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May 1981

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Document:	VMS Internals and Data Structures 2.2 1981
Order Number:	AA-K785A-TE
Revision:	0
Pages:	703
Original Filename:	VMS_Internals_and_Data_Structures_2.2_1981.pdf

OCR Text

VAX/VMS
Internals and Data Structures

April 1981

This manual explains the internal control paths and data structures used by the
VAX/VMS operating system.

VAX/VMS

Intern als and Data Structures
Order No. AA-K785A- TE

SUPERSESSION/UPDATE INFORMATION:

This is a new document for this release.

OPERATING SYSTEM AND VERSION:

VAX/VMS V2.2

SOFTWARE VERSION:

Not Applicable

digital equipment corporation

maynard, massachusetts

F i r s t P r i n t i ng , Apr i l 1 9 8 1

The i n fo rma t i o n i n t h i s d o c um e n t i s s ub j e c t t o c h a ng e w i t h o u t n o t i c e
a nd
should
no t b e c o n s t r ued
a s a c omm i tme n t b y D i g i t a l E q u i pm e n t
Co r po r a t i o n .
D i g i t a l E q u i pment Co r po r a t i o n a s s um e s n o
r e s pons i b i l i ty
f o r a n y e r ro r s tha t m a y a ppe a r i n th i s d o c um e n t .
Th e s o f t wa r e d e sc r i b ed i n th i s d o c um e n t i s f u r n i shed und e r
a l i c en s e
a nd m a y o n l y b e u s e d o r c o p i ed i n a c c o rd a n c e wi th t h e t e rms o f s uc h
l i c en s e .
No r e spo n s i b i l i ty i s a s s umed for the u s e o r r e l i a b i l i t y o f so f twa r e o n
e qu i pm e n t tha t i s n o t s upp l i ed by D I G I TA L o r i t s a f f i l i a t ed compa n i e s .

C o py r i g h t

P e rm i s s i o n
to
a c knowl edged .

r e p r i nt

1 9 8 1 by D i g i t a l E q u i pm e n t C o r po r a t i o n
Al l R i gh t s Re s e r v e d .

the

f o l l o w i ng

m a te r i a l

g ra te f u l l y

F r om Th e Hobb i t b y J . R . R .
To l k i e n .
C o py r i g h t
@ 1 9 6 6 by J . R . R .
To l k i e n .
R e p r i n t ed
1 n the
Un i t ed S t a t e s b y pe rm i s s i o n o f Ho ug h to n
M i f f l i n Compa ny .
Re p r i n t ed o u t s i d e the Un i t ed S t a t e s b y pe rm i s s i o n o f
G e o r g e A l l en & U n w i n , Ltd .
F r o m Th e Re t u r n o f t h e K i ng , Be i ng the Th i r d Pa r t o f Th e Lo rd o f
the
R i ng 7 b y J . R . R .
Copy r i g h t
@ 1 9 6 5 by J . R . R . To l k i e n .
To l k i e n .
R e p r1n t ed i n the Un i t e d
S t a t e s b y p e rm i s s i o n o f
Ho ug h t o n M i f f l i n
Rep r i n t ed o u t s i d e the Un i ted S t a t e s by pe rm i s s i o n of G e o r g e
Compa n y .
A l l e n & Unwi n , Ltd .

The po s tag e p r e pa i d READER ' S C OMM ENTS f o rm o n the l a s t pag e o f t h i s
d o c um e n t r eq ue s t s
the
use r ' s c r i t i c a l
e va l ua t i o n
to a s s i s t u s i n
p r e pa r i ng f u t u r e d o c um e n ta t i o n .

The fo l l ow i ng a r e t r ad em a r k s o f D i g i ta l Equ i pm e n t C o r po r a t i o n :
DEC
D E CU S
D IG I TA L
PDP
UN I B U S
VAX
D E Cn e t

DEC s ys tem- 1 0
DEC S Y S TEM - 2 0
DECw r i te r
D I BOL
EduSys t em
!AS
MAS S B US

3/83-14

PDT
RSTS
RSX
VMS
VT

�omoomo

C ONTENTS

Page
PRE FAC E

xxvii

PART I

I N TRODUC T I ON

C HA PTER 1

S Y S T EM OVE RV I EW

PROC E S S , JOB , AND I MAG E
1.1
1. 1. 1
Process
Ha r d wa r e Co n t e x t
1. 1. 1. 1
So f twa r e Co n t ext
1. 1.1.2
V i r t ua l Ad d r e s s S pa c e De s c r i p t i o n
1.1.1.3
Imag e
1. 1.2
Job
1.1.3
FUNC T I ONA L I TY PROV I DE D B Y VAX/VM S
1.2
Ope r a t i ng Sy s t em Ke r n e l
1. 2. 1
I / 0 S u b s y s tem
1.2.1.1
Memo r y Ma n ag em e n t
1 . 2.1.2
S c h ed u l i ng a nd P r o c e s s Co n t r o l
1.2. 1. 3
M i s c e l l a n e o us S e r v i c e s
1.2.1.4
Da t a Ma n ag em e n t
1 . 2. 2
User Inter face
1 . 2. 3
1.2. 3. 1
I m ag e s I n s t a l l ed w i t h P r i v i l eg e
O t h e r P r i v i l eg e d I m a g e s
1.2.3.2
1 . 2. 3. 3
Imag e s Th a t L i n k w i t h SY S $ SYS TEM : S YS . STB
1.2.4
I n t e r f a c e b e twe e n Ke r n e l S u b s ys t em s
I / 0 S u b s y s t em Re que s t s
1.2.4.1
Memo r y Ma n ag em e n t Re qu e s t s
1 . 2. 4. 2
S c h e d u l e r Re q u e s t s
1.2.4.3
HARDWARE I M P LEM ENTAT I ON O F O P E RAT ING S Y S T EM
1.3
K E RN E L
VAX A r c h i t ec t u r e Fe a t u r e s E x p l o i t ed b y VM S
1.3.1
VAX- 1 1 I n s t r uc t i o n Se t
1 . 3.2
I m p l em e n t a t i o n o f VM S Ke r n e l Ro u t i n e s
1. 3.3
P r o c e s s Co n t e x t a nd Sy s t em S t a t e
1 . 3. 3. 1
P r o c e s s - B a s e d Ro u t i n e s
1 . 3.3. 2
Sys t em S e r v i c e s
1 . 3. 3. 2. 1
Pag e Fa u l t H a nd l e r
1 . 3.3.2.2
I n t e r r u p t S e r v i c e Ro u t i n e s
1.3.3.3
1 . 3. 3. 4
Spec i a l P r o c e s s e s - Swa ppe r a nd N u l l
1.3.3.5
Spec i a l S u b r o u t i n e s
1.3.4
Memo r y Ma n ag em e n t a nd Ac c e s s Mo d e s
1.3.5
Ex c e pt i o n s , I n t e r r up t s , a nd RE I
1. 3.5. 1
Compa r i s o n o f E x c e p t i o n s a nd I n t e r r up t s
1 . 3. 5. 2
O t h e r U s e s o f E x c e p t i o ns a nd I n t e r r up t s
1. 3. 5. 3
Th e RE I I n s t r uc t i o n
1 . 3.6
P r o c e s s S t r uc t u r e
OTHER SYSTEM C ONC E PT S
1.4
1.4.1
Re s o u r c e C o n t r o l
1.4.1.1
H a r d wa r e P r o t e c t i o n
P r o c e s s Pr i v i l eg e s
1 . 4. 1. 2
1.4.1.3
Q uo t a s a nd L i m i t s
1.4.1.4
Us e r I d e n t i f i c a t i on Code ( U I C )
iii

1-1
1-1
1-1
1-3
1-3
1-3
1-4
1-4
1-4
1-4
1-4
1-6
1-6
1-6
1-6
1 -7
1 -7
1-9
1-9
1-1 0
1-1 0
1-1 0
1-1 0
1-1 0
1-1 1
l-1 2
1-1 3
1-1 4
1-1 4
1-1 5
1-1 5
1-1 5
1-16
1-1 6
1-1 7
1-1 7
1-1 8
1-1 8
1-18
1-19
1-19
1-19
1-19
1-20
1-20

C ONTENTS
1.4.2
Ot h e r Sys t em P r i m i t i v e s
1 . 4 . 2. 1
S yn c h r o n i z a t i o n
1.4.2. 2
Dyn am i c Memo r y Al l o c a t i o n
1.4.2. 3
Log i c a l Na m e s
LAYO UT O F VI RTUA L ADDR E S S S PACE
1.5
Sy s t em V i r t ua l Ad d r e s s Spa c e
1 . 5. 1
Th e Co n t r o l Reg i o n ( P l S pa c e )
1.5.2
Th e P r o g r am Reg i o n ( P O S pa c e )
1.5.3
PART I I

C ONTROL M EC HAN I S M S

C HA PTER 2

C OND I T I ON HAND L I NG

2.1
2.1.1
2.1.2
2.2
2.2.1
2.2.1.1
2.2.1. 2
2.2.1.3
2.2.1.4
2.2.2
2 . 2 . 2. 1
2 . 2 . 2. 2
2.3
2.3.1
2. 3.2
2.3.2.1
2. 3. 2. 2
2 . 3 . 2. 3
2.3.3
2.3.3.1
2.3.3.2
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.5
2.5
2.5.1
2.5.2
2 . 5. 3
2.5.3.1
2.5.3.2
C HAPTER 3
3.1
3.2
3.2.1
3.2.2
3.3
3.3.1
3.3.2
3.3.3
3.3.4

OVERVI EW OF TH E C OND I T I ON HANDL I NG FAC IL I TY
Go a l s o f VAX- 1 1 C o nd i t i o n Hand l i ng Fa c i l i t y
Fe a t u r e s o f VAX- 1 1 C o nd i t i o n Hand l i ng Fa c i l i t y
G E N E RAT I ON OF E XC E PT I ON S
E x c ept i o n s Th a t O r i g i n a t e i n the Ha r d wa r e
E x c ep t i o n s Th a t VM S T r e a t s i n a Spec i a l Wa y
O t h e r Ha r d wa r e E x c ept i o n s
I n i t i a l Ac t i o n o f E x c e p t i o n S e r v i c e Ro ut i n e s
Mo r e S p e c i a l Ca s e s i n E x c ept i o n D i s pa tch i ng
Ex c e p t i o n s De t e c ted by S o f twa r e
Pa s s i ng S t a t u s f r om a P r o c ed u r e
I n i t i a l Ope r a t i o n o f L I B $ S I GNA L
UN I F ORM E XC E PT I ON D I S PATC H ING
Es t a b l i sh i ng a Co nd i t i o n Ha nd l e r
Th e S e a r c h fo r a Cond i t i o n Ha nd l e r
P r i m a r y a nd S e c o nd a r y E x c ept i o n Ve c to r s
Ca l l F r am e C o nd i t i o n H a nd l e r s
La s t Ch a n c e Cond i t i o n H a nd l e r
M u l t i p l y Ac t i v e S i g n a l s
Common Ca l l S i t e fo r C o nd i t i o n Hand l e r s
E x ampl e o f M u l t i pl y Ac t i v e S i g n a l s
C OND I T I ON HANDLE R ACT I ON
C o n t i n u e o r Re s i g n a l
Un w i nd i ng t h e C a l l S t a c k
E x ampl e o f Unw i nd i ng t h e Ca l l S t a c k
Po t e n t i a l I n f i n i t e Lo o p
Unwi nd i ng M u l t i pl y Ac t i v e S i g n a l s
D E FAULT ( VM S - S U PP L I E D ) C OND I T I ON HANDLERS
T r a c e b a c k Ha n d l e r E s t a b l i shed by Ima g e S t a r t up
Ca t c h Al l Cond i t i o n Ha nd l e r
Ha n d l e r s Us ed by Ot h e r Ac c e s s Mo d e s
Ex c ept i o n s i n Ke r n e l o r Ex ec u t i v e Mo d e
C o nd i t i o n Ha n d l e r U s e d b y DC L o r MCR

1-20
1-20
1-21
1-21
1-21
1-21
1-22
1 -2 4

2-1
2-1
2-2
2-3
2-3
2-7
2-7
2-8
2-9
2-1 4
2-1 4
2-1 4
2-1 6
2-1 6
2-1 8
2-1 8
2-1 8
2-1 8
2-2 0
2-20
2-21
2-2 3
2-2 3
2-24
2-2 4
2-27
2-28
2-28
2-30
2-3 0
2-30
2-31
2-31

S Y S T EM S ERVI C E D I S PATC H ING
S YS TEM S ERVI C E VE C TORS
C HANG E MODE I NS TR UC T I ON S
C HM K , CHM E
C HM S , C HM U
C HANG E M ODE D I S PA TCH ING I N VM S
Ope r a t i o n o f the Ch a n g e Mod e D i s pa t c h e r
Ch a ng e -Mo d e- to-Ke r ne l D i s p a tche r
Ch a ng e -Mod e- t o - E x e c u t i ve D i s p a t c h e r
RM S D i s pa t c h i ng
iv

3-1
3-4
3 -4
3-4
3-4
3-5
3-1 0
3-10
3-10

C ONTENTS
Re t u r n Pa th f o r Sys t em S e r v i c e s
3.3.5
Re t u r n Pa th f o r RMS S e r v i c e s
3.3.6
Wa i t S t a t e As so c i a t ed w i t h RMS Requ e s t s
3.3.6.1
RM S E r r o r De t e c t i o n
3.3.6.2
U S E R-WR I TT EN SYSTEM S ERVI C E D I S PATC H ING
3.4
Pe r - P r o c e s s U s e r -Wr i t t e n D i s pa t c h e r
3.4.1
Pr i v i l eg ed Sha r e a b l e Imag es
3.4.2
Sys t em-W i d e U s e r -Wr i t t e n D i s pa tc h e r
3. 4.3
RELATE D SYS TEM S ERVI C E S
3. 5
Se t Sys t em Se r v i c e Fa i l u r e E x c e p t i o n s Sys tem
3.5.1
Se r v i c e
Ch a ng e Mo d e Sy s t em Se r v i c e s
3.5.2
C HAPTER 4
4. 1
4.1.1
4.1.2
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
C HAPTER 5
5.1
5. 1 . 1
5. 1 . 2
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5. 3
5. 3.1
5. 3 . 2
5.3.3
5. 4
5.4.1
5 . 4. 2
5 . 4. 3
5 . 4. 4
5 . 4. 5
5 . 4. 6
5.5
5. 5. 1
5.5.2
5. 5 . 3
5.5.4
5.5.4.1
5.5.4.2
C HAPTER 6
6.1
6.1.1

3-1 0
3-12
3-12
3-1 3
3-1 3
3-13
3-1 3
3-17
3-17
3-17
3-18

S OFTWARE INTERR U PTS
THE S OFTWARE INTERR U PT
H a r d wa r e Mec h a n i sm o f So f twa r e I n t e r r up t s
So f twa r e I n t e r r up t S e r v i c e Ro u t i n e s
S OFTWARE INTERR U PT LEVE LS I N VAX/VM S
Fo r k P r o c e s s i ng
So f t wa r e T i m e r
I /0 Po s t p r o c e s s i ng
Re s c h e d u l i ng I n t e r r up t
A S T De l i v e r y I n t e r r up t

4-1
4-1
4-3
4-3
4-4
4-6
4-7
4-7
4-8

A S T D E L I VE RY
HARDWARE ASS I STANC E TO AST DE L I VE RY
RE I I n s t r uc t i o n
A S T LVL P r o c e s s o r Reg i s t e r ( PR $ ASTLVL )
Q U E U ING AN AST TO A PROC E S S
AST C o n t r o l B l o c k
Ac c e s s Mo d e a n d AST Que u i ng
Sp e c i a l Ke r n e l Mo d e ASTs
Comp u t a t i o n o f a New Va l ue fo r ASTLVL
DE L I VE R ING AN AST TO A PROC E S S
AST De l i v e r y I n t e r r up t
Arg um e n t L i s t
A S T E x i t Pa th
S PE C IAL KERN E L ASTS
I /0 Po s t p r o c e s s i ng in Pr o c e s s Co n t e x t
P r o c e s s S u s pe n s i o n
P r o c e s s De l e t i o n
$G E TJ P I Sys tem Se r v i c e
Powe r Re c o v e r y ASTs
O t h e r Sys t em U s e o f ASTs
ATTENT I ON A STS
Se t At t e n t i o n Me c ha n i sm
De l i v e r y o f At t e n t i o n ASTs
Fl ush i ng a n At t e n t i o n AST L i s t
Ex amp l e s i n VAX/VM S
Te r m i n a l D r i v e r a nd CTRL/Y No t i f i c a t i o n
Ma i l b o x D r i v e r

5-l
5-l
5-2
5-2
5-2
5 -4
5-5
5-5
5-6
5-6
5-8
5-8
5-9
5-1 0
5- 1 0
5-1 1
5-1 1
5-12
5-1 2
5-1 2
5-1 3
5-1 3
5-14
5-1 5
5-1 5
5-1 5

HARDWARE INTERRU PTS
HARDWARE I NTERRUPT D I S PATC H ING
I n t e r r up t D i spa tch i ng
v

6-1
6-2

C ONTENTS
S y s t em Co n t r o l B l o c k
6.1.2
6.1.2. 1
VAX- 1 1 / 7 5 0 E x t e r n a l Ad a p t e r s
6. 1.2.2
VAX- 1 1 /7 8 0 E x t e r n a l Ad a p t e r s
6.1.2.3
Ad a p t e r Co n f i g u r a t i o n
VAX/VM S I N TERRUPT S ERVI C E R O UT INE S
6.2
6.2.1
Re s t r i c t i o n s Impo sed o n I n t e r r upt S e r v i c e
Ro u t i n e s
6.2.2
S e r v i c i ng UN I B US I n t e r r up t s
6.2. 2. 1
VAX- 1 1 /7 5 0 UN I B US I n t e r r upt S e r v i c e Ro u t i n e s
6.2. 2. 2
VAX- 1 1 / 7 8 0 UN I B US I n t e r r upt S e r v i c e Ro u t i n e s
MAS S B U S I n t e r r u p t S e r v i c e Ro ut i n e s
6.2.3
DR 3 2 I n t e r r up t S e r v i c e Ro u t i n e
6.2.4
6.2.5
MA7 8 0 I n t e r r up t D i s p a tch i ng
CONNEC T-TO- I NTERRUPT M E C HAN I SM
6.3
C HA P T E R 7

6-4
6-4
6-5
6-6
6-6
6-6
6-7
6-7
6-9
6-1 0
6-1 3
6-1 3
6-1 5

E RROR HAND L ING

E RROR LOGG I NG
7.1
Ove r v i ew o f the E r r o r Logg i ng S ubsys t em
7.1.1
De v i c e D r i v e r E r r o r s
7.1.2
O t h e r E r r o r Log Me s s ag e s
7. 1.3
Ope r a t i o n o f the E r r o r Lo g g e r Ro u t i n e s
7.1.4
Wa k i ng the ERRFMT P r o c e s s
7.1. 4. 1
7.1.5
Cu r so r y Ov e r v i ew o f the E RR FMT P r o c e s s
E r r o r L o g Ma i l bo x
7.1.6
S y s t em Se r v i c e Ca l l
7.1.6.1
Ac t i o n o f the E RRFMT P r o c e s s
7.1.6.2
SYS TEM CRA S H E S ( BUGC HECKS )
7.2
B UGC H E C K M e c h a n i sm
7.2.1
Ope r a t i o n o f BUG C HECK Ro u t i n e
7.2.2
B ug c h e c k s f r om Us e r a nd S u pe r v i so r Mo d e
7.2.2.1
VM S U s e o f Bug c hec k s
7.2.2.2
Sys tem Dump Fi l e
7.2. 3
MAC H IN E C H E C K M E C HAN I SM
7.3
VAX- 1 1/7 5 0 Ma ch i n e Ch e c k
7.3. 1
VAX- 1 1 /7 8 0 Ma c h i n e Ch e c k
7.3.2
M a c h i n e Ch e c k Re c o ve r y Bl o c k s
7.3. 3
7.3.3. 1
Us i ng t h e Recove r y Mech a n i sm
PART I I I

S C H E D U L ING AND T IM E R S U PPORT

C HA PTER 8

S C HE D U L ING

PROC E S S S TATES
8.1
P r o c e s s Co n t r o l B l o c k
8.1.1
S o f t wa r e P r i o r i t y
8.1.2
Re a l -T i m e Pr i o r i t y Ra ng e
8.1.2. 1
No rma l P r i o r i t y Ra ng e
8.1. 2. 2
P r i o r i ty Ad j u s tm e n t
8.1.2. 3
Qua n t um E x p i r a t i o n
8.1.2.4
S t a te Que u e s
8.1.3
Comput a b l e S t a t e s
8.1.3.1
Wa i t S t a t e s
8.1.3.2
Vo l un t a r y Wa i t S t a t e s
8.1.3.2.1
8.1.3.2.2
Memo r y Ma n ag em e n t Wa i t S t a t e s
M i s c e l l a n e o u s Wa i t S t a t e ( MWA I T )
8.1. 3.2.3
Commo n Ev e n t B l o c k s
8.1. 3. 3
SYS TEM EVENTS
8.2
vi

7-1
7-1
7-2
7-2
7-2
7-3
7-3
7-3
7-4
7-4
7-4
7-4
7-5
7-5
7-6
7-9
7-9
7-1 0
7-1 1
7-1 2
7-1 2

8-1
8-1
8-3
8-3
8-4
8-5
8-5
8-9
8-9
8-9
8-9
8-1 1
8-11
8-1 4
8-15

C ONTENTS
8.2.1
S y s t em Ev e n t s a nd P r o c e s s S t a t e s
P r o c e s s S t a t e Ch a ng e s
8.2.1.1
Wa i t S t a t e s a nd A S T De l i ve r y
8.2.1.2
S y s tem S e r v i c e Wa i t S t a t e s
8.2.1.2.1
Mem o r y Ma n a g em e n t Wa i t S t a t e s
8.2.1.2.2
Spec i a l Cases
8.2.1.2.3
Ev e n t R e po r t i ng
8.2.2
Sy s t em Even t s a nd As s o c i a t ed P r i o r i t y Bo o s t s
8.2.3
R E S C HE DU L I NG I NTERRUPT
8.3
Ha r dwa r e Co n t e x t
8.3.1
Remov a l o f C u r r e n t P r o c e s s f r om E x e c u t i o n
8.3.2
S e l e c t i o n o f Nex t P r o c e s s fo r Ex e c u t i o n
8.3. 3
Summa r y Lo ngwo r d a nd Compu t a b l e S t a t e Que ue s
8.3.4
Ha r d wa r e As s i s t a n c e i n Co n t e x t Swi tc h i ng
8.3.5
SVPC T X I n s t r uc t i o n
8.3.5.1
LDPC TX I n s t r uc t i o n
8.3. 5.2
C HA PTER 9

PROC E S S C ONTROL AND C OMMUN ICAT I ON

E VENT F LAG S E RVI C E S
9.1
Lo c a l E v e n t F l ag s
9.1. 1
Common E v e n t F l ag s
9.1.2
E v e n t F l ag Wa i t S t a t e s
9.1. 3
S e t t i ng a nd C l e a r i ng E v e n t F l ag s
9.1.4
Ot h e r E v e n t Fl ag S e r v i c e s
9.1.4.1
AFFECT I NG THE C OM PUTAB I L I TY OF ANOTHER PROC E S S
9.2
Common E v e n t Fl ag s
9 . 2. 1
P r o c e s s Co n t r o l S e r v i c e s
9 . 2. 2
P r i v i l eg e Ch e c k s
9 . 2. 2. 1
P r o c e s s C r e a t i o n a nd De l e t i o n
9.2.2.2
Hi b e r n a t e /Wa k e
9.2. 2. 3
S u s pe nd / Re s um e
9.2.2.4
Process Suspens i on
9.2.2.4.1
Ope r a t i o n o f the Re s ume Sys t em S e r v i c e
9.2.2.4.2
Ex i t a n d Fo r c e d Ex i t
9.2.2.5
M i s c e l l a n eo u s P r o c e s s At t r i b u t e C h a ng e s
9.2. 3
Se t P r i o r i t y
9.2. 3.1
S e t P r o c e s s Name
9.2. 3. 2
P r o c e s s Mo d e S e r v i c e s
9.2. 3. 3
I NT E R PROC E S S C OMMUN I C AT I ON
9.3
E v e n t F l ag s
9.3. 1
Ma i l bo x e s
9.3.2
Log i c a l Nam e s
9.3.3
G l o ba l S e c t i o n s
9.3.4
I n t e r p r o c e s s o r Commun i c a t i o n wi th t h e MA7 8 0
9.3.5
C HAPTER 1 0

8-15
8-1 5
8-1 5
8-16
8-1 6
8- 1 6
8-17
8-1 8
8-2 0
8-20
8-22
8-22
8-23
8-26
8-26
8 - 27

9-1
9-1
9-1
9-4
9-6
9 -7
9-8
9-8
9-8
9-8
9-8
9-9
9-9
9-9
9-1 0
9-1 0
9-1 0
9-1 1
9-1 1
9-1 1
9-1 3
9-1 3
9- 1 3
9-1 4
9-1 4
9-14

T IM E R S U P PORT

10. 1
T I M E KE E P I NG I N VAX/VM S
10. 1 . 1
Ha r dwa r e C l o c k s
Interval Clock
10. 1.1. 1
10. 1 . 1 . 2
T i m e - o f-D a y C l o c k
10. 1.2
S o f t wa r e T i m e
10. 1.3
S e t T i m e Sy s t em S e r v i c e
10. 1.3.1
$ S E T I M E S y s tem T i m e Re c a l i b r a t i o n Re que s t s
10. 1.3. 2
$ S E T I M E T i me-o f-D a y Re a d j u s tm e n t Reque s t s
10. 2
HARDWARE C LOCK I NTERRUPT S ERVI C E ROUT INE
10. 2. 1
Sy s t em T i m e Upd a t i ng
10. 2. 2
T i m e r Qu e ue Te s t i ng
vi i

1 0- 1
1 0- 1
1 0- 1
1 0- 3
1 0- 3
1 0- 4
1 0-4
1 0- 5
1 0- 5
1 0- 6
1 0-6

C ONTENTS
10. 3
10. 3. 1
10. 3. 2
10. 3. 3
10. 3. 4
10. 3. 5
10. 4
10.4.1
10. 4. 2

S O FTWARE T I M E R INTE RRUPT S E RVI C E ROUT INE
Qua n t um Ex p i r a t i o n
T i m e r Qu e ue a n d T i m e r Qu e ue E l em e n t s
T i m e r Reque s t S e r v i c i ng
S c h ed u l e d Wa k e u p
Pe r i od i c Sys t em P r o c ed u r e s
T I MER SYS TEM S E RVI C E S
$ S E T I M R Re q u e s t s
S c h e d u l ed Wa k e up

PART I V

M EM ORY MANAG EM E NT

C HA PTER 1 1

MEMORY MANAG EM E NT DATA S TRUC TUR E S

1 0-6
1 0-6
1 0-7
1 0-8
1 0- 9
1 0- 9
1 0- 1 0
1 0-1 0
1 0-1 1

1 1-1
PROC E S S DATA S TRUC TURES ( PROC E S S HEAD E R )
11. 1
1 1-2
P r o c e s s Pa g e Ta b l e s
11. 1.1
P r o c e s s S e c t i o n Ta b l e I n d e x
1 1-4
11. 1.1.1
Pa g e F i l e V i r t u a l B l o c k Num b e r
1 1-4
11.1.1.2
G l o b a l Pa g e Ta b l e I n d e x
1 1-4
11. 1.1.3
Page in Trans i t ion
1 1-7
11.1.1.4
Dem a n d Z e r o Pag e s
1 1-7
11. 1.1.5
1 1-7
Wo r k i ng S e t L i s t
11.1.2
1 1-7
D i v i s i o n o f t h e Wo r k i ng S e t L i s t
11. 1 . 2. 1
1 1-1 1
P r o c e s s Se c t i o n Ta b l e
11.1.3
P r o c e s s He a d e r Pa g e A r r a ys
1 1-1 1
11.1.4
1 1-14
PFN DATA BASE
11 .2
1 1-16
PTE Ar r a y
11. 2. 1
1 1-16
BAK A r r a y
11.2. 2
1 1-16
S TATE A r r a y
11. 2. 3
1 1-17
TYPE Ar r a y
11.2. 4
Fo r wa r d and B a c kwa r d L i n k s
1 1-17
11. 2. 5
1 1-18
RE FCNT A r r a y
11.2.6
1 1 -1 9
S HRCNT A r r a y
11. 2.7
1 1-20
WS LX A r r a y
11.2.8
SWPVBN A r r a y
1 1 -2 0
11.2.9
DATA S TRUC TURES FOR G LOBAL PAG E S
1 1-20
11.3
G l o b a l Se c t i o n De s c r i p to r
11. 3. 1
1 1-20
Th e Sys tem He ad e r and G l o ba l S e c t i o n Ta b l e
11. 3. 2
1 1-20
En t r i e s
G l oba l Pa g e Ta b l e En t r i e s
11. 3. 3
1 1-23
G l o b a l Pag e T a b l e a nd Sys t em Pag e Ta b l e
11. 3. 4
1 1-24
P r o c e s s PT Es fo r G l o b a l Pag e s
1 1-26
11.3.5
SWAPP I NG DATA S TRUCTURES
1 1-27
11.4
1 1-27
Bal ance Slots
11.4.1
1 1-27
Ba l a n c e S l o t Ar r a ys
11.4.2
Comme n t o n E q u a l S i z e Ba l a n c e S l o t s
11.4. 3
1 1-30
DATA S TRUC TUR E S THA T D E SC R I B E THE PAG E F I LE S AND
11.5
1 1-30
SWAP F I L E S
11. 5. 1
Pag e a n d Swa p F i l e Ve c to r
1 1-30
11. 5. 2
Pa g e F i l e Da t a Ba s e
1 1-30
Swa p F i l e Ta b l e E n t r i e s
11. 5. 3
1 1-32
11.6
SWAPPER AND M OD I F I E D PAG E WR I TE R PAGE TAB LE
ARRAYS
1 1-32
11. 6. 1
1 1-34
D i r e c t I /O and Sc a t t e r/G a th e r
11.6.2
Swa ppe r I /0
1 1-34
11.6. 3
Mo d i f i e d Pa g e Wr i t e r PTE A r r a y
11-35
11.6.4
No n r e e n t r a n c y o f Swa ppe r a nd Mod i f i ed Pag e
1 1-3 5
Wr i t e r
11.7
DATA S TRUC TUR E S US E D W I TH S HARED M EM ORY
1 1-3 5
vi i i

CONTENTS
11.7 . 1
11.7 . 1 . 1
11.7 . 1 . 2
11.7 . 1 . 3
11.7. 2
11.7. 3
11.7 . 4
C HAPT E R 1 2

Sh a r ed Memo r y C o n t r o l S t r uc t u r e s
Ph y s i c a l La yo u t o f Sha r ed Memo r y
Sh a r ed Memo r y Commo n Da t a Pag e
P r o c e s so r -S pe c i f i c C o n t r o l
G l o ba l S e c t i o n s i n Sh a r ed Mem o r y
Ma i l bo x e s i n Sh a r ed Memo r y
Comm o n Ev e n t F l a g C l u s t e r s i n Sh a r ed Memo r y
PAG I NG DYNAM I C S

OVERVI EW O F PAG E R O P E RAT I ON
12. 1
H a rdwa r e Ac t i o n
12. 1 . 1
I n i t i a l Pa g e r Ac t i o n
12. 1 . 2
PAG E FA U LTS FOR PROC E S S PR IVATE PAG E S
12. 2
Pag e Lo c a t ed i n a n Imag e Fi l e
12. 2 . 1
Imag e Pa g e Th a t I s No t Co py o n Re f e r e nc e
12. 2. 1 . 1
Pag e Fa u l t s o u t o f T r a n s i t i o n S t a t e s
12. 2 . 1 . 2
Co py-on-Re f e r e n c e Pa g e
12. 2. 1 . 3
Demand Z e r o Pa g e s
12. 2.2
G l o b a l C o p y-on-Re f e r e n c e Pa g e s
12. 2. 3
Pa g e Lo c a t ed i n the Pag e Fi l e
12. 2.4
PAG E FAU LTS FOR G LOBAL PAG E S
12. 3
Pa g e Fa u l t fo r G l o b a l Re ad-On l y Pag e
12. 3.1
G l o b a l Re a d /Wr i t e Pag e s
12. 3.2
G l o ba l Co py-on-Re f e r e n c e Pag e s
12. 3. 3
WORK I NG S E T R E PLAC EMENT
12. 4
S c a n o f Wo r k i ng Set L i s t
12. 4.1
S k i pp i ng Wo r k i ng S e t L i s t E n t r i e s
12. 4.2
I N PUT AND O UT PUT THAT S U PPORT PAG I NG
12. 5
Pa g e Re a d s
12. 5.1
Pag e Re a d C l u s t e r i ng
12. 5. 1 . 1
T e rm i n a t i ng Co nd i t i o n fo r C l u s t e r ed Re ad s
12. 5. 1.1.1
Ma t c h i ng Co nd i t i o ns Wh i l e Sc ann i ng P a g e
12. 5.1.1.2
Tabl e
Ma x im um C l u s t e r S i z e fo r Pa g e Re ad
12. 5. 1.1.3
Pag e Re a d Compl e t i o n
12. 5. 1 . 2
Mod i f i ed P a g e Wr i t i ng
12. 5. 2
Ope r a t i o n o f the Mo d i f i ed Pa g e Wr i t e r
12. 5 . 2. 1
Mo d i f i e d Pa g e Wr i t e C l us t e r i ng
12. 5.2.2
Ba c k i ng S t o r e Ad d r e s s e s fo r Mo d i f i ed Pag e s
12. 5.2.3
Ex am p l e o f Mo d i f i ed Pa g e Wr i t e t o a Pag e
12. 5.2. 4
Fi l e
Mo d i f i ed Pa g e Wr i t e Compl e t i o n
12. 5. 2 . 5
12. 5. 3
Upd a t e S e c t i o n Sy s t em S e r v i c e
Pag e S e l e c t i o n
12. 5.3. 1
Wr i t e Compl e t i o n
12. 5 . 3 . 2
12. 6
PAG I NG AND S C HEDUL ING
Pa g e Fa u l t Wa i t S t a t e
12. 6.1
12. 6.2
F r e e P a g e Wa i t S t a t e
Co l l i d ed P a g e Wa i t S t a t e
12. 6.3
No Av a i l a b l e S p a c e i n the Pa g e F i l e
12. 6.4
C HAPTER 1 3

1 1 - 37
1 1 - 37
1 1-38
1 1-38
1 1-39
1 1-42
1 1-4 2

1 2-1
1 2-1
1 2-1
1 2-3
1 2-3
1 2 -4
1 2 -7
1 2-8
1 2- 1 0
1 2-1 0
1 2-1 2
1 2-1 2
1 2- 1 2
1 2- 1 5
1 2- 1 6
1 2 - 17
1 2-17
1 2- 1 8
1 2-19
1 2-20
1 2-20
1 2-20
1 2-21
1 2-21
1 2-24
1 2-25
1 2-2 5
1 2-25
12-26
1 2-28
1 2-28
1 2-29
1 2-29
1 2-29
1 2-30
1 2-30
1 2-30
1 2-30
1 2- 3 1

M EM ORY MANAG EM ENT SYS TEM S E RV I C E S

D I S PATC H ME THOD F OR M EMORY MANAG EM ENT S Y S TEM
S E RVI C E S
VI RTUAL ADDR E S S C R EAT I ON AND DE L E T I ON
13. 2
Ad d r e s s S p a c e C r e a t i o n
13. 2.1
13. 2. 1. 1
L i m i t s o n Vi r t ua l Ad d r e s s Sp a c e C r e a t i o n
13. 1

1 3 -1
1 3-2
1 3-2
1 3 -3

C ONTENTS
13.2. 1.2
E x p a n d Reg i o n Sy s t em S e r v i c e
13.2.1.3
Au t oma t i c Us e r S t a c k E x pa n s i o n
13.2.2
Ad d r e s s Spa c e De l e t i o n
13.2. 2. 1
D e l e t e V i r t u a l Ad d r e s s Spa c e Sys t em S e r v i c e
13.2.2.2
Pag e De l e t i o n a n d Sc h ed u l i ng
13.2. 2.3
Co n t r a c t Reg i o n Sy s t em S e r v i c e
13.2.3
Co n t r o l l ed Al l oc a t i o n o f V i r t ua l Memo r y
13. 3
PR I VA T E AND G LOBAL S ECT I ONS
13.3.1
C r e a t e a nd Ma p S e c t i o n Sys t em S e r v i c e
13.3.1.1
Pr i v a t e Sec t i on C r e a t i on
G l o ba l Sec t i on C r ea t i on
13.3. 1. 2
G l o b a l S e c t i o n s i n Sh a r ed Memo r y
13.3.1.3
Ma p by PFN
13.3.1.4
Ma p G l o b a l S e c t i o n Sy s t em S e r v i c e
13. 3.2
De l e t e G l o b a l S e c t i o n Sys t em S e r v i c e
13.3.3
Upd a t e S e c t i o n Sys t em S e r v i c e
13.3.4
R E LATED S Y S T EM S ERVI C E S
13.4
Wo r k i ng S e t S i ze Ad j u s tme n t
13.4.1
13.4.1. 1
Ad j u s t Wo r k i ng S e t S i ze Sy s t em S e r v i c e
S E T WO R K I NG S E T C omma nd
13.4. 1.2
Au t oma t i c Wo r k i ng Set S i z e Ad j us tm e n t
13.4.1.3
Pu r g e Wo r k i ng S e t Sys t em S e r v i c e
13.4.1.4
Lo c k i ng a n d Un l o c k i ng Pag e s
13.4.2
Lo c k i ng Pag e s i n th e Wo r k i ng S e t
13.4.2. 1
Lo c k i ng P a g e s i n Memo r y
13.4.2.2
Un l o c k i ng P a g e s
13.4.2. 3
P r o c e s s Swa p Mo d e
13.4.3
Al t e r i ng Pag e P r o t e c t i o n
13.4.4
C HAPTER 1 4

1 3-3
1 3-3
1 3-4
1 3-5
1 3-5
1 3-5
1 3-6
1 3-6
1 3-6
1 3-6
1 3 -7
1 3 -7
1 3 -8
1 3 -8
1 3-9
1 3- 1 0
1 3- 1 0
1 3- 1 0
1 3-1 1
1 3- 1 2
1 3- 1 2
1 3- 1 4
1 3- 1 4
1 3- 1 5
1 3- 1 5
1 3- 1 6
1 3- 1 6
1 3- 1 6

SWAPP I NG

SWAPP I NG OVERVI EW
Swa ppe r Re s po n s i b i l i t i e s
Swa ppe r Impl em e n t a t i o n
Compa r i so n o f Pag i ng a n d Swa pp i ng
SWAP S C HE D U L ING
S e l e c t i o n of I n s wa p C a nd i d a t e
S e l e c t i o n o f O u t s wa p C a nd i d a t e s
Sy s t em Ev e n t s Th a t T r i g g e r Swa ppe r Ac t i v i t y
SWAPP E R ' S US E OF MEMORY MANAG EM E NT DATA
S TR UC TUR E S
P r o c e s s He ad e r
14. 3.1
Wo r k i ng S e t L i s t
14. 3 . 1 . 1
P r o c e s s Pa g e T a b l e s
14. 3. 1. 2
P r o c e s s He ad e r P a g e A r r a ys
14.3.1.3
14. 3 . 2
Swa ppe r I /G Da t a S t r uc t u r e s
14. 3.2. 1
Swa p F i l e Ta b l e E n t r i e s
14. 3 . 2. 1 . 1
Swa p F i l e I n i t i a l i z a t i o n
14. 3. 2 . 1 . 2
Al l o c a t i o n o f S wa p S l o t s
14. 3. 2. 2
Swa ppe r PTE A r r a y
OUTSWAP O P E RAT I ON
14. 4
14. 4. 1
Se l ec t i o n o f O u t swa p Ca nd i d a te
Ou t swa p o f t h e P r o c e s s Bo d y
14.4.2
Sc a n n i n g t h e Wo r k i ng S e t L i s t
14 . 4 . 2 . 1
Pag e s w i th D i r e c t I /0 i n P r o g r e s s
14. 4. 2. 2
G l o b a l Pag e s
14.4.2. 3
Ex ampl e o f P r o c e s s Bo d y O u t s wa p
14. 4. 2. 4
14.4. 3
O u t swa p o f P r o c e s s He ad e r
Pa r t i a l O u t s wa p
14. 4. 3. 1
Sc a n n i ng t h e F r e e Pag e L i s t
14.4.3.2
14. 1
14. 1 . 1
14 . 1. 2
14 . 1 . 3
14. 2
14. 2 . 1
14. 2. 2
14. 2. 3
14. 3

1 4-1
1 4-1
1 4-2
1 4-2
1 4-2
1 4-4
1 4-4
1 4 -8
1 4- 1 0
1 4- 1 0
1 4- 1 0
1 4- 1 0
1 4-1 1
1 4-1 1
14-11
1 4-1 2
1 4- 1 2
14-12
1 4-1 3
1 4-1 3
1 4-1 3
1 4- 1 3
1 4- 1 4
1 4- 1 4
14-15
1 4- 2 0
1 4-20
1 4- 2 0

C ONTENTS
F l u s h i ng t h e Mod i f i ed Pag e L i s t
14. 4. 3 . 3
O u t swa p o f t h e P r o c e s s He ad e r
14. 4. 3. 4
I N SWAP O P E RAT I ON
14 . 5
Se l e c t i o n o f a n In s wa p C a nd i d a t e
14 . 5. 1
I n s wa p o f t h e P r o c e s s H e a d e r
14 . 5. 2
Re b u i l d i ng t h e P r o c e s s Head e r
14 . 5. 2 . 1
14 . 5. 2 . 2
P l W i n d o w to the P r o c e s s H e a d e r
Re b u i l d i ng t h e P r o c e s s Bo d y
14. 5. 3
Re b u i l d i ng t h e Wo r k i ng S e t L i s t a n d P r o c e s s
14 . 5. 3 . 1
Pag e Ta b l e s
Pag e s w i t h I /0 i n P r o g r e s s Wh e n O u t s wa p
14.5.3.2
Oc c u r r e d
Re s o l u t i o n o f G l o b a l Re a d - On l y Pag e s
14. 5. 3 . 3
Ac t i ve T r a n s i t i on Pag e s
14. 5. 3. 4
Ex ampl e o f a n I n swa p Ope r a t i o n
14 . 5. 3 . 5
F i n a l P r o c e s s i ng o f the I n swa p Ope r a t i o n
14 . 5. 3 . 6
PART V

I N PUT/ O UT PUT

C HA PTER 1 5

VAX/VM S DEVI C E DR IVE R S

D I SK DR IVE R S
15. 1
ECC E r r o r Re c o ve r y
15. 1.1
Of f s e t Re c o ve r y
15. 1.2
Dy n am i c B a d B l o c k Ha n d l i ng
15. 1.3
Mul t i pl e- B l o c k No nc o n t i g uous Vi r t u a l I /0
15. 1.4
Ma ppi ng In fo rm a t i o n
15. 1.4.1
15. 1.4.2
No AC P I n t e r v e n t i o n
AC P I n t e r v e n t i on
15. 1.4.3
MAGN E T I C TAPE DR IVERS
15. 2
TERM I NAL DR I VE R
15. 3
Al t e r n a t e Te rm i n a l D r i v e r s
15. 3. 1
Fu l l Dupl e x Op e r a t i o n
15. 3.2
C h a n n e l s a nd t h e DZ l l
15. 3.3
Typ e -Ah e ad B u f f e r
15. 3.4
15. 4
PS E UDO DEVI C E DR I VE R S
Nu l l Dev i c e D r i v e r
15. 4.1
Ne two r k Dev i c e D r i v e r
15. 4.2
Ma i l box D r i v e r
15. 4. 3
P r o c e s s i ng S e t Mo d e Reque s t s
15.4.3.1
P r o c e s s i ng a Ma i l box Re a d Re que s t
15.4. 3.2
P r o c e s s i ng a Ma i l box Wr i t e Reque s t
15. 4. 3.3
C ON S O L E INTE RFAC E
15. 5
VAX- 1 1 / 7 5 0 C o n s o l e I n t e r f a c e
15. 5. 1
VAX- 1 1 /7 8 0 Co n s o l e I n t e r f a c e
15. 5. 2
Da t a T r a n s f e r b e twe e n the VAX- 1 1 C PU a nd
15. 5. 3
C o n s o l e Dev i c e s
Co n s o l e I n t e r r upt D i s pa t c h i ng
15. 5.4
Co n s o l e Te rm i n a l I n t e r r upts
15. 5. 4 . 1
Co n s o l e B l o c k S t o r ag e Dev i c e I /0
15. 5. 4 . 2
Do ub l e Ma p p i ng o f B u f f e r Pag e s
15. 5. 4. 3
C HAPTE R 1 6

1 4-21
1 4-21
1 4-21
1 4-22
1 4 -2 2
1 4 -2 3
1 4-23
1 4 -2 4
1 4-24
1 4-24
1 4-25
1 4 -2 6
1 4 -2 6
1 4-27

1 5-1
1 5 -2
1 5- 3
1 5 -4
1 5 -4
1 5-4
1 5- 5
1 5-5
1 5- 6
1 5 -7
1 5 -7
1 5 -9
1 5-1 0
1 5- 1 1
1 5-1 1
1 5- 1 1
1 5-1 1
1 5-1 2
1 5-1 2
1 5-1 3
1 5-1 5
1 5-16
1 5-1 6
1 5-1 6
1 5- 1 7
1 5-1 8
1 5- 1 8
1 5-1 8
1 5-1 9

I /0 SYSTEM S ERVI C E S

A S S IGN ING AND D E AS S I GN ING C HANNE LS
16. 1
Ch a nn e l As s i g nm e n t
16. 1.1
Lo c a l Dev i c e As s i g nm e n t
16. 1.1.1

1 6-1
1 6-1
1 6- 2

C ONTENTS
Spec i a l Ac t i o n Wh e n As s i g n i ng a S p o o l ed
Dev i c e
As s i g n i ng a Ch a n n e l t o the Ne t wo r k Dev i c e
16 . 1 . 1 .3
Dev i c e s Loc a t e d o n An o th e r No d e
16 . 1 . 1 .4
Ch a nn e l De a s s i g nm e n t
16 . 1 . 2
DE V I C E AL LOCAT I ON AND DEALLOCAT I ON
16 . 2
Dev i c e Al l o c a t i o n
16 . 2. 1
Dev i c e De a l l o c a t i o n
16 . 2. 2
$ Q I O S Y S TEM S E RVI C E
16 . 3
Dev i c e - I nd e pe n d e n t P r e p r o c e s s i ng
16 . 3 . 1
FDT Ro u t i n e s
16 . 3. 2
I /0 Po s t p r o c e s s i ng
16 . 3. 3
D i r e c t I /0 Compl e t i o n
16 . 3 . 3.1
B u f f e r ed I /0 Comp l e t i o n
16. 3. 3. 2
I /0 CANC E L LAT I ON
16 . 4
MA I LB O X C R EAT I ON AND D E LE T I ON
16 . 5
Ma i l bo x C r e a t i o n
16 . 5 . 1
Ma i l b o x C r e a t i o n i n Sh a r ed Memo r y
16. 5. 2
Ma i l bo x De l e t i o n
16 . 5 . 3
B R OADCAST S Y S TEM S E RVI C E
16. 6
I N FORMAT I ONA L S E RVI C E S
16.7
Dev i c e - I n d e pend e n t I n f o rm a t i o n
16 . 7 . 1
G e t Ch a n n e l /De v i c e I n fo rm a t i o n
16 . 7 . 1 .1
Dev i c e -D e p e nd e n t I n fo rma t i o n
16 . 7 . 2
16 . 1. 1 . 2

PART VI

PROC E S S C REAT I ON AND D E L E T I ON

C HAPTER 1 7

PROC E S S C REAT I ON

17 . 1
17 . 1 . 1
17 . 1 . 2
17 . 1 . 3
17 . 1 . 4
17 . 2
17 . 2 . 1
17 . 2. 2
17 . 3
17 . 3 . 1
17 . 3. 2
C HAPTER 1 8

C R EATE PROC E S S SYS TEM S E RVI C E
Con t r o l F l o w o f C r e a te P r o c e s s
E s t a b l i s h i ng Q uo t a s fo r t h e N e w P r o c e s s
Th e PC B Ve c to r
Fa b r i c a t i o n o f P r o c e s s I Ds
T H E S H E L L PROC E S S
I n s wa p f r o m S H E L L
Co n f i g u r a t i o n o f the P r o c e s s He a d e r
PROC E S S CREAT I ON I N THE C ONTE XT O F THE N EW
PROC E S S
Ope r a t i o n o f PROC S TRT
C a tch Al l Co nd i t i o n Hand l e r

1 6-3
1 6- 3
1 6- 3
1 6- 3
1 6 -4
1 6- 5
1 6- 5
1 6-6
1 6-6
1 6- 7
1 6 -8
1 6 -8
1 6- 9
1 6-1 0
1 6-1 1
1 6- 1 1
1 6- 1 3
1 6- 1 6
1 6- 1 6
1 6- 1 8
1 6- 1 8
1 6- 1 9
1 6- 1 9

1 7- 1
1 7- 1
1 7 -8
1 7-9
1 7-9
1 7-1 2
1 7- 1 3
1 7-1 3
1 7- 1 6
1 7-1 6
1 7-1 9

I MAG E AC T I VA T I ON AND TERM I NA T I ON

18 . 1
IMAG E I N IT IAT I ON
18 . 1 . 1
Imag e Ac t i v a t i o n
Impl em e n t a t i o n o f the Im a g e Ac t i v a t o r
18 . 1 . 1 . 1
18 . 1 . 1 . 2
Ov e r v i e w o f I m ag e Ac t i v a t i o n
Ac t i v a t i o n o f a n Imag e w i th No G l o b a l
18 . 1 . 1 .3
Se c t i o n s
Ac t i v a t i o n o f Imag e Co n t a i n i ng G l o b a l
18 . 1 . 1 .4
Sec ti ons
18 . 1 . 1.5
I n i t i a l Ac t i v a t i o n o f Known Imag e
18 . 1. 1. 6
La t e r Ac t i v a t i o n o f Known Imag e
18 . 1 . 1.7
Ac t i v a t i o n o f Compa t i b i l i t y Mo d e I ma g e s
Imag e S t a r t u p
18 . 1 . 2
18 . 1. 2. 1
T r a n s f e r Ve c to r Ar r a y
18 . 1. 2. 2
I m a g e S t a r t up Sys t em S e r v i c e
xii

1 8-1
1 8-1
1 8-3
1 8-5
1 8-5
1 8-1 1
1 8-1 2
1 8-1 5
1 8-1 5
1 8- 1 6
1 8- 1 6
1 8-1 7

C ONTENTS
18.1.2.3
E x c e p t i o n H a nd l e r f o r Tr a c e b a c k
18.2
I MAG E E X I T
Co n t r o l F l ow o f t h e E x i t Sys t em Se r v i c e
18.2.1
Ex amp l e o f Te r m i n a t i o n H a nd l e r L i s t P r o c e s s i ng
18. 2 . 2
18. 3
IMAGE AND PROC E S S RUNDOWN
18.3.1
C o n t r o l F l ow o f Rund own
PROC E S S PR I VI LEG E S
18. 4
18. 4 . 1
P r o c e s s P r i v i l eg e Ma s k s
S e t P r i v i l eg e Sy s t em Se r v i c e
18. 4. 2
C HAPTER 1 9
19. 1
19. 1.1
19. 2
19. 2. 1
19. 2.2
19. 2. 3
C HAPT E R 2 0

1 8- 1 7
18-18
1 8- 1 8
1 8- 1 9
18-20
18-21
18-23
18-24
18-24

PROC E S S D E LE T I ON
PROC E S S DE L E T I ON IN C ONT E XT OF CALLER
De l e t e P r o c e s s Sys t em Se r v i c e
PROC E S S DE L ET I ON IN C ONTE XT OF PROC E S S B E ING
DE LETED
S p e c i a l Ke r n e l AST f o r P r o c e s s De l e t i o n
De l e t i o n o f a P r o c e s s Th a t Own s S ubp r o c e s s e s
Ex amp l e o f P r o c e s s De l e t i o n wi t h Sub p r o c e s s e s

1 9-1
1 9-1
1 9-2
1 9-2
1 9-5
1 9-6

INT E RAC T I VE AND BATC H JOBS

T H E JOB C ONTRO L L E R AND UNS O L I C I T E D I N PUT
20 . 1
2 0-1
Un s o l i c i ted Te rm i n a l I n pu t
2 0-1
20. 1 . 1
20-4
Th e S U BM I T Comma nd
20. 1 . 2
Un s o l i c i t ed C a r d Read e r I n pu t
2 0 -4
20. 1. 3
20-5
T H E LOG I NOUT I MAG E
20 . 2
20-5
I n t e r a c t i v e Jo b s
20. 2. 1
LOG INOUT Ope r a t i o n fo r Ba t c h Jo b s
2 0 -8
20 . 2. 2
2 0-8
Th e Lo g o u t Ope r a t i o n
20. 2. 3
C OM MAND LANG UAG E INTE R PRETERS AND I MAG E E XE C UT I ON 2 0 -9
20. 3
C L I In i ti a l i za t i on
2 0-9
20. 3. 1
20-11
Comma n d P r o c e s s i ng Lo o p
20. 3. 2
20-12
I m a g e I n i t i a t i o n b y DC L
20. 3. 3
I m a g e Te r m i n a t i o n
20-14
20. 3 . 4
2 0-1 4
Ab n o rm a l I m ag e Te rm i n a t i o n
20. 3. 5
CTR L/Y P r o c e s s i ng
20-1 4
20. 3. 5 . 1
2 0-1 5
20. 3. 5. 2
Th e Pa u s e C a pa b i l i t y
Th e S t a te o f I n t e r r up t ed Imag e s
20-1 5
20. 3. 5 . 3
C ONT I N U E Comma nd
20-16
20. 3. 5. 4
20-16
DE BUG Comm a n d
20. 3. 5. 5
20-16
E X I T Comm a n d
20. 3 . 5 . 6
20-1 6
STOP C o mmand
20. 3 . 5 . 7
PART VI I

S Y S TEM I N I T IA L I Z AT I ON

C HAPTER 2 1

B OOTSTRA P PROC EDUR ES

PROC E S S OR - S PEC I F I C I N I T IA L I Z ATI ON
21. 1
VA X-1 1 /7 5 0 I n i t i a l Bo o t s t r a p Ope r a t i o n
21. 1 . 1
VAX- 1 1 /7 5 0 C o n so l e P r o g r am
21. 1. 1 . 1
Dev i c e - S pe c i f i c ROM P r o g r am
21. 1 . 1 . 2
Bo o t B l o c k P r o g r am
21. 1 . 1 . 3
BOOT 5 8
21 . 1 . 1 . 4
VAX- 1 1 /7 8 0 I n i t i a l Boo t s t r a p Ope r a t i o n
21. 1.2
PR IMARY B O OTSTRA P PROGRAM
21 . 2
Mo t i va t i o n fo r Two Boo t s t r a p P r o g r am s
21. 2. 1
xii i

21-1
2 1-1
2 1-2
2 1-2
21-5
21-5
2 1-6
2 1 -7
2 1-8

CONTENTS
21. 2 . 2
21. 2.3
21 . 2 . 4
21 . 3
21 . 3 . 1
C HAPTER 2 2

Ope r a t i o n o f VMB
Boo t s t r a p D r i v e r and I /O S u b r o u t i ne s
F i l e Ope r a t i o n s
S E C ONDARY BOOTSTRA P PROG RAM ( S YSBOOT )
De t a i l ed Ope r a t i o n o f S Y S B OOT
O P E RATING SYS TEM I N I T I A L I Z AT I ON

22. 1
I N I T IA L E XE C U T I ON OF THE E XE C UT I VE ( I N I T )
22. 1 . 1
Tu r n i ng o n Memo r y Ma n ag em e n t
Do ub l e Ma p p i ng o f I N I T b y SYSB OOT
22. 1 . 1 . 1
I n s t r uc t i o n s Th a t Tu r n o n Memo r y Ma n ag em e n t
22. 1 . 1 . 2
I n i t i a l i za t i on o f the Execut ive
22. 1 . 2
I /O Ad a pt e r I n i t i a l i za t i o n
22. 1 . 3
C PU-De p e nd e n t Ro u t i n e s
22. 1 . 4
22. 2
I N I T I A L I Z AT I ON I N PROC ES S C ONTEXT
S Y S I N I T Pr o c e s s
22. 2 . 1
Po o l Usag e by SYS I N I T
22. 2 . 1 . 1
D e t a i l ed Ope r a t i o n o f SYS I N IT
22. 2. 1 . 2
22. 2 . 2
Th e S TARTUP P r o c e s s
S TARTUP . C OM
22. 2 . 2. 1
S i t e- S p e c i f i c S t a r t up Command F i l e
22. 2 . 2. 2
22. 3
THE S Y S G E N PR OGRAM
22. 3 . 1
C o n t e n t s o f Pa r am e t e r B l o c k
U s e o f Pa r am e t e r F i l e s b y SYSBOOT
22. 3 . 2
U s e o f Pa r am e t e r F i l e s b y SYSGEN
22. 3 . 3
C HAPTER 2 3

2 1 -9
21-14
21-14
2 1-1 5
21-1 5

2 2-1
22-1
22-2
22-3
22-5
2 2-1 0
2 2-1 1
2 2- 1 3
2 2-1 3
2 2- 1 5
22-1 5
2 2- 1 7
22-18
2 2-1 8
22-19
22-19
22-19
2 2-2 3

POW ERFA I L REC OVERY

POWERFAI L S E QUENC E
23. 1
POW E R R E C OVE R Y
23 . 2
23. 2 . 1
I n i t i a l S t e p i n Po we r Re c ov e r y
Po we r Rec o v e r y o n the VAX- 1 1 /7 5 0
23 . 2 . 1 . 1
Po we r Rec o v e r y o n t h e VAX- 1 1/7 8 0
23. 2 . 1 . 2
Ope r a t i o n o f t h e Re s t a r t Ro u t i n e
23. 2. 2
Dev i c e No t i f i c a t i o n
23. 2 . 3
P r o c e s s No t i f i c a t i o n
23. 2 . 4
$ S E T PRA Sys tem S e r v i c e
23. 2 . 4 . 1
D e l i v e r y o f Powe r Re c o v e r y ASTs
23. 2.4.2
MULT I P L E POW E R FA I LURES
23. 3
N e s t ed Powe r Fa i l I n t e r r up t s
23. 3 . 1
P r ev e n t i o n o f Ne s t ed Re s t a r t s
23. 3 . 2
Dev i c e Dr i v e r Ac t i o n
23. 3 . 3
23. 4
POW E R FA I LURE O N THE UN I B US
UN I B US Powe r Fa i l u r e o n the VAX- 1 1 /7 5 0
23. 4 . 1
UN I B US Powe r Fa i l u r e o n the VAX- 1 1 /7 8 0
23. 4 . 2
PART VI I I

M I S C E L LANEOUS TOP I C S

C HA PTER 2 4

SYNC HRON I Z AT I ON TECHN I QU E S

E L EVAT E D I PL
24 . 1
Us e o f I P L $ S YN C H
24. 1 . 1
24. 1 . 2
Ot h e r I P L Leve l s Used fo r Sync h r o n i za t i o n
24. 1 . 2 . 1
I PL 3 1
24. 1.2.2
I PL 24
De v i c e I P L
24. 1.2.3
x iv

2 3-1
2 3-1
2 3-3
2 3- 3
23-4
23-5
2 3-7
2 3-8
2 3-8
2 3-8
23-9
23-9
23-9
23-10
2 3- 1 0
2 3-1 1
2 3- 1 1

2 4 -1
24-3
2 4-3
24-4
24-4
2 4-4

C ONTENTS
Fo r k I PL
24 . 1 . 2 . 4
I P L $ Q U E UEAST
24 . 1 . 3
I PL 2
24. 1 . 4
S E R IA L I Z E D AC C E S S
24 . 2
Fo r k P r o c e s s i ng
24 . 2 . 1
I /0 Po s t p r o c e s s i ng
24 . 2 . 2
MUTUA L E XC LUS I ON S EMAPH OR E S ( MUTEXE S)
24 . 3
Lo c k i ng a M u t e x fo r Re a d Ac c e s s
24 . 3 . 1
Lo c k i ng a M u t e x fo r Wr i t e Ac c e s s
24 . 3 . 2
Mu t e x Wa i t S t a t e
24 . 3 . 3
Un l o c k i ng a M u t e x
24 . 3 . 4
Re s o u r c e Wa i t S t a t e
24. 3. 5
C HAPTER 2 5
25. 1
25. 1 . 1
25. 1 . 2
25. 1 . 3
25. 1 . 4
25. 2
25. 2. 1
25. 2. 2
25. 3
25. 3. 1
25. 3. 2
25. 3. 3
C HAPTER 2 6
26. 1
26 . 1 . 1
26 . 2
26 . 2 . 1
26 . 2 . 2
26 . 2 . 3
26. 2. 4
26 . 2 . 5
C HAPTER 2 7

24-4
24-5
24-5
2 4-6
24-6
24-7
2 4-7
24-9
24-9
2 4- 1 0
24-1 0
24-1 1

DYNAM I C M EMORY A L LOCAT I ON
A L LOCAT I ON S TRATEGY AND I M P LEM ENTA T I ON
Al l o c a t i o n o f Dyn am i c Memo r y
De a l l o c a t i o n o f Dyn am i c Memo r y
S yn c h r o n i z a t i o n
G r a n u l a r i t y o f Al l o c a t i o n
PREA LLOCATED I /0 R E Q U E S T PAC K E T S
Al l o c a t i o n f r om t h e Lo o k a s i d e L i s t
De a l l o c a t i o n t o the Lo o k a s i d e L i s t
US E O F DYNAM I C M EM ORY ·
P r o c e s s Al l o c a t i o n Re g i o n
P a g e d Dyn am i c Mem o r y
No n pa g e d Dy n a m i c Memo r y

2 5-1
2 5- 1
2 5-2
2 5- 7
2 5-9
2 5-9
2 5-9
2 5-1 0
2 5- 1 1
2 5-1 1
2 5-1 1
2 5-1 3

LOG I C A L NAM E S
L OG I C AL NAM E TAB L E S
Log i c a l N a m e B l o c k
LOG I CA L NAM E SYS TEM S ERVI C E S
P r i v i l eg e a n d P r o t e c t i o n Ch e c k s
Log i c a l Name Ta b l e M u t e x e s
Log i c a l Name C r e a t i o n
Lo g i c a l Name De l e t i o n
Lo g i c a l Name T r a n s l a t i o n

26-1
26-1
26-3
26-4
2 6-4
26-4
2 6-4
2 6- 5

M I SC E LLANEOUS S YS T EM S ERVI C E S

C OMMUN I C AT I ON W I TH S Y S TEM PROC E S S E S
27. 1
Ac c o un t i ng Ma n ag e r ( Jo b Co n t r o l l e r )
2 7 . 1 . 1.
Symb i o n t Ma n ag e r ( Jo b Co n t r o l l e r )
27 . 1 . 2
Op e r a t o r Commun i c a t i o n s
27 . 1 . 3
E r r o r Logg e r
27 . 1 . 4
SYS T EM M E S SAG E F I LE S ERVI C E S
27 . 2
G e t Me s s ag e Sys t em S e r v i c e
27. 2. 1
F i n d i ng t h e Me s s ag e F i l e s
27 . 2 . 1 . 1
S e a r c h i ng a Lo c a t e d Me s sag e S e c t i o n
27 . 2 . 1 . 2
P u t Me s s a g e Sy s t em S e r v i c e
27. 2 . 2
P r o c ed u r e E XE $ E XCMSG
27 . 2 . 3
PROC E S S INF ORMAT I ON ( $G E TJ P I )
27 . 3
Ope r a t i o n o f t h e $ G E TJ P I Sys tem S e r v i c e
27 . 3. 1
$G E TJ P I Spec i a l Ke r n e l A S Ts
27 . 3 . 2
W i l d C a r d S uppo r t i n $G E TJ P I
27 . 3. 3
FORMATT I NG S U P PORT
27 . 4
T i m e C o nv e r s i o n S e r v i c e s
27 . 4 . 1
F o r m a t ted A S C I I O u t p u t
27. 4. 2

27-1
2 7- 1
2 7-2
2 7- 3
27-3
2 7- 4
2 7- 4
27-5
2 7- 6
27-6
2 7-7
2 7-7
2 7-8
27-9
27-1 0
2 7- 1 0
27- 1 1
27-1 1

C ONTENTS
Pag e

APPEND I C ES
APPEND I X A

US E OF L I S T ING AND MAP F I L ES

H I NTS IN R EAD ING T H E E XE C UT IVE L I S T INGS
A.1
S t r uc t u r e of a MAC RO L i s t i ng F i l e
A.1. 1
$ x y z D E F Ma c r o s
A. l. l. l
Th e Ro u t i n e B o d y
A. 1. 1. 2
The VA X- 1 1 I n s t r uc t i o n S e t a nd Ad d r e s s i ng Mo d e s
A. 1 . 2
Te c h n i que s fo r I n c r e a s i ng In s t r uc t i o n Speed
A. l . 2. 1
Un us ua l I n s t r uc t i o n a nd Ad d r e s s i ng Mo d e Us a g e
A. l . 2. 2
Us e o f the R E I I n s t r uc t i o n
A. 1. 3
Reg i s t e r C o n v e n t i o n s
A. 1 . 4
E l i m i n a t i o n o f S e l d om - U s ed Cod e
A. l . 5
E l i m i n a t i ng the Bo o t s t r a p P r og r am s
A. 1 . 5. 1
S e l d om-U s e d Sys t em Ro u t i n e s
A. 1 . 5. 2
Dyn am i c a l l y Lo c k i ng Co d e o r Da t a i n to Memo r y
A. 1 . 6
Lo c k i ng Pag e s i n Ex t e r n a l Imag e s
A. l . 6 . 1
Pl a c i ng Co d e i n t h e No n pag ed E x e c u t i v e
A. 1 . 6 . 2
Dy n am i c Lo c k i ng o f Pag e s
A. l . 6. 3
US E O F MAP F I LE S
A. 2
The Ex e c u t i v e Ma p SYS . MAP
A. 2. 1
RMS . MAP a nd DC L . MAP
A. 2.2
D e v i c e D r i v e r Ma p F i l e s
A. 2. 3
C PU-D e p e nd e n t Ro u t i n e s
A. 2. 4
O t h e r Ma p F i l e s
A.2. 5
T H E S YS TEM D UM P ANA LY Z E R ( S DA )
A. 3
G l o b a l Lo c a t i o n s
A. 3 . 1
L a yo u t o f Sy s t em V i r t ua l Ad d r e s s Spa c e
A. 3. 2
La yo u t o f P l S pa c e
A. 3. 3
I NTERPR E T I NG MDL F I L E S
A. 4
S a m p l e S t r uc t u r e De f i n i t i o n s
A. 4. 1
Common l y Us ed M D L Comma nd s
A. 4 . 2
$ S TRUC T D i r e c t i v e
A. 4 . 2. 1
F Di r e c t i ve
A.4. 2. 2
L Di r ect ive
A. 4. 2. 3
E Di r ec t i v e
A. 4 . 2. 4
S Di r ec t i ve
A.4. 2. 5
C Di r e c t i ve
A. 4 . 2 . 6
M a nd P D i r e c t i v e s
A. 4 . 2. 7
B i t F i e l d De f i n i t i o n s - Th e V D i r e c t i v e
A.4. 3
APPEND I X B
B.l
B. 1. 1
B.1.2
B.l. 3
B.1.4
B.l.5
B.1.6
B.1.7
B.l.8
B.1.9
B . l . lO
B. 1 . 11
8. 1 . 12
8. 1 . 13
8 . 1 . 14

A- 1
A- 1
A-1
A-2
A- 4
A- 5
A- 7
A-8
A- 1 0
A- l l
A- l l
A- l l
A- 1 2
A- 1 2
A- 1 2
A- 1 3
A-1 4
A-1 4
A- 1 5
A- 1 6
A- 1 6
A- 1 6
A- 1 6
A- 1 7
A- 1 7
A- 1 7
A- 1 7
A- 1 8
A-1 8
A- 1 8
A- 2 2
A- 2 2
A- 2 2
A- 2 2
A- 2 2
A- 2 3
A- 2 3

E X E C U T I VE DATA AREAS
B-1
S TAT ICALLY A L LOCATED E XE C UT IVE DATA
B-1
Sy s t em S e r v i c e Ve c to r A r e a ( $ $ $ 0 0 0 )
F i l e Sys tem Pe r f o rm a n c e Mo n i to r Da t a ( $ $ $ 0 0 0 PM S ) B-2
B-2
M i s c e l l a n e o us Bug c hec k I n fo rma t i o n ( $ $ $ 0 2 5 )
Da t a S t r uc t u r e s fo r D r i v e r s L i n k ed wi th VMS
B-2
($$$100)
D r i v e r P r o l og u e Ta b l e s ( $ $ $ 1 0 5 PROLOG U E )
B-3
L i n k ed D r i v e r Cod e ( $ $ $ 1 1 5 D R I V E R )
B-4
Mem o r y Ma n ag em e n t Da t a ( $ $ $ 2 1 0 )
B-4
B-5
Pag e Fa u l t Mo n i to r Da t a ( $ $ $ 2 1 5 )
S c h ed u l e r Da t a ( $ $ $ 2 2 0 )
B-5
M emo r y Ma n ag em e n t Da t a ( $ $ $ 2 2 2 )
B-7
P r o c e s s Da t a fo r Sy s t em P r o c e s s e s ( $ $ $ 2 3 0 )
B-7
Co n so l e I n t e r r up t D i s p a t c h Da t a ( $ $ $ 2 5 0 )
B-8
S YS C OMMON - M i s c e l l a n e o u s Ex e c u t i v e Da t a
B-8
( $$$260 )
S t a t i s t i c s U s ed by D I S PLAY ( $ $ $ 2 7 0N P )
8- 1 2
xvi

C ON TENTS
E n t r y Po i n t s fo r C PU-D e p e nd e n t Ro u t i n e s
B. 1 . 15
Ta b l e o f Ad j us t a b l e SYS B OOT Pa r am e t e r s ( $ $ $ 9 1 7 )
B. 1 . 16
Rem a i nd e r o f E x e c u t i v e Imag e
B. 1 . 17
DYNAM I CA L LY A L LOCATED E XE C UT IVE DATA
B.2
Re s t a r t Pa r am e t e r B l o c k
B. 2. 1
PFN D a t a Ba s e
B.2. 2
Pag ed Dyn a m i c Mem o r y
B.2. 3
N o n p a g e d Dyn am i c Memo r y
B.2.4
I n t e r r u pt S t a c k
B.2.5
Sys t em Co n t r o l B l o c k
B.2.6
Ba l ance Slot Area
B.2.7
Sy s t em He a d e r
B.2.8
Sys t em Pag e Ta b l e
B.2.9
G l o b a l Pa g e Ta b l e
B.2. 10
PROC E S S -S PE C I F I C E XE C UT I VE DATA
B. 3
P l Po i n t e r Pa g e
B. 3. 1
O t h e r P l Spa c e D a t a A r e a s
B.3. 2
Da t a Pag e s fo r Command Lang uag e I n t e r pr e t e r
B.3.2.1
P r o c e s s A l l o c a t i o n Reg i o n
B. 3. 2 . 2
Compa t i b i l i t y Mo d e Co n t e x t Pag e
B. 3. 2. 3
P r o c e s s I /O Segme n t
B. 3. 2 . 4
A PPEN D I X C
C.1
C.2
C.3
A P PEND I X D

B-1 3
B-1 4
B-2 2
B-22
B-22
B-22
B-22
B-2 3
B-2 3
B-23
B-2 3
B-2 3
B-23
B-23
B-24
B-24
B-26
B-2 6
B-2 7
B-27
B-27

NAM ING C ONVENT I ONS
P UB L I C SYMBOL PATTERNS
OBJECT DATA TYPE S
FAC I L I TY PREF I X TAB L E

C-1
C-8
C-9

DATA STRUC TURE D E F I N IT I ONS

E XE C UT I VE DATA STR UC TUR E S
D. l
ACB - AST C o n t r o l B l o c k
D. l. l
ACC - Ac c o un t i ng a nd Te rm i n a t i o n Me s s ag e B l o c k
D. l . 2
ARB - Ac c e s s R i g h t s B l o c k
D. l . 3
B RD - B r o ad c a s t Me s s ag e D e s c r i pto r B l o c k
D. 1.4
C E B - Common Ev e n t B l o c k
D. l . 5
C HF - C o nd i t i o n H a nd l e r A r g um e n t L i s t A r r ay s
D. l . 6
DM P - H e a d e r B l o c k o f Sy s t em Dump F i l e
D. l . 7
EMB - E r r o r Lo g Me s s a g e B l o c k
D. l . 8
EMB , CR - C r a sh / Re s t a r t E r r o r Log En t r y Fo rma t
D. l . 8 . 1
EMB , HD - Lo ngwo rd H e a d e r fo r A l l En t r i e s
D. l . 8 . 2
FKB - Fo r k B l o c k
D. l . 9
G S D - G l o b a l S e c t i o n De sc r i pto r
D. l . l O
IAC - Imag e Ac t i v a t i o n Co n t r o l F l ag s
D. 1 . 11
I FD - Imag e F i l e De sc r i pto r B l o c k
D. 1. 12
I Hx - Imag e He a d e r F i e l d s
D. 1 . 13
I HA - I m a g e He a d e r Tr a n s f e r Ad d r e s s A r r a y
D. l . l3. 1
I H D - I m a g e He a d e r Re c o r d De f i n i t i o n s
D. 1 . 1 3 . 2
Imag e
He ad e r
Id e n t i f i c a t i o n Se c t i o n
IHI
D. 1 . 13 . 3
I H P - I m ag e He a d e r Pa t c h Se c t i o n
D. 1 . 13 . 4
I H S - I m ag e He a d e r
Symbo l
Ta b l e a n d De b ug
D. 1 . 1 3 . 5
Sec t i o n
I S D - Imag e Sec t i o n De sc r i pto r
D. 1 . 14
J I B - Job I n fo rma t i o n B l o c k
D. 1 . 15
KFH - Known F i l e Head e r
D. 1 . 16
D. l . l7
K F I - Known F i l e En t r y
K F P - Kn own F i l e Po i n t e r B l o c k
D. l . l8
LOG - Log i c a l Name B l o c k
D. l . l9
M B X - Sh a r ed Memo r y Ma i l box Co n t r o l B l o c k
D. l . 20
xvi i

D-3
D-3
D-3
D-4
D-4
D-4
D-4
D- 5
D-5
D-5
D-5
D-5
D- 6
D- 6
D-6
D-6
D-6
D-7
D-7
D-7
D-7
D-7
D-7
D-7
D-8
D-8
D-9
D-9

C ONTENTS
0. 1 . 21
MCHK - Ma c h i ne Ch e c k E r r o r Ma s k B i t De f i n i t i o n s
0. 1 . 22
MPM - M u l t i po'r t Memo r y Ad a p t e r Reg i s t e r s
0. 1 . 23
MTX - M u t e x ( Mu t u a l E x c l u s i o n S em a ph o r e }
PC B - P r o c e s s Co n t r o l B l o c k
0 . 1 . 24
So f t wa r e P r o c e�s C o n t r o l B l o c k
0 . 1 . 2 4,. 1
0 . 1 . 24 . 2
Ha r dwa r e P r o c e s s C o n t r ol B l o c k
PF L - P a g e F i l e Co n t r o l B l o c k
0. 1 . 25
PFN - PFN Da t a Ba s e De f i n i t i o n s
0. 1 . 26
PHD - P r o c e s s He a d e r
0 . 1 . 27
P LV - P r i v i l eg ed L i b r a r y Ve c to r
0 . 1 . 28
P QB - P r o c e s s Quo t a B l o c k
0. 1 . 29
PRM - P a r ame t e r De sc r i pto r B l o c k
0 . 1 . 30
PS L - P r o c e s so r S t a t u s Longwo rd
0. 1 . 31
PT E - P a g e Ta b l e E n t r y Fo rma t s
0. 1 . 32
PTR - P o i n t e r Co n t r o l B l o c k
0 . 1 . 33
RBM - R e a l - T i m e B i tma p
0. 1 . 34
R PB - R e s t a r t Pa r am e t e r B l o c k
0. 1 . 35
S E C - S e c t i o n Ta b l e En t r y
0. 1 . 36
S F T - S wa p F i l e Ta b l e E nt r y
0 . 1 . 37
S H B - S h a r ed Memo r y Co n t r o l B l o c k
0. 1 . 38
S H D - S h a r ed Memo r y Da t a Pag e
0 . 1 . 39
S T S - R e t u r n S t a t u s F i e l d De f i n i t i o n s
0. 1 . 40
T Q E - T i m e r Qu e ue E l eme n t
0. 1 . 41
VA - V i r t ua l Ad d r e s s F i e l d D e f i n i t i o n s
0 . 1 . 42
WQH - S c h e d u l e r Wa i t Que ue H e ad e r
0. 1 . 43
WS L - Wo r k i ng Se t L i s t E n t r y F i e l d De f i n i t i o n s
0. 1 . 44
CONSTANT S
0. 2
B T D - B o o t s t r a p Dev i c e Co d e s
0.2.1
C A - C o nd i t i o n a l As s emb l y Pa r ame t e r s
0. 2. 2
DYN - D a t a S t r uc t u r e Typ e De f i n i t i o n s
0. 2. 3
I 0 7 x x - I /O Spa c e Ad d r e s s S p e c i f i c a t i o n s
0. 2. 4
! 0 7 5 0 - VAX- 1 1 /7 5 0 Phys i c a l Ad d r e s s Spa c e
0. 2. 4 . 1
De f i n i t i o n s
! 0 7 8 0 - VAX- 1 1 /7 8 0 Ph ys i c a l Ad d r e s s Spa c e
0. 2. 4 . 2
De f i n i t i ons
I P L - P r o c e sso r P r i o r i t y Le v e l De f i n i t i o n s
0. 2. 5
J P I - $G E TJ P I Da t a I d e n t i f i e r De f i n i t i o n s
0. 2.6
MSG - S y s t em Wi d e Ma i l bo x Me s s a g e Type s
0. 2 . 7
NOT - N e x u s ( Ad a pt e r ) D e v i c e Type
0. 2 .8
P Q L - P r o c e s s Quo t a L i s t C o d e s
0. 2.9
P R - P r o c e sso r Reg i s t e r De f i n i t i o n s
0. 2 . 10
0. 2 . 11
PR I - P r i o r i t y I n c r emen t C l a s s De f i n i t i o n s
0. 2. 12
P R T - P r o t ec t i o n F i e l d D e f i n i t i o n s
PRV - P r i v i l eg e B i t De f i n i t i o n s
0. 2 . 13
R S N - R e s o u r c e Name De f i n i t i o n s
0. 2. 14
SGN - S YS G E N Pa r am e t e r C o n s t a n t De f i n i t i o n s
0. 2 . 15
S S - S y s t em S e r v i c e Compl e t i o n Cod e s
0. 2. 16
S TATE - S c h e d u l i ng S t a t e s
0. 2 . 17
DATA S TR UC TUR E S US ED B Y T H E I / 0 SYS TEM
0. 3
DATA S TR UC TUR E S US ED BY F I LE S - 1 1
0. 4
M I S C E L LAN EOUS DATA S TR UC TUR E S AND C ONSTANTS
0. 5

xvi i i

D- 9
D-9
D-9
D-9
D-1 0
D- 1 0
D- 1 0
D- 1 0
D-1 3
D-1 3
D-13
D-13
D-16
D-16
D-16
D-16
D-16
D-1 7
D-17
D-17
D-17
D-17
D-1 7
D- 1 8
D- 1 8
D-18
D-18
D-18
D- 18
D- 1 9
D- 1 9
D-19
D- 2 1
D- 2 1
D- 21
D- 2 1
D- 2 2
D- 2 2
D- 2 2
D- 2 2
D- 2 3
D- 2 3
D- 2 3
D- 2 4
D- 2 4
D- 2 4
D- 2 5
D- 2 6
D- 2 7

CONTENTS
A PP E ND I X E
E.l
E.l. l
E.l.2
E.l.3
E.2
E. 2. 1
E.2.2
E . 2. 3
E.2.4
E.3
E. 3.1
E.3.2
E.4
A P PEND I X F
F. l
F.l.l
F.l . 2
F. 2
F.2.1
F.2.2

S I Z E OF SYS TEM VI RTUA L ADDR E S S S PAC E
S I Z E OF PROC E S S H EADE R
P r o c e s s Pa g e Ta b l e s
Wo r k i ng S e t L i s t and P r o c e s s S e c t i o n Tab l e
P r o c e s s He ad e r Pag e A r r a y s
S Y S T EM V I R TUA L ADDR E S S S PA C E
S y s t em V i r t ua l Ad d r e s s S p a c e a nd SYSB OOT
Pa r am e t e r s
S y s t em P a g e T a b l e a nd t h e PFN Da t a Ba s e
App r o x i ma t i o n U s ed b y S Y S B OOT
Re n o r ma l i za t i o n of S PTREQ
P HYS ICAL M EMORY R E QU I R EM ENTS OF THE E XE C UT I VE
Ph y s i c a l Memo r y U s e d by the E x e c u t i v e
Sy s t em P r o c e s s e s
S I Z E S O F P I EC E S O F P l S PAC E

E-1
E-3
E-3
E-3
E-5
E- 1 0
E- 1 3
E- 1 4
E- 1 5
E- 1 5
E- 1 5
E- 1 7
E- 1 8

VAX/VM S VE R S I ON 2 . 2 E NHANC EMENTS
S E COND LOOKAS I DE L I S T
I n i t i a l i z a t i o n o f S e c o nd Lo o ka s i d e L i s t
No n pag e d Po o l Al l o c a t i o n a nd De a l l o c a t i o n
C HANG E T O S U PPORT A LARG E NUMB E R O F PROC ES S E S
Swa p F i l e I n i t i a l i z a t i o n
Process Lim i ts

F-1
F-2
F-2
F-3
F-3
F-3
Index-1

I NDE X

xix

CONTENTS
Pag e
F IGUR E S
F I GURE

1-1
1-2
1-3
1-4
1-5
1-6
1-7
1 -8

Da t a S t r uc t u r e s Th a t De sc r i be P r o c e s s Co n t e x t
L a ye r ed De s i g n o f VAX/VM S
I n t e r ac t i o n Be twe e n Compo n e n t s o f VMS Ke r n e l
Me th o d s fo r A l t e r i ng Ac c e s s Mo d e
Pa t h s i n to Compo n e n t s o f VM S K e r n e l
L a yo ut o f Sy s t em V i r t ua l Ad d r e s s S pa c e
La yo u t o f P l S pa c e
P O Spa c e Al l o c a t i o n

1-2
1-5
1-9
1-12
1-1 3
1-22
1-23
1-25

2-1
2-2

S y s t em Co n t r o l B l o c k
S i g n a l A r r a y Bu i l t by Ha r d wa r e
a nd
Exc e pt i o n
Ro u t i n e s
Rem ova l o f C a l l F r am e by L I B $ S IGNA L
S i g n a l a nd Mec h a n i sm A r r a ys
O r d e r o f S e a r c h fo r C o n d i t i o n Ha nd l e r
Mo d i f i ed S e a r c h wi th M u l t i pl y Ac t i v e S i g n a l s
C a l l F r a m e Mod i f i c a t i o n b y SYS $UNW IND
Mo d i f i ed Unw i nd wi t h Mul t i pl y Ac t i v e S i g n a l s

2-4

2 -3
2-4
2-5
2-6
2-7
2-8
3-1
3-2
3-3
3-4
3-5
3 -6
3-7
3-8
3-9
4-1
4-2
5-1
5-2
6-1
6-2
6-3
6-4
6-5
6-6
6-7
8-1
8-2
8-3

2-9
2-1 5
2-17
2-1 9
2-22
2-2 5
2-29

Co n t e n t s o f t h e Sys t em S e r v i c e Ve c to r s
C o n t r o l F l o w o f Sy s t em
S e r v i c e s Th a t Ch a n g e
Mo d e
C o n t r o l F l ow o f Sy s t em S e r v i c e s Th a t Do
No t
Ch a ng e Mo d e
C o n t en t s o f t h e VM S Ch a ng e Mo d e D i s pa tche r s
E r r o r Ro ut i n e s a nd Common Ex i t Pa t h fo r Sys t em
S e r v i c e s a n d RM S C a l l s
C o n t r o l F l o w o f RM S D i s pa tch i ng
Sta te o f
the
S t a c k W i th i n
a
Us e r -W r i t t e n
Di spa tch e r
D i s p a tc h i ng t o Us e r -W r i t t e n Sy s t em S e r v i c e s
S t r uc t u r e o f P r i v i l eg ed Sh a r e a b l e Imag e

3-1 4
3- 1 5
3- 1 6

Co n t e n t o f S o f twa r e I n t e r r up t Re que s t Reg i s t e r
a nd So f twa r e I n t e r r up t S umma r y Reg i s t e r
L a yo u t o f Fo r k Bl o c k

4-2
4-5

A S T Co n t r o l B l o c k a nd AST Que ue
in
So f twa r e
PC B
A r g um e n t L i s t P a s s ed to AST by D i s pa tche r

5-3
5-8

Sys t em C o n t r o l B l o c k Ve c to r Fo rm a t
Sy s t em C o n t r o l
B l o c k Ve c to r s
fo r
Ha r d wa r e
I n t e r r up t s
C o n t r o l F l ow i n S e r v i c i ng a UN I B U S I n t e r r up t
C o n t r o l F l ow i n S e rv i c i ng a MAS S B US I n t e r r upt
Con t r o l Fl ow in S e r v i c i ng a DR 7 8 0 I n t e r r up t
Co n t r o l Fl ow i n S e r v i c i ng a MA7 8 0 I n t e r r up t
Ex t e nd i ng In t e r r up t D i s pa tch Mec h a n i sm w i th
the Co n n e c t - t o - I n t e r r up t Fa c i l i ty
Process
Co n t r o l
Block
Fi elds
Used
in
S c h e d u l i ng
S o f twa r e P r i o r i t i e s a nd P r i o r i ty Ad j us tm e n t s
Compu t a b l e ( Ex e c u t a b l e ) S t a t e Que u e s
XX

3-2
3-6
3 -7
3 -8
3-9
3-1 1

6-2
6-3
6-8
6-1 2
6-1 4
6-1 5
6-17
8-2
8-6
8-1 0

C ONTENTS
( F IG URES , c ont. )
8-4
8-5
8-6
8-7

Fo rma t o f Wa i t S t a t e Q u e ue Head e r s
S t a te T r a n s i t i o n D i a g r am
H a r dwa r e P r o c e s s Co n t r o l B l o c k
S c h ed u l e r Ro u t i n e Th a t S e l e c t s Ne x t
C a nd i d a t e

9-1
9-2
9-3
9 -4
9-5

S o f twa r e PC B F i e l d s Th a t S u ppo r t Eve n t Fl ag s
L a yo u t o f Comm o n E v e n t B l o c k
Common Ev e n t F l ag Wa i t Q u e u e s
R e l a t i o n sh i p B e twe e n Ma s t e r a nd S l a v e C E B
Sh a r ed
Memo r y
Comm o n
Ev e n t
Fl ag
Da t a
S t r uc t u r e s

9-3
9-4
9-5
9-1 6

1 0- 1

La yo u t o f a T i me r Que ue E l eme n t

1 0-7

1 1-1
1 1-2
1 1-3
1 1-4
1 1-5
1 1-6
1 1 -7
1 1 -8
1 1 -9
1 1 -1 0
1 1-11
1 1-1 2
1 1-1 3

D i s c r e t e Po r t i o n s o f t h e P r oc e s s He a d e r
P r o c e s s Pa g e T a b l e s
D i f f e r e n t Fo rms o f Pag e Ta b l e En t r y
Wo r k i ng S e t L i s t
Fo rma t o f Wo r k i ng S e t L i s t En t r y
P r o c e s s S e c t i o n Ta b l e
La yo u t o f P r o c e s s S e c t i o n Ta b l e En t r y
P r o c e s s H e a d e r Pag e A r r a y s
PFN Da t a B a s e Ar r a y s
Po s s i b l e C o n t e n t s o f PFN BAK Ar r a y E l em e n t
Co n t e n t s o f PFN S TATE Ar r ay E l em e n t
Co n te n t s o f PFN TYPE Ar r a y E l em e n t
Ex ampl e o f
Fr e e
Pa g e
L i s t Showi n g
L i n ka g e
Me thod
L a yo u t of G l o b a l S e c t i o n De sc r i pto r
The
Sy s t em H e ad e r
Co n t a i n i ng
the
Sy s t em
Wo r k i ng S e t L i s t a nd t h e G l o b a l Se c t i o n T a b l e
La yo u t o f G l o b a l o r Sys t em Sec t i o n T a b l e E n t r y
Lo c a t i o n o f G l o b a l Pag e Ta b l e a t V i r t ua l
End
o f Sy s t em Pa g e T a b l e
Re l a t i o n s h i ps Amo ng
Gl obal
Sec t i on
Da t a
S t r uc t u r e s
Re l a t i o n sh i p B e twe e n P r o c e s s PT Es a nd G l o b a l
PTEs
Ba l a n c e S l o t s Co n t a i n P r o c e s s H e ad e r s
P r o c e s s H e a d e r Ve c to r Ar r a ys
Pag e F i l e Da t a Ba s e
Swa p Fi l e Da t a B a s e
Swa ppe r a n d Mo d i f i ed Pa g e Wr i te r PTE Ar r a y s
Phys i c a l L a yo u t o f Sh a r ed Memo r y
Co n t e n t s o f Sh a r ed Memo r y Co n t r o l B l o c k
Contents o f
Sha r ed
Mem o r y G l o b a l
Sec t i on
De s c r i pto r

1 1-2
1 1-3
1 1-5
1 1-8
1 1-1 0
1 1-1 2
1 1-1 3
1 1-1 4
1 1 -1 5
1 1-1 6
1 1- 1 7
1 1-18

1 1-14
1 1- 1 5
1 1-1 6
1 1- 1 7
1 1-18
1 1-19
1 1-20
1 1-21
1 1-22
1 1- 2 3
1 1-24
1 1-2 5
1 1 - 26
1 1-2 7
1 2- 1
1 2-2
1 2-3
1 2-4
1 2-5

Execut i on

Fo rma t o f V i r t ua l Ad d r e s s Showi ng F i e l d s
Used
t o Lo c a t e Pa g e Ta b l e En t r y Th a t Ma ps the Pag e
S t a te o f
the
Ke r n e l
Stack
Fo l l owi ng
a
T r a n s l a t i o n-No t-Va l i d Fa u l t
S t a t e D i a g r am
S h o w i ng
Pag e Trans i t i o n s
fo r
P r i va t e
Sec t i on
Pag e
Th a t
I s No t Co py o n
Re f e r e n c e
S t a te D i a g r am
Sh o w i ng
Page Trans i t i ons
fo r
P r i v a t e a n d G l o b a l C o py-o n-Re f e r e n c e Pag e s a nd
f o r Dema n d Z e r o Pag e s
T r a n s i t i o n s f o r Pag e s Lo c a t ed i n a
Pag e
Fi l e
xxi

8-10
8-1 2
8-21
8-24

9-1 7

1 1-1 9
1 1- 2 1
1 1-22
1 1-23
1 1-24
1 1-2 5
1 1-26
1 1- 2 8
1 1-29
1 1-31
1 1-33
1 1- 3 6
1 1-38
1 1- 4 0
1 1-41
1 2- 2
1 2- 2
1 2- 5
1 2- 9

C ON TENTS
( F I G URES , c o n t . )

1 2-6
1 2-7
1 2-8
1 4-1
1 4-2
1 4-3
1 4-4
1 4-5
1 4-6
1 4 -7
1 5-1
1 5-2
1 5-3
1 5-4
1 6-1
1 6-2
1 6-3
1 6-4
1 6 -5
1 7-1
1 7-2
1 7-3
1 7-4
1 7-5
1 7- 6
1 8-1
1 8-2
1 8-3
1 8-4
1 8- 5
1 8-6
1 8-7
1 8-8
1 8-9

( Co n t i n ua t i o n o f F i g u r e 1 2 - 4 )
Examp l e o f Pag e Tr a n s i t i o n s Ma d e by a
G l obal
Pa g e Ma pped b y Two P r o c e s s e s
Trans i t ions
Examp l e
of
Pag e
fo r
G l oba l
Co py-on-R e f e r e n c e Pag e s
Examp l e o f C l u s t e r ed Wr i t e to a P a g e F i l e
Pa r a l l e l s Be twe e n I n swa p C a nd i d a t e
S e l ec t i o n
by
the
Swa p pe r
a nd
E x e c u t i o n C a nd i d a t e
S e l e c t i o n by t h e S c hed u l e r
Ex ampl e Wo r k i ng S e t L i s t B e f o r e Ou t s wa p S c a n
Examp l e Wo r k i ng S e t L i s t A f t e r O u t s wa p S c a n
P r o c e s s Pa g e
Ta b l e
Ch a n g e s A f t e r
Swa p pe r ' s
Wr i t e Comp l e te s
Wo r k i ng
Set
L i s t a nd
Swa ppe r Ma p
B e fo re
Ph ys i c a l Pa g e A l l o c a t i on
Wo r k i ng
Set
L i s t a nd
Swa ppe r
Ma p
Af t e r
Ph ys i c a l Pa g e A l l o c a t i o n
Wo r k i ng S e t L i s t and Re bu i l t Pag e Ta b l e s
Te rm i n a l I /0 S y s t em
Comm a n d s t h a t As s em b l e a nd L i n k t h e
Te r m i n a l
Dr i v e r
Ro l e o f N E TDR I VE R i n
P r o c e s s i ng Ne t wo r k
I /0
Reque s t s
La yo u t o f Ma i l bo x M e s s ag e B l o c k
Da t a
S t r uc t ur e s
As so c i a t e d
wi t h
Ma i l bo x
Crea ti on
Co n t e n t s o f a S h a r ed Memo r y Ma i l bo x C o n t r o l
Block
Da t a S t r uc t ur e s As s o c i a t ed wi th Sh a r ed Mem o r y
Ma i l box C r e a t i o n
La yo u t o f a B r o a d c a s t De sc r i pto r B l o c k
La yo u t o f a Wr i t e B u f f e r Pa c k e t
Sampl e Mo vem e n t o f
Pa r am e t e r s
in
Process
Crea t i on
Re l a t i o n sh i p B e twe e n J I B a nd PC Bs o f
Seve ral
P r o c e s s e s i n t h e Same Job
Sampl e PC B Ve c to r
Fa b r i c a t i o n o f P r o c e s s I Ds
Lo c a t i o n o f S h e l l
Process
in
the
Exec u t i ve
Imag e F i l e
Remova l o f
Process
Pa r am e t e r s
f r om
Process
Quo t a B l o c k
Co n t e n t s o f Imag e He a d e r
G e n e r a l Fo rm o f I m a g e S e c t i o n De sc r i p to r
I S D a nd Pa g e Ta b l e E n t r i e s fo r P r o c e s s Pr i v a t e
Se c t i o n
I S D a n d Pa g e Tab l e
En t r i e s
fo r
Dem a nd
Z e ro
Se c t i o n
I S D a nd Pa g e Ta b l e E n t r i e s fo r G l o b a l Sec t i o n
Fo rma t o f Known F i l e En t r y
Tr a n s f e r Ve c t o r A r r a y
Samp l e Te r m i n a t i o n H a nd l e r L i s t s
Lo w Ad d r e s s E n d o f P l S p a c e Th a t I s De l e t ed a t
Imag e Ex i t

xx i i

1 2-1 1
1 2- 1 3
1 2- 1 6
1 2- 2 7

1 4-5
1 4-1 7
14-18
1 4- 1 9
1 4-28
1 4-29
1 4-30
1 5-7
1 5-8
1 5- 1 2
1 5- 1 4
1 6-1 3
1 6- 1 4
1 6-1 5
1 6- 1 7
1 6- 1 8
1 7-3
1 7-5
1 7-8
1 7- 1 1
1 7- 1 2
1 7- 1 7
1 8-6
1 8-7
1 8-9
1 8-1 0
1 8-1 3
1 8-1 4
1 8- 1 6
1 8-1 9
1 8- 2 2

C ONTENTS
( F I G UR E S , c o n t . )
1 9- 1

S am p l e J o b to I l l u s t r a t e P r o c e s s De l e t i o n w i t h
Subprocesses

2 0- 1

S t e ps I n vo l v ed i n
In i t i a t i ng
an
I n t e r ac t i ve
Job
S t e ps
I n v o l ved
in
I n i t i a t i ng
a
Ba t c h Jo b
Th r o ug h
a
S UBM I T Comma nd a nd Th r o ug h a Ca r d
Read e r
S i mpl i f i e d
Co n t r o l
F l ow Th r o ug h
a
Comm a n d
L a ng u a g e I n t e r p r e t e r
A r g um e n t L i s t Pa s s e d to a n Imag e b y PROC S TRT
o r a CLI

2 0- 2
20-3
20-4
21-1
21-2
22-1

Ph y s i c a l
Memo r y L a yo u t s U s e d b y VMB
a nd
S Y S B O OT
Ph ys i c a l Mem o r y La yo u t U s e d by the Ex ec u t i v e

1 9-6
2 0-2
2 0-3
20-1 0
20-1 3
21-1 3
21-19

22-5

Do ub l e U s e o f Sy s t em
Page Ta b l e
Ent r i e s
by
!NIT
Ad d r e s s S pa c e Ch a ng e s a s Memo r y Ma n a g e m e n t
Is
E n a b l ed b y ! N I T
L i nkag e
a nd
Cont r o l
Flow
Ex ampl e
fo r
C PU-De p e n d e n t Ro u t i n e s
Mo v em e n t o f
Pa r am e t e r
Da t a b y SYS BOOT a nd
SYS I N I T
Mo vem e n t o f Pa r am e t e r Da t a b y SYSGEN

24-1
24-2

Ma c r o s U s ed by VM S t o Chang e I P L
Fo rma t o f Mu t u a l E x c l u s i o n Sem a pho r e ( MUTE X )

24-2
2 4 -9

2 5- 1
2 5-2
25-3
2 5-4

La yo u t o f Un u s e d Ar e a s i n Dyn a m i c Mem o r y Po o l s
Ex ampl e s o f Al l o c a t i o n f r om Dyn am i c Mem o r y
Ex ampl e s o f De a l l o c a t i o n to Dyn am i c Mem o r y
P r e a l l o c a ted I /O Re q u e s t Pa c k e t s

2 5-2
2 5-3
2 5-5
2 5- 1 0

26-1
2 6-2

G l o b a l L i s th e ad s fo r Log i c a l N a m e Ta b l e s
Log i c a l Name B l o c k

2 6-2
26-3

A- 1

S t a c k Mo d i f i c a t i o n D u e
I n s t r uc t i o n

D-1
D-2

De t a i l ed La yo u t o f J o b I n f o rm a t i o n B l o c k ( J I B )
D e t a i l ed La yo u t o f
So f twa r e
Process
Co n t r o l
B l o c k ( PC B )

E-1

La yo u t o f Sy s t em V i r t ua l Ad d r e s s S pa c e

2 2-2
2 2-3
2 2-4

xxi i i

PO PL

(SP)

Ps e ud o

2 2-2
2 2-4
2 2- 1 4
22-22
22-24

A-9
D-8
D- 1 1
E-5

C ONTENTS

Pa g e
TAB L E S
TAB LE

1-7

1-1

Sy s t em P r o c e s s e s a nd P r i v i l eg ed Imag e s

2-1

Us e o f F i r s t 2 0 Lo c a t i o n s
in
Sy s t em Co n t r o l
Block
E x c e pt i o n s Th a t Us e t h e D i s pa t ch e r
i n Mo d u l e
E XC E PT I ON
S i g n a l Nam e s fo r A r i thme t i c E x c e p t i o n s

2-1 0
2-1 2

3-1

Sys tem S e r v i c e s a nd R M S S e r v i c e s Th a t U s e E a c h
Fo r m o f Sy s t em S e r v i c e Ve c t o r

3-3

4-1

So f twa r e I n t e r r up t Leve l s Us ed b y VAX/VM S

4-4

6-1

S t a nd a r d
SBI
VAX- 1 1/ 7 8 0

7-1

Co n t e n t s o f Dump F i l e He ad e r B l o c k

8-1
8-2
8-3

P r o c e s s S c h ed u l i ng S t a t e s
Type s o f MWA I T S t a t e
Sy s tem Ev e n t s a nd As s o c i a t ed P r i o r i t y Bo o s t s

8-2
8-1 3
8-19

9-1
9-2

S umma r y o f P r o c e s s C o n t r o l Sys tem S e r v i c e s
M e a n i ng
of Flags
in
PC B
Sta tus
Lo ng wo r d
( PC B $ L_S T S )

9-2
9-12

10-1

VAX/VM S Ha r dwa r e C l o c k s a nd So f twa r e T i m e r s

1 0-2

11-1

Memo r y Ac c e s s P r o t e c t i o n Co d e s i n
Pag e
Ta b l e
Ent r i e s
PFN Da t a Ba s e A r r a y s
Co n te n t s o f Sh a r ed Memo r y Common Da ta Pag e

1 1 -6
1 1-9
1 1-39

12-1

De s c r i p t i o n o f I /0 Re que s t s I s s ued
Ma n ag eme n t

1 2- 2 2

1 3- 1
1 3-2

Wo r k i ng S e t L i s t L i m i t s a nd Quo t a s
P r o c e s s a nd
S y s tem
P a r am e t e r s
U s ed
Automa t i c Wo r k i ng S e t S i ze Ad j u s tm e n t

14-1
1 4 -2

Compa r i so n o f Pa g i ng a nd Swa pp i ng
Ord e r
of
Se a r ch
fo r
Po t e n t i a l
O u t s wa p
Cand i d a te
Ev e n t s Th a t C a u s e t h e Swa ppe r o r Mod i f i ed Pag e
W r i t e r to Be Awa k e n ed
Sc a n o f Wo r k i ng S e t L i s t o n O u t s wa p
Re b u i l d i ng
t h e Wo r k i ng
Set
L i s t a nd
the
P r o c e s s Pa g e Tab l e s at I n s wa p

2-2
2-3

11-2
11-3

14-3
14-4
14-5

Ad a p t e r

As s i g nm e n t s

the

2-5

6-5
7-8

Memo r y

1 3-1 1
1 3-1 3
1 4- 3
1 4-7
1 4-9
1 4-1 6
1 4-25

1 5- 1

S p e c i a l Us e s o f t h e C o n s o l e PR $_TXDB Reg i s t e r

1 5- 1 7

1 7- 1

Pa r ts o f P r o c e s s C r e a t i o n Th a t Oc c u r
D i f f e r e n t P r o c e s s Co n t e x t s
Co n t e n t s o f t h e P r o c e s s Quo t a B l o c k

1 7- 2
1 7- 4

1 7- 2

xxiv

C ONTENTS
( TAB LE S , c o n t . )
F l ag s
in
the
S t a t us
Lo ngwo r d
in
the
PC B
( PC B $ L S T S )
Th a t
Can
Be
Se t a t
Process
c r e a t ion
S t o r ag e A r e a s fo r P r o c e s s Quo t a s
Co n t e n t s o f t h e
In i t i a l
Swa p
Imag e
in
the
Sh e l l P r o c e s s

1 7-1 3

1 8-1

P r o c e s s P r i v i l eg e Ma s k s

1 8- 2 5

1 9-1

Co n t e n t s o f Te rm i n a t i o n Ma i l box
Me s s ag e
Sent
t o Ac co un t i ng Ma nag e r a nd to P r o c e s s C r e a t o r

1 9- 4

2 0-1

Ge n e r a l
Ac t i o n s
Pe r f o r m ed
by
a
Comm a n d
La ng uag e I n t e r p r e te r
Comma n d s Ha nd l ed by C L I I n t e r n a l P r o c ed u r e s

20-1 1
20-1 2

1 7-3
1 7-4
1 7-5

2 0-2
2 1 -1
2 1 -2
21-3
2 1 -4

a nd
U s e d D u r i ng
P r o g r am s
Fi les
Sequence
I n p u t t o VMB
( Pr ima ry
Reg i s t e r
P r o g r am )
Co n t e n t s o f Re s t a r t Pa r am e t e r B l o c k
Reg i s t e r I n p u t t o I N I T f r om SYS B OOT

Boo t s t r a p
Bo o t s t r a p

1 7 -7
1 7-1 0

21-3
2 1 -1 0
2 1 -1 2
21-1 6

22-1
2 2 -2
2 2-3
2 2-4

Us e of No n p ag e d Po o l by Mo d u l e I N I T
Ex t e r n a l Ad a p t e r I n i t i a l i z a t i o n
Compa r i so n o f S Y S B OOT a nd SYSGEN
I n f o r ma t i o n
S t o r ed
fo r
Ea c h
Ad j us t a b l e
Pa r am e t e r b y SYS B OOT a nd SYSGEN

2 3-1

Da t a S a v ed by Powe r f a i l Ro u t i n e
D u r i ng P o we r Rec ove r y

24-1
2 4-2

Commo n
I PL Leve l s
Used
by
VAX/VM S
for
Syn c h r o n i z a t i o n
L i s t o f Da t a S t r uc t u r e s P r o t e c ted b y Mu t e x e s

24-3
2 4-8

2 5 -1
2 5 -2

G l o ba l L i s t h e ad s f o r E a c h Po o l A r e a
Compa r i so n o f D i f f e r e n t Po o l Ar e a s

2 5-8
2 5-1 2

A- 1

MDL
Desc r i pt i o n
a nd
Re s u l t a n t
Sym bo l
De f i n i t i o n s f o r Lo g i c a l Name B l o c k
E x ampl e s o f t h e S D i r e c t i v e
S a m p l e Va r i a b l e Le ng th B i t F i e l d De f i n i t i o n s

A-1 9
A-2 0
A-2 1

A-2
A-3
D- 1
D-2
D-3
D-4
E-1
E-2
E-3
E-4

a nd

Re s to r ed

Summa r y o f
Arb i t rary
Div i s i on
of
Da t a
S t r uc t u r e s i n Th i s App e nd i x
O f f s e t s i n to S o f t wa r e P r o c e s s Co n t r o l B l o c k
O f f s e t s i n to
F i x ed
Po r t i o n o f
the
Process
Head e r
Dyn am i c Da t a S t r uc t u r e Type Cod e s
Di s c r e te
De t a i l ed
S pa c e
Di v i s i on
No n pag e d
De t a i l ed

Po r t i o n s o f t h e P r o c e s s He a d e r
La yo u t o f
Sy s t em V i r t ua l
Ad d r e s s
o f S y s t em V i r t u a l Ad d r e s s S p a c e
a nd Pa g ed P i e c e s
L a yo u t o f P l S pa c e

X XV

i n to

2 2-6
2 2 -1 2
2 2-2 0
2 2 -2 1
2 3-2

D-2
D- 1 2
D-1 4
D- 2 0
E-2
E-6
E-1 6
E-1 9

PREFAC E

MANUAL OBJECTIVE S
Th i s m a n ua l e x p l a i n s h o w t h e VAX/VM S e x e c u t i v e wo r k s .
In d o i ng s o , i t
d e sc r i b e s
t h e d a ta
s t r uc t u r e s ma i n t a i n ed
a nd m a n i pu l a t e d by VM S ,
d i sc u s s e s the me c h a n i sms t h a t t r a n s f e r c o n t r o l b e twe en use r
processes
a nd VM S
a nd wi t h i n VM S i t s e l f , a nd d e s c r i b e s some o f the f e a t u r e s o f
the VAX h a r d wa r e a s t h e y a r e u s ed b y VM S .
Th i s d e sc r i pt i o n i nc l ud e s a l l the m a j o r c om po n e n t s o f
the
executive
i nc l ud i ng
s ys t em
i n i t i a l i za t i o n a nd
t h e o pe r a t i o n o f a l l s y s t em
s e rv i c e s .
I t does not
i n c l ud e a g e n e r a l
d i sc us s i o n o f
the
I /O
s ub s y s t em b ec a u s e
tha t
s ub j e c t
i s a l r e a d y d e sc r i b ed i n t h e VAX/VM S
Gu i d e to Wr i t i ng a
D ev i c e D r i v e r .
Ho we v e r ,
t h e d e ta i l s o f
some
VAX/VM S dev i c e d r i v e r s ,
as
we l l
as
t h e o pe r a t i o n s of I /O r e l a t ed
sys tem s e rv i c e s , a r e i nc l ud ed in th i s m a n ua l .
INTENDED AUD I ENC E
Th i s m a n ua l i s i n t e nd ed f o r s ys t em p r o g r amme r s
a nd
o the r
use r s o f
VAX/VM S wh o wi sh t o und e r s t a nd t h e i n t e r n a l wo r k i ng s o f the e x e c u t i v e .
A tho r o ug h knowl e d g e o f VAX- 1 1 MACRO p r og r amm i ng i s a s s umed .
Re a d e r s
wi th a s y s t ems l ev e l b a c kg r o und o n o th e r o p e r a t i ng s ys t ems wh o h a v e a
wo r k i ng k n owl e d g e o f VAX a nd VM S c o n c e p t s c an g a i n some
und e r s t a nd i ng
o f how t h e VAX/VM S o pe r a t i ng s ys tem wo r k s .
Th e wr i t i ng l ev e l o f t h i s
m a n ua l a s s um e s t h a t the
r e ad e r
is
f am i l i a r w i th VM S p r o g r amm i ng ,
pa r t i c u l a r l y wi th
the
use
of
s ys t em
s e rv i c e s .
Knowl ed g e o f VM S
c o n c e p t s a nd the VAX a r c h i t e c t u r e i s a l s o a s s umed .
In e x p l a i n i ng the o pe r a t i o n o f
a
s ub s ys t em o f
the
e x e c u t i ve ,
the
emph a s i s
i s on
the d a ta
s t r uc t u r e s m a n i pu l a ted by th a t c ompo n e n t ,
r a th e r t h a n on d e ta i l ed f l o w d i a g r ams o f m a j o r r o u t i n e s .
Th e d e ta i l ed
d e sc r i p t i o n o f d a ta s t r uc t u r e s sho u l d ena b l e sys tem m a n ag e r s t o m a k e
mo r e i n t e l l i g e n t d ec i s i o n s wh en c o n f i g u r i ng s y s t ems fo r spa c e o r
t i me
c r i t i cal
a pp l i c a t i o n s .
Th e a pp l i c a t i o n d e s i g n e r wi l l a l s o b e ne f i t by
b e i ng a b l e to r e a l i z e the e f f e c t s ( i n s pe ed or in memo r y c o n s ump t i o n )
o f d i f f e r e n t d e s i g n a nd impl emen t a t i o n d e c i s i o n s .
NOTE
Th i s m a n ua l
i s d i f f e r en t
f r om
the
r e f e r e n c e m a n ua l s t h a t m a k e up t h e r e s t
o f t h e VAX/VM S d o c um e n t a t i o n s e t i n th a t
i t d e sc r i b e s
i nte rna l
o pe r a t i o n s a nd
d a t a s t r uc t u r e s .
Wh i l e i t
is
unl i ke l y
t h a t a n y c ompo n e n t d e sc r i b ed
i n th i s
ma n ua l wi l l be d r a s t i c a l l y c h ang ed
wi th
any ma j o r
r e l e a s e of VAX/VM S , t h e r e i s
no g u a r a n t e e tha t a n y d a t a s t r uc t u r e o r
s u b r o u t i n e i n t e r f a c e d e s c r i b ed h e r e wi l l
r em a i n t h e s ame f r om r e l e a s e to r e l e a s e .
a ppl i c a t i o n
p r og r ams
th a t
P r i v i l eg e d
r e l y o n d e t a i l s c o n t a i n e d i n th i s m a n u a l
mus t b e t e s t ed
aga i n wi th each new
ve r s i o n o f VAX/VM S .

xxvii

S TRUC TURE OF TH I S DOC UMENT
Th i s m a n ua l i s b r o k e n up i n to e i g h t pa r t s , w i th e a c h pa r t d e s c r i b i ng a
d i f f e r e n t f un c t i o n o f the o pe r a t i ng s ys t e m .
•

•

Th e f i r s t c h a p t e r ( Pa r t I ) p r e s e n t s a n o v e r v i e w o f VAX/VM S
a nd
r e v i ews
tho s e c o n c e p t s
that a re
c r uc i a l
to
l ater
u nd e r s t a nd i ng o f t h e wo r k i ng s o f t h e s y s t em .
Pa r t I I d e s c r i be s the d i f f e r e n t t ec h n i qu e s th a t a r e
u s ed
to
pass control
b e t we e n
user
p r og r am s a nd VM S .
I nd i v i d ua l
c h a p te r s d e s c r i b e e x c e p t i o n s , s ys tem s e rv i c e d i spa t c h i ng , the
u s e of so f t wa r e i n t e r r upts , a s yn c h r o no u s s ys t em t r a ps ( AS Ts ) ,
a nd h a r d wa r e
i n t e r r up t d i s pa tc h i ng .
Th e
faul t
r e po r t i ng
m ec h a n i sms
u s ed
by VM S a r e a l s o d i s c u s s e d .
Th e s e i n c l ud e
e r r o r l o gg i ng , m a c h i ne c h ec k s , a nd
BUGC HECKs ,
t h e s ys t em ' s
wa y o f r e po r t i ng i n te r n a l i n c o n s i s t e nc i e s .
Th e n e x t s e c t i o n ( P a r t I I I ) d e s c r i b e s
the
s c h ed u l e r - r e l a t ed
s y s t em
s u ppo r t .
Inte rproc ess
c ommun i c a t i o n ,
i nc l ud i ng
c ommun i c a t i o n b e t we e n p r o c e s so r s u s i ng
t h e MA 7 8 0 m u l t i po r t
m emo r y
i s d i sc u s s ed .
A d e s c r i p t i o n o f t i m e r s uppo r t a nd
s ys t em t i m e k e e p i ng c o n c l ud e s t h i s s ec t i o n .
Memo r y m a n ag em e n t i s d i sc u s s e d i n the n e x t s e c t i o n ( Pa r t I V ) .
Th e d a t a
s t r uc t u r e s t h a t a r e u s ed by bo th t h e pag e r a nd the
s wa ppe r a r e d i s c u s s e d f i r s t .
Th e o pe r a t i o n o f the
pag e r
in
r e s po n s e t o
t yp i c a l pag e f a u l t s i s t h e n d e sc r i b ed .
Many o f
t h e c o d e p a th s th r o ug h the pag e r a r e d e s i g ned
t o d e a l w i th
r a re
but
t r o ub l e s ome c a s e s .
Th e s e
r o ut i ne s a r e
no t i n
g en e r a l d i sc ussed .
VM S a l s o
p r ov i d e s c o n t r o l
ove r
the
pag i ng
a nd
s wa pp i ng
e nv i r o nm e n t
i n the fo rm of s ys t em s e rv i c e s r e l a te d to m emo r y
m a n ag em e n t .
Th e s e s e r v i c e s a r e c om p l i c a t ed e n o ug h t o wa r r a n t
t h e i r o wn
c h a pt e r .
Th e o pe r a t i o n o f t h e swa ppe r c o nc l ud e s
t h e d e sc r i p t i o n o f m em o r y m a n ag eme n t .

•

Th e n e x t s e c t i o n ( Pa r t V ) d e sc r i b e s a no th e r m a j o r
c om po n e n t
o f VM S ,
the
I / O s ubsys tem .
Th i s s e c t i o n a s s um e s t h a t t h e
r e ad e r i s f am i l i a r w i th t h e f i r s t f i ve c h a pt e r s o f VAX/VMS
Guide
to
Wr i t i ng
a Dev i c e D r i v e r .
Th e o pe r a t i o n o f d ev i c e
d r i v e r s , i n c l ud i ng a c om p l e t e d i sc u s s i o n f r om s t a r t to f i n i sh
of a
Q I O r e que s t i s p r e s e n t e d t h e r e .
Th i s m a n ua l b u i l d s o n
t h a t d i s c us s i o n b y d e sc r i b i ng
t h e d e ta i l s o f VM S d ev i c e
d r i v e r s a n d e x pl a i n i ng
h o w t h e I /O r e l a t ed s ys t em s e r v i c e s
wo r k .
The c r e a t i o n a n d d e l e t i o n o f a p r o c e s s i nv o l v e s a s i g n i f i c a n t
po r t i o n o f
VM S a nd
f o rm s
t h e s ub j e c t o f
Pa r t VI .
Th e
a c t i va t i o n a nd t e rm i n a t i o n o f a n i m a g e i n the c o n t e x t o f a
p ro c e s s a r e
a l so d e sc r i b ed .
Be c a u s e
the
i n i t i a t i o n a nd
t e rm i n a t i o n o f i m a g e s i n a n i n t e r a c t i ve o r b a tc h e n v i r o nm e n t
i s s uc h a c ommo n v a r i a t i o n t o t h e s i t u a t i o n j us t d e sc r i b ed , a
s e pa r a t e c h a p t e r i s d evo ted to t h e b e h a v i o r o f
i n t e r a c t i ve
a nd ba t c h j o b s .
Pa r t VI I d e a l s w i t h s ys t em i n i t i a l i za t i o n .
M a n y o f t h e d a ta
s t r uc t u r e s
a nd
e v e n s om e o f t h e c o d e u s e d by VM S c a nno t b e
c r e a te d u n t i l t h e s ys tem h a s b e e n c o n f i g u r ed w i th a
set o f
S Y S B OOT p a r am e t e r s .
Th i s s e c t i o n o f the m a n u a l d e sc r i b e s the
o pe r a t i o n o f the boo t s t r a p p r og r am s ( VM B a nd
SYS B OOT )
th a t
i n i t i a l i ze
VM S a nd
a l so
the
f i r s t c o d e i n VMS ( i n mod u l e
I N I T ) tha t e x ec u te s .
B e c a u s e t h e po we r
d o wn
a nd
powe r f a i l
xxviii

r e c o v e r y p r o c ed u r e s
a re
r e l a t ed to the boo t s t r a p s e qu e nc e ,
t h e y a r e d e s c r i b ed i n t h i s s e c t i o n .
•

•

Th e
f i nal
section o f
the m a n ua l
{ Pa r t VI I I )
d i s c us s e s
m i s c e l l a n e o u s t o p i c s th a t a r e n o t c o n v e n i e n t l y p i g e o nho l ed i n
a ny c o nv en t i o n a l
b r e a kd own o f o pe r a t i ng
s ys t e m s .
Th e
t e chn i que s
used
by VM S
fo r
s yn c h r o n i z a t i o n a n d d yn am i c
s t o r ag e a l l o c a t i o n and d e a l l o c a t i o n a r e d e sc r i b ed f i r s t .
Th e
i mp l em e n t a t i o n o f l o g i c a l nam e s , a powe r f u l t o o l f o r b o t h the
s y s t em a n d for u s e r s i s e x pl a i n ed n ex t .
Th e r ema i n i ng s ys t e m
s e rv i c e s
that
do
not
f i t i n to any o f t h e p r ev i o u s s e c t i o n
h e ad i ng s a r e d i s c u s s e d i n the f i n a l c h a p t e r .
Th e m a n ua l i n c l ud e s s i x a ppend i c e s tha t w i l l
be
e sp e c i a l l y
u s e f ul
fo r th o s e r e ad e r s who wi s h to p u r s ue th i s m a t e r i a l b y
r e ad i ng t h e m i c r o f i c h e l i s t i ng s o f VM S .
Th e f i r s t a pp e nd i x i n c l ud e s h e l p f ul h i n t s fo r r e a d i ng the
l i s t i ng s
a nd i nd i c a t e s h o w the m a ps of t h e e x e c u t i v e and
o th e r c ompo n e n t s c a n b e
used
wh i l e d o i ng
th i s .
Th e
s y s t em d um p a n a l y ze r
{ S DA )
i s a l s o a v a l ua b l e to o l i n
e x am i n i ng tho s e s t r uc t u r e s t h a t a r e n o t b u i l t
un t i l
the
A d e sc r i pt i o n o f t h e s t r uc t u r e
s ys t em
is
i n i t i a l i z ed .
d e f i n i t i o n l a ng u a g e { MD L ) th a t
is
u s ed
t o d e f i ne
the
e x e c ut i v e d a ta
s t r uc t u r e s
in a
l a ng uag e
i nd e pe nd e n t
f a s h i o n i s a l s o i nc l ud ed .
Th e r e a r e t h r e e i mpo r ta n t po i n t e r a r e a s used
by
VM S
to
l oc a te
d yn am i c a l l y
c o ns t r uc ted
d ata
bloc k s .
Th e s e
po i n t e r a r e a s a r e pa r t o f t h e s ta t i c e x e c u t i v e d a t a
tha t
i s a pa r t o f the e x e c u t i v e i m a g e Th e d e t a i l ed c o n t e n t s o f
t h e s t a t i c d a t a a r e a s a r e l i s t ed i n Appe nd i x B .
Th e s ym bo l nam i ng c o nv e nt i o n s tha t we r e a d h e r ed
to
wh e n
VM S wa s o r i g i n a l l y wr i t t e n m a k e
it
e a s y to r e a d t h e
sour c e cod e .
Th e s e s ymbo l n am i ng c o nv e n t i o n s a r e
l i s t ed
in Ap pend i x C .
Mo s t o f t h e o pe r a t i o n s o f VM S c a n b e
e a s i l y und e r s to od
once
t h e c o n te n t s o f
the
va r i o us d a t a s t r uc t u r e s a r e
k n o wn .
Many o f t h e s e s t r uc t u r e s a r e d e s c r i b ed th r o ug h o u t
the m a n ua l .
Mo s t o f the s t r uc t u r e s u s e d by VM S , e x c e p t
tho s e r e l a t ed to d ev i c e d r i v e r s a nd the f i l e s y s t em ,
are
d e s c r i bed
i n Append i x D .
Th e d a ta s t r uc t u r e s r e l a t ed to
d ev i c e d r i ve r s a r e d e sc r i b ed i n VAX/VM S G u i d e to
W r i t i ng
Th e d a t a s t r uc t u r e s t h a t a r e s pe c 1 f 1 c
a D e v i c e D r i ve r .
t o t h e f i l e s ys t em a r e n o t l i s t ed a n ywh e r e a t t h i s t i m e .
App e nd i x E shows h o w t h e s i z e o f e ac h p i e c e o f s ys t em
v i r t ua l
add r e s s
s pa c e d epe nd s on the v a l ue s o f SY S B OOT
pa r am e t e r s .
{ Th i s c a l c u l a t i o n a l s o r e l a t e s t h e
s i ze
of
the
process head e r t o
the v a l u e s o f s ev e r a l SY S B OOT
pa r am e t e r s . ) A f t e r a l l the s e s i ze s h a ve b e en c a l cu l a t ed ,
the
amo un t o f phys i c a l memo r y u s e d by VM S a s a fun c t i o n
o f S Y S B OOT pa r am e t e r s i s a l s o p r e s e n t ed .
App e nd i x F m e n t i o n s two c h a ng e s to the e x e c u t i v e t h a t a r e
mad e
by a ppl y i ng
t h e Ve r s i o n 2 . 2 b i n a r y upd a t e to VM S .
Th e s e t wo c h a ng e s a r e a ppl i ed by p a t c h i ng
the
ex e c u t i ve
imag e
SYS . E X E .
Th i s a ppe nd i x
i s t h e o n l y p l a c e wh e r e
th i s f un c t i o n a l i t y i s c u r r e n t l y d e sc r i b ed .

xxix

A S S OC IATED DOCUM ENTS
S e v e r a l d o c um e n ts i n the VAX/VM S d o c um e n t s e t sho u l d
be
r e a d b e fo r e
a t t empt i ng
to
r ead
t h i s m a n ua l .
Th e fo l l o w i ng m a n ua l s a r e the mo s t
i mpo r ta n t p r e r e qu i s i t e r e ad i ng f o r th i s m a n ua l .
•

VAX/VM S S y s tem S e r v i c e s Re f e r e n c e Ma n ua l

•

VAX- 1 1 S o f twa r e I n s t a l l a t i o n G u i d e

•

Ch a p t e r 6 o f t h e VAX- 1 1 Run -T i me L i b r a r y Re f e r e n c e Ma n ua l

•

VAX/VM S Re a l - T i m e Us e r ' s G u i d e

•

Ch a p t e r s 1 2 a nd 1 3 o f the VAX/VM S Sys t em Ma n ag e r ' s G u i d e

Th e c o n c e p t s o f VAX a n d VM S a r e d i sc u s s ed i n
•

VAX/VM S S umma r y De sc r i pt i o n a n d G l o s s a r y

•

VAX So f twa r e H a n d bo o k

a nd i n

E a c h o f t h e s e two d o c um e n ts a l s o p r o v i d e s a g l o s s a r y o f the t e rms used
t o d e sc r i b e t h e VA X a r c h i t e c t u r e a nd t h e VM S o pe r a t i ng s y s t em .
Th e fo l l o w i ng d o c um e n ts w i l l
r ea d i ng th i s m a n ua l .

h e l pful

r e f e r en c e s

•

VA X/VM S G u i d e to Wr i t i ng a Dev i c e D r i v e r

•

VAX- 1 1 A r c h i t e c t u r e H a n d b o o k

•

VAX Ha rdwa r e H a n d bo o k

wh i l e

yo u

a re

A n e x c e l l e n t d e sc r i p t i o n o f
t h e VAX a r c h i t e c t u r e ,
a
as
a s we l l
d i sc u s s i o n o f
some o f
the
d e s i g n d ec i s i o n s m a d e
the f i r s t
fo r
i mp l em e n t a t i o n , th e VAX- 1 1 /7 8 0 , c a n be fo und i n
Comp u t e r P r o g r amm i ng a n d A r c h i t e c t u r e
Dig i ta l Press , 1 98 0
Th i s b o o k a l s o c o n t a i n s a
b i b l i og r a ph y
d e a l i ng w i th o pe r a t i ng s y s t e m d e s i g n .

s om e

Th e VAX- 1 1
of

the

l i te r a t u r e

C ONVENTIONS US ED I N T H I S DOCUM ENT
In a l l p i c t u r e s o f m em o r y t h a t
v i r t ua l
a d d r e s s a ppe a r s a t t h e
t o wa rd t h e b o t tom o f t h e pag e .
g r owth i s t o wa rd t h e t o p o f t h e

a ppe a r
in
t h i s m a n ua l ,
the
l o we s t
t o p o f t h e pag e a nd ad d r e s s e s i nc r e a s e
Th i s m e a n s t h a t the d i r e c t i o n o f s t a c k
p ag e .

I n f i g u r e s t h a t d i sp l a y mo r e d e t a i l s uc h a s b y t e s w i th i n
l o ng wo r d s ,
add resses
a l so
i nc r e a s e
f r om
r ight
to
left .
Th a t i s , the l o we s t
a d d r e s s ed b y t e ( o r b i t ) i n a l o ng wo r d i s o n t h e r i g h t h a nd s i d e
of
a
f ig ure
a nd
the m o s t s i g n i f i c a n t b y t e ( o r b i t ) i s o n the l e f t h a nd
s ide .
Th e wo r d " s ys tem " o r " VM S " i s u s ed to d e sc r i b e
the
enti re
s o f twa r e
p a c ka g e
tha t
i s a pa r t o f a VA X- 1 1 s y s tem .
Th i s i nc l ud e s p r i v i l eg ed
p r o c e s s e s , u t i l i t i e s , a nd
o th e r
s uppo r t
s o f twa r e
a s we l l
as
the
execut i ve i ts e l f .
XXX

Th e wo r d " e x e c u t iv e " r e f e r s to t ho s e
p a r t s o f VMS th a t
r e sid e i n
s ys tem vi r t ua l add r e s s s pa c e .
Thi s i nc l ud e s t h e c o n t e n t s o f the fi l e
SYS . E XE , d evi c e d riv e r s , a nd o th e r c od e and d a ta s t r uc t u r e s l o ad ed
at
i n i t i a l i za tion time , i nc l ud i ng RMS a nd the s ys tem m e s s ag e fi l e .
Wh e n e i th e r " p r o c e s s c o n t r o l
b loc k "
or
" PC B "
i s used
wi tho u t a
it
r e f e r s to the so f twa r e s t r uc t u r e used by t h e sch e d u l e r .
modi fie r ,
Th e d a ta s t r uc t u r e t h a t c o n t a i n s c o pi e s o f the g en e r a l r eg i s t e r s ( th a t
t h e h a r d wa r e
l oc a t e s th r o ug h t h e PR$ PCBB r egis te r ) i s a l wa ys c a l l ed
the " h a r d wa r e PC B " .
Wh e n r e f e r r i ng to a c c e s s m od e s , t h e t e rm " inne r
a c c e s s m od e s "
means
tho s e a c c e s s m o d e s wi th m o r e p r ivi l eg e .
Th e t e rm " o u t e r a c c e s s m od e s "
m e a n s tho s e a c c e s s m od e s wi th l e s s p r ivi l eg e .
Th us ,
t h e in n e rmo s t
a c c e s s mod e i s k e r n e l a nd the o u t e rm o s t a c c e s s m o d e i s us e r .
Th e t e rm " SYSB OOT pa r am e t e r " i s used to d e sc ri b e a n y o f t h e a d j u s t a b l e
pa r am e t e r s tha t a r e u s ed by t h e s e c o nd a r y boo t s t r a p p r og r am SYSB OOT t o
c o n fig u r e t h e sys tem .
Th e
a d j u s ta b l e
pa r am e t e r s i n c l ud e bo th t h e
d yn amic
pa rame t e r s
t h a t c a n b e c h a ng ed o n t h e r unning s y s t e m a nd t h e
s ta t i c pa r am e t e r s tha t r eq ui r e a r eboo t i n o rd e r fo r t h e i r
v a l ue s
to
c h a ng e .
Th e s e pa r am e t e r s
are
r e f e r r ed to by thei r pa r am e te r n am e s
r a th e r t h a n by t h e g l o b a l l o c a ti o n s wh e r e
th e i r
v a l ue s a r e
s to r e d .
App e nd i x B
r e l a t e s the SYSB OOT p a r am e t e r n am e s to thei r c o r r e s po nd ing
g l o b a l l o c a ti o n s .
Th e t e rm s " by t e i n d e x " , " wo r d ind ex " , " l o ng wo r d ind ex " ,
a nd
so
on ,
refer
to
a m e thod
of
a c c e s s tha t u s e s the VAX- 1 1 c o n te x t i nd e x i ng
ad d r e s si ng c a pa bi l i ty .
Th a t i s , t h e i nd ex va l ue wi l l be m u l tipl i ed by
o n e , t wo , f o u r , o r e ig h t ( d e pend i ng o n wh e the r a byte , wo r d , l o ng wo rd ,
o r quad wo r d i s b eing r e f e r en c ed ) a s pa r t o f o pe r a nd
e v a l ua ti o n i n
o rd e r to c a l c u l a t e t h e e f f e c ti v e a d d r e s s o f t h e o pe r a nd .
I n g e n e r a l , t h e c ompo n e n t c a l l ed !N I T r e f e r s to a mod u l e o f t h a t n a m e
i n the e x e c utive a nd n o t the vo l um e i n i ti a l i z a tion uti l i ty .
Wh e n th a t
u t i l i ty p r og r am i s b eing r e f e r en c ed , i t wi l l b e c l e a r l y s p e c i fi ed .
Th e r e a r e th r e e c o nv e n tio n s tha t a r e o b s e r ved f o r l i s t s th a t a ppe a r i n
thi s m a n ua l .
•

•
•

I n l i s t s s uc h a s
this
o ne ,
wh e r e
the r e i s n o o r d e r o r
hiera rchy ,
l i s t e l em e n t s
a r e i nd i c a t ed by l ea d i ng b u l l e t s
Sub l i s t s wi tho ut h i e r a r c h y a r e i nd i c a t e d by d a s h e s ( - ) .
(e) .
Li s t s t h a t i ndic a t e an o rd e r ed s e t o f o pe r a t i o n s a r e n umbe r e d
( o r l e t t e r ed ) .
N umb e r ed l i s t s wi th t h e
n umbe r s e nc l o s ed i n p a r e n th e s e s
i nd i c a t e a
c o r r e s po nd e n c e b e twe e n i n d ivid u a l l is t e l em e n t s
a nd n um b e r ed i t ems i n a f ig u r e .

xxxi

PART I

I NTRODUC T I ON

Fo r t h e f a sh i o n o f M i n a s T i r i th wa s s uc h t h a t
s ev e n l e v e l s , e a ch d e l v ed
i t wa s b u i l t o n
i n to a h i l l , a nd abo u t e a c h wa s s e t a
wa l l ,
a nd i n e a c h wa l l wa s a g a t e .
Th e Re t u r n o f the K i ng ,
Be i ng th e Th i r d Pa r t o f
Th e Lo r d' o f t h e R i ng s
J . R . R . To l k i e n

C HA PTER 1
S YS TEM OVERV I EW

Th i s c h a p t e r i n t r o d uc e s the b a s i c c o n c e p t s t h a t a r e u s ed
to
d e sc r i b e
the VAX/VM S o pe r a t i ng
s ys tem .
Spec i a l
a t te n t i o n
i s pa i d to the
h a rd wa r e f e a t u r e s of t h e VAX a r c h i t e c t u r e th a t a r e e i t h e r e x p l o i ted b y
VM S o r e x i s t so l e l y t o s uppo r t a n o pe r a t i ng sys tem .
I n ad d i t i o n , s om e
o f the d e s i g n g o a l s
t h a t g u i d ed
the
i mpl em e n t a t i o n
of
VM S a r e
d i sc u s s e d .

1.1

PROC E S S , JOB , AND I MAG E

The f und am e n t a l u n i t i n VAX/VM S ,
the ent i ty t h a t
is
s e l e c t ed
fo r
e x e c ut i o n
by
the
s c h ed u l e r ,
is
the p r o c e s s .
I f a proc e s s c r eates
s ub p r o c e s s e s ,
t h e c o l l e c t i o n o f t h e c r e a to r
process ,
all
the
s ub p r o c e s s e s c r e a t e d
by
it,
a nd
al l
s ub p r o c e s s e s
c r ea t ed b y i t s
d e s c e nd a n t s , i s c a l l ed a j o b .
Th e p r og r am s tha t a p r o c e s s e x e c u t e s i n
o rd e r to a c compl i s h m e a n i ng f u l wo r k a r e c a l l ed i m a g e s .

1.1.1

Process

A p r o c e s s i s f u l l y d e s c r i b ed by h a r d wa r e c o n t ex t ,
s o f twa r e
contex t ;
a nd
a v i r t u a l a d d r e s s s pa c e d e sc r i p t i o n .
Th i s i n fo rma t i o n i s s t o r e d
i n s e v e r a l d a t a s t r uc t u r e s l o c a t e d i n d i f f e r e n t p l a c e s i n the
p r ocess
a d d r e s s s pa c e .
Th e d a t a s t r uc t u r e s tha t c o n t a i n t h e v a r i o u s p i e c e s o f
p r o c e s s c o n t e x t a r e p i c t u r ed i n F i g u r e 1 - 1 .

1 . 1 . 1 . 1 H a r d wa r e Co n t e x t - Th e h a r d wa r e c o n t e x t c o n s i s t s o f c o p i e s o f
the g e n e r a l
p u r po s e
r eg i s t e r s , the fo u r pe r - p r o c e s s s t a c k po i n t e r s ,
the p r og r am c o u n t e r ( PC ) , t h e p r o c e s s o r s t a t u s l o ng wo r d ( P S L ) , a nd t h e
p r o c e s s - s pe c i f i c
processo r
r eg i s te r s i n c l ud i ng the m emo r y m a n a g em e n t
r eg i s t e r s a nd the A S T l ev e l r eg i s t e r .
Th e h a r d wa r e c o n t ex t r e s i d e s i n
a data
s t r uc t u r e c a l l ed
t h e h a r d wa r e p r o c e s s c o n t r o l b l o c k t h a t i s
u s e d p r i ma r i l y wh e n
a process
is
r emoved
f r om o r
s e l e c t ed
fo r
execut ion .
Ano the r pa r t o f p r o c e s s c o n t e x t t h a t i s r e l a t ed
to
h a r d wa r e
is
the
ex i s tence
o f fo u r pe r - p r o c e s s s t a c k s , one fo r e a c h of the fo u r a c c e s s
mod e s .
A n y code tha t e x e c u t e s o n beha l f o f a p r o c e s s u s es o n e o f tha t
proce s s ' s four stacks .

1-1

1 . H a r d w a r e c o n t e x t is stored
i n h a r d w a r e PCB

• Per-Process

Stacks

(Control Reg i o n )
P 1 Space

2. Softw are context i s spread
around in PCB. PHD. JIB
a nd P1 space

3. V i r t u a l address space

Proc ess Control
Block
Job Information
Block
•

Pooled Q uo t a s

...til_
"""'

• Process Name

• Scheduling Info

This JIB p o i n t e d
t o by a ll o t h e r
proc e s s e s ( i f a n y )
i n s a me job

•

Process 10

• Pointers to

RMS Data

• I mage Data

t---1 80000000

System Space

d e s c r i p t i o n i s stored in
PO and P 1 pa g e t ables

•

��

>�

P roce ss Head e r

'�

� - - - - - - -

- - -

� - - - - - - •

Working Set List

• Process Sec t ion

Table

• Accounting Info

other struc tures

JIB

- or---..,

Hardware Process
Control Blocks

Hardware PCB

PCB

PO Page Table

��

• General Registers

• PC, PSL

\
\

• Per-Process

Stack Pointers
• Memory
Management
Registers
• ASTLVL
( Hardware Contex t)

(Virtual
Address Space
Description) � �
P 1 Page Table

PHD
Figure 1-1

Da t a S t r uc t u r e s Th a t De sc r i b e P r o c e s s Co n t e x t

en
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en

..a
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3

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�

SYSTEM OVERVI EW
1 . 1 . 1 . 2 S o f twa r e Co n t e x t - So f t wa r e c o n t e x t c o n s i s t s o f a l l th e d a t a
r e q u i r ed
by v a r i o u s p a r t s o f t h e o pe r a t i ng s y s t em to m a k e s c h ed u l i ng
a n d o th e r d e c i s i o n s a b o u t a p r o c e s s .
Th i s d a t a i nc l ud e s
the process
so f twa r e
pr i o r i ty ,
i t s c u r r e n t sc h ed u l i ng s t a t e , p r o c e s s p r i v i l eg e s ,
q uo t a s a nd l i m i t s , a nd m i s c e l l a n e o u s i n fo rm a t i o n s uch a s p r o c e s s
n am e
a nd p r o c e s s I D .
Th e i n fo rm a t i o n abo u t a p r o c e s s th a t mus t b e i n memo r y a t a l l t i m e s i s
s to r ed
i n a d a ta s t r uc t ur e c a l l ed t h e so f twa r e p r o c e s s c o n t r o l b l o c k
( PC B ) .
Th i s d a ta i n c l ud e s t h e s o f twa r e pr i o r i t y o f t h e p r o c e s s ,
i ts
un i que
process
id ent i f i c a t i o n
( PID) ,
a nd t h e pa r t i c u l a r sch ed u l i ng
s t a t e th a t the p r o c e s s i s i n a t a g i v e n po i n t i n t i me .
Some p r o c e s s
quo t a s
a nd
l imi ts a re
s to r e d i n t h e so f twa r e PC B .
( Th e q uo t a s a nd
l i m i t s tha t a r e sha r ed amo ng a l l p r o c e s s e s i n the s am e j o b a r e
s to r ed
i n a sha r e d d a t a s t r uc t ur e c a l l ed t h e j o b i n f o rm a t i o n b l o c k . )
Th e i n fo rma t i o n abo u t a p r o c e s s tha t d o e s n o t h a v e to
b e pe rm a n e n t l y
r e s i d e nt
( s wa ppab l e p r o c e s s c o n t ex t ) i s c o n t a i ned i n a d a t a s t r uc t ur e
c a l l ed t h e p r o c e s s h e a d e r .
Th i s i n f o rm a t i o n i s o n l y n e ed e d
wh e n
the
process
i s r e s i d e n t a nd c o n s i s t s m a i n l y o f i n fo rma t i o n u s ed b y memo r y
Th e d a t a i n the p r o c e s s h e a d e r
is
m a n ag em e n t wh e n pag e f a u l t s o c c u r .
a l so
used
by the
swa ppe r wh e n
t h e p r o c e s s i s r em o v e d f r om memo r y
( o u t swa ppe d ) o r b r o ug h t b a c k i n to memo r y
( i n swa pped ) .
Th e
h a r d wa r e
PC B ,
wh i c h
conta i ns
t h e h a r d wa r e c o n t e x t o f a p r o c e s s , i s a p a r t o f
I n f o rma t i o n i n t h e p r o c e s s h e a d e r i s a v a i l a b l e to
the proc ess h e ad e r .
s u i t a b l y pr i v i l eg e d
code wh e n e v e r t h e p r o c e s s i s r e s i d e n t ( i s in the
bal ance se t ) .
Al l o th e r r e f e r e n c e s to the p r o c e s s h e a d e r m u s t be mad e
i n the c o n t e x t o f the p r o c e s s wh o s e p r o c e s s h e a d e r i s b e i ng e x am i n ed .
O t h e r p r o c e s s - s p ec i f i c i n f o rm a t i o n i s s t o r e d i n the P l po r t i o n o f
the
p r o c e s s v i r t ua l
ad d r e s s
sp a c e
( the contr o l
r eg i o n ) .
Th i s d a t a
i n c l ud e s e x c e p t i o n d i s pa tch i ng
i n fo rm a t i o n ,
RM S d a t a
tables ,
a nd
i n f o rm a t i o n a b o u t the i m ag e t h a t i s c u r r e n t l y e x e c u t i ng .
I n f o rm a t i o n
t h a t i s s t o r ed. i n P l s pa c e i s o n l y a c c e s s i b l e wh en
the
proc ess
is
e x e c u t i ng
(is
the
cur rent proces s )
b e c ause
P l s pa c e
i s process
s pe c i f i c .

1 . 1 . 1 . 3 V i r t u a l Ad d r e s s Spa c e D e sc r i pt i o n - Th e v i r t u a l a d d r e s s s pa c e
o f a p r o c e s s i s d e sc r i b ed b y t h e p r o c e s s P O a n d P l pag e t a b l e s , s t o r e d
i n t h e h i g h ad d r e s s e nd o f t h e p r o c e s s h e a d e r .
Th e
p r o c e s s v i r t ua l
address
s pa c e i s a l t e r ed wh e n a n i m a g e i s i n i t i a l l y a c t i v a t ed , d u r i ng
i m a g e e x e c u t i o n th r o ug h s e l ec ted sys t em s e r v i c e s , a n d
wh e n
an
i m ag e
t e rm i n a t e s .
Th e p r o c e s s pag e t a b l e s r e s i d e i n sys tem v i r t ua l a d d r e s s
s pa c e a nd a r e i n t u r n d e sc r i b ed by e n t r i e s i n t h e sys t em pag e
t ab l e .
Un l i k e
the
o th e r
po r t i o n s o f
t h e p r o c e s s h e a d e r , t h e p r o c e s s pag e
t a b l e s a r e them s e l v e s pag e a b l e ,
and
are
f a u l t ed
i n to
the process
wo r k i ng s e t o n l y wh e n t h e y a r e n e e d e d .

1.1.2

Image

Th e p r o g r ams t h a t e x e c u t e i n t h e
c o n tex t o f
a
process
a r e c a l l ed
imag e s .
Imag es
u s ua l l y r e s i d e i n f i l e s tha t a r e p r o d uc ed by o n e o f
t h e VAX/VM S l i n ke r s .
Wh e n the u s e r i n i t i a t e s i m ag e e x e c u t i o n ( a s pa r t
of
p r o c e s s c r ea t i o n o r t h r o ug h a DC L o r MCR c o mma nd i n a n i n t e r a c t i v e
o r ba tch j o b ) , a com po n e n t o f the e x e c u t i v e c a l l e d t h e i m a g e a c t i v a to r
sets
up
t h e p r o c e s s pag e ta b l e s to po i n t to the a pp r o p r i a t e s e c t i o n s
o f th e i m a g e f i l e .
VM S u s e s t h e same pag i ng m e c h a n i sm th a t i mp l em e n t s
i t s v i r t ua l memo r y s uppo r t t o r e ad i m ag e pag e s i n to memo r y a s t h e y a r e
n e ed ed .
1-3

SYS TEM OVE RVI EW
1.1.3

Job

Th e c o l l e c t i o n of s ub p r o c e s s e s th a t h a s a
c ommo n
r oo t
process
is
c a l l ed
a
j ob .
Th e c o n c e p t o f a j o b ex i s t s so l e l y f o r the p u r po s e o f
s h a r i ng r e s o u r c e s .
Some quo t a s a n d l i m i t s , s o - c a l l ed po o l e d
quo t a s ,
a r e s h a r ed among a l l p r o c e s s e s i n the s ame j o b .
Th e c u r r e n t v a l u e s o f
these
q uo t a s
a re
c o n t a i n ed
i n a d a ta
s t r uc t u r e c a l l e d
a
j ob
i n fo r m a t i o n b l o c k ( F i g u r e 1 - 1 ) th a t i s sha r e d by a l l p r o c e s s e s i n the
s ame j o b .

1.2

FUNC T I ONAL I TY PROV I D E D BY VAX/VMS

Any o pe r a t i ng s ys t em p r o v i d e s s e r v i c e s a t m a n y l ev e l s
so
that use r
a ppl i c a t i o n s m a y e x e c u t e
e a s i l y and e f fect ive l y .
Th e f un c t i o n a l i t y
p r ov i d ed by VAX/VM S i s p i c t u r ed i n F i g u r e 1 - 2 .
Th e f i g u r e i s d e s i g n ed
to
show the
l a ye r ed
des ign of
the VAX/VM S o p e r a t i ng s y s tem .
In
g e ne r a l , c ompo n e n t s i n a g i v e n l a ye r c a n m a k e u s e o f t h e f a c i l i t i e s i n
a l l i nn e r l a ye r s .

1.2. 1

Ope r a t i ng S y s t em Ke r n e l

the I /0
Th e m a i n to p i c o f t h i s m a n u a l i s t h e ope r a t i ng s y s t em k e r n e l ;
s ub s ys tem ,
memo r y m a n ag em e n t ,
t h e s c h e d u l e r , a nd t h e VAX/VM S s y s t em
s e rv i c e s th a t s uppo r t a nd c ompl eme n t th e s e c ompo n e n t s .
Th e
a pp r o a c h
that
is
used
i n d i s c u s s i ng
th e s e
th r e e c ompo n e n t s a nd
other
m i s c e l l a n e o u s pa r t s o f t h e o pe r a t i ng s ys tem k e r n e l f o c u s e s o n t h e d a t a
s t r uc t u r e s
tha t a r e m a n i pu l a t ed by a g i v en c om po n e n t .
By d i s c u s s i ng
wh a t e a c h m a j o r d a t a s t r uc t u r e r e p r e s e n t s , a n d h o w t h a t
s t r uc t u r e
is
a l t e r ed b y d i f f e r e n t
s e q u e nc e s o f e v e n t s
in
the s ys tem , we w i l l
d e sc r i b e t h e d e t a i l ed o pe r a t i o n s o f e a c h m a j o r p i e c e o f the e x e c u t i v e .

1.2. 1 . 1
I /0 S u b s y s t em - Th e I /0 s ub s ys tem c o n s i s t s o f d e v i c e d r i v e r s
a nd
the i r
a s s o c i a t ed
data
s t r uc t u r e s ,
d e v i c e i nd e pe nd e n t r o u t i n e s
w i t h i n the e x e c u t i v e , a nd s ev e r a l s y s t em s e rv i c e s , t h e m o s t
i m po r t a n t
of
wh i c h i s the $ Q I O r e qu e s t , t h e e v e n t u a l I /0 r e que s t t h a t i s i s s u ed
b y a l l o u t e r l a ye r s of t h e s ys tem .
Th e I /0 s u b s y s tem i s d e sc r i b ed
in
g r e a t d e ta i l
f r om t h e po i n t o f v i e w o f a d d i ng a d ev i c e d r i v e r t o VM S
i n t h e VAX/VM S G u i d e to Wr i t i ng a Dev i c e Dr i v e r .
Ch a p te r s 1 5
and
16
of
t h i s m a n ua l d e s c r i b e
f e a t u r e s o f the I /0 s ub s ys t em th a t a r e n o t
d e sc r i b ed th e r e .

1 . 2 . 1 . 2 Memo r y Ma n a g em e n t - Th e m a i n c ompo n e n t s
of
the
memo r y
m a n ag em e n t
s ub s ys t em a r e t h e pag e f a u l t h a nd l e r , wh i c h i m pl em e n t s the
v i r t u a l mem o r y s uppo r t of VAX/VM S , a n d the s wa ppe r , wh i c h
a l l o ws
the
s ys t em
to m o r e
f u l l y u t i l i z e t h e amo un t of phys i c a l memo r y that i s
ava i l able .
Th e d a t a s t r uc t u r e s u s ed a nd m a n i p u l a t ed by t h e pag e r
a nd
s wa ppe r i n c l ud e t h e PFN d a t a b a s e a nd th e pag e t a b l e s o f e a c h p r o c e s s .
Th e PFN d a t a b a s e d e sc r i b e s e a c h
pag e o f phys i c a l
memo r y t h a t
is
a v a i l a b l e fo r pag i ng and s wa pp i ng .
V i r t u a l a d d r e s s s pa c e d e sc r i p t i o n s
o f e a c h c u r r e n t l y r e s i d e n t p r o c e s s a r e c o n t a i n ed i n
the i r
r e spec t i v e
pag e tab les .
Sy s t em s e r v i c e s a r e a v a i l a b l e to a l l o w a u s e r ( o r the s y s t em on b e h a l f
of
t h e us e r ) to c r e a t e o r d e l e t e s p e c i f i c po r t i o n s o f v i r t u a l add r e s s
s pa c e o r ma p a f i l e i n t o a s pe c i f i ed v i r t ua l a d d r e s s r a ng e .
1-4

P r i v i leged I m a ges

P r o g r a m Dev el o pmen t Too l s

I mages I nstalled with Privilege
Other Privileged I mages
Images Linked with
system symbol table
•

•

I-'
I
U1

• Tex t E d i t o rs
• Linker
• MACRO A ssembler
• S y s t e m Message

File System
I nformational
Utilities

Compiler

Run T i m e
Li b rary

Run Time
Li b rary

( S p ec ific )

(General )
•

• FO RTRA N

•

• PASCA L
• PL/ 1

•

Lay e red P rod uc t s
•
•

•

Math Library
Stri ng
M a n ipulati o n
Screen
Formatt i n g

A s s o rted U t i l i t i e s
•

Language Compilers
DATATRI EVE
Forms Utilities

SORT

• File M a nipulation

• H E LP

• DIRECTORY

Figure 1-2

La ye r e d De s i g n o f VAX/VM S

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SYSTEM OVERVI EW
1. 2. 1 . 3
Sched u l i ng a nd P r o c e s s C o n t r o l - Th e thi r d ma j o r c om po n e n t o f
t h e k e r n e l i s the s c h ed u l e r , wh i c h s e l e c t s p r o c e s s e s fo r e x e c u t i o n a nd
r em o v e s p r o c e s s e s f r om ex e c u t i o n tha t c a n
no
l o ng e r e x e c u t e .
Th e
s c h ed u l e r
a l so
h a nd l e s
c l o c k s e r vi c i ng
a nd i n c l ud e s t ime r r e l a t e d
sys t em s e rv i c e s .
Sys tem s e rv i c e s a r e a v a i l a b l e to a l l o w a p r o c e s s ( o r
p r og r amme r )
to c r e a t e
o r d e l e t e o th e r
processes .
O t h e r s e rv i c e s
p r ov i d e o n e p r o c e s s the a b i l i t y t o c o n t r o l t h e e x e c u ti o n o f a n o t he r .

1 . 2 . 1 . 4 M i sc e l l a n e o u s S e rv i c e s - O n e a r e a o f
the
o pe r a ting
s ys tem
ke r nel
tha t
is
not
pi c t u r ed
i n Fig u r e 1 - 2 i nvo l v e s
the m a n y
m i s c e l l a n e o us s e rv i c e s th a t a r e
avail ab l e
in
t h e o pe r a t ing
sys tem
k e r nel .
Some
of
these
s e r vi c e s ,
s uc h as l og i c a l n am e c r e a ti o n o r
s t r ing f o rm a t t i ng , a r e a v a i l a b l e to the u s e r i n
the
fo rm o f
s y s t em
servi ces .
Ot h e r s ,
s uc h
as
po o l
m a nipu l a ti o n
r o u t i n e s a nd
s ync h r o n i z a tio n t e c hnique s , a r e o n l y u s e d by t h e k e r n e l a nd p r ivi l eg e d
ut i l i t i e s .

1. 2. 2

D a t a Ma n a g e m e n t

VAX/VMS p r o v i d e s d a t a m a n ag em e n t f a c i l i ti e s a t two l ev e l s .
Th e r e c o r d
s t r uc t u r e
th a t e x i s t s w i thin a
file
i s i n t e r p r e t ed b y t h e VAX - 1 1
Re c o r d Ma nag em e n t S e r vi c e s ( RM S ) , whi c h e x i s t s i n a l aye r j us t o u t s i d e
the
ke rnel .
RMS e x i s t s a s a s e r i e s o f p r oc e d u r e s l o c a t e d i n sys tem
spa c e , s o i t i s i n some wa ys j u s t l i k e
the
r es t o f
the
o pe r a t i ng
sys tem
ke rnel .
Mo s t o f
t h e p r o c ed u r e s i n RM S e x e c u t e i n e x e c ut i v e
a c c e s s m o d e , p r ov i d i ng a t h i n wa l l o f p r o t ec t i o n b e twe e n RM S a n d
the
ke rnel i tsel f .
Th e pl a c em e n t o f f i l e s o n m a s s s to r ag e v o l um e s i s c o n t r o l l ed b y o n e o f
the
disk o r
t a pe
AC Ps
( Anc i l l a r y Co n t r o l
Process ) .
AC Ps
are
i m p l em e n t ed a s s e pa r a t e p r o c e s s e s b e c a u s e many o f
their
o pe r a t i o n s
mus t b e
s e r i a l i zed
to
avoid
s yn ch r ono us
access confl icts .
Th e s e
p r o c e s s e s i n t e r a c t w i th t h e k e r n e l bo th
th r o ug h
the
sys t em
s e rv i c e
i nter face
a nd a l so b y us i ng s om e o f t h e u t i l i ty r o u t i n e s th a t a r e no t
a c c e s s i b l e to the g e n e r a l u s e r .

1.2.3

User Interface

Th e i n t e r f a c e tha t i s p r e s e n ted t o t h e
use r
( a s d i s tinc t
f r om
the
a pp l i c a ti o n p r og r amme r
wh o
is
us i ng
s y s tem
s e r v i c e s a nd Run-T i m e
Li b r a r y p r o c ed u r e s ) i s o n e o f the c ommand l a ng uag � i n t e r p r e t e r s ( C L I ) .
Some o f
the
s e r v i c es
p e r fo rmed
by a
C L I c a l l RM S o r the s ys tem
s e rv i c e s d i r e c t l y .
Oth e r s r e s ul t i n
the
exec u t i o n o f
a n e x t e r na l
i m ag e .
Th e s e
imag e s a r e g e n e r a l l y n o d i f f e r e n t f r om u s e r -w r i t t e n
a pp l i c a t ions i n tha t t h e i r o n l y i n te r f a c e to t h e e x e c u t i v e i s
t h r o ug h
the sys t em s e r v i c e s a nd RM S c a l l s .
Some func t i o n s a v a i l a b l e to t h e us e r a r e pe r f o rmed by i mag e s th a t
use
und o c um e n ted i n te r f a c e s into t h e k e r n e l .
Th e s e i m a g e s u s ua l l y r e qu i r e
p r i v i l eg e s i n o r d e r to e x e c u t e , and a r e a l s o l i n k e d w i th
the
s ys tem
s ymbo l t a b l e SYS $ S Y ST EM : S YS . S TB .

1-6

SYS TEM OVERVI EW
1. 2. 3. 1
Imag e s I n s ta l l ed w i t h P r i v i l eg e - Some o f
the
i n fo r m a t i o n a l
ut i l i ti e s a nd d i s k a nd t a pe vo l um e m a nipu l a tion u t i l i t i e s r eq ui r e t h a t
s e l e c ted po r ti o n s o f p r o t e c t ed d a t a s t r uc t u r e s b e r e ad o r wr i t t e n i n a
c o n t r o l l ed
f a shio n .
Imag es
t h a t r e qui r e p r iv i l eg e to pe r fo r m thei r
f un c t i o n c a n b e i n s t a l l ed ( ma d e known to VM S ) by t h e s y s t e m m a n ag e r s o
that
th e y c a n pe r f o rm t h ei r f un c tio n i n a n o rd i n a r i l y n o n p r iv i l eged
p r o c e s s e nvi r o nm e n t .
I mag e s t h a t fit this d e sc r i p t i o n a r e
D I S PLAY ,
VMO UNT ( th e vo l um e m o u n t u t i l i t y ) , S E T , a n d SHOW .
Tabl e 1 - 1 li sts a l l
th o s e imag e s t h a t a r e i n s t a l l ed
wi th p r ivi l eg e
in a
t yp i c a l VM S
s y s t em .

1.2. 3. 2
O t h e r P r i v i l eg ed Ima g e s - O t h e r
imag e s
tha t
pe r f o rm
p r ivi l eg e d
f un c t i o n s
are
n o t i n s t a l l ed wi th p r iv i l eg e b e c a u s e thei r
f un c ti o n s a r e l e s s c o n t r o l l ed a nd c o u l d d e s t r o y t h e sys tem i f e x e c u t ed
by
n a iv e o r m a l i c i o us
use r s .
Th e s e im ag e s c an o n l y b e e x e c uted by
p r ivi l eg e d u s e r s .
Ex ampl e s o f
these
imag es i nc l ud e
SYSGEN
( fo r
l o a d i ng
d evi c e d r iv e r s ) ,
I N S TALL
{ wh i c h m a k e s i m a g e s p r ivi l eg ed o r
sha r e a b l e ! ) , o r the im ag e s i nv o k e d by a C L I to m a n i p u l a te
print o r
b a tc h q u e ue s .
Imag es
t h a t r e qu i r e p r ivi l eg e to e x e c u t e b u t a r e no t
i n s t a l l ed wi t h p r ivi l eg e i n a t ypi c a l VAX/VM S s y s t em a r e a l s o
l i s ted
in Tab l e 1 - 1 .
Ta b l e 1 - 1
Sys tem P r o c e s s e s a nd Pr ivi l eg ed Imag e s
Sys tem P r o c e s s e s

Imag e Name

L i n ked wi th
SYS . STB

C C P . E XE
F l lAAC P . EXE
F l lBAC P . EXE
M TAAAC P . EXE
R EMAC P . EXE

Ye s
Ye s
Ye s
Ye s
Ye s

Imag e fo r NETAC P
F i l e s - 1 1 AC P f o r St r uc tu r e Lev e l 1
F i l e s- 1 1 A C P f o r S t r uc t u r e Lev e l 2
Mag n e t i c Ta pe AC P
Rem o t e Te rm i n a l AC P

ERRFMT . EXE
I N PSM B . EXE
JOBCTL . E XE
O PC OM . EXE
PRTSM B . EXE

Ye s
Ye s
Ye s
Ye s
Ye s

Er r o r Log Bu f fe r Fo rma t Pro c e s s
Ca r d Re ad e r Inpu t Symb i o nt
Job Co n t r o l l er / Sym b i o n t Man ag e r
Ope r a to r Commun i c a t i o n Fac i l i ty
Pr i n t Symb i o n t

De sc r i pt i o n

Imag e s In s ta l l ed wi th Pr i v i l eg e
( i n a typ i c a l VM S system)

I m ag e Name

L i n ke d wi th
SYS . STB

D I SMOUNT . E XE
D I S PLAY . EXE
I N IT . E XE
LOG I NO UT . EXE
MAI L . EXE
R E QU E S T . EXE
S E T . EXE
S ET P O . EXE
S H OW . EXE
S UBM I T . EXE

Ye s
Ye s
Ye s
Ye s

VMOUNT . EXE

Ye s

De sc r i pt i o n
Vo l ume Di smo un t Ut i l i ty
Sys tem Sta t i st i c s Ut i l i ty
Vo l um e In i t i a l i za t i o n Ut i l i ty
Log i n/Log o u t Imag e
Ma i 1 Ut i 1 i t y
Ope r a to r Requ e s t Fa c i l i t y
SET Command Pro c e sso r
SET Command Pro c e sso r
SHOW Comma nd Pro c e s so r
Ba tch a nd Pr i n t Job Subm i s s i on
Fac i l i ty
Vo l um e Mo un t Ut i l i ty

Ye s
Ye s
Ye s

1-7

S Y S TEM OVERVI EW
Ta b l e 1 - 1

( co n t . )

Sy s t em P r o c e s s e s a n d P r i v i l eg ed Imag e s

Imag e s Th a t Re qu i r e Pr iv i l eg e
Th a t Ar e Typ i c a l l y No t I n s ta l l ed
L i nked wi th
SYS . STB

Imag e Nam e
I N F O . EXE
I N S TA L L . EXE
NC P . EXE
O PCCRA S H . E XE
QUEMAN . EXE
R E PLY . EXE
RM S S HA R E . EXE
RTPA D . EXE
R UNDE T . EXE
S DA . EXE
S YS G E N . EXE

(*)

TALK . EXE
US ERS . EXE

(*)
( *)

( *)

De sc r i pt i o n
P r o c e s s In fo rma t i o n Ut i l i ty
Kn o wn Imag e In sta l l a t i o n Ut i l i t y
Ne two r k Co n t r o l P r o g r am
Sys tem Sh utd o wn Fa c i l i ty
Que ue Ma n i pu l a t i o n Command Proc e s so r
Me s sa g e B r o ad c a s t i ng Fa c i l i ty
F i l e Sh a r i ng Ut i l i ty
Rem o te Te r m i n a l Command I n te r fa c e
RUN Pr o c e s s Command Pr o c e sso r
Sys tem Dump �n a l y ze r
Sys t em G e n e r a t i o n and Co n f i g ur a t i o n
Ut i l i ty
I n t e r te rm i n a l Commun i c a t i o n Ut i l i t y
I n te r a c t i v e Us e r s D i spl a y

Ye s
Ye s
Ye s
Ye s
Ye s
Ye s

Ye s
Yes

Th e se imag e s a r e no t s uppo r te d by D I G I TA L .

Imag es Wh o se Ope r a t i o n s Ar e Pr o te c ted b y Sys t em U I C o r Vo l um e OWn e r sh i p
Li nked wi th
SYS . STB

Imag e Na me

Oe se r i pt i o n

B A D . EXE
DSC 1 . EXE

Bad B l o c k Lo c a to r
Di s k S a v e and Compr e s s Ut i l i ty
f o r S t r uc t u r e Lev e l 1
Di s k Sa v e and Compr e s s Ut i l i ty
fo r St r uc t u r e Lev el 2
Di s k Quo ta Ut i l i ty
Fi l e St r uc t u r e Ve r i f i c a t i o n Ut i l i ty
fo r St r uc t u r e Lev e l 1
F i l e St r uc t u r e Ve r i f i c a t i o n Ut i l i ty
f o r St r uc t u r e Lev e l 2

DSC 2 . EXE
D I S KQUOTA . EXE
VFY l . EXE

Ye s

VFY 2 . EXE

M i s c e l l aneo us Imag e s L i n ked wi th SYS $ S YS TEM : SYS . S TB

Imag e Na me
DC L . EXE
MCR . EXE
RM S . EXE

Li n ked wi th
SYS . STB

Oe se r i pt i o n
DC L Command In te r pr e te r
MCR Comma nd In te r pr e te r
Re c o rd Ma nag em en t Se r v i c e s Imag e

Ye s
Ye s
Ye s

1-8

S YS TEM OVE RVI EW
1.2. 3. 3
I m a g e s Th a t L i n k w i th S Y S $ SY STEM : SY S . S TB - Ta b l e 1 - 1
a l so
l i sts
t ho s e c om po n e n t s
t h a t a r e l i n k e d w i th t h e s ys t em s ym b o l t a b l e
( S YS $ S YS T EM : S YS . S T B ) .
Th e s e i m a g e s a c c e s s
k n o wn
l oc a t i ons
in
the
s y s t em
i m ag e
( S YS . E X E )
t h r o ug h g l o b a l s ym b o l s a nd m u s t b e r e l i n k e d
e a c h t i m e t h e s ys t e m i t s e l f i s r e l i n k e d .
Us e r a pp l i c a t i o n s o r s pe c i a l
c om po n e n t s
s uc h
a s d ev i c e d r i v e r s t h a t i n c l ud e SYS . S TB wh e n t h e y a r e
l i n k e d m u s t b e r e l i n k e d wh e n e v e r a n e w v e r s i o n o f t h e s ym b o l t a b l e
is
r e l e a s e d , u s u a l l y a t e a c h m a j o r r e l e a s e o f VAX/VM S .

1.2.4

I n t e r f a c e b e twe e n Ke r n e l S ub s ys t ems

Th e c o up l i ng b e t we e n the th r e e m a j o r s ub s ys t em s p i c t u r e d i n F i g u r e 1 - 2
is
s o m e wh a t m i s l e a d i ng
i n t h a t t h e r e i s a c t ua l l y l i t t l e i n t e r a c t i o n
b e twe e n t h e t h r e e
c om po n e n t s .
In
add i t ion ,
e a ch
of
the
three
c om po n e n t s h a s i t s o wn s e c t i o n o f e x e c u t i v e d a t a s t r uc t u r e s t h a t i t i s
r e s po n s i b l e fo r .
Wh e n o n e o f t h e o th e r p i e c e s o f t h e s ys t e m w i s h e s t o
access
s uc h d a t a
s t r uc t u r e s ,
i t does
so
t h r o ug h s o m e c o n t r o l l ed
i n te r fa c e .
F i g u r e 1 - 3 s h o ws t h e
sma l l
am o u n t o f
i n terac t i on
that
occurs
b e t we e n t h e
th r e e m a j o r
s ub s ys t ems i n t h e o pe r a t i ng s y s t em
ke rnel .
Lock/U nlock Physical
Pages for
Direct 1/0

Page Fault Read
l nswap/Outswap
Modified Page Write

Wait for 1/0 Request

Wake Up

1/0 Request

Swapper

Complete

Page Fault Wait
Page Fault Read Complete
Free Page Wait
Physical Page Available
l nswap Complete
Outswap Complete

Figure 1-3

I n t e r a c t i o n B e t we e n Compo n e n t s o f VM S K e r n e l

1-9

SYSTEM OVERV I EW
1.2. 4. 1
I /0 Subsys tem Re que s t s
Th e I /0 s ub s y s t em ma k e s a r e q u e s t to
memo r y m a n a g eme n t
to
l o c k d o wn
s pe c i f i ed
pag e s
f o r a d i r e c t I /0
r eques t .
Th e pag e r o r swa ppe r
i s n o t i f i ed
d i r e c t l y wh e n
the
I /0
r e q ue s t tha t j us t c om p l e t ed wa s i n i t i a t e d b y e i th e r o n e o f them .
-

I /0 r e q ue s t s c a n r e s u l t i n the r e q ue s t i ng p r o c e s s b e i ng
p l a c ed
in
a
wa i t s t a t e ,
un t i l
the
r e q u e s t c om p l e t e s .
Th i s r eq u i r e s t h a t the
I n a d d i t i o n , I / 0 c o mpl e t i o n c a n a l s o
c ause
a
s c h ed u l e r b e no t i f i ed .
p r o c e s s to c h a ng e i t s s c h ed u l i ng s ta t e .
Ag a i n , t h e s c h ed u l e r wo u l d b e
c a l l ed .

1 . 2 . 4 . 2 Memo r y Ma nag e me n t Reque s t s
B o th
the p ag e r
a nd
swa ppe r
r e qu i r e
i n p u t a nd
o u t pu t o pe r a t i o n s
i n o rd e r
to
f ul f i l l
the i r
f un c t i o n s .
Ne i th e r c a l l s $ Q I O d i r e c t l y b e c a us e m a ny o f t h e p r o t ec t i o n
checks
tha t
$ Q I O m a k e s a r e unne c e s s a r y a nd wo ul d s l ow d o wn pag e I /0
a nd swa p I /0 .
I n s t e ad , t h e y u s e spec i a l e n t r y po i n t s
i n to
the
I /0
s y s t em
th a t a l l o w p r eb u i l t
I /0 r e qu e s t s to b e q u e ued d i r e c t l y to a
d r iver .
-

I f a p r o c e s s i nc u r s a pag e f a u l t t h a t r e s u l t s i n a r e a d f r om d i s k ,
or
if a
process
r e qu i r e s phys i c a l
memo r y a nd n o n e i s a v a i l a b l e , t h e
p r o c e s s i s p u t i n t o o n e o f t h e memo r y m a n ag em e n t wa i t s t a t e s b y t h e
s c h ed u l e r .
Wh e n
the
pag e r e a d c ompl e te s o r phys i c a l memo r y b e com e s
a v a i l a b l e , t h e p r o c e s s i s m a d e c omput a b l e a g a i n .

1.2.4.3
S c h e d u l e r Req u e s t s - Th e s c h ed u l e r
act ively
i nte r a c ts
ve r y
l i ttle
wi th
t he
rest
o f t h e sys tem .
I t s e rv e s a m o r e pa s s i v e r o l e
wh e n c o o pe r a t i o n w i th m emo r y m a n ag eme n t o r
the
I /0 s ub s ys t em
is
r e q u i r ed .
On e e x c e p t i o n
t o th i s pa s s i v e r o l e i s t h a t t h e s c h ed u l e r
a wa k e n s the s wa ppe r wh e n a
process
that
is
n o t c u r r e n t l y m emo r y
r e s i d e n t b e c om e s c om p u t a b l e .

1.3

HARDWARE I MPLEMENTAT I ON OF OPERATING SYSTEM KERN E L

Th e m e t ho d o f i m p l eme n t i ng
t h e many s e rv i c e s p r ov i d ed
b y VAX/VMS
i l l us t r a tes
t h e c l o s e c o nn e c t i o n b e twe e n t h e h a r d wa r e d e s i g n a n d the
o p e r a t i ng
sys tem .
Many o f
the g ene r a l
features
of
the
VAX
a r ch i t e c t u r e
a r e u s e d to a d v a n t ag e by VAX/VMS .
Oth e r f e a t u r e s o f the
a r ch i t e c t u r e e x i s t e n t i r e l y t o s uppo r t a n o pe r a t i ng s ys t em .

1 . 3. 1

VAX A r c h i te c t u r e Fe a t u r e s E x pl o i t e d by VMS

S e v e r a l f e a t u r e s o f t h e VAX a r c h i t ec t u r e th a t
us e r s a r e used fo r s p e c i f i c p u r po s e s b y VM S .
•

•

a re

ava i l ab l e

all

Th e g e ne r a l p u r po s e c a l l i ng m e ch a n i sm
is
the p r i m a r y pa th
i n t o VM S
f r om a l l o u t e r l a ye r s o f the s ys t em .
Becaus e a l l
s ys t em s e r v i c e s a r e p r o c e d u r e s , t h e y a r e
ava i l ab l e
to
all
n a t i v e mod e l a ng u a g e s .
As me n t i o n ed a b ove , t h e m emo r y m a n ag em e n t p r o t ec t i o n
s c h em e
is
used
to
protec t
c o d e a nd d a t a u s e d by mo r e p r i v i l eg e d
a c c e s s mod e s f r om mod i f i c a t i o n b y l e s s p r i v i l eg e d m od e s .
Re a d - o n l y po r t i o n s o f t h e e x e c u t i v e a r e p r o t e c t ed i n t h e same
manne r .
1-1 0

SYSTEM OVERVI EW
•

•

Th e r e i s i mp l i c i t p r o t e c t i o n b u i l t i n to s pe c i a l
i n s t r uc t i o n s
Because only the
t h a t m a y o n l y b e e x e c u t e d f r om k e r n el m o d e .
e x e c ut i v e
( a n d s u i t ab l y p r i v i l eg ed
p r o c e s s-ba sed
c od e )
e x ec ut e s
in
k e r n e l m od e , s uc h i n s t r uc t i o n s a s MTPR , L D PC TX ,
a nd HA LT a r e p r o t e c t ed f r om ex e c u t i o n b y n o np r i v i l eg e d u s e r s .
Th e o pe r a t i ng s y s t em u s e s i n t e r r up t pr i o r i t y l ev e l ( I P L )
fo r
s eve r a l
p u r po s e s .
At
i t s m o s t e l em e n ta r y l e v e l , I PL i s
e l e v a ted
so
tha t
certain
i n t e r r up t s
a re
blocked .
Fo r
e x ampl e ,
c l oc k
i n t e r r up t s m u s t b e b l o c k e d wh i l e t h e s ys t em
t i m e ( s t o r e d in a q u a d wo r d ) i s c h e c ked b e c a u s e th i s
c h e c k i ng
t a ke s mo r e
than one
i n s t r uc t i o n .
Clock
i n t e r r up t s
are
b l o c k e d t o p r ev e n t t h e s ys tem t i me f r om b e i ng
upd a t e d
wh i l e
i t i s b e i ng c h e c k e d .
I P L i s a l so u s ed a s a s yn c h r o n i z a t i o n to o l .
Fo r e x ampl e , a n y
r o u t i n e t h a t a c c e s s e s a s ys tem-w i d e d a t a s t r uc t ur e m u s t r a i s e
I PL to 7 ( c a l l ed
I P L $ S YNC H ) .
Th e a s s i g nm e n t o f v a r i o u s
h a r dwa r e
a nd
so f twa re i n t e r r upt s
to
s pe c i f i c
I P L v a l ue s
e s t a b l i s h e s a n o rd e r
of
i mpo r t a n c e
to
t h e h a r d wa r e
a nd
s o f t wa r e i n t e r r up t s e r v i c e s th a t VM S pe r f o rm s .
S e v e r a l o th e r f e a t u r e s o f t h e VAX a r c h i t e c t u r e a r e
used
by
l a ter
in
spec i f i c
c ompo n e n t s o f VM S a n d
a r e d e s c r i b ed
c h apte r s .
Th e y i n c l ud e
t h e c h a n g e m o d e i n s t r uc t i o n s ( C HM E a nd C HM K ) th a t a r e the
only me a n s a v a i l a b l e
fo r d e c r e a s i ng
access
mode ( t o
g r ea t e r p r i v i l eg e ) ( F i g u r e 1 - 4 ) ,
the i nc l us i on o f m a ny p r o t e c t i o n
chec ks
a nd
p e nd i ng
i n t e r r up t c h e c k s
in
the s i ng l e i n s t r uc t i o n t h a t i s t h e
c o mmo n i n t e r r u p t e x i t pa th , RE I ,
s o f t wa r e i n te r r up t s , a nd
ha r d wa r e c o n t e x t a nd t h e s i ng l e i n s t r uc t i o n s
LDPC TX ) t h a t s a v e a nd r e s t o r e i t .

1. 3.2

( S VPC TX

and

VAX- 1 1 I n s t r uc t i o n S e t

Wh i l e t h e VAX- 1 1 i n s t r uc t i o n s e t , d a t a
t ype s ,
a nd
a d d r e s s i ng m o d e s
we r e d e s i g n ed
to be
somewh a t c ompa t i b l e w i t h t h e PD P- 1 1 , s e v e r a l
f e a t u r e s t h a t we r e m i s s i ng
in
the
PD P- 1 1 we r e a d d ed
to
the
VAX
a r c h i tec t ur e .
T r ue
contex t
i nd e x i ng
a l l o ws
a r r a y e l em e n t s to b e
ad d r e s s e d by e l em e n t n um b e r , w i t h t h e h a r d wa r e a c c o un t i ng f o r the s i z e
( by t e ,
wo r d ,
l o ngwo r d ,
o r q u a d wo r d ) o f e a ch e l em e n t .
Sho r t l i t e r a l
ad d r e s s i ng wa s a d d ed i n r e c o g n i t i o n o f t h e f a c t tha t the m a j o r i ty o f
l i te r a l s
t h a t a ppe a r i n a p r og r am a r e sm a l l n um b e r s .
Va r i a b l e l e ng th
b i t f i e l d s a nd c h a r ac t e r d a t a t ype s we r e ad d ed to s e rv e the
need s o f
s eve r a l c l a s s e s o f u s e r s , i n c l ud i ng o pe r a t i ng s ys tem d e s i g n e r s .
Th e i n s t r uc t i o n s e t i nc l ud e s m a n y i n s t r uc t i o ns t h a t a r e u s e f u l to
any
d e s i g n e r a nd o c c u r o f t e n i n t h e VM S e x e c u t i v e .
Th e q u e ue i n s t r uc t i o n s
a l l o w t h e c o n s t r uc t i o n o f d o u b l y l i nk e d l i s t s a s a c ommo n d yn am i c d a t a
s t r uc t u r e .
C h a r a c t e r s t r i ng i n s t r uc t i o n s a r e u s e f u l wh en d e a l i ng wi th
Bi t
any d a t a s t r uc t ur e th a t c a n be t r e a ted as
an
a r ray o f byt e s .
f i e l d i n s t r uc t i o n s a l l o w e f f i c i e n t o pe r a t i o n s o n f l ag s a nd m a s k s .

1-1 1

SYS TEM OVE RV I EW

Access mode fields in the PSL are not directly accessible to the programmer or
to the operating system.

The only way to reach a
LESS privileged access
mode is through the REI
instruction.

The only way to reach a
MORE privileged access
mode is through one of
the CHMx instructions.

The boundaries between the access modes are nearly identical to the layer
boundaries pictured in Figure 1 -2 .
•

Nearly a l l o f t h e system services execute i n kernel mode.

•

RMS and some system services execute i n executive mode.
Command Language I nterpreters normally execute I n supervisor mode.

•
•

Utilities, application programs, Run-Time Library procedures, and so on
normally execute i n user mode. Privileged utilities sometimes execute in
kernel or executive mode.

Figur e 1 - 4

M e t h o d s f o r Al t e r i ng Ac c e s s Mo d e

One o f t h e mo s t im po r t a n t f e a t u r e s o f
t h e VAX a r c h i t e c t u r e
is
the
c a l l i ng
s t a nd a r d .
An y p r o c ed u r e th a t a d h e r e s to th i s s t a nd a r d c a n b e
c a l l ed
f r om a n y n a t i v e
l a ng u a g e ,
a n a d va n tag e
fo r
any
l a rg e
a pp l i c a t i o n th a t w i s h e s t o ma k e u s e o f t h e f e a t u r e s o f a wi d e r a ng e o f
l a ng ua g e s .
VM S ad h e r e s t o th i s s t and a rd
in
i ts
i nter faces
to
the
o u t s i d e wo r l d th r o ug h t h e sys t em s e r v i c e i n t e r f a c e , RMS e n t r y po i n t s ,
a nd t h e Run-T i m e L i b r a r y p r o c ed u r e s .
Al l
s ys t em
s e rv i c es
a nd
RM S
r o ut i nes
a r e wr i t t e n a s p r o c e d u r e s t h a t c a n b e a c c e s s e d by i s s u i ng a
CALLx to a b s o l u t e
location
SYS $ s e r v i c e
in
s ys tem v i r t ua l
add r e s s
s pa c e .
Run-T i m e
Li b r a r y p r o c ed u r es
a r e i n c l ud ed i n a use r ' s i m a g e
i n s t e a d o f b e i ng l o c a t ed i n s ys t em spa c e .

1 . 3. 3

Impl eme n ta t i o n o f VMS Ke r n e l Ro u t i n e s

I n t h e p r ev i o u s
sec t ion ,
w e d i v i d ed
t h e VM S k e r n e l
i n to
th r e e
f un c t i o n a l
p i ec e s a nd t h e sys t em s e rv i c e i n t e r f a c e t o t h e r e s t o f the
wo r l d .
An a l t e rna t i v e me thod of
pa r t i t i o n i ng
t h e o pe r a t i ng
s y s t em
ke rnel
is
a c c o rd i ng
to t h e m e thod u s e d to g a i n a c c e s s to e a c h pa r t .
Th r e e c l a s s e s o f r o u t i n e s w i th i n the k e r n e l a r e p r o c ed u r e - b a s e d
c od e ,
e x c ep t i o n
s e rv i ce
r o ut i ne s ,
a nd
i n te r r up t s e r v i c e r o u t i n e s .
Oth e r
s ys t em-w i d e
f un c t i o ns ,
the
s wa pp i ng
a nd mod i f i ed
pag e
wr i t i ng
1-1 2

S Y STEM OVERVI EW
pe r f o rmed
b y t h e swa ppe r , a r e i mp l em e n ted a s a s e pa r a t e p r o c e s s t h a t
r e s i d e s i n s ys t e m s pa c e .
F i g u r e 1 - 5 s h ows
the v a r i o u s
e n t r y pa t hs
i n to t h e o pe r a t i ng s y s tem k e r n e l .
E x t e r n a l Device

� Hard w a re Interrupts
� ( IPL 20 .. 23)
=

Device Driv e r
F o r k Proce ssing
Softw a re I n t e rrupts

T r a n s l a t i o n - not - V a lid
Fault
(Page Fault)

'
)l

( IPL = 8 1 1 )

( Ex c e p t i o n , not Interrupt)

....- 1 / 0 Post processing
Software Interrupt
(IPL = 4 )

�

R e s c h e d uling
Sof t w a re I n t e r ru p t

AST Delivery
Softw a re I n t e rrupt
( IPL = 2 )

( IPL = 3)
Softw are Timer
Inter rupt

H a rdware C l o c k
Interrupt

(IPL = 7 )

( IPL = 24)

Figure 1-5

Pa t h s i n to Compo n e n t s o f VM S Ke r n e l

1 . 3. 3. 1
P r o c e s s C o n te x t a nd Sys t em S t a t e - Th e f i r s t s e c t i o n o f
th i s
c h a p t e r d e sc r i b e d the p i ec e s o f t h e s y s tem tha t a r e u s ed to d e s c r i b e a
process .
P r o c e s s c o n t ex t
i n c l ud e s
a
c ompl e t e
add r e ss
s pa c e
d e sc r i p t i o n ,
quo tas ,
p r i v i l eg e s ,
s c h ed u l i ng
data ,
a n d so on .
An y
po r t i o n o f t h e s ys t em th a t e x e c u t e s i n the c o n t e x t o f a
process
can
c o u n t o n a l l o f t h e s e p r o c e s s a t t r i b u t e s b e i ng av a i l a b l e .

Th e r e i s a po r t i o n o f t h e k e r n e l , h o we v e r , t h a t o pe r a t e s o u t s i d e
the
c ontex t of
a
s pe c i f i c
process .
Th e l a rg e s t c l a s s o f r o u t i n e s th a t
f a l l i n to th i s c a t e g o r y a r e i n t e r r up t
s e rv i c e
r o ut i nes ,
i nvoked
in
r e s po n s e t o e x t e r n a l e v e n t s wi th n o r eg a r d f o r t h e c u r r e n t l y e x e c u t i ng
process .
Po r t i o n s o f t h e i n i t i a l i z a t i o n s e q ue n c e a l s o f a l l i n to
th i s
c a teg o r y .
I n a n y c a s e , t h e r e a r e n o p r o c e s s f e a t u r e s s uc h a s a k e r n e l
s t ac k o r a pag e
f a u l t h a nd l e r
a v a i l a b l e wh e n t h e s e
rout i nes
are
e x e c u t i ng .

1-13

SYSTEM OVERV I EW
B e c a u s e o f t h e l a c k o f a p r o c e s s , t h i s s ys t em s t a t e o r i n t e r r up t s t a t e
c a n b e c h a r a c t e r i z e d b y t h e f o l l o w i ng l i m i t e d c o n te x t .
•
•

•

Al l s t a c k o pe r a t i o n s t a k e p l a c e o n t h e s ys tem-w i d e
s tack .

i n t e r r upt

Th e pr i m a r y d e s c r i pt i o n o f
s y s t em
or
i n t e r r up t
s ta t e
is
c o n ta i n ed
i n t h e p r o c e s so r s t a t u s l o ng wo r d ( PS L ) .
Th i s wi l l
i nd i c a t e t h a t t h e i n t e r r up t s t a c k i s b e i ng
u s ed ,
that
the
c u r r en t a c c e s s mode
is
ke rnel
mode ,
and tha t the I PL i s
h i gh e r than I PL 2 .
Th e s ys t em c o n t r o l b l o c k , t h e d a ta
s t r uc t ur e
tha t
contro ls
t h e d i s p a tc h i ng o f i n t e r r up t s a nd e x c e p t i o n s , c a n b e tho ug h t
o f a s t h e s e c o nd a r y s t r uc t u r e th a t d e sc r i b e s s y s t em s t a te .
Co d e t h a t e x e c u t e s i n t h i s s o - c a l l ed s ys tem c o n t e x t c a n o n l y
refer
to
s ys tem v i r t u a l a d d r e s s e s .
I n pa r t i c u l a r , the r e i s
no P l space a va i l abl e .
Th i s r e q u i r e s
that
the
s ys tem-w i d e
i n t e r r up t s t a c k b e l oc a t e d i n s ys t em s p a c e .
No pag e f a u l t s a r e a l l o we d .
Th e pag e f a u l t h a nd l e r g e ne r a t e s
a
f a t a l b ug c h e c k i f a pag e f a u l t o c c u r s a nd t h e I P L i s a b o v e
I PL 2 .
No e x c ep t i o n s a r e a l l o we d .
E x c e p t i o n s , l i k e pag e f a u l t s , a r e
a s s o c i a t ed
wi th
a
process .
Th e
e x c e p t i o n d i spa t c h e r
g e ne r a t e s a f a t a l b ug c h e c k i f a n e x c ep t i o n o c c u r s a bove I PL 2
o r wh i l e t h e p r o c e s so r i s e x e c u t i ng on t h e i n t e r r up t s t a c k .
A S Ts , a s yn c h r o no u s ev e n t s t h a t a l l o w
n o t i f i c a t i o n wh e n e x t e r n a l
ev e n t s
( Th e A S T d e l i v e r y i n te r r up t
a l l owed .
d r o ps b e l o w
I PL 2 ,
an
i nd i c a t i o n
l e a v i ng i n t e r r up t s t a t e . )

a
process
to . r e c e i v e
h av e o c c u r r e d , a r e no t
i s d e l i v e r ed
wh en
I PL
tha t
the
proc esso r i s

No s ys tem s e r v i c e s a r e a l l o we d i n s ys t em
s t a te .
( In
fact ,
s ys t em s e r v i c e s c a nn o t e v e n b e c a l l ed f r om p r o c e s s c o n t e x t a t
I PL 2 .
Sys t em s e r v i c e s c a n o n l y b e c a l l e d a t I P L 0 . )

1 . 3 . 3 . 2 P r o c e s s - B a s ed Ro u t i n e s - P r o c e d u r e - b a s e d c o d e
( th e
s e rv i c e s )
and
except ion
s e rv i c e
rout ines
us ua l l y e x e c u t e
c ontex t of the c u r r e n t p r o c e s s ( on the kernel
s t ac k wh e n
in
mode ) .

sys tem
in the
k e r ne l

1.3. 3.2. 1
S y s tem S e r v i c e s - Th e s ys t em s e rv i c e s
a re
i m pl em e n t ed
as
p r o c ed u r e s .
Th i s m a k e s t h em ava i l a b l e to a l l n a t i v e m o d e l a ng ua g e s .
I n a d d i t i o n , t h e f a c t t h a t t h e y a r e p r o c ed u r e s m e a n s t h a t t h e r e
is
a
call
f r ame
on
the
stac k .
Th u s ,
e r r o r s d e te c t ed
by
a
ut i l i t y
s ub r o u t i n e u s e d by a s ys t em s e rv i c e c a n
return
an error
s i mpl y by
p u t t i ng
the
e r r o r s t a t u s i n to R O a n d i s s u i ng a RET i n s t r uc t i o n .
Al l
s u pe r f l uo us
i n fo rm a t i o n
i s c l e a n ed
off
the
s t ac k b y
the
RET
i n s t r uc t i o n .
Th e s ys t e m s e r v i c e d i s pa t c h e r s , a c t ua l l y t h e d i spa tc h e r s
f o r t h e C HMK a nd C HM E e x c ep t i o n s , a r e e x c e p t i o n s e r v i c e r o u t i n e s .
Sys t em s e rv i c e s m u s t b e c a l l ed f r om p r o c e s s
c o n tex t .
Th e y a r e no t
ava i l able
f r om
i n t e r r up t
serv i c e
r o u t i n e s o r o th e r c o d e ( s uc h a s
1-1 4

SYSTEM OVERVI EW
po r t i o n s o f t h e i n i t i a l i za t i o n s e q u e n c e )
th a t e x e c u t e s o u t s i d e t h e
c o n t ex t o f
a
process .
One
r e a so n
fo r
th i s
i s tha t the v a r i o us
s e rv i c e s a s s um e t h a t t h e r e
is
a
p r o c e s s who s e p r i v i l eg e s c a n b e
c h e c k ed
a nd
who s e quo t a s
c a n b e c h a r g ed
as pa r t
o f t h e n o rma l
o p e r a t i o n o f t h e s e rv i c e .
Some s ys t em s e rv i c e s r e f e r e n c e l o c a t i o n s i n
P l s pa c e , a po r t i o n o f a d d r e s s s pa c e o n l y ava i l ap l e wh i l e e x e c u t i ng i n
process contex t .
Sys tem s e rv i c e s a l s o m a k e a s s um p t i o n s a b o u t I P L a nd
t h a t wo u l d b e v i o l a ted i f t h e y we r e c a l l ed f r om o th e r
s yn ch r o n i z a t i o n
t h a n p r o c e s s- b a sed cod e e x e c u t i ng a t I P L 0 .

1. 3. 3 . 2. 2
Pa g e Fa u l t Hand l e r - Th e pag e r
i s a n except ion
s e rv i c e
r o u t i n e t h a t i s i nv o k e d i n r e s po n s e t o a t r a n s l a t i o n - n o t - v a l i d f a ul t .
Th e pag e r thus s a t i s f i e s pag e f a u l t s i n t h e c o n t e x t
of
the process
that
i n c u r r ed
the
f a ul t .
Be c a u s e pag e f a u l t s a r e a s so c i a t ed w i t h a
process ,
the
s ys t em
c anno t
to l e r a t e
page
f a ul t s
that occ ur
in
i n te r r upt
s e rv i c e r o u t i n e s o r o t h e r r o u t i n e s t h a t e x e c u t e o u t s i d e t h e
context o f a process .
Th e a c t u a l r e s t r i c t i o n i mp o s ed b y t h e pag e r
is
even mo re
s t r i ng e n t .
Pag e f a ul t s a r e n o t a l l o we d a bo v e I P L 2 .
Th i s
r e s t r i c t i o n a pp l i e s t o p r o c e s s - b a s e d co d e e x e c u t i ng a t e l e v a t ed I P L a s
we l l a s t o i n t e r r up t s e r v i c e c o d e .

1.3.3.3
I n te r r up t S e r v i c e Ro u t i n e s - By
t he i r
a s yn ch r o n o us n a t u r e ,
i n t e r r up t s e x e c u t e w i tho u t
the
s uppo r t o f p r o c e s s c o n t e x t ( o n the
s ys tem-w i d e i n t e r r up t s t a c k )
•

•

I /0 r e qu e s t s a r e i n i t i a t ed th r o ug h the $ Q I O s ys t em
s e rv i c e ,
wh i c h c a n
be
i s s ued
d i r e c t l y by t h e
use r
o r b y some
i n t e rm e d i a r y s uc h as RM S on th e u s e r ' s b e h a l f .
On c e
an
I /0
r e qu e s t h a s
b e e n pl a c e d i n a d ev i c e que ue , i t r em a i n s t h e r e
un t i l t h e d r i v e r
is
t r i g g e r ed ,
u s ua l l y b y a n
i n t e r r up t
g e n e r a t ed i n t h e e x t e r n a l d ev i c e .
Two c l a s s e s o f s o f twa r e
i n t e r r up t s e r v i c e
r o ut i ne s
ex i s t
solely
to
s uppo r t
the
I /0 s ub s ys t em .
Th e
fo r k
l ev e l
i n t e r r up t s a l l o w d ev i c e d r i v e r s t o l o we r I P L i n a
c o n t r o l l ed
f a sh i o n .
F i n a l p r o c e s s i ng o f I /0 r e que s t s i s a l so d o n e i n a
s o f t wa r e i n t e r r up t s e r v i c e r o u t i n e .

•

Th e t i m e r f unc t i o n s
i n VM S
i nc l ud e s uppo r t
i n bo th the
a s o f t wa r e
h a r dwa r e c l o c k
i n te r r up t
s e rv i c e
r o ut ine
a nd
i nd i v i d u a l
i n t e r r up t s e r v i c e r o u t i n e th a t a c t ua l l y s e r v i c e s
t ime r reque s t s .
An o t h e r
s o f twa r e
i n t e r r up t
pe r f o rm s
the
r e s c h e d u l i ng
f un c t i o n ,
wh e r e o n e
process
i s r emoved f r om e x e c u t i o n a nd
a n o t he r s e l e c t ed a nd p l a c ed i n to e x e c u t i o n .

1.3.3.4
Spec i a l P r o c e s s e s - Swa ppe r a nd N u l l - Th e
s wa ppe r
and
the
nul l
process
a r e d i f f e r e n t f r om a ny o th e r p r o c e s s e s t h a t e x i s t i n a
VAX/VM S s ys tem .
Th e d i f f e r e n c e s l i e n o t i n t h e i r
o pe r a t i o n s ,
wh i c h
a r e c ompl e t e l y no rm a l , b u t i n the i r l i m i t ed c o n t e x t .

1-1 5

S Y S TEM OVERVI EW
The l i m i t e d c o n tex t o f e i th e r o f t h e s e p r o c e s s e s i s d u e , i n p a r t ,
to
the
fact
that
t h e s e t wo p r o c e s s e s e x i s t a s pa r t o f t h e s y s t em i m ag e
SYS . EXE .
Th e y d o n o t h a v e to
be
c r e a t ed
wi th the
C r e a te
Process
s ys tem
s e rv i c e .
Spe c i f i c a l l y ,
th e i r
PC Bs
a nd p r o c e s s h e a d e r s a r e
a s s e m b l e d ( i n m o d u l e PDA T ) a n d l i n k e d i n to t h e
sys tem
imag e .
Oth e r
c h a r a c t e r i s t i c s o f t h e s e two p r o c e s s e s a r e l i s t ed h e r e .
•

Th e i r pr o c e s s h e a d e r s a r e s t a t i c .
Th e r e i s n o wo r k i ng
set
l i s t a nd n o p r o c e s s s e c t i o n t a b l e .
Th i s i mpl i e s t h a t n e i th e r
p r o c e s s s uppo r t s pag e f a u l t s .
Al l c o d e e x e c u t ed
b y e i th e r
p r o c e s s m u s t b e l o c k e d i n to m em o r y i n some wa y .
I n fac t , the
c o d e o f b o th o f t h e s e
pr ocesses
is
pa r t
of
t h e n o n pag ed
execut ive .

•

Bo t h p r o c e s s e s
e l im i nates
the
modes .

•

N e i th e r p r o c e s s h a s a P l s p a c e .
Th e k e r n e l s t ac k f o r
p r o c e s s i s l o c a t ed i n s ys tem s p a c e .

•

Th e n u l l p r o c e s s d o e s n o t h a v e
a
P O s pa c e
e i th e r .
Th e
s wa ppe r
u s e s a n a r r a y a l l o c a t e d f r om no npag ed po o l a s i t s P O
p a g e t a b l e f o r a s p e c i a l po r t i o n o f
process
c r ea t i o n ,
the
p a r t t h a t t a k e s p l a c e i n t h e c o n t e x t o f t h e swa ppe r p r o c e s s .

execute
ent i r e l y
i n ke rnel
mo d e .
Th i s
need
fo r
s t a c k s f o r the o th e r th r e e a c c e s s
e i th e r

De s p i t e t h e i r l i m i t ed c o n t ex t s , b o th o f t h e s e p r o c e s s e s b e h a v e
in a
n o rma l
f a sh i o n
i n e v e r y o th e r wa y .
Th e s wa ppe r a nd t h e n u l l p r o c e s s
a r e s e l e c t ed f o r e x e c u t i o n b y t h e
sched ul e r
j us t
l i ke
a n y o th e r
process
in
the
s y s t em .
Th e
s wa ppe r
s p e nd s
i ts i d l e t ime i n the
h i b e r n a t e s t a t e un t i l s o m e c o m po n e n t i n the s ys tem r e c og n i z e s a
n e ed
fo r
o n e o f t h e swa ppe r f un c t i o n s , a t wh i c h t i m e i t i s a wa k e n ed .
Th e
n u l l p r o c e s s i s a l wa ys c om p u t a b l e , b u t s e t to the l o we s t p r i o r i t y
in
the
s y s t em
( pr i o r i ty 0 ) .
A l l C P U t i m e no t used by a n y o t h e r p r o c e s s
i n t h e s ys t em w i l l b e u s ed by t h e n u l l p r o c e s s .

1.3.3.5
S p e c i a l S ub r o u t i ne s - Th e r e a r e s e v e r a l
u t i l i ty s ub r o u t i n e s
w i t h i n VM S
r e l a ted
to
s c h ed u l i ng
a n d r e so u r c e a l l o c a t i o n tha t a r e
c a l l ed f r om bo th p r o c e s s - b a s e d c o d e s uc h a s s ys t em s e rv i c e s a nd
f r om
s o f t wa r e
i n t e r r up t
s e rv i c e
rout ines .
Th e s e
s ub r o u t i n e s
are
c o n s t r a i n ed t o e x e c u t e w i th t h e l i m i t ed c o n t e x t o f i n t e r r upt o r s ys t em
s t a te .

1 . 3.4

Memo r y Ma n a g e m e n t a nd Ac c e s s Mod e s

Th e a d d r e s s t r a n s l a t i o n m e c h a n i sm i s d e sc r i b ed
in
t h e VAX H a r d wa r e
Two s i d e e f f e c t s o f t h i s o pe r a t i o n a r e o f s pe c i a l i n t e r e s t
Ha n d boo k .
t o VM S .
Wh e n a pag e i s no t v a l i d , a
t r a ns l a t i o n-no t-va l i d
e x c e pt i o n
i s g en e r a ted
tha t
t r a n s f e r s c o n t r o l to a n e x c ep t i o n s e r v i c e r o u t i n e
t h a t c a n t a k e wh a te v e r s t e ps a r e r e q u i r e d
to m a ke
the
pag e v a l i d .
Th i s e x c e p t i o n t r a n s f e r s c o n t r o l f r om a h a r d wa r e m e c h a n i sm , a d d r e s s
t r a n s l a t i o n , t o a s o f twa r e e x c ep t i o n s e r v i c e r o u t i n e , t h e pag e
faul t
h a nd l e r ,
a nd
a l l o ws VM S
to g a in control
on
add r ess t r ansl a t ion
f a i l u r e s i n o rd e r t o impl em e n t i t s d yn am i c m a pp i ng o f oag e s wh i l e
a
p r og r am i s e x e c u t i ng .

1-1 6

SYS TEM OVERVI EW
Be f o r e t h e ad d r e s s t r a n s l a t i o n m e c h a n i sm
chec k s
the val id
bi t ,
a
protec t i o n chec k
i s mad e
to d e t e rm i n e wh e th e r t h e r eque s t ed a c c e s s
wi l l be g r anted .
Th e c h e c k u s e s t h e c u r r e n t a c c e s s m o d e
in
the
PS L
( PS L < 2 5 : 2 4 > ) , a p r o t ec t i o n c o d e th a t i s d e f i ned fo r e a c h v i r t ua l pag e ,
and t h e t ype o f a c c e s s ( r e a d , m o d i f y , o r wr i te ) to m a k e i t s d e c i s i o n .
Th i s p r o t e c t i o n
check
a l l o ws VM S t o m a k e r e a d - o n l y po r t i o n s o f t h e
e x e c u t i v e i n a c c e s s i b l e to
anyo n e
(all
access mod es )
fo r
wr i t i ng ,
p r ev e n t i ng
c o r r up t i o n
o f o pe r a t i ng
s ys tem
code .
In add i t ion ,
p r i v i l eg e d d a t a s t r uc t u r e s c a n b e p r o t e c t ed f r om e v e n r e ad
access by
no npr i v i l eg e d u s e r s , p r e s e r v i ng o p e r a t i ng s ys t em s e c u r i t y .

E x c e p t i o n s , I n te r r up t s , a nd RE I

1.3. 5

Be f o r e m e n t i o n i ng
o t he r
features o f
the
e x c e p t i o n a nd
i n t e r r up t
m e c h a n i sm s
used
b y VM S , i t wo ul d b e h e l p f u l t o c ompa r e a nd c o n t r a s t
t h e s e two m e c h a n i sm s .

1.3.5.1
C ompa r i s o n o f E x c e p t i o n s a nd I n t e r r up t s - Th e fo l l o w i ng
l ist
s umma r i z e s some o f t h e c h a r a c t e r i s t i c s o f e x c e p t i o n s a nd i n te r r up t s .
•

I n t e r r up t s o c c u r a s yn ch r o n o u s l y to
t h e c u r r e n t l y e x e c u t i ng
i n s t r uc t i o n
s t r e am .
Th e y a r e a c t ua l l y s e r v i c ed
b e twe e n
i nd i v i d u a l i n s t r uc t i o n s o r a t we l l d e f i n e d po i n t s w i t h i n
the
exec ut i on
of
a
g i v en
i n s t r uc t i o n .
E x c ept i o n s
occur
s yn c h r o n o u s l y a s a d i r e c t e f f ec t
o f the
execut ion
of
the
c u r r e n t i n s t r uc t i o n .

•

Bo th m e c h a n i sm s
pa s s
control
t o serv i c e
rout ines
wh o s e
ad d r e s s e s
are
s to r ed
i n t h e sys tem c o n t r o l b l o c k .
Th e s e
r o u t i n e s pe r fo rm e x c e pt i o n- s p e c i f i c
or
i n t e r r up t - s p e c i f i c
p r o c e s s i ng .

•

Ex c e p t i o n s a r e g e ne r a l l y a pa r t o f
t h e c u r r e n t l y e x e c u t i ng
process .
Th e i r s e r v i c i ng i s a n ex t e n s i o n o f t h e i n s t r uc t i o n
s t r e am t h a t i s c u r r e n t l y e x e c u t i ng o n b e h a l f o f t h a t p r o c e s s .
I n t e r r up t s a r e s ys tem-w i d e e v e n t s tha t c a n n o t r e l y o n s uppo r t
o f a p r o c e s s i n the i r s e rv i c e r o u t i nes .

•

A c o n s e q uenc e o f th i s
l ast
i t em
is
that
the
s y s t em-w i d e
i n te r r up t
s t a c k i s u s u a l l y u s e d t o s to r e t h e PC a nd PS L t h a t
r e pr e s e n t t h e ma c h i ne s t a t e t h a t wa s i n te r r upted .
Except i on s
are
us ua l l y s e rv i c ed o n t h e pe r - p r o c e s s k e r n e l s t a c k .
Wh i c h
s t a c k to u s e i s a c t ua l l y d e t e r m i ned by c o n t r o l
b i ts
in
the
s y s t em c o n t r o l b l o c k e n t r i e s f o r e a ch e x c ep t i o n o r i n t e r r upt .

•

I n t e r r u p t s c a u s e a PC / P S L p a i r to be p u s h e d o n to
the
s t ac k .
Ex c e p t i o n s o f t e n c a u s e
e x c e p t i o n - s p e c i f i c pa r am e t e r s to b e
s t o r e d a l o ng w i th a PC/ P S L p a i r .

•

I n t e r r up t s c a u s e t h e I P L t o c h a ng e .
E x c ep t i ons
u s ua l l y d o
( Ma c h i n e c h e c k s
no t h a v e a n I P L c h ange a s s o c i a t ed w i th t h em .
a nd k e r n e l - s t a c k-no t-va l i d e x c e p t i o n s e l ev a t e I P L t o 3 1 . )

•

A c o r o l l a r y o f th i s p r ev i o u s s t e p i s t h a t i n t e r r up t s
can be
b l oc ked
b y e l ev a t i ng
I PL t o
a va l ue a t o r above t h e I PL
a s s o c i a t ed
wi t h
the
i n t e r r up t
tha t
is
to
be
b l o c k ed .
Except i on s ,
on
t h e o th e r h a nd , c a nno t b e b l o c ked .
Howev e r ,
some e x c e p t i o ns c a n be d i s a b l ed ( by c l e a r i ng a s s o c i a t ed
b i ts
i n t h e PSW) .
1-17

S Y STEM OVERVI EW
•

Wh e n an i n t e r r up t o r e x c e p t i o n o c c u r s , a n e w PS L
is
f o rmed
tha t
s umma r i z e s the n ew I PL , the c u r r e n t a c c e s s m o d e ( a l mo s t
a l wa y s k e r n e l ) , wh e th e r t h e i n t e r r up t s t a c k i s i n u s e , a nd s o
on .
On e d i f f e r en c e b e t we e n e x c e p t i o n s
a nd i n t e i r up t s , a
d i f f e r e n c e t h a t r e f l ec t s t h e f a c t
tha t
i n t e r r up t s
are not
r e l a ted
to
the
i n t e r r up t ed i n s t r uc t i o n s t r e am , i s t h a t t h e
p r ev i o us a c c e s s m o d e f i e l d i n t h e n e w PS L i s
set
to
ke rnel
fo r
i n t e r r up t s wh i l e t h e pr ev i o u s m o d e f i e l d f o r e x c e p t i o n s
r e f l e c t s t h e a c c e s s m o d e i n wh i c h t h e e x c e p t i o n o c c u r r e d .

1 . 3 . 5 . 2 O th e r Us e s o f E x c e p t i o n s a nd I n te r r up t s - I n a d d i t i o n t o
the
t r a n s l a t i o n - n o t-va l i d
f a ul t
used
by mem o r y m a n a g em e n t s o f twa r e , VM S
a l so
uses
t h e c h a ng e -mo d e- t o - k e r n e l
a nd
c h a ng e -mo d e- t o - e x e c u t i v e
e x c ep t i o n s a s e n t r y p a t h s to the ex e c u t i v e .
Sy s tem s e r v i c e s t h a t m u s t
e x e c u t e i n a m o r e p r i v i l eg e d a c c e s s m o d e u s e e i th e r t h e C HM K o r
C HM E
i n s t r uc t i o n
to g a i n
access
r ights
( Fi g ure 1-4 ) .
VM S h a nd l e s m o s t
o th e r e x c ep t i o n s b y p a s s i ng t h em t h r o ug h a c ommo n e x c e p t i o n d i spa t c h e r
d e s c r i b ed i n Ch a p t e r 2 .
Ha r dwa r e i n t e r r up t s t em po r a r i l y s u s pe nd
code
tha t
is
e x e c u t i ng
in
o rd e r
th a t a n i n t e r r up t - s pe c i f i c r o u t i n e c a n s e r v i c e t h e i n t e r r up t .
I n t e r r up t s h a v e a n I P L a s s o c i a t ed w i t h t h em .
Th e
i n te r n a l
p r o c e s so r
p r i o r i ty l ev e l ( I PL ) i s r a i s ed wh e n the i n t e r r upt i s r ec og n i zed .
High
l ev e l i n t e r r up t s e r v i c e r o u t i n e s t h us pr ev e n t t h e r e c og n i t i o n o f l o we r
l ev e l
i n te r r up t s .
Lo we r
l ev e l
i n t e r r up t
s e rv i c e
r o u t i nes c a n b e
i n te r r up t ed
b y s ub s e q ue n t h i g h e r
l ev e l
i n t e r r up t s .
Ke r n e l mo d e
r o ut i nes c a n a l so b l o c k
i n te r r up t s
a t c e r t a i n l ev e l s b y ma n ua l l y
r a i s i ng t h e I P L .
Th e VAX a r c h i t e c t u r e a l s o d e f i n e s
a
ser ies
of
s o f twa r e
i n t e r r up t
l ev e l s
t h a t c a n b e u s e d fo r a v a r i e t y o f p u r po s e s .
VM S u s e s t h em fo r
s c h ed ul i ng , I /0 c ompl e t i o n r o u t i n e s , a nd f o r s yn c h r o n i z i ng
access
to
c e r t a i n c l a s s e s o f d a t a s t r uc t u r e s .

1 . 3 . 5 . 3 Th e RE I I n s t r uc t i o n - Th e RE I i n s t r uc t i o n i s t h e c ommo n e x i t
pa t h
fo r
i n t e r r up t s
a nd
e x c e pt i o n s .
Ma ny p r o t e c t i o n a nd pr i v i l eg e
c h e c k s a r e i n c o r po r a t e d i n to t h i s i n s t r uc t i o n .
Be c a u se m o s t f i e l d s i n
the proc esso r
status
l o ng wo r d a r e no t a c c e s s i b l e t o t h e p r og r amm e r ,
t h e RE I i n s t r uc t i o n p r o v i d e s t h e o n l y m e a n s f o r c h a ng i ng
access mode
to
a
l e s s p r i v i l eg e d m o d e ( F i g u r e 1 - 4 ) .
I t i s a l s o t h e o n l y wa y t o
r e a c h c om pa t i b i l i t y m o d e .
Al tho ug h the I P L f i e l d o f t h e PS L i s a c c e s s i b l e
t h r o ug h
the
PR$ I P L
processo r
r eg i s t e r ,
e x e c u t i o n o f a n RE I i s a c ommo n wa y t h a t I PL i s
l o we r ed d u r i ng no rma l e x e c u t i o n .
Bec ause a ch ange i n
I PL can
al ter
t h e d e l i v e r ab i l i ty o f p e nd i ng i n te r r up t s , m a ny h a rd wa r e a nd e s pec i a l l y
s o f twa r e
i n t e r r up t s
a r e d e l i v e r ed
a f te r
an
RE I
i n s t r uc t i o n
is
e x e c u t ed .

1.3. 6

P r o c e s s S t r uc t u r e

Th e VAX a r c h i t e c t u r e a l s o d e f i n e s a d a t a s t r uc t u r e c a l l ed
a h a r d wa r e
process
c o n t r o l b l o c k t h a t c o n t a i n s c o p i e s o f a l l a p r o c e s s ' s g e ne r a l
r eg i s t e r s wh e n the p r o c e s s i s n o t a c t i v e .
Wh e n a p r o c e s s i s
s e l ec t e d
fo r
execut ion ,
t h e c o n t e n t s o f t h i s b l o c k a r e c o p i ed i n to t h e a c t ua l
1-18

SYSTEM OVERV I EW
r eg i s t e r s i n s i d e the p r o c e s s o r w i t h a s i ng l e i n s t r uc t i o n , LDPCTX .
Th e
c o r r e s po nd i ng
i n s t r uc t i o n
that
s a v e s t h e c o n t e n t s o f t h e g e ne r a l
r eg i s t e r s wh en t h e p r o c e s s i s r emoved f r om e x ec u t i o n i s SVPC TX .

1.4

O THER SYS TEM C ON C E PTS

i mpo r ta n t c o nc e p t s
in
We b eg a n t h i s c h a p t e r by d i s c u s s i ng the m o s t
VM S ,
p r o c e s s a nd
i m ag e .
Th e r e a r e s ev e r a l o th e r f un d am e n t a l i d e a s
tha t
sho u l d
be a t
l e a s t m e n t i o n ed
b e fo r e w e b eg i n a
d e t a i l ed
d e s c r i pt i o n o f VM S
i n ternal s .
Some o f t h e s e
ideas are br iefly
d e s c r i b ed h e r e .

1.4.1

Re s o u r c e C o n t r o l

VAX/VM S p r o t e c t s
i tsel f
a nd
o th e r
p r ocesses
in
the
s ys t em
f r om
c a rel e ss o r m a l i c i o us
u s e r s w i th h a r d wa r e a nd s o f twa r e p r o t e c t i o n
m e c h a n i sm s , s o f twa r e p r i v i l eg e s , a nd s o f twa r e q uo t a s a nd l i m i t s .

1.4.1.1
Ha r d wa r e P r o t e c t i o n - Th e
m emo ry
m a n a g em e n t
p r o t ec t i on
m e c h a n i sm
that
is
r e l a t ed
to
access mode
is
used
to
pr ev e n t
un a u t h o r i z e d u s e r s f r om m o d i fy i ng ( o r e v e n r e a d i ng )
p r i v i l eg ed d a t a
s t r uc t u r e s .
Ac c e s s m o d e p r o t e c t i o n i s a l s o u s ed to k e e p p r og r am c o d e
a nd r e a d - o n l y d a t a s t r uc t ur e s , w i th i n e i th e r t h e e x e c u t i v e o r
a
use r
p r og r am , f r om b e i ng mod i f i e d by p r og r amm i ng e r r o r s .
A m o r e s ub t l e b u t pe r h a p s mo r e i m po r t a n t a spec t o f p r o t ec t i o n p r o v i d ed
by
t h e memo r y m a n ag em e n t a r c h i t e c t u r e
i s t h a t t h e p r o c e s s ad d r e s s
s pa c e o f o n e p r o c e s s ( P O s pa c e a n d P l s pa c e ) i s n o t a c c e s s i b l e to c o d e
r un n i ng i n t h e c o n t ex t o f a n o the r p r o c e s s .
Wh e n s uc h a c c e s s i b i l i t y i s
d e s i r ed to s h a r e c ommo n r o u t i n e s o r d a t a , VM S p r o v i d e s a
c o n t r o l l ed
a c c e s s th r o ug h g l o b a l s e c t i o n s .
An o th e r d i m e n s i o n to a c c e s s i b i l i t y i s
t h a t s ys t em v i r t ua l
add ress
s pa c e
is
ava i l ab l e
to
all
processes
( a l tho ug h pag e - by-page
pr o t ec t i o n m a y d e ny r e ad o r w r i t e a c c e s s t o
s p e c i f i c s ys t em v i r t ua l pag e s fo r c e r t a i n a c c e s s m o d e s ) .

1 . 4 . 1 . 2 P r o c e s s P r i v i l e g e s - Ma n y o pe r a t i o n s t h a t
are
pe r fo rmed
by
s ys tem s e rv i c e s c o u l d d e s t r o y o pe r a t i ng s ys tem c o d e o r d a t a o r c o r r u pt
e x i s t i ng f i l e s
i f pe r f o rmed
carelessly .
Oth e r
s e rv i c e s
a l l ow a
p r o c e s s to a d v e r s e l y a f f e c t f e a t u r e s i n o th e r p r o c e s s e s i n the s ys tem .
VM S r e q u i r e s t h a t
proc esses
w i sh i ng
to
execute
these
po t e n t i a l l y
d am a g i ng o pe r a t i o n s b e
s u i t a b l y p r i v i l eg e d .
Pr o c e s s p r i v i l eg e s a r e
a s s i g ned wh e n a p r o c e s s i s c r e a t ed , e i th e r b y t h e c r e a to r , o r
th r o ug h
t h e us e r ' s r e c o rd i n t h e a u t ho r i z a t i o n f i l e .
Th e s e p r i v i l eg e s a r e d e s c r i b ed i n t h e VAX/VM S Sy s t em Ma n ag e r ' s G u i d e
in
the VAX/VM S Sys t em S e r v i c e s Re f e r e n c e Ma n ua l .
a nd
Th e p r i v i l eg e s
t h em s e l v e s a r e spe c i f i c b i t s i n a
q u a d wo r d
tha t
is
s to r ed
in the
( Th e l o c a t i o n s a nd m a n i pu l a t i o n s o f
b eg i nn i ng
o f the p r o c e s s head e r .
t h e s ev e r a l p r o c e s s p r i v i l eg e m a s ks t h a t VM S ma i n t a i n s
a r e d i sc u s s ed
in
Ch a pt e r 1 8 . ) Wh e n a VM S s e rv i c e t h a t r eq u i r e s p r i v i l eg e i s c a l l ed ,
t h e s e r v i c e c h e c k s to s e e wh e th e r t h e a s so c i a t ed b i t
in
the
process
p r i v i l eg e ma s k i s s e t .

1-19

SYSTEM OVERVI EW
1.4.1.3
Quo t a s a nd L i m i t s - VM S
a l so
contro l s
a l locat ion of
i ts
s ys t em w i d e
r esources
s uc h a s n o n pag ed d yn am i c memo r y a nd pag e f i l e
s pa c e th r o ug h the use o f q uo t a s a nd l i m i t s .
Th e s e p r o c e s s
a ttr i butes
are
a l so
a s s i g ned
wh e n t h e p r o c e s s i s c r e a t ed .
B y r e s t r i c t i ng s uc h
i t ems a s t h e n umb e r o f c o nc u r r e n t I /0 r e que s t s o r
p e n d i ng
ASTs ,
VM S
exerc i se s
c o n t ro l
ove r
t h e r e s o u r c e d r a i n th a t a s i ng l e p r o c e s s c a n
ex e r t on
s y s t em
r e so u r c e s
s uc h a s n o npag e d d yn am i c m em o r y .
In
g e ne r a l , a p r o c e s s c a nno t p e r f o rm c e r t a i n o pe r a t i o ns ( s uc h a s q u e u e a n
AS T ) un l e s s i t h a s s u f f i c i e n t q uo t a
( no n z e r o
PC B $W A S TCNT
in
th i s
c a se ) .
Th e l o c a t i o ns a nd v a l ue s o f t h e v a r i o u s q uo t as a nd l i m i t s u s e d
by VM S a r e d e sc r i b ed i n Ch a pt e r 1 7 .

1.4.1.4
U s e r I d e n t i f i c a t i o n C o d e ( U I C ) - VM S u s e s u s e r i d e n t i f i c a t i o n
c o d e ( U I C ) f o r two d i f f e r e n t p r o t e c t i o n pur po s e s .
I f a p r o c e s s w i sh e s
t o pe r fo rm some c o n t r o l o p e r a t i o n ( S u s pe nd , Wa k e , De l e t e , a nd s o o n )
o n a n o t h e r p r o c e s s , i t r e q u i r e s WOR LD p r i v i l eg e i n o rd e r t o a f f e c t a n y
p r o c e s s i n the s ys t em .
A p r o c e s s w i t h G R O U P p r i v i l eg e c a n o n l y a f f e c t
o the r
p r o c e s s e s wi th
t h e s a m e g r o up n um b e r .
A p r o c e s s w i th n e i th e r
WOR LD no r G R O U P p r i v i l eg e c a n o n l y a f f e c t
s ub p r o c e s s e s t h a t
it
has
c r e a t ed .
( Th i s m e a n s t h a t a
p r o c e s s w i th n e i th e r G R O U P n o r WOR LD
p r i v i l eg e c a nno t a f f e c t any o t h e r p r o c e s s i n the sys tem ,
even
if
it
h a s t h e s a m e U I C , un l e s s t h e t a r g e t p r o c e s s wa s c r e a t e d by t h e p r o c e s s
in ques t i o n . )
Th e U I C i s a l s o the p a r am e t e r th a t d e t e rm i n e s wh e th e r a u s e r c a n
r ead
f r om
o r w r i te to a g i v e n f i l e .
Th e o wn e r o f a f i l e c a n d e te rm i n e h o w
m u c h a c c e s s to h i s f i l e s h e g r a n t s t o h i ms e l f , t o o th e r
processes
in
t h e s am e g r o up , a nd to a r b i t r a r y p r o c e s s e s i n t h e s ys t e m .
Th e s ame U I C p r o t e c t i o n th a t e x i s t s f o r f i l e s i s a l s o u s ed
f o r o th e r
d a t a s t r uc t u r e s i n th e s ys t em .
Bo th l o g i c a l n am e s a nd g l o b a l s e c t i o n s
e x i s t i n two v a r i e t i e s , g r o up n am e s a nd s e c t i o n s o r s ys t em
n am e s a nd
secti ons .
Th e g r o up v a r i e t y i s o n l y a v a i l a b l e to o th e r p r o c e s s e s i n
t h e s am e g r o u p .
Commo n e v e n t f l ag s , f l ag s t h a t c a n b e
s h a r ed
am o ng
s e v e r a l p r o c e s s e s , a r e r e s t r i c t e d to p r o c e s s e s i n t h e s am e g r o u p .

1.4.2

Oth e r Sys t em P r i m i t i ve s

S e v e r a l o t h e r s i mpl e t o o l s u s e d b y VM S a r e m e n t i o n e d f r e e l y t h r o ug h o u t
t h i s m a n ua l b u t a r e n o t d e sc r i b e d un t i l th e f i n a l s e c t i o n , i n Ch a pt e r s
2 4 t h r o ug h 2 6 .

1 . 4 . 2 . 1 Synch r on i za t i o n - Any m u l t i p r og r amm i ng
s ys t em
must
ta k e
me a su r e s
to
p r ev e n t
s imul taneous
a c c e s s to s ys tem d a t a s t r uc t u r e s .
VM S u s e s two s i mpl e s yn c h r o n i z a t i o n t e c h n i q ue s .
By e l ev a t i ng
I PL ,
a
s ub s e t o f
i n t e r r up t s c a n b e b l o c k e d , a l l o w i ng un r e s t r i c t e d a c c e s s t o
s ys t em w i d e d a t a s t r uc t u r e s .
Th e m o s t c ommo n s yn ch r o n i z a t i o n I PL u s ed
by VM S i s I PL 7 , c a l l ed I P L $ _S YNC H .
Fo r some d a t a s t r uc t u r e s , e l ev a t e d I PL i s e i th e r an
unne c e s s a ry t o o l
or
a
po t en t i a l s ys t e m d eg r ad a t i o n .
Fo r e x ampl e , p r o c e s s e s e x e c u t i ng
a b ov e I P L 3 c a nn o t b e r e s c h ed u l ed ( r em o v e d f r om
execution ) .
Onc e a
p r o c e s s g a i ns c o n t r o l o f a d a t a s t r uc t u r e p r o t e c ted by e l ev a t e d I P L ,
i t g i v e s u p i ts
i t w i l l n o t a l l o w a n o th e r p r oc e s s t o e x e c u t e u n t i l
o wn e r sh i p .
I n ad d i t i o n , pag e f a u l t s a r e no t a l l o we d a bo v e I PL 2 a nd
1-2 0

S Y S TEM OVERV I EW
s o a n y d a t a s t r uc t u r e tha t e x i s t s i n pag e a b l e a d d r e s s s pa c e c a nno t
s yn c h r o n i z e d w i t h e l e v a t e d ! P L .

VM S r e qu i r e s a
s e c o nd
s yn c h r o n i z a t i o n
to o l
t o a l l o w s yn c h r o n i z e d
access
to
pag e a b l e d a t a
s t r uc t u r e s .
Th i s
too l m us t a l so a l l o w a
p r o c e s s to b e r em o v e d f r om e x e c u t i o n wh i l e i t m a i n t a i n s o wn e r sh i p o f
the
s t r uc t u r e
i n que st ion .
Th e s yn c h r o n i z a t i o n to o l t h a t f u l f i l l s
t h e s e r e q u i r em e n t s i s c a l l e d a m u t ua l
exc l us i o n
s em a pho r e
( M UTE X ) .
Syn c h r o n i z a t i o n , i n c l ud i ng t h e u s e o f m u t e x e s , i s d i s c u s s e d i n Ch a p t e r
24 .

1 . 4 . 2 . 2 Dyn am i c Memo r y A l l o c a t i o n - Th e
s ys t em
m a i n ta i n s
th r e e
d yn am i c m em o ry a r e a s f r om wh i c h b l o c k s o f m em o ry c a n b e a l l o c a t e d a nd
d ea l l o c a ted .
No n pag e d po o l c o n t a i n s tho s e s ys t em -w i d e s t r uc t u r e s t h a t
m i ght b e man ipul a ted
by
( h a rdwa r e o r
so f t wa r e ) i n t e r r up t s e rv i c e
r o u t i n e s o r p r o c e s s - b a sed c o d e
e x e c u t i ng
a b ov e
I PL 2 .
Pag ed
po o l
c o n ta i n s
s ys t em-w i d e
s t r uc t u r e s
tha t
d o n o t h av e t o b e k e p t m em o r y
r e s id ent .
Th e pr o c e s s a l l o c a t i o n r eg i o n , a po r t i o n o f t h e p r o c e s s
Pl
s pa c e ,
i s used
fo r pag e a b l e d a t a s t r uc t u r e s th a t wi l l n o t b e s h a r e d
among s ev e r a l p r o c e s s e s .
Dyn am i c memo r y a l l o c a t i o n
a nd d e a l l o c a t i o n
a r e d i s c u s s ed i n d e t a i l i n Ch a p t e r 2 5 .

1.4.2. 3
Log i c a l Names - Th e
s ys t em
uses
l og i c a l
n am e s
fo r
m a ny
p u r po s e s ,
i n c l ud i ng
a
t r a nspa r e n t
wa y
of
i m pl em e n t i ng
a
d ev i c e- i n d e pend e n t
I /0 s ys t em .
Th e
use
of
l og i c al
n am e s
as
a
p r og r amm i ng to o l i s d i s c u s s e d i n t h e VAX/VM S Sy s t em Se r v i c e s Re f e r e n c e
Ma n ua l .
Th e i n t e r n a l ope r a t i o n s o f t h e l og i c a l n am e sys tem
s e rv i c e s ,
a s we l l
a s t h e i n t e r n a l o rg a n i z a t i o n o f t h e l o g i c a l name t a b l e s , a r e
d e s c r i b ed i n Ch a pt e r 2 6 .

1.5

LAYOUT OF V I RTUAL ADDRES S S PAC E

Th i s s e c t i o n shows t h e a pp r o x i m a t e c o n t e n t s
pa r t s o f v i r t ua l ad d r e s s spac e .

1.5. 1

the

three

d i fferent

Sys t em V i r t ua l Ad d r e s s S p a c e

Th e l a yo u t o f s ys t em v i r t u a l
ad d r e s s
s pa c e s ys t em v i r t ua l
add ress
s pa c e
l a yo u t
is
p i c t u r ed
in Figure 1-6 .
De t a i l s s uc h a s No-Ac c e s s
g ua r d pag e s a t e i th e r end o f t h e i n t e r r up t s t a c k a r e om i t t ed t o
avo i d
c l u t t e r i ng t h e d i ag r am .
Ta b l e E - 2 i n Ap pend i x E l i s t s a mo r e c o m p l e t e
l a yo u t o f s ys tem spac e , i n c l ud i ng
t h e s e g ua r d
p ag e s ,
sys tem
pag e s
a l l o c a t e d b y d i s k d r i v e r s , a n d o th e r d e t a i l s .
Th i s f i g u r e wa s p r o d u c ed f r om two l i s t s p r ov i d ed b y t h e
s ys t em
d um p
analyzer
( th e
s ys t em pag e t a b l e a nd t h e c o n t e n t s o f a l l g l o b a l d a t a
a r e a s i n s ys t em s p a c e ) a nd f r om
t h e s ys t em m a p SYS $ S YS TE M : SY S . MA P .
Th e
r e l a t i o n s b e twe e n t h e v a r i a b l e s i z e p i e c e s o f s ys t em spa c e a n d
t h e i r a s s o c i a t ed S YS B OOT pa r am e t e r s a r e g i v e n i n App e nd i x E .

1-21

SYSTEM OVERV I EW
80000000

S y s t e m Service Vectors
Linked Driver Code and D a t a Structures
Nonpaged E x ecutive D a t a
Nonp a ge d E x ecutive C o d e

P a g e a ble Ex ec utive Routines
s t a t ic Portion ( SY S .E X E )

X D E LTA ( usually unmapped), INIT
S y s t e m Virtual Pages
M a p p e d to 1 / 0 Addresses

D ynamically m apped a t
in itia lization time

RMS I m a ge
(RMS.EXE)

System Message File
( SY SMSG.EXE)

�

Pool of Unmapped System P a g e s

��

Restart Parameter Block
PFN D a t abase

Paged Dynamic Memory

Nonpaged Dynamic Memory
Interrupt Stack
System Control Block

��

Balanc e Slots

��

System Header
System P a ge Table
High address end
of system virtual
address space

Fi gur e 1 - 6

1 . 5. 2

Global Page Table

La yo u t of Sys t em V i r t ua l Ad d r e s s Spa c e

Th e C o n t r o l Reg i o n

(Pl Space )

F i g u r e 1 - 7 s h ows t h e l a yo u t o f P l s pa c e .
Th i s
f i g u r e wa s p r o d uc ed
m a i n l y f r om
i n fo rma t i o n c o n t a i n ed in m o d u l e S H E L L , wh i c h c o n t a i n s a
p r o to type o f a P l pag e t a b l e
that
is
used
wh e n ev e r a
process
is
c r e a t ed .
An S DA l i s t i ng o f p r o c e s s pag e t a b l e s wa s u s e d to d e t e rm i n e
t h e o r d e r a nd s i z e o f t h e po r t i o ns o f P l s p a c e n o t d e f i n ed i n S HE LL .

1-22

SYSTEM OVE RV I EW

40000000
Ima g e-Specific Porti o n
of P 1 Space

User S t ac k

(Dele ted at Image E x i t
\ by MMGSIMGRESET

Image 1/0 Segment

)

Per-Process Message Section (s)
CLI S ymbo l Table

Dyn amic Permane n t
Portion of P 1 Space

+---e ::CTLSGL..CTLBASVA

(

CLI Image

P1 W indow to Process Header

Locates Initial low
address end of P1
space for each process
as It Is created

Process 1 / 0 S e g ment

Static Permanent
Portion of P 1 Space

Per Proc ess C o mmon Area

Per Proc e s s Co mmon Area
Compa tibility Mode Data Page

(no longer used)

Process Alloca tion Region

Generic CLI Data P a ge s
I mage Activ a tor Scratch P a g es
Debu gger Co nt e x t
Vec tors l o r Messages a n d User-Written System Services

Image Header Buffer
Kernel Stack
E x ecutive Stack
Superv i s or Stack
P 1 Poi n t er P a g e

Debugger Sy mbol Table
(not mapped if debugge r not present )

Figure 1-7

7 F F FFFFF

L a yo u t of P1 S p a c e

1-2 3

)

+---e : :MMGSG L - CTLBASVA

Channel Control Block Ta ble

)

Locates border between
image -specific a nd
process-permanent
pieces of P 1 space

SYSTEM OVERVI EW
Some o f t h e p i ec e s o f
Pl
s p a c e a r e c r e a t ed
d y n a m i c a l l y wh e n t h e
p r o c e s s i s c r e a t ed .
Th e s e i n c l ud e a P l m a p o f p r o c e s s h e ad e r pag e s , a
c ommand l a ng uag e i n t e r p r e t e r i f o n e i s b e i ng u s ed , a nd a s ymb o l
tab l e
fo r that C L I .
Th e two p i e c e s o f P l s pa c e a t the l o we s t v i r t ua l ad d r e s s e s
( th e u s e r
s t a c k a nd t h e i m a g e I /0 s egme n t ) a r e c r e a ted d yn am i c a l l y e a c h t i me a n
i m a g e e x e c u t e s a nd a r e d e l e te d a s pa r t o f i m a g e
r un d o wn .
Append i x E
c o n ta i ns
a d e sc r i p t i o n o f
the
s i ze s o f the d i ffe rent p i ec e s o f P l
s pa c e .
Ta b l e E - 4 i n App e nd i x E sh ows a c om p l e t e l a yo u t o f
Pl
s pa c e ,
i n c l ud i ng d e t a i l s
s uc h
a s m em o r y m a n a g em e n t pag e p r o t e c t i o n a nd t h e
n a m e o f t h e s ys tem c ompo n e n t t h a t m a ps a g i v e n po r t i o n .

1. 5. 3

The Prog r am Reg i o n ( P O Spac e )

F i g u r e 1 - 8 s h ows a t yp i c a l l a yo u t o f P O s pa c e f o r b o th a
n a t i ve mode
( p r o d uc e d
by t h e VAX- 1 1 L i n k e r ) a n d a c ompa t i b i l i t y m o d e i m ag e
imag e
( p r o d uc e d by t h e RSX- l l M t a s k b u i l d e r ) .
Th i s
f ig ure
i s m uc h m o r e
c o n c e p t ua l
than
t h e p r ev i o us two i l l us t r a t i o n s b e c a u s e P O s p a c e d o e s
n o t c o n t a i n p i ec e s o f t h e e x e c u t i v e l i k e P l s p a c e a nd s ys t em s pa c e d o .
Th e f i g u r e d o e s s h o w t h e d e f a u l t o rd e r o f P O s p a c e i n t h e a b s e n c e o f
e x p l i c i t i n s t r uc t i o n s t o t h e l i n k e r .
Th e o rd e r i n wh i ch v i r t u a l spa c e
i s a l l o c a t ed i s a l s o s h o wn .
By d e f a u l t , t h e f i r s t pag e o f P O s p a c e
{0
to
l FF )
i s no t
ma pped
{ p r o t ec t i o n
set
to
No
Ac c e s s ) .
Th i s e n a b l e s e a s y
d e t e c t i o n o f t wo c ommo n p r og r amm i ng e r r o r s , u s i ng z e r o
or
a
sma l l
n um b e r a s t h e ad d r e s s o f a d a t a l oc a t i o n o r u s i ng s uc h
a sma l l n um b e r a s t h e d e s t i n a t i o n o f a c o n t r o l t r an s f e r .
( A l i n k t i m e r e que s t o r a s ys tem s e rv i c e c a l l c a n
a l te r
the
p r o t ec t i o n o f v i r t ua l pag e z e r o .
No t e a l s o th a t pag e z e r o i s
a c c e s s i b l e t o c ompa t i b i l i t y m o d e i m ag e s . )
(1)

An y p r ev i o u s l y l i n k e d
sh a r ed
image
that
i s n o t po s i t i o n
i nd epend e n t
( P I C ) i s p l a c ed a t i t s p r ev i o u s l y s pe c i f i ed b a s e
add res s .

(2)

Pa r t s o f t h e u s e r i m a g e t h a t a r e
b eg i n n i ng a t a d d r e s s 2 0 0 { h e x ) .

(3)

I f the r e i s a n y r o om be twe e n the t wo p i e c e s a l r e a d y p l a c ed i n
P O s pa c e ,
th i s
r o om i s f i l l ed f i r s t wi t h p r ev i o u s l y l i nk e d
P I C code and d a ta

(4)

a nd t h en w i t h P I C c o d e a nd d a t a t h a t a r e
u s e r i m ag e .

(5)

I f t h e Run- T i m e L i b r a r y ( P I C a nd s h a r ed ) i s r e q u i r e d and no t
o ve r r i d d en
( w i t h a /NOSYS SHR q u a l i f i e r to the L I NK c omma nd ) ,
t h i s b e c ome s t h e l a s t p i e c e o f t h e i mag e .

(6)

I f t h e d e b ug g e r o r t h e t r a c e b a c k f a c i l i ty i s r eq u i r ed ,
these
i m ag e s a r e
a d d ed
at
exec u t i o n
t ime
{ even
i f /DEBUG wa s
s e l e c t ed a t l i n k t i m e ) by pr o c ed u r e S Y S $ I MG S TA .
Th i s m a pp i ng
i s d e s c r i be d i n d e t a i l in Ch a pt e r 1 8 .

1-24

not

PIC

are

ad d ed

pa r t

nex t ,

the

Native Mode Image

No Access Page

This part of
PO space Is
defined by the ...
linker and
mapped by the
Image activator

0
0

NON-PIC Image
PIC Shared and
PIC Image
(As much as- fits)
NON-PIC shared
code and data
(Previously linked)

The AME is
mapped b y the
image activator
when i t detects
tha t it is
a ctiv ating a
compatibility
mode ima g e

RTL Vectors

G)
This part of
PO space Is
not defined at
link time
If either of
these pieces Is
required, It It
mapped

�

This portion
of PO space
is defined by
the R S X-1 1
task builder
and mapped
by the AME

Compa tibility Mode Image
0

Compatibility
Mode Image
End of Compatibility
Mode Image

not mapped

The rest of PIC
Shared and PIC Image
(If any)

- - - - - - - - - -

�
I
N
U1

Run Time Library
VMSRTL.EXE

( If needed a nd n o t e x cluded)

Debugger ( LIB$DEBUG )

RSX- 1 1 M AME
( RSX.EXE)
(BACKTRANS.EX E )
.

Nativ e M o d e Image

��

(If requested at link,
run, or execution time)

...

Tra c eback (LIB$TRACE )

��

(If not overridden at link
time and needed)

not mapped

POLR Pages

��

3FFFFFFF

Figure 1-8

1 7 7 7 7 7 8 = FFFF 16

PO Spa c e A l l o c a t i o n

not mapped

POLR Pages

��

3FFFFFFF

PART I I

C ONTROL MECHAN I SMS

" Wo u l d yo u t e l l me , p l e a s e , wh i c h wa y I o ug h t
t o g o f r om h e r e ? "
" Th a t d e pend s a g o o d d e a l on wh e r e
to g e t to , " s a i d t h e Ca t .

yo u

wa n t

Al i c e ' s Ad v e n t u r e s i n Wo nd e r l a nd
Lewi s Ca r r o l l

C HAPTER 2
C OND I T I ON HANDLI NG

One o f t h e d e s i g n g o a l s o f t h e VAX a r c h i te c t u r e wa s a g e ne r a l i z e d
u n i fo rm
c o nd i t i o n h a nd l i ng
f a c i l i ty f o r
b o th h a r d wa r e d e t e c t e d
e x c e p t i o n s a nd s o f twa r e g e n e r a t ed c o nd i t i o n s .
I n add i t ion
t o m a k i ng
t h i s f a c i l i t y a v a i l ab l e to u s e r s , VAX/VM S u s e s m a ny o f t h e f e a t u r e s o f
t h e c o nd i t i o n h a nd l i ng f a c i l i ty f o r i t s o wn p u r po s e s .

2. 1

OVERVI EW OF THE C OND I T I ON HANDL ING FAC I L ITY

Th e g e ne r a l i z e d c o nd i t i o n h a nd l i ng f a c i l i ty t h a t i s i n c l ud ed
as pa r t
of
t h e VAX a r c h i t e c t u r e p r ov i d e s u s e r s a nd the s ys t em w i t h a po we r f u l
t o o l i n h a nd l i ng
except ional
c o nd i t i o n s
that
a r i se
d u r i ng
no rma l
p r og r am
e x ec u t i o n .
I n add i t io n ,
s o f twa r e d e t e c t ed c o nd i t i o n s ( no t
n e c e s s a r i l y i nd i c a t i ng a n e r r o r ) c a n b e pa s s ed t o VM S t o a l l o w t h em to
be h a nd l ed in e x a c t l y t h e s am e m a n ne r as h a r d wa r e d e te c t e d e x c e p t i o n s .
Th e o p t i o n s t h a t a r e a v a i l a b l e t o u s e r p r og r am s t o a l l o w t h em
to
use
the
features
o f t h e VAX- 1 1 c o nd i t i o n h a nd l i ng f a c i l i ty a r e d e s c r i bed
i n the VAX/VM S
Re f e r en c e Ma n ua l
a nd
t h e VAX- 1 1
sy s t em S e rv i c e s
Run-T i m e
L i b r a r y Re f e r e n c e Ma n ua l .
Th i s c h a p t e r d i s c u s s e s h o w t h e
t o o l s d e sc r i b e d
in
tho s e
t wo m a n u a l s a c t ua l l y
i m pl em e n t
the i r
f e a tu r e s .

G o a l s o f VAX- 1 1 Cond i t i o n H a nd l i ng F a c i l i ty

2.1.1

S o m e o f t h e g o a l s o f t h e VAX- 1 1 c o nd i t i o n h and l i ng
f a c i l i t y r e f l ec t
goals
o f t h e VAX- 1 1 p r o c ed u r e c a l l i ng s t a nd a r d .
O t h e r g o a l s r e f l ec t
t h e d e s i r e t o p l a c e a n e a s y- t o - u s e g e n e r a l p u r po s e m e c h a n i sm i n to
the
o pe r a t i ng
s ys tem s o
th a t a pp l i c a t i o n p r og r am s a nd
o th e r l a ye r ed
p r od uc t s
s uc h
a s c om p i l e r s c a n
use
t h i s m e c h a n i sm
r a th e r
than
i nv e n t i ng
t h e i r o wn a pp l i c a t i o n - s p e c i f i c to o l s .
Some o f t h e e x pl i c i t
a nd i mpl i c i t g o a l s o f t h e VAX- 1 1 c o nd i t i o n h a nd l i ng f a c i l i t y a r e t h e
f o l l o w i ng .
1.

the
i nc l ud ed
in
be
Th e c o nd i t i o n h a nd l i ng f a c i l i ty sho u l d
a r c h i t e c t u r e s o th a t i t i s a v a i l a b l e a s a pa r t
base mach i ne
so f t wa r e
some
a nd
a s pa r t o f
no t
o f the
base mac h i ne
f o r c o nd i t i o n h a nd l e r
r es e rved
s pa c e
Th e
c ompo n e n t .
f r am e
the
call
of
l o ng wo r d
the f i rs t
in
add resses
a c c omp l i sh e s t h i s .

2-1

C OND I T I ON HANDL I NG
2.

By i n c l ud i ng t h e h a nd l e r spe c i f i c a t i o n a s a p a r t o f t h e c a l l
f r am e ,
s ignal
h a nd l i ng
i s a n i n t eg r a l pa r t o f a p r o c e d u r e ,
r a th e r
than a g l obal
f a c i l i ty w i t h i n a
proc ess .
Th i s
cont r i butes
t o t h e g e ne r a l g o a l o f m o d u l a r p r o c ed u r e s .
Th i s
a l so a l l ows c o nd i t i o n h a nd l e r s
t o b e n � s t ed ,
wh e r e
i nn e r
h a nd l e r s c a n
e i th e r s e r v i c e a d e t ec t ed e x c e p t i o n o r pa s s i t
a l o ng t o some o u t e r h a nd l e r i n the c a l l i ng h i e r a r c h y .

S o m e l a ng uag e s s uc h a s BAS I C a nd
PL/I
h ave
s i g n a l l i ng
and
e r r o r h a nd l i ng a s pa r t o f t h e l a ng uag e s pe c i f i c a t i o n .
Th e s e
l a ng uag e s c a n u s e the g e ne r a l m e c h a n i sm r a th e r t h a n i nv e n t i ng
t h e i r o wn p r o c ed u r e s .

Th e r e s h o u l d be l i t t l e o r no c o s t to p r o c ed u r e s t h a t d o
no t
e s t a b l i sh h a nd l e r s .
Fu r th e r ,
p r o c ed u r e s t h a t d o e s t a b l i sh
h a nd l e r s s h o u l d i n c u r l i t t l e o v e r h e a d f o r e s t a b l i s h i ng
t h em ,
w i th t h e
expense
in
t ime
b e i ng
i n c u r red
wh e n a n e r r o r
a c t ua l l y o c c u r s .

As f a r a s t h e u s e r o r a ppl i c a t i o n p r og r amme r
is
c o n c e r n ed ,
'
t h e r e s h o u l d be n o d i f f e r e nc e i n t h e a ppe a r a n c e o f e x c e p t i o n s
i n i t i a l l y d e t e c t e d b y t h e h a r d wa r e a nd s i g n a l s g e n e r a t e d b y
s o f twa r e .

Fe a t u r e s o f VAX- 1 1 C o nd i t i o n Hand l i ng Fa c i l i ty

2.1.2

Some o f t h e f e a t u r e s o f t h e VAX- 1 1 c o nd i t i o n h a nd l i ng
fac i l i ty show
h o w t h e s e g o a l s we r e a t t a i n ed .
Oth e r s r e f l ec t t h e g e ne r a l d e s i r e t o
p r od uc e a n e a s y- t o - u s e
b u t g en e r a l
c o nd i t i o n h a nd l i ng m e c h a n i sm .
Fe a t u r e s o f
the VAX- 1 1
c o nd i t i o n h a nd l i ng
f a c i l i ty
i n c l ud e
the
f o l l o w i ng .
1.

A c o nd i t i o n h a nd l e r h a s th r e e o p t i o n s a v a i l a b l e to
it.
Th e
h a nd l e r c a n f i x t h e c o nd i t i o n ( c o n t i n u i ng ) .
Th e h a nd l e r m a y
n o t be c a p a b l e o f f i x i ng
t h e c o nd i t i o n
so
i t pa s s e s
the
c o nd i t i o n o n
to
the
n e x t h a nd l e r i n t h e c a l l i ng h i e r a r c h y
( r e s i g n a l l i ng ) .
Th e h a nd l e r c a n a l t e r the
f l ow o f cont rol
( un w i nd i ng t h e c a l l s t ac k ) .

Be c a u s e c o nd i t i o n h a nd l e r s a r e
t h em s e l v e s p r o c ed u r e s ,
they
have the i r
o wn c a l l f r ame w i th i t s o wn s l o t fo r a c o nd i t i o n
h a nd l e r
add r e s s .
Th i s g i v e s h a nd l e r s t h e
a b i l i ty
to
e s tabl i sh
t h e i r o wn h a nd l e r s t o f i e l d e r r o r s t h a t t h e y m i g h t
c a use .

Th e g o a l s r e l a t ed to c o s t i n s pa c e a nd t i m e we r e r e a l i z e d b y
u s i ng
only a
s i ng l e
l o ng wo rd pe r p r o c ed u r e a c t i v a t i o n f o r
h a nd l e r a d d r e s s s to r ag e .
Th e r e
i s no
cost
in
t i me
fo r
p r o c ed u r e s
t h a t d o no t e s t ab l i s h h a nd l e r s .
P r o c ed u r e s t h a t
do
e s t a b l i sh h a nd l e r s
can d o so
wi th a
s i ng l e
MOVAx
i n s t r uc t i o n .
No t i me i s s pe n t l o o k i ng f o r c o nd i t i o n h a nd l e r s
u n t i l a s i g n a l i s a c t ua l l y g e ne r a t ed .

Th e m e c h a n i sm i s d e s i g ned to wo r k e v e n i f a c o nd i t i o n h a nd l e r
is
wr i t t e n
in
a
l a ng uag e
t h a t d o e s n o t p r o d uc e r e e n t r a n t
code .
Th u s ,
if a
c o nd i t i o n h a nd l e r
wr i t t e n
i n FORTRAN
g enera ted
an
e r r o r , th a t e r r o r wo u l d n o t be r e po r ted to th e
s am e h a nd l e r .

2-2

C OND I T I ON HANDL I NG
I n f a c t , t h e s pe c i a l a c t i o n s th a t a r e t a k e n
in
r e s po n s e
m u l t i pl y a c t i v e s i g n a l s h a s a s e c o nd b en e f i t , n ame l y t h a t
c o nd i t i o n h a nd l e r h a s
t o wo r r y a bo u t
e r ro r s
th a t
g ene r a tes ,
b e c a use
a
h a nd l e r
wo u l d
n ev e r b e c a l l ed
r e s po n s e to i t s o wn s i g n a l s .

2. 2

to
no
it
in

Un i f o rm ex c e p t i o n d i spa tch i ng
f o r h a r d wa r e a nd
so f twa r e
except i ons
is
a c compl i shed by p r ov i d i ng p a r a l l e l m e c h a n i sms
fo r
the
t wo
f o rm s
of
e x cept i o n s .
So f twa r e
d e t e c ted
ex cept i ons
a r e g e n e r a ted
by c a l l i ng
a
p r o c ed u r e
in t h e
Run-T i m e L i b r a r y .
Ha r d wa r e e x c ep t i o n s t r an s f e r co n t r o l to a n
e x c e p t i o n d i s pa t c h e r
i n the execut ive .
Wh i l e t h e i n i t i a l
e x e c u t i o n o f th e s e two m e c h a n i sm s d i f f e r s s l i g h t l y t o r e f l e c t
t h e i r d i f f e r i ng
i n i t i a l co nd i t i o n s , t h e y e v e n t ua l l y e x e c u t e
nea rly
i d ent i c a l
i n s t r uc t i o n
sequenc es
so
th a t
the
i n fo rm a t i o n
r e po r t ed to c o nd i t i o n h a nd l e r s i s i nd e pend e n t o f
t h e i n i t i a l d e t e c t i o n m e c h a n i sm .

By m a k i ng c o nd i t i o n h a nd l i ng a pa r t o f a
proced ur e ,
h igh
l ev e l
l a ng uag e s h av e
t h e c a pa b i l i ty to e s t a b l i s h h a nd l e r s
t h a t c a n e x am i n e a g i v e n s i g n a l
a nd d e t e rm i n e wh e th e r
the
s ignal
wa s g e n e r a ted
a s a pa r t o f t h a t l a ng u a g e ' s s uppo r t
l ibrary.
I f so , t h e h a nd l e r · c a n a t tempt to f i x t h e e r r o r
in
the manner
d e f i ned
b y the
l a ng ua g e .
I f n o t , t h e h a nd l e r
p a s s e s t h e s i g n a l a l o ng to pr oced u r e s
f u r th e r
up t h e c a l l
stack .

GENERAT I ON OF E XC E PT I ONS

On e wa y of c l a s s i f y i ng the c o nd i t i o n s th a t occ u r i n a r un n i ng VAX/VM S
s y s tem
is
to
s e pa r a t e tho s e c o nd i t i o n s tha t o r i g i n a t e i n the VAX- 1 1
h a r dwa r e f r om tho se th a t
are
i n i t i a t ed
b y so f twa r e .
Th e p r i m a r y
d i f f e r e n c e s b e twe e n t h e two s e t s o f i n i t i a l c o nd i t i o n s a r e th e i n i t i a l
s t a t e o f the s t a c k t h a t c o n t a i n s
the
e x c e pt i o n p a r a m e t e r s a n d
the
l oc a t i o n of
t h e r o u t i n e th a t pe r f o rm s t h e d i s pa t c h i ng .
Th e i n i t i a l
e x e c u t i o n o f the two d i spa tc h e r s
r e f l e c t s t h e s e d i f f e r i ng
initial
c o nd i t i o n s .

2. 2. 1

E x c e p t i on s Th a t O r i g i n a t e i n t h e H a rdwa r e

Wh e n a n e x c e p t i o n i s d e t e c t ed b y t h e h a r d wa r e , t h e e x c e p t i o n P C a nd
PS L
( a n d po s s i b l e e x c e p t i o n - s p e c i f i c pa r ame t e r s ) a r e p u s h e d o n to t h e
a pp r o p r i a t e s t a c k .
Th e a pp r o p r i a t e s ta c k i s d e te rm i n ed b y t h e
access
mode
i n wh i ch
t h e e x c e p t i o n o c c u r red
and
wh e th e r
t h e C P U wa s
p r ev i o u s l y e x e c u t i ng on the i n t e r r up t s t a c k .
•

I f t h e e x c e p t i o n o c c u r r ed i n a ny mod e o th e r t h a n
ke rnel
a nd
t h e e x c e p t i o n wa s
n o t a C HMU , C HMS , o r C HM E e x c e pt i o n , t h e
kernel
stack
is
used .
( Th e
i nt e r r up t
s tac k
is
not a
cons i d e ra t i on
i n t h i s c a s e b e c a u s e i t i s i m po s s i b l e to be o n
t h e i n t e r r up t s t a c k i n o th e r t h a n ke r n e l m o d e . )

•

I f t h e e x c ep t i o n o c c u r r e d i n k e r n e l m o d e a nd t h e k e r n e l s t a c k
wa s
i n use ,
t h e k e r n e l s t a c k i s a l s o u s e d a s th e ex c e p t i o n
s ta c k .

2-3

C OND I T I ON HANDL ING
•

I f t h e e x c e p t i o n o c c u r r ed i n k e r n e l m o d e a nd
the
i n t e r r up t
s t a c k wa s
in
use ,
the
i n t e r r upt
s ta c k
is
used
as the
e x c ept i o n s t a c k .
VM S d o e s n o t
e x pe c t
except i o ns
to
occur
wh e n i t i s o pe r a t i ng o n t h e i n t e r r up t s t a c k .
I f an ex c ep t i o n
s h o u l d o c c u r o n t h e i n t e r r up t s t a c k , t h e e x c ep t i o n d i s pa t ch e r
g e n e r a t e s a VM S - r e q u e s t ed
s ys t em c r a sh
c a l l ed a b ug c h e c k
( Ch a p te r 7 ) w i th a B UG $_I NVE XC E PTN c o d e .

Th e a c t ua l s t a c k ( i n t e r r upt o r k e r n e l ) th a t
is
used
to
s e rv i c e
an
e x c ep t i o n
o r i n t e r r up t i s d e t e rm i n ed b y t h e l o w-o r d e r two b i t s i n th e
S C B e n t r y a nd wh e th e r t h e i n t e r r up t s t a c k
i s a l ready
in
use .
Th e
rules
j us t
f o rm u l a ted
r e f l ec t t h e b e h av i o r o f VM S , wh e r e e x c e p t i o n s
a r e a s s o c i a t e d w i th a p r o c e s s a nd s e rv i c ed o n
tha t
process ' s
ke rnel
s t a c k ( b e c a u s e t h e l o w-o r d e r two b i t s i n t h e S C B e n t r y a r e z e r o ) .
Th e
i n te r r up t s t a c k i s o n l y u s ed
if
i t wa s a l r e a d y
i n u s e wh e n t h e
e x c ep t i o n o c c u r r e d .
No t e t h a t two s e r i o u s a b o r t s ( ma c h i n e c h e c k a nd
k e r n e l s t a c k n o t va l i d ) , e x c ept i o n s t h a t a l s o c h a ng e I P L
to
31 ,
are
s e rv i c ed o n t h e i n t e r r u pt s t a c k b y VM S .
Af t e r a l l o f t h e e x c e p t i o n i n fo rm a t i o n h a s b e e n p u s h e d o n to t h e s t a c k ,
control
i s t h e n pa s s ed to a n e x c e p t i o n - s pec i f i c s e r v i c e r o u t i n e who s e
ad d r e s s i s s to r e d i n t h e S y s tem Co n t r o l B l o c k ( F i g u r e 2 - 1 ) .
Th e
use
of
the
f i r s t twe nty l o c a t i o n s o f th i s tab l e a r e l i s t ed i n Ta b l e 2 - 1 .
Mo s t o f t h e e x c e p t i o n s t h a t a r e l i s t ed i n th i s t a b l e a r e h a nd l ed i n a
un i fo rm wa y by VM S .
Th e a c t i o n s t h a t VM S t a k e s i n r e s p o n s e to th e s e
e x c e p t i o n s wi l l b e t h e s ub j e c t o f mo s t o f th i s c h a p t e r .
Some o f t h e
except i ons ,
h owe ve r ,
r e s ul t
in
s pe c i a l
a c t i o n o n th e pa r t o f VM S .
Th e s e e x c e p t i o ns a r e d i s c u s s ed i n t h e pa r ag r a ph s th a t f o l l o w a n d a r e
i nd i c a t e d i n Tab l e 2 - 1 b y a n a s t e r i s k .
.-tiiiL
�

E x ceptions ( 20)

·�

P ro c e s s o r F a u l t s ( 1 2 )
S o f t w a r e I nt e r r u p t s ( 1 6 )

PR$-SCBB

T h e Sy stem Control Block
B a s e R e g i s te r ( SC B B )
c o n t a in s t h e p hy s i c a l
address of t h e page
a ligned System Control
B l o c k ( SC B )

C l o c k a nd C o n s o l e ( 1 6 )

Ex t e r n a l A d a p t e r

1 1 -

I n t e rr u p t s

I : : E X E $ G L_SC B

The s y s t e m v i rt u a l a d d r e s s
of t h e S C B i s s t o r e d
in g l o b a l l o c a t i o n E X E $ G L_S C B
T h e VAX-1 1 /750 system control block is
two pages long. The second page Is
used for directly vectored UNI BUS d evice interrupts.

S y s t e m C o n t ro l B l o c k

Figur e 2-1

The VAX-1 1 /780 system control block is
one page long.

Sys t em C o n t r o l B l o c k

2-4

Ta b l e 2 - 1
U s e o f F i r s t 2 0 Loc a t i o n s i n Sys tem Co n t r o l B l o c k
Byte
f r om

Of f s e t

E x c e p t i o n Name

S C B Ba s e

Un u s ed

Mac h i ne

�e r n e l

Ch e c k
Stac k

Ex t r a

Type ( Ab o r t ,

No t e s o n VM S

Pa r am e t e r s

Fa u l t , Tr a p )

D i s pa tc h i ng

No t e
n o t Va l i d

Po we r f a i l

Note

Commen t s

No t e

( Ch a pt e r

Abo r t

No te

I PL = 3 1 ,

I n t e r r up t

No te

I PL = 3 0

7)
I n t e r r up t

( Ch a pt e r

l\J

lJ1

Re s e r v e d / P r i v i l eg ed

C u s t ome r

Re s e r v ed

R e s e r v ed

Op e r a nd

R e s e r v ed

Ad d r e s s i ng

Ac c e s s

Tr ansl a t io n

I n s t r uc t i o n

Mo d e

Vi o l a t i o n
no t

Va l i d

(1)

Th e ma c h i n e c h e c k e x c e p t i o n i nd i c a t e s
and
ke rnel
mod e
cause
b ug ch ec k s .
n o r m a l e x c e p t i o n d i s pa t c h m e t h o d .

(2)

Th e

ke rnel

( 3)

Powe r f a i l

(4)

Th e

(5)

I f e x e c u t i v e d e b ug g i ng
pend i ng a r e a l t e r ed t o

(6)

except i o n

serv ice

causes

r o u t i ne

i n t e r r up t

t r a n s l a t i o n - n o t-va l i d

fo r
tha t

faul t

the

Fa u l t

Abo r t/ Fa u l t

Faul t

Fa u l t

Faul t

s t a c k no t va l i d

control

e n t r y pa th

the

i n to

a bo r t

p o we r fa i l

the

pag i ng

( XD E LTA ) i s s e l e c t ed a t S Y S B OO T t i m e , t h e
po i n t i n to XDE LTA f a u l t h a nd l e r s ( Ch a p t e r

Th e c h a ng e-mod e - t o - k e r n e l
RM S p r o c ed u r e s .

a nd

XF C

No te

p r o c e s s o r d e te c t e d i n t e r n a l
Ma c h i n e c h e c k s i n s upe r v i so r

pa s s e s
the

c h a n g e-mo d e - t o- e x e c u t i v e

t r a ps

a re

St a c k

23)

I n s t r uc t i o n

( Ch a pte r

12)

e r ro r .
Ma c h i n e
chec ks
in
exec ut i ve
a n d u s e r m o d e a r e r e po r ted t h r o ug h t h e

i ssues

b ug c h ec k .

h a nd l e r .
fac i l i ty
except ion

i n VM S .
v e c to r s

for

B PT

and

trace

22) .
the

entry paths

i n to

s y s t em

service

and

( co n t i nued on next pag e )

Ta b l e 2 - 1

( co n t . )

U s e o f F i r s t 2 0 Loc a t i o n s i n Sys t em Co n t r o l B l o c k
Byte Of f s e t
f r om S C B Ba se

Ex c ept i o n Name

Ex t r a
Pa r am e t e r s

Type ( Abo r t ,
Fa ul t , Tr ap)

No t e s on VM S
D i s pa tc h i ng

T r a c e Pend i ng

Faul t

No te

B PT I n s t r uc t i o n

Fa u l t

No t e

Compa t i b i l i t y Mo d e

Abo r t/ Fa ul t

A r i t hm e t i c

Fa u l t / T r a p

Commen t s

VM S mod i f i e s c o d e
( Ta b l e 2 - 3 )

Unused

C HM K

Trap

No te

U s e s Ke r n e l St a c k
( Ch a p t e r

C HM E

Trap

No t e

U s e s Ex e c u t i v e St a c k
( Ch a p t e r 3 )

C HM S

Trap

Us e s Supe r v i so r St a c k

C HM U

Trap

Us e s Us e r St a c k

COND I T I ON HANDL I NG

2.2. 1. 1
Ex cept i o n s Th a t VMS T r e a ts i n a Spec i a l Way
A l t h o ug h
VM S
p r o v i d e s u n i f o r m h a nd l i ng
o f mo s t e x c e p t i o n s g e n e r a t ed by u s e r s ,
s ev e r a l po s s i b l e e x c e p t i o n s a r e u s e d a s e n t r y p o i n t s
i n to
p r i v i l eg ed
s y s t em p r o c ed u r e s .
O th e r e x c e p t i o n s c a n o n l y be a c t ed upo n b y t h e
e x e c ut i v e .
It makes no
sense
to
pa s s
i n f o rm a t i o n a b o u t
the s e
e x c e p t i o n s a l o ng t o u s e r s .
-

Th e ma c h i ne c h e c k e x c ep t i o n i s a p r o c e s so r - spec i f i c c o nd i t i o n
tha t m a y o r m a y not be
r ec o v e r ab l e .
Th e m a c h i n e c h e c k
e x c e p t i o n s e r v i c e r o u t i n e i s d i s c u s sed i n Ch a pt e r 7 .

A k e r ne l - s t a c k-no t-va l i d e x c ep t i o n i nd i c a t e s th a t th e
ke rnel
s ta c k
wa s
not val id
wh i l e
t h e p r oc e s s o r wa s p u s h i ng
i n fo rm a t i o n o n t o
the
s ta c k d u r i ng
the
i n i t i a t ion o f
an
e x c ept i on
or
i n t e r r up t .
Th e e x c ep t i o n s e r v i c e r o u t i n e f o r
th i s
except i on
g ene r a tes
a
fatal
b ug ch e c k
wi th
a
B UG $ KRN L S TAKNV c o d e .

Th e po we r f a i l e n t r y po i n t t h a t a ppe a r s a s o n e o f t h e f i r s t 2 0
entr ies
in
the
SCB
i s n o t a n except ion .
B e c a u s e a po we r
f l uc t u a t i o n o c c u r s a s ynch r o no u s l y w i th
r e spe c t
to
the
c u r r e n t l y e x e c u t i ng
i n s t r uc t i o n
s t r e am ,
i t i s a c t ua l l y a n
i n t e r r up t .
Th e f a c t th a t po we r f a i l i s a n i n t e r r up t , w i t h
an
a s s o c i a t ed
IPL,
i m p l i e s t h a t t h e po we r f a i l i n te r r up t c a n b e
b l o c k e d s im p l y b y r a i s i ng I PL t o 3 0 o r 3 1 .
Th e
s t eps
th a t
VM S t a ke s
in
r e spo n s e to powe r f a i l u r e a s we l l a s o n po we r
r e c o v e r y a r e d e s c r i b ed i n Ch a p t e r 2 3 .

Th e
t r an s l a t i o n-no t-va l i d
e x c ep t i o n
is a
s ignal
tha t a
r e f e r e n c e wa s mad e to a vi r t ua l a d d r e s s th a t i s n o t c u r r e n t l y
m a pped t o phys i c a l m emo r y .
Th e pag e f a u l t h a nd l e r
th a t
is
i nv o k e d
i n r e spo n s e to th i s e x c e p t i o n i s d i s c u s s e d i n d e ta i l
i n Ch a p t e r 1 2 .

Th e
c h a ng e-mo d e - to - k e r n e l
a nd
c h ang e -m o d e- t o - e x e c u t i v e
e x c e p t i o n s a r e t h e m e c h a n i sm s u s e d b y t h e VM S s ys t em s e rv i c e s
a nd b y RMS t o r e a c h a mo r e p r i v i l eg ed a c c e s s mo d e .
Th e
d i spa t c h i ng
s c h em e
fo r
s ys tem
s e rv i c e s a nd
RM S c a l l s i s
d e s c r i b ed i n Ch a p t e r 3 .

Th e l a s t t wo e x c ep t i o n s i n t h e l i s t ( th e t wo c h a ng e m o d e e x c e p t i o n s )
a r e pa ths i n to t h e o pe r a t i ng s y s t em th a t a l l o w nonpr i v i l eg ed us e r s t o
r e a c h a p r i v i l eg ed a c c e s s m o d e i n a c o n t r o l l ed f a sh i o n .

2.2.1.2
O th e r Ha r dwa r e Except i o n s - Th e
r est
of
the
except ions
d e t e c t ed
b y h a rd wa r e a r e h and l ed un i fo rm l y by t h e i r e x c ep t i o n s e r v i c e
r out ines .
Th e s e e x c e p t i o n s a r e a l l
r e po r t ed
t o c o nd i t i o n h a nd l e r s
e s t a b l i sh e d
by the
us e r
o r b y t h e s ys t em , r a th e r t h a n r e s u l t i ng i n
s p e c i a l s y s tem ac t i o n s uc h a s o c c u r s f o l l o w i ng a c h a ng e -mo d e- to - k e r n e l
e x c e p t i o n o r a t r a n s l a t i o n - no t-v a l i d f a u l t ( pa g e f a u l t ) .

Wh e n a h a r d wa r e-d e t e c t ed e x c e p t i o n o c c u r s , t h e PS L a nd PC a t the
t ime
of
the e x c e p t i o n a r e p u sh ed o n to t h e s t a c k .
Th e u s u a l s t ac k t h a t i s
u s e d i s t h e ke r n e l s t a c k b u t t h e C HMx e x c e p t i o n s u s e t h e s ta c k o f
the
d es t inat i o n mode .
Fo r e x ampl e , a C HM S e x c ep t i o n push e s th e P C a nd PS L
o f the
e x c ep t i o n o n to
the
s upe r v i so r
s t ac k .
No t e t h a t a
CHMx
i n s t r uc t i o n
i s s ued f r om an i nn e r acc e s s m o d e i n an a t t em p t to r e a c h a
l e s s p r i v i l eg ed ( o u t e r ) a c c e s s mod e wi l l n o t h a v e t h e d e s i r ed
e f f ec t .
Th e m o d e
i nd i c a t ed
b y t h e i n s t r uc t i o n i s m i n im i zed wi t h t h e c u r r e n t
a c c e s s mod e t o d e t e rm i n e t h e a c t ua l ac c e s s m o d e t h a t wi l l b e
used .
Fo r
e x am p l e , a CHMS i n s t r uc t i o n i s s ued f r om k e r n e l m o d e w i l l g e n e r a t e
2-7

CONDITION HANDLING

a n e x c e p t i o n th r o ug h t h e c o r r e c t SCB v e c to r ( th e o n e f o r C HM S ) b u t t h e
f i na l
a c c e s s m o d e wi l l
st i l l
be
ke rnel .
I n o th e r
wo r d s ,
as
i l l u s t r a t ed i n F i g u r e 1 - 4 , t h e C HMx i n s t r uc t i o n s c a n o n l y r e a c h e q ua l
o r mo r e p r i v i l eg ed a c c e s s m o d e s .
Th e PC t h a t i s p u s h e d d e pe nd s o n th e n a t u r e o f t h e e x c e p t i o n , t h a t i s ,
wh e th e r the e x c e p t i o n i s a f a u l t , a t r a p , o r a n a b o r t .
•

•

E x c e p t i o n s t h a t a r e f a u l ts ( Ta b l e 2 - 1 ) c a us e t h e
PC o f
the
f a u l t i ng i n s t r uc t i o n to b e push ed .
Wh e n f a u l ts a r e d i sm i s s ed
wi th
an
RE I
i n s t r uc t i o n ,
the
f a u l t i ng
i n s t r uc t i o n w i l l
e x e c u te aga i n .
Ex c e p t i o n s t h a t a r e t r aps ( Ta b l e 2 - 1 ) p u s h t h e PC o f the n e x t
i n s t r uc t i o n o n t o
t h e d e s t i na t i o n s t ac k .
I n s t r uc t i o n s t h a t
c a us e t r a p s d o n o t r e e x e c u t e wh e n t h e e x c e p t i o n i s d i sm i s s e d
wi th a n R E I i n s t r uc t i o n .
A th i r d c l a s s o f e x c e p t i o n , a n ab o r t ,
c a uses
a
PC
in
the
midd l e
o f t h e i n s t r uc t i o n to b e p u s h e d o n to th e s t a c k .
Th i s
i m p l i e s t h a t a b o r t s a r e no t r e s t a r t ab l e .
Some
a bo r t s a l s o
r a i se
I PL
to 3 1 , b l o c k i ng a l l o th e r a c t i v i ty o n t h e sys t em .
I P L i s u s ua l l y n o t a f f e c t ed wh e n e x c e p t i o n s o c c u r , o n e o f t h e
f e a t u r e s t h a t d i s t i ng u i sh e s t h em f r om i n t e r r up t s .
Ex c e pt i o n s
t h a t a r e a b o r t s i n c l ud e ke r n e l s t a c k no t v a l i d , some m a c h i n e
c h e c k c o d e s , and some r e s e rved ope r a nd e x c e p t i o n s .

Fo r a l l e x c e p t i o n s th a t wi l l
e v e n t ua l l y
be
r e po r t ed
to
c o nd i t i o n
h a nd l e r s ,
t h e h a r d wa r e h a s pushed a PC/PS L p a i r o n to th e d e s t i n a t i o n
s t ac k .
I n ad d i t i o n , f r om z e r o to
two
e x c e p t i o n - s pec i f i c
pa r ame t e r s
are
p u sh ed
o n to
t h e d est ina t ion
s ta c k
( Ta b l e 2 - 1 ) .
Fi na l l y , t h e
h a r d wa r e pa s s e s c o n t r o l t o the e x c e p t i o n s e r v i c e r o u t i n e wh o s e add r e s s
VM S p l a c ed i n to t h e S C B wh en the sys t em wa s i n i t i a l i z ed .

2. 2.1.3
I n i t i a l Ac t i o n o f E x c e p t i o n S e r v i c e Ro u t i n e s - Th e s e
ex cept i on
s e rv i c e r o u t i n e s a l l pe r f o rm a pp r o x ima t e l y t h e s ame a c t i o n .
Th e e x c e p t i o n n ame ( o f t h e
f o rm S S $ e x c ept i o n- n am e )
a nd
t h e to t a l
n um b e r
o f e x c e p t i o n pa r ame t e r s ( f r om t h e e x c e p t i o n n ame t o the s a v ed
PS L i n c l u s i v e ) a r e p u s h e d o n to the s t a c � so th a t t h e d e s t i n a t i o n s t a c k
n o w c o n t a i n s a l i s t , c a l l e d t h e s i g n a l a r r a y , t h a t r e s emb l e s a VA X- 1 1
a r g um e n t l i s t
used
by the
CALLx
i n s t r uc t i ons
( Fi g u r e 2-2 ) .
Th e
ex c e p t i o n s th a t VM S h a nd l e s i n th i s un i f o rm wa y , i n c l ud i ng t h e i r n am e s
a nd to t a l num b e r o f s i g n a l a r r a y e l em e n t s , a r e l i s t ed i n Tab l e 2 - 2 .

Af t e r VM S h a s b u i l t
th i s
a rray ,
control
i s p a s s ed
to
a g ene r a l
e x c ep t i o n d i s p a tc h e r th a t m u s t l o c a t e a n y c o nd i t i o n h a nd l e r s th a t h a v e
b e e n e s t a b l i sh ed i n t h e a c c e s s m o d e
of
th e
except ion .
Th e
se a r ch
m e thod
a nd
the
l i s t o f i n fo rma t i o n p a s s e d to c o nd i t i o n h a nd l e r s i s
d e sc r i b ed i n S e c t i o n 2 . 3 be l ow .
Al l
h a r d wa r e
except ions
( e x c e pt
fo r
CHM E ,
C HM S ,
a nd C HM U )
are
i n i t i a l l y r e po r t ed o n t h e k e r n e l s t ac k ( a s s um i ng t h e p r o c e s s o r i s n o t
a l r e ad y o n t h e i n t e r r u pt s t a c k ) .
I n ad d i t i o n , t h e h a rd wa r e e x c e pt i o n
r e po r t i ng m e c h a n i sm
a s s um e s th a t
the
ke rnel
s tack i s val id .
Th e
d e c i s i o n to u s e t h e k e r n e l
s t a c k wa s m a d e
to
avo i d
the c a se
of
a t t em p t i ng t o r e po r t a n e x c e p t i o n o n , l e t u s s a y , t h e u s e r s t ac k , o n l y
t o f i nd th a t t h e u s e r s t a c k i s
c o r r u pted
in
som e wa y
{ i nva l i d
or
o t h e r wi s e
i naccess i b l e ) ,
r e s u l t i ng
i n a no th e r
ex cept ion .
If
a
k e r n e l - s t a c k -no t-va l i d
except ion
i s g e n e r a t ed
wh i l e
r e po r t i ng
an
e x c e p t i o n , VM S c a u s e s a f a t a l b ug ch e c k to o c c u r .
2-8

C OND I T I ON HANDL I NG

SS$_exception-name

:=�

From 0 to 2
exception-specific
parameters (Table 2-1 )
Exception PC

}

Pushed
by software

N is the number of longwords from
SS$_exception-name to the exception
PSL. It ranges from 3 to 5.

Pushed
by hardware

Arguments are pushed onto the kernel
stack except for CHMS and CHMU
exceptions where the supervisor or
user stack is used.

:: �

Exception PSL

Figur e 2-2

S i g n a l Ar r a y B u i l t by Ha r dwa r e a nd Ex c e p t i o n Ro u t i n e s

Howe v e r , t h e e x c e p t i o n m u s t e v e n t u a l l y b e r e po r ted b a c k t o t h e a c c e s s
mode
i n wh i c h
t h e ex cept i o n occ u r r ed .
B e f o r e t h e d i spa tch e r b e g i n s
i t s s e a r c h , i t c r e a t e s s pa c e o n t h e s t a c k o f t h e m o d e
i n wh i c h
the
ex cept i o n o c c u r red .
Th e e x c e p t i o n pa r am e t e r l i s t s a r e t h e n c o p i e d to
t h a t s t ac k wh e r e they w i l l b e c om e the a rg um e n t l i s t th a t i s pa s s e d
to
c o nd i t i o n h a nd l e r s .

2.2.1.4
M o r e Spec i a l C a s e s i n E x c e p t i o n D i spa tch i ng - Al t h o ug h
the
p r o c ed u r e d e sc r i b e d
above
is
a
r e a s o n ab l e
a pp r o x i m a t i o n
to
the
o p e r a t i o n o f the e x c e p t i o n s e r v i c e r o u t i n e s i n VM S , t h e r e a r e d e t a i l ed
d i ffe rences
that
o c c u r i n t h e d i spa tc h i ng o f s e v e r a l e x c e p t i o n s t h a t
d e s e r v e spec i a l m e n t i o n .
Th e s e s p e c i a l c a s e s a r e l i s t ed h e r e .

Us e r S t a c k Ov e r f l o w i s d e tec t ed by t h e h a r d wa r e a s a n
access
v i o l a t i on
at
t h e l o w a d d r e s s e nd o f P l s pa c e .
Th e a c c e s s
vio lation
f a u l t h a nd l e r
t e s t s wh e th e r
the
i na c c e s s i b l e
v i r t ua l add r e s s i s a t t h e l o w e nd o f P l s pa c e .
I f i t i s , the
s t a c k i s e x p a nd ed a nd
th e
e x c e p t i o n d i sm i s s e d .
Use r
a nd
s y s tem c o nd i t i o n h a n d l e r s wo u l d o n l y be n o t i f i e d a b o u t s uc h
a n e x c e p t i o n i f th e s t a c k e x pa n s i o n we r e un s uc c e s s f u l .

Th e r e a r e t e n po s s i b l e a r i thme t i c e x c e p t i o n s th a t c a n o c c u r .
Th e y a r e d i s t i ng u i shed i n the h a r d wa r e by d i f f e r e n t e x c e p t i o n
p a r am e t e r s .
Howev e r , t h e e x c e p t i o n s e r v i c e r o u t i n e d o e s
no t
s impl y
push a g ene r i c
e x c e p t i o n n ame
o n to
the
stac k ,
r e s u l t i ng i n a f o u r
pa r a m e t e r
s ig nal
array .
Ra t h e r ,
the
e x c e p t i o n pa r am e t e r i s u s e d by t h e e x c e p t i o n s e r v i c e r o u t i n e
t o f a s h i o n a un i que e x c e p t i o n n am e f o r e a c h o f
the
po s s i b l e
a r i thm e t i c
ex cept i ons .
Th e
e x c e p t i o n pa r a m e te r s a nd t h e i r
a s s o c i a t ed s i g n a l nam e s a r e l i s t ed i n Ta b l e 2 - 3 .

2-9

Ta b l e 2 - 2
E x c e p t i o n s Th a t Us e t h e D i s pa tc h e r i n Mod u l e E XC E PT I ON
Ex c ept i o n Nam e

Nam e i n
S i g na l Ar r a y

Ac c e s s Vi o l a t i o n

S S $_ACCVI O

No t e s o n VM S
D i s pa t c h i ng
( Sec t i o n 2 . 2 . 1 . 4 )
I t em 1

S i ze o f
S i g na l Ar r a y

Ex t r a Pa r am e t e r s
i n S i g n a l Ar r a y
(No t e 1 )
S i g na l
S i g na l

Ar i thm e t i c Ex c e pt i o n

( Ta b l e 2 - 3 )

I t em 2

No t e 2

A S T De l i v e ry S t a c k Fa u l t
( So f t wa r e ex c e pt i o n )

S S $_A S TF LT

I t em 3 a .

S ignal
Signal
S i g na l
S i g na l
S i g na l
Signal

!'\)

I
....

(1)

(2)

Ad d i t i o n a l

(3)

(2)

R e a so n Ma s k
I n a c c e s s i b l e Vi r t ua l Ad d r e s s

S P Va l ue a t Fa u l t
A S T Pa r am e t e r o f fa i l ed AST
( No t e 3 )
( 4 ) = PC a t AST d e l i v e r y i n te r r upt
( 5 ) = PS L a t AST d e l i v e r y i n t e r r up t
( 6 ) = PC to wh i c h AST wo u l d ha v e
b e en d e l i v e r ed
( 7 ) = PS L a t wh i c h AST wo u l d h a v e
b e en d e l i v e r ed
(3)

Pa r am e t e r s i n t h e s i g n a l a r r a y a r e r e p r e s e n ted i n t h e f o l l o wi ng wa y .

S i g na l

(0)

Si gnal

(1)

E x c e pt i o n name

Si gnal

(2)

F i r s t add i t i o n a l pa r am e t e r

S i g na l

(3)

S e c o nd a d d i t i o n a l pa r am e t e r

Signal

( N- 1 )

E x c e p t i o n PC

Signal

(N)

E x c e p t i o n PS L

N um b e r o f a d d i t i o n a l l o ng wo r d s i n s i g n a l a r r a y

Th e a r i thme t i c e x c e p t i o n h a s n o ex t r a pa r a m e t e r s , d e s p i t e t h e f a c t t h a t t h e h a r d wa r e pus h e s a n
e x c e pt i o n
code
onto the ke rnel stac k .
VMS mod i f i e s t h i s h a r d wa r e c o d e i n to a n e x c e pt i o n- s p e c i f i c e x c e p t i o n n a m e ( Ta b l e 2 - 3 ) .
Si gnal

(3)

(2)

(1)

8 * c o d e + S S $_ARTR E S

Th e AST d e l i v e r y c o d e e x c h a ng e s t h e i n t e r r up t PC/ P S L pa i r a nd t h e PC/ P S L to
d e l i v e r ed .

wh i c h

the

AST

wo u l d

have

been

( cont inued on next page )

Ta b l e 2 - 2

{ co n t . )

E x c e p t i o n s Th a t Us e the D i s pa tc h e r i n Mo d u l e E XC E PT I ON

Except io n Name

Name i n
S i gnal Ar ray

B PT I n s t r uc t i o n

S S $_B REAK

C h a ng e Mo d e to S u pe r v i so r

S S $_CMODS U PR

I t em

S i g na l

(2)

C h a n g e mod e c od e

Ch a n g e Mo d e t o Us e r

S S $_CM ODUS ER

I t em

S i g na l

(2)

C h a n g e mod e c od e

Co mpa t i b i l i t y Mo d e

S S $_C OMPAT

I t em

S i g na l

(2)

Compa t i b i l i ty e x c e pt i o n c o d e

De b ug S i g na l
( S o f t wa r e e x c ept i o n )

S S $_D E B UG

I t em 3

Ma c h i n e Ch e c k

S S $_MC HE C K

S S $_0 PC C US

C u s t om e r Re s e r v ed

In s t r uc t i o n

Re s e r v e d / P r i v i l eg ed

No tes on VMS
Di spa tch i ng
( Sec t i o n 2 . 2 . 1 . 4 )

Si ze o f
Signal Ar ray

S S $_0 PC DEC

I t em 5

Pag e Fa u l t Re a d E r r o r
( So f twa r e ex c e pt i o n )

S S $_PAGRDERR

I t em 3 b .

Re s e r v ed Ad d r e s s i ng Mo d e

S S $_RADRM OD

Re s e r v ed Ope r a nd

S S $_R O PRAND

Sys t em Se r v i c e Fa i l u r e
( S o f t wa r e e x ce p t i o n )

S S $_S S FA I L

Trace Pend i ng

S S $_TB I T

(4)

In s t r uc t i o n

Ex tra Pa ramete r s
in S i g na l Ar ray
( No te 1 )

I t em 3 c .

No t e

S i g na l
S i g na l

(2)
(3)

S i g na l

(2)

=
=

Re a so n Ma s k
I n ac c e s s i b l e Vi r t ua l Ad d r e s s

Sys t em s e r v i c e f i n a l s t a t u s

Mac h i n e c h e c k e x c e p t i o n s t h a t a r e r e po r t e d to a p r o c e s s d o no t h a v e a n y e x t r a pa r am e t e r s i n the
s i g na l
array.
Th e
mach i ne
c h ec k pa r ame t e r s h a ve b e e n e x a m i n ed , wr i t t en t o t h e e r r o r l og , a n d d i s c a r d ed b y t h e m a c h i n e c h e c k
h a nd l e r ( Ch a p t e r 7 ) .

C OND I T I ON HANDL ING
3.

Th e r e a r e th r e e e x c e pt i o n s th a t a r e l i s t ed i n Tab l e 2 - 2
that
a r e d e t ec ted
b y s o f twa r e r a th e r th a n by h a r d wa r e .
Ho we v e r ,
Ra th e r ,
t h e s e c o nd i t i o n s a r e n o t g e n e r a t ed
by
L I B $ S I GNAL .
t h e y a r e d e t e c t e d by t h e e x e c u t i v e a nd c o n t r o l i s pa s s e d to
the
same
r o ut ines
tha t
a re
u s ed
fo r
d i spa t c h i ng
h a r dwa r e -d e t e c t e d
except ions .
Th e r e a so n wh y t h e y d i s pa tc h
t h r o ug h t h e e x e c u t i v e i s th a t t h e y a r e typi c a l l y d e t e c ted
in
k e r n e l mod e
b u t m u s t b e r e po r ted b a c k t o s o m e o th e r a c c e s s
m od e .
Th e c o d e t o a c compl i s h
th i s
access mode
swi tch
is
c o n ta i ned
in
E XC E PT I ON .
L I B $ S I GNA L h a s n o c o r r e s po nd i ng
f un c t i o n a l i t y .
Th e th r e e
except i o n s
that
fa l l
i n to
th i s
c a t ego r y a r e
s y s tem
s e rv i c e f a i l u r e e x c e p t i o n s , pag e f a u l t
r e ad e r r o r s , a nd i n s u f f i c i e n t s t a c k s pa c e wh i l e a t t empt i ng to
d e l i v e r an AST .
Ta b l e 2 - 3
S i g n a l Nam e s fo r Ar i t hm e t i c Ex c e pt i o n s

Ex c e pt i o n Type

Co d e Pu shed
By Ha rdwa r e

Re sul t i ng Ex c e pt i o n
Re po r ted by VMS

No tes

Tr a ps
In t eg e r Ov e r fl ow

S S $ INTOVF

I n teg e r Di v i d e by Z e r o

S S $ I NTDIV

F l o a t i ng Ov er f l ow

S S $_F LT OVF

No te 3

F l o a t i ng /Dec imal

S S $_F LTD IV

No te 3

Fl o a t i ng Und e r fl ow

S S $_F LTUND

No tes 2 , 3

Dec ima l Ov er f l ow

S S $_D E.C OVF

No te 1

Subsc r i pt Ra ng e

S S $_S UBRNG

Fl o a t i ng Ov er f l ow

S S $ F LTOVF F

No te 3

F l o a t i ng Di v id e by Z e r o

S S $_F LTDIV_F

No te 3

F l o a t i ng Und e r flo w

S S $_F LT UND_F

No te 3

No te 1

D i v ide by Zero

Fa ul ts
-

(1)

I n t eg e r over f l o w enab l e and dec imal over f l ow enab l e b i t s i n
t h e PSW c a n b e a l te r ed e i th e r d i r ec t l y o r thro ug h the
pr o c ed u re en t r y mask .

(2)

Th e fl o a t i ng und e r f l ow enab l e b i t i n the
PSW c a n onl y b e
al t e r ed d i r �c tl y .
Th e r e
i s n o c o r r e spo nd i ng b i t i n the
pr o c ed u re e n t r y ma s k .

(3)

On the VAX-1 1 /7 5 0 , t h e s e t h r e e f l o a t i ng po i n t ex c e pt i o n s a r e
fa ul ts .
On the VA X-1 1 /7 8 0 , they a r e t r a ps .

2-1 2

COND I T I ON HANDL ING
•

Th e S S $ S S FA I L e x c e pt i o n i s r e po r t ed wh e n a p r o c e s s h a s
e n a b l e d - s ys t em
s e rv i c e
f a i l u r e e x c e p t i o n s a nd a s ys t em
s e r v i c e r e t u r n s un s uc c e s s f u l l y w i th a
s t a t u s o f e i th e r
S T S $ K E RROR o r S T S $ K S EVE R E .
Th e S S $ PAG RDERR e x c e p t i o n i s
r e po r t e d
wh en a
process
i n c u r s -a
pag e
faul t
fo r
a pag e o n wh i c h a r e ad e r r o r
o c c u r r ed i n r e s po n s e t o a p r ev i o u s p a g e f a u l t .
-

•

Th e S S $ A ST F LT e x c e pt i o n i s r e po r t e d wh e n a n i n a c c e s s i b l e
s t a c k is d e t e c t ed wh i l e a t t em p t i ng to d e l i v e r an AST to a
process .

A f o u r th s o f twa r e d e t e c t ed e x c e p t i o n i s l i s t e d
i n Tab l e 2 - 2
a l tho ug h
it
does
no t have
a g l o ba l e n t r y po i n t i n m o d u l e
E XC E PT I ON .
Th e s i g n a l S S $ DE BUG i s g e n e r a t ed by e i th e r
the
DC L o r
MC R c omma nd
l a nguag e
i n te r p r e te r in r e sponse to a
D E B UG c ommand wh i l e a n i m ag e e x i s t s i n a n i n t e r r up t ed
s tate .
Th e DEBUG c omma nd
p r o c e s so r
pushes
t h e PC a nd PS L o f t h e
i n t e r r up t e d i m a g e , t h e e x c e p t i o n n am e
( S S $ D E B UG ) ,
a nd
the
s i ze
of
the
s i g n a l a r r a y ( 3 ) o n to t h e s upe r v i so r s t ac k a n d
j umps t o
EXE $RE FLECT ,
a g l ob a l
entry
ad d r ess
in mod ul e
E XC E PT I ON .
Th e r e a s o n t h a t a C L I
u s e s t h i s m e c h a n i sm
fo r
t h e D E B UG
s i g na l
r a th e r
than
s i mpl y c a l l i ng
L I B $ S I GNAL i s th a t t h e
D E BUG c ommand i s i s s u ed wh i l e
in
s upe r v i so r m o d e b u t
the
except i on h a s
to
be
r e po r t e d
back
to
us e r m o d e .
Th i s
i nv o l v e s m o v i ng t h e e x c e p t i o n pa r am e t e r s f r om o n e
s tac k
to
f un c t i o n a l i t y t h a t d o e s n o t e x i s t i n L I B $ S I GNA L b u t
a n o th e r ,
does ex i st
in
E XC E PT I ON b e c a u s e mo s t
h a rdwa r e - d e t e c t e d
e x c e pt i o n s a r e r e po r t ed o n t h e k e r n e l s t a c k .
4.

Th e e x c e p t i o n d i s pa t c h i ng f o r t h e C HMS a nd
C HM U e x c e p t i o ns
a nd
f o r c ompa t i b i l i ty m o d e e x c e pt i o ns c a n be sho r t c i r c u i t ed
by use o f the
De c l a r e
Ch a ng e Mo d e o r
Comp a t i b i l i t y Mo d e
H a nd l e r s y s t em s e r v i c e .
Wh e n t h i s s y s t em s e rv i c e i s ex e c u t ed , o n e o f
three
l o ng wo rd
l oc a t i ons
i n the Pl po i n t e r pag e ( Append i x B) is l o ad ed w i th
the a d d r e s s o f the h a nd l e r
pa s s e d
as
a
pa r ame t e r
to
the
s y s t em s e r v i c e .
Wh e n t h e
d i s pa t c h e r
fo r
the
c h a ng e -mo d e - to - s up e r v i s o r
or
c h a ng e-mo d e- t o - u s e r
e x c e pt i o n
f i nd s n o n z e r o c o n t e n t s i n t h e
a s s o c i a t e d l o ng wo r d i n P l s p a c e , i t t r a n s f e r s c o n t r o l to
the
r o u t i n e wh o s e a d d r e s s
is
s to r ed i n t h a t l o c a t i o n wi t h t h e
e x c e pt i o n s t a c k ( s up e r v i s o r o r
use r )
i n exac t l y the
s am e
s t a t e i t wa s i n f o l l o w i ng t h e e x c e p t i o n .
Th a t i s , t h e c h a ng e
mod e c o d e i s o n t h e t o p o f the stac k , a n d t h e ex cept i o n
PC
a nd e x c e p t i o n PS L o c c u py t h e n e x t t wo l o ng wo r d s .
Th e d i s pa t c h e r f o r c ompa t i b i l i t y m o d e
e x c e p t i o ns
transfers
control
to
t h e u s e r - d e c l a r ed c o m pa t i b i l i t y m o d e h a nd l e r ( i f
o n e wa s d e c l a r ed ) wi t h t h e u s e r s t a c k i n t h e
s ame
state
it
wa s b e f o r e
t h e c om pa t i b i l i ty mod e e x c e p t i o n o c c u r r ed .
Th a t
i s , n o p a r am e t e r s a r e
passed
to
t h e c om pa t i b i l i t y m o d e
h a nd l e r
on the use r s tac k .
Th e c ompa t i b i l i ty mo d e c o d e , t h e
e x c e p t i o n P C a nd PS L , a nd t h e c o n t e n t s o f R O t h r o ug h
R6
are
s aved
in the
f i r s t t e n l o ng wo r d s o f t h e c om pa t i b i l i t y mod e
c o n t e x t pag e i n P l s pa c e a t g l o b a l
locat ion
C T L $ A L CM CNTX
( Append i x B ) .
2-1 3

C OND I T I ON HANDL ING
5.

Th e Re s e r v e d
I n s t r uc t i o n
f aul t
i s g e n e r a t ed
wh e n ev e r
an
un r e c og n i z e d
o pc o d e
i s d e t e c t ed b y t h e i n s t r uc t i o n d e c o d e r .
Th e s am e e x c e p t i o n i s g e n e r a t e d wh e n a p r i v i l eg ed i n s t r uc t i o n
i s e x e c u t e d f r om o th e r t h a n k e r n e l mo d e .
VM S u s e s th i s f a u l t a s a pa th i n to t h e o pe r a t i ng s y s tem c r a s h
c o d e c a l l ed
t h e b ug ch e c k m e c h a n i sm .
Opc o d e FF , f o l l o wed b y
F E o r FO , t e l l s t h e r e s e r v e d
i n s t r uc t i o n
except i o n
service
routine
tha t
t h e e x c e p t i o n i s a c t ua l l y a b ug c h ec k .
Co n t r o l
i s passed to
t h e b ug c h e c k
r o ut ine
tha t
i s d e sc r i b ed
in
Ch a p t e r 7 .

2. 2. 2

E x c ep t i o n s De t e c ted b y S o f twa r e

On e o f t h e g o a l s o f t h e d e s i g n o f t h e VAX a r ch i t e c t u r e wa s to
have a
c ommo n
c o nd i t i o n
h a nd l i ng
f a c i l i ty
fo r
both
h a r d wa r e a nd
so f twa r e -d e t e c ted c o nd i t i o n s .
Th e d i spa t c h i ng f o r c o nd i t i o n s th a t a r e
initially
d e t ec t ed
by
the
h a r d wa r e
( a nd
fo r
fo ur
s pe c i a l
so f t wa r e - d e t e c t ed e x c e p t i o n s ) i s pe r f o rmed b y t h e
routines
in
the
execut ive modul e
E XC E PT I ON .
Th e
Run-T i m e L i b r a r y p r o c ed u r e c a l l ed
L IB $ S I GNAL p r ov i d e s a s i m i l a r c a pa b i l i ty to
a ny u s e r
of
a
VAX/VMS
s ys tem .

2. 2. 2. 1
P a s s i ng S t a t us f r om a P r o c ed u r e - Th e r e
are
u s ua l l y
t wo
m e thod s a v a i l a b l e f o r a p r o c ed u r e to i nd i c a t e to i t s c a l l e r wh e th e r i t
c om p l e ted s uc c e s s f u l l y .
On e m e tho d i s t o i nd i c a t e a r e t u r n s t a t u s
in
RO .
Th e o th e r i s t h e s i g n a l l i ng m e c h a n i sm .
Th e s i g n a l l i ng mec h a n i sm
i nvo l v e s a c a l l to t h e VAX- 1 1 Run-T i m e L i b r a r y p r o c ed u r e L I B $ S I GNAL to
i n i t i a te
a
sequence
of
events
exac tly
l i ke
tho s e
tha t o c c u r i n
r e s po n s e t o a h a r d wa r e -d e t e c t ed e x c e p t i o n .
On e o f
the cho i c e s
th a t
m u s t b e m a d e wh e n d e s i g n i ng
a m o d u l a r p r o c ed u r e i s th e m e th o d fo r
r e po r t i ng e x c e pt i o n a l c o nd i t i o n s b a c k to t h e c a l l e r .
Th e r e a r e t wo r e a so n s wh y s i g n a l l i ng m a y b e cho s e n o v e r c om p l e t i o n
s t a t us .
I n some p r o c ed u r e s s uc h a s t h e m a thema t i c s p r o c ed u r e s i n th e
Run-T i m e L i b r a r y , R O i s a l r e a d y u s e d fo r a n o t h e r p u r po s e ,
n am e l y t h e
r e tu r n
of
a
f un c t i o n va l ue , a n d i s t h e r e f o r e unava i l a b l e fo r e r r o r
r e turn s ta tus .
I n th i s c a s e , th e p r o c e d u r e m u s t u s e
the
s i g n a l l i ng
mech a n i sm
to
i nd i c a t e
e x c e p t i o n a l c o nd i t i o n s , s uc h a s an a t t em p t to
t a ke the s qua r e r o o t o f a n eg a t i v e n umb e r .
Th e s e c o nd c ommon u s e o f s i g n a l l i ng o c c u r s i n an a pp l i c a t i o n
th a t
is
u s i ng
an
i nd e te rm i n a t e n um b e r
o f p r o c ed u r e c a l l s to pe r f o rm some
a c t i o n , s uc h as a r e c u r s i v e p r o c ed u r e
tha t
pa r s e s
a
command
l i ne ,
wh e r e
t h e u s e o f a r e t u r n s t a t u s i s o f t e n c um b e r some a nd d i f f i c u l t to
code .
In th i s c ase ,
the
VAX- 1 1
s i g n a l l i ng m e c h a n i sm p r o v i d e s a
g r ac e f u l
wa y to n o t o n l y i nd i c a t e th a t an e r r o r h a s o c c u r r ed b u t a l s o
r e t u r n c o n t r o l ( th r o ug h SYS $ UNW I ND ) to a kn own a l t e r n a t e r e t u r n po i n t
i n t h e c a l l i ng h i e r a r c hy .

2. 2. 2. 2
I n i t i a l Ope r a t i o n o f L I B $ S IGNAL - Wh e n t h e
p r o c ed u r e
th a t
d e te c t s a n e r r o r wi s h e s t o s i g n a l i t , t h e p r o c ed u r e c a l l s L I B $ S I GNAL
wi th t h e n ame of the e x c ept i o n a nd wh a t ev e r add i t i o n a l
pa r am e t e r s
it
wi she s to pa s s to t h e c o nd i t i o n h a nd l e r s t h a t h a v e b e e n e s t a b l i s h e d b y
t h e u s e r a nd b y t h e s ys t em .
Th e s t a t e o f t h e s t ac k f o l l o w i ng
a
call
to L I B $ S I GNA L i s p i c t u r e d i n F i g u r e 2- 3 .

2-1 4

State of the stack Immediately
after the CALLS to LIB$SIGNAL

!",'
'

0 � No condition handler
Register save
mask, etc.

Saved

Saved AP

Saved FP

Saved PC

PSW

®
G)
0

N
I
....

32-blt status code
(signal name)

lJ1

)
,,,

/
/

,/,/

• ol

�- - -

.. ..�

,_l.:

:fig ��
''•
'
"4<
<
' ' -t '•

''
'��
o..,

Argument list
passed to
LIB$SIGNAL or
LI B$STOP

---

copied from elsewhere to
signal array. Rest of
call frame discarded
In same fashion.

)

Figure 2-3

Signal/Stop code

1 � LIB$SIGNAL 2 � LI B$STOP

---

The argument list Is
shifted up 8 bytes
to make room for
PC/PSL pair so
that hardware and
software signal arrays
look the same

,.o
,�

== �
'

- - - ---

N Is the size of the
signal array (N=M+2)

Additional arguments
(If any) passed
to LIB$SIGNA'L
or LIB$STOP

..
...
N

== �

Signal
Array

passed to
Condition
Handlers

' '"{9.,.,,.,, ' '
'

Location of PC/PSL
pair for quick exit

32-blt Status code
(signal name)

"o-�
'
1-o:fl)
'
'
'�.
'
'
1}.,� '
.
'
'

---- - - - -

If CALLG Instead of
CALLS, then argument list

Saved PC � signal array

�

Saved FP � FP

::: �

to LIB$SIGNAL
or LIB$STOP

Saved

Mechanism Array
will go here

Exit from LIB$SIGNAL
---with
��- -�
---REI and
not RET.
-

. .r' '> . 40C ' �
.. �,/,......'-, �0�o '

Additional arguments
(If any) passed

(

f2\
\V
f3\
\V
f4\
\V

,...� "' '

�

::: �

bytes

M Ia the size of the
argument list

,
"

State of the stack after

LIB$SIGNAL has removed
the call frame

Saved PSW � low 1 6
bits of PSL I n signal
array

Call
,,
frame for
,'
LIB$SIGNAL
or LIB$STOP

0 .. 3 stack alignment

��

Call frame Is discarded before
handlers are called

1'.,
, r;
...... ,

PC of Instruction
following CALLx
PSL that existed
before CALLx

Value of SP before
call and push
of argument list

Remova l o f Ca l l F r ame b y L I B $ S IGNAL

0
G)

.._

�

C OND I T I ON HANDL ING
B e f o r e L I B $ S I GNAL b eg i n s i t s s e a r c h f o r c o nd i t i o n h a nd l e r s , i t r emov e s
the
c a l l f r am e ( a nd po s s i b l y t h e a r g um e n t l i s t ) f r om th e s t a c k .
Th i s
c a u s e s t h e s t a c k t o a ppe a r a l mo s t e x a c t l y t h e s am e t o L I B $ S I GNAL a s i t
d o e s to EXC E PT I ON f o l l owi ng a h a r d wa r e e x c e p t i o n ( F i g u r e 2 - 3 ) .
Th i s p r o c ed u r e
EXC E PT I ON
to
t h i s p r o c ed u r e
s t ac k s w i t c h
take s p l ace o n

2. 3

us e s a n i d e n t i c a l s e a r c h m e c h a n i sm to the o n e
used
by
l o c a t e c o nd i t i o n h a nd l e r s .
Th e o n l y d i f f e r e n c e b e twe e n
a nd t h e c o d e c o n t a i n ed i n
the
execut ive
is
th a t n o
is
r e q u i r ed
here .
Th e s e a r ch f o r cond i t i o n h a nd l e r s
th e s ta c k o f t h e c a l l e r o f L I B $ S IGNA L .

UN I FORM E XC E PT I ON D I S PATCH ING

At
th i s
po i n t ,
t h e d i f f e r e n c e s b e twe e n h a rd wa r e
and
so f twa r e
e x c ep t i o n s a r e n o
l o ng e r
i mpo r ta n t .
Th e o p e r a t i o n o f e x c e p t i o n
d i s pa tc h i ng w i l l b e d i sc u s s ed i n g e n e r a l t e rm s a nd e x p l i c i t m e n t i o n o f
E XC E PT I ON o r L I B $ S IGNAL w i l l o n l y b e mad e wh e r e t h e y d e pa r t f r om e a c h
o th e r i n th e i r ope r a t i o n .
Be f o r e the sea rch
fo r
a
c o nd i t i o n h a nd l e r
b eg i n s ,
the
e x c e pt i o n
d i s pa tc h e r m u s t b u i l d a s e c o nd d a t a s t r uc t u r e o n t h e s t a c k th a t wi l l
b e u s ed to r e po r t t h e
except ion .
Th e
add r e s s o f
th i s
s t r uc t u r e ,
c a l l ed
t h e m e c h a n i sm
a r ray ,
a l ong
wi th
the
a d d r e s s o f t h e ta b l e
c o n t a i n i ng t h e e x c e p t i o n a rg um e n t s w i l l b e th e two a rg um e n t s t h a t a r e
passed
t o a ny c o nd i t i o n h a nd l e r s th a t a r e c a l l ed b y t h e d i s pa tc h e r
( Fi g u r e 2-4 ) .

2.3.1

E s t a b l i sh i ng a Cond i t i o n H a nd l e r

VM S p r o v i d e s
h a nd l e r s .
•

•

two

d i f fe r ent

m e tho d s

fo r

e s t a b l i s h i ng

c o nd i t i o n

One m e th o d u s e s th e c a l l s t a c k a s so c i a t ed
wi th e a c h a c c e s s
mod e .
Each ca l l
f r am e
i n c l ud e s a l o ng wo r d to c o n t a i n the
a d d r e s s of a c o nd i t i o n h a nd l e r a s s o c i a t ed wi th th a t f r am e .
Th e s e c o nd me tho d u s e s so f twa r e e x c e p t i o n v e c to r s , s e t a s i d e
i n t h e c o n t r o l r eg i o n ( P l s p a c e ) fo r e a c h o f t h e f o u r a c c e s s
mod e s .
Ve c t o r e d
h a nd l e r s d o n o t po s s e s s
the
modul a r
p r o pe r t i e s
a s s o c i a t ed
wi th c a l l
f r am e h a nd l e r s
a nd
are
i n t e n d e d p r im a r i l y f o r d e b ug g e r s a nd pe r f o rma n c e m o n i to r s .

C a l l f r am e h a nd l e r s a r e e s t a b l i s h ed by p l ac i ng
th e ad d r e s s o f
the
h a nd l e r
in
the
f i rst
l o ng wo r d
of t h e c u r r e n t l y a c t i v e c a l l f r am e .
Th i s i s a c compl i s hed i n a s s em b l y l a ng uag e wi th a s i ng l e i n s t r uc t i o n
MOVAB

n e w-h a nd l e r , ( FP )

Be c a u se t h e f r am e po i n t e r i s g e n e r a l l y n o t a v a i l a b l e t o h i g h
l ev e l
l a ng uag e p r og r amme r s , t h e Ru n - T i m e L i b r a r y p r o c ed u r e L I B $ E S TAB L I S H c a n
b e c a l l ed i n t h e fo l l o w i ng wa y
o l d-h a nd l e r

L I B $ E S TAB L I S H ( n e w-h a nd l e r )

to a c c om p l i s h the same r e s u l t .

2-1 6

C OND I T I ON HANDL I NG

address of
signal array

....
-

address of
m e c h a n i sm a rr a y

These two longwords are
used and modified by
handler search procedure

Because VAX-1 1 calling
standard dictates that
RO and R1 are not saved
across calls, they must be
preserved In some other way

(

[l
[l

FP of e s t a b lisher f r a m e

Exception generated
by call to LIB$SIGNAL
o r LIB$STOP
Argument list passed
by call to LIB$SIGNAL
or LIB$STOP. PC and PSL
are added before handlers
are called. See Figure 2-3.

�

depth argument

s av ed R 1

) (

""""-

1\)

s a v e d RO

If lists are built by LIB$SIGNAL, there are
two extra longwords between mechanism
array and signal a rray. See Figure 2-3.

Condition handlers can pass
status back to mainline code
by modifying saved RO (and R1 )

If lists are built by EXCEPTION, mechanism
array Is adjacent to signal array

Argu ment count is nu mber of
longwords i n signal array ( N 2: 3)

�
"'

e x c e ption or s i gn a l name
A d d ition a l e x c e p t i o n p a r a m e ters
� p u s hed by h a r d w a re o r
� � a d d i ti o n a l a rguments p a s s e d t o
LIB$SIGNAL or LIB$STOP

E x c e ption PC or PC following
c a l l to L I B $ S I G N A L o r L I B $ S T O P

r'lll

Exception dispatched through
hardware dispatcher

��

�

E x c e p t ion P S L

Figure 2-4

.JII(

Parameters pushed Initially onto
kernel stack (except for CHMS
and CHMU) by hardware and copied
to exception stack by software.
Exception name and argument count
are added by software before
handlers are called.
Value of SP before
exception

S i g n a l a nd Me ch a n i sm A r r ay s

C o n d i t i o n h a nd l e r s a r e r em o v e d by c l e a r i ng the f i r s t l o ng wo r d
c u r r e n t c a l l f r am e .
Th e i n s t r uc t i o n
C LR L

)

the

( FP )

a c c ompl i s h e s
th i s
in
a s s emb l y l a ng u a g e .
c o un t e r pa r t to L I B $ E S TA B L I S H i s L I B $ R EVE R T .

Th e

Run-T i m e

L i b ra ry

Ex c e p t i o n v e c to r h a nd l e r s a r e e s t a b l i s h e d and
r em o v e d
wi th
the
Set
E x c e p t i o n Ve c to r sys tem s e r v i c e , wh i c h s i mp l y l o ad s t h e ad d r e s s o f t h e
s pe c i f i ed h a nd l e r i n to t h e spec i f i ed e x c e p t i o n v e c to r , l o c a t e d i n t h e
po i n t e r pag e i n P l s pa c e .

2-17

C OND I T I ON HANDL ING
2. 3.2

Th e S e a r ch f o r a Cond i t i o n H a n d l e r

At t h i s po i n t i n the d i spa t c h
s e q ue nc e ,
t h e s ig nal
a nd m e c h a n i sm
a r r a ys h a v e b e en
set
up o n
the s t a c k o f t h e a c c e s s mo d e tha t the
e x c ep t i o n w i l l b e r e po r ted to .
Th e e s t a b l i sh e r f r am e a rg um e n t i n
the
m e c h a n i sm
a r ra y
( F i g u r e 2 - 4 ) wi l l b e used b y t h e s e a r c h p r o c ed u r e to
i nd i c a t e how f a r a l o ng the s e a r c h h a s g o n e .
Th e d e pth a rg um e n t i n the
m e c h a n i sm
a r r a y n o t o n l y s e rv e s as us e f u l i n fo rm a t i o n to c o nd i t i o n
h a nd l e r s th a t w i sh to unw i nd b u t a l s o a l l o ws t h e s e a r ch
p r o c ed u r e t o
d i s t i ng u i sh
call
f r am e h a nd l e r s
( no nn eg a t i v e d e pth ) f r om e x c e p t i o n
v e c to r h a nd l e r s ( n eg a t i v e d e pth ) .

2. 3. 2. 1
P r ima r y a nd S e c o nd a ry E x c ept i o n Vec to r s - Th e
sea rch
fo r
a
c o nd i t i o n h a nd l e r b e g i n s
w i th
the
p r ima r y e x c ep t i o n v e c to r o f the
a c c e s s m o d e in wh i c h t h e e x c ep t i o n o c c u r r ed .
If the v e c t o r
conta ins
t h e ad d r e s s o f a c o nd i t i o n h a n d l e r ( a n y n o n z e r o c o n te n t s ) , t h e h a nd l e r
i s c a l l ed w i t h a d ep th a rg um e n t o f - 2
( th i r d
l o ng wo r d
i n m e c h a n i sm
a r ray ,
Figure 2-4 ) .
I f tha t h a n d l e r r e s i g n a l s o r i f n o n e e x i s t s , t h e
s am e s t e p i s pe r fo rmed fo r the s e c o nd a r y e x c e p t i o n v e c to r ,
wh e r e
the
d e pth a rg um e n t i s now - 1 .

C a l l F r ame Co nd i t i o n Hand l e r s - I f the s e a r c h i s to
con t i nue
( no h a nd l e r y e t pa s s ed b a c k a s ta t us o f S S $ C ONT INUE ) , t h e c o n t e n t s o f
t h e c u r r e n t c a l l f r am e a r e e x am i n ed n ex t . If the
f i rs t
l o ng wo r d
in
the c u r r e n t c a l l f r am e i s n o n z e r o , t h a t h a nd l e r i s c a l l ed n ex t .
I f no
h a nd l e r i s fo und th e r e or i f tha t h a nd l e r r e s i g n a l s , t h e p r ev i o us c a l l
f r am e i s e x am i n ed by u s i ng the s a v ed f r am e po i n t e r i n t h e c u r r e n t c a l l
f r am e ( F i g u r e 2- 5 )
2.3.2.2

•

Th e s e a r c h c o n t i n u e s un t i l some h a nd l e r pa s s e s b a c k a s t a t u s c o d e o f
S S $ C ONTI NUE o r un t i l a
s a v ed
f r ame
po i n t e r o f
ze ro
is
f o und
( i nd i c a t i ng the e nd of the c a l l
f r am e cha i n ) .
Wh en
the
except i o n
d i s pa t c h e r r e c e i v e s a r e t u r n s t a t u s o f S S $ C ONT INUE ( a n y c o d e w i th t h e
l ow b i t o f R O s e t wi l l d o ) , t h e s t a c k i s cle a n e d o f f , R O
and Rl
are
r e s t o r ed
f r om
th e m e c h a n i sm a r r a y , a nd t h e e x c e p t i o n i s d i sm i s se d b y
i s s u i ng a n R E I , us i ng the s a v ed PC a n d PS L t h a t
fo rm
th e
l ast
two
e l em e n t s o f t h e s i g n a l a r r a y .
No t e tha t L I B $ S IGNA L pa s s e s c o n t r o l b a c k to i t s
caller
wi th a n RE I
b e c a us e
i t d i sc a r d ed
the c a l l
f r am e
th a t wa s s e t up wh e n i t wa s
c a l l ed .
Th a t i s , L I B $ S I GNAL m o d i f i e s i t s s t a c k to l o o k j u s t l i k e
the
s t a c k u s e d b y E XC E PT I ON ( F i g u r e 2 - 3 ) .

2. 3. 2. 3
La s t Ch a n c e Cond i t i o n Ha nd l e r - I n
the
event
that
al l
h a nd l e r s r e s i g n a l , t h e s e a r c h t e rm i n a t e s wh e n a s a ved f r am e po i n t e r o f
z e r o i s l o c a ted .
Th e e x c e p t i o n d i spa tc h e r
t h e n c a l l s t h e h a nd l e r
wh o s e a d d r e s s
is
s to r ed
i n the l a s t c h anc e e x c e p t i o n v e c to r w i th a
d e pth a rg um e n t o f - 3 .
( Th i s h a nd l e r i s a l s o c a l l e d i n th e e v e n t
tha t
a ny e r ro r s
o c c u r wh i l e
s e a r c h i ng
the s t ac k
fo r th� e x i s t e n c e o f
c o nd i t i o n h a nd l e r s . ) Th e u s ua l h a nd l e r fo und i n the l a s t c h a n c e v e c to r
is
the
s o -c a l l ed c a tc h a l l c o nd i t i o n h a nd l e r e s t a b l i sh ed a s pa r t o f
i mag e i n i t i a t i o n .
Th e
act ion o f
th i s
sys t em - s upp l i ed h a nd l e r
is
d e sc r i b ed a t the end o f th i s c h a p t e r .

2-1 8

COND I T I ON HANDL ING

Signal array

Mechanism array

Signal and
mecha nism
arrays for
signal S
generated by
procedure C

Establisher FP

4
-

.1
G)

Depth � 1

RO
R1

�
�

Name of signal S

=�

Other parameters

==;:::

Exception PC in C
Exception PSL

�

Direction of
stack growth
Call frame for
procedure C
Saved FP

Saved PC in B

�
�

Call frame for
procedure B
Saved FP
Saved PC in

AH
Call frame for
procedure

Saved FP
Saved PC

Figure 2-5

To previous frame

O r d e r o f S e a r c h fo r C o nd i t i o n Ha nd l e r

2-1 9

C OND I T I ON HANDL I NG
I f th e l a s t c h a n c e h a nd l e r r e t u r n s to t h e d i spa tc h e r
( i t s s t a t us
is
i g n o r ed )
or
if
the
l a s t c h ance v e c to r
is
emp t y ,
t h e e x c ept i o n
d i s pa tc h e r i nd i c a t e s th a t n o h a nd l e r wa s fo und .
Th i s no t i f i c a t i o n
is
p e r fo rmed b y a
p r o c ed u r e c a l l ed
E XE $ E XC M SG
( Ch a pte r 2 7 )
i n the
ex ecut ive .
I t s t wo i n p u t pa r am e t e r s a r e a n ASC I Z
s t r i ng
c o n t a i n i ng
m e s sag e
t ex t ,
a nd t h e a r g um e n t l i s t t h a t wa s pa s s e d to a n y c o nd i t i o n
h a nd l e r s .
Fo l l o w i ng th e c a l l to EXE $ E XC M SG ( Ch a pte r 2 7 ) , t h e i m a g e i s
t e rm i n a t e d
w i th
a s t a t us i nd i c a t i ng e i th e r th a t n o h a n d l e r wa s fo und
or t h a t a b a d s t a c k wa s d e tec ted
wh i l e
s e a r c h i ng
fo r
a
c o nd i t i o n
h a nd l e r .

2. 3.3

M u l t i pl y Ac t i ve S i g n a l s

I f a n e x c e p t i o n o c c u r s i n a c o nd i t i o n h and l e r
or
i n s o m e p r o c ed u r e
c a l l ed
by a
c o nd i t i o n h a nd l e r ,
a s i t ua t i o n c a l l ed m u l t i pl y a c t i v e
s i g na l s i s r eached .
I n o r d e r to avo i d a n i n f i n i t e l o o p o f e x c e p t i o n s ,
t h e p r o c ed u r e t h a t s e a r c h e s f o r cond i t i o n h a n d l e r s mo d i f i e s i t s s e a r c h
a l g o r i thm so t h a t tho s e f r am e s s e a r c h e d
wh i l e
s e r v i c i ng
the
fi rst
c o nd i t i o n a r e s k i pped wh i l e s e rv i c i ng t h e s e c o nd c o nd i t i o n .
I n o rd e r f o r th i s s k i pp i ng to wo r k c o r r e c t l y , t h e h a r d wa r e e x c e pt i o n
d i s pa t c h e r
( mod u l e
EXC E PT I ON )
a n d t h e so f twa r e e x c e pt i o n d i spa tche r
m u s t e a c h know wh e n t h e o th e r i s c u r r e n t l y s e r v i c i ng
a n except i on .
Th i s
is
a c compl i shed by r e q u i r i ng b o t h d i s pa tc h e r s to c a l l c o nd i t i o n
h a nd l e r s th r o ug h a c ommo n c a l l s i t e
l o c a t ed
in
the
s ys tem
s e rv i c e
v e c to r a r e a .

2 . 3 . 3 . 1 Commo n C a l l S i t e f o r Co nd i t i o n H a nd l e r s - Be fo r e t h e d i spa t c h
to
t h e h a nd l e r o c c u r s , t h e s t ac k i s s e t u p to c o n t a i n t h e s i g n a l a nd
m e c h a n i s m a r r a ys a nd the h a nd l e r
a rg um e n t l i s t
( F i g u r e 2- 4 ) .
Th e
h a nd l e r
a d d r e s s i s l o ad ed i n to Rl by t h e h a nd l e r s e a r c h p r o c ed u r e a nd
c o n t r o l i s pa s s e d to t h e c ommo n d i s pa t c h s i t e w i th t h e i n s t r uc t i o n
JSB

@ # SYS $ C A L L_HAND L

Th e c o d e l o c a t ed a t SYS $ C A L L HAND L s i mp l y c a l l s
the
p r o c ed u r e
ad d r e s s i s s to r ed i n R l a nd re t u r n s to i t s c a l l e r wi th a n RSB .

wh o s e

SYS $CALL HAND L : :
CA L LG
4 ( SP) , (Rl )
RSB
Th e c a l l i ns t r uc t i o n l e a v e s t h e r e t u r n ad d r e s s SYS $CALL HAND L + 4 , t h e
ad d r e s s
of
t h e RSB i n s t r uc t i o n , i n i t s c a l l f r am e .
Thu s , t h e un i q u e
i d e n t i fy i ng c h a r a c t e r i s t i c o f
a
c o nd i t i o n h a nd l e r
is
the
add r e s s
SYS $CALL HANDL + 4
i n t h e s a v ed P C o f i t s c a l l f r am e .
Th i s s i g n a t u r e
i s n o t o nl y u s ed b y t h e s e a r c h p r o c ed u r e b u t a l s o by t h e Unwi n d s ys t em
s e rv i c e , a s d e sc r i b ed b e l o w .

2- 2 0

C OND I T I ON HANDL ING
2 . 3. 3. 2
E x am pl e o f Mul t i p l y Ac t i ve S i g n a l s - Th e
m o d i f i ed
search
p r o c ed u r e c a n b e s t b e
i l l us t r a te d
t h r o ug h a n e x am p l e .
F i g ur e 2 - 5
s h ows the s t a c k a f t e r p r o c ed u r e c , c a l l ed f r om B c a l l ed
f r om A ,
has
g e n e r a t ed
s ignal
s.
We a r e a s s um i ng th a t th e p r i m a r y a nd s e c o nd a r y
c o nd i t i o n h a nd l e r s ( i f t h e y e x i s t ) r e s i g n a l l ed .
Co nd i t i o n h a nd l e r
CH
a l s o r e s i g na l l ed .
(1)

P r o c ed u r e A c a l l s p r o c ed u r e B wh o c a l l s p r o c ed u r e

(2)

P r o c ed u r e C g e n e r a t e s s i g n a l

(3)

Th e
search
p r o c ed u r e m o d i f i e s
e s t a b l i sh e r f r am e a rg um e n t .

the

d e pth

I f we
a s s um e
t h a t h a nd l e r C H r e s i g n a l s ,
a rg um e n t i s 1 wh e n BH i s c a l l ed .

a rg um e n t
then

the

a nd
d e p th

(4)

Th e c a l l f r am e f o r h a nd l e r B H i s l o c a t ed
(at
l o we r v i r t ua l
add resses)
on top o f
the
s i g n a l a nd m e c h a n i sm a r r a y s f o r
s ig n a l S ( Fi g u r e 2- 6 ) .
( Th e o n l y i n t e r v e n i ng i t em s a r e
the
s aved
r eg i s t e r s
a nd
s t a c k a l i g nm e n t b y t e s i nd i c a t ed b y t h e
r eg i s t e r s a v e ma s k i n the u ppe r by t e o f t h e
s e c ond
l o n g wo r d
o f t h e c a l l f r am e f o r h a nd l e r B H . ) Th e s av e d f r am e po i n t e r i n
t h e c a l l f r a m e f o r B H p o i n t s t o th e f r am e f o r p r o c ed u r e C .

(5)

Hand l e r B H now
{ Fi g u r e 2-6 ) .

(6)

P r o c e d u r e Y g e n e r a te s s i g n a l
f r am e s t o b e e x am i n ed i s :
t h e n f r ame A .
F r ame s B a n d C
we r e e x am i n e d wh i l e s e r v i c i ng

(7 )

Th e s e a r c h p r o c ed u r e p r o c e ed s i n
i t s n o rm a l
f a sh i o n .
Th e
p r i ma r y a nd s e c o nd a r y v e c to r s a r e e x am i n ed f i r s t ( no s k i pp i ng
here) .
Th e n f r am e s Y , X , a nd BH a r e e x am i n ed ,
r e s u l t i ng
in
h a nd l e r s YH , XH , a nd B H H b e i ng c a l l ed i n t u r n .
Le t us a s s um e
t h a t a l l t h e s e h a nd l e r s r e s i g n a l .
Af t e r h a nd l e r BHH r e t u r n s
to
t h e d i s pa tc h e r w i th a c o d e o f S S $ R E S IGNAL , t h e s e a r c h
p r o c ed u r e no t e s
th a t
th i s
is
t h e f ram e o f
a
c o nd i t i o n
h a nd l e r ,
b e c a us e
i ts
s av e d
PC
is
SYS $ C A L L HAND L + 4
( Fi g u r e 2-6 ) .

c alls

p r o c ed u r e

wh o

calls

p r o c ed u r e

T.
Th e d e s i r ed
s equenc e o f
f r am e Y , f r am e X , f r ame B H , a nd
s h o u l d b e s k i pped b e c a use
they
c o nd i t i o n S .

(8)

Th e s k i pp i ng i s
a c compl i s h ed
by
l o c a t i ng
the
f r ame
th a t
e s t a b l i sh e d
th i s h a nd l e r .
Th e
add r e s s
o f ' th a t f r ame i s
l o c a t e d i n t h e m e c h a n i sm a r r a y f o r s i g n a l s .
To l o c a t e t h e m e c h a n i sm a r r a y f o r s i g n a l S , t h e v a l u e o f
SP
b e f o r e t h e c a l l t o B H m u s t b e c a l c u l a t ed , u s i ng th e r e g i s t e r
s av e m a s k a n d s t a c k a l i g nm e n t b i t s i n t h e c a l l f r am e .

(9)

One
extra
l o ng wo r d ,
the
r eturn
PC
f r om
the
JSB
to
S Y S $ C A L L HAND L ,
mus t b e s k i pped t o l o c a t e the a rg umen t l i s t
( a n d t h us t h e me c h a n i sm a r r a y ) f o r s i g n a l s .

2-21

C OND I T I ON HANDLING

Signal array

Signal and
mechanism
arrays for
signal T
generated by
procedure Y

Depth
RO
R1

Name of signal T

Other parameters
Exception PC in Y
Exception PSL

Direction of
stack growth

Call frame for
procedure Y
Saved FP
Return PC in X

XH
To call frame for
procedure A
in Figure 2-5

Call frame for 1---�
procedure X
Saved FP

Return PC in BH

+--

BHH
R.S.M.
Call frame fo r
procedure BH

Saved FP

Dispatcher call site

:::: :::

Saved registers and
stack alignment
bytes indicated
by register save
mask (R.S. M.) in
call frame BH
Return PC from JSB

F i g u r e 2-6

��

0
@

.. ,
To call fra me for
procedu re C
in Figure 2-5

Mod i f i ed S e a rch w i th Mu l t i pl y Ac t i v e S i g na l s

2-22

C OND I T I ON HANDL ING
(10)

B e c a us e t h e f r am e po i n t e d to b y t h e m e c h a n i sm
a r r a y e l em e n t
has
a l r e a d y b e e n s e a r c h ed ,
t h e n e x t f r am e e x am i n ed b y t h e
s e a r c h p r o c ed u r e i s t h e f r ame po i n t ed to b y t h e
s a v ed
f r am e
po i n t e r
i n t h e c a l l f r am e o f p r o c ed u r e B , wh i c h i n th i s c a s e
i s t h e f r am e fo r p r o c ed u r e A .
Th e d e p th s t h a t a r e pa s s ed
to
h a nd l e r s a s a r e s u l t o f t h e m o d i f i ed s e a r c h a r e 0 fo r Y H , 1
f o r XH , 2 f o r BHH , a n d 3 f o r AH .

(11)

Th e f r ame f o r the s e a r ch p r o c ed u r e o r fo r a n y o f t h e h a nd l e r s
YH ,
XH ,
BHH , a nd AH wh en t h e y a r e c a l l ed wi l l b e l o c a t e d o n
t o p o f t h e s i g n a l a nd m e ch a n i sm a r rays fo r s i g n a l T ( a t l owe r
v i r t ua l
addresses) .
( On e
e x ampl e
i s s h o wn i n F i g u r e 2 - 8 ,
wh i c h
i l l ustra tes
the
opera t io n of
the
$ UNW I ND
s ys t em
s e rv i ce . )

2. 4

C OND I T I ON HANDLER ACT I ON

C o nd i t i o n h a nd l e r s h a v e s ev e r a l � p t i o n s a v a i l a b l e to them .

2. 4. 1

•

Th e y c a n f i x t h e e x c e p t i o n a nd a l l o w e x ec u t i o n to c o n t i n ue a t
t h e i n t e r r upted po i n t i n t h e p r og r am .

•

Th e y c a n p a s s the
r e s i g n a l l i ng .

•

r e s um e
at
any a r b i t r a ry
Th e y c a n a l s o a l l o w e x e c u t i o n
to
place
in
t h e c a l l i ng
h i e r a r c h y by
unwi nd i ng a n um b e r o f
f r am e s f r om the c a l l s t a c k .

except ion

a l o ng

ano the r

h a nd l e r

C o n t i n ue o r Re s i g n a l

A h a nd l e r f i r s t d e t e rm i n e s t h e n a t u r e o f t h e e x c e p t i o n b y e x am i n i ng
the s ignal
name
in
the
s i g n a l a r r a y ( Fi g u r e 2 - 4 ) .
I f the h a nd l e r
d e te rm i n e s t h a t i t i s n o t c a pa b l e o f r e so l v i ng t h e c u r r e n t e x c e p t i o n
f o r wh a t e v e r
r e a so n ,
it
i n f o rm s t h e e x c ep t i o n d i spa t c h e r th a t t h e
s e a r ch fo r a h a nd l e r m u s t g o o n .
Th i s i s c a l l ed r e s i g n a l l i ng
and
is
p e r f o rmed b y p a s s i ng a r e t u r n s t a t u s c o d e o f S S $ R E S IGNA L b a c k t o t h e
d i spa tch e r .
( Re c a l l th a t c o nd i t i o n h a nd l e r s a r e -f un c t i o n p r o c ed u r e s
t h a t r e t u r n a s t a t u s t o the i r c a l l e r i n R O . )
On t h e o th e r h a nd , i f t h e cond i t i o n h and l e r i s a b l e
to
r e so l v e
the
ex cept i o n
( i n s o m e u n s p e c i f i ed wa y ) , i t i nd i c a te s t o t h e d i s p a tc h e r
t h a t t h e p r og r am t h a t wa s i n t e r r up t ed wh e n the e x c e p t i o n o c c u r r ed
c an
c o n t i n ue .
Th i s
1 s d o ne
b y p a s s i ng
the
r etur n
s t a t us c o d e o f
S S $_C ONT INUE b a c k t o t h e c a l l e r .
Wh e n t h e d i s pa tc h e r d e t e c t s t h i s r e t u r n s t a t us c o d e ,
it
r em o v e s
the
a rg um e n t
l i s t a nd m e c h a n i sm
a r r a y f r om t h e s t a c k
( Figure 2-4 ) ,
r e s to r i ng RO and Rl i n t h e p r o c e s s .
I t t h e n r emov e s a l l o f t h e s i g na l
a r r a y e x c e p t t h e e x c e p t i o n P C a n d PS L f r om t h e s t a c k .
Fi nal l y , these
a r e r emoved w i th t h e RE I i n s t r uc t i o n th a t d i sm i s s e s t h e e x c e p t i o n a nd
pa sse s
control
back to
t h e p r og r am
th a t wa s i n t e r r up t e d wh e n t h e
e x c e p t i o n o c c u r r ed .
I f the ex c ep t i o n th a t o c c u r r ed wa s a h a r d wa r e f a u l t ( s u c h a s a n a c c e s s
v i o l a t i o n ) , t h e i n s t r uc t i o n t h a t c a us ed t h e e x c e p t i o n w i l l b e r e p e a t e d
b e c a u s e t h e PC o f t h a t i n s t r uc t i o n wa s pushed o n to t h e s ta c k wh e n t h e
e x c e p t i o n o c c u r r ed .
If
the
e x c ep t i o n wa s a h a r d wa r e t r a p ( s uc h a s
i n teg e r o v e r f l o w ) ' t h e n e x t i n s t r uc t i o n i n t h e i n s t r uc t i o n s t r e am wi l l
2-2 3

COND I T I ON HANDL I NG
be
the
f i rs t
to
execute .
In
th e e v e n t th a t a c o nd i t i o n h a nd l e r
c o n t i n u e s f r om a n e x c e pt i o n th a t wa s
i n i t i a t ed
th r o ug h
a
call
to
L I B $ S I GNA L ,
t h e f i r s t i n s t r uc t i o n t o ex e c u t e w i l l be the i n s t r uc t i o n
f o l l o w i ng the CALLx i n s t r uc t i o n .

2.4. 2

Unwi nd i ng t h e C a l l S t a c k

An o th e r powe r f u l to o l a v a i l a b l e t o c o nd i t i o n hand l e r s a l l o ws
t h em
to
al ter
the
f l ow o f cont r o l
wh e n an ex c e p t i o n o c c u r s .
Th i s t o o l i s
c a l l ed u n w i nd i ng a n d a l l o ws t h e c o nd i t i o n h a nd l e r t o pa s s c o n t r o l b a c k
to
a
p r ev i o u s
l ev e l
in
the
c a l l i ng
h i e r a r c h y by th r o w i ng awa y a
s pe c i f i ed ( o r d e f a u l t ) n um b e r o f c a l l f r am e s .
Th e Unw i nd Ca l l S t a c k s ys t em
s e rv i c e
is
c a l led
w i th
two
o pt i o n a l
a rg um e n t s , t h e f i r s t o f wh i c h i nd i c a t e s t h e n um b e r o f f r ame s t o r emove
f r om t h e c a l l s t a c k a nd t h e s e c o nd of wh i c h g i v e s a n a l t e r n a t e
return
P C t o wh i c h c o n t r o l w i l l b e r e t u r n ed .
Th e Unwi nd s ys t em s e rv i c e d o e s n o t a c t ua l l y r emove
f r am e s
f r om t h e
s ta c k .
Ra th e r ,
i t c h ang e s t h e r e t u r n PC i n t h e s p e c i f i e d n umbe r o f
f r am e s t o po i n t t o a s pe c i a l r o u t i n e i n t h e
execut ive
th a t w i l l
be
e n t e r ed a s e a ch p r o c ed u r e e x i t s w i th a R E T i n s t r uc t i o n .
Th e e f f ec t o f
c a l l i ng Unw i nd
is
p i c t u r ed
in
Figure 2-7 .
If
the
a l ternate
PC
a r g um e n t h a s
a l so
b e e n p a s s e d to Unwi n d , t h e r e t u r n PC i n the n e x t
c a l l f r am e i s a l t e r ed to t h e s p e c i f i ed a rg um e n t ( F i g u r e 2 - 7 ) .
As e a c h p r o c ed u r e i s s u e s a R E T i n s t r uc t i o n , c o n t r o l i s pa s s ed
to
the
e x e c u t i v e r o ut i n e t h a t e x am i n e s th e c u r r e n t f r am e f o r the e x i s t e n c e o f
a c o nd i t i o n h a nd l e r .
I f s uc h a h a nd l e r e x i s t s , i t i s c a l l ed wi t h
the
e x c e p t i o n n am e SS$ UNW I N D .
Wh e n the c o nd i t i o n h a nd l e r r e t u r n s to the
unwi nd r o u t i n e , a RET i s i s s ued b y the unwi nd r o u t i n e on b e h a l f of the
p r o c ed u r e
t o d i sc a r d
t h e c u r r e n t c a l l f r ame .
Th i s s e q ue n c e g o e s on
un t i l the s pec i f i ed n umbe r o f c a l l f r am e s h av e been
d i s c a r d ed .
Th i s
t e c h n i que o f c a l l i ng h a nd l e r s a s a pa r t o f the unwi nd s e q u e n c e a l l o ws
h a nd l e r s t h a t p r ev i o u s l y r e s i g n a l l ed an e x c ep t i o n
to
r eg a i n c o n t r o l
a nd pe r fo rm p r o c ed u r e - s p e c i f i c c l e a n u p .

2.4.3

E x ampl e of U n w i nd i ng th e C a l l S t a c k

An e x ampl e o f a n unwi nd s e quenc e i s i l l u s t r a t ed h e r e w i th t h e h e l p o f
Figure 2-7 .
Th e s i t ua t i o n b eg i n s wi th a s e q u e n c e e x a c t l y l i k e t h e o n e
p i c t u r ed i n F i g u r e 2 - 5 .
P r o c ed u r e A c a l l s p r o c ed u r e
B who
calls
p r o c ed u r e
c.
P r o c ed u r e C g e n e r a t e s
s ignal
s.
Th e p r i m a r y a nd
s e c o nd a r y h a nd l e r s ( i f the y e x i s t ) s i mpl y r e s i g n a l .
H a nd l e r s C H a nd
BH , l o c a ted ne x t by t h e s e a r c h p r o c ed u r e , a l s o r e s i g n a l .

2-24

COND I T I ON HANDL I NG
Return PCs in these
frames after they
have been modified by
EXE$UNWIND

Call fram e s on e ntry
to EXE$UNWIN D
SYS$UNWIND's h andler
Call frame for
system service
SYS$UNWIND
(EXE$UNWI N D
executes i n
access mode
of caller.)

�

Saved AP
Saved FP
Return PC in AH

Return PC i n A H

AHH ( i f established)

.Jill
�

This AP locates
the signal and
mechanism arravs
passed to
handler AH

Call frame for
condition handler
AH

Saved FP
Return PC in exception dispatcher
(SYS$CALL_HANDL � 4)
Signal and mechanism arrays for
initial condition located here
(Figure 2-5)

+- J

STARTUNWI N D
Signal array contains return PC
in procedure C which is
bypassed if u nwinding any frames

CH (if established)
Call frame for
procedure C

Saved FP
Return PC in B

LOOPUNWI N D

(alternate return PC)

BH (if established)
Call frame for
procedure B

Saved FP
Return PC in A

AH
Call frame for
procedure A

Saved FP

Return PC in calle r of A
previous call
frame

F i g u r e 2- 7

C a l l F r am e Mod i f i c a t i o n by SYS $ UNW I ND

2-2 5

C ONDI T I ON HANDL ING
F i n a l l y , h a nd l e r AH i s c a l l ed .
AH d e c i d e s to unw i nd
the c a l l
stack
back
to
i t s e s ta b l i sh e r
f r am e .
( Th i s i s n o t t h e d e f a ul t c a s e . ) To
a c c ompl i sh th i s , AH m u s t c a l l SYS $ UNW I N D w i t h a d e pth a r g um e n t e q u a l
to
t h e v a l ue c o n t a i n e d i n t h e m e c h a n i sm a r r a y .
I n th i s e x ampl e , the
d e p th a rg um e n t is 2 .
Af t e r the c a l l to SYS $ UNWI ND , wh i c h e x e c u t e s
in
the a c c e s s m o d e o f
i ts c a l l e r ,
b u t b e fo r e the f r am e mod i f i c a t i o n
o c c u r s , t h e s t a c k h a s t h e fo rm p i c t u r ed
on
the
l e f t h and
side of
Figure 2-7 .
Th e o pe r a t i o n o f f r ame mo d i f i c a t i o n b y t h e $ UNW I ND s ys tem
s e rv i c e n o w p r o c e e d s a s fo l l o ws .
(1)

Unwi nd l o o k s b a c k d o wn the c a l l
s t ac k
un t i l
i t l ocates a
c o nd i t i o n h a nd l e r .
Re c a l l
th a t
a
c o nd i t i o n h a nd l e r
is
i d e n t i f i ed b y a s av e d PC o f SYS $CALL HAND L + 4 .
I f h a nd l e r
A H h a d c a l l ed
another
p r o c ed u r e - i n th i s e x am p l e , no th i ng
wo u l d h a v e h a pp e n e d to
th a t p r o c ed u r e ' s c a l l
f r am e .
Th e
f i r s t c a l l f r am e m od i f i ed by Unw i nd i s t h e f r am e o f the f i r s t
h a nd l e r t h a t i t e nc o un t e r s , wh i c h
in
th i s
e x amp l e
is
the
f r am e fo r AH .

(2)

Unwi nd d o e s n o t mod i fy i t s o wn f r am e .
c o n t r o l i s p a s s ed b a c k to h a nd l e r A H .

(3)

Th e f i r s t f r am e th a t Unwi nd mo d i f i e s
is
the
f r am e o f
the
f i r s t c o nd i t i o n h a nd l e r
th a t i t e nc o un t e r s b y t r a c i ng bac k
the c a l l s t ac k .
I t r epl aces the r et u r n add r e s s
f o und
the r e
w i th
the a d d r ess
of
a
rout ine
( S TARTUNW I N D ) i n t e r n a l to
i ts e l f .

Wh e n i t i s s ue s a

RET ,

Wh e n h a nd l e r AH i s s ue s i t s RE T , c o n t r o l w i l l n o t g o b a c k to
th e
e x c ep t i o n
d i spa tc h e r .
I n s t e ad ,
the
i n s t r uc t i o n s
b e g i nn i ng a t STARTUNW I N D e x e c u t e .
No t e t h a t n o t r e t u r n i ng t o
t h e e x c e p t i o n d i s pa tc h e r m e a ns th a t c o n t r o l w i l l n eve r g e t
b a c k t o p r o c ed u r e C , b e c a u s e i t s r e t u r n P C i s s to r ed
in
the
m e c h a n i sm a r r a y a nd wo u l d b e r e s to r ed b y t h e RE I i n s t r uc t i o n
i s s ued b y t h e e x c e p t i o n d i spa t c h e r .
(4)

Unwi nd
c on t i nues
to mod i f y t h e
s a v ed
PC
l o ngwo r d s
in
s uc c e s s i v e
f r am e s o n
the c a l l
stack
un t i l t h e n umb e r o f
f r am e s s pe c i f i e d ( o r i m p l i ed ) i n t h e SYS $ U NW I N D a r g um e n t l i s t
h a v e b e e n mo d i f i ed .
Al l f r am e s e x c ep t the fi r s t h a v e the i r
s a ved PC r e p l a c ed w i th a d d r e s s LOO PUNW I N D , a n o t h e r
l a be l
in
t h e i n t e r n a l unw i nd r o u t i n e ( F i g u r e 2 - 7 ) .
I t i s th i s r o u t i n e
that checks
wh e th e r
the c u r r e n t
f r am e h a s
a
h a nd l e r
e s t a b l i s hed
and ,
if
so , c a l l s t h a t h a nd l e r w i th t h e s i g n a l
n am e
S S $ U NW I ND
to
a l low
the
h a nd l e r
to
pe r f o rm
p r o c ed u r e -sp e c i f i c c l e a n u p .
I f a h a nd l e r c a l l ed i n th i s wa y c a l l s
SYS $ UNW I N D
( w i th
the
s ignal
a r r a y c o n t a i n i ng
SS$ U NW I ND as the s i g n a l nam e ) , an
e r r o r s t a t u s of SS$ U NW I N D I NG T s r e t u r n ed , i nd i c a t i ng th a t a n
unwi nd i s a l r e a d y i n p r og r e s s .

(5)

I f the a l t e r n a t e PC a r g um e n t wa s a l s o s uppl i ed to SYS $ UNW I ND ,
t h e c a l l f r ame i n to wh i ch th i s a rg um e n t wo u l d be i n s e r t ed i s
t h e n e x t f r am e b eyo nd the l a s t f r am e s p e c i f i ed
(or
i m p l i ed )
in
the
f i rs t
SYS $ UNWIND a r g um e n t .
In
th i s
c a se , i f a n
a l t e r n a t e P C a r g um e n t we r e p r e s e n t , i t wo u l d b e p l a c ed
i n to
the c a l l f r am e fo r p r o c ed u r e A .

2-26

C OND I T I ON HANDL ING
Now t h a t a l l the f r am e s h a v e b e e n mo d i f i e d ,
the
a c t ua l
un w i nd i ng
occurs .
Th e s e q u e n c e o f s t eps i s a pp r o x i m a t e l y t h e f o l l o w i ng .
1.

Unw i nd r e t u r n s c o n t r o l t o h a nd l e r AH .

Ha n d l e r AH d o e s wh a t ev e r e l s e i t n e ed s to d o to
s e rv i c e
the
c o nd i t i o n .
Wh e n i t h a s c om p l e t ed i t s wo r k , i t r e t u r n s t o th e
c o d e b e g i n n i ng a t
l abel
STA RTUNW I ND i n mod u l e
S Y S UNW I ND .
( Be c a us e n o n e o f the unwi nd r o u t i n e s c h e c k r e t u r n s t a t u s , i t
d o e s n o t ma t t e r wh a t s t a t us
i s p a s s ed
b a c k b y AH a s
it
returns . )

Th e r o u t i n e b eg i nn i ng a t S TARTUNW I ND f i r s t r e s t o r e s R O a nd R l
f r om t h e m e c h a n i sm
a r ray .
I t then pe r f o rm s t h e fo l l o w i ng
th r e e s t e ps .
a.

I f a h a nd l e r i s e s ta b l i sh ed fo r th i s f r ame ,
i s c a l l ed w i th the s i g n a l n am e S S $_UNW I ND .

the

h a nd l e r

I f e i th e r R O o r Rl i s s pe c i f i ed
in
the
r eg i s te r
save
ma s k ,
the
unwi nd
rout i ne
r eplaces
the
v a l ue o f th a t
r e g i s t e r i n t h e r eg i s t e r s a v e a r ea o f the c a l l f r am e wi th
t h e c u r r e n t c o n t e n t s o f t h e r eg i s t e r .

Co n t r o l i s r e t u r n ed t o wh a t ev e r ad d r e s s i s
th e
s aved
PC
l o ng wo r d
of
the c u r r e n t
i s s u i ng a RE T .

s pe c i f i ed
in
c a l l f r am e b y

Th e RET
i s sued
in
s tep 3c
d i sc a r d s
the c a l l
f r am e
fo r
p r o c ed u r e C ,
p a s s i ng
c o n t r o l to LOOPUNW I N D wh e r e the th r e e
s t e p s 3 a t h r o ug h 3 c a r e a g a i n e x e c u t ed .

Th e R E T t h a t d i s c a r d s the c a l l f r am e f o r p r o c e d u r e
B pa sses
control
back
t o t h e po i n t i n p r o c ed u r e A f o l l o w i ng t h e c a l l
to p r o c ed u r e B ( i f we a s s ume no a l t e r n a t e PC a r g um e n t )
wh e r e
e x ec u t i o n w i l l r e s ume .

I n e f f e c t , S TARTUNW I ND a nd
LOOPUNW I N D s i mul a t e
r e t u r ns
f r om
each
n e s t ed
p r o c ed u r e t h a t
is
b e i ng
unwo und .
Th e s e p r o c ed u r e s n ev e r
r ec e i ve c on t r o l aga i n .
Howeve r ,
t h e o u t e rmo s t p r o c ed u r e
r ec e i ves
c o n t r o l a s i f a l l o f the n e s t ed p r o c ed u r e s h ad r e t u r ned no rm a l l y .

2. 4.4

Po t en t i a l I n f i n i t e Lo o p

Th e r e
i s o n e po s s i b l e
p i tf a l l
that
can
h a ppe n
w i th
th i s
I n the
p r ev 1 o u s s e c t i o n ,
we po i n t e d o u t th a t the
i mpl em e n t a t i o n .
e x c ep t i o n d i s pa tc h e r t a k e s c a r e ( wh e n m u l t i pl e s i g n a l s a r e a c t i v e ) no t
to
sea r ch
f r am e s
f o r the s e c ond c o nd i t i o n th a t we r e e x am i n ed o n t h e
f i r s t pa s s .
I f a c o nd i t i o n h a nd l e r g e n e r a t e s a n e x c e p t i o n , i t i s n o t
c a l l ed
i n r e s po n s e to i t s o wn s i g n a l ( un l e s s i t e s t a b l i sh e s i t s e l f t o
h a nd l e i t s o wn s i g n a l s ! ) .
Ho we v e r , Unw i nd c a nno t pe r f o rm s uc h
a check .
I t must cal l
each
c o nd i t i o n h a nd l e r
th a t
i t e nc o un te r s a s i t r em o v e s f r am e s f r om t h e
s ta c k .
Th u s , a poo r l y wr i t t e n c o nd i t i o n h a n d l e r ( o n e
th a t g e n e r a t e s
an ex cept i on )
c o ul d
resul t
in
a n i n f i n i te l oo p of e x c ept i o n s i f a
h a nd l e r h i g h e r up i n th e c a l l i ng h i e r a r c h y unwi nd s the f r am e i n wh i c h
th i s
po o r l y wr i t t e n h a nd l e r i s d e c l a r ed .
Th i s h a s no e f f e c t o n t h e
s ys tem b u t e f f e c t i v e l y d e s t r o ys t h e p r o c e s s
in
wh i ch
th i s h a nd l e r
ex i s ts .
2-27

C OND I T I ON HANDL ING
Unwi nd i ng Mul t i p l y Ac t i ve S i g na l s

2.4.5

Th e r e i s a s l i g h t c h a ng e t o th e Unw i nd s y s t em
s e rv i c e wh en m u l t i pl e
s i g na l s a r e a c t i v e .
Wh i l e m o d i f y i ng saved PCs i n c a l l f r ame s , Unwi nd
c o un t s the
n um b e r
of
f r am e s
t h a t h a v e b e e n m o d i f i ed
un t i l
the
r e que s ted
n um b e r h a s b e en r e a c h e d .
Th e o n l y c h a ng e th a t o c c u r s w i th
m u l t i pl y a c t i v e s i g n a l s i s t h a t the
l o o p s to p s
c o un t i ng
wh i l e
the
s k i pped f r am e s a r e b e i ng m o d i f i e d .
Th e e x ampl e o f m u l t i pl y a c t i v e s i g n a l s p i c t u r ed i n F i g u r e s 2 - 5 and 2 - 6
can be
used
to
i l lustrate
th i s .
Re c a l l
t h a t p r o c ed u r e A c a l l ed
p r o c ed u r e B wh o c a l l ed
p r o c ed u r e C wh o
s i g n a l l ed
S.
Hand l e r
CH
r e s i g n a l l ed .
Hand l e r B H c a l l ed p r o c ed u r e X who c a l l ed p r o c ed u r e Y wh o
s i g n a l l ed T .
Hand l e r s Y H , XH ,
and
BHH a l l
r e s i g n a l l ed .
F i nal l y ,
h a nd l e r A H wa s c a l l ed f o r s i g n a l T w i th a d e p th o f 3 .
I f AH c a l l s SYS $UNW I ND , t h e
top o f
the
s tack
i s a s p i c t u r ed
in
Figure 2-8 ,
w i th t h e c o n t i n ua t i o n s o f th i s f i g u r e i n F i g u r e 2 - 6 .
Le t
u s f u r the r a s s ume t h a t t h e d e p th a rg um e n t pa s s e d to SYS $ UNW I N D i s
3,
t a ke n
f r om
the m e ch a n i sm a r r a y ( me a n i ng unw i nd t o the e s t a b l i s h e r o f
AH ) a n d t h e a l t e r n a t e P C a r g um e n t i s n o t p r e s e n t .
Th e e nd r e s u l t o f the o pe r a t i o n o f Unwi nd i n th i s c a s e i s a s fo l l o ws .

2. 5

locates
it
a
Unw i nd l o o k s b a c k d own the c a l l
stack
un t i l
Th e s a v ed PC i s
c o nd i t i o n h a nd l e r , wh i c h i n th i s c a s e i s AH .
m o d i f i e d t o START UNW I N D .

Th e s a ved PC l o ng wo r d s i n f r am e s Y a nd
X a r e a l t e r ed
to
conta i n add ress
L O O PUNW I N D .
No t e th a t we h a v e now a l t e r ed
th r e e f r am e s .

Be c a use
the
nex t
f r ame
on
the
s tac k ,
BH ,
i nd i c a t e s
a
c o nd i t i o n h a n d l e r
( s aved
PC o f
SYS $CALL HANDL + 4 ) ,
i ts
a s s o c i a t ed m e c h a n i sm a r r a y i s l o c a t ed ( by c lim b i ng o v e r s a v ed
r eg i s te r s , s t a c k a l i g nm e n t byt e s , a n d a s a ved PC f r om th e J S B
i n s t r uc t i o n ) .
Th e s a v e d PC s i n a l l f r am e s up t o
the
f r am e
po i n t ed
to
by
t h e m e c h a n i sm a r r a y a r e m o d i f i ed ( b u t n o t
c o un t ed t owa r d t h e n um b e r s pe c i f i ed i n t h e a r g um e n t pa s s ed to
SYS $ UNW I N D )
to
c o nta i n
add r ess
L O O PUNW I ND .
Th i s c a u s e s
f r am e s B H a n d C
to
get
the i r
s av ed
PCs
a l te r ed
in
the
e x ampl e .

Th e saved PC i n t h e f r am e fo r p r o c ed u r e B i s no t a l t e r ed
so
t h a t wh e n t h e unwi nd t a k e s p l a c e , c o n t r o l wi l l r e t u r n to the
c a l l s i t e o f p r o c ed u r e B i n p r o c ed u r e A .

DEFAULT ( VMS-S U P PL I E D ) C OND I T I ON HANDLERS

A l t h o ug h
the
use
o f c o nd i t i o n h a nd l e r s
is
total ly g eneral
a nd
c ompl e t e l y i n the h a nd s o f t h e u s e r , s om e a c t i o n s wi l l a l wa ys o c c u r a s
t h e r e s u l t o f d e fa u l t c o nd i t i o n h a nd l e r s th a t a r e e s t ab l i s h e d b y VM S
a s a pa r t o f p r o c e s s c r e a t i o n o r i m a g e a c t i v a t i o n .
Th e d i sc u s s i o n s o f p r o c e s s c r e a t i o n i n Ch a p t e r 1 7 a nd i m a g e i n i t i a t i o n
in
C h a p t e r 1 8 po i n t
out
ex a c t l y wh en a nd h o w e a ch o f t h e h a nd l e r s
d e sc r i b ed i n th i s s e c t i o n i s e s t a b l i shed .
Th e a c t i o n o f e a c h o f th e s e
h a nd l e r s , o n c e t h e y a r e i nv o k e d , i s b r i e f l y d e sc r i b ed h e r e .

2-28

C OND I T I ON HANDL ING

SYS$UNWIND's handler
Call frame for
system service
SYS$UNWIN D
(EXE$UNWIND
executes in
access mode
of caller)

Saved AP
Saved FP
Return PC in AH

""""....

AHH (if established)

Call frame for
condition
handler AH

R.S.M.

Direction of
stack growth
-

Saved FP
Return PC in
exception dispatcher

::�

Saved registers and
stack alignment
bytes indicated
by register save
mask R.S.M. in
call frame AH

��

::;:;

To fram e for
proced ure Y
in Figure 2-6

Return PC fro m JSB

Signal and
mechanism arrays
for signal T

Sig nal array
M echanism array

2
-

��.I �,

,.. -.,.,

To signal
array
in Figure 2-6

Figure 2-8

Mod i f i ed Un w i nd w i th Mu l t i pl y Ac t i v e S i g n a l s

2-2 9

C OND I T I ON HANDL ING
2.5.1

T r a c e b a c k Hand l e r E s tab l i s h ed by Imag e S t a r t up

Wh e n a n imag e i n c l ud e s e i th e r the d eb ug g e r o r t h e
t r a c eb a c k h a nd l e r ,
a n o th e r
f r am e
is
put on
t h e u s e r s t a c k b e fo r e t h e i m ag e i t s e l f i s
c a l l ed ( Ch a p t e r 1 8 ) .
Th e c o d e th a t e x e c u t e s b e fo r e c a l l i ng the
i m ag e
pl aces
the
add r e s s
of a
c o nd i t i o n h a nd l e r i n to th i s f r ame s o th a t
s ub s e q ue n t c o nd i t i o n s th a t a r e n o t h a nd l ed b y a n i n t e r v e n i ng c o nd i t i o n
h a nd l e r w i l l be p i c k e d up b y t h i s t r a c eb a c k h a nd l e r .
Th i s h a nd l e r f i r s t c h e c k s wh e th e r
the e x c e p t i o n
t h a t o c c u r r ed
wa s
I f s o , i t m a ps the d e b ug g e r i n t o P O s p a c e ( i f n o t a l r e a d y
S S $ D E B UG .
m a pped ) a n d pa sse s c o n t r o l to i t .
Th i s c o nd i t i o n i s
s i g n a l l ed
by a
C L I i n r e s po n s e to a D E B UG c omma nd .
Th i s f e a t u r e a l l o ws a n i m ag e th a t
wa s n o t l i n k e d o r r un w i t h d eb ug g e r s uppo r t t o b e i n t e r r upted a n d have
that s uppo r t a d d ed .
Fo r a l l o the r e x c e p t i o n s , i f t h e s ev e r i t y l ev e l i s wa r n i ng , e r ro r ,
or
s ev e r e
e r r o r , the h a nd l e r m a ps th e t r ac eb a c k f a c i l i ty i n to the t o p o f
P O s p a c e a nd pa s s e s c o n t r o l t o
it.
Th e
t r ac ebac k
f a c i l i ty p a s s e s
i n f o rm a t i o n a b o u t t h e
except ion
to
S Y S $ 0 UTPUT a nd t e rm i n a t e s the
i m ag e .
I f the s ev e r i ty l ev e l i s o the r t h a n the th r e e l i s t ed i n
the p r ev i o us
p a r ag r a ph ,
t h e t r a c e b a c k c o nd i t i o n h a nd l e r r e s i g n a l s the c o nd i t i o n ,
wh i c h u s ua l l y m e a n s t h a t the c o nd i t i o n i s b e i ng pa s s e d o n to th e c a tc h
a l l c o ud i t i o n h a nd l e r .

2. 5. 2

C a t c h Al l C o nd i t i o n Ha nd l e r

Th e a d d r e s s o f th i s h a nd l e r i s pl a c ed i n a n i n i t i a l c a l l f r ame o n
the
use r
stack
a nd
in the l a s t c h a n c e ex c e p t i o n v e c t o r f o r user m o d e by
e i the r PROC S TRT wh e n the p r o c e s s i s c r ea ted or by a
c ommand
l a ng uage
i nterprete r
b e f o r e a n i m ag e i s c a l l e d .
Th i s h a nd l e r i s a l wa ys c a l l ed
i f no o th e r h a nd l e r s e x i s t o r i f a l l o th e r h a nd l e r s r e s i g n a l .
Bec ause
t h e ad d r e s s o f t h e h a nd l e r i s d u pl i c a t ed i n th e l a s t c h a n c e v e c to r , i t
w i l l a l s o b e c a l l ed i n the e v e n t o f some e r r o r wh i l e
l o o k i ng
th r o ug h
t h e us e r s t a c k .
Th e
f i rst
s t ep t h a t
th i s h a nd l e r
takes
is
to c a l l
SYS $ P UTM SG
( Ch a p t e r 2 7 ) .
If
the
h a nd l e r
wa s c a l l e d
th r o ug h t h e l a s t c h a n c e
e x c e p t i o n v e c t o r ( d epth a r g um e n t i n m e c h a n i sm a r r a y i s - 3 ) , o r i f t h e
s e ve r i t y
l ev e l
of
the
e x c e p t i o n n ame i n th e s i g n a l a r r a y i nd i c a t e s
s eve r e ( e x c e p t i o n - n a m e < 2 : 0 > G E QU 4 ) , th en SYS $ E XCMSG
( Ch a p t e r 2 7 )
is
c a l l ed
t o pr int a
s umma r y m e s s ag e a nd
the
i m ag e i s t e rm i n a t e d .
O t h e r w i s e , t h e i m a g e i s c o n t i n u ed .

2. 5. 3

H a nd l e r s U s e d by O th e r Ac c e s s Mod e s

I n a d d i t i o n t o the h a nd l e r s th a t VM S s uppl i e s t o h a nd l e e x c e p t i o n s
that
o c c u r i n u s e r m o d e , i t a l s o s e t s up h a nd l e r s t h a t wi l l d e t e rm i n e
s ys tem b e h a v i o r i f a n e x c e p t i o n o c c u r s
i n one o f
the
o the r
th r e e
access modes .

2-3 0

C OND I T I ON HANDLING
2 . 5. 3. 1
E x c e p t i o n s i n K e r n e l o r E x e c ut i v e Mo d e - I n
r e s po n s e
to
an
e x c ept i o n
in
k e rne l
mode ,
t h e e x c e p t i o n d i spa tc h e r ma k e s s pe c i a l
c h e c k s t o d e t e rm i n e wh e th e r
the
p r oc e s so r
wa s o pe r a t i ng
on
the
i n t e r r up t
s t a c k wh e n t h e ex c e p t i o n o c c u r r ed o r wh e th e r I P L wa s a b o v e
I PL $ ASTDE L ( I P L 2 ) .
E i t h e r o f t h e s e i t ems c o u l d
i nd i c a t e
th a t
the
I n any c a s e , i f e i th e r o f
e x c ept i o n i s n o t a s s o c i a t ed w i th a p r o c e s s .
t h e s e c o nd i t i o n s h o l d s ,
an
Inva l i d
Ex c e p t i o n
fatal
b ug ch e c k
( BUG $ I NVE XC E PTN ) i s g e n e r a t ed .
Ro u t i n e s wh i c h f a l l i n to the c a t eg o r y
t h a t fo r b i d s e x c e p t i o n s i n c l ud e
i n te r r up t
s e rv i c e
rout ines ,
d ev i c e
d r ivers
( e x c e pt
f o r t h e i r FDT r o u t i n e s ) , a nd p r o c e s s - b a sed c o d e th a t
h a ppe ns t o b e ex e c u t i ng a b o v e I P L $ A S TDE L ( s uc h a s po r t i o n s o f c e r ta i n
s ys t em s e rv i c e s ) .
I f a ke r ne l m o d e e x c e p t i o n i s a s so c i a t ed w i th p r o c e s s - b a sed
code
fo r
wh i ch
e x c ept i on s
a r e a l l o we d ( I P L i s l e s s th a n o r e q ua l to 2 a n d t h e
e x c e pt i o n o c c u r r ed o n th e k e r n e l s t a c k ) ,
th en
e x c e p t i o n d i s p a t c h i ng
p r o c e ed s
i n i t s usual manne r .
Th e p r i m a r y e x c e p t i o n v e c to r s f o r bo th
ke r n e l
a nd
exec ut i ve mod e s
are
i n i t i a l i zed
in
modul e
SHELL
( Ch a p t e r 1 7 )
to c o n t a i n
the
add resses
o f r o u t i n e s th a t g e n e r a t e a
b ug c h e c k c o d e o f Un e x pe c t ed Sy s t em Se r v i c e E x c e p t i o n .
Th e d i f f e r e n c e
b e twe e n t h e b ug c h e c k s
f o r t h e two a c c e s s m o d e s i s t h a t t h e b ug c h e c k
g e n e r a t e d b y t h e k e r n e l m o d e p r i m a r y ex c e p t i o n h a nd l e r i s f a t a l
wh i l e
t h e c o r r e s po nd i ng
b ug c h e c k g e n e r a t ed
by t h e e x e c u t i v e m o d e p r i m a r y
e x c e p t i o n v e c to r i s n o t .
Fa t a l b ug c h e c k s c a u s e the s ys tem t o c r a s h .
No n f a t a l
b ug c h e c k s
resul t
in
e rror
l og
entr ies .
Th e b ug c h e c k
o pe r a t i o n i s d e sc r i b ed i n Ch a p t e r 7 .
Th i s m e a n s th a t i f a n ex c e p t i o n eve r o c c u r s wh i l e
the
s ys tem
is
in
e i th e r
k e r n e l o r e x e c u t i v e m o d e , t h e s ys t em w i l l b ug c h e c k b e c a u s e t h e
p r i m a r y e x c e p t i o n v e c to r ' s h a nd l e r
is
f o und
f i rst .
Ro u t i n e s
th a t
e x e c u t e i n e x e c u t i v e m o d e i n c l ud e RM S , pa r t s o f the e x e c u t i v e , a nd a n y
u s e r -wr i t t e n p r o c ed u r e t h a t i s e n t e r ed th r o ug h e i th e r
a
u s e r -w r i t t e n
s ys tem
s e rv i c e d i s pa tc h e r
or
t h r o ug h
t h e Ch a ng e Mo d e t o E x e c u t i v e
s ys tem s e rv i c e .
Ro u t i n e s th a t e x e c u t e i n ke r n e l m o d e ( th a t c a n
c a us e
th i s b ug c h e c k a nd
no t t h e
I nv a l i d Ex c e p t i o n b ug c h e c k b e c a u s e t h e y
e x ec u t e a t I P L 0 o r I P L 2 ) i n c l ud e po r t i o n s o f
al l
s ys tem s e r v i c e s ,
m a n y e x c e p t i o n s e r v i c e r o u t i n e s , d ev i c e d r i v e r FDT r o u t i n e s , i n c l ud i ng
tho s e th a t a r e wr i t t e n b y u s e r s , a nd p r o c ed u r e s th a t a r e c a l l ed b y t h e
e i th e r
a use r -w r i t t e n s ys tem s e rv i c e d i s pa tc h e r o r b y t h e Ch a ng e Mo d e
t o Ke r n e l s ys t em s e r v i c e .

2 . 5 . 3 . 2 Cond i t i o n H a nd l e r U s e d b y DC L o r MCR - Th e
DC L
a nd
MCR
c o mmand
l a ng u a g e
i n te r p r ete r s
e s t a b l i s h n e a r l y i d e n t i c a l c o nd i t i o n
h a nd l e r s a t the b eg i n n i ng o f t h e i r c ommand l o o p s to
f i el d
except i ons
t h a t o c c u r i n s upe r v i so r mo d e .
Th e f i r s t s t e p t h a t t h e c o nd i t i o n h a nd l e r t a k e s i s to a l t e r the
entry
po i n t c o n t a i n ed
in the
s u pe rv i so r m o d e t e rm i n a t i o n h a nd l e r c o n t r o l
b l o c k f r om i t s n o rm a l c o n t e n t s t o
a
p r o c ed u r e
tha t
s i mpl y r e t u r n s
s uc c e s s f u l l y .
Th i s s t ep c a u s e s s upe r v i so r m o d e e x c e p t i o n s ( e x c e p t i o n s
e nc o un te r ed
wh i l e t h e C L I
is
e x e c u t i ng ) ,
to
r esul t
in process
deletion .
( As we
wi l l
s e e i n Ch a p t e r 2 0 , t h e m e a n s b y wh i c h a C L I
p r events p r o c e s s d e l et i on
f o l l o w i ng
i m a g e ex i t
is
th r o ug h
the
s up e rv i s o r m o d e t e rm i n a t i o n h a nd l e r tha t h a s j u s t b e e n e l i m i n a t e d . )

2-31

C OND I T I ON HANDL ING
Th e o n l y o th e r s t e p t a k e n by t h e s up e r v i s o r m o d e c o nd i t i o n h a nd l e r
is
t o cal l
t h e c a tc h a l l h and l e r d i r e c t l y , w i th a d e pth a rg um e n t o f - 3 .
As we s a w i n t h e d e sc r i pt i o n o f t h e c a t c h
al l
h a nd l e r ,
wh e n
it
is
c a l l ed
t h r o u g h t h e l a s t c h a n c e v e c to r ( d e t e rm i n ed b y a d e p t h a r g um e n t
o f - 3 ) , i t fo r c e s i mag e e x i t .
Th u s ,
an
exc ept ion
i n c u r red
wh i l e
e x e c u t i ng
in
s upe r v i so r m o d e r e s u l t s i n p r o c e s s d e l e t i o n , a f t e r some
m e s s a g e s have b e e n sent to SYS $ 0 UT P U T ( a n d po s s i b l y SYS $ ERROR ) .

2-3 2

C HAPTER 3
SYSTEM SERVI C E D I S PATCH ING

Ma n y o f the o pe r a t i o n s th a t VMS p e r f o r m s o n b e h a l f o f
the
user
are
i m p l emen ted
a s p r o c ed u r e s c a l l ed s y s tem s e rv i c e s .
Th e s e p r o c ed u r e s
a r e l i n ked a s pa r t o f t h e e x e c u t i v e ,
reside
in
s y s t em
space ,
have
g l o ba l
e n t r y p o i n t n am e s o f
the
f o rm
EXE $ s e r v i c e , a nd t yp i c a l l y
e x ec u t e i n k e r n e l o r e x e c u t i v e a c c e s s mod e s o th a t t h e y c a n r e a d
or
wr i t e d a ta s t r uc t u r e s p r o t e c t ed f r om a c c e s s by l e s s p r i v i l eg ed a c c e s s
mod es .
Some s e r v i c e s a r e i nvo ked d i r e c t l y by a ppl i c a t i o n p r og r am s .
O t h e r s a r e c a l l ed
o n b e h a l f o f t h e u s e r by c ompo n e n t s s uc h a s RM S .
Th i s c h apte r d e s c r i b e s h o w c o n t r o l i s pa s sed f r om a
u s e r p r og r am
to
t h e p r o c ed u r e s i n the e x e c u t i v e t h a t e x e c u t e s e r v i c e - s pec i f i c co d e .

3. 1

SYS TEM S ERVI C E VECTORS

Th e l o we s t t h r e e pag e s o f
s ys tem v i r t ua l
add r e s s
s pa c e
( add r e s s e s
8 0000000
to
8 0 00 05FF)
are
r e se rved
fo r en t r y po i n t s t o t h e s ys t em
s e rv i c e s a nd to RM S s e r v i c e r o u t i n e s .
Th e g l o b a l e n t r y po i n t nam e o f
e ach
s ys tem s e rv i c e v e c t o r
is
SY S $ s e rv i c e ,
a s d i s t i ng u i s h e d f r om
E XE $ s e rv i c e , the g l ob a l name of t h e p r o c ed u r e in the
execut i ve
i m ag e
t h a t pe r fo rm s t h e a c t ua l wo r k o f t h e s ys tem se r v i c e .
As n e w s e rv i c e s a r e a d d ed to f u t u r e r e l e a s e s o f
VAX/VM S ,
t h e v e c to r
a r ea w i l l g r o w t o ma k e r o om fo r n e w e n t r y po i n t s .
I n ad d i t i o n , t h e
a bso l ute
l oc a t i ons
of
the
SYS $ s e r v i c e
entry
po i n t s
of
ex i s t i ng
s e rv i c e s w i l l
r ema i n
f i x ed
fo r ev e r , s o t h a t ex i s t i ng us e r p r o g r am s
w i l l no t h a v e t o b e r e l i n k e d a t e a c h n ew r e l e a s e o f VM S .
E a c h s e rv i c e e n t r y po i n t c o n ta i n s e i g h t b y t e s o f c o d e a nd d a t a c a l l ed
a sys tem s e rv i c e v e c t o r .
E a c h v e c to r c o n s i s t s o f a g l o b a l en t r y po i n t
n amed SYS $ s e rv i c e , a r eg i s t e r s a v e m a s k ,
a
s i ng l e
i n s t r uc t ion
th a t
t r a n s fe r s
cont r o l
e v e n t ua l l y t o a s e r v i c e- s p e c i f i c p r o c ed u r e i n th e
e x e c u t i v e , a nd a n i n s t r uc t i o n ( u s ua l l y a RE T ) t h a t pa s s e s c o n t r o l b a c k
t o th e c a l l e r .
Mo s t o f t h e s ys t em s e r v i c e s e x e c u t e i n k e r n e l mod e a nd
t h e v e c to r s f o r th e s e s e r v i c e s c o n t a i n
a
C HMK
i n s t r uc t i o n .
A
f ew
s e rv i c e s
a nd
all
of
the
RMS s e r v i c e v e c t o r s c o n t a i n
a
C HM E
i n s t r uc t i o n .
S o m e se r v i c e s
s uc h a s
the
tex t
fo rma t t i ng
serv ices
exec ute
i n t h e a c c e s s m o d e o f the c a l l e r a nd d i s pa t c h d i r e c t l y t o th e
s e rv i c e - s p e c i f i c c o d e i n VM S w i th a
JMP
i n s t r uc t i o n .
Figure 3-1
i l l u s t r a t e s t h e th r e e s e t s o f i n s t r uc t i o ns f o und i n th e sys t em s e r v i c e
v e c to r a r ea .
Ta b l e 3 - 1 l i s t s t h e VM S s ys t em s e r v i c e s th a t u s e e a c h o f
t h e th r e e i l l us t r a t ed m e tho d s o f i n i t i a l d i s pa tc h .

3-1

SYSTEM SERVIC E D I S PATCH ING

Ve c to r c on t e n t s fo r s e rv i c e s tha t c ha ng e mod e to ke r ne l
S YS $ s e rv i c e : :

; En t r y po i n t fo r s e r v i c e s tha t
;
e x e c u t e i n k e r ne l mod e

. WOR D

e n t r y-ma s k

C HMK

# s e rv i c e- spec i f i c - c o d e

RET
. B LKB

; Th i s m a s k i s i d en t i c a l to the
;
ma s k f o und at l oc a t i o n
;
E XE $ s e rv i c e

; Re t u r n to c a l l e r
; Sp a r e b y t e to m a k e vec to r
;
e i g h t b yt e s l o ng

Ve c to r c o n te n t s fo r se r v i c e s tha t c ha ng e mod e to ex ecut i v e
; E n t r y po i n t fo r se r v i c e s tha t
;
e x ec ut e i n ex ecut i v e mod e

S YS $ s e rv i c e : :
. WORD

e n t r y -ma s k

C HM E

# s e r v i c e- s pec i f i c -c o d e
; Re t u r n to c a l l e r

RET
. B LKB

; Th i s m a s k i s i d en t i c a l to the
;
ma s k f o und at l o c a t i o n
;
E XE $ s e r v i c e

; Sp a r e b yt e to make v e c to r
;
e i g h t b y t e s l o ng

; Mo s t v e c to r s fo r RM S s e r v i c e c a l l s r epl a c e t h e se l a st t wo
;
byt e s wi th a b r a n c h to an RM S s yn c h r o n i za t i o n r o ut i n e .

Ve c to r c o n te n t s fo r s e r v i c e s tha t d o no t c h a ng e mod e
; En t r y po i n t fo r se r v i c e s th a t
;
e x ec u t e i n the a c c e s s mod e
;
o f the cal l e r

S YS $ s e rv i c e : :

. WORD

e n t r y-ma s k

JM P

@ # E XE $ s e r v i c e + 2
;
;

F i g ure 3 -1

; Th i s m a s k i s i d en t i c a l t o the
;
ma s k fo und at l o c a t i o n
;
E XE $ s e rv i c e
; T r a n s f e r c o n t r o l to
f i r s t i n s t r uc t i o n a f t e r the
e n t r y m a s k a t EXE $ s e r v i c e

C o n t e n t s o f t h e Sys t em Se r v i c e Ve c to r s

3-2

SYS TEM S E RVI C E D I S PATC H ING
Ta b l e 3 - 1
S y s t em Se r v i c e s a nd RM S Se r v i c e s Th a t Us e
Ea c h Fo rm o f Sys t em Se r v i c e Ve c to r

Th e s e s ys t em s e rv i c e s i n i t i a l l y e x ec u t e i n ke r ne l mod e .
A DJS TK
ADJW S L
AL LOC
ASC EFC
A S S IGN
B RDC S T
CANC E L
C ANE XH
CANT IM
CANWAK
C LR EF
C M KR N L
C NTREG

C R E LOG
C REMB X
C R E PRC
C RETVA
C RM PSC
DAC EFC
DA L LOC
DA S S GN
DC LAS T
DC LCMH
DC LEXH
DE L LOG

DE LM B X
DE L PRC
DE LTVA
DE R LM B
DGB LSC
DLC EFC
EXI T
E XPREG
F ORC E X
GETC HN
GETDEV
G E TJ P I

G E TPT I
H I B ER
LC KPAG
LKW S E T
MGB LSC
PURGW S
QIO
Q I OW
R EADEF
R E S UM E
R UN DWN
S C HDWK

S E TA S T
S ETEF
S E TE XV
S E T IM E
S E T IM R
S ETPFM
S ET PRA
S E T PR I
SETPR N
S ET PR T
S ETPR V
S E TRWM

S E TS FM
SETSWM
S NDE R R
S US PN D
TRNLOG
UL KPAG
ULW S E T
U PDS EC
WA ITFR
WAKE
WFLAND
WFLOR

Th e s e s ys t em s e rv i c e s i n i t i a l l y e x ec ute i n e x e c ut i v e mod e .
C M EXEC
G E TM SG

G E TT IM
I MGAC T

N UM T IM

SNDSMB

SNDACC

SNDO PR

Th e s e s ys t em s e r v i c e s e x ec u t e i n t h e a c c e s s mod e o f t h e c a l l e r .
A S C T IM
B I N T IM

E XCMSG
FAO

FAOL

IMGS TA

PUTM SG

UNW IN D

Th e se RM S s e rv i c e s b r a n c h to a s yn c h r o n i z a t i o n r o u t i n e
b e fo r e r e t u r n i ng t o the c a l l e r .
C LO S E
C ONN E C T
C R EATE
DE LETE
D I S C ONNE C T
D I S PLAY
ENTER
E RAS E

E XTEND
F IND
F LUS H
F REE
GET
M ODIFY
N XTVO L
O PEN

PAR S E
PUT
R EA D
R E LEASE
R EM OVE
R E NAM E
R EW IN D
S EARC H

S PAC E
TRUNC ATE
U PDA TE
WA IT
WRITE

Th e v e c to r s fo r t h e s e RM S s e rv i c e s c o nta i n RET i n st r uc t i o n s
r a the r tha n a b r a n c h t o a n RM S s yn c h r o n i za t i o n r o u t i n e .
RM SRUN DWN

S ETDDIR

S E TDF PR OT

3-3

S SVE XC

SYS TEM SERV I C E D I S PATC H ING
3.2

C HANGE MODE INSTRUC T I ON S

Wh e n a c h a ng e mode i n s t r uc t i o n i s e x e c u ted , a n e x c e p t i o n i s
g enera ted
th a t p u s h e s t h e PS L , t h e PC o f the n ex t i n s t r uc t i o n , a n d the c o d e th a t
i s the s i ng l e ope r a nd o f t h e c h a ng e m o d e i n s t r uc t i o n o n to
the
s tac k
( As a l r e a d y po i n t ed o u t i n the p r ev i o us
i nd i c a t ed i n the i n s t r uc t i o n .
c h a p t e r , t h e a c t u a l a c c e s s m o d e i s the m i n im um o f the
a c c e ss mode
i nd i c a t ed
b y t h e i n s t r uc t i o n a nd t h e c u r r e n t a c c e s s m o d e c o n t a i n ed i n
t h e PS L . ) Fo r e x ampl e , t h e e x ec u t i o n o f a
C HM E
#5
i n s t r uc t i o n wi l l
pu sh
a PS L , t h e PC o f t h e i n s t r uc t i o n f o l l o w i ng t h e C HM E i n s t r uc t i o n ,
a n d a 5 o n t o the ex e c u t i v e s t a c k .
Co n t r o l
is
t h e n pa s s e d
to
the
ex cept i o n
s e rv i c e r o u t i n e wh o s e ad d r e s s i s l o c a t e d in the a pp r o p r i a t e
e n t r y i n the s ys tem c o n t r o l b l o c k ( S C B )
•

3.2.1

C HM K , CHME

A t i n i t i a l i z a t i o n t i m e , VM S f i l l s i n th e SCB e n t r i e s fo r C HM K and CHME
w i t h the a d d r e s s e s o f c h a n g e mode d i spa t c h e r s th a t pa s s c o n t r o l to th e
p r o c ed u r e s t h a t pe r fo rm s e rv i c e - s p e c i f i c c o d e .
Th e a c t i o n o f
the s e
t wo d i s pa t c h e r s i s d i s c u s sed i n the n e x t s e c t i o n .

3. 2. 2

C HMS , C HM U

Th e S C B e n t r i e s f o r C HM S a nd C HMU a r e f i l l ed i n w i th the a d d r e s s e s o f
except i on
s e rv i c e
r o ut i ne s
t h a t u s u a l l y pa s s c o n t r o l to the g e n e r a l
e x c e p t i o n d i s pa tc h e r d e s c r i b ed i n t h e p r ev i o u s c h a p t e r .
I n th i s c a s e ,
a
C HM S o r
C HMU e x c e p t i o n wo u l d be r e po r ted to a p r o c e s s th r o ug h t h e
n o rm a l s i g na l a nd m e c h a n i s m a r r a y s .
Th e pa r t i c u l a r e x c e p t i o n . n ames
a r e S S $_CMODS U PR a nd S S $ _CMODUS ER r e spe c t i v e l y .
Howe v e r , a u s e r c a n sho r t c i r c u i t t h e n o rm a l e x c e p t i o n d i s pa t c h i ng
in
t h e c a se o f
e i th e r
o f t h e s e ex c e p t i o n s b y u s i ng the $ DC LCMH s y s t em
s e rv i c e
to
e s t a b l i sh
a
p e r - p r o c e s s c h a ng e -mo d e - to - s upe r v i so r
or
c h a ng e -m o d e - t o - u s e r
ex c e pt i o n h a nd l e r .
Th i s s e r v i c e f i l l s l o c a t i o n
C T L$G L CMSUPR o r C T L$G L C M U S E R i n t h e P l po i n t e r p a g e wi th the a d d r e s s
of
t he u s e r -wr i t t e n ch a ng e mod e d i s pa tch e r .
Th e e x c e p t i o n s e r v i c e
r o u t i n e s fo r the C HM S a nd C HMU e x c e p t i o n s c h e c k
these
l oc a t i ons
for
n o n z e r o c o n t e n t s a n d d i s pa t c h a c c o r d i ng l y .
Th e DC L a nd MCR c ommand l a ng u a g e
i n terpreters
use
th i s
service
to
c r e a te
a
s p e c i a l c h a ng e -mo d e- t o - s upe r v i s o r h a nd l e r .
Th i s h a nd l e r i s
u s e d wh e n i t i s n ec e s s a r y t o g e t to s upe r v i so r m o d e
f r om
use r mode
wh e n
an
imag e
is
i n t e r r up t e d w i th a
CTRL/Y .
Th e
use
of
the
c h a ng e-mo d e - t o - s upe r v i s o r h a nd l e r i s d i sc u s s ed in Ch a pt e r 2 0 .
Th e j o b
c o n t r o l l e r us e s a c h a ng e -mod e - t o - u s e r d i s p a tch e r f o r i t s p r o c e s s i ng o f
e r ro r messag e s .

3. 3

C HANGE MODE D I S PATCHING IN VMS

Th e c h a ng e m o d e d i spa t c h e r t h a t r ec e i v e s c o n t r o l f r om the C HMK o r CHM E
i n s t r uc t i o n
in
the
s ys tem
s e rv i c e v e c to r m u s t d i spa t c h
to
the
p r o c ed u r e i nd i c a t ed b y t h e c od e th a t i s f o und o n t h e t o p o f the s t a c k .
In
add i t ion ,
b e c a u s e t h e s e rv i c e r o u t i n e s a r e wr i t t e n a s p r o c ed u r e s ,
t h e d i spa t c h e r m u s t c o n s t r uc t a c a l l f r am e o n the s ta c k .
Th i s c o u l d
b e a c c ompl i shed
b y u s i ng a CALLx i n s t r uc t i o n a nd a d i spa t c h t ab l e o f
s e rv i c e e n t r y po i n t s .
3-4

SYSTEM SERV I C E D I S PATCHING
Howev e r , t h e c a l l f r am e th a t m u s t b e b u i l t
is
i d ent i c a l
fo r
each
se rv i c e .
In
add i t ion ,
the
r eg i s t e r s
th a t
the
s e r v i c e - spec i f i c
p r o c e d u r e w i l l m o d i fy h a v e a l r e a d y b e e n
s a v ed
b e c a use
the
r eg i s t e r
save mask
i n t h e v e c to r a r e a ( a t g l o b a l l o c a t i o n SYS $ s e r v i c e ) i s t h e
s a m e a s t h e r eg i s t e r
save ma s k
at
locat ion
EXE $ s e r v i c e .
So
the
d i spa tc h e r
avo ids
the
ove rhead
of
the g eneral
p u r po s e
CALLx
i n s t r uc t i o n a nd b u i l d s i t s c a l l f r am e b y h a nd .
Fu r th e r s pe ed i m p r o veme n t i s a c h i e v e d i n th i s c ommo n l y e x e c u t ed
code
pa th b y o v e r l a pp i ng memo r y wr i t e o pe r a t i o n s ( b u i l d i ng t h e c a l l f r ame )
wi th
r eg i s te r - t o - r eg i s t e r
o pe r a t i o n s
a nd
i n s t r uc t i o n
s t r e am
r e fe r e nc e s .
Th e a c t ua l d i s pa tch to t h e s e r v i c e - s p e c i f i c p r o c ed u r e i s
t h e n a c compl i s hed wi th a CAS EW i n s t r uc t i o n tha t u s e s t h e C HMx c o d e
as
i ts
i nd ex
i n to t h e c a s e t a b l e .
F i g u r e 3 - 2 p i c t ures the c o n t ro l f l ow
f r om t h e us e r p r og r am a l l t h e wa y t o t h e
s e rv i c e- s pec i f i c
p r o c ed u r e .
Th i s
f l ow
i s i l l u s t r a t e d f o r b o th k e r n e l a nd ex ec u t i v e a c c e s s m o d e s .
F i g u r e 3 - 3 s h ows t h e c o r r e s pond i ng f l o w f o r tho s e s e r v i c e s th a t d o n o t
c h a ng e mo d e .

3. 3. 1

Ope r a t i o n o f t h e C h a ng e Mo d e D i spa t c h e r

Th e ope r a t i o n o f the c h a ng e m o d e d i spa t c h e r s i s a l m o s t
i d en t i ca l
fo r
k e rne l
a nd e x e c u t i v e m o d e s .
Th i s s e c t i o n d i s c u s s e s t h e c ommo n po i n t s
o f the d i s pa tc h e r s f o r k e r n e l a nd e x e c u t i v e mo d e s .
Th e n e x t
sec t i o ns
po i n t
o ut
the
o n l y d i f f e r enc e s b e twe e n the d i spa t c h e r s f o r t h e t wo
a c c e s s mod e s .
F i g u r e 3 - 4 c o n t a i n s t h e c o d e fo r th e s e two d i s p a t c h e r s ,
c o p i ed
f r om t h e m o d u l e CMODS SDS P .
Th e i n s t r uc t i o n s a r e n o t l i s t ed i n
e x a c t l y t h e same o r d e r t h a t t h e y a ppe a r i n the so u r c e m o d u l e .
Ra t h e r ,
th e
i n s t r uc t i o n s
a r e s h o wn i n t h e o r d e r tha t t h e y a r e fo und wh e n a l l
th e PS E C Ts h a v e b e e n so r t e d o u t a t l i n k t i m e .
Fig ur e 3 - 5 conta i ns the
e r ro r
rout ines
tha t
are
b r a n c h ed
to
f r om
the chec ks mad e
in
Fig ure 3-4 .
Th e f i r s t i n s t r uc t i o n o f
t h e d i spa t c h e r
po ps
the
except i o n cod e ,
un i q ue
fo r
each
s e r v i c e , f r om t h e s t a c k i n to R O .
Th e c a l l f r am e i s
b u i l t o n t h e s t a c k by t h e f o l l o w i ng f o u r i n s t r uc t i o n s .
Ke r n e l Mo d e D i s p a t c h e r
P U S HAB
PUS H L
PUSHL
C LRQ

B A K S RVE X I T
FP
AP
- (SP)

E x e c u t i v e Mo d e D i s pa t c h e r
P U S HAB
P US HL
P US HL
C LRQ

B A S RVE X I T
FP
AP
- (SP)

Wh i l e t h e c a l l f r ame i s b e i ng b u i l t , t wo c h e c k s a r e pe r f o rmed
on the
a rg um e n t l i s t .
Th e n um b e r o f a r g um e n t s a c t ua l l y p a s s e d ( f o und i n t h e
f i r s t b y t e o f t h e a rg um e n t l i s t ) i s
c ompa red
to
a
s e r v i c e - s pec i f i c
ent r y
i n a p r e b u i l t t ab l e to d e t e rm i n e wh e th e r t h e r e q u i r e d n um b e r o f
a rg um e n t s f o r th i s se r v i c e h a v e b e e n pa s s ed .
Re a d a c c e s s i b i l i t y o f
t h e a rg um e n t l i s t i s c h e c k e d ( w i th t h e PROB ER i n s t r uc t i o n g e n e r a ted by
the I FNORD m a c ro ) .
If e i th e r o f t h e s e c h e c k s f a i l s , c o n t r o l i s p a s s e d
b a c k to t h e c a l l e r wi th a n e r r o r i nd i c a t i o n i n R O .
F i n a l l y , a CASEW i n s t r uc t i o n i s e x e c u t ed , us i ng t h e un i q ue c o d e i n
RO
as an
i nd ex
i n to t h e c a s e t a b l e .
Th e c a se t a b l e h a s b e e n s e t u p a t
a s s em b l y t i m e t o c o n t a i n the ad d r e s s e s o f
the
f i rst
i n s t r uc t i o n o f
each
s e rv i c e-spec i f i c
rout i ne .
B e c a u s e e a c h s e r v i c e i s wr i t t e n a s a
p r o c ed u r e wi th a g l o b a l e n t r y po i n t n am e d EXE $ s e rv i c e po i n t i ng
to
a
r eg i s t e r
save ma s k ,
the c ase
t a b l e c o n t a i n s a d d r e s s e s o f th e fo rm
E XE $ s e r v i c e + 2 .
Th i s i s i l l u s t r a t ed i n F i g u r e 3 - 4 .
If
contro l
is
p a ssed
to
the
e nd
of
the
c a s e t a b l e , t h e n a C HMx i n s t r uc t i o n wa s
e x e c u t ed wi th a n i m p r o pe r c o d e a nd e r r o r p r o c e s s i ng d e s c r i b ed
in
the
n e x t s e c t i o n i s pe r f o rmed .
3-5

PO
Space

User Program
C A L Lx
•
•

System Space

r:J

hange
Dispatcher

System
Service Vector
SYS$service ::

EXE$CMODx x x x : :

1) Build call frame
2) Check argument
list
CASEW
•
•
•

•

w
I

�

offsets
•
•
•

•
•

•

Service-Specific
Procedure

process ille� al
chan �e mo e
code

EXE$service : :
entry mask
•
•
•

(Jl
t<
til
�
twl
3:
til

twl

::a
<

H
n
twl

t::l

H
til

>
toi
n
=
H

2!
G'l

(K)SRVEXIT:
•
•
•

REI
I

Figure 3-2

C o n t r o l F l o w o f Sys tem Se r v i c e s Th a t Ch a ng e Mo d e

PO
Space

System Space

User Program
•

•

w
I

-..J

•

SY S$service ::

Service-Specific
Procedure

JMP -.

entry mask

•

RET

Figure 3-3

rn
rn
t<

�
tzl

entry mask
EXE$service : :

CALLx
•

System
Service Vector

Co n t r o l F l o w o f Sys t em Se r v i c e s Th a t Do No t Ch a ng e Mo d e

m
tzl

�H

n
tzl

H
m

>
�
n
0::
H
z
Cl

SYSTEM SERV I C E D I S PATCH ING

Th e s e r o ut i n e s a r e t h e c ha ng e mod e d i spa t c h e r s u s e d by VMS to
transfer
contr o l
to
s ys tem
s e rv i c e s o r RM S s e rv i c e s .
Th e two d i s pa t c h e r s a r e
n ea r l y i d en t i c a l .
Tho se
entr ies
c o n t a i n i ng
* * * * * * i nd i c a te pl a c e s
wh e r e
the
two
c h a ng e
mod e
d i spa t c h e r s
d i f fe r .
Comme n t s h a v e b e en
r em o v e d a n d i n s t r uc t i o n s a ppe a r i n the o rd e r tha t t h e y
a ppe a r
in
the
e x ec ut i v e
i m ag e ,
no t
n ec e s s a r i l y
in
the
o rd e r t h a t they a ppe a r i n
mod u l e CM ODS S DS P .

Ch a ng e Mo d e to Ex ec u t i v e D i s pa tche r

Ch a ng e Mo d e t o Ke r n e l D i s pa tc he r

E XE $CMODEXEC : :
P O PR
# "" M < R O >

E X E $CMODKRN L : :
POPL
RO
B E QL
ASTE X I T
B "" K S RVE X I T
P U S HAB
R O , R1
MOVZ B L
FP
PUS H L
MOVZ B L W"" B KRN LARG [R 1 ] , R1
AP
PUS H L
@ # 4 [ R 1 ] , FP
MOVA L
C LR Q
- (S P )
F P , ( AP ) , ACCVI O
I FNORD
p ro b e r
# O , fp , ( ap )
beql
accv io
MOVL
S P , FP
CM PB
( AP ) , R1
K INSARG
B LS S U
K ERDS P :
S C H $G L C UR PC B , R 4
MOVL
R 0 , # 1 , tKCASMAX
CAS EW

******

P U S HAB
MOVZ B L
PUS HL
MOVZ B L
PUS HL
MOVAL
C LR Q
I F NORD

MOVL
CM PB
B LS S U
E XEDS P :

******

CAS EW

B "" SRVE X I T
RO, R1
FP
W "" B E XE C NARG [ R 1 ] , R 1
AP
@ # 4 [R 1 ] , FP
- (SP)
F P , ( AP ) , E XAC CVI O
prober
# O , fp , ( ap)
beql
exaccv io
S P , FP
( AP ) , R 1
E X I NSARG

R O , # O , S ""' ECASMAX

EXE $ s e r v i c e + 2

o f f s e t to E XE S s e rv i c e + 2

o f f s e t to

******

JSB

@ CT L $ G L_RM SBASE

B SBW
M OVL
B EQL
JSB
M OVL
B E QL
JSB
B RW

C HEC KARGL I S T
@ # C T L $G L_US RC HM E , R 1
10$
(R1)
L "" EXE $G L_U S RC HM E , Rl
20$
(R1)
I L LS ER

I L LC HM K :
B S BW
MOVL
B E QL
JSB
10$:
M OVL
B EQL
JSB
2 0$ :
NOP
NOP
I L LS ER :
MOVZW L
RET

C HE C KARG L I S T
@ # C T L $G L U S RC HM K , R 1
10$
(R1 )
L "" EXE $G L U S RC HM K , R 1
20$
(R1 )

1 0$:

20$:

# S S $_I L LS ER , R O

Figure 3-4

C o n t e n t s o f t h e VM S Ch a ng e Mo d e D i s pa tc h e r s

3-8

SYSTEM SERV I C E D I S PATCH ING

The se rout i nes a r e i nvoked i f t he arg ument l i st ' i s i nacc es s i b l e o r
i f a n i n suff i c i e n t number o f a rg uments was passed to the serv i c e .
EXACCVIO :
BRW

ACCVIO

EXINSARG :
CMPW

R O , fRCASCTR

BGE QU
BRW

; Fr om EXE $CMODEXEC

; On l y r e po r t INSARG f o r RMS a nd
, and bui l t i n func tions
; Other wi se , g et back in l in e
; Re po r t e r ro r to c al l er

E XEDS P
INSARG

CHECKARGL I S T :
I FNORD
MOVZ BL
ASHL
I FNORD
RSB

t 4 , ( AP) , ACCVIO RET
( AP ) , Rl
f 4 , Rl , Rl
R l , 4 (AP) , ACCVI O_RET

ACCVI O :

MOVL
ACCVI O RET:
MOVZWL
RET
KINSARG :

INSARG :

; Check a rg ument l i st fo r
, r ead access ib i l i ty
; Fi r s t chec k coun t
; Then g et count
; Co nv e r t to b yte coun t
; Now check r e st o f l i st

; Se t FP so tha t RET wo rks

S P , FP
ISS $_ACCVI O , RO

CMPW
BGE QU

R O , #KCASCTR
KERDS P

MOVZWL
RET

#SS $_INSFARG , RO

; I s t h i s a r ecog n i zed cod e?
; No . Get bac k in l in e

Th i s r o ut i ne i s t h e common ex i t pa th fo r al l system s e rv i c e and
RMS s e r v i c e c al l s .
The usua l ex i t pa th is the RE I i ns t r uc ti o n .
The al te rnate ex i t pa th i s to repo rt a SS $SSFAIL except i on .
SRVEXIT :
SRVRE I :
SSFA I L :

BLBC

R O , SSFA I L

REI
BITL
BEQL

#7 , RO
SRVRE I

BRW

SSFA I LMAIN

; Check fo r mere wa rn i ng
; I f so , d o no t g en e r a te
, except io n
; Go t o SSFAI L l og i c

RO , l O $

; Ke rn e l mod e ex i t pa th
; Br anch i f abno rmal compl e t i o n

KSRVE XI T :
B LBC
REI
S E T I PL
10$ :
BRB

; Do no t use e l eva ted I PL o n
; e r r o r path .
; check fo r SSFA I L except i on

SSFA I L

SSFAILMAIN :
MOVL
TS'IW
BNEQ
E XTZV
ADDL

10$:
20$:

SCH$G L CURPCB , Rl
PCB $W MTXCNT
; Check fo r own e r sh i p o f a m utex
; I f so , BUGCHECK
20$
#PS L$V-C URMOD , #PSL$8 C URMOD, 4 (S P ) , - (S P )
#PCB$V-S SFEXC , ( S P) ; Ar e sys tem s e rv i c e
; fa i l ur e except i ons enabl ed
, fo r c a l l e r ' s access mod e
( S P+) , PCB$L-STS ( R l ) , 1 0 $ ; If not , d i sm i ss the
BBC
, except ion
; I f so , pass control to the
EXE $SSFAIL
BRW
, g en e r a l ex cept i o n d i spa tcher
; Re tu r n f rom se rv i c e wi th
REI
, e r r o r sta t us
M TXCNTNONZ , FATAL
B UG CHECK

Figure 3-5
E r r o r Ro u t i n e s a nd Commo n Ex i t P a t h
f o r Sy s t em Se r v i c e s a nd R M S Ca l l s

3-9

SYS TEM S E RVI C E D I S PATCH ING
3.3.2

C h a ng e -Mo d e - to -Ke r ne l D i spa tch e r

Th e r e a r e two s t e p s pe r fo rm ed by t h e c h a ng e -mo d e - to- k e r n e l
d i spa t c h e r
a r e n o t pe r fo rm ed
by t h e c h a ng e -m o d e - t o - e x e c u t i v e d i s pa tch e r .
th a t
B e f o r e c o n t r o l i s p a s s e d to tho s e
s e rv i c e s
tha t execute
in
kernel
mod e ,
t h e a d d r e s s o f t h e PC B f o r t h e c u r r e n t p r o c e s s ( f o und a t g l o b a l
l o c a t i o n S C H $G L C UR PC B ) i s p l a c ed i n to R 4 .
Th e s ec o nd d i f f e r en c e
is
t h a t C HMK # 0 i s a s p e c i a l e n t r y p a th i n to k e r n e l m o d e th a t i s used b y
t h e A S T d e l i v e r y r o u t i n e fo l l o w i ng t h e c a l l to the AST p r o c ed u r e .
If
t h e C HM K c o d e r em o v e d f r om t h e s t a c k i s a z e r o , c o n t r o l i s p a s s e d to a
r o u t i n e c a l l ed ASTEX I T .
Th e a c t i o n o f th i s r o u t i n e
i s d e sc r i b ed
in
Ch a pt e r 5 .

3. 3.3

Ch a ng e-Mo d e - t o -E x e c u t i ve D i s p a tch e r

Th e c h a ng e -m o d e - t o - e x ec u t i v e d i spa tc h e r pe r fo rms o n e s t e p un i que
to
execut i v e mode .
If t h e C HM E code i s not a r ec og n i z ed sys t em s e r v i c e ,
t h e CAS EW i n s t r uc t i o n pa s se s c o n t r o l to t h e e nd o f t h e c a s e t a b l e .
At
tha t
po i n t , t h e c h a ng e -m o d e - t o - e x ec u t i v e d i spa tch e r t r a n s f e r s c o n t r o l
to t h e RM S d i s pa tc h e r to d e t e rm i n e wh e th e r th i s wa s a v a l i d
RM S c a l l
b e f o r e d r o p p i ng i n to t h e e r r o r p r o c e s s i ng d e sc r i b ed b e l o w .

3. 3 . 4

RMS D i s p a tc h i ng

Th e
RM S d i s p a t c h e r ,
i l l u s t r a t ed
i n Figure 3-6 ,
cons i sts o f
two
i n s t r uc t i o n s .
Th e
CAS EW
i n s t r uc t i o n
wi l l
d i spa t c h
to
RM S
s e r v i c e- s pe c i f i c p r o ced u r e s f o r l eg i t i m a t e RM S s e rv i c e c o d e s .
Th e s e
p r o c ed u r e s wi l l
e x i t w i th a RET b a c k t o S RVE X I T .
I f a n i l l eg a l c o d e
wa s
i s s u ed ,
( th a t i s , a c o d e n o t r e c o g n i z e d a s a n RM S s e r v i c e c a l l )
the
RSB i n s t r uc t i o n f o l l o w i ng the CAS EW i n s t r uc t i o n w i l l pa s s c o n t r o l
b a c k to EXE $ CMODEXEC f o r n o rm a l e r r o r p r o c e s s i ng .

3. 3.5

Re t u r n P a t h f o r Sys t em S e r v i c e s

Wh e n t h e s e rv i c e- s p e c i f i c p r o c ed u r e h a s c ompl e t ed
i t s o pe r a t i o n ,
it
pl a c e s
a
s t a t us
code
i n RO
and
i s s u e s a RET i n s t r uc t i o n .
Th i s
i n s t r uc t i o n r e t u r n s c o n t r o l
to
the code a t
l ab e l
( K ) S RVE X I T i n
F i g u r e 3 - 5 b e c a us e th i s a d d r e s s wa s p u t i n to the s a v ed PC a r e a o f t h e
c al l
f r am e b u i l t b y t h e c h a ng e m o d e d i s pa tc h e r .
Th e
rout ine
( K ) S RVE X I T f i r s t c h e c k s wh e t h e r
a n e r ro r
o c c u r r ed .
I f no e r ro r
o c c u r red o r i f t h e e r r o r wa s m e r e l y a wa r n i ng
( R 0 < 2 : 0 >= 0 ) ,
t h e CHMx
except ion
is d i sm i s sed w i th an RE I i n s t r uc t i o n th a t pa s s e s c o n t r o l to
the
i n s t r uc t i o n
f o l l o w i ng
the
C HMx
in
the v e c to r
a rea .
Th i s
i n s t r uc t i o n i s a RET wh i c h f i n a l l y r e t u r n s c o n t r o l t o the us e r prog ram
f o l l o w i ng t h e c a l l t o S YS $ s e r v i c e ( F i g u r e 3 - 1 ) .
On e a d d i t i o n a l s t e p i s t a k e n by r o u t i n e KSRVE X I T , t h e e x i t r o u t i n e fo r
s e rv i c e s
that
exec ute
i n k e r n e l mod e .
I PL i s e x p l i c i t l y l o we r ed to
zero .
Th i s s t e p i s unnec e s s a r y un l e s s t h e p r o c e s s h a s e n a b l ed
sys tem
s e rv i c e
f a i l u r e e x c ept i o n s b e c a u s e t h e RE I i n s t r uc t i o n th a t d i sm i s s e s
t h e C HMK e x c e p t i o n w i l l l o we r
I PL .
Howe v e r ,
if
a
sys t em s e r v i c e
fa i l ur e
e x c ep t i o n
is
t o b e g e n e r a ted ,
t h e e x c e p t i o n c o d e m us t b e
e n t e r ed w i th I P L s e t t o z e r o .
( A s im i l a r check
i s n o t n e e d ed
fo r
e x e c u t i v e mod e
s e r v i c e s b e c a u s e o n l y k e r n e l mod e c od e c a n e x e c u t e a t
e l ev a t ed I P L . )
3-1 0

PO
Space

Change
Mode Dispatcher
RMS Service Vector I
User Program

I-'

•
•
•
CA x
•

•

System Space

I EXE$CMODEXEC::

1 ) Build Call Frame
2) Check Argument
List

SYS$service::
e n t ry m a s k

CASEW
•
•
•

C H M E •code

RMS Dispatcher
RMSSDISPATCH:

/' :

cA Ew
•
offsets
•
•
•
RSB

offsets
•

•
•
JSB
RMS Service-Specific
Procedure

I
I

RMS$servlce: :

I I

Ro u t i n e
Common Exit Path

R MSCHK_STALL:
....
•
•
•
RET

SRVEXIT:
•

Figure 3-6

•
•
REI

Co n t r o l F l o w o f RM S D i s pa t c h i ng

entry mask
•
•
•
RET

00
00
1-'3
tzl
3:
00
tzl
::c
<
1-4
(')
tzl
t:1
1-4
00
1-(

>
t-3

(')
::c
1-4

2!
G)

S Y S TEM S E RV I C E D I S PATCH ING
I f an e r r o r o r s ev e r e e r r o r o c c u r r e d , a c h e c k i s mad e to
s e e wh e th e r
the
proc ess
own s
a ny m u t ex .
I f so , a f a t a l b ug c h e c k i s g e n e r a t ed .
( Ch a p t e r 7 d e s c r i b e s b ug c h e c k p r o c e s s i ng .
M u t e x e s a r e d e s c r i b ed
in
Ch a p t e r 2 4 . ) I f t h e m u t e x c h e c k s uc c e e d s , a c h e c k i s mad e to d e t e rm i n e
wh e th e r t h i s p r o c e s s h a s e n a b l e d s y s t em
s e r v i c e ex c e p t i o n s
fo r
the
c a l l i ng
a c c e s s mo d e .
I f i t h a s , c o n t r o l i s p a s s e d t o the e x c e p t i o n
d i spa tc h e r a t g l o b a l l a b e l EXE $ S S FA I L .
Th e
ex cept ion
tha t wi l l
be
r e po r t ed
t o the c a l l e r i n the s i g n a l a r r a y i s S S $ S S FA I L .
Oth e r w i s e ,
c o n t r o l i s pa s s ed b a c k to the c a l l e r
wi th R O
cont a i n i ng
the
error
s t a t us c o d e .

3. 3.6

Re t u r n Pa t h f o r RMS S e r v i c e s

Th e r e t u r n pa th fo r RMS s e r v i c e s i s s l i g h t l y mo r e c ompl i c a t ed t h a n t h e
r e t u r n pa th
fo r
s ys t em
s e rv i c e s .
Th e l a s t two b y t e s o f t h e v e c to r
c o n t a i n a b r a nch ( B RB ) to a n RM S s yn c h r o n i z a t i o n r o u t i n e ( c o n t a i n e d i n
mod ul e CMODS S DS P ) .
Th i s
r o u t i n e f i r s t c h e c k s wh e th e r the c a l l e r o f
the RMS s e rv i c e wi sh e s t o wa i t .
Th i s i s t h e u s ua l c a s e b u t RM S d o e s
( Th e r e t u r n s t a t u s c o d e i s s e t t o
a l l o w a s yn c h r o n o u s I /O o p e r a t i o ns .
RM S $ S TA L L by RM S i n the u s ua l s t a t e ,
wh e r e
the
p r o c e s s m u s t wa i t
un t il t h e RMS o pe r a t i o n h a s c ompl e t ed . )

3 . 3 . 6 . 1 Wa i t S t a te As s o c i a t ed wi t h RMS Reque s t s
If
a
sta l l
is
i nd i c a t ed ,
the c a l l e r
i s p u t i n t o a n ev e n t f l ag wa i t s t a t e , wa i t i ng
f o r the e v e n t f l ag a s so c i a t ed w i th t h e I /0 r e que s t t h a t RMS h a s
j us t
i s s ued .
Th e
c r uc i a l po i n t i n th i s i mpl em e n t a t i o n i s th a t the c a l l e r
i s wa i t i ng a t the a c c e s s m o d e a s so c i a t ed wi t h t h e o r i g i n a l c a l l to RMS
and
no t
in e x e c u t i v e a c c e s s m o d e , t h us a l l o w i ng AST d e l i v e r y f o r a l l
a c c e s s m o d e s a t l e a s t a s p r i v i l eg e d a s t h e c a l l e r
o f RM S .
( In
the
u s ua l
case
wh e r e RM S i s c a l l e d f r om us e r m o d e , th i s a l l o ws bo th us e r
a nd s upe r v i s o r ASTs a s we l l
as
e x ec ut i ve
a nd
ke rnel
ASTs
t o be
d e l i v e r ed wh i l e wa i t i ng fo r t h e RM S o pe r a t i o n to c ompl e t e . )
-

Wh e n th e o r i g i n a l
I /0 c ompl e t e s ,
RM S g a i n s c o n t r o l
f i rst i n an
e x e c u t i v e m o d e A S T t h a t i t a s s o c i a t ed w i th i t s $ Q I O r e q u e s t .
If it
d e t e rm i n e s t h a t the o r i g i n a l r e qu e s t i s c om p l e t e , i t s e t s f i n a l s t a t us
in
the d a t a s t r uc t ur e ( FAB o r RAB ) a s s o c i a t ed wi th the o pe r a t i o n a nd
r e t u r n s f r om i t s AST .
Th e c a l l e r n o w d r ops
t h r o ug h
the
even t
f l ag
wa i t
in
the
s yn c h r o n i z a t i o n
rout ine
( because
the
I /0 c ompl e t i o n
r o u t i n e s e t t h e e v e n t f l ag ) .
Th e s ynch r o n i z a t i o n
r o u t i n e d e t e rm i n e s
tha t
the
RM S o pe r a t i o n
is
c ompl e t e ( b e c a u s e t h e FAB o r RAB s t a t us
f i e l d c o n t a i n s n o n z e r o ) , a n d e x e c u t e s a R E T , p a s s i ng c o n t r o l
back
to
the po i n t wh e r e t h e i n i t i a l c a l l to R M S wa s i s s ued .
I f the RM S e x e c u t i v e mo d e AST d e t e rm i n e s t h a t m o r e I /0 i s r e q u i r e d
to
c ompl e t e
the o r i g i na l
r e que s t
( s uch as o c c u r s wh e n r e a d i ng a l a rg e
r e c o rd f r om a s e q ue n t i a l f i l e w i th
sm a l l
i n te r nal
buf f e r s o r
wh e n
o pe r a t i ng
o n a n ! S AM f i l e ) , RM S i s s ue s t h e n e x t $ Q I O a nd r e t u r n s f r om
i t s AS T .
B e c a u s e the p r ev i o us I /0 c o mpl e t i o n s e t th e a s s o c i a t ed e v e n t
f l ag ,
the process
i s n o w c ompu t a b l e .
Ho we v e r , t h e RM S o pe r a t i o n i s
n o t ye t c ompl e t e .
Fo r th i s r e a so n , t h e RMS s yn c h r o n i z a t i o n
r o ut i ne
( ex e c u t i ng i n the c a l l e r ' s a c c e s s m o d e ) c h e c k s t h e s t a t u s f i e l d i n t h e
RAB o r F A B f o r z e r o , i nd i c a t i ng th a t RM S h a s m o r e
to d o .
In
th i s
c a se ,
the c al l e r
is
ag a i n
pl a c ed
i n to
the
L E F s t a t e b y t h e RM S
s yn c h r o n i z a t i o n r o u t i n e .
I n o th e r wo r d s , a t a
pr i m i t i v e
l ev e l ,
the
Howe v e r ,
p r o c e s s i s p l a c ed i n to a L E F s t a t e by RMS o n e o r mo r e t i m e s .
t h e a c t ua l i nd i c a t i o n t h a t the RMS o pe r a t i o n h a s c ompl e t ed i s n o n z e r o
c o n t e n t s i n t h e s t a t u s f i e l d o f t h e FAB o r RAB .
3-1 2

SYSTEM S ERVI C E D I S PATC H ING
3. 3. 6.2
RMS E r r o r De t e c t i o n - Wh e n th e
RM S s yn c h r o n i z a t i o n
rout i ne
f i na l l y d e c i d e s
t h a t RM S h a s c om p l e t ed i t s wo r k , i t c h e c k s t h e f i na l
status .
I f th i s s t a t u s i nd i c a t e s e i th e r s uc c e s s o r wa r n i ng , a RET
is
e x e c uted .
If
e i th e r
a n e r r o r o r a s ev e r e e r r o r o c c u r r e d , a s p e c i a l
RM S c a l l { $ S SVE XC ) i s i s s ued .
Th i s s e rv i c e s i m p l y r e po r t s
the
e r ro r
s t a t us
t h r o ug h
t h e no r m a l VM S
s e rv i c e ex i t p a th
{ S RVE X I T ) th a t
d e te rm i n e s wh e th e r t h e p r o c e s s h a s
e nab led
s ys t em
s e rv i c e
fa i l ure
e x c e pt i o n s .
B e c a us e
RM S e r r o r s
are
r e po r t ed
th r o ug h t h e s ys t em
s e rv i c e d i s pa t c h e r , t h e y a r e t r e a t ed i n e x a c t l y t h e
s ame m a nne r
as
s ys t em s e rv i c e e r r o r s .

3. 4

U S ER-WR I TTEN SYS TEM S E RV I C E D I S PATC H I NG

Th e VAX a r c h i t e c t u r e r e s e r v e s C HMx i n s t r uc t i o n s
w i th n eg a t i v e
codes
f o r c u s tome r u s e .
VM S s ys t em s e rv i c e d i spa tch i ng a c k n o wl ed g e s th i s i n
i t s d i s pa t c h s c h em e a nd c o n t a i n s h o o k s th a t a l l o w a p r i v i l eg ed us e r to
wr i t e h i s o wn s ys tem s e rv i c e s .
Th e m e thod f o r d o i ng th i s i s d e s c r i b ed
i n the VAX/VM S Re a l -T i m e Us e r ' s G u i d e .
Th i s s e c t i o n me r e l y d e s c r i b e s
h o w c o n t r o l i s pa s s ed t o us e r -w r i t t e n s y s t em s e rv i c e s .
F i g u r e 3 - 4 i l l us t r a t e s t h e e r r o r p r o c e s s i ng c o d e th a t f o l l o ws the c a s e
table
fo r
t h e c h a ng e -mod e - t o - k e r n e l
o r c h a ng e-mo d e- t o - e x e c u t i v e
d i s pa t c h e r .
Th e o n l y d i f fe r e n c e s b e twe en these two r o u t i n e s
a re
the
n am e s o f the g l o b a l po i n t e r s th a t a r e r e f e r e nced .

3. 4 . 1

Per- P r o c e s s U s e r -W r i t t e n D i s p a t c h e r

I f c o n t r o l i s pa s s ed t o t h e e nd o f the c a s e t a b l e , th i s i nd i c a t e s th a t
a
C HMK o r
C HM E
i n s t r uc t i o n wa s e x e c u t ed wi th a n i nv a l i d c o d e .
VM S
a t t emp t s to pa s s c o n t r o l to a
u s e r -wr i t ten ch ang e mod e d i s pa t c h e r .
Fi r st ,
a
location
i n P l s p a c e { C T L $G L U S RC HMK o r C T L $ G L U S RC HM E ) i s
c h e c k e d t o s e e wh e th e r
a
p e r - p r o c e s s -d i s pa t c h e r
ex i s ts .
No n z e r o
c o n tents o f
th i s
l oca t i on
a re
i n t e r p r e t ed
as
the
add r ess o f a
u s e r -w r i t ten d i spa tc h e r a nd c o n t r o l i s p a s sed to i t w i th the s t a c k
as
s h o wn
in
Figure 3-7 .
Th e a s s um p t i o n b e i ng m a d e b y VM S a t th i s po i n t
t r an s f e r
i s th a t a v a l i d c h a ng e m o d e c o d e w i l l r e s u l t i n t h e ev e n t u a l
of
control
t o { K ) S RVE X I T w i th a R E T i n s t r uc t i o n .
I f t h e pe r - p r o c e s s
d i s pa t c h e r r e j e c t s t h e c o d e , i t r e t u r n s c o n t r o l t o the c o d e l i s t ed
in
F i g u r e 3 - 4 w i t h a n RSB i n s t r uc t i o n .

3. 4. 2

P r i v i l eg ed Sh a r e a b l e Imag e s

Th e us u a l c o n t e n t s o f CT L $G L U S RC HMK a nd CTL$G L U S RC HM E a r e
add resses
w i t h i n t h e t wo
pag e s
i n P l s p a c e s e t a s i d e by VM S f o r u s e r -wr i t t e n
s y s tem s e rv i c e s a nd imag e - s p e c i f i c m e s s a g e pr o c e s s i ng .
Ke r n e l
mo d e
a nd
e x ec u t i ve mode
each have
o ne h a l f pag e { 2 5 6 byt e s ) d ev o t ed t o
s ys t em s e rv i c e d i spa tch i ng .
Th e i n i t i a l c o n t e n t o f t h e f i r s t b y t e o f
e a c h d i s pa t c h a r e a { s e t up b y PR OC STRT ) i s a n R S B i n s t r uc t i o n .
W i th
the d i s p a tch s c h em e d e s c r i b ed
in
the
p r ev i o u s
sec t i on ,
there
is
e f fe c t i v e l y n o pe r - p r o c e s s c h a ng e m o d e d i s pa tch i ng .

3-1 3

SYSTEM S E RVI C E DISPATCH ING

Direction of
stack growth
r e t u r n PC in CMODSSDSP

.-sP

0 ( c o n d i t i o n h a n d l e r a d d r es s )
0 ( PSW / re g i s t e r s a v e m a s k )
s a v e d AP
s a v ed FP

(K)SRVEXIT (return PC)
PC following CHMx instruction
PSL following CHMx instruction
Figure 3-7

S t a t e o f t h e S t a c k Wi t h i n a U s e r -Wr i t t e n D i s pa tc h e r

Howe v e r , i f a n imag e
executes
th a t wa s p r ev i o u s l y
l i n k e d wi th a
p r i v i l eg ed
shareab l e
i m ag e
( l i n k e d wi th t h e / PROTECT a n d / S HAREABLE
o p t i o n s a n d i n s t a l l ed w i th t h e / PROTECTED a nd / S HARED o p t i o n s ) ,
the
i m ag e
a c t i v a to r
r e pl a c e s
the
RSB
i n s t r uc t i o n wi t h a
J S B to the
u s e r -w r i t t e n c h a ng e mode
d i spa tc h e r
s pe c i f i ed
as
a
p a r t of
the
p r i v i l eg ed
sha reable
i m ag e
( Figure 3-8 ) .
VM S a l l o ws m u l t i pl e
p r i v i l eg ed s h a r e a b l e i m ag e s to b e
l i n ked
i n to
the
same
exec utab l e
i m ag e .
( Th e r e i s a l i m i t o f 4 2 u s e r -wr i t t e n d i sp a tc h e r s o f e a c h t ype .
Ho w t h e s e d i spa tc h e r s a r e c o l l e c t ed i n to pr i v i l eg ed
shareable
i m ag e s
d e te rm i n e s
t h e n umb e r
of
p r i v i l eg ed
shareab l e
i m ag e s th a t c a n b e
i nc l ud ed i n a s i ng l e e x e c u t a b l e i m ag e . ) A n RSB i n s t r uc t i o n fo l l o ws t h e
l ast JSB
i n s t r uc t i o n
i n the d i s pa t c h a r e a .
Th e e x ampl e p i c t u r ed i n
F i g u r e 3 - 8 s h ows t h r e e p r i v i l eg e d sh a r e a bl e i m ag e s .
Wh e n
the
i m a g e a c t i v a to r
( Ch a p t e r 1 8 )
e n c o u n te r s
a
pr i v i l eg ed
s h a r e a b l e i m ag e a s a pa r t o f t h e e x e c u t ab l e imag e i t i s a c t i v a t i ng , i t
m a ps the s e c t i o n ( s ) c o n t a i n i ng t h e u s e r -wr i t t e n s ys tem s e r v i c e s i n the
u s ua l
manne r .
Ho we v e r , i t a l s o u s e s i n f o rm a t i o n s to r ed i n th e f i r s t
e i g h t l o ng wo r d s o f t h e i m a g e ( a pr i v i l eg ed l i b r a r y v e c to r p i c t u r ed
in
Figure 3-9 )
t o m o d i f y t h e P l s p a c e d i spa t c h a r e a .
Fo r e x amp l e , i f a
p r i v i l eg ed
sha reable
i m ag e
c o n t a i n ed
a
c h a ng e -mo d e - to- k e r n e l
d i spa tch e r ,
the
i m ag e a c t i v a to r wo u l d i n se r t a J S B i n s t r uc t i o n i n P l
s p a c e th a t t r a n s f e r r ed c o n t r o l t o
t h e d i spa tc h e r
s p e c i f i ed
by t h e
P LV$ L_K E RN E L l o ngwo r d i n the pr i v i l eg ed l i b r a r y v e c to r .

3-1 4

PO
Space

I IIIIo.
I

U s e r P ro g r a m
•

•

__...

C A LLx
•

Jill""

•

�

��

w
I
I-'
U1

I•

Dispatcher A

RSB -@

�

Dispatcher 8

I
I

��

. ENTRY

�

�--------•

- - - - - -

...(b

� I
....
""'111"

Figure 3-8

This Vector i s built
by the I mage
Activator
(CTL$A_DISPVEC)

I
I
I
I

__...
....

en
�
en
t-3
tz::l
3

E X E $ C M O Dx x x x : :
1 ) Build c a l l f rame
2) Check a r g u m e n t
list
CA SEW
•
•
•

en
tz::l

�
1-1

n
tz::l

offsets
•
•
•

SB
-®- •Jpro
cess illegal

1-1

c h a n g e mode c o d e s

Change Mode
Dispatcher

�----------------

� C H Mx 1
RET
� cA-se- :.(5)----. ENTRY
: ®
a t us
RO 4:
RET

....

Sp
- ace
@J S 8 A
�JS8 8
JS8 C
RS8

S y s t e m S p a ce

��

��
Common E x it P a t h

----..
....

(K)SRVEXIT :

D i spa tc h i ng to U s e r-Wr i t t e n Sys tem Se r v i c e s

•

·®
•

REI

�t-3

n
=
1-1

z
Cl

SYS TEM S ERVI C E D I S PATCH ING

{

l
/" ..J'

.ENTRY
CHMX
RET

#CO

1 E n t r y V e c tors
/" o/

( 1 p e r s e rv ic e )

V e c t o r Type
System Version
-

Kernel Dispatcher

Privileged
Library V e c t o r
( 1 per image )

E x e c u t i v e D i s p a t ch e r

A d d ress Check
"'
,

CASE RO,
RSB
CASE RO,
RSB

""
,

ENTRY
•

��

Executive Dispatc her

••.

Kernel Disp atcher

mask

•

Functional Routines

•

MOVZWL
RET
F i g u r e 3-9

.•.

# status,

� � ( 1 per serv i c e )

S t r uc t u r e of P r i v i l eg ed Sha r e a b l e Imag e

O n c e the i m ag e c o n t a i n i ng u s e r-wr i t t e n s ys t em s e rv i c e s
is
a c t i v a t ed ,
e x ec u t i o n p r o c e e d s
no rm a l l y un t i l
o n e o f t h e s e r v i c e s i s i n v o k ed .
D i s p a tc h i ng p r o c e ed s a s f o l l o ws ( F i g u r e 3 - 8 ) .
(l)

A CALLx i n s t r uc t i o n t r a n s f e r s c o n t r o l to
a
se rv i c e- spec i f i c
entry mask i n PO space .
Th e C HMx ( C HM K o r C HM E ) i n s t r uc t i o n
l o c a t ed t h e r e
t r an s f e r s
control
t o t h e VM S c h a ng e m o d e
d i spa t c h e r .

(2)

E x e c u t i o n p r o c e ed s a s i f a VM S s e rv i c e wa s
i nvo k e d
e x c e pt
that the
c h a ng e m o d e c o d e
is
not
r e c og n i zed by t h e VM S
d i spa tc h e r a nd c o n t r o l pa s s e s to t h e end o f
the c a se
tab l e
( Fi g u r e 3 - 4 ) .

(3)

Th e J S B i n s t r uc t i o n i n CMODS S DS P p a s s e s c o n t r o l
to
the
Pl
s pa c e d i s p a t c h a r e a
wh e r e
a no th e r J S B i n s t r uc t i o n pa s s e s
c o n t r o l t o t h e f i r s t d i s pa tc h e r .

(4)

Th e cha ng e m o d e c o d e i s r e j e c t ed by t h e f i r s t d i spa tc h e r
by
s i mp l y e x e c u t i ng
an RSB b a c k t o the Pl s p a c e v e c t o r wh e r e a
s e c o nd J S B i s e x e c u t ed .

3-1 6

SYSTEM S E RVI C E D I S PATCH ING
(5)

Th e s e c o nd d i s pa tch e r r ec o g n i z e s
t h e c h a ng e m o d e c od e a s
v a l i d a n d d i spa t c h e s ( p r o b a b l y w i th a CAS Ex i n s t r uc t i o n ) t o a
s e r v i c e - s pec i f i c p r o c ed u r e
that
i s a l so
a
pa r t o f
the
p r i v i l eg ed sh a r e a b l e i m ag e .

(6)

Wh e n the s e r v i c e c ompl e t e s ( s u c c e s s f u l l y o r
un s uc c e s s f u l l y ) ,
it
l o ad s
a
f i n a l s t a t u s i n to R O a nd ex i t s wi t h a RET wh i c h
p a s s e s c o n t r o l to ( K ) S RVE X I T .
At
th i s
po i n t ,
u s e r -w r i t t e n
s y s t em s e r v i c e d i spa tch i ng m e r g e s w i th VM S s ys t em s e r v i c e
d i s p a tch i ng .

I f e a c h d i spa tc h e r r e j e c t e d t h e ch a ng e m o d e c o d e
( by e x e c u t i ng
an
RSB ) ,
control
wo u l d
e v e n t ua l l y
r e a c h the R S B i n s t r uc t i o n i n t h e P l
s p a c e v e c to r .
Th i s R S B i n s t r uc t i o n pa s s e s c o n t r o l
back
to
the
VMS
c h a ng e m o d e d i s pa tc h e r i n CMODS SDS P wh e r e a sys t em w i d e d i s p a t c h e r i s
c h e c k e d fo r n e x t .

3.4.3

Sys t em -Wi d e Us e r -Wr i t t e n D i s pa tc h e r

I f t h e P l s pa c e
l ocat ion conta ins
a
ze ro ,
or
if
no
pe r - p r o c e s s
d i s pa t c h e r s
a re
i nv o k e d ,
or
if
the
l a s t pe r - p r o c e s s u s e r -wr i t t e n
d i spa tc he r r e t u r n s to t h e r o u t i n e i n CMODS SDS P w i th a n RSB , a l o c a t i o n
in
s ys tem s p a c e ( E XE $G L U S RC HMK o r E XE $G L U S RC HM E ) i s c h e c k ed f o r th e
e x i s t e nc e o f a s y s t em-w i de u s e r -wr i t ten d i spa tc h e r .
If
none ex i s ts
( contents a r e
ze ro ,
i t s u s u a l c o n ten t s i n a VM S s ys t em ) , o r i f th i s
d i spa tc h e r pa s s e s c o n t r o l b a c k w i th a n R S B , a n i l l eg a l s y s t em
se rv i c e
cal l
( S S $ I L LS E R )
is
r e po r ted
b a c k t o the u s e r i n R O .
Th i s s c heme
a s s um e s that u s e r -wr i t t e n s ys t em s e r v i c e s tha t c om p l e t e
success f u l l y
w i l l e x i t wi t h a R E T b a c k t o ( K ) S RVE X I T , wh e r e a n RE I i n s t r uc t i o n w i l l
d i sm i s s the C HMK o r CHM E e x c e p t i o n .

3. 5

R E LATED SYSTEM S ERVI C ES

T h e r e a r e f o u r s ys t em s e rv i c e s i n VM S
th a t a r e c l o s e l y r e l a ted
to
s ys tem s e r v i c e d i spa t c h i ng
and
the
c h a ng e m o d e i n s t r uc t i o n s .
Th e
$ D C LCMH s y s t em s e r v i c e wa s d e sc r i b ed i n S e c t i o n 3 . 2 . 2 .
Th i s
sec t i on
d e sc r i b e s t h e $ S E TS FM s e rv i c e a nd t h e c h a ng e mo d e s ys t em s e rv i c e s .

3. 5. 1

Se t Sys t em Se rv i c e Fa i l u r e E x c ep t i o n s Sys tem S e rv i c e

Th e $ S ETSFM s ys t em s e rv i c e e i th e r e n a b l e s o r d i s a b l e s
th e g ene r a t i on
of
e x c e p t i o n s wh en a n e r r o r i s d e t e c t ed by t h e s ys t em s e rv i c e c ommon
e x i t pa th .
Th e s e rv i c e i t s e l f s i mpl y s e t s ( t o enab l e ) o r c l e a r s
( to
t h e b i t i n t h e p r o c e s s s t a t u s l o ng wo r d ( a t o f f s e t PC B $ L S T S
d i sa b l e )
i n t h e so f twa r e PC B ) fo r t h e a c c e s s mo d e f r om wh i c h t h e s y s t em se rvi c e
wa s c a l l ed .

3-1 7

SYSTEM SERVI C E D I S PATCHING
3. 5. 2

Chang e Mod e Sys t em Se rv i c e s

Th e $ CMKRN L a nd $ CMEXE C s ys t em s e rv i c e s p r ov i d e a
s i m p l e pa th
fo r
p r i v i l eg e d p r o c e s s e s
to
execute code
i n k e r n e l o r e x e c u t i v e mo d e .
Th e s e s e rv i c e s c h ec k f o r t h e a pp r o p r i a t e p r i v i l eg e ( CMKRN L o r CMEXE C )
and
then d i s pa t c h
( wi th a CALLG i n s t r uc t i o n ) to the p r o c ed u r e wh o s e
a d d r e s s i s s uppl i ed a s a n a rg um e n t to
the
s e rv i c e .
( No t e
th a t
if
$ CMKRN L i s c a l l ed f r om e x e c u t i v e m o d e , n o p r i v i l eg e c h e c k i s m a d e . )
Th e p r o c ed u r e th a t e x e c u t e s i n k e r n e l o r e x e c u t i v e mod e m u s t
l o ad
a
r e t u r n s ta tu s c o d e i n to R O .
I f n o t , t h e p r ev i o us c o n t e n t s o f RO w i l l
b e u s ed t o d e t e rm i n e wh e th e r a n e r r o r o c c u r r ed .

3-1 8

CHAPTER 4
S OFTWARE INTERRUPTS

Th e so f twa r e i n t e r r up t m e c h a n i sm th a t is p r ov i d ed a s a n i n t eg r a l
pa r t
o f t h e VAX a r ch i t e c t u r e i s r e l i ed o n h e a v i l y b y VAX/VM S f o r s ev e r a l
pu r po s e s .
Th e s c h e d u l e r i s i nv o k e d a s a
s o f twa r e
i n te r r up t s e r v i c e
rout ine .
So f twa r e
i n t e r r up t s
p r ov i d e d ev i c e d r i v e r s a c l e a n m e thod
for l o we r i ng I P L .
S e v e r a l I/0 c ompl e t i o n
ro u t i n e s
r un
as
s o f twa r e
i n t e r r up t
serv i c e rout ines .
Th i s c h a p t e r f i r s t d e sc r i b e s the g e n e r a l
s o f twa r e i n t e r r upt m e c h a n i sm a n d th en l i s ts s ev e r a l u s e s o f
s o f twa r e
i n t e r r up t s i n VAX/VM S .

4.1

THE S OFTWARE I NTERRUPT

A s o f twa r e i n t e r r up t i s a c t ua l l y a h a r d wa r e m e c h a n i sm , s i m i l a r
to
an
i n t e r r upt g e n e r a t e d by a n ex t e r n a l d ev i c e .
I t c a u s e s a PC/ PS L p a i r to
b e pushed o n to a n a pp r o p r i a t e s t a c k ( u s ua l l y the i n t e r r up t s t a c k )
and
pa s s e s c o n t r o l to a n i n t e r r up t s e r v i c e r o u t i n e wh o s e a d d r e s s is s to r ed
i n the s ys tem co n t r o l b l o c k .
L i k e h a r d wa r e i n t e r r up t s , VM S i n t e r p r e t s
s o f twa r e
i n t e r r up t s
as
s ys tem-w i d e
events
th a t a r e
s e r v i c ed
i nd e pe nd e n t l y o f
the contex t o f
a
spec i f i c
process .
Th e
AST
i n t e r r upt ,
d i scussed
b r i e f l y at the e nd of t h i s c h a p t e r a nd in g r e a t
d e ta i l i n Ch a p t e r 5 , i s t h e o n l y v a r i a t i o n f r om th i s a s s um p t i o n .
Th e
b ig
d i f f e r e nc e
b e twe e n
so f twa r e
i n t e r r upts
and
h a rd wa r e
i n t e r r up t s ,
a nd
t h e r e a so n fo r t h e n am e , i s t h a t so f twa r e i n t e r r up t s
a r e g e ne r a t e d by a n e x p l i c i t
r eq u e s t
f r om
s o f twa r e .
Th e
t yp i c a l
so f twa r e
i n t e r r up t
r e q ue s t o c c u r s
as
the
r esul t o f
a h a r d wa r e
i n t e r r upt
or
wi th i n
a n o th e r
so f twa r e
i n te r r up t
serv i c e
rout i ne .
Howe v e r ,
there a re
e x ampl e s w i th i n VM S o f so f twa r e i n t e r r u p t s b e i ng
i s s ued f r om c o d e e x e c u t i ng i n p r o c e s s c o n t ex t .

4.1.1

Ha rdwa r e Mec h a n i sm o f So f twa r e I n t e r r up t s

Th e VAX a r ch i t e c t u r e
p r ov i d e s
15
s o f t wa r e
i n te r r u pt
l ev e l s ,
f r om
Th e r e a r e 1 5 e n t r i e s i n t h e s ys tem c o n t r o l
I P L 1 5 d o wn
to
I PL 1 .
b l o c k ( S C B ) f o r a d d r e s s e s o f so f twa r e i n t e r r up t s e r v i c e r o u t i n e s ,
one
fo r e a c h
I P L l ev e l .
A s o f twa r e
rout ine
( u s ua l l y a h a r d wa r e o r
so f twa r e i n te r r upt s e r v i c e r o u t i n e ) r e que s t s a so f t wa r e i n t e r r up t a t a
g i v en
I P L l ev e l by wr i t i ng th e d e s i r e d I P L v a l u e i n to the pr i v i l eg ed
r eg i s t e r So f t wa r e I n t e r r up t Re q u e s t Reg i s te r ( P R $ S I RR ) .
Wr i t i ng
to
th i s
r eg i s t e r c a u s e s a b i t in the So f t wa r e I n t e rr upt Summ a r y Reg i s t e r
( PR $ S I S R ) to b e s e t .
Th e b i t
in
the
S I SR
is
c l ea r ed
wh e n
the
i n te r r up t
is
f i n a l l y t a ken .
Th e
l a yo u t of
these
two p r o c e s s o r
r eg i s t e r s i s p i c t u r ed i n F i g u r e 4 - 1 .
Al l s o f t wa r e i n te r r upt
r e que s t s

4-1

SOFTWARE INTERRUPTS
i n VM S u s e the SOFT INT m a c r o to wr i t e the S I RR .
m a c ro i s
. MAC RO

S O F T INT I PL

MTPR

I P L , S A # PR $_S I RR

. ENDM

S O F T INT

Th e e x pa n s i o n of th i s

4 3
IGNORED

REQUEST

Softw a re Interrupt Request Register
(Write Only)

P R $ _ S I RR

PENDING SOFTWARE INTERRUPTS

MBZ

P R $_ S I S R

Softwa re Interrupt Summary Register
( R e a d / Wri t e )

Figure 4-1
C o n t en t o f So f twa r e I n t e r r u pt Re q u e s t Reg i s t e r
a n d So f twa r e I n t e r r up t S umm a r y Reg i s t e r
Th e us ua l s i t ua t i o n i n VM S i s tha t t h e r e q ue s t e d
I P L l ev e l
is
l e ss
than o r
equa l
to t h e c u r r e n t I P L ( a s d e t e rm i n ed by PS L < 2 0 : 1 6 > ) .
In
th i s c a se , t h e i n t e r r upt i s d e f e r r ed un t i l th e
I P L d r ops b e l o w t h e
r e q ue s t ed l ev e l .
Th e d e f e r r a l o f p e nd i ng so f twa r e i n t e r r up t s b a s e d o n
c u r r e n t I P L i s e x a c t l y t h e wa y th a t pe nd i ng
h a r d w� r e
i n t e r r upts a r e
t r ea t e d .
Th i s l owe r i ng o f I P L u s u a l l y o c c u r s a s t h e r e s u l t o f an RE I
i n s t r uc t i o n b u t c o u l d a l s o o c c u r i f p r i v i l eg ed c o d e d i r e c t l y a l t e r ed
th e c u r r e n t I PL by w r i t i ng to the PR $ I P L r eg i s t e r ( wi th t h e S E T I P L o r
t h e ENB I NT m a c r o s , d e sc r i b ed i n Ch a pt er 2 4 ) .
I f the r e q u e s t ed I P L v a l u e i s h i g h e r
than
the
l ev e l
a t wh i c h t h e
processo r
is
c u r r e n t l y r un n i ng ,
t h en the i n t e r r upt s e r v i c e r o u t i n e
wh o s e
ad d r e s s
is
i n the
s e l ec ted
slot
in
the SCB
is
e n t e r ed
i mmed i a te l y .
( Th i s
i s t h e s ame wa y t h a t pe nd i ng h a r d wa r e i n t e r r up t s
a r e t r e a t ed . )
Th e r e a r e a f e w o c c u r r e n c e s i n VM S o f a so f twa r e i n t e r r up t r e que s t a t
an
I P L l ev e l g r e a t e r t h a n t h e p r oc e s s o r i s c u r r e n t l y r un n i ng a t .
Fo r
e x ampl e , d ev i c e d r i v e r FDT r o u t i n e s m a y s i g n a l c om p l e t i o n
by c a l l i ng
th e r o u t i n e s E XE $ F I N I S H I O o r EXE $ F I N I SH I OC .
Th e s e r o u t i n e s e x e c u t e a t

4-2

S OFTWARE INTERRUPTS
I PL 2 a nd te rm i n a t e by
r e que s t i ng
the
I /0 po s t p r o c e s s i ng
so f twa r e
i n t e r r up t a t I P L 4 .
I n th i s c a se , t h e i n t e r r u pt i s t a k e n i mmed i a te l y .
Th e f i l e sys tem AC P u s e s t h e same t e c h n i q ue t o s i g n a l
I /0 c ompl e t i o n
f o r r e que s t s i n wh i c h i t wa s i nv o l v e d .

4. 1.2

So f twa r e I n t e r r up t S e rv i c e Ro u t i n e s

Th e r e a r e s e v e r a l f e a t u r e s a b o u t t h e u s e o f so f twa r e i n t e r r up t s i n VM S
tha t a r e
i nd e pe nd e n t o f t h e p u r po s e s o f i nd i v i d u a l i n t e r r up t s e r v i c e
r o ut i n e s .
Some o f the s e a r e d i c t a t e d b y the
pa r t i c u l a r
wa y t h a t
so f twa r e i n t e r r up t s a r e t r e a t ed i n t h e h a r d wa r e .
Be c a u s e the VAX a r ch i t e c t u r e s upp l i e s n o mech a n i sm f o r d e t e rm i n i ng h 9 w
m a n y t i m e s a so f twa r e i n t e r r up t h a s b e en r eque s t e d b e f o r e i t i s t a k e n ,
VM S
uses
s o f twa r e m u s t s uppl y some p r o to c o l f o r d e t e rm i n i ng
th i s .
queues
( d o ub l y l i nk e d
l i s ts m a n i pu l a t ed b y t h e I N S QU E a nd REMQUE
i n s t r uc t i o n s ) f o r
th i s
p u r po s e .
I n g e ner a l ,
e a ch
queue
e l em e n t
r epresents
a
spec i f i c
o pe r a t i o n th a t m u s t b e pe r f o rmed .
Th e u s e o f
q ue ue s , p a r t i c u l a r l y t h e u s e o f t h e I N S Q U E a nd
REMQUE
i n s t r uc t i o n s ,
a l l ows o th e r o p t i m i z a t i o n s to b e m a d e .
•

•

4.2

I n g e n e r a l , so f twa r e i n t e r r up t r e q u e s t s a r e mad e by c o d e th a t
is
e x e c u t i ng
at
e l ev a ted
I P L , o f t en b y h a r d wa r e i n t e r r upt
s e rv i c e r o u t i nes .
Th e s e
so f twa r e
i n t e r r up t
r eque sts a r e
u s ua l l y a c c ompa n i ed
by
t h e i n s e r t i o n o f some type o f q u e ue
e l em e n t
i n to
a wo r k
l i s t w i th
an
I NSQUE
i n s t r uc t i o n .
C o nd i t i o n c o d e s
( i n pa r t i c u l a r ,
t h e s e t t i ng o f t h e Z - b i t )
i nd i c a t e wh e t h e r t h e que ue wa s p r ev i o u s l y n o t em pty
( a nd
by
i mpl i c a t i o n
wh e t h e r
the
so f twa r e
i n t e r r up t
r equest h a s
By us i ng th i s i n f o rm a t i o n , VM S m a k e s t h e
a l r e ady b e e n mad e ) .
s o f twa r e
i n t e r r up t
r e q ue s t o n l y o n c e , a v o i d i ng t h e o v e r h e a d
o f t h e M T PR i n s t r uc t i o n f o r a d d i t i o n a l
u n n ec e s s a r y so f t wa r e
i n t e r r up t r e qu e s t s .
Th e so f t wa r e i n t e r r up t
serv i c e
rout ine
c an
a l so
use
the
i n fo rm a t i o n p r o v i d e d b y c o nd i t io n cod e s e t t i ng s , th i s t i me a s
the
r e s ul t o f
e x e c u t i ng
a
REMQUE
i n s t r uc t i o n .
Th a t
i n s t r uc t i o n
r e t u r n s t h e V-b i t s e t
i f t h e q u e ue wa s emp ty
b e fo r e t h e i n s t r uc t i o n b eg a n e x e c u t i o n ,
an
i nd i c a t i o n
th a t
t h e wo r k o f
th i s
pa r t i c u l a r
i n te r r up t s e r v i c e r o ut i n e i s
compl e t e .
By c o d i ng so f twa r e i n t e r r up t s e r v i c e r o ut i n e s
so
th a t
they
keep
r emov i ng wo r k l i s t e l em e n t s f r om a q u e u e un t i l th e r e i s
no mo r e wo r k t o d o , i t i s po s s i b l e to s im p l y i g no r e e r r o n e o us
s o f t wa r e
i n t e r r up t
r eque s t s .
I n f a c t , a l l o f t h e so f t wa r e
i n t e r r up t s e r v i c e r o u t i n e s i n VM S , i nc l ud i ng
tho s e
th a t d o
n o t u s e q u e ue s , wo r k e v e n i n the e v e n t o f s p u r i o us i n t e r r up t s
r e que s t s .

S OFTWARE INTE RRUPT LEVE LS IN VAX/VMS

VM S u s e s t h e so f twa r e i n t e r r up t m e c h a n i sm f o r s ev e r a l p u r po s e s .
•

De v i c e d r i v e r s u s e fo r k p r o c e s s e s so tha t t h e y c a n e x ec u t e a t
a n I P L b e l o w d ev i c e I P L .

4-3

S OFTWARE INTERRUPTS
•

Th e s o f t wa r e t i m e r s e rv i c e r o ut i n e pe r fo rms t im e r o pe r a t i o n s
t h a t wo u l d b o g t h e s ys t em d o wn ( b e c a u s e I /O d ev i c e i n t e r r up t s
a r e b l o c k e d ) i f t h ey we r e p e r fo rmed a t I PL 2 4 , t h e l ev e l
at
wh i c h the h a r dwa r e c l o c k i n t e r r up t s .

•

Th e n e ed f o r I / O po s t pr o c e s s i ng
c an b e
f l agg ed
by d ev i c e
d r iver
i n t e r r up t s e r v i c e r o u t i n e s b u t the a c t ua l p r o c e s s i ng
d e f e r r ed wh i l e a n o th e r pend i ng I /0 r e q ue s t i s s ta r t ed .

•

R e s c h e d u l i ng ,
the
r emova l
of
the c u r rent process
f r om
e x ec u t i o n and
t h e s e l e c t i o n o f a n e w p r o c e s s fo r ex ec u t i o n ,
i s i mpl em e n t ed a s a s o f twa r e i n t e r r up t s e rv i c e r o u t i n e .

•

Th e AST d e l i v e r y i n t e r r up t i s
t h e o n l y so f twa r e
i n t e r r up t
t h a t i s t r e a t ed a s a p r o c e s s - sp e c i f i c i n t e r r up t r a th e r t h a n a
s ys t em -w i d e e v en t .

T a b l e 4 - 1 l i s t s a l l t h e so f twa r e i n t e r r up t l ev e l s used by VAX/VM S .
Ta b l e 4 - 1
So f t wa r e I n t e r r up t Lev e l s Us e d b y VAX/VM S
I PL

4. 2. 1

Use

Stack

1 5-1 2

Unused

I n t e r r up t

I PL = l l Fo r k D i s pa t c h i ng

In t e r r up t

I PL = l O Fo r k D i s pa t c h i ng

In t e r r up t

I PL = 9 Fo r k Di s pa t c h i ng

I n t e r r upt

I PL=8 Fo r k D i s pa t c h i ng

In t e r r upt

So f t wa r e T i m e r Se r v i c e Ro u t i n e

I n t e r r upt

I PL = 6 Fo r k D i spa t c h i ng

I n t e r r up t

Us ed to En t e r XD E LTA

I n t e r r upt

I /0 Po s t p r o c e s s i ng

In t e r r up t

R e s c hed ul i ng In t e r r up t

Ke r n e l

A S T De l i v e r y In t e r r up t

Ke r n e l

Unused

Fo r k P r o c e s s i ng

One u s e o f so f twa r e i n t e r r up t s i s fo und i n t h e m e c h a n i sm c a l l ed
fo r k
p r o c e s s i ng
empl o ye d b y d ev i c e d r i v e r s .
Th e i n t e r r up t n e s t i ng s c h em e
d e f i n ed b y t h e VAX a r c h i t e c t u r e i s n o t g o i ng to wo r k c o r r e c t l y i f a n
i n t e r r up t
s e rv i c e
rout ine
l o we r s
I P L b e l ow t h e l ev e l a t wh i c h the
i n t e r r up t o c c u r r ed .
Howe v e r ,
d ev i c e
d r iver
i n t e r r up t
s e rv i c e
r o u t i nes ,
i n i t i a l l y e n te r ed o r i nvo k e d a t d ev i c e I P L ( typ i c a l l y 2 0 to
2 3 d e c i m a l ) , o f t e n mus t pe r fo rm l e ng t h y p r o c e s s i ng th a t d o no t r e qu i r e
d ev i c e i n t e r r up t s to b e b l o c k e d , t h e us ua l r e a so n fo r m a i n t a i n i ng h i g h
4-4

S OFTWARE INTERRUPTS

I PL .
Som e mech a n i sm i s r e qu i r ed t o a l l o w d ev i c e d r i v e r s to l owe r
w i tho u t d e s t r o y i ng the i n t e r r up t n e s t i ng s c h eme .

I PL

S e v e r a l I PL v a l u e s ( 6 , a n d 8 to 1 1 ) and th e i r a s so c i a t ed SCB s l o ts a r e
u s ed b y d ev i c e d r i v e r s t o a l l o w t h em t o c o n t i n ue t h e i r e x e c u t i o n a t
l o we r I PL , a s s o - c a l l ed fo r k p r o c e s s e s .
Th e r e a r e a l s o
six
q u a d wo r d
l i s th e a d s
a ssoc i a ted
wi th
the
fo r k
I PLs .
( Be c a us e I PL 7 s o f twa r e
i n t e r r up t s a r e used by t h e s o f twa r e t i me r , t h i s l i s th e a d i s n o t
u s ed
by the
f o r k p r o c e s so r
b u t m e r e l y s e rv e s a s a p l a c e s a v e r so th a t
c o n t e x t i nd ex ed ad d r e s s i ng c an b e used b y t h e fo r k p r o c e s so r
a nd
the
f o r k d i s pa t c h e r
wi th
the I P L v a l ue a s a n i nd ex . ) Th e queue e l em e n t s
t h a t d e sc r i b e e a c h i nd i v i d ua l o pe r a t i o n
th a t m u s t b e pe r fo rmed
at
l o we r
I P L a r e c a l l ed fo r k b l o c k s a nd a r e u s ed to pa s s c o n t ex t b e t we e n
d r iver
i n t e r r up t
service
r o u t i n e s a nd
the
fo r k
l ev e l
s o f twa r e
i n t e r r up t
s e rv i c e r o u t i n e s .
A f o r k b l oc k ( p i c t u r ed i n F i g u r e 4 - 2 ) i s
o f t en pa r t o f a l a rg e r s t r uc t ur e s u c h a s a un i t c o n t r o l b l o c k .

Fork Queue Forward Link

Fork Queue Backward Link

Fork IPL

Size

Type

Saved PC

Figure 4-2

Saved

L a yo u t o f Fo r k B l o c k

Wh en a d r i v e r wi she s t o l o we r i t s I P L ( by c r e a t i ng a fo r k p r o c e s s ) , i t
calls
rout i ne
E XE $ F ORK wi th R S c o n t a i n i ng t h e a d d r e s s o f t h e f o r k
b l ock .
Th a t r o u t i n e s a v e s t h e d r i v e r c o n tex t ( R 3 , R 4 , a nd
s a v ed
PC )
in
the
fo r k b l o c k , i n se r t s the fo r k b l oc k i n to the a pp r o p r i a t e fo r k
q ue ue , a nd r e que s t s a so f twa r e i n t e r r up t a t the
r eque s ted
I P L l ev e l
(if
the
q u e ue wa s p r ev i o u s l y emp t y ) .
Th e a c t ua l i n s t r uc t i o n s i n
r o u t i n e EXE $ FORK t h a t pe r f o rm
these
f un c t i o n s
a r e l i s t ed
here
to
i l l u s t r a t e how wo r k
que ue s a nd
so f twa r e
i n t e r r up t
r e que s t s
a re
m a n ag e d .
E XE $ F ORK : :
R 3 , FKB $ L F R 3 ( R 5 )
MOVQ
F KB $ L FPC ( R S )
POPL
MOVZ B L FKB $ 8-F I PL ( R S ) , R4
W� SW I $G L F QF L- < 6 * 8 > [ R 4 ] , R 3
M OVAQ
( R S ) , @ 4 ( R3 )
I N S QUE
1 0$
BNEQ
S OF T INT R 4
RSB
1 0$ :

4-5

SOFTWARE INTERRUPTS
The fo r k d i s pa tch e r , wh i c h i s the so f t wa r e i n t e r r up t
s e rv i c e
r o ut i n e
that
executes
in
r e s po n s e
to
the
r e q u e s t ed
i n t e r r up t ,
ex ecutes
a pp r o x i m a te l y th e fo l l o w i ng s e que n c e o f i n s t r uc t i o n s th a t r em ov e s e a c h
queue
e l em e n t
in
t ur n
f r om
t h e a � s o c i a t ed q u e ue a n d p r o c e s s e s i t .
Th i s p r o c e s s i ng c o n t i n u e s un t i l t h e q u e ue i s emp t y , a t wh i c h t i m e
the
s o f twa r e i n t e r r up t i s d i sm i s s ed w i th an RE I
•

AL IGN
E XE $ F ORKD S PTH : :
PUS HR
M F PR
10$:
M OVAQ
REMQUE
BVS
M OVQ
M OVL
•

LONG
i � M< R O , R l , R 2 , R 3 , R 4 , R S >
i P R $ I PL , R O
W � SWI$G L F QF L- < 6 * 8 > [ R O ] , Rl
@ ( R l ) + , RS
20$
F KB $ L F R 3 ( R 5 ) , R 3
F KB $ L=F PC ( R S ) , R l

JSB

(Rl)

BRB

10$

20$ :

P O PR
REI

i A M< R O , Rl , R2 , R 3 , R 4 , R S >

4.2.2

S o f twa r e T i m e r

Mo s t o f t h e t i me r o pe r a t i o n s i n VM S e x ec u t e i n r e s po n s e t o a
so f twa r e
i n t e r r up t
at
I PL 7 .
Th e s e o pe r a t i o n s
a r e d e s c r i b ed i n d e t a i l i n
Ch a p t e r 1 0 .
Th e u s e o f
s o f twa r e
i n t e r r upts by the
t imer
s uppo r t
r o u t i n e s i s d e sc r i b ed h e r e .
Wh e n t h e h a rdwa r e c l o c k
i n te r r up t
serv i c e
rout i ne
( e x e c u t i ng
at
I PL 2 4 )
d e te rm i n e s
th a t
f u r th e r s e r v i c e i s r eq u i r e d ( d ue t o q u a n t um
e x p i r a t i o n o r b e c a u s e t h e f i r s t e l em e n t i n the c l o c k q u e ue h a s c om e
d ue ) ,
i t r e qu e s t s a so f twa r e i n t e r r up t a t I P L 7 ( I P L $ T I M E R ) .
Un l i k e
the f o r k que ue d e sc r i b e d i n t h e p r ev i o us s e c t i o n , q u e ue e l em e n t s a r e
n o t p l a c ed
i n to t h e
t imer
q u e u e b y a n i n t e r r up t s e r v i c e r o u t i n e .
Ra the r , t h e y a r e u s ua l l y p l a c ed t h e r e by
one o f
the
timer
r e l a t ed
s ys tem s e rv i c e s
( s uch a s $ S E T I M R o r $ S C HDWK ) .
Th e k e y to th e t i m e r
que ue i s th a t th e q u e ue e l em e n t s a r e o rd e r ed
by e x p i r a t i o n
time so
that only the f i r s t TQE has
t o b e e x a m i n ed b y t h e h a r d wa r e c l o c k
s e rv i c e r o u t i ne .
Th e s o f twa r e i n t e r r up t s e r v i c e r o u t i n e r e c h e c k s f o r q u a n t um e x p i r a t i o n
a nd
t a ke s
action
i f n e c e s sa r y .
After
a n y r e q u i r ed
q ua n t um end
p r o c e s s i ng h a s o c c u r r ed , the so f twa r e t i m e r s e rv i c e
r o ut i ne
e x am i n e s
the
t imer
q u e u e fo r a n y t i m e r r eq ue s t s t h a t h a v e e x p i red .
An y t i m e r
que ue e l em e n t th a t h a s a n e x p i r a t i o n t i m e
earl i e r
than
the c ur rent
s ys tem
t ime
is
then
r em o v e d
f r om
the
t imer
que ue a nd se r v i c ed .
B e c a u s e o f t h e t i me o r d e r i ng o f t h e t i m e r q u e ue ,
th i s
r em o v a l
takes
pl ace
f r om
t h e b eg i nn i ng
of
the l i st .
Wh e n n o m o r e e x p i r ed t i m e r
q u e ue e l em e n ts r em a i n ( th e e x p i r a t i o n t i m e o f t h e
f i r s t TQE
in
the
q u e ue
is
l a t e r than t h e c u r r e n t s y s t em t i m e ) , the s o f t wa r e i n t e r r upt
i s d i sm i s s e d .
No t e th a t a s e c o nd
d i f fe r e n c e b e twe e n
th i s
s o f twa r e
i n t e r r up t
s e rv i c e
rout i ne
a nd
f o r k p r o c e s s i ng i s th a t th e so f twa r e
( th e o n e s
th a t
t i m e r s e rv i c e r o u t i n e m a y l e a v e t im e r q u e u e e l em e n t s
h av e n o t ye t ex p i r ed ) i n t h e que ue wh e n i t d i sm i s s e s t h e i n t e r r up t .
4-6

S OFTWARE INTERRUPTS
4.2. 3

I /O Po s tpr o c e s s i ng

Wh e n a d ev i c e d r i v e r o r FDT r o u t i ne d e tec t s
tha t
a
pa r t i c u l a r
I /0
r equest
i s c ompl e t e ,
i t c a l l s a r o u t i n e tha t p l a c e s the I /0 r e que s t
pa c k e t ( po i n t ed t o b y R 3 ) a t t h e t a i l o f t h e I /0 po s t p r o c e s s i ng
que u e
( l o c a t ed
th r o ug h g l o b a l po i n t e r I OC $G L P S B L ) a n d r e que s t s a s o f twa r e
i n t e r r u p t a t I P L 4 ( I P L $ I O POS T ) i f t h e que u e
wa s p r ev i o u s l y empt y .
Th e
fo l l o w i ng
s e t o f i n s t r uc t i o n s ( f r om r o u t i n e I OC $ R E QC OM i n m od u l e
I O S UB N PAG ) shows
the
s i m i l a r i t i e s b e twe e n
the
s o f twa r e
i n t e r r up t
( Othe r r o ut i n e s
r e que s t s
fo r f o r k p r o c e s s i ng a nd I /0 po s t p r o c e s s i ng .
t h a t r e que s t a n I P L $ I O PO S T s o f twa r e i n t e r r upt , $ Q I O c o mpl e t i o n c o d e
a nd ACP r o u t i n e s , e xec u t e s i m i l a r i n s t r uc t i o n s . )

10$ :

I N S Q UE
( R 3 ) , @ WA I O C $G L P S B L
BNEQ
1 0$
S O FT INT # I P L $ I O PO S T

Th e I /0 po s t pr o c e s s i ng so f twa r e i n t e r r upt s e r v i c e r o u t i n e r emov e s e a c h
IRP
in
t ur n
f r om t h e b eg i nn i ng o f t h e queue ( l o c a ted th r o ug h g l o b a l
po i n t e r I OC $G L P S F L } a n d p r o c e s s e s i t .
Wh e n t h e que ue i s
empt y ,
the
I PL 4
s o f twa re i n t e r r u p t i s d i sm i s s e d .
Th e s i m i l a r i t i e s b e twe e n f o r k
p r o c e s s i ng a nd I /0 po s t p r o c e s s i ng a r e a l s o fo und i n
the i r
r e spec t i ve
so f twa r e
i n t e r r up t s e r v i c e r o u t i n e s .
Th e fo l l o w i ng i n s t r uc t i o n s f r om
mod u l e I OC I O PO S T i l l u s t r a t e these s i m i l a r i t i e s .
I O C $ I O PO S T : :
M OVQ
MOVQ
M OVQ
I O PO S T : REM QUE
BVC
M OVQ
MOVQ
M OVQ
RE I

R4 , - ( S P)
R2 , - ( SP)
RO , - ( S P )
@WA I O C $G L P S F L , R S
10$
( S P ) + , RO
( S P ) + , R2
( S P ) + , R4

10$ :

Compl e t e p r o c e s s i ng o f th i s r e q u e s t
B Rx

4. 2. 4

I O PO S T

Re s c h ed u l i ng I n t e r r up t

Th e r o u t i n e tha t r em o v e s a p r o c e s s
f r om
e x ec u t i o n a nd
s e l ec ts
the
h i g h e s t pr i o r i t y p r o c e s s
fo r
execution
is
i nv o k e d
a s a s o f t wa r e
i n t e r r up t s e rv i c e r o u t i n e a t I P L 3 ( I P L $ S C HED ) b y t h e r o u t i n e
th a t
makes
a
p r o c e s s c om p u t a b l e .
Wh e n e v e r th e s t a t e o f a p r o c e s s b e c o m e s
c ompu tab l e a nd i t s pr i o r i t y i s g r e a t e r th a n o r e q u a l to
the p r i o r i ty
o f t h e c u r r e n t p r o c e s s , t h i s s o f twa r e i n t e r r up t i s r eq u e s t e d .
Because
s ev e r a l p r o c e s s e s c o u l d a l l b e c o m e c om p u t a b l e a t e f f e c t i v e l y t h e s a m e
t ime ,
there could
b e m u l t i pl e r eq ue s t s fo r th i s s o f twa r e i n t e r r up t
s e rv i c e r o u t i n e .

4-7

S OFTWARE INTERRUPTS
Th e r e sc h ed u l i ng i n te r r up t
is
not
to ta l l y
i nd e pend e n t o f
process
c o ntex t
l i ke
the
f o r k p r o c e s s i ng a nd I /O p o s t p r o c e s s i ng i n t e r r up t s .
Th e S C B e n t r y f o r t h i s i n t e r r up t ( Ta b l e 4 - 1 ) i nd i c a t e s th a t i t sho u l d
b e s e r v i c ed
o n t h e k e r n e l s t ac k .
I n f a c t , i t s f i r s t o pe r a t i o n i s to
r emove the c u r r e n t p r o c e s s f r om e x e c u t i o n w i t h a
SVPC TX
i n s t r uc t i o n .
Howeve r ,
that
i n s t r uc t i o n pe r fo rm s
a
s t ac k s w i t c h f r om t h e ke r n e l
s t ac k t o t h e i n te r r up t s t a c k s o t h e r e s t o f t h e r e s c h e d u l i ng i n t e r r up t
s e rv i c e
r o u t i n e i s pe r fo rmed i n s y s t em c o n t e x t .
Th e o pe r a t i o n o f t h e
s c he d u l e r ,
i nc l ud i ng
a d e ta i l ed
d e sc r i pt i o n o f
the
r e sched ul i ng
i n te r r up t , i s d i sc u s s ed i n Ch a pt e r 8 .
U n l i k e f o r k p r o c e s s i ng o r I /0 p o s t p r o c e s s i ng
r e q ue s t s ,
the re
is
no
n e ed to c o un t r e que s t s f o r the r e s c h ed u l i ng i n t e r r up t b e c a u s e o n l y o n e
p r oc e s s c a n b e c u r r en t a t a g i v e n t i me .
Th e
so f twa r e p r i o r i t i e s
of
t h e c omp u t a b l e p r oc e s s e s d e te rm i n e wh i c h o f
them
i s c ho s en f o r
e x ec u t i o n .
Th e s c h ed u l e r wi l l s e l e c t t h e p r oc e s s
w i th
the h i g h e s t
s o f twa r e
p r i o r i ty .
Th e
rest
of
the
p r o c e s s e s wi l l r ema i n i n the
c omputa b l e s t a t e un t i l
some
s ys t em
event o c c u r s
that
a l te r s
the
s c h e d u l i ng
b a l a n c e o f t h e sys t em and c a u s e s one of these p r o c e s s e s to
be s e l e c t ed f o r ex e c u t i o n .
Fo r e x ampl e , i f a h i g h e r p r i o r i t y p r o c e s s
we r e t o
b ecome c om p u t a b l e ,
an
I PL 3
s o f twa r e
i n t e r r up t wo u l d b e
r eque s t ed .
( I f t h e c u r r e n t p r o c e s s we r e to
enter
a
wa i t s t a t e ,
a
d i f f e r e n t pa th
i s t a k e n th r o ug h t h e s c h ed u l e r , o n e th a t bypa s s e s the
s o f twa r e i n t e r r up t r eq u e s t a nd e x e c u t e s
the
code
c o n t a i n ed
in
the
s e co nd h a l f o f the r e s c h ed u l i ng i n te r r up t s e rv i c e r o u t i n e . )

4 . 2. 5

AST De l i v e r y I n t e r r up t

Th e so f t wa r e i n t e r r up t t h a t i nd i c a t e s t h a t th e r e i s a n AST to
del iver
d i f f e r s i n s ev e r a l r e s p e c t s f r om t h e o t he r s o f twa r e i n t e r r up t s .
•
•

•

Th e A S T d e l i v e r y i n t e r r up t
is
a s s o c i a t ed
wi th a
spec i f i c
p r o c e s s a nd i s s e r v i c ed o n the k e r n e l s t ac k o f th a t p r o c e s s .
Th e i n t e r r up t r e q u e s t i s m a d e i n two
s t eps .
Ro u t i n e s
that
r e c og n i z e
tha t
the r e
is
a n A S T t h a t c a n b e d e l i v e r ed to a
p r o c e s s i n d i c a t e t h a t b y wr i t i ng th e a c c e s s m o d e a s s o c i a t ed
w i th
the A S T
i n to a pe r - p r o c e s s p r i v i l eg e d r eg i s t e r c a l l ed
t h e A S T l e v e l r eg i s t e r
( PR $ A S T LVL ) .
Th e . RE I
i n s t r uc t i o n
c ompa r e s
th e
c o n ten ts o f th i s r eg i s t e r wi th t h e a c c e s s m o d e
t h a t i t i s r e s to r i ng to d e t e rm i n e wh e th e r to r e q ue s t an I P L 2
s o f twa r e i n t e r r up t .
As th i s m e c h a n i sm s ug g e s t s , I P L 2 s o f twa r e i n t e r r up t s h a v e
s e c o nd d i m e n s i o n a s so c i a t ed wi th t h em , n am e l y a c c e s s mo d e .

Th e u s e o f ASTs i n VM S i s so i mpo r t a n t th a t t h e y a r e
s e pa r a te c h a pt e r ( Ch a p t e r 5 ) .

4-8

d e sc r i b ed

a
a

CHAPTER 5
AST D E L I VE RY

A s yn c h r o n o u s sys t e m
t r aps
( ASTs )
a r e a m e c h a n i sm
fo r
s i g n a l l i ng
a s ynch r o no u s e v e n t s
to
a
process .
Spec i f i c a l l y ,
a p r o c ed u r e ( o r
r o u t i n e ) d e s i g n a t ed b y e i th e r the p r o c e s s o r the
s ys t em
executes
in
the contex t
of
the p r o c e s s .
ASTs a r e c r e a t ed i n r e s po n s e to s y s t em
s e rv i c e s
s uc h a s
$QIO,
$ S E T IM R ,
a nd
$ DC LA S T .
Ad d i t i o n a l l y ,
u n r e que s ted ASTs o c c u r a s i m p l i c i t r e s u l t s o f o t h e r o pe r a t i o n s s uc h a s
I /0 c om p l e t i o n , p r o c e s s s u spe ns i o n , a n d o b t a i n i ng
i n fo rm a t i o n
about
a n o th e r p r o c e s s w i th the $G E TJ P I s ys tem s e r v i c e .
Th e r e a so n th a t A STs
a r e u s e d fo r the s e o p e r a t i o ns i s t h a t i t i s ne c e s s a r y f o r a
p i ece
of
c od e
to
execute
i n the c o n tex t o f a s p e c i f i c p r o c e s s .
ASTs f u l f i l l
th i s n e ed .
AST e n q u e u i ng i s a s ys t em e v e n t t h a t m a y
r e sul t
in
a
r e s c h ed u l i ng
A S T d e l i v e r y o c c u r s i n the c o n t e x t o f t h e p r o c e s s th a t i s
i n ter r upt .
t o a c t ua l l y r e c e i v e t h e A S T .
Th i s c h a p t e r
d i sc us s e s
how ASTs
a re
e nque ued and d e l i v e r ed to a p r o c e s s .
Se v e r a l e x amp l e s o f h o w A S Ts a r e
u s ed b y VM S a r e a l s o i n c l ud ed .

5. 1

HARDWARE ASS I STANC E TO AST D E L I VE RY

The d e l i v e r y o f A S Ts i s o n e e x am p l e o f
t h e VAX h a r d wa r e p r o v i d i ng
a s s i s t a n c e to VM S .
Th r e e h a r d wa r e c om po n e n t s o r m e c h a n i s�s c o n t r i b u t e
to AST d el ivery :
•

th e RE I i n s t r u c t i o n ,

•

th e PR$ _A S T LVL p r o c e s s o r r eg i s te r , and

•

the I P L 2 s o f t wa r e i n t e r r upt .

Th e f i r s t t wo f e a t u r e s a r e d i sc u s s ed
in
th i s
sec t i o n .
Th e
i n t e r r u p t s e r v i c e r o u t i n e , AS TDE L , i s d i s c u s se d i n Sec t i o n 5 . 3 .

5. 1 . 1

I PL 2

RE I I n s t r uc t i o n

Th e r e t u r n f r om
except i o n o r
i n t e r r upt
rout i ne
i n s t r uc t i o n ,
RE I ,
p rov i d e s
the
initial
s t ep
in
the d e l i v e r y o f a n A S T t o a p r o c e s s .
Am o ng t h e o pe r a t i o n s pe r f o rm e d by t h e RE I m i c r o c o d e a r e the fo l l o w i ng .
1.

A c h e c k i s m a d e to d e t e r m i n e wh i c h s t a c k w i l l b e a c t i v e a f t e r
th e
re turn .
N o A S Ts a r e d e l i v e r ed i f t h e i n t e r r u pt s t a c k i s
ac t i ve .

5-l

AAS T D E L I VE RY
2.

Th e va l u e i n t h e A S T l ev e l p r o c e s so r r eg i s t e r , PR$ A S T LVL , i s
co mpa r e d w i t h
the
a c c e s s mod e
to
wh i c h c o n t rol i s b e i ng
pa s s ed .
I f t h e " d e s t i n a t i o n " a c c e s s m o d e n umb e r i s l e s s t h a n
t h e va l u e i n PR $ _A S T LVL , n o A S Ts c a n b e d e l i v e r ed .

I f the i n t e r r upt s t a c k i s no t g o i ng to b e u s ed a nd t h e a c c e s s
mod e n um b e r i s g r e a t e r t h a n o r e q u a l t o t h e PR $ A S T LVL v a l u e ,
t h e n a n A S T c a n be d e l i v e r ed .
Th e RE I i n s t r uc tio n m i c r o c o d e
r e qu e s t s
a
so f t wa r e
i n t e r r upt
at
I PL 2 .
( No t e th a t t h e
r e q u e s t e d I P L 2 i n t e r r upt w i l l
n o t a c t ua l l y b e d e l i v e r ed
unt i l
the
I P L d r o p s b e l o w 2 . ) Th e I P L 2 s o f twa r e i n t e r r u pt
s e rv i c e
ro ut i ne
is
f o und
at g l o b a l
location
S C H $AS TDE L
( Sec t i on 5 . 3 ) .

A S TLVL P r o c e s so r Reg i s t e r

5.1. 2

( PR $_AS T LVL )

Th e p r o c e s s o r r eg i s t e r , P R $ A S T LVL , i s a pe r - p r o c e s s h a r d wa r e r eg i s t e r
i nd i c a t i ng
th e d e l i v e r a bTl i t y o f
A S Ts
to
the
c u r r en t process .
PR $ A S T LVL i s pa r t o f t h e h a r d wa r e c o n t e x t o f t h e p r o c e s s
( l o ad ed b y
LDPCTX )
and
is
r e c o rd ed
in
t h e h a r d wa r e p r o c e s s c o n t r o l
block
( Ch a p t e r 8 ) .
PR$ _A S T LVL c a n c o n t a i n t h e f o l l o w i ng v a l u e s :
A k e r n e l mod e AS T i s d e l i v e r a b l e .
An e x e c u t i v e m o d e A S T i s d e l i v e r ab l e .
A s upe r v i s o r m o d e A S T i s d e l i v e r a b l e .
A u s e r mod e A S T i s d e l i v e r a b l e .
No AST i s d e l i v e r a b l e .

0
1
2
3
4

Th us , i f an AST i s d e l i v e r ab l e , PR$ A S T LVL c o n t a i n s
the
access mode
va l u e
fo r
the m o d e i n wh i c h t h e AST i s t o e x e c u t e .
Th e " n u l l " v a l ue
o f f o u r i s c h o s e n so th a t t h e RE I t e s t , d e s c r i b e d
a b ov e ,
wi l l
fai l ,
r eg a r d l e s s
of
the
" d e s t i n a t i o n " a c c e s s m o d e o f t h e RE I i n s t r uc t i o n .
I f t h e a c c e s s m o d e o f t h e d e l i v e r a b l e A S T i s a t l e a s t a s p r i v i l eg ed a s
the
d e s t i n a t i o n a c c e s s m o d e o f t h e RE I i n s t r uc t i o n , t h e A S T d e l i v e r y
i n te r r up t w i l l b e r e q u e s t e d .

5. 2

Q U E U ING AN AST TO A PROC E S S

ASTs a r e
que ued
to
a
proc ess
as
the
c o r r e s po n d i ng
events
( I /0
compl e t i o n ,
t i me r
expi ra t i on ,
and
so
on) occur .
Th e AST q u e ue i s
ma i n t a i n ed a s a l i s t s t r uc t u r e o f AST c o n t r o l b l o c k s ( ACBs )
w i th
the
l i s th e ad
c o n t a i n ed
in
the
s o f twa r e p r o c e s s
co n t r o l
block
( PC B )
( Fi g u r e 5- l ) .

AST C o n t r o l B l o c k

5. 2. 1

Th e A S T c o n t r o l b l o c k
d e l i ve r a n AST

( AC B )

d e f i ne s

the

nec e s s a r y

i n f o r ma t i o n

•

to t h e c o r r e c t p r o c e s s a nd A S T r o u t i n e ,

•

i n t h e c o r r e c t a c c e s s mo d e , a n d

•

wi t h t h e a pp r o p r i a t e pa r am e t e r pa s s e d t o t h e r o u t i n e .

5-2

AST DE L I VE RY
the
{ spec i f i c a l l y ,
Th e AC B i s a l l o c a ted f r om no npag ed d yn am i c memo r y
I / 0 r e qu e s t pa c k e t l o o k a s i d e l i s t , d e s c r i b ed i n Ch a p te r 2 5 ) b e f o r e t h e
q u e u i ng o f a n AST t o a p r o c e s s i s r e q u e s t ed .
r e l ev a n t
the
F i g u r e 5 - l s h ows the fo rm a t o f a n A S T c o n t r o l b l o c k a nd
ACB $ L A S T Q F L a nd A C B $ L_A S T QB L l i n k t h e AC B i n to
s o f t wa r e P C B f i e l d s .
the
is
que ue
th i s
of
Th e l i s th e ad
th e A S T q u e ue f o r the p r o c e ss .
Th e f i e l d
PCB $ L A S T QF L a nd PC B $ L A S T QB L .
f i elds ,
of
pa i r
l o ng wo r d
AC B $ B_RMOD p r o v i d e s t h r e e t ype s o f - i n f o rm a t i o n .
1.

B i t s 0 a n d 1 ( AC B $ V RMOD ) c o n t a i n t h e va l u e c o r r e s po nd i ng
the a c c e s s mod e i n wh i c h the AST r o u t i n e i s to e x e c u t e .

the
B i t 6 ( AC B $V Q U O TA ) i n d i c a t e s wh e the r the a l l o c a t i o n o f
f o r i n the p r o c e s s A S T q uo t a ,
a c c o un t e d
is
s t r uc tur e
d a ta
PC B $W A S TCNT .

B i t 7 ( AC B $V KAS T ) i n d i c a t e s t h e p r e s enc e o f a s p e c i a l k e r n e l
mod e A S T ( S e c t i o n s 5 . 2 . 3 a n d 5 . 4 ) .

Software Pro c ess Control Blo c k (PCB)
I

ASTEN I ASTACT
ASTQFL
ASTQBL
����----------�

AST Control Block (ACB)
�::::::::::�A�S�T�Q�F�L��==�:J������
ASTQBL
�.
SIZE
RMOD I TYPE I
PID
AST
ASTPRM
KAST

I\._

�---------�------------------------�

ASTCNT

RMOD Bits:
7 6 5

2 1 0

I I C>SJ j
U

SPARE MODE
QUOTA
KAST

Figure 5-l

A S T Co n t r o l B l o c k a nd AST Qu e ue i n So f t wa r e PCB

AC B $ L A S T
AC B $ L P I D i d e n t i f i e s wh i c h p r o c e s s i s to r e c e i v e t h e A S T .
a nd ACB $ L A S T PRM a r e t h e e n t r y po i n t o f the d e s i g n a t ed A S T r o u t i n e a nd
AC B $ L KA S T c o n t a i n s t h e e n t r y po i n t
th e A S T par am e t e r , r e sp e c t i v e l y .
the
if
mode A S T r o u t i n e
k e r nel
s p ec i a l
sys tem- r e qu e s ted
a
of
AC B $V KAS T b i t o f AC B $ B_RM O D i s s e t ( i t em 3 a bove ) .

5-3

AST DE L IVE RY
ACBs a r e c r e a te d by th r e e t ype s o f a c t i o n .
1.

Th e p r o c e s s e x p l i c i t l y d e c l a r e s a n A S T .
Th e
$ DC LAST s ys tem
s e r v i c e s i m p l y a l l o c a t e s a n AC B , f i l l s in the ACB i n fo rma t i o n
f r om i t s a rg um e n t l i s t , a n d r eq ue s t s t h e q u e u i ng o f t h e ACB .
Two c h e c k s a r e m a d e to e n s u r e tha t
•
•

t h e A S T q uo t a f o r t h e p r o c e s s
r e q ue s t , a nd

not

the

th e a c c e s s m o d e i n wh i c h t h e A S T r o u t i n e i s t o e x e c u t e i s
n o mo r e
p r i v i l eg ed
t h an the a c c e s s m o d e f r om wh i c h t h e
s y s tem s e r v i c e wa s c a l l ed .

Th e AC B$V Q U O TA b i t i s s e t
to
i nd i c a t e
c o un t e d aga i n s t t h e p r o c e s s AST q uo t a .
2.

e x c e e d ed

th a t

thi s

AST

Th e p r o c e s s r e q ue s t s a n AST to b e a s s o c i a t ed
wi t h
an
event
s uc h a s
th e c om p l e t i o n
of
a n I /0 r e qu e s t ( $ Q I O o r Upd a t e
S e c t i o n s ys t em s e r v i c e ) o r a t i m e r
r eq ue s t
( $ S E T IM R s ys t em
Sys t em s e r v i c e s s uc h a s th e s e h a v e a r g um e n t s t h a t
service)
Th e
i nc l ud e a n A S T r o u t i n e e n t r y po i n t a nd a n A S T pa r am e t e r .
d el ivery o f
a n AS T i s
a c c o un t ed
f o r i n the PC B $W A S TC NT
f i eld .
Th e c o n t r o l b l o c k ( AC B ) i s a c t ua l l y a
r e u s e of
the
I /0 r e qu e s t pa c k e t ( I R P ) o r t i m e r q u e u e e l em e n t ( TQE ) us ed i n
( Co mpa r e t h e ACB f o rm a t p i c t u r ed
in
t h e i n i t i a l o pe r a t i o n .
F i g u r e 5 - l wi th
the
TQE f o rma t s h o wn i n Ch a p t e r 1 0 and t h e
I R P l a yo u t s h o wn
i n App e n d i x A o f
t h e VAX/VM S G u i d e
to
W r i t i ng a Dev i c e D r i v e r .
•

5. 2. 2

Th e s y s t em , o r a no th e r p r o c e s s , c a n r e que s t a n A S T to e x e c u t e
c od e
in
th e c o n t e x t
o f t h e s e l e c t ed p r o c e s s .
E x am pl e s o f
t h i s t ype o f a c t i o n
i n c l ud e
I/0 c o mp l e t i o n ,
$G ETJ P I
f r om
a no th e r
p r o c e s s , Fo r c ed Ex i t s ys t em s e r v i c e , a nd wo r k i ng s e t
a d j us tm e n t a s pa r t o f t h e q u a n t um e nd e v e n t ( Ch a p t e r 8 ) .
AST
c o n t r o l b l o c k s u s ed in th e s e s i t ua t i o n s a r e not d ed uc t ed f r om
the
AST q u o t a o f
the
t a rg e t p r o c e s s b e c a u s e o f
the i r
i nvo l un t a r y n a t u r e .

Acc e s s Mo d e a nd AST Que u i ng

Th e ACB $V RMOD b i t s o f t h e AC B $ 8 RMOD f i e l d d e t e rm i n e
the
i nse r t i on
po s i t i o n -o f a n A S T c o n t r o l b l o ck wh e n i t i s que ued to a p r o c e s s .
Th e
AS T q u e ue i s m a i n t a i ned a s a f i r s t - i n f i r s t - o u t ( F I F O ) l i s t fo r
each
a c c e s s mo d e .
A S T s o f d i f f e r e n t a c c e s s mod e s a r e pl a c e d i n to t h e q u e ue
i n a s c end i ng a c c e s s m o d e o r d e r , t h a t i s , k e r n e l m o d e
ASTs
f i r s t a nd
us e r m o d e A S Ts l a s t .
Wh e n the s ub r o u t i n e
S C H $ QA S T
( i n m o d u l e A S TDE L )
is
i nv o k e d ,
the
p r e a l l o c a t ed a n d p r e i n i t i a l i z ed AST c o n t r o l b l o c k i s i n s e r t ed i n to t h e
I P L $ _S YNC H .
Th e
fo l l o w i ng
A S T q u e ue o f t h e a pp r o p r i a t e p r o c e s s
at
s t eps a r e pe r fo rmed .
1.

I f t h e p r o c e s s i s nonex i s t e n t , t h e ACB i s d e a l l o c a t ed and t h e
A S T e v e n t i s i g n o r ed .
A n e r r o r s t a t us c o d e i s r e t u r n ed .

I f t h e A S T q u e u e i s emp t y ( th e c o n t e n t s o f
PCB $ L ASTQF L a r e
e q ua l
to
i ts
ad d r e s s ) ,
t h e AC B
i s i n s e r ted as the f i r s t
e l em e n t i n t h e A S T q u e ue .
5-4

AST DE L IVE RY
3.

5. 2. 3

Ot h e r w i s e , t h e que u e e l em e n t s ( AC Bs ) a r e s c anned u n t i l e i th e r
t h e end o f
t h e q u e u e i s r e a c h e d o r a n ACB i s f o und w i th a n
a c c e s s mod e l e s s p r i v i l eg ed t h a n t h e o n e b e i ng i n s e r t ed ( th a t
is,
t h e A C B $V RMOD v a l u e
i s h ig h e r ) .
Th e n e w AST c o n t r o l
b l o c k i s i n s e r ted a t t h i s po i n t .
Th u s ,
ASTs
are
f i r s t- i n
f i r s t - o u t w i th i n a n a c c e s s m o d e a nd g r o up e d b y a c c e s s m o d e i n
d e c r e a s i ng amo u n t o f p r i v i l eg e .
Us e r m o d e ASTs a r e a l wa y s
p l a c ed a t t h e t a i l o f t h e q u e ue .

S p e c i a l Ke r n e l Mo d e ASTs

S p e c i a l k e r n e l mode ASTs r e p r e s e n t a f i f t h
type
o f AST .
Th e y a r e
ma i nta i ned
a s a s e p a r a t e g r o up i n the AST q u e ue .
Sp e c i a l k e r n e l m od e
ASTs a r e i nd i c a t ed b y t h e ACB$V KAST b i t
of
t h e ACB $ B RMOD f i e l d .
Inse r t i on o f
a s pe c i a l k e r n e l -m9d e AST w i l l o c c u r a f t e r -a n y p r e v i o us
s pe c i a l k e r ne l mod e ASTs , b u t b e fo r e any " no rm a l " A S Ts o f a n y a c c e s s
m o d e ( i nc l ud i ng k e r n e l ) .
Th u s , t h e o rg a n i z a t i o n o f t h e A S T que ue i s :
l i s th e a d - s p e c i a l - " n o rma l " ..-. e x ec- - s upe r - -- u s e r
( PC B )
ut ive
v i so r
k e r ne l
ke rnel
Sec t i on 5 . 4 d i sc us s e s spec i a l k e r ne l
s ev e r a l e x am p l e s .

5. 2. 4

ASTs

mo r e

f ul ly

a nd

prov i d e s

Comput a t i o n o f a New Va l ue f o r ASTLVL

An AST c a n be enque ued to a p r o c e s s a t a n y t im e , b e c a u s e the
s o f twa r e
PC B a n d t h e AST c o n t r o l b l o c k s a r e n e i t h e r pag e d no r swa ppe d .
Each
t i m e a n A S T c o n t r o l b l o c k i s i n s e r ted i n to t h e q u e u e ,
the
a s s i g nm e n t
of
a v a l ue
to A S T LVL ( p r o c e s so r r eg i s t e r a n d ha r d wa r e PCB f i e l d ) i s
a t t em p t ed .
Howe v e r , t h e p r o c e s s c a n b e i n a ny o n e o f
th ree
po s s i b l e
s i t ua t i o n s
t h a t d e t e rm i n e t o wh a t d eg r e e th e s t a t e o f the AST q u e ue
c a n be upd a t ed .
•

•

I f a p r o c e s s i s o u t s wa pped ,
t h e A S T LVL c a nno t b e
bec a use
the
process
h e a d e r ( i n c l ud i ng t h e h a r d wa r e
c o n t r o l b l o c k ) i s no t av a i l a b l e .
Wh e n
the
process
r e s i d e n t and
compu t a b l e
at
a
later
t i m e , ASTLVL
c a l c u l a t ed by t h e s wa ppe r ( by i n v o k i ng S C H $ N EWLVL
in
AS TDE L ) .

upd a t e d
proc e s s
becomes
wi ll be
mod ul e

If
the p r o c e s s
i s m em o r y r e s i d e n t b u t
not
cur rently
e x e c ut i ng ,
th e n e w v a l ue fo r A S T LVL w i l l b e r e c o r d ed i n t h e
h a rdwa r e PCB f i e l d b u t n o t i n th e p r o c e s s o r r eg i s te r .
I f t h e p r o c e s s i s c u r r e n t l y e x e c u t i ng , t h e n e w
wi l l
be
s t o r ed
in
both
the
h a r d wa r e
PC B
p r o c e s s o r r eg i s t e r , PR$_ASTLVL .

ASTLVL va l u e
f i e l d and the

Th e AS T LVL v a l u e i nd i c a t e s the d e l i v e r a b i l i t y a nd a c c e s s mod e o f
the
f i rst
pend i ng
AST
in
the
que ue .
Th e r e
is
n o i nd i c a t i o n o f t h e
d e l i v e r a b i l i ty o f a n y o t he r pend i ng ASTs .
A S T LVL i s c a l c u l a t ed i n t h e
f o l l o w i ng s t eps .
1.

I f t h e f i r s t p e nd i ng A S T i s a s pec i a l ke r n e l
mode
a l so S e c t i o n s 5 . 2 . 3 a n d 5 . 4 ) , AST LVL b e c o m e s 0 .

5-5

AST

( see

AST DE L I VE RY
2.

I f the p r o c e s s a l r e ad y h a s a n a c t i v e A S T a t the
same access
mo d e a s
th e
f i rst
pend i ng
AST ,
ASTLVL i s s e t t o 4 .
Th e
e x i s t e n c e o f an a c t i v e AST i n a n y a c c e s s m o d e i s i nd i c a t ed by
s e t t i ng
t h e c o r r e s po nd i ng
bit
in
the
PC B $ 8 A S TACT f i e l d
( Fi g ure 5 - l ) .
De l i v e r y o f
an AST sets
th i s b i t ,
a nd
c ompl e t i o n o f an A S T c l e a r s i t ( S e c t i o n 5 . 3 ) .

I f t h e p r o c e s s h a s d i s a b l ed t h e d e l i v e r y o f a n y AST
in
the
a c c e s s mod e
of
the
fi rst
p e nd i ng A S T , ASTLVL i s a l s o s e t
to 4 .
D i s a b l i ng A S T d e l i v e r y f o r a
pa r t i c u l a r
access mode
r equ i res
c l e a r i ng
t h e c o r r e s po nd i ng b i t o f t h e PC B $ 8 ASTEN
f i e ld ( Fi g ure 5- l ) .
By d e f a ul t , a l l a c c e s s mod e s a r e enab l ed
fo r
AST d e l i ve ry .
Th e $ S E TA S T s y s tem s e r v i c e s e t s o r c l e a r s
t h e PC B $ B _A S T E N b i t c o r r e s po nd i ng t o t h e a c c e s s m o d e o f
i ts
caller .

I f , f o r t h e a c c e s s m o d e o f the f i r s t pe nd i ng AS T , th e r e i s no
a c t i v e AST a nd
t h e d e l i v e r y o f A S Ts is ena b l e d , then the
ASTLVL r e g i s t e r i s l o ad ed w i th t h e v a l u e of tha t a c c e s s m o d e
( a v a l u e f r om z e r o th r o ug h th r e e ) .

Th e v a l ue o f ASTLVL p r o d u c e d by th i s a l g o r i thm w i l l b e e x am i n ed
each
t ime
a n RE I i n s t r uc t i o n r e t u r n s c o n t r o l to t h e p r o c e s s f r om i n t e r r up t
o r e x c e p t i o n s e r v i c e r o u t i n e s ( s uc h a s t h e s c h ed ul e r and
the
pag e r ) .
Th e r o l e o f the RE I i n s t r uc t i o n wa s d e sc r i b ed i n S e c t i o n 5 . 1 .

5. 3

D E L I VE R ING AN AST TO A PROC E S S

A n A S T i s d e l i v e r ed to a p r o c e s s wh e n a n
RE I
i n s t r uc t i o n d e t e rm i n e s
( f r om
t h e d e s t i n a t i o n a c c e s s m o d e a nd t h e PR $ ASTLVL r eg i s te r ) th a t a
pend i ng
AST
i s del ive rabl e
( S e c t i o n s 5 . 1 and
5.2) .
A s o f twa r e
i n t e r r up t i s r e q ue s ted a t I P L 2 .
Th e am o un t o f t i me b e f o r e t h e A S T i s
a c t ua l l y d e l i v e r ed i s d e pend e n t upo n t h e
i n t e r r upt
a c t i v i ty o f
the
s ys t em .
Wh e n I P L f i n a l l y d r ops b e l o w t wo , the AST d e l i v e r y i n t e r r upt
s e r v i c e r o u t i n e w i l l b e e x e c u t ed .

AST De l i v e r y I n t e r r upt

5. 3. 1

Ro u t i n e S C H$ASTDE L ( i n mod ul e A S TDE L ) i s the I P L 2
i n te r r u pt
s e rv i c e
rout i ne .
I ts
f un c t i o n
is
to r em o v e t h e f i r s t pe nd i ng AST f r om the
q u e u e a nd d i s p a t c h to the
a pp r o p r i a t e
AST
r o u t i ne
in
the
correct
a c c e s s mod e .
S C H $ A S TDE L p e r fo rm s t h e f o l l o w i ng o p e r a t i o n s .
l.

A f t e r r a i s i ng t h e I P L to SYNC H , t h e f i r s t AST c o n t r o l
block
is
r em o v ed
f r om th e A S T q u e ue o f t h e p r o c e s s .
I f t h e que ue
wa s
empt y ,
the
rout ine
i mm e d i a t e l y e x i t s wi th
an
RE I
i n s t r uc t i o n .

Th e r em o v e d AC B i s t e s t e d
fo r
a
s pe c i a l
k e r n e l m o d e AST
( us i ng
ACB$V KAST i n ACB $ 8 RM OD ) .
If the AST i s a s pe c i a l
k e r n e l A S T , a -s h o r tened s e q uenc e o f s t eps o c c u r s :
a.

I P L i s d r o pped f r om SYN C H t o I P L $ A S TDE L ( I P L 2 ) .

5-6

AST DE L IVERY
b.

Th e s pe c i a l k e r n e l m o d e r o u t i n e i s d i s pa t c h ed
t h r o ug h
a
JSB
i n s t r uc t i o n w i th
t h e ACB a d d r e s s i n R 5 a n d t h e PC B
add r e s s i n R4 .

On r e t u r n f r om t h e spec i a l k e r n e l mod e r o u t i n e , ASTLVL i s
r e c om p u t e d ( S e c t i o n 5 . 2 . 4 ) , a nd the r e t u r n to th e p r o c e s s
o c c u r s t h r o ug h a n R E I i n s t r uc t i o n f r om I P L 2 .

I f the A S T r em o v e d f r om t h e q u e ue i s n o t a
spec i a l
ke r ne l
mod e AST ,
t h e n a c h e c k i s m a d e t o c o n f i rm th a t t h e mod e o f
t h e A S T i s a t l e a s t a s p r i v i l eg e d a s the d e s t i n a t i o n
of
the
RE I
i n s t r uc t i o n
that
i n i t i a t ed
AST d e l i v e r y .
Th i s
is
a c c ompl i s h ed b y c h e c k i ng the s a ved PS L o n the
ke rnel
s t ac k .
If
t h e m o d e o f t h e A S T i s n o t c o r r e c t , t h e AC B i s r e i n s e r t e d
a t the h e a d o f t h e q u e u e a nd t h e r o u t i n e
ex i ts
th r o ug h
the
RE I
i n s t r uc t i o n .
S i m i l a r checks a r e mad e fo r a l read y a c t i ve
A S Ts
and
f o r d i sa b l ed
access modes .
Th e c o r r e s pond i ng
AC B $ B_ASTACT b i t i s u n c o nd i t i o n a l l y s e t .

I f t h e A S T i s d e l i v e r ab l e , t h en the fo l l o w i ng o p e r a t i o ns
p e r fo rmed b e f o r e d i s pa tc h i ng to the AST r o u t i n e .

a re

I f t h e A C B i s a c c o un t ed f o r i n
the
PC B $W A S TCNT q uo t a ,
t h e n t h e c o u n t i s i n c r em e n t e d to s h o w d e l ive r y o f t h e A S T
a nd d e a l l o c a t i o n o f t h e ACB t o no npag ed po o l .

A S T LVL i s r ec ompu t ed bec a u s e t h e r emo v a l o f the f i r s t AC B
a l t e r s t h e s t a t e o f t h e A S T q ue ue .

A k e r n e l m o d e AST d o e s n o t r e qu i r e c h a ng i ng a c c e s s m o d e ,
Fo r
and
the
a pp r o p r i a t e
stack
is
a l read y ac t i ve .
the
e x e c u t i v e , s upe r v i s o r , a n d u s e r mode ASTs ,
h o wev e r ,
i n a c t i v e s t a c k po i n t e r i s o b t a i n ed .

A n a r g um e n t l i s t ( d e s c r i b ed i n t h e n e x t s e c t i o n )
o n t h e s t a c k o f t h e AS T ' s a c c e s s m o d e .

Fo r A S Ts fo r t h e o u t e r th r e e a c c e s s m o d e s , a PC/ P S L p a i r
o f l o ng wo r d s i s p u s h e d o n to the ke r n e l s t a c k .
Th e s to r ed
PC i s t h e l o c a t i o n E XE $ A S TD E L , the A S T d i s pa tc h e r .
Th e
s t o r ed
PS L c o n t a i n s t h e a c c e s s m o d e i n wh i c h t h e A S T i s
t o b e d e l i v e r ed i n b o th i t s
c u r r en t mod e
a nd
p r ev i o u s
mod e f i e l d s .

Th e AC B i s d e a l l o c a t e d a nd r e t u r n ed to
memo r y .

EXE $AS TDE L e x ec u t e s i n the a c c e s s m o d e o f t h e AS T .
Fo r
ke r n e l mod e ,
t h i s me r e l y � e q u i r e s d r o p p i ng t h e I P L t o
ze r o .
Fo r t h e o th e r a c c e s s mod es ,
t r ans f e r
of
control
a n d c h a ng e o f a c c e s s m o d e i s a c compl i sh e d th r o ug h a n R E I
i n s t r uc t i o n , t h e o n l y wa y t o
r each
a
l e s s p r i v i l eg ed
access mode
( Fi g u r e 1-4 ) .
( Th e PC a nd PS L u s e d b y t h e
R E I i n s t r uc t i o n a r e d e sc r i b ed a bove i n i t em 4 e . ) A CALLG
i n s t r uc t i o n
i s e x e c u t ed , t r a n s f e r r i ng c o n t r o l to th e AST
p r o c ed u r e , w i t h t h e a rg um e n t po i n t e r ( AP ) po i n t i ng t o t h e
a r g um e n t l i s t .

5-7

no npag ed

is bui l t

d yn am i c

AST D E LIVERY
5.3.2

A r g umen t L i s t

Us e r-wr i t t e n ASTs a r e p r o c ed u r e s , wh i c h m e a n s th a t t h e y c a n b e w r i t t en
I f they a r e w r i t te n i n a s s emb l y l a ng uag e , t h e y m u s t
i n a ny l a ng u a g e .
b eg i n w i th an en t r y m a s k a nd r e t u r n c o n t r o l to the i r c a l l e r
( th e AST
d i s pa t c h e r ) w i th a RET i n s t r uc t i o n .
F i g u r e 5 - 2 s h ows the a rg um e n t l i s t pa s s e d to a n AST p r o c ed u r e b y the
i n t e r r up t s e rv i c e r o u t i n e , ASTDE L .
Th e AS T p a r am e t e r i s o b t a i n e d f r om
th e AC B wh e r e it wa s i n i t i a l l y s to r ed by a
s ys tem s e rv i c e s uc h a s
$ S ETIMR,
o r $ DC LAS T .
Th e pa r am e t e r wa s o r i g i n a l l y a n a rg um e n t
$QIO,
t o th a t s ys tem s e rv i c e .
Th e i n t e r p r e ta t i o n o f the AST p a r am e t e r
is
the
r e s po n s i b i l i t y o f
the o r ig i na l
c a l l i ng
r o ut i ne
a nd
t h e AST
p r o c ed u r e .

ASTPRM
SAVED RO
SAVED R1
SAVED PC
SAVED PSL
Figure 5-2

� AP

A r g um e n t L i s t Pa s s ed t o AST by D i s p a tc h e r

Th e g e n e r a l pur po s e r eg i s t e r s , R O and R l , a r e s a v e d
i n t h e a rg um e n t
l i st beca use
the
p r o c ed u r e c a l l i ng c o n v e n t i o n d o e s n o t p r e s e r v e the
v a l u e s o f t h e s e r eg i s t e r s .
Th e a s yn c h r o n o u s n a t u r e o f ASTs
i mp l i e s
t h a t t h e R O a nd Rl c o n t e n t s a r e u n p r e d i c t a b l e a nd c a nno t b e d e s t r o yed .
Th e r eg i s t e r s a r e s a v e d a n d r e s to r ed b y t h e AST d e l i v e r y m e c h a n i sm .
Th e s a v ed PC a n d PS L v a l u e s a r e the r eg i s t e r c o n t e n t s o r i g i n a l l y s a v ed
wh e n
the
I PL 2
i n t e r r up t wa s i n i t i a t ed by the h a r d wa r e .
Th e v a l u e s
a r e n o rm a l l y t h e pa i r th a t wa s a b o u t t o b e u s ed b y t h e o r i g i n a l
RE I
i n s t r uc t i o n r eq ue s t i ng t h e AST d e l i v e r y .

5. 3. 3

AST Ex i t Pa t h

Wh e n t h e A S T r o u t i n e i s s ue s t h e R E T i n s t r uc t i o n , c o n t r o l
is
r e t u r n ed
to
the
l oc a t i o n
E XE $ASTRET i n the a c c e s s mod e o f the AST .
Th e c a l l
f r am e , b u t n o t t h e a rg um e n t l i s t , wa s r em o v e d f r om the c u r r e n t
s t ac k
Th e a rg um e n t l i s t r ema i n s b e c a u s e a CA LLG
by
the
R E T i n s t r uc t i o n .
r a th e r t h a n a CALLS i n s t r uc t i o n wa s u s ed to e x e c u t e the AST r o u t i n e .
Th e f o l l o w i ng s t e ps then o c c u r
•

Th e a r g um e n t c o un t a nd the AST p a r am e t e r a r e r emoved f r om the
s t a c k , l e a v i ng t h e R O , R l , PC , a nd PS L v a l ue s .

A
C HM K

=IJ: A S T E X I T

i n s t r uc t i o n i s e x e c u t ed , i nv o k i ng
the c h a ng e -mod e - t o - k e r n e l
s ys tem s e r v i c e d i s pa t c h e r
( d e sc r i b ed
i n Ch a pt e r 3 ) .
Th e
s e r v i c e c o d e o f z e r o ( A STEX I T
0 ) c a us e s the
no r m a l
kernel
m o d e d i s pa t c h i ng m e c h a n i sm t o b e bypa s s ed .
=

5-8

AST D E L IVERY
3.

I n s t e ad , wh i l e i n k e r n e l m o d e ,
e

t h e I PL i s r a i s e d to S YN C H ,

•

t h e a pp r o p r i a t e PC B $ B A S TACT b i t i s c l e a r e d t o s i g n a l AST
c ompl e t i o n , a n d

•

t h e ASTLVL v a l u e i s r ec o m p u t e d .

Th e s e f i e l d s c a n o n l y be wr i t t e n f r om k e r n e l m o d e .
Th i s
is
wh y
i t i s n e c e s s a r y f o r t h e AST d i spa tc h e r to r e e n t e r k e r ne l
m o d e a f t e r t h e AS T r e t u r n s c o n t r o l
t o t h e d i s pa t c h e r
a nd
be f o r e t h e AST d e l i v e r y i n t e r r upt i s d i sm i s s ed .
4.

An RE I i n s t r uc t i o n , s t i l l i n m o d u l e CMODS SDS P , d r o ps t h e
to z e r o , a nd r e t u r n s the a c c e s s m o d e to tha t o f t h e AST .

Co d e , i n t h e mo d u l e ASTDE L , r e s um e s a t
mo d e a n d I P L 0 by

the

•

r e s to r i ng t h e s a v e d RO and R l va l u e s , a nd

•

i s s u i ng a n o th e r RE I i n s t r uc t i o n .

p r ev i o u s

Th i s R E I i n s t r uc t i o n r e t u r n s c o n t r o l to the a c c e s s
l o c a t i o n o r i g i na l l y i n te r r up t ed by AST d e l i v e r y .

I PL

access

mod e

a nd

No te th a t t h e R E I i n s t r uc t i o n s
i n CMODS S D S P a nd ASTDE L m a y c a u s e
a no t h e r
I P L 2 i n t e r r upt t o o c c u r , d e p e nd i ng u po n t h e ASTLVL v a l u e a nd
the access mod e t r ans i t i o n s .

5. 4

S PE C IAL KERNEL ASTS

S p e c i a l k e r ne l m o d e ASTs a r e d i f f e r e n t f r om " n o rm a l " AS Ts
m a j o r wa ys :

seve r a l

Th e ASTs r e p r e s e n t un so l i c i te d o r i nv o l un ta r y s ys t e m a c t i o n s
th a t m u s t o c c u r i n t h e c o n t e x t o f t h e p r o c e s s .
Th e s e a c t i o n s
a r e f r e qu e n t l y r e q u e s t ed wh e n t h e p r o c e s s
is
not c u r r ently
e x e c u t i ng .

Th e spe c i a l k e r n e l mod e A S T r o u t i n e s a r e d i s pa t c h e d a t
I PL 2
and
ex ecute
at
tha t
l ev e l
o r h ighe r .
Syn c h r o n i z a t i o n i s
prov i d ed b y the
i n te r r up t m e c h a n i sm
i t se l f ,
r a th e r
than
r e q u i r i ng a d d i t i o n a l PC B $ B A S TACT a nd PC B $ 8 ASTEN b i t s .
On l y
o n e s pe c i a l k e r n e l m o d e A ST c a n b e a c t i ve a t a n y m o m e n t
b e c a u s e t h e AST d e l i v e r y i n t e r r up t i s b l o c k e d .

Th e s pe c i a l k e r n e l m o d e A S T r o u t i n e s a r e
i nvo k e d
by a
JSB
i n s t r uc t i o n
r a th e r
than a
CALLG i n s t r uc t i o n .
Th e r e i s n o
a rg um e n t l i s t ( t h e PC B a d d r e s s i s i n R4 a n d th e AC B a d d r e s s
is in R5)
•

Th e AS T r o u t i n e i s r e s po n s i b l e f o r th e
d eal locat ion of
the
AC B ( t o n o n pag ed poo l ) ( Fo r no rm a l ASTs , t h i s d e a l l o c a t i o n i s
d o n e b y t h e AST d e l i v e r y r o u t i n e . )

Th e r e t u r n f r om t h e AST r o u t i n e
( w i th
a n RS B
i n s t r uc t i o n )
pa s s e s c o n t r o l t o a n RE I i n s t r uc t i o n i n mod u l e ASTDE L .
Th i s
i n s t r uc t i o n
a t t emp t s t o p a s s c o n t r o l
to
the
o r i g i na l l y
i n t e r r up t e d
PC / P S L pa i r .
I P L w i l l d r o p f r om two to z e r o a t
t h e s am e t i m e .
5-9

AST D E L I VE RY
Th e n e x t f o u r s e c t i o n s b r i e f l y d e s c r i b e f o u r ex ampl e s o f
k e r n e l mod e A S T m e c h a n i sm .

the

spec i a l

I /O Po s tp r o c e s s i ng i n P r o c e s s C o n t e x t

5.4. 1

Pa r t o f the
s equence
of
c ompl e t i ng
an
I /0
r e q ue s t
i nv o l v e s
the
d e l i v e r y o f a spec i a l k e r n e l mod e AST t o t h e r e q ue s t i ng p r o c e s s .
I /0
p o s t p r o c e s s i ng i s d e s c r i b ed i n the VAX/VM S G u i d e to Wr i t i ng
a Dev i c e
D r i ve r .
Th i s
r e q ue s t
i s mad e
by
t h e I PL 4 ( I /O po s t p r o c e s s i ng )
i n t e r r u pt s e r v i c e r o u t i n e b y q ue u i ng t h e fo rme r I /0 r e que s t pa c k e t a s
a n ACB .
Th e o pe r a t i o n s pe r fo rmed by t h e I /0 c ompl e t i o n AST r o u t i ne
a r e tho s e th a t mu s t e x e c u t e i n p r o c e s s c o n t e x t ,
p a r t i c u l a r l y tho s e
tha t
r e fe r e n c e
process
v i r t ua l
add r esses .
Th e p r i m a r y o p e r a t i o n s
{ e x e c u t ed a t I PL 2 ) a r e the f o l l o w i ng .
1.

Fo r b u f f e r ed r e ad I/0 o pe r a t i o n s o n l y , t h e d a t a i s moved f r om
the
sys t em b u f f e r to the u s e r b u f f e r , and the sys t em b u f fe r
i s d e a l l o c a t e d t o nonpa g e d d yn am i c memo r y .

Th e b u f f e r ed o r d i r e c t I /0 c o un t f i e l d o f the p r o c e s s
i s i n c r emen t e d f o r a c c o un t i ng i n fo rm a t i o n .

I f a u s e r d i ag n o s t i c b u f f e r wa s
s pe c i f i ed ,
t h e d i a g no s t i c
i n f o rm a t i o n i s m o v ed f r om the s ys t em d i ag n o s t i c b u f f e r b e f o r e
i t i s d e a l l o c a t ed .

Th e c h a n n e l c o n t r o l b l o c k { i n the c o n t r o l r eg i o n ) i s
upd a t ed
t o show I /0 c omp l e t i o n .
Th i s may m a k e the c h a n n e l i d l e .

I f a n I/0 s ta tus block ( I OSB)
wa s
s p e c i f i ed ,
th e
wr i t t en f r om i n f o r ma t i o n i n the I /0 r e q u e s t pa c k e t .

I f a n AS T wa s s pec i f i ed
w i th
the
$ Q I O r e qu e s t ,
then
the
AC B $ V QUOTA b i t wa s
set
in
the
I RP .
Th e AST p r o c ed u r e
a d d r ess a nd t h e o p t i o n a l A S T p a r ame t e r we r e o r i g i n a l l y s to r ed
in
the
I RP
{ no w a n AC B ) .
Th e f o rme r I R P i s que ued to the
p r o c e s s a g a i n i n t h e a c c e s s m o d e of the r e q ue s t o r .

O t h e r wi s e , t h e I R P/AC B i s
m em o r y .

d e a l l o c a ted

no n pa g ed

header

I O SB

d yn am i c

P r o c e s s S u spen s i o n

5. 4. 2

Wh e n a $ S US PN D s ys tem s e r v i c e r e que s t spec i f i e s a p r o c e s s o th e r
th a n
the
r eque s to r ,
t h e s u s p e nd mec h a n i sm r eq u i r e s a s pe c i a l k e r n e l mod e
A S T t o e n t e r the c o n te x t o f the t a rg e t p r o c e s s .
Wh en the spec i a l k e rne l mod e AST i s d e l i v e r ed , t h e
a r e pe r fo rmed .

f o l l o wi ng

ac t i o n s

Th e ACB i s d e a l l o c a t ed to no npag ed d yn a m i c memo r y .

Af t e r
r a i s i ng
I P L f r om A S TDE L
{ I PL 2 )
to
S YNC H ,
the
PC B $V RE S PE N b i t
i s c l e a r ed .
I f a r e s ume wa s pend i ng , t h e n
t h e r e s um e h a s p r e c ed enc e .
Th a t i s , t h e A S T r o u t i ne e x i t s
w i thout
s us p e n d i ng
t h e p r o c e s s ( a f te r d r o pp i ng I PL b a c k t o
A S TDE L )
•

5-10

AST D E L I VE RY
3.

I f no r e s um e wa s p e nd i ng , t h e n th e p r o c e s s i s pl a c e d i n to the
SUSP wa i t s t a t e .
Th e p r o c e s s h a r d wa r e c o n t e x t i s s a v e d wi th
a SVPC TX i n s t r uc t i o n ( d e s c r i b ed in d e t a i l in Ch a p t e r 8 ) .
Th e
p r o c e s s q u a n t um f i e l d i n t h e p r o c e s s h e a d e r i s c h a r g ed w i th a
v o l un t a r y wa i t i n t e r v a l ( d e t e rm i n ed
by
the
spe c i a l
s ys t em
p a r am e t e r
I OTA ,
d e sc r i b ed i n Ch a pt e r 8 ) .
Co n t r o l i s p a s s e d
t o t h e s c h ed u l e r a t S C H $ S C H E D t o s e l e c t t h e n e x t p r o c e s s
fo r
e x e c ut i on .

Wh e n t h e p r o c e s s
f i n a l l y e x ec u t e s
ag a i n
( a f te r
a
$ R E S UM E s ys t em
s e rv i c e c a l l ) , the PC B $V S US P EN b i t i s unc o nd i t i o n a l l y c l e a r e d a nd t h e
p r o c e s s i s m a d e c om p u t a ble .

P r o c e s s De l e � i o n

5. 4. 3

Th e m a j o r po r t i o n o f t h e s t e ps i nv o l v e d i n p r o c e s s d e l e t i o n o c c u r i n a
s p e c i a l k e r n e l m o d e AST r o u t i n e q u e ued i n r e s po n s e to a $ D E LPRC s ys tem
s e rv i c e c a l l .
A d e t a i l ed e x p l a n a t i o n o f p r o c e s s d e l e t i o n i s p r o v i d ed
i n Ch a pt e r 1 9 .
Th e
use
of
the
s pe c i a l ke r n e l mod e A S T m e c h a n i sm
p r o v i d e s t h e f o l l o w i ng ben e f i t s .
•

Execut i on a s the c ur rent process
i s a c c o m p l i s h ed
b y AST
del ivery .
Ne a r l y a l l wa i t i ng p r o c e s s e s a r e m ad e c om p u t a b l e
$D E L PRC e n s u r e s the d e l e t i o n o f
b y AST d e l i v e r y ( Ch a p t e r 8 ) .
a s us p e n d ed p r o c e s s b y i s s u i ng a $ R E S UM E f i r s t .
E x e c ut i o n a s the c u r r e n t p r o c e s s
is
r e q u i r ed
fo r
p r oc e s s
v i r t u a l a d d r e s s t r a n s l a t i o n a nd o th e r o pe r a t i o n s t h a t r e q u i r e
p r o c e s s c o n t e x t { pa r t i c u l a r l y i n
o b t a i n i ng
the
i n fo rm a t i o n
c o n t a i n e d i n t h e c o n t r o l r eg i o n ) .

•

Th e d e l i v e r y o f d e l e t i o n ASTs
c a nn o t b e p r e v e n t ed
by the
$ S E TAST s ys t em s e r v i c e .
A p r o ces s can o n l y a v o i d d e l e t i on by
r a i s i ng I P L t o ASTDE L ( I PL 2 ) o r above
to
p r ev e n t a l l
AST
d e l i ve r i e s .
B e c a us e I PL c a n o n l y b e e l e v a t ed wh i l e i n k e r n e l
m od e , o n l y p r i v i l eg ed p r o c e s s e s ,
or
th e
s ys t em
a c t i ng
on
b eh a l f
of
some p r o c e s s ,
c a n e x pl i c i t l y p r ev e n t p r o c e s s
delet i on .

$GETJ P I Sys t em Se rv i c e

5.4.4

Th e
$ G E TJ P I
s ys tem
s e rv i c e
i s d e sc r i b ed
in
Ch a pt e r 2 7 .
Wh e n
i n fo r m a t i o n
is
r e q u e s t e d f o r a p r o c e s s o th e r th a n t h e r e q u e s to r , the
t a r g e t process mus t execu t e
t o e s t a b l i sh p r o c e s s c o n t e x t .
In
add i t ion ,
i f the
t a r g e t p r o c e s s i s o u t swa pped , t h e e n q u e u i ng o f the
s pe c i a l k e r n e l mode A S T w i l l make t h e
p r o c e ss
an
i n s wa p c a nd i d a t e .
Th i s a c t i o n b r i ng s
i n b o th
t h e wo r k i ng s e t a nd t h e p r o c e s s h e ad e r
{ wh e r e m uc h o f t h e a c c o un t i ng i n fo rm a t i o n i s ma i n t a i n ed ) .
I n g en e r a l t e r m s , t h e $ G E TJ P I A S T a c t i v i ty i s a s f o l l o ws .
1.

An AC B i s c o n s t r uc t ed f o r a s p e c i a l
k e r ne l
AST .
A s ys tem
b u f f e r i s a l so a l l o c a te d and a po i n t e r to i t i s p l a c ed i n the
AC B .

5-11

AST DELIVE RY
2.

Wh e n t h e s p e c i a l k e r ne l m o d e A S T r o u t i n e
ex ecutes
in
the
c o n tex t of
t h e t a r g e t p r o c e s s , t h e r eq u e s t ed i n fo rm a t i o n i s
m o v ed i n t o t h e s ys t em b u f fe r .
( Th e r eq ue s t s h a d b e e n e n c o d ed
in
the ACB . )
Th e
ACB
is
t h e n r e s e t to d e l i v e r a s p e c i a l
k e r n e l mod e AST t o t h e r e q ue s t i ng p r o c e s s .

Th e s e cond s p e c i a l k e r n e l mod e AST m o v e s d a t a f r om th e sys tem
buffer
i n to
a u s e r b u f f e r in t h e r e que s t i ng p r o c e s s .
Othe r
a c t i o n s i nc l ud e
•

d e a l l o c a t i ng t h e s ys t em b u f f e r ,

•

s e t t i ng a n e v e n t f l ag , a nd

•

d e l i v e r i ng an A S T i n t h e a c c e s s m o d e o f
r e que s t e d .

the

cal ler i

I f a n AS T i s d e l i v e r ed , t h e ACB i s u s e d f o r t h e
th i r d
I f no AS T i s d e l i v e r e d , t h e n th e AC B i s d e a l l o c a t e d .

5. 4. 5

t i me .

Po we r Recove r y ASTs

A f i na l e x a m p l e o f t h e u s e o f
s pe c i a l
k e r ne l
ASTs o c c u r s
in
the
i mp l em e n ta t i o n o f powe r r e c ov e r y ASTs , a t o o l th a t e n ab l e s p r o c e s s e s
t o r e c e i v e n o t i f i c a t i o n th a t a po we r f a i l u r e a nd
s uc c e s s f u l
r e s ta r t
h a v e o c c u r r ed .
( Po we r
f a i l u r e a nd powe r r e c ov e r y a r e d e sc r i b ed i n
Ch a pt e r 2 3 . )
Wh e n a s uc c e s s f u l po we r
r ecove r y o c c ur s ,
all
processes
th a t h a v e
e s ta b l i s h e d
a po we r
r e c o v e r y A S T a r e no t i f i ed f i r s t wi th a s p e c i a l
k e r n e l AST .
Th i s AST r e t r i ev e s i n fo rm a t i o n f r om t h e P l po i n t e r
pa g e
t h a t a l l o ws
the
u s e r - r e q u e s t ed A S T t o b e d e l i v e r ed .
Th e A S T i s
r e q u i r ed b e c a u s e P l s p a c e i n f o rm a t i o n i s o n l y a v a i l ab l e
f r om p r o c e s s
c o n tex t .

5.4.6

O t h e r Sys t em U s e o f ASTs

Th r e e o th e r f e a t u r e s w i th i n
the
execut ive
are
i m pl emented
th r o ugh
AS Ts ,
but
these
ASTs
a re
not
s pe c i a l k e r n e l ASTs .
Th e a u tom a t i c
wo r k i ng s e t ad j u s tm e n t th a t t a k e s pl a c e a t q ua n t um end ( Ch a p t e r s 8 a nd
1 3 ) a n d t h e C PU t i m e l i m i t ex p i r a t i o n a r e bo th i mpl em e n ted wi th no r m a l
Th e Fo r c e Ex i t s ys t em s e rv i c e ( Ch a p t e r s 9 and 1 8 ) c a u s e s
k e r ne l ASTs .
a u s e r m o d e A S T t o b e d e l i v e r ed to t h e t a r g e t p r o c e s s

5. 5

ATTENT I ON AST S

Ano th e r c a t eg o r y o f AST u s e i s t h e a t te n t i o n AST m e c h a n i sm .
At t e n t i o n
ASTs
a r e u s ed i n a s s o c i a t i o n w i t h I /0 o p e r a t i o n to no t i f y o n e o r m o r e
p r o c e s s e s o r r o u t i n e s o f a s p e c i f i c ( a nd u s ua l l y u n s o l i c i t ed ) ev e n t i n
a d ev i c e .

5-1 2

AST D E L I VE RY
S e t At t en t i o n Mecha n i sm

5. 5. 1

I n o r d e r to e s t ab l i sh a n a t t e n t i o n AST f o r a p a r t i c u l a r d ev i c e ,
the
user mus t
i s s ue
a $ Q I O s y s t em s e rv i c e r e q ue s t w i th t h e I /O f un c t i o n
I O $ S ETM ODE ( o r I O $ S E TC HAR f o r some d ev i c es )
Th e k i nd o f
a ttent i o n
AST- r e q u e s ted i s i ndi c a t ed b y a f un c t i o n mo d i f i e r .
•

Th e f o l l o w i ng s t ep s a r e p r ov i d ed
by
the
r o u t i ne
C OM $ S E TATTNAST i n
m o d u l e C OMDRVS UB .
( Th i s
r o u t i n e r e q u i r e s p r o c e s s c o n tex t a n d so i s
c a l l ed o n l y f r om d ev i c e d r i v e r FDT r o u t i n e s . )
1.

I f t h e u s e r AST r o u t i n e ad d r e s s ( t h e $ Q I O P l
p a r am e t e r )
is
zero ,
th e
r e que s t
is
i n t e r p r e t ed a s a f l ush a t t e n t i o n AST
1 i s t r e que s t ( S e c t i o n 5 . 5 . 3 )
•

An ex pa nd e d ACB ( th a t i s , a n I R P ) i s a l l o c a t e d f r om n o n pa g ed
d yn a m i c m em o r y .
Th e ACB i s d e d uc t ed f r om t h e p r o c e s s quo t a ,
PC B $W_A S TCNT .

I n f o r ma t i o n f r om t h e I /0 r e que s t pa c k e t
( s uch a s
t h e AST
rout i ne
e n t r y po i n t ,
AST p a r am e t e r , d e v i c e c h a n n e l n umbe r ,
a nd p r o c e s s I D ) i s moved i n to t h e AC B .

Th e AC B i s l i n k ed t o t h e un i t c o n t r o l
block
( UC B )
of
the
a s s o c i a t ed
d ev i c e
in
a
s i ng l y l i n k e d ,
l a st- i n f i r s t-out
( L I FO ) l i s t .

De l i v e r y o f A t t en t i o n ASTs

5. 5. 2

Th e occ u r r e n c e o f a s i t ua t i o n
fo r
wh i c h
a t te n t i o n ASTs h a v e b e e n
d e f i ned c a u s e s t h e d e l i v e r y o f a l l s uc h a t t e n t i o n AS Ts .
Th e m e c h a n i sm
o f d e l i v e r y i s i mpl emented i n t h e
rout i ne
C OM $ D E LATTNA ST o f m od u l e
C OM $ D E LATTNAST
is
u s ua l l y i nv o k e d by a d ev i c e d r i v e r a t
C OMDRVS UB .
d ev i c e I PL
( I PL 2 0
th r o ug h
23) ,
a fte r
s pec i f y i ng
wh i c h
l ist of
a t t e n t i o n AST f o r k b l o c k s/ACBs i s to b e u s e d .
Ea c h AC B i s o r i g i na l l y f o r m a t t e d a s a fo r k b l o c k w i th t h e AST f i e l d s
( Th e f i r s t s i x l o ng wo r d s o f t h e Un i t
l o c a t ed
a t d i f fe r ent o f fsets .
Co n t r o l B l o c k p i c t u r ed i n Append i x A o f the VAX/VM S G u i d e to Wr i t i ng a
t h e m o s t c ommon
e x ampl e o f a fo r k b l o c k . ) Th e
Dev i c e D r i v e r a r e
c o n t r o l b l o c k c o n t a i n s r e l e v a n t a d d i t i o n a l i n fo r m a t i o n s uc h a s
s a v ed
PC ,
R 3 , a n d R4 va l u e s , t h e c h a n n e l n um b e r fo r t h e d ev i c e , a nd the I PL
v a l u e fo r p r oc e s s i ng t h e AST
( I P L $ Q U E UEAST
I PL 6 ) .
Du r i ng
fo r k
p r o c e s s i ng , t h e c o n t r o l b l o c k i s r e form a t ted i n t o a s t a nd a r d ACB .
=

Wh e n C OM $ D E LATTNAST b eg i n s e x e c u t i o n , t h e CPU i s u s ua l l y e x e c u t i ng
at
d ev i c e I PL .
Th e q ue u i ng o f A S Ts i s a n o pe r a t i o n us i ng I P L $ SYNCH a s a
s yn c h r o n i z a t i o n m e c h a n i sm ( Ch a p te r 2 4 ) .
Spe c i f i c a l l y ,
I PL m u s t b e
r a ised
to
SYNC H .
T o a c compl i s h c o r r e c t s yn c h r o n i z a t i o n , t h e I P L 6
f o r k d i s pa tc h e r i s u s ed .
Th e fo l l o w i ng s t eps s umma r i z e t h e d e l i v e r y o f a t t e n t i o n ASTs .
1.

At
I PL 2 0
t h r o ug h
23,
e a c h a t t e n t i o n AST f o r k c o n t r o l
b l o c k/AC B i s r em o v ed f r om t h e a pp r o p r i a t e l i s t i n the r e v e r s e
o rd e r o f d ec l a r a t i o n .
Ea c h b l o c k i s e n que ued
to the
I PL 6
f o r k q u e ue l i s t h e ad .

Th e r o u t i n e i nv o k e s t h e FORK s ys tem m a c r o to no t i f y t h e
d i s pa t c h e r t h r o ug h t h e I P L 6 s o f twa r e i n te r r up t .
5-1 3

fo r k

AST D E L I VERY
3.

As t h e i n t e r r up t p r i o r i t y l ev e l o f t h e CPU d r o p s be l o w s i x ,
the
fo r k
i n te r r up t
is
ta ken .
Th e
I P L $ Q U E UEAST f o r k
d i s p a t c h e r r emov e s e a c h f o r k c o n t r o l b l o c k f r om i t s q u e u e a nd
p a s s e s t h e c o n t r o l b l o c k b a c k to a l o c a t i o n i n C OM $D E LATTNAST
a t I PL 6 .

At I P L 6 t h e f o r k c o n t r o l b l o c k i s t h e n r e f o r m a t t e d
i n to
an
AC B ,
r e p r e s e n t i ng
a n AST in the access mod e of the o r i g i na l
r equesto r .

Th e AC B i s t h e n que u e d t o the p r o c e s s th r o ug h S C H $ QAST ( wh i c h
w i l l i mmed i a t e l y r a i s e I P L to I P L $_S YNC H ) .

5. 5. 3

Fl u sh i ng a n A t t e n t i o n A S T L i s t

Th e l i s t o f a t te n t i o n A S Ts i s f l u s h e d a s t h e
r esul t o f
a n expl i c i t
use r
r e q ue s t , a c a n c e l I /0 r e q ue s t , o r a d e a s s i g n c h a n n e l r e que s t f o r
t h e a s s o c i a t e d d ev i c e .
An e x p l i c i t u s e r r e q ue s t t o f l u s h t h e a t t e n t i o n AST l i s t i s
pe r f o rmed
as
the
r esul t o f
a
s e t a t t en t i o n A S T r e que s t w i th a n AST r o u t i n e
add r e s s o f ze ro
( Se c t i on 5 . 5 . 1 ) .
C OM $ S E TATTNAST t h e n b r a n c h e s
to
C OM $ F L U S HATTNS .
Dev i c e d r i v e r s c a n r e q ue s t the f l u s h i ng o f t h e a t t e n t i o n AST l i s t b y
e i th e r
i nvo k i ng C OM $ S E TATTNA S T w i t h a n A S T r o u t i n e a d d r e s s o f z e r o o r
by d i r ec t l y i nv o k i ng C OM $ F L USHATTNS w i th t h e
channel
n um b e r
of
the
d ev i c e i n R 6 .
C OM $ F LUS HATTN S pe r fo rm s t h e fo l l o w i ng o pe r a t i o n s .
l.

Th e I PL i s r a i s ed to t h e h a r d wa r e I P L o f t h e
t h r o ug h 2 3 )

d ev i c e

( I PL 2 0

•

As e a c h c o n t r o l b l o c k i n t h e a t t e n t i o n AST l i s t i s f o und , t h e
process
I D o f t h e p r o c e s s r e que s t i ng t h e f l u s h i ng o pe r a t i o n
i s c ompa r e d w i th t h e p r o c e s s I D s t o r ed i n t h e c o n t r o l b l o c k .
An A S T c o n t r o l b l o c k i s r e t a i n ed i n t h e a t t e n t i o n AST l i s t i f
t h e p r o c e s s I Ds d o no t m a t c h .

I f t h e p r o c e s s I Ds m a t c h ,
then
the channel
n umbe r s m u s t
match .
On e
channel
number
i s pa s s ed i n R 6 f r om t h e f l ush
r e q u e s t , a nd the o th e r i s
in
the c o n t r o l
block
f r om
the
d e c l a r a t i o n o f t h e AS T .
I f the c h a n n e l n um b e r s d o n o t m a tc h ,
t h e n t h e c o n t r o l b l o c k i s r e t a i n e d i n t h e a t t e n t i o n AST l i s t .
O t h e r wi s e ,
the
contr o l
b l o c k i s r emoved f r om the a t t e n t i o n
AST l i st .

I PL i s d ro pp e d f r om d ev i c e i n t e r r up t
2 3)

l ev e l

( I PL 2 0

t h r o ug h

•

Th e ASTCNT q uo t a i s i nc r em e n ted to i nd i c a t e
the cont rol block .

5-14

d ea l loc a t i on

AST DELIVE RY

5 . 5. 4

Th e c o n t r o l b l o c k i s d e a l l o c a t e d to no npag ed d yn am i c memo r y .
Th i s o pe r a t i o n r e qu i r e s e x e c u t i o n t h r o ug h t h e fo r k d i spa t c h e r
a t I PL $ Q U E UEAST t o e n s u r e p r ope r s yn ch r o n i z a t i o n wi th
! PL .
( Ac t ua l - d e a l l o c a t i o n
i s done
at
I PL 1 1
a s d e sc r i b ed i n
Ch a p t e r 2 5 . )

P r o c e s s i ng c o n t i n u e s un t i l the e n t i r e a t t e n t i o n AST l i s t
b e en sc anned .

has

E x a mp l e s i n VAX/VMS

Two d ev i c e s tha t c ommo n l y h a v e a t t e n t i o n ASTs a s s o c i a t e d wi th t h em a r e
t e rm i n a l s a nd ma i l bo x e s .
B r i e f d e sc r i p t i o n s o f
the
s uppo r t f o r
a t te n t i o n ASTs i n t h e s e d ev i c e d r i v e r s c o n c l ud e s t h i s c h a p t e r .

5 . 5 . 4 . 1 Te rm i n a l Dr i v e r a n d C TRL/Y No t i f i c a t i o n - Th e
t e rm i n a l
I O $ S E TMODE a n d
I O $ S E TCHAR f un c t i o n s m a y t a k e
I O $M CTRLCAST a nd
I O $M C TR LYAS T f un c t i o n mo d i f i e r s .
Wh e n
a
C TRL/C
i s -t ype d
on a
t e rm i n a l ,
t h e C T R L/C a t t en t i o n AST l i s t i s empt i e d by d e l i v e r i n g e a c h
C TRL/C A S T a s so c i a t ed w i th t h e t e rm i n a l .
I f n o C TRL/C a t t e n t i o n AST
i s d e c l a r ed , t h e n the C TRL/C i s i n te r p r e t ed a s a C TRL/Y a nd th e CTR L/Y
A S T l i s t i s s e a r c h ed i n s t e a d .
I f a CTR L/Y i s t yped , o n l y the
CTR L/Y
a t t e n t i o n AST l i s t i s empt i e d .
B e c a u s e the l i s t i s empt i e d e a c h t i m e a C TR L /Y o r a CTRL/C
is
t yped ,
b o th C TRL/C a n d CTRL/Y a t t e n t i o n ASTs m u s t b e r e e n a b l ed e a c h t i m e th e y
a r e d e l i v e r ed to a p r o c e s s .

5 . 5 . 4 . 2 Ma i l bo x D r i v e r - Th e I O $ M READATTN a n d I O $M WRTATTN
f unc t i o n
m od i f i e r s
p r ov i d e
n o t i f i c a t i o n- o f ma i l bo x
r e que s t s
f r o m o th e r
processes .
I O $M WRTATTN p r o v i d e s n o t i f i c a t i o n o f un so l i c i t ed i n p u t to
a m a i l bo x .
I O$M R EADATTN n o t i f i e s
the
e n ab l i ng
p r o c e s s wh e n a n y
p r o c e s s i s s ue s a r�a d t o a m a i l bo x wh en no m e s s a g e i s a v a i l a b l e .
Mu l t i p l e a t te n t i o n ASTs o f e a c h type m a y b e d e c l a r ed by p r o c e s s e s
fo r
the
s am e m a i l bo x .
Wh e n a c o nd i t i o n co r r e s pond i ng to an a t t e n t i o n AST
o c c u r s i n a ma i l bo x , a l l A S Ts of t h e a pp r o p r i a t e type
a r e d e l i v e r ed .
On l y t h e f i r s t p r o c e s s to i s s ue a r e s po nd i ng I /0 r e que s t wi l l be a b l e
t o compl e t e the t r a n s f e r o f d a t a s i g n a l l ed b y t h e a t t e n t i o n ASTs .
Re a d a nd wr i t e a t t e n t i o n ASTs m u s t b e r e e n ab l ed a f t e r d e l i v e r y b e c a u s e
the ent i re
a t te n t i o n AS T l i s t i s d e l i v e r e d ( a nd r emoved ) a f t e r e a c h
o c c u r r en c e o f t h e s pe c i f i e d c o nd i t i o n .

5-1 5

CHAPTER 6
HARDWARE INTERRUPTS

VM S i s an i n t e r r upt-d r i v e n o pe r a t i ng s ys tem .
I t conta i n s a co l l e c t i on
of
i n t e r r up t
serv i c e
rout ines
t h a t e x e c u t e i n r e s po n s e to h a r d wa r e
i n t e r r u p t s f r om e x t e r n a l d ev i c e s a nd
i n te r n a l
dev i c e s
such
as
the
c l oc k .
VM S d o e s n o t h a v e a s o f twa r e - b a s e d c e n t r a l d i s p a t c h i ng mod u l e
t h a t r e c e i v e s no t i f i c a t i o n o f a l l s y s t em events ( th a t i s ,
i n t e r r up t s )
and
d ec i d e s
wh a t
to
do
nex t .
I n s t ead ,
VM S
re l i es o n a
h a r d wa r e- c o n t r o l l ed i n t e r r upt d i s pa tch i ng sc heme
th a t
a l wa ys
forces
t h e h i g h e s t pr i o r i t y i n te r r upt o n t h e s ys t em to b e se rv i c ed f i r s t .

6.1

HARDWARE INTERRUPT D I S PATC H I NG

Th e VAX a r c h i t e c t u r e p r ov i d e s 1 6 h a r d wa r e
i n t e r r up t p r i o r i t y l e v e l s
( I PL ) ,
f r om
I PL
3 1 d o wn to I P L 1 6 .
Th e t o p 8 l e v e l s a r e fo r u s e by
u r g e n t c o nd i t i o n s i n c l ud i ng se r i o u s e r r o r s ( s uch
as m a c h i n e
chec k ) ,
the
s y s t em
c l o c k , a n d powe r f a i l u r e .
Th e s e c o nd i t i o n s a r e d i s c u s s e d
i n c h a p t e r s 7 , 1 0 , a nd 2 3 r e spe c t i v e l y .
Th e l o we r
e ight
l ev e l s
are
u s ed b y pe r i ph e r a l d e v i c e s .
Wh e n a pe r i ph e r a l d e v i c e g e ne r a t e s a n
i n te r r up t ,
th a t
i n t e r r up t
is
r eque s ted a t a pa r t i c u l a r h a r d wa r e I P L ( f i x ed fo r a g i v e n d e v i c e ) .
As
i n t h e c a s e o f s o f twa r e i n t e r r u p t s , i f
the
r e que s t ed
I PL v a l u e
is
h ighe r
t h a n the l ev e l a t wh i c h t h e p r o c e s s o r i s c u r r e n t l y r un n i ng ( a s
d e t e r m i n ed by PS L < 2 0 : 1 6 > ) , t h e n th e i n t e r r up t s e r v i c e
r o u t i n e wh o s e
a d d r e s s i s i n t h e s e l e c ted v e c t o r i n t h e Sy s t em Co n t r o l B l o c k ( S C B ) i s
e n t e r ed i mmed i a t e l y .
Ot h e r w i s e , t h e
i n t e r r upt
servi�e
is
d e f e r r ed
u n t i l I P L d r o ps b e l o w t h e l ev e l a s so c i a t ed w i th t h e i n t e r r up t .
Wh e n a n i n t e r r up t i s s e r v i c ed , t h e c u r r e n t p r o c e s s o r
s t a tus mus t be
p r e s e rved
so
th a t
the
i n t e r r upted
th r e a d
of
executi o n
( e i th e r
p r o c e s s - b a s e d c o d e o r a n i n t e r r up t s e r v i c e r o u t i n e ex e c u t i ng a t
l o we r
I PL }
c a n c o n t i n u e no rm a l l y a f t e r the i n t e r r upt i s d i sm i s s ed .
Th i s i s
a c c ompl i shed ( b y the h a r d wa r e ) by a u tom a t i c a l l y s a v i ng t h e PC and
PS L
on
the
s ta c k .
Th e s e a r e l a te r r e s t o r e d wi th a n RE I i n s t r u c t i o n th a t
d i sm i s s e s t h e i n t e r r up t .
O t h e r e l em e n t s o f the p r o c e s s c o n t e x t ,
s uc h
a s g ener a l
r eg i s t e r s ,
m u s t b e s a v e d and r e s to r ed b y t h e r o u t i n e ( s )
h a nd l i ng t h e i n t e r r up t .
I n o r d e r to
r ed uc e
i n t e r r upt
ove rhead ,
no
m emo r y m a pp i ng
i n fo rma t i o n
i s c h a ng ed
wh en a n
i n t e r r u pt o c c u r s .
Th e r e f o r e , t h e
i n s t r uc t i o n s
a nd
d a ta
r e f e r e n c ed
by
an
i n t e r r up t
s e r v i c e r o u t i n e m u s t b e i n s ys tem ad d r e s s s p a c e .

6-1

HARDWARE INTERRUPTS
I n t e r r up t D i s p a t c h i ng

6.1.1

Th e f o l l o wi ng l i s t o u t l i n e s the p r i m a r y s e q u e n c e o f e v e n t s tha t
i n i n t e r r upt d i s pa tc h i ng .

occur

An i n t e r r up t i s r e q ue s ted .

Th e c u r r e n t i n s t r uc t i o n f i n i s h e s o r r e a c h e s a
we l l d e f i n e d
po i n t wh e r e t h e i n s t r uc t i o n s t a t e i s c ompl e t e l y c o n t a i n e d i n
t h e g e n e r a l r eg i s t e r s , PC , a nd
PS L
( wh i c h h a ppe n s
in
the
( S ome
i n s t r uc t i o n s c a n a l so
be
s t r i ng
i n s t r uc t i o ns ) .
i n t e r r up t e d a t we l l d e f i n ed
po i n t s
s uc h th a t ,
a f te r
the
i n te r r upt
d i sm i s s a l ,
they
are
r e s t a r t ed ,
r a th e r
th a n
c o n t i n ued . )

Th e i n t e r r up t s e q u e n c e i s i n i t i a t ed by t h e h a r d wa r e ,
push i ng
t h e c u r r e n t PC s a nd PS L o n the s t a c k .
VM S u s e s the i n te r r up t
stack
fo r
all
h a rd wa r e
i n t e r r up t
s e r v i c i ng .
Th i s
is
i nd i c a ted
by p l a c i ng
a
01
i n b i t s < 1 : 0 > o f e a c h h a r d wa r e
i n t e r r upt v e c to r i n the s ys tem c o n t r o l b l o c k ( F i g u r e 6 - 1 ) .
Mo s t s o f t wa r e i n t e r r up t s a r e a l so s e r v i c ed o n t h e
i n t e r r upt
stack .
On
the o th e r
h a nd ,
the
pe r - p r o c e s s
i n t e r r upt
a s s o c i a t ed w i th AST d e l i v e r y a nd n e a r l y a l l
except i ons a r e
s e r v i c ed o n t h e pe r - p r o c e s s k e r n e l s t a c k .
31

0
Address of longword-aligned
interrupt service routine

Code

SCB vector

Meaning

Code
00

Service event on kernel stack u nless currently on interrupt stack; in which
case, use interrupt stack.

Service event on interrupt stack; if event is an exception, raise IPL to 31 .

Service event i n Writable Control Store (WCS), passing bits <1 5:2> to micro
code; if WCS does not exist or is not loaded, the operation is UNDEFI NED
(the VAX-1 1 /750 and the VAX-1 1 /780 will HALT).

Operation i s UN DEFINED {the VAX-1 1 /750 and the VAX-1 1 /780 will HALT).

Figure 6-1

Sy s t em Co n t r o l B l o c k Ve c to r Fo rma t

A n e w PC i s l o a d ed ( f r om t h e a pp r o p r i a t e S C B v e c to r ) ,
and
a
n e w PS L
is
c r e a ted
( w i th
PS L < 2 0 : 1 6 >
c o n t a i n i ng
the I P L
a s s o c i a t ed w i th t h e i n t e r r upt , a nd the p r ev i o u s a c c e s s mo d e ,
c u r r e n t a c c e s s m o d e , CM , T P , FPD , DV , FU , I V , T , N , z , a nd C
b i t s c l e a r e d by t h e h a r d wa r e ) .

Th e i n t e r r up t s e r v i c e r o u t i n e i d e n t i f i e d by the PC i n the SCB
is
exec uted ,
and
ev e n t u a l l y e x i t s w i th a n RE I i n s t r uc t i o n
th a t d i sm i s s e s t h e i n te r r up t .

Th e PC a n d PS L a r e r e s to r ed
by
the
e x ec ut i o n o f
the
RE I
i n s t r uc t i o n , a nd t h e i n t e r r upted th r ead o f e x e c u t i o n { p r o c e s s
o r l e s s i mpo r t a n t i n te r r up t s e r v i c e r o u t i n e ) c o n t i n u e s wh e r e
it l eft off .
6-2

HARDWARE INTERRUPTS
Unl i k e so f twa r e i n t e r r up t d i spa t c h i ng ,
th e r e
i s not a
one- to-one
c o r r e sp o nd e n c e b e t we e n h a r d wa r e I PL a nd a n i n t e r r up t s e r v i c e r o u t i n e
v e c to r i n the SCB ( F i g u r e 6 - 2 ) .
Th e SCB c o n ta i n s
the
add r esses o f
sever a l
i n te r r up t
s e rv i c e
routines
fo r
a g i v e n d ev i c e ! P L .
Al so ,
t h e r e a r e no r eg i s t e r s c o r r e s po nd i ng to t h e So f t wa r e I n t e r r upt Re qu e s t
Reg i s t e r ( PR $ S I RR ) o r S o f twa r e I n t e r r up t S umma r y Reg i s te r ( P R $ S I S R ) .
Th e d ev i c e m ust c o n t i n ue to r e q u e s t a n i n t e r r up t un t i l
the
p r oc e s s o r
I PL d r o ps l ow e n o ug h so t h a t t h e i n t e r r up t i s g r a n ted .
SCB (System Control Block)

•

SCBB
{physical
address
of start
of SCB)

•
•
•

Various exceptions and
software Interrupts
(Figure 2-1 )

offsets
In
SCB

•
•

.
.

•

1 0016
IPL 20
interrupts

•
•

1 4016
IPL 21
interrupts

•

.
.

1 8016
IPL 22
interrupts

l
J1

)

16 vectors,
one for
each
number

I 16 vectors
)

)

1 6 vectors

)

1 6 vectors

•
•

1 C01&

IPL 23
interrupts

•
•
•

A second SCB page exists on
the VAX-11nso for directly

vectored UNI BUS device Interrupts

Figure 6-2

Sys t em Co n t r o l B l o c k Ve c to r s f o r Ha r d wa r e I n t e r r up t s

6-3

HARDWARE INTERRUPTS
6.1.2

Sys t em Co n t r o l B l o c k

Th e Sy s t em Co n t r o l B l o c k ( S C B ) c o n t a i n s t h e v e c to r s u s e d
to d i spa tch
( s o f twa r e a nd
h a r d wa r e )
i n te r r up t s
a nd
ex cept i on s .
Th e s t a r t i ng
ph ys i c a l a d d r e s s o f t h e S C B i s f o und i n t h e Sys t em Co n t r o l B l o c k Ba s e
Reg i s t e r
( PR $ S C B B ) .
Th e
s i ze
of
t h e S C B v a r i e s d e pend i ng o n
p r oc e s s o r t ype: Th e VAX- 1 1 / 7 5 0 s ys t em c o n t r o l b l oc k
is
t wo
pag e s
l o ng .
Th e VAX- 1 1 / 7 8 0 s ys t em c o n t r o l b l o c k c o ns i s t s o f a s i ng l e pag e .
Th e f i r s t pag e o f t h e s y s tem c o n t r o l b l o c k i s t h e o n l y pag e d e f i n e d b y
t h e VAX a r c h i t e c t u r e .
It
conta ins
t h e a d d r e s s e s o f s o f t wa r e a nd
h a r d wa r e i n t e r r upt s e r v i c e
r out ines
a s we l l
as
ex cept i o n
serv i c e
r o ut i n e s .
Th e l a yo u t o f t h e f i r s t S C B p a g e i s p i c t u r ed i n F i g u r e 2 - 1 .
Ta b l e 4 - 1 c o n t a i n s mo r e d e t a i l s
about
the
SCB v e c to r s u s ed
fo r
s o f twa r e
i n t e r r up t s .
F i g u r e 6 - 2 s h ows h o w t h e s e c o nd h a l f o f t h e
f i r s t pag e
is
d i v i d ed
amo ng
1 6 po s s i b l e
e x t e r n a l d ev i c e s ,
e a ch
i n t e r r up t i ng
a t f o u r po s s i b l e I P L v a l ue s .
Th e s e c o nd SCB pag e o n th e
VAX- 1 1 /7 5 0 i s u s e d fo r d i r e c t l y v e c t o r ed UN I B U S d ev i c e i n te r r up t s .
E a c h v e c to r i n t h e SCB i s a l o ng wo r d th a t i s e x am i n ed by t h e p r o c e s s o r
wh e n a n ex c e p t i o n o r i n t e r r up t o c c u r s , t o d e t e rm i n e h o w t o s e r v i c e t h e
event .
F i g u r e 6 - 1 i l l us t r a t e s t h e f o rm a t o f a v e c t o r i n the SCB ,
a nd
i nd i c a t e s wh i c h
stack
i s u s e d to s e rv i c e a n ex c e pt i o n o r i n t e r r up t .
I n VAX/VM S , a l l h a r d wa r e i n t e r r up t s ( a nd a l l s o f twa r e i n t e r r up t s a b o v e
I PL 3)
are
s e r v i c ed
on
the
s ys t em-w i d e
i n t e r r upt
s t ac k .
Th e
r e s c h e d u l i ng s o f twa r e i n te r r up t ( I P L 3 ) m a y b eg i n e x e c u t i o n o n t h e
ke rnel
s tac k but
i mmed i a t e l y c h a ng e s to t h e i n te r r up t s t a c k wh e n i t
e x e c u t e s a SVPCTX i n s t r uc t i o n ( Ch a p t e r 8 ) .
AST d e l i v e r y
( I PL 2 )
is
s e r v i c ed u s i ng a p r o c e s s - s p e c i f i c k e r n e l s t a c k .

6 . 1 . 2 . 1 VAX- 1 1 /7 5 0 E x t e r n a l Ad a pt e r s - Th e b a c kpl a n e i n t e r c o n n e c t o n
t h e VAX- 1 1 /7 5 0 , c a l l ed th e CM I ( C PU t o memo r y i n t e r c o n n e c t ) , c o nnec ts
Each
t h e C P U , memo ry c o n t r o l l e r s , a nd UN I B US
or
MAS SBUS a d a p t e r s .
c o nn e c t i o n
to
t h e CM I i s i d e n t i f i e d b y i t s s l o t n um be r .
Th e r e a r e a
t o t a l o f 3 2 s l o t s , t h e f i r s t 1 6 o f wh i c h a r e
used
fo r
the o p t i o n a l
wr i t ab l e c o n t r o l
store
( WC S ) .
Th e n e x t 1 0 s l o t s a r e r e s e r v ed f o r
memo r y c o n t r o l l e r s a nd UN I B U S o r MAS S B U S a d a pt e r s .
Th e s e 1 0 s l o t s a r e
c a l l ed
f i x ed
s l o t s b e c a u s e t h e m a pp i ng o f c o n t r o l l e r / a d a pt e r to s l o t
n umb e r i s
f i x ed .
Th a t
is,
a
pa r t i c u l a r
s l o t c an h a v e onl y a
pa r t i c u l a r
a d a p te r
p l a c ed
in
it.
F i v e o f the t e n f i x ed s l o t s a r e
c u r r e n t l y u s e d by e x t e r n a l a d a p t e r s .
Th e s e ad apte r s a r e :
Memo r y Co n t r o l l e r
U p t o th r e e MAS S B U S Ad a p t e r s
UN I BUS Ad a p t e r

Slot 0
S l o t s 4 th r o ug h 6
Slot 8

Th e l a s t s i x
s l o ts a r e
r e se rved
fo r
a d a pt e r s
r eg i s t e r s , a nd a r e c a l l ed f l o a t i ng s l o t s .

w i th

conf ig ura tion

E a c h s l o t h a s f o u r SCB v e c to r s i n t h e f i r s t S C B pa g e a s s i g ned
to
it,
one
fo r
e ach
I P L v a l u e f r om 2 0 t o 2 3 .
As s h o wn i n F i g u r e 6 - 2 , t h e
f i r s t 1 6 v e c to r s a r e a s s i g n e d t o I P L 2 0 a n d s o o n .
Th e
s e c o nd
SCB
pag e
on
t h e VAX- 1 1 / 7 5 0
i s u s ed fo r d i r e c t l y v e c to r ed UN I B US d e v i c e
i n t e r r up t s .
E a c h S C B v e c to r c o r r e s po nd s to a
UN I B US v e c to r
in
the
r a ng e f r om 0 to 7 7 4 ( o c t a l ) .

6-4

HARDWARE INTERRUPTS
6 . 1 . 2 . 2 VAX- 1 1/7 8 0 E x t e r n a l Ad a p t e r s - On
the
VAX- 1 1 /7 8 0 ,
the
Sync h r o n o u s
Ba c k p l a n e
Inte r connec t
( SB I )
c o n ne c t s
the C PU , m emo r y
contro l lers
( i n c l ud i ng MA7 8 0 s ) ,
DR7 8 0 s ,
a nd
UN I B US
or
MAS S B US
a d a pte r s .
E a c h c o n n ec t i o n to t h e S B I i s a s s i g n ed a t r a n s f e r r e q u e s t
( TR ) n um b e r t h a t i d e n t i f i e s i t s S B I p r i o r i t y .
T R n um b e r s r a ng e f r om 0
( h i g h e s t p r i o r i ty )
to
1 5 ( l o we s t p r i o r i ty ) .
Th e r e i s a l i m i t o f 1 5
c o n n ec t i o n s t o t h e S B I
( Ta b l e 6 - 1 ) .
TR 0
is
used
fo r
a
spec i a l
pu r po s e o n the S B I a n d h a s n o c o r r e s po nd i ng ex t e r n a l a d a pt e r .
Ta b l e 6 - 1
S t a nd a r d SB I Ad a pt e r As s i g nm e n t s o n the VA X- 1 1 /7 8 0

E x t e r n a l Ad a pt e r Type

VAX-1 1 /7 8 0
As s i g nm e n t

TR 0

F i r s t Memo r y Co n t ro l l e r

TR 1

S e c o nd Mem o r y Co n t r o l l e r

TR 2

Commen t s

Ho l d L i n e fo r n e x t c yc l e
Th i s i s t h e h i g h e s t T R l ev e l .
( Th i s TR l ev e l i s no t
a s s i g ned to a d ev i c e . )

F i r s t MA78 0 S h a r ed Memo ry
Se c o nd MA7 8 0 Sh a r ed Memo r y
F i r s t UN IB US Ad a pt e r

TR 3

S e c o nd

TR 4

UN I B US Ad a pt e r

Th i r d UN IB US Ad a pt e r

TR 5

Fo u r th UN I B U S Ad a pt e r

TR 6
TR 7

F i r s t MASSB US Ad a pt e r

TR 8

S e c o nd MAS SB US Ad a pt e r

TR 9

Th i rd MAS S B U S Ad a p t e r

TR 1 0

Fo u r th MA S S B US Ad a pt e r

TR 1 1

DR7 8 0 S B I

TR 1 2

In t e r fa c e

Re s e r ved

TR 1 3

R e s e r v ed

TR 1 4

R e s e r ved

TR 1 5

Re s e r ved

TR 1 6

Th e C PU has i m pl i c i t TR 1 6 .
Th i s i s the l owe s t TR l ev e l .

An a d a p t e r i s n o t r e s t r i c t ed to h av i ng a spec i f i c TR n um be r .
H o we v e r ,
the
r e l a t i v e p r i o r i t i e s o f t h e v a r i o u s a d a pte r s m a y n o t c h a ng e .
Th a t
i s , a s ys t em c a nno t h av e a n MBA w i th a h i g h e r
p r i o r i ty
{ l o we r
TR
n umbe r )
than a
UBA .
Fo r i n s t a n c e , i f a s ys t em h a s t wo l o c a l m em o r y
c o n t r o l l e r s a nd a n MA7 8 0 s h a r ed m emo r y c o n t r o l l e r ,
the
f i r s t UN I B US
a d a pt e r
on
tha t sys t em c o u l d h a v e TR n umbe r 4 , w i th t h e MA 7 8 0 h a v i ng
TR n um b e r 3 , a nd the m emo r y c o n t r o l l e r s h av i ng TR n umb e r s 1 a n d 2 .

6-5

HARDWARE INTERRUPTS
6 . 1 . 2 . 3 Ad apte r C o n f i g u r a t i o n - O n bo th p r o c e s so r s , the
pr esence o f
a n ad a p te r a t a pa r t i c u l a r s l o t o r T R n um b e r i s c h e c k e d b y t e s t i ng the
f i r s t l o ng wo r d i n the a d a pt e r ' s I /0 r eg i s t e r spa c e , a nd
c h e c k i ng
fo r
n o n e x i s t e n t m emo r y .
Th e p r e s e n c e o r a b s e n c e o f a n e x t e r n a l a d a pt e r i s
d e t e r m i n ed b y th e p r i m a r y b o o t s t r a p p r og r am VMB ( Ch a p t e r 2 1 )
a s pa r t
of
that
p r og r am ' s m emo r y s i z i ng o pe r a t i o n .
S p e c i f i c a l l y , VMB l o ad s
t h e m a c h i n e c h ec k v e c to r i n t h e SCB w i t h t h e a d d r e s s o f a
spec i a l
r o u t i n e wh i l e
it
is
s 1 z 1 ng
memo r y a nd d e t e rm i n i ng wh i c h e x t e r n a l
a d a pt e r s a r e p r e s e n t .
I f a n o n e x i s t e n t memo r y m a c h i ne c h e c k o c c u r s ,
there
is
no
c o nn e c t ed
a d a pt e r
at
t h e l o c a t i o n b e i ng t e s t e d .
Th e
r e s u l t o f th i s t e s t i ng
is
s to r ed
in a
1 6 -by t e a r r a y i n a
d a ta
s t r uc t u r e c a l l ed a r e s t a r t pa r am e t e r b l o c k ( RPB ) .
La t e r s t a g e s o f t h e
i n i t i a l i z a t i o n u s e t h e i n fo rm a t i o n o b t a i n e d b y VMB a n d s to r ed
in
the
R PB wh e n t h e y c o n f i g u r e s p e c i f i c a d a pt e r s i n to t h e s y s tem .
On bo t h t h e VAX- 1 1 /7 5 0 a n d t h e VAX- 1 1 /7 8 0 , o n l y I PL l ev e l s 2 0
t h r o ug h
23
a r e u s ed
f o r d ev i c e
i n t e r r up t s .
W i th i n
t h e SCB , v e c to r s a r e
r e s e r v ed f o r e a c h I P L l ev e l a v a i l a b l e to
e a c h a d a pt e r
( Fi g u r e 6 - 2 )
Wh e n e v e r
an
ad a p t e r g e ne r a te s a n i n t e r r up t fo r a d ev i c e c o n n e c t e d to
i t , t h e s l o t n um b e r o r TR n um b e r o f the a d a p t e r a nd the d ev i c e I PL a r e
u s ed
by
t h e h a r d wa r e
to
i nd ex
i n to
the
SCB f o r the a pp r o p r i a t e
i n t e r r upt
s e rv i c e
r o u t i ne .
S o m e a d a pte r s
s uc h
as
l o c a l m emo r y
c o n t r o l l e r s d o n o t g e n e r a t e i n t e r r up t s .
•

6.2

VAX/VMS INTERRUPT S E RV I C E ROUT I N E S

Th e i n te r r up t s e rv i c e r o u t i n e s u s ed by VM S o pe r a te
in
th e
l i m i t ed
s ys t em c o n t e x t o r
i n t e r r up t
c o n t e x t d e sc r i b ed in Ch a pt e r 1 .
Th e s e
r o u t i n e s e x e c u t e a t e l ev a t ed I P L o n th e i n t e r r up t
s t a c k o uts i d e
the
contex t o f a process .

6.2.1

Re s t r i c t i o n s I mpo s e d o n I n te r r up t S e r v i c e Ro u t i n e s

Th e r e a r e s ev e r a l r e s t r i c t i o n s i m po s ed o n i n t e r r upt
service
r o u t i nes
b y e i th e r
t h e VAX a r ch i t e c t u r e o r b y s yn c h r o n i z a t i o n t e c h n i que s used
b y VM S .
Th e s e r e s t r i c t i o n s r e s u l t f r om t h e l i m i t ed
c o n tex t
th a t
is
ava i l ab l e t o any r o ut i ne
that executes o uts ide
the c o n t e x t o f a
process .
Th e fo l l o w i ng l i s t o f i t em s i nd i c a t e s some o f
the
spe c i f i c
o pe r a t i o n s a nd d a t a
r e fe rences
t h a t c a nno t o c c u r i n a n i n t e r r upt
s e rv i c e r o u t i ne .
Th e d e s c r i pt i o n of i n t e r r upt c o n t e x t
in
Ch a p t e r 1
c o n t a i n s a m o r e g e n e r a l l i s t o f t h e s e a nd o t he r r e s t r i c t i o n s .
•
•
•

•

I n t e r r up t s e r v i c e r o u t i n e s sho u l d be v e r y s h o r t ,
l i t t l e p r o c e s s i ng a s po s s i b l e a t d ev i c e I P L .

a nd

An y r eg i s t e r s u s ed b y a n i n t e r r up t s e r v i c e r o u t i n e mus t f i r s t
b e s a ved .
Al t h o ug h a n i n t e r r up t s e r v i c e r o u t i n e
c a nno t l o we r
I PL b e l ow t h e
l ev e l
i n t e r r up t o c c u r r ed .

c an
e l ev a t e
I PL ,
it
a t wh i c h the o r i g i n a l

Th e s i z e o f t h e
i n t e r r up t s t a c k ,
the
h a r d wa r e
i n t e r r up t
s e rv i c e
rout ines ,
S YS B OOT p a r am e t e r I N T S TK PAG E S ( wh i c h h a s
in
all
pa r am e t e r
f i l e s d i s t r i b uted
p a r ame t e r d e t e rm i n e s t h e amo u n t of s t a c k
i n t e r r up t s e r v i c e r o u t i n e s .
6-6

s t a c k u s e d by a l l
i s c o n t r o l l ed b y the
a v a l u e of two pag es
Th i s
by D I G I TA L ) .
s t o r a g e a v a i l a b l e to

HARDWARE INTERRUPTS
•

•

•
•

•

6.2.2

An y e l em e n t s p u s h ed o n t o t h e s t a c k by an
i n t e r r up t
serv i c e
r o u t i n e m u s t b e r em o v e d b e f o r e the i n t e r r upt i s d i sm i s s e d i n
o r d e r t h a t RE I wo r k s c o r r e c t l y .
Be c a u s e
the
l o w two
b i ts o f
i n te r r u pt s e r v i c e
rout i ne
add resses
in
the
Sy s t em
Co n t r o l
Bl o c k a r e u s e d fo r s t a c k
s e l ec t i on ,
i n t e r r up t
s e rv i c e
r o u t i ne s mus t
be
l o ng wo r d
a l i g ned .
No pag e a b l e r o u t i n e s o r d a t a s t r uc t u r e s c a n b e r e f e r e nc ed .
No d a t a s t r uc t u r e s th a t a r e s yn c h r o n i z e d by e i th e r
e l e v a ted
I PL
( I P L $ S YNC H o r fo r k I P L ) o r by m u t e x e s c a n be r e f e r e n c e d
by
i n t e r rup t
service
r o ut ines
wi tho u t
d e s t r o y i ng
the
s ync h r o n i z a t i o n .
No r e f e r e nc e s to p e r - p r o c e s s a d d r e s s sp a c e
s pa c e ) a r e a l l owed .

(PO

s pa c e

S e r v i c i ng UN I B US I n t e r r up t s

E a c h d ev i c e o n t h e UN I B US
has one
(or more)
vec to r
number ( s )
to
i d e n t i f y t h e d ev i c e ,
and
a
b u s r e que s t ( B R ) p r i o r i t y to a l l o w the
UN I B U S to a r b i t r a t e am o ng
d ev i c e s wh en m u l t i pl e
i n t e r r up t s o c c u r .
Th e r e a r e
4
BR
l e v e l s , c a l l ed BR4 , B R 5 , BR6 , a nd BR7 .
BR7 h a s the
h i g h e s t p r i o r i ty .
If m u l t i pl e i n t e r r up t s o c c u r fo r d e v i c e s
wi th
the
s am e
BR l ev e l ,
the d ev i c e
e l e c t r i c a l l y c l o s e s t to the UBA has the
h i g h e s t pr i o r i ty .
Th e d ev i c e I P L u s e d equa l s
the
BR p r i o r i t y + 1 6 .
Fo r e x am p l e , B R 4 c o r r e s po nd s to I P L 2 0 .

6 . 2 . 2 . 1 VAX- 1 1 / 7 5 0 UN I BU S I n te r r up t S e rv i c e Ro u t i n e s - UN I B US
i n t e r r up t s
on t h e VAX- 1 1 / 7 5 0 a r e d i r e c t l y v e c to r ed th r o ug h the s e c o nd
pag e o f t h e Sys t em Co n t r o l B l o c k .
Th e Sy s t em Co n t r o l
Bl o c k conta i n s
s e pa r a t e
ad d r e s s e s
f o r t h e i n t e r r u pt s e r v i c e r o u t i n e s f o r a l l o f the
UN I B U S i n t e r r up t v e c to r l o c a t i o n s .
Wh en a
un i t
is
c o n n e c ted
( wi th
SYSG E N ) , the a pp r o p r i a t e f i e l d s i n the SCB a r e i n i t i a l i z ed to po i n t to
the i n t e r r upt s e r v i c e r o u t i n e s f o r the d ev i c e v e c t o r s .
Th e
i n t e r r upt
s e r v i c e r o u t i n e s e v e n t ua l l y t r a n s f e r c o n t r o l to the a pp r o p r i a t e d e v i c e
d r i v e r i n t e r r up t s e r v i c e r o u t i n e s .
Th e VAX/VM S G u i d e
to
Wr i t i ng
a
Dev i c e D r i v e r d e s c r i b e s the d a t a s t r uc t u r e s i n t h e I /0 d a t a b a s e , a nd
c o n t a i n s a m o r e c om p l e t e d i s c u s s i o n o f d r i v e r
i n t e r r upt
service
r o u t i n e s t h a n wh a t i s p r e s e n t ed h e r e .
Wh e n a UN I B US d ev i c e g e ne r a t e s a n i n t e r r upt o n
i n t e r r up t
is
v e c to r e d
d i r e c t l y th r o ug h
the
i mm e d i a t e l y t r a n s f e r r e d to a
P U S HR

the
VAX- 1 1 / 7 5 0 ,
the
SCB ,
and
cont r o l i s

# A M < R O , R l , R2 , R 3 , R4 , R 5 >

i n s t r uc t i o n i n t h e a pp r o p r i a t e d ev i c e c o n t r o l l e r ' s c h a n n e l
r e q ue s t
b lock
( C RB ) .
Th e n e x t i n s t r uc t i o n i n the CRB i s a J S B to the d r i v e r
i n te r r up t s e r v i c e r o u t i n e ( F i g u r e 6 - 3 ) .
Th e
l o n g wo r d
f o l l o wi ng
the
JSB
i n s t r uc t i o n c o n t a i n s
the ad d r e s s o f a n6 t h e r d a t a s t r uc t u r e ( th e
I DB , I n t e r r up t D i spa t c h B l o c k ) .
Th i s a d d r e s s i s p u s h e d o n
the s ta c k
( a s t h e r e t u r n PC f o r t h e J S B i n s t r uc t i o n ) .
Ho we v e r , c o n t r o l i s n ev e r
r e t u r n ed t h e r e b e c a u s e t h a t a d d r e s s i s r em o v ed f r om th e s t a c k
by
the
d r i v e r i n t e r r up t s e r v i c e r o u t i n e .
6-7

VAX-1 1/780
SCB
Interrupt
occurs,
_

__.

hardware
responds
to Interrupt

UBA ADP
UBA Interrupt Service Routine
• Saves RG-RS

�

• Reads BRRVR register In UBA

• Uses vector read as Index

1--- --1

Executing process Is Interrupted;
software response to Interrupt
Is Initiated.

Into vector table
�-------+--""
•
....

• JMP

vector table contains
device CRB addresses

...

VAX-1 1 /750
SCB

Device CRB

PUSHR RG-RS
JSB
�--�t!-t:::::::::::::::�
..
--

lOB pointer

0'\
I
co

�
_..
._
-....-----------1-�-�

In Device Driver
Second page

Device IDB

�

Device Driver Interrupt Service
Routine
• Uses lOB address on stack

to locate:

Device CSR :•�+---!"�
UCB address :--�---....

Device UCB
Fork Block
• R3
• R4
• PC

- Device registers
- Device UCB
• Restores R3 and R4 from

fork block In UCB
• Transfers control to PC in
•

I nterrupted
process
continues ...,.!�-_....
execution
.-__

Figure 6-3

fork block (via JSB)
When driver issues RSB,
- Restores RG-RS
- Issues REI to dismiss
the interrupt

Co n t r o l F l o w i n S e r v i c i ng a UN I B US I n t e r r up t

Device registers

HARDWARE INTERRUPTS
A f t e r the J S B i n s t r uc t i o n i n the CRB t r an s f e r s c o n t r o l to
the
i n t e r r up t s e r v i c e r o u t i n e , t h e f o l l o w i ng e v e n t s t a k e pl a c e .

dr iver

Th e d r i v e r i n t e r r up t s e rv i c e r o u t i n e r em o v e s t h e I DB p o i n t e r
f r o m th e
stac k ,
a nd u s e s
i t t o o b t a i n the a d d r e s s o f t h e
d ev i c e c o n t r o l l e r ' s c o n t r o l / s t a t u s r eg i s t e r
( CSR) ,
a nd
the
a d d r e s s o f t h e UC B f o r t h e d ev i c e g en e r a t i ng t h e i n t e r r up t .

H a v i ng
f o und
the
UCB ,
the
i n te r r upt
s e rv i c e
rout i ne
d e t e rm i n e s wh e t h e r t h e i n t e r r upt wa s e x pe c t ed o r no t , a nd , i f
e x p e c t ed , r e s to r e s t h e d r i v e r c o n tex t s to r ed i n the UC B ,
a nd
t r a n s f e r s c o n t r o l to t h e s a v ed PC .

Wh e n t h e d r i v e r f i n i sh e s p r o c e s s i ng t h e i n t e r r up t , i t
an RSB .

Co n t ro l i s t r a n s f e r r ed b a c k t o the d r i v e r
i n t e r r up t
serv i ce
rout ine ,
wh i c h
r e s to r e s the r eg i s te r s ( R O t h r o ug h R S ) s a v ed
by t h e PUS HR i n s t r uc t i o n a nd d i sm i s s e s t h e i n t e r r up t w i th
an
RE I .

i s s ue s

I f the i n t e r r up t wa s u n s o l i c i t ed , t h e d r i v e r m a y t a k e some a pp r o p r i a t e
action ,
or
s i mpl y d i sm i s s the i n t e r r up t by r e s to r i ng R O t h r o ug h R S ,
a n d i s s u i ng a n RE I .

6 . 2 . 2 . 2 VAX- 1 1/7 8 0 UN I B US I n te r r up t S e r v i c e Ro u t i ne s - Wh e n a d ev i c e
o n t h e UN I B US
r e q ue s t s
a n i n t e r r up t , t h e U B A c o nv e r t s th a t r e q u e s t
i n to a n i n te r r upt o n the S B I .
Th e S B I i n t e r r upt i s v e c t o r ed
th r o ug h
t h e S C B t o a UN I B U S Ad a p t e r i n t e r r up t s e r v i c e r o u t i n e .
In the case o f
i n t e r r up t s g e n e r a t e d b y a
UN I B US d ev i c e o n
the VAX- 1 1 / 7 8 0 ,
the
c o r r e s po nd i ng ad a p t e r r e c e i v e s d ev i c e i n t e r r up t s , d e t e rm i n e s wh i c h h a s
t h e h i g h e s t p r i o r i t y , a n d g e n e r a t e s a n i n te r r up t o f i t s o wn
for
the
C PU
( o n beha l f o f
th e
i n t e r r up t i ng
d ev i c e ) .
It
is the adapter
i n t e r r up t th a t i s v e c to r ed th r o ug h t h e S C B
( us i ng
th e
i n t e r r upt i ng
d ev i c e ' s
IPL,
a nd
t h e ad a p t e r ' s TR n um b e r ) , t o a n a d a p t e r i n t e r r up t
s e rv i c e r o u t i n e .
Th e a d a p t e r i n t e r r up t s e r v i c e
r o ut i ne
saves
some
( a d a p t e r - spec i f i c )
r eg i s t e r s ,
a nd
pa s s e s c o n t r o l
to
an i n t e r r up t
s e r v i c e r o u t i n e i n the d ev i c e d r i v e r f o r the i n t e r r up t i ng d ev i c e .
Th e
d r iver
i n te r r upt s e r v i c e r o u t i n e c a n t h e n r e s po nd to the i n t e r r up t i n
a d ev i c e-d e pend ent
f a sh i o n .
Af t e r
s e rv i c i ng
the
i n t e r r up t ,
the
r eg i s t e r s
s aved by the
a d a p te r
i n t e r r upt
s e r v i c e r o ut i ne m u s t be
r e s to r e d , a nd a n RE I i n s t r uc t i o n i s s ued to d i sm i s s t h e i n te r r up t .
Th e r e a r e fo u r i n t e r r up t s e r v i c e r o u t i n e s fo r e a c h UBA , o n e
fo r
each
B R l ev e l a t wh i c h UN I B U S d ev i c e s r e q ue s t i n t e r r up t s .
Th e y d i f f e r o n l y
i n wh i c h i n t e r n a l UBA r eg i s t e r t h e y r e ad
t o d e t e rm i n e wh i c h d e v i c e
r e que s t ed
the
i n t e r r up t .
Th e s e i n t e r r up t s e r v i c e r o u t i n e s a r e f o und
i n a d a t a s t r uc t u r e d e sc r i b i ng th e UBA ( t h e Ad a p t e r
Co n t r o l
Bloc k ) ,
t h a t i s c r e a t ed wh e n the s ys t em i s b o o t s t r a pped ( f r om m o d u l e I N I TAD P ) .
UN I B US i n t e r r upt s e r v i c i ng on t h e VAX- 1 1 / 7 8 0 beg i n s
UN I B US a d a p te r i n t e r r up t s e rv i c e r o u t i n e s .
1.

Th e
UBA
i n te r r u p t s e r v i c e
r eg i s t e r s R O th r o ug h R S .

6-9

r o ut ines

one

( Figure 6-3 )

fo ur
save

HARDWARE INTERRUPTS
2.

A UBA i n t e r n a l r eg i s t e r ( B RRVR )
is
r ead
to
d e t e rm i ne
the
i d e n t i ty o f
the
i n t e r r up t i ng
d ev i c e .
Each BRRVR r eg i s t e r
c o nta i ns
t h e v e c to r
n um b e r c o r r e spo nd i ng
t o t h e d ev i c e
i n te r r upt ,
or
a n i nd i c a t i o n th a t the UBA i s i n t e r r up t i ng o n
beha l f of i ts e l f , not
fo r
s o m e d ev i c e .
( Th e r e
are
four
BRRVRs i n t h e UBA , o n e fo r e a c h B R l ev e l . )

I f t h e UBA i s
i n t e r r up t i ng
o n beha l f o f
i tse l f ,
it
is
n o rma l l y i nd i c a t i ng a n ad a p t e r e r r o r c o nd i t i o n .
Th e s e e r r o r s
u s ua l l y r e s ul t wh e n a r e f e r e n c e
i s mad e t o a
nonex i s tent
address
in
UN I B US
I /O
space .
Th e y m a y i nd i c a t e o n l y a
t r a n s i e n t h a rdwa r e e r r o r , o r a b ug i n a d ev i c e d r i v e r .
Th e s e
errors a r e
l og g ed ,
up t o
a m a x i m um o f 3 i n a n y g i v e n 1 5
m i n u t e pe r i o d , a nd t h e i n t e r r up t i s d i sm i s s e d .

Fo r a d ev i c e i n t e r r up t , t h e v e c to r n um b e r i s used a s a n i nd ex
i n to
a v e c to r t a b l e .
Th e v e c to r t a b l e c o n t a i n s a po i n t e r to
the JS B i n s t r uc t i o n i n s i d e the C RB .
Co n t r o l
is
transfer red
to
th e J S B
i n s t r uc t i o n b y a JM P i n s t r uc t i o n i n the ad a pt e r
i n te r r up t s e r v i c e r o u t i n e .
( Th e v e c t o r t a b l e e n t r y po i n t i ng to the CRB , a s we l l
as
the
add ress
f i elds
in
the
CRB , a r e f i l l ed i n b y SYSGEN a t t h e
t i m e t h e d ev i c e d r i v e r i s
l o ad ed
i n to
the
s ys t em w i th a
S YS G E N C ONNECT c omma n d . )

At t h i s po i n t , i n t e r r upt d i spa t c h i ng p r o c e e d s e x a c t l y a s i n
the case
of
t h e VAX- 1 1 /7 5 0 .
No t e
t h a t d ev i c e d r i v e r s n e ed
no t concern
t h em s e l v e s wi th wh e th e r
they a r e on a
VAX- 1 1 / 7 5 0 o r
VAX- 1 1 /7 8 0 ,
because
the i r
i n t e r r upt
s e rv i c e
r o ut i n e s wi l l
be
ente r ed
in a
t r a n s pa r e n t m a n ne r .

MAS SBUS I n te r r upt S e r v i c e Ro u t i n e s

6.2. 3

Un l i k e UN I B US i n t e r r up t d i spa tc h i ng , t h e MAS S B U S
i n te r r up t
s e qu e n c e s
f o r the VAX- 1 1 / 7 5 0 a nd t h e VAX- 1 1/7 8 0 MAS S B U S a r e i d e n t i c a l .
Wh e n the
s ys t em i s b o o t s t r a pped , e n t r i e s
a r e mad e
in
the
SCB t o
transfer
contro l
to
l o ca t i ons
in
t h e CRB
for
the MAS S B US Ad a pt e r .
Th e
i n s t r uc t i o n s i n t h e MBA C RB a r e a P U S HR f o r R2 t o R S , and a J S B to the
MBA i n t e r r up t s e r v i c e
r o u t i n e MBA $ I N T
( wh i c h
i s pa r t
of mo d u l e
MBA I NTDS P )
•

MBA i n t e r r up t s a r e h a nd l ed d i f f e r e n t l y f r om UN I B US i n te r r up t s ,
pa r t l y
because
o n e MBA i n t e r r up t m a y i nd i c a t e tha t m u l t i pl e d ev i c e s o n the
a d a p t e r n e ed s e rv i c i ng .
Th e MBA i n t e r r up t s e r v i c e
rout i ne
reads an
a ttent i o n
s umm a r y r eg i s t e r t o d e t e rm i n e wh a t i t m u s t d o to r e s po nd t o
a n i n t e r r up t .
I f t h e i n t e r r up t e n ab l e b i t i n the MBA i s s e t , a n MBA i n t e r r upt c a n b e
c a u s e d b y a n y o f t h e fo l l o w i ng o pe r a t i o n s .
•

A d a t a t r a n s f e r c om p l e t e s .

•

An a t t e n t i o n l i n e i s a s s e r ted wh i l e the MBA i s no t b u s y .

•

An MBA e r r o r o c c u r s wh i l e the MBA i s n o t b u s y .

•

Th e powe r i s t u r n ed o n fo r t h e MBA .

6-1 0

HARDWARE INTERRUPTS
Dev i c e s on the MASSB US c a n a s s e r t the a t t e n t i o n l i n e
•

i f a n e r r o r o c c u r s , wh e th e r
pl a c e ,

•

wh e n a m e c h a n i c a l mo t i o n s uc h a s a d i s k s e e k o r
c om p l e t e s , o r

•

wh e n a d ev i c e c h a ng e s i t s s t a t e .

not

t r an s f e r

t a k i ng

t a pe

r e w i nd

I n g e n e r a l , MAS S B U S d ev i c e d r i v e r s d o n o t r e que s t own e r sh i p o f t h e MBA
un t i l
they
n e ed i t t o pe r f o rm a t r a n s f e r .
Th e MBA i n t e r r u p t s e r v i c e
r o u t i n e a s s um e s t h a t i f t h e MBA o wn e r i s e x pe c t i ng a n i n t e r r up t ,
then
the
i n t e r r up t c u r r e n t l y b e i ng s e r v i c ed i nd i c a t e s th a t a t r a n s f e r h a s
c om p l e ted o r b e e n abo r ted .
Th a t i s , wh e n
a n MBA i n t e r r up t o c c u r s ,
MBA$ I NT d i s p a t c h e s
to
t h e o wn e r o f the MBA f i r s t .
I t then c h e c k s
Th e
UCB
l i st
wh e t h e r o t h e r d ev i c e s o n t h e MAS S B U S n e ed
a t te n t i o n .
c o n t a i n ed
in the
! DB a l l o ws MBA $ I N T t o a s s o c i a t e UCB ad d r e s s e s w i th
d ev i c e s tha t a r e r e que s t i n g s e r v i c e .
MBA $ I NT r e s po nd s to an i n t e r r upt i n o n e o f
th r e e wa ys
( Figure 6-4 ) .
I t m a y p e r fo rm
all
th r e e o f
these
act ions
to
s e rv i c e m u l t i pl e
a t te n t i o n r e que s t s i n r e s po n s e to a s i ng l e i n te r r upt .
•

Fo r an e x p e c t e d i n te r r up t fo r
a
s i ng l e - un i t c o n t r o l l e r
(a
d isk) ,
MBA$ I N T
i ssues a
JSB
i n s t r uc t i o n th a t
transfe r s
c o n t r o l d i r e c t l y t o the f o r k PC s t o r ed
in
th e
UCB o f
the
i n t e r r up t i n g d ev i c e .
Th e d r i v e r r e t u r n s to MBA $ I NT wh e n i t
h a s c ompl e t ed i t s wo r k .

•

Fo r an u n s o l i c i t ed i n t e r r upt f o r
a
s i ng l e- un i t c o n t r o l l e r ,
MBA$ I N T
i s s ue s a J S B i n s t r uc t i o n th a t t r a n s f e r s c o n t r o l to a
d r i v e r - s upp l i e d u n e x pe c t ed i n t e r r upt s e r v i c e r o u t i n e ,
wh i c h
w i l l r e t u r n t o MBA$ I NT .

•

Fo r a m u l t i - d ev i c e c o n t r o l l e r ( a mag t a pe ) , MBA$ I NT t r a n s f e r s
c o n t ro l
to
th e C RB f o r t h e d ev i c e c o n t r o l l e r .
Th e d ev i c e
c o n t r o l l e r CRB d i s p a tc h e s to a c o n t r o l l e r
i n t e r r up t
s e rv i c e
r o ut i ne
th a t s a v e s
R2
to
R S and t r a n s f e r s c o n t r o l t o t h e
d r i ve r
i n t e r r up t
serv i c e
rout i ne .
Th i s
serv i c e
r o ut i ne
e v e n t u a l l y r e t u r n s c o n t r o l to MBA$ I NT .

Th e wa y MBA $ I NT d e c i d e s wh e t h e r a n e n t r y i n
the MBA I DB
is
a
UCB
ad d r e s s
( s i ng l e- un i t
contro l l e r ) ,
or
a
po i n t e r
i n to
a
CRB
( m u l t i -d ev i c e c o n t r o l l e r ) i s by c h e c k i ng the
l ow o rder
bi t o f
the
entry
i n t h e M B A I DB f o r t h e c o n t r o l l e r .
I f t h e b i t i s s e t , th e n t h e
e n t r y i s f o r a m u l t i - d ev i c e c o n t r o l l e r .
If
the b i t
is
c lear ,
the
entry
r e pr e s e n t s
the
UC B a d d r e s s f o r t h e d ev i c e o n a s i ng l e- d ev i c e
contro l l e r .
UC Bs , l i k e CRBs , a r e a l wa ys
l o ng wo r d
a l i g ned
( th e
low
o rde r
two
b i ts a re c l ea r ) .
Wh e n a C RB i s c r e a t e d fo r a m u l t i - d ev i c e
c o n t r o l l e r , a nd i t s ad d r e s s s to r ed i n t h e M BA I DB ,
the
ad d r e s s
is
i nc r em e n t e d b y l s o
th e
l o w o r d e r b i t w i l l b e se t .
Co n t r o l i s
a c t ua l l y t r a n s f e r r ed t o the
P U S H R i n s t r uc t i o n
in
t h e m u l t i - d ev i c e
c on t r o l l e r C RB v i a a
JSB

- (RS)

i n s t r uc t i o n ( wh e r e R S c o n t a i n s t h e MBA I DB e n t r y ) ,
so
th a t
o r d e r b i t i s c l e a r ed b e f o r e c o n t r o l i s a c t ua l l y t r a n s f e r r ed .

6-l l

the

low

� MBA registers

Interrupt
occurs;

�

hardware

responds

1---,.�-1

...

M B A CSR

M BA CRB

�

PUSHR R2-R5

MBA Interrupt Service
Routine ( M BA$1 NT: : )
Executing process
is interrupted;
software response
initiated.

Interrupted
process
continues
execution

�

CASE 1' slngle-un• (disk)
controller expecting
interrupt
JSB

••-'�
.:,.

i:J

�
•I
1e...... expectmg mterr�:
,
•-•----•-• -•-•-•- � '
• •
CASE 3: multi-unit (tape) -e,- �
•
controller
JSB - i
..•,.
,
CASE 2: single-unit (disk)

� �

con roll r not

�

L.--------------------�·
�_.

Fork Block
• R3

List of CRBs

• R4
• PC

a nd UCBs for

-�---,.._
-----+-----t
� -.C:��!!!!._
II. ro-1
M BA IDB &.
JSB

interrupt

to interrupt is

Device UCB f or single-unit controller

MBA I D B

SCB

�

devices o n ---+------'
MASSBUS .-.

Device Driver

..
..

I n struction awaiting ...,
interrupt (PC stored
in UCB fork block)

•'
•
-- 1- \- - - - - - - ·�
, U n solicited interrupt
•
routine

�

• exits with RSB

�

1rt-' ,,

•
- •'

Interrupt service

"-•

routine JSB ____,
• rest ores R2-R5

• exits with REI

� - ,, -. - - ..... ,
. •
.... 'e
....

Device UCB for

multi-unit
-

Device CRB
PUSHR R2-R5

:------....Device controller I D B :�-&---'
JSB -.

Device I D B

:---tl-- --.

Device CSR •

[.;...

:+---+---'

List of UCBs •
for devices on
thi s controller

controller
Fork Block
• R3
• R4

• PC

controiJer registers

Figure 6-4

C o n t r o l F l ow i n S e r v i c i ng a MAS SB U S I n t e r r up t

HARDWARE INTERRUPTS
MBA $ I N T a l wa ys c h e c k s the
MBA a t ten t i o n s umm a r y r eg i s t e r
after a
dr iver
i n t e r r up t s e rv 1 c e
r o u t i n e r e t u r n s c o n t r o l to i t to d e t e rm i n e
wh e th e r a n o t h e r d ev i c e o n t h e MAS S B U S r e que s ted a n i n t e r r up t wh i l e the
MAS S B U S o wn e r wa s
t r a n s f e r r i ng d a t a , or wh i l e t h e c u r r e n t i n t e r r up t
wa s b e i ng
proces sed ,
b e c a us e d a ta
t ransfer
f unc t i o n s b l o c k
the
i n t e r r up t s
f r om
nontr ans f e r
f un c t i o n s
un t i l
the d ata
t r an s f e r
c om p l e t e s .

DR 3 2 I n te r r up t S e r v i c e Ro u t i ne

6.2.4

DR 3 2 i n t e r r upt d i s pa t c h i ng
i s h a nd l ed
s i m i l a r l y to
MBA i n t e r r up t
d i s pa t c h i ng .
Wh e n t h e s ys t em i s b o o t s t r a pp e d , e n t r i e s a r e m a d e i n th e
S C B t o t r a n s f e r c o n t r o l to l o c a t i o n s i n the CRB
for
the
DR 3 2 .
Th e
i n s t r u c t i o n s i n the CRB a r e a P U S HR f o r R 2 t o R 5 , a n d a J S B .
Th e DR 3 2
I DB a d d r e s s fo l l o ws t h e J S B i n s t r u c t i o n i n the DR 3 2 CRB ( F i g u r e 6 - 5 ) .
I n i t i a l l y , t h e J S B i n t h e DR 3 2 C RB t r an s f e r s c o n t r o l to r o u t i n e DR $ I NT
i n m o d u l e DR INTHAND .
Th i s r o u t i n e s i m p l y
1.

c l e a r s t h e a d a p t e r powe r up a nd po we r d o wn
c o n t r o l r eg i s t e r ,

c a l l s o n a c o n t r o l l e r i n i t i a l i za t i o n
DR 3 2 ( a nd d i s a b l e DR 3 2 i n t e r r up t s ) ,

r e s to r e s r eg i s t e r s R 2 t o R 5 , a nd

i s s ue s a n R E I i n s t r uc t i o n .

b i ts

ro u t i ne

DR 3 2

reset

the

Wh e n the DR 3 2 d r i v e r ( XFDR I VE R )
is
l o ad ed
by
SYSG E N
(as
pa r t o f
AUTOCONF I G UR E wh e n
the
s ys t e m
i s b o o t s t r a pped ,
o r b y a n expl i c i t
CONN E C T c ommand ) , t h e J S B i n s t r uc t i o n i s o v e rwr i t t e n to po i n t
to
the
i n t e r r up t s e r v i c e r o u t i n e in t h e d r i v e r .
Th i s r o u t i n e

6. 2. 5

r e s po nd s to t h e v a r i o us t ype s o f DR 3 2 i n t e r r up t s ,

r e s to r e s r eg i s t e r s R 2 t o R 5 , a nd

i s s u e s a n R E I i n s t r uc t i o n .

MA7 8 0 I n te r r up t D i s pa tc h i ng

Al tho ug h t h e
s t a nd a r d
MS 7 8 0 m em o r y c o n t r o l l e r
d o e s n o t g en e r a t e
i n te r r up t s , t h e sh a r e d m em o r y ( MA7 8 0 ) c o n t r o l l e r d o e s .
I n t e r r up t s a r e
r e que s t e d b y a d r i v e r o r t h e e x e c u t i v e t o i n te r r up t a n o th e r
p r o c e s so r
Th i s o c c u r s wh e n e v e r a s h a r ed m em o r y
c o n n e c t ed
to t h e sh a r ed memo r y .
e v e n t f l ag i s s e t , o r a s h a r e d m em o r y m a i l b ox m e s s a g e i s wr i t t e n .

6-13

l"%j
1-'•
1.0
c
t;
CD
0"\

SCB

CASE

()

Interrupt

DR32 CRB

0
::s

t;
0
f--J

PUSHR R2-R5
JSB

responds
to interrupt

Path
taken
until the
DR32

DR$1NT: :
•

Disables DR32
interrupts

• Restores R2-R5
•

REI

l"%j

f--J
0

�

1-'•

0"\

::s

f--J

Cl.l

�

CD
t;

1-'•
()
1-'•

Executing
process is interrupted;
software response
to interrupt is
initiated

• Respond to interrupt;

DR32 CSR

::s

1.0

Device UCB

0.1

t:l
:::0

Fork Block
• R3
• R4
• PC

-...J
co
0
H

DR32 Driver Interrupt Service Routine

DR32 lOB
Path
taken
after the
DR32
driver
is loaded

e.g., queue AST to
user process to
inform L!Ser of interrupt
• Restore R2-R5
• REI

DR32
registers

::s

rt
CD
t;
t;

c
"0
rt

F i gure 6 - 5

Contro l F l ow in Servic ing a DR7 8 0 Interrup t

Interrupted
process
continues
execution

>
:;cl

�::0

tzl
H
z
1-i

tzl

::0
c:
.,
1-i
en
:;cl

HARDWARE INTERRU PTS
Wh e n t h e s y s t e m i s b o o t s t r a pped , m o d u l e I N I TADP p l a c e s e n t r i e s
i n to
the
S C B t o t r a n s f e r c o n t r o l t o l o c a t i o n s i n th e MA7 8 0 ADP wh e n MA 7 8 0
i n t e r r up t s o c c u r ( F i g u r e 6 - 6 ) .
Th e l o c a t i o n s i n
t h e ADP c o n t a i n
a
P U S HR
i n s t r uc t i o n
s av i ng
RO
to
R5 ,
a nd
a JSB
i n s t r uc t i o n th a t
t r a n s f e r s c o n t r o l t o r o u t i n e MA$ I N T ( i n MAHAN DLER ) .
1.

Wh e n MA$ INT o b t a i n s c o n t r o l , i t r em o v e s t h e v a l u e pu s h e d o n to
the
s tack
by t h e J S B i n s t r uc t i o n i n t h e ADP , a nd u s e s i t t o
d e t e rm i n e the a d d r e s s o f t h e MA 7 8 0 ' s ADP .

I t u s e s f i e l d s i n t h e AD P t o l o c a t e ad a p t e r r eg i s t e r s i n
the
MA 7 8 0 ,
and
to
d e te rm i ne
wh i c h po r t r e qu e s t e d a n i n t e r r u p t
( a nd wh a t k i n d o f i n t e r r up t wa s r e qu e s t e d ) .

I f t h e i n t e r r up t i s fo r a p r o c e s s o r b e i ng
connec ted
to
the
m em o r y ,
t h e i n te r r up t i s d i sm i s s ed by r e s t o r i ng R O t o R S a n d
i s s u i ng a n RE I .

Ot h e r w i s e , MA$ I N T s e r v i c e s the i n t e r r up t .

An d f i n a l l y , t h e i n t e r r up t i s d i sm i s s ed by r e s t o r i ng R O to R S
a nd i s s u i ng a n RE I .
MA780 registers

SCB
MA$1 NT: :

MA780 ADP
Interrupt

MA780 CSR ----4�

PUSHR RO-RS

• Com putes a d dress of

ADP from pointer o n
stack

responds

• Servic es interrupt

to
interrupt

• Restores RO-RS
• Exits with REI

E xecuti n g process is
interrupted; software
respo n s e to interrupt
i s initiated.

I nterrupted
process
c o nti n u es
executio n .

Figure 6-6

6.3

Co n t r o l Fl ow i n S e rv i c i ng a MA 7 8 0 I n t e r r u p t

C ONNECT-TO- I NTERRU PT MECHAN I SM

Th e c o nnec t - t o - i n t e r r up t m e c h a n i sm a l l o ws a pr o c e s s to be no t i f i e d
of
a UN I B U S d ev i c e i n t e r r up t b y the d e l i v e r y o f a n AST , b y t h e s e t t i ng o f
a n e v e n t f l ag , o r b o th .
Th e p r o c e s s c a n
a l so
spec i f y a n
i n t e r r up t
s e rv i c e r o u t i n e t h a t w i l l r e s po nd to d ev i c e i n t e r r up t s .
can
A s u i t a b l y p r i v i l eg ed p r o c e s s ( w i th CMKRNL a nd PFNMAP p r i v i l eg e s )
r e s po nd
to
an
i n t e r r upt b y r e ad i ng o r wr i t i ng d ev i c e r eg i s t e r s , a n d
po s s i b l y , b y i n i t i a t i ng f u r th e r d ev i c e a c t i v i t y .
Howev e r , i n o r d e r t o
d i r e c t l y m a n i pu l a te d ev i c e r eg i s te r s , t h e p r o c e s s m u s t f i r s t m a p t h e
UN I B U S I/0 pa g e ( s ) c o n t a i n i ng the r eg i s t e r s fo r t h e d ev i c e
i n to
i ts
6-1 5

HARDWARE INTERRUPTS
o wn
process
s pa c e
( PO
or
Pl) .
Th e VAX/VM S Re a l T i m e U s e r ' s G u i d e
c o n t a i n s a d i s c us s i o n o f m a pp i ng the UN I B U S I /0 p ag e ,
a nd
us i ng
the
c o n n e c t - to - i n t e r r up t c a pa b i l i t y .
C h a pt e r
1 3 c o n t a i n s m o r e d e t a i l ed
i n fo rma t i o n o n h o w t h e m a pp i ng i s a c t ua l l y pe r f o rmed .
No t e tha t t h e phys i c a l a d d r e s s e s o f t h e UN I B US I/0 p a g e d i f f e r o n t h e
VAX- 1 1 / 7 8 0
a nd VAX- 1 1 / 7 5 0 .
Th e r e f o r e ,
d i f f e r en t PFNs m u s t b e u s e d
wh e n m a ppi ng t h e UN I B U S I /O p a g e .
UN I B U S
I /O
add ress
space
s ta r ts
( ph ys i c a l l y )
a t 2 0 0 0 0 0 0 0 ( h e x ) fo r t h e VAX- 1 1 / 7 8 0 , a nd F 2 0 0 0 0 ( h e x ) f o r
t h e VAX- 1 1 / 7 5 0 .
Th e d e t a i l s o f m a pp i ng to the I /0 p a g e a r e d e s c r i b e d
i n t h e VAX/VMS Re a l -T i m e Us e r ' s G u i d e .
Append i x D c o n t a i n s a l i s t o f
s ym bo l s d e f i n ed b y t h e $ I 0 7 5 0D E F a nd $ I 0 7 8 0D E F m a c r o s
to make
th i s
m a pp i ng a s s ym bo l i c a s po s s i b l e .
Th e c o nn e c t - to - i n te r r upt f a c i l i t y i s a n e x t e n s i o n o f
the
i n t e r r up t
d i s pa tc h i ng
s c h em e .
I n o rd e r
to
u s e i t , t h e c o nn e c t - to - i n t e r r up t
d r i v e r ( C ON I NTERR ) m u s t b e a s s o c i a t ed wi th t h e i n t e r r up t v e c to r .
Th e
a s s o c i a t i o n i s m a d e u s i ng t h e S Y S G E N C ONNE C T c ommand , s pe c i f y i ng
•
•
•

a n a m e f o r t h e d ev i c e
( to
c o nn e c t s to the i n t e r r up t ) ,

the
i n t e r r up t v e c to r
i n t e r r up t s , a nd

wh i c h

u s ed

by
the

the

process

d ev i c e

tha t

g ene r a te s

t h e C ON I NTERR d r i v e r , wh i c h i n i t i a l l y r e s pond s t o the
i n t e r r up t s .

d ev i c e

Wh e n the d ev i c e g e ne r a t e s a n i n t e r r up t , t h e n o rm a l
UN I B US
i n te r r up t
d i s pa tc h i ng
s e que n c e
i s f o l l o we d , a s d i sc u s s e d i n s e c t i o n s 6 . 2 . 1 a n d
6.2.2.
Ho we v e r , the C ON I NT E RR
i n t e r r up t
s e rv i c e
r o u t i ne
t r an s f e r s
control
t o the
u s e r - s uppl i ed
i n te r r upt s e r v i c e r o u t i n e ( i f o n e wa s
s up p l i ed ) u s i ng a JS B o r CALL i n s t r uc t i o n ( a s r e que s t e d by t h e
use r ) .
Th i s
is
i l l us t r a ted i n F i g u r e 6 - 7 .
Wh e n the u s e r - s uppl i ed i n t e r r up t
s e rv i c e r o u t i n e i s s u e s a n R S B
(or
RET ) ,
t h e C ON I N T E RR
i n t e r r up t
s e rv i c e
r o ut i ne
r eg a i n s c o n t r o l .
Be fo r e
r e s to r i ng
RO
to R 5 a n d
i s s u i ng a n RE I , t h e C ON I NT E RR i n t e r r up t s e r v i c e r o u t i n e que u e s a n A S T
to
the p r o c e s s ( i f r e que s t ed ) t o no t i f y the p r oc e s s th a t a n i n t e r r up t
h a s o c c u r r ed ( v i a the AST , o r b y s e t t i ng a n e v e n t f l ag )
•

I n o r d e r f o r the p r o c e s s - s uppl i ed
i n t e r r up t
s e rv i c e
r o ut i ne
to
be
access ibl e
to
t h e C ON INT E RR i n t e r r up t s e r v i c e r o u t i n e , t h e C ON I NT E R R
add r e s s
s pa c e .
Th e
d r i v e r d o ub l e maps the u s e r r o u t i n e i n to sys �m
d o ub l e m a pp i ng r e q u i r e s e no ugh s ys tem pag e t iO� e e n t r i e s ( r e s e r v ed b y
t h e REALT I M E S PTS SYS BOOT p a r am e te r ) t o m a p t he u s e r - s uppl i ed r o u t i n e s
( o t h e r d r i ver
r o u t i n e s b e s i d e s a n i n t e r r upt s e rv i c e r o u t i n e m a y b e
s pe c i f i ed
wh e n c o n n e c t i ng
to
an
i n te r r up t ) .
Wh e n
the
proc ess
d i s connec t s
f r om t h e i n t e r r upt , t h e S PTs used to m a p t h e r o u t i n e s fo r
t h a t p r o c e s s a r e mad e a v a i l a b l e f o r l a t e r u s e b y o th e r p r o c e s s e s .

6-1 6

HARDWARE INTERRUPTS

CONINTERR Interrupt
Service Routine

Device CRB
JSB

..
-

�

• JSB (or CALL)

I DB address :

• Request delivery

Device IDB
Device CSR :

Device UCB :

I r

�

if requested by user

..
-

of AST to process
or set an event
flag, if desired
by user
• Restore RO-RS
• Issue an REI

to dismiss interrupt

Device UCB
Fork Block
• R3
• R4
• PC

Figure 6-7

�
This portion of the interrupt
dispatch scheme is an
explicit example of the general
.
.
UN IBUS mterrupt dispatch
scheme illustrated in Figure 6-3

User-supplied Interrupt
Service Routine
• Responds to interrupt

In device-dependent
fashion
• Exits with RSB

I
I
I

This portion of the interrupt
dispatch scheme is specific
to the connect-to-interrupt driver

E x t end i ng I n t e r r upt D i s pa tch Me c h a n i sm wi t h
t h e Co n n e c t - to - I n t e r r up t Fa c i l i t y

6-1 7

C HAPTER 7
ERROR HANDL I NG

Th e r e a r e s e v e r a l l ev e l s fo r
r e po r t i ng
s y s t em-w i d e
( Pro c essand
imag e-spec i f i c
e r r o r s a r e h a nd l ed
m e c h a n i sm d e s c r i b ed i n Ch a p t e r 2 . )
•

•

7.1

e r ro r s
i n VM S .
b y t h e ex c e p t i o n

Th e e r r o r l ogg i ng s ub s y s t em a l l o ws d ev i c e d r i v e r s a nd
o th e r
s ys t em c ompo n e n t s t o r e c o rd e r r o r s a nd o th e r e v e n t s fo r l a t e r
i n c l u s i o n i n a n e r r o r l og r e po r t .
Th e BUG C HECK m e c h a n i sm i s u s e d by VM S t o s h u t d o wn t h e s y s t em
i n a n o r d e r l y f a s h i o n wh e n i n t e r n a l i n c o n s i s t e n c i e s o r o th e r
i r r e c o v e r a b l e e r r o r s a r e d e t e c ted .
A mach ine check i s
an
ex cept ion
th a t
i nd i c a t e s
p r o c e s s o r has d e t e c ted some C P U - s p e c i f i c e r r o r .

th a t

the

ERROR LOGG I NG

Th e e r r o r l og g i ng s ub s ys t em i s u s e d to r e c o r d d ev i c e e r r o r s , p r o c e s s o r
d e t e c t ed c o nd i t i o n s , a n d o th e r n o t e wo r thy e v e n t s s uc h a s v o l um e m o un t s
a nd s ys tem s t a r t ups .

Ove r v i ew o f t h e E r r o r Log g i ng S ubsys tem

7.1.1

E r r o r l og g i ng o c c u r s in th r e e s t e p s .
1.

Co mpo n e n t s s uc h a s d ev i c e d r i v e r s th a t w i s h to l o g
an
e r ro r
c a l l r o u t i n e s i n t h e e x e c u t i v e tha t wr i te e r r o r m e s s ag e s i n to
o n e o f t wo b u f f e r s pe rm a n en t l y a l l o c a t e d
in
the
e x ec ut i v e
i m ag e .

Wh e n t h e b u f f e r a l l o c a t i o n r o u t i n e d e t e c t s th a t a b u f f e r
is
f ul l ,
i t a wa k e n s
the
E RRFMT p r o c e s s s o
th a t t h e b u f f e r
contents
c an
be
wr i tten
to
the
error
l og
file
[ S YS E RR] E RRLOG . SYS .

Th e c o n t e n t s o f t h i s f i l e c a n b e a s s emb l ed i n t o a
t h e r e po r t g en e r a to r u t i l i t y SYE .

7-1

r e po r t

E RROR HANDL ING
Dev i c e D r i ve r E r r o r s

7.1.2

Th e r e a r e t wo r o u t i n e s i n t h e e r r o r
l og
s ub s ys tem
us ed
b y d ev i c e
d r ivers .
E R L $DEVI C ERR
is
used
to
r e po r t d ev i c e- sp e c i f i c e r r o r s .
E R L $ D EVI C TM O c a n b e c a l l ed b y a d r i v e r to r e po r t a d ev i c e t i m e o u t .
In
e i th e r c a s e ,
1.

a n e r r o r message b u f f e r i s a l l o c a ted ,

t h e b u f fe r i s l o ad e d w i t h i n fo rm a t i o n o b t a i n e d f r om th e
un i t
c o n t r o l b l o c k a nd f r om t h e c u r r e n t I /0 r e que s t pa c k e t , a nd

t h e d r i v e r i s c a l l ed a t i t s r eg i s t e r d um p r o u t i n e e n t r y po i n t
to
s t o r e d ev i c e - s p e c i f i c i n f o rma t i o n i n to t h e e r r o r m e s s a g e
b u f fe r .

O th e r E r ro r Lo g Me s s a g e s

7.1.3

VM S u s e s t h e e r r o r l og s ub s ys t em to r ec o rd o th e r
i n fo rm a t i o n b e s i d e s
d ev i c e e r r o r s .
Th e k i nd s o f i t e m s w r i t t e n t o the e r r o r l og i nc l ud e
•
•
•

Co l d s ta r t e n t r i e s .
Th e s e
s y s tem boo t s t r a p a t t emp t s .

entr i es

A l l b ug c h e c k s , f a t a l a nd o th e r w i s e .
i n the nex t s ec t i o n .

•

Ma c h i n e c h e c k o c c u r r e n c e s .

•

Vo l um e m o u n t s a nd d i sm o un t s .

•

7. 1. 4

Wa r m s t a r t e n t r i e s .
Th e s e
r e c o ve r i e s f r o m powe r f a i l u r e .

r ec o r d

r e co rd

al l

Bug c h e c k s a r e

s uc c e s s f u l
s uc c e s s f u l
d e s c r i b ed

Any m e s s a g e s wr i t t e n to the e r r o r m e s s a g e b u f f e r by the
Send
Me s s ag e
to
Error
Log g e r
s ys tem
s e rv i c e .
Th e u s e o f th i s
s ys tem s e r v i c e r e qu i r e s BUGC HK p r i v i l eg e .

Ope r a t i o n o f t h e E r r o r Lo g g e r Ro u t i n e s

E r r o r m e s sag e b u f fe r a l l o c a t i o n o c c u r s a t
I PL 3 1 .
Th i s
a l l o ws
a l loc a t i o n
r o ut i ne
( E R L $ A L LOC EM B )
to be c a l l ed f r om anywh e r e in
s y s t em ( i n c l ud i ng m a c h i n e c h e c k h a nd l e r s ,
wh i c h
ex e c u t e
at
I PL
w i tho ut c a u s i ng
I P L p r o b l em s .
I P L i s r e s to r ed to the c a l l e r ' s
b e f o r e c o n t r o l i s pa s s ed b a c k t o the c a l l e r .

the
the
31)
I PL

Th e r e a r e two 5 1 2-by t e b u f f e r s u s e d fo r ho l d i ng m e s s a g e s .
A f l i p- f l o p
s wi t c h ( E R L $GB_B U F I N D ) i nd i c a t e s wh i c h o f t h e two b u f f e r s i s c u r r e n t l y
act ive .
Al l o c a t i o n i nv o l v e s f i nd i ng eno ug h f r e e spac e i n t h e b u f f e r
i nd i c a t ed b y E R L$GB B U F I N D t o h o l d a m e s sag e .
Wh en t h e c u r r e n t b u f f e r
i s f i l l ed , t h e swi tch i s th r o wn t o a c t i v a t e t h e o th e r b u f f e r
a nd
the
E RRFMT p r o c e s s i s awa ke ned to wr i t e the f i l l ed b u f fe r t o t h e e r r o r l og
file .
A f t e r a m e s s ag e b u f f e r
is
s uc c e s s f u l l y a l l o c a ted ,
i ts add ress
is
r e t u r ned t o t h e c a l l e r o f the a l l o c a t i o n r o u t i n e , wh o l o a d s t h e b u f f e r
w i th i n fo rm a t i o n spec i f i c t o
t h e m e s sa g e b e i ng
l o g g ed .
Onc e
the
i n fo rma t i o n h a s
been
s to r ed ,
a
s e c o nd
r o u t i n e ( E R L $ R E LEASEM B ) i s
c a l l e d to wr i t e mo r e i n f o rma t i o n i n t o t h e m e s s ag e h e a d e r ,
i nd i c a t i ng
th a t t h e m e s sa g e i s v a l i d .
7-2

E RROR HANDLING
7 . 1 . 4 . 1 Wa k i ng the E RRFMT P r o c e s s - Th e r o u t i n e ERL $WAKE i s c a l l ed a t
l e a s t o n c e a s e c ond .
Th i s r o u t i n e i s a l s o c a l l ed wh e n o n e o f t h e t wo
l og b u f f e r s i s f i l l ed .
Th e r o u t i n e d o e s n o t a u tom a t i c a l l y wa k e
the
ERRFMT p r o c e s s .
Ra th e r , i t d e c r em e n t s a c o un t e r ( E R L $G B B U F T I M ) a n d
o n l y wa ke s E RRFMT i f th e c o un t e r g o e s to z e r o .
I f t h e c o un t e r g o e s to z e r o , i t i s a l s o r e s e t .
Th e
c u r r e n t s t a r t i ng
( Th i s va l u e i s a n a s s em b l y t i m e
v a l ue
fo r t h e e r r o r l og t i m e r i s 3 0 .
pa r am e t e r , no t ad j us t a b l e wi th S Y S G E N . ) Th a t i s , t h e r o u t i n e c a n b e
c a l l ed
a m a x i m um o f 3 0 t i m e s b e f o r e E RRFMT i s a wa k e n ed .
Th i s m e a n s
t h a t a m a x i m um o f th i r t y s e c o nd s c a n e l a ps e wi tho u t ERRFMT ' s b e c om i ng
c om p u t a b l e .
Th i s f o r c e s e r r o r m e s s a g e s to be wr i t t e n to th e e r r o r l o g
f i l e a t r e a s o n a b l e i n t e r v a l s , e v e n o n s ys tems
th a t h a v e v e r y f e w
e r r o r s o c c u r r i ng .
Th i s t i m i ng m e c h a n i sm i s e x p l o i t ed by t h e a l l o c a t i o n a n d d e a l l o c a t i o n
rout ines
if
t h e y w i sh
to
f o r c e a n a wa k e n i ng o f E RRFMT .
E i th e r o f
t h e s e r o u t i n e s s i mpl y l o ad s a 1 i n to E R L $ G B BUFT IM .
Th e n e x t c a l l
to
E R L $WAKE
( wh i c h m u s t be d o n e
at
I P L 7- so c a nno t b e done d i r e c t l y
e i th e r b y t h e a l l o c a t i o n o r d e a l l o c a t i o n
r o ut i ne )
i s g ua ranteed
to
wa k e ERRFMT .
Th e a l l o c a t i o n r o u t i n e fo r c e s a wa ke wh enev e r i t i s fo r c ed
to
s wi t c h
buf fe r s beca use
the
c ur rent buffe r
is
f ul l .
Th e b u f f e r r e l e a s e
r o ut i n e f o r c e s a wa ke i f t h e c u r r e n t m e s sag e b u f f e r
conta i ns
10
or
m o r e messag es .

C u r so r y Ove r v i ew o f the ERRFMT P r o c e s s

7. 1. 5

Th e ERRFMT p r o c e s s c o p i e s a pr ev i o u s l y f i l l ed e r r o r m e s s a g e b u f f e r
t h e e r r o r l og f i l e [ S YS E RR ] E R R L OG . S YS .
Th i s o c c u r s i n two s t e ps .

i n to
the
Th e c o n t e n t s o f t h e m e s s a g e b u f f e r a r e
c o p i ed
I PL 3 1
space
of
ERRFMT .
Th i s c o pyi ng
occ urs a t
s yn c h r o n i z e w i th the a l l o c a t i o n s u b r o u t i n e .

PO
to

On c e t h e
add ress
SYE , the
messages

I f a p r o c e s s h a s d e c l a r ed a n e r r o r l og ma i l bo x , e a c h m e s s a g e
i n t h e e r r o r l og b u f f e r i s a l s o s e n t to th a t m a i l bo x .

m e s s ag e b u f f e r c o n t e n t s a r e a c c e s s i b l e
in
ERRFMT ' s
space ,
t h e y c a n b e put i n to a fo rma t a c c e p t a b l e t o
e r r o r l og r e po r t g e n e r a to r .
Th e
r e f o rm a t t e d
error
a r e wr i t t e n t o [ S Y S E RR ] E RR LOG . S YS .

Af t e r ERRFMT h a s c om p l e t e d i t s
h i bernate ( H I B ) s tate .

7.1.6

o u t put

ope rat i ons ,

r eente r s

the

E r r o r Log Ma i l bo x

Th e e r r o r
l og g i ng
s ub s ys t em p r o v i d e s
t h e c a pa b i l i ty
( c u r r en t l y
ava i l ab l e
f o r i n t e r n a l u s e by D I G I TA L ) f o r a p r o c e s s to mo n i to r e r r o r
l og g i ng a c t i v i t y a s i t i s h a ppe n i ng r a th e r
than wa i t
fo r
off
l ine
p r o c e s s i ng
wi th the
f o rma t t i ng
p r og r am
SYE .
Th i s c a pa b i l i t y i s
p r ov i d ed th r o ug h a n u n s uppo r t e d s ys t em s e rv i c e c a l l ed
De c l a r e
E r ro r
Lo g Ma i l box ( S YS $ D E R LM B ) .

7-3

E RROR HANDL ING
7 . 1 . 6 . 1 S y s t em S e r v i c e C a l l - A p r o c e s s tha t h a s D I AGNOS E p r i v i l eg e
c an c a l l
t h e $ D E R LM B s ys t em s e rv i c e w i th a s i ng l e a rg um e n t , t h e un i t
n umb e r o f t h e ma i l bo x t o r e c e i v e e r r o r l og m e s s ag e s .
I f the e r r o r l og
m a i l bo x
i s n o t i n u s e ( th e e r r o r l og m a i l bo x d e s c r i p to r E XE $ G Q E R LM B X
c o n ta i n s a z e r o ) , t h e un i t n um b e r i s s to r ed i n t h e f i r s t wo rd o f t h e
m a i l bo x d e sc r i p t o r a nd t h e P I D o f t h e r e q ue s t i ng p r o c e s s i s s to r ed i n
t h e s e c o nd l o ng wo r d .
I f th i s s e rv i c e i s c a l l ed w i t h a un i t n um b e r o f z e r o ,
t h e d e sc r i pt o r
i s c l e a r ed ,
d i s ab l i ng t h e e r r o r l og m a i l bo x f e a t u r e .
Th e d e s c r i pt o r
i s a l so
u n c o nd i t i o n a l l y c l e a r ed
by
the
i m ag e
r un d o wn
r o ut i ne
( Ch a p t e r 1 8 ) .

7 . 1 . 6 . 2 Ac t i o n o f the E RRFMT P r o c e s s - I f t h e E RRFMT p r o c e s s d e t e c t s
tha t
the
e r r o r l og ma i l bo x f e a t u r e i s e n a b l ed , i s s e nd s e a c h m e s sag e
tha t i t ex t r a c t s
f r om
th e
e r ro r
l og
buf fer
to
tha t
e s t a b l i sh ed
m a i l bo x .
Th us a p r o c e s s c a n m o n i to r m e s s ag e s th a t t h e E RRFMT p r o c e s s
i s wr i t i ng to t h e e r r o r l og f i l e .

7.2

SYSTEM C RASHES

( B UGCHECKS )

Wh e n VM S d e t e c t s a n i n t e r n a l i nc o n s i s t e n c y s uc h a s
a
c o r r up t e d d a t a
s t r uc t u r e
o r an unexpe c t ed e x c e p t i o n , i t d e c l a r e s a b ug c h e c k .
I f the
s ys tem c a n c o n t i n ue r un n i ng , a no n f a t a l b ug ch e c k
i s d e c l a r ed ,
wh i c h
r esul ts
in
an e r ror
l og
entry .
S e r i o us
e r ro r s
resul t in fatal
b ug ch e c k s , t h r o ug h wh i c h t h e s ys tem
is
s h u t d o wn
in a
c o n t r o l l ed
f a sh i o n .
1.

Th e c o n t e n t s o f ph ys i c a l memo r y a r e wr i t t e n
to
the
s ys tem
d um p f i l e ( un l e s s i nh i b i t ed by a SYS BOOT f l ag , DUM P B UG ) .

Af t e r t h e s y s t em i s h a l t e d ,
i t may r e s ta r t
i ts e l f
( ag a i n
a c c o r d i ng t o t h e s e t t i ng o f a SYSBOOT f l ag , BUG R E B O OT ) .

B UGCHECK M e c h a n i sm

7.2.1

Th e p a th i n t o th e b ug ch e c k r o u t i n e
a ppe a r s
in
source code
as
the
i nvo c a t i o n o f
the
B UG C H E C K ma c r o .
Th i s m a c r o e x pa n d s i n to o pc o d e
A XF F , a b y t e c o n t a i n i ng �XF E , a nd a wo r d c o n ta i n i ng
the
pa r t i c u l a r
b ug c he c k c o d e .
Th e e x e c u t i o n o f
o pc o d e
A X FF
results
in
an
r e se rved
i n s t r uc t i o n
e x c e p t i o n ( S S $ O PC DEC , o pc o d e r e s e r v e d t o D I G I TA L ) , c a us i ng c o n t r o l to
be
t r a n s f e r red
th r o ug h
the
Sy s t em
Co n t r o l
Bl o c k
to
an
e x c ep t i o n - s p e c i f i c s e rv i c e r o u t i n e .
Th i s r o u t i n e c h e c ks wh e th e r
•

t h e o pc od e i s A XF F a nd

•

t h e by t.e fo l l o w i ng t h e r e s e r v ed
o pc o d e
is
e i th e r
A XF E o r
A XF D .
( A A XF E i nd i c a t e s th a t t h e b ug c h e c k c o d e i s c o n t a i ned
in the n e x t wo r d .
A A XFD i nd i c a t e s th a t the b ug ch e c k code i s
c o n ta i ned
in
t h e n e x t l o ng wo r d .
VM S d o e s n o t c u r r e n t l y u s e
l o ng wo r d b ug c h e c k c o d e s . )

7-4

ERROR HANDLING
I f b o t h o f t h e s e c h e c k s s uc c ee d , VMS i n t e r p r e t s th i s e x c e p t i o n
as a
b ug ch e c k
a nd
t r an s f e r s c o n t r o l to r o u t i n e EXE $ B UG C H EC K .
Oth e r w i s e ,
t h e i l l eg a l o pc o d e e x c ep t i o n i s t r e a t ed i n t h e u s ual m a n n e r d e sc r i b ed
i n Ch a pt e r 2 .

Ope r a t i o n o f BUGC HECK Ro u t i n e

7. 2. 2

Th e b ug c h e c k r o u t i n e pe r fo rm s s ev e r a l s t eps , d e pe nd i ng o n t h e
access
mode
i n wh i c h t h e b ug c h e c k o c c u r r ed
a nd wh e th e r t h e b ug c h e c k wa s
( Th e f a t a l i ty o f t h e b ug c h e c k i s d e te r m i n ed
by
the
seve r i ty
f a ta l .
f i eld
< 2 : 0>
i n t h e b ug ch e c k c o d e .
I f t h e B UG C H E C K m a c r o c a l l
is
i n c l ud e s t h e pa rame t e r FATAL , a c o d e o f S T S $K S EVE R E (v a l ue o f
4)
p l a c ed
i n to
th i s
f i eld .
O t h e rwi s e , a z e r o- i s p l a c ed th e r e . ) I f t h e
SYS B OOT f l ag B UG C H E C KFATAL i s s e t , a l l bug c h e c k s a r e t r e a ted a s f a t a l ,
i n d e pe nd e n t o f
the
s e v e r i t y c o d e i n t h e l o w o r d e r th r e e b i t s o f t h e
b ug ch e c k c o d e .
Th e BUG C H ECKFATAL f l ag i s c l e a r i n a l l pa r am e t e r f i l e s
d i s t r i b u t ed
by D I G I TA L ,
wh i c h m e a n s th a t n o n f a t a l b ug ch e c k s d o n o t
c a u s e t h e s ys tem t o c r a s h .

7 . 2. 2. 1
B ug c h e c k s f r o m Us e r a nd S up e rv i s o r Mo d e - I f
a
b ug c h e c k
is
g en e r a ted
f r om
e i th e r
user
o r s upe rv i s o r m o d e , a n d th e p r o c e s s h a s
B UG C H E C K p r i v i l eg e , a m e s s ag e ( o f
t ype
u s e r - g e n e r a ted
b ug c h e c k )
is
wr i t t e n t o t h e e r r o r l og b u f f e r .
•

I f t h e b ug c h e c k i s f a t a l , t h e $ E X I T s ys tem s e r v i c e i s
c a l l ed
w i th
the
c o d e S S $ B UG C H E C K a s t h e f i n a l i m a g e s t a t us .
Wh a t
h a pp e n s a s a r e s ul t-o f
th i s c a l l d e pend s o n wh e th e r
the
process
is
e x e c u t i ng
a
s i ng l e
imag e
( no s up e rv i s o r m o d e
t e rm i n a t i o n h a nd l e r h a s b e e n e s t a b l i s h ed ) o r t h e p r o c e s s
is
a n i n t e r a c t i v e o r b a tc h j o b .
I f the proc e s s i s
e x e c u t i ng
a
s i ng l e
i m ag e ,
a
fatal
b ug c h e c k
f r om u s e r o r s upe rv i so r m o d e r e s u l t s i n p r o c e s s
deletion.
W i th t h e c u r r e n t
use
of
s upe r v i so r m o d e
t e rm i n a t i o n
h a nd l e r s ,
a f a t a l b ug c h e c k i s s ue d f r om an i n t e r a c t i v e o r
b a t c h j o b c a u s e s t h e c u r r e n t l y ex e c u t i ng
i m ag e t o e x i t
and control
t o b e pa s s e d to the C L I t o r e c e i v e t h e n e x t
c omma n d .
In
e i ther
case ,
t h e o n l y d i f f e r e n c e b e twe e n
us e r
a nd
s upe rv i s o r mo d e
is
t h a t u s e r m o d e t e rm i n a t i o n h a nd l e r s a r e
no t c a l l ed i f a f a t a l
b ug c h e c k
is
i s s ued
f r om
s upe r v i so r
mo d e .

•

I f t h e b ug c h e c k c o d e i s n o t f a t a l , t h e e x c e p t i o n ( th e i n i t i a l
pa th
i n to
t h e b ug c h e c k
code )
i s d i sm i s s ed a nd e x e c u t i o n
c o n t i n u e s w i th t h e i n s t r uc t i o n fo l l o w i ng t h e BUG CHECK ma c r o .

Th e BUG C H EC KFATAL f l ag h a s no e f f e c t o n b ug c he c k s i s s ue d f r om u s e r
or
s u pe r v i s o r m o d e .
Th e s e v e r i t y f i e l d i n t h e b ug ch e c k c o d e i s u s e d to
d e t e rm i n e wh e t h e r a g i v e n b ug ch e c k i s
fatal .
In add i t i on ,
n e i th e r
u s e r no r s upe r v i so r m o d e b ug c h e c k s c a u s e t h e s ys tem t o s h u t d o wn .

7-5

E RROR HANDL I NG
7 . 2 . 2 . 2 VMS U s e o f B ug c h e c k s - Th e b ug ch e c k s t h a t VM S
o wn pu r po s e s a r e i s s ue d f r om e x e c u t i v e o r k e r n e l mo d e .

uses

fo r

i ts

If
t h e b ug c h ec k
i s not
fata l
a nd
the
SYSB OOT pa r am e t e r
f l ag
BUGC H E C KFATAL wa s t u r ned o f f , t h e b ug ch e c k r o u t i n e p r o c e ed s a s i t d o e s
f o r n o n f a t a l b ug ch e c k s f o r t h e o u t e r two a c c e s s m o d e s .
A m e s sag e
is
sent t o
the e r r o r
l og g e r
a nd
t h e e x c e pt i o n i s d i sm i s s ed , pa s s i ng
c o n t r o l b a c k t o t h e c a l l e r a t the i n s t r uc t i o n f o l l o w i ng
t h e b ug c h e c k
i nv o c a t i o n .
A f a t a l b ug c h e c k r e s u l t s i n a n o rd e r l y s h u td own o f t h e s ys t em .
Ra th e r
t h a n d e sc r i b e e a c h s t e p th a t t h e b ug ch e c k r o u t i n e t a k e s t o ac c ompl i s h
th i s s h utd o wn , we w i l l d e sc r i b e s e v e r a l i t em s o f g e n e r a l
i n te r e s t
in
t h e o p e r a t i o n o f t h e o r d e r l y s h utd o wn .
•

•

Al l d i s k I /0 p e r fo rmed
by
t h e b ug ch e c k
r o ut i n e
uses
the
b o o t s t r a p d i s k d r i v e r u s ed b y t h e i n i t i a l i z a t i o n p r og r am s VMB
a nd S YS B OOT ( Ch a p t e r 2 1 ) and l o a d ed
i n to
n o n pag ed
po o l
by
! N I T ( Ch a p t e r 2 2 ) .
Th e u s e o f t h i s d r i v e r a l l o ws a d um p f i l e
t o b e wr i t t e n e v e n i f the s ys tem d i s k d r i v e r i s c o r r up t ed .
Mo s t o f t h e bug c h e c k r o u t i n e a n d a l l t h e b ug c h e c k
c o d e s a nd
a s soc i a ted
text
a re not
r es i d ent .
Th e y a r e s t o r e d i n the
e x e c u t i v e i m ag e S Y S . EXE and read i n to m emo r y
( by t h e b o o t
driver) .
Th i s c o d e a n d d a t a a r e r e a d i n to s ys tem spa c e o n
top o f a
r e a d - o n l y po r t i o n o f t h e ex ec u t i v e .
G l o b a l l a b e l BUG $ FATA L
d e f i n es t h e b eg i n n i ng o f t h e b u f f e r i n to wh i c h t h e b ug ch e c k
c o d e a nd d a t a w i l l be r e ad .
Th i s l a b e l i mmed i a t e l y p r e c ed e s
t h e b l a n k p r og r am s e c t i o n ( n am e d
BLANK
a nd
l o c a t ed
at
a d d r e s s 8 0 0 0 7 0 6 8 i n Ve r s i o n 2 o f VAX/VM S ) .
•

Th e c o d e a nd d a t a th a t a r e r e ad
i n c l ud e :

•

i n to

m emo r y

th i s

t i me

t h e b u l k o f t h e b ug c h e c k s e r v i c e r o u t i n e ,
a t empl a t e fo r t h e m e s s ag e th a t i s t yp e d on
t e rm i n a l ,

the

c o n so l e

some p r i m i t i v e c o nso l e t e rm i n a l o u t put r o u t i n e s , a nd
the
t e x t ua l
m e s s ag e s .

d e sc r i p t i o n

all

po s s i b l e

b ug c h e c k

Th e r e a r e t wo impl i c a t i o n s o f r e ad i ng c o d e i n to memo r y on to p
o f e x i s t i ng c o d e .
N o n e o f the r o u t i n es d e s t r o ye d by BUG C HE C K
is
ava i l ab l e
for
u s e b y t h e b ug ch e c k c o d e .
Th i s i s m o s t i mpo r t a n t i n
d e c i d i ng h o w t h e n o npa g ed e x e c u t i v e i s l a i d o u t .
Po r t i o n s o f t h e d ump m a y l o o k s t r a ng e wh e n
i n s pe c t ed b y
S DA .
Fo r
ex ampl e ,
it
i s i m po s s i b l e t o d e t e rm i n e i f a
po r t i o n o f t h e i n s t r uc t i o n s t r eam
i s c o r r up t e d
bec a u s e
S DA d i spl a y s b ug c h e c k c o d e a nd
d a ta
i n s t e ad
o f the
o r i g i n a l i n s t r uc t i o n s a nd r e ad o n l y d a ta .

7-6

ERROR HANDL ING
e

A h e a d e r b l o c k f o r t h e d um p f i l e i s c o n s t r uc t e d
i n the
512
b yt e s
i mm e d i a t e l y p r e c e d i ng the a r ea i n to wh i c h t h e b u g ch e c k
c o d e a n d d a t a we r e w r i t t e n .
Th i s a r e a
conta i ns
mo r e
r e a d - o n l y po r t i o n s
of
t h e no npag ed e x e c u t i v e .
( Th e s ys t e m
v i r t ua l a d d r e s s r a ng e
wh o s e c on t e n t s a r e
a l t e r ed b y the
o pe r a t i o n
of
b ug c h e c k ,
i n c l ud i ng
the
5 1 2 b y t e d um p f i l e
h e ad e r b l o c k ,
e x t e nd s
f r om
800 06E68
to
8 0 0 0 91 2 3 .
Th e s e
n um b e r s a r e v a l i d fo r Ve r s i o n 2 o f VM S a n d a r e a l m o s t c e r ta i n
t o c h a ng e w i th t h e n e x t m a j o r r e l e a s e o f t h e s ys t em . )
Th e c o n t e n t s o f the d ump f i l e h e a d e r
block
are
l i sted
in
Ta b l e 7 - 1 .
No t e
that
t h e e r r o r l og e n t r y a s so c i a t e d wi th
th i s b ug c h e c k i s wr i t t e n i n to th e h e a d e r
to
avo i d
loss o f
i n f o rma t i o n
if
the
e r ro r
l og
b u f f e r s we r e f u l l wh e n t h e
b ug c h e c k o c c u r r e d .
Th i s e r r o r l og e n t r y w i l l b e wr i t t e n i n to
o n e o f t h e e r r o r l og b u f f e r s by SYS IN I T ( Ch a p t e r 2 2 ) wh e n t h e
r e s t o f t h e e r r o r l og m e s s ag e s ( b l o c k s 2 a nd 3
in
t h e d um p
f i l e ) a r e p u t b a c k i n to t h e b u f f e r s .
( I f t h e r e i s no r o om i n
t h e e r r o r l og b u f f e r s ,
t h e b ug ch e c k
e n t r y wi l l
neve r b e
wr i t t e n t o
th e e r r o r
l og
file,
a l tho ug h
the
entry
is
p r e s e r v ed i n th e d ump f i l e . )

•

A sm a l l amo un t o f
i n fo rm a t i o n d e s c r i b i ng
th e b ug c h e c k
is
wr i tten
to
t h e c o n s o l e t e rm i n a l .
Th i s i n f o rm a t i o n i n c l ud e s
t h e c o n t e n t s o f g e ne r a l r eg i s te r s , t h e k e r n e l
a nd
ex e c u t i v e
s tacks ,
the
c o n t e n t s o f p r o c e s s o r i n t e r n a l r eg i s te r s , a nd a
s umm a r y o f t h e r e a so n f o r t h e bug chec k .
Th i s o u tput o c c u r s
b e fo r e t h e d ump f i l e i s wr i t t e n a nd sho u l d no t b e i n t e r r up t e d
b y h a l t i ng t h e VAX p r o c e s so r f r om the c o n s o l e t e rm i n a l .
Suc h
an
i n t e r r upt i o n wo u l d
p r ev e n t
the d ump f i l e
f r om be i ng
wr i t t e n .
Th e d um p h e a d e r , t h e c o n t e n t s o f the two e r r o r
l og
buf fe r s ,
a n d t h e c o n t e n t s o f phys i c a l m em o r y a r e wr i t t e n to the s ys t em
d ump f i l e .
Th i s
step c an be
i nh i b i t ed
b y c l e a r i ng
the
S Y S B OOT pa r am e t e r
f l ag
DUM PB UG .
Th e
sys tem d um p f i l e i s
d e s c r i b ed i n some d e t a i l i n the n e x t s e c t i o n .
Th e l a s t s t e p i n t h e b ug ch e c k
rout ine
r eboo ts
the s ys t em .
Th i s
is
a c c om p l i s h e d by w r i t i ng a s p e c i a l c o d e ( A XF 0 2 ) i n to
t h e c o n s o l e t r a n sm i t d a t a b u f f e r
( PR $ TXDB ) .
( Th e s pe c i a l
u s e s o f t h e c o n so l e r eg i s t e r s a r e d esc r i b ed i n Ch a pt e r 1 5 . )
Af t e r t h e b o o t s t r a p c o d e i s wr i t t e n , a
HALT
i n s t r uc t i o n
is
executed
th a t a l l o ws
c o n so l e m i c r o c o d e to g a i n c o n t r o l a nd
p r o c e s s t h e boo t s t r a p c ommand .
On a VAX- 1 1 / 7 5 0 s ys t em ,
t h e bo o t s t r a p d ev i·c e s e l e c to r
s w i t c h mus t b e pr o pe r l y s e t a nd t h e s ys t em d i s k m u s t b e
un i t 0 i n o r d e r f o r t h e sys tem t o a u t o m a t i c a l l y r e b o o t
f o l l owi ng a b ug c h ec k .
On a VAX- 1 1 / 7 8 0 s ys t em ,
t h e c on t e n ts o f the
file
DE FBOO . CMD o n the c on s o l e f l o ppy m u s t c o n t a i n c omma n d s t o
d i r e c t a r eb o o t f r om th e s y s t em d i s k .
Th e a u toma t i c r eb o o t f o l l o w i ng a b ug c h e c k c a n b e p r e v e n ted b y
c l e a r i ng
t h e SYS B OOT p a r am e t e r f l ag BUGRE BOOT .
Th i s f l ag i s
a l so m a n ua l l y c l e a r ed b y O PC CRASH , t h e p r o g r a m th a t ex e c u t e s
a s p a r t o f t h e o rd e r l y s h utd own p r o c e d u r e S H UTDOWN . C OM .
Wh e n
a u t om a t i c r e bo o t i ng i s i nh i b i ted , t h e s ys t em l o o ps a t I PL 3 1 ,
wa i t i ng f o r a c ommand to b e e n te r ed a t t h e c o n s o l e t e rm i n a l .
7-7

ERROR HANDL I NG
Ta b l e 7 - 1
Co n t e n t s o f Dum p F i l e He a d e r Bl o c k

Desc r i pt i on

S i ze

La st error l og sequence number ( unused )

long wo rd

Dump f i l e flag
( Lo w b i t set i f d ump f i l e anal yzed )
Dump f i l e ver s i o n
( Co nta ins 1 if Ver s i o n 2 . 0 fo rmat )

wo rd
wo rd

Contents o f SBR , SLR , KS P , ESP , SSP, US P , I S P

7 l ongwo rds

Quadwo rd memory desc r i pto rs fo r u p t o e ight
memo ry contr o l l ers ( each quad wo rd is
b ro ken d own as fo l lows :
Pag e count
TR n umber fo r thi s c ontro l l er
Ba se PFN fo r thi s c ontrol l er

quadwo rds
2 4 b i ts
8 b i ts
3 2 b i ts

System v e r s i o n number

longwo rd

One ' s complement of prev i o us l ongwo rd

longwo rd

Er r o r l og ent r y fo r c rash/resta r t
( Se e d e sc r ipt ion bel ow)

1 25 wo rds

Co ntents of so ftwa re PCB o f c u r r ent process
( Table D-2 )

140 bytes

( Co n te n t s o f E r r o r Me ssag e B u f f e r fo r C r a sh / Re s t a r t En t r y)

E r r o r Me ssag e Buf f e r Head e r
S i ze in bytes o f buffe r
Al l oc a t i o n buffer i nd i c a to r
E r r o r message val id i nd ic ato r

l o ngwo rd
wo rd
byte
byte

En try type ( conta ins EMB$K CR

wo rd

3 7 d ec imal }

System t ime when c rash occur r ed
( fr om EXE $G Q_SYS T IM E )

quad wo rd

E r ro r l og sequenc e number
( l ow o rd e r wo rd of ERL$G L_S EQUENC E )

wo rd

Co ntents o f KS P, E S P , SSP, US P , I S P

5 longwo rds

Co ntents o f RO t o Rl l , AP , FP , SP, PC , PS L

1 7 long wo rd s

Co ntents o f POBR, POLR , PlBR, P lLR , SBR, S LR ,
PCB B , SCBB , ASTLVL , S IS R , ICCS, ICR,
TODR , ACCS

14 long wo rd s

Co ntents o f CPU-spec i f i c reg i ste rs

21 long wo rds

( Fo r the VAX- 1 1 /7 5 0 th i s a r ea c onta i n s
Tr ansl a t i o n b u f f e r d i sab l e reg i ster ( PR$_TBDR)
Cache d i sa b l e r eg i ster ( PR $ CADR }
Mac h i n e chec k e r ro r summa r y- ( PR$ MCESR )
Cache e r r o r r eg i ster ( PR$ CAER } CM I e r r o r summary r eg i ster ( PR$_CM I ERR )

long wo rd
long wo rd
l ong wo rd
l ongwo rd
long wo rd

( Fo r the VAX-1 1/7 8 0 th i s a rea c onta i n s
SB I faul t sta tus ( PR$ S B I F S )
SB I compa r a to r r eg i ster ( PR $ S B I SC )
SB I ma intenanc e reg i ster ( PR$ SB IMT )
SB I e r r o r r eg i ster ( PR$ S B ITA)
SB I t i meout add r ess r egTster ( PR $_S B IS )

l o ng wo rd
long wo rd
long wo rd
long wo rd
long wo rd

Bug chec k c rash code

longwo rd

Leng th i n byte s of so ftwa r e PCB

wo rd

The e r r o r l og entry fo r a non f a ta l bug chec k conta i n s the same
i n fo rm a t i o n as the entry fo r a fata l bugcheck except fo r the
3 5 longwo rds set a s i d e fo r a rchi tec tural and CPU -spec i f i c
proc esso r r eg i ste r s .

7-8

ERROR HANDL ING
Sys t em Dump F i l e

7. 2. 3

Th e m o s t i mpo r ta n t o pe r a t i o n t h a t i s pe r f o rmed b y t h e b ug ch e c k r o u t i n e
is
to
wr i t e
the
c o n t e n t s o f phys i c a l m em o r y a nd o th e r i m po r t a n t
i n fo rm a t i o n t o t h e d ump f i l e .
I n t h e c a s e o f s ys t em c r a s h e s , t h e d um p
file
c a n b e e x am i n ed by t h e Sys t em Dump An a l y z e r ( S DA } to d e t e rm i n e
t h e r e a so n fo r th e c r a sh .
Th e d ump f i l e c o n t a i n s
th r e e d i s t i n c t
p i ec e s .
1.

Th e p r ev i o us l y c o n s t r uc t e d d ump h e a d e r
to the f i r s t block in the f i l e .

Th e t wo e r r o r l og b u f f e r s a r e wr i t t e n to t h e n e x t two b l o c k s .
Th e s e b u f f e r s wi l l be c o p i ed b a c k i n to th e e r r o r l og b u f f e r s
i n m emo r y f r om th e d um p f i l e b y SYS I N I T ( Ch a p t e r 2 2 } a s p a r t
of
the
i n i t i a l i za t i o n code .
In
th i s
wa y ,
n o e r r o r l og
i n f o rm a t i o n i s l o s t a c r o s s a
s ys tem c r a s h o r
an
o pe r a to r
r e que s t ed s h u td own .

Th e r e s t o f t h e d um p f i l e i s f i l l ed wi th t h e c u r r e n t c o n t e n t s
of
phys i c a l m emo r y .
B ug c h e c k u s e s t h e m em o r y d e s c r i p t o r s i n
t h e Re s t a r t
Pa r am e t e r
Block
( RPB }
c o n s t r uc t ed
by
VMB
( Ch a p te r 2 1 }
to
p r ov i d e
an accurate
l a yo u t o f ph y s i c a l
I f a MA7 8 0 s h a r ed m emo r y a d a p t e r
i s present
add ress space .
o n t h e s y s t em ,
i ts contents
a r e a l s o wr i t t e n t o t h e d ump
file.

( Ta b l e 7 - 1 }

i s wr i t t e n

Th e s i z e o f t h e d um p f i l e m u s t b e f o u r b l o c k s l a rg e r t h e n
the n um b e r
( Th e f o u r th b l o c k i s no t c u r r e n t l y
of
phys i c a l
pag e s i n t h e sys t em .
u s ed . } I n o r d e r t o i n s u r e th a t a c r a s h d um p c a n b e a n a l y z e d w i th
S DA ,
I f a d ump f i l e i s
i t i s i mpo r t a n t tha t t h e d ump f i l e b e l a r g e eno ug h .
t o o sm a l l , o n l y t h e ph y s i c a l pag e s th a t f i t i n to
the
und e r c o n f i g u r ed
I n a t yp i c a l VM S c o n f i g u r a t i o n , t h e m o s t
d ump f i l e w i l l be wr i t t e n .
c r uc i a l c o n t e n t s o f
phys i c a l
memo r y ,
t h e s ys tem pa g e
tabl e ,
a re
l o c a ted a t t h e l a rg e s t phys i c a l a d d r e s s e s ( Ch a p t e r 2 1 } and w i l l n o t b e
wr i t t e n , m a k i ng a pa r t i a l d um p u s e l e s s .
Th a t i s , S DA c a nno t b e
used
t o ex am i n e a d ump f i l e t h a t d o e s n o t c o n t a i n a l l o f ph ys i c a l m em o r y .

7. 3

MAC H INE C HECK M E C HAN I SM

A m a c h i n e c h e c k i s a n e x c e pt i o n tha t i s r e po r t e d wh e n t h e
C PU o r
an
e x t e r n a l a d a pt e r d e t e c t s a n i n t e r n a l e r r o r .
Th e i n i t i a l pro c e s s i ng o f
a ma c h i n e c h e c k e x c e p t i o n i s C P U s p e c i f i c .
Th i s s e c t i o n c o n t a i n s
an
o v e r v i e w o f m a c h i n e c h e c k h a nd l i ng .
Co n s u l t t h e VAX H a rdwa r e H a n d bo o k
o r o th e r h a r d wa r e- r e l a t e d l i t e r a t u r e fo r i n fo rma t i o n a b o u t a
spec i f i c
t ype o f m a c h i n e c h e c k .
Th e b a s i c ph i l o s o ph y o f a n y o f t h e m a c h i n e c h e c k h a nd l e r s i s to
keep
as much of
t h e s y s t em r un n i ng a s po s s i b l e .
Th e r e a r e two impo r t a n t
p i e c e s o f i n fo rm a t i o n th a t d e t e rm i n e h o w s e r i o u s a pa r t i c u l a r m a c h i n e
check
is :
t h e n a t u r e o f the m a c h i n e c h e c k i t s e l f a nd the a c c e s s m o d e
i n wh i c h t h e m a c h i n e c h e c k o c c u r r ed .
•

I f the mac h i n e check i s r ecove rab l e , the s impl e a c t io n i s
to
l og
an
e r ro r .
Th i s s t e p i s t a k e n i nd e pe nd e n t of t h e a c c e s s
m o d e i n wh i c h t h e m a c h i n e c h e c k o c c u r r ed .
In
ad d i t i o n ,
the
e r ro r
t ime
is
r e c o r d ed .
I f m a c h i n e c h e c k s s t a r t o c c u r r i ng
t o o q u i c k l y ( mo r e th an o n e m a c h i n e c h e c k p e r
1 0 m i l l i s e c o nd
i n t e rva l } , t h e n t h e h a nd l e r a s s um e s th a t s o m e th i ng s e r i o u s i s
7-9

ERROR HANDL ING
wr o ng a nd t r e a t s a r e c o v e r a b l e m a c h i n e c h e c k in the s a m e wa y
t h a t i t t r e a t s an a b o r t .
Th e d i s t i n c t i o n b e twe e n r e c o v e r a b l e
m a c h i n e c h e c k s a n d a b o r t s i s C P U s pe c i f i c .
Th e VAX H a rdwa r e
t h e m o d u l e MCHEC K x x x ( MC HE C K 7 5 0 o r MCHEC K 7 8 0 )
Ha n d b o o k o r
c o n t a i n s i n fo rma t i o n a b o u t t h e m a c h i n e c h e c k s th a t c a n o c c u r
o n a pa r t i c u l a r p r o c e s s o r .
•

I f t h e m a c h i n e c h e c k h a s p u t t h e sys tem
i n to
a
state
f r om
wh i c h
it
c annot
r ecove r ,
the
a c t i o n t a k e n by the m a c h i n e
c h e c k h a nd l e r d e pend s o n t h e a c c e s s m o d e i n wh i c h t h e m a c h i n e
I f t h e p r ev i o u s m o d e wa s s up e r v i s o r o r us e r ,
c h e c k o c c u r r ed .
a m a c h i n e c h e c k e x c e p t i o n i s r e po r t ed to
th a t
a c c e s s mo d e .
( Un l e s s
t h e p r o c e s s h a s t a k e n s pe c i a l a c t i o n , th i s s t e p wi l l
r e s u l t i n i m a g e e x i t . ) I f the p r ev i o u s m o d e wa s e x ec u t i v e o r
ke rnel ,
an
i r r ec ov e r ab l e mach i n e chec k c a us e s
a
fatal
b ug c h e c k ( wi th t h e b ug c h e c k c o d e BUG $_MAC H I N ECHK ) .

VAX- 1 1 /7 5 0 M a c h i n e Ch e c k

7. 3. 1

Wh e n a m a c h i n e c h e c k o c c u r s o n a VAX- 1 1 / 7 5 0 , I P L i s e l e v a t e d t o 3 1 a nd
t h e i n t e r r up t s t a c k c o n t a i n s t h e fo l l o w i ng i n fo r m a t i o n .
•

Th e l e ng th i n byt e s o f
the
e x c e p t i o n - spec i f i c
i n f o rma t i o n
p u s h ed o n t h e s t a c k .
( Th i s c o un t d o es n o t i n c l ud e e i th e r th e
PC/ P S L pa i r
or
t h e c o un t
l o ng wo r d
i tse l f . )
Th e r e
are
c ur r en t l y
1 0 l o ngwo r d s i n th i s l i s t , wh i c h r e s u l t i n a v a l u e
of 2 8 hex o n the s tac k .

•

Ma c h i n e c h e c k e r r o r c o d e

•

Vi r tua l a d d r e s s o f t h e l a s t f e t c h o r s t o r e o pe r a t i o n

•

P r o g r am c o un t e r a t the t i m e o f t h e e r r o r

•

Mem o ry d a t a o f the l a s t f e tch o r s to r e o pe r a t i o n

•

S a v e d mod e r eg i s t e r

•

Re a d l o c k t i m e o u t r eg i s t e r

•

T r a n s l a t i o n b u f f e r pa r i t y e r r o r r eg i s t e r

•

Ca c h e e r r o r r eg i s t e r

•

Bus e r r o r r eg i s t e r

•

E r r o r s umm a r y r eg i s t e r

•

PC o f a b o r t e d o pc o d e

•

PS L a t t h e t i m e o f t h e a bo r t

Th e m a c h i n e c h e c k e r r o r c o d e ( t h e s e c ond i t em o n the s t a c k ) d e t e r m i n e s
the
s pe c i f i c
ac t i o n o f
t h e m a c h i n e c h e c k h a nd l e r .
I f the mac h i ne
c h e c k i s a n abo r t ( PC l e f t i n a n i nd e te rm i n a t e s t a t e ) ,
then
r ecovery
is
i mpo s s i b l e .
I n ad d i t i o n ,
a
s ub s e t o f
t h e VAX- 1 1 i n s t r uc t i o n
( Th e
l i st o f
the se
o pc o d e s o n t h e VAX- 1 1 /7 5 0 c a n no t b e r e s t a r t ed .
i n s t r uc t i o n s c a n b e fo und i n m o d u l e MCHEC K 7 5 0 . )

7-1 0

ERROR HANDL ING
I n a d d i t i o n t o the VAX- 1 1 / 7 5 0 m a c h i n e c h e c k s th a t a ppe a r a s e x c e p t i o n s
( th r o ug h
the
S C B v e c to r
a t o f f s e t 4 ) , t h e r e a r e two m a c h i n e c h e c k s
t h a t a ppe a r a s i n t e r r up t s t h r o ug h d e d i c a t ed S C B v e c to r s .
Wh e n
e i th e r
of
these occur s ,
o n l y t h e PC a n d PS L a r e p u s h e d o n to the i n t e r r up t
s t ac k .
•

A " c o r r e c t e d memo r y d a t a " c o nd i t i o n ( CRD ) w i l l
i n t e r r upt
at
I PL
26
t h r o ug h
S C B v e c to r 5 4 ( h e x ) .
Th i s e x c ept i o n s i m p l y
c a u s e s a n e r r o r l o g e n t r y ( i nd i c a t i ng a s o f t m emo r y e r r o r ) to
b e wr i t t e n .
( I f e r r o r s o c c u r too q u i c k l y , the CRD i n te r r up t
b i t i n t h e memo r y c o n t r o l l e r i s t u r ned
o f f by the mach i ne
c h e c k h a nd l e r . )

•

i n te r r up t a t
I PL
29
A " wr i t e b u s e r r o r "
c o nd i t io n w i l l
th r o ug h S C B v e c to r
60
( hex ) .
Th i s e r r o r i s t r e a t e d a s a n
i r r e c o ve r a b l e e r r o r a nd f u r th e r
p r o c e s s i ng
d e pe nd s o n
the
p r ev i o us a c c e s s m o d e .

VAX- 1 1 /7 8 0 M a c h i n e Ch e c k

7. 3. 2

Wh e n a m a c h i n e c h e c k o c c u r s o n a VAX- 1 1 /7 8 0 , I P L i s e l eva t e d to 3 1 a nd
t h e i n t e r r up t s t ac k c o n t a i n s t h e fo l l o w i ng i n fo rm a t i o n �
•

Th e l e ng th i n by t e s o f
the
e x c e pt i o n - s p e c i f i c
i n f o rm a t i o n
p u s h e d o n the s t a c k .
( Th i s c o u n t d o e s no t i n c l ud e e i th e r t h e
PC/P S L p a i r
or
t h e c o un t
l o ng wo r d
i tse l f . )
Th e r e
a re
c ur r ently
1 0 l o ng wo r d s i n th i s l i s t , wh i c h r e s u l t i n a v a l ue
o f 2 8 hex on the s t ac k .

•

Ma c h i n e c h e c k s umma r y pa r am e t e r

•

CPU e r ro r s ta t us

•

T r a pped m i c r o PC , t h e m i c r o c o de e r r o r l o c a t i o n

•

Vi r t u a l a d d r e s s a t f a u l t t i m e

•

C P U D r e g i s te r a t f a u l t t i m e

•

Tr a n s l a t i o n b u f f e r s t a t us r eg i s t e r 0

•

Tr a n s l a t i o n b u f f e r s t a tus r eg i s t e r 1

•

Ph ys i c a l a d d r e s s c a u s i ng S B I t i m e o u t

•

Ca c h e pa r i t y e r r o r s t a t u s r eg i s te r

•

S B I e r r o r r eg i s t e r

•

PC o f i n s t r uc t i o n t h a t c a us e d t h e m a c h i n e ch e c k

•

PS L o f ma c h i n e a t f a u l t t i m e

Th e m a c h i n e c h e c k s umma r y pa r am e t e r d e t e rm i n e s t h e spe c i f i c a c t i o n o f
I f the m a c h i n e c h e c k i s a n a b o r t ( PC l e f t
t h e m a c h i n e c h e c k h a nd l e r .
i n a n i nd e t e rm i n a t e s t a t e ) , t h e n r ec o v e r y i s i m po s s i b l e .
I n add i t i on ,
a s ub s e t o f t h e VA X- 1 1 i n s t r uc t i o n o pc o d e s o n t h e VAX- 1 1 / 7 8 0 c a n n o t b e
r es t a r ted .
( Th e l i s t o f th e s e i n s t r uc t i o n s c a n b e
f o und
in modul e
MC HEC K 7 8 0 . )
7-1 1

ERROR HANDLING
Th e r e a r e
a l so
s ev e r a l
error
c o nd i t i o n s o n
the VAX- 1 1 / 7 8 0
g e n e r a t e i n t e r r up t s i n s t e a d o f m a c h i n e c h e c k e x c e p t i o n s .
•

A " c o r r e c t e d r e a d d a t a " c o nd i t i o n o r a " r e a d d a t a s ub s t i t u t e "
c o nd i t i o n
i n t e r r up t s
t h r o ug h SCB v e c to r 5 4 ( h ex ) a nd r a i s e s
I PL t o 2 6 .

•

An " S B I a l e r t "

i n t e r r up t s th r o ug h v e c to r 5 8 a t I P L 2 7 .

•

An " S B I f a u l t "

i n t e r r up t s th r o ug h v e c to r 5 C a t I P L 2 8 .

•

tha t

An " a s yn c h r ono u s wr i t e e r r o r " i s r e po r t ed th r o ug h SCB
60 at IPL 2 9 .

v e c to r

Th e f i r s t th r e e o f t h e s e e r r o r s
r esul t
in
e r ro r
l og
entr ies .
An
a t t empt
i s mad e
t o c o n t i n ue f r om the e r r o r .
Th e a s yn c h r o n o us wr i t e
e r r o r c a u s e s a f a t a l b ug ch e c k i f i t o c c u r r ed i n
ke r n e l
or
exec ut i ve
mo d e o r i f a n e r r o r o c c u r red wh i l e upd a t i ng a pag e t a b l e .

M a c h i ne Ch e c k Re c ov e r y B l o c k s

7. 3. 3

VM S p r o v i d e s a c a pab i l i t y f o r a b l o c k o f k e r n e l mod e c o d e
to protect
i t s e l f f r om m a c h i n e c h e c k s wh i l e t h e p r o t e c t ed c o d e i s e x e c ut i ng .
Fo r
e x ampl e , VM S u s e s th i s f e a t u r e i f a n i n t e r r upt
i s g en e r a ted
f r om
a
p r ev i o u s l y
unco n f i g u r ed
adapte r .
If
the code
th a t
r ead
the
c o n f i g u r a t i o n r eg i s t e r
we r e n o t
p r o t e c t ed
a nd
the
i n t e r r up t wa s
spur i o us ,
t h en
the
configurat ion
r eg i s t e r d o e s n o t e x i s t a nd t h e
r e f e r e nc e t o a n o n e x i s t e n t I /0 s p a c e a d d r e s s wo u l d c r a sh t h e sys tem .
Th e r e a r e s ev e r a l r e s t r i c t i o ns o n t h e p r o t e c ted c o d e .
1.

I t m u s t b e e x e c u t i ng i n k e r n e l m o d e .

Th e s t a c k c a nno t be u s ed a c r o s s t h e e n t r y i n to o r
the
ex i t
o ut o f
th e p r o t e c t ed
code block .
Th i s r e s t r i c t i o n e x i s t s
b e c a u � e a c o r o u t i n e m e c h a n i sm i s u s ed t o pa s s c o n t r o l b e twe e n
the
p r o t e c t ed
b l o c k a nd t h e VM S r o u t i n e s t h a t e s t ab l i sh t h e
p r o t e c ted c o d e .

VM S e l ev a t e s I P L to 3 1 s o a l i m i t ed
s h o u l d be i nc l ud e d i n the b l o c k .

R O i s d e s t r o yed by the m e c h a n i sm .

n um b e r

i n s t r uc t i o n s

7. 3. 3. 1
U s i ng t h e Re c o v e r y Mech an i sm - S e v e r a l m a c r o s a r e p r o v i d ed i n
the
mac ro
l ibrary
S YS $ L I B RARY : L I B . M LB t o u s e
th i s p r o t e c t i o n
Th e m a c r o
m e c h a n i sm .
$ PRTC T I N I

LABE L , MAS K

d e f i n e s t h e b eg i nn i ng o f the b l o c k .
Th e l a b e l a r g um e n t
t o the l a b e l a r g um e n t a s so c i a t ed w i th th e m a c ro
$ PRTCTEND

ident ical

LAB E L

t h e m a c r o th a t d e f i n e s t h e e nd o f t h e b l o c k .
If
no
error
occur red
wh i l e
the
p r o t e c t e d c o d e wa s e x e c u t i ng , R O c o n t a i n s t h e s u c c e s s c o d e
S S $ _NORMA L .
Ot h e r w i s e , t h e l o w b i t o f R O i s c l e a r .
7-12

ERROR HANDLING
Th e m a s k a rg um e n t a l l o ws t h e b l o c k o f
d i ffe rent c la sses
o f e r ro r s .
Th e
d e f i ne d by t h e $ MC HKDE F m a c r o , a r e

c od e t o
spec i f i c

protec t
i tse l f
f r om
t ype s o f p r o t e c t i o n ,

MCHK$M L OG

I nh i b i t e r r o r l og g i ng f o r t h e e r r o r

MC HK$M MCK

P r o te c t ag a i n s t m a c h i n e c h e c k s

MC HK$M_N E XM

P r o te c t a g a i n s t n o n e x i s t e n t m em o r y

MCHK$M_U B A

P r o t e c t ag a i n s t UN I B U S a d a p t e r e r r o r i n t e r r up t s

Th e r e a r e two o th e r f e a t u r e s u s ed b y VM S
p r o t ec t i o n m e c h a n i sm .
Th e m a c ro
$ PRTCTEST

tha t

a re

pa r t

th i s

ADDRE S S , MAS K

a l l ows VM S to d e t e rm i n e wh e th e r a r e c ov e r y b l o c k i s i n e f f e c t a nd t a ke
a c t i o n a c c o r d i ng l y .
Th e
s t a tus i s r e tur ned i n RO .
Th e l ow b i t s e t
i nd i c a t e s t h a t a r ec o v e r y b l o c k i s i n e f f e c t a nd
th a t t h e s p e c i f i ed
m a s k i s b e i ng u s ed .
Th e m a c r o
$ B UG PRTCT
i s used by the m a c h i n e c h e c k h a nd l e r s
fo r
t h e VAX- 1 1 / 7 5 0
a nd
the
VAX- 1 1 /7 8 0 b e fo r e
i s s u i ng a f a t a l b ug c h e c k .
I f no r ec o v e r y b l oc k i s
i n e f f e c t , c o n t r o l i s pa s s e d b a c k t o the l o c a t i o n wh e r e th i s m a c r o wa s
i nv o k e d ,
wh e r e
a b ug c h e c k i s u s ua l l y i s s ue d .
I f a r ec o v e r y b l o c k i s
i n e f f e c t , c o n t r o l i s pa s s e d t o the end o f t h e p r o t e c ted b l o c k w i th R O
c o n t a i n i ng a n e r r o r c o d e o f S S $ _MCHE C K .

7-1 3

PART I I I

S C H EDUL ING AND T I M ER S U PPORT

It i s e q u a l l y bad wh e n one s p e ed s on
the g u e s t unwi l l i ng
to g o , a nd wh e n he ho l d s b a c k o n e
who i s h a s t en i ng . Ra the r
o n e sho u l d b e f r i e nd t h e g u e s t who i s th e r e ,
b u t speed h i m wh e n h e w i s h e s
Th e Od y s s e y
Ho rn e r

CHAPTER 8
S C H E DU L I NG

S c h e d u l i ng i s c o n c e r n ed w i th t h e o r d e r o f e x e c u t i o n o f p r o c e s s e s a n d
the o c c u r rence
of
ev e n t s o v e r
t i me .
Th e s c h e d u l e r i d e n t i f i e s a n d
e x e c u t e s the h i g h e s t p r i o r i t y , m em o r y- r e s i d e n t p r o c e s s .
Th e
abi l i ty
of
a p r o c e s s to be s c h ed ul e d ( o r t h e n a t u r e o f t h e e v e n t o r r e s o u r c e
f o r wh i c h t h e p r o c e s s m a y b e wa i t i ng ) i s r e f l e c t ed i n t h e p r o c e s s o r
s c h ed u l i ng
s t a te
of
the
process .
T r a n s i t i o n s f r om o n e s t a t e t o
a n o t h e r o c c u r a s t h e r e s u l t o f s ys t em e v e n t s s uc h t h e
s e t t i ng
of
an
event
f l ag ,
e n q ue u i ng
a n AS T , a Wa k e s ys tem s e r v i c e , a n d s o fo r th .
Th i s c h a p t e r
d e sc r i b e s
the
i n t e r a c t i o ns o f
so f t wa r e p r i o r i t i e s ,
process
s t a tes ,
a nd
s y s tem
e v e n t s , a s we l l a s t h e o p e r a t i o n o f t h e
s c h ed ul e r .

8.1

PROC E S S S TATES

Th e s t a t e of a p r o c e s s d e f i n e s the r e a d i n e s s o f
the
process
to
be
s c h ed u l ed
fo r execut ion .
I n ad d i t i o n , t h e p r o c e s s s t a t e m a y i nd i c a t e
wh e th e r t h e p r o c e s s i s m emo r y r e s i d e n t o r o u t swappe d .
If a process i s
wa i t i ng f o r t h e a v a i l a b i l i t y o f a s ys t em r e so u r c e o r the o c c u r r e n c e o f
a n e v e n t , t h e n the p r o c e s s s t a t e
i s o n e o f s e ve r a l
d i s t i n c t wa i t
s ta tes .
Th e wa i t s t a t e r e f l e c t s t h e pa r t i c u l a r c o nd i t i o n t h a t m u s t b e
s a t i s f i ed fo r t h e p r o c e s s t o b e c om e c om p u t a b l e ag a i n .

8.1.1

Process Control Block

Th e ma j o r d a t a s t r uc t u r e d e s c r i b i ng
the
s tate
a nd
pr i o r i ty o f a
process
is
the
s o f twa r e
process control
b l o c k ( PC B ) .
Figure 8-1
i l l us t r a tes the f i e l d s o f
the
s o f twa r e P C B t h a t
are
pa r t i c u l a r l y
i m po r t a n t t o
s c h e d u l i ng .
Th e
f i e l d PC B $W_S TATE c o n t a i n s a n um e r i c
va l u e a s s o c i a t ed w i th a pa r t i c u l a r p r o c e s s s t a t e .
Th e p r o c e s s
state
is
e s t a b l i sh ed
b y m o v i ng t h e a pp r o p r i a t e v a l ue i n t o PC B $W S TATE a nd
i n s e r t i ng th e PCB i n to t h e c o r r e s po nd i ng s t a t e que ue by m e a ns o f
the
s t a t e q u e ue
l i nk
f ields ,
PCB $ L S QF L and
PCB $ L S QB L .
Append i x D
c o n t a i n s a c om p l e t e d e sc r i pt i o n o f- t h e s o f twa r e PCB� Ta b l e 8 - 1
l ists
the process
s t a t e n ame s
a nd
t h e c o r r e s po nd i ng PC B $W S TATE v a l ue s .
Ot h e r s o f twa r e PC B f i e l d s d e f i n e t h e s c h ed u l i ng o r
s o f twa r e
pr i o r i ty
of
the
p r o c e s s a nd
i n d i c a t e wh e th e r
the p r o c e s s i s i n m emo r y o r
o u t s wa pped .
Th e l o c a t i o n o f a d a t a s t r uc t u r e c o n t a i n i ng t h e h a r d wa r e
con tex t
of
the
proc ess
i s a l so
s to r ed
in
the
so f t wa r e
PC B
( PC B $ L_PHYPC B ) .

8-1

S C HEDUL ING

SQFL
SQBL

Software PCB

PRI

I
PHYPCB
STS

PRIB

STATE

"�

�,

F i g u r e 8 - 1 P r o c e s s Co n t r o l B l o c k Fi e l d s Us ed i n S c h ed u l i ng
Ta b l e 8 - 1
P r o c e s s Sc h e d u l i ng S t a te s

S t a t e Na m e
Co l l i d ed Pag e Wa i t
M i sc e l l a n e o us Wa i t
Mu t e x Wa i t
Re s o u r c e Wa i t
Co mmon Ev e n t Fl ag Wa i t
Pa g e Fa u l t Wa i t
Lo c a l Ev e n t Fl ag Wa i t ( Re s i d e n t )
Lo c a l Ev en t Fl ag Wa i t ( Ou t s wa pped )
H i b e r n a t e Wa i t ( Re s i d e n t )
H i b e r na t e Wa i t
( Ou t swa pped )
S u s pe nd Wa i t ( Re s i d en t )
S u s pe nd Wa i t
( Ou t swa ppe d )
F r e e Pa g e Wa i t
C o mp u t a b l e ( Re s i d e n t )
C o m pu t a b l e
( Ou t swa p pe d )
C u r r en t l y Ex e c u t i ng P r o c e s s

8-2

Mn em o n i c

Va l ue

C O L PG
MWA I T

1
2

C EF
PFW
LEF
LEFO
H IB
H IB O
S US P
S US PO
F PG
C OM
C OM O
C UR

3
4
5
6
7
8
9
10
11
12
13
14

S C HEDUL I NG
8.1.2

S o f twa r e P r i o r i ty

S o f t wa r e pr i o r i t y ( a s d i s t i n c t f r om
i n t e r r upt
pr i o r i t y ,
a
h a r d wa r e
m e c h a n i sm ) i s used i n d e t e rm i n i ng t h e r e l a t i v e p r e c ed e n c e o f p r o c e s s e s
f o r ex e c u t i o n a nd m emo r y r e s i d e n c e .
So f twa r e p r i o r i t y i s a v a l ue
in
the
r a ng e
f r om
0
to
31 .
Th e n u l l
p r o c e s s e x e c u t e s a t so f t wa r e
p r i o r i t y l ev e l 0 , a n d t h e h i g h e s t pr i o r i t y r e a l - t i m e p r o c e s s ex e c u t e s
at
so f twa r e pr i o r i t y l e v e l
31.
Th e r a ng e o f 3 2 s o f t wa r e pr i o r i t y
l e ve l s i s d i v i d ed e v e n l y b e twe e n the no rma l pr o c e s s l ev e l s o f 0 to
15
and
th e r e a l - t i me pro c e s s l e v e l s o f 1 6 to 3 1 .
Th e e x e c ut i o n b e h a v i o r
o f a p r o c e s s i s s i g n i f i c a n t l y a f f e c t ed b y t h e type o f p r o c e s s
( no rm a l
o r r e a l t i m e ) and t h e a s s i g n ed s o f twa r e pr i o r i t y l ev e l .
Two f i e l d s o f the so f t wa r e p r o c e s s c o n t r o l b l o c k d i r ec t l y d e sc r i b e t h e
s c h ed u l i ng
or
s o f t wa r e pr i o r i t y o f the p r o c e s s .
Th e f i e l d PC B $ 8 P R I
( F i g u r e 8 - 1 ) d e f i n e s t h e c u r r e n t so f twa r e p r i o r i ty o f
the
p r o ces s ,
wh i c h
is
u s ed
t o ma ke s c h ed u l i ng d e c i s i o n s .
PC B $ 8 PR I B d e f i n e s t h e
b a se pr i o r i ty of the p r o c e s s ,
f r om wh i c h
t h e c u r r e n t pr i o r i t y
is
c a l c u l a t ed .
Fo r
no rma l
or
t i m e s h a r i ng
processe s ,
t h e s e pr i o r i t y
v a l u e s a r e some t i m e s d i f f e r e n t , wh i l e r e a l - t i m e pr o c e s s e s a l wa ys h a v e
i d e nt i c a l
cur rent
a nd
base
pr i o r i t y v a l u e s .
Each f i eld may have a
v a l u e f r om 0 to 3 1 .
Howe v e r , t h e v a l u e s i n
these
f i elds a re
s t o r ed
i n te r nal l y i n
an
i n v e r ted o r d e r .
Th a t i s , t h e b a s e a nd c u r r e n t pr i o r i t i e s o f 0 f o r t h e
nul l process a r e s to r ed i n terna l l y i n t h e P C B f i e l d s
as
31 .
Th e
h ighest
pr i o r i t y p r o c e s s
po s s i b l e wo u l d h a v e
i n t e r n a l l y s t o r ed
s o f t wa r e pr i o r i t y v a l u e s o f 0 .
Th us , t h e i n t e r n a l
f i eld val ues a re
s t o r ed
as
3 1 m i n u s the so f t wa r e pr i o r i t y v a l ue .
Th i s i n v e r t e d v a l ue
c a uses
pr i o r i t y p r om o t i o n s o r
boosts
to
be
i m pl em ented
t h r o ug h
s ub t r a c t o r
d e c r emen t
i n s t r uc t i o n s .
Sys tem u t i l i t i e s s uc h a s S DA ,
D � S P LAY , a n d the DC L c omma n d
S H OW SYSTEM
i n te r p r e t
the se
i n v e r t ed
v a l u e s a nd d i s pl a y e x t e r n a l v a l u e s , wh e r e 0 i s the l o we s t pr i o r i t y a nd
3 1 i s the h i ghest .
Ex te r n a l v a l u e s a r e a l s o r e t u r n ed by
the
$ G E TJ P I
s ys tem s e r v i c e wh e n a pr o c e s s p r i o r i t y i s r e que s t ed .
NOTE
Al l d i scu s s i ons
in
th i s m a n ua l
abo u t
s o f t wa r e pr i o r i t y t r e a t pr i o r i t y a s a n
i n c r e a s i ng e n t i t y f r om 0 ( f o r
the n u l l
p r o c e s s ) to 3 1 ( f o r the h i g h e s t pr i o r i t y
rea l-t i me process ) .
Pl e a s e
take
th i s
i n to
a c c o un t wh e n r e l a t i ng d e sc r i pt i o n s
i n th i s m a n u a l t o t h e ac t ua l r o u t i n e s i n
the
l i s t i ng s ,
wh i c h m a n i pu l a t e
the
i nv e r t e d p r i o r i t i e s .

8.1.2.1
Re a l -T i me P r i o r i t y Ra ng e - P r o c e s s e s wi th
s o f t wa r e
pr i o r i t y
l e ve l s
16
t h r o ug h
3 1 a r e c o n s i d e r ed r e a l - t i m e p r o c e s s e s .
Th e r e a r e
two s c h ed u l i ng c h a r a c t e r i s t i c s th a t d i s t i ng u i s h r e a l - t i m e pr o c e s s e s .
1.

Th e s o f t wa r e pr i o r i t y o f a r e a l - t i m e pr o c e s s d o e s n o t c h a ng e
over
time ,
un l e s s
the r e
is
a
d i r e c t p r o g r a m o r o pe r a t o r
r e qu e s t t o c h a n g e i t ( w i t h a Se t Pr i o r i t y s ys t em se r v i c e o r a
S E T PROC E S S/ P R I O R I TY c omma nd ) .
Th i s
i m pl i e s tha t the b a s e
p r i o r i t y a nd th e c u r r e n t pr i o r i t y o f a r e a l - t i m e pr o c e s s
a re
i d ent i c a l ,
and
no
dyn am i c
pr i o r i t y
a d j u s tm e n t
( S e c t i o n 8 . 1 . 2 . 3 ) i s a p pl i e d by VM S .
8-3

S C HED � L I NG
2.

A r e a l - t i m e p r o c e s s e x e c u t e s un t i l i t i s e i th e r p r e empted
by
a h i g h e r p r i o r i t y p r o c e s s o r i t e n t e r s one of the wa i t s t a t e s
( Se c t ion 8 . 1 . 3 . 2 ) .
Th u s ,
a
r e al - t ime
process
is
not
s u s c ept i b l e
to q u a n t um e n d eve n t s ( S e c t i o n 8 . 1 . 2 . 4 ) , a nd i s
n o t r em o v e d
f r om
ex ec u t i o n
( r e s c h ed u l ed )
bec a u s e
some
i n t e r va l of e x e c u t i o n t i m e h a s e x p i r ed .

Ta k e n i n i s o l a t i o n , t h e r e a l - t i m e r a ng e
o f VM S s o f twa r e
pr io r i t i es
p r ov i d e s
a s c h ed u l i ng env i r o nm e n t l i k e t r a d i t i o n a l r e a l - t i m e sys tems ,
p r e em p t i v e , p r i o r i t y -d r i v e n sc h ed u l i ng wi t h o u t t i m e s l i c e s o r q u a n t a .

8 . 1 . 2 . 2 No rma l P r i o r i ty Rang e - No rma l p r o c e s s e s i n c l ud e
i n te r a c t i v e
t e rm i n a l
sess ions ,
b a tch
j obs ,
a nd a l l sys tem p r o c e s s e s e x c e p t the
swa ppe r .
Th e s c h e d u l i ng b e h a v i o r o f a
no rma l
process
i s d i f fe r ent
f r om th a t o f a r e a l - t i me p r o c e s s .
1.

Th e c u r r e n t so f twa r e p r i o r i ty o f the p r o c e s s v a r i e s o v e r t i me
wh i l e
the
b a s e p r i o r i t y r em a i n s c o n s t a n t ( un l e s s a l t e r e d by
the Set P r i o r i t y s y s t em s e r v i c e o r by a
S E T PROC E S S /PR I OR I TY
c o mm and ) .
Th i s b e h a v i o r
i s t h e r e s u l t o f d yn am i c p r i o r i t y
a d j u s tm e n t a pp l i e d by VM S to f av o r I /O-bo und a nd
i nterac t i ve
processes
a t the
expense
o f c ompute -bo und ( a nd f r e q u e n t l y
a l so batch) p r o c e s s e s .
Th e m e c h a n i sm o f p r i o r i t y
ad j u s tm e n t
i s d i sc u s s e d i n the f o l l o w i ng s e c t i o n .

No rma l
processes
r un
in a
t i m e s h a r i ng
e nv i r o nm e n t
that
a l locates
CPU
t i me s l i c e s ( o r q ua n t a ) to p r o c e s s e s i n t u r n .
Th e r e f o r e , a n e x e c u t i ng no rm a l p r o c e s s wi l l c o n t r o l
the
CPU
unt i l
•
•
•

i t i s p r e em p t ed b y a h i g h e r p r i o r i t y , c omputab l e
( s e e Fi g u r e 8 - 2 , e v e n t 5 f o r e x amp l e ) ,

process

i t e n te r s a r e s o u r c e o r e v e n t wa i t s t a t e
e v e n t 7 fo r e x amp l e ) , o r

( see F i g u r e 8-2 ,

th e c u r r e n t qua n t um o r t i m e
sl ice
F i g u r e 8 - 2 , e v e n t 1 7 f o r examp l e ) .

been

has

used

( see

P r o c e s s e s w i th i d e n t i c a l c u r r e n t pr i o r i t i e s a r e s c h ed u l ed o n
a
r o un d
robin ba s i s .
Th a t
is,
each
p r o c e s s a t a g i v en
s o f twa r e p r i o r i t y l ev e l e x e c u t e s in
t u r n b e fo r e
a ny o th e r
process
at
th a t
l ev e l
executes
ag a i n .
Al tho ug h
th i s
m ec h a n i sm
a pp l i e s t o
r e a l -time proc esses a s
we l l ,
it
g en e r a l l y h a s n o e f f e c t b e c a use
r e a l - t i me p r o c e s s e s a r e
u s u a l l y a s s i g ned to un i que s o f twa r e p r i o r i t y l ev e l s a n d the i r
p r i o r i t i e s d o n o t c h a ng e .
No r m a l p r o c e s s e s d o e x pe r i e n c e
r o und r o b i n s c h ed u l i ng b o th b e c a u s e the r e a r e us ua l l y m o r e o f
t h em o n a g i v e n s ys t em and b e c a u s e the d e f a u l t b e h a v i o r ( f r om
C r e a t e P r o c e s s a r g um e n t s o r f r om the u s e r a u tho r i z a t i o n f i l e )
is to
a s s ign a b a s e p r i o r i ty o f fo ur t o a l l user proc esse s .
Th u s s o f twa r e p r i o r i t y l ev e l s f o u r th r o ug h n i n e
t e nd
to
be
o c c up i ed b y s e v e r a l p r o c e s s e s s i m u l t a ne o us l y .

8-4

S C H EDUL I NG
8.1.2. 3
P r i o r i ty Ad j u s tm e n t - No r ma l
processes do
no t
g en e r a l l y
execute
at a
s i ng l e
s o f t wa r e p r i o r i t y l ev e l .
Ra t h e r , a p r o c e s s
s o f t wa r e p r i o r i t y c h a ng e s o v e r t i m e i n a r a ng e o f ze r o t o s i x s o f t wa r e
pr io r i ty
l evel s
above
the
base
p r o c e s s pr i o r i ty .
Two m e c h a n i s m s
p r ov i d e t h i s p r i o r i t y ad j us tm e n t .
As
a
c o nd i t i o n
fo r
wh i c h
the
process
has
b e e n wa i t i ng
i s s a t i s f i ed o r a n e e d ed r e s o u r c e b e c o m e s
a v a i l a b l e , a b o o s t o r pr i o r i t y i n c r em e n t m a y be a ppl i e d
to
the
base
pr io r i ty
to
i mp r o v e
the
s c h ed u l i ng
r e s po n s e
fo r
the
process
( Sec t i on 8 . 2 . 3 ) .
Ea c h
t i me
the process
e x e c u t e s wi tho u t
f u r th e r
s ys t em
ev e n t s
( Section 8 . 2 )
or
q u a n t um
expi r a t i o n
( see
the nex t
s e c t i o n ) o c c u r r i ng , t h e c u r r e n t pr i o r i t y
i s moved
t o wa rd
the
base
p r i o r i t y ( o r d em o ted ) b y o n e p r i o r i t y l ev e l ( S e c t i o n 8 . 3 ) .
Ov e r t i m e ,
c o mpu t e - bo und p r o c e s s p r i o r i t i e s t e nd to r ema i n a t t h e i r ba s e p r i o r i t y
l e v e l s , wh i l e I / O-bo und a nd i n t e r a c t i v e p r o c e s s e s t e nd to h a v e a v e r a g e
c u r r e n t p r i o r i t i e s s o mewh a t h i g h e r
than
the i r
base
pr i o r i ty .
An
e x am pl e o f
p r i o r i t y ad j u s tm e n t
t h a t o c c u r s o v e r t i me f o r s e v e r a l
p r o c e s s e s i s i l l u s t r a t ed i n F i g u r e 8 - 2 .

Q UANTUM
8.1.2.4
Quan t um E x p i r a t i o n - Th e
SYSBOOT
pa r am e t e r
d e t e rm i n e s ,
f o r mo s t
process
s ta tes ,
t h e m i n i m um am o un t o f t i m e a
p r o c e s s c a n r em a i n i n m em o r y a f t e r an i n swa p o pe r a t i o n , b u t i t i s n o t
a n a b s o l u t e g u a r a n t e e o f m emo r y r e s i d e nce .
( Th e swa ppe r ' s u s e o f t h e
i n i t i a l q u a n t um f l a g i s d e sc r i b ed i n
Ch a p t e r 1 4 . )
Th e qua n t um
a l so
def i nes
the
s i z e o f the t i m e s l i c e f o r r o und r o b i n s c h ed u l i ng no r m a l
processes .
Th e v a l u e o f QUANTUM
is
the
n umbe r
of
1 0 m i l l i s ec ond
( c l o c k t i c k s ) i n t h e qua n t um .
Th e d e f a u l t QUANTUM v a l u e o f
i n te rv a l s
3 0 t h e r e fo r e p r o d uc e s a
s c h ed u l i ng
i n te r v a l
of
3 0 0 m i l l i s e c o nd s .
Af t e r
each
1 0 m i l l i s e c o nd
i n te rva l ,
t h e ha r d wa r e c l o c k i n t e r r up t
s e r v i c e r o u t i n e upd a t e s t h e qua n t um- r ema i n i ng
f i eld
in
the
process
head er
o f the cu r rent
process .
Wh en th i s v a l ue b e c om e s z e r o , t h e
so f twa r e t i m e r r o ut i n e s i g n a l s a qu a n t um end
event by
i nv o k i ng
the
s ub r o u t i n e S C H $ Q E ND i n mod ul e R S E .
An a d d i t i o n a l d ed uc t i o n f r om t h e QUANTUM i s g o ve r n e d
by
the
s pe c i a l
SYSB OOT p a r am e t e r
I O TA .
Th i s v a l ue ( i n un i t s o f 1 0 m i l l i s e c o nd s ) i s
d e d uc t ed f r om t h e r em a i n i ng q u a n t um v a l u e e a ch t i m e a p r o c e s s e n t e r s a
wa i t s t a t e .·
Th e r e f o r e ,
the d e fa ul t
I O TA v a l ue
of
2 cha r g e s 2 0
m i l l i s e c o nd s a g a i n s t the q u a n t um o f t h e p r o c e s s .
Th i s m e c h a n i sm
is
p r o v i d ed
to ensur e
th a t a l l p r o c e s s e s e x pe r i e n c e q ua n t um end e v e n t s
wi th s o m e r eg u l a r i t y .
P r o c e s s e s th a t
a r e c o m p u t e b o und
expe r i ence
qu a n t um e nd
as
a
resul t of
us i ng
a c e r t a i n a m o u n t o f C PU t i m e .
P r o c e s s e s th a t a r e I /0 bo und expe r i e n c e q u a n tum end
as a
resu l t
of
pe r fo rm i ng
a r e a s o n a b l e n um b e r o f I /O r e q u e s t s .
Th i s g ua r a n t e e s th a t
p r o c e s s e s tha t s pe nd mo s t o f t h e i r t i m e i n some wa i t
s ta te c a n a l so
a c c ompl i sh u s e f u l wo r k b e fo r e t h e y a r e o u t s wa pped .
Th e r o u t i n e
S C H $ QEND i s
e x e c u t ed
at
the
end
of
e v e r y q u a n t um ,
r eg a rd l e ss o f
the
so f t wa r e p r i o r i t y o f the c u r r e n t p r o c e s s .
Fo r
r e a l - t i m e p r o c e s s e s , howe v e r , t h e o n l y a c t i o n pe r f o rmed
is
to
r eset
t h e p r o c e s s h e ad e r
q ua n t um
f i eld
t o t h e f u l l q u a n t um v a l u e a nd t o
clear
the
init ial
qu a n t um
bit
in
the
PCB
s t a t us v e c to r
(bit
PC B $V I N QUAN
in
the
f i eld
PC B $ L S T S , p i c t u r ed i n F i g u r e 8 - 1 ) .
Th e
c l e a red i n i t i a l
qua n t um b i t m a k es a
process mo r e
l i ke l y
to
be
o u t swa pped , i f p r o c e s s swa p m o d e h a s n o t b e en d i s a b l ed .

8-5

QUANTUM

TYPE
PROCESS
BASE PRIORITY
A
COMPUTE BOUND
4
1 / 0 BOUND
B
4
c
REAL TIME
18

�

EVENTS
1/0 REQUEST

PREEMPTION
QUANTUM END

20
18
16

SOFTWARE
PRIORITY 1 2
LEVELS

[§:]
-

EwAPPERI

[§:]
-

[§:]

[§:]
-

m
-

(X)

"'
I

10
8
6
4
2

E VE N TS

CD ®

Figure 8-2

@§) COO)® ® @ @ @ @ @ @ @ @ @
TIME ---+
So f twa r e P r i o r i t i e s a nd Pr i o r i t y Ad j u s tm e n t s

S CHEDUL ING
No t e s o n Fi g u r e 8 - 2

(1)

P r o c e s s " C " bec om e s c omput a b l e .

Pr o c e s s " A"

i s p r e empted .

(2)

" C" h i b e r nate s .
l o we r .

ag a i n ,

pr i o r i ty

(3)

" A" ex pe r i e n c e s qua n t um e n d and i s r e s c h ed u l ed
pr io r i ty .
" B " i s c om p u t a b l e o u t s wa pped .

(4)

Th e Swa ppe r p r o c e s s e x e c ut e s t o i n s wa p " B " .
f o r ex ec u t i o n .

(5)

" B " i s pr e em pt ed b y " C " .

(6)

" B " ex ec u t e s ag a i n , o n e pr i o r i t y l ev e l l o we r .

(7)

" B " r e qu e s t s
an
I /O o pe r a t i o n
e x ec u t e s a t i t s b a se pr i o r i t y .

(8)

" A " r e qu e s t s a t e r m i n a l o u t pu t o pe r a t i o n .
e x ec ute s .

(9)

ex e c ut e s
" A"
pr io r i ty + 3 .

(10)

" A " i s p r e em p t ed b y

(11)

" A " e x e c u t e s ag a i n , o n e pr i o r i t y l ev e l l o we r .

( 12)

" A"
e x pe r i e n c e s qua n t um
p r i o r i t y l ev e l l o we r .

end

(13)

" A " i s p r e empted by " B " .
a ppl i ed
to
" B"
bec a us e
c u r r e n t pr io r i t y .

A p r i o r i ty boost o f
2
i s no t
the
r e s u l t wo u l d b e l e s s t h a n the

(14)

" B"

(15)

" B " ex ec u t e s ag a i n , o n e pr i o r i t y l ev e l l o we r .

(16)

" B " r e qu e s t s a n I /0 o pe r a t i o n .
p r io r i t y .

ex ec u t e s

i ts

b a se

(17)

" A " e x pe r i e nc e s qua n t um end and i s r e s c h ed u l ed
p r io r i t y ( i t s b a s e pr i o r i t y ) .

the

same

(18)

" A"

e x ec u t e s

( no t

one

" B"

I /0
c ompl e t i o n
fo l l o w i ng
( Th e a ppl i ed bo o s t wa s 4 . )

i ts

b a se

i s s c hed u l ed

t e rm i n a l
Th e

l ev e l

I /O ) .
Nul l

" A"

pr o c e s s
b a se

i ts

"C" .

and

r e s c h ed u l ed

o ne

i s p r e em p t ed by " C " .

" A"

i s p r e em pted b y " C " .

F i g ur e 8 -2

( Co n t . )

So f twa r e P r i o r i t i e s a nd Pr i o r i t y Ad j u s tm e n t s

8-7

S CHEDUL ING
Fo r no rm a l p r o c e s s e s , h o we v e r , t h e o c c u r r e n c e
i nv o l v e s s e v e r a l d i f f e r e n t o pe r a t i o n s .

q u a n t um

ex p i r a t i o n

As
w i th
r e a l - t ime p r o c e s se s ,
no r m a l
proc e s s e s have
the
p r o c e s s h e ad e r q u a n t um
f i e l d r e s e t a nd t h e i n i t i a l q u a n t um
b i t c leared .

I f th e r e a r e a ny i n s wa p c a nd i d a t e s ( S C H $G L C OMOQS i s n o n z e r o ,
i nd i c a t i ng
at
l e a s t o n e n o n e m p t y C OM O- s t a t e que ue ) , t h e
c u r r e n t p r i o r i t y o f t h e p r o c e s s i s s e t to i t s b a s e
p r i o r i ty .
( If
S C H $G L C OM O QS c o n t a i n s a
ze r o ,
the
pr i o r i ty i s l e ft
a lone . )

Ro u t i ne S C H $ SWPWAKE i s c a l l ed to
d e t e rm i n e wh e th e r
s wa pp e r
a c t i v i t y i s r e qu i r ed .
Th e swa ppe r p r o c e s s i s a wa kened i f
•

t h e r e i s a t l e a s t o n e c om p u t a b l e o u t swa pped p r o c e s s ,

•

i n d i c a t ed b y
mod i f i ed pag e wr i t i ng i s r e q u i r e d
as
fo r
the
free
uppe r
a nd
l o we r
l im i t
th r e sh o l d s
m o d i f i ed p ag e l i s t s ,

•

th e r e i s a t l e a s t o n e p r o c e s s h e ad e r o f a d e l e t ed p r o c e s s
s t i l l i n the bal ance s l o ts , or

•

a powe r f a i l r e c ov e r y h a s j u s t o c c u r r ed .

the
a nd

Th e s e c h e c k s a v o i d n e ed l e s s a wa k e n i ng o f t h e
s wa ppe r ,
w i th
the
a s s o c i a t e d c o n t e x t s w i t c h o v e r h e a d , o n l y to d e t e r m i n e
t h a t the s wa pp e r h a s no u s e f u l wo r k t o d o .
Th e swa ppe r p r o c e s s d o e s n o t e x e c u t e i mmed i a t e l y b u t m u s t b e
s c h ed u l e d
fo r
exec ut ion .
As a
c omputab l e ( a f t e r wa k i ng )
r e s i d ent r e a l - t i m e p r o c e s s o f
s o f t wa r e p r i o r i t y
16 ,
the
s wa ppe r i s l i k e l y to b e t h e n e x t p r o c e s s s c h ed u l e d .
4.

Th e C P U l i m i t f i e l d o f t h e p r o c e s s h e a d e r i s n e x t c h e c ked
to
d e te rm i n e
if
a C PU l i m i t has b e e n i m po sed and i f tha t l i m i t
I f t h e C PU l i m i t h a s e x p i r e d , e a c h a c c e s s m o d e
h a s e x p i red .
wi l l
h a v e a n i n t e r v a l o f t i m e t o c l e a n u p o r r un d o wn be f o r e
t h e i m ag e ex i t s a nd th e p r o c e s s i s d e l e t ed .
Th e s i z e o f
the
wa rn i ng
i n t e r v a l g i v e n to each ac c e s s mod e is d e f i n ed by t h e
S Y S B OOT pa r am e t e r E XTRACPU .
( Th i s p a r am e t e r
has
a d e f a ul t
v a l u e o f o n e s e c o nd . )

I f no C P U l i m i t ex p i r a t i o n h a s o c c u r r e d , then
the
a u toma t i c
wo r k i ng
set
ad j u s tm e n t c a l c u l a t i o n s t a k e pl a c e i f t h e y a r e
e n ab l ed .
Th e SYS B OOT p a r am e t e r WS INC m u s t be z e r o to d i s a b l e
a u tom a t i c
wo r k i ng
s e t ad j u s tm e n t s .
Th e s i z e o f the pr o c e s s
wo r k i ng
set may be
e x p a nd ed
or
c o n t r a c ted
by
amo u n t s
s p ec i f i e d
by t h e
SYS B O OT p a r am e t e r s WS I NC o r WSDE C .
F i ve
t h r e s ho l d v a l u e s a pp l y to the a u toma t i c ad j us tm e n t s .
•

Th i s p r o c e s s m u s t h a v e a c c um u l a t ed AWST IM E u n i t s
of
CPU
t i m e ( e a c h c l o c k t i c k a c co un ts f o r 1 0 m i l l i s e c o nd s ) s i n c e
t h e l a s t a d j u s tm e n t fo r a n e w a d j u s tm e n t to t a k e p l ac e .

•

Th e pag e f a u l t r a t e m u s t b e l a rg e r th a n PFRATH f a ul t s pe r
1 0 s e c o nd s o r l e s s t h a n PFRATL f a ul t s pe r 1 0 s e c o nd s .

•

Th e wo r k i ng s e t c a nno t c o n t r a c t b e l o w AWSM I N
above AWSMAX p a g e s .

8-8

no r

ex pand

S C HEDULING
Au t om a t i c wo r k i ng s e t ad j us tm e n t i s d i sc u s s e d f r om the m em o r y
m a n a g em e n t po i n t o f v i e w i n Ch a pt e r 1 3 .
6.

8.1.3

F i n a l l y , a s c h e d u l i ng i n t e r r up t a t I P L 3 w i l l b e r e q u e s t e d to
r em o v e
the
cur rent
p r o c e s s f r om ex ec u t i o n and s c h e d u l e t h e
h i g h e s t pr i o r i ty ,
m em o r y r e s i d e n t c ompu t a b l e
proc ess
fo r
execut i on .
No te
th a t o n
a
qu i e t
sys t em ,
the c ur r e n t l y
e x e c u t i ng p r o c e s s m a y b e s e l ec t ed fo r ex ec u t i o n ag a i n .

S t a t e Que ue s

Wi th t h e e x c e p t i o n o f t h e s i ng l e p r o c e s s e x e c u t i ng a t a g i v e n mome n t ,
all
processes
in
the
sys t em
are
in a
pr o c e s s wa i t
s ta te , the
c ompu t a b l e r e s i d e n t s t a t e , o r the c o m p u t a b l e o u t swa pped
state .
Th e
p r o c e s s s t a t e i s i nd i c a t ed by t h e PC B $W S TATE f i e l d and th e l i n k i ng o f
t h e p r o c e s s c o n t r o l b l o c k i n to a que ue of s i m i l a r PCBs .
Th e l i s th e a d s
fo r
a l l wa i t que ue s , c omp u t a b l e r e s i d e n t ( C OM ) que ue s , a nd c o m p u t a b l e
o u t swa pped ( C OMO ) que ue s , a s we l l a s the po i n te r to
the
PCB o f
the
c u r r e n t ( C UR ) p r o c e s s , a r e d e f i n ed i n the m o d u l e SDA T .

8.1.3.1
Compu t a b l e S t a t e s - P r o c e s s e s i n the c om p u t a b l e o r e x e c u t a b l e
s tate
a r e n o t wa i t i ng fo r e v e n t s o r r e s o u r c e s , o th e r t h a n a c q u i r i ng
c o n t r o l o f t h e C P U f o r e x e c ut i o n .
Comp u t a b l e r e s i d e n t ( C OM ) p r o c e s s e s
a r e pl a c ed i n o n e o f 3 2 p r i o r i t y que ue s , w i th t h e que ue c h o s e n by t h e
i n t e r n a l v a l ue fo r
the
cur rent
so f t wa r e
pr i o r i t y o f
the
process
( Figure 8 - 3 ) .
Th e r e i s a s i m i l a r s e t o f 3 2 quadwo r d l i s th e a d s f o r the
c om p u t a b l e o u t swa pped
( C OM O )
s t a te .
Processes
in
the
c om p u t a b l e
o u t swa pped
s tate
a re
wa i t i ng
f o r t h e swa ppe r p r o c e s s t o b r i ng t h em
i n to m em o r y .
As
c om p u t a b l e
r es i d ent processes
they c an
then be
s c h ed u l ed fo r ex e c u t i o n .
P r o c e s s e s m u s t b e i n the c om p u t a b l e r e s i d e n t
s t a t e t o b e c o n s i d e r ed f o r s c h ed u l i ng .
P r o c e s s e s a r e c r e a ted
in
the
c ompu t a b l e o u t swa pped ( C OM O ) s t a t e .
De l e t i o n of p r o c e s s e s o c c u r s f r om
th e c u r r e n t ( C UR ) s t a t e .

8 . 1 . 3 . 2 Wa i t S t a t e s - Th e l i s t h e a d s f o r
the p r o c e s s
control
block
q u e ue s c o r r e s po nd i ng
to
all
p r o c e s s wa i t s t a t e s e x c ept t h e c ommo n
e v e n t f l ag wa i t s t a t e ( C E F ) l o o k l i k e F i g u r e 8 - 4 .
( Common e v e n t
f l ag
wa i t que u e s
a r e d e sc r i b ed i n Ch a pt e r 9 . ) Th e f i r s t two l o ng wo r d s a r e
t h e l o ng wo r d l i n k s to the PCBs i n th i s q ue ue .
Th e S TATE f i e l d o f
the
que ue h e a d e r c o n t a i n s the n ume r i c a l v a l u e c o r r e s po nd i ng to th e p r o c e s s
s tate .
Al l PC Bs i n a s t a t e que ue h a v e PC B $W S TATE v a l ue s i d e n t i c a l to
the
STATE v a l u e o f
the
wa i t s t a t e q ue ue h e a d e r .
Re c o g n i z e d S TATE
v a l u e s a nd the c o r r e s po nd i ng s t a t e n am e s a r e s umma r i z e d in
Ta b l e 8 - 1 .
Th e C O UNT f i e l d o f t h e wa i t s t a t e que ue h e a d e r i s s i mpl y t h e n um b e r o f
p r o c e s s c o n t r o l b l o c k s c u r r e n t l y i n th i s s t a t e and q u e ue .

8 . 1 . 3 . 2 . 1 Vo l un t a r y Wa i t S t a t e s
Th e r e a r e
two
process
s tates
a s s o c i a t ed
w i th l o c a l
e v e n t f l ag wa i t s .
Re s i d e n t pr o c e s s e s wa i t i ng
fo r l o c a l ev e n t f l ag s a r e p l a c ed i n to the LEF s t a t e , wh i l e o u t s wa pped
p r o c e s s e s o c c upy the LE F O s t a t e .
Th e r e a r e s e pa r a t e que ue s m a i n t a i n ed
f o r the s e s t a t e s , a nd a n LEF s t a t e p r o c e s s b e i ng o u t swa pped m u s t be
r emoved
f r om
the
LE F q u e u e
and
pl a c ed i n to t h e LEFO s t a t e que ue .
P r o c e s s e s e n t e r t h e L E F s t a t e a s a r e s u l t o f i s s u i ng $ WA I TFR ,
$WFLOR ,
a nd
$WF LAND s ys t em
s e rv i c e s d i r e c t l y o r
i nd i r e c t l y ( w i th a $ Q I OW
s ys tem s e r v i c e c a l l , i s s ue d e i th e r by t h e use r o r o n h i s b e h a l f b y
-

8 9
-

SC HEDULING
s om e
s y s tem c om po n e n t s uc h a s
RMS ) .
Remo v a l f r om t h e L E F o r L E F O
s t a t e s t o t h e c om p u t a b l e ( C OM ) o r c om p u t a b l e o u t swa pped ( C OMO )
states
c a n o c c u r a s a r e s u l t o f m a t c h i ng t h e e v e n t f l ag wa i t m a s k , e n q ue u i ng
a n a s yn c h r o no u s s y s t em t r a p ( AS T ) , o r p r o c e s s d e l e t i o n .
For

BITS 3 1

State COM

: :�L�
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
E��;.�=:�U::::QUEUE)
PRIORITIES
31

QUEUE 0
PRIORITY 3 1
30

For

BITS 3 1

•

lilliE

•

QUEUE HEADERS
: :SCH$AQ_COMH
: :SCH$AQ_COMT

State COMO

111111111111111111111111111111111

��:::�g ���: BIT MAP
O
(CLEAR
BIT
IMPLIES EMPTY QUEUE)
3t
QUEUE HEADERS
: :SCH$AQ_COMOH
---1
: :SCH$AQ_COMOT

PRIORITIES 0

QUEUE 0
....,._
PRIORITY 3 1

PRIORITY 3 1

PRIORITY 30

PRIORITY 29

Figur e 8 - 3

Compu t a b l e

{ Ex e c utab l e )

W a it Queue
Forward Link

liE

,..
Wait Queue
Backward Link
Count

State

Figure 8-4

S t a t e Que u e s

Fo rma t o f Wa i t S t a t e Q u e ue He a d e r s

8-1 0

S C HEDUL I NG
S im i l a r l y , the re a r e
sepa rate
r e s i d e n t a nd
o u t s wa pped
states and
q u e ue s
f o r h i b e r n a t i ng
a nd
s u s p e nd ed p r o c e s s e s .
Th e H i b e r n a t e a n d
S u s pe nd s ys tem se rv i c e s c a us e p r o c e s s e s t o
enter
the
r e s i d e n t wa i t
s ta te s .
H i b e r na t i ng
p r o c e s s e s c a n l e a v e the H I B a nd H I B O s t a t e s a n d
e n t e r t h e C OM a nd C OMO s t a t e s a s a r e s u l t o f
$ WAKE
s y s t em
s e rv i c e s ,
A S T e n q ue u i ng , o r pr o c e s s d e l e t i o n .
S u s pe nd ed pr o c e s s e s a r e s e n s i t i v e
t o o n l y $ R E S UM E s y s t em s e r v i c e s a nd
process d el e t ion
( be c a u s e ASTs
c a nno t b e d e l i v e r ed
to
p r o c e s s e s wh i l e
t h e y a r e s u s pe nd ed ) .
Th e
t r a n s i t i o n s b e twe e n s t a t e s a r e d i ag r ammed i n F i g u r e 8 - 5 .

8 . 1 . 3 . 2 . 2 Memo r y Ma n a g e m e n t Wa i t S t a te s - Th r e e p r o c e s s wa i t
states
E a c h s t a t e i s r e p r e s e n t ed by a
a r e a s s o c i a t ed wi th memo r y m a n ag eme n t .
s i ng l e
queue
a nd
l i s th e a d
of
the
f o rm
s h o wn
in
Fig ure 8-4 .
Di f fe rent iat ion o f
r e s i d e n t a nd o u t swa pped pr o c e s s e s i n th e s e s t a te s
i s o n l y a c compl i sh e d b y m e a n s o f t h e PC B $V R E S b i t
of
the
PCB $ L S T S
f i eld .
Th e o u t s wa ppi ng o f p r o c e s s e s i n the se s t a t e s d o e s n o t i nvol v e
r em o v a l f r om a nd i n s e r t i o n i n to q u e ue s .
Th e PC B $V R E S b i t
is
s impl y
c l e a r ed
i n the process c o n t r o l b l o c k .
( Memo r y m ana g e m e n t wa i t s t a t e s
a r e d i s c u s s e d f r om a n o th e r po i n t o f v i ew i n Ch a pt e r 1 2 . )
Th e pag e f a u l t wa i t s t a t e ( PFW) i s e n t e r ed wh e n a p r o c e s s r e f e r s to
a
pag e
that
i s not
in
phys i c a l
memo r y .
Wh i l e the pag e r e ad i s i n
p r og r e s s , t h e p r o c e s s i s p l a c ed i n to the PFW s t a t e .
Compl e t i o n o f t h e
pa g e r e ad , A S T e n q u e u i ng , o r p r o c e s s d e l e t i o n c a n c a u se the p r o c e s s t o
b e c ome c ompu t a b l e ( C OM ) o r
c ompu t a b l e o u t s wa pped
( C OM O ) ,
d e pend i ng
upo n i t s PC B $V_R E S b i t v a l u e wh e n the s a t i s f y i ng c o nd i t i o n o c c ur s .
Th e f r e e pag e wa i t s t a t e ( F PG ) i s e n t e r ed wh en a
process
r eque sts
a
pag e to be add ed to i t s wo r k i ng s e t , b u t t h e r e a r e no f r e e pag e s to b e
a l l o c a t ed f r om t h e f r e e
pag e
l i st .
Th i s
state
is
essent i a l l y a
r e s o u r c e wa i t
unt i l
t h e s uppl y o f f r e e pag e s i s r e pl e n i s h e d th r o ug h
mod i f i e d pag e wr i t i ng , p r o c e s s o u t s wa ppi ng , o r v i r t ua l
add r e s s
s pa c e
deletion .
Th e c o l l i d ed pag e wa i t s t a t e
( C O L PG )
u s ua l l y o c c u r s wh e n
s ev e r a l
processes
c a u s e pag e f a u l t s o n t h e s ame sh a r ed pag e a t th e same t i m e .
Th e i n i t i a l f a u l t i ng p r o c e s s e n t e r s t h e PFW s t a t e ,
wh i l e
th e
second
and
s u c c eed i ng
p r o c e s s e s e n t e r t h e C O L PG s t a t e .
Th e C O L PG s t a t e c a n
a l s o b e e n t e r ed wh e n a p r o c e s s
refers
to
a pr i v a t e pag e
th a t
is
a l ready i n t r ans i t ion
f r om
the d i s k .
Al l C O LPG p r o c e s s e s a r e m a d e
c omp u t a b l e o r c om p u t a b l e o u t s wa pped wh e n the r e ad o pe r a t i o n c ompl e t e s .
( A mo r e d e t a i l ed
d i s c u s s i o n o f c o l l i d ed pag e s
i s c o n t a i n ed
in
Ch a p t e r 1 2 . )

8 . 1 . 3 . 2 . 3 M i s c e l l a n e o u s Wa i t S t a t e ( MWA I T ) - Th e m i s c e l l a n e o us wa i t
s ta te
( MWA I T ) i s used t o i nd i c a t e p r o c e s s e s wa i t i ng fo r r e s o u r c e s n o t
ma n ag e d by a ny o f t h e o th e r p r o c e s s wa i t s t a t e s .
Th e r e
is
a
s i ng l e
MWA I T q u e ue
fo r memo r y r e s i d e n t a nd o u t swa ppe d p r o c e s s e s .
Tab l e 8 - 2
l i s t s t h e r e s o u r c e s a s s o c i a t e d w i th t h e two fo rms o f the MWA I T s t a t e .

8-1 1

S C H E D U L I NG

OUTSWAP

EVENT, AST, DEL

WAIT CEF

OUTSWAP

DELETE

AST, DEL,
MUTEX OR RESOURCE
AVAILABLE
AST
DEL
*

AST enqueuing
Process deletion

Transitions from memory-resident
walt states to COM are not
labeled to avoid cluttering
the figure. They are caused
by the same events shown for
transitions to the COMO state.

Represents a process state
with a single queue

Represents a process state
with a multiple queues

Fi g ur e 8 - 5

S t a t e T r a n s i t i o n D i ag r am

8-1 2

S C H E D U L I NG
Ta b l e 8 - 2
Ty pe s o f MWA I T S t a t e
Re a s o n fo r Wa i t

Co n t e n t s o f PCB $ L_EFWM
Symb o l i c

Mu t e x Wa i t s
S y s t em Log i c a l Nam e Tab l e
G r o up Lo g i c a l Na m e Ta b l e
I /O Da t a Ba s e
Common E v e n t B l o c k L i s t
P a g ed Dyn am i c Mem o r y
G l o b a l S e c t i o n De sc r i pto r L i s t
S h a r ed Mem o r y G l o b a l Sec t i o n De sc r i p t o r Ta b l e
S h a r ed Memo r y Ma i l bo x e s
E n que ue/De q u e u e Ta b l e s { No t Cu r r e n t l y U s e d )
K n o wn F i l e En t r y Ta b l e
L i n e P r i n t e r Un i t Co n t r o l B l o c k { 2 )

L OG $A L MUT E X
I OC $G L MUTE X
E XE $G L-C EBMTX
EXE $G L-PGDYNMTX
E XE $G L-G S DM TX
E XE $G L-S HMGSMTX
E XE $G L-S HMMBMTX
E XE $G L-EN QM TX
EXE $ G L-KF IM TX
UCB $ L_LP_MUTEX

Sym b o l i c

Re so u r c e Wa i t s
A S T Wa i t ( Wa i t fo r sys t em o r s pe c i a l k e r n e l A S T }
Ma i l bo x Fu l l
N o n pa g ed Dyn am i c Memo r y
Pag e F i l e Fu l l
P a g ed Dyn a m i c Memo r y
B r e a k t h r o ug h { Wa i t fo r b r o a d c a s t m e s s a g e )
I m a g e Ac t i v a t i o n Lo c k
J o b Po o l ed Quo t a ( no t c u r r en t l y u s e d )

R S N $ AS'IWA I T
RSN $-MA I LB O X
RSN $-N PDYNM EM
RSN $-PG F I LE
RSN $-PG DYNM EM
R S N $-B RKT HR U
R S N $-I AC LO C K
R S N $=J Q UO TA

(1)

Th e s ym bo l i c c o n t en t s o f PC B $ L E FWM w i l l p r o bab l y r em a i n
the
s a m e f r o m r e l e a s e to r e l e a se .
Th e n um e r i c c o n t e n t s fo r m u t e x
wa i t s a r e a l m o s t c e r ta i n to c h a ng e w i t h e a c h m a j o r r e l e a s e o f
t h e o pe r a t i ng s ys t em .

{2)

Th e m u t e x a s s o c i a t ed w i t h e a c h l i n e
pr i n te r
un i t d o e s
no t
have
a
f i x ed
add r e s s
l i ke
the
o th e r m u t e x e s .
I t s v a l ue
d e pe nd s o n wh e r e the UCB f o r tha t un i t i s a l l o c a t e d .

Num e r i c

{1)

{ he x )

80 0024F4
8 0 0 0 24F8
80002620
80002624
80002628
8 0 0 0 2 6 2C
80002630
80002634
80002638
8 0 0 0 2 6 3C
{No te 2 )

Num e r i c

( hex)

00000001
00000002
00000003
0 0 0 0 0 0 04
00000005
00000006
00000007
00000008

Th e m i s c e l l a n e o us
r e so u r c e wa i t
state
is
used
t o wa i t
fo r
the
ava i l ab i l i ty
of a d e pl e t ed or l o c k e d r e s o u r c e .
A p r o c e s s may e n t e r a
r e s o u r c e wa i t i f the r e s o u r c e r e que s t ed ha s a l r e a d y b e e n
a l l o c a ted .
Common e x ampl e s a r e
t h e d e pl e t i o n o f no npag ed d ynam i c memo r y o r no
r o om in ma i l bo x e s .
Th e
process
wi l l
b e c ome c omputa b l e
wh e n
the
r e s o u r c e b e c om e s ava i l a b l e ag a i n .
Th e n um b e r of the r e so u r c e (a sma l l
i n t eg e r d e f i n ed b y t h e $ R SNDEF m a c r o )
is
s t o r ed
in
the
PC B $ L E FWM
f i e l d ( Ta b l e 8 - 2 ) , and t h e PC B $W S TATE i s c h a ng e d to MWA I T t o i ndTc a t e
a m i sc el l aneous
r e so u r c e
wa i t�
Wh e th e r
a process
can
be m a d e
e x e c u t a b l e b y t h e e n que u i ng o f a n A S T t o t h e p r o c e s s i s d e pe nd e n t upon
t h e i n t e r r up t p r i o r i t y l ev e l of t h e c a l l e r of
the
r o ut i ne
d e c l a r i ng
the
r e so u r c e wa i t .
If
the
I PL
i s t h e s a v e d PS L i n th e h a r d wa r e
p r o c e s s c o n t r o l b l o c k i s two o r l a r g e r , t h e p r o c e s s wi l l r e e x e c u t e t h e
r e so u r c e
wa i t
code
a nd b e pl a c ed
back
i n to
the MWA I T s t a t e
i mmed i a te l y .
I f the s a v ed I P L i s sm a l l e r th a n two ,
an
AST d e l i v e r y
i n te r r upt w i l l
occur ,
r e s ul t i ng
i n t h e e x e c u t i o n o f t h e p r ev i o u s l y
e n que u e d AST .
Th e S e t Re s o u r c e Wa i t Mo d e s ys tem
s e rv i c e
( $ S E TRWM)
can
fo r c e
the
i mmed i a t e
r e turn
of
an
error
s t a t u s c o d e r a th e r th a n p l a c i ng the
p r o c e s s in the
MWA I T s t a t e .
$ S ETRWM d o e s th i s b y s e t t i ng
the
PC B $V S S RWA I T b i t
of
t h e PC B $ L STS f i e l d .
D i s a b l i ng r e so u r c e wa i t s
a f f e ct s m a n y d i r ec t l y r e que s t ed ope r a t i o n s s uch a s
I /0 r e que s t s
or
t imer
r e que s t s b u t h a s n o e f f e c t o n a l l o c a t i o n r e qu e s t s b y t h e s y s tem
on b e h a l f of t h e us e r .
An ex ampl e of
th i s
s i tua t i o n
is
the
pag e r
8-1 3

S CHEDUL ING
r e qu i r i ng
a n I /O r e q u e s t p a c k e t t o pe r f o rm a pag e r e ad o pe r a t i o n .
If
n o npag e d d y n am i c m em o r y i s d e pl e t ed , t h e p r o c e s s w i l l e n t e r the MWA I T
s t a te ,
even
i f $ S ETRWM h a d b e e n u s e d t o d i sa b l e r e s o u r c e wa i t s .
Th e
r e a so n fo r th i s d i s t i n c t i o n
is
that
a
process can
r e s pond
to
a
d e pl e t ed
r e so u r c e
e r r o r f r om a s ys t em s e rv i c e c a l l o r an RMS r e q u e s t
b u t h a s no m e a n s o f r e ac t i ng t o a s i m i l a r e r r o r i n t h e e v e n t o f
an
u n e x p e c t ed e v e n t s uc h a s a pag e f a u l t .
Sys t em r o u t i n e s tha t a c c e s s d a t a s t r uc t u r e s p r o t e c ted b y m u t e x e s w i l l
pl ace a
process
i n t h e MWA I T s t a t e i f t h e r e q u e s te d m u t e x o wn e r sh i p
c a nno t be g r a n t e d ( Ch a pt e r 2 4 ) .
Th u s , t h e m u t e x wa i t s t a t e
i nd i c a t e s
a
l o c k ed
r e so u r c e a nd
n o t n ec e s s a r i l y a d e p l e t e d o n e .
Th e l og i c a l
n am e s ys tem s e rv i c e s o pe r a t i ng o n t h e sys tem a nd g r o up l o g i c a l
name
tables
a re
o n e e x am p l e o f th i s t ype of o pe r a t i o n . Wh e n t h e o wn e r o f
t h e r e que s t e d m u t e x
rel eases
it,
t h e r e q ue s t i ng
p r o c e s s b e c om e s
( C OM ) a n d r eq ue s t s o wn e r sh i p o f t h e m u tex ag a i n .
r e s i d e n t c ompu t a b l e
A S T e n que u i ng c a nno t m a k e a m u t e x -wa i t i ng p r o c e s s c om p u t a b l e fo r
l o ng
because the
I PL
i n the s to r ed PS L i s I P L $ A S TDE L ( I P L 2 ) , d i s a b l i ng
th e A S T d e l i v e r y i n te r r up t .
Th e m u t ex wa i t s t a t e i s d i s t i ng u i s h e d f r om t h e r e s o u r c e wa i t s t a t e
by
s to r i ng
t h e s ys t em v i r t ua l
ad d r e s s
of
t h e r e q ue s t e d m u t ex i n t h e
PC B $ L E FWM f i e l d .
( Wh e n t r e a t e d a s a s i g n ed i n t eg e r , t h e c o n t e n t s o f
t h i s -f i e l d
a r e po s i t i v e a nd sm a l l wh e n t h e p r o c e s s i s wa i t i ng f o r a
r e so u r c e .
Wh en t h e p r o c e s s i s wa i t i ng f o r a m u t e x , t h e c o n t e n t s
are
n eg a t i v e , a s l i s te d i n Ta b l e 8 - 2 . ) Fo r e x am p l e , i f a p r o c e s s w i sh e s to
a l l o c a t e a b l o c k o f pag e d d yn am i c memo r y , i t m u s t f i r s t a c q u i r e
the
pag ed
po o l m u t ex
t o a l l o w i t to s e a r c h the l i n k e d l i s t o f a v a i l a b l e
b l o c k s ( Ch a p t e r 2 5 ) .
I f a n o t h e r p r o c e s s i s a l r e a d y l o o k i ng
a t pag ed
po o l ,
th i s p r o c e s s i s put i n to a m u t e x wa i t s t a t e ( w i t h 8 0 0 0 2 6 2 8 , t h e
a d d r e s s o f t h e pag ed po o l m u t ex ,
s to r ed
in
PC B $ L E FWM ) .
On c e
the
m utex
i s avai l ab l e
a nd
t h e n o wn e d by t h i s p r oce s s , p a g ed po o l i s
s e a r c h ed fo r a b l o c k o f t h e r e q ue s t ed s i z e .
If
the r e
i s no block
l a rge
e no ugh t o s a t i s f y t h e a l l o c a t i o n r e q ue s t , t h e p r o c e s s i s pl a c ed
i n to a r e so u r c e wa i t s t a t e ( wi th 0 0 0 0 0 0 0 5 , t h e v a l ue o f RS N $ PG DYNM EM ,
s t o r ed
in
PCB $ L E FWM ) .
Th e p r o c e s s
r em a i n s i n th i s s t ate un t i l a
b l o c k o f pag e d pool i s d e a l l o c a t e d .

8 . 1 . 3 . 3 Common Eve n t B l o c k s - P r o c e s s e s wa i t i ng
fo r o n e
or
mo r e
c ommo n e v e n t f l ag s a r e e nque ued t o d a t a s t r uc t u r e s c a l l ed c ommo n e v e n t
b l oc k s ( CEBs )
Th e s e d a t a
s t r uc t ur e s a r e a l l o c a t e d
f r o m nonpa g ed
d yn am i c m em o r y wh e n p r o c e s s e s c r e a t e c ommon e v e n t f l ag c l us t e r s .
Th e
c o n t e n t s o f a C E B i n c l ud e t h r e e l o ng wo r d s th a t e x a c t l y c o r r e s po nd to a
wa i t s t a t e q u e u e h e ad e r ( F i g u r e 8 - 4 ) .
Th e e n t i r e fo rma t o f the c ommo n
e v e n t b l o c k i s s h o wn i n Ch a p t e r 9 .
•

Th e n um b e r o f C E F s t a t e que ue s d e pe nd s upo n th e n umbe r o f c ommo n e v e n t
f l ag
c l us te r s
th a t e x i s t o n a pa r t i c u l a r s ys tem a t a n y g i v e n t i m e .
( Ad d i t i o n a l p r o c e s s e s a s s o c i a t i ng
w i t h e x i s t i ng
common e v e n t
f l ag
c l us t e r s d o n o t c r e a t e
f u r th e r
C E Bs o r
C E F q u e ue s . ) O u t s wa pped
p r o c e s s e s wa i t i ng f o r c ommo n
event
f l ag s a r e d i f f e r en t i a t ed
f r om
s i m i l a r memo ry
r e s id ent
processes
by
the
PC B $V R E S b i t o f
the
PCB $ L S T S f i e l d o n l y .
I n a d d i t i o n to s a t i s f y i ng t h e-ev e n t
f l ag
wa i t
ma s k ,- the
s ys t em c a n a l s o ma ke
a
C E F p r o c e s s c o m pu t a b l e by AST
e n qu e u i ng or pr o c e s s d e l e t i o n .

8-1 4

S CHEDULING
8.2

S YS TEM EVENTS

Sys tem e v e n t s a r e o c c u r r e n c e s o f o pe r a t i o n s tha t c h a ng e the s t a t e s o f
processe s .
A s ys t em e v e n t m a y m a k e
a p r o c e s s c om p u t a b l e , m em o r y
r e s i d en t L
or
o u t s wa pped .
S y s tem e v e n t s
prov i d e t h e t r ans i t i on s
b e twe e n t h e p r o c e s s s t a t e s d i ag r ammed i n F i g u r e 8 - 5 .

8.2.1

Sys t em Ev e n t s a nd P r o c e s s S t a t e s

A p r o c e s s i n i t i a l l y e n t e r s a wa i t s t a t e f r om th e c u r r e n t s t a t e
( CUR ) .
Th a t
is ,
a
p r o c e s s e i th e r d i r e c t l y o r i nd i rec t l y ex ecutes a r e q u e s t
fo r a s ys tem o pe r a t i o n fo r wh i ch i t. m u s t wa i t .
Di rect
r eque s t s
s uc h
a s $ Q I OW ,
$H IBER ,
$ S US PN D ,
a nd
$ WA I TFR pl a c e t h e p r o c e s s i n th�
v o l un t a r y wa i t s t a t e s L E F , C E F , H I B , a n d S U S P .
S u b s e q u e n t o u t s wa pp i ng
( f r om
t h e p r o c e s s v i ewpo i n t a n un r e q ue s t ed s ys t em o pe r a t i o n ) m a y m o v e
a p r o c e s s t o the LEFO , H I B O , o r S U S PO s t a t e s .

8.2.1.1
P r o c e s s S t a t e Ch a ng e s - I nd i r e c t wa i t
r e quests o c c ur
as
a
r e s u l t o f p a g i ng o r c o n t e n t i o n fo r s y s t em r e so u r c e s .
A process does
n o t r e q ue s t PFW ,
FPG ,
C O L PG ,
or
MWA I T t r a n s i t i o n s .
Ra t h e r ,
the
t r an s i t i o n s to th e s e wa i t s t a t e s o c c u r b e c a u s e d i r e c t s e r v i c e r e q u e s t s
to t h e s ys t em c a n n o t b e c om p l e t ed o r s a t i s f i e d a t t h e mome n t .
A p r o c e s s c a n b e come
c om p u t a b l e
fo r
a
va r i ety o f
reasons .
Th e
av a i l a b i l i t y o f
a
r eque sted
r e so u r c e o r the s a t i s f a c t i o n o f a wa i t
c o nd i t i o n ( s uc h a s a n e v e n t f l ag s e t t i ng o r
a
$ WAKE
s ys t e m s e r v i c e
cal l )
w i l l m a k e t h e p r o c e s s c om p u t a b l e .
I n a l l p r o c e s s s t a t e s e x c e pt
S US P a nd S US PO , the e n que u i ng of a n A S T w i l l m a k e a p r o c e s s c om p u t a b l e
even
if
t h e wa i t c o nd i t i o n i s n o t s a t i s f i ed .
( Be c a u s e p r o c e s s e s a r e
u s ua l l y p u t i n to the MWA I T s t a t e a t I PL 2 , t h e A S T i s n o t a b l e
to
be
d e l i v e r ed
unt i l
t h e m i s c e l l a n eo us wa i t
is
s a t i s f i ed .
Th u s , the
t yp i c a l p r o c e s s in an MWA I T s t a t e wi l l not b e c ome c omput a b l e fo r
l o ng
d ue
to the e nq ue u i ng o f a n A S T .
In pa r t i c u l a r , p r o c e s s e s wa i t i ng f o r
r e s o u r c e s o r m u t e x e s t yp i c a l l y c a nn o t be d e l e t ed . )
Process dele t ion ,
i m pl e m e n t ed
w i th
a
s p e c i a l k e r n e l m o d e A S T , w i l l m a k e a l l pr o c e s s e s
tha t a r e b e i ng d e l e t e d c o m p u t a b l e ( i n c l ud i ng pr o c e s s e s i n t h e S US P o r
S U S PO s t a t e s ) b e c a u s e t h e t a rg e t p r o c e s s i s r e s um ed b e f o r e t h e A S T i s
que ued .
E x c h a ng e s o f p r o c e s s e s b e twe e n the c u r r e n t e x e c u t i ng s t a t e
( C UR )
a nd
t h e c om p u t a b l e m em o r y- r e s i d e n t s t a t e
( C OM )
a r e pe r f o rmed
by the
sched ul e r r o ut i n e ( Se c t i o n 8 . 3 ) .
Th e movem e n t o f a p r o c e s s
i n to
and
out o f
t h e b a l a n c e s e t i s t h e r e s po n s i b i l i t y o f t h e swa ppe r pr o c e s s
( Ch a pt e r 1 4 ) .

8 . 2 . 1 . 2 Wa i t S t a t e s a nd AST De l i v e r y - On e o f th e r e spon s i b i l i t i e s o f
the
r o ut i ne s
th a t p l a c e p r o c e s s e s i n to wa i t s t a t e s i s to i n s u r e t h a t
t h e s e p r o c e s s e s w i l l c o r r ec t l y e n t e r
the i r
a pp r o p r i a t e wa i t
s t a tes
a fter
s uc c e s s f u l
del ivery of
a n AS T .
Th e r e
a r e th r e e d i f f e r e n t
t e chn i q u e s u s e d , d e pend i ng o n t h e pa r t i c u l a r wa i t s t a t e b e i ng e n t e r ed .

8-15

S C H E D U L I NG
8.2.1.2. 1
S y s t e m Se r v i c e Wa i t S t a t e s - I n t h e c a s e wh e r e a p r o c e s s i s
e n t e r i ng
a wa i t s t a t e a s a r e s u l t o f e x e c u t i ng a sys t em se rv i c e ( B I B ,
L E F , o r C E F ) , t h e wa i t r o u t i n e i s e n t e r e d w i th the PC a n d PS L o f
the
t h e s ys tem s e r v i c e C HM K e x c ept i o n ( Ch a p t e r 3 ) o n the t o p o f t h e s t a c k .
Th e f i r s t i m p l i c a t i o n o f th i s i s th a t the p r o c e s s w i l l
wa i t
in
the
a ccess
m o d e i n wh i c h t h e sys t em s e r v i c e wa s i s s u ed .
Bec ause ASTs a r e
e nque ued a nd d e l i v e r ed b a s ed o n a c c e s s m o d e , th i s a l l o ws , f o r e x a m p l e ,
a s upe r v i s o r m o d e A S T t o b e d e l i v e r e d to a p r o c e s s wa i t i ng o n an e v e n t
f l ag a s a r e s u l t o f a $ Q I OW c a l l i s sued f r om u s e r o r s up e rv i s o r mo d e .
I n ad d i t i o n , the wa i t c o d e b a c k s up the s a v e d PC by f o u r
so
th a t
it
po i n t s
to
the
C HM x
i n s t r uc t i o n
1n
the
s ys t em
s e r v i c e v e c to r
( Figure 3-1 ) .
I f a p r o c e s s r e c e i v e s a n A S T wh i l e
in
s uc h
a
wa i t
s tate ,
t h e AST
i s d e l i v e r ed
a nd
executes .
Wh e n t h e AST d e l i v e r y
r o u t i n e pa s s e s c o n t r o l
bac k
to
the ma i nl i ne ,
t h e s ys tem
serv ice
executes
ag a i n , p l a c i ng t h e p r o c e s s r i g h t b a c k i n to t h e wa i t s t a t e i t
wa s i n be f o r e the A S T wa s d e l i v e r ed .

8 . 2 . 1 . 2 . 2 Memo r y Manag e m e n t Wa i t S t a t e s - Th e pag e
faul t
h a nd l e r
( Ch a p t e r 1 2 )
is
so l e l y r e s po n s i b l e
fo r
p l a c i ng p r o c e s s e s i n t o the
t h r e e wa i t s t a t e s a s s o c i a t ed w i t h m emo r y m a n ag em e n t ( P FW , FPG , C O L PG ) .
Th i s r o u t i n e p l a c e s a p r o c e s s i n to a wa i t s t a t e wi th t h e PC a nd PS L o f
t h e pag e f a u l t a s t h e s a v ed p r o c e s s c o n t e x t .
On c e a g a i n , b e c a u se
the
PS L r e f l e c t s the a c c e s s mod e in wh i c h the f a u l t o c c u r r ed , ASTs c a n be
d e l i v e r ed f o r th a t a nd
all
i nn e r
access modes .
( No t e
th a t
th i s
r o ut i n e d o e s no t n e ed
t o c h a ng e t h e PC t h a t i t f i nd s o n t h e s t a c k
b e c a u s e pag e f a u l t
ex c ept i o n s
are
faul ts
a nd
no t
t r aps .
Fa u l t s
( Ch a p te r 2 ) c a us e t h e P C o f t h e f a u l t i ng i n s t r uc t i o n and no t t h e PC o f
t h e n e x t i n s t r uc t i o n t o b e p u s h ed o n to t h e e x c e p t i o n s t a c k . )
I f a n A S T i s d e l i v e r e d to a nd ex e c u t e s i n s uc h a p r o c e s s , the ma i n l i n e
wi l l
execute the
f a u l t i ng i n s t r uc t i o n ag a i n .
I f the r e a s o n fo r the
f a u l t has b e en r em o v e d ( a f r e e pag e b e c ame a v a i l a b l e or the pag e
r ead
c ompl e t ed )
wh i l e
the
A S T wa s b e i ng d e l i v e r ed o r wa s e x e c u t i ng , t h e
p r o c e s s w i l l s i mp l y c o n t i n ue w i th i t s e x e c u t i o n .
If ,
on
t h e o th e r
h a nd ,
t h e s i t ua t i o n t h a t c a u s e d th e p r o c e s s t o wa i t s t i l l ex i s t s , t h e
p r o c e s s w i l l r e i nc u r t h e pag e f a u l t a nd b e p l a c ed b a c k i n to o n e o f the
m emo r y m a n a g em e n t wa i t s t a t e s .
( No t e
tha t a
process
tha t wa s
i n i t i a l l y i n a PFW s t a t e wo u l d b e p l a c ed i n to a C O LPG s t a t e by s uc h a
s e qu e n c e o f e v e n t s . )

8 . 2 . 1 . 2 . 3 S p e c i a l C a s e s - Th e two r em a i n i ng
wa i t s t a t e s
( S US P a nd
MWA I T )
a r e hand l ed
i n a s p e c i a l wa y b y t h e wa i t r o u t i n e .
A process
s u spe n s i o n o c c u r s a s a r e s u l t o f e x e c u t i ng a spec i a l k e r n e l AST .
ASTs
c a nno t b e d e l i v e r ed t o s u sp e n d ed p r o c e s s e s .
Th a t i s , an AST q u e u e d to
a s us p e n d ed p r o c e s s h a s i t s AST c o n t r o l b l o c k i n s e r t e d
i n to
the
AST
q u e ue
in
t h e so f twa r e PCB .
Ho we v e r , t h e AST e v e n t i s i g no r ed b y the
( I n f a c t , wh i l e a p r o c e s s i s s u s pe nd ed , t h e saved PC i s an
s c h ed u l e r .
ad d r e s s in t h e s p e c i a l k e rne l AST t h a t c a u s e d t h e p r o c e s s to e n t e r the
s us pe nd s t a t e .
Th e s a ved PS L i n d i c a t e s ke r n e l mod e a nd I PL 2 . )
Wh e n a p r o c e s s i s p l a c ed
i n to
a wa i t s t a t e wa i t i ng
fo r
a m u t ex
( Ch a p t e r 2 4 ) , i t s s av e d PC i s e i th e r S C H $ L OC KR o r S C H $ LOCKW , d e pe nd i ng
o n wh e th e r i t i s a t tempt i ng to l o c k t h e m u t ex f o r r e a d a c c e s s o r wr i t e
access .
Th e s a v ed PS L i nd i c a t e s k e r n e l mo d e a nd I PL 2 , wh i c h i m p l i e s
t h a t p r o c e s s e s i n an MWA I T s t a t e wa i t i ng f o r a m u t e x
c a nno t
rece ive
ASTs .

8-16

SCHEDUL I NG
A p r o c e s s c a n a l s o be p l a c ed i n to an MWA I T s t a t e wh i l e wa i t i ng fo r
an
a r b i t r a r y s ys t em
r e so u r c e .
In
th i s c a se , t h e c a l l e r o f S C H $ RWA I T
c o n t r o l s t h e PC and PS L t h a t a r e s a v e d wh e n the p r o c e s s i s p l a c ed i n to
t h e MWA I T s t a t e .
I n pa r t i c u l a r , t h e c u r r e n t a c c e s s m o d e a nd I PL i n
t h e s a v ed PS L d e t e rm i n e wh e th e r a n y ASTs c a n be d e l i v e r ed to a pr o c e s s
t h a t i s wa i t i ng fo r a r e s o u r c e .

8.2. 2

E v e n t R e po r t i ng

E v e n t s a r e r e po r t ed to t h e s c h ed u l e r f r om m a n y s ys tem r o u t i n e s th r o ug h
t h e RPT EVT m a c r o , wh i c h g e n e r a t e s t h e fo l l o wi ng c o d e :
B S BW
. BYTE

SCH$RSE
EVT $ e v e n t-name

wh e r e t h e byte v a l ue s t o r ed d e pend s upo n t h e e v e n t b e i ng
d e c l a r ed by
the
s ys t em
r o ut i ne .
Th e ad d r e s s o f t h e v a l ue wi l l b e p u s h ed o n the
s tac k by
the
BSBW i n s t r uc t i o n .
Ad d i t i o n a l
pa r am e t e r s
( pr i o r i ty
i n c r em e n t c l a s s and PC B a d d r e s s o f t h e a f f e c t ed p r o c e s s ) a r e pa s s e d i n
r eg i s t e r s .
Th e r o u t i n e S C H $ R S E

( i n modul e RSE )

pe r fo rm s the fo l l o w i ng o pe r a t i o n s .

Th e ev e n t n um b e r i s l o ad e d i n to a r eg i s t e r and the r e t u r n
PC
v a l ue
(on
th e s t a c k a s a r e s u l t o f the BSBW i n s t r uc t i o n ) i s
a d j u s t e d to po i n t to t h e a d d r e s s a f t e r the s to r ed b y t e
event
va l ue .

Th e s t a t e
a nd
the
event
a r e checked
fo r
a
s i gn i f i cant
t r an s i t i o n .
E a c h ev e n t ( o r s t a t e t r a n s i t i o n ) h a s a b i t m a s k
d e f i n i ng wh i c h s t a t e s t h i s e v e n t c a n a f f e c t .
Th e
state
of
t h e p r o c e s s i s o b t a i n e d f r om t h e PC B $W_S TATE f i e l d .
•
•

•

Fo r
ex ampl e ,
a
wa k e
event
i s o n l y s i g n i f i c ant
p r o c e s s e s t h a t a r e h i b e r n a t i ng ( H I B o r H I B O s t a t e s ) .

fo r

An o u t s wa p e v e n t i s o n l y s i g n i f i c a n t f o r t h e th r e e s t a t e s
( H IB ,
LEF ,
and
S US P )
wh e r e
a wa i t q u e ue
c h a ng e i s
r e qu i r ed .
Th e e n que u i ng o f a n AST i s s i g n i f i c a n t
to
nea r l y a l l
process
s tates .
On l y
if
the process i s i n a SUSP o r
S US PO s t a t e
is
the
enque u i ng
o f a n AST
i g no r e d
by
S C H $ RS E .

I f the e v e n t i s no t s i g n i f i c a n t
fo r
the c u r r e n t pr o c e s s
s ta te ,
the
even t
is
i g n o r ed ( a nd S C H $ R S E s i mpl y i s s u e s a n
RSB) .
3.

Fo r s i g n i f i c a n t e v e n t s , o n e o f t h e f o l l o wi ng a c t i o n s i s t a k e n .
•

An o u t s wa p e v e n t p r o d uc i ng
an
LEF-LE F O ,
HI B-H IBO ,
or
S US P-S US PO
t r ans i t i on
s i mpl y r em ov e s t h e
PC B o f the
p r o c e s s f r om the r e s i d e n t wa i t que u e and
i nse r ts
it
in
the
c o r r e s po nd i ng
o u t swa pped
wa i t
que ue .
Th e
c o r r e s po nd i ng wa i t q ue ue h e a d e r
c o un t f i e l d s
are
a l so
ad j us t ed .

8-1 7

SCHEDULING
•

•

An o u t swa p e v e n t p r o d uc i ng a C OM-C OMO t r an s i t i o n
r emov e s
t h e P C B f r om
t h e C OM p r i o r i t y q u e ue co r r e s pond i ng to
PCB $ B PR I a nd i n s e r t s
it
i n to
the
c o r r e spond i ng
C OMO
p r i o r Tt y q ue ue .
Th e
S C H $G L C OMQS s t a t us b i t v e c to r i s
a l so mod i f i ed
if
the
C OM q ue u e
i s n o w emp t y .
Th e
a pp r o pr i a t e S C H $ G L_C OM O QS b i t i s un c o nd i t i o n a l l y s e t .
Fo r t r a n s i t i o n s f r om t h e L E F ( i mpl i ed
res i d en t )
or CEF
r e s i d e n t s t a te
to
the
C OM s t a t e , the s a v ed P C i n t h e
h a r d wa r e PC B s t o r ed i n t h e p r o c e s s h e ad e r i s
i n c r em e n t e d
by
f o u r to po i n t pa s t t h e C HMx i n s t r uc t i o n .
Th i s a l l o ws
t h e p r o c e s s to b eg i n e x e c u t i o n immed i a t e l y f o l l o wi ng
the
s ys tem s e r v i c e c a l l r a th e r than g o i ng th r o ug h a Wa i t f o r
Ev e n t Fl ag s ys t em s e rv i c e f o r a f l ag t h a t i s a l r e a d y s e t .
Th e
r e s i d e n c e c h e c k i s n e c e s s a r y b e c a u s e the s a v e d PC o f
n o n r e s i d e n t pr o c e s s e s i s
u s ua l l y n o t a v a i l a b l e .
( Th e
s av e d P C
is
s to r ed
i n the h a r d wa r e PC B i n the p r o c e s s
h e a d e r , wh i c h m a y b e o u t swa pped i f t h e p r o c e s s
is not
r e s i d ent . )
Fo r t h e
r em a i n i ng
t r ans i t ions
(all
o f wh i c h m a k e
a
p r o c e s s comp u t a b l e ) , t h e p r o c e s s i s r emoved f r om the wa i t
q u e ue a n d t h e wa i t que ue h e a d e r
c o un t
i s d e c r em e n t e d .
Th e
PC B
is
i n s e r t ed
i n to
a
COM o r COM O s t a t e que ue
d e pend i ng u po n wh e th e r the p r o c e s s i s mem o r y - r e s i d e n t o r
o u t swa pped .
Th e pa r t i c u l a r p r i o r i t y que ue o f the COM o r
COM O s t a t e i s s e l e c t ed f o r
i n se r t i o n
a fter
a
pr i o r i t y
a d j us tm e n t i s a t t emp t e d ( s e e the fo l l o w i ng s e c t i o n ) .
Th e
SCH$G L C OMQS o r SC H$G L C OM O QS s umma r y b i t c o r r e s pond i ng
to the-s e l e c t ed p r i o r i ty q u e ue i s uncond i t i o n a l l y s e t .

Sub s e qu e n t s c h e d u l i ng o r s wa pp i ng a c t i v i t y
i s n e c e s s a r y to
e x e c u t e o r i n swa p the now c omputab l e proc e s s .
Th e swa ppe r i s
po s s i b l y a w& k e n ed ( r o u t i n e SCH$ SWPWAKE i s c a l l ed ) i f the n o w
c o mp u t a b l e p r o c e s s i s p r e s e n t l y o u t swa pped ( S e c t i o n 8 . 1 . 2 . 4 ,
i t ern 3 )
•

Th e
s c h ed u l e r
is
r e que s t ed ,
t h r o ugh
an
I PL 3
so f t wa r e
i n t e r r up t ,
if
t h e now c omputa b l e p r o c e s s i s m em o r y- r e s i d e n t
a n d h a s a pr i o r i ty g r e a t e r th a n
or
e qua l
to
tha t o f
the
c u r r e n t l y e x e c u t i ng
process .
Th i s p r i o r i ty c h e c k avo i d s
n e ed l e s s c o n t e x t s w i t c h e s
wi th
the i r
a ssoc i a ted
overhead ,
o n l y to d e t e rm i n e th a t t h e p r ev i o u s l y e x e c u t i ng p r o c e s s wi l l
ag a i n e x ec u t e .

8. 2. 3

Sys t em Ev e n t s a n d As s o c i a t ed P r i o r i ty Boo s t s

Sy s t em r o u t i n e s th a t r e po r t e v e n t s t o t h e s c h ed u l e r no t o n l y d e sc r i b e
t h e e v e n t a nd the p r oc e s s t h a t i s r e spo n s i b l e , b u t a l so s p e c i f y one o f
f i v e c l a s s e s o f p r i o r i ty i n c r em e n t s o r bo o s ts tha t m a y b e a pp l i ed
to
the
b a se
p r io r i t y o f
the p r o c e s s .
Ta b l e 8 - 3 l i s t s the e v e n t s , t h e
p r i o r i t y c l a s s , a n d the po t e nt i a l amo un t o f p r i o r i t y i n c r em e n t a pp l i ed
to
the proce ss .
Th e t a b l e d o e s n o t s h o w AST enqu e u i ng bec a u s e sys t em
r o u t i n e s enque u i ng ASTs to a p r o c e s s c a n s e l e c t a n y o f
the pr i o r i ty
i n c r em e n t c l a s s e s to be a s so c i a t ed wi th the e n que u i ng o f a n AS T .

8-18

S C HEDUL I NG
Ta b l e 8 - 3
Sy s t em Ev e n t s a n d As s o c i a te d P r i o r i t y Bo o s t s

Sy s t em Ev en t

P r i o r i ty
Cl ass { * )

Pa g e Fa u l t Re ad Compl e t e
Qua n t um End
O t h e r Ev e n t s wi t h No Bo o s t

0
0
0

{ PR I $_NULL )

0
0
0

D i r ec t I /0 Compl e t i o n
No n t e r m i n a l Bu f f e r ed I /O Compl e t i o n
Upd a t e S e c t i o n Wr i t e Compl e t i o n
S e t Pr i o r i t y

1
1
1
1

( PR I $_I OC OM )

2
2
2
2

Re so u r c e Av a i l ab l e
Wa ke a P r o c e s s
Re s um e a P r o c e s s
De l e t e a Pr o c e s s
T i m e r Re que s t Ex p i r a t i o n

2 { PR I $_R E SAVL )
2
2
2
2 ( PR I $_T IM ER )

3
3
3
3
3

Te rm i n a l Ou t pu t Compl e t i o n

( PR I $_T OC OM )

Te rm i n a l I n pu t Compl e t i o n
Process Creation

4
4

( PR I $_T I C OM )

6
6

( *)

P r i o r i ty
Bo o s t

Ro u t i n e s tha t r e po r t s ys t em
even t s
pa ss a n
i nc r em en t
cl ass
to
the s c h ed ul e r .
Th e s c h ed u l e r u s e s t h i s c l a s s
a s a b y t e i nd ex i n to a
t ab l e
of va l ue s
{ local
l ab e l
B P I NC i n mod ul e R S E ) t o c om p u t e t h e a c t ua l boo s t .

Th e a c t u a l s o f twa r e p r i o r i t y o f
f o l l o wi ng s t e ps .

the

process

d e t e r m i ned

the

Th e p r i o r i t y i n c r eme n t f o r the
event c l a s s
( Ta b l e 8 - 3 )
a d d ed to t h e b a s e pr i o r i t y o f t h e p r o c e s s { PC B $ B_PR I B ) .

I f the p r o c e s s h a s a c u r r e n t p r i o r i t y h i g h e r th a n t h e
r esul t
o f s t e p o n e , t h e c u r r e n t p r i o r i t y wi l l b e r e t a i n e d ( s u c h a s
o c c ur s i n F i g u r e 8 - 2 , event 1 3 ) .

I f the h i g h e r p r i o r i ty o f s t e p s o ne and two i s a b o v e 1 5 , t h e n
( No t e t h a t th i s
the
base
pr i o r i ty o f the process is used .
t e s t a c c ompl i s h e s two c h e c k s a t t h e same
t ime .
Fi rst ,
all
r e a l - t i m e p r o c e s s e s f i t th i s c r i t e r i o n , w i th t h e r e s u l t t h a t
r e a l - t i m e p r o c e s s e s d o no t h a v e t h e i r p r i o r i t i e s a d j us t e d
in
r e s po n s e
to
s ys t em
events .
S e c o nd , p r i o r i ty b o o s t s c a nno t
m o v e a no rm a l p r o c e s s i n to the r e a l - t i me p r i o r i t y r a ng e . )

A s i d e e f f e c t o f s t e p t h r e e i s tha t r e a l - t i m e p r o c e s s e s a l wa ys e x e c u t e
at
the i r
base
pr io r i t i es .
Fu r the r , no te tha t no r m a l pr o c e s s e s w i th
b a s e p r i o r i t i e s f r om
1 0 to
1 5 wi l l
no t a l wa ys
r ec e i ve
pr i o r i ty
i n c r em e n t s
a s events occur .
As t h e b a s e p r i o r i t y o f a n o r m a l p r o c e s s
i s moved c l o s e r t o 1 5 , t h e p r o c e s s wi l l s pe nd a g r e a t e r amo un t o f t i me
at
i ts
base pr io r i ty .
P r i o r i ty 14
a n d 1 5 p r o c e s s e s e x p e r i e n c e no
p r i o r i ty b o o s t s .
Th u s , th i s s t r a t eg y b e n e f i t s
tho s e p r o c e s s e s
th a t
m o s t n e ed i t , I /0 bo und a nd i n te r a c t i v e p r o c e s s e s wi th b a s e p r i o r i t i e s
o f 4 th r o ug h 9 .
P r o c e s s e s w i th e l ev a t e d
base pr i o r i t i es do
not
r e q u i r e th i s a s s i s t a n c e a s t h e y a r e a l wa ys a t t h e s e l ev e l s .
8-19

S C HEDUL ING
8.3

RESCHEDUL ING INTERRUPT

Th e I PL 3 i n te r r up t s e r v i c e r o u t i n e , S C H E D ,
sc h e d u l e s p r o c e s s e s
fo r
execut ion .
Th e
a c t ua l
wo r k o f
the
s c hed ul e r
i s pe r f o rm ed
at
I PL $ S YNC H to b l o c k c o nc u r r e n t
access
a nd mod i f i c a t i o n o f
the
s c h ed u l e r ' s d a t a b a s e b y o th e r
s y s t em
compo n e n t s .
Th e p r i n c i pa l
p u r po s e o f the s c h e d u l e r i s t o r emove t h e c u r r e n t l y e x e c u t i ng
process
b y s to r i ng
t h e c o n t e n t s o f t h e p r o c e s s p r i v a te p r o c e s s o r ( ha r d wa r e )
r e g i s te r s a nd r e p l a c i ng
th e
r eg i s t e r
contents
wi th
tho s e o f
the
h i g h e s t p r i o r i ty c om p u t a b l e r e s i d e n t p r o c e s s .
Th i s o pe r a t i o n , k n o wn
a s c o n t e x t swi tch i ng , i s a c c om p a n i e d by mod i f i c a t i o n s to the
a f f ec ted
processes
in
t e rm s o f p r o c e s s
s ta te ,
c u r r en t p r i o r i t y , a nd s t a t e
q u e ue .

Ha r d wa r e C o n t ex t

8.3.1

Th e d e f i n i t i o n o f a p r o c e s s f r om t h e v i ewpo i n t o f
t h e h a r d wa r e
is
c o n t a i ne d i n t h e h a r d wa r e c o n t e x t .
Th i s c o l l e c t i o n o f d a t a i s t h e s e t
o f h a r d wa r e p r o c e s s o r r eg i s t e r s
who s e c o n t e n t s
a re
un i que
to
the
p r oce s s .
Th e s e i nc l ud e the f o l l o w i ng c a t eg o r i e s of i n f o rm a t i o n :
•

•

t h e g e n e r a l p u r po s e r eg i s te r s , R O t h r o ug h R l l ,
t h e a r g um e n t
po i n t e r ( AP ) , t h e f r am e po i n t e r ( F P ) , and t h e p r og r am c o u n t e r
( PC ) ;
t h e pe r - p r o c e s s
a c c e s s mod e
s t a c k po i n t e r s
fo r
ke rnel ,
e x ec u t i v e ,
s upe r v i s o r ,
a nd
u s e r s tac k s .
One o f th e s e fo u r
r eg i s te r s c o n t a i n s t h e c u r r e n t s t a c k po i n te r fo r t h e p r o c e s s ,
a s i nd i c a t e d by th e c u r r e n t m o d e f i e l d i n th e s a v ed PS L ;

•

t h e p r o c e s s o r s t a t u s l o ng wo r d

•

t h e AST l e v e l p r o c e s s o r r eg i s te r

•

( PS L ) ;
( ASTLVL ) ;

a nd

t h e p r o c e s s pag e t a b l e r eg i s t e r s f o r the p r og r am and
r eg i o n s ( P O B R , P O L R , P l B R , a nd P l LR ) .

contro l

W i th the e x c e p t i o n s o f the ASTLVL r eg i s t e r v a l u e a nd t h e c o n t e n t s o f
t h e m em o r y m a n ag em e n t r eg i s t e r s fo r t h e p r og r am and c o n t r o l r eg i o n s ,
t h e c u r r e n t v a l u e s f o r the
var ious
r eg i s t e r s f o rm i ng
the h a r d wa r e
c o n te x t o f
the
c u r r e n t p r o c e s s a r e m a i n t a i n ed o n l y i n t h e p r o c e s so r
r eg i s t e r s .
Wh en a p r o c e s s i s n o t ex e c u t i ng ,
t h e c omp l e t e h a r d wa r e
conte x t
i s c o n t a i n ed
in
a po r t i o n o f t h e p r o c e s s h e a d e r c a l l ed the
h a r d wa r e p r o c e s s c o n t r o l b l o c k .

8-20

S CHEDUL ING
Th e h a r d wa r e p r o c e s s c o n t r o l b l o c k ( F i g u r e 8 - 6 ) i s a pa r t o f t h e f i x ed
po r t i o n o f
the
p r o c e s s h e ad e r fo r e a c h p r o c e s s .
I t i s r e s i d en t i n
m em o r y wh e n ev e r t h e c o r r e s po nd i ng
process
is
i n t h e b a l anc e
set .
Ac c e s s b y t h e o pe r a t i ng s y s t e m o c c u r s n o rma l l y th r o ug h o f f s e t s f r om
t h e s t a r t i ng a d d r e s s o f t h e p a r t i c u l a r
p r o c e s s h e ad e r .
Howe v e r ,
d u r i ng c o n t e x t swi t c h i ng o pe r a t i ons t h e h a r d wa r e m u s t a c c e s s th i s d a t a
s t r uc t u r e d i r ec t l y w i tho u t a d d r e s s t r a n s l a t i o n .
Th i s i s
a c c o m p l i shed
by u s i ng the c u r r en t v a l u e in the p r o c e s s c o n t r o l b l o c k b a s e r eg i s te r
( PR $ P C B B ) .
Th i s
r eg i s te r
conta ins
the
phys i c a l
add r e s s o f
the
h a r d wa r e
process control
b l o c k f o r the c u r r e n t l y e x e c u t i ng p r o c e s s .
VM S s t o r e s t h e phys i c a l a d d r e s s o f t h e h a r d wa r e p r o c e s s c o n t r o l
block
fo r e a c h r e s i d e n t p r o c e s s ( c a l c u l a t e d wh e n the p r o c e s s i s swa pped i n to
memo r y ) in
the
PC B $ L PHYPCB f i e l d
of
the
c o r r e s pond i ng
so f twa r e
p r o c e s s c o n t r o l b l o c k (F i g u r e 8 - 1 ) .

Hardware PCB

KSP
ESP
SSP
USP
RO
R1
R2
R3
R4
RS
R6
R7
R8
R9
R 10
R11

FP
PC
PSL
POBR

PR$_PCBB

The process control block
base register contains
the physical address
of this structure
for the currently
executing process

26 25 24

XI ��� IX1 1
><J
2

P1BR

Figure 8-6

POLR

P 1 LR

H a rdwa r e P r o c e s s Co n t r o l B l o c k

8-2 1

SCHEDUL ING
Remov a l of C u r r e n t P r o c e s s f r om E x e c u t i on

8.3.2

Th e e n t r y po i n t
S C H $ R E SC HE D i n the m o d u l e
SCHED p e r f o rm s
the
o pe r a t i o n s
of
r e sc h ed u l i ng ,
p r e s e r v i ng
the h a r d wa r e c o n t e x t o f t h e
c u r r e n t l y e x e c u t i ng p r o c e s s a nd r emov i ng i t f r om e x e c u t i o n .
Th i s
is
a c c ompl i s hed b y t h e f o l l o w i ng s t e p s .
1.

Th e h a rd wa r e c o n t e x t o f t h e c u r r en t p r o c e s s i s s av ed b y t h e
SVPCTX i n s t r uc t i o n .
Th e d e s t i n a t i o n o f
t h e d a ta i s t h e
h a r dwa r e p r o c e s s c o n t r o l
b l o c k wh o s e phys i c a l
add r e s s
is
c o n t a i ne d
in
the
process control
block base
r eg i s t e r ,
PR $ PCBB .
Ad d i t i o n a l o p e r a t i o n s o f
the
S VPC TX i n s t r uc t i o n
a r e-d e sc r i b ed i n S e c t i o n 8 . 3 . 5 . 1 .

Th e a d d r e s s o f the s o f twa r e p r o c e s s c o n t r o l
bloc k
fo r
the
c u r r e n t p r o c e s s i s o b t a i n ed f r om t h e po i n t e r S C H $G L CURPC B i n
t h e modul e S DAT .
( A s i ng l e l o ng wo r d po i n t e r i s r e qu i r e d
fo r
t h e c ur r e n t
state
( C UR ) ,
r a th e r t h a n a qua d wo r d l i s th e a d ,
b e c a us e t h e r e i s o n l y o n e c u r r e n t p r o c e s s a nd no t a que ue
of
s e v e r a l s uc h p r o c e s s e s . )

Th e c u r r e n t p r i o r i t y o f t h e p r o c e s s i s d e te rm i n ed
f r om
the
PC B $ 8 PR I
f i eld .
Th i s
i s u s ed
to d e t e rm i n e wh i c h of the
r e s i d en t c omp u t a b l e s t a te que ue s i s to i nc l ud e th i s PC B .
Th e
p r o c e s s i s i n s e r ted a t t h e t a i l o f t h e c o r r e s po nd i ng p r i o r i t y
queue .

Th e s t a t e o f the p r o c e s s i s c h a ng ed to
upd a t i ng the PC B $W_S TATE f i e l d .

At th i s po i n t , the r e i s n o c u r r e n t p r o c e s s , a nd
next p r o c e s s to e x e c u t e b eg i n s .

8 . 3.3

comput a b l e

( C OM )

the

for

the

S e l e c t i o n o f Nex t P r o c e s s f o r E x e c u t i o n

Th e e n t r y p o i n t S C H $ S C HE D b eg i n s t h e po r t i o n o f c o d e th a t s e a r c h e s f o r
the
next
process
to
be
s c h e d u l ed
fo r
exec ut i o n .
Und e r
some
c i r c um s t a nc e s ( s uc h as s y s t em
i n i t i a l i za t i o n ,
p l a c i ng
the p r ev i o u s
process
i n to a wa i t s t a t e , o r d e l e t i o n o f t h e p r ev i o u s p r o c e s s ) th e r e
m a y no t b e a c u r r e n t p r o c e s s t o b e s a v e d b y SCH$RESC H ED .
In
th e s e
c ases ,
s ys tem
rout ines
t r ansfe r
c o n t r o l d i r e c t l y to SC H $ S C HED f o r
p r oc e s s se l ec t i on .
( Th e d i f f e r e n c e b e twe e n t h e two
e n t r y po i n t s
is
d e t e rm i n ed b y wh e th e r
the
p r ev i o u s p r o c e s s
i s s t i l l computab l e .
Typ i c a l l y , a p r o c e s s
e n t e r i ng
a
wa i t
state wi l l
c a use
entry a t
S C H $ S C H E D wh i l e a h i g h e r
p r i o r i ty p r o c e s s b e c o m i ng comput a b l e w i l l
c a use e n t r y ( v i a a so f twa r e i n t e r r up t ) a t S C H $ R E SCHED . )
Th e
SC H$RE SCHED l o g i c
f l o ws d i r e c t l y
i n to
SC H $ S C HE D .
As
wi th
r e sched u l i ng ,
the
s e a r c h f o r and mod i f i c a t i o n o f the nex t p r o c e s s to
be e x e c uted m u s t be pe r fo rm e d at I P L $ S YNC H to b l o c k o th e r
po t e n t i a l
s y s t em o pe r a t i o n s o n t h e sc h ed u l e r d a ta b a s e .

8-22

SCHEDUL ING
Th e fo l l o wi ng ope r a t i o n s a r e i nvo l ved i n s e l e c t i ng a n d
next process .
1.

e x e c u t i ng

the

Th e f i r s t s o f twa r e p r o c e s s c o n t r o l b l o c k ( PCB ) i n t h e h i g h e s t
p r i o r i t y n o n em p t y c om p u t a b l e
r e s i d e n t ( C OM ) s t a t e que ue i s
r emoved f r om t h e q u e u e a nd po i n t ed to b y S C H $G L CURPC B a s t h e
cur rent process .
Co n s i s t e n c y c h e c k s a r e m a d e to e n s u r e tha t
the q u e ue r e a l l y h a d a t l e a s t o n e
PC B a n d
th a t t h e d a t a
s t r uc t u r e
r emoved wa s a c t ua l l y a PCB .
Fa i l u r e o f e i th e r o f
t h e s e t e s t s r e s u l t s i n a f a t a l b ug chec k ( BUG $_Q U E UEMPTY )
•

8. 3. 4

Th e s t a t e o f t h e pr o c e s s i s m a d e c u r r e n t
by
i n s e r t i ng
the
a pp r o p r i a t e v a l ue ( S C H$C_C UR ) i n t o the PC B $W S TATE f i e l d .

Th e c u r r e n t p r o c e s s p r i o r i t y
i s e x am i n ed
a nd
po t e n t i a l l y
mo d i f i e d .
I f t h e pr o c e s s i s a r e a l - t i me p r o c e s s o r i f i t i s
a no rma l p r o c e s s a l r e a d y a t
i ts
b a se
pr i o r i ty ,
t h en
the
process
is
s c h e d u l ed
a t i t s c u r r ent o r b a s e p r i o r i t y ( th e y
a r e t h e s am e ) .
If the cur rent process is
a
no rma l
process
a b ove
i ts base
pr i o r i ty ,
t h en
a d e c r e a s e o f o n e so f twa r e
p r i o r i t y l evel
i s pe r f o rmed
b e fo r e
s c h ed u l i ng .
Th us ,
p r i o r i ty
" d em o t i o n s "
a l wa ys o c c u r b e fo r e e x e c u t i o n , a n d a
p r o c e s s e x e c u t e s a t the p r i o r i t y o f the q u e u e
to
wh i c h
it
wi l l
be
r e turned
( a nd
not
the p r i o r i t y o f t h e que ue f r om
wh i c h i t wa s
r emove d ) .
See
Figure 8-2 ,
event 2
fo r
an
e x ampl e .

Th e phys i c a l a d d r e s s o f the h a r d wa r e p r o c e s s
con t r o l
bloc k
for
the
s c h ed u l ed
process
is
l o ad e d
i n to
the
PR $ PC B B
r eg i s t e r f r om t h e so f t wa r e p r o c e s s c o n t r o l b l o c k PC B $ L PHYPC B
f i eld
and
a
l o ad
process
c o n t e x t , LDPC TX , i n s t r uc t i o n i s
e x e c u ted ( S e c t i o n 8 . 3 . 5 . 2 ) .

Co n t r o l i s p a s s e d to the s c h ed u l ed p r o c e s s
by
e x e c u t i ng
an
RE I
i n s t r uc t i o n .
Th i s
is
po s s i b l e b e c a u s e
the
LDPCTX
i n s t r uc t i o n l e f t the PC and PS L o f the sched u l ed p r o c e s s o n
the k e r n e l s t a c k .
Pa s s i ng c o n t r o l to the p r o c e s s t h r o ug h t h e
RE I i n s t r uc t i o n u s u a l l y
•

d r ops t h e i nt e r r up t pr i o r i t y l evel f r om I PL $_S YNC H ,

•

c h a ng e s the a c c e s s m o d e f r om k e r n el to a l e s s
one , and

p r i v i l eg ed

•

p e rm i t s t h e po te n t i a l d e l i v e r y o f o n e o r mo r e
Ch a p t e r 5 ) .

ASTs

( se e

S umma r y Lo ngwo rd a nd Comput a b l e S t a t e Que u e s

Th e s e a r c q fo r t h e h i g h e s t p r i o r i t y c om p u t a b l e
re s i d ent process and
the
r emova l
of
i ts
PC B
f r om
the c om p u t a b l e s t a t e ( C OM ) q u e ue i s
a c h i e v e d i n th r e e i n s t r uc t i o n s ( F i g u r e 8 - 7 ) .
Th e e f f i c i e n c y o f
th i s
o pe r a t i o n
i s d ue
to
the
i n s t r uc t i o n
s e t a nd
the d e s i g n o f the
s c h e d ul e r d a t a b a s e fo r t h e comput a b l e ( C OM ) and compu t a b l e o u t s wa pped
( c OM 0 ) s t a t e s ( F i g u r e 8 3 )
-

•

8-23

RESC HEDUL ING INTERRUPT HANDLER
SC H$RESCHED R ESCHEDULING INTERRUPT HANDL

SCHED
V 0 2 -0 0 1

(X)

O O O O ' CF
52
08 Al
52
0 0 O O O O ' CF
oc
2C A 1
0000 'CF42
53
61
93

I
N
�

OOOO 'CF
53

00
3D
0000 'CF42
54
93
3C
06

07
DO

E2
BO
7E
OE

EA
13
7E
OF
1D
12

0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0003
0004
0009
O O OD
001 3
0017
0 0 1D
0020
0020
0020
0020
0020
0020
0020
0020
0020
0023
0 0 2A
0 0 2C
0032
0035
0037

6 -APR-1 9 8 0 1 9 : 4 4 : 4 1 VAX-1 1 Mac ro V0 2 . 4 5
Pag e
1 -APR - 1 98 0 1 0 : 2 4 : 4 5 _DBB O : [ E XEC . SRC ] SC HED . MAR ; 3

3
(1)

SBTTL SCH$RESCHED RESCHEDULING INTERRUPT HANDLER
41
42 ; ++
43
S CH$R ESCHED - RESCHEDULING INTERRUPT HANDLER
44
THIS ROUT INE I S ENTERED VIA THE I PL 3 RESCHEDULING INTERRUPT .
45
T H E VECTOR FOR THIS INTERRUPT IS CODED TO CAUS E EXE C UT ION
46
ON THE KERNE L STAC K .
47
48
ENVIRONM ENT :
49
I PL=3 MODE=KERNE L I S=O
50
INPUT :
51
O O ( S P ) =PC AT RESC HEDULE INTERRUPT
52
04 ( S P ) =PS L AT INTERRUPT .
53
54
. ALIGN LONG
55
; RESC HEDULE INTERRUPT HANDLER
5 6 SC H$R ESCHED : :
; S YNC HRON I Z E SC HEDULER W ITH EVENT R E PORT ING
S E T I PL # I PL$ SYNC H
57
; SAVE CONTEXT OF PROC ESS
SVPC TX
58
WA SCH$GL C URPCB , R1
; G ET ADDRESS OF CURRENT PCB
MOVL
59
; C URRENT PR I OR ITY
MOVZ BL PCB $8 PRl ( R l ) , R2
60
; MARK QUE UE NON-EM PTY
B B SS
R 2 , WASCH$GL C OMQS , 1 0 $
61
#SCH$C C OM , PC B $W S TATE ( R 1 ) ; S ET STATE TO RES COM PUTE
62 1 0 $ :
.l\1 0VW
; C OM PUTE ADDRESS O F QUE UE
WA SC H $AQ C OMT [ R 2] , R 3
MOVAQ
63
; INS ERT AT TA I L OF QUEUE
INS QUE ( R 1 ) , @ ( R3) +
64
65
66 ; +
SCH$SCHED - SC HEDULE NEW PROC ESS F OR EXEC UT I ON
67
11 8 ,
6 9 ; T H IS ROUT INE S E LECTS THE H IGHEST PR IOR ITY EXEC UTABLE PROC ESS
7 0 ; AND PLAC ES IT IN E XECUT ION .
71 ; ; SCHE DULE FOR EXECUT ION
7 2 S C H$SCHED: :
; S YNCHRON I Z E SC HEDULER WITH EVENT REPORT ING
S ET I PL # I PL$ SYNC H
73
# 0 , # 32, WA SCH$GL COM QS , R2
; F IND F IRST F ULL S TATE
FFS
74
SCH $ I DLE
;NO EXECUTAB LE PROC ES S ? ?
B EQL
75
; C OM PUTE QUE UE HEAD ADDR ESS
WA SC H$AQ C OMH [ R 2 ] , R 3
MOVAQ
76
; G ET HEAD OF QUE UE
REM QUE @ ( R 3 ) + , R4
77
; BR I F QUE UE WAS EM PTY ( B UG C HE C K )
QEMPTY
BVS
78
; Q U E U E NOT EM PTY
BNEQ
79
20$

Figure 8-7

•

S c h ed u l e r Ro u t i n e Th a t Se l e c t s Nex t
Execut i o n Cand i d a t e

00 O O O O ' CF

OA A 4

2E
2C A4
OE
OOOO 'CF
54
OB A 4
2F A4
08
04
03 OB A4
OB A4
O O O O ' CF
OB A4
10
18 A4

BO
DO
91

13
E1
96
90
DA
06
02

0039
0 0 3F
003F
004 3
0045
004 9
004E
0053
0053
0055
0 0 5A
0 0 5D
0063
0067
0068
0069
0069
0069

80
81
82
83
84
85
86

BBCC

20$ :

C M PB
BNEQ
M OVW
M OVL
C M PB

B E QL
88
89
BBC
I NC B
90
91 30$ :
M OVB
92
M T PR
L D PC TX
93
REI
94
95
9 0 S C H $ I DLE :
S E T I PL
97

R 2 , WA SC H $G L

C OM QS , 2 0 $
_

; S E T QU E UE EM PTY
'

; M U S T B E A PR OC E S S C ONTR O L B LOC K
# D YN $C_PC B , PC B $B_T Y PE ( R 4 )
; OT H E RW I S E FATA L E R R OR
QEM PT Y
# S C H $ C C UR , PC B $W S TATE ( R 4 ) ; S ET S TATE TO C UR R E NT
R 4 , WA SCH $G L C UR PCB
; N OTE C UR R ENT PC B LOC
PC B $B_PR I B ( R4 ) , PC B $B_PR I ( R 4 ) ; C H E C K F OR B A S E
; PR I OR I T Y=C URR ENT
; Y E S , DONT F LOA T PR I OR I T Y
3 0$
; DONT F LOAT R EA L T IM E PR I O R I T Y
# 4 , PC B $ B P R I ( R 4 ) , 3 0 $
; M OVE TOWAR D B A S E PR I O
PC B $B PRI ( R 4 )
_
PC B $ B PR I ( R 4 ) , WA S C H $G B PR I
; S ET G L O B A L PR I O R I T Y
PC B $ L=P H Y PC B ( R 4 ) , # P R $_PC B B
; S E T PC B BAS E PHYS ADDR
; R E S TOR E C ONTEXT
; N ORMAL R ETURN

# I P L $ _S C H E D

; N O AC T I VE , E X E C UTAB LE PR OC ES S
; DR O P I PL T O S C HE DU L I NG L E VE L

C/l
n
ti:
t'Z'J
t:1
c:
t""'

(X)
I
1\.)
U1

2!
(j')
H

SCHED
V 0 2 -0 0 1

R E S C H E DU L I NG I NT E R R U PT HAND L E R
S C H $ R E S C H E D R ES C H E D U L I N G I NT E R R UPT HANDL
O O O O ' CF

20
AD

90
11

0 0 6C
0071
0073
0073
0077
0077

F i g u r e 8-7

99
1 00
1 0 1 QEM PT Y :
1 02
1 03

( Co n t . )

M OVB
B RB

6 -A PR - 1 9 8 0 1 9 : 4 4 : 4 1
1 -A PR - 1 9 8 0 1 0 : 2 4 : 4 5

# 3 2 , WA SC H $G B_PR I
SC H $ S C H E D

B UG C HE C K Q U E UEM PT Y , FATA L

Pag e
VA X - 1 1 Ma c r o V0 2 . 4 5
D B B O : [ E XE C . SRC ] S C HE D . MAR ; 3
_

; S E T PR I OR I T Y TO - 1 ( 3 2 )
; AND T R Y AGA I N
; S C HE DU L I NG QU E UE EM PTY

. EN D

S c h ed u l e r Ro ut i n e Th a t S e l e c t s Ne x t
Ex e c u t i o n C a n d i d a t e

TO S I GNA L I DL E

4
(1)

S CHEDUL ING
(1)

A f i nd f i r s t s e t ( FF S )
i n s t r uc t i o n wi l l
l o c a te
the
l east
s ign i f icant
set b i t
i n t h e l o ng wo r d
S C H $G L COM QS .
Th e
l o c a t e d b i t po s i t i o n i nd i c a t e s th e h i g h e s t p r i o r it y n o n em p t y
computab l e
r e s i d e n t s t a t e q u e ue .
Th e swa ppe r ' s s e a r c h f o r
t h e f i r s t PC B i n th e
h i g h e s t p r i o r i ty n o nempty c om p u t a b l e
o u t s wa pped
( C OMO )
q u e ue
us e s
the
same
o pe r a t i o n s
( Ch a pt e r 1 4 ) .
On e r e a s o n f o r s to r i ng t h e so f twa r e p r i o r i t y i n
i nv e r t e d
or
3 1 -c ompl em e n t
fo rm s h o u l d b e o bv i o u s .
By m a k i ng
bit 0
c o r r e s po nd t o so f twa r e p r i o r i t y 3 1 , a nd so
on ,
the h i ghest
p r i o r i t y q u e ue s w i l l
be
s c anned f i r s t .
Conve r s i o n i n t h e
v a r i o u s us e r i n t e r f a c e s o c c u r s b e c a u s e
s ys t em s a nd
use r s
g ene r a l l y a s soc i a te
h igher
p r i o r i t y n um b e r s wi th h i g h e r
p r i o r i t y j o b s , t a s ks , o r p r o c e s s e s .

(2)

Th e l i s t h e a d o f t h e s e l e c t ed
comput a b l e
r e s i d e n t que ue
is
f o und by u s i ng
t h e no n em p t y q u e ue b i t po s i t i o n a s a n i nd ex
i n to t h e c o n t i g uo u s l i s th e ad s .

(3)

Th e f i r s t PC B i n t h e s e l e c t ed que ue i s
r em o v e d by
r e f e r e nc e t h r o ug h t h e fo r wa r d l i n k o f t h e l i s th e ad .

(4)

in
t h e q u e ue ,
the
I f t h e r emoved PC B wa s
the onl y one
c o r r e s po nd i ng
SC H$G L C OMQS b i t m u s t n o w b e c l e a r ed b e c a us e
t h e q u e ue i s now empty .

8.3. 5

i nd i r e c t

Ha r d wa r e As s i s t a n c e i n C o n t e x t S w i t c h i ng

Th e VAX a r c h i tec t u r e wa s d e s i g n ed to a s s i s t t h e so f twa r e i n pe r f o rm i ng
One ex ampl e i s t h e d e l i v e r y
critical ,
c o mmo n l y p e r f o rmed o pe r a t i o n s .
o f a s yn c h r o no u s s y s t em t r aps th r o ug h t h e R E I i n s t r uc t i o n
( Ch a p t e r 5 ) .
Th e m e c h a n i sm o f r e p l a c i ng t h e h a r d wa r e c o n t e x t o f t h e c u r r e n t p r o c e s s
wi th t h e c o n t e x t o f t h e h i g h e s t p r i o r i t y r e s i d e n t p r o c e s s
is
a n o th e r
e x amp l e o f h a r d wa r e a s s i s ta n c e t o t h e o pe r a t i ng s ys t em .
Th e s w i t c h i ng
o f h a rd wa r e c o n t e x t i s pe r f o rmed by t wo spec i a l pu r po s e
i n s t r uc t i o n s ,
SVPC TX a nd LDPCTX .

8. 3. 5. 1
S VPCTX I n s t r uc t i o n - Th e s a v e
process c o n te x t
i n s t r uc t i o n ,
SVPCTX ,
p e r fo rm s s e v e r a l
o pe r a t i o n s
and
a s s um e s a spec i a l s e t o f
i n i t i a l and f i n a l c o nd i t i o n s .
Th e fo l l o wi ng
initial
c o nd i t i o n s
are
a s s um ed .
1.

Th e c u r r e n t a c c e s s m o d e m u s t b e k e r n e l .

Th e p r og r am c o un t e r ( PC ) a n d p r o c e s s o r s t a t u s l o ng wo r d
( PS L )
a r e o n t h e c u r r e n t s t a c k ( e i th e r ke r n e l o r i n t e r r up t s t a c k ) .
I f t h e SVPC TX i n s t r uc t i o n th a t ex e c u t e s i s
the one
in
the
r e sc h e d u l i ng i n t e r r up t s e r v i c e r o u t i n e , t h e PC a nd PS L a r e o n
t h e k e r n e l s t a c k a s a r e s u l t o f t h e I PL 3 s o f twa r e i n t e r r up t .

Th e p r o c e s s c o n t r o l b l o c k b a s e r eg i s t e r
( PR $ PC B B )
c o n ta i n s
t h e ph ys i c a l
ad d r e s s o f
t h e h a r d wa r e PC B-f o r t h e c u r r en t
p r o c e ss .

Th e c u r r e n t v a l u e s o f ASTLVL , P O B R , P O L R , P l B R , a nd P l LR
a l r e ady s to r ed i n t h e h a r d wa r e PC B .
8-2 6

are

SC HEDULING
Th e o pe r a t i o n s o f t h e SVPC TX i n s t r uc t i o n i n c l ud e
1.

m o v i ng t h e p e r - p r o c e s s s ta c k po i n t e r s
m o d e s t a c k s t o t h e ha r d wa r e PC B ,

fo r

the

fo u r

access

m o v i ng t h e g e n e r a l p u r po s e r eg i s te r s ,
RO
t h r o ug h R l l ,
the
a r g um e n t po i n te r
( AP ) ,
a nd
the
f r am e po i n te r ( FP ) to the
h a rdwa r e PC B , a nd

po pp i ng t h e p r og r am c o un t e r
( PC )
a nd
the process
s t a t us
l o ngwo r d ( P S L ) f r om t h e c u r r e n t s t ac k to th e h a r d wa r e PC B .

Fi nal ly , i f
the c u r r en t
s tac k
i s the
k e rne l
stac k ,
the
S VPC TX
i n s t r uc t i o n
saves
t h e c u r r e n t s t ac k po i n t e r ( S P ) in th e k e r n e l s t a c k
f i e l d o f t h e h a r d wa r e
process
control
b l o c k a nd
swi t c h e s
to
the
i n te r r up t
stac k
( by s e t t i ng t h e PS L$V I S b i t a nd c o py i ng th e PR $ I S P
r eg i s t e r c o n t e n t s i n to the S P r eg i s te r ) � Swi tch i ng to the s ys tem-w i d e
i n t e r r up t
s t a c k i s e s se n t i a l b e c a u s e the r e i s n o c u r r e n t p r o c e s s o n c e
t h e i n s t r uc t i o n c om p l e t e s .
Th e ASTLVL , P O B R , P O L R , P l B R , a nd P l L R f i e l d s o f t h e h a r d wa r e
process
control
b l o c k a r e n o t c h a ng ed .
It
is
the r e s po n s i b i l i t y o f t h e
v a r i o us s ys tem compo n e n t s t h a t a l t e r th e s e
f ields
to
a l wa ys
upd a t e
b o th
t h e h a r d wa r e
p r o c e s s c o n t r o l b l o c k f i e l d s a nd the pe r - p r o c e s s
p r o c e sso r r eg i s t e r s .
AST LVL i s un u s ua l i n th a t i t c a n b e a l t e r e d e v e n
wh en
the p r o c e s s i s n o t c u r r e n t .
I n th a t c a s e , o n l y t h e h a r d wa r e PC B
f i e l d i s a l te r ed .
Th e p r o c e s so r r eg i s t e r i s no t a l t e r e d b e c a u s e
the
p r o c e s s d o e s no t o wn t h a t r eg i s te r wh e n i t i s n o t t h e c u r r e n t pr o c e s s .
Th e s e f i e l d s d o n o t c h a n g e f r e q ue n t l y c o mpa r ed
to
the
f r equency o f
context
swi tch i ng .
Th e o v e r h e a d
of
s t o r i ng
the s e
f i e l d s i n the
h a r d wa r e p r o c e s s c o n t r o l b l o c k i s i n c u r r ed o n l y wh e n the f i e l d v a l ue s
c h a ng e .
Th e SVPC TX i n s t r u c t i o n o c c u r s i n s e v e r a l l o c a t i o n s i n th e e x e c u t i v e .
•

Th e
r e s c h ed u l i ng
i n t e r r up t
serv i c e
rout i ne conta ins
the
i n s t a n c e o f th i s i n s t r uc t i o n wh e n t h e c u r r e n t p r o c e s s r em a i n s
c omp u t a b l e a f t e r i t i s r emove d f r om ex e c u t i o n .

•

Mo d u l e S YSWA I T c o n t a i n s ano the r ex ampl e o f
the
i n s t r uc t i o n
wh en
th e
c u r r e n t p r o c e s s i s b e i ng pl a c ed i n to a s c h e d u l i ng
wa i t s t a t e .

•

Th e pag e r ( mo d u l e
PAG E FAULT )
i s s ue s a
SVPCTX i n s t r uc t i o n
d i r e c t l y wh e n
it
pl aces
a
p r o c e s s i n t o o n e o f t h e m emo r y
m a n a g em e n t wa i t s t a t e s ( P FW , FPG , C O L PG ) .

•

On e o f t h e l a s t s t e ps o f p r o c e s s d e l e t i o n
i nv o l v e s
the
process
b e i ng
d e l e t ed
f r om
ex e c u t i o n wi th
i n s t r uc t i o n .

r em o v i ng
a SVPC TX

8.3.5.2
LDPC TX I n s t r uc t i o n - Th e l o ad
process contex t
i n s t r uc t i o n ,
LD PC TX ,
p e r f o rm s t h e o pe r a t i o n s r e q u i r ed i n e s t a b l i s h i ng the h a r d wa r e
c ontext o f the p r o c e s s .
As wi th the SVPC TX
i n s t r uc t i o n ,
a s s um p t i o n s
a r e mad e abo u t
t h e i n i t i a l a nd f i n a l c o nd i t i o n s o f t h e i n s t r uc t i o n .
Th e fo l l o wi ng i n i t i a l c o nd i t i o n s a r e a s s um e d .
1.

Th e p r o c e s s o r mus t be i n k e r n e l mo d e , u s i ng e i th e r t h e k e r n e l
or
the
i n t e r r up t
s t ac k .
( Th e
p r o c e s s o r i s a l wa ys o n t h e
stack
for
the one o cc ur r ence
of
the
LDPCTX
i n t e r r up t
i n s t r uc t i o n i n VM S . )
8-27

S CHEDUL I NG
2.

Th e p r o c e s s c o n t r o l
b loc k b a s e
r eg i s t e r
( P R $ PC B B )
mus t
conta i n
t h e phys i c a l ad d r e s s o f t h e h a r d wa r e p r o ce s s c o n t r o l
b l o c k to b e u s ed ( f r om t h e PC B $ L PHYPC B f i e l d o f t h e so f t wa r e
process control bloc k )
-

•

Th e LDPCTX i n s t r uc t i o n i nc l ud e s t h e fo l l o w i ng o pe r a t i o n s .
1.

Th e
pe r - p r o c e s s h a l f
of
the
trans l a t ion
buffer
is
i nva l i d a t e d .
Al l o f t h e p r ev i o u s t r a n s l a t i o n b u f f e r e n t r i e s
b e l o ng ed to t h e p r e v i o u s p r o c e s s .
Th ey a r e
i nv a l i d a t e d
to
p r e v e n t m i s t r a n s l a t i o n o f v i r t u a l add r e s s e s a nd to p r o t e c t
t h e d a t a o f t h e p r ev i o u s p r o c e s s .

Th e p e r - p r o c e s s a c c e s s m o d e s t a c k po i n te r s
( KS P ,
ESP,
SSP ,
a nd US P ) a r e l o ad ed f r om t h e h a r d wa r e p r o c e s s c o n t r o l b l o c k .

Th e g e n e r a l p u r po s e r eg i s t e r s , R O t h r o ug h R l l ,
the
a r g um e n t
po i n te r
( A P ) , a nd t h e f r am e po i n t e r ( F P ) a r e l o ad ed i n to the
c o r r e spond i ng p r o c e s s o r r eg i s t e r s .

Th e mem o r y m a n a g em e n t m a p p i ng r eg i s t e r s
( P OBR ,
P OLR ,
PlBR,
a nd
P l LR )
are
c h e c k e d f o r l eg a l va l u e s a n d l o ad ed f r om the
h a r dwa r e p r o c e s s c o n t r o l
block .
No t e
th a t a l tho ug h
the
S VPCTX
i n s t r uc t i o n d o e s not s a v e t h e s e r eg i s te r s , t h e LDPCTX
m u s t l o a d t h em .
Un t i l t h e y a r e l o ad ed ,
the v a l ue s
in
the
r eg i s t e r s b e l ong to th e p r ev i o u s p r o c e s s .

Th e AS TLVL r eg i s t e r i s l o ad ed .
Th i s r eg i s t e r
s a v e d by t h e SVPCTX i n s t r uc t i o n .

wa s

a l so

not

I f the i n s t r uc t i o n b eg a n e x e c u t i o n u s i ng th e i n t e r r upt s t a c k ,
t h e n t h e fo l l ow i ng o pe r a t i o n s a r e pe r f o rmed .
•

Th e c o n t e n t s o f t h e c u r r e n t s t a c k po i n t e r
r eg i s t e r
(SP)
a r e s a v e d i n the i n t e r r upt s t a c k po i n t e r r eg i s te r ( I S P ) .

•

Th e PS L $V I S b i t i s c l e a r e d to i nd i c a t e the s w i t c h to the
ke r n e l s tac k .

•

Th e c u r r e n t s t a c k po i n te r i s u pd a t ed w i th t h e c o n t e n t s o f
t h e k e r n e l s t a c k po i n te r r eg i s t e r ( KS P ) .

F i n a l l y , t h e s a v e d p r o g r am c o un t e r ( PC ) a nd p r o c e s s o r
s ta t us
l o ngwo r d
( PS L )
are
pushed
onto
the k e r n e l s t a c k f r o m the
h a r d wa r e p r o c e s s c o n t r o l b l o c k .
Th e s e v a l u e s a r e no t s to r ed
i n to
the
a pp r o p r i a t e
r eg i s t e r s .
Th i s pa r t i c u l a r o pe r a t i o n
o c c u r s b e c a u s e t h e n ex t
i n s t r uc t i o n
( in the
sched ul e r
r o ut i n e )
i s e x p e c ted t o b e a n R E I i n s t r uc t i o n .
Th e RE I pops
t h e two l o ng wo r d s , v e r i f i e s t h e PS L fo rm a t , and
i ns e r t s
the
t wo l o ng wo r d s i n to t h e a pp r o p r i a t e r eg i s t e r s .

Th e o n l y o c c u r r e n c e o f a LDPC TX i n s t r uc t i o n i n t h e e n t i r e VM S s ys tem
is
the
one
s h o wn i n F i g u r e 8 - 7 , the s e c o nd h a l f of t h e r e s c h ed u l i ng
i n te r r up t s e r v i c e r o u t i n e .

8-28

C HAPTER 9
PROC E S S C ONTROL AND C OMMUN I CAT I ON

VM S p r ov i d e s m a n y s e r v i c e s
that
a l l ow
mul t i pl e
processes
to
c ommun i c a t e a nd a l low one p r o c e s s t o c o n t r o l th e e x e c u t i o n of a no t h e r .
Eve n t f l ag s a r e t h e m o s t p r i m i t i ve
cont r o l
a nd
c ommun i c a t i o n
tool
ava i l ab l e
( in
t e rms
o f a m o u n t o f i n f o rm a t i on ) .
O th e r c ommu n i c a t i o n
t e c h n i que s
i nc l ud e
l og i c a l
names ,
m a i l bo x e s ,
g lobal
s h a r ed d a t a
sect ions ,
a n d s h a r ed f i l e s .
Sys t e m s e r v i c e s a l l o w a p r o c e s s to a l t e r
s o m e o f i t s p a r am e t e r s ( s u c h a s name o r p r i o r i t y ) .
Oth e r
s e rv i ce s
a l l o w a p r o c e s s to a f f e c t t h e sc h ed u l i ng s t a t e o f i t s e l f o r a n o t h e r
process .
A s umma r y o f p r o c e s s c o n t r o l s y s tem s e r v i c e s
is
l i sted
in
Tab l e 9 - 1 .

9.1

E VENT FLAG S E RVI C E S

E v e n t f l ag s a r e u s ed w i th i n a s i ng l e p r o c e s s
fo r
synch r o n i z a t i o n o f
I /0
r e qu e s t s , $G E TJ P I s y s t em s e rv i c e c a l l s , and t i m e r r e que s t s .
Th e y
c a n a l s o b e u s ed e i th e r w i t h i n a
s i ng l e p r o c e s s
or
among
seve r a l
processes
in
the
same g r o up a s a ppl i c a t i o n - s p e c i f i c s yn c h r o n i z a t i o n
to o l s .
Sys tem s e r v i c e s
a re
p r ov i d ed
to
r ead ,
se t ,
or
clear
c o l l ec t i o ns o f
event
f l ag s .
Oth e r s e rv i c e s a l l o w a p r o c e s s t o wa i t
fo r one o r a col l e c t i o n o f event fl ags .

9.1. 1

Lo c a l E ve n t F l ag s

Each process h a s ava i l ab l e t o i t
64
local
{ p r o c e s s - s pec i f i c )
event
f l ag s
a nd
64
s h a r ea b l e
event
f l ag s
( among p r o c e s s e s i n the s a m e
g r o up ) .
Th e 6 4 l o c a l e v e n t f l ag s a r e s t o r ed d i r e c t l y i n the
so f twa r e
PCB ,
a t o f f s e t s PC B $ L E F C S a nd PC B $ L E FC U ( F i g u r e 9 - 1 ) .
Loc a l e v e n t
f l ag s 0 to 3 1 a r e l o c a ted i n l o ng wo r d PC B $ L E FCS .
Loc a l
ev e n t
f l ag s
3 2 t o 6 3 a r e l o c a t e d i n l o ngwo r d PC B $ L_E FCU�

9.1.2

Common Eve n t F l a g s

Commo n e v e n t f l ag c l us t e r s d o n o t
i n i t i a l l y ex i s t .
Th e y m u s t b e
c r e a ted
by the
f i rst process
th a t c a l l s t h e As s o c i a t e E v e n t F l ag
C l u s t e r s y s t e m s e r v i c e fo r a g i v e n c l u s te r .
Th i s s e r v i c e a l l o c a t e s a
s t r uc t u r e c a l l ed a c ommo n e v e n t b l o c k ( F i g u r e 9 - 2 ) f r om n o n pa g ed po o l
a nd l o ad s i t s a d d r e s s i n t o the PC B p o i n t e r f i e l d
( e i th e r
P C B $ L E FC 2 P
or
PCB $ L E FC 3 P ) .
Th e c ommo n e v e n t b l o c k i s l i n k e d i n to a s ys tem w i d e
l i s t o f commo n e v e n t b l o c k s l o c a t ed b y g l o ba l
l i s th e a d
S C H $ G Q C E BHD
( Fi g u r e 9 - 3 ) .

9-1

PROC E S S C ONTROL AND C OMMUN ICAT ION
Table 9 - 1
Summa ry o f P roce s s Contro l S y stem Serv i c e s
Af f e c t O t h e r P r o c e s s e s

Pr i v i l eg e Ch ec ks

C r e a te Common Ev e n t Fl ag C l u s t e r

S a m e g ro up o n l y

De l e t e Comm o n Ev e n t Fl ag C l us t e r

Same g r o up o n l y

PRMCEB ( fo r pe rman e n t
c l us t e r s o n l y )
PRMCEB

Se r v i c e Name

Wa i t fo r S i ng l e Eve n t F l ag
Wa i t fo r Log i c a l AND o f E v e n t F l ag s
Wa i t fo r Log i c a l O R o f Ev e n t Fl ag s

(1 )

No n e
G R O U P o r WORLD

Hi bernate
Wa ke

No
YES

S c h ed u l e Wa k e up
C a n c e l Wa k e up

YES
YES

GROUP o r WORLD
GROUP o r WORLD

S u s pend
R e s um e

YES
YES

GROUP o r WORLD
GROUP o r WORLD

Ex i t
Fo r c ed Ex i t

No
YES

No n e
GROUP o r WORLD

C r ea t e Proc ess

YES

De l e t e P r o c e s s

YES

DETAC H fo r o t h e r tha n
s ub p r o c e s s e s
G R O U P o r WORLD

Set
Se t
Se t
Set
Se t
Se t
Set

No
No
YES
No
No
No
No

Ac c es s Mo d e Ch ec k
Ac c es s Mo d e Ch e c k
G R O U P o r WORLD
No n e
No n e
PSWAPM
Ac c e s s Mo d e Ch e c k

A S T En a b l e
Powe r Rec ov e r y AST
P r i o r i ty
P r o c e s s Name
Re so ur c e Wa i t Mo d e
Swa p Mo d e
Sys t em Fa i l u r e Mod e

G e t Jo b/ P r o c e s s

(1)
(2)

In fo rm a t i o n

(2)
(2)
( 2)

YES

GROUP o r WORLD

As pa r t of the C r e a t e P r o c e s s s ys tem s e rv i c e , a pr o c e ss c an spec i fy tha t the
p r o c e s s b e i ng c r ea ted h i b e r n a te b e fo r e the spe c i f i ed i m ag e e x ec u t e s .
Th e s e t h r e e fea t u r e s c an be spec i f i ed
s e rv i c e .

as a pa r t o f t h e C r e a t e P r o c e s s system

As a d d i t i o n a l p r o c e s s e s a s so c i a t e w i th th i s c l us te r , t h e C E B l i s t
is
s e a r c hed
i n o r d e r t o l o c a t e t h e C E B , t h e e v e n t f l ag c l u s t e r po i n t e r s
i n the i r PC Bs a r e u pd a ted , a nd t h e r e f e r e n c e c o un t fo r th a t c l us t e r i s
upd a t ed .
As p r o c e s s e s d i s a s so c i a t e f r om a c l us t e r ( wi th the $ DAC E FC
s y s tem s e rv i c e ) ,
the
r e fe r enc e
c o un t
i s d ec r em e n t ed .
Wh e n
the
r e f e r e nc e
c o un t f o r a t empo r a r y c l u s t e r g o e s to z e r o , t h e c l u s t e r i s
a u tom a t i c a l l y d e l e t ed a nd the C E B d e a l l o c a ted .
Pe rma n e n t c l us t e r s m u s t b e e x p l i c i t l y d e l e t ed ( $ DLC E FC s ys tem s e r v i c e )
i n o rd e r
t o c a u s e the C E B t o b e d e a l l o c a ted wh e n t h e r e f e r e n c e c o u n t
goes to ze ro .
Al t e r n a t i v e l y , pe rm a n e n t c l us t e r s c a n c o n t i n u e to ex i s t
wi tho u t
r e q u i r i ng
th a t
t h e y b e a s so c i a t e d wi th a n y p r o c e s s e s .
In
f a c t , t h e o n l y o pe r a t i o n pe r fo rmed b y the
De l e t e Commo n
Even t
F l ag
Cl u s t e r
s ys tem
se rv i c e
is
to t u r n o f f the C E B $V PERM b i t .
( I f the
r e f e r e n c e c o un t o f t h e c l u s t e r i s
z e r o wh e n
the -p e r m a n e n t b i t
is
t u r n ed o f f , t h e c l u s t e r i s d e l e t ed . )

9-2

PROC ESS CONTROL AND COMMUN I CATI ON

Software PCB
SQFL
SQBL
I

I WEFC

STATE

EFWM /POB
EFCS
EFCS
EFCU
EFC2P
EFC3P

�

Figure 9-1

S o f twa r e PC B F i e l d s Th a t S uppo r t Ev e n t F l ag s

9-3

PROC E S S C ONTROL AND C OMMUN I CAT I ON

CEB Forward Link

� - - - - - - - - - - - - - - - - - - - - - --·

CEB Backward Link
Type

Status

Size

Process ID of Creator
Event Flags
Walt Queue Forward Link
Walt Queue Backward Link
CEF State Number

Walt Count

UIC of Creator
Reference Count

Protection Mask
Count

Cluster Name
(up to 15 characters)
(counted ASCII string)

Figure 9-2

9.1.3

L a yo u t o f Common E v e n t B l o c k

Event F l ag Wa i t S t a t e s

P r o c e s s e s a r e p l a c ed i n to e v e n t f l ag wa i t s t a t e s i mp l i c i t l y
•
•
•

b y e x ec u t i ng a $ Q I OW s ys t em s e rv i c e ,
by u s i ng the RM S s e rv i c e s
u s ua l wa y t h e y a r e c a l l ed ,

s yn c h r o no us

o pe r a t i o n s ,

o r e x pl i c i t l y by e x e c u t i ng o n e o f t h e th r e e e v e n t
s e r v i c e s ( $WA I TFR , $WFLOR , $WF LAND ) .

9-4

f l ag

the
wa i t

PROC ESS C ON TROL AND C OMMUN I CAT I ON

�

SCH$GQ_CEBHD: :

CEB
Wait Queue

...
,

....

PCB

+--

1.._.:.

PCB

....

PCB

CEB Name
CEB

""
�

Wait Queue

+-__lo.
,.

.,
....

CEB

""
,..

W a i t Queue

....

--"'
,.

PC B

+---

PCB

....
J

PCB

CEB

""'
,

W a i t Q ueue

Figure 9-3

No processes waiting
for flags in this
common event flag cluster

Common Ev e n t F l ag Wa i t Qu e ue s

I f t h e f l ag o r f l ag s i n q ue s t i o n a r e a l r e a d y s e t , t h e s ys tem s e rv i c e
i mmed i a t e l y r e t u r n s s uc c e s s f u l l y
to
i ts c a l l e r .
O th e r w i s e ,
the
p r o c e s s i s p l a c ed i n to e i th e r a l o c a l o r c ommo n ev e n t f l ag wa i t s t a t e .
Th e
saved
PC
i n the h a r d wa r e PC B i s b a c k ed up b y 4 ( Ch a p t e r 8 ) to
a l l o w ASTs to be d e l i v e r ed t o th e p r o c e s s wh i l e i t i s wa i t i ng fo r
the
f l ag ( s )
to
be
set .
Th e e v e n t f l ag c l u s t e r n umbe r ( 0 or 1 f o r l o c a l
c l u s te r s a nd 2 o r 3 fo r g l o b a l c l u s te r s ) , i nd i c a t i ng wh i c h f l ag s a r e
b e i ng wa i t ed
fo r ,
i s s to r ed i n t h e PC B ( a t o f f s e t PC B $B WE FC ) .
Th e
l i s t { ma s k ) o f e v e n t f l ag s b e i ng
wa i ted
fo r
is
s to r ed - { i n o n e ' s
c om p l eme n t fo rm ) i n PC B $ L_EFWM .
•

If
the process
i s wa i t i ng
fo r
a
s i ng l e
even t
f l ag
{ S YS $WA I T FR ) ,
the
PC B $ L E FWM m a s k c o n t a i n s a 1 i n eve r y b i t
e x c e p t t h e b i t n um be r c o rre s po nd i ng to t h e f l ag b e i ng
wa i t ed
for .

9-5

PROCESS CONTROL AND C OMMUN ICAT I ON
•

•

I f t h e p r o c e s s i s wa i t i ng f o r a n y o n e o f s e v e r a l f l ag s to
be
set
( S YS $WFLOR ) ,
th e
PC B $ L E FWM m a s k c o n t a i n s t h e o n e ' s
c omp l em e n t o f t h e m a s k p ass e d
to
the
SYS $WFLOR s ys t em
s e rv i c e .
( Th e $WA I TFR ma s k i s t h u s a spec i a l c a s e of a wa i t
fo r a n y o n e o f a g r o up o f f l ag s t o be s e t . )
I f a ny o f
the
f l ag s in the r e q u e s t e d m a s k i s s e t wh en $WF LOR i s c a l l ed , the
p r o c e s s i s not p l a c ed
i n to
a wa i t s t a t e .
Ins tead ,
the
s e r v i c e i mm ed i a t e l y r e t u r n s a s uc c e s s code to i t s c a l l e r .
I f a p r o c e s s c a l l s t h e $WFLAND s y s tem s e r v i c e ,
i nd i c a t i ng
a
wa i t
fo r
a l l f l ag s i n a g i ven m a s k to be s e t , the wa i t m a s k
i s mod i f i ed s o tha t e v e n t f l ag s t h a t a r e s e t wh en the s e r v i c e
I n ad d i t i o n ,
i s c a l l ed a r e no t r e p r e s e n t ed i n the wa i t m a s k .
a bit
in
the
process
s t a t us
l o ng wo r d
( PC B $ V WA L L
in
PC B $ L S TS )
is
s e t , i nd i c a t i ng t h a t a l l f l ag s r e p r es e n t e d by
the mas k mus t b e set b e f o r e the wa i t i s sa t i s f i e d .

Th e r e ex i s t two l o c a l e v e n t f l ag wa i t s t a t e s ( L E F a nd
L E FO )
and
two
c o r r e spo nd i ng
wa i t que u e
l i s t h e a d s ( S C H$ G Q L E FWQ a nd S C H $ G Q L E F OW Q )
f o r t h e e n t i r e s ys tem .
O n t h e o th e r h a nd ,
the r e e x i s t s o n e- c ommo n
event
f l ag
wa i t que ue
l i s th e ad
f o r e a c h c ommon ev e n t c l u s t e r th a t
cur rently ex i sts .
E a c h c ommo n
event
f l ag
wa i t q u e u e
l i s th e a d
is
l o c a t ed
i n t h e c o r r e spo nd i ng c ommo n e v e n t b l o c k ( F i g u r e 9 - 2 ) and h a s
t h e same o v e r a l l s t r uc t u r e a s a ny o f t h e o th e r
wa i t que ue
l i s theads
( Fi g ur e 8 - 4 ) .

S e t t i ng a nd C l e a r i ng Eve n t F l ag s

9.1.4

Ev e n t f l ag s c an b e s e t d i r e c t l y b y a p r o c e s s b y c a l l i ng t h e Se t
Ev e n t
Fl ag sys t em s e r v i c e .
A p r o c e s s c o u l d u s e th i s s e r v i c e a t A S T l ev e l t o
c ommun i c a t e w i t h i t s m a i n l i n e c o d e .
I t c an a l so
s e t common e v e n t
f l ag s
to
c ommun i c a t e wi th o th e r p r o c e s s e s .
E v e n t f l ag s a r e a l s o s e t
i n r e s po n s e to I /0 c o mp l e t i o n , t i me r e x p i r a t i o n ,
a nd d e l i v e r y o f
a
$ G E TJ P I
r e que s t .
Bo th t h e sys t em s e rv i c e a nd t h e spec i a l pa ths c a l l
t h e s am e r o u t i n e ( S C H $ P O S TE F ) to pe r f o rm t h e a c tua l ev e n t f l ag s e t t i ng
and ch e c k f o r po s s i b l e sched u l i ng i mp l i c a t i o n s .
Th e o pe r a t i o n o f S C H $ PO S TE F d e pend s o n wh a t
b e i ng s e t .
•

•

k i nd

event

f l ag

I f the ev e n t f l ag th a t i s b e i ng s e t i s l o c a l , a ch e c k i s m a d e
to d e t e rm i n e wh e th e r th i s f l ag s a t i s f i e s t h e p r o c e s s ' s wa i t
r e ques t .
Fo r a $ WF LOR c a l l , th i s f l ag me r e l y h a s
to m a t c h
one
of
t h e f l ag s b e i ng wa i ted f o r .
Fo r a $WF LAND c a l l , a l l
o f the f l ag s be i ng wa i t ed fo r mus t b e s e t i n o r d e r to s a t i s f y
t h e p r o c e s s ' s wa i t
r e que s t a nd
r e po r t a n
e v e n t t o the
schedul e r .
Wh e n a c ommo n ev e n t f l ag i s s e t , t h e
l i st of
PC Bs
in
the
c ommon ev e n t b l o c k
is
sc anned
to d e t e rm i n e i f any of the
p r o c e s s e s wa i t i ng fo r f l ag s in
t h i s c l us t e r
s a t i sfy the i r
wa i t
r e que s t a s a
r e s u l t o f s e t t i ng th i s f l ag .
A s y s t em
e v e n t i s r e po r t e d fo r e a c h s uc h p r o c e s s .
Al l such p r o c e s s e s a r e mad e c om p u t a b l e .
I f the
p r i o r i ty o f
a n y o n e o f t h em i s g r e a t e r than the p r i o r i t y o f the c u r r e n t l y
e x e c u t i ng p r o c e s s , a r e s c h ed u l i ng i n te r r up t i s r e que s t e d .
As
wi th a l l
o th e r
c a s e s i n the sys tem wh e r e seve r a l p r o c e s s e s
b e c ome c omp u t a b l e a s a r e s u l t o f t h e s a m e s ys t em wi d e
event ,
9-6

PROC ESS CONTROL AND COMMUN ICAT I ON

t h e p r o c e s s w i th
the
s e l e c t ed fo r e x e c u t i o n .
•

h ighest

s o f twa r e

p r i o r i ty

wi l l be

Fo r commo n e v e n t f l ag s l o c a ted i n sha r ed m emo r y , t h e r e i s o ne
mo r e
l ev e l
o f c ompl i c a t i o n .
Th e e v e n t f l ag m u s t b e s e t i n
t h e m a s t e r C E B l o c a ted i n s h a r ed m emo r y a nd o th e r
p r oc esso r s
c o nn e c ted
t o th i s s h a r ed m emo r y u n i t m u s t b e no t i f i ed th a t a
s h a r ed memo r y c ommo n e v e n t f l ag wa s j us t s e t .
( Sh a r ed memo r y
c ommo n e v e n t f l ag d a t a s t r uc t u r e s a r e d i s c u s s e d a t t h e e nd o f
th i s chapte r .
Oth e r
sha r ed
mem o r y d a ta
s t r uc t u r e s a r e
d e s c r i b ed i n Ch a p t e r 1 1 . )
An y o th e r p r o c e sso r c o n n ec ted to the same g l o b a l
event
f l ag
c l us t e r
r ec e i ve s
init ial
not i f i cation
th r o ug h a n MA7 8 0
i n te r r up t .
Th e i n te r r up t s e r v i c e r o ut i n e d e t e rm i n e s th a t t h e
i n t e r r up t wa s d u e to a n eve n t f l ag i n s h a r ed memo r y g e t t i ng
s e t , c o p i e s t h e e n t i r e s e t o f e v e n t f l ag s f r om t h e m a s t e r CEB
to
the
s l av e C E B ,
a nd c h e c k s wh e th e r a n y of t h e p r o c e s s e s
wa i t i ng f o r f l a g s i n th i s c l u s t e r a r e n o w c o m p u t a b l e .

9. 1.4. 1
Oth e r Ev e n t F l ag S e r v i c e s - Th e
s e r v i c e s i mpl y c l e a r s the e v e n t f l ag
•
•
•

C l ea r

Ev e n t

F l ag

s y s t em

common

event

i n t h e s o f twa r e PCB f o r a l o c a l ev e n t f l ag ,
i n t h e c ommo n e v e n t f l ag b l o c k fo r
f l ag , a nd

r eg u l a r

i n t h e m a s t e r CEB o n l y f o r c ommo n e v e n t f l ag c l u s t e r s l o c a t ed
i n sh a r ed m emo r y .
It
i s n o t n e c e s s a r y to c o py the s e t o f
f l ag s f r om t h e m a s te r
CEB t o t h e s l av e
CEBs o n o th e r
p r o c e s s o r s wh e n a n e v e n t f l ag i s c l e a r ed fo r t h e fo l l o w i ng
t wo r e a s o n s .
Th e e ve n t f l ag wa i t s e r v i c e s o n l y u s e the m a s t e r CEB wh en
c h e c k i ng wh e th e r to p l a c e a p r o c e s s i n to a wa i t s t a t e o r
r e t u r n i mmed i a t e s uc c e s s .
Th e e v e n t f l ag po s t i ng r o u t i n e co p i e s the m a s t e r
set of
f l ag s t o t h e l o c a l s l ave CEB b e fo r e t e s t i ng wh e th e r a n y
p r o c e s s wa i t r eque s t s a r e s a t i s f i ed .
Th e m a s t e r
set
of
f l ag s
i s c o p i ed i n to a l l o th e r s l av e CEBs a s a r e s u l t o f
no t i f y i ng o th e r p r o c e s so r s tha t a f l ag h a s b e e n s e t .

Th e Re a d Ev e n t Fl ag sys tem s e rv i c e i s s i mpl y i n fo rm a t i o na l .
I t h a s no
e f fec t
on
the c om p u tab i l i ty o f a n y p r o c ess on a n y p r o c e s s o r .
Th e
e v e n t f l ag c l u s t e r
1s
r ead
f r om
the
same d e s t i n a t i o n s a s
tho s e
a f f e c ted b y t h e C l e a r Ev e n t F l ag sys tem s e rv i c e .
•

Lo c a l e v e n t f l ag c l u s t e r s a r e r e a d f r om t h e so f t wa r e PC B .

•

Reg u l a r c ommo n e v e n t f l ag c l u s t e r s a r e r e ad f r om the CEB .

•

Common e v e n t f l ag c l u s te r s l o c a t e d i n sha r ed m emo r y a r e
f r om t h e ma s te r C E B l o c a t ed i n sha r ed memo r y .

9-7

r ead

PROC ESS CONTROL AND COMMUN I CAT I ON

9. 2

AFFECTING THE C OMPUTAB I L I TY OF ANOTHER PROC E S S

I n a n y m u l t i p r o c e s s i ng a pp l i c a t i o n , i t i s n e c e s s a r y fo r o n e p r o c e s s t o
control
wh e th e r
a nd
wh e n o th e r
processes
in
the a pp l i c a t i o n c a n
execute .
VMS c o n t a i n s s ev e r a l s e rv i c e s th a t p r ov i d e th i s c o n t r o l .

9.2. 1

Common Ev e n t F l ag s

Commo n e v e n t f l ag s d e sc r i b ed i n the p r ev i o u s s e c t i o n a r e o n e m e thod o f
s ynch r o n i z a t i o n c on t r o l .
On e p r o c e s s c a n r e a c h a c r i t i c a l po i n t i n
i ts e x e c u t i o n a n d wa i t o n a g l o b a l ev e n t f l ag .
Ano the r
process can
a l l o w th i s p r o c e s s
to c o n t i n u e i t s e x e c u t i o n b y s e t t i ng t h e f l ag i n
quest i on .
Commo n e v e n t f l ag s a r e a l so u s ed a s s em a ph o r e s f o r mo r e c om p l i c a t e d
f o rms
of
i n t e r p r o c e s s c ommun i c a t i o n tha t use l o g i c a l n a m e s o r g l o b a l
sec t i on s .

9.2. 2

P r o c e s s C o n t r o l S e rv i c e s

S e v e r a l s ys tem s e r v i c e s
a l low o ne p rocess
s c h e d u l i ng s ta te o f a no the r p r o c e s s .

d i rectly

a l te r

th e

9.2. 2.1
Pr i v i l e g e Ch e c k s
Al l
s ys tem
s e rv i c e s
th a t
pe rm i t
one
p ro c es s
to
d i r e c t l y a f f e c t a no the r a l l ow the p r o c e s s to be s pe c i f i ed
b y e i th e r p r o c e s s n a m e o r b y p r o c e s s ! D .
I n e i th e r
c a se ,
VMS m u s t
d e te rm i n e wh e th e r t h e spec i f i ed p r o c e s s e x i s t s a nd wh e th e r t h e c a l l e r
h a s the p r i v i l eg e { G R O U P o r WOR LD ) t o a f f e c t the o th e r p r o c e s s .
Th i s
wo r k
i s c en t r a l i z e d i n a r o u t i n e c a l l ed EXE $NAM P I D th a t i s c a l l ed by
a l l s uc h s ys t em s e rv i c e s .
-

I f the spec i f i ed p r o c e s s e x i s t s , a nd t h e c a l l e r i s s u i t a b l y p r i v i l eg ed
( GR O U P o r WORLD ) t o a f f e c t the s pe c i f i ed p r o c e s s , EXE $NAM P I D r e t u r n s
s uc c e s s f u l l y { a t I P L 7 ) w i t h the PC B a d d r e s s o f the spec i f i ed
process
in
R4 .
No t e th a t
th i s r e t u r n c o nd i t i o n a l t e r s t h e c o n t e n t s o f R4 ,
wh i c h u s ua l l y c o n t a i n s the c a l l e r ' s PC B a d d r e s s .
A s e c o nd
i mpo r ta n t
i t em a s so c i a t ed w i t h EXE $NAMP I D i s th a t i f a p r o c e s s i s d e s i g n a ted by
n a m e , and i f a P r o c e s s ID a r g um e n t i s
present
{ th e o n l y c a s e
he r e
o c c u r s wh e n a z e r o i s pa s s ed b y r e f e r e nc e ) , the P I D o f the spe c i f i e d
p r o c e s s w i l l be r e t u r n e d to t h e c a l l e r a t the d e s i g n a t ed l o c a t i o n .

9 . 2 . 2 . 2 P r o c e s s C r e a t i o n a nd De l e t i o n
An o bv i o u s f i r s t s t e p
in a
m u l t i p r o c e s s a pp l i c a t i o n
r equi r e s
t h a t a c o n t r o l l i ng p r o c e s s c r e a t e
o the r p r o c e s s e s fo r d e s i g n a ted wo r k .
Th e s e p r o c e s s e s m a y b e d e l e t ed
wh e n
they have
compl e ted
t h e i r wo r k o r they may e x i s t in some wa i t
s ta t e i n a n t i c i pa t i o n o f a d d i t i o n a l wo r k .
Th e d e ta i l ed
ope r a t i o n o f
p r o c e s s c r ea t i o n
i s d e sc r i b ed
i n Ch a p t e r 1 7 .
Process d el et ion i s
d e sc r i b ed i n Cha pt e r 1 9 .
-

9-8

PROCE S S CONTROL AND COMMUN ICAT I ON
9. 2. 2. 3
H i be r n a te/Wa k e - Th e r e a r e t wo d i f f e r e n t wa ys tha t a
process
can be
t empo r a r i l y h a l t e d ,
c a l l ed h i b e r n a t i o n a nd s uspe n s i o n .
Th e
d i f f e r e nc e s b e twe e n t h e s e t wo wa i t s t a t e s a r e l i s te d
i n t h e VAX/VM S
Sys tem S e r v i c e s Re f e r e n c e Ma n u a l ( i n T a b l e 7 - 2 i n tha t m a n u a l ) .

( Th a t
is ,
a
A p r o c e s s c a n o n l y p u t i t s e l f i n to th e h i b e r n a t e s t a t e .
p r o c e s s c a nno t
put
a n o th e r p r o c e s s i n t o the H I B s t a t e . ) I f the wa k e
p e nd i ng f l ag i s n o t s e t
( th i s
f l ag
ch e c k a l s o
c l ea r s the
f l ag ) ,
i nd i c a t i ng
th a t a n a s s o c i a t e d wa k e h a s no t p r e c e d ed th e h i b e r n a t e
c al l , the process
is
p l a c ed
i n to
t h e h i be r na te
wa i t s t a te .
As
d e sc r i b ed
i n t h e p r ev i o u s c h a p t e r , t h e s a v ed P C i s b a c k e d u p b y 4 s o
t h a t t h e p r o c e s s w i l l b e p u t b a c k i n to t h e h i b e r n a t e s t a t e i n c a s e
it
( No t e th a t t h e c h e c k o f t h e
r ec e i v e s ASTs
wh i l e
i t i s h i b e r n a t i ng .
wa k e p e nd i ng f l ag b y t h e H i b e r n a t e sys tem s e rv i c e
i n c l ud e s
the case
wh e r e
a
p r o c e s s f i r s t h i b e r n a t e s a nd th e n i s a wa k e n ed b y a Wa k e c a l l
i s s u e d f r om a n A S T . )
A
Th e Wa k e sys tem s e rv i c e i s th e c om p l eme n t a r y s e r v i c e to H i b e r n a t e .
p r o c e s s m a y a wa k e n i t s e l f ( by c a l l i ng Wa k e f r om an AS T ) o r i t m a y b e
a wa k e n e d bec a u s e a no th e r p r o c e s s c a l l ed Wa k e wi th e i th e r t h e n a m e o r
the p r o c e s s
ID of
the
ta rg e t process .
Th i s s e r v i c e s e t s the wa k e
p e nd i ng f l ag i n t h e so f twa r e P C B a nd r e po r t s t h e a wa k e n i ng
event
to
the
s c h ed u l e r .
Th e p r o c e s s i s r emoved f r om t h e H I B o r H I B O q u e ue a nd
p l a c ed i n to the C OM o r C OMO s t a t e i n the q u e ue
c o r r e s po nd i ng
to
i ts
( A Wa k e e v e n t r e s u l t s i n a p r i o r i t y boo s t c l a s s o f
upd a te d
p r i o r i ty .
PR I $_R E SAVL , wh i c h i s e qu i v a l en t to a boo s t o f 3 . )
Th e n e x t t i me t h e p r o c e s s e x e c u t e s ,
the h i bernate
s e rv i c e
ex e c u t e s
( because
t h e PC wa s b a c k e d up by 4 ) .
Be c a u s e the wa k e p e nd i ng
aga i n
f l ag i s n o w s e t , t h e p r o c e s s r e t u r n s i mm e d i a te l y f r om the h i b e r n a t e
cal l
( wi th t h e wa k e pend i ng
f l ag n o w c l e a r ) .
No t i c e tha t i f the
p r o c e s s i s in a n y s t a te o th e r t h a n HIB o r H I B O wh en
it
is
a wa ke n e d ,
the net
r esul t
is
to l e av e the wa k e p e nd i ng f l ag s e t wi th n o o th e r
c h a ng e i n i t s sched u l i ng s t a t e .

9.2.2. 4
S uspend/Re s ume - P r o c e s s
s u spe n s i o n
is
sl ig h t l y
mo r e
c ompl i c a t ed
i n te r na l l y t h a n h i b e r n a t i o n b e c a u s e a
process c a n be
pl a c ed i n to
t h e S U S P s t a t e b y o the r
p r o c e s s es .
Th e
s c h e d u l i ng
ph i l o s o ph y o f VM S , i l l u s t r a t ed i n F i g u r e 8 - 5 , a s s um e s tha t p r o c e s s e s
e n t e r v a r i o u s wa i t s ta t e s f r om t h e s t a t e o f be i ng t h e c u r r e n t p r o c e s s
a nd
i n n o o the r wa y .
Th i s a s s umpt i o n r e qu i r e s t h a t the p r o c e s s b e i ng
s u spe nd ed
( th e
ta rg e t )
b e c om e c u r r e n t ,
r e p l a c i ng
the
cur rently
e x e c u t i ng p r o c e s s , t h e c a l l e r o f t h e Suspe nd sys t em s e rv i c e .

VMS a c c ommod a t e s th i s s c h ed u l i ng c o n s t r a i n t by u s i ng a spec i a l
ke rne l
t h e s ame to o l th a t i t u s e s wh e n i t n e ed s a c c e s s to a po r t i o n o f
AS T ,
process a d d r e s s spac e .
I n th i s c a s e , i t i s no t
the
proce ss a d d r e s s
s pa c e
tha t
is
s o impo r ta n t .
Ra t h e r , t h e p r o c e s s m u s t f i r s t b e m a d e
c u r r e n t b e fo r e i t i s p l a c ed i n to the S US P s t a t e .

9.2.2.4.1
P r o c e s s Suspe n s i on - P r o c e s s
s u spe n s i o n o c c u r s
in
t wo
pi eces .
Th e
po r t i o n o f the s e r v i c e th a t ex e c u t e s i n the c o n t e x t o f
t h e c a l l e r s e t s the s u s p e nd p e nd i ng b i t i n the
s o f twa r e
PCB o f
the
t a rg e t
process
a nd
q u e ue s
t h e spec i a l k e r n e l A S T ( th e r o u t i n e th a t
pe r fo rm s the a c t ua l s u s pe n s i o n ) to t h a t p r o c e s s .
Th i s
impl em e n t a t i o n
i nc l ud e s the spec i a l c a s e wh e r e a p r o c e s s s us pe nd s i t s e l f .

9-9

PROC E S S CONTROL AND COMMUN I CATI ON

Th r o ug h t h e n o rma l s c h ed u l i ng s e l e c t i o n p r o c e s s ,
the
t a rg e t p r o c e s s
e v en t ua l l y e x ec u t e s .
Th e
spec i a l A S T t h a t pe r fo rm s t h e s u s p e n s i o n
e x e c u t e s f i r s t un l e s s t h e r e a r e p r ev i o us l y que ued spec i a l k e r n e l ASTs .
Th i s AST f i r s t c h e c k s
( a nd
c l ea r s )
the
r e s um e pend i ng
f l ag i n
PCB $ L S T S .
( Th i s c h e c k a vo i d s t h e d e ad l o c k t h a t c o u l d o th e r w i se o c c u r
i f t he a s s o c i a t ed Re s um e p r e c ed ed t h e S u s pend . ) I f t h e r e s ume pend i ng
f l ag i s s e t , t h e p r o c e s s
s impl y c l ea r s
the
s us p e nd
pend i ng
bit,
r e t u r n s f r om t h e AS T , a nd c o n t i n u e s w i th i t s e x e c u t i o n .
O t h e rwi s e , i t i s p l a c ed i n to t h e
SUS P wa i t s t a t e .
Th e
s a v ed
PS L
c onta ins
I PL 2 ,
p r ev e n t i ng
d e l i v e r y o f ASTs wh i l e a
process i s
s us pe nd ed .
( In add i t ion ,
t h e AST s y s t em
event
is
i g n o r ed
fo r
p r ocesses
i n e i th e r the S U S P o r the S U S PO s t a t e . ) Th e saved PC i s a n
a d d r e s s w i th i n th e s u spend spe c i a l k e r n e l AST .
Wh en t h e p r o c e s s
is
r e s umed
( th e o n l y wa y t h a t a s u s p e nd ed p r o c e s s c a n c o n t i nue w i th i t s
e x e c u t i o n ) , i t r e e x e c u t e s the c h e c k o f t h e r e s ume pend i ng f l ag ,
wh i c h
i s now s e t ,
c a us i ng
the p r o c e s s
to
r e t u r n s u c c e s s f u l l y f r om t h e
s pe c i a l AST .

9. 2.2.4. 2
O pe r a t i o n o f t h e Re s ume S y s t em S e rv i c e - Th e Re s ume
s ys t em
s e rv i c e
i s v e ry s i mp l e .
Th e r e s um e pend i ng f l ag i n PC B $ L S T S o f the
t a rg e t p r o c e s s is s e t a nd ( i f th e t a r g e t p r o c e s s of the Resume
is
in
e i th e r
the
SUSP o r
S US PO s t a t e ) a r e s ume event i s r e po r ted t o the
s c hed u l e r .
As wi th a l l o th e r sys t em even t s , t h i s r e po r t may r e s u l t i n
a r e sched u l i ng pa s s , a r e que s t t o wa k e the swa ppe r p r o c e s s , o r n o th i ng
at all .

9 . 2 . 2 . 5 Ex i t a nd Fo r c ed Ex i t - Th e Ex i t s ys t em s e r v i c e t e rm i n a t e s t h e
c u r r e n t l y e x e c u t i ng i m ag e .
I f the p r o c e s s i s ex ec u t i ng a s i ng l e i m ag e
( i t i s n e i th e r a n i n t e r a c t i v e n o r
b a tc h
j ob ) ,
i mag e ex i t
usua l l y
r e s u l ts i n p r o c e s s d e l e t i o n .
A d e ta i l ed d i s c us s i o n o f the Ex i t s ys t em
s e rv i c e , i n c l ud i ng the c a l l i ng s e q ue n c e o f
t e rm i na t i o n hand l e r s ,
is
d i sc u s s ed i n Ch a p te r 1 8 .
Th e Fo r c e E x i t sys t em s e r v i c e i s a t o o l t h a t a l lows o n e p r o c e s s
to
execute
the
Ex i t
s ys tem s e rv i c e on b e h a l f of a n o the r p r o c e s s .
Th e
s e rv i c e s i mp l y s e t s t h e fo r c e
e x i t pend i ng
f l ag
in
PC B $ L S TS a nd
q u e ue s a u s e r mode AST t o the t a r g e t p r o c e s s .
Th i s AS T , e x e c u t i ng i n
u s e r mod e , c a l l s t h e Ex i t sys t em s e r v i c e a f te r c l e a r i ng the AST a c t i v e
f l ag by e x e c u t i ng a
C HMK

#ASTEXI T

i n s t r uc t i o n ( Ch a p t e r 5 } .
Th e c a l l to Ex i t i s e x e c uted i n the
context
of
t h e t a rg e t p r o c e s s .
E x e c u t i o n p r o c e e d s i n e x a c t l y t h e s ame m a n n e r
a s i t wo u l d i f the t a rg e t p r o c e s s h a d c a l l ed Ex i t i t s e l f .

9.2. 3

M i s c e l l an e o u s P r o c e s s A t t r i b u t e Ch a ng e s

F i n a l l y , th e r e a r e seve r a l s y s t em s e rv i c e s th a t a l l o w a
process
to
a l te r
i ts
character i stics ,
s uc h
as
i t s r e sponse to s ys t em se rv i c e
f a i l u r e s , i t s so f twa r e p r i o r i ty , a nd i t s p r o c e s s n a m e .
Some o f
these
c h a ng e s
( s uc h a s
p r i o r i ty e l ev a t i o n
or
swa p d i s a b l i ng }
requ i r e
p r i v i l eg e .
Th e S e t
P r i o r i t y s ys tem
s e rv i c e
is
t h e o n l y se rv i c e
d e sc r i b ed
i n th i s s e c t i o n tha t c a n b e i s s ued fo r a p r o c e s s o th e r t h a n
the c a l l e r .

9-1 0

PROCESS CONTROL AND COMMUN I CAT I ON
9. 2. 3. 1
S e t P r i o r i ty - Th e
Se t
P r i o r i ty s ys t e m s e r v i c e a l l ows a
process
to
a l te r
i t s o wn so f twa r e p r i o r i t y o r the p r i o r i t y o f o th e r
p r o c e s s e s tha t i t i s a l l o wed ( th r o ug h GROUP o r WORLD p r i v i l eg e s )
to
I f a p r o c e s s h a s the ALTPR I p r i v i l eg e , i t c a n c h a ng e p r i o r i t y
a f fec t .
to a ny v a l ue b e twe e n 0 a n d 3 1 .
A p r o c e s s wi tho u t th i s p r i v i l eg e
is
r e s t r i c ted
t o the r a ng e b e twe e n 0 a n d i t s o wn b a s e p r i o r i t y , i mp l y i ng
th a t a n o n p r i v i l eg ed p r o c e s s c a n l o we r b u t no t
ra i se
i ts
s o f twa r e
p r i o r i ty .
( Be c a u s e VM S d o e s n o t k e ep a pe rma n e n t c o py o f the p r o c e s s
p r i o r i t y o b ta i n ed
f r om
t h e a u tho r i z a t i o n
record ,
a
n o n p r i v i l eg ed
process
tha t l owe r s i t s s o f twa r e p r i o r i ty c a nno t r a i s e i t bac k to i t s
a u tho r i z e d va l ue w i t ho u t l ogg i ng o u t . )

Fo r mo s t s c h ed u l i ng s t a te s ( ev e r yth i ng e x c e p t C OM , C OM O , a nd C UR ) , t h e
Se t
P r i o r i ty s ys t em s e rv i c e s i m p l y c h a ng e s the b a s e so f twa r e p r i o r i t y
i n the so f twa r e PC B ( a t o f f s e t PC B $ B PR I B ) .
If a process
a l te r s
i ts
o wn
p r i o r i ty ,
not only
i t s b a s e -b u t a l s o i t s c u r r e n t p r i o r i t y ( a t
o f f s e t PC B $ B P R I ) i s c h a ng ed .
Wh e n
the
p r io r i ty o f a
c ompu t a b l e
process
( e i th e r
C OM o r C OMO ) i s a l t e r ed , t h e p r o c e s s i s r emoved f r om
t h e C OM o r C OM O q u e ue c o r r e s po nd i ng to i t s c u r r e n t p r i o r i t y a nd p l a c ed
i n to
a C OM o r C OM O q u e u e c o r r e s po nd i ng to i t s n e w p r i o r i t y ( th e n e w
b a s e w i th a b o o s t o f 2 ) .
I n a d d i t i o n , t h e sched u l e r i s no t i f i ed .
If
t h e n e w p r o c e s s p r i o r i t y ( n ew b a s e pl us a bo o s t o f 2 ) i s g r e a te r th a n
or
e q ua l
to
t h e c u r r e n t pr i o r i ty o f
the cur rent
process ,
a
r e s c h e d u l i ng i n te r r up t i s r e que s t ed .

9.2.3.2
S e t Pr o c e s s Name - Th e Se t P r o c e s s Name a l l o ws a
process
to
c h a ng e
i t s p r oc e s s n am e .
Th e new n am e c a nno t c o n t a i n mo r e t h a n 1 5
cha r a c te r s .
I f no o th e r p r o c e s s i n the s ame g r o up h a s the same
n am e ,
t h e n e w n ame i s p l a c ed i n to t h e so f twa r e PCB ( a t o f f s e t PC B $ T LNAME ) .
( No t e tha t th i s s e rv i c e a l l o ws mo r e
f l ex i b i l i ty
in
e s t a b l i sh i ng
a
p r o c e s s n am e
than
i s ava i l a b l e f r om t h e u s ua l c h a n n e l s , s uc h a s t h e
a u tho r i z a t i o n f i l e o r a $ J O B c a r d .
Th i s
is
b e c a use
th e r e
a r e no
r estr ic t i ons
i mpo s ed
by
th i s s e r v i c e o n c h a r a c t e r s tha t c a n m a k e up
the p r o c e s s name . )

P r o c e s s Mo d e S e r v i c e s - Th e r e
are
seve r a l
m i sc e l l aneous
sys tem s e r v i c e s wh o s e
o n l y a c t i o n i s to s e t o r c l e a r a b i t i n some
f i e l d i n t h e s o f twa r e PCB .
I n pa r t i c u l a r , the so f twa r e PC B c o n t a i n s a
s ta tus
l o ng wo rd ( no t to be co n f u sed w i th the h a r d wa r e e n t i t y � t h e PS L
o r p r o c e s s o r s t a t u s l o ngwo r d ) t h a t r ec o r d s the c u r r e n t s o f twa r e s t a t u s
of the proce sso r .
Ta b l e 9 - 2 l i s t s e a c h o f t h e f l ag s i n th i s l o ng wo r d ,
a nd the d i r e c t o r i nd i r e c t wa ys
that
the s e
f l ag s
can
be
se t o r
c l e a r ed .

9.2.3.3

Th e Se t Re so u r c e Wa i t Mo d e , S e t Sys t em Se r v i c e Fa i l u r e E x c e p t i o n Mod e ,
and
Set
Swa p Mo d e
sys tem s e r v i c e s a l l s e t ( o r c l e a r ) b i t s i n th i s
s t a t us l o ng wo r d .
Th e a b i l i ty t o d i s a b l e swa pp i ng i s p r o t e c t ed b y t h e
PSWAPM p r i v i l eg e .
Th e
o th e r
two
serv i ces
r e q u i r e n o p r i v i l eg e .
S e v e r a l o the r sys tem s e r v i c e s ( s uch a s $ D E L PRC , $ FORC E X ,
$ R E S UM E ,
or
$ S U S PND )
se t o r c l e a r b i t s i n t h e s ta t us l o ng wo r d a s a n i nd i c a t i o n o f
the i r pr ima ry ope r a t i o n .
Th e S e t AS T s y s tem
s e rv i c e
sets o r c lea r s
( enab l e s o r d i sab l e s )
d e l i v e r y o f ASTs
fo r a g i v e n a c c e s s mo d e .
Th e AST e n ab l e f l ag s a r e
s to r e d a t o f f s e t PC B $ B ASTEN .
Th e u s e o f t h e s e f l ag s i s d i sc us s e d
in
Ch a p t e r 5 .

9-1 1

Tab l e 9- 2
Mean i ng of F l ag s

\0
....

S ym bo l i c Name

Me a n i ng o f Fl ag

PC B $V R E S
PC B $V-D E L PEN
PCB $V-F ORC PEN
PC B $V-I N QUAN
PCB $V-PSWAPM
PCB $V-R E S PE N
PCB $V-S S F E XC
PCB $V-S S F E XC E
PCB $V-S S F EXC S
PC B $V=S S F E XC U

in P C B S tatus Longword

i f Se t

( PC B $ L STS )
_

Fl ag Se t b y

Fl ag Cl ea r ed by

P r o c e s s i s r e s i d en t ( i n t h e b a l a n c e s e t )
P r o c e s s d e l e t i o n i s pe nd i ng
Fo r c ed ex i t i s pend i ng
P r o c e s s i s i n i t s i n i t i a l q ua n t um ( fo l l o wi ng i n s wa p )
P r o c e s s s wa pp i ng i s d i s a b l ed
Re s um e i s pend i ng ( s k i p s us pe nd )
En a b l e s y s t e m s e rv i c e e x c e p t i o n s fo r k e r ne l mod e
En a b l e s ys t e m s e rv i c e e x c e pt i o n s fo r ex ec u t i v e m o d e
En a b l e s ys t e m s e rv i c e e x c e p t i o n s fo r s upe r v i so r mod e
E n a b l e s ys t e m s e rv i c e ex c e pt i o n s fo r u s e r mod e

Swa ppe r
$DE LPRC
$ F ORCEX
Swa ppe r
$S ETSWM ,
$ R E S UM E
$ S ETSFM
$ S ETSFM
$ S ETSFM
$ S ETSFM ,

Swa ppe r

PC B $V S S RWA I T
PC B $V-S US PEN
PC B $V=WAKE PE N

D i s a b l e r e so u r c e wa i t mod e
S u s pe nd i s pe nd i ng
Wa k e i s p e nd i ng ( s k i p h i b e r na te )

PC B $V WA L L
PC B $V-BATC H
PCB $V-N OACNT
PC B $V-SWPVB N
PC B $V-AS TPEN
PC B $V-P H DR E S
PC B $V-H I B ER
PCB $V-L OG I N
PC B $V-N E 'IWRK
PC B $V=PW RA S T

Wa i t fo r a l l e v e n t f l ag s i n m a s k
P r o c e s s i s a b a tc h j o b
Do n o t wr i te an a c c o un t i ng r e c o rd fo r t h i s p r o c e s s
Mo d i f i e d pag e wr i te to t h e swa p f i l e i s i n p r og r e s s
A S T i s pend i ng ( No l o ng e r u s ed )
P r o c e s s h e ad e r i s r e s i d en t
H i b e r n a t e a ft e r i n i t i a l i m ag e a c t i v a t i o n
Log i n w i tho u t r ea d i ng t h e a u t ho r i za t i o n f i l e
P r o c e s s i s a n e t wo r k j o b
P r o c e s s h a s d ec l a r ed a powe r r ec o v e r y AST

$S ETRWM , $CRE PRC
$ S US PND
$WAKE , e x p i r a t i o n o f
s c h e d u l ed wa k e up
$WF LAND
$CRE PRC
$ C R E PRC
Mo d i f i ed pa g e wr i t e r

PCB $V_N OD E L E T

Do no t d e l e t e t h i s p r o c e s s

( No t u s e d )

Swa ppe r
$ C R E PRC
$ C R E PRC
$ C R E PRC
$S ETPRA

$ C R E PRC

$CRE PRC

I m ag e and pr o c e s s r und own
Qua n t um end ro ut i n e
$ S E TSWM
S u s pend s pe c i a l AST
$S ETSFM , p r o c e s s r un d o wn
$S E TSFM , p r o c e s s r un d o wn
$S E TS FM , p r o c e s s r un d o wn
$S E TS FM , i m ag e and
p r o c e s s r un d o wn
$ S E TRWM
S u s pe nd s pe c i a l AST
$ H I B ER
Th e n e x t $WFLOR o r $WA I TFR
Mod i f i ed pag e wr i t e r
Swa ppe r

Ro u t i n e tha t q u e u e s
r e c o v e r y ASTs , i m ag e
a nd p r o c e s s r un d o wn

PROCE S S CONTROL AND C OMMUN ICAT I ON

9.3

INTERPROC ESS COMMUN I CAT I ON

I n a n y a pp l i c a t i o n i nv o l v i ng mo r e t h a n o n e p r o c e s s ,
it
i s necessa ry
f o r d a ta
t o b e s h a r ed among the s ev e r a l p r o c e s s e s o r fo r i n fo rma t i o n
t o b e s e n t f r om o n e p r o c e s s to a no t h e r .
VM S p r o v i d e s s e v e r a l s e r v i c e s
t h a t a c c ompl i sh
t h i s i n f o rm a t i o n e x c h a ng e .
Th e s e r v i c e s v a r y i n th e
a m o un t o f i n fo rm a t i o n t h a t c a n be t r a n sm i t t ed , t h e t r a n s pa r e n c y o f t h e
t r a n sm i s s i o n , a nd t h e a m o un t o f s yn c h r o n i z a t i o n p r o v i d ed by VM S .

9.3.1

Event F l a g s

G l o b a l o r c ommon e v e n t f l ag s c a n b e t r e a ted a s a m e thod
fo r
seve r a l
p r o c e s s e s t o s h a r e s i ng l e b i t s o f i n f o rm a t i o n .
I n f a c t , t h e t yp i c a l
u s e o f c ommon ev e n t f l ag s i s a s a s yn ch r o n i z a t i o n to o l f o r o th e r m o r e
c ompl i c a t ed
commun i c a t i o n
t e c hn i que s .
Th e
i nternal
o pe r a t i o n s o f
c ommo n e v e n t f l ag s a r e d e sc r i b ed i n t h e beg i nn i ng o f th i s c h a p t e r .

9. 3. 2

Ma i l bo x e s

Ma i l bo x e s p r o v i d e t h e m o s t t r a n s pa r e n t fo rm o f c omm un i c a t i o n p r ov i d ed
Ma i l b o x e s
a re
I /0 d ev i c e s i n th a t t h e y a r e w r i t t e n to a nd
b y VM S .
r e a d f r om by t h e no rm a l VM S I /0 s y s t em , e i th e r th r o ug h RM S o r wi th t h e
$QIO
i n te r fa c e .
Al tho ug h p r o c e s s - s p e c i f i c o r s ys t em-w i d e pa r am e t e r s
m a y c o n t r o l t h e amo un t o f d a t a th a t c a n b e wr i t t e n to a m a i l b o x i n o n e
o pe r a t i o n ,
there
i s n o l i m i t i n t h e t o t a l amo un t o f i n fo rm a t i o n th a t
c a n b e pa s s e d th r o ug h a m a i l bo x wi t h a s e r i e s o f r e a d s a nd w r i t e s .
Th e r e a r e two f o rms o f
s yn c h r on i za t i o n p r ov i d ed
fo r m a i l bo x
I /0 .
B e c a u s e m a i l bo x e s a r e I /0 d ev i c e s , a s i mpl e b u t r e s t r i c t i v e t e c h n i qu e
wo u l d h a v e t h e r e c e i v i ng p r o c e s s i s s ue a r e a d
f r om
the m a i l bo x
a nd
wa i t un t i l th e r e a d c ompl e t e s .
Th i s c o u l d n o t o c c u r un t i l t h e p r o c e s s
wr i t i ng t o th e m a i l bo x
comp l e ted
i ts
t r a nsm i s s i o n o f d a t a .
Th e
l im i t a t i on o f
t h i s t e c h n i q u e i s t h a t t h e r e c e i v i ng p r o c e s s c a nno t d o
a ny t h i ng e l s e wh i l e i t i s wa i t i ng
fo r d a ta .
Ev e n
if
the process
i ssues
a s yn c h r o no u s
I /O r e que s t s , a n I /O r e que s t m u s t b e o u t s t a n d i ng
a t a l l t i m e s i n o rd e r to r e c e i v e n o t i f i c a t i o n wh e n some o th e r
process
w r i t e s t o t h e m a i l bo x .
I n some a pp l i c a t i o n s , t h e s e l i m i t a t i o n s m a y b e
a c c e p t a b l e a nd s o th i s t e c h n i que c a n b e used .
O th e r a ppl i c a t i o n s m a y h a v e a
r e c e i v i ng
process
th a t c a n
pe r f o rm
d i fferent tasks ,
d e pe nd i ng
on the
i n fo r ma t i o n
ava i l ab l e
to
it.
Pu t t i ng s uc h a p r o c e s s i n to a wa i t s t a t e fo r o n e t a s k p r e v e n t s i t f r o m
s e r v i c i ng
a n y o f i t s r e que s t s .
Fo r s uc h a ppl i c a t i o n s , VM S p r ov i d e s a
s p e c i a l $ Q I O r e que s t c a l l ed S e t At t e n t i o n AST th a t a l l ows a p r o c e s s t o
r ec e i v e not i f i c a t i o n
t h r o ug h a n A S T wh e n a nyo n e w r i t e s i n to i t s
m a i l bo x .
Th i s t e c hn i que a l l ows a p r o c e s s
to
c o n t i nue
i t s ma i nl i ne
p r oc e s s i ng
a nd
h a nd l e
r e que s t s
f r o m o th e r p r o c e s s e s o n l y wh e n s uc h
wo r k i s n e ed ed , w i tho u t h av i ng
an
I / 0 r e que s t o u t s t a nd i ng
at
all
t imes .

9-13

PROCE S S CONTROL AND COMMUN I CAT ION

9.3. 3

Log i c a l Names

Log i c a l n am e s ( Ch a pt e r 2 6 ) a r e used
e x t e n s i v e l y by VM S t o
p r ov i d e
t o ta l
d ev i c e
i nd e pe nd e n c e i n the I /O s y s t em .
Howe v e r , l og i c a l n a m e s
c a n b e u s ed f o r many o t h e r
pu r po s e s
a s we l l .
Spe c i f i c a l l y ,
one
p r o c e s s c a n pa s s i n f o rma t i o n t o a n o th e r p r o c e s s by c r e a t i ng a l og i c a l
n a m e ( i n the g r oup o r s ys t em t a b l e ) wi t h
i n fo rm a t i o n s t o r ed
in
the
e q u i v a l enc e
s t r i ng .
Th e r e c e i v i ng p r o c e s s s i mpl y t r a n s l a t e s the n a m e
t o r e t r i ev e t h e d a ta .
Al tho ug h some fo rm o f s yn c h r o n i z a t i o n i s p r o v i d ed by a n e r r o r
r eturn
( S S $ NOTRAN ) f r om th e T r a n s l a te Log i c a l Nam e sys tem s e rv i c e , p r o c e s s e s
u s i ng s uc h a t e c h n i q ue
sho u l d
use event
f l ag s
(or
a n e qu i v a l e n t
m e tho d )
t o synch r o n i z e th i s c ommun i c a t i o n t e c h n i que .
O n e u s e o f th i s
t ec h n i que wh e r e s yn c h r o n i z a t i o n i s n o t r eq u i r ed o c c u r s wh e n a
process
c r ea t e s a
s ub p r o c e s s
or
d e ta c h ed p r o c e s s a nd pa s s e s i t d a t a i n t h e
e qu i v a l e nc e s t r i ng s f o r SYS $ I N PUT , S YS $ 0 UTPUT , o r SYS $ E RROR .
In
th i s
c a se ,
t h e r e i s n o po s s i b i l i ty fo r t h e t r a n s l a t i o n to o c c u r b e fo r e the
c rea t ion .

9.3.4

G l oba l S e c t i o n s

G l o b a l s e c t i o n s p r o v i d e t h e f a s t e s t m e thod f o r o n e p r o c e s s
to
pa s s
i n fo rma t i o n
to
a n o th e r
process .
Be c a u s e the two p r o c e s s e s h a v e t h e
d a ta a r e a m a pped i n to the i r ad d r e s s s p a c e , n o movem e n t o f
d a ta
t a ke s
p l ac e .
I n s t e ad ,
t h e m e thod p r ov i d e s fo r a sha r i ng o f t h e d a ta .
Th e
m e thod i s n o t t r a n s pa r e n t i n tha t e a c h p r o c e s s m u s t m a p t h e g l oba l
s ec t i on
t h a t wi l l be u s e d to sha r e d a t a .
I n add i t i on , the processes
m us t pe r f o rm th e i r own s yn c h r o n i za t i o n to p r ev e n t t h e
r ec e i ve r
f r om
r e ad i ng
d a ta b e fo r e i t h a s b e e n m a d e a v a i l a b l e by the s e nd e r .
Common
e v e n t f l ag s a r e one m e thod fo r a c c om p l i s h i ng th i s a l tho ug h p r o c e s s e s
c o u l d u s e a c c e s s f l ag s i n the s e c t i o n i t s e l f .

9.3.5

I n t e r p r o c e sso r Commun i c a t i o n w i th the MA7 8 0

VM S s uppo r t f o r t h e MA 7 8 0 s h a r ed memo r y un i t p r o v i d e s a
t r a n spa r e n t
c omm u n i c a t i o n
pa th fo r i n t e r p r o c e s s c ommun i c a t i o n e v e n wh e n p r o c e s s e s
a r e l o c a t e d o n d i f f e r e n t p r o c e s s o r s c o nn e c ted th r o ug h a s h a r e d memo r y
un i t ( MA7 8 0 ) .
Th e th r e e c ommun i c a t i o n pa ths p r o v i d ed a r e c ommo n e v e n t
f l ag s , ma i l bo x e s , a n d g l o b a l s e c t i o n s .
Each o f these ent i t i es
is
d e sc r i b ed
by a
name .
Wh e n a
process
c o nn e c t s
t o o n e o f t h e m ( w i th the As s o c i a t e Commo n Ev e n t F l ag C l u s t e r
s ys te m s e rv i c e , t h e C r e a t e Ma i l bo x s y s tem s e rv i c e , o r t h e C r e a t e
a nd
Ma p S e c t i o n o r Ma p G l o b a l S e c t i o n s ys t em s e r v i c e s ) , a l og i c a l name
t rans l a t i o n
i s pe r fo rmed
on
the
name
of
the o b j e c t .
If
the
e q u i v a l enc e n ame is o f the fo rm
s h a r ed -m emo r y- n am e : o b j e c t-name
the s e r v i c e m a k e s the a pp r o p r i a t e c o nne c t i o n be twe e n the
process
a nd
t h e d a ta s t r uc t u r e d e s c r i b i ng the o b j e c t th a t ex i s ts i n sha r e d memo r y .
I f t h e sha r ed memo r y d a t a s t r uc t u r e d o e s n o t ex i s t ,
it
is
c r e a t ed .
( Ma p G l o b a l
Se c t i o n d o e s n o t c r e a t e g l o ba l
s e c t i o n s t h a t d o no t
e x i s t . ) Th e d a t a s t r uc t u r e s th a t VMS u s e s to
d e sc r i b e
s h a r e d memo r y
a re
p i c t u r ed
in
Ch a p t e r 1 1 .
In
add i t ion ,
m emo r y m a n ag ement d a ta
s t r uc t u r e s , i n c l ud i ng tho s e s t r uc t ur e s
t h a t d e sc r i b e
s h a r e d memo r y
g l o b a l s e c t i o n s , a r e f o und i n th a t c h a p t e r .

9-1 4

PROC E S S CONTROL AND COMMUN I CAT ION
•

Fo r a c ommo n e v e n t f l ag c l u s t e r i n sha r ed memo r y ,
the event
f l ag c l u s t e r i n the s o f twa r e PC B ( PC B $ L E FC 2 P o r PC B $ L E FC 3 P }
po i n ts t o t h e s l av e C E B f o r th i s p r o c e sso r .
Th e
s l ave C E B
c o n ta i n s
i n fo rm a t i o n
t h a t d e sc r i b e s the m a s t e r C E B t h a t i s
l o c a t ed i n t h e s h a r ed m em o r y ( F i g u r e 9 - 4 } .
I f t h e s l av e
C E B a l r e a d y e x i s ts ,
s i mpl y po i n t s t h e PC B to t h e C E B .
I f the sl ave CEB d o e s not
( th e r e a r e c u r r e n t l y n o
th i s C PU } , t h e n a s l av e C E B
t h e m a s t e r i s s to r ed i n t h e
s l av e i s s to r ed i n th e PC B .

the

s y s t em

se r v i c e

ex i s t but
the m a s te r
does
r e f e r e n c e s t o t h i s c l us t e r o n
i s c r ea t ed ,
the address o f
s l av e , a nd t h e a d d r e s s o f the

I f t h e m a s t e r C E B d o e s no t ex i s t e i th e r ,
it
i s c r e a ted
f i rst
in
the
s h a r ed memo r y .
Th e n t h e s l av e i s c r e a t e d
a nd e x e c u t i o n p r o c e e d s a s d e sc r i bed i n the p r ev i o us c a s e .
Th e wa y i n wh i c h c ommon e v e n t f l ag s a r e s e t a nd
c l ea red
is
d e s c r i be d
i n the beg i nn i ng o f th i s c h a p t e r .
Th e d i f f e r e nc e s
b e twe e n s h a r ed memo r y c o mmon e v e n t b l oc k s ( ma s t e r a nd
s l av e }
and
l o c a l memo r y c ommo n e v e n t b l o c k s
a r e p i c tured
in
( A l o c a l mem o r y c ommo n event b l o c k
i s p i c t u r ed
Figure 9-5.
in Figure 9-2 . )
•

Fo r a m a i l bo x i n sha r ed m em o r y , th e r e a r e a l s o th r e e c a s e s .
•

•

I f t h e m a i l bo x a l r e a d y e x i s t s o n th i s
po r t ,
the
Create
Ma i l bo x
s y s t em
s e rv i c e
s i mpl y a s s i g n s a c h a nn e l to i t .
Th i s m e a n s t h a t the UC B po i n t e r i n a n
ava i l a b l e
Ch a n n e l
Cont r o l
Block
is
l o ad ed
wi th the
a d d r e s s o f t h e UCB
d e s c r i b i ng th i s s h a r ed mem o r y m a i l bo x .
I f t h e m a i l bo x i s b e i ng c r e a t e d
on
th i s
node
fo r
the
f i r s t t i m e , a UC B i s a l l o c a ted a nd l o a d ed w i th pa r am e t e r s
t h a t d e s c r i b e t h e ma i l box .
A bi t is
set
i n a m a i l bo x
d e pend e n t
field
i nd i c a t i ng
th a t
th i s ma i l bo x
UCB
d e s c r i b e s a m a i l bo x
in
sha r ed memo r y .
Final ly,
the
add ress
of
the
s h a r ed memo r y ma i l bo x c o n t r o l b l o c k i s
l o ad ed i n to th e UCB .
( Fi g u r e 1 6-2 )
I f t h e sha r ed memo ry m a i l box c o n t r o l b l o c k
d o e s no t e x i s t
( th i s
is
the
i n i t i a l c r e a t i o n o f the
ma i l box } , i t i s c r e a t ed b e f o r e the r e s t of the o pe r a t i o n s
d e s c r i b ed i n the p r ev i o us s t e p a r e pe r fo rmed .

data
s t r uc t u r e s
are
p i c t u r ed
in
Sh a r ed memo r y ma i l box
Ma i l bo x c r e a t i o n i s d e sc r i b ed i n mo r e
F i g u r e s 1 6 - 2 and 1 6 - 3 .
d e t a i l i n Ch a p te r 1 6 .

9-15

Shared Memory

Processor 1 Local Memory
SCH$GQ_CEBHD::

��

Slave CEB
PCB

�

..
-

BETA

Local CEB
...

PCB

...

PCB

...,

ALPHA

Local CEB
...

PCB

GAMMA

...

Master CEB
for shared
memory CEF
cluster

BETA

J�
..
-

F igure 9 - 4

�

Processor 2 Local Memory

Master CEB
for shared
memory CEF
cluster

GAMMA

Slave CEB
-

..
-

BETA

I
....

::SCH$GQ_CEBHD

A�

---

...

PCB

Slave CEB
...

..
-

GAMMA
'l

PCB

Local CEB
...

ALPHA

Re l a t ionship Between Ma s ter and S l ave CEB

...

PCB

PROC E S S CONTROL AND COMMUN I CAT I ON

The master CEB resides In
shared memory
Valid and Interlock Bits
Unused
Type

Status

Size
Unused

Event Flags

Deletor
Port

Unused
Unused
InterNumber
Creator
of Processes processor
Port
Lock
UIC of Creator
The slave CEB resides In
processor local memory

Protection Mask

Unused

Count
Cluster Name
(up to 15 characters)
(counted ASCII string)

Same as
Local Memory
Common Event
Block

VA of Processor 0 Slave CEB

VA of Shared Memory Control Block

��

VA of Processor N Slave CEB
Processor 0
Processor 1
Reference Count
Reference Count
=�

Index to
Master CEB
VA of Master CEB

��

Processor N
Reference Count

Figure 9-5

Processor N-1
Reference Count

Sh a r e d Memo ry Commo n E v e n t F l ag Da t a S t r uc t u r e s

9-1 7

PROCE S S CONTROL AND COMMUN I CAT I ON
•

Fo r a g l ob a l s e c t i o n
i n sh a r e d m emo r y ,
a
spec i a l g l obal
s e c t i o n d e sc r i pt o r
is
a l l o c a ted
t h a t d e sc r i b e s t h e g l ob a l
s e c t i o n i n s h a r ed m emo r y .
U n l i k e g l o b a l s ec t i o n s t h a t
ex i st
in
l o c a l memo ry , t h e r e a r e no g l o b a l pag e t a b l e e n t r i e s s e t
u p fo r g l o b a l s ec t i o n s i n sh a r e d memo r y .
Wh e n a p r o c e s s m a ps to the s h a r ed m emo r y g l o ba l s e c t i o n ,
i ts
p r o c e s s p a g e t a b l e s a r e s e t up c o n t a i n t h e PFNs o f the sh a r ed
memo r y pag e s a nd m a r k e d as v a l i d .
Such pag e s a r e n o t c o un t ed
ag a i ns t
the
p r o c e s s wo r k i ng s e t .
Th a t i s , pag e s i n s h a r ed
m em o r y do no t pag e .
Th e y a r e a l wa ys v a l i d .
Th i s a l l o ws t h em
to be d e sc r i b ed w i t h a s i mpl e d e sc r i pto r tha t i s c o n t a i n ed i n
t h e g l o ba l s e c t i o n d e sc r i pt o r , r a th e r th a n a
set of global
pag e
table
entr i es
r e qu i r ed fo r g l o b a l pag e s t h a t e x i s t i n
local
memo ry .
Mem o ry m a n ag em e n t
d a ta
s t r uc t u r e s
a re
d e s c r i bed
i n Ch a pt e r 1 1 .
Th e m emo r y m a n ag e m e n t s ys t em
s e r v i c e s a r e d i s c u s s ed i n Ch a pt e r 1 3 .

9-1 8

C HAPTER 1 0
T IMER SUPPORT

The r e a r e s e v e r a l a c t i v i t i e s t h a t r eq u i r e e i t h e r t h e t i m e o f d a y a nd
d a te
or
t h e m e a s u r em e n t o f a n
i n t e r v a l of t i m e .
Th e s uppo r t fo r
t i m e - r e l a t ed a c t i v i t i e s i s i m p l em e n te d bo th i n t h e VAX- 1 1 h a r d wa r e a nd
i n VA X/VM S .

10. 1

T IMEKE E P I NG IN VAX/VMS

Two h a r d wa r e c l o c k s a r e upd a t ed a t
r eg u l a r
in te r va l s ,
the
i n te rval
c lock
a nd
the
t i m e - o f-d a y c l o c k .
Th e s e c l o c k s a r e u s e d b y VM S t o
m a n ag e two d i f f e r e n t t i m e s , t h e s y s tem t i m e a nd t h e t i m e b e c a u s e
the
s ys t em wa s
l a s t b o o t s t r a pp e d .
Ad d i t i o n a l l y ,
th e
s o f twa r e
t i me r
p r o v i d e s t i m e r s e r v i c e s s uc h a s s c h ed u l ed wa ke ups b y m a i n t a i n i ng
a
t i m e - o r d e r ed
q u e u e o f r e q u e s t s a nd d e l i v e r i ng t h em a s th e e x p i r a t i o n
t imes occur .

10. 1. 1

H a r d wa r e C l o c k s

Th e h a r d wa r e c l oc k s a r e a s e t o f p r o c e s so r r eg i s t e r s t h a t a r e used
or
u pd a t e d
r eg u l a r l y b y t i m i ng c i r c u i t r y .
In i t i al i za t i o n , c a l i b r a t ion ,
a n d i n t e r p r e t a t i o n o f t h e r eg i s t e r s
a r e pe r f o rmed
by VM S
rout i ne s
d u r i ng s y s tem i n i t i a l i z a t i o n a nd no rm a l o pe r a t i o n s .
Th e
p r o c e s so r
r eg i s t e r s
that
i mp l em e n t
the
h a r d wa r e
c locks
are
th a t
s umma r i z e d
in
Ta b l e 1 0 - 1 ,
a l o ng
wi th t h e memo r y l o c a t i o ns
i mp l em e n t the v a r i o u s s o f t wa r e t i m e v a l u e s .

10. 1.1.1
I n te rv a l C l o c k - Th e i n t e r v a l c l oc k i s i mp l em e n t e d a s a
set
of
th r e e
3 2 -b i t p r o c e s s o r
r eg i s t e r s .
Th e c l oc k
" ticks"
a t one
m i c r o s e c o nd i n t e r v a l s w i th a n a c c u r a c y o f a t l e a s t
0 . 01%
( l ess
than
n i ne
s e c o nd s pe r d a y ) .
Th e
f r e q u e nc y a t wh i c h t h e i n t e r v a l c l o c k
c a u s e s an i n t e r r upt i s d e t e rm i n e d b y t h e v a l ue i n o n e o f t h e p r o c e s s o r
r eg i s t e r s , PR $ _N I CR .
Th e t h r e e i n t e r v a l c l o c k r eg i s t e r s
1.

( Ta b l e 1 0 - 1 )

a r e u s e d a s fo l l o ws .

Th e
i nterval
clock
c o n t r o l / s ta tus
r eg i s t e r
( PR $ I C C S )
contro l s
the
i n t e r r up t
s t a t us o f th e i n t e r v a l c l o c k .
Th i s
r eg i s t e r i s s e t b y t h e C P U h a rdwa r e and
th e n
r e s e t b y the
h a rdwa r e c l o c k i n t e r r up t s e r v i c e r o ut i n e ( S e c t i o n 1 0 . 2 ) each
t i m e t h e i n t e r v a l c l oc k i n t e r r up t s .

1 0-1

Tab l e 1 0 - 1
VAX/VMS Hardware C locks and S o f tware T ime r s

f-'
0
I
N

S i ze
( b i ts)

Un i t s

Fr eque n c y

Upd a ted by

1 m i c ro sec o nd

1 m i c r o s e c o nd

CPU h a r dwa r e

Nex t i n te r v a l

1 m i c ro second

( No te 1 )

S y s t e m i n i t i a l i za t i o n

PR $ -I C C S

Interval clock
control/sta tus

PR $ T ODR

T i m e - o f - d ay
c l oc k

1 0 m i l l i s ec o nd s

1 0 m i l l i s econd s

EXE $G Q_S YS T IM E

Sys tem t i m e

1 0 0 n a no sec o nd s

1 0 m i l l i s econd s

E XE $G L_AB S T IM

Sys tem a b so l ut e
t ime

1 s e c o nd

1 s e co nd

EXE $G L_TODR

T i m e - o f-y e a r
b a s e v a l ue

1 0 m i l l i second s

( No t e 2 )

$ S E T I M E s ys t em se rv i c e

EXE $G Q_TODCBASE

T i m e - o f -y e a r
b a s e v a l ue
( i n s y s t em
t i m e fo rma t )

1 0 0 n a n o s e c o nd s

( No te 2 )

$ S ET I M E s ys t em s e r v i c e

Nam e

Use

PR $-I C R

Interval clock

PR $ N I CR

c o n t r o l / s t a t us
b i ts

(1)

PR $_N I CR i s wr i t t e n o n l y a t sys t em i n i t i a l i za t i o n t i m e .

(2)

E X E $G L_T ODR and EXE $G Q_T ODCBASE a r e mod i f i ed onl y wh en
•

•

1 0 m i l l i s econd s

the t i m e - o f - d a y i s c h a ng ed b y a
$ S ET I M E s ys tem
se rv i c e
r eque s t
( e i th e r
expl i c i t l y
o r a s a n i n teg r a l pa r t o f t h e s ys t em boo t s t r a p
o pe r a t i o n ) o r
t h e PR$_TODR h a s b e e n l o s t d ue t o a pro l o ng ed powe r fa i l u r e .

Ha rdwa r e c l o c k i n t e r r upt
serv i c e rout i n e
C PU h a r d wa r e ,
$S ETIME s ys t em se rv i c e
Ha r d wa r e c l oc k i n t e r r upt
s e rv i c e r o u t i n e ,
$ S E T IM E s ys t em s e r v i c e
Sy s t em i n i t i a l i za t i o n ,
EXE $T IM E OUT r e pea t i ng
s ys t em s ub r o u t i n e

TIMER SUPPORT

Th e n e x t i n t e r v a l c o un t r eg i s te r ( PR $ N I C R ) d e f i n e s how o f t e n
the
i n te rv a l
c l o c k wi l l c a u s e a h a rdwa r e i n t e r r up t .
D u r i ng
s ys tem i n i t i a l i z a t i o n , t h e r o u t i n e ! N I T l o a d s th i s
p r o c e s so r
r eg i s te r wi th
a v a l ue o f - 1 0 0 0 0 .
Th i s d e f i n e s th� h a r d wa r e
c lock
i n t e r r up t
i nte rva l
to be
1 0 m i l l i s e c o nd s
( 10000
m i c r o s e c o nd s )
•

Th e i n t e rva l c o un t r eg i s t e r ( PR$ I C R )
is
i n c r em e n t e d
every
m i c r o s e c o nd
f r om
the
PR$ N I CR v a l ue
towa r d
zero .
Wh e n
PR$ I C R b e c ome s z e r o , the reg i s te r
ove r f l o ws ,
c a u s i ng
the
f o llowi ng a c t i o n s .
a.

Th e PR$ N I C R v a l ue is c o p i ed i n to PR $_I CR to
n e x t i nt e r v a l .

d e f i ne

the

Th e PR$ I C C S r eg i s t e r i s s e t
to
i nd i c a te
the o v e r f l o w
c o nd i t ion .
Th i s o pe r a t i o n c a u s e s a h a r d wa r e i n t e r r up t
( I PL 2 4 )
to
occur ,
s e rv i c ed
by t h e h a r d wa r e
c l oc k
i n te r r up t s e r v i c e r o u t i n e .

Th e PR$ I C C S i s r e s e t by the ha r d wa r e c l o c k i n t e r r up t s e r v i c e
r o u t i n e- to i nd i c a t e s e r v i c i ng o f the i n t e r r upt a nd r e e n a b l i ng
o f t h e h a r d wa r e c l o c k .

1 0 . 1 . 1 . 2 T i me - o f -Day C l o c k - Th e
t i m e - o f -d a y c l o c k
is
a h a r d wa r e
c ompo n e n t c o n s i s t i ng
o f o n e 3 2 -b i t p r o c e s s o r r eg i s t e r a n d a ba t te r y
b a c k u p s u pp l y f o r a t l e a s t 1 0 0 ho u r s o f o pe r a t i o n .
Th e
t i m e-o f-d a y
c l oc k h a s a n a c c u r a c y o f a t l e a s t 0 . 0 0 2 5 % ( a b o u t 6 5 s e c o nd s pe r m o n th )
a nd
a
r e so l u t i o n o f
1 0 m i l l i s e c o nd s .
The b a s e
t i me
fo r
the
t i m e - o f-d a y c l o c k
is
0 0 : 0 0 : 0 0 . 0 0 o ' clock
of Ja n ua r y f i r s t o f the
Th e t i me - o f - d a y c l o c k o v e r f l o ws a f t e r 4 9 7 d a ys .
c u r r e n t ye a r .
Th e p r e s e n c e o f the t i m e-o f - d a y c l o c k o p t i o n i s d e te rm i ned
a t s ys tem
i n i t i a l i za t ion
t i me .
If
the c o n t e n t s of the t i me-o f-d a y c l o c k a r e
v a l i d , the
i n i t i a l i za t i o n process ,
SYS I N I T ,
wi l l
no t p r ompt
the
o pe r a to r fo r the t i me .
Va l u e s i n PR$ TODR a r e b i a s e d by 1 0 0 0 0 0 0 0 ( h e x ) .
Va l ue s sma l l e r
than
th i s
i nd i c a te l o s s
of
powe r
or
t i me - o f - d a y o v e r f l o w , c o nd i t i o n s
c a u s i ng t h e t i me-o f -d a y c l o c k t o b e r e s e t b y ope r a to r
i n put
( th r o ug h
t h e $ S E T I M E s y s t em s e rv i c e } .
B e c a u s e the t i m e - o f -d a y c l o c k h a s a b e t t e r a c c u r a c y th a n the
i nterval
c l oc k , t h e t i me - o f-d a y c l o c k i s u s e d f o r r e c a l i b r a t i ng the sys tem t i m e
a t s y s t em i n i t i a l i z a t i o n a n d a t o th e r t i m e s wh e n
the
$ S E T I M E s ys tem
s e rv i c e is c a l l ed ( S e c t i o n 1 0 . 1 . 3 ) .

10. 1. 2

So f twa r e T i me

S o f twa r e t i me i s m a n ag e d by VM S r o u t i n e s a s a r e s u l t o f c h a ng e s i n the
h a r d wa r e c l o c k s .
Th e
s y s t em
t ime
i s d e f i n e d by a q u a d wo r d v a l ue
m e a s u r i ng the n umbe r o f 1 0 0 n a no s e c o nd i n te r v a l s s i n c e 0 0 : 0 0
o ' clock ,
Novemb e r
17,
1 8 58
( th e
t i me b a s e
f o r the Sm i th s o n i a n I n s t i t u t i o n
a s t r o nom i c a l c a l e nd a r ) .
E X E $G Q S Y S T I M E ( Ta b l e 1 0 - 1 ) i s upd a t ed
eve r y
i n t e r r up t s e r v i c e r o u t i n e
1 0 m i l l i s e c o nd s b y t h e h a r d wa r e c l o c k
( S ec t i o n 1 0 . 2 ) .
Th i s
q u a d wo r d
is
the
r e f e r e nc e
fo r nea r l y a l l
t i m e - r e l a t ed
so f twa r e
activ i t i es
in
the
s ys t em .
Fo r e x ampl e , t h e
1 0-3

TIMER S UPPORT
$ G E TTIM s ys t em s e r v i c e
u s e r -d e f i ned bu f f e r .

s impl y

wr i tes

th i s

q u a d wo r d

val ue

i n to

E XE $G L AB S T I M m e a s u r e s the n umbe r o f o n e s e c o nd
i n te r v a l s
tha t h a v e
e l a p s e d s i nc e th e s y s t e m wa s l a s t boo t s t r a pped .
Th i s a bso l u t e t i m e i s
u s ed t o pe r i o d i c a l l y c h e c k f o r I / O d ev i c e t i me o u t s a nd
i s a l so
the
v a l ue
fo r
" s ys t em
upt ime "
i n t e r p r e ted
a nd
d i s p l a y e d b y the
$ S HOW SYS T EM DC L c omma n d .
E X E $ G Q TODCBAS E c o n ta i n s t h e q u a d wo r d sys tem t i m e v a l ue e qu i v a l en t
to
the ba s e
t i me
fo r
t h e t i me - o f - d a y c l o c k .
EXE $G L TODR c o n ta i n s the
PR $ TODR v a l ue e q u i v a l e n t to the base t i m e of t h e
tTm e - o f - d a y c l o c k .
Th e-b a s e t i m e v a l ue s r e p r e s e n t t h e mo r e r ec e n t o f
•

0 0 : 0 0 o ' c l o c k o f J a n ua r y 1 o f the c u r r e n t ye a r , o r

•

t h e l a s t t i m e tha t the t i me - o f -d a y wa s r ed e f i n e d b y $ S E T I M E .

E XE $G L TODR
( as
1 0 0 0 0 000 ( h e x )

wi th

PR $_TODR )

b i a s ed

f a c to r

•

10. 1 . 3

S e t T i me S y s t em Se r v i c e

Th e $ S ET I M E s ys t em s e r v i c e a l l ows a
s ys tem m a n ag e r o r o pe r a to r
to
c h a ng e
the
s ys tem t i m e wh i l e VM S i s r un n i ng .
Th i s may be n ec e s s a r y
b e c a u s e o f a po we r f a i l u r e l o ng e r t h a n the b a t t e r y b a c k up t i me o f
the
t i me - o f-d a y c l o c k or b e c a u s e of c h a ng e s b e twe e n s ta nd a r d a nd d a y l i g h t
s a v i ng t i m e , fo r e x am p l e .
Th e n e w s y s tem t i m e
( a bso l u t e
t i me ,
not
r e l a t i v e t i m e ) i s pa s s e d a s t h e o p t i o n a l s i ng l e a rg um e n t o f t h e sys t em
s e rv i c e .
$S ETIME i s a l so
i nv o k e d d u r i ng
s ys t em
i n i t i a l i za t ion
to
r e s e t the sys tem t i m e ( a nd po s s i b l y t h e t i m e - o f -d a y c l o c k ) .
I f the r e qu e s t i ng p r o c e s s d o e s no t h a v e the
p r o c e s s p r i v i l eg e s
OPER
and
LOG I O , the r o u t i n e r e t u r n s w i th a n SS$ NOPR I V e r r o r s t a t us c o d e .
I f the i np u t qua d wo r d c a nno t b e r e a d ,
t h e ro u t i n e
r e t u r n s wi th
an
S S $ ACCVI O e r r o r s t a t u s c o d e .

10 . 1 . 3. 1
$ S ETIME Sys t em T i me Rec a l i b r a t i o n Requ e s ts - I f no
a r g um e n t
wa s pa s sed to t h e sys t em s e rv i c e o r the t i me a rg um e n t i s a z e r o va l u e ,
t h e n the r e que s t i s c o n s i d e r ed a r e c a l i b r a t i o n r e q ue s t .
Th e fo l l o w i ng
a c t i on s take place .
1.

Th e nex t s y s t em t i m e ,
f o l l o wi ng e q ua t i o n :
E X E $ G Q_S Y S T I M E

EXE $G Q_S YS T I M E ,

computed

E X E $G Q TODC BAS E
+ ( (PR$_TODR - E XE $G L_TODR )

the

* 100000)

E XE $G Q_S Y S T I M E a n d
EXE $G Q T ODC BAS E a r e q ua d wo r d
" s ys t e m "
PR $ TODR a nd E X E $G L TODR
i n un i t s o f 1 0 0 n a n o se c o nd s .
t imes
a r e l o ngwo r d " t i me - o f - d a y " t i m e s i n un i t� o f 1 0 m i l l i s e c�nd s .
Th e
mul t i pl i e r
of
100000
repr esents
the
n umbe r
of
1 0 0 n a n o s e c o nd i n t e r v a l s i n 1 0 m i l l i s e c o nd s .
2.

Ea c h e l em e n t i n t h e
timer
queue
( Sec t i on 1 0 . 3 . 2 )
has
i ts
a bso l ut e
expi r a t i o n
t i m e ad j u s ted by the d i f f e r e n c e b e t we en
the p r e v i o us s ys t em t i m e a nd the n e w s ys t em t i m e .
1 0-4

T I MER S U PPORT
Fo r t i me r r e q u e s t s t h a t e x p r e s s ed t h e i r e x p i r a t i o n t i m e a s a n
i n t e r va l ,
th i s
r e c a l i b r a t i o n c a us e s e a c h t i m e r r e q ue s t to
e x p i r e a f t e r the s ame i n te r v a l as o r i g i na l l y r e q u e s t e d .
Fo r t i m e r r e q u e s t s t h a t ex p r e s s ed t h e i r e x p i r a t i o n t i m e a s a n
a b so l u t e
t i m e , th i s r e c a l i b r a t i o n c a u s e s t h e e x p i r a t i o n t i me
t o b e r e a d j us t e d j u s t as
the
s ys tem t i me wa s
r e a d j us t e d .
Such r e q u e s t s w i l l e x p i r e a t a d i f f e r e n t t i me t h a n o r i g i na l l y
r e q u e s ted .
Ho wev e r , the i n t e r v a l b e twe e n the o r i g i n a l sys t em
t i me
and
the o r ig i n a l
r e q u e s t t i me
is
i d e n t i c a l to the
i n te r v a l b e twe e n the n ew s y s t em t i m e a nd the
new e x p i r a t i o n
t i me .
3.

Th e
ent i re
col lection o f
s ys tem
i nc l ud i ng
pa r am e t e r s ,
i s wr i t t e n bac k
to the
E XE $G Q TODCBAS E
a nd
E XE $ G L TODR ,
sys t em- i m a g e f i l e .

10. 1.3.2
$ S E T IME T i me - o f -Da y Re a d j us tm e n t Re qu e s t s - If
a
non z e ro
t ime v a l ue
i s s uppl i ed a s an a r g um e n t to $ S ET IME , then the fo l l o w i ng
o pe r a t i o n s o c c u r .
1.

Th e i n p u t a r g ume n t ,
spec i f i e d
in
" s y s t em t i m e
un i t s "
of
1 0 0 n a n o s e c o nd s ,
1s
c o nv e r ted i n to " t i m e -o f-d a y un i t s " ( th e
n umb e r o f 1 0 m i l l i s e c o nd
i n te r v a l s a f t e r
0 0 : 0 0 o ' c lock o f
J a n u a r y 1 o f the b a s e ye a r )
•

10 . 2

Th e c o nv e r ted spec i f i ed t i m e i s
E XE $ G L_TODR .

wr i t t e n

i n to

Th e
unconve r t ed
spec i f i ed
t ime
E XE $G Q_TO DC BASE a n d E XE $G Q_S YST IME .

F i n a l l y , the t i m e r q ue ue i s upd a t ed and the
new v a l u e s
fo r
the
t i me-o f-d a y c l o c k b a s e a r e wr i t t e n to the sys t em i m ag e
f i l e ( a l o ng w i th the sys tem pa r ame t e r s ) .
( S e e s t e ps 2 a nd
3
d e sc r i bed above i n Se c t i o n 1 0 . 1 . 3 . 1 ) .

PR $ TODR
wr i t t e n

a nd
i n to

HARDWARE C LOCK INTERRUPT SERV I C E ROUT INE

Th e h a r d wa r e c l oc k i n t e r r upt s e r v i c e r o u t i n e , EXE $ HWC L K I N T
i n mod u l e
T I M E S C HDL ,
s e rv i c e s
the I PL 2 4 h a rdwa r e i n t e r r upt s i g n a l l ed wh e n the
i n t e r v a l c l o c k , PR$ I C R , r e a c h e s z e ro .
Th e
i n te r v a l
c lock
is
set
( th r o ug h PR $_N I C R ) to i n t e r r upt ev e r y 1 0 m i l l i se c o nd s .
The h a r d wa r e c l oc k i n t e r r upt s e r v i c e r o u t i n e h a s two m a j o r f un c t i o n s .
•
•

upd a t i ng the sys tem t i me

( a nd po s s i b l y p r o c e s s a c c o un t i ng )

and chec k i ng t h e t i me r que ue fo r t i me r e v e n t s to be
now .

1 0-5

r e po r ted

T I MER S UP PORT
10. 2.1

S y s t em T i me U pd a t i ng

Th e upd a t i ng o f the s y s tem t i me a nd t h e po t e n t i a l upd a t i ng o f
a c c o un t i ng f i e l d s r e q u i r e s s e ve r a l d i s t i nc t a c t i o n s .

process

Th e PR $ I C C S r eg i s t e r i s r e s e t to i nd i c a t e th e
s e r v i c i ng
t h e i n te r r up t a nd t h e r e e n a b l i ng o f t h e h a r d wa r e c l o c k .

Th e s y s t em t i m e , EXE $G Q S Y S T I M E , i s u pd a t ed
by a d d i ng
e q u i v a l e n t o f 1 0 m i l l i sec o nd s to t h e q u a d wo r d va l ue .

the

I f the h a r d wa r e c l o c k i n t e r r u p t s wh i l e a p r o c e s s i s e x e c u t i ng
( th e
f o r m e r c u r r e n t s t a c k wa s no t t h e i n t e r r up t s t a c k ) , t h e n
t h e a c c umu l a t e d
CPU u t i l i z a t i o n
a n d q u a n t um va l u e
are
i n c r emen ted i n t h e p r o c e s s h e ad e r .
Th e q ua n t um va l u e i s u s e d
to d e t e rm i n e q u a n t um e n d ( S e c t i o n 1 0 . 3 . 1 a n d Ch a p t e r 8 ) .
If
t h e q u a n t um va l u e r e a c h e s z e r o , a n I PL 7 s o f t wa r e i n t e r r upt ,
s e r v i c ed by t h e s o f twa r e t i m e r r o u t i n e ,
is
r e q u e s t ed .
Th e
c h e c k f o r wh e th e r the i n t e r r u pt o c c u r r ed wh i l e a l r e a d y o n th e
i n t e r r up t s t a c k p r e ven t s a p r o c e s s f r om be i ng c h a r g ed fo r C PU
t i me th a t t h e s y s tem wa s u s i ng to s e r v i c e i n t e r r up t s .

10. 2.2

T i m e r Queue T e s t i ng

Th e t i me r q u e ue i s d i s c u s s ed w i th
the
s o f twa r e t i m e r
in
the n e x t
s ec t i o n .
Th e h a r d wa r e
c l oc k
i n te r r up t
s e rv i c e
r o u t i ne has
the
r e s po n s i b i l i t y to d e t e rm i n e i f t h e s o f twa r e t i m e r m u s t b e r e que s t e d t o
If
t h e f i r s t t i m e r q u e u e e l em e n t h a s a n
s e rv i c e
the
t ime r
que u e .
e x p i r a t i o n t i me l e s s t h a n o r equa l t o the n ewl y upd a ted
s y s tem t i m e ,
then
t h e t i m e r e v e n t i s d ue .
Th e s o f twa r e t i m e r r o u t i n e i s r e que s t e d
th r o ug h t h e I P L 7 i n t e r r up t .

10. 3

S OFTWARE T IMER INTERRUPT S E RVI C E ROUT INE

Th e so f twa r e t i m e r i n t e r r upt s e r v i c e r o u t i n e , E XE $ SWT I M I NT
in mod u l e
T I M E SC HDL ,
is
i nv o k e d
t h r o ug h
the
I P L 7 s o f t wa r e i n t e r r upt .
Th e
s o f twa r e t i me r i s r e q ue s t ed
bec a use
e i th e r
the
first
t imer queue
e l em e n t m u s t b e
s e r v i c ed o r t h e c u r r e n t p r o c e s s h a s r e a c h ed qua n t um
e nd .
I f t h e s ys t em t i m e , E XE $G Q S YS T I M E , i s g r e a t e r t h a n o r
e q ua l
to
th e
exp i r a t i on
t i me o f
t h e -f i r s t e l em e n t i n t h e t i m e r q u e ue , then t h e
t i m e r e v e n t i s d ue .
Th e c ompa r i s o n wi th
the
s ys tem
t i me mus t b e
pe r fo rmed a t I P L 2 4 t o b l o c k t h e h a r d wa r e c l o c k i n t e r r up t .
I f a t i m e r r e que s t i s d u e , then t h e TQE
is
r emoved
f r om
the
t imer
que u e ,
the
I P L d r o pped bac k t o I P L $ T I MER ( I P L 7 ) , a nd o n e o f th r e e
s e q u e n c e s o f c o d e i s p e r f o rm ed ( d epend Tng upon t h e typ e o f r e que s t ) .

10. 3.1

Qua n t um Exp i r a t i o n

Th e e x p i r a t i o n o f t h e q u a n t um i n t e r va l
for
the c u r rent process
is
d e t e rm i n ed
by
t e s t i ng
the
PHD$W Q UANT f i e l d .
Th i s
f i eld
is
i nc r emen ted by t h e h a r d wa r e c l o c k s e r vic e
rout i ne .
A z e r o qu a n t um
va l ue i nd i c a t e s qua n t um e x p i r a t i o n .
Th e p r o c e s s i ng o f t h e q u a n t um end
1 0-6

T IMER S U PPORT
e v e n t i s pe r fo rmed by t h e s c h ed u l e r
d e sc r i b e d i n Ch a p t e r 8 .

10. 3.2

rout ine

S C H $ Q E ND ,

wh i c h

T i me r Q u e u e a n d T i m e r Que u e E l em e n t s

T i m e r r e que s t s a r e ma i n ta i n ed i n a d o ub l y l i n ked l i s t th a t i s
o r d e r ed
by
the
e x p i r a t i o n t i me o f the r e q ue s t s .
E XE$G L T Q F L a nd EXE $G L T QB L
a r e a pa i r o f l o ng wo r d s ( d e f i n ed i n the mod u l e SYS C OMMON )
th a t -fo rm
th e l i s th e a d of the t i m e r q u e u e .
E l em e n t s i n the t i me r que ue a r e d a t a
s t r uc t u r e s t h a t a r e g e n e r a l l y a l l o c a t ed f r om no npag ed d yn am i c m emo r y
a nd
i n i t i a l i zed
as
a
r e s ul t
of
$ S E T IMR sys tem
serv i ce
calls
( Sec t i on 1 0 . 4 . 1 ) .
Th e a l l o c a t i o n o f t i m e r queue
e l em e n t s
( TQEs )
is
g o ve r n e d b y the po o l ed j o b quo ta J I B $W_T QCNT .
Th e fo rma t o f the t i m e r que ue e l em e n t i s shown
in
Figure 1 0-1 .
Th e
l i n k f i e l d s ( T QE $ L T Q F L a nd TQE $ L T QB L ) , the TQE $W S I Z E f i e l d , a nd the
TQE $ B TYPE
f i eld
a r e cha r a c te r i s t i c
of
s y s t em- d a t a
s t r uc t u r e s
a l l o c a ted
f r om d yn am i c m emo r y .
Th e T QE $ 8 RQTYPE f i e l d d e f i n e s the
t ype of t i m e r r e que s t ( p r o c e s s t i m e r r e q ue s t , -pe r i od i c s y s tem
r o ut i ne
r e qu e s t ,
or
process
wa k e
r e que s t )
a nd wh e the r
the
r eque s t i s a
o n e - t i m e o r r e pe a t i ng r e que s t ( s e e the l i s t o f TQE
r eque st
t ype s
in
Figure 1 0-1 ) .
Bit 6
o f TQE $ B R QTYPE
is
set
if
a n AST i s to be
d e l i v e r ed wh e n the t i m e r e v e n t occ u r s .
Th i s b i t i s e q u i v a l e n t to
the
AC B $V_Q U O TA b i t o f the AST c o n t r o l b l o c k d e sc r i b ed in Ch a pt e r 5 .

RQTYPE I

TQFL
TQBL
TYPE
SIZE
P I D / PC
AST/FR3
ASTPRM / FR4

TIME

DELTA

EFN

RQPID

R MOD

TQE $ 8- RQTY PE
3 2 1 0

7 6 5

.______IIIIC 1

Figure 1 0-1

Process timer request
System subroutine request
Scheduled wake request
One-time request
Repeat request
(not allowed for process
timer requests)
AS T is associated with
timer event

L a yo u t of a T i m e r Que ue E l eme n t

1 0 -7

T IMER SUPPORT

Th e i n t e r p r e t a t i o n o f the n e x t
three
l o ng wo rd
f i e l d s d e p e nd s
upo n
wh e th e r
the
r e que s t
is
f r om a sys t em s u b r o u t i n e o r a use r p r o c e s s .
Fo r s y s t em s ub r o u t i n e r e q ue s ts , t h e f i e l d s c o nta i n the PC , R 3 , a n d
R4
r eg i s t e r v a l ue s to b e l o a d ed b e fo r e pa s s i ng c o nt r o l t o the s ub r o u t i n e .
Fo r p r o c e s s t i m e r r e qu e s t s , t h e f i e l d s d e f i n e the p r o c e s s
ID o f
the
process
t o r e po r t t h e e v e n t , t h e a d d r e s s o f a n AST r o u t i n e to e x e c u t e
( i f r eque s t ed ) , a nd a n o p t i o n a l A S T pa r am e t e r .
TQE $ Q T IM E i s the quadwo r d abso l u t e s ys t em t i m e a t wh i c h a
pa r t i c ul a r
t i me r - e v e n t
i s t o occur .
TQE $ Q D E LTA i s t h e qu a d wo r d d e l t a t i m e f o r
r ep e a t i ng r e que s t s .
Th e a c c e s s mod e o f the
r e que s t o r
i s s to r ed
in
TQE $ 8 RMO D .
Th e
event
f l ag
t o s e t wh e n the t i me r e v e n t o c c u r s i s
d e f i ned b y TQE $8 E FN .
Th e TQE $ L RQP I D c o n t a i n s t h e p r oc e s s I D o f
the
p r oc e s s
t h a t made the i n i t i a l tTm e r r e q ue s t .
( Th e r e que s t i ng p r o c e s s
i s n o t n e c e s s a r i l y t h e s a m e a s t h e t a rg e t p r o c e s s . )
I f a n AST i s r e q u e s t e d , t h e t i m e r que ue e l em e n t wi l l
be
i nto an A S T c o n t r o l b l o c k ( AC 8 ) wh e n t h e event o c c u r s .

10. 3. 3

r e fo rm a t t ed

T i me r Re q ue s t S e rv i c i ng

I f t h e TQE i s a p r o c e s s t i m e r r eq ue s t ( c r e a t ed
by a
$ S E TIMR s y s t em
s e rv i c e c a l l and i nd i c a t e d by a TQE $ 8 RQTYPE v a l ue o f z e r o ) , t h e n t h e
f o l l o w i ng ope r a t i o n s a r e pe r fo rmed .
1.

Th e e v e n t f l a g a s s o c i a te d wi th th i s t i m e r
event
is
s e t by
u s i ng
the
TQE $ L P I D
a nd TQE $ 8 E FN f i e l d s a nd i nvo k i ng t h e
S C H $ POSTEF r o u t i n e .
A s o f twa r e pri o r i ty i nc r em e n t o f
th r e e
w i l l b e a pp l i ed wh e n t h e p r o c e s s n e x t e x e c u t e s ( Ch a pt e r 8 ) .

I f the t a r g e t p r o c e s s i s n o l o ng e r i n the sys t em , t h e TQE
s i m p l y d e a l l o c a ted wi t ho u t f u r th e r a c t i o n .

O t h e rwi s e , t h e J I 8 $W T QCNT quo t a i s i nc r em e n t e d
to
i nd i c a t e
i m p e nd i ng
the
d el ivery
o f - the
t ime r
event
and
the
d e a l l oc a t i o n o f the TQE .

I f a n AST wa s r e q u e s t e d ( i nd i c a ted by b i t 6 o f TQE $ 8 RQTYPE ) ,
t h e n t h e TQE $ 8 RMOD f i e l d
i s moved
to
TQE $ 8 RQTYPE
to
r e f o rma t the TQE- i n to an AST c o n t r o l b l o c k ( AC 8 ) . -Th e AC8 i s
t h e n q u e ued to the t a rg e t p r o c e s s , i n the a c c e s s m o d e o f t h e
o r ig inal t imer
reque s t ,
by c a l l i ng
the
rout i ne
S C H $ QAST
( Ch a pte r 5 ) .

Wh e n t h e p r o c e s s i ng o f th i s t i m e r que ue e l em e n t h a s
b e e n c ompl e ted ,
t h e s o f twa r e t i m e r r o u t i n e c h e c k s to s e e i f ano th e r TQE e l em e n t c a n b e
r emoved f r om the que ue .
No t e t h a t p r o c e s s t i m e r r e que s t s a r e s t r i c t l y o n e - t i m e r e que s t s .
An y
r e pe t i t i o n o f t i m e r r e que s t s m u s t be i mpl em e n ted wi th i n the r e qu e s t i ng
process .

1 0 -8

TIMER SUPPORT

10 . 3. 4

Sched u l ed Wa k e up

Th e s e c o nd t ype o f t i me r q u e ue e l eme n t i s a s s o c i a t ed
wi th a
r e que s t
fo r
a s c h ed u l ed $WAKE t o a h i b e r na t i ng p r o c e s s .
Th i s t yp e o f r e q ue s t
m a y b e e i th e r o n e - t i m e o r r e pe a t i ng a nd m a y b e r e q ue s t ed by a p r o c e s s
o th e r th a n t h e t a r g e t p r o c e s s .
Th e f o l l o w i ng o pe r a t i o n s a r e pe r f o rm e d fo r s c hed u l ed wa ke TQE s .
1.

Th e t a rg e t p r o c e s s ( i n d i c a te d by TQE $ L P I D )
i s a wa ke ne d
by
e x e c ut i ng
the r o u t i n e SCH$WAKE .
If the t a rg e t p r o c e s s i s no
l o ng e r
in
the
s y s t em ,
the
PC B $W ASTCNT q uo t a
of
the
Ts
r e qu e s t i ng
pr o c e s s
( T QE $ L RQP I D )
i nc r em e n t e d
a nd
�� e
c o n t r o l b l o c k i s d e a l l o c a t e d to nonpaged d ynam i c memo r y .

I f the r e que s t i s a o n e - t i m e r e que s t ( i nd i c a t ed b y a
c l e a r ed
T Q E $ V RE PEAT
bit
in
the
TQE $ 8 RQTY PE
f i e ld ) ,
then
the
d e a l loc a t i o n o p e r a t i o n i s t h e
s ame
as
tha t d e sc r i bed
in
i t em 1 .

I f the r eque s t i s a r e pe a t i ng t ype , th en the r e pe a t
i nterval
( T QE $ Q D E LTA )
i s a d d ed to the r e que st t i me ( T QE $ Q T I M E ) , a nd
t h e t i me r que ue e l emen t i s r e i n s e r t ed i n the t i m e r que ue .

Th e so f t wa r e t i me r r o u t i n e t h e n c h e c k s
to
r e que s t c a n a l s o be pe r f o rmed a t th i s t i m e .

10 . 3 . 5

see

the

t imer

Pe r i o d i c Sys t em P r o c ed u r e s

Th e th i r d t ype o f t i m e r que ue
e l em e n t d e f i n es
a
s ys tem
s ub r o u t i n e
A r e que s t o f
th i s
t ype i s n o t the r e s u l t o f a n y p r o c e s s
r e que s t .
r e qu e s t , b u t i s a s ys tem- r e q ue s t e d t i m e - d e pe nd e n t eve n t .
Th e so f t wa r e
t i m e r i n t e r r upt s e r v i c e r o u t i n e h a nd l e s th i s type o f TQE by
•

TQE $ L FR3 a nd
TQE $ L FR4
f i elds
l o a d i ng R 3 a n d R 4 f r om the
as the TQE $ L_AS T a nd TQE $ L_AST PRM f i e l d s )
( n o rma l l y d e f i ned
a nd

•

the
a JSB
u s i ng
i n s t r uc t i o n
e x e c u t i ng
( no r ma l l y d e f i n ed a s t h e TQE $ L_P I D f i e l d ) .

TQE $ L F PC
-

f i eld

On r e t u r n f r om the s ys tem s ub r o u t i n e , the TQE $V RE PEAT b i t i s
tested .
I f the b i t i s s e t , then the TQE i s r e i n s e r ted i n the t i me r que ue us i ng
the TQE $ Q DE LTA t i me f i e l d .
I f the r e que s t wa s a
n o n r e pe a t i ng
one ,
then
the - t i m e r r o u t i n e i mm ed i a t e l y c h e c k s the t i m e r que ue fo r f u r the r
TQEs to s e r v i c e .
Th e TQE i s n o t d e a l l o c a ted bec a u se the s e r e que s t s d o
not
u s e d yn am i c m emo r y .
Th i s
t ype
of
TQE
is d e f i ned in s t a t i c
nonpag ed po r t i o n s o f s ys tem s pa c e , s uc h a s the mod ul e SYSCOMMON i n the
c a s e of the EXE $T IME OUT s ub r o u t i n e .
r e pe a t i ng
s ys tem
One e x amp l e o f th i s t ype o f r e qu e s t ,
a
execut ion o f
the
is
r e que s t ,
o n c e - pe r - s e c o nd
the
E XE $ T I M E O UT .
1.

Th e r o u t i n e SCH$ SWPWAK E i s c a l l ed
swa ppe r p r o c e s s ( Ch a p t e r 1 4 ) .

1 0-9

po s s i b l y

s ub r o u t i n e
s ub r o u t i n e
a wa k e n

the

T IMER S UPPORT
2.

Th e E XE $ T I M E OUT s u b r o u t i n e upd a t e s the E XE $G L ABST IM f i e l d to
i nd i c a t e t h e pa s s i ng o f o n e s e c o nd o f sys t em upt i m e .

Th e r o u t i n e ERL$WAKE i s c a l l ed to po s s i b l y a wa k e n the
p r o c e s s ( Ch a p t e r 7 ) .

Th i s s ub r o u t i n e s c a n s t h e I /O d a t a b a s e fo r d ev i c e s t h a t h a v e
e x c e ed ed
the i r
t imeout i n terva l s .
D r i v e r s f o r s u c h d ev i c e s
a r e c a l l ed a t th e i r t i m e o u t e n t r y po i n t s a t d ev i c e
I PL .
A
p a t h th r o ug h t h i s s ub r o u t i n e c h e c k s fo r t e rm i n a l t i med r e a d s
t h a t h a v e e x p i r ed .

ERRFMT

Th e TQE f o r th i s s ub r o u t i n e
i s p e rma nen t l y d e f i n ed
in
the mod u l e
SYSCOMMON ,
a nd t h e t i m e r queue i s i n i t i a l i z ed a t boo t s t r a p t i me wi th
t h i s d a ta s t r uc t u r e a s the f i r s t e l emen t i n the que ue .
Th e t e rm i n a l d r i v e r a l s o u s e s a
r e pe a t i ng
sys t em
timer
r o ut i ne
to
i m p l em e n t i t s mo d em po l l i ng .
Th e c o n t r o l l e r i n i t i a l i z a t i o n r o u t i n e i n
t h e t e rm i n a l d r i v e r l o ad s the ex p i r a t i o n t i me f i e l d i n a
TQE
in
the
t e rm i n a l d r i v e r wi th t h e c u r r e n t s ys tem t i m e , s e t s the r e pea t b i t , a nd
l o ad s t h e r e pe a t i n t e r v a l wi t h t h e
SYSBOOT pa r am e t e r
TTYS CANDE LTA .
Wh e n t h e t i m e r r o u t i n e e x p i r e s , i t po l l s e a c h mod em l o o k i ng fo r s ta t e
c h a ng e s .

10 . 4

T IMER S YSTEM S ERVI C E S

Two sys tem s e rv i c e s a r e u s ed to i ns e r t e n t r i e s
in
the
t imer
queue ,
S c h ed u l e Wa k e r e que s t ( $ S C H DWK ) a nd Se t T i m e r r e que s t ( $ S ET I MR ) .
Bo th
of
the s e
s e rv i ces
a r e c o n ta i n ed
in
the mod u l e
SYSSC HEVT .
Two
c ompl em e n t a r y s e r v i c e s d e l e t e
e n t r i e s f r om the t i m e r queue , $CANWAK
a nd
$ CANT I M .
Th e s e s ys t em
s e rv i c e
rout i n es a r e
in
the mod ul e
SYSCANEVT .

10 . 4 . 1

$ S ETIMR Requ e s t s

$ S E T IMR s ys t em s e r v i c e c a l l s p r o d uc e t i m e r que ue e n t r i e s o f the s i ng l e
process
r e que s t
t ype ,
TQE $ C_TMSNG L .
Th e
fo l l o w i ng
s t eps
are
pe r fo rmed .
1.

Th e e v e n t f l ag spec i f i ed a s a n a rg um e n t to the s ys tem s e r v i c e
is
c l e a r ed
in
p r ep a r a t i o n
fo r
s ub s e que n t s e t t i ng
at
e x p i r a t i o n t i me .

Th e r e que s t i s c h e c k e d t o m a k e s u r e tha t
•
•

•

the d e l t a t i me l o c a t i o n i s ac c e s s i b l e by t h e r e que s t o r ,
the
PC B $W A S TCNT o f the
r e que s t i ng
process
is
not
e x c eed ed { i f a n A S T i s to b e a s soc i a t ed w i th th i s t i m e r
r e qu e s t ) , a nd
the J I B $W_T QCNT o f t h e r e que s t i ng j o b i s n o t e x c e ed ed .

A t i m e r q u e u e e l em e n t
i s a l l o c a ted
f r om no npag ed d yn am i c
memo ry a nd
the TQE
i s i ni t i a l i z e d f r om the s ys t em s e r v i c e
a r g umen t s ( d e l ta t i m e , r e que s t t ype , and p r o c e s s I D ) .

1 0- 1 0

T IMER S U P PORT
4.

If the e x p i r a t i o n
t i me
wa s
e x p r e s s ed
as
an
i nterval
(a
n eg a t i v e
a r g um e n t ) , t h e n t h e a b s o l u t e e x p i r a t i o n t i m e o f t h e
r e que s t i s c a l c u l a te d by a d d i ng t h e d e l ta t i m e o f the r eq u e s t
t o t h e c u r r en t sys tem
t i m e , EXE $G Q S Y S T I M E .
Th e a b s o l u t e
e x p i r a t i o n t i m e i s s t o r ed i n t h e TQE $ Q=T I ME f i e l d .

Th e J I B $W T QCNT f i e l d o f t h e po o l ed j ob quo t a s i s d ec r em e n t e d
t o i nd i c ate t h e a l l o c a t i o n o f t h e TQE .

Th e a c c e s s mod e o f the s y s tem s e rv i c e c a l l e r i s s t o r ed i n t h e
TQE $ 8 RMOD f i e l d .
If
a n AST r o u t i ne wa s s p e c i f i ed a s a n
a r g umen t t o t h e $ S E T IMR c a l l , t h e n the p r o c e s s
PC B $W ASTCNT
i s d e c r em e n t e d to i nd i c a t e the f u t u r e AST d e l i v e r y a nd b i t 6
o f TQE $ B_RMOD i s s e t to i nd i c a t e the AST a c c o un t i ng .

Th e AST p a r am e t e r ( r e q u e s t
i d en t i f i c a t i o n )
n um b e r a r g um e n t s a r e c o p i ed to t h e TQE .

Th e TQE i s t h e n i n s e r t ed i n t o t h e t i m e r q u e ue a nd the r o u t i n e
r e turns .

a nd

ev e n t

f l ag

Th e $ CANT IM s ys t em s e rv i c e r emo v e s o n e o r mo r e
t i me r
que u e e l em e n t s
b e fo r e
expi ra t i on .
Two
a rg um e n t s ,
r e que s t
i d e n t i f i c a t i o n /AST
p a r am e t e r a nd a c c e s s mo d e , c o n t r o l t h e a c t i o n s t a k e n by th i s r o u t i n e .
1.

Th e a c c e s s mo d e r e que s t e d
i s m a x i m i zed w i t h t h a t o f
the
caller .
( Th a t
is ,
no
r e que s t s c a n be d e l e t ed fo r a c c e s s
mod e s mo r e p r i v i l eg ed t h a n t h e c a l l e r . )

E a c h TQE i n t h e t i m e r q u e u e tha t m e e t s a l l o f
c r i t e r i a i s r emoved a nd d e a l l o c a t e d .
•
•
•

10 . 4 . 2

the

f o l l o w i ng

Th e p r o c e s s I D o f the $ C ANT IM s ys tem s e r v i c e
t h e same a s the p r o c e s s I D s t o r e d i n the T QE .

cal ler

Th e a c c e s s m o d e o f t h e c a l l e r i s a t l e a s t
a s t h e a c c e s s mod e s to r ed i n the TQE .

p r i v i l eg ed

Th e r e que s t i d e n t i f i c a t i o n/A S T p a r am e t e r a rg um e n t i s
the
s a m e a s t h a t s to r ed i n t h e TQE .
I f the a rg um e n t v a l ue i s
z e r o , t h e n a l l TQEs m e e t i ng t h e f i r s t two
c r i te r i a
are
r emoved .

S c h ed u l ed Wa k e up

Th e l og i c f o r m a n ag i ng s c h ed ul ed wa k e up r eque s t s i s s i m i l a r
to
tha t
fo r
$ S ETIMR r e que s t s .
Two d i f f e r enc e s a r e the ab i l i t y to s p e c i f y
r e pe a t i ng s c h ed u l ed wa k e up r e que s t s a nd the a b i l i t y to sched u l e wa k e up
r eque sts
f o r a n o th e r p r o c e s s .
Th e f o l l o w i ng s t eps c r e a t e a s c h ed u l ed
wa k e up r e q u e s t .
1.

Th e t a rg e t p r o c e s s I D
i s v e r i f i ed
f r om a
sys t em s e rv i c e
a rg um e n t .
If
t h e t a rg e t p r o c e s s i s n o t i n the sys t em , t h e
s c hed u l ed wa k e up r e que s t i s i g no r ed .

I f t h e t a rg e t p r o c e s s e x i s t s , a nd i f the c u r r e n t p r o c e s s
is
s u i ta b l y p r i v i l eg ed ( G ROUP o r WOR LD ) wi th r e s pe c t to i t , t h e n
t h e r e pe a t t i m e i s t e s t e d to d e t e rm i n e wh e th e r the r e que s t i s
a
one- t ime o r
r e pe a t i ng
s c h ed u l ed wa k e up , TQE $ C WKSNG L o r
T QE $ C_WKR E PT o f t h e TQE $ B_RQTYPE f i e l d .

1 0-1 1

TIMER S UPPORT
3.

Th e r e q u e s t e d r e pe a t t i m e i s fo rma t t e d f o r i ns e r t i o n
in
the
TQE .
I f t h e r e pe a t t i m e i s l e s s t h a n 1 0 m i l l i s e c o nd s , i t i s
i n c r e a s e d t o t h a t v a l ue ( th e r e so l ut i o n o f the h a r d wa r e c l o c k
i n t e r r up t )
•

A T QE i s a l l o c a t e d f r om n o npag ed d yn am i c memo r y .

Th e r e pe a t t i m e , r e q ue s t type ,
i n s e r t e d i n to t h e TQE .

I f t h e i n i t i a l s c h e d u l ed
wa k e u p t i m e
i s e x p r e s s ed
as an
i nt e rva l ,
th e
the
ini tial
a b s o l ut e
expi r a t i on
t ime
is
c a l c u l a t e d a s i n $ S ET IMR f r om t h e i n i t i a l d e l t a t i m e a nd
the
c u r r e n t s ys tem t i m e .

Th e AS TCNT q uo t a o f the r eq ue s t i ng p r o c e s s i s d ec r em e n t e d
a c c o un t f o r th e a l l o c a t i o n of t h e TQE .

Th e TQE i s i n s e r te d i n to the t i m e r q u e u e .

a nd

target

process

are

E x p i r a t i o n t i me wi l l c a us e a p r o c e s s wa k e up
to
the t a r g e t p r o c e s s
( Sec t i on 1 0 . 3 . 4 } .
Dea l l o c a t i o n o f t h e TQE o c c u r s a f t e r d e l i v e r y o f a
o n e - t i m e s c h ed u l ed wa k e u p r e que s t o r a s a r e s u l t o f a
$ CANWAK s ys t em
s e rv i c e c a l l .
Th e $ CANWAK s ys t em s e rv i c e c a nc e l s a l l o n e- t i m e a nd
r epe a t s c h e d u l ed
wa k e up
r e que s t s
fo r
a
t a rg e t p r o c e s s .
E a c h c a nc e l l ed
TQE
is
d ea l l o c a t e d to n o n pag ed d yn am i c memo r y a nd
t h e PCB $W ASTCNT o f t h e
i n i tial
r e que s t i ng
process
is
i nc r em e n ted
to- i nd i c a t e t h e
d ea l l o c a t i on .

10-1 2

PART I V

MEMORY MANAG EMENT

" I c o n s i d e r t h a t a ma n ' s b r a i n o r i g i na l l y
is
l i ke
a
l i tt l e
empty a t t i c , a nd yo u h a v e to
s to c k i t wi th s uc h f u r n i t u r e as
yo u c ho o s e .
No w ,
the
ski l l ful
wo r km a n
i s very
c a r e f u l i nd e ed a s to wh a t h e t a k e s
i n to
his
b r a i n- a t t i c .
H e wi l l
h a ve n o t h i ng b u t t h e
to o l s wh i c h m a y h e l p h i m i n d o i ng
h i s wo r k ,
but o f
t h e s e h e h a s a l a rg e a s s o r tm e n t , a nd
a l l i n the m o s t pe r f e c t o r d e r .
It
is
a
m i s ta ke
to
th i n k
tha t tha t l i t t l e r o om h a s
e l a s t i c wa l l s a nd c a n d i s t e nd t o a n y e x t e n t .
De pend
upo n
i t , t h e r e c om e s a t i m e wh e n f o r
ev e r y a d d i t i o n o f
knowl edg e
yo u
f o rg e t
s om e t h i ng
that
yo u
knew b e fo r e .
It is of
h i g h e s t i mpo r ta n c e , th e r e f o r e ,
n o t t o have
u s e l e s s f a c t s e l bowi ng o u t the u s e f u l o n e s . "
A S t ud y i n Sc a r l e t
S i r A r th u r C o n a n Do y l e

CHAPTER 1 1
MEMORY MANAG EMENT DATA STRUCTURES

Vi r t ua l memo r y s uppo r t i n VAX/VM S i s impl em e n ted b y s e v e r a l
d i s t i nc t
p i ec e s o f
the
e x ec u t ive .
Th e
t r a n s l a t i o n- no t-va l i d f a u l t h a nd l e r
( pa g e r ) i s t h e e x c e pt i o n s e r v i c e r o u t i n e th a t r e s po nd s t o pag e
f a u l ts
a nd
b r i ng s p r o c e s s v i r t ua l pag e s i n to m emo r y on beha l f o f a p r o c e s s .
Th e s wa ppe r p r o c e s s k e e ps t h e h i g h e s t p r i o r i t y c omputa b l e p r o c e s s e s i n
phys i c a l
memo r y ,
r emov i ng
tho s e p r oc e s s e s th a t a r e b l o c k e d f o r some
r e a s o n in f a v o r of n o n r e s i d e n t c ompu t a b l e p r o c e s s e s .
Seve r a l
s ys t em
s e rv i c e s
a l low a
p r og r am to e x e r c i s e some cont r o l o v e r i t s b e h a v i o r
wh i l e i t i s e x e c u t i ng .
Th e s ys tem ma i n t a i n s m a n y t a b l e s , s ome
process
s pe c i f i c
a nd
o th e r s
s ys tem wi d e ,
t h a t m u s t b e m a n i pu l a t e d b y the ma j o r c ompo n e n t s o f the
memo r y ma n a g em e n t s ub s ys t em .
B e f o r e we d i sc us s
each
c ompo ne n t ,
we
wi l l d e sc r i b e the s e t a b l e s .
Th e d a t a s t r uc t u r e s a r e p r e s e n t e d i n f o u r
s e pa r a t e s e c t i o n s .
Th e p r o c e s s - s p e c i f i c d a t a ,
f o und m o s t l y
in
the
p r o c e s s h e ad e r , i s d e sc r i b ed f i r s t .
Th e d a ta th a t i s used to a c c o un t
f o r phy s i c a l memo r y , t h e so - c a l l ed PFN d a t a b a s e , i s
then p r e s e n t ed .
Th e
s pe c i a l
s t r uc t u r e s
that
a re
u s ed
f o r g l o b a l pag e s h a v e the i r
p r o c e s s - s pe c i f i c a n a l og u e s b u t
a re
put
i n to
a
s e pa r a t e
sec t ion .
Fi nal l y ,
tho s e
s t r uc t u r e s
th a t s uppo r t the MA 7 8 0 s h a r ed m emo r y a r e
p r e s e n t ed .

11. 1

PROC ESS DATA STRUCTURES

( PROC E S S HEADER )

Th e mo s t i mpo r t a n t p r o c e s s - s pe c i f i c d a ta s t r uc t u r e s th a t a r e
used
by
t h e memo r y m a n a g em e n t s ub s ys t em a r e c o n t a i n ed in th e p r o c e s s h e a d e r
( Fi g ure 1 1 -1 ) .
Th e
process
h e ad e r
conta i n s
all
of
the
p r o c e ss- spec i f i c d a ta
tha t c a n b e r emoved f r om m emo r y wh e n a p r o c e s s
i s o u t swa ppe d .
Th e a d d r e s s o f t h e p r o c e s s h e ad e r
is
s to r ed
in
the
s o f twa r e PCB .
F i g u r e 1 1 - 1 s h ows the po r t i o n s o f t h e
s pe c i a l i n t e r e s t to m emo r y m a n ag em e n t .
o f the p i eces o f
t h e p r o c e s s h e ad e r
p a r am e t e r s sho wn i n t h e f i g u r e .

p r o c e s s h e ad e r
th a t a r e o f
App e nd i x E s h o ws h o w t h e s i ze s
a re
rel a ted
t o the
SYSB OOT

Th e PO and Pl p a g e t a b l e s a r e the l a rg e s t c o n t r i b u to r to
the
s i ze
of
the p r o c e s s h e a d e r
a nd c o n t a i n
the c om p l e t e
d e s c r i pt i o n o f t h e v i r t ua l a d d r e s s s pa c e c u r r e n t l y b e i ng u s e d
by t h e p r o c e s s .

Th e wo r k i ng s e t l i s t d e sc r i b e s the
s ub s e t o f p r o c e s s pag e
t a b l e e n t r i e s t h a t a r e c u r r e n t l y v a l i d b u t c a n b e c om e i nv a l i d
i n the f u tu r e .
PFN-ma pped pag e s a nd pag e s i n
sha r ed m emo r y
a r e v a l i d f o r t h e e n t i r e t i m e tha t they a r e m a pped a nd d o no t
a ppe a r i n t h e wo r k i ng s e t l i s t .

1 1-1

MEMORY MANAG EMENT DATA STRUCTURES
3.

Th e p r o c e s s s e c t i o n t a b l e c o n t a i n s i n fo rma t i o n
p a g e r wh e n a pa g e r e s i d e s i n a n imag e f i l e .

used

the

B e c a use t h e s i z e s o f t h e d i f f e r e n t p i e c e s o f
the
process
h e ad e r v a r y f r om s y s t em to sys t em , t h e r e mus t b e s o m e me thod
of d e te rm i n i ng wh e r e e a c h p i ec e
is
l o c a ted .
Po i n t e r s o r
i nd i c e s i n t h e f i x ed po r t i o n o f t h e p r o c e s s h e ad e r s e r v e th i s
p u r po s e .
P r o c e s s a c c o un t i ng i n fo rm a t i o n , s om e o f wh i c h
is
used b y the
pag e r
o r the swa ppe r , i s a l s o l o c a t e d i n th i s
a rea .

Th e r e a r e s e v e r a l a r r a ys t h a t c o n t a i n i n fo rm a t i o n abo u t e a c h
p r o c e s s h e a d e r pag e .
Th i s i n fo rma t i o n i s u s e d b y t h e swa ppe r
wh e n i t i s n e c e s s a r y to o u t swa p t h e p r o c e s s h e ad e r .

Where Size o f This
P ortion is Stored

SY S B OOT Parameters Affecting
Size of Thi s Portion
Fix ed Portion of Process Header

PHD$1LLENGTH
(not a SYSBOOT parameter)
PQLDWSDEFAULT

SWP$GW_WSLPTE
pages

P ROCSECTCNT

Process Section Table
Empty Pages

WSMAX,PQL_DW S DEFAULT
Size in bytes of
e ntire proce s s header

Arrays f o r Process Header Pages

SWP$GW_EMPTPTE
p ages
SWP$GW_BAKPTE
pages

PO Page Table

•

SGN$GL_PTPAGCNT
pages

VIRTUALPAGECNT

P 1 Page Table

Figure 1 1-1

11.1. 1

D i sc r e t e Po r t i o ns o f t h e P r o c e s s H e a d e r

P r o c ess Pag e Ta b l e s

Th e p r o c e s s page t a b l e s a r e t h e f i r s t s t e p i n to mem o r y m a n ag em e n t d a t a
s t r uc t u r e s t a k e n b y e i th e r h a r d wa r e o r s o f twa r e .
Th e pag e t ab l e e n t r y
c o n t e n t s a r e used b y t h e h a r d wa r e t o t r a n s l a t e a v i r t ua l
add ress
to
i ts phys i c a l c o un t e r pa r t .
Pag e t a b l e e n t r y c o n t e n t s a r e a l so used by
the pag e r wh e n t r a n s l a t i o n f a i l s t o d e t e rm i n e the ph ys i c a l l o c a t i o n o f
a n i nv a l i d pag e .

1 1-2

MEMORY MANAG EMENT DATA STRUCTURE S

F i g u r e 1 1 - 2 s h ows t h e po r t i o n o f t h e p r o c e s s h e ad e r d ev o ted to the
PO
a nd
P l pag e tabl e s .
I t a l s o shows tho s e f i e l d s i n t h e f i x ed po r t i o n
t h a t a r e u s ed to l o c a t e d i f f e r e n t p i e c e s o f t h e P O o r P l pag e t a b l e .
1.

Th e P O pag e t a b l e c o n t a i n s pag e tab l e e n t r i e s fo r
al l
pag e s
c u r r e n t l y d e f i ned i n P O s pa c e .
Th e numb e r o f pag e s i s s to r ed
i n o f f s e t PHD $ L_P O LR ( a n d moved i n to PR $ P O LR by LDPC TX wh e n
the process
is
s e l ec ted
fo r e x e c u t i on) .
Th e v i r t ua l pag e
n umb e r o f t h e f i r s t unma pped pag e i n P O s pa c e , the
i nd e x
of
the
fi rst
nonex i s t e n t
POPTE ,
is
s to r ed
at o ffset
PHD$L FRE P OVA .

I n a s i m i l a r m a nne r , t h e P l pag e t a b l e c o n t a i n s pag e
t ab l e
e n t r i e s f o r the pag e s c u r r e n t l y d e f i n ed i n P l s p a c e .
L i ke P l
space
i tsel f ,
the Pl
pag e
t a b l e g r o ws
towa r d
sm a l l e r
add resses .
To s i m p l i f y t h e ad d r e s s t r a n s l a t i o n l og i c , t h e P l
b a s e r eg i s t e r c o n t a i n s t h e v i r t ua l a d d r e s s o f t h e pag e
t ab l e
e n t r y t h a t wo u l d m a p v i r t ua l ad d r e s s 4 0 0 0 0 0 0 0 .
Th e P l l e ng th
r eg i s t e r c o n t a i n s the n umbe r o f Pl pag e t a b l e e n t r i e s tha t d o
no t
ex i s t .
Th e v i r t ua l pag e n um b e r o f t h e h i gh a d d r e s s e nd
o f the unm a pped po r t i o n o f P l s pa c e ( F i g u r e 1 1 - 2 )
is
s t o r ed
a t o f f s e t PHD$ L FR E P lVA .

Th e num b e r o f pag e t a b l e e n t r i e s a v a i l a b l e fo r the
e x pa n s i o n
of
e i ther
PO
space o r
Pl
s pa c e
is
s t o r ed
i n o f fset
PHD$ L FRE PTECNT .
Th e n um b e r o f e n t r i e s h e r e d e pe nd s o n
the
S Y S B OOT p a r am e t e r VI RTUA L PAG E CNT , m i nus t h e c u r r e n t s i z e s o f
t h e P O a n d P l pag e t a b l e s .

PCB$L_PHD
(PHD)

Process Header

�

F REPOVA
FREPTECNT
FREP 1 VA

��

These four values
are stored i n the
H a rdware PCB, a
p a rt of the fixed
portion of the
process h eader

POBR
Virtual address
POBR + 4* POLR
(F REPOVA )

(FREP 1 VA )
P 1 BR +4* P 1 LR
P 1 BR+(4 * 221 )
Virtual address

{

to �

�
-

1��

POBR
POLR
P 1 BR
I P 1 LR
Rest of Fix ed Portion
WSL, PST, Empty Pages,
PHD page Arrays

PO Page Table
(Maps Virtual Addresses from
0 to FREPOVA- 1 )
Room for Expansion of either

��

}

PO Page Table
or
P1 Page Table
"""

...

Fix ed Portion of
Process Header

P Page Table
(Maps Virtual Addresses from
(FRE P 1 VA+ 200,J to 7FFFFFFF)

F REPTECNT e ntries
•

End of Process Header

F i g u r e 1 1 -2

P r o c e s s Pag e Ta b l e s
1 1-3

POLR entries

(2 2 1

P 1 LR) e ntries

MEMORY MANAG EMENT DATA S TRUCTURE S

Wh e n a p r o c e s s r e f e r e n c e s a v i r t ua l a d d r e s s
tha t
i s not val id ,
it
i nc u r s a
pag e f a u l t , a n e x c e p t i o n t h a t t r an s f e r s c o n t r o l to the pag e
f a u l t h a nd l e r .
O n e o f t h e e x c e pt i o n - s p e c i f i c pa r a me t e r s p u s h e d
o n to
the s t a c k
i s t h e i nv a l i d v i r t ua l a d d r e s s .
Th i s a d d r e s s e n a b l e s t h e
pag e r t o r e t r i e ve t h e
pag e
tab l e e n t ry
fo r
the
i nv a l i d
pag e
to
d e te rm i n e wh e r e t h e pag e i s l o c a ted .
Th e pag e t a b l e e n t r i e s f o r i nv a l i d pag e s a r e s e t up i n s uc h a wa y t h a t
t h e y c o n ta i n
e i th e r the l o c a t i o n o f the pag e o r a po i n t e r to f u r th e r
i n f o rma t i o n about t h e pag e .
Figure 1 1-3
s h o ws t h e d i f f e r e n t
f o rms
tha t a n
i nva l i d pa g e t a b l e e n t r y can t a k e .
A va l i d pag e t a b l e e n t r y
i s i nc l ud ed fo r c om pa r i s o n .
No t i c e
tha t b i t s
<31>
( va l id
bit) ,
< 3 0 : 27 >
( p r o t ec t i o n
cod e ) ,
a nd < 2 4 : 2 3 > ( o wn e r a c c e s s mod e ) h a v e the
s am e m e a n i ng in a l l po s s i b l e f o rm s of pag e
tab l e
entr y .
Ta b l e 1 1 - 1
l i s t s t h e s ym bo l i c a nd n um e r i c f o rms o f po s s i b l e p r o t e c t i o n c o d e s .
Th e pag e r u s e s b i t s 2 6 a nd 2 2 i n
the
i nv a l i d
pag e
tab l e
e n t r y to
d i s t i ng u i sh
the d i f f e r e n t PTE f o rms .
( Be c a us e p r o t ec t i o n c h e c k s a r e
mad e b e fo r e the v a l i d
bit
i s c h ec k e d ,
PTE < 3 0 : 2 7 > m u s t c o n t a i n a
p r o t ec t i o n c od e , e v e n wh e n the v a l i d b i t i s c l e a r . ) Th e va r i o u s f o rms
a r e d e s c r i b ed in the f o l l o w i ng pa r ag r a ph s , s t a r t i ng a t the b o t tom o f
the f i g u r e .

11. 1.1.1
P r o c e s s S e c t i o n Ta b l e I n d e x - Wh e n a pag e i s l o c a ted
i n an
imag e
file,
the pag e t a b l e e n t r y c o n ta i n s a n i nd e x i n to th e p r o c e s s
s ec t i o n tabl e .
Th i s i nd e x l o c a t e s a
proc ess sec t i on
tab l e e n t r y ,
wh i c h c o n t a i n s i n f o rm a t i o n a b o u t wh e r e t h e i m ag e f i l e i s l o c a ted , a nd
wh i ch b l o c k i n th e i m ag e f i l e c o n t a i n s
the
f a u l t i ng
pa g e .
Co n t r o l
b i t s i nd i c a t e wh e th e r t h e s e c t i o n i s a g l o b a l se c t i o n ( p r o c e s s s e c t i o n
t a b l e e n t r i e s a l wa ys h a v e th i s b i t c l e a r ) , wh e th e r i t i s wr i t a b l e , a nd
wh e the r
the s e c t i o n i s c o py o n r e f e r e n c e .
Process sec t i on tab l e s a r e
d i sc us s e d i n Se c t i o n 1 1 . 1 . 3 a nd f u r th e r i n Ch a pt e r 1 2 .

1 1 . 1 . 1 . 2 Pag e F i l e V i r t u a l B l o c k Numbe r - Wh e n a v i r t ua l pag e r e s i d e s
in a
pag e f i l e , i t s a s s o c i a t ed page t a b l e e n t r y c o n ta i n s t h e v i r t ua l
b l o c k n um b e r wi th i n t h e pag e f i l e wh e r e t h e pag e
is
l oca ted .
Wh i c h
pag e
file
is
in
u s e b y th i s
process
is
i nd i c a ted by the f i e l d
PHD$ B PAG F I L i n t h e p r o c e s s h e a d e r .
PHD$ L PAG F I L ,
a
l o ng wo rd
f i eld
that - c onta ins
ove r l a ps
ze ro
in
i ts
l o w-o r d e r -th r e e b y t e s a nd
PHD $ B PAG F I L i n the h i g h - o r d e r byte , i s t h e o r i g i n a l c o n t e n t s o f
any
e n t r y t h a t a c q u i r e s a pag e f i l e ba c k i ng s to r e a d d r e s s .
A
pag e -t ab l e
v i r t ua l b l o c k n um b e r o f z e r o i nd i c a t e s th a t a b l o c k i n the
pag e
file
h a s no t ye t b e e n r e s e r v e d .

1 1 . 1 . 1 . 3 G l o ba l Pag e Ta b l e I n d e x - An i nv a l i d p r o c e s s pag e m a pped
to
a g l ob a l
pag e c o n t a i n s an i nd e x i n to the g l ob a l pag e t a b l e , wh e r e an
a s s o c i a t ed g l o b a l pa g e t a b l e e n t r y c o n t a i n s f u r the r
i n f o rma t i o n
used
to
l oc a t e
the
pag e .
Th e g l o b a l
pag e
tab l e
is
d e sc r i b e d
in
Sec t i on 1 1 . 3 .
Pa g e f a u l t s i nv o l v i ng g l oba l
pag e s a r e d i s c u s s e d
in
Ch a p t e r 1 2 .

1 1 -4

.---� M o d i f y B i t
3 1 30
V a lid PTE

Protection
C o de

�

�
Different
Forms of
I nv a l id PTE s

2 5 24 23 22

Protection

Code

1--

(See

0 Table 1 1 - 1 ) 1

1
30

� X
O w ne r
Access
Mode

�
�
�
�
X

0
0
Owner
Access
Mode

- S e t by H a rd w a r e o n Write o r
Mod i f y Access to P a ge
.-....� window B i t - I nd ic a t es Page Ma pped by PFN r./il«� l"'��
20 1 9 1 8 1 7 1 6 1 5

2 5 24 23

Page is Active
and V alid

P a g e Fra me Number ( PF N )

tz.:l

�
�

Demand Zero
Page

Invalid Global
Page

P a g i n g F i l e V i rt u a l B l o c k N u m b e r

Page is in
Paging File

D
z
R
0

c
R
F

Page is in

Image F ile

Proc e s s S e c t i o n Ta b l e I n d e x

---�

TY PO B i t - Low O rd e r Bit of PTE Typ e
....��� TY P 1 Bit - H i g h O rd e r B i t of PTE Type
........
,.
�
_
V a l i d B i t - P a g e Table E n t ry V a l i d B i t

....___

.._______

D i f f e r e n t Fo rms o f Pag e Ta b l e En t r y

>
2:

/���

Global P a g e Table Index

(
J r

Pogo Is In
Transition

P a g e F ra m e N u m b e r ( P F N )

XXX

Figure 1 1-3

3
0
�
�

'='
>
�
>

Ta b l e 1 1 -1
Mem o r y Ac c e s s P r o t e c t i o n Co d e s i n Pag e Ta b l e En t r i e s

1-'
1-'

0'1

Pro tec t i o n

S YM B O L

No Ac c e s s Al l owed
Re s e r v ed
Ke r n e l Wr i t e ( Ke r n e l Re ad }
Ke r n e l Re ad ( N O Wr i t e }
Us e r Wr i t e ( Us e r Re ad }
Ex ec u t i v e Wr i t e { Ex e c u t i v e Re ad }
E x e c u t i v e Re ad , Ke r n e l Wr i t e
E x e c u t i v e Re ad (NO Wr i t e )
S u p e r v i so r Wr i t e ( S u p e r v i so r Re ad )
S u p e r v i so r Re ad , Ex e c u t i v e Wr i t e
S u pe r v i s o r Re ad , Ke r n e l Wr i t e
S u pe r v i so r Re ad ( N O Wr i t e )
Us e r Re ad , Supe rv i so r Wr i t e
U s e r Re a d , Ex e c u t i v e Wr i t e
Us e r Re a d , Ke r n e l Wr i t e
Us e r Re ad (NO Wr i t e )

PR T$C NA
PR T $ C -R E S ERVE D
PRT $C KW
PRT$C -KR
PRT$C-UW
PRT$C -EW
PRT $ C -ERKW
PRT$C -E R
PRT$C -SW
PR T$C -S R EW
PR T$C -S RKW
PRT$C -S R
PR T$C =U R SW
PR T$C U R EW
PR T $ C -URKW
PRT$C UR

b i n a r y v a l ue

=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=

Pr o t e c t i o n Ma s k

0 000
0001
0010
0011
0100
0 1 01
0110
0111
1 000
1 001
1 010
1 011
1 1 00
i l Ol
1110
1111

PTE $C NA

PT E $ C KW
PT E $C -KR
PT E $C -UW
PT E $ C -EW
PT E $C ERKW
PT E $ C -ER
PT E $C -SW
PTE $C -SREW
PTE $C-SRKW
PT E $C =S R
PT E $C URSW
PT E $ C UREW
PT E $ C =URKW
PT E $ C UR

=
=
=
=
=
=
=
=
=
=
=

=
=
=

00000000
1 0000000
18000000
20000000
28000000
3 0000000
38000000
40000000
48000000
50000000
58000000
60000000
68000000
70000000
78000000

{1}

I f a g i v en ac c e s s mod e ha s wr i te ac c e s s t o a spec i f i c pag e , t h e n tha t a c c e s s
mod e a l so h a s r e ad a c c e s s to tha t pag e .

(2)

I f a g i v en a c c e s s mod e c a n r e ad a spec i f i c pag e , t h e n
a c c e s s mod e s c a n r e ad the same pag e .

al l

mo r e

p r iv i l eg ed

(3)

I f a g i ven ac c e s s mod e c a n wr i te a s pe c i f i c pag e , then a l l
a c c e s s mod e s c a n wr i t e the same pag e .

mo r e

p r iv i l eg ed

(4)

Ac c e s s t h a t i s i mpl i ed ( r a t h e r
than
expl i c i tl y
p r o tec t i o n nam e ) i s i nc l ud ed i n pa r en the s e s .

pa r t

the

s ym bo l i c

3:
�
3

"
t<

3:
>
z
>

G'l
�
3:
�
1-i

0
>

1-i
>

(/)
1-i
"
c
()
1-i
c
"
�
(/)

MEMORY MANAGEMENT DATA STRUCTURES

11. 1. 1. 4
Pag e in Tr an s i t i o n - Th e r e a r e s ev e r a l d i f f e r en t s i t ua t i o n s
wh e r e
a
v i r tua l pag e c a n b e a s s o c i a t e d w i th a ph ys i c a l pag e , a n d ye t
t h e pag e i s n o t v a l i d , n o t i n th e p r o c e s s wo r k i ng s e t .
Fo r
e x am p l e ,
wh e n a pag e i s r em o v e d f r om a p r o c e s s wo r k i ng s e t , i t i s no t d i sc a r d ed
b u t put o n to the f r e e pag e l i s t o r mo d i f i ed pag e l i s t .
Such a pag e i s
c a l l ed
a
t r an s i t i o n pag e .
Th e p r o c e s s pag e t a b l e e n t r y c o n t a i n s a
PFN , b u t t h e v a l i d b i t i s c l e a r .
Th e
two
type b i t s
( PTE < 2 6 >
and
PTE < 2 2 > ) a r e a l s o c l e a r .
Tr a n s i t i o n pag e s a r e d e sc r i b e d by t h e e n t r i e s fo r
th e
phys i c a l
pag e
fo und
in
the
PFN d a ta b a s e ( S e c t i o n 1 1 . 2 ) .
I n pa r t i c u l a r , t h e PFN
S TATE a r r a y d e s i g n a t e s the pa r t i c u l a r t r an s i t i o n
s ta te
the
ph ys i c a l
pag e i s i n .

1 1 . 1 . 1 . 5 Demand Z e r o Pag e s - A s pe c i a l fo rm o f
the
t r a n s i t i o n pag e
t ab l e
e n t r y fo rma t h a s
a
z e r o i n t h e PFN f i e l d .
Th i s i nd i c a t e s a
s p e c i a l fo rm o f pag e c a l l ed d em a n d - a l l o c a t e , z e r o - f i l l o r d em a nd
zero
fo r
sho r t .
Wh e n a
pag e
f a ul t o cc u r s
fo r s uc h a pag e , t h e pag e r
a l l o c a t e s a phys i c a l p ag e , f i l l s the pag e wi th z e r o s , i n s e r t s the
PFN
i n to
the
PTE , s e t s the v a l i d b i t , a nd d i sm i s s e s the e x c e p t i o n .
( Fo r
th i s r e a so n , a nd a s e c ond
r ea son
e x pl a i n e d b e l o w
( Sec t i on 1 1 . 2 . 5 ) ,
phys i c a l pag e z e r o c a nno t b e u s e d by memo r y manag em e n t . )

11. 1. 2

Wo r k i ng S e t L i s t

Th e wo r k i ng s e t l i s t c o n t a i n s the s ub s e t o f
a p r o c e s s ' s pag e
tab l e
e n t r i e s th a t a r e c u r r e n t l y v a l i d .
Th e wo r k i ng s e t l i s t i s u s e d b y the
pag e r to d e t e rm i n e wh i c h v i r t ua l pag e to d i sc a r d
( to m a r k
i nv a l i d )
wh e n
it
i s n e c e s s a r y t o t a k e a phys i c a l pag e awa y f r om t h e pr o c e s s .
Th e wo r k i ng s e t l i s t i s a l s o used by t h e swa ppe r
to
d e t e r m i n e wh i c h
v i r t ua l
pag e s n e ed t o b e wr i t t e n t o t h e swa p f i l e wh e n t h e p r o c e s s i s
o u t swa pped .
F i g u r e 1 1 - 4 sh ows the wo r k i ng s e t l i s t i n th e p r o c e s s h e ad e r , and
the
var i o us
f i elds
in
the f i x e d po r t i o n th a t l o c a t e d i f f e r e n t p i e c e s o f
the l i s t .
E a c h o f th e s e f i e l d s , i n c l ud i ng the quo ta f i e l d s ,
c o n ta i n s
a
l o ng wo r d
i nd e x
( m ul t i pl y c o n t e n t s
by
f o u r o r u s e c o n t e x t i nd e x
a d d r e s s i ng ) to the wo r k i ng s e t l i s t e n t r y i n que s t i o n .

1 1 . 1 . 2 . 1 D i v i s i o n o f the Wo r k i ng S e t L i s t - Th e wo r k i ng
set
l i st
c o ns i s t s o f
th r e e p i e c e s .
Th e quo ta f i e l d s d e te rm i ne h o w l a rg e the
wo r k i ng set l i s t may g r ow in r e s po n s e t o d i f f e r e n t wo r k i ng
set
s i ze
a d j u s tmen ts .
1.

Th e pe rma nen t l y l o c k e d po r t i o n o f the wo r k i ng s e t l i s t
( f rom
W S L I S T to WS LOC K ) c o n t a i n s t h e pag es tha t a r e fo r e v e r a pa r t
o f the p r o c e s s wo r k i ng s e t .
Th e s e i n c l ud e
•

the k e r n e l s t a c k ,

•

the P l po i n te r p ag e ,

•

th e P l p a g e ta b l e pag e tha t m a ps the k e r n e l s t a c k a nd the
P l po i n t e r pag e ,

1 1 -7

MEMORY MANAG EMENT DATA STRUCTURE S
•
•

(

the P l p a g e ta b l e p a g e th a t m a ps the
p r o c e s s h e a d e r , a nd

w i nd o w

the

the p r o c e s s h e a d e r pag e s t h a t a r e no t pag e
ta b l e p a g e s .
Th i s
i n c l ud e s
the
f i x e d po r t i o n , t h e wo r k i ng s e t l i s t ,
the p r o c e s s s e c t i o n t a b l e , a n d the p r o c e s s h e a d e r
pag e
a r r a ys .
•

PCB$ L-PHD
(PHD)

)

A ll working s et list
fields in the f i x e d
portion a re longword
indice s f rom the
top o f the
process header
P H D + 4*WSLIST

WSAUTH
WSDY N
WSLAST

WSLIST
WSLOCK
WSNEXT

DFWSCNT

WSOUOTA

��

•

PHD + 4*WSLOCK

Rest of Fix ed Portion
of Process Header

Fix ed Portion of
Process Header

��

Pages Permanently
Locked in
Working Set
Pages Locked by
User Request
( $ LKWSET )

PHD + 4*WSDY N

Working
Set List

Working Set
List
Dynamic Space

PHD + 4*WSNEXT
PHD + 4*WSLAST

..,

PHD + 4*WSOUOTA

Room for Ex pansion of WSL

, ...

Figure 1 1 -4

Rest of Process Header

Wo r k i ng Se t L i s t

Th e po r t i o n o f the wo r k i ng s e t l i s t b e t we e n WS LOC K a nd WS DYN
conta ins
all
pag e s
that
are
l o c k ed
by
user
r e qu e s t ,
s pec i f i c a l l y w i th
th e
Lo c k
Pag e s
i n Wo r k i ng
Se t s ys t em
service .

Th e d yn am i c po r t i o n o f the wo r k i ng s e t i s th e po r t i o n th a t i s
u s ed
fo r
pag e
r e p l a c eme n t .
It
i s d e l i m i t ed b y WSDYN a nd
W S LAS T .
Th e e n t r y t h a t wa s
j u s t put
i n to
th e
tabl e
is
po i n t ed
t o b y WSN E XT .
Th e r e p l a c em e n t a l g o r i t hm , expl a i n ed
i n d e ta i l i n Ch a p t e r 1 2 , i s a m o d i f i ed
f i r s t- i n ,
f i r s t-out
s c h em e .

Th e d yn am i c b o t tom o f t h e wo r k i ng s e t l i s t i s WS LAST .
Pa r t
of
the
i m a g e r e s e t l og i c , i n vo k e d a t i m ag e e x i t , r e s e t s the
end o f the wo r k i ng s e t l i s t to DFWSCNT .

Th e max i m um v a l u e th a t WS LAST c a n a t ta i n i s g i ven b y WS QUOTA .
WSQ UOTA c a n
be a l t e r ed i n i n t e r a c t i v e a nd b a t ch j o bs by the
SET WORK I NG S E T/QUOTA c o mmand .
Th e m e a n i ng s o f
th e
va r i o u s
wo r k i ng
set
l i s t q uo t a s a nd
l im i ts a r e
s umm a r i z e d
in
Ta b l e 1 3 - 1 .
1 1 -8

Ta b l e 1 1 - 2
PFN Da t a Ba s e Ar r a ys

G l ob a l Ad d r e s s o f
Po i n t e r to
St a r t o f Ar r a y

S i ze o f Ar r a y
E l em e n t

Sys t em V i r t ua l Ad d r e s s
o f Pa g e Ta b l e En t r y

PFN $A L_PTE

Lo ngwo rd Ar r a y

Ba c k i ng Sto r e Ad d r e s s

PFN $AL_BAK

Lo ng wo rd Ar r ay

( Fi g ur e 1 1 -1 0 )

Ph ys i c a l Pa g e S t a t e

PFN$AB STATE

By t e Ar r a y

( Fi g ur e 1 1 -1 1 )

Pag e Typ e

PFN $AB TYPE

By t e Ar r a y

( Fi g ur e 1 1 -1 2 )

Fo r wa rd Li n k

PFN $AW F L INK

Wo rd Ar r a y

( Fi g u r e 1 1 -1 3 )
Ov e r l a ys the
SHRCNT a r r a y

Ba c kwa r d Li n k

PFN $AW B L I NK

Wo rd Ar r a y

( Fi g ur e 1 1 -1 3 )
Ov e r l a ys the
WSLX Ar r a y

Re f e r e n c e Co un t

PFN $AW R EFCNT

Wo rd Ar r a y

G l o b a l Sh a r e Co u n t

PFN $AW S HRCNT

Wo rd Ar r a y

Ov e r l a ys t h e
FLINK Ar r a y

Wo r k i ng Se t Li s t Ind ex

PFN $AW WS LX

Wo rd Ar r a y

Ov e r l a ys t h e
B L I NK Ar r a y

Swa p Fi l e Vi r t ua l Bl o c k Num b e r

PFN $AW SW PVB N

Wo rd Ar r a y

Ar r a y E l em e n t Co n t e n t s

....
....
I
\0

Commen t

MEMORY MANAG EMENT DATA S TRUCTURE S
Th e f o rma t o f a wo r k i ng
set
l i st
entry
i s shown
in
Figure 1 1-5.
No t i c e tha t the v i r t ua l pag e n um b e r i s c o nta i ned i n the uppe r 2 3 b i t s ,
i n the s a m e l o c a t i o n th a t v i r t ua l pag e n um b e r s a r e
f o und
i n v i r t ua l
add resses .
Th i s a l l o ws
th e WS L E t o b e pa s s ed t o s e v e r a l u t i l i t y
r o u t i n e s a s a v i r t ua l
add r e s s ,
wh e r e
the
byte o f f s e t b i t s
( WS LE
control
b i ts ) a r e n o t l ooked a t .
Th e m e a n i ng s o f the v a r i o u s c o n t r o l
b i t s a r e a s f o l l o ws .
1.

Wh e n the v a l i d b i t i s c l e a r , t h e wo r k i ng s e t l i s t
entry
b e u s ed w i t h o ut r emov i ng a pag e f r om t h e wo r k i ng s e t .

Th e type f i e l d ( a d up l i c a t e o f the c o n t e n t s o f the
PFN TYPE
a r r a y ) d i s t i ng u i sh e s pag e s th a t r e q u i r e d i f f e r e n t ac t i o n wh e n
r emoved f r om a p r o c e s s wo r k i ng s e t .

Th e PFN L o c k b i t i nd i c a t e s t h a t
th i s pag e
is
locked
i n to
ph ys i c a l m emo r y wi th t h e Lo c k Pag e s i n Memo r y s ys t em s e rv i c e .
S u c h pag e s a r e a l s o l o c k e d
i n to
the p r o c e s s wo r k i ng
set .
( Th e wo r k i ng s e t l o c k b i t i s n o t s e t b u t th e WS LEs a r e m o v ed
i n to t h e po r t i o n o f t h e wo r k i ng s e t l i s t th a t c o n t a i n s pag e s
l o c k e d b y u s e r r eque s t . )

Th e Wo r k i ng S e t Lo c k b i t
i nd i c a t e s tho s e
pag e s
tha t a r e
pe rmane n t l y o r d yn am i c a l l y l o c k e d i n to the p r o c e s s wo r k i ng
set .
Th e o n l y pag e s t h a t c a n b e d yn am i c a l l y l o c k e d a r e
pag e
t a b l e pag e s tha t m a p c u r r en t l y v a l i d pag e s .
( Pa g e s th a t a r e
p e rma n e n t l y l o c k e d o r l o c k e d by u s e r r e que s t a l so h a v e
th i s
b i t s e t i n th e i r wo r k i ng s e t l i s t e n t r i e s . )

9 8 7 6

5 4

1 0

Virtual Page Number

Saved Modify Bit
( G o odpage bit) Keep in WS for One More Pass .,___..
Page Locked in Working Set 4-----..
Page Locked in M emory .,_____..
Page Type .,_______..
WSL Entry Valid •---..,.
Code

Page Type

Process Page

System Page

Global Read-Only Page

Global Read/Write Page

Process Page Table Page

Global Page Table Page
Figure 1 1-5

Fo r m a t o f Wo r k i ng S e t L i s t En t r y

1 1-10

can

MEMORY MANAG EMENT DATA STRUCTURES

Th e G o o d p a g e b i t i s u s ed
b y the
swa ppe r
to d e sc r i b e
the
d i f f e r en t
type s
of
wo r k i ng s e t l i s t e n t r i e s f o r o u tswapped
processes .
I t s use is f u r th e r d e sc r i b e d in Ch a p t e r 1 4 .

Th e Mod i f y b i t i n t h e WS L E
i s u s e d wh e n th e
process
is
o u t s wa pped
t o r e c o r d the l og i c a l OR o f the mod i f y b i t i n the
p a g e t a b l e e n t r y a nd th e s av e d mod i f y b i t in
th e
PFN S TATE
a r ray .

11. 1.3

P r o c e s s S e c t i o n Ta b l e

Th e p r o c e s s s e c t i o n
t a b l e c o n ta i n s p r o c e s s
sec t i on
tab l e
entr ies
( PS TE ) ,
d a t a s t r uc t u r e s t h a t a r e u s ed t o l o c a t e i m ag e s e c t i o n s wi th i n
imag e f i l e s .
Th e l o c a t i o n o f t h e p r o c e s s s e c t i o n
t a b l e wi th i n
the
p r o c e s s head e r
i s p i c t u r ed
in F i g u r e 1 1 - 6 .
O f f s e t PH D $ L P S TBAS OFF
c o n t a i n s the byte o f f s e t t o the b o t tom o f t h e p r o c e s s
s e c t ion
tab l e .
Al l
process
sec t ion
t a b l e e n t r i e s wi th i n the t a b l e a r e th e n l o c a t e d
th r o ug h n eg a t i v e l o ng wo r d i nd i c e s f r om th e b o ttom o f the PS T .
Wh e n i t i s n e c e s s a r y t o e x p a nd the wo r k i ng s e t l i s t
i n to
the
a r ea
a l r e a d y o c c up i ed
b y t h e p r o c e s s s e c t i o n tab l e ( Ch a p t e r 1 2 ) , s pa c e i s
a l l o c a ted f r om th e emp t y pag e a r e a ( i f i t ex i s t s ) , the e n t i r e
PST
is
moved
i n to
the
a l l o c a ted
spa c e ,
a nd
a n e w v a l ue o f PS TBASOFF i s
i n s e r t e d i n to the f i x ed po r t i o n o f
the
process h e ad e r .
Al l
o the r
r e f e r ences
to i nd i v i d ua l p r o c e s s s e c t i o n t a b l e e n t r i e s a r e una f f e c ted
b y th i s c h a ng e .
Th e
f o rm a t o f a
process
sec t i o n
t ab l e
entry
is
p i c t u r ed
in
F i g u r e 1 1 -7 .
Th e
i mpo r t a n t
f i e l d s i n the PS TE a s f a r a s l o c a t i ng a
b l o c k i n a n i m a g e f i l e a r e t h e f o l l o wi ng .
1.

Th e WCB po i n t e r l o c a t e s t h e w i ndow c o n t r o l
block
for
the
i mag e
file.
Th e WCB c o n t a i n s the m a pp i ng i n f o rma t i o n tha t
r e l a t e s v i r t ua l b l o c k n um b e r s i n a
file
to
l og i c a l
block
n umb e r s o n a v o l um e .

Th e s t a r t i ng
v i r t ua l
pag e
n umbe r
fo r
the
sec t i o n ,
wh e n
s ub t r a c ted f r om t h e v i r t ua l pag e numbe r o f t h e f a u l t i ng pa g e ,
g i v e s t h e pag e o f f s e t i n to the s e c t i o n .

Th e s ta r t i ng v i r t ua l b l o c k n um b e r o f the s e c t i o n i s a d d ed
to
the
d i f f e r e n c e c om p u t ed in s t ep 2 to g i v e the v i r t ua l b l o c k
n um b e r o f t h e f a u l t i ng pa g e wi th i n the imag e f i l e .

11 . 1 . 4

P r o c e s s H e a d e r Pag e A r r ay s

Wh e n a p r o c e s s h e a d e r
is
o u t s wa pped ,
s ome
i n f o rma t i o n a b o u t
each
p r o c e s s h e a d e r pag e mus t b e s t o r e d i n the o u t s wa pped p r o c e s s h e a d e r .
Th e p r o c e s s h e ad e r pag e a r r a y s p r ov i d e a n a r e a wh e r e th i s
i n fo rm a t i o n
c a n b e s to r ed ( F i g u r e 1 1 - 8 ) .
Two o f t h e a r r a ys , th e BAK a r r a y a nd the
W S L X a r r a y , s a ve i n fo rm a t i o n f r om the PFN d a t a base abo ut each p r o c e s s
h e ad e r
pag e i n t h e wo r k i ng s e t .
Th e o th e r two a r r a ys k e e p s t a t i s t i c s
a b o u t e a c h pa g e t a b l e
pag e .
Th e s e
f o u r a r r a ys a r e d e s c r i b ed
in
g r e a t e r d e ta i l i n Ch a p t e r 1 4 .

1 1-1 1

(

Process Header

)

P C B $ L_ P H D ---.
(PHD)
P S T L A S T a n d PSTF R E E a re
b o t h n e g a t i v e l o n g w o rd
i n d i c e s f ro m the b o t t o m
o f the proce s s sec tion t a bl e

PSTL A ST

PSTBASOFF
PSTF R E E

STB A S M A X

Fixed Portion,
Working Set List

R e s t of

....
....
I
....

PHD + PSTBASOFF
+ 4i•IPASTLAST
(End of Process Section Table)

Room for Expansion of PST

Process
Section
Table

F i x e d P o r t i o n of
Proc e s s H e a d e r

Movable Boundary
between WSL and PST

All proc ess se c tion
table entries are
located via a
(negative) longword
index from the base
of the PST.
I

� -·�---�
l
--"""'i��--Pro c ess Header Page Arrays,
PO Page Table, P 1 Page Table
PHD 4 •.PSTBASMAX ---�J�
"'���41-- The process se c tion table
(Longword Ind ex)
c annot ex tend beyond
this point
PHD + PSTBASOFF
(Byte I ndex)
+

F i g u r e 1 1 -6

P r o c e s s S e c t i o n Ta b l e

Pointer to Cha nnel Control Block
B a c kward Link
Index
Page
Fault
Cluster

Forward Link
Index

Control F l a g s Word in Proce s s / Global Sectio n Table Entry

Starting Virtual
Page Number (22 bits)

Address of Window Control Bloc k
I-'
I-'
I
I-'
w

Base Virtual Block Number
for this Section

:><==:

Control
Flags

I
I

I I
I
I

Global
...._...,.

Demand Zero
..____...,.

Writable

....,. Shared Memory Global
.._
L...--..,. On Delete Pending List (Set)
On Normal List (Cieart
L---..,. Access Mode for Writing
____

L-----------....

�---�

Count of PTEs R eferencing
This Section
Number of Pages in
This Section

F i g u r e 1 1 -7

Copy on Reference

L a yo ut o f P r o c e s s S e c t i o n Ta b l e En t r y

Access Mode of Section
Permanent
System Global (Set)
Group Global (Clear)

MEMORY MANAG EMENT DATA STRUCTURES

PCB $ L _ PHD
( PHD)

WSLX

BAK

��

��
PTWSLELCK

Fixed Portion of
Process Header

PTWSLEVAL

PHD +4* WSLX
( Longword Index )

•

PHD +4* BAK
( Longword Index )

•

PHD + PTWSLELCK
( Byte Index )

•

PHD + PTWSLEVAL
( Byte Inde x )

•

PTCNTVAL

PTCNTLCK

PTCNTMAX

PTCNTACT

Rest of Fixed Portion,
WSL, PST,
Empty Pages

��

WSL Index Save Area
(One Word for Each
Process Header Page)

Process Header
Page Arrays

Backup Address Save Area
(One Longword for Each
Process Header Page)

( Eight bytes per
process header
page, rounded up
to page boundary )

Locked WSLE Counts Array
(One Byte per Page Table Page)
(-1 => none)
Valid WSLE Counts Array
(One Byte per Page Table Page)
(-1 => none)

IV
F i g u r e 1 1-8

11. 2

��

PO and P1 Page Tables

P r o c e s s He ad e r Pag e Ar r ays

PFN DATA BAS E

Th e memo r y m a n ag em e n t d a ta s t r uc t u r e s i nc l ud e
i n fo rm a t i o n a bo u t
the
av a i l a b l e pag e s
of
phys i c a l m emo r y .
Th e f a c t th a t th i s i n fo rm a t i o n
m u s t b e a v a i l a b l e wh i l e
the pag e
i s b e i ng
u s ed
pr e v e n t s
th i s
i n f o rma t i o n
f r om b e i ng
s t o r ed i n t h e pag e i t s e l f .
I n a d d i t i o n , th e
c a c h i ng s t r a t eg y o f the f r e e pag e l i s t a nd mod i f i ed pag e l i s t r e qu i r e s
phys i c a l
pag e
i n f o rm a t i o n t o b e
a v a i l a b l e even wh e n pag e s a r e no t
c u r r e n t l y a c t i v e a nd v a l i d .
A po r t i o n o f the n o n pag ed
execut ive
is
s e t a s i d e f o r th i s a c c o un t i ng d a t a , c a l l ed the PFN d a t a b a s e .
A PFN d a t a b a s e e n t r y i s n o t a t a b l e o r i e n t e d s t r uc tu r e , l i ke m a n y o f
the o th e r
e x e c ut i v e d a t a
s t r uc t u r e s .
Ra t h e r ,
th e
same
i t em o f
i n f o rma t i o n abo u t a l l phys i c a l pag e s i s s to r ed i n s uc c e s s i v e
e l em e n t s
of
an a r ra y ( Fi g u r e 1 1 - 9 ) .
Th e pag e f r am e n umbe r i s t h e n u s e d a s a n
i nd e x i n to e a ch a r r a y .
Ta b l e 1 1 - 2 l i s t s e a c h i t em o f
i n f o rma t i o n
in
the
PFN d a t a b a s e ,
i n c l ud i ng th e g l o b a l name o f the po i n t e r to th e
b eg i nn i ng o f e a c h a r r a y .

1 1-14

PFN data for
Process or Global
Page In Process
Working Set

I
p N

1-'
1-'
I
1-'
U1

A rr a y
of
L o n g w o rd s

A rr a y
of
Words

A rray
of
Words

A rr a y
of
Longwords

Array
of
Words

These t w o a rrays
a re o v e rl a id

Figure 1 1-9

PFN d ata for page
on free or m odified
page list
P F N Da t a Ba s e Ar r ays

MEMORY MANAGEMENT DATA STRUCTURES

11. 2. 1

PTE Ar r a y

Th e PFN PTE l o ngwo r d a r r a y c o n ta i n s the s ys t em v i r t ua l a d d r e s s of
the
pag e t a b l e e n t r y t h a t m a ps e a c h ph y s i c a l pag e .
PFN PT E a r r a y e l em e n t s
f o r g l o b a l pag e s po i n t to t h e g l o b a l pag e t a b l e e n t r i e s .

11. 2. 2

BAK A r r a y

Th e PFN BAK l o ng wo r d a r r a y s to r e s the o r i g i na l PTE c o n t e n t s .
Wh e n a
phys i c a l
pag e
is
r e u s ed ,
i ts
PTE m u s t b e
r e s e t to i t s o r i g i n a l
contents .
Th e PFN PTE a r r a y e l em e n t l o c a t e s
th e
PTE t h a t m u s t b e
Th e BAK a r r ay e l em e n t i nd i c a t e s wh a t g o e s b a c k i n to th e PTE .
a l te r ed .
F i g u r e 1 1 - 1 0 shows t h e two d i f f e r e n t c o n t e n t s o f a BAK a r r a y e l ement .
I n t e rm s o f po s s i b l e pag e t a b l e e n t r y c o n t e n t s ( F i g u r e 1 1 - 3 ) , the o n l y
f o rms o f PTE tha t c an g o i n to t h e BAK a r r a y a r e a
p r o c e s s s ec t i on
t a b l e i nd ex o r a pag e f i l e v i r t ua l b l o c k n um b e r .

2 4 2322 2 1

P a ge File Index

0 0

Page File Virtual Block Number

24 2322 2 1

Process PTE < 2 1 :0>

2 4 2322 2 1

Global PTE < 2 1 :0 >

(This form o n l y appears in IRP while read i s in progress.
I t does not a ppear in PFN BAK array element. )
Figure 1 1-1 0

11. 2. 3

Po s s i b l e Co n t e n t s o f PFN BAK Ar r a y E l em e n t

STATE A r r a y

Th e PFN S TATE a r r a y ( F i g u r e 1 1 - 1 1 ) i nd i c a t e s
the
phys i c a l
s ta t e o f
e a ch
phys i c a l
pag e .
Th e
l ow th r e e b i t s c o n t a i n the pag e l o c a t i o n
c od e .
Th e uppe r b i t i n a S TATE a r r ay e l em e n t i s e x t r em e l y
impo r ta n t .
It
i s the s e t t i ng o f th i s b i t th a t d e t e rm i n e s wh e th e r a phys i c a l pag e
i s put o n to the f r e e pag e l i s t o r the mod i f i ed pag e l i s t wh e n the pag e
i s r e l ea sed .
Wh e n a pag e i s r emoved f r om a p r o c e s s wo r k i ng s e t , t h e s e t t i ng o f
the
mod i fy b i t
in
t h e pag e t a b l e e n t r y i s l og i c a l l y ORed i n to the saved
mod i f y b i t i n the S TATE a r r a y .
Th e s e t t i ng of t h e mod i f y b i t
in
the
t ab l e e n t r y i s o n l y o n e wa y i n wh i ch t h e s a v ed mod i f y b i t c a n b e
pag e
set .
Th e e x e c u t i v e r o u t i n e th a t l o c k s d own pag e s f o r d i r e c t I /0 s e t s
th i s
b i t fo r
all
pag e s t h a t c o n t a i n r e ad b u f f e r s .
Pag e f a u l t s f o r
c o py- o n - r e f e r e n c e pag e s c a u s e th i s b i t to b e s e t a s pa r t o f
t h e pag e
f aul t
r eso l ut io n
to
f o r c e a wr i t e to the pag e f i l e wh e n the pag e i s
r emoved f r om the p r oc e s s wo r k i ng s e t .
11-16

MEMORY MANAG EMENT DATA STRUCTURES

..____....�

STATE A r ray Element
Loc a tion of Page ( See Below)

.._---t� D e l e t e PFN Contents When

Reference Count Goes To 0

..._--1� Saved Modify Bit from PTE

Code
0

Location
Page on Free Page List

Page on Modified Page List

Page on Bad Page list

Release Pending (when reference count goes to 0, put page on
free or modified page list)

Read Error Occurred While Page Read Was in Progress

Write in Progress by Modified Page Writer

Read in Progress by Page Fault Handler

Page is Active and Valid

Figure 1 1-1 1

Co n t e n t s o f PFN S TATE Ar r a y E l em e n t

Th e wo r d " d e l e t e " h a s a s pec i a l m e a n i ng
wh en r e f e r r i ng
to
phys i c a l
pa g e
contents .
Wh e n
the r e f e r e n c e c o un t o f a phys i c a l pa g e g o e s to
ze r o , a l l t i e s w i th a v i r t ua l
page
( P FN PTE
a r r ay contents )
are
d e s t r o yed .
Th e
phys i c a l
pag e
i s th e n put a t the f r o n t o f the f r e e
pag e l i s t wh e r e i t w i l l b e r e used a s qu i c k l y a s po s s i b l e .

11 . 2 . 4

TYPE Ar r ay

Th e PFN TYPE a r r a y ( F i g u r e 1 1 - 1 2 ) d i s t i ng u i sh e s t h e d i f f e r e n t t ype s o f
v a l i d pa g e s .
Th e r e a s o n f o r th i s d i s t i nc t i o n i s th a t e i t h e r the pag e r
o r s wa ppe r m u s t t a k e d i f f e r e n t a c t i o n d ep e nd i ng o n wh a t type
o f pag e
i s b e i ng a c ted o n .
Th e c o l l i d ed pa g e b i t i n th e TY PE a r r a y e l em e n t i s
s e t wh e n a pag e f a u l t o c c u r s wh i l e t h e pag e i s a l r e a d y b e i ng
read
in
f r om
i t s b a c k i ng s t o r e a d d r e s s .
Co l l i d ed pag e s a r e d e sc r i b e d b r i e f l y
i n Ch a p t e r 1 2 .

11. 2.5

Fo rwa rd and Bac kwa r d L i n k s

Th e th r e e pag e l i s t s ( f r e e pag e l i s t , m o d i f i ed pag e l i s t , a nd b a d pag e
l i st )
mus t a l l
b e d o ub l y l i n ked l i s t s b e c a u s e a n a r b i t r a r y pag e i s
o f te n r emoved f r om t h e m i d d l e o f the l i s t .
Howe v e r , t h e l i n k s c a nno t
ex i s t
in
t h e pag e s them s e l v e s b e c a u s e the o r i g i na l c o n t e n t s o f pag e
mus t be prese rved .
Two wo r d a r r a ys , t h e F L I NK a r r a y a nd
th e
BLINK
a r ra y ,
c o n ta i n e l em e n t s
tha t a r e
i n t e r p r e t e d a s t h e ph ys i c a l pag e
numbe r s o f the s uc c e s s o r a n d p r ed e c e s s o r to a g i v e n ph ys i c a l p ag e .

1 1-1 7

MEMORY MANAGEMENT DATA STRUCTURES

TY P E Arr a y E l e m e n t
----� Page Type

( See below )

----� Collided Page

( Empty COLPG state
when page read completes )
..._--� Bad Page Bit ( When Reference
Count = 0, put page on Bad Page List)
..._
....� Report Event on 1/0 Completion
__________

Code

Page Type

Process Page

System Page

Global Read-Only Page

Global Read/Write Page

Process Page Table Page

Global Page Table Page

Figure 1 1 -1 2

C o n t e n t s o f PFN TYPE A r r ay E l em e n t

A z e r o i n o n e o f t h e l i n k f i e l d s i nd i c a t e s the e n d o f the l i s t ( a nd i s
n o t a po i n t e r to ph ys i c a l pag e z e r o ) .
Fo r th i s r e a so n , phys i c a l pag e
ze r o c a nno t b e u s e d i n a n y d yn am i c f unc t i o n b y VMS b u t m a y b e ma pped
by
some
s y s t em v i r t ua l
pag e
tha t
is
a l wa ys r e s i d e n t .
Th e u s u a l
c o n t e n t s o f phys i c a l
pag e
zero
a re
the
Re s t a r t
Pa r ame t e r
Block
( Ch a pt e r 2 1 ) .
F i g u r e 1 1 - 1 3 shows a n e x ampl e o f pag e s o n the f r e e
l i st ,
a l o ng
wi th
the
c o r r e s pond i ng
F L I N K a nd
B L I N K a r r ay e l em e n t s .
Th e STATE a r r ay
e l em e n t s fo r a l l o f t h e s e pag e s c o n t a i n
ze ro ,
i nd i c a t i ng
th a t
the
phys i c a l pag e s a r e o n t h e f r e e pag e l i s t .

11. 2. 6

REFCNT Ar r ay

Th e PFN REFCNT a r r ay c o un t s t h e n um b e r o f r e a so n s wh y a
pag e
sho u l d
no t b e p u t o n to
th e
f r ee
or
mod i f i ed pag e l i s t .
On e r e a s o n f o r
i nc r em en t i ng th e r e f e r e n c e c o un t i s
tha t a
pag e
is
in a
process
wo r k i ng s e t .
Pag e s a r e l o c k e d d own f o r d i r e c t I /O b y i nc r emen t i ng the
r e f e r e n c e c o un t .
I /0 c ompl e t i o n a nd wo r k i ng s e t r e p l a c em e n t u s e
the
same
rout i ne
to
d e c r em e n t the
r e f e r e n c e c o un t .
I f the r e f e r en c e c o un t g o e s to ze r o ,
t h e phys i c a l pag e i s r e l e a s ed to the f r e e o r m od i f i e d
pag e
l i st a s
i nd i c a ted
by
the
s a v ed mod i f y b i t
in
the
PFN S TATE a r r a y .
Ma n i pu l a t i o n s o f t h e r e f e r e nc e c o u n t a r e i l l us t r a t ed i n th e d i sc us s i o n
o f pag i ng d yn am i c s i n Ch a p t e r 1 2 .

1 1 -1 8

MEMORY MANAG EMENT DATA STRUCTUR E S

Head o f
Free Page List
•
•
•

::PFN$AW_BLINK

::PFN$A W_FLINK

BLINK
PFN
array J _

FLINK
PFN
array J ----

28
15
5

5
10
15

15
33
11

20
25

5
10
15
20

previous
30
11

30
35

Tail o f
Free Page List

STATE
·array J

::PFN$AB_STATE

..._..-

•
•
•

Fi g ur e 1 1 -1 3

11.2.7

E x ampl e o f F r e e Pag e L i s t Sh o w i ng L i n kag e Me thod

SHRCNT Ar r ay

A s e c o nd fo rm o f r e f e r en c e c o un t i s k e p t fo r g l o b a l
pa g e s .
Th e
PFN
S HRCNT a r r a y c o un t s the n um b e r of p r o c e s s pag e t a b l e e n t r i e s tha t a r e
m a ppe d to a pa r t i c u l a r g l o b a l pag e .
Wh e n the S HRCNT f o r a
pa r t i c ul a r
p ag e g o e s
f r om
z e r o t o one ,
the
r e f e r e n c e c o un t i s i n c r em e n t e d .
Fu r th e r add i t i o n s to th e s h a r e
c o un t d o n o t a f f e c t
th e
refe rence
c o un t .
As t h e g l o b a l pag e i s r emoved f r om t h e wo r k i ng
set o f
each process
m a pped
t o t h e pag e , t h e s h a r e c o u n t i s d e c r em e n t e d .
Wh e n t h e s h a r e
c o un t f i n a l l y r e ac h e s z e r o , t h e r e f e r e n c e c o un t f o r the pag e
i s a l so
d e c r e m e n ted .
Wh e n a phys i c a l pag e h a s a n o n z e r o s h a r e c o un t , i t c a nno t b e o n o n e o f
the
pag e l i s t s .
Th e f o rwa r d a nd b a c k wa rd l i n k wo r d s a r e n o t n e ed e d .
Th e g l oba l
sha r e count a r r a y ove r l ays
the
f o r wa r d
l ink a rray .
( PFN$AW F L I N K a n d PFN $AW S HRCNT a r e the s ame g l oba l l o c a t i o n i n s ys t em
s p a c e . ) -Th e g l o b a l sh a r e-c o u n t i s o n l y u s ed fo r g l o b a l pa g e s .
Th e S H RCNT a r r a y i s u s e d f o r a s e c o nd p u r po s e wh e n t h e
ph ys i c a l
pag e
i n qu e s t i o n i s a p r o c e s s p a g e t a b l e pag e o r a g l o b a l pag e t a b l e pag e .
I n e i th e r o f th e s e c a s e s , t h e a r r a y e l ement c o u n t s
t h e n umbe r
of
a c t i ve
pag e
tab l e
e n t r i e s i n the p r o c e s s o r g l o b a l pag e t a b l e pag e .
Th i s i s the m e a s u r e th a t , wh e n i t pa s s e s f r om z e r o to no n z e r o ,
c a us e s
p r o c e s s pag e
t a b l e pag e s t o b e d yn am i c a l l y l o c k e d i n to t h e p r oc e s s
wo r k i ng s e t a nd c a u s e s g l oba l pag e t a b l e pag e s t o b e l o c k e d
i n to
the
s y s tem wo r k i ng s e t .
1 1-19

MEMORY MANAG EMENT DATA STRUCTURES

11. 2. 8

WS LX A r r a y

The wo r k i ng s e t l i s t i nd e x a r r a y c o n ta i n s a n i nd ex i n to a
process o r
s ys tem wo r k i ng ? e t l i s t
fo r
v a l i d pag e s .
Th e c o n t e n t o f a n a r r a y
e l em e n t i s a l o ng wo r d i nd e x f r om th e b eg i nn i ng o f t h e p r o c e s s
{or
sys t e m ) h e ad e r t o th e wo r k i ng s e t l i s t e l em e n t i n que s t i o n .
B e c a u s e a phys i c a l pag e th a t i s i n s om e wo r k i ng s e t i s n o t o n o n e o f
the
pag e
l i sts ,
t h e l i n k wo r d s a r e a v a i l a b l e fo r o th e r us e s .
Th e
wo r k i ng s e t l i s t
i nd e x
a r r a y ov e r l ays
t h e b a c kwa r d
l i nk a r ray .
{ PF N $ AW B L I NK a nd
PFN $AW WS LX a r e the same g l o b a l l o c a t i o n i n s ys t em
s p a c e . ) -Th e WS LX a r r a y i s no t used f o r g l o b a l pag e s .

11.2.9

SWPVBN Array

Th e swa p v i r t ua l b l o c k � um b e r a r r a y is used to s uppo r t t h e o u t s wa p o f
a
p r o c e s s wi th
I /0
1 n p r og r e s s .
Wh e n s u c h a n o u t swa p o c c u r s , t h e
v i r t ua l b l o c k n umbe r i n t h e swa p f i l e wh e r e the l o c k e d d o wn pag e wo u l d
go
is
r e c o rd ed i n th e SWPVB N a r r a y .
Th e mod i f i ed pag e w r i te r c h e c k s
th i s a r r a y f o r n o n z e r o c o n te n t s a nd , i f n o n z e r o , d i v e r ts t h e pag e f r om
i ts
no rm a l
b ac k i ng s to r e ad d r e s s to the d e s i g na t ed b l o c k i n th e swa p
file .

11. 3

DATA STRUCTURES FOR G LOBAL PAG ES

Th e t r e a tm e n t of g l ob a l pag e s
is
not
a wh o l e
lot
d i f fe rent
f r om
p r o c e s s p r i v a te pag e s .
Ho we v e r , t h e s ys tem i s r e qu i r ed to k e e p some
s ys t em w i d e d a ta base of t h e v a r i o u s g l oba l pag e s in t h e s ys tem .

11 . 3 . 1

G l o b a l Se c t i o n De s c r i p to r

Wh e n a g l o b a l se c t i o n i s c r e a t e d , a s t r uc t u r e c a l l ed a g l o ba l
section
is
a l l o c a ted
f r om pag e d d yn am i c m emo r y a nd l o ad ed
d e sc r i pto r
{GSD)
w i th i n f o r ma t i o n
tha t d e sc r i b e s
the
sec t ion
{ Fi g ur e 1 1 - 1 4 ) .
Th e
i n fo rma t i o n a bo u t the s e c t i o n s to r ed i n the G S D i s o n l y u s e d wh e n the
s e c t i o n i s c r e a t ed or d e l e t ed , o r wh en some p r o c e s s a t tempts to map to
the s e c t i o n .
Th e pag e r d o e s n o t use th i s d a ta s t r uc t u r e .
Th e G S D i s l i n k ed i n to o n e o f two G S D l i s t s tha t the s ys t em ma i n t a i n s .
Al l
sys t em g l oba l
s ec t i ons a r e
put
i n to o n e l i s t .
G r o up g l o b a l
s e c t i o n s { i nd e pe nd e n t o f g r oup n umb e r ) a r e put i n to
the
o the r
l i st .
Th e g l o b a l
s e c t i o n ta b l e i nd e x f i e l d con t a i n s an i nd e x t h a t a l l o ws a
s e c o nd s t r uc t u r e c a l l ed a g l o b a l s e c t i o n ta b l e e n t r y to be l o c a t ed .

11. 3.2

Th e Sys tem H e a d e r and G l o ba l S e c t i o n Ta b l e En t r i e s

Th e s ys tem ma i n ta i n s two d a t a
s t r uc t u r e s
for
i tsel f
th a t pa r a l l e l
s t r uc t u r e s ma i n ta i ne d f o r e a c h p r o c e s s i n the s ys tem .
Th e s ys t em PCB
a n d s ys tem h e ad e r a r e u s ed by the pag e r to a l l o w pag e f a u l ts of s ys tem
pag e s to
be
t r e a t ed
a l mo s t
i d e n t i c a l l y to pag e f a u l t s f o r p r o c e s s
pag e s .

1 1-2 0

MEMORY MANAG EMENT DATA S TRUCTURES

R e g u l a r G l o b a l S e c t i o n D e s c riptor
\

G S D Forw a r d Link

Size

\ Ex t e nd e d G l o b a l S e c t i o n D e sc r i p t o r
\

UIC o f Creator o f S e c tion
UIC of File Owner

This portion of a GSD
appears in extended
GSDs (used for
map-by-PFN) and
shared memory GSDs
(Figure 1 1-27)

G lobal Section
Table Index

Pro tection
Mask

Global Section ldent
count
Sec tion Name

( u p t o 15 charac ters )
( co u n t e d ASCII string)

�---�- !
Section Flags
I
Figure 1 1-1 4

for M a p - b y - P F N G lo b a l S e c ti o n s

l
.,. ..,

R e g u l a r Global
S e c t 1. o n D e s c n. p t o r

B a s e PFN

'r-'

N u m ber o f P a g e s i n Section

Reference Count

L a yo u t of G l o b a l S e c t i o n De s c r i p to r

Th e s ys tem h e ad e r ( F i g u r e 1 1 - 1 5 ) c o n ta i n s the wo r k i ng
set
l i st
th a t
g o v e r n s pag e r e p l a c em e n t f o r s ys tem pag e s .
Th e s e c t i o n t a b l e a r e a i n
t h e s y s tem h e a d e r c o n t a i n s s e c t i o n t ab l e e n t r i e s f o r the
i m ag e
fi les
th a t c o n t a i n pag e a b l e s ys tem p ag e s .
Th e s e i nc l ud e th e e x e c u t i v e i m a g e
SYS . EX E , RMS . E XE , a nd t h e s ys tem m e s s a g e f i l e S YSMSG . E XE .
Th e s e c t i o n t a b l e a r e a i n the s y s tem h e ad e r se r v e s a
s e c o nd
pu r po s e .
Wh e n a g l o b a l s e c t i o n i s c r e a t ed , a s e c t i o n tab l e e n t r y th a t d e s c r i b e s
t h e g l ob a l i m a g e f i l e i s c r ea t ed a nd p l a c ed i n to
the g lobal
s ec t i o n
tabl e ,
a s t h i s a r e a i n the s y s t em h e ad e r i s c a l l ed .
Th e fo rma t o f a
g l ob a l s e c t i o n t a b l e e n t r y ( F i g u r e 1 1 - 1 6 ) i s n e a r l y i d e n t i c a l
to
the
f o rm a t o f a p r o c e s s s e c t i o n t a b l e e n t r y .
Th e o n l y d i f f e r e n c e i s th a t
the f i r s t l o ng wo rd po i n ts t o the g l o ba l s e c t i o n d e sc r i p to r ( i n s t e ad o f
the c h a n n e l c o n t r o l b l o c k ) .
G l o b a l s e c t i o n t a b l e e n t r i e s a r e a c c e s sed i n e x a c t l y t h e s ame wa y a s
p r o c e s s s e c t i o n ta b l e e n t r i e s , w i th a n eg a t i v e l o ng wo rd i nd e x f r om the
b o t tom of t h e g l ob a l s e c t i o n t a b l e .
Th e g l oba l s e c t i o n t a b l e i nd ex i n
the g l o b a l
s e c t i o n d e sc r i p to r
i s s uc h a n i nd e x , a s s o c i a t i ng a G S TE
wi th a GSD.

11-21

M M G $ G L_SY S P H D
( PHD)

--+1

1
' r'

,r'

P S T L A S T a n d PSTF R E E
are both negative
l o n g w o r d i n d i c e s f ro m
the bottom of the
g l o b a l s e c t i o n t a bl e

PSTFREE

��

PSTLAST

Rest o f Fixed Portion,
System W o r k i n g S e t List
Room f o r E x p a n s i o n of

PHD + PSTBASOFF
+ 4 ' PSTLAST
( E n d of Global Section Table )

, ..

II(

GSTE

Table

...

, ..,

Fix ed Portion of

Syste m Header

Boundary b e t w e e n
System working set
l i s t a nd g l o b a l
s e c t i o n t a ble

Last Allo c a t e d GSTE

Section

Figure 1 1-1 5

��

Global S e c t i o n Table

Global (System )

P H D + PSTB A S O F F
( B yte Index )

PST B A S O F F

System P a g e T a b l e

All global section
t a ble e n t ries a re
loc a t e d v ia a ( ne g a t i v e )
long word i n d e x f ro m
the b a s e o f the G S T
•

,.�,

Th e Sy s t em He a d e r Co n t a i n i ng t h e Sys t em Wo r k i ng S e t
L i s t a nd t h e G l o b a l Se c t i o n Ta b l e

M EMORY MANAG EMENT DATA S TRUCTURES

Global Sec tion Descriptor Address
Forward Link
Index
Starting Virtual
Page Number (22 bits)
Pointer to Window Control Block
(for Virtual to Logical Mapping)
Base Virtual Block Number
for this Section
Control Flags
Count of PTEs Referencing
This Section
Number of Pages in the Section
Page
Fault
Cluster

Figure 11-16

11. 3. 3

L a yo u t o f G l o b a l o r Sys t em S e c t i o n Ta b l e En t r y

G l oba l Pag e Ta b l e E n t r i e s

A t h i r d s e t o f d a t a i s a l so c r e a t ed f o r
e ach g l ob a l
sec t i on .
Each
pag e
in
the g l ob a l s e c t i o n i s d e sc r i b e d by a g l o b a l pag e t a b l e e n t r y
i n t h e g l oba l pag e t a b l e { F i g u r e 1 1 - 1 7 ) .
Th e pag e r u s e s g l o b a l
pag e
tab l e
entr ies
j u s t l i k e p r o c e s s pag e t a b l e e n t r i e s t o l o c a te g l o b a l
pa g e s .
G l o b a l pag e t a b l e e n t r i e s a r e r e s t r i c t ed to
i l l us t r a t ed i n F i g u r e 1 1 - 3 .

s ub s e t

the

fo rms

Th e g l o ba l pag e t a b l e e n t r y c an b e v a l i d , i nd i c a t i ng t h a t t h e
g l o b a l pag e i s i n a t l e a s t o n e p r o c e s s wo r k i ng s e t .

Th e g l o b a l pag e t a b l e
entry can
i nd i c a t e
some
trans i t i on
s ta te .
Th e PFN S TATE a r r a y i nd i c a te s wh i c h t r a n s i t i o n s t a t e
i n t h e u s ua l m a n n e r .

Th e g l o b a l pag e c a n b e i n a g l o b a l i m ag e f i l e , i n wh i c h c a s e
the g l o b a l
pag e t a b l e e n t r y c o n ta i n s a g l o b a l s e c t i o n t ab l e
i nd e x .

No t e t h a t g l o b a l d em a n d z e r o pag e s d o n o t c on t a i n a
PFN o f
zero .
Ra t h e r , t h e G PT E c o n t a i n s a G S TX a nd h a s the DZ R O b i t s e t i n the G PT E .
S uc h a pag e wi l l n o t r eq u i r e a r e ad a t t h e i n i t i a l
faul t .
Th e pag e
wi l l
b e m a r k e d a s mo d i f i ed a nd wr i t t e n b a c k to the g l o b a l imag e f i l e
b y t h e mod i f i ed pag e wr i t e r .

1 1 -2 3

MEMORY MANAG EMENT DATA STRUCTURES

MMG$GLSYSPHD:

=••t---4�
System
Header

MMG$GLSPTBASE: :

··�---�-.

System
Page
Table
•
•

MMG$GLGPTE: :

•

··�---.-.

Global
Page
Table
•

•
.

Global Page Table Entry
GPTE
GPTE

Global Page Table Entries May
Indicate Pages That Are:

1. Valid

2. In Transition
3. In a Global Image File.
In this case, the
Global Page Table Entry
contains an Index into
the Global Section Table
in the System Header.
·

Global Page Table Entries are
located with a virtual page
number from the beginning
of the System Page Table.

GPTE
GPTE
GPTE
GPTE
GPTE
•

Figure 11-17

11. 3.4

Lo c a t i o n o f G l o b a l Pa g e Ta b l e a t Vi r t ua l End
of Sys tem Pag e T a b l e

G l oba l Pag e Ta b l e and Sys t em Pag e Ta b l e

G l o b a l p a g e t a b l e e n t r i e s a r e l o c a ted i n e x a c t l y t h e same m a n n e r
as
process
or
s ys t em pag e
table
entr i e s .
Lo c a t i o n MMG $G L G PTBA S E
c o n ta i n s t h e add r e s s o f the
base
of
the g l obal
pag e
t a b le .
Al l
r e f e r e nc e s
to g l o b a l p a g e t a b l e e n t r i e s use wh a t c a n be tho ug h t o f a s
a v i r t ua l pag e n um b e r a s a n i nd e x i n to th e g l ob a l pag e t a b l e .

1 1-2 4

M EMORY MANAG EMENT DATA STRUCTUR E S

Th e i n te r e s t i ng th i ng to n o t e about th i s a pp r o a c h i s th a t the b a s e
of
the g l ob a l
page
tab l e c o i n c i d e s w i t h
the b a s e o f t h e sys tem pag e
tabl e .
Fu r the r , th e v i r t ua l pag e n um b e r s t h a t a r e
used
as
i nd i c e s
i n to
t h e g l o b a l pag e t a b l e a r e sys t em v i r t ua l pag e n umbe r s .
In fac t ,
wh e n l o o k i ng a t s y s t em v i r t ua l a d d r e s s s pa c e , t h e g l o b a l
pag e
tab l e
s i mpl y a ppe a r s
a s a n e x t e n s i o n t o the s y s tem pag e t a b l e .
Th e g l o b a l
pag e t a b l e i nd e x a s s o c i a t e d w i th t h e f i r s t g l o b a l pag e i s o n e g r ea t e r
th a n t h e l a rg e s t s ys t em v i r t ua l pag e n um b e r fo r a g i v e n c o n f i g u r a t i o n .
Th i s l og i c a l e x te n s i o n o f t h e
s ys tem p a g e
tab l e
ex i s t s
o n l y wh en
l o o k i ng
at
s ys t em v i r t ua l a d d r e s s s pa c e .
Th e g l o b a l pag e t a b l e d o e s
n o t e x i s t i n phys i c a l pag e s a d j a c e n t t o t h e sys tem pag e
tab l e .
Th e
s y s tem
l e ng th
r eg i s t e r
o n l y r e co r d s t h e numb e r o f r e a l s y s t e m pa g e
t a b l e e n t r i e s , n o t t h e l og i c a l ex t e n s i o n s .
I n o th e r
wo r d s ,
global
pag e s a r e
n o t m a pped
i n to sys t em v i r t ua l ad d r e s s s pa c e a n d a r e no t
a c c e s s i b l e th r o ugh s y s t em v i r t ua l ad d r e s s e s .
Th i s p s e ud o e x t e n s i o n to
the
s ys tem pag e
t a b l e i s o n l y a v a i l a b l e to the so f twa r e r o u t i n e s i n
t h e m emo ry m a n ag em e n t s ub s ys t em .
F i g u r e 1 1 - 1 8 s h ows how t h e g l o b a l pag e t a b l e
relates
to
the
s ys t em
pag e t a b l e .
I t a l s o shows t h e r e l a t i o n s h i p be twe e n the g l o b a l s e c t i o n
d e s c r i p t o r , th e g l ob a l s e c t i o n ta b l e e n t r y , and t h e g l o b a l pag e
ta b l e
entr ies
fo r a g i v e n se c t i o n .
Th e r e a r e seve r a l r e l a t i o n sh i ps b e twe e n
t h e s e th r e e s t r uc t u r e s .
1.

Th e c e n t r a l s t r uc t ur e
is
the g l oba l
sec t i on
tab l e
entry
( Figure 1 1-16) .
Th e f i r s t l o ng wo r d i n t h e G S T E po i n t s t o t h e
g l o b a l s e c t i o n d e sc r i p to r .

Th e v i r t u a l pag e n um b e r f i e l d ( l a b e l l ed ( B ) i n F i g u r e 1 1 - 1 8 )
c o n t a i n s t h e pse ud o s ys t em v i r t ua l pag e n um b e r t h a t s e r v e s a s
a l o ngwo r d i nd e x t o the f i r s t g l o b a l pag e
tab le
entry that
maps th i s sec t i o n .

Global Section
Table Entry
-

System Header

...

W C B Address

System Working
Set List
GSTE

--------------- -

�

-------------- - -

Base VBN

I
I

System
Page Table
Global
Page Table

Global Section Desc riptor
Section
Name

Figure 1 1-1 8

GPTE
GPTE
GPTE
GPTE
GPTE
GPTE

Global
Page
Table
Entries

R e l a t i o n s h i ps Am ong G l o b a l Se c t i o n Da t a S t r uc t u r e s
1 1-25

MEMORY MANAG EMENT DATA S TRUCTURE S

Th e g l o b a l s e c t i o n d e sc r i p to r c o n ta i n s a g l o b a l s ec t i o n t a b l e
i nd e x ( l a b e l l e d ( A ) i n the f i g u r e ) t h a t a l l o ws t h e G S T E t o b e
l o c a ted f r o m t h e G S D .

Th e o r i g i n a l f o rm o f e a c h g l o b a l
pag e
t ab l e e n t r y
is
a
section
ta b l e
i nd ex
( i d en t i c a l
to
the G S T X f o und i n the
g l o ba l s e c t i o n d e s c r i pto r ) , e f f e c t i v e l y po i n t i ng to the G S T E .
Wh e n a n y g i v e n G PT E
i s e i th e r va l i d o r i n t r a n s i t i o n , t h e
G S TX i s s t o r ed i n the P F N B A K a r r ay .

11.3.5

P r oc e s s PTEs fo r G l oba l Pag e s

Wh e n a p r o c e s s m a ps a po r t i o n o f i t s v i r t ua l a d d r e s s s pa c e t o a g l o b a l
section ,
i ts process
pag e t a b l e e n t r i e s tha t m a p the s e c t i o n a r e o f
t h e fo rm g l o b a l
pag e
tab l e
i nd ex
( F i g u r e s 1 1 - 3 a nd
1 1-19) .
Th e
process
PTE t h a t m a ps the f i r s t g l ob a l s e c t i o n pag e c on t a i n s the G PTX
o f the f i r s t pag e in the g l o b a l s e c t i o n .
E a c h s uc c e s s i ve p r o c e s s pa g e
t ab l e e n t r y c o n ta i n s
the n e x t p s e ud o
s y s tem v i r t ua l pag e n um b e r
( G PTX ) , s o tha t e a c h P T E e f f e c t i v e l y po i n t s to the G PT E t h a t m a ps th a t
pa r t i c u l a r pag e i n t h e g l ob a l s e c t i o n .

Global Page Table

MMG$GL_GPTBASE: : ----4,.�

N Entries
Global Page Table Entry

Proc ess P a ge Table

G PTE

I
I
I
I

G PT Index

GPTE

G PT Index

GPTE

G PT Index

G PTE

G PT Index

G PTE

G PT Index

G PTE

G PT Index

G PTE

G PT Index

1 30

.... _

27 26 25 24 23 22 2 1

.... .... _

- -

G lobal Page Table Index

Figure 1 1 -1 9

Rel a t i o n sh i p B e twe e n P r o c e s s PTEs a nd G l o b a l PT E s
1 1 -26

._,Q

MEMORY MANAG EMENT DATA STRUCTURES

A l l of the d a ta s t r uc t u r e s a s s o c i a t ed w i th g l oba l
sec t i ons wi l l
be
d e sc r i b e d
i n d eta i l
i n Ch a p t e r 1 2 wh e n pag e f a u l t s fo r g l o b a l pag e s
a r e d i sc u s se d .
Th e i n i t i a l a l l o c a t i o n o f
these
s t r uc t u r e s w i l l
be
b r i e f l y d e sc r i b ed
wh e n t h e
C r e a t e a nd
Ma p S e c t i o n a nd Ma p G l o b a l
S e c t i o n s y s t em s e rv i c e s a r e d i sc u s se d .

11 . 4

SWAPP ING DATA STRUCTURES

Th e r e a r e th r e e d a ta s t r uc t u r e s t h a t a r e used p r i m a r i l y b y the swa ppe r
but
i nd i r e c t l y b y t h e p ag e r .
Th e
SYS B OOT pa r am e t e r
BALS E TCNT
d e t e rm i n e s t h e m a x i m um n um b e r of c o nc u r r e n t l y r e s i d e n t p r o c e s s e s .
In
pa r t i c u l a r , i t d e te rm i n e s the amo un t of s y s t em add r e s s s pa c e set a s i d e
f o r p r o c e s s h e ad e r s .

11. 4. 1

B a l a n c e S l o ts

Wh e n the sys t em i s i n i t i a l i z e d , a n amoun t o f v i r tu a l
add ress
s pa c e
equal
to
the s i ze
o f a p r o c e s s h e a d e r t i m e s BALS ETCNT i s a l l o c a t e d
e x c l us i v e l y f o r p r o c e s s h e ad e r s ( F i g u r e 1 1 - 2 0 ) .
Each of these process
h e ad e r
a reas
is
c a l l ed
a
b a l anc e s l o t .
Th e l o c a t i o n o f t h e f i r s t
b a l a n c e s l o t i s s to r ed i n g l o b a l l o c a t i o n SWP$G L BA LBAS E .
Th e s i z e o f
a
process
h e ad e r
( in
pa g e s )
is
s to r ed - i n g l o b a l
locat ion
SWP $G L B S LOTS Z .
Th e c a l c u l a t i o n s pe r f o rmed b y S Y S BOOT t o d e t e rm i n e
t h e s i ze o f t h e p r o c e s s h e a d e r a r e d e s c r i b e d i n App e nd i x E .

11.4.2

B a l a n c e S l o t A r r ays

Th e s ys t em m a i n ta i n s two wo r d s of i n fo rm a t i o n a b o u t t h e p r o c e s s wh o s e
process heade r
is
s to r ed i n a s p e c i f i c b a l a n c e s l o t ( F i g u r e 1 1 - 2 1 ) .
Th e n um b e r o f the b a l a n c e s l o t tha t a
r e s i d e n t p r o c e s s o c c up i e s
is
s to r e d
i n the
f i x ed
po r t i o n o f
the p r o c e s s h e a d e r a t o f f s e t
PHD $W_PHVIND E X .
Th e a r r a y l o c a t ed b y g l o ba l po i n t e r PHV$G L R E FCBAS c o un t s
the
n umbe r
of
r e a s o n s wh y t h e p r o c e s s h e a d e r c ann o t be r emoved f r om memo r y .
Sp�c i f i c a l l y , th i s a r r a y e l em e n t c o un t s t h e n umbe r o f pag e t a b l e pag e s
t h a t c o n t a i n e i th e r v a l i d o r t r a n s i t i o n PT E s .
Th e a r r a y l o c a t ed by g l o ba l po i n te r PHV$G L P I XBAS c o n t a i n s a n
i nd e x
i n to
still
ano th e r
a r ray ,
th i s o n e lo c a ted b y g l o b a l
po i n t e r
S C H $G L PCBVE C , th a t c o n t a i n s PCB po i n t e r s .
Figure 1 1-2 1
i l l u s t r a te s
h o w the
ex ecut ive
turns
the add r e ss
o f a p r o c e s s h e ad e r i n t o the
a d d r e s s of the PCB f o r t h e
s am e p r o c e s s ,
us i ng
the
entry
in
the
p r o c e s s i nd e x a r r a y ( l o c a ted th r o ug h PHV$G L_P I XBAS ) .
I f the p r oc e s s h e a d e r a d d r e s s i s k n o wn , t h e b a l a n c e s l o t i nd e x c a n b e
c a l c ul a t ed
( a s d e sc r i b ed
in
th e n e x t s e c t i o n ) .
B y u s i ng th i s a s a
wo r d i nd e x i n to the p r o c e s s i nd e x a r r a y , t h e l o ngwo r d i nd e x
i n to
the
PC B v e c to r
is
f o und .
Th e
a r r a y e l em e n t in th e PC B v e c to r i s t h e
a d d r e s s o f the PCB ( wh o s e PC B $ L PHD e n t r y po i n t s b a c k to
the
process
h e ad e r ) .
A m o r e d e ta i l ed d e scr i pt i o n o f t h e PC B v e c to r c a n b e f o und
i n Ch a p t e r 1 7 , wh e r e i t s use b y the C r e a t e P r o c e s s s ys tem s e rv i c e
is
d i sc u s s e d .

1 1 -27

�

�W

FNSALPTE

PSGLBALBASE

Balance
Slot 0

Process Header

PHVINDEX
S V A PT E

Balance
Slot 1

Working Set List

Process Section Table
....
....

I
N
00

��

P T E L o n gw o rd
A rr ay in PFN
Database

Proce s s H e a d e r
Page Arrays

��

...._.

Balance
Slot M

t
F i g u r e 1 1 -2 0

PFN

P 1 Page Table

All balance slots
are exactly the same
size.

��

PO Page Table

}
}

��

The size of a
balance slot in
pages Is stored in
global location
SWP$GLBSLOTSZ

��
Last
Balance Slot

Ba l a n c e S l o t s Co n t a i n P r o c e s s Head e r s

There are
BALSETCNT slots

(

HV$GL_REFCBAS

HV$GL_PIXBAS

Contents of
PHD$W_PHVINDEX
are used as a
word Index Into
each of these arrays

)
Ref. Count

BALSETCNT
entries In
each array

Process Index

t:HS

@SCH$GL_PCBVEC __.....
..
�..
'r
+ 4*(Process I ndex)

PCB of process
whose PHD Is
In balance slot
M

.,;

GL_PCBVEC

Pointer to PCB

....

PCB Vector

Figure 1 1-21

�

P r o c e s s He a d e r Ve c to r Ar r a ys

MAX PROCESSCNT
entries

MEMORY MANAG EMENT DATA STRUCTURES

11.4.3

Comm e n t on Equal S i ze Ba l an c e S l o t s

Th e cho i c e o f e q ua l s i z e
b a l anc e
s l ots ,
a t f i r s t s i g h t s e em i ng l y
i ne f f i c i en t ,
h a s some
s ub t l e b e n e f i t s t o po r t i o n s o f the memo r y
m a n ag em e n t s ub s y s t em .
Th e r e
a re
seve ral
i nstanc e s ,
mo s t n o t a b l y
wi th i n
t h e mod i f i ed
pag e w r i te r ,
wh e n i t i s n e c e s s a r y to o b t a i n a
p r o c e s s h e a d e r a d d r e s s f r om a ph y s i c a l pag e ' s pag e f r a m e n umbe r ( P FN ) .
Wi th f i x ed s i ze b a l a n c e s l o t s , th i s o pe r a t i o n i s s t r a i g h t f o r wa rd .
Th e c o n te n t s o f t h e
PFN PTE a r r ay po i n t
to
a
pag e
tab l e
entry
s omewh e r e
in
the b a l ance
slot
a rea .
S ub t r a c t i ng t h e c o n t e n t s o f
SWP$G L BALBA S E f r om th e PFN PTE a r r a y c o n t e n t s a nd d i v i d i ng th e r e s u l t
by
the s i z e o f a b a l a n c e s l o t ( th e s i ze o f a p r o c e s s h e ad e r ) i n b y t e s
p r o d uc e s t h e b a l a n c e s l o t i nd ex .
I f th i s i nd ex i s m u l t i pl i ed
by the
s i ze
of
the process head e r
in
b yt e s a nd a d d ed to the c o n t e n t s o f
SWP $ G L BALBAS E , t h e f i n a l r e s u l t i s the a d d r e s s o f t h e p r o c e s s h e a d e r
tha t co n t a i n s t h e pag e
table
e n t r y t h a t m a ps t h e phys i c a l pag e i n
ques t i o n .

11.5

DATA STRUCTURES THAT DESCR I BE THE PAG E F I LE S AND SWAP F I LE S

Th e pag e a nd swa p f i l e s u s e d b y t h e memo r y m a nag em e n t s ub s ys t em
to
b a c k u p e i th e r phys i c a l
pa g e c o n t e n t s o r p r o c e s s wo r k i ng s e t s a r e
d e sc r i b ed
by s im i l a r d a ta
s t r uc t u r e s .
Th e c o n t r o l
blocks
tha t
d e sc r i b e e a ch f i l e a r e a c c e s s ed th r o ug h a c ommon t a b l e , l e ad i ng to a t
l e a s t o n e s i m i l a r i ty b e twe e n the two k i nd s o f f i l e s .

11. 5. 1

Pag e and Swa p F i l e Ve c to r

F i g u r e 1 1 - 2 2 i l l u s t r a t e s the f i r s t l i nk t o the pag e
a nd
swa p f i l e
contr o l
b l oc ks .
Lo c a t i o n MMG $ G L PAG SWPVC po i n ts
to
an a r ray o f
l o ng wo rd po i n te r s , o n e f o r e a c h page f i l e o r swa p f i l e i n the
s y s t em .
Th e
n um b e r
o f l o ng wo r d s i s e q u a l to the s um o f t h e two a s s emb l y t i m e
pa ram e t e r s SGN $ C S FTMAX a nd SGN $ C PAG F I LCNT .
Th i s a r r a y i s
a l l o c a t ed
in mod u l e SWAPF ILE .

11. 5. 2

Pag e F i l e Da ta B a s e

Th e l a s t SGN$C PAG F I LCNT l o ng wo r d s in the
a r ray
( th e r e a r e
two
in
Ve r s i o n 2
o f- VAX/VM S )
po i n t
to
pag e
file
control
b l o c ks
( F i g u r e 1 1 - 2 2 ) , a l s o s t a t i c a l l y a l l o c a te d
1 n mod u l e
SWAPF I LE .
Th e
pag e
f i l e c o n t r o l b l o c k f o r SYS $ S Y S TEM : PAG E F I L E . SYS i s i n i t i a l i z e d by
the SYS I N I T p r o c e s s ( Ch a pt e r 2 2 ) .
Th e f i l e is o p e n e d , t h e a d d r e s s o f
t h e w i ndow c o n t r o l
block
is
s to r ed ,
a nd
the pag e f i l e b i tm a p i s
a l l o c a t ed f r om nonpag ed po o l a nd i n i t i a l i z e d t o a l l b i t s s e t .
block
Th e l o c a t i o n s o f t h e w i ndow c o n t r o l b l o c k
field ,
t h e v i r t ua l
n umbe r
f i e l d , a nd t h e pag e f a u l t c l u s te r f a c to r f i e l d a r e i n t h e s ame
r e l a t i v e o f f s e t s i n th i s s t r uc t u r e a s th e y a r e
in a
section
table
e n t r y ( a nd a l so a s wa p f i l e t a b l e e n t r y ) .
Th i s a l l ows I /O r e que s t s to
s t r uc t u r e
be p r o c e s s e d by c ommo n c o d e , i nd e p e nd e n t o f the
d a ta
that
d e sc r i b e s t h e f i l e b e i ng r e ad o r wr i t t e n .

1 1-3 0

: : M MG$GL_PAGSWPVC

Page File Control Bloc k
Address of Start of Bitmap
(Bit = 1 • Bloc k is Available Starting Byte Offset to Sc an

Entry for S HELL
(filled in by INIT )

J
I
I
I

Entry for
SWAPFILE.SY S .

1-'
1-'

( filled in b y SY SINIT)

w
1-'

Entry for
Second Swap File
(filled in by SYSGEN)

Longword Array is
indexed by page
or swap file nu mber
(Offset PH D$B_PAGFI L
contains index of page
file used by process)

�

Cluster

�

( filled in by SYSINIT)

( filled in by SY SGEN)

l Type

Size

Pointer to Window Control Block

Page Fault

I
I
I

Control Block
for PAGEFILE.SYS

Control Block for
Second Page File

Base Virtual Bloc k Number

Size in Bytes of Bitmap
Count 1 of Pages which may be
Allocated
Count 1 of Pages which may be
Reserved
-

Figure 1 1-2 2

Pag e F i l e Da t a Ba s e

Page File

Bitmap
One Bit per
Block in the
Page File
Bit Set •

Block Available

MEMORY MANAG EMENT DATA STRUCTURE S

A s e c ond pag e f i l e c o n t r o l b l o c k e x i s t s to a l l o w th e c r e a t i o n o f a
s e c o nd
pag e
f i l e w i th
the
I N S TA LL/PAG E F I LE c omma n d t o the S Y S G E N
u t i l i ty .
I f a s e c ond pag e f i l e i s i n s t a l l e d ,
a l l processes c r e a ted
f r om
th a t po i n t o n u s e the n e w pag e f i l e .
No t e th a t th i s c ommand i s
t h e o n l y wa y t o p l a c e t h e pag e f i l e o n a vo l um e o th e r than the
sys t em
d i sk .

11. 5. 3

Swap F i l e Ta b l e En t r i e s

Th e f i r s t SGN$C S F TMAX l o ng wo r d s i n t h e
a r ray
( th e r e a r e
th r e e
in
Ve r s i o n 2 o f VAX/VM S ) po i n t t o s wa p f i l e t ab l e e n t r i e s ( F i g u r e 1 1 - 2 3 ) .
Th e r e a r e t h r e e swa p f i l e t a b l e e n t r i e s s ta t i c a l l y a l l o c a ted i n m o d Ql e
SWAPF I LE .
Th e
f i r st
s wa p f i l e
t ab l e e n t r y ,
i n i t i a l i z e d by ! N I T
( Ch a pt e r 2 2 ) , d e sc r i b e s t h e Sh e l l p r o c e s s , a s k e l e to n swa p i m ag e
th a t
is
used
wh e n ev e r a
process
i s c r e a t ed
as
i ts
initial
context
( Ch a p t e r 1 7 ) .
Th e swa p f i l e t a b l e e n t r y fo r SYS $ S YS TEM : SWAPF I LE . SYS
is
i n i t i a l i zed
b y S YS I N I T .
A k e y s t e p i n th i s i n i t i a l i z a t i o n i s t h e d i v i s i o n o f the
swa p f i l e i n to equa l s i z e d swa p s l o t s .
Th e s i z e of t h e swa p f i l e
is
Th i s n um b e r i s m i n i m i z e d w i th
d i v i d ed b y t h e SYSB OOT pa r am e t e r WSMAX .
1 2 8 , the s i z e o f the b i tm a p i n the s wa p f i l e t a b l e e n t r y .
Th e sm a l l e r
n um b e r
r e p r e s en t s t h e n um b e r o f s l o t s i n th i s swa p f i l e .
( No t e th a t
t h e swa p f i l e b i tm a p c o nta i n s o n e b i t pe r s l o t wh i l e
the
pag e
file
b i tm a p c o n ta i n s o n e b i t fo r e a c h b l o c k i n th e f i l e . )
Th e n um be r o f swa p s l o t s ( p l u s t wo to a c c o u n t fo r th e
two
proc e ss e s ,
SWAPPER a nd N U L L , t h a t n e v e r swa p ) i s a l s o c om pa r ed w i th the n um b e r o f
p r o c e s s e s a l l o wed fo r th i s s ys tem ( S C H$GW PROC L I M ) .
If
the ad j us ted
In
s wa p s l o t c o un t
is
sma l l e r ,
t h e n i t re p l a c e s th e old m a x i m um .
o th e r wo r d s , t h e s ys t em wi l l no t a l l o w a p r o c e s s t o ex i s t un l e s s th e r e
i s a swa p s l o t fo r i t .
Th e s i z e o f the b i tm a p l i m i t s the n um b e r o f p r o c e s s e s th a t a swa p f i l e
c a n ho l d a nd , by i m p l i c a t i o n , t h e n um b e r o f p r o c e s s e s tha t the s ys tem
wi l l a l low .
A s ys tem w i th o n e ( th e s t a nd a rd ) swa p f i l e w i l l a l l o w no
more
than 1 3 0 p r o c e s s e s .
A s ys t em th a t ad d s a s e c o nd s wa p f i l e ( wi th
t h e S Y S G E N I N S TA L L/SWAPF I L E c ommand ) c a n s uppo r t a max i m um o f
2 58
p ro c e s se s .
VM S c u r r e n t l y
r e s t r i c t s the n umbe r o f swa p f i l e s to two
( pl us SHELL) .
NOTE
A s l i g h t c h a ng e to
th i s
a l g o r i thm h a s
been
pa tch ed
i n to
VM S
w i th
the
Ve r s i o n 2 . 2 b i n a r y upd a t e .
Th i s c h a ng e
r em o v e s the r e s t r i c t i o n o f 2 5 8 p r o c e s s e s
Th e d e t a i l s o f
th a t p r e v i o u s l y e x i s t e d .
th i s c h a ng e a r e d e sc r i b ed i n Append i x F .

11 . 6

SWAPPER AND MOD I F I ED PAGE WR ITER PAG E TAB L E ARRAYS

Th e VAX/VM S I /0 s ys t em a l l o ws d i r ec t I /0 r e que s t s ( DMA t r a n s f e r s )
to
v i r t ua l l y c o n t i g uo u s b u f f e r s .
Th e r e i s no r e q u i r em e n t th a t pag e s i n
t h e b u f f e r b e ph ys i c a l l y c o n t i g uo u s o r even h a v e a n y r e l a t i o n sh i p to
e a c h o th e r .
1 1 -3 2

Each swap slot contains
WSMAX blocks

Swap File Table Entry
Slot
Count

Slot Size
Spa re
Page

F ault
Cluster

S iz e

Pointer to Window Control
Bloc k for Swap File
Base Virtual Block
Number of First Slot
S W A P FILE

Bitmap
( 1 28 Bits)
One Bit per Swap Slot

....
....

I
w
w

I 7l I"I

PCB

./
index
�--�--

c o n t ain virtual

block number of
beginning of slot
alloc a ted to this
process

non Page Table
Process Header
pages

index into swap and

2) L o w e r t h r e e bytes

�

VBN of slot

1 1 Upper byte contains
p a ge file v e c t o r

}

s L oT

Spare

PCBSL -WSSWP

\
\
\

I
I

Bit S e t .,. S i o t Available

Active
Pag e Ta ble s

APTC NT
Bit PCBSV_RES in PCBSL_srs
indicates residency o f pro cess

PCB$W_APTCNT
pages

1 .. Re s i de n t

0 .. O u tswa ppe d

Figure 1 1-23

S wa p F i l e Da t a Ba s e

Process Body

IPO and P 1 pages I

MEMORY MANAG EMENT DATA STRUCTURES

11. 6. 1

D i r e c t I/0 a nd S c a t te r/G a th e r

Th e I /O Lo c k i ng mec h a n i sm i nvo k ed a t t h e FDT l ev e l
b r i ng s
e a c h pag e
i n to
the
wo r k i ng
s e t o f t h e r e que s t i ng p r o c e s s , m a k e s i t v a l i d , a nd
i n c r eme n t s t h a t pag e ' s
r e f e r e n c e c o un t
( in
PFN RE FCNT a r r a y )
to
r e f l ec t
the pe nd i ng r e a d o r w r i te .
Th e b u f f e r i s g e ne r a l l y d e s c r i b ed
i n t h e I /O r e qu e s t p a c k e t th r o ug h th r e e f i e l d s .
•
•

I R P $ L S VAPTE c o n t a i n s t h e s y s t em v i r t ua l ad d r e s s o f t h e f i r s t
PTE tha t m a ps t h e b u f f e r .
I R P$W B O F F a nd I R P$W BCNT t o g e th e r d e sc r i b e the b u f f e r
s i ze
th a t - i s
u s e d to c alc u l a t e how m a n y PTE s a r e r e qu i r ed to map
the b u f f e r .

Wh e n a d r i v e r p r o c e s s e s th i s I /O r e q u e s t , i t a l l o c a t e s
the
r e q u i r ed
n um b e r o f MBA o r UBA ma pp i ng r eg i s t e r s a nd l o a d s th em wi th the pag e
f r am e n um be r s f o und i n the pag e t a b l e e n t r i e s .
Th e a d a p t e r h a r d wa r e
h a nd l e s t h e m a p p i ng f r om i t s a d d r e s s s pa c e t o VAX phys i c a l a d d r e s s e s .
The a b i l i ty to t r a n s f e r to d i s c o n t i g uo u s ph y s i c a l pag e s ( th e s o - c a l l ed
s c a t t e r - r e ad g a the r - w r i t e c a pa b i l i ty ) i s a b e n e f i c i a l s i d e e f f e c t o f
t h i s ma pp i ng .

11 . 6 . 2

Swa ppe r I/O

The s wa ppe r i s p r e s e n t ed w i th a m o r e d i f f i c u l t p r o b l em .
I t m u s t wr i t e
a
c o l l e c t i o n o f pag e s to d i s k tha t a r e no t even v i r t ua l l y c o n t i g uo us .
I t s o l v e s t h i s p r o b l em e l eg a n t l y .
Wh e n the s ys t em
is
i n i t i a l i z ed ,
a n a r r a y o f WSMAX l o ng wo r d s
is
a l l o c a t ed
f r om no npag ed po o l f o r u s e a s the swa ppe r ' s I /0 t a b l e .
Th e
s ta r t i ng ad d r e s s o f t h i s a r r a y i s s to r ed i n g l o b a l po i n t e r SWP $G L MAP .
( Th e
add r e s s
i s a l so
s to r e d
in
the s a v e d P O b a s e r eg i s t e r i n the
s wa ppe r ' s p r o c e s s h e ad e r
so
the
pag e s m a pped
by t h i s
a r r ay a r e
e f f e c t i v e l y th e
s wa ppe r ' s R O s pa c e .
Th i s u s e
i s d i scussed
in
Ch a pt e r 1 7 . )
Wh e n th e s wa ppe r s c a n s the wo r k i ng
s e t l i st o f
the
p r o c e s s b e i ng
o ut swa pped ,
th e pag e
f r am e n umbe r s
i n e a c h v a l i d PTE a r e moved to
s uc c e s s i v e e n t r i e s in the s wa ppe r ' s I /0 t a b l e .
Th e a d d r e s s o f
the
b a se
of
the
ta b l e
i s put
i n to t h e SVAPTE f i e l d o f the I R P b y the
s wa ppe r b e f o r e the IRP i s pa s s ed o n to the d r i v e r .
( Th e
s wa ppe r
can
exerc i se
th i s c o n t r o l
because
it
b u i l d s a po r t i o n o f i t s o wn I R P ,
r a th e r th a n u s i ng the e n t i r e $ Q I O m e c h a n i sm . ) Th e I /O t a b l e l o o k s j us t
l i ke
a ny o the r pag e t a b l e t o the m a pp i ng r eg i s t e r s ub r o u t i n e s c a l l ed
by t h e d r i v e r .
Th e PFNs a r e e x t r a c t ed f r om th i s a r r a y a nd l o ad ed i n to
ad a p t e r m a pp i ng r eg i s t e r s .
Wh a t the s wa ppe r h a s s uc c e e d ed i n d o i ng i s m a k i ng pag e s th a t a r e
no t
v i r t ua l l y c o n t i g uo us
a ppe a r
to
b e v i r t ua l l y c o n t i g uo u s to the I /O
s ub s y s tem .
( A d i f fe rent
i nterpretation
is
that
the
pag e s
are
v i r t ua l l y c o n t i g uo u s i n th e P O s p a c e o f t h e swa ppe r , t h e p r o c e s s tha t
i s a c t ua l l y pe r fo rm i ng t h e I /0 . ) At t h e s am e t i me
tha t e a c h
PTE
is
b e i ng
p r o c e s sed ,
a n y s pe c i a l
a c t i o n s b a s e d o n the t ype o f pag e a r e
a l so
t a k e n c a re
of .
Th e who l e
o pe r a t i o n o f o u t s wa p ,
a nd
the
c ompl em e n t a r y s t e p s
t a k e n wh e n
the
process
i s s wa pped back i n to
m em o r y , a r e d i s c u s s e d in Ch a p t e r 1 4 .

1 1- 3 4

MEMORY MANAG EMENT DATA STRUCTURES

11.6. 3

Mod i f i ed Pag e Wr i te r PTE Ar ray

Th e m o d i f i ed pag e wr i te r , i n
i ts
a t tempt
to wr i t e m a n y pag e s
to
b a c k i ng
s t o r e w i th a
s i ng l e wr i t e r eque s t { so -c a l l ed mod i f i ed pag e
wr i te c l us t e r i ng ) , i s f a c ed w i t h a p r o b l em s i m i l a r
to
the
swa ppe r ' s
p r o b l em ,
w i th o n e a d d i t i o n a l twi s t .
Wh e n the m od i f i ed pag e w r i te r i s
b u i l d i ng a n I /0 r e qu e s t , th e r e a r e th r e e fo rms o f pag e
tha t
i t can
e nco un te r .
Pag e s
th a t a r e b o un d fo r the swa p f i l e ( SWPVBN n o n z e r o )
a r e wr i t t e n i nd i v i d ua l l y .
Pag e s t h a t a r e bo und fo r a n i m ag e f i l e a r e
a l so v i r t ua l l y c o n t i g uo u s .
Ho we v e r , pag e s o n the m od i f i ed pag e l i s t
t h a t a r e t o b e wr i t t e n t o a pag e f i l e m a y b e n o t o n l y d i s c o n t i g uo us
w i th i n a
p r oc e s s
ad d re s s
s pa c e b u t m a y a l so
b e l ong
to s ev e r a l
p r o c e s se s .
Th e m o d i f i ed pag e wr i te r b u i l d s a
tab l e o f
PTE s
in
a
m a n n e r s i m i l a r to t h e swa ppe r .
At i n i t i a l i z a t i o n t i m e ( i n m od u l e I N I T ) , two a r r a y s a r e a l l o c a t e d f r om
n o npag e d po o l fo r the m od i f i ed pag e wr i te r ( F i g u r e 1 1 - 2 4 ) .
Each a r ray
Th e l o ng wo r d a r r a y w i l l
be
f i l l ed
c o nt a i n s M PW WRTC LUS TER e l em e n t s .
w i �h pag e tab l e e n t r i e s c o n t a i n i ng PFNs a na l og o us to t h e swa pp e r m a p .
Th e wo r d a r r a y c o n t a i n s a n i nd ex i n to the p r o c e s s h e ad e r v e c to r
fo r
e a c h pag e i n the m a p .
I n th i s wa y , e a ch pag e t h a t i s p u t i n to th e m a p
a nd wr i t te n to i t s b a c k i ng s t o r e l o c a t i o n i s r e l a t e d
to
the process
h e ad e r
c o n t a i n i ng
t h e PT E t h a t m a ps th i s pag e .
Th e o pe r a t i o n o f the
m od i f i ed pag e wr i te r , i n c l ud i ng i t s c l u s te r ed wr i t e s to a
pag e
fi le ,
i s d i sc u s s e d i n d e t a i l i n Ch a pt e r 1 2 .

11. 6. 4

N o n r e e n t r a ncy o f Swappe r a nd Mod i f i ed Pag e W r i t e r

Th e u s e o f the se a r r a ys to ho l d pag e ta b l e e n t r i e s f o r the I /0
s y s t em
makes
the
swa ppe r
a nd t h e m od i f i ed pag e wr i t e r n o t r e e n t r a n t .
Th a t
i s , t h e swa ppe r p r o c e s s c a n pe r fo rm o n l y two s i m u l t a n e o u s o pe r a t i o n s .
•

•

An i n s wa p o r o u t s wa p o pe r a t i o n t h a t
uses
the
swa ppe r m a p .
Th i s a c t i o n i s r e c o r d ed b y s e t t i ng th e swa p i n p r o g r e s s f l ag
( SC H $V_S I P ) i n l o c a t i o n S C H$GB_S I P .
A m od i f i ed pag e wr i t e to
a pag e f i l e ,
an i m ag e f i l e , o r
a s wa p f i l e VBN .
Th e mod i f i ed pag e wr i t e i n p r og r e s s f l ag ( S C H $V MPW )
in
s am e g l o ba l l o c a t i o n ( S C H$G B_S I P ) r e c o r d s th i s ac t i o n .

11.7

th e

DATA STRUCTURES USED WITH SHARED MEMORY

Th e MA7 8 0
s h a r ed memo r y un i t c a n be
used
as
an
i n t e r p r oc e s s o r
c ommun i c a t i o n pa th wi th c ommo n
event
f l ag s ,
m a i l bo x e s , o r g l o b a l
secti ons .
Th i s VM S s uppo r t r eq u i r e s d a t a s t r uc tu r e s
l o ca ted
in
the
sha r ed m emo r y th a t d e sc r i b e
the
sha r ed m emo r y
i tsel f ,
a nd d a ta
s t r uc t u r e s tha t d e sc r i b e the s h a r ed m emo r y c ommo n ev e n t f l ag c l us t e r s ,
m a i l box e s ,
o r g l obal s ec t i o n s .
I n a d d i t i o n , e a c h p r o c e s s o r c o nn e c t e d
t o the sha r ed memo r y r e q u i r e s d a t a s t r uc t u r e s l o c a t e d i n l o c a l
memo r y
t h a t d e sc r i b e t h e s h a r ed m em o r y d a t a s t r uc t u r e s .
1 1-3 5

SWPSGL _MAP :: •
(This address is s to red
in the swapper's P 0
base register.)

•

��

....
....

I
w

MPW$AL-PTE :: •

Swapper's
1/0
Page Table
Entry
Array of
Long words

•

�� >

WSMAX
elements
(This number is stored in
the swapper's PO length
register.)

Modified
Page Writer's
1/0
1� Page Table �� > MPW-WRTCLUSTER
elements
Entry
Array of
Longwords

· -

F i g u r e 1 1 -2 4

.... :: MPWSAW-PHVINDEX

MPW's
Pro c ess
Header
oe � � Ve c tor � �
Index
Array
of
Words
_ ...._
_
_....

Swa ppe r a nd Mod i f i ed Pag e Wr i t e r PTE Ar r a ys

MEMORY MANAGEMENT DATA STRUCTURES

11. 7.1

Sh a re d Memo r y Con t r o l S t r uc t u r e s

Th e sha r ed memo r y un i t c o n s i s t s o f
a
series of
pag e s
of
phys i c a l
memo r y .
Th e
b o o t s t r a p s e qu e n c e
r e c o r d s t h e p r e s e n c e o f t h e s h a r ed
memo r y un i t b u t d o e s n o t c o n f i g u r e the phys i c a l pag e s i n t o th e sys t em .
Th i s
a l l o ws
t h e u s e r to i n c l ud e s h a r ed memo r y i n a s i t e - s pec i f i c wa y
i n s t e a d o f a l l o wi ng VM S to p r ov i d e
t r a n s pa r e n t s uppo r t .
In
e i th e r
t h e phys i c a l memo r y pag e s m u s t b e v i r t ua l l y ma pped so th a t t h e y
case ,
a r e a c c e s s i b l e t o p r og r am c o d e ( b e c a u s e memo r y m a n ag emen t i s e n ab l ed )
•

I n a ny c a s e , i t i s e x t r em e l y un l i k e l y t h a t t h e v i r t ua l m a pp i ng u s e d b y
o n e p r o c e s so r t o a c c e s s s h a r ed memo ry pag e s i s t h e s a m e a s t h e v i r t ua l
m a p p i ng
u s e d b y a n o th e r
processo r .
Fo r
th i s
reaso n ,
the d a t a
s t r uc t u r e s t h a t VMS u s e s to m a n i p u l a t e i t s d a t a s t r uc t u r e s l o c a t e d i n
sh a r e d memo r y a r e s e l f - r e l a t i v e q u e ue e l em e n ts .
( Se l f- r e l a t i ve
q u e ue
e l em e n ts a r e d e s c r i b ed i n the VAX- 1 1 A r c h i t e c t u r e Handboo k . )
I n add i t i on ,
VM S c a n no t
use o ne o f
i ts
u s ua l
s ynch r o n i z a t i o n
t e c h n i que s ,
e l ev a t e d
I PL ,
to contr o l
a c c e s s t o sh a r ed m emo r y d a t a
s t r uc t u r e s .
E l e v a t ed I PL b l o c k s i n t e r r up t s , b u t o n l y o n t h e
local
I n s t e ad ,
a l l a c c e s s e s to s h a r ed memo r y d a t a th a t m u s t b e
p r o c e s so r .
s ync h r o n i z e d
a r e d on e w i th o n e o f
the
i n t e r loc ked
i n s t r uc t i o n s
p r o v i d ed
fo r
j us t th i s
p u r po s e
in
t h e VAX a r ch i t e c t u r e .
Th e s e
i n s t r uc t i o n s a r e :
I N S QH I
I N S QT I
REMQH I
REMQT I
BB S S I
BBCC I
ADAWI

I n s e r t E n t r y i n to Qu e ue at H e a d , I n t e r l o c k e d
I n s e r t �n t ry i n to Q u e ue a t Ta i l , I n t e r l o c ked
Remove E n t r y f r om Queue at H e a d , I n t e r l o c k e d
R e m o v e En t r y f r om Q u e u e a t Ta i l , I n t e r l o c k e d
B r a nch o n B i t S e t a nd S e t I n t e r l o c k e d
B r a n c h o n B i t C l e a r a nd C l e a r I n t e r l o c k e d
Ad d Al i g n e d Wo r d I n t e r l o c k e d

Th e f o u r i n s t r uc t i o n s th a t m a n i pu l a t e
s e l f - r e l a t i v e q u e ue s a c t ua l l y
p r ov i d e two
l ev e l s o f
i n t e r l o c k i ng .
Because
s e l f - r e l a t i v e q ue ue
e l em e n t s mus t b e quadwo r d a l i g ned , the l ow th r e e a d d r e s s b i t s
( al l
ze r o )
a r e a v a i l a b l e f o r o th e r us e s .
Th e l o w o r d e r b i t i n the f o r wa r d
l i n k i s used
as a
s e c o nd a r y
i n te r l o c k .
Wh e n
th i s b i t
is
set ,
i n t e r l o c ked
access
to th e h e a d o r ta i l o f the queue i s d e n i ed .
Th i s
i n t e r l o c k b i t i s r e ad i n a n i n t e r l o c k ed f a sh i o n th a t i s
used b y the
o th e r th r e e i n s t r uc t i o n s i n the l i s t ( BB S S I , BBCC I , a nd ADAW I ) .

1 1 . 7 . 1 . 1 Ph ys i c a l Layo ut o f Sh a r ed Memo ry - I f the sha r ed m emo r y
is
to b e s uppo r t ed b y VM S , i t m u s t b e c o n f i g u r ed i n to the s ys t e m wi th t h e
SYSGEN u t i l i ty .
Th i s i n s t a l l a t i o n s t e p i s d e sc r i b ed
in
t h e VAX/VM S
Sys tem Ma n ag e r ' s G u i d e .
Th e
r e s u l t i ng
ph ys i c a l
l a yo u t o f s h a r ed
memo r y i s
i l l us t r a ted
in
Figure 11-2 5 .
Th e
VMS d a t a a r e a s
a re
i n i t i a l i z e d wh e n the f i r s t p r o c e s s o r { po r t ) conn e c t s t h e sh a r e d memo r y
un i t .
As o th e r po r t s m a k e the i r c o nn e c t i o n , t h e i r l o c a l m em o r y d a ta
s t r uc t u r e s a r e s i mpl y i n i t i a l i z e d to po i n t to th e sh a r ed s t r uc t u r e s .

11-37

MEMORY MANAG EMENT DATA S TRUCT URES

Lowest physical
address

: :::

Balance of memory
available for
shared memory
global sections

��

Global page allocation bit map

Pool space

Table for shared memory CEBs

Mailbox table

Table for shared memory GSDs

One page reserved for each port

Shared memory common data page

Figu r e 1 1 - 2 5

Highest physical
address

Ph ys i c a l La yo u t o f Sha r ed Memo r y

1 1 . 7 . 1 . 2 S h a r ed Memo r y Common Da t a Pag e - Th e sha r ed memo r y pag e wi th
the h i g h e s t phys i c a l a d d r e s s i s u s ed b y VMS to c o n ta i n the i n f o rm a t i o n
tha t d e sc r i b e s t h i s s h a r ed memo r y un i t .
Th i s pag e
is
c a l l ed
the
c ommo n d a ta
pag e .
Because
th i s pag e may b e v i r t ua l l y mapped i n
d i f f e r e n t wa ys o n e a c h po r t ( a nd m a y n o t even e x i s t a t the
s am e
phys i c a l
a d d r e s s ) , e a c h po i n t e r i n th e c ommon d a ta pag e i s a r e l a t i v e
po i n t e r f r om t h e b a s e v i r t ua l a d d r e s s o f th e common d a t a
pag e .
Th e
c o n t e n t s o f t h e c ommo n d a t a pag e a r e l i s t ed i n Tab l e 1 1 - 3 .

1 1 . 7 . 1 . 3 P r o c e s s o r - S p e c i f i c Co n t r o l - As
e ac h
processo r
connec ts
i tse l f
to t h e s h a r e d mem o r y un i t , a d a ta s t r uc t u r e i n p r o c e s s o r l o c a l
memo r y i s i n i t i a l i ze d th a t a l l o ws t h a t p r o c e s so r t o l o c a t e t h e c ommo n
d a ta
pag e .
Th a t s t r uc t u r e a l so c o n t a i n s phy s i c a l pag e i n fo rm a t i o n
tha t a l l o ws t h e sha r ed phys i c a l memo r y to b e v i r t ua l l y ma pped on
th a t
p r o c e s so r .
Th e l a yo u t o f the sha r e d m emo r y c o n t r o l b l o c k i s p i c t u r ed
i n F i g ur e 1 1 -2 6 .
1 1-38

M EMORY MANAG EMENT DATA S TRUCTURES
Table 1 1 - 3
Conten t s o f Shared Memory Common Data P ag e

S i ze

I t em

Mnemon i c
S HD $ L MBXPTR
S HD $ L-G S DPTR
S HD $ L-C EFPTR
S HD $ L-G S B I TMAP
S HD$ L=G S PAGCNT
S HD $ L G S PF N
S HD$W-G S DMAX
S HD$W-MBXMAX
S HD$W=C EFMAX
S HD$T_NAM E
S HD$Q_I N I T T IM E

Re l a t i v e Po i n te r to Ma i l box Ta b l e
Re l a t i v e Po i n t e r t o G S D Ta b l e
Re l a t i v e Po i n t e r to C EB Ta b l e
R e l a t i v e Po i n t e r to Gl o b a l Pag e B i tma p
Co u n t o f Pag es Al l o c a ted fo r
Gl obal Sec t i o n s
Re l a t i v e PF N o f F i r s t G l o b a l S e c t i o n Pag e
S i ze o f G S D Ta b l e
S i ze o f MB X Ta b l e
S i ze o f C E B Ta b l e
( spa r e wo rd fo r a l i g nm en t }
Name o f Sh a r ed Memo ry
( Co un t ed A SC I I S t r i ng }
I n i t i a l i za t i o n T i m e

l o ng wo rd
l o ng wo rd
l o ng wo rd
l o ng wo rd
l ong wo rd
l o ng wo rd
wo rd
wo rd
wo rd
wo rd
16 byt e s
quad wo r d

Th i s i s the e n d o f t h e c o n s t a n t a r ea o f the sha r ed m emo ry c ommon d a ta pag e .

S HD$L C RC
S HD$W-G S DQUOTA
S HD$W-MBXQUOTA
S HD$W-C EFQUOTA
S HD$8-PORTS
S HD$8-I N I T LC K
S HD$8-B ITMAPLC K
S HD$8-F LAGS
S HD$8-G S DLOCK
S HD$8-MBXLOCK
S HD$ B=C E F LOCK
SHD $W_PR QWA I T
S HD$W_POLL
S HD$W_R E SWAIT
S HD$W_R E SAVA I L
S HD$W_R E S S UM
S HD$Q PRQ
S HD$Q-POOL
S HD$Q=PRQWRK

11.7.2

S i ze

I t em

Mn emo n i c

C RC o f F i e l d s i n Co n s t a n t A r e a
Co un t o f G S Ds C r ea ted ( o ne pe r po r t }
Co u n t o f Ma i l bo x e s C r e a ted ( on e pe r po r t )
Co u n t o f C EB s C r ea ted ( o n e pe r po r t )
Number o f Po r t s
Own e r o f I n i t i a l i za t i o n Lo c k
Own e r o f G l ob a l Pag e B i tmap Lo c k
Fl ag s fo r Lo c k i ng Da t a S t r uc t u r e s
Own e r o f G S D Tab l e Lo c k
Own e r o f MBX Tab l e Lo c k
Own e r o f C EF Ta b l e Lo c k
( spa r e byt e fo r a l ig nm en t )
Po r ts Wa i t i ng fo r In t e r p r o c e s so r
Re que s t B l o c k s ( o n e b i t pe r po r t )
Po r t s Ac t i v e l y Us i ng . t h e Memo ry
( o ne b i t pe r po r t )
Po r ts Wa i t i ng fo r a Re s o u r c e
( o ne b i t pe r po r t )
( o ne wo rd m a s k pe r r e so u r c e )
Po r ts Need i ng t o Re po r t Re so u r c e Ava i l ab l e
( o ne b i t pe r po r t )
( o ne wo rd m a s k p e r r e so u r c e )
Po r t s w i th Re s o u r c e s to Re po r t
( o ne b i t pe r po r t )
( 3 s pa r e wo r d s fo r a l i g nmen t )
F r e e I n t e r pr o c e s so r Re qu e s t B l o c k Li s thead
Free Po o l B l o c k Li st h e ad
I n t e rproc e s so r Reque s t Wo r k Que ue L i s th e ad s
( One l i s t h e ad pe r po r t )

l o ng wo rd
16 wo r d s
1 6 wo r d s
1 6 wo rd s
byte
byt e
byte
byte
byte
byte
byte
wo rd
wo rd

16 wo r d s
1 6 wo r d s
wo rd
3 wo rd s
quad wo r d
qua d wo rd
1 6 quadwo rd s

G l ob a l S e c t i o n s i n Sha r ed Memo ry

Th e c r e a t i o n a nd m a p p i ng o f a g l o b a l
sect ion
in
s h a r ed memo r y a r e
s l i g h t l y d i f f e r en t
f r om
t h e c o r r e s po nd i ng a c t i o n s f o r l o c a l memo r y
g l obal s e c t i o ns .
Th e g l ob a l s e c t i o n i s r e cog n i z e d a s a sh a r ed memo r y
g l o ba l
s e c t i o n b ec a u s e i t s n am e t r a n s l a t e s t o a n e qu i va l e n c e n a m e o f
t h e fo rm
s h a r e d -memo r y-nam e : s e c t i o n-name
1 1- 3 9

MEMORY MANAGEMENT DATA STRUCTUR E S
A shared memory control block
resides in local memory. One
such structure describes each shared memory.
Link to next SHB

VA of common data page

Flags

Type

Size

Reference count

Base PFN for global section pages

Port
number

TR number
of memory

Address past last byte of pool

Address of adapter control block

Figure 1 1-26

C o n t e n t s o f Sh a r ed Memo r y C o n t r o l B l o c k

Th e C r e a t e a nd M a p Sec t i on
s ys t em
s e rv i c e t h e n
s t r uc t u r e s n e c e s s a r y t o d e s c r i b e th i s s e c t i o n .
•

•

c reates

Th e g l ob a l
sec t i o n
d e sc r i pto r
fo r
s uc h
( Figure 1 1 -2 7 )
is
l oc a ted
in
sha r ed m emo r y
i n f o rma t i o n u s ed t o m a p t h e s e c t i o n .

the

data

a
sec t i o n
a nd c o n t a i n s

On l y th e po r t th a t c r e a t e s t h e g l oba l s e c t i o n h a s a g l o b a l
s ec t i on
table
entry
( in
th a t p r o c e s so r ' s
l o c a l m emo r y )
d e sc r i b i ng t h e s ec t i o n .
Th i s s e c t i o n t a b l e e n t r y i s u s e d
by
the I NS TA L L u t i l i ty t o l o ad t h e phys i c a l pag e s of the s e c t i o n
w i th t h e c o n t e n t s o f the d e s i g na t e d f i l e wh e n the s e c t i o n
is
c r e a t ed .
Th e G S TE i s a l s o us ed i f t h e Upd a t e S e c t i o n sys t em
s e r v i c e i s c a l l e d to wr i t e t h e c o n t e n t s o f a wr i ta b l e g l o b a l
s ec t i on
l o c a t ed
i n s h a r ed m em o r y bac k to i t s o r i g i n a l f i l e .
( Th e Upd a t e S e c t i o n s ys t em s e r v i c e wi l l no t h a v e a n y e f f e c t
i f i t i s i s s ue d f r om a n y po r t o th e r than t h e c r e a t o r po r t . )
B e c a us e t h e pag e s o f
a
sh a r ed
memo r y g l o b a l
sec t ion a r e
a l wa ys v a l i d , t h e r e i s n o n e e d f o r g l o b a l pag e t a b l e e n t r i e s
f o r the s ec t i on .
I n s t e ad , wh e n a
p r o c e s s maps t o
s uc h a
sect i on ,
i ts
p r o c e s s pag e t a b l e e n t r i e s a r e l o a d ed wi th t h e
pag e f r am e n um b e r s o f the s h a r ed memo r y s e c t i o n a nd m a r k e d
va l id .
Th e s e p ag e s a r e
n o t c h a rg ed
ag a i n s t t h e p r o c e s s
wo r k i ng s e t .

1 1 -4 0

MEMORY MANAG EMENT DATA S TRUCTURES

Shared memory flags

See Figure
Rest of regular
global section descriptor

:�
Deletor
port

::�
Interprocessor
lock

Number of
processor
ref. counts

Creator
port

11-14

Base PFN for section pages
- -

- -

Number of pages

Second base PFN page count pair

The assembly
time parameter
GSD$C_PFNBASMAX
(currently
4)
defines the
number of
discontiguous
pieces in a
single section

Thir-d base PFN page count pair

Fourth base PFN page count pair

PTE count for first processor
One longword for each additional port

Figure 1 1-27

C o n t e n t s o f Sha r ed Mem o r y G l o b a l Se c t i o n De s c r i p to r

Due to the way th a t VM S u s e s
s h a r ed memo r y f o r g l o b a l
sec t i o ns ,
p u t t i ng
g l o b a l s e c t i o n s i n to sha r ed memo r y , even wh e n the m emo r y un i t
i s not
c on ne c t e d
to
a n o th e r p r o c e s s o r ,
p r ov i d e s b e t t e r
s y s t em
uti l i za t ion .
E a c h p r o c e s s u s i ng t h e s h a r ed s e c t i o n s i s g e t t i ng a f r e e
e x t e n s i o n t o i t s wo r k i ng s e t .
Th e r e i s n o d emand pl a c e d o n t h e g l o b a l
pag e
tabl e .
Th e
local
phys i c a l m emo r y th a t wo u l d o th e r w i s e b e
r e q u i r e d to c o n t a i n s uc h e n t i t i e s a s DC L o r t h e Run-T i m e
Li bra ry
is
a v a i l a b l e f o r o th e r u s e s s uc h a s a n e x p a nd ed ph ys i c a l pa g e c a c h e ( f r e e
pag e 1 i s t )
•

1 1-4 1

MEMORY MANAG EMENT DATA S TRUCTURE S

11. 7 . 3

Ma i l bo x e s i n Sha r e d Memory

Wh e n a m a i l box i s c r e a t ed in s h a r ed m em o r y ,
it
is
d e sc r i b ed
by a
s h a r ed m emo r y m a i l bo x d e sc r i p to r
b l o c k ( MB X ) l o c a ted i n the s h a r ed
memo r y ( F i g u r e 1 6 - 2 ) .
I n a d d i t i o n , e a ch po r t c o n ne c t ed to the
s h a r ed
memo r y m a i l box h a s a un i t c o n t r o l b l o c k ( UC B ) i n i t s l o c a l mem o r y I /O
d a t a b a s e t h a t m a k e s t h e c o nnec t i o n b e twe e n t h e l o c a l I /0 s ys tem a nd
t h e s h a r ed memo r y m a i l bo x .
Th e r e l a t i o n s h i ps o f s h a r ed memo r y m a i l bo x
d a t a s t r uc t u r e s a r e p i c t u r e d i n F i g u r e 1 6 - 3 .

11. 7. 4

Common Event F l a g C l us t e r s i n Sha r ed Memo ry

As wi th g l ob a l s e c t i o n s and m a i l bo x e s ( a nd the s h a r e d memo r y i t s e l f ) ,
th e r e
a r e d a ta
s t r uc t u r e s
i n sh a r ed memo r y a n d o t he r s t r uc t u r e s i n
l o c a l memo r y r e q u i r ed to f u l l y d e sc r i b e a c ommo n e v e n t f l ag
c l us t e r
l oc a ted
i n sha r ed memo r y .
Th e s h a r ed memo r y d a ta s t r uc t u r e i s c a l l ed
a ma s te r CEB ( c ommon e v e n t b l o c k ) a nd c o n t a i n s the o n l y v a l i d
set o f
event
f l ag s .
E a c h po r t c o n n e c ted t o th i s c ommon e v e n t f l ag c l us t e r
h a s a s l a v e C E B t h a t l o c a t e s th e m a s te r .
Th e r e l a t i o n sh i p b e twe e n th e
m a s te r
CEB a nd th e s l a v e C E Bs i s p i c t u r ed i n F i g u r e 9 - 4 .
Th e l a yo uts
o f t h e m a s te r
a nd
s l av e c ommo n
event
b l o c k s a r e p i c t u r ed
in
Figure 9-5 .

1 1-42

CHAPTER 1 2
PAG ING DYNAM I C S

In
the
p r ev i o u s c h a p t e r ,
the v a r i o u s d a t a
s t r uc t u r e s
th a t a r e
ma i n t a i n ed b y m em o r y m a n ag em e n t we r e d e sc r i b ed i n a somewh a t s t e r i l e
f a sh i o n , o u t o f the c o n t e x t i n wh i c h
they a r e
used .
Th i s c h a pt e r
s h o ws h o w t h e v a r i o u s
s t r uc t u r e s
a r e m a n i pu l a t ed b y t h e pag e r i n
r e s p o n s e t o d i f f e r e n t fo rms o f pag e f a u l t s .
Al t h o ug h pag e r a c t i o n i s d e sc r i b ed h e r e , i t
i s n o t p r e s e n t ed
in a
f l o wc h a r t o r d e c i s i o n f a s h i o n .
Ra t h e r , the a c t i o n s a r e d e s c r i b ed i n
t e rm s o f mod i f i c a t i o n s t o d a t a s t r uc t u r e s .

12. 1

OVERVIEW OF PAG ER OPERAT I ON

Be f o r e we b eg i n d i s c u s s i ng how the pag e r r e a c t s to d i f f e r e n t fo rms o f
pag e
f a u l ts ,
we
wi l l
b r i e f l y d e sc r i b e the o v e r a l l o pe r a t i o n o f the
pag e r .

12. 1 . 1

Ha r d wa r e Ac t i o n

Al l p r og r am r e f e r e n c e s g e n e r a t ed b y t h e C P U a r e
v i r t ua l
ad d r e s s e s .
Each add ress mus t be
t r a n s l a t ed
to
a
phys i c a l
a d d r e s s b e fo r e a
r e f e r e n c e to memo r y ( o r a n I /O s p a c e pag e ) c a n b e m ad e .
Th e v i r t ua l
add ress
( F i g u r e 1 2 - 1 ) i s used by the a d d r e s s t r a n s l a t i o n m e c h a n i sm to
f i nd the pag e t a b l e e n t r y th a t wi l l be used to t r a n s l a t e th e a d d r e s s .
I f the pag e t a b l e e n t r y i s v a l i d , i t s c o n t e n t s a r e used
to
t r a n s l a te
the v i r t u a l a d d r e s s to a phys i c a l a d d r e s s a nd e x e c u t i o n c o n t i n u e s .
If
the
pag e
table
entry
is
i nv a l i d
( PT E < 3 1 >
0) ,
then
a
t r a n s l a t i o n - no t-va l i d f a u l t i s g en e r a ted .
F i g u r e 1 2 - 2 shows the s t a t e
o f t h e k e r n e l s t ac k f o l l o w i ng a pag e f a u l t .
=

12 . 1 . 2

I n i t i a l Pag e r Ac t i o n

Be f o r e the pag e r d o e s a n y wo r k , i t pe r f o rm s a c o n s i s t e n c y c h e c k b y
d em a n d i ng th a t the I P L b e no h i g h e r t h a n 2 .
I f the I PL i s h i g h e r t h a n
2 , a f a t a l b ug c h e c k i s g e n e r a t ed .
Th i s c h ec k i s mad e fo r two r e a so n s .
•

Co d e t h a t i s ex e c u t i ng a t a h i g h e r I P L n e e d s
to
pe r f o rm a
se r i e s
o f i n s t r uc t i o n s wi tho u t b e i ng i n t e r r upted .
I f a pag e
f a u l t h a p p e n s , the f a u l t i ng p r o c e s s m i g h t
be
r emoved
f r om
execut i on ,
a l l o w i ng
a n o th e r
p r o c e ss
to
exec ute the same
r o u t i n e o r a c c e s s the s ame p r o t e c ted d a t a s t r uc t u r e .

12-1

PAG ING DYNAM I C S
•

Pag e f a u l t s a r e e x c e p t i o n s tha t h a pp e n to a
process .
Wh en
the
sys t em i s e x e c u t i ng at I P L h i g h e r th a n 2 , i t i s o f te n o n
t h e i n t e r r upt
s t ac k ,
a c t i ng
i n r e s po n s e
to
an external
t r igger .
Th e r e
is
n o t n ec e s s a r i l y a p r o c e s s th a t c a n b e
c ha rg ed f o r th e pag e f a u l t .

31 30 29

Virtual Page N umber

Byte Offset

P1 Space I ndicator if VA<31 >

'---� System Virtual Address Space

Indicator

VA<31 : 30> Selects the page table
0 PO Page Table
1 P1 Page Table
2 System Page Table
3 reserved
VA<29:9> is used as a longword
i ndex i nto the selected table

F i g u r e 1 2- 1
Fo rma t o f Vi r t ua l Ad d r e s s Showi ng F i e l d s Us e d
to Lo c a t e Pa g e Ta b l e En t ry Th a t M a ps t h e Pag e

stack growth

Reason Mask

�

Invalid Virtual Address �

PC of Faulting Instruction
PSL at Time of Fault

State of the Kernel Stack
following a Translation not - Valid Fault

Reason Mask for Translation Not - Valid Fault

This Bit is Always 0 for
Translation - Not - Valid Faults
,.pTE Reference
O....,. V irtual Address Not Valid
1 ....,.A ssociated PTE not Valid
....-----+!Intended A ccess Type
O....,. Read Access
1 ....,. M odify or Write Access
....___

F i gu r e 1 2 - 2
S t a t e o f the Ke r n e l S t a c k Fo l l o w i ng
a T r a n s l a t i o n-No t-Va l i d F a u l t

1 2-2

PAG ING DYNAM I C S

Th e n e x t s te p tha t the pag e r t a k e s i s to r e t r i ev e th e i nv a l i d
v i r tual
add r e s s
f r om t h e k e r n e l
s t ac k .
I t u s e s th i s a d d r e s s to l o c a t e t h e
pag e t ab l e e n t r y th a t m a ps th i s pag e b y p e r f o rm i ng the s a m e o pe r a t i o n s
th a t t h e a d d r e s s t r a n s l a t i o n m e c h a n i sm u s e s .
1.

Th e u ppe r two b i t s o f t h e v i r t ua l add r e s s ( VA < 3 1 : 3 0 > )
wh i c h pag e t a b l e ( o r wh i c h b a s e r eg i s t e r ) to u s e .

Th e v i r t u a l a d d r e s s f i e l d ( VA < 2 9 : 9 > )
i nd e x i n t o t h e pag e t a b l e .

i s u s ed

sel ect
l o ng wo r d

B e f o r e t h e pag e t ab l e e n t r y i s e x am i n ed , the pag e r d e t e rm i n e s
wh e th e r
the
s ys tem v i r t ua l
pa g e c o n t a i n i ng
t h e pag e t a b l e e n t r y i s i t s e l f
va l id .
( Th i s
check avo id s
t h e n e c e s s i t y o f ma k i ng
the
pag e r
r ec u r s i v e . )
If
not ,
t h e pag e t a b l e pag e i s mad e va l i d f i r s t .
No te
th a t t h e pag e r pe r f o rm s th i s c h e c k w i tho u t u s i ng t h e f l ag b i t
in
the
e x c e p t i o n pa r a m e t e r .
takes d i ffe r ent
Onc e t h e pag e t ab l e e n t r y i s ava i l a b l e ,
t h e pag e r
( See
a c t i o n s d e pe nd i ng o n the n a t u r e o f the i nva l i d pag e ta b l e e n t r y .
Th e
F i g u r e l l - 3 f o r t h e d i f f e r e n t fo rms o f i nva l i d pag e ta b l e e n t r y . )
next
s ev e r a l
sect i ons
w i l l d e s c r i b e some o f the ma j o r pa th s th r o ug h
r e ad
and
wr i t e
t h e pag e r .
Ex t r a o rd i n a r y c o nd i t i o n s s uc h a s
e r ro rs
wi l l o n l y b e m e n t i o ne d i n pa s s i ng .

12 . 2

PAGE FAU LTS FOR PROC E S S PR IVATE PAG ES

Th e f i r s t s e t o f
pag e
faul ts
th a t
a r e d i s c u s s ed
conc e r n
proc e s s
pr i va te
pag e s .
Th e d i f f e r en t pa th th r o ug h the pag e r wh e n s h a r i ng i s
i nvo l v ed i s d i s c u s s ed i n the n e x t s e c t i o n .
Th e r e a r e fo u r c a s e s
th a t
m u s t b e d e sc r i b ed .
•

•
•

12. 2. 1

Two o f t h e c a s e s i nv o lve a pag e tha t
i s o r ig i na l l y
f a u l ted
f r om a n
imag e
file .
Th e
two c a s e s a r e d i s t i ng u i sh e d by
wh e th e r o r not t h e s e c t i o n i s c o py on r e f e r e nc e .
A th i r d p r i v a t e s e c t i o n c a n c o n s i s t o f
z e r o pag e s .

se r i es

d em a nd

resul t
f r om bo th
F i n a l l y , a n i n t e rm e d i a te s t a t e
th a t c a n
z e r o pag e s h a s
the
c o py-on- r e f e r e n c e
pag e s a nd
d em a nd
f a u l t i ng pag e r e s i d i ng i n a pag e f i l e .

Pag e Lo c a ted i n a n Ima g e F i l e

Th e r e a r e two d i f f e r e n t type s o f pag e th a t c a n i n i t i a l l y r e s i d e
in
a
pr i va te
i m ag e f i l e .
Th e pag e t a b l e e n t r y f o r e a c h c o n t a i n s a p r o c e s s
s e c t i o n ta b l e i nd ex .
Th e o n l y
init ial
d i f f e r e n c e b e t we e n t h e
two
pag e s
i s the
s e t t i ng o f t h e c o py-on- r e f e r e n c e b i t i n th e pag e t a b l e
entry ( Figure 1 1-3 ) .

1 2-3

PAG ING DYNAM ICS

12. 2. 1 . 1
Imag e Pag e Th a t I s No t Copy o n Re f e r en c e - Th e f i r s t t ype o f
pag e
f a u l t tha t i s d e sc r i b ed i nvo l v e s a pag e i n a n i m ag e f i l e t h a t i s
n o t c o py o n r e f e r e nc e .
Th e v a r i o u s t r a ns i t i o n s th a t s uc h a
pag e
can
po s s i b l y m a k e a r e i l l u s t r a t ed i n F i g u r e 1 2 - 3 .
Th e n umbe r s i n c i r c l e s
a r e k e yed t o expl a na t i o n s o f e a c h t r a n s i t i o n th a t a r e
l i s t ed b e l o w .
( Fo r
s i mpl i c i ty ,
c l u s t e r ed
r e ad s
a nd wr i t e s a r e
i g no r e d
i n th e
S e c t i o n 1 2 . 5 d i s c u s s e s a l l a s pe c t s o f pag i ng
d i s c us s i o n th a t f o l l o ws .
I /0 . )
Th e pag e t a b l e e n t r y i s i n i t i a l l y s e t to th e f o rm i l l u s t r a ted
a t th e
top o f Figure 1 2-3 .
I t c o n t a i n s a p r o c e s s s e c t i o n ta b l e i nd ex ( PS T X )
w i th t h e c o py-on- r e f e r e n c e b i t ( PT E < l 6 > ) c l e a r .
(1)

A page faul t o cc u r s .
Th e pag e r
uses
the v i r tua l
add r e s s
e x c e pt i o n p a r am e t e r to l o c a t e the pag e t a b l e e n t r y .
Th e f o rm
o f the pag e t a b l e
entry
i s process
sec t ion
tabl e
i nd e x .
I n f o rma t i o n c o n t a i n ed
in
the p r oc e s s
s e c t i on tab l e ent r y
i n d i c a t e s wh i ch v i r t ua l b l o c k i n t h e
i mag e
file
sho u l d b e
r ead .
Th e
pag e r a l l o c a t e s a phys i c a l pag e f r om the h e a d o f
t h e f r e e pag e l i s t .
Th e pag e i s a d d ed t o t h e p r o c e s s wo r k i ng
set .
Th i s s t e p m a y r e q u i r e the p ag e r to r emove a no the r pag e
f r om the wo r k i ng s e t i n o r d e r
to
make
r o om
fo r
the
pag e
c u r r e n t l y b e i ng a d d ed .
Th e PFN a r r a ys a r e
i n i t i a l i ze d .
Th e
S TATE a r r a y e l em e n t
i nd i c a t e s
th a t a r e ad i s i n p r og r e s s .
Th e P T E a r r a y e l em e n t
po i n ts to t h e p r o c e s s pag e t a b l e e n t r y .
Th e wo r k i ng s e t l i s t
i nd e x
a r r a y e l em e n t l o c a t e s the wo r k i ng l i s t e n t r y j u s t s e t
up .
Th e
BAK a r r a y e l em e n t
is
l o ad ed w i th
the
initial
c o n tents o f
th e p ag e t a b l e e n t r y , th e p r o c e s s s e c t i o n t ab l e
i nd ex .
Th e r e f e r e n c e c o un t a r r a y e l em e n t c o n t a i n s a two , o n e
for
b e i ng
in
t h e wo r k i ng
s e t a nd
one
fo r
t h e r e ad i n
p r og r e s s .
Th e pag e r b u i l d s a n I /0 r e qu e s t p a c k e t
( Se c t i on 1 2 . 5 )
th a t
Th e p r o c e s s i s p l a c e d
d e sc r i be s t h e r e ad th a t i s b e i ng d o n e .
i n to a pag e f a u l t wa i t s ta t e .

(2)

Be c a us e mo s t o f the wo r k wa s d o ne i n r e s po n s e to the
initial
to
pag e r e a d
l i ttl e
f a ul t ,
l eft
do wh e n th e
the r e
is
( b ut s t a ys
i s d e c r em e n t e d
c ompl e te s .
Th e r e f e r e n c e c o un t
The s ta t e o f t h e
a bo v e
s p e c i a l h a ppe n s )
zero
s o n o th i ng
F i na l l y , the va l i d
pag e i s c h a ng ed to a c t i v e a nd v a l i d .
bit
set
in
is
p r o c e s s pag e t a b l e e n t r y a nd the p r o c e s s i s
th e
r emoved f r om t h e pag e f a u l t wa i t s t a t e .
Th e n e x t
t i me
th a t
the proces s
i s s e l e c t ed f o r e x e c ut i o n , i t wi l l e x e c u t e t h e
s am e i n s t r uc t i o n th a t c a used t h e i n i t i a l pag e f a u l t .
•

( 3)

O n e t r a n s i t i o n tha t a v a l i d
pag e c a n und e rg o
( a nd
stil l
r em a i n v a l i d ) o c c u r s wh e n t h e pag e i s modi f i ed a s a r e s u l t o f
i n s t r uc t i o n e x e c u t i o n .
Th e h a rdwa r e s e t s the mod i fy b i t
in
t h e pag e
tab l e entr y .
Th e c h ang e i s no t n o t ed a t th i s t i m e
in the PFN d a ta base .

1 2-4

PAG ING DYNAMI C S

PFN Data

PTE contains
Process Section
Table lndex(PSTX)

Page NOT in
physical memory No PFN data

from bottom
of page

Read in Progress
REFCNT - 2
BAK = PSTX

- PTE � Transition
- in Working Set

r- - -.

I
I
I
I
I
�---

- PTE is valid
- in Working Set
- Modify Bit Clear

.,...,

1---{ 3 ,_

- PTE is valid
- in Working Set
- Modify Bit Set

-l
I
I
I
I
_.I

_ _ _

I
I
I

PTE � Transition

I
I

Saved Modify Bit Set

Active and Valid
REFCNT > 0
BAK = PSTX

Release Pending
REFCNT > 0
BAK - PSTX

I
I
I
I

-&1

Modified Page List
REFCNT 0
BAK
PSTX

I
I

f.
I
I
I

-- - - - -

_ _ _

I
I

4V-

--0-

PTE � Transition

Write in Progress
1
REFCNT
BAK PSTX

Saved Modify Bit Clear

Free Page List
REFCNT
0
BAK
PSTX

PTE > Transition
Saved Modify Bit Clear

to top
of page

Figure 1 2-3

Page Fault Transition

Other Transitions

Figure 1 2-3

S t a t e D i a g r am Sh o w i ng Pag e T r a n s i t i o n s f o r P r i v a t e
S e c t i o n Pag e Th a t I s No t C o py o n Re f e r e nc e

12-5

PAG ING DYNAMI C S

(4)

Wh e n the pag e
is
r emoved
s ev e r a l th i ng s h a ppen .

f r om

the

process

wo r k i ng

set ,

Th e wo r k i ng s e t l i s t e n t r y i s m a d e a v a i l a b l e .

Th e WS LX a r r a y e l eme n t i s c l e a r ed .

Th e mod i f y b i t i n the pag e t ab l e e n t r y i s l og i c a l l y
i n to the PFN s t a t e a r r a y e l eme n t .

ORed

Th e VA L I D , TY P O ,
a nd
TY P l b i t s
in
the
c l ea r e d .
Th e PFN f i e l d i s l e f t a l o n e .

all

Th e
RE FCNT a r r a y e l em e n t i s d e c r em e n t e d .
If
the
refe rence
count goes
t o z e r o , th e pag e i s put o n to the
f r e e or mod i f i ed pag e l i s t , a c c o r d i ng to the
s e t t i ng
of
the s a ved mod i fy b i t i n the PFN STATE a r r a y e l em e n t .
Th e
new l o c a t i o n o f the pag e
is
i n se r t ed
i n to
the
S TATE
array.

PTE

are

No t e tha t pag e s a r e no t r emoved f r om the wo r k i ng
s e t un t i l
r o o m i s r e q u i r ed f o r o th e r pa g e s , u n t i l th e v i r t ua l pag e s a r e
d e l e t ed , o r i n r e s po n s e t o a $ PURGW S s y s t em s e r v i c e c a l l .
(5)

I f the r e f e r e n c e c o un t d o e s n o t g o to
zero ,
th i s
i nd i c a t e s
th a t t h e r e
is
o u t s t a nd i ng I /O f o r th i s pag e .
Th e s t a t e i s
c h a ng ed to r e l e a s e pend i ng .
Th e u l t i ma t e d e s t i na t i o n f o r the
pag e
( f r e e o r mod i f i ed l i s t ) i s r e c o rd ed i n th e s a v ed m o d i fy
b i t i n the STATE a r r a y .

(6)

Th e I /O c o mpl e t i o n r o u t i n e d e c r emen t s
r e f e r e n c e c o un t s
fo r
pag e s
tha t a r e l o c k e d d o wn .
Wh e n th i s r o u t i n e d e t e c ts t h a t
t h e c o un t h a s g o n e to z e r o , i t pl a c e s t h e pag e o n e i th e r
the
f ree
l i st or
th e mo d i f i ed l i s t as a pp r o p r i a t e .
Th e STATE
a r r a y e l em e n t i s c h a ng ed .

(7)

Th e mod i f i ed pag e wr i te r wi l l ev e n t ua l l y wr i te th i s
ph ys i c a l
pag e t o
i t s b a c k i ng s t o r e a d d r e s s , wh i c h i s l o c a t ed i n the
PFN BAK a r r a y .
Wr i t a b l e pag e s th a t a r e no t c o py on r e f e r e n c e
a r e wr i t t e n b a c k to the i mag e f i l e th a t th e y o r i g i n a l l y c am e
f r om .
Th e s t a t e o f t h e pag e i s s e t t o wr i t e i n p r og r e s s .
Th e s a ved
mod i fy b i t
i s c l e a r ed .
Th e r e f e r e n c e c o un t o f one r e f l e c t s
th i s o u t s tand i ng o u t put o p e r a t i o n .
I t i s wo r th no t i ng a t th i s t i m e th a t wr i ta b l e p r i v a te pag e s
t h a t a r e n o t c o py o n r e f e r e n c e a r e n o t usua l p r od uc t s o f the
l i nke r .
Such s e c t i o n s must
b e c r e a ted manua l l y wi th
the
C r e a t e a nd Ma p ( P r i v a t e ) S e c t i o n s y s tem s e r v i c e .

(8)

Wh e n the mod i f i ed pag e wr i te c ompl e t e s , the pag e i s p l a c ed o n
the
f r e e pa g e l i s t ( by t h e s ame r o u t i n e th a t d ec r ements the
r e f e r e n c e c o un t , n o t e s t h a t i t we n t to z e r o , a nd
no t e s
that
the s a v e d mod i f y b i t i s c l e a r ) .

(9)

Wh i l e the phys i c a l pag e h a s r em a i n e d a t t a c h ed to the p r o c e s s ,
t h e pa g e
ta b l e e n t r y h a s a l wa ys c o n t a i ned a PFN a n d the PFN
PTE a r r a y h a s a l wa ys c o n t a i n e d the
add r e ss o f
the
process
pag e ta b l e e n t r y .

1 2-6

PAG ING DYNAM I C S

Wh e n th e ph y s i c a l pa g e i s r e u s e d f o r a n o th e r pu r po s e , s ev e r a l
s t e ps m u s t b e t a k e n
t o b r e a k the t i e s b e twe e n the p r o c e s s
v i r t ua l pag e a nd t h e phys i c a l
pag e
th a t
is
a b o ut
to
be
r e used .
Th e p r o c e s s PTE mus t be a l t e r ed to r e f l e c t t h e b a c k i ng
stor e
add ress o f
the
pag e .
( Th e PFN PT E a r r a y i s u s e d to l o c a t e
t h e pag e t a b l e e n t r y . ) I n th i s c a s e , the PTE i s r e s e t so th a t
it
conta i ns
a
p r o c e s s s e c t i o n tab l e i nd e x ( P STX ) , t h e s am e
c o n t e n t s t h a t i t h a d b e f o r e t h e i n i t i a l pa g e f a u l t .
Th e PFN a r r a y e l em e n t s f o r th i s phys i c a l pag e a r e a l l c l e a r ed
b e f o r e t h e pag e i s pa s s e d o n to the new own e r o f the phys i c a l
pag e .
In
pa r t i c u l a r ,
t h e PTE a r r a y e l em e n t ,
the o n l y
connec t i on
f r om t h e PFN d a t a b a s e t o the p r o c e s s pag e t a b l e ,
i s c l e a r ed .

12. 2. 1. 2
Pag e Fa u l t s o u t o f T r a n s i t i o n S t a t e s - F i g u r e 1 2 - 3
a l so
shows t h e t r a n s i t i o n s tha t a pag e m a k e s wh en a pa g e f a u l t o c c u r s wh i l e
the phys i c a l pag e i s i n the t r a n s i t i o n s t a t e .
Wh i l e the c h a ng e s b a c k
to
the
ac t i ve
s t a t e a r e somewh a t s t r a i g h t fo r wa r d , the r e a r e d e t a i l s
a bo u t e a c h f a u l t t h a t sho u l d b e m e n t i o n e d .
No t e th a t e a c h o f
th e s e
pag e
faul ts
r equi res
t h a t a n e w wo r k i ng s e t l i s t e n t r y b e a c q u i r e d ,
wh i c h m a y i nv o l v e t h e r emo v a l o f some o th e r pag e
f r om
the
process
wo r k i ng s e t .
1.

A pag e f a u l t f r om the f r e e pag e l i s t i s r e s o l v e d
by p l a c i ng
t h e pag e b a c k i n to the a c t i v e a nd v a l i d s t a t e , r e s e t t i ng th e
PTE , a nd i n c r eme n t i ng the r e f e r e n c e co unt .

A pag e f a u l t f r om t h e m o d i f i ed
l i st has
e x ac t l y the
s ame
e f fec t .
Th e
fact th a t t h e pag e wa s p r e v i o us l y mo d i f i ed but
n e v e r wr i t t e n to
i ts
b a c k i ng
s to r e a d d r e s s
is
r e f l ec ted
p i c to r i a l l y by p u t t i ng t h e pag e b a c k i n to i t s m od i f i e d s t a t e .
I n f a c t , t h e mod i f y b i t i n the P T E i s n o t a c t ua l l y t u r ne d
on
b y th e p ag e r .
Ra the r , th e s a v e d mod i fy b i t i n the PFN S TATE
a r r a y r e c o r d s the f a c t tha t the pag e has no t been b a c k e d u p .

A pag e f a u l t f r om t h e r e l e a s e p e nd i ng s t a t e h a s
no
spec i a l
e f fects .
Ag a i n ,
the
s t a t e i s c h a ng ed to a c t i v e , t h e v a l i d
b i t i n th e PT E i s t u r ned
on ,
and
th e
r e f e r e nc e c o un t
is
i n c r em e n t e d .
A l i ttl e
artistic
l i c en s e
is
t a ke n
in
th e
f igure
to
d i f fe rent i a te
phys i c a l
pag e s
t h a t we r e mod i f i ed f r om pag e s
th a t we r e no t .
Ag a i n , t h e o n l y d i f f e r e n c e b e twe e n t h e
t wo
pag e s i s t h e s e t t i ng o f t h e s av e d mod i f y b i t i n the PFN S TATE
a r r a y , n o t the s e t t i ng of t h e m o d i fy b i t in th e PTE .

Th e t r a n s i t i o n tha t d e s e r v e s s pe c i a l c omme n t i s a pag e
faul t
th a t o c c u r s wh i l e
t h e mo d i f i ed pag e wr i t e r i s wr i t i ng the
pag e t o i t s b a c k i ng s t o r e a d d r e s s .
Th e s a v e d mod i f y b i t
is
c l e a r ed
b e f o r e t h e wr i te b eg i n s s o th a t th e pag e w i l l b e
p l a c e d o n t h e f r e e l i s t wh e n the wr i te c om p l e te s .

1 2 -7

PAG ING DYNAM I C S

A l thoug h t h e pag e h a s no t ye t b e e n comp l e t e l y b a c k e d u p ,
th e
a s s um p t i o n i s mad e tha t the wr i te w i l l c ompl e te s uc c e s s f u l l y .
Pag e f a ul t s c a n
th us p u t t h e pag e
i n to
the
a c t i v e but
u nmod i f i ed s t a t e .
Th e o n l y d i f f i c u l t y o c c u r s i n t h e e v e n t o f
a wr i t e e r r o r .
Th e I /0 comp l e t i o n r o u t i ne d e t e c t s th i s s ta t e
o f a f fa i r s a nd t u r n s t h e s a v ed mod i fy b i t b a c k o n .

1 2 . 2 . 1 . 3 Copy-o n-Re fe renc e Pag e - A mo r e commo n
type o f wr i ta b l e
p r o c e s s p r i v a t e pag e
is
c a l l ed
c o py o n r e f e r en c e .
F i g u r e 1 2-4
i l l u s t r a t e s t h e t r a n s i t i o n s tha t s uc h a pag e m a k e s
f r om
i ts
i ni tial
pag e f a u l t un t i l i t i s wr i t t e n to som e b a c k i ng s to r e a d d r e s s .
Many o f t h e t r a n s i t i o n s tha t o c c u r h e r e a r e no d i f f e r e n t f r om t h e c a s e
j us t d e sc r i b ed .
Th i s s e c t i o n wi l l n o t e e a c h t r a n s i t i o n b u t o n l y
e l abo r a t e o n tho s e a r e a s t h a t a r e d i f f e r en t .
(1)

Th e i n i t i a l s e t t i ng o f the pag e t a b l e e n t r y ( S TART-I
in
the
f igure)
is
ag a i n process
s ec t i o n t a b l e
i nd ex ,
but
the
c o py-on- r e f e r e n c e b i t ( PT E < l 6 > ) i s now s e t .
Wh e n a
pag e
f a ul t o c c u r s , t h e pag e r a g a i n a l l o c a t e s a ph ys i c a l pag e , s e t s
i t s PFN i n to t h e PT E , a nd i n i t i a t e s the r e a d .
Two
i m po r ta n t
s teps
are
taken
a t t h i s t i me th a t d i f f e r f r om t h e p r ev i o us
case .
F i r s t , t h e s a v ed mod i f y b i t i n t h e PFN S TATE a r r a y i s
t u r ne d
on.
Th i s g u a r a n t e e s
tha t
t h e pag e w i l l b e wr i t t e n t o i t s
b a c k i ng s to r e a d d r e s s wh e n r emov e d f r om th e
p r o c e s s wo r k i ng
set ,
r eg a r d l e s s o f wh a t i n s t r uc t i o n s o r I /0 o pe r a t i o n s the
p r o c e s s c ho o s e s t o e x e c u t e .
S e c o nd , t h e BAK a r r a y e l emen t i s s e t to
po i n t
to
th e
pag e
file,
w i th a n
i nd i c a t i o n
th a t
no
block has
ye t b e e n
a l loca ted .
At th i s t i m e , a l l t i e s t o t h e o r i g i n a l i m ag e f i l e
a r e b r o ke n .
Wh e n t h e mo d i f i e d pag e wr i te r wa n t s to wr i te
t h i s pag e to i t s b a c k i ng s to r e a d d r e s s ( a s i t c e r t a i n l y w i l l
b e c a us e th e
s a v ed mod i fy b i t wa s j u s t t u r ned o n ) , i t w i l l
a l l o c a t e a b l o c k i n t h e pag e f i l e a nd wr i te t h e c o n t e n t s o f
t h e ph y s i c a l pag e t he r e .

(2)

Wh e n the r e a d c ompl e t e s , the pag e i s
v a l i d ( a nd e f f ec t i v e l y mod i f i ed ) .

ma r k e d

active

a nd

(4)

Wh e n the pag e i s r emoved f r om th e p r o c e s s wo r k i ng
set
( and
the
r e f e r e nc e c o un t
is
z e r o ) , the pag e i s un c o nd i t i o n a l l y
p l a c ed o n t h e mod i f i ed pag e l i s t .

(5)

I f the r e f e r e n c e c o un t d i d n o t g o to z e r o wh e n the
pag e wa s
r emoved
f r om th e p r o c e s s wo r k i ng s e t , the ph ys i c a l pag e i s
p l a c ed
i n to
the
r e l e a s e p e nd i ng
s t a te
un t i l
th e
I /O
c ompl e t e s .

(6)

At tha t t i m e , t h e pag e i s p l a c ed on the mod i f i ed pag e l i s t .

A pa g e f a ul t f r om e i th e r
the
r e l e a s e p e nd i ng
s t a te o r
f r om
th e
mod i f i ed page l i s t p u t s t h e pag e b a c k i n to the a c t i v e ( b u t e f f e c t i v e l y
mod i f i ed ) s t a te .
Th a t i s , t h e s av e d mod i f y b i t i n th e PFN S TATE a r r a y
r ema i n s s e t , c a us i ng t h e pag e to b e put b a c k o n the mod i f i ed pag e l i s t
wh e n i t i s r emoved f r om t h e wo r k i ng s e t a g a i n .

1 2-8

PAG I NG DYNAM I C S

- I
PTE contains
PSTX,CRF

PTE contains GPTX
GPTE contains
GSTX,CRF

- PTE => Transition
- In Working Set
- Saved Modify Bit Set

PTE =>
Demand Zero Page

The area within
doHed lines Is also
shown In Figure 1 2-7

Page NOT In
physical memory no PFN data

Read In Progress
REFCNT = 2
BAK = PGFLX,O

Active and Valid
REFCNT >0
BAK
PGFLX,O

PTE => Transition
Saved Modify Bit Set

P - - - - - - - - - �
I

PTE => Transition
Saved Moj:ilfy Bit Set

to
Figure 1 2-5

P - .!

Release Pending
REFCNT >0
BAK = PGFLX,O

Modified Page List
REFCNT = 0
BAK = PGFLX,O

- --®- - �

Page Fault Transition

Other Transitions

Figur e 1 2-4
S t a t e D i a g r am Showi ng Pag e T r a n s i t i o n s fo r P r i v a t e
a nd G l o b a l Copy-o n-Re f e r e n c e Pag e s a nd fo r Demand Z e r o Pag e s

1 2-9

PAG I NG DYNAM I C S
Th e t r a n s i t i o n f r om th e mod i f i ed pag e l i s t
th a t
is
t a k e n wh e n
th e
m o d i f i ed
pag e wr i t e r wr i tes t h e pag e to i t s b a c k i ng s to r e a d d r e s s ( i n
t h e pag e f i l e ) f i t s i n to the t r a n s i t i o n d i ag r am f o r
f a u l ts
f r om
the
pag e
file
( Figure 1 2 -5 ) .
Th e
c o n n e c t i o n b e twe e n
F i g u r e 1 2 - 4 a nd
F i g u r e 1 2 - 5 i s i nd i c a t e d by p a th C i n the two f i g u r e s .

12. 2. 2

Demand Z e r o Pag e s

Th e i n i t i a l s e t t i ng o f a pa g e t a b l e e n t r y c a n b e s e t t o d emand z e r o a s
a
r e s u l t o f a C r e a t e Vi r t ua l Ad d r e s s o r E x p a nd Reg i o n s ys tem s e r v i c e .
O n e o f t h e s e s e r v i c e s c a n be i s s ue d e x p l i c i t l y by th e
p r o c e s s o r on
i ts
b e ha l f by t h e
s ys t em
( a s pa r t
o f i mag e a c t i v a t i o n o r i n the
L I B $G E T_VM Run-T i m e L i b r a r y p r o c ed u r e ) .
Wh e n the pag e r d e t e c t s a pag e f a u l t f o r a d em a nd z e r o pag e ,
t h e fo l l o wi ng s t eps .

takes

A phys i c a l pa g e i s a l l o c a ted f r om t h e beg i n n i ng o f
page l i s t .

the

free

Th e PFN a r r a y e l em e n t s
a re
i n i t i a l i zed .
Th e
e l em e n t po i n t s to the p r o c e s s pag e t a b l e e n t r y .

PTE

a r r ay

Th e BAK a r r a y e l em e n t d e no t e s a
t h e pag e f i l e .

block

Th e pag e i s f i l l ed w i th z e r o s .
Th i s i s d o ne wi th
a MOVC 5
i n s t r uc t i o n
tha t u s e s a z e r o - l eng th so u r c e s t r i ng a nd a n u l l
f i l l cha r a c te r .

Th e r e f e r e nc e c o un t i s i nc r em e n ted , the pa g e i s a d d ed to
p r o c e s s wo r k i ng s e t , a nd t h e s t a t e is set to a c t i v e .

F i n a l l y , the f a u l t i s d i sm i s s ed a nd c o n t r o l i s p a s s e d bac k to
t h e us e r p r o c e s s wi tho ut i n te r r u pt i o n .

Th e s e s t e p s a l l t a k e p l a c e
po r t i o n o f F i g u r e 1 2 - 4 .

12 . 2 . 3

a l o ng

p a th 3

n o t-ye t-a l l o c a ted

the

uppe r

r ight

the

h a nd

G l o b a l Co py-on -Re f e r e nc e Pag e s

Th e r e i s o n e o the r f o rm o f pag e tha t me r g e s i n to t h e s a m e s e t o f s t a t e
t rans i t ions
a s p r i v a t e c o py-on- r e f e r e n c e
s e c t i o n s a nd d em a nd z e ro
pag e s .
Th i s fo rm i s a g l oba l c o py-o n- r e f e r e n c e pa g e .
Th e d e t a i l s o f
g l o b a l pa g e f a u l t r e so l u t i o n a r e d i sc u s s e d i n Sec t i o n 1 2 . 3 .
Fo r n o w , l e t us s i mpl y s t a t e tha t g l ob a l c o py-on- r e f e r e n c e pa g e s a r e
i n i t i a l l y f a u l ted f r om a g l oba l imag e f i l e b u t , f r om th a t t i m e o n , a r e
i nd i s t i ng u i sh a b l e f r om p r o c e s s p r i v a t e pag e s .

12-10

PAG ING DYNAM I C S

PTE contains
Page File VIrtual
Block Number (PGFLVB)

Page NOT In
physical memory no PFN data

from bottom
of page

Read in Progress
REFCNT = 2
BAK = PGFLVB

PTE => Transition
in Working Set

Active and Valid
REFCNT >0
BAK = PGFLVB

- PTE Is Valid
- in Working Set
- Modify Bit Set

- PTE Is Valid
- In Working Set
- Modify Bit Clear

- �

1-C 1

Release Pending
REFCNT >0
BAK = PGFLVB

I
I
PTE => Transition
Saved Modify Bit Set

� - - - - - - - - - - - - - - I

PTE => Transition
Saved Modify Bit Clear

_.1

from
Figure 1 2-4

Modified Page List
REFCNT = 0
BAK = PGFLVB

Write in Progress
REFCNT = 1
BAK = new PGFLVB

Free Page List
REFCNT = 0
BAK = new PGFLVB

to top
of page

Page Fault Transition

Other Transitions

Figure 1 2-5

T r a n s i t i o n s f o r Pag e s Lo c a t ed i n a Pag e F i l e
( Co n t i n ua t i o n o f F i g u r e 1 2 - 4 )

1 2- 1 1

PAG I NG DYNAM I C S

12.2.4

Pag e Loc a te d i n t h e Pag e F i l e

Th e t r a n s i t i o n s tha t a pag e f a u l t ed f r om the pag e
f i l e g oes
t h r o ug h
( Figure 1 2- 5 )
a r e no
d i f fe r en t
f r om
the t r a n s i t i o n s d e sc r i b ed f o r
pag e s
t h a t a r e n o t c o py o n
r e f e r en c e
( F i g u r e 1 2 -3 ) .
Th e o n l y
d i f f e r enc e
in
the
PFN d a ta b e twe e n the two f i g u r e s i s th a t the BAK
a r r a y e l em e n t i n F i g u r e 1 2 - 5 i nd i c a te s tha t the pag e b e l o ng s
i n the
pag e
file.
Th e B A K a r r ay e l em e n t i n F i g u r e 1 2 - 3 c o n t a i n s a p r o c e s s
s e c t i o n t a b l e i nd e x .
Th e o the r d i f f e r e nc e b e twe e n t h e two f i g u r e s i s the e n t r y po i n t
i n to
the
t r a n s i t i o n d i ag r am .
Pag e s c a n s ta r t o u t i n a n i m a g e f i l e ( PT E
c o n t a i n s PS TX ) b u t pag e s c a n n ev e r s ta r t o u t
in
a
pag e
file.
Th e
e n t r y i n to F i g u r e 1 2 - 5 i s f r om F i g u r e 1 2 - 4 , f r om o n e o f th r e e i n i t i a l
s t a t e s th a t even t ua l l y r e s u l t i n
the phys i c a l
pag e c o n te n t s be i ng
wr i t te n to the pag e f i l e .

12 . 3

PAGE FAULTS FOR G LOBAL PAG E S

Th e pag e f a u l t r e s o l u t i o n f o r g l o b a l pag e s c a n b e d e sc r i b e d i n e x ac t l y
t h e same wa y a s p r o c e s s p r i v a t e pag e s a r e d e s c r i b e d .
Howe v e r ,
f o l l o w i ng the
t r a n s i t i o n o f a g l oba l
pa g e
t a b l e e n t r y a nd
i ts
a s so c i a t e d
PFN d a t a b a s e
e n t r i e s a d d s n o th i ng to the i n f o rma t i o n
a l r e a d y p r e s e n ted i n F i g u r e 1 2 - 3 .
A m o r e i n te r e s t i ng a pp r o a c h i s to
l oo k a t
the
i n te rac t i on o f
the
p r o c e s s pa g e tab l e e n t r i e s a nd t h e g l o b a l pag e tab l e e n t r i e s th a t t h e y
po i n t to .
Th i s wi l l b e d o n e w i th a spec i f i c e x amp l e r a th e r th a n a s
a
g e n e r a l c a s e , to a l l o w s pe c i f i c n umb e r s to b e used .

12. 3.1

Pag e Fa u l t f o r G l o b a l Re ad-On l y Pag e

Figure 1 2-6 i l lustrates
the
t r an s i t i o n s
th a t o c c u r
fo r
a g lobal
r ea d - o n l y pag e t h a t i s ma pped b y two p r o c e s s e s .
Th e ma pp i ng i s sho wn
s e pa r a t e l y f r om the o pe r a t i o n o f
section c reat ion
to
s i mpl i fy t h e
f ig u r e .
A s e cond
s impl i f i c a t i o n
i n t h e f i g u r e i s th a t t h e pag e i s
a s s um e d to b e r e ad o n l y .
Th e i m p l i c a t i o n s o f a r e a d / wr i te g l o b a l pa g e
a r e d e sc r i b ed wi tho u t t h e b e n e f i t o f a f i g u r e .
( S TART )

Wh e n the g l o b a l
sect ion
is
i n i t i a l l y c r e a t ed ,
the d a ta
s t r uc t u r e s d e s c r i b ed i n the p r e v i o u s c h a pt e r a r e a l l s e t u p .
Th e g l oba l pag e t a b l e e n t r y fo r
the
pag e we wi l l
fo l l o w
c o n ta i n s a
g l oba l
sect ion tabl e
i nd ex , wh i c h l o c a t e s t h e
g l o b a l s e c t i o n t a b l e e n t r y c o nta i n i ng i n fo rm a t i o n abo ut t h e
g l o b a l i m ag e f i l e .

(1)

Wh e n P r o c e s s A m a ps to the s e c t i o n , t h e
e n t r y conta i ns
a g l o ba l
pag e
tab l e
po i n t e r t o the g l o ba l pag e t a b l e e n t r y .

(2)

Wh e n Pr o c e s s B m a p s to the
sect i o n ,
i t s pag e
ta b l e e n t r y
c o n t a i n s e x a c t l y t h e s a m e g l o b a l pag e t a b l e i nd ex a s fo und i n
P r o c e s s A ' s PTE .

1 2-1 2

p r o c e s s pag e
ta b l e
i nd e x , e f f ec t i v e l y a

PAG ING DYNAM I C S

Process A

Process B

'
I
I ..._
L

GPTE = GSTX

no change

2
-

PTE = GPTX

- -- - ---

iiO'change

___,r--- 1

No PFN data

....__

____,

PTE = GPTX

- - -,

GPTE = GSTX

PTE = GPTX

_ __

No PFN data

PTE contains
Global Page Table
Index (GPTX)

r--- 2

Page NOT In
physlcel memory no PFN ciN

GPTE contains
Global Section Table
Index (GSTX)

_ _ _

_ __ _ _ _

PTE = GPTX

_j
Read In Progress
AEFCNT = 2
SHACNT = 1
BAK = GSTX
PTE => GPTE

GPTE => Transition

no change

- PTE Is Valid
- In Working Set

PTE = GPTX

GPTE Is Valid

•
E
•
•
•

no change

- PTE Is Valid
- In Working Set

f
=
•

GPTE Is Valid

- PTE Is Valid
- In Working Set

•
•
•

•
•

no change

PTE = GPTX

- PTE Is Valid
- In Working Set

GPTE Is Valid

PTE = GPTX

GPTE => Transition

•
.c

....

Active and Valid
AEFCNT = 1
SHACNT = 1
BAK = GSTX
PTE => GPTE

Active and Valid
AEFCNT = 1
SHACNT = 2
BAK = GSTX
PTE => GPTE

·Active and Valid
AEFCNT = 1
SHACNT = 1
BAK = GSTX
PTE => GPTE

no change

PTE = GPTX

r---r- ------,- -------no change

no change

�HPn I I �HPn I I

�

Free Page List
AEFCNT = 0
SHACNT = 0
BAK = GSTX
PTE => GPTE

__,I I

TX
GPTE = GS
r---

No PFN data

L - - - - - - - - - - - -- - - - - - -- - - - - - J
F i g u r e 1 2-6

E x am p l e o f Pag e T r a n s i t i o n s Ma d e b y a G l oba l Pag e
Mapped by Two P r o c e s s e s

12-13

PAG ING DYNAM I C S

(3)

P r o c e s s B h a pp e n s to i nc u r a pag e f a u l t o n th i s
f i rst .
S e v e r a l th i ng s h a ppe n .
a.

g loba f

pag e

Th e pag e r n o t e s th a t t h e p r o c e s s
PTE c o n t a i n s a G PT X .
Th i s
is
used
to
l o c a te
the g l o b a l
pag e t a b l e e n t r y
( G PTE )
•

(4)

(5)

Th e G PT E c o n t a i n s a
i nd i c a t i ng
th a t
Ex a c t l y
somewh e r e .
the r e a d h e r e a s i n

g l o b a l s e c t i o n ta b l e
i nd ex
( GSTX) ,
the
g l oba l
page
r e s i d es on d i s k
the s am e th i ng s a r e d o ne to
i n i t i ate
the c a s e o f a p r o c e s s p r i v a t e pag e .

A phys i c a l p a g e i s a l l o c a ted .

I t s s t a t e i s s e t to r e a d i n p r og r e s s .

Th e r e f e r e nc e c o un t i s i nc r em e n ted .

Th e BAK a r r a y e l em e n t i s l o ad e d w i th the G S TX .

No te tha t t h e PFN PTE a r r a y e l em e n t i s
l o ad ed
w i th t h e
add ress
o f the G PT E , no t t h e add r e s s o f th e p r o c e s s PTE .
No t e a l s o th a t , wh i l e t h e r e a d i s i n prog r e s s ,
the GPTE
conta i ns
th e
t rans i t ion
PTE b u t th e p r o c e s s PTE s t i l l
c o n t a i n s t h e G PTX .

Th e r e fe r e n c e c o un t i s t wo , o n e fo r the r e a d i n p r og r e s s
and one to
r ec o rd
th e
f a c t th a t th e pag e i s i n some
p r o c e s s wo r k i ng s e t ( th e g l o b a l sh a r e co un t i s
non z e r o ) .
Th e g l o b a l s h a r e c o un t a r r a y e l eme n t c o n t a i n s a one wh i l e
th e r e ad i s i n p r og r e s s .

S e v e r a l s t eps a r e t a k e n wh e n the r e ad compl e t e s .
a.

Th e s t a t e o f the pa g e i s c h a ng ed to a c t i v e a nd v a l i d .

Th e g l oba l pag e t a b l e e n t r y i s s e t to va l i d ,
to
record
th e f a c t t h a t th i s pag e i s i n some p r o c e s s wo r k i ng s e t .

Th e p r o c e s s pag e
sto red
i n the
e x a c t l y t h e s am e
w i th
the v a l i d
b i ts .

Th e r e f e r e n c e c o un t a nd s h a r e c o un t a r e bo th o n e a t
po i n t .

t a b l e e n t r y , l o c a ted th r o ug h i t s ad d r e s s
I /O r e que s t pa c k e t , i s s e t u p t o c o n t a i n
c o n t e n t s a s the g l oba l pa g e t a b l e e n t r y ,
b i t s e t and the PFN s t o r ed i n the l o w 2 1
th i s

Wh e n P r o c e s s A f a u l t s t h e same g l o b a l pag e , t h e i n i t i a l pag e r
a c t i on
is
the
s am e
as
i t wa s i n S t e p 4 , bec a us e the pag e
tabl e entry
is
ag a i n
a g lobal
pa g e
ta b l e
i nd e x .
Now ,
h owe ve r ,
the
pag e r
f i nd s a v a l i d G PTE .
Re so l u t i o n o f th i s
pag e faul t i s t r i v i a l .
A wo r k i ng s e t l i s t i s c r e a t ed fo r P r o c e s s A .
Th e g l o b a l pag e
tabl e
e n t r y i s s i mpl y c o p i ed to P r o c e s s A ' s pag e t a b l e .
Th e
s h a r e c o un t i s i nc r em e n ted a nd the f a u l t i s d i sm i s s e d .

1 2- 1 4

PAG ING DYNAM I C S

(6)

Wh e n t h e g l o b a l pag e i s r emoved f r om P r o c e s s B ' s wo r k i ng s e t ,
the
sh a r e
c o un t i s d e c r em e n ted .
B e c a u s e t h e s h a r e c o un t i s
s t i l l po s i t i v e , n o th i ng
d r am a t i c
h a ppens t o th e
phys i c a l
p ag e .
A t th i s t i m e , P r o c e s s B ' s pag e t a b l e e n t r y m u s t b e r e s to r e d
t o i ts prev i o us s ta t e .
( Th e pag e t ab l e e n t r y d o e s n o t a s s um e
s ome t r a n s i t i o n f o rm . ) Th e P T E a r r a y e l em e n t c o n t a i n s
the
address
of
the g lobal
pag e t a b l e e n t r y s o the g l o b a l pag e
t a b l e i nd e x mus t b e r e c a l c u l a t ed .
Th e c a l c u l a t i o n i s t r i v i a l .
Th e c o n t e n t s o f MMG $G L G PTBAS E
a re
s ub t r a c t e d
f r om
the
PTE a r r a y e l eme n t , t h e res u l t i s
d i v i d ed by
four
( to
c r e a te
a
l o ngwo r d
i nd e x ) ,
and
the
q uo t i e n t s t o r e d
in t h e p r o c e s s pag e ta b l e e n t r y in the G PTX
f i eld .

(7)

Wh e n the g l o b a l pag e i s r emoved f r om P r o c e s s A ' s wo r k i ng s e t ,
t h e p r o c e s s pa g e
tab l e
entry
i s r e s to r e d a s d e s c r i b ed i n
Step 7 .
Th e s h a r e c o un t i s d e c r emen ted .
Now t h e sha r e c o un t
r eaches
zero
so
the
r e fe rence c ount
is
a l so d e c r em e n ted .
I f we
a s s um e
th a t
t h e pag e
is
unmo d i f i ed
a nd
th e r e
is
no
o u t s t a nd i ng I /0 , t h e phys i c a l pa g e is pl a c ed o n t h e f r e e pag e
l i st .
Th e G PTE c o n ta i n s a t r a n s i t i o n PT E .
i nd i c a t e s
f ree
l i st .
Th e o th e r
u n c h a ng ed .

(8)

Th e STATE a r r a y e l em e n t
P F N a r r a y e l em e n t s a r e

Wh e n the phys i c a l pag e i s r e u s e d , the
t i e s mus t
be
broken
b e twe e n t h e phys i c a l pag e a nd , i n th i s c a s e , t h e g l o b a l pag e
( N o n e o f the p r o c e s s e s m a pped to th i s pag e
are
tabl e entry .
a f f e c ted i n a n y wa y b y th i s s t e p . )
Th e c o n t e n t s o f the BAK a r r ay e l em e n t ( a G S T X )
are
i ns e r ted
i n to
th e G PTE
l o c a ted b y t h e c o n t e n t s o f t h e PFN P T E a r r a y
e l em e n t .
Th e PFN PTE a r r ay e l em e n t i s then c l e a r e d , b r e a k i ng
t h e c o nn e c t i o n b e twe e n t h e phys i c a l pag e a nd the g l o b a l pa g e
tabl e .
Th i s puts t h e p r o c e s s a nd g l o b a l
pag e
ta b l e s b a c k
to
the
s tate
they we r e i n fo l l o w i ng S t e p 2 ( a l th o ug h i t i s p i c t u r ed
h e r e a s a d i f f e r e n t s t a t e to ma k e the f i g u r e s i mpl e ) .

12. 3.2

G l o b a l Re a d /Wr i t e Pag e s

Th e t r a n s i t i o n s th a t o c c u r fo r g l o b a l wr i t ab l e pag e s a r e no
d i f f e r en t
f r om t h e
t r an s i t i o n s
f o r a p r o c e s s pr i v a t e pag e t h a t i s n o t c o py o n
r e f e r e nc e .
Th e o n l y d i f fe r e n c e b e twe e n
s uc h t r a n s i t i o n s
a nd
the
t r ans i t i ons
i l l u s t r a t ed
in F i g u r e 1 2 - 3 i s th a t the g l o b a l pag e t a b l e
entry ,
n o t t h e p r o c e s s pag e
t ab l e
entry ,
i s a f fec ted
by
the
t r a n s i t i o n s t h a t th e phys i c a l pag e m a k e s .
Th e p r o c e s s pag e t a b l e e n t r y f o r g l o b a l pag e s c o n t a i n s a g l o b a l
pag e
t ab l e
i nd e x up un t i l t h e t i m e th a t the pag e i s mad e v a l i d .
On l y t h e n
i s a P F N i n se r t ed i n to the p r o c e s s
PT E .
As soon a s
the
pag e
is
r emoved
f r om
th e p r o c e s s wo r k i ng s e t , t h e p r o c e s s PTE r e v e r t s to the
G PTX f o rm .
Al l t i e s to the PFN d a t a b a s e a r e mad e th r o ug h the g l o b a l
pag e
t a b l e e n t r y , wh i c h r e t a i n s t h e PFN wh i l e t h e phys i c a l pa g e i s i n
the va r i o us t r ans i t i o n s ta te s .
12-15

PAG ING DYNAM I C S

12 . 3. 3

G l o ba l Copy-o n-Re f e r en c e Pag e s

Th e g l o b a l pag e s j u s t d e sc r i b ed a r e a l l s h a r ed
pa g e s .
One
f o rm o f
g l o b a l pa g e i s s h a r ed o n l y i n i t s i n i t i a l s t a t e .
As soon as the faul t
o c c u r s , th e pag e i s t r e a t ed e x a c t l y l i k e a p r o c e s s p r i v a t e pa g e .
Th e s e p ag e s a r e g l o b a l c o py-on- r e f e r e nc e pag e s a n d c ommo n l y o c c u r
in
sha r e ab l e
i m ag e s tha t c o n t a i n impu r e d a ta a r e a s .
Fo r e x ampl e , a l l o f
t h e l o c a l va r i a b l e s i n a F ORTRAN s h a r e a b l e i m a g e wo u l d b e i n a g l o b a l
c o py - o n - r e f e r e nc e s e c t i o n .
E a c h p r o c e s s th a t u s e s t h e i m a g e wo u l d g e t
i t s o wn p r i v a te c o py o f the l o c a l v a r i a b l e s , b u t a l l
p r o c e s s e s wo u l d
g e t t h e s ame i n i t i a l v a l u e s f o r t h e v a r i a b l e s .
F i g u r e 1 2 -7 i l l u s t r a t e s
c o py - o n - r e f e r e n c e pag e .

r - - - - - - -,

I
I
I
I
I
I

PTE = GPTX

- PTE � Transition
- In Working Set
- Saved Modify Bit Set

t r ans i t i o n s

I
I
I
I
I

--, G r - _j
L �
to
Figure 1 2-4

tha t

occur

Process A

GPTE contains
Global Section Table
Index (GSTX),CRF

PTE contains

GPTE = GSTX, CRF

fo r

Page NOT In
physical memory no PFN data

no change

PTE = GPTX

GPTE = GSTX, CRF

no change

PTE = GPTX

GPTE = GSTX, CRF

No PFN data

z
IL.
G.
CD
c
0

Read In Progress
REFCNT = 2
BAK = PGFLX,O
PTE .... Process B's
page table entry

no change
z
IL.
G.

- PTE � Transition
- In Working Set

GPTE = GSTX, CRF

- Saved Modify Bit Set

c
•

:»

;:;
Ill

to
Figure 1 2-4

F i g u r e 1 2-7

g l ob a l

No PFN data

Global Page Table
Index (GPTX)

Process B

<¥

the

E x ampl e o f Pa g e T r a n s i t i o n s f o r G l o b a l
C o py-o n-Re f e r e n c e Pag e s

1 2- 1 6

Read In Progress
REFCNT = 2
BAK = PGFLX,O
PTE .... Process A's
page table entry

PAG ING DYNAM I C S

(1)

i d ent ical
c o nd i t i o n s a r e
to
initial
Th e
th o s e
used
in
Th e s e c t i o n i s c r ea t ed and th e G PT E s c o n t a i n a
F i g u r e 1 2-6 .
G STX , a l th o ug h h e r e t h e c o py-on- r e f e r e n c e b i t i s s e t .

( 2)

P r o c e s s A m a p s the pag e a nd h a s i t s
G PTX .

( 3)

P r o c e s s B m a p s t h e pag e a nd g e t s the same G PT X
N o th i ng i s d i f f e r en t u p t o th i s po i n t .

(4)

Now wh e n P r o c e s s B i nc u r s a pag e f a u l t , the pag e r f o l l o ws t h e
G PTX to th e G PT E , n o t i ng t h a t the pag e i s l o c a t ed i n a g l o b a l
i mag e f i l e a n d i s c o py o n r e f e r e nc e .
A r e a d i s i n i t i a t e d a nd
the
f o l l ow i ng
mod i f i c a t i o n s a r e m a d e to the p r o c e s s PT E a nd
the PFN d a t a b a s e .

set

PTE

c o n ta i n

i ts

PTE .

Th e g l o b a l pag e t a b l e e n t r y i s n o t to uc h e d .
i t s G S TX c o n t e n t s .

Th e p r o c e s s pag e t a b l e e n t r y i s s e t to a t r a n s i t i o n PTE .

Th e s t a t e
p r og r e s s .

Th e BAK a r r a y e l em e n t c o n t a i n s a pag e f i l e i nd ex
b l o c k a l l o c a ted ye t )

the

ph y s i c a l

pag e

set

r e ta i ns

read

( w i th n o

•

Th e PT E a r r a y e l em e n t c o n t a i n s the ad d r e s s o f P r o c e s s B ' s
PTE .

No t e tha t a l l t i e s b e twe e n P r o c e s s B a nd the g l o ba l
sect ion
are
bro ken .
Th e pag e i s now t r e a t ed e x a c t l y l i k e a p r i v a t e
c o py-on- r e f e r e n c e pag e .
Th e
two
box e s
for
Process B
in
Figure 1 2 -7
are
the box e s wi th i n
the d a sh e d
o u tl i ne i n
Figure 12-4 .
(5)

Wh e n P r o c e s s A f a u l ts the same pag e , e x a c t l y the
same
s teps
a r e t a k e n , th i s t i me w i th a to ta l l y d i f f e r e n t phys i c a l pag e .

Th u s , bo th P r o c e s s A a nd P r o c e s s B g e t e x a c t l y the s a m e
initial
c o py
o f the g l o b a l pag e f r om the g l o b a l i m ag e f i l e b u t , f r om tha t po i n t o n ,
e a c h p r o c e s s h a s i t s o wn p r i v a t e c o py o f t h e pag e
to
mod i f y a s
it
wi shes .

12 . 4

WORK ING S ET REPLAC EMENT

Th e wo r k i ng s e t l i s t r e p l a c em e n t a l g o r i thm th a t VMS u s e s i s a mod i f i e d
f i r s t- i n
f i r s t- o u t s c h em e .
Th e pag e tha t h a s b e en i n th e wo r k i ng s e t
l i s t fo r the l o ng e s t t i m e i s t h e f i r s t c a nd i d a te f o r r e p l ac em e n t .

12. 4. 1

Sc a n o f Wo r k i ng S e t L i s t

Wh e n the pag e r n e e d s a n empty wo r k i ng s e t l i s t en t r y , i t c a l l s r o u t i n e
MMG $ FREWS LE .
Th i s
r o ut i n e
m a n i pu l a t e s
the wo r k i ng
set
l i st
( F i g u r e 1 1 - 4 ) i n t h e fo l l o w i ng f a sh i o n .
1.

I f the W S L E i nd ex ed b y PHD$W WSN E XT i s a l r e a d y f r e e
a r e z e r o ) , th a t e n t r y i s u s ed .
1 2- 1 7

( contents

PAG ING DYNAM I C S

I f n o t , t h e WSNE XT po i n t e r i s
i nc r em e n t ed .
If
the WSNE XT
po i n te r
e x c eed s the e nd o f the l i s t ( WS LA S T ) , i t i s r e s e t to
the beg i nn i ng o f the d yn am i c wo r k i ng s e t l i s t
( WS DYN ) ,
th u s
i mpl em e n t i ng th e wo r k i ng s e t l i s t a s a c i r c u l a r b u f f e r .
I f the n e wl y i nd e x ed WS LE i s a v a i l a b l e ,
u s ed .

then

s impl y

I f the n e w WS LE i s l o c k ed i n to the d yn am i c
po r t i o n o f
the
wo r k i ng
set
l i s t , t h a t e n t r y i s s k i pped .
( Th i s m e a n s g o i ng
b a c k to S t e p 2 . ) On l y p r o c e s s pag e t a b l e pag e s c a n b e
loc ked
i n to
t h e d yn am i c
po r t i o n
of
t h e wo r k i ng s e t l i s t .
Pag e s
l o c k e d b y u s e r r e que s t r e s u l t i n a s h u f f l i ng o f t h e wo r k i ng
s e t l i s t ( Ch a p t e r 1 1 a nd Ch a pt e r 1 3 ) .

D r o pp i ng th r o ug h t h e p r ev i o us c h ec k s i nd i c a t e s tha t the v i r t oa l
pag e
i nd i c a t ed
by
t h e WSLE mus t be r emoved b e fo r e th i s WS LE c a n b e u s e d .
I f wo r k i ng s e t l i s t s k i pp i ng ( d e sc r i b ed i n the n e x t
sec t i o n )
i s no t
e na b l ed , t h e wo r k i ng s e t l i s t e n t r y i s r emoved , wh a t ev e r i t s s t a t e .
Fo r g l o b a l pag e s , t h e s h a r e c o un t i s d e c r em e n ted .
g o e s t o z e r o , t h e r e f e r e n c e c o un t i s d e c r em e n t e d .

I f the sh a r e

c o un t

Fo r p r o c e s s p r i va te pag e s , th e r e f e r e nc e c o un t i s d e c r em e n ted .
I f the
pag e
i s pl a c ed
i n to
a t r a n s i t i o n s t a t e , the b a l a n c e s l o t r e f e r e nc e
c o un t f o r th i s p r o c e s s h e a d e r i s i n c r em e n ted to p r e v e n t the o u tswa p o f
t h e p r o c e s s h e ad e r .

12. 4.2

S k i pp i ng Wo r k i ng S e t L i s t E n t r i e s

Th e s pe c i a l SYS B OOT pa r am e t e r S K I PWS L ( d e f a ul t va l u e o f z e r o ) i s u s ed
by
t h e wo r k i ng
set
r emov a l r o u t i n e to pe rm i t f r e q ue n t l y r e f e r e nc e d
pag e s to r ema i n i n the wo r k i ng s e t .
Th i s a l l o ws VM S to mod i f y i t s
str ict
f i r s t- i n
f i r s t - o u t pag e
r e pl a c emen t a l g o r i thm wi th some
f r eque n c y of u s e i n f o rm a t i o n .
Th e m o d i f i ed a l g o r i thm wo r k s i n the f o l l o wi ng m a n n e r .
As wo r k i ng
set
l i st entr i es
are
sc ann ed ,
a n y va l i d
pa g e
is
s k i pped o v e r a f t e r
c l e a r i ng t h e va l i d b i t i n t h e PT E .
Th e pag e r ema i n s
i n t h e wo r k i ng
s e t l i s t a nd i t s PFN s t a t e i nd i c a t e s a c t i v e and va l i d .
Th e r e a r e two
po s s i b l e f u t u r e c o u r s e s f o r th i s pa g e ,
c a l l ed
an
act ive t rans i t ion
pag e .
•

Th e pa g e wi l l b e r e f e r e nc ed
ag a i n ,
c a u s i ng
a
pag e
faul t
because
the va l i d b i t i s o f f .
Th e pag e r r e so l v e s th i s pag e
f a u l t by s i mp l y t u r n i ng th e va l i d
b i t bac k on .
Th e r e
is
n o th i ng
e l se
to d o b e c a u s e
the wo r k i ng s e t l i s t s c a n d i d
n o th i ng e x c e p t to t u r n the va l i d b i t o f f .
Th i s type o f pag e
f a u l t i s t h e f a s t e s t pa th th r o ug h the pag e r .
Th e ma i n r e a s o n f o r th i s e f f i c i e n c y i s th a t the wo r k i ng
set
l i st does
n o t h a v e t o b e s c anned , l o o k i ng fo r a WSLE t o
d i sca r d .
Th a t wo r k i ng s e t s c a n i s
wh e r e
th e pag e r
spend s
mo s t o f i t s t i m e wh e n r e s o l v i ng pag e f a u l ts f r om the f r e e o r
mod i f i ed pag e l i s t s o r wh en a pag e f a u l t o c c u r s f o r a g l ob�l
pag e
th a t
is
a l r e ad y
in
the
wo r k i ng
set
of some o the r
process .

12-18

PAG ING DYNAM I C S
•

Th e pag e w i l l n o t b e r e f e r e nc ed a g a i n s o o n .
O n th e n e x t pa s s
th r o ug h
th e wo r k i ng s e t l i s t , t h e pag e wi l l s t i l l be i nv a l i d
( a c c o r d i ng t o t h e v a l i d b i t i n the PTE ) b u t a c t i v e ( a c c o r d i ng
to
the PFN S TATE a r r a y ) .
On th i s s e c o nd pa s s , the pag e w i l l
b e r emoved f r om th e wo r k i ng s e t .

Th e S K I PW S L p a r am e t e r
is
used
b y t h e wo r k i ng
set
l i st
scan
to
d e t e rm i n e
how m a n y WS LEs
to
scan ahead
l o o k i ng
for
a s u i tab l e
c a nd i d a t e f o r r emova l b e fo r e a b a nd o n i ng the s e a r c h .
B e f o r e the s e a r c h
b eg i n s ,
the
f i r s t wo r k i ng l i s t e n t r y t h a t wi l l b e e x am i n ed i s s a v e d
f o r po s s i b l e r emov a l
i f no
a c t i ve
t r a n s i t i o n pag e
is
f o und
a nd
r emoved .
A n um b e r
o f wo r k i ng l i s t e n t r i e s up to S K I PWS L i s sc a nn e d
u n t i l e i th e r
•
•

a pag e i n a n a c t i v e t r a n s i t i o n s t a t e i s fo und .
r emoved f r om the wo r k i ng s e t l i s t .
Or

•
•

S K I PWSL e n t r i e s h a v e b e e n e x am i n ed a nd no
ac t i v e
t rans i t ion
pag e
f o und .
In
th i s c a se ,
th e
f i r s t e n t r y loo ked a t i s
r em oved f r om t h e wo r k i ng s e t l i s t , r eg a r d l e s s o f
i ts
s ta t e .
By
r emov i ng the f i r s t e n t r y r a th e r th a n a n y o th e r , a pag e i s
n o t p r ema t u r e l y r emoved f r om the wo r k i ng s e t by th i s m o d i f i e d
a l g o r i thm .

Th e fo l l o wi ng pag e s i n t h e
m od i f i ed s c a n .
•

Th i s pag e

Pag e s th a t a r e va l i d
pag e s . )

set

s k i pped

ove r

th i s

( Th e va l i d b i t i s t u r n ed

off

fo r

s uc h

wo r k i ng

are

Pag e s t h a t a r e i n t h e r e ad - i n - p r o g r e s s t r a n s i t i o n s t a t e
G l o b a l pag e s wh e r e t h e g l o b a l pag e t a b l e e n t r y
i nd i c a t e s
t r a n s i t i o n s t a t e ( wh i c h m u s t b e r e ad i n p r og r e s s )

I f no a c t i v e t r a n s i t i o n pag e i s fo und a f t e r S K I PW S L pag e s h a v e
been
s k i pped ,
th e
f i rst
e n t r y l o o k e d a t i s r emoved f r om th e wo r k i ng s e t ,
r e g a rd l e s s o f i t s s t a t e .
Th e d e fa u l t v a l u e o f t h e S K I PWS L s pe c i a l SYSB OOT p a r am e t e r
is
zero ,
wh i c h t u r n s o f f
th i s
e n t i r e mo d i f i c a t i o n o f the wo r k i ng s e t l i s t
r e pl a c em e n t a l g o r i thm .
I n a d d i t i o n , i f S K I PWSL i s z e r o ,
then a c t i v e
t r a n s i t i o n pag e s w i l l
n ev e r
ex i s t ,
b e c a us e
th e y o n l y c o m e i n to
e x i s t e n c e d u r i ng t h e m o d i f i ed wo r k i ng set l i s t s c a n .
Ca r e
sho u l d
be
e x e r c i s e d wh e n us i ng th i s f e a t u r e ( s e t t i ng S K I PW S L t o n o n z e r o ) b e c a u s e
c e r t a i n a sp e c t s o f th i s mod i f i c a t i o n d e f e a t t h e o pt i m i za t i o n s a c h i eved
b y c l u s t e r ed
I /O a nd th e phys i c a l pag e c a c h e s .
To o l a rg e a va l ue o f
S K I PWS L a l s o c a u s e s m o r e t i m e to b e s pe n t e a c h t i me
the wo r k i ng
set
l i s t i s s c anned l o o k i ng f o r a pag e t o b e r e p l a c ed .

12. 5

IN PUT AND O UTPUT THAT SUPPORT PAG ING

Th e r e i s v e r y l i t t l e spec i a l p u r po s e c o d e
in
the
I /O s ub s ys t em
to
s uppo r t pag e r
I /0 a n d s wa ppe r I /0 .
Th e pag e r and swa ppe r each b u i l d
th e i r o wn I /O r e qu e s t pa c k e t s b u t t h e s e
pa c k e t s a r e que ued
to
the
d ev i c e d r i v e r i n the n o rma l f a sh i o n .
Th e s e a r e the o n l y d i f f e r e n c e s .
•

Mo d u l e S Y S Q I OR E Q c o n t a i n s s pe c i a l e n t r y po i n t s f o r pag e r
a nd
s wa ppe r
I /O
tha t i n s e r t s pec i a l I /O f unc t i o n cod e s i n to th e
I /O r e que s t p a c k e t .
12-19

PAG ING DYNAM I C S
•

Th e s e c o d e s a r e d e t e c t ed by t h e
I /O
po s tp r o c e s s i ng
s e rv i c e
rout i ne .
Th e r e a r e
spec i a l compl e t i o n pa ths f o r pag e r e a d
( p r o c e s s i s r emoved f r om PFW s t a te a nd mad e c om p u t a b l e )
and
f o r o t h e r f o rms o f I /O ( a d d r e s s o f s p e c i a l ke r n e l A S T s t o r ed
i n I R P $ L ASTPRM f i e l d i s u s e d to n o t i f y mod i f i ed pa g e wr i t e r
o r swa pper th a t I /O h a s c ompl e t ed ) .

I n o rd e r to m a k e r e ad i ng a nd wr i t i ng a s e f f i c i e n t a s po s s i b l e ,
the
pag e r
s uppo r t s
a
f e a t u r e c a l l ed c l us t e r i ng , wh e r e i t c h e c k s to s e e
wh e th e r pag e s a d j a c e n t t o th e v i r tua l pag e
th a t
it
is
r e a d i ng
are
l o c a ted
i n the
same
file
i n ad j a c e n t v i r t ua l
blocks .
I f so , a
m u l t i pl e b l o c k r e ad i s i s s ued a nd s ev e r a l pag e s a r e b r o ug h t
i n to
the
wo r k i ng s e t a t o n e t i me .
Th e mod i f i ed pag e wr i t e r a nd t h e Upd a t e Se c t i o n
s ys tem s e r v i c e
a l so
c l us te r t h e i r wr i t e o pe r a t i o n s , b o th to m a k e t h e i r wr i t e s a s e f f i c i e n t
a s po s s i b l e a nd t o a l l o w s ub s e q u e n t c l us te r ed r e a d s f o r t h e pag e s tha t
a r e b e i ng wr i t t e n .

12. 5 . 1

Page Re ad s

Wh e n the pag e r d e t e rm i n e s tha t a r e a d i s r e qu i r ed to
sa t i s f y a
pag e
f a u l t , i t a l l o c a t e s a n I /O r e qu e s t pa c k e t a nd f i l l s i t wi th pa r am e t e r s
tha t d e sc r i b e t h e r e a d .
Ta b l e 1 2 - 1 l i s t s tho s e f i e l d s tha t a r e
used
f o r spec i a l p u r po s e s by t h e pag e r .

12. 5 . 1 . 1
Pag e Re ad C l u s te r i ng - Th e
pag e r a t tempt s
to
c reate
a
c l us t e r
o f pag e s to r e a d .
Th e m a nne r i n wh i c h th i s c l u s t e r i s f o rmed
d e pe nd s on the i n i t i a l s t a t e of the f a u l t i ng pag e ta b l e en t r y .

1 2 . 5 . 1 . 1 . 1 Te rm i na t i ng Co nd i t i o n fo r C l us te r ed Re ad s - The
pag e r
scans
PTEs
th a t m a p l a rg e r
v i r t ua l
add resses ,
c h e c k i ng f o r mo r e
v i r t ua l pag e s tha t a r e l o c a t ed i n t h e
s a m e b a c k i ng
sto r e
loc a t i on ,
un t i l
the d e s i r ed
c l us t e r
s i ze
is
r e ached
or
un t i l
one o f th e
f o l l o w i ng o the r t e rm i n a t i ng c o nd i t i o n s i s r e a c h ed .
•
•
•
•
•

A pag e t a b l e e n t r y d i f f e r e n t f r om the o r i g i n a l
is en c o un t e r e d .

f a u l t i ng

PTE

Th e c l u s t e r s i z e i s r e a c h e d .
Th e pa g e t a b l e pag e i s i t s e l f n o t v a l i d .
( S a t i s f y i ng
f a ul t wo u l d o f f s e t t h e b e n e f i t s g a i ned by c l u s t e r i ng . )

th i s

No mo r e wo r k i ng s e t l i s t e n t r i e s a r e a v a i l a b l e .
i n the c l u s te r i s a d d ed to the wo r k i ng s e t . )

pag e

{ Each

No phys i c a l pag e i s a v a i l a b l e .

I f , a f t e r sc a n n i ng t h e a d j a c e n t pag e
t a b l e e n t r i e s towa r d h i g h e r
v i r t ua l
add resses ,
no
p ag e s h a v e
been c l us te r ed ,
the p r o c e s s i s
r e p e a ted towa r d l o we r v i r t ua l
a d d r e s s e s wi th
the
same
t e rm i n a t i ng
c o nd i t i o n s .

1 2-2 0

PAG I NG DYNAM ICS
Th e s c a n i s m a d e i n i t i a l l y t o wa r d h i g h e r
v i r t ua l
a d d r e s s e s b e c a us e
p r og r am s
t yp i c a l l y
execute
s e qu e n t i a l l y t o wa r d h i g h e r
v i r t ua l
a d d r e s s e s a n d th e s e pag e s a r e
l i k e l y t o b e n e e d ed
soon .
If
the
fo rwa r d
a t t empt
fa i l s ,
the pag e r a t temp t s to r e ad pag e s a d j a c e n t to
the f a u l t i ng pag e on the a s s ump t i o n t h a t even pag e s at
l o we r
v i r t ua l
a d d r e s s e s b u t n e a r t h e f a u l t i ng pag e a r e l i ke l y t o b e n e e d ed so o n .

1 2 . 5 . 1 . 1 . 2 Ma t c h i ng Co nd i t i o n s Wh i l e S c a nn i ng Pag e Ta b l e - Th e m a tc h
that
is
l ooked
f o r wh en
s c a n n i ng
the a d j a c e n t pa g e t a b l e e n t r i e s
d e pend s o n t h e f o rm o f t h e i n i t i a l pag e t a b l e e n t r y .
•
•

•

I f the o r i g i na l PT E c o n ta i n s a p r o c e s s s e c t i o n t ab l e
s uc c e s s i v e PTEs mu s t c o n t a i n e x a c t l y the same PSTX .

i nd ex ,

I f the o r i g i n a l
P T E c o n ta i n s a
pag e
f i l e v i r t ua l
block
s uc c e s s i v e
PTEs m u s t c o n t a i n PTEs w i th s u c c e s s i v e l y
n um b e r ,
i nc r e a s i ng ( o r d e c r e a s i ng ) v i r t ua l b l o c k n umb e r s .
I f the o r i g i n a l pag e t a b l e e n t r y c o nta i n s a g l o ba l pag e t a b l e
s uc c e s s i ve
PTEs mus t c o n t a i n s uc c e s s i ve l y I n c r e a s i ng
i nd e x ,
{ o r d e c r e a s i ng ) i nd i c e s .
I n a d d i t i o n , t h e g l o b a l pag e
t ab l e
e nt r i e s mus t a l l
conta i n
ex a c t l y the s a m e g l o b a l s e c t i o n
t a b l e i nd ex .

1 2 . 5 . 1 . 1 . 3 Ma x i m um C l us t e r S i z e f o r Pag e Read - Th e m a x i m um n um b e r o f
pag e s
tha t c a n b e
in a
c l us t e r
i s d e term i n e d
i n s e v e r a l wa ys ,
d e pend i ng o n the type o f pag e b e i ng r e ad .
•
•

G l o ba l pag e t a b l e p ag e s a r e n o t c l u s t e r ed .
Th e c l u s t e r f a c t o r fo r p r o c e s s pag e ta b l e pag e s i s t a k e n f r om
o ffset
PHD$8 PGTB PFC
in
the
f i x ed po r t i o n of the p r o c e s s
head e r .
Un l es s some u s e r -wr i t t e n k e r n e l m o d e
r o ut i n e h a s
mod i f i ed
th i s
field ,
t h e v a l u e o f th i s f i e l d i s t a k e n f r om
the s pe c i a l S Y S B OOT p a r am e t e r PAGTB LPFC f o r a l l p r o c e s s e s
in
the s y s tem .
Th e d e f a u l t va l u e f o r th i s p a r am e t e r i s two .
Th i s v a l ue
is
chosen
to avo i d a n a r t i f i c i a l end to b u i l d i ng a c l us t e r wh e n
t h e pag e t a b l e pag e a l s o had to b e f a u l ted .
Two
pa g e
tab l e
pag e s a r e g ua r a n t e ed
to
s p a n 1 2 7 pag e s , r eg a rd l e s s o f the
i n i t i a l f a u l t i ng v i r t ua l a d d r e s s .
Dec r e a s i ng th i s v a l ue m a y
I n c r e a s i ng i t a bove two i s l i ke l y t o
d e f e a t c l us t e r ed r e ad s .
h a ve n eg l i g i b l e e f f e c t s i n mo s t s y s tems .

•

Th e c l u s t e r f a c to r f o r pag e f i l e
pag e s
is
ta ken
f r om
th e
P F L $ 8 PFC
f i e ld
of
the
pag e
file
c on t r o l
bloc k
Th e u s ua l c o n t e n t s o f th i s f i e l d
are
zero .
{ F i g ure 1 1 - 2 2 ) .
In
th a t
c a se ,
the c l us t e r
f a c to r
is
ta ken
f r om
the
PHD$8 D F PFC f i e l d o f t h e p r o c e s s h e a d e r .
I n the
absence o f
u s e r -wr i t t e n mod i f i c a t i o n ,
t h e v a l ue p l a c ed i n to th i s f i e l d
i s t h e S Y S 8 00T pa r am e t e r PFC D E FAU LT .

1 2-2 1

PAG ING DYNAM I C S
Ta b l e 1 2 - 1
De s c r i pt i o n o f I /O Reque s t s I s s ue d b y Memo r y Ma n ag em ent

�

P r i o r i ty

P r o c e s s Pag e Read

Imag e F i l e ( 1 )

Pag e

2.
3.

Pag e i n Pag e F i l e
Pag e Ta b l e Pag e

Pro c e s s

I R P $B_PR I

I R P $ L_P I D

Pr i o r i t y o f
Fa ul t i ng
Process

PID o f
Fa ul t i ng
Process

Sys t em Pag e Re a d

Pr i o r i t y o f
" Sy s t e m "
Process
16

1 . Sys tem Pag e ( 2 )

PID o f
" Sy s tem "
Process

S y s tem V i r t ua l
Add r e s s o f PTE

AST Add re s s

I R P$ L_SVAPTE

IRP$L_AST

P OPT/ P l PT

2.
3.

P O PT/P l PT
S PT

S PT

0
3. 0

G l oba l Pag e

G PT

Gl oba l

P r o c e s s Pag e Ta bl e

3 . Ma s t e r PTE

CRF Pag e

S l av e PTE
Ad d r e s s ( < O )
Co nten t s ( > O )

G l o b a l Pag e
Ta b l e Pag e

To
To

To Swa p Fi l e
( SWPVBN=O )

Upd a t e Sec t i o n
Pag e Wr i te ( 4 )

Swa ppe r

(1)

(2)

Po i n t s t o
Mod i f i ed
Pag e Wr i te r ' s
Ma p

Pr i o r i ty
o f Ca l l e r

PI D o f
Ca l l e r

a . P r o c e s s Pag e Ta b l e
b . G l o b a l Pag e Tab l e

SWP PR I O

PID o f
Swa ppe r

Po i n t s to
Swa ppe r Ma p

I /0

O n e f i e l d in the I /0 r eque st pa c k e t
sec t i o n
is
sensi t ive
to
wh e th e r
c a s e s a r e d i s t i ng u i sh e d a s :
a.
b.

PID of
Mo d i f i ed
Pa g e Wr i te r
(PID of
Swa ppe r )

Pa g e F i l e
I m ag e F i l e ( 3 )

1.
2.

MPW P R I O

Pag e Wr i te

Mo d i f i ed

S PT

AST Add r e s s
( i f s pe c i f i e d )

( I R P S L AS TPRM ) fo r pag e r ead s f rom a
pr i v a t e
t h e s ec t i o n i s c o py o n r e f e r en c e .
The se two

No t Co py o n Re fe r enc e
Co py on Re f e r enc e

P ag e a b l e ex ecut i v e r o u t i n e s o r i g i na te in
o ne
of
t h r ee
imag e
f i l es
( S YS . EXE ,
RMS . E XE ,
a nd
S YSMSG . EXE ) d e sc r i b ed by t h r e e sys t em s e c t i o n tab l e en t r i e s ( S STE )
l oc a ted i n the s ys t em h e ad e r .
The s t a t i c ex e c ut i v e d a ta is a l l l o c a ted in the
no npag ed
e x ec ut i v e .
The
onl y
pag e ab l e
wr i tab l e
d a ta
is t h e pag ed po o l a r ea , wh i c h st a r t s o u t as a se r i e s o f
d emand ze ro pag e s .
Pag ed po o l pag e s a r e wr i t t e n to a nd sub s e que n t l y f a u l ted f r om
the pag e f i l e .
The se two c a s e s a r e d i s t i ng u i sh ed a s :
a.
b.

(3)

T h e mod i f i ed pag e wr i te r t a k e s spec i a l n o t e o f wh e th e r
b a c k t o a n imag e f i l e a r e pa r t o f a
a.
b.

(4)

Pag e a b l e ex e c u t i v e r o ut i n e s
Pag ed po o l pag e s
tha t

are

wr i t te n

Pr i v a t e s e c t i o n
Gl o b a l se c t i o n

I n a s i m i l a r m a n ne r ,
the
Upd a te
Se c t i o n
s ys t em
d epend i ng on wh e th e r t h e pag e s a r e pa r t o f a
a.
b.

pag e s

Pr i v a t e s e c t i o n
G l o b a l se c t i o n

12-22

s e rv i c e

beha v e s

d i f fe r en t l y

PAG I NG DYNAM I C S
Ta b l e 1 2 - 1

( cont . )

De s c r i pt i o n o f I /0 Re q u e s t s I s s ued by Memo r y Ma n ag em e n t
A S T Pa r am e t e r

Ad d r e s s o f Wi ndow
C o n t r o l Bl o c k

I R P S L A S TPRM

I R P $ L_W IND

la . O
l b . PSTX

2. 0
3. 0

l.
2.

GSTX
( PFN!:V G B LBAK
is s e t)

4. 0

Ad d r e s s o f
M PW ' s spe c i a l
k e r n e l AST
( WR I T EDON E )

A S T Pa ram e t e r
( i f spec i f i ed )

Swa ppe r • s
( I O DONE )

(7)

From PFL
From P F L ( S )

p f c / PFCDEFAULT ( 6 )

PFCDEFAULT
PAGTB L PFC

Pr io r i t y
Bo o s t a t I/O
Compl e t i o n

Cl ass=O
Bo o s t = O

KAST

l a . From S S TE
l b . From P F L
2 . From G S TE

la . SYS PFC
l b . PFCDEFAULT
2 . p f c / P F CDEFAULT ( 6 )

From G S TE

p f c / PFCDEFAULT ( 6 )

From P F L ( S )

a.
b.

PS TE
GSTE

S F TE

1.
2.

Pa g e

Re ad

Pag e i n Pa g e Fi l e
Pa g e Ta b l e Pa g e

I m ag e

System Pa g e ( 2 )

Gl obal

Pa g e

Gl obal

CRF Pag e

3.
4.

G l o b a l Pag e
Ta b l e Pag e

Mod i f i ed

MPW WRTC LUS TER
MPW-WRTC LUSTER

l.
2.

To
To

Pag e Wr i te

Pag e Fi l e
!mag e F i l e ( 3 )

To Swap Fi l e
( SWPVBN=O )

MPW WRTCLUSTER

C l ass=l
Boost=2

Upd a t e Se c t i o n
P a g e Wr i te ( 4 )

No t Appl i c ab l e

No ne ( 7 )

swa ppe r

P r o c e s s pag e tab l e s a nd g l o b a l pag e t a b l e s o r i g i n a te
a r e wr i t t e n to and f a u l ted f r om the pag e f i l e .

as d emand

zero

pag es

tha t

Th e c l us t e r f a c to r fo r a pr i v a te sec t i o n o r a g l ob a l sec t i o n c an b e spe c i f i ed
at
l i nk
t i m e o r when t h e sec t i o n i s m a pped b y e x pl i c i t l y d e c l a r i ng a c l us te r f a c to r
( pfc ) .
In the absen c e o f s uc h a spec i f i c a t i o n , the pag e r u s e s the d e fa ul t s ys tem
c l us t e r fac to r d e t e r m i n ed b y t h e SYS B OOT pa r am e t e r PFCDEFAULT.
Th e swappe r ( a nd by i mpl i c a t i o n the mod i f i ed pag e wr i te r )
a nd i s t he r e fo r e n o t s ub j ec t to pr i o r i ty b o o s t s .

12-23

is a

Fi l e ( l )

Sys tem Pag e Read

No ne ( 7 )
l . From PFL
2 a . From PSTE
2b . From G S TE
3 . From S F TE

Process
l.
2.

Cl a s s = O
Bo o s t = O

(6)

From

(5)

PSTE

Cl uster
Fa c to r

r ea l - time

proc e s s

I/O

PAG ING DYNAM I C S
•

Th e c l us t e r f a c to r f o r p r o c e s s o r g l o b a l
sec t i o n s
is
t a k en
f r om t h e
SEC$8 PFC
f i e l d o f the p r o c e s s o r g l o b a l sec t i o n
t a b l e e n t r y { F i gur e s 1 1 - 7 a n d 1 1 - 1 6 ) .
Th e se
f i e ld s
u s ua l l y
c o n t a i n v a l ue s o f z e r o , i n wh i ch c a se , t h e d e fa u l t pag e f a u l t
{ J u s t a s f o r c l us t e r ed r e a d s f r om t h e pag e
c l u s t e r i s u s ed .
f i l e , t h i s d e f a ul t i s t a k e n f r om t h e PHD $ 8 DFPFC f i e l d i n t h e
p r o c e s s h e ad e r , wh i c h i s
u s ua l l y e q ua l to
the
PFCDEFA U LT
S YS B OOT p a r am e t e r . )
Th e r e a r e two m e tho d s a v a i l a b l e t o t h e us e r
to
c l u s te r
f a c to r o f p r o c e s s o r g l o b a l s e c t i o n s .
the opt i ons l i n e

the
control
By i n c l ud i ng

C LUSTER = c l us t e r -n a m e , [ b a s e - ad d r e s s ] , [ p f c ] , f i l e - s p e c [ ,

•

]

i n the l i n k e r o p t i o n s f i l e , t h e pag e f a u l t c l us t e r f a c to r
in
t h e i m a g e s e c t i o n d e sc r i pto r c a n b e s e t t o n o n ze r o c o n t e n t s .
S e c t i o n s t h a t a r e m a pped m a n ua l l y by t h e u s e r { wi th a
C r e a te
a nd
Ma p { P r i va te o r G l o ba l ) S e c t i o n s ys t em s e rv i c e ) c a n h a v e
t he i r pag e f a ul t c l u s te r f a c to r spec i f i ed
b y i nc l ud i ng
the
o pt i o n a l p f c a rg um e n t i n t h e s ys t em s e rv i c e c a l l .

1 2 . 5 . 1 . 2 Pag e Read Compl e t i o n - Th e pag e r e a d compl e t i o n i s d e te c t ed
by
t h e I /0 po s t p r o c e s s i ng r o u t i ne { I PL = 4 s o f twa r e i n t e r r up t s e r v i c e
r o u t i n e ) b y the spec i a l c o d e i n s e r t ed i n to the I R P b e f o r e t h e
r e que s t
wa s que ued .
Pa g e r e ad c ompl e t i o n i s n o t r e po r ted to the f a ul t i ng
process
i n the
n o rma l
f a sh i o n w i t h a
s pe c i a l
k e rn e l
AST b e c a u s e
none
of
the
po s t p r o c e s s i ng h a s t o b e pe r f o rmed i n
t h e c o n t ex t o f
the
f a u l t i ng
p r o c es s .
I n s t e ad ,
t h e wo r k i s d o ne by th i s s e r v i c e r o u t i n e a nd t h e
p r o c e s s m a d e c om p u ta b l e b y r e po r t i ng a pag e r e a d c ompl e t i o n e v e n t
to
t h e s c h ed u l e r .
Th e d e ta i l s tha t t h e s e r v i c e r o u t i n e t a k e s c a r e o f wh en a
pag e
read
s uc c e s s f u l l y c ompl e te s i nc l ud e t h e f o l l o w i ng s teps fo r e a c h pag e .
1.

Th e r e f e r en c e c o un t i s d e c r em e n ted , i nd i c a t i ng t h a t t h e
i n p ro g r e s s h a s c o mp l e t ed .

read

Th e phys i c a l pa g e s t a t e i s s e t to ac t i v e a nd v a l i d .

Th e va l i d b i t i n t h e pag e t a b l e e n t r y i s s e t .

I f t h e pag e i s a g l o ba l pag e , t h e v a l i d b i t s e t i n S t e p 3 wa s
in
the g l o ba l
pag e t a b l e e n t r y .
I n th i s c a s e , the p r o c e s s
{ s l a v e ) P T E m u s t b e l o a d ed w i t h t h e PFN a nd mad e v a l i d .

Af t e r the i nd i v i d ua l pag e s h av e b e e n t e nd ed
to ,
the
sched u l e r
is
n o t i f i ed
th a t a
pag e
r e a d h a s c om p l e ted { by r e po r t i ng a pag e f a u l t
c om p l e t i o n e v e n t w i th a n u l l p r i o r i ty i nc r emen t ) s o th a t t h e p r o c e s s
t h a t wa s p u t i n to a pag e f a u l t wa i t s ta t e wh e n t h e r e a d wa s i n i t i a t ed
{ I f a n y o f t h e pag e s j us t r e a d we r e c o l l i d ed
c a n b e m a d e c om p u t a b l e .
pag e s ,
t h e c o l l i d ed
pag e wa i t q u e u e i s a l s o emp t i ed .
Th a t i s , a l l
p r o c e s s e s i n th a t s t a te
a r e mad e c om p u t a b l e .
C o l l i d ed
pag e s a r e
d i sc us s ed i n the n e x t s e c t i o n . )

1 2- 2 4

PAG ING DYNAMI C S

12. 5. 2

Mod i f i ed Pag e Wr i t i ng

Th e mod i f i ed
pag e w r i te r
a l so
a t t em p t s
to c l us t e r wh e n wr i t i ng
mod i f i ed
page s
to
the i r b ac k i ng s to r e a d d r e s s e s .
Th e r e a r e n o t so
many s pe c i a l c a s e s h e r e as t h e r e a r e i n t h e pag e r e ad s i t ua t i o n .
Th e
th r e e d i f f e r e n t c a s e s enco u n t e r ed b y the mod i f i ed pag e wr i t e r d e pend
on the th r e e po s s i b l e b ac k i ng
s to r e
locat ions
tha t pag e s on
the
mod i f i ed pa g e l i s t c a n have .

1 2 . 5 . 2 . 1 Ope r a t i on o f the Mod i f i ed Pag e Wr i te r - Th e mod i f i ed
wr i te r p r o c e ed s i n a pp r o x i m a t e l y the f o l l o wi ng f a sh i o n .

pag e

Th e f i r s t pag e i s r emoved f r om the mod i f i ed pag e l i s t .
Its
pag e t a b l e e n t r y ad d r e s s i s r e t r i ev ed f r om t h e PFN PTE a r r a y .

Ad j a c e n t pag e t a b l e e n t r i e s a r e s c anned ( f i r s t
towa r d
l o we r
v i r t ua l
add r esses
a nd then towa r d h i g h e r v i r t ua l a d d r e s s e s )
l o o k i ng f o r t r a n s i t i o n pag e t ab l e e n t r i e s th a t m a p pag e s o n
t h e mod i f i ed pag e l i s t un t i l e i th e r th e d e s i r ed c l us t e r s i z e
i s r e a ch e d o r un t i l o n e o f t h e o th e r
t e rm i n a t i ng
cond i t i ons
i s r e a ch e d .
Th i s s c a n beg i n s f i r s t t o wa r d sma l l e r v i r t ua l
add r e s s e s
fo r
the
same
r e a so n t h a t t h e r e a d c l u s t e r r o ut i n e b eg i n s towa rd
l a rg e r a d d r e s s e s .
I f t h e p r og r am i s mo r e l i ke l y to r e f e r e n c e
t h e mo d i f i ed page wr i t e r d o e s n o t wa n t to
h i gh e r add r e s ses ,
i n i t i a t e a wr i te o pe r a t i o n , o n l y to have the pag e i mmed i a t e l y
f a ul ted
{ and
l i k e l y m o d i f i ed
ag a i n ) .
Th e mod i f i ed pag e
wr i t e r c ho o s e s to f i r s t wr i te
tho s e pag e s w i th a
sma l l e r
l i k e l i ho o d o f b e i ng r e f e r e n c ed i n the n e a r f u t u r e .

Th e w r i te i s i n i t i a t ed , the s t a t e o f a l l
of
the pag e s
is
c h a ng e d
to wr i t e i n p r og r e s s , a nd th e i r r e f e r e n c e c o un ts a r e
i n c r em e n ted .

Th e mod i f i ed pag e wr i te r r e t u r ns to i t s c a l l e r un t i l n o t i f i ed
by
i ts
spec i a l
k e r n e l AST t h a t the mod i f i ed pag e wr i t e h a s
c ompl e t ed .

1 2 . 5 . 2 . 2 Mod i f i ed Pag e Wr i t e C l u s t e r i ng - Th e t e rm i n a t i ng
f o r t h e sc a n o f t h e pag e t ab l e i n c l ud e t h e f o l l o w i ng .
•

•
•
•

c o nd i t i o n s

th e r e
Th e pag e ta b l e pag e i s n o t v a l i d .
Th i s
i mp l i e s t h a t
Th e s p e c i a l
a r e n o t r a n s i t i o n pag e s i n t h i s pag e ta b l e pag e .
c h e c k i s mad e to a v o i d a n unn ec e s s a r y pag e f a u l t .
Th e pag e t a b l e e n t r y d o e s n o t i nd i c a t e a t r a n s i t i o n f o rm a t .
Th e pag e t a b l e e n t r y i nd i c a t e s a pag e i n t r a n s i t i o n , b u t
phys i c a l pag e i s no t on the m od i f i ed pag e l i s t .

the

Th e phys i c a l page n um b e r i s g r e a t e r
tha n
the c o n t e n t s o f
g l o ba l
l o c a t i o n MMG $G L MAX PF N .
Th i s c h e c k avo i d s pag e s i n
s h a r ed memo r y , wh i c h h a ve n o PFN d a ta a s so c i a t ed w i th them .

1 2- 2 5

PAG ING DYNAM I C S
•

•

Th e SWPVBN a r r a y e l em e n t m u s t b e z e r o .
Pag e s wi th non z e r o
SWPVBN c o n t e n t s a r e t r e a ted i n a s pe c i a l wa y by th e mod i f i ed
p a g e wr i te r .
I f the c o n t e n t s o f t h e BAK a r r a y i nd i c a t e s t h a t th e b a c k i ng
store
l oc a t i on
fo r
t h e pag e i s a ( p r i v a t e o r g l o ba l ) i m ag e
f i l e , t h e s e c t i o n i nd e x m u s t b e t h e same f o r a l l pag e s i n the
c l us t e r .
I f the BAK a r r ay e l em e n t i nd i c a t e s tha t th e pag e s a r e
to
be
wr i tten
to
the pag e f i l e , t h e c o n t e n t s o f the v i r t ua l b l o c k
n um b e r f i e l d a r e i g no r ed .
Howe v e r , a l l
pag e s m u s t c o n t a i n
t h e s am e pag e f i l e i nd ex i n t h e i r BAK a r r a y e l em e n t s .

12. 5 . 2 . 3
Bac k i ng S t o r e Add r e s s e s fo r Mod i f i ed Pag e s
Th e r e a r e th r e e
d i f f e r e n t k i nd s o f b a c k i ng s to r e a d d r e s s tha t t h e mod i f i ed pag e wr i te r
e nc o un t e r s a s the mod i f i e d pag e wr i t e r r em ov e s pag e s f r om th e mod i f i ed
page l i s t .
-

•

I f the SWPVB N a r r a y e l em e n t i s n o n z e r o , th i s
i nd i c a t e s
th a t
the proces s
i s o u t s wa pped
a nd
th i s pa g e r ema i n ed beh i nd ,
p r o ba b l y d u e to a n o u t s t a nd i ng r e ad
r e que s t .
Th e mod i f i e d
p a g e wr i t e r d o e s n o t a t tempt to c l u s te r .
I n s t e ad , a wr i t e o f
a s i ng l e pag e t o t h e d e s i g n a t ed b l o c k i n
th e
swa p f i l e
is
i s s ue d .
A d e sc r i pt i o n o f how t h e SWPVBN a r r a y e l em e n t c a n b e
l o a d ed i s f o und
i n C h a pte r 1 4 ,
wh e r e
the
e n t i r e o u t s wa p
o pe r a t i o n i s d i s c u s s e d .
I f the ba c k i ng s to r e a d d r e s s i s a s e c t i o n , t h e mod i f i ed
pag e
wr i t e r c r e a t e s
a
c l us t e r
( up
to th e v a l ue o f t h e SYSBOOT
p a r ame t e r M PW WRTC LUSTER ) .
An y o f the t e rm i n a t i ng c o nd i t i o n s
l i s t ed a b o v e w i l l l i m i t t h e s i z e o f t h e c l us t e r .
I f the b a c k i ng s to r e a d d r e s s i s a pag e f i l e ,
ad j a c e n t pag e s
b o und
fo r
t h e s ame
pag e f i l e a r e a l s o wr i tten a t t h e same
t i me .
Th e mod i f i ed pag e wr i t e r a t tempts to
a l l o c a te a
n umbe r o f
b l o c k s i n t h e pag e f i l e e q ua l t o M PW WRTC LUSTER .
Th e d e s i r e d
c l u s t e r f a c t o r i s r ed uc ed to the n umbe r o f b l o c k s
a c t ua l l y
a l l o c a ted .
Th e a c t ua l c l u s t e r c r e a t ed fo r
a
wr i t e
to
the
pag e
file
c o n s i s t s o f s e v e r a l sm a l l e r c l u s t e r s , e a ch o n e r e p r e s e n t i ng a
s e r i e s o f v i r t ua l l y c o n t i g uo u s pag e s ( F i g u r e 1 2 -8 ) .
1.

Th e mod i f i ed pag e wr i t e r c r e a t e s a c l u s t e r o f v i r t ua l l y
c o n t i g uo u s pag e s , a l l bound f o r th e s ame pag e f i l e .

I f t h e d e s i r ed c l u s t e r s i z e h a s n o t ye t b e e n r e a c h ed , the
mod i f i ed
pa g e
l i st
is
s e a r c hed u n t i l ano th e r ph ys i c a l
pag e b o und fo r the s ame pag e f i l e i s fo und .

Pag e s v i r t ua l l y c o n t i g uo u s to th i s pag e fo rm the sec o nd
m i n i c l us ter
that
i s a d d ed to the e v e n tua l c l us t e r to be
wr i t t e n to the pag e f i l e .

1 2-26

PAG I NG DYNAM I C S
4.

Th i s p r o c e s s c o n t i n ue s un t i l e i th e r t h e c l us t e r
s i ze
is
r e a ch e d
o r n o m o r e pag e s o n the mod i f i ed pag e l i s t h a v e
the d e s i g na t e d pag e f i l e a s the i r b a c k i ng s t o r e a d d r e s s .

Th e mod i f i ed pag e wr i t e r i s b u i l d i ng
a
l a rg e c l u s t e r
th a t
c o n s i s t s o f a s e r i e s o f s ma l l e r c l u s te r s .
Th e l a rg e c l u s t e r
o n l y t e rm i n a t e s wh e n t h e d e s i r ed
s i ze
is
r eached
or
the
mod i f i ed
page
l i s t c o n t a i n s n o mo r e pag e s b o un d to th e pag e
f i l e i n qu e s t i o n .
E a c h sma l l e r c l us t e r c a n te rm i n a t e o n a n y
of
t h e c o nd i t i o n s
l i s te d
a b o v e , o r o n t h e two t e rm i n a t i ng
c o nd i t i o n s f o r the l a rg e c l us t e r .
Modified Page List
SWP$GL_BALBASE : :
(Balance Slot Area)

BAK

PTE

pgflx

gptx

PFN D

pgflx

gstx

pgflx

pgflx
correct pgflx but cluster is full

pgflx
.
.
.

transition PTE ( free list)

PFN H

PFN F

PFN A

MPW$AL_PTE : :
(Modified Page Writer's Map)
1

PFN H

PFN F
PFN A

PFN E

PFN ( valid)

PFN G

process section table Index

PFN G

PFN B

PFN J

PFN D

PFN J
demand zero PTE

Figure 1 2-8

E x amp l e o f C l u s te r e d Wr i t e to a Pag e F i l e

1 2-2 7

::J

PAG ING DYNAM I C S
12 . 5 . 2 . 4
E x amp l e o f Mod i f i ed Pag e W r i te to a P a g e F i l e - F i g u r e
1 2-8
i l l u s t r a t e s a sampl e c l u s t e r f o r wr i t i ng to a pag e f i l e .
Th e mod i f i ed
pa g e l i s t ( p i c t u r ed i n t h e uppe r r i g h t h a nd o f t h e f i g u r e } i s s h o wn a s
a s e que n t i a l a r r a y t o s i mpl i f y the f i g u r e .
1.

Th e f i r s t pag e o n t h e mo d i f i ed
pag e
l i st
is
PFN A .
By
s c a n n i ng
b a c kwa r d s ,
f i r s t P FN F a nd then PFN H a r e l o c a t ed .
Th e PTE p r e c e d i ng the o n e
th a t c o n ta i n s
PFN H
i s a l so
a
trans i t i on
PTE b u t the pag e i s o n t h e f r e e pag e l i s t .
Th i s
pag e t e rm i n a t e s t h e b a c kwa r d s e a r c h .

Th e mod i f i ed pag e wr i t e r m� p b eg i n s wi th
PFN H ,
PFN F ,
and
PFN A.
Th e
s e a rch
n o w g o e s i n t h e f o rwa r d d i r e c t i o n , w i th
e a c h p a g e b o und f o r the pag e f i l e ad d ed to the map up t o
a nd
i n c l ud i ng
P FN E .
Th e n e x t pag e t ab l e e n t r y i s v a l i d so t h e
f i r s t m i n i c l u s t e r i s t e rm i n a t ed .

Th e nex t pag e o n the m o d i f i ed pag e l i s t , PFN B , l e a d s to
the
a d d i t i o n o f a s e c o nd c l u s t e r to the ma p .
Th i s c l u s t e r b eg i n s
Th e b a c kwa r d
s e a r c h wa s
w i th P F N G a nd e nd s w i th P F N J .
t e rm i n a ted
wi th a PT E c o n t a i n i ng a s e c t i o n t ab l e i nd ex .
Th e
f o rwa r d s e a r c h t e rm i n a t e d w i th a d emand z e r o PTE .
No te th a t t h i s s e c o nd c l u s t e r c o n s i s t s o f pag e s b e l o ng i ng
to
a
d i f fe r ent proc e s s
f r om
th e
f i r s t c l us te r .
Th i s
is
r e f l ec t e d i n th e wo r d a r r a y e l em e n t fo r e a c h PTE i n
the m a p
that conta i ns a
process
h e a d e r vec to r i nd ex f o r e a c h pag e
( Figure 1 1 - 2 4 } .

Th e nex t pag e o n the m od i f i ed pag e l i s t i s PFN c .
Th i s pag e
b e l ongs i n a g l o b a l i m a g e f i l e a nd i s s k i pped ove r d u r i ng the
c u r r e n t wr i t e a t t em p t .

PFN D l e a d s to a th i r d c l u s t e r th a t wa s t e rm i n a t e d
i n the
b a c kwa r d d i r e c t i o n w i th a pag e t a b l e e n t r y th a t c o n t a i n s a
g l o b a l pag e ta b l e i nd ex .
Th e s e a r c h i n the fo r wa r d d i r e c t i o n
t e rm i n a ted
wh e n
the d e s i r ed c l u s t e r s i z e wa s r e a c h e d , even
t h o ug h the next P T E wa s b o und to the same pag e
file .
Th i s
s i ze
is
e i th e r M PW WRTC LUSTER o r a
n um b e r o f v i r t ua l l y
c o n t i g uo u s b l o c k s a v aTl a b l e i n the pag e
file ,
wh i c h ev e r
1s
sm a l l e r .
In
any c a s e , th i s c l us te r wi l l b e wr i t t e n wi th a
s i ng l e wr i t e r e que s t .

No t e th a t r e a ch i ng th e d e s i r ed s i z e r e s u l ted i n l e a v i ng
some
pag e s o n the mod i f i ed pa g e l i s t b o und f o r the same pag e f i l e ,
s uc h a s PFN I i n the f i g u r e .

1 2 . 5 . 2 . 5 Mod i f i ed Pag e W r i te C ompl e t i on - The mod i f i ed pag e wr i t e r i s
n o t i f i ed
th a t
the
wr i te
i s c ompl e t e by a s pe c i a l k e rne l AST ( wh o s e
ad d r e s s wa s s to r ed i n t h e ASTPRM f i e l d o f t h e I R P wh i l e th e wr i t e
wa s
i n p r og r e s s ) .
Mo d i f i ed pag e wr i t i ng i s r e co rd ed i n the I R P a s a s wa p
wr i te t o a l l o w th i s c ompl e t i o n m e tho d t o b e used .
Fo r the p u r po s e s o f
the I / 0 po s t p r o c e s s i ng r o u t i n e , t h e o n l y f o rm o f pag e wr i t e r e q u e s t i s
t h e o n e i s s ue d by th e Upd a t e S e c t i o n s ys tem s e rv i c e .
Th i s k e r n e l AST d e c r em e n t s v a r i o u s r e f e r e n c e c o un t s tha t
wr i t e
in p r og r e s s .
I f the r e f e r e n c e c o u n t i s n o w z e r o ,
pl a c ed o n the f r e e pag e l i s t .
I f the n um b e r o f pag e s o n
pa g e
l i st
( S C H $G L_MFYCNT ) i s s t i l l a b o v e the l o w l i m i t
1 2-28

i nd i c a ted the
th e pag e s a r e
the mod i f i ed
th r e sho l d fo r

PAG I NG DYNAM I C S
t h e mod i f i ed pag e
l ist
( S C H $ G L MFY L O L IM ) ,
t h e n t h e mod i f i ed
pag e
wr i te r
r em o v e s
t h e n ew f i r s t- pag e f r om t h e mod i f i ed pag e l i s t a nd
s ta r ts a l l ove r .

12. 5.3

Upd a t e S e c t i o n Sy s t em Se r v i c e

Th e Upd a t e S e c t i o n s ys t em s e r v i c e a l l o ws a p r o c e s s t o wr i t e pag e s i n a
s ec t i o n
to
th e i r
b a c k i ng
s to r e
a d d r e s s e s i n a c o n t r o l l ed f a sh i o n ,
w i tho ut wa i t i ng f o r the mod i f i ed pag e wr i te r to d o the b a c k u p .
Th i s
s y s tem s e rv i c e i s e spec i a l l y u s e f u l f o r f r e que n t l y a c c e s sed pag e s th a t
m a y n ev e r b e wr i t t e n b y t h e m od i f i ed p a g e wr i t e r ,
b e c a us e
they a r e
a l wa ys b e i ng f a ul t ed f r om the mod i f i ed pag e l i s t b a c k i n to the wo r k i ng
s e t b e f o r e t h e y a r e b a c ked up .
Th i s sys tem s e rv i c e i s a c r o s s b e twe e n mod i f i ed
pag e wr i t i ng
a nd
a
n o rm a l
wr i t e
r eq ue s t .
L i ke a n y Que u e d I / 0 r e que s t , th i s s e r v i c e c a n
r ec e i v e c omp l e t i o n no t i f i c a t i o n w i th a n e v e n t f l ag , a n A S T , o r th r o ug h
an
I /O s t a t us b l oc k .
Th e n um b e r o f pag e s wr i t t e n i s spec i f i ed by t h e
a d d r e s s r a ng e pa s s ed a s
an
i np u t pa r am e t e r
to
the
serv i ce .
Th e
c l us te r
f a c to r
i s t h e m i n imum o f M PW WRTC LUSTER a nd th e n um b e r o f
pag e s i n t h e i n put r a ng e .
Th e d i r ec t i o n o f s e a r c h fo r mod i f i ed
pag e s
is
d e t e rm i n ed b y t h e o rd e r tha t t h e a d d r e s s r a ng e i s spec i f i e d t o the
s e rv i c e .

12. 5. 3. 1
Page S e l e c t i o n - I f th e s e c t i o n th a t i s b e i ng b a c k e d up i s a
process
pr i va te
s e c t i o n , o n l y tho s e pag e s tha t h a v e the mod i f i ed b i t
s e t i n the pag e t a b l e e n t r y ( o r i n the PFN s t a t e a r r a y f o r t r a n s i t i o n
pag e s ) a r e w r i t t e n o u t .
I f the s e c t i o n i s a g l o b a l s e c t i o n , then i n f o rm a t i o n a bo ut wh e th e r the
pag e i s mod i f i ed i s f o und i n b o th the PFN d a t a base a nd the pag e t a b l e
( Th e mod i f y b i t
e n t r i e s o f a l l p r o c e s s e s m a pped t o th i s g l ob a l pag e .
in
the g l o b a l
pag e
t ab l e
entry
is
i n a c c e s s i b l e t o h a r d wa r e a nd
c o n t a i n s no u s e f u l i n f o rm a t i o n . ) B e c a u s e t h e r e a r e
no
b a c k po i n t e r s
f o r va l i d
g l o b a l pag e s , th i s i n f o rma t i o n i s un a v a i l a b l e .
Th e r e fo r e ,
a l l pag e s i n a g l o b a l s e c t i o n a r e
wr i t t e n
to
th e i r
b ac k i ng
s to r e
l o c a t i o n , r eg a r d l e s s o f wh e th e r t h e pag e s h a v e b e e n mod i f i e d .
I f the f l ag s pa r a m e t e r p a s s e d to Upd a t e S e c t i o n h a s i t s l ow b i t
set ,
th i s
i nd i c a t e s
that
the
caller
is
the
o n l y p r o c e s s c a pa b l e o f
mod i f y i ng t h e s ec t i o n .
I n th a t c a s e , t h e p r o c e s s pag e
tab l e
entr i es
( a nd th e PFN d a t a b a s e ) a r e u s e d to s e l e c t c a nd i d a t e pag e s fo r b a c k i ng
On l y mod i f i ed pag e s a r e wr i t t e n .
up .

1 2 . 5 . 3 . 2 Wr i t e Compl e t i o n - Th e
proc e s s
tha t
i s s ued
the
Upd a t e
Se c t i o n s ys t em s e r v i c e i s f i r s t n o t i f i ed a bo u t wr i t e compl e t i o n wi th a
s pe c i a l k e r n e l AS T .
Th i s AST f i r s t c h e c k s wh e th e r
all
the
pag e s
r e que s t ed
b y t h e o r i g i n a l c a l l h a v e b e e n wr i t t e n o r wh e th e r a n o th e r
wr i t e i s r eq u i r ed .
I f mo r e pag e s h a v e t o b e wr i t t e n , a no the r
c l us te r
is
s e t u p a nd q u e ued .
I f a l l r e que s t ed pag e s h a v e b e e n wr i t t e n , the
n o rma l I /0 c omp l e t i o n pa th i nvo l v i ng event f l ag s , I /0 s t a t u s b l o c k s ,
a nd u s e r - r e q ue s ted ASTs i s e n t e r e d a nd th e p r o c e s s no t i f i ed .

1 2-29

PAG I NG DYNAM I C S
12. 6

PAG ING AND SCHEDUL ING

Pag e f a u l t h a nd l i ng c a n i n f l ue n c e the s c h ed u l i ng s t a t e o f p r o c e s s e s i n
s ev e r a l
d i f f e r e n t wa ys .
If
a
r ead
i s r eq u i r ed to sa t i s f y a pag e
f a u l t , t h e f a u l t i ng p r o c e s s i s p l aced i n to a pag e
f a u l t wa i t
s ta t e .
If a
r e so u r c e
s uc h
a s phys i c a l m emo r y o r pag e f i l e s pa c e i s n o t
av a i l a b l e , t h e p r o c e s s i s p l a c ed
i n to
a n a pp r o p r i a t e wa i t
state .
Th e r e
are
s ev e r a l wa i t s ta t e s tha t a p r o c e s s m a y b e p l a c ed i n to a s a
r e s u l t o f a pag e f a u l t .

12. 6. 1

P a g e Fa u l t Wa i t S t a t e

Th e m o s t o bv i o u s wa i t
s ta t e
is
pag e
f a u l t wa i t
( PFW ) ,
wh i c h
is
r e q u i r ed i f a r e a d i s r eq u i r ed to r e so l v e t h e fa u l t .
Th e p r o c e s s t ha t
r eq u i r e s the r e a d to r e so l v e i t s pag e f a u l t
i s p l a c ed
i n to
a pag e
f a u l t wa i t s ta t e .
Th e I /O c ompl e t i o n r o u t i n e d e te c t s t h a t a pag e r e a d
h a s c ompl e t ed a nd
r e po r t s
a
pag e
f a ul t c om p l e t i o n ev e n t t o
the
s c h ed ul e r .
Th e s c h ed u l e r r em o v e s the p r o c e s s f r om t h e pag e f a u l t wa i t
s t a t e a nd m a k e s i t c om p u ta b l e .
Th e r e i s n o p r i o r i t y i nc r e m e n t d ue
to
pag e f a u l t r e ad c om p l e t i o n so the s c h ed u l i ng d e c i s i o n i s m a d e b a s e d o n
t h e p r o c e s s ' s c u r r en t pr i o r i ty .

12. 6. 2

F r e e Pag e Wa i t S t a t e

I f the r e i s n o t e n o ug h phys i c a l m emo r y a v a i l a b l e t o s a t i s f y the
faul t ,
t h e p r o c e s s i s p l a c ed i n to a f r e e pag e wa i t s t a t e ( FPG ) .
phys i c a l pag e m a n ag e r ( mod u l e A L LOCPFN ) c h e c k s f o r p r o c e s s e s
in
s ta t e wh e ne v e r
pag e s a r e
a d d e d to a n empty l i s t .
I f the f r e e
wa i t s t a t e
is
not
empty ,
all
processes
in
the
state
a re
c om p u t a b l e .

pag e
Th e
th i s
pag e
mad e

Th e phys i c a l pag e ma n ag e r m a k e s n o s c h ed u l i ng d e c i s i o n a b o u t wh i c h
p r o c e s s w i l l g e t the pa g e .
Th e r e i s n o f i r s t- i n f i r s t- o ut a pp r o ach to
the f r e e pag e wa i t s t a t e .
Ra t h e r , a l l p r o c e s s e s wa i t i ng fo r the pag e
a r e mad e c om p u t a b l e .
Th e n e x t p r o c e s s to e x e c u t e wi l l be cho s e n b y
t h e sched ul e r , u s i ng t h e n o rma l a l g o r i thm th a t t h e h i g h e s t p r i o r i t y
r e s i d e n t c omputa b l e p r o c e s s e x e c u t e s n ex t .

12. 6 . 3

C o l l i d ed P a g e Wa i t S t a t e

I t i s po s s i b l e fo r a pag e f a u l t t o o c c u r f o r a pag e wh i c h
is
al ready
b e i ng
r e ad f r om d i s k .
S u c h a pag e i s r e f e r r ed to a s a c o l l i d ed pag e .
Th e c o l l i d ed b i t ( i n the PFN TYPE a r r a y ) i s s e t a nd t h e pr o c e s s p l ac ed
i n to the c o l l i d ed pag e ( C O L PG ) wa i t s t a t e .
One o f t h e d e ta i l s th a t th e pag e r e ad c ompl e t i o n r o u t i n e ch e c k s i s t h e
c o l l i d ed
b i t i n th e TYPE a r r a y e l em e n t fo r t h e pag e .
I f the c o l l i d ed
b i t i s s e t , the c o l l i d ed pag e wa i t s t a t e
i s empt i ed .
Th e r e
i s no
chec k
fo r
the pag e tha t i s b e i ng wa i t ed f o r by each p r o c e s s as i t i s
mad e c omput ab l e .

1 2-30

PAG ING DYNAM I C S
Th i s l a c k o f c h e c k h a s two a d v a n ta g e s .
•

•

12. 6.4

As wa s t h e c a s e fo r
f r ee
pag e av a i l a b i l i t y ,
the r e
is
no
s pe c i a l
code
t o d e t e rm i n e wh i ch pr o c e s s w i l l g e t th e pag e
f i rst .
Al l p r o c e s s e s a r e m a d e c ompu t a b l e and
the n o rm a l
s c h e d u l i ng a l g o r i thm s e l e c t s t h e p r o c e s s th a t e x e c u t e s n e x t .
Th e p r o b a b i l i t y o f a c o l l i d ed pag e i s sm a l l .
Th e p r o b a b i l i t y
of
two
d i f f e r e n t c o l l i d ed
pag e s
is
e v e n sm a l l e r .
If a
p r o c e s s wa i t i ng fo r ano th e r c o l l i d ed
pa g e
is
s e l e c ted
for
e x e c ut i o n ,
th a t p r o c e s s wi l l i n c u r a pag e f a u l t a nd g e t put
r i g h t b a c k i n to t h e c o l l i d ed
wa i t s t a t e .
No th i ng
un u s ua l
occ u r s
and VM S a v o i d s a l o t o f s pe c i a l c a s e c o d e to h a nd l e a
s i t ua t i o n th a t r a r e l y i f ev e r o c c u r s .

No Ava i l a b l e S pa c e i n the Pag e F i l e

Wh e n a n e n t r y f o r a c o py-on- r e f e r e nc e pag e o r a d emand
ze ro
pa g e
is
mad e
in
t h e wo r k i ng
s e t , a pa g e m u s t b e r e s e rved i n the pag e f i l e .
{ Th e a c tua l a l l o c a t i o n o f a s p e c i f i c b l o c k d o e s n o t o c c u r
un t i l
the
m o d i f i ed
pa g e wr i t e r
b a c k s t h e pag e up . ) If th e r e is no r o om in the
pag e f i l e , t h e p r o c e s s i s p l a c ed i n to a r e s o u r c e wa i t
s tate
{ MWA I T ) .
Th e
pa r t i c u l a r
r e s o u r c e b e i ng
wa i t ed
fo r
i s pag e
file
s pa c e
{ RS N $_PG F I L E ) .
As v i r t ua l a d d r e s s s pa c e i s d e l e t e d { by spec i f i c r e que s t o r a s a
side
e f fe c t o f
i mag e
ex i t o r p r o c e s s d e l e t i o n ) , pag e f i l e s pa c e b e c o m e s
ava i l ab l e .
Th e pa g e f i l e d e a l l o c a t i o n r o u t i n e c h e c k s f o r
t rans i t ions
f r om
th e empty s t a t e a nd no t i f i e s t h e s c h ed u l e r tha t t h e r e so u r c e o f
pag e f i l e s pa c e i s n o w a v a i l a b l e .
Th e s c h e d u l e r { s p e c i f i c a l l y r o u t i n e
S C H $ RAVA I L )
d e t e rm i n e s wh e th e r
a ny p r o c e s s e s a r e wa i t i ng fo r th i s
r e so u r c e a nd ma k e s them compu t a b l e ag a i n .

1 2-3 1

CHAPTER 1 3
MEMORY MANAG EMENT SYSTEM S ERVI C E S

Th e p r ev i o u s two c h a p t e r s d e sc r i b ed t h e d a t a s t r uc t u r e s
used by
the
m em o r y m a nag em e n t s ub s ys t em to d e sc r i b e ph ys i c a l and v i r t ua l memo r y ,
a nd t h e a c t i o n o f t h e pag e f a u l t h a nd l e r wh e n a pag e wa s r e f e r e n c e d i n
wh i c h
the v a l i d
b i t wa s n o t s e t .
Th i s c h a p t e r d e s c r i b e s t h e sys t e m
s e r v i c e s a v a i l a b l e to the u s e r ( a n d a l so u s e d i n t e r n a l l y b y VM S )
th a t
a l l o c a t e t h e s e s t r uc t u r e s a nd i n i t i a l i z e t h e i r c o n t e n t s .
Th e s e r v i c e s
a r e d i v i d ed i n to f o u r s e pa r a t e c a t eg o r i e s .

13. 1

Some s y s tem s e r v i c e s a r e
a s s o c i a t ed
spe c i f i c a l l y w i th
the
l a yo u t
o f v i r t u a l ad d r e s s s pa c e .
V i r t ua l a d d r e s s s pa c e c a n
b e c r e a t ed o r d e l e t ed a l m o s t a t wi l l wi th i n
the
l im i ta t i on s
i mpo s ed
b y p r o c e s s quo t a s a nd l i m i t s a nd the c o n s t r a i n t s o f
the
S Y S B OOT pa r am e t e r s
set
up
wh e n
the
sys tem
wa s
i n i t i a l i zed .

P r i v a t e and g l o b a l s e c t i o n s c a n b e c r e a t ed
th a t
a l low the
blocks
of
a
file
to
b e m a pped a s a po r t i o n o f a p r o c e s s
add ress
spac e .
Al th o ug h t h e
sec t i o n s e rv i c e s
are
a l so
a s s o c i a t ed w i th t h e l a yo u t o f v i r t ua l a d d r e s s s pa c e , t h e y a r e
t r e a t ed i n a s e pa r a t e s e c t i o n b e c a u s e o f the i r a d d e d l ev e l o f
c om p l e x i t y .

S y s t em s e rv i c e s a l l o w u s e r s t o l o c k po r t i o n s o f the i r wo r k i ng
sets
i n to m emo r y ,
a v o i d i ng
the o v e r h e a d o f pag e f a u l t s o r
a l l ow i ng po r t i o n s o f c o d e to
e x e c u t e a t e l ev a ted
! PL .
A
p r o c e s s c a n a l so d i sa b l e
s wa pp i ng , p r eve n t i ng i t s e l f f r om
b e i ng r emoved f r om memo r y .

Th e r e a r e o th e r m i s c e l l a n e o us o pe r a t i o n s a s s o c i a t e d w i th
the
m em o r y m a n a g em e n t a v a i l a b l e to a p r o c e s s s u c h a s f o r c i ng t h e
c o n t e n t s o f a l l mod i f i ed pag e s to b e wr i t t e n to the i r b a c k i ng
s t o r e ad d r e s s e s
( Upd a t e
S e c t i o n s ys t e m se r v i c e ) o r p u r g i ng
s o m e o r a l l p ag e s f r om th e p r o c e s s wo r k i ng s e t .

D I S PATCH METHOD FOR MEMORY MANAG EMENT SYSTEM S E RV I C E S

A l mo s t a l l o f t h e m em o r y m a n ag em e n t s y s tem s e rv i c e s spe c i f y a d e s i r ed
address
r a ng e
as an
i n put p a r am e t e r .
Th e
pag e
tabl e en t r i e s
a s s o c i a t ed w i th t h e s e a d d r e s s e s c o n t a i n a n o wn e r f i e l d
( Fi g u r e 1 1 -3 ) ,
i nd i c a t i ng wh e th e r t h e c a l l e r o f e a c h s e r v i c e c an m a n i p u l a te t h e pag e s
i n t h e d e s i r ed f a sh i o n .
An o th e r p e c u l i a r i t y o f t h e m em o r y m a n ag em e n t
s ys tem s e rv i c e s
is
t h a t m a n y o f t h e s e r v i c e s c a n pa r t i a l l y s u c c e e d
( b e c a u s e th e y a r e d o n e o n a pag e- by-p a g e b a s i s ) .
Th i s p a r t i a l s uc c e s s
is
i nd i c a t e d
b y r e t u r n i ng
an
e r r o r code c om b i n ed w i th t h e a d d r e s s

13-1

MEMORY MANAG EMENT S YS TEM S E RV I C E S
r a ng e
over
p a r am e t e r ) .

wh i c h

the

o pe r a t i o n

wa s

c ompl e t ed

( in

A c ommo n d i s pa t c h m e th o d i s used by m o s t o f t h e memo r y
s ys t em s e r v i c e s t o r e f l e c t the s i m i l a r i ty o f t h e se r v i c e s .
•

•

13.2

the

RE TADR

m a n ag emen t

I n fo rma t i o n a bo u t t h e s p e c i f i c s e rv i c e , i nc l ud i ng
the
i nput
pa r ame t e r s , i s pl a c ed on t h e s t a c k f o r l a t e r r e t r i e v a l .
Pag e own e r s h i p i s c h e c k e d to i n s u r e t h a t
a
l e s s p r i v i l eg ed
a c c e s s mod e i s n o t a t tem p t i ng t o a l t e r t h e p r o pe r t i e s o f s o m e
pag e s o wn e d b y a m o r e pr i v i l eg e d a c c e s s mo d e .

•

Th e a d d r e s s o f a
pag e - by-pa g e
r o u t i ne
to
a c compl i s h
the
d e s i r e d a c t i o n o f t h e o r i g i n a l s e rv i c e i s pl a c ed i n t o R6 .

•

A c ommon
rout ine
i s c a l l ed
th a t pe r fo rms g e n e r a l
pag e
p r o c e s s i ng a n d c a l l s the s i ng l e pag e s e r v i c e - s p e c i f i c r o u t i n e
f o r e a c h pag e i n t h e d e s i r ed r a ng e .

•

Th e a d d r e s s r a ng e a c t ua l l y o pe r a ted on
c a l l e r ( i f r e q u e s t ed ) .

r e t u rned

the

VI RTUAL ADDRESS C REAT I ON AND D E L E T I ON

Th e f i r s t l ev e l o f m em o r y m a n ag em e n t a v a i l a b l e to
a
process
is
the
c rea t ion
or
d el et ion
of
v i r t ua l a d d r e s s s pa c e .
Th e s e s e r v i c e s a r e
a l s o u s ed by t h e s ys t em wh e n a n
i m ag e
f i r s t b eg i n s e x e c u t i ng
( th e
imag e
a c t i v a to r
cal l s
seve ral
se rv i ces
to
c r e a t e p r o c e s s add r e s s
s pa c e ) a n d a s pa r t o f i m a g e e x i t ( t h e i m ag e r e se t r o u t i n e d e l e t e s
all
of
P O s pa c e a nd
a
sm a l l pa r t o f P l s p a c e ) .
Th e memo r y m a n a g em e n t
pe r f o rmed b y t h e
s ys tem
a s pa r t
of
imag e
a c t ivation
or
process
d e l e t i o n i s d e sc r i b ed i n Ch a pt e r 1 8 .

13. 2. 1

Ad d r e s s Sp a c e C r e a t i o n

Ad d r e s s s pa c e c r e a t i o n i s e s s e n t i a l l y a s i m p l e o p e r a t i o n .
A series of
d em a nd
ze r o
pag e s
a r e c r ea t ed , e i th e r a t the end o f the d e s i g n a t ed
a d d r e s s s pa c e ( E x p a nd
Reg i o n )
or
in
the
spe c i f i e d
add ress
r a ng e
( C r e a t e Vi r t ua l
Ad d r e s s
Spa c e ) .
I f a ny p a g e s a l r e a d y e x i s t i n the
r e que s ted r a n g e , they m u s t be d e l e t ed f i r s t .
Th e s e two sys tem s e rv i c e s c a n pa r t i a l l y s uc c e e d .
Th a t i s , a n umbe r o f
pag e s
sm a l l e r
than o r i g i na l ly
r e que s t ed m a y b e c r e a ted .
Onc e the
s pe c i f i ed a d d r e s s r a ng e is
d e te r m i n ed ,
t h e d em a nd
zero
pag e s
are
c r e a ted o n e a t a t i m e .
I t i s po s s i b l e t o r un i n to o n e o f the l i m i t s
o n t h e n um b e r o f pag e s th a t c a n b e c r e a ted a f t e r
s ev e r a l
pag es h a v e
a l r e a d y b e en s uc c e s s f u l l y c r e a t ed .
Fo r th i s r e a s o n , i t i s e s pec i a l l y
i m po r t a n t f o r t h e c a l l e r o f e i t he r $ C R E TVA o r $ E X PREG to l o o k a t
the
RETADR a r g um e n t to d e t e rm i n e wh e th e r the s e r v i c e ( $ CRETVA or $ E XPREG )
wa s pa r t i a l l y s uc c e s s f u l .

1 3 -2

MEMORY MANAG EMENT SYSTEM S ERVI C E S
13.2.1.1
L i m i t s o n Vi r t ua l Ad d r e s s Spa c e C r e a t i o n - Th e r e a r e t h r e e
l im i t a t i o n s o n
the
amo u n t o f v i r tu a l
add ress
s pa c e
tha t c a n be
c r ea t e d .
e

•

Th e
S Y S B OOT p a r am e t e r V I RTUA L PAG E CNT c o n t r o l s
the
total
n um b e r
o f pag e
t a b l e e n t r i e s ( P O PTEs p l u s P l PTE s ) th a t a n y
p r o c e s s c a n have i n i ts p r o c e s s h e a d e r .
Th e d i v i s i o n o f
t h e s e p a g e s b e twe e n
PO
s p a c e a nd
Pl
s pa c e
is
to t a l l y
I t i s o n l y t h e s um o f PO a nd
a r b i t r a r y a nd p r o c e s s s pe c i f i c .
P l p a g e s t h a t i s l i m i t ed b y t h e SYS B O OT p a r am e t e r . )
Th e s i ze o f a p r o c e s s wo r k i ng s e t a l s o c o n t r o l s t h e
s i ze
of
tha t
p r o c e s s ' s a d d r e s s s pa c e .
Wh e n a p r o c e s s p a g e i s �q l i d ,
t h e pag e t a b l e pag e f o r th a t pag e i s no t o n l y v a l i d b u t
a l so
d yn am i c a l l y l o c k e d
i n to the wo r k i ng s e t .
Fo r sm a l l a d d r e s s
s pa c e s , t h e s e t o f v a l i d p r o c e s s pag e s c a n b e r e p r e s e n t e d b y
a sm a l l n um b e r o f pag e t a b l e pag e s .
As t h e a d d r e s s s pa c e g r ows , t h e p r o ba b i l i ty tha t a g i v e n pag e
t a b l e p a g e m a ps m o r e t h a n o n e v a l i d p r o c e s s pag e d e c r e a s e s .
( Th e l i m i t i ng c a s e , o n e t h a t c a n u s ua l l y be r e a c h e d o n l y w i th
v e r y l a rg e p r o c e s s ad d r e s s s pa c e s , r e qu i r e s two wo r k i ng s e t
l i s t e n t r i e s f o r e a c h v a l i d p r o c e s s pag e . ) I n a n y c a s e , t h e r e
is
a n i mp l i c i t l i m i t t o the p r o c e s s a d d r e s s spa c e i m po s e d b y
t h e p r o c e s s wo r k i ng s e t quo t a s .
Th e s p e c i f i c c h ec k t h a t i s m a d e i s wh e th e r the
s i ze
of
the
d yn am i c wo r k i ng
set
l i s t c a n l o c k a l l t h e pa g e t a b l e pag e s
n e c e s s a r y t o m a p t h e p r o c e s s a d d r e s s spa c e a nd
stil l
l eave
e no ug h
f l u i d wo r k i ng s e t ( PH D $W F LU I D ) to a l l o w t h e p r o c e s s
t o pe r fo rm u s e f u l wo r k .
I f th i s ch e c k f a i l s , t h e wo r k i ng s e t
l ist
is
e x pa nd ed .
I f t h e wo r k i ng s e t i s a t i t s l i m i t , t h e
v i r t ua l
ad d r e s s c r e a t i o n
fa ils
wi th
the
sta tus
of
S S $ I N S FWS L .

•

Th e th i r d c o n s t r a i n t o n t h e to t a l s i z e o f t h e p r o c e s s a d d r e s s
space
is
t h e pag i ng f i l e q uo t a .
E a c h d em a nd ze r o pag e a n d
e a c h c o py-on- r e f e r e n c e s e c t i o n pag e i s
c h a r g ed
ag a i n s t
the
j o b ' s pag i ng f i l e q u o ta ( J I B $ L_PG F LCNT ) .

1 3 . 2 . 1 . 2 E x pa nd Reg i o n Sys t em S e r v i c e - Th e
Ex pand
Reg i o n
s y s t em
s e rv i c e
is
a spec i a l c a s e o f the C r e a t e Vi r t ua l Ad d r e s s S p a c e sys t em
se rv i c e .
Th e r e que s t ed n um b e r o f pag e s i s s i mpl y c o nv e r ted i n to a
PO
o r P l pag e r a ng e a nd c o n t r o l i s p a s sed t o a pag e c r e a t i o n r o u t i n e th a t
i s c ommo n b e twe e n the two s e r v i c e s .

1 3 . 2 . 1 . 3 Au toma t i c Us e r S t a c k E x p a n s i o n - A s p e c i a l fo rm o f P l s pa c e
e x pa n s i o n o c c u r s wh e n a
r e q ue s t
fo r
u s e r s t a c k s pa c e e x c e e d s t h e
r em a i n i ng s i z e o f the u s e r s t a c k .
S u c h a r e que s t c a n b e
r e po r t e d
by
t h e h a r d wa r e
as
an
a c c e s s v i o l a t i o n e x c e pt i o n , o r by s o f twa r e wh e n
i n s u f f i c i e n t use r s t a c k s pa c e i s
d e t e c ted .
( S o f twa r e d e t e c t i o n
is
d o ne b y t h e AS T d e l i v e r y r o u t i n e a nd the Ad j u s t S t a c k s ys tem se r v i c e
i f t h e r e q ue s t i s fo r u s e r m o d e s t ac k s pa c e ) .
Th e r o u t i n e E XE $ E XPANDS TK i s c a l l ed
d i r e c t l y by
the
two
s o f t wa r e
r o u t i n e s a nd i nv o k e d b y t h e Ac c e s s Vi o l a t i o n e x c e p t i o n hand l e r i f t h e
access v i o l a t i on occur red i n user mode .
Th i s r o u t i n e c h e c k s
th a t a
1 3- 3

MEMORY MANAG EMENT SYS TEM S ERVI C E S
l e ng t h v i o l a t i o n
( a s o pp o s e d to a p r o t e c t i o n v i o l a t i o n ) o c c u r r ed a n d
t h a t the i n a c c e s s i b l e a d d r e s s i s i n P l s p a c e .
If
so ,
Pl
space
is
e x pa nd e d
f r om
i ts
c u r r en t
l ow a d d r e s s e nd
to
the
spec i f i ed
i n ac c e s s i b l e a d d r e s s .
Fo r t h e u s u a l c a s e ,
one
i n wh i c h
a
p r o g r am
r e qu i r e s m o r e
use r
s t a c k s pa c e
than
r e q ue s t e d
a t l i n k t ime , the
e x pa n s i o n typ i c a l l y o c c u r s o n e pag e a t a t i m e .
Because
t h i s a u toma t i c
e x pa n s i o n
c a nno t
be
d i s a b l ed
on
a
p r o c e s s - spec i f i c o r s ys t em-wi d e b a s i s , a r un a wa y p r o g r am ( o n e tha t i s
u s i ng s t a c k s pa c e w i tho u t r e t u r n i ng i t ) wi l l no t b e a b o r t e d
un t i l
it
exceeds
t h e v i r t ua l
add ress
s i z e d e t e rm i n ed by t h e VI RTUA L PAG E CNT
S Y S B O O T p a r am e t e r ( wh i c h i s i nd i c a t ed by $ C R E TVA
r e t u r n i ng
an
e r ro r
s t a t u s o f S S $ VAS F U L L ) .
I n a d d i t i o n , a p r og r am th a t m a k e s a r a nd om
( a nd p r o b a b l y i nc o r r e c t ) r e f e r e n c e to an a r b i t r a r y P l a d d r e s s
sm a l l e r
than
the
t o p o f t h e u s e r s t a c k w i l l p r o ba b l y c o n t i n u e t o e x e c u t e
( a f t e r t h e c r ea t i o n o f m a n y d em a nd z e r o pag e s )
r a th e r
than
e x i t i ng
w i th some e r r o r s t a t us .
I f t h e s ta c k e x pa n s i o n f a i l s f o r wh a te v e r r e a s o n ( th e C r e a t e Vi r t ua l
Ad d r e s s s ys tem
s e rv i c e c a n f a i l fo r s ev e r a l r e a so n s ) , t h e p r o c e s s i s
n o t i f i e d i n a wa y t h a t d e p e nd s o n wh o o r i g i n a l l y c a l l ed E XE $ E XPAND S TK .
•
•

•

13. 2. 2

Th e Ad j u s t S t a c k s ys t em s e rv i c e f o r u s e r m o d e c a n
s ev e r a l o f the e r r o r c o d e s r e t u r n ed by $ C RETVA .

fa i l

w i th

An a t t empt to d e l i v e r a n A S T to a p r o c e s s w i th
i nsuff i c i ent
user
stack
s pa c e
r esul ts
i n a n AS T d e l i v e r y s t a c k f a u l t
e x c e pt i o n b e i ng r e po r t e d to the p r o c e s s .
( E no ug h i n fo rma t i o n
is
r em o v e d
f r om
the
s ta c k by the e r ro r ro u t i ne that the
e x c e pt i o n d i s pa tc h e r c a n a t l e a s t g e t s t a r t ed
in
r e po r t i ng
the e x c ept i on . )
I f t h e u s e r s t a c k c a nno t b e e x pa nd ed
i n r e s po n s e
to
a
Pl
space
l e ng th v i o l a t i o n ,
then an a c c e s s v i o l a t i o n faul t i s
r e po r t ed t o t h e p r o c e s s .
I f the r e i s n o t e n o ug h
user
s tac k
to
r e po r t th e e x c e p t i o n , t h e no rma l c o nd i t i o n h a nd l e r s e a r c h
i s byp a s s e d a nd t h e e x c e p t i o n i s
r e po r t e d d i r e c t l y t o
the
l a s t c h a n c e h a nd l e r ( Ch a p t e r 2 ) .
In the d e faul t c ase , th i s
h a nd l e r c a u s e s th e c u r r e n t l y e x e c u t i ng i m ag e t o te rm i n a t e .

Ad d r e s s Spa c e De l e t i o n

Fo r a c o up l e o f r ea so n s , p a g e d e l e t i o n i s mo r e c ompl i c a t ed
c rea t i on .

than

pag e

C r e a t i o n i nv o l v e s t a k i ng t h e p r o c e s s
f r om o n e
k n o wn
s ta t e
( ad d r e s s
s pa c e d o e s n o t ye t e x i s t ) t o ano th e r k n o wn s t a t e
( t h e pag e t a b l e e n t r i e s c o n t a i n d em a n d
ze ro
PTE s ) .
Pag e
d e l e t i o n mus t d e a l w i th i n i t i a l c o nd i t i o n s tha t i n c l ud e a l l
t h e po s s i b l e s t a t e s t h a t a v i r tua l p a g e c a n b e i n .

Th e s e c o nd r e a so n i s t h a t pag e c r e a t i o n m a y f i r s t
r e qu i r e
that the
s p e c i f i ed
pag e s be d e l e te d
i n o r d e r t o put the
Th a t
is ,
pag e
p r o c e s s pag e t a b l e s i n to t h e i r known s t a t e .
d e l e t i o n i s o f t en an i n t eg r a l pa r t o f p a g e c r e a t i o n .

1 3-4

MEMORY MANAG EMENT SYS TEM SERVI C E S
13. 2. 2. 1
De l e t e V i r t u a l Ad d r e s s Spa c e Sys t em Se r v i c e - Wh e n a pag e i s
d e l e t ed ,
all
process
a nd
s y s t em r e so u r c e s a s s o c i a t ed w i th t h e pag e
mus t b e r e t u r ned .
Th e s e i n c l ud e
1.

a pag e f r am e f o r v a l i d a nd t r a n s i t i o n pa g e s ,

a pa g e f i l e v i r t ua l
block
fo r
pag e s wh o s e
a d d r e s s i n d i c a t e s an a l r e a d y a l l o c a t ed b l o c k ,

a wo r k i ng s e t l i s t e n t r y f o r a pag e i n
s e t l i s t , a nd

p a g e f i l e q uo t a f o r a l l pag e s w i t h a pag e f i l e b a c k i ng
s to r e
a dd r e s s ,
i n c l ud i ng pag e s tha t h a v e no t ye t a l l o c a t e d a b l o c k
i n t h e pag e f i l e .

the

b a c k i ng
process

s to r e
wo r k i ng

P r i v a t e s e c t i o n pag e s th a t a r e d e l e t e d c a u s e the
r e f e r e n c e c o un t
the
proc ess
s e c t i o n t a b l e e n t r y ( F i g u r e 1 1 - 7 ) t o b e d e c r em e n t ed .
t h e r e f e r e n c e c o un t g o e s to z e r o , th e PSTE i t s e l f c a n b e r e l e a s ed .

in
If

I n a d d i t i o n , v a l i d o r m o d i f i ed pag e s
w i th a
s e c t i o n ba c k i ng
s to r e
add r e s s
( a s o ppo s e d
t o a pag e f i l e b a c k i ng s to r e add r e s s ) m u s t h a v e
t h e i r l a t e s t c o n t e n t s wr i t t e n b a c k t o the s e c t i o n f i l e .
( Th e c o n t e n t s
of
p a g e s wi th a pag e f i l e ba c k i ng s to r e a d d r e s s a r e un i mpo r t a n t a f te r
the v i r t ua l pag e i s d e l e t ed and d o n o t h a v e to
be
s a v ed
b e fo r e
the
phys i c a l pag e i s r e u s e d . )

Pag e De l e t i o n a nd Sc h ed u l i ng - Pag e s t h a t
have
I /O
in
13. 2. 2.2
p r og r e s s
c a nno t b e d e l e t ed u n t i l the I /0 c ompl e t e s .
Such processes
a r e p l a c ed i n to a pag e f a u l t wa i t s t a t e
( r e que s t i ng
th a t
a
s ys tem
event
be
r e po r ted
wh e n
I /0 c ompl e t e s ) un t i l t h e pag e r e a d o r wr i t e
c ompl e t e s .
Pag e s i n the wr i t e- i n - p r o g r e s s t r a ns i t i o n s t a t e wi l l c a u s e
the
s am e
e f fe c t .
Pag e s i n t h e r e a d - i n- p r og r e s s t r a n s i t i o n s t a t e a r e
f a u l t ed , wi th t h e i mmed i a t e r e s u l t t h a t t h e p r o c e s s i s p l a c ed i n t o the
c o l l i d ed
pag e wa i t s t a t e .
Sp e c i a l a c t i o n m u s t be t a k e n f o r g l o b a l
pag e s wi th I /0 i n p r og r e s s b e c a u s e the r e i s n o wa y to d e t e rm i n e i f the
p r o c e s s d e l e t i ng
the
pag e is a l s o r e s po n s i b l e f o r t h e I /0 .
In s uc h
c a s e s , th e p r o c e s s i s p l a c ed i n to a m i s c e l l a n e o u s wa i t s t a t e
( MWA I T )
( I f t h e p r o c e s s h a s no d i r e c t I /0 i n
un t i l
i t s d i r e c t I /0 c o mpl e t e s .
p r og r e s s , t h e p r o b l em d o e s no t
arise
in
the f i r s t
pl a c e a nd
the
d e l e t i o n is a l l o we d t o p r o c eed . )
On c e a l l r e a s o n s f o r k e e p i ng th e pag e a r o und have b e e n t a k e n c a r e o f ,
t h e pag e
is
d e l e t ed .
De l e t i o n o f
a phys i c a l pa g e m e a n s th a t the
c o n t e n t s o f t h e PFN PTE a r r ay a r e c l e a r e d , d e s t r o y i ng a l l t i e s b e twe e n
the
phys i c a l
pag e a nd a n y p r o c e s s v i r t ua l add r e s s .
I n ad d i t i o n , t h e
pag e i s p l a c ed a t t h e h e ad o f t h e f r e e pag e l i s t ,
c a us i ng
it
to
be
u s ed b e f o r e o th e r pag e s wh o s e c o n t e n t s a r e s t i l l u s e f u l .

13 . 2. 2. 3
Co n t r a c t Reg i o n Sys t em S e r v i c e - Th e Co n t r a c t Reg i o n s y s t em
se rv i c e
is
a spec i a l c a s e o f t h e De l e t e Vi r t ua l Ad d r e s s Spa c e s ys t em
s e rv i c e .
Th e r e q ue s t ed n um b e r o f pag e s i s s i mpl y c o nv e r t e d i n to a
PO
o r P l pag e r a ng e a nd c o n t r o l i s pa s s e d t o a pag e d e l e t i o n r o u t i n e th a t
i s c o mmon b e t we e n t h e two s e rv i c e s .

1 3-5

M EMORY MANAG EMENT SYSTEM S E RVI CES
13. 2. 3

C o n t r o l l ed A l l o c a t i o n of V i r tu a l Memo r y

Th e r e i s a s e c o nd l ev e l o f m em o r y m a n ag em e n t a v a i l a b l e t o
a process .
Th e
Ru n - T i m e
L i b r a r y p r o c ed u r e s L I B $G E T VM a nd L I B $ F R E E VM p r ov i d e a
m e c h a n i sm
f o r a l l o c a t i ng
sma l l
b l o c k s - o f v i r t ua l
memo r y
in
a
c o n t r o l l ed f a sh i o n .
A l l o c a t i o n f r om t h e f r ee memo r y po o l i s pe r fo r m e d
i n m uc h the s am e wa y a s po o l s pa c e i s a l l o c a t e d b y VMS
( Ch a pt e r 2 5 ) .
If
t h e r e i s n o t a b l o c k o f m emo r y i n t h e po o l l a rg e e n o ug h to s a t i s f y
t h e r eq ue s t , P O s pa c e i s e x p a nd ed ( by c a l l i ng $ E XPREG ) a nd t h e po o l i s
e x t e nd e d t o i nc l ud e t h e n e wl y c r e a t ed v i r t ua l a d d r e s s s p a c e .

13. 3

PRIVATE AND G L OBAL SECT I ONS

A s e c o n d m e thod o f c r e a t i ng a d d r e s s s pa c e i s
a v a i l ab l e .
Th e
Create
a nd Ma p S e c t i o n s ys t e m s e rv i c e a l l o ws a p r o c e s s to a s so c i a t e a po r t i o n
o f i t s a d d r e s s spac e w i t h a spe c i f i ed po r t i o n o f a f i l e .
Th e
sec t i on
m a y b e s p e c i f i c to a p r o c e s s ( p r i v a t e s e c t i o n ) o r s h a r e d amo ng s e v e r a l
processes ( g l obal s ec t i o n )
Th e M a p G l o b a l
Sec t i on
s ys t em s e r v i c e
a l l o ws
a
p r o c e s s t o m a p a po r t i o n o f i t s v i r tua l a d d r e ss s pa c e t o a n
a l r e a d y e x i s t i ng g l o b a l s e c t i o n .
Th e s e t wo s e r v i c e s a r e used b y t h e
i m ag e a c t i v a to r ( Ch a p t e r 1 8 ) to m a p po r t i o n s o f p r o c e s s a d d r e s s s pa c e
t o e i th e r t h e i mag e f i l e o r p r ev i o u s l y i n s ta l l ed g l o b a l s e c t i o n s .
•

Th e C r e a t e a nd Ma p S e c t i o n sys tem se r v i c e a l so
p r o v i d e s t wo
spe c i a l
opt i ons .
Ra the r t h a n m a pp i ng a po r t i o n o f p r o c e s s a d d r e s s s pa c e t o a
file, a
s u i tab l y p r i v i l eg ed
process
( wi th
PFNMAP p r i v i l eg e )
can
a ssoc i a te
( ma p )
v i r t ua l
add r es s e s
to
s pe c i f i c ph ys i c a l ad d r e s s e s .
G l o b a l s e c t i o n s c a n b e c r e a t e d and m a ppe d i n sha r ed m em o r y a s we l l
as
i n l o c a l memo r y .

13. 3.1

C r e a te a nd M a p S ec t i o n Sys t em S e r v i c e

Th e C r e a t e a nd Ma p S e c t i o n s ys t em se r v i c e i s t h e sys t e m se r v i c e
th a t
( I n a s e n s e , t h e Ma p G l o b a l S e c t i o n
pe r fo rm s a l l o f t h e s e o pe r a t i o n s .
s ys tem s e rv i c e i s a spec i a l c a s e o f $ C RMP S C wh e r e t h e s e c t i o n d o e s no t
have
t o b e c r e a t ed . )
Th e p a r t i c ul a r p a th th a t i s t a k e n th r o ug h t h e
s e r v i c e i s d e t e r m i n ed b y t h e c o n t e n t s o f t h e f l ag s a rg um e n t p a s s e d
to
the s e r v i c e .
( Th e
VAX/VM S
Sys tem S e r v i c e s Re f e r e n c e Ma n ua l l i s t s
tho se
f l ag s
tha t
can be
used
tog e th e r
a nd
tho s e
tha t
a re
i nc ompa t i b l e . )
O n e wa y o f l o o k i ng a t t h e a c t i o n o f th i s s e r v i c e i s t o
e x am i n e t h e d a ta s t r uc t u r e s t h a t a r e c r e a t e d a s a r e s u l t o f e x e r c i s i ng
o n e o f t h e seve r a l o p t i o n s a v a i l a b l e to i t .

13. 3.1. 1
P r i v a t e S e c t i o n C r e a t i o n - Wh e n a p r o c e s s p r i va t e s e c t i o n i s
c r e a t ed , a p r o c e s s s e c t i o n t a b l e e n t r y ( F i g u r e 1 1 - 7 ) i s a l l o c a t e d f r om
t h e a r e a o f the p r o c e s s h e a d e r se t a s i d e f o r PSTEs .
Th e
i n fo rm a t i o n
tha t
a s so c i a t e s
t h e v i r t ua l a d d r e s s r a ng e w i t h v i r t ua l b l o c k s i n t h e
f i l e i s l o ad ed i n to the P S T E .
( Wh e n
the
pr ivate sec t i on
is
b e i ng
c r e a t ed
a s a pa r t o f i m a g e a c t i v a t i o n a s d e sc r i b ed i n C h a pt e r 1 8 , t h e
o r i g i n a l s o u r c e fo r m u c h o f t h e d a ta s to r ed i n t h e P S T E
is
an
imag e
s e c t i o n d e sc r i p to r
c o n ta i n e d
i n t h e i m ag e f i l e . ) I n a d d i t i o n , e a c h
p r o c e s s pag e t a b l e e n t r y i n t h e d e s i g n a t e d
add r e ss
r a ng e
is
l o ad ed
wi th
i d en t i c a l
c o n tents ,
n am e l y a
p r o c ess sec t i o n tab l e
i nd ex
( Figure 1 1-3 ) .

1 3-6

MEMORY MANAGEMENT SYS TEM S ERVI C E S
Bec ause
of
t h e wa y s pa c e
is
a l l o c a t ed
i n the
process
h e ad e r
( Append i x E ) ,
it
is
po s s i b l e th a t the s pa c e t o ho l d a s e c t i o n t ab l e
e n t r y m a y e x t end i n to th e wo r k i ng s e t l i s t .
Wh en t h i s o c c u r s ,
the
ent i re
p rocess
sec t ion
tabl e
c an
s l i d e d o wn i n t o o n e o f t h e empty
p ag e s set a s i d e in t h e p r o c e s s h e ad e r fo r e x a c t l y th i s p u r po s e .
Al l
r e f e r e nc e s to p r o c e s s s e c t i o n t a b l e e n t r i e s a r e r e l a t i v e to th e b o t to m
( h i g h ad d r e s s e nd )
of
the
t ab l e
that
is
loca ted
th r o ug h o f f s e t
PHD $ L PS TBAS O F F .
Th a t
is ,
the
ent i re
s t r uc t u r e
is
po s i t i o n
i nd e pend e n t .
H e a d e r e x p a n s i o n i nvo l v e s m a pp i ng the f i r s t empty p ag e ,
m o v i ng
the
ent i r e
s t r uc t u r e
d o wn
one
pag e ,
and
c h a ng i ng
P H D $ L P S TBAS OFF to l o c a t e t h e n e w b o t tom o f t h e ta b l e .

1 3 . 3 . 1 . 2 G l o b a l S e c t i o n C r e a t i o n - Th e c r e a t i o n o f a g l o b a l
sect i on
( l o c a t ed
i n l oc a l
memo r y )
i s s i m i l a r to t h e c r e a t i o n o f a p r i v a t e
s e c t i o n e x c e p t th a t t h e d a t a s t r uc t u r e s a r e
located
in
the
s ys t em
h e ad e r ( F i g u r e s 1 1 - 1 5 a n d 1 1 - 1 8 ) i n s t e ad o f t h e p r o c e s s h e a d e r .
1.

A g l o b a l s e c t i o n d e sc r i p to r ( F i g u r e 1 1 - 1 4 ) i s a l l o c a t e d
f r om
pag ed
d yn am i c memo r y a nd
l o a d ed w i th
i n fo rma t i o n
th a t
d e s c r i b e s t h e n am e a nd p r o t e c t i o n a t t r i b u t e s o f t h e
s ec t i o n .
Th i s
d a t a s t r uc t u r e i s u s ed by s ub s e qu e n t Ma p G l o b a l S e c t i o n
s ys t em s e r v i c e c a l l s t o d e t e rm i n e wh e th e r th e
n am ed
sec t i on
ex i s ts
and
to
l o c a t e t h e G l o b a l Se c t i o n T a b l e En t r y i n t h e
s y s t em h e a d e r t h a t m o r e f u l l y d e sc r i b e s the se c t i o n .

A g l obal s e c t i o n tab l e e n t r y
( Figure 1 1-1 6 )
in
the
header
( Fi g u r e 1 1 -1 5 )
is
the
a n a l og o u s
s t r uc t u r e
process sec t i on tab l e entr y .

A s e r i e s o f g l o ba l
pa g e
tab l e
entr i e s a re
c r e a ted
in
a
v i r t ua l e x t e n s i o n to t h e s ys t em h e ad e r ( F i g u r e 1 1 - 1 7 ) .
Th e s e
pag e tab l e e n t r i e s co n t a i n
i n fo rm a t i o n
th a t d e s c r i b e s
the
c u r r en t s t a t e
o f e a c h g l ob a l pag e i n the s e c t i o n .
Th e y a r e
no t a v a i l a b l e t o th e m emo r y m a n ag em e n t h a r d wa r e b u t a r e
u s ed
by
t h e pag e f a u l t h a nd l e r wh e n a p r o c e s s i n c u r s a pag e f a u l t
f o r a g l o ba l pag e .

A g l o b a l s e c t i o n c a n b e c r e a ted and m a pped b y a s i ng l e s ys t em
s e rv i c e c a l l .
Al te r n a t i v e l y , t h e s e c t i o n c a n b e c r e a t e d i n
o n e s t e p a n d ma pped l a t e r o n b y e i th e r the c r e a t i ng
process
or
by a n y o th e r p r o c e s s a l l o we d t o m a p t h e s e c t i o n .
In any
c a s e , m a pp i ng t o a g l o b a l s e c t i o n r e s u l ts i n n o
c h a ng e s
to
the g l oba l
d a ta b a se .
Ra th e r , t h e p r o c e s s pa g e t a b l e h a s a
s e r i e s o f p a g e t a b l e e n t r i e s o f t h e fo rm g l o b a l
pag e
tab l e
i nd e x ( Fi g u r e 1 1 - 1 9 ) a d d ed t o d e s c r i b e the d e s i g na t e d a d d r e s s
r a ng e .
Th e p r o c e s s pa g e t a b l e e n t r i e s fo r g l o b a l
pag e s c a n
be
i n one o f
two
states ,
e i th e r va l i d o r c o n ta i n i ng t h e
a pp r o p r i a t e g l o b a l pag e t a b l e i nd e x .

s ys t em
to t h e

1 3 . 3 . 1 . 3 G l o b a l S e c t i o n s i n S h a r e d Memo r y - G l o b a l s e c t i o n s t h a t a r e
l oca ted
i n s h a r ed m em o r y a r e t r e a t e d i n a s l i g h t l y d i f f e r e n t f a s h i o n
f r om l o c a l memo r y g l ob a l s e c t i o n s .
Th e s e c t i o ns a r e
c r e a t ed
by the
I N S TA L L u t i l i ty a f te r
s h a r ed
m em o r y h a s b e en
i n i t i a l i zed .
( See
Ch a p t e r 1 1 f o r a d e s c r i p t i o n o f
the d a ta
s t r uc t ur e s t h a t d e s c r i b e
g l o b a l s e c t i o n s i n s h a r e d mem o r y . )

1 3-7

MEMORY MANAG EMENT SYSTEM SERV I C E S
1.

A s pe c i a l g l o b a l s e c t i o n d e s c r i pt o r ( F i g u r e 1 1 - 2 7 ) i s c r e a t e d
th a t c o n t a i n s ,
a m o n g o th e r
th i ng s , a l i s t o f t h e ph ys i c a l
p a g e s i n s h a r e d memo r y t h a t w i l l c o n t a i n
the
sec t i on .
Th e
s e c t i o n i s t empo r a r i l y m a pped by I N STALL a n d e a c h pag e o f t h e
s e c t i o n i s l o a d e d f r om t h e i m ag e f i l e .

A g l o b a l s e c t i o n t a b l e e n t r y i s c r e a t e d o n l y o n the CPU th a t
o r ig i na l l y c r e a t e s the s ec t i o n .
Th i s G S T E a l l ows t h e i n i t i a l
r e ad t o b e pe r fo r m e d a n d a l l o ws
s ub s e q u e n t
sec t i o n
upd a te s
( w i th S YS $ U PD S E C )
fo r
wr i t ab l e
sec t i o ns .
Pag e s a r e a l s o
wr i t t e n b a c k to t h e i m a g e f i l e o n the c r e a t i ng C P U wh e n t h e
s e c t i on is d e l e ted .

No g l o b a l pag e t a b l e e n t r i e s a r e n e ed ed fo r g l o b a l
sec ti ons
i n sh a r e d memo r y b e c a u s e t h e s ta t e o f e a c h pa g e i s k n o wn t o
be val id .
Th e PFN i n fo rm a t i o n n e c e s s a r y to
a l low processes
to map
i n to
th i s s e c t i o n i s c o n t a i ned i n t h e sh a r ed memo r y
GSD.

Wh e n a p r o c e s s m a ps t o t h e s h a r ed memo r y g l o b a l s e c t i o n ,
the
p r o c e s s pa g e
table
entr i es a r e
set
to
val id
wi th
the
a pp r o p r i a t e p a g e f r am e n um b e r s l o ad ed i n to the
PTEs .
Th e s e
p a g es a r e n o t c o un ted ag a i n s t t h e p r o c e s s wo r k i ng s e t .

1 3 . 3 . 1 . 4 Map by PFN
Th e
C r e a t e a nd
Ma p Sec t i o n
s ys t e m s e r v i c e
a l l o ws
a
p r i v i l eg e d
process
( o n e wi th
PFNMA P p r i v i l eg e ) t o m a p a
po r t i o n o f i t s v i r t ua l ad d r e s s s pa c e to s pe c i f i c
ph ys i c a l
add r ess es .
Al t h o ug h
the
pr ima ry
i n te n t i o n o f th i s s e r v i c e i s to a l l o w p r o c e s s
a d d r e s s s pa c e to b e m a pped to I /0 a d d r e s s e s , i t c a n a l s o b e
used to
m a p s pe c i f i c ph ys i c a l memo r y p ag e s .
-

Wh e n a p r i v a t e PFN-m a pped s e c t i o n i s c r e a t ed , t h e o n l y e f f e c t
is
to
add
a s e r i e s of v a l i d PTEs to t h e p r o c e s s pag e t a b l e .
Th e PFN f i e l d s
i n t h e s e PTEs c o n t a i n
the
r e que s t e d
ph ys i c a l
pa g e n um b e r s .
Th e
PTE $V W I NDOW b i t
in
the
PTE
( Fi g u r e 1 1 - 3 )
is
s e t i n e a c h PTE t o
i nd i c a t e tha t e a c h o f th e s e v i r t ua l pag e s i s P F N m a pped .
Th e s e
pag e s
a r e n o t c o unted
ag a i ns t
the
p r o c e s s wo r k i ng s e t .
In add i t i on , no
r e c o rd i s m a i n t a i n ed i n t h e PFN d a t a b a s e
tha t s uc h pag e s a r e
PFN
m a pped .
Wh e n a g l o b a l PFN m a p ped s e c t i o n i s c r e a ted , t h e o n l y d a t a
s t r uc t u r e
c r e a ted t o d e sc r i b e s uc h a m a ppi ng r e que s t i s a spec i a l fo rm o f g l oba l
s e c t i o n d e sc r i pto r ( F i g u r e 1 1 - 1 4 ) .
Th e r e a r e no
g lobal
pag e
tab l e
entr ies
no r
is
the r e
a g l o b a l s e c t i o n t a b l e en t r y .
Wh e n a p r o c e s s
m a ps t o s uc h a s e c t i o n , i t s p r o c e s s pag e
table entr i es a r e
set
to
val id ,
m a pped
by PFN
( P F N $ V W I NDOW i s s e t ) , a nd th e PFN f i e l d s a r e
f i l l ed
i n a c c o r d i ng
to
t h e- c o n t e n t s
of
the
ex t e n d ed
GSD
( Fi g u r e 1 1 -1 4 ) .

13. 3.2

M a p G l o b a l S e c t i o n Sys t em S e r v i c e

Th e Ma p G l o b a l S e c t i o n s y s t em s e r v i c e c a n b e c o n s i d e r e d a s p e c i a l c a s e
of
t h e C r e a t e a nd
Ma p
( G l oba l )
S e c t i o n s ys tem s e r v i c e , wh e r e the
g l ob a l s e c t i o n a l ready ex i sts .
Th i s s e r v i c e us u a l l y has no e f f e c t o n
t h e g l oba l
d a ta
b a se
( o th e r
t h a n t o i n c l ud e t h e l a t e s t m a pp i ng i n
v a r i o u s r e f e r e n c e c o un t s ) .
Ra th e r , t h i s s e r v i c e a l l o ws a
r a ng e o f
p r o c e s s a d d r e s s e s t o b e c o m e m a pped t o the n amed g l o b a l se c t i o n .
1 3-8

M EMORY MANAG EMENT SYS TEM S E RVI C E S
Th e a c t ua l e f f e c t o f th i s s e r v i c e i s t o l o ad e a c h
of
t h e d e s i g na t ed
process
PTEs
w i th
a
g l ob a l
page
tab l e
i nd ex
( Fi g ur e 1 1 - 3 ,
Figure 1 1-1 9 ) .
Th e s e g l ob a l
pag e
t ab l e
i nd i c e s a r e e f f e c t i v e l y
po i n t e r s
t o g l o b a l pag e t ab l e e n t r i e s i n the s ys t em h e ad e r , wh e r e th e
c u r r e n t s t a t e o f e a c h g l ob a l pag e i s a c t ua l l y r e c o r d ed .
Wh e n a p r o c e s s m a p s to a g l o b a l s e c t i o n
i n sha r e d m em o r y o r
to
a
section
th a t i s PFN-m a ppe d , t h e r e a r e no g l o b a l pag e t a b l e e n t r i e s to
be po i n t e d t o .
I n s t e ad , e a c h p r o c e s s pag e t a b l e e n t r y i s s e t to va l i d
w i th
t h e PFN f i e l d c o n t a i n i ng a ph ys i c a l pag e n um b e r e i th e r i n s h a r ed
m emo r y ( f o r sha r ed m emo r y g l o b a l s e c t i o n s )
o r a n ywh e r e
i n ph y s i c a l
a d d r e s s s pa c e ( a s i nd i c a t ed b y t h e e x t e n d e d G S D f o r PFN-mapped g l o b a l
sections )
•

De l e t e G l o b a l S e c t i o n Sys t em S e r v i c e

13. 3.3

L i k e t h e De l e t e V i r t ua l
Ad d r e s s
Spa c e
s ys t em s e r v i c e ,
t h e De l e t e
G l obal
S e c t i o n s y s tem s e rv i c e i s m o r e c ompl i c a t e d than g l o b a l s e c t i o n
c r e a t i o n b e c a u s e t h e s e c t i o n m u s t b e r e d uc ed f r om o n e o f m a n y s t a t e s
In
ad d i t i o n ,
g l o b a l wr i t ab l e pag e s m u s t b e wr i t t e n to
t o n o th i ng .
t h e i r ba c k i ng s to r e ad d r e s s e s b e fo r e a g l o b a l
s e c t i o n c an
be
ful ly
d e l e ted .
Fo r
these
r e a so n s ,
t h e g l obal sec t i on d e l e t i on i s o f ten
s e pa r a t ed i n t i m e f r om t h e s ys t em s e r v i c e c a l l .
Wh e n t h e De l e t e G l o b a l S e c t i o n s ys tem s e r v i c e
i s c a l l ed ,
t h e named
section
i s ma r k ed fo r d e l e te .
Th i s m e a n s tha t t h e G S D i s moved f r om
th e n o rm a l d o ub l y l i nk e d G S D l i s t to t h e d e l e t e
pend i ng
l i st .
Th e
d e l ete
pend i ng
bit
in
the GSD i s set .
I n a d d i t i o n , t h e pe rm a n e n t
i nd i c a to r i n t h e G S D i s
t u r ned
off .
Howe v e r ,
the
ac tual
sect ion
d e l e t i o n c a nno t o c c u r u n t i l t h e r e f e r e nc e i n t h e g l o b a l s e c t i o n t a b l e
e n t r y , t h e c o un t o f p r o c e s s pa g e t a b l e e n t r i e s m a pped t o the
sec t i on ,
g o es
to
zero .
Al t h o ug h i t i s po s s i b l e fo r th e r e f e r e n c e c o unt to b e
z e r o wh e n t h e s e c t i o n i s m a r ked f o r d e l e t e , t h e m o r e
t yp i c a l g l o b a l
sect i on d e l e t i o n o cc u r s a s a s i d e e f fec t o f v i r tua l add r e s s d e l e t ion
( wh i c h i t s e l f m i g h t o c c u r
as
a
resul t of
imag e ex i t
or
proc ess
deletion)
•

Wh e n t h e r e f e r e n c e c o un t g o e s to z e r o , th i s
i nd i c a t e s
th a t
no
more
p r o c e s s pag e
t a b l e e n t r i e s a r e m a pped t o t h e s e c t i o n .
A t th a t t i m e ,
t h e d a t a s t r uc t u r e s tha t d e sc r i b e the s ys tem c a n b e d e a l l o c a t ed .
•

Th e g l o b a l pag e t a b l e e n t r i e s i n the s ys t em h e ad e r a r e
f r e ed
fo r
f u r th e r
use .
If
an
e n t i r e pag e of g l o b a l p a g e t a b l e
e n t r i e s i s f r e ed , t h a t p a g e c a n b e un l o c k e d f r om
th e
s ys tem
wo r k i ng s e t .

•

Th e g l o b a l s e c t i o n
tab l e
entry in
the
sys tem h e ad e r
is
r emoved
f r om
th e a c t i v e l i s t a nd p l a c ed o n t h e f r e e l i s t o f
s y s t em s e c t i o n t a b l e en t r i e s f o r po s s i b l e l a t e r u s e .

•

Th e g l o b a l s e c t i on d e sc r i pt o r i s pl a c ed o n the f r e e
l i st o f
G S Ds .
Wh e n a g l o b a l s e c t i o n i s l a t e r c r e a t e d , th i s l i s t i s
c h e c k e d f o r a G S D b e fo r e a n ew s t r uc t u r e
is
a l l o c a t ed
f r om
p a g e d d yn am i c memo r y .

1 3-9

MEMORY MANAGEMENT SYSTEM S E RVI CES
G l o b a l s e c t i o n s in
sh a r ed m emo r y a nd
PFN m a pped g l o b a l
sect i ons
e x e r c i s e s o m e o f t h e s a m e l og i c wh en t h e s e c t i o n s a r e d e l e te d b u t t h e
e f fe c t s a r e d i f f e r e n t b e c a u s e n o t a l l o f t h e g l o b a l d a t a
s t r uc t u r e s
ex i st
fo r
thes e
spec i a l
g loba l
sections .
A PFN m a pped s e c t i o n i s
d e sc r i b ed
ent i r ely b y a n
e x t end e d
g lobal
sec t i o n
d e sc r i pt o r
( Fi g u r e 1 1 - 1 4 ) .
In
add i t io n ,
n o r e f e r e n c e c o un ts a r e k e p t f o r s u c h
s e c t i o ns
so
t h e G S D c a n b e p l ac e d
on the
f r ee
l ist
o f G S Ds
i mmed i a t e l y .
Wh e n a s h a r ed memo r y g l ob a l s e c t i o n i s d e l e t e d , t h e r e a r e
no
global
pag e
table
entr ies
to d e l ete .
I n ad d i t i o n , a g l ob a l s e c t i o n t a b l e
e n t r y o n l y e x i s t s o n t h e po r t f r om wh i ch t h e s e c t i o n wa s c r ea t e d
( to
a l lo w the
s ec t i o n t o b e l o ad ed wh e n i t wa s i n i t i a l l y c r ea t ed and to
a l l o w the Upd a t e S e c t i o n s ys t em
s e rv i c e o r
De l e t e G l o b a l
Sect i on
s ys tem s e rv i c e t o p r e se r v e i t s c o n t e n ts ) .

13. 3.4

Upd a te S ec t i on S y s t em S e r v i c e

Th e Upd a t e S e c t i o n s ys tem s e rv i c e r e que s t s th a t a spec i f i e d
r a ng e
of
p r oc e s s p r i v a t e o r g l o b a l
pag e s b e wr i t t e n t o the i r b ac k i ng s to r e
a d d r e s se s .
Wh e n a p r i v a t e s ec t i o n i s b e i ng upd a t ed , o n l y t h o s e p a g e s
t h a t h a v e b e e n mod i f i ed ( a s i nd i c a t ed e i th e r by t h e PTE $V MOD I FY b i t
i n t h e PT E o r b y t h e PFN$V MOD I FY b i t i n t h e
PFN S TATE a r r a y )
are
wr i tten .
W i th g l o b a l
pag e s , t h e m o d i f y s t a t e o f a phys i c a l pag e i s
t h e l og i c a l OR o f th e PFN S TATE a r r ay m o d i fy b i t a nd th e m o d i f y b i t s
in all of
t h e p r oc e s s pag e
t ab l e e n t r i e s m a pped to t h e s e c t i o n .
Bec au s e the r e a r e
no
b a c k po i n t e r s
to a l l
of
these
PTEs ,
th i s
i n fo r ma t i o n
i s not ava i l ab l e .
I n s t e ad ,
wh en a g l ob a l s e c t i o n i s
u pd a ted , a l l pag e s i n the d e s i g n a t e d a d d r e s s r a ng e a r e wr i t t e n b a c k t o
( Wh e n t h e " e x c l u s i v e wr i t e r " f l ag i s pa s s e d to
the g l obal imag e f i l e .
t h e Upd a t e S e c t i o n s ys tem s e rv i c e , o n l y tho s e pag e s m o d i f i ed
by t h e
c a l l e r a r e w r i t t e n . ) Th e i n te r a c t i o n b e twe e n t h e Upd a t e S e c t i o n s ys t em
s e rv i c e a nd t h e I /0 s ub s ys t em i s d e sc r i b ed i n Ch a p t e r 1 2 .

13. 4

R E LATED S YSTEM S ERVI C E S

O th e r m em o r y m a n ag em e n t s ys tem s e rv i c e s a l l o w a p r o c e s s to c o n t r o l i t s
wo r k i ng
se t ,
a l ter
pag e p r o t ec t i o n , a nd l o c k pag e s i n to the wo r k i ng
s e t o r i n to ph y s i c a l memo r y .

13. 4 . 1

Wo r k i ng S e t S i z e Ad j u s tme n t

I t i s po s s i b l e t o m a k e
t h e p r o c e s s wo r k i ng
s e t e i th e r
l a rg e r
or
sma l l e r ,
e i th e r m a n ua l l y w i th
t h e Ad j us t Wo r k i ng S e t L i m i t s ys t em
s e rv i c e o r a u toma t i c a l l y a s a pa r t o f t h e q ua n t um end
rout i ne .
Wh e n
t h e wo r k i ng s e t i s e x pa nd ed , n e w pag e s c an b e a d d e d t o the wo r k i ng s e t
w i tho u t
r em ov i ng
a l r e ad y v a l i d
entr ies .
Th i s
decreases
the
p r o b a b i l i ty o f a p r o c e s s i n c u r r i ng a pag e f a u l t .
I t i s un l i k e l y t h a t a p r o g r am w i l l v o l un t a r i l y r ed uc e i t s wo r k i ng
set
l i m i t , u n l e s s i t h a s a g o od und e r s t a nd i ng o f i t s pag i ng b e h a v i o r .
Th e
s ys t em r ed uc e s a p r o c e s s wo r k i ng
set as a
pa r t o f
the
a u tom a t i c
wo r k i ng
s e t a d j u s tme n t .
I n a d d i t i o n , a p r o c e s s wo r k i ng s e t l i m i t i s
r e s e t t o i t s d e f a u l t v a l ue a s a pa r t o f t h e
i m ag e
r un d o wn
p r o c ed u r e
( Ch a p t e r 1 8 )
th a t
is
i nvo k e d wh e n a n i m a g e e x i t s .
Ta b l e 1 3 - l l i s t s
t h e p r o c e s s - s p e c i f i c a n d s ys tem-w i d e wo r k i ng s e t l i s t pa r am e t e r s .
1 3-1 0

MEMORY MANAG EMENT SYSTEM S ERVI CES
Tab l e 1 3 - 1
Working Set L i s t s Lim i t s and Quotas

De sc r i pt i o n

Loc a t i o n or Name

Comments

Beg i nn i ng o f Wo r k i ng Se t Li st

PHD$W_WS L I S T

Alwa ys h a s t h e val ue 6 0 ( he x )
( Th i s i s < PHD$K_LENGTH I 4 > )

Beg i n n i ng of l i st o f
pe rman e n t l y l oc k ed entr i e s

PHD$W_WS LOCK

The same fo r a l l pro c es s e s
i n a g i ven sys tem

Beg i nn i ng o f d ynam i c po r t i o n
o f wo r k i ng set l i st

PHD$W WSDYN

Iden t i c a l to WS LOC K u n l ess t h i s
process h a s c a l l ed SYS $LKWSET
or SYS $LC KPAG

I nd ex o f m o s t r ec en t l y i nser ted
wo r k i ng s e t l i s t e n t r y

PHD$W_WSNEXT

Upd a ted each t ime an e n t r y
i s add ed t o the wo r k i ng s e t

E n d o f wo r k i ng se t l i st

PHD$W_WSLAST

Upd a ted by c a l l ing SYS $ADJWSL a nd
at imag e ex i t

De f a ul t wo r k i ng set s i ze

PHD$W_DFWSCNT

S e t by LOG INOUT , a l te r ed
by SET WORKI NG_S ET/L IM IT = command

Upper l im i t to wo r k i ng set s i ze

PHD$W_WSQUOTA

Set by LOG INOUT , a l te r ed
by SET WOR K ING_S ET/QUOTA= c ommand

Upper l im i t to wo r k i ng se t quo ta

PHD$W_WSAUTH

S e t by LOG INOUT , c anno t be a l t e r ed

Lowe r l im i t to s i ze o f d yn am i c
wo r k i ng s e t s i ze

PHD$W_WSFLUI D

Set up by S HE L L , equal to the v a l ue
of M I NWSCNT SYSBOOT pa r am e t e r

S i ze o f d yn a m i c wo r k i ng s e t a ft e r
a l l ow i ng r o o m fo r PHD$W WSFLU I D
pr o c e s s pag e entr i e s a nd a
r e a so nab l e n umber pag e tab l e pag es

PHD$W_ E XT DYNWS

Upd a ted each t i me s i ze o f d yn am i c
wo r k i ng s e t i s c hang ed

Autho r i zed d e fa u l t wo r k i ng s e t s i ze

UAF $W_DFWSCNT

Lo ad ed i n to PHD$W_DFWSCNT

Autho r i zed d e fa ul t wo r k i ng s e t l im i t

UAF $W_WSQUOTA

Load ed in to bo th PHD$W_QUOTA
and PHD$W_WSAUTH

System w i d e m i n imum wo r k i ng se t s i ze

M INWSCNT

SYSBOOT pa rameter

Sys tem w i d e max im um wo r k i ng se t s i ze

WSMAX

S YS B OOT pa rameter

Wo r k i ng set s i ze fo r s ys t em pag i ng

SYSMWCNT

S YS B OOT pa rameter

De f a ul t val ue fo r wo rki ng s e t s i ze
d e fa ul t ( us e d by SYS $CREPRC )

PQL_DWSDEFAULT

SYSBOOT pa r ame t e r

M i n imum val ue fo r wo r k i ng s e t s i ze
d e fa ul t ( us e d by SYS $C REPRC )

PQL_MWSDEFAULT

SYSBOOT pa ram e t e r

D e faul t va l ue fo r wo rki ng s e t quo ta
( us ed by SYS $CREPRC )

PQL_DWS QUOTA

SYS B OOT pa r ame t e r

M i n imum va l ue fo r wo r k i ng s e t quo ta
( us ed by SYS $C R E PRC)

PQL_MWSQUOTA

SYSBOOT pa rameter

1 3 . 4 . 1 . 1 Ad j us t Wo r k i ng S e t S i z e Sys t e m S e r v i c e - Th e
e f fe c t i ve
r e s u l t o f a l t e r i ng the p r o c e s s wo r k i ng s e t s i z e i s to c h ang e t h e v a l ue
o f the WS LA S T wo r k i ng s e t l i s t po i n te r ( F i g u r e 1 1 - 4 ) .
I n th e c a s e o f wo r k i ng s e t l i s t e x p a n s i o n , t h e wo r k i ng
set
s i ze
is
l i m i t ed b y t h e wo r k i ng
s e t quo t a ( P HD$W WSQUOTA ) .
I f the e x pa nd ed
wo r k i ng s e t e x t e nd s i n to the p r o c e s s s e c t i on t a b l e ( F i g u r e 1 1 - 1 ) ,
the
1 3-11

MEMORY MANAG EMENT SYS TEM SERV I C ES
p r oc ess
sect ion
t a b l e i s m o v ed d o wn i n e x a c t l y t h e s am e m a n n e r a s i s
d o ne to a c c ommod a t e p r o c e s s s e c t i o n t a b l e e x pa n s i o n .
Th e r e i s
a l wa ys
e n o ug h
r o om i n t h e p r o c e s s h e ad e r to a c c ommod a t e t h e e x pand e d wo r k i ng
s e t l i s t b e c a u s e t h e p r o c e s s h e a d e r s i z e i s d e te rm i n ed by WSMAX
( a nd
PROC S E C TCNT )
a nd
the
wo r k i ng
s e t pa r am e t e r s
( PHD$W WS Q UOTA a nd
PHD$W WSAUTH ) a r e m i n im i z e d w i th WSMAX .
( Th e c a l c u l a t i o n-o f the s i z e s
o f e ach p i e c e o f t h e p r o c e s s h e a d e r a r e d e sc r i b e d i n Append i x E . )
I n t h e c a s e o f wo r k i ng s e t l i s t c o n t r a c t i o n , t h e wo r k i ng se t c a nno t b e
contrac ted
b e l o w M I NWSCNT
(a
S Y S B OOT p a r am e t e r ) .
I n a d d i t i o n , the
e x t r a d yn am i c wo r k i ng set
s i ze
( P HD$W E XT DYNWS )
c a nno t b e
r ed uc ed
below z e ro .
I f t h e PHD$W WS N EXT po i nte r l o c a t e s a n e n t r y b e yo nd the
n ew e nd of t h e l i s t , i t i s re s e t to po i n t to the new end .
If
the r e
are
any val id
entr ies
i n t h e po r t i o n o f t h e l i s t th a t i s n o l o ng e r
b e i ng u s ed ( b e twe e n t h e o l d a n d t h e n ew PHD$W WS LAST po i n t e r s ) ,
they
a r e moved
i n to the d yn am i c po r t i o n o f the l Ts t i n t o the a r e a l o c a t ed
b y the PHD$W WSN E XT po i n t e r .
( Th e a t t empt to
l oc a t e
f r ee
slots
in
wh i c h
t o move a n y a c t i v e e n t r i e s c a n c a u s e t h e p r o c e s s t o b e pl a c ed
i n to a r e so u r c e wa i t s t a t e , wa i t i ng f o r s pa c e i n th e pag e f i l e . )

1 3 . 4 . 1 . 2 SET WORK I NG S E T Comm a nd - Th e S E T WORK I NG S E T c omm a n d a l l o ws
t h e d e f a u l t wo r k i ng se t s i z e ( P HD$W D FWSCNT ) o r the wo r k i ng s e t quo t a
( P HD$W WSQUOTA ) to b e a l t e r e d a t the-c ommand l ev e l .
Ne i th e r the q uo ta
no r
t he
l i m i t can b e s e t to a v a l ue l a rg e r th a n the a u tho r i z e d uppe r
l i m i t ( PHD$W_WSAUT H ) .
•
•

I f t h e q uo t a i s a l t e r ed ,
i t c h a ng e s
the
uppe r
l im i t
fo r
f u t u r e c a l l s to t h e Ad j u s t Wo r k i ng S e t L i m i t s ys tem s e r v i c e .
I f the l im i t
( d e f a ul t s i ze )
i s a l te r ed ,
i t a f fects
the
wo r k i ng
set
l i s t r e s e t o pe r a t i o n pe r f o rmed by the r o u t i n e
MMG $ I MG R E S E T i nv o k e d a s a r e s u l t o f i m a g e e x i t .
I f the l i m i t
i s s e t t o a v a l u e l a r g e r th a n the c u r r e n t quo t a , bo th the
q uo t a a nd t h e l i m i t a r e a l te r e d to the new v a l u e .
(Note that
a u toma t i c
wo r k i ng s e t ad j us tm e n t i s d i s a b l ed fo r a n y p r o c e s s
th a t h a s i t s q uo t a
a nd
d e fa u l t
( l im i t )
set
to
t h e s am e
va l ue . )

1 3 . 4 . 1 . 3 Automa t i c Wo r k i ng S e t S i z e Ad j u s tmen t - I n
add i t i o n
to
manual
wo r k i ng
s e t ad j u s tm e n t
as
a
resul t
of
e x p l i c i t c a l l s to
S YS $ ADJW S L or as a s i d e e f f e c t o f
i m ag e e x i t ,
VM S a l s o
p r ov i d e s
a u toma t i c wo r k i ng
s e t ad j u s tm e n t t o k e e p a p r o c e s s ' s pag e f a u l t r a t e
w i th i n l i m i t s s e t by o n e o f s e v e r a l SYS B OOT pa r am e t e r s
( Ta b l e 1 3 - 2 ) .
Al l o f t h e SYS B OOT p a r am e t e r s l i s t ed i n th i s t a b l e a r e d ynam i c a nd c an
b e a l t e r e d w i tho u t r e boo t i ng t h e s ys t em .

1 3-1 2

M EMORY MANAG EMENT SYSTEM S E RVI C E S
Tab l e l 3 - 2

P ro c e s s and S y s tem Paramet e r s U s ed b y Automatic Working S e t S i z e Adj u s tmen t s

De sc r i pt i o n

Lo c a t i o n o r Name

Comments

To tal amoun t of CPU t ime cha rged
to th i s proce ss

PHD$L_C PU T IM

Upd a ted by h a r d wa r e c l o c k
s e rv i c e r o u t i n e

Amoun t o f CPU t ime when l a st
ad j ustment took pl ace

PHD$L_T IMREF

Upd ated by quantum end ro ut i ne
when ad j ustment check is made

To tal number o f pag e faul ts
fo r thi s pro c ess

PHD$L_PAGEFLTS

Upd ated each t ime th i s
process i nc u r s a pag e faul t

Number o f pag e fa ul ts when l ast
ad j ustment took pl ace

PHD$L_PF LREF

Upd ated by quantum end r o ut i n e
when ad j ustment check is made

Mo st r ec ent pag e fau l t r ate
fo r thi s process

PHD$L_PFLTRATE

Recorded but not used each
t ime an ad j ustment chec k is mad e

Amoun t o f CPU t ime tha t process
mus t accumul a te b e fo re a pag e
faul t r a te chec k i s mad e

AWST IM E ( S )

Lowe r l im i t pag e faul t rate

PFRATL ( S )

Amoun t by wh ich to d ec rease
wo r k i ng se t s i ze

WSDEC ( S )

Lowe r bound fo r dec r eas i ng
wo r k i ng set s i ze

AWSM IN ( S )

Uppe r l im i t pag e fa ul t r ate

PFRATH ( S )

Amount by wh i ch to inc rease
wo r k i ng set s i ze

WS INC ( S )

D i sables a utomat i c adj ustment fo r
enti re system i f zero

Uppe r bound fo r d ec reas i ng
wo r k i ng set s i ze

AWSMAX ( S )

Do no t ad j ust i f PCB $W PPGCNT i s
g reater than o r equal -to th i s val ue

(S)

Do no t adj ust i f PCB $W PPGCNT i s
l ess than o r equal to-th i s val ue

These va l ue s a r e SYSBOOT pa rame te rs .

Th e a u toma t i c wo r k i ng s e t a d j u s tm e n t t a k e s p l a c e a s pa r t o f
the
q u a n t um
end
r o ut i n e
( Ch a p t e r 8 ) .
Th i s i s a r e f l e c t i o n o f t h e f a c t
th a t a p r o c e s s th a t c a nno t e x ec u t e f o r even a s i ng l e q u a n tum w i l l
no t
b e ne f i t
f r om an i nc r e a s e d wo r k i ng s e t s i z e .
( No t e th a t no ad j us tm e n t
t a ke s p l a c e f o r r e a l - t i m e p r o c e s s e s . ) Th e a d j us tm e n t t a k e s p l a c e
in
seve r a l steps .
1.

I f t h e WS I NC pa r am e t e r i s s e t
to
zero ,
the
ad j u s tm e n t
d i s a b l ed o n a s y s tem-w i d e b a s i s s o n o t h i ng i s d o n e .

I f t h e p r o c e s s d e f a ul t wo r k i ng s e t s i z e
( PH D $W D FWSCNT )
e qua l
to
i t s q uo t a
( PH D $W WSQUOTA ) ,
t h e n ad j us tm e n t
d i s a b l ed f o r th i s p r o c e s s so , -a g a i n , no th i ng i s d o n e .

is
is

I f t h e p r o c e s s h a s n o t b e en e x e c u t i ng l o ng e n o ug h s i nc e
the
l a s t a d j u s tm e n t
( d i f f e r e n c e b e twe en a c c um u l a t ed C PU t i m e ,
PHD$ L C PU T I M ,
and
t im e
of
l ast
a d j us tmen t
a t tempt ,
PHD$ L-T I M RE F , i s l e s s t h a n th e SYSB OOT pa r am e t e r AWS T IM E ) , no
a d j u stm e n t
i s d o ne a t th i s
t ime .
If
the
process has
a c c um u l a ted
e no ug h C PU
t i m e , t h e r e f e r e n c e t i m e i s upd a t ed
( P HD$ L C PUT IM i s
l o ad ed
i n to
PHD$ L_T I M REF )
and
the
r a te
c h e c k s- a r e m a d e .
1 3-1 3

MEMORY MANAGEMENT SYSTEM S E RVI C E S
4.

Th e c u r r e n t pa g e
f a ul t
r ate
i s c a l c ul a t e d .
Th e g u i d i ng
ph i l o s o ph y t o
t h e a u toma t i c wo r k i ng s e t ad j us tm e n t c o n s i s t s
o f two p i e c e s .
I f t h e pag e f a u l t r a t e i s to o l o w , t h e s ys tem
c an bene f i t
f r om
a
sm a l l e r wo r k i ng s e t s i z e ( b e c a u s e m o r e
phys i c a l pag e s b e c o m e a v a i l a b l e ) w i tho u t h a r m i ng t h e p r o c e s s
( by c a us i ng i t t o i n c u r m a n y pag e f a u l t s ) .
I f the pag e f a u l t
r a te i s too h igh , the
p r o c e s s c a n b e n e f i t f r om
a
l a rg e r
wo r k i ng
set
s i ze
( by i n c u r r i ng
f e we r
faul ts )
wi tho u t
d eg r ad i ng t h e s ys t e m .
•

•

I f t h e c u r r e n t pag e f a u l t r a t e i s t o o h i g h ( g r e a t e r
th a n
or
equa l
to
PFRATH ) ,
t h e wo r k i ng s e t i s i n c r e a s e d ( by
WS I NC ) .
Ho wev e r , i f t h e c o n t e n t s o f
PC B $W P PG C NT a r e
g reater
than o r
e q ua l
t o AWSMAX , n o ad j ustmen t t a k e s
pl a c e .
Th e
a s s um p t i o n b e i ng m a d e h e r e
is
th a t
the
p r o g r am
is
not
we l l b eh a v ed
(makes many nonloc a l i zed
ad d r e s s r e f e r e n c e s ) a nd w i l l p r o ba b l y n o t b e n e f i t
f r om
a n y mo r e wo r k i ng s e t .
Th e s ys t em w i l l c e r t a i n l y s u f f e r
by l o s i ng s t i l l m o r e phys i c a l m em o r y to th i s p r o c e s s .
I f t h e c u r r en t pag e f a u l t r a t e i s t o o l o w ( s t r i c t l y l e s s
than
PFRATL ) ,
t h e wo r k i ng s e t i s d ec r e a s ed ( by WSDEC ) .
Howe v e r , i f t h e c o n t e n t s o f PC B $W P PGCNT a r e l e s s t h a n o r
Th i s d e c i s i o n
equal
AWSM I N ,
n o a d j u s tm e n t t a kes p l a c e .
i s b a s e d o n t h e a s s umpt i o n th a t m a n y o f t h e pag e s i n
the
wo r k i ng
set
a r e g l obal
pag e s a n d th e sys tem w i l l no t
b e n e f i t ( a nd t h e p r o c e s s m a y s u f f e r ) i f the wo r k i ng
set
i s d ec r ea sed .

Th e a c t u a l
wo r k i ng
s e t a d j u s tm e n t
is
a c c ompl i s hed
by a
r eg u l a r k e r n e l AST t h a t e x e c u t e s a n Ad j u s t Wo r k i ng S e t s ys t em
s e rv i c e .
Th e AS T p a r am e t e r pa s s e d to t h i s AST i s t h e
a m o un t
o f p r e v i o us l y d e t e rm i n ed i n c r e a s e o r d e c r e a s e .
Th i s s t ep i s
r e q u i r ed b e c a u s e t h e
s ys t em
s e r v i c e m u s t b e c a l l ed
f r om
p rocess context
(at
I PL 0 )
and t h e qua n t um end r o u t i n e i s
e x e c u t i ng i n r e s po n s e t o the I P L 7 s o f twa r e t i m e r i n t e r r up t .

13.4. 1 . 4
Pu r g e Wo r k i ng S e t S y s t em S e r v i c e - Th e
Pu r g e Wo r k i ng
Set
s ys t e m s e rv i c e
r e q ue s t s
tha t
all
v i r t ua l
pag e s
i n t h e s p e c i f i ed
a d d r e s s r a ng e th a t h a ppen t o b e i n the wo r k i ng s e t b e r em o v e d f r om t h e
wo r k i ng s e t .
A p r og r am co u l d u s e t h i s s e r v i c e i f i t r e c og n i z ed t h a t a
c e r ta i n
set of
r o ut i n e s o r d a ta we r e
no
l o ng e r
r e q u i r ed .
By
v o l un t a r i l y r em ov i ng
entr i es
f r om
t h e wo r k i ng
set , a process can
e x e r c i s e a l i tt l e
control
ove r
t h e wo r k i ng
set l i st
r e p l a c em e n t
a l g o r i thm ,
i n c r e a s i ng t h e c h a n c e s fo r f r eq u e n t l y u s ed pag e s t o r em a i n
i n t h e wo r k i ng s e t .
VM S u s e s
th i s
s e r v i c e a s pa r t o f
the
i mag e
s t a r t u p s e quenc e
( Ch a pt e r 1 8 )
to
i nsure
t h a t a p r og r am s t a r t s i t s
e x e c u t i o n w i tho u t unn e c e s s a r y p a g e s s uc h a s C L I
c o mmand
p r o c e s s i ng
r o u t i n e s i n i t s wo r k i ng s e t .

13. 4. 2

Lo c k i ng a n d Un l o c k i ng P a g e s

Fo r t i me c r i t i c a l a pp l i c a t i o n s a nd o th e r s i t ua t i o n s wh e r e
a
p r og r am
wi s h e s
to
a c c e s s c o d e o r d a t a wi tho u t i n c u r r i ng a pag e f a u l t , s ys t em
s e rv i c e s a r e p r ov i d ed to l o c k pag e s i n to the p r o c e s s wo r k i ng
set o r
i n to m em o r y .

1 3-14

M EMORY MANAG EMENT SYS TEM SERVI C ES
13. 4.2. 1
Lo c k i ng Pag e s i n the Wo r k i ng Se t - A s e t o f v i r t ua l
pag e s
c a n b e l o c ked i n to t h e p r o c e s s wo r k i ng s e t t o p r e v e n t pa g e f a u l t s f r o m
o c c u r r i ng o n r e f e r e n c e s t o the s e pag e s .
Th i s g ua r an t e e s
th a t wh e n
th i s p r o c e s s
is
e x e c u t i ng ( i s t h e c u r r e n t p r o c e s s ) , t h e s e pag e s a r e
a l wa ys i n the p r o c e s s wo r k i ng s e t .
I n a d d i t i o n to the o bv i o u s b e n e f i t
of
th i s
serv i c e ,
i t c a n a l s o b e u s e d by r o u t i n e s th a t e x e c ute a t
e l ev a ted I PL ( a b o v e I PL 2 ) bec a u s e VM S d o e s n o t a l l o w pag e
f a ul ts
to
occu r
a bo v e
I PL 2.
Th e r e i s no i mp l i c a t i o n t h a t the s e pag e s r ema i n
r e s i d e n t wh en t h e p r o c e s s i s n o t c u r r e n t b e c a u s e
the
e n t i r e wo r k i ng
se t
c an
be
o u t s wa pped .
( Re s i d e n c y
i s gua r anteed
by e i th e r
a
c omb i n a t i o n o f th i s s ys t e m se r v i c e
a nd
the Set
Swa p Mo d e
s ys t e m
se r v i c e o r by u s i ng t h e Lo c k Pag e s i n Memo r y sys t em se rv i c e . )
Al l pag e s i n the s pe c i f i ed r ang e a r e f a u l ted i n t o t h e wo r k i ng
set
if
they a r e not a l ready val id .
Th e wo r k i ng s e t l i s t ( F i g u r e 1 1 - 4 ) mus t
be r eo r g a n i z e d s o th a t the l o c k e d pag e s a ppe a r i n t h e
l i st
f o l l o w i ng
Th i s
i s a c c ompl i shed by e x c h a ng i ng the l o c k e d
the WSLOC K po i n te r .
WS L E wi t h t h e e n t r y po i n t e d to by WSDYN , a nd then
i nc r emen t i ng WSDYN
t o po i n t t o the n e x t e l em e n t i n the l i s t .
Th e WS LX PFN a r r a y e l em e n t s
fo r t h e two v a l i d p ag e s m u s t a l s o b e e x c h a ng ed .
In
add i t i on ,
the
WS L $ V_WS LOCK b i t i s s e t i n t h e wo r k i ng s e t l i s t en t r y .
A c h e c k i s m a d e to i n s u r e tha t t h e p r o c e s s wi l l be
l e f t w i th e no ug h
d yn a m i c
wo r k i ng
s e t a f t e r the s p e c i f i ed numb e r o f pag e s a r e l o c k ed .
Eno ug h d yn am i c wo r k i ng s e t m e a n s t h a t t h e e x t r a d yn am i c wo r k i ng
set
s i ze ,
t h e s i ze
of
t h e d y n am i c wo r k i ng
s e t a f t e r s pa c e h a s b e e n
a l l o c a t ed fo r pag e t a b l e p ag e s a nd a m i n i m um wo r k i ng
set s i ze ,
is
g reater
than
zero .
( L i k e mo s t o f
the mem o r y manag em e n t s ys tem
s e rv i c e s , th i s s e r v i c e c a n
pa r t i a l l y s uc c e ed .
In
th i s
case ,
the
add r e s s
r ang e
tha t
is
a c t ua l l y l o c k e d is r e t u r ne d to the c a l l e r by
m e a n s of t h e R E TADR a r g um e n t . )
Wh e n a p r o c e s s
i s b e i ng
o u t swa pped ,
g l o ba l
r e a d /wr i t e
pag e s a r e
d r o pped
f r om t h e p r o c e s s wo r k i ng s e t ( Ch a pt e r 1 4 ) t o avo i d c umbe r so m e
a c c o u n t i ng p r o b l em s a b o u t wh e t h e r t h e o u t swa pped
pag e c o n t a i n s
the
mo s t up- to -d a t e i n fo rma t i o n .
Fo r th i s r e a so n , g l oba l r e a d /wr i t e pag e s
c a nno t b e l oc k e d i n to the p r o c e s s wo r k i ng s e t .
( S u c h pag e s c a n b e
loc ked
i n to m emo r y b e c a u s e
t h e Lo c k Pag e s i n Mem o r y s y s t em s e r v i c e
p r e v e n t s o u t s wa p o f e i th e r the p r o c e s s h e a d e r
or
the
loc ked
pag e s ,
a vo i d i ng t h e swa pp i ng s i t u a t i o n a l t og e th e r . ) Th e swa ppe r a l s o pe r fo rm s
a n o p t i m i z a t i o n w i t h g l ob a l r e ad - o n l y pag e s b y d r o pp i ng them f r om
th e
wo r k i ng
s e t o n o u t s wa p i f t h e g l o b a l s h a r e c o un t i s l a rg e r th a n o n e .
I f s uc h pag e s a r e l oc ked i n to the wo r k i ng s e t , t h e y a r e no t d r o pped
f r om
t h e wo r k i ng
s e t , i nd e p e nd e n t of t h e c o n t e n t s o f the PFN S HRCNT
a rray .

13. 4 . 2. 2
Lo c k i ng Pag e s i n Memo r y - Th e Lo c k
Pa g e
i n Memo r y s ys tem
s e rv i c e
i s s i m i l a r t o the Lo c k Pa g e in the Wo r k i ng Set s e r v i c e e x c e p t
tha t the WS L $ V PFNLOCK b i t i n the WS LE i s s e t a nd t h e p r o c e s s h e a d e r
is
l o c k ed i n to m em o r y .
Th i s s e r v i c e p e r f o rms a n i m p l i c i t wo r k i ng se t
l o c k i n add i t i o n t o g ua r a n t e e i ng pe rma n e n t r e s i d e nc y to the
spec i f i ed
v i r t ua l
add r e s s
r a ng e .
Bec ause
t h i s o pe r a t i o n
i s pe r m a n e n t l y
a l l o c a t i ng a s ys tem r e so u r c e , phys i c a l m emo r y , i t r e q u i r e s a pr i v i l eg e
( P SWAPM )
•

1 3-1 5

MEMORY MANAG EMENT S Y S TEM S ERVI C E S
1 3 . 4 . 2 . 3 Un l oc k i ng P a g e s - Th e c o nve r s e o f e i th e r o f t h e two
l o c k i ng
s e r v i c e s un l o c k s pag e s f r om e i th e r the wo r k i ng s e t o r phys i c a l memo r y .
I n ad d i t i o n , t h e wo r k i ng s e t l i s t e n t r i e s m a y h a v e
to
b e e x c h a ng ed
w i th o t he r l oc ked e n t r i e s to pl a c e t h e u n l o c k e d e n t r i e s b a c k i n to the
d yn am i c po r t i o n of t h e l i s t .
As w i th
the
e x c h a ng e a s s o c i a t e d w i th
l o c k i ng
pag e s ,
t h e WS LX P FN a r r a y e l em e n t s m u s t a l s o b e e x c h a ng ed .
F i na l l y ,
t h e a pp r o p r i a t e b i t
in
the
WSLE
( WS L $V WS LOCK
or
WS L$V_PFNLOC K ) i s c l e a r e d .

13. 4. 3

P r o c e s s Swa p Mo d e

A p r o c e s s w i th PSWAPM p r i v i l eg e c a n p r ev e n t i t s e l f f r om be i ng
r em o v ed
f r om mem o r y .
Th i s
service
s i mpl y s e t s t h e PC B $ V PSWAPM b i t i n the
s t a t u s l o ng wo r d ( PC B $ L S TS ) in t h e so f twa r e PC B .
When t h e swa ppe r
is
s e a r c h i ng f o r s u i t a b l e-o u t s wa p c a nd i d a t e s , p r o c e s s e s wi th th i s b i t s e t
a r e pa s s ed o v e r .

13. 4.4

Al t e r i ng Pag e P r o t e c t i o n

I t i s po s s i b l e fo r a p r o c e s s to a l t e r the pag e p r o t e c t i o n o f a s e t o f
pag e s
in
i ts add r e ss
r a ng e w i th the S e t P r o t e c t i o n o n Pag e s s ys t em
s e r v i c e ( $ S E T PRT ) .
I n g e ne r a l ,
t h e o pe r a t i o n o f
th i s
service
is
s t r a i g h t fo r wa rd .
Ho weve r , t h e r e i s o n e i n t e r e s t i ng s i d e e f f e c t .
If a
s e c t i o n pag e f o r
a
r ea d - o n l y s e c t i o n h a s
i ts protec t i o n set
to
wr i t a b l e ,
the c o py-on- r e f e r e n c e b i t i s s e t .
Th i s w i l l fo r c e the pag e
to h a v e i t s b a c k i ng s t o r e add r e s s c h ang ed to t h e pag e
f i l e wh e n
the
pa g e
is
f a u l ted ,
p r e v e n t i ng
a
l a te r a t t empt to wr i t e the mo d i f i ed
s e c t i o n pag e s b a c k to a f i l e to wh i c h t h e p r o c e s s m a y b e d e n i e d
wr i t e
access .
Th e s ymbo l i c d e b ug g e r u s e s th i s s e r v i c e to
i m pl em e n t
i t s wa t c h po i n t
f a c i l i ty .
Th e pa g e c o n t a i n i ng t h e d a t a e l em e n t i n que s t i o n i s s e t to
no wr i t e a c c e s s fo r u s e r m o d e .
Wh en the p r og r am a t temp t s
to
access
t h e pag e ,
an access v i o l a t i on occur s ,
wh i c h
is
f i e l d ed
by the
d eb ug g e r ' s c o nd i t i o n h a nd l e r .
Th i s h a nd l e r
1.

is
the
add r e s s
c h e c k s wh e t h e r t h e i na c c e s s i b l e
wa t c hed and r e po r t s t h e m o d i f i c a t i o n i f i t i s ,

pa g e
sets
the
mod i f i c a t i o n ,

s e t s the TB I T i n the PS L to g i v e t h e d e b ug g e r
the i n s t r uc t i o n c ompl e t e s ,

a n d d i sm i s s e s t h e e x c e pt i o n .

pro tec t i o n

PRT $ C UW

one

b e i ng

al low

the

control

after

Wh e n t h e i n s t r uc t i o n c ompl e t e s ,
t h e d e b ug g e r ' s
TB I T h a nd l e r g a i n s
control ,
s e ts
the
pag e
p r o t ec t i o n b a c k t o no wr i t e a c c e s s fo r u s e r
mod e , a nd a l l o ws t h e p r og r am t o c o n t i n ue i t s e x e c u t i o n .

1 3 -1 6

C HAPTER 1 4
SWA P P I NG

VA X/VM S d o e s n o t a l l o w t h e a m o un t o f phys i c a l memo r y to to ta l l y l i m i t
the
n um b e r
o f processes
a l l o we d i n the s ys tem .
Ph ys i c a l m emo r y i s
e f f e c t i v e l y e x tend ed b y k e e p i ng o n l y a s u b s e t o f t h e to t a l
n um b e r
of
a c t i ve
p r oc e s s e s
r e s i d ent
a t a g i ven t ime .
Th e r em a i n i ng p r o c e s s e s
r e s i d e i n b ac k i ng s t o r e
l o c a t i o ns .
Th e movemen t o f
l ow pr i o r i ty
processes
to
b a c k i ng s t o r e a nd t h e s ub s e q u e n t f i l l i ng o f memo r y w i th
h i g h p r i o r i t y c omp u t a b l e
processe s
i s the
r e s po n s i b i l i t y o f
the
s wa ppe r .

14. 1

SWAPP I NG OVERV I EW

B e f o r e we d i sc u s s t h e d e t a i l s o f
swa ppe r
o pe r a t i o n wh i c h
i nv o l v e s
m o v i ng
a process
i n to
or
o u t o f m emo r y , we w i l l r e v i e w s ome b a s i c
s wa ppe r conc e pt s .
We w i l l a l s o po i n t o u t t h e spec i f i c u s e s o f e a c h o f
t h e m emo r y m a n ag em e n t d a ta s t r uc t u r e s m a n i pu l a t ed b y the swa ppe r .

14. 1.1

Swa pp e r Re s po n s i b i l i t i e s

Th e swa ppe r h a s two m a i n r e spon s i b i l i t i e s .
•

Th e s u b s e t o f p r o c e s s e s t h a t a r e c u r r e n t l y r e s i d e n t s h o u l d
represent
th e h i g h e s t
p r i o r i t y e x e c u t a b l e p r o c e s s e s i n the
s y s t em .
Wh e n no n r e s i d e n t p r o c e s s e s b e c om e c ompu t a b l e ,
the
s wa ppe r mus t b r i ng them b a c k i n to m emo r y .

•

Th e swa ppe r i s a l s o r e s po n s i b l e fo r
k e e p i ng
t h e n um b e r
of
pag e s o n
the
f r ee
pag e l i s t above the l o w l i m i t th r e sho l d
e s t a b l i s h e d b y t h e SYS B OO T pa r ame t e r FRE E L I M .
Re qu e s t s
for
phys i c a l
pag e s c om e f r om s e v e r a l s o u r c e s .
On e r e que st c om e s
f r om t h e pag e r i n r e s o l v i ng a pag e f a u l t fo r a pag e
th a t
is
not
cur rentl y
i n m emo r y .
An o th e r
o r ig i na tes
wi th
the
swa ppe r ' s a t t empt i ng to
a c q u i r e e n o ug h ph ys i c a l
pag e s
to
i n s wa p a c ompu t a b l e but o u t swa pped p r o c e s s .
Th e r e a r e th r e e
o pe r a t i o n s t h a t t h e
swa ppe r
pe r fo rm s t o
ful f i l l
th i s
r e spon s i b i l i t y .
1.

P r o c e s s h e ad e r s o f pr ev i o u s l y o u t swa pped
process bod i es
may be
el ig i ble
f o r o u t swa p .
( Process headers
for
a l r e a d y d e l e t e d p r o c e s s e s a r e s i mpl y d e l e t ed . )

1 4-l

SWAPPING

14. 1 . 2

Th e swa ppe r w i l l wr i t e m od i f i ed pag e s unt i l t h e n um b e r o f
pa g e s o n t h e mo d i f i ed
l i st
f a l l s b e l o w the l ow l im i t
th r e sho l d s t o r e d i n g l o b a l l o c a t i o n S C H $G L_MFYLOL I M .

As a l a s t r e s o r t to m a i n t a i n i ng t h e s i ze o f t h e f r e e pag e
l i st ,
the
s wa ppe r
wi l l
s e l e c t a n e l i g i b l e p r o c e s s fo r
o u t s wa p a n d r emove t h a t p r o c e s s f r om memo r y .

Swa ppe r I mp l em e n t a t i o n

Th e swa ppe r i s a s e pa r a t e p r o c e s s i n VAX/VM S .
A s s uc h ,
i t can be
f o r e x e c u t i o n j u s t l i ke a ny o th e r p r o c e s s i n t h e s ys tem .
It
s e l e c t ed
a l s o h a s i t s own r e s o u r c e s
a nd
q uo t a s t h a t a r e c h a r g ed
wh e n
the
swa ppe r d o e s I /0 .
By m a k i ng t h e swa ppe r a s e pa r a te p r o c e s s , t h e p i e c e s o f
the
s ys t em
th a t d e tec t a n e ed fo r o n e o f t h e s wa p pe r ' s d u t i e s s i mpl y h a v e to wa k e
t h e swa ppe r u p { by i s s u i ng a J S B t o r o u t i n e S C H $ SWPWAKE ) .
A s a l r ea d y
no ted
i n Ch a p t e r 8 ,
th i s
r o u t i n e d o e s n o t s i mp l y wa ke t h e swa ppe r .
I n s t e a d , i t pe r f o rms a s e r i e s o f c h e c k s to d e te r m i n e wh e th e r t h e r e
is
a n e ed fo r s wa ppe r a c t i v i ty .
I f s o , t h e swappe r pr o c e s s i s awa k e n ed .
I f n o t , t h e r o ut i n e s i mpl y r e t u r n s .
By p e r fo rm i ng
these checks
in
th i s
r o ut i n e
r a th e r than i n t h e s wa ppe r p r o c e s s i t s e l f , t h e ov e r h e a d
o f t wo n e e d l e s s c o n t e x t s w i t c h e s i s a v o i d ed .
Wh e n the swa ppe r i s the
c u r r en t
process ,
it
executes ent i rel y
in
k e r ne l
mode .
Al l o f t h e swa ppe r c o d e r e s i d e s i n sys t em s p a c e .
{ Th e
swa p pe r m a k e s u s e o f i t s P O
s pa c e wh e n
it
s wa ps a
n e wl y c r e a t ed
process
f r om mod ul e S H E L L in the e x e c ut i v e i m ag e .
Th i s o pe r a t i o n i s
d e sc r i b ed i n Ch a p t e r 1 7 . )

14. 1 . 3

Compa r i s o n o f Pag i ng and Swapp i ng

VM S u s e s two d i f f e r e n t t e c h n i q ue s to m a k e e f f i c i e n t u s e o f av a i l a b l e
phys i c a l m emo r y .
Th e a b i l i t y t o s uppo r t p r o g r am s wi th v i r t ua l a d d r e s s
s pa c e s l a rg e r t h a n ph ys i c a l memo r y i s t h e r e s po n s i b i l i t y o f t h e pag e r .
Th e
s wa ppe r
a l l o ws a r un n i ng s ys t em to s uppo r t mo r e a c t i v e p r o c e s s e s
than c an
fit
i n to
phys i c a l
m emo r y a t o n e
t i me .
Th e
swa ppe r ' s
r e spons i b i l i t i es
a r e mo r e g l o b a l
o r s ys tem w i d e t h a n t h e pag e r ' s .
Ta b l e 1 4 - 1 c ompa r e s a nd c o n t r a s t s the pag e r
a nd
swa ppe r
i n seve r a l
d e ta i l s .

14. 2

SWAP S C HEDUL ING

Th e swa ppe r i s a
pa r t o f
the
s ys t em t h a t
pe r fo rms b o th m emo r y
m a n a g em e n t
a nd
s c h e d ul i ng
f unc t i o n s .
Th e s c h e d u l i ng a s pe c t s o f the
swa p pe r a r e d i sc u s s ed f r om two po i n t s o f v i e w .
Fi r s t ,
the
ac t i ons
that
the
s wa ppe r
takes
to d e te r m i n e wh e th e r t o i n swa p o r o u t s wa p a
pa r t i c u l a r p r o c e s s a r e d i sc u s s e d .
Th e n ,
those
s ys t em e v e n t s
th a t
t r i g g e r s wa ppe r a c t i v i t y a r e m e n t i o n ed .

1 4-2

SWA P P I NG
Ta b l e
Co m pa r i so n o f

1 4 -1

Pag i ng

and

Swa pp i ng

D i f f e r enc e s

P a g i ng

Swa pp i ng

Pag i ng s uppo r t s p r o g r am s
wi th
v e r y l a rg e ad d r e s s s pa c e s .

Swa ppi ng
s uppo r t s
a
l a rg e
n um b e r
o f c o nc u r r en t l y a c t i v e
processes .

Pr o c e s s wi d e c ompo n en t o f
tha t
ex ec u t i v e
i n to
a nd
out
wo r k i ng s e t s .

The

pag e

the

Sys t em wi d e c om po n e n t

m ov e s
pag e s
of
proc ess

f a u l t h a nd l e r

e x ec ut i v e
tha t
proc esses
i n to
p h ys i c a l m emo ry .

Th e

swa ppe r

the

mov e s
enti re
and
out
of

s e pa r a t e

e x c ept i o n s e rv i c e r o u t i n e t h a t
e x e c u t e s i n t h e c o n t ex t o f the
p r o c e s s t h a t i n c u r r ed t h e pa g e
fa ul t .

pr o c e s s
t h a t i s a wa k e n ed f r om
h i b e r na t i ng
s t a te
i ts
by
c ompo n en t s
t h a t d e te c t a n e ed
f o r s wa ppe r ac t i v i t y .

The
un i t
of
pag i ng
is
the
a l tho ug h
t he
pag e r
pag e ,
a t t empt s t o r ea d mo r e t h a n o n e
pag e wi th a s i ng l e d i s k r e ad .

Th e un i t o f
s wa pp i ng
is
the
proc e s s
(or
mo r e ac c u r a t e l y ,
the p r o c e s s wo r k i ng s e t ) .

Pag e r e ad r e q u e s t s fo r p r o c e s s
pa g e s a r e q u e u e d to t h e d r i v e r
ac c o rd i ng t o t h e b a se p r i o r i t y

Swa ppe r
I /0
r e que s t s
are
q u e ued
a c c o rd i ng t o t h e v a l u e
pa r am e t e r
t he
SYSB OOT
of
SWP PR I O .

of
the
p r o c e s s i nc u r r i ng the
pa g e
faul t .
Mo d i f i ed
pag e
wr i t e
r eque s t s
a re
q u e ued
acco rd i ng
the
S Y S B OOT
to
pa r am e t e r M PW_PR I O .

Simi l a r i ties

(1)

The

pa g e r

a nd

s wa ppe r

wo r k

f r om a

c ommo n d a ta

b a se .

i m po r t a n t
s t r uc t ur e s
that
a re
u s ed
fo r
both
swa ppi ng a r e the p r o c e s s pag e t a b l e s , the wo r k i ng
a nd t h e PFN d a t a b a se .

Th e mo s t
pag i ng and
set
l i st ,

(2)

Th e pag e r a nd s wa ppe r d o c o nv e n t i o n a l I /0 .
Th e r e
are
onl y
sl ight
d i f f e r e nc e s
in
d e ta i l b e t we e n pag e r I /O a nd swa ppe r
I /0 on the o n e hand a nd no rm a l Q u e ued
I /0
r e que s t s
on
the
o the r .

(3)

Bo th c ompo n en t s a t t empt to m a x 1m 1 z e the n um b e r o f b l oc ks r e ad
or
wr i t t e n w i th a g i v en I /O r e que s t .
Th e pag e r a c c ompl i sh e s
t h i s w i th r e ad a nd wr i t e c l us t e r i ng .
Th e swa ppe r a t t empt s to
i n swa p
or
n um b e r o f )

o u t s wa p the e n t i r e
I /O r e que s t ( s ) .

wo r k i ng

1 4 -3

set

one

(or

sm a l l

SWAPPING
S e l e c t i o n o f I n swap C a nd i d a te

14. 2. 1

Th e
s c h ed u l e r m a i n ta i n s
3 2 q u a d wo r d
l i s th e a d s
fo r
o u t swa pped
c ompu t a b l e
( C OMO )
processes ,
one
fo r
e a c h s o f t wa r e p r i o r i t y
Th e s e q u e u e s a r e i d e n t i c a l to the 3 2 q u e u e s m a i n t a i ned
( Fi g u r e 8 - 3 } .
for
t h e c om p u t a b l e
r es i d ent
( C OM }
processes .
Th e s t eps tha t the
s wa ppe r t a k e s to l o c a t e an i n swa p c a nd i d a t e ( o n c e i t has d e c i d ed
tha t
an
i n swa p c a n b e pe r f o r m e d )
e x a c t l y pa r a l l e l
the s t eps tha t the
r e s c h ed u l i ng i n te r r up t s e r v i c e r o u t i n e t a k e s ( Ch a p t e r 8 ) to se l ec t the
n ex t c a nd i d a t e f o r e x ec u t i o n .
1.

the
C OM O queue
s umm a r y
l o ng wo r d
A FFS
i n s t r uc t i o n o n
the h i g h e s t p r i o r i ty no n empty C OMO
( S C H$G L_C OM O QS )
l ocates
q u e ue .

Th e f i r s t p r o c e s s i n th i s que ue i s r em o v e d and
b e i ng s wa pped i n to memo r y .

p r e pa r ed

fo r

F i g u r e 1 4 - 1 s hows t h e p a r a l l e l b e t we e n the i n swa p c a nd i d ate
se l ec t ion
a nd
t h e o pe r a t i o n o f t h e r e s c h ed u l i ng i n te r r up t s e r v i c e r o u t i n e .
Th e
key
i n s t r uc t i o n s
in
the
two
r o u t i ne s a r e
i d ent i c a l .
Th e o n l y
d i f f e r e nc e s
a re
in
the g lobal
d a ta
i tems
r e f e r en c ed b y the
i n s t r uc t i o n s .
A f t e r a p r o c e s s h a s b e en c h o s e n f o r
i n swa p ,
the
s wa ppe r
chec ks
if
the r e
a re
e no ug h pag e s o n the
f r ee
pag e l i s t to ho l d the i n s wa p
c a nd i d a t e a nd l e a v e a t l e a s t FRE E L I M pag e s r em a i n i ng o n the l i s t .
If
so ,
the
i n swa p p r o c e ed s .
I f no t , t h e s wa ppe r a t temp t s t o m a k e mo r e
pag e s a v a i l a b l e b y o u t swa pp i ng o n e o r mo r e p r o c e s s e s , wr i t i ng mod i f i ed
p ag e s , o r d e l e t i ng p r o c e s s h e ad e r s o f a l r e a d y d e l e t ed p r o c e s s bod i e s .
Th e r e i s o n e o p t i m i z a t i o n t h a t the swa ppe r pe r f o r m s tha t m a y p r ev e n t
a n o u t swa p .
Th e
swa ppe r
onl y
i n swa ps c om p u t e bo und l o w p r i o r i t y
p rocesses a t a
r a t e d e t e r m i n ed
by
the
s pe c i a l
SYSB OOT pa r am e t e r
SWPRA T E .
Th e d e f i n i t i o n
of
s uc h a
proc ess
i s o n e who s e c u r r e n t
p r i o r i t y i s e q ua l t o i t s b a se p r i o r i t y , wh i c h p r i o r i t y i s l e s s t h a n o r
e qua l t o t h e SYS B OOT p a r am e t e r DEFPR I .
If
•

t h e swa ppe r i s a t t em p t i ng t o i n swa p s uc h a p r o c e s s ,

•

and t h e p r o c e s s w i l l no t f i t ,

•

and t h e SWPRATE i n t e rv a l h a s n o t ye t e x p i r ed ,

the
i n swa p a t t empt
is
a bandoned .
Ea c h
t ime
tha t
the
swa ppe r
s uc c e s s f u l l y
i n swa ps o n e o f
t h e s e s o - c a l l ed c r un c h e r p r o c e s s e s , i t
r e s e t s i t s i n swa p c l oc k t o c o n t a i n the c u r r e n t t i m e pl us SWPRATE .

14. 2. 2

S e l ec t i o n o f O u t swa p C a nd i d a t e s

Wh e n t h e swa ppe r d e t e rm i n e s t h a t i t m u s t o u t s wa p a p r o c e s s ( e i th e r
to
f r ee
up phys i c a l
pag e s o r
to make
r o om
fo r
a h i g h e r pr i o r i t y
c ompu t a b l e b u t o u t swa pped p r o c e s s ) , i t m u s t
s e l ec t s uc h a
proce ss .
Th e
o rd e r i n wh i c h po t e n t i a l o u t swa p c a nd i d a t e s a r e e x am i n ed a t t em p t s
t o r em o v e f i r s t t ho s e p r o c e s s e s tha t b e n e f i t the l e a s t f r om
r em a i n i ng
r e s i d en t .

1 4-4

The f i r s t ha l f o f
The r o ut i n e SCH$SCHE D t ha t sel ec ts the n e x t e x ecut i o n c and i d a te ha s an ex ac t pa r a l l el in the swappe r .
the
pa r a l l el
shows
t he
swa ppe r ' s s e l ec t i o n o f the n ex t i n swa p c and i d a te a nd the n e a r l y i d en t i c a l i n s t r uc t i o n s i n the
schedul e r .
Swa ppe r ' s Se l ec t i o n o f Inswa p Cand i d a te
QEM PTY :

B UG C HECK QUE UEM PTY , FATAL

SWAPS C HE D :
DSB INT
BBSS
FFS
BNEQ
BBCC
ENB INT
5$ :
RSB
10$:
....
.b

U"1

No t e s

PUSHR
M OVA Q
MOVL
CMPB
BNEQ

U PL $ S YNCH
S A t SCH$V S I P , WA SC H $GB S I P , S $
t O , t 3 2 , W�SC H $G L C OMOQS, R2
1 0$
S A t S C H$V_S I P , WA SCH$GB_S I P , 5 $

t A M <R 6 , R7 , R8 , R 9 , R l 0 , R l l , AP , F P >
WA SCH$AQ C OM OH [ R 2 ] , R 3
(R 3 ) , R4 tDYN $C PCB , PC B $8 TYPE ( R 4 )
QEM PTY-

(1)

Sc hed ul e r ' s Se l ec t i o n o f Ex ecut i o n Cand i d a te
S C H $ I DLE :
S ET I PL
MOVB
BRB

I I PL $ S C HE D
1 3 2 , W�SC H$GB PR I
SCH$SC HE D

SCH$SCHED : :
S ET I PL

U PL $_S YNC H

(2)

FFS
B E QL

f O , f 3 2 , WA SC H $G L C OM QS , R 2
S C H $ I DLE

(3)

MOVAQ
R EM QUE

WA SCH$A Q C OM H [ R 2 ] , R 3
@ ( R 3 ) + , R4

(4)

It then t a k e s t he s t e ps n ec e ssa r y to b r i ng th i s p r o c e s s
i n to
At t h i s po i n t , t h e swa ppe r h a s fo und an i n swa p c a nd i d a te .
memo r y .
Th e s c hed ul e r , on the o th e r hand , c o n t i n u e s e x ec ut i o n .
Th e REM QUE i n s t r uc t i o n shown above fo r the sc hed u l e r i s
d upl i c a ted b e l o w to em ph a s i ze tha t , wh i l e a l ong t i me e l a ps e s b e twe en i n swa p c and i d ate se l ec t i o n and compl e t i o n o f
the
i n swa p , t h e r e is no t i me l a pse fo r ex ec u t i o n se l ec t i o n .

(1)

I PL i s r a i sed to SYNC H to sync h r o n i ze acc e ss to the sc hed ul e r ' s d a ta b a s e .

(2)

Th e h i g h e s t pr io r i t y ( c omputa b l e b u t o u t swa pped/computa b l e )

(3)

Th e add r e s s o f i t s fo rwa r d po i n t e r i s l o ad ed i n to R 3 .

(4)

Th e add r e s s o f t h e sel ec ted PCB i s l o ad ed i n to R 4 .

que ue i s s e l ec ted .

( continued o n next page )
F i g u r e 1 4 -1
Pa r a l l e l s Be twe e n I n swa p C a nd i d a t e S e l e c t i o n
by t h e Swa ppe r a nd E x e c u t i o n Cand i d a t e S e l e c t i o n by t h e S c h e d u l e r

Som e t i m e l a t e r , t h e i n swa p o pe r a t i o n c ompl e te s .
The swa ppe r r eb u i l d s t h e wo r k i ng se t l i s t and the proc e s s pag e t a b l e s .
Th e pa r a l l e l r e s um e s wh en the swappe r c a l l s t h e s c hed u l e r to m a ke the n ewl y i n swapped pr o c e s s c ompu t a b l e .

Sta t e Ch a ng e f r om C OM O t o C OM

No t e s

S t a te Ch ang e f r om Compu t ab l e t o Cu r r en t

S C H $ S C HE P :

5$:
1 0$ :

I-'
�

0'\

30$:
40$:

(5)

R EM QUE

( R 4 ) , Rl

BNE Q
M OVZW L
BBC
M OVZ B L
B LB C
ADDL
B BCC
M OVB
MOVL
.

10$
PC B $W S TATE ( R 4 ) , R l
R l , E XES TATE , l O $
PC B $ B P R I ( R 4 ) , R l
PC B $W-S TATE ( R 4 ) , 5 $
# 3 2 , Rl
R l , W"" SC H$G L C OM QS , 1 0 $
R O , PC B $B PRI ( R 4 )
# S C H $C_COM , R l

M OVW
MOVAQ
BBSS
I N S QUE
RSB

R l , PC B $W S TATE ( R 4 )
L "" S C H $A Q-COMT [ R O ] , R l
R O , W"" SC HGL C OM QS , 4 0 $
( R 4 ) ,@ ( R l ) +

R EM QUE
BVS
BNE Q

@ ( R 3 ) + , R4
QEM PTY
20$

B B CC

R 2 , W"" SC H $G L_C OM QS , 2 0 $

CM PB
BNE Q

iDYN $C PC B , PC B $8 T Y PE ( R 4 )
QEM PTY-

(8)

M OVW

# S C H $C_C UR , PC B $W_S TATE ( R 4 )

�"'0

(9)

MOVL

R 4 , W"" SC H $G L_C UR PC B

G')

(6)

(7 )

20$ :

At t h i s po i n t , t h e pa r a l l e l e nd s .
I f t h e p r o c e s s j us t m a d e c o m pu t a b l e i s o f h i g h e r
pr i o r i ty ·than
the
swa p pe r ,
tha t
process
wi l l be s c h e d u l ed as s o o n a s t h e I PL i s l o we r ed b e l o w 3 a n d t h e r e sc hed u l i ng i n te r r up t o c c u r s .
I n o the r c a s e s ,
t h e p r o c e s s w i l l n o t e x e c u t e u n t i l i t b ec om e s t h e h i g he s t pr i o r i t y c om p u t a b l e p r o c e s s .
Th e sched u l e r ' s s e r v i c e
rout ine
c o n t i n u e s i t s o pe r a t i o n , p l ac i ng t h e s e l e c ted p r o c e s s i n to ex e c u t i o n .
(5)

Rem o v e the s e l ec t ed PC B f r om i t s fo rm e r s t a t e

( C OM O/ C OM ) .

(6)

B i a s Rl so tha t i s po i n t s to SC H $G L C OM O QS , t h e s umma r y l o ng wo rd fo r the
c o m pu t a b l e
b ut
o ut s wa pped
state .
( Th i s i s n o t a pa r a l l e l s t ep b u t i s m e r e l y no ted so t h e BBCC i n s t r uc t i o n m a k e s s e n s e . )

(7)

I f t h e r em ov a l o f t h e PC B empt i ed t h e q u e u e ,
l o ng wo r d .

(8)

Lo a d t h e STATE f i e l d

(9)

F i n a l l y , p l a c e t h e PC B i n to

c l ea r

i n t h e PC B wi th t h e n e w s ta te

the

a s so c i a ted

( COM/ C UR ) .

pr i o r i t y

bit

the

o f the proc ess .

i t s n e w s c h e d u l i ng q u e u e .

F i g u r e 1 4 - 1 { Co n t . )
Pa r a l l e l s Be t we e n I n s wa p C a nd i d a t e S e l e c t i o n
b y t h e Swa ppe r a nd E x e c u t i o n C a nd i d a t e S e l e c t i o n b y t h e S c h e d u l e r

s umm a r y

(J)

"'0
H
z

SWA P PING
Th e swa ppe r m a i n t a i n s a t a b l e ( i n m o d u l e
OSWPS C HE D )
t h a t d e te rm i n e s
t h e o rd e r
i n wh i c h
the v a r i o us
r e s i d e n t s c h e d u l i ng
states
a re
e x a m i n ed .
Tab l e 1 4 - 2
s h ows
thi s
o rd e r
a nd
m en t i o n s
o th e r
c o n s i d e r a t i o n s th a t a r e m a d e i n f i nd i ng a s u i t ab l e o u t s wa p c a nd i d a t e .
Ta b l e 1 4 -2
O r d e r o f Se a r c h f o r Po t e n t i a l Ou t swa p Ca nd i d a te s
Pr o c e s s St a t e

S u s pend ed

( Mn emo n i c )

( S US P )

Lo c a l Ev e n t Fl ag Wa i t
H i b e r na t i ng

( H IB )

Commo n Ev e n t Fl ag Wa i t
Fr e e Pa g e Wa i t

( CEF)

( F PG )

Co l l i d ed Pag e Wa i t )
Mi sc e l l an e o u s Wa i t

( C OLPG )
( MWA I T )

Common Ev e n t Fl ag Wa i t

Lo c a l Ev e n t Fl ag Wa i t

Pag e Fa ul t Wa i t
Comput a b l e

( LE F )

( C OM )

( PFW)

( CEF)

( LE F )

P r i o r i ty
Impo r t a n t

In i t i a l
Qua n t um

Ad d i t i o na l No t e s

YES

YE S

D i r ec t I /O Co un t
Ca n no t Be Z e ro

YES

YE S

D i r ec t I/O Co un t
Ca n no t Be Z e r o

YES

YE S

YES

YE S

D i r ec t I /O Co u n t
Mu s t Be Z e r o

D i r ec t I /O Co un t
Mu s t B e Z e r o

(1)

The pr io r i ty tha t i s used fo r c om pa r i so n i s fo und
in
g l obal
location
SWP $GB I SWPR I .
If
the
pr io r i t y o f the po ten t i a l
o ut s wa p c a nd i d a te i s g r ea t e r than
( but
not
e qua l
to )
the
p r i o r i ty
of
the
po ten t i a l
i ns wa p p r o c e s s ,
the
o ut s wa p
c and i d a t e i s bypa s sed .

(2)

An a s s umpt i o n i s mad e abo ut d i r ec t I /O fo r p r o c e s s e s i n l oc a l
o r g l ob a l ev e n t f l ag wa i t s t a te s .
Th e a s s umpt i o n i s tha t the
event f l ag
wa i t
wi l l
be
sa t i s f i ed
wh en
the
d i rect
I /O
c ompl e te s .
Such a p r o c e s s i s pa s s ed ov e r , r a th e r than i n c u r the
o v e r he a d
of
s wa pp 1 ng
it,
o n l y to h a v e the p r o c e ss b ecome c omputab l e
v e r y s o o n , pe r h a ps e v en b e fo r e the o ut swa p i s c ompl e t e .

Th e r e a r e th r e e g e ne r a l c o n s i d e r a t i o n s tha t
a c c o un t wh en c h e c k i ng e a c h p r o c e s s s ta t e .
•

the

swa ppe r

takes

i n to

Fo r some o f t h e s t a t e s t o wa r d the bo t t om o f t h e
l ist
( tho se
states
l o o k e d at l a s t ) , the swa ppe r t e s t s the s e t t i ng of the
i n i t i a l q u a n t um f l ag ( PC B $V I N QUAN i n PC B $ L S T S ) .
Pr o c e s s e s
r e s i d e n c y -a nd i n o n e o f the
in
the i r
initial
q ua n t um- o f
s c h e d u l i ng
s t a t e s wh e r e
the
s e t t i ng
of
th i s
f l ag
is
1 4 -7

SWAPP I NG
s i g n i f i cant wi l l
b e b ypa s s ed
wh e n l o o k i ng fo r a s u i t a b l e
o u t s wa p c a nd i d a t e .
Fo r o th e r p r o c e s s s ta t e s , t h e s e t t i ng
of
t h i s f l ag i s i g n o r e d .
Th e s e t t i ng o f t h e i n i t i a l q u a n t um f l ag i s a l s o i g no r ed und e r
a
d i f f e r ent
s e t o f c i r c um s t a nc e s .
Th e swa ppe r m a i n t a i n s a
f a i l u r e c o un t e r t h a t r ec o rd s t h e n umbe r o f
t imes
tha t
it
a t t empt ed
to
l o c a t e a n o u t s wa p c a nd i d a te a nd f a i l ed .
Wh e n
t h i s c o un t r e a c h e s a v a l ue e q ua l
to
the
SYS B OOT pa r am e t e r
SWPFA I L ,
th e
s wa ppe r
b eg i n s
i g no r i ng
the s e t t i ng o f th i s
i n i t i al
qu a n t um
f l ag
fo r
po te n t i a l
o u t s wa p
c a nd i d a t e s ,
i nd e p en d e n t o f p r o c e s s s ta t e .
Th e c o un t e r i s r e s e t e a c h t i m e
t h a t a n o u t s wa p c a nd i d a t e
is
s uc c e s s f u l l y l o c a t e d .
( Th e
actual
i mp l eme n t a t i o n
r e s e t s t h e c o u n t pa r am e t e r to SWPFA I L
a nd d e c r em e n t s t h e c o un t fo l l o w i ng e a c h f a i l u r e .
Th e i n i t i a l
q u a n t um f l ag i s i g n o r ed o n c e the c o un t g o e s t o ze r o . )
•

•

14. 2. 3

P r o c e s s e s i n tho s e s t a t e s wh e r e p r i o r i t y i s l i s t ed
a s b e i ng
i mpo r ta n t a r e o n l y s e l e c t e d fo r o u t s wa p i f the i r p r i o r i t y i s
sm a l l e r t h a n o r e q u a l to the p r i o r i t y o f the po t e n t i a l i n s wa p
p r o c e s s ( s t o r e d i n g l o b a l l o c a t i o n SW P$GB_I SWPR I ) .
Th e swa ppe r d o e s n o t
initially
r emove
proc e s s e s
tha t a r e
p r e s um a b l y d o i ng
d i r e c t I /0 .
( I f a p r o c e s s i s d o i ng d i r e c t
I /0 , a n d t h e p r o c e s s i s wa i t i ng o n a n e v e n t f l ag , t h e swa ppe r
a s s um e s
th a t
the even t
f l ag
wa i t
i s a s so c i a t e d wi th t h e
d i r e c t I /0 . ) Th e mo t i v a t i o n b eh i nd
th i s d e c i s i o n
is
the
d e s i r e to a v o i d t h e o v e r h e a d o f s wa pp i ng t h e p r o c e s s , o n l y to
h a v e t h e p r o c e s s ' s s t a t e c h ang e
to
C OM ,
e v e n b e fo r e
the
o u t s wa p c ompl e t e s .

Sys t em Eve n t s Th a t T r i g g e r Swappe r Ac t i v i t y

Th e swa ppe r s pend s i t s
idle
t ime
i n a h i b e r n a t i ng
state .
Tho s e
c om po n e n t s wh o d e t e c t a n e e d f o r s wa ppe r a c t i v i t y wa ke the s wa ppe r ( by
c a l l i ng r o u t i n e SCH$ SWPWAKE ) .
Ta b l e 1 4 - 3 l i s t s the s ys t em e v e n t s th a t
t r i gg e r
a
n e ed
fo r
s wa ppe r
a c t i v i t y , t h e mod ul e th a t c o n t a i n s t h e
r o u t i n e tha t d e te c t s e ac h n e e d , a nd t h e r e a s o n wh y t h e
s wa ppe r n e ed s
t o b e i n fo rmed a b o u t th e s e s ys t em eve n t s .
Th e s wa ppe r d o e s n o t wo r r y a b o u t " h y i t wa s a wa k e n e d .
Eve r y t i me tha t
it
is
a wa ke n ed ,
it
t e nd s to a l l o f i t s r e s po n s i b i l i t i e s .
Th e m a i n
l oo p o f t h e s wa ppe r l o o k s l i ke the fo l l o w i ng .
1.

Th e f r e e pag e c o un t i s b a l a nc ed .
Th i s m i g h t
r e s ul t
in
an
o u t s wa p
of
a p r o c e s s i f m o d i f i e d pag e wr i t i ng ( S t e p 2 ) w i l l
n o t f r e e e n o ug h phys i c a l pag e s .

Mo d i f i ed pag e s
a r e wr i t t e n .
Ev e r y t i me
the
s wa ppe r
is
a wa k e n e d , t h e m o d i f i ed pag e wr i t e r i s c a l l ed .
I f the s i ze o f
th e m o d i f i ed pag e l i s t
exceeds
i ts
uppe r
l im i t
th r e sh o l d
( S C H$G L MFY L IM ) ,
mod i f i ed
pag e s w i l l
b e wr i t t e n un t i l the
s i ze or t h e
l i st
f a l l s b e l o w the
l ow l im i t
thr esho l d
( S C H $G L _M FY L O L IM ) .
Th e r e a r e t i m e s wh e n the swa ppe r wa n t s to
f l ush the en t i r e
m o d i f i ed pag e
l i st .
Th e l og i c o f t h e mod i f i ed pag e wr i t e r
r e qu i r e s t h a t bo th o f t h e s e t h r e sh o l d
pa r ame t e r s b e z e r o ed
for
th i s
to
h a pp e n .
Th e l a s t s te p tha t th e m o d i f i ed pag e
1 4-8

SWAPP I NG
w r i t e r t a k e s b e fo r e e x i t i ng i s to r e s to r e
the
two m od i f i e d
pag e
l i s t t h r e sh o l d s to t h e v a l ue s d e s c r i b e d by t h e SYS B OOT
p a r am e t e r s M PW_H I L I M and MPW L O L I M .
3.

Th e swa ppe r a t t emp t s to i n swa p a p r o c e s s i n the
C OMO s t a t e
(if
one ex i sts ) .
Th i s
a t t e m p t c a n f a i l i f t h e r e a r e no t
e no ug h ph ys i c a l pag e s t o a c c ommo d a t e th e o u t swa ppe d
process
a nd
none o f
th e
r e s i d en t
processes
a r e s u i t a b l e o u t s wa p
c a nd i d a t e s .
Th e fa c t tha t the swa ppe r i s a s e pa r a te p r o c e s s th a t e x e c u t e s
fa i r ly
f r e que n t l y
(at
l e a s t o nc e
a
s e c o nd )
makes
it a
c o nv e n i e n t v e h i c l e fo r t e s t i ng wh e th e r a po we r f a i l
r ec o v e r y
h a s o c c u r r ed
and ,
i f s o , no t i f y i ng a l l p r o c e s s e s th a t h a v e
r e que s t ed powe r
r e co v e r y AST no t i f i c a t i o n
( wi th the
Se t
Powe r f a i l
Re c o v e r y A S T s ys tem s e rv i c e ) .
Th e d e t a i l s o f th i s
d e l i v e r y m e c h a n i sm a r e d e sc r i b ed i n Ch a pt e r 2 3 .
F i n a l l y , t h e swa ppe r p u t s i t s e l f i n to
the h i b e r n a t e
state ,
a f te r
c h e c k i ng
i t s wa k e p e nd i ng f l ag .
I f a n yo n e ( i n c l ud i ng
t h e s wa ppe r i t s e l f i n o n e o f i t s t h r e e m a i n s ub r o u t i n e s )
has
r e q u e s t e d swa ppe r a c t i v i t y s i n c e t h e swa ppe r beg a n e x e c u t i o n ,
t h e h i b e r n a t e i s s k i pped a nd the swa ppe r g o e s b a c k t o S t e p 1 .
Ta b l e 1 4 - 3
Ev e n t s Th a t Ca u s e t h e Swa ppe r o r
Mo d i f i e d Pa g e Wr i t e r t o Be Awa k e n ed
Ev e n t

Mo d u l e

Ad d i t i o n a l Comm en t s

P r o c e s s tha t i s o ut swa pped
b e c omes c omputab l e

RSE

Swa ppe r wi l l a t t empt t o m a k e
th i s process r e s i dent .

Qua n t um End

RSE

Ou t swa p p r ev i o us l y b l oc ked by
i n i t i a l qua n t um f l ag se t t i ng may
now b e po ss i b l e .

CPU T i me Ex p i r a t i o n

RSE

Pr oc e s s may be d e l e t ed , a l l o wi ng
p r ev i o u s l y b l oc ked i n swa p to o c c u r .

Pro c e s s En t e r s Wa i t Sta te

SYSWAIT

Pr o c e s s tha t e n t e r ed wa i t s t a te
may be s u i tab l e o ut swa p c and i d a te .
( Fo r ex ampl e , p r i o r i ty may n o t b e
i m po r ta n t fo r th i s wa i t s t a t e . )

Mod i f i ed Pag e Li s t Exc eed s
Uppe r Li m i t Th r e sho l d

A LLOCPFN

Mo d i f i ed pag e wr i t i ng
by s wa ppe r .

Fr e e Pag e Li s t Dr o ps Be l ow
Lo w L i m i t Th r e sho l d

A L LOC PFN

Swa ppe r Mus t Ba l anc e F r e e Pag e Co un t b y :

i s pe r fo rmed

1 . Wr i t i ng mod i f i ed pag e s

Swa pp i ng h e ad e r s o f p r ev i o us l y
o ut swapped pr o c e s s b od i e s
Swa pp i ng mo r e pr o c e s s e s

Fr e e Pag e L i m i t Exc eed s
H i g h Li m i t Th r e s ho l d

A LLOC PFN

Pr o c e s s tha t co u l d no t b e i n swa pped
d ue to l ac k of phys i c a l pag e s
may n o w f i t .

Ba l anc e S l o t o f De l e ted
Pr o c e s s Becomes Ava i l abl e

SYS DE LPRC

Pr ev i o u s l y b l oc ked i n swa p m a y now
b e po s s i b l e .

P r o c e s s Head e r Re fe r en c e
Co un t Go e s t o Z e ro

PAGEFAULT

P r o c e s s h e ad e r c an now b e o ut swa pped
to j o i n pr ev i o us l y o u t swa pped
p r o c e s s bod y .

Sys t em Ti m e r Sub r o u t i n e
Ex ec u t e s

T IMESCHDL

Th e swa ppe r i s a wa ke n ed ev e r y s ec o nd
to c h e c k i f t h e r e i s a n y wo r k
t o b e d o ne .

1 4-9

SWAPPING
14 . 3

SWAPPER ' S U S E OF M EMORY MANAGEMENT DATA STRUCTURE S

I n Ch a pt e r 1 1 , t h e m em o r y m a n ag em e n t d a ta s t r uc t u r e s tha t a r e used b y
bo th
the
pag e r a nd t h e swa ppe r we r e d e sc r i b ed .
We wi l l r ev i e w tho s e
s t r uc t u r e s h e r e , a nd a d d d e sc r i pt i o n s o f
tho s e
s t r uc t u r e s
tha t a r e
u s ed e x c l u s i v e l y by the s wa ppe r .

14 . 3 . 1

P r o c e s s H e ad e r

Th e b u l k o f i n fo r m a t i o n t h a t the s wa ppe r u s e s i n m a n ag i ng the d e t a i l s
o f e i th e r i n swa p o r o u t s wa p a r e c o n t a i n ed i n the p r o c e s s h e a d e r .
Th e
p r o c e s s pag e ta b l e s c o n t a i n a
c ompl e te d e sc r i pt i o n o f
the
add r e s s
s pa c e f o r a g i v e n p r o c e s s .
Th e wo r k i ng s e t l i s t d e sc r i b e s tho s e PTEs tha t a r e v a l i d .
Th i s l i s t
is
c r u c i a l f o r the swa ppe r b e c a us e i t i s o n l y the p r o c e s s wo r k i ng s e t
tha t wi l l be wr i t t e n t o b ac k i ng s t o r e wh e n th e p r o c e s s i s o u t swa pped .
In a
s i m i l a r f a sh i o n , wh e n i t i s t i m e fo r a p r o c e s s to be i n swa pped ,
t h e wo r k i ng s e t l i s t i n the p r o c e s s h e a d e r i n
the
s wa p
image of
a
p r o c e s s d e sc r i b e s wh a t the r e s t o f the swa p i m a g e l o o k s l i k e .

1 4 . 3 . 1 . 1 Wo r k i ng S e t L i s t - Th e wo r k i ng s e t l i s t d e s c r i b e s the s ub s e t
of
a
p r o c e s s v i r t ua l a d d r e s s s pa c e t h a t m u s t b e wr i t t e n t o t h e swa p
f i l e wh e n t h e p r o c e s s i s o ut s wa pped .
Th e r e a r e f o u r d i f f e r e n t s ta t e s
t h a t a pag e i n t h e p r o c e s s wo r k i ng s e t c an b e i n .
1.

Th e pag e i s v a l i d .

Th e pag e i s i n t r an s i t i o n b u t the PFN S TATE a r r a y
i nd i c a t e s
t h a t t h e pag e i s a c t i v e .
( I f the S K I PW S L pa r am e t e r i s ze r o ,
i t s d e f a ul t v a l u e , t h i s s t a t e c a n n e v e r ex i s t . )

Th e pa g e i s c u r r e n t l y b e i ng r e ad i n to m em o r y .
Th e
swa ppe r
t r e a t s pag e
r e ad s
l i k e a n y o the r
I /O
in
p r og r e s s wh e n
s wa pp i ng
a
process .
Th i s
t r e a tm e n t
is
in
d e sc r i b ed
Se c t ion 1 4 . 4 .

Th e p r o c e s s pag e t a b l e c o n t a i n s a g l o b a l pag e t a b l e i nd e x and
the
i n d e x ed g l o b a l
pag e t a b l e ent r y i nd i c a t e s a t r a n s i t i o n
state .
Th e s wa ppe r h a nd l e s g l o b a l pag e s i n a spec i a l manne r
wh e n o u t swa pp i ng a p r o c e s s .
Th i s t r e a tm e n t i s a l s o d e sc r i b ed
in S e c t i o n 1 4 . 4 .

Th e o pe r a t i o n o f t h e swa ppe r ' s sc a n o f t h e p r oc e s s wo r k i ng s e t l i s t a t
o u t swa p i s d i sc u s s e d i n S e c t i o n 1 4 . 4 .

1 4 . 3 . 1 . 2 P r o c e s s P a g e Ta b l e s - Th e wo r k i ng s e t l i s t d o e s no t s upp l y
the
swa ppe r
wi t h a l l t h e i n f o rm a t i o n n ec e s s a r y to o u t s wa p a p r o c e s s .
O th e r i n fo rma t i o n i s c o n t a i n e d i n e i the r the v a l i d ( o r t r an s i t i o n ) PTE
o r in o n e of the PFN a r r a y e l em e n t s a s s o c i a t ed wi th the ph ys i c a l pa g e .
E a c h wo r k i ng s e t l i s t e n t r y e f fe c t i v e l y po i n t s to a d i f f e r e n t p r o c e s s
pag e t a b l e e n t r y tha t c o n t a i n s a pag e f r am e n umbe r .
Th e
(or
sys tem )
PTE i s c o p i ed to the s wa ppe r • s I /0 m a p a n d then the c o n t e n t s o f the
BAK a r r a y e l em e n t f o r th i s phys i c a l pag e a r e p u t b a c k i n t o the pr o c e s s
PTE .
Th i s e l i m i n a t e s a n y t i e s b e twe e n a n o u t swa pped
p r o c e s s ' s pag e
t a b l e s a nd ph ys i c a l memo r y .
1 4-1 0

SWAPP I NG
1 4 . 3 . 1 . 3 P r o c e s s Hea d e r Pag e A r r ays - Th e b r e a k i ng
of
t i e s b e twe en
p r o c e s s PTEs a nd phys i c a l m emo r y i s s t r a i g h t fo r wa r d f o r p r o c e s s pag e s .
Th e c o n t e n t s o f t h e BAK a r r ay e l em e n t i s s i mpl y m e r g e d i n to
the
PTE .
Howe v e r ,
p r oc e ss
h e a d e r p ag e s a r e a l s o a pa r t o f t h e p r o c e s s wo r k i ng
se t .
Th e s e pag e s r e s i d e i n s ys tem s pa c e a nd a r e m a pped by s ys t em pag e
tab l e
entr ies
tha t m a p t h e b a l a n c e s l o t i n wh i c h t h e p r o c e s s h e ad e r
r es i d es .
Th e r e l i n q u i sh i ng o f the b a l anc e s l o t i mpl i e s th a t
these
S PTEs m us t
a l s o b e s u r r e nd e r ed .
Th e r e i s no a n a l og o u s wa y t o s to r e the BAK a r r a y
c o n t e n t s fo r p r o c e s s h e ad e r pag e s .
Th i s i s wh y
the
process header
pag e
a r r a ys
( Fi g u r e 1 1 -8 ) ex i s t i n t h e process head e r .
Th e r e e x i s t s
a n a r r a y e l em e n t fo r e a c h pag e i n t h e p r o c e s s h e ad e r .
Wh e n a p r o c e s s
i s o u t swa pped , tho s e p r o c e s s h e ad e r pag e s c u r r e n t l y i n t h e wo r k i ng s e t
h a v e th e i r BAK ad d r es s e s p u t i n to t h e c o r r e s pond i ng a r r a y e l em e n t s
in
the
p r o c e s s h e a d e r pag e B AK a r r a y .
Wh e n the p r o c e s s i s swa pped bac k
i n to memo r y , t h e p r o c e s s h e ad e r pag e s c a n
be
s c anned
a nd
the
BAK
c o n t e n t s c o p i ed
f r om
th e a r r a y b a c k i n to the PFN BAK a r r a y e l emen t s
fo r t h e phys i c a l pag e s t h a t c o n t a i n the p r o c e s s h e a d e r .
I n a s i m i l a r m a nn e r , i t i s n e c e s s a r y to r emem b e r
wh e r e
each process
head e r
pag e
f i ts
i n to t h e wo r k i ng s e t .
Th i s i s d o n e b y s to r i ng the
WS LX PFN a r r a y e l em e n t i n t o the c o r r e s po nd i ng p r o c e s s h e a d e r pag e WS LX
a r r a y e l eme n t .
Th e
use
of
th i s a r r a y wh i l e t h e p r o c e s s h e a d e r i s
b e i ng r eb u i l t fo l l o w i ng i n s wa p p r ev e n t s a p r o h i b i t i v e l y l o ng s e a r c h o f
t h e wo r k i ng s e t l i s t f o r e a c h p r o c e s s h e ad e r pag e .

14. 3 . 2

Swa ppe r I /O Da t a S t r uc t u r e s

L i ke t h e pag e r , t h e swa ppe r u s e s the c o nv e n t i o n a l VM S
I /0
s ub s ys tem .
I t a l locates
i t s o wn
I /0
r e q ue s t pa c k e t a n d f i l l s i n some o f the
f i e l d s t h a t wi l l b e
i nte r p r e ted
in a
s pe c i a l
manner
by the
I /0
po s t p r o c e s s i ng
rout ine .
Af t e r
t h e s e f i e l d s h a v e b e e n f i l l ed i n , i t
j umps to o n e o f t h e swa ppe r
I / 0 e n t r y po i n ts
i n mod u l e
SYS Q I ORE Q
( E XE $ B LD PKTSWPR o r
E XE $ B LDPKTSWPW )
th a t
fills
in
a n a pp r o p r i a t e
f unc t i o n c od e a nd q u e ue s t h e p a c k e t to the
a pp r o p r i a t e d i s k d r i v e r .
Tab l e 1 2 - 1 sh ows h o w t h e I /0 r e qu e s t pac k e t i s u s ed by t h e swa pp e r fo r
i t s I /0 a c t i v i t i e s .
Two o th e r s t r uc t u r e s a r e u s ed by t h e swa ppe r .
Th e r e i s a
swa p
file
t ab l e e n t r y f o r
each
swap
f i l e i n the s ys t em .
Th e s wa ppe r u s e s a
s pe c i a l I /0 a r r a y t h a t a l l o ws i t to r e ad o r wr i t e
a
p r o c e s s wo r k i ng
set ,
a c o l l ec t i o n o f v i r t u a l l y d i s c o n t i g uo u s pag e s , i n o n e o r a sma l l
n umb e r o f I /0 r e q u e s t s .

1 4 . 3 . 2 . 1 Swa p F i l e Ta b l e En t r i e s - F i g u r e 1 1 - 2 2 sh ows t h e l a yo u t o f a
swa p
file
t a b l e e n t r y , t h e s t r uc t u r e t h a t a l l o ws t h e swa p f i l e to be
l oca ted on d i sk .
No t i c e t h a t t h e w i ndow c o n t r o l
b l o c k po i n t e r
a nd
v i r tua l
b l o c k n um b e r
f i eld
a r e l o c a ted a t th e s a m e o f f s e t s i n swa p
f i l e t ab l e entr i e s , page f i l e c o nt r o l b l o c k s , and
p r o c e s s o r g l oba l
sec t i on
tab l e
entr ies .
Th i s a l l o ws t h e s e d a t a s t r uc t u r e s to b e used
by c o mmon r o ut i n e s t h a t need no t d i s t i ng u i sh t h e
t ype o f s t r uc t u r e
b e i ng u s ed to d e sc r i b e a m emo r y m a n ag em e n t I /0 r e qu e s t .

1 4-1 1

SWA P P ING
14 . 3 . 2 . 1 . 1
Swap F i l e I n i t i a l i z a t i o n - Wh e n the s ys t em i s i n i t i a l i z ed ,
the
S Y S I N I T p r o c e s s i n i t i a l i z e s t h e s wa p f i l e SWAPF I L E . SYS .
Th e s i z e
o f t h e swa p f i l e i s d i v i d ed b y t h e m a x i m um po s s i b l e wo r k i ng
set s i ze
( g o v e r n ed
b y SYSB OOT p a r am e t e r WSMAX ) to y i e l d t h e n um b e r o f s l o t s i n
the f i l e .
( Th e s l o t s a r e a l l t h e s a m e
s i ze ,
e a c h s l o t c a pa b l e o f
h o l d i ng WSMAX n um b e r o f pag e s . )
Th e n um b e r o f ava i l a b l e s l o t s c a n a l s o c a us e
the m a x i m um n um b e r
of
processes
that the
s ys t em c a n s uppo r t t o d ec r e a s e .
Th e s wa p s l o t
c o u n t ( p l u s two t o a c c o u n t f o r t h e two p r o c e s s e s ,
N U L L a nd
SWA P PE R ,
that d o
n o t swa p )
i s c ompa r ed to MAXPROC E S SCNT a nd the sm a l l e r i s
c ho s e n a s t h e a c t ua l m a x i m um n um b e r o f p r o c e s s e s th a t t h e s ys t em w i l l
s uppo r t .
I f a s e c o nd s wa p f i l e i s i n s t a l l ed ( w i t h t h e SYSGEN I N S TA L L c omm and ) ,
i ts
S F TE
is
i n i t i a l i zed .
I t i s a l s o pa r t i t i o ned i n to swa p s l o t s o f
e q ua l s i z e ( s t i l l WSMAX pag e s ) .
Th e ad d i t i o n a l n um b e r
of
s l o t s c an
i nc r e a s e
t h e max i m um n umbe r o f p r o c e s s e s t h a t c a n e x i s t i n the s y s tem
( b u t n e v e r m o re than t h e i n i t i a l v a l u e of MAXPROC E S SCNT ) .
N O TE
A s l i g h t c h a ng e to
th i s
a l g o r i thm h a s
been
pa t c h ed
i n to
VM S
w i th
the
Th i s c h a ng e
Ve r s i o n 2 . 2 b i n a r y upd a t e .
r em o v e s t h e r e s t r i c t i o n o f 2 5 8 p r o c e s s e s
Th e d e ta i l s o f
t h a t p r e v i o u s l y e x i s t ed .
t h i s c h a n g e a r e d e sc r i b ed i n Appe nd i x F .

1 4 . 3 . 2 . 1 . 2 A l l o c a t i o n o f Swap S l o t s - Th e i nd i c a t i o n o f wh i c h S FTE to
use
i s c o n t a i n ed i n the so f t wa r e PC B i n f i e l d PC B $ L WS SWP .
Th e uppe r
b y t e i s a l o ng wo r d i nd e x i n to the a r r a y o f po i n t e r s ( F i g u r e 1 1 - 2 2 )
to
S F TEs
a nd page f i l e c o n t r o l b l o c k s .
Wh e n a pr o c e s s i s f i r s t c r e a t ed ,
t h i s f i e l d i s c l e a r , wh i c h i mpl i e s v i r t ua l b l o c k z e r o
in
s wa p f i l e
z e r o , the She l l process .
Wh e n a p r o c e s s i s s e l e c ted f o r o u t s wa p f o r the f i r s t t i m e , a swa p s l o t
is
a l l o c a ted
fo r
it.
Th e
swa p f i l e n umbe r a nd t h e v i r t ua l b l o c k
n umbe r o f t h e beg i nn i ng o f t h e s l o t a r e r ec o r d e d
in
the
PC B .
Th i s
s wa p s l o t
r ema i n s
a l l o c a ted
to
th i s
process
fo r t h e l i f e o f the
proc e s s .

14 . 3. 2 . 2
Swappe r PTE A r r a y - Th e n e ed f o r the swa ppe r PTE a r r a y tha t
a l l o ws
it
to
wr i t e pag e s
tha t
a r e v i r t ua l l y d i s c o n t i g uo u s i n the
c o n t e x t o f the p r o c e s s b e i ng
s wa pped wa s d e sc r i b ed
i n Ch a pt e r 1 1 .
Th i s a r r a y c o n ta i n s WSMAX l o ngwo r d s a nd i s used fo r bo th o u t s wa p a nd
i n swa p o pe r a t i o ns .
At o u t s wa p , the PFN o f e a c h pag e t h a t wi l l be wr i t t e n to the swa p f i l e
is
l o ad ed
i n to
the
a r r ay .
Th i s a r r a y i s t h e n pa s s e d o n to the I /0
s y s t em to p e r f o rm t h e w r i t e .
At
i n swa p ,
the
swa ppe r
a l l oc a tes a
n umbe r o f PFNs to ho l d t h e p r o c e s s a nd r e a d s the swa p i m ag e i n to th e s e
pag e s .
E a c h PFN i s t h e n pl a c ed i n to t h e a pp r o p r i a t e pag e ta b l e a s the
wo r k i ng s e t l i st a nd p r o c e s s pag e t a b l e s a r e r e b u i l t .

1 4-1 2

SWAPPING
14. 4

OUTSWAP OPERATI ON

O u t sw a p i s d e sc r i b ed b e f o r e i n swa p b ec a u s e i t
is
i ns wa p i n t e rm s o f wh a t
the
s wa ppe r p u t i n to
s wa ppe r
does
not
r emove
processes
f r om
P r o c e s s e s a r e o n l y r emoved i f
i nd i sc r i m i n a t e l y .
phys i c a l pag e s by a h i g h e r p r i o r i t y p r o c e s s .

14. 4 . 1

eas i e r
to
e x pl a i n
the swa p f i l e .
Th e
the
bal ance
set
the r e i s a n e e d f o r

S e l e c t i on o f O u t swap Cand i d a t e

As we m e n t i o ne d i n S e c t i o n 1 4 . 2 , t h e o u tswa p se l ec t i o n
is d r iven by
t ab l es
tha t c o n t a i n a we i g h t fo r e a c h r e s i d e n t s c hed u l i ng s t a t e .
Th e
s wa ppe r s e l e c t s t h e p r o c e s s tha t i t j ud g e s w i l l b e ne f i t the l e a s t f r om
r em a 1 n 1 ng
i n m em o r y .
On c e a c and i d a t e
is
s e l ec te d , t h e swa ppe r
p r epa r e s the wo r k i ng s e t o f tha t p r o c e s s f o r o u t s wa p .

14. 4 . 2

Outswa p o f the P r o c e s s Bo d y

Th e swa ppe r o u t s wa ps t h e p r o c e s s b o d y ( P O
a nd
P l pag e s )
s e pa r a t e l y
f r om t h e p r o c e s s h e a d e r .
Th e r e a r e two r e a s o n s fo r d o i ng th i s .
•

F i e l d s i n t h e p r o c e s s h e a d e r ( mo s t no t a b l y wo r k i ng
s et
l ist
entr i es
and
p r o c e s s pag e t a b l e e n t r i e s ) a r e m o d i f i ed a s t h e
wo r k i ng s e t l i s t i s p r o c e s s ed :

•

Th e p r o c e s s h e a d e r m a y n o t b e swa ppa b l e a t th i s • t i m e d ue
to
o u t s t a nd i ng
I /0 ,
pag e s o n
the m o d i f i ed pag e l i s t , o r s o m e
o th e r r e a s o n .

14. 4 . 2. 1
S c a n n i ng th e Wo r k i ng S e t L i s t - Th e p r o c e s s body i s p r e pa r ed
fo r
o u t s wa p by
s c ann i ng
t h e wo r k i ng
set l i st .
E a c h pag e i n t h e
wo r k i ng s e t l i s t m u s t b e l o o k e d a t to d e t e rm i n e i f a n y s pe c i a l
ac t i on
is
r eq u i r ed .
Th e
s wa ppe r
l ooks
a t a c om b i n a t i o n o f the pag e t ype
( f o und in t h e wo r k i ng set l i s t e n t r y as we l l a s the
PFN TYPE a r r a y )
a nd t h e v a l i d b i t .
Ta b l e 1 4 - 4 l i s t s a l l c om b i n a t i o n s o f pag e t ype a nd
v a l i d b i t s e t t i ng tha t t h e swa ppe r e nc o un t e r s a nd the a c t i o n
tha t
it
t a k e s fo r e a c h .
Seve r a l c a s e s a r e d i s c u s s e d f u r the r he r e .
Th e b a s i c s t ep tha t the swa ppe r m u s t t a k e a s i t s c a n s t h e wo r k i ng
set
l i st
i s t o move e ac h s wa ppa b l e pag e i n to t h e s wa ppe r ' s I /O ma p .
Th i s
c a u s e s the v i r t u a l l y d i s c o n t i g uo u s pag e s i n the p r o c e s s ' s wo r k i ng
set
to
a ppe a r
v i r t ua l l y c o n t i g uo u s
t o t h e I /0 s y s t em ( F i g u r e s 1 4 - 3 a n d
1 4-6)
Th e s t e p s tha t the swa ppe r t a k e s f o r e a c h pag e a r e t o
•

l o c a t e t h e pag e t a b l e e n t r y f r om
the
f i e l d i n t h e wo r k i ng s e t l i s t e n t r y ,

d e t e rm i n e a n y s p e c i a l ac t i o n b a s ed o n pag e v a l i d i ty a nd
t yp e ,

m o v e the PFN f r om th e pag e t a b l e e n t r y to the s wa ppe r m a p ,

r e c o r d t h e mod i f y b i t ( l o g i c a l OR o f PTE mod i f y b i t and
PFN
STATE a r r a y s av e d mod i f y b i t ) i n the wo r k i ng s e t l i s t e n t r y ,
and
1 4-1 3

v i r t ua l

pag e

n umbe r
pag e

SWAPP ING
5.

s e t th e De l e t e Co n t e n t s b i t i n the PFN S TATE a r r a y e l em e n t .
Th i s w i l l c a u s e t h e pag e to be p l a c ed a t the h e a d o f the f r e e
p a g e l i s t wh e n i t s r e f e r e n c e c o un t g o e s t o z e r o
( wh i c h
in
n o r m a l c i r c um s t a n c e s wi l l be wh e n the s wa p w r i t e c o m pl e t e s ) .

No t e t h a t t h e swa ppe r d o e s no t h av e t o e x pl i c i t l y p u t the c o n t e n t s o f
Th a t h a pp e n s n a t u r a l l y wh e n the pa g e
the PFN BAK a r r a y i n t o e a c h PTE .
i s r e l e a s e d { a f t e r t h e s wa p wr i t e c om p l e t e s a nd a l l o th e r
r e f e r enc e s
t o the pag e a r e e l i m i n a t ed ) .

1 4 . 4 . 2 . 2 Pag e s w i t h D i r e c t I/0 i n P r og r e s s - I f a { mo d i f i ed ) pa g e h a s
o u t s t a nd i ng
I /0 wh i l e
t h e p r o c e s s i s b e i ng o u t swa pped , t h e swa ppe r
t a k e s n o t e o f t h i s by l o ad i ng t h e SWPVBN PFN a r r ay e l em e n t wi th
th e
v i r t ua l
b l o c k n umbe r i n the s wa p f i l e wh e r e t h e pag e i s b e i ng wr i t t e n
to .
Th e pag e i s n ev e r th e l e s s s wa pped a t th i s t i m e to r e s e r v e a p l a c e
fo r i t i n t h e swa p f i l e .
I f the I /0 o pe r a t i o n i s a r e a d { o r i t i s a w r i te a nd some o th e r a c t i o n
h a s c a us ed the pag e t o b e mo d i f i ed ) , t h e phys i c a l pag e wi l l b e p l a c ed
o n t h e mo d i f i ed pag e
l i s t wh en
the
I / 0 c ompl e te s .
{ Th i s o c c u r s
b e c a u s e MMG $ R E L PFN , t h e r o u t i n e tha t r e l e a s e s t h e pag e , p u t s pag e s o n
t h e m od i f i ed pag e l i s t i f e i th e r t h e m o d i f y b i t i n t h e PFN S TATE a r r a y
i s s e t o r i f the PFN SWPVB N a r r a y h a s n o n z e r o c o n te n t s . )
Th e mod i f i ed pag e wr i te r t a k e s s pe c i a l a c t i o n f o r mod i f i ed pag e s w i th
n o n z e r o c o n t e n t s in t h e SWPVBN a r r a y .
Th a t i s , i t wr i t e s each pag e t o
the d e s i g na t ed b l o c k i n t h e
swa p f i l e
r a th e r
than
to
i t s n o rma l
ba c k i ng s t o r e a d d r e s s .
I f the I /0 o pe r a t i o n i s a wr i te { f r om memo r y to m a s s s t o r ag e ) and
the
pag e wa s n o t o th e r w i s e m od i f i e d , t h e c on t e n t s t h a t a r e c u r r e n t l y b e i ng
wr i t t en to the s wa p f i l e a r e g o od .
Th e pag e wi l l
be
pl a c ed
on
the
f r e e l i s t wh e n the wr i t e c ompl e t e s .

1 4 . 4 . 2 . 3 G l o ba l Pag e s - G l o ba l pag e s a r e a l s o g i ven spec i a l t r e a tmen t
a t o u t s wa p .
If
t h e g l o b a l pag e i s wr i t a b l e , i t i s d r o pped f r om the
p r oc e s s wo r k i ng set b e fo r e the p r o c e s s i s s wa pped to d i s k .
Th e
task
o f r e c o rd i ng wh e the r t h e c o n t e n t s t h a t a r e swapped a r e u p to d a t e wh e n
the p r o c e s s i s b r o ug h t bac k
i n to m em o r y
i s m o r e c ompl i c a t ed
than
s i mpl y
r e f a u l t i ng
t h e pag e
( o f t e n w i tho u t I /0 ) wh e n the p r o c e s s i s
swa pped bac k i n to memo r y .
G l o b a l r e ad - o n l y pag e s a r e o n l y s wa pped i f t h e g l oba l sha r e c o un t { PFN
S HRCNT a r r a y )
i s o ne .
I n a l l o th e r c a s e s , t h e pa g e is d r o ppe d f r om
the wo r k i ng s e t a nd m u s t be r e f a u l ted { mo s t l i k e l y w i tho u t
I /0 )
wh e n
the
process
is
i n swa ppe d .
(Gl obal
pag e s
tha t a r e e x pl i c i t l y o r
i m pl i c i t l y l o c k e d i n to the p r o c e s s wo r k i ng s e t a r e no t d r o pped
f r om
th e wo r k i ng
se t . )
G l o ba l t r a n s i t i o n pag e s a r e a l s o d r o pped f r om the
p r o c e s s wo r k i ng s e t .

1 4-1 4

SWAPPING
14. 4.2.4
E x ampl e o f P r o c e s s Bod y O u t swap - F i g u r e s 1 4 - 2 t h r o ug h
1 4-4
s h o w s om e o f t h e s pe c i a l c a s e s e nc o un t e r ed b y t h e swa ppe r wh i l e i t i s
s c a n n i ng t h e p r o c e s s wo r k i ng s e t l i s t .
As m e n t i o n e d
i n c onnec t i o n
wi t h Tab l e 1 4 - 4 , t h e k e y i n f o r m a t i o n abo u t e a c h pag e i s a c om b i n a t i o n
o f t h e PTE va l i d b i t a nd t h e phy s i c a l pag e t ype .
Th e
o rd e r
of
the
sc an
i s d e te rm i ned
b y t h e o rd e r d e f i n ed b y the wo r k i ng s e t l i s t .
F i g u r e 1 4 - 2 s h ows t h e p r o c e s s wo r k i ng s e t , t h e p r o c e s s pag e
tabl e s ,
a nd the a s s o c i a t ed PFN d a t a b a s e e n t r i e s b e fo r e t h e swa ppe r beg i n s i t s
wo r k i ng s e t s c a n .
F i g u r e 1 4 - 3 s h ows t h e m od i f i ed wo r k i ng s e t a nd
the
swa ppe r m a p a f t e r t h e wo r k i ng s e t l i s t sc an b u t b e fo r e t h e I /0 r e qu e s t
i s i n i t i a t ed .
F i g u r e 1 4 - 4 s hows t h e s ta t e o f t h e pag e
tab l e entr i e s
a fter
the
s wa p wr i t e h a s c omp l e te d and the ph ys i c a l pag e s h a v e b e e n
r e l e a sed .
1.

Th e f i r s t wo r k i ng s e t l i s t e n t r y i s a g l o b a l r e a d - o n l y pag e .
Th e
VPN f i e l d o f t h e wo r k i ng s e t l i s t e n t r y l o c a t e s t h e pag e
table entry .
Th e PFN f i e l d o f t h e PTE l o c a t e s t h e
PFN d a t a
a s s o c i a t ed w i t h
th i s
phys i c a l
pag e .
In
pa r t i c u l a r , t h e
( Th i s
p r oc e s s
is
g l o b a l s h a r e c o un t f o r th i s pag e i s o n e .
the
o n l y p r o c e s s tha t c u r r e n t l y h a s th i s pag e i n i t s wo r k i ng
s e t . ) Th e swa ppe r wi l l wr i te th i s pag e o u t a s p a r t o f
the
s wa p
i m ag e
f o r th i s p r o c e s s .
Th u s , P F N A i s t h e f i r s t pag e
i n t h e swa ppe r ' s PTE a r r a y ( F i g u r e 1 4 - 3 ) .
Wh e n t h e swa ppe r ' s wr i t e o pe r a t i o n com p l e t e s , t h e
pag e
wi l l
b e d e l e te d .
Th a t i s , t h e PTE a r r ay e l emen t w i l l be c l e a r ed
a nd t h e pag e w i l l be p l a c ed a t t h e head o f t h e f r e e pag e l i s t
( Fi g u r e 14-4) .

The s e c ond wo r k i ng s e t l i s t e n t r y i s a p r o c e s s pag e tha t a l s o
h a s I /0 i n p r o g r e s s ( R E FCNT
2) .
Th i s pag e wi l l be swa pped .
Th i s i s i l l u s t r a ted by t h e i nc l u s i o n o f PFN C i n t h e
s wa ppe r
map .
=

I f t h e pag e wa s p r ev i o u s l y mod i f i ed ( e i the r PTE m o d i f y b i t o r
s a v e d mod i f y b i t i n S TATE a r r a y was s e t ) , t h e v i r t ua l b l o c k
n um b e r i n th e s wa p f i l e w i l l b e l o ad ed i n to t h e SWPVBN a r r a y .
Th i s w i l l f o r c e t h e pag e to t h e m od i f i ed pag e l i s t wh e n i t i s
r e l e a s ed .
I f the p r oc e ss i s s t i l l
o u t s wa pped b y t h e
t i me
tha t
t h e m o d i f i ed
pag e w r i te r g e ts a r o und to wr i t i ng th i s
p ag e , t h e pag e w i l l be wr i t t e n t o the b l o c k r e se r v ed
fo r
it
wh e n t h e p r o c e s s i s f i r s t o u t swa pped .
Th a t i s , wh e n
the
r e f e r en c e
Th e p a g e i s m a r k e d f o r d e l e t e .
c o un t f o r
t h e pag e r e a c h e s z e r o ( d ue t o c ompl e t i o n o f bo th
the o u t s ta n d i ng I/0 and the swa ppe r ' s wr i t e ) ,
the
pag e
is
p l aced
at
t h e h ea d o f t h e f r e e pag e l i s t a nd i t s PTE a r r a y
e l em e n t c l e a r e d .
3.

T h e t h i r d wo r k i ng s e t l i s t e n t r y i s a g l o b a l r e ad/wr i t e pa g e .
Th e
pa g e
is
d r o pped
f r om
the p r o c e s s
wo r k i ng
set
( Fi g u r e 1 4 - 3 ) .
Th i s m e a n s tha t t h e p r o c e s s pag e t a b l e
entry
is
r e pl a c ed
w i th a g l ob a l
p a g e ta b l e i nd e x ( th a t l o c a t e s
g l oba l pag e t a b l e e n t r y R ) a nd t h e sha r e c o un t fo r
PFN B
is
d e c r emen ted .
No t i c e tha t PFN B i s no t a pa r t o f t h e s wa ppe r
m a p , wh i c h c o n t a i n s a l i s t o f t h e phys i c a l pag e s t h a t w i l l b e
w r i t t e n t o t h e s wa p f i l e .

Th e l a s t wo r k i ng s e t
p a g e w i t h no t h i ng
t h e s wa ppe r m a p ( P FN
Th e d e l e t i o n w i l l
o pe r a t i o n c o mpl e t e s .

l i s t e n t r y i n th i s e x am p l e i s a
process
s pe c i a l abo u t i t .
Th i s pa g e i s a d d ed t o
D ) a nd i t s c o n t e n t s m a r k e d
fo r d e l e te .
a c t ua l l y o c c u r wh en th e swa ppe r ' s wr i t e
1 4 -1 5

SWA P P I NG
Ta b l e 1 4 -4
S c a n o f Wo r k i ng Se t L i s t o n Ou t swa p
Th e sc a n o f the wo r k i ng s e t l i s t o n o u t swa p i s k e yed o f f a
phys i c a l pag e type ( WS L < 3 : 1 > ) and the v a l i d b i t ( PT E < 3 1 > ) .

Type o f Pag e

Va l i d

P r o c e s s Pag e

Tr a n s i t i o n

comb i n a t i o n

t he

Ac t i o n o f Swa ppe r fo r Th i s Pag e
a.

( S TATE = Re a d i n Prog r e s s )
Tr e a t a s pag e wi th I /O i n prog r e s s .
Sp e c i a l ac t i o n m a y be t a k e n at i n swa p
o r by mod i f i ed pag e wr i te r .

( S TATE = Ac t i v e )
Ou t s wa p b u t s e t Go odpag e b i t i n WSLE .
Pag e wi l l be put b a c k i n to ac t i v e
t r a n s i t i o n s ta te a t i n swa p t i me .

( S TATE = Re a d Er r o r )
DR OP f r om wo r k i ng se t .

d . No o th e r t r a n s i t i o n s t a t e s a r e po s s i b l e
fo r a pag e i n the wo r k i ng se t .

Pro c e s s Pag e

Va l i d

Out swa p pag e .
I f the r e i s o u t s t a nd i ng I /0 and
t h e pag e is mod i f i ed , l o ad SWPVBN a r r a y
e l em e n t wi th b l o c k i n swa p f i l e wh e r e
t h e upd a ted pag e c o n t e n t s sho u l d b e
wr i t ten wh e n the I /0 com pl e t e s .

Sys t em Pa g e

G l ob a l Read On l y

G l ob a l Re ad On l y

6 . G l ob a l Re ad /Wr i te

Pa g e Ta b l e Pa g e

Impo s s i b l e fo r sys tem pag e to be i n
p r o c e s s wo r k i ng s e t . Swa ppe r g en e r a te s
an e r ro r .
Trans i t i on

Va l i d

I f the pr o c e ss pag e tab l e e n t r y
s t i l l conta i n s a PFN , th i s i s a n ac t i v e
t r an s i t i o n pag e . Ou t s wa p t h e pag e b u t
s e t the Go od pag e b i t i n t h e WSLE .

If t h e pr o c e s s pag e tab l e e n t r y c o nta i n s
a g l obal pag e ta b l e i nd ex , t he n the
g l obal pag e tab l e m u s t c o n t a i n a
t r a n s i t i o n PTE . The pag e i s d ro pped
f r om the pro c e s s wo r k i ng se t .

I f S HRCNT = 1 ,

I f S HRCNT > 1 , DRO P f r om wo r k i ng se t .
I t i s h i g h l y l i ke l y tha t pr o c e s s c a n faul t
pag e l a t e r w i tho u t I /0 . Th i s c h e c k avo i d s
m u l t i pl e c o p i e s o f s a m e pag e i n swa p f i l e .

t h e n o ut s wa p .

DR OP f rom wo r k i ng se t . I t i s ex t r emel y
d i f f i c ul t to d e t e r m i n e wh e th e r pag e i n
memo ry wa s m od i f i ed a f t e r th i s c o py wa s
wr i t ten to the swa p f i l e .
No t pa r t o f proc e s s bod y . Ho we v e r , wh i l e
s c a n n i ng pro c e s s b od y , VPN f i e l d i n WSL
i s mod i f i ed to r e f l ec t o f f s e t f rom beg i nn i ng
p r o c e s s h e ad e r b e c a us e pag e ta b l e pag es wi l l
p r o b ab l y b e l o c a te d a t d i f f e r en t v i r t ua l
a d d r e s s e s fo l l ow i ng i n swa p .

1 4-1 6

Process Header for
swapped process

WSLX

Fix ed Portion
Working Set List
vpn
y
GRO w s le 1
vpn
PPG wsle 2
z
vpn w
GRW w s l e 3
vpn
X
PPG w s l e 4

A
B
c

wsle 2

wsle 4

PTE

BAK

gpte R

gstx

gpte a

gstx

pte Z

pgflx

pte X

pstx

Proce s s Section
Table. etc.

TYPE

STATE

� IGR o l l
� I I l
� I I I
� I I

other
s H RC N T : 1

GRW

sHRCNT :

PPG

REFCNT =

PPG

PFN D a t a b a s e A r r a y s

PO P a g e T a b l e

pte W

vpn W
....

�
I
....

-...J

vpn X

pte X

vpn Y

pte Y

global p a g e t a b l e

gpte a

SWP$GL -MAP

Swapper's
1 / 0 Map

1:J

gpte R

vpn Z
P 1 Page Table

F i g u r e 1 4 -2

E x amp l e Wo r k i ng Se t L i s t Be fo r e O u t s wa p S c a n

til

�

ttl
ttl

H
2:
C)

Process Header for
swapped process
A

Fixed Portion
Working Set List
y

vpn
vpn
... ·

vpn

wsle 2

PPG

.
.•·

wsle 1

GAO
.

wsle 3

. •

.
· ·. ·.. ·

wsle 4

PPG

W S LX

PTE

gpte 0

gstx

gpte

BAK

w s le 2

pte Z

pgflx

wsle 4

pte X

pstx

Process Sec t ion
Table. etc.

S T A TE

TY PE

other

I
B l cRo l I
B I l I �H�QNT: = ff I
2
I
B [§] I
B I I
SHRCNT = 1

GRw

REFCNT =

PPG

P F N D a t a b a se A r r a y s

PO Page Table
vpn W

0
.

�J>t:x JAJ

· ·.. •

pte W

vpn X

pfn D

pte X

vpn Y

pfn A

pte Y

g l o b a l p a g e t a b le

gpte a

gpte R
vpn Z

pfn C

v a li d , pfn A
�---�

SWP$GL-MAP "

=j:J

S w a p p er's
1/0 M a p

v alid, pfn B
�---�

pte z

P 1 Page Table

Fi g ure 1 4 -3

E x amp l e Wo r k i ng Set L i s t Af t e r O u t s wa p Sc a n

C/l

�

.,
.,

1-t

z
Cl

Process Header for
swapped process
A

Fixed Portion
Working Set List
vpn
vpn
vpn

GRO

w sle 1

PPG

w sle 4

PPG

wsle 2

wsle 3

S LX

I BUNK

PTE

BAK

gpte a

gstx

gpte

wsle 2

pte Z

BLINK

Process Section
Table. etc.

pgflx

STATE

TYPE

other

[�r&�'l 1 GRo I ($,�'�"� +'o�l
B I GRW I I SHRCNT 3 1
B I I l �t.,�. Cf.lt==· tl
ltreeJ �
=

PPG

PFN D a tabase Arrays

PO Page Table
vpn W

gptx (R)

pte W

vpn X

pstx

pte X

vpn Y

9PJl!. (0)

pte Y

vpn Z

pfn C

g l o b a l page ta ble

gpte a

trans, pfn A

gpte R

v a li d , p f n B
�---�

SWP$GL - MA P

"==i:]

S w a pp e r' s
1/0 Map

pte Z

P 1 Page Table

Figure 1 4-4

P r o c e s s Pag e Ta b l e Ch a ng e s Af t e r Swa ppe r ' s
Wr i t e Compl e t e s

SWAPP I NG
14 . 4. 3

O u t swap o f P r oc e s s He a d e r

Th e p r o c e s s h e a d e r i s n o t o u t swa pped un t i l a f t e r t h e p r o c e s s bod y h a s
b e e n s uc c e s s f u l l y w r i t t e n t o t h e swa p f i l e .
Th e r ea so n f o r th i s
i l l us t r a t e s two o th e r c a s e s
th a t c a n
keep the process head e r
in
m em o r y .
B e fo r e t h e p r o c e s s h e a d e r c a n b e o u t s wa pped , a l l t i e s t o
ph ys i c a l m em o r y tha t e x i s t i n t h e p r o c e s s pag e t a b l e s m u s t b e s ev e r ed .
Th i s
i nc l ud e s n o t o n l y tho s e pag e s t h a t we r e i n t h e p r o c e s s wo r k i ng
s e t a nd wr i t te n to the s wa p f i l e b u t a l so tho s e pag e s th a t a r e i n som e
t rans i t i o n
s ta t e ,
m o s t n o t a b l y p a g e s o n t h e f r e e a nd mod i f i ed pag e
l i s ts .

14. 4. 3. 1
P a r t i a l Outswa p - Af t e r
the
p rocess
body
has
been
o u t swa pped , t h e p r o c e s s h e ad e r b e c om e s e l i g i b l e f o r o u t s wa p .
I n fac t ,
t h e h e a d e r o f a n o u t s wa pped
process
is
the
f i r s t th i ng
th a t t h e
s wa ppe r l o o k s f o r i n a n a t tempt t o b a l a n c e t h e f r e e pag e l i s t .
Th e i nd i c a t i o n tha t t h e p r o c e s s h e ad e r c an n o t
be o u t s wa pped y e t
is
f o und
in
the
p r oc e s s
h e ad e r
v e c to r
r e f e r e nc e c o un t a r r a y
( Fi g u r e 1 1-2 1 ) .
Th i s a r r a y c o un t s t h e n um b e r o f
r easons
( trans i t i o n
pag e s ,
a c t i v e pag e
t a b l e pag e s , a nd s o o n ) t h a t p r ev e n t the p r o c e s s
h e a d e r f r om be i ng o u ts wa pped .
B e c a u s e t h e o u t swa p o f t h e h e ad e r d o e s n o t h a v e t o i mmed i a t e l y f o l l o w
th e b o d y o u t swa p , i t i s po s s i b l e ( ev e n p r o b ab l e ) th a t a p r o c e s s h e a d e r
wi l l no t b e swa pped i n t h e
t i m e b e twe en wh e n a
process body i s
o u t swa pped
a nd wh e n tha t p r o c e s s i s b r o ug h t b a c k i n to memo r y .
Such a
s i t ua t i o n i s r e f e r r e d to a s a pa r t i a l
o u t s wa p .
I t h a s a n o bv i o u s
c o u n t e r pa r t ,
a
pa r t i a l
i n swa p ,
wh e r e t h e swa ppe r d o e s no t h av e t o
a l l o c a t e a b a l a nc e s l o t a nd
b r i ng
t h e p r o c e s s h e ad e r
i n to m emo r y
b e c a u se t h e h e a d e r i s a l r e a d y r e s i d e n t .
An i mpo r ta n t sys t e m m a n ag em e n t po i n t
is
i l l us t r a t ed
he re .
Process
bod i es ,
wh i c h c o n s um e phys i c a l memo r y , a r e r e l a t i v e l y e a s y t o r em o v e
f r om memo r y .
P r o c e s s h e ad e r s c o n s um e a
sma l l e r
amo un t o f phys i c a l
memo r y b u t
t h e y a l so o c c upy a b a l a n c e s l o t .
Th e b a l a n c e s l o t i s n o t
f r e e d f o r o th e r u s e u n t i l the e n t i r e h e a d e r
i s o u t s wapped .
If
the
S Y S BOOT p a r am e t e r
BALS ETC NT
i s se t to t o o sma l l a v a l ue , the sys t e m
c a n r e a c h t h e un fo r t un a t e
s t a t e wh e r e
the r e
i s mo r e
than
eno ug h
phys i c a l m em o r y b u t c om p u ta b l e p r o c e s s e s c a nno t be b r o ug h t i n to memo r y
b e c a u s e the
bal ance
s l o ts
a re
sti l l
t i ed
t o a l r e ad y o u t swa ppe d
processes .
Th i s s i t ua t i o n c a n be a v o i d ed by s e t t i ng BALS ETCNT to a n
ad e q u a t e v a l u e .

1 4 . 4 . 3 . 2 S c a n n i ng t h e F r e e Pag e L i s t - Wh e n t h e
swa ppe r
loc a te s
a
p r o c e s s h e ad e r
tha t c a n
be r emoved f r om i t s b a l a n c e s l o t , i t t a ke s
wh a t eve r a c t i o n s a r e r e qu i r e d t o r emove the t i e s th a t b i nd the p r o c e s s
head e r
to
phys i c a l
m em o r y .
Th e f i r s t s uch s t e p i s t o e l i m i n a t e a n y
t r a n s i t i o n PTEs wh e r e t h e phys i c a l pag e i s o n t h e f r e e pag e l i s t .
Th i s i s a c c ompl i s hed by s c a n n i ng t h e e n t i r e f r e e pag e l i s t a nd l o o k i ng
f o r pag e s wh o s e PTE a r r a y c o n t e n t s l i e wi t h i n t h e PO o r Pl pa g e ta b l e s
o f the p r o c e s s h e ad e r b e i ng e x am i n ed .
Wh e n e v e r s uch a pag e i s
fo und ,
the process
PTE
is
r eset
to
the c o n t e n t s o f t h e BAK a r r a y , the
r e f e r e n c e c o un t a nd PTE a r r ay e l em e n t s a r e c l e a r ed , a nd
the pag e
is
moved f r om i t s c u r r e n t l o c a t i o n to the h e a d o f t h e f r e e pag e l i s t .

1 4-20

SWAPP ING
14. 4.3.3
Fl ush i ng t h e Mo d i f i ed Pag e L i s t - Be c a us e t h e f r e e pag e l i s t
i s o n l y o n e o f s e v e r a l t r an s i t i o n s ta t e s , t h e s c a n o f t h e f r e e pag e
l i s t m a y n o t f r e e t h e p r o c e s s h e a d e r f o r r em o va l .
Pag e s m a y b e
1n
some o th e r
t r a n s i t i o n s ta t e .
T r a n s i t i o n s ta t e s t h a t r e p r e s e n t s o m e
f o rm o f I /O i n p r og r e s s ( r e l e a s e pend i ng , r e ad i n p r og r e s s ,
wr i t e
in
p r og r e s s ) a r e l e f t a l o n e b e c a u s e the r e i s n o th i ng th a t the s wa ppe r c a n
d o u n t i l t h e I /0 c ompl e t e s .
Howe v e r , t h e m od i f i e d pag e
l i s t c a n b e m a n i pu l a t e d .
Th e d e s i r ed
e f fec t
is
r em o v a l o f a l l pag e s f r om t h e m o d i f i ed pag e l i s t .
Th i s i s
t r i g g e r e d by s e t t i ng t o z e r o bo th t h e l o we r a nd uppe r l i m i t th r e s h o l d s
fo r
t h e m od i f i ed p a g e l i s t .
C l e a r i ng the uppe r l i m i t g ua r a n t e e s tha t
a nonempty l i s t h a s e x c e ed ed i t s th r e sho l d , i n i t i a t i ng a r e q u e s t
fo r
mod i f i ed
pag e w r i t i ng .
C l e a r i ng th e l owe r l i m i t c a u s e s mod i f i e d pag e
wr i t i ng to c o n t i n ue un t i l t h e l i s t
is
empty
( be l ow the
l ow l im i t
t h r e sh o l d ) .

14. 4. 3.4
Out swa p o f t h e P r o c e s s Head e r - O n c e the r e f e r e n c e c o u n t f o r
the
p r o c e s s h e a d e r r e a c h e s z e r o , t h e h e ad e r c a n b e o u t swa pped and t h e
b a l a nc e s l o t f r e ed .
Th e o u t s wa p o f t h e
process head e r
is
en t i r e l y
a n a l og o us t o t h e o u t swa p o f a p r o c e s s b od y .
Th a t i s , the h e a d e r pag e s
tha t a r e n o t pag e t a b l e pag e s a nd the
a c t i v e pag e
t a b l e pag e s a r e
sc a n n ed
a nd
put
i n to
the
s wa ppe r ' s
PTE a r r a y t o fo rm a v i r t u a l l y
c o n t i g uo u s b l o c k f o r the I /0 s y s t em .
Th e r e a r e s e v e r a l d i f f e r e n c e s b e twe e n the o u t swa p o f a pr o c e s s h e a d e r
a nd
a
process
body .
Wh e n a p r o c e s s b o d y i s o u t s wa pped , t h e h e a d e r
tha t m a ps tha t b o d y i s
still
r e s i d en t .
Wh en
the
swa ppe r ' s wr i t e
c ompl e t e s
a nd
e a c h phys i c a l pag e i s d e l e t ed , t h e c o n t e n t s o f t h e BAK
a r r a y e l em e n t f o r e a c h pag e a r e put b a c k i n to the p r o c e s s PT E .
P r o c e s s h e a d e r pag e s a r e m a pped by s ys tem pag e t a b l e e n t r i e s f o r
tha t
bal ance
slot .
Th e
S PT E s
a r e not
a v a i l a b l e to ho l d th e BAK a r r a y
c o n te n t s b e c a u s e the y w i l l b e
u s ed
b y t h e n e x t o c c upa n t o f
th i s
One o f the p r o c e s s h e ad e r pag e a r r a ys ( Ch a p t e r 1 1 ) i s
bal ance
slot .
set aside
fo r
exac tl y th i s
p u r po s e .
As
the
p r o c e s s h e ad e r
is
p r o c e s sed
fo r
o u t s wa p , t h e c o n t e n t s o f t h e BAK a r r a y fo r e a c h a c t i v e
h e a d e r pag e a r e s to r ed i n the c o r r e s po nd i ng p r o c e s s h e ad e r pag e
a r ra y
e l em e n t .
At t h e s ame t i m e , t h e l o c a t i o n o f e a c h h e a d e r pag e wi th i n th e
wo r k i ng
set
l i st
is
s to r ed
in
t h e WS LX a r r a y .
Th i s a r r a y p r ev e n t s a
p r o h i b i t i v e l y l o ng s e a r c h to
r eb u i l d
the
p r o c e s s h e ad e r
wh e n
the
p r o c e s s i s swa pped b a c k i n to m emo r y .
On c e t h e h e ad e r i s s uc c e s s f u l l y o u t swa pped , the h e a d e r
r e s i d en t b i t
( PC B $ V P HDRE S ) i n th e PC B i s c l e a r ed a nd t h e b a l a n c e s l o t i s ava i l ab l e
fo r f urth e r u s e .

14. 5

INSWAP OPERAT I ON

The i n s wa p i s e x a c t l y the oppo s i t e o f
t h e o u t s wa p o pe r a t i o n .
Th e
s wa ppe r
b r i ng s
the p r o c e s s h e a d e r , i n c l ud i ng a c t i v e pag e t a b l e s , a n d
t h e p r o c e s s b o d y b a c k i n to phys i c a l m emo r y .
I t then u s e s t h e c o n t e n t s
of
t h e wo r k i ng
set
l i st
to r eb u i l d t h e p r o c e s s pa g e ta b l e s , wh i c h
mo s t l y m e a n s upd a t i ng e a c h v a l i d PTE t o r e f l ec t the PFN th a t c o n t a i n s
it.
At
the s a m e t i me tha t e a c h pag e i s b e i ng p r o c e s s e d , t h e s wa ppe r
1 4-21

SWAPPING
c a n r e so l v e a n y s pe c i a l
o u t swa pped .

cases

tha t

ex i s ted

wh e n

the

proc e s s

wa s

S e l ec t i o n o f a n I n swa p C a n d i d a te

14. 5. 1

As m e n t i o ne d e a r l i e r i n t h e c h a p t e r , t h e s wa ppe r s e l e c t s a p r o c e s s fo r
i n swa p e x a c t l y l i k e t h e s c h ed ul e r s e l e c t s a c a nd i d a t e fo r e x ec u t i o n .
Po t e n t i a l c a n d i d a te s fo r i n swa p m a y b e
•
•
•

n ewl y c r e a t ed p r o c e s s e s ,
p r o c e s s e s i n s o m e o u t swa pped wa i t s ta t e t h a t we r e
c omp u t a b l e , o r

m ad e

p r o c e s s e s t h a t we r e o u t s wa pped wh i l e i n th e compu t a b l e s t a t e .

Th e h i g h e s t p r i o r i ty p r o c e s s i n t h i s co l l e c t i o n i s
for i n s wa p .

14. 5. 2

j us t

the

one

s e l e c ted

I n swa p o f t h e P r o c e s s Head e r

I f t h e p r oc e s s h e a d e r wa s o u t s wa pped wh e n t h e bod y wa s o u t s wa pped ,
it
m u s t b e b ro ug h t b ac k
i n to m emo r y b e fo r e t h e p r o c e s s bod y c a n b e
r e con s t r uc t ed .
Un l i ke t h e s p e c i a l o pe r a t i o n s tha t too k p l a c e wh e n t h e
process
wa s o u t s wa ppe d , a n o u t s wa pped p r o c e s s h e a d e r m e r e l y ad d s two
d e ta i l s to t h e i n s wa p o pe r a t i o n .
1.

I f t h e h e ad e r i s r e s i d e n t , t h e n um b e r o f
f r om
t h e s i z e o f t h e o u t s wa p
s ub t r a c t e d
the h e a d e r
wh e th e r
is
is,
file.
Th a t
d e t e rm i n e s t h e to t a l n um b e r o f b l oc k s tha t
t h e swa p f i l e a nd t h e v i r t ua l b l oc k n umbe r
s h o u l d b eg i n .

I f the h e a d e r wa s swa pped , t h o s e p r o c e s s pa r am e t e r s t h a t
are
t i ed
to
a
spec i f i c
b a l a nc e s l o t ( th a t i s , s pec i f i c s y s t em
v i r t ua l o r phys i c a l a d d r e s s e s ) m u s t b e a d j us ted
to
r e f l ec t
the new l o c a t i ons
i n v i r t ua l
o r phys i c a l add r e s s s p a c e .
Th e s e i n c l ud e t h e fo l l o w i ng .
•
•

•

h e a d e r pag e s
is
i m a g e i n the s wa p
r e s i dent or
no t
m u s t b e r e ad f r om
wh e r e
the
r e ad

Obv i o u s l y , e a ch S PTE m u s t b e l o a d ed
w i th
the
PFN
c o n ta i n s t h e c o n t e n ts o f e a c h p r o c e s s h e a d e r pag e .

tha t

Th e v i r t u a l a d d r e s s e s o f t h e P O and P l pag e
tab l es m u s t
b e c a l c u l a t ed
a nd
l o ad ed
i n to
the i r l o c a t i o n s i n the
h a r d wa r e PCB .
Th e
phys i c a l
add ress o f
t h e h a r d wa r e
PC B m u s t
be
l o a d ed
and
c a l c u l a ted
i n to
t h e so f t wa r e PC B ( i n f i e l d
PC B $ L_P H Y PCB ) .
F i n a l l y , t h e P l pag e s t h a t d o ub l e m a p the p r o c e s s h e a d e r
pag e s
t h a t a r e n o t pag e t a b l e pag e s m u s t b e l o a d ed w i th
t h e new pag e f r am e n umbe r s tha t c o n t a i n t h e s e pag es .

14-22

SWAPPING

1 4 . 5 . 2 . 1 Reb u i l d i ng t h e P r o c e s s He a d e r - Wh e n a
p r o c e s s h e ad e r
is
r e ad
f r om
t h e s wa p i m ag e i n t o a n ew b a l a n c e s l o t , t h e S PTEs t h a t m a p
e ac h b a l a n c e s l o t pag e m u s t b e l o ad ed w i t h t h e PFNs f r om t h e
s wa ppe r
m a p t h a t c o n t a i n e a c h h e ad e r pag e .
I n ad d i t i o n , t h e PFN d a t a b a s e
m us t b e s e t u p fo r e a c h o f t h e s e phys i c a l pag e s .
Th e swa ppe r d o e s a l l
th i s wo r k i n a v e r y s i mpl e l o o p t h a t i t e x e c u t e s f o r e a c h h e a d e r pag e .
Th e s i mpl i c i t y ( a nd s pe ed ) o f th e l o o p r e s u l t s f r om th e u s e o f the two
process head e r
pag e
a r r a ys tha t ex i s t i n t h e p r oc e s s h e ad e r .
Th e s e
a r r a y s a l l o w t h e PFN BAK a nd WS LX a r r a ys
to be l oaded wi th
t he i r
p r ev i o u s c o n t e n t s ( b e c a u s e t h e two h e a d e r a r r a y s we r e l o ad ed wh e n the
p r o c e s s wa s o u t swa pped ) .

1 4 . 5 . 2 . 2 P 1 W i nd ow t o t h e P r o c e s s He a d e r - A l l o f the p r o c e s s h e a d e r
pag e s e x c e p t p r o c e s s pag e t ab l e s a r e d o ub l e ma pped w i th a r a ng e o f P l
add r e ss e s .
Th i s i s d o n e fo r t h e f o l l o w i ng
r eason .
Wh e n a
process
h ead e r
is
o u t s wa pped a nd s ub s e q ue n t l y i n swa pped , i t p r o b ab l y r e s i d e s
i n a d i f f e r e n t b a l ance s l o t .
Any r o u t i n e
that
s to r e s
tha t
process
h e a d e r a d d r e s s i n a r eg i s t e r a nd t h e n r e f e r e n c e s h e ad e r l o c a t i o n s w i th
a d i s p l a c e m e n t f r om th i s r eg i s t e r m i g h t b e r e f e r e nc i ng t h e h e ad e r
of
a no t h e r
p r oc e s s
if
some
s c h ed u l i ng
a nd
swa pp i ng o c c u r r e d b e twe e n
o b t a i n i ng t h e h e a d e r b a s e ad d r e s s a nd l a t e r r e f e r e nc e s .
To avo i d t h i s p r o b l em , a r a ng e o f P l s pa c e i s s e t up by t h e s wa ppe r to
map
these
s am e h e ad e r p ag e s .
Th e P1 pag e s a r e m a pped in s uc h a wa y
tha t ,
even
if
a n o u t s wa p a nd
l a te r
i n swa p o c c u r
b e t we e n
two
i ns t r uc t i o n s ,
t h e P 1 v i r t ua l a d d r e s s e s o f the p r o c e s s h e ad e r pag e s d o
n o t c ha ng e .
Th e c o n v e n t i o n s tha t VM S o b s e r v e s a b o u t h e a d e r r e f e r e n c e s
a re these .
•

•
•

An y r e f e r e n c e to t h e p r o c e s s h e a d e r sho u l d u s e t h e P l a d d r e s s
( C T L $ G L PHD c o n t e n t s po i n t
to
the
Pl map of the process
h e ad e r ) �
Any r e f e r e n c e to t h e s y s t e m s p a c e h e a d e r
I P L 7 ( I PL $ _S YN C H ) t o p r e v e n t a swa p .

m us t

ex ec ute

An y r e f e r e n c e t o p r o c e s s pag e t a b l e s m u s t ex ec u t e
at
b e c a us e t h e pag e t a b l e pag e s a r e n o t d o ub l e mapped .

I PL 7

Th e r e a r e two i mp l i c a t i o n s f o r VM S h e r e .
•

•

Th e s e ph ys i c a l pag e s a r e n o t k e pt t r ac k o f i n a n y wa y t h r o ug h
r e f e r e n c e c o un t s
or
a n y o th e r t e c h n i qu e .
Howe v e r , a l l o f
t h e s e h e ad e r pag e s a r e a
pe r m a n e n t pa r t o f
the
process
wo r k i ng s e t .
Th e P l pag e t a b l e pag e t h a t m a ps t h e s e pag e s m u s t a l so
p e r m a n e n t memb e r o f t h e p r o c e s s wo r k i ng s e t .

1 4-23

SWA P P I NG
14. 5. 3

Re b u i l d i ng t h e P r o c e s s Bo d y

Th e pr o c e s s h e ad e r m u s t b e p u t i n to a kn own s t a t e b e f o r e t h e p r o c e s s
b o d y c a n b e p u t bac k i n t o t h e a pp r o x i m a t e sh a pe i t wa s i n b e f o r e t h e
p r o c e s s wa s o u t swa ppe d .
I f t h e h e a d e r wa s n e v e r o u t swapped , t h e r e
is
v e r y l i t tl e
that has t o be done .
I f the h e a d e r wa s o u t swa pped , t h e
s t e ps j u s t d e sc r i b ed a r e t a k e n t o p u t t h e p r o c e s s h e a d e r ba c k tog e th e r
ag a i n .

1 4 . 5 . 3 . 1 Re b u i l d i ng t h e Wo r k i ng S e t L i s t a nd P r o c e s s Pag e Tab l e s 
Th e
r e b u i l d i ng o f t h e p r o c e s s b o d y i nvo l v e s a s i mpl e s c a n o f bo th t h e
swa ppe r m a p a nd the p r o c e s s wo r k i ng s e t l i s t .
Re c a l l tha t a t o u t s wa p ,
t h e k e y to e a c h s pe c i a l c a s e wa s t h e c om b i n a t i o n o f phys i c a l pag e t yp e
a nd t h e s e t t i ng o f th e v a l i d b i t i n t h e pag e t a b l e e n t r y .
On
i n swa p ,
the
k e y t o e a c h s p e c i a l c a s e i s t h e c o n t e n t s o f t h e pag e t a b l e e n t r y
l o c a t ed b y t h e v i r t ua l pag e n um b e r
f ield
i n t h e wo r k i ng
set l is t
ent r y .
An a pp r o x i ma t i o n o f
s wa ppe r
a c t i v i t y f o r e a c h pag e i s a s
fo l l o ws .
1.

Th e pag e t a b l e e n t r y i s l o c a t ed f r om t h e
WSLE .

VPN

f i eld

the

I n the u s ua l c a s e , t h e o r i g i na l c o n t e n t s o f t h e PTE a r e
put
i nto
t h e P F N B AK a r r a y a nd t h e P F N f r om th e swa ppe r m a p i s
l o ad ed i n t o t h e n o w v a l i d PTE .

I f f o r s o m e r e a s o n a c o py o f
the
pag e a l r e a d y e x i s t s
in
memo r y ,
t h e n t h a t pag e i s p u t i n to t h e p r o c e s s wo r k i ng s e t
a nd t h e d u pl i c a t e pag e f r om t h e swa ppe r m a p
is
rel eased
to
t h e f r o n t o f t h e f r e e pag e l i s t .

Tab l e 1 4 - 5 c o n t a i n s a d e t a i l ed l i s t o f t h e d i f f e r e n t c a s e s
tha t
the
swa ppe r
c a n e n c o un te r wh e n r e b u i l d i ng the p r o c e s s pag e t a b l e s .
Th r e e
o f t h e c a s e s d e s e r v e s p e c i a l c ommen t .

14. 5 . 3 . 2
Pag e s wi t h I / O i n P r og r e s s Wh e n O u t swa p Oc c u r r ed
Pag e s
tha t h a d I /0 i n p r og r e s s wh en t h e p r o c e s s wa s o u t swa pped we r e wr i t t e n
t o t h e swa p f i l e a n ywa y t o r e s e r v e s pa c e .
I f t h e pag e wa s p r ev i o u s l y
unm o d i f i ed , t h e n i t wo u l d b e p u t o n to the f r e e pag e l i s t wh en bo th t h e
s wa p wr i te a nd t h e o u t s t a nd i ng w r i t e o pe r a t i o n c ompl e t ed .
I f the pag e
wa s
p r ev i o u s l y mo d i f i ed , t h e n i t wo u l d be p u t o n to t h e m o d i f i ed pag e
l i s t wh e n b o th t h e swa p w r i t e
a nd
t h e o u t s t a nd i ng
wr i t e o pe r a t i o n
c om p l e ted ( b e c a u s e t h e c o n t e n t s o f t h e SWPVBN a r r a y we r e n o n z e r o )
-

•

I n e i th e r c a s e , i t i s po s s i b l e f o r the p r o c e s s to be swa pped
bac k
in
b e f o r e o n e o f t h e s e phys i c a l pag e s wa s r e u s e d .
Th e swa ppe r us e s th e
phys i c a l p a g e tha t i s a l r e ad y c o n t a i ned
in
the process
PTE
( as
a
t ra ns i t i on
pag e )
and
r el eases
t h e d upl i c a t e ph ys i c a l pag e f r om th e
swa ppe r m a p to t h e f r o n t o f t h e f r e e pag e l i s t .
I n t h e c a s e o f a pag e o n t h e f r e e pag e l i s t , t h i s d e c i s i o n
i s s impl y
o �e o f c o nv e n i e n c e .
I n t h e c a s e o f a pag e o n t h e mod i f i ed pag e l i s t ,
t h e c o n t e n t s o f the pag e i n t h e swa p i m ag e a r e o u t o f d a t e a nd
th e
swa ppe r h a s no cho i c e b u t to u s e the phys i c a l pag e tha t i s a l r e a d y i n
m em o r y .

14-24

SWAPP ING
Ta b l e 1 4 - 5
Re b u i l d i ng the Wo r k i ng Se t L i s t and t h e
P r o c e s s Pa g e Ta b l e s a t I n swa p

At i nswap t ime , the swapper uses the contents o f the page tab l e entry to
d eterm i n e wha t a c t i o n to take fo r each pa r ti c ul ar pag e .
Type o f Pag e Tab l e Entry
1 . PTE i s v a l id
2.

Ac t ion o f Swa ppe r fo r Th i s Pag e
Pag e i s l oc ked i n to memo r y and
wa s never o utswapped .

PTE i nd i cates a tran s i t io n pag e
{ probabl y d ue to outstand i ng I/0
when proc e ss wa s o utswapped )

Fa ul t tran s i t i o n pag e into proc ess
wo r k i ng set . Re l ease d upl i c a te pag e
tha t wa s j ust swapped i n .

PTE conta ins a g lobal pag e
tab l e i nd ex ( G PTX)

Swa ppe r ac t i o n i s based o n the contents
o f the g l obal pag e tab l e entry ( G PTE )

( Pag e must b e g lobal
r ead -onl y because g lobal
read/wr i te pag e s we re
d ropped from the wo r k i ng set
a t outswap t ime . )

a . I f the g lobal pag e tabl e entry i s val id ,
add the PFN i n the GPTE to the process wo r k i ng
set and rel ease the d upl i c a te pag e .
b . I f the g lobal pag e tabl e entry i nd icates a
transi tion pag e , make the g lobal pag e tabl e
e n t ry val id , add tha t phys i c a l pag e to the
process wo r k i ng se t , and rel ease the d upl i c a t e
pag e .
c . I f the g lobal pag e tabl e entry i nd icates a
g lobal sec t i o n tabl e i nd ex , then keep the
pag e j ust swapped i n , and make that the maste r
pag e in the g lobal pag e tab l e entry as we l l a s
t h e s l ave pag e in t h e process pag e tabl e en tr y .

PTE cont a i n s a pag e f i l e i nd ex
o r a process sect i o n tab l e i nd ex

Th i s i s the usual contents fo r pag es
tha t d id not have o utstand i ng I /0 or
o ther pag e r e fe renc es when the
process wa s o ut swapped .
The PFN i n the swappe r map i s i ns e r ted
i n to the proc ess p�g e tab l e . The PFN
a r r ays a r e i n i t i a l i zed fo r that pag e .

1 4 . 5 . 3 . 3 Reso l ut i o n o f G l oba l Re a d -On l y Pag e s - Th e
only
po s s i b l e
g l obal
pag e t h a t c o u l d b e i n t h e s wa p f i l e i s a g l o b a l r e ad - o n l y pag e
t h a t h a d a sh a r e c o un t o f o n e wh e n the p r o c e s s wa s o u t s wa pped
(or
a
pag e t h a t wa s e x p l i c i t l y l o c k e d ) .
Al l o th e r g l o b a l pag e s we r e d r o pped
f r om the p r o c e s s wo r k i ng s e t b e f o r e t h e p r o c e s s wa s o u t s wa pped .
Th e r e a r e
t wo d i f f e r e n t c a s e s
tha t
the
swa ppe r
wi l l
f i nd
wh e n
r eb u i l d i ng
t h e p r o c e s s pa g e t a b l e s .
In e i th e r c a s e , t h e p r o c e s s pag e
t a b l e e n t r y c o n t a i n s a g l o b a l pag e
table
i nd e x
so
the
d e t e rm i n i ng
f a c t o r i s t h e c o n t e n t s o f the g l ob a l pag e t ab l e e n t r y .
1.

Th e g l ob a l p a g e t a b l e e n t r y c o n t a i n s a g l o b a l
sec t i o n
tab l e
i nd e x .
I n t h i s c a s e , t h e phys i c a l pag e f r om t h e swa ppe r m a p
i s a d d ed t o t h e g l oba l
page
t a b l e e n t r y a s we l l
as
the
p r o c e s s pag e t a b l e en t r y .

I t i s po s s i b l e t h a t t h e g l ob a l pag e wa s
r e f e r e n c ed b y s o m e
o th e r p r o c e s s wh i l e
t h i s p r o c e s s wa s o u t swa pped .
I n tha t
c a s e , th e g l o b a l pag e t a b l e e n t r y m i g h t c o n t a i n a
t r an s i t i on
o r v a l i d PTE .
I n e i th e r c a s e · , t h e PFN th a t i s a l r e a d y i n t h e
g l obal pag e
tabl e entry
i s kept .
(If
t h e G PTE
is
in
t r an s i t i on ,
it
i s m a d e v a l i d . ) Th e d upl i c a t e PFN f r om t h e
swa ppe r m a p i s r e l e a s e d t o t h e f r o n t o f t h e f r e e pag e l i s t .

14-25

SWAPP I NG
1 4 . 5 . 3 . 4 Ac t i ve T r a ns i t i o n Pages - O n e o th e r
f o rm o f PTE d e s e rv e s
no t e .
Rec a l l
f r om
Ch a p t e r 1 2
that
it
is
po s s i b l e t o mod i fy t h e
wo r k i ng s e t l i s t s c a n by s e t t i ng the s pe c i a l S Y S B OO T pa r am e t e r S K I PWS L
Th e m od i f i ed s c a n o f t h e wo r k i ng s e t l i s t t u r n s o f f t h e
to
nonz e r o .
v a l i d b i t f o r pag e s o n i t s f i r s t pa s s , l e a v i ng the pag e s i n the a c t i v e
t r a n s i t i on state .
Th e s wa ppe r s i g n a l s s uc h pag e s wh e n a p r o c e s s i s o u t swa pped by s e t t i ng
i n th e WSLE f o r the a c t i v e t r a n s i t i o n pag e s .
a bit
( WS L $V G OO D PAG E )
Wh e n s uc h pag es a r e e nc o u n te r ed
a s pa r t o f
the
i n s wa p l o o p ,
th e
swa ppe r t r e a t s them e x a c t l y l i k e v a l i d pag e s e x c e p t tha t the v a l i d b i t
i n t h e PTE i s n ev e r t u r n e d o n .
I n th i s
wa y ,
t h e o cc u r r en c e o f a n
o u t s wa p d o es n o t
i n t e r f e r e i n a n y wa y w i th t h e m o d i f i ed s c a n o f t h e
( I f S K I PW S L i s s e t to z e r o , i t s d e fa u l t v a l u e , s uc h
wo r k i ng s e t l i s t .
a c t i ve t r a n s i t i o n pag e s c a n n ev e r e x i s t . )

14. 5. 3. 5
Ex ampl e o f a n I n swap O pe r a t i o n - To i l l us t r a t e a t l ea s t s o m e
of
the
s pe c i a l c a s e s th a t t h e swa ppe r e n c o un t e r s wh e n a p r o c e s s bod y
i s s wa pped bac k i nto memo r y ,
Figures 1 4-5
t h r o ug h
1 4-7 conta i n an
e x ampl e o f a n i n swa p o pe r a t i o n .
No t e tha t t h i s e x ampl e i s no t r e l a te d
to the o u t s wa p e x am p l e
u s ed
b e fo r e
( Fi g u r e s 14-2
to
1 4-4 ) .
Th i s
e x am p l e
is
t a i l o r ed
to i l l u s t r a te the i n t e r e s t i ng c a s e s the swa ppe r
c a n e nc o un te r d u r i ng a n i ns wa p o pe r a t i o n .
F i g u r e 1 4 - 5 s hows th e s ta t e o f the p r o c e s s h e ad e r a f t e r
the p r o c e s s
h a s b e e n s e l e c ted a s a n i n swa p c a nd i d a t e .
F i g u r e 1 4 - 6 s hows th a t f o u r
phy s i c a l pag e s h a v e b e e n a l l o c a t ed to c o n t a i n t h e f o u r wo r k i ng pag e s
tha t the e x ampl e i s d e sc r i b i ng .
F i g u r e 1 4 - 7 s h o ws the r e b u i l t p r o c e s s
pag e t ab l e s a nd t h e P F N d a t a b a s e c h a ng e s tha t r e s u l t f r om
r e b u i l d i ng
th e wo r k i ng s e t a nd p r o c e s s p a g e t a b l e s .
1.

Th e
f i r s t wo r k i ng
set l i st
e n t r y l o c a t e s v i r t ua l
pag e
Th i s PTE c o n ta i n s a g l o b a l pag e tab l e i nd e x .
Th e
n um b e r X .
r e f e r e nc ed g l o b a l pag e t a b l e e n t r y ( G PTE T ) c o n ta i n s a g l oba l
s e c t i on
table
i nd e x ,
i nd i c a t i ng th a t th e g l o b a l pag e ta b l e
entry i s no t val i d .
Th e pag e f r am e n um b e r ( PFN D ) i s put i n to
the p r o c e s s pag e
tabl e .
It
i s a l so
a d d ed
to the g l o b a l pag e d a ta b a s e b y
m a k i ng t h e G PTE v a l i d ( F i g u r e 1 4 - 7 ) , p u t t i ng PFN D
i n to
the
G PTE ,
a nd
upd a t i ng
the P F N d a t a
fo r
phys i c a l pa g e D t o
r e f l ec t i t s new s t a t e .

Th e nex t wo r k i ng s e t l i s t e n t r y i s a p r o c e s s pag e m a pped by
PTE W
( Fi g u r e 1 4-6 ) .
Th i s PTE c o n ta i n s a p r o c e s s s e c t i o n
t a b l e i nd e x .
Th e PT E i s u pd a t ed t o c o n t a i n PFN C a nd
the
PSTX i s
s t o r ed
in
the BAK a r r a y e l emen t f o r th a t pag e
( Fi gu r e 1 4 - 7 ) .
O t h e r PFN a r r ay s a r e u pd a ted a c c o r d i ng l y .

Th e n e x t wo r k i ng s e t l i s t e n t r y
( th a t l o c a t e s
PTE Y )
is
e x a c t l y l i ke
the
f i rst ,
a s f a r a s the process d a ta i s
conce rned .
Howe v e r , t h e g l o b a l pag e t a b l e e n t r y ( G PTE S )
is
val id ,
i nd i c a t i ng
t h a t a no th e r
c o py o f th i s pag e a l r e a d y
ex i sts .
( Th i s c o ul d o n l y h a v e h a pp e n e d
i f ano the r
process
f a u l t ed t h e pa g e wh i l e th i s p r o c e s s wa s o u t swa pped . )
Th e d up l i c a te pag e ( PFN E ) i s r e l e a s e d to the
f r o n t o f the
f ree l i st .
Th e
p r o c e s s pag e
t ab l e e n t r y i s upd a t ed to
c o n t a i n th e phys i c a l pag e tha t a l r e a d y e x i s t s ( PFN B) and th e
s h a r e c o un t
fo r
t h a t pag e
is
i nc r em e n ted ( f r om th r e e to
fou r )
14-26
•

SWAPPING
4.

Th e f o u r th wo r k i ng s e t l i s t e n t r y l o o k s j us t l i k e the s e c o nd .
Howev e r ,
th e p r o c e s s pa g e t a b l e e n t r y i nd i c a t e s a t r a n s i t i o n
pag e .
( Th i s i mp l i e s th a t the h e ad e r
in
th i s
e x am p l e wa s
n ev e r o u t swa pped . )
Th e a c t i o n t a k e n h e r e i s s i m i l a r to s t e p 3 , wh e r e a d up l i c a t e
g loba l
pag e
wa s d i sc o v e r ed .
Th e pag e j us t r e a d ( PFN F ) i s
r e l e a s ed t o th e h e a d o f the f r e e l i s t .
Th e
t r a n s i t i o n pag e
( PFN A )
is
f a ul ted
back
i n to
the p r o c e s s wo r k i ng s e t by
r em o v i ng t h e pag e f r om the f r e e l i s t , s e t t i ng
i ts
s ta te
to
a c t i v e , and t u r n i ng the v a l i d b i t i n th e PTE b a c k o n .

14. 5. 3. 6
F i n a l P r o c e s s i ng o f t h e I n swa p Ope r a t i o n - A f t e r the wo r k i ng
s e t l i st h a s b een
s c anned a nd the p r o c e s s pag e ta b l e s r eb u i l t , the
p r o c e s s i s r ead y t o h av e
i ts
s t a t e c h a ng ed
f r om c om pu ta b l e but
o u t swa pped
to c om p u t a b l e
a nd
r e s i d ent .
Seve r a l
o th e r s c h e d u l i ng
d e ta i l s m u s t be t a k e n c a r e o f b e fo r e the s c h ed u l e r i s no t i f i ed .
1.

A n ew v a l u e o f A S T LVL
i s c a l c u l a t ed
and
l o ad ed
i n to
the
h a r d wa r e
PC B
in
the
process header .
ASTs may have b e e n
e n q u e ue d
to
the p r o c e s s
wh i l e
i t wa s o u t s wa pped .
The
h a rdwa r e
PC B ,
wh i c h c o n t a i n s a c o py o f the A S T LVL r eg i s t e r ,
wa s no t a v a i l a b l e wh i l e the h e ad e r wa s n o t r e s i d e n t .

Th e r e s i d e n t b i t a n d the i n i t i a l q u a n t um b i t
l o ngwo r d i n th e so f twa r e PC B a r e s e t .

A n e w q u a n t um i n t e r v a l i s l o ad ed i n to the p r o c e s s h e ad e r .

Finally ,
the
c om p u t a b l e .

sc h ed u l e r

1 4-27

c a l l ed

make

the

s t a t us

process

Process Header for
swapped process
Fixed Portion
Working Set List

wsle 1

wsle 2

wsle 3

wsle 4
Proc ess S e c t i o n
Table. etc.

[

I
cl
ol

WSLX
BLINK

PTE

pgflx

gpte s

gstx

BLINK

•

STATE

BAK

pte Z

P F N D a t a b a s e A rr a y s

TY PE

o t her

G Ro

S HRC N T = 3

� D
B I l I
� D
� D

•

PO Page Table
vpn W

....
�
I
1\.)
co

pte W

vpn X

gpte S

vpn Y

g l o b a l page t a b l e

S W P $ G L- M A P

"�

S w a pp e r' s
1/0 Map

gpte T

v pn

Figure 14-5

Wo r k i ng Se t L i s t a nd Swa ppe r Ma p Be fo r e Ph ys i c a l Pag e Al l o c a t i o n

Process Header for
swapped process
Fixed Portion
Working Set List
vpn X
G R O wsle 1
vpn w
PPG wsle 2
vpn y
G R O wsle 3
vpn z
PPG wsle 4
Table. et c .

vpn W

PO Page Table
pstx

vpn X

gptx (T)

pte X

gptx ( S )

pte Y

pfn A
P 1 Page Table

pte Z

vpn Y
vpn Z

Figure 1 4-6

pte W

PTE
pte Z

A I BLINK
W S LX

gpte S

gpte T

gpte S

0
0

gstx

ST A TE TYPE
I free f D

valid, pfn

B
�---�

other

� I G R ot lsH R CNT :;: 31
D
D
D
D

PFN Database A rr a y s

global page table
gstx

pgflx
BAK

SWP$G L_MAP "

Swapper's
1/0 Map

l':J

�---�

Wo r k i ng Se t L i s t a nd Swa ppe r Ma p Af t e r Ph ys i c a l Pag e A l l o c a t i o n

Process Header tor
swapped process

W S LX

Fixed Portion
Working Set List
vpn
vpn
�·
vpn
vpn

I-"
�
I
w
0

GRO
GRO

PPG

wsle 3
wsle 4

c
0
E

PO P a g e Table

pfn C

vpn X

pfn 0

vpn Z

wsle 2

Process Section
Table. etc.

vpn W

vpn Y

wsle 1

1 ..

p fn B

pte W

.·.

pfn A

pt e Y

BAK
pgflx

gpte s

gstx

w sle 4 I I
I I
I I
I I
2
I I e¥� w I I
I I gpt'J I I
I I 0 I I
BLINK
I I
I I
w sle

BUNK

p${�
gst.x

STATE

TY PE

tr��t I

IPRG]
B IGRol

global page t able

gpte S

v a l i d , pfn B
�---�

gpte T

�------�--����

SWP$GL-MAP

''=i:]

S w a p pe r s
1/0 Map
'

pte Z

P 1 Page Table

F i g u r e 1 4 -7

other

B I PPG)
B lGRo J lsHRCNT : 1 1
l rree l D
ltr�e l D

P F N D a t a b a se A rr a y s

pte X

�

PTE

pte z

Wo r k i ng S e t L i s t a nd Re b u i l t Pa g e Ta b l e s

PART V

I N PUT/O UTPUT

De l a y no t C a e s a r . Re ad i t i n s t a n t l y .
J u l i u s Ca e s a r

III , l

He r e i s a l e t t e r , r e ad i t a t yo u r l e i s u r e .
Me r c h a n t o f Ve n i c e

V, l

CHAPTER 1 5
VAX/VMS DEVI C E DR I VERS

A VAX/VM S d ev i c e d r i v e r i s a c o l l e c t i o n o f t a b l es a nd r o u t i n e s u s e d to
c on t r o l
I /0 o pe r a t i o n s o n a pe r i ph e r a l d ev i c e .
Th e VAX/VM S Gu i d e to
W r i t i ng a D e v i c e D r i v e r d e s c r i be s t h e g e ne r a l s t r uc t u r e o f a d r i v e r ,
a nd
I n t r o d uc e s t h e s ys t em r o u t i n e s c ommo n l y c a l l ed by d ev i c e d r i v e r s .
Th i s c h a p t e r h i g h l i g h t s v a r i o u s t e c h n i q u e s
used
by s e l e c ted
s ys t em
d r ive r s ,
a nd
d oc um e n t s
s ome
of
the d ev i c e - s pe c i f i c
p r o c e s s i ng
pe r f o rmed b y t h e m .
Th e i n t e n t i s to p r e s e n t tho s e t e c h n i q ue s th a t a r e
hel pful
in
und e r s t a nd i ng
the VAX/VM S
I /0 s ub s y s t em b u t a r e no t
d e sc r i b ed i n t h e VAX/VM S G u i d e to Wr i t i ng a De v i c e Dr i v e r .
No a t t e m p t
i s m a d e to d i sc u s s e a c h VAX/VM S d ev i c e d r i v e r , no r i s e v e r y f e a t u r e o f
a pa r t i c u l a r d r i v e r d e s c r i b ed .
Fo r d e t a i l ed d e sc r i p t i o n s o f
the
f e a t u r e s a nd
c a pa b i l i t i e s
p r ov i d ed by e a ch s uppo r t ed d ev i c e d r i v e r ,
s e e the VAX/VM S I /O Us e r ' s G u i d e .

15. 1

D I S K DR I VERS

D i s k s a r e r a nd om a c c e s s ma s s s to r ag e d ev i c e s pl a c ed
e i th e r o n
the
MAS SBUS
( RM 0 3 ,
RM 0 5 ,
RM 8 0 ,
RP0 6 )
o r on the
UN I B US ( R L 0 2 , RX0 2 ,
RK 0 6 / 7 ) .
Th e d r i v e r s wr i t t e n fo r t h e s e d ev i c e s a r e d e s i g n ed to
•

t a ke a d v a n tag e of the h a r d wa r e e r r o r r e c o v e r y a nd
co r r e c t i on
c a pa b i l i t i e s
s uc h
a s d a ta
c h e c k i ng ,
o f f s e t r e c o v e r y , a nd
e r ro r c o d e c o r r ec t i o n ( ECC ) ,

•

o p t i m i z e c o n t r o l l e r o p e r a t i o n s by o ve r l a pp i ng s e e k
t r a n s f e r o pe r a t i o n s ,

•

pe r f o rm dynam i c b a d b l o c k h a nd l i ng ,

•

s u ppo r t o n- l i n e d i ag no s t i c s a nd e r r o r l og g i ng , a nd

•

s u ppo r t I /0 r e qu e s t s a t t h e l og i c a l and phys i c a l l e v e l s ,
c o o pe r a t e wi t h a n An c i l l a r y Co n t r o l
Processo r
( AC P )
s uppo r t v i r t ua l I/O r e que s t s .

a nd

d a ta

a nd
to

Th e VAX/VM S I /0 Us e r ' s G u i d e c o n t a i n s a g e n e r a l d i s c u s s i o n o f some o f
t h e d i s k d r i v e r c h a r a c t e r i s t i c s l i s t e d above .
Th e fo l l o w i ng s e c t i o n s
s uppl em e n t t h e i n f o rma t i o n p r e s e n t e d th e r e .

1 5- 1

VAX/VMS DEVI C E DRIVERS
15. 1. 1

ECC E r r o r Re c o v e r y

E C C e r r o r s o c c u r on l y o n r e ad o pe r a t i o n s ( r e ad d a t a , r e ad
h e ad e r
a nd
d a ta ,
wr i t e
c h e c k d a t a , a n d w r i t e c h e c k h e ad e r and d a t a ) .
Th ey a r e
c o r r e c ted by a pp l y i ng a h a r d wa r e- s p e c i f i ed
c o r r e c t i o n ma s k
to
the
a pp r o p r i a t e memo r y d a t a .
Th e
transfer
i s then c o n t i n u e d a s i f a n
e r r o r n e v e r o cc u r r e d .
Th e a c t u a l e r r o r c o r r e c t i o n c o d e c o n s i s t s o f
1.

an
1 1 -b i t m a s k
tha t mus t
a pp r o p r i a t e memo r y d a t a , a nd

e x c l us i v e

a b i t n umb e r w i t h i n t h e s e c to r tha t s pe c i f i e s
t h e e r ro r b u r s t .

ORed
the

wi th
s ta r t

the
of

D i s k d r iv e r s c al l
rout ine
I OC $ A P P LY E C C
( i n mod ul e
I O S UB RAM S )
to
I OC $APP LYECC r eq u i r e s t h e u s e o f a
a c t ua l l y a pp l y the ECC c o r r e c t i o n .
s y s tem p a g e t ab l e e n t r y
( S PT E ) .
Dev i c e d r i v e r s
th a t s uppo r t ECC
r e c o v e r y s pe c i f y the DPT$V SVP f l ag i n the f l ag s a rg um e n t t o the DPTAB
mac ro .
Wh e n th i s f l ag i s se t , the S Y S G E N C ONN E C T c omma nd a l l o c a te s a n
S PTE
f o r e ac h un i t a nd s to r e s t h e s ys tem v i r t ua l pag e n umb e r i n f i e l d
UC B $ L S VPN i n t h e un i t c o n t r o l b l o c k .
Th e s y s tem pag e ta b l e e n t r y
is
u s e d - t o d o ub l e m a p a
b y t e t o b e c o r r e c t ed .
Th e d r i v e r mus t a l s o
s pe c i fy t h e n um b e r o f byt e s tha t we r e t r a n s f e r r ed i n to m emo r y ( up t o ,
b u t n o t i nc l ud i ng , t h e b l o c k to b e c o r r e c t ed ) .
Th i s c a n be c a l c u l a t ed
by a d d i ng the r ema i n i ng byte c o un t
( l o a d ed
b y the d r i v e r
f r om a
MAS S B U S a d a p t e r
c on t r o l
r eg i s t� r ,
MBA $ L B C R , i n to t h e un i t c o n t r o l
b l o c k , i n f i e l d UC B $W B C R ) t o t h e t r a n s f e r -b y t e c o un t
( UC B $W BCNT ) .
Th e f o l l o w i ng s t eps are pe r f o rmed to a pp l y t h e c o r r e c t i o n .
1.

Th e t r a n s f e r r ed b y t e c o un t i s d e c r em e n ted ,
a nd
t h e n ANDed
w i t h A X l F F to c a l c ul a t e the b y t e o f f s e t f r om t h e s t a r t of the
b u f f e r to t h e b l o c k tha t c o n t a i n s t h e d a t a to be c o r r e c ted .

Th e s t a r t i ng b i t n umb e r o f t h e e r r o r b u r s t ( a n umb e r
i n the
r a nge
f r om
1
to
4096)
i s d ec r em e n t e d to c o nv e r t i t to a
r e l a t i v e b i t n umb e r , a nd the r e s u l t i s s e pa r a t e d i n to a b y t e
o f f s e t wi th i n b l o c k a nd a ma s k s h i f t c o un t .

Th e by t e o f f s e t w i th i n b l o c k i s ad d ed to the b y t e o f f s e t f r om
buffer
c a l c u l a t ed
i n s tep 1 .
Th e r e s u l t i s the b y t e o f f s e t
w i th i n bu f f e r t o t h e s t a r t o f t h e e r r o r b u r s t .

Th e e x c l us i v e OR pa t t e r n m a s k i s s h i f t ed
s h i f t c o un t c a l c u l a t ed i n s t e p 2 .

left

the

mask

At th i s po i n t t h e l o ng wo r d e x c l u s i v e OR pa t t e r n and the byte
o f f s e t w i th i n b u f f e r t o t h e f i r s t b y t e to be c o r r e c t ed have
be e n c a l c u l a t ed .
A l l th a t r ema i n s i s to d o ub l e m a p the d a t a
b l o c k t o b e c o r r ec t ed , a nd e x c l u s i v e OR t h e pa t t e r n m a s k w i th
memo r y .
Ho we v e r , t h e fo l l o w i ng c o n s i d e r a t i o n s m u s t b e mad e .
a.

Th e t r a ns f e r m a y h a v e b e e n s a t i s f i ed pa r t wa y t h r o ug h t h e
l a s t b l o c k , a nd t h e e r r o r c o r r e c t i o n i s o u t s i d e the d a t a
� f i n te r e s t .
Fo r
e x am p l e ,
t h e b y t e c o un t
t e rm i n a t ed
a f te r
20 byt e s i n to the s e c to r , a nd the c o r r e c tab l e d a t a
s t a r t s a t byt e 3 5 .

1 5- 2

VAX/VMS DEVI C E DR I VERS
b.

Th e t r an s f e r m a y h av e b e e n s a t i s f i ed
l a s t b l o c k , a nd t h e e r r o r c o r r e c t i o n
p a r t l y o u t s i d e t h e d a ta o f i n t e r e s t .
byt e c o un t t e rm i n a t ed a f t e r 2 0 byt e s
t h e c o r r e c t a b l e d a ta s t a r t ed a t byt e

pa r t wa y t h r o ug h
i s pa r t l y i n s i d e
Fo r
ex ampl e ,
i n to t h e s e c t o r ,
19.

the
and
the
a nd

Th u s , t h e c o r r e c t i o n m u s t b e a pp l i ed
one byte a t a
t ime .
S t e ps 5 t h r o ug h 7 a r e r e pe a t ed f o u r t i m e s , i f n e c e s s a r y .
5.

Th e o f f s e t t o t h e n e x t b y t e t o b e c o r r e c t e d i s c ompa r ed
wi th
the t r a n s f e r by t e c o un t .
I f the o f f s e t byt e c o un t i s g r e a t e r
than or
e qua l
to the t ransfer
byt e
c o un t ,
r em a i n i ng
c o r rect i ons a r e o uts i d e
the
a rea o f i nte r e s t .
Step 8 i s
e x e c u t ed n e x t .

Th e b y t e to b e c o r r e c t e d i s d o ub l e m a pped
u s i ng
the
s ys t em
v i r t ua l pag e n um b e r s to r ed i n UC B $ L SVPN , a n d t h e t r a n s l a t i o n
b u f f e r i s i nva l i d a t e d f o r tha t pag e�

Th e n e x t by t e
( l o we s t )
o f the
l o ng wo r d pa t t e r n ma s k
is
e x c l us i v e ORed w i t h t h e m emo r y d a t a , t h e o f f s e t i n b u f f e r i s
i nc r em e n t e d , a n d t h e pa tte r n m a s k i s r i g h t sh i f t ed
8
b i ts .
If
a l l f o u r c o r r e c t i o n b y t e s h a v e n o t b e e n a pp l i ed , s t e ps 5 ,
6 , a nd 7 a r e r e p e a t ed .

Th e t r a n s f e r i s c o n t i n ued
by
r e ex e c u t i ng
the a pp r o p r i a t e
f un c t i o n a f t e r upd a t i ng t h e c u r r e n t t r a n s f e r pa r am e te r s ( by t e
c o un t , d i s k ad d r e s s , a nd s y s t em v i r t ua l a d d r e s s o f
the
nex t
pag e t a b l e e n t r y t h a t m a ps t h e t r a n s f e r ) .

15. 1.2

O f f s e t Re cove r y

Of f s e t r ec o ve r y i s a t e c h n i q ue wh e r e by t h e d r i v e r e ad head s a r e moved
in
sma l l
i n c r em e n t s
( us ua l l y 2 0 0 to 4 0 0 m i c r o i nc h e s ) f r om the t r a c k
c e n t e r l i n e i n a n a t t empt t o p i c k u p a s t r o ng e r
r e ad i ng
s ignal .
Th e
t ec h n i q u e
i s pe r fo r m ed
o n l y f o r r e a d o pe r a t i o n s s uc h a s r e a d h e ad e r
a nd d a t a , w r i t e c h e c k d a t a , a nd wr i t e c h e c k h e ad e r a nd d a t a .
Upo n e nc o un t e r i ng an
error
tha t m a y be
c o r r ec tabl e
us i ng
r ec o v e r y , t h e fo l l o w i ng s t eps a r e t a k e n b y a d i s k d r i v e r .

o ffset

Th e r e a d h e a d s a r e r e t u r n ed to t h e c en t e r l i n e .

Up
to
16
a t t emp t s
c e n t e r l i ne .

Th e h e a d s
a re o f fs e t an
i nc r em e n t ,
a nd
2
retr ies
are
p e r fo rmed a t t h a t o f f s e t .
Th i s p r o c ed u r e i s r e pe a t ed up to 6
t imes .

I f a f te r 2 8 a t t emp t s ( 1 6 a t the c e n t e r l i n e , a nd 2 a t e a c h o f
6
o f f s e t po s i t i o n s )
t h e d a ta s t i l l c a nno t b e r e t r i e v e d , a
f a i l u r e i s r e turned .

a re

mad e

1 5-3

r e ad

the

d a ta

the

VAX/VMS DEV I C E DR I VERS
15. 1.3

Dynam i c Bad B l o c k Ha nd l i ng

Dyn a m i c bad b l o c k h a nd l i ng i s
i mp l em e n te d
as
a c o o pe r a t i v e e f f o r t
b e twe e n d r i v e r
FDT
r o u t i ne s , I /O po s tp r o c e s s i ng r o ut i n e s , a nd AC Ps .
FDT r o u t i ne s f o r
I O $ R EADVB LK a nd
I O $ WR I TEVB LK c o n s t r uc t
an
I /0
packet
( IRP) ,
a nd se t
the v i r t ua l
bit
in
the
I R P s t a t u s wo r d
( I RP $ V V I RTUA L i n I R P $W S TS ) .
Th e
I /0 po s tp r o c e s s i ng
rout i nes
( in
m od u l e
I OC I O PO S T )
d i scov e r t r a n s f e r e r r o r s o n v i r t ua l I /O f un c t i o n s ,
a nd r o u t e t h e I R P to the a pp r o p r i a t e AC P .
Th e AC P , u s i ng i n fo rm a t i o n
in
the
I RP ,
ca lcul ates
the b a d b l o c k
address ,
a nd
stores
tha t i n f o rm a t i o n .
In add i t i on , a b i t i s s e t i n
t h e f i l e c o n t r o l b l o c k ( FC B ) th a t c a us e s the e n t i r e c l us t e r c o n t a i n i ng
t h e b ad b l o c k to be r ec o r d ed i n t h e bad b l o c k f i l e ( [ O , O ] BADB LK . SYS ; l )
wh e n t h e f i l e i s d e l e t ed .
No te th a t a bad b l o c k i s n o t d i sc o v e r ed u n t i l i t i s a l r e a d y pa r t o f
a
f ile ,
a nd
i s n o t r e c o r d ed a s b ad u n t i l tha t f i l e i s d e l e t ed . Wh e n a
b ad
block
i s d i s c ov e r ed
wh i l e wr i t i ng
a
file ,
t h e bad
block
i n fo rm a t i o n
i s r ec o rd e d , a b i t i s s e t i n the FCB f o r the f i l e , a nd a n
e r r o r i nd i c a t i o n i s r e t u r n ed t o t h e r eq ue s t i ng p r o c e s s .
B a d b l o c k s uppo r t i s r e s t r i c t ed to v i r t ua l
I /O f un c t i o n s
( th a t
is,
file
I /0 ) .
Pr o c e s s e s pe r f o rm i ng
l og i c a l o r phys i c a l I /O f unc t i o n s
m u s t p r o v i d e the i r o wn b a d b l o c k h a nd l i ng .

15. 1.4

Mul t i p l e - B l o c k Nonc o n t i g uo u s V i r t u a l I /0

Wh e n a r e a d o r wr i t e v i r t ua l I /0 f u n c t i o n i s p r o c e s s e d
by
the
$QIO
s ys tem s e rv i c e ( by r o u t i n e EXE $ Q I O i n mo d u l e S YS Q I ORE Q ) , a n a t tempt i s
m a d e to pe r f o rm t h e t r a n s f e r
w i tho u t
the
i n te r v e n t i o n o f a n AC P .
C o n v e r s i o n o f v i r t ua l
b l o c k n um b e r s
to
l og i c a l
b l o c k n umbe r s i s
a c c ompl i shed us i ng m a pp i ng i n fo rm a t i o n c o nta i ned i n a d a t a
s t r uc t u r e
c a l l ed
a Wi n d o w Co n t r o l B l o c k ( WC B ) th a t wa s p r ev i o u s l y c r ea t ed by a n
A C P wh e n t h e c o r r e s pond i ng
f i l e wa s
f i r st accessed .
If
t h e WCB
c o n ta i n s
e no ug h m a pp i ng
i n fo rm a t i o n t o
c o nv e r t the e n t i r e v i r t ua l
r a ng e o f t h e t r a n s f e r i n to c o r r e s po nd i ng l og i c a l b l o c k n umbe r s on
the
t h en the v i r t u a l I /0 t r a n s f e r w i l l be h a nd l ed d i r e c t l y by the
v o l ume ,
d r i v e r a nd I / 0 c ompl e t i o n r o u t i n e s , even i f t h e t r a n s f e r
cons i s ts
of
seve ral
n o n c ont i g uo u s
p i ec e s .
If
t h e WC B d o e s n o t c o n t a i n e n o ug h
i n fo rma t i o n t o e n t i r e l y m a p t h e v i r t ua l r a ng e o f t h e
transfe r ,
the
i n te rven t i on
of
a n AC P w i l l
be
r eq u i r ed a t some t i me in o r d e r to
c ompl e t e t h e t r a n s f e r .

1 5 . 1 . 4 . 1 Mapp i ng I n f o rma t i o n
The WC B i s po i n t ed to by the
Ch a n n e l
Co n t r o l B l o c k ( CC B ) , wh i c h i s e s t a b l i shed b y t h e As s i g n Ch a n n e l sys t em
s e rv i c e ( a s d e sc r i b ed i n Ch a p t e r 1 6 ) .
Th e WCB c o n t a i n s a b a s e v i r t ua l
b l o c k n um b e r
a nd a va r i a b l e n umb e r o f m a p e n t r i e s ( c o n t r o l l ed b y t h e
/W I NDOW S =n q u a l i f i e r
to
the
I N I T IA L I Z E DC L c omma nd ,
and
by
the
ACP WI NDOW S Y S B OOT pa r am e t e r
f o r d i s k s m o un ted / S Y S T EM ) .
Th e m a p
e n tri e s f o rm a s ub s e t o f t h e f i l e r e t r i e v a l i n fo rm a t i o n f o r t h e
file.
E a c h m a p e n t r y c o n s i s t s o f a n e x t e n t s i z e a nd a s t a r t i ng l og i c a l b l o c k
n umbe r .
Th e m a p e n t r i e s
r epr esent
a v i r t u a l l y c o n t i g uo u s
set
of
b l oc k s t h a t a r e n o t nec e s s a r i l y phys i c a l l y c o n t i g uo u s o n t h e d i s k .
-

Wh e n a v i r t ua l r e a d
or
f i elds
t wo
i n i t i a l i ze

wr i t e
r e que s t
is
the
I RP t h a t
in
1 5-4

s pe c i f i e d ,
FDT r o u t i n e s
wi l l
be
u s ed by t h e I /0

VAX/VMS DEV I C E DR I VERS
po s t pr o c e s s i ng r o u t i n e s .
Th e t o t a l byte c o un t i n the o r i g i n a l r e q ue s t
is
s to r e d
i n t h e o r i g i na l
b y t e c o un t
f ield
( I R P $W OBCNT ) .
Th e
a c c um u l a t ed byte c o u n t f i e l d ( I R P$W_ABCNT ) , a c o un t o f byte s
a c t ua l l y
t r a n s f e r r ed , i s s e t t o z e r o .
Ro u t i ne I OC $MAPVB LK i s
t h e n c a l l ed
to
c o nve r t
the v i r t ua l
r a ng e
s pe c i f i ed
i n t h e t r a n s f e r to a l og i c a l b l o c k r a ng e , u s i ng i n fo rma t i o n
i n t h e WC B .
Th e r e a r e th r e e po s s i b l e c a s e s tha t c a n o c c u r h e r e .
•
•

•

Th e v i r t ua l
r a ng e
is
l og i c a l l y c o n t i g uo u s a nd
m a pp i ng
i n f o rma t i o n i s c o n t a i n ed i n t h e w i ndow c o n t r o l b l o c k .
Th e w i n d o w c o n t r o l b l o c k c o n t a i n s m a pp i ng i n fo r m a t i o n f o r t h e
b eg i n n i ng
of
t h e v i r t ua l r a ng e b u t the v i r t ua l r a ng e i s no t
v i r t ua l l y c o n t i g uo u s .
Th e ma p p i ng i n fo rm a t i o n tha t m a ps the f i r s t v i r t ua l b l o c k
t h e r a ng e t o i t s l og i c a l c o un te r pa r t i s no t i n the WC B .

15. 1.4.2
No AC P I n t e rve n t i o n - I n e i the r
o f the
f i rst
t wo c a s e s ,
I OC $MAPVB LK r e t u r n s
a n o n z e r o n um b e r o f b y t e s m a pped , a nd a s t a r t i ng
l og i c a l b l o c k n umbe r .
Th e s e
a re
l o a d ed
i n to
the
IRP
(at
f i elds
I RP$W BCNT a nd I RP $ L M E D I A r e s pe c t i v e l y ) a nd the I /0 r e que s t pac k e t i s
q ue u ed to the d r i v e r� Fu r th e r p r o c e s s i ng o f th i s r e que s t t a k e s
place
in
the
I /0 po s t p r o c e s s i ng r o u t i n e s .
Th e s e ro ut i n e s ( f o und i n m o d ul e
I OC I O PO S T ) p r o v i d e t h e a d d i t i o n a l p r o c e s s i ng ne c e s s a r y to
e f fec t
the
tota l
t r a n s fe r .
Th ey a r e
r e s po n s i b l e
fo r
a c c um u l a t i ng t h e to ta l
n um b e r o f b y t e s t r a n s fe r r e d , a nd fo r p r o pag a t i ng f u r th e r p r o c e s s i ng o f
the r e q u e s t , i f n e c e s s a r y .
Wh ene v e r t h e I /0 po s t p r o c e s s i ng c od e e n c o unte r s a n I / 0 r e que s t p a c ke t
( IRP)
w i th
t h e v i r t ua l
bit
set
( I R P $ V V I RTUAL
i n I R P$W ST S ) , i t
upd a t e s t h e a c c um u l a t ed b y t e c o un t ( s t o r ed Tn I R P $W ABCNT )
by a d d i ng
the
n umb e r o f byt e s
j us t
t r a n s f e r r ed
( I RP $W BCNT ) .
Th i s upd a t ed
a c c um u l a t ed byte c o un t i s then c ompa r ed w i th the or i g i n a l
byte
c o un t
( s to r ed
in
I R P $W OBCNT ) .
If
th e t wo n umbe r s ag r e e , the r e q u e s t i s
c om p l e ted e x a c t l y li ke o th e r d i r e c t
I /0
r e que s t s
( a s d e s c r i b ed
in
Ch a p t e r 1 6 ) .
O t h e r w i s e , t h e r ema 1 n 1 ng b y t e c o un t i s p l a c ed i n to I R P $W BCNT , a nd t h e
s eg m e n t
s t a r t i ng
v i r tual
b l o c k n um b e r ( I RP$ L S EGVBN ) - i s r e t r i e v ed .
Ro u t i ne I OC $MAPVB LK i s ag a i n c a l l ed
to m a p the
r ema 1 n 1 ng
v i r t ua l
I f the m a p p i ng i s s uc c e s s f u l ( a n o n z e r o c o un t o f t h e n um b e r o f
r a ng e .
by t e s m a pped i s r e t u r n ed ) , t h e I R P$W BCNT a nd I R P $ L MEDIA f i e l d s
a re
upd a ted
a nd
t h e I R P i s a g a i n q u e ued to t h e d r i v e r� I n th i s wa y , t h e
v i r t ua l r e que s t c o n t i n u e s un t i l i t c ompl e t e s o r un t i l a v i r t ua l
r a ng e
tha t c a n n o t b e m a pped by i n fo r m a t i o n i n t h e WCB i s e n c o un t e r e d .

1 5 . 1 . 4 . 3 AC P I n t e r v e n t i o n - I f r o u t i n e I OC $MAPVB LK c a nno t c o nv e r t a
v i r t ua l
r a ng e
to
i ts
l og i c a l c o un t e r pa r t , t h e f i l e s AC P a s s o c i a t ed
w i th the v o l ume i nvo l v ed i n the t r a n s f e r m u s t be c a l l ed upo n t o o b t a i n
the
r eq u i r ed m a pp i ng
i n fo rm a t i o n .
No t e th a t
th i s f a i l u r e c a n b e
d e t e c t ed by F D T r o u t i n e s a t t h e b eg i nn i ng o f the t r an s f e r o r
by
the
I /O po s t p r o c e s s i ng
rout ines
a f te r
the
r e que s t
h a s b e e n pa r t i a l l y
s a t i s f i ed .
I n e i th e r c a s e , t h e I RP i s pl a c ed i n to a wo r k q u e u e
a nd
the a s s o c i a t ed ACP i s a wa k e n ed .

1 5-5

VAX/VMS DEVI C E DR I VERS
Wh e n the AC P p r o c e s s e s th i s I RP , i t r e a d s the f i l e h e a d e r
to
obta i n
t h e m a pp i ng i n fo rma t i o n n e c e s s a r y f o r t h e t r a n s f e r i n q u e s t i o n .
Th i s
i n fo rma t i o n i s s to r ed i n the WCB ,
pe rh a ps
r e pl a c i ng
o th e r m a pp i ng
i n fo rma t i o n a l r e a d y c o n t a i n ed
th e r e .
Th e AC P t h e n upd a te s t h e B CNT
a nd M E D I A f i e l d s i n the I RP i n o r d e r t o t r a n s f e r the
f i r s t p i ece
of
the
r em a 1 n 1 ng v i r t ua l
r a ng e ,
a nd
queues
the I R P t o the d r i v e r to
c o n t i n u e the t r a n s f e r .
Wh e n t h e I /O po s tp r o c e s s i ng
r o u t i ne
r ec e i v e s
t h i s pac k e t , i t w i l l u s ua l l y f i nd t h a t t h e r em a i n i ng v i r t ua l r a ng e c a n
b e ma pped , a l l o wi ng
the
r e que s t
t o c ompl e t e wi tho u t
f u r th e r
AC P
i n t e rv e n t i o n
( ev e n
tho ug h
s e v e r a l d i sc r e t e
t r a n s f e r s may s t i l l b e
r e q u i r ed ) .
Th e o n l y t i m e th a t m o r e t h a n o n e AC P
i n t e rv e n t i o n ,
a
s o - c a l l ed w i ndow t u r n ,
o c c u r s i s wh en a f i l e i s s o bad l y f r agmen ted
that
i t c a n n o t be m a pped
by t h e n umbe r
of
r e t r i ev a l
po i n t e r s
e s t a b l i shed f o r th i s v o l um e .

15. 2

MAGNE T I C TAPE DR I VERS

M a g n e t i c t a pe s a r e
s equent i a l
a c c e s s m a s s s to r ag e d ev i c e s pl a c ed
e i th e r
o n t h e MAS S B U S ( T E 1 6 , T U 4 5 , TU 7 7 ) o r o n the UN I B U S ( TS l l ) .
Up
to e i g h t TE 1 6 or T U 4 5 t a pe d r i v e s o r up t o f o u r TU7 7 t a pe d r i v e s m a y
b e p l a c ed
o n e a c h TM 0 3 mag n e t i c t a pe c o n t r o l l e r ( a l th o ug h d i f f e r e n t
d r i v e s c a nno t b e c o nn e c t ed to
the
s ame
contro l l e r ) .
I n o rd e r
to
p e r fo rm d a ta t r a n s f e r o pe r a t i o n s , t h e MAS S B U S mag n e t i c t a pe d r i v e r ( i n
TMD R I VE R ) h a s to o b t a i n o wn e r s h i p o f b o t h t h e TM 0 3 c o n t r o l l e r ( pr i m a r y
c h a nne l )
a nd
the MAS S B US Ad a p t e r ( s e c o nd a r y c h a nn e l ) b y i s s u i ng the
R E Q PC HAN a nd REQSC HAN m a c r o s , r e s pe c t i v e l y .
At t i me s ,
the
s e co nd a r y
c h a nn e l m a y b e r e l e a s e d ( u s i ng t h e R E LSCHAN m a c r o ) s o th a t o th e r d i s k s
m a y u s e t h e MASSB U S .
Appe nd i x F o f t h e VAX/VMS G u i d e
t o Wr i t i ng
a
Dev i c e D r i ve r conta i n s
i n f o rm a t i o n o n ho w d r i v e r s a r e wr i t t e n fo r
d ev i c e s o n t h e MAS S B US .
The VAX/VM S I /0 Us e r ' s G u i d e d e sc r i b e s the f e a t u r e s
a nd
c a pa b i l i t i e s
p r o v i d ed b y t h e m ag n e t i c t a pe d r i v e r s , a nd d i sc us s e s the g e n e r a l e r r o r
r ec o v e r y a nd d a t a c h e c k
l og i c
empl o yed b y them .
Th e
s pe c i f i c
a l g o r i t hm us ed t o c o r r e c t NRZ I
( no n- r e t u r n- t o - z e r o - i nv e r ted ) r e ad
e r r o r s i s t h e fo l l o w i ng .
1.

I f the e r r o r o c c u r r ed wh i l e r e a d i ng i n the fo r wa rd d i r e c t i o n ,
t h e t a pe i s b a c k s pa c ed , a nd the r ec o rd i s r e ad a g a i n .

I f a n e r r o r o c c u r s wh i l e r e ad i ng i n the r e v e r s e d i r e c t i o n ( a s
the
resul t o f
a r e a d ph ys i c a l b l o c k r ev e r s e f unc t i o n ) , t h e
f o l l owi ng s t e ps a r e t a k e n .
a.

Th e r e c o rd i s r e a d i n t h e f o r wa r d d i r e c t i o n to s e t up the
e r r o r c o r r e c t i o n in t h e h a r d wa r e .

Th e t a pe i s b a c k s pa c ed o v e r the r ec o rd j us t r e ad .

Th e r e c o rd i s r e r e ad i n the fo r wa r d
the e r ro r c o r rec t i o n .

Th e t a pe i s b a c k s pa c ed ov e r the r ec o rd
to
po s i t i o n
the
t a pe p r o p e r l y ( b e c a u s e t h e i n i t i a l r e que s t wa s fo r a r e a d
i n t h e r ev e r se d i r ec t i o n ) .

A m a g n e t i c t a pe AC P i s c a l l ed f r om va r i o us
pe r fo rm f un c t i o n s l i ke wr i t i ng t a pe l ab e l s .

1 5-6

d i r ec t i o n

d river

FDT

a pp l y

r o ut i nes

VAX/VMS DEVI CE DR IVERS
15. 3

TERMINAL DR I VER

Th e t e rm i n a l I /O s y s t em i s a
c o l l ec t i o n o f
rout ines
( i n s e p a r a te
m od u l e s ) t h a t p r ov i d e a f l ex i b l e a pp r o ac h to te rm i n a l i nput a nd o u tput
Th e
l og i c a l
VAX/VM S
I / O Us e r ' s G u i d e ) .
( a s d e sc r i b ed
in
the
c ompo n e n t s
o f t h e t e rm i n a l I /O s y s t em a r e i l l us t r a t ed i n F i g u r e 1 5 - 1 .
( Th e c o n s o l e i n t e r f a c e
i s d i sc ussed
in a
l a te r
s ec t i o n o f
th i s
c h a p te r . )

User Issues $QIO request

Terminal Independent FDT Routines
(module TTYFDT)

Terminal

r -- -------- -

Driver

- - - - - - - - - - -,

I
I

Device and Terminal I ndependent Routines
Executing at Fork and Interrupt IPLs.
(modules: TTYCHARI , TTYCHARO,TTYDRVDAT, TTYSTRSTP, TTYSUB )

Device-Dependent
Interrupt Level
Routines for DZ-1 1
Interface

Device-Dependent
Interrupt Level
Routines for Console
Interface

(module TTZINTDSP)

(module CONINTDSP )

---- -

terminal interrupt

F i g u r e 1 5-1

15. 3. 1

- - -

- -

I
I
I
I
I
I
I
I
I
�

console interrupt

Te rm i n a l I /0 Sys tem

A l t e r n a te Te r m i n a l D r i v e r s

Wh e n the sys t em i s b o o t s t r a pped , mo d u l e I N I T r e a d s t h e t e rm i n a l d r i v e r
( wh i c h mus t b e c o n t i g uo u s ) i n to n o n pag ed po o l .
Th e t e rm i n a l
i m ag e
d r i v e r i m ag e i s a s e pa r a t e , l o ad ab l e i m ag e .
I t i s n o t l i n k ed w i th t h e
execut i ve .
Th e r e f o r e ,
c h a ng e s c a n b e mad e to th e t e rm i n a l d r i v e r
m od u l e s ,
a nd
tho s e mo d u l e s c a n
then b e a s s em b l ed
and
l i n ked
i nd e pend e n t o f the e x e c u t i v e ( F i g u r e 1 5 - 2 ) .
1 5-7

Comm a n d

Bu i l d Ph a s e
Ma c ro L i b r a r y C r e a t i o n

$ L I B RARY/CREATE/MAC R O S YS $S YS TEM : TTYL I B SYS $ S YS TEM : TTYU C B DEF . MAR

As s em b l y Ph a s e

$ MAC RO/ L I S T=S YS $ S YS TEM : ' mod u l e ' /OBJECT=S YS $ S YS TEM : ' mod ul e ' S YS $ S YS TEM : ' mo d ul e ' + 
SYS $ L I B RARY : L I B / L �B RARY+
SYS $ S YS TEM : TTYL I B/ L I B RARY
$!
$!
$!
$!
$!
$!
$!
$!
$!

1-'
U1
I
co

L i n k Ph a s e

Th i s i s d o n e fo r e a c h o f the fo l l owi ng mod ul e s
TTYS UB
TTYF DT
TTYDRVDAT
TTYC HAR I
TTYC HARO
TTYS TRS T P
TTZ I N T DS P

$ L I N K / S HARE=S YS $ S YS TEM : TTDR I VE R/ C ONT IGUOUS/MAP=S YS $S YS TEM : TTDR I VER/ FU L L /CROS S S YS $ S YS TEM : TTYDRVDAT , TTYF DT , TTYS TRS TP , TTYC HAR I , TTYC HARO , TTYS UB 1 TTZ I N T DS P , S YS $ S YS TEM : SYS . S TB/ S E LEC T I VE S EARC H , 
S YS $ S YS TEM : O PT IONS/ O PT I ONS
$!
$!
$!

Figure 1 5-2

wh e r e the f i l e OPT I ONS . OPT c o n t a i n s t h e s i ng l e l i n e
BAS E = 0

Comma n d s th a t As s emb l e a nd L i n k the Te rm i n a l D r i v e r

VAX/VMS DEVI C E D R I VERS
Wh e n the s y s t em i s r e b o o t e d , t h e n e w t e rm i n a l d r i v e r can be t e s t e d .
A
r e bo o t
is
nec e s sa ry
to u s e t h e new t e rm i n a l d r i v e r o n , f o r e x ampl e ,
a u to c o n f i g u r ed D Z l l s b e c a u s e the SYSGEN R E LOAD c omma nd wi l l n o t r e l o ad
a d r iver
wh i l e a d ev i c e un i t s e r v i c ed by t h e d r i v e r i s b u s y , a nd the
t e rm i n a l f r om wh i c h the R E LOAD c omma nd i s b e i ng i s s ued is a l wa ys b u s y .
Th e f a c t t h a t the t e rm i n a l d r i v e r i s l o ad ed by I N I T h a s
i m pl i c a t i o n s
fo r
a n yo n e wh o wr i t e s a n e w t e rm i n a l d r i v e r .
A s ys t em d i s k w i t h t h e
o r i g i n a l t e rm i n a l d r i v e r m u s t b e k e pt a r o und to r e bo o t the
s ys t em
in
the
event
tha t
t h e m o d i f i ed
t e rm i n a l
d r i v e r c o n t a i n s e r r o r s th a t
pr e v e n t t h e s ys t em f r om c ompl e t i ng i t s i n i t i a l i z a t i o n s e q u e n c e .
(or
r e pl a c ed )
No rma l l y , t h e o n l y mo d u l e t h a t w i l l n e ed to b e a l t e r ed
i s TTZ I N TDS P to p r ov i d e t h e d ev i c e d e pend e n t pr o c e s s i ng fo r a s p e c i f i c
d ev i c e ( s u c h a s a D L l l ) .
I f the d ev i c e i s t o o pe r a t e i n a DMA ( d i r e c t
m em o r y a c c e s s )
mo d e , t h e n t h e e n t i r e d r i v e r i n t e r f a c e m a y h a v e t o b e
c h a ng ed .
TTZ I NTDS P c o n t a i n s t h e d r i v e r p r o l o g ue t a b l e ( wh i c h h a s some
n o n s t a nd a r d ,
but
r e q u i r ed ,
CRB
i n i t i a l i za t ion
i n s t r uc t i o n s i n the
RE INIT s e c t i o n
to
p r ov i d e
l i n k ag e s
to
the
d ev i c e
i nd e pend e n t
p r o c e s s i ng r o u t i n e s ) , a n d some s e l f - r e l a t i v e o f f s e t s wh i c h a r e u s e d b y
I N I T t o l o ad t h e d r i v e r .

15. 3.2

Fu l l Dup l e x Ope r a t i o n

Th e
t e rm i nal
d r iver
i m p l eme n ts
ful l
d u p l ex
o pe r a t i o n
( un l e s s
s pe c i f i c a l l y a s ke d
to
o pe r a t e
i n h a l f d up l e x mod e f o r a pa r t i c u l a r
t e r m i n a l ) b y ut i l i z i ng a n a l t e r n a t e s ta r t I /0 e n t r y po i n t
( s pe c i f i ed
as
the A L T S TART pa r am e t e r
to
the
DDTAB mac r o ) . Wh e n e v e r a wr i t e
r e q u e s t i s i s s u ed t o a f u l l d upl e x t e rm i n a l ,
t h e wr i t e
FDT
rout i ne
( TTY$ FDTWR I T E
i n TTYFDT )
a l l o c a t e s a nd
i n i t i a l i z e s a wr i t e b u f f e r
pa c k e t t o d e sc r i b e t h e wr i te r eq u e s t , a nd c a l l s r o u t i n e
E XE $ALTQUE PKT
( i n S YS Q I OR E Q ) to e n t e r the a l te r n a t e s ta r t I /0 r o u t i n e o f the d r i v e r .
I n t h e h a l f d up l e x c a s e , r o u t i n e EXE $ Q I ODRVP KT , a l s o i n SYS Q I OR E Q ,
is
c a l l ed .
No rma l l y , FDT r o u t i n e s c a l l on EXE $ Q I ODRVPKT to i nv o k e the
s ta r t
I /0
r o u t i ne o f t h e d r i v e r , i f t h e un i t i s n o t b us y , o r to q u e ue t h e I R P t o
t h e UC B i f t h e un i t i s b u s y .
E XE $ A LT QU E PKT d i f f e r s f r o m EXE $ Q I ODRVPKT
i n s ev e r a l r e s pe c t s .
1.

No c h e c k i s mad e t o s e e i f t h e
UC B i s b u s y
( UC B $V B S Y
in
UC B $W STS ) .
Th e r e f o r e ,
th e
r e q ue s t i s n ev e r q u e ued t o the
U C B by EXE $ A LTQU E PKT .
Th i s i s d e s i r a b l e bec a u s e
t h e r e may
c u r r en t l y b e a r e a d r e q ue s t i n p r og r e s s , a nd i f t h e I R P we r e
q u e ue d u n t i l t h e r e ad r e que s t
f i n i shed ,
a nd
the
bus y b i t
c l e a r e d , f u l l d u p l e x ope r a t i o n wo u l d no t be po s s i b l e .

Th e c a nc e l a n d t i m e o u t b i t s
in
the
UCB
( UC B $V CANC E L a nd
UC B $V T I MO U T
in
UC B $W S TS )
a r e una f f e c ted
( not c l e a r ed )
b e c a use t h e y m a y b e b e i ng u s ed by t h e c u r r e n t I R P , i f t h e UC B
i s bus y .

Th e SVA PT E , BCNT , a nd B O F F f i e l d s a r e n o t c o p i ed f r om t h e I R P
to
th e UC B b e c a u s e
t h i s wo u l d
effect the cur rent
I /0
o pe r a t i o n i f t h e UC B i s b u s y .

Th e a l t e r n a t e s t a r t I /0 r o u t i n e
i n the d r i ve r
( r a th e r t h a n t h e r eg u l a r s t a r t I /O r o u t i n e ) .

1 5- 9

e n t e r ed

VAX/VMS DEVI C E DR IVE RS
TTY $WRTSTART I O ( i n TTYS TRS T P ) i s th e a l t e r n a t e s t a r t I /0 r o ut i n e e n t r y
po i n t .
Th i s e n t r y po i n t i s a l s o u s ed by t h e b r o a d c a s t s ys t em s e rv i c e ,
as d e s c r i b ed i n Ch a p t e r 1 6 .
Th i s r o u t i n e r a i s e s I PL to d ev i c e I PL
to
b l o c k d ev i c e
i n t e r r up t s
f r om the c u r r e n t I /0 o p e r a t i o n , i n c a s e the
d ev i c e is b u s y , a nd p r o c e s s e s the pac k e t as f o l l o ws .
1.

I f a wr i t e i s c u r r e n t l y i n p r og r e s s , t h e wr i te b u f f e r
i s q u e ued .

pac k e t

I f a r e ad i s o c c u r r i ng , b u t t h e b uf f e r h e ad e r s pe c i f i e s wr i t e
b r e a k th r o ug h , t h e wr i t e i s s t a r t ed .

I f a r e a d i s o c c u r r i ng , b u t no c h a r a c te r s h a v e b e e n
ye t , the wr i t e i s s t a r t ed .

O t h e r w i s e , t h e w r i t e b u f f e r i s q ue u e d .

r ec e i v ed

I n o rd e r to c ompl e t e wr i te I /0 r e q ue s t s f o r f ul l d up l e x o pe r a t i o n , t h e
d r iver
e x i t s b y c a l l i ng r o u t i n e C OM $ P O S T ( i n C OMDRVS U B ) r a th e r t h a n
i s s u i ng t h e R E QC OM ma c r o .
C OM $ P O S T p l a c e s t h e I / 0 r e que s t pa c k e t
in
the
po s t p r o c e s s i ng
q u e u e , r eq ue s t s a n I P L $ I O PO S T s o f twa r e i n t e r r upt
i f t h e queue wa s p r ev i o u s l y em p t y ( Ch a p t e r 4 ) , a nd
returns .
Ro ut i n e
I OC $ R E QC OM
is
a v o i d ed
s o th a t the n e x t I R P que ued to the UC B ( wh i c h
m u s t b e a r e a d r e q ue s t ) i s n o t i n i t i a t ed
( be c a u s e
the c ur rent
r e ad
r e qu e s t , i f a n y , h a s n o t ye t t e rm i n a t ed ) .
Al so , the s t a t u s o f the UCB
b u s y b i t i s un a l te r e d b y C OM $ P O S T .
Al l r e ad
r eq u e s t s ,
h o wev e r ,
are
t e rm i n a ted by i nvo k i ng t h e R E Q C OM m a c r o , s o th a t t h e nex t r e a d r e q u e s t
m a y b e p r o c e s s ed i n t h e no rm a l f a sh i o n .
I n f u l l d upl ex o pe r a t i o n the d ev i c e c an b e e x pe c t i ng mo r e
than one
i n t e r r upt
at a
t i me
( one
fo r
a r e ad r e q ue s t , a n d o n e fo r a wr i t e
r e q ue s t ) .
Th e r e fo r e , t wo f o r k PC s m u s t be s to r ed .
( Us u a l l y d r i v e r s
o n l y e xpect o n e
i n t e r r up t
at
a
t ime ,
a nd
s to r e t h e fo r k PC i n
UC B $ L F PC . ) Th e te rm i n a l d r i v e r
s to r e s m o r e t h a n o n e
f o r k P C by
a l t e rTng
t h e v a l u e o f R S ( wh i c h no r ma l l y po i n t s to the UC B ) , to po i n t
t o the w r i te b u f f e r pac k e t o r t h e I RP b e f o r e f o r k i ng ( by i nv o k i ng
the
F ORK m a c r o ) .
A fork
b l o c k i s t h e r e f o r e f o rmed i n t h e wr i t e buf f e r
pa c k e t o r i n t h e I RP ( c o n t a i n i ng R 3 , R 4 , a nd t h e f o r k PC ) .
Th e
fo rk
block
i n t h e UC B i s n o t u s e d f o r r e a d o r wr i t e r e que s t s , a l tho ug h i t
i s u s e d a t o the r t i m e s , s uc h a s wh e n a l l o c a t i ng a type - a h e a d b u f f e r o r
wh e n h a nd l i ng un so l i c i t e d d a t a .
Th e t e c h n i q u e o f a l t e r i ng R S b e fo r e fo r k i ng c a n e a s i l y be e x t e nd ed
by
any d r iv e r
to
a l l o w mo r e
than
o ne
o u t s t a nd i ng
i n t e r r up t fo r a
pa r t i c u l a r d ev i c e , p r ov i d ed the d r i v e r c a n d i s t i ng u i sh wh i c h i n te r r upt
is
a s s o c i a t ed
w i th wh i c h
fo r k b l oc k .
Th e r e f o r e ,
a n y n umbe r o f
o u t s t a nd i ng I /O r e q ue s t s m a y b e h a nd l ed b y a
d r i v e r e n t e r ed
a t the
a l t e r n a te
s ta r t I /0 e n t r y po i n t .
O f c o u r s e , the d r i v e r m u s t m a i n t a i n
que ue s f o r o u t s t a nd i ng I /0 r e q ue s t s , a nd s yn c h r o n i ze
I /0 o pe r a t i o n s .
Th � d r i v e r
shQu l d o pe r a t e
a l mo s t e x c l u s i v e l y a t d ev i c e I PL ( a s t h e
t e rm i n a l d r i v e r d o e s ) , t o b l o c k o u t d ev i c e
i n t e r r up t s
in
o rd e r
to
a c h i e v e s yn c h r o n i z a t i o n w i th m u l t i pl e I /0 r e q ue s t p r o c e s s i ng .

15. 3. 3

Channe l s a nd th e DZ l l

The DZ l l h a s no c o n t r o l l e r c h a n n e l c o n c e p t .
Th e r e fo r e ,
the
t e rm i n a l
d r i v e r n ev e r
r eq u e s t s
or
r el ea s e s a
c o n t r o l l e r c h a n n e l ( wi th t h e
Th e l oc a t i o n s n o rm a l l y u s e d i n the C RB
R E QC HAN a nd R E LC HAN m a c r o s )
as
l i s th e ad s
fo r
the
c o n t r o l l e r c h a n n e l wa i t que ue ( CRB $ L_WQF L a nd
•

1 5- 1 0

VAX/VMS DEVI C E DR I VERS
C RB $ L WQB L )
are
i ns tead
u s ed
i n f o r ma t i o n
( a nd
are
r e named
C RB $ 8 TT E X P E C by TTZ I NTDS P ) .

15. 3 . 4

to
to

c o n t a i n m o d em
c on t r o l
s ta t u s
C RB $ L_TT_D I A L , CRB $ B_TT_ATTN , a n d

Type -Ah e a d B u f f e r

A t ype- a h e ad bu f f e r i s a l l o c a ted f r om n o np a g e d po o l fo r e a c h t e rm i n a l .
Ev e r y c h a r a c t e r
t yped
i s p l a c ed
i n to
the b u f fe r , even i f a read
I f t h e b u f f e r i s w i th i n 8 c h a r a c t e r s o f b e i ng f u l l
r eque s t is a c t i v e .
a nd
the
t e rm i n a l
is
i n h o s t - s yn c m o d e ,
t h e d r i v e r s e nd s a n XOF F
c h a r ac t e r t o t h e t e rm i n a l t o t e l l i t to s to p s e nd i ng d a ta .
A n XON
c h a r ac t e r i s n o t s e n t to the t e rm i n a l t o t e l l i t t o s t a r t s e nd i ng d a t a
un t i l t h e b u f f e r i s empt i ed .
Us i ng th i s t e c hn i que p r ev e n t s c h a r a c t e r s
f r om b e i ng l o s t i n b l o c k I /0 t r a n sm i s s i o n s f r om h i g h - s pe ed t e rm i na l s .

15. 4

PS EUDO DEVICE DR I VERS

VM S s uppo r t s d r i v e r s fo r d e v i c e s th a t do no t ph y s i c a l l y e x i s t
( ps e ud o
d ev i c e s ) ,
i n c l ud i ng t h e n u l l d ev i c e ( N L : ) , the n e t wo r k d ev i c e ( N ET : } ,
a nd m a i l bo x e s ( MB : ) .
U s e r s c a n a s s i g n c h a n n e l s to t h e s e d ev i c e s a n d
i s sue
I /0
r eque s t s ,
j us t
as
t ho ug h
t h e y we r e r e a l d ev i c e s .
Th e
f o l l o w i ng s e c t i o n s h i g h l i g h t s o m e o f
the
features o f
t h e s e p s e ud o
d ev i c e d r i v e r s .

15. 4 . 1

N u l l Dev i c e D r i ve r

Th e n u l l d ev i c e d r i v e r ( i n N L DR I VE R } i s a s s embl e d and l i n k e d w i th
the
s ys t em i ma g e ( S YS . E XE } .
I t i s a v e r y s i mpl e d r i v e r , c o ns i s t i ng o f two
FDT r o u t i n e s ( o n e to h a nd l e r e a d r e q ue s t s , a nd o n e
to
h a nd l e wr i t e
r eque s ts } .
Th e
FDT r o u t i n e s
i n t h e n u l l d r i v e r r e spond to r e a d
r e que s t s b y r e t u r n i ng a n S S $ ENDOF F I LE s t a t us c o d e t o
the
use r ,
and
t h e y r e s po nd to wr i t e r e que sts by r e t u r n i ng a n S S $ N O RMAL s t a t u s c o d e .
No d a ta i s t r a n s f e r r ed , n o r a r e a ny p r i v i l eg e o r quo ta c h e c k s m ad e .

15.4.2

N e t wo r k Dev i c e D r i v e r

Th e n e t wo r k d ev i c e d r i v e r ( i n N E TDR I VE R } i s used t o i m pl eme n t s o m e o f
the
DECn e t
i n t e r p r o c e s so r
c ommun i c a t i o n p r o t o c o l s ( s e e the VAX/VM S
DECne t-VAX U s e r ' s G u i d e a n d D E Cn e t-VAX S y s t em Ma n ag e r ' s G u i d e } .
Th i s
d r iver
i s not a
pa r t o f
t h e s ys t em i m ag e .
I t m u s t b e ex pl i c i t l y
l o ad e d
w i th a
C ONNECT c ommand ,
u s ua l l y a s a
pa r t
of
DECn e t
i n i t i a l i za t i o n .
Al l D E Cn e t u s e r s a s s i g n a c h a n n e l to d ev i c e NE T O ,
a t wh i c h
t i me a
n e t wo r k
UC B
i s c r ea t ed
to
d esc r ibe
the
l og i c a l l i n k f o r m ed wi th
a no th e r p r o c e s s on a n o th e r CPU , a nd th a t UCB is g i v e n a un i que n umbe r ,
s uc h a s N E Tl O O .
Th e c h a nn e l n umbe r r e t u r ned to the u s e r po i n t s to t h e
n ewl y c r e a t ed UC B , wh i c h w i l l b e d e l e t ed
wh en
the
use r
no
l o ng e r
d e s i r e s t h e l og i c a l l i n k .
Al l r e a d a nd wr i te r e que s t s ( f r om a l l
D E Cn e t u s e r s )
a r e pa s s e d
to
N E T DR I VE R .
N E TDR I VE R
c ons i s ts p r ima r i l y o f
FDT r o u t i n e s
th a t
p r e p r o c e s s t h e I /0 r e q ue s t , a nd q u e u e the I R P t o a
s e pa r a t e p r o c e s s ,
1 5-1 1

VAX/VMS DEVI C E DR I VE RS
N ETAC P
( th e n e two r k AC P ) ,
by c a l l i ng
routine
EXE $ Q I OAC PPKT
( in
S YS Q I O R E Q ) .
NE TAC P h a s a c h a n n e l a s s i g n ed to the
r ea l
c omm un i c a t i o n
d ev i c e
(a
DMC - 1 1 ) ,
and
i ssues
I /0 r e q ue s t s to the r e a l d ev i c e on
b eh a l f o f the u s e r , wh i c h a r e p r o c e s s ed
by the
real
d ev i c e d r i v e r
XMDR I VE R
is
t h e n am e o f t h e d ev i c e d r i v e r fo r the
( Fi g u r e 1 5-3 ) .
DMC - 1 1 .

Responds to
user $QIO
for network
operations

Figure 1 5-3

XMDRIVER

N ETACP

N ETDRIVER

Issues $QIOs
on behalf of
user to
real device

...
-

Controls the
real device
DMC-1 1

Ro l e o f N E TDR I VER i n P r o c e s s i ng Netwo r k I /0 Reque s t s

Th e c omm un i c a t i o n d ev i c e ( DMC - 1 1 ) i s no rma l l y a
n o n s h a r e a b l e d ev i c e ,
a nd
t h e r e f o r e o n l y o n e p r o c e s s c a n have a c h a n n e l a s s i g n ed to i t .
In
o rd e r to i m p l em e n t DECn e t p r o t o c o l s , NETAC P mu s t a s s i g n a
channel
to
the d ev i c e .
Oth e r p r o c e s s e s , th e r e fo r e , c a n no t a s s i g n c h anne l s to the
d ev i c e ,
b e c a u s e a s s i g n i ng
a
channel
to
a
nonsha r ea b l e
d ev i c e
i mpl i c i t l y a l l o c a t e s
t h e d ev i c e ,
a s d e sc r i b ed i n Ch a p t e r 1 6 .
Th e
p s e u d o d ev i c e N E T i s th e r e f o r e u s e d to a l l o w m a ny u s e r
proc e s s e s
to
i s s u e I/O r e q ue s t s f o r the n e t wo r k , wh i c h may be pa s s ed to NETAC P , a nd
eve n t u a l l y t o the d r i v e r fo r t h e
n o n sha r e a b l e
c ommun i c a t i o ns d ev i c e
( i n e ffec t ,
m a k i ng
t h e d ev i c e sha r eab l e ) .
N E TAC P a nd N E TDR IVE R a r e
r e s p o n s i b l e fo r manag i ng a l l
of
the
l og i c a l
l i nks
e s tabl i shed
by
use r s ,
a nd
r e t u r n i ng
st atus
i n fo rma t i o n
to
the
a pp r o p r i a t e us e r
r eg a r d i ng e a c h I /0 r e q ue s t .

15. 4 . 3

M a i l b ox D r i v e r

Ma i l box e s a r e so f t wa r e - impl eme n t ed d e v i c e s tha t c a n pe r f o rm
r e ad
and
wr i t e o p e r a t i o n s .
No rm a l l y ,
ma i l b ox e s a r e
used fo r c o mmun i c a t i o n
b e t we e n p r o c e s s e s .
Al though m a i l bo x e s t r a n s fe r
i n fo rma t i o n
i n much
the
s am e
wa y tha t o th e r I /0 d e v i c e s d o , t h e y a r e not a c tua l d e v i c e s .
Th e fo l l o w i ng s e c t i o n s d e sc r i b e ho w t h e m a i l bo x d r i v e r ( i n MBDR I VE R , a
mod ul e i n t h e s ys t em i m ag e ) b u f f e r s m e s s a g e s wr i t t e n to ma i l bo x e s , a nd
s e r i a l i z e s m a i l box r e ad r e q u e s t s .

15. 4. 3 . 1
P r o c e s s i ng S e t Mo d e Requ e s t s - A
process
may
r e que s t
not i f i c a t i on of
a ma i l bo x
r e ad
o r wr i t e r e que s t b y i s s u i ng a $ Q I O
r e q u e s t w i th a n I O $ S E TM ODE f unc t i o n c o d e
( a nd
an
I O $ READATTN o r
S e e th e VAX/VMS I / O- Us e r ' s G u i d e
I O $ WRTATTN f un c t i on c o d e mo d i f i e r ) .
f o r -d e t a i l s .
Th e m a i l bo x d r i v e r ' s
FDT
r o ut i nes
r e s pond
to
the se
r e que s t s b y
1.

v e r i f y i ng tha t t h e p r o c e s s m a y a c c e s s the m a i l bo x ,

1 5-1 2

VAX/VMS DEVI C E DR I VE R S
2.

r·eque s t
que ue i ng
th e
to
the
a pp r o p r i a t e
l i s th e a d
wr i t e
( UC B $ L MB W AST fo r
r e q ue s t s ,
o r UC B $ L MB R A S T f o r
r e a d re quest s )
by c a l l i ng
r o ut i ne
on
C OM $ SETATTNAS T
in
C OMDRVS UB
( wh i c h a l l o c a t e s ,
i n i t i a l i z e s , and que ue s a n AST
s p e c i f i ed
c o n t r o l b l o c k to the
l i s t head ,
a s d e s c r i bed
in
Ch a p t e r 5 ) ' a n d

r a i s i ng I P L to I P L $ MA I LBOX ( I P L 1 1 ) , a n d c h e c k i ng to s e e
if
t h e no t i f i c a t i o n c ond i t i o n r e q u e s ted i s p r e s e n t ( c u r r e n t r e a d
o r wr i t e r e que s t o u t s t a nd i ng ) .
I f so , r o u t i n e C OM $ D E LATTNAST
in
C OMDRVS UB
i s c a l l ed
to
queue the a t te n t i o n AST t o the
r e q u e s t i ng p r o c e s s ( Ch a p t e r 5 ) .
Oth e r w i s e , t h e a t te n t i o n AST
r eque s t
r ema i n s q u e ued
to
t h e m a i l bo x
UC B ,
b u t the I /0
r e q u e s t i s c o mp l e t e d by c a l l i ng EXE $ F IN I S H I OC .
Th e a t te n t i o n
AST w i l l
be
que ued
to
the
process
wh en a r e ad o r wr i t e
r e q u e s t , a s a pp r o p r i a te , i s i s s ued f o r t h e m a i l bo x .
No t e
th a t m a i l bo x e s
use
fo r k
I PL $ MA I L BOX
( I PL 1 1 ,
the
h i g h e s t f o r k I P L ) , to avo i d po s s i b l e syn c h r o n i z a t i o n p r o b l ems
w i t h o t h e r d r i v e r s th a t r e f e r e n c e ma i l bo x e s wh i l e
at
the i r
r e s pe c t i v e
fo r k
I PLs ( f o r ex ampl e , to s e nd a " d ev i c e i s o f f
l i n e " me s s ag e to t h e o p e r a to r ' s ma i l box ) .

15. 4. 3.2
P r o c e s s i ng a Ma i l bo x Re a d Reque s t
Wh e n a
use r
i ssues
a
r e ad m a i l bo x
$QIO,
t h e m a i l bo x d r i v e r
FDT
r o u t i n e s pe r fo r m t h e
fo l l o w i ng g e n e r a l f unc t i o ns .
-

Th e us e r r e qu e s t i s va l i d a ted to ma ke
sure
th e
r e qu e s t i ng
process ' s
UIC
i s g i ven access
to
the ma i l bo x , th a t t h e
m e s s a g e s i z e r e q u e s t ed i s a l l o wed fo r t h e m a i l bo x ,
a nd
th a t
t h e u s e r h a s wr i t e a c c e s s t o the b u f f e r s pe c i f i e d ( i n to wh i c h
t h e ma i l bo x me s s ag e w i l l be pl a c ed ) .

Th e a d d r e s s o f t h e s pe c i f i ed b u f f e r , i n to wh i c h
the
m e s s a g e w i l l b e wr i t ten , i s s a v ed i n I R P$ L M E D I A .

Th e I R P $ V MB X I O b i t i n I RP $W S T S
is
set
so
th a t
the
I /0
po s t p r o c e s s i ng
r o u t i n e s w i lT r ec og n i z e a ma i l bo x I /0 r e que s t
c ompl e t i o n a n d a n n o u n c e t h e av a i l a b i l i ty o f t h e RS N $ MA I LB OX
resource .

I f t h e I O $M N OW f u nc t i o n c od e mo d i f i e r wa s n o t
spec i f i e d
in
the
$ Q I O ca l l ,
t h e r e que s t i s que ued t o the d r i v e r ' s s t a r t
I /0 r o u t i n e .

I f t h e I O $M N OW mo d i f i e r wa s s pe c i f i ed ,
I PL
is
r a i sed
to
I P L $ MA I LBOX
( I PL 1 1 ) ,
and
i f a n y m e s s ag e s a r e a v a i l a b l e
( UC B$W M SGCNT i s
n o n ze ro )
t h e r equest
is
q ue ued
to
the
d r i v e rTs
sta r t
I /0
r o ut i ne .
O t h e rwi s e , t h e S S $ ENDO F F I L E
m e s s a g e i s r e t u r n ed to the u s e r , and
the
I /O o pera t i o n
is
compl e t ed .

ma i l bo x

Th e ma i l bo x d r i v e r ' s s t a r t I /0 r o u t i n e pe r f o rms th e fo l l o w i ng s t e ps .
1.

I t f i r s t t r i e s to d e que ue a m e s sa g e wr i t t e n
to
( me s s a g e s
a re
que ued
to
the
UC B ,
w i th
UCB $ L_MB_MSG Q ) .

1 5 -1 3

the ma i l bo x
l i s th e a d
at

VAX/VMS DEVI C E DR I VERS
2.

I f no me s s a g e i s fo und , a ny pend i ng r e a d a t te n t i o n ASTs
a re
q u e ue d to th e i r p r o c e s s ( e s ) ( by pa s s i ng the l i s th e a d a d d r e s s ,
UC B $ L MB R A S T ,
to
C OM $D E LATTNAS T ,
as
d e s c r i b ed
in
C h a p te r 5) :-

Th e m a i l bo x UC B r em a i ns " b u s y " ( th e UC B $V B S Y b i t i s s e t
in
UC B $W_S T S ) ,
a l tho ug h n o
f u r th e r
p r o c ess i ng o c c u r s un t i l a
w r i t e r e qu e s t i s i s s ue d .
S u b s e q u e n t r ea d r e q u e s t s w i l l
wa i t
t o en te r
the
s ta r t
I /0
r o ut i ne
( a l th o ug h
t h e y w i l l be
p r e p r o c e s s e d by FDT r o u t i n e s ) , bec a u s e the busy b i t
is
set .
As
soon as
th i s
r ea d
r eque s t
t e rm i n a t e s ,
t h e nex t r e a d
r e q ue s t wi l l b e p r o c e s s ed by the s ta r t I /0 r o u t i n e .

I f a me s s ag e wa s fo und ( o r a wr i te r e q u e s t o c c u r s a nd a
read
r e q u e s t i s o u t s t a nd i ng , a s d i sc u s s e d i n s t ep 3 ) , t h e n spec i a l
a c t i on i s t a ke n .
a.

Th e ad d r e s s o f t h e m e s s a g e b l o c k b u i l t by t h e wr i t e
FDT
routine
( Fi g u r e 1 5-4 )
i s p l a c ed i n I R P $ L S VA PTE i n the
r e ad
request ' s
I R P so
th a t
the
I /0
po s t p r o c e s s i ng
r o u t i ne s c a n l oc a t e
t h e m e s sag e a nd c o py i t i n to th e
u s e r ' s buf fe r .

pointer to start of data

pointer to user buffer

mailbox
IPL

block
type

-._.
--

lll..
,

size of block

saved packet address
(low word)

size of message
in bytes

process ID of sender
(low word)

saved packet address
(high word)

MAILBOX
MESSAGE
DATA

F i g u r e 1 5 -4

L a yo u t o f Ma i l bo x Me s s ag e B l o c k

1 5- 1 4

VAX/VMS DEVI C E DR I VERS
b.

Th e
f i r s t t wo
l ong wo r d s
i n the m e s sag e b l o c k
a re
i n i t i a l i ze d
to
c o n ta i n v a l ue s e x pe c t ed
by
the
I/0
po s t p r o c e s s i ng r o u t i ne s .
( Th e f i r s t l o ng wo r d po i n t s
to
the m e s s ag e d a t a ,
s to r ed i n the m e s sa g e b l o c k , a nd the
s e c o nd l o ngwo r d po i n t s t o t h e us e r b u f f e r , wh e r e th e d a t a
w i l l be c o p i ed by t h e I /O c ompl e t i o n spec i a l k e r n e l AS T . )
Th e a d d r e s s o f t h e u s e r ' s b u f f e r i s
r e t r i eved
f r om
th e
I RP $ L_M E D I A f i e l d i n t h e r e a d r e qu e s t ' s I RP .

Th e o u t s tand i ng m e s s ag e
m a i l bo x i s d e c r em e n t e d .

p l a c ed
is
in
r eque s t
the
r ead
ID of
process
Th e
become the h i gh-o r d e r
i t wi l l
( so
tha t
I RP $ L M E D I A+ 4
l o ngwor d o f t h e I O S B f o r t h e wr i te r eq u e s t $ Q I O ) , a n d t h e
S S $ N O RMAL s uc c e s s c o d e i s p l aced i n t h e l o w- o r d e r wo r d
o f th e I O S B ( I RP $ L_M ED I A )

c o un t

( UC B $W_M SGC NT )

fo r

the

•

Ro u t i n e C OM $ P O S T ( i n C OMDRVS UB ) i s c a l l ed to
i n s e r t the
wr i te
r e que s t ' s
I R P on
the
I /0 po s t p r o c e s s i ng queue .
Th i s r o u t i n e i s c a l l ed , r a th e r than
i s s u i ng
the
R E QC OM
mac ro ,
so th a t a n o t h e r I RP i s n o t d e q u e ued ( b e c a us e o n l y
r e a d r e que s t I RPs a r e q ue ued to the UC B wa i t i ng to
enter
the start
I /0
routine) .
A l s o , t h e b u s y s t a t us o f t h e
un i t i s no t c h ang e d ( UC B $V_B SY i n UCB $W_S TS ) .

Wh e n C OM $ PO S T r e t u r n s c o n t r o l ,
the
process
ID o f
the
wr i t e
r e que s t ' s I RP i s pl a c ed in Rl ( a nd w i l l even t ua l l y
b e c om e t h e h i g h - o r d e r
l o ng wo r d o f
the
r e ad
r e que s t ' s
I OS B ) ,
and
the
R E QC OM m a c r o i s c a l l ed to compl e t e the
r ead r eque s t .
Th e n ex t
r e ad
r e que s t
( i f any)
wi l l
a u toma t i c a l l y b e d eq u e ued ,
and
t h e s t a r t I /0 s e q uenc e
r e pea t e d .
I f no r e ad r e que s t i s o u t s t a nd i ng ,
the
busy
b i t w i l l be c l e a r ed .

15. 4 . 3. 3
P r oc e s s i ng a Ma i l bo x Wr i t e Reque s t - Wh e n a
us e r
i ssues a
wr i t e m a i l bo x
$QIO,
t h e ma i l bo x
d r i ve r
FDT
r o u t i n e s pe r f o rm the
fo l l o wi ng g e n e r a l f unc t i o n s .
1.

Th e s a m e va l i d a t i o n c h e c k s t h a t we r e mad e i n s t e p s 1 a n d 2 o f
the
r ead
$ Q I O F DT r o u t i n e s a r e pe r fo rmed h e r e , e x c e pt th a t
t h e b u f f e r c o n t a i n i ng t h e d a t a t o b e wr i t t e n i s c h e c k e d
fo r
r e ad a c c e s s i n s t e a d o f wr i t e a c c e s s .

A m e s s a g e b l o c k i s a l l o c a t e d f r om no npa g ed po o l
( by
routine
E XE $ A LONON PAG E D ) ,
a n d i n i t i a l i z e d ( a s s h o wn i n F i g u r e 1 5 - 4 ) .
Th e d a t a t o be wr i t t e n to t h e m a i l box
i s c o p i ed
i n to
the
message block .
Th e r e a r e 22 byt e s of o v e r h e a d ( no t m e s sag e
d a t a ) i n th e me s s a g e b l o c k .

I P L i s r a i s ed to I P L $ MA I LB OX , a n d the m a i l bo x i s e x am i ned to
see
i f t h e r e i s e no ugh r oom f o r the m e s s ag e .
I f n o t , I PL i s
r e s to r e d , t h e me s s ag e b l o c k i s d e a l l o c a t ed , a nd
the
r e qu e s t
is
p l a c ed
in a
r e s o u r c e wa i t s t a t e
( wa i t i ng
fo r
the
R S N $_MA I LBOX r e s o u r c e )
•

Th e m e s sa g e b l o c k i s i n s e r t e d o n the que ue o f m e s sag e s w i th
l i s th e a d
UCB $ L MB M S G Q+ 4
( un l e s s the r e
1 s a r e a d r e que s t
o u t s t a n d i ng , i n-whTc h c a se c o n t r o l i s t r an s f e r r ed to
s tep
4
i n t h e s t a r t I /0 r o u t i n e , d i s c u s sed i n the p r ev i o u s s e c t i o n ) .
1 5 -1 5

VAX/VMS DEVI C E DRIVERS
5.

An y q u e ued w r i t e a t t e n t i o n A S Ts a r e d e l i v e r ed ( by pa s s i ng the
l i s th e a d
ad d re s s ,
UC B $ L MB W A S T ,
to
COM $ D E LATTNAS T ,
as
- - d e s c r i b ed i n Ch a p t e r 5 ) .

I P L i s l o we r ed to wh a t i t wa s b e fo r e s t e p 3 wa s e x ec u t ed , a nd
a c h e c k i s m a d e to s e e i f the I O $ M N OW f un c t i o n c o d e mo d i f i e r
wa s s pe c i f i ed i n t h e $ Q I O c a l l .

I f s pec i f i e d , t h e wr i t e I /O r e qu e s t i s c ompl e t e d ( by c a l l i ng
E XE $ F I N I S H I OC ) .
Oth e rwi se ,
t h e p r o c e s s i ng o f t h e wr i t e I /0
r e q u e s t i s s u s p e n d ed ( un t i l a r e a d r eq u e s t
is
i s s u ed ) ,
a nd
control
i s pa s s e d t o EXE $ Q I ORETURN , s o some o th e r p r o c e s s i n
t h e s y s tem m a y r e s um e ex e c u t i o n .

15. 5

C ONSOLE INTERFAC E

Th e c o n s o l e i n t e r f a c e , t h e po r t i o n o f t h e p r o c e s s o r th a t
i n i t i ates a
b o o t s t r a p o pe r a t i o n a nd
pe rm i t s m i c r od i ag no s t i c s to e x e c u t e , i s n o t
s p e c i f i ed by t h e VAX a r c h i te c t u r e b u t
is
C PU s pe c i f i c .
Th e VAX
Ha r d wa r e
Ha nd b o o k c o n t a i n s m o r e d e ta i l s a b o u t the c o n so l e i n te r f aces
fo r each CPU .

15. 5. 1

VAX- 1 1 /7 5 0 Conso l e I n t e r f a c e

Th e c o n s o l e i n t e r f a c e o n t h e VAX- 1 1 / 7 5 0 c o n s i s t s o f a t e rm i n a l , a TU 5 8
cartr idge
d ev i c e ,
a n opt i on a l
r emo t e d i ag n o s i s po r t ,
a nd
some
m i c r o c o d e i n the VAX- 1 1 / 7 5 0 p r o c e s s o r .
Wh e n t h e c o n s o l e p r og r am h a s
c o nt r o l
( th e th r e e a ng l e b r a c k e t p r ompt h a s b e en t yped on t h e c o n s o l e
t e rm i n a l ) , t h e VAX- 1 1 / 7 5 0 p r o c e s so r
i s n o t e x e c u t i ng m a c r o
code
( b e c a u s e i t i s e x e c u t i ng t h e c o n s o l e m i c r o c o d e ) .
Th e r e a r e e i g h t p r o c e s s o r i n t e r n a l r eg i s t e r s o n t h e VAX- 1 1 / 7 5 0
c ommun i c a t i ng w i t h t h e the t wo c o n s o l e d ev i c e s .
In add i t ion , the
a r c h i te c t u r e spec i f i e s t h a t t h e PR $ T XDB r eg i s te r i s to
be
u s ed
c ommun i c a t i o n f r om VAX ma c ro c ode
to
the c o n s o l e s ub s ys t e m .
s p e c i a l u s e s o f t h i s r eg i s t e r ( so m e o f wh i c h a r e
not
u s ed
by
VAX- 1 1 / 7 5 0 ) a r e l i s t ed i n Tab l e 1 5 - 1 .

15. 5. 2

fo r
VAX
fo r
Th e
the

VAX- 1 1/7 8 0 Conso l e I n t e r f a c e

Th e VAX- 1 1 / 7 8 0 c o n so l e i n te r f a c e c o n s i s t s o f a n LS I - 1 1
m i c r o c om p u t e r ,
a
f l o ppy d i s k , t h e c o n s o l e t e rm i n a l , a nd a n o p t i o n a l r emo te d i a g no s i s
po r t ( a s d e sc r i b ed i n t h e VAX Ha r dwa r e Ha nd boo k }
Th e c o n s o l e p r og r am
e x ec u t e s o n t h e
L S I - 1 1 ( u s i ng t h e PD P- 1 1 i n s t r uc t i o n s e t )
Bec a use
t h e c o n s o l e p r og r am i s
e x e c u t i ng
on a
s e pa r a t e
p r o c e s so r ,
it
is
po s s i b l e
fo r
the c o n s o l e
s ub s ys t em
t o pe r f o rm a
l i m i t ed s e t o f
f un c t i o n s w i tho ut h a l t i ng t h e VAX - 1 1 /7 8 0 C P U .
•

•

Th e VAX- 1 1 / 7 8 0 u s e s f o u r p r o c e s so r i n t e r n a l r eg i s t e r s
to
c ommun i c a t e
to
the two c o n s o l e d ev i c e s .
Th a t i s , u n l i k e the VAX - 1 1 / 7 5 0 , t h e same
r eg i s t e r s a r e u s ed to c omm un i c a t e to two d ev i c e s .
Th e d ev i c e
ID
is
e nc o d ed
i n to
the cont r o l
b i ts
to
a l l o w VAX- 1 1 m a c r o c o d e
to
d i s t i ng u i sh b e twe e n
the
two
d ev i c e s .
Al l
c o n s o l e d a ta
t rans f e r
o pe r a t i o n s a r e pe r fo rmed b e twe e n the VAX- 1 1 /7 8 0 C PU a n d th e LS I - 1 1 C PU
u s i ng t h e s e fo u r i n t e r n a l p r o c e s s o r r eg i s te r s .
Th a t
is,
no
d i rect
1 5- 1 6

VAX/VMS DEVI C E DR IVERS
t r a ns f e r s a r e m a d e b e twe e n t h e VAX- 1 1 /7 8 0 CPU a nd t h e c o n so l e t e rm i na l
o r f l o ppy d i s k .
As w i th t h e VAX - 1 1 /7 5 0 , t h e P R $ TXDB r eg i s t e r i s a l so
u s ed fo r c ommun i c a t i o n t o the c o n s o l e p r og r am ( Tab l e 1 5 - 1 ) .
Ta b l e 1 5 - 1
Spe c i a l Us e s o f t h e Co n so l e PR $ TXDB Reg i s t e r
Re g i s t e r
Co nten t s

Me an i ng

Comments

FOl

So ftwa r e Do ne

Used by the VAX-1 1 /7 8 0 Mem o r y
ROM p r og ram t o no t i f y con so l e
p r og ram tha t i t h a s l oca ted
6 4 K byt e s o f g ood memo r y

F02

Rebo o t the CPU

U s ed b y t h e b ug c hec k r o ut i n e
t o r eboo t t h e sys tem a f te r a
f a t a l bug c h e c k

F03

C l ea r Wa rm- sta r t
Fl ag

Th i s fl ag i s ma i n ta i n ed b y the
prog ram .
VAX- 1 1 /7 8 0 c o n so l e
Th e r e i s no ana l og ue on the
VAX- 1 1 /7 5 0 .

F04

Cl ea r Co l d -sta r t
Fl ag

Th i s fl ag i s ma i n ta i n ed by the
c onso l e p r og ram
on
e i th e r
p r o c e s so r to pr event nested
boo t s t r a p a t tempt s .

15. 5. 3

Da ta T r a n s f e r be twe e n th e VAX- 1 1 CPU a nd Conso l e Dev i c e s

Th e i n t e r n a l p r o c e s s o r r eg i s t e r s , PR$ TXC S a nd PR $ R XC S ( a nd
PR $ C S R S
a nd
PR $ C S TS o n t h e VAX- 1 1 /7 5 0 )
a re used
f or c o n t r o l a nd s ta t us
i n f o rm a t i o n ( to e n a b l e i n te r r up t s a nd to i nd i c a t e
tha t
a d ev i c e
is
Th e o th e r two i n t e r n a l r eg i s t e r s , PR $ RXDB a nd PR $ T XDB ( a n d
r ea d y ) .
PR $ C SRD a nd PR$ C S TD o n th e VAX- 1 1 /7 5 0 ) a r e used
t o t r a n sfe r d a t a .
Th e - TXxx
( a nd CS Tx ) r e g i s t e r s a r e u s ed f o r t r a n sm i t o pe r a t i o n s ( wi th
r e s pe c t to the VAX- 1 1 C PU ) wh i l e t h e RXx x
( a nd
C S Rx )
r eg i s t e r s a r e
u s ed f o r r ec e i v e o pe r a t i o n s .
Mo s t d r i v e r s t r e a t d ev i c e r eg i s t e r s a s i f t h e y we r e memo r y l o c a t i o n s ,
u s i ng
MOVB o r M OVW i n s t r uc t i o n s
to
r ea d
o r w r i te d a t a i n tho s e
r eg i s te r s .
I n t h e c a s e o f t h e c o n so l e , t h e MTPR a n d MFPR i n s t r uc t i o n s
a r e u s e d t o t r a n sm i t a nd r ec e i v e d a ta , r e spec t i v e l y .
Fo r e x amp l e , t h e
fo l l o w i ng i n s t r uc t i o n s o n t h e VAX- 1 1 /7 8 0
M T PR

d a t a , # P R $ _TXDB

t r a n sm i t d a t a

MFPR

# P R $ _RXDB , d a t a

r ec e i ve d a t a

t r a n sm i t a nd r ec e i ve d a ta .
Th e d a ta
is
sent
or
r e c e i ve d
as a
l on g wo r d ,
w i th b i ts
<7 : 0>
c o n t a i n i ng th e AS C I I c ha r a c t e r , a nd b i t s
< 1 1 : 8 > i d e n t i f y i ng wh i ch c o n s o l e d ev i c e ( t e rm i n a l o r f l o ppy d i s k )
is
s en d i ng
or
r ec e i v i ng
t h e d a ta .
On t h e VAX - 1 1 /7 5 0 , t h e d i s t i nc t i o n
b e t we en d ev i c e s i s m a d e b y c ho i c e o f r eg i s t e r i n s t e a d o f by i nc l ud i ng
a d ev i c e c o d e i n a d a t a b u f f e r r eg i s t e r .
No t e t h a t a l l d a t a i s pa s s e d
a c h a r a c t e r at a t ime , even to the
f l o ppy d i s k .
Th e r e fo r e ,
it
is
r ec omm e nd ed
that a
sepa rate
f i l e s ACP b e r e que s te d t o s e rv i c e t h e
c o n so l e b l o c k s to r a g e d ev i c e .
1 5- 1 7

VAX/VMS DEVI C E DRI VERS
15. 5. 4

C o n s o l e I n te r r up t D i spa t c h i ng

As t h e p r ev i o u s d i sc u s s i o n o f p r o c e s s o r r eg i s t e r s i nd i c a t e s ,
the
two
c o n s o l e d ev i c e s
( t e rm i n a l
a nd
b l o c k s to r a g e d ev i c e )
a r e t r e a t ed
s l i g h t l y d i f fe r e n t l y on the VAX- 1 1/7 5 0 and
the
VAX- 1 1 /7 8 0 .
On
the
VAX- 1 1 /7 5 0 ,
t h e b l o c k s to r ag e d ev i c e ( a T U 5 8 c a r t r i d g e ) h a s i t s o wn
c o n t r o l r eg i s te r s a nd i t s o wn i n t e r r up t v e c to r s .
On
the
VAX-1 1 / 7 8 0 ,
the
two
d ev i c e s
a re
h a nd l ed mo r e
a s a s i ng l e e n t i t y , w i th c ommo n
r o u t i n e s d i s t i ng u i sh i ng
t e rm i n a l
o pe r a t i o n s
f rom
f l o ppy
d i sk
o pe r a t i o n s .
Th i s d i f f e r e n c e i s a l s o r e f l e c t e d i n th e d i f f e r e n t fo r m s
o f i n t e r r upt d i spa tc h i ng o n the two p r o c e s so r s .

15. 5 . 4 . 1
Co n s o l e Te rm i na l I n t e r r up t s - Wh e n
the
s ys t em
is
bo o t s t r a pped ,
t h e Sy s t em Co n t r o l B l o c k ( S C B ) i s i n i t i a l i z ed ( f r om t h e
SCB t empl a t e i n S C BVE C TOR ) so tha t t h e two v e c to r s a t o f f s e t s
F 8 a nd
FC
( h e x ) po i n t to c o n s o l e i n t e r r up t s e r v i c e r o u t i n e s ( CON $ I NTD I S I f o r
c o n s o l e i n put a nd C ON $ I NTD I S O f o r
c o n so l e o u t pu t )
B o th
r o ut i n e s
r e s po nd
to
an
i n t e r r up t by s a v i ng
r eg i s t e r s R O
th r o ug h R 5 , a nd
t r a n s f e r r i ng c o n t r o l to r o u t i n e s i n C ON I NTDS P ( C ON $ I N T I N P fo r
c o n so l e
i n p u t , C ON $ I NTOUT f o r c o n s o l e o u tpu t ) .
•

C ON $ I NT I N P r e ad s t h e d a ta a nd c o n s o l e d ev i c e i d en t i f i c a t i o n
f r om t h e
PR $ R XDB
r eg i s te r
a nd
d e te r m i n e s wh e th e r the i n te r r upt wa s f r om t h e
c o nso l e t e rm i n a l o r b l o c k s to r a g e d ev i c e .
I f t h e i n t e r r up t wa s
f r om
t h e c o n s o l e t e rm i n a l , t h e n the c h a r a c t e r r e a d o pe r a t i o n i s h a nd l ed by
the t e rm i n a l d r i v e r ' s c h a r ac t e r b u f f e r i ng
r o ut i ne who s e
add ress
is
s to r ed
i n g loba l
l o c a t i o n TTY$G L P U TNXTC H .
Th e c h a r a c t e r i s a l s o
e c h o ed b a c k t o the c o n s o l e t e rm i n a l by b e i ng p l a c ed
i n the
PR $ _TXDB
r eg i s t e r .
Ro u t i n e C ON $ I NTOUT t r a n sm i t s d a ta t o the c on s o l e t e rm i n a l th r o ug h
the
PR $ _TXDB
r eg i s te r
a nd
d e te rm i n e s wh e th e r the r e s u l t i ng i n t e r r up t i s
f r om t h e t e rm i n a l
or
t h e c o n s o l e b l o c k s to r ag e d ev i c e .
If
the
i n t e r r upt wa s c a used by t h e t e rm i n a l , t h e n t h e t e rm i n a l o u tpu t r o u t i n e
( wh o s e ad d r e s s i s s to r e d i n l o c a t i o n TTY$G L G E TNXTC H ) i s c a l l ed to g e t
t h e n e x t c ha r a c t e r f o r o u t pu t .
No t e t h a t the h a nd l i ng o f c o nso l e t e rm i n a l I /O i s d o n e by
the no rma l
t e rm i n a l d r i v e r r o u t i n e s .
On l y the i n i t i a l f i e l d i ng o f i n te r r up t s a nd
t h e d ev i c e r eg i s t e r s th a t a r e
r e ad
o r wr i t te n d i s t i ng u i sh c o n s o l e
t e rm i n a l
I /O
f r om o pe r a t i o n s t h r o ug h the r eg u l a r te rm i n a l i n te r f a c e .
No t e a l s o tha t the c o n s o l e t e rm i n a l a l wa ys i n te r r up t s a t
I PL 2 0
( th e
l owe s t d ev i c e
I P L u s ed
by d r i v e r s ) o n bo th t h e VAX-1 1 /7 5 0 a n d t h e
VAX- 1 1 /7 8 0 .

1 5 . 5 . 4 . 2 Conso l e B l o c k S to r a g e Dev i c e I /0 - Th e d ev i c e d r i v e r
a nd
a s so c i a t e d d a t a b a se
fo r
t h e c on s o l e b l o c k s to r a g e d ev i c e a r e n o t
l o ad ed un t i l a n e x pl i c i t C ONNE C T C ON S O L E c ommand i s i s s u e d to
SYSGEN .
At t h a t t i me , t h e d ev i c e d r i v e r a nd d a t a s t r uc t u r e s a pp r o p r i a t e to the
spec i f i c p r o c e s so r a r e l o a d ed i n to m emo r y a nd i n i t i a l i z e d .
A C ONN ECT C ON S O L E c omma nd tha t i s i s s ued to
SYSGEN o n a
VAX- 1 1 /7 5 0
c a us e s t h e
TU5 8 d r i v e r
( c a l l ed
DDDR I VE R )
t o b e l o ad ed and d a ta
s t r uc t u r e s f o r a d ev i c e c a l l ed C SA 1 to be
bui l t .
I n a dd i t i on ,
two
d ed i c a t ed
v e c t o r s i n the SCB ( a t o f f s e t s F O a nd F 4 h e x ) a r e l o a d ed to
po i n t t o i n te r r up t d i s pa tc h c o d e c o n t a i n e d i n t h e CRB f o r CSA1 .

1 5- 1 8

VAX/VMS DEV I C E DR IVERS
Th e DDDR IVER t h us r e s po nd s t o c o n s o l e T U 5 8 i n te r r up t s in
exa c t l y the
s a m e wa y t h a t
it
r e s p o nd s to i n t e r r up t s g e n e r a t ed b y a T U 5 8 o n t h e
UN I B U S .
Th e o n l y d i f f e r e n c e b e twe e n
the
two
i n t e r r up t s
is
tha t
conso l e TU58
i n t e r r up t s o c c u r a t I P L 2 3 wh i l e UN I B US T U 5 8 i n t e r r up t s
o c c u r a t I PL 2 0 .
A C ONNE C T C ON S OLE c omma nd tha t i s i s s ue d to
SYSGEN o n a
VAX- 1 1 /7 8 0
c a us e s
the
c o n s o l e f l o ppy d i s k d r i v e r ( c a l l ed DXDR I VE R ) t o b e l o ad ed
a nd d a t a s t r uc t u r e s fo r a d ev i c e c a l l ed C SA l to be b u i l t .
B e c a u s e the
c o n s o l e f l o ppy i n te r r up t s th r o ug h the s a m e vec to r s u s e d b y t h e c o n so l e
t e rm i n a l , n o f u r th e r S C B mod i f i c a t i o n i s r eq u i r ed a t th i s t i m e .
Wh e n a c o n s o l e d ev i c e i n t e r r upt o c c u r s , t h e i n t e r r up t se r v i c e
r o ut ine
d e te r m i n e s wh e th e r the i n t e r r up t wa s f r om t h e c o n s o l e t e r m i n a l o r f r om
I f the i n te r r up t wa s f r om the b l o c k s to r ag e
the b l o c k s to r ag e d ev i c e .
d ev i c e ,
if
the
c o n s o l e h a s b e en c o n n e c ted ( a UCB e x i s t s f o r d ev i c e
C SA l ) , a nd i f the i n t e r r up t wa s e x pe c t ed ( th e UC B $V ! NT b i t i s s e t
in
the
s ta t us wo r d i n t h e UC B ) , t h e n t h e d r i v e r c o n t ext i s r e s t o r ed f r om
t h e U C B a nd t h e d r i v e r p r o c e s s i s r e s um e d a t the s a v ed PC ( UC B $ L F PC ) .
O th e r w i s e , t h e i n t e r r up t i s c o n s i d e r ed s p u r i o us a nd s i mpl y d i sm i ss e d .

1 5 . 5 . 4 . 3 Do u b l e Ma pp i ng o f Buf f e r Pag e s - One i n t e r e s t i ng f e a t u r e o f
the
TU58 d r iver
a nd
t h e f l o ppy d i s k d r i v e r , d r i v e r s tha t t r a n s f e r s
d a ta o n e c h a r a c t e r
at a
t ime ,
is
tha t they use
the
r o ut i n e s
I OC $ F I L S PT ,
I OC $M OVFRUS E R , a nd I OC $MOVT O US E R ( i n BUFFERC T L ) t o d o ub l e
m a p a pag e i n the u s e r ' s d a t a b u f f e r i n to
s ys t em ad d r e s s s pa c e
( so
tha t d a ta c a n b e t r a n s f e r r ed d i r e c t l y t o a nd f r om the u s e r ' s b u f f e r ) .
U s e r b u f f e r pag e s a r e n o t no rm a l l y a c c e s s i b l e b e c a us e d ev i c e d r i v e r s
execute
i n s ys t em c o n t e x t a nd
d o n o t h a v e p r o c e s s a d d r e s s s pa c e
ava i l a b l e t o t h em .
B y d o ub l e m a pp i ng a
b u f f e r pag e
i n to
a
s y s tem
add r e s s
r a ng e ,
t h e e n t i r e u s e r b u f f e r c a n be a c c e s s ed by t h e d ev i c e
d r i v e r o ne pag e a t a t i m e .
Th e sys t em pag e ta b l e en t r y u s e d
t o map
the
pag e
is
r e s e r v e d i n t h e d r i v e r , b y s e t t i ng the DPT $V S VP b i t i n
the F LAG S a r g um e n t to t h e D PTAB m a c r o .
By m a k i ng
the user
buffer
i s a c c e s s i b l e th r o ug h s ys t em v i r t ua l
add r e s se s ,
t h e s e two d r i v e r s c a n u s e VM S d i r e c t I /0 , e v e n tho ug h t h e y
a r e n o t DMA d ev i c e s .
Th i s a l l o ws t h em t o i s s ue v i r t ua l I /0
r e que s t s ,
call
e x i s t i ng
A C P FDT r o u t i n e s , a nd u s e the v i r t ua l I /0 c ompl e t i o n
r o u t i n e s i n t h e I /0 po s tp r o c e s s i ng c od e .

1 5-19

C HAPTER 1 6
I/0 SYSTEM S ERVI C E S

A l l I /0 o p e r a t i o n s pe r f o r m e d o n a d ev i c e a r e r e q u e s t e d u s i ng
th e
I /0
Som e t im e s ,
the
I /O s y s t em s e rv i c e s a r e c a l l ed o n
s ys tem s e rv i c e s .
b eh a l f o f a u s e r by s ys t em c ompo n e n t s
s uc h a s
RM S .
Th i s c h a pt e r
d e sc r i be s
•
•
•
•

16. 1

wh a t m u s t b e d o n e b e fo r e a n I /O r e qu e s t c an b e mad e
a s s i g nme n t a nd d ev i c e a l l o c a t i o n ) ,

( c h a nne l

h o w a n I /O r e q u e s t i s s e n t t o a d ev i c e d r i v e r ,
h o w a u s e r i s no t i f i ed o f t h e c ompl e t i o n o f a n
a nd
h o w a u s e r c a n o b t a i n i n f o rm a t i o n abo u t a
o r I /O r e q ue s t .

I/0

pa r t i c u l a r

r e q ue s t ,
d ev i c e

A S S IGN I NG AND D EASS IGN ING CHANN E L S

I n o rd e r t o r e q u e s t a n I /0 o pe r a t i o n o n a d ev i c e , a p r o c e s s n e e d s to
to
t he s ys tem .
i d ent i fy
the
d ev i c e
Th e so f twa r e m e c ha n i sm u s ed to
l ink a process
to
a d ev i c e
i s c a l l ed
a channel .
Onc e a
use r
e s ta b l i sh e s a c h a nn e l to a d ev i c e ( us i ng t h e $ A S S IGN s y s tem s e r v i c e ) ,
t h e u s e r m a y i s s u e I /O r e q u e s t s ( wi th the
$ Q I O s ys t em s e r v i c e )
fo r
tha t d ev i c e by s pe c i f y i ng t h e c h a n n e l n um b e r a s s i g n ed to t h e d ev i c e .
I f t h e u s e r no l o ng e r wa n ts to u s e t h e d ev i c e ,
the
$ DA S SGN s ys tem
s e r v i c e c a n b e u s ed t o d e a l l o c a t e the c h a n n e l a s s i g ne d to the d ev i c e .

16. 1. 1

C h a n n e l As s i g nm e n t

A c h a nn e l i s d e sc r i b e d by a Ch a n n e l Co n t r o l B l o c k ( CC B ) , l o c a t e d i n a
d ed i c a t ed po r t i o n o f P l s pa c e ( F i g u r e 1 - 7 , Tab l e E - 4 ) .
Wh e n a c h a n n e l
i s a ss i g ne d
t o c e r t a i n n o n s h a r e a b l e d ev i c e s ,
the
u s e r m a y a l so
a s s o c i a te
a m a i l bo x
w i th
t h a t d ev i c e t o r ec e i ve s t a t u s i n f o rm a t i o n
s uc h a s t h e a r r i v a l o f u n so l i c i t ed i nput f r om a t e rm i n a l .
I t is up to
t h e d ev i c e d r i v e r
for
e ac h d ev i c e
t o e i th e r
u s e o r i g no r e th i s
a s s o c i a t ed m a i l bo x .
Appe nd i x A o f t h e VAX/VMS G u i d e
to Wr i t i ng
a
Dev i c e D r i ve r c o n t a i n s a c om p l e t e d e sc r i pt i o n o f t h e C C B .
Th e $ A S S I G N s ys tem s e r v i c e c a l l s o n I OC $ FFCHAN a n d
I OC $ S EARC HDEV
( in
I O S UB PAG D )
to
f i nd
a
f r ee
I /0 c h a n n e l ( CC B ) , a n d to f i nd t h e Un i t
Co n t r o l Bl o c k ( UC B ) f o r t h e d ev i c e t h a t
i s b e i ng
a s s i gned .
Af t e r

1 6-1

I/0 SYS TEM SERVI C E S
tha t ,
one
d ev i c e i s

the f o l l o w i ng pa th s i s t a k e n , d e pend i ng on wh e th e r the

•

a l ocal

•

a s po o l ed d ev i c e ,

•

th e n e two r k d e v i c e N E T : , o r

•

a r em o t e d e v i c e

{ no t a n e t wo r k )

d ev i c e ,

{ a d ev i c e l o c a t ed o n a n o th e r nod e ) .

16. 1.1. 1
Lo c a l Dev i c e A s s i g nment - Th i s i s t h e
t h e As s i g n C h a n n e l s ys t em s e rv i c e .
1.

n o rma l

pa th

t h r o ug h

Th e DEV$V S HR b i t i n UC 8 $ L D EVC HAR i s c h e c ked to s e e
if
the
d ev i c e i s -a s h a r e ab l e d ev i ce .
I f t h e d ev i c e i s n o n s h a r e a b l e ,
t h e n t h e d e v i c e i s i m pl i c i t l y a l l o c a t ed t o t h e
process
{ by
pl a c i ng t h e p r o c e s s I D , f r om PC 8 $ L_P I D , i n to UC 8 $ L_P I D ) .
Th e UC8 a d d r e s s i s s t o r ed i n C C 8 $ L U C 8 .
Wh e n e v e r
the
use r
i ssues an
I /0 r e q u e s t , t h i s po i nte r i s u s e d to i d e n t i f y t h e
d ev i c e .
I n th i s wa y , t h e d ev i c e c an b e
fo und m uc h
faster
th a n b y r e pe a t ed l y c a l l i ng o n I OC $ S EARC HDE V , wh i c h f i nd s a
d ev i c e UC 8 f r om t h e d ev i c e n am e { s uc h a s TT8 3 ) .

I f a n a s s o c i a t ed ma i l bo x wa s r e que s t ed , i t i s
i d e n t i f i ed
by
p l a c i ng
the
UC 8 a d d r e s s
{ o f the ma i l bo x ) in th e UC 8 $ L AM8
f i e l d of t h e UC B f o r the d ev i c e to wh i c h t h e c h a n n e l i s be i ng
a s s i g n ed .
Th e UC B $W R E FC f i e l d o f t h e a s s o c i a t ed m a i l bo x i s
i n c r eme n t ed , a n d t h e CC 8 $V AM8 f l ag i s s e t i n
CC8 $ 8 STS
to
i nd i c a t e th a t a n a s s o c i a t ed ma i l bo x i s p r e s e n t .
No t e-th a t no
a s s o c i a t i o n i s mad e i f
•
e
•

the d e v i c e i s a f i l e - o r i e n t ed d ev i c e { i d e n t i f i ed
P EV$V_F OD b i t i n UC 8 $ L_DEVC HAR ) ,
t h e d e v i c e i s sh a r e a b l e

the

{ D EV$V_S HR i n UC 8 $ L_DEVC HAR ) , o r

the d e v i c e a l r e ad y h a s a n
UC8 $ L_AM8 f i e l d i s n o n z e r o ) .

a s s o c i a t ed

{ UC 8 $W_R E FC )

ma i l bo x

{ th e

Th e d e v i c e r e f e r e n c e c o un t

Th e a c c e s s mod e { p l u s o n e ) a t wh i c h
the c h a n n e l
i s b e i ng
a s s i g ned
is
s to r ed i n C C 8 $ 8 AMOD .
I OC $ F FCHAN i d e n t i f i e s a n
u n u s e d C C 8 by l o o k i ng i n the CC 8 $ 8 AMOD f i e l d .
I f t h e v a l ue
s t o r e d th e r e i s a z e r o , t h e C C 8 i s-n o t b e i ng u s ed .

An y f l ag s a s s o c i a t ed w i t h the
c h a nn e l
( s uch
a s C C 8 $V AM8
i nd i c a t i ng
th a t an a s s o c i a t ed m a i l bo x i s p r e s e n t ) a r e s tor ed
i n C C 8 $ 8_STS .

Th e c h a n n e l n um b e r { r e a l l y a n i nd e x i n to
the
CC8 t a b l e
in
process
P 1 s p a c e , p r ov i d ed b y I OC $ F FC HAN ) i s r e t u r n ed t o the
u s e r at
the add r e s s
s pe c i f i ed
in
the
CHAN a rg um e n t
to
$ASS I GN .

Th e no r m a l
s uc c e s s f u l
r e t u r n ed to t h e us e r .

c ompl e t i o n

1 6-2

i s i n c r em e n t e d .

code

{ S S $_N ORMAL )

I /0 SYSTEM S ERVI C ES
1 6 . 1 . 1 . 2 Spe c i a l Ac t i o n When As s i g n i ng a Spo o l ed Dev i c e - I f
the
D E V $ V S PL b i t i n UC B $ L DEVC HAR i s s e t , then the d ev i c e b e i ng a s s i g ne d
i s a spo o l ed d ev i c e .
The o n l y d i f fe r en c e i n c h a n n e l
a s s i g nm e n t
fo r
s po o l ed
d ev i c e s i s tha t the s ta t u s f i e l d i n the c h a nn e l c o n t r o l b l o c k
Th e d ev i c e a s s o c i a t ed w i t h the s po o l ed d ev i c e
( C C B $ 8 S T S ) i s c l e a r ed .
i ts UC B a d d r e s s s to r ed i n the UC B $ L A M B f i e l d wh e n t h e d ev i c e wa s
had
Wh e n a n I /0 r e q ue s t i s pa s s ed to
a
s po o l ed d ev i c e ,
s e t to s po o l ed .
the
$ Q I O sys tem
s e rv i c e
r ec og n i z e s tha t the d ev i c e i s s po o l ed a nd
a c t ua l l y pe r f o rm s t h e I /0 r e que s t to t h e a s s o c i a t ed d ev i c e .

1 6 . 1 . 1 . 3 Ass i g n i ng a Ch a n n e l to the Ne two r k Dev i c e - I f
the
d ev i c e
b e i ng
a s s i g n ed
i s a n e t wo r k d ev i c e ( th a t i s , t h e u s e r i s a s s i g n i ng a
channel
to
t h e N E T d ev i c e ,
p r obab l y
to
pe r fo r m
t a s k - to - t a s k
c omm un i c a t i o n ) , t h e n t h e f o l l o w i ng s t e p s a r e t a k e n .
1.

A n e two r k U C B i s c r ea t ed by I OC $ C REATE_U C B ( i n I O S U B PAGD ) .

Th e U C B i s mad e t o l o o k l i k e a m a i l bo x UC B t h a t i s ma r k ed f o r
d e l e te
( th e UC B $V D E LMBX b i t i n UC B $W DEVS T S i s s e t ) .
Wh e n
t h e u s e r d e a s s i g n s th e c h a n ne l , t h e UCB-w i l l b e d e l e t ed .

Th e u s e r ' s by t e c o un t q uo t a a nd l im i t a r e r ed uced b y t h e s i z e
o f the UCB .

Fu r th e r p r o c e s s i ng p r o c e ed s
n o n s h a r e a b l e d ev i c e .

the

c a se

l oc a l ,

1 6 . 1 . 1 . 4 Dev i c e s Lo c a te d o n Ano th e r Nod e - I f
the
d ev i c e
b e i ng
a s s i g n ed
i s a r emo t e d ev i c e ( th a t i s , tb e f i l e spe c i f i c a t i o n c o n ta i n s
a d o ub l e c o l o n ) , t h e n a m e s s a g e m u s t b e t r a n sm i t ted t o th a t nod e .
1.

Th e d ev i c e n ame i s t r a n s l a t e d i n c a s e i t i s a l og i c a l name .

An $ A S S IGN i s i s s ued o n
d ev i c e .

A $ Q I O ( w i t h the
I O$ ACCESS
f un c t i o n c od e )
is
i s s ue d
on
beha l f
of
th e
u s e r - ( s pec i f y i ng
even t
f l ag num be r 3 1 ) to
e s t a b l i s h a n e two r k c o nn e c t i o n .
If
the
$QIO fa i l s ,
the
c h a n n e l i s d e a s s i g n ed u s i ng t h e $ DA S SGN s y s t em s e r v i c e .

Th e c h a nn e l n um b e r to the N E T :
use r .

Th e S S $ R EMOTE s uc c e s s f u l c om p l e t i o n s t a t u s
the u s e r .

16. 1 . 2

beha l f

the

d ev i c e

use r

r e t u r ned
is

the

r e t u r ned

NET :

the
to

C h a n n e l De a s s i g nm e n t

Th e $ DAS SGN s ys t em s e rv i c e d e a s s i g n s a p r ev i o u s l y a s s i g ned I /O c h a nn e l
a nd
clears
the
l i n kag e a nd c o n t r o l i n f o rma t i o n i n the c o r r e s po nd i ng
CCB .
Th i s i s a c compl i shed w i th the f o l l o w i ng s t eps .

1 6-3

I /0 SYSTEM S ERVI C E S
1.

An y o u t s t a n d i ng I /O i s c a nc e l l ed .
( A $ CANC E L s y s tem s e r v i c e
c a l l i s i s s ue d f o r t h e c h a n n e l o n b e h a l f o f t h e u s e r . )

I f a f i l e i s o p e n o n t h e c h a nn e l
( i nd i c a t e d
by CCB $ L W I N D
b e i ng n o n z e r o ) , t h e n t h a t f i l e i s c l o s ed ( by i s s u i ng a $Q I OW
w i t h t h e I O $ D EACC E S S f un c t i o n c od e ,
a nd
s pe c i f y i ng
eve n t
f l ag n um b e r 3 1 ) .

I f any I /O i s s t i l l o u t s t a nd i ng ( i nd i c a t ed by CCB $W r oc b e i ng
nonze ro ) ,
the
process
i s pl a c ed i n to an RSN$ A STwA I T wa i t
state
( wa i t i ng
fo r
the
I /0 c ompl e t i o n
AST(s )
to
be
d e l i v e r ed ) .
Ch a p te r 8 d i s c u s s e s wa i t s t a t e s i n d e ta i l .

Th e c h a n n e l i s a c t ua l l y d e a s s i g ned by c l e a r i ng th e CCB $ B_AMOD
f i eld .

If
th i s wa s
the
last
( UC B $W R E FC c o n t a i n s a
c l e a r ing UC B $ L_P I D ) .

I f the d ev i c e i s m a r k e d f o r d i sm o u n t ( th e DEV$V DMT b i t
in
UC B $ L D EVC HAR
i s s e t ) a n d i t wa s m o un ted w i th a-VM S AC P ( th e
f o r e i g n b i t D EV$V F O R
is
c lea r ) ,
t h e d i sm o un t , m o un t ed
( D EV$V MNT ) , r e a d che c k ( D EV$V RCK ) , wr i te c h e c k ( D EV$V WC K ) ,
a nd s oftwa r e wr i t e l o c k e d ( D EV$V SWL ) b i t s
i n UC B $ L DEVC HAR
a re cl ea red .
Th e
UC B $ L VC B fi e l d i s c l e a r e d , a n d - i f th a t
f i e l d wa s n o t z e r o , t h e Volum e Co n t r o l B l o c k po i n t ed
t o by
tha t
f i e l d i s d ea l l o c a ted .
Al s o , the vo l um e p r o t e c t i o n m a s k
( UC B $W P RO T ) a n d t h e s o f twa r e vo l um e va l i d
bit
( UC B $V VA L I D
i n UC BSW_ S T S ) a r e c l e a r ed .

Th e a s s o c i a t ed d ev i c e d r i v e r ' s c a nc e l I /0 r o u t i n e
i s c a l l ed
to
pe r fo r m a n y d ev i c e - d epend e n t o pe r a t i o n s ( s e e the VAX/VM S
UC B $W R E FC
is
G u i d e to Wr i t i ng a De v i c e D r i v e r ) , u n l e s s the
g re a te r
than
1,
a n d t h e d ev i c e i s no t a l l o c a t e d ( o r un l e s s
t h e d ev i c e i s n o t a l l o c a t e d t o t h e c u r r en t p r o c e s s ) .

I f a ma i l b o x wa s a s so c i a t e d wi th t h e d ev i c e wh e n the c ha nn e l
wa s
a s s i g n e d ( i nd i c a t e d b y C C B $ V A M B i n C C B $ B S T S ) , then t h e
l i n kag e wi t h t h e m a i l bo x i s c l e a r ed b y

16 . 2

c h ann e l
a s s i g n ed
to
the
d ev i c e
0) ,
t h e d ev i c e i s d e a l l o c a t e d ( by

c l e a r i ng UC B $ L_AMB ,

d e c r em e n t i ng UC B $W_R E FC fo r the m a i l bo x UC B , a n d

c a l l i ng I OC $ D E LM B X ( i n I O SUBNPAG ) to s e e i f t h e m a i l bo x
UCB s h o u l d be d e l e t e d ( i n c a s e t h i s wa s the l a s t p r o c e s s
r e f e r e n c i ng a t em po r a r y ma i l bo x ) .

I f t h e d ev i c e t o wh i c h t h e c h a n n e l wa s a s s i g ne d wa s a m a i l bo x
( i n d i c a t e d b y t h e DEV$V M B X b i t i n UC B $ L DEVC HAR ) , I OC $D E LM B X
i s a g a i n c a l l ed to s e e Tf t h a t m a i l bo x sho u l d b e d e l e t e d .

DE VI C E A L LOCAT I ON AND DEA LLOCAT I ON

A p r o c e s s a l l o c a t e s a d ev i c e ( us i ng
the
$ A L L OC s ys tem s e r v i c e )
to
r e s e r v e t h a t d ev i c e fo r e x c l u s i v e u s e .
A p r o c e s s d e a l l o c a te s a d ev i c e
( u s i ng t h e $ DA LL OC s ys t em s e rv i c e ) to r e l i nq u i sh e x c l us i v e o wn e r sh i p .

1 6-4

I / 0 SYS TEM S ERVI C E S
Dev i c e Al l o c a t i o n

16. 2. 1

Th e fo l l o w i ng s t e p s a r e t a k e n by E X E $ A L LOC t o a l l o c a te a d ev i c e .
1.

Th e p r o c e s s I D ( PC B $ L P I D )
f i e l d ( UC B $ L_P I D ) .

s to r ed

the

d ev i c e

Th e d ev i c e a l l o c a t e d b i t

Th e d e v i c e r e f e r e nc e c o un t

Th e a c c e s s m o d e a t wh i c h t h e d ev i c e i s a l l o c a t e d i s p l a c ed i n
UCB $ B AMOD .

( D EV$V_A L L i n UC B $ L_DEVC HAR )
( UC B $W_R E FC )

o wn e r
i s set .

i s i nc r em e n t ed .

An y o f the fo l l o w i ng c o nd i t i o n s wi l l p r ev e n t d ev i c e a l l o c a t i o n .
•

Th e d e v i c e i s a l r e a d y a l l o c a ted by a n o th e r p r o c e s s
is nonze r o ) .

•

Th e d ev i c e r e f e r e n c e c o un t ( UC B $W_R E F C )

Th e mo un ted b i t

•

16. 2. 2

( UC B $ L_P I D

i s no n z e r o .

( UC B $V_MNT i n UC B $ L_DEVC HAR )

Th e spo o l e d b i t ( UC B $V S P L i n UC B $ L DEVC HAR )
p r o c e s s d o e s no t have AL L S PO O L p r i vil eg e .

i s set .
i s s e t , a nd

the

Th e d e v i c e i s n o n s h a r e a b l e , a nd t h e r e qu e s t i ng
process
does
no t h a v e a c c e s s r i g h t s ( l o c a t ed th r o ug h PC B $ L ARB ) a l l o w i ng
i t t o a l l o c a t e the d ev i c e ,
a s d e t e r m i ned
by -the d e v i c e ' s
own e r U I C ( U C B $ L_OWNU I C ) .

Dev i c e De a l l o c a t i o n

A p r o c e s s m a y c h o o s e t o d e a l l o c a t e a s i ng l e d ev i c e ,
or
all
d ev i c e s
a l l o c a t ed
to
it.
Fo r e a c h d ev i c e
tha t
is
t o be d e a l l o c a ted ,
E XE $ DA L LOC f i nd s i t s UC B a d d r e s s
e i th e r
d i re c t l y ,
f r om
the
DEVNAM
a r g um e n t
i n the $ DAL LOC c a l l , o r by e x am i n i ng e a c h UCB i n the s y s tem .
E a c h UCB i n the s ys t e m c a n be fo und by
f o l l o w i ng
a
l i n k ed
l i st of
Dev i c e Da t a
Bl o c k s
( D DB s ) ,
t h a t n am e e a c h d ev i c e c o n t r o l l e r i n the
s y s t em ( t h e f i r s t DDB i s po i n t ed t o by g l oba l s ymbo l
I OC $G L DEVL I S T ) .
E a c h DDB c o n ta i n s a po i n t e r to t h e f i r s t d ev i c e UCB on t h e con t r o l l e r ,
a nd a l l o f t h e UCBs fo r the d ev i c e s o n a g i v e n c o n t r o l l e r
a re
l i n ked
t o g e th e r .
A d ev i c e i s d eal l o c a ted i f
1.

t h e UC B $ L P I D f i e l d ma t c h e s
p r o c e s s i s s u i ng t h e $ DA L L OC ,

t h e a c c e s s m o d e a t wh i c h t h e d e a l l o c a t e r e q u e s t i s b e i ng mad e
is
at
l e a s t a s p r i v i l eg ed a s the a c c e s s m o d e a t wh i c h t h e
d ev i c e wa s a l l o c a t ed ,

t h e a l l o c a ted b i t ( D EV$V_A L L i n UC B $ L D EVC HAR )

t h e r e f e r e nc e c o un t ( UC B $W_R E FC )

1 6-5

the

PC B $ L P I D

e q ua l s 1 .

f i eld

i s s e t , a nd

the

I /0 S YS TEM S ERVI C E S
Th e d ev i c e i s d e a l l o c a t e d b y
1.

c l e a r i ng
the
UC B $ L_D E VC HAR ) ,

bit

( D EV$V_A L L

c l e a r i ng t h e d ev i c e o wn e r p r oc e s s i d f i e l d

( UC B $ L_P I D ) ,

d e c r emen t i ng t h e d e v i c e r e f e r e n c e c o un t

c a l l i ng t h e d e v i c e d r i v e r ' s c a nc e l I /0 r o u t i n e , a nd

r e t u r n i ng t h e n o r m a l s uc c e s s f u l c om p l e t i o n c o d e t o
i n R O ( S S $ _N ORMAL ) .

d ev i c e

a l l o c a t ed

( UC B $W_R E FC ) ,

the

use r

$ Q I O SYSTEM S ERVI C E

16. 3

Th e $ Q I O s ys t em s e rv i c e ( i n S YS Q I O RE Q ) p r o v i d e s t h e c a pa b i l i t y f o r
a
u s e r to i n i t i a t e a n I /0 o pe r a t i on by q ue u i ng a r e que s t to t h e d ev i c e ' s
On c e t h e I /0 o pe r a t i on h a s b e en i n i t i a t e d , c o n t r o l
a s s o c i a t ed d r i v e r .
wi l l
be
r e t u r ned
t o t h e u s e r , wh o c a n s yn c h r o n i z e I /0 c om p l e t i o n i n
o ne o f th r e e wa ys .
•

•

Th e p r o c e s s c a n e n t e r an e v e n t f l ag wa i t s t a t e un t i l the
I /O
r e q u e s t c o mpl e t e s , wa i t i ng f o r t h e s pe c i f i ed e v e n t f l ag to b e
set .
Th e add r e s s o f a n AST r o u t i n e tha t w i l l be e x e c u t e d wh en
the
I /0 c ompl e t e s c a n b e p a s s e d
to
$QI O .
I n th i s c a s e , t h e
p r o c e s s c a n c o n t i n u e e x e c u t i ng
or
wa i t ,
d e pend i ng
on
the
pa r t i c ul a r m e thod of s yn c h r o n i za t i o n .
Th e I /0 s t a t u s b l o c k c a n b e po l l ed f o r a c ompl e t i o n
sta tus .
Th e
s ta tus
f i eld
i n t h e I O S B i s c l e a r ed by $ Q I O a nd s e t by
the s p e c i a l k e r n e l AST t h a t c ompl e te s
an
I /O
r e q ue s t
in
process contex t .

wh i c h
is
A l te r na t i ve l y ,
the
$ Q I OW s ys t em s e rv i c e may b e u s ed ,
e qu i v a l en t
to
the
$ Q I O s ys t em s e rv i c e fo l l o wed by a $WA I TFR s y s tem
s e rv i c e g ua r a n t e e s
tha t
the
I /O
s e rv i c e .
Us i ng t h e $ Q I OW s ys t em
control
i s t r a n s f e r r ed b a c k to the
o pe r a t i o n w i l l c ompl e t e b e fo r e
us e r .

16. 3. 1

Dev i c e - I nd e pend ent P r e p r o c e s s i ng

E XE $ Q I O b eg i n s p r e p r o c e s s i ng an I /O r e q ue s t b y
1.

v a l i d a t i ng th e d ev i c e- i nd epend e n t $ Q I O p a r ame t e r s ( ev e n t f l ag
n um b e r ,
channel
n umb e r ,
I /0
f un c t i o n co d e , a nd I /0 s t a tus
block) ,

c h e c k i ng f o r n o n z e r o AS TCNT q uo t a i f an AST a d d r e s s
i s pr esen t ,

c l e a r i ng t h e s pe c i f i ed e v e n t f l ag
no e v e n t f l ag wa s s p e c i f i ed ) ,

1 6-6

a rg um e n t

( o r e v e n t f l ag n um b e r 0

I /0 SYS TEM S ERVI C E S
4.

c l e a r i ng t h e I /O s t a t u s b l o c k ( i f o n e wa s s pe c i f i ed ) , a nd

v e r i f y i ng
th a t t h e d ev i c e
UC B $W S TS m u s t b e s e t )

l i ne

( UC B $V_ON L I N E

•

An I /0 r e que s t pac k e t ( I R P )
i s a l l o c a ted
f r om n o npag ed
po o l .
If
po s s i b l e ,
th i s
a l lo c a t i on
i s d o ne f r om a q u e u e o f p r e a l l o c a ted I R Ps
( po i n t ed to b y
I OC $G L I RPF L ) .
Othe rwi se ,
r o u t i ne
EXE $A L LOC I R P i n
M EM ORYA LC
i s c a l l e d to a l l o c a t e a n I R P f r om t h e g en e r a l nonpag ed po o l
a r ea .
Ob t a i n i ng a n I R P f r om t h e p r e a l l o c a t ed q u e u e
takes
l ess
t ime
t h a n c a l l i ng t h e a l l o c a t i o n r o u t i n e .
Th e d ev i c e- i nd e p e nd e n t s e c t i o n o f t h e I RP
the fo l l o w i ng f i e l d s :

i n i t i a l i ze d ,

•

t h e d ev i c e- i nd ep e nd e n t $ Q I O pa r am e t e r s

•

t h e p r o c e s s b a s e p r i o r i t y ( f r om PC B $ B_P R I B )

•

t h e p r o c e s s I D ( f r om PC B $ L_P I D )

•

t h e d e v i c e UC B a d d r e s s

•

f l ag
in
t h e I RP $V B UF I O
b u f f e r ed - I /0 o pe r a t i o n ,
o pe r a t i o n )

is
I RP $W S T S
( wh i c h
a
a nd -c l e a r e d
for

i n c l ud i ng

a
fo r
set
d i rect
I /0

Th e p r o c e s s ' s p r i v i l eg e s a r e c h e c k e d to g ua r a n t e e t h a t i t m a y pe r f o rm
the
r e q ue s t e d
I /0
f unc t i o n .
In
the c o u r s e
o f c h e c k i ng p r o c e s s
p r i v i l eg e s , a r ea d o r wr i te v i r t ua l
I /0
r e que s t
f unc t i o n c o d e
is
c o nv e r t e d
i n to
t h e c o r r e s po nd i ng r e ad o r wr i t e l og i c a l f un c t i o n cod e
( un l e s s t h e v i r t ua l r e que s t i s f o r a f i l e -o r i e n t ed
d ev i c e ,
DEV$V FOD
i n UC B $ L_D EVC HAR i s s e t )
-

•

I f a n A S T wa s r eq u e s t ed , t h e A S T q uo t a ( PC B $W ASTCN T ) i s d e c r em e n ted ,
a nd t h e AST q uo t a upd a te f l ag ( AC B $V_Q U OTA ) is s e t i n I R P $ B_RMOD .
C o n t r o l i s t h e n t r a n s f e r r ed to a f un c t i o n d ec i s i o n t a b l e ( FDT ) r o u t i n e
( by a J S B ) i n the s e l e c t e d d ev i c e d r i v e r .
Th i s r o u t i n e i s r e s p o n s i b l e
f o r i n t e r p r e t i ng t h e d ev i c e-d e pe nd e n t $ Q I O pa r am e t e r s ( P l t o P 6 ) .
If
the
FDT r o u t i ne
returns control
to
E XE $ Q I O
( by i s s u i ng a n R S B ) ,
E XE $ Q I O c a l l s a n o th e r FDT r o u t i ne i n
the d r ive r
( a nd
r e pe a t s
th i s
p r o c e s s un t i l s ome FDT r o u t i ne ex i t s u s i ng a me thod o th e r th a n RSB ) .

16. 3 . 2

FDT Ro u t i n e s

Func t i o n d ec i s i o n t a b l e ( FDT ) r o u t i n e s a r e d ev i c e - sp e c i f i c
ex tens i on s
to
$QIO .
Th e i r
p r i m a r y p u r po s e i s t o v a l i d a t e t h e d ev i c e - d epend en t
$ Q I O pa r am e t e r s ( P l t o P 6 ) .
A d ev i c e d r i v e r c a n
i nc l ud e c us tom i z e d
FDT
r o ut i ne s o r
u s e some o f t h e g e n e r a l p u r po s e r o u t i n e s t h a t a r e a
p a r t o f the s ys t em i m ag e .
A l t h o ug h s ome FDT r o u t i n e s a r e i n c l ud ed
in
a d r i v e r i m ag e , t h e y a r e l og i c a l l y a d ev i c e -d epend e n t ex t e n s i o n o f t h e
$ Q I O s y s tem s e rv i c e .
FDT r o u t i n e s e x e c u t e i n t h e c o n t e x t o f t h e p r o c e s s
th a t
i s s ue d
the
$ Q I O r e que s t .
Th e r e f o r e ,
t h ey h av e a c c e s s to d a t a i n the u s e r ' s P O
a nd P l a d d r e s s s pa c e .
FDT r o u t i n e s c ommun i c a t e i n f o r ma t i o n abo ut
the
I /O
r e que s t
to
the
d r iver
by
pa s s i ng
i n fo rm a t i o n
in
th e
d ev i c e - d epend e n t s ec t i o n o f t h e I R P .
1 6-7

I /0 SYSTEM SERVI C E S
FDT r o u t i n e s f o r d i r e c t I /0 ( I /0 d o n e d i r e c t l y t o
a
use r buf fe r )
insure
tha t
e a c h b u f f e r pag e i s v a l i d a nd l o c k e d i n to m emo r y .
( Th i s
i s d o ne b y i n c reme n t i ng t h e r e f e r e n c e c o un t i n t h e
PFN d a t a b a s e
fo r
e a c h phys i c a l
pag e
i nv o l v ed
in
the
t r an s fe r . )
FDT
r o u t i ne s fo r
b u f f e r ed I /0 o p e r a t i o n s m u s t a l l o c a t e a b u f f e r f r om n o n pa g ed po o l th a t
wi l l
b e u s ed b y t h e d r i v e r f o r t h e a c t ua l t r an s f e r .
I f t h e o pe r a t i o n
wr i t te n
1s
c o p i ed
i nto
i s a b u f f e r ed wr i t e , t h e d a t a t h a t i s b e i ng
th i s
buf f e r .
Sys t em s p a c e b u f f e r s a r e r e q u i r ed b e c a u s e the d r i v e r
p r o c e s s e s t h e I /0 r e qu e s t i n s y s t em c o n tex t a nd
only has access to
s ys t em v i r t ua l a d d r e s s s pa c e .
FDT r o u t i n e s a r e d e sc r i b ed i n d e t a i l i n
the VAX/VM S G u i d e t o Wr i t i ng a De v i c e D r i v e r .

16. 3 . 3

I /O Po s t p ro c e s s i ng

A f t e r a d ev i c e d r i v e r c om p l e t e s
an
I /0 o pe r a t i o n ,
it
i nv o k e s
the
R E QC OM m a c r o .
Th i s m a c r o p l a c e s t h e I R P o n t h e I /0 po s t p r o c e s s i ng
q u e u e , a n d r e q ue s t s a so f twa r e i n t e r r upt a t I PL $ I O PO S T ( I PL 4 ) .
Th e
I / O po s t p r o c e s s i ng
r o u t i ne
( I O C $ I O PO S T ,
i n lOC I O PO S T )
r un s a s a
r e s po n s e
to
the
so f twa r e
i n t e r r upt .
It
i mpl em e n t s
the
d ev i c e - i n d e p e nd e n t
facets
of
I /0 c ompl e t i o n , a nd h a nd l e s pag i ng I /0
c ompl e t i o n a s we l l ( s e e c h a p t e r 1 2 ) .
Some o f t h e I /0 po s tp r o c e s s i ng o pe r a t i o n s ( fo r ex ampl e , s e t t i ng
event
f l ag s , un l o c k i ng b u f f e r pag e s , a nd d e a l l o c a t i ng b u f f e r s ) a r e pe r fo rmed
in t h e I /0 p o s t p r o c e s s i ng
i n te r r up t s e r v i c e
r o u t i ne
( I OC $ I OPOS T ) ,
wh i l e o th e r
o pe r a t i o n s
( s uc h
a s wr i t i ng t h e I /0 s t a t u s b l oc k ) a r e
pe r f o rmed b y a s pe c i a l k e r n e l A S T r o u t i n e ( wh i c h e x e c u t e s
i n process
c o n t e x t , a nd th e r e f o r e h a s a c c e s s t o p r o c e s s ad d r e s s s p a c e ) .
Wh e n an I RP
is
r emoved
f r om
the
I /0 po s tp r o c e s s i ng
l i sthead
I OC $G L P S F L ) ,
I OC $ I O PO S T f i r s t d e te r m i n e s
o pe r a t i o n wa s a buf f e r ed o r d i r e c t r e q ue s t .

q u e ue
( w i th
if
the
I/O

16. 3. 3. 1
D i r ec t I / 0 Compl e t i o n
P o r t i o n s o f d i r e c t I /0
r e que s t c a n
b e c ompl e ted i n the I P L 4 I /0 p o s t p r o c e s s i ng i n t e r r up t s e r v i c e r o u t i n e
w i tho u t t h e b e ne f i t o f p r o c e s s c o n t e x t .
-

Th e p r o c e s s d i r e c t I /0 c o un t i n t h e so f twa r e PC B
( at o ffset
PC B $W D I OCNT ) i s i n c r em e n t e d , i nd i c a t i ng o n e l e s s o u ts t a nd i ng
d i r e ct I /0 r e qu e s t .

Th e b u f f e r po i n t ed to by I RP $ L S VA PT E i s un l o c k e d , u s i ng
the
I R P $ W B CNT a nd I R P$W B OF F f i e lds to d e t e rm i n e t h e s i z e o f t h e
l o c k ed b u f f e r .
B u f fe r pag e s a r e
un l o c k e d by d e c r eme n t i ng
t h e i r a s s o c i a t ed r e f e r e n c e c o un t s i n the PFN d a t a b a s e .
Th i s
s t e p m a y r e s u l t i n t h e i r b e i ng p l a c ed on the f r e e o r mod i f i ed
pag e l i s t .

Th e I R P $V E XT E ND b i t i n I R P $W S T S i s c h e c ked .
I f tha t b i t i s
set ,
i t - i nd i c a t e s a n I R P ext e n s i o n ( I RPE ) i s po i n t ed to by
I R P $ L E XTEND .
Th e I R P E m a y c o nta i n up to two l o c k e d b u f f e r s
( po i n t ed
t o by I R PE $ L S VA PT E l a n d I R PE $ L SVA PT E 2 , w i th s i z e s
d e t e rm i ned b y I R P E $W BOF F l a nd I R PE $ L BCNTl , and I R PE $W B O F F 2
a nd
I R PE $ L B CNT2 , res p e c t i v e l y ) .
Thes e buf fe r s , i f p res e n t ,
a r e un l o c k ed , a nd a c h e c k i s mad e to s e e i f t h e I RPE $V E XT E ND
bit
in
I R PE $W S TS
is
set .
If
s o , t h e s ame p r o c edu r e i s
r e p e a ted , un t i l - t h e l a s t I RPE i n the l i n k e d
l ist
is
f o und ,
a nd i t s b u f f e r s un l o c k e d .
1 6-8

I /0 SYSTEM S ERVI C E S
4.

Th e e v e n t f l ag s pe c i f i ed i n t h e $ Q I O c a l l i s s e t ( by c a l l i ng
r o ut i ne
S C H $ P O S TE F ,
wh o s e
o pe r a t i o n
i s d i sc us s ed
in
Ch a p t e r 9 ) .

Th e d i r e c t I /0 s pe c i a l k e r ne l AST ( D I RPO S T i n
I OC I O PO S T )
is
q u e ued
to t h e p r o c e s s ( u s i ng t h e I R P $ L P I D f i e l d to i d en t i f y
t h e p r o c e s s to wh i c h the A S T s ho u l d be que ued ) .
Th e
I RP
is
u s ed
as
the AST c o n t r o l
block
fo r
r o u t i n e S C H $ QA S T ( a s
d e sc r i bed i n Ch a p te r 5 ) .

Th e r ema i nd e r o f I /0 c om p l e t i o n f o r a d i r e c t I /0 r e q ue s t
takes
i n p r oc e s s c o n t e x t i n t h e s pe c i a l k e r n e l A S T c a l l ed D I R PO S T .

place

Th e ac c um u l a t ed d i r e c t I /0 c o un t ( s to r ed i n PHD $ L D I OCNT )
is
i n c r em e n ted .
Th i s
i s a n a c c o un t i ng
s t a t i s tTc
th a t
is
r e po r ted to t h e a c c o u n t i ng manag e r ( th e j o b c o n t r o l l e r )
wh e n
t h e p r o c e s s i s d e l e t ed .

Th e I /0 i n p r o g r e s s c o un t e r
( C C B $ W_ I OC ) i s d e c r emen t e d .

I f th i s wa s t h e l a s t I /0 f o r the c h ann e l ,
a nd
th e r e
is
a
d e a c c e s s r e q ue s t fo r t h e c h a n n e l p e nd i ng ( C C B $ L D I RP d o e s n o t
e q u a l z e r o ) , tha t d e a c c e s s r e que s t i s queued to - the AC P
( so
th a t a f i l e c an be p r o p e r l y c l o s e d o r s ome s i m i l a r o pe r a t i o n
pe r f o rme d ) , b y c a l l i ng r o u t i n e I OC $WAKAC P .

I f a n I /0 s t a t u s b l o c k wa s
r e q u e s ted b y t h e
user ,
it
is
wr i t t e n
us i ng
th e q ua d wo r d
s t a r t i ng a t I R P $ L I O S T l ( s ame
o f f s e t as I R P $ L_ME D I A ) .

I f a n y I R PEs we r e u s ed , t h e y a r e d e a l l o c a t e d .

I f t h e us e r r e q u e s t ed an A S T f o r t h e $ Q I O c a l l ,
the
IRP i s
ag a i n u s ed a s a n AST c o n t r o l b l o c k , a nd i s que ued to the u s e r
( th e I R P w i l l be d e a l l o c a t ed by t h e no rma l
AST p r o c e s s i ng
s c h eme , a s d i s c u s s e d i n Ch a p t e r 5 ) .

I f t h e u s e r d i d n o t r e que s t a n A S T t o be d e l i v e r ed
upo n
c o mpl e t i o n o f th e $ Q I O c a l l , t h e I R P i s d e a l l o c a t e d .

the

channel

control

bloc k

th e

1 6 . 3 . 3 . 2 B u f f e r ed I /O Comp l e t i o n - Th e po r t i o ns o f
b u f f e r ed
I/O
c ompl e t i o n
that
take
place
in
t h e I PL 4 i n te r r up t s e r v i c e r o u t i n e
d i f f e r f r om t h e d i r e c t I /0 c a s e b e c a u s e o f t h e d i f f e r e n c e s i n t h e wa y
t h e two k i nd s o f r eq u e s t s a r e p r o c e s s ed .
1.

Th e p r o c e s s b u f f e r ed I /0 c o un t { PC B $W B I OCNT ) , t h e c o un t
o u t s t a nd i ng b u f f e r ed I /0 o pe r a t i o n s , Ts i n c r em e n t e d .

Th e b y t e c o un t q uo t a th a t wa s a l l o c a t ed fo r the s ys tem b u f f e r
i s g i v e n b a c k b y a d d i ng I R P $W_B O F F t o J I B $ L_B YTCNT .

I R P $W S T S
I f t h e I /0 f u n c t i o n wa s a r e ad { b i t I R P$V F UNC
in
i s s e t ) , t h e B U F P O S T r o u t i n e { i n mod u l e I OC I O PO S T ) i s u s e d a s
the spec i a l ke r nel AST r o u t i ne add r e s s .

Oth e r w i s e , D I RPOST i s u s ed a s the s pe c i a l k e r n e l AST r o u t i n e
add r e s s ,
a n d t h e b u f f e r u s ed to h o l d the d a t a w r i t t e n to t h e
d e v i c e , i f a n y , i s d e a l l o c a t ed ( th e b u f f e r ' s a d d r e s s i s f o un d
i n I R P$ L_SVA PT E ) .
1 6-9

I /0 SYSTEM S E RVI C E S
5.

I n e i th e r c a s e , b e fo r e t h e s p e c i a l k e r n e l AST i s q u e u e d ,
the
event
f l ag
s p e c i f i ed
in
the
$ Q I O c a l l is set ( a s in the
d i r e c t I /0 c a s e ) .

Th e s pe c i a l k e r ne l A S T c a l l ed B U F P O S T i s
u s ed
fo r
the
case
of a
buf f e r ed
r e ad
o pe r a t i o n ,
because
t h e d a t a m u s t b e c o p i ed f r om t h e
s ys t em bu f f e r t o t h e b u f f e r s p e c i f i ed i n the o r i g i n a l $ Q I O r e q u e s t .
1.

Af t e r t h e d a t a i s c o p i ed , t h e
s ys t em b u f f e r
n e ed ed s o i t i s d e a l l o c a t ed t o n o npag ed po o l .

Th e a c c um u l a t ed
b u f f e r ed
I /0 c o un t a c c o un t i ng
( s t o r e d i n PHD$ L_B I OCNT) i s i n c r em e n ted .

l o ng e r

s tat i st i c

Th e r em a i n i ng s t eps tha t t h i s r o u t i n e m u s t p e r fo rm a r e
i d en t i c a l
to
the
o pe r a t i o n s p e r fo rm e d by D I RPOST .
B UF PO ST c o n t i n u e s a t s t e p 2 i n
tha t r o u t i n e .

16 . 4

I /0 CANC E LLAT I ON

Th e $ C ANC E L s y s t em s e rv i c e c an c e l s a l l I /O i s s ue d to a d ev i c e
f r om a
s pe c i f i ed c h a nn e l by s c a n n i ng a l l o f t h e I RPs q u e u e d to th e d ev i c e UC B
( s t a r t i ng a t UC B $ L I O QF L ) .
S e v e r a l c ond i t i o n s m u s t h o l d
fo r
an
I /O
r e q u e s t t o b e c ancel l ed .
•

•
•

Th e r e qu e s t c a n n o t b e a v i r tua l
r e que s t
( i nd i c a t e d
by t h e
s e t t i ng o f t h e I RP $ V V I RTUA L b i t i n I RP $W S T S ) .
I n g en e r a l ,
I /O c a nno t b e c a n c e l led on d i s k o r t a pe d evi c e s .
Dr i ve r s fo r
t h e s e d ev i c e s i n s u r e tha t t h e I RP $V V I RTUA L b i t i s s e t o n a l l
r e q ue s t s t h a t c a nno t b e c a nc e l l ed . Th e r e q ue s t i ng p r o c e s s
ID
p r o c e s s I D i n I R P $ L _P I D .

( PC B $ L_P I D )

ma tche s

the

s to r ed

Th e r e que s t e d c h a nn e l n umbe r i n the C HAN a rg um e n t t o
m a t c h e s t h e s t o r ed c h a n n e l n umb e r i n I R P$W C HAN .

$ C ANC E L

Th e I /0 i s c a nc e l l ed by
1.

c l e a r i ng the b u f f e r ed r e ad b i t ( I R P$V FUNC i n I R P $W S TS )
fo r
b u f fe r ed
I /0
f un c t i o n s
( i d e n t i fied
by
I R P $V-B UF I O
in
I R P $W_ S T S ) ,

p l a c i ng t h e S S $ C ANC E L f unc t i o n c o d e i n the l o w o rd e r wo rd o f
t h e I /0 s t a t us b l o c k , a nd

p l a c i ng
the
IRP
in
the
I /O po s tp r o c e s s i ng
q u e ue ,
and
r e q ue s t i ng
an
I /O po s t pr o c e s s i ng
s o f twa r e
i n t e r r upt
( at
I PL $ _I O POS T ) a f t e r t h e f i r s t I R P i s pl ac ed o n to the que u e .

Th e d r i v e r c a nc e l I /0 r o u t i n e i s c a l l e d t o a l l o w t h e d r i v e r to pe r f o rm
any d e s i r ed
c l e a n up o pe r a t i o n s ,
a nd
to
c ancel
the
I /O
r e que s t
c u r r e n t l y i n p r og r e s s .
I f t h e r e i s a n y o u t s t a nd i ng I /0 , o r AC P - c o n t r o l l ed
f i l e a c t i v i ty i n
p r og r e s s , E XE $ C ANC E L a l l o c a t e s a nd i n i t i a l i z e s a n I R P o n beha l f o f the
u s e r ( a nd c h a rg e s t h e u s e r ' s b u f f e r ed I /O q uo t a , PCB $W B I OC NT , fo r
an
I/O
r eque s t ) .
Th e
IRP
i s que ued to t h e AC P f o r f urth e r p r o c e s s i ng
( us i ng r o u t i n e E XE $ Q I OAC P P KT
in
SYS Q I OR E Q ) .
Th e
I R P s pe c i f i e s a
1 6-1 0

I /0 SYSTEM S E RVI C E S
f unc t i o n c od e
of
I O $ A C PC ONTRO L ,
i nd i c a t e I /0 c ompl e t i o n�

16. 5

a nd

u s e s e v e n t f l ag n um b e r 3 1 t o

MA I LBOX C R EAT I ON AND D E L ET I ON

Ma i l bo x e s a r e v i r t ua l d ev i c e s
used
fo r
i nterprocess
c ommun i c a t i o n .
Th e y a r e c r e a t ed by t h e $ C REMBX s ys t em s e rv i c e .
The r e a r e two k i nd s
o f m a i l bo x e s ,
t empo r a r y a nd
p e rm a n en t .
Tempo r a r y m a i l bo x e s a r e
d e l e t ed a u toma t i c a l l y wh e n no m o r e p r o c e s s e s h a v e c h a n n e l s a s s i g n ed t o
them , wh i l e pe rm a n e n t m a i l bo x e s m u s t b e e x p l i c i t l y m a r k e d
fo r d e l e t e
us i ng
t h e $ D E LMBX s y s t em s e r v i c e .
( Af t e r b e i ng ma r k e d fo r d e l e t e ,
pe rm a n e n t m a i l bo x e s a r e d e l e t e d wh e n no mo r e pr o c e s s e s h a v e c h a nne l s
a s s i g ned to th em )
•

16. 5. 1

Ma i l bo x C r e a t i o n

Th e $ C R EMBX s ys t em s e rv i c e c r e a t e s a v i r t ua l ma i l bo x d e v i c e named MBn :
a nd a s s i g n s a n I /0 c h a n n e l to i t .
E XE $ C R EMBX beg i n s b y t r an s l a t i ng t h e l og i c a l
n ame
s p e c i f i ed
by t h e
user
in
the
L OGNAM pa r a m e t e r
( i f a n y ) , a nd f i nd i ng a f r e e c h a n n e l
( CC B ) to a s s i g n to t h e m a i l bo x ( u s i ng I OC $ FFCHAN ) .
I t a l so
ver i f i e s
tha t the u s e r h a s the a pp r o p r i a t e p r i v i l eg e ( s ) f o r the type o f m a i l bo x
b e i ng c r e a t ed :
PRMMBX
TM PMBX
S HM EM

fo r a pe rmanen t m a i l bo x
f o r a t empo r a r y m a i l bo x
f o r a ma i l bo x i n sha r e d memo r y

I f a l og i c a l n a m e h a s b e en s pe c i f i e d , E XE $ C REMBX s e a r c h e s a l l ex i s t i ng
ma i l bo x
UCBs to s e e i f a ma i l bo x wi th th a t n ame a l r e a d y ex i s t s .
If a
m a t c h i s fo und , t h e r e f e r e n c e c o un t f o r th a t ma i l bo x
( UC B $W_R E FC )
is
i nc r emen ted , a nd a c h a n n e l i s a s s i g n ed by
1.

p l a c i ng t h e ma i l bo x UCB a d d r e s s i n C CB $ L_U C B ,

p l a c i ng th e a c c e s s mo d e a t wh i c h
( p l u s o n e ) i n C C B $ B_AMOD ,

the

r e t u r n i ng
the
pa r am e t e r , a nd

r e t u r n i ng w i th a n S S $_N ORMAL c ompl e t i o n s ta t us c od e .

channel

n um be r

c h a nn e l
the

user

wa s

a s s i g ned

the

C HAN

If
a
t empo r a r y m a i l box
i s b e i ng
c r e a t ed
( th e m a i l bo x d i d
no t
p r ev i o u s l y
ex i st ) ,
the process
b u f f e r ed
I /0 b y t e c o un t quo t a
( J I B $ L B YTCNT ) i s c h ec ked to d e te rm i n e i f the p r o c e s s h a s e n o ug h quo t a
to
s uppo r t
the c rea t i on
of
a m a i l bo x
UCB ,
to
buf f e r mes sag e s
( a c c o r d i ng t o the v a l u e s pe c i f i e d i n t h e BUF QUO pa r am e t e r t o $ CREMB X ) ,
a nd to a l l o w f o r o v e r h e a d ( 2 5 6 byt e s ) i n c a s e o f p r o c e s s d e l e t i o n .
If
the
BUFQU O pa r am e t e r
i s not
s pe c i f i ed ,
the
SYSB OOT
p a r a me t e r
DE FMBXB UFQUO
( s t o r ed
at
I OC $GW MBXB FQ U O )
i s u s ed f o r the amo u n t o f
s pa c e r e s e rved t o b u f f e r m e s sa g e s�
A l o g i c a l name b l o c k i s a l l o c a t ed , i f r e q u i r ed , wh i c h wi l l c o n t a i n t h e
l og i c a l
n ame
s pe c i f i ed
fo r
the m a i l bo x by t h e u s e r i n t h e $ C REMBX
cal l .
1 6-1 1

I/0 SYSTEM SERVI C ES
Ro u t i ne I OC $C REATE UCB ( i n I O S UB PAGD ) i s c a l l ed to a c t ua l l y c r e a t e t h e
m a i l bo x
UC B .
The r o u t i n e a l l o c a t e s s pa c e f o r the UC B f r om n o npag ed
po o l , a nd i n i t i a l i z e s f i e l d s i n the UC B ( u s i ng a
templ a te
UCB
f o und
th r o ug h M B $ U C B O i n DEV I C EDA T ) .
1.

Th e ma i l b o x i s m a r k e d on l i n e
UC B $W_S T S ) .

Th e r e f e r e n c e c o un t ( UC B $W_R E F C )

Th e U I C o f t h e c r e a t i ng p r o c e s s ( PC B $ L U I C ) i s e s ta b l i shed a s
t h e own e r o f t h e m a i l bo x ( by l o ad i ng UCB $ L_OWNU I C ) .

Th e UC B i s i d en t i f i ed
a s b e i ng
a
s h a r e a b l e m a i l bo x
DEV$V_S HR a n d DEV$V_MBX b i t s a r e se t i n UCB $ L_D E VC HAR ) .

( th e

Th e UC B i s l i n k e d i n to th e m a i l b o x c o n t r o l l e r ' s
( v i a UC B $ L_L I N K ) .

l ist

A u n i t n um b e r i s a s s i g n ed to the UC B
( in
UC B $W UN I T ) .
Th e
n um b e r
i s i n t h e r ang e o f 1 t o 6 5 5 3 5 ;
wh e n a l l -un i t n um b e r s
i n t h e r a ng e h a v e b e e n u s ed , t h e un i t n umb e r s s ta r t ag a i n a t
1.

Th e m a i l bo x
i nc r em e n t e d .

control ler ' s

( th e UCB $V O N L I N E b i t i n s e t i n
i s s e t to 1 .

d ev i c e

c o un t

d ev i c e

( C R B $W_REFC )

Af t e r I OC $ C R EATE UCB r e t u r n s c o n t r o l , E XE $ C REMBX
1.

p l a c e s t h e b u f f e r q uo t a c a l c u l a t ed e a r l i e r i n UC B $W_B UFQUO ,

p l a c e s t h e p r o t e c t i o n m a s k s pe c i f i ed
PROM SK pa r am e t e r i n UC B $W_VPROT ,

c l e a r s t h e d e v i c e own e r p r o c e s s I D f i e l d

4.
5.

the

user

the

( UC B $ L P I D) I
p l a c e s t h e b u f f e r quo t a p l us UCB s i z e i n UC B $W_C HARG E , a n d

p l a c e s t h e m a x i m um me s s ag e s i z e s pe c i f i ed b y t h e u s e r i n t h e
MAXM SG pa r ame t e r
in
UC B $W D EVB UF S I Z .
( If
MAXM SG wa s no t
s p e c i f i ed ,
t h e S Y S B OOT param e t e r
DEFMBXM XM S G ,
s to r ed
at
I OC $GW_MBXM XM SG , i s u s ed ) .

I f the m a i l bo x
is a
UC B $W DEVS T S
i s set .
t empora r y ma i lbox .
e

p e rm a n e n t m a i l bo x ,
t h e UC B $V P RMMBX b i t
in
Th r e e o th e r s t eps a r e t a k e n i f th e m a i l bo x i s a

Th e UC B$V D E LMBX b i t i n
UC B $W DEVS T S
is
set
to m a r k
the
I t w i l l be d e l e t ed wh e n th e l a s t c h a n n e l
ma i l bo x for d e l e te .
a s s i g n ed t o i t i s d e a s s i g n ed .

•

Th e pr o c e s s byt e c o un t l i m i t ( J I B $ L_BYTLM )

i s r e d uc ed .

•

Th e pr o c e s s by t e c o un t quo ta

i s r ed uc ed .

( J I B $ L_B YTCNT )

I f a l og i c a l name wa s spec i f i e d f o r the m a i l bo x ,
a
l og i c a l name
is
c r e a t ed
us i ng
the
l og i c a l
name b l o c k a l l o c a t e d
ea r l i e r .
Th e
I f no
a s s o c i a t i o n w i th the l og i c a l n ame i s mad e th r o ug h UC B $ L L OGADR .
l og i c a l
n am e wa s
s pec i f i ed ,
UC B $ L L OGADR i s c l e a red .
Fi nal l y , a
the m a i l bo x
c h a n n e l i s a s s i g n ed to the m a i l bo x i n-t h e s am e wa y a s i f
had
a l r e a d y e x i s t ed .
Th e
r e l a t i o n s h i ps among t h e d a t a s t r uc t u r e s
a s s o c i a t ed w i th m a i l bo x c r e a t i o n a r e p i c t u r ed i n F i g u r e 1 6 - 1 .
1 6-1 2

I /0 SYSTEM SERVICES

Process Z
(P1) address space
-

CCB for
Process Z

for
Process A
CCB

Process A
(P1) address space

I
I

Static Executive Data

Paged Pool

Mailbox
unit control
block 0

(optional)
Logical name
block

Template for
other units

_MBn:

System virtual
address space
...
-

...
-

Mailbox
message queue

� - - - - - ------

First
message
��

Mailbox
unit control
block n

Second
message
•

Nonpaged pool
Figure 1 6-1

16.5.2

•

D a t a S t r uc t u r e s As s o c i a t e d w i t h Ma i l bo x C r e a t i o n

Ma i l bo x C r e a t i o n i n S h a r ed Memo r y

No t e tha t a l tho ug h t h e f o rm a t o f
a
s h a r ed
memo r y ma i l bo x
UCB
is
s omewh a t d i f f e r e n t f r om a l o c a l memo r y UC B , t h e g e ne r a l s teps i nv o l v ed
i n the c r e a t i o n o f t h e m a i l bo x a r e t h e s ame .
Al l
of
the
l og i c
is
c o n t a i ned w i th i n t h e s a m e m od u l e ( S YSMA I LB X ) .
One ex t r a l ev e l o f d a ta s t r uc t u r e i s r eq u i r ed
to d e s c r i b e a
s h a r ed
memo r y m a i l bo x .
Th i s s t r uc t u r e ,
c a l l ed
a s h a r ed m emo r y ma i l bo x
c on t r o l b l o c k ( F i g u r e 1 6 - 2 ) , i s l o c a ted i n t h e s h a r ed
memo r y .
Th e
UCBs o n e ac h po r t a s s o c i a t ed w i th the sha r ed m emo r y m a i lbox c o n t a i n
t h e ( po r t- s p e c i f i c ) v i r tua l a d d r e s s o f t h e MB X .
Th e r e a r e th r e e c a s e s
t h a t t h e C r e a t e M a i l bo x s ys t em s e r v i c e c a n enc o un t e r wh e n c r e a t i ng a
m a i l bo x i n s h a r ed m emo r y .
•

I f t h e s h a r ed memo r y m a i l bo x c o n t r o l b l o c k ( F i g u r e 1 6 - 2 ) d o e s
no t ex i s t
( th i s i s t h e i n i t i a l c r e a t i o n o f t h e ma i l bo x ) , i t
i s c r ea t e d f i r s t .
Th e n , t h e u n i t c o n t r o l
block
in
local
m em o r y i s c r e a ted .
A l og i c a l n ame b l o c k i s a l l o c a ted b e c a u s e
1 6-1 3

I /0 SYSTEM S E RVI C ES
s h a r ed memo ry s t r uc t u r e s a l wa ys h av e a n a m e a s so c i a t e d
w i th
t h em .
Fi n a l l y ,
a
channel
i s a ss i g ned
fo r
the c r e a t i ng
process .
•

•

I f the m a i l bo x i s b e i ng c r e a t e d o n th i s po r t
fo r
the
f i rst
t ime ,
a
UC B
is
a l l o c a ted
a nd l o ad ed w i th pa r am e te r s tha t
d e s c r i be t h e ma i l bo x .
A b i t is set
i n a m a i l bo x - d e p e nd e n t
f i e l d i nd i c a t i ng t h a t t h i s m a i l bo x UC B d e sc r i be s a m a i l bo x i n
s h a r ed memo r y .
F i n a l l y , the add r es s o f
the
sh a r ed m emo r y
m a i l bo x c o n t r o l b l o c k i s l o ad ed i n to t h e UC B .
I f the ma i l bo x a l r e a d y e x i s t s o n th i s po r t ,
the
Create
Ma i l bo x s y s t em s e rv i c e s i mpl y a s s i g n s a c h a n n e l t o i t .

Message queue llsthead
- - - - - -

- - - -

- -

(Self relative queue)
Creator
port

Unit number

Flags

Waiting reader

Reference flags

Waiting write AST

Waiting read AST

Current
message count

Maximum
message size

Protection mask

Buffer quota

Owner UIC

Count

Mailbox name
(up to 15 characters)
(counted ASCII string)

Figure 16-2

Co n te n t s o f a S h a r ed Memo ry Ma i l bo x Co n t r o l Bl o c k

Th e d a t a s t r uc t u r e s r eq u i r e d t o d e sc r i b e a sh a r ed m emo r y
p i c t ur ed i n F i g u r e 1 6 - 3 .

1 6- 1 4

m a i l bo x

are

Processor 1 Local Memory

Processor 2 Local Memory

Shared Memory

(Creator Port)

Logical name
block

Second

Logical name

message

block
(Implicit pointer)

(Implicit pointer)

First
SHMEM:MBn

message

SHMEM : MBm
CCB for
Process X

Message queue

....
m

....
U1

....

til
t<
til
�
1:1:1
3:

CCB for
Process A

Shared memory
Mailbox
unit control
block

CCB for
Process B
for Unit n

Figure 16-3

mailbox
control block

til
tzl

"
<

Mailbox
unit control

....

(")

block

1:1:1
til

CCB for
Process Z
for Unit m

D a t a S t r uc t ur e s As s o c i a ted wi th Sha r ed
Memo r y Ma i l box C r e a t i o n

I /0 SYSTEM S ERVI C E S
Ma i l box D e l e t i o n

16. 5. 3

Th e $ D E LMBX s ys t em s e r v i c e i s u s e d t o ma r k
a pe rma n e n t ma i l bo x
for
d e l e t i on .
Th e
m a i l bo x
is
a c t ua l l y d e l e te d b y I OC $D E LMBX
( in
I O S UB N PAG ) wh e n i t s r e f e r e nc e c o un t ( UC B $W R E F C ) g o e s to
ze r o
( a fter
t h e l a s t c ha n n e l a s s i g n ed t o i t h a s b e en-d e a s s i g n ed , a s d e s c r i b ed i n
s ec t i o n 1 6 . 1 . 2 ) .
Th e ma i l bo x to b e m a r k e d f o r d e l e t e i s i d en t i f i ed by t h e C HAN a rg um e n t
in
the
$ D E LMBX c a l l .
Th e c ha n n e l n um b e r i s u s e d to l oc a t e the CCB ,
f r om wh i c h t h e m a i l bo x UCB a d d r e s s c a n b e f o und ( i n CCB $ L_UCB ) .
E XE $DE LM B X v e r i f i e s t h a t
1.

t h e UC B i s f o r a m a i l b o x
U C B $ L_D E VC HAR ) ,

( th a t t h e DEV$V_MBX b i t

t h e ma i l bo x i s a pe rma n e n t ma i l bo x
i s s e t i n UC B $W_DEVS TS ) , a n d

t h e pr o c e s s h a s PRMMBX p r i v i l eg e .

set

( th a t the UCB $V P RMMB X b i t

I f the a b o v e c o nd i t i o n s a r e m e t , t h e m a i l bo x i s m a r k e d f o r
s e t t i ng t h e UC B $V_D E LM B X b i t i n UC B $W_D EVS T S .

d el e t e

I OC $D E LM B X a c t u a l l y d e l e t e s a m a i l bo x b y
1.

v e r i fy i ng
that
t h e d ev i c e
t o b e d e l e te d
is
a ma i l bo x
( D EV$V M B X i s s e t i n U C B $ L D EVC HAR ) , tha t t h e r e f e r e n c e c o un t
( UC B $W-R E FC ) i s z e r o , a nd th a t t h e m a i l bo x h a s b e e n m a r k e d
f o r d ele t e ( UC B $V_D E LM B X i s s e t i n UC B $W_DEVS T S ) ,

r e l i n k i ng t h e o th e r m a i l bo x UC Bs
fo r
th i s
ma i l bo x
contro l l er
c o n t r o l l e r a r e l i n k e d t og e th e r ) ,

d e c r em e n t i ng
the
( C RB $W_R E FC ) ,

r emov i ng t h e l og i c a l n am e fo r the m a i l bo x ( i f a n y s pe c i f i e d ,
via a
no n z e r o v a l u e i n UC B $ L_LOGADR ) f r om the l og i c a l name
t a b l e , a nd

d e a l l o c a t i ng t h e l og i c a l name b l o c k u s e d f o r the ma i l bo x .

controller ' s

UC B $ L L I N K
( v i a the
t h e -UC B s
( because
d ev i c e

r e f e r enc e

f i eld)
fo r
a
c o un t

If
t h e m a i l bo x wa s a
t empo r a r y ma i l bo x
( UC B $V PRMMBX c l e a r
in
UC B $W D EVS T S ) ,
th e b y t e c o un t l i m i t ( J I B $ L BYTLM ) and the b y t e c o un t
quo t a- ( J I B $ L BYTCNT ) a r e upd a t e d ( b e c a u s e the c r e a t i o n o f a
tempo r a r y
ma i l bo x r eq uir ed tho s e r e s o u r c e s ) .
An y un p r o c e s s ed m e s s ag e s th a t we r e
q u e u e d t o t h e m a i l bo x ( a nd a r e s t i l l
s to r ed
i n no npag ed poo l )
are
d eal l o c a ted
( by c a l l i ng
E XE $ D EANON PAG E D i n MEMORYA LC ) .
Th e UCB fo r
t h e ma i l bo x i s d e a l l o c a t ed ( by c a l l i ng E XE $D EANON PAG E D ) .

16. 6

BROADCAST S Y S TEM S E RV I C E

Th e $ B RDC S T s y s tem se rv i c e ( E XE $ B RDC S T i n S Y S BRDC S T )
a l l o ws m e s s ag e s
to be
s en t
to one
o r m o r e t e rm i n a l s ( e v e n i f a n I /0 o pe r a t i o n i s
c u r r e n t l y i n p r og r e s s o n t h e t e rm i n a l ) .

1 6-1 6

I /0 SYSTEM S ERV I C E S
A f t e r c h e c k i ng
t h e b u f f e r q uo t a
( to m a k e s u r e e n o ug h q uo t a
is
a v a i l a b l e t o b u f f e r t h e m e s s ag e ) , a b r o ad c a s t d e sc r i pt o r b l o c k ( BRD )
i s a l l o c a t e d a nd i n i t i a l i z e d .
( S e e F i g u r e 1 6 -4 f o r the
f o rm a t o f
a
BRD . )

BRD$L_FLINK

Broadcast queue forward link

BRD$L_BLINK

Broadcast queue backward link

BRD$W_SIZE
BRD$B_TYPE
BRD$L_PCB

C><

BRD$L_PID

Type

Size

Requesting process PCB

Requesting process PID

BRD$W_REFC
BRD$W_MSGLENGTH

Message length

BRD$L_DATA

N umber of terminals

Broadcast
Message

F i g u r e 1 6-4

L a yo u t o f a B r o ad c a s t Desc r i pto r B l o c k

I f t h e m e s s a g e i s to b e s e n t to a s i ng l e t e r m i n a l , t h e n EXE $ B RDC S T
1.

l o c a t e s t h e UC B a d d r e s s f o r t h e t e r m i n a l
( spec i f i ed
DEVNAM pa r am e t e r ) b y c a l l i ng I OC $ S EARCHDE V ,

v e r i f i e s th a t t h e pr o c e s s e i th e r o wn s t h e t e rm i n a l
e q u a l s PC B $ L_P I D ) , o r h a s O P E R p r i v i l eg e ,

in
terminal
( D EV$V TRM s e t
v e r i f i e s th a t t h e UC B i s f o r a
Ts
the
on
l i ne
t e rm i na l
UC B $ L D EVC HAR ) ,
and
th a t
( UC B $V_ON L I N E i n UCB $W_S T S ) ,

p l a c e s t h e BRD i n a q u e ue o f B ROs t o be b r o a d c a s t , a n d

sta rts a broadca s t .

I f the m e s sa g e i s
t o b e sent t o a l l
t e rm i n a l s ,
p e r fo rm s s t e ps 3 t o 5 above f o r e a c h t e rm i n a l UCB .

then

the

( UC B $ L_P I D

EXE $ B RDC S T

S t a r t i ng a b r o ad c a s t i nvo l v e s s ev e r a l s t eps .
1.

A wr i t e b u f f e r pa c k e t th a t po i n t s to the B RD ( F i g u r e 1 6 - 5 )
a l l o c a t ed a nd i n i t i a l i z ed .

Th e wr i t e b u f f e r p a c k e t i s p a s s e d to
the
te rm i n a l
d r iver ' s
a l te rnate
start
I /0
e n t r y po i n t
( by c a l l i ng
r o u t i ne
EXE $ALTQUE PKT i n
SYS Q I ORE Q ) .
Th i s r o u t i n e a c t i v a t e s
the
d r i ve r
r eg a r d l e s s o f wh e th e r
or
n o t a n I /0 r e q u e s t i s i n
p r o g r e s s f o r t h e d ev i c e .
1 6- 1 7

I /0 S Y S TEM S E RVI C ES
3.

Th e te rm i n a l d r i v e r then a c c e p t s the
b r o a d c a s t m e s sag e ,
or
i nd i c a t e s
t h a t t h e m e s s a g e c a n n o t b e b r o a d c a s t ( be c a u s e , f o r
e x ampl e , th e u s e r i s s u ed a S E T T E RM I NA L /N O B ROADCAST c ommand ) .

I f the m e s s ag e i s n o t a c c e p t e d
b u f f e r pa c k e t i s d e a l l o c a t ed .

I f t h e m e s s ag e i s
a c c e p t ed
by
the d r i v e r ,
r e f e r e n c e c o un t i s i n c r emen ted ( B RD $W_R E FC ) .

the

TTY$LWB_FLIN K

Forward Link

TTY$LWB_BLINK

Backward Link

TTY$W_WB_SIZE
TTY$B_WB_TYPE
TTY$B_WB_FIPL

FIPL

the

wr i t e

b r o ad c a s t

SIZE OF BLOCK

TYPE

TTY$LWB_NEXT

Address of start of data

TTY$LWB_END

Address of end of data

TTY$LWB_IRP

Figure 1 6-5

d r iver ,

L a yo ut o f a Wr i t e Bu f f e r Pa c k e t

Wh i l e t h e d r i ve r i s w r i t i ng t h e m e s s a g e t o t h e s pe c i f i ed
t e rm i n a l ( s ) ,
t h e p r o c e s s i s s u i ng t h e $ B RDC S T c a l l i s p l a c ed i n a n RSN$ B RKTHRU wa i t
s ta t e .
As s o o n a s B RD$W R E FC g o e s t o
zero ,
i nd i c a t i ng -a l l o f t h e
b r o a d c a s t m e s s a g e s h a ve b e e n s e n t to t h e s pe c i f i e d t e rm i n a l { s } , th e
p r o c e s s i s r emoved f r om t h e wa i t s t a t e , t h e BRD
i s d ea l l o c a ted ,
and
the s ys t em s e rv i c e c ompl e te s .

16. 7

I NFORMAT I ONAL S ERVI C ES

Appl i c a t i o n p r og r am s f r e q u e n t l y r e q u i r e i n fo rm a t i o n
a bo u t pa r t i c u l a r
d ev i c e s
on
the
s ys t em .
VM S a l l ows
a
use r
t o o b ta i n s p e c i f i c
i n f o rm a t i o n abo u t a pa r t i c u l a r d ev i c e u s i ng
one o f sever a l
system
se rv i ce s
( $QIO,
$G E TDEV ,
$ G ETCHN ) .
Th e i n fo rma t i o n o b t a i n ed may b e
e i th e r c ommo n t o a l l t h e d ev i c e s o n t h e s ys tem
( dev i c e
i nd e pe n d e n t ) ,
o r s p e c i f i c to a pa r t i c u l a r d ev i c e t ype ( d ev i c e d e p e nd e n t ) .

16. 7. 1

Dev i c e - I nd epend e n t I n f o rma t i on

Dev i c e - i nd epend e n t i n fo rm a t i o n r e f e r s to i n fo rm a t i o n th a t
i s present
fo r
e a c h d ev i c e o n t h e s ys tem ( s uch a s t h e d ev i c e un i t n umbe r , d ev i c e
c h a r a c t e r i s t i c s , a nd t h e d ev i c e t ype ) .
It
i s o b t a i n ed b y r e ad i ng
f i e l d s i n t h e UCB t h a t h a v e t h e s ame i n t e r p r e t a t i o n fo r a l l d ev i c e s o n
t h e s ys t em .
1 6-1 8

I /0 SYS TEM S E RVI C E S
1 6 . 7 . 1 . 1 G e t Ch a n n e l /Dev i c e I n f o rma t i o n - Two
s ys t e m
s e rv i c e s
( $ G E TDEV a nd
$ G E TC HN ,
l o c a t ed
i n S Y S G E TDEV) a r e p r o v i d ed to r e t u r n
d ev i c e - i nd e pend e n t i n fo rm a t i o n a bo u t a
d ev i c e
in
a
u s e r - s uppl i ed
b u f f e r ( s e e t h e VA X/VM S Sys t em S e r v i c e s Re f e r en c e Ma n ua l fo r a l i s t i ng
o f the f i e l d s r e t u r n ed ) .
Two s e t s o f i n f o rm a t i o n a r e o p t i o n a l l y r e t u r n ed ,
c a l l ed
th e
pr imary
d ev i c e c h a r a c t e r i s t i c s
a nd
the
s e c o nd a r y d ev i c e c h a r a c t e r i s t i c s .
Th e s e two s e t s o f c h a r a c t e r i s t i c s a r e
i d en t i c a l
un l e s s o n e o f
the
fo l l o w i ng c o nd i t i o n s ho l d s .
•

•

Th e d ev i c e h a s a n a s s o c i a t ed m a i l bo x
( no n z e r o
entry i n
U C B $ L AM B ) ,
i n wh i c h c a s e
t h e p r ima r y c h a r a c t e r i s t i c s a r e
t h o s e-o f t h e d e v i c e , a n d the
s e c o nd a r y c h a r a c t e r i s t i c s a r e
t h o s e o f t h e a s s o c i a t ed ma i l bo x .
Th e d e v i c e i s s po o l ed ( D EV$V S P L i s se t i n UC B $ L DEVC HAR ) , i n
wh i c h c a s e
the
p r ima r y cha r a c t e r i s t i c s
a re
tho s e o f the
i n t e rm e d i a te d e v i c e , and the
s e c o nd a r y c h a r a c t e r i s t i c s a r e
t h o s e o f t h e s po o l ed d e v i c e .
I f t h e d e v i c e r e p r e s e n t s a l og i c a l l i n k
in a
n e t wo r k ,
the
s e c o nd a r y c h a r a c t e r i s t i c s c o n t a i n i n f o rma t i o n a b o u t the l i n k .

EXE $G E TDEV a nd E XE $G E TC HN d i f f e r o n l y i n h o w they i n i t i a l l y f i nd
the
d e s i r ed
d ev i c e ' s
UCB a d d r e s s .
In
the $ G E TC HN c a s e , the CCB $ L UCB
f i e l d for t h e C C B i d e n t i f i ed by the C HAN a r g ume n t
is
used .
I n -the
$G ETDEV c a s e , r o u t i n e I OC $ S EARC HDEV i s c a l l ed to f i nd the UCB a d d r e s s
f r om t h e DEVNAM a r g umen t .
On c e
the
UCB add ress
is
f o und ,
the
d ev i c e - i nd e pe nd e n t
i n fo rm a t i o n
i s c o p i ed f r om th e pr i m a r y UC B t o t h e
user b u f fe r ( i f a p r ima ry buffer
wa s
s pe c i f i ed ) .
Af t e r
th a t ,
the
d ev i c e - d e pe n d e n t i n fo rm a t i o n i s c o p i ed f r om t h e s e c o nd a r y U C B ( l o c a ted
by UC B $ L AMB in the p r ima ry UC B , o r , i f th a t va l ue i s 0 ,
the pr i m ary
UC B
i s -a g a i n
u s ed )
i n to the u s e r b u f f e r ( i f a s e c o nd a r y bu f f e r wa s
s pe c i f i ed ) .

16. 7 . 2

Dev i c e -Depend e n t I n f o rm a t i o n

Dev i c e - d epend e n t i n f o rm a t i o n r e f e r s to i n f o rma t i o n th a t i s p r e s e n t fo r
a pa r t i c u l a r d ev i c e
t ype on the s ys t em , b u t no t fo r e v e r y d ev i c e o n
the sys tem .
( Fo r e x ampl e , a un i t c o n t r o l
block
for
a
c a rd
r e ad e r
i nd i c a t e s
wh e t h e r
t h a t c a r d r e a d e r i s t r a n s l a t i ng c a r d s a c c o rd i ng to
the 0 2 6 k e ypunch c o d e o r the 0 2 9 k e yp unch c o d e . )
Dev i c e - d e p e nd e n t i n f o rm a t i o n c a n b e mad e a v a i l ab l e to a
us e r
process
b y pl a c i ng
th a t
i n f o rm a t i o n i n to t h e h i g h o r d e r l o ng wo rd o f t h e I /0
s ta tus b l o c k fo r a $ Q I O r eque s t .
Th e i n fo rma t i o n i s p l a c ed
the r e by
the d r i v e r
( by p l a c i ng
that
i n fo rm a t i o n
in Rl be f o r e i s s u i ng th e
REQC OM m a c r o to c ompl e t e t h e I /0 r e q u e s t ) , and c a n b e a n yth i ng
the
d r iver
wr i t e r
fee l s
is
a pp r o p r i a t e
for a pa r t i c u l a r $ Q I O f unc t i o n
c od e .
Th a t i s , t h e i n f o rm a t i o n p l a c ed the r e c a n
take
on
d i f f e rent
me a n i ng s f o r d i f f e r e n t f un c t i o n c o d e s .
O f t e n , d ev i c e d r i v e r s s uppo r t s p e c i a l f un c t i o n c o d e s t h a t o n l y r e t u r n
d ev i c e - d e pe n d e n t
i n fo rm a t i o n
in
t h e h i g h o r d e r l o ng wo rd o f t h e I /0
s t a t u s b l o c k , a nd tha t d o n o t
i n i t i a te
a ny d ev i c e
ac t i v i ty .
Th e
f un c t i o n c od e s m o s t f r e q u e n t l y u s ed i n th i s wa y a r e I O $ S EN S EMODE a nd
I O $ S E N S E C HAR .
Fo r
e x ampl e ,
t h e mag t a pe d r i v e r
r e spo nd s
to
the
I O $=S E N S EMODE
$ Q I O by r e t u r n i ng t h e t a pe c h a r a c t e r i s t i c s in th e I /0
1 6-1 9

I /0 SYSTEM SERVICES
s t a t u s b l oc k .
Co r r e spo nd i ng
I O $ S E TMODE a nd
IO$ S ETC HAR f un c t i o n
c o d e s a r e a l s o us ua l l y p r o v i d ed so -tha t the u s e r c an-c h a ng e t h e d ev i c e
m o d e o r c h a r a c t e r i s t i c s i f t h e c u r r e n t o ne s a r e n o t a c c e p t ab l e .
I n a d d i t i o n , the $ G E TC HN a nd $ G E TDEV s ys t em
s e rv i c e s
r eturn
in
the
u s e r ' s b u f f e r a d ev i c e - d e p e n d e n t f i e l d ( UC B $ L DEVD E PEND ) , wh i c h can be
used f o r d i f f e r e n t p u r po s e s by d i f fe r e n t d evic e s .
Th e VAX/VMS
I /0
U s e r ' s G u i d e c o n t a i n s c om p l e t e d e sc r i p t i o n s o f ho w t h e i n fo rm a t i o n i n
t h a t f i e l d s h o u l d b e i n t e r p r e t ed
fo r
ev e r y s uppo r t e d d ev i c e t ype .
Th a t m a n ua l
a l so c o n t a i n s a d e ta i l ed e x p l a na t i o n o f wh a t i n f o rm a t i o n
i s r e t u r ne d by t h e I O $ S EN S EMODE a nd
I O $ S ENSECHAR $ Q I Os
f o r each
d ev i c e t h a t s uppo r t s t ho s e f un c t i o n c od e s . -

1 6- 2 0

PART V I

PROC E S S C R EAT I ON AND DELET I ON

f o r d u s t yo u a r e
a nd unto d u s t yo u sh a l l r e t u r n .
Genes i s 3 , 1 9

C HAPTER 1 7
PROC E S S C REAT I ON

Th e c r e a t i o n o f a n e w p r o c e s s
p i ec e s o f the e x ec ut i v e .
•
•

•

r equ i r e s

the

c o o pe r a t i o n

C r e a t i o n b eg i n s i n the c o n t e x t o f an
e x i s t i ng
e x e c u t e s a C r e a t e Pr o c e s s sys tem s e rv i c e c a l l .

sev e r a l

process

th a t

Th e i n i t i a l s c h e d u l i ng s t a t e
of
the
new p r o c e s s
is
C OM O
( c ompu t a b l e b u t o u t s wa pped )
in
a
spec i a l
swa p
i m ag e i n
S YS . EXE c a l l ed Sh e l l and s o f u r th e r e x e c u t i o n
is
s u pp r e s s ed
u n t i l t h e Swa ppe r mo v e s the n ew p r o c e s s i n to the b a l a n c e se t .
Th e f i n a l s t e ps o f p r o c e s s i n i t i a l i z a t i o n t a k e pl a c e
in
c o n t e x t of t h e new p r o c e s s in a r o u t i n e c a l l e d PROC S TRT .

the

Ta b l e 1 7 - 1 s umma r i z e s t h e p i e c e s o f p r o c e s s c r ea t i o n th a t
take
place
i n t h e c o n t e x t o f e a c h o f the th r e e p r oc e s s e s th a t a r e i n v o l v ed .

CREATE PROC E S S SYS TEM SERV I C E

17 . 1

Th e C r e a t e P r o c e s s s ys t em s e r v i c e e s t a b l i s h e s the
pa r am e te r s o f
the
n ew p r o c e s s .
S o m e o f t h e s e p a r a m e t e r s a r e pa s s e d to t h e se rv i c e by
the c a l l e r .
O t h e r s a r e t a k e n f r om the c o n t e x t of
the c a l l e r ;
f r om
the
PC B , the p r o c e s s h e a d e r , the j o b i n f o rma t i on b l o c k ( J I B ) , o r f r om
the c o n t r o l r eg i o n ( F i g u r e 1 7 - 1 ) .
Th o s e pa r am e t e r s th a t b e l o ng in the
PC B o r
the
J I B o f the n ew p r o c e s s c a n b e p l a c ed th e r e by the C r e a t e
P r o c e s s s ys tem s e rv i c e .
Th o s e p a r a m e t e r s tha t b e l ong
e i th e r
in
the
proc ess h ead e r
or
in
t h e c o n t r o l r eg i o n of the n e w p r o c e s s m u s t b e
s to r ed i n a t em po r a r y s t r uc t u r e
un t i l
the new process
c om e s
i n to
e x i s te n c e
a nd has a v i r t ua l add r e s s s pa c e a nd p r o c e s s h e a d e r th a t c a n
be accessed .
Th e P r o c e s s Quo t a B l o c k ( P QB ) s e rves the pu r po s e o f th i s
t empo r a r y d a t a s t r uc t u r e .
I t s c o n t e n t s a r e l i s t ed i n Tab l e 1 7 - 2 .

17. 1 . 1

Co n t r o l F l o w o f C r e a t e P r o c e s s

Th e C r e a t e P r o c e s s s ys tem s e r v i c e a l l o c a t e s a
PCB ,
a
JIB
( d e t a c h ed
process c rea t i on onl y) ,
and
a PQB a n d f i l l s t h e s e th r e e s t r uc t u r e s
w i th t h e i mp l i c i t a nd e x p l i c i t pa r am e t e r s pa s s ed t o
it.
A l i st o f
o pe r a t i o ns pe r f o rm ed by t h e s e r v i c e i s l i s t e d h e r e .
1.

I f t h e U I C a r g um e n t i s p r e s e n t , t h i s i nd i c a t e s th a t
the n e w
process wi l l
b e a d e t a c h ed p r o c e s s .
Th e c r e a t o r m u s t h a v e
D E TAC H p r i v i l eg e i n o rd e r f o r t h e s e r v i c e to s uc c e ed .

1 7- 1

PROC E S S CREAT I ON
Tab l e 1 7 - 1
P a r t s o f Proc e s s Creat ion
That Occur i n D i f f erent Proc e s s Contexts

Th e Cr e a t e Pr o c e s s s ys t em se rv i c e , e x ec u t i ng in
o f the c r e a to r , pe r fo rms the fo l lowi ng s t e ps .

the

c ontext

It m a k e s pr i v i l eg e and quo ta chec k s .

I t l o ad s the PC B , po s s i b l y the JIB i f c r e a t i ng a d e tac hed
pro c e s s , a nd the p r o c e s s quo ta b l oc k wi th expl i c i t
SYS $CREPRC a rg uments a nd impl i c i t pa r am e te r s ta ken f r om
the c o n tex t o f the c r e a to r .

I t pl ac e s the n ew p r oc e s s i n to the sched ul e r ' s d a ta base .

The fo l l owi ng s t e ps a r e
swa ppe r p r o c e s s .

pe r fo rm ed

the

c o n t ex t

the

The swa ppe r i nswa ps the
templ a te pr o c e s s c o n tex t
SHE LL , a po r t i o n o f the ex ec u t i v e i mag e SYS . EXE .

f r om

The process head e r i s b u i l t acco rd i ng to
the
SYSB OOT pa r amet e r s fo r th i s c o n f i g u r a t i o n .

val ues

Th e fo l l owi ng s t eps a r e pe r fo rmed i n the c o ntex t o f the n ewl y
c r ea ted process .
a.

The a rg uments f r om the PQB a r e moved
to
pl a c e s i n the p r o c e s s h e ad e r and P l s pa c e .

the i r

prope r

Th e imag e a c t iva to r i s c a l l ed to ac t i v a te the imag e .

Th e i mag e i s c a l l ed a t i t s e n t r y po i n t .

A PC B a nd PQB a r e a l l o c a ted f r om no npag ed po o l .

I f a d e t a c hed p r o c e s s
i s b e i ng
c re a ted ,
a J I B must be
a l l o c a ted f r om n o npag ed poo l .
Th e J I B po i n t e r ( PC B $ L J I B ) i n
t h e n e w PC B po i n t s
to
t h e n ewl y a l l o c a t ed J I B and
the
i n fo rma t i o n
fi elds
( all
b u t the
12
b y t e s o f h e ad e r ) a r e
c l e a r ed .
I f a s ub p r o c e s s i s b e i ng c r e a t e d , t h e J I B po i n t e r i n the
PC B
po i n t s t o
t h e J I B o f the c r e a to r ( wh i c h i s a c t ua l l y the J I B
o f t h e m a s te r p r o c e s s o f t h e j o b . ) Th e
r e l a t i o n sh i p b e t we e n
t h e J I B a nd th e PC B s o f s ev e r a l p r o c e s s e s i n t h e s ame j o b i s
p i c t u r ed i n F i g u r e 1 7 - 2 .
The p r o c e s s c o un t f i e l d
( i n the
JIB)
is
i n c r eme n t e d
a nd
c h e c ked
to
see th a t i t i s s t i l l
w i th i n l i m i t s .
No t e t h a t t h e PRCCNT f i e l d s w i th i n e ac h
PC B
( PC B $W PRCCNT )
c o un t t h e n um b e r
of
s ubp r o c e s s e s c r e a t ed by th a t pro c e s s .
Th e PRCCNT f i e l d w i t h i n the J I B
( J I B $W PRC CNT )
c o un ts t h e
t o t a l n umb e r o f s ub p r o c e s s e s i n t h e j o b and mus t b e l e s s th a n
o r e q ua l t o t h e c o n t e n t s o f J I B $W_PRC L I M .

17-2

PROC E S S CREAT I ON

( New JIB a lloc ated
o nly if creating
detached proc e s s )

Cre ator

JIB
( Pooled
Q u ot a s )

PCB

New Process
PCB

$ C REPRC
a rg u m e nts

C o n t ro l
R e g io n

Proc e s s
Quota
Blo c k
( PQ B )

P ro c e s s
Header

Figure 17-1
4.

S a mpl e Movem e n t o f Pa r am e t e r s i n P r o c e s s C r e a t i o n

S e v e r a l f i e l d s i n t h e PC B a r e i n i t i a l i z e d to n o n z e r o v a l u e s .
a.

Th e AST q u e ue i s s e t up a s empty .

ASTs a r e e n a b l ed f o r a l l a c c e s s mod e s .

Th e po i n t e r to t h e Ac c e s s R i g h t s B l o c k i s i n i t i a l i z e d
po i n t to the PC B $ Q_P R I V f i e l d o f the PC B .

Th e Ac c e s s R i g h t s B l o c k i s c u r r e n t l y l o c a t ed
w i th i n
the
PC B
( F i g u r e D- 2 ) .
Howe v e r ,
r o u t i n e s s uc h a s AC Ps and
d ev i c e d r i v e r s th a t w i sh
to check a
process ' s
access
r igh ts
u s e t h e ARB po i n t e r t o l o c a t e t h e p r i v i l eg e m a s k
a nd U I C s o
th a t ,
i f t h e ARB b e c om e s a n
i nd e pend e n t
s t r uc t u r e
i n a f u t u r e r e l e a s e o f VAX/VM S , tho s e p r o g r ams
w i l l c o n t i n ue to wo r k w i tho u t m od i f i c a t i o n .
d.

Th e un i t n um b e r o f a t e r m i n a t i o n m a i l b o x i s f i l l ed i n .
A
u n i t n um b e r o f z e r o w i l l i nd i c a t e to t h e p r o c e s s d e l e t i o n
r o u t i n e t h a t no t e r m i n a t i o n m e s s a g e i s to be s e n t b a c k to
the c r e a to r .

Th e p r o c e s s pag e c o u n t i s i n i t i a l i z ed
pag e s i n t h e S H E L L p r o c e s s .

1 7-3

the

c o un t

PROC E S S CREAT ION
Tab l e 1 7 - 2
Content s o f the Proc e s s Quota B l o c k

S i ze ( Bytes )

I t em
P r i v i l eg e Mas k

S i z e o f PQB

Type Co d e

S t a t u s Fl ag s

Im ag e Name

Eq u i v a l enc e Name fo r SYS $ ERROR

Equ i v a l enc e Nam e fo r SYS $ IN PUT

Equ i v a l enc e Name fo r SYS $0UT PUT

Equ i v a l ence Nam e fo r SYS $D I S K

A S T Lim i t

B u f f e r ed I/0 Lim i t

B u f f e r ed I/0 By te Li m i t ( N OT US ED )

C PU T i me Li m i t

D i r ec t I /0 Li m i t

Open Fi l e Lim i t ( N OT US E D )

Pag i ng Fi l e Quo ta

( N OT US ED )

S ubpr o c ess Li m i t ( N OT US ED )

T i m e r Que ue En t r y Li m i t ( N OT US ED )

Wo r k i ng Se t Quo ta

( L im i t )

Wo r k i ng Set De fa ul t

U s e r name fo r Subproc e s s

Ac c o un t Nam e fo r Subproc ess

De fa ul t Di r ec to ry St r i ng

1 7 -4

PROC E S S C REAT I ON

name

PID
1 0035
2
PRCCNT
OWNER
J IB

name

PID
1 0033
PRCCNT
0

PID

OWNER 1 0035

JIB

name

1 . Pro c e s s W cre a t ed
bot h X a nd Y
2 . Pro c e s s Y c re a t ed

Pro cess Z

Figure 17-2

J IB for
all processes
in this job

""
,

1 003 1
1
PRCCNT

pooled
quotas

MPID : 1 0035
-

PRCCNT 3

1 002E
PID
PRCCNT
0
OWNER 1 003 1
JIB

Re l a t i o n sh i p Be twe e n J I B a nd PC Bs o f Seve r a l P r o c e s s e s
i n t h e Same Jo b

Th e p r o c e s s n ame i s l o ad ed i n to the PC B .

Th e p r o c e s s p r i v i l eg e s o f the n ew p r oc e s s a r e d e t e rm i ned
and
l o ad ed
i n to
the
PQB .
I f no p r i v i l eg e a rg um e n t i s p r e s e n t ,
t h e c u r r e n t p r i v i l eg e s o f the c r e a t o r a r e u s ed .
( Ta b l e 1 8 - 1
s umma r i z e s
t h e v a r i o u s p r i v i l eg e m a s k s a s so c i a t ed w i th a
process . )
I f a p r i v i l eg e a r g um e n t i s p r e s e n t and the c r e a to r h a s S E T PRV
p r i v i l eg e ,
then
the
p r i v i l eg e
a rg um e n t
is
u s e d w i th n o
mod i f i c a t i o n .
I f a p r i v i l eg e a rg um e n t i s p r e s e n t and the c r e a to r d o e s n o t
have
S E TPRV p r i v i l eg e , t h e n the p r i v i l eg e s pa s s e d to the n e w
p r o c e s s a r e t h e l og i c a l AND o f the p r i v i l eg e s o f the c r e a to r
a nd
t h e p r i v i l eg e s s p e c i f i ed
i n the
a rg um e n t to C r e a t e
Pr o c e s s .

1 7- 5

PROC E S S C REAT I ON
7.

Th e s o f twa r e p r i o r i ty o f t h e n e w p r o c e s s
i s d e t e r m i n ed
a nd
l oaded
i n to
t h e PCB i n b o t h t h e b a s e p r i o r i ty f i e l d and the
c u r r e nt p r i o r i ty f i e l d .
( Be c a us e th i s a r g um e n t i s pa s s e d by
i t i s a l wa ys p r e s e n t , w i th a d e f a u l t va l u e d e t e rm i ned
va l ue ,
by t h e
t r e a tm e n t of
m i s s i ng
a rg um e n t s by t h e
l a ng uag e
p r o c e s s o r . ) I f t h e c r e a to r h a s A LT PR I p r i v i l eg e , t h e p r i o r i t y
s p e c i f i e d i n t h e a rg um e n t l i s t i s used .
I f t h e c r e a to r d o e s n o t h a v e ALTPR I p r i v i l eg e , t h e sm a l l e r o f
his
b a s e p r i o r i t y a nd t h e p r i o r i t y i n t h e a rg um e n t l i s t wi l l
b e u s ed .

Th e U I C o f the n e w p r o c e s s i s d e te rm i n ed and l o ad ed i n to
the
PC B .
If
a
UIC
a r g um e n t
i s presen t , the new p r o c e s s i s a
d e t a c hed p r o c e s s a nd the a rg um e n t i s i t s U I C .
I f a U I C a r g um e n t i s n o t p r e s e n t , t h en the n e w p r o c e s s
is
a
s ubp r o c e s s .
Th e
U I C o f the c r e a t o r i s u s e d .
In add i t i on ,
t h e P I D o f t h e c r e a to r i s p u t i n to the PCB $ L OWN E R f i e l d o f
the
PC B o f
the
n ew p r o c e s s .
Th i s w i ll i nd i c a t e t o the
p r o c e s s d e l e t i o n r o u t i n e th a t t h i s is a s ubpr o c e s s fo r
wh i c h
s p e c i a l a c t i o n mu s t b e t a k e n .

A c h e c k i s ma d e to i n s u r e t h a t t h e
p r o c e s s name
is
un i que
Th i s i s d o n e by e x am i n i ng th e p r o c e s s n am e
w i th i n the g r o up .
f i e l d s o f a l l PC Bs i n the s ys t e m w i th the s am e g r o up n umbe r .
Rec a l l
tha t a
p r o c e s s c a n o n l y r e f e r to a n o th e r p r o c e s s by
n am e ( Wa k e , S u s pe nd , Re s um e , De l e t e , a nd so o n ) i f the t a r g e t
p r o c e s s i s i n t h e s am e g r o up .

10.

S e v e r a l t ex t s t r i ng s a r e l o ad ed i n to the PQB .
Th e i m a g e name
a nd
the
e q u i v a l e n c e n am e s
fo r
SYS $ I N PUT , SYS $0UT PUT , a nd
SYS $ E RROR a r e t a k e n f r om the a rg um e n t l i s t to C r e a t e P r o c e s s .
Th e
e q u i v a l e n c e n am e
fo r
SYS $D I S K
i s o b t a i n ed
f r om the
Trans l a te
Lo g i c a l
Name s ys t e m s e rv i c e .
Th e
use r
name ,
a c c o un t n a m e , a nd d e f a u l t d i r e c to r y s t r i ng a r e o b t a i n ed f r om
the c o n t r o l r eg i o n o f the c r e a to r .

11.

Th e s t a t u s f l ag s f o r the n e w p r o c e s s a r e ex t r a c ted
f r om the
Create
P r o c e s s a rg um e n t l i s t a nd set in the PC B $ L S T S f i e l d
i n th e n e w PCB .
Some
of
these
f l ag s
r e q u i r e -p r i v i l eg e
( Ta b l e 1 7 - 3 ) .
Th e pr i v i l eg e m a s k tha t i s c h e c ked i s th a t o f
the n ew p r o c e s s .

12.

Th e q uo t a s a r e d e te rm i n ed f o r t h e new p r o c e s s a nd l o a d ed i n to
the
PQB .
Th e n e x t s e c t i o n d e s c r i b e s the seve r a l s t eps ta k e n
to d e t e rm i n e t h e q uo t a l i s t fo r the new p r o c e s s .

At t h i s po i n t , t h e PC B a n d PQB h a v e b e e n l o ad ed
r e a d y t o b e a c t i v a t ed .
Th i s
s impl y means
i n s e r t ed i n to t h e s c h ed ul e r ' s d a t a b a s e .
13.

Th e a d d r e s s o f t h e PQB
the
PC B $ L P QB f i e l d .
a s t h e e v en t f l ag wa i t
ava i l ab l e because the
e v e n t f l ag s .

a nd
the
proc ess
is
t h e PC B w i l l be
tha t

i s s to r e d i n the PCB ( F i g u r e 1 7 - 1 )
in
Th e PQB po i n te r u s e s the s am e l o ng wo r d
ma s k f i e l d , PC B $ L E FWM .
Th i s f i e l d i s
p r o c e s s c a n n o t yet b e wa i t i ng f o r a n y

1 7- 6

PROC E S S CREAT I ON
Table 1 7 - 3
F l ag s i n the S tatus Longword i n PCB ( PCB $ L STS )
That Can Be Set at P roce s s Creat ion

F l ag i n
PC B $ L_S TS

B i t Num b e r
i n $ C R E PR C
A r g um e n t

PCB $V_S S RW A I T

PC B $V_S S F EXC U

PC B $V_PSWAPM

I n h i b i t P r o c e s s Swa pp i ng

PC B $V_N OACNT

S up p r e s s Ac c o un t i ng

PCB $V_B ATC H

Ba tch

PC B $V_H I B ER

H i b e r n a t e P r o c e s s B e fo r e Ca l l i ng

PCB $V_L O G I N

L o g i n W i tho ut Re ad i ng the Au t ho r i za t i o n
Fi l e

DETAC H

PC B $V_N E TWRK

P r o c e s s I s a N e two r k Co n n ec t Ob j ec t

NETM B X

Me a n i ng

Pr i v i l eg e
R e qu i r ed

( i f Se t )

D i s a b l e Sy s t em S e r v i c e Re so u r c e Wa i t Mo d e

No n e

E n a b l e Sys t em S e r v i c e E x c e pt i o n s
f o r Us e r Ac c e s s Mo d e

No n e

( no n i n te r ac t i v e )

NOACNT
No n e

pr o c e s s
Imag e

No n e

14.

prevent m u l t i p l e
to
( I PL 7 )
I P L $ S YNC H
to
I P L is r a i s ed
PC B v e c to r
Th e
s c h edu l e r ' s d a t a b a s e .
the
to
accesses
is
( p i c t u r ed i n F i g u r e 1 7 - 3 a nd d e s c r i b ed i n S e c t i o n 1 7 . 1 . 3 )
s e a r c h ed f o r a n emp t y s l o t .

15.

( contents o f
I f the ma x i m um p r o c e s s c o un t h a s b e en e x c e ed ed
SCH$GW PROCCNT wo u l d be l a rg e r than SCH $GW PROC L I M ) o r i f n o
swa p slo t i s a v a i l ab l e ( c o n t e n t s o f SWP $G L SLOTCNT h a v e g o n e
Oth e r wi s e , a p r o c e s s
to z e r o ) , t h e n t h e c r e a t i o n i s a b o r ted .
I D i s f a b r i c a ted ( S e c t i o n 1 7 . 1 . 4 ) and pu t i n to t h e PC B o f the
new p r o c e s s .

16.

PC B v e c t o r
the
in
Th e PC B a d d r e s s i s l o ad ed i n to the s l o t
I f a d e t a c h e d p r o c e s s i s b e i ng
th a t wa s l o c a ted i n s t ep 1 4 .
the
c r e a t e d , i t s P I D i s l o ad e d i n to the m a s t e r P I D f i e l d o f
J I B ( J I B $ L_M P I D ) .

17.

( a nd
Th e s c h ed u l e r i s c a l l ed to m a k e th i s pr o c e s s e x e c u t a b l e
the b a s e
to
be g i ven
6 wi l l
A boo s t o f
o u t swa pped ) .
d e t e rm i n e
I t i s th i s boo s t ed pr i o r i t y t h a t w i l l
pr i o r i ty .
wh e n t h e new p r o c e s s i s s wa pped i n f r om S H E LL .

18.

s ubpr o c e s s e s
I f a s ub p r o c e s s i s b e i ng c r e a t ed , the c o un t o f
PCB $W_PRCCNT ) i s
field
in
( s t o r ed
owned b y the c r e a t o r
i n c r em e n t e d a t th i s po i n t .
I n a d d i t i o n , i f the c r e a to r h a s a
no n z e r o C PU t i m e l i m i t ( C PU t i me l i m i t i n e f f e c t ) , t h e amo un t
the
f r om
o f C P U t i m e pa s s e d to the n e w p r o c e s s i s d ed uc t ed
c r e a to r .

19.

the
to
r e t u r n ed
is
new process
the
Fi n a l l y , t h e P I D o f
c r e a t o r ( i f r e que s t e d ) , I P L i s r e s t o r ed t o a l l o w s ys tem ev e n t
r e po r t i ng , a n d c o n t r o l i s pa s sed bac k t o t h e c a l l e r .

1 7-7

PROC ESS CREAT I ON

:: S C H $ G L _PCBVEC

PCB
of
SWAPPER

free slot
•

•

PCB
of
NULL
PROCESS

free slot

PCB
of
OPCOM

JOR£0NTROL �---� PCB
DBAOACP
PRTSYMB 1

PCB
of
PRTSYMB1

Figure 1 7-3

17.1.2

of
Job
Controller

S ampl e PC B Ve c to r

E s t a b l i s h i ng Quo t a s f o r t h e New P r o c e s s

Th e r e a r e two ta b l e s i n t h e e x e c u t i v e tha t a r e u s ed b y C r e a t e
Process
wh e n t h e q uo t a s a r e s e t u p fo r the n ew p r o c e s s .
Ea c h quo ta o r l i m i t
i n the s ys t em h a s a n e n t r y i n bo th the m i n i m um tab l e and
the d e f a u l t
t ab l e .
Th e c o n t e n t s o f
t h e m i n i m um
t a b l e a r e d e t e rm i n ed by t h e
SYSBOOT p a r ame te r s who s e n am e s a r e o f t h e fo rm PQL Mquo t a wh i l e
the
contents o f
the d e f a u l t t a b l e a r e o f t h e fo rm P Q L-D q uo t a .
Th e l og i c
tha t d e te rm i n e s the v a l u e f o r e a c h q uo ta o r l i m i t tha t
i s pa s s ed
to
t h e n ew p r o c e s s fo l l ows .
1.

Th e d e f a u l t v a l ue s fo r e a c h q uo ta a r e put
a s s umed i n i t i a l v a l u e s .

Ea c h q uo t a t h a t i s i nc l ud ed i n the a rg um e n t l i s t
P r o c e s s r e p l a c e s t h e d e f a u l t va l u e i n t h e l i s t .

E a c h q uo ta i s f o r c ed to a t l e a s t i t s m i n i m um v a l ue .

1 7-8

i n to

the
to

PQB

Create

PROC E S S C REAT I ON
4.

A check
i s mad e
to
i ns u r e
tha t t h e c r ea to r
po s s e s s e s
to cover
wh a t
it
i s g i v i ng t o t h e n e w
s u f f i c i e n t quo t a
process .
Th i s c h e c k i s p e r f o rmed i n the fo l l o w i ng wa y .
a.

I f a d e ta c hed p r o c e s s i s b e i ng c r ea t e d , t h e n no c h e c k
is
pe r f o rmed .
Po o l ed
q uo t a s a r e pl a c ed d i r e c t l y i n to the
n ewl y a l l o c a ted J I B .

I f a s ubp r o c e s s i s be i ng c r e a ted and the quo ta i s n e i th e r
po o l ed
n o r d ed uc t i b l e , t h en t h e s ubp r o c e s s quo t a m u s t b e
sm a l l e r t h a n o r e q u a l t o t h e c r e a t o r ' s quo t a .

Po o l ed q uo t a s r e q u i r e no spec i a l ac t i o n wh e n a s ubp r o c e s s
is
b e i ng c r e a t e d b e c a u s e they a l r e ad y r e s i d e i n t h e J I B ,
a s t r uc t u r e tha t i s s h a r ed by a l l p r o c e s s e s
in
the
j ob
( Figure 17-2) .

I f a s ub p r o c e s s i s b e i ng
c rea ted
a nd
the quo ta
is
a
d e d uc t i b l e q uo ta
( th e o n l y d ed uc t i b l e
quo t a
tha t i s
c u r r e n t l y i m p l eme n t ed i s C PU t i m e ) , t h e n t h e c r e a t o r m u s t
r e ta i n a t
l east
t h e m i n i m um va l u e fo r th i s quo ta a f t e r
wh a t i t i s g i v i ng awa y h a s b e en s ub t r a c ted .

Ta b l e 1 7 - 4 l i s t s the quo t a s t h a t a r e pa s s ed to a n e w p r o c e s s
wh e n
it
is
c r e a t ed ,
wh e t h e r
e a c h q uo ta i s d ed uc t i b l e o r
poo l ed , a nd wh e r e t h e l i m i t i s s to r ed i n the c o n t ex t o f
the
new process .
Fu r th e r d i s c u s s i o n o f quo t a s c a n b e fo und i n
t h e VAX/VM S S y s t em Ma n a g e r ' s G u i d e and i n t h e VAX/VM S S y s t em
S e r v i c e s Re f e r e n c e Ma n ua l .
5.

17. 1 . 3

Th o s e quo t a s a nd wo r k i ng
va l u e s
( Ta b l e 1 7 - 4 ) a r e pl a c ed t h e r e .

tha t

b e l o ng

the

PC B

Th e PCB Ve c to r

Wh e n the sys tem i s i n i t i a l i z ed , a n a r r a y o f MAXPR OC E S SCNT l o ng wo r d s i s
a l l o c a ted
f r om
nonpa g ed
d yn a m i c m em o r y .
Th i s a r r a y w i l l b e used t o
l oc a t e the PC B o f e a c h p r o c e s s i n t h e s ys t em a t a n y g i v e n
t i me .
Th e
f i rst
two
e n t r i e s i n the t a b l e po i n t to the PC B s o f t h e n u l l p r o c e s s
a nd t h e swa ppe r p r o c e s s r e spe c t i v e l y .
Al l o th e r e n t r i e s i n t h e
tab l e
i n i t i a l l y po i n t t o the PCB o f the n u l l p r o c e s s .
Th e i nd i c a t i o n o f a n
empty s l o t i n th i s t a b l e i s a n e n t r y t h a t po i n t s t o
the
PC B o f
the
nul l
process
b u t h a s n o n z e ro i nd e x .
( Th e e n t r y th a t l o c a t e s t h e PC B
o f the n u l l p r o c e s s tha t h a s a n i nd e x o f z e r o i s t h e " r e a l "
po i n t e r . )
Th e
scan
f o r a n empty s l o t b eg i n s a t the bo t tom o f t h e t a b l e so th a t
tho s e
system processes
t h a t a r e c r e a t ed
a s a pa r t o f
s ys t em
i n i t i a l i za t i o n w i l l have t h e i r PC B po i n te r s l o c a ted n e a r th e bo t to m o f
t h e tab l e .
An ex ampl e o f t h e c o n t e n t s
of
th i s
tabl e
is
s h o wn
on
Figure 17-3 .

17 . 1 . 4

Fabr i c a t ion o f Process IDs

Th e i nd ex i n to the P C B v e c t o r tha t l o c a t e s t h e PC B o f a p r o c e s s
fo rms
the
l ow o rde r 1 6 b i ts of the process I D .
Th e h i g h o rd e r 1 6 b i t s a r e
t a k e n f r om a n o t h e r a r r a y ( o f wo r d s ) a l l o c a t e d f r om no npag ed
po o l
at
s ys t e m i n i t i a l i z a t i o n t i m e .
Th i s a r r a y o f s e que n c e n um b e r s ( i n i t i a l l y
s e t to z e r o ) i s u s e d a s a c o ns i s t e n c y c h e c k to d e t e rm i n e tha t a n umbe r
a l l eg ed
to
be a
process
I D c o r r e s po nd s
to a r e a l p r o c e s s i n t h e
s ys tem .
1 7- 9

PROC E S S C REAT I ON
Tab l e 1 7 - 4
Sto rage Areas for P ro c e s s Quotas
Loc a t i o n o f
Ac t i v e Co unt

Quo ta/L i m i t Name

AST Lim i t
Bu f fe r ed

I /0 L i m i t

Deduc t i b l e Quo t a s

PCB $W_ASTCNT

PHD$W_ASTLM

C/P

PCB $W_B I OCNT

PCB $W_B I O LM

C/C

PCB $W_D I O LM

C/C

No te 2

PHD$W_WSQUOTA

Wo r k i ng Se t De f a ul t

No te 2

PHD$W_DFWSCNT

PHD$L_C PUTIM

PHD$L_CPULIM

No t e 3/P

PCB $W_D I OCNT

C P U T i m e L im i t

J I B $L_BYTCNT

J I B $ L_BYTLM

No te 4

Open Fi l e L i m i t

J I B $W_F I LCNT

J I B $W_F I LLM

No te 4

Pag e Fi l e Pag e L i m i t

J I B $L_PGF LCNT

J I B $ L_PGF LQUOTA

No te 4

B u f f e red
Po o l ed Quo ta s
( Sha r ed by a l l
processes in the
s ame j ob )

Co un t/L im i t
Sto r ed by ( No t e 1 )

Wo r k i ng Se t Quo t a

Di r ec t I/0 L i m i t

No nd ed uc t i b l e
Quo ta s

Loc a t i o n o f
Pro c e s s L i m i t

I /0 B y t e L i m i t

S ubpr o c e s s L i m i t

J I B $W_PRCCNT

J I B $W_PRC L IM

No te 4

T i m e r Que ue En t r y L i m i t

J I B $W_TQCNT

J I B $W_T QLM

No te 4

W i th the e x c ept i o n of CPU t im e l im i t and subproc e s s c o un t , a l l ac t i ve c o u n t s s ta r t
at
the i r
proc e s s
l im i t
v a l ue s
a nd d e c r ement t o z e r o .
An ac t i v e c o un t o f zero
ind i c a te s no quo t a rema 1 n 1 ng .
An ac t i v e c o un t equa l to the c o r r e s po nd i ng
process
l im i t i nd i c a te s n o o u t s t and i ng reque s ts .
(1)

The s l a sh

( /)

s e pa r a t e s the c o un t f r om the l im i t .

C/ i nd i c a te s tha t the c o unt v a l ue i s s to red by the C r e a t e P r o c e s s s ys t em s e rv i c e .
/C i nd i c a tes tha t the 1 im i t v a l ue i s s to red by the C r e a t e P r o c e s s s ys t em s e rv i c e .
/P i nd i c a te s tha t the l im i t v a l ue

i s s to red by PROC STR T .

( 2 ) Wo r k i ng Se t Li s t quo t a s a r e h a nd l ed d i f f e r en t l y f r om o th e r quo t a s ( Ch a pte r 1 2 ) .
( 3)

C PU T i m e s t a r t s a t z e ro and i n c r ements fo r e a c h c l oc k t i c k tha t
the
proc e s s
is
c u r rent .
If
l im i t
c hec k i ng i s i n e f fec t ( CPULIM n o n z e ro ) , then C PUT IM m a y no t
e x c eed C PU L IM .

( 4 ) Th e c o n t e n t s o f the J I B a r e l oa d ed b y C r e a te P r o c e s s wh en a d e tac hed
c r eated .

pro c e s s

Subp r o c e s s c r ea t i o n uses an ex i s t i ng J I B .

Wh e n an emp t y s l o t i n t h e P C B v e c to r
is
located ,
t h e c o r r e s pond i ng
e n t r y i n t h e s e q u e n c e v e c t o r ( F i g u r e 1 7 - 4 ) i s i nc r emented a nd u s e d a s
t h e h i g h o r d e r 1 6 b i t s o f t h e p r oc e s s I D .
S e qu e n c e n umb e r s c yc l e t o 0
a f te r
r e a c h i ng
3 2767 .
Th i s m e a n s
tha t process
I Ds
a r e a l wa ys
po s i t i v e .
Th i s i s d o n e to a l l o w a spec i a l
f o rm o f
I /0 c ompl e t i o n .
Th e I /0 po s t p r o c e s s i ng i n t e r r up t s e r v i c e r o u t i n e i n te r p r e t s a n eg a t i ve
P I D i n th e I RP $ L P I D f i e l d o f a n I /0 r e qu e s t pa c k e t a s
the
( s y s t em
v i r t ua l ) a d d r e s s-o f a n i n t e r n a l I /0 c ompl e t i o n r o u t i n e .
Wh en a p r o c e s s i s l a te r r e f e r r ed to by p r o c e s s I D , t h e v a l i d i ty o f the
P I D c a n be c h e c ked
by u s i ng
the l ow 1 6 b i t s as a n i nd e x i n to the
s e q u e nc e v e c t o r a nd c ompa r i ng t h e v a l u e
f o und
t h e r e w i th
the h i g h
o rd e r
1 6 b i ts o f the P I D .
W i th t h i s s c h eme , a s e c ond c h e c k m u s t a l so
be made .
Th e c o r r e s po nd i ng e n t r y i n the PC B v e c to r mus t b e c ompa r ed
to
the
PCB ad d r e s s o f
the n u l l
p r o c e s s to c h e c k wh e th e r the o l d
p r o c e s s h a s g o ne a wa y b u t t h e s l o t n o t y e t r e u s e d .

1 7- 1 0

: :SCH$GL_PCBVEC

....1,

..._____.____

N ULL
Same index value
used to locate array
element In either array
forms low 16 bits
of process 1 0 .

SWAPPER

O PC O M
JOB CONTROL

to PCB o f
n e w proc ess
F igure 1 7 - 4

sequence no.

index

Process ID
Fabr i c a tion o f Proce s s I D s

: SCH$GL_SE QVEC

PROC E S S C R EAT I ON
Th e t wo c o n c ep t ua l c h e c k s d e sc r i b ed
in
the
p r ev i o u s pa r ag r a ph a r e
a c t ua l l y p e r fo rmed
i n o n e s t e p ( i n r o u t i n e E XE $NAM P I D ) b y u s i ng t h e
l ow o r d e r 1 6 b i ts of the PID as a n
i nd e x
i n to
the
PCB v e c to r
a nd
c ompa r i ng
the P I D i n the PC B po i nted to by t h e i nd e x ed v e c to r e l em e n t
w i th t h e P I D th a t i s b e i ng c h ec k ed .
I f the p r o c e s s s p e c i f i ed h a s b e e n
( PC B v e c to r
n o w po i n t s t o PCB of n u l l p r o c e s s ) but t h e s l o t
d e l e t ed
h a s n o t y e t b e e n r e used ( s e q u e nc e n um b e r n o t ye t
i nc r em e n ted ) ,
the
s e q u e n c e n umbe r
a r r a y e l em e n t w i l l m a tc h t h e h i g h - o r d e r wo r d i n t h e
p r o c e s s I D b u t t h e f u l l 3 2 -b i t P I Ds w i l l n o t m a t c h .
Fo r e x ampl e , s u ppo se a p r o c e s s h a s b e e n d e l e t ed
but
i ts
PCB vec to r
s l o t h a s n o t ye t b e en r e u s e d .
Th en t h e c o n t e n t s o f t h e se q u e n c e a r r a y
e l em e n t m a t c h e s t h e h i g h o r d e r wo r d
o f the process
!D .
B u t the
i nd e x e d
PC B p o i n te r l o c a t e s t h e PC B of the n u l l p r o c e s s , wh i c h h a s a
p r o c e s s I D o f 1 0 0 0 0 and d o e s n o t m a tch
the v a l u e o f
the
PID in
If,
o n t h e o th e r h a nd , t h e s l o t h a s b e en r e us e d , then the
q ue s t i o n .
l ow-o r d e r wo rd of the p r o c e s s I D , t h e p r o c e s s i nd e x , a g r e e s w i th
the
l o w-o r d e r wo rd o f the p r o c e s s I D .
Ho we v e r , t h e h i g h- o r d e r wo r d i n the
PC B ( o r the c o n t e n t s of t h e s eq u e nc e a r r a y e l em e n t ) is o ne l a rg e r than
the s e quenc e num b e r f i e l d i n the o r i g i n a l p r o c e s s I D .
Ag a i n , n o m a tch
occur s .

17. 2

THE S HE L L PROC E S S

A process
c om e s
i n to
ex i s tenc e
in
the
s c h e d ul i ng
s tate
C OM O ,
c om p u t a b l e b u t o u t swa pped .
Howev e r , t h e swa p i m a g e o f a n e wl y c r e a t e d
p r o c e s s d o e s no t r e s i d e i n t h e s wa p f i l e .
I n s t e ad ,
a
spec i a l
swa p
i m ag e ex i s t s a t t h e e nd o f t h e e x e c u t i v e i m a g e f i l e SYS $ S Y S TEM : SYS . EXE
( Fi g u r e 1 7- 5 ) .
Th i s i m ag e c o nta i n s a m i n i m a l p r o c e s s h e a d e r
a nd
Pl
s pa c e .
Th e a c t ua l
contents
of
the
swa p i m ag e fo und i n Sh e l l a r e
l i s t ed i n Ta b l e 1 7 - 5 .
Process B
is b e i n g
created

PC B
for
Process B
Swap File Table

WSSWP

Entry 0
Locates SHELL

Entry 1
Locates SWAPFILE. SYS
Process X
a lready
exists
and is
currently
outswapped

PCB
for
Process X

•
•
•

SWAPFILE.SYS
WSSWP
Swap Slot
L for
Process

F i g u r e 1 7- 5

Lo c a t i o n o f Sh e l l P r o c e s s i n t h e E x e c ut i v e Imag e F i l e
17- 1 2

PROC E S S CREAT I ON
Tab l e 1 7 - 5
Conten t s o f the I n i t i a l Swap Image i n the S he l l Proc e s s
I t em

P r o c e s s Head e r
( Fi x ed + W S L + P S T )
P l Pag e Ta b l e Pag e s

S i ze

No te

Perman e n t l y Lo c ked
i n Wo r k i ng s e t ?

Pag e No .
i n SHE L L

Yes

Yes ,

1 Pag e o n l y

Yes

2, 3

Ye s ,

2 Pag e s

I s Pag e Read f r om SHE LL
b y SWAPPER Pro c e s s ?

P l Po i n t e r Pag e

Yes

Yes ,

1 Pag e

Pr o c e s s I /0 Segmen t

Ye s ,

1 Pag e

Proc e s s Al l oc a t i o n Reg i o n

Yes ,

1 Pag e

Yes

7,8

Ye s ,

Fi rst

Ke r n e l

St a c k

Re s t o f P r o c e s s He a d e r

No te

Yes

Pag e Ta b l e Pag e Ar r a ys

No te

Yes

No te 3

N o te 4

TOTALS

2 Pag e s

(1)

Th e s i ze of the to p o f the proc e s s
header
d epend s
on
the
v a l ue s
of
several
SYSB OOT
pa r am e t e r s .
See
Append i x
E
fo r
d e ta i l s on h o w t h e s i ze the p r o c e s s
h e a d e r i s c a l c u l a ted b y SYS B OOT .

(2)

Th e r e a r e e i g h t byt e s pe r proc e s s h e ad e r pag e
f o r d e ta i l s .

(3)

(4)

17. 2. 1

See

in t h e s e a r r ays .

Append ix

Th e r e a r e s i x P l pag e s , two P l pag e t a b l e pag e s , and a va r i a b l e n um b e r o f pro c e s s
h e a d e r pag e s ( no te s 1 a nd 2 ) t h a t c o n t r i b u t e to S H E L L .
Th e number o f pe rma n en t l y l oc ked pag e s i s t h e r es ul t i n
nonpe rmanent pag e s .

No te

m i n us

the

two

I n swap f r om S H E LL

At sys tem i n i t i a l i z a t i o n t i m e , ! N I T f i l l s i n f i e l d s i n the f i r s t s wa p
file
tab l e e n t r y so
tha t
t h e po r t i o n o f the e x e c u t i v e i m a g e th a t
c o n t a i n s S H E L L l o o k s l i k e a swa p f i l e .
Swa p
file
table entry zero
{ Ch a pte r
14)
c o n ta i n s the c o r r e c t w i nd o w po i n te r t o l o c a t e th i s pa r t
o f the executive on d i sk .
A n e wl y c r e a t ed p r o c e s s h a s a z e r o
in
i ts
PCB $ L_WS SWP f i e l d
i nd i c a t i ng s wa p f i l e ze r o and v i r t ua l bl o c k n umbe r
zero .
Th e s e l e c t i o n o f a ne wl y c r e a t ed p r o c e s s fo r
i n s wa p a nd
the
actual
i n swa p o pe r a t i o n
a re
pe r f o rmed by t h e swa ppe r i n e x a c t l y t h e same
f a sh i o n as a n i n s wa p o f a pr ev i o u s l y o u t swa pped p r o c e s s f r om a r eg u l a r
Sh e l l wa s c o n s t r uc t ed wh e n the e x e c u t i v e i m ag e SYS . EXE wa s
swa p f i l e .
l i n k e d to l oo k e x a c t l y l i k e a n o u t swa pped p r o c e s s .
Howev e r , a pr o c e s s
head e r
c a nno t b e e n t i r e l y c o n f i g u r ed
w i tho ut
t a k i ng i n to ac c o un t
s ev e r a l SYSB OOT p a r am e t e r s .

17. 2. 2

C o n f i g u r a t i o n o f t h e P r o c e s s He a d e r

To a c c ompl i sh the f i n a l
c on f i g u r a t i o n o f
the p r o c e s s h e a d e r ,
the
swa ppe r m a k e s o ne c h e c k { a f t e r the p r o c e s s h a s b e e n r e ad i n b u t b e f o r e
the wo r k i ng s e t i s r eb u i l t ) t o d e t e rm i n e wh e th e r
th i s
is
an
i n s wa p
f r om S H E L L .
I f i t i s , a s p e c i a l s ub r o u t i n e i s c a l l ed t o c o n f i g u r e t h e
p r o c e s s h e a d e r b e fo r e t h e f i n a l o pe r a t i o n s o f i n s wa p a r e c ompl e t ed .

1 7-1 3

PROC ESS C REAT I ON
Th i s r o u t i n e , a s ub r o u t i n e o f
the
swa ppe r ,
does not
e x e c ute v e r y
o f t en ,
o n l y as pa r t o f t h e c rea t i on o f a n e w process .
To avo i d u s i ng
up s pa c e i n the r e s i d e n t e x e c u t i v e , t h e r o u t i n e i s p u t
i n to
some o f
the
pag e s
tha t a r e r e ad i n f r om S H E L L .
Re c a l l f r om Ch a p t e r 1 4 t h a t
t h e swapp e r ' s p s e ud o
pag e
t ab l e
( as
fa r
as
the
I /0 s ys t em
is
c o nc e r n ed )
i s a l so
i t s P O pag e ta b l e ( a s f a r a s a d d r e s s t r a n s l a t i o n
r o u t i n e s a r e c o nc e r n ed ) .
Th i s
s pe c i a l
s ub r o u t i n e
exec utes
in
PO
a d d r e s s e s i n t h e c o n t e x t o f t h e s wa ppe r p r o c e s s .
Wh e n t h e n e w p r o c e s s
pag e t ab l e s a r e s e t u p , t h e phys i c a l pag e s tha t c o n t a i n th i s cod e w i l l
become the k e r n e l s t a c k .
Th e d e t a i l s th a t th i s s pe c i a l s ub r o u t i n e m u s t
h e re .

a t t e nd

are

l i s t ed

Pag es t h a t a r e a pa r t o f She l l ( a nd a l s o
pe rm a n e n t l y l o c k ed
i n to
th e wo r k i ng
s e t ) b u t a r e not r e a d in f r om the c o py o f
Th e s e
Sh e l l i n t h e e x e c u t i v e i m a g e a r e f i l l ed w i th
zeroes .
pag es a r e
a l l but
the
f i r s t pag e o f t h e b eg i nn i ng o f the
p r o c e s s h e a d e r , one pag e of t h e k e r n e l s t a c k ,
a nd
the
pa g e
t a b l e pa g e a r r a ys ( Ta b l e 1 7 - 5 ) .
No n e o f t h e i n f o rm a t i o n tha t
w i l l be p u t i n t h e s e pag e s wa s a s s embl ed i n to
the
ex ec u t i v e
Th e i r c o n t e n t s a r e d e t e rm i ned dynam i c a l l y .
image .

Th e s y s t em pag e t a b l e e n t r i e s tha t m a p t h e f i x ed
po r t i o n o f
the p r o c e s s h e ad e r ,
t h e wo r k i ng s e t l i s t , a nd the p r o c e s s
s e c t i o n ta b l e a r e t empo r a r i l y m a pped so th a t th i s r o u t i n e m a y
access
t h em .
Th e
i n i t i a l c o n t e n t s o f e a c h S PTE a r e s i mp l y
th e c o n t e n t s o f t h e swa ppe r ' s I /0 pag e t a b l e ( F i g u r e 1 1 - 2 4 ) .

Th e s y s t em pag e t a b l e e n t r i e s tha t m a p t h e em pty pag e s o f the
process
header
( us ed
fo r
wo r k i ng
set
l i s t e x pa n s i o n ,
Ch a p t e r 1 1 ) a r e l e f t a s no a c c e s s
pag e s .
Th e
sys tem pag e
t a b l e e n t r i e s t h a t m a p t h e pag e ta b l e pag e a r r a ys i n the
p r o c e s s h e a d e r ( Ch a p te r 1 1 , Ch a p t e r 1 4 ) a r e a l so
t empo r a r i l y
m a pped s o th a t th i s r o u t i n e m a y a c c e s s t h em .

Th e t r a n s l a t i o n bu f f e r i s i nv a l i d a t ed .

Th e b a l a n c e s l o t i nd ex i s s to r ed i n the p r o c e s s h e a d e r .
Th i s
n umbe r
is
s uppl i ed t o S H E LL by t h e swa ppe r , wh o r ec o r d s t h e
n umbe r o f t h e s l o t tha t h a s j us t b e e n f i l l ed .

Th e S YS B OOT pa r am e t e r s t h a t d e te rm i n e the d e f a u l t pag e
faul t
c l us te r
s i ze ,
th e d e f a u l t pag e f i l e i nd e x , a nd the d e f a u l t
pa g e t a b l e pag e f a u l t c l us t e r s i z e a r e s to r ed i n t h e p r o c e s s
h e ad e r .

Th e
i nd e x
to
t h e b eg i nn i ng
of
the wo r k i ng
set
l ist
( P HD$W_W S L I S T )
a n d t h e po i n t e r
to t h e e n d o f t h e p r o c e s s
s e c t i o n t a b l e ( P HD $ L_P S TBAS O F F ) a r e c a l c u l a ted a nd s to r ed .

Th e po i n te r s to t h e fo u r a r r a y s i n t h e pag e t a b l e pag e
ar ray
po r t i o n o f
t h e p r o c e s s h e a d e r ( F i g u r e 1 1 - 8 ) a r e c a l c u l a ted
a nd s to r e d .
Th e pag e t ab l e pag e a r r a ys ( th a t c o un t v a l i d and
l oc ked
pag e s
in
e ac h pag e
of
pag e
t a b l e ent r i e s )
are
i n i t i a l i z e d t o - 1 , i nd i c a t i ng n o v a l i d o r l o c k e d pag e s .
Th e
next to
l a s t pag e
t ab l e pag e i n P l s p a c e h a s i t s e n t r i e s
c o r r e c t ed t o r e f l e c t fo u r l o c k e d pag e s a nd s i x v a l i d
pag e s .
Th e f o u r l o c k e d pa g e s a r e the P l po i n t e r pag e and t h r e e pag e s
o f ke r n e l s t a c k .
Th e t wo pag e s t h a t a r e v a l i d b u t no t l o c k e d
a r e o n e pag e
of
p r o c e s s a l l o c a t i o n r eg i o n and one pag e o f
p r o c e s s I /0 s egmen t .
1 7-1 4

PROC E S S C REAT I ON
9.

Th e f o u r c o un t e r s i n t h e f i x ed po r t i on o f
the head e r
that
c o un t l o c k e d pa g e s , v a l i d pag e s , a c t i v e pag e t a b l e pag e s , a n d
tho s e PTEs w i th n o n z e r o e n t r i e s ( F i g u r e 1 1 - 8 ) a r e i n i t i a l i z e d
t o t h e n umb e r o f a c t i v e P l pa g e ta b l e e n t r i e s .
Th e r e a r e two
s uc h pag e s f o r Ve r s i o n 2 . 0 o f VAX/VM S .

10.

Th r e e wo r k i ng s e t l i s t po i n t e r s ( WS LOC K , WSDYN ,
WSN E XT )
are
ad j us ted
f r om
the i r
i n i t i a l v a l u e s a s semb l ed i n t o S H E L L t o
r e f l e c t t h e ad d i t i o na l pag e s f r om
the
to p o f
th e
process
h e ad e r
tha t a r e a
pe r m a n e n t pa r t o f t h e wo r k i ng s e t .
Th e
wo r k i ng s e t l i s t e n t r i e s f o r t h e two pag e s th a t a r e v a l i d b u t
no t
l o c k e d ( s t e p 8 ) a r e s l i d d o wn t o m a k e r o om fo r t h e WS L E s
f o r t h e p r o c e s s h e a d e r pag e s .

11.

Th e pag e s th a t c ompr i s e t h e t o p o f the p r o c e s s h e ad e r
( f i x ed
po r t i o n ,
wo r k i ng
set
l i s t , p r o c e s s s e c t i o n t a b l e , a n d pag e
t a b l e pa g e a r r ay s ) a r e a d d ed t o the p r o c e s s wo r k i ng s e t l i s t .
In
add i t i o n ,
t h e PFN a r r a ys fo r the phys i c a l pag e s tha t a r e
ma pped a r e u pd a t ed to i nd i c a t e
tha t these
pag e s
a re
pag e
tabl e pag es
( TY PE a r r a y ) , a c t i v e ( S TATE a r r a y ) , a nd i n t h e
p r o c e s s wo r k i ng s e t ( WS LX a r r a y ) .

12.

Th e sys t em pag e t a b l e e n t r i e s tha t m a p t h e p r o c e s s pag e t a b l e
en t r i e s
are
i n i t i a l i zed
t o d em a nd z e r o pa g e s .
Th e t wo P l
pag e ta b l e pag e s tha t a r e a pe rm a n e n t pa r t o f the wo r k i ng s e t
are
a d d ed
to
the wo r k i ng s e t l i s t .
Th e PFN a r r a ys f o r t h e
phys i c a l pag e s t h a t t h e y a r e m a pped
to
are
upd a t e d
as
in
s tep 1 1 .
Finally ,
the
s ys tem
pag e t a b l e e n t r i e s th a t m a p
t h e s e P l pag e t a b l e pag e s a r e s e t u p s o tha t the s e pag e s
a re
acces s i bl e .

13.

Th e o f f s e t s f r om t h e b eg i nn i ng o f the p r o c e s s h e a d e r t o
the
b eg i n n i ng
of
the
P O pag e t a b l e and t h e e nd o f t h e P l p a g e
t a b l e a r e c a l c u l a ted , r e f l ec t i ng t h e s i z e o f the beg i n n i ng o f
t h e p r o c e s s h e a d e r ( Ch a p t e r 1 1 , Append i x E ) .
Th e a d d r e s s o f
t h e f i r s t f r e e v i r t ua l a d d r e s s i n P l s p a c e
( s to r ed
in
the
process
head e r
a t o f f s e t PHD $ L FREP lVA ) and the c o n t e n t s o f
t h e c o py o f t h e P l l e ng th r eg i s ter ( s to r ed
in
the
h a r d wa r e
PC B
in
t h e p r o c e s s h e ad e r ) a r e a l s o ad j us t ed to r e f l ec t t h e
s i z e o f t h e p r o c e s s h e ad e r , wh i c h i s m a pped i n to P l s pa c e .

14.

Th e swa ppe r I /0 p a g e
tab l e
( Fi g u r e 1 1 -2 4 )
i s ad j u s t e d
to
r e f l ec t
the cur rent
s ta t e
of
t h e wo r k i ng s e t l i s t .
Th e
a d d r e s s o f t h e P l w i nd o w to t h e to p o f t h e p r o c e s s h e ad e r
is
( Al t h o ug h the
c a l c u l a ted
and s t o r e d i n l o c a t i o n CTL$G L PHD .
s wa ppe r i s the c u r r en t p r o c e s s , i t is a b le to a c c e s s
the
Pl
add ress
of
the n ewl y c r e a t e d p r o c e s s b e c a u s e i t s pag e s a r e
mapped a s swa ppe r P O a d d r e s s e s a s a pa r t o f t h e
swa ppe r
I /0
page
t a b l e . ) Wh e n c o n t r o l i s pa s s ed b a c k to the swa ppe r , t h e
c ompl e t i o n o f t h e i n s wa p o pe r a t i o n wi l l r e f l e c t
th e
correct
s ta te
of
t h e wo r k i ng
set
l i s t and t h e l o c a t i o n o f t h e P l
w i ndow t o t h e p r o c e s s h e ad e r .

15.

Th e p r o c e s s h e ad e r i s m a r k e d r e s i d e nt
i n PC B $ L_S TS ) .

16.

Th e WS Q U OTA a nd WSAUTH po i n te r s a r e i n i t i a l i z e d to the
v a l ue
of
the
S Y S B O OT pa r am e t e r WSMAX .
Th e WSFLU I D c o un t e r i s
i n i t i a l i z e d to t h e v a l u e o f t h e SYS BOOT pa r am e t e r
M I NWSCNT .
Th e
end
of
the wo r k i ng
s e t l i s t ( WS LAS T ) and t h e d e f a u l t
c o un t ( D FWSCNT ) i n i t i a l l y r e f l e c t the v a l u e o f t h e
S Y S B OOT
pa r am e t e r P Q L_DWS DEFAU L T .
1 7 -1 5

( i n f i e ld

PC B $V P HDRES

PROC E S S C REATI ON
17.

F i n a l l y , t h e PO and P l b a s e r eg i s t e r s a r e ad j us ted to r e f l ec t
th e v i r t u a l a d d r e s s o f t h e p r o c e s s h e ad e r .
Th e c a l c u l a t i o n s
s t ep 13
a d j u s t ed
the va l ue s
of
these
two
r eg i s t e r s
in
r e l a t i ve
t o t h e b eg i nn i ng o f t h e p r o c e s s h e ad e r .
Af t e r th i s
f i n a l s t ep , t h e c o p i e s o f t h e s e
t wo
r eg i s t e r s c o n t a i n
the
v i r tual
a d d r e s s e s o f t h e t h e b eg i nn i ng o f the P O a n d P l pag e
t a b l e s , e x a c t l y wh a t i s r eq u i r ed f o r ad d r e s s t r a n s l a t i o n .

Th e s p e c i a l s ub r o ut in e i n S H E L L r e t u r n s c on t ro l to t h e swa ppe r ' s m a i n
i n swa p r o u t i n e wh e r e
the
f i na l
s t eps o f t h e i n swa p o pe r a t i o n a r e
c ompl e ted .
Th e o pe r a t i o n o f
the
swa ppe r
process
i s d e sc r i be d
in
Ch a p t e r 1 4 .

PROC E S S CREATI ON IN THE C ONTEXT O F THE N EW PROC E S S

17. 3

Th e f i n a l s t eps o f p r o c e s s c r e a t i o n t a k e p l a c e i n t h e c o n t e x t o f t h e
n ewl y c r ea t ed p r o c e s s .
S H E L L c o n t a i n s a n i n i t i a l h a rdwa r e c o n t e x t fo r
the p r o c e s s .
I n pa r t i c u l a r , t h e s a v ed PC i n the h a r d wa r e PCB
is
the
add r e s s
of
a
r o u t i ne c a l l ed E XE $ PROCSTRT .
Th e s a ved PS L i nd i c a t e s
k e r n e l mod e a t I P L 2 .
Th us , t h e
f i r st code
tha t e x e c u t e s
in
the
contex t
of
a n ew l y c r e a t ed p r o c e s s i s the s ame fo r ev e r y p r o c e s s i n
t h e s ys tem .

17. 3. 1

O pe r a t i o n o f PROCSTRT

By the t i me tha t PROC S TRT e x e c u t e s , the PC B
a nd
the
p r o c e s s h e ad e r
have
been
p r ope r l y c o n f i g u r ed .
I n a d d i t i o n , a l l i n fo rma t i o n p a s s ed
f r om t h e c r e a to r th a t b e l o ng s i n t h e PC B h a s a l r e a d y b e e n p u t th e r e .
PROC S TRT m u s t ta k e t h e i n fo rma t i o n tha t i s t empo r a r i l y l o c a t ed i n the
P r o c e s s Quo t a B l o c k a nd p u t i t i n to i t s p r o pe r pl a c e s in
the
process
h e ad e r
a nd
in
P l s pa c e
( Figure 1 7-6 ) .
PROC STRT then p r e pa r e s fo r
ex ec u t i o n the i m a g e wh o s e name wa s pa s s e d by
t h e c r e a t o r a nd
calls
tha t i m ag e .
Th e s t eps tha t a r e pe r fo rmed by PROC STRT a r e
l i s t ed
here .
PROC STRT
b eg i n s e x e c u t i o n
i n k e r n e l m o d e a t I P L 2 to p r ev e n t p r o c e s s d e l e t i o n
un t i l t h e P QB h a s b e en d e a l l o c a t ed .
1.

Th e ad d r e s s o f the RM S d i s pa tc h e r a nd the ad d r e s s o f t h e b a s e
of
the c o n t r o l
r eg i o n
( th e ad d r e ss
o f th e P l m a p t o the
p r o c e s s h e a d e r , the pa r t of P l s pa c e tha t i s
at
the
l o we s t
v i r t ua l a d d r e s s ) a r e p u t i n to t h e P l po i n t e r pag e .

Th e Pl s p a c e
per-proc ess
po i n t to RSB
d i s p a t c h i ng
Ch a p te r 3 . )

Th e ac c o un t n am e , u s e r name , a nd d e f a u l t d i r ec to r y s t r i ng a r e
t a k e n f r om t h e P QB
a nd p u t i n to th e i r p r o p e r pl a c e s i n P l
spac e .

Tho se quo t a s tha t a r e s to r ed i n t h e p r o c e s s h e ad e r ( c ur r e n t l y
o n l y C P U t i m e l i m i t a nd A S T l i m i t ) a r e m o v ed f r om t h e PQB to
t h e i r p r o pe r pl a c e s i n the p r o c e s s h e ad e r ( Ta b l e 1 7 - 4 ) .

v e c to r s fo r
u s e r -wr i t t e n s ys t em se rv i c e s
a nd
or
imag e - s pec i f i c m e s s ag e s a r e i n i t i a l i z e d to
i n s t r uc t i o n s .
( Th e
use o f
t h e s e v e c to r s
in
to
u s e r -wr i t ten s ys t em s e r v i c e s i s d i sc ussed i n

1 7- 1 6

PROC E S S C REAT I ON

JIB

N e w Proc e s s

( N ot i n v o l v e d
i n PROCS. TRT
operation )

PC B
-

( S a m pl e p a r a m e t er s
t h at a r e m o v e d f ro m

��
P ro c e s s

Q uo t a

PQB t o n e w p roces s )

.?
�

I mage name, Use: :
Default Directory

Block

( PQB )

Privilege Mask,
Working Set Quotas

Control
Region

� Process
Header

Figure 17-6

Remo v a l o f P r o c e s s Pa r ame t e r s f r om P r o c e s s Quo t a B l o c k

Th e wo r k i ng s e t l i s t po i n te r s a r e i n i t i a l i z ed t o r e f l ec t
the
q uo t a s pa s s e d
f r om th e c r e a to r ( a f t e r m i n i m i z a t i o n wi t h the
s y s t em-w i d e wo r k i ng set ma x i m um ) .

Th e p r o c e s s p r i v i l eg e ma s k i s l o ad ed i n to the f i r s t q u a d wo rd
of
the
process head e r
{ th e wo r k i ng
p r i v i l eg e ma s k ) , the
p e rma n e n t p r i v i l eg e ma s k ( a t l o c a t i o n C T L $G Q PROCPR I V in
the
P l po i n t e r pag e ) , a nd the a u tho r i z e d pr i v i l ege m a s k { i n f i e l d
PHD $ Q AUTHPR I V) .
Th e us e o f e a c h o f t h e s e p r i v i l eg e m a s k s i s
d e s c rTbed i n Ch a p t e r 1 8 .

At t h i s po i n t , t h e en t i r e P QB i s c o p i ed to the s t a c k a nd
the
PQB d e a l l o c a ted to nonpag ed po o l .
Th i s step i s t a k e n to g i v e
b a c k d yn am i c mem o r y a s
q u i c k l y a s po s s i b l e ,
pa r t i c ul a r l y
b e fo r e t h e t i m e - c o n s um i ng p r o c e s s o f l og i c a l n am e c r e a t i o n .

Th e l o g i n t i m e i s s aved .

1 7- 1 7

PROC E S S C REAT I ON
9.

On c e t h e PQB h a s b e e n d e a l l o c a ted ,
I PL c a n be
l o we r ed
to
zero ,
a l l ow i ng t h e p r o c e s s to be d e l e t ed .
By k e e p i ng I PL a t
2 u n t i l t h e PQB h a s b e e n g i v e n up , t h e n e ed fo r spec i a l c a s e
c o d e i n De l e t e P r o c e s s i s a v o i d ed .
Th e r e i s no n e ed t o chec k
i n De l e t e P r o c e s s wh e th e r the p r o c e s s b e i ng d e l e t ed
is only
pa r t i a l l y c r e a t ed
a nd s t i l l own s a P r o c e s s Quo t a B l o c k f r om
n o npag ed po o l .
Ano the r mo r e ph i l o so ph i c a l i n t e r p r e t a t i o n
is
th a t a t th i s
po i n t i n the c r e a t i o n o f a p r o c e s s , we f i n a l l y h a v e som e th i ng
th a t i s c a pa b l e o f b e i ng d e l e t ed , a f u l l f l ed g ed p r o c e s s .

10.

Log i c a l
n am e s
a r e c r e a ted
fo r
SYS $ IN PUT ,
SYS $0UTPUT ,
SYS $ E RROR ,
TT , a n d SYS $D I S K .
Th e i ma g e name i s moved to the
i ma g e h e a d e r
buf f e r
fo r
s ub s e q u e n t
use
by
the
imag e
a c t iva to r .
Th e PQB c o py i s r emoved f r om th e s t a c k .

A t t h i s po i n t , PRO C S TRT h a s moved a l l the i n f o rm a t i o n f r om the c r e a to r
to
the c o n t e x t o f the n ew p r o c e s s .
I t i s now r e ad y to a c t i v a t e the
i m a g e tha t w i l l e x e c u t e
in
the
context o f
the
new p r o c e s s .
It
p e r fo rms t h e f o l l o w i ng s t eps t o a c c ompl i sh th i s .
11.

Ac c e s s m o d e i s c h a ng ed to e x e c u t i v e b y f a b r i c a t i ng a
PS L o n
t h e s t a c k a nd e x e c u t i ng a n RE I i n s t r uc t i o n .
Th e e x e c u t i o n o f
a n RE I i n s t r uc t i o n i s the o n l y wa y t o g e t t o a n o u t e r
( l ess
p r i v i l eg e d ) a c c e s s m o d e .

12.

Th e imag e a c t i v a to r i s c a l l ed to s e t up the pag e
t a b l e s a nd
pe r fo rm
th e
o t he r
s t eps n ec e s s a r y
to a c t i v a t e the i m ag e .
Im a g e a c t i v a t i o n i s d e sc r i b ed i n t h e nex t c h a p t e r .

13.

An ex e c u t i v e m o d e t e rm i n a t i o n h a nd l e r i s d e c l a r ed
t h a t wi l l
call
RM S $ RUNDWN
fo r
e a c h o pen f i l e .
Th i s h a nd l e r wi l l be
i nv o k e d wh en S Y S $ E X I T i s c a l l ed f r om e x e c u t i v e a c c e s s mo d e ,
wh i c h wi l l u s ua l l y h a ppen wh e n the p r o c e s s i s d e l e t ed .

14.

Ac c e s s m o d e i s c h ang ed to us e r by f a b r i c a t i ng a
s t a c k and e x e c u t i ng a n RE I i n s t r uc t i o n .

15.

Th e f r am e po i n t e r ( F P ) i s c l e a r ed .
Th i s g u a r a n t e e s tha t
the
s e a r c h o f the s t a c k fo r a c o nd i t i o n h a nd l e r by the e x c e p t i o n
d i s pa t c h e r w i l l t e rm i n a t e ( Ch a p te r 2 ) .

16.

An i n i t i a l c a l l f r am e i s s e t up o n t h e s t a c k by
CALLG i n s t r uc t i o n i n l i n e .

PS L

e x e c u t i ng

the

C A L LG
1 5$ :

. WORD
0
n e x t i n s t r uc t i o n

; E n t r y Ma s k

Th e ad d r e s s o f a c a t c h a l l c o nd i t i o n hand l e r
is
e s t a b l i s hed
in
th i s
f r am e a nd a l so i n the l a s t c h a n c e e x c e p t i o n v e c to r
f o r us e r mo d e .
Th e p u r po s e a nd a c t i o n o f
th i s h a nd l e r
a re
d i scus sed i n the nex t sec t i o n .
17.

An a r g um e n t l i s t t h a t i s n e a r l y i d en t i c a l to the o n e used
by
one o f
the
c ommand
l a ng uag e
i n t e r p r e t e r s ( Ch a p t e r 2 0 ) i s
b u i l t o n the s tac k .
Th i s a rg um e n t l i s t a l l o ws a n
i m ag e
to
e x e c u t e wi th n o c o nc e r n o v e r wh e th e r i t wa s a c t i v a ted f r om
Th e a d d r e s s o f a d ummy C L I c a l l b a c k
PRO C S TRT o r f r om a C L I .
1 7- 1 8

PROC E S S CREAT I ON
r o ut i ne
i s p u t i n to th i s a rg um e n t l i s t a nd a l so i n l o c a t i o n
C T L $ A L C L I CA LB K .
If
an
imag e
tha t wa s a c t i v a t ed
f r om
PRO C S TRT a t temp t s
to c ommun i c a t e w i th a C L I ( wh i c h d o e s no t
e x i s t ) , a n e r r o r o f C L I $_I NVR E QTYP w i l l b e r e t u rned .
18.

F i n a l l y , t h e i m ag e i s c a l l ed a t i t s i n i t i a l t r a n s f e r add r e s s .
If
the
imag e
t e rm i n a t e s w i th a RET
( i n s t e ad o f c a l l i ng
SYS $ E X I T d i r e c t l y ) ,
PR OC STRT c a l l s
SYS $ E X I T
i tsel f .
In
g en e r a l ,
t h e r e i s n o d i f f e r e n c e b e twe e n a n i m ag e t e r m i n a t i ng
wi t h a R E T o r wi th a c a l l to S YS $ E X I T .
I f t h e p r o c e s s wa s i n i t i a l l y c r ea t ed w i th t h e h i b e r n a t e f l ag ,
it
is
pl a c ed
i n to
h i b e r n a t i o n b e fo r e the i m ag e i s c a l l ed .
Wh e n c o n t r o l i s pa s s ed
bac k
to
PROC S TRT f o l l o w i ng
i m ag e
te rmi nat i on ,
the h i b e r n a t e
f l ag
i s ag a i n c h e c ked .
I f no
e r r o r o c c u r r ed a nd t h e h i b e r n a te f l ag is s e t , the p r o c e s s
is
p u t b a c k i n to the h i b e r n a t e s ta t e .
I n th i s i n s t a n c e , t h e r e
i s a d i f f e r e n c e b e twe en
RET a nd
SYS $ E X I T .
If
a
p r o c e s s w i sh e s to be p u t b a c k to s l e e p fo r
f u t u r e a wa k e n i ng s , i t m u s t RET b a c k to PROC STRT r a th e r
than
t e rm i n a t e w i th a c a l l to SYS $ E X I T .

17. 3. 2

C a t c h Al l Co nd i t i o n H a nd l e r

Th i s c o nd i t i o n h a nd l e r i s e s t a b l i shed i n the o u t e rmo s t c a l l
f r am e by
PR O C S TRT a nd b y the c omma nd l a ng uag e i n t e r p r e t e r s b e f o r e a n i mag e i s
c a l l ed .
An y c o nd i t i o n tha t i s r e s i g n a l l ed ( n o t p r o pe r l y h a nd l e d )
by
o th e r
h a nd l e r s
(or
un f i e l d ed
bec a use
no o th e r h a nd l e r s have b e en
e s t a b l i shed ) w i l l ev e n t ua l l y b e pa ssed to th i s h a nd l e r .
Th e h a nd l e r
wi l l
i s sue
a m e s sag e us i ng the SYS $ P U TM SG s e r v i c e and , d e pend i ng on
t h e s e v e r i t y l e v e l of the c o nd i t i o n , f o r c e i m ag e ex i t .
The d e t a i l s o f the c a tc h a l l c o nd i t i o n h a nd l e r a r e l i s t ed h e r e .
1.

I f the c o nd i t i o n i s S S $ S S FAI L , t h en sys tem
s e rv i c e
fa i l ure
e x c e p t i o n mod e
is
d i sa b l ed
t o avo i d
a n i n f i n i t e l o o p i ng
s i t ua t i o n .

I f the e x c e p t i o n wa s g e n e r a t ed b y a c a l l t o L I B $ S IGNAL , ( th a t
is,
th e
e x c e p t i o n d i d no t p a s s th r o ug h t h e mod ul e EXC E PT I ON
i n the e x e c u t i v e ) , t h e a rg um e n t l i s t i s ad j us ted
to
conta i n
o n l y tho s e a r g um e n t s pa s s ed t o L I B $ S IGNAL a nd no t the PC a nd
PS L f a b r i c a t ed
i n to
the
s i g na l
a r r a y by
t h a t p r o c ed u r e
( Ch a p t e r 2 ) .

SYS $ P UTM SG i s c a l l ed to wr i t e an e r r o r m e s s ag e to
SYS $ 0 UT PUT
( a n d to SYS $ E RROR i f d i f f e r e n t f r om SYS $ 0 UT P UT ) .
Th e s e r v i c e
SYS $ P UTMSG
i s d e sc r i b ed
in
the
Se r v i c e s
VAX/VM S
Sys tem
Re f e r e nc e Ma n ua l a n d i n t h e VAX- 1 1 Run-T i m e L i b r a r y Re f e r e n c e
Th e i n t e r n a l o p e r a t i o n o f
the
Put Me s s ag e
sys t em
Ma n ua l .
s e r v i c e i s d i s c u s sed i n Ch a p t e r 2 7 .

1 7-1 9

PROC E S S CREAT I ON
4.

I f th i s h a nd l e r wa s c a l l ed th r o ug h the
l a s t c h a n c e v e c to r
( i nd i c a t ed by a d e pth o f - 3 ) , o r i f the e r r o r l ev e l i s s eve r e
or g reate r ,
t h e n a n exc ept ion
s umm a r y
is
wr i t t e n
to
SYS $ 0 UTPUT by
the
rout ine
E XE $ E XCMSG .
Th i s
r o ut i n e
is
d e sc r i b ed i n Ch a p t e r 2 7 .
( by
I n a l l o th e r c a s e s , t h e i mag e
i s a l l o wed
to c o n t i nue
the
e x c e pt i o n
r e t u r n i ng
a
s t a t us
of
S S $_C ONT INUE
to
d i spa tch e r ) .

1 7- 2 0

CHAPTER 1 8
I MAG E ACT IVAT I ON AND TERM I NAT I ON

to
p r e pa r e
s t e ps
Be fo r e a n i mag e c a n e x e c u t e , VM S m u s t ta k e s e v e r a l
the
i mag e
fo r
execut ion .
P r o c e s s pag e
ta b l e s a nd o th e r
d a ta
s t r uc t u r e s m u s t be s e t up to l o c a t e the c o r r e c t imag e
f i l e on d i sk .
Th e c a pab i l i t y o f i nv o k i ng a d eb ug g e r m u s t b e i n c l ud ed .
At imag e e x i t , t e rm i n a t i o n h a nd l e r s d e c l a r ed by th e
user
or
by VM S
must
be
c a l l ed .
I f the i m a g e i s e x e c u t i ng i n a b a tc h o r i n t e r a c t i v e
e nv i r o nme n t , a l l t r ac e s o f t h e i ma g e m u s t be el i m i n a te d
so
tha t
the
next i m ag e c a n b eg i n e x e c u t i o n w i th no s i d e e f fec t s f r om the e x e c u t i o n
o f the p r e v i o u s i m ag e .

18 . 1

I MAG E IN I T IAT I ON

VM S c o n t a i n s no s pe c i a l c od e to r e ad i m a g e s i n to memo r y fo r
initial
execut ion .
I n s t e ad , t h e pag i ng mech a n i sm th a t b r i ng s i n pag e s f r om a n
i m ag e f i l e o n d em a nd i s u s e d wh e n a n imag e i n i t i a l l y e x e c u t e s a s we l l
a s l a te r
on .
I n o rd e r
fo r
th i s s c h em e to wo r k , t h e p r o c e s s pag e
t a b l e s m u s t be p r o p e r l y s e t up to r e f l ec t the s ta t e o f a l l
t h e pag e s
Th i s s e t u p i s pe r f o rmed by the i m a g e a c t i va to r .
i n the i ma g e f i l e .
Th e a c t ua l t r a n s f e r o f c o n t r o l to the i m ag e a l s o t a k e s p l ac e
th r o ug h
VM S s o tha t ho o k s c a n b e i n s e r t e d t o a l l o w l a t e r i nc l us i o n o f e i th e r a
d e b ug g e r o r the t r a c e b a c k f a c i l i ty .
Th i s pa th th r o ug h VM S , c a l l ed t h e
d e b ug
boo t s t r a p ,
a l wa ys e x e c u t e s un l e s s e x pl i c i t l y e x c l ud ed a t l i n k
t i m e w i th a /NOTRAC EBAC K q u a l i f i e r t o t h e L I NK c ommand .

I m ag e Ac t i va t i o n

18. 1 . 1

Th e mod u l e tha t c o n t a i n s t h e i m a g e ac t i v a to r ( S YS I MGAC T ) i s o n e o f t h e
l a rg e s t m od u l e s
in
the
e x ec u t i ve .
Al t h o ugh
t h e c o n c e p t o f i mag e
a c t i v a t i o n i s v e r y s i mp l e , t h e r e a r e s e v e r a l a l t e r n a t e
pa th s
th r o ug h
the
i m ag e a c t i v a to r th a t t a k e i n to a c c o u n t the m a n y s pe c i a l c a s e s o f
i m ag e a c t i va t i o n .
Some o f the s e c a se wi l l
b e d i sc u s s ed
expl i c i t l y .
Ot h e r s wi l l onl y b e m e n t i o ne d i n p a s s i ng .
Th e t ype s o f
i nc l ud e :
•

i m ag e

a c t i va t i on

tha t

wi l l

d i s c u s s ed

Ac t i va t i o n o f a " s i mpl e " i m ag e , o n e th a t c o n t a i n s
secti ons .

1 8-1

expl i c i tl y
no

g lobal

I MAG E ACT I VAT I ON AND TERM INAT I ON
Th i s i s a n a r t i f i c i a l s e pa r a t i o n f r om t h e n e x t c a se ,
s impl y
t o i l l us t r a t e t h e d i f f e r e n c e i n c a l l s to t h e i mag e a c t i v a to r .
•

Ac t i v a t i o n o f a n i m a g e t h a t c on t a i n s g l oba l s e c t i o n s .
B e c a use a l mo s t eve r y h i g h l ev e l l a ng uag e p r o c e s s o r
inc l ud e s
l i b r a r y r o u t i n e s , th i s c a se i nc l ud e s eve r y i m a g e e x c e p t tho s e
wr i t t en e n t i r e l y i n VAX- 1 1 MACRO w i t h no e x p l i c i t s h a r i ng
of
g loba l sec t i ons .

•

I n i t i a l a c t i va t i o n o f k n o wn i m ag e s .
Wh e n th e I N S TA L L u t i l i ty e x e c u t e s
to make
p r i v i l eg ed
or
sha r eable
i m a g e s k n o wn t o the s ys tem , the i m a g e a c t i v a to r i s
c a l l ed w i th a n o a c t i v a t e o p t i o n , o n l y p r e pa r i ng the i m ag e fo r
l a ter a c t ivat ion .

•

La t e r a c t i v a t i o n o f k n o wn i m ag e s .
Th e
a c t i v a t i on o f
images
th a t h a v e b e e n
i n s t a l l ed
is
s t r e aml i n e d by t h e d a ta s t r uc t u r e s tha t we r e c r e a t ed wh e n the
i m a g e wa s i n i t i a l l y i n s t a l l ed .

•

Ac t i v a t i o n o f c ompa t i b i l i ty mod e i m ag e s .
Wh e n th e i m ag e a c t i v a to r i s a s k e d to a c t i v a t e a c ompa t i b i l i t y
mod e
i m a g e , i t a c t ua l l y a c t i v a t e s the RSX- l l M AME a nd pa s s e s
t h e c ompa t i b i l i ty mo d e i mag e n am e
to
t h e AME f o r
f u r th e r
p r o c e s s i ng .

Th e r e a r e s ev e r a l o th e r opt i o n s t h a t t h e i m a g e
a c t i v a to r m u s t c h e c k
Th e s e wi l l
o n l y b e m e n t i o n ed i n the spec i f i c pa r t s o f i m ag e
fo r .
a c t i v a t i o n wh e r e t h e y c a u se s pe c i a l a c t i o n t o b e ta ken .
Th ey i n c l ud e :
•

I m ag e a c t i v a t i o n a t s ys t em i n i t i a l i z a t i o n t i me .
Du r i ng i n i t i a l i z a t i o n o f the s ys tem , two i m ag e f i l e s m u s t b e
o pe n ed w i tho u t t h e
s uppo r t o f e i th e r RM S o r the d i s k AC P .
Th e s e i m ag e s a r e SYS I N I T a nd t h e s ys tem d i s k AC P i t s e l f .
Th e
i m a g e a c t i v a t o r c a l l s t h e s pe c i a l c o d e i n the ex e c ut i v e th a t
p e r fo rms th e s i mpl e r AC P o pe r a t i o n s w i tho ut a c t ua l l y us i ng
t h e AC P .
Th e s e r o u t i n e s a r e b r i e f l y d e sc r i b ed a l o ng w i th the
r e s t of s y s t em i n i t i a l i z a t i o n in Ch a p te r s 2 1 a nd 2 2 .

•

Me r g e d i m a g e a c t i v a t i o n .
Th i s i s t h e t e c h n i qu e th a t the e x ec u t i v e u s e s f o r m a pp i ng
a
d e b ug g e r ,
the
t r a c e b a c k h a nd l e r ,
or a
c ommand
l a ng uag e
i n t e r pr e t e r i n t o a n u n u s e d a r ea o f P O o r
Pl spac e .
Ra th e r
th a n us i ng t h e v i r t u a l a d d r e s s d e sc r i pto r s fo und i n t h e i m ag e
h e a d e r o f t h e m e rg ed i m ag e , t h e i m ag e a c t i v a t o r
s i mpl y u s e s
th e n e x t a v a i l a b l e po r t i o n o f P O o r P l s pa c e .
Th e u s e r s t a c k
a n d i m a g e I /0 s e gme n t a r e no t m a pped fo r a m e r g ed i m ag e .
Th e
RM S
i n i t i a l i za t i o n r o u t i n e s a r e n o t c a l l ed e i th e r bec a u se a n
i m a g e i s a l r e a d y e x e c u t i ng a nd h a s RM S c o n tex t tha t c a nno t b e
d e s t r oyed .

1 8-2

I MAG E ACTIVATI ON AND TERM I NAT I ON
•

P O -o n l y i m ag e s .
i mag e s
tha t c o nta i n a l l
t empo r a r y
Th e l i n k e r c a n p r o d uc e
the user
s t ac k a nd the I /O i m ag e I /O
s t r uc t u r e s
i n c l ud i ng
Th e i m a g e a c t i va to r m u s t r e c og n i z e th i s
s egmen t i n P O s p a c e .
t ype o f
a n i m a g e s o tha t the t wo s t r uc t u r e s u s ua l l y l o c a t e d
of
P1
s pa c e
are
c o r r ec t l y
i n t h e l owe s t ad d r e s s po r t i o n
ma pped .
P O - o n l y i m ag e s a r e u s ed wh e n e v e r i t i s
n ec e s s a r y t o e x t e n d
t h e pe r ma n e n t p a r t o f t h e l ow a d d r e s s e nd o f P 1 s p a c e .
Fo r
e x ampl e , t h e
S E T M E S S AG E c omma nd
causes
a
P O -on l y
i m ag e
c a l l ed
S E T P O . EXE
t o ex e c u t e .
Th i s i m ag e m a p s t h e i nd i c a t e d
m e s s a g e s e c t i o n i n to the l o w a d d r e s s e nd
of
P1
s pa c e a nd
a l te r s
l oc a t i on
CTL$G L C T LBASVA to r e f l ec t the new b o und a r y
b e twe e n t h e t empo r a r y a nd pe rm a n e n t pa r t s o f P l s pa c e .
Th i s
last
step
i s c r i ti cal
i f t h e m e s sa g e s e c t i o n i s t o r em a i n
ma pped wh e n l a t e r i m ag e s t e rm i n a t e .

•

P r i v i l eg ed s h a r e a b l e i m ag e s .
Th e s e i n c l ud e pr i v i l eg ed s h a r e a b l e s e c t i o n s u s e d to i m p l emen t
u s e r -w r i t t e n
s y s t em
se rv i c es
a nd
the
a b i l i ty
to
add
pe r -p r o c e s s
or
i ma g e - s p e c i f i c
ent r i e s
to
the
m e s s ag e
f ac i l i ty .

•

Imag e s tha t d o n o t r e s i d e o n a
d ev i c e .

r a nd om

access

mass

s t o r ag e

Th e i mag e
a c t i v a to r c a n ac t i vate
i mag e s
f r om s e qu e n t i a l
d ev i c e s ( ma g t a pe ) and i m a g e s tha t a r e l o c a t ed o n a no th e r nod e
o f a n e two r k .
An a d d r e s s s pa c e l a rg e e no ug h to
conta i n
th e
e n t i r e i m a g e i s f i r s t c r e a t ed .
Th e i m ag e i s then c o p i ed i n to
th i s add r e s s spac e .
Th i s c a u s e s a l l i m ag e pag e s ,
i n c l ud i ng
r e a d -o n l y pa g e s ,
t o be s e t up a s wr i t a b l e , a nd d e s t i ned fo r
t h e pa g e f i l e wh e n t h e y a r e r emoved f r om ph y s i c a l m em o r y .

18. 1 . 1 . 1
Imp l emen t a t i o n o f t h e Imag e Ac t i va to r - Th e i m ag e a c t i va to r
is
i m pl eme n t e d
as a
s ys t em s e rv i c e , a l tho ug h i t i s n o t m e a n t to b e
c a l l ed d i r e c t l y by us e r s .
Th e r e a s o n f o r th i s f o rm o f
i m pl em e n t a t i o n
is
tha t
the i m ag e a c t i v a to r w i l l be i nd i r ec tl y c a l l ed by u s e r s , bo th
th r o ug h a CLI wh e n r unn i ng a n i m a g e wi th some c omm and , a nd th r o ug h th e
I N S TA L L u t i l i ty , wh e n the s ys t em m a n ag e r o r some o th e r p r i v i l eg ed u s e r
i s i n s t a l l i ng p r i v i l eg ed o r sh a r e ab l e i m ag e s .
s ys t em
se rv i c e
Th u s , t h e i m a g e a c t i v a to r h a s i t s
o wn
slot
in
the
vec to r
a r e a a nd
is
i m p l em e n t ed
as a
p r o c ed u r e .
Th e r e a r e s e v e n
Th e y a r e :
a rg um e n t s tha t c a n b e pa s s ed to the i m ag e a c t i v a to r .
nam e

S t r i ng d e s c r i pt o r o f i m ag e tha t i s b e i ng a c t i v a t ed

d f l n am

S t r i ng d e s c r i pt o r f o r d e f a u l t f i l ename

hd r b u f

Ad d r e s s of 5 1 2 byt e bu f f e r in wh i c h
the
i m ag e h e ad e r
a nd
i ma g e f i l e d e s c r i p to r a r e r e t u r n ed .
Th e f i r s t two
l o ngwo r d s i n t h e b u f f e r a r e the add r e s s e s
( wi t h i n
th e
buffer )
of
the
i m ag e head e r
a nd
the
i m ag e
file
d e s c r i pto r r e spec t i v e l y .

18-3

I MAG E ACT I VAT I ON AND TERM I NAT I ON
i mg c t l

Image
ac t i va t i o n c o n t r o l
pa r am e t e r s .
Th e s e
f l ag s
contro l
the
fo rm
t h a t the ac t i va t i o n wi l l take .
Th e
po s s i b l e o p t i o n s a r e :
Bit

Me a n i ng

N OACT , s e t i f n o t a c t i v a t i ng the
i m ag e .
Th i s f l a g i s u s e d by th e I N S TA L L u t i l i ty
t o c o mpl e t e t h e
i n s ta l l a t i o n o f
known
f i l e entr ies .

WRI TAB L E , s e t i f i mag e i s s uppo sed to b e
wr i tabl e .

S HAREAB L E ,
set
if
the
image
is
a
shareable
imag e tha t i s b e i ng a c t i v a t ed
a s a p i e c e o f an e x e c u t a b l e i m ag e .
Th i s
f l a g i s o n l y u s e d i n a r e c u r s i v e c a l l to
the i m ag e a c t i v a to r .

PR IVI L E G E , s e t i f e x e c u t a b l e
imag e h a s
ampl i f i ed
p r i v i l eg e s .
Th i s
f l ag
r e qu i r e s th a t t h e sha r e a b l e
i mag e
tha t
a c t i v a t ed
be
i n s t a l l ed a s a
i s b e i ng
k nown f i l e .
I t a l so r e qu i r e s
tha t
the
S HAREABLE b i t be s e t .

M E RG E , set
i f m e r g i ng o n e
e x ec ut a b l e
i mag e i n to t h e a d d r e s s s pa c e o f a n o the r .
Th e s e t t i ng o f th i s b i t c a u s e s the
us e r
s tack ,
the
i m ag e
I/O segme n t , a nd the
p r i v i l eg e ampl i f i c a t i o n to
be
i g no r ed .
Th i s
bi t mus t be set
if
the
i m ag e
a c t i v a to r i s c a l l ed f r om us e r mod e .

E XPR E G , s e t i f t h e i n ad r
a r g um e n t
( see
next
i t em )
d o e s no t g i v e a n a c t ua l
a d d r e s s r a ng e b u t m e r e l y i nd i c a t e s
i n to
wh i c h
a d d r e s s s pa c e
( PO
s pa c e
or Pl
Th i s
s pa c e ) t h e i m ag e i s to b e m a pped .
f l ag
i s o n l y u s ed d u r i ng a m e r g ed i m ag e
a c t i v a t i on .

i nad r

the v i r t ua l
a d d r e s s o f a 2 - l o ng wo r d a r r a y c o nta i n i ng
add ress
r a ng e
i n to
wh i c h
t h e i mag e i s t o be m a pped .
Th i s a r g um e n t i s u s ua l l y om i t ted ,
i n wh i c h c a s e
the
add r e s s
r a ng e s
d e s i g n a t ed
by th e
i m ag e s e c t i o n
d e s c r i p t o r s i n t h e i m ag e h e ad e r a r e u s e d .

r e ta d r

a d d r e s s o f a 2 - l o ng wo r d a r r a y to r ec e i ve
the
s t a r t i ng
a nd
end i ng a d d r e s s e s i n to wh i c h the i ma g e wa s a c t ua l l y
mappe d .

ident

a d d r e s s o f a q ua d wo r d c o n t a i n i ng the v e r s i o n n umb e r a nd
m a t c h i ng c r i t e r i a fo r a sha r e a b l e i ma g e .
Th e l a s t th r e e
a rg um e n t s a r e
s i m i l a r t o the
i n put
a r g um e n t s
f o r v a r i o us o th e r memo r y m a n ag em e n t sys t em
s e r v i c e s th a t a r e d e sc r i b ed i n Ch a p t e r 1 3 .

1 8-4

I MAG E A C T I VAT I ON AND TERM I NAT I ON
1 8 . 1 . 1 . 2 Ove r v i ew o f Ima g e Ac t i v a t i o n - Th e r e a r e
essent i a l ly
two
s t eps t h a t the i m a g e a c t i v a to r pe r f o rms e a c h t i m e th a t i t a c t i v a t e s a n
i m ag e .
F i r s t , i t o p e n s t h e i m ag e f i l e , wh i c h a l l o ws
the
s ys tem
to
pe r fo rm a l l
o f i ts f i l e protec t i o n chec ks .
Th e n t h e i m ag e h e a d e r i s
r e a d a nd t h e i m a g e th a t i s d e sc r i b ed the r e i s m a pped i n to
the
user ' s
v i r tua l
add r e s s
s pa c e .
Th e mo s t
i m po r ta n t c o n t e n t s o f the imag e
h e a d e r a r e a s e r i e s o f i m a g e s e c t i o n d e s c r i p to r s , o n e fo r e a c h s e c t i o n
in
the
imag e .
E a c h o f the s e s t r uc t u r e s d e sc r i b e s a po r t i o n o f t h e
i m a g e ' s v i r t ua l add r e s s s pa c e , a nd the i r c o n t e n t s wi l l b e u s ed by t h e
image
a c t i va to r a s i n put pa r am e t e r s to o th e r m emo r y m a n ag emen t sys tem
s e r v i c es .
Th e ov e r a l l s t r uc t u r e of a n imag e h e a d e r
is
p i c t u r ed
in
Figure 1 8-1 .
Th e g e n e r a l
f o rm o f a n
i m ag e sec t i o n d e sc r i pt o r i s
p i c t u r ed i n F i g u r e 1 8 - 2 .

1 8 . 1 . 1 . 3 Ac t i va t i o n o f a n Imag e w i th No G l o b a l S e c t i o n s - Mo s t o f t h e
c ommo n o pe r a t i o n s
tha t
a r e pe r f o rmed by t h e i m a g e a c t i v a to r w i l l b e
d e sc r i b ed i n the a c t i v a t i o n o f a n i m ag e
tha t does
no t c o n t a i n a n y
g l o ba l
sec t i ons .
Th i s s e c t i o n c a n b e i n t e r p r e t ed a s t h e g e ne r a l f l o w
th r o ug h t h e i m ag e a c t i v a to r .
O th e r
f o r m s o f a c t i v a t i o n wi l l
be
e x p l i c i t l y d e sc r i b ed
i n l a te r s e c t i o ns b u t wi l l b e m e n t i oned i n th i s
s e c t i o n wh en a pp r o p r i a t e .
1.

Th e i m a g e a c t i v a t o r sc r a tc h a r e a i n P l s pa c e i s i n i t i a l i z e d .

Th e i m ag e f i l e i s o pe n ed a s a p r o c e s s pe rm a n e n t f i l e .

I f t h e i m ag e i s b e i ng
a c t i v a t ed
f r om a
sequen t i a l d ev i c e
( ma g t a pe o r
ac ross a
n e two r k ) ,
then the a d d r e s s r a ng e i s
c r ea t ed a n d t h e e n t i r e i mag e r e ad f r om
th e s e q ue n t i a l
file
i n to v i r t ua l
a d d r e s s s pa c e .
Al l f ut u r e pag e f a u l ts w i l l b e
r e s o l v ed f r o m t h e pa g e f i l e .

Th e f i r s t b l o c k o f t h e i m ag e h e a d e r i s r e a d i n to memo r y .
At
t h i s po i n t , the c h e c k f o r a c ompa t i b i l i t y mod e i m ag e is mad e .
Th e c o n t e n t s o f t h e l a s t wo r d o f t h e f i r s t b l o c k o f the i mag e
h e ad e r i nd i c a t e e i th e r a n i m ag e p r od uc ed by t h e VAX- 1 1 L i n k e r
( - 1 ) o r a n i m a g e p r od uc ed by s ome o th e r l i n k e r ( 0 o r po s i t i v e
contents)
•

At p r e s e n t , o n l y o n e t ype
o f c om pa t i b i l i t y mod e
i m ag e
is
s u ppo r t ed .
An i m ag e p r od uc ed by t h e RSX- l l M t a s k b u i l d e r h a s
a z e r o i n th e c o d e wo r d a nd
wi l l
cause
the
a c t i va t ion o f
SYS $ S YS TEM : RSX . EXE .
Fu r th e r d e t a i l s a b o u t the a c t i v a t i o n o f
a c o mpa t i b i l i t y m o d e i m a g e a r e fo und i n S e c t i o n 1 8 . 1 . 1 . 7 .
5.

A t th i s po i n t , t h e i m ag e a c t i v a to r b eg i n s i t s mo s t
i mpo r ta n t
wo r k ,
th e
s e t t i ng
u p o f t h e p r o c e s s pag e t a b l e s t o r e f l ec t
t h e a d d r e s s s pa c e p r od uc ed b y t h e l i n k e r .
I t pe r f o rms
th i s
wo r k by r e a d i ng
e a c h i mag e s e c t i o n d e sc r i pt o r c o n t a i n ed i n
the i mage h e ad e r
( F i g u r e 1 8 -2 ) ,
d e t e rm i n i ng
the
type o f
s e c t i o n th a t i s b e i ng d e s c r i b ed , a nd c a l l i ng the a pp r o p r i a t e
m emo r y m a n a g eme n t s y s tem s e rv i c e
to
pe r f o rm
th� a c t ua l
m a pp i ng .

1 8- 5

�

Image Header

1-'
00

Image Itself

0'\

Debug a n d
Other Symbol
Tables

Image File

...,.

,,' ®
®

�

®
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Fixed Portion of
Image Header

Transfer Address
Array

Debug and Global
Symbol Table Offsets

Image Section
I'�
D e s c p to rs
\
\ ._________
n_-________

Image Header

Spare

Offset to @

Offset to @
minor ID

�lr

Spare

Patch Data (only found
in patched images)

I'�

Size of Header

�

Image Name and
JOENT S t ri n g s

'\®

Offset to @

\
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Offset to ©

major 1 0

Privilege Mask
Requested

\
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Image 1/0
Segment Pages

Image Flags

1/0

Global Section 10

Image Header

Header
Blocks

Channels

System Version Number
(if linked with SY S.STB )

Fixed Portion o f
Image Header

F igure 1 8 - 1 Contents of

image
type

n u m ber of pages
in this section
page fault
c luster

size of ISO
(in bytes)

I mage Section Flags

s t a rt i n g v i r t u a l p a g e
number for this sec tion

type
o • norm a l

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end of demand
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ze r o s e c t i o n d e s c r i p t or --..
base v irtual block number

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e n d o f pro c e s s
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in image file for this section

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count

global section name

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Global

Copy on Reference

Demand Zero

Writable

4-6

Match Control Field

Last Cluster i n PO
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Vector Contained
in I mage Section

I m age Section
is Protected

e n d o f glo b a l
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F igure 1 8 - 2

General Form of Image S ec tion D e s c r iptor

t-1

3:
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G'l
tz:l

(')
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1-i

t-1

�1-i
t-1

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t-1

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I MAG E ACT I VAT I ON AND TERM INAT I ON
a.

Th e mo s t c ommo n f o rm o f
i m ag e s e c t i o n d e sc r i pto r
tha t
occurs
in
a " s i mpl e " i m ag e d e s c r i b e s a p r i v a te se c t i o n .
Th i s
t ype o f
sec t i o n may be
e i th e r
r ead-on l y
or
r e a d/wr i t e ,
d e pend i ng o n t h e a t t r i b u t e s o f the p r og r am
s e c t i o n s th a t mad e up e a c h s uc h i m ag e
sec t i o n .
Ini tial
pag e f a u l t s fo r e a c h pag e i n th i s t ype o f s ec t i o n w i l l b e
s a t i s f i e d f r om t h e a pp r o p r i a t e b l o c k s i n t h e i mag e f i l e .
Wh e n t h e i m a g e
a c t i v a to r
e nc o un t e r s a n
image sec t i o n
d e sc r i pto r
th a t d e sc r i b e s a p r i v a t e se c t i o n , i t us e s t h e
c o n tents o f
the
i m ag e
s e c t i o n d e sc r i pt o r
as
i nput
a r g um e n t s
t o the C r e a t e a nd Ma p ( P r i va t e ) S e c t i o n s ys t em
service ( Fi g ur e 1 8 - 3 ) .
Th i s r e s u l t s i n a s e r i e s o f pag e
ta b l e
entr i es
th a t a r e p r o c e s s s e c t i o n t a b l e i nd i c e s .
Th e n um b e r o f PTEs i s e q ua l to t h e pag e c o un t c o n t a i n e d
in
th e
ISD.
No t i c e tha t a l l o f t h e PT E s i nd ex t h e s a m e
process sec t i o n .

Ano th e r fo rm o f i m a g e
s ec t i o n d e sc r i pto r
that may be
fo und
in
a n imag e 1 s a d emand z e r o s e c t i o n .
Th e l i n k e r
p r o d uc e s s uc h a s e c t i o n wh ene v e r t h e r e a r e f i v e ( o r
some
u s e r - s p e c i f i ed d e f a u l t n um b e r o f ) c o n s e c u t i ve pag e s i n
t h e i m a g e f i l e tha t c o n t a i n a l l z e r o e s .
Th e
i m ag e
file
does no t c onta i n
tho s e pag e s , b u t me r e l y a n i nd i c a t i o n
( i n t h e I S D ) tha t a c e r t a i n
r a ng e o f v i r t ua l
add r e s s
s pa c e c o n t a i n s a l l z e r o e s .
Wh e n th e i m a g e ac t i v a to r e n c o u n t e r s s uc h an i m a g e s e c t i o n
d e sc r i p t o r ,
i t uses
the c ontents o f the I SD a s i nput
a r g umen t s t o the
C r e a t e Vi r t ua l
Ad d r e s s
Spa c e s ys t em
service
( Fi g ure 1 8 -4 ) .
Th i s r e s u l t s i n a s e r i e s o f pag e
ta b l e e n t r i e s tha t
i nd i c a t e d em a nd
ze ro
pag e s .
Th e
n umbe r
of
PTEs
i s e q ua l to the pag e c o un t c o n t a i n ed i n
the I S D .
No te tha t o n e s uc h s e c t i o n i s the
a rea
in
Pl
sp a c e
that
conta ins
the
us e r
stac k .
Th e
l i n ke r
d i f f e r e n t i a t e s th i s
s pe c i a l
d em a nd
ze r o
sect i on
f r om
o th e r s
by a spec i a l c o d e b y t e i n the t ype d e s i g na to r i n
the I S D .
Th e i m ag e a c t i v a to r p u t s o f f t h e m a pp i ng o f t h e
us e r s t a c k u n t i l l a te r i n t h e a c t i v a t i o n .

Th e th i r d f o rm o f i m ag e s e c t i o n d e sc r i p to r tha t the i m a g e
a c t i v a to r m a y f i nd
i nd i c a t e s
tha t a r a ng e o f v i r t u a l
a d d r e s s s p a c e i s to
b e m a pped
to
a n e x i s t i ng g l o b a l
sec t i on .
Wh e n t h e
i mage
a c t i v a to r enco un t e r s s uc h a n
i m ag e s e c t i o n d e sc r i pto r , i t
cal l s
i ts e l f
r ec u r s i v e l y ,
r e q u e s t i ng
th a t
the g l o b a l
i m ag e
f i l e c o n t a i n i ng t h e
r e q u e s t e d g l o ba l s e c t i o n b e a c t i v a t ed a s a
pa r t o f
the
ac t i va t i o n
o f a no r ma l e x e c u t a b l e i m ag e .
Th e d e t a i l s o f
th i s a c t i va t i o n w i l l b e d e sc r i b ed i n the n e x t s e c t i o n .

A f t e r t h e i m ag e a c t i v a to r h a s p r o c e s s e d a l l the i m a g e s e c t i o n
d e s c r i p t o r s , i t c a l l s the C r e a t e V i r t ua l Ad d r e s s Spa c e s ys t em
s e r v i c e to c r e a t e the i m ag e I /O s egme n t .
Th e
s i ze of
th i s
a rea
i s d e t e r m i ned by t h e s pe c i a l SYS B OOT pa r am e t e r IMG I OCNT
( d e f a u l t v a l ue o f 3 2 ) but may b e o v e r r i d d e n wi th a n
I O S EGM ENT

n [ , [ N O ] P OBUFS ]

entry i n a l i nk e r opt ions f i l e .
I f a P O - on l y i m a g e i s b e i ng
a c t i v a t ed , t h i s a r e a i s l o c a t ed a t t h e h i gh a d d r e s s end o f P O
s pa c e w i th a n E x pa nd Reg i o n sys t e m s e r v i c e .
1 8-8

N u mber of P a g e s

Pro c e s s S e c t i o n
T a b le i n
Process Header

S ize

•

P a g e F ault
C l us t e r

B a se V irtual Page Number

Type

Section Flags

Backw ard Link
P r o c e s s S e c ti o n

Page Fault
Cluster

Table Entry

Base Virtual Block Number

PO P a g e
Table

Image S e c tion D escriptor for
Process Priv a t e Section
0

\.0

N u mber
of Pages
Protection

Owner
Proc ess Section Table Index

3 1 30

2 726

24 23 22

Base VPN

PSTX
PSTX
PSTX

Base Virtual Block Number
\

spare
\

I Control Flags

Count of PTEs
'

Number of Pages

Protection is either
UR or UW
F i gure 1 8 - 3

I Forward Link

Ptr. to W indow C ontrol Block

in Image File
....
00

Ptr. to Channel Control Block

I S D a n d P a g e Tab le Entr i e s for P roc e s s P r ivate S e c t ion

N umber of Pages
Page F a ult
Cluster

Size = 32

GPTX

Base VIrtual Block Number

GPTX

G PTX

GPTX

Minor 10

I count

Image Section Description
for Global Section
-

Owner

I t><J

Pro tection

2 7 26

_..

1 I

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24 23 2 2 2 1

Protection is either
U R or UW
F igure 1 8 - 4

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,

G PTX

Image Section Name

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0
0

Major 10 :

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Base VPN

Section Flags

Type

Global Page Table

PO Page Table

GPTX

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,

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Global Page Table Entry
GPTE
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Global Page Table Index
0

Global page table entries can
take one of three forms.
•
GPTE Is valid.
•
GPTE Indicates a
transition state.
•
GPTE contains a
Global Section Table Index.

I S D and Page Tab l e Entr i e s for Demand Z ero S e c tion

IMAGE ACT IVAT I ON AND TERM INAT I ON
7.

F i n a l l y , t h e ad d r e s s s pa c e t h a t i s to c o n ta i n the u s e r s ta c k
i s c r e a t€d ( wi t h a n E x pa nd Reg i o n s ys t em s e rv i c e ) .
Th e u s ua l
l o c a t i o n o f t h e u s e r s t ac k i s a t the l ow a d d r e s s e nd
of
Pl
spac e ,
wh e r e t h e a utom a t i c s ta c k e x pa n s i o n f a c i l i ty o f t h e
e x c e p t i o n d i s pa t c h e r c a n a d d u s e r s t a c k s pa c e a s n e ed ed .
Th e
l o c a t io n o f
t h e u s e r s ta c k i n P O -o n l y i m ag e s i s a t the h i g h
a d d r e s s e n d o f the P O i m ag e .
Th e d e f a ul t s i z e o f the u s e r s t ac k i s 2 0 p ag e s .
c a n b e o v e r r i d d e n w i th a n
S TACK

Th i s

v a l ue

ent ry i n a l i n k e r opt ions f i l e .
8.

Th e i n i t i a l v a l u e o f the u s e r s ta c k po i n t e r is s to r ed in
the
Pl
s p a c e po i n t e r pag e a nd l o ad ed i n to t h e p r o c e s s o r r eg i s t e r
PR$ USP.
Th i s v a l ue w i l l b e l o ad ed i n to g e n e r a l r eg i s t e r
14
( SP)
wh e n a n RE I
i n s t r uc t i o n
r e t u r n s the p r o c e s s to us e r
mod e , wh i c h u s u a l l y o c c u r s
f o l l o w i ng
the return
f r om
the
i m a g e a c t i v a to r .

Th e p r i v i l eg e s th a t wi l l b e i n e f f e c t wh i l e t h i s
i mag e
is
e x e c u t i ng
a r e c a l c u l a t ed .
Th e l og i c a l AND o f the p r i v i l eg e
m a s k f o und
in
the
i m ag e h e ad e r
( c u r r e n t l y e n a b l i ng
all
p r i v i l eg e s a n d s o
e f fec t i vel y unused )
w i th the
proce s s
pe rma n e n t p r i v i l eg e
mask
( fo und
at
g l oba l
loc a t i on
C T L $ G Q PROCPR I V i n th e P l po i n t e r pag e ) i s t h e n ORed wi th t h e
p r i v i leg e e nh a n c em e n t s f o r a
p r i v i l eg ed
known
i m ag e .
Th e
r e s ul t
is
l o a d ed i n to the p r o c e s s p r i v i l eg e m a s k i n t h e PCB
( PC B $ Q P R I V ) and i n to two
p r i v i l eg e m a s k s
i n the p r o c e s s
h e a d e r� a t o f f s e t
PHD $ Q PR I VMSK ( th e m a s k t h a t i s ac t ua l l y
c h e c k e d by o t h e r
r o u t i n e s- i n
the
sys t e m )
a nd
at o ffset
PHD $ Q I MAG PR I V .
Th e u s e s o f t h e va r i o u s pr i v i l eg e ma s ks by
the sys t em i s d e sc r i b ed S e c t i o n 1 8 . 4 .

10.

A c h e c k i s m a d e to d e te rm i n e wh e th e r
the
i m ag e wa s
l i n k ed
w i th
the
sys t em s ymbo l t a b l e SYS $ S YS TEM : SY S . S TB .
If s o , a
c h e c k i s mad e t o d e t e rm i n e th a t the v e r s i o n o f t h e s ymb o l
tabl e
a g r e e s w i th t h e c u r r e n t l y r unn i ng s ys t e m v e r s i o n .
If
t h e v e r s i o n n um b e r s d i s ag r e e , CMKRN L and
CMEXEC p r i v i l eg e s
are
t u r n ed o f f i n t h e c u r r e n t p r i v i l eg e m a s k .
Th i s p r e v e n t s
m a n y d i f f e r e n t s p u r i o u s e r r o r s tha t c a n o c c u r i f t h e o u td a t e d
i m a g e we r e t o e x e c u t e .

11.

At th i s po i n t , t h e i m ag e a c t i v a to r h a s f i n i sh ed i t s wo r k .
It
l oad s a
f i na l
s t a t us
i n to
R O and
returns t o i ts cal l e r
( e i th e r PROC STRT o r a C L I ) t o a l l o w t h e i m a g e
i tse l f t o be
c a l l ed .

1 8 . 1 . 1 . 4 Ac t i v a t i o n o f I m a g e C o n t a i n i ng G l o ba l S e c t i o n s - As
m e n t i o n ed i n the p r ev i o u s s e c t i o n , wh en the i m ag e a c t i v a to r e n c o un t e r s
a n i m a g e se c t i o n d e sc r i p to r tha t d e sc r i b e s a g l o b a l s e c t i o n , i t c a l l s
i tsel f
r ec ur s i ve l y ,
a l tho ug h
a d i f f e r e n t i mag e f i l e i s i nd i c a t e d o n
t h e r e c u r s i v e c a l l a nd d i f f e r e n t f l ag s a r e s e t .
Th e pu r po s e o f t h e r e c u r s i v e c a l l i s to p r ev e n t a
n o n p r i v i l eg ed
user
wh o h a s
l i nked
his
i m ag e
to
a
p r i v i l eg ed
sha reab l e
i mag e f r om
a c q u i r i ng una utho r i z e d p r i v i l eg e .
Put s i mp l y , VM S d o e s n o t t r u s t
the
1 8-1 1

I MAG E ACT IVAT I ON AND TERMINAT ION

s e c t i o n d e sc r i p to r s
tha t
it
f i nd s
i n t h e us e r ' s i m a g e f i l e
i ma g e
b e c a u s e t h e u se r c a n p u t a lm o s t a ny t h i ng h e p l e a s e s th e r e .
Th e i m a g e a c t i v a to r wo u l d l i k e to
r ea d
t h e o r i g i na l
i m ag e s e c t i o n
d e sc r i pt o r
tha t
is
f o und
in
the
s h a r e a b l e i mag e f i l e , p r e s um a b l y
p r o t e c t e d f r om w r i t e a c c e s s b y n o n p r i v i l eg ed us e r s .
Th e s i mpl e s t wa y
to a ccompl i sh
th i s i s to h av e t h e i m a g e a c t i v a to r c a l l i t s e l f , wh i c h
w i l l r e s u l t i n the sha r e a b l e i m ag e f i l e b e i ng
o pe n e d ,
b u t w i th a n
i mp l i c i t p r o t ec t i o n c h e c k b e i ng p e r fo rmed f o r t h e c u r r e n t u s e r .
Wh e n t h e i m ag e a c t i v a to r p r o c e s s e s t h e i m ag e s e c t i o n d e s c r i pto r s
fo r
e ac h
sec t i on
i n t h e sha r e a b l e i m ag e , i t a l s o maps e a c h s e c t i o n i n to
t h e u s e r ' s a d d r e s s s pa c e w i th a
Ma p G l o b a l
Sec t i on
s ys t em s e rv i c e
( Fi g u r e 1 8- 5 ) .
Any v e r s i o n c h e c k i ng
( to i n s u r e th a t t h e i n s t a l l ed
s h a r e a b l e i m a g e i s c ompa t i b l e w i th t h e s h a r e a b l e i m ag e th a t wa s l i n k e d
i n to
the
u s e r ' s e x e c u ta b l e
imag e )
i s pe r f o rmed by t h e Ma p G l o b a l
S e c t i o n s y s t e m s e r v i c e a nd no t d i r e c t l y b y t h e i m ag e a c t i v a to r .
One b e n e f i c i a l
s ide
effect o f
the
r ec u r s i v e c a l l
to
the
i m ag e
a c t i va t o r
fo r
sha r e a b l e
imag e s
is
tha t
t h e y d o no t h a v e to b e
fo r
( I n f a c t , t h e i m a g e a c t i v a to r o n l y a l l o ws th i s o pt i o n
i n s t a l l ed .
r ea d - o n l y s h a r e a b l e
i m ag e s . )
In
t h e c a s e th a t the r e q u e s ted g l o b a l
s e c t i o n d o e s no t e x i s t , t h e i m a g e a c t i v a to r pe r fo rms a C r e a t e a nd
Ma p
( Pr i va t e )
S e c t i o n s ys t em
s e rv i c e .
In
the c a s e o f
an i n s t a l l ed
s h a r e ab l e i m ag e , a C r e a t e ( Bu t Do
No t Ma p )
Global
S e c t i o n s ys tem
s e rv i c e wa s p r ev i o u s l y e x e c u ted b y t h e i m ag e a c t i v a to r a s a pa r t o f
t h e i n i t i a l i ns ta l l a t i o n o f a known s h a r e a b l e i m ag e .

18. 1. 1. 5
I n i t i a l Ac t i va t i o n o f Known Ima g e - Known i m ag e s
two m a i n p u r po s e s i n VAX/VM S .
•

•

ex i s t

fo r

Imag e s th a t r e q u i r e e n h a n c ed pr i v i l eg e s b u t mus t e x e c u t e
in
n o n p r i v i l eg ed
p r o c e s s c o n t e x t ( s uc h a s MOUNT , S E T , and S HOW )
m u s t h a v e some me thod f o r a c q u i r i ng the i r e l eva t ed pr i v i l eg e s
b e f o r e th e
imag e
e x e c u t e s a nd r e s t o r i ng p r o c e s s pr i v i l eg e s
wh e n th e i m a g e t e rm i n a t e s .
Sh a r e a b l e i m a g e s ( e spec i a l l y tho s e
tha t
i n c l ud e pr i v i l eg ed
s e c t i o n s a nd tho se th a t e x i s t i n sh a r ed memo r y ) m u s t a l so b e
m a d e k n o wn t o t h e sys t em .

Th e I N S TA L L u t i l i ty i s u s e d to r e q u e s t the i n i t i a l ac t i va t i o n o f known
i m ag e s .
It cal ls
t h e i m ag e a c t i v a to r w i th the NOAC T I VATE f l ag s e t ,
t e l l i ng t h e i ma g e a c t i v a to r
to
go
th r o ug h
the mo t i o n s o f
i m ag e
a c t i v a t i o n b u t no t to a c t ua l l y a l t e r the a d d r e s s s pa c e o f the p r o c e s s
i n wh i c h I N S TA L L i s ex e c u t i ng .
Th e c r uc i a l s t ep tha t t h e
i m ag e a c t i v a to r
pe r f o rms wh e n
it
f i rst
acti vates
a
kn own i mag e i s t h e c r e a t i o n o f a d a ta s t r uc t u r e c a l l ed a
k n o wn f i l e e n t r y ( F i g u r e 1 8 - 6 ) i n the known f i l e e n t r y l i s t .
On l a t e r
o pe n s
of
th i s f i l e , RMS w i l l r e t u r n t h e a d d r e s s o f th i s s t r uc t u r e t o
t h e i m a g e a c t i v a to r , i nd i c a t i ng t h a t a k n o wn i m a g e i s b e i ng ac t i v a ted .

1 8-12

Process Page Table

Size

Number of Pages

Page Fault
Cluster

Base VIrtual Page Number

Type

Section Flags

....
(X)

I m a g e S e c t i o n D e s c ri p t o r f o r
Demand Z ero Section

I
....
w

Number
of
Pag es

Demand Z e ro

Demand Z ero

Demand Z e r o

Demand Z e ro

Demand Z ero

Demand Z eJ"o

,
,

Protec t ion

Owner
All Z eros

31 30

27 26

24 23 2 2

F igure 1 8 - 5

I S D and P age Tab l e Entr i e s for G l ob a l S e c tion

K n o w n File H e a d e r ( K F H )

K n o w n F il e E n t ry ( K F I )
�
'

Known File Queue Forward Link

Known File Queue Backward Link
C o n t rol
Bits
1-zj

.....
I.Q
c
1"1
ro
....
00
I

0'\

....
00
I
....
�

Byte Offsets
within Structure
to. . .

File

D;•ecto•y

Name

KFI
KF I
Sequence Q -Number
Number
Globel Section C o unt

Address of A ss o c i a t e d K F I

Spare

�

De•;ce
Name

Reference Count

Known Image Flags

Type

Size of KFH

Image Header of Known
File that was Installed
/HEADER._RESIDENT

��

Usage C o unt e r
Pointer to WCB if file opened
File ID/ Sequence Number if not

0
Hl

I"%J
.....
....
ro

Size of KFI

Type

I"%J
0
1"1
9
Ill
rt
:;:.;:
:;:3
0
�
:;:3

Type

Address o f End o f KFH

Image Header Address
if Header Resident

Privileged Image

Privilege Mask

tzl
:;:3
rt
1"1
"<

AME Code
Number f ro m
Image Header

S p a re

One of these I n Paged
Pool for each known file
lnstalled/HEADER_RESIDENT

Match
Control

Global Section Identification

,�

Counted Strings for
Device Name. Directory.
File Name. File T YP e

One of these for each
Installed Image
F i gure 1 8 - 6

l" v

Format o f Known F i le Entry

L
�

IMAGE ACT IVATI ON AND TERM INATI ON

Th e r e i s a t h i r d b e n e f i t to m a k i ng i m ag e s known to t h e sys t e m .
Th e i r
a c t i v a t i o n m a y b e f ac i l i ta t e d b y o n e o f s e v e r a l o p t i o n s g i v e n wh e n t h e
i m a g e i s i n s ta l l ed .
1.

At th e v e r y l e a s t , t h e i mag e a c t i v a to r s a v e s the f i l e I D a nd
s equenc e
n umbe r wh e n
i t o r i g i n a l l y a c t i v a t e s t h e i m ag e s o
t h a t f u t u r e o pe n s m a y b e b y f i l e I D r a t h e r than by f i l e n a m e .

Th e i m a g e f i l e c a n be i n s t a l l ed / O PEN , wh i c h wi l l
l eave
the
In
th i s c a se , t h e a c t ua l O PEN c a l l to RMS i s
f i l e o pened .
e s s e n t i a l l y a n u l l o pe r a t i o n .

Th e /H EADER R E S I D ENT o p t i o n c a n b e spe c i f i ed to
the
I N S TA L L
u t i l i t y , whTch d i r e c t s t h e i m ag e a c t i v a to r t o k e e p t h e e n t i r e
i ma g e h e ad e r r e s i d e n t i n pag e d d yn am i c m emo r y .
Th i s
saves
the add i t i o nal
r e ad s
tha t a r e r eq u i r ed to b r i ng th e h e a d e r
i n t o memo r y e a c h t i m e t h a t t h e i m ag e i s a c t i v a t ed .

18. 1.1.6
La t e r Ac t i v a t i o n o f Known Imag e - Wh e n a
known
i m ag e
is
a c t i va t ed ,
the
i m ag e a c t i v a to r
is
i n f o rmed by RM S , wh o pl a c e s t h e
a d d r e s s o f t h e k n o wn f i l e e n t r y i n t h e
CTX f i e l d
of
the
FAB .
Of
c o u r se ,
t h e o pe n m a y h a v e b e e n e a s ed by o n e o f t h e o p t i o n s m e n t i o n ed
in the p r ev i o u s s e c t i o n .

Th e a c t i v a t i o n o f a k n o wn i m ag e
r eg u l a r i m ag e , a l tho ug h some o f
pe r f o rm i n the r eg u l a r c a s e c a n
k n o wn i m ag e t h a t h a s i t s h e a d e r
b e c a u s e the I /0 o v e r h e a d c a n b e

p r o c e e d s i n muc h t h e
s am e wa y a s
a
the wo r k t h a t the imag e a c t i v a to r m us t
be a v o i d ed
here .
I n pa r t i c u l a r ,
a
r e s i d e n t c a n be ac t i va ted mo r e q u i c k l y
avo i d ed .

In a ny c a se , t h e i m ag e s e c t i o n d e sc r i p to r s m u s t s t i l l be p r o c e s s e d and
the
pag e
tab l e
entr i e s
set
up s o tha t the i m ag e m a y e x e c u t e .
In
ad d i t i o n ,
the
i m ag e ac t i v a t o r m u s t upd a t e t h e u s a g e
stat i st i c s
( F i g u r e 1 8 - 6 ) f o r th i s known i m ag e .

18. 1 . 1 . 7
Ac t i v a t i o n o f Compa t i b i l i ty Mo d e Imag e s - Wh e n
the
i m ag e
a c t i v a to r d e t e rm i n e s th a t i t i s a t temp t i ng to a c t i v a t
compa t i b i l i t y
mod e i m a g e , i t d o e s a c h a ng e o f c o u r s e a nd a c t i v a t e s an AM E
th a t
is
d e s i g n a t e d b y t h e c o d e wo r d i n t h e l a s t wo rd o f t h e f i r s t b l o c k o f t h e
i m ag e h e a d e r .
At
the
present
t ime ,
there
is
only one
fo r m o f
c ompa t i b i l i ty m o d e
imag e
a nd
o n e AM E s uppo r t ed .
Th e R S X- l l M AM E
( S YS $ S YS TEM : RSX . EXE )
wi l l
be
a c t i v a t ed
wh eneve r
an
i ma g e h e a d e r
c o n t a i n s a ze r o i n the c o d e wo r d .
u

An AME i s i t s e l f a n a t i v e m o d e i m a g e t h a t i s r e s po n s i b l e
f o r m a pp i ng
the
c omp a t i b i l i t y m o d e
image
i n to
the add r e s s r a ng e be t we en 0 a n d
1 0 0 0 0 ( h e x ) ( F i g u r e 1 - 8 ) , p a s s i ng c o n t r o l to th a t i mag e wh i l e
t u r n i ng
o n the c ompa t i b i l i t y mod e b i t ( w i th a n RE I i n s t r uc t i o n ) , a nd f i e l d i ng
all
c om pa t i b i l i ty m o d e
a nd
o th e r
e x c e pt i o n s g e n e r a ted
by
the
c om pa t i b i l i ty m o d e i m ag e .
F r om th e po i n t o f v i e w o f i m a g e a c t i v a t i o n , o n c e t h e
i mage
a c t i v a to r
d e te rm i n e s
that
it
i s a c t i v a t i ng
a c ompa t i b i l i t y mod e i m ag e , i t
c o n t i n u e s wi th a c t i v a t i o n , b u t a c t i v a t i o n o f t h e
AME a nd
no t
the
c ompa t i b i l i t y m o d e i m ag e .
Th e n a m e o f t h e c ompa t i b i l i t y m o d e i m a g e i s
s to r ed
i n the
c om pa t i b i l i ty
mod e
pag e
( at
g l obal
location
C T L $ AG C M E DATA )
i n P l s p a c e wh e r e i t wi l l be r e t r i ev ed by t h e AME a nd
m a pped - i n to the l o we s t 6 4 K b y t e s o f P O s pa c e .
18-1 5

IMAGE ACTI VATI ON AND TERM INAT ION

18 . 1 . 2

Imag e S t a r t up

A f t e r t h e pag e t ab l e s h a v e b e en s e t up b y t h e
imag e a c t i va to r ,
the
i m ag e
i s c a l l ed a t i t s t r a n s f e r a d d r e s s .
De pend i ng o n ho w the i mag e
wa s l i n k e d , t h e i n i t i a l t r an s f e r o f c o n t r o l m a y be to a d eb ug g e r , to a
u s e r - s uppl i ed i n i t i a l i z a t i o n p r o c ed u r e , o r to t h e u s e r i m a g e i t s e l f .

18. 1. 2. 1
T r a n s f e r Ve c to r Ar r a y - I n add i t i o n
to
the
i m ag e
sec t i on
d e sc r i p to r s d i s c u s s e d
i n the
p r ev i o u s s ec t i o n ,
the
l i nk e r
a l so
i nc l ud e s a d a ta s t r uc t u r e c a l l ed a t r a n s f e r v e c to r a r r a y i n the
imag e
Th i s a r r a y c o nta i n s t h e use r s upp l i ed t r a n s f e r a d d r e s s a nd
h e ad e r .
a l s o the m e a n s f o r i nc l ud i ng a d eb ugg e r o r a t r a c eb a c k h a nd l e r i n
the
u s e r imqg e .
Th e f o r m a t o f the t r an s f e r v e c t o r a r r a y i s p i c t u r ed
i n Figure 1 8-7 .
I f a d eb ug t r ans f e r a d d r e s s i s spec i f i ed o r i mpl i ed , i t appe a r s f i r s t
in
the
l ist .
An
i ma g e - s p e c i f i c
i n i t i a l i za t ion
p r o c ed u r e ,
if
s pe c i f i ed ,
o c c u r s n ex t .
Th e l a s t e n t r y i n the l i s t i s the t r a n s f e r
a d d r e s s o f t h e u s e r i m ag e , e i th e r the a rg um e n t o f a . END d i r e c t i v e f o r
a
VAX- 1 1 MACRO p r o g r am
or
t h e f i r s t s t a t e m e n t o f t h e m a i n p r o g r am
wr i t t e n i n a h i g h l ev e l l a ng u a g e .
A f o u r th s l o t c o n t a i n i ng a z e r o
is
the
e nd o f l i s t i nd i c a t i o n , n o m a t te r wh a t o p t i o n s we r e pa s s ed to t h e
l i nke r .

SYS$1MGSTA

Transfer address of
user image

no entries in PSECT
LIB$1NITIALIZE

LIB$ INITIALIZE

Transfer address of
user image

$LINK
or
$LINK/DEBUG
or
$LINK/DEBUG filespec
=

Transfer address of
user image

Transfer address of
user image
-

LIB$ INITIALIZE

0
-

SYS$1MGSTA

$LINK/NOTRACEBACK

non-zero c ontribution to
PSECT LIB$1NITIALIZE

Figure 1 8-7

T r a n s f e r Ve c to r Ar r a y

Th e i n i t i a l i za t i o n t r a n s f e r a d d r e s s i s d e sc r i b ed i n Appe nd i x E o f
the
VAX - 1 1
Run - T i m e
L i b r a r y Re f e r en c e Ma n ua l a nd w i l l no t be d i s c u s s ed
here .
1 8- 1 6

IMAGE ACT I VAT I ON AND TERM INAT I ON

I f the /D E B UG= f i l e s pec o p t i o n i s i nc l ud ed a s a q ua l i f i e r to
the
L I NK
c omma n d ,
the
l i n k e r p l a c e s t h e t r a n s f e r a d d r e s s f o und in f i l e s pec i n
t h e f i r s t e l em e n t i n t h e t r a n s f e r v e c t o r a r r a y .
I f the
/NOTRAC EBAC K
o pt i o n
is
i nc l ud ed
{ and
no t o v e r r i d d e n i mp l i c i t l y by i nc l ud i ng a n
e xp l i c i t / D E B UG o pt i o n ) , t h e n t h e r e i s n o d eb ug t r a n s f e r a d d r e s s .
In
a l l o th e r c a se s , t h e l i n k e r p l a c e s t h e a d d r e s s o f SYS $ IMG S TA ( fo und i n
t h e sys t e m s e r v i c e v e c to r a r e a ) i n t h e f i r s t e l ement o f t h e
transfer
v ec t o r a r r a y .

I m a g e S t a r t up S y s tem S e rv i c e - Un l e s s e x p l i c i t l y s upp r e s s e d
( w i t h t h e /N OTRAC E BAC K q ua l i f i e r ) ,
all
imag es e x ec ute
t h e Imag e
S t a r t up s ys t e m s e rv i c e , s om e t i m e s c a l l ed t h e d e b ug g e r boo t s t r a p .
Th i s
p r o c ed u r e
e x am i n e s
the v a r i o us
l i nk
a nd
C L I f l a g s a nd d e t e r m i n e s
wh e t h e r
t o s ta r t
the
user
i mag e d i r e c t l y o r m a p t h e d e b ug g e r
( s pec i f i ed
b y t r an s l a t i ng t h e l og i c a l n a m e L I B $DE BUG ) i n to t h e u s e r ' s
P O s pa c e a nd t r a n s f e r r i ng c on t r o l t o i t .
18. 1. 2. 2

I n a n y c a s e , a c o nd i t i o n h a nd l e r i s e s t a b l i shed i n t h e c u r r e n t c a l l
f r am e
th a t w i l l e v e n t ua l l y g a i n c o n t r o l o n s i g n a l s t h a t t h e u s e r d o e s
n o t hand l e d i r e c t l y .
On e o p t i o n tha t th i s h a nd l e r c a n ex e r c i s e i s t o
map the
t r a c ebac k
f a c i l i ty
t h a t w i l l p r i n t a s ym bo l i c d um p o f the
e x c e pt i o n .
1.

Imag e S t a r t up f i r s t p u r g e s the e n t i r e proc e s s wo r k i ng s e t o f
all
P O and P l p a g e s .
Th i s h a s t h e e f f e c t o f e l i m i n a t i ng C L I
p a g e s a n d o th e r pa r t s o f t h e a d d r e s s s p a c e t h a t w i l l
no t b e
n e ed ed b y th e i m ag e t h a t i s a bo u t t o e x e c u t e .

Th e nex t s t e p t h a t Imag e S t a r t up pe r fo rm s i s a po t e n t i a l m a p
of a
d e b ug g e r i n to P O s pa c e .
Th i s m a p wi l l o c c u r und e r two
d i f f e r e n t c o nd i t i o n s .
a.

I f t h e p r og r am wa s l i nk e d L I NK/D E B UG a nd s i mpl y r un
i s , n o t r un w i th a RUN/NODEBUG c omma nd ) .

( tha t

If
t h e p r og r am wa s
r un w i th a
RUN/D E B UG
c omma n d ,
i nd e pend e n t o f wh e th e r the d eb ug g e r wa s r e q u e s t ed a t l i n k
t i me .

Th e d e bug g e r w i l l n o t b e m a pped i f t h e i m ag e i s
r un w i th a
R UN/N ODE B UG c omma n d o r i f t h e / D E B UG o pt i o n wa s o m i t te d f r om
b o th th e L I N K c o mma n d a nd the RUN c omma nd .
3.

F i n a l l y , a c o nd i t i o n h a nd l e r i s e s t a b l i sh e d
i n the c ur rent
c a l l f r am e , t h e a r g um e n t l i s t i s a l te r ed to po i n t to t h e n e x t
a d d r e s s i n t h e t r a n s f e r v e c to r a r r a y , a nd c o n t r o l
i s pa s s ed
to
the nex t
t rans fer
address .
Th i s w i l l
be e i th e r the
Run - T i m e L i b r a r y p r o c ed u r e
LI B $ I N I TIALI Z E o r
th e
t r ansfer
a d d r e s s o f t h e u s e r i m ag e .

18. 1.2. 3
Except i o n Ha nd l e r fo r T r a c eb a c k - Th e c o nd i t i o n h a nd l e r th a t
wa s e s ta b l i sh e d b e fo r e t h e imag e wa s c a l l ed h a s two p u r po s e s .
•
•

I t i n vo k e s a d e b ug g e r i f a DEBUG c omma nd i s
i ma g e i s i n t e r r up t ed w i th a C TRL/Y .

t yped

after

I t i nvo k e s t h e t r a c e ba c k h a nd l e r to prod uc e a s ymbo l i c
d ump i f a n u n f i e l d ed c o nd i ti o n o c c u r s .
1 8- 1 7

s tac k

I MAGE ACT I VATION AND TERM INAT I ON

I f a n o n p r i v i l eg ed i m ag e i s i n t e r r up t e d w i th a
CTRL/Y ,
and
a DEBUG
c omma nd
i s e x e c u t ed , t h e DC L ( o r M C R ) c omma nd i n t e r p r e t e r g e ne r a t e s a
s i g n a l o f the f o rm S S $ D E B UG .
( P r i v i l eg ed i m a g e s a r e
s i mpl y r un d o wn
in
r esponse
to
a C TRL/Y . ) As s um i ng t h a t any hand l e r s e s t a b l i shed b y
the
i m ag e
r es i g na l
the
S S $ DEBUG e x c e pt i o n ,
t h i s h a nd l e r
wi l l
e v e n t ua l l y g a i n c o n t r o l .
I t s re s po n s e to a S S $ D E B UG s i g na l i s to m a p
t h e d eb ug g e r s pe c i f i ed b y t h e l og i c a l n a m e L I B $DE BUG
(if
it
is
no t
a l r e a d y ma pped ) a n d t r a n s f e r c o n t r o l to i t .
No t i c e th a t a n i ma g e th a t
wa s n e i th e r l i nk ed no r r un w i th the d eb ug g e r c a n
s t i l l b e d eb ug g ed
( a l b e i t w i tho u t a d eb ug s ymbo l t a b l e ) i f t h e p r og r am r e a c h e s some ug l y
s ta t e s uc h a s a n i n f i n i t e l o o p .
Th e s e c o nd p u r po s e o f th i s h a nd l e r i s t o f i e l d
any e r ro r
c o nd i t i o n s
( wh e r e
t h e s eve r i t y l ev e l i s WARN I NG , ERROR , o r S E VE R E ) a n d pa s s them
on t o
the
t r aceba c k
f ac i l i ty .
Th i s
r eq u i r e s
th a t
the
f ac i l i ty
( d e n o ted
by
the
l og i c a l
n am e L I B $ TRAC E ) be m a pped i n to the us e r P O
s pa c e .
An y c o nd i t i o n s t h a t h a v e a s ev e r i t y l ev e l o f e i th e r NORMAL o r
I NF O a r e
r e s i g n a l l ed , wh i c h i mp l i e s t h a t th e y w i l l b e h a nd l ed by t h e
c a t c h a l l c o nd i t i o n h a nd l e r e s t a b l i s h e d by e i th e r PROC STRT o r the C L I
t h a t c a l l ed t h e i m a g e .

I MAGE EXIT

18. 2

Wh e n a n i ma g e wi s h e s
to
pa s s c o n t r o l
b a c k t o VM S a f t e r
i t has
i t s wo r k , i t c a l l s S YS $ E X I T e i th e r d i r e c t l y o r by r e tu r n i ng
c om p l e t ed
t o i t s c a l l e r ( e i th e r PROC S TRT o r some c ommand
l a ng uag e
i n t e r p r e te r )
who
executes
the c a l l
to
SYS $ E X I T .
Th e p r o c ed u r e SYS $ E X I T s i m p l y
c a l l s wh a t eve r t e r m i na t i o n h a nd l e r s h a v e b e e n d ec l a r e d by t h e pr o c e s s
a nd th e n d e l e te s t h e p r o c e s s .
Te r m i n a t i o n h and l e r s a l l o w a n i m ag e to pe r fo rm i m a g e - s p e c i f i c
c l e a n up
o pe r a t i o n s b e fo r e
the
i mag e g oe s
a wa y .
Th e y a l so a l l o w i m a g e s t o
e x e r t s om e c o n t r o l o v e r wh e th e r a nd wh e n they w i l l t e rm i n a t e .
Th e u s e
of
a
s upe r v i s o r m o d e t e rm i n a t i o n h a nd l e r by t h e VM S c omma nd l ang ua g e
i n t e r p r e t e r s t o p r ev e n t p r o c e s s d e l e t i o n
f o l l o w i ng
imag e ex i t
is
d i sc us s ed i n Ch a pt e r 2 0 .

18. 2.1

Co n t r o l Fl ow o f the Ex i t Sys tem S e r v i c e

Th e s t e ps l i s ted b e l o w s h o w h o w t h e Ex i t s y s t e m s e r v i c e ,
a
p r o c ed u r e
t h a t exec utes
i n k e r n e l m od e ,
calls
a
s uc c e s s i o n o f t e rm i n a t i o n
h a nd l e r s f o r a g i v e n a c c e s s mod e a nd
i l l us t r a t e s h o w t e rm i n a t i o n
h a nd l e r s c a n b e
u s ed
to
p r ev e n t
i m ag e e x i t .
Th e VAX/VMS Sys tem
S e r v i c e s Re f e r enc e Ma n ua l
d e s c r i b e s h o w t e rm i n a t i o n h a nd l e r s a r e
d ec l a r ed
a nd
t h e a rg um e n t
l i s t tha t w i l l be pa s s ed to t h e h a nd l e r s
wh e n t h e y a r e c a l l ed b y t h e E x i t s y s t e m s e rv i c e .
1.

Th e f i n a l s t a t u s o f t h e i m ag e ( th e s i ng l e a rg um e n t
to
the
E x i t s y s tem
s e rv i c e )
i s s to r ed i n t h e P l po i n t e r pag e f o r
po s s i b l e i n s e r t i o n
by De l e t e P r o c e s s
i n to a
t e rm i na t i o n
m a i l bo x .
Th e f o r c e e x i t p e nd i ng f l ag i n t h e s t a t us l ong wo r d
( PC B $ L_S TS ) i n t h e P C B i s c l e a r ed .

I f SYS $ E X I T wa s c a l l ed f r om k e r n e l m o d e , t h e n the p r o c e s s
is
s i m p l y d e l e t ed .
I f SYS $ E X I T wa s c a l l ed f r om any o th e r a c c e ss
mod e , t h e n t h e
t e rm i n a t i o n h a nd l e r
l ist
( Fi g ur e 1 8-8 )
is
s e a r ch e d f o r h a nd l e r s th a t h a v e b e en d ec l a r ed , b eg i nn i ng wi th
the a c c e s s m o d e o f the c a l l e r
a nd
p r o c e ed i ng
towa r d
i nn e r
( mo r e p r i v i l eg e d ) a c c e s s m o d e s .
18-18

I MAG E ACT I VATI ON AND TERM INAT I ON

On c e a n o n z e r o l i s t po i n t e r i s f o und , a c c e s s mod e
is
r a i s ed
( p r i v i l eg e
l o we r ed }
w i t h a n RE I
a nd t h e l a s t t e rm i n a t i o n
h a nd l e r t h a t wa s d e c l a r ed i s c a l l ed .
Wh e n ( i f } tha t h a nd l e r
r e turns
to
S YS $ E X I T � t h e n e x t h and l e r i n the l i s t i s c a l l ed
a nd so o n un t i l t h e l i s t i s e x h a u s t ed .

SYS $ E X I T a v o i d s a n i n f i n i te l o o p by s to r i ng the l i s t po i n t e r
in
a
r eg i s t e r
a nd
c l e a r i ng t h e l i s t po i n te r i t s e l f .
Wh e n
t h i s l i s t po i n t e r i s n e x t e x am i n ed ( s te p 4 ) , the l i s t w i l l b e
emp t y .
4.

On c e a l l t h e t e rm i n a t i o n h and l e r s fo r
a g i ven a c c e s s m o d e
have been p r o c essed ,
SYS $ E X I T m u s t g e t
bac k
to
a mo re
p r i v i l eg ed a c c e s s m o d e .
I t a c c om p l i sh e s
th i s by c a l l i ng
i tse l f .
I f none
of
the e x i t h a nd l e r s
i n the l i s t j us t
p r o c e s s e d h a v e d o n e a ny t h i ng e x t r a o r d i n a r y ( s uc h a s d e c l a r i ng
a no t h e r
t e rm i n a t i o n h a nd l e r } ,
t h e n the l og i c d e s c r i b ed i n
s t e p 3 w i l l f i nd the l i st emp t y a nd p r o c e ed to the n e x t i nn e r
a c c e s s mo d e i n i t s s e a r c h fo r m o r e t e rm i n a t i o n h a nd l e r s .

E x ampl e o f T e rm i n a t i o n Hand l e r L i s t P r o c e s s i ng

18. 2 . 2

To i l l u s t r a te the p r o c e s s i ng o f t e rm i n a t i o n h a nd l e r s , s uppo se
th a t
a
process
has
i ts
t e rm i n a t i o n h a nd l e r
l i sts set
up a s s h o wn
in
Figure 1 8-8 .
Wh e n the
i m ag e c a l l s
SYS $ E X I T f r om us e r mod e ,
the
fo l l o w i ng s t eps a r e t a k e n .

0
(ex ec)

(exec)

(declared
first)

(declared
second)

1---1

0
( super)
D

(user)
A
( declared
first,
called last

address in which to store
reason for exit
<!! � additional arguments
J.�

(user)
B

(declared
second)

F i g ur e 1 8-8

: : CTL$GL_THSUPR

forward link
exit handler address
0

: : CTL$ GL_THEXEC

I N

S amp l e Te rm i n a t i o n Hand l e r L i s t s

use r
Th e t e rm i n a t i o n h a nd l e r l i s t i s s e a r c h e d beg i nn i ng w i th
the
mod e .
A
nonze ro
l i s th e a d
is
fo und ,
po i n t i ng
to
the
l ast
t e rm i n a t i o n h a nd l e r c o n t r o l b l o c k f o r p r o c e d u r e C ,
t e rm i n a t i o n h a nd l e r d e c l a r ed f o r u s e r mode .

18-19

I MAGE ACTIVAT I ON AND TERMINAT I ON

Th i s a d d r e s s i s s to r ed i n RO a n d t h e l i s th e ad fo r
u s e r mod e
i s c l e a r ed .
Ac c e s s m o d e i s r a i s e d to u s e r a nd p r o c ed u r e C i s
c a l l ed .
Wh e n C r e t u r n s , p r o c ed u r e B a n d f i n a l l y p r o c e d u r e A
a r e c a l l ed .
Wh en A r e t u r n s , SYS $ E X I T d e t e rm i n e s th a t t h e
l i s t f o r us e r mod e i s e x h a u s t e d ( be c a us e i t s fo r wa rd
po i n t e r
conta i ns a z e r o ) .
SYS $ E X I T i s c a l l ed ag a i n f r om us e r m od e .

As i n s t e p 1 , t h e s e a r c h f o r t e rm i na t i o n h a nd l e r s b eg i n s wi th
u s e r mo d e
but th i s l i s t is n o w emp t y .
Th e s e a r c h c o n t i n ue s
t o s upe r v i s o r mod e wh e r e t h e s i ng l e t e rm i n a t i o n hand l e r D h a s
b e e n d e c l a r ed .
Th e
s upe r v i so r l i s th e a d i s c l e a r ed , a c c e s s
mod e i s r a i s ed to
s upe r v i so r ,
a nd
p r o c ed u r e D
i s c a l l ed .
Wh e n D
r e turns ,
SYS $ E XI T
i s a g a i n c a l l ed , th i s t i m e f r om
s upe rv i s o r mo d e .

Now t h e s e a rch
fo r
t e rm i n a t i o n
h a nd l e r s
b eg i n s
wi th
s upe rv i s o r mo d e , wh o s e l i s t is empty .
Th e l i s t fo r e x e c u t i v e
mod e c o n t a i n s two t e r m i n a t i o n h a nd l e r s , F a nd E ,
wh i c h wi l l
b e c a l l ed
in turn
f r om
e x e c u t i v e a c c e s s mod e . Wh e n th e y
r e tu r n ,
SYS $ E X I T wi l l
ag a i n b e c a l l ed ,
th i s
t ime
f r om
e x ec u t i v e
a c c ess mod e .
Th e s e a r c h th a t n o w beg i n s wi th the
e x e c u t i v e mod e l i s th e ad wi l l f a i l a nd
the
process wi l l
be
d e l eted .

Th e l og i c i l l u s t r a t e d h e r e shows h o w a
proc ess c an prevent
i mag e
t e rm i n a t i o n th r o ug h the u s e o f t e rm i n a t i o n h a nd l e r s .
Fo r e x am p l e , i f
a ny o f t h e hand l e r s c a l l ed
i n s upe r v i so r m o d e we r e to d e c l a r e a
( fo r
s upe r v i so r mod e ) , t h e s e a r c h th a t i s b eg un
t e rm i n a t i o n h an d l e r
a f te r SYS $ E X I T i s c a l l ed f r om s upe r v i so r mode wi l l l o c a t e the h a nd l e r
j u s t d e c l a r ed
t h a t , wh e n c a l l ed , wi l l d ec l a r e ano t h e r h a nd l e r a nd s o
I n f a c t , t h i s i s j u s t t h e m e c h a n i sm u s ed by DC L a nd
o n a d i n f i n i t um .
MCR
to
a l l o w m u l t i pl e
i m ag e s to e x e c u t e , o n e a f t e r ano th e r , i n t h e
same process .
Th i s m e c h a n i sm
i s d i s c u ssed
i n mo r e d e t a i l
in
Ch a p t e r 2 0 .
No t e th a t a t e rm i na t i o n h a nd l e r tha t i s d e c l a r e d l a t e r ( wh i ch
i mpl i e s
tha t
i t wi l l
b e c a l l ed
earl ier )
c a n p r ev e n t p r ev i o us l y d e c l a r e d
h a nd l e r s f o r t h e s a m e a c c e s s m o d e f r om e v e n b e i ng
c a l l ed
by s i mpl y
i s s u i ng a c a l l to SYS $ E XI T .
I n the e x ampl e d e s c r i b e d above , p r o c ed u r e
C c o u l d p r ev e n t t e rm i n a t i o n h a nd l e r s B a nd A f r om be i ng
c a l l ed b y
c a l l i ng SYS $ E X I T i t s e l f .

18 . 3

IMAGE AND PROC E S S RUNDOWN

In a n i n t e r a c t i v e o r b a tc h e nv i r o nm e n t t h a t a l l o ws m u l t i pl e images
to
exec ute
one a f ter
ano t h e r , s ev e r a l s t eps m u s t b e t a k e n to p r e v e n t a
l a te r i m ag e f r om i nhe r i t i ng
e i th e r
e nh a n c em e n t s
( s uch a s
e l ev a t ed
p r i v i l eg e s )
or
d eg r ad a t i o n s
( s uch
as a r ed uc ed wo r k i ng s e t ) f r om a
p r ev i o u s i m ag e .
I n a d d i t i o n , wh e n a p r o c e s s i s d e l e t ed , a l l t r a c e s o f
i t m u s t b e e l i m i n a t ed
f r om
t h e s y s t e m t a b l e s a nd
a l l r e us a b l e
r e so u r c e s r e t u r ned t o the sys t em .
Th e p r o c ed u r e SYS $ R UNDWN a c c ompl i sh e s m u c h o f the wo r k f o r
bo th o f
t he s e
p u r po s e s .
I t d i s t i ng u i sh e s b e twe e n i m ag e r undown a nd p r o c e s s
r und own b y i t s s i ng l e i np u t pa r a m e t e r , a c c e s s m o d e .
( Th i s f l e x i b i l i t y
r e qu i r e s t h a t SYS $ R UNDWN e x e c u t e i n k e r n e l mod e . ) SYS $RUNDWN i s c a l l ed
wi t h an a r g ume n t o f u s e r by b o th DC L a nd MCR ( Ch a pt e r 2 0 ) to c l e a n
up
a fter
an
imag e t h a t h a s j us t t e rm i n a t e d a nd b e f o r e the nex t i m ag e i s
a c t i va ted .
SYS $ R UNDWN i s a l s o c a l l ed f r om the De l e t e
Process
s ys t em
1 8-2 0

I MAG E ACT I VAT I ON AND TERM I NAT I ON
s e r v i c e ( Ch a p t e r 1 9 ) wi th a n a r g umen t o f k e r n e l mod e to c l e a n up a f t e r
a p r o c e s s tha t i s b e i ng d e l e t ed .
Much o f t h e a c t i v i ty pe r f o rmed by Rund own i s a c c ompl i shed wi t h
sys tem
s e rv i c e s .
Rund own s i mpl y pa s s e s i t s i n put a rg um e n t to th e s e s e r v i c e s
to a l l o w them t o d e t e rm i n e h o w much wo r k
t o do .
Fo r
e x am p l e ,
the
De l e t e
Log i c a l Name sys tem s e r v i c e ( Ch a pt e r 2 6 ) c a n b e c a l l ed wi th an
a c c e s s mod e a rg um e n t a nd
the
i mpl i c i t
i n s t r uc t i o n
to d e l e te
all
l og i c a l
names
f o r th i s a nd o u t e r a c c e s s mod e s .
I f Rund own i s c a l l ed
f r om us e r m od e , t h e c a l l to De l e t e Log i c a l Name wi l l o n l y d e l e t e
user
mode
( imag e
a s s o c i a t ed )
l og i c a l
nam e s .
I f Rund own i s c a l l ed f r om
k e r n e l mo d e , t h e n a l l p r o c e s s l og i c a l names wi l l be d e l e t ed .

18 . 3 . 1

C o n t r o l F l o w o f Rund o wn

Th e fo l l o w i ng s t eps d e t a i l the
wo r k pe r fo rmed
by
S Y S $ R UNDWN .
Th e
a c c e s s mod e a rg um e n t i s m a x i m i z e d wi t h t h e acc e s s mod e o f t h e c a l l e r
( by r o u t i n e E XE $MAXAC MODE ) .
Th a t i s , t h e l e s s p r i v i l eg ed a c c e s s mod e
is
used .
Th e
ph r a s e
" ba s e d
o n a c c e s s mod e " m e a n s " pe r f o r m th i s
o pe r a t i o n fo r th i s a c c e s s mod e a nd a l l o u t e r ( l e s s p r i v i l eg ed )
access
mod e s . "
Tho s e o pe r a t i o n s
tha t a r e pe r f o rmed b y s y s t em s e r v i c e s h a v e
the n a m e o f the s e r v i c e i n c l ud ed .
1.

I f a powe r f a i l
e l imi n a t ed .

AST

h ad

been

p r ev i o u s l y

d e c l a r ed ,

Th e i m a g e c o un t e r tha t
to an
i ma g e tha t h a s
th i s
syn c h r o n i z a t i o n
$G ETJ P I s y s t em s e r v i c e

Th e f o u r P l spa c e vec to r s f o r
u s e r -wr i t t e n
s ys t em
se r v i c e s
a nd i m ag e - s p e c i f i c me s s a g e s e c t i o n s ( F i g u r e 3 - 8 ) a r e r e s e t t o
c o n t a i n R S B i n s t r uc t i o n s .

Al l c h a n n e l s wi tho u t o pe n f i l e s a r e d ea s s i g ned
( S Y S $DASSGN ) ,
b a s e d o n a c c e s s mod e .
Th e a c c e s s mode c h e c k p r e ven t s p r o c e s s
p e r ma n e n t f i l e s f r om b e i ng c l o s ed
wh e n a n
i m ag e
is
b e i ng
r und own
( i n put a r g um e n t i s u s e r mod e ) .
Oth e r channe l s tha t
w i l l no t be d e a s s i g n ed a t th i s s t a g e o f i mag e r un d o wn i n c l ud e
the
image
f i l e a nd a n y o th e r f i l e tha t i s m a pped to a r a ng e
o f v i r t ua l add resses .

Th e i m ag e pag e s a r e r e s e t ( by c a l l i ng
MMG $ I MG R E S E T ) .
Th i s
r o ut i ne
pe r fo rms a l l
the
i m ag e c l ea n up t h a t i s a s s o c i a t e d
w i t h mem o r y m a n ag em e n t .
Th e s t eps pe r fo rmed by th i s
r o u t i ne
a r e l i s t ed h e r e .

p r ev e n t s t h e d e l i v e r y o f $ G E TJ P I
ASTs
t e rm i n a t ed i s i n c r em e n ted .
Th e use o f
t e chn i q ue
i n t h e o pe r a t i o n o f
the
is d e sc r i b e d i n C h a pt e r 2 7 .

Al l o f P O s p a c e i s d e l e t ed .
Th i s w i l l f r e e up the
i mag e
file
a nd a ny o th e r f i l e th a t i s m a pped .
Ph ys i c a l pag e s
wi l l b e r e l e a s e d a nd b l o c k s i n
the
pag e
file
wi l l
be
d e a l l o c a ted .

Th e no n pe rm a n e n t p a r t o f P l s p a c e i s d e l e t ed .
Th e
two
pa r t s o f P l s pa c e tha t a r e d e l e t ed by t h i s o pe r a t i o n a r e
t h e us e r s t a c k a nd the i m ag e I /O s egme n t
( Fi g ur e 1 8-9 ) .
In
add i t i on ,
a ny e x pa n s i o n s
to
Pl
s pa c e ( a t sm a l l e r
vi r tual
add resses
than
the
use r
s ta c k )
that
we r e
pe r fo rmed b y the u s e r a r e a l s o d e l e t e d .
1 8- 2 1

IMAGE ACT I VAT I ON AND TERM INAT I ON

d i rection of g rowth

Cre ated
by
Image
Activator
for
Each
- !!'l!g !.
C re a ted
a s P a rt
of
Process
Creation

�

User Stack
( De f ault S ize of 20 Pages)
Image 1/0 Segment
( D ef ault S ize of 3 2 Pages)
-+---t-

CLI Image and Data,
Other Stacks, etc.
•
•
•

De leted
at
Image
Ex it
by
Image
R_!S_!t_

Ex ists
for
Life of
the
Process

� : :CTL$GL_CTLBASVA
Location CTL$GL._CTLBASVA
contains the address of
the boundary between
the temporary and
permanent parts of
P1 space .

Figure 1 8 -9

Low Ad d r e s s End o f P l Sp a c e Th a t Is De l e t ed a t Imag e Ex i t

Th e wo r k i ng s e t i s r e s e t to i t s d e fa u l t v a l ue ,
und o i ng
any e x pa n s i o n o r c o n t r a c t i o n o f
the wo r k i ng s e t a s a
r e s u l t o f a c a l l to SYS $ADJW S L ( e i th e r e x p l i c i t l y o r a s a
resul t o f
the
a u toma t i c
wo r k i ng s e t s i z e ad j u s tm e n t ) .
Wo r k i ng s e t s i z e c h a ng e s a r e d e s c r i b ed i n Ch a p te r 1 3 .

Th e p r o c e s s pr i v i l eg e ma s k i n the f i r s t q u a d wo rd o f
the
p r o c e s s h e ad e r is r e s e t to i t s pe rm a n e n t va l ue , fo und at
l o c a t i o n C T L$G Q PROC PR I V .
Th i s s t e p e l i m i n a t e s
any
pr i v i l eg e
e n h anc em e n t s
to
the p r o c e s s d ue
to
the
e x e c u t i o n of a p r i v i l eg e d k n own i mag e .

Th e same c h a nne l d e a s s i g nm e n t l o o p pe r fo rmed
i n s te p 4
is
e x e c ut ed .
Howe v e r ,
b e c a us e the i m a g e f i l e a nd o th e r m a pped
f i l e s h a v e now b e e n d i s a s s o c i a t ed f r om v i r t ua l add r e s s s pa c e ,
t h e c h a nn e l s a s so c i a t ed
wi t h
tho s e
f i l e s wi l l
a l so
be
d ea s s ig ned .
As in s tep 4 ,
th i s d e a s s i g nm e n t
is
based on
a c c e s s mo d e ,
i m p l y i ng
t h a t p r o c e s s pe r m a n e n t
f i l es
a re
u n a f f e c t e d by i m a g e r und own .

Al l d e v i c e s a r e d e a l l o c a ted
a c c e s s mo d e s .

Al l t i me r r e q u e s t s a r e c a n c e l l ed
o u t e r a c c e s s mo d e s .

( S YS $CANT I M )

fo r

Common
eve n t
f l ag
c l uste r s
i nd e pend e n t o f a c c e s s mo d e .

a nd

d i s a s s o c i a t ed ,

( S YS $DA LLOC )

fo r th i s

are

a nd
th i s

o uter
a nd

10 .

Th e nex t s e v e r a l s t eps m u s t e x ec u t e a t
I P L $ S YNC H
( I PL 7 )
b e c a u s e sys t em wi d e d a t a s t r uc t u r e s a r e b e i ng man i pu l a te d .

11 .

I f th i s p r o c e s s h a s d e c l a r ed a n e r r o r
l og m a i l bo x ,
it
is
e l i m i n a t ed .
Th e me thod fo r d e c l a r i ng a n e r r o r l og ma i l bo x i s
d e s c r i b e d i n Ch a p t e r 7 .
18-22

I MAGE ACT IVAT I ON AND TERM INAT I ON

12.

A l l p e nd i ng A S T c o n t r o l b l o c ks a r e r emoved f r om the l i s t
{ in
the
PC B )
a n d d e a l l o c a ted
to n o npag ed po o l b a s e d on a c c e s s
mo d e .
Th i s i s a c compl i s hed b y s t a r t i ng a t t h e
ta i l
of
the
l i st
a nd p r o c e ed i ng towa rd the h e a d o f t h e l i s t un t i l a n AST
control block i s
f o und
w i t h a m o r e p r i v i l eg ed
( sm a l l e r )
a c c e s s mo d e
than
the
Run d own
a rg um e n t ,
o r u n t i l t h e AST
p e nd i ng q u e u e i s emp t y .
( Re c a l l f r om Ch a pt e r 5 t h a t ASTs a r e
e n que ued i n o r d e r o f i n c r e a s i ng a c c e s s mode . )

13.

Any c h a ng e mod e h a nd l e r s f o r th i s a nd o u t e r a c c e s s mod e s a r e
e l i m i n a t ed .
B e c a us e ch a ng e mod e h a nd l e r s o n l y e x i s t fo r u s e r
a nd s upe rv i s o r mod e s , t h i s s t ep r e s u l ts i n e l i m i n a t i o n o f a
c h a ng e mo d e to u s e r h a nd l e r eve r y t i me a n i m a g e e x i t s a nd t h e
e l i m i n a t i o n o f a c h a n g e mod e to s upe r v i s o r h a nd l e r wh e n
the
p rocess is d e l e t ed .

14 .

Any t e rm i n a t i o n h a nd l e r s fo r t h i s a nd o u t e r a c c e s s mod e s a r e
c a nc e l l ed .
Te r m i n a t i o n h a nd l e r s c a n e x i s t fo r e x e c u t i v e ,
s upe r v i s o r , a nd us e r m o d e s .

15.

E x c e p t i o n h a nd l e r s fo und i n the p r i ma r y , s e c o nd a r y , a nd
last
c h a n c e ve c to r s
are
e l im i n a ted
fo r
th i s
a nd o u t e r a c c e s s
mo d e s .

16.

Th e AST a c t i v e b i t s fo r
th i s
a nd
o ute r
a c c e s s mod e s a r e
c l e a r ed .
Th e A S T e n a b l e b i t s fo r t h i s a nd o u t e r a c c e s s mod e s
a r e se t .

17.

S y s t em s e rv i c e f a i l u r e e x c e p t i o n s a r e d i s a b l e d fo r
o u t e r a c c e s s mod e s .

18.

that h a s
Any c ompa t i b i l i t y m o d e h a nd l e r
e l i m i n a ted ,
i n d e pe nd e n t o f
the
access
Rund own .

19.

rout ine
SCH$N EW LVL )
A n e w va l u e o f A S TLVL i s c a l c u l a t ed { by
r e s u l t i ng f r om
to
ref l ec t
t h e c h a ng e
in
t h e AST q u e ue
s tep 1 2 .

20 .

Th e fo rc e e x i t pend i ng f l ag in the PC B i s c l e a r ed .
Th i s
is
t h e l a s t s t e p t h a t mus t b e pe r f o rmed a t I P L $ S YNC H , so I PL i s
l owe r ed to i t s p r ev i o u s va l u e .

21.

The l a s t s t e p t h a t Rund own pe r f o rm s b e fo r e r e t u r n i ng
to
i ts
c a l l e r i s to d e l e t e a l l p r o c e s s l og i c a l nam e s b a s e d on a c c e s s
mod e .
A t i mag e e x i t , a l l l og i c a l names c r e a t ed
f r om wi t h i n
the
imag e
( w i t h a c a l l t o SYS $ C R E LOG ) a nd a l l l og i c a l n am e s
c r e a ted wi t h t h e AS S IGN/U S E R c omma nd wi l l b e e l im i n a t ed .
At
p r o c e s s d e l e t i o n , a l l p r o c e s s l og i c a l nam e s w i l l be d e l e t ed .

18 . 4

been
mode

th i s

d e c l a r ed
a rg ume n t

a nd
is
to

PROC E S S PR IVI L EG E S

O n e o f t h e c o n t r o l s e x e r c i s ed b y VM S to p r ev e n t un a u tho r i zed
use
the
s ys tem
is
the
set o f
process
p r i v i l eg e s .
O n e o r mo r e o f t h e s e
p r i v i l eg e s i s r e q u i r ed to pe r f o rm m a n y o f t h e sys tem s e r v i c e s , e x e c u t e
c e r t a i n c ommand s , o r u s e p r i v i l eg ed u t i l i t i e s .

18-2 3

IMAGE ACT I VAT I ON AND TERM INAT I ON

18 . 4 . 1

P r o c e ss P r i v i l eg e M a s k s

VM S m a i n t a i ns s ev e r a l p r i v i l eg e m a s ks

( Ta b l e 1 8 - 1 )

fo r e a c h p r o c e s s .

Th e f i r s t q u a dwo r d
of
the
p r o c e s s h e ad e r
( PH D $ Q P R I VM S K )
conta ins
the wo r k i ng p r i v i l eg e m a s k , t h e o n e c he c ked by a l l
VM S s e r v i c e s t h a t
r eq u i r e
p r i v i l eg e .
Th i s m a s k m a y b e
a l t e red
each
t ime
a n i m ag e e x e c u t e s , c a n be a l t e r ed b y t h e
Se t
P r i v i l eg e
s y s tem s e rv i c e ,
a nd
is
r eset
to
the
p r o c e s s - p e rma n e n t p r i v i l eg e m a s k ( C T L $ G Q PROC PRI V ) a s a pa r t
o f i ma g e r und own .

Th e p r o c e s s p r i v i l eg e m a s k i n the Ac c e s s R i g h t s B l o c k
( ARB )
( PC B $ Q P R I V )
is
a l wa y s a n e x a c t d up l i c a t e o f the p r i v i l eg e
m a s k i n t h e p r o c e s s h e ad e r .
Th e Acc e s s R i g h t s B l o c k
is
c u r r en t l y a pa r t o f the so f twa r e PC B .

Th e p r o c e s s -pe r ma n e n t pr i v i l eg e m a s k i s
l o c a t ed
in
the
Pl
po i n te r
pag e
a t g l ob a l
l o c a t i o n C T L$G Q PROC PR I V .
Th e
c o n t e n t s o f th i s l o c a t i o n a r e wr i t t e n to
the- PHD p r i v i l eg e
mas k
( and a l so
t h e ARB o r PC B p r i v i l eg e m a s k ) a s a pa r t o f
i ma g e e x i t b y t h e i ma g e r e s e t r o u t i n e
( MMG $ IMGRESE T ) .
Th i s
f i e l d i s i n i t i a l i z e d wh e n the p r o c e s s i s c r e a t ed .

Th e a u th o r i zed
pr i v i l eg e m a s k
in
the
process
h e ad e r
i s u s ed by t h e S e t Pr i v i l eg e sys t em s e r v i c e
( P HD$ Q AUTHPR I V )
to a l l ow a n o n p r i v i l eg ed p r o c e s s ( a
p r o c e s s w i tho ut
SETPRV
p r i v i l eg e )
to
r emove o n e o f
i t s p e r m a n e n t pr i v i l eg e s a nd
l a t e r r eg a i n th a t p r i v i l eg e .
Th i s f i e l d i s a l so
i n i t i a l i z ed
wh e n t h e p r o c e s s i s c r e a t e d .

Th e
i m ag e
p r i v i l eg e
mas k
in
the
pr o c e s s
h e ad e r
( P HD$Q I MAG PR I V ) co n t a i n s t h e p r i v i l eg e m a s k fo r a pr i v i l eg ed
Th i s m a s k
is a
k n own Tm a g e wh i l e t h a t i m a g e i s e x e c u t i ng .
c o nv e n i e n t to o l u s ed by the S e t Pr i v i l eg e s y s t e m s e r v i c e tha t
a l l ows i ma g e s i n s t a l l ed w i th p r i v i l eg e
to
i s s ue
the
Se t
Pr i v i l eg e s y s t em s e rv i c e w i tho u t l o s i ng p r i v i l eg e s .

18 . 4 . 2

S e t P r i v i l eg e Sys t em S e rv i c e

Th e Se t Pr i v i l eg e
s ys t e m s e r v i c e
a l l o ws a
process
to
a l te r
i ts
i m ag e - spec i f i c
( P HD$Q P R I VM S K a nd
PC B $ Q PR I V )
o r p r o c e s s - pe rman e n t
( C T L $G Q PROC PR I V ) p r i vil eg e ma s ks , g a i n i ng -o r l o s i ng pr i v i l eg e s a s a
r e s u l t . - In ad d i t i o n , t h e s e r v i c e c a n r e t u r n the p r ev i o us s e t t i ng s o f
e i the r
the
i ma g e - s pe c i f i c
or
p r oc e s s - pe r ma n e n t
pr i v i l eg e s ,
if
r e que s t ed .
Th e d i s a b l e p r i v i l eg e pa th r e q u i r e s no s pec i a l
p r i v i l eg e a nd
clears
the r e que s t ed p r i v i l eg e b i t s i n t h e i m ag e - s pe c i f i c ( a nd o p t i o n a l l y t h e
p r o c e s s -pe rma n e n t ) p r i v i l eg e m a s ks .

18-24

Tab l e 1 8 - l
Proc e s s P r iv i lege Ma s k s

(X)
I
N
I-'

Sym bo l i c Na m e

Lo c a t i o n

Us e o f Th i s Ma s k

Mo d i f i ed by

Re f e r e n c ed b y

P H D $ Q_PR I VM S K

P r o c e s s He ad e r

Th i s i s t h e wo r k i ng pr i v i l eg e
mask
tha t
is
t e s t ed
by
all
system
s e r v i c e s t h a t r eq u i r e p r i v i l eg e .

PR OC STRT
LOG I N OUT
Imag e Ac t i v a to r
$S ETPRV

A l l sys t em s e r v i c e s
t h a t r e qu i r e pr i v i l eg e

PCB $Q_PR I V

S o f t wa r e PC B
{ Ac c e s s Ri g h t s
Bl oc k )

Th i s m a s k i s a n ex ac t d up l i c a t e
t h e p r o c e s s h e ad e r m a s k .

Same a s fo r
PHD$Q_PR I VM S K

Dev i c e d r i v e r s
a n d AC Ps

C T L $G Q_PR OC PR I V

P l Po i n t e r Pa g e

Th i s m a s k r ec o rd s
the
pe r m a n e n t l y
e n a b l ed pr i v i l eg e s fo r t h e p r o c e s s .
Th e wo r k i ng p r i v i l eg e m a s k i s r e s e t
to t h i s v a l ue ev e r y
t i me
tha t
an
i m ag e e x i t s .

PR OC STRT
LOG I N O UT
$ S ETPRV

Imag e Ac t i v a t o r
MMG $ I MGR E S E T
S E T U I C c ommand

PHD$Q_A UT H PR I V

P r o c e s s Head e r

the
pr i v i l eg e s
r ec o rd s
Th i s m a s k
t h a t t h i s p r o c e s s i s a l l o we d to use
i ts
a c c o rd i ng
a u t ho r i za t i o n
to
r ec o rd .

PR OC STRT
LOG I N O UT

$S ETPRV

PHD$Q- I M AG PR I V

P r o c e s s Head e r

Th i s
mask
r ec o r d s
the
pr i v i l eg e
m a s k fo r a n imag e tha t i s i n s t a l l ed
wi t h e n h a n c ed pr i v i l eg e s .

Imag e Ac t i v a t o r

$ S E T PRV

UAF $Q_PR I V

A u t ho r i za t i o n
R e c o rd

Th i s m a s k
r e c o rd s
the
pr i v i l eg e s
tha t th i s u s e r i s a l l o wed to u s e .

AUTHOR I Z E

LOG I N O UT

KF I $Q_PROC PR I V

Known Fi l e En t r y
fo r pr i v i l eg ed
i n s t a l l ed i m a g e

Th i s m a s k
r ec o r d s
the
add i t i o nal
pr i v i l eg e s
r e q u i r ed
by
an
i m ag e
tha t i s i n s t a l l ed wi th pr i v i l eg e .

I N S TA L L

I m ag e Ac t i v a t o r

I HD $ Q_PR I VR E QS

Imag e He ad e r o f
a n y i m ag e

Th i s m a s k i s c u r r e n t l y
unused .
c o n ta i n s
all
ones ,
e n ab l i ng
p r i v i l eg e s •

Li nker

I m ag e Ac t i v a to r

It
all

IMAGE ACTIVAT I ON AND TERMINAT I ON

Th e e na b l e p r i v i l eg e pa th
r e qu i r e s n o p r i v i l eg e
if
the
r e q u e s ted
p r i v i l eg e
is
i nc l ud ed
i n the l i s t o f p r i v i l eg e s a u tho r i z e d fo r th i s
p r o c e s s ( PHD$ Q AUTHPR I V ) .
I f a p r o c e s s w i she s a pr i v i l eg e tha t i s n o t
in
i t s a u tho r i z ed
l i st ,
one
of
two
c o nd i t i o ns m u s t h o l d o r t h e
r e q u e s t ed p r i v i l eg e i s n o t g r an ted .
•

Th e p r o c e s s m u s t h a v e S E TPRV p r i v i l eg e .
A p r o c e s s wi th
th i s
p r i v i l eg e c a n a c q u i r e a n y o the r p r i v i l eg e wi th e i th e r the Se t
P r i v i l eg e s y s t em s e r v i c e o r the
$ S E T PROC E S S/ P R I VI LEG E S = ( p r i v i l eg e [ ,

•

] )

c ommand .
•

Th e sys tem s e r v i c e wa s c a l l ed f r om e x ec u t i v e o r k e r n e l mo d e .
Th i s m e c ha n i sm
i s a n e sc a pe
tha t a l l o ws e i th e r VM S o r
u s e r -wr i t t e n s y s t em s e r v i c e s t o a c qu i r e wh a te v e r
pr i v i l eg e s
t h e y n e ed w i tho u t r eg a r d f o r wh e th e r t h e c a l l i ng p r o c e s s h a s
S E TPRV p r i v i l eg e .
S u c h p r o ced u r e s m us t o f c o u r s e d i s a b l e
p r i v i l eg e s g r a n t ed
i n t h i s f a sh i o n a s pa r t o f th e i r r e t u r n
p a th .

No t e t h a t the i mp l em e n ta t i o n o f the S e t P r i v i l eg e sys tem s e r v i c e d o e s
not
r eturn an e rro r
if a
n o n p r i v i l eg ed
process
a t t empts t o add
un a u tho r i z e d p r i v i l eg e s .
I n such a
c ase ,
the
serv i c e c lears
all
un a u tho r i z e d b i t s i n the r eque s t ed p r i v i l eg e m a s k , l o ad s the mod i f i ed
p r i v i l eg e m a s k , a nd r e t u r n s s uc c e s s .

18-26

C HAPTER 1 9
PROC E S S DELETION

Th e De l e te P r o c e s s s y s tem s e rv i c e a l l o ws a p r o c e s s to d e l e t e i t s e l f o r
a ny o the r
proc e s s
i n the s ys t em tha t i t h a s t h e p r i v i l eg e t o a f f e c t
( a c c o rd i ng t o wh e th e r i t h a s GRO U P o r WORLD p r i v i l eg e ) .
Th e d e l e t i o n
i s a c c ompl i shed
i n t wo s te p s .
Th e p r o c e s s i s m a r ke d fo r d e l e t i o n i n
the c o n t e x t o f t h e p r o c e s s i s s u i ng the De l e t e P r o c e s s s ys t em
se rv i c e .
I n ad d i t i o n , a s p e c i a l k e r n e l A S T i s qu e ued to the t a rg e t pr o c e s s .
Th i s AST e x e c u t e s i n t h e c on t e x t o f
t h e p r oc e s s
b e i ng d e l e t ed
a nd
pe r fo rm s
the
a c t ua l
d e l e t i o n ope ra t i on .
P r o c e s s d e l e t i o n r e qu i r e s
tha t s ev e r a l o pe r a t i o n s b e pe r f o rmed .
•

Al l t r a c e s o f t h e p r oc e s s mus t be r emoved f r om the sys t e m .

•

Al l sys t em r e so u r c e s m u s t b e r e t u r ned .

•
•

•

19. 1

Ac c o un t i ng i n fo rma t i o n mus t
m a n ag e r , t h e j o b c o n t r o l l e r .

pa ssed

the

a c c o un t i ng

I f t h e p r o c e s s b e i ng d e l e t ed i s a s ubp r o c e s s , a l l quo t a s
a nd
l im i ts
t a ke n
f r om
the c r e a to r wh e n the p r o c e s s wa s c r e a t e d
mus t b e r e t u r n ed .
F i n a l l y , i f t h e c r e a to r r eque s t ed
not i f i c a t i o n o f d e l e t i o n
t h r o ug h a t e r m i n a t i o n m a i l bo x , s uc h a m e s s a g e m u s t b e s e n t .

PROC E S S DELET ION IN C ONTEXT OF CALLER

The i n i t i a l ope r a t i o n o f the De l e t e P r o c e s s s ys t em s e rv i c e t a k e s p l a c e
i n t h e c o n t e x t o f t h e p r o c e s s i s s u i ng t h e s ys t em s e rv i c e c a l l .
Th i s
pa r t o f the o pe r a t i o n pe r f o rms a s i mpl e s e t o f p r i v i l eg e c h e c k s
a nd
then que u e s a
s pe c i a l
kernel
AST t h a t w i l l c a u s e the d e l e t i o n to
c o n t i n ue i n the c o n t e x t o f the p r o c e s s a c t ua l l y b e i ng d e l e t ed .

19. 1. 1

De l e te P r o c e s s Sys t em S e r v i c e

Th e De l e te P r o c e s s s y s t em
s e rv i c e
i n i t i a l ly calls
the
s ub r o u t i n e
EXE $NAMP I D to c o nv e r t e i th e r a p r o c e s s n ame o r a P I D to the a d d r e s s o f
the PC B o f the p r o c e s s b e i ng d e l e t ed .
Th i s s ub r o u t i n e c h e c k s tha t the
n ame
or
PID c o r r e sp o nd s
to
a n a c t ua l
p r oc e s s .
In add i t i o n , i t
v e r i f i e s t h a t the p r o c e s s i s s u i ng the d e l e t e h a s
the
pr i v i l eg e
to
d e l e t e the spec i f i ed p r o c e s s .

1 9- 1

PROCE S S DE LET I ON

The De l e t e P r o c e s s s ys t em s e rv i c e t h e n p e r fo rm s the fo l l owi ng s t e p s .
1.

Th e ta r g e t p r o c e s s i s m a r k e d f o r d e l e te .
I f i t wa s a l r e a d y
ma r ked
fo r
d e l e t e , t h e s ys t em s e r v i c e s i mp l y r e t u r ns t o the
cal ler .

Th e t a rg e t p r o c e s s i s r e s um e d i n c a se i t wa s s uspend ed .
If
the
pr o c e s s we r e t o r em a i n s uspe n d ed , n o AST , i nc l ud i ng the
d e l e t e s p e c i a l k e r ne l AST , c o u l d b e d e l i v e r ed t o i t .

An AST c o n t r o l b l o c k i s a l l o c a t e d a nd
i n i t i a l i ze d w i t h
the
P I D of
the
t a rg e t p r o c e s s
a nd the a d d r e s s o f t h e s p e c i a l
k e r n e l A S T ( D E LETE ) th a t w i l l
pe r fo rm the a c t ua l
process
deletion .

Th e AST i s que ued to the t a r g e t p r o c e s s ,
b o o s t o f 3 t o i t s so f twa r e p r i o r i t y .

wi th

po t e n t i a l

I n o th e r wo r d s , v e r y l i t t l e e x c e p t the q ue u i ng o f a n AST t o the t a rg e t
p r o c e s s i s p e r fo rmed i n the c o n t e x t o f t h e p r o c e s s i s s u i ng t h e d e l e t e .

19. 2

PROC E S S DE LET I ON IN C ONTEXT OF PROC E S S BEING DE LETED

A l mo s t the e n t i r e o pe r a t i o n o f p r o c e s s d e l e t i o n t a k e s p l a c e
in
the
c o n t e x t o f the p r o c e s s b e i ng d e l e ted .
Th e que u i ng of the spec i a l AST
t o th i s p r o c e s s m a k e s i t c om p u ta b l e a nd
c a us e s
the p r o c e s s
to be
eventua l l y s e l e c ted
fo r
e x ec u t i o n b y t h e s c h ed u l e r .
As s um i ng th a t
the r e a r e n o o th e r p e nd i ng s p e c i a l k e r n e l A S Ts , t h e d e l e t e spec i a l AST
be the f i r s t c o d e t o e x ec u t e in the c on t e x t o f the p r o c e s s b e i ng
wi l l
d e l e t ed .
process d elet ion
i n proc ess c o n tex t ,
the
t a rg e t
By pe r fo rm i ng
process ' s address
s pa c e a nd
p r o c e s s h e a d e r a r e r e ad i l y a c c e s s i b l e .
Sys tem s e rv i c es s uc h a s $ D E LTVA a nd $ D E L LOG a nd
RM S c a l l s
s uc h a s
SYS $ RM S RUNDWN c a n a l s o b e used .
Spe c i a l c a s e s s u c h a s the d e l e t i o n o f
a p r o c e s s t h a t i s o u t s wa pped s i mpl y d o n o t e x i s t .

19. 2. 1

S p e c i a l K e r n e l AST f o r P r o c e s s Del e t i o n

T h e s t e p s tha t a r e pe r f o rm ed by t h e
he r e .

spec i a l

ke r n e l

AST

are

l i s t ed

Re s o u r c e wa i t mod e i s e na b l ed .

RM S $ R UNDWN i s c a l l ed f o r
e a c h o pe n
file .
Th i s p r o c ed u r e
i nsures
th a t a l l
RM S
I/0 a c t i v i t y i s c ompl e te , c l o s e s a l l
f i l e s , a nd r e s e t s t h e i n t e r n a l FAB a n d RAB t a b l e s .

I f the p r o c e s s o wn s a ny s ub p r o c e s s e s , t h e s e s ubp r o c e s s e s mus t
b e d e l e t ed
b e fo r e d e l e t i o n o f t h e o wn e r c a n con t i nue .
Th e
l o g i c th a t i s pe r fo rmed a t th i s po i n t
is
l i s t ed h e r e .
An
e x ampl e o f p r o c e s s d e l e t i o n wh e n s ubp roc e s s e s a r e i nv o l v ed i s
f o und i n t h e n e x t s e c t i o n .
a.

Th e PC B v e c to r i s sc anned un t i l a l l the PC Bs wi t h the P I D
of
t h e c r e a to r i n the i r o wn e r f i e l d s a r e fo und .
Ea c h o f
t h e s e p r o c e s s e s i s m a r ked fo r d e l e t e .
Th a t i s , a De l e te
1 9-2

PROCE S S DE LETI ON
P r o c e s s s y s t em
s e rv i c e c a l l
i s made fo r each o f these
p r o c e s s e s , r e s u l t i ng i n the que u i ng o f t h e d e l e t e spec i a l
AST t o e a c h o f t h em .
b.

Th e c o un t o f o wn e d s ubp r o c e s s e s ( i n
f ield
PC B $W PRCCNT )
of
t h e pr o c e s s c u r r en t l y b e i ng d e l e t ed i s c he c k ed to s e e
i f i t h a s r e a c h ed z e r o .
If not , the process
is
p l a c ed
i n to
the
r e s o u r c e wa i t s ta t e ( MWA I T ) .
Th e p r o c e s s w i l l
b e c ome comp u t a b l e ag a i n wh e n the spec i a l k e r n e l AS T t h a t
r e t u r n s quo t a s f r om o n e o f t h e s ubpr o c e s s e s i s e nque ued .

Th e d e l i v e r y o f t h e spec i a l AST tha t
r e t u r n s d ed uc t i b l e
quo t a s ( C P U t i me l i m i t o n l y ) f r om o n e o f t h e s ub p r o c e s s e s
wh e n i t i s d e l e t ed w i l l r emove t h e p r o c e s s f r om t h e wa i t
state ,
a t wh i c h t i me
the c h e c k
i n S t e p 3 b wi l l be
r e p e a ted .

Th e p r o c e s s i s
r un d own
f r om k e r n e l m od e .
SYS $RUNDWN i s d e s c r i b ed i n Ch a p t e r 1 8 .

Th e v i r t ua l pag e s a s so c i a t ed wi th a n y s e c t i o n s a r e d e l e t ed .

Al l p r o c e s s p r i va t e vo l um e s a r e d i sm o un t ed .

Al l a l l o c a t e d d ev i c e s a r e d e a l l o c a t e d .

I f th i s p r o c e s s i s i ts e l f
a
s ubp r o c ess
( PC B $ L OWN ER f i e l d
nonzero ) ,
t h e n a l l r em a i n i ng quo t a s m u s t b e r etu r n ed to the
o wn e r p r o c e s s .
Th e l og i c o f r e t u r n i ng quo t a s to the own e r o f
a s ubp r o c e s s i s l i s ted h e r e .

Th e

p r o c ed u r e

Th e c o un t o f o wn e d s ubp r o c e s s e s i n the PC B $W PRCCNT f i e l d
I f t h e own e r Ts a l s o be i ng
of
t h e own e r i s d ec r em e n ted .
d e l e t ed , t h e n t h e o wn e r i s c u r r e n t l y
in a
wa i t s ta t e ,
wa i t i ng fo r t h e c o n t e n t s o f t h i s f i e l d to b e c o m e z e r o .

An I /O r e q u e s t pac k e t i s a l l o c a ted
fo r
u s e a s a n AST
control
b l oc k .
Th e e x t r a s pa c e a t the b o t tom of the IRP
w i l l b e us e d t o ho l d the q uo t a s be i ng
r e turned
to
the
own e r .

Th e a d d r e s s o f the r e t u r n q uo t a
spec i a l
AST
( RETQUOTA )
a nd
t h e P I D o f t h e own e r a r e put i n to t h e AST c o n t r o l
b l oc k .

Th e unused q uo ta s a r e put i n to the b o t tom o f
the
IRP.
Th e o n l y quo t a
t h a t m u s t b e r e tu r n ed to t h e c r e a t o r i s
u n u s ed C P U t i m e .
A l l o th e r quo t a s a r e e i th e r po o l ed
or
n o nd ed uc t i b l e ( Ch a p t e r 1 7 ) .

F i n a l l y , t h e s pe c i a l AS T i s queued to the c r e a t o r , g i v i ng
i t a p r i o r i ty b o o s t o f 3 .

A t e rm i n a t i o n m e s s a g e i s c o n s t r uc ted on t h e s t a c k t o s end
to
the
j ob c o n t r o l l e r in i t s r o l e as a cc o un t i ng m a n ag e r .
Th i s
m e s s a g e w i l l a l wa y s b e s e n t un l e s s e xp l i c i t l y p r e v e n t e d
by
Th e c o n te n t s o f
t h e NOACNT f l ag
at p r o c e s s c r e a t i o n t i m e .
t h i s me s sag e a r e l i s t ed i n Ta b l e 1 9 - 1 .

1 9- 3

PROC E S S DE LET I ON
Ta b l e 1 9 - 1
Co n t e n t s o f Te rm i n a t i o n Ma i l box Me s s ag e Se n t to
Ac c o un t i ng Ma n ag e r and to Pr o c e s s C r e a to r

F i e l d i n Me ssag e Bl o c k

So u r c e o f In fo rma t i o n

No t e s
No t e 1

Me s s ag e Type

M SG $ DE LPR OC

F i n a l Ex i t St a t us

C TL $G L_F INALS TS

P r o c e ss ID

PC B $ L_P I D

Jo b I D

0 fo r now

Lo g o u t T i m e

E XE $G Q_S YS T IM E

Ac c o un t Nam e

C TL $G T ACC O UNT

Us e r Nam e

C T L $G T U S ERNAME

C PU T i m e

PHD$L C PUT IM

No t e 3

N um b e r o f Pa g e Fa ul t s

PH D$L PAG E F LTS

No t e 3

P e a k Pag i ng Fi l e Us a g e

0 f o r now

Pe a k Wo r k i ng Se t S i z e

C T L $G L_WS PEAK

B u f f e r ed I /O Co un t

PHD$L B I OC NT

No te 3

D i r ec t I /O Co un t

PH D$L D I OC NT

No t e 3

Co un t o f Mo un t ed Vo l um e s

C T L $G L_VOLUM ES

Log i n T i m e

C T L $G Q_L OG I N

P I D o f OWn e r

PC B $ L_OWNER

Mo s t o f
the
i n fo rm a t i o n a b o u t
the d e l e ted
pr o c e s s i s fo und in the P l po i n t e r pag e at the
g l ob a l
locatio ns
i nd i c a t ed
in
the
s e c o nd
co l um n .
Th e e x c e pt i o n s a r e the s e .
(1)

MSG$ DE L PR OC i s a c o n s t a n t i nd i c a t i ng tha t
t h i s- i s a p r o c e s s t e rm i n a t i o n m e s s ag e .

(2)

PCB $ L P I D a nd PC B $ L OWNER a r e o f fs e t s i n to
the PCB o f t h e proces s b e i ng d e l e t ed .

(3)

Names o f t h e fo r m PHD$L name a r e o f fs e t s
i n to
t h e p r o c e s s h e ade r
o f t h e pro c e s s
b e i ng d e l e ted .

1 9- 4

No te 2

No t e 2

PROC E S S DELET ION
10.

Th e s a m e m e s s a g e wi l l b e s e n t to the c r e a to r o f a
s ubp r o c e s s
if a
t e rm i n a t i o n m a i l bo x m e s s a g e wa s
r e que s t ed wh e n the
p r o c e s s wa s c r e a t ed .

11 .

Th e r em a i nd e r o f P l s p a c e i s d e l e t ed .
{ Th e a c t ua l pa r am e te r s
p a s s e d t o $ D E LTVA a r e 4 0 0 0 0 0 0 0 t o 7 FFFFFFF . ) Some o f P l s pa c e
i nc l ud i ng t h e us e r s t a c k m i g h t h a v e a l r e ad y b e e n d e l e t ed a s a
r e s u l t o f a p r ev i o us i m ag e r e s e t c a l l .

12.

At
th i s
po i n t ,
t h e p r oc e s s m u s t b e
r emoved
f r om
the
schedul e r ' s d a ta base .
To avo i d m u l t i pl e a c c e s s e s to th i s
d a t a , t h e r e s t o f the c o d e i n the d e l e t e spec i a l
ke rnel
AST
e x e c u t e s at I P L$ S YNC H .
Th e
process
i n s t r uc t i o n )

r emoved

f r om

execut ion

{ w i th

S VPC TX

•

13.

Th e a d d r e s s o f the PCB o f the n u l l p r o c e s s i s put i n to g l o b a l
l oc a t i o n
SC H$G L C URPCB
{ ma k i ng t h e n u l l p r o c e s s t h e c u r r e n t
p r o c e s s ) a n d a l so i n to the s l o t i n the
PC B vec to r
fo r m e r l y
o c c up i e d b y the p r o c e s s b e i ng d e l e t ed { th us f r e e i ng th i s s l o t
f o r f u r the r us e ) .

14 .

Th e pag e s t h a t we r e pe rmanen t l y l o c k e d i n to the wo r k i ng
set
but
are
n o t s ys t em pag e s
( k e r n e l s t a c k , P l po i n t e r pag e ,
e t c . ) a r e d e l e t ed and p l a c ed a t t h e beg i nn i ng o f
the
free
pag e
l ist .
Th e
p r o c e s s h e ad e r pag e s th a t a r e a pe rma n e n t
p a r t o f t h e wo r k i ng s e t wi l l b e d e l e t ed by the
swa ppe r
wh e n
t h e p r o c e s s h e ad e r i s d e l e t ed .

15.

An y r em a i n i ng AST c o n t r o l b l o c k s a r e
r emoved
q u e ue a nd d e a l l o c a t ed to n o npag ed po o l .

16.

Th e p r o c e s s swa p s l o t i s d e a l l o c a t e d .

17.

Th e p r o c e s s c o u n t f i e l d
in
the
j ob
i n fo rm a t i o n b l o c k
is
d e c r eme n t ed .
If
th i s
i s n o t the d e l e t i o n o f a s ub p r o c e s s ,
t h e n t h e J I B mus t be d e a l l o c a t ed .
( Th i s c h e c k
i s mad e
by
c ompa r i ng
the PID of
the
process
b e i ng d e l e t ed wi t h t h e
m a s te r P I D f i e ld of the J I B . )

18.

Th e PCB i s d e a l l o c a ted to n o n pa g ed po o l .

19.

Th e num b e r o f p r o c e s s e s i n
the
s ys tem a nd
the
p r o c e s s e s i n the b a l a n c e s e t a r e d e c r em e n ted .

20 .

Th e swa ppe r i s a wa k e n ed a nd i n fo rmed th a t th e r e i s a
p r oc e s s
h e a d e r to b e r emoved f r om t h e b a l a n c e s l o t a r e a { Ch a pte r 1 4 ) .

21 .

Fi n a l l y , t h e d e l e t e s p e c i a l k e r n e l AST e x i t s by j um p i ng
to
the s c h ed u l e r ( a t e n t r y SCH$ S C HED ) to s e l ec t the n e x t p r o c e s s
f o r e x e c u t i o n ( Ch a p t e r 8 ) .

19. 2. 2

f r om

the

n um b e r

PC B

D e l e t i o n o f a P r o c e s s Th a t Own s S u b p r o c e s s e s

Wh e n a p r o c e s s o wn s s ubpr o c e s s e s , t h e d e l e t i o n o f
t h e own e r
p rocess
m u s t b e d e l a yed un t i l a l l s ub p r o c e s s e s o wn ed b y i t a r e d e l e t ed .
Th i s
mus t b e d o ne to i n s u r e tha t a l l quo t a s
t a ken
f r om
the c r e a t o r
are
r e t ur ned .
19-5

PROC ESS DELET ION
D u r i ng t h e e x e c u t i o n o f t h e d e l e te spec i a l A S T , a c h e c k
i s made
to
d e t e rm i n e wh e th e r the p r o c e s s b e i ng d e l e ted o wn s any s ubp r o c e s s e s .
If
i t d o e s , t h e s e p r o c e s s e s mus t b e l oc a t e d
and m a r ked
fo r d e l e te .
M a r k i ng
a process
f o r d e l e t e s i m p l y m e a n s i s s u i ng a De l e te P r o c e s s
s ys tem s e rv i c e fo r i t .
As F i g u r e 1 9 - 1 sh ows , t h e r e a r e n o f o rwa r d po i n t e r s i n the PCB o f a n
o wn e r p r o c e s s t o i nd i c a t e wh i c h s ub p r o c e s s e s i t h a s c r e a t e d .
Th e o n l y
i nd i c a t i o n t h a t a p r o c e s s h a s c r e a t e d s ub p r o c e s s e s i s a n on z e r o e n t r y
in
the
PCB $W PRC CNT f i e l d .
Th e se p r o c e s s e s c a n o n l y b e l o c a ted by
s c a nn i ng a l l the PC Bs in t h e s ys t em un t i l t h e r e q u i r ed n umbe r of
PCBs
a r e l o c a ted w i th the P I D o f the c r e a to r in the own e r f i e l d .

name

OTG

name

B ERT

F i g u r e 1 9- 1

ERNIE

S ampl e Jo b to I l l u s t r a te P r o c e s s De l e t i o n
w i t h S ub p r o c e s s e s

Af t e r e a c h o wn ed
s ub p r o c e s s
i s m a r k ed
fo r d e l e t i o n ,
t h e c r e a to r
p r o c e s s e n t e r s a wa i t s t a t e u n t i l the c o un t o f own e d s ub p r o c e s s e s g o e s
to zero .
Th e a c t u a l wa i t s t a t e tha t i s e n t e r ed i s r e so u r c e wa i t s t a t e
( MWA I T ) .
Th e pa r t i c u l a r
r e so u r c e
th a t
i s b e i ng wa i t ed fo r i s the
s pe c i a l A S T u s ed b y the s ub p r o c e s s to r e t u r n d e d uc t i b l e quo t a s to
the
o wn e r .

19. 2. 3

E x a mp l e o f P r o c e s s D e l e t i o n wi t h S ubpro c e s s e s

Th e d e t a i l s o f th i s s i t ua t i o n c an b e b e s t i l l us t r a t ed w i th a n e x am p l e .
F i g u r e 1 9 - 1 s hows a p r o c e s s
( PID

1 0035

NAME

O TG )

t h a t own s t wo s ub p r o c e s s e s
( PID

1 0033

, NAM E

B ERT ) a nd

1 9-6

( PID

1 003

, NAME

E RN I E ) .

PROC E S S DELET I ON

Ne i the r o f the s e s ub p r o c e s s e s o wn s a n y f u r the r s ub p r o c e s s e s . We
wi l l
l i st
the
s teps
tha t o c c u r
as a
r e s u l t o f t h e p r o c e s s OTG b e i ng
d e l e ted . We w i l l
a s s um e
tha t
the
pr i o r i t i e s
a re
s uch
tha t
the
p r o c e s s e s ex e c u t e i n the o rd e r OTG , BE RT , a nd f i na l l y E RN I E .
1.

Th e d e l e t i o n o f p r o c e s s OTG p r o c e ed s no rm a l l y un t i l
it
is
d e t e r m i n ed
th a t
th i s p r o c e s s h a s c r e a t e d two s ubpro c e s s e s .
Th e PC B v e c to r i s s c a nned un t i l the two PC B s w i th
10035
in
the own e r f i e l d a r e l o c a ted .
Th e s e two p r o c e s s e s a r e m a r k ed
for deletion .
Th i s m e a n s tha t the d e l e t e spec i a l AST i s n o w
q u e ued
to
th e two s ubp r o c e s s e s a nd they a r e now c ompu t a b l e .
P r o c e s s OTG i s pl a c ed i n to a wa i t s t a t e be c a u s e the c o u n t o f
own ed s ubp r o c e s s e s i s non z e r o ( a c t ua l l y 2 a t th i s po i n t ) .

Th e a s s umpt i o n a bo u t pr i o r i t i e s
i mpl i e s
th a t p r o c e s s
B E RT
wi l l
e x ec u t e n e x t .
I t s d e l e t i o n p r o c e e d s pa s t the po i n t
wh e r e p r o c e s s OTG s t o pped b e c a u s e i t o wn s n o
s ubproc e s s e s .
Howe v e r ,
t h e n e x t s t e p i n the d e l e t e s pe c i a l AST d e t e rm i n e s
th a t p r o c e s s B E RT i s a s ub p r o c e s s a nd m u s t r e t u r n quo t a s
to
i ts
own e r .
As
l i s t ed a bove , t h i s i s a c c ompl i shed wi th t h e
q ue u i ng o f a s p e c i a l A S T ( R ETQU OTA ) t o p r o c e s s OTG ,
c h a ng i ng
i ts
state
back
to c om p u t a b l e .
Howe v e r , t h e c o un t o f own ed
s ubpr oc e s s e s i s s t i l l no t z e r o ( d own to 1 n o w ) so p r o c e s s OTG
i s put
r i g h t b a c k i n to the r e so u r c e wa i t s t a t e .
( Th e co un t
o f o wned s ubp r o c e s s e s wa s d e c r em e n t ed
as a
pa r t o f
the
r o u t i n e th a t s e nd s the RE TQUOTA AST to the own e r . )

O u r a s s um p t i o n a b o u t pr i o r i t i e s i nd i c a t e s tha t p r o c e s s
B E RT
wi l l
co n t i n u e
to
e x e c u t e u n t i l i t d i s a ppe a r s e n t i r e l y f r om
P r o c e s s E RN I E now b eg i n s e x e c u t i o n o f the d e l e t e
the s y s t em .
spec i a l
AST .
Ag a i n ,
t h e che c k
fo r
o wn ed
s ubpro c e s s e s
i nd i c a t e s n o n e b u t
the
chec k
tha t th i s
is
a
s ubp r o c e s s
i nd i c a t e s
tha t
it
is .
Th e RETQUOTA A S T i s ag a i n que ued to
p r o c e s s OTG a n d the c o un t o f owned
s ub p r o c e s s e s d e c r em e n t e d
( f i n a l l y to z e r o ) .

Now p r o c e s s OTG w i l l r e s ume e x ec u t i o n a s
a
resul t o f
the
d e l i v e r y o f t h e RE TQU OTA AST a nd f i nd tha t the c o un t o f o wn ed
s ubp r o c e s s e s h a s g o ne to z e r o .
In
fac t ,
process
OTG w i l l
con t i nue
to b e d e l e t ed
a t th i s po i n t , e v e n tho ug h p r o c e s s
Th i s i s s i mp l y a r e s u l t
ERN I E h a s n o t b e e n e n t i r e l y d e l e t e d .
o f o u r a s s umpt i o n a b o u t so f twa r e pr i o r i t i e s and h a s no e f f e c t
o n a n yth i ng .
Th e i mpo r ta n t po i n t i s th a t the quo t a s g i v en t o
p r o c e s s ERN I E h a v e b e en r e t u r n ed t o the own e r .
On c e th a t A S T
i s q u e ued , i t i s i r r e l ev a n t wh i c h p r o c e s s e x e c u t e s n e x t .

I n the g e ne r a l c a s e o f a s e r i e s o f s ub p r o c e s s e s a r r a ng ed
in a
t r ee
s t r uc t u r e ,
i f s om e
a rb i t r a r y process
i s d e l e t ed , a l l s ubp r o c e s s e s
f u r the r d o wn i n the t r e e wi l l b e d e l e t ed f i r s t .

1 9-7

C HAPTER 2 0
INTERAC T I VE AND BATCH JOBS

T h e p r ev i o u s t h r e e c h a p t e r s h av e d e sc r i b ed the c r e a t i o n a nd d e l e t i o n
o f a p r o c e s s tha t e x e c u t e s a s i ng l e i m ag e .
Th i s c h a p t e r d e sc r i b e s t h e
s pe c i a l a c t i o n s t h a t m u s t b e t a k e n to a l l o w s e ve r a l imag e s to
exec ute
c onsec ut i v e l y
in
t h e c o n t e x t o f t h e s ame p r o c e s s .
Bec a use th i s mode
o f o pe r a t i o n o c c u r s i n a l l
i n te r ac t i ve
a nd
ba t c h
j o bs ,
i t m e r i ts
s p e c i a l d i sc u s s i o n .
Howeve r , t h e to t a l o pe r a t i o n o f a VAX/VM S c omma nd
l a ng uag e i n te r p r e t e r w i l l n o t b e d i sc u s s ed .

20 . 1

THE JOB C ONTROLLER AND UNS O L I C I TED INPUT

T h e j o b c o n t r o l l e r is t h e p r o c e s s t h a t c o n t r o l s the c r e a t i o n o f n e a r l y
all
i n te r a c t i v e
a nd
batc h
j o bs .
I n t e r ac t i ve
j o bs
are
u s ua l l y
i n i t i a t ed by un so l i c i t e d
t e rm i n a l
i np u t .
Batch
j obs a r e
u s ua l l y
i n i t i a t ed t h r o ug h t h e S UBM I T c omma nd , a l tho ug h un so l i c i t ed c a r d r e ad e r
i nput wi l l a l s o r e s u l t i n the c r e a t i o n o f a b a tc h j o b .
Th e c r uc i a l s t ep t h a t i s pe r fo rmed
by
the
j ob c o n t r o l l e r
is
the
c r e a t i o n o f a p r o c e s s t h a t e x e c u t e s t h e imag e LOG INOUT .
Th i s i mag e i s
a c t i v a t ed a nd c a l l ed e x a c t l y l i k e a ny o th e r
imag e a s d e sc r i b ed
1n
Ch a p t e r s 1 7 a nd 1 8 .
T h e ac t i o n s t h a t i t t a k e s , e s pec i a l l y t h e mappi ng
of
a
c omma nd
l a ng ua g e
i n te r p r e t e r
i n to
Pl
s pa c e ,
are
wh a t
d i f f e r e n t i a t e i n t e r a c t i v e a nd b a t c h j o bs f r om the s i ng l e i m ag e p r o c e s s
d e sc r i b ed
i n the
p r ev i o u s
t h r e e c h a p te r s .
Th e
c r e a t i on o f
an
i n te r a c t i v e
j ob
is
p i c t u r ed
s c h em a t i c a l l y i n F i g u r e 2 0 - 1 .
Th e
c r e a t i o n o f a b a t c h j o b i s p i c t u r ed i n F i g u r e 2 0 - 2 .

20 . 1 . 1

Unso l i c i ted Te rm i n a l Input

Th e t e rm i n a l i n te r r upt s e r v i c e r o u t i n e p e r fo rm s s pec i a l a c t i o n wh e n a n
unex pe c t ed i n te r r up t o cc u r s .
A c h e c k i s mad e t o d e t e rm i n e wh e th e r t h e
d ev i c e i s o wn ed .
I f the o wn e r p r o c e s s h a s r eque s t ed
no t i f i c a t i o n o f
un so l i c i t ed
i n te r r up t s ,
it
w i l l b e n o t i f i ed .
O t h e rw i s e ,
the
c h a r a c t e r s wi l l b e pl a c ed i n to a type - a h ead buf f e r .
I f the d ev i c e i s n o t o wn ed , t h e j o b c on t r o l l e r i s no t i f i ed th r o ug h i t s
m a i l bo x t h a t a n un o wn e d t e rm i n a l h a s r ec e i v ed an un e x p e c t ed i n te r r up t .
I n a s e n s e , t h e j o b c o n t r o l l e r i s t h e d e fa ul t own e r o f a l l
o th e r wi s e
unc l a i m e d t e rm i n a l s .

20-1

Termin.a l
Driver

TTcu :

Job
Controller
Job Controller's
Mailbox
Creates
Process

Contex t of Job
Controller Process
Conte x t of Newly
Created Process

SY SSINPUT

[\)
0
I
[\)

SYSSOUTPUT
SYSSERROR
SYSSCOMMAND

TTcu :

1) Verify Usern a m e / Password
a g a inst record in the
a uthorization file

2) Alter process characteristics
according to authorization record.
Set up process permanent flies
for SYS$1NPUT, SYS$0UTPUT,
SYS$ERROR, and SYS$COMMAND

3) Map requested CLI into P 1 space,
stack login c ommand file, a nd
pass control to CLI in supervisor
mode ( Figure 20-4)

F i g u r e 2 0-1

S t e p s I n vo l ve d i n I n i t i a t i ng a n I n t e r a c t i v e Job

INTERACT I VE AND BATCH JOB S

Job Controller's
Mailbox
Job
Controller

D ri v e r

Creates
Input
Symbiont
Process

C o n t e x t of Job
Con t r o l l e r Proc e s s

Conte x t o f Input
S y m b i o n t P roc e s s

Context of
Requesting Process

Job Controller- m a k e s entry i n
response t o $SNDSMB f rom either
input symbiont o r SUBMIT utility

....------....

$ S U B M IT X . C O M
CLI a c t i v a t e s
S U B M IT u t i l i t y

SUBMIT u t i l i t y notif ies
Job Controller of
r e q u e s t ed b a tch
job I S SNDSMB

Job
Controller

C re a t e s
proce s s

S o m e t i m e l a t e r . job con troller
removes q ueue entry and c re a t e s
reques ted p r o c e s s with specif ied
charac teristics

SY S $ 1 NPUT
SY S $ C O M M A N D

The two chief differences between batch
and interactive jobs are:
No user name/password verification has
to occur
2) SYS$1NPUT and SYS$0UTPUT are different

SY S $ 0 UTPUT
SY S $ ERROR

X . LOG

Figure 2 0-2

There is only a trivial difference between batch
jobs initiated with a SUBMIT command and batch
jobs read from the card reader. This is the method
of creating the batch command file.
The remaining operations performed by
LOGINOUT for batch jobs are the same as
those performed by interactive jobs
P roces s c ha racter lsti c s a ltered accord i ng to
authorization record
__
_.
2) Map CLI and pass control to it.
..•••••••••-•••.•••••••-.•••••••

�����·-·-1•)

S t e ps I n v o l v ed i n I n i t i a t i ng a Ba t c h Jo b Th r o ug h a
S UBM I T Comma nd a nd Th r o ug h a C a r d Re a d e r

2 0-3

INTERACT I VE AND BATCH JOBS
The j o b c o n t r o l l e r r o u t i n e t h a t r e spo nd s to u n so l i c i t e d t e rm i n a l input
s i mpl y c r e a t e s a p r o c e s s w i th the pa r a m e t e r s
P r o c e s s Name

TTc u :

UIC

[10, 40]

Imag e Name

SYS $ S Y S TEM : LOGI NOUT . E XE

S YS $ I N P U T

TTc u :

S YS $ 0 UT PUT

TTc u :

S YS $ ERROR

TTc u :

Ba s e P r i o r i ty

DEFPR I

( S YS B OOT Pa r am e t e r )

P r i v i l eg e Ma s k

Al l P r i v i l eg e s

wh e r e TTc u i nd i c a t e s t h e c o n t r o l l e r/ un i t o f t h e
t e rm i n a l
wh e r e
the
u n so l i c i t e d
i np u t wa s
t yped .
No t e t h a t a l l i n t e r a c t i v e j o b s beg i n
w i th a
name
i nd i c a t i ng
the i r
i np u t/o u t put d ev i c e a nd
the
i m ag e
LOG INOUT a s th e i m a g e tha t w i l l e x ec u t e ( F i g u r e 2 0 - 1 ) .

20 . 1 . 2

Th e S UBM I T Command

Wh e n the S UBM I T c omma nd i s e x e c u t ed , a m e s s ag e i s s e n t to the s ym b i o n t
m a n ag e r ( th e j ob c on t r o l l e r ) , wh i c h p l a c e s the r eq u e s t ed j o b i n o n e o f
i ts j o b q u e u e s . Wh e n the n umb e r o f a c t i ve j o bs i n o n e o f t h e b a tc h
q u e u e s d r o p s b e l o w i t s m a x i m um va l ue , t h e j o b c o n t r o l l e r s e l e c t s the
h i g h e s t p r i o r i ty p e nd i ng j o b f r om o n e o f
i t s q ue ue s a nd
c rea tes a
p r o c e s s w i th the s pe c i f i e d ba tch s t r e a m a s SYS $ I N PUT a nd a l og f i l e i n
a n a pp r o p r i a t e d i r e c to r y a s SYS $ 0 UTPUT ( F i g u r e 2 0 - 2 ) .
Th e i m a g e
tha t
wi l l
execute
is
LOG I NOUT ,
wh i c h
a l l o ws
the l a ng uag e o f t h e i n p u t
s t r e am to b e a
c omma nd
l a ng uag e b e c a u s e
LOG I NO UT w i l l m a p t h e
a pp r o p r i a t e C L I i n t o the p r o c e s s P l s pa c e .

20. 1 . 3

U n so l i c i te d C a rd Re a d e r I nput

An a l t e r n a t i v e m e t hod f o r s t a r t i ng ba tc h j o bs u t i l i z e s
the
s o - c a l l ed
ho t c a r d
r ea d e r
feature
tha t
is
a p a r t o f the c a rd r e a d e r d r i v e r
i n t e r r upt s e r v i c e
rout ine .
L i ke
the
t e rm i n a l
d r i ve r ' s
i n t e r r up t
s e rv i c e
r out i ne ,
t h e c a rd
r ea d e r d r i v e r i n f o rm s t h e j o b c o n t r o l l e r
tha t a n u n ex p e c t ed i n te r r up t h a s o c c u r r ed o n a n un own ed d ev i c e .
Th e
j ob c o n t ro l l e r c rea tes a
p r o c e s s s i m i l a r to the p r o c e s s c r e a t ed i n
r e spo n s e
to
un so l i c i t e d
t e rm i n a l
i np u t e x c e p t
tha t
the
i m ag e
I N PSMB . E XE ,
the
i np u t
s ym b i o n t , e x e c u te s i n p l a c e o f LOG INO UT .
Th e
p r o c e s s pa r a m e t e r s tha t a r e p a s s e d by t h e j o b c o n t r o l l e r to t h e C r e a t e
P r o c e s s s y s t e m s e rv i c e a r e

2 0-4

INTERACT IVE AND B ATCH J O B S
P r o c e s s Name

C Rc O :

UIC

[10, 40]

Im a g e Name

SYS $ S YS TEM : I N PSMB . E XE

SYS $ I N PUT

C Rc O :

S YS $ 0 UTPUT

C Rc O :

S YS $ E RROR

C Rc O :

Ba s e Pr i o r i t y

DE FPR I

P r i v i l eg e Ma s k

Al l P r i v i l eg e s

{ S YS B OOT Pa r am e t e r )

Th e f a c t tha t t h i s p r o c e s s h a s a c a rd r e a d e r fo r i ts o u t p u t d ev i c e
i r r e l ev a n t b e c a u s e
i t d o e s n o wr i t i ng
t o e i th e r
SYS $ 0 UT PU T
SYS $ E RROR .

is
or

Th e i n p u t s ymb i o n t r e ad s t h e $JOB a nd $ PAS SWORD c a rd s a nd
pe r f o rm s
a
val i d a t i on
s im i l a r
to
the one
pe r f o rm ed b y LOG INOUT .
Af t e r
d e t e rm i n i ng
the
u s e r ' s d e fa u l t d i r e c to r y f r om
t h e a u th o r i z a t i o n
r ec o rd ,
the
i n put
s ymb i o n t o pe n s a f i l e i n tha t d i r e c t o r y a nd r e ad s
t h e r e s t o f t h e j o b c a r d s i n to tha t f i l e .
Te rm i n a t i ng
c o nd i t i o ns
of
th i s r e ad a r e a n e nd o f f i l e , a n $ E OJ c a r d , o r ano t h e r $ J O B c a r d .
On c e t h e i n p u t s t r e a m h a s b e e n r e ad i n to
the
u s e r ' s d i r ec t o r y ,
the
s ymb i o n t s e nd s a m e s sag e
to
the
j ob c on t r o l l e r ,
a nd t h e
i nput
o pe r a t i o n p r o c e ed s f r om t h i s po i n t i n e x a c t l y t h e s am e m a n n e r
as
fo r
the
S UB M I T c omma nd .
Th a t
is ,
the
j o b c o n t r o l l e r w i l l ev e n t ua l l y
c r ea t e a p r o c e s s wi th t h e c a r d f i l e a s S YS $ I N PUT ,
s ome
l og
file
as
SYS $ 0 UTPUT , a n d LOG IN OUT { wh i c h wi l l m a p a C L I ) a s the i m ag e t h a t w i l l
e x ec ute { F i g u r e 2 0 - 2 ) .

20 . 2

THE LOG INOUT IMAG E

Th e LOG INOUT i mag e i s r e s p o n s i b l e
f o r v e r i f y i ng
that
the
use r
is
a u tho r i z ed
t o u s e t h e s ys t em , r e ad i ng h i s r e c o r d i n t h e a u th o r i z a t i o n
f i l e , a nd a l t e r i ng t h e p r o c e s s
chara c te r i s t i c s
to
r e f l e c t wh a t
is
f o und
ther e .
Th e m o s t
i mpo r ta n t
s te p tha t t h i s i m ag e pe r f o rm s i n
a l t e r i ng t h e p r o c e s s i s t o m a p a c omm a nd l a ng uag e i n t e r p r e t e r i n to i t s
r e s e rved
pl a c e
in
P l s pa c e
{ p i c t u r ed
i n F i g u r e 1 - 7 a nd l i s t ed i n
Ta b l e E- 4 ) .

20 . 2 . 1

I n t e r a c t i ve Jobs

Wh e n LOG INOUT e x e c u t e s in r e s p o n s e t o u n so l i c i t ed t e rm i n a l
i np u t ,
it
m u s t v e r i f y t h a t t h e u s e r h a s a c c e s s t o t h e s ys t em b e fo r e i t p r o c e e d s
wi t h t h e r e s t o f i t s o pe r a t i o n s .
I t d o es
t h i s b y pe r fo rm i ng
the
fo l l o wi ng s t e p s .
1.

A Ch a ng e Mo d e
to
Ex ec u t i v e
s ys t em s e rv i c e
i s e x e c u t ed .
LOG INOUT pe r f o r ms
all
o f i t s o pe r a t i o n s i n e x e c u t i v e m o d e ,
b e c a u s e i t mus t wr i t e p r o t e c t ed d a t a s t r uc t u r e s .
Th e PC
a nd
PS L p a i r t h a t a r e p u s h e d o n the s ta c k i n r e s po n s e to t h e C HM E
e x c e p t i o n w i l l a l so b e t h e v eh i c l e
tha t w i l l
be
u s ed
to
t r a n s f e r c o n t r o l to t h e C L I i n s upe rv i so r m od e .
2 0-5

I N TERAC T I VE AND BATCH J O B S
2.

A n e x e c u t i v e m o d e e x c e p t i o n h a nd l e r
i s e s t a b l i sh e d
in
the
p r i m a r y e x c e p t i o n v e c to r t o s e r v i c e a n y e x c e p t i o n s th a t o c c u r
wh i l e L OG I N O UT i s e x e c u t i ng .
I f t h i s h a nd l e r i s i nv o k ed ,
it
wi l l c a l l
SYS $ RMSRUNDWN f o r
e a c h o pe n f i l e , a nd then c a l l
S YS $ E X I T f r o m e x e c u t i v e m o d e .
Th i s w i l l
result
i n the
e v e n t ua l d e l e t i o n o f t h e p r o c e s s .

Th e l o g i c a l n am e s S YS $ I N PUT , S Y S $ 0 UTPUT ,
a nd
SYS $ E RROR a r e
t r a n s l a t ed a n d t h e r e s u l t a n t s t r i ng s a r e s a v ed f o r l a te r u s e .

Th e p r o c e s s
I /0 s egme n t
in
P l s pa c e
is
i n i t i a l i ze d .
S YS $ I N PUT
is
o pe n ed .
Because
a n i n t e r a c t i v e j o b i s b e i ng
c r e a t ed , th i s
i mp l i e s t h a t
SYS $ 0 UT PUT a n d
SYS $ E RROR a r e
a l r e a d y o pe n ed .
RAB s a r e c o n n e c t ed to the FAB s o th a t RMS
o pe r a t i o n s m a y p r o c e ed .

Th e u s e r n a m e a nd pa s swo r d a r e p r om p t e d fo r a nd r e a d f r om t h e
r e q u e s t i ng t e rm i n a l .
Th e r e c o r d a s s o c i a t ed w i t h th i s u s e r i s
read
f r om t h e
a u t ho r i z a t i o n
f i le
and
the
pa s s wo r d
is
v e r i f i ed .

I f the pa s s wo r d i s c o r r e c t a n d the i n te r a c t i v e j o b c o un t h a s
n o t b e e n e x c e ed ed , t h e l og i n o pe r a t i o n wa s a s uc c e s s .
Th i s
s uc c e s s i s i nd i c a t ed by t h e a nno u n c em e n t m e s sag e
We l c om e to VAX/VM S Ve r s i o n V 2 . 2

Fo u r by t e s c o n t a i n i ng
RM S
i n fo rm a t i o n a r e
a d d ed
to
the
b eg i n n i ng o f t h e r e s u l t a n t s t r i ng s f o r SYS $ I N PUT , SYS $ 0 UT PU T ,
a nd SYS $ E RROR .
Th e s e fo u r by t e s a r e < e s c a pe > , < n u l l > , and
a
wo r d c o n t a i n i ng t h e i n te r n a l f i l e i d e n t i f i c a t i o n ( I F I ) o f t h e
SYS $ I N PUT .
New l o g i c a l
n am e s a r e c r e a ted
fo r
SYS $ I N PU T ,
SYS $0UTPUT
and
SYS $ E RROR u s i ng
t h e mod i f i ed
r e s u l ta n t
s t r i ng s .
Wh e n RMS r e c e i v e s s uc h a m o d i f i e d name a s a
resu l t
o f l o g i c a l n am e t r a n s l a t i o n , i t u s e s t h e I F I a s a n i nd e x i n to
one of i t s i n t e r n a l t a b l e s .
A l o g i c a l name i s a l s o c r e a t ed
fo r
SYS $ C OMMAND ,
us i ng
the
s am e
trans l a t i on as
ex i s ts
fo r SYS $ I N PUT .
SYS $COMMAND i s
t h e n i d e n t i c a l t o the z e r o th l ev e l SYS $ I N PUT .
( No te th a t t h e
l og i c a l
name
SYS $ C OMMAND
i s a p r o d uc t o f LOG I N O UT a nd d o e s
no t ex i s t f o r p r o c e s s e s tha t d o no t e x e c ute tha t i m ag e . )
Wh e n RM S pe r fo rms l o g i c a l n ame t r a n s l a t i o n o f o n e o f t h e s e
l og i c a l
nam e s ,
the
two b y t e c omb i n a t i o n i nd i c a t e s th a t t h e
n e x t wo r d o f th e r e s u l t a n t s t r i ng i s a n i nd e x i n to o n e o f i t s
tables .
Th i s a l l ows e x t r em e l y f a s t a c c e s s to the se c ommon l y
used f i l e s .

Th e c omm a nd l a ng uag e
i n te r p r e t e r
i s m a pped
i n to
the
l ow
a d d r e s s end
o f P l space ( Fi g u r e l-7 ) .
Th i s i s a c compl i sh e d
by a m e r g ed i m a g e
ac t i v a t i o n
of
the
se l e c ted
CLI .
( Th e
p r o c ed u r e
L I B $ P l M E RGE
f i r s t m e r g e s t h e C L I i n to P O s p a c e to
d e t e rm i n e i t s s i z e ,
d e l etes
the
PO
spa c e ,
a nd maps
the
c o r r e c t amo u n t o f P l s pa c e .
G l o b a l l o c a t i o n C T L $G L C T LBASVA
i s a l t e r ed to r e f l e c t the n e w l o w a d d r e s s e nd o f Pl spa c e . )

2 0-6

INTERACT I VE AND BATCH JOBS
9.

10 .

Th e c ommand l a ng u a g e i nd e pend e n t d a ta
a rea ,
i nc l ud i ng
the
s ymb o l
tabl es ,
is
i n i t i a l i zed .
P l s pa c e is e x pa nd ed by a
n umb e r o f p a g e s e q ua l to the S YS B OOT pa r am e t e r
C L I S YMTB L t o
a c c ommo d a t e
t h e C L I s ymbo l t a b l e .
Th e s e s ym bo l t a b l e s h a v e
the s a m e s t r uc t u r e a s t h e l og i c a l n a m e t a b l e s d e sc r i b e d
in
Ch a p t e r 2 6 .
Ma ny o f
the
a u tho r i z a t i o n
o v e r wr i t i ng the
Th e s e
c r ea ted .

process
a tt r ibutes
e x t r a c ted
f r om
the
file
a re put
i n to
t he i r
p r o pe r
pl a c e s ,
a t t r i b u t e s p l a c ed the r e wh en the pr o c e s s
wa s
i n c l ud e

•

De f a ul t D i r e c t o r y S t r i ng

•

Us e r Name

•

Ac c o un t Name

•

De f a ul t P r i v i l eg e Ma s k

•

P r o c e s s Quo t a s ( b e c a us e th i s i s a d e t a c h e d p r o c e s s )

•

Ba s e S o f t wa r e P r i o r i t y

•

UIC

LOG INOUT a t t emp t s to c h a ng e t h e p r o c e s s n ame f r om TTc u :
to
the us e r n a m e .
Th i s wi l l f a i l i f ano the r p r o c e s s Tn t h e s a m e
g r o u p a l r e a d y h a s the s am e n a m e .
( Th e mo s t c ommon o c c u r r e n c e
of
th i s
i s wh e n t h e s ame u s e r i s l ogg ed i n a t mo r e th a n o n e
t e rm i n a l . ) I n t h e c a s e o f fa i l u r e , t h e p r o c e s s wi l l
r e ta i n
the n a m e o f _TTc u : ,
g ua r a n t e ed
to b e un i que f o r a g i v e n
s ys tem .
11.

Th e l og i n c ommand
f i le
( e i ther
LOG I N . C OM
i n t h e d e fa u l t
d i r e c to r y o r an a l t e r n a t e f i l e i nd i c a ted i n the a u th o r i z a t i o n
r e co rd ) i s o pe n ed a nd s e t u p a s
the n e x t
l ev e l
S YS $ I N PUT .
Wh e n
t h e C L I i s f i r s t e n t e r ed , i t i s a c t ua l l y o n e l ev e l d e e p
i n i n d i r e c t f i l e s , e x t r a c t i ng i t s c omma nd s
f r om t h e
l og i n
c ommand
file.
Wh e n the e nd o f th i s f i l e i s r e a c h e d , c o n t r o l
pa s s e s b a c k t o t h e z e r o th l ev e l , t h e te rm i n a l
o n wh i c h
the
p r o c e s s wa s o r i g i n a l l y c r e a t e d .

12.

At th i s po i n t , LOG INOUT h a s
f i n i shed
i t s wo r k a nd
pa s s e s
contro l
to
t h e a l r e ad y m a pped
C LI .
Th i s
transfe r
is
a c compl i s hed by a l t e r i ng the C HM E e x c ept i o n PC
to
po i n t
to
the
l o we s t
ad d r e s s in the C L I , a nd a l t e r i ng the m o d e f i e l d s
i n t h e e x c e p t i o n PS L t o i nd i c a t e tha t the p r ev i o u s mod e
a nd
the c u r r e n t mod e
are
s upe r v i so r .
Th e
return
f r om
the
e x e c u t i v e m o d e p r o c ed u r e g o e s
bac k
to
the
s ys t em
se rv i c e
d i s pa t c h e r ,
but
the
RE I
t h a t d i sm i s s e s the CHME e x c ept i o n
d o e s no t pa s s c o n t r o l b a c k to the sys tem s e r v i c e vec to r a r e a .
Ra the r ,
the
RE I p a s s e s c o n t r o l to the f i r s t add r e s s i n the
ma pped C L I , e x e c u t i ng in s upe r v i s o r mo d e .

2 0-7

I NTERACT IVE AND BATCH JOBS

20 . 2 . 2

LOG I NOUT O pe r a t i o n f o r B a t c h Jobs

Many o f t h e o pe r a t i o n s pe r fo rmed by LOG INOUT f o r i n t e r a c t i v e j o b s m u s t
a l s o o c c u r wh e n a
b a tc h
j o b i s b e i ng c r e a t ed .
Fo r ex ampl e , i t i s
s t i l l n ec e s s a ry t o o pe n the i np u t a nd o u tp u t s t r eams a nd m a p t h e
CLI .
Howe v e r ,
pa s s wo r d
ve r i f i c a t i on
i s n o t n e c e s s a ry , e i th e r b e c a u s e the
i np u t s ym b i o n t a l r e a d y d i d i t o r b e c a u s e i t i s not n e c e s s a r y i n
the
c a s e of a S UBM I T c omm a nd .
Ra t h e r t h a n d e s c r i b e t h e s t e p s pe r f o rmed by LOG INOUT
s i mpl y l i s t tho s e d i f f e r e n c e s fo r b a tc h j o b s .

aga i n ,

wi l l

Th e f i r s t i nd i c a t i o n t h a t LOG INOUT h a s tha t i t i s c r e a t i ng
a
b a tc h
j ob
is
that
t h e r e s u l t a n t s t r i ng s f o r SYS $ I N PUT a nd
S YS $0UTPU T a r e d i f f e r e n t .
Th i s m e a n s tha t i t m u s t o pe n
two
f i l e s a s p r o c e s s pe r m a n e n t f i l e s r a th e r th a n o n e a nd p r e s e r v e
t wo I F i s f o r l a t e r u s e .

Th e p r o mp t ed
r e ad
fo r
u s e r n am e
a nd
pa s swo rd
a nd
the
a n n o un c em e n t
of
t h e s ys t em a r e s k i pped b e c a u s e th i s s t e p i s
unnece s sa ry .

New l o g i c a l
n am e s a r e
aga i n
c r e a t ed
fo r
SYS $ I N PUT ,
S YS $0UTPUT , SYS $ E RROR a n d SYS $C OMMAND .
Bec a u s e two f i l e s a r e
i nvo l v ed , d i f f e r e n t I F i s w i l l b e ad d ed t o t h e b eg i n n i ng
of
t h e r e s u l t a n t s t r i ng s b e fo r e C r e a t e Log i c a l Name i s c a l l ed .
One I F I i s u s ed fo r S YS $ I N PUT a nd SYS $ C OMMAND .
Th e o th e r I F I
i s u s e d f o r SYS $ 0 UT PU T a nd SYS $ E RROR .

Th e r e wr i t e o f p r o c e s s a t t r i b u t e s f r om the a u th o r i z a t i o n f i l e
c a n a l s o b e sk i pped .
B e c a u s e the j o b c o n t r o l l e r knows m uc h
mo r e a b o u t a b a tc h j o b t h a n a n i n te r a c t i v e j o b wh e n i t
c al l s
C r e a t e P r o c e s s , mo s t o f t h e s e a t t r i b u t e s a r e a l r e a d y i n p l a c e
a nd n e e d no t b e wr i t t e n b y LOG INOUT .

Th e m a pp i ng o f t h e C L I a nd t h e t r a n s f e r o f c o n t r o l
to
i t h a ppen
in
e x a c t l y t he s am e wa y a s t h e y d o fo r a n i n te r a c t i v e j o b .
Th u s i n bo th
c a s e s , the f i r s t c omma nd s t h a t e x e c u t e a r e the c ommand s in t h e
use r ' s
l og i n c omma nd
file.
I f a l o g i n c ommand f i l e i s spec i f i e d a s pa r t o f
t h e u s e r ' s a u tho r i z a t i o n r e c o rd , t h e n tha t f i l e i s u s e d .
I f no t , then
the f i l e LOG I N . COM i n t h e u s e r ' s d e f a u l t d i r ec t o r y i s u s ed .

20 . 2 . 3

Th e Log o u t Ope r a t i o n

Th e same i m a g e t h a t pe r f o rms t h e i n i t i a l i z a t i o n o f a n
i nterac t i ve or
b a tch
j ob
is
u s ed t o c a u s e the ev e n t u a l d e l e t i o n o f s uc h a p r o c e s s .
Th e i nd i c a t i o n t h a t a l og o u t i s r e qu i r e d i s th a t the f i l e SYS $ I NPUT i s
a l r e a d y o pe n ed .
LOG IN OUT t a k e s wh a t e v e r s pec i a l a c t i o n i s r e q u i r e d
b e f o r e c a l l i ng d e l e t e p r o c e s s , wh i c h w i l l c o n t i n ue w i th tho s e pa r t s o f
process d e l et ion
t h a t a r e i nd e pe nd e n t o f t h e k i nd o f p r o c e s s th a t i s
b e i ng d e l e t ed .
1.

Th e l o g o u t m e s s ag e i s s e n t to SYS $ 0 UTPUT , e i th e r
the
user ' s
t e rmi na l
fo r a n i n t e r a c t i v e j o b o r the b a t c h l og fo r a b a tc h
j ob .

SYS $ 0 UTPUT i s c l o s e d .
I f th i s i s a b a tc h j ob , t h e n S YS $ I NPUT
i s d i f f e r e n t a nd m u s t a l s o b e c l o s ed .

2 0-8

INTERAC T I VE AND BATCH JOBS

20 . 3

SYS $ RMSRUNDWN i s c a l l ed fo r e a c h o pe n f i l e .

F i n a l l y , S YS $ E X I T i s
c a l l ed
f r om
e x e c u t i v e m od e .
As
we
d i s cus sed
i n Ch a p te r 1 8 , t h e se a r c h fo r t e r m i n a t i o n h a n d l e r s
w i l l o n l y l o o k a t the
e x ec u t i ve mode
l i st ,
b ypa s s i ng
the
s upe r v i s o r mo d e te rm i n a t i o n h a nd l e r e s t a b l i s h e d by the C L I to
p r e v e n t p r o c e s s d e l e t i o n f o l l o w i ng i mag e e x i t .

A f t e r the e x e c u t i v e m o d e t e rm i n a t i o n hand l e r
h a s pe r fo rmed
i t s wo r k ,
the Ex i t s ys t em s e rv i c e wi l l c a l l De l e te P r o c e s s ,
wh i c h w i l l c a u s e the l og g e d o u t p r o c e s s to d i s a pp e a r f r om the
s y s t em .

C OMMAND LANGUAG E INTERPRETERS AND I MAG E EXECUT I ON

O n c e the c omma nd l a ng uag e i n te r p r e t e r g a i n s c o n t r o l , i t pe r fo r m s
some
i n i t i a l i za t ion
a nd
then
r e ad s a nd p r o c e s s e s s uc c e s s i v e r e co r d s f r om
SYS $ I N PUT .
S e v e r a l of t h e s e o p e r a t i o ns i nv o l v e fancy comm a nd l a ng uag e
features .
We
a re
onl y
i n te r e s t ed i n tho s e c ommand s th a t r e s u l t i n
j o bs
wi th
s i mpl e
i m ag e e x e c u t i o n , t o co n t r a s t i n te r a c t i v e a nd batch
p r o c e s s e s d e sc r i b ed i n p r ev i o u s c h a p t e r s .
VAX/VM S s u ppo r ts two c omma nd l a ng u ag e i n t e r pr e t e r s , DC L and MCR .
Th e
c h i e f d i f f e r e nc e b e t we e n
the s e c ommand
l a ng uag e s
l ies
in
the i r
t r e a tm e n t o f i nd i r e c t f i l e s ,
a
to p i c
tha t d o e s n o t a f f e c t
i m ag e
execut ion .
In
fact ,
t h e s t e p s t a k e n by e i the r C L I i n a c t i v a t i ng a n
i m a g e a r e n e a r l y i d e n t i c a l . W e w i l l d e sc r i b e the o pe r a t i o n o f DC L
in
d e t a i l , a nd o n l y m e n t i o n MCR wh e r e i t d i f f e r s f r om DC L .
Th e m o s t i mpo r t a n t s t e p tha t th e C L I pe r fo rms a s f a r a s the " l i f e o f a
process "
is
c o nc e r n ed
is
the d ec l a r a t i o n o f a
s upe r v i so r mod e
t e rm i n a t i o n h a nd l e r .
I t i s th i s h a nd l e r
tha t w i l l
prevent
proc ess
delet ion
f o l l o w i ng
i m ag e e x i t a nd a l l o w t h e s uc c e s s i v e e x e c u t i o n o f
m u l t i pl e i mag e s wi th i n t h e s ame p r o c e s s .
A s i mpl i f i e d f l o w o f c o n t r o l
t h r o ug h t h e C L I i s p i c t u r ed i n F i g u r e 2 0 - 3 .

20 . 3 . 1

C L I I n i t i a l i za t i o n

Th e f i r s t c o d e t h a t e x e c u t e s i n DC L pe r fo rms
seve r a l
i n i t i a l i za t i o n
s t eps b e fo r e i t e n t e r s the ma i n comm a nd p r o c e s s i ng l o o p .
1.

SYS $ R UNDWN i s c a l l ed w i th a n a rg umen t o f u s e r mod e to r und own
the L OG INOUT i m a g e .

A c h a ng e m o d e to s upe r v i so r h a nd l e r i s e s t a b l i s h e d ( by u s i ng
the
$DC LCMH s ys tem s e r v i c e ) .
Th i s h a nd l e r a l l ows DC L to g e t
b a c k t o s upe r v i s o r mod e f r om u s e r m o d e wh e n i t n e ed s t o wr i t e
p r o t e c t ed d a t a
s t r uc t u r e s .
One
i n s tance
wh e r e
th i s
is
r e q u i r e d i s i n s ymbo l d e f i n i t i o n , b e c a u s e DC L ' s s ymbo l t a b l e s
a r e p r o t ec t ed f r om wr i t e a c c e s s b y u s e r mode .

A C ONTRO L/Y AST i s d e c l a r ed
so
c o n t r o l wh e n C TR L/Y i s typed .

F i n a l l y , c o n t r o l i s pa s s ed to the f i r s t
i n s t r uc t i o n o f
the
m a i n command p r o c e s s i ng l o o p ( a t g l oba l l a b e l DC L $ RE S TART o r
M C R $ R E S TART ) .
2 0-9

tha t

DC L

a l wa ys

r ece ives

CLI Initialization
Code

....�------ from LOGINOUT

Establish CH M S
handler
to Exception
Dispatcher

Rundown LOGINOUT
Image

DEBUG Command

Generate
SS$_DEBUG
signal

�---� r---��

Beginning of CLI
Command
Processing Loop

-·--�--

STO P Command
(Close all flies,
rundown Image, and
get next command)

Determine whether
command executes
Internally or requires
external Image

.... .

Internal
Routine

[\.)
0
I
....
0

�
External
�Image
�

� command and

Service Internal

�
CONTINUE Command

go back to
top of main loop.

If CO NTINUE, STOP,
EXIT, or DEBUG, go
there.

(If previously executing
Image was Interrupted
with iCTRLIY
then return control)

t-·------Rundown previous
Image
Redeclare supervisor
mode termination
handler

r+'

$EXIT System Service

1-- -------Ralse access
mode to supervisor

Call supervisor mode
termination handler .,_I-

Activate the Image
Raise access mode to
user

CTRL/Y AST

.,_ •
(Save context of
Interrupted Image and
..
get next command)

Set up call frame
and condition handler
transfer-address: :

EXIT Command

Portion of CLI that
activates and calls
external Images

RET
Image Code

11,...

�

��������; :::
M

n
dler
Declared by Cl.l
1--------Ciose all open flies
Purge Input stream
of data records
Rundown Image
Restore stack
to known stack
Go back to top
of main loop

....

Build argument list

CALL Imago

CALL SYS$EXIT ... 1-

Call SYS$EXIT ...-+--------------------------�

Figure 20-3

S i mp l i f i e d Co n t r o l F l o w Th r o ug h a Command La ng u a g e I n t e r p r e t e r

INTERACT I VE AND BATCH JOBS

20. 3. 2

Command P r o c e s s i ng Lo o p

Th e ma i n c ommand p r o c e s s i ng l o o p r e ad s a
r e c o rd
f r om
SYS $ I N PUT a n d
t a k e s wh a t e v e r a c t i o n i s d i c t a ted by t h e c ommand .
Some a c t i o n s c a n b e
pe r fo rmed d i r e c t l y by DC L { o r MCR ) .
O t h e r s r e qu i r e the e x e c u t i o n o f a
s e pa r a t e
i m ag e .
Ta b l e 2 0 - 1 l i s t s t h e g en e r a l ope r a t i o n s pe r fo rmed by
DC L { o r MCR) a nd i nd i c a t e s tho s e
a c t i ons
tha t r equ i r e
an external
imag e .
Ta b l e 2 0 - 1
G e n e r a l Ac t i o n s Pe r fo rmed by a
Comma nd La ng ua g e In te r pr e te r

Ge n e r a l C L I Op e r a t i o n s

Sampl e Co mma n d s

Co mma nd s tha t Re qu i r e
Ex t e r n a l Imag e s

C OPY
LINK
So me S E T Comma nd s
Some S H OW Command s

Command s tha t Re qu i r e
In t e r n a l Pr o c e s s i ng and
an Ex t e r n a l Imag e

LOGOUT
MCR
RUN

Fo r e i g n Comma nd s

s t r i ng : = = " $ imag e- f i l e - s pe c "

Oth e r Ope r a t i o n s tha t
De s t r o y an .Im ag e

STOP
EXIT
Inv o k i ng a Comma nd Pr o c ed u r e
CTR L/Y i n te r r up t i ng a
p r i v i l eg ed i m ag e

Command s tha t C L I
Ca n Ex e c u t e I n t e r n a l l y

E XAM INE ,
S E T DE FAULT
{ Ta b l e 2 0 -2 )

Oth e r I n t e r n a l Op e r a t i o n s

Sym b o l De f i n i t i o n

I f t h e r e c o r d t h a t i s r e ad f r om t h e
i nput
s t r e am
is
a
r e c og n i z e d
c omm a nd ,
DC L
( o r MC R ) m u s t a l so d e t e rm i n e wh e th e r i t c a n p e r fo r m t h e
r eq u e s t e d a c t i o n i t s e l f o r a c t i v a t e a n e x t e r n a l
i m ag e .
Tab l e 2 0 - 2
l i s t s t ho s e
c omma nd s
tha t
c a n b e e x e c u t e d b y DC L o r MCR wi tho u t
( Sp e c i a l c omm and s u s ed by t h e
d e s t ro y i ng a c u r r e n t l y e x e c u t i ng i ma g e .
M C R i nd i r e c t c omm a nd
f i l e p r o c e s s o r a r e n o t i n c l ud ed i n t h e t a b l e . )
Any o th e r c ommand e i th e r r e qu i r e s a n i m ag e i n o rd e r to
execute
( s uch
as
C O PY or
L I NK )
or d i r e c t l y a f f e c t s the c u r r en t l y e x e c u t i ng i m ag e
( s uch a s STO P ) .

2 0-1 1

INTERACT I VE AND BATCH JOBS
Ta b l e 2 0 - 2
Comma nd s Ha nd l ed b y C L I I n t e r n a l Pr o c ed u r e s
Command

De sc r i pt i o n

ALLOCATE
ASS IGN
C LO S E
C ONT INUE
DEA LLOCATE
DEA S S IGN
DEBUG
$DECK
DEF INE
DE POS IT
DELETE/ SYMBOL
$ E OD
EXAM I N E
EXI T

Al l oc a t e a d ev i c e
C r e a t e a l og i c a l name
C l o se a process pe rman ent f i l e
Re s um e i n t e r r upted i m ag e
Dea l l oc a te a d ev i c e
De l ete a l og i c a l name
Invoke the symbo l i c d eb ug g e r
Del im i t t h e beg i nn i ng o f a n i n put str eam
C r e a te a l og i c a l name
Mod i fy a memo ry l ocat i o n
De l e te a symbol d e f i n i t i o n
Del im i t t h e end o f an i n put s t r e am
E x am i n e a memo ry l o c a t i o n
Ex i t a c ommand proced u r e
Rundown an imag e a ft e r i nvo k i ng
t e rm i n a t i o n hand l e r s
Tr a n s f e r c o n tro l w i th i n a command
p r oced u r e
Co nd i t i o n a l command ex ec ut i o n
I n t e r a c t i v e l y a s s i g n a v a l ue to a symbol
De f i n e c o nd i t i o n a l ac t i o n
Open a pr o c e s s pe rmanent f i l e
Read a r ec o rd i n to a symbol

(D)
(D )
(D)
(D )
(D)
(D)

GOTO
IF
I N QU I R E
ON
O PEN
R EAD
Some S E T
SET
SET
SET
SET
SET

(D)
(D )

Commands
[ N O ] C ONTROL-Y
DEFAULT
[ N O ] ON
PROTEC T ION
UIC

(D)
(D)

De t e rm i n e C TRL/Y a c t i o n
De f i n e d e fa ul t d i r ec to ry s t r i ng
De t e rm i n e e r ro r proc e ss i ng
De f i n e d e f a u l t f i l e pro tec t i o n
Ch a ng e p r o ce ss U IC a n d d e fa ul t
d i r ec to ry s t r i ng
De t e rm i n e echo i ng of command
p r o c ed u r e c ommands

S E T [ NO ] VE R I FY
Some SHOW
SHOW
SHOW
SHOW
SHOW

SHOW SYMBOL
S HCM TIME
SHOW TRANS LAT I ON

S TOP
WAI T
WR I T E

(D)

Command s
DE FAULT
PROTEC T I ON
QUOTA
STATUS

(D)
(D)

Di spl a y d e fa ul t d i r ec to ry s t r i ng
Di spl a y d e fa ul t f i l e pro tec t i o n
Di spl ay c u r rent d i sk f i l e usag e
Di spl a y s ta tus o f cur rentl y e x ec ut i ng
i mag e
Di spl a y v a l ue o f s ymbol ( s )
Di spl a y c ur r ent t ime
Sho w t r an s l a t i o n of s i ng l e l og i c a l name
Rundown a n imag e bypa ss i ng
t e rm i n a t i o n hand l e r s
Wa i t fo r spec i f i ed i n te rval to e l a pse
Wr i te the v a l ue of a symbol to a f i l e

Th e s e c omma nd s a r e ava i l a b l e i n t h e DC L
b ut n o t i n the MCR c ommand i n t e r p r e t e r .

20. 3 . 3

c ommand

i n t e r pr e te r

I m ag e I n i t i a t i o n by DC L

I f o n e o f the o pt i o n s t h a t r eq u i r e s a n e x t e r n a l
i mag e wa s d e t e c ted ,
DC L
f i r s t pe r fo rms
some
c omma nd - s pec i f i c
s t e ps .
I t then ente r s a
c ommo n r o u t i n e to fo rma l l y a c t i v a t e a nd c a l l
the
1 m ag e .
Th e
s t e ps
tha t
i t t a k e s a r e n e a r l y i d e n t i c a l to the s teps pe r f o rmed by PR OCSTRT
t h a t a r e d e sc r i b ed i n C h a p t e r 1 7 .

2 0- 1 2

INTERACT IVE AND BATCH JOB S

Th e p r ev i o u s i m ag e ( i f any ) i s r und own by c a l l i ng SYS $ R UNDWN .
Th i s
c a l l r emo v e s any t r a c e s o f a p r ev i o u s l y e x e c u t i ng i m ag e
b e f o r e a n o t h e r i m ag e i s a c t i v a ted .
In
the
case
wh e r e
the
p r e v i o u s i m a g e t e rm i n a t ed n o rm a l l y , th i s c a l l i s unnec e s s a r y .
Ho we v e r , a CTR L/Y f o l l o we d b y a n e x t e r n a l
c ommand
bypa s s e s
t h e no rma l i m a g e t e r m i n a t i o n pa th , r e q u i r i ng th i s e x t r a s t e p
t o i n s u r e t h a t a pr ev i o u s i m ag e i s e l i m i n a t ed b e f o r e a no th e r
i s a c t i va ted .

Th e s upe r v i s o r m o d e t e r m i n a t i o n h a nd l e r tha t w i l l
a l l o w DC L
to
r eg a i n
control
at
i mag e ex i t i s d ec l a r ed .
Re c a l l f r om
Ch a p t e r 18 th a t an ex i t h a nd l e r m u s t b e r e d e c l a r e d a f te r e a c h
use .

The i m ag e i s a c t i v a t ed by c a l l i ng SYS $ I MGAC T ( Ch a p te r 1 8 ) .

Ac c e s s mod e i s r a i s ed to u s e r .

Th e c a l l f r ame c h a i n i s t e rm i n a t e d by c l e a r i ng F P .

An i n i t i a l c a l l f r ame i s c r e a ted
o n the
us e r
stac k .
Th e
add ress o f
the
c a tc h
a l l c o nd i t i on h a nd l e r i s pl a c ed i n to
t h i s f r ame a n d a l s o i n to t h e l a s t c h anc e e x c e p t i o n v e c t o r .

Th e a r g um e n t l i s t ( F i g u r e 2 0 - 4 ) th a t wi l l be
pa s s e d
to
the
i m ag e
( a nd to a n y i n te r v e n i ng p r o c ed u r e s s uc h a s SYS $ I MG S TA )
i s b u i l t o n th e u s e r s t a c k .

Address of Transfer Address Array
Address of C LI Utility Dispatcher
Address of Image Header
Add ress of I m a ge File Descriptor
Link Flags from Image Header
CLI Flags
( 0 from PROCSTRT)

Figure 2 0-4
8.

Arg um e n t L i s t Pa s s ed to an Imag e by PROC S TRT o r a C L I

Th e i m a g e i s c a l l e d a t t h e
f i r s t add r e s s
in
the
transfer
add ress
a r r a y d e s c r i b ed i n C h a p t e r 1 8 .
As men t i o n ed i n t h e
d i s c u s s i o n o f Imag e S t a r t up , t h i s wi l l u s ua l l y be t h e a d d r e s s
of
t h e d e b ug
bo o t s t r a p t h a t wi l l e s ta b l i s h t h e t r a c e b a c k
e x c e p t i o n h a nd l e r a n d m a p t h e d eb ug g e r i f r e q u e s t e d .

2 0-1 3

INTERAC T I VE AND BATC H JOBS
9.

20 . 3 . 4

Th e i n s t r uc t i o n fo l l o w i ng the c a l l to the i mag e i s a c a l l
to
S YS $ EX I T .
Un l i k e
the c h e c k m ad e in PR OC S TRT , the cod e pa th
t h r o ugh DC L m a k e s i t i r r e l ev a n t wh e th e r a n
imag e
t e rm i n a t e s
w i th a R E T o r a c a l l t o S YS $ E X I T .
Othe r r e a so n s , d e s c r i b ed
i n Append i x
E
of
the VAX- 1 1 Run- T i m e
L i b r a r y Re f e r en c e
Ma n ua l ,
s t i l l m a k e t h e R E T i n s t r uc t i o n t h e p r e f e r r ed m e th o d
o f i mag e t e rm i n a t i o n .

Imag e Te rm i na t i o n

Wh e n a n i m a g e i n a n i n t e r a c t i v e o r b a tc h
j ob
t e rm i n a t e s ,
the
Ex i t
s e rv 1 c e w i l l
e v e n t ua l l y c a l l the s upe r v i so r mod e t e rm i n a t i o n
s y s t em
h a nd l e r
e s t a b l i shed
by
DC L b e fo r e
the
i m ag e wa s c a l l ed .
Th i s
t e rm i n a t i o n h a nd l e r
pe r fo rms
s ev e r a l
c l e a n up s t eps b e f o r e pa s s i ng
c o n t r o l to the b eg i nn i ng o f t h e m a i n c omma nd
loop
to
a l l o w DC L to
p r o c e s s the n ex t c omma nd .
1.

An y f i l e s l e f t o pe n
by t h e
i mag e
SYS $ RMSRUNDWN f o r e a c h o p e n f i l e .

An y d a t a r e c o r d s i n the i nput s t r eam
( r ec o r d s
tha t d o n o t
beg i n w i th a d o l l a r s i g n fo r DC L o r a r i g h t a ng l e b r a c k e t fo r
MCR ) a r e d i s c a r d ed a nd a wa r n i ng m e s s ag e i s s ued .

Th e
i m ag e
tha t
j us t t e rm i n a t ed
is
r und own
SYS $ R UNDWN w i th an a r g um e n t of u s e r m od e .

F i n a l l y , c o n t r o l i s pa s s e d
to
the b eg i nn i ng
of
the ma i n
c ommand
l o o p so
tha t DC L c a n
read
a nd p r o c e s s the nex t
c ommand .
Th i s i s a c compl i s hed by
r e s to r i ng
the
s upe rv i s o r
s ta c k
po i n te r
to a
known
state
( w i t h the
add ress o f
DC L $ R E S TART o n t h e t o p o f the s t a c k ) and i s s u i ng a n RSB .

20 . 3 . 5

a re

c l o s ed

c a l l i ng

Abno rma l Imag e T e r m i n a t i o n

Wh e n a n i m ag e t e r m i n a t e s no rma l l y , i t i s r undown a s a
pa r t o f DC L ' s
t e rm i n a t i o n h a nd l e r
a nd c o n t r o l i s pa s s e d to DC L a t the s t a r t o f i t s
c ommand l o o p .
An i m ag e c a n a l s o b e i n te r r upted by t yp i ng a CTR L/Y o r
b y us i ng the C OB O L o r F ORTRAN p a u s e c a pa b i l i ty .
Fu r th e r ex e c u t i o n o f
the i m a g e d e pend s o n the s e q u e n c e o f c omm a nd s tha t e x e c u t e
wh i l e
the
i m ag e i s i n te r r upted .

2 0 . 3 . 5 . 1 CTRL/Y P r o c e s s i ng - Wh e n a C TRL/Y ( o r po s s i b l y a C TR L/C )
is
typed a t the t e r m i n a l , c o n t r o l i s p a s s e d by the te rm i n a l d r i v e r to the
AS T t h a t wa s e s t a b l i sh e d b y DC L a s a pa r t o f i t s i n i t i a l i z a t i o n .
Th e
f i rst
s t e p pe r fo rmed
by t h i s AST i s to r ed e c l a r e i t s e l f .
Th i s wi l l
c a u s e f u t u r e C TR L/Ys to be pa s s e d to the same AST .
The p r ev i o u s mod e
of
t h e PS L i s then c h e c ked .
I f the p r ev i o u s mode wa s s upe r v i so r , DC L
c h e c k s wh e th e r a S E T NOC ONTRO L Y c omma nd h a s b e en e x e c uted .
If
so ,
the
i n te r r up t
is
s i mpl y d i sm i s s ed .
I f n o t , DC L i s r e s to r ed to i t s
i n i t i a l s t a t e ( w i th no n e s t i ng o f
i nd i r e c t l ev e l s )
and
control
is
pa s s e d t o the beg i n n i ng o f t h e m a i n c ommand l o o p .

20-1 4

INTERACTIVE AND BATCH JOBS
If the p r ev i o us m o d e wa s u se r , t h e n an i m ag e wa s i n t e r r upted .
If
the
i n t e r r up t ed
i mag e
is
i n s t a l l ed
w i th e nh a n c ed p r i v i l eg e s , t h e n t h e
i ma g e i s r un d o wn , p r ev e n t i ng t h e u s e r f r om b e n e f i t t i ng f r om p r i v i l eg e s
t o wh i ch h e i s n o t e n t i t l ed .
A s i d e e ff e c t o f th i s pro tec t i o n check
p r e v e n t s i n te r r up t e d p r i v i l eg ed imag e s f r om b e i ng
c o n t i n ued
a ft e r
a
CTRL/Y .

2 0 . 3 . 5 . 2 The P a u s e Capab i l i ty - Th e VAX- 1 1 C OB O L a nd VAX- 1 1
F ORTRAN
l a ng uag e s p r ov i d e
t h e c apa b i l i ty to i n te r r upt a n i m ag e und e r p r og r am
c o n t ro l .
E i t h e r o f t h e Run-T i me L i b r a r y p r o c ed u r e s i mpl emen t i ng
th i s
f e a t u r e c o u l d a l so b e c a l l ed f r om a n y o th e r l ang uag e .
•

Th e C O B O L s t a t em e n t
STOP l i t e r a l
g e n e r a t e s a c a l l t o the Run-T i m e L i b r a r y p r o c ed u r e C OB $ PAUS E ,
wh i c h s e nd s
t h e m e s sag e " l i t e r a l " to SYS $ 0 UTPUT a nd p a s s e s
c o n t r o l t o t h e C L I a t t h e b eg i nn i ng o f i t s m a i n c omma nd l o o p .

Th e FORTRAN s t a t em e n t
PAUS E

[d i sp]

g e n e r a t e s a c a l l to the Run-T i m e L i b r a ry pr o c ed u r e FOR$ PAU S E ,
wh i c h s e nd s
t h e m e s sag e
" d i sp "
to
SYS $ 0 UTPUT a n d pa s s e s
c o n t r o l t o t h e C L I a t t h e b eg i nn i ng o f i t s m a i n c omm and l o o p .
If
the
" d i sp "
a rg um e n t
i s o m i t ted ,
FOR $ PAU S E s end s t h e
d e f a ul t m e s s a g e
F ORTRAN PAUS E
to S Y S $ 0 UTPUT .

2 0 . 3 . 5 . 3 Th e S t a te o f Inte r r upted Imag e s - I f a n o n p r i v i l eg ed
imag e
wa s
i n t e r r upted ,
t h e i mag e c o n t e x t i s s a v ed a nd c o n t r o l i s p a s s e d to
the b eg i nn i ng of t h e m a i n c omma nd l o o p t o a l l o w t h e
use r
to
e x ec u t e
c ommand s .
I f DC L c a n p e r fo rm t h e
r eque s t ed
action
i n te r n a l l y
( Ta b l e 2 0 - 2 ) , t h e n the i mag e c an po ten t i a l l y be c o n t i n u e d .
Howe ve r , a ny c omma nd t h a t r e qu i r e s a n e x t e r n a l i m ag e wi l l d e s t r o y t h e
c ontex t of
t h e i n t e r r upted i mag e .
In add i t ion , i f the use r ex e c u t e s
a n i nd i r ec t c omm and f i l e wh i l e a n i mag e i s i n t e r r up t e d , t h a t i mag e
is
d e s t r o ye d ,
even
tho ug h t h e c omm a n d s i n the i nd i r e c t c omma nd f i l e c an
b e pe r fo rm ed i n te r na l l y by DC L .
Fo u r c omma nd s t h a t the u s e r c a n ex e c u t e h a v e spec i a l i m po r ta n c e i f a n
i mag e h a s b e en
i n t e r r up t e d b y C TRL/Y .
Th e s e c ommand s a r e C ONT IN U E ,
D E B UG , E X I T , a nd S TO P .

2 0 -1 5

INTERAC T I VE AND BATCH JOBS

2 0 . 3 . 5 . 4 CONT INUE Command - I f a C ON T INUE c omma nd i s typed wh i l e a t
C ONTRO L/Y AST l ev e l
a nd
t h e p r ev i o u s mod e wa s
us e r , the AST i s
d i sm i s s e d a nd c on t r o l i s p a s s e d b a c k t o t h e i m a g e a t the
po i n t wh e r e
i t wa s i n t e r r upted .

2 0 . 3 . 5 . 5 DEBUG Command - As d e s c r i b ed i n Ch a pt e r 1 8 , a DE B UG c ommand
c a use s
DC L to g e n e r a t e
a
SS$ D E B UG s i g n a l th a t wi l l e v e n t ua l l y be
f i e l d ed b y t h e c o nd i t i o n h a nd l e r es t a b l i s h ed by Imag e
S t a r t up .
Th i s
h a nd l e r
wi l l
r e spo nd t o the S S $ D E B UG s i g n a l b y m a pp i ng the d eb ugg e r
to
it.
Th i s
( i f i t i s n o t a l r e a d y m a pped ) a nd -t r a n s f e r r i ng c o n t r o l
techn i que
a l l o ws t h e d eb ugg e r to b e u s e d , even wh e n the imag e wa s no t
l i nk ed w i t h the / D E B UG q u a l i f i e r .
( I n o rd e r fo r
th i s c a pa b i l i t y t o
wo r k ,
the
i mag e c a nno t b e
l i nk e d w i th t h e /NOTRAC EBAC K qua l i f i e r .
Th a t qua l i f i e r p r ev e n t s Imag e S t a r t u p f r om e x ec u t i ng , wh i c h m e a n s tha t
the
h a nd l e r
tha t
d yn am i c a l l y
m a ps
the d eb ug g e r n ev e r g e t s
e s t a b l i sh e d . )

20. 3 . 5. 6
E X I T Command - Th e
EXI T c omma n d c a u s e s
a n Ex i t
s ys tem
s e rv i c e
t o b e i s s u e d f r om u s e r mode .
Te r m i n a t i o n h a nd l e r s a r e c a l l ed
a nd the i m a g e i s r und o wn .

20 . 3 . 5. 7
STOP Command - Th e S T O P
c omma n d
pe r fo rm s
e s sen t i a l l y the
s am e c l e a n up o pe r a t i o n s tha t o cc u r f o r a no rma l l y t e rm i n a t i ng i m ag e .
Howe ve r , S TOP d o e s i t s o wn wo r k a nd d o e s n o t c a l l
SYS $ E X I T .
Th i s
me a n s t h a t use r m o d e t e rm i n a t i o n h and l e r s a r e n o t c a l l ed wh e n a n i mag e
t e rm i n a t e s wi th a C TR L/Y S TO P s e quenc e .
Th e STOP c omma nd p r o c e s so r f i r s t d e te rm i n e s wh e th e r
an
imag e o r a
proc ess
i s b e i ng
s t o pped .
( Th e v a r i o u s po s s i b l e STOP c omma nd s a r e
d e sc r i b ed i n the VAX/VMS C omma nd La ngu ag e U s e r ' s Gu i d e . ) I f
an
i mag e
i s b e i ng s to pped , a l l o pe n f i l e s a r e c l o s ed by c a l l i ng SYS $ RM S RUNDWN .
Th e i m a g e i t s e l f i s t h e n r und o wn ( by c a l l i ng
SYS $ R UNDWN ) .
Fi nal ly ,
c o n t r o l i s pa s s e d t o the b eg i nn i ng o f the m a i n c omma nd l o o p .
No t e t h a t
STOP p e r fo rm s
nea r l y i dent i c a l
o pe r a t i o n s
to
t h e DC L
t e rm i n a t i o n h a nd l e r ,
i nv o k e d a s a r e s u l t o f a c a l l to SYS $ E X I T o r a n
EXI T c omma nd .
Th e o n l y d i f f e r e n c e b e twe e n e i th e r
E X I T s e qu e n c e and
the S T O P c omma nd i s t h a t u s e r m o d e t e rm i n a t i o n h a nd l e r s a r e no t c a l l ed
f i rs t .
Th us
i n most c ases ,
the
STOP a nd
EXI T
c ommand s
are
i n t e r c h a ng e ab l e .
On e us e f u l a s pec t o f t h e STOP c ommand i s t ha t i t c a n
b e u s ed to e l i m i n a t e a n i m ag e t h a t c on t a i n s a
u s e r m o d e t e rm i na t i o n
h a nd l e r
tha t
is
p r ev e n t i ng
that
i mag e f r om compl e te l y g o i ng awa y ,
e i th e r i n t e n t i o n a l l y o r a s a r e s u l t o f a n e r r o r .

20-1 6

PART VI I

SYSTEM I N I T IALI ZAT I ON

a n t e ma r e e t t e r r a s e t q uo d t eg i t omn i a c a e l um
u n u s e r a t to to n a t u r a e v u l t u s i n o r b e ,
q uem d i x e r e Ch a o s
Me t amo r pho s e s
Ov i d

C HAPTER 2 1
BOOTS TRAP PROC EDURES

Be fo r e a VAX/VM S s y s t em c a n ope r a t e , s ome i n i t i a l i z a t i o n p r og r am s
(or
b oo t s t r a p p r og r ams ) m u s t e x e c u t e t o c o n f i g u r e t h e sys tem and r e a d th e
P a r t s o f the b o o t s t r a p o pe r a t i o n a r e
spec i f i c
e x e c u t i v e i n to m emo r y .
to
one
t ype
o f VAX C PU .
O th e r s a r e c ommo n a c r o s s a l l VAX f am i l y
membe r s .
Ta b l e 2 1 - 1 s umma r i z e s the
p r og r ams
th a t
e x e c u t e a nd
the
f i l es
tha t a r e
r e f e r e n c ed
in o rd e r to i n i t i a l i z e a VAX/VM S s y s t em .
Th i s c h a p t e r d e sc r i b e s a l l ph a s e s o f
t h e bo o t s t r a p o pe r a t i o n
tha t
o c c u r b e fo r e c o d e c o n t a i n ed i n the e x ec u t i v e imag e ( S YS . EXE ) ex ec u t e s .

21 . 1

PROC ESS OR-S PEC I F I C IN I T IAL I Z AT I ON

The i n i t i a l s t eps t h a t o c c u r i n the i n i t i a l i z a t i o n o f a VAX/VM S s y s t em
d e p e nd
on
the pa r t i c u l a r VAX p r o c e s s o r t h a t i s b e i ng u s ed .
The n e x t
s e c t i o n s b r i e f l y d e sc r i b e
the
p r o c e s s o r - s pe c i f i c
s t eps
tha t o c c u r
befo re
t h e p r ima r y b o o ts t r a p p r og r am VMB g a i n s c o n t r o l and b eg i n s
execut ion .
Th e mo s t o bv i o u s p r o c e s so r - s pe c i f i c i t em t h a t a f f e c t s
the boo t s t r a p
o pe r a t i o n
is
t h e c o nso l e co n f i g u r a t i o n .
An o v e rv i e w o f t h e c o n so l e
s ub s ys t em fo r a s p e c i f i c VAX- 1 1 f am i l y mem b e r c a n b e fo und i n the
VAX
Ha r d wa r e Ha n d bo o k .

21 . 1 . 1

VAX- 1 1 / 7 5 0 I n i t i a l Boo t s t r a p Ope r a t i o n

Th e c o n s o l e p r og r am on t h e VAX- 1 1 / 7 5 0
resides
in
r e a d - o n l y m emo r y
wi t h i n t h e C P U .
Wh en the C P U i s i n c o n so l e mod e , th i s p r og r am ( a n d
n o t h i ng e l s e , s uc h a s a u s e r p r og r am
or
VM S
i tsel f )
1s
e x e c u t i ng .
Wh e n a
VAX- 1 1 /7 5 0
s y s t em i s i n i t i a l i z e d , the c o n s o l e prog r am i s t h e
f i r s t in
a
se r i e s
of
p r og r ams
th a t e x e c u t e b e fo r e
the pr ima r y
Th e s e p r o g r ams i nc l ud e
boo ts t r a p p r og r am VM B e x e c u t e s .
1.

the c o n so l e s u b s y s t em , wh i c h i n i t i a l i z e s the C PU ,
locates
a
byte
b l o c k o f g o od m emo r y ,
a nd
pa s s e s c o n t r o l to a
d ev i c e - s p e c i f i c ROM p r og r am ,

a d e v i c e ROM , wh i c h r e a d s l og i c a l b l o c k n umb e r 0 ( LBN 0 ,
the
s o - c a l l ed
bo o t b l o c k )
f r om
the boo t s t r a p d ev i c e i n to t h e
f i r s t pag e o f t h e g o od memo r y b l o c k , a nd

the bo o t b l o c k p r o g r am , wh i c h r e ad s a f i l e f r om the b o o t s t r a p
d e v i c e i n to memo r y . Wh en a VM S s ys t em i s b e i ng boo t s t r a pp e d ,
th i s f i l e w i l l u s ua l l y be VM B , t h e pr ima r y b o o t s t r a p p r og r am .

64K

2 1-1

BOOTSTRAP PROC EDURES

A l i s t o f the p r og r ams t h a t e x e c u te d u r i ng th e
initial
pha s e o f i n i t i a l i za t i o n i s c o n ta i n e d i n T a b l e 2 1 - 1 .

C PU-d epend e n t

2 1 . 1 . 1 . 1 VAX- 1 1 / 7 5 0 Con so l e P r og r am - Th e c o n so l e
p r og r am
on
a
VAX- 1 1 /7 5 0 i s s to r ed i n r e a d - o n l y m em o r y w i th i n the C PU .
Th i s p r og r am
c a n i n i t i a t e a b oo t s t r a p s eq u e n c e fo r f i v e d i f f e r e n t r e a s o n s .
•
•
•
•

Th e s y s tem i s powe r ed o n a nd the po we r - o n s e l e c to r swi t c h
i n t h e b o o t s t r a p po s i t i o n .
Th e B ( Bo o t )
mod e .

c o mmand i s typed wh i l e t h e sys t em i s i n

A HA LT i n s t r uc t i o n i s e x e c u t ed
a nd
s w i t c h i s i n t h e boo t s t r a p po s i t i o n .

the

powe r - o n

c onso l e
s e l ec to r

Th e i n s t r uc t i o n
M T PR
i s e x e c u t ed .
Th e VM S b ug c h e c k r o ut i ne u s e s th i s mecha n i sm o n
all
C PU s
to
a u toma t i c a l l y r e boo t the sys tem a f t e r a f a t a l
s o f t wa r e c r a s h .
( Th i s a u toma t i c
r eb o o t c a pa b i l i ty c an b e
i nh i b i t ed b y c l e a r i ng t h e B UG R E B OOT SYS BOOT f l ag . )

•

An a t tempt t o
r e s ta r t
the
s ys t em
a f te r
a
po we r
fa i lure
r e c o ve r y d o e s n o t s uc c e ed , a nd t h e po we r - o n s e l e c to r s w i t c h
i s i n t h e r e s t a r t/bo o t s t r a p po s i t i o n .

No te tha t the i mp l em e n t a t i o n o f
the VAX- 1 1 / 7 5 0 p r e v e n t s
una t t e n d ed
( th e
l a s t th r e e o p t i o n s ) un l e s s t h e sys t em d ev i c e i s un i t 0
r esta r ts
o n the f i r s t c o n t r o l l e r o f a g i v e n type
s uc h
a s the
f i r s t MAS S B US
a d apte r .
Th e i mpo r ta n t s te p s t h a t a r e pe r f o rmed by t h e c o nso l e p r og ram i n c l ud e
•
•

•
•

l o c a t i ng 6 4 K b y t e s o f c o n t i g uo u s
e r r o r - f r e e pag e- a l i g n ed
memo r y to be u s ed b y l a t e r s tag e s o f the boo t s t r a p ,
l o ad i ng t h e f i r s t 1 2 8 m a p r eg i s t e r s i n the UN I B US a d a p t e r
to
add ress
t h i s b l oc k o f m emo r y , ( a s t ep n o t t a k e n wh e n us i ng
t h e c o n so l e b l o c k s to r ag e d ev i c e a s a boo t s t r a p d ev i c e ) ,
l o ad i ng the g e n e r a l r eg i s t e r s wi th p a r am e t e r s to be
l a t e r s t ag e s o f the b oo t s t r a p , a nd
pa s s i ng c o n t r o l to the d ev i c e ROM s e l ec ted by
d e v i c e s e l e c t o r swi tch .

the

u s ed

boo t s t r a p

ROM
p r og r am
2 1 . 1 . 1 . 2 Dev i c e - S p e c i f i c ROM P r og r am - Th e
d ev i c e
c o ns i s t s
o f two m a i n p i e c e s , a co n t r o l r o u t i n e a nd a d ev i c e - s pec i f i c
s ub r o u t i n e .
Th i s p r og r am s i m p l y r e ad s t h e b o o t b l o c k ( LBN 0 )
of
the
s e l e c t ed
d ev i c e
i n to
the
fi rst
pag e
of t h e g ood mem o r y b l o c k a nd
pa s s e s c o n t r o l to i t ( a t a n add r e s s 1 2 b y t e s pa s t the beg i n n i ng o f the
p r og r am ) .

2 1-2

Ta b l e 2 1 - 1
P r o g r am s a nd Fi l e s Used Du r i ng Bo o t s t r a p Se quenc e
( C PU - I nd epend e n t Bo o t s t r a p S e q u e n c e )
P r og ram Ex ec u t i ng
( pr oc e s s cont e x t )

Pu r po s e of Th i s Prog ram

Fi l e s

VM B . EXE ( N o t e 1 )
( s tand a l o n e prog r am)

P r i m a r y Bo o ts t r a p Prog ram

SYSBOOT. EXE

SYSBOOT . EXE ( C )
( s tand a l one prog r am)

S e c o nd a r y Boo t s t r a p Prog ram
co n f i g ur e s system
and reads exec u t i v e
i n to memo ry

Pa r am e t e r F i l es
Created by SYSGEN
SYS . EXE ( C )
TTDR IVER . EXE ( C )
SYSLOAx x x . EXE ( C )
yyDR I VE R . E X E ( C )

E xecut i v e

TTDR IVER . E X E ( C )
SYSLOAx x x . EXE ( C )
yyDR IVER . EXE ( C )

Loaded
Loaded
Loaded

Fi r s t P r o c e s s
S e l ec ted f o r Ex ec u t i o n

SYS I N I T . EXE

Image Spec i f i ed

SYS I N I T . EXE ( C )
( S YS I N I T p r o c e s s )

Co n t i nue I n i t i a l i za t i o n
i n P r o c e s s Co n t e x t

RMS.EXE (C)
[ S YSMSG ] S YSMSG . EXE
PAGEF I LE . SYS ( C )
SWAPF I L E . SYS ( C )
DUMPF I L E . SYS ( C )
Fl l z AC P . E X E ( C )
JOB C T L . EXE
ERRFMT. EXE
OPCOM. EXE
STARTU P . COM
LOGINOUT . EXE

LOGINOUT . EXE
( S TARTUP P r o c e s s )

I n i t i a l I m a g e tha t Ex ecutes
i n I n t e r a c t i v e Job

DC L . EXE
( No te 2 )

Mapped i n to P l Spa c e o f STARTUP Pr o c e s s
wi th Me r g e d Image Ac t i v a t i o n

I N S TA L L . EXE
( S TARTUP Proc e s s )

Ins t a l l Pr i v i l eg ed and
Sh a r eab l e Imag es

Al l Pr i v i l eg ed , Sh a r eab l e ,
and o the r wi se I n s ta l l ed
Images

Al l I n s t a l l ed Imag es a r e S e t up
a s Known Imag es

SYSGE N . EXE
( S TARTUP P r o c e s s )

Autoc o n f i g u r e I /O Dev i c e s ,
Load Dr i v e r s , a nd C r eate
I /O Data Ba se

Al l Dev i c e Dr i v e r s Loaded
as a Re s u l t o f
AUTOCONFIGURE A L L

Dr i v e r s for Al l Co n f i g ur ed Dev i c e s
a r e Loaded i n to Nonpaged Po o l

RMSSHAR E . EXE
( S TARTUP P r o c e s s )

Al l oc a t e B l o c k of Paged
Po o l fo r F i l e Sh a r i ng

none

SYS . EXE (Mod ul e IN IT )
( no p r o c e s s ye t )

(C)

SYS . EXE (Mod ul e SWAPPER)
( SWAPPER proc e s s )

(C)

Th e se

(1)

VMB must b e c o n t i g uo us beca use
o n the VAX- 1 1 /7 8 0 .

(2)

In i t i a l i za t i o n

Used

by Th i s Prog ram

U s e of

Opened a n d Read

( C)

(C)

Used

i s l oaded b y e i the r

i n to Memo ry

to Co n f i g u r e System

Opened and
Opened
Opened
Opened

Read

i n to Mem o r y

i n to Memory
i n to Memory
i n to Memory

Create

Pr o c e s s

Mapped a s Pag e ab l e S ys t e m Sec t i o n
Mapped a s Pag eab l e System Sec t i o n
Opened and In i t i a l i zed
Opened and In i t i a l i zed
Opened and In i t i a l i zed
Imag e that Ex ecutes i n DxcuACP Process
Image that Ex ec u t e s i n JOB CONTROL P r o c e s s
I m a g e Spec i f i ed to C r e a t e ERRFMT Proc e s s
Im a g e Spec i f i ed to C r e a t e OPCOM Proc e s s
SYS $ I N PUT f o r STARTUP Pr o c e s s
Im a g e Spec i f i ed to Cr e a t e STARTUP P r o c e s s

f i l es m ust be c o n t i g uo us becaus e they a r e l oaded b y t h e pr i m i t i v e AC P r o u t i n e s th a t a r e
it

Th i s Fi l e

pa r t

o f t h e e x ecut i v e

imag e .

the b o o t b l o c k prog ram o n the VAX- 1 1 / 7 5 0 o r the c o n so l e prog ram CONS O L . SYS

The autho r i za t i o n f i l e i s n o t used b y LOGINOUT h e r e beca use the STARTUP p r o c e s s i s c r ea ted wi t h a f l ag t ha t d i c t a t e s tha t
a utho r i za t i o n
sho u l d
be
s k i pped .
Th i s
is
done
to a l l o w t o ta l l y a utoma t i c i n i t.i a l i za t i o n and to e l i m i n a t e the need
fo r an i n i t i a l i za t i o n account in the autho r i za t i o n f i l e .
(continued o n ne xt page )

Ta b l e 2 1 - 1

( cont . )

P r o g r ams a nd Fi l e s Used Du r i ng Bo o t s t r a p S e qu e n c e
( Initial Bootstrap Programs for VAX-11/7 5 0 )
Al l

prog rams e x ec u t e

i n t h e VAX-1 1/7 5 0 C PU ,

The r e

i s no f r o n t e n d processo r pe r fo rm i ng

any o f t h e boo t s t r a p o pe r a t i o n s .

Prog r am Ex ec u t i ng

Wh e r e Prog ram

C onso l e Prog r am
( ex ec u t e s m i c rocod e )

Re a d-only m em o r y in
VAX-1 1 /7 5 0 C PU

Dev ic e-Spec i f i c
Prog ram i n ROM

Re a d-only memory in
a d d res s s pa c e o f
VAX-1 1 / 7 5 0 C PU

Boot B l o c k

Log i c a l B l o c k Number o f
System Dev i c e

Loc a te Pr i m a r y Bo o ts t r a p Prog ram
o n system dev i c e (or c o n so l e sto r ag e d ev i c e )
l og i c a l bl oc k number and pa ss c o n t r o l to i t

VM B . EXE

Spec i f i c Log i c a l Bl o c k
N u m b e r o n syst em dev i c e

( S ee f i r s t pa r t o f tabl e )

BOOT 58
( no t used d u r i ng
no rma l bo o t s t r a p )

Spec i f i c Lo g i c a l Bl o c k
Number o n c o n so l e b l o c k
sto rag e d e v i c e

U s e Ind i r ec t Command Fi l es o r
enhanced c o n so l e commands

P r og ram Ex ec u t i ng

Wh e r e Prog r am i s Lo c a ted

LS I - 1 1 ROM Bo o t s t r a p

ROM

Fl o ppy Bo o t Bl ock

Prog ram

Loc a ted

( In i t i a l

Pu r po se o f Th i s Prog r am
Locate b l o c k o f g ood mem o r y
D e t e r m i n e a c t i o n to be ta ken and pa s s
c o n t r o l to d ev i c e-spec i f i c prog r am

I/O

Load boot b l o c k ( LB N 0) o f
d e s i g nated d ev i c e i n to
memo ry and pa s s c o n t r o l to

Bo o t s t r a p Prog rams for

VAX-1 1 /7 8 0 )

CPU Used by Prog r am

P u r po s e o f Th i s Prog r am

LS I - 1 1

Read f l oppy boot b l o c k i n to
memo ry and execute code
c o nta i n ed the r e

Log i c a l B l o c k 0 o n
Co n so l e Fl oppy

LS I-1 1

L o c a t e CONSOL . S YS , r ead i t i n to
mem o r y , and pa ss c o n t r o l to i t

CONS O L . SYS

Somewh e r e o n Co n so l e Fl o ppy ,
an RT- 1 1 d i r ec to ry
s t r uc t u r ed d ev i c e

LS I - l l

Put VAX- 1 1 / 7 8 0 i n to known s t a t e ,
l oad g e n e r a l r eg i s t e r s , a nd
i nvoke mem o r y s i z i ng prog r am

Good Memo r y Lo c a t e r

R OM i n f i r s t mem o r y
c o nt r o l l e r o n SB I

VAX- l l / 7 8 0

L o c a te
error

LS I - 1 1

L o a d V M B i n to VAX mem o r y a nd
t r a n s f e r c o n t r o l to i t

VAX- 1 1 /7 8 0

( Se e

Prog ram

LS I - 1 1

CONSOL . SYS
( a f t e r wa i t i ng fo r
memo r y ROM p rog ram
to compl ete )

VMB . EXE

Conso l e Fl o ppy

I /0 Spa c e

64K byte b l o c k o f
f r ee mem o r y

f i r st pa r t o f t a b l e )

B OOTSTRAP PROCEDURES

2 1 . 1 . 1 . 3 Bo o t B l o c k P r og r am - Th i s boo t b l o c k p r og r am
has
a
s i ng l e
p u r po s e ,
wh i c h d e pe nd s o n the t ype o f b o o t s t r a p d ev i c e spec i f i ed to
the c o n so l e p r og r am .
Wh e n a po t e n t i a l sys t em d ev i c e is spec i f i ed , the
boo t b l o c k p r og r am l o a d s t h e p r i m a r y b o o t s t r a p p r og r am VMB i n to m emo r y
a nd pa s s e s c o n t r o l t o i t .
Wh e n t h e c o n s o l e b l o c k s to r ag e d ev i c e
is
s e l e c t ed ,
the b o o t b l o c k p r og r am c a n p a s s c o n t r o l to a n e nh a n c ed
c omm and p r o c e sso r c a l l ed B O OT 5 8 .
Th e b o o t b l o c k
p r og r am d o e s no t
conta i n
a ny
I / 0 s uppo r t .
I t u s e s the d r i v e r s ub r o u t i n e c o n t a i n e d i n
the d ev i c e ROM p r og r am .
Th e r e a r e t h r e e l o ng wo r d s o f h e a d e r i n fo rm a t i o n b e f o r e the bod y o f the
boo t b l o c k p r og r am .
Th e s e l o ng wo r d s c o n t a i n
1.

t h e s i ze o f the p r i m a r y b o o t s t r a p p r og r am ,

t h e s t a r t i ng l og i c a l b l o c k n umbe r o f
p r og r am , and

a r e l a t i v e o f f s e t i n to the b l o c k of g o od
p r og r am i s t o b e l o a d ed .

the

pr ima ry
memo r y

boo t s t ra p
wh e r e

th i s

Th e s e l o ng wo r d s a r e l o ad ed b y t h e p r og r am WR I T EB OOT wh en
the
boo t
b l oc k
1 s wr i t t e n .
No t i c e
tha t
the b o o t b l o c k h a s the LBN o f the
p r ima r y b o o t s t r a p p r og ram h a rd c od ed i n to the b l o c k .
If the
po s i t i o n
o f t h e p r ima r y b o o t s t r a p p r og r am o n t h e vo l ume c h a ng e s , WR I TE B OOT m us t
b e e x e c u t ed t o r ewr i t e the b o o t b l o c k wi th n e w i n f o rm a t i o n .
No te tha t the l o c a t i o n o f VM B by t h e VAX- 1 1 /7 5 0 bo o t b l o c k p r o g r am
is
the
o n l y s i t ua t i o n
in all
o f VAX/VM S wh e r e a f i l e i s l o c a t e d by a
l og i c a l b l o c k n um b e r c od ed i n to
a no t h e r
p r og r am .
Th us ,
VMB o n a
VAX- 1 1 / 7 5 0
s y s t em d i s k
is
t h e o n l y f i l e tha t i s n o t f r e e to move
wi tho u t some e x t e r n a l i n t e r v e n t i o n
( r unn i ng WR I T E B OOT )
to
prese rve
s ys tem i n teg r i t y .

2 1 . 1 . 1 . 4 BOOT 5 8 - Th e c o n s o l e b l o c k s to r ag e d ev i c e o n the VAX- 1 1 /7 5 0
( T U 5 8 c a r t r id g e )
i s not
used
d u r i ng a no rma l boo t s t r a p o pe r a t i o n .
( Th i s i s i n c o n t r a s t to the VAX- 1 1 /7 8 0 boo t s t r a p , wh i c h a l wa ys
r eads
VMB a nd a c omm a nd f i l e f r om t h e c o nso l e f l o ppy . ) Howe v e r , t h e r e i s a n
a l t e r n a t e b o o t s t r a p pa th th a t u s e s t h e TU 5 8 tha t p r o v i d e s
•

i nd i r e c t c omma nd f i l e c a pa b i l i ty ,

•

a n e n h a n c ed c o nso l e c ommand l a ng u ag e , a n d

•

t h e a b i l i t y to boo t s t r a p a s ys t em i n t h e e v e n t
b l o c k b e c ome s c o r r upted .

tha t

boo t

A s t and a l o n e p r og r am c a l l ed BOOT 5 8
i s a n e nha n c ed
c o n s o l e c o mmand
processo r
l o a d ed
f r om the T U 5 8 t h a t p r ov i d e s the s e f e a t u r e s .
BOOT 5 8
i s l o ad ed b y s e l e c t i ng t h e c o n s o l e b l o c k s to r ag e d ev i c e ( DDA O : ) a s the
boo t s t r a p d ev i c e , e i th e r b y the d ev i c e s e l e c t o r swi tch or wi th a
> > > B OOT DDA O :
c omma nd .
Th e b o o t b l o c k o n the T U 5 8 c o n t a i n s a p r og r am j us t l i k e
the
boo t b l o c k p r og r am o n a s y s t em d ev i c e .
Th i s prog r am c o n t a i n s the LBN
o f BOOT 5 8 ( b e c a u s e i t wa s put t h e r e b y WR I TE B OOT ) .
On q e BOOT 5 8 p r i n t s
i t s p r om p t ,
c omma nd s
o r i nd i r e c t c omm a nd f i l e s p e c i f i c a t i o n s c a n b e
e n t e r ed .
2 1-5

BOOTSTRAP PROC EDURES

21. 1 . 2

VAX- 1 1 /7 8 0 I n i t i a l Boo t s t r a p Ope r a t i o n

Th e c o n so l e
s ub s ys t em o n t h e
VAX- 1 1 /7 8 0 c o ns i s t s
of
a
s e pa r a t e
processo r ,
a n LS I - 1 1
wi th
i t s o wn m a s s s to r ag e d e v i c e ( RX O l f l o ppy
d i s k) and
t e rm i n a l .
Th e
fac t
th a t
the
c onso l e
s ub s ys t em on
a
VAX- 1 1 /7 8 0
i nc l ud e s i t s o wn p r o c e s s o r i m p l i e s tha t the c o n so l e sys t em
c a n pe r f o rm c e r t a i n ( b u t no t a l l ) o pe r a t i o n s wh i l e the VAX- 1 1 /7 8 0 C PU
i s pe r f o rm i ng i t s o wn o pe r a t i o n s .
Th e i n i t i a l boo t s t r a p p r og r am s ( Ta b l e 2 1 - 1 ) t h a t e x e c u t e i n o r d e r
to
i n i t i a l i ze
a VAX/VM S s ys tem o n a VAX- 1 1 /7 8 0
a r e PD P- 1 1 p r og r ams
e x e c u t i ng i n the LS I - 1 1 .
Th i s m e a ns th a t the s e p r og r am s
( C ON S O L . S YS
a nd
the b o o t b l oc k p r og r a m ) e x ec u t e PD P- 1 1 i n s t r uc t i o n s a s o ppo s e d to
VAX- 1 1 i n s t r uc t i o n s ( wh i c h a r e e x e c u t ed by t h e r e s t o f VM S a n d a l so by
t h e VAX- 1 1 / 7 5 0 boo t s t r a p p r og r am s ) .
1.

Th e f i r s t p r og r am th a t e x e c u t e s i n the LS I - 1 1 i s a b o o t s t r a p
p r o g r am
loca ted
in
r e a d - o n l y memo r y
( ROM )
th a t c a u s e s a
p r og r am l o c a te d o n l og i c a l b l o c k n um b e r z e r o o f
the
c onso l e
f l o ppy ( s e c to r s 1 , 3 , 5 , a n d 7 ) t o b e l o a d ed i n to LS I m emo r y .

Th i s p r og r am i s a c o py o f t h e boo t s t r a p p r og r am u s e d b y the
RT- 1 1
o p e r a t i ng
s ys t em .
Th e
RT- 1 1
boo t s t ra p ,
wh i c h
u n d e r s t a n d s t h e RT- 1 1 f i l e sys tem , l o o k s f o r a spec i f i c
file
( th e mo n i t o r ) , l o a d s i t i n to memo r y , a nd t r a n s f e r s c o n t r o l to
it.
( Th e RT- 1 1 d i r e c to r y s t r uc t u r e a nd boo t s t r a p p r og r am a r e
d e sc r i b e d i n t h e RT- 1 1 S o f twa r e S u pp o r t Ma n ua l . )
Th e boo t s t r a p p r og r am t h a t i s fo und o n t h e VAX- 1 1 /7 8 0 c o n so l e
f l o ppy d i s k e t t e l o o k s f o r a p r og r am c a l l ed C ONSOL . SYS .

Th e c o n s o l e p r o g r am l o a d s the f i l e WC Sxxx . PAT f r om the f l o ppy
d i s k e tte
i n to
the VAX- 1 1 /7 8 0 d i ag no s t i c c o n t r o l s to r e a nd
t h e n pr i n t s i t s pr ompt
>>>
o n the c o n so l e t e rm i n a l .
If
the r e
is a
v e r s i o n m i sm a tch
b e twe e n
t h e WC S a nd
e i th e r
the PC S o r the F P LA , a n e r r o r
m e s s a g e i s d i s p l a ye d o n the c o n s o l e t e rm i n a l .

Th e r e a r e many c omma n d s tha t
the c on s o l e c ommand
l a ng uag e
u n d e r s t a nd s .
Al l
t h r e e c ommand s tha t c a us e a VM S s ys t em to
be boo t s t r a pp e d ex e c u t e c ommand f i l e s l o c a t e d o n the
conso l e
f l o ppy .
Th e c o mm a n d s a nd th e i r a s s o c i a t e d c ommand f i l e s a r e
Command

Command F i l e

BOOT
B OO T d e v
@ f i l e spec

DE FBOO . CMD
d evBOO . CMD
f i l e s pe c

Th e s e c omma n d
f i les
i d e n t i f y t h e s y s t e m d i s k a nd
o th e r
c h a r a c t e r i s t i c s o f t h e b o o t s t r a p o pe r a t i o n by l o ad i ng g e n e r a l
r eg i s t e r s R O
th r o ug h
R 5 wi th pa r ame t e r s
tha t w i l l
be
i n te r p r e t e d by the p r i m a r y b o o t s t r a p p r og r am VMB .

2 1-6

BOOTSTRAP PROC EDURES

Th e y a l s o c o n t a i n the f o l l o w i ng command s :
S TART 2 0 0 0 3 0 0 0
WA I T
Th e s e two c o mmand s c a u s e
a
p r og r am l o c a ted
in
r e ad - o n l y
m emo r y
i n t h e f i r s t memo r y c o n t r o l l e r o n t h e S B I to e x e c u t e .
Th e c o mmand f i l e wa i t s un t i l the m emo ry ROM p r og r am compl e t e s
( Th e memo r y R OM p r og r am
b e fo r e
e x e c u t i ng
i t s n ex t c ommand .
s i g n a l s t h e c o n so l e p r og r am th a t i t i s d o ne b y wr i t i ng
the
" s o f twa r e d o n e "
s ignal
i n to
one
o f the c o n s o l e r eg i s t e r s
w i th a n
MTPR
i n s t r uc t i o n .
Th e p r o g r am i n the m em o r y c o n t r o l l e r ROM pe r f o rm s a pr im i t i v e
memo r y s i z i ng
o pe r a t i o n i n a n e f fo r t t o l o c a t e 6 4 K byt e s o f
e r r o r - f r e e c o n t i g uo u s pag e - a l i g n ed phys i c a l memo r y t h a t c an
b e u s e d by t h e r e m a i n i ng boo t s t r a p prog r am s .
Th e o u t p u t o f th i s p r og r am i s
an
add r ess
200
( hex )
b yt e s
b e yo nd t h e b e g i n n i ng o f t h e f i r s t g o od pag e .
Th i s a d d r e s s i s
l o a d e d i n to S P .
( I n a t yp i c a l s ys t em , o n e wi th n o e r r o r s
in
t h e f i r s t 6 4 K b y t e s , the c o n t e n t s o f S P a r e 2 0 0 . )

Th e n e x t th r e e c o mma n d s
EXAM I N E S P
LOAD VMB . EXE / S TART : @
S TART @
c a u s e t h e pr i m a r y b o o t s t r a p p r og r am VMB to be l o ad ed f rom the
f l o ppy d i s k
i n to
the g o od
6 4 K byte b l o c k o f VAX memo r y ,
l e a v i ng the f i r s t pag e f r e e .
Th i s pag e wi l l c o n t a i n a d a ta
s t r uc t u r e c a l l ed a r e s ta r t pa r am e t e r b l o c k ( R P B ) th a t i s u s e d
b y bo th VMB a nd b y the r e s t a r t r o u t i n e s i n
the
event o f a
powe r f a i l
or
o th e r
s ys t em
fa i l ure .
The
S TART c ommand
t r a n s f e r s c o n t r o l to VMB at i t s f i r s t l o c a t i o n .

21 . 2

PRIMARY BOOTSTRAP PROGRAM

Th e f i r s t p r og r am tha t i s c ommo n to a l l VM S
s ys tem s ,
i nd e pe nd en t o f
CPU
t ype ,
i s t h e p r i m a r y b o o t s t r a p p r og r am VMB .
Th e o n l y d i f fe r e nc e
b e twe e n the i n i t i a t i o n o f
VMB o n a
VAX- 1 1 /7 5 0 s ys t em and o n a
VAX- 1 1 /7 8 0
s ys tem
i s t h e so u r c e o f t h e p r og r am ( sys tem d i s k o n a 7 5 0
s ys t em v e r s u s the c o n s o l e f l oppy o n a 7 8 0 s ys t em ) and the l o c a t i o n o f
t h e p r og r am th a t pa s s e s c o n t r o l t o VMB ( bo o t b l o c k VAX- 1 1 p r og r am o n a
VMB p e r fo rms
two
7 5 0 v e r s u s t h e c o n s o l e PDP- 1 1 p r og r am o n a
780) .
ma j o r s t e p s .
•
•

I t d e t e rm i n e s t h e amo u n t o f phys i c a l memo r y o n the sys tem and
the p r e s enc e of o th e r e x t e r n a l ad a p t e r s .
I t l o c a t e s t h e s e c ond a r y b o o t s t r a p p r o g r am ,
memo r y , a n d t r a n s f e r s c o n t r o l to i t .

2 1-7

l o ad s

i n to

BOOTSTRAP PROC EDURES
21 . 2 . 1

Mo t i v a t i o n f o r Two Boo t s t r a p P r og r am s

VMB a n d the s e c o n d a r y boo ts t r a p p r og r am SYSBOOT a r e c o n c e pt u a l l y o n e
p r og r am .
Th e VAX- 1 1 /7 8 0
i n i t i a l i za t io n
( i n i t i a l l y i mpl em en ted f o r
Ve r s i o n 1 . 0 o f VM S ) r e q u i r ed tha t t h e i n i t i a l boo t s t r a p p r og r am r e s i d e
on
the c o n s o l e f l o ppy .
Ra t h e r t h a n i m po s e a r t i f i c i a l r e s t r i c t i o n s o n
the s i z e o f the b oo t s t r a p p r og r am , i t wa s d i v i d ed i n to two p i e c e s :
•
•

a p r ima r y p i e c e , wh i c h r e s i d e s o n t h e f l o ppy d i s k a nd
wh o s e
o n l y r e a l p u r po s e i s to l o c a t e the sec o nd a r y p i e c e , a n d
a s e c o nd a r y p i e c e tha t r e s i d e s o n the s ys t em
real
l im i ts on
i ts
s i ze )
th a t pe r f o rms
boo t s t r a p o pe r a t i o n .

d i sk
( w i th n o
the b u l k o f t h e

On c e th i s d i v i s i o n wa s a c h i e v ed , VM B b e c am e a mo r e f l ex i b l e to o l
th a t
c o u l d be
u s ed
t o l o ad
p r og r am s o th e r than t h e s e c o nd a r y boo t s t r a p
p r og r am SYSB OOT .
I n o rd e r t o p r e s e r v e th i s f l e x i b i l i t y a nd m a i n t a i n
a s m u c h C P U i n d e pend e n c e a s po s s i b l e
in
the l a t e r s t ag e s o f the
bo o t s t r a p , t h e d i v i s i o n of the bo o t s t r a p i n to
p r i m a r y a nd
s e c o nd a r y
p i e c e s wa s p r e s e r v ed a nd e nh a n c ed f o r Ve r s i o n 2 . 0 o f VAX/VM S .
VMB t h us b e c o m e s a g en e r a l p u r po s e boo t s t r a p p r og r am tha t c a n be
used
for
seve r a l
o p t i o n s o the r than i n i t i a l i z i ng a VM S s ys t em .
Th e r e a r e
th r e e o pt i o n s c u r r e n t l y a v a i l a b l e
i n add i t ion
to
i n i t i a l i z i ng
a
VAX/VM S s y s t em by l o ad i ng S YS B OOT .
e
•

Th e d i a g no s t i c
s upe r v i so r
l o a d ed i n p l a c e o f SYSBOOT .

[ S YSMA I NT ] D I AGBOOT . E XE

c an

VMB c a n be d i r e c ted to so l i c i t f o r the n a m e o f a n y s t a nd a l o n e
p r o g r am
to be l o ad ed i n to VAX memo r y .
Th i s p r og r am m i g h t b e
a
s t a nd a l o n e d i ag no s t i c
p r og r am ,
an al ternate
s e c o nd a r y
boo t s t r a p , o r e v e n a n o th e r o pe r a t i ng s ys t em .
Th e f i l e s ys tem
r o u t i n e s a nd c o n t r o l t r an s f e r mech a n i sm u s ed
by VMB p l a c e
some r e s t r i c t i o n s o n th i s f i l e .
Th e vo l ume ( th e sys t e m d i s k ) c o n ta i n i ng the f i l e tha t VMB
wi l l l o a d m u s t b e a F i l e s - 1 1 v o l um e ( S t r uc t u r e Lev e l 1 o r
2)
•

Th e f i l e c o n t a i n i ng t h i s p r og r am mus t b e co n t i g uo us .
I t s t r a n s f e r a d d r e s s m u s t be the f i r s t
locat ion
i n the
( I f t h e f i l e i s l i n ked a s a sys t e m i m a g e wi th a
p r o g r am .
base add r e s s o f z e r o , i ts t r an s f e r
a d d r e s s mus t b e a t
locat ion zero . )
Th e c o d e i n the p r og r am m u s t b e po s i t i o n i nd epend e n t .
•

VMB c a n l o ad the c o n t e n t s
of
a b o o t s t r a p b l oc k
f r om the
sys t em d i s k a nd e x e c u t e the p r og r am t h a t i t f i nd s th e r e .
In
g e n e r a l , t h i s bo o t b l o c k i s l og i c a l b l o c k n umbe r z e r o o n t h e
vo l ume .
Th e
VAX- 1 1 /7 8 0
boo t s t r a p s e q u e n c e a l l o ws
an
a l t e r n a t e bo o t b l o c k n um b e r to b e p a s s e d t o VMB i n R 4 .
Pa s s i ng co n t r o l to a boo t b l o c k p r og r am i s t h e
feature
tha t
m a k e s VMB a n e x t r em e l y f l ex i b l e to o l .
One po s s i b l e us e fo r a
boo t s t r a p p r og r am i s s uppo r t f o r a
file
s ys t em o th e r
than
F i l e s- 1 1 .

2 1-8

BOOTSTRAP PROCEDURES

Th e bo o t b l o c k o p t i o n i s o n l y u s e f u l on
a
VAX- 1 1 /7 8 0 .
Th e
VAX- 1 1 /7 5 0 b o o t s t r a p s e q ue n c e
a l l o ws c o n t r o l to b e pa s s ed
d i r e c t l y f r om t h e c o n so l e prog r am to
a boo t block
p r og r am
wi thout
us i ng
VMB a t a l l .
Th a t i s , i f a s p e c i a l bo o t s t r a p
t h r o ug h a
b o o t b l o c k p r og r a m wa s
r e q u i r ed ,
t h e no rma l
VAX- 1 1 /7 5 0 s e qu e n c e c o u l d be u s ed b u t the s p e c i a l VAX- 1 1 /7 8 0
o pt i o n wo u l d b e r eq u i r ed .
I f none o f these o p t i o n s i s
s e l e c t ed
by s e t t i ng
t h e c o r r e s po nd i ng
f l ag s
i n R5 ,
VM B e n t e r s
i t s d e f a u l t p a th ,
wh i c h l o ad s the VM S
s e c o nd a r y b o o t s t r a p p r o g r am S Y S B O O T i n to mem o r y a nd t r a n s f e r s c o n t r o l
to i t .

21. 2.2

Ope r a t i o n o f VMB

VMB d e t e rm i n e s the t ype of b o o t s t r a p tha t i s b e i ng pe r fo rmed , a nd
the
i d e n t i ty o f
the s ys t em d i s k , b y the c o n t e n t s o f r eg i s t e r s R O t h r o ug h
R5 .
T a b l e 2 1 - 2 s umma r i ze s t h e i n p u t pa r am e t e r s
tha t a re
pa s s e d
to
VMB .
Th e s e
pa r am e t e r s a r e s a v ed by VM B i n a d a t a s t r uc t u r e c a l l ed a
Re s t a r t Pa r am e t e r B l o c k ( Ta b l e 2 1 - 3 ) f o r u s e by l a t e r p r o g r am s i n
the
b o o t s t r a p s e quenc e .
1.

The f i r s t s te p th a t VMB t a k e s i s to s e t up a
Sys t em Co n t r o l
B l o c k wi t h a l l
i n t e r r up t a nd e x c e pt i o n v e c to r s e x c e p t TB I T
a nd B PT e x c e p t i o n s po i n t i ng to a s i ng l e s e r v i c e r o u t i n e .
Th e
v e c to r s
fo r
TB I T a nd
B PT e x c e p t i o n s a r e l o ad ed w i th the
ad d r e s s e s o f e x c e p t i o n s e r v i c e r o u t i n e s in XDE LTA , l i n k ed
as
a pa r t o f t h e VMB i m ag e .
F i g u r e 2 1 - 1 i l l u s t r a t e s t h e l a yo ut o f
VMB h a s s e t up i t s S C B .

phys i c a l

m emo r y

o nc e

VMB
then
r ea d s
the
p r o c e s so r
I D r eg i s t e r
( PR $ S I D )
to
d e t e rm i n e
the
C PU t ype .
VMB uses the C P U type as th e b a s i s
o f d e c i s i o n s a b o u t wh i c h p i ec e o f C PU-d e pe nd e n t c o d e
to
execute .
A s im i l a r
s t e p i s p e r fo rmed l a t e r by SYS B OOT f o r
t h e u s e o f b o th SYSB OOT a nd the e x e c ut i v e .

I f t h e b o o t s t r a p b r e a k po i n t f l ag
( RPB $V B OOB PT ,
R5< 5 > )
is
set ,
VM B e x e c u t e s a B PT i n s t r uc t i o n , wh i ch t r a n s f e r s c o n t r o l
to
XDE LTA ,
l i nked
as a
pa r t o f t h e VMB
i m ag e .
Th i s
b r e a k po i n t i s u s e f u l i n l oc a l i z i ng h a r d wa r e p r o b l ems t h a t a r e
p r e v e n t i ng a s y s tem f r om b e i ng s t a r ted .

Th e i n put pa r am e t e r s to
VMB a r e
Pa r ame t e r B l o c k ( Ta b l e 2 1 - 3 ) .

A b i tm a p i s s e t up th a t d e sc r i b e s a l l ph ys i c a l memo r y .
Th i s
m a p i n c l ud e s a b i t tha t i s s e t fo r eve r y phys i c a l memo r y pag e
i n t h e s y s tem t h a t i s f r e e f r om
e r ro r s .
Th e
r o ut i ne
that
t e s ts
fo r memo r y e r ro r s i s C P U s pec i f i c .
A s id e e ffect of
the
C PU - s p e c i f i c memo r y t e s t i ng
s ub r o u t i ne
causes
all
e x t e r na l
ad a p te r s t o b e i d en t i f i ed .
Th e i r c o d e s a r e s to r ed
i n t h e 1 6 -byte
a r r ay
in
the
RPB t h a t b eg i n s a t o f f s e t
R PB $ 8 C ONFREG .

Th e bus a d a pt e r f o r t h e b oo t s t r a p d ev i c e i s i n i t i a l i z e d
C PU-spec i f i c f a s h i o n ) .

2 1 -9

l o ad ed

i n to

the

Re s t a r t

( in a

BOOTSTRAP PROC EDURES
Ta b l e 2 1 - 2
Reg i s te r In put to VMB ( P r i m a r y Bo o t s t r a p Prog r am )
( Reg i s t e r Co n t e n t s )
Co n te n t s

Reg i st e r

boo tstr a p d ev i c e type c o d e

< 3 1 : 1 6 > typ e - s pec i f i c i n fo rm a t i o n
MASSBUS : MBZ
UN IBUS :
o pt i o n a l v e c to r add re s s
0 => use d e fa ul t v ec to r
<1 5: 8>

MBZ

<7 : 0>

boo ts t r a p d ev i c e type c od e
0
1
2
3-6 3
64

MASSB US d ev i c e ( RM 0 3/S , RP 0 4 / 5 /6 , RM 8 0 )
RK 0 6/7
R L 0 1 /2
R e s e rved fo r UN IB US d ev i c e s
C o n so l e b l o c k s to rag e d ev i c e

boo ts t r a p d ev i c e ' s bus a d d r ess

1 1/7 8 0

< 3 1 : 4>
< 3 : 0>

MBZ
T R n um b e r o f a d a pt e r

1 1/7 5 0

< 3 1 : 24> MBZ
< 2 3 : 0>
a dd r e ss o f the I /O pag e fo r the
b o o t d ev i c e ' s UN I B US

boo t s t r a p d ev i c e c ont r o l l e r

i n fo rm a t i o n

UN I B US :

<3 1 : 1 8 > MBZ
< 1 7 : 0>
UN I B US a d d ress o f the d ev i c e ' s C SR

MASSBUS :

<3 1 : 4>
< 3 : 0>

MBZ
ad a p t e r ' s c o n t r o l l e r / fo rm a t te r n umber

bo o t d ev i c e un i t n um b e r

l og i c a l b l oc k n umber o f b o o t b l o c k

s o ftwa r e boo t c o n t r o l

( VAX-1 1 /7 8 0 o n l y )

f l ag s

Th e ha r d wa r e o r the C ONS OLE p rog r am se t s up the n ex t 3
r eg i st e r s
a fter
a
s ys tem c ra sh o r po we r f a i l ur e .
Th e se r eg i st e r s a r e no t
used by VM B .
RlO
Rll
AP

h a l t PC
h a l t PS L
h a l t c od e

The memo ry ROM prog r am r e t u r n s i n fo rma t i o n abo ut a b l o c k o f
m em o r y in S P .
SP

<ba se-add r e s s

g ood

A X 2 0 0 > o f 6 4Kb o f g ood m emo r y

{ cont inued o n next page )

2 1-1 0

BOOTSTRAP PROC EDURES

Ta b l e 2 1 -2

( co nt . )

Reg i s t e r I n pu t t o VMB ( P r i m a r y Bo o t s t r a p P r o g r am )
( Bo o t s t r a p Co n t r o l F l ag s i n R S }
Bi t

Po s i t i o n

Mean i ng

RPB$V_CONV

Conve r sa t i o nal boo t .
At v a r i o us po in t s in the
system
boo t
p r o c ed ur e ,
the boo t s t r a p cod e sol i c i ts pa r a m e te r s a nd othe r
i nput f rom the c o nso l e term inal .

RPB $V_DEBUG

Debug..
XDELTA
s ys tem .

RPB $V_I N IB PT

In i t i a l b r ea kpo i n t .
BPT
i n s t r uc t ion
in
mapping .

If th i s f l ag i s s e t ,
VMS
d ebug g e r
i n to the system

maps
the
cod e · fo r
the
page tabl e s of the r un n i ng

RPB$V DEBUG

i s se t ,

VM S

e x ec ut e s

modul e IN I T immed i a tel y a f t e r

enabl i ng

RPB $V_B B LOCK

Second a r y boot from boot b loc k .
Second a r y
b oo t s t r a p
s i ng l e 5 1 2 -byte b l oc k , whose LBN i s spec i f i ed in R 4 .

RPB $V_D IAG

Di agnost i c
boot .
Second a r y
[ S YSMA INT ] D IAGBOOT . EXE .

RPB $V_B OOBPT

Bootstrap
b r ea kpo i n t .
Stops
the
pr i m a r y
and
second a r y
boo t s t r aps
wi th
b r ea kpo i n t
i n s t r uc t i o n s
b e fo r e
te st i ng
memo r y .

RPB $V_HEADER

Image head e r .
Ta k e s t h e t r a n s f e r a d d r e s s o f
the
second a r y
boots t r a p
i mag e
f rom
that
file ' s
imag e
head e r .
If
RPB$V HEADER i s n o t s e t , t r an s f e r s control to the f i r s t byte
of the second a r y boot f i l e .

RPB $V_NOTEST

Memo ry t e s t i nh i b i t .
Se t s a b i t i n the PFN b i t map fo r each
Do e s no t t e s t the memo r y .
pag e of mem o ry pr esen t .

RPB $V_S O L I C T

File
name .
VMB
bootstrap f i l e .

RPB $V_HALT

Ha l t b e fo r e t r a n s fer .
Ex ecutes a
HALT
i n st r uc t i o n
t r an s f e r r i ng con t r o l t o t h e second a r y bootst r a p .

RPB $V_N O PFND

N o PFN d e l e t i o n ( no t c u r r entl y u s ed ) .
Intended t o t e l l
VMB
not
to read a f i l e from the boo t d ev i c e tha t i d en t i f i e s bad
or r e s e rved memory p ag e s , so tha t VMB d o e s
not
ma r k
these
pag es a s v a l i d i n the PFN b i tm a p .

Symbo l i c Name

p rompts

boo t s t r a p

fo r

the

name

image

c a l l ed

second a r y

b e fo r e

Th e s e c o nd a r y b o o t s t r a p i m ag e i s i d en t i f i ed ( by R S f l ag s a nd ,
o p t i o na l l y , i n fo rm a t i o n so l i c i t ed f r om the c o n so l e t e rm i n a l } .
Th e o r d e r o f p r e c ed enc e i n c ho o s i ng
a
s e c o nd a r y boo t s t r a p
i m ag e i s t h e f o l l ow i ng .
a.

I f t h e R S f l ag c a l l ed RPB $V B B LOCK i s s e t , a b o o t b l oc k
p r o g r am
is
r ea d
f r om t h e s y s t em d i s k .
R 4 c o n ta i n s t h e
l og i c a l n um b e r
of
t h e d i s k b l oc k t h a t c o n ta i n s
the
( Th i s f un c t i o n i s u s e d o n l y
s e c o nd a r y b o o t s t r a p
i m ag e .
o n t h e VAX- 1 1 /7 8 0 p r o c e s so r . }

I f t h e R S f l ag c a l l ed RPB $V S O L I C T i s s e t ,
t h e nam e o f
t h e s e c o nd a r y b o o t s t r a p imag e
i s expl i c i tl y r eques ted
f ro m t h e c o nso l e t e r m i na l .

I f t h e R S f l ag c a l l ed RPB $V D I AG i s s e t ,
t h e d i a g no s t i c
s up e r v i so r
i s l o ad ed .
This o pt i o n c a u s e s a f i l e c a l l ed
[ S YSMA IN T ] D IAGB OOT . EXE t o b e
used
as
the
s e c o nd a r y
b o o t s t r a p i mag e .

Th e a b s e n c e o f a n y o f t h e th r e e o pt i o n s
(a,
b,
or c)
c a us e s
[ S YS EXE ] S YS B O OT . EXE t o b e used a s t h e s e c o nd a r y
boo t s t r a p p r og r am .
Th i s i s t h e n o r m a l p a t h o f e x e c u t i o n
wh e n a VM S s ys t em i s b e i ng i n i t i a l i zed .

2 1-1 1

Ta b l e 2 1 - 3
Co n t e n t� o f Re s t a r t Pa r am e t e r Bl o c k
Mnemo n i c

R PB $L_BASE

....

I
....

S i ze i n Byt e s

Ph ys i c a l Ba se Ad d r e s s of 6 4 K B l oc k

R PB $ L_RESTART

Ph ys i c a l Ad d re s s o f RESTART Ro u t i ne

RPB $L_C HKS UM

Ch e c k s um o f Fi r s t

R PB $ L_RSTSTFLG

Re s t a r t

R PB $L HALT PC
R PB $L-HA LTPS L
RPB $L -HALTCODE
R PB $L-BOOTRx
R PB S L:::: I OVEC

Item

31 Longwo r d s o f RESTART Ro u t i ne

in Prog r e s s F l ag

PC a t HALT/Re sta r t
PS L a t HALT/Re s ta r t
Cod e De sc r i b i ng Re a so n fo r Re sta r t
Saved Bo o t s t r a p Pa r ame te r s ( R O t h r o ug h R S )
Add re ss o f $ Q I O Vec to r in Boo t s t r a p Dr i v e r

R PB $ L_I S P

S i ze ( i n b yt e s ) o f Boo ts t r a p $ Q I O Ro u t i n e
Log i c a l B l o c k Number o f Second a r y Bo o t s t r a p Fi l e
S i ze ( i n b l o c k s ) o f Second a r y Bo o t s t r a p Fi l e
Desc r i pto r o f PFN B i tm a p
S i ze ( i n byt e s ) o f P F N B i tmap
Phys i c a l Ad d r e s s of Sta r t o f PFN B i tm a p
Co un t o f Ph ys i c a l Pag es
Sys tem V i r tua l Add r e s s of Sys tem Pag e Ta b l e
Ph ys i c al Ad d r e s s o f UBA Dev i c e CSR
Vi r t ua l Add re s s of UBA Dev i c e CSR
Ph ys i c al Ad d re s s o f Ad a pt e r Co n f i g u r a t i o n Reg i st e r
Vi r t ua l Add re s s o f Ad a pt e r Co n f i g ur a t i o n Reg i st e r
De sc r i pto r o f Bo o t s t r a p Dev i c e
Un i t Num b e r
Dev i c e Type Cod e
S l av e Un i t Num b e r
S e c o nd a r y Boo ts t r a p Fi l e N a m e ( Co un ted ASC I I S t r i ng
Byte Ar r a y o f Ad a p t e r Types
Co unt of Head e r Pag es in Second a r y Bo o ts t r a p Imag e
s pa r e ( to p r e s e r v e n a t u r a l a l i g nmen t )
Powe r fa i l Inte r r upt Stack Po i n t e r

R PB $L_PCBB

Saved Pr o c e s s Co n t r o l B l o c k Ba s e Reg i s t e r

R PB $L_SBR

Saved Sys tem Ba se Reg i s t e r

R PB $ L_SCBB

Saved Sys t em Co n t ro l

R PB $L I OVEC S Z
R PB $L-F I LLBN
R PB $L-F I LS I Z
R PB $Q::::P FNMAP

RPB $ L PFNCNT
RPB $ L-SVA S PT
R PB $L-C SRPHY
RPB $L-C SRV I R
RPB $L-ADPPHY
R PB $L::::A DPVI R
RPB$W U N I T
RPB $B-DEVTYP
R PB $B-SLAVE
RPB $T-F I LE
RPB $B-C ONFREG
RPB $B::::H DRPGCNT

B l o c k Ba s e Reg i st e r

R PB $L_S I SR

Saved So ftwa r e I n t e r r upt Summa r y Reg i s t e r

RPB $L_SLR

Saved Sys t em Leng th Reg i s t e r

RPB SL_MEMDSC

Lo ngwo rd A r r a y o f Mem o r y De sc r i pto r s

4
4

Lo a d ed by

Spec i a l

VMB

Used t o Loc a t e RPB
( Co n t e n t s�Add r e s s )
Used to Loc a te
RESTART Ro ut i n e
Co n s i s t e n c y Che c k
o n RPB and
RESTART Ro u t i n e
Prevent Ne s ted Re sta r t

I N IT

S e t by Ha rdwa r e

4
4
4
24
4

Cl e a r ed by I N I T
C l e a red by
RESTART
VMB
VMB
VMB
VMB
VMB , IN IT

4
4
4
8
(4)
(4)
4
4
4
4
4
4
4
(2)
(1)
(1)
40
16
1
3
4
4
4

4
4

Us e s

Us ed b y BUGC HEC K to
d ump phys i c a l mem o r y

VMB
VMB
VMB
VMB

VMB
! N IT
VMB
INIT
VMB
! N IT
VMB

U s e d by RESTART

VMB
VMB
VMB
Powe r Fa i l
Ro ut i n e
Powe r Fa i l
Ro u t i ne
I N I T , Powe r
Fa i l Ro ut i ne
I N I T , Powe r
Fa i l Ro u t i ne
Powe r Fa i l
Ro u t i ne
I N I T , Powe r
Fa i l Ro u t i ne
VMB

Re s t o r ed by
RESTART Ro u t i n e
Re sto r ed b y
RESTART Ro u t i n e
Re s t o r ed b y
RESTART Ro ut i n e
Re sto r ed b y
RESTART Ro u t i n e
Re sto r ed b y
RESTART Ro ut i n e
Re sto r ed by
RESTART Ro ut i n e
Us ed b y BUGCHECK to
d ump phys i c a l mem o r y

S P ---..

Physical State

after VMB Begins Execution

after SYSBOOT Begins Execution

Restart Parameter Block
(RPB)

(Loaded by VMB)

(

Primary
Bootstrap
Program
VMB

(

PR$_SCBB __,.
System Control Block (SCB)
for VMB

N
1--'
I
1--'
w

(

R1 0 contains HALT PC
R1 1 contains HALT PSL
AP contains HALT code
RO through RS contain
initial bootstrap parameters.
These are loaded i nto RPB
by VMB. (See Table 21-2)

Primary
Bootstrap
Program

\
)

Read i nto m emory
by console program

\
}

Set up by first few
instructions in VMB

(

Filled in by VMB
to reflect
presence of
each physical page

.-- R1 1

VMB

)

System Control Block (SCB)
for VMB

PFN Bitmap
(4 Pages)

Bootstrap Stack

Used by both VMB
and SYSBOOT

(3 Pages)

� S P , R1 0

(

Read i nto m emory
by VMB

(

)

Set u p by first few
i nstructions in SYSBOOT

Figure 2 1 -1

Secondary
Bootstrap
Program
SYSBOOT

)

.,..._ PR$_SCBB

System Control Block (SCB)
for SVSBOOT

Ph ys i c a l Memo r y L a yo u t s U s e d by VMB a nd SYSB OOT

BOOTSTRAP PROCEDURES

Th e i m ag e i s r e a d i n to m emo r y ( F i g u r e 2 1 - 1 )
and
co n t r o l
is
p a s sed
to
i t at
i ts
t r a n s f e r ad d r e s s .
Th i s a d d r e s s i s
n o rma l l y t h e f i r s t b y t e i n the i m ag e .
Ho we v e r ,
s e t t i ng
the
f l ag R PB $V H EADER
in R S d i r ec t s VMB to use the t r a n s f e r
a d d r e s s s t ored i n the i m ag e h e a d e r o f the s e c o nd a r y boo ts t r a p
p r og r am .
( Th i s
o f c o u r se
a s s um e s t h a t the
s e c o nd a r y
b o o ts t r a p i m ag e wa s p r o d uc e d by t h e VAX- 1 1 L i nke r . )

21. 2. 3

Boo t s t r a p D r i v e r and I/0 S ub ro ut i ne s

VMB c o n t a i n s a s ke l e to n Q u e u e I /O Reque s t r o u t i n e a nd d ev i c e d r i v e r t o

pe r fo rm
i ts
I /0 .
Th i s d r i v e r a nd r o u t i n e a r e l o a d ed i n to nonpag e d
po o l b y I N I T f o r po s s i b l e l a t e r u s e b y t h e b ug ch e c k c o d e ( Ch a p t e r 7 ) .

Th e VMB i m ag e a c t ua l l y c on t a i n s s i mp l e d r i v e r s f o r a l l po s s i b l e sys t e m
d ev i c e s .
On c e
i t h a s d e te rm i ned
t h e n am e o f t h e boo t s t r a p d ev i c e
( f r om r eg i s t e r c o n t e n t s ) , VM B mov e s t h e d r i v e r c od e fo r
the
s e l ec t e d
d ev i c e
so
tha t i t i s a d j a c en t to the $ Q I O r o ut i n e .
( Th i s a l l o ws t h e
e nt i re
boo t s t r a p
I /0 s y s t em to b e moved w i t h a
s i ng l e
MOVCx
i n s t r uc t i o n . )
Th e
l o c a t i o n a nd t h e s i z e o f t h e $ Q I O r o ut i ne pl us t h e
s e l e c t ed d r i v e r a r e l o a d ed i n to the Re s t a r t Pa r am e t e r B l o c k fo r
later
u s e b y IN I T .
Th i s s i mpl e o pe r a t i o n by VMB p r ev e n t s n o npag ed po o l f r om b e i ng
l oad ed
wi t h a s e t o f b o o t s t r a p d ev i c e d r i v e r s t h a t a r e n eve r u s e d .
Th a t i s ,
t h e o n l y boo ts t r a p d r i v e r t h a t i s p r e s e r v ed f o r
the
l i f e o f a VM S
s ys tem
i s the boo t s t r a p d ev i c e d r i v e r s e l e c t e d t h r o ug h i n put to VM B .
Al l o th e r b o o t s t r a p d r i v e r s a r e
l i n ked
i n to
t h e VM B
i m ag e b u t
d i s a pp e a r a l ong w i th t h e r e s t o f VM B wh e n VM S i s f i na l l y i n i t i a l i z ed .

21 . 2. 4

F i l e Ope r a t i o n s

On e o f the p r o b l em s th a t m u s t b e so l v ed
i n a n y b o o t s t r a p o pe r a t i o n
i nvo l v e s
l oc a t i o n o f
f i l e s b e f o r e the f i l e sys t e m i t se l f i s i n f u l l
ope r a t i on .
In a VM S s ys tem , t h e p r o b l em
is
f a c e d wi th eve r y f i l e
o pe r a t i o n t h a t m u s t b e pe r f o rm ed b e f o r e the sys t em d i s k AC P (Anc i l l a r y
Co n t r o l P r o c e s s o r ) i s c r e a t e d .
VM S s o l ve s th i s
p r o b l em
by
i nc l ud i ng
two
spec i a l
o b j ec t mod u l e s
( F I L ER EAD a nd
F I LERW I O ) i n th e e x e c u t i v e i m ag e .
Th e mod u l e s c o n s i s t
o f a ser ies o f
s ub r o u t i n e s
tha t c a n
pe r f o rm some p r i m i t i v e
file
o pe r a t i o n s o n a F i l e s- 1 1 vo l ume .
On e o f the se m o d u l e s ( F I LE READ ) i s
a l s o l i nked i n to b o th the VM B a nd S YS B OO T imag e s .
I n o rd e r
to
keep these
s ub r o u t i n e s
r el a t ive l y
sm a l l ,
s ev e r a l
r e s t r i c t i o n s a r e i m po s ed o n f i l e s t h a t c an b e a c c e s s ed wi th them .
•
•
•

Th e vo l um e c o n t a i n i ng the f i l e m u s t b e a F i l e s- 1 1 vo l ume .
c a n u s e e i th e r S t r uc t u r e L ev e l 1 o r 2 .

Th e f i l e m u s t b e c o n t i g uo u s .
I f th e vo l um e u s e s S t r uc t u r e Lev e l 2 , t h e f i l e m u s t r e s i d e i n
a r o o t d i r e c to r y .
Th e s ub r o u t i n e s c a nno t fo l l o w s ubd i r e c to r y
spe c i f i c a t i o n s .

F i l e s tha t mus t b e c o n t ig u o u s
i nd i c a t ed i n T a b l e 2 1 - 1 .

beca use
21-14

the s e

res t r i c t i ons

a re

BOOTSTRAP PROCEDURES

21 . 3

S ECONDARY BOOTSTRAP PROGRAM

( SYSBOOT )

Th e s e c o nd a r y b o o t s t r a p p r og r am SYSB OOT e x e c u t e s wh e n VMB i s d i r e c t ed
to
l o ad
a
VM S s y s t e m .
Mo s t o f t h e o pe r a t i on s t h a t a r e pe r fo rmed by
c od e t h a t e x e c u t e s b e f o r e VM S e x i s ts a r e pe r fo rmed
by SYSBOOT .
VMB
h a s a l ready t e sted
ph ys i c a l m em o r y ,
r e ad SYSBOO T i n to m emo r y , a nd
t r a n s f e r r ed c o n t r o l to i t .
S Y S B O OT p e r fo rm s th r e e m a j o r f un c t i o n s .
•

•

Th e
s y s t em
a d j us t a b l e
s y s t em o r a
bo o t s t r a p )
d e pe nd
on
c a l c u l a t ed .

i s c o n f i g u r ed .
Th i s m e a n s
that
a
set
of
S Y S B O OT pa r am e t e r s ( e i th e r the o n e s f r om the l a s t
s e t e x p l i c i t l y s e l e c ted th r o ug h a
c o nv e r s a t i o n a l
is
l o ad ed .
O t h e r s ys t em pa r am e t e r s wh o s e v a l u e s
t h e v a l ue s o f
the a d j us tab l e pa r am e t e r s
a re

A po r t i o n o f
s ys t em c o n f i g u r a t i o n t h a t d e s e r v e s s e pa r a te
m e n t i o n i nvo l ve s t h e m a p p i ng o f s ys tem v i r t ua l add r e s s spac e .
Th e s i z e s o f m a ny o f t h e
p i e c e s o f s ys t em
add r e s s s pa c e
d e pe nd o n th e v a l ue s o f o n e o r mo r e S YS B OO T p a r am e t e r s .
Th e
c a l c u l a t i o n s t h a t SYSB OOT p e r fo rm s a nd the r e s u l t s o f
the s e
c a l c u l a t i o n s a r e d e ta i l ed i n Append i x E .
I n a d d i t i o n t o s i z i ng t h e p i e c e s o f s y s t em
spac e ,
SYS B OOT
a l so
s e t s up the s ys t e m pag e t a b l e to map many o f the p i e c e s
o f t h e no npag ed a n d pa g ed
execut ive .
In a
r e l a ted
s te p ,
S YS B OOT
p r e pa r e s
a
P O pag e
table
tha t
a l l o ws m emo r y
m a n ag em e n t t o b e t u r n ed o n .
( Th i s l a s t s te p i s d e sc r i b ed
in
Ch a pt e r 2 2 . )

•

Th e l a s t ma j o r s t e p th a t S YS B OOT p e r fo rm s i s to
l o c a te
the
e x ec ut ive
( S YS . EXE ) a n d r e ad the v a r i o u s po r t i o n s of i t i n to
t h e ( ph y s i c a l ) pag e s s e t a s i d e wh e n the sys t e m pag e t a b l e wa s
set
up .
Oth e r f i l e s ( Ta b l e 2 1 - 1 ) a r e a l so l o c a t e d and the i r
l o c a t i o n s pa s s ed
on
to
!NIT
in
g ene r a l
r eg i s t e r s
( Ta b l e 2 1 - 4 ) .

Th e r e i s l i t t l e C PU -d e pend e n t c o d e
in
SYS BOO T .
Mo s t
d e pe nd e nc i e s h av e a l r e a d y b e en t a k e n c a r e o f by VMB .

21. 3.1

the

CPU

De t a i l e d Ope r a t i on o f SYS BOOT

SYS B OOT b eg i n s o pe r a t i o n w i th the phys i c a l m emo r y l a yo u t p i c t u r ed
in
Figure 21-1 .
R l l po i n t s t o
t h e b eg i nn i ng o f t h e Re s t a r t Pa r am e t e r
Block .
1.

S YS B OO T i mmed i a t e l y a l l o c a t e s a phy s i c a l pag e a n d s e t s
up a
s ys t em c o n t r o l b l o c k w i th a l l vec t o r s c o n ta i n i ng the a d d r e s s
o f a s e r v i c e r o u t i n e i n SYS B OOT .
Th e v e c to r s
for
TB I T a nd
B PT a r e
r e d i r e c ted to e x c e p t i o n s e r v i c e r o u t i n e s i n XDE LTA ,
l i n ked a s a pa r t o f t h e SYS B OOT i ma g e .
Th e m a c h i n e c h e c k
v e c to r i s mod i f i e d t o po i n t t o a c u s tom i z ed e x c ept i o n s e r v i c e
r o ut i ne .

I f the boo t s t r a p b r ea k po i n t
f l ag
( RPB $V B O O B PT ,
RS<S> )
is
set ,
S Y S B OOT e x e c u t e s
a
B PT
i n s t r uc tTo n , wh i c h t r a n s f e r s
c o n t r o l t o XD E LTA , l i nk ed a s a pa r t o f t h e SYSB OOT i mag e .
No t e t h a t t h e same f l ag c o n t r o l s b r ea kpo i n t e x e c u t i o n i n bo th
VM B a nd
SYS B OOT .
Th i s
f l ag
c an be
used
i n l o c a t i ng a
h a rdwa r e p r o b l em o r o th e r p r o b l em t h a t i s
p r e v en t i ng
s ys t em
i n i t i a l i za t i o n .
21-1 5

BOOTSTRAP PROC EDURES
Ta b l e 2 1 - 4
Reg i s t e r I n put to

!N I T f r om S YSB OOT

Reg i s te r

Co n te n ts

Ph ys i c a l Ad d r e s s o f EXE $ I N I T

Log i c a l

S i ze

( i n byt e s )

o f Te r m i n a l Se r v i c e

S i ze

( i n b l o c ks )

o f Ex e c u t i v e I m ag e

Log i c a l

Bl o c k Num b e r o f Ex e c u t i v e Imag e

Log i c a l

Bl o c k Num b e r o f Sys t em D i s k Dr i v e r

S i ze

Log i c a l

S i ze

Rll

Phys i c a l Ad d r e s s o f R PB

SBR

Ph ys i c a l Ad d r e s s o f Ba s e o f Sy s tem Pag e Tab l e

S LR

Le ng th o f Sy s t em P a g e Tab l e

POBR

Se t u p s o tha t pag e c o n ta i n i ng
EXE $ I N I T
m a pped a s a P O v i r t ua l pag e ( Fi g u r e 2 2 -1 )

P OL R

C o n ta i n s t he v a l ue o f t h e PFN
t�

E XE $ I N I T

Bl o c k Num b e r o f Te rm i n a l

( i n byt e s )

Se r v i c e

( S YS . E XE )

o f Sys t em D i s k D r i v e r

Bl o c k Numb e r o f Lo ad ab l e C P U C o d e

( i n byt e s )

( TTDR I VER . EXE )

( S YS LOAx x x . EXE )

o f Lo ad a b l e C P U C o d e

c o n t a i n i ng

i d en t i c a l l y

p l us

Th e PR $ S I D r eg i s t e r i s r e ad to d e t e r m i n e the C P U t ype .
Th i s
t ype
i s s to r ed f o r l a te r u s e by c o d e wh o s e e x e c u t i o n d e pend s
o n the s p e c i f i c C P U t ype .
Th i s v a l ue ,
s to r ed
i n g loba l
l o c a t i o n E XE $G B_C PUTYPE , i s u s ed i n s ev e r a l wa ys .
•

•

I t wi l l d e t e rm i n e wh i c h p i e c e s o f C PU-d epend e n t c o d e
wi th i n
SYSB OOT e x e c u t e .
Fo r e x ampl e , t h e r e i s a c h e c k
wh e th e r t h e h a r d wa r e E C O s t a tus i s a t the l ev e l
r equ i r ed
to
s u ppo r t a
VAX/VMS
s y s tem .
On
a VAX- 1 1 /7 5 0 , the
h a rdwa r e ECO l ev e l a nd m i c r o c o d e r ev i s i o n l ev e l
a re
the
va l u e s
th a t a r e
c h e c k ed .
On a VAX- 1 1 /7 8 0 , th i s t e s t
r e q u i r e s c ommun i c a t i o n w i th t h e c o n s o l e p r og r am t o o b t a i n
the v e r s i o n n um be r s o f t h e PC S , WCS , a nd FPLA .
Th e C PU t yp e w i l l d e t e rm i n e
the n a m e o f
the
s e pa r a t e
i m ag e f i l e ( S YS LOA7 5 0 . EXE o r SYS LOA7 8 0 . EXE ) t h a t c o n t a i n s
C PU-d e pend e n t r o u t i ne s .
Th i s i m ag e i s o pe n e d
( l ocated )
by SYSBOO T a nd r e ad i n to no n pag e d po o l by !N I T .

2 1- 1 6

BOOTSTRAP PROC EDURE S
•

•

Tho s e po r t i o n s o f C PU-spe c i f i c cod e th a t a r e s e l e c t e d a t
e x ec u t i o n
t ime
( wi th
sui table
test
a nd
b ranch
i n s t r uc t i o n s ) w i l l u s e t h e C P U t ype a s t h e o b j e c t o f
the
t e s ts .
Th e s i z e o f t h e s ys tem c on t r o l
block ,
a
pa r t o f t h e
s 1 z 1 ng
ove r a l l
e f fo r t o f s y s t e m add r e s s s pa c e d e s c r i b ed
i n s t e p 7 a nd Append i x E , d e pend s on the C PU t ype .

Th e d i f f e r e n t
s t r a t eg i e s
tha t a r e
used
to
d e pend e n c i e s a r e d e sc r i b ed i n the n e x t c h a p t e r .

h a nd l e

C PU

Th e e x e c u t i ve i ma g e i s o pened .
I t s l oc a t i on
( l og i c a l
bloc k
n umb e r )
on
the
s ys t em d i s k
i s s to r ed f o r l a t e r use .
Th e
po r t i o n o f t h e ex ec u t i v e i mag e th a t con t a i n s pa r am e te r s
is
r e ad
i n to
SYSBOOT ' s wo r k i ng t a b l e .
Th e l a s t se c t i o n o f t h e
next
chapter
d e s c r i be s
i n mo r e d e ta i l
the movem e n t o f
pa ram e t e r i n fo rma t i o n d u r i ng the i n i t i a l i za t i o n se que nc e .

Seve r a l o th e r f i l e s a r e o pened a nd
Th e s e f i l e s i n c l ud e

the i r

l oc a t i on s

•

t h e sys t em d i s k d r i v e r ,

•

t h e t e rm i n a l d r i v e r , a n d

•

t h e i m a g e c o n t a i n i ng the C PU-d e pend e n t mod u l es .

s to r e d .

Th e a d d r e s s e s o f the s e f i l e s a r e pa s s ed to ! N I T so tha t t he i r
conten t s c a n
be
r e ad
i n to
a p p r o pr i a t e
pl a c e s
i n s y s t em
add r e s s s p a c e a f t e r m emo r y m a n ag emen t i s t u r ned on .
6.

At th i s po i n t , SYS BOOT d e t e rm i n e s i f the ope r a to r r e que s t ed a
c o nv e r s a t i o n a l
bo o t s t r a p b y s e t t i ng
t h e RPB $V C ONV f l ag ,
R 5 < 0 > , a s i n p u t to VMB .
I f s o , S Y S B OOT w i l l p r ompt to
a llow
I n a n y c a se ,
i n t e r a c t i v e a l t e r a t i o n o f t h e pa r am e te r v a l ue s .
S YS B OOT e n t e r s t h e n e x t ph a s e wi t h some s e t o f ad j us t a b l e
pa r am e t e r s .

Th e s i ze o f t h e p r o c e s s h e ad e r a nd the
s i ze s o f p i e c e s o f
s ys t em a d d r e s s s p a c e a r e c a l c u l a t ed .
I n pa r t i c u l a r , t h e s i z e
o f t h e s y s t em pag e tab l e i s c a l c u l a ted .
Th e d e ta i l s o f t h e s e
c a l c u l a t i o n s a r e d e sc r i b ed i n Append i x E .

Th e f i r s t pag e o f the s ys t em co n t r o l b l o c k , f o und o n b o t h t h e
VAX-1 1 /7 5 0 a nd th e VAX-1 1/7 8 0 , i s l o ad ed w i t h the c o n t e n t s o f
mod u l e S C BVECTOR , wh i c h c o n t a i n s t h e e n t r y po i n t s
fo r
the
i n te r r up t a nd e x c ept i o n s e r v i c e r o u t i n e s l o c a ted i n S YS . EXE .

Th e s y s t em h e ad e r i s c o n f i g u r ed .
Al l e n t r i e s i n t h e
s y s t em
h e ad e r wh o s e c o n t e n t s d epend on c o n f i g u r a t i o n pa r am e t e r s a r e
f i l l ed i n a t t h i s
t ime .
Th i s s t e p i s a n a l og o u s
to
the
p r o c e s s h e ad e r c o n f i g u r a t i o n tha t
i s p e r fo rmed b y c o d e i n
S H E LL a s a pa r t o f p r o c e s s c r ea t i o n ( Ch a pt e r 1 7 ) .

10.

P i eces o f the
e x ec u t i v e
tha t n ev e r pag e
( Ta b l e E - 3 )
are
ma pped
i n to the h i g h e s t po r t i o n o f phys i c a l m emo r y .
Th e s e
phys i c a l pag e s wi l l n o t b e a c c o un ted fo r i n t h e PFN d a ta b a s e
b e c a u s e t h e i r s t a te w i l l neve r c h a ng e .

21-17

BOOTSTRAP PROC EDURES

11.

Th e pag e ab l e po r t i o n s o f SYS . E X E ( th e sys tem s e rv i c e v ec to r s
a nd t h e pag e a b l e ex e c u t i v e r o u t i n e s ) a r e a l so m a pped t o a l l o w
t h e e x ec u t i v e t o b e r e a d i n to memo r y .
I f t h e SYS PAG I NG f l ag
i s s e t ( i t s u s ua l s t a t e ) , t h e phys i c a l pag e s t h a t c o n t a i n the
pag e a b l e e x ec u t i ve w i l l b e r e l e a s ed to the f r e e l i s t b y !N IT .

12.

Th e e x ec u t i ve i m ag e i s
r ead
i n to m em o r y .
B e c a use memo r y
m a n a g em e n t
has
not
yet
been
e n a b l ed ,
none o f
the
c ompl i c a t i o n s o f sc a t t e r ed r e ad s i n to memo r y a r e a pp l i c a b l e
here.

13.

Th e c o n t e n t s o f SYSB OOT ' s i n t e r n a l p a r ame t e r t ab l e a r e c o p i ed
to
the po r t i o n o f
t h e m emo r y i mag e o f the e x e c u t i v e tha t
c o n ta i n s a l l t h e a d j u s ta b l e pa r am e t e r s .
Th i s s t e p p r e s e r v e s
t h e c u r r e n t pa r am e t e r
s e t t i ng s
( be c a us e SYSB OOT i s g o i ng
a wa y ) u n t i l t h e y c a n be wr i t t e n b a c k to the d i s k i m ag e o f the
e x ec u t i ve by SYS I N I T ( Ch a p t e r 2 2 ) .

14.

SYS B OOT l o ad s the b a s e a nd l eng t h r eg i s t e r s fo r
the
PO
and
s y s t em pag e
tab les
s o tha t !NIT c an t u r n m emo r y m a n ag em e n t
on .
E n a b l i ng memo r y m a n ag em e n t i s d e sc r i b ed i n mo r e d e t a i l
i n t h e n e x t c h a pt e r .

15.

F i n a l l y , SYS B O OT t r a n s f e r s c on t r o l
to
e x e c ut i v e .
Th i s t r a n s f e r mus t be d o ne
b ec a us e m emo r y m a n ag em e n t h a s n o t b een
d e s c r i pto r s a nd o th e r i n f o rm a t i o n t h a t
a r e s t o r ed i n r eg i s t e r s ( Ta b l e 2 1 -4 ) .
memo r y i s p i c t u r ed i n F i g u r e 2 1 - 2 .

2 1-1 8

!N I T
in
the
mod u l e
to a phys i c a l l o c a t i o n
e n a b l ed ye t .
Th e f i l e
SYSB OOT p a s s e s to ! N I T
Th e s t a t e o f
phys i c a l

BOOTSTRAP PROC EDURES
0

""' I"'

MMG$GL_MAXPFN
_,.
(Physical Page N umber)

(

Dynamic Pages
Process Working Sets System
Working Set, Free Page
List, Modified Page List
'

) 1
....

�

These pages are
described by
entries In the PFN
data base.

PFN Database

Nonpaged Executive
Code and Data

Nonpaged Dynamic Memory

The PFN database
contains no Information
about the physical
pages containing a ny
of these pieces of
the executive.

Interrupt Stack
PR$_SCBB
(Physical Address)
System Control Block

System Header
PR$_SBR
(Physical Address)
System Page Table
Largest PFN
(Physical Page N umber) __..

F i g u r e 2 1 -2

Ph ys i c a l Memo r y La yo u t Used by the E x ec u t i v e

2 1-1 9

CHAPTER 2 2
O PERAT ING SYSTEM I N I T IALI ZAT I ON

Th e s e c o nd ma j o r ph a s e o f s y s t em i n i �ia l i z a t i o n i s pe r fo rmed
•
•

by c o d e t h a t i s a pa r t o f the e x e c u t i v e

( modu l e ! N I T ) a n d

by a s p e c i a l p r o c e s s ( S YS I N I T ) t h a t i s
c r e a ted
t o compl e t e
tho s e p i e c e s o f i n i t i a l i za t i o n t h a t r e qu i r e pr o c e s s c o n t e x t
i n o r d e r to e x e c u t e .

! N I T t u r n s o n m emo r y m a n ag emen t a nd
sets
up tho s e d a t a
s t r uc t u r e s
wh o s e
s i ze
or
c o n t e n t s d e pend o n S Y S B OO T pa r am e t e r s .
SYS I N I T o pe n s
s ys tem f i l e s , c r e a t e s s ys t em p r o c e s se s , m a ps RM S a nd t h e m e ssag e f i l e ,
a nd c r e a t e s t h e p r o c e s s tha t i nvo k e s the s ta r tup c ommand f i l e .

22. 1

I N I T IAL E XECUT I ON OF THE EXECUT IVE

( IN I T )

Th e f i n a l i n s t r uc t i o n
in
SYSBOOT t r a ns f e r s c o n t r o l
to
( ph ys i c a l )
ad d r e s s
EXE $ I N I T ,
an add r e s s
i n m o d u l e !N I T .
! N I T t u r n s o n m emo r y
m a n ag em e n t ,
config ures
the
I /0
adapte r s ,
i n i t i a l i ze s
seve r a l
s c h ed u l i ng a nd memo r y m a n ag em e n t d a ta s t r uc t ur e s , a nd f i na l l y r e l e a s e s
t h e pag e s tha t i t o cc up i e s s o tha t c o d e t h a t ex e c u t e s o n l y o n c e d u r i ng
t h e l i f e o f t h e s ys t em d o e s n o t c o n s ume s ys t em r e so u r c e s .

22. 1. 1

Tu r n i ng on Memo ry Manag ement

Th e f i r s t ( a nd pe rh a ps m o s t i m po r ta n t ) s t e p tha t ! N I T t a k e s t u r n s o n
m emo r y m a n ag emen t .
Be fo r e SYSBOOT t r a n s f e r s c o n t r o l t o ! N I T , i t s e t s
u p the s ys tem pag e
t ab l e t o m a p t h e
e x e c u t i v e a nd d yn am i c d a ta
s t r uc t u r e s .
In
a d d i t i o n , a P O pag e t a b l e i s c o ns t r uc ted so tha t t h e
ph ys i c a l pag e c o n ta i n i ng E XE $ I N I T i s m a pped a s a P O v i r t ua l pag e wh e r e
t h e v i r t ua l
p ag e
n um b e r
is
i d en t i c a l t o the phys i c a l pag e n um be r .
Th i s m e a n s tha t E XE $ I N I T c a n b e r e f e r e n c ed a s a
PO v i r tua l
address
tha t
is
i d en t i c a l l y eq ua l t o t h e phys i c a l ad d r e s s o f EXE $ I N I T .
Th e
r e a so n tha t P O s pa c e i s used f o r th i s d o ub l e m a pp i ng i s t h a t t h e
PO
s pa c e add r e s s
r a ng e
f r om 0
t o 4 0 0 0 0 0 0 0 i s t h e same a s t h e m a x i m um
ph ys i c a l add r e s s r a ng e p e rm i t ted by t h e VAX a r c h i t e c t u r e .
Th a t i s , n o
m a t t e r h o w m u c h phys i c a l memo r y i s p u t o n a VAX p r o c e s so r , the r e w i l l
a l wa ys b e a P O a d d r e s s r ang e w i th i d en t i c a l a d d r e s s e s .

22-1

OPERAT ING SYSTEM I N I T IALI ZAT I ON

2 2 . 1 . 1 . 1 Do ub l e Mapp i ng o f ! N I T by SYSBOOT - Th i s PO
pag e
t ab l e
is
c o n s t r uc t ed
b y l o ad i ng
the P O b a s e a nd l eng t h r eg i s t e r s wi th v a l ue s
th a t a c c e s s a po r t i o n o f t h e sys t em pag e t ab l e { F i g u r e 2 2- 1 ) .
I f we
a s s um e t h a t E XE $ I N I T i s l o c a t ed i n PFN n , t h e n P O LR i s l o ad ed wi th n + 2
a nd POBR i s l o ad ed w i th a sys tem v i r t ua l a d d r e s s tha t
is
n l o ngwo rd s
sma l l e r t h a n t h e s ys tem v i r t ua l add r e s s o f t h e sys tem pag e t ab l e e n t r y
th a t maps E XE $ I N I T .
System Page Table
PR$_SBR contains
physical address of
this SPTE
SPTE for zeroth SVP
•
•
•

(

EXE$1NIT Is contained
In system virtual page
VI and In physical
page PI

)

1-----------------i
•
•

,._

PR$_POBR contains the virtual
address of this longword
This longword becomes the PO
PTE for the zeroth POVP
The relative sizes of PI and VI deter
mine whether the longword pointed
to by POBR lies within the sysJem
page table •

•

PI 5 VI => within system page table

PI > VI => outside the system page
table
Pt-1

(

SPTE for virtual page VI
This system virtual
page contains EXE$1NIT

)

Valid, PROT,
etc.

Whether this longword lies within the
system page table Is of no concern
to address translation.

PFN

Pt+1

P1+2

(

POPTE for PO virtual page that
contains EXE$1NIT.
This Is the P1th PO
page table entry

)

PR$_POLR Is loaded with P1 + 2
There are PI + 1 longwords Inclusive
from the longword located by POBR
to the SPTE that maps I N IT. By put
ting PI + 2 Into POLR, EXE$1NIT can
extend Into a second page.

•
•
•

SPTE for last SVP

F i g u r e 2 2 -1

Do ub l e U s e o f Sys t em Pag e Ta b l e En t r i e s by IN I T

Th e n e t
r es u l t of
all
th i s m a pp i ng
is
t h a t t h e ph ys i c a l
pa g e
c o n t a i n i ng E XE $ I N I T c a n ( a nd w i l l ) b e a c c e s s e d i n th r e e d i f f e r e n t wa ys
( F igure 2 2-2 ) .
Th e s e d i f f e r e n t m a pp i ng s a r e l i s t ed h e r e in o rd e r
of
m a pp i ng
c om p l i c a t i o n ,
a nd n o t
i n the o rd e r i n wh i c h th e y a r e used .
EXE $ I N I T c a n b e a c c e ssed

2 2- 2

OPERATING SYSTEM IN I T IALIZATION
•
•
•

a s a p h ys i c a l add r e s s ,
a s a s y s t em v i r t ua l a d d r e s s ( 8 0 0 1 2F F 8 i n Ve r s i o n 2 )
m a pped by t h e s y s t em pag e t a b l e ,

tha t

o r a s a P O v i r t ua l a d d r e s s t h a t i s l o c a ted by t h e s u b s e t o f
t h e s y s tem pa g e ta b l e tha t i s a l so u s ed a s a P O pag e t ab l e .

22 . 1 . 1 . 2
I n s t r uc t i o n s Tha t Tu r n on Memo ry Managem e n t - Wh e n
INIT
b eg i n s e x ec u t i o n , m emo r y manag em e n t i s d i s ab l ed .
Th e PC c o n t a i n s t h e
phys i c a l add r e s s o f EXE $ I N I T .
(1)

Th e f i r s t i n s t r uc t i o n
MOVL

RPB $ L_B OOTRS ( R l l ) , FP

e x e c u t e s i n phys i c a l s pac e .
I t s e f fe c t
t u r n i ng mem o r y m a n ag em e n t o n .
(2)

no t

r e l a te d

Th e s e c o nd i n s t r uc t i o n
MTPR
a c t ua l l y t u r n s memo r y m a n a g em e n t o n .
Th a t
is ,
all
add r e s s
r e f e r enc e s
f r om t h a t po i n t o n m u s t b e t r a n s l a te d .
No t e t h a t
t h e i n s t r uc t i o n d o e s n o t c a use a t r a n s f e r o f c o n t r o l .
Th e PC
is
s i mpl y
i n c r em e n t ed b y th r e e , the numb e r o f byt e s i n t h e
i n s t r uc t i o n .
Ho we v e r ,
the
next
PC r e f e renc e
wi l l
be
t r a n s l a t e d b e c a use memo r y ma n ag emen t has b e en e n a b l ed .
Be c a us e o f t h e m a pp i ng s e t up b y S YSB OOT ,
the
i nc r em e n t ed
( ph y s i c a l )
PC
( th e
add r e s s o f
t h e JM P i n s t r uc t i o n ) , wh e n
t r a n s l a t e d us i ng t h e P O pag e
t a b l e , y i e l d s t h e phys i c a l
a d d r e s s o f t h e JMP i n s t r uc t i o n .

(3)

Th e th i rd i n s t r uc t i o n
JMP

@#10$

i s t h e o n l y i n s t r uc t i o n tha t e x e c u t e s wi th a
P O p r og r am
counte r .
Th i s i n s t r uc t i o n i mmed i a t e l y t r a n s f e r s co n t r o l to a
sys t em v i r t ua l a d d r e s s th a t wa s c a l c u l a ted wh en the e x e c u t i v e
wa s
l i nked .
Wh e n th i s s ys tem v i r t ua l add r e s s i s t r a n s l a t ed ,
i t r e s u l t s i n t h e phys i c a l add r e s s o f the n e x t i n s t r uc t i o n i n
the phys i c a l pa g e c o n t a i n i ng E XE $ I N I T .
Th e th r e e i n s t r uc t i o n s f r om
MTPR
to
MOVL

E XE $G L_INTSTK , S P

execute
in
th r e e d i f f e r e n t m a pp i ng
contexts
( so l i d
l i ne
in
Figure 2 2-2 ) .
Ho we v e r , the m a ppi ng tha t wa s s e t up b y SYSB OOT r e s u l t s
i n a s e l e c t i o n o f s uc c e s s i v e i n s t r uc t i o n s f r om the s am e ph ys i c a l pag e .

2 2- 3

OPERAT ING SYSTEM IN I T IA L I ZAT I ON

from SYSBOOT

PO
Space

I
....---�

I
I

}

MOVL RPB$LBOOTR5(R1 1 ),FP

MTPR

# 1 ,S- # MAPEN

System

1. Instructions that execute with
physical (no) mapping
2. Instruction that executes
from PO space
3. Instructions that execute

from system virtual
address space

Space

F i gure 2 2 - 2

Addr e s s Space Changes a s Memory Management
is Enabled by I N I T

2 2- 4

OPERATING S YSTEM I N I T I AL I Z AT I ON

22. 1 . 2

I n i t i a l i za t i o n o f t h e E x e c u t i ve

Onc e !N I T h a s s uc c e ed ed i n t u r n i ng o n memo r y manag emen t , i t i s f r e e t o
make
r e f e r e nc e s t o s ys t em a d d r e s s e s .
I n pa r t i c u l a r ,
it
is now
po s s i b l e t o
i n i t i a l i z e d yn am i c d a ta
s t r uc t u r e s
tha t h a v e
the i r
l i sthead s
s to r ed i n s t a t i c g l o b a l l o c a t i o n s i n s y s t em spa c e .
Some o f
t h e s e s te p s i nvo l v e a l l o c a t i o n f r om no npag ed d y n am i c m emo r y .
( Th e
n o npag ed po o l s pac e a l l o c a t ed b y ! N I T , a nd t h e SYSB OOT pa r am e t e r s t h a t
c o n t r o l t h e amoun t o f a l l o c a ted s pa c e , a r e l i s t ed i n Tab l e 2 2 - 1 . )
Th e
d e t a i l ed
s t eps t h a t ! N I T t a k e s o nc e mem o r y m a n ag em e n t h a s b e e n t u r n e d
o n a r e l i s t ed h e r e .
1.

Th e f i l e d e sc r i p to r s a n d o th e r a rg um e n t s tha t we r e pa s s e d
to
!NIT
f r om SYSBOO T i n
r eg i s t e r s a r e s a v e d in co r r e s po nd i ng
g loba l l o ca t i o ns .

Th e
swa p
f i l e t ab l e
entry fo r
the
Sh e l l
process
is
i n i t i a l i z e d t o po i n t to the e x e c u t ive i mag e ( F i g u r e s 1 1 - 2 2 ,
1 1-2 3 , and 1 7- 5 ) .

Th e Sy s t em Co n t r o l B l o c k Ba s e Reg i s t e r
i s l o ad ed
w i th
the
phys i c a l
ad d r e s s o f
the SCB that c o n t a i n s the add r e s s e s o f
e x c e p t i o n a n d i n t e r r up t s e r v i c e r o u t i n e s
in
the e x e c u t i v e .
Th i s b l o c k wa s a l l o c a t e d a nd i n i t i a l i z ed by SYSBOOT .

or
E x e c u t i v e d e b ug g e r s up po r t
is
e i th e r
i n i t i a l i z ed
e l i m i n a ted ,
a c c o rd i ng
to
the
s e t t i ng
of
t h e d e bug f l ag
( R PB $V_D E B UG , R 5 < 1 > ) o n i n put t o VM B .
a.

I f d e b ug s uppo r t i s s e l ec t ed , t h e B PT a nd TB IT
v e c to r s a r e l o ad ed
wi th
the
ad d r e s s e s o f
s e r v i c e r o u t i n e s w i th i n XDE LTA .

I f d e bug s uppo r t i s n o t s e l e c t ed , t h e B PT i n s t r uc t i o n
in
!NIT
( a t add r e s s
IN I $ BRK )
i s c o nve r ted to a NO P .
In
a d d i t i o n , the pag e s c o n t a i n i ng
XDE LTA
( s e e App e nd i x E )
are
i nc l ud ed i n t h e l i s t o f p a g es tha t ! N I T w i l l r e l e a s e
t o t h e f r e e pag e l i s t a s pa r t o f i t s ex i t r o ut i n e .

except i o n
except i on

Th e a nno unc em e n t m e s sag e i s p r i n t ed on the c o nso l e
t e rm i na l .
No t e
t h a t t h i s i mpo r ta n t m i l e s to n e , wh i l e no t v e r y f a r i n to
! N I T , i nd i c a t e s t h a t the e x e c u t i v e h a s b e e n r e a d i n to m emo r y
a n d memo r y m a n a g eme n t t u r ned o n , b o th s i g n i f i c a n t s t e p s i n
b r i ng i ng the s y s t em o n the a i r .

No n pag ed po o l i s i n i t i a l i z ed

I f t h e i n i t i a l b r e a kpo i n t f l ag ( RPB $V I N I BPT , R S < 2 > ) wa s
set
o n i n pu t to VMB , t h en ! N I T e x e c u t e s a B PT i n s t r uc t i o n a t t h i s
po i n t .

I f the SYSPAG I NG S YSB OOT f l ag i s s e t ,
i nd i c a t i ng
that
the
pag e a b l e
ex e c u t i v e
r o u t i nes
a r e g o i ng
to pag e , t h e n t h e
phys i c a l pag e s o c c up i ed by t h i s pa r t o f
the
e x ec u t i v e
are
r e l e a s ed
t o t h e f r e e pag e l i s t a nd the S PTEs fo r th e s e pag e s
are se t up to
c o n ta i n
s ys t em
sect ion
tab l e
i nd i c e s .
In
a d d i t i o n , t h e f i r s t s ec t i o n t a b l e e n t r y i n t h e sys tem s e c t i o n
t a b l e ( F i g u r e 1 1 - 1 5 ) i s i n i t i a l i z e d to po i n t to the e x e c u t i ve
i mag e SYS . EXE .

2 2- 5

( Ch a p t e r 2 5 ) .

Tab l e 2 2 - 1
U s e o f Nonpaged Pool by Modu l e I N I T
G l ob a l Ad d r e s s o f Po i n te r

Fa c to r s Th a t Af f e c t S i ze

R e a l -T i m e B i tm a p

E XE $G L_R TB I TMAP

RBM $K L E NGTH + 4 *R EALT I M E S PT S
( but o n l y pr e se n t wh e n
REA LT I M E_S PTS n o n ze r o )

Ad a pt e r Co n t r o l B l o c k s
f o r I /O Ad a pt e r s

I OC $G L ADPL I S T

Num b e r and Type o f Ex t e r n a l Ad a pt e r s
( Ta b l e 22-2 )

(NH)

PCB Ve c to r and Se q u e n c e Ve c to r

SC H $G L PCBVEC
SC H $G L=S E QVEC

6 * ( MAXPROC E S S C NT + l )
( No te 1 )

(NH )

P r o c e s s He ad e r Ve c to r s

PHV$G L P I XBAS
PHV$G L=R EFCBAS

4 * ( BA LS E TC NT + l )
(No te 2 )

(NH )

Swa ppe r Ma p

SWP$G L_MAP

4 *WSMA X + 4
( No te 3 )

(NH )

Mo d i f i ed Pag e Wr i t e r Ar r a ys

M PW $A L PTE
M PW $AW P HVI N DE X

6 * M PW WRTC LUSTER

(NH )

Bo o t s t r a p I /O Ro ut i n e s

R PB $ L_I OVE C

S i z e o f Dr i v e r

(NH )

C PU -De pend e n t Co d e

E XE $ A L_L OAVEC

Log i c a l Nam e Bl o c k s fo r
S YS $D I S K a nd SYS $ S YS D I S K

LOG $G L_S LTF L

Te rm i n a l Dr i v e r a nd I t s
As s o c i a ted Da ta S t r uc t u r e s

( N o te 7 )

S i ze o f Imag e TTDR I VE R . EXE

Sy s tem D i s k Dr i v e r a nd I t s
As s o c i a ted Da ta St r uc t u r e s

( No t e 7 )

S i ze o f d i s k d r i v e r

Item

( No te 4 )
( No t e 5 )
(No te 6 )

Itsel f

S i ze o f I m ag e SYS LOAx x x . E XE

constant

( No te 6 )

i m ag e

OPERATING SYSTEM IN I T IAL I Z ATION

Ta b l e 2 2 - 1

( cont . )

U s e o f No n pag ed Po o l by Mo d u l e !N I T
( No t e s )
(NH )

Th e s e s t r uc t u r e s a r e a l l o c a t ed w i tho ut a 1 2 byt e head e r
tha t
conta ins a
s i ze
a nd
t ype
f i eld .
Th i s
i s no t a pro b l em
bec a use the se s t r uc tu r e s a r e n ev e r d e a l l o c a ted .
Ho wev e r ,
an
i n te r e s t i ng
s i d e e f fe c t o f t h i s ab s e nc e o f a h e a d e r i s tha t
S DA i n te r pr e t s d a ta a s s t r uc t u r e s i ze a nd
i nco r r ec t l y d um ps
the b eg i nn i ng o f n o n pag ed po o l .

(1)

On e ex t r a s l o t
i n e a c h a r r a y fo r
s ys tem
p r o c e s s h a s p r o c e s s i nd ex o f MAXPR OC ES SCNT .

PCB .

(2)

On e ex t r a s l o t i n e a c h a r r a y fo r
s ys t em
h e a d e r ha s b a l a n c e sl o t i nd ex of BALS ETCNT .

h e ad e r .

(3)

Ex t r a l o ng wo r d conta i n s a ze r o , a n e nd o f l i s t i nd i c a to r .

(4)

Th e boo t s t r a p I /O r o ut i n e s a r e l o c a t ed thro ug h a n
the Re s t a r t Pa r ame t e r B l o c k .

(5)

Lo a d a b l e r o u t i n e s a r e
JM P
to
a rg um e n t s
( Fi g u r e 22- 3 ) .

(6)

Th e l og i c a l name b l o c k s a r e c o n s t a n t b ec a use
the
s i ze s o f
b o th the l og i c a l name s t r i ng s ( S YS $D I S K a nd SYS $ S YS D I S K ) and
the equ i v a l enc e name
s t r i ng s
( D Dc u : )
a r e c on stan t .
Th e
l og i c a l
name b l o c k s a r e l i n k e d - i n to the s ys t em l og i c a l name
tab l e in the u s ua l m a n ne r .

(7)

Dev i c e d r i v e r s a nd
the i r
a s so c i a t ed d a ta
s t r uc t u r e s a r e
l i n ked
i n to
the
I /O d a t a b a s e
i n s ev e r a l wa ys .
Se e t h e
VAX/VM S Gu i d e to Wr i t i ng a Dev i c e Dr i v e r fo r d e ta i l s .

c o nnec ted
to
i n s t r uc t i o n s

2 2-7

the
in

" Sy s t em "
Sys tem

o ffset

ex ec u t i v e
th r o ug h
modul e
S YS LOAVEC

OPERAT ING SYSTEM IN I T IAL I Z AT I ON

Th e f i e l d s i n the r e s t a r t pa r am e t e r b l o c k u s e d by t h e r e s t a r t
r o u t i n e ( Ch a p t e r 2 3 ) a r e i n i t i a l i z e d .

10.

Th e phys i c a l pag e s r e p r e s e n t e d by t h e PFN b i tm a p s e t
up by
VMB a r e
p l a c ed o n t h e f r e e pag e l i s t .
( No t e th a t the pag e s
t h a t c o n ta i n t h e PFN b i tm a p m u s t b e m a pped v i r t ua l l y b e fo r e
t h e y c a n b e a c c e s s ed . )

11.

Th e s y s t em pag e t a b l e e n t r i e s f o r pag ed d yn am i c m emo r y a r e
s e t up .
I f pag e d
poo l
i s g o i ng t o pag e ( th e POO L PAG ING
SYSBOOT f l a g i s s e t ) , t h e n the S PTEs a r e s e t
up
to
conta i n
d emand
z e r o f o rma t PTEs .
I f po o l pag i ng i s t u r n ed o f f , then
phys i c a l pag e s a r e a l l o c a ted , t h e i r PFNs a r e l o ad ed i n to
the
S PTEs ,
the p r o t e c t i o n c od e s ( URKW ) a r e l o a d ed , a nd the v a l i d
b i t s a r e t u r ned o n .

12.

Th e p r e a l l o c a t ed
I /0
r e que s t pa c k e t s
a re
r emoved
f r om
n o n pag ed
po o l
and l i n ked tog e the r .
( Th e I R P l o o k a s i d e l i s t
i s d e sc r i bed i n Ch a p t e r 2 5 . )

13.

I f the SYS B OOT p a r am e t e r REALT IME S PTS
i s set
to
non z e r o ,
t h a t n um b e r o f
S PT E s
is
t a k e n f r om the l i s t o f a v a i l a b l e
S PTEs
{ Append i x E )
a nd d e s c r i b ed
in a
r e a l - t i m e b i tm a p
c o n t r o l b l o c k , a l l o c a t ed f r om n o npag ed po o l .

14.

Th e
a d a pte r
m a pped .
Th e e x t e r n a l
I / O a d a pt e r s
a re
r e co r d ed i n the
c o n f i g u r a t i o n wa s d e te rm i n ed
by VMB a nd
r e s ta r t pa r am e t e r b l o c k .
Th e r e a r e two d i s t i n c t
s t e ps to
i n i t i a l i z i ng e a c h a d a p t e r :
•
•

c r e a t i ng sys t em v i r t ua l pag e s tha t map t h e ph ys i c a l pag e s
c o n t a i n i ng ad a p t e r ad d r e s s e s a nd
i n i t i a l i z i ng
r eg i s te r s .

the

Ad a p te r i n i t i a l i z a t i o n
s ec t i on .

con ten ts
is

d i sc u s s ed

the s e

now

f u r th e r

access i bl e
in

the

nex t

15.

The PC B v e c to r a nd s e q u e n c e n umbe r vec to r
( Ch a pt e r 1 7 )
are
a l loca ted
f r om nonpa g ed po o l a nd i n i t i a l i z e d .
Al l s e q u e n c e
n umbe r s a r e i n i t i a l i z e d to z e r o .
Al l PC B v e c to r
slots are
s e t u p t o po i n t t o the PC B o f the n u l l p r o c e s s .
No te th a t
Th e
o n e e x t r a e n t r y i s a l l o c a t ed a t the end o f e a c h a r r a y .
e x t r a e n t r y i n the PC B v e c to r po i n t s to the sys tem PCB .
( Th e
s y s tem PCB i s d e f i n ed i n mod u l e PDAT .
I t s d ynam i c
contents
a r e l o ad ed by !N I T . )

16.

Th e s c h e d u l e r i s c a l l ed to m a k e c om p u ta b l e the two
proc esses
tha t are
a s sem b l ed
as
a
pa r t o f t h e e x e c u t i v e i m ag e , the
s wa ppe r a n d the n u l l p r o c e s s .

17.

Th e p r o c e s s h e a d e r vec to r s ( Ch a p t e r 1 1 ) a r e
i n i t i a l i zed
fo r
e a c h b a l a n c e sl o t .
Th e r e f e r e nc e c o un t a r r a y i s i n i t i a l i z ed
to c o n t a i n a neg a t i v e one in e ac h a r r a y e l em e n t .
Th e p r o c e s s
i nd e x
a r r a y i s i n i t i a l i z ed to c o n t a i n z e r o s , i nd i c a t i ng f r e e
ba l ance s l o ts .

2 2-8

OPERAT ING SYSTEM IN I T IALI ZATION

( Th e n u l l p r o c e s s i s the p r o c e s s wi t h
z e ro .
Be c a u s e t h e n u l l p r o c e s s d o es
r e qu i r e a ba l an c e s l o t .
Th i s a l l o ws a n
u s ed
fo r
a n o the r
p u r po s e ,
n ame l y to
s l o ts . )

a
proc ess
i nd ex
of
n o t swa p , i t d o e s n o t
i nd ex o f z e r o
to
be
i nd i c a t e f r ee b a l a n c e

As Append i x E i l l u s t r a t e s , the s ys tem head e r and sys t em pa g e
tabl e
i mmed i a t e l y f o l l o w t h e ba l a nc e
s l o t a r e a i n sys t em
a d d r e s s spa c e .
I n f a c t , po r t i o n s o f
the m emo r y manag em e n t
s ub s y s t em
t r e a t the
s y s t em h e ad e r a s
t h e o c c upa n t o f a n
a d d i t i o n a l ba l a nc e s l o t , o n e w i th a s l o t n um b e r e q ua l t o t h e
S YS B OOT pa r am e t e r
BALS ETCNT .
Th e t wo p r o c e s s head e r vec to r
a r r a ys h a v e o n e e x t r a e n t r y a t the end
to
r e f l ec t
th i s
f e a t ur e .
18 .

Th e swa ppe r m a p
( Ch a pt e r s l l
a nd
14)
i s a l loca ted
f r om
n o n pag ed
po o l .
I t s add ress
i s s to r e d i n g l o b a l l o c a t i o n
SWP $G L MAP a n d a l s o i n t h e swa ppe r ' s P O b a s e r eg i s t e r .
Pag e s
th a t appe a r
i n t h e swa ppe r m a p a r e a c c e s s i b l e a s P O v i r t ua l
pag e s wh e n t h e swa ppe r i s the c u r r e n t pr o c e s s .

19 .

Th e mod i f i ed pag e wr i t e r
a r r a ys
a l l o c a t e d f r om no npag ed po o l .

20 .

Th e boo t s t r a p I /O r o u t i n e s tha t a r e a pa r t o f VMB a r e c o p i ed
to no n pag ed po o l .
{ As wi t h the PFN b i tm a p , the pa g e s th a t
c o n ta i n these r o ut i nes mus t be
t empo r a r i l y ma pped
t o ma ke
t h em a c c e s s i b l e
to
IN I T ,
wh i c h
i s wo r k i ng
w i th m emo r y
m a n a g em e n t e n a b l ed . ) S o m e mo r e pa r am e t e r s tha t wi l l
be
u s ed
by t h e
r e s ta r t
r o ut i ne
( Ch a pt e r 2 3 )
are
l o a d ed i n to the
r e s t a r t pa r am e t e r b l o c k .

21 .

Th e C PU-d epend e n t c o d e i s l o ad ed
i n to po o l .
Th e v e c to r ed
l i nkage
to
th e se
r o u t i n e s , d e sc r i b ed i n a l a t e r sec t i o n o f
t h i s c h a p t e r , i s e s t a b l i shed .

22 .

Log i c a l
name
bloc ks
fo r
SYS $D I S K and
SYS $ S Y S D I S K
are
a l l oca ted
f r om n o npag ed po o l , even tho ugh a l l o th e r l og i c a l
name b l o c k s f o r s ys t em o r g r o up l og i c a l n a m e s a r e a l l o c a t ed
f r om pa g ed po o l .
Th i s i s b ec a u se pag e d po o l a l l o c a t i o n i s
n o t po s s i b l e above I PL 2 .
Th e two l og i c a l
n ame b l o c k s a r e
l i n k ed i n to t h e sys tem l og i c a l name t a b l e .

23 .

Th e t e rm i n a l d r i v e r ( S YS $ S YS TEM : TTDR I VER . E XE ) i s l o ad ed
i n to
n o n pag ed
po o l .
Th e e n t r y po i n t s o f t h e d r i v e r a r e l o a d ed
i n to t h e d e v i c e d a t a b l o c k ( DDB )
fo r
th e c o n so l e t e rm i n a l
( O PA O ) .
Th e d a t a s t r uc t u r e s f o r add i t i o n a l t e rm i n a l s wi l l be
e s t a b l i shed a s a r e s u l t of the AUTOC ONF I G URE ALL c omm and th a t
i s pa s s e d to SYSGEN a s pa r t o f t h e c ommand f i l e STARTU P . COM .

24 .

Th e d r i v e r fo r th e sys t em d ev i c e
i s l o ad ed
i n to n o n pa g ed
po o l .
Fi e l d s
in
i ts a s s o c i a t ed d a t a s t r uc t u r e s ( DDB , UC B ,
CRB , I DB , AD P ) a r e l o a d ed wi th i n fo rm a t i o n tha t d e pend s o n
wh i c h spec i f i c un i t a nd c o n t r o l l e r l oc a t e t h e sys t em d i s k .

25.

On c e the s ys t em d ev i c e c o n t r o l l e r a nd
un i t d e s i g na t o r s a r e
d e t e rm i n ed ,
the
equi va l en c e
n am e s
fo r
SYS $D I S K a nd
SYS $ S YS D I S K a r e s t o r ed
in
the i r
r e spe c t i ve
l og i c a l
n ame
bl ocks .

2 2-9

( Ch a pt e r s l l

a nd

12)

are

OPERATING SYSTEM I N I T IALI ZAT I ON

26.

Th e d r i v e r p r o l o g ue ta b l e s f o r the
th r ee d ev i c e s
{ ma i l bo x ,
n u l l d ev i c e ,
a nd c o n s o l e
t e rm i n a l )
th a t a r e l i n ked w i th
SYS . EX E , a nd a l so the D PTs f o r the t e rm i n a l d r i v e r
a nd
the
s y s tem d i s k d r i v e r ,
a re
l i n k ed
i n to t h e d r i v e r d a t a b a s e
{ l o c a t e d th r o ug h l i s thead I O C $G L_D PTL I S T ) .

27.

A p ag e o f phys i c a l memo r y { th e so -c a l l ed b l a c k h o l e pag e o r
r a bb i t ho l e pag e ) i s r e s e r v e d fo r UN I B US a d a p t e r po we r f a i l o n
t h e VAX- 1 1 /7 8 0 .
Wh e n powe r
fa i l ure occurs on a
UN I B US
ad apte r ,
a l l v i r t ua l pag e s m a pped to UBA r eg i s te r s o r UN I BUS
I/0 s p a c e { 2 4 p a g e s i n a l l ) a r e
r ema pped
to
th i s phys i c a l
p ag e .
Th i s
p r even t s d r i v e r s
fo r
UN I B US d ev i c e s
f r om
g e n e r a t i ng mul t i pl e m a c h i n e c h e c k s wh i l e the powe r i s o f f f o r
t h e UBA .
Powe r f a i l o p e r a t i o n s a r e d i s c u s s ed i n mo r e d e ta i l
i n Ch a pte r 2 3 .
Ma c h i n e c h e c k o pe r a t i o n i s b r i e f l y d i sc us s e d
i n Ch a p t e r 7 .

28 .

Th e m a x i m um a l l o wa b l e
n e c es s a ry)
to
r e f l ec t
memo r y .

wo r k i ng
set
is
r e ad j us ted
{if
the
amoun t o f a v a i l ab l e phys i c a l

Spe c i f i c a l l y , t h e n um b e r
of
phys i c a l
pag e s u s ed b y the
execut ive
{ Append i x E) i s s ub t r a c ted f r om a v a i l a b l e phys i c a l
memo r y .
Sy s t em usage i n c l ud e s n o t o n l y nonpaged
c o d e a nd
d a ta b u t a l s o
the s ys t em wo r k i ng s e t , M PW L O L IM IT pag e s o n
f r e e pag e
the mod i f i ed pag e l i s t , a nd FRE E L IM pag e s o n t h e
l i s t { b u t n o t t h e pag e s used by !N I T ) .
Th e v a l ue o f WSMAX i s
t h e n m i n im i zed w i t h th i s d i f f e r enc e .
29 .

Two f l ag s used by t h e r e s ta r t c od e

{ Ch a pte r 2 3 )

a r e c l ea r ed .

30 .

F i na l l y , ! N I T f r e e s up t h e pag e s tha t i t o c c up i ed
a nd
j umps
to
the sched u l e r .
Th i s m e a n s tha t the p r o t e c t i o n f i e l d s fo r
t h e s e s y s t em v i r t ua l pag e s a r e s e t to No Ac c e s s i n the sys t em
page
t a b l e and
the phys i c a l pag e s a r e pl ac e d o n to the f r e e
page l i st .
! N I T a c c ompl i sh e s th i s
by
c o pyi ng
a
sma l l
r o ut i n e
i n to
nonpag e d po o l and t r an s f e r r i ng c o n t r o l to th a t r o u t i n e .
Th e
r o u t i n e i t s e l f v a n i sh e s a s a r e s u l t o f the
f i rst a l locat i on
f r om po o l ,
because the
u s e o f th i s b l o c k o f po o l wa s no t
r e co r d e d a n ywh e r e .

22. 1 . 3

I /0 Ad a pt e r I n i t i a l i za t i on

Wh e n VMB p e r fo rmed i t s m emo r y s i z i ng , i t a l so i d e n t i f i ed t h e p r e s e n c e
a nd i d en t i t y o f e x t e r n a l a d a p t e r s .
T h e r e s u l t s o f th i s o pe r a t i o n we r e
s to r e d i n a 1 6 byte t ab l e i n the Re s t a r t Pa r ame te r
Bl o c k
{ at o f fset
RPB $ B C ONFREG ) .
!N I T u s e s th i s i n f o rm a t i o n t o i n i t i a l i ze e a c h o f the
a d a p ter s f o r l a te r u s e by SYSGEN ' s c o n f i g u r a t i o n o pe r a t i o n s .
{ Some o f
the
r o u t i n es
c a l l ed b y !N I T a r e fo und i n so u r c e mod ul e I N I TADP , a
l og i c a l ex t e n s i o n o f t h e cod e c o n t a i n ed i n m od u l e ! N I T . )

2 2-1 0

OPERATING SYSTEM INITIAL I Z ATION

Al t h o ug h some o f t h e i n i t i a l i z a t i o n th a t I N IT p e r fo r m s d e pend s o n t h e
nature
of
t h e ex t e r n a l I /0 a d a pt e r , the r e a r e two g en e r a l s te p s th a t
a r e t a k e n fo r e ac h a d a pt e r .
•

•

An a d a p t e r c o n t r o l b l o c k
tha t
i d en t i f i e s
the a d a pt e r
and
conta ins
i n fo rm a t i o n
a bo u t h o w t h e a d a p te r ' s
i n t e rn a l
r eg i s t e r s a r e m a pped i s a l l o c a te d
f r om no npag ed
poo l
and
l o a d ed .
Sys t em v i r t ua l spac e i s s e t
u p to m a p to
the
I /O
space
add resses
fo r i n t e r n a l a d a pt e r r eg i s te r s a nd o th e r I /O s pa c e
a s s i g nm e n t s .

Ta b l e 2 2 - 2 l i s t s the d i f f e r enc e s i n ADP s i z e a nd m a pp i ng
fo r e a c h o f t h e po s s i b l e e x t e r n a l a d a pte r s .

22 . 1 . 4

r e qu i r emen t s

C PU-Depend e n t Ro u t i ne s

Th e r e a r e two d i f f e r e n t type s o f C PU-d e p e nd e n t c o d e
th a t a ppe a r
in
Ve r s i o n 2
o f VM S a nd
two
c o r r e spond i ng m e tho d s th a t VMS u s e s f o r
i nc o r po r a t i ng the c od e .
•

•

Wh e n th e r e a r e o n e o r two
i n s t r uc t i o n s o r d a t a
r e fe renc e s
th a t d e pend o n the s pe c i f i c typ e o f C PU th a t i s b e i ng u s e d ,
the s y s tem u s ua l l y i nc l ud e s the c o d e o r d a t a s e q u e n c e f o r a l l
C PUs i n l i n e a nd u s e s the c o n t e n t s o f l o c a t i o n EXE $G B C PUTYPE
( Th i s
t o d e t e rm i n e wh i c h p i e c e o f the c od e or d a t a to
use .
l o c a t i o n wa s p r ev i o u s l y l o ad ed by SYSB OOT f r om the c o n t e n t s
o f t h e PR $_S I D r eg i s t e r . )
In the c a s e o f e n t i r e r o u t i n e s ( s uch a s the p u r g e d a t a pa th
rout ine ,
I OC $ P URGDATAP )
or
e n t i r e mod u l e s
( s uc h a s
the
m a c h i n e c h e c k h a nd l e r ) th a t a r e
C PU-d e pend e n t ,
a v e c to r ed
e n t r y po i n t t e c hn i que i s u sed .

Th e v e c to r ed e n t r y po i n t m e thod wo r k s
in
the
fo l l o wi ng
wa y .
Each
r e f e r e n c e w i th i n t h e
execut i ve
i m ag e t o a C PU-d e pend e n t r o u t i n e i s
d i spa tc h ed to a JMP i n s t r uc t i o n i n m o d u l e SYS LOAVE C
l i n k ed wi t h t h e
execut i ve
i m ag e SYS . EXE .
Th e C PU-d e pe n d e n t r o u t i n e s ( on e r o u t i n e f o r
e a c h C PU ) a r e l i n k ed tog e th e r i n to a s e r i e s o f CPU-depend e n t
i mag e s
wi th n am e s o f the fo rm SYS LOAx x x . EXE ( S YS L OA7 5 0 . EXE o r SYS LOA 7 8 0 . EXE ) .
! N IT u s e s the
C PU t ype
to
l o ad
the c o r r e c t C PU -d e pend e n t
image
SYS LOAx x x . EXE i n to n o n pa g ed po o l a s a pa r t o f s ys t em i n i t i a l i z a t i o n .
An o th e r v e c to r mod u l e c a l l ed
LOAVE C
( a c t ua l l y the
same mod u l e
as
SYS LOAVE C w i th a d i f f e r en t s e t t i ng o f a c o nd i t i o n a l a s s em b l y f l ag ) ,
l i n k ed i n to e a c h C PU-d e pe nd e n t i mag e SYS LOAx x x . EXE , c o n t a i n s a n o f f s e t
i n to
the
l o ad a b l e
i mag e
f o r e a c h o f t h e C PU -d epend e n t s u b r o u t i ne s .
! N I T us e s the i n fo rm a t i o n i n th i s t a b l e to ad j us t the a rg um e n t s o f t h e
JM P
i n s t r uc t i o n s
( i n mod ul e
SYS LOAVEC )
so
th a t they po i n t to t h e
c o r r e c t r o u t i n e s i n SYS LOAx x x . EXE .
Th e i n i t i a l
d e s t i na t i o n s o f a l l
the JMP
i n s t r uc t i o n s
is
EXE $ L OAD ERROR , a g l o b a l a d d r e s s o f a HA LT
i n s t r uc t i o n w i th i n m od u l e SYS LOAVEC - i n SYS . EXE .
If
a ny of
th e s e
C PU-d e pe nd e n t
rout i n e s
is
r e fe r enced
b e fo r e ! N I T h a s c ompl e t ed i t s
i n i t i a l i za t i o n , the s ys t em wi l l h a l t .

2 2- 1 1

OPERATING SYSTEM I N IT IALI ZAT I ON
Ta b l e 2 2 - 2
Ex t e r n a l Ad apte r I n i t i a l i za t i o n

Ad apt e r Type

S i ze o f Ad apt e r
Co n t r o l B l o c k ( byt e s )

Number o f Sys t em Vi r tua l
Pag e s Ma pped fo r Ad a pt e r

Lo c a l Memo ry

No n e ex i s t s

On e Pag e

MA7 8 0 Sh a r ed Memo r y
( VAX- 1 1 /7 8 0 o n l y )

112 + 4*16
(No te 1 )

UN I B US Ad a pt e r
(VAX- 1 1/7 5 0 )
(VAX-1 1 /7 8 0 )

One Pag e

1 76

8 + 16
112
1 1 2 + 1 48 + 4*128
( No te 2 }

772

(No te 3 )

MAS SBUS Ad ap t e r

8 Pag e s

DR 7 8 0 I n t e r fa c e
( VAX- 1 1 /7 8 0 o n l y )

4 Pag e s

Un o c c up i ed Ne xus Sl o t

No n e Ex i s t s

On e Pag e t o Al l o w Ac c es s

(1}

Th e r e a r e 1 1 2 byt e s i n t h e bod y o f the ADP pl us spa c e fo r
v ec to r s .

l o ng wo rd

(2)

Th e VAX- 1 1 /7 5 0 ADP c o nta i n s 1 1 2 byt e s o f d a ta a nd no th i ng el s e .
UN I B US
v ec to r s a r e c o n t a i n ed i n the sec ond pag e o f the sys tem con t r o l bloc k .
the
i n te r r upt
serv i c e
Th e VAX- 1 1 /7 8 0 ADP c o n ta i n s 1 1 2 byt e s o f d a ta ,
r o ut i n e
fo r
t h e UBA wh i c h i s 1 4 8 byt e s l o ng ( i n Ve r s i o n 2 . 0 ) , and 1 2 8
l o ng wo rd v ec to r s ,
c o r r e spo nd i ng
to
UN IBUS
v ec to r s
f r om
0
to
774
( oc ta l ) .

(3}

E i g h t pag e s m a p t h e UBA i n te r nal r eg i s t e r s s u c h a s mapp i ng
r eg i s t e r s ,
d a t a pa th
r eg i s t e r s ,
a nd
the
l i ke .
S i x t e en pag e s map the UN IBUS I/0
pag e to a l l o w v i r t ua l ac c e s s to d ev i c e CSRs , d a ta r eg i s t e r s , a nd so o n .

2 2- 1 2

OPERATING SYSTEM I N ITIAL I ZATION

Th e c o s t o f s e pa r a t i ng o u t C PU-d e pend e n t
r o ut i ne s
f r om the s ys t em
i m ag e ,
o ne e x t r a
l ev e l o f
i nd i r ec t i o n ,
i s f a r o utwe i g h ed b y t h e
b en e f i t s , f ewe r ex ec u t i o n t i m e d ec i s i o n s a nd no n e ed
fo r
sepa r a te
e x e c u t i ve
i mag e s
fo r
e a c h C PU .
Th e l i n ka g e tha t i s e s ta b l i sh ed b y
INIT f o r C PU-d e pe nd e n t r o u t i n e s i s i l l us t r a t ed i n F i g u r e 2 2 -3 .

22. 2

IN I T IAL I ZATION IN PROC ESS CONTEXT

F u r the r s t eps i n s ys t em i n i t i a l i z a t i o n r equ i r e tha t th e y be
pe r fo rmed
Sys tem s e rv i c e s c an o nl y b e c a l l ed wh i l e ex e c ut i ng i n
by a
process .
p r o c e s s c o n te x t b ec a u s e
the q uo t a a nd p r i v i l eg e c h e c k s a r e m a d e
ag a i nst
p r o c e s s d a ta s t r uc t u r e s .
A c omma nd l a ng uag e i n t e r p r e te r c an
e a s i l y b e ma pped i n to P l s p a c e ,
a
pe r - p r o c e s s po r t i on o f v i r tu a l
ad d r e s s
s pa c e tha t
i s o n l y a v a i l ab l e wh en e x ec u t i ng
i n process
c o n t ex t .
Th e p r o c e s s ph a s e o f s y s t em i n i t i a l i za t i o n i s d i v i d ed
i n to
two p i e c e s , t h a t pe r fo rmed by a s p e c i a l p r o c e s s c a l l ed SYS INIT a nd the
s te p s pe r fo rmed by t h e c omma nd f i l e STARTU P . C OM .

SYS IN IT P r o c e s s

22 . 2 . 1

Wh e n the
s c hed u l e r
exec utes ,
i t s e l ec t s t h e
h ighest
p r i o r i ty
c omputa b l e
process
fo r
e x ec u t i o n .
Bec ause
the r e a r e o n l y t wo
p r o c e s s e s i n e x i s t e n c e a t th i s t i m e , the s wa ppe r
process
i s a l wa ys
s e l e c ted
( be c a u s e
i t has a p r i o r i ty o f 1 6 and the n u l l p r o c e s s h a s a
p r i o r i ty o f 0 ) .
Th e
swa pp e r
i mmed i a t e l y c r ea t e s a n o the r
proce s s ,
c a l l ed
S YS I N I T ,
t h a t p e r f o r m s tho se a spe c t s o f s ys t em i n i t i a l i za t i o n
t h a t r equ i r e p r o c e s s c o n t ex t .
In o ne s e n s e ,
S YS INIT
i s a n e x t e n s i o n o f the
swa ppe r p r o c e s s .
Howe ve r ,
the
i n i t i a l i za t i o n c o d e i s i so l a t ed to p r e v e n t e n c umbe r i ng
t h e swa pp e r w i th c od e tha t o n l y e x ec u t e s o nc e d u r i ng
the l i fe
of a
s ys t em .
( Th i s
i s o ne o f s ev e r a l
techn i que s u s ed d u r i ng s ys t em
i n i t i a l i za t i o n a nd p r o c e s s c r e a t i o n
to c a us e s e l d om
u s ed cod e
to
d i s a ppe a r a f te r
it
is
used .
A l i s t o f s uc h techn i qu e s a pp e a r s i n
Append i x A . )
Th e m a j o r f un c t i o n s tha t SYS INIT pe r fo rms c a n be
g ro ups .
•
•
•

g ro u pe d

i n to

th r e e

Th e pa g e f i l e , s wa p f i l e , a nd d um p f i l e a r e
all
o pened
a nd
the i r l o c a t i o n s o n d i s k s to r ed i n r e spec t i ve d a ta s t r uc tu r e s .
RMS a nd
th e
s ec t i o n s .

s ys t em

m e s sag e

file

Sys t em p r o c e s s e s
( d i s k ACP ,
Jo b
f o rma t t e r , a nd O PC OM ) a r e c r e a ted .

2 2- 1 3

a re

m a pped

Co n t ro l l e r ,

s ys t em

the

error

SYS.EXE
JSB

G " IOC$PURGDATAP

SYSLOAxxx.EXE

(This linkage Is established at
link time to vector In
module SYSLOAVEC.)

(vector for purge datapath routine
.LONG IOC$PURGDATAP - .)

module
SYSLOAVEC
Each vector In SYSLOAVEC
Initially contains a JMP (with
absolute addressing) to an
Internal error routine. If a
loadable routine were called
before the linkage Is estab
lished, that error routine will
halt.

(vector for purge datapath
routine)
IOC$PURGDATAP:

(

··---�·

this linkage dynamically
established by INIT

JMP @ # ....._____..

}

(

Each vector In LOAVEC con
tains a self relative displace
ment (offset) to the routine In
question.

IOC$PURGDATAP: :
real purge datapath routine
RSB

Modules LOAVEC and SYSLOAVEC are
produced from the same source with
alternate settings of an assembly
time parameter

I N IT modifies the destina
tions of the JMP Instructions
after It loads
SYSLOAxxx.EXE.

F i gure 2 2 - 3

module
LOAVEC

L inkage and Contro l F l ow Examp l e for
CPU-Dependent Routines

)

OPERATING SYSTEM IN I T IAL I Z ATION

2 2 . 2 . 1 . 1 Po o l Usag e by SYS INIT
S Y S I N I T , l i ke ! N I T ,
c o ns um e s
l a rg e
amoun t s o f n o npag ed po o l a nd s ome pag ed po o l .
Howe v e r , t h e s i z e s o f
v a r i o u s b l o c k s a r e n o t d i r e c t l y r e l a t ed
t o SYS BOOT pa r am e t e r s .
In
add i t i o n ,
w i th o n e e x c e p t i o n ,
all
b l o c k s a l l o c a ted d i r e c t l y o r
i nd i r e c t l y b y SYS IN IT i n c l ud e a 1 2 b y t e head e r tha t c o n t a i n s a
s i ze
f ield
a nd
un i q ue
ident i f i e r
fo r
e ac h s t r uc t u r e .
A s am p l e l i s t o f
s t r uc t u r e s tha t a r e a l l o c a ted f r om n o npag ed po o l a s a
resul t o f
the
e x e c u t i o n o f S YS I N IT i n c l ud e
-

•
•
•
•

s o f twa r e PC Bs a nd J I B s fo r s ys t em p r o c e s s e s ,
f i l e c o n t r o l b l o c k s a nd wi n d o w c o n t r o l b l o c k s fo r a l l
f i les ,

ope ned

a vo l um e co n t r o l b l o c k f o r the sys t em d i s k , a nd
Th e s e s t r uc t u r e s
ma i l bo x e s fo r the Jo b C o n t r o l l e r a nd O PC OM .
a r e a c t ua l l y c r e a t ed
as
a
r esul t o f exec ut i on o f
the
p r o c e s s - s p e c i f i c i m ag e s .

The o ne b l o c k of n o npag ed poo l a l l o c a t ed
by SYS INIT th a t does
no t
c o n t a i n a t ype c od e i s the pag e f i l e b i tm a p .
Th i s s t r uc t u r e i s e a s i l y
i d en t i f i a b l e i n a n S DA d ump a s a l a rg e b l o c k o f UN KNOWN t ype tha t h a s
a n umbe r o f b i t s equa l to the s i z e i n b l o c ks o f PAG EF I L E . SY S .

2 2 . 2 . 1 . 2 De ta i l ed Ope r a t i o n o f SYS I N I T
S YS I N I T t a k e s a r e l i s t e d h e r e .
1.

Th e

d e t a i l ed

s t e ps

that

Sys tem l og i c a l
n am e s
a r e c r e a t ed
fo r
SYS $ S YS T EM
a nd
SYS $ S HARE .
Th e c r e a t i o n o f the se name s c a nno t be d e l a yed
u n t i l the c r e a t i o n of the S TARTUP p r o c e s s b e c a use th e s e names
a r e n e e d ed a s a pa r t of t h e c r ea t i o n of th a t p r o c e s s .
•
•

Th e n am e o f t h e i mag e
tha t
is
p r o c e s s i s S YS $ S YS TEM : LOG INOUT .

pa s s ed

the

STARTUP

Th e LOG INOUT i ma g e pe r fo rm s a m e rg ed
i mag e a c t i v a t i o n
( Ch a p t e r 1 8 )
to ma p t h e DC L c ommand l a ng uag e i n t e r pr e t e r
i n to P l spa c e .
Th e i m a g e
a c t i v a to r
uses
l og i c a l
n am e
SYS $ S HARE to
loca te
the
sha r e a b l e i m ag e DC LTAB LES . E XE
t h a t c o n t a i n s the c ommand d a t a b a s e fo r the
DC L c ommand
l a ng u a g e i n t e r p r e t e r .

Th e s y s t em t i m e i s c a l c u l a t ed a nd s to r ed .
I f t h e S E TT IM E f l a g wa s pa s s ed to SYSB OOT , o r i f t h e c o n t e n t s
of
t h e TODR r eg i s t e r i nd i c a t e tha t i t c o n t a i n s a m e a n i ng l e s s
n um b e r ( Ch a p t e r 1 0 ) , t h e n a n e w v a l ue fo r t h e sys t em t i m e
is
so l i c i t ed f r om the c o n so l e t e rm i n a l .
In any case ,
the
c a l c ul a te a
n ew
copi es t h e cur rent
m emo r y t o t h e d i s k

Set Time
s y s t e m se rv i c e
i s c a l l ed
to
s ys t em
t i me .
I n ad d i t i o n , t h a t s e r v i c e
pa r a m e t e r s e t t i ng s f r om t h e i r l o c a t i o n s i n
i m ag e o f the e x e c ut i v e ( S YS . E XE ) .

2 2-1 5

OPERAT ING SYS TEM IN I T IAL I ZAT I ON
3.

I f t h e UAFALTERNATE
SYSBOOT
f l ag
is
set ,
then a
s ys t em
l og i c a l
n am e
c a l l ed
SYS UAF i s c r ea t ed wi th the eq u i v a l en c e
n am e SYS UAFALT .
Th i s f e a t u r e a l l o ws
•

•

s e l e c t i o n o f a n a l t e r n a t e a u tho r i za t i o n f i l e i f a log i c a l
n ame
c a l l ed
SYS UAFALT
is
c r e a ted
l a te r
in
the
i n i t i a l i za t i o n s eque n c e tha t t r a n s l a t e s to th i s a l te r n a t e
file , or
a u toma t i c l og i n w i th s ys tem m a nag e r p r i v i l eg e s to a n yo n e
i f no
l og i c a l
n a m e c a l l ed SYSUAFALT i s c r e a t ed .
Th i s
po s s i b i l i t y i s u s e f u l i f the sys tem m a n ag e r
f o rg e t s h i s
p a s swo r d .
{ U s e o f th i s c apa b i l i ty sho u l d be a c compa n i ed
by a spec i a l pa rame t e r f i l e o r s ta r t up c ommand f i l e
tha t
p r ev e n t s un r e s t r i c t ed a c c e s s to the sys t em . )

Th e fo l l ow i ng f i l e s a r e o pe n e d by t h e AC P r o u t i n e s l o c a t ed i n
t h e execut ive :
[ S YS E XE ] PAG E F I L E . SYS
[ S YS EXE ] S YS DUM P . DM P
[ S YS EXE ] SWAPF I L E . S YS
[ S YS E XE ] RM S . EXE
[ S YSMSG ] S YSMSG . EXE

Th e pag e
file
is
i n i t i a l i z ed .
Th i s r eq u i r e s tha t
the
i n f o rm a t i o n o b t a i n ed
in
t h e p r ev i o u s s te p b e l o ad ed i n to a
w i n d ow c o n t r o l b l o c k
t h a t d e sc r i b e s
t h e pag e
file .
Th e
a d d r e s s o f t h a t WCB i s s to r e d i n the pag e f i l e c o n t r o l b l o c k
{ F i g u r e 1 1 - 2 2 ) fo r th e i n i t i a l
pag e
file
{ th e b l o c k w i th
i nd e x 3 ) .
I n a d d i t i o n , a b i tm a p t h a t d e sc r i b e s the av a i l a b i l i ty o f e a c h
b l ock
in
t h e pag e f i l e i s a l l o c a ted f r om nonpa g ed po o l a nd
i n i t i a l i z ed to a l l o n es
to
i nd i c a t e
tha t a l l
b l o c ks
a re
a va i l a b l e .

Th e a d d r e s s { l og i c a l b l o c k n umbe r ) a nd s i z e o f t h e d ump
a r e s t o r ed { a t g l o b a l l o c a t i o n EXE $G Q_S YSDM P ) .

f i le

Th e s wa p f i l e i s i n i t i a l i z e d .
As wa s d o ne fo r the pag e f i l e ,
a
w i n d o w c o n t r o l b l o c k i s a l l o c a ted f r om nonpag ed po o l .
Its
a d d r e s s i s s t o r ed i n the swa p f i l e t a b l e e n t r y
{ Ch a pt e r 1 1 )
f o r th e f i r s t swa p f i l e { th e o ne wi th i nd ex 1 ) .
Th e swa p f i l e i s d i v i d ed i n to equa l
s i z e s wa p s l o t s ,
each
s l o t equa l
in
s i ze
to
the
SYSB OOT pa r am e t e r WSMAX .
Th e
n um b e r o f s l o t s i n the f i l e ( m i n im i zed wi th 1 2 8 , t h e m a x i m um
n um b e r o f
s l o ts
i n a s i ng l e swa p f i l e ) i s r ec o r d ed i n t h e
S FTE .
I n a d d i t i o n , t h e m a x i m um n um b e r o f p r o c e s s e s t h a t
the
s ys tem c a n s uppo r t { s to r ed i n g l o b a l l o c a t i o n S C H$GW PROC L I M )
i s t a k e n a s t h e m i n imum o f
s wa p f i l e
s l o t c o u n t -a nd
the
i n i t i a l MAXPROC ES SCNT SYS BOOT p a r am e t e r .
( Th e c o n t e n t s o f
S C H $GW PROC L I M c a n b e i n c r e a sed l a t e r b y i n s t a l l i ng a s e c o nd
s wa p fTl e . )
A s l i g h t c h a ng e to th i s i n i t i a l i z a t i o n , r emov i ng the l i m i t o f
1 2 8 o n t h e s i z e o f the b i tm a p , h a s b e e n a d d e d to Ve r s i o n 2 . 2
o f VAX/VM S .
Th i s c h a ng e i s d e sc r i bed i n Append i x F .

2 2-1 6

O P E RATING SYSTEM IN ITIAL I Z AT I ON
8.

RM S a n d the s ys t em m e s s a g e f i l e a r e s e t up a s pag e a b l e s y s t em
sec t i ons .
Th e
sec t i on
t ab l e e n t r i e s
t h a t d e s c r i be t h e s e
s ec t i ons a r e i n i t i a l i zed as
the
second
a nd
th i r d
sec t i on
tabl e entr i e s
in
the
s ys t em h e ad e r .
( Th e
f i r s t s ys t em
sec t i on tab l e e n t r y , the one
t h a t d e sc r i b e s
the
e x e c u t i ve
i mag e i t s e l f , wa s s e t up by IN I T . )

Th e s e c o nd a n d th i r d b l o c k s o f
t h e d um p f i l e c o n ta i n
the
c o n t en t s of t h e e r r o r l og bu f f e r s i f t h e s ys t em j u s t c r a sh e d .
Th e s e b u f f e r s we r e wr i t t e n to the d ump f i l e by t h e b ug c h e c k
c o d e ( Ch a p t e r 7 ) s o t h e i r c o n t e n t s wo u l d no t b e l o s t .
I f the
sys t em is r e b o o t i ng a f t e r a c r a sh , SYS I N I T c o p i e s the
s e c o nd
a nd
th i r d b l o c k s o f
t h e d ump f i l e b a c k to the e r r o r l og
b u f f e r s so t h e i r
contents wi l l
e v e n t ua l l y be
wr i t t e n
to
[ S YS ERR ] ERRLOG . S Y S .
Th e bug c h e c k
r o u t i ne
i nc l ud ed
the e r ro r
l og
e n t r y th a t
d e s c r i be s t h e r e a so n f o r the c r a sh i n the f i r s t b l o c k o f the
d um p f i l e as pa r t of t h e d um p f i l e h e a d e r b l o c k .
Th i s wa s
d o n e to avo i d the l o s s o f t h i s d a ta i n the even t th a t th e two
e r r o r l og bu f f e r s we r e f ul l a t the t i me o f
t h e c r a sh .
If
t h i s wa s
t h e c a se wh e n the s ys t e m c r ashed , SYS I N I T w i l l b e
u n a b l e to c o py t h i s e r r o r l og e n t r y to o n e o f t h e e r r o r
l og
In
tha t c ase ,
t h e e r r o r l og e n t r y th a t ac t ua l l y
buffe r s .
d e s c r i b e s t h e c r a sh wi l l n ev e r a ppe a r i n a n e r r o r l og r e po r t .
Howev e r ,
in
a l l c a s e s i nc l ud i ng t h i s r a r e o c c u r r e n c e o f t wo
f ul l e r r o r l o g bu f f e r s , t h e r e a so n f o r the
s ys t em c r a sh
is
c o n t a i n e d i n t h e d um p f i l e .

10.

Th e s y s tem d i s k i s m o un t ed .
A d i r e c t r es u l t o f th i s
c r e a t i o n of the d i s k AC P f o r the s ys tem d i s k .

the

F r om t h i s po i n t o n , t h e AC P i s ava i l ab l e f o r f i l e o pe r a t i o n s .
Th e
p r i m i t i v e AC P r o u t i n e s tha t a r e a pa r t o f SYS . EXE a r e n o
l o ng e r r e qu i r ed a nd w i l l d i s a ppe a r
in
t i m e d ue
to
s ys t em
wo r k i ng
set
r e pl a c em e n t .
Th e pa r t i c u l a r c o n s t r a i n t th a t i s
r emoved i s t h a t f i l e s a c c e s s ed f r om th i s po i n t o n a r e
no t
r e qu i r ed to b e c o n t i g uo us a nd c a n r e s i d e i n s ubd i r e c to r i e s .
11 .

Th r e e mo r e sys t em p r o c e s s e s
J o b C o n t r o l l e r ( J OB C ONTRO L )
Ope r a to r Commun i c a tTo n P r o c e s s ( O PC OM )
E r r o r Log B u f f e r Fo rma t P r o c e s s ( E RRFMT )
a r e c r e a t ed .

12.

22 . 2 . 2

F i n a l l y , a p r o c e s s c a l l ed STARTU P i s c r ea t ed .
Th e
i mpo r ta n t
po i n t a b o u t
th i s p r o c e s s
is
tha t
it
e x e c u t e s the i m a g e
LOG INOUT ,
wh i c h m a ps
a
c omma nd
l a ng uag e
i nterpreter
( Ch a pt e r 2 0 ) .

Th e S TARTUP P r o c e s s

Th e
S TARTU P
process
c rea ted
by
SYS I N I T
c ompl e te s
s ys t em
i n i t i a l i za t i o n .
Th i s p r o c e s s i s the f i r s t p ro c e s s i n t h e sys t em tha t
i nc l ud e s a c omma nd l ang uag e i n t e r p r e te r .
Th e i nc l us i o n o f DC L a l l ows
the o pe r a t i o n o f th i s p r o c e s s to be d i r e c ted by s i mpl e c omma nd s .

2 2-17

OPERAT ING SYSTEM IN I T IAL I ZAT I ON

2 2 . 2 . 2 . 1 S TARTUP . COM - Th e m a j o r s t eps tha t a r e pe r f o rmed by c ommand s
i n t h i s f i l e c an b e d i v i d ed i n to th r e e m a j o r s t eps .
1.

S e v e r a l s ys t em l o g i c a l nam e s a r e c r e a t ed .
•

Th e s e i nc l ud e :

VM S - s pe c i f i c n am e s
S YS $ L I B RARY
SYS $ M E S SAG E
SYS $ H E L P
•
•
•

Log i c a l n am e s u s ed by t h e s ymbo l i c d e b ug g e r
Name s r e qu i r ed b y l ang uag e r un- t i m e sys tems
C O B O L- 7 4 a nd VAX- 1 1 PASCAL

fo r

VAX- 1 1

Lo g i c a l names r eq u i r ed by c ompa t i b i l i ty mod e u t i l i t i e s

Th e
INSTALL u t i l i ty
is
i nv o k e d
to
s h a r e a b l e i m a g e s k n o wn to the s ys tem .

make

Th e SYSGEN u t i l i t y i s
i nv o k e d
to
a utoma t i c a l l y c on f i g u r e
e x t e rna l
I /O d ev i c e s .
( If
a
us e r -wr i t ten d r i v e r m us t be
l o ad ed b e fo r e n o rm a l VM S d r i v e r s ,
S TARTU P . C OM s h o u l d be
m od i f i ed
to
i n c l ud e
LOAD a nd CONNEC T c omma nd s b e fo r e the
AUTOC ONF IGURE ALL c omma nd to S YSGEN . )

Th e RM S S HARE u t i l i ty e x e c u t e s a nd a l l o c a t e s a b l o c k o f pag ed
po o l { d e fa u l t o f 2 0 pa g e s ) to c o n t a i n the d a ta s t r uc t u r e s f o r
s h a r ed f i l e s .

F i n a l l y , a s i t e - s pe c i f i c c omma nd
i s i n vo k e d .

file

p r i v i l eg ed

[ S YSMGR ] S YSTARTUP . C OM

2 2 . 2 . 2 . 2 S i t e- S p e c i f i c S t a r t up Comma nd F i l e - Th e
c ommand
f i l e tha t i s d i s t r i b u t ed w i th VM S i s emp t y .
used to :

s i t e - spec i f i c
Th i s f i l e c a n be

•

S t a r t ba t c h a n d p r i n t que u e s

•

Se t t e r m i n a l s p e ed s a nd o th e r d ev i c e c h a r a c t e r i s t i c s

•

C r e a t e s i t e - s p e c i f i c sys tem l og i c a l n am e s

•

I n s t a l l mo r e p r i v i l eg e d a nd s h a r e ab l e i m ag e s

•

Lo ad us e r -wr i t t e n d ev i c e d r i v e r s

•

Mo un t vo l um e s o th e r than t h e s ys t em d i s k

•

•
•

Lo ad the c o n so l e b l o c k s to r ag e d r i v e r
C ONNECT C ONSOLE c omma nd
to
SYSGEN
m ed i um

a nd

(if
a nd

d e s i r ed )
wi th a
m o un t t h e c o n s o l e

S t a r t D E Cn e t { i f p r e s e n t o n the s ys tem )
Run SDA t o p r e s e rv e the p r ev i o u s d um p f i l e i n c a s e the sys t em
c r a shed

2 2-1 8

OPERAT ING SYSTEM I N I T IALI Z ATION
•

P r o d u c e a n e r r o r l og r e po r t

•

An n o un c e s y s t em av a i l ab i l i ty

22. 3

THE SYSGEN PROGRAM

Th e SYSGEN p r og r am
un r e l a te d wa ys .
e
•

f i ts

i n to

the

i n i t i a l i za t i o n

I t i s i nv o k e d d i r e c t l y by S TARTUP . COM
e x t e r n a l I / O d ev i c e s .

s e q u e nc e

two

AUTOCON F IGURE

the

I t i n t e r a c t s i nd i r ec t l y by p r od uc i ng pa r am e te r f i l e s tha t m a y
b e u s e d by SYS B OOT f o r f u t u r e boo t s t r a p o pe r a t i o n s .

Th e r o l e o f SYSGEN i n a u t o c o n f i g u r i ng the I /O s ys tem i s d e s c r i b ed
in
the VAX/VM S Gu i d e
to Wr j t i ng a Dev i c e D r i v e r .
Th i s s e c t i o n b r i e f l y
c ompa r e s a nd c on t r a s t s the o p e r a t i o n s tha t SYSBOOT a nd S YSGEN pe r f o rm
o n pa r a m e t e r f i l e s .
Ta b l e 2 2 - 3 s umma r i z e s th i s c om pa r i s o n .

22. 3. 1

C o n t e n t s o f Pa r am e t e r B l o c k

A c ommo n mod ul e c a l l ed PARAMETER i s l i nk e d i n to bo th t h e SYS B OOT a nd
S YSGEN i m ag e s .
Th i s mod u l e c o n t a i n s i n fo rma t i o n abo ut e a c h a d j us ta b l e
pa r am e t e r ( Ta b l e 2 2 - 4 ) .
Th i s d a ta n ev e r c h a ng e s .
I n ad d i t i o n ,
e ac h
pa r am e t e r o c c up i e s
a
c e l l i n a tab l e o f wo r k i ng v a l u e s .
I t is th i s
t ab l e tha t i s
•

d i s pl ayed by S H OW pa r am e t e r - name c ommand s ,

•

a l t e r e d by S E T pa r am e t e r - name va l u e c ommand s , a nd

•

o v e rwr i t t e n by a USE c ommand

Th e r e i s a l so a c o py o f the wo r k i ng tab l e l i n k ed
i n to
the
e x ec u t i ve
( Th i s ta b l e i s p r od uc ed f r om the same so u r c e m od u l e
i ma g e ,
SYS . EXE .
a s PARAMETER w i th a
d i f f e r e n t s e t t i ng
o f a c o nd i t i o n a l
a s s em b l y
pa r am e t e r .
Th e r e s u l t a n t mod u l e i s c a l l ed SYSPARAM . )

22. 3. 2

Us e o f Pa r ame t e r F i l e s by SYSBOOT

F i g u r e 2 2 - 4 s hows the f l ow o f pa r a m e te r v a l ue d a t a d u r i ng a boo t s t r a p
Th e n umbe r s i n the f i g u r e d e sc r i b e the s i g n i f i c a n t s t e ps
o pe r a t i o n .
i n s e t t i ng v a l ue s o r m ov i ng d a t a .
(1)

Th e f i r s t
s t e p tha t
SYSB OOT p e r fo rm s
is
to
l o c a te
the
execut i v e
i m ag e a nd
r e ad
the
pa r amete r s e t t i ng s f r om the
e x e c u t i v e i ma g e i n to i t s wo r k i ng t a b l e .
In the
l a ng uag e o f
SYS BOOT a n d S YSGEN c omma nd s , t h i s s t ep i s a n i m p l i ed
U S E C URRENT
c o mmand .
Th i s o pe r a t i o n c a u s e s the sys tem to be
i n i t i a l i z ed
wi th
the
pa r am e t e r
s e t t i ng s
used d u r i ng
th e p r e v i o us
c o n f i g u r a t i o n o f the sys t em ( d ue to step 5 ) .
2 2 -1 9

OPERAT ING SYSTEM I N I T IA L I ZAT I ON
Table 2 2 - 3
Compar i so n o f SYS BOOT and SYSGEN
SYSGEN

SYSB OOT

Pu r po s e

SYSB OOT

SYSGEN has

us i ng
t he
s ys tem
c o n f i g u r es
t h e e x ec u t i v e i m ag e o r
fi l e .

pa r am e t e r s
f r om
f r om a pa r am e t e r

•
•

It
in

•

Sy s t em

p u r po s e s .

c r e a t e s pa r am e t e r f i l e s
fo r
f u t u r e boo t s t r a p o pe r a t i o n s .

l o ad s d ev i c e

d r ivers

a nd

s t r uc t ur e s .

i n s ta l l s

c r e a te s a nd
a nd

use

pa rame t e r s
in
wi t h the WRITE

a s s o c i a t ed d a ta

page

un r e l a t ed

d yn am i c
I t mod i f i e s
system
r unn i ng
the
ACTIVE command .

•

Use

fo u r

the i r

a d d i t i o nal

s wa p f i l es .

I n i t i a l i za t i o n

o c c up i e s
The o nl y pl ac e tha t SYSGEN
in
se quenc e is r e l a ted
i n i t i a l i za t i o n
the
is
It
to i t s d r i v e r func t i o n .
i nv o ked
t o AUTOCONF IGURE a l l I /0 d ev i c e s .

the
SYSB OOT
boo t s t r a p
is
s e c o nd a r y
but
VM B
tha t
executes
a ft e r
p r og r am
to
the
is
pa s s ed
be fo r e
control
ex e c u t i v e .

Env i ronmen t

SYSGEN
executes
in
the
n o rmal
a u t i l i ty prog r am .
of
e nv i r o nm ent
Th e
d r i v e r and swap/pag e
f unc t i o n s
r e qu i r e
A
( CMKRN L ) .
WRITE
p r i v i l eg e
ACTIVE
c ommand a l so r e qu i r e s CMKRNL
pr i v i l eg e .
Th e
pa r am e te r
file
o pe r a t i o n s
are

SYSB OOT r un s in a s t a nd a l o n e env i r o nment
wi t h
no f i l e system , m em o r y manag emen t ,
any
o th e r
or
c o ntex t ,
proc e s s
env i r o nm e n t prov i d ed by VM S .

p r o t e c ted

Va l i d

t h r o ug h t h e

f i l e s ys tem .

Command s

USE

US E

U S E f i l es pe c
US E CURRENT
US E DEFAULT
U S E ACTIVE

US E f i l e s pec
U S E CURRENT
USE DEFAULT
no equ i v a l ent c ommand
S ET

S ET

SHOW
CONTINUE ( E X I T )
no equ i v a l en t c ommand

S H OW
E X I T ( C ONT INUE )
WR ITE

eq u i v a l en t c omma nd s

Comma nd s As s o c i a ted

wi th Dev i c e

equ i v a l en t comma nd s

Command s As s o c i a ted
a nd Swa p Fi l e s

wi th Ad d i t i o n a l

In i t i a l

Cond i t i o n s

Impl i e d

Impl i ed

U S E ACTIVE

US E CURRENT

c ommand

command

2 2-2 0

Dr i v e r s
Pag e

OPERATING SYSTEM I N I T IAL I Z ATION
Tab l e 2 2 - 4
I n formation S tored for E ach Ad j u stable P a r ameter
by SYSBOOT and SYSGEN
( Th i s s t r uc t u r e i s d e f i n ed
in
b o th
SYS B OOT
SYSGEN by i nvo k i ng t h e $ PRMDEF m a c r o . )
I t em
Ad d r e s s o f Pa r am e t e r

a nd

S i ze o f I t em
( i n SYS . EXE )

L o ng wo rd

De f a ul t Va l ue o f Pa r am e te r

Lo ngwo r d

Mi n imum Va l ue Th a t Pa r am e t e r Ca n As s um e

Lo ng wo r d

Ma x imum Va l ue Th a t Pa r am e t e r C a n As s um e

Lo ng wo r d

Pa r am e t e r Fl ag s

Wo rd

DYNAM I C Pa r am e t e r
S TA T I C Pa r am e t e r
SYSGEN Pa r am e t e r
AC P Pa r am e t e r
JBC Pa r am e t e r
RMS Pa r am e t e r
S Y S Pa r am e t e r
S PEC I A L Pa r am e t e r
D I S PLAY Pa r am e t e r
C ONTROL Pa r am e � e r
MAJOR Pa r am e t e r
PQL Pa r am e t e r
N E G Pa r am e t e r

S HOW /DYN
S HOW
S HOW
S HOW
S HOW
S HOW
S HOW

/GEN
/ACP
/JO B
/RM S
/ S YS
/ S PEC I A L

S HOW /MAJOR
S H OW /PQL

S i ze o f Th i s Pa r am e t e r

Byt e

B i t Po s i t i o n i f Pa r am e t e r i s Fl ag

Byte

Nam e S t r i ng fo r Pa r am e t e r

1 6 Byt e s

Nam e S t r i ng fo r Un i t s

1 2 By t e s

Wo r k i ng Va l ue o f Pa r am e t e r

Lo ngwo r d

The wo r k i ng va l ue o f e ac h pa r a m e t e r i s
fo und
no t
onl y
i n i n te r n a l tab l es i n SYSB OOT a nd SYSGEN but
a l so i n the e x ec u t i v e i t s e l f .
I n f ac t , t h e pa r a m e t e r a d d r e s s ( f i r s t i tem ) s to r ed
fo r
each
pa r am e t e r
l oc a te s t h e wo r k i ng v a l ue o f
e ac h
pa r am e t e r
in
the
m emo r y
i mag e
of
the
execut ive .

(2)

I f a c o nv e r s a t i o n a l boo t s t r a p wa s se l ec t ed

( R S < O > wa s s e t a s
i n p u t t o VM B ) , t h e n SYSBOOT w i l l p r ompt f o r c ommand s t o a l t e r
c u r r e n t pa r ame t e r
se t t i ng s .
A USE c o mmand
to
SYSB OOT 1 s
p r ompt r e s u l t s i n the wo r k i ng t a b l e be i ng o v e rwr i t t e n wi th a n
e n t i r e s e t o f pa r am e t e r v a l u e s .
Th e r e a r e
t h r e e po s s i b l e
s o u r c e s o f t h e s e v a l ue s .
•

U S E f i l e spec d i r e c t s SYSB OOT to the
f i l e f o r a n ew s e t o f v a l ue s .

2 2-21

i nd i c a t e d

pa r am e t e r

USE CURRENT

Default

SYSBOOT
Table

Parameter
Settings
Internal
to

N
N

N
N
I

SYSBOOT

USE
DEFAULT

of
Working

Values

Parameter
Settings
SYSBOOT
action

I n Memory
Image of

SYSINIT
action

Executive

USE filespec

F i gure 2 2 - 4

USE
SET
CONTI NUE (EXIT)

Movement of P arameter Data by SYS BOOT and SYS I N I T

OPERATING SYSTEM I N I T IAL I Z ATI ON
•

•

Th e r e s e rved n am e DE FAU LT c a us e s
the wo r k i ng
table
in
S Y S B OOT t o b e f i l l ed
wi th the d e f a u l t v a l ue s fo r e a c h
p a r am e t e r .
Th e r e s e r v ed n am e C URRENT c a u s e s the pa r am e t e r v a l ue s
in
the execut ive
i m a g e t o b e l o ad ed i n to SYSB OOT ' s wo r k i ng
tabl e .
( A U S E C URRENT c ommand i s r ed und a n t i f i t i s
the
f i r s t command pa s s e d to SYSBOOT . )

(3)

Onc e the i n i t i a l c o nd i t i o n s h ave b e e n e s ta b l i shed , i nd i v i d ua l
pa r ame t e r s
can
be
a l t e r ed
w i th
S E T c ommand s .
Th e
c o nve r s a t i o n a l ph a s e o f SYSB O OT i s t e rm i n a t ed w i th a C ONT INUE
( o r EXI T ) c ommand .

(4}

Af t e r SYSB OOT h a s c a l c u l a t ed the s i z e s o f the v a r i o us p i e c e s
of
s y s tem spa c e , b u t b e f o r e i t t r an s f e r s c o n t r o l t o I N I T , i t
c o p i e s t h e c o n t e n t s o f i t s wo r k i ng t a b l e to the c o r r e s po nd i ng
t a b l e i n t h e m emo r y i m a g e o f the e x e c u t i v e .

( 5}

One o f t h e f i r s t
s t eps
pe r f o rmed
by the
SYS I N I T p r o c e s s
copi es the pa ramete r
t ab l e
f r om t h e m emo r y i m a g e o f t h e
e x ec u t i v e to i t s d i s k i m ag e .
B e c a u s e SYSB OOT a l wa ys d o e s
an
i mp l i e d
US E C URRENT a s i t s f i r s t s t ep , t h i s g ua r a n t e e s t h a t
a l l s ub s e qu e n t bo o t s t r a p s w i l l
u s e the
l a t e s t pa r am e t e r
s e t t i ng s , e v e n i f no c o n v e r s a t i o n a l boo t s t r a p i s se l e c t ed .

22. 3. 3

U s e o f P a r ame t e r F i l e s by SYSGEN

S YSGEN ' s i n t e r a c t i o n w i th p a r am e t e r f i l e s i s not a n i n t eg r a l
pa r t
the
boo t s t r a p
o pe r a t i o n .
Ho we v e r ,
i ts
action ,
p i c t u r ed
F i g u r e 2 2 - 5 , c l o se l y p a r a l l e l s t h a t o f SYSBOOT .
( 1}

Th e i n i t i a l c o n t e n t s o f S YSGEN ' s wo r k i ng t a b l e
are
the
v a l ue s
t a ken
f r om
t h e m emo r y image of the e x e c u t i v e .
d a t a movemen t p i c t u r ed i n F i g u r e 2 2 - 5 i s a movem e n t f r om
m emo r y a r e a
to
ano t h e r
r a the r
than
t h e r e s u l t o f an
o pe r a t i o n .

of
in
the
Th e
one
I /O

I n a n y e v e n t , SYSGEN beg i n s i t s e x e c u t i o n wi th a n impl i ed
US E AC T I VE
c omma nd , a
SYSB OOT ' s
SYSGEN a nd
i m ag e o f
exec ut i ve )
( 2}

s e t o f i n i t i a l cond i t i o n s tha t wo u l d d i f f e r
f r om
initial
s t a te o n l y i f
som e o n e
had a l r e a d y r un
wr i t t e n pa r am e t e r s to
e i the r
C URRENT
( the d i s k
t h e ex e c u t i v e ) o r AC TIVE { th e m emo r y i m ag e o f t h e
•

S YSGEN c a n c ho o s e i n i t i a l s e t t i ng s f o r i t s wo r k i ng
e x a c t l y the s am e f a sh i o n a s SYSB OOT .

ta b l e

Th e r e i s a n a d d i t i o n a l r e s e r v e d f i l e s pec a v a i l a b l e to SYSGEN .
A US E AC T I VE
c omma nd
c a us e s
t h e pa r am e t e r t a b l e f r om the
m emo r y i m ag e o f the e x e c u t i v e
to
be c o p i ed
i n to
SYSGEN ' s
wo r k i ng t a b l e .

2 2-2 3

Parameter
Settings
I n Memory
Image of
Executive

implied
USE ACTIVE

J:ll:l

::0

SYSGEN
Table
of
Working
Values

N
N
I
N
�

>
t-3

1-1

z
Cl
til
t<
til
t-3
tzl
3

WRITE filespec

Default
Parameter
Settings
Internal
to
SYSGEN

USE
SET
WRITE
EXIT(continue)

F igure 2 2 - 5

1-1

Movement of P arame ter Data by S YSGEN

1-1

t-3

1-1

Parameter
Settings
In Memory
Image of
Executive

t""
>

1-1
N

>
t-3
1-1

0
z

O PERAT ING SYSTEM I N I T IA L I ZAT I ON

(3)

S E T c om ma nd s c a n b e
used
to
a l ter
i nd i v i d ua l
pa r am e t e r
v a l ue s .
Typ i c a l l y ,
a n EXI T ( o r C ONTINUE ) c ommand wo u l d n o t
be u s ed un t i l t h e f i na l s e t t i ng s we r e p r e s e rved wi t h a WR I T E
c omma nd .

(4)

Th i s i s the s te p tha t
wo r k i ng t a b l e .
•
•

•

prese rves

the

contents

S YSGEN ' s

WR ITE f i l e spec c r e a t e s a new p a r ame t e r f i l e tha t c o n t a i n s
t h e c o n t e n t s o f SYSGEN ' s wo r k i ng t a b l e .
WR I TE C URRENT a l t e r s the c op y o f the pa r am e t e r
tabl e
in
the d i sk
i m ag e o f the
execut i ve .
Th e nex t boo t s t r a p
o pe r a t i o n wi l l
u s e the se v a l ue s a utoma t i c a l l y
( ev e n
wi t h o u t a c o nv e r s a t i o n a l bo o t s t r a p o pt i o n ) .
Se v e r a l pa r am e t e r s d e te rm i n e
the
s i ze o f po r t i o n s o f
s y s tem add r e s s
s pa c e .
O th e r pa r ame t e r s d e t e rm i n e t h e
s i z e o f b l oc k s o f p o o l s pac e a l l o c a t ed
by !N I T .
Th e s e
pa r am e t e r s
c a nno t b e c h a ng ed
in a
r unn i ng
s y s tem .
Ho we v e r , m a n y pa r am e t e r s a r e n o t used i n c o n f i g u r i ng
the
s y s t em .
Th e s e p a r am e t e r s
a r e d e s i g n a t ed a s DYNAM I C
( Ta b l e 2 2 - 4 )
•

s e t t i ng s o f
A WRITE ACTIVE c ommand to SYSGEN a l te r s the
d yn am i c
pa r am e t e r s o n l y
in
the m emo r y i m a g e o f t h e
execut i ve .
A wo rd o f c a u t i o n i s i n o rd e r h e r e .
B e f o r e e x pe r i m e n t i ng wi th a
new
c o n f i g u r a t i o n , t h e pa r a me t e r s f r om a wo r k i ng sys tem sho u l d b e s a v ed i n
a pa r am e t e r f i l e .
I f the new c o n f i g u r a t i o n c r e a t e s a sys tem th a t
is
unusab l e ,
the
s ys t em c a n b e r e s t o r e d
to
i ts
p r e v i ous s t a t e by
d i r ec t i ng SYSB OOT t o u s e the s aved pa r am e t e r s .

2 2 -2 5

C HAPTE R 2 3
POWERFAI L RECOVERY

Powe r f a i l r e co v e r y s uppo r t a l l o ws s u i t a b l y e q u i pped VAX/VM S s ys tems to
s u r v i v e po we r f l uc t ua t i o n s a nd powe r o u t ag e s o f sho r t d u r a t i o n w i th no
l o s s of o p e r a t i o n .
Th e s uppo r t i s p r o v i d ed by h a r d wa r e
f e a t u r e s a nd
VM S s o f t wa r e r o u t i n e s .
VM S s o f t wa r e s uppo r t i n c l ud e s a po we r
f a i l ur e serv i c e
routine
tha t
s av e s
t h e vo l a t i l e s t a t e o f
the m a c h i n e b e f o r e the po we r f a i l s , a
po we r r e c o v e r y r o u t i n e th a t r e s to r e s t h a t s t a te ,
a n d d ev i c e - spec i f i c
c o d e wi th i n m a ny VAX/VM S d ev i c e d r i v e r s .
Some d r i v e r s a r e a b l e to
r e s ume I /0 o p e r a t i o n s tha t we r e in p r og r e s s wh e n
the
po we r
f a i l ed .
O th e r s
s i mpl y a b o r t
the
r eque s t
th a t wa s
i n p r og r e s s .
VM S a l so
p r ov i d e s p r o c e s s no t i f i c a t i o n by m e a n s o f po we r r ec o v e r y ASTs .

23 . 1

POWERFA I L S EQUENCE

Wh e n a f l uc t ua t i o n or
d r o p i n o pe r a t i ng vo l t ag e o c c u r s ,
the
CPU
g e n e r a t e s a po we r f a i l i n t e r r u p t .
Th i s i n t e r r up t c a u s e s c o n t r o l to b e
p a s s e d to t h e r o u t i n e wh o s e ad d r e s s i s s to r ed
in o f f s e t
12
in
the
Sys t em Co n t r o l
Block ,
at t h e s am e t i m e r a i s i ng I P L to 3 0 .
Th e fac t
t h a t po we r f a i l i s a n i n t e r r up t w i th a f i n i t e I P L a s soc i a t ed
w i th
it
a l l o ws po we r f a i l
i n t e r r up t s
to
b e b l o c ked f o r a sho r t s e qu e n c e o f
i n s t r uc t i o n s , a v o i d i ng m a n y po t e n t i a l s yn c h r o n i z a t i o n pr o b l em s .
Th e VM S powe r f a i l i n t e r r up t s e r v i c e r o u t i n e s ave s t h e vo l a t i l e m a c h i n e
s ta t e
( tho s e
r eg i s te r s wh o s e c o n t e n t s a r e � o t p r e s e r v ed by s om e so r t
o f b a t t e r y b a c k up ) i n m a i n m em o r y
( wh i c h
1 s p r e s e r v ed b y b a t t e r y
b a c k up) ,
e i th e r
o n the
i n t e r r up t s t a c k o r i n the Re s t a r t P a r am e t e r
Bloc k .
A l i s t o f the r eg i s t e r s p r e s e r v e d by the po we r
fa i l
s e rv i c e
rout i ne
a nd
r e s t o r ed b y t h e r e s t a r t r o u t i n e i s f o und i n T a b l e 2 3 - 1 .
Th e s e r v i c e r o u t i n e then wa i t s i n a t i g h t l o o p
10$ :

BRB

10$

u n t i l t h e h a r d wa r e g e n e r a t e s a HALT o pe r a t i o n .
( Th e
BRB
i n s t r uc t i o n
wa s c h o s e n o v e r a n e x p l i c i t HALT i n th e so ftwa r e s e r v i c e r o u t i n e to
avo i d c o n f u s i ng the r e s t a r t l og i c b y t r i g g e r i ng a r e s t a r t t o o s o o n . )

23. 2

P OWER RECOVERY

Th e powe r r e co v e r y s e q u e n c e pe r f o rm s v a r i o u s v a l i d i t y c h e c k s
in a
C PU - d e pe nd e n t
f a sh i o n a nd
t h e n pa s s e s c o n t r o l
to th e VM S r e s t a r t
rout i ne .
Th i s r o u t i n e r e s to r e s the saved s t a t e
of
the mach i ne
and
then no t i f i e s
each d ev i c e d r i v e r in the s ys tem th a t po we r has f a i l ed
so t h a t
the d r i v e r s c a n
t a k e d ev i c e - spec i f i c
a c t i on
to
r e s to r e
i n te r r upted I /0 r e q ue s t s .

2 3 -1

POWERFAI L RECOVERY
Ta b l e 2 3 - 1
D a t a Sa v ed b y Po we r fa i l Ro u t i n e a nd Re s t o r ed Du r i ng P o we r Re c ov e r y
The fo l l owi ng e l em e n t s a r e l i sted i n the o rd e r
r e sto r ed b y t h e powe r r ec ov e r y r o u t i n e .

that

they

are

Th e s e f i r s t e l em e n t s a r e r e s t o r ed b e fo r e memo r y
m a n ag ement
r e enab l ed .
The Resta r t Pa r am e t e r B l o c k i s a c c e s sed t h r o ug h
phys i c a l ad d r e s s .

is
i ts

E l em e n t

Wh e r e Sto r ed

System Ba s e Reg i s t e r
Sys tem Leng t h Reg i s t e r
So ftwa r e I n t e r r upt Summa r y Reg i s t e r
Sy s t em Co n t r o l B l o c k Ba se Reg i s t e r
Pr o c e s s Co n t r o l B l o c k Ba s e Reg i s t e r
In t e r r upt Sta c k Po i n t e r

Re s t a r t Pa r am e te r
Re s t a r t Pa r am e te r
Re s t a r t Pa r am e t e r
Re s t a r t Pa r am e te r
Re s t a r t Pa r ame t e r
Re s t a r t Pa r ame t e r

The fo l l owi ng e l em e n t s a r e l i st e d i n t h e o rd e r
that
they
are
r e sto r ed
by
t h e powe r r ec ov e r y r o u t i n e .
Th i s i s d o n e t o m a k e
t h i s l i s t ag r e e w i t h t h e o rd e r o f e l em e n t s t h a t a r e
s to r ed
on
t he s t a c k .
Th e s e e l em e n t s a r e a l l r e sto r e d
a fter
m em o r y
ma nag ement
has
b e e n r e enab l ed , wh i c h a l l o ws t h e i n t e r r upt s t a c k to b e a c c e s sed
t h r o ug h i t s no rma l s y s t e m v i r t ua l add r e s s .

E l emen t

Wh e r e Sto r ed

C PU -Spec i f i c P r o c e s so r
( S e e Be l ow )

Reg i s t e r s

In t e r r upt

St a c k

P r o c e s s -Spe c i f i c P r o c e s so r Reg i s t e r s
P l Leng t h Reg i s t e r
P l B a s e Reg i s t e r
P O L e ng t h Reg i s t e r
P O B a s e Reg i s t e r
Pe r fo rmanc e Mo n i to r Enab l e
AST Level Reg i s te r

In t e r r upt

Stack

Fo u r

I n t e r r upt

Stack

Pe r - P r o c e s s

Stack

Po i n t e r s

T h e fo l l owi ng e l ements a r e n o t
r e cov e r y
s t eps
d e sc r i b ed
in
powe r fa i l i n te r r upt d i sm i s sed .
The PC / PS L pa i r
are
r e s t o r ed
d i sm i s s e s the i n t e r r upt .

r e s t o r ed un t i l the
o th e r
powe r
the
tex t a r e pe r fo rmed and the

El em e n t

Ge n e r a l

the

REI

i n s t r uc t i o n

that

Wh e r e Sto r ed

Reg i s t e r s

I n t e r r upt P C a nd

(RO

t h r o ug h

FP)

PS L

( C PU-Spec i f i c

Reg i s t e r s

S a v ed

The fo l l owi ng C PU -spec i f i c p r o c e sso r
r e sto r ed f r om the i n te r r upt s t a c k .

Stac k

In t e r r upt

Stack

by Powe r fa i l

Ro u t i n e )

r eg i s t e r s a r e saved

C PU

E l em e n t

T r a n s l a t i o n Bu f f e r
Memo r y Ca c h e

I n t e r r upt

Di s a b l e Reg i s t e r

VAX- 1 1 /7 5 0
VAX-1 1 /7 5 0
VAX-1 1 /7 8 0

S B I Ma i ntenanc e Reg i s t e r

2 3-2

and

Bloc k
B l oc k
B l oc k
Block
Block
B l oc k

POWERFA I L REC OVE RY
23 . 2 . 1

I n i t i a l S t e p i n Powe r Re c ov e r y

Th e i n i t i a l s t e p i n r ec o v e r y f r om a powe r
fai l ure
i s pe r f o rmed
by
Th e g e n e r a l
e i th e r
h a r d wa r e o r m i c r o c o d e
a nd
is
CPU-d e pe nd e n t .
p u r po s e o f a n y o f t h e s e r o u t i n e s i s to
•

v e r i f y t h a t t h e c o n t e n t s o f m emo r y s u r v i v ed the po we r o u ta g e ,

•

l o c a t e t h e powe r r e c o v e r y r o u t i n e , a nd

•

pa s s c o n t r o l to tha t r o u t i n e .

23. 2. 1 . 1
Powe r Re c o ve r y o n t h e VAX- 1 1 /7 5 0 - Th e
conso l e
p r og r am
( Ch a p t e r 2 1 ) i s the f i r s t p r og r am t h a t e x e c u t e s i n r e s po n s e to a po we r
r e co v e r y o n the VAX- 1 1 /7 5 0 .
Th i s p r og r am f i r s t c h e c k s the s e t t i ng
of
the
Po we r - o n Ac t i o n s w i t c h .
I f the s w i tch i s i n e i th e r the HALT o r
If
B OOT po s i t i o n , the c o n s o l e p r og r am pe r f o r m s the d e s i g n a t ed ac t i o n .
the swi tch i s i n e i t he r the RESTART/ BOOT o r RESTART/ HA LT po s i t i o n , t h e
c o n so l e p r og r am a t temp t s a r e s t a r t .
On l y i f th e r e s t a r t f a i l s i s
the
s e cond o p t i o n ( B OOT o r HALT ) u s ed .
Th e c o n s o l e p r og r am then a t temp t s
to
locate
the
Re s t a r t
Pa r ame t e r
Block .
A t t h e s ame
t i me ,
t h e c o n t e n t s o f m emo r y a r e t e s t ed to
d e t e r m i n e wh e th e r m emo r y s uc c e s s f u l l y s u r v i v ed the po we r o u t ag e .
Th i s
t e s t c an
i d e n t i f y two d i f f e r e n t c o nd i t i o n s , e i the r o f wh i c h p r e v e n t s
s uc c e s s f u l r e cov e r y .
Th e s e c o nd i t i o n s a r e
•
•

a s y s t em t h a t d o e s n o t h a v e b a t t e r y bac k up ,
i n wh i c h
c a se ,
t h e c o n t e n t s o f memo r y we r e l o s t wh e n the po we r fa i l ed , o r
a s i t ua t i o n wh e r e the po we r wa s
o f f fo r
l o ng e r
than
ten
m i n u t e s , t h e amo un t o f t i me tha t b a t t e r y b a c k u p i s c a pa b l e o f
p r e s e r v i ng the c o n t e n t s o f memo r y .
{ Th i s t i m e d e pend s o n the
amo un t
of
memo r y p r e s e n t b u t
is
not
sho r ter
than
ten
mi nutes . )

Th e o pe r a t i o n a l d e f i n i t i o n o f a r e s t a r t pa r ame t e r
bloc k
is
a
pag e
a l i g ned b l o c k o f ph ys i c a l mem o r y wh o s e f i r s t fo u r l o ng wo r d s c o n t a i n
1.

the phys i c a l a d d r e s s o f the RPB
add ress o f l o c a t i o n ) ,

( c o n te n t s o f l o c a t i o n

the ph ys i c a l ad d r e s s o f the r e s t a r t r o u t i n e ,

a c h e c k s um o f t h e f i r s t 3 1 l o ngwo r d s i n the r e s t a r t
a nd

a wa rm r e s t a r t f l ag .

equa l s

r o u t i ne ,

I f a va l i d RPB c a n n o t b e l o c a t ed , o r i f the r e s t a r t f l ag i s s e t ,
the
r esta r t
a t t empt h a s
f a i l ed
a nd
t h e c o n so l e
p r o g r am t a k e s
i ts
a l t e r na t i v e o p t i o n .
I f a v a l i d RPB i s l o c a t e d ,
t h e c o n so l e
prog r am
t r an s fe r s c o n t r o l
to the r e s t a r t r o u t i n e wh o s e a d d r e s s wa s s to r ed i n
the Re s t a r t Pa r ame t e r B l o c k .

2 3-3

POWERFA I L R E C OVE RY
23 . 2. 1 . 2
Powe r Re c o v e r y on the VAX- 1 1 /7 8 0 - Wh e n po we r i s r e s to r ed on
the
VAX- 1 1 /7 8 0 ,
t h e c o n so l e s ub s ys t em ( L S I - 1 1 ) g o e s th r o ug h the same
s e qu e nc e tha t it d o e s wh e n a s ys t em i s b e i ng i n i t i a l i z ed ( Ch a p t e r 2 1 ) .
I f po we r
i s a l s o b e i ng r e s to r e d o n the LS I - 1 1 , CONS O L . SYS i s l o aded
f r om the c o n so l e f l o ppy .
No s t a t e fo r the LS I - 1 1 i s p r e s e r v ed
across
a po we r fa i l u r e .
The c o n s o l e p r og r am then p r o c eed s wi th i t s n o rm a l
powe r o n a c t i o n s .
I f t h e a u to r e s t a r t swi tch o n the f r o n t o f the p r o c e s s o r c a b i n e t i s i n
the OFF po s i t i o n , o r i f t h e wa rm s t a r t i nh i b i t f l ag ma i n t a i n e d b y the
c o n so l e p r og r am
i s s e t , the c o n s o l e p r og r am s i mp l y p r i n t s i t s p r ompt
on
the
c o n so l e
t e rm i n a l
a nd
wa i t s
fo r
i nput .
( No te
th a t
the
a uto r e s t a r t
swi tch
on
the
f r o n t p a n e l sho u l d be swi tched o f f wh en
f i r s t t u r n i ng o n a VAX- 1 1 /7 8 0 s y s t em to a v o i d a n
unnec e s s a r y r e s t a r t
a t tempt . )
I f the a u to r e s ta r t s w i t c h i s i n the ON po s i t i o n a nd
the wa rm
start
i nh i b i t
f l ag
is
c l ea r , t h e c o n s o l e p r og r am u s e s t h e c o n t e n t s o f the
Be fo r e
RESTAR . CMD
c ommand f i l e R E S TAR . CMD t o d i r e c t f u r th e r ac t i o n .
execut e s ,
t h e d i ag no s t i c c o n t r o l s to r e c o n t e n t s a r e r e l o a d e d f r om the
c o n s o l e f l o ppy ( f rom f i l e WC Sx x x . PAT ) .
Th e c o n t e n t s o f WC S we r e no t
p r e s e rved
by t h e
b a t t e r y b a c k up t h a t p r e s e rved the c o n te n t s o f ma i n
memo r y .
No t e
tha t
r e l o a d i ng
WC S ma k e s po we r
r e c ove r y o n
the
VAX- 1 1 / 7 8 0 somewha t s l o we r than in the VAX- 1 1 /7 5 0 , wh e r e I/O i s no t an
i n teg r a l pa r t of po we r r e c o v e r y .
Th e f i l e RESTAR . CMD c a n c o n t a i n a ny v a l i d
c omma nd s .
Th e
RE S TAR . CMD
tha t
i s d i s t r i b u t e d wi th VMS c o n t a i n s c omma nd s d e s i g ned to r e s t a r t a
r unn i ng VM S s ys tem .
( On
s y s tems wi t h mo r e
than
t wo
m emo r y
control l e r s ,
t h e UN I B US a d a p t e r
i s not
l o c a t ed a t T R 3 .
On s uc h
s ys t e m s , RESTAR . CMD mus t be a l t e r ed s o tha t R l i s l o ad ed wi t h
t h e TR
n umbe r o f the UN I B US a d a p t e r . )
HALT
INIT
D E PO S I T/ I 1 1 2 0 0 0 3 8 0 0
DE PO S I T R O 0
DE PO S I T R l X X X
D E PO S I T R2 0
DEPO S I T R3 0
D E PO S I T R4 0
DE PO S I T R S 0
DE PO S I T F P 0
S TART 2 0 0 0 3 0 0 4

Ha l t p r o c e s s o r
I n i t i a l i ze proc e s so r
Se t a d d r e s s o f S C B b a s e
C l e a r un u s ed r eg i s t e r
TR n umbe r fo r UN I B US a d apte r
C l e a r un u s e d r eg i s t e r
C l e a r un u s e d r eg i s t e r
C l e a r u n u s ed r eg i s t e r
C l e a r u n u s ed r eg i s t e r
No m a c h i n e c h e c k e x pe c ted
Sta r t res t a r t refe ree

Th e START c omma n d p a s s e s c o n t r o l to t h e
s am e p r o g r am
tha t
i s used
d u r i ng
s y s t em
i n i t i a l i za t i o n ,
e x c e p t t h a t the p r og r am is e n t e r ed at
i t s r e s ta r t e n t r y p o i n t .
Th e m emo r y ROM p r og r am a t temp t s to l o c a t e the Re s t a r t Pa r am e t e r B l o c k ,
a
pag e a l i g ned b l o c k o f phys i c a l m emo r y wh o s e f i r s t fo u r l o ngwo r d s
conta i n
1.

t h e ph y s i c a l a d d r e s s o f the RPB
add ress o f loca tion) ,

t h e ph y s i c a l add r e s s o f the r e s t a r t r o u t i n e ,

a s i mp l e c h e c k s um o f the f i r s t 3 1 l o ng wo r d s
r o u t i n e , a nd

a wa rm r e s t a r t f l ag .
2 3-4

( contents o f loc at i o n

the

e q ua l s

r e sta r t

POWERFAI L RECOVERY
I f a v a l i d R PB c a nno t b e fo und , o r i f t h e wa rm r e s t a r t f l ag i n t h e RPB
is
c l ea r ,
the
ROM p r og r am
r e t u r n s c o n t r o l to th e c o n so l e pr og r am ,
wh i c h a t t e m p t s a c o l d s t a r t ( bo o t s t r a p ) .
Th i s i nd i c a t i o n i s
a c t ua l l y
m a d e by t h e m emo r y ROM p r og r am wr i t i ng a " r e boo t " s i g n a l i n to o n e o f
t h e c o n so l e r eg i s t e r s wi t h a
MTPR
i n s t r uc t i o n .
O t h e r w i s e , t h e m em o r y ROM p r og r am pa s s e s c o n t r o l to
the
r esta rt
routine
( wh o s e
add r e s s
i s s t o r ed i n t h e RPB ) .
Th e s p e c i a l
u s e s o f t h e PR $ TXDB r e g i s te r fo r commun i c a t i o n f r om t h e VAX C PU
to
t h e c o n s o l e p r og r am a r e d e sc r i b ed i n Ch a p t e r 1 5 .

23. 2. 2

Ope r a t i o n o f t h e Re s t a r t Ro u t i n e

Th e VM S r e s ta r t r o u t i n e r e c e i v e s c o n t r o l
•

i n k e r n e l mo d e ,

•

o n t h e i n t e r r up t s t ac k ,

•

w i th m emo r y m a n ag em e n t d i s a b l e d ,

at IPL 31 .

Th e s e i n i t i a l c o nd i t i o n s a r e s i m i l a r to t h e e n t r y to VM B , e x c e p t
th a t
t h e RPB h a s a l r e a d y b e en
l o ad ed .
On e m o re s i m i l a r i t y b e t we e n t h e
e n t r y to t h e r e s t a r t r o u t i n e a nd VM B i s t h a t S P po i n ts 2 0 0 ( h e x ) byt e s
pa s t t h e RPB .
Th i s s e r v e s two p u r po s e s .
Th e c o n t e n t s o f S P a r e u s e d
to l o c a t e t h e R PB .
Th e
last
s ev e r a l
l o ngwo r d s
in
the
pa g e
th a t
conta i ns
the
RPB w i l l b e u s e d a s s t a c k s pa c e by t h e r e s t a r t r o u t i n e
u n t i l t h e s av ed i n t e r r upt s t ac k po i n t e r i s r e s to r ed .
Th e r e s t a r t r o u t i n e f i r s t c l e a r s two wa rm s t a r t i n h i b i t f l ag s .
On e o f
these
f l ag s i s C PU-d e pe nd e n t and i s c l e a r ed b y wr i t i ng a s p e c i a l cod e
i n to the c o nso l e t r a n sm i t d a t a b u f f e r r eg i s t e r .
MT PR
Th e o th e r f l ag i s l o c a ted
in
the
Re s t a r t
Pa r am e t e r
B l o c k a nd
is
c l e a r ed
wi th
a
BICL
i n s t r uc t i o n .
Th e
use o f
these
s o - c a l l ed
l o o pb r e a k e r f l a g s i s d i sc u s s e d f u r th e r a t t h e e nd o f t h i s c h a p t e r .
Al l i n fo rm a t i o n s t o r e d i n the RPB by t h e po we r f a i l s e rv i c e r o u t i n e i s
r e s t o r ed
n ex t ( Ta b l e 2 3 - 1 ) .
Mo s t o f th i s i n f o rma t i o n i s n e c e s s a r y to
t u r n mem o r y m a n ag em e n t b a c k o n .
A d ummy PO pag e ta b l e is s e t up ( j u s t
l i ke
the o n e s e t
u p b y SYS BOOT )
s o th a t t h e pag e c o n t a i n i ng t h e
r estart
rout ine
i s m a pped
as
a
P O v i r t ua l
add r e s s
th a t ,
wh e n
t r a n s l a t ed ,
yi elds
t h e i d e n t i c a l phys i c a l add r e s s .
Ch a p t e r 2 2 s h o ws
h o w t h e c o n t e n t s o f P O B R a r e d e t e r m i n ed
to
prod uc e
th i s
i d en t i ty
m a pp i ng .
Af t e r the PO p a g e t a b l e i s s e t up , m emo ry m a n ag em e n t i s e n a b l e d
t h e same two i n s t r uc t i o n s used by I N I T .

1 0$ :

MTPR
JM P

( De t a i l s o f
Ch a p t e r 2 2 . )

u s i ng

# l , # P R $ MAPEN
@# 1 0 $ th i s

t e c h n i que

c an

23-5

fo und

the

b eg i nn i ng

POWERFAI L RECOVERY
O n c e memo r y m a n ag em e n t h a s b e en e n a b l ed , the r e s t a r t r o u t i n e
i s ab l e
to
r e s to r e
the d a t a
t h a t wa s s a v e d o n t h e i n t e r r upt s t a c k .
Be fo r e
t h i s h a ppe n s , a c h e c k i s m a d e to d e t e rm i n e wh e th e r
the
r e s t a r t wa s
i n i t i a t ed
a s a pa r t o f r e c o v e r y o r i n r e s po n s e to some o th e r r e s t a r t
c o nd i t i o n d e tec t ed by t h e c o n so l e
l og i c .
Al l
o th e r
r e a so n s
for
r estart
a re
errors .
Th e VM S r e s t a r t
routine
s i mpl y
i ssues a
r e a s o n - s pec i f i c b ug c h e c k
( wh i c h w i l l
r es u l t
in
a cold
star t ,
a
boo tst r a p ,
i f the
SYS B OOT f l ag
BUGRE BOOT
is
set) .
By c a us i ng a
b ug c h e c k , VM S h o pe s to m a k e mo r e i n f o rm a t i o n a v a i l a b l e abo u t the e r r o r
c o nd i t i o n
th r o ug h
a c r a s h d ump t h a n i s no rma l l y p r ov i d ed b y h a r d wa r e
a l one .
Tab l e 2 3 -1
i nd i c a t e s
the
i n fo rm a t i o n
tha t
is
r e s to r ed
f r om the
i n t e r r up t s t a c k .
Th e r e s t a r t r o u t i n e d o e s not u s e S P to r e s to r e th i s
d a ta .
Ra th e r , i t u s e s a sc r a tc h r eg i s t e r ( R 6 ) to t r a ve r s e
the
stack
to
prevent
the d a t a o n t h e
s tac k
f r om b e i ng ove rwr i t t e n i n c a s e
a no th e r powe r f a i l u r e o c c u r s wh i l e t h e d a ta i s b e i ng
r e s to r ed .
Th i s
a l l o ws
the
r e s t a r t r o u t i n e to b e r e pe a t ed a s m a n y t i m e s a s n e c e s s a r y
w i tho u t t a k i ng a n y s pec i a l a c t i o n .
Af t e r e v e r yth i ng e x c e p t t h e g e n e r a l r eg i s t e r s h a s b e e n
r e s t a r t r o u t i n e t a k e s t h e fo l l o w i ng s t eps .

r e s t o r ed ,

the

A n e w s y s t em t i m e i s c a l c u l a t ed .
( Th e
t i me -o f -y e a r
clock
k e p t r un n i ng wh i l e the po we r wa s o f f .
Its contents a re used
to r e c a l i b r a t e E XE $G Q_S YS T IME . )

Th e t i m e r q u e u e i s s c a n n e d .
Al l t i me r q u e u e e l em e n t s
th a t
h a v e e x p i r ed h a v e t h e r ec a l i b r a t e d t i m e s ub s t i t u t e d fo r the i r
abso l ut e d ue t im e .
Th i s i s d o ne
to
a l l o w pe r i o d i c
t imer
r e que s t s to r e e s t ab l i sh i n t e r n a l s yn c h r o n i z a t i o n .
To i l l u s t r a t e the
p u r po s e
of
th i s
s tep ,
s uppo s e
th a t a
pe r i o d i c
t i mer
r e q u e s t wa s d e c l a r ed
wi th a pe r i od o f o n e
m i n u te a n d t h e po we r wa s o f f
for
th r e e m i n u t e s .
W i th n o
a d j u s tm e n t
of
the
a b s o l u t e d ue t i me , t h r e e r e q u e s t s wo u l d
ex p 1 r e
i mmed i a t e l y
f o l l o wi ng
po we r
r ecove r y .
Th e
r e ad j us tm e n t c a u s e s o n e r e que s t to come d u e i mmed i a t e l y , wi th
the n e x t r e que s t no t o c c u r r i ng un t i l one m i n u t e l a t e r .
No t e th a t r e l a t i v e s yn c h r o n i z a t i o n b e twe e n s e v e r a l
r eque s t s
m a y b e l o s t a s a r e s u l t o f a po we r f a i l u r e .
Fo r e x ampl e , i f
o n e r e que s t i s d ue to ex p i r e i n two m i n u t e s , a s e c o nd i s d ue
to e x p i r e i n f i v e m i n u t e s ( o r th r e e m i n u t e s a f te r the f i r s t ) ,
a nd the powe r i s o f f f o r m o r e t h a n f i v e m i n u t e s ,
then bo th
r eque s t s w i l l
be d e l i v e r ed
at
the
s ame
t ime .
A powe r
r e c o v e r y AST m i g h t be u s ed
to
a l l o w m u l t i pl e
r e que s t s
to
r e e s t a b l i sh t h e i r r e l a t i ve s yn c h r o n i z a t i o n .

A powe r r e c o v e r y e n t r y i s m a d e i n the e r r o r l og .

Ex t e r n a l a d a pt e r s a r e i n i t i a l i z e d .

Al l e x t e r n a l d ev i c e s a r e n o t i f i ed th a t a
po we r
f a i l u r e a nd
r e c o v e r y s e q ue n c e h a s o c c u r r e d .
Th i s s t e p i s d e t a i l ed i n the
next s e c t i o n .

23 6
-

POWE RFA I L RECOVERY
6.

Fi nal l y ,
•
•
•
•

23. 2. 3

S P i s s e t up to po i n t t o t h e s a v ed g e n e r a l
t h e i n t e r r up t s t a c k ,

r eg i s t e r s

t h e l a s t s a n i t y c h e c k f l ag , EXE $G L PFA I LT I M ,
_

i s c l ea r ed ,

t h e g e n e r a l r eg i s t e r s a r e r e s t o r e d , a n d
the
po we r
fa i l
i n s t r uc t i o n .

i n te r r u pt

d i sm i s s ed

w i th

RE I

Dev i c e No t i f i c a t i o n

Ex t e r n a l d e v i c e s a r e no t i f i e d t h a t a po we r f a i l u r e h a s o c c u r r e d i n two
s t ag e s .
Wh i l e t h e powe r r e c o v e r y r o u t i n e i s
e x e c u t i ng
( at
I PL
31
so
tha t
a no t h e r
po we r
f a i l i n t e r r upt c a nno t o c c u r ) , e a c h d r i v e r i s c a l l ed a t
i t s c o n t r o l l e r i n i t i a l i z a t i o n r o u t i n e f o r e a c h c o n t r o l l e r an d
at
i ts
un i t
i n i t i a l i za t ion
rout ine
fo r
each
un i t .
Th e
powe r
fa i l b i t
UC B $ V POW E R i n t h e UC B s t a t u s wo r d UC B $W S T S
i s set
to
al low each
d r i v er r o u t i n e
to
d i f f e r e n t i a t e b e t ween po we r r e c o v e r y a n d o r d i n a r y
i n i t i al i za t ion .
I n ad d i t i o n , t h e e n t i r e I /0 d a t a b a s e i s s c a n n e d ,
l o o k i ng
fo r
un i t s
tha t a r e
e x p e c t i ng
i n t e r r up t s .
Th e po we r r e c o v e r y r o u t i n e c l e a r s
t h e i r i n t e r r u pt- e x pe c ted b i t s , s e t s t h e i r t i m e o u t - e x pe c t ed
b i ts ,
a nd
sets
the i r
d ue
t i m e s to z e r o .
Th i s c a u s e s e a c h d e v i c e to a ppe a r t o
h a v e t i med o u t .
Th e c h e c k f o r d ev i c e t i m e o u t o c c u r s a s
a
r e sul t o f
the
s ys t em s ub r o u t i n e th a t e x e c u t e s o n c e a s e c ond .
Th a t r o u t i n e w i l l
not execute unt i l
1.

t h e h a r d wa r e c l o c k
d r o pped b e l o w 2 4 )

a nd t h e so f twa r e
t imer
executes
a s pa r t o f t h e
s ys t em
s ub r o ut i ne
th a t h a s p r o b a b l y e x p i r ed
wh i l e t h e po we r wa s
d o wn .
( Th i s w i l l n o t h a ppe n u n t i l t h e I P L i s
l o we r ed
below
7. )

i n te r r u p t s

( wh i c h

means

that

I PL

has

Th u s , e a c h d ev i c e t h a t wa s e x pe c t i ng an i n t e r r upt w i l l a ppe a r to
have
t i med
out .
A d r iver ' s
t ime
o u t r o u t i n e c a n d i f f e r e n t i a t e b e twe e n
g e n u i ne t i m e o u t a nd po we r f a i l u r e b y c h e c k i ng the UCB $V_POWER b i t .
I n a VM S s ys t em , t h e m a j o r i t y o f t h e wo r k d o n e to r e c o v e r f r om a po we r
fa i l u r e o c c u r s i n d r i ve r s .
VM S d i s k d r i v e r s a nd mag ne t i c t a p e d r i v e r s
a r e c a pa b l e o f r e s t a r t i ng wh a t ev e r r e que s t t h e y we r e p r o c e s s i ng
wh e n
t h e powe r
f a i l ed
in
s uc h a
wa y t h a t t h e po we r f a i l u r e i s to t a l l y
t r a n spa r e n t t o t h em .
( I f a m a g n e t i c t a pe un i t l o s t v a c u um ,
o pe r a t o r
i ntervent ion
is
r eq u i r ed
to
r e e s tab l i sh
t h e v a c uum and r e w i nd t h e
t a pe .
Onc e t h a t i s d o n e , t h e d r i v e r a u tom a t i c a l l y r e s t a r t s
the
I /0
r e q u e s t t h a t wa s i n p r og r e s s wh e n t h e powe r f a i l e d . )

2 3 -7

POWE RFA I L R E C OVERY
23. 2. 4

P r o c e s s No t i f i c a t i o n

VMS a l so a l l o ws p r o c e s s e s to b e no t i f i ed , by r e c e 1 v 1 ng a n AST , th a t a
powe r
fa i l ure
a nd
s ub s eque n t r e c o v e r y h a pp e n e d .
A p r o c e s s r e que s t s
th i s no t i f i c a t i o n b y us i ng t h e S e t Powe r Re c o v e r y A S T s ys t em s e r v i c e .

23 . 2 . 4 . 1
$ S ETPRA S y s tem S e r v i c e - Th e S e t Po we r Re c o ve r y AST s ys t em
s e r v i c e i s an e x t r eme l y s i m p l e s e r v i c e t h a t pe r fo rm s two s t e p s .
•

•

t h e AST
is
s to r ed
i n g l oba l
location
Th e a d d r e s s o f
in
t h e P l po i n t e r pag e .
Th e a c c e s s mod e i n
C T L $G L POWERAST
b e d e l i v e r ed
is
s to r ed
i n l oc a t i on
wh i c h th e AST w i l l
C T L $G B PWRMODE .
Th e powe r AST f l ag { PC B $V PWRAS T ) i n the s t a tus
l o ng wo r d
in
the
PC B
is
set .
Th i s-f l ag w i l l b e u s e d by t h e swa ppe r i n
s c ann i ng t h e PC B v e c to r f o l l o wi ng powe r r e c o v e r y .

Th e e f f e c t o f th i s s y s t e m s e rv i c e i s e l i m i n a t ed a s a r e s u l t
r und own { Ch a pt e r 1 8 ) .

i m ag e

2 3 . 2 . 4 . 2 De l i v e r y o f Powe r Re c ove r y ASTs - Th e d e l i v e r y o f t h e s e ASTs
o c c u r s i n s eve r a l d i s t i nc t s t e p s .
l.

Th e po we r r ec o v e r y r o u t i n e s to r e s the d u r a t i o n o f
t h e powe r
fa i lure
in
loc a t i on
EXE $G L PFAT I M .
{ Th i s
is
s i m p l y the
c u r r e n t c o n t e n t s of PR $ TODR mi n u s EXE $G L P FA I LT I M , t h e
t i me
at wh i c h the po we r f a i l ed . ) N o n z e r o c o n tent s in t h i s l o c a t i o n
a c t a s a t r i g g e r t o the swa ppe r the nex t t i me th a t i t r un s .
No t e th a t no s p e c i a l a c t i o n i s t a k e n a t th i s po i n t to wa ke up
the swa ppe r .
In f a c t , b e c a u s e th i s r o u t i n e is r un n i ng at I P L
3 1 , t h e s wa ppe r c o u l d no t h a v e i t s sc h e d u l i ng
s t a te c h a ng ed
wi tho ut po t e n t i a l s ynch r o n i z a t i o n p r o b l em s .

A pa r t o f t h e swa ppe r ' s m a i n l o o p o f e x e c u t i o n
{ Ch a pte r 1 4 )
c a l l s r o u t i n e E XE $ POWE RAST i f l o c a t i o n EXE $G L PFAT I M c o n t a i n s
no n ze r o .
Th i s s ub r o u t i n e s c a n s the PC B v e c tor and d e l i v e r s a
s pe c i a l
k e r n e l AST to e a c h p r o c e s s th a t h a s the PC B $V PWRAST
f l ag se t .
Th a t f l ag i s c l e a r e d to p r ev e n t m u l t i p l e ASTs
if
m u l t i pl e powe r f a i l u r e s o c c ur b e f o r e t h e p r o c e s s ex e c u t e s .

Th e spec i a l ke r ne l AST i s r e q u i r e d b e c a u s e the a d d r e s s
{ a nd
a c c e s s mo d e )
of the r ec o v e r y AST a r e s to r ed in the Pl s pa c e
o f th e r e que s t i ng p r o c e s s .
Th e
spec i a l
k e r nel
A S T s i mpl y
loads
th e
ad d r e s s
a nd
access mode
f r om the i r
P l s pa c e
l o c a t i o n s i n to t h e A S T Co n t r o l B l o c k a nd que ue s t h e
r e cove r y
A S T to t h e r e qu e s t i ng p r o c e s s .

Fi nal l y ,
the
r e c o ve r y AST
i tsel f
i s d e l i v e r ed
to
the
r e que s t i ng p r o c e s s .
Th e AST p a r am e t e r i s the d u r a t i o n of the
powe r f a i l u r e , in 10 msec un i t s .

2 3 -8

POWERFA I L R E C OVE RY
23 . 3

M U LT I PLE POWER FA I LURES

A c omb i n a t i o n o f h a r d wa r e a nd
s o f twa r e
f l ag s
ex i sts
to
prevent
i n f i n i te
l o o p i ng
or
r e l a t ed p r o b l em s i n r e s po n s e to a po we r fa i l u r e
t h a t o c c u r s wh i l e e i th e r the powe r f a i l se r v i c e r o u t i n e
i s e x e c u t i ng
o r wh i l e t h e r e s t a r t r o u t i n e i s e x e c u t i ng .

23 . 3 . 1

Ne s ted Powe r Fa i l I n t e r r up t s

O n e o f t h e f i r s t s t eps t a k e n by t h e powe r f a i l se r v i c e
routine
saves
the c ontents
of
the
PR $ TODR r eg i s te r i n l o c a t i o n EXE $G L PFAI L T I M .
Th i s l o c a t i o n r e t a i n s n o n z e ro c o n t e n t s un t i l j u s t b e f o r e
th e r e s t a r t
r o ut i ne
i s s ue s
i ts
RE I
i n s t r uc t i o n ,
d i sm i s s i ng
the
po we r
fa i l
i n t e r r up t .
I f a po we r f a i l i n t e r r upt o c c u r s wh i l e t h i s l o c a t i o n c o n t a i n s n o n z e r o
( i nd i c a t i ng
that
a no th e r
f a i l u r e / r e co v e r y
i s a l r e a d y i n p r og r e s s ) ,
t h i s l a te r i n t e r r u pt i s i g no r ed .
Some m a c h i n e s t a t e wa s
saved
as
a
r e s u l t o f the f i r s t po we r f a i l i n t e r r u pt .
Th a t s t a t e wi l l be r e s t o r ed
e v e n t u a l l y by the r e s t a r t r o u t i n e .
Th e p r e v i o u s s t e p i s a n e x ampl e o f e x t r eme c a u t i o n tha t
i s n ec e s s a r y
wh e r e
powe r
fa i l u r e
i s c o nc e r n e d .
A n a i v e und e r s t a nd i ng o f the wa y
i n te r r up t s a r e d e f i n ed i n the VAX a r c h i t e c t u r e i nd i c a t e s t h a t a s e c o nd
powe r
fa i l
i n te r r u pt
c a nno t o c c u r wh i l e
I PL
i s a t o r a bo v e 3 0 .
Bec ause
I PL
is
not
l o we r ed
un t i l
the
po we r
fa i l
i n t e r r upt
is
d i sm i s s ed ,
I PL s e em s
to
c o v e r th i s s i t ua t i o n .
Th e EXE $G L PFA I L T I M
c h e c k , a n e x t r a s a n i ty c h e c k t h a t i s to t a l l y und e r t h e c o n t r o l o f
the
s o f t wa r e ,
p r ev e n t s
n e s ted
powe r f a i l i n t e r r upts o n a s ys t em th a t i s
e x pe r i enc i ng some o b sc u r e beh a v i o r th a t wo u l d o th e r w i s e
b e e x t r em e l y
d i f f i c u l t t o d i a g no s e .

23 . 3 . 2

P r eve n t i o n o f N e s ted Re s t a r t s

Th e p r e v i o u s two c h e c k s c o v e r a l ong t i m e a nd a r e d e s i g n ed to
prevent
a
s e c o nd powe r f a i l i n t e r r upt wh i l e a f i r s t i s b e i ng s e r v i c ed .
Th e r e
i s a l s o a f l ag d e s i g n ed t o p r e v e n t n e s t e d r e s t a r t a t t empts .
Th i s f l ag i s l o c a ted i n the Re s t a r t Pa r am e t e r
Block ,
i s c l ea red
by
INIT
a nd
by t h e
r es ta r t
r o ut i ne ,
a nd s e t by the C PU - s p e c i f i c ROM
r o u t i n e th a t l o o k s fo r a v a l i d RPB .
I f the R PB s e a r c h r o u t i n e l o c a t e s
a n o the r w i se v a l i d
RPB wi th t h e RPB $ L RS TRTF LG s e t , i t a s s um e s th a t
t h e Re s t a r t Pa r am e t e r
Block
is
in
e r ro r
a nd
abo r ts
the
r e s ta r t
a t tempt .
On
t h e VAX- 1 1 / 7 5 0 ,
f u r th e r
a c t i on
i s c o n t r o l l ed by t h e
s e t t i ng o f t h e po we r o n a c t i o n s w i tch o n
the
front
pa ne l .
On
the
VAX- 1 1 /7 8 0 ,
the c o nso l e p r og r am a bo r t s t h e r e s t a r t a t t empt a nd p r i n t s
i t s p r ompt o n t h e c o n s o l e t e rm i n a l .
A s e c o nd f l ag , l o c a t ed wi th i n the c o nso l e
l og i c o n
the
VAX - 1 1 / 7 8 0 ,
I t i s s e t by h a r d wa r e a t t h e b eg i n n i ng
f unc t i o n s i n a s i m i l a r mann e r .
o f t h e r e s t a r t a nd c l e a r ed by t h e r e s t a r t r o u t i n e by e x ec ut i ng a
MTPR
i n s t r uc t i o n .
I f the r es ta r t r o ut ine d e tects that
th i s
f l ag
is
set
wh i l e
a t tempt i ng
a r e s t a r t , i t a bo r t s the r e s t a r t a nd t a k e s the s a m e
p r o c e s s o r - s pec i f i c a c t i o n a s i t wo u l d i f the r e s t a r t pa r am e t e r
block
f l ag
we r e s e t .
( Th e r e i s no a n a l og ue t o th i s f l ag on the VAX - 1 1 / 7 5 0 .
Th e C PU m i c r o c od e t u r n s th i s pa r t i c u l a r MTPR i n s t r uc t i o n i n to
a nul l
ope r a t i o n . )
2 3 -9

POWERFA I L RECOVERY
One m o r e b i t of c a u t i o n i s e v i d e n t i n the m a nne r in wh i c h t h e r e c o v e r y
r o ut i n e
r e s to r e s d a t a
f r om t h e i n t e r r up t s t a c k .
A s c r a tc h r eg i s t e r
( R 6 ) i s u s e d to t r a v e r s e t h e s t a c k .
I f a n o the r po we r
fa i l
i n t e r r up t
we r e
t o o c c u r wh i l e d a t a wa s b e i ng r e s to r ed , no d a t a w i l l b e l o s t d ue
to t h e p u s h o f t h e PC a n d PS L o n to
the
i n t e r r upt
s tack because
SP
po i n t s
to
the
e nd
of
t h e pag e c o n t a i n i ng the R PB a n d no t i n to t h e
m i d d l e o f t h e d a t a b e i ng r e s to r ed .

Dev i c e D r i v e r Ac t i o n

23. 3. 3

Dr i v e r s d o not h a v e t o c o nc e r n t h em s e l v e s d i r ec t l y w i th
t h e m u l t i pl e
E v e n th o ug h t h e b u l k o f d r i v e r r e c o v e r y i s d o ne i n
r es ta r t
p r ob l em .
r e s po n s e t o a n I P L 7 so f twa r e i n t e r r up t wh e n a s e c o nd powe r f a i l u r e i s
po s s i b l e , d r i v e r s a r e p r o t e c t e d b y o n e o f t h e fo l l o w i ng s i t ua t i o n s .
•

•

Th e d r i v e r c o n t r o l l e r a nd un i t
i n i t i a l i za t i o n
rout i ne s a r e
c a l led
a t I P L 3 1 b e f o r e EXE $ G L PFAI LT IM i s c l e a r ed .
D r i ve r s
a r e p r o t e c t e d h e r e b y t h e s am e sa n i t y c h e c k s
t h a t VM S
uses
fo r i ts el f .
I f t h e d r i v e r d o e s n o t g e t c a l l ed a t i t s t i m e o u t e n t r y po i n t
b e fo r e t h e powe r
fa i l s ag a i n ,
t h e p r e s e r v ed d r i v e r s t a t e
i nd i c a t e s a un i t t h a t h a s a l r e a d y t i med o u t .
Wh e n po we r
is
f i na l l y
r e s to r ed
pe rm a n en t l y ,
t h e d r i v e r w i l l b e c a l l ed a t
i t s t i m e o u t e n t r y po i n t .
it
I f t h e d r i v e r i s i n the m i d d l e o f i t s t i me o u t
r o ut i ne ,
s t i l l a ppea r s to t h e s ys tem a s a un i t th a t h a s t i m e d o u t .
It
w i l l be c a l l e d a t i t s t i m e o u t e n t r y po i n t ag a i n wh e n t h e
mach i ne f i na l ly stabi l i zes .
I f t h e d r i v e r s uc c e ed s i n r e t u r n i ng con t r o l to the o pe r a t i ng
s y s tem w i th , f o r ex ampl e , o n e o f t h e fo l l o w i ng c a l l s ,
WF i x x C H
I O FORK
RE QC OM
t h e r e q u e s t h a s e i th e r b e e n c ompl e t ed o r th e d r i v e r
i s back
i n t o a s t a t e ( s uch a s e x p e c t i ng a n i n t e r r upt ) wh e r e t h e po we r
r e co v e r y l o g i c wi l l c a u s e t h e d r i v e r to be c a l l ed a t i t s t i me
o u t e n t r y p o i n t wh e n the powe r i s f i na l l y r e s t o r e d .

23 . 4

POWER FA I L URE ON THE UN I B US

UN I B U S powe r f a i l u r e is h a nd l e d d i f f e r e n t l y o n the VAX- 1 1 / 7 5 0 a n d
the
VAX- 1 1 / 7 8 0 .
Th e
UN I B US
is
an
i n t eg r a l
pa r t
of
the
VAX- 1 1 / 7 5 0
processo r .
Th e UN I B U S o n a VAX- 1 1 /7 8 0 i s c o nnec ted to the S B I t h r o ug h
a UN I B U S a d apte r ( DW 7 8 0 )
•

2 3 -1 0

P OWERFA I L RECOVERY
23. 4. 1

UN I B US Po we r F a i l u r e o n t h e VAX- 1 1/ 7 5 0

Th e UN IBUS o n the
VAX- 1 1/7 5 0
c a n n o t e x pe r i e n c e
i nd e pend e n t po we r
fa i l ur e .
I f po we r f a i l s o n the VAX- 1 1/7 5 0 U N I B U S , i t h a s a l s o fa i l ed
on the p r o c e s so r .
As a r e s u l t , a po we r f a i l i n te r r up t i s g e ne r a ted .

23. 4. 2

UN I B US Powe r F a i l u r e o n t h e VAX- 1 1 / 7 8 0

Bec a us e a UN IBUS f a i l u r e d o e s n o t n e c e s s a r l i y i nd i c a t e th a t the en t i r e
s ys tem
is
i n e r r o r , VM S a l l ows UNIBUS e r r o r s , i n c l ud i ng UN I B US p o we r
f a i l u r e c a u s e d by t u r n i ng o f f t h e powe r to th e UBA o r t h e
BA- l l K ,
to
o c c u r wi tho u t c r a sh i ng the e n t i r e s ys tem .
Wh e n s uc h a n e r r o r o c c u r s , t h e UBA i n te r r up t s o n beha l f o f
i tsel f
( bi t < 3 1 >
of
the
a pp r o p r i a te
BRRVR i s s e t ) .
Th e i n t e r r upt s e r v i c e
r o u t i n e fo r the a f f ec t e d UBA d e t e c t s tha t a UBA i n t e r r up t ( a s o ppo s e d
t o a UN IBUS d ev i c e i n t e r r up t ) h a s o c c u r r ed a n d t r a n s fe r s c o n t r o l to a n
e r ro r rout i n e that
•
•
•

c h e c k s t h a t t h e i n t e r r upt i s d u e to the po we r f a i l u r e o f
U B A o r UN I B US ,

the

wr i t e s an e r r o r l og e n t r y ,
r em a p s t h e s ys t em v i r t ua l add r e s s e s
tha t p r ev i ous l y ma pped
t h e UBA
i t s e l f a nd the UN IBUS I /O page ( 2 4 p a g e s in a l l ) s o
t h a t t h e s e pag e s n o w po i n t to t h e s o - c a l l ed b l a c k ho l e pag e
r e s e r v ed a t i n i t i a l i z a t i o n t i me .
Th i s m a pp i ng t e ch n i que p r ev e n t s s ub s eque n t m a c h i n e c h e c k s
or
r e l a t ed
e r r o r s f r om d ev i c e d r i v e r s tha t r e f e r e n c e the UBA o r
d ev i c e r eg i s t e r s wh i l e the UBA o r UN I B US powe r i s o f f .

I f the UN I B US ha s g o n e a wa y e i th e r bec a u s e t h e powe r wa s t u r ned o f f o r
fo r
s om e o th e r
r e a so n , d e v i c e s tha t we r e wa i t i ng f o r I /0 compl e t i o n
wi l l t ime o ut .
Th e p r og r am t h a t i s s ued the i n i t i a l I /0
r e que s t w i l l
( Th i s a s s um e s
p r e s um a b l y r e c e i v e a n a ppr o p r i a t e e r r o r no t i f i c a t i o n .
tha t no d r i v e r i s s i t t i ng i n a t i g h t l o o p a t d ev i c e I PL wa i t i ng fo r
a
s ta t us b i t to c h a ng e s t a t e . )
Wh e n the po we r i s r e s to r ed , t h e s ys tem v i r t ua l pag e s a r e
r em a pped
to
po i n t
to
the UBA r eg i s te r s a nd the UN I B U S I/O pag e .
If any d ev i c e s
we r e r emoved wh i l e t h e powe r wa s t u r ned o f f , t h e y wi l l be m a r k e d
off
l i n e a s pa r t o f t h e po we r r e c o v e r y o pe r a t i o n .
Th i s f e a t u r e , new w i th Ve r s i o n 2 o f VM S , h a s i m pl i c a t i o n s
fo r
peo p l e
a t t em p t i ng
to d e b ug d e v i c e d r i v e r s .
I n v e r s i o n 1 o f VM S , a r e f e r en c e
to a non e x i s t e n t C S R o r
o th e r
s uc h e r r o r
c a us e d
t h e s y s t em
to
bug c h e c k ,
a d rastic
but
i mmed i a te n o t i f i c a t i o n
tha t a n e r r o r h a d
occur red .
Th e r e commend ed m e t ho d
fo r
d eb ug g i ng
UN I B U S d ev i c e d r i v e r s o n
a
Ve r s i o n
2
VMS s ys tem
is
to
p l a c e a n XDE LTA b r e a kpo i n t a t g l o b a l
l o c a t i o n EXE $DW7 8 0 INT ( a t
locat ion
8 0 0 0 2B C 6
i n Ve r s i o n 2 ) .
Th i s
t e c h n i que
a l so a l lo ws i mmed i a t e e r r o r n o t i f i c a t i o n wi tho u t ta k i ng t h e
s ys tem d o wn and wi t ho u t t h e wa i t f o r the s ys t em to r e boo t i t s e l f .
Of
c o u r se ,
the e r r o r
l og
c a n a l s o b e l o o k e d a t t o o b t a i n i n f o rm a t i o n
a bo u t the e r r o r .

2 3 -1 1

PART VI I I

M I S C E L LANEOUS TOP I C S

Of s h o e s - a n d s h i ps - a n d s e a l i ng wa x Of c a bbag e s - and k i ng s And wh y t h e s e a i s b o i l i ng h o t And wh e th e r p i g s h a v e w i ng s .
Th r o ug h t h e Lo o k i ng G l a s s
Lewi s Ca r r o l l

C HAPTER 2 4
SYNCHRON I ZATION TECHN I QUES

One o f the mo s t i mpo r t a n t i s s u e s i n the d e s i g n o f an o pe r a t i ng
sys tem
is
s ynch r o n i za t i o n .
Espec i a l l y i n a s ys t em tha t i s i n t e r r up t d r i v e n ,
c e r ta i n s eque n c e s o f i n s t r uc t i o n s m u s t b e a l l owed to
e x e c u t e w i tho ut
i n t e r r up t i o n .
VM S u s e s spec i a l I PL v a l ue s to b l o c k c e r ta i n i n t e r r up t s
d u r i ng t h e e x e c u t i o n o f c r i t i c a l cod e pa t h s .
An y o pe r a t i ng s y s t e m m u s t a l so t a k e p r ec a u t i o n s to i n s u r e tha t
sh a r ed
d a ta
s t r uc tu r e s
are
not
b e i ng
s i m u l t a ne o u s l y mod i f i ed by s ev e r a l
r o u t i n e s o r b e i ng
r ead
by one
r o u t i ne
wh i l e a n o the r
r o ut i ne
is
mod i fy i ng
the
s t r uc t u r e .
VM S u s e s a
c om b i n a t i o n o f
s o f t wa r e
t e c h n i que s a nd f e a t u r e s o f t h e VAX h a r dwa r e t o s yn c h r o n i z e
access to
s h a r e d d a ta s t r uc t u r e s .
Th e t e c hn i q u e s d e sc r i b ed i n th i s c h a pt e r a r e

24 . 1

•

t h e u s e o f I P L a s a s ynch r o n i z a t i o n to o l ,

•

se r i a l i za t i o n o f a c c e s s , a nd

•

mu t ua l ex c l us i o n sema pho r e s , c a l l ed m u t e x e s .

E LEVATED I PL

Th e p r i m a r y p u r po s e fo r r a i s i ng I PL i s
to
block
i n t e r r up t s
at
the
s e l e c t ed
I PL v a l ue
a nd
all
l o we r v a l u e s of I PL .
Fo r e x ampl e , by
r a i s i ng I PL t o 2 3 , a l l d ev i c e i n t e r r u p t s a r e b l o c ked ;
but the
cloc k ,
wh i c h i n t e r r upts a t I P L 2 4 , c a n s t i l l c a us e i n te r r upt s .
VM S a l s o u s e s
s e l e c t ed I P L v a l u e s fo r pe r fo rm i ng c e r t a i n a c t i o n s o r
fo r
a c c e s s i ng
c e r t a i n s t r uc t u r e s .
I PL
Th e I PL , s to r e d i n P S L < 2 0 : 1 6 > , i s a l t e r ed by wr i t i ng the d e s i r ed
v a l ue
to
the p r i v i l eg ed r eg i s t e r PR $ I P L w i th the MTPR i n s t r uc t i o n .
Th i s i s u s ua l l y a c c ompl i shed i n VM S w i th o n e o f t wo m a c r o s , SET I PL o r
DS B IN T , who s e m a c ro d e f i n i t i o n s a r e l i s t ed i n Fi g u r e 2 4 - 1 .
Th e DSB I NT
m a c r o i s u s ua l l y used wh en a l a te r s e qu e n c e o f c o d e w i s h e s to
r e s to r e
the
I PL t o t h e s a v e d va l ue ( wi t h t h e ENB I NT mac r o ) .
Th e S E T I P L m a c r o
i s u s ed wh en the I P L wi l l l a t e r be e x pl i c i t l y l owe r ed
w i th a n o the r
S E T I P L o r s i mpl y a s a r e s u l t o f e x ec u t i ng a n RE I i n s t r uc t i o n .
Th a t
i s , t h e v a l ue o f the s aved I PL i s n o t i mpo r ta n t t o the r o u t i n e th a t i s
us i ng the S E T I PL m a c r o .
Th e s uc c e s s f u l u s e o f I P L a s a s yn c h r o n i za t i o n to o l r e qu i r e s th a t
I PL
be
r a i sed
{ no t l owe r ed )
to
t h e a pp r o p r i a t e s ync h r o n i z a t i o n l ev e l .
Lowe r i ng I PL d e f e a t s a n y a t tempt a t s yn c h r o n i z a t i o n a nd r un s t h e
r i sk
o f a r e s e r v ed o pe r a n d f a u l t wh e n a n RE I i n s t r uc t i o n i s l a t e r ex e c u t ed .
{ An RE I i n s t r uc t i o n tha t a t t emp t s to e l ev a t e
I P L c a us e s a
r e s e rved
o pe r a nd f a u l t . )

2 4-1

SYNCHRON I ZATION TECHN I QUES

Th e S E T I PL m a c r o c h a ng e s I PL t o the s pe c i f i ed v a l ue .
i s p r e s e n t , I PL i s e l ev a te d to 3 1

a rg um e n t

•

MAC RO

S ET I PL

I PL

#31

M T PR

I PL , S "' # PR $_I PL

. ENDM

S E T I PL

Th e DS B INT m a c r o f i r s t s a v e s t h e c u r r en t I PL b e fo r e e l ev a t i ng
I PL to
the
s p e c i f i ed v a l ue .
I f no a l t e r n a t e d e s t i n a t i o n i s s pe c i f i ed , t h e
o l d I PL i s s a v ed o n the s t a c k .
Th e d e fa u l t I PL v a l ue i s 3 1
•

MAC RO

DS B INT

MFPR

S "' ft PR $ I PL , DS T

M T PR

I PL ,

. ENDM

DSB INT

•

I PL

31 ,

DS T

- (SP)

S "' # PR $_I PL

Th e ENB INT m a c r o i s the c o un te r pa r t to the DS B INT m a c r o .
It s e t s
I PL t o the v a l ue tha t i t f i nd s i n the d e s i g na t ed so u r c e a rg um e n t

the

•

MAC RO

ENB INT

SRC

(SP) +

M T PR

SRC , S "' # PR $_I PL

. ENDM

ENB INT

Th e SAVI PL m ac r o d o e s n o t a l te r the c u r r en t I PL
v a l ue i n the d e s i g n a ted d e s t i n a t i o n a rg um e n t

but

d o es

•

. SAVI PL

DS T

MFPR

S "' # PR $_I PL , DS T

. ENDM

SAVI PL

Figure 24-1

- (SP)

M a c r o s Us ed by VM S to Ch a ng e I P L

24-2

s to r e

i ts

SYNCHRON I ZAT I ON TECHN I QUES

24 . 1 . 1

Use of I PL $ SYNCH
_

A s po i n t ed out i n Ch a p t e r
4,
I PL 7
( I P L$ SYNC H )
is
used
as
the
i n t e r r up t
l ev e l
f o r the s o f twa r e t i m e r r o ut i n e s , tho se r o u t i n e s th a t
I PL 7
is
s e r v i c e t i me r q ue ue e n t r i e s a nd h a nd l e qua n t um e x p i r a t i o n .
a l so
u s ed
a s t h e l ev e l t h a t I P L m u s t be r a i s ed to fo r a n y r o u t i n e to
a c c e s s a s ys t em-w i d e d a ta s t r uc t u r e .
By r a i s i ng I PL t o 7 ,
all
o th e r
r o u t i ne s
tha t might acce s s
t h e s am e sys t em-w i d e d a t a s t r uc t u r e a r e
b l o c k ed f r om e x e c u t i o n un t i l I P L i s l owe r ed .
Wh i l e the p r o c e s s o r i s e x e c u t i ng a t I P L 7 , c e r t a i n sys t em-wi d e e v e n t s
s uc h a s s c h e d u l i ng a nd I /O po s t p r o c e s s i ng a r e b l o c ked .
Ho we v e r , o th e r
m o r e impo r ta n t o pe r a t i o n s s uc h a s h a r d wa r e
i n t e r r up t
s e r v 1 c 1 ng
a nd
d ev i c e d r i v e r f o r k p r o c e s s i ng c an c o n t i n ue .
Th u s , t h e amo un t o f t i me
t h a t VMS s pe n d s at I P L 7 d o e s not
a ffect more
i mpo r ta n t a c t i v i t i e s
s uc h a s
s e rv i c i ng
external
d ev i c e s .
Th e f a c t t h a t I / O p r o c e s s i ng
i nc l ud i ng
fo rk
p r o c e s s i ng
i s mo r e
i mpo r ta n t
t h a n o th e r
s y s tem
o pe r a t i o n s
( s uch
as
s a t i s f y i ng
a
pag e
f a u l t ) r e f l ec t s o n e of the
und e r l y i ng ph i l o so ph i e s of VM S , t o k e ep e x t e r n a l d ev i c e s
as b u s y a s
po s s i b l e .

24 . 1 . 2

Othe r I PL Leve l s Used fo r Synch ro n i za t i o n

T a b l e 2 4 - 1 l i s t s seve r a l I PL l ev e l s tha t a r e used fo r
s yn c h r o n i za t i o n
p u r po s e s b y VM S .
Some o f t h e s e l ev e l s a r e used to c o n t r o l a c c e s s to
s h a r ed d a ta s t r uc t ur e s .
O t h e r s a r e used to
prevent c e r ta i n events ,
s uc h a s a c l o c k i n t e r r upt o r p r oc e s s d e l e t i o n , f r om o c c u r r i ng wh i l e a
b l o c k o f i n s t r uc t i o n s i s e x e c uted .
Ta b l e 2 4 - 1
Common I PL Va l ue s Used by VA X/VM S fo r Syn c h r o n i za t i o n

Va l ue
( d ec i m a l )

Nam e

Me a n i ng

I PL $ P OWER

D i s a b l e a l l i n t e r r up t s

I PL $ HWC L K

B l o c k c l oc k a nd d ev i c e i n t e r r upts

UC B $B D I PL

(*)

2 0 -2 3

B l o c k i n te r r up t s f r om s pe c i f i c d ev i c e s

UC B $B F I PL

(*)

8 -1 1

Dev i c e d r i v e r fo r k l ev e l s

I PL $ S YNC H

Syn c h r o n i ze a c c e s s to a n y s ys t em-w i d e
d a ta s t r uc t ur e s

I P L $_QUE UEAST

bev i c e d r i v e r fo r k I PL t h a t a l l o ws
d r i v e r s to el ev a te I PL to 7

I PL $ AS TDE L

B l o c k d e l i v e r y o f ASTs
( P r ev e n t p r o c e s s d e l e t i o n �

(*)

Th e s e s ym bo l s a r e o f f s e t s i n to a d ev i c e un i t c o n t r o l b l o c k .

24-3

SYNC HRON I Z AT I ON TECHN I QUES
24 . 1 . 2 . 1
I PL 31 - Ro u t i n e s i n VM S wi l l r a i s e I PL t o 31 to
block
i n te r r up t s
fo r
a
sho r t pe r i o d
of
t i me
( u s ua l l y l e s s
tha n
i n s t r uc t i o n s o nc e the s ys t em i s i n i t i a l i z ed ) .
•
•

•

all
ten

Th i s
i s d o ne
by d ev i c e d r i v e r s
j us t b e fo r e
they c a l l
I OC $WF i x x C H t o p r e v e n t a po we r f a i l i n t e r r up t f r om o c c u r r i ng .
Th e e n t i r e boo t s t r a p s e q ue nc e o pe r a t e s a t
I PL 3 1
for
a
in
o rder
t o put
t h e s ys t em i n to a known s t a t e b e f o r e a l l o wi ng
i n t e r r up t s to o c c u r .
Bec a u se t h e e r r o r l og g e r r o u· t i n e s c a n be c a l l ed f r om a nywh e r e
in
the
execut i ve ,
i n c l ud i ng
faul t
service
r o u t i n e s th a t
e x e c ute a t I P L 3 1 s uc h a s m a c h i n e c h e c k h a nd l e r s ,
a l locat i on
of
an e r ro r
l og
buffe r
c a n onl y exec ute
a t I PL 3 1 .
A
c o r r o l a r y o f th i s r e q u i r em e n t d em a nd s th a t the E RRFMT p r o c e s s
e x e c ute
a t I PL 3 1 wh e n i t i s c o py i ng t h e e r r o r l og b u f f e r t o
t h e e r r o r l og f i l e .
( As d e sc r i b ed i n Ch a p t e r 7 , th i s c o py i ng
i s done
i n two
s t eps .
Th e e r r o r l og b u f f e r c o n t e n t s a r e
c o p i ed t o t h e ERRFMT p r o c e s s P O s pa c e a t I PL 3 1 .
Th e n I PL i s
l owe r ed t o
ze r o ,
t h e m e s sag e s a r e fo rm a t ted , a nd they a r e
wr i t t en t o the e r r o r l og f i l e . )

24 . 1 . 2. 2
I PL 2 4 - Wh e n I PL i s r a i s ed to 2 4 , t h e l ev e l
a t wh i c h t h e
h a rd wa r e c l o c k i n te r r upts , c l o c k i n te r r upts a r e b l o c ked .
Th e so f t wa r e
t i m e r i n te r r upt s e r v i c e
rout i ne uses
th i s
I PL l ev e l
wh e n
it
is
c om pa r i ng
two
q ua d wo r d s y s t em t i m e v a l ue s .
Th i s p r e v e n ts t h e sys t em
t i m e f r om b e i ng u pd a t ed wh i l e i t i s b e i ng compa r ed to some o th e r
t i me
va l ue .
( Th i s
1s
r e qu i r ed
b ec a u se
the VAX a r ch i t e c t u r e d o e s n o t
c o n t a i n a CMPQ i n s t r uc t i o n . )

24. 1 . 2. 3
Dev i c e I PL - De v i c e d r i v e r s wi l l r a i s e I PL to the
l ev e l
at
wh i c h
the
a s so c i a t ed d ev i c e i n t e r r up t s t o p r ev e n t d ev i c e i n t e r r up t s
wh i l e d ev i c e r eg i s te r s a r e b e i ng r e ad o r wr i t t e n .
Th i s
s t e p u s ua l l y
p r e c ed e s the f u r the r e l ev a t i o n o f I PL t o 3 1 j u s t d e sc r i bed .

24 . 1 . 2 . 4
Fo r k I P L - Fo r k I P L ( a v a l ue spec i f i c to e a c h
d ev i c e t ype )
i s used
by VM S
to
s yn c h r o n i z e
a c c e s s to e a c h un i t c o n t r o l b l o c k .
Th e s e b l o c k s a r e a c c e s s e d b y d ev i c e d r i v e r s a nd
b y p r o c ed u r e b a s e d
c od e
s uc h
as
the compl e t i o n pa th o f the $ Q I O s y s tem s e r v i c e a nd t h e
Ca n c e l I /0 s y s tem s e rv i c e .

Dev i c e d r i v e r s a l s o use the i r a ss o c i a t ed fo r k I PL a s a synch r o n i za t i o n
l ev e l
wh e n a c c e s s i ng
d a t a s t r uc t u r e s tha t c o n t r o l sha r ed r e so u r c e s ,
s uc h a s m u l t i - u n i t c o n t r o l l e r s ,
o r d a ta pa th
r eg i s t e r s
or
map
r eg i s t e r s .
I n o rd e r
fo r t h i s s yn c h r o n i za t i o n to wo r k p r o pe r l y , a l l
d ev i c e s s ha r i ng a g i v e n r e s o u r c e m u s t use the same fo r k I P L .
Th e use o f f o r k I P L t o synch r o n i ze a c c e s s to un i t c o n t r o l b l o c k s wo r k s
the s am e wa y tha t e l ev a t i ng I PL to 7 d o e s .
Th a t i s , o n e p i e c e o f c o d e
e l e v a t e s I PL to the spec i f i ed fo r k I PL ( fo und
a t o f f s e t UC B $ B_F I PL )
a nd b l o c k s a l l o the r po t en t i a l a c c e s s e s to the UC B .
Fo r k p r o c e s s i ng ,
the t e c h n i q ue wh e r eby d ev i c e d r i v e r s l o we r I PL b e l o w d ev i c e
i n te r r up t
l ev e l
in
a man n e r c o n s i s t e n t wi th the i n te r r up t n e s t i ng sc h em e , a l so
u s e s t h e s e r i a l i z a t i o n t e c h n i que d e sc r i b ed i n the n e x t s e c t i o n .

2 4-4

SYNC HRON I ZAT ION TECHN I QUES

24 . 1 . 3

I PL$ QUEUEAST
_

Pe r h a ps the e x ampl e tha t b e s t i l l u s t r a t e s
the
sync h r o n i za t i o n
rules
fo l l o wed b y VM S i s the u s e o f I P L 6 ( I PL $ QUE UEAST ) b y d ev i c e d r i v e r s .
The r e a r e i n s t a nc e s wh e r e d ev i c e d r i v e r s f i nd i t nec e s s a r y to i n t e r a c t
wi t h t h e s c h ed u l e r .
Fo r
e x ampl e ,
t h e t e rm i n a l d r i v e r n o t i f i e s a
r e que s t i ng p r o c e s s a bo u t u n so l i c i t ed i np u t o r a CTRL/Y th r o ug h a n AST
( Ch a p t e r 5 ) .
Th e m a i l bo x d r i v e r a l s o c a n no t i f y r e que s t i ng p r o c e s s e s
a b o u t r e a d s o r wr i t e s to a m a i l bo x .
Th e e nq u e u i ng o f a n AST m u s t o c c u r
at
I PL$ S YNC H ,
to
s yn c h r o n i z e
a c c e s s t o the sched u l e r ' s d a t a b a s e .
As a l r e aay po i n ted o u t , I PL mus t
b e e l ev a t e d ( no t l owe r ed ) to 7 to a c h i ev e th i s
s yn c h r o n i za t i o n .
Th e
fo r k
I PL a t
I PL 6
a l l o ws d ev i c e d r i v e r s tha t e x e c u t e a t fo r k I PL
( I PL 8
t h r o ug h
I PL 1 1 )
to
m a ke
the s e
s c h e d u l i ng
r e q ue s t s .
Spec i f i c a l l y ,
the d r i v e r
c a l l s a r o u t i n e c a l l ed C OM $DE LATTNAS T tha t
c r e a t e s a n I PL 6 f o r k r e q ue s t .
Th a t i s , a fo r k b l o c k i s p l a c ed
i n to
the
I P L 6 f o r k que ue a nd an I P L 6 s o f twa r e i n t e r r up t r e que s t ed .
Wh e n
tha t i n t e r r upt o c c u r s , t h e fo r k b l oc k i s u s e d a s a n AST c o n t r o l
block
a nd p a s s e d t o S C H $ QAST , wh o wi l l e l e v a t e I P L t o 7 , i n k e e p i ng wi th the
r u l e tha t
I P L mus t b e
r a i s ed
to
I P L $ S YNC H to
prese rve
p r o pe r
i n t e r r up t n e s t i ng .
An o bv i o u s que s t i o n i n r e s po n s e to the a bo v e d e s c r i p t i o n
is
wh y t h e
I PL 7
fork
i n te r r upt c a nno t b e u s e d to a c h i eve t h e s am e r e s u l t .
Th e
a n s we r i s tha t i f the I P L 7 so f twa r e i n t e r r upt we r e n o t b e i ng used fo r
a no t h e r
p u r po s e ,
t h a t wo u l d
be
a
pe r f e c t l y a c c e p t a b l e so l u t i o n .
Ho we v e r , the so f twa r e t i m e r s e r v i c e r o u t i n e i s e n t e r ed a s a r e s u l t o f
the
I P L 7 s o f t wa r e i n t e r r upt .
So th i s s ynch ron i z a t i o n t e c h n i que u s e s
the f i r s t f r e e I P L b e l ow 7 ,
the
I P L 6 s o f t wa r e
i n t e r r u p t c a l l ed
I PL $_Q U E U EAST .
I PL 6 i s used i n a s e c o nd i n s t a n c e b y d ev i c e d r i v e r s
th a t
i n te r a c t
wi th
t h e sche d u l e r .
As d e sc r i b ed i n t h e n e x t c h a p t e r , n o npag ed po o l
c anno t b e d e a l l o c a ted f r om c od e e x e c u t i ng i n r e spo n s e t o a n
i n t e r r up t
a bo v e
I PL 7 ,
b e c a u s e n o n pag ed
po o l i s a s ys t em-w i d e r e s o u r c e wh o s e
a v a i l a b i l i ty
mus t
be
r e po r ted
to
the
schedul e r .
Ro u t i n e
C OM $ DRVD EALM EM
c reates
an
I PL 6
fo r k proc ess
tha t
a l l o ws
the
d e a l l o c a t i o n to t a k e p l a c e i n r e spo n s e to a n I P L 6 s o f twa r e i n t e r r up t ,
a l l o w i ng the s c h ed u l e r to p r o pe r l y s yn c h r o n i z e i t s d a t a b a s e a c c e s s e s .
Th e a c t ua l po o l m a n i pu l a t i o n t a k e s p l a c e a t I PL 1 1 to s ync h r o n i z e wi th
the a l l o c a t i o n r o u t i n e .

24 . 1 . 4

I PL 2

Th i s i s t h e l ev e l a t wh i c h the so f twa r e i n t e r r up t a s s o c i a ted wi th AST
del ivery occur s .
Wh e n s ys t em s e rv i c e p r o c ed u r e s r a i s e I PL to 2 , t h e y
a r e b l o c k i ng the d e l i v e r y o f a l l ASTs , b u t pa r t i c u l a r l y t h e
spec i a l
In o th e r wo r d s , i f a p r o c e s s
ke rnel AST tha t c a uses process d e l e t i o n .
i s e x e c u t i ng a t I P L 2 ( o r abov e ) , th a t p r o c e s s c a nno t b e d e l e t ed .
Th i s t e ch n i q u e i s used i n s eve r a l p l a c e s to p r ev e n t
proc e s s d e l e t i on
b e twe e n
t h e t i me
tha t
s ome sys t em r e so u r c e ( s uc h a s s ys tem d yn am i c
m emo r y ) i s a l l o c a t ed a nd t h e t i me t h a t own e r sh i p o f t h a t
r e so u r c e
is
r ec o rd ed ( s uch a s t h e i n s e r t i o n o f a d a t a s t r uc t u r e i n to a l i s t ) .
Fo r
e x a m p l e , the $ Q I O s y s tem s e rv i c e e x e c u t e s a t I P L 2 f r om th e t i me
tha t
an
I /0 r e que s t pac k e t i s a l l o c a ted f r om no npag ed d yn am i c memo r y u n t i l
t h a t pa c k e t i s que ued to a un i t c o n t r o l b l o c k o r pl a c ed i n to
the
I /0
po s t pr o c e s s i ng queue .

24-5

SYNCHRON I Z AT I ON TECHN I QUES

I PL 2 a l so has s i g n i f i c a n c e fo r an e n t i r e l y d i f fe r e n t r e a so n .
Th i s i s
the
h ighest
I PL l ev e l a t wh i c h pag e f a u l t s a r e pe rm i t te d .
I f a pag e
f a u l t o c c u r s a t I PL a b o v e
2,
a
fatal
b ug ch e c k
( BUG $ PG F I PLH I )
is
i s s ue d .
If
the r e
is
a ny po s s i b i l i ty t h a t a pag e f aul t c a n o c c u r ,
b e c a us e e i th e r the c o d e
tha t
is
e x e c u t i ng
or
the d ata
tha t
it
r e f e r e nc e s
i s pag e ab l e ,
then
t h a t c o d e c anno t ex e c u t e above I PL 2 .
Th e c onv e r s e o f th i s c o n s t r a i n t i s tha t a n y c o d e tha t e x e c u t e s above
I PL 2 ,
a nd
a l l d a ta
r e f e r en c ed
b y s uc h c od e , must be l o c k ed i n to
memo r y i n some wa y .
Append i x A s hows some o f t h e techn i qu e s th a t VMS
uses
to
d yn am i c a l l y l o c k c o d e o r d a ta i n to memo r y s o t h a t I PL c a n b e
e l eva t ed a b o v e I P L 2 .

24 . 2

S ER IAL I Z ED ACC E S S

Th e s o f t wa r e i n te r r up t c apab i l i ty d e sc r i b ed in C h a p t e r 4
p r o v i d e s no
m e thod
f o r c o un t i ng t h e n um b e r of r e que s t ed so f t wa r e i n te r r up t s .
VMS
u s e s a c om b i na t i o n o f s o f twa r e i n t e r r up t s a nd d o ub l y l i n ke d
l i sts
to
c ause
s ev e r a l r eque s t s fo r the s am e d a ta s t r uc t u r e or p r o c e d u r e to b e
s e r i a l i zed .
Th e mo s t i m po r ta n t e x ampl e o f th i s i n V M S i s the
use o f
f o r k p r o c e s s e s b y d ev i c e d r i v e r s .
Th e I /0 po s tp r o c e s s i ng s o f twa r e
i n t e r r up t i s a s e c o nd e x amp l e o f s e r i a l i ze d a c c e s s .

24 . 2 . 1

Fo r k Proc e s s i ng

Fo r k p r o c e s s i ng i s t h e t ec h n i q ue tha t a l l o ws d ev i c e d r i v e r s
to
l owe r
I PL
i n a m a n n e r c o n s i s t e n t w i th t h e i n t e r r up t n e s t i ng s c h eme d e f i n ed
Fo r k p r o c e s s i ng i n VM S i s e x p l a i n ed by f i r s t
by the VAX a r ch i t ec t u r e .
d e sc r i b i ng how i t wo r k s a nd then i l l u s t r a t i ng the s i t ua t i o n tha t i t i s
d e s i g n ed t o av o i d . Wh en a d ev i c e d r i v e r r ec e i v e s c o n t r o l i n r e s po n s e
i t pe r fo rm s wh a t eve r s t eps a r e n ec e s s a r y to
to
a d ev i c e
i n t e r r upt ,
se rv i c e
the
i n t e r r upt
at d ev i c e
I PL .
Fo r
exampl e ,
any d ev i c e
r eg i s te r s
who s e c o n t e n t s wo ul d b e d e s t r o yed b y ano th e r i n t e r r upt mus t
b e r e ad b e f o r e d i sm i s s i ng the d ev i c e i n t e r r upt .
Us u a l l y , t h e r e i s some p r o c e s s i ng
t h a t c an
be d e f e r r ed .
Fo r
DMA
d ev i c e s ,
a n i n te r r up t s i g n i f i e s e i th e r c ompl e t i o n o f t h e o pe r a t i o n o r
a n e r ro r .
Th e c o d e tha t d i s t i ng u i sh e s t h e s e two c a s e s
a nd pe r f o rms
e r ro r
p r o c e s s i ng
i s u s ua l l y l e ng t h y a nd to e x e c ute at d ev i c e I PL f o r
e x t e nd ed pe r i od s o f t i me wo u l d
s l ow d own
the sys t em .
Fo r n o n DMA
d ev i c e s
tha t d o n o t
i n t e r r upt
a t too
r ap i d
a
r a te ,
i n te r r up t
p r o c e s s i ng c an b e d e f e r r e d i n favo r o f o the r mo r e
i mpo r ta n t d ev i c e
s e r v i c i ng .
I n e i th e r c a se , t h e d r i v e r s i g n a l s tha t i t wi s h e s
to
d e l a y f u r th e r
p r o c e s s i ng
un t i l
the
I PL
i n t h e s ys t em d ro ps b e l o w a p r ed e t e r m i ned
v a l u e , the fo r k I P L a s s o c i a t ed wi t h th i s d r i v e r .
Th i s
s i g n a l l i ng
is
a c c om p l i s hed b y c a l l i ng
a
rout i ne
i n the e x e c u t i ve tha t s a v e s the
ad d r e s s of the nex t i n s t r uc t i o n in the d r i v e r
in
a d a ta
s t r uc t u r e
c a l l ed
a fo r k b l o c k ( F i g u r e 4 - 2 ) .
Th e fo r k b l o c k i s t h e n i n s e r t e d a t
t h e e nd o f t h e fo r k q u e u e fo r
tha t
I PL va l ue .
If
t h e que ue wa s
p r e v i o u s l y empt y ,
a
s o f twa r e
i n te r r up t
a t the a pp r o p r i a t e I PL i s
r e que s t e d .
( I f t h e que u e wa s n o t p r ev i o u s l y emp t y ,
the
r e que s t h a s
a l r e a d y b e en mad e a nd t h e ove r h e a d a s soc i a t ed wi th a n e e d l e s s so f twa r e
i n t e r r up t r e que s t c a n b e avo i d ed . )

2 4 -6

SYNCHRON I Z ATION TECHN I QUES

24 . 2 . 2

I/O Po s tproc e s s i ng

Upo n c ompl e t i o n o f a n I /O r e qu e s t , t h e r e a r e a s e r i e s o f c l e a n up s te ps
t h a t m u s t b e p e r fo rmed .
Th e e v e n t f l ag a s s o c i a t ed wi t h t h e r e qu e s t
must be set .
A s pec i a l k e r n e l A S T t h a t wi l l p e r fo rm f i n a l c l e a n up
1n
t h e c o n tex t o f t h e p r o c e s s tha t i n i t i a l l y i s s ued the $ Q I O c a l l m u s t b e
que ued to the p r o c e s s .
Th i s c l e a n up m u s t b e c omp l e ted
fo r
o ne
I /0
I n o th e r wo r d s , I/O po s tp r o c e s s i ng
r e qu e s t b e fo r e a no th e r i s h a nd l ed .
m u s t b e s e r i a l i z ed .
Th i s s e r i a l i z a t i o n i s a c c om p l i shed by pe r fo rm i ng
the po s t p r o c e s s i ng
o pe r a t i o n a s a so f t wa r e i n t e r r up t s e r v i c e r o u t i n e ( a t I PL 4 ) .
Wh e n a
r e que s t i s r ec og n i zed a s b e i ng c om p l e te , t h e
I /0
r e que s t pa c ke t
is
p l a c ed a t t h e t a i l o f t h e I /O po s tp r o c e s s i ng q ueue ( a t g l o b a l l i s th e a d
I OC $G L P S B L ) .
If th i s pac ke t i s the f i r s t in
the
l i st ,
a
so f t wa r e
i n te r r up t at I P L 4 i s r e que s t ed .
Wh en t h e d ev i c e d r i v e r r ec og n i z e s t h a t a n I /O
r e que s t h a s c om p l e ted
( e i th e r
s uc c e s s f u l l y o r un s uc c e s s f u l l y ) , i t c a l l s r o ut i n e I OC $ R E QC OM ,
wh i c h m a k e s t h e I PL 4 s o f twa r e i n t e r r up t r e que s t a t fo r k I PL ( I PL 8 to
I PL 1 1 ) , a nd s o the po s t p r o c e s s i ng i n te r r up t i s d e f e r r ed un t i l the I PL
d rops b e l ow 4 .
Some I /O r e q ue s t s d o n o t r eq u i r e d r i v e r a c t i o n .
Wh en
the
$ Q I O s y s tem s e rv i c e o r d ev i c e - sp e c i f i c FDT r o u t i n e s d e t e c t t h a t
t h e r e que s t c a n b e c ompl e t ed w i tho u t d r i v e r i n t e r v en t i o n , o r
if
they
d e t ec t
an e r ro r ,
they c a l l
o ne
of
the
r o u t i ne s EXE $ F IN I SH I O o r
E XE $ F I N I S H I OC .
Th e s e t wo
r o u t i ne s
execute
at
I PL 2
and
so
the
r e q ue s t ed
s o f twa r e
i n t e r r up t
i s t a k e n i mmed i a t e l y .
AC Ps a l so p l a c e
I /O r e que s t pac k e t s d i r e c t l y i n to t h e po s t p r o c e s s i ng q u e u e a nd r e qu e s t
t h e I PL 4 s o f twa r e i n t e r r up t .

24 . 3

MUTUAL E XC LUS ION S EMAPHORES

( MUTEXE S )

Th e
s yn ch r o n i z a t i o n
t e c h n i qu e s d e sc r i b ed
so
far
all
execute
at
e l eva t ed
I PL ,
t h us b l oc k i ng c e r t a i n o pe r a t i o n s s uc h a s a r e sc h ed u l e
f r om t a k i ng p l a c e .
Th e r e a r e s ome sha r ed d a ta s t r uc t u r e s tha t m u s t b e
p r o t e c ted
f r om m u l t i pl e a c c e s s wh e r e e l ev a t ed I PL i s a n un a c c ept a b l e
t ec h n i que fo r s yn c h r o n i za t i o n , b e c a u s e the p r oc e s so r wo u l d have
to
r ema i n a t an e l ev a ted
I P L f o r a n u n s pe c i f i ed l eng t h o f t i me .
Fo r
e x ampl e , t h e s ys t em l og i c a l
n ame
t ab l e c anno t h a v e
two
proc esses
m a k i ng
entr i es
at the
s am e t i m e .
Howev e r , t h e sys t em l og i c a l n ame
t ab l e c a n b e v e r y l o ng , a nd the s e a r c h o f
the
t ab l e
fo r
d up l i c a te
n am e s c a n b e v e �y t i m e c o n s um i ng .
A s e c ond
s i t ua t i o n wh e r e
e l ev a ted
I PL
i s n o t a c c e p ta b l e a s a
s yn c h r o n i za t i o n
too l
o cc u r s wh e n t h e d a t a s t r uc tu r e t h a t i s b e i ng
p r o tec t ed i s pag ed .
Th e memo r y m a n ag em e n t s ub sys t em d o e s n o t a l l o w
pag e
faul ts
to occur
wh e n I PL i s above 2 .
Th u s , a n y pag e ab l e d a ta
s t r uc t u r e c a nn o t b e p r o t e c t e d b y e l ev a t i ng I PL to 7 .
Fo r
these
two
r easons ,
a n o th e r mech a n i sm
is
r eq u i r ed
fo r c o n t r o l l i ng acc e s s to
sh a r e d d a ta s t r uc tu r e s .
VM S u s e s m u t e x e s ,
m u t ua l
e x c l us i o n
s em a pho r e s ,
for
th i s pu r po se .
M u t ex e s a r e
e s s e n t i a l l y f l ag s
tha t
i nd i c a te
wh e th e r a g i v e n d a ta
s t r uc t u r e i s b e i ng
e x am i n ed
o r mod i f i ed
b y o n e o f a g r o up o f
c o ope r a t i ng
processes .
Th e
i m p l em e n ta t i o n a l l o ws
e i th e r mul t i pl e
Ta b l e 2 4 - 2
l i s ts those
r e ad e r s o r o n e wr i te r o f a d a ta
s t r uc t u r e .
d a ta s t r uc t u r e s i n VM S t h a t a r e p r o t ec t ed b y m u t ex e s .

2 4-7

S YNCHRON I Z AT ION TECHN I QUES

Ta b l e 2 4 - 2
L i s t o f Da t a S t r uc t u r e s P r o tec ted b y Mu t e x e s

Da t a St r uc t u r e

Gl o b a l Ad d r e s s
o f Mu t e x
{ No t e 1 }

Va l ue i n
Ve r s i o n 2 . 0
{No te 1 }

Sy s t em Lo g i c a l Nam e Ta b l e

LOG $AL MUT E X

8 0 0 0 2 4F 4

G r o up Lo g i c a l Nam e Ta b l e

8 0 0 0 2 4F 8
I OC $G L MUT E X

80002620

Commo n Ev e n t B l o c k L i s t

E XE $G L C EBM TX

80002624

Pag ed Dyn am i c Mem o r y

EXE $G L PGDYNM TX

80002628

G l ob a l Sec t i o n De sc r i p to r L i s t

E XE $G L G S DM TX

8 0 0 0 2 6 2C

S h a r ed Mem o r y Gl o b a l Sec t i o n
De sc r i pto r Ta b l e

E XE $G L_S HMG S MTX

80002630

Sh a r ed Mem o r y Ma i l box
De sc r i pto r Ta b l e

EXE $G L S HMMBMTX

80002634

E n qu e ue/Dequeue Ta b l e s
( No t Cu r r e n t l y Us ed )

E XE $G L_E N QM TX

80002638

Known F i l e En t r y Ta b l e

E XE $G L K F IMTX

8 0 0 0 2 6 3C

L i n e Pr i n t e r Un i t Co n t r o l
Bl o c k { No te 3 )

UC B $ L LP MUT EX

(No te 3 )

I /0 Da ta Ba s e

{ No te 2 }

{1)

Wh e n a pr o c e s s i s p l a c ed i n to a n MWA I T s t a te wa i t i ng
fo r
a m u t ex ,
the
add r e s s o f t h e m u t ex i s pl a c ed i n to the
PC B $ L E FWM f i e l d of the PC B .
Th e
s ym bo l i c
contents o f
PC B $ L-E FWM w i l l p r o b ab l y r em a i n t h e same f r o m r e l e a se to
r e l e a se .
Th e n ume r i c
c o n te n t s a r e
a lmost
c e r ta i n
to
c h a ng e wi t h e a c h m a j o r r e l e a se o f the o pe r a t i ng sys t em .

(2)

Th i s m u t e x i s used by t h e As s i g n Ch a n n e l
a nd Al l o c a t e
Dev i c e s ys t em se rv i c e s wh en s e a r c h i ng t h r o ug h the l i n k ed
l i s t o f d ev i c e d a ta b l o c k s fo r
a d ev i c e wi t h a g i v en
I t i s a l so used by the MOUNT u t i l i ty a nd the f i l e
n am e .
s ys t em AC Ps to l o c k the f i l e s ys t e m d a ta s t r uc t u r e s .

{3)

Th e mutex a s so c i a t e d wi t h e ac h l i n e p r i n t e r u n i t d o e s no t
have a
f i x ed ad d r e s s l i ke the o th e r m u t ex e s .
I t s v a l ue
d e pe nd s o n wh e r e t h e UC B fo r tha t un i t i s a l l o c a ted .

Th e m u t e x i t se l f c on s i s t s o f a
s i ng l e
l o ng wo r d
th a t c o n t a i n s
the
n um b e r of o wn e r s of t h e m u t ex { MT X $W OWNC NT ) in t h e low o r d e r wo r d and
s t a t u s f l ag s { MTX$W S T S ) i n t h e h i g h o rd e r wo r d
{ Fi g ur e 2 4 -2 ) .
Th e
o wn e r c o un t b eg i ns a t - 1 s o th a t a m u t e x w i t h a z e r o i n t h e l o w o r d e r
wo r d h a s o ne o wn e r .
Th e o n l y f l ag
cur r en t l y
i mp l eme n ted
i nd i c a t e s
wh e th e r
a
wr i te o pe r a t i o n i s e i th e r i n p r og r e s s o r pend i ng fo r th i s
m u t e x { MTX$ V_WRT ) .

2 4-8

SYNC HRON I Z AT I ON TECHN I QUES
31

1 7 1 6 15

Status

Figure 24-2

24.3 . 1

O w n e rship Count
W r i t e - in- Progress or
Write P e n d i ng Flag

Fo rma t o f Mu t ua l E x c l u s i o n Sema pho r e

( MUT E X )

Loc k i ng a Mu t e x fo r Read Ac c e s s

Wh e n a p r o c e s s w i shes to g a i n r ea d a c c e s s to a d a t a s t r uc t u r e tha t
is
p r o t e c t ed b y a mutex , i t p a s s e s the a d d r e s s o f t h a t m u t ex to a r o u t i n e
c a l l ed S C H $ L O C KR .
I f the r e i s n o wr i t e o pe r a t i o n e i th e r
i n prog r e s s
or
pend i ng ,
t h e o wn e r c o un t o f
th i s m u t e x
( MTX$W OWNCNT )
is
at
i nc r emen t ed , t h e c o un t o f m u t e x e s o wn ed by th i s p r o c e s s - ( s to r ed
o f fset
PC B $ L M TXCNT
in
the
so f twa r e
PC B ) i s a l so i n c r emented , a nd
c o n t r o l i s p a ss e d bac k to the c a l l e r , un l e s s th i s i s
the
onl y mutex
o wn e d by th i s p r o c e s s .
I f t h e m u tex c o un t fo r th i s p r o c e s s ( PC B $W MTXCNT ) i s o n e ,
i nd i c a t i ng
that
the
p r o c e s s o wn s
no
o th e r m u t ex e s ,
t h e c u r r e n t a nd
base
p r i o r i t i e s a r e s to r ed i n t h e u ppe r two b y t e s o f PC B $ L WT I M E ,
a
field
in
the
s o f twa r e
PC B t h a t i s n o l o ng e r u s ed b y VM S . - I n a d d i t i o n , i f
the p r o c e s s i s n o t a r e a l - t i me p r o c e s s ( p r i o r i t y sm a l l e r than 1 6 ) , t h e
s o f twa r e p r i o r i t y
( bo th c u r r e n t p r i o r i t y and b a s e p r i o r i t y ) o f t h e
p r o c e s s i s e l ev a t ed to 1 6 .
Th i s i s d o ne to i n s u r e th a t the mutex wi l l
b e o wn ed fo r a s l i t t l e t i m e a s po s s i b l e .
No t i c e t h a t the chec k o n t h e
n um b e r o f own ed m u t ex e s p r ev e n t s a p r o c e s s that g a i n s o wn e r sh i p o f two
o r m o r e m u t ex e s f r om r e c e i v i ng a pe rma n e n t pr i o r i t y e l ev a t i o n i n t o the
r e a l - t ime r a ng e .
( Th e p r i o r i t y a l t e r a t i o n a l g o r i thm d e s c r i b ed h e r e i s
a pa r t o f a b i n a r y upd a t e a nd d o e s n o t ag r e e e n t i r e l y w i th the l i s t i ng
o f mod u l e MUTEX i n the e x e c u t i v e m i c r o f i c h e . )
Ro u t i n e S C H $ LOCKR a l wa ys r e t u r n s s uc c e s s f u l l y i n the s e n s e th a t i f t h e
mutex
is
c u r r e n t l y un a v a i l a b l e ,
t h e p r o c e s s i s p l a c ed i n to a m u t ex
wa i t s ta t e ( MWA I T ) un t i l t h e m u t ex i s f r e ed up .
At t h e t i me tha t
the
process
even t ua l l y g a i n s o wn e r sh i p o f the m u t ex , c o n t r o l wi l l th e n b e
p a s s e d b ac k .
I PL i s s e t t o I PL $ A S TDE L
( I PL 2)
to
p r ev e n t p r o c e s s
d e l e t i o n wh i l e t h e m u t ex i s o wn ed b y t h i s p r o c e s s .
Th i s m u s t b e d o n e
b e c a use t h e De l e t e P r o c e s s sys t em s e r v i c e h a s no
internal
chec k s o n
wh e the r
t h e p r o c e s s b e i ng d e l e t ed own s a n y m u t e x e s .
I f the del etion
s uc c e ed ed , t h e l o c k ed d a ta s t r uc t u r e wo u l d b e l o s t t o the sys t em .

24 . 3 . 2

Loc k i ng a Mu t e x f o r Wr i te Ac c e s s

A p r o c e s s wi sh i ng to g a i n wr i t e a c c e s s to a pro t e c t ed
d a ta
s t r uc t u r e
pa s s e s t h e a d d r e s s
of
t h e a pp r o p r i a t e mutex
to a r o u t i n e c a l l e d
S C H $ LOCKW .
Th i s r o u t i n e r e t u r n s c o n t r o l to the c a l l e r wi th the m u t e x
l o c k ed
fo r
wr i t e
access
if
the mutex
is
c u r r e n t l y unowned .
In
ad d i t i o n ,
b o th m u t e x c o un t s
( MTX$W OWNC NT a nd
PCB $ L MTXCNT )
are
i nc r em e n t e d ,
the process
s o f twa r e pr i o r i t y i s po s s i b l y-a l te r e d , a n d
I PL i s s e t to 2 .
A n a l t e r n a t e e n t r y po i n t ,
S C H $ LO C KNOWA I T ,
returns
control
t o t h e c a l l e r w i th R O < O > c l e a r ed ( i nd i c a t i ng f a i l u r e ) i f t h e
r e q u e s ted m u t ex i s a l r e a d y own ed .

24-9

SYNCHRON I Z AT I ON TECHN I QU E S

Fo r the r � g ul a r e n t r y po i n t ( S C H $ L OC KW ) , i f th i s m u t e x i s o wn e d ,
the
process
1s
p l a c ed
i n to
t h e m u t ex wa i t s ta t e ( MWA I T ) .
Howe v e r , the
wr i t e pend i ng b i t i s set so tha t f u t u r e r e que s t s fo r r e a d a c c e s s wi l l
I n a s e n s e , t h i s s c h em e i s p l a c i ng r e que s t s fo r wr i t e
a l so b e d en i ed .
a c c e s s a h e a d o f r e que s t s f o r r e ad
access .
Howeve r ,
all
that
th i s
c h ec k
is
r e a l l y d o i ng
is
p r ev e n t i ng
a c o n t i n uo u s s t r e am o f r e a d
a c c e s s e s k e e p i ng the m u t ex c o un t
( MTX$W OWNCNT )
no n z e r o .
Wh e n t h e
m u t ex
c o un t g o e s to - 1 ( no o wn e r s ) , i t i s d ec l a r e d ava i l a b l e a nd t h e
h i g h e s t p r i o r i t y p r o c e s s wa i t i ng f o r the m u tex i s the o n e
tha t wi l l
g e t f i r s t a c c e s s t o the m u t ex , i nd e pend e n t o f wh e th e r i t i s r e q ue s t i ng
a r e ad a c c e s s o r a wr i te a c c e s s .

24 . 3 . 3

Mutex Wa i t S t a te

Wh e n a p r o c e s s is p l a c ed i n to a m u t ex wa i t s t a t e , i t s s t a c k i s set
up
so
tha t
the
saved
PC
is
the
e n t r y po i n t of e i th e r the r e ad - l o c k
r o u t i ne o r t h e wr i te- l o c k r o u t i n e .
( I n the l a t t e r c a s e , the PC po i n t s
to
a
b r an c h to SCH$ LOCKW . ) The PS L i s ad j us ted so tha t t h e saved I PL
is 2.
Th e add r e s s o f the m u t e x th a t i s b e i ng r e qu e s t ed i s p l a c ed i n to
the
s o f twa r e PC B a t o f f s e t PC B $ L E FWM .
( Be c a us e the p r o c e s s i s n o t
wa i t i ng o n a n ev e n t f l ag , t h i s f i e l d i s a v a i l ab l e fo r o th e r p u r po s e s . )
Ta b l e s 8 - 2 a nd 2 4 - 2 l i s t the c o n t e n t s o f the PC B $ L E FWM f i e l d fo r e a c h
MWA I T s t a te .

24 . 3 . 4

Un l o c k i ng a Mutex

A p r o c e s s r e l i nq u i sh e s o wn e r sh i p o f a m u t e x b y p a s s i ng the a d d r e s s o f
the m u t ex to be r e l e a sed to a r o u t i n e c a l l ed S C H $ UN LOC K .
Th i s r o u t i ne
d e c r em e n t s the n umber o f m u t e x e s o wned by th i s p r o c e s s r eco r d ed i n i t s
PC B .
If
this
p r o c e s s d o e s n o t own a n y mo r e m u t e x e s ( PC B $W MTXCNT
c o n t a i n s z e r o ) t h e s av ed
b a s e a nd
c u r r e n t pr i o r i t i e s
( in
f ields
PC B $ L WT I M E + 2 a n d PC B $ L WT IME + 3 ) a r e e s t a b l i sh e d a s t h e p r o c e s s ' s
I f t h e r e a r e c omputa b l e
( C OM )
c u r r e n t p r i or i t i e s .
n ew b as e a nd
p r o c e s s e s w i th h i gh e r
pr i o r i t i es
than
th i s p r o c e s s ' s n ew c u r r en t
p r i o r i t y , a r e sc h ed ul i ng i n t e r r up t i s r eque s t ed .
S C H $ UN LOC K a l s o d e c r em e n t s
t h e n um b e r o f own e r s o f t h i s m u t e x
( MTX $W OWNCNT ) .
If
the o wn e r c o un t o f th i s m u t e x d o e s n o t g o to - 1 ,
t h e r e a r e o th e r o u t s t a nd i ng own e r s o f t h i s m u tex so c o n t r o l i s
s imply
p a s s ed b a c k to the c a l l e r .
I f the c o un t d o e s b e come - 1 ,
th i s
i nd i c a t e s
tha t
t h i s mu tex
is
c u r r e n t l y unown ed .
If
t h e wr i te- i n-prog r e s s b i t i s c l e a r , t h i s
i nd i c a t e s t h a t t h e r e a r e n o p r o c e s s e s
wa i t i ng o n th i s m u t e x ,
and
contro l
i s pa s s ed
back
to the c a l l e r .
( A wa i t i ng wr i te r wo u l d s e t
th i s b i t .
A po t en t i a l r e ad e r i s o n l y b l o c k ed i f the r e i s a c u r r e n t o r
pend i ng
wr i t e r . ) I f th e r e a r e o th e r p r o c e s s e s wa i t i ng fo r t h i s m u t ex ,
t h e y a r e a l l mad e c omputa b l e .
Th i s i s a c compl i shed
by s c a nn i ng
the
MWA I T q u e ue
fo r
all
p r o c e s s e s wh o s e
PC B $ L E FWM f i e l d m a tc h e s the
a d d r e s s o f the u n l o c ked m u t ex .
I f the p r i o r i t y o f a ny o f t h e p r o c e s s e s r emoved f r om the m u tex wa i t
s ta t e
i s g reater
than
the
p r i o r i ty o f
the
cur rent process ,
a
r e s c h e d u l i ng pa s s wi l l o c c u r tha t wi l l
select
the h i g h e s t
pr i o r i ty
p r o c e s s fo r exe c u t i o n .
As n o t ed a bove , the r e i s no d i f f e r e n c e b e twe e n
p r o c e s s e s wa i t i ng fo r r e a d a c c e s s
a nd
p r o c e s s e s wa i t i ng
fo r wr i t e
a c c e ss .
Th e c r i t e r i o n
tha t d e te rm i n e s who w i l l g e t f i r s t c h a n c e a t
o wn e r sh i p o f the m u t e x i s s o f twa r e p r i o r i ty .
24-10

SYNCHRON I ZATI ON TECHN I QUES

24 . 3. 5

Re s o u r c e Wa i t S t a te

Th e r o u t i n e s t h a t pl a c e a p r o c e s s i n to a r e so u r c e wa i t s t a t e a nd m a k e
r e so u r c e s a v a i l ab l e
sha r e
some c od e w i th t h e m u t e x
l o c k i ng and
un l oc k i ng r o u t i n e s a nd wi l l be b r i e f l y d e sc r i b ed
here .
De t a i l s o f
r e so u r c e s
t h a t a r e c o n t e s t ed
fo r
among
p r o c e s s e s c a n b e fo und i n
Ch a p t e r 8 .
Wh e n a p r o c e s s r eq u i r e s a r e s o u r c e t h a t i s unav a i l a b l e , i t
i s p l a c ed
i n to
a
r e so u r c e wa i t s t a t e , wh i c h s h a r e s the same s t a t e n umbe r a n d
wa i t que ue h e a d e r w i th t h e m u t ex wa i t s t a t e .
Th e r e so u r c e n umbe r
is
s to r ed
i n the PC B ( a t o f f s e t PC B $ L E FWM ) i n s t ead o f the m u t e x a d d r e s s
( Ta b l e 8 - 2 ) .
I n a d d i t i o n , a b i t c orr e s po nd i ng t o th i s r e so u r c e i s s e t
in
a
r e so u r c e wa i t m a s k ( fo und a t g l ob a l l o c a t i o n S C H $ G L RE SMAS K ) .
Th e s a v ed
PC
a nd
PS L a r e d e t e rm i ned
by
the
c a l l e r of r o u t i n e
S C H $ RWA I T .
Wh e n a r e so u r c e b ec ome s a v a i l a b l e , t h e a pp r o p r i a t e b i t i n the r e s o u r c e
wa i t m a s k
i s c l e a r ed .
I f t h e b i t wa s p r ev i o u s l y s e t , t h i s i nd i c a t e s
t h a t t h e r e a r e o th e r p r o c e s s e s wa i t i ng o n
th i s
r e so u r c e .
The
same
r out ine
tha t f r ee s up p r o c e s s e s wa i t i ng o n a mutex is e n t e r ed at th i s
po i n t .
O f f s e t PC B $ L E FWM n o w c o nta i n s a r e so u r c e n umbe r i n s t e a d o f a
m u t e x a d d r e s s b u t thTs i s a c o nc e p t ua l d i f f e r ence th a t i s i nv i s i b l e to
t h e cod e tha t is a c t ua l l y e x e c u t i ng .
Th e MWA I T s t a t e q u e u e i s s c a n n ed fo r a l l
p r o c e s s e s wh o s e
PC B $ L E FWM
f i e l d m a tc h e s
t h e n um b e r
o f the r ec e n t l y f r e ed r e so u r c e .
Al l s uc h
p r o c e s s e s a r e mad e c om p u ta b l e .
I f the n ew p r i o r i t y o f a n y o f
these
processes
is
l a rg e r
than
t h e p r i o r i t y o f the c u r r e n t l y e x ec u t i ng
In
any event ,
all
p r o c e s s , a r e s c h ed u l i ng i n te r r upt i s r eq u e s ted .
p r o c e s s e s wa i t i ng fo r t h e n o w a v a i l a b l e r e s o u r c e wi l l compe te fo r th a t
r e s o u r c e b a sed o n so f twa r e p r i o r i t y .

2 4-1 1

CHAPTER 2 5
DYNAM I C MEMORY AL LOCAT I ON

Th e s ys tem m a i n t a i n s th r e e s e pa r a t e a r e a s f o r
s to r ag e .
•
•

•

d yn am i c

a l loc a t i on

Th e p r o c e s s a l l o c a t i o n r eg i o n ho l d s d a t a s t r uc t u r e s tha t
o n l y r e q u i r ed by a s i ng l e p r o c e s s .

a re

Pa g ed d yn am i c memo r y c o n t a i n s d a t a s t r uc t u r e s tha t a r e
used
by s e v e r a l
p r o c e s s e s but
a re not
r e q u i r ed
to b e memo r y
r e s i de n t .
Th e nonpa g ed poo l c o n t a i n s d a t a s t r uc t u r e s and c o d e
th a t
is
by t h e
po r t i o n s
o f VM S th a t a r e n o t p r o c ed u r e b a s e d ,
used
such a s i n t e r r u p t s e r v i c e r o u t i n e s a nd d ev i c e d r i v e r s .
Th e s e
po r t i o n s o f VM S c a n o n l y u s e sys tem v i r t ua l add r e s s spa c e a nd
u s ua l l y e x e c u t e a t
e l ev a ted
I PL ,
r e qu i r i ng
nonpa g ed
po o l
spa c e r a th e r t h a n pag ed po o l s pa c e .
Th e n o n p a g e d po o l a l s o c o n ta i n s d a ta s t r uc t u r e s a nd c o d e t h a t
are
sh a r ed by s eve r a l p r o c e s s e s a nd m us t n o t be pag ed .
Th i s
r e q u i r em e n t i s us ua l l y d i c ta t ed by t h e f a c t tha t pag e
fa u l t s
a r e n o t p e rm i t t ed a b ove I P L 2 .

25 . 1

AL LOCAT I ON S TRATEGY AND IMPLEMENTAT I ON

E a c h o f the
three
po o l
a re a s h a s
the
s am e
s t r uc t u r e
so
c ommo n
a l l o c a t i o n a nd
d ea l l o c a t i o n
r o u t i n e s c a n b e u s ed .
Th e f i r s t two
l o ngwo r d s o f e ac h un used b l o c k i n o n e o f t h e po o l a r e a s a r e
used
to
d e sc r i b e the b l o c k .
As i l l u s t r a t ed in F i g u r e 2 5 - 1 , the f i r s t l o ng wo r d
i n a b l oc k c o n ta i n s t h e v i r t ua l a d d r e s s o f t h e n e x t
un us ed b l o c k
in
the
l i st .
Th e
s e c o nd
l o ngwo r d
con ta i n s
the s i ze i n b y t e s o f the
unused b l oc k .
E a c h s uc c e s s i v e un u s e d b l o c k
i s f o und
at a
h igher
v i r t ua l
add r e s s .
Th u s ,
e a ch po o l a r e a fo rms a s i ng l y l i n k e d mem o r y
o rd e r e d l i s t .

25. 1.1

Al l oc a t i o n o f Dyn am i c Memo ry

Wh e n the a l l o c a t i o n r o u t i n e is c a l l ed , i t s e a r c h e s f r om the b eg i n n i ng
o f the l i s t u n t i l i t e n c o un t e r s the f i r s t un u s e d b l o c k l a r g e e n o ug h t o
s a t i s f y the r eq ue s t .
I f the f i t
is
exac t ,
the a l l o c a t i o n
rout ine
s i mpl y a d j us t s
t h e p r ev i o us po i n t e r t o po i n t t o t h e nex t f r e e b l o c k .
I f the f i t i s n o t ex a c t , i t s ub t r a c t s t h e
a l lo c a ted
si ze
f r om
the
o r i g i na l
s i ze
of
the b l o c k , puts the n e w s i z e i n to t h e r em a i nd e r o f

2 5- 1

DYNAM I C MEMORY ALLOCATI ON

t h e b l o c k , a nd a d j u s t s the p r ev i o u s po i n t e r to po i n t to the
of
the b l o c k .
Th e
two
po ss i b l e
a l l o c a t i o n s i t ua t i o n s
i n ex a c t f i t ) a r e i l l u s t r a t ed i n F i g u r e 2 5 - 2 .

r ema i nd e r
( ex a c t a nd

Beginning of P ool Area
(Filled in When
System is Initialized)

0
Address of First
Free Blo c k
(Modified b y Allocation
and Deallocation Routines)
(Zero in Pointer
Signifies End of List)

Figure 25-1

25. 1 . 2

L a yo u t o f Unused Ar e a s i n Dyn am i c Memo r y Poo l s

Dea l l o c a t i o n o f Dynam i c Memo ry

Wh e n a b l o c k i s d e a l l o c a te d , i t m u s t be pl a c ed b a c k i n to the
l i st
in
i t s p r o pe r
p l a c e , a c co r d i ng to i t s add r e s s .
Th i s i s a c compl i shed by
f o l l o wi ng the unused a r e a po i n t e r s un t i l an add r e s s
l a rg e r
than
the
ad d r e s s o f
the b l oc k t o b e d e a l l o c a t e d
is
e nc o un t e r ed .
If the
d e a l l o c a ted b l o c k is a d j a c e n t to ano th e r un used b l o c k , the two
b l o c ks
a r e me rged i n to a s i ng l e un used a r e a .
Th i s m e r g i ng , o r agg l om e r a t i o n ,
c a n o c c u r a t the e nd o f the p r e c ed i ng unus ed b l o c k o r a t the beg i n n i ng
of
the
f o l l o wi ng
bloc k
(or
bo th ) .
Th r e e
samp l e d e a l l o c a t i o n
s i t ua t i o n s , two o f wh i c h i l l u s t r a t e m e rg i ng , a r e shown i n F i g u r e 2 5 - 3 .
B e c a u s e m e r g i ng oc c u r s a u tom a t i c a l l y a s a pa r t o f d e a l l o c a t i o n , t h e r e
i s n o n e ed f o r a ny e x t e r n a l l y t r i g g e r ed g a r b a g e c o l l ec t i o n r o u t i n e s .
Th e d e a l l o c a t i o n r o u t i n e a s s umes t h a t the wo rd a t o f f s e t 8
conta ins
the
s i ze
o f t h e b l oc k b e i ng
d e a l l o c a ted .
Al l o f t h e d yn am i c a l l y
a l l o c a t ed b l oc k s use b y VM S adhe r e t o th i s c o nv e n t i o n .
Th e t ype
code
l o c a ted
in
the b y t e
at
o f f s e t 1 0 i s a l s o u s ed by the d e a l l o c a t i o n
r o u t i n e t o d i s t i ng u i sh b e twe en s t r uc t u r e s a l l o c a ted f r om l o c a l m emo r y
( type cod e
is
po s i t i v e ) a nd s t r uc t u r es a l l o c a t ed f r om sh a r ed m emo r y
( type cod e i s n eg a t i v e ) .

2 5-2

DYNAM I C MEMORY ALLOCATI ON
Th i s s i z e wo r d , a s we l l a s t h e type c o d e s to r ed i n the
ad j a c e n t b y t e
at
o f fs e t
10,
a l l ow S DA to c o r r ec t l y
i n te r pr e t
t h e po r t i o n s o f
n o npag ed po o l t h a t a r e c u r r e n t l y
i n use .
S ev e r a l d a t a
s t r uc t u r e s
a l l o c a t ed
d u r i ng
the
i n i t i a l i za t i on
s eq uenc e
a nd me n t i o ned
in
Ch a p t e r 2 2 d o no t h a v e a 1 2 byte h ead e r th a t a l l o ws th i s s i ze a nd type
i n fo rm a t i o n
to be s to r ed .
As a r e s u l t , SDA i n t e r p r e t s a c t ua l d a t a a s
h e ad e r
i n fo rma t i o n a nd
i n co r r ec t l y
i n te r p r e t s t h e b eg i nn i ng
of
n o npag ed
po o l e
Th i s m i s i n t e r p r e t a t i o n w i l l a ppe a r a s s t r uc t u r e s o f
UN KN OWN t ype a nd u n u s u a l s i z e s .

I n t h i s ex ampl e , t h e pag ed po o l
i n i t i al l y has
the
s t a te
sho wn
Al l oc a ted b l o c k s o f m em o r y a r e i nd i c a t ed onl y a s t h e to t a l
he r e .
n um b e r o f b yt e s b e i ng u s e d , i g no r i ng e i th e r the n um b e r o r s i z e o f
t h e i nd i v i d ua l d a ta s t r uc t u r e s .

MMG $G L PAG E DYN : :
. ADDRESS

E XE $G L PAGED : :
. ADDRESS
. LONG

X + 1 76
0

; L i s t h e ad
-

1 7 6 byt e s i n u s e

X:
X+l 7 6 :

X+2 0 8 :
X+3 0 4 :

X+3 6 8 :
X +4 3 2 :

UN US E D B LOC K
Ne x t
S i ze

X+3 0 4
32

9 6 b yt e s i n u s e
UN US ED B LOC K
Ne x t
S i ze

X+4 3 2
64

6 4 b yt e s i n u s e
UNUS E D B LOC K
Ne x t
S i ze

X +4 8 0 :

2 0 8 byt e s i n u s e

X +6 8 8 :

e tc .

F i g u r e 2 5-2

X+6 8 8
48

�

J
J
J

; Ad d r e s s o f n e x t b l oc k
; S i ze o f t h i s b l oc k

; Ad d r e s s o f n e x t b l o c k
; S i ze o f t h i s b l ock

; Ad d r e s s o f n ex t b l o c k
; S i ze of th i s b l o c k

( co n t i nued o n n ex t page )

Ex ampl e s o f Al l oc a t i o n f r om Dyn am i c Memo r y

2 5-3

DYNAM I C M EM ORY A LL OC AT I ON

Fo l l owi ng a l l o c a t i o n o f a b l oc k o f 6 4 byt e s { a n e x a c t
s t r uc t u r e o f t h e pag ed po til no w l o o k s l i ke th i s .

fit) ,

the

f r om l i s t h e ad

1 7 6 byt e s i n u s e
�_ _ _ _
UN US ED B LOC K
X+l 7 6 :
Ne x t
S i ze
X:

X+2 0 8 :

2 2 4 byt e s i n use

X+4 8 0 :

2 0 8 byt e s i n u s e

X+6 8 8 :

e tc .

X+4 3 2
32

I
�

; Po i n t e r h a s c hang ed

{ 2 2 4 =9 6 +6 4 +6 4 )

UNUS E D B LOC K
Nex t
S i ze

X+4 3 2 :

__,

__
________
__
__

X+6 8 8
48

If i ns t e ad , an a l l oc a t i o n r eque s t o f 4 8 byt e s wa s m ad e , the
f i nal
s t a te
of
the po o l wo u l d look l i k e t h i s .
Th e 4 8 byt e s a r e t a k e n
f r om the f i r s t empt y b l oc k l a rg e eno ug h to ho l d i t s o the
fit
is
no t
exac t .
No t i c e tha t a l l oc a t i o n i s d o ne f r om the l ow a d d r e ss
e n d o f t h e un used b l oc k .

f r om l i s t head

1 7 6 byt e s i n us e
UN US ED B LOC K
Nex t
S i ze

X+l 76 :

X+2 0 8 :

1 4 4 byt e s i n use

X+3 6 8 :

; Po i n t e r ha s c h a ng ed

{ 1 4 4 = 9 6 +4 8 )

UNUS E D B LOC K
Nex t
S i ze

X+3 52 :

X+3 5 2
32

X+4 3 2
16

; B l oc k now b eg i n s h e r e
; S i ze i s now 1 6 byt e s

6 4 byt e s i n u s e
UN US E D B LOC K
Nex t
S i ze

X +4 3 2 :

X +4 8 0 :

2 0 8 byt e s i n use

X +6 8 8 :

e tc .

F igure 2 5 - 2

{ cont . )

X+6 8 8
48

E xamp l e s of A l l o c at ion f rom Dynamic Memory

2 5- 4

DYNAM IC MEMORY ALLOCAT ION

I n th i s ex ampl e , t h e pag ed po o l
i n i t i a l l y h a s the
s t a te
sho wn
here .
Th r e e c o n t i g uo us l og i c a l name b l o c k s a r e fo und somewh e r e i n
the m i d d l e o f the po o l .
Th r e e po s s i b l e ex ampl e s o f d e al l oc a t i o n
a r e i l l us t r a t ed b y d e l e t i ng o n e o f the t h r e e l og i c a l nam es .
f r om p r ev i o us b l o c k
o r f r om l i s th e a d
UNUS E D
Ne x t
S i ze

Y+ 6 4 :

Lo g i c a l Na m e Bl o c k
48
S i ze
Log i c a l Na m e AB C

Y+ l l 2 :

Lo g i c a l Na m e Bl o c k
S i ze
80
Log i c a l Name JKL

Y+ l 9 2 :

Lo g i c a l Na m e Bl o c k
S i ze
64
Log i c a l Na m e XY Z

Y+ 2 5 6 :

UN US E D
Ne x t
S i ze

Y+2 5 6
64

-...-

Y+? ? ?
176

-...

; Ad d r e s s o f n e x t b l o c k
; S i ze o f t h i s b l o c k

; Ad d r e s s o f n ex t b l o c k
; S i z e o f th i s b l oc k
,�

Y+4 3 2 : e t c .

I f the l og i c a l name AB C wa s d e l e t ed , t h e i n i t i a l s t r uc t u r e o f t h e
po o l
wo u l d
b e a l t e r ed s o tha t i t l o o k s l i ke th i s .
I n th i s c a se ,
the d e a l l o c a t ed b l o c k i s ad j ac en t to the h i g h add r e s s
end
o f an
unused b l o c k .
On l y the s i z e o f t he un used b l o c k i s d i f fe r en t t h a n
i t wa s b e fo r e d e a l l oc a t i o n .
f r om pr ev i o us b l o c k
o r f r om l i s t h e ad
UN US E D
Ne x t
S i ze

Y+l l 2 :

Lo g i c a l Na me Bl o c k
S i ze
80
Log i c a l Name J K L

Y+l 9 2 :

Lo g i c a l Na m e Bl o c k
S i ze
64
Log i c a l Nam e XYZ

Y+ 2 5 6 :

UN US E D
Nex t
S i ze

Y+2 5 6
112

Y+? ? ?
1 76

Y +4 3 2 : e tc .

; On l y s i ze i s a l t e r ed

-,,
( co n ti nued o n n e x t page )

F i g u r e 2 5 - 3 E x ampl es o f De a l l o c a t i o n to Dyn am i c Mem o r y
25-5

DYNAMI C MEMORY ALLOCATION

I f t h e l og i c a l name JKL wa s d e l e t ed i n s t e ad ,
the
po o l
wo u l d
be
a l te r ed
to
the
fo rm
i l l us t r a t ed h e r e .
In
th i s c a se ,
the
d e a l l o c a ted b l o c k i s n o t ad j a c en t to an
unused
b l oc k a t
e i th e r
end .
Th e pr ev i o us
po i n t e r m u s t b e
a l te r ed t o l oc a t e the n ew
unused b l o c k .
f r om p r ev i o us b l oc k
o r f r om l i s th e ad
UN US E D
Ne x t
S i ze

Y+l 1 2
64

Y +6 4 :

Lo g i c a l Nam e Bl o c k
S i ze
48
Log i c a l Nam e AB C

Y+ l l 2 :

UN US E D
Nex t
S i ze

Y+l 9 2 :

Lo g i c a l Nam e Bl o c k
S i ze
64
Lo g i c a l Name
XYZ

Y+2 5 6 :

UN US E D
Next
S i ze

Y+2 5 6
80

Y+? ? ?
176

; Po i n t e r i s a l te r ed

; No w a n un used b l o c k

Y+4 3 2 : e tc .

Fi n a l l y , i f l og i c a l name XY Z wa s d e l e t ed , t h e po o l wo u l d l o o k l i ke
th i s .
In th i s c a se , the d e a l l o c a ted b l o c k i s a d j a c e n t to the l o w
add r e s s e nd o f an u n used b l o c k .
Bo t h t h e i n i t i a l ad d r e s s o f t he
block
a nd
i ts
s i ze
a r e d i ffe r en t
than
t h e y we r e b e fo r e
dea l l oc a t i o n .
f r om p r ev i o us b l oc k
o r f r om l i s t h e ad
UNUS E D
Next
S i ze

Y+l 9 2
64

Y+6 4 :

Lo g i c a l Nam e Bl o c k
48
S i ze
Log i c a l Nam e AB C

Y+l l 2 :

Lo g i c a l Nam e B l o c k
80
S i ze
Log i c a l Name JKL

Y+l 9 2 :

UN US E D
Nex t
S i ze

Y+? ? ?
240

; Po i n te r h a s c hang ed

; S i z e ha s c ha ng ed
,

Y+4 3 2 : e tc .
F igure 2 5 -3

( cont . )

Examp l e s o f Dea l lo ca t ion to Dynamic Memory

25-6

DYNAMI C M EMORY ALLOCATI ON

25. 1 . 3

Synch r on i za t i o n

S o m e me thod i s r e q u i r ed to s yn c h r o n i z e a c c e s s t o
the po o l
areas
to
avo id
s ev e r a l
p r o c e s s e s o r ex e c u t i v e r o u t i n e s s e a r c h i ng o n e of t h e s e
l i s t s s i m u l ta neo u s l y .
Th e r e i s n o l o c k i ng m e ch a n i sm c u r r e n t l y used f o r e i t h e r
the process
a l loca t i on
r eg i o n o r
a ny o f t h e l i s t s ( s uch a s t h e p r o c e s s l og i c a l
n am e t a b l e o r the moun ted p r i v a t e v o l um e l i s t ) f o und th e r e .
Howev e r ,
t h e a l l o c a t i on
r o u t i n e e x e c u t e s i n k e r n e l mod e a t I PL 2 , e f f e c t i v e l y
b l o c k i ng any o the r m a i n l i n e o r AST c o d e
f r om e x ec u t i ng
a nd
pe r h a ps
a t tempt i ng
a
s i m u l t a neo us
a l locat ion
f r om the p r o c e s s a l l o c a t i o n
r eg i o n .
Pag ed po o l i s p r o t e c ted by a m u t ex .
Be f o r e
a b l o c k o f m emo r y
is
e i th e r a l l o c a ted o r d e a l l o c a t ed f r om the pag ed po o l , t h i s m u t e x , f o und
at g l oba l l ab e l E X E $ G L_PG DYNMTX , i s l o c k ed fo r wr i t e a c c e s s .
E l eva t ed I PL i s � s e d to c o n t � o l a l l o c a t i o n o f nonpag e d po o l .
Th e
I PL
tha t
is
used
1 s s to r ed
1n
the l ong wo r d immed i a t e l y p r ec ed i ng the
( Ta b l e 2 5 - 1 ) .
po i n t e r t o the f i r s t unused b l o c k i n the n on pag ed po o l
Th e a l l o c a t i o n r o u t i n e fo r n o n pag e d po o l r a i s e s I PL t o the v a l ue fo und
h e r e b e f o r e p r o c e ed i ng .
Wh i l e the system i s
r un n i ng ,
thi s
l o ng wo rd
us ua l l y c o nta i n s
an
11.
Th e v a l u e o f 1 1 wa s c ho s e n b e c a u s e d ev i c e
d r i v e r s r un n i ng a t f o r k l eve l f r eq ue n t l y a l l o c a te d y n am i c s to r ag e a nd
I PL 1 1
r e p r e se n t s
the h ighest
f o r k I PL c u r r en t l y u s ed i n VM S .
( An
i m p l i c a t i o n o f th i s s yn c h r o n i z a t i o n I PL v a l ue i s tha t d ev i c e d r i v e r s
m u s t n o t a l l o c a t e n o n pag ed
po o l
wh i l e exe c u t i ng i n r e s po n s e t o a
d ev i c e i n t e r r upt . )
D u r i ng i n i t i a l i za t i o n , t h e c o n t e n t s o f t h i s l o ng wo r d
are
set
to
31
b e c a use
the
r es t o f t h e c o d e i n ! N I T e x ec u t e s a t I PL 3 1 t o b l o c k a l l
i n te r r up t s .
Ch a ng i ng the c o n t e n t s o f t h i s
l o ng wo r d
avo i d s
l o we r i ng
I PL a s
a
s ide
e f f e c t o f a l l o c a t i ng s pa c e f r om no npa g ed po o l .
Th e
v a l ue i s r e se t to 1 1 a f t e r ! N I T h a s f i n i sh ed i t s a l l o c a t i o n b u t b e f o r e
!N I T pa s s e s c on t r o l to t h e s c h ed ul e r .
I P L i s a l s o a c o n s i d e r a t i o n fo r d e a l l o c a t i o n o f nonpa g ed po o l , b u t f o r
a d i f f e r e n t r e a so n .
Al t h o ug h n o n p a g e d poo l c a n be a l l o c a ted f r om fo r k
p r o c e s s e s r un n i ng a t I PL l ev e l s u p to I PL 1 1 , i t c a n n o t b e d ea l l o c a t ed
as
a r e s u l t o f an i n t e r r up t a bove I PL 7 .
Th e r e a so n f o r th i s i s t h a t
n o n pag ed po o l i s a
s ys t em-wi d e r e so u r c e
that processes m i ght be
wa i t i ng
fo r .
Th e d e a l l o c a t i o n r o u t i ne n o t i f i e s th e s c h ed u l e r t h a t a
r esource i s ava i l ab l e .
Th e
s c h ed u l e r
in
turn checks
wh e th e r
any
processes
a r e wa i t i ng
fo r
the n o n pag ed po o l r e so u r c e .
Al l o f t h i s
s c h ed u l i ng mus t t a k e p l a c e a t I PL$ S YNC H , a nd the
i n te r r up t n e s t i ng
s c heme r e q u i r e s tha t I PL n ev e r b e lowe r ed b e l o w the I PL v a l ue a t wh i c h
t h e c u r r e n t i n t e r r up t o c c u r r ed .
Th i s r ul e d i c t a t e s t h a t a l l
po o l
be
d e a l l o c a t ed a t I PL 7 o r l o we r .
Th e r e ma y be i n s ta nc e s wh e r e c o d e e x e c u t i ng above I P L 7 mus t use
some
m e c h an i sm
f o r d e a l l o c a t i ng
n o npag ed
po o l .
Ro ut i ne C OM $DRVD EALMEM
e x i s ts f o r th i s p u r po s e .
Th i s r o u t i n e t a k e s the b l o c k t h a t i s
to
be
d e a l l o c a t ed ,
t u r n s i t i n to a f o r k b l oc k ( F i g u r e 4 - 2 ) , a nd r eque s t s a n
I PL 6 f o r k p r o c e s s .
Th e c o d e t h a t exec u t e s a s t h e f o r k p r o c e s s
( th e
saved
PC i n t h e f o r k b l oc k ) s i mpl y i s s u e s a J M P to EXE $ D EANON PAG E D t o
d e a l loca te the bloc k .
Ho we v e r , b e c a u s e E XE $D EANON PAG E D i s e n t e r ed
at
I PL 6
a nd no t a t f o r k I PL , t h e syn ch r o n i zed acc e s s to t h e s c h ed u l e r ' s
d a t a b a s e i s p r e s e r v ed .
Th i s t ec h n i que i s s i m i l a r to the o n e used
by
d e v i c e d r i v e r s t h a t n e ed to i n t e r a c t wi th the sched u l e r by d e c l a r i ng
ASTs .
Th e a t te n t i o n AST m e c h a n i sm i s b r i e f l y d e sc r i b ed i n Ch a p t e r 2 4
a nd d i s c u s s ed i n g r ea t e r d e ta i l i n Ch a p t e r 5 .
25 7
-

DYNAM I C MEMORY ALLOCAT ION
Table 2 5 - 1
Global L i s theads for Each Poo l Area

Poo l Area

Global Add ress
o f Po i n t e r

S i ze

Nonpaged Poo l

EXE$G L_NONPAG�D

3 longwo rds

Sta t i c or
Dynam i c ( 1 )

Use o f These F i e l d s

l o ngwo rd
l o ng wo rd
l o ngwo rd

Synchron i za t i o n
I PL
for
nonpaged
pool a l l oc a t i on
Add ress o f nex t ( f i r s t ) free b l oc k
Dummy s i ze ( o f ze ro )
fo r
l i s thead
to speed up a l l oca t i o n rout i n e

Dynamic
Dynam i c
Sta t i c

Nonpaged Pool

MMG$GL_N PAGEDYN

l o ngwo rd

Add ress o f
poo l a r ea

nonpaged

Sta t i c

Nonpaged Pool

EXE $G L_S PLITADR

l ongwo rd

Add,ress o f bound a r y between g en e r a l
nonpaged po o l a r ea
and
looka s i d e
l i st

Sta t i c

Looka s i d e L i s t

IOC$GL_I RPFL

l ongwo rd

IOC $GL_IRPB L

l o ngwo rd

EXE $G L_PAGED

2 longwo rds

Paged Poo l

MMG$G L_PAGEDYN

l ong wo rd

Process Al l oc a t i o n
Reg i o n

CTL$G Q_ALLOCREG

2 l o ngwo rds
l o ngwo rd
l o ngwo rd

(2)

Dynam i c

Add ress o f nex t ( f i r s t ) f r e e b l o c k
Dummy s i ze ( o f ze ro )
fo r
l i sthead
to speed up a l loc a t i on rout i n e

Dynam i c
Sta t i c

Add ress o f beg inn ing o f paged
a r ea

Sta t i c

po o l

Add ress of nex t ( f i r s t ) free b l o c k
Dummy s i ze ( o f ze ro )
fo r
l i sthead
to speed up a l loca t i o n rout i n e
The r e i s
no g lobal
po i nter
l oc a tes
the
beg i n n i ng
of
process a l loc a t i o n reg ion .

Process Al loca t i on
Reg i o n

(1)

Fo rwa rd l i nk
fo r
l ooka s i d e
l i st .
IRPs a r e a l loca ted f rom
th i s
end
of the l i s t .
Backwa rd l ink f o r
l ooka s i d e
l i st .
IRPs a re d eal loca ted to
th i s
end
of the l i st .

l o ngwo rd
l o ngwo rd
Paged Poo l

beg inn i ng

Dyn am i c
Sta t i c

tha t
the

Sta t i c po inters a r e loaded at i n i t i a l i za t i o n t ime .
The
contents o f
these
l oc a t i o ns do
no t
chang e
d u r i ng
the
l i fe
of the s ys tem .
Dynam i c po in t e r s gene r a l l y change the i r conten ts each
t i me a block is a l l oc a ted f rom or d ea l l oc ated to a po o l a r ea .
The synchro n i za t i o n I PL i s changed to 3 1 b y INIT wh i l e i t i s exec ut i ng but, i s reset
rema i n s a t that val ue fo r the l i fe o f the sys tem .

25-8

and

(2)

DYNAM IC MEMORY ALLOCATI ON

25. 1 . 4

G r a n ul a r i ty o f Al l o c a t i o n

Th e a l l o c a t i o n r o u t i n e s fo r bo th pag ed a nd
nonpag ed
po o l
r o und
the
r eq ue s te d
s i ze
u p t o t h e n e x t m u l t i pl e o f 1 6 byt e s .
Th i s i s d o n e t o
i mpo s e a g r a n u l a r i ty o n bo th t h e a l l o c a ted a nd unused a r e a s .
Be c a u s e
bo th po o l a r e a s a r e i n i t i a l l y pag e a l i g ned , t h i s r o und i ng c a us e s e v e r y
s t r uc t u r e a l l o c a t ed f r om o n e o f the two sys t em-wi d e po o l a r e a s t o b e
a t l e a s t quadwo r d a l i g n ed .
Th e r e i s n o g r a n u l a r i ty i mpo s ed o n the a l l o c a t i o n s i ze fo r t h e p r o c e s s
a l loca tion
r eg 1 o n .
Howev e r ,
t h e two s t r uc t u r e s a l l o c a ted f r om t h i s
po o l b y t h e sys t e m { l og i c a l name b l o c k s fo r proc e s s l og i c a l name s
a nd
moun ted
vo l um e l i s t e n t r i e s fo r p r i v a te v o l umes ) a r e bo th a n i n t e g r a l
numbe r o f qua d wo r d s l o ng .
Th i s i m p l i e s tha t any b l o c k a l l o c a t ed
f r om
the process
a l l oc a t i on
r eg i o n i s qua d wo r d a l i g n ed .
I t a l so i m p l i e s
tha t the sma l l e s t po s s i b l e s i ze
o f a n un a l loc a t ed b l o c k
is
e ight
bytes .
Any us e r -wr i t ten p r i v i l eg ed p r og r am tha t a l l o c a t e s s pa c e f r om
the p r o c e s s a l l o c a t i o n r eg i o n
sho u l d
i ns u r e tha t
i t r eq ue s t s a n
i n teg r a l n um b e r o f q u a d wo r d s t o k e e p th i s r eg i on quadwo r d a l i g ned .

25. 2

PREALLOCATED I /0 REQUES T PACKETS

Wh i l e mo s t of the s t r uc t u r e s fo und i n the n o n pag ed po o l a r e
a l l o c a t ed
a nd d e a l l o c a ted i n f r e que n t l y , I /0 r e que s t pa c ke t s a r e c o n s t a n t l y b e i ng
a l l o c a ted a nd d e a l l o c a t ed .
To avo i d the o v e rhead o f s e a r c h i ng
for
blocks o f
f r e e m emo r y o f s u f f i c i en t s i z e
to a c c ommod a t e I R Ps , a
po r t i o n o f the n o npag ed po o l { c a l l ed the l o o k a s i d e l i s t ) i s d ed i c a t e d
to
the
a l locat i on
a nd d e a l l o c a t i o n
o f I /O r e que s t pa c k e t s a n d any
o th e r s t r uc t u r e t h a t is t h e s am e s i z e o r sma l l e r than a n I RP .
Spec i f i c a l l y , a t i n i t i a l i z a t i o n t i m e , a pe r c en tag e o f nonpaged
po o l
{ l a r g e eno ug h t o a c c ommod a t e I RPC OUNT I /0 r e que s t pa c k e t s b u t n o t m o r e
t h a n h a l f the to t a l spac e ) i s r emoved f r om t h e h i g h a d d r e s s e nd o f t h e
po o l
a nd
pa r t i t i o ned i n to a s e r i e s o f e l em e n t s 9 6 b y t e s l o ng .
Th e s e
e l emen ts a r e then e n t e r ed i n to a d o ub l y l i n ked l i s t { wi th t h e
I N S QU E
i n s t r uc t i o n )
so
tha t t h e
l oo ka s i d e l i s t i s a d o ub l y l i n k e d l i s t o f
f i x ed s i z e l i s t e l em e n t s .
A s e c ond l o o ka s i d e l i s t h a s b e e n a d d ed to VAX/VMS a s a
pa r t o f
the
Ve r s i o n 2 . 2 b i n a r y upd a t e .
Th i s a d d i t i o n i s d e sc r i b ed i n App e nd i x F .

25. 2. 1

Al l o c a t i o n f r om the Loo k a s i d e L i s t

Wh e n a r o u t i ne { s uc h a s the $ Q I O s ys tem s e rv i c e ) n e ed s a n I /0
r e qu e s t
pac ket ,
i t s impl y
i ssues a
REMQUE f r om t h e b eg i nn i ng o f t h i s l i s t
{ fo und th r o ug h g l ob a l l ab e l I OC $G L I RPF L ) .
On l y i f t h e l i s t i s
empty
{ i nd i c a ted
b y t h e V-b i t
in
the PSW s e t )
wo u l d the mo r e g en e r a l
a l l oc a t i on
r o ut i ne have
to b e c a l l ed .
Be c a u s e a l l o c a t i o n
a nd
d ea l loc a t i on
f ro m
t h e l oo ka s i d e l i s t a r e so m uc h mo r e e f f i c i e n t than
t h e g ene r a l r o u t i n e s tha t a l l o w a n y s i z e b l o c k t o b e a l l o c a t e d
or
d ea l l o c a ted ,
a
s pe c i a l c h e c k i s b u i l t i n to the g en e r a l nonpag e d po o l
a l l o c a t i o n r o u t i n e t o d e t e rm i ne wh e th e r the
r eque s t e d b l oc k c a n b e
a l l o c a t ed
f r om
t h e l oo ka s i d e l i s t .
Th e l og i c o f th i s r o ut i n e i s
a pp r o x i m a t e l y t h e fo l l owi ng .

2 5- 9

DYNAM IC MEMORY ALLOCAT ION

Th e a l l o c a t i o n s i z e i s r o unded up t o the n e x t m u l t i pl e o f 1 6 .

I f the r o un d e d s i z e i s L E QU t h e r o unded s i z e o f a n
IRP
(96
by t e s )
a nd
the
l oo k a s i d e l i s t i s no t empty , then the f j r s t
I R P i s r emoved f r om t h e l i s t a nd r e t u rned to the c a l l e r .

I f the r e qu e s t e d b l o c k i s too l a rg e , o r i f the l o o ka s i d e l i s t
is
emp t y ,
t h e n t h e g ene r a l a l l o c a t i o n r o ut i n e i s c a l l ed to
s e a r c h f o r the f i r s t f r e e b l oc k l a rg e eno ug h
to a c c ommod a t e
t h e r e qu e s t .

No te tha t b ec a u se a l l o c a t i o n i s d o ne wi th a s i ng l e i n s t r uc t i o n ,
the r e
i s n o n eed
fo r
a ny o th e r s yn c h r o n i za t i o n than t h a t p r o v i d ed b y t h e
REMQUE i n s t r uc t i o n .
Th e o th e r c onc e r n o f
t h e g e ne r a l
a l loca t i on
r o u t i ne s ,
t h e b l o c k g r a nu l a r i t y , i s a l s o i r r e l ev a n t h e r e b e c a u se a l l
b l o c ks o n the l oo k a s i d e l i s t a r e the same s i ze .

25. 2. 2

Dea l l oc a t i o n t o the Lo o k a s i d e L i s t

Wh e n the r o u t i n e t o d e a l l o c a t e a b l o c k o f n o npag ed po o l i s c a l l ed ,
it
f i r s t c h ec k s wh e th e r the b l o c k wa s a l l o c a t e d f r om t h e m a i n po r t i o n o f
the po o l o r f r om t h e l oo k a s i d e l i s t .
Th i s c he c k
is
a c compl i shed
by
c ompa r i ng the add r e s s o f the b l o c k to b e d e a l l o c a t ed wi th t h e c o n t e n t s
o f g l o b a l l o c a t i o n EXE $G L S PL I TADR , wh i c h c o n ta i n s the add r e s s o f
the
b o und a r y b e twe en
the ma i n pa r t o f t h e po o l a nd the l oo ka s i tl e l i s t .
Th i s a d d r e s s wa s f i l l ed
i n by
! N I T wh en
the
l o o ka s i d e l i s t wa s
i n i t i a l i ze d .
F i g u r e 2 5 - 4 s h o ws the r e l a t i o n sh i p o f the l o o ka s i d e l i s t
to the r e s t o f n o npag ed po o l .

<111�--· : : MMG$GL-NPAGEDYN

Rest of
Non paged
Pool

: : EXE$GL-NONPAGED

first
unused
block

•••

: : IOC$GL-IRPFL
Lookaslde
List

Figure 2 5-4

: : IOC$GL-IRPBL

P r e a l l o c a ted I /O Re que s t Pac ke t s

2 5-10

DYNAM I C MEMORY ALLOCAT I ON
I f the b l o c k wa s o r i g i n a l l y a l l o c a te d f r om the l o o ka s i d e l i s t ,
it
is
r e t u r ned the r e b y i n se r t i ng i t a t t h e e nd o f the l i s t ( a t g l o b a l l ab e l
I O C $G L I R PB L ) w i t h a n I N S QU E i n s t r uc t i o n .
No te
th a t b y a l l o c a t i ng
pa c k e ts f r om o n e e nd o f t h e l i s t a nd p ut t i ng them bac k a t the o th e r
e nd , a t r a n s a c t i o n h i s to r y a s l o ng a s t h e l i s t i t s e l f
i s m a i n ta i ned .
If
t h e b l o c k wa s o r i g i n a l l y a l l o c a t ed f r om the g en e r a l poo l a r ea , t h e
g e n e r a l d e a l l o c a t i o n r o u t i n e i s c a l l ed .
Th e d i f f e r e nc e s b e twe e n
the
l o o k a s i d e l i s t a nd
the g ene r a l
n o npag ed po o l
a r e s umma r i z e d i n
Ta b l e 2 5 - 2 .
Al thoug h the a l l o c a t i o n f r om the l oo ka s i d e l i s t r eq u i r ed no add i t i o n a l
synch r o n i z a t i o n
i n add i t i o n
to the REMQUE i n s t r uc t i o n , d e a l l oc a t i o n
m u s t b e d o ne a t I P L 7 o r be l o w f o r the r e a so n a l r e a d y s t a t ed ,
n am e l y
t h a t n o n pag ed
po o l i s a r e so u r c e who s e a v a i l a b i l i ty m u s t b e r epo r t ed
to t h e s c h ed u l e r wh o wi l l e l ev a t e
I PL
to
7.
Al l
d ea l l o c a t i o n to
n o n pag ed
po o l
i s d one
t h r o ug h t h e
r o u t i n e E XE $ DEANON PAG E D , wh i c h
sho u l d n o t b e c a l l ed a bove I P L 7 .

25. 3

U S E OF DYNAMI C M EMORY

A l mo s t a l l o f t h e d a ta s t r uc t u r e s tha t a r e d yn am i c a l l y c o n f i g u r ed
are
pl a c ed
i n e i th e r the n o npag ed o r pag ed poo l a r e a s .
On l y t h e PFN d a ta
b a s e , t h e g l o b a l a nd s ys t em pag e t ab l e s , t h e sys t em h e ad e r ,
a nd
the
i n t e r r up t s ta c k h av e s e pa r a t e v i r t u a l add r e s s spa c e a l l o c a t e d .
Mo s t
pe r - p r o c e s s d a t a s t r uc t u r e s ,
o n the o th e r
hand ,
a r e a s s i g ne d
to
d ed i c a t ed
a r ea s o f
Pl
s pa c e ,
as
d e f i ned
in t h e mod u l e S H E L L a nd
i l l us t r a ted i n F i g u r e 1 - 7 a nd l i s t ed i n Ta b l e E - 4 .
One pe r - p r o c e s s
d a ta
s t r uc t u r e ,
t h e p r o c e s s h e ad e r ,
r e s i d e s i n t h e a r e a o f s ys t em
s pa c e c a l l ed t h e b a l a nc e s l o t a r e a .

25. 3 . 1

P r o c e s s Al l o c a t i o n Reg i o n

Th e p r o c e s s a l l o c a t i o n r eg i o n i s c u r r en t l y 4 6 pag e s l o ng .
I t s s i ze i s
f i x ed b y a n a s semb l y t i m e pa r am e t e r i n mod u l e S H E LL .
I t s p r o tec t i on
i s s e t to UREW .
Th a t i s , i t c an be w r i t te n f r om e x e c u t i v e a nd
ke rnel
mod e s a nd
r ead
f r om a ny a c c e s s mod e .
On l y t h e p r o c e s s l og i c a l name
t ab l e a nd the m o un ted vo l um e l i s t fo r p r i va te vo l um e s a r e f o un d in t h e
p r o c e s s a l l oc a t i o n
r eg i o n .
Th e r e
is
e no ugh
r o om
i n the p r oc e s s
a l l o c a t i o n r eg i o n f o r p r i v i l eg ed
a pp l i c a t i o n s o f t wa r e t o a l l o c a t e
r e a s o na b l y s i ze d p r o c e s s - s p e c i f i c d a ta s t r uc t u r e s .

25. 3.2

Pag ed Dynam i c Memo r y

S e v e r a l d a ta s t r uc t u r e s a r e l o c a t ed i n the pag ed po o l a r e a .
•
•

Bo th t h e g r o up a nd
th e r e .

s ys t em

l og i c a l

name

tabl es

are

fo und

G l o b a l s e c t i o n d e sc r i p to r s , r e qu i r ed o n l y wh e n a
se c t i o n
m a pped o r unmapped , a r e a l s o l o c a ted i n pag ed po o l .

2 5-1 1

Tabl e 2 5 - 2
Compari son o f D i f f erent Poo l Are a s

Poo l Area

Al l oc a t i on
Qua n t um

Type of Li s t
( No te s 1 a nd 2 )

Synchron i za t i o n
Techn i que

Typi c a l St r uc tu r e s
Al loc a ted He r e

Nonpag ed Poo l

1 6 byt e s

Va r i a b l e s i ze
( No t e 1 )

El evated I PL

B u f f e r ed I /0 b u f f e r (GTRU 96 byt e s )
Dr i v e r Prolog ue Tab l e ( D r i v e r S t r uc tu r e )
Job In fo rma t i o n Block
Netwo r k Da ta St r uc tu r e s
Process Con t r o l Bl oc k
Pr ocess Quo ta Bl ock
Un i t Con t r o l Block ( D r iver St r uc tu r e )

Loo ka s i d e Li st

9 6 byte s

Fi x ed s i ze b l oc ks
( 9 6 byt e s )
( No te 2 )

No ne requ i red

Bu f fe r ed I /0 b u f f e r ( LE QU 96 byte s )
Channel Request B l o c k (Dr iver St r uc tu r e )
Common Event Bl o c k
Dev i c e Da ta Block ( D r i v e r St r uc tu r e )
Fi l e Co ntrol Bl ock
I /0 Request Pac k e t
Inte r r upt Di s pa tch Bl oc k ( D r iver St r uc t ur e )
Timer Queue El ement
Vo l um e Con t r o l Bl ock
Wi ndow Co ntrol Bl ock

Pag ed Pool

16 byt e s

Va r i abl e s i ze
( No t e 1 )

Mutex

Global Sec t i o n De sc r i pto r s
Known Fi l e En t r i e s
Known Fi l e Head e r s
Log i c a l Nam e Bl oc ks fo r g ro up
and system log i c a l names
Mo un ted Vo l ume L i s t En t r y fo r vol um e s
mounted /SYSTEM o r /GROUP

Process Al l oc a t i o n
Reg ion

none

Va r i abl e s i ze
( No t e 1 )

Acc e s s mode

Log i c a l Nam e Blocks fo r
process l og i c a l names
Mo un ted Vo l ume Li st En t r y fo r pr i v a te
v o l um e s ( /S HARE OR /NOSHARE )

(1)

The l oo ka s i d e l i st has e x t r emel y e f f i c i en t ( s i ng l e i n s t r uc ti o n ) a l l o c a t i o n and d ea l l oc a t i o n r o ut i nes .
Bec ause the b l o c ks a r e f i x ed s i ze , i n te rnal f r agmenta t io n ( un us ed spa c e wi thi n ind i v i d ua l bl oc k s ) can
resul t .

(2)

The g e n e r a l poo l a reas a l l o w v a r i a b l e s i zed al l oc a t i o n r eque s t s ( and conta i n v a r i a b l e s i zed empty a r ea s ) .
The a l l o c a t i o n and d eal l oc a t i o n r o ut i n e s must search a t l ea s t a po r t i o n o f the empty l i st . Ex te r nal
f r agmenta t i o n ( un used blocks equa l to the a l l oc a t i o n qua n t um ) near the beg i nn i ng o f the l i s t can r es u l t
from th i s type o f a l l o c a t i o n scheme .

DYNAM I C MEMORY ALLOCAT ION
•

Th e I N S TALL u t i l i ty a l l o c a t e s the d a ta s t r uc t u r e s r equ i r ed to
d e s c r i be k n o wn
i m a g e s f r om pag e d d yn am i c memo r y .
An y i m ag e
th a t i s i n s t a l l ed h a s a known f i l e en t r y c r e a t ed t o d e sc r i b e
it.
Some f r e que n t l y a c c e s s ed known i m ag e s a l so have
the i r
imag e
h e ad e r s p e rma n e n t l y
resident .
Th e s e d a ta
s t r uc t u r e s a r e
d e sc r i b ed i n mo r e d e ta i l i n Ch a p t e r 1 8 .

•

F i n a l l y , t h e mo u n t ed vo l ume l i s t fo r vo l um e s th a t a r e
among s eve r a l p r o c e s s e s i s f o und i n pag ed po o l .

s h a r ed

Th e s i z e o f pag ed d yn am i c m emo r y
i s d e te rm i ned
by
the
S Y S B OO T
pa r am e t e r PAG E DYN .
I t s p r o t e c t i o n i s s e t to URKW .
Th e pag e s o f pag ed
d yn a m i c m em o r y u s ed by RMS f o r the sha r ed f i l e d a ta
base
have
the i r
p r o t e c t i o n a l t e r ed
to EW ( e i th e r r e ad o r wr i t e a c c e s s f r om ex e c u t i v e
o r k e r n e l mod e ) by RM SSHARE ,
the
i m ag e
tha t e x e c u t e s a s pa r t o f
STARTU P . C OM to i n i t i a l i ze the s h a r ed f i l e d a ta b a s e .

25. 3 . 3

Nonpaged Dyn am i c Memo ry

No n pa g ed po o l s e rv e s s e v e r a l p u r po s e s .
At i n i t i a l i z a t i o n
t i me ,
data
s t r uc t u r e s wh o s e s i ze a nd c o n t e n t s d epe nd on SYSB OOT pa r am e t e r s wi l l
b e a l l o c a t ed f r om n o npag ed po o l
a nd
i n i t i a l i z ed .
Th e s e
s t r uc t u r e s
i nc l ud e
t h e P C B v e c to r
a nd s eque n c e v e c to r , t h e swa ppe r ' s I / 0 pag e
t a b l e , t h e pag e f i l e b i tm a p , mod i f i ed
pag e wr i te r
a r r a ys ,
a nd
the
ada pte r
c on t r o l b l o c k s f o r a l l e x t e r n a l a d a p t e r s l o c a ted at boo t s t r a p
t i me .
The d e t a i l ed
use of
n o npag ed
po o l
by t h e
ini tial i zat ion
r o u t i n e s i s d e s c r i b ed i n Ch a p t e r 2 2 .
A s e c ond g e ne r a l somewh a t s ta t i c u s e o f n o n pag ed po o l
i s t o conta i n
d ev i c e d r i v e r c od e a nd a s so c i a t ed d a t a s t r uc t u r e s fo r a l l d ev i c e s tha t
a r e e i th e r l o c a t ed t h r o ug h t h e a u to c o n f i g u r e pha s e o f
SYSGEN o r
a re
expl i c i t l y l o ad ed w i th a LOAD o r C ONNECT S YSGEN c ommand .
Th e d e t a i l s
o f t h e s e s t r uc t u r e s a r e d e sc r i b ed i n the VAX/VMS Gu i d e to Wr i t i ng
a
Dev i c e D r i ve r .
Th e r e a r e m a n y d a ta s t r uc t u r e s tha t a r e
a l l o c a t ed d yn am i c a l l y f r om
Ta b l e 2 5 - 2 c o n t a i n s a r e p r e s e n t a t i v e l i s t o f i t ems
no n pag ed
po o l .
c o n t a i n e d the r e . Wh i l e t h i s l i s t i s not e x h a u s t i v e , i t g i v e s a n
idea
o f t h e many s t r uc t u r e s
that
a r e c o n s t a n t l y b e i ng
a l l o c a t e d and
d e a l l o c a t ed .
Th e s i ze o f n o n pag ed d yn am i c memo r y , i nc l ud i ng the
a rea
d ev o t ed
t o the l oo k a s i d e l i s t , i s d e te rm i n ed b y t h e SYS B OO T pa r am e t e r
N PAG E DYN .
Th e f r ac t i o n o f
t h i s s pa c e
tha t
i s d ed i c a t e d
to
the
l o o ka s i d e l i s t
is
d e t e rm i n ed by t h e SYS B OOT pa r am e te r I R PC OUNT ( an d
Th e
impl i c i t l y by t h e r o und ed s i z e o f a n I RP , c u r r en t l y 9 6 b y t e s ) .
pag e
p r o tec t i o n o f b o th t h e l oo k a s i d e l i s t a nd the g en e r a l n o n pag ed
po o l a r e a is set to ERKW .

2 5- 1 3

C HAPTER 2 6
LOG I CAL NAMES

Log i c a l n am e s prov i d e a po we r f u l to o l fo r a s i ng l e pr o c e s s o r
seve r a l
processes
t o u s e a s a c ommun i c a t i o n t o o l .
Log i c a l nam e s a l s o a l l o w
t h e s ys tem a n d a pp l i c a t i o n p r og r am s to i m pl eme n t a t r a n s pa r en t fo rm o f
d ev i c e
i nd e pe nd e nc e
a nd I /O r e d i r ec t i o n .
Th i s c h a pt e r d e s c r i b e s the
i n t e r n a l impl em e n ta t i o n of l og i c a l nam e s .

26. 1

LOG ICAL NAME TABL E S

Wh e n a l og i c a l name is
c r ea t ed ,
the
l og i c a l
name
s t r i ng
a nd
i ts
e qu i v a l e n c e n ame s t r i ng a r e p u t i n to a d a ta s t r uc t u r e c a l l ed a l og i c a l
name b l oc k .
Th i s s t r uc t u r e i s then i n s e r t ed i n to o n e o f th r e e d o ub l y
l i nked
l i s ts , d e pend i ng o n wh e th e r the l og i c a l name i s b e i ng i n se r ted
i n to the p r o c e s s , g r o up , or s ys t em l og i c a l name t a b l e .
Th e p r oc e s s l og i c a l name t a b l e i s l o c a ted i n the p r o c e s s a l l o c a t i o n
r eg i o n i n P l s p a c e .
Th e g r oup a nd s ys tem l og i c a l name t a b l e s a r e bo th
al l o c a ted f r om pag e d d y n am i c memo r y .
Th e
l i s the ad s
fo r
the
th r e e
tables a re
l o c a ted
t h r o ug h t h e
l o ng wo r d
a r r a y a t g l obal l oc a t i o n
LOG $AL L OGTBL .
Ea c h o f t h e l o ngwo r d s i n
t h i s a r r a y po i n t s
to
the
q ua d word l i s t h e ad fo r one of t h e th r e e l og i c a l nam e t a b l e s .
Th e th r e e
l og i c a l n ame t ab l e s a nd t h e i r l i s t h e a d s a r e p i c t u r ed i n F i g u r e 2 6 - 1 .

26. 1 . 1

Log i c a l Name B l o c k

Th e c o n t e n t s o f a l og i c a l name
block
a r e p i c tur ed
in
Figure 2 6- 2 .
Bo th
the
l og i c a l
n am e
a nd
the
e q u i v a l e nc e n am e m a y be up to 6 3
c h a r a c t e r s i n l eng th .
B e fo r e t h e m emo r y b l oc k i s a l l o c a t e d , t h e
s i ze
r eq u i r ed f o r the s um o f the two s t r i ng s p l us the f i x ed s i z e i s r o und ed
up to the n ex t qua d wo r d so t h a t , a l tho ug h l og i c a l name b l o c k s
a re o f
v a r i ab l e
l eng th ,
t h ey a r e a l wa ys a n i n teg r a l numbe r o f qua d wo r d s i n
l e ng th .
Th e a c c e s s m o d e f i e l d i s o n l y u s e d wh e n a l og i c a l name b l o c k a ppe a r s
in
the
proc e s s
l og i c a l
n am e t a b l e .
Wh e n a proc e s s l og i c a l name i s
c r e a t ed , i t s l og i c a l name b l oc k i s i n s e r ted i n to the
process
l og i c a l
name t a b l e i n o rde r o f d ec r e a s i ng a c c e s s mo d e .
I n o the r wo r d s , a u s e r
m o d e l og i c a l name XYZ a ppe a r s i n t h e l i s t b e f o r e a
s upe r v i s o r mod e
l og i c a l
n ame XYZ .
Wh e n l og i c a l n am e XY Z i s t r a n s l a t ed , t h e us e r mod e
e q u i va l e n c e n ame i s r e t u r ned .

26-1

LOG I CAL NAMES

LOG$ALLOGTBL: :

Array of Logical Name
Table Listhead Pointers

LOG$GLGLTFL:

� ::_-__

� ====

Group
Logical
Name
Table

LOG$GLGLTBL:
Group Logical Name
Table Listhead

LOG$GLSLTFL: :

� ::::==
System
Logical
Name
Table

LOG$GLSLTBL:
System Logical Name
Table Listhead
(defined in module SYSCOMMON)

CTL$GLPLTFL: :

System Space

System Space (Paged Dynamic Memory)

P1 Space (P1 Pointer Page)

P1 Space (Process Allocation Region)

•

r-------�--��
� ====
Process
Logical
Name
Table

CTL$GLPLTBL: :
Process Logical Name
Table Llsthead
(defined In module SHELL)

F igure 2 6 - 1

Glob a l L i stheads for Log i c a l Name Tab l e s

26-2

..
� -------

LOG I CAL NAM E S

Logical Name Table Forward Link

Logical Name Table Backward Link

Table

Type

Size

Access Mode

Creator's Group

Mailbox UCB Address

Logical Name String

��

count

(up to 63 characters)

��

Equivalence Name String
.... L,.,

count
':' "'

( u p to 63 characters

Table N umber

Table

System Name Table
Group Name Table
Process Name Table

Figure 2 6 -2

Log i c a l Name B l o c k

Th e g r oup f i e l d i s o n l y r e l ev a n t wh en the l og i c a l name b l o c k a ppe a r s
i n the g r o up l og i c a l name t a b l e .
Th e r e i s o n l y o n e g r o up l og i c a l name
t ab l e fo r the e n t i r e s ys t em a nd a l l g r oup l og i c a l
name b l o c k s a r e
pl a c ed
i n to
th i s l i st .
An o pe r a t i o n tha t s e a r c h e s the g r o up l og i c a l
name t ab l e l oo k s fo r a m a tch b e twe en the g ro up cod e
in
the
l �g i c a l
name b l o c k a nd t h e g r o up n umbe r o f t h e c a l l e r o f the sys tem se r v i c e .
Th e a s s o c i a t ed m a i l bo x f i e l d i s u s ed wh en the l og i c a l name i s c r e a t ed
as a
pa r t o f ma i l bo x c r e a t i o n .
In add i t i o n , the MOUNT u t i l i ty u s e s
th i s f i e l d wh en i t c r e a t e s a l og i c a l n a m e i n c o n n e c t i o n wi th mo un t i ng
a vo l ume .

26 . 2

LOG I CAL NAME SYSTEM S ERVI C E S

Th e r e a r e
th r e e s ys t em s e rv i c e s
ava i l a b l e
fo r
l og i c a l
n am e
man i pu l a t i o n .
Log i c a l
n am e s c a n b e c r e a t ed , t r an s l a t ed , o r d e l e t ed .
Pr i v i l eg e s c o n t r o l a c c e s s to b o th the g ro up a nd
sys tem l og i c a l
n am e
tabl es .
B e fo r e d i sc u s s i ng t h e i nd i v i d u a l s e r v i c e s , s ome c h e c k s t h a t
a r e c ommo n to m o r e than o ne o f the s e rv i c e s a r e d e sc r i b ed .
2 6-3

LOG I CAL NAM E S

26 . 2 . 1

P r i v i l eg e a nd P r o tec t i o n Ch e c k s

L i k e a n y o the r s ys t em s e rv i c e s t h a t u s e a c c e s s mod e
a s a n a rg um en t ,
t h e l og i c a l
name
sys t e m s e rv i c e s c a l l the r o ut i n e EXE $ MAXACMODE t o
m a x i m i z e the m o d e p a s s ed a s a n a rg um e n t w i th t h e a c c e s s mod e
of
the
( f o und i n the p r ev i o u s m o d e f i e l d o f t h e PS L ) .
A p r o c e s s th a t
caller
wi s h e s to c r e a t e o r d e l e te a g ro up o r s ys t em l og i c a l
name m u s t h a v e
t h e a p p r o p r i a t e p r i v i l eg e , GRPNAM o r SYSNAM r e spec t i ve l y .
Seve r a l a c c e s s c h ec k s m u s t b e mad e b y the s e
s e rv i c es .
Because a l l
th r e e
s e r v i c e s p a s s a t l e a s t o ne s t r i ng d e sc r i pto r a s a n a rg um e n t
( C r e a t e Log i c a l Name h a s two ) , t h e
r ead
a c c e s s i b i l i ty o f bo th t h e
s t r i ng
d e sc r i p to r
a nd the s t r i ng mus t b e c h e c ked .
T r a n s l a te Log i c a l
Name m u s t c hec k w r i te a c c e s s i b i l i ty o f the a rg um e n t s th a t a r e used
to
pa s s i n fo rma t i o n b a c k to the c a l l e r .

26 . 2 . 2

Log i c a l Name Tab l e Mute x e s

Bo th t h e g r o up a nd s y s t e m l og i c a l
n am e
t ab l e s a r e p r o t e c ted
f r om
s imul t aneous a cc e ss
by m u t e x e s ( Ch a pt e r 2 4 ) .
The Tr a n s l a te Log i c a l
Name sys tem s e rv i c e l o c k s t h e t ab l e tha t i s c u r r e n t l y b e i ng
sea rched
fo r
r e ad
access .
Th i s d o e s n o t p r ev e n t o th e r p r o c e s s e s f r om r e ad i ng
Log i c a l
( t r a n s l a t i ng ) l og i c a l nam e s i n the s am e l og i c a l name
tabl e .
name c r e a t i o n a nd d e l e t i o n b o th r e q u i r e tha t the t a b l e b e i ng mod i f i ed
b e l o c k ed f o r wr i t e a c c e s s .
Th i s p r ev e n t s o th e r p r o c e s s e s
f r om e v e n
r e a d i ng the l oc k e d tab l e wh i l e the t a b l e i s b e i ng mod i f i ed .

26 . 2 . 3

Log i c a l Name C r e a t i on

Af t e r the p r e l i m i n a r y c h e c k s h a v e b e e n ma d e , t h e C r e a t e
Log i c a l
Name
s ys t em s e rv i c e a l l o c a t e s a b l o c k of m emo r y fo r the l og i c a l name b l o c k .
Th e b l o c k i s a l l o c a t e d f r om t h e p r o c e s s a l l o c a t i o n r eg i o n f o r
proc e s s
l og i c a l
n am e s
a nd
f r om p a g e d d yn am i c memo ry fo r g ro up a nd sys t em
l o g i c a l n am e s .
Th e s i z e o f t h e b l o c k i s the s um o f the l eng ths o f t h e
l og i c a l
a nd e qu i v a l e n c e s t r i ng s p l u s the s i ze o f the c o n s t a n t pa r t o f
a l og i c a l name b l o c k .
B e fo r e t h e a l l o c a t i o n r o u t i n e
is
c a l l ed ,
the
s i ze i s r o und e d to a n i n teg r a l n um b e r o f qua d wo r d s .
Af t e r a l l the pa r am e t e r s h a v e b e e n p l a c ed i n to the a l l o c a ted b l o c k , i t
is
i n s e r t ed
i n to
the
a pp r o p r i a t e t ab l e , u s ua l l y a t the end .
I f an
i d en t i c a l l og i c a l n a m e a l r e a d y e x i s t s , the o l d n am e i s
f i r s t d e l e t ed
a nd
the
s ta t u s o f
S S $ S U PE R S EDE i s r e t ur ned to the c a l l e r .
I f the
l og i c a l n ame is b e i ng p u t- i n to the p r o c e s s l og i c a l name t a b l e a nd
an
i d en t i c a l n a m e i s fo und wi th a d i f f e r e n t a c c e s s mo d e , the l og i c a l name
b l oc k i s i n s e r t e d i n to the t ab l e i n s uc h a wa y as to pl a c e the h i g h e s t
( l e a s t pr i v i l eg ed ) a c c e s s m o d e c l o s e s t to t h e b eg i nn i ng o f the tab l e .

26. 2. 4

Log i c a l Name De l e t i o n

Af t e r the u s ua l s e t o f p r i v i l eg e a nd p r o tec t i o n c h e c k s a r e pe r f o rmed ,
t h e De l e te
Log i c a l Nam e s ys tem s e rv i c e chec k s wh e th e r th i s o pe r a t i o n
If all
sys t e m
i s d e l e t i ng a s i ng l e l og i c a l name o r a g r oup o f n am e s .
n am e s a r e
to b e d e l e t ed ,
they a r e .
I f a l l g r o up n am e s a r e to b e
d e l e te d , t ho s e l og i c a l n am e s tha t h a v e the
s ame g r o up c o d e
as the
caller
a r e d e l e t ed .
If
all
p r o c e s s n am e s a r e to b e d e l e te d , a l l
2 6- 4

LOG I CAL NAMES

l og i c a l n ame s f o r t h e spec i f i ed a c c e s s mode a nd
a c c e s s m o d e s a r e d e l e t ed .

all

l ess

p r i v i l eg ed

Th e d e l e t i o n o f a s i ng l e l og i c a l n ame r e q u i r e s
tha t
the
a pp r o p r i a t e
t ab l e b e
s e a r ch ed .
I f the l og i c a l n ame i s i n the p r o c e s s t a b l e , a n
a c c e s s m o d e c h e c k i s pe r f o rm ed .
Th e a c t ua l d e l e t i o n o pe r a t i o n
fi rst
r emoves
the l og i c a l name b l o c k f r om the l i s t , c l e a r s the UC B $ L LOGADR
f i e l d i n a n a s s o c i a t ed UCB i f t h e L OG $ L MBXUCB in the l og i c a l f Te l d i s
nonze r o ,
a nd
f i na l l y d e a l l o c a t e s t h e bl o c k t o the a pp r o p r i a t e m emo r y
po o l .

26. 2. 5

Log i c a l Name T r a n s l a t i o n

Log i c a l n ame t r an s l a t i o n h a s s ev e r a l
s pe c i a l
opt i o n s t h a t
i t mus t
c h ec k
fo r
i n a d d i t i o n to the usua l p r i v i l eg e a nd p r o t e c t i o n c h e c k s .
I f the l og i c a l name b eg i n s w i th the und e r s c o r e cha r a c t e r ( ) , t h e n the
e qu i v a l e n c e
s t r i ng that i s r e t u r ned i s s i mpl y the l og i c a l -name s t r i ng
wi th the und e r s c o r e r emoved .
I n ad d i t i o n , t h e c a l l e r c a n spec i f y t h a t
the s e a r c h o n l y o c c u r i n some o f t h e t a b l e s .
As s um i ng t h a t none o f the t ab l e s h a s b e en e l i m i n a t ed ,
the
se r v i c e
s e a r c h e s f o r a m a t c h i n f i r s t t h e p r o c e s s t a b l e , then the g r o up t a b l e ,
a nd f i n a l l y t h e s ys t em t a b l e .
Th e r e i s n o a c c e s s mod e c h e c k m a d e
fo r
the
proc ess
tab l e .
I f a p r o c e s s h a s the same l og i c a l name w i th mo r e
t h a n o n e a c c e s s mod e , t h e n a m e a s so c i a t ed w i th t h e
l e a s t pr i v i l eg ed
( l a r g e s t ) a c c e s s m o d e i s r e t u r n ed .
Th e s e a r c h of the g r o up t a b l e d o e s
r e q u i r e t h a t t h e g r o up n umbe r s m a tc h .
As e a c h l o g i c a l name b l o c k i s p r o c e s s ed , a c h ec k i s f i r s t mad e to
see
if
the
s t r i ng l eng t h s o f the l og i c a l n a m e b e i ng s e a r c hed fo r a nd the
l og i c a l n am e i n the b l oc k a r e i d e n t i c a l .
If they a r e no t , th i s b l o c k
i s pa s s ed ove r a nd t h e s e a r c h c o n t i n ue s wi tho ut the c o s t l y ove r h e a d o f
a CMPC i n s t r uc t i o n t h a t i s b o und t o f a i l .

2 6- 5

CHAPTER 2 7
M I SCE LLANEOUS SYSTEM SERVI CES

Th i s c h a p t e r i nc l ud e s b r i e f d i s c u s s i o n s of
the
s ys tem se rv i c es
not
in
the p r ev i o u s c h a p t e r s .
Th e s e s e r v i c e s d o n o t g e n e r a l l y
m e n t i o n ed
_ma k e i n t e n s i v e u s e o f the i n t e r n a l s t r uc t u r e s and m e c h a n i sm s o f
VM S .
De t a i l ed d i sc u s s i o n s o f t h e a rg um e n t s , r e t u r n s t a tus cod e s , r e q u i r ed
p r o c e s s p r i v i l eg e s , a nd sys tem s e rv i c e o p t i o n s c a n
be
fo und
in
the
VAX/VMS S y s t em Se r v i c e s Re f e r enc e Ma n ua l .

27 . 1

COMMUN ICAT I ON W I TH SYS TEM PROC ES S E S

Some of t h e o pe r a t i o n s o f t e n a s s o c i a t ed wi th an o pe r a t i ng
sys tem
are
pe r f o rmed
i n VAX/VM S b y i nd e pend e n t n o rm a l pro c e s s e s , r a the r th a n by
code in t h e l i n ked sys tem i m ag e .
Ex am p l e s
of th i s
type
of
s y s t em
a c t i v i ty i n c l ud e
•

g a th e r i ng o f a c c o un t i n g i n fo rm a t i o n abo u t ut i l i z a t i o n o f
s ys tem r e s o u r c e s ,

•

manag i ng pr i n t and b a t c h j o b s a nd queue s ,

•

c ommun i c a t i ng w i th o n e o r mo r e sys t em o pe r a to r s , a nd

•

r e po r t i ng d ev i c e e r r o r s .

Fo u r s ys tem s e rv i c e s a r e d e f i ned i n the mod u l e SYS SNDM SG
c ommun i c a t i o n s wi t h t h e a pp r o p r i a t e sys tem p r o c e s s e s .

27 . 1 . 1

Ac c o un t i ng Ma n ag e r

the

prov i d e

( Jo b Co n t ro l l e r )

The a c c o un t i ng m a n ag e r i s a
pa r t o f
the
j ob contro l l er
( pr o c ess
J O B C ONTRO L
r un n i ng
imag e J O B C T L . E XE ) .
It
is
r e s po n s i b l e
fo r
r e co rd i ng the u t i l i z a t i o n o f s y s tem r e so u r c e s i n the a c c o un t i ng f i l e .
Re que s t s
to
the
a c c o un t i ng m a n ag e r
are
sent
th r o ug h
the
j ob
c o n t r o l l e r ' s ma i l box by t h e $ S NDACC s ys tem s e rv i c e .
E x p l i c i t $ SNDACC
r e que s t s c a n b e i s s ued by u s e r s t o r eque s t a c t i o n s no rma l l y a v a i l a b l e
t h r o ug h the S E T ACC OUNT I NG c omma nd .

2 7-1

M I S C E L LANEOUS SYSTEM S E RVI C E S
Th e $ SNDACC s ys tem s e r v i c e r o u t i ne pe r fo rms t h e fo l l o w i ng ope r a t i o ns .
1.

Th e me s s a g e t yp e i s d e f i n ed a s
MSG $ SNDACC a n d
th e
m a i l bo x
i s d e f i ne d
a s t h e j ob c o nt r o l l e r ' s m a i l bo x
d e f i n ed i n mo d u l e DEVI C EDAT)

t a rg e t
( MBAl : ,

•

Th e r e que s t i s c h e c k e d fo r po s s i b l e e r r o r s s uc h a s t o o
l a rg e
a m e s s ag e , i n s u f f i c i e n t p r i v i l eg e s , o r a c c e s s v i o l a t i o n s .

Th e me s s a g e b u f fe t i s a l l o c a t e d o n t h e c u r r e n t s t a c k
e x e c u t i v e mod e s t a c k ) , a nd the b u f f e r i s f i l l ed wi th
•
•

27 . 1 . 2

( th e

the me s s ag e type ,
the r ep l y m a i l bo x c h a nn e l
a rg um e n t ) ,

( i f spec i f i ed

opt i onal

•

the p r i v i l eg e m a s k , U IC , u s e r n am e , a n d a c c o un t n am e ,

•

the p r o c e s s b a s e p r i o r i t y ( Ch a pt e r 8 ) , a n d

•

the u s e r -d e f i ned m e s s a g e t ex t ( a r e qu i r ed a rg um e n t ) .

Th e me s s ag e i s wr i t te n
k e r ne l m od e .

Symb i on t Ma nag e r

the

m a i l bo x

a f te r

c h a ng i ng

( Jo b Co n t r o l l e r )

Th e s ym b i o n t manag e r i s a l s o pa r t o f t h e j ob c o n t r o l l e r p r o c e s s .
It
is
r e s po n s i b l e
fo r t r a n s a c t i o n s t o and f r om the q u e ue f i l e i nc l ud i ng
t h e c r e a t i o n and d i s pa t c h i ng o f b a tc h a nd p r i n t que u e s a nd j o b s .
Re que s t s to the sym b i o n t m a n ag e r a r e
sent
to
the
j ob contro l l e r ' s
ma i l bo x b y the $ SNDSMB s y s tem s e rv i c e .
Expl i c i t $ SNDSMB r e que s t s c a n
b e i s s ued by use r s to r e que s t a c t i o n s n o rm a l l y ava i l a b l e
th r o ug h
the
f o l l o w i ng DC L c omma nd s :
S ET DEVI C E/ S POOLED
S E T QUEUE
S TART/QUEUE
S T O P/ABORT
S T O P/QUEUE
S T O P/REQUEUE
S UBM I T

AS S IGN/MERGE
AS S IGN/QUE UE
DEAS S I GN/Q U E U E
DE LETE/ENTRY
DE LETE/QU E UE
I N I T I ALI Z E/QUEUE
PR INT

Th e $ S NDSMB sys tem s e rv i c e
pe r fo rms e x a c t l y t h e s am e o pe r a t i o n s
( c ommon c od e )
as
the
$ SNDAC C s ys tem s e rv i c e ( a s d e s c r i b ed i n the
p r ev i o u s s e c t i o n ) , e x c e p t tha t the m e s s ag e type
is
d e f i ne d
to b e
MSG $ S NDSMB .

27-2

M I SC E LLANEOUS SYS TEM S E RVI CES

27 . 1 . 3

Ope r a to r Commun i c a t i on s

Ope r a to r c ommun i c a t i o n s a r e h a nd l ed b y a s y s t em p r o c e s s ( p r o c e s s O PC OM
r un n i ng i m a g e O PC OM . EXE ) .
O PC OM h a s the r e s po n s i b i l i t i e s o f
•

d e f i n i ng wh i c h t e rm i n a l s a r e o pe r a to r t e rm i n a l s a n d fo r
wh a t
cl ass
of
a c t i v i ty
( s uch a s d i s k o r t a pe o pe r a t i o n s ) th e s e
t e rm i n a l s w i l l r e c e i v e m e s s a g e s ,

•

r e p l y i ng t o o r c a n c e l i ng a u s e r r eque s t to a n ope r a to r , a nd

•

m a n a g i ng t h e o pe r a to r l og f i l e .

Re qu e s t s to O PC OM a r e s e n t t h r o ugh O PC OM ' s m a i l bo x b y t h e
$ S NDO PR
s y s tem s e rv i c e .
E x p l i c i t $ S NDOPR r e que s t s c a n be i s s ued by u s e r s t o
r eq ue s t a c t i o n s
n o rma l l y a va i l a b l e
th r o ugh
th e D C L us e r c ommand
REQUEST a nd the ope r a to r c omma nd RE PLY .
Wi t h e x c e p t i o n s o f a d i f f e r e n t m a i l bo x ( MBA2 : , d e f i ned i n
the mod u l e
DEVI C EDAT )
a nd a d i f f e r e n t m e s sag e t ype ( MSG $ O PRQS T ) , $ S NDO PR s h a r e s
c ommo n c o d e wi t h $ SNDACC a nd $ S NDSMB ( d e s c r i b ed i n S e c t i o n 2 7 . 1 . 1 ) .

E r r o r Log g e r

27 . 1 . 4

A s d e sc r i b ed i n Ch a pt e r 7 , t h e e r r o r
three pi eces .
•

•

l og g i ng

s ub s ys t em

cons i s ts

Th e ke r n e l i t s e l f c o n t a i n s r o u t i n e s tha t m a i n t a i n a
set o f
e r r o r m e s s ag e b u f f e r s .
Th e s e
r o u t i n e s a r e c a l l ed b y t h e
k e r n e l a nd d ev i c e d r i v e r s i n o rd e r th a t e r r o r m e s s a g e s c a n b e
wr i t t e n to some a v a i l a b l e spa c e i n o n e o f t h e s e b u f f e r s .
Th e e r r o r f o rma t t i ng p r o c e s s ( pr o c e s s ERRFMT r un n i ng
i mag e
E RRFMT . EXE )
i s a wa k e n ed wh e n
it
i s n ec e s s a r y t o c o py t h e
f o rma t t ed c o n t e n t s o f t h e s e
e r r o r message b u f fe r s
to
the
e r r o r l og f i l e f o r s u b s e q ue n t a n a l ys i s .
Th e SYE p r o g r am r e a d s the e r r o r m e s sa g e s
in
the e r r o r
l og
f i l e a nd p r od uc e s a n e r r o r l og r e po r t , b a s e d on the c o n t e n t s
o f t h e e r r o r l og f i l e a nd t h e o p t i o n s s e l e c ted wh e n S Y E wa s
r un .

No rma l i n t e r a c t i o n s wi th t h e e r r o r
l og g i ng
rout ines
i n the
k e rne l
occur
i n d ev i c e d r i v e r s b y i s s u i ng d ev i c e e r r o r o r d ev i c e t i m e o u t
r e que s t s .
Us e r s c a n a l s o s e nd m e s sag e s
to the e r ro r
l og g e r
( pu t
me s s ag e s i n to o ne o f the e r r o r m e s sag e b u f f e r s ) fo r l a t e r t r a n sm i s s i o n
to t h e e r r o r l og f i l e .
b y i s s u i ng
a
$ S NDERR s ys tem s e rv i c e
( th i s
r e qu 1 r e s
the
B UGC HK p r i v i l eg e ) .
Unl i ke
the $ SNDAC C , $ SNDSMB , a n d
$ S NDOPR s ys tem s e rv i c e s , t h e $ S NDERR s ys t em s e r v i c e
•
•

e x e c u t e s i n k e r n e l mo d e

( r a th e r t h a n exec u t i v e mod e ) , a nd

a l l o c a t e s a n e r r o r m e ssag e
m a i l bo x me s s ag e )
•

27-3

b u f fe r

( r a th e r

th a n

s e nd i ng

M I S C E LLANEOUS SYS TEM SERVI CES

Th e $ SNDERR s ys tem s e r v i c e r o u t i n e pe r fo rms these a c t i o n s .
1.

Th e r e qu e s t i s c h e c ked fo r a c c e s s a nd p r i v i l eg e v i o l a t i o n s .

A b u f f e r i s a l l o c a t ed f r om t h e e r r o r l og g e r ' s m e s s ag e po o l .

Th e m e s s a g e b u f f e r
is
f i l l ed
wi t h
the
m e s s ag e
t ype
( EM B $ C S S ) , the m e s s a g e s i z e , and t h e m e s sag e t e x t .
An e r r o r
l og s equen c e n um b e r a nd t h e c u r r e n t t i me a r e a l s o a pa r t o f
e v e r y e r r o r m e s s ag e .

Th e bu f f e r i s r e l e a s ed to
the e r r o r
l ogg i ng
s ub s e qu e n t o u t p u t to t h e e r r o r l og f i l e .

r o ut i nes

Ch a pte r 7 co n ta i n s a d i sc u s s i o n o f the e r r o r l og r o u t i n e s a nd a
d e sc r i p t i o n o f the E RRFMT p r o c e s s .

27 . 2

fo r
bri ef

SYSTEM MESSAG E F I LE SERVI C ES

VAX/VM S Ve r s i o n 2 . 0 p r o v i d e s t h r e e l ev e l s o f m e s s a g e f i l e c a pa b i l i t y .
Th e c r e a t i o n a nd d e c l a r a t i o n o f i m ag e- s p e c i f i c a nd p r o c e s s - pe rma n e n t
m e s s ag e f i l e s a r e d i s c u s sed i n t h e VAX- 1 1 U t i l i t i e s Re f e r en c e Ma n u a l
Th e sys tem m es s a g e
La nguag e Us e r ' s G u i d e .
a nd
t h e VAX/VMS C omma nd
f i l e ( S YSMSG . EXE ) i s ma pped i n to s ys tem a d d r e s s s pa c e a s a
p ag e a b l e
s ec t i o n .
Th i s
i n i t i a l i za t i on
i s pe r fo rmed b y SYS I N I T d u r i ng sys t em
i n i t i a l i z a t i o n ( Ch a pt e r 2 2 ) .
Two sys t em s e rv i c e s p r o v i d e t h e a b i l i t i e s to
•
•

s e a r c h f o r a m e s s ag e t e x t c o r r e s p o nd i ng
c o d e ( $G E TM SG ) , a nd

g i ven

s t a t us

wr i t e o n e o r mo r e m e s sag e t e x t s to S Y S $ 0UT PUT ( $ PUTM SG ) .

A th i rd p r o c ed u r e ( E XE $ E XCMSG ) d o e s n o t u s e t h e va r i o us m e s sag e
f i l es
but
is
a l so o n e o f t h e m e s s ag e o u t pu t p r o c ed u r e s th a t c a n b e i nv o k ed
E XE $ E XCMSG i s c a l l ed by L I B $S IGNAL a nd
a s p a r t o f c o nd i t i o n h a nd l i ng .
E XC E PT I ON to wr i te t h e c o n t e n t s o f t h e g e ne r a l r eg i s t e r s to SYS $0UTPUT
i f a c o nd i t i o n is n o t h a nd l ed in any o the r wa y .

27 . 2 . 1

G e t Me s sag e Sys t em S e r v i c e

Th e Ge t Me s s ag e sys t em s e rv i c e ( $G E TM SG ) e x e c u t e s i n e x e c u t i v e mod e .
It
s e a r c h e s e a ch o f t h e th r e e l ev e l s o f me s s ag e f i l e s fo r a ma t c h to
t h e s t a t us c od e p r o v i d ed a s a n a rg um e n t .

27-4

MISCELLANEOUS SYSTEM SERVI CES

27 . 2 . 1 . 1
F i nd i ng the Me s sag e Fi l e s - Th e f i r s t s tep of the
r e t r i ev a l
of
a
m e s sa g e
i nv o l v e s d e t e rm i n i ng wh i ch type s o f m e s s ag e f i l es h av e
b e e n d e f i ned .

I f an i mag e mes sag e sec t i o n h a s b e e n
d e f i ned ,
then
it
has
been
i nco rpo r a t ed
as
a
p r og ram reg i o n i mag e s e c t i o n .
Th e
c o n t r o l r eg i o n l o c a t i o n CTL$G L G E TM SG po i n ts to th e pe r- i mag e
mes sag e
s ec t i o n
vecto r
i n the c o n t r o l reg i on ( Append i x E ) .
Th e v e c t o r i s i n i t i a l i z ed wi th a va l ue
c o r re spond i ng
to
an
RSB
i n s t r uc t i o n .
If
an
im ag e
h a s d e f i ned
a ny message
s ec t i o n s , t h e n th i s v e c to r i s ch ang ed by the imag e
ac t i va to r
to the c od e s e que n c e
JSB
JSB

@ t < P O - l o c a t i on 1 >
@ # < P O - l o c a t i on 2 >

JSB
RSB

@ # <PO-loca t i on n>
_

Each P O l o c a t i o n i s in a d i f f e r e n t me s sag e sec t i o n ( up
to
a
max imum o f 4 2 d i s t i nc t me s s a g e s e c t i o ns i n a g i ve n imag e ) and
c o n ta i n s a
JSB

( RS )

i n s t r uc t i o n .
Th i s i nvo ke s the v e c t o r s e a r c h r o u t i ne f o r
the
i mage
me s s ag e
s e c t i on d e s c r i b ed b e l ow b e c a u se R S wa s l o ad ed
wi th the r o u t i n e ' s s t a r t i ng add r e s s .

I f no ma tch i s f o und i n the f i r s t sec t i o n , the f i r s t
mes sag e
d i spa t c h e r
i ssues
an RSB b a c k to the Pl space v e c to r , wh i ch
i s s ue s a J S B to the s econd m e s sag e d i spa tc h e r and so o n .

I f no i mag e me s s a g e s ec t i on h a s been
d e f i n ed
or
the
i nput
s t a tus v a l ue c o u l d not be fo und in a ny i mag e m e s s a g e s ec t i o n ,
then a t e s t i s mad e fo r a p r o c e s s- pe rma n e n t m e s sag e
s ec t i o n
( e s t a b l i sh e d
by
the SET MESSAG E c omma nd ) .
Th e a b s e n c e o f a
p r o c e s s-pe rma n e n t m e s s a g e s e c t i o n i s i nd i c a ted by a
zero
in
the
control
r eg i o n
l oc a t i on ,
CTL$G L PPMSG .
If
a
p r o c e s s-pe rma n e n t
m e s sag e
sect ion
has
been
d e f i ned ,
CTL$G L PPMSG
po i n t s
to
a
control
reg i o n
ad d r e s s
in
a
p r o c e s s-pe rma n e n t s e c t i o n vecto r ( Append i x E ) .
Th e
l oc a t i o n
c o n ta i ns t h e e q u i v a l e n t o f a
JSB

( RS )

i ns t r uc t i o n .
Th i s
i n s t r uc t i on
i nv o k e s
the
v e c to r
search
rout i ne
fo r
the
p r o c e s s -pe rm a n e n t mes sag e
sec t i o n
in
a
s i m i l a r f a sh i o n a s fo r the i mag e sec t i on c a s e abov e .

I f a p r o c e s s-pe rma n e n t m e s s ag e s e c t i o n h a s no t
b e en
d e f i ned
or
the
i n put
s ta t u s
v a l ue
could
no t
be
fo und
in
the
p r o c e s s-pe rman e n t me s s a g e se c t i o n , then
the
sys t em me s s ag e
file
is
s e a r c h ed .
Th e
l o ca t i o n EXE $G L SYSMSG po i n ts to a
sys tem l o c a t i on i n a sys tem
sec t i on
v e c to r .
Th e
l oc a t i o n
co nta i n s t h e e qu i v a l ent o f a
JSB

(RS)

i n s t r uc t i o n .
Th i s
i n s t r uc t i on
i nv o k e s
r o u t i ne f o r the s ys t em m e s s a g e f i l e .

2 7- 5

the

v e c to r

sea rch

M I SC E LLANEOUS SYS TEM SERVI C ES
I f no m e s sag e f i l e i s fo und o r
none o f
t h e d e f i ne d m e s s a g e
f i l es
c o n ta i n s
the
s p e c i f i ed s t a t u s c o d e , then t h e s t a tus c o d e i s i n s e r t ed
i n to
a d e f a u l t m e s s ag e
tex t
a nd
the
s e rv i c e r e t u r n s w i t h t h e
S S $_MSGNOTFND c od e .

2 7 . 2 . 1 . 2 Search i ng a Lo ca ted Me ssag e Sec t i on - Wh e n a m e s s ag e s e c t i o n
is
l o ca t e d ,
t h e s ta r t i ng
ad d r e s s a nd l eng t h o f t h e m e s s a g e s ec t i o n
i nd ex a re c a l c u l a ted .
A b i na ry s e a r c h o f t h e m e s s a g e s e c t i o n i nd e x i s
t h e n pe r fo rmed t o d e t e rm i n e i f t h e spec i f i ed s t a t us c o d e i s i nc l ud ed .
I f no m e s sag e i s d e f i n ed wi th i n the s ec t i o n fo r the
spec i f i ed
s t a t us
If
code ,
a c h ec k i s m a d e in o th e r m e s s ag e s e c t i o n s o f t h e s a m e type .
is
then c o n t r o l
n o f u r the r m e s s a g e s ec t i o n s o f t h e s am e type e x i s t ,
r e t u r n ed to t h e $ G E TM SG m a i n l i ne th r o ug h a s e r i e s o f RSB i n s t r uc t i o n s .
sys t em
$G E TMSG t h e n c h e c k s t h e n e x t type o f m e s s a g e s e c t i o n un t i l the
me s s ag e f i l e h a s b e en s e a r ch ed .
I f a m e s s ag e c o r r e spo nd i ng to t h e s pe c i f i ed
s t a t us c o d e
is
l o c a t ed
w i t h i n a m e s s ag e s e c t i o n , t h e n t h e i n fo rma t i o n se l e c t e d b y t h e $ G E TM SG
F LAGS a rg um e n t i s c o p i ed i n to t h e
u s e r -d e f i ned b u f f e r .
Th e s e a r c h
r o u t i ne r e t u r n s c o n t r o l ( w i th a n R E T i n s t r uc t i o n ) t o the c a l l e r o f t h e
$G E TMSG s y s t em s e rv i c e .

27 . 2 . 2

Put Me s sag e Sys t em S e r v i c e

Th e $ PU TMSG s ys t em s e rv i c e p r ov i d e s t h e a b i l i ty to wr i te o ne o r mo r e
e r r o r m e s s ag e s t o SYS $ E RROR ( a nd SYS $0UT PUT i f i t i s d i f fe r e n t f r o m
SYS $ E RROR ) .
I t e x e c u tes i n the a c c e s s m o d e o f i t s c a l l e r ,
a nd
us e s
$G E TMSG t o r e t r i ev e t h e a s s o c i a t ed t ex t f o r a pa r t i c u l a r s t a t u s c o d e .
Th r e e a rg um e n ts a r e p r ov i d ed to $ P U TMSG :
1.

a m e s sag e a rg um e n t v e c to r d e sc r i b i ng the m e s sag e s i n t e rms o f
s t a tus codes ,
m e s s ag e
f ield
s e l e c t i o n f l ag b i t s , a nd $ FAO
a rg um e n t s ( S e c t i o n 2 7 . 4 . 2 ) ,

a n o p t i o n a l a c t i o n r o u t i n e to be c a l l ed
m e s s a g e t ex t s , a nd

a n o p t i o n a l f a c i l i ty n am e to be
m e s s ag e wr i t ten .

b e fo r e

a s so c i a ted

wi th

wr i t i ng
the

the
fi rst

Th e c o n s t r uc t i o n o f the m e s sag e a rg um e n t v e c to r i s . d i sc u s s e d
i n the
VAX/VMS Sys t em
S e r v i c e s Re f e r en c e Ma n ua l .
O th e r u s e s o f the $ PUTM SG
s y s t em s e rv i c e a r e d e sc r i bed i n t h e VAX- 1 1 Run- T i me L i b r a r y Re f e r en c e
Ma n ua l .
Ea c h a rg um e n t o f the m e s sag e a rg um e n t v e c to r i s p r o c e s s ed a s fo l l o ws .
1.

Th e f a c i l i ty c o d e o f
the
r e que s t
i s d e t e r m i ned
to
be
a
s y s t em ,
RM S ,
or
s ta nd a rd
f a c i l i ty c o d e .
Sys t em a nd RMS
f a c i l i ty c o d e s d o n o t use a s s o c i a t ed $ FAO a rg um e n t s
in
the
m e s s ag e a rg um e n t v e c to r .
S t a nd a rd
f a c i l i ty c o d e s r equ i r e
s uc h $ FAO a rg um e n t s .

$G E TMSG i s c a l l ed w i th t h e s ta t u s c o d e a nd
f i eld
s e l ec t i o n s
( ba s ed upo n t h e se l ec t i o n b i t s a nd $ FAO a rg umen t s ) .

2 7- 6

M I SC E LLANEOUS SYSTEM SERV I C E S
3.

$ FAOL i s c a l l ed to a s semb l e a l l t h e po r t i o n s o f
the message
to
b e wr i t t e n ( s uppl i ed f a c i l i t y c o d e , opt i o n a l l y s pe c i f i ed
d e l i m i t e r s , o u t p u t f r om $ G E TM SG ) .

Th e u s e r ' s a c t i o n r o u t i n e i s c a l l ed , i f o ne wa s s pe c i f i ed .

I f the a c t i o n r o u t i n e r e t u r n s a n e r r o r s t a t us , the m e s s a g e i s
not
wr i t t e n .
O th e rwi s e , t h e fo rma t ted m e s sag e i s wr i t t e n to
SYS $ E RROR b y a n RM S $ P UT r e que s t .
I f SYS $ 0UTPUT i s d i f f e r e n t
f r om SYS $ E RROR , t h e n t h e f o rm a t t ed m e s s ag e i s a l so wr i t t e n to
SYS $ 0 UTPUT .

Wh en a l l o f t h e a rg um e n t s i n the m e s sa g e a rg um e n t vec to r have
p r o c e s s ed , t h e $ P UTMSG s y s t em se rv i c e r e t u r n s t o i t s c a l l e r .

27 . 2 . 3

been

P r o c ed u r e E XE $ E XC M SG

Th i s p r o c ed u r e i s used i n t e r n a l l y by the c a t c h a l l
c o nd i t i o n
h a nd l e r
a nd
L I B $ S IGNAL t o
r e po r t a c o n d i t i o n
tha t h a s no t b e e n p r o pe r l y
h a nd l ed b y a n y c o nd i t i o n h a nd l e r s f a r th e r u p the c a l l s t a c k .
Th e
two
i n p u t a rg um e n t s
to th i s p r o c ed u r e a r e the add r e s s o f a n ASC I Z s t r i ng
and the add r e s s o f the a rg um e n t l i s t pa s s ed to the c o nd i t i o n h a n d l e r s
( Ch a p t e r 2 ) .
Th e p r o c ed u r e wr i tes a fo rm a t t ed d ump o f the g e ne r a l r eg i s te r s and the
s ignal
a r r a y , a s we l l as the c a l l e r ' s m e s s a g e tex t to SYS $ 0 UTPUT ( a nd
to SYS $ ERROR i f d i f f e r e n t f r om SYS $ 0UTPUT ) .
Th i s m e s sag e a pp e a r s
fo r
all
f a ta l
e r r o r s t h a t o c c u r i n imag e s t h a t we r e l i n k e d wi tho u t the
t r a c eb a c k h a nd l e r .
Al th o ug h th i s p r o c ed u r e h a s a n a s so c i a t ed en t r y po i n t
in
the s ys t em
s e rv i c e vec t o r
a rea ,
i t c a nno t
b e c onven i e n t l y c a l l ed
f rom any
l a ng uag e s ex c e p t VAX- 1 1 MAC RO a n d VAX- 1 1 B L I S S - 3 2 .
Th i s
restr i c tion
i s i m p o s ed b y t h e s pe c i f i c a t i o n o f the s e c o nd a rg um e n t , wh i c h r eq u i r e s
a c c e s s t o the g en e r a l r eg i s t e r AP , a c a pa b i l i ty d e n i ed
to most h igh
l ev e l l a ng uag e s .

27 . 3

PROC E S S I N FORMAT I O N

( $G E TJ P I )

Th e $ G E TJ P I s ys t em s e rv i c e p r o v i d e s
s e l ec t ed
i n fo rma t i o n a bo u t a
s pec i f i ed p r o c e ss ( wh i ch m a y no t n e c e s s a r i l y be the p r o c e s s r e que s t i ng
t h e $ G ETJ P I s e r v i c e )
Th e a rg umen t s to $ G E TJ P I i n c l ud e
•

•
•
•
•

the e v e n t f l ag num b e r t o s e t wh e n t h e s e r v i c e h a s c ompl e ted ,
the p r o c e s s I D o f the p r o c e s s f r om wh i c h i n fo rma t i o n i s to b e
c o l l ec ted ,
the p r o c e s s name o f the t a rg e t p r o c e s s ,
the ad d r e s s o f a n i tem l i s t t h a t i nc l ud e s ( fo r e a c h r e que s t e d
i t em )
wh i c h
i t em o f i n fo rma t i o n i s to b e r e t u r ned , t h e s i z e
a nd a d d r e s s o f the b uf f e r to
hold
the
i n fo rma t i o n ,
a nd
a
l o c a t i o n to i n s e r t the s i z e o f t h e r e t u r n ed i n f o rm a t i o n ,

2 7-7

M I S C E LLANEOUS SYSTEM SERVI C E S
•
•

an
I /0 s t a t u s b l o c k
i n fo rma t i o n , a nd

( I OS B )

r ec e i ve

f inal

s t atus

t h e e n t r y po i n t a nd
pa r am e t e r
fo r
a n AS T r o u t i ne
i nv o ked wh e n t h e sys tem s e rv i c e h a s c om p l e ted .

A d e ta i l ed d i sc us s i o n o f t h e fo rma t a nd s pe c i f i c a t i o n o f the i t em l i s t
i s d e sc r i b ed i n t h e VAX/VMS Sys t em Se r v i c e s Re f e r e n c e Ma n ua l .

27 . 3 . 1

Ope r a t i on o f the $G ETJ P I Sys t em Se rv i c e

Th e $G E TJ P I s ys t em s e rv i c e , e x e c u t i ng i n
f o l l o w i ng o pe r a t i o n s .

ke r n e l

mod e ,

pe r fo rms

Th e I OS B , i f s pe c i f i ed , a nd t h e eve n t f l ag a r e c l e a r ed .

Each
i t em
in
c o nd i t i o n s .
•
•

the

l i st

c h ec k e d

Th e b u f f e r d e sc r i pto r mus t b e
wr i t a b l e .

fo r

r ea d a b l e

the
a nd

the

f o l l o w i ng
th e

buffer

Th e r e q u e s ted i t em mus t b e a r ec og n i zed o n e .

I f these cond i t i o n s a r e m e t , t h e n t h e r e q ues t e d i t em c a n b e
r e t r i ev e d .
Al l
d a ta a b o u t t h e c u r r e n t p r o c e s s a nd PCB a nd
J I B d a ta
a b o u t a no the r
process c an
be
o b t a i ned wi tho u t
e n t e r i ng
the
context of
the
t a rg e t p r o c e s s .
Al l
s uc h
i n fo rma t i o n i s m o v e d to t h e u s e r -d e f i ned b u f f e r s f o r e a c h
c o r r e s po nd i ng i tem .

I f no i n f o rm a t i o n r ema i n s to b e g a th e r ed ,
s e r v i c e r e t u r n s to the c a l l e r a f t e r

then

•

s e t t i ng t h e s pec i f i ed eve n t f l ag ,

•

d e c l a r i ng the r e que s ted AST i f spec i f i ed , a nd

•

wr i t i ng t o t h e I OS B i f s uppl i ed .

th e

s y s t em

I f the r e i s r ema i n i ng i n fo rm a t i o n t h a t c o u l d no t b e r e t r i eved
b y s t e p 3 a bo v e , then the i n fo rma t i o n
•
•

i s a bo u t a p r o c e s s o th e r t h a n t h e c a l l e r , a nd
i s s to r ed i n e i th e r the c o n t r o l
h e ad e r .

r eg i o n

the

process

Th i s i n fo rma t i o n m u s t b e r e t r i ev ed
b y e x e c u t i ng
i n the
c o n tex t
of
the t a r g e t p r o c e s s .
To d o th i s a spec i a l ke r n e l
mo d e AST ( Ch a p t e r 5 ) i s queued to the
t a rg e t p r o c e s s .
Two
d a t a s t r uc t u r e s a r e a l l o c a t ed f r om n o npag ed d yn am i c memo r y .
•

•

An e x t end e d AST c o n t r o l b l o c k i s b u i l t t o c o n t a i n the
no r m a l
f i e l d s p l u s d e sc r i p to r s of a l l of the un sa t i s f i ed
r e q u e s t s t h a t mus t b e r e t r i ev ed
b y e x e c u t i ng
i n the
c o n t e x t o f the o th e r p r o c e s s .
A b u f f e r i s c r e a t ed to r e c e i v e t h e r e t r i eved
fo r
t r a n sm i s s i o n
to the r eq ue s t i ng p r o c e s s
to t h e J I B $ L_BYTCNT q uo t a )
•

2 7 -8

i n fo rma t i o n
( a nd cha rg ed

M I S C E LLANEOUS SYST EM S E RVI CES

Th e AC B i s then q u e ue d to the t a rg e t p r o c e s s un l e s s
i t no
l o ng e r
ex i sts ,
or
i t i s i n t h e s u s pe nd ed ( S US P ) , s us pend e d
o u tswa pped ( S U S PO ) , o r t h e m i sc e l l a neous wa i t ( MWA I T )
states
( Ch a p t e r 8 ) .
If any of
these
c o nd i t i o n s ho l d s , t h e t wo
b l o c k s o f n o n pag e d po o l a r e d e a l l o c a t ed and a n e r r o r
return
i s pa s s ed b a c k to t h e c a l l e r .
Th e s ta t u s o f S S $ S US PENDED i s
r e t u r n e d f o r the t h r e e l o ng wa i t s t a te s o f S US P ,
S U S PO ,
a nd
MWA I T .
I f t h e p r o c e s s h a s b e en d e l e t e d o r i s i n t h e p r o c e s s
o f b e i ng d e l e t ed ( h a s t h e d e l e t e pend i ng b i t s e t i n
the PCB
s t a t us
l o ngwo r d ) ,
a s t a tus o f S S $ NON E XPR i s pa s s ed b a c k t o
the c a l l e r .
No t e t h a t
the c om p l et i o n m e c ha n i sm s a r e
all
t r i g g e r ed
i f one o f these e r ro r s occur s .
Tha t i s , the e v e n t
f l ag i s s e t , a use r - r e qu e s ted AST i s que ued , a nd a n
IOSB
is
wr i t t e n w i t h the f a i l u r e s t a t u s .
On e f i n a l p i e c e o f i n f o rm a t i o n i s ad d ed to the ex t e nd ed AST
control
block .
Th e r e
is
an
image
c o un t e r s t o r ed i n t h e
p r o c e s s h e a d e r ( a t o f f s e t PHD $ L I MGCNT) th a t
is
i nc r e m e n t e d
each t ime
th a t a n
i mag e
is
r und own
( Ch a p t e r 1 8 ) .
Th i s
c o un t e r p r e v e n t s o n e i m a g e f r om r eq ue s t i ng i n fo rma t i o n a b o u t
a no the r
process
a nd
t h e n ex i t i ng ,
o n l y to h a v e
a n AST
d e l i v e r ed o r an I OS B wr i t t e n l a t e r o n to
the
r e que s t e d
PO
a d d r e s s e s i n a no th e r i m ag e .
6.

27. 3 . 2

F i n a l l y , t h e sys tem s e r v i c e r e t u r n s to
t h e c a l l e r wh o
can
e i th e r wa i t f o r
the i n fo rm a t i o n t o b e r e t u r n ed o r c o n t i n u e
p r o c e s s i ng .

$G E TJ P I Spe c i a l Ke r n e l ASTs

I f some o f the i n fo r ma t i o n abo u t the t a rg e t ( o the r
than
the c a l l e r )
resides
i n the p r o c e s s h e ad e r o r i n the P l s pa c e o f the t a r g e t , t h e n
c od e mus t e x e c u t e i n tha t t a rg e t ' s c o n tex t to ac c e s s the
i n fo rma t i o n .
Onc e the i n fo rma t i o n h a s b e en r e t r i ev e d , i t mus t b e pa s s ed b a c k t o t h e
c a l l e r so tha t i t c a n b e wr i t t e n to t h e c a l l e r ' s ad d r e s s s p a c e .
VMS
u s e s s pe c i a l ke r n e l ASTs f o r bo th p i e c e s o f th i s t r i p .
A s umma r y o f t h e o pe r a t i o n s pe r fo rmed by t h e s e spec i a l k e r n e l ASTs
l i s t ed h e r e .

Wh e n t h e spec i a l k e r n e l mod e AST m a ke s
the
t a rg e t p r o c e s s
c ompu t a b l e ,
t h e r eque s ted i n fo rma t i o n i s d e t e rm i n ed f r om t h e
e x t e n d e d AC B a nd s t o r ed i n t h e a s so c i a t ed s y s t em b u f fe r .
Th e
c omp l e t i o n o f
the
s pe c i a l
k e r ne l mod e AST r o u t i ne o c c u r s
a f te r t h e e x t e nded ACB i s r e f o rm a t ted t o d e l i v e r
a
s e c o nd
s pe c i a l k e r ne l mo d e AST , t h i s t i m e to the r e que s t i ng p r o c e s s .

Th e s e c o nd k e r n e l mo d e AST r o u t i n e e x e c u t e s i n the c o n t e x t o f
the
r e ques t i ng p r o c e s s .
If the image c o un t e r s do n o t a g r e e ,
then the r e q ue s t i ng image h a s g o ne awa y .
I n th i s
c a se ,
the
t wo
b l o c k s o f n o npag ed
po o l
a r e d e a l l o c a t ed , t h e p r o c e s s
BYTCNT q uo t a i s r e s to r ed , a nd the s pe c i a l k e r ne l A S T s i mpl y
r e turns .
I f t h e i m ag e c o un t e r i n the p r o c e s s h e a d e r
ag r e es w i t h
i m ag e
c o un t e r
in
t h e e x t e nd ed A S T c o n t r o l
b l oc k ,
r e t r i ev ed d a t a i s moved
f r om
th e sys t em bu f f e r
i nto
v a r i o u s u s e r -d e f i ned b u f f e r s .

27-9

the
the
the

M I S C E L LANEOUS SYS TEM SERVI C E S

Th e sys t em b u f f e r is d e a l l o c a t e d , t h e ev e n t f l ag is s e t ,
a nd
the
I O SB
is
wr i t t e n
if
i t wa s s pe c i f i e d .
No te t h a t the
a s yn c h r o n o u s n a t u r e of th i s a sp e c t
of
the
sys tem
serv i c e
r e qu i r e s
th a t
the
I O SB
be
p r o bed
ag a i n fo r
wr i te
a c c e s s i b i l i ty .
Th i s c h e c k i n s u r e s tha t the o r i g i na l
cal ler
of
$G E TJ P I h a s no t a l t e r ed the p r o t e c t i o n o f the I O SB i n the
i n t e r v a l b e twe e n the c a l l to $G E TJ P I and the d e l i v e r y o f
the
r e t u r n s p e c i a l k e r n e l AST .

I f a n AST wa s r e que s t ed then t h e AST c o n t r o l
block
i s u s ed
fo r
t h e t h i r d t i me to q u e u e an AST to the r eq u e s t i ng p r o c e s s
i n t h e a c c e s s mo d e o f t h e c a l l e r .
Othe r w i se ,
t h e ACB
is
d e a l l o c a t e d t o n o npag ed m emo r y .

27 . 3 . 3

W i l d Ca r d S uppo r t i n $ G E TJ P I

Th e $ G E TJ P I a l so p r ov i d e s so- c a l l ed w i l d c a rd s uppo r t , th e a b i l i ty t o
o bta i n
i n fo rma t i o n
about a l l
p r o c e s s e s i n t h e s ys tem .
A wi ld c ard
r e que s t i s i nd i c a t e d b y p a s s i ng a n eg a t i v e p r o c e s s I D t o
t h e $ G E TJ P I
s ys t em s e rv i c e .
Th e i n t e r n a l r o u t i ne i n $G E TJ P I t h a t d e te rm i n e s t h e
i d e n t i t y o f the t a r g e t p r o c e s s r e c og n i z e s a
wi l d c a rd
r eque s t a n d
pa sse s
i n fo rm a t i o n
b a c k to the c a l l e r a bo u t the f i r s t p r o c e s s i n t h e
PCB v e c to r a f te r the s wa ppe r a nd t h e n u l l p r o c e s s ( Ch a p t e r 1 7 ) .
I n a d d i t i o n , t h e p r o c e s s i nd e x f i e l d o f t h e c a l l e r ' s P I D a r g um e n t
is
a l t e r ed
to c o n ta i n t h e p r o c e s s i nd ex o f t h e t a rg e t p r o c e s s .
Wh e n the
c a l l e r of $ G E TJ P I i s s u e s a s e c ond c a l l , the n eg a t i v e
sequence
n umbe r
( i n t h e h i g h o r d e r wo r d o f t h e p r o c e s s I D ) i nd i c a t e s t h a t a w i l d c a r d
o pe r a t i o n i s i n p r og r e s s b u t a po s i t i v e p r o c e s s i nd ex i nd i c a te s wh e r e
in
the
PCB v e c to r
t h e s e a r c h sho u l d c o n t i n ue .
No t e t h a t the u s e r
p r og r am w i l l no t wo r k c o r r e c t l y i f the c a l l e r a l t e r s the v a l ue o f
the
p r o c e s s ID a r g ume n t b e twe en c a l l s t o $G E TJ P I .
Th e use r c o n t i n u e s to i s s ue c a l l s to $G E TJ P I u n t i l a s t a t us c o d e o f
S S $ N OMOREPR OC
is
r e t u r n ed ,
i nd i c a t i ng
that
the PC B vec to r s e a r c h
r o ut i n e h a s r ea c h ed t h e e n d o f t h e PC B v e c to r .
An ex ampl e o f t h e w i l d
c a rd
use of
the
$G E TJ P I s ys t em s e rv i c e i s c o n t a i n ed i n the VAX/VMS
Sys tem Se r v i c e s Re f e r e n c e Ma n ua l .

27 . 4

FORMATTING S UPPORT

fo r
T h e f i n a l g r o up o f s ys t em s e rv i c e s p r ov i d e s c o nve r s i o n s uppo r t
I/O o f ASC I I c h a r a c t e r
t i m e - r e l a t ed
r eq u e s t s
a nd
fo r
fo rm a t ted
s t r i ng s .

2 7-1 0

M I S C E LLANEOUS SYS TEM S ERVI CES
27 . 4 . 1

Time Co nve r s i on S e rv i c e s

Th e
t i m e c o nv e r s i o n s ys tem
s e rv i c e s a r e d e f i ne d
in
t h e mod u l e
SYS CVRT IM .
Th e $ N UMTIM s ys t em s e rv i c e e x e c u t e s i n e x e c u t i ve mod e a nd
c o nv e r t s a b i na r y quad wo r d t i m e v a l u e i n s y s tem t i m e f o rm a t ( d e sc r i b e d
i n Ch a pt e r 1 0 ) i n to s e v e n n um e r i c a l wo r d l e ng th f i e l d s :
y e a r s s i nc e 0
m o n th o f ye a r
d a y o f m o n th
ho ur o f d a y
m i n u t e o f ho u r
s ec o nd o f m i n ut e
h und r ed t h s o f s e c ond
A po s i t i v e t i m e a rg umen t i s c o nv e r t e d i n to the c o r r e s pond i ng
a bso l u t e
s y s tem
t ime .
A z e r o - v a l u ed t i m e a rg um e n t r eque s t s t h e c o nv e r s i o n o f
t h e c u r r e n t s ys tem t i me .
A n eg a t i v e t i m e a rg um e n t i s i n t e r p r e ted a s a
t i m e i n t e rv a l f r om the c u r r e n t s ys tem t i m e .
Th e $ A S C T IM s y s t em s e rv i c e e x e c u t e s i n the a c c e s s mod e o f
the c a l l e r
a nd
c o nve r t s
a
sys tem
t i m e fo rma t quadwo r d i n to a n ASC I I c h a r a c t e r
s t r i ng .
Th e i n put b i na r y t i m e a rg um e n t i s
pa ssed
t o $ N UMT I M .
Th e
s ev e n
f i elds
r e t u r n ed
f r om
$ N UM T I M a r e then c o nve r t e d i n to ASC I I
c h a r a c t e r f i e l d s wi th t h e s e l ec t i o n d e t e rm i ned by wh e th e r
the
i np u t
t i m e wa s a n a b s o l u t e
o r d e l t a t i m e a nd wh e th e r c o n v e r s i o n f l ag wa s
s e t , i nd i c a t i ng conve r s i o n o f d a y a nd t i m e o r on l y t h e t i me po r t i o n .
Th e
$ FAO s ys tem
s e rv i ce
( d e sc r i b ed i n the n e x t s e c t i o n ) i s u s ed to
c o n c a t e n a t e a nd fo rm a t the
s t r i ng
compo n e n t s b e fo r e
r e t u r n i ng
the
s t r i ng to the c a l l e r .
Th e $ B INTIM s ys t em s e r v i c e e x e c u t e s i n the a c c e s s mod e o f
the c a l l e r
a nd
c o nv e r t s
a n ASC I I t i me s t r i ng i n to a quadwo r d a b s o l u t e o r d e l t a
t ime .
I f the i np u t s t r i ng
e x p r e s s e s a n a b so l u t e t i m e ,
then
the
cur rent
s ys t em
t i me
is
c o nv e r t ed
by
$NUMTIM t o s u pp l y a n y f i e l d s
om i t t ed i n ASC I I s t r i ng .
E a c h ASC I I
f i eld
is
t h e n c o nv e r ted
to
n um e r i c a l v a l u e s a nd s to r ed i n th e s e v e n wo rd f i e l d s u s e d b y $NUMTIM .
Th e s e v e n wo r d f i e l d s a r e th e n comb i ned i n to a b i n a r y q ua d wo rd v a l ue .
Th e
r e s u l t i ng
va l u e
i s n eg a ted i f a d e l t a t i me wa s s p e c i f i ed i n t h e
AS C I I s t r i ng .

27 . 4 . 2

Fo rma t ted ASC I I Ou tput

Th e $ FA O a nd $ FAOL s ys tem s e r v i c e s p r ov i d e fo rma t t i ng
a nd
c o nv e r s i o n
fac i l i t i e s
f r om b i na r y a nd ASC I I i n p u t pa r ame t e r s t o a s i ng l e ASC I I
o u t p u t s t r i ng .
Th e t wo s y s tem s e rv i c e s e x e c u t e i n t h e a c c e s s m o d e o f
the c a l l e r
a nd use c ommo n c od e .
Th e o n l y d i f f e r e n c e b e t we e n them i s
wh e th e r the pa r am e t e r s a r e pa s s ed a s a l i s t o f a rg um e n t s ( $ FAO ) o r a s
t h e ad d r e s s o f t h e
f i r s t pa r am e t e r ( $ FAOL ) .
Th e c o n t r o l s t r i ng i s
pa r s ed c h a r a c t e r b y c h a r a c t e r .
I n fo rm a t i o n th a t i s n o t p r ec e d ed b y
the control
cha r a c te r ,
! ,
i s c op i ed i n to t h e o u tput s t r i ng wi tho u t
f u r th e r a c t i o n .
Wh en a
control
c h a r a c t e r a nd o pe r a t i o n c o d e a r e
e n c o un t e r ed
in the control
s t r i ng , t h e n t h e a pp r o p r i a t e c o nve r s i o n
r o u t i n e i s e x e c u t ed
to
process
zero ,
one ,
or
two
of
the
i np u t
pa r am e t e r s
to
the
s ys t em s e rv i c e .
Wh e n t h e co n t r o l s t r i ng h a s b e e n
c om p l e t e l y pa r s ed , the s e r v i c e r e t u r n s to the c a l l e r w i t h a
no r m a l
s tatus
code .
If
the o u tput
s t r i ng
l eng t h
i s ex c e ed ed , a b u f f e r
ove r f l o w e r ro r s t a t us i s r e t u r ned .
Th e d e sc r i pt i o n o f t h e $ FAO s ys t em
s e rv i c e
in
t h e VAX/VMS Sys tem Se r v i c e s Re f e r en c e Ma n ua l con t a i n s
d e t a i l s a b o u t how t o s pe c 1 fy S FAO r e que s t s .

2 7- 1 1

APPEND I C E S

Wh e n t h o u h a s t d o n e , t h o u h a s t n o t d o n e ,
Fo r I h a v e mo r e .
A Hymn e to G o d t h e Fa th e r
Jo h n Do n n e

On t h e t a b l e i n the l i g h t o f a b i g l amp w i t h
a
r ed
s h ad e
h e s p r e a d a p i e c e o f pa r c hm e n t
r a t h e r l i k e a ma p .

" Th e r e
i s o n e po i n t
tha t
yo u
haven ' t
n o t i c ed , "
s a i d t h e w i za rd , " a nd th a t i s t h e
s e c r e t ent r anc e .
Yo u s e e t h a t
r un e
on
the
We s t s i d e ,
a nd t h e h a nd po i n t i ng to i t f r om
t h e o th e r r un e s ? "
Th e Ho bb i t , o r Th e r e a nd Ba c k Ag a i n
J . R . R . To l k i e n

APPEND I X A
U S E OF L I S T ING AND MAP F I LES

Th i s m a n ua l
has
p r e s e n t ed
a d e t a i l ed
o v e r v i ew of
the
VAX/VM S
e x ec ut i ve .
Howe v e r ,
the
u l t i m a t e a u th o r i t y on how the e x e c u t i v e o r
a n y o th e r compo n e n t o f t h e s ys t em wo r k s i s t h e so u r c e
cod e
fo r
tha t
c ompo n e n t .
Th i s a pp e nd i x shows how t h e l i s t i ng and m a p f i l e s p r o d uc ed
b y t h e l a ng uag e p r o c e s s o r s and t h e VAX- 1 1
L i nk e r can be
used
wi th
o the r
too l s
to
und e r s t a nd
how a
g i ven c ompo n e n t wo r k s o r wh y t h e
s ys t em i s ma l f un c t i o n i ng .

A. l

H I NTS IN READ I NG THE EXEC UT I VE L I S T I NG S

Th e so u r c e s fo r the VAX/VM S o pe r a t i ng
s ys t em
are
av a i l ab l e
in
t wo
Th e
sourc e
l i s t i ng k i t i n c l ud e s m i c r o f i c h e l i s t i ng s fo r a l l
fo rms .
b und l ed c ompo n e n t s e x c e p t c e r t a i n c ompa t i b i l i t y mod e u t i l i t i e s .
Th i s
kit
is
i nc l ud ed
w i th e a c h VAX/VM S s y s t em .
So u r c e f i l e s and comm a nd
p r o c ed u r e s a r e a l s o d i s t r i b u t ed on m a g n e t i c
t a pe
fo r
c u s t ome r s
who
p u r c h a s e a so u r c e l i c e n s e .
Th e i d e a s e x p r e s s ed i n t h i s a pp e nd i x a r e g e a r e d
towa rd
r e ad i ng
the
mod u l e s
tha t m a k e
up t h e e x e c u t i v e a nd the i n i t i a l i z a t i o n ro u t i n e s ,
a l l o f wh i c h a r e wr i t t e n i n VAX- 1 1 MACRO .

A. l . l

St r uc t u r e o f a MACRO L i s t i ng F i l e

Th e mod u l e s t h a t m a k e u p t h e e x e c u t i v e a r e a l l wr i t t e n f r om a c ommo n
t em p l a t e
th a t i n c l ud e s a mo d u l e h e a d e r d e s c r i b i ng e a c h r o u t i n e i n t h e
mod u l e .
Th e g e ne r a l
fo rm a t
of
a
VAX- 1 1 MACRO l i s t i ng
file
is
Fe a t u r e s
d e s c r i b ed
in
the
VAX- 1 1 MAC RO La ng u ag e Re f e r e nc e Ma n ua l .
t h a t a r e pec u l i a r t o l i s t i ng s i nc l ud ed i n the s o u r c e l i s t i ng
kit
are
d e s c r i b ed h e r e .

A. l . l . l
$ x y z D E F Ma c r o s - One o f t h e f i r s t pa r t s o f e a c h mod u l e
tha t
r e qu i res
e x pl a n a t i o n
is
the
i nv o c a t i o n o f a s e r i e s o f ma c r o s t h a t
d e f i n e symbo l i c o f f s e t s i n to d a t a s t r uc t u r e s r e f e r e nc ed i n t h e mod u l e .
Th e g e n e r a l f o rm o f t h e s e mac r o s i s
$ xy z D E F
wh e r e x y z r e p r e s e n t s t h e d a t a s t r uc t u r e wh o s e
o f fsets a re
r e q u i r ed .
Fo r
e x am p l e , a mod u l e t h a t d e a l s w i th t h e I / 0 s ubsys t em w i l l p r o ba b l y
i nvo k e t h e $ I R PDEF a nd $ UC BDEF mac r o s t o d e f i n e o f f s e t s
i n to
I /0
A- 1

U S E OF L I S T I NG AND MAP F I L E S
R e qu e s t
Pa c k e t s a nd Un i t Co n t r o l B l o c k s .
S o m e o f the $ xy z DEF ma c r o s
s uc h a s $ S S DE F , $ I ODEF , a nd $ PRDEF d e f i n e
constants
( s ys t em s e r v i c e
s ta tus
returns ,
I/0
f unc t i on c od e s
a nd mod i f i e r s ,
a nd p r o c e s s o r
r eg i s t e r d e f i n i t i o n s ) r a th e r than o f f s e t s i n to d a ta s t r uc tu r e s .
S t r uc t u r e s a nd c o n s t a n t s t h a t a r e used i n s ys tem s e r v i c e s h a v e
th e i r
$ x y z D E F ma c r o s d e f i n ed i n S TARL E T . M LB , t he d e fa u l t m a c r o l i b r a r y t h a t
is
a u tom a t i c a l l y s e a r c h ed
by the a s s embl e r .
Mo s t o f
t h e d a ta
s t r uc t u r e s
used
by
the
e x e c u t i v e h av e
the i r m a c r o d e f i n i t i o n s
c o n t a i n ed i n a spec i a l m a c r o l i b r a r y c a l l ed L I B . ML B .
Th e d i s t i nc t i o n
b e t we e n
the s e
two m a c r o l i b r a r i e s i s d i s c us s e d i n Append i x D , wh e r e
m a n y o f the d a t a s t r uc t u r e s d e sc r i b ed i n t h i s m a n u a l a re l i s t ed .
On e wa y to o b t a i n t h e s ymbo l d e f i n i t i o n s r e s u l t i ng f r om t h e s e ma c r o s
i s t o l oo k a t t h e s ymbo l t a b l e tha t a ppe a r s a t the end o f t h e a s semb l y
l i s t i ng .
Howe ve r , t h e i n fo rma t i o n p r e s e n t e d t h e r e i s o f t e n i nc ompl e t e
or
no t
i n a s u i t a b l e f o rm .
An a l t e r n a te r e p r e s e n t a t i o n o f t h e d a t a
c a n be o b t a i n e d f r om t h e f o l l o wi ng s e q u e n c e o f DC L command s .
$ CREATE x y z D E F . MAR
$ xy zD E F G LO BAL
. END
Az

$ MAC RO x y z DEF+SYS $ L I BRARY : L I B . MLB/ L I BRARY
$ L I NK/NOEXE/MAP/ F U L L x y zDEF
$ PRINT x y z DE F . MAP
Th i s c omma nd s e q u e n c e p r o d uc e s a s i ng l e o b j e c t mod u l e
t h a t c on t a i n s
all
t h e s ymbo l s p r od u c e d by the $ xy zD E F m a c r o .
Th e a r g um e n t G LOBAL
ma k e s a l l the s ymbo l s p r od uc ed by the m a c r o g l o ba l .
( Th i s
a rg um e n t
must
a ppe a r
1n
uppe r
c a se
to b e p ro p e r l y
i n te r p r e t e d
by the
a s s em b l e r ' s m a c r o p r o c e s so r . } Th a t i s , t h e s ym bo l names a nd v a l ue s a r e
pa s s ed
f r om
the a ssembl e r
to
the
l i nker
so
tha t t h e y a ppe a r o n
wh a t e v e r m a p t h e l i n k e r p r o d uc e s .
Th e f u l l ma p c o n t a i n s t wo l i st s o f
s ymbo l
d e f i n i t i ons ,
one
i n a l ph a b e t i c a l
o rd e r
a nd o n e i n n ume r i c
o rd e r .

A . l . l . 2 The Ro u t i n e Body - I n g e n e r a l , t h e r o u t i n e s tha t m a ke
e x ec u t i v e we r e c o d ed a c c o rd i ng to s t r i c t s ta nd a rd s tha t r e s u l t
th a t i s e a s i l y m a i n ta i n e d .
One s i d e e f f e c t o f t h e s e s ta n d a r d s
the code
is
e a sy t o
read
fo r som e o n e a t t empt i ng to l e a r n
wo r k s .
S e v e r a l i t ems a b o u t t h e i n s t r uc t i o n s t h a t a ppe a r i n
a r e wo r th d e s c r i b i ng .
•

the

up t h e
i n cod e
i s th a t
how VM S

mod u l e

bod y

Da t a s t r uc t u r e r e f e r e nc e s a r e u s ua l l y mad e us i ng d i s p l a c em e n t
mod e a d d r e s s i ng .
Fo r e x ampl e , t h e i n s t r uc t i o n
MOVL

R 3 , UC B $ L_I R P ( R 5 )

l o a d s the c o n t e n t s o f R 3 ( p r e s um a b l y the a d d r e s s o f a n I /O
r e que s t pa c k e t ) i n to the I RP po i n t e r f i e l d ( a l o ng wo r d ) i n a
un i t c o n t ro l b l o c k po i n t e d to by R S .
Suc h
i n s t r uc t i o ns a r e
p r a c t i c a l l y s e l f d o c um e n t i ng .
Th e
o v e r a l l a r r a ng ement o f
d a t a i n a pa r t i c u l a r s t r uc t u r e d o e s n o t n e ed t o b e known
in
o r d e r t o und e r s t a n d s uc h i n s t r uc t i o n r e f e r en c e s .

A- 2

U S E OF L I S T ING AND MAP F I LE S
•

Wh e n e v e r a s e q u e n c e o f i n s t r uc t i o ns m a k e s a n a s s ump t i o n a b o u t
the
r e l a t i ve
l oc a t i o n s
of
f i e l d s wi t h i n a d a ta s t r uc t u r e ,
t h e r e i s a po s s i b i l i ty o f f a i l u r e
i f the
s t r uc t u r e s h o u l d
Two
i n s ta n c e s wh e r e s uc h a s s umpt i o n s m i g h t be u s e d
c h a ng e .
a r e t h e f o l l ow i ng .
•
•

Two ad j a c e n t l o ngwo r d
f i elds
s i ng l e MOVQ i n s t r uc t i o n .

c o uld

A s t r uc t u r e c o ul d be
t r a v e r s ed
a u tod ec r em e n t a d d r e s s i ng .

us i ng

l o a d ed

wi th

a uto i nc r emen t

Th e AS S UM E ma c r o { l i s ted i n [ E XEC . SRC ] S YSMAR . MAR a nd d e f i n ed
in
SYS $ L I BRARY : L I B . MLB )
i s o f ten used to i mmed i a t e l y d e t e c t
these fa i lures by
i s s u i ng
a n a s s emb l y t i me
e r ro r .
Fo r
if
a d ev i c e d r i v e r wa n t ed to c l e a r a d j a c e n t f i e l d s
ex ampl e ,
i n a un i t c o n t r o l b l o c k , t h e fo l l o w i ng i n s t r uc t i o n a nd m a c r o
s e que n c e s e q u e n c e wo u l d p r ev e n t f u t u r e s ub t l e e r r o r s i f the
l a yo u t of the un i t c o n t r o l b l o c k c h a nged .
C LRQ
ASSUM E
ASSUM E

UC B $ L SVAPTE { R S )
UC B $ L B OFF E Q <UCB $ L SVAPTE + 4 >
UC B $ L=B CNT E Q <UC B $ L=SVAPTE + 6 >

Th e o p t i o ns a v a i l a b l e wi th t h i s m a c r o c a n b e d e te rm i ned
by
e x am i n i ng
i ts defini t ion
in
the m i c r o f i c h e l i s t i ng in the
E XE C c ompo n e n t .
•

Th e r e a r e some c ommo n l y u s e d i n s t r uc t i o n s e q u e nc e s tha t o c c u r
so
f r e quen t l y t h a t
t h e a u tho r o f a m o d ul e u s e d a n a s s e m b l y
t i me ma c r o to
r epresent
the
i n s t r uc t i o n
s e q u e nc e .
Othe r
i n s t r uc t i o n s e quenc e s , p a r t i c ul a r l y tho s e t h a t r e a d o r wr i t e
t h e i n t e r n a l p r o c e s so r r eg i s t e r s , a r e mo r e r e a d a b l e i f h i d d e n
in
a ma c r o d e f i n i t i o n .
Howeve r , b e c a u s e m a c r o s a r e r a r e l y
e x pand ed a s a pa r t o f t h e a s s embl e r l i s t i ng ,
t h e r eade r o f
l i s t i ng f i l e s mus t b e a b l e t o l o c a t e the m a c r o d e f i n i t i o n s .
Th e r e a r e
VAX/VM S .

th r e e

l eve l s

wh i c h

ma c r o s

a re

d e f i n ed

I n th i s c a se ,
the
A m a c r o m a y be l o c a l to a mo d u l e .
m a c r o d e f i n i t i o n a ppe a r s
as p a r t of the mod u l e h e a d e r .
Such mac r o s a r e o f te n used to g e ne r a t e d a ta
t a b l e s used
by a s i ng l e m o d u l e .
A m a c r o m a y b e a p a r t o f a spec i f i c f ac i l i ty , s uc h a s DC L
or
the RSX- l lM AME .
Th e m a c ro s th a t a r e a pa r t o f a
spec i f i c f a c i l i ty a r e i nc l ud ed a s p a r t o f the m i c ro f i c h e
l i s t i ng
fo r
th a t
f ac i l i t y .
Fo r ex ampl e ,
the
DC L
m i c r o f i c h e i n c l ud e s n o t o n l y a l l mod u l e s t h a t m a k e up the
DC L
i m ag e s but a l so the ma c r o s tha t a r e u s ed t o a s s embl e
tho s e mod u l e s .
A m a c r o m a y b e used by m a ny c omponen t s o f VMS .
In
th i s
case ,
th e m a c r o d e f i n i t i o n i s fo und o n e i th e r the E XEC
m i c r o f i c h e { fo r e x ampl e , in SYSDEF . MDL o r SYSMAR . MAR )
or
the VMS L I B m i c r o f i c h e
{ fo r e x ampl e , i n STARDE F . MDL o r
S SMSG . MDL ) .
Mo s t o f the ma c ro d e f i n i t i o n s
in
th i s
c a t eg o r y a r e d a t a
s t r uc t u r e d e f i n i t i on s , b u t t h e r e a r e
many c ommo n i n s t r uc t i o n s equenc e s a ppe a r i ng
i n seve r a l
c ompo n e n t s
tha t
a re
d e f i n ed
i n the
f i l e c a l l ed
SYSMAR . MAR .
A- 3

USE OF L I STING AND MAP F I LES

Th e d e f in i t i o n s of a l l s y s t em ma c r o s
tha t a re
used
in
b u i l d i ng
VMS
are
i nc l ud ed
i n the m a c r o
l ibrary
SYS $ L I BRARY : L I B . M LB t h a t i s s uppl i ed a s a
pa r t o f
the
VAX/VMS b i na r y d i s t r i b u t i o n k i t .
App l i c a t i o n s s uc h a s
us e r -wr i t t e n d ev i c e d r i v e r s o r
u s e r -w r i t t e n
s y s t em
se r v i c e s
can
a l so
u s e th i s m a c r o
l i bra ry .
Such
appl i c a t i o n s m u s t b e r ea s s e m b l e d or r ecomp i l ed wi th e a c h
new r e l e a s e
of
L I B . MLB , wh i c h u s ua l l y o c c u r s w i th e a c h
m a j o r r e l e a s e o f VAX/VM S .
Th e d e f i n i t i o n s o f a l l m a c r o s tha t a r e i n t end e d
fo r
use
in
nonpr i v i l eg ed
a pp l i c a t i o n s
s uc h a s sys t em s e r v i c e
cal l s
can
be
f o und
in
the
macro
l ibrary
SYS $ L I BRARY : S TARL E T . MLB
that
i s a l s o s upp l i ed a s a pa r t
o f the VAX/VM S b i n a r y d i s t r i b u t i o n
kit .
Th i s ma c r o
l ibrary
i s a u to m a t i c a l l y s e a r c hed
by t h e a s s emb l e r to
r e s o l ve und e f i ned
ma c r o s .
Append i x D
conta i ns
a
d e s c r i p t i o n o f the d a t a s t r uc tu r e s d e f i ned i n STARDEF . MDL
a nd SYSDE F . MD L .
•

Ano th e r s e a r c h t ha t the r e ad e r o f l i s t i ng s h a s to
emba r k o n
i nv o l v e s
l o o k i ng
fo r
d e s t i na t i o ns o f
i ns t r uc t i o n s
tha t
t r a ns f e r c o n t r o l o r r e f e r e nc e s t a t i c d a ta l o c a t i o n s .
If
the
d e s t i na t i o n
or
d a ta
l ab e l
i s o u t s i d e the mod u l e c u r r e n t l y
b e i ng l o o k ed a t , t h e s ym bo l a ppe a r s i n t h e s ym bo l
tab l e
at
t h e e n d o f t h e a s sembl e r l i s t i ng a s a n und e f i n ed g l o b a l .
Th e
m o d u l e tha t d e f i n e s t h a t s ymbo l c an b e d e t e r m i ned
wi th the
m a p f i l e fo r tha t c ompon e n t ( S e c t i o n A . 2 ) .
Symbo l s tha t a r e l o c a l to a m od u l e a r e u s ua l l y e a s y to
f i nd
b e c a us e mo s t o f t h e mod u l e s t h a t ma ke up the e x e c u t i v e o r a n y
o th e r c o mpo n e n t a r e n o t v e r y
l a rge .
Howe v e r ,
the
l i s t i ng
f i l e s fo r some mo d u l e s a r e l o ng e r tha t 5 0 pag e s .
Th e r e a r e a
c o upl e o f s t e ps th a t c a n b e t a k e n b e fo r e
the
r ea d e r
scans
e v e r y pag e
of
the l i s t i ng , l o o k i ng fo r the p l a c e wh e r e t h e
s ym bo l i s d e f i n ed .
Th e symbo l i n q u e s t i o n o r s ome tex t ua l
refe rence
to
may app e a r i n the t a b l e o f c o n t e n t s fo r th i s mod u l e .

Th e va l ue o f the s ym bo l
appe a r s
i n the
s ym bo l
tabl e .
B e c a use
the
a s sem b l e r i nc l ud e s the v a l ue o f the c u r r e n t
l o c a t i o n c o un t e r i n eve r y l i ne o f t h e l i s t i ng , t h e r e ad e r
c a n d e t e rm i n e a pp r o x i m a t e l y wh e r e
in
the l i s t i ng the
symbo l is d e f i n ed .
( Th i s t e c h n i que i s n o t
fo o l p r o o f .
Th e va l ue o f
the
s ymbo l
th a t a ppe a r s
i n t h e s ym bo l tab l e i s r e l a t i v e t o
t h e beg i nn i ng
of
the
PSECT
i n wh i c h
the
symbo l
is
d e f i n ed .
Mo d u l e s w i th mo r e than o n e r e l o c a t a b l e PSECT
m a y have to be sea r c h ed mo r e c a r e f u l l y . )

A. l . 2

Th e VAX- 1 1 I n s t r uc t i o n S e t a nd Ad d r e s s i ng Mod e s

O n e o f t h e d e s i g n g o a l s o f t h e VAX- 1 1
i n s t r uc t i o n s e t wa s
tha t
it
c o n ta i n
u s e f u l i ns t r uc t i o n s wi th a n a t u r a l numbe r o f o pe r a nd s .
Th us ,
the r e a r e two a nd t h r e e o pe r a nd f o rms o f the a r i thme t i c
i n s t r uc t i o n s
ADD , S UB , MUL , a nd D I V .
Th e r e a r e a l s o b i t m a n i pu l a t i o n i n s t r uc t i o n s ,
A-4

U S E OF L I STING AND MAP F I LES
a c a l l i ng s t a nd a rd , c h a r a c t e r s t r i ng i n s t r uc t i o n s , a nd s o o n .
Al l
of
t h e s e a l l o w t h e a s s e mb l y l a ng uag e p r og r amme r t o p r o d uc e cod e tha t i s
n o t o n l y e f f i c i en t b u t a l s o h i g h l y r e ad a b l e .
Howe v e r , the r e a r e c e r t a i n p l a c e s i n the
e x e c u t i v e wh e r e
the mo s t
o bv i o us c ho i c e o f i n s t r uc t i o n o r a d d r e s s i ng mod e wa s n o t used , b e c a u s e
a sho r t e r o r f a s t e r
a l t e r n a t i ve wa s a v a i l a b l e .
I n t e r r upt
serv i c e
r o u t i n e s , r o u t i n e s tha t e x e c u t e a t e l ev a ted I PL , a nd c ommo n l y e x ec u t e d
cod e pa ths s uc h a s the s ys t em s e rv i c e d i spa tc h e r a nd the ma i n pa t h s i n
the
pag e r
are
all
e x ampl e s wh e r e c l a r i t y o f the s o u r c e c o d e wa s
s a c r i f i c ed fo r e x e c u t i o n s p e ed .
One que s t i o n tha t mus t b e a n swe r ed a t t h i s po i n t i s wh y the r e
is
a
conce rn
ov e r
i ns t r uc t i o n
l eng th o n a mach i n e wi th p r a c t i c a l l y
un l i m i ted v i r t ua l add r e s s spac e .
Th e r e a r e a t l e a s t
a n s we r s
two
to
tha t q ue s t i o n .
Mo s t of the a r e a s wh e r e i n s t r uc t i o n s i z e is an i s s u e
a r e wi th i n
the
pe rma n en t l y r e s i d e n t e x e c u t i ve .
Th i s po r t i o n o f the sys t e m c o n s um e s a
f i x ed pe r c e n t ag e o f
the
phys i c a l m emo r y t h a t
i s pr e s e n t
in
the
con f i g u ra t i on .
Ke e p i ng
i n s t r uc t i o n s i ze sma l l i s o n e of t h e e f fo r t s
tha t c a n be m ad e to k e e p th i s r e a l memo r y c o s t to a m i n i m um .
the VAX - 1 1 /7 8 0 m a k e
A s e c o nd an swe r i s tha t bo th the VAX- 1 1 /7 5 0 a nd
use
of
an
i n s t r uc t i o n l o o k a h e a d b u f f e r tha t c o n t a i n s t h e n e x t e i g h t
b yt e s i n t h e i n s t r uc t i o n s t r e am .
If
the buffe r
emp t i e s ,
the next
i n s t r uc t i o n o r
ope r a nd
c anno t b e ev a l ua t ed
unt i l
the b uf f e r i s
r e p l e n i shed .
By k e e p i ng i n s t r uc t i o n s sma l l i n k e y a r e a � ,
th i s
wa i t
c a n b e avo i d ed
a nd the i n s t r uc t i o n b u f f e r c a n b e f i l l ed i n pa r a l l e l
wi th o the r C P U o pe r a t i o n s .

A . l . 2 . 1 Tech n i qu e s fo r I n c r e a s i ng I n s t r uc t i o n Spe e d - Th i s s ec t i o n i s
a
l i s t o f s ome o f the t e c hn i q u e s emp l oyed to r ed uc e i n s t r uc t i o n s i z e
o r i nc r e a s e e x e c u t i o n spe ed .
Th e l i s t
i s h a rd l y e x h a u s t i v e b u t a
pa t t e r n eme r g e s h e r e
tha t c an
be
a pp l i ed to o th e r mod ul e s i n the
e x e c u t i v e tha t a r e n o t e x pl i c i t l y m e n t i o ned h e r e .
Each
l i st
e l em e n t
cons i s ts
of
a g ene r a l
t e c hn i que
a nd m a y a l s o c o n t a i n a spec i f i c
e x ampl e , i n c l ud i ng the n ame o f the mod ul e wh e r e
th i s
t ec h n i que
is
empl o y ed .
•

Th e MOVAx and PUS HAx i n s t r uc t i o n s c ombi ned wi th d i spl a c em e n t
mod e
ad d r e s s i ng
a r e eq u i v a l e n t to an ADDLx i n s t r uc t i o n wi th
the ad d i t i o n b e i ng
pe r fo rmed
i n o rd e r
to c a l c u l a t e
the
e f fe c t i ve
add r e s s
of
t h e o pe r and .
Fo r
e x ampl e ,
the
i n s t r uc t i o n
PUS HAB

1 2 (R3 )

i s e q u i v a l e n t to
ADD L 3

# 1 2 , R3 , - ( S P )

b u t i s o n e byte sho r t e r t h a n the ADD L3 i n s t r uc t i o n
faste r .

A- 5

a nd

a l so

U S E OF L I ST ING AND MAP F I LE S
•

Th e us e o f MOVAx a n d PUS HAx d e sc r i b ed i n the
p r ev i o us
i tem
c a n be comb i n ed w i th i nd ex ed mod e add r e s s i ng to a c compl i sh a
m u l t i pl y by 2 , 4 , o r 8 .
Fo r e x am p l e , t h e i n s t r uc t i o n
MOVA L

@#4 [Rl] , Rl

mul t i pl i e s the co ntents of Rl by 4 , add s 4
to
the
p r o d uc t ,
a nd pl a c e s the r e s u l t b ac k i n to R l .
Th i s i ns t r uc t i o n i s used
b y the c h a ng e mo d e d i spa t c h e r s
( i n mod ul e CMODS SDS P )
to
c a l c u l a te
the
l e ng th of an a rg um e n t l i s t f r om the n um b e r o f
a rg umen t s .
•

Th e i n s t r uc t i o n
MOVAB

( R O ) + , R2

f o und i n r o u t i ne EXE $AL LOCATE i n mo d u l e MEMORYALC p e r fo rm s
t wo
s t e ps a t o nc e .
I t s o s t e n s i b l e p u r po s e i s t o p l a c e t h e
a d d r e s s o f t h e a l l o c a te d b l o c k o f memo r y i n to
R 2 wh e r e
it
w i l l be p i c k ed
up b y t h e c a l l e r .
Howeve r , b e c a us e t h e
a l l o c a t ed b l o c k i s a l wa ys a t l e a s t q ua d wo r d a l i g ned , the b y t e
c o n t e x t o f t h e i n s t r uc t i o n f o r c e s a n i nc r em e n t o f R O by o n e ,
s e t t i ng t h e l o w b i t o f R O .
Th i s w i l l
be
i n t e r p r e ted
as a
s uc c e s s i nd i c a to r by t h e c a l l e r .
•

Wh e n two s uc c e s s i ve wr i tes to memo r y o c c u r , t h e s e c o nd wr i te
m u s t wa i t
fo r
the
f i r s t to c om p l e t e .
I f s uc c e s s i ve wr i te
o pe r a t i o n s c a n b e ove r l a pped
w i th
r eg i s t e r - t o - r eg i s te r
o pe r a t i o n s ,
i n s t r uc t i o n
s t r eam
r e f e r e nc e s ,
or
o th e r
o pe r a t i o n s th a t d o n o t g e ne r a t e wr i t e s to memo r y ,
then s o m e
o th e r
i n s t r uc t i o n c a n b eg i n e x ec u t i o n wh i l e the m emo r y wr i te
i s c ompl e t i ng .
Th e r e a r e th r e e p l a c e s i n the e x ec u t i v e wh e r e th i s
t e c h n i qu e
is
u s ed .
Th e y a r e among
t h e m o s t c ommo n l y e x e c u t ed c od e
p a th s i n t h e en t i r e sys tem .
Th e pa g e f a u l t h a nd l e r s a v e s R O t h r o ug h
RS w i th
s e pa r a t e
M OVQ
i n s t r uc t i o n s
i n t e r s pe r s ed
i n s t r uc t i o n s th a t d o no t wr i te to memo r y .

th r e e
among

Th e i n t e r r up t se r v i c e r o u t i n e fo r the VAX- 1 1 /7 8 0 UN I B U S
ad a p t e r
a l so
s a v e s RO
t h r o ug h R S w i th
th r e e MOVQ
i n s t r uc t i o n s .
He r e , the wr i te s to memo r y a r e ove r l a pped
wi th
r e f e r e nc e s to I /O s pa c e a d d r e s s e s , spec i f i c a l l y UBA
i n t e r n a l r eg i s t e r s , as we l l a s r eg i s t e r m a n i pu l a t i o n s .
Th e c h a ng e mod e d i spa tc h e r s
fo r
e x e c u t i ve a nd
ke r n e l
mod es b u i l d
c us tom i z ed c a l l f r am e s o n t he i r s t a c k s .
As
F i g u r e 3 - 4 i l l u s t r a t e s , t h e wr i te s to memo r y
( th e
s ta c k
o pe r a t i o n s )
a r e ove r l a pped w i th r eg i s t e r a nd i n s t r uc t i o n
s t r e am r e f e r e nc e s .
•

Wh e n i t i s n e c e s s a r y t o i nc l ud e a t e s t a nd b r a n c h o pe r a t i o n ,
a
dec i s i on
as
to
wh i c h s e n s e o f the t e s t to b r a n c h o n a n d
wh i c h s e n s e to a l l o w t o c o n t i n ue i n l i ne
is
r eq u i red .
On e
bas i s
fo r
th i s d ec i s i o n
is
to
a l l o w the c ommo n ( us ua l l y
e r r o r - f r e e ) c a s e t o c o n t i n ue
in
l i ne ,
o n l y r e q u i r i ng
th e
( s l owe r ) b r a nc h o pe r a t i o n i n unus u a l c a s e s .

A- 6

U S E OF L I S T ING AND MAP F I LES
A . l . 2 . 2 Un u s ua l I n s t r uc t i o n a nd Ad d r e s s i ng Mod e U s a g e - Th e r e
a re
s e v e r a l i n s ta nc e s i n the e x e c u t i v e wh e r e the pu r po s e o f a n i n s t r uc t i o n
i s n o t a t a l l o bv i o u s .
Th i s l i s t i nc l ud e s the mo s t c ommo n o c c u r r en c e s
o f u n u s ua l u s e o f t h e i n s t r uc t i o n s e t a nd a d d r e s s i ng mo d e s .
•

Th e r e a r e m a n y i n s t a n c e s o f the i n s t r uc t i o n s e q u e n c e
10$ :

BBSS

b i t a r g um e n t s , 1 0 $

wh e r e the i n i t i a l s e t t i ng o f the b i t h a s
no
e f fec t o n the
f l ow o f
control .
Th i s s e q ue nc e i s used wh ene v e r the b i t to
b e set ( o r c l e a r ed wi th a n e q u i v a l e n t s e quenc e us i ng BBCC ) i s
i d e n t i f i e d by b i t numbe r o r b i t po s i t i o n .
I n o r d e r to s e t ( o r c l e a r ) t h e b i t wi th a
B I Sx
(or
( B I Cx )
i n s t r uc t i o n ,
a m a s k mus t
f i r s t b e c r e a ted wi th a 1 i n the
d e s i g n a t ed po s i t i o n , r e q u i r i ng e i th e r two i n s t r uc t i o n s or
an
i mmed i a t e ma s k
that m i g h t occ upy a
l o ng wo r d .
( Th e o n l y
e x c e p t i o n t o th i s i nv o l v e s a b i t i n the f i r s t s i x
po s i t i o n s ,
wh e r e t h e ma s k c a n be c o n t a i n ed i n a sho r t l i t e r a l c o n s t a n t . )
No t e
th a t a
BBC S
i n s t r uc t i o n
i s equ i v a l en t
to a
BBSS
i n s t r uc t i o n
wh e n
the
b r a nch d e s t i n a t i o n
is
the n e x t
Th e r e a r e some o c c u r r e nc e s o f BBCS wh e r e a B B S S
i n s t r uc t i o n .
s e ems
to
a c c ompl i s h the s am e p u r po s e .
P r o b a b l y , t h e cho i c e
wa s mad e by l o o k i ng a t the u s ua l s e n s e o f the b i t i n que s t i o n
befo re
the i n s t r uc t i o n a nd c ho o s i ng the i n s t r uc t i o n t o a v o i d
the b r a nch i n t h e us ua l c a se .
•

Th e r e
are
seve r a l
i ns tances o f
a u to i nc r em e n t
defer red
a d d r e s s i ng wh e r e
t h e n e ed f o r the i nc r em e n t o f t h e r eg i s t e r
i s no t a ppa r en t .
Fo r e x ampl e , the i n s t r uc t i ons
I N S QU E

( R l ) ,@ ( R 3 ) +

REMQUE

@ ( R 3 ) + , R4

a nd

o c c ur i n the r e s c h ed u l i ng i n te r r upt se r v i c e r o u t i n e i n mod ul e
S C HED .
In
bo th c a s e s ,
R3
conta ins
the add r e s s o f the
l i s th e a d
of
s o m e d o ub l y l i n ked
l i s t b e fo r e
i n s t r uc t i o n
e x e c ut i o n .
I t s c o n te n t s
a f t e r the i n s t r uc t i o n i s ex e c u t ed
a r e i r r e l ev a n t .
I n f a c t , th e i nc r em e n t i s t o t a l l y unne c e s s a r y .
Al l
th a t
is
n e e d ed
i s d o ub l e d e f e r r a l f r om a r eg i s t e r .
I n o th e r wo r d s ,
the a d d r e s s i ng mo d e @ O ( R 3 ) wo u l d be
equa l l y a pp r o p r i a t e
if
the c o n t e n t s o f R 3 a r e n o t i mpo r ta n t .
Howe v e r , d e f e r r e d b y t e
d i spl a c emen t a d d r e s s i ng c o s t s
an extra
byte
to ho l d
the
d i spl a c eme n t .
In
th i s c ommo n l y e x e c u t ed
c o d e pa th , t h e
s a v i ng s o f a byte wa s ex t r em e l y impo r ta n t .
I t i s wo r th n o t i ng t h a t the r e i s no s i m i l a r
p r o b l em wh e n a
s i ng l e
l ev e l
o f d e f e r r a l f r om a r eg i s t e r i s r e qu i r ed .
Th e
a s s emb l e r
is
sma r t e n o ug h
to g e ne r a t e
s i mpl e
r eg i s t e r
d e f e r r ed mod e
( c o d e 6 ) wh e n i t enc o un t e r s byte d i s p l a c em e n t
( O ( r eg ) )
i n t h e so u r c e
mod e wi th a d i s pl a c emen t o f z e ro
c od e .

A-7

U S E OF L I STING AND MAP F I LES
•

Th e pe rma n e n t s ymbo l t a b l e o f t h e VAX- 1 1 MACRO a s sem b l e r
r e c o g n i ze s
t h e mnemo n i c
P O PL even tho ug h t h e r e i s n o POPL
i n s t r uc t i o n s e t .
i n s t r uc t i o n i n th e VAX- 1 1
Th e g en e r a ted
code for a
POPL

dst

ps e ud o i n s t r uc t i o n i s i d e n t i c a l t o a
MOVL

( S P) + , d st

i n s t r uc t i o n .
Th a t i s , t h e mnemo n i c g e ne r a tes two b y t e s
( fo r
i n s t r uc t i o n
o pc o d e
a nd
source
o pe r a nd
spe c i f i e r )
pl us
wh a t eve r i s r e qu i r ed to spec i f y t h e d e s t i n a t i o n ope r a nd .
Fo r ex ampl e , t h e p s e ud o i n s t r uc t i o n
POPL

the f i r s t i n s t r uc t i o n i n the c h a ng e -mod e - to-k e r n e l d i spa t c h e r
i n mo d u l e CMODS S DS P r emov e s t h e c h a n g e m o d e c o d e f r om the
s t a c k ( so th a t RE I wi l l wo r k c o r r ec t l y ) and l o ad s i t i n to R O .
A c omb i n a t i o n o f t h i s i n s t r uc t i o n w i th a n u n u s ua l
a d d r e s s i ng
mod e
occ u r s
in
the
except i on
d i spa t c h e r
fo r
c h a ng e -mod e - to - s up e r v i s o r a n d c h a ng e -mod e - t o - u s e r
except i ons
wh e r e
i t i s n e c e s s a r y t o r emove t h e s e c o nd l o ng wo r d f r om the
stack .
Th e a c t ua l i n s t r uc t i o n ,
POPL

(SP)

h a s th e e f f e c t o f r emov i ng the n e x t - to - l a s t
i t em f r om
the
s ta c k a n d d i s c a r d i ng
it,
l e av i ng
the s t a c k i n the s t a t e
p i c t u r ed i n F i g u r e A- 1 .
•

The i n s t r uc t i o n
MOVQ

R O , RO

f o l l owed by s ome
c o nd i t i o na l
b r a n ch
i n s t r uc t i o n pe r fo rms
e x a c t l y the
same f unc t i o n a s a T S TQ i n s t r uc t i o n , wh i c h d o e s
n o t ex i s t .
Th i s c u r i o us
i n s t r uc t i o n
is
f o und
i n mod u l e
SYSSCH EVT ,
wh e r e
the
Se t T i m e r Requ e s t a nd Sched u l e Wa k e up
s y s tem s e r v i c e s a r e i mp l em e n ted .

A. l . 3

U s e o f t h e RE I I n s t r uc t i o n

Th e o n l y p e rm i s s i b l e m e a n s o f r e a c h i ng a l e s s p r i v i l eg ed
a c c e s s mode
f r om a mo r e pr i v i l eg ed mod e is t h r o ug h the R E I i n s t r uc t i o n .
Th e r e a r e
two s l i g h t l y d i f f e r e n t t e c h n i q ue s th a t a c compl i sh t h i s .

A- 8

USE OF L I S T ING AND MAP FILES

POPL dest

MOVL(SP)+,dest
after POPL (SP)

before POPL (SP)

X+4:
...

X +8:

X + 1 2:

X + 1 6:

X+1 6:

X+8:

C (or Indeterminate)

Direction of
stack growth

F i g u r e A- 1

S t a c k Mo d i f i c a t i o n Due to PO P L { S P ) Ps e ud o I n s t r uc t i o n

Th e m o s t g en e r a l t e c h n i qu e o f e l ev a t i ng a c c e s s mod e a l l o ws the f l o w o f
e x e c ut i o n t o b e a l t e r ed a t the s am e t i me .
Th i s s ame t e c hn i que i s a l so
u s ed
by
the
RSX- l l M AM E
to
get
i n to
c ompa t i b i l i ty m od e .
Th e
i n s t r uc t i o n s e quenc e
PUSHL
PUSHL
RE I

new- P S L
n ew-PC

a c c ompl i s h e s the d e s i r ed r e s u l t .
No te tha t the many p r o t e c t i o n c h ec k s
bui l t
i n to t h e RE I i n s t r uc t i o n p r ev e n t th i s techn i que f r om be i ng used
b y a n o n p r i v i l eg ed us e r to g e t i n to a mo r e p r i v i l eg ed a c c e s s mod e o r
t o e l ev a t e I PL , two o pe r a t i o n s tha t wo u l d a l lo w s uc h a u s e r t o d am ag e
the sys t em .

A- 9

US E OF L I S T ING AND MAP F I LE S

A s e c o nd t e c hn i qu e c an b e u s e d wh e n i t i s
only necessa r y to change
a c c e s s m od e .
N o a c compa n y i ng c h a ng e i n c o n t r o l f l ow i s r e q u i red .
Th e
i ns t r uc t i on seque nce l i s t ed h e r e ( pa t t e r ned a f t e r c o d e c o n t a i n ed
in
mod u l e PROC S TRT ) shows t h i s s e c o nd t e c h n i que .
PUS H L
BSBB

e x e c u t i v e -mod e-PS L
DORE I
; Do p r o c e s s i ng i n
; execut ive access mode

PUSHL
BSBB

u s e r -mod e - P S L
DORE I
; Do p r o c e s s i ng i n
; u s e r a c c e s s mod e

DORE I :

REI

A. l . 4

Reg i s t e r Conve n t i o n s

; R E I u s e s pushed PS L a n d PC
; th a t B S B B p u t o n s t a c k

E a c h o f the m a j o r s ub s ys t em s o f t h e e x e c u t i ve u s e s a s e t
of
r eg i s t e r
c onve n t i o n s
in
i ts ma i n
rout ines .
Th a t i s , t h e same r eg i s t e r s a r e
used t o h o l d the same c o n t e n t s f r om r o u t i n e t o r o u t i n e .
Some o f the
mo r e c ommo n c o nv e n t i o n s a r e l i s t ed h e r e .
•

•

R4 u s ua l l y c o n ta i n s the a d d r e s s o f the
PC B o f
the c u r r en t
process .
Nea r l y a l l
s ys tem s e rv i c e s a nd the s c h ed u l e r us e
th i s c o nve n t i o n .
I n f a c t , a s i l l us t r a ted i n F i g u r e 3 - 4 ,
the
c h a ng e -mod e - to - k e r n e l sys tem s e r v i c e d i spa t c h e r l o ad s the PC B
of
the c a l l e r
i n to
R4
be f o r e p a s s i ng
c on t r o l
to
the
s e r v i c e - s pec i f i c
p r o c ed u r e .
Wh en i t is n e c e s s a· r y to s t o r e a
PHD add r e s s , RS i s u s ua l l y c h o sen .
( E x c e pt fo r
the
swa ppe r
a nd c e r t a i n memo r y m a n ag em e n t c od e tha t e x e c u te s a t I PL 7 , R S
c o n t a i n s t h e add r e s s o f t h e P l w i ndow to t h e p r o c e s s h e a d e r . )
Th e memo r y m a n a g em e n t s ub s ys t em u s e s R 2 to c o n t a i n a n i nv a l i d
add r e s s
a nd
R 3 t o c o n t a i n the sys tem v i r t ua l add r e s s o f the
pag e t a b l e e n t r y th a t m a ps the pag e .
Wh en a ph ys i c a l pag e i s
e v e n t ua l l y a s s o c i a t e d wi t h the pag e , t h e PFN i s s to r ed i n R O .
Th e
I /O
sys t em
us e s t wo
n e a r l y i d en t i c a l
c o n v en t i o n s ,
d e pend i ng o n wh e th e r i t i s e x e c u t i ng i n p r o c e s s c o n t e x t ( i n
the $ Q I O sys tem s e r v i c e o r i n d ev i c e d r i v e r FDT r o u t i n e s )
or
in
r e sponse t o a n
i n t e r r up t .
Th e mo s t c ommo n r eg i s t e r
c o n t e n t s a r e t h e c u r r e n t I R P a d d r e s s s to r ed i n R 3 a nd t h e UC B
add ress
i n RS .
I n p r o c e s s c o n t ex t , R4 c o n t a i n s t h e a d d r e s s
of the PCB o f
the
r eque s t i ng
process .
W i th i n
i n t e r r up t
service
r o ut i n e s ,
R 4 c o n t a i n s the v i r t ua l add r e s s t h a t m a ps
o n e o f t h e C SRs o f t h e i n te r r upt i ng d ev i c e .
A mo re
c ompl e t e
l i s t of
r eg i s t e r
u s ag e b y d ev i c e d r i ve r s a nd
the
I /0
s ub s y s t em c a n b e f o und i n the VAX/VM S G u i d e
to
Wr i t i ng
a
Dev i c e D r i v e r .

A- 1 0

U S E OF L I ST ING AND MAP F I LE S
A. l. S

E l i m i n a t i o n o f S e l d om - U s e d Cod e

Th e r e a r e s e v e r a l d i f f e r e n t techn i q ue s tha t a r e u s e d t o e l i m i n a t e c o d e
o r d a ta
tha t
i s no t
used ve ry o f ten .
Fo r e x ampl e , n o n e o f t h e
p r og r a m s u s e d d u r i ng t h e i n i t i a l i z a t i o n o f a VMS s ys tem r ema i n s a f t e r
i t s wo r k i s a c c om pl i s h e d .
P r o c e s s c r e a t i o n i s a n e x ampl e o f a com pl ex
sys t em s e r v i c e tha t d o e s n o t e x e c u t e o f te n d u r i ng the
l i fet ime o f a
typ i c a l sys t em .
VMS u s e s s e ve r a l t e c h n i q ue s tha t a l l o w the s e r o u t i n e s
to d o the i r wo r k a s e f f i c i e n t l y a s po s s i b l e
a nd
ye t e l i m i n a t e
them
a f t e r the y h a ve d o n e the i r wo r k .

A. l . S . l
E l i m i n a t i ng the Bo o t s t r a p P r o g r ams - Th e
fo l l owi ng
l i st
i l l ustrates
some o f
the
techn i q ue s
used
to
r emove the bo o t s t r a p
p r og rams f r om t h e sys t em a f t e r the y h a v e d o n e the i r wo r k .
1.

Bo t h VMB and S Y S B OOT e x ec u te i n phys i c a l pag e s tha t a r e n o t
r e c o r d ed
a n ywh e r e .
Wh e n mod ul e
I N I T pl a c e s a l l phys i c a l
pag e s e x c e pt
tho s e o c c up i ed
b y t h e pe rman e n t l y
res ident
e x e c u t i v e o n t o t h e f r e e pag e l i s t , t h e pag e s u s e d b y VMB a nd
SYS B OO T a r e i n c l ud ed .
Th e i r
c o n t e n t s a r e o v e r wr i t t e n
the
f i r s t t i me th a t e a c h phys i c a l pag e is u s e d .

Th e mod u l e IN I T i s a pa r t o f the l i n k ed e x e c u t i v e a nd
c a n no t
be e l i m i n a t ed qu i t e so e a s i l y .
Ch a pt e r 2 1 d e sc r i b e s how I N I T
p u t s t h e phys i c a l pag e s tha t i t o c c up i ed o n to t h e
f r ee
pag e
l i s t a f t e r i t s wo r k wa s d o ne .
•
•

Th e r o u t i n e th a t puts the phys i c a l pag e s o n the f r e e pag e
l i s t pe r f o rms a s t r a i g h t f o rwa r d f un c t i o n .
Th e un u s ua l pa r t o f t h i s s t e p i s tha t
th i s
r o u t i n e wa s
f i r s t co p i ed
to a n u n u s e d po r t i o n o f n o npag ed po o l , b u t
t h e po o l spac e wa s n o t
fo rm a l l y a l l o c a t e d .
Wh e n
the
rout i ne
has a c c ompl i shed i t s wo r k a nd r e t u r n ed , the c o d e
r em a i n s u n t i l t h e po r t i o n o f po o l
tha t
it
o c c upi ed
is
used
later
on ,
wh e n
the
l ast
traces of
INIT a re
e l i m i n a t e d f r om the s y s t e m .
No t e
tha t t h i s
t ec h n i que
a s s um e s
th a t n o po o l a l l o c a t i o n t a k e s pl a c e un t i l i t i s
done .
Th e
f a c t tha t
I PL
r em a i n s a t
3 1 wh i l e
INIT
e x e c ute s i n s u r e s tha t n o s uc h a l l o c a t i o n o c c u r s .

Th e sys t em i n i t i a l i z a t i o n tha t t a k e s pl a c e i n p r o c e s s c o n t e x t
c a n be
th o ug h t o f a s a pa r t o f t h e swa ppe r p r o c e s s b e c a u s e
t h e swa ppe r c r e a t e s SYS I N I T , wh o i n t u r n c r e a t e s t h e
START U P
process .
Bec a u s e b o th
SYS I N I T a nd
S TARTUP a r e s e pa r a t e
p r o c e s s e s , howe v e r , they d i s a ppe a r
a fter
the y a r e d e l e t e d
( wh e n they h a v e c ompl e t ed the i r wo r k ) .

by
A . l . 5 . 2 S e l d om-Used Sys t em Ro u t i n e s - Th e s i mpl e s t t e c h n i que used
the
sys tem
to
prevent
s e l d om- u s ed
c o d e f r om pe rm a n e n t l y o c c upy i ng
memo r y i s to put i t i n to t h e pag ed e x e c u t i v e .
Th e n o rm a l ope r a t i o n o f
s ys tem wo r k i ng s e t r e pl a c em e n t wi l l e v e n t ua l l y f o r c e tho s e pag e s tha t
a r e r e f e r en c ed o nc e a nd n e v e r ag a i n o u t o f t h e s ys tem wo r k i ng s e t .
Th i s t e c h n i que i s used by s ev e r a l sys t em s e rv i c e s tha t a r e no t c a l l ed
very o ften ,
s uc h a s
the Se t T i m e sys tem s e rv i c e , wh i c h c h a ng e s the
sys t em t i m e .
P r o c e s s c r ea t i o n a nd d e l e t i o n a r e a l s o
events
tha t d o
A- l l

U S E OF L I STING AND MAP F I LE S
no t occur v e r y o ften .
B e c a u s e p r o c e s s c r e a t i o n i s s p r e a d th r o ug h o u t
t h e s ys t em , seve r a l t e c hn i que s a r e emp l o yed t o e l i m i n a t e t h e cod e f r om
t h e sys tem a f t e r the p r o c e s s i s c r ea t ed .

A. l . 6

Th e r o u t i n e s i n t h e C r e a t e P r o c e s s s y s t em s e rv i c e
( and
a l so
·
t h e De l e t e P r o c e s s sys t em s e rv i c e a nd i t s a s s o c i a t ed spec i a l
ke r n e l AST ) a r e l o c a ted i n the pag e d ex e c u t i ve .

Th e swa ppe r h a s a spec i a l s ub r o u t i n e th a t i t c a l l s wh en
it
i n s waps
a n e wl y c r e a t ed p r o c e s s f r om S h e l l .
Th i s s ub r o u t i n e
i s l o c a t e d i n two o f the pag e s t h a t
the
swa ppe r
j us t
r ead
i n to mem o r y .
Be c a use
o f t h e wa y t h a t the swa ppe r d o e s i t s
I / 0 , t h e s e pag e s a r e ma pped a s
PO
pag e s
i n the
swa ppe r ' s
add ress
spac e .
Th e s e pag e s b ecome t h e k e r n e l s t a c k o f t h e
n e w p r o c e s s ( wh i c h c a nno t e x e c u t e un t i l the swa ppe r m a r k s t h e
process
as
C OM ,
a fter
it
is
f i n i s h ed
wi th t h e spec i a l
s ub r o u t i n e ) .
Th e swa ppe r
has
s uc c e ed ed
i n e x e c u t i ng
two
pag es wo r th o f cod e ( th a t a r e o n l y u s e d the f i r s t t i me th a t a
p r o c e s s i s i n swa pped ) wi tho u t r e q u i r i ng a n y phys i c a l memo r y .

Th e f i n a l s t e ps o f p r o c e s s c r e a t i o n t a k e p l a c e i n the c o n t e x t
of
th e new p r o c e s s i n r o u t i n e EXE $ PROCSTRT , l o c a t ed i n t h e
pag ed e x e c u t i ve .

Dynam i c a l l y Loc k i ng Cod e o r Da t a i n to Memo r y

Th e f r e q u e n c y o f u s e i s n o t t h e o n l y c r i t e r i o n t h a t i s used t o d e c i d e
wh e t h e r
to
put
a r o u t i n e i n to the pag ed o r no npag ed ex ec u t i v e .
Th e
pag e f a u l t h a nd l e r a s s um e s tha t i t w i l l nev e r i nc u r a pag e f a u l t above
I PL 2 .
( Th i s a s s um p t i o n i s e n fo r c ed by i s s u i ng a f a t a l b ug c hec k i f i t
i s v i o l a t ed . )
S e v e r a l sys tem s e rv i c e s t h a t a r e n o t used ve r y o f ten ( i nc l ud i ng C r e a t e
P r o c e s s a nd
De l e t e
Process )
m u s t e l ev a t e
I PL to 7 to synch r o n i ze
a c c e s s to the s c h e d u l e r ' s d a t a b a s e .
Th e r e a r e
seve r a l
d i ffe rent
t e c h n i q u e s used t o m i n i m i z e the c o n t r i b u t i o n t h a t t h e s e r o u t i n e s m a k e
to t h e nonpag ed e x e c u t i v e .

A. l . 6 . 1
Lo c k i ng Pag e s i n E x t e r n a l Imag e s - Th e s i mpl e s t t echn i que fo r
l o c k i ng d own pag e s wh i l e e x e c u t i ng
a t I P L 7 i s used by p r i v i l eg ed
u t i l i t i e s t h a t use the $ CM KRN L sys t em s e r v i c e .
Th e s e prog r ams c a n use
the
$ L KWSET s ys t em s e rv i c e to l o c k d o wn the code a nd d a t a pag es tha t
a r e r e f e r e n c ed wh i l e I PL i s e l ev a t ed a bove 2 .
Th i s t ec h n i que
is not
a v a i l a b l e to exec u t i v e r o u t i n e s o r u s e r -wr i t t e n sys tem se rv i c e s .

A . l . 6 . 2 P l a c i ng C o d e i n t h e No npag ed E x e c u t i v e - Th i s techn i que
puts
the
sm a l l e s t po s s i b l e b l o c k of code i n to the n o n pag ed exec ut i v e a nd
pl a c e s the r e s t o f the r o u t i n e i n to the pag ed
e x e c ut i v e .
A con t r o l
t r a n s f e r a l l o ws t h e n o n pag ed cod e t o e x ec ute .
Th e fo l l owi ng v a r i a t i o n
on a
r o u t i n e w i th i n t h e $ G E TJ P I
s y s tem s e rv i c e
i l l ustr ates
the
t e c h n i que .
Th e
reason
tha t
the
ent i re
r o u t i n e c a nno t ex i s t i n
pag e ab l e pag e s i s b e c a use r o u t i n e EXE $NAMP I D r e t u r n s a t I P L 7 .

A- 1 2

U S E OF L I S T ING AND MAP FI LES

. PS EC T Y E XE PAG ED
. ENAB LE LOCAL B LO C K
P r o c e s s i ng beg i n s i n pag ed c o d e
JSB
25$
. SAVE P S E C T
25$ :

. PS ECT
JSB
SE T I P L
RSB

AE XENON PAG E D
EXE $NAM P I D
#0

Th i s i s o n l y nonpag ed p i e c e

. RE S TORE P S E C T
P r o c e s s i ng c o n t i n ue s i n pag ed c o d e

A . l . 6 . 3 Dynam i c Lo c k i ng o f Pag e s - Th e p r e c ed i ng p i e c e o f
code onl y
contr i butes
t e n b y t e s to the n o n pag ed e x e c ut i v e .
Th e C r e a t e P r o c e s s
a nd De l e t e Pr o c e s s sys tem s e r v i c e s mus t e x e c ute m a n y mo r e i n s t r uc t i o n s
at
I PL 7.
Th e y empl oy a t e c h n i que th a t d yn am i c a l l y l o c k s o n e o r two
pag e s i n to mem o r y .
( Th e s y s t em c a nno t use the $ L KWSET s ys t em s e r v i c e
to
l o c k pag e s
i n to
the s ys t em wo r k i ng s e t . ) Th i s t e c h n i que i s a l s o
n e c e s s a r y f o r us e r -wr i t t e n s ys t em s e r v i c e s
t h a t m us t
execute
a bove
I PL 2
bec a u se
t h e y m u s t a l s o l o c k pag e s i n to memo r y a nd , in g e n e r a l ,
c a nno t use the $ L KWS E T sys tem s e r v i c e .
Th i s t e chn i que r e l i e s on the a s s ump t i o n tha t once I PL i s
e l eva ted
to
I PL $_S YNC H ,
no
ev e n t s
r e l a t ed
to pag e f a u l t i ng o c c u r , pa r t i c u l a r l y
r emov i ng a pag e f r om t h e p r o c e s s o r sys tem wo r k i ng s e t .
; P r o c e s s i ng beg i n s i n pag ed cod e
B EG I N LOC K :
DSB INT

LOCK I P L
No pag e f a u l ts wi l l o c c u r he r e

ENB INT
Pa g e f a u l ts c an o c c u r ag a i n
LOC K I P L :
. LONG
END L OC K :

I P L$ SYNC H

AS S UME < E ND LOCK-BEG IN L OCK> L E 5 1 2
The k e y to th i s t e c h n i que i s tha t the DS B I NT m a c r o
MTPR

( wh i c h e x pa nd s to a

s r c , # PR$ I P L

i n s t r uc t i o n )
c a nno t
s uc c e s s f u l l y c ompl e t e unt i l
bo th
the
pag e
c o n t a i n i ng
the i n s t r uc t i o n a nd t h e pag e c o n t a i n i ng the so u r c e o p e r and
A- 1 3

U S E OF L I ST ING AND MAP F I LES
a r e va l i d .
Onc e t h e i n s t r uc t i o n c ompl e t e s ( i m pl y i ng t h a t b o th pag e s
a r e v a l i d ) , I PL i s s e t a t 7 , p r eve n t i ng f u r th e r pag i ng a c t i v i t y un t i l
t h e I P L i s l owe r ed ( w i th the ENB I N T m a c r o ) .
Th e A S S UM E mac r o i s n ec e s s a r y to m a k e s u r e tha t t h e D S B INT m a c r o
and
source
o p e r and
a re no t mor e
than
o ne pag e a pa r t , p r eve n t i ng the
po s s i b i l i ty of a n
i nv a l i d
p a g e b e twe e n the
t wo
val id
pag e s ,
an
o c c u r r e nc e
tha t wo u l d
s ub v e r t
t h i s t e c h n i que .
An y e x amp l e o f th i s
t ec h n i que a l so h a s some i n s t r uc t i o n tha t t r a n s f e r s c o n t r o l s o th a t the
l o n g wo r d c o nta i n i ng I PL $_S YNC H i s not i n t e r p r e t ed as an i n s t r uc t i o n .
A n a t u r a l que s t i o n a t t h i s po i n t i s wh y t h e f i r s t t e c h n i que ,
t h e one
u s ed
b y $G ETJP I , is n e c e s s a r y a t a l l .
It s e ems that the c a l l s i t e to
EXE $NAM P I D c o u l d b e l o c ked d own u s i ng th i s t e c h n i que .
Th e a n swe r
to
I t a c c e s s e s the
t h i s i s th a t E XE $NAM P I D c a n n o t be c a l l ed above I PL 2 .
c a l l e r ' s a rg um e n t l i s t , a d a ta r e fe r e n c e tha t c o u l d po t e n t i a l l y c a us e
a pag e f a u l t , a nd pag e f a u l t s a r e n o t a l l o we d above I PL 2 .

A.2

U S E O F MAP F I LE S

O n e i nd i spens a b l e to o l f o r r e ad i ng the e x e c u t i ve l i s t i ng s i s
the map
file
SYS . MAP f o und
i n d i r e c to r y SYS $ S YS T EM .
Th i s f i l e wa s p r o d uc ed
wh e n t h e e x ec u t i v e i m ag e wa s l i n k ed a nd c o n t a i n s
the
s ys t em v i r t ua l
add resses
o f a l l g l o b a l s ymbo l s i n t h e e x e c u t i v e .
Mo r e impo r ta n t l y
f r om t h e po i n t o f v i e w o f r e ad i ng t h e l i s t i ng s , i t c o n ta i n s a
c ross
r e f e r ence
l i s t i ng
of mod u l es
tha t d e f i n e a nd r e f e r e n c e e a c h g l o b a l
sym bo l .
Th e t e c h n i q ues tha t
a r e d e sc r i b ed
fo r
us i ng
th i s
f i l e a r e a l so
a pp l i c a b l e
to o th e r m a p
f i l es .
M a p f i l e s f o r d ev i c e d r i v e r s a r e
Th e m a p f i l e s
fo r
RM S
n e c e s s a r y wh en d eb ug g i ng a n ew d ev i c e d r i v e r .
a nd
DC L a r e a l s o d e sc r i b ed b ec a u se th e s e imag e s d o no t e x e c u t e i n the
u s ua l s e n s e but r a th e r a r e m a pped
i n to
s ys t em o r p r o c e s s v i r t ua l
a d d r e s s s pa c e .

A. 2 . l

Th e Exec u t i ve M a p SYS . MAP

Th e r e are two ma i n uses fo r the s ys tem m a p f i l e .
One of th e s e o c c u r s
wh e n
t h e sys tem c r a s h e s .
Th e a d d r e s s e s tha t a r e r e po r ted o n e i th e r
t h e c o n so l e t e rm i n a l o r i n t h e s ys tem d um p f i l e m u s t b e
r e l a t ed
to
r o u t i n e s i n s ys t em a d d r e s s spa c e .
Th e po r t i o n o f the m a p tha t
a c t ua l
l i s t s i n a sc e nd i ng o rd e r a l l p r og r am s e c t i o n s tha t c o n t r i b ute
to
the
exec u t i ve
is
use f u l
here .
Th e a d d r e s s i n que s t i o n i s c ompa r ed wi th
e a c h P S E C T c o n t r i b u t i o n un t i l the mod u l e tha t d e f i n e s
the
s ymbo l
is
f o und .
Th e b a s e a d d r e s s o f th i s mo d u l e i s s ub t r a c ted f r om the a d d r e s s
th a t i s b e i ng exam i n ed t o p r o d uc e a n o f f s e t i n to t h e c o r r e c t mod u l e .
Th i s o f f s e t c a n
be
used
w i t h the a s s embl e r l i s t i ng to l o c a te the
i n s t r uc t i o n or d a t a r e f e r e n c e th a t c a used the e r r o r .
Such a n e r r o r s i t ua t i o n c o u l d a r i s e a s a r e s u l t o f a b ug
i n VM S b u t
mo r e
l i k e l y i s d u e to s o m e us e r -wr i t t e n mod i f i c a t i o n t o t h e e x ec ut i v e
s u c h a s a d ev i c e d r i v e r , a c u s tom i z ed
s ys te m se r v i c e ,
or
s i mpl y a
p r o c ed u r e
th a t
i s c a l l ed t h r o ug h the Ch a ng e Mo d e to Ke r n e l o r Ch a ng e
Mo d e to E x e c u t i v e s y s t em s e r v i c e .
Th e o n l y l i m i t a t i o n to t h e u s e o f
the map
in
th i s
wa y o c c u r s wh e n a sys t em v i r t ua l a dd r e s s i s l a rg e r
t h a n t h e h ig h e s t a d d r e s s
in
the execut ive
i m ag e .
Th i s p r o b ab l y
i nd i c a t e s
th a t t h e a d d r e s s i s f o und i n a r o u t i n e t h a t i s d yn am i c a l l y
A- 1 4

U S E OF L I S T ING AND MAP F I LES
l o ad ed , s uc h as RM S ,
a
d ev i c e d r i v e r ,
or
C PU - d e pend e n t
rout i ne s .
Ta b l e E-2
l i s ts
the g l ob a l
po i n t e r s th a t
l o c a t e e a c h d ynam i c a l l y
m a pped po r t i o n o f s ys t em a d d r e s s s pa c e .
B y e x am i n i ng t h e c o n t e n t s o f
t h e s e l o c a t i o n s , t h e c ompo n e n t th a t c o n t a i n s the o f f e nd i ng add r e s s c an
b e d e t e r m i n ed .
Th e s e c o nd u s e o f SYS . MAP o c c u r s wh e n r e ad i ng p r a c t i c a l l y a n y r o u t i n e
in
the
e x ec ut i ve .
Due
to
the m o d u l a r
c o n s t r uc t i o n o f VM S , m a n y
r o u t i n e s th a t a r e r e f e r e nc ed b y t h e r o u t i n e t h a t
is
c u r r e n t l y b e i ng
l o o ked
a t a r e fo und i n some o th e r mod u l e .
Th e s i mpl e s t wa y to l o c a t e
t h e s e e x t e r n a l s ymbo l s i s to l o o k i n t h e a l ph a b e t i c a l c r o s s
r e f e r ence
map fo r
the
e x t e r n a l s ymbo l n ame .
Th e f i r s t i t em o f i n fo rma t i o n i s
t h e name o f t h e m od u l e th a t d e f i n e s th i s
s ym bo l .
Al l
mod ul e s
tha t
r e f e r e n c e th i s s ymbo l a r e l i s t ed i n s uc c e ed i ng co l umns .

A. 2. 2

RM S . MAP a nd DC L . MAP

The s ame c r o s s r e f e r e n c e c a pa b i l i t y me n t i o n ed
fo r
SYS . MAP o bv i o u s l y
a pp l i e s
t o a n y c ompo n e n t o f VM S t h a t c o n t a i n s many mod u l e s . Wh i l e
r e ad i ng a mod ul e i n DC L fo r e x ampl e , t h e r e ma y be a
r e fe rence
to
an
exte rnal
s ub r o u t i n e .
Th e mo d u l e
c o n t a i n i ng that s u b r o u t i n e can be
d e t e rm i n ed wi th the c r o s s r e fe r e n c e l i s t i ng in the map f i l e DC L . MAP .
RM S a nd the c ommand l a ng uag e i n t e r p r e t e r s p r e s e n t a s e c o nd p r o b l em
to
a nyo n e
a t t emp t i ng
to
r e l a te code o r d a ta
i n v i r t ua l m emo r y wi th
r e f e r e n c e s in an a s sembl e r l i s t i ng or i n a m a p f i l e .
Bo th i m ag e s a r e
m a pped
i n to
a
v i r t ua l
add r e s s
r a ng e th a t
i s n o t known un t i l the
m a pp i ng o c c u r s .
Th e m a p s m e a nwh i l e c o n t a i n a d d r e s s e s b eg i n n i ng at 0 .
Th e t e c h n i q ue to r e l a t e m a p add r e s s e s t o v i r t ua l m emo r y l o c a t i o n s
for
e i th e r
of
the s e
i m ag e s i s a s fo l l o ws .
De s p i te t h e f a c t th a t RM S i s
m a pped i n to s ys t em v i r t ua l ad d r e s s s pa c e a nd DC L i s m a pped
i n to
Pl
s pa c e , t h e t e c h n i que em pl oye d i n e a c h c a s e i s the s ame .
Wh e n RM S i s m a pped by SYS I N I T , t h e b a s e add r e s s o f the
RM S
i m ag e
is
s to r ed
i n g lobal
l o c a t i o n MMG $G L RM SBAS E .
( Th e c o n t e n t s o f t h i s
l o c a t i o n a r e c o p i ed t o l o c a t i o n C T L$ GL RM S BAS E i n the P l po i n t e r
pag e
by
PROC STRT wh e n a
proc ess
i s c rea t ed . )
Th e b a s e a d d r e s s o f a n y
Comma nd La ng uag e I n t e r p r e t e r i s s to r ed i n the f i r s t l o ng wo rd a t g l o b a l
l o c a t i o n C T L $AG C L IMAG E .
Be c a u s e b o th
RM S a nd DC L a r e l i n ked a s
the se
two
s ys tem i m ag e s wi th a b a s e ad d r e s s o f z e r o , t h e c o n t e n t s o f
l o c a t i o n s c a n be used a s s i mpl e o f f s e t s to r e l a t e an a d d r e s s e x t r a c ted
f r om the map to a v i r t ua l add r e s s i n a r unn i ng sys tem .
Fo r e x ampl e , i f a n e r r o r o c c u r r ed a t l o c a t i o n X i n sys t em s pa c e , a nd X
wa s l a rg e r than the c o n t e n t s o f MMG $G L RM SBAS E , d eno ted by Y , t h e n the
r e l a t i v e o f f s e t i n to the RM S i m a g e is s impl y Y
X.
( Obv i o u s l y ,
if
th i s d i f fe r ence
is
l a rg e r
than
the
s i z e o f the RM S i m a g e , then
a d d r e s s Y i s no t in RM S . )
-

To g i v e an e x amp l e tha t g o e s i n t h e o th e r d i r e c t i o n ( f r om a
r e l a t ive
a d d r e s s on an a s s em b l e r l i s t i ng to a v i r t ua l m emo r y l o c a t i o n ) , s uppo s e
t h a t w e wi s h to l o c a t e a s p e c i f i c
i n s t r uc t i o n
1 n mod ul e
DC Labc x y z ,
p a r t o f t h e DC L i m ag e .
Th e r e l a t i v e o f f s e t i n the a s s e m b l y l i s t i ng i s
a d d ed to the b a s e add r e s s o f mod u l e DC Labcxyz ( ta k e n f r om DC L . MA P )
to
f o rm the o f f s e t i n to t h e DC L i m ag e .
Th i s s um is a d d ed to t h e c o n t e n t s
o f g l o b a l l o c a t i o n C T L $ AG C L IMAG E t o fo rm t h e P l v i r t u a l
add r e s s o f
t h e i n s t r uc t i o n .

A- 1 5

USE OF LI S T I NG AND MAP F I LES

A.2. 3

Dev i c e Dr i v e r Map F i l e s

Dev i c e d r i v e r s a r e l o ad ed i n to n o n pag ed po o l b y t h e SYSGEN u t i l i t y .
Th e
S H OW /DEVI C E c omma nd t o th i s u t i l i ty d i s pl ays among o th e r p i e c e s
o f i n f o rma t i o n t h e add r e s s
r a ng e
i n t o wh i c h t h e d r i v e r
image
is
l o ad ed .
Th e s um o f t h e s ta r t i ng a d d r e s s f r om SYSGEN a nd t h e s i z e o f
t h e $ $ $ 1 0 5 PROLOGUE p r o g r am s e c t i o n f r om the d r i v e r m a p g i v e s t h e b a s e
ad d re s s
t ha t
i s u s e d to t r a n s fo rm b e twe e n a d d r e s s e s o n t h e a s semb l y
l i s t i ng and sys t em v i r t ua l a d d r e s s e s .
De bug g i ng d ev i c e d r i v e r s
is
d i sc u s s ed
i n m o r e d e ta i l
i n t h e VAX/VMS Gu i d e to Wr i t i ng a Dev i c e
Dr i ve r .

A. 2. 4

C PU-Depe n d e n t Ro u t i n e s

Th e b a s e ad d r e s s o f t h e C PU-d e pe n d e n t c od e ( Ch a pte r 2 2 ) c a n b e fo und
in
the
f o l l o w i ng
wa y .
Lo c a t i o n EXE $AL L OAVEC i s the a d d r e s s of the
f i r s t v e c to r tha t i s l o ad ed b y !N I T , t h e ma c h i ne c h e c k h a nd l e r .
Th a t
v ec t o r
c o n t a i n s a JMP i n s t r uc t i o n t o the C PU-d e pe nd en t ma c h i n e c h e c k
h a nd l e r i n nonpag ed po o l .
B e c a us e a b s o l u t e a d d r e s s i ng
is
used
wi th
the
JM P i n s t r uc t i o n , t h e c o n t e n t s o f EXE $AL L OAVE C + 2 a r e the sys t em
v i r t ua l add r e s s o f EXE $MCHK .
By s ub t r a c t i ng -t h e a d d r e s s o f EXE $MCHK
o b ta i ned
f r om t h e map f i l e ( S YS LOA7 5 0 . MAP o r SYS LOA7 8 0 . MAP ) , t h e b a s e
a d d r e s s o f the C PU -d e pend e n t i mag e i s d e t e rm i ned .

A. 2. 5

O th e r Ma p F i l e s

A l l o th e r m a p
f i l e s c a n a l so
be
used
for
the c r o s s
r e f e r en c e
I n a d d i t i o n , m o s t o th e r compo n e n t s o f
c a pa b i l i t i e s a l r e a d y men t i o n ed .
VM S e x e c u t e a s r eg u l a r i m ag e s , a nd s o n o b a s e a d d r e s s e s h a ve t o b e
u s ed
t o l o c a t e a d d r e s s e s i n v i r t ua l add r e s s s pa c e .
Th e a d d r e s s e s o n
t h e m a p c o r r espo nd t o the v i r t ua l a d d r e s s e s tha t
a re used
wh e n t h e
i m ag e e x e c u t e s .
Th e o n l y e x c e p t i o n s to th i s a r e s h a r e a b l e i m ag e s .
Howe v e r , t h e m a p f i l e f r om a n e x e c u t a b l e i m ag e t h a t i nc l ud e s a g i v e n
sha r ea b l e
i mag e c a n b e
u sed
t o d e t e rm i n e
the
base address of a
s h a r e a b l e i mag e i n a s pe c i f i c i n s ta nc e .

A. 3

T H E SYS TEM DUMP ANALY Z ER ( SDA )

Be c a u s e some o f the r o u t i n e s a nd mo s t o f the d a t a s t r uc t u r e s used
by
VAX/VMS a r e l o a d ed o r c o n s t r uc ted d y n am i c a l l y , t h e m a p f i l e i s l i m i t ed
In
i n i t s a b i l i ty to r e l a te a d d r e s s e s to d a ta s t r uc t u r e s o r r o u t i n e s .
add i t i on ,
t h e ma p f i l e c an o n l y s upp l y a d d r e s s e s o f s ta t i c d a ta
s to r ag e a r e a s i n VM S ,
and n o t
the i r conten t s .
Th e
s ys t em d ump
a na l yz e r
i s a to o l th a t o v e r c ome s t h e se l i m i t a t i o n s of the m a p f i l e s .
Th e u s e o f the s ys tem d ump a na l y z e r i s d e sc r i b ed i n the VAX/VMS Sys t em
Dump Ana l y z e r Re f e r e n c e Ma n ua l .
Th i s s e c t i o n m e n t i o n s s e v e r a l o f t h e
m a n y S DA c ommand s t h a t a r e e spec i a l l y u s e f u l
wh en s t ud y i ng h o w VM S
wo r k s .

A- 1 6

U S E OF L I STING AND MAP F I LE S
A. 3 . 1

G l o b a l Loc a t i on s

Ma n y o f t h e d yn am i c d a t a
s t r uc t u r e s ,
l o c a te d
i n pa r t s
o f s ys te m
ad d r e s s spa c e tha t a r e b e yo nd t h e l a s t a d d r e s s i n t h e e x e c u t i ve i m ag e ,
a r e l o c a t ed
th r o ugh g l o b a l
po i n te r s
in
the
s t a t i c pa r t o f t h e
e x e c ut i v e
( th e pa r t
f o und
in
the
i mag e
SYS . EXE ) .
Th e s e s t a t i c
l o c a t i o n s a r e l o ad ed wh e n t h e s t r uc t u r e s i n que s t i o n a r e c r e a t e d o r
mod i f i ed ,
e i the r
as a
pa r t o f s ys t em i n i t i a l i za t i o n o r some o th e r
l o a d i ng m e c h a n i sm .
By us i ng t h e
SHOW SYMBOLS /ALL
c ommand to S DA , n o t o n l y the a d d r e s s e s but a l so the
c ontents o f a l l
g lobal
loca t i ons
in
the
e x ec u t i v e a r e put i n t o SDA ' s o u t put f i l e .
Th i s l i s t , t og e the r w i th
t h e m a p f i l e SYS . MAP ,
enab l e s any d a t a
s t r uc t u r e
t o b e l oc a ted i n sys tem ad d r e s s s pa c e i f t h e g l ob a l name o f
the l i s t h e a d tha t l o c a t e s t h e s t r uc t u r e i s known .
Append i x B c o n ta i n s
a c ompl e t e l i s t o f t h e s t a t i c d a t a l o c a t i o n s used b y VM S .

A. 3 . 2

La yo u t o f Sys t em V i r t ua l Ad d r e s s Spa c e

A s e c ond use f u l a ppl i c a t i o n o f S DA i nvo l v e s c r e a t i ng
a
p i c ture o f
As
F i g u r e 1 - 6 s h ows , m a n y o f the p i e c e s o f
s ys tem add r e s s s pa c e .
s ys tem a d d r e s s s pa c e a r e
c o n s t r uc ted
at
i n i t i a l i za t i o n
t i me .
Th e
s i zes o f
the v a r i o u s p i e c e s
a r e d e t e r m i ned by SYS B OOT pa r a m e t e r s
( Append i x E ) .
By i s s u i ng the
SHOW PAGE_TABLE / S YS TEM
S DA c omma nd , the c o n t e n t s o f the en t i r e sys tem pa g e t a b l e a r e
l i s ted .
Th i s
l i s t i ng ,
the s ym bo l t a b l e p r o d uc ed i n the p r ev i o u s e x ampl e , a nd
the exec u t i v e m a p f i l e SYS $ S Y S T EM : SYS . MAP a l l ow a n a c c u r a t e p i c t u r e o f
s ys tem v i r t ua l add r e s s s pa c e to b e d r a wn .
I n f a c t , t h i s t ec hn i qu e wa s
used to g e ne r a t e F i g u r e 1 - 6 , F i g u r e E - 1 , a nd Ta bl e E - 2 .

A. 3 . 3

L a yo u t o f P l S p a c e

S DA c a n a l s o b e used to o b t a i n the l a yo ut o f P l s pa c e .
Mo s t
of
the
pi eces
of
Pl
s pa c e
( F i g u r e 1 - 7 , Tab l e E - 4 ) a r e f i x ed s i z ed p i e c e s .
Th e Pl pag e ta b l e s d e f i n ed i n mod u l e S H E LL d e te rm i n e
the
s i ze s o f
the s e p i e c e s .
Oth e r p i e c e s m a y n o t even ex i s t fo r some p r o c e s s e s .
In
a n y c a se , the S DA c omm a nd
S HOW PROC ESS/PAG E_TAB L E S
p r o d uc e s a c ompl e t e l a yo u t o f P l s pa c e .
g e n e r a t e F i g u r e 1-7 a nd Ta b l e E - 4 .

A. 4

Th i s t e c h n i q ue

wa s

used

INTERPRET ING MDL F I L E S

Th e r e a r e v e r y many d a t a s t r uc t u r e s a nd o th e r
sys t em wi d e c o n s t a n t s
u s e d by t h e exec ut i v e a nd o th e r sys tem componen ts .
Th e s e s t r uc t u r e s
a r e d e f i n ed wi th a s pe c i a l s t r uc t u r e d e f i n i t i o n l a ng uag e c a l l ed
MDL .
Th i s
l a ng uag e a l l ows d a t a
s t r uc t u r e s
to
be d e f i n ed f r om a s i ng l e
so u r c e b u t used i n e i t he r VAX- 1 1 MACRO o r B L I S S - 3 2 .
A- 1 7

U S E OF L I S T ING AND MAP F I LE S
Wh e n a VM S s ys tem i s b u i l t f r om so u r c e , a p r e p r o c e s s i ng p r o g r am c a l l ed
MDL
r e ad s a l l
s y s t em d a ta s t r uc t u r e d e f i n i t i o n s ( f r om the t wo f i l e s
[ E XEC . S RC ] S YS DE F . MD L a nd
[ VM S L I B . SRC ] S TARDE F . MDL )
a nd
p ro d u c e s
two
o ut p u t
f i l e s fo r each i nput f i l e .
One o f t h e s e o u t p u t f i l e s c o n t a i n s
mac r o d e f i n i t i o n s f o r u s e b y VAX - 1 1 MACRO .
Th e o th e r o u t p u t
file
is
used b y t h e B L I S S c om p i l e r t o p r od uc e B L I S S m a c r o d e f i n i t i o n s .
Th i s
s ec t i o n i s no t a n e x h a u s t i v e d i sc u s s i o n o f e v e r y MDL d i r e c t i ve .
Ra t he r ,
i t a t t em p t s
to
show how t h e MDL d e s c r i p t i o n o f a d a t a
s t r uc t u r e c an b e r e l a ted to e i th e r a p i c t u r e o f the s t r uc t u r e o r
the
r e s u l t i ng VAX- 1 1 MACRO o r B L I S S - 3 2 d e f i n i t i o n s .

A. 4 . 1

S ampl e S t r uc tu r e De f i n i t i o n s

Th e s i m p l e s t wa y t o i l l u s t r a t e t h e wa y t h a t a s t r uc t u r e i s d e f i ne d
is
to
l o o k a t t h e r e s u l t a n t symbo l d e f i n i t i o n s .
One wa y t o a c c ompl i sh
t h i s i s to c ompa r e the MDL d e f i n i t i o n o f a g i ven s t r uc t u r e w i th
the
r e s u l ta n t VAX- 1 1 MACRO o r
B L I S S - 3 2 s ym bo l s .
Th e s e s ym bo l s can be
fo und
in
a ny l i s t i ng
tha t
uses
the
s t r uc t u r e
in
q ue s t i o n .
A l t e r na t i ve l y ,
t h e c omma nd p r o c ed u r e l i s t ed i n the b eg i n n i ng o f th i s
a ppend i x c a n b e u s ed .
Th e r e a r e th r e e t ab l e s l i s ted h e r e to show the r e s u l t s o f
s i m p l e MDL
d i r ec t i ves .
Ind i v i d ua l
MDL c omma nd s
a r e b r i e f l y d e sc r i b ed in the
fo l l o w i ng s e c t i o n s .
Tab l e A - 1 shows the r e s u l t of
the c ompl e t e MDL
d e f i n i t i on
of
the
l og i c a l
n ame
bloc k
( p i c t u r ed
in F i g u r e 2 6 - 2 ) .
No t i c e
tha t
the
s t r uc t u r e h a s a
v a r i ab l e
l eng th .
Th e
s ymbo l
LOG$K L ENGTH o n l y
r e p � e s e n t s the l eng t h o f the f i x ed s i z e po r t i o n o f
t h e s t r uc t u r e , e x c l ud i ng t h e s to r ag e a r e a s fo r the
l og i c a l
name a nd
equ i v a l e n c e name c o un ted s t r i ng s .
Ta b l e A- 2 i l l u s t r a t e s the s ev e r a l
uses o f
the
S d i r e c t i ve ,
us i ng
ex c e r p t s
f r om
the d e f i n i t i ons
fo r the PC B ( Ta b l e D- 2 ) , the p r o c e s s
head e r
( Ta b l e D- 3 ) ,
a nd
the
t i m e r q ue ue e l emen t
( Fi g u r e 1 0-1 ) .
Ta b l e A- 3
i l l us t r a t e s
the
even t ua l
r e s u l ts o f u s i ng MDL t o d e f i n e
v a r i a b l e l eng th b i t f i e l d s .
Th e AST c o n t r o l
block
i s p i c t u r ed
in
Figure 5 -l .
Th e s pe c i f i c f i e l d s wi t h i n a v i r t ua l add r e s s a r e p i c t u r ed
i n F i g u r e 1 2 -1 .

A. 4 . 2

Common l y U s ed MDL Comm a nd s

Th i s s e c t i o n d e sc r i b e s the MDL d i r e c t i v e s c ommo n l y u s ed
i n d e f i n i ng
s t r uc t u r e s
used by VMS .
Emph a s i s i s o n r e ad i ng the MDL f i l e s used by
Ra th e r ,
the
VM S .
A c ompl e t e s yn ta x of each c omma nd is
not g i v e n .
f e a t u r e s of e a c h d i r ec t i v e tha t a r e used b y VMS a r e emph a s i zed .

A. 4 . 2. 1
$ STRUCT D i r ec t i v e - E a c h s t r uc t u r e d e f i n i t i o n b eg i n s
wi th a
$ S TRUC T s t a teme n t .
Th i s
s t a t eme n t d e f i n e s t h e p r e f i x c h a r a c t e r s i n
e a c h s ymbo l d e f i n i t i o n .
Fo r e x ampl e ,
$ S TRUCT PC B
d e f i ne s the PC B s t r uc t u r e , wh e r e e a c h s ym bo l d e f i n i t i o n b eg i ns wi t h
t h e c ha r a c t e r s
PCB .
In
t h e d e fa u l t
c a s e ( us e d by VMS ) , the n e x t
c h a r a c t e r i n e a c h r e s u l t a n t s ym bo l name i s the c u r r en c y s ymbo l
($) .
Co n s t a n t d e f i n i t i o n s c a n h a v e a n u nd e r s c o r e ( ) , a C , o r a K a s t h e
F i e l d d e f i n i t i o n s h a v e a cha r a c t er ( B , W , L, o r Q )
n e x t c ha r a c t e r ( s ) .
tha t
r ep r esents
the
s i ze o f t h e f i e l d .
Th e n am i ng conven t i o n s t h a t
MDL s ymbo l s a d h e r e to a r e l i s te d i n App e nd i x c .
A- 1 8

Tab l e A- 1
MDL D e s c r iption and Re sul tant Symbo l D e f in iti ons for Log i c a l Name B lo ck

MDL D i r ec t i v e

M e a n i ng o f D i r ec t i v e

Re s u l t a n t
Sym bo l Nam e

$ S TR UC T LOG

B eg i n LOG s t r uc t u r e
defini tion
Lo ng wo r d f i e l d
Lo ng wo rd f i e l d
Wo r d F i e l d
Byt e f i e l d
By t e f i e l d
Wo rd F i e l d
Byt e f i e l d
S k i p o n e s pa r e b yt e

LOG $ L L T F L
LOG $ L L T B L
LOG $W S I Z E
LOG $B TYPE
LOG $ 8 T.AB LE
LOG $W G R OU P
LOG $ B=.AM OD
none

F
F
F
F
F
F
F
F

L TF L , L
L TB L , L
S IZ E , W
T Y PE , B
T.AB LE , B
G R OU P , W
.AM OD , B
,B

F
L

M B XUC B , L
L E NGTH

Sym b o l Va l ue
( d ec i m a l )

0
4

10
11
12
14

E f f e c t o n I n t e r na l
Co un t e r Va l ue

I n c r e a se b y 4
I nc r e a se b y 4
I n c r ea s e b y 2
I nc r e a s e b y 1
I n c r e a se b y 1
I n c r e a se b y 2
I n c r e a se b y 1
Inc r e a s e b y 1
( ev en tho ug h no
s ym b o l d e f i n ed )
I n c r e a se b y 4
none
none
n o n e ( bec a us e s i ze
i s ze r o )

N.AM E , T , O

Lo ng wo rd f i e l d
De f i n e s t r uc t u r e l eng th
t o t h i s po i n t
A t e x t s t r i ng b eg i n s h e r e

LOG $ L MBXU C B
LOG $C L ENGT H
LOG $ K L E NGTH
LOG $ T=N.AME

16
20
20
20

c
c
c

S Y S TEM , O
GR O U P , l
PR OC ES S , 2

D e f i n e a c on s t a n t
D e f i n e a c on s t a n t
D e f i n e a c on s t a n t

0
1
2

none
n o ne
none

N.AM LENGT H , 6 4

LOG $C S YS TEM
LOG $C G R OU P
LOG $ C=P R OC E S S

D e f i n e a c o n s ta n t

LOG $C_N.AM LENGTH

none

Te rm i n a t e s t r uc t u r e
definition

USE OF LIST ING AND MAP FI LES

Tab l e A- 2
Examp l e s of the S D i rect ive

Resul tant
Symbol Name

Symbol Val ue
(dec imal )

Ef fect on Internal
Coun ter Val ue

PCB$L ARB
PCB$L-U IC
PCB$W=MEM

1 32
136
136

PCB$W_GRP

1 38

PCB$C LENGTH
PCB$K=LENGTH

140
140

Increase by 4
Inc rease by 4
none ( se t subfi eld
counter to 2 )
none ( se t subfield
counter to 4 )
none

Longwo rd Field
Byte Subfi eld
wi th o r i g i n o f 3
Longwo rd Field

PHD$L PAGFIL
PHD$B=PAGF IL

28
31

Increa se by 4
none

PHD$L_PSTBASOFF

Inc rease by 4

Longwo rd Field
Byte Sub f i eld
wi th o r i g i n o f 3
Longwo rd Field

PHD$L P OLRASTL
PHD$B=ASTLVL

200
203

Inc rease by 4
none

PHD$L_P 1BR

204

Inc rease by 4

TQE$L PID
TQE$L-FPC
TQE$L-AST
TQE $L-FR3
TQE$L-ASTPRM
TQE $L-FR4
TQE$Q=T IME

12
12
16
16
20
20
24

Inc rease by 4
none
Increase by 4
none
Increase by 4
none
Inc rease by 8

MDL Di recti ve

Mean ing of Di rec tive

$STRUCT PCB

Beg in De f i n it ion o f
PCB Struc ture

.
.

ARB , L
UIC , L
MEM , O , W

GRP, 2 , W

LENGTH

F
F

Longwo rd Fi eld
Longwo rd Fi eld
Wo rd Subfi eld
wi th o r i g i n o f 0
Word Sub f i eld
wi th o r i g i n o f 2
De f ine Length o f PCB

Terminate PCB De f i n i t ion

$STRUCT PHD

Beg in Def i n i t ion
of PHD Struc ture

PAGF I L , L
PAGF I L , 3 , B
PSTBASOFF, L

POLRASTL
ASTLVL , 3 , B

P lBR, L

Terminate PHD De f i n i tion

$STRUCT TQE

Beg in De f i n i t ion
of TQE Struc tur e

PID, L
FPC , , L
AST, L
FR3 , , L
ASTPRM , L
FR4 , , L
TIME , Q

F
s

F
E

Longwo rd Fi eld
Sub f i eld wi th same val ue
Longwo rd Fi eld
Sub f i eld wi th same val ue
Longwo rd Field
Sub f i eld wi th same val ue
Quad wo rd Fi eld
Terminate TOE De f i n i tion

A- 2 0

Table A- 3
S amp l e Var i ab l e Length B i t F i e l d Def initions

MDL Di r ec t i v e

Mean i ng of Di r ec t iv e

$S TRUCT ACB

Beg i n De f i n i t i o n o f ACB S t r uc tu r e

Byte F i e l d
Beg i n Bi t F i e l d De f i n i t ions
B i t Field o f S i ze 2 and Or ig i n 0

RMOD , B
V<
M ODE , 2
,4
QUOTA , , , M
KAST

PID, L

S k i p 4 Spa r e B i ts
S i ng l e B i t F i e l d wi th Ma s k De f i n i t i o n
S i ng l e Bi t F i e l d
E n d Bi t F i e l d De f i n i t i o n s
Longwo rd F i e l d

Te rm i nate ACB De f i n i t i o n

$STRUC T VA

Beg i n VA B i t F i e l d De f i n i t i ons

v <

BYTE , 9 , , M

Beg i n Bi t F i e l d De f i n i t i o ns
B i t Fi e l d o f S i ze 9 and Or ig i n 0

VPN , 2l , , M

B i t F i e l d of S i ze 2 1 and Or ig i n 9

Pl, , ,M

S i ng l e Bi t Fi e l d at Bi t 3 0

S YS TEM , , , M

S i ng l e B i t Fi e l d a t Bi t 3 1

>
v <

,9
VPG , 2 3 , , M

End Bi t F i e l d De f i n i t i ons
Beg i n New Se t of B i t Fi e l d De f i n i t i o n s
Sk i p o v e r t h e F i r s t N i n e B i ts
B i t Field of s i ze 23 a nd Or ig i n 9
End Second Set o f Bi t De f i n i t i o n s
Te r m i n a te VA De f i n i t i o n

Resul tant
Symbol Names

Symbol Va l ue
{ d ec imal }

ACB $B_RMOD

ACB $V MODE
ACB $S=MODE

0
2

ACB $V QUOTA
ACB$M-QUOTA
ACB $V=KAST

6
0 0 0 0 0 0 4 0 {hex }
7

ACB $L_PI D

VA$V BYTE
VA$S-BYTE
VA$M-BYTE
VA$V-VPN
VA$S-VPN
VA$M-PFN
VA$V-P l
VA$M-P 1
VA$V-SYSTEM
VA$M=SYSTEM

0
9
O O O OO lF F
9
21
3FFF F E O O
30
40000000
31
80000000

VA$V VPG
VA$S-VPG
VA$M=VPG

9
23
FFFFF E O O (hex }

{ hex }
{hex }
{hex }
( hex }

In t e r nal Bi t Co un ter
{ be fo re }
{ a f te r }

2
6

6
7

beyo nd l im i t

U S E OF L I S T ING AND MAP F I LE S
A . 4 . 2 . 2 F D i r ec t i ve - F i e l d s i n a d a t a s t r uc t u r e a r e d e f i n ed w i t h the
F
d i r ec t i ve .
Th e
n am e
of
e a c h f i e l d is the f i r s t a rg um e n t of the
f i e l d d e f i n i t i o n a nd f o rm s the b a l a n c e of a s ym bo l name .
Th e v a l ue o f
the
s ymbo l
name
i s s e t e qua l to a n i n t e r n a l c o un t e r .
As e a c h f i e l d
d e f i n i t i o n i s p r o c e s s ed , t h e i n t e r n a l c o un t e r va l ue
is
i nc r e a s ed b y
t h e s i ze o f t h e f i e l d ( 1 , 2 , 4 , o r 8 ) .
Th e d e fa u l t s i ze o f a f i e l d i s
f o u r , r ep r e s e n t i ng a l o ng wo rd .
Th i s d e fa u l t c a n b e ov e r r i d d en b y
i nc l ud i ng a s ec o nd p a r ame t e r to the F d i r ec t i ve .
Leg a l c h a r a c t e r s a r e
B , W , L , Q , a nd T .
Th e f i r s t f o u r po ss i b i l i t i e s c o r r e spo nd
to
the
l og i c a l or i n teg e r VAX- 1 1 d a t a t ype s .
Th e T a rg um e n t i nd i c a t e s a t e x t
s t r i ng , wh o s e s i ze a ppe a r s a s t h e th i r d a rg um e n t .
( A c o un t
( th i rd )
a rg umen t
f o r a ny
f i e l d t ype i nc r e a s e s th e i n t e r n a l po i n t e r v a l ue b y
t h e s i ze o f t h e f i e l d m u l t i pl i ed b y t h e c o un t . )

A . 4 . 2 . 3 L D i r ec t i ve - Th e L d i r ec t i v e i s used to c r e a t e a l ab e l a t a
spec i f i ed
po i n t
in a
d a ta
s t r uc t u r e .
VMS u s e s the L d i r e c t i v e to
d e f i n e the l eng th o f a s t r uc t u r e b y g i v i ng
the
r e s u l t a n t n am e
the
s u f f i x LENGTH .

A . 4 . 2 . 4 E D i r ec t i ve - Th e s t r uc t u r e d e f i n i t i o n i s t e rm i n a ted wi th
E d i r ec t i ve .

A. 4 . 2. 5
S D i r ec t i ve - I t i s o f t e n d e s i r ab l e
to g i v e a
f i eld
two
n am e s .
I n add i t i o n ,
s ub f i e l d s wi th i n
a f i e l d o f t e n ex i s t .
Th e S
d i r ec t i ve d e f i n e s a s ym bo l w i th the i nd i c a t ed name a nd a v a l ue d e r i v ed
f r om
the
i n te r na l
po i n t e r
wh en the c u r r e n t F d i r ec t i v e wa s i s s ued .
Th e s e c o nd a rg umen t i nd i c a t e s how f a r
i n to
the c u r r e n t
f i eld
the
s ub f i e l d
ex i s t s .
Th e
th i r d
a rg umen t
i nd i c a t e s
the
s i ze
of the
s ub f i e l d .
Fo r e x ampl e , t h e fo l l o w i ng l i n e s
f r om
the
PC B s t r uc t u r e
d e f i n i t i on
F
S
S

UIC , L
MEM , O , W
GR P , O , W

r e s u l t i n a symbo l PCB $W MEM th a t h a s the s am e v a l ue a s PC B $ L U I C
and
a
s ec o n d
s ymbo l
PC B $W-GRP t h a t
is
two
l a rg e r th a n the oth e r two
s ym bo l s .
Ta b l e A-2 shows s ev e r a l ex ampl e s o f the s d i r e c t i v e .

A . 4 . 2 . 6 C D i r ec t i ve - Th e C d i r ec t i v e a l l o ws a c o n s t a n t o r a
se r i es
of cons tan t s t o
b e d e f i ned .
Depend i ng o n wh a t o th e r pa r am e t e r s a r e
s uppl i ed , t h e C d i r ec t i v e prod uc e s symbo l s o f t h e
f o rm x y z $C n am e ,
x y z $K name ,
o r x y z $ name .
Th e e x amp l e i n Ta b l e A- 1 i l l us t r a tes o ne
u s e o f t h e c d i r ec t i ve .
Th e r e a r e s eve r a l o th e r ex ampl e s o f cons t a n t
d e f in i t i ons
in
e i th e r
SYS DE F . MD L o r
STARDE F . MDL ,
such as
the
d e f i n i t i o n s of t h e DYN $ symbo l s th a t d e sc r i b e d yn am i c a l l y a l l o c a ted
s t r uc t u r e s o r the J P I $ s ymbo l s , t h e c od e s t h a t d e sc r i b e a n i n f o rm a t i o n
l i s t to the $G E TJ P I s y s t em s e r v i c e .

A- 2 2

U S E OF L I ST ING AND MAP F I LE S

A . 4 . 2 . 7 M a nd P D i r e c t i v e s - Th e M a nd P d i r e c t i v e s a r e u s ed tog e th e r
to
al low the
s am e
f i el d s
i n a d a ta
s t r uc t u r e to have d i f f e r e n t
d e f i n i t i o n s d epend i ng o n t h e c o n t e x t i n wh i ch t h e y a r e u s ed .
Fo r
e x am pl e ,
the
UCB d e f i n i t i o n c o n t a i n s f i e l d d e f i n i t i o n s a t the e n d o f
t h e s t r uc t u r e tha t d e pend o n the d ev i c e tha t i s d e sc r i b ed b y a g i v e n
UC B .
Th e M d i r ec t i v e
( fo l l owed
by a
n ume r i c
a rg um en t ) ma r k s a
s pe c i f i c po s i t i o n ( i n t e r n a l byte c o un t e r va l ue ) i n t h e s t r uc t u r e .
Th e
P d i r ec t i v e ( fo l l owe d by a n um e r i c a rg umen t ) r e s to r e s the v a l ue o f t h e
i n t e rna l c o un t e r to t h e v a l ue
a s s o c i a t ed
wi th
tha t n umbe r e d ma r k
po s i t i o n .

A. 4 . 3

B i t F i e l d De f i n i t i o n s - Th e V D i r ec t i ve

B i t f i e l d s r e qu i r e two n um b e r s to
c ompl e te l y d e sc r i b e t h em ,
a
bit
po s i t i o n a nd a s i z e .
MDL a l wa ys d e f i ne s a b i t po s i t i o n ( i nd i c a t ed b y
a V
i n t h e s ym bo l nam e ) .
Th e s i z e o f a f i e l d ( i nd i c a ted b y S
in the
s ymbo l
n am e )
i s a l wa ys d e f i ned wh e n t h e f i e l d s i z e i s d i f f e r en t f r om
I t i s o f t e n c o n v e n i e n t to d e f i n e a ma s k s ymbo l ( i nd i c a t ed b y M
one .
in
the s ym bo l n ame ) t h a t h a s o ne s i n e a c h b i t po s i t i o n d e f i n ed b y t he
b i t f i e l d a nd
zeros
e l s e wh e r e .
MDL d e f i n es
s uc h s ymbo l s
i f so
r e q u e s ted .
Bec a use th i s s e c t i o n i s n o t t r y i ng to e x pl a i n the e n t i r e
MDL
s yn t a x
but
r a th e r
s h o w wh a t sym bo l s r e s u l t f r om a g i v en M D L d e f i n i t i o n , t h e
s i mpl e s t wa y t o d e sc r i b e t h e b i t f i e l d s yn t a x i s w i th s o m e e x am p l e s .
Ta b l e A-3 i nc l ud e s MDL d i r e c t i v e s ex t r a c ted f r om t h e d e f i n i t i o n o f t h e
AST C o n t r o l B l o c k ( AC B ) t h a t i s p i c t u r ed
in
Figure 5-l .
No t e
tha t
o n l y the q uo t a
f i e l d h a s a ma s k s ymbo l d e f i n ed .
Ta b l e A-3 a l so
c o n t a i n s t h e MDL d e sc r i pt i o n o f
the b i t
f i e l d s w i th i n a v i r t ua l
( Fi g u r e 1 2-1 ) .
Th e d e f i n i t i o n s o f t h e PS L b i t f i e l d s a nd t h e
add r e s s
S T S b i t f i e l d s ( bo th l o c a t e d
in
STARDE F . MD L )
a r e m o r e c ompl i c a t e d
i l l us t r a t i o n s o f the s yn t a x tha t t h e s e e x am p l e s d e sc r i b e .

A- 2 3

APPENDI X B
EXECUT IVE DATA AREAS

Th e wr i t ab l e
execut ive cons i s ts
of
seve r a l d yn am i c a l l y a l l o c a t e d
t a b l e s a s we l l a s s t a t i c a l l y a l l o c a ted d a t a s t r uc t u r e s t h a t a r e a pa r t
o f the e x e c u t i v e imag e SYS . EXE .
Th i s a ppend i x s umma r i z e s a l l o f t h e s e
d a t a a r e a s , w i th a n emph a s i s o n t h e s t a t i c e x e c u t i v e d a t a b a s e th a t i s
r e l a t ed to o th e r m a t e r i a l i n th i s m a n ua l .
Th e
i n fo rm a t i o n
p r e s e n t ed
in th i s
a ppend i x wa s a c c um u l a t ed
by
i n co r po r a t i ng
data
f r om
t h e sys tem m a p ( S YS . MAP ) wi th c o n te n t s o f
s pe c i f i c s o u r c e mod ul e s .
I n fo rma t i o n o u t s i d e th e sc o pe o f t h i s m a n u a l
Th e r e
i s no a t tempt to i nc l ud e ev e r y g l o b a l
is
s i mpl y s umma r i z ed .
symbo l i n SYS . E XE i n th i s a ppend i x .
Da t a b l o c k s ( s uch a s un i t c o n t r o l
blocks or
t im e r queue
e l em e n t s ) a r e r e f e r e nced as s i ng l e en t i t i e s .
G l o b a l l a b e l s wi th i n
such
s t r uc t ur es
are
i g no r ed .
Global
l abe l s
a s so c i a t ed w i th b a c kwa rd l i n k po i n t e r s o f d o ub l y l i nked l i s t s a r e a l so
om i t ted .
Nam e s th a t a ppe a r i n t h e
" G l o b a l Symbo l "
co l umn
in
l o we r
c a se
r epresent
local
s ymbo l s ,
n ame s
th a t a r e o n l y u s e d w i th i n t h e
m o d u l e i n wh i c h t h e y a r e d e f i n ed .

B. l

STAT I CALLY AL LOCATED EXECUT IVE DATA

Th e c e l l s t h a t c o n t a i n the d a ta d e sc r i b ed
i n th i s s e c t i o n
can be
i d e n t i f i ed wi th s p e c i f i c s o u r c e m o d u l e s i n t h e e x ec u t i v e .
Th o s e c e l l s
t h a t c a n b e a d d r e s s ed d i r e c t l y wi t h a g l o b a l name a r e
so
i nd i c a t ed .
P r og r am s e c t i o n
nam e s
( . PS EC T n ame s )
a r e i n c l ud ed i n e a c h s e c t i o n
t i t l e t o a l l o w e a sy l o c a t i o n o f a g i v e n d a t a a r e a .
P r o g r am
sec t ions
of
zero
l e ng th d e c l a r ed
i n mod u l e MDAT f o r t h e pu r po se o f d e f i n i ng
g l o b a l l a b e l s th a t s e p a r a t e m a j o r s e c t i o n s o f SYS . E XE a r e no t i n c l ud ed
he re .
Th e y a r e l i s t ed . i n Ta b l e E - 2 a n d c a n a l s o be fo und by e x am i n i ng
SYS . MAP .

B.l. l

Sys t em Se r v i c e Ve c to r Ar e a

($$$000)

Th e f i r s t th r e e pag e s o f s y s tem v i r t ua l
add ress
spa c e c o n t a i n
the
sys t em
s e rv i c e v e c t o r s .
Th e s e p ag e s a r e r e ad o n l y .
Th e g l o b a l l ab e l
MMG $A ENDVE C , d e f i n ed i n mod ul e MOAT , r e pr e s e n t s t h e h i g h -ad d r e s s
end
o f the sys t em se rv i c e v e c to r pag e s .

B-1

EXECUTIVE DATA AREAS

Pi l e System Pe r fo rmance Mo n i to r Da ta ( $ $ $ 0 0 0 PMS )

B.l.2

Th i s a r e a c o n s i s t s o f two b l o c ks , e a ch 7 0 l o ng wo r d s l o ng , t o d e sc r i b e
t h e c um u l a t i v e b e h a v i o r
of
t h e f i l e ACPs s e rv i c i ng bo th S t r uc t u r e
Lev e l 1 a nd S t r uc t u r e Lev e l 2 .
G l o b a l Symbo l

Modul e

S i ze

De s c r i p t i o n o f D a t a

PMS $G L F C P

PMSDAT

7 0 l o ngwo r d s

PMS $G L F C P 2

PM S DA T

7 0 l o ng wo r d s

F i l e s y s t em s t a t i s t i c s
L ev e l 1 AC P .
F i l e sys t em s ta t i s t i c s
L ev e l 2 ACP

B.l.3

M i sc e l l aneous Bug c h e c k I n fo rma t i on

Mod u l e B UGC HECK ma i n t a i n s two l o ng wo r d s
p r og r e s s .
G l o b a l Symb o l

Mod u l e

f a t a l_s psav

B UGC HECK

l o ng wo r d

E XE $G L B UGCHECK

B UG C H E C K

l o ng wo r d

B.l.4

S i ze

for
for

($$$025)

about

fatal

b ug chec k

De s c r i p t i o n o f Da t a
Fa t a l b ug ch e c k
i n p r og r e s s
s ta c k po i n t e r
Saved f a ta l b ug ch e c k c o d e

D a t a St r uc t u r e s fo r Dr i ve r s L i nked wi th VMS

($$$100 )

Mod u l e DEV I C EDAT c o n ta i n s d a t a s t r uc t u r e s fo r
the d ev i c e s
th a t a r e
Th e s e d ev i c e s a r e
l i n k ed a s a pa r t of the e x e c u t i v e imag e SYS . E XE .
•

the n ul l d ev i c e ,

•

a ma i l bo x , a nd

•

the c onso l e t e rm i n a l .
Th e d a ta s t r uc t u r e s
fo r d ev i c e O PA O
are
a s s emb l ed
i n to
VAX/VM S .
Th e t e rm i n a l d r i v e r i ts e l f
( TTDR I VE R . EXE ) i s l o aded by I N I T .

Th e r e a r e un i t c o n t r o l
blocks
fo r
th r e e m a i l bo x e s s e t a s i d e i n
DEV I C E DAT .
Un i t c o n t r o l b l o c k ze r o i s a s k e l e to n UC B tha t i s c o p i ed
i n to a n y o th e r UCB wh e n a ma i l bo x i s c r e a t ed .
Th e Job Co n t r o l l e r ' s
m a i l bo x a nd O PC OM ' s ma i l bo x a l s o u s e p r e a l l o c a t e d UCBs .
S i ze

G l oba l Symbo l

Mod u l e

I OC $G L D EVL I S T

DEV I C EDAT

l o ng wo r d

I OC $G L ADPL I S T

DEVI C E DAT

l o ng wo r d

I OC $G L_D PTL I S T

DEV I C EDAT

q uadwo r d

SYS $G L_B OOTDDB

DEV I C EDAT

5 2 byt e s

SYS $G L_B OOTUCB

DEVI C E DAT

2 0 4 byt e s

B-2

De s c r i p t i o n o f Da t a
L i s th e a d o f DDBs o f a l l
d ev i c e s i n the sys t em
L i s th e a d o f a l l Ad apte r
Con t ro l Blocks
L i s th e a d o f D r i v e r Pro l og u e
Tabl es
Dev i c e Da t a B l o c k fo r sys t em
d i sk
Un i t Co n t r o l B l o c k f o r
s y s t em d i s k ( 2 2 e x t r a
l o ngwo rd s )

EXECUT IVE DATA AREAS

G l o b a l Sym bo l

Mo d u l e

O PA $G L_DDB

DEV I C EDAT

5 2 by t e s

O PA $ U C B O

DEV I C E DAT

2 1 2 bytes

TTY$G L_G E TNXT C H

DEVI C EDA T

l o ngwo r d

TTY $G L P UTNXTC H

DEVI C EDAT

l o ng wo r d

TTY$G L U C B S E T U P

DEVI C EDAT

l o ng wo r d

O PA $ CRB

DEVI C EDAT

6 8 bytes

opa$ idb

DEVI C E DAT

3 2 byt e s

MB $G L DDB

DEVI C EDAT

5 2 byt e s

MB $ UC B O

DEVI C EDAT

1 1 6 bytes

SYS $G L J OBC TLMB

DEV I C EDAT

1 1 6 bytes

S Y S $G L_O PRMBX

DEVI C EDAT

1 1 6 byte s

N L $G L D DB

DEVI C E DA T

52 bytes

NL$GL UCBO

DEVI C EDAT

1 1 6 bytes

NET$WC B

DEV I C EDA T

3 6 by t e s

s ys_c r b

DEVI C E DAT

5 6 bytes

B.l . 5

Dr i v e r P r o l og ue Tab l e s

S i ze

De s c r i p t i o n o f Da t a
Dev i c e Da t a B l o c k f o r
c o n so l e t e rm i n a l
Un i t C o n t r o l B l o c k f o r
c o n so l e t e rm i n a l { 2 4
e x t r a l o ng wo r d s )
Ad d r e s s wi th i n t e rm i n a l
d r i v e r o f r o u t i n e t o r e ad
the next cha r a c t e r
Ad d r e s s wi t h i n t e r m i n a l
d r i v e r o f r o u t i n e to
wr i t e the n e x t c h a r a c t e r
Ad d r e s s wi t h i n t e rm i n a l
d r iver o f r o ut i ne t o s e t
u p UCB
Ch a nne l Re que s t B l o c k f o r
c o nso l e d ev i c e
I n t e r r up t D i spa tch B l o c k f o r
c o n so l e d ev i c e
Dev i c e Da t a B l o c k fo r
ma i l bo x
Un i t Co n t r o l B l o c k Temp l a t e
u s ed i n ma i l bo x c r e a t i o n
( Th i s UC B i s no t l i n k e d
i n to ma i l bo x DDB ' s UCB
1 ist)
Un i t Con t r o l B l o c k f o r J o b
Co n t r o l l e r ' s Ma i l b o x
{ Un i t 1 )
Un i t Co n t r o l B l o c k f o r
Ope r a to r ' s Ma i l bo x
( Un i t 2 )
Dev i c e Da t a B l o c k f o r n u l l
d ev i c e
Un i t Co n t r o l B l o c k f o r n u l l
d ev i c e
Wi ndow Con t r o l B l o c k f o r
n e two r k ps e ud o d ev i c e
Ch a nn e l Re que s t B l o c k f o r
ma i l bo x d ev i c e s

( $ $ $ 1 0 5 PROLOGUE )
_

Th e d r i v e r p r o l og ue t a b l e s fo r th e s e d r i v e r s a r e
a l so
a s s em b l ed
a nd
l i nked
i n to
the
ex e c u t i v e i m ag e .
Th e c o n t r i b u t i o n s to th i s pa r t o f
t h e wr i ta b l e e x ec u t i ve c om e f r om t h e th r e e d r i ve r mod u l e s
{ MB DR I VE R ,
NLDR I VE R , a nd C ON I NTDS P ) th a t a r e l i n k ed wi th SYS . EXE .
G l o b a l Symbo l

Mo d u l e

MB$DPT

MBDR IVE R

40 bytes

NL$ DPT

N LDR I VE R

4 0 bytes

O P $DPT

C ON INTDS P

4 0 bytes

S i ze

B-3

D e s c r i pt i o n o f Da t a
D r i ve r P r o l og ue Ta b l e f o r
ma i l bo x d r i v e r
D r i ve r P r o l og ue Ta b l e f o r
n u l l d ev i c e d r i v e r
D r i v e r P r o l og ue Ta b l e f o r
c o nso l e t e rm i n a l d ev i c e
d r iver

EXECUT IVE DATA AREAS
8.1.6

L i n k e d Dr i ve r Co d e ( $ $ $ 1 1 5_DRIVE R )

Th e r e i s a r e ad o n l y s e c t i o n ( 5 pag e s l o ng ) th a t c o n t a i n s
the d r i v e r
code
fo r
t h e s e d r i v e r s as we l l as c od e fo r t h e MA7 8 0 s h a r ed m emo r y ,
t h e DR7 8 0 i n t e r f a c e , a n d
i n te r r up t d i spa tc h c o d e
fo r
the MASS8US
l abe l s
a d a pt e r .
Th i s
sec t i o n
i s b o un d ed b y t h e two g l o b a l
MMG $AL_8 EGDR I VE a nd MMG $ A L_ENDDRIVE , d e f i n ed i n mod u l e MOAT .

8. 1 . 7

M em o r y Ma nag eme n t Da t a

($$$210)

Th e m emo r y m a n ag em e n t d a ta c o n s i s t s
dyn am i c a l l y a l l o c a ted s t r uc t u r e s .

ma i nl y

S i ze

l i s th e a d s

fo r

De sc r i p t i o n o f Da t a

G l o b a l Symbo l

Mod u l e

PFN$AW H EAD

A L LOC PFN

6 wo r d s

p f n $ a l_co un t

AL LOC PFN

3 l o ngwo r d s

PFN$G L PHYPGCNT

A L LOC PFN

l o ng wo r d

PFN$AL H I L I M I T

A L LOC PFN

3 l o ngwo r d s

PFN $AL_LOL IM I T

A L LOC PFN

3 l o ngwo r d s

S C H $G L MFYL IMSV

A L LOC PFN

l o ngwo rd

S C H $G L MFYLOSV

ALLOC PFN

l o ng wo rd

PAG E FAU LT

1 5 l o ngwo r d s

Pa g e f a u l t s t a t i s t i c s fo r
D I S PLAY

M PW$AL PTE

WRTM FY PAG

l o ngwo rd

M PW$AW PHVI NDEX

WRTMFY PAG

l o ngwo rd

Po i n t e r to mod i f i ed pag e
wr i t e r PTE a r r a y
Po i n t e r t o p r o c e s s h e a d e r
vec to r i nd ex a r r a y u s ed
by the mod i f i ed pag e
wr i t e r

MMG $G L I AC LOCK

S YS IMGACT

l o ngwo rd

Imag e Ac t i v a to r I n t e r l o c k

MMG $G L_PFNLOCK

S YS LKW S E T

l o ng wo r d

Down c o un te r o f pag e s
r em a i n i ng th a t m a y b e
l o c k ed i n memo r y

8-4

L i s th e a d s f o r t h e f r e e ,
mod i f i ed , a n d b a d pag e
l i s t s ( 3 fo rwa rd l i n k
wo r d s fo l l owed b y 3
b a c kwa rd l i n k wo r d s )
Co un t o f pag e s o n e a c h o f
the three l i s t s
Co un t o f a v a i l ab l e phys i c a l
pag e s
H i g h l im i t th r esho l d s fo r
e a ch o f the th r e e l i s t s
Lo w l i m i t t h r esho l d s f o r
e a c h o f the th r e e l i s ts
Saved h i gh l i m i t t h r e sho l d
o f mod i f i ed pa g e l i s t
Saved l o w l i m i t th r e sho l d o f
mod i f i ed pag e l i s t

E XECUT I VE DATA AREAS
B.l.8

Pag e Fa u l t Mo n i to r Da t a

($$$215)

Th e pag e f a u l t mo n i to r s ub sys t em m a i n t a i n s 3 l o ngwo r d s o f i mpu r e d a t a .
G l o b a l Symbo l

Mod u l e

PFM $G L S I Z E
PFM $G L PMBLST

SYS S ET PFM
SYSSETPFM
SYSSE T PFM

B. l . 9

Si ze
l o ng wo r d
l o ng wo r d
l o ngwo r d

De s c r i p t i o n o f Da ta
S i z e of a l l o c a t ed b l o c k
Po i n t e r t o PMB l i s t
Co un t o f p r o c e s s e s us i ng
mo n i to r

Schedul e r Da t a ( $ $ $ 2 2 0 )

Th e s c h e d u l e r ' s d a t a b a s e i s d e f i n ed p r i ma r i l y i n mod u l e S DAT .
Th i s
mod ul e conta i ns
t h e queue h e ad e r s f o r e a c h o f the s c h ed u l i ng s t a t e s
a nd r e l a t ed c o u n t e r s .
Seve r a l
o th e r m o d u l e s
( ma i n l y SWAPPER a nd
SWAPF I LE ) a l s o co n t r i b u t e to th i s p r og r am s e c t i o n .
G l o b a l Symbo l

Mo d u l e

S i ze

S DAT

quadwo r d

S C H $AQ_C OMH

S DAT

3 2 q ua d wo r d s

SC H$AQ_C OMOH

SDAT

3 2 q u a d wo r d s

S C H $AQ_WQH DR

S DAT

1 3 2 bytes
( 1 32
1 1*12)
=

S C H $G L C URPC B

SDAT

l o ngwo r d

SC H $G L_C OM QS

SDAT

l o ngwo r d

SC H $G L_C OMOQS

S DAT

l o ngwo r d

S C H $G B S I P

S DAT

byte

SCH$V S I P
SCH$V SWP S C H E D
SCH$V-MPW

bit
bit
bit

SCH$V DG B L S C

bit

S C H $GW PROCCNT

S DAT

byte
wo r d

S C H $GW PROC L IM

SDAT

wo r d

SC H $G Q_C EB HD

S DAT

wo r d
q u adwo r d

B-5

De s c r i p t i o n o f Da ta
Spa r e quadwo r d to t e rm i n a t e
o u t s wa p s c h e d u l i ng s c a n
L i s th e ad s fo r c om p u t a b l e
s t a t e s fo r a l l 3 2
so f twa r e p r i o r i ty l ev e l s
L i s th e a d s f o r c omputa b l e
o u t swa pped s t a t e s f o r a l l
3 2 so f twa r e p r i o r i ty
l ev e l s
Wa i t que ue h e ad e r s fo r 1 1
wa i t s t a t e s ( Wa i t q ue ue
h e ad e r fo r CEF s t a t e i s
no t u s ed )
Ad d r e s s o f PCB o f c u r r e n t
process
Que ue s umma r y l o ng wo r d fo r
C OM s t a te
Que ue s umma r y l o ng wo r d fo r
C OM O s t a t e
Swa p i n p r og r e s s f l ag s
Swa p i n p r og r e s s
Swa p sched u l e t r i g g e r
Mo d i f i ed pag e wr i t e r i s
active
Gl o b a l s e c t i o n s n e e d t o
b e d e l e t ed
Spa r e fo r a l i g nm e n t
Cu r r e n t n um b e r o f p r o c e s s e s
wh i ch r e q u i r e swa p f i l e
( d o e s no t c o un t NU L L o r
SWAPPER )
Ma x i m um n um b e r o f p r o c e s s e s
th a t th i s s ys tem a l l o ws
Spa re fo r a l i g nm e n t
L i s th e a d fo r commo n e v e n t
bl ocks

EXECUT IVE DATA AREAS

G l o b a l Symbo l

Mod u l e

S C H$GW_C E B CNT

S DAT

wo r d

S C H $GW D E L PHDC T

S DAT

wo r d

SWP $G L S H E L L
SWP $G L I N PC B

S DAT
S DAT

l o ngwo r d
l o ng wo r d

SWP $ G L I S PAGCNT
SWP $GW= I BALS E TX

S DAT
S DAT

l o ngwo r d
wo r d

SWP $G B I SWPR I

S DAT

SWP $ G L I SWPC NT
SWP $G L O SWPCNT
SWP $G L H O SWPCNT
SWP $G L H I SWPCNT
S C H $G L R E SMASK
S C H $G B P R I

S DAT
S DAT
S DAT
S DAT
S DAT
S DAT

byte
byte
l o ng wo r d
l o ng wo r d
l o ng wo r d
l o ngwo r d
l o ng wo r d
byte
3 by t e s

SWP $G L S WT IM E

OSWPS C HE D

l o ngwo r d

E a r l i e s t t i m e fo r n e x t
e x chang e swa p

E XE $G L PWRDONE

POWERFA I L

l o ng wo r d

E XE $G L PWR INTVL

POWERFA I L

l o ng wo r d

End t i m e fo r po we r r ec o v e r y
i nterval
Al l owa b l e r e c o v e r y i n t e r v a l
i n 1 0 ms e c un i t s

SWP $G L S FTBAS

SWAPF I L E

4 0 byt e s

SWAPF I L E

4 0 bytes

SWAPF I L E

4 0 by t e s

SWAPF I L E

3 2 by t e s

SWAPF I LE

3 2 bytes

SWAPF I L E

l o ngwo rd

SWAPF I L E

36 b y t e s

MMG $A PAG F I L

MMG $G L PAGSWPVC

S i ze

1 6 by t e s
l o ng wo r d
l o ngwo r d
l o ngwo r d
l o ng wo r d
l o ngwo r d

B-6

De s c r i p t i o n o f Da t a
Num b e r o f c ommo n event
b l ocks
Num b e r o f p r o c e s s h e ad e r s o f
a l r e a d y d e l e ted p r o c e s s e s
She l l p r o c e s s swa p a dd r e s s
PC B a d d r e s s o f p r o c e s s b e i ng
s wa pped i n to memo r y
I n s wa p pag e c o un t
Ba l an c e s l o t i nd e x fo r
i nswa p p r o c e s s
P r i o r i ty o f i n s wa p p r o c e s s
Spa r e fo r a l i g nm e n t
C o un t o f i n swa ps pe r fo rmed
Co un t o f o u t swaps pe r fo rmed
Co un t of h e ad e r o u t s wa ps
C o u n t o f h e a d e r i n s wa ps
Re so u r c e wa i t mask v e c to r
P r i o r i ty o f c u r r e n t p r o c e s s
Spa r e fo r a l i g nm e n t

Swa p f i l e t a b l e e n t r y fo r
S h e l l p r o c e s s i n SYS . E XE
Swa p f i l e t a b l e en t r y f o r
SWAPF I LE . SYS
Spa c e fo r swa p f i l e t a b l e
e n t r y fo r s e c o nd swa p
f i le
Pag e f i l e c o n t r o l b l o c k fo r
PAG E F I LE . SYS
Spa c e fo r pag e f i l e c o n t r o l
b l o c k fo r s e c o nd pag e
file
Ad d r e s s o f a r r a y ( wi th i n
po i n te r c o n t r o l b l o c k ) o f
a d d r e s s e s o f S FTEs and
P F Ls
Po i n t e r Co n t r o l B l o c k to
S FTEs and PFLs
H e a d e r of po i n t e r c o n t r o l
block
Ad d r ess o f S FTE fo r She l l
process
Ad d r ess o f S F T E f o r
SWAPF I LE . SYS
Ad d r e s s of spa r e S FTE
Ad d r ess of PF L fo r
PAGE F I LE . SYS
Ad d r e s s of spa re PF L

EXECUT I VE DATA AREAS
G l o b a l Sym bo l

Mod u l e

i o rout i ne

SWAP PER

l o ngwo r d

i oea
r ws swp

SWAPPER
SWAPPER

l o ngwo r d
l o ngwo r d

r sv a pte

SWAP PER

l o ngwo r d

r pg c n t
o s wppg s
o swppc b

SWAP PER
SWAPPER
SWAP PER

wo r d
wo r d
l o ngwo r d

SWP $GW_BA LCNT

SWAP PER

wo r d

S C H $GW SWPFCNT

SWAPPER

wo r d

B. l. lO

S i ze

De s c r i p t i o n o f Da t a
Ad d r e s s o f p r o pe r ( r e a d o r
wr i t e ) bu i l d pac k e t
r o ut i ne
I /O end a c t i o n r o u t i n e
Rem a i n i ng wo r k i ng s e t swa p
address
Rem a i n i ng s ys tem v i r t ua l
a d d r e s s o f pag e t a b l e
entr i es
Rema i n i ng pag e c o un t
Ou t s wa p pag e c o un t
Ad d r e s s o f PC B o f o u t s wa p
process
Co un t o f p r o c e s s e s i n
b a l a n c e s e t ( Swa ppe r a nd
Nu l l p r o c e s s e s n o t
c o un t ed )
Co un t o f s uc c e s s i v e o u t s wa p
sched u l e f a i l u r e s

Memo r y Ma n ag em e n t Da t a ( $ $ $ 2 2 2 )

Th i s p r og r am s e c t i o n c o n t a i n s t h e d a t a c e l l
c o n t r i b u t i o n o f mod ul e
MOAT to the e x e c u t i ve .
MOAT a l s o d e f i n es g l o b a l l a b e l s tha t s e pa r a t e
d a t a a r e a s f r om r e a d - o n l y s ec t i o n s , a nd s e pa r a t es pag e a b l e c o d e f r om
n o npa g e d
rout i nes .
In
a d d i t i o n , MOAT a l l o c a t e s pa tch a r e a s fo r the
execut i ve .
G l o b a l Symbo l

Mod u l e

PHV$G L_P I XBAS

MOA T

l o ngwo r d

PHV$G L_REFCBAS

MOA T

l o ngwo r d

MMG $ A L_S B IC ONF

MOAT

1 6 l o ng wo r ds

MMG $G L_RM SBAS E

MOA T

l o ngwo r d

B.l.ll

S i ze

De s c r i p t i o n o f Da t a
Ad d r e s s o f p r o c e s s i nd e x
a r ray
Ad d r e s s o f p r o c e s s h e a d e r
r e f e r ence count a r r a y
Ar r a y o f po i n t e r s t o sys t em
v i r t ua l ad d r e s s o f
co n f i g u r a t i o n r eg i s t e r
fo r a d a p t e r
Po i n t e r to b a s e a d d r e s s o f
RM S i ma g e

P r o c e s s Da ta fo r Sy s tem P r o c e s s e s ( $ $ $ 2 3 0 )

Two p r o c e s s e s e x i s t a s a pa r t o f
the
s ys t em
i m ag e .
Th e y a r e the
s wa ppe r
a nd
the nul l
pr o cess .
I n ad d i t i o n , t h e r e ex i s t s a sys tem
h e ad e r c o n t a i n i ng the s ys tem pag e t a b l e
( Ch a p t e r 1 1 a nd Appe nd i x E )
a nd a sys tem PCB t o s uppo r t sys tem pag i ng .

B-7

EXE C UT IVE DATA AREAS

Mo d u l e

S i ze

PDAT

3 2 l o ng wo r d s

PDAT

1 6 0 l o ngwo r d s

n u l phd

PDAT

384 byt es

SC H $G L N U L L PC B

PDAT
PDAT
PDAT

1 4 0 byte s
l o ng wo r d
3 8 4 byte s

MMG $AL S YS PC B
S C H $G L-PCBVE C

PDAT
PDAT
PDAT
PDAT

1 4 0 byte s
1 o ng wo r d
1 4 0 b yt e s
l o ng wo r d

SC H$G L MAXP I X

PDAT

l o ngwo r d

S C H $ G L_S E QVE C

PDAT

l o ng wo r d

G l o b a l Sym bo l

swpphd
SC H $G L SWPPC B

B. l . l2

C o n so l e I n te r r up t D i spa tch Da t a

D e s c r i p t i o n o f Da t a
Ke r n e l s t a c k f o r the n u l l
process
Ke r n e l s t a c k f o r the swa ppe r
process
M i n im a l p r o c e s s h e ad e r
{ f i x ed po r t i o n o n l y ) fo r
nul l process
PCB for nul l process
Spa r e fo r a l i g nm e n t
M i n im a l p r o c e s s h e ad e r
{ f i x ed po r t i o n o n l y ) f o r
swappe r p r o c e s s
PC B f o r swa ppe r p r o c e s s
Spa r e f o r a l i g nm e n t
Sys tem PC B
Add r e ss o f PCB v e c to r o f
l o ngwo r d s
Ma x im um p r o c e s s i nd e x f o r
th i s s y s tem
Ad d r e s s of s e q u e n c e vec to r
o f wo r d s

{ $ $$ 2 50 )

Th e c o n so l e d ev i c e d r i v e r m a i n t a i n s a sma l l amo un t o f i mp u r e s t o r ag e .
G l o b a l Symbo l

B. 1 . 13

Mod u l e

S i ze

C ON I NTDS P

byte

C ON I NTDS P
C ON I NTDS P

byte
wo r d

De s c r i p t i o n o f Da t a
Cu r r e n t un i t e x pe c t i ng
o u tp u t comp l e t i o n
Nex t un i t a wa i t i ng o u t p u t
Ne x t d a t a fo r o u t p u t

SYSCOMMON - Mi s c e l l a n e o u s E x ec u t i ve Da t a

($$$260)

Mo d ul e
SYSC OMMON c o n t a i n s mo s t o f
t h e m i sc e l l a n e o us
l i s t h e ad s ,
c o un t e r s ,
s emaph o r e s , a nd o th e r d a ta t h a t i s no t d i r e c t l y t i ed to o ne
o f t h e m a j o r s ub s ys t ems .
Mod u l e E RROR L OG a l s o m a k e s a
s i gn i f i cant
c o n t r i b u t i o n to t h i s p r og r am s e c t i o n .
G l ob a l Symbo l

Mo d u l e

E XE $G Q_S TAREXE

SYSC OMMON

EXE $G Q_S Y S DM P

S Y S C OMMON

S i ze

Desc r i p t i o n o f Da t a

2 l o ngwo r d s

De sc r i p to r o f e x e c u t i v e
i m ag e SYS . EXE

l o ngwo r d
l o ngwo r d

S i z e of f i l e in pag e s
S t a r t i ng l og i c a l b l o c k
n umbe r o f f i l e

2 l o ng wo r d s

Desc r i p to r o f s ys tem d um p
f i l e SYSDUM P . DM P

l o ngwo r d
l o ngwo r d

S i ze o f f i l e i n pag e s
S t a r t i ng l og i c a l b l o c k
n um b e r o f f i l e

B-8

EXECUTIVE DATA AREAS

G l o b a l Symbo l

Mo d u l e

E XE $G Q_SWAPF

SYSCOMMON

S i ze

De s c r i p t i o n o f Da t a

2 l o ng wo r d s

De sc r i pto r o f swa p f i l e
SWAPF I L E . SYS

l o ngwo r d
l o ngwo r d
E XE $G L DM PCHK

SYSCOMMON

l o ngwo rd

EXE $G L F LAG S

SYSCOMMON

l o ngwo r d

E XE $G Q_E R LMBX

S YS C OMMON

q u a dwo rd
wo r d
wo r d
l o ngwo r d

E XE $G L U S RCHMK

S YS COMMON

l o ngwo r d

E XE $G L U S RC HME

SYSCOMMON

l o ngwo rd

SW I $G L_F QFL

SYSCOMMON

6 quadwo r d s

LOG $A L LOG TB L

S YS COMMON

3 l o ng wo r d s

LOG $AL MUTEX

S YS COMMON

4 wo r d s

l o g $ g l_g l t f l

SYSCOMMON

q u ad wo r d

LOG $G L S LTFL

SYS COMMON

q u a d wo r d

E XE $G L S Y S UCB
F I L $G T-DDDEV

SYSCOMMON
S Y S C OMMON

l o ngwo r d
1 2 byt e s

I OC $G L P S F L

S YS COMMON

q u adwo r d

I OC $G L_I R PF L

S Y S COMMON

q u a d wo rd

I OC $G L AQB L I S T
I OC $G Q=MOUNT LST

SYSCOMMON
SYS COMMON

l o ngwo r d
q u ad wo r d

I O C $G Q_BRDC S T

SYS COMMON

q u ad wo r d

EXE $G L G S DGRPF L

S YS COMMON

q u a d wo r d

EXE $G L G S DSYS F L

SYS COMMON

q u a d wo r d

EXE $G L G S DFREFL

S Y S COMMON

q u a d wo r d

B-9

S i ze of f i l e in pag e s
S t a r t i ng l og i c a l b l o c k
n umbe r o f f i l e
Ch e c k s um fo r s ys t em d um p
file
Sys tem f l ag s l o ng wo r d ( S e e
SYS PARAM d e s c r i pt i o n )
De sc r i p to r o f e r r o r l og
ma i l bo x
Un i t n um b e r ( 0 = > no n e )
Spa r e f o r a l i g nm e n t
Process I D of a s s i g n e r
Ad d r e s s o f s ys t em-w i d e
u s e r -wr i t t e n
c h a ng e -mod e- to -k e r n e l
d i spa tc h e r
Ad d r e s s o f s y s t em-wi d e
u s e r -wr i t t e n
c h a ng e-mo d e- to-ex e c u t i v e
d i spa tc h e r
Fo r k q u e ue l i s t h e a d s f o r I P L
l e v e l s 6 to 1 1 ( I P L 7 i s
u s ed o n l y a s a p l a c e
ho l d e r )
Ad d r e s s e s o f l i s th e a d s f o r
sys t em , g r o up , and
p r o c e s s l o g i c a l name
tab l e s
Mutex e s fo r s ys tem and g r o up
l o g i c a l name t ab l e s
L i s th e a d fo r g r o up l og i c a l
name t a b l e
L i s th e ad fo r s ys t em l o g i c a l
n am e t a b l e
Ad d r e s s o f s ys t em d i s k UC B
Co un t e d ASC I I s t r i ng f o r
d e f a u l t d ev i c e
L i s th e a d fo r I /0
po s tp r o c e s s i ng que ue
L i s th e ad fo r I R P l o o k a s i d e
l i st
AC P Qu e ue B l o c k l i s th e a d
Sy s t em-w i d e mo un t ed vo l ume
l i st
Te rm i n a l b r o ad c a s t m e s sag e
l i s th e a d
L i s th e a d fo r g r o up g l o b a l
s e c t i o n d e s c r i pto r l i s t
L i s th e a d fo r sys t em g l o b a l
s e c t i o n d e s c r i pto r l i s t
L i s th e a d fo r g l o b a l s e c t i o n
d e s c r i p to r b l o c k
loo ka s i d e l i s t

EXECUT I VE DATA AREAS

G l o b a l Symbo l

Mod u l e

E XE $G L G S DDE LFL

SYSCOMMON

q u a dwo r d

E XE $G L_WCBDE LFL

S YS C OMMON

q u a d wo r d

EXE $G L S YSWC B F L

S YS C OMMON

q u a d wo r d

E XE $G L S YSWCB

SYS C OMMON

4 2 byt e s

PM S $G L_K E RNE L

SYSCOMMON

6 l o ngwo r d s

EXE $G L AB S T IM

SYS C OMMON

l o ng wo r d

E XE $G Q_S YS T I M E

S Y S C OMMON

q u a dwo r d

E XE $G L PFA I LT IM

SYSCOMMON

l o ngwo r d

EXE $G L PFAT IM

SYSCOMMON

l o ngwo r d

E XE $G L_T QF L

SYSCOMMON
SYSC OMMON

q u a d wo r d
4 0 byt e s

SYS C OMMON

3 2 by t e s

I OC $G L MUT E X
E XE $G L-C E BMTX

S Y S C OMMON
S YS C OMMON

2 wo r d s
2 wo r d s

E XE $G L PG DYNMTX
EXE $G L-G S DMTX

S YS C OMMON
S YS C OMMON

2 wo r d s
2 wo r d s

E XE $G L_S HMG S MTX

S Y S C OM MON

2 wo r d s

E XE $G L S HMMBMTX

S Y S C OMMON

2 wo r d s

EXE $G L E N QMTX
EXE $G L-KF IMTX
E XE $G L-KNOWN F I L

SYS C OMMON
S YS C OMMON
SYSCOMMON

2 wo r d s
2 wo r d s
l o ngwo r d

KF I $G L_F l lAAC P

SYSCOMMON

l o ngwo r d

E XE $G L G PT

SYSCOMMON

l o ng wo r d

SYS C OMMON

l o ngwo r d

SYS $G Q_VE RS I ON

S YS C OMMON

q u a d wo r d

SYS $GW I JOBCNT

SYSCOMMON

3 wo r d s

E XE $G L S YS M SG

SYSCOMMON

l o ng wo r d

S i ze

3 wo r d s
B-1 0

D e s c r i p t i o n o f Da t a
L i s thead f o r g l o b a l s e c t i o n
d e sc r i p to r b l o c k d e l e t e
p e nd i ng l i s t
L i s thead f o r w i nd ow c o n t r o l
b l o c k d e l e t e que ue f o r
G S D w i nd ows
L i s thead fo r sys t em wi nd o w
control block l i st
Wi ndow c o n t r o l b l o c k ( wi th
one r e t r i ev a l po i n te r }
f o r s y s t em i m ag e SYS . E XE
T i m e r s ta t i s t i c s f o r t i m e
s p e n t i n e ac h a c c e s s
mo d e , o n th e i n te r r up t
s t a c k , a nd i n
c ompa t i b i l i t y mod e
Ab s o l u t e t i me i n s e c o nd s
( fo r d ev i c e d r i v e r
t i m eo u t }
Sys t em t i me i n un i t s o f 1 0 0
n a n o s e c o nd s
Co n t ents o f PR $ T ODR a t l a st
po we r f a i l u r e
Du r a t i o n o f m o s t r e c e n t
powe r f a i l u r e ( i n un i t s
o f 1 0 m i l l i s econd s }
T i m e r q u e u e l i s th e ad
T i m e r q u e ue e l em e n t f o r
s ys tem s ub r o u t i ne
Pe rma n a n t l a s t e n t r y i n
t i me r que ue
I /O d a t a b a s e mutex
Common event b l o c k l i s t
mutex
Pag ed d yn am i c memo r y mutex
G l o b a l s e c t i o n d e s c r i pto r
l i s t m u t ex
Sha r ed m emo r y g l o ba l s e c t i o n
d e sc r i p to r l i s t m u t ex
Sh a r ed memo r y m a i l bo x l i s t
mutex
Enque ue/d equeue t a b l e s m u t ex
Kno wn f i l e t a b l e m u t e x
Ad d r e s s o f known f i l e l i s t
v e c to r
Ad d r e s s o f KF I fo r sys tem
d i s k AC P
Ad d r e s s o f f i r s t f r e e g l o b a l
pag e t a b l e e n t r y
Dummy co u n t o f n umb e r o f
G PTEs i n l i s th e a d
ASC I I s t r i ng th a t c o n t a i n s
sys tem v e r s i o n n um b e r
C u r r e n t c o un t s o f
i n te r a c t i v e , n e two r k , a nd
b a tch l og i n s
Ad d r e s s o f s y s tem wi d e
m e s s ag e s e c t i o n
Spa r e fo r a l i g nm e n t

EXECUT IVE DATA AREAS

S i ze

G l o b a l Symbo l

Mo d u l e

E X E $G L_NONPAG E D

S YS COMMON

l o ng wo rd

SYSC OMMON

l o ng wo r d

SYSCOMMON

l o ngwo r d

EXE $G L_S P L I TADR

SYSCOMMON

l o ngwo r d

EXE $G L PAG E D

S YS COM MON

l o ngwo r d

SYSCOMMON

l o ngwo r d

RM S $G L S FDBAS E

SYSCOM MON

l o ngwo rd

EXE $G L S HB L I S T

SYSCOM MON

l o ngwo r d

EXE $G L RTB I TMAP

S YS COM MON

l o ngwo r d

MCH K $G L_MASK

SYSCOMMON

l o ng wo r d

MCHK$G L_S P

SYSCOMMON

l o ng wo r d

I O $ G L U BA I N T O
E XE $G L B LAKH OLE

S Y S C OM MON

l o ngwo r d

SYSCOMMON

l o ng wo r d

EXE $G L_S I TE S PE C

SYSCOMMON

l o ngwo r d

De s c r i p t i o n o f Da t a
I PL a t wh i c h n o npag ed po o l
a l l o c a t i on w i l l o c c u r
Ad d r e s s .o f f i r s t f r e e b 1 o c k
o f no npag ed po o l
Dummy s i z e o f z e r o fo r
l i s th e a d
Ad d r e s s o f b o und a r y b e twe e n
r eg u l a r no npag ed po o l a nd
l oo ka s i d e l i s t
Ad d r e s s o f f i r s t f r e e b l o c k
o f pag ed po o l
Dummy s i z e o f z e r o fo r
l i sthead
Ad d r e s s o f s h a r ed f i l e d a t a
base
Ad d r e s s o f sh a r ed memo r y
control block l i st
Ad d r e s s o f r e a l t i me S PT E
b i tm a p
Func t i o n m a s k f o r c u r r e n t
m a c h i ne c h e c k r e co v e r y
b lock
Saved s t a c k po i n t e r f o r
r e t u r n a t end o f r ec o v e r y
Co un t o f UBA i n t e r r up t s
t h r o ug h v e c to r 0
Phys i c a l pag e u s ed to r em a p
a d d r e s s e s o f ad a pt e r s
t h a t h a v e e x pe r i e n c ed
powe r f a i l u r e
Longwo r d th a t i s a va i l ab l e
t o p r i v i l eg ed us e r s

Mod u l e ERRORLOG ma k e s a s i g n i f i c an t c on t r i b u t i o n t o p r og r am s ec t i o n
Mo s t o f t h e s p a c e i s o c c up i ed b y two 5 1 2 -byte e r r o r m e s s a g e
$$$260.
b u f fe r s .
S i ze

G l o b a l Symbo l

Mo d u l e

E R L $AL_B UFADR

E RRORLOG
ERROR LOG
ERROR LOG

5 1 2 byt e s
51 2 bytes
2 l o ngwo r d s

ERL$GB B UF IND

E RROR LOG

byte

ERL$GB B U F F LAG
ERL$GB=BUFPTR

E RRORLOG
E RROR L OG

byte
byte

E R L $G B BUFTIM
E R L $G L-E R L P I D

E RROR L OG
E RRORLOG

byte
l o ng wo r d

ER L $G L_S E QUENCE

E RRORL OG

l o ng wo r d

B- 1 1

De s c r i p t i o n o f Da t a
F i r s t e r r o r l og bu f f e r
S e c o nd e r r o r l o g b u f f e r
Ad d r e s s e s o f two e r r o r l og
buf f e r s
Cu r r en t b u f f e r a l l o c a t i o n
i nd i c a to r
Bu f f e r s t a tus f l ag s
Fo rma t p r o c e s s ( E RRFMT )
b u f f e r i nd i c a to r
Fo rma t p r o c e s s wa ke u p t i m e r
P r o c e s s I D o f e r r o r f o rma t
process
Un i v e r s a l e r r o r s eque n c e
n umb e r

E XECUT IVE DATA AREAS

8 . 1 . 14

S ta t i s t i c s Used by D I S PLAY

( $ $ $ 2 7 0N P )

Mo d ul e PM S DAT c o n t a i n s m o s t o f t h e d a t a
tha t
is
p resen ted
by the
D I S PLAY u t i l i ty .
M a n y o f t h e c e l l s d e f i n ed i n th i s m o d u l e , e sp e c i a l l y
tho s e a s so c i a t ed w i th the t e rm i n a l d r i v e r , a r e n o t c u r r e n t l y u s ed b u t
we r e i n s e r t ed w i th po s s i b l e f u t u r e pe r fo r m a n c e m o n i to r i ng i n m i nd .
G l o b a l Symbo l

Mod u l e

S i ze

PM S $G L D I R I O

PM SDAT

l o ng wo r d

PMS $G L B U F I O

PM SDAT

l o ngwo r d

PM S $G L L OGNAM

PM SDAT

l o ngwo r d

PM S $G L MBREADS

PMSDAT

l o ngwo r d

PMS $G L MBWR I T E S

PM S DAT

l ongwo r d

PMS $G L TREADS

PMS DAT

l o ng wo r d

PM S $G L_TWR I T E S

PMS DAT

l o ngwo r d

PMS $G L_I O PFMPDB

PMS DAT

l o ng wo r d

PMS $G L_I O PFM S E Q

PM S DAT

l o ng wo r d

PMS $G L_PAG E S

PMS DAT

l o ng wo r d

PMS $GW BATC H
PMS $GW- I NTJOBS
PMS $A L-R EADTB L

PMS DAT
PMS DAT
PM SDAT

wo r d
wo r d
1 0 l o ngwo r d s

PM S $A L_WR ITETB L

PM SDAT

1 0 l o ng wo r d s

PM S $G L_R EADC NT

PMS DAT

l o ng wo r d

PM S $G L_WRTCNT

PM SDAT

l o ng wo r d

PM S $G L PAS SALL

PM SDAT

l o ng wo r d

PM S $G L RWP

PMSDAT

l o ng wo r d

PM S $G L LRGRWP

PM SDAT

l o ng wo r d

PM S $G L RWPS UM

PM SDAT

l o ng wo r d

PM S $G L N O S TDTRM

PMSDAT

l ong wo r d

PM S $G L RWPNO S TD

PMSDAT

l o ng wo r d

PM S $G L_LDPCTX

PMSDAT

l o ng wo r d

B-1 2

De s c r i p t i o n o f Da t a
Numbe r o f d i r e c t I /O
o pe r a t i o n s
Numb e r o f b u f f e r ed I /O
o pe r a t i o n s
N umbe r o f l og i c a l name
t r an s l a t i o n s
Numbe r o f m a i l bo x r ea d
o pe r a t i o n s
Numbe r o f m a i l bo x wr i t e
o pe r a t i o n s
Numbe r o f t e rm i na l r e a d
o pe r a t i o n s
Numbe r o f t e rm i na l wr i t e
o pe r a t i o n s
Ad d r e s s o f p e r fo rmanc e d a t a
b l oc k
Ma s t e r I /O p a c k e t s e q u e n c e
n umbe r
Num be r o f phys i c a l pag e s o f
m em o r y i n c o n f i g u r a t i o n
Num b e r o f c u r r en t b a tch j o bs
Num b e r of i n t e r ac t i v e us e r s
1 0 c e l l h i s tog r am t o c o un t
n umb e r o f c h a r a c t e r s pe r
t e rm i n a l r e a d o pe r a t i o n
1 0 c e l l h i s tog r am to c o un t
n umbe r o f c h a r a c t e r s pe r
te rm i n a l wr i te op e r a t i o n
To t a l n umbe r o f t e rm i na l
c h a r a c te r s r e ad s i nc e
bo o t s t r a p
To t a l numbe r o f t e rm i n a l
c h a r a c te r s wr i t t e n s i nc e
bo o t s t r a p
Numbe r o f r e ad s i n PAS SALL
mod e
Numbe r o f r e a d - w i th-prompt
r eads
Num b e r o f r e a d -w i th-pr om p t
r e ad s o f mo r e than 1 2
c h a r a c te r s
To t a l numbe r o f c h a r a c t e r s
r e ad i n p r ompt mode
Numbe r of r e ad s no t us i ng
s t a nd a r d t e rm i n a l s
Numbe r o f r e a d -w i th-prompt
r e ad s not us i ng s ta nd a r d
te rm i n a l s
Numbe r o f LDPC T X
i n s t r uc t i o n s

EXECUT IVE DATA AREAS

G l o b a l Symbo l

Mo d u l e

Si ze

PM S $G L SWITCH

PM S DAT

l o ng wo r d

PMS $G L T URN
PM S $G L-S PL I T

PM S DAT
PMS DAT

l o ngwo r d
l o ngwo r d

PMS $G L H I T

PMS DAT

l o ng wo r d

PMS $G L O P EN

PM S DAT

l o ngwo r d

PMS $G L O PENS
PM S $G L-D O S TATS

PM SDAT
PMS DAT

l o ngwo r d
byte
3 byt e s

B. l . l5

De sc r i pt i o n o f Da t a
Num b e r o f sw i tc h e s f r om t h e
c ur rent process
Numb e r o f wi n d o w t u r n s
Num b e r o f s p l i t I /0
t r an s f e r s
Num b e r o f t r an s f e r s n o t
r e qu i r i ng w i nd o w t u r n s
Num b e r o f c u r r en t l y o pe ned
f i l es
To t a l n umbe r o f f i l e o pe n s
F l ag to t u r n s t a t i s t i c s c o d e
on and o f f
Spa r e fo r a l i g nm e n t

E n t r y Po i n t s f o r C PU-De pend en t Ro u t i ne s

( $$$500 )

Mod ul e S Y S LOAVEC c o n ta i n s e n t r y po i n t s fo r e a c h C PU -d e pe nd e n t r o u t i n e .
Each
entry
po i n t
conta ins
a JMP
i n s t r uc t i o n
( w i t h a b so l ut e
a d d r e s s i ng ) .
Th e d e s t i n a t i o n o f e a c h JMP i s a l t e r ed b y !N I T t o po i n t
t o the
a pp r o p r i a te
r o u t i n e i n the C PU-d epend e n t i mag e SYS LOAx x x . EXE
( S YS LOA 7 5 0 . E XE o r SYS LOA7 8 0 . E XE ) th a t is l o ad ed i n to no npag e d po o l
by
!N I T .
Th e r e a r e two t ype s o f r o u t i n e s h e r e .
Tho s e r o u t i n e s t h a t a r e e n t e r ed
th r o ug h t h e sys t em c o n t r o l b l o c k m u s t h a v e th e i r e n t r y po i n t s l o ng wo r d
a l i g ned .
Each o f these rout ines has
two
spa r e b y t e s
to
prese rve
the
six
b y t e JM P
O th e r
r o ut i n e s can have
l o ngwo r d
a l i g nm e n t .
i n s t r uc t i o n s p a c k e d tog e t h e r .
G l o b a l Symbo l

Mod u l e

E XE $W N UMALGVE C

S YS LOAVE C

wo rd

EXE $W N UM PKDVE C

S YS LOAVE C

wo rd

S YS LOAVE C

4 0 byt e s

Si ze

Num b e r of l o ng wo r d a l i g n ed
vec to r s
Num b e r of p a c k e d vec to r s

E XE $MC HK

8 bytes

E XE $ I NT 5 4

8 bytes

E XE $ I N T 5 8

8 bytes

E XE $ I NT S C

8 by t e s

E XE $ I NT6 0

8 bytes
SYS LOAVE C

De s c r i p t i o n o f Da t a

5 4 byt e s

ECC $ RE ENAB LE

6 byt e s

E XE $ADP I N I T

6 bytes

E XE $ D UM PC PUREG

6 bytes

B-1 3

F i v e l o ngwo r d a l i g n e d
vec to r s
Ma c h i ne c h e c k e x c e p t i o n
s e rv i c e r o u t i n e
I n t e r r upt s e rv i c e r o u t i ne
fo r SCB vec to r 5 4
I n t e r r upt s e rv i c e r o u t i ne
fo r S C B v e c to r 5 8
I n t e r r upt s e rv i c e r o u t i n e
f o r SCB vec to r 5 C
I n t e r r upt s e rv i c e r o ut i n e
fo r SCB vec to r 6 0
N i n e pa c k ed v e c to r s
Re e n a b l e m emo r y e r r o r
t imers
I n i t i a l i z e a d a pt e r fo r
s y s t em d i s k
Dump C PU-spec i f i c
r eg i s t e r s t o e r r o r
l og b u f f e r

EXECUT IVE DATA AREAS

G l o b a l Symbo l

Mo d u l e

S i ze

E XE $REGRES TOR

6 byt e s

EXE $REG SAVE

6 byt e s

EXE $TEST C S R

6 by t e s

I OC $ PURGDATAP

6 byt e s

E X E $DW7 8 0 I NT

6 byt e s

E X E $MC HK_ERRCNT

6 byt e s

E XE $ L OAD_E RROR

B . l . l6

SYS LOAVEC

byte

De s c r i p t i o n o f Da t a
Re s to r e C PU-spec i f i c
r eg i s t e r s o n po we r
r ec o v e r y
Save C PU-spec i f i c
r eg i s t e r s a t powe r
f a i l ur e
Te s t UN I B US C S R f o r
e x i s te n c e
Pu r g e UN I BUS b u f f e r ed
d a t a pa th
DW7 8 0 UBA a d a pt e r e r r o r
i n te r r up t r o ut i n e
Po i n t e r t o e r ro r c o un te r s
i n mach i n e c he c k
routine
HALT i n s t r uc t i o n .
Ini tial
d e s t i n a t i on o f JMP
i n s t r uc t i o n s in v e c to r s

Ta b l e o f Ad j us t a b l e SYS BOOT Pa r am e te r s

($$$917 )

As d e sc r i b ed i n Ch a pt e r 2 2 , t h e e x ec u t i v e imag e c o n t a i ns a c o py o f t h e
wo r k i ng v a l ue
of
e a c h SYSB OOT p a r ame t e r .
Th i s t ab l e o f v a l ue s i s
w r i t t e n i n to t h e memo r y i m a g e o f t h e e x e c u t i v e b y SYSB OOT a nd cop i ed
back
to
the
execut ive d i sk
i mag e by
SYS I N I T .
G l oba l
l abel
MMG $A SYS PARAM , d e f i n ed i n mod u l e MOAT , l o c a t e s t h e t h e b eg i nn i ng o f
t h e pa r ame t e r
a rea .
G l o ba l l a b e l E XE $A S Y S PARAM , d e f i ned i n mod u l e
S YS PARAM , h a s the s ame v a l ue .
I n t h e f o l l o w i ng l i s t , t h e n am e o f e a c h pa r am e t e r
p a r t o f i t s d e sc r i p t i o n .
G l o b a l Symbo l

Mo d u l e

E XE $G Q_TODCBAS E

SYS PARAM

q ua d wo r d

E XE $G L TODR

SYS PARAM

l o ng wo r d

S GN $GW_DF PFC

SYS PARAM

wo r d

SGN$G B_PG TB PFC

SYS PARAM

byt e

SGN$G B_S YS PFC

SYS PARAM

byte

S G B $ G B_KF I LSTCT

SYS PARAM

byte

SGN $GW G B LS ECNT

SYS PARAM

byte
wo r d

S GN $G W MAXG PGC T
.S GN$GW-MAXPRC CT

SYS PARAM
SYS PARAM

wo r d
wo r d

S i ze

B-1 4

i nc l ud ed

De sc r i p t i o n o f Da t a
Ba s e v a l u e o f t i me-o f -d a y
c l o c k i n sys t em t i me
fo rma t ( no t a pa r am e t e r )
Ba s e v a l ue i n t i me-o f -ye a r
c l o c k ( no t a pa r a m e t e r )
De f a u l t pag e f a u l t c l us t e r
s i ze ( PFCDEFAULT )
De f a u l t pag e t a b l e pag e
f a u l t c l us t e r s i z e
( PAGTB LPFC )
Pag e f a u l t c l us t e r f a c to r
f o r sys t em pag i ng
( S YS PFC )
Num b e r o f known f i l e l i s t s
( K F I LSTCNT )
Spa r e fo r a l i g nment
G l o b a l sec t i o n c o un t
( G B LSECT I ONS )
G l o b a l pag e c o u n t ( G B LPAG E S )
Ma x i m um p r o c e s s c o un t
( MAXPROC E S SCNT )

E X E C U T I VE DATA AREAS
S i ze

G l o b a l Symbo l

Mod ul e

SGN $GW MAXP S TCT

SYS PARAM

wo rd

SGN $GW MINWSCNT

SYS PARAM

wo rd

SGN $GW_PAG F I LCT

S YS PARAM

wo rd

SGN $GW P F L I BAS

SYS PARAM

wo rd

SGN $GW S FTMAX

S YS PARAM

wo rd

SGN $G L PG F L S I Z

SYS PARAM

2 byt e s
l o ng wo r d

SGN $GW S YS DWSCT

SYS PARAM

wo rd

SGN $GW I S PPGCT

SYS PARAM

wo rd

SGN$GB DE FPG F L

S YS PARAM

byte

SGN $ G L BALS E TC T

SYS PARAM
SYS PARAM

3 bytes
l o ng wo r d

SGN $ G L I R PC NT

SYS PARAM

l o ng wo r d

SGN $ G L MAXWSCNT

SYS PARAM

l o ngwo r d

SGN $ G L N PAG E DYN

S YS PARAM

l o ng wo r d

SGN $G L PAG E DYN

S YS PARAM

l o ngwo r d

SGN $G L MAXVPGCT

SYS PARAM

l o ng wo r d

SGN $G L_S PTRE Q

S YS PARAM

l o ngwo r d

SGN $G L E XU S R S TK

S YS PARAM

l o ng wo r d

S GN $GW PC HANC NT

SYS PARAM

wo r d

SGN $GW I MG I OCNT

S YS PARAM

wo rd

S C H$GW_QUAN

SYS PARAM

wo rd

MPW$GW MPWPFC

SYS PARAM

wo rd

MPW$GW H I L I M

SYS PARAM

wo rd

MPW$GW L O L I M

SYS PARAM

wo rd

B-1 5

D e s c r i pt i o n o f Da t a
Pr o c e s s s e c t i o n c o un t
( PROC S ECTCNT )
M i n i m um wo r k i ng s e t s i z e
( M I NWSCNT )
Num b e r o f pag e f i l e s
( PAGF I LCNT )
Ba s e v a l ue fo r pag e f i l e
i nd ex ( no t a pa r am e t e r )
Num b e r o f swa p f i l e s
( SWPF I LCNT )
Spa r e fo r a l i g nm e n t
S i z e o f pag i ng f i l e
( PAGE F I LS I Z E )
S i ze o f s ys t em wo r k i ng s e t
c o un t ( S YSMWCNT )
S i z e i n pag e s o f i n t e r r up t
s t a c k ( I NTS TKPAG E S )
De f a u l t pag i ng f i l e i nd ex
( no t a SYSB OOT pa r am e t e r )
Spa r e fo r a l i g nm e n t
Ba l a n c e s e t c o un t
( BALS ETCNT )
Co un t o f p r e a l l o c a t e d I/0
r e que s t pa c ke t s
( I R PC OUNT )
Ma x i m um s i ze o f p r o c e s s
wo r k i ng s e t ( WSMAX )
Num b e r o f byt e s o f n o npag ed
po o l ( N PAG E DYN )
( T r un c a ted to pag e
b o und a r y by SYSB OOT )
Num b e r o f b yt e s o f p a g ed
po o l ( PAGE DYN ) ( T r un c a t ed
t o pag e bo und a r y b y
SYSBOOT )
Max i m um v i r t ua l pag e c o un t
( VI RTUA LPAG E CNT )
Num b e r o f add i t i o n a l S PTEs
t o a l l o c a t e ( S PTRE Q )
Ex t r a us e r s t a c k s pa c e ( i n
b y t e s ) a l l o c a t ed by i ma g e
a c t i v a to r ( E XUSRS TK )
Pe r m a n e n t I /0 c h a nn e l c o un t
( C HANNE LCNT )
De f a ul t n umbe r o f pag e s
m a pped fo r i m a g e I /O
s egme n t ( I MG I OCNT )
Leng th ( i n 1 0 m s e c u n i t s ) o f
q ua n t um ( QUANTUM )
Mod i f i ed pag e wr i t e r c l us t e r
f a c to r ( MPW WRTC LUSTER)
High l i m i t th resho l d o f
m od i f i ed pag e l i s t
( MPW H I L I M )
Low l i mT t t h r e sho l d o f
m od i f i e d pag e l i s t
( MPW_LOLIMI T )

EXECUTIVE DATA AREAS

G l o b a l Symbo l

Mod u l e

S i ze

MPW $ G B PR I O

S Y S PARAM

byte

SWP $G B PR I O

SYS PARAM

byte

SGN$GW WS LMXS K P

S Y S PARAM

wo r d

MMG $G L P HYPGCNT

S YS PARAM

l o ngwo r d

S C H $G L P FRAT L

S YS PARAM

l o ngwo rd

S C H$G L PFRATH

SYS PARAM

l o ng wo rd

S C H$G L PFRATS

S YS PARAM

l o ngwo rd

S C H $G L WS INC

SYS PARAM

l o ngwo r d

S C H $G L WSDEC

SYS PARAM

l o ng wo r d

S C H $GW AWSMIN

SYS PARAM

wo rd

S C H $GW AWSMAX

S YS PARAM

wo rd

S C H $G L AWS T I M E

SYS PARAM

l o ngwo r d

S C H$G L SWPRATE

SYS PARAM

l o ngwo rd

S C H$GW I OTA

SYS PARAM

wo rd

S C H $GW SWPFA I L

SYS PARAM

wo r d

S G N $G L E XTRAC PU

SYS PARAM

l o ngwo rd

E XE $G L S YS U I C

SYS PARAM

l o ngwo r d

I OC $GW MAXBUF

SYS PARAM

wo rd

I OC $GW_MBXBFQUO

SYS PARAM

wo rd

I OC $GW M B XMXM SG

S YS PARAM

wo rd

I OC $GW MBXNMMSG

SYS PARAM

wo rd

B- 1 6

Des c r i pt i o n o f Da t a
P r i o r i t y a t wh i c h mod i f i ed
pag e wr i t e s w i l l b e
q u e ued ( MPW PR I O )
P r i o r i t y a t wh Tc h swa ppe r
I /0 r e q u e s t s wi l l b e
q u e ued ( SWP PR I O )
Numbe r o f wo r kTng s e t l i s t
entr ies t o skip i n
mo d i f i ed s c a n o f WS L
( S K I PWS L )
Max i m um n um b e r o f phys i c a l
pag e s t o u s e
( PH Y S I CALPAG E S )
Low l i m i t pag e f a u l t r a te
th r e sho l d ( PFRATL )
H i g h l i m i t pag e f a u l t r a te
th r e sho l d ( PFRATH )
Pag e f a ul t r a te th r e sho l d
f o r sys t em pag i ng
( PFRATS )
Wo r k i ng s e t i nc r em e n t
( WS INC )
Wo r k i ng s e t d e c r em e n t
( WSDEC )
M i n i m um v a l ue o f a utom a t i c
o r k i ng s e t ad j us tm e n t
( AWSM IN )
Ma x i m um va l u e o f a u tom a t i c
wo r k i ng s e t ad j us tmen t
( AWSMAX )
Wo r k i ng s e t m e a s u r em e n t
i n te rva l ( i n 1 0 m s e c
un i t s ) ( AWST IM E )
Swa p r a t e f o r c ompu t e bo und
j o b s ( SW PRATE )
Amo un t o f t ime ( i n 1 0 m s e c
un i t s ) t o c h a rg e ag a i n s t
q u a n t um wh e n p r o c e s s g o e s
i n to wa i t s ta te ( I OTA )
Numb e r o f o u tswa p f a i l u r e s
t o h a ppe n b e f o r e
mod i fy i ng s e l ec t i o n
a l go r i thm ( SWPFA I L )
E x t r a C PU t ime a f t e r C PU
t ime exp i r a t i on
( E XTRAC P U )
Max i m um g r o up c o d e fo r
s ys t em U I C ( S Y S U I C )
Ma x imum b u f f e r ed I /O r e que s t
s i ze ( MA XB U F )
D e f a u l t b u f f e r quo t a f o r
ma i l bo x c r e a t i o n
( D E FMBXB UFQUO )
D e f a u l t m a x i m um m e s s a g e s i z e
f o r ma i l bo x c r e a t i o n
( DE FMBXM XMSG )
D e f a u l t n um b e r o f m e s s ag e s
fo r ma i l bo x c r e a t i o n
( D E FMBXN UMMSG )

EXECUTIVE DATA AREAS

G l o b a l S ymbo l

Mod u l e

S GN $G L FRE E L I M

S YS PARAM

l o ng wo r d

E XE $G L_LOCKRTRY

S YS PARAM

l o ng wo r d

I OC $GW XFMXRATE
I OC $GW=LAMAPREG

S YS PARAM
S YS PARAM

wo r d
wo r d

E XE $G L_RT I M E S PT

S YS PARAM

l o ngwo r d

E XE $G L C L I TAB L

SYS PARAM

l o ngwo r d

E XE $G L_D E F F LAG S

S YS PARAM

l o ng wo r d

S i ze

E XE $V_C RDENABLE

bit

E XE $V B UGDUM P

bit

E XE $V FATA L B UG
E XE $V M U LTAC P

bit

E XE $V_N OAUTOCNF

bit

E XE $V N OC LOC K

bit

E XE $V N OC LU S TER

bit

E XE $V_POO LPG ING

bit

E XE $V S B I E RR

bit

E XE $V S E TT I M E

bit

E XE $V S HR F l lAC P

bit

E XE $V S YS PAG I NG

bit

E XE $V S YS UAFA LT

bit

E XE $V S YSWRTAB L

bit

E XE $V RESALLOC

bit

TTY$G L DE LTA

S Y S PARAM

l o ngwo r d

TTY$GB D I A LTY P

S YS PARAM

byte

De s c r i p t i o n o f Da t a
Low l im i t t h r e sho l d o f f r e e
pag e l i s t ( FREE L I M )
N umbe r o f r e t r i e s wh e n
a t temp t i ng t o l o c k a
m u l t i pr o c e sso r d a t a
s t r uc t u r e ( LOCKRETRY )
Max i m um DR 7 8 0 d a ta r a t e
Numbe r o f UN I B US m a p
r eg i s t e r s t o p r e a l �o c a t e
fo r LPA l l ( LAMAPREG S )
Numbe r o f p r e a l l o c a ted S PT E s
fo r c o n n e c t to i n t e r r up t
( REALT I M E S PTS )
Numbe r o f page s f o r C L I
s ym b o l t a b l e ( C L I SYMTB L )
Sys tem f l ag s l o ng wo r d ( no t a
pa r am e t e r i t s e l f )
CRD e r r o r e n a b l e
( CRDENAB LE )
Wr i t e sys t em d um p o n
b ug c h e c k ( D UM PB UG )
Ma k e a l l b ug ch e c k s f a t a l
( B UG C H ECKFATA L )
C r e a te s e pa r a t e AC P f o r
e a c h vo l um e
( AC P MULT I P L E )
I nh i b i t-a u t o c o n f i g u r a t i o n
o f I /0 d ev i c e s
( N OAUTOCONF I G )
Do no t s t a r t i n t e rv a l
t i m e r ( N OC LOC K )
I n h i b i t pag e r e a d
c l us t e r i ng ( NOC L U S T E R )
Ena b l e pag i ng o f pag e d
po o l ( POOLPAG I NG )
E n a b l e d e t ec t i o n o f S B I
e r r o r s ( S B I E RRENAB LE )
P r ompt fo r sys tem t i m e i n
SYSBOOT ( S E TT IM E )
Enab l e s h a r i ng o f f i l e
AC P ( AC P S HARE )
Enab l e pag i ng o f pag e ab l e
s y s t em c o d e
( S Y S PAG ING )
Se l e c t a l t e r n a t e
a u tho r i z a t i o n f i l e
( UAFALTERNATE )
Leave e n t i r e e x e c u t i v e
wr i ta b l e ( WR I TAB LE SYS )
Enab l e r e s o u r c e
a l l o c a t i o n c h e c k i ng
( RE SALLOC )
Del ta t i me fo r d i a l up t i m e r
s c a n ( TTYS CANDE LTA )
D i a l up f l ag s ( D I ALTYPE )
(1
> Un i ted K i ng d om ,
> e l s e wh e r e )
0
=

B 17
-

EXECUT IVE DATA AREAS

S i ze

G l oba l Symbo l

Mod ul e

TTY$G B_D E F S PE ED

S Y S PARAM

byte

TTY$GW_D E FBUF

SYS PARAM

wo r d

TTY$G L_D E F C HAR

S Y S PARAM

l o ng wo r d

TTY$GW_TYPAHD S Z

S Y S PARAM

wo r d

TTY$GW_PR OT

S Y S PARAM

wo r d

TTY$G L_OWN U I C

S Y S PARAM

l o ng wo rd

S YS $G B_DFMBC

S Y S PARAM

byte

S Y S $G B_DFMB FSDK

S Y S PARAM

byt e

S YS $G B_DFMBFSMT

S Y S PARAM

byte

S Y S $G B DFMB F S UR

S Y S PARAM

byte

S YS $ G B_DFMBFRE L

S YS PARAM

byt e

S Y S $G B_DFMB F I DX

S Y S PARAM

byte

SYS $ G B_DFMB FHSH

S Y S PARAM

byte

PQL$AL_D E FAULT + 4 S Y S PARAM

byte
1 2 l o ng wo r d s

P Q L $AL_M I N + 4

S Y S PARAM

1 2 l o ng wo r d s

PQL$AB_FLAG + 1

S YS PARAM

1 2 bytes

AC P$GW_MAPCAC H E

S Y S PARAM

wo r d

AC P$GW_HDRCAC H E

S Y S PARAM

wo rd

AC P$GW_D I RCACHE

S Y S PARAM

wo rd

AC P$GW_WORKS ET

SYS PARAM

wo r d

AC P$GW_F I DCACHE

SYS PARAM

wo rd

AC P$GW_E XTCACHE

SYS PARAM

wo r d

AC P$GW_E XT L I M I T

S Y S PARAM

wo r d

B-1 8

De s c r i pt i o n o f D a ta
De f a ul t s pe ed f o r t e rm i na l s
( TTY S PE E D )
De f a ul t-t e rm i na l l i n e w i d th
( TTY B U F )
De f a u l t-te rm i n a l
c h a r a c te r i s t i c s
( TTY D E FC HAR )
S i z e o f-t ype - a h e ad b u f f e r
( TTY TYPAHDS Z )
De f a u l t-t e rm i na l a l l oc a t i o n
p r o t e c t i o n ( TTY PROT )
De f a ul t te rm i n a l own e r U I C
( TTY OWN E R )
De f a u l t-mul t i b l o c k c o u n t
( RM S DFMB C )
De f a ul t-mul t i bu f f e r c o un t
fo r s e que n t i a l d i s k I /O
( RM S DFMBFSDK )
De f a u l t-mul t i b u f f e r c o un t
f o r mag tape I /0
( RM S DFMB FSM T )
De f a u l t-mu l t i b u f f e r c o un t
fo r un i t r e co r d d ev i c e s
( RM S DFMBFS UR )
De f a ul t-mul t i b u f f e r c o un t
fo r r e l a t i v e f i l e s
( RMS DFMBFRE L )
De f a u l t-mul t i b u f f e r c o un t
fo r i nd e x ed f i l e s
( RM S DFMBF I DX )
De f a u l t-mul t i b u f f e r c o un t
h a sh ed ( RMS DFMBFHS H )
Spa r e fo r a l i gnme n t
Tab l e o f p r o c e s s quo ta l i s t
d e f a u l t v a l ue s
( Ta b l e 1 7 - 4 )
Ta b l e o f p r o c e s s quo ta l i s t
m i n imum va l ue s
( Ta b l e 1 7 - 4 )
Ta b l e o f p r o c e s s quo ta l i s t
f l ag s
Numb e r o f b l o c ks i n b i tmap
c a che ( AC P MAPCACHE )
Numb e r o f b l ock s i n f i l e
h e ad e r c a c h e
( AC P HDRCAC HE )
Numbe r of b l oc ks i n f i l e
d i r e c to r y c a c h e
( AC P D I RCAC H E )
AC P wo rki ng s e t s i z e
( AC P WORKS E T )
Numbe r of c a c h ed i nd e x f i l e
s l o ts ( AC P F I DCACHE )
Num b e r o f c a ched d i s k
e x te n t s ( AC P E XTCACHE )
Fr a c t i o n o f d i sk to c ac h e
( AC P_E XT L I M I T )

EXECUTIVE DATA AREAS

S i ze

G l o b a l Symbo l

Mod u l e

ACP $GW_Q U OCAC HE

S Y S PARAM

wo r d

ACP $GW_S YSACC

S Y S PARAM

wo r d

AC P$G B_MAXREAD

S Y S PARAM

byt e

ACP$G B WI NDOW

S YS PARAM

byte

AC P $G B WR ITBACK

S YS PARAM

byte

AC P $G B DATAC HK

S Y S PARAM

byte

Numbe r o f quo t a f i l e e n t r i e s
to c a c h e ( AC P QUOCAC H E )
De f a u l t a c c e s s for s ys t em
vo l um e s ( AC P S YSAC C )
Ma x i m um n um b e r of b l o c k s t o
r e a d a t o n c e fo r
d i r e c to r i e s ( AC P MAXREAD )
De f a u l t w i nd ow s i z e - f o r
s y s t em vo l um e s
( AC P W INDOW )
Enab l e de fe r r ed c a c h e wr i t e
b a c k ( AC P WR I T E BACK )
AC P d a t a c h e ck e n ab l e f l ag s
( AC P_DATAC H E C K )

bit
bit

AC P$V READC HK
AC P $V=WR I TE C HK
AC P$GB_BAS E PR I O

S Y S PARAM

byt e

ACP$GB SWAPF LG S

S YS PARAM

byt e
bit

AC P$V SWAPG RP

bit

AC P$V SWAP PRV

bit

AC P$V_SWAPMAG

bit
SYS PARAM

byte

S YS $GB D E FPR I

S YS PARAM

byte

S YS $GW_I JOB L IM

S YS PARAM

wo r d

S Y S $GW BJOB L IM

SYS PARAM

wo r d

SYS $GW_NJOB L IM

SYS PARAM

wo r d

Do d a t a c h e c k o n r e a d s
D o d a t a c h e c k o n wr i t e s
A C P b a s e so f twa r e p r i o r i t y
( AC P BAS E PR I O )
AC P s wap f l ag s
( AC P_SWAPF LGS )

AC P$V_SWAPS YS

SYS $GB MXPRTSYM

De s c r i p t i o n o f Da t a

Swa p ACPs f o r /SYSTEM
vo l um e s
Swa p AC Ps f o r /G ROUP
vo l um e s
Swa p AC Ps f o r p r i v a t e
vo l um e s
Swa p mag t a pe AC Ps
Max i m um n umb e r o f p r i n t
s ymb i on t s ( MAXPR I NTSYMB )
De f a u l t p r i o r i ty f o r j o b
i n i t i a t i o n s ( DE FPR I )
( a l so uppe r l i m i t o n
" c r un c h e r " p r o c e s s
p r i o r i ty )
L i m i t f o r i n t e r a c t i v e j o bs
( I JOB L I M )
L i m i t f o r b a tc h j o b s
( BJOB L I M )
L i m i t fo r n e two r k j o b s
( NJOB L I M )

8-1 9

E XECUTIVE DATA AREAS

Th e r e s t o f m o d u l e SYS PARAM c o n s i s t s o f o th e r sys tem wi d e pa r ame te r s
who s e v a l ue s a r e n o t d i r e c t l y a d j us tab l e w i th SYSB OOT o r SYSGEN b u t
wh i c h d e pe nd
d i r ec t l y o n
the v a l ue s o f o n e o r mo r e ad j us ta b l e
pa r am e t e r s .
G l o b a l Symbo l

Mod u l e

S i ze

SWP $G L_S H E L LS I Z

S Y S PARAM

l o ng wo r d

SWP $GW BAKPTE

SYS PARAM

wo rd

SWP $GW EMPTPTE

S Y S PARAM

wo r d

SWP $GW WS LPTE

S Y S PARAM

wo rd

SWP $G B S H L P l PT

S Y S PARAM

byte

SWP $G L_B S LOTS Z

SYS PARAM

byte
l o ng wo r d

SWP $G L MAP

S YS PARAM

l o ng wo r d

SWP $G L PHDBASVA

S Y S PARAM

l o ng wo r d

SGN $G L PHDAPCNT
SGN $G L=PHDLWCNT

S Y S PARAM
S Y S PARAM

l o ng wo r d
l o ngwo r d

SGN $G L P l LWCNT

S Y S PARAM

l o ng wo r d

SGN$G L PHDPAG C T

S Y S PARAM

l o ng wo rd

SGN$G L P T PAGCNT
MMG $G L=C T LBASVA

S Y S PARAM
S Y S PARAM

l o ng wo r d
l o ng wo rd

E XE $AL_S TACKS

SYS PARAM

2 l o ngwo r d s
l o ngwo r d

EXE $G L I NT S TK

l o ng wo r d

MMG $G L_G PTBAS E

S Y S PARAM

l o ngwo r d

MMG $G L G PT E

S Y S PARAM

l o ngwo r d

MMG $G L MAXG PTE
MMG $G L=MAXSYSVA

S YS PARAM
S Y S PARAM

l o ngwo r d
l o n g wo r d

MMG $G L_S PTBAS E

S Y S PARAM

l o ng wo r d

MMG $G L S PT LEN
MMG $G L-SYS PHD

S Y S PARAM
S YS PARAM

l o ng wo r d
l o ng wo r d

8-2 0

De s c r i p t i o n o f Da t a
Pag e s r e qu i r ed fo r Sh e l l
process
Numbe r o f p r o c e s s h e a d e r
pag e s f o r p r o c e s s h e ad e r
pag e a r r a ys
Numbe r of emp t y p r o c e s s
h e ad e r pag e s f o r wo r k i ng
s e t l i s t expans i o n
Numbe r o f p r o c e s s h e ad e r
pag e s f o r f i x ed a r e a ,
wo r k i ng s e t l i s t , a nd
p r o c e s s s e c t i o n t ab l e
Numbe r o f P l pag e t a b l e
pag e s r e q u i r ed fo r Sh e l l
Spa r e f o r a l i g nm e n t
S i z e ( i n p ag e s ) o f b a l a n c e
slot
Ad d r e s s o f swa ppe r ' s I /0
pag e t a b l e
Ba s e a d d r e s s o f p r o c e s s
h e a d e r w i ndow
C o un t of Sh e l l he ad e r pag e s
C o un t o f l o ng wo r d s i n
p r o c e s s h e ad e r
Co u n t o f l o ng wo r d s t o e nd o f
P l pag e t a b l e
C o u n t o f a l l p r o c e s s h e ad e r
pag e s e x c l ud i ng pag e
t a b l e pag e s
Co un t o f p a g e t ab l e pag e s
I n i t i a l l o w a d d r e s s e nd o f
P l s pa c e
Ar r a y o f k e rne l mod e sys tem
spa c e s t a c k s
Ad d r e s s o f swa ppe r ' s
ke rnel stack
Ad d r e s s o f i n t e r r up t
s ta c k
Ba s e a d d r e s s o f g l o b a l pag e
table
Ad d r e s s o f f i r s t G PTE
{ ps e ud o S PTE ) at e nd o f
s ys t em pag e t a b l e
H i g h e s t G PTE a d d r e s s
H i g h e s t s y s tem v i r t ua l
a d d r e s s { pl us one )
Ba s e v i r t u a l add r e s s o f
sys t em pag e t a b l e
Leng th o f sys tem pag e t a b l e
V i r t 4a l ad d r e s s o f sys tem
h e ad e r

EXE C UT I VE DATA AREAS

Si ze

G l o b a l Symbo l

Mo d u l e

MMG $G L S YS PHD LN

S Y S PARAM

l o ng wo rd

SWP$G L_BALBAS E

S YS PARAM

l o ngwo rd

SWP$G L_BALS PT

SYS PARAM

l o ng wo rd

MMG $ G L S B R

SYS PARAM

l o ng wo rd

MMG $G L_N PAG EDYN

SYS PARAM

l o ngwo rd

MMG $G L_PAG E DYN

S YS PARAM

l o ng wo rd

MMG $G L MAXPFN

SYS PARAM

l o ng wo r d

EXE $G L_R PB

SYS PARAM

l o ng wo r d

B OO $G L_S PTFREL

S YS PARAM

l o ng wo rd

BOO$G L S PTFREH

SYS PARAM

l o ngwo r d

E XE $G L S C B

SYS PARAM

l o ng wo r d

EXE $GB C PUTYPE

SYS PARAM

PFN $A BAS E

SYS PARAM

byte
3 byt e s
8 l o ng wo r d s

PFN $ A L P T E
PFN $AL-BAK

l o ngwo r d
l o ngwo r d

PFN$AW_R E FCNT

l o ngwo r d

PFN$AW_F L I NK , PFN$AW_S HRCNT

l o ngwo r d

PFN$AW_B L INK , PFN$AW_WS LX

l o ngwo r d

PFN$AW SWPVBN

l o ngwo r d

PFN$AB S TATE

l o ngwo r d

PFN$AB TYPE

l o ngwo r d

E XE $GT S TART UP

S YS PARAM

3 3 bytes

B-2 1

De s c r i p t i o n o f Da t a
S i ze ( i n b y t e s ) o f s ys tem
h e ad e r
Base v i r tua l add r e s s o f
ba l ance s l o t a rea
Ba s e v i r t u a l a d d r e s s i n
s y s tem pag e t a b l e f o r
m a pp i ng b a l a n c e s l o t s
Phys i c a l a d d r e s s o f sys tem
pag e t a b l e ( Dupl i c a t e s
c o n t e n t s o f PR $ S B R )
V i r t u a l add r e s s o f-b eg i nn i ng
o f no np� g e d po o l
V i r t ua l ad d r e s s o f beg i nn i ng
o f pag ed po o l
Ma x i m um PFN a c c o un t ed fo r i n
PFN d a t a b a s e
V i r t u a l add r e s s o f r e s t a r t
pa r ame t e r b l o c k
V i r t u a l pag e numbe r o f l o we r
e nd o f po o l o f un u s ed
S PT E s
Vi r t u a l pag e n um be r o f uppe r
end o f po o l o f unused
S PT E s
V i r t u a l add r e s s o f sys tem
c o n t ro l b l o c k
C PU t ype r e ad f r om P R $ S I D
Spa r e fo r a l i g nm e n t
Ad d r e s s e s o f e i g h t PFN d a t a
b a s e a r r a ys
Ad d r e s s o f PTE a r r a y
Ad d r e s s o f b a c k i ng s t o r e
add r e s s a r r a y
Ad d r e s s o f r e f e r e n c e
c o un t a r r a y o f wo r d s
Ad d r e s s o f c omb i n e d
f o r wa r d l i n k /g l o b a l
sha r e c o un t a r r a y o f
wo r d s
Ad d r e s s o f comb i n e d
b a c kwa r d l i n k/wo r k i ng
s e t l i s t i nd ex a r r a y
o f wo r d s
Ad d r e s s o f swa p i m ag e
v i r t ua l b l o c k n umbe r
a r r a y o f wo r d s
Ad d r e s s o f STATE a r r a y o f
byt e s
Ad d r e s s o f TYPE a r r a y o f
bytes
C o un t ed ASC I I s t r i ng o f n a m e
o f s t a r t up c ommand f i l e

EXEC UT IVE DATA AREAS

8 . 1 . 17

Rema i nd e r o f Ex e c u t i ve Imag e

Th e r e s t o f t h e e x e c u t i ve imag e c o n s i s ts o f
r ead-onl y code a r eas ,
r e ad - o n l y
tables ,
a nd
pa tch
spac e .
Al l
o th e r d a ta
a reas a re
d yn am i c a l l y c r e a t ed a s a pa r t o f s y s tem i n i t i a l i za t i o n .
G l ob a l l abel
MMG $ FRSTRONLY ,
d e f i n ed
i n mod u l e MOAT ,
locates
the
b eg i nn i ng
of the n o n pag ed e x e c u t i v e r o u t i ne s .
Th e pag ed e x e c u t i v e i s
a l so
d e l i m i t ed
by the
l a b e l s MMG $AL PGOC OO a nd MMG $AL_PGDC OOEN ,
d e f i n ed i n MOAT .

8.2

DYNAM I CALLY ALLOCATED EXECUT IVE DATA

M a n y o f t h e d a ta s t r uc t u r e s a nd a r e a s o f s y s t em ad d r e s s s p a c e a r e n o t
a
pa r t o f
the
e x e c u t i ve i ma g e b u t i n s t e a d a r e c o n s t r uc ted wh e n the
sys tem is i n i t i a l i z e d .
Th e s i z e s o f some of t h e s e a r e a s d e pe nd o n the
v a l u e s o f S YS 8 00T p a r am e t e r s .
O th e r a r e a s d e pe nd o n t h e pa r t i c u l a r
phys i c a l c o n f i g u r a t i o n .

8.2. 1

Re s ta r t Pa r am e t e r B l o c k

Th e r e s ta r t p a r am e te r b l o c k i s f i l l ed i n a t i n i t i a l i z a t i o n t i me w i th
b o o t s t r a p pa r am e t e r s .
Th e
powe r
f a i l u r e i n t e r r up t s e rv i c e r o u t i n e
l o ad s the v o l a t i l e m a c h i n e s t a t e i n to th e R PB b e fo r e the sys t em h a l t s .
Du r i ng
powe r r e c o v e r y , t h e r e s ta r t pa r am e t e r b l o c k a l l o ws t h e c o n so l e
l og i c to d e t e rm i n e wh e th e r memo r y c o n t e n t s s u rv i v ed t h e powe r o u t ag e .
Th e u s e o f t h e r e s ta r t pa r am e t e r b l o c k i s d i sc us s ed i n Ch a p te r s 2 1 a nd
23.

8.2. 2

PFN Da t a Ba s e

Th e PFN d a t a b a s e c o n s i s t s o f s eve r a l a r r a ys who s e c o n t e n t s d e sc r i b e
t h e s t a t e o f e a c h pag e i n phys i c a l memo r y .
( To s a v e memo r y , pag e s
tha t c o n t a i n the pe r m a n e n t l y r e s i d en t €X e c u t i v e a r e no t a c c o un ted
fo r
in
the
PFN d a t a b a s e . ) Th e PFN a r r a ys a r e d e sc r i b ed i n Ch apte r 1 1 .
Th e i r u s e d u r i ng pag e f a u l t r e so l u t i o n
i s d i sc us s ed
i n Ch a p t e r 1 2 .
PFN a r r a y m a n i pu l a t i o n d u r i ng
s wa ppe r o pe r a t i o n s
i s d i s c us s ed i n
Ch a p t e r 1 4 .

8.2.3

P a g ed Dyn am i c Memo r y

Pag ed dyn am i c memo r y c o n ta i n s a l l
s y s t em-w i d e d ynam i c a l l y a l l o c a ted
s t r uc t u r e s
that do
not
h av e
to b e pe rma n e n t l y r e s i d e n t .
Typ i c a l
s t r uc t u r e s
a l l o c a ted
f r om pag ed
d yn am i c m emo r y a r e
l i s ted
in
Ch a p t e r 2 5 .

8- 2 2

EXECUT I VE DATA AREAS

B.2.4

No n pa g ed Dyn am i c Mem o r y

No n pag ed po o l c o n ta i n s a l l d yn am i c a l l y a l l o c a ted s t r uc t u r e s tha t mus t
b e r e s i d en t a t a l l t i m e s .
Th e s e s t r uc t u r e s m a y c o n t a i n e i th e r cod e o r
Th e no rma l
n o n pag ed
d a ta .
Th e r e a r e a c t ua l l y t wo po o l a r e a s h e r e .
po o l uses t h e same a l l o c a t i o n r o u t i n e as is u s e d fo r pag ed po o l .
Th i s
po o l a r e a c a n h a v e b l o c k s o f a ny s i z e a l l o c a ted
f r om
it.
A s e co nd
po o l
a r ea c o n ta ins
f i x ed
s i ze
blocks
( c u r r en t l y 9 6 byt e s ) l i nk e d
tog e th e r so t h a t a b l o c k m a y b e i n s e r ted o r r emoved wi th t h e
I N S QU E
a n d REMQU E
i n s t r uc t i o n s .
Th i s
s e c o nd
a rea
i s o f t e n c a l l ed the
l o o ka s i d e l i s t .
Th e u s e of n o n pag ed po o l is d e s c r i b ed in Ch a pt e r 2 5 .

B. 2. 5

I n t e r r up t S t a c k

Th e i n t e r r up t s t a c k i s u s e d to s e r v i c e a l l h a r d wa r e i n t e r r up t s a nd a l l
so f twa r e i n t e r r up t s e x c e p t AST d e l i v e r y .

B.2.6

Sys t em Co n t r o l B l o c k

Th e sys tem c o n t r o l b l o c k i s s t r i c t l y s pe a k i ng
no t a
wr i t a b l e d a t a
s t r uc t u r e a l tho ug h e n t r i e s
a re
some t i me s mo d i f i ed by the e x e c u t i v e
d eb ug g e r XDE LTA .

B.2.7

Ba l an c e S l o t Ar e a

Th e b a l a n c e s l o t a r e a i s d evo ted e x c l u s i v e l y t o p r o c e s s h e ad e r s .
An y
r e s i d en t p r o c e s s h a s i t s p r o c e s s h e ad e r i n o n e o f the b a l a n c e s l o t s .
Ba l anc e s l o t s a r e d e sc r i b ed i n Ch a pt e r 1 1 .
Th e i r u s e by
the
swa ppe r
i s d i s c u s s ed i n Cha p t e r 1 4 .

B.2.8

Sys t em He a d e r

Th e s ys t em h e ad e r i s a sys tem a n a l og u e t o p r o c e s s h e ad e r s th a t a l l o ws
s y s t em c o d e
to be pag e ab l e .
Th e s t r uc t u r e s w i th i n the sys t em h e ad e r
tha t a r e o f t e n a l t e r ed a r e t h e sys t em wo r k i ng s e t l i s t a nd the s y s t em
s e c t i o n tab l e tha t c o n t a i n s g l ob a l s e c t i o n t a b l e en t r i e s .

B. 2.9

Sys t em P a g e Tab l e

Th e po r t i o n o f the sys tem pag e t a b l e tha t und e rg o e s the m o s t c h a ng e i s
O th e r ope r a t i o n s c a n c a u s e
tha t pa r t th a t m a ps t h e b a l a n c e s l o t a r e a .
o the r a r e a s o f t h e sys t em pa g e t a b l e t o c h a ng e .

8 . 2. 10

G l o ba l Pag e Ta b l e

Th e g l o b a l p a g e t ab l e i s a p s e ud o e x t e n s i o n o f t h e sys tem pag e t a b l e
tha t a l l ows G PT E s to b e a c c e s s ed w i th SVPNs .
Th e g l o b a l pag e t ab l e i s
a l t e r ed wh en g l oba l s e c t i o n s a r e c r e a ted and d e l e t ed .
In
ad d i t i o n ,
G PTEs c a n c h a ng e a s a r e s u l t o f pag e f a u l t s .
B- 2 3

EXE C UT I VE DATA AREAS

B.3

PROC ESS-SPEC I F I C EXECUT IVE DATA

S ome p r o c e s s - s pe c i f i c d a t a i s s to r ed i n t h e p r o c e s s h e a d e r .
Th a t d a t a
i s a c c e s s i b l e ( s ub j e c t to s yn c h r o n i za t i o n c o n s i d e r a t i o n s ) wh e n ev e r th e
process i s res ident .
Mo s t o f t h e p r o c e s s - s p e c i f i c d a t a i s f o und i n P l
space .
P l s pa c e i s o n l y a d d r e s s a b l e wh e n the p r o c e s s i s t h e c u r r e n t
process .
Th e e x e c u t i v e us e s ASTs t h a t e x e c u t e i n p r o c e s s c o n t e x t wh e n
it
is
n e c e s s a r y to
a c qu i r e
o r mod i f y s uc h d a ta f r om some o th e r
proc e s s .

B.3.1

Pl Po i n te r Pag e

Th e P l po i n t e r pag e i s a pe rm a n e n t m em b e r o f the p r o c e s s wo r k i ng
Th e e n t i r e po i n t e r pag e i s d e f i n ed i n e x e c u t i v e mod u l e S H E L L .
G l o b a l Sym b o l

Da t a Ar e a

S i ze

C T L$GW NM I OC H
CT L$G W-C H INDX
CTL$G L-RM S P P

P l Po i n t e r Pag e
P l Po i n t e r Pag e
P l Po i n t e r Pag e

wo r d
wo r d
l o ng wo rd

CT L$G L RM S I P

P l Po i n t e r Pag e

l o ng wo r d

P l Po i n t e r Pag e

l o ng wo rd

P l Po i n t e r Pag e

l o ng wo r d

P l Po i n t e r Pag e

l o ng wo rd

P l Po i n t e r Pag e

l o ng wo rd

P l Po i n t e r Pag e

l o ng wo r d

C T L$G L P L T F L

P l Po i n t e r Pag e

l o ng wo r d

CTL$G L P LTBL

P l Po i n t e r Pag e

l o ngwo rd

CTL$G L CMS UPR

P l Po i n t e r Pag e

l o ng wo r d

C T L$G L C MUS ER

P l Po i n t e r Pag e

l o ng wo r d

CTL$G L C M HANDLR

P l Po i n t e r Pag e

l o ng wo r d

CTL$AQ_E XCVE C

P l Po i n t e r Pag e

8 l o ng wo r d s

C T L $ G L_TH E XE C

P l Po i n t e r Pag e

3 l o ng wo r d s

CTL$AL S TAC K

B-24

set .

D e s c r i pt i o n o f Da t a
Num b e r o f I /0 c h a nn e l s
Ma x i m um cha n n e l i nd ex
Po i n t e r to RM S p r o c e s s
I /0 s egm e n t
Po i n t e r t o RM S i m ag e I /O
s egmen t
Ma x i m um e x t e n t ( l ow
ad d r e s s l i m i t ) o f
ke rnel s ta c k
I n i t i a l v a l ue o f k e r n e l
s t a c k po i n t e r
I n i t i a l v a l ue o f
e x ec u t i v e s t a c k
po i n t e r
I n i t i a l v a l ue o f
s up e r v i s o r s t a c k
po i n t e r
I n i t i a l v a l ue o f us e r
s t a c k po i n t e r
L i s th e ad ( fo r wa rd l i n k )
fo r p r o c e s s l og i c a l
name t a b l e
Ba c kwa rd l i n k f o r p r o c e s s
l og i c a l n a m e ta b l e
Ad d r e s s o f
chang e -mod e- to
s upe r v i s o r h a nd l e r
Ad d r e s s o f
chang e -mod e - to-us e r
h a nd l e r
Ad d r e s s o f compa t i b i l i t y
mod e h a nd l e r
Ad d r e s s e s o f p r i m a r y a nd
s e c o nd a r y e x c e p t i o n
h a nd l e r s f o r e a c h o f
t h e f o u r a c c e s s mod e s
Te r m i n a t i o n h a nd l e r
l i s th e ad s f o r
e x e c ut i v e , s upe r v i so r ,
a nd us e r a c c e s s mod e s

EXECUT I VE DATA AREAS

G l o b a l Symbo l

Mo d u l e

S i ze

C T L $ G Q_C OMMON

P l Po i n t e r Pag e

quad wo rd

C T L $ G L G E TMSG

Pl Po i n t e r Pag e

l o ng wo rd

C T L $AL S TACKS I Z

P l Po i n t e r Pag e

4 l o ngwo r d s

C T L $ G L C T LBASVA

P l Po i n t e r Pa g e

l o ng wo r d

C T L $ G L I MG HDRBF

P l Po i n t e r Pag e

l o ng wo r d

C T L $ G L RUNDNFLG

P l Po i n t e r Pa g e

l o ng wo rd

RND $V IAC LOCK

Desc r i pt i o n o f Da t a
D e s c r i p to r ( s i z e a nd
add r e s s ) o f
pe r - p r o c e s s c ommo n
a rea
Ad d r e s s o f pe r - p r o c e s s
m e s s ag e d i spa t ch e r
S i ze o f s tac k fo r e ach
a c c e s s mod e
Lo w a d d r e s s e nd o f
pe r m a n e n t pa r t o f P l
sp a c e
Ad d r e s s o f i ma g e
a c t i v a to r ' s imag e
h e ad e r b u f f e r
Imag e r und own c o n t r o l
f l ag

bit

Imag e a c t i v a to r l o c k
mus t be r e s e t
Ad d r e s s o f P l wi ndow
th a t d o u� l e maps the
p r o c e s s h e ad e r pag e s
th a t a r e n o t pag e
t a b l e pag e s
L i s th e a d fo r t h e p r o c e s s
a l l o c a t i o n r eg i o n
L i s th e a d fo r the p r o c e s s
p r i v a t e mo unted vo l um e
l i st
Ex i t s t a t u s o f l a t e s t
imag e t o execute
Pe a k v i r t ua l s i z e f o r
process
Pe a k wo r k i ng s e t s i z e f o r
p r oc es s
C o unt o f mo un ted vo l um e s
Us e r name f o r p r o c e s s
( b l a n k - f i l l ed ASC I I
s t r i ng )
Ac c o un t n ame fo r p r o c e s s
( b l a n k - f i l l e d ASC I I
s t r i ng )
Pe r m a n e n t p r o c e s s
p r i v i l eg e m a s k
Ad d r e s s o f pe r - p r o c e s s
c h a ng e -mo d e - to - k e r n e l
d i spatche r
Ad d r e s s o f p e r - p r o c e s s
ch ang e-mo d e - to 
e x e c u t i v e d i spa tc h e r
Ad d r e s s o f powe r r e c o v e r y
AST f o r p r o c e s s
Ac c e s s m o d e fo r po we r
r e cove r y AST
Spa r e f o r a l i g nm e n t

C T L $ G L PHD

Pl Po i n t e r Pa g e

l o ng wo rd

C T L $ G Q_A LLOCREG

P l Po i n t e r Pag e

quad wo r d

C T L $ G Q_MOUNT LST

P l Po i n t e r P a g e

q u a d wo rd

C T L $G L F I NALS TS

P l Po i n t e r Pa g e

l o ng wo r d

C T L $G L V I RTPEAK

P l Po i n t e r Pag e

l o ng wo rd

C T L $G L WS PEAK

P l Po i n t e r Pag e

l o ng wo rd

C T L $G L VO LUM E S
C T L $ T US ERNAM E

P l Po i n t e r Pag e
P l Po i n t e r Pag e

l o ng wo r d
1 2 byt e s

C T L $ T ACCOUNT

P l Po i n t e r Pag e

8 byt e s

C T L $ G Q_PROC PR I V

P l Po i n t e r Pag e

quad wo r d

C T L $G L U S RC HMK

P l Po i n t e r Pag e

l o ng wo r d

C T L $G L U S RC HM E

P l Po i n t e r Pag e

l o ng wo r d

C T L $G L POWERAS T

P l Po i n t e r Pag e

l o ng wo rd

C T L $G B PWRMODE

P l Po i n t e r Pag e

byte
3 by t e s

B-2 5

EXECUTIVE DATA AREAS

G l o b a l Symbo l

Mod u l e

S i ze

C T L $ G Q _L OG I N

P l Po i n t e r Pag e

q uad wo rd

C T L $ A L F I NA L E XC

P l Po i n t e r Pag e

4 l o ngwo r d s

C T L$G L_C C 8 8AS E

P l Po i n t e r Pa g e

l o ng wo rd

C T L $ G Q_D8GAREA

P l Po i n t e r Pag e

q uad wo r d

CTL$G L RM S8ASE

P l Po i n t e r Pag e

l o ng wo rd

C T L $G L_P PM SG

P l Po i n t e r Pag e

l o ng wo r d

C T L $ G 8 MSGMASK

P l Po i n t e r Pag e

byte

C T L $ G 8_D E F LANG

P l Po i n t e r Pag e

byte
2 byt e s

8.3.2

De sc r i pt i o n o f Da t a
Sys t em t i me at p r o c e s s
c reat ion
Ad d r e s s o f l a s t c h a n c e
e x c ep t i o n h a nd l e r s fo r
each o f the four
a c c e s s mod e s
Ad d r e s s of b a s e o f I /0
c h a nn e l a r e a
Desc r i pto r { s i z e a nd
add r e s s ) f o r d eb ug
s ymbo l t a b l e
Po i n t e r to b a s e o f RM S
image
Ad d r e s s o f
p r o c e s s-pe rma n e n t
m e s s a g e s ec t i o n
De f a ul t m e s s ag e d i s p l a y
f l ag s
De f a ul t m e s s ag e l a ng uag e
Spa r e fo r a l i g nm e n t

Oth e r P l S p a c e Da t a A r e a s

Th e l a yo u t o f P l s pa c e
is
p i c t u r ed
i n Ch a pt e r 1
a nd d e ta i l ed
in
Ta b l e E - 4 l i s t s the g l o b a l l a b e l s tha t d e l im i t e ac h a r e a
App e nd i x E .
i n P l s pa c e .
Th e r em a i nd e r o f th i s a ppe nd i x s umma r i z e s d a t a l o c a t i o n s
in
s p e c i f i c P l a r e a s tha t a r e d e f i n ed i n modul e SHE L L .
Th e a r e a s a r e
p r e s e n t ed i n o r d e r o f d e c r e a s i ng P l v i r t ua l add r e s s e s .
Th a t
is ,
the
CLI
d a t a pag e s a r e p r e s e n t ed f i r s t a nd o c c upy the h i g h e s t P l a d d r e s s
r a ng e .
Th e p r o c e s s I /0 s e gme n t o c c up i e s t h e l o we s t P l
address
r a ng e
o f t h e a r e a s p r e s e n ted he r e a nd i s l i s t e d l a s t .

8 . 3 . 2 . 1 Da ta Pag e s fo r Command Language I n t e r p r e t e r - Mo d u l e
s e ts a s i d e a n a r e a fo r the g e ne r i c C L I d a t a pag e s .
G l o b a l Symbo l

Da t a A r e a

C T L $AL_C L I CALBK

Gene r i c CLI
Da t a Pag e s
Gene r ic CLI
Da t a Pa g e s
Gene r i c CLI
Da t a Pag e s

C T L $AG C L IMAG E
C T L $ AG_C L I DATA

S i ze

SHELL

De s c r i p t i o n o f Da t a

2 l o ng wo r d s

C a l l b a c k v e c to r fo r C L I

2 l o ng wo r d s

V i r t ua l ad d r e s s r a ng e i n to
wh i c h C L I i s m a pped
Re s t o f C L I d a t a a r e a

B- 2 6

EXEC UT IVE DATA AREAS
8.3. 2. 2
Process Al locat i o n Reg i o n - Th e p r o c e s s a l l o c a t i o n a r e a i s
a
p e r - p r o c e s s po o l
a r e a c o n s t r uc t ed
e x a c t l y l i ke pag ed a nd nonpa g ed
d yn am i c m em o r y .
I t i n i t i a l l y r e q u i r e s t wo
l o ngwo rd s .
On e
l o ng wo r d
d e sc r i b e s
the
i n i t i a l s i ze o f t h e b l o c k .
Th e o th e r c o n t a i n s a z e r o ,
i nd i c a t i ng t h a t th e r e a r � n o o th e r u n u s e d b l o c k s i n the po o l .

G l o b a l S ymbo l

Da t a Ar e a
P r o c e s s Al l o c a t i o n
Reg i o n
P r o c e s s Al l o c a t i o n
Reg i o n

Si ze
l o ng wo r d
l ong wo r d

De s c r i p t i o n o f Da t a
I n i t i a l fo r wa rd l i n k
( co n t a i n s z e r o )
I n i t i a l s i z e o f r eg i o n

8.3. 2. 3
Compa t i b i l i ty Mo d e Co n t ex t Pag e - Ano th e r P l d a ta
area that
modul e S H E LL d e f i n e s s ymbo l s fo r i s t h e pag e used b y t h e c ompa t i b i l i ty
mod e e x c e p t i o n s e r v i c e r o u t i n e .

G l o b a l Sym b o l

Da t a Ar e a

C TL$AL_CMCNTX

Compa t i b i l i ty 1 0 l o ng wo r d s
Mo d e Co n t e x t
Pag e

S i ze

7 l o ngwo r d s
1 l o ngwo r d
2 l o ngwo r d s

Compa t i b i l i ty r e s t o f pag e
Mo d e Co n t e x t
Pa g e

De sc r i p t i o n o f Da t a
G en e r a l r eg i s t e r c o n t e n t s
s to r ed by e x c ept i o n
s e rv i c e rout i ne
Saved RO th r o ug h R6
Saved c ompa t i b i l i t y mod e
e x c ept i o n c o d e
S a v ed e x c e p t i o n P C a nd
PS L
Used by c ompa t i b i l i t y
mode em u l a to r

8.3. 2. 4
Process I/0 Segment - Th e p r o c e s s I /O s egme n t i s used to h o l d
all
o f t h e RM S c o n t e x t t h a t e x i s t s fo r t h e l i fe o f t h e p r o c e s s .
Th i s
i nc l ud e s a l l i n fo rma t i o n a b o u t p r o c e s s p e rma n e n t f i l e s ,
a s we l l
as
po i n t e r s
i n to
the
i mag e I /0 s egmen t , t h e RMS c o n tex t a r e a t h a t o n l y
e x i s t s wh i l e a n imag e i s a c t i v e .
Th e r e i s
a
s e c o nd
a rea
i n Sh e l l
c a l l ed t h e p r o c e s s I /O s egmen t .
Th i s po r t i o n o f P l s pa c e i s n o l ong e r
u s ed .

B- 2 7

EXECUTIVE DATA AREAS

G l o b a l Symbo l

Da ta Area

P I O $G L_FMLH

P r o c e s s I /O
Segment
P r o c e s s I /O
Segment
P r o c e s s I /0
S e g me n t
P r o c e s s I /O
Segment
P r o c e s s I /O
S e g me n t
P r o c e s s I /O
Segme n t
P r o c e ss I /O
S e g me n t

P I O $G L I I OF S P L H
P I O $GW S TATUS
P I O $G T ENDSTR
P I O $GW_DFPROT
P I O $G B DFMBC
P I O $G B_DFMBFSDK

S i ze
2 l o ng wo r d s

wo r d

F r e e m emo r y l i s th e a d f o r
p r o c e s s I /O s egme n t
F r e e memo r y l i s t h e a d f o r
i mag e I /O s egment
RM S ov e r a l l s t a tus

16 bytes

End of d a ta s t r i ng

wo r d

De f a u l t f i l e p r o t e c t i o n

byt e

byte

De f a u l t m u l t i b l o c k c o un t
( RM S DFMBC )
De f a u l t-m u l t i b uf f e r c o un t
f o r s e q u e n t i a l d i s k I /0
( RMS D FMBFSDK )
De f a u l t-m u l t i b uf f e r c o un t
fo r m ag t a pe I /0
( RMS DFMBFSMT )
De f a ul t-m ul t i bu f f e r c o un t
fo r un i t r eco r d d e v i c e s
( RMS D FMBFS UR )
De f a ul t-m u l t i b uf f e r c o un t
fo r r e l a t i ve f i l e s
( RMS D FMB FRE L )
De f a ul t-m ul t i b u f f e r c o un t
fo r i nd ex ed f i l e s
( RM S DFMB F I D X )
De f a ul t-m u l t i b uf f e r c o un t
h a shed ( RMS DFMBFHS H )
Spa r e fo r a l i g nm e n t

8 4 byt e s

De f a u l t d i r e c to r y s t r i ng

2 l o ngwo r d s

D i r e c to r y c a c h e l i s th e a d

l o ng wo r d

F r e e l i s t f o r d i r e c to r y
c a c h e nod e s ( s i ng l y
l i nked )
P r o c e s s I /O Segmen t
contex t a r ea
Imag e I /O Segme n t
contex t a r ea
RM S t e rm i n a t i o n h a nd l e r
con t r o l block
F r e e a r e a th a t f i l l s r e s t
o f pag e

2 l o ngwo r d s

byte

P I O $ G B DFMB FSMT

P r o c e s s I /O
S e g me n t

byt e

P I O $ G B DFMBFSUR

P r o c e s s I/O
Segment

byte

P I O $ G B DFMBFRE L

P r o c e s s I /O
S e g me n t

byte

P I O $ G B D FMBF I DX

P r o c e s s I /O
Seg m e n t

byte

P I O $GB_DFMBFHS H

P r o c e s s I /O
S e g me n t
P r o c e s s I /O
Segment
P r o c e s s I /O
Segment
P r o c e ss I /0
Segment
P r o c e s s I /O
Segme n t

byte

P I O$GT DDSTR I NG
P I O$G L D I RCAC H E
P I O $G L D I RCFRHL
P I O $GW_P I O IMPA
P I O $GW_I I O IM PA
P I O $AL RMS EXH

P r o c e s s I /0
Segment
P r o c e s s I /O
S e g me n t
P r o c e s s I /O
S e g me n t
P r o c e s s I /O
S e g me n t

Desc r i pt i o n o f Da t a

3 5 l o ngwo r d s
4 1 l o ngwo r d s
4 l o ngwo r d s
1 3 l o ngwo r d s

B- 2 8

APPENDI X C
NAM I NG C ONVE N T I ONS

Th e c o nve n t i o n s d e sc r i b ed
i n th i s
a ppe nd i x we r e
i mp l emento r s
i n p r od uc i ng m e a n i ng f u l p ub l i c nam e s .
a l l names tha t a r e g l o b a l { k nown to the
l inke r )
or
pa r am e t e r o r m a c r o d e f i n i t i o n f i l e s .

d e r i v ed
to
a id
Pub l i c n a m e s a r e
th a t a pp e a r
in

Th e s e pub l i c n am e s a r e a l l c o n s t r a i n ed to f o l l o w t h e s e r u l e s
f o l l o w i ng r e a s o n s .
•

•

fo r

the

Us i ng r e s e rved n am e s i n s u r e s tha t c us tom e r -wr i t ten
so f t wa r e
wi l l
no t b e
i nv a l i d a t ed
b y s ub s e q ue n t r e l e a s e s o f D I G I TA L
p r o d u c t s tha t a d d n ew s ym b o l s .
Us i ng d e f i n i t e pa t t e r n s f o r d i f f e r e n t u s e s a l l o ws the
r e ad e r
to
j ud g e
the
type o f o b j e c t tha t i s b e i ng r e f e r e n c ed .
Fo r
e x am p l e , t h e f o rm o f a m a c ro n am e i s d i f f e r e n t f r om
tha t o f
a n o f f s e t , wh i c h i s d i f f e r e n t f r om that o f a s t a t u s c o d e .
Us i ng c e r t a i n c o d e s wi th i n a p a t t e r n a s s o c i a t e s the
s i ze
of
a n o b j e c t w i th i t s name .
Th i s i n c r e a s e s the l i ke l i ho o d tha t
r e f e r e n c e to th i s o b j e c t w i l l u s e the c o r r e c t i n s t r u c t i o n s .
Us i ng a f a c i l i t y c o d e i n s ym b o l d e f i n i t i o n s g i v e s the
reader
an
i n d i c a t i o n o f wh e r e
the
s ym b o l
i s d e f i ned .
S e pa r a t e
g r o ups o f i mp l emen to r s a r e a l l o we d t o c h o o s e f a c i l i t y c o d e
n am e s th a t w i l l n o t c o n f l i c t w i th o n e a no th e r .

To f u l l y c o n f o rm wi th t h e s e s ta nd a rd s , l o c a l syn o n ym s sho u l d n e v e r
be
d e f i n ed
fo r p ub l i c s ym bo l s .
Th e f u l l p ub l i c sym bo l sho u l d b e u s e d i n
ev e r y r e fe r e n c e t o g i ve m a x i m um c l a r i t y t o the r e ad e r .

�� S YMBOL PATTERNS
A l l D I G I TAL s ymbo l s c o n t a i n a c u r r e n c y s i g n .
Th u s ,
c u s tom e r s a nd
a pp l i c a t i o n s d ev e l o pe r s a r e s t r o ng l y a d v i sed
to
use
u nd e r sc o r e s
i n s t e a d o f c u r r en c y s i g n s to avo i d f u t u r e c o n f l i c t s .
Pub l i c symbo l s sho u l d be c o n s t r uc t ed to c o nvey a s m uch i n f o rm a t i o n a s
po s s i b l e a b o u t
the
ent i t i es
t h e y n am e .
F r e qu e n t l y , pr i v a t e n a m e s
fo l l o w a s i m i l a r c o nv e n t i o n .
Th e p r i v a t e n am e c o nvent i o n i s t h e n
the
same a s the p ub l i c one w i th t h e und e r s c o r e r e p l ac i ng t h e c u r r e n c y s i g n
i n s ymbo l nam e s .
Pr i v a t e n a m e s a r e u s ed bo th wi th i n a mod u l e ,
a nd
g l o b a l l y b e twe e n m od u l e s o f a f a c i l i t y t h a t i s n ev e r i n a l i b r a r y .
A l l nam e s th a t m i g h t eve r b e b o und i n to a u s e r ' s p r og r am mus t f o l l o w
the
r ul es
f o r p ub l i c n am e s .
In the c a s e o f i n t e r n a l nam e s , a d o ub l e

C-1

NAM ING CONVENTI ONS

c u r r e n c y s i g n c onv e n t i o n c a n
fo l l o w i ng l i s t .
1.

u s ed

s h o wn

i tem 5

the

Sys tem s e r v i c e m a c r o n am e s a r e o f the f o rm :
$ s e r v i c e -name
A t r a i l i ng
S o r G d i s t i ng u i sh e s the
s t a c k f o rm f r om
th e
s e pa r a t e
a rg um e nt l i s t
fo rm .
De t a i l s a b o ut the nam e s o f
s y s tem s e r v i c e m a c r o s c a n b e f o und
i n the VAX/VMS Sys tem
S e r v i c e s Re f e r en c e Ma n ua l .
Th e s e
n am e s
a ppe a r
in
the
s y s tem
mac ro
l ibrary
SYS $ L I B RARY : S TARL E T . MLB a nd
r e p r e s e n t a c a l l t o one o f t h e
VAX/VM S s y s t em s e r v i c e s o r RM S s e r v i c e s .
Ex ampl e s o f th i s f o rm o f s ym bo l n am e a r e :
$AS C E FC S
$ C LO S E $ TRN LOG G

As so c i a t e Common E v e n t F l ag C l us t e r
C lose a Fi l e
T r a n s l a t e Log i c a l Name

Fa c i l i t y- s p e c i f i c publ i c m a c ro n a m e s a r e o f t h e fo rm :
$ f a c i l i t y_m a c r o n ame
Th e e x e c u t i v e d o e s n o t u s e any s ymbo l n am e s of th i s fo rm .

Sys t em m a c r o s us i ng l o c a l s ymbo l s o r m a c r o s a l wa ys use
o f the f o rm :

n am e s

$ f a c i l i t y $m a c r o n ame
Th i s i s t h e fo rm to be used bo th f o r s ymbo l s g en e r a ted by a
macro
and
i n c l ud ed
i n c a l l s to i t , a nd f o r i n t e r n a l m a c r o s
th a t a r e n o t d o c umen t ed .
Th e e x e c u t i v e d o e s n o t use a ny s ym bo l names o f th i s fo rm .
4.

S t a t us c o d e s a nd c o nd i t i o n v a l ue s a r e o f the fo rm :
f a c i l i t y $_s t a t u s
Ex ampl e s o f th i s f o rm o f s ymbo l name a r e :
RM S $ FNF
S S $ IL L E FC
S S $ -WAS C LR

F i l e No t Fo und
I l l eg a l Ev e n t Fl ag Cl us t e r
F l ag Wa s P r ev i o us l y C l e a r

G l oba l e n t r y po i n t n am e s a r e o f the f o rm :
f a c i l i t y $ e n t r y-name
Ex ampl e s o f th i s fo rm of s ym bo l n ame a r e :
EXE $ALOPAG E D
I OC $WF I KPCH
MMG $ PAG E FAULT

A l l o c a t e Pag e d Dyn am i c Memo r y
Wa i t fo r I n t e r r upt and K e e p Ch a nne l
Pag e F a u l t E x c ept i o n H a nd l e r

G l o ba l e n t r y po i n t nam e s
tha t a r e
i n t e nd ed
for
use onl y
w i th i n a
set o f
r e l a t ed p r o c ed u r e s b u t no t by a n y c a l l i ng
p r og r ams o u t s i d e t h e s e t a r e o f the fo rm :

C-2

NAM ING CONVENTIONS

f a c i l i t y $ $ e n t r y-name
Th e e x e c u t i v e d o e s
not
use
s ym bo l names o f
th i s
f o rm .
Ho we v e r ,
the Run - T i m e
L i b r a r y c o n t a i n s s ev e r a l ex ampl e s o f
s ymbo l nam e s th a t f o l l o w th i s c o nv e n t i o n , s uc h a s :
BAS $ $N UM ! N I T
FOR $ $ S I GNAL S TO
O TS $ $G E T LUN
6.

I n i t i a l i z e the BAS I C NUM f unc t i o n
S i gnal a
FORTRAN e r r o r
a nd
cal l
L I B $ S TO P
G e t Log i c a l Un i t Numbe r

G l o b a l e n t r y po i n t nam e s th a t h av e
e n t r y po i n t nam e s ) a r e o f the fo rm :

no n s t a nd a rd

calls

(JSB

f a c i l i t y $ e n t r y-name_Rn
wh e r e Rn i nd i c a t e s t h a t RO t h r o ug h Rn a r e n o t p r e s e r v e d
by
the
r ou t i n e .
No te
tha t
the c a l l e r o f s uc h an e n t r y po i n t
m u s t i n c l ud e a t l e a s t r eg i s t e r s R 2 th r o ug h R n
in
i ts
own
e n t r y ma s k so tha t a s t a c k unwi nd wi l l r e s t o r e a l l r eg i s te r s
p r ope r l y .
The e x e c u t i v e d o e s no t use th i s c o nv en t i o n f o r i t s J S B e n t r y
po i n ts b u t t h e Run - T i m e L i b r a r y c o nta i n s seve r a l e x am p l e s o f
i t s u s e , s uc h a s :
C O B $ CVTFP R 9
MTH$ S I N R4
S TR $ C O PY DX R 8
7.

C o nve r t F l o a t i ng to Pa c k ed
S i ng l e P r e c i s i o n S i n e Func t i o n
J S B e n t r y to g e ne r a l s t r i ng c o py i ng
r o ut i ne

G l o b a l v a r i a b l e n a m e s a r e o f the fo rm :
f a c i l i ty$G t_v a r i a b l e-name
Th e l e t t e r G i nd i c a t e s
a g lobal
va r i a b l e .
Th e
l e t te r
r e pr e s e n t s the t yp e o f va r i a b l e a s d e f i n ed i n Se c t i o n C . 2

Ex amp l e s o f th i s f o rm o f sym bo l n ame a r e :
C T L $ G Q PROC PR I V
EXE $G L-NONPAG ED
S C H$G L-C UR PC B
8.

P r o c e s s P r i v i l eg e Ma s k
F i r s t F r e e Bl o c k i n No npag ed Po o l
Ad d r e s s o f PC B o f C u r r e n t P r o c e s s

Ad d r e s s a b l e g l o b a l a r r ays u s e t h e l e t t e r A
l e t t e r G ) and a r e of t h e f o rm :

( i nstead

the

f a c i l i t y $At_a r r a y- n ame
Th e
l e t t e r A i nd i c a te s a g l o b a l
a r ray.
Th e
l etter
t
i nd i c a t e s t h e t yp e o f a r r a y e l em e n t a s d e f i n e d i n Se c t i o n C . 2
Ex ampl e s o f th i s f o rm o f s ym bo l n am e a r e :
C T L$AQ_E XCVE C
L OG $A L LOG T B L
PFN$AW F L I NK

A r r ay o f
Pr i ma r y a nd
S e c o nd a r y
E x c e p t i o n Ve c to r s
A r r ay
of
Log 'i c a l
Name
Ta b l e
L i s th e a d s
A r r ay o f Fo r wa r d
Li nks
fo r
PFN
Li sts

C-3

NAM I NG C ONVENT I ONS
9.

I n the a s s emb l e r , p ub l i c s t r uc t u r e o f fs e t n am e s
f o rm :

a re

the

s t r uc t u r e $ t f i e l d - n ame
Th e l e t t e r t i nd i c a t e s t h e d a ta type of the f i e l d a s d e f i n e d
in
Sec t i o n C . 2 .
Th e v a l ue o f t h e p ub l i c sym bo l i s the b y t e
o f f s e t to t h e s t a r t o f t h e d a ta e l em e n t i n t h e s t r uc t ur e .
Ex ampl e s o f th i s fo rm o f sym bo l n am e a r e :
C E B $ L E FC
GS D$W G S TX
PC B $ B PR I
10.

E v e n t Fl ag C l us t e r ( i n Common E v e n t
Block)
I nd e x
G l obal
Sec t i on Tab l e
( in
G l o b a l S e c t i o n De s c r i pto r )
Pr i o r i ty
Cur r en t
( in
Process
So f twa r e PC B )

I n the a s s em b l e r , p ub l i c
s t r uc t u r e
s i ng l e b i t nam e s a r e o f t h e fo rm :

bit

f i el d

o f f s e ts

a nd

s t r uc t u r e $ V f i e l d -n ame
Th e va l u e of the p ub l i c s ymbo l i s the b i t o f f s e t f r om th e
s t a r t o f t h e f i e l d t h a t c o n t a i n s the d a t um ( a nd no t f r om the
s t a r t of t h e c o n t r o l b l o c k )
•

Ex ampl e s o f th i s f o rm o f symbo l name a r e :
AC B $V Q UOTA
PS L$V-C URMOD
UCB $V-CANC E L
11.

Ch a rg e A S T to P r o c e s s AST Quo t a
C u r r e n t Ac c e s s Mo d e
C a n c e l I /0 o n th i s u n i t

I n the a s s emb l e r , p ub l i c s t r uc t u r e b i t f i e l d s i z e
o f the fo rm :

names

are

s t r uc t u r e $ S f i e l d - n ame
Th e va l ue of the pub l i c s ymbo l i s the n umb e r o f b i t s
f i eld .

the

Ex ampl e s o f th i s fo r m o f s ymbo l name a r e :
AC B $ S MODE
PS L $ S -C URMOD
PTE $ S -PROT
12.

Ac c e s s Mo d e of Re q u e s to r ( 2 b i t s )
C u r r e n t Ac c e s s Mo d e ( 2 b i t s )
M emo r y P r o te c t i o n o n Pag e ( 4 b i t s )

Fo r B L I S S , t h e f unc t i o n s o f the symbo l s i n the p r ev i o u s th r e e
i t ems
are
c omb i n ed
i n to a s i ng l e name u s ed t o r e f e r e n c e a n
a r b i t r a r y d a t um .
Names a r e o f t h e fo rm :
s t r uc t u r e $ x_f i e l d - n am e
wh e r e x i s t h e s am e a s t fo r s t a nd a rd s i z e d d a t a
(B,
w,
L,
a nd
Q ) a n d x s t and s f o r V f o r a r b i t r a r y a nd b i t f i e l d s .
Th e
m a c ro i n c l ud e s t h e o f f s e t , po s i t i o n , s i z e , a nd s i g n ex t e n s i o n

C-4

NAMING C ONVENTI ONS

s u i t a b l e f o r use i n a R E F B LOC K s t r uc t ur e .
t h i s n a m e i s d e f i na b l e a s
MAC RO

s t r uc t u r e $ V f i e l d - n ame
s t r uc tur e $ t f i e l d-nam e ,
s t r uc t u r e $ V- f i e l d - n am e ,
s t r uc t u r e $ S-f i e l d - n am e ,
< s i g n e x t e ns i o n > % ;

Mo s t

t yp i c a l l y ,

13.

! a s s em b l e r m e a n i ng

Pub l i c s t r uc t u r e m a s k n am e s a r e o f the fo r m :
s t r uc t u r e $ M f i e l d -name
Th e va l u e of t h e pub l i c s ymbo l is a mask w i th b i ts
set
fo r
e a ch b i t
in
the
f i el d .
Th i s m a s k i s n o t r i g h t j us t i f i ed .
Ra the r , i t h a s s t r uc t u r e $V_f i e l d - n ame ze r o b i t s o n the r i g h t .
Ex ampl e s o f th i s fo r m o f s ym bo l name a r e :
C EB $M VA L I D
PS L $ M-C URMOD
PTE $M-PROT

14.

Sh a r ed memo r y m a s t e r CEB i s v a l i d
C u r r en t Ac c e s s Mo d e
Memo r y P r o tec t i o n o n Pag e

Pub l i c s t r uc t u r e c o n s t a n t n am e s a r e o f t h e f o r m :
s t r uc t u r e $ K c o n s t a n t - n am e
E x ampl e s o f th i s fo r m o f s ym bo l n a m e a r e :
PC B $ K L ENG TH
S RM $ K-FLT OVF F
S T S $ K-S EVERE -

Leng th ( i n by t e s ) o f So f t wa r e PCB
Cod e fo r F l o a t i ng Ov e r f l ow Fa u l t
F a t a l E r r o r Cod e

Fo r h i s to r i c a l r e a s o n s , m a ny o f the
cons t a n t s
u s e d b y the
e x e c u t i v e h a ve
the l e t t e r C i n s te ad of a K t o i nd i c a t e tha t
t h e o b j e c t d a t a type i s a c o n s t a n t .
E x amp l e s o f th i s fo rm o f s ymbo l n am e a r e :
DYN $ C PCB
E XE $ C-CMSTKS Z
PT E $ C URKW

S t r uc t u r e Type i s S o f twa r e PCB
S i z e of S t a c k S pa c e Ad d e d b y Ch a ng e
Mo d e H a nd l e r
P r o t e c t i o n Cod e o f
Use r
Read ,
Ke r n e l Wr i t e

C-5

NAM ING C ONVENTIONS

15.

. PS ECT n a m e s a r e o f t h e fo rm :
f a c i l i t y $mnemo n i c
a nd wh e n put i n to a l i b r a r y
f a c i l i t y $mnem o n i c
E x ampl e s o f s ymbo l s o f the f i r s t k i nd a r e :
C O PY $ C O PY F I L E

F i l e c o py i ng m a i n
r o u t i n e p r og r am
s ec t i on
sec t i on
sec t i o n
th a t
P r og r am
c o n ta i ns
most
code
fo r
the
DC L c ommand i n t e r p r e te r
P r og r am s e c t i o n c o n t a i n i ng the Job
Co n t r o l l e r ' s
m e s sag e
o u tput
r o u t i ne

DC L $ Z C ODE
J B C $MSGOUT

Th i s c o nv e n t i o n i s n o t a d h e r ed to a s s t r i c t l y a s t h e o the r
n am i ng
c o nv e n t i o n s b e c a us e . PS EC T n am e s c o n t r o l the wa y t h a t
t h e l i n k e r a l l o c a t e s v i r t ua l a d d r e s s spac e .
Nam e s wi l l o f ten
b e cho s e n to a f f e c t t h e r e l a t i v e l o c a t i o n s of r o u t i n e s a nd
t h e d a t a th a t they r e f e r e n c e .
Some s am p l e . PS EC T n am e s f r om
the
e x ampl e s o f t h e s e c ond c o nve n t i o n .
L I B $ C ODE

Run - T i m e

Li b r a r y

show

General
Library
( Re ad-On l y )
Code
Sec t i on
Da t a S e c t i o n i n Ma them a t i c s L i b r a r y
Lang uag e
Po r t i o n
of
Cod e
I n d e pe nd e n t Suppo r t L i b r a r y

MTH$DATA
-O TS $ C ODE

Th e e x e c u t i v e d o e s n o t u s e th i s c o nv e n t i o n wh e n fo r m i ng
i ts
. PS ECT n am e s .
Ra th e r , i t use s n a m e s th a t c a use the d e s i r ed
s e c t i o n s to b e pl a c ed i n the c o r r e c t pa r t s o f
sys t em spa c e .
Fo r e x ampl e ,
. PS E CT n ame s c o n t r o l
tho s e
p i ec e s o f
the
e x e c u t i v e t h a t a r e pag e ab l e .
I n a d d i t i o n , . PS E C T names a l l o w
d a ta a r e as
a nd c o d e t h a t r e f e r en c e s th a t d a t a to b e p l a c ed
w i th i n 6 4 k byt e s s o tha t wo rd d i spl a c em e n t a d d r e s s i ng ( r a the r
t h a n l o ngwo r d d i s p l a c em e n t )
can
be
u s e d to r e f e r e nc e the
d a ta .
Some e x ampl e s o f . PS E C T n ame s tha t a r e u s ed i n the ex ec a r e :
$$$220

On e

of
the
f i r s t d a ta
p r og r am
s e c t i o n s i n the e x e c u t i v e
No npag ed Ex ec u t i v e Co d e
Pag e a b l e Ex e c u t i v e Ro ut i ne s

$AE XENONPAG ED
Y E XE PAG E D
16.

Mo d u l e n am e s a r e o f t h e fo rm :
f a c i l i ty $mnemo n i c
Th e
mod u l e
is
" f a c i l i t ymnemo n i c "
fac i l i ty .

s to r ed
in
a

C-6

in
wi th
a
file
f i l ename
to
the
d i r e c to r y c o r r e s po nd i ng

NAM ING CONVENTI ONS

Ex ampl e s o f th i s c o nven t i o n a r e :
Mo d u l e :
Fi l e :
Mo d u l e :
Fi l e :

L I B $ S I GNA L
[ R T L . S RC ] L I B S IGNAL . MAR
MTH $ S INCOS
[ RT L . SRC ] MTHS INCOS . MAR

Cond i t i o n
Gene r a t i o n
P r o c ed u r e s
a nd
S i ne
Func t i o n s

Co s i n e

Th e e x ec u t i v e i nc l ud e s the f a c i l i t y p r e f i x S Y S i n som e o f i t s
mod u l e
nam e s
( u s ua l l y mo d u l e s
tha t
i n c l ud e
the
s ys t em
s e rv i c e s ) a n d om i t s i t i n o th e r s .
No n e o f the mod u l e s i n the
e x e c u t i v e h a s a c u r r en c y s i g n in i t s n ame .
Some e x am p l e s o f
e x ec u t i v e m o d ul e n am e s a nd a s so c i a t ed f i l e s a r e :
Mo d u l e :
Fi l e :
Mo d u l e :
Fi l e :
17 .

I O S UBNPAG
[ E XE C . S RC ] I O S UBNPAG . MAR
S Y S S E T PRV
[ E XE C . SRC ] S YS S E TPRV . MAR

I /0
No n pag ed
Ro u t i n e s

Dr i v e r

Set

Sys c em

P r i v i l eg e
Service

Publ i c s t r uc t u r e d e f i n i t i o n m a c ro names a r e o f the fo rm :
$ f a c i l i t y_s t r uc t u r e DEF
I nvo k i ng
th i s m a c r o
s t r uc t u r e $ x x x x x x .

d e f i nes

all

symbo l s

the

fo rm

Mo s t of t h e pub l i c s t r uc t ur e d e f i n i t i o n s used b y VM S do
no t
i nc l ud e t h e
f a c i l i ty
i n the m a c ros tha t d e f i n e s t r uc t � r �
o f f s e ts .
Ra t h e r , m a c ros o f t h e f o rm :
$ s t r uc t u r e D E F
a r e used to d e f i n e s t r uc t ur e $ x x x x x x sym bo l s .
E x ampl e s o f t h e s e m a c r o s a r e :
$ LOG D E F
$ PC BDE F
$ S S DE F

O f f s e t s i n to Log i c a l N a m e B l o c k
Of f s e t s
i n to
So f twa r e
Process
Co n t r o l B l o c k
Sys tem S e rv i c e S t a tus Cod e s

C-7

NAM ING C ONVE N T I ONS
C.2

OBJ E C T DATA TYPE S

Th e fo l l o w i ng a r e the l e t t e r s used f o r the v a r i o us d a t a type s
r e s e rved fo r the f o l l o w i ng p u r po s e s :
Le t t e r
A
B
c

D
E
F
G
H
I
J
K
L
M
N
0
p

Q
R
s

u
v
w

y
z

are

Da t a Type o r U s a g e
Ad d r e s s
By t e I n t eg e r
S i ng l e Ch a r a c t e r �
Do ub l e P r e c i s i o n F l o a t i ng
Re s e rved to D I G I TAL
S i ng l e P r e c i s i o n F l o a t i ng
G e n e r a l Va l ue
I n t eg e r Va l ue fo r Co un t e r s
Re s e r v e d fo r I n t eg e r E x t e n s i o n s
Re s e r v ed to C u s tome r s f o r E s c a pe to Oth e r Co d e s
Co n s t a n t
Lo ngwo r d I n t eg e r
F i e l d Ma s k
Nume r i c S t r i ng ( Al l By t e Fo rms )
Re se r v ed to D I G I TAL a s an E s c a pe to O th e r Cod e s
Pa c k e d S t r i ng
Quadwo r d I n t eg e r
Re s e rved fo r Re co r d s ( S t r uc t u r e )
Fi e l d S i ze
Te x t ( Ch a r a c t e r ) S t r i ng
Sm a l l e s t Un i t o f Ad d r e s s a b l e S t o r ag e
F i e l d Po s i t i o n ( VAX- 1 1 MACRO ) ; F i e l d Re f e r e n c e ( B L I S S )
Wo r d I n t eg e r
C o n t e x t De pend e n t ( G e n e r i c )
Co n t e x t Depend e n t ( G e n e r i c )
Un spe c i f i ed o r No n s t a n d a rd

� I n many of the s ymbo l s used by VAX/VMS , C i s used a s a
s ynonym
fo r
K.
Al tho ug h
K
i s the p r e f e r r ed i nd i c a to r fo r c o n s t a n t s ,
mo s t c o n s t a n t s used i n VM S a r e i nd i c a t ed by a C i n t h e i r
n ame .
Some
c o n s t a n t s , s uc h a s l e ng ths o f d a t a s t r uc t u r e s , h a ve b o th a
C f o rm a nd a K fo r m .
N , P , a n d T s t r i ng s a r e t yp i c a l l y v a r i a b l e l e ng t h .
I n s t r uc t u r e s o r
I /0
r eco rds ,
t h e y f r e que n t l y c o n t a i n a byte- s i zed d i g i t o r c h a r a c t e r
c o un t p r e c ed i ng t h e s t r i ng .
I f so , t h e l o c a t i o n o r o f f s e t i s
to
the
c o un t .
Co un t ed s t r i ng s c a nno t b e pa s s e d i n p r o c ed u r e c a l l s .
I n s t e ad ,
a s t r i ng d e s c r i pto r m u s t b e g e n e r a t ed .

C- 8

NAM ING CONVENT I ONS

C.3

FAC I L I TY PREF I X TAB LE

Fo l l o w i ng
is
a
l i st o f
f a c i l i ty p r e f i x e s f o r
D I G I TAL- s uppl i ed
so f twa r e .
Th i s l i s t wi l l g r o w o v e r t i m e a s n e w f a c i l i ty pr e f i x e s a r e
chosen .
No o n e sho u l d u s e a n e w c o d e w i tho ut
r eg i s t e r i ng
it
in a
c ommo n pl a c e .
No t e tha t b i t < 2 7 > , the c u s tome r f a c i l i t y b i t , i s c l e a r i n a l l o f
the
f a c i l i ty c o d e s
l i s ted
here .
Cu s tome r s
a r e f r e e to use a n y o f the
f a c i l i ty codes l i s ted h e r e , p r ov i d ed
th a t th e y set b i t < 2 7 > .
Th e
d e f a u l t a c t i o n o f the me s s ag e c omp i l e r i s to s e t th i s b i t .
Th e l o c a t i o n o f t h e f a c i l i t y c o d e w i th i n a s t a tus c o d e , as we l l a s the
me a n i ng
of
the o th e r
f i elds
in
the
s t a t us c o d e , is d e sc r i b ed i n
Ch a p t e r 8 o f t h e VAX- 1 1 U t i l i t i e s Re f e r e n c e Ma n ua l .
P re f i x

Condi t ion
F ac i l i ty D e s c r iption

< 27 : 16>

Nuc l eu s and Sys tem Proce s s e s

S YS T EM
RM S
D E B UG
CLI
JBC
O PC OM
RSX
ERF
TRACE

Sys tem S e rv i c e S t a t u s Cod e s
RMS I n t e r n a l s a nd S t a t u s Co d e s
S ymbo l i c De b ug g e r
Comma nd La ng uag e I n t e r p r e t e r s
Jo b Co n t r o l l e r
Ope r a to r Commun i c a t i o n
RSX- l l M Ap pl i c a t i o n M i g r a t i o n Ex e c u t i v e
E r r o r Logg e r Fo rma t P r o c e s s
T r a c e b a c k Fac i l i ty

0
1
2
3
4
5
6
8
9

Run - T i m e L i b r a r y Compo n e n t s
BLI
LIB
MTH
OTS
FOR
C OB
BAS
B32
S ORT
C74
PLI
XPO
PAS
C OR
S TR
LBR
FDV
SCR

B L I S S T r a n s po r t a b l e Run - T i m e L i b r a r y
G e n e r a l Pu r po s e L i b r a r y ; G l o b a l S e c t i o n s
Ma thema t i c s L i b r a r y
Lang u a g e I n d e pe nd e n t Obj ec t T i m e Sys t em
VAX- 1 1 FORTRAN Run-T i m e L i b r a r y
VAX- 1 1 C O B O L Ru n - T i m e L i b r a r y
VAX- 1 1 BAS I C Run-T i m e L i b r a r y
B L I S S - 3 2 S p e c i f i c Run - T im e L i b r a r y
VAX- 1 1 S ORT
C OBOL- 7 4 S p e c i f i c Run - T i m e L i b r a r y
P L / I Run - T i m e L i b r a r y
T r a n s po r t a b i l i t y Su ppo r t L i b r a r y
VAX- 1 1 PAS CAL Run - T i m e L i b r a r y
C ORA L - 6 6 Run-T i m e L i b r a r y
S t r i ng Ma n i pul a t i o n P r o c ed u r e s
L i b r a r i a n Su b r o u t i n e Pa c k a g e
FMS - 3 2 Fo rms D r i v e r L i b r a r y
S c r e e n Fo rma t t i ng Pa c ka g e

C-9

20
21
22
23
24
25
26
27
28
29
30
32
33
34
36
38
41
44

NAM ING C ONVENTI ONS

Pr e f i x

F a c i l i ty De sc r i pt i o n

Cond i t i o n
<27: 16>

U t i l i t i e s and Compi l e r s
L I NK
CREF
DS U P
C O PY
B TRAN
S Y S M SG
F ORT
C OB 7 4
DIFF
PAT C H
PAX
B LS 3 2
APPEND
MOUNT
D I SM
UETP
!NIT
HELP
SET
S H OW
D I RE C T
AUT HOR
INS
SYSGEN
MAC RO
MA I L
DSM
PAS CAL
C ORAL
COBOL
S UM
E DT
L I B RAR
P L IG
BAS I C
FED
FUT
C OB 7 4 T
RENAM E
C R EATE
UN LOC K
DE LETE
P URG E
TYPE
R UNOFF
M E S SAG E
C LE D I T

VAX- 1 1 L i n k e r
C r o s s Re f e r e nc e Fa c i l i t y
D i ag n o s t i c S u p e r v i so r
C O PY Ut i l i t y
AME Ba c k T r a n s l a to r
Sys tem Me s s ag e Ma ke r
VAX- 1 1 FORTRAN Comp i l e r
VAX- 1 1 COB O L - 7 4 Comp i l e r
F i l e Di f f e r e nc e s Ut i l i t y
VAX- 1 1 Imag e F i l e Pa t c h Ut i l i t y
VAX- 1 1 Ob j e c t Mo d u l e Pa tch Ut i l i t y
VAX- 1 1 B L I S S - 3 2 Comp i l e r
A P PE ND Ut i l i t y
Vo l um e Mo u n t
Vo l um e D i smo un t
Us e r Env i r o nm e n t Te s t Pa c k ag e
Vo l ume I n i t i a l i z a t i o n
H e l p Fa c i l i t y
S ET Ut i l i t y
S HOW Ut i l i t y
D I R EC TORY U t i l i t y
Us e r Autho r i z a t i o n Ma n ag e r
I NS TALL U t i l i t y
Sys tem G e n e r a t i o n a nd Dr i v e r Lo a d e r Ut i l i t y
VAX- 1 1 MAC RO As s emb l e r
VA X/VM S MA I L U t i l i t y
D I G I TAL S t and a rd MUMPS
VAX- 1 1 PAS CAL Com p i l e r
C ORAL - 6 6 Comp i l e r
C OBO L- 7 9 Comp i l e r
So u r c e Upd a t e M e r g e U t i l i t y
DEC S t a nd a r d Ed i t o r
VAX- 1 1 L i b r a r i a n
VAX- 1 1 P L/ I Le v e l -G Com p i l e r
VAX- 1 1 BAS IC Com p i l e r
Fo rms Ed i t o r
Fo rms Ut i l i t y
C OBOL - 7 4 to VAX C OB O L T r a n s l a to r
RENAME Ut i l i ty
C REAT E Ut i l i t y
UN LOC K U t i l i ty
DE LETE Ut i l i ty
PURG E Ut i l i ty
TYPE Ut i l i t y
DEC S t a nd a rd RUNOFF
Sys tem Me s s ag e Comp i l e r
C L I Da t a Ba s e Ed i to r

C- 1 0

100
101
102
103
1 04
105
106
107
108
109
110
111
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
132
133
1 34
135
137
139
140
143
144
145
146
147
148
149
150
1 51
155

NAM I NG C ONVE N T I ONS

Fa c i l i ty D e s c r i p t i o n

Prefix

Co nd i t i o n
<27 : 16>

Ne two r k S u ppo r t U t i l i t i e s
NET
DAP
FAL
NCP
NIC
DLE
B SC P T P
H LD
REM

DECn e t AC P a nd N S P Pr o to c o l ; DTS/DTR
D E Cn e t DAP P r o c e d u r e s a nd P r o to c o l
DEC n e t F i l e Ac c e s s L i s t e n e r a nd P r o to c o l
D E Cn e t Ne two r k Co n t r o l P r o g r am a nd P r o to c o l
D E Cn e t N I C E P r og r am a n d P r o t o c o l
D E Cn e t D i r e c t L i n e Ex ec u t i v e
2 7 8 0 / 3 7 8 0 B I SYNC Po i n t to Po i n t Em u l a to r
D E Cn e t Ho s t Lo a d Pr o to c o l
DECn e t Rem o t e Te r m i n a l ACP a nd P r o t o c o l

501
502
503
504
505
506
507
508
510

Te s t Fa c i l i t i e s
SYSTST
RMS TS T

S y s tem Te s t s
RM S Te s t s

1000
1001

I nd i v i d ua l p r o d uc t s s uc h a s c omp i l e r s a l s o g e t un i q ue
f ac i l i ty c od e s
fo rmed
f r om t h e p r o d uc t n ame .
Th ey m u s t b e s i g n ed o u t i n the a b o v e
l i st .
Fa c i l i t y p r e f i x e s sho u l d b e cho s e n t o avo i d con f l i c t w i th
file
type s .
S t r uc t u r e name p r e f i x e s a r e typi c a l l y l o c a l to a f a c i l i t y .
Re f e r
to
the i nd i v i d ua l f a c i l i t y d o c um e n t a t i o n f o r i t s s t r uc t u r e n ame p r e f i x e s .
a nd
Th i s d o e s no t c a u s e p r o b l em s b e c a u s e t h e s e n a m e s a r e no t g l o b a l ,
are
th e r e f o r e n o t k n o wn to the l i n k e r .
Th ey b e come known a t a s s e m b l y
o r c omp i l e t i m e o n l y b y e x p l i c i t l y i nvo k i ng
t h e m a c r o d e f i n i ng
the
f a c i l i ty s t r uc t u r e .
codes
tha t
Fo r e x ampl e , t h e m a c r o $ F ORDE F d e f i n e s a l l o f the
s tat us
Th e f a c i l i t y
c a n b e r e t u r n e d f r om the VAX- 1 1 F ORTRAN s u ppo r t l i b r a r y .
the
status
c o d e o f 2 4 i s i nc l ud ed i n t h e uppe r 1 6 b i t s o f e a c h o f
c o d e s d e f i n ed wi th th i s m a c r o .
NOTE
D I G I TAL d o e s no t p r ov i d e a
r eg i s t r a t i o n
s e r v i c e f o r t h e c u s tom e r f a c i l i t y c o d e s .

C-1 1

APPEND I X D
DATA S TRUCTURE DE F I N I T I ONS

Th i s m a n ua l
has
d e sc r i b ed VM S p r im a r i l y
in
te r m s
of
the d a t a
s t r uc t u r e s
tha t a r e u s e d by t h e v a r i o u s c ompo n e n t s o f the e x e c u t i ve .
Th e d a ta s t r uc t u r e s u s e d by VM S a r e d e f i n ed i n a l a ng uag e c a l l ed
MDL
( Append i x A) in one of two f i l e s .
Th e s e f i l e s a l s o d e f i n e mo s t o f the
s ymbo l i c c o n s t a n t s m e n t i o n ed th r o ug h o u t t h i s m a n ua l .
•

•

A f i l e c a l l ed [ E XEC . SRC ] S YS D E F . MDL c o n t a i n s a l l s t r uc t u r e a nd
constant d e f i n i t i ons
u s e d i n t e r n a l l y by VM S .
Th e r e s u l t a n t
mac r o d e f i n i t i o ns a r e s to r ed i n
t h e spec i a l m a c r o
l ib r a ry
SYS $ L I BRARY : L I B . M LB
used
to
a s sem b l e a l l c ompo n e n t s o f VM S
a nd a v a i l a b l e to
user s
for
s pec i a l
a ppl i c a t i o n s s uc h a s
u s e r -w r i t t e n d ev i c e d r i v e r s a nd s ys t em s e r v i c e s .
A f i l e c a l l ed [ VM S L I B . S RC ] S TARDE F . MD L c o n t a i n s a l l
s t r uc t u r e
a nd
cons tant d e f i n i t i ons
tha t
a r e ava i l ab l e
fo r g e n e r a l
a ppl i c a t i o n s ( s u c h a s s ys tem s e r v i c e c a l l s . )
The
resul tant
mac r o d e f i n i t i o n s a r e
s to r ed
i n t h e d e f a u l t m a c ro l i b r a r y
SYS $ L I BRARY : S TAR LE T . MLB ( a s we l l as L I B . M LB ) .
i n th i s m a n u a l
M i s c e l l a n e o u s d e f i n i t i o n s me n t i o n ed
d e f i n ed
in
o th e r
f i l es .
In
pa r t i c u l a r ,
the
[ VM S L I B . SRC ] S SMSG . MDL d e f i n e s a l l
the
symbo l s o f
S S $ name .

are
file
f o rm

Th e d i s t i nc t i o n b e t we e n the two f i l e s SYS DE F . MDL a nd
STARDEF . MDL
is
tha t
s t r uc t u r e s a nd
c o n s t a n t s d e f i n ed i n STARD E F , b e c a u s e the y a r e
s to r ed i n the l i b r a r y S TARL E T . M LB a nd a r e u s ed
i n c o n j un c t i o n w i th
s ys t em s e rv i c e s ,
wi l l
p r o b a b l y n o t c h a ng e f r om r e l e a s e to r e l e a s e .
S t r uc t u r e s a nd c o n s t a n t s d e f i n ed i n SYSDEF
( a nd
s t o r ed
in
L I B . M LB )
c a r r y no
s uc h g ua r an t e e ,
r e q u i r i ng
t h a t p r og r am s
tha t
u s e s uc h
s t r uc t u r e d e f i n i t i o n s m u s t b e r e a s s embl ed a nd r e l i n k ed w i th e a c h m a j o r
r el ease
o f VAX/VM S .
Th e u s e o f L I B . MLB i n a s s em b l y l a ng uag e s o u r c e
p r og r am s ( o r L I B . L 3 2 i n B L I S S - 3 2 p r og r am s ) i s i n th i s wa y a n a l og o us t o
p r og r ams
l i n ked w i th
SYS $ S YS TEM : SYS . STB t h a t m u s t b e r e l i n k ed w i th
e ac h m a j o r r e l e a s e of VAX/VM S .
Th i s a ppe nd i x s umma r i ze s the p r i m a r y d a t a
s t r uc t u r e s
used
by t h e
c ompo n e n t s d e sc r i b ed i n th i s m a n ua l .
A s omewh a t a r b i t r a r y d i v i s i o n o f
d a t a s t r uc t u r e s i s mad e i n o rd e r t o k e e p the
s i ze
of
th i s a ppend i x
m a n ag e a b l e .
Ta b l e D - 1
l i sts a l l
the d a ta s t r u c t u r e s a nd c o n s t a n t s
d e f i n ed i n SYSDEF a nd S TARDE F , showi ng how t h i s a r b i t r a r y d i v i s i o n
is
m ad e .
On l y the f i r s t two c l a s s e s a r e d e sc r i b ed i n a ny d e t a i l i n th i s
a ppe nd i x o r e l sewh e r e i n th i s m a n u a l .

D-1

Ta b l e D-1
Summa r y o f A r b i t r a r y D i v i s i o n o f Da t a S t r uc t u r e s in Th i s Append i x
Th e fo l l ow i ng ac ro nyms i nd i c a te c o n s t a n t s o r d a ta s t r u c t u r e s tha t � r e d e f i ned i n
t h e f i l e [VM S LIB . SRC ] STARDE F . MDL .

Sys tem Wi d e
Da ta S t r u c t u r e s
ACC
DMP
IAC
PLV
PS L
SEC
STS

Symbo l ic Co nst a n t s
JPI
M SG
PQL
PR
PRT
PRV

S t r uc tu r e s Used by
t h e I /O Subsys t em

S t r u c t u r e s Used by
the Fi l e System

M i s c e l l aneo us
Da ta S t r uc tu r e s

CR
DC
DEV
DIB
IO
LA
LP
MT
PCC
TT

ATR
FIB
FID

C LI
C L I S ERV
C L I VERB
DJI
OPR
SJH
SMQ
SM R
SQH
SQR
SYM
TPA

XF
XM

Th e fo l l owi ng a c ronyms i nd i c a te c o n s t a n t s o r d a ta s t r uc tu r e s that a r e d e f i ned i n
t h e f i l e [ EXEC . SRC ] SYS DEF . MD L .

Sys tem Wi d e
Da ta S t r uc t u r e s
MBX
ACB
MCHK
ARB
MPM
BRD
C EB
MTX
C HF
PCB
EMB , CRDEF PFL
EM B , HDDEF PFN
PHD
FKB
GSD
PQB
PRM
IFD
PTE
I HA
PTR
IHD
RBM
!HI
IHP
RPB
S FT
IHS
S HB
ISO
SHD
JIB
KFH
TQE
KF I
VA
KF P
WQH
LOG
WSL

Symbol i c Co nstants
BTD
CA
DYN
! 07 5 0
!0780
I PL
NDT
PR I
RSN
SGN
STATE

S t r uc tu r e s Used by
the I / O Subsys tem

S t r uc tu r e s Used by
the Fi l e System

Mi scel l aneous
Da ta St r uc tu r e s

ADP
AQB
CCB
CRB
D DB
DDT
DPT
! DB
IRP
I R PE
MBA
TTY
UBA
UB I
UCB
VEC

AIB
BBS
CXB
EOl
E02
E03
FCB
HDl
HD2
HD3
MT L
MVL
NMB
RVT
RVX
VCA
VCB
VL l
WCB

ABD
ACF
C IN
EMB , BCDEF
EMB , DVDEF
E M B , E TDE F
EMB, MCDEF
EMB , SBDEF
EMB , SEDEF
EMB , SSDEF
EMB , SUDEF
EMB , TSDEF
EMB , UEDEF
EMB , UIDEF
EMB , VMDEF
ERL
IHX
I P
PBH
PDB
PIB
PMB
PRQ
RDP
UAF

DATA STRUCTURE DEFIN I T IONS

Th e f i v e c l a s s e s o f s t r uc t u r e s tha t a r e l i s t ed h e r e a r e :
•

Da ta s t r uc t u r e s u s ed by m em o r y m a n ag em e n t , t h e sched ul e r , a nd
m i s c e l l a n e o us c om po n e n t s .
Th e r e
i s a t l e a s t o ne fi g u r e o r
t a b l e i n th i s m a n ua l tha t d e sc r i b e s each o f · t h e s e s t r uc t u r e s .

•

Co n s t a n t s s uc h a s c o nd i t i o n c od e s ,
d a ta s t r uc t u r e t ype s , a nd so o n .

•

s ta t e

codes ,

Da ta s t r uc t u r e s a n d d ev i c e - s p e c i f i c c o ns t a n t s used by t h e I/0
s y s t em , i nc l ud i ng d ev i c e d r i v e r s .

•

Da ta s t r uc t u r e s u s ed
by
the
f i l e c on t r o l
r e l a t ed u t i l i t i e s s uc h a s MOUNT a nd IN I T .

•

D. l

sched u l i ng

p �o c e s s e s

a nd

M i s c e l l a n e o u s d a t a s t r uc t u r e s a nd c o n s t a n t s .
Some o f t h e s e
a r e d e f i n ed i n o th e r m a n ua l s i n t h e VMS d o c um e n t a t i o n s e t .

EXECUT IVE DATA S TRUCTURES

Th i s f i r s t sec t i o n me n t i o n s e a c h d a ta · s t r uc t u r e tha t i s d e sc r i be d
in
th i s m a n ua l , i nc l ud i ng a b r i e f s umma r y o f t h e s t r uc t u r e a nd r e f e r e n c e s
t o a mo r e c ompl e t e d e s c r i pt i o n e l s e wh e r e i n the m a n ua l .
Th r e e d a t a
s t r uc t u r e s ,
the
s o f twa r e
PC B ,
the
P r o c e s s Head e r ,
a nd
t h e Jo b
I n fo rma t i on B l o c k a r e pa r t i a l l y d e sc r i b ed i n seve r a l pl a c e s t h r o ug h o u t
the
tex t .
Th e y a r e d e sc r i b ed h e r e i n th e i r en t i r e t y , wi th r e f e r en c e s
to o th e r pa r t i a l d e sc r i pt i o n s .

D. l . l

ACB - AST Co n t r o l B l o c k

Pu r po s e :
Us ua l Lo c a t i o n :
Al l o c a ted f rom :
Re f e r e n c e s :
Spec i a l No t e s :

D. l . 2

De sc r i b e s pend i ng AST f o r a p r o c e s s
A S T q ue ue w i th l i s t h e ad i n so f twa r e PC B
No n pag ed po o l
Figure 5-l
ACBs a r e u s ua l l y a pa r t o f a l a rg e r s t r uc t u r e ,
an
I /0
r e que s t pa c k e t
( IRP)
or
a
t i me r q u e ue
e l emen t ( T QE ) .

ACC - Acco un t i ng and Te rm i na t i o n Me s sa g e Blo c k

Pu r po s e :

Us ua l Lo c a t i o n :
Re f e r e n c e s :

Us ed
to
s e nd
t e rm i n a t i o n m e s s a g e
to
the
j ob
c o n t r o l l e r wh e n a p r o c e s s i s d e l e te d .
Th e s am e
m e s s a g e i s a l s o s en t to t h e t e rm i n a t i o n ma i l bo x
of
th e c r e a to r o f t h e p r o c e s s .
Th e s t r uc t u r e
i s a l so
u s ed
i n t h e Send Me s s a g e t o
the
Ac c o un t i ng Ma n ag e r sys t em s e rv i c e .
Th e t e rm i n a t i o n m e s sag e
resides
on
the
kernel
s t ac k .
Ta b l e 1 9 - 1 o f th i s m a n ua l , Pa r t I I o f the VAX/VMS
Sys t em Se r v i c e s Re f e r en c e Ma n u a l

D- 3

DATA STRUCTURE DE F IN I TI ONS

D. l . 3

ARB - Ac c e s s R i g h ts B l oc k

Th e a c c e s s r i g h t s b l o c k c u r r en t l y c o ns i s t s o f the p r i v i l eg e m a s k
a nd
U I C l o c a te d a t t h e
e nd o f the so f twa r e PCB .
Th a t i s , t h e ARB i s
c u r r e n t l y a pa r t o f t h e so f twa r e PC B .
Th e ARP po i n t e r
( PC B $ L_ARB )
c u r r e n t l y po i n t s to t h i s o ve r l a i d d a ta s t r uc t u r e .
F i g u r e D-2 s h o ws a n
ARB w i t h i n a so f twa r e PC B .
F i g u r e D-1
s hows
tha t
the
fi rst
fo u r
l o ng wo rd s
i n a J I B c a n a l so b e c o n s i d e r e d a n ARB .
Prog r am r e f e r e nc e s
tha t u s e t h e ARB po i n t e r i n t h e so f twa r e PC B t o l o c a t e t h e ARB o r
any
f i e l d s w i th i n t h e ARB s uc h a s a pr i v i l eg e ma s k wi l l c o n t i n u e t o wo r k
wi tho u t m od i f i c a t i o n
sho u l d
t h e ARB b e c om e a n
i nd e pe nd e n t d a ta
s t r uc t u r e in a f u t u r e r e l e a se of VAX/VM S .
De f i n e s p r o c e s s a c c e s s r ig h t s a nd p r i v i l eg e s
C u r r e n t l y a p a r t o f t h e so f twa r e PC B
T a b l e 1 8 - 1 , Fi g u r e s D- 1 and D-2

Pu r po s e :
Lo c a t i o n :
Re f e r e nc e s :

D. l . 4

BRD

B r o a d c a s t Me s s ag e Desc r i pto r B l ock

Pu r po s e :
Us ua l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e nc e s :

D. l . S

l ist

( l i s th e a d

C EB - Common E v e n t B l o c k

Pu r po s e :
Lo c a t i o n :

Al l o c a t ed f r om :
Re f e r e n c e s :

D. l . 6

C o n t a i n s b r o ad c a s t m e s s ag e
b r o ad c a s t
t e rm i n a l
In
I OC $G L B RDC S T )
No n pag ed pool
F i g u r e 1 6-4

C o n t a i n s d e sc r i pt i o n a nd wa i t que ue
f o r c ommo n
e v e n t f l ag c l u s t e r
In
c ommo n
event
block
l i st
( l i s th e ad
S C H $ G Q C EB HD ) .
( Ma s t e r C EBs a r e l o c a ted i n s h a r ed
m emo r y-a nd po i n ted to b y a f i e l d i n the s l av e
CEB
l o c a t ed
in
t h e c ommo n event b l o c k l i s t o n e a c h
processo r . )
N o n pa g ed po o l .
( Ma s t e r CEBs a r e a l l o c a ted f r om a
C EB t a b l e l o c a ted i n s h a r ed memo r y . )
F i g u r e s 9 - 2 , 9 - 3 , 9 - 4 , a nd 9 - 5

CHF - Cond i t i o n Hand l e r Argumen t L i s t Ar r ays

P u r po s e :
Us u a l Lo c a t i o n :
Re f e r e n c e s :

Spec i a l No t e s :

D e s c r i b e s c o nd i t i o n o r e x c e p t i o n
to
cond i t i o n
h a nd l e r
O n s ta c k o f a c c e s s m o d e
i n wh i c h e x c e pt i o n o r
c o nd i t i o n o c c u r r ed
F i g u r e s 2 - 2 a nd 2 - 4 o f th i s m a n ua l ,
Ch a pt e r 9 o f
t h e VAX/VMS Sys t em S e r v i c e s Re f e r en c e Ma n ua l ,
Ch a p t e r 6 o f
the
VAX- 1 1
Run -T i m e
L i b r a ry
Re f e r en c e Ma n ua l
Th e $ C HFDEF m a c r o d e f i n e s o f f s e t s
i n to
no t o n l y
t h e p r ima r y a rg um e n t l i s t b u t a l so t h e s i g n a l
a n d m e c h a n i sm a r r a y s .

0- 4

DATA STRUCTURE DEF I N I T I ONS

D. l . 7

DMP - Head e r B l o c k o f Sys t em D u mp F i l e

De sc r i b e s c o n t e n t s o f d um p f i l e
F i r s t v i r t ua l b l o c k o f
SYS $ SYS T EM : SYS DUMP . DM P
a n y o th e r d um p f i l e
Ta b l e 7 - 1

Pu r po s e :
Loc a t i o n :
Re f e r e nc e s :

D. l.8

E M B - E r r o r Log Me s s ag e B l o c k
De sc r i b e s a pa r t i c u l a r e r r o r l og e n t r y i n o n e o f
the e r ro r
l og
buf fe rs .
Th e r e
are
sever a l
Th e y a r e a l l
d i f f e r en t f o rms o f e r r o r m e s s ag e .
i nv o k e d wi t h t h e
$ EMBDE F m a c r o wi th o n e o f
s e ve r a l s e c o nd pa r am e t e r s .
Fo r
e x am p l e ,
the
f o l l ow i ng i nvoc a t i o n f r om mod ul e ERROR LOG

Pu r po s e :

$ EMBDEF <DV, S U , TS , U I >
d e f i n e s s ym bo l s o f the fo rm
EMB $ x DV a b c
EMB $ x-S U-a b c
EMB $ x-T S-a b c
EMB $ x-U I -a bc
Almo s t a l l o f t h e
e r r o r me s s a g e
fo r m a t s a r e
r e l a t ed
t o a s pe c i f i c type o f e r r o r .
On l y o n e
e r ro r
t yp e
of
e r r o r m e s s ag e
buffe r ,
the
c r a s h/ r e s t a r t e r r o r m e s s ag e a s s o c i a t ed wi th a
f a t a l b ug c h e c k , i s r e f e r e n c ed i n th i s m a n ua l .

D. l . 8 . 1

EMB , CR - C r a s h/Re s t a r t E r ro r Log E n t ry Fo r m a t

De f i n e s o f f s e t s f o r e r r o r l og
e n t r i e s a s s o c i a t ed
b ug c h e c k s
( No n f a t a l
f a ta l
b ug c h e c k s .
wi th
ent r y ,
r e s ul t i n a s l i g h t l y d i f fe r e n t f o rm o f
d e s i g n a t e d by BC i n s t e ad of C R . )
Ta b l e 7 - 1

Pu r po s e :

Re f e r en c e s :

EMB , HD - Lo ngwo rd Hea d e r f o r Al l En t r i e s - Th e f i r s t l o ng wo rd

D. l.8.2
i n all
r ec o rd .

error

Pu r po s e :
Re f e r enc e s :

D.l.9

l og

entr ies

i s a h e ad e r tha t d e f i n e s t h e r e s t o f t h e

De sc r i b e s t h e r e s t o f the e r r o r l og e n t r y
Ta b l e 7 - 1

FKB - Fo r k B l o c k

P u r po s e :
U s u a l Lo c a t i o n :
A l l o c a t e d f r om :

S t o r e s m i n i m um c o n t e x t
fo r d r i v e r p r o c e s s o r
s ys tem t i m e r s ub r o u t i n e
F i r s t s i x l o ng wo r d s o f d ev i c e un i t c o n t r o l
block
o r t i m e r q u e ue e l em e n t o f s y s t em s ub r o u t i n e
No npag ed po o l ( e x c e pt f o r st a t i c a l l y a l l o c a t ed TQE
o r UCB )
D-5

DATA STRUCTURE DEF IN IT I ONS

Re f e r e nc e s :

Spec i a l No t e s :

D. l . lO

F i g u r e 4 -2 fo r g ene r a l
l a yo u t ,
Figure 1 0-1
fo r
f o r k b l o c k c o n ta i n ed 1 n TQE , Append i x A o f the
VAX/VM S G u i d e to Wr i t i ng a Dev i c e D r i v e r
fo r
I /0 f o r k b l o c k
Th e o n e u s e o f a sys tem t i m e r s u b r o ut i ne i n VMS i s
a s ta t i c a l l y a l l o c a t ed t i m e r que ue e l em en t .

GSD - G l oba l Sec t i o n Desc r i pto r

Pu rpo s e :

Us ua l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e nc e s :
S p e c i a l No t e s :

C o n t a i n s i d en t i f y i ng i n fo rma t i o n a b o u t a g l o b a l
s ec t i on .
G r o up o r sys t em G S D l i s t .
( Sh a r ed memo r y G S Ds a r e
l o c a t e d i n sha r ed m emo r y . )
Pag ed po o l .
( Sh a r ed memo r y G S Ds a r e a l l o c a t e d
f r o m pag e s
in
sha r ed m emo r y s e t
a s i d e fo r
s h a r ed m emo r y G S Ds . )
F i g u r e s 1 1 - 1 4 , 1 1 - 1 8 , a nd 1 1 - 2 7
Th e r e a r e t h r e e d i f f e r e n t fo rms o f G S D :
•

•

D. l . ll

Us ua l Lo c a t i o n :
Re f e r en c e s :

D e s c r i b e s a c t i v a t i o n o p t i o n s to
Imag e Ac t i v a t i o n
s y s tem s e r v i c e
Fo u r th a rg um e n t i n a rg um e n t l i s t t o sys tem s e r v i c e
Sec t io n 1 8 . 1 . 1

I FD - Imag e F i l e D e s c r i p to r B l o c k

Pu r po s e :
U s u a l Lo c a t i o n :
Re f e r e nc e s :

D. l . l3

Re t u r n s
i n fo rma t i o n a b o u t
i m ag e
f r om
i m ag e
a c t i v a to r to i t s c a l l e r
I n a d d r e s s s pa c e o f c a l l e r o f i m ag e a c t i va to r
Sec t i o n 1 8 . 1 . 1

I Hx - Imag e H e a d e r F i e l d s

Th e imag e h e ad e r c o n t a i n s s e v e r a l
r ec o r d s
tha t
f u l l y d e sc r i b e
imag e .
Th e I Hx s t r uc t u r e s d e f i n e the f i e l d s wi th i n e a c h r ec o r d .

D. l . l3. 1

IAC - Imag e Ac t i v a t i o n C o n t r o l F l a g s

Pu r po s e :

D. l . 12

No rma l g l o b a l s e c t i o n d e sc r i pto r
De s c r i pto r fo r PFN-ma pped s e c t i o n
De s c r i pto r
fo r
sec t ion
tha t
r e s i d es
s h a r ed
m emo r y

I HA - Imag e H e ad e r T r a n s f e r Ad d r e s s A r r a y

Pu r po s e :
Re f e r e nc e s :

De f i n e s t r a n s f e r add r e s s ( e s )
Figure 18-7

D-6

fo r i m ag e

the

DATA S TRUCTURE DEF IN IT I ONS
D. l . l3 . 2
I HD - Imag e He a d e r Rec o rd De f i n i t i on s - Th i s
is
the
fi rst
r ec o r d
in
the i m a g e h e a d e r .
Amo ng o the r th i ng s , t h i s po r t i o n o f the
image h e ad e r c o n t a i n s o f f s e t s to the o th e r r e c o rd s .
Pu r po s e :
Re f e r e n c e s :

De sc r i b e s t h e r e s t o f the imag e h e ad e r
F i g u r e 1 8-1

D. l . l3 . 3
IHI
Imag e H e ad e r
I d en t i f i c a t i o n S e c t i o n - Th i s s e c t i o n
c o n t a i n s s uch i n fo rm a t i o n a s the i mag e n am e a nd the d a te a nd t i m e tha t
the l i n k wa s pe r fo rmed .

D. l . l3 . 4
I H P - Imag e Head e r Pa t c h S e c t i o n - Th i s
the p a t c h l ev e l o f t h e i m ag e .

s ec t i o n

d e sc r i be s

D. l . l3 . 5
I HS - Imag e He ad e r Symbo l
Tabl e a nd De b ug
S e c t i o n - Fo r
e x e c u ta b l e
i mag e s
t h a t h ave
i nc l ud ed
DEBUG s uppo r t , th i s s e c t i o n
l o c a te s t h e d eb ug s ymbo l t a b l e w i th i n t h e i m a g e f i l e .
Fo r
sha r e a b l e
i m ag e s ,
t h i s s ec t i o n l o c a t e s t h e un i v e r s a l s ymbo l t ab l e a t t h e e n d o f
t h e i m ag e f i l e .

D. l . l4

I S D - Imag e S ec t i o n Desc r i pt o r

Pu r po s e :
Lo c a t i o n :
Re f e r e n c e s :

D. l . lS

D e s c r i b e s v i r t ua l add r e s s r a ng e a nd
c o r r e s po nd i ng
i n fo rma t i o n
{ v i r t ua l
bloc k
r a ng e ,
g l o ba l
s e c t i o n n am e ) to i mag e ac t i v a to r
Imag e h e a d e r
F i g u r e s 1 8-2 to 1 8-5

J I B - Job I n fo rma t i o n B l o c k

Th e Jo b I n fo rm a t i o n B l o c k a ppe a r s i n s ev e r a l f i g u r e s i n
th i s m a n ua l .
F i g u r e D-1
sh ows
all
of
the
f i e l d s c u r r en t l y d e f i ned
in
th i s
s t r uc t u r e .
Some o f t h e s e f i e l d s a r e n o t c u r r e n t l y u s e d .
Pu r po s e :
Lo c a t i o n :
Al l o c a t ed f r om :
Othe r Re f e r e n c e s :

D. l . l6

C o n t a i n s quo t a s po o l ed by a l l
processes
same j o b .
Po i n t ed to b y PC B $ L J I B f i e l d o f a l l PC B s
s ame j o b .
No n pag ed po o l
F i g u r e 1 - 1 , F i g u r e s 1 7 - 1 , 1 7 - 2 , a nd 1 7 - 6

the

KFH - Known F i l e He a d e r

Pu r po s e :
Usua l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e n c e s :

C o n t a i n s i mag e h e a d e r f o r any k n o wn i mag e th a t
is
i n s t a l l ed /H EADER RE S I DENT
Lo c a t ed th r o ug h KF I $L I MG HDR po i n t e r
i n KF I
fo r
t h a t known i mag e Pag ed po o l
F i g u r e 1 8-6
D-7

DATA STRUCTURE DE F I N I T I ONS
Job I nformation Block (JIB)

Only the shaded
fields within the
J I B are currently
used

USE RNA ME

F i g u r e D- 1

D . l . l7

(JIB)

K F I - Known F i l e En t r y

Pu r po s e :
U s ua l Lo c a t i o n :
Al l o c a ted f r om :
Re f e r e nc e s :

D . l . l8

De t a i l ed L a yo u t o f Jo b I n fo rma t i on B l o c k

De sc r i b e s a n imag e t h a t h a s b e e n m a d e known to the
s ys t em wi t h the INSTA L L u t i l i ty
I n o n e o f t h e k nown f i l e l i s t s .
Th e r e i s o n e l i s t
fo r
e a c h d i r ec to r y tha t h a s i mag e s i n s t a l l ed
f r om i t .
Pag ed po o l
F i g u r e 1 8-6

K F P - Known F i l e Po i n te r B l o c k

Pu r po s e :
U s u a l Lo c a t i o n :
A l l o c a t ed f r om :

Ac t s a s l i s t h e ad f o r a l l KF i s i n a g i v e n d i r e c to r y
I n known f i l e l i s t ( l i s thead EXE $G L_KNOWNF I L )
Pag ed po o l

D-8

DATA S TRUCTURE DEFIN I T I ONS

0. 1 . 19

LOG - Log i c a l Name B l o c k

P u r po s e :
U s u a l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e nc e s :

0 . 1 . 20

MBX - S h a r e d Memo r y Ma i l bo x C o n t r o l B l oc k

Pu r po s e :
U s ua l Lo c a t i o n :
Re f e r e nc e s :

0 . 1 . 21

De s c r i b e s e a c h m a i l bo x
th a t e x i s t s
i n sha r ed
memo r y
m a i l bo x
Pag e s
in
sha r ed m emo ry d ed i c a t ed
to
con t r o l b l ocks
F i g u r e s 1 6 - 2 and 1 6 - 3

MCHK - M a c h i ne Chec k E r ro r Ma s k B i t De f i n i t i o n s

P u r po s e :
Re f e r e nc e s :

0. 1 . 22

C o n t a i n s l og i c a l and e qu i v a l en c e n am e s t r i ng s fo r
a g i v e n l og i c a l n ame
I n one o f th r e e
l og i c a l
name
tabl e s :
process ,
g r o up , o r sys t em
Pag ed po o l f o r g r o up a nd s ys t em l og i c a l names ,
P r o c e s s a l l o c a t i on r eg i on f o r
process
l og i c a l
n am e s
F i g u r e s 1 6 - 1 a nd 1 6 - 3 , F i g u r e s 2 6 - 1 a nd 2 6 - 2

D e s c r i b e s pa r t i c u l a r s e t o f m ac h i n e c h e c k e r r o r s
th a t
a b lock of
ke r n e l
mod e cod e wi sh e s to
p r o t e c t i t s e l f ag a i n s t
Sec t ion 7 . 3 . 3

MPM - M u l t i pa r t Memo ry Ad a p t e r Reg i s t e r s

Lo c a t i o n :

S ym bo l i c n am e s
fo r
r eg i s te r s
tha t
o pe r a t i o n o f MA7 8 0 mul t i pa r t m emo r y
I / 0 pag e s s e t a s i d e fo r t h i s a d a p t e r

D . l . 23

( Mu t u a l Exc l u s i o n S em apho r e )

Pu r po s e :

MTX - M u t e x

P u r po s e :
U s u a l Lo c a t i o n :
Re f e r enc e s :

D . l . 24

cont r o l

M u t e x e s c o n t r o l p r o c e s s a c c e s s to
p r o t e c t ed d a ta
s t r uc t u r e s
S t a t i c a l l y a l l o c a ted l o ng wo r d s i n mod u l e SYSC OMMON
F i g u r e 2 4 - 2 , Ta b l e 8 - 2 , Ta b l e 2 4 - 2

PCB - P r o c e s s C o n t r o l B l o c k

Th e t e r m p r o c e s s c o n t r o l b l o c k c a n r e f e r to two d i f f e r e n t s t r uc t u r e s
i n t h e VAX l i te r a t u r e .
Al l
so f twa r e d o c umen t a t i o n i n c l ud i ng th i s
m a n ua l r e f e r s to the s o f twa r e p r o c e s s c o nt r o l blo c k a s s i mp l y PC B a nd
a l wa ys p r e f i x e s the h a r d wa r e p r o c e s s c o n t r o l
b l o c k w i t h the wo rd
" h a r d wa r e " .

D-9

DATA STRUCTURE DEFIN I T I ONS

0. 1 . 24 . 1
So f twa r e P r o c e s s Con t r o l B l o c k - Th e s o f twa r e PCB a ppe a r s i n
s ev e r a l
f ig u r e s
i n t h i s m a n ua l .
Howeve r , e a c h o f the s e f i g u r e s o n l y
s h o ws tho s e f i e l d s r e l a te d to the p u r po se o f
the pa r t i c u l a r
f i g ur e .
Th e
s o f twa r e
PCB
i s i l l us t r a te d i n F i g u r e D- 2 .
Th e m e a n i ng o f e a c h
f i e l d i s l i s t ed i n Tab l e D - 2 .
Pu r po s e :
Lo c a t i o n :
Al l o c a t e d f r om :
O th e r Re f e r enc e s :

D . l . 24 . 2

Ha rdwa r e P r o c e s s Con t r o l B l o c k

Pu r po s e :
Lo c a t i o n :
Re f e r en c e s :

0. 1 . 25

C o n t a i n s h a r d wa r e c o n t e x t o f a p r o c e s s wh i l e i t i s
no t e x ec u t i ng
Pa r t o f the f i x ed po r t i o n o f t h e p r o c e s s h e ad e r .
Figure 1-1 , Figure 8-6

PFL - Page F i l e Con t r o l B l o c k

Pu r po s e :
Al l o c a ted f r om :
Re f e r e nc e s :

D . l . 26

C o n t a i n s a l l t h e p e rmanen t l y r e s i d en t
i n f o rma t i o n
a bo u t a p r o c es s .
On e o f t h e s c h ed u l i ng s t a t e q u e ue s .
Al s o
po i n ted
t o by one o f the PCB ve c to r e l em e n t s .
No npag ed poo l
F i g u r e 1 -1 , F i g u r e 5 - l ,
F i g u r e 8 -1 ,
Figures 9-1 ,
9-3 ,
and
1 9- 4 ,
F i g u r e 1 1-2 1 ,
Fig ures 1 7-1 ,
1 7 - 2 , 1 7 - 3 , a nd 1 7 - 6 , F i g u r e 1 9- 1

C o n t a i n s d a ta n ee d ed by pag e r to
r ea d
f r om pag e
f i le
and
by mod i f i ed
pag e
to wr i t e �o pag e
file.
S t a t i c a l l y a l l o c a t ed i n m od u l e SWAPF I LE
F i g ur e 1 1- 2 2

PFN - PFN Da t a B a s e De f i n i t i o n s

Th e $ P FNDE F mac r o d e f i ne s f i e l d s i n t h e
e l emen t s .
Pu r po s e :
U s u a l Lo c a t i on :
Re f e r enc e s :

STATE ,

TYPE

a nd

BAK

a r r ay

PFN d a ta b a s e d e sc r i b e s d ynam i c phys i c a l pag e s
S e pa r a t e a r e a i n s ys t em add r e s s s pa c e
F i g u r e s 1 1 -9 to 1 1 -1 3

D- 1 0

DATA S TRUCTURE DEFIN I T IONS
Software Process Control Block (PCB)
SQFL
SQBL
PRI

TYPE

SIZE

MTXCNT

ASTEN
ASTQFL

ASTACT

ASTQBL
PHYPCB
OWNER
WSSWP
STS
WTIME
PRIB

WEFC

STATE

TMBU

APC NT

PPGCNT

GPGCNT

BlOC NT

ASTCNT

DIOCNT

BIOLM

PRCCNT

DIOLM

TERMINAL
PRCCNT

D IOLM
TERMINAL
EFWM/PQB

EFCS
EFCU
EFC2P

....
)-

EFC3P
PID
PHD

LNAME

ARB contained
within PCB

F i g u r e D-2

JIB
PRIV
ARB

---

UIC

De t a i l ed L a yo u t o f So f twa r e Pr o c e s s Co n t r o l
B l o c k ( PC B )

D- 1 1

Ta b l e D-2
Of f s e t s i n to So f t wa r e P r o c e s s Co n t r o l Bl o c k
F i g u r e o r Ta b l e
Re f e r en c e s i n Th i s Ma nua l

Th i s F i e l d

Symbo l i c Name

S i ze o f F i e l d

Use of

PCB SL_S QF L

l o ng wo rd

S c h e d u l i ng

PCB $ L S QB L
PCB $W-S I Z E
PCBSB-TYPE
PC B $ B-PR I
PCB $B-ASTACT
PCBSB-ASTEN
PCB $W-MTXCNT
PC B $ L-ASTQFL
P C B $ L-ASTQBL
PCB $L-PHYPCB
P C B $ L O WNER

l o ng wo rd
wo rd
byte
byte
byte
byte
wo rd
1 o ngwo rd
l o ng wo rd
l o ng wo rd
l o ng wo rd

PCB $ L WSSWP
PCB $ L-STS
PC B $ L-WT I M E
PCB $W-S TATE
PCB $B-WEFC
PCB $B-P R I B
PCB $W-A PTCNT
PCB $W-TM BU
PCB $W-G PGCNT
PCB $W-P PGCNT
PCB $W-ASTCNT
P C B $W-B IOCNT
PCB $W-B I O LM
PCB $W-D I OCNT
PCB $W-D I O LM
PCB $W-PRCCNT
PCB $T-TER M IN AL
PCB $ L E FWM

l o ngwo rd
1 o ngwo rd
l o ng wo rd
wo rd
byte
byte
wo rd
wo rd
wo rd
wo rd
wo rd
wo rd
wo rd
wo rd
wo rd
wo rd
8 byt e s
l o ngword

S c h ed ul i ng s t a t e q u e ue b a c kwa rd l i n k
S i ze of s o f twa r e PCB
S t r uc t u r e type c o d e ( DYN $C_PCB )
Cu r r en t so f t wa r e p r io r i ty
Ac c e s s m ode s wi th a c t i v e ASTs
Access mod e s wi th ASTs e n ab l ed
Co unt of owned m u t e x e s
A S T q u e u e fo rwa rd l i n k
A S T q u e u e b a c kwa rd l i n k
Ph ys i c a l add r e ss o f h a r d wa r e PCB
P r o c e s s I D o f own e r p r o c e s s i f s ub p r o c e s s
( ze r o i m p l i e s n o t a subproc e s s )
Swa p f i l e d i s k a d d r e s s
So f t wa r e s t a tus f l ag s l o ngwo rd
Time a t s t a r t of wa i t ( no l ong e r used )
Cur r en t s c h ed ul i ng s t a t e cod e
Wa i t i ng event f l ag c l us t e r
B a s e so ftwa r e pr i o r i t y
Ac t i v e pag e tab l e c o u n t
Te r m i n a t i o n m a i l box un i t n um b e r
G l o b a l pag e c o un t i n wo r k i ng s e t
Pro c e s s pag e count i n wo r k i ng s e t
A S T count r ema i n i ng
Bu f f e r ed I /O c o u n t r ema i n ing
Bu f fe r ed I /O l i m i t
Di r e c t I /0 c o u n t r ema i n i ng
Di r ec t 1 /0 l im i t
Co unt of owned s ub proc e s s e s
Te rm i n a l d e v i c e n am e s t r i ng fo r i n t e r ac t i v e j obs
E v e n t f l ag wa i t m a s k

::::

s t a t e queue

fo rwa rd

l in k

Figure 8 - 1 , Figure 8-3 ,
Figure 8-4 , Figure
Fig ure 9 - 4
S a m e a s fo r wa r d l i n k

9-3 ,

Figure 8-1
Figure 5 -1
Figure 5 -1
Figure 5 -1
Figure 5 -l
Figure 1-1 , Figure 8-1
Figure 17-2 , Figure 1 9-1 ,
Ta b l e 1 9 - 1
Figure 11-23, Figure 17-5
F i g u r e 8 -1 , Ta b l e 9 - 2
Figure 8-1
Figure 9-1
F i g u r e 8 -1

F i g u r e 5 - l , Ta b l e 1 7 -4
Ta b l e 1 7 -4
Ta b l e 1 7 -4
Ta b l e 1 7 -4
Ta b l e 1 7 -4
F i g u r e 1 7 -2 , F i g u r e 1 9 - 1
Figure

9 -1

Figure

1 7- 1 ,

S am e l o ngwo rd ho l d s r eso u r c e number o r
m u t e x ad d r e s s w h e n p r o c e s s i s i n MWA I T s t a te
PCB S L_PQB

S am e l o ngword ho l d s add r e s s o f P r o c e s s Quo t a
B l o c k d u r i ng p r o c e s s c r e a t i o n

PC B $ L E F C S
PCB $ L-EFCU
P C B $ L=EF C 2 P

l o ngword
l o ngwo rd
l ongword

Lo c a l event f l ag c l us t e r ( sy s t em )
Lo c a l event f l ag c l us t e r ( us e r )
Ad d r e s s o f g l o b a l c l us t e r 2

l ong wo rd

Ad d r e s s o f g l o b a l

PCB S L_P I D

l o ngword

Process

PCB$L_EFC3P

c l us t e r

PCB $ L_PHD

l o ngwo rd

Ad d r e s s o f p r o c e s s h e a d e r

PC B $ T LNAME
PC B $ L=J I B

16 byte s
l o ngwo rd

Pro c e s s name
Ad d r e s s o f Jo b

P C B $ Q PR I V
PCB $ L-ARB
PCB $ L U I C

quadwo rd
l o ngwo rd
l o ngwo rd

Cu r r en t p r o c e s s pr i v i l eg e m a s k
Ad d r e s s of a c c e ss r ig h t s b l o c k
Us e r i d e n t i f i c a t i o n c od e o f p r o c e s s

PCB $W MEM
PCB$W G R P

::::

wo rd
wo rd

In fo rma t i o n B l o c k

Membe r cod e of U IC
G r o up code o f U I C

Fig u r e

1 7-6

F i g u r e 9 -1
Figure 9-1
F i g u r e 9 -1 , F i g u r e 9 - 3 ,
F i g u r e 9 -4
F i g u r e 9 -1 , F i g u r e 9-3 ,
Fig ure 9 - 4
F i g u r e 1 7 - 2 , F i g ur e 1 9- 1 ,
Ta b l e 1 9 - 1
Fig ure 1-1 , Figure 1 7 - 1 ,
F i g ur e 1 7 -6
F i g u r e 1 7 - 2 , F i g u r e 1 9- 1
F i g ur e 1 - 1 , F i g u r e 1 7 - 1 ,
F i g u r e 1 7 - 2 , F i g u r e 1 7 -6
Ta b l e 1 8 - 1

DATA STRUCTURE DEF I N I T I ONS

D . l . 27

PHD - P r o c e s s He a d e r

Th e p r o c e s s h e ad e r c o n t a i n s p r o c e s s - s pe c i f i c m emo r y m a n ag em e n t d a t a
a nd o th e r p r o c e s s c on t e x t tha t c an b e s wa ppe d .
Of f s e t s i n to t h e f i x ed
po r t i o n o f t h e p r o c e s s h e ad e r a r e d e f i ne d wi th the $ P HDDEF m a c r o
a nd
l i s t ed i n Ta b l e D - 3 .
Pu r po s e :
Us u a l Lo c a t i o n :

Re f e r e n c e s :

O t h e r Re f e r e n c e s :

D. l . 28

PLV - P r i v i l eg ed L i b r a ry Ve c to r

Pu r po s e :
Us u a l L o c a t i o n :
Re f e r e n c e s :

D. l . 29

( co n ta i n i ng
Desc r i b e s p r i v i l eg ed sha r e a b l e
i mag e
to
imag e
sys t em
user
wr i t t e n
s e rv i c e s )
a c t i v a to r
i m ag e ,
Pa r t o f p r i v i l eg ed
shar eab l e
u s ua l l y
r e s i d i ng i n PO s pa c e
F i g u r e 3 - 9 , Ch a p t e r 6 o f
t h e VAX/VM S Re a l - T i m e
U s e r ' s Gu i d e

--�---------------

PQB - P r o c e s s Quo ta B l o c k

Pu r po s e :

Us u a l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e n c e s :

D. l . 30

Th e p r o c e s s h e a d e r c o n ta i n s a l l
process conte x t
t h a t mus t
r es i d e
in
sys t em s pa c e b u t c a n b e
o u t swapped .
P r o c e s s h e ad e r s a l wa ys r e s i d e i n the b a l a n c e s l o t
a r ea
i n s ys tem spac e .
P r o c e s s h e ad e r pag e s
t h a t a r e no t pag e t a b l e pag e s a r e d o ub l e mapped
b y a r a ng e of Pl space a d d r e s s e s .
Th e e n t i r e f i x ed po r t i o n o f t h e p r o c e s s h e ad e r
a ppe a r s n o wh e r e
i n t h i s m a n ua l .
Ta b l e D - 3
s umma r i z e s t h e f i x ed
po r t i o n o f
the proc e s s
h e ad e r .
F i g u r e 1 - 1 , Fig u r e s 1 1-1 , 1 1-2 , 1 1-4 , 1 1-6 ,
1 1-1 5
( Sy s t em He a d e r ) ,
1 1 -1 8
( Sy s t em He a d e r ) , a nd
1 1-20

Us ed d u r i ng p r o c e s s c r e a t i o n to
s to r e pa r ame t e r s
f o r n ew p r o c e s s tha t b e l o ng i n p r o c e s s h e a d e r
a nd
i n P l s pa c e u n t i l
tho s e
a reas
a re
accessible
Po i n ted t o b y l o ng wo r d ( PC B $ L_E FWM f i e l d )
in
the
PCB
Nonpag ed po o l
Ta b l e 1 7 - 2 , F i g u r e s 1 7 - 1 a nd 1 7 - 6

PRM - Pa r ame t e r Desc r i pto r B l o c k

Pu r po s e :
Us u a l L o c a t i o n :
Re f e r e n c e s :

Used by SYSB OOT a nd SYSGEN to f u l l y d e s c r i b e
a d j us t a b l e pa r am e t e r
Ad d r e s s s pa c e o f SYSB OOT o r SYSGEN p r og r am
Ta b l e 2 2 - 4

D- 1 3

each

Ta b l e D- 3
Of f s e t s i n to Fi x ed Po r t i o n o f t h e P r o c e s s He ad e r
S i ze o f F i e l d

Use of Th i s F i e l d

PHD$Q PR IVMSK
PHD$W-WS L I S T
PHDSW-WSAUTH
PHD$W-WSLOCK
PHD$W-WSDYN
PHD$W-WS LAST
P H D S L-REFERFLT
PHD$W=WSQUOTA

quad wo rd
wo rd
wo rd
wo rd
wo rd
word
l o ngwo rd
wo rd

P r o c e s s pr i v i l eg e m a s k
Ind ex to beg i nn i ng o f Wo r k i ng Se t Li s t ( WS L )
Ma x i mum autho r i zed WS L i nd e x
Index to beg i n n i ng o f d ynam i c a l l y l oc ked WSLEs
Ind ex to d yn a m i c WSL
Index to c u r rent end o f W S L
Re f e r ence Fa ul t Co unt
Ma x imum i nd e x that SADJWSL can reach

PHD$W_DFWSCNT

wo rd

De f a u l t WS L i nd e x

P H D S L_PAGF I L

l o ngwo rd

Longwo rd whose upper byte c o n ta i n s pag e f i l e i nd ex

PHD$B_PAGF I L
PHDSL PSTBASOFF
PHD$W-PSTLAST
PHD$W-PS TFREE
PHDSL-F R E P OVA
PHDS L=FREPTECNT

I-'
�
I

F i g u r e or Ta b l e
Re fe r ences i n Th i s Ma nua l

Symbo l i c Name

byte
l o ng wo rd
wo rd
wo rd
1 ongwo rd
l o ngwo rd

PHD$L_F R E P 1 VA

l o ngwo rd

PHD$8 D F PF C
PHD$8-PGTBPFC
PH D$W=F LAGS

byte
byte
wo rd

PHD$V PFMFLG
PHDSV-DA LCSTX
PHDSV=WS PEAKCHK

bit
bit
bit

r e s t o red by Imag e Rundown

O f f s e t to upper byte of tha t l ongword
Byte o f f s e t to high a d d ress end o f process sec t i o n tab l e
Ind ex ( n eg a t i v e f rom PSTBASOFF) o f l a st PSTE
Ind ex ( neg a t i ve from PSTBASOFF) o f f i r s t ava i l ab l e PSTE
Fi r s t f r ee v i r t ual ad d r e ss at end of PO space
Co unt o f free PTEs between the ends of
t h e P O and P l page t a b l es
F i r s t f r ee v i r t ua l ad d re s s a t
( l ow a d d r e s s ) end o f P l space
De faul t page faul t c l us t e r fo r process pag e s
De faul t p a g e faul t c l us t e r fo r p r o c e s s head e r pages
Fl ag s wo rd

PHDSL_CPUTIM

l o ng wo rd

Ac c um u l a ted CPU t i m e ( i n 10 msec un i t s )

wo rd
wo rd
wo rd
wo rd
wo rd

PHD$W_WS LX

wo rd

Ac c umul a ted C P U t ime s i nc e l a st quantum expi r a t i o n
Subpr o c e s s 1 i m i t
AST 1 i m i t
P r o c e s s h ead e r vecto r i n d e x
Longwo rd i n d ex t o bac kup a d d r e s s v e c to r
fo r process header pag e s
Longwo rd index to W S L X s a v e a r e a
f o r process h e a d e r pag es

PHDSW_PSTBASMAX

wo rd

P H D S L_PTWSLELC K

l o ngwo rd
l o ngwo rd
l o ngwo rd
l ong wo rd
l o ngwo rd
b yte
3 bytes
l o ngwo rd

PHD$L_PTWSLEVAL

l o ngword

PHD$W_PTCNTLCK

wo rd

PHDSW_PTCNTVAL

wo rd

PHD$W PTCNTACT
PHD$W-PTCNTMAX
PHD$W-WSF L U I D
PHD$W=E XTDYNWS

wo rd
wo rd
wo rd
wo rd

PHD$L PAGEFLTS
P H D $ L-PG F L T I O
PHD$L-DIOCNT

PHD$L-B IOCNT

PHD$B=CPUMODE
P H D $ L-C P U L I M

18-1
1 3- 1 , Fig ure
1 3 - 1 , Figure
13-1, Figure
1 3- 1 , F i g u r e
1 3 -1 , F i g u r e

1 1 -4
1 1 -4
1 1 -4
1 1 -4
1 1 -4

Ta b l e 1 3 -1 , F i g u r e 1 1 - 4 ,
Ta b l e 1 7 - 4
Ta b l e 1 3 - 1 , F i g u r e 1 1 -4 ,
Ta b l e 1 7 - 4
Figure 1 1-22
Figure
Figure
Figure
Figure
Figure

1 1 -6
1 1 -6
1 1 -6
1 1 -2
1 1 -2

F i g u r e 1 1 -1 5

F i g u r e 1 1 -2
Ta b l e 1 2 -1
Tab l e 1 2 -1

Page fa u l t mon i to r ing enab l ed
Need to d eal l oc a t e sec t i o n i nd i c e s
Ch eck f o r new peak wo r k i ng s e t s i ze

PHDSW QUANT
PHD$W-PRCLM
PHD$W-ASTLM
P HDSW-PHVINDEX

PHD$W=BAK

Tab l e
Ta b l e
Ta b l e
Ta b l e
Ta b l e
Ta b l e

Synonym fo r l a st e n t r y ( a l so end of empty pag e a r e a )
C o u n t o f a c c umul a t ed p a g e f a ul ts
Co unt of pag e f a ul t I/0 o pe ra t i o n s
Co unt o f d i rec t I / 0 o pe r a t i o n s
Co un t o f b u f fe r ed I / O o pe r a t i o n s
CPU t i me l im i t fo r p r o c e s s
Ac c e s s mode to no t i fy on CPU t i m e l im i t expi r a t i o n
spa r e
B y t e o f fs e t to a r r a y o f c ounts o f l o c ked
WSLEs in this page tab l e pag e
Byte o f fs e t to a r ray of c o un t s of v a l i d
WSLEs i n th i s page tab l e page
Co un t of page table pages conta i n i ng
o ne or m o r e l oc ked WSLEs
Count of page tabl e pages c onta i n i ng
o n e or mo r e va i l d WSLEs
Co u n t of a c t i v e page tab l e pages
Maxi mum count of page tabl e pages that have nonze r o PTEs
Gua r a n teed number of f l u i d wo r k i ng set l i st entr i e s
E x t r a dynam i c WSLEs above r equi red WSFLUID m i n imum

Ta b l e 1 3 -2 , Ta b l e 1 7 - 4 ,
Ta b l e 1 9- 1
Table 1 7 - 4
F i g u r e l l -2 0
F i g u r e l l -8
F i g u r e 1 1 -8
Fi g ur e 1 1 -6
Tab l e 1 3 -2 , Ta b l e 1 9- 1
Table 1 9-l
Ta b l e 1 9 -1
Ta b l e 1 7 -4
F i g u r e 1 1 -8
F i g u r e 1 1 -8
F i g ur e 11-8
F i g u r e 1 1 -8
F i g u r e 1 1 -8
F i g u r e 1 1 -8
Table 1 3-1
Table 1 3-1

(continued o n next page)

Ta b l e D- 3

( cont . )

Of f s e t s i n to Fi x ed Po r t i o n o f t h e Pr o c e s s He ad e r
the
Th e n e x t 2 4 l o n g wo rd s c o n ta i n t h e h a r d wa r e PC B :
c o p i e s o f t h e g en e r a l r eg i s t e r s ,
The
pe r p r o c e s s s t a c k po i n t e r s , a nd t h e m em o r y m a n ag em e n t a nd ASTLVL r eg i s t e r s .
fo u r
fo r
each
o ffse t s
Symbo l i c
h a r d wa r e PC B i s t r e a t ed i n t h e t a b l e a s a s i ng l e e n t i t y .
i nd i v i d ua l e l em e n t a r e n o t i n c l ud ed i n t h e ta b l e .
S i ze o f F i e l d

Us e o f Th i s F i e l d

PHDSL PCB

2 4 l o ng wo r d s

Co n t a i n s h a r d wa r e p r o c e s s c o n t e x t wh e n
p r o c e s s i s n o t c u r r e n t l y e x e c u t i ng

Ad d i t i o na l p r o c e s s - s p e c i f i c d a ta
PC B .

0
I
1--'
Ul

F i g u r e o r Tab l e
Re f e r en c e s i n Th i s Ma n ua l

Sym bo l i c Na m e

i s fo und

i n the proc e s s

h ead e r

Fig ur e

bel ow

the

Symbo l i c Na m e

S i ze o f Fi e l d

Us e o f Th i s F i e l d

P H D $W EM PT PG
PHD $W-R E S PGCNT
PHD $W-R E QPGCNT
PHD $W-C W S L X
P H D S Q A UT H PR I V
P H D $ Q I M AG PR I V
PHD S L R E S LS TH
P H D $ L I MG C NT
P H D S L-P F LTRATE
P H D $ L-P F LR E F
P H D $ L-T I M REF

wo rd
wo rd
wo rd
wo rd
q u a d wo r d
q u ad wo r d
1 o ng wo rd
1 o ng wo r d
l o ng wo rd
l o ng wo rd
l o ng wo rd
l o ngwo rd

Co un t of empty p r o c e s s h e a d e r pag e s
Re s i d e n t pag e c o un t
Re q u i r ed pag e c o un t
Co n t i n ua t i o n WS LX
Pr i v i l eg e s m a s k f r o m a u t ho r i za t i o n f i l e
P r i v i l eg e s m a s k f o r i m a g e i n s t a l l ed w i t h p r i v i l eg e
s pa r e
Re s o u r c e l i s t h e a d ( no t u s e d )
Imag e c o un te r i n c r em e n t e d by i m ag e r und o wn
Pag e f a u l t r a t e ( fo r a ut om a t i c wo r k i ng s e t a d j u s tmen t )
Num b e r of pag e f a u l t s a t e n d o f l a s t i n t e r v a l
Time at end of l a s t i n te r v a l

l o ng wo r d s

s pa r e

1-1 ,

Figure

8 -6

h a r d wa r e
F i g u r e o r Tab l e
Re f e r en c e s i n Th i s Ma n ua l

Tab l e 1 8 -1
1 8-1

Ta b l e

Tab l e 1 3-2
Ta b l e 1 3-2
Ta b l e 1 3-2

DATA S TRUCTURE DE F IN I T I ONS

D. l . 31

PS L - P r o c e s s o r S t a tus Longwo r d

Pu r po s e :
Lo c a t i o n :
Re f e r e nc e s :

D. l . 32

Re f e r en c e s :

Us ua l Lo c a t i o n :
Al l o c a ted f r om :

Re f e r e nc e s :

De s c r i b e s s t a t e a nd l o c a t i o n o f e a c h v i r t ua l pag e
P r o c e s s h e a d e r c o n t a i n s P O a nd P l pag e ta b l e s t h a t
d e sc r i b e
p r o c e s s a d d r e s s s pa c e .
Th e s ys t em
pag e t a b l e i n the sys tem h e ad e r c o n t a i n s
the
s y s t em pa g e t a b l e .
Fig ure 1 1-3

Ac t s a s b l oc k h e ad e r fo r a r b i t r a r y d a t a s t r uc t u r e .
VM S u s e s o n e to c o n ta i n the a r r a y o f po i n t e r s
to
swa p
file
table
e n t r i e s a nd
pag e
file
con t r o l
blocks .
A s e cond i s u s e d to c o n t a i n
t h e a r r a y o f po i n t e r s t o e a c h known f i l e l i s t .
Depend s o n i t s u s e
Th e pag e f i l e a nd swa p f i l e v e c to r
is
s ta t i c a l l y
a l l oca ted
i n m od u l e SWAPF I LE .
Th e known f i l e
l i s th e a d i s a l l o c a t ed
f r om no npag ed po o l
by
SYS I N I T .
Impl i c i t r e f e r e n c e s i n F i g u r e 1 1 - 2 2

RBM - Re a l -T i me B i tmap

Pu r po s e :
Us u a l Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e nc e s :

D. l . 35

Sys tem

PTR - P o i n t e r C o n t r o l Bl o c k

Pu r po s e :

D . l . 34

VAX/VMS

PTE - Pag e Ta b l e En t r y Fo rma ts

Pu r po s e :
Us u a l Lo c a t i o n :

D. l . 33

De s c r i b e s s t a t e o f p r o c e s so r
P r o c e s so r i n t e r n a l r eg i s t e r
VAX- 1 1 A r c h i t e c t u r e Hand boo k ,
S e r v i c e s Re f e r e n c e Ma n u a l

D e s c r i b e s a v a i l a b l e S PT E s fo r conn e c t- to- i n te r r up t
dr iver
Po i n ted t o b y E XE $G L R TB I TMAP
No n pag ed poo l
Ta b l e E-2

RPB - Re s t a r t P a r am e t e r Bl o c k

Pu r po s e :

Us u a l Lo c a t i on :
Re f e r e nc e s :

U s e d by powe r f a i l a nd r ec o v e r y r o u t i n e s
to
save
vo l a t i l e
p r o c e s so r s t a t e .
Us ed b y b ug ch e c k to
l o c a t e b o o t s t r a p I /0 d r i v e r
a nd
a s so c i a t ed
s ub r o u t i n e s
Ph ys i c a l pag e z e r o o n s ys t em wi th no b ad m emo r y i n
the f i r s t 6 4 K bytes
T a b l e 2 1 - 3 , Tab l e 2 3 - 1

D- 1 6

DATA S TRUCTURE DE F I N I T I ONS

D. l . 36

S EC - S e c t i on Ta b l e E n t r y

Pu r po s e :
U s ua l Lo c a t i o n :
Re fe r e n c e s :

D. l . 37

U s u a l Lo c a t i o n :
Al l o c a t ed f r om :
Re fe r e nc e s :

U s ua l Lo c a t i o n :

Re f e r e n c e s :

D e sc r i b e s s h a r ed m emo r y c o nn e c t e d
to
s pe c i f i c
p r o c e s so r
I n l i s t o f s h a r ed memo r y c o n t r o l b l o c k s
( l i s th e a d
EXE $G L S HB L I ST ) i n p r o c esso r l o c a l memo r y
Nonpag ed po o l
Figure 1 1-26

I n i t i a l d e sc r i p t i o n o f a
spec i f i c
sh a r ed m emo r y
control le r
( I ts
La s t phy s i c a l
pag e o f
sha r ed
memo r y .
p r o c e s s o r - s pec i f i c v i r t ua l a d d r e s s i s s to r ed i n
t h e s h a r ed memo r y c o n t r o l b l o c k o n e a c h po r t
c o n n e c ted t o the sha r ed memo r y . )
Table 1 1- 3

STS - Re t u r n S t a tus F i e l d De f i n i t i on s

Pu r po s e :
Re fe r e n c e s :

D. l . 41

F u l l y d e s c r i b e s e a c h swa p f i l e i n t h e sys t em
S t a t i c a l l y a l l o c a ted i n modul e SWAPF I LE
F i g u r e s 1 1 - 2 2 a nd 1 1 - 2 3 , F i g u r e 1 7 - 5

S HD - Sha r ed Memo r y Da ta Pag e

Pu r po s e :

D. l . 40

the

SHB - Sh a r ed Memo r y Con t r o l B l o c k

Pu r po s e :

D . l . 39

fo r

SFT - Swa p F i l e Ta b l e En t r y

Pu r po s e :
U s ua l Lo c a t i o n :
Re f e r e n c e s :

D . l . 38

D e s c r i b e s p r o c e s s , g l oba l , o r s ys t em s e c t i o n
I n p r o c e s s o r s ys tem h e ad e r i n a r e a a l l o c a ted
sec t i o n table entr i e s
F i g u r e s 1 1 -6 , 1 1 -7 ,
a nd
1 1-1 6 ,
Pa r t I I o f
VAX/VM S Sys t em Se r v i c e s Re f e r e nc e Ma n u a l

De sc r i b e s r e t u r n s t a t us f r om p r o c ed u r e
( i nc l ud i ng
De sc r i b e s c o nd i t i o n name to
s y s t em s e r v i c e ) .
c o nd i t i o n h a nd l e r .
C h a pte r 8
of
the VAX/VM S U t i l i t i e s
Re f e r en c e
Ma n ua l ,
Append i x C o f t h e VAX-1 1
Run-T i m e
L i b r a r y Re f e r e n c e Ma n ua l

TQE - T i m e r Queue El ement

Pu r po s e :
Lo c a t i o n :
Al l o c a t ed f r om :
Re f e r e n c e s :

De sc r i b e s p e nd i ng
t i me r
or
sched u l ed
r e que s t
I n t i me r queue ( 1 i s thead EXE $G L_T QF L )
N o n pag ed po o l
F i g u r e 1 0-1

D- 1 7

wa k e up

DATA S TRUCTURE DE F I N I T I ONS

D. l . 42

VA - Vi r tua l Add r ess F i e l d De f i n i t i o n s

Pu r po s e :
Re f e r e nc e s :

0. 1. 43

WQH - Sched u l e r Wa i t Que ue He ad e r

P u r po s e :
Usua l Lo c a t i o n :
Re f e r e nc e s :

0. 1 . 44

L i s thead
fo r
al l
PC Bs
o f p r oc e s s e s
sched ul i ng s ta te
S t a t i c a l l y a l loca ted in mod u l e SDAT
Figure 8 - 4

g i ven

WS L - Wo r k i ng Se t L i s t En t ry F i e l d De f i n i t i ons

Pu r po s e :
U s u a l Lo c a t i o n :
Re f e r e nc e s :

D. 2

pag e n umbe r
fo r
S e l e c t s pag e t a b l e and v i r t ua l
and pag e f a ul t
add ress
t r a n s l a t i o n m e c han i sm
h a nd l e r
F i g u r e 1 2 -1

D e s c r i b e s v i r t u a l pag e t ha t i s a m embe r o f p r o c e s s
o r s y s t em wo r k i ng s e t
I n wo r k i ng s e t l i s t i n p r o c e s s o r sys tem h e ad e r
F i g u r e s 1 1 - 4 a nd 1 1 - 5

C ONSTANTS

s ym bo l i c c o d e s
Th e f i l e s SYSDEF a nd S TAROEF d e f i ne many s ys tem-w i d e
r e so u r c e s , quo ta s , p r i o r i t i e s , a nd s o on .
tha t
i d en t i f y s t r uc t u r e s ,
Many o f t h e s e c o n s t a n t s a r e
l i s t ed
i n e i th e r
the VAX/VMS Sys tem
Se r v i c e s R e f e r e nc e Ma n u a l o r the VAX/VM S I /O Us e r ' s Gu i d e .
Tho s e tha t
a r e m o s t c l o s e l y t i ed t o the m a t e r i a l p r e s e n t ed
in
t h i s m a n ua l
are
l i sted h e r e .

0. 2. 1

BTD - Boo t s t r a p Dev i c e Cod e s

Th e boo t s t r a p d ev i c e c od e s a r e u s ed to i n t e r p r e t t h e c o n t e n t s o f RO t o
VMB , t h e p r ima r y bo o t s t r a p p r og r am .
B TD $ K MB
BTD$K-DM
B TD $ K-D L
B TD $ K=C ONSOLE

0
1
2
64

MAS S B US Dev i c e
R K 0 6 / RK 0 7
R L0 2
Co n so l e B l o c k S to r ag e Dev i c e

Th e boo t s t r a p d ev i c e t ype cod e s a r e l i s t ed in Tab l e 2 1 - 2 .

D. 2. 2

CA - Co nd i t i o n a l As s em b l y Pa rame t e r s

Th e c o nd i t i o na l a s s emb l y p a r a m e t e r s c o n t r o l wh e th e r c e r t a i n c o d e
is
i nc l ud ed
wh e n c om po n e n t s o f VM S a r e a s s em b l ed .
Th e s e pa r ame t e r s we r e
i mpo r ta n t d u r i ng t h e i n i t i a l d ev e l o pm e n t o f VM S b u t a r e n o
l o ng e r
us ed .
Al l
s i m u l a to r
cod e
h a s b e en r emoved .
Al l m e a s u r em e n t c o d e
( u s ed b y D I S PLAY ) i s a l wa ys i nc l ud ed .

D- 1 8

DATA STRUCTURE DEFIN I T I ONS

CA$ S IMULATOR
CA$ M EASURE
CA$ MEASURE I OT
-

D.2. 3

1
2
4

VMS Runn i ng on S i m u l a to r
Ac c um u l a t e Sta t i s t i c s f o r D I S PLAY
C o un t I /0 T r a n s a c t i o ns f o r D I S PLAY

DYN - Da t a S t r uc t u r e Type De f i n i t i ons

Al l s t r uc t u r e s a l l o c a t e d f r om no npag ed and pag ed d ynam i c m em o r y have a
un i q u e c od e i n a t ype f i e l d ( a t o f f s e t x y z $ B TYPE = 1 0 ) .
SDA u s e s the
c o n t e n t s o f t h i s f i e l d in d ump i ng po o l a nd i n a utoma t i c f o r m a t t i ng
of
a d a ta s t r uc t u r e wi th t h e F ORMAT c ommand .
Th e r e s u l t s o f i nv o k i ng th e
$ DYNDEF ma c ro a r e s umma r i ze d i n Ta b l e D-4 .

D. 2. 4

I 0 7 x x - I /0 Spa c e Ad d r ess Spec i f i c a t i o n s

Th e d i v i s i o n o f phys i c a l add r e s s b e twe en ma i n m emo r y a d d r e s s e s and I / O
s pa c e add r e s s e s i s C PU d e pe nd e n t .

D. 2 . 4 . 1
I 0 7 5 0 - VAX- 1 1 / 7 5 0 Phys i c a l Add r ess Spa c e De f i n i t i o n s Phys i c a l
add ress
s pa c e o n the
VAX- 1 1/7 5 0
i s d e f i n ed by a 2 4 -b i t
a d d r e s s a nd i s e v e n l y d i v i d ed b e twe e n m a i n m emo r y ( Phys . Ad d r . < 2 3 >
0)
a nd I /O s pa c e a d d r e s s e s ( Ph ys . Ad d r . < 2 3 > = 1 ) .
Ten o f t h e s i x t e e n s l o t
po s i t i o ns a r e f i x ed .
Th u s i t i s po s s i b l e t o
i d en t i f y t h e ad d r e s s
s pa c e fo r UB I O r eg i s t e r s a nd MASS BUS 0 r eg i s t e r s .
=

I 0 7 5 0 $AL I OBASE

F20000

( hex )

I 0 7 5 0 $AL MBBAS E

F 2 8 0 00

( hex )

I 0 7 5 0 $AL UBBASE

F 30000

(hex )

I 0 7 5 0 $AL NNEX
I 0 7 5 0 $AL PERNEX

16
2000

(d ec )
( hex )

I 0 7 5 0 $AL UB O S P

FCO O O O

(hex )

Ba s e Ad d r e s s o f Reg i s t e r
S pa c e fo r Sl o t 1 6
Reg i s t e r
B a s e Ad d r e s s o f
S pa c e fo r MAS S B U S 0
Reg i s t e r
B a s e Ad d r e s s o f
Spa c e fo r UN I B US 0
Numbe r o f Ad a p t e r s
S i z e o f Reg i s t e r Spa c e fo r
E a c h Nexus
Ba s e Ad d r e s s o f UN I B US
0
Ad d r e s s Spa c e

Ad a pt e r a s s i g nm e n t s fo r t h e f i r s t t e n s l o t s a r e f i x ed .
c o n s ta n t s d e sc r i b e the s e a s s i g nm e n t s .
I 0 7 5 0 $C S L M EM O
- I 0 7 5 0 $C S L M PM O
- I 0 7 5 0 $ C S L M PM 1
- I 0 7 5 0 $ C S L M PM 2
- I 0 7 5 0 $ C S L MB O
- I 0 7 5 0 $ C S L MB 1
- I 0 7 5 0 $ C S L MB 2
- I 0 7 5 0 $ C S L MB 3
- I 0 7 5 0 $ C S L UB O
- I 0 7 5 0 $ C S L UB 1

0
1
2
3
4
5
6
7
8
9

Memo r y Co n t r o l l e r
M u l t i pa r t Memo r y 0
M u l t i pa r t Memo r y 1
Mul t i pa r t Memo r y 2
MAS SBUS 0
MAS SBUS 1
MAS S B US 2
MAS SB US 3
UN I B US 0
UN I B US 1

D- 1 9

Th e

fo l l owi ng

DATA STRUCTURE D E F IN I T I ONS

Ta b l e D - 4
Dyn am i c Da t a S t r uc t u r e Type Cod e s
St r uc t u r e Type

Symbo l i c Nam e

Co d e

DYN $C ADP
DYN $C ACB
DYN $C AQB
DYN $C C EB
DYN $C C RB
DYN $C DDB
DYN $C FCB
DYN $C FRK
DYN $C I DB
DYN $C I R P
DYN $C LOG
DYN $C PCB
DYN $C P QB
DYN $C RVT
DYN $C T QE
DYN $C UCB
DYN $C VC B
DYN $C WCB
DYN $C B UF I O
DYN $C TYPAHD
DYN $C G S D
DYN $C MVL
DYN $C N E T
DYN $C KF I
DYN $C MTL
DYN $C B RDC S T
DYN $C C XB
DYN $C NDB
DYN $C S SB
DYN $C D PT
DYN $C J PB
DYN $C PB H
DYN $C PDB
DYN $C P I B
DYN $C PF L
DYN $C S F T
DYN $C PTR
DYN $C K F H
DYN $C RVX
DYN $C E XTGSD
DYN $C S HMGS D
DYN $C S HB
DYN $C MBX
DYN $C I R PE
DYN $C S LAVCEB
DYN $C S HM C EB
DYN $C J I B
DYN $C TWP
DYN $C RBM
DYN $C=VCA

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
32
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50

Ad a pt e r Co n t r o l Bl o c k
AST Co ntr o l Bl oc k
ACP Que ue B l o c k
Common Ev e n t Bl oc k
Channe l Reque s t Bl oc k
Dev i c e Da t a B l o c k
F i l e Co n t r o l B l o c k
Fo r k B l oc k
I n te r r upt D i s pa tch Bl o c k
I /O Re que s t Pac ke t
Log i c a l Name B l o c k
So ftwa r e P r o c e s s Co n t r o l Bl oc k
P r o c e s s Quo ta Bl o c k
Re l a t i v e Vo l ume Ta b l e
T i m e r Que ue El emen t
Un i t Co n t r o l Bl oc k
Vo l um e Co n t r o l B l o c k
W i ndow Co n t r o l Bl o c k
Bu f fe red I /O Bu f f e r
Te r m i n a l Type-Ah e ad Bu f f e r
G l o b a l Sec t i o n De sc r i pto r
Mag ne t i c Ta pe Vo l um e Li s t
N e two r k Me s sag e B l o c k
Known Fi l e En t r y
Mounted Vo l um e L i s t En t r y
B r o ad c a s t Me s sag e B l o c k
Compl e x Cha i n ed Bu f f e r
N e two r k No d e De sc r i pto r Bl o c k
Log i c a l L i n k Subcha nnel Sta t us B l oc k
Dr i v e r Pro l og ue Tab l e
Job Pa ram e t e r Bl o c k
Pe r fo rmanc e Bu f f e r He ad e r
Per fo rm anc e Da ta B l o c k
Pe r fo rman c e I n fo rma t i o n B l oc k
Pag e F i l e Co n t r o l Bl oc k
Swa p F i l e Tab l e En t r y
Po i n t e r Co n t r o l Bl o c k
Known Fi l e Imag e He ad e r
R e l a t i v e Vo l um e Tab l e Ex tens i o n
Ex tend ed G l obal Sec t i o n De sc r i pto r
Sha r ed Mem o ry G l o b a l Sec t i o n Desc r i pto r
Sha r ed Mem o ry Co n t r o l Bl oc k
Ma i l bo x Co n t ro l B l o c k
Ex tend ed I /O Reque s t Pa c k e t
S l ave Common Ev e n t B l o c k
Sh a r ed Mem o ry Ma s t e r Common Ev e n t B l o c k
J o b In fo rma t i o n B l o c k
Te rm i n a l D r i v e r Wr i te Pa c ke t ( $ TTYDEF)
Real T i m e S PT B i tm a p
D i s k Vo l um e Ca che Bl oc k

DYN $C S PEC IAL
DYN $C S HRBUF I O

128
1 28

Cod e tha t d e f i n e s b eg i nn i ng o f s pec i a l cod e s
Sh a r ed Mem o ry Bu ffe r ed I/O Bu f fe r

D- 2 0

DATA STRUCTURE DEF IN I T I ONS
0. 2. 4 . 2
I 07 8 0 - VAX- 1 1/ 7 8 0 Phys i c a l Add r e s s S pa c e De f i n i t i o n s Ph ys i c a l
add r e s s
s pa c e
o n t h e VAX- 1 1 / 7 8 0
i s d e f i ned by a 3 0 -b i t
0)
a d d r e s s a nd i s eve n l y d i v i d ed b e twe e n m a i n memo r y ( Phys . Ad d r . < 2 9 >
a nd I /O spa c e a d d r e s s e s ( Ph ys . Ad d r . < 2 9 >
1) .
=

I 0 7 8 0 $AL I OBAS E

20000000

(hex )

I 0 7 8 0 $A L NNEX
I 0 7 8 0 $AL-P E RNE X

16
2000

( d ec )
( h ex )

I 0 7 8 0 $A L UB OS P

20100000

(hex )

0. 2 . 5

Ba s e Ad d r e ss o f Reg i s t e r
Spa c e fo r TR 0
N umbe r o f Ad a pt e r s ( N e x u s )
S i z e o f Reg i s t e r S pa c e f o r
Each N e x u s
Ba s e Ad d r e s s o f UN I B US
0
Ad d r e s s Spa c e

I PL - P r o c e s s o r P r i o r i ty Leve l De f i n i t i o n s

I PL l ev e l s tha t a r e u s e d f o r s yn c h r o n i za t i o n a nd o th e r pu r po s e s by VM S
a r e g i ven s ymbo l i c n a m e s .
I P L $ ASTD E L
I P L$ -S C H E O
I PL $- I O PO S T
I PL $ -Q U E UEAST
I PL $-S YN C H
I PL $-T IM E R
I PL $-MA I LB OX
I PL $-HWC LK
I PL $=POWER

2
3
4
6
7
7
11
24
31

AST De l i v e r y I n t e r r up t
R e s c h e d u l i ng I n t e r r up t
I /O · Po s t p r o c e s s i ng In t e r r up t
Fo r k L e v e l Used fo r AST Que u i ng
S y s t em Wi d e Syn c h r o n i za t i o n Lev e l
S o f twa r e T i m e r I n t e r r up t
Fo r k I PL f o r Ma i l box D r i v e r
H a rdwa r e C l o c k I n t e r r up t
B l o c k Po we r Fa i l I n t e r r up t

A powe r fa i l i n te r r upt c a u s e s I P L to be r a i s ed to 3 0 , no t 3 1 .
Ra i s i ng
I PL
to
31
b l o c k s a l l i n te r r up t s a nd s e r i o u s c o nd i t i o n s un t i l I PL i s
l owe r ed .
Th e I PL va l ue s u s e d f o r
s yn c h r o n i z a t i o n a r e
l i s t ed
i n Tab l e 2 4 - 1 .
Th o s e v a l u e s tha t c o r r e s po nd to s o f twa r e i n t e r r upt I PL v a l u e s a r e a l so
l i s t ed i n Ta b l e 4 - 1 .

0. 2 . 6

J P I - $GETJ P I Da t a I d e n t i f i e r De f i n i t i on s

Th e $ J P I DE F m a c r o i s u s e d i n a rg umen t l i s t s
to
the
$G E TJ P I
s ys tem
s e rv i c e to i d en t i f y tho s e d a t a e l em e n t s t h a t a r e be i ng r e q u e s t ed .
Th e
s ym bo l i c n ame s d e f i n ed by th i s m a c r o a r e
l i sted
i n Pa r t I I o f
the
VAX/VM S Sys t em Se r v i c e s Re f e r enc e Ma n ua l .

0. 2 . 7

MSG - Sys t em Wi d e Ma i l bo x Me s s a g e Types

Th e $MSG D E F m a c ro d e f i n e s codes t o
i d en t i f y m a i l bo x m e s s ag e s .
Th e
s ymbo l i c n ame s d e f i n ed by th i s m a c r o a r e l i s t ed i n Append i x A o f the
VAX/VMS Sy s t em S e rv i c e s Re f e r enc e Ma n ua l .

0- 2 1

DATA STRUCTURE DEF IN I T I ONS
D. 2. 8

NDT - Nexus

( Ad a pt e r ) Dev i c e Type

Ea c h e x t e r n a l a d a p t e r h a s an a s s o c i a t ed c o d e
that
is
used
by VMB ,
IN I T ,
a nd
the
powe r
r ec o v e r y
r o ut i ne
to
d e t e rm i ne wh i c h
e ac h
a d a pte r - s pe c i f ic
ac t i on
sho u l d b e t a k e n
to
( re ) i n i t i a l i ze
adapte r .
NDT$ MEM 4N I
NDT$-M EM 4 I
NDT $-M EM 1 6N I
NDT $-M EM 1 6 I
NDT $-M B
NDT $-UB O
NDT$-UB l
N DT $-UB 2
N DT$-UB 3
NDT $-DR 3 2
NDT$-M PM O
NDT $-M PM l
NDT$-M PM 2
NDT$=M PM 3
D. 2.9

8
9
16
17
32
40
41
42
43
48
64
65
66
67

4 K Memo r y - No t I n t e r l e a ved
4 K Memo r y - I n te r l eaved
1 6K Mem o r y - No t I n te r l ea v ed
1 6K Mem o r y - I n t e r l eaved
MAS S B US
UN I B US 0
UN I BUS 1
UN I B US 2
UN I B US 3
DR 3 2
Mul t i pa r t Mem o r y 0
Mul t i pa r t Memo r y 1
Mul t i pa r t Memo r y 2
Mul t i pa r t Memo r y 3

PQL - P r o c e s s Quo t a L i s t C o d e s

Th e $ P QLDEF m a c r o d e f i n e s s ym bo l i c c o d e s t h a t a r e pa s s ed t o t h e C r e a te
P r o c e s s s ys tem s e rv i c e .
Th e s e s ym bo l s a r e l i s t ed i n Pa r t I I o f the
VAX/VM S Sys tem Se r v i c e s Re f e r enc e Ma n ua l .

D. 2. 10

PR - P r o c e s so r Reg i s t e r De f i n i t i o n s

Th e $ PRDE F ma c r o d e f i n e s sym bo l i c names
fo r
t h e processo r
internal
r eg i s t e r s .
Some
of
the s e
r eg i s t e r s a r e d e f i n ed a s pa r t o f t h e VAX
a r c h i t ec t u r e a nd a r e fo und i n a l l p r o c e sso r s .
O th e r s a r e spec i f i c
to
a
s i ng l e C PU .
Th e
internal
p r o c e s so r
r eg i s t e r s a r e l i s t ed
in
Append i x A o f the VAX/VM S Sy s t em S e r v i c e s Re f e r e n c e Ma n ua l .
P r o c e sso r
r eg i s t e r s a r e d e sc r i b ed i n t h e VAX Ha rdwa r e Ha ndbo o k .

D. 2 . 11

PRI - P r i o r i ty I n c r em e n t C l a s s De f i n i t i o n s

Th e $ PR I DE F m a c r o d e f i n e s
the pr i o r i ty
i nc r em e n t c l a s s e s .
Th e s e
c o n s t a n t s a r e t yp i c a l l y l o ad ed i n to R2 b e fo r e S C H $ C HS E o r SC H $ C HS E P i s
c a l l ed t o m a k e a p r o c e s s c om p u t a b l e .
PR I $ N U L L
PR I $- I OC OM
PR I $-R E SAVL
PR I $-T IMER
PR I $ -TOC OM
PR I $-T I C OM

0
1
2
2
3
4

No Pr i o r i ty Bo o s t
I /O Compl e t i o n
Re so u r c e Av a i l a b l e
T i m e r Re qu e s t Compl e t e
Te rm i n a l Output Compl e t i o n
Te rm i n a l Output Compl e t i o n

Ta b l e 8 - 3 s hows t h e c o r r e s po nd e n c e be twe en i nc r em e n t c l a s s e s
a c t ua l boo s ts .

D- 2 2

a nd

the

DATA STRUCTURE DEFIN I T I ONS

D. 2. 12

PRT

P r o t e c t i o n F i e l d D e f i n i t i ons

Th e $ PRTDE F m ac r o d e f i n e s the d i f f e r e n t c o n t e n t s o f
the
p r o te c t i o n
f i eld
in a
pag e
t ab l e e n t r y .
( Th e $ PTEDEF m a c r o d e f i n e s s i m i l a r
c on s t a n t s , e x c e p t t h a t t h e PRT $ C x x x s ym bo l s a r e v a l u e s i n t h e r a ng e
f rom
0
to
1 5 wh i l e t h e PTE $ C-x x x s ym bo l s have sh i f t e d t h e s e v a l u e s
i n to b i t po s i t i o n s < 3 0 : 2 7 > .
PRT $ C NA
PRT $C-R E S E RVE D
PRT $C-KW
PRT $C-KR
PRT $C-UW
PRT $C-EW
PRT $C-E RKW
PRT $C-E R
PRT $C-SW
PRT $C-S R EW
PRT $C-S RKW
PRT $C-S R
PRT $C-URSW
PRT $C-UREW
PRT $C-URKW
PRT $C-UR

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

No Ac c e s s
R e s e rved
K e r n e l Wr i t e
K e r ne l Re ad
U s e r Wr i t e
E x e c u t i v e Wr i t e
E x e c u t i ve Read , Ke r n e l Wr i t e
E x e c u t i v e Re ad
S u pe rv i so r Wr i t e
S upe rv i so r Read , E x e c u t i v e Wr i te
Supe rv i so r Re ad , Ke r n e l Wr i te
S upe rv i so r Re ad
U s e r Re ad , Supe rv i so r Wr i t e
U s e r Read , Ex e c u t i v e Wr i te
U s e r Re ad , Ke r n e l Wr i t e
U s e r Read

Th e p r o tec t i o n c od e s a r e l i s t ed i n Ta b l e 1 1 - 1 .

0. 2 . 13

PRV - P r i v i l eg e B i t De f i n i t i o n s

Th e $ PRVOE F ma c r o d e f i n e s
s ymbo l i c n am e s f o r
all
r e c og n i zed VMS
p r i v i l eg e s .
Th e
s ymbo l i c n am e s p r od uc ed by th i s m a c r o a r e d e sc r i b ed
i n Pa r t I I o f t h e VAX/VM S Sys tem Se r v i c e s Re f e r en c e Ma n ua l .

0. 2. 14

RSN

R e so u r c e Name De f i n i t i o ns

Th e $ RSNDE F m a c r o d e f i n e s c o n s ta n t s
tha t
i nd i c a t e
t h e pa r t i c u l a r
r e so u r c e a p r o c e s s i s wa i t i ng f o r wh e n i t i s i n the MWA I T s ta te .
Th e
r e so u r c e n um b e r i s s to r ed i n the PC B $ L E FWM f i e l d i n t h e PC B .
RSN$ A S TWA I T
RSN $ -MA I LB OX
RSN$-N PDYNMEM
RSN$-PG F I L E
RSN$ -PG DYNMEM
RSN $ -B RKTHRU
RS N $- IAC LOCK
RSN $ -J QUOTA
RSN$=MAX

1
2
3
4
5
6
7
8
9

Wa i t f o r De l i v e r y o f a n AST
Wa i t f o r Ma i l b ox Spa c e
Wa i t f o r No n pag ed Po o l Spa c e
Wa i t f o r Spa c e i n t h e Pag e F i l e
Wa i t fo r Pag ed Po o l Spa c e
Te rm i n a l B r o ad c a s t
I m ag e Ac t i v a t i o n I n t e r l o c k
J o b Po o l ed Quo ta
Ma x i m um Re s o u r c e Numb e r

Re s o u r c e s a r e l i s t ed i n Ta b l e 8 - 2 .

0- 2 3

DATA S TRUC TURE DEF I N I T I ON S
D. 2 . 15

S G N - SYSG EN Pa r am e t e r C o n s t a n t De f i n i t i o n s

T h e $ SGNDE F m a c r o i s used b y m od u l e s i n t h e ex ec ut i v e
fo r
pa r a me t e r s
t h a t h a v e n o t b e e n mad e a d j us ta b l e b y SYSBOOT .
Mo s t o f t h e s ym bo l i c
c o n s t a n t s d e f i n ed b y th i s m a c r o o n l y h av e h i s to r i c a l i n t e r e s t a nd
are
no
l ong e r
u s ed
b y VM S .
On l y t h e c o n s ta n t s s t i l l u s ed b y VM S a r e
l i sted h e r e .
SGN $ C S FTMAX
SGN $ C-S YSVE C PG S

3
3

SGN $ C M INWSCNT

N umb e r o f Swa p F i l e Tab l e En t r i e s
Num b e r o f Pag e s Used f o r Sys t em
S e r v i c e Ve c to r s
Abso l u t e M i n i m um Wo r k i ng S e t S i z e

Two o th e r SGN $ C n am e c o n s t a n t s a r e d e f i ned i n mod u l e SWAPF I L E a nd u s ed
by VM S .
SGN $ C PAG F I LCNT
SGN $ C-PF L I BAS

D. 2 . 16

N umbe r o f Pag e F i l e s
Ba s e I nd ex f o r Pag e F i l e s

2
3

S S - S y s t em S e rv i c e Compl e t i on Cod e s

Th e $ S S D E F m a c r o d e f i n e s a l l s ys t em w i d e s t a t us c o d e s .
Append i x A o f
t h e VAX/VMS Sys tem Se rv i c e s Re f e r enc e Ma n u a l l i s t s the symbo l i c names
o f a l l SS$ name symbo l s .
( Th e s e sym bo l s a r e d e f i n ed
in a
s e pa r a t e
f i l e c a l l ed [ VM S L I B . SRC ] SSMSG . MDL . }

D. 2 . 17

S TATE - Sched u l i ng S t a t e s

Th e $ S TATEDEF ma c r o d e f i n e s s ymbo l i c n am e s fo r a l l s c h ed u l i ng
s ta t e s .
No te
tha t
the
pref i x
fo r
each o f
the
sym bo l s i s SCH$C_ and no t
S TAT E $ C
•

S C H $ C C O LPG
S C H $ C-MWA IT

1
2

S C H $C CEF
S C H $C-PFW
S C H $ C- L E F
S C H $C- L E FO
S C H $ C-H I B
S C H $ C-H I B O
S C H $ C-S U S P
S C H $C -S US PO
S C H $ C-FPG
S C H $ C-C OM
S C H $C -C OMO
S C H $ C-C UR

3
4
5
6
7
8
9
10
11
12
13
14

Th e
sc hed u l i ng
Figure 8 - 5 .

states

are

C o l l i d ed Pag e Wa i t
M i sc e l l a n e o u s Wa i t
( Re so u r c e Wa i t )
( Mu t e x Wa i t }
C ommon Ev e n t Fl ag Wa i t
Pag e Fa ul t Wa i t
Lo c a l Ev e n t F l ag Wa i t ( Re s i d en t }
Lo c a l Even t Fl ag Wa i t ( O u t swa pped }
H i b e r n a t i ng ( Re s i d e n t }
H i b e r n a t i ng ( Ou t swa pped }
S u s pe nd ed ( Re s i d e n t }
S u spend ed ( Ou t swa pped )
F r e e Pag e Wa i t
Comput a b l e ( and Re s i d e n t }
Comput a b l e ( Ou t s wa pped }
C u r r ent Process
l i s t ed

D- 2 4

Ta b l e 8 - 1

a nd

p i c t u r ed

DATA STRUCTURE DEF IN I T IONS

D. 3

DATA STRUCTURES USED BY THE I/0 SYSTEM

Th e r e a r e
t wo
c la sses o f
s ymbo l i c d e f i n i t i o n s
u s e d by
the
I /0
s ub s y s tem .
Da t a s t r uc t u r e s
used
by d ev i c e d r i v e r s a r e p i c t u r ed i n
( r e f e r r ed
Appe nd i x A o f the VAX/VM S G u i d e t o Wr i t i ng a Dev i c e D r i v e r
to a s " Dev i c e D r i v e r s " ) .
Symbo l i c d e f i n i t i o n s s p e c i f i c to e a c h d ev i c e
c l a s s a r e l i s t ed i n t h e a ppr o p r i a t e c h a p t e r s o f the VAX/VMS I /0 U s e r ' s
f unc t i o n c od e s a nd D ev 1 c e
I /0
Th e
Us e r ' s G u i d e ) .
( " I /O
Guide
Sys tem S e r v i c e s
I n fo rma t i o n B l o c k a r e a l s o d e sc r i b ed i n t h e VAX/VM S
Re f e r e nc e Ma n ua l ( " Sys t em S e r v i c e s " ) .
Da t a S t r uc t ur e s Us ed by Dev i c e Dr i v e r s
( De f i ned i n S Y S D E F a nd s to r ed i n L I B . M LB )
S t r uc t u r e Name

Ad a p t e r C o n t r o l B l o c k
A C P Q u e ue B l o c k
C h a nne l Co n t r o l B l o c k
Ch a n n e l ( Co n t r o l l e r ) Re que s t B l o c k
Dev i c e Da t a B l o c k
D r i v e r D i s pa tch Ta b l e
D r i v e r P r o l og ue Ta b l e
I n t e r r up t D i spa tch B l o c k
I /0 Re qu e s t Pa c k e t
I /0 R e qu e s t Pa c k e t Ex t e n s i o n
MAS S B US Ad a p t e r Reg i s t e r O f f s e t s
Te rm i n a l D r i ve r Wr i t e Reque s t B l o c k
UN I B U S Ad a p t e r Reg i s t e r Of f s e t s
UN I B US I n t e r c o n n e c t Reg i s t e r O f f s e t s
Un i t C o n t r o l B l o c k
C R B I n t e r r up t T r a n s f e r Ve c to r S t r uc t u r e

Ac ronym

Desc r i bed i n

ADP
AQB
CCB
CRB
DDB
DDT
DPT
!DB
IRP
I RPE
MBA
TTY
UBA
UB I
UC B
VE C

Dev i c e D r i v e r s
Dev i c e
Dev i c e
Dev i c e
Dev i c e
Dev i c e
Dev i c e
De v i c e
Dev i c e
Dev i c e

Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i ve r s
Dr i v e r s

Dev i c e
Dev i c e
Dev i c e
Dev i c e

Dr i v e r s
Dr i v e r s
Dr i v e r s
Dr i v e r s

Da t a S t r uc t u r e s Used b y Dev i c e Dr i v e r s
( De f i ned i n S TARD E F a nd s to r ed i n bo t h S TARLE T . MLB a nd L I B . MLB )
Ac r o nym

De sc r i bed i n

Ca rd Read e r S t a tus B i t s
Dev i c e Ad a p t e r , Typ e ,
a nd C l a s s De f i n i t i o n s
Dev i c e Ch a r ac te r i s t i c s
Dev i c e I n fo rma t i o n B l o c k

CR
DC

I /0 Us e r ' s G u i d e
I /0 Us e r ' s G u i d e

DEV
DIB

I /0 Func t i o n Co d e De f i n i t i o n s

L PA- 1 1 Cha r a c t e r i s t i c s
L i n e P r i n t e r Ch a r a c t e r i s t i c s
Mag t a pe S t a t us B i t s
P r i n te r/Te rm i n a l Ca r r i ag e Co n t r o l
Spec i f i e r s
Spec i a l Symbo l s fo r Te rm i n a l D r i v e r
DRl l -W Dev i c e C h a r a c t e r i s t i c s
DR 3 2 Command Ta b l e and Pa c k e t De f i n i t i o n s
DMC - 1 1 S t a t us a nd Ch a r a c t e r i s t i c s

LA
LP
MT
PC C

I /0 U s e r ' s G u i d e
I /O Us e r ' s G u i d e
Sys t em Se r v i c e s
I /O Us e r ' s G u i d e
Sys t em Se r v i c e s
I /O Us e r ' s G u i d e
I /O Us e r ' s G u i d e
I / O Us e r ' s Gu i d e

S t r uc t u r e Name

D- 2 5

TT
XA
XF
XM

I/0
I /0
I /0
I /0

User ' s
Us e r ' s
Us e r '· s
Use r ' s

Gu i d e
Gu i d e
Gu i d e
Gu i d e

DATA STRUCTURE DEF I N I T I ONS

D. 4

DATA STRUCTURES USED B Y F I LES-1 1

Th e d a t a s t r uc t u r e s used by t h e f i l e AC P s a nd
a s so c i a te d
util ities
s uc h a s
I N I T a nd MOUNT a r e o ut s i d e t h e s c o pe o f t h i s m a n ua l and a r e
l i s t ed
h e re
fo r
c ompl e te n e s s .
Any
i nc i d en t a l
r e fe r e n c e s
are
i nd i c a te d .
Th e ANS I m a g n e t i c t a pe l a b e l s a r e p i c t u r ed i n Append i x B
o f the VAX- 1 1
Re c o rd Ma n ag em e n t S e r v i c e s Re f e r en c e Ma n ua l
( " RMS
Re f e r en c e " ) .
Th e
At t r i b u t e
Li s t
De sc r i pto r
( ATR )
and
Fi l e
Id e n t i f i c a t i o n B l o c k ( F I B ) a r e d e sc r i b ed i n the VAX/VMS
I /O
Us e r ' s
Gu i d e .
Da t a S t r uc t u r e s U s ed by t h e F i l e Sys tem
( De f i ned in SYSDEF a nd s t o r ed in L I B . MLB )

S t r uc t u r e Name

Ac ronym

AC P I /0 B u f fe r Pa c k e t
AC P Me s s a g e to B a d B l o c k S c a n
Compl e x Ch a i ned B u f f e r
E O F l ANS I Mag n e t i c T a pe La b e l
E O F 2 ANS I Mag ne t i c Ta pe La b e l
E O F 3 ANS I Mag n e t i c Ta pe La b e l
Fi l e Con t r o l B l o c k
HDR l ANS I Magne t i c Ta pe La b e l
HDR 2 ANS I M a g ne t i c Ta pe La be l
HDR 3 ANS I Mag n e t i c Ta pe La b e l
Mo un t e d Vo l um e L i s t En t r y
Mag n e t i c Ta pe Vo l um e L i s t
F i l e Name B l o c k
Re l a t i ve Vo l um e Ta b l e
Re l a t i v e Vo l um e Ta b l e Ex t e n s i o n
Vo l ume C a c h e B l o c k
Vo l ume C o n t r o l B l o c k
VO L ! ANS I Ma g n e t i c Ta pe La b e l
Wi nd ow C o n t r o l B l o c k

AIB
BBS
C XB
EOl
E02
E03
FCB
HD l
HD2
HD3
MTL
MVL
NMB
RVT
RVX
VCA
VC B
VL l
WCB

Desc r i bed i n

RMS Re f e r e n c e
RMS Re f e r e nc e
RM S Re f e r e n c e
RM S Re f e r e n c e
RM S Re f e r e nc e
RMS Re f e r e n c e

RM S Re f e r e nc e

Da t a S t r uc t u r e s U s ed by t h e F i l e Sys tem
( De f i n ed in S TARDEF and s to r ed in bo t h S TARLE T . M LB a nd L I B . MLB )

S t r uc t u r e Name

At t r i b u t e Li s t De s c r i pt i o n
Fi l e Iden t i f ic a t i o n Block
F i l e I d en t i f i c a t i o n

D- 2 6

Ac ro n ym

Desc r i b ed i n

ATR
FIB
FID

I /0 Us e r ' s Gu i d e
I /0 Us e r ' s G u i d e

DATA S TRUCTURE DEFIN I T I ONS
D. S

M I SCELLANEOUS DATA STRUCTURES AND C ONSTANTS

Th i s s ec t i o n l i st s t h e d a ta s t r uc t u r e s a nd c o n s t a n t s t h a t a r e d e f i ne d
in
SYSDE F . MDL o r S TARDE F . MDL b u t a r e no t m e n t i o n e d i n th i s m a n ua l .
A
d e s c r i p t i o n o f a n y o f the s e s t r uc tu r e s c an b e o b t a i ne d by l o o k i ng
at
t h e m i c ro f i c h e l i s t i ng o f t h e f i l e i n wh i c h the s t r uc t u r e i s d e f i n ed .
Ve r y f e w o f t h e s e
s t r uc t u r e s a r e d e sc r i b ed
e l s e wh e r e
in
the
d o c um e n t a t i o n s e t .
T h e c onnec t- to- i n t e r r up t f ac i l i ty i s d e sc r i b e d i n
t h e VAX/VM S Re a l - T i m e
Us e r ' s Gu i d e
( " Re a l -T i m e " ) .
Some
of
the
s ym b i o n t manag e r
r eq ue s t c od e s
are
l i s t ed
in
t h e VAX/VM S Sys tem
S e r v i c e s Re f e r enc e Ma n ua l .
Th e T PARS E c o n t r o l b l o c k
i s p i c t u r ed
in
the VAX- 1 1 Run- T i m e L i b r a ry Re f e r en c e Ma nua l ( " RT L Re f e r e nc e " ) .
M i sc e l l a n e o us Da t a S t r uc t u r e s
( De f i ned i n SYS D E F a nd s to r ed i n L I B . M LB )
S t r uc t u r e Name

Ac ronym

Gen e r a l i z e d Name S t r i ng De s c r i pto r
Co n f i g u r a t i o n C o n t r o l B l o c k
C o n n e c t - to - I n t e r r up t De f i n i t i o n s
E r r o r L o g Al l o c a t i o n Bu f f e r Head e r
C r o s s L i n k e r Imag e He a d e r Fo rm a t
RM S Impu r e A r e a O f f s e t De f i n i t i o n s
Pe r fo rma n c e Bu f f e r He ad e r
Dev i c e Pe r fo rma n c e Da t a B l o c k
Pe r fo rma n c e I /O I n f o rm a t i o n B l o c k
I n t e r pr o c e s so r Re que s t B l o c k De f i n i t i o n s
Remo t e Dev i c e P r o to c o l De f i n i t i o n s
U s e r Au t ho r i za t i o n F i l e Re c o r d Fo rma t

ABD
AC F
C IN
ERL
I HX
IMP
PB H
PDB
PIB
PRQ
RDP
UAF

De sc r i be d i n

Re a l -T i m e

M i sc e l l a n e o us Da t a S t r uc t u r e s
( De f i n ed i n S TARD E F a nd s to r ed i n bo th S TARL E T . M LB a nd L I B . MLB )

Ac ronym

S t r uc t u r e Name
Comma nd La ng uag e I n t e r f a c e De f i n i t i o n
C L I S e r v i c e Re que s t Cod e s
G e n e r i c Cod e s f o r Command Ve r b s
D e t a c hed J o b I n i t i a t e Me s s ag e
Ope r a t o r Commun i c a t i o n Me s s ag e Typ e s
S ymb i o n t Ma nag e r Jo b Re c o r d He a d e r
Symb i o n t Ma n ag e r Qu e ue He a d e r
S ymb i o n t Ma n ag e r Re q ue s t Cod e s
Symb i o n t Que ue He a d e r Rec o r d
Symb i o n t Manag e r Que u e Re c o r d
Sym b i o n t Que ue Re c o r d Enve l o pe S t r uc t u r e
T PARSE Co n t r o l B l o c k

D-2 7

CLI
C L I S E RV
C L IVE RB
DJ I
O PR
SJH
SMQ
SMR
S QH
S QR
SYM
T PA

De sc r i be d i n

Sys t em Se r v i c e s

RTL Re f e r e n c e

DATA S TRUCTURE D E F I N I T I ONS
Th e $ EMBDEF mac r o , wi th o n e of f o u r t e e n d i f f e r e n t pa r am e t e r s ,
d e f i ne s
the v a r i o u s e r r o r m e s s ag e b u f f e r s u s e d b y t h e e r r o r l og g e r .
Th e
b u f f e r h e ad e r a nd the e r r o r l og e n t r y f o r s ys t em c r a s h e s a r e d e sc r i b ed
i n Ta b l e 7 - 1 .
Th e y a r e i nc l ud ed i n th i s l i s t fo r compl e t en e s s .
E r r o r Log Me s s ag e Bu f f e r s
( De f i n ed i n S Y S D E F a n d s to r ed i n L I B . M LB )
Ac r onym

S t r uc t u r e Name
Bu f f e r H e a d e r
En t r y Type De f i n i t i o n s

EMB , HDDE F
EMB , ETDEF

No n f a t a l B ug c h e c k E r r o r
C r a sh/Re s t a r t E r r o r ( Fa t a l Bug c h e c k )
Dev i c e E r r o r
Ma c h i n e Ch e c k Log
S B I Fa ul t s a nd As yn c h r o no us Wr i t e E r r o r s
So f t ECC E r r o r s a n s S B I Al e r t
Sys tem Se r v i c e M e s sag e s
Sys tem S t a r t up M e s sag e
T i m e S tamp M e s sag e
UN I B US E r r o r S umm a r y
UN I B US Ad a p t e r Und e f i n ed I n t e r r up t
Vo l ume Mo un t/D i sm o un t Me s s ag e

EMB , BCDEF
EMB , CRDE F
EMB , DVD E F
EMB , MC D E F
EMB , S BDEF
EMB , S EDEF
EMB , S SDEF
EMB , SUDEF
EMB , TSDEF
EMB , UEDEF
EMB , U I DE F
EMB , VMDEF

D- 2 8

APPEND I X E
S I Z E OF SYSTEM VI RTUAL ADDRES S SPAC E

The e x e c u t i v e i ma g e SYS $ S YS TEM : SYS . EXE c o n ta i n s the o pe r a t i ng
s ys tem
code fo r VM S but v e r y l i t t l e of the d a ta .
Many o f the d a t a s t r uc t u r e s
t h a t VMS u s e s a r e n o t c r e a t ed un t i l t h e s ys t em
i s b o o t s t r a pped ,
so
that
the
s t r uc t u r e
s i z e s c a n b e d e t e rm i ned
f rom the appro p r i a t e
S YSBOO T pa r am e t e r s .
Th i s a ppend i x d e sc r i b e s the r e l a t i o n sh i ps b e twe e n
these
SYSB OOT p a r ame t e r s
a nd
t h e po r t i o n s o f s ys t em add r e s s s pa c e
who s e s i z e s t h e y d e t e rm i n e .
I n t h e equa t i o n s tha t a ppe a r i n th i s
a ppe nd i x ,
t wo
c ommo n
features
d om i n a t e .
One
feature
i s d i v i s i o n b y 5 1 2 , the n umbe r o f b y t e s i n a
p ag e .
Th i s i s d o ne wh e n ev e r the i n put pa r am e t e r i s a n umbe r o f b y t e s ,
s uc h a s the N PAG E DYN S Y S B OO T p a r am e t e r o r a n e x p r e s s i o n fo r the n umbe r
o f bytes i n a process head e r .
I f 5 1 1 i s added to an e x p r e s s i o n f o r
a
n umbe r
o f b yt e s b e fo r e
the
i n t eg e r d i v i s i o n
t a k e s pl ace ,
th i s
r e p r e s e n t s a r o und i ng u p t o the n ex t h i g h e s t pag e bo und a r y .
Th e s e c o nd f e a t u r e i s the n umbe r 1 2 8
a ppe a r i ng
i n expr ess i ons
tha t
c o un t a n umbe r o f pag e s
f o r wh i c h s ys t em pag e t a b l e e n t r i e s a r e
n e ed ed .
Th e s i g n i f i c a n c e o f t h e n umbe r 1 2 8 i s t h a t a pag e t a b l e e n t r y
is
four bytes
l o ng
so
tha t
a pag e o f pag e t a b l e e n t r i e s m a ps 1 2 8
pag es .
I n th i s c a se , t h e r o un d i ng t e rm t h a t i s a d d ed i s 1 2 7 .

E.l

S I Z E O F PROC ESS HEADER

B e fo r e the v a r i o u s po r t i o n s o f s ys tem a d d r e s s spa c e a r e c a l c u l a te d , we
wi l l
r e l a te
t h e s i ze o f the p r o c e s s h e ad e r to the SYSB OOT p a r am e t e r s
t h a t a f f e c t i t s s i ze .
Ta b l e E - 1 l i s t s each po r t i o n
of the process
h ea d e r ,
the
SYSB OOT p a r am e t e r s t h a t a f f e c t i t s s i ze , a nd t h e g l o b a l
l o c a t i o n wh e r e t h e s i z e o f t h a t po r t i o n i s s to r ed .
Th e
t a b l e a l so
i n t r od uc e s t h e n o t a t i o n u s ed i n the f i r s t s e t o f e qua t i o n s to d e s c r i b e
e a ch p i ec e o f the p r o c e s s h e ad e r .

E-1

Ta b l e E - 1
D i sc r e te Po r t i o n s o f t h e Pr o c e s s He ad e r

I t ems s to r ed i n
t h i s pa r t o f t h e
p r o c e s s h e ad e r

Fa c to r s Af f e c t i ng
s i ze o f t h i s pa r t
o f p r o c e s s h e ad e r

Gl o b a l l oc a t i o n
wh e r e s i z e o f t h i s
pa r t i s s t o r ed

PHD ( ws l_ps t )

Fi x ed Po r t i o n
Wo r k i ng Se t L i s t
Pr o c e ss Sec t i o n Ta b l e

PHD$K L ENGTH
PR OC SEC TC NT
WSMAX
PQL_DW S DE FAULT

SW P $GW_WS L PT E

PHD ( empt y )

No Ac c e s s Pag e s fo r
wo r k i ng s e t l i st
e x pa n s i o n

WSMAX
PQL_DW SDE FAULT

SW P $GW_EM PT PTE

PHD ( ba k )

P r o c e s s He ad e r
Pa g e Ar r a ys a nd
Pag e Ta b l e Pag e Ar r a ys

S i ze o f t he
Pr o c e s s He ad e r

SW P $GW BAKPTE

PHD ( p t e )

P O and P l Pag e Ta b l e s

VI RTUA L PAGE CNT

SGN $G L_PT PAGC NT

Symbo l i c Nam e
fo r Eq u a t i o n s

t:rl
I

Th e fo l l o wi ng g l o b a l l o c a t i o n s c o n t a i n
s ev e r a l o f t he p i e c e s l i s t e d a b ov e .
e

@ S GN $G L P H DAPC NT

@ S GN SG L PHDPAGC T

•

@ SW P $G L_B S LOTSZ

PHD ( ws l_ps t )

s um s

s i ze s

+ P H D ( ba k )

PHD ( ws l_ps t ) + P H D ( em p t y )
PHD ( ws l _ ps t )

the

+ PHD ( b a k )

+ P H D ( em p t y ) + PH D ( ba k )

+ PHD ( pag e_ta b l e s )

S I Z E OF SYSTEM VI RTUAL ADDRES S S PACE
E. l.l

Process Pag e Ta b l es

Th e ma j o r i t y o f t h e p r o c e s s h e ad e r i s t a k e n up by t h e PO and
P l pag e
t ab l e s .
Th e
to t a l
n um b e r
o f pag e s a l l o c a ted fo r the pr o c e s s pag e
t a b l e s d e pend s o n t h e p a r a m e t e r VIRTUALPAG E CNT .
VIRTUALPAGECNT + 127
PHD( page_ tables ) = ---128

E.l.2

E.1.1

Wo r k i ng Se t L i s t and Proc e s s Sec t i o n Ta b l e

Th e wo r k i ng s e t l i s t a nd p r o c e s s s e c t i o n t a b l e a r e l o c a ted a t the
low
a d d r e s s e nd
o f t h e p r o c e s s h e ad e r immed i a t e l y a f te r the f i x ed s i z e
a r e a a nd g r o w towa r d e a c h o the r .
Th e
s i ze o f t h e p r o c e s s
sec t i o n
t a b l e d epend s o n
the
pa r am e t e r
PROC S EC TCNT .
Th e n a i v e a pp r o a c h
d i c ta te s tha t t h e wo r k i ng s e t l i s t s i z e d e pend s o n t h e pa r am e t e r
WSMAX .
Howe v e r ,
b e c a u se
the p r o c e s s h e ad e r pag e s th a t a r e n o t pag e
t a b l e pag e s a r e l oc ked i n to
the
p r o c e s s wo r k i ng
set ,
they a l wa ys
r e q u i r e phys i c a l
pag e s .
In mo s t s ys t ems , many p r o c e s s e s wi l l h av e
wo r k i ng s e t s tha t a r e m uc h sm a l l e r
than
the
a l l o wed max i m um .
Th e
i n i t i a l wo r k i ng s e t l i s t s i z e i s c a l c u l a t ed to t a k e th i s i n to a c c o un t .
Th e a s s ump t i o n i s m a d e t h a t m o s t p r o c e s s e s wi l l h a v e wo r k i ng s e t s th a t
a r e a pp r o x i m a t e l y e q ua l to the pa r am e t e r PQL_DW SDEFAU L T .
Equa t i o n E . l . 2 c a l c u l a t e s the max i m um n um b e r o f pag e s r e qu i r ed fo r t h e
f i x ed
po r t i o n o f
the
p r o c e s s h e ad e r , the wo r k i ng s e t l i s t , a nd t h e
p r o c e s s s ec t i o n t a b l e .
Th e e x t r a s pa c e r e s e r v ed fo r wo r k i ng s e t
l i st
e x pa n s i o n
i s c a l c u l a t ed
in
Equa t i o n E . l . 3 .
Th e d i f f e r e n c e b e t we e n
t h e s e two n umbe r s ( Equa t i o n E . l . 4 ) i s t Q e n um b e r o f pag e s
initially
a v a i l a b l e fo r the f i x ed po r t i o n , the wo r k i ng s e t l i s t , a nd the p r o c e s s
s ec t i o n
t ab l e .
Th e
s i g n i f i c anc e o f
the
num b e r s
4 a nd
32
in
Equa t i o n E . l . 2
is
tha t
a wo r k i ng s e t l i s t e l em e n t i s a l o ng wo r d ( o r
f o u r byt e s , WS L $ C L E NG T H ) a nd a p r o c e s s
s ec t i o n t ab l e e n t r y
is
32
by t e s l o ng ( S E C $ K=L ENGTH ) .

PHD(temp) =

(

PHD$K_LENGTH + 4 * WS MAX
+ 32 * PROCSECTCNT + 5 1 1
512

PHD(empty)

WS MAX - PQL_DWSDEFAULT

)

E . 1.2

E. 1.3

128
PHD(wsl_pst)

E.l.3

PHD(temp) - PHD(empty)

E . 1 .4

Proc e ss He a d e r Pag e A r r ays

Th e pr o c e s s head e r pag e a r r a ys i nc l ud e two a r r a ys tha t c o n t a i n a r r a y
e l emen ts
fo r
e ac h pag e i n the p r o c e s s h e ad e r .
( Th e s e two a r r a ys a r e
used b y the swa ppe r t o s to r e i n fo rma t i o n a b o u t p r o c e s s h e ad e r
pag e s
wh i l e t h e h e a d e r
is
o u t swa pped . ) Th e r e a r e a l s o two b y t e a r r a ys i n
E-3

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE

t h i s po r t i o n o f the p r o c e s s h e ad e r tha t c o n t a i n an a r r a y e l em e n t
for
e a c h pag e t a b l e p ag e .
T o s i mpl i f y t h e c a l c u l a t i o n o f t h e s i z e o f th i s
po r t i o n o f the p r o c e s s h e a d e r , s pa c e i s a l l o c a ted a s i f the
l as t
two
a r r a ys c o n t a i n ed a n e l em e n t fo r e ac h p r o c e s s h e ad e r pag e .
Be c a u s e the
pag e t a b l e s compr i s e a pp r o x i m a t e l y 9 0 % of
the p r o c e s s h e ad e r
in a
t yp i c a l sys tem , t h i s i s a v e r y g o od a pp r o x i m a t i o n .
Bec a u s e the r e s u l t
i s r o und ed up t o t h e n e x t pag e b o und a r y ,
th e r e
i s a b s o l ut e l y n o
d i f f e r en c e fo r a lmo s t a l l c om b i n a t i o n s o f SYSB OOT pa r am e t e r s .
B e c a u s e the p r o c e s s h e a d e r p ag e a r r a ys a r e
l o c a ted
i n the
process
head e r ,
t h e s pa c e
a l l o c a ted
fo r t h i s a r e a d epend s o n i t s o wn s i z e .
Th e c a l c u l a t i o n o f t h i s po r t i o n o f t h e
p r o c e s s h e ad e r
proceeds
i t e r a t i ve l y .
A n a p p r o x i m a t e s i z e o f t h e a r e a i s d e t e r m i n ed , b a s ed o n
t h e s i z e s o f t h e o th e r th r e e a r e a s .
Th e n t h e e s t i m a t e s a r e
r e f i n ed
un t i l two s uc c e s s i v e c a l c u l a t i o n s r e a c h t h e same r e s u l t .
De f i n e

PHD(the_rest)

PHD(bak,O)

PHD(wsl_pst)
+ PHD(empty)
+ PHD(page_tables)

Pe r fo rm t h e fo l l owi ng c a l c u l a t i o n ( Eq u a t i o n E . l . 5 )

PHD(bak,N)
PHD( bak , N)

un t i l

PHD(bak,N-1)
8*

(PHD(the_rest)

)

PHD(bak,N- 1)
512

511

E.1.5

Ca l l the r e s u l t of th i s c a l c u l a t i o n PHD ( ba k ) .
PHD(bak)

PHD(bak,N)

Th e s um o f t h e fo u r p i ec e s o f t h e p r o c e s s h e ad e r y i e l d s
i t s s i ze
in
pag e s .
Th e
r e s u l t o f t h i s c a l c u l a t i o n i s s to r ed i n g l o b a l l o c a t i o n
SWP $G L B S LOTS Z .
PHD(total)

PHD (wsl_pst)
+ PHD(empty)
+ PHD(bak)
+ PHD(page_tables)

E-4

E . 1 .6

S I Z E OF SYSTEM VI RTUAL ADDRE SS S PACE
E.2

SYSTEM VI RTUAL ADDRESS S PAC E

Onc e the s i z e o f the p r o c e s s h e ad e r h a s b e e n c a l c u l a t ed , t h e s i ze s o f
the
d yn am i c
p i ec e s o f
s ys t em a d d r e s s
s pa c e c an b e c om p u ted .
F i g u r e E - 1 p i c t u r e s s ys t em a d d r e s s s pa c e a nd the nomenc l a t u r e used
to
d e s i g na t e e a c h p i e c e .
Ta b l e E-2 l i s t s e a c h p i e c e , the g l ob a l l o c a t i o n
o f t h e po i n t e r
to e ac h p i e c e ,
and
t h e SYS B OOT pa r ame t e r s
tha t
d e te r m i n e i ts s i ze .

SVAS( sptskel)

System Service Vectors

80000000

Linked Driver Code and Data Structures "'
Nonpaged Executive Data
Nonpaged Executive Code

� SVAS ( non paged_exec)
(No PFN Data)

Pageable Executive Routines
XDELTA ( usually unmapped), INIT
System Virtual Pages
Mapped to 1/0 Addresses

SVAS(spt req)

(

RMS Image
(RMS.EXE}

Dynamically mapped at
initialization time
by SYSBOOT

System Message File
( SYSMSG.EXE)

� ��

Pool of Unmapped System Pages

SVAS(rpb )

Restart Parameter Block

SVAS(pfn)

PFN Database

SVAS( nonpaged_pool)
SV AS(int-&tack)
SVAS(scb)
SVAS(balance-slots)

��

( No PFN Data)

Paged Dynamic Memory

SV AS(paged_pool)

��

Nonpaged Dynamic Memory

(No PFN Data)

Interrupt Stack
System Control Block

( No PFN Data)
( No PFN Data)

Balance Slots

��

System Header

(No PFN Data)

SVAS(spt)

System Page Table

(No PFN Data)

SVAS(gpt)

Global Page Table

SVAS(sysphd)

Figure E-1

La yo u t o f S y s t em V i r t ua l Ad d r e s s Spa c e

E-5

)

Static Portion (SYS .EXE)

Tabl e E.,.. 2
Deta i l ed Layout of S y s tem Virtua l Addre s s Spa c e
(F ixed S i z e Portion )

The fo l lowi ng p i ec e s o f the execut i v e o r ig i na te i n the exec u t i v e imag e f i l e SYS $SYS TEM : SYS . EXE .
each o f these pi eces r ema i n unchang ed un t i l a new maj o r rel ease o f the o pe r a t i ng system .

The sys t em add resses o f

G l oba l Add re s s

Add ress ( 1 )

S i ze i n pag es

Pro t

OWne r

Pag eab l e

Mapped by

System Se r v i c e Vec to r s

SYS $QI OW

80000000

3 pag es

Yes

SYSB OOT

Nonpag ed Ex ecut i v e Da ta
FCP Data Ar ea
L i n ked Dr i v e r Da ta
S t r uc tures

MMG$A ENDVEC
8 0 00 0 6 0 0
PMS$G L FCP
80000600
EXE $GL=B UGCHECK
80000834

4 pag es
( 5 6 4 . bytes )
( 1 4 8 4 . bytes )

UREW ( 2 )
URKW ( 2 )

SYSB OOT

Li nked Dr iver Cod e

MMG$AL B EGDR IVE
DR$INT-

8 0 0 00EOO
8 0000EOO

5 pag es

SYSB OOT

80001 800
8 0 0 0 1 80 0

13 pag es

URKW

SYSBOOT

Item

Nonpag ed Ex ecut ive Da ta
Nonpag ed Ex ecut ive Ro ut i nes

MMG$AL ENDDR IVE
PFN$AW=HEAD

=
=

MMG$FRSTRONLY
EXE $RESTART

8 0 0 03200
8 0 00 3 2 0 0

5 5 pag es

URKW

SYSB OOT

Pag eabl e Execut ive Ro ut i nes

MMG$AL_PGDCOD

8 0 0 0A O O O

6 7 pag es

Yes

SYSB OOT

Us ua l l y Unmapped Pag es
XDE LTA
! N IT
BUGC HECK

MMG $AL_PGDCODEN

8 0 0 1 24 0 0
(80012400)
( 8 0 0 1 2E O O )
( 8 00 1 4 2 0 0 )

3 2 pag es
( 5 pag e s )
( 1 0 pag e s )
( 1 7 pag e s )

NA
URKW ( 3 )

End of F i x ed Si zed Po r t i o n o f
Sys tem Vi r tua l Add ress Spac e

SWP$GL_S HE L LBAS

80016400

No ( 3 )

SYSBOOT

Tabl e E - 2

(cont . )

Deta i l ed Layout o f System Virtual Addre s s Space
( Var iable S i z e Port ion
Mapped toward Increas ing Vi r tua l Add r e s s e s )
��

Th e fo l l owi ng pi e c e s o f the sys t em a r e no t a pa r t o f the execut i v e i m ag e SYS . EXE .
Th e i r s i ze s a r e no t f i x ed but
r a th e r
d e pend
on t h e va l ue s o f s pec i f i c SYSBOOT pa r am e t e r s o r o n the pa r t i c u l a r d ev i c e a n d mem o r y c on f i g ur a t i on .
Th e s e p i e c e s
a r e l oc a t ed by s to r ing the i r sta r t i ng add r e s s e s i n po i n t e r f i e l d s , who se add r e s s e s a r e l i s ted he r e .
The f i r s t i tems l i sted a r e mapped by I N I T a nd SYS IN IT .
i s , t h e conn e c t - to- i n te r r upt pag e s a r e s e t a s i d e f i r st ,

I t em

tzl

G l obal

Ad d re s s o f Po i n te r

Beg i n n i ng o f Va r i a b l e
S i zed Po r t i o n o f
Sys t em Vi r tua l Ad d r e s s Spa c e

SWP$G L_S HE LLBAS

Sys t em Vi r tua l Pag es fo r
Co nnec t t o I n te r r upt

RBM $L S PTFREL i n
Re a l �T i m e SPT B i t Ma p

Ma ppi ng

MMG$AL_S B I C ONF

fo r

I /O Ad d r e s s e s

I tems a r e mapped towa rd
I / O a d a pt e r s a r e m a pped

l a rg er s ys t em v i r tua l
nex t , a n d s o o n .

Fa c to r s Th a t
Af f e c t S i ze

Pro t

REALT I M E S PT S

Ph ys i c a l
Co n f i g u r a t i on
( Types o f Ex t e r nal
Ad a pt e r s )

(6)

...J

(5)

INIT

(5)

I N IT

(5)

!NIT

URKW

Yes

SYS I N IT

URKW

Yes

SYS I N I T

Number o f
Di s k Un i ts

S PTREQ
( Se v e r a l Othe r
De ta i l s )

UCB $ L SVPN i n
Un i t-Co n t r o l B l o c k
fo r Sys t em Di s k

constant

RMS

MMG $GL_RMSBASE

S i ze o f RM S
Imag e ( 1 31 pag e s )

pag e

Sys t em Me s s a g e Fi l e

nul l

constant
EXE $G L_S YSMSG

pag e )

(1 pag e )

S i ze of Sys t em
Me s sag e Fi l e
( 2 57 pag e s )

pag e

S y s t em Vi r t ua l Pag es
fo r o th e r d i s k d r i v e r s

UCB $ L SVPN i n
Un i t-Co n t r o l B l o c k
fo r Eac h Un i t

Po o l

BOO$G L S PTFREL
BOO$G L:s PTFR.EH

of ava i l ab l e s ys t em pag es

(7)
(7 )

Mapped by

Sys t em Vi r t ua l Pag e
fo r Sys t em Di s k Dr i v e r

nul l

Pag ea b l e

Th a t

8 0 0 1 6 2 00

Imag e

owne r

add r e s se s .

(4 )

(5)

S YSGEN i n
STARTUP. C OM
o r when
d r iver i s
l oa d ed

(continued on next page)

Tabl e E - 2

( cont . )

Deta i l ed Layout of Sys tem Virtual Addr e s s Space
(Virtual S i z e Port ion - - Mapped toward Sma l l e r Vir tua l Addr e s s e s )
The s e pi e c e s a r e a l so pa r t o f the d yn am i c a l l y c o n f i g u r ed po r t i o n of s ys t em
v i r tua l
add r e ss
spac e .
Th e i r
s i ze s
are
d e t e r m i ned b y SYSB OOT pa ramete r s .
Th e s e pi ec e s a r e l oc a ted b y s to r i ng the i r s ta r t i ng add r e s s e s i n po i n te r f i e l d s , who se
add r e s s e s a r e l i sted he r e .

Th i s pa r t o f s ys tem add ress spa c e i s mapped by
Ex c e s s pag e s a r e add ed

I t em

Re sta r t

Ba se

Pag ed Dynam i c Memo ry

tzl
I
(X)

the

po o l

G l ob a l

Pa r am e t e r Bl o c k

P F N Da ta

SYSBOOT s t a r t i ng at the h i g h e s t sys tem v i r t ua l ad d r e s s a nd wo r k i ng

of a v a i l ab l e S PTEs

Ad d r e s s o f Po i n t e r

l i s ted

the

pr ev i o us pag e .

Fa c to r s Tha t
Af f e c t S i ze

( 1 pag e )

EXE $G L_R PB

constant

PFN$A BASE
PFN$AL_PT E

( Ev e r yt h i ng )

MMG$G L_PAGE DYN

PAGEDYN

down .

Pr o t

Own e r

URKW

SYSB OOT

Yes

INIT

ERKW

SYSB OOT

Pag eabl e

(8)

URKW

Ma pped

S YS B OOT

URKW
No npag ed

Dyn am i c Mem o r y

MMG$G L_N PAGEDYN

NPAGEDYN

( 1 pag e )

No Ac c e s s g ua rd pag e

constant

I n t e r r upt

INTSTKPAGES

Sta c k

K
K

N o Ac c e s s g ua rd pag e

EXE $G L_I NTSTK

S y s t em Co n t r o l

EXE $G L SCB
PR$_SCBB ( P )

constant ( 9 )
( 1 o r 2 pag e s )

ERKW

Ba l an c e S l o t Ar e a

SWP$G L_BA LBASE

BALS ETCNT
S i ze of Proc e s s
He ad er

SRKW

Yes

Sys t em He a d e r

MMG $G L S YS PHD

S YSMWCNT
GB LS ECT I ONS

ERKW

SYSB OOT

Sys t em Pag e Ta bl e

MMG $G L S PTBASE
MMG$GL-G PTBASE
MMG$GL-S B R ( P )
PR$_SBR ( P )

( Ev e r yt h i ng )

ERKW

SYSB OOT

G l ob a l

MMG$G L_G PTE

GB LPAGES

URKW

Yes

Block

Pag e Ta b l e

End o f Sys t em V i r t ua l
Ad d r e s s Spa c e

(S)

NA
ERKW

MMG $G L MAXS YSVA
MMG$G L-FRESVA
MMG$G L:MAXG PTE

consta n t

pag e )

(10)

(11)

SWAP PER

S YS B OOT

(P)

G l oba l addresses o r processo r reg i ste r s ( PR$ nam e ) who se names a r e fo l lowed wi th ( P ) conta i n phys i c a l add resses
r a th e r than sys tem v i r tua l add resses . The two phys i c a l add resses r e l evant to th i s tabl e a r e the base o f the sys tem
pag e tab l e ( i n PR$_SBR) and the base of the sys tem contro l b l o c k ( i n PR$_SCBB) .

(S)

The i n te r rupt s ta c k g rows towa rd sma l l e r v i rtua l add resses .
po i n t to the g ua rd page that fol lows the i n ter rupt s tac k .

(1)

Some g l obal add resses l i sted here a re o n l y c o i n c i d enta l l y a t the beg i nn i ng o f the named reg i on . Othe r s , those who se
names beg i n wi th MMG $ , a r e d e f i ned i n mod ul e MOAT s o l e l y a s symbo l i c l abel s to del im i t the po r t i o n s o f the l i nked
execut ive .

(2)

Al tho ugh only 5 6 4 bytes a r e used for f i l e sys tem s t a t i st i cs , the pro tec t ion g r anul a r i ty d e f i ned by the
a rc h i tec ture i s a pag e , 5 1 2 byte s . Fo r th i s r ea son , two ent i r e pag es , 1 0 2 4 byte s , a r e set to UREW pro tec t i on .
r ema i n ing two pag e s i n th i s a rea a r e s e t to URKW .

VAX
The

(3)

The pages conta i n i ng XDE LTA only r ema i n ma pped i f the R5 f l ag ( Chapter 2 1 ) reque s t i ng the exec ut i ve d ebugg er i s
when the sys tem is i n i t i a l i zed .

set

(4)

The pag e s set a s i d e fo r connec t to i nt e r r upt are only ma pped No Access a s pa r t o f i n i t i a l i za t ion .
a l l o c a ted i n response to spec i f i c r eque s t s .

are

(5)

I t i s mean ing less to a s k wh ether sys tem v i r tua l pag es tha t a r e ma pped to I/0 add resses a re pag eabl e .

(6)

MMG $AL_SB ICONF i s the address o f a 1 6-longwo rd a r ray . Each l o ng wo rd _ a r r ay
address o f the f i rst pag e tha t maps I /O addresses fo r tha t ad a pte r .

(7)

Loc a t i ons BOO$G L SPTFREL and BOO$G L S PTFREH do not conta i n sys tem v i rtua l add resses .
sys tem v i r tua l page numbers of the fi r s t and l a s t pag e s in the poo l o f ava i l able SPTEs .

(8)

(9)

Th i s i s why

the

contents

e l ement

loca t i on

conta i n s
Ra ther ,

EXE $G L_INTSTK

These

the

SPTEs

sys tem

they

v i r t ua l

conta i n

the

The Resta r t Pa rame ter B l o c k d o es not pag e . Howeve r , i t i s not l o c a ted in h i gh phys i c a l memory a s the rest o f the
The Re s t a r t Pa rame ter Block i s l ocated in the f i r s t pag e o f the the good 6 4K byte segment
nonpag ed exec u t i ve i s .
l ocated by the memo ry bootst r a p ROM . The pag e is not pl aced i n to the sys tem wo r k i ng set so the re is no way memory
management can ma ke the pag e i nva l i d .
The sys tem cont r o l b l o c k on the VAX- 1 1/7 5 0 i s two pag es l ong .
page l ong .

Th e system cont r o l b l o c k on

the

VAX- l l/7 8 0

one

( 10)

The process head e r s that res i d e i n the b a l a nce s l o t a rea a r e a pa r t o f the process wo r k i ng set to wh i ch they a r e
a sso c i a ted .
Al though po rt i o n s o f t h e process h e a d e r do no t pag e , t h e phys i c a l pages l o cked down i n th i s manne r are
accounted for i n process wo r k i ng s e ts and d o not count towa rd the execut i ve ' s use o f memory .

(11)

G l obal pag e tab l e s a r e pag eab l e . However , i f a g l obal pag e table pag e conta i n s a t l ea s t one va l id g lobal page tabl e
entr y , then that pag e i s l ocked i n to the sys tem wo r k i ng s e t .

S I Z E OF SYSTEM VIRTUAL ADDRESS SPACE
E.2.1

S ys t em V i r tua l Add re s s Spa c e a nd SYSBOOT Pa r am e t e r s

Th e s i ze s o f mo s t o f t h e p i ec e s o f s ys t e m add r e s s
s pa c e l i s te d
in
Ta b l e E - 2 a r e e i th e r c o n s t a n t o r s im p l y r e l a t ed t o o n e o r two SYSB OOT
p a r ame t e r s .
Th e i r s i z e s a r e c om p u t e d i n a s t r a i g h t fo r wa r d m a nn e r by
SYSBOOT .
Th e s i z e s o f the sys t em pag e t ab l e a nd th e PFN d a t a b a s e a r e
a l i t t l e mo r e c om p l i c a t ed a nd a d i sc us s i on o f the i r s i z e s i s po s t po ne d
unt i l the n e x t s ec t i o n .
Wh e n SYSBOOT c a l c ul a t e s the s i ze o f t h e sys t em pag e t ab l e , i t f o rms a
s um o f
t h e s i ze s o f the p i ec e s o f sys tem v i r tua l add r e s s spa c e , a nd
a l l o c a t e s a n S PTE f o r e a c h pag e .
Th e c a l c u l a t i o n
tha t
i s p r e s en t e d
here
p r e s e n t s e ac h p i ec e o f
s ys tem spa c e
i n o rd e r o f i n c r e a s i ng
v i r tua l add r e ss , r a th e r than i n t h e o rd e r tha t
SYS BOOT pe r fo rm s
the
c a l c ul a t i o n .
1.

Th e f i r s t pag e s o f sys tem a d d r e s s
s pa c e ,
c o n ta i n i ng
the
s y s t em s e r v i c e v ec to r s
a nd t h e FCP s t a t i s t i c s b l oc ks , h a v e
t h e i r s i z e a c c o un ted
fo r
in
the
a ss emb l y t i m e pa r am e t e r
MMG $ C S PTSKE L d e f i ne d i n mod u l e S PTSKE L .
S VAS(sptskel)

E.2.1

Th e FC P d a t a a r ea is l e s s t h a n two pag e s l o ng .
Howeve r ,
the
g r a n ul a r i ty of
access
p r o t e c t i o n is the pag e .
Th i s i s wh y
pa r t o f t h e f i r s t pag e o f t h e l i n ked d r i v e r d a ta
s t r uc t u r e
a r e a h a s a p r o tec t i o n o f UREW wh i l e the r e s t o f th a t a r e a i s
URKW .
2.

Th e a r e a t h a t wi l l c o n t a i n
the
l i n ked e x e c u t i v e ,
the
RMS
i m ag e , a nd t h e sys tem m e s s a g e f i l e h a s i t s s i ze d e t e rm i n ed by
the SYSB OOT p a r am e t e r S PTRE Q .
In
add i t i o n ,
t h e r e mus t be
e n o ug h e x t r a
pag e s i n t h i s a r e a to map the I/0 a d a p t e r s a nd
to r e s e rve a sys tem v i r t ua l pag e fo r e a c h d ev i c e d r i v e r
tha t
r e ques t s o n e .
I f th e r e a r e a n y s y s tem pag e
tab l e ent r i e s
r equ i r ed
fo r
m a pp i ng
by
PFN
fo r r e a l - t i m e d ev i c e s , t h e r eque s t ed n um be r
( S YS B OOT p a r am e t e r REALT IME S PTS } i s a d d ed to sys tem v i r t ua l
a d d r e s s r e q u i r emen t s a t t h i s t i m e .
SVAS(sptreq)

SPTREQ + REALTIME_SPTS

E.2.2

Af t e r the s i z e of the sys t em pag e
t ab l e
is
c a l c u l a ted
and
r o u n d ed
up
to
the n ex t pag e b o und a r y ,
any e x t r a pag e s
a c qu i r ed a r e a d d ed to t h e po o l o f a v a i l ab l e sys t em pag e t a b l e
ent r ies .
3.

Th e Re s ta r t Pa r am e t e r B l o c k i s a l wa ys o ne pag e l o ng .
no t a t i o n o f F i g u r e E - 1 , t h i s i s e x p r e s s ed as
SVAS(rpb)

the

E.2.3

Th e s i ng l e pag e r e qu i r ed fo r the Re s t a r t Pa r am e t e r
Bloc k
is
n o t c o un t ed wh e n d e te rm i n i ng the i n i t i a l s i z e o f the sys tem
E- 1 0

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE
pag e t a b l e .
I t i s a s s umed t h a t pag e r o und i ng o r o n e o f the
a p p r o x i m a t i o ns w i l l
add t h e s i ng l e S PT E r e qu i r ed to map the
R PB .
4.

Th e n umbe r o f pag e s i n t h e PFN d a t a b a s e
the n e x t sec t i o n .

Th e spa c e r e s e r v e d f o r t h e pag ed a nd nonpag ed d yn am i c m emo r y
a r e a s d e pend s o n t h e S YS B OO T p a r am e t e r s PAG E DYN a nd N PAG E DYN
r e spec t i ve l y .
Bo t h pa r am e t e r s ,
e x p r e s s i ng
po o l
s i zes
in
byt e s ,
are
t r un c a t ed
t o the nex t sma l l e s t pag e b o und a r y t o
g i ve
th e po o l
s i zes
in
p ag e s .
SYSB OOT
mod i f i e s
the
p a rame t e r s thems e l v e s
so
tha t the nex t b o o t s t r a p o pe r a t i on
w i l l r e f l ec t t h e t r un c a t e d po o l s i z e s .

SVAS(pagecLpool)

d e f e r r ed

PAGEDYN

un t i l

E.2.4

----

512

Th e pa g e s i n t h e m i d d l e o f pag ed d yn am i c m emo r y t h a t h a v e
p r o tec t i on of
E W a r e a l l o c a ted
b y t h e u t i l i ty p r og r am
RM S S HARE to a c c o mmod a t e the d a ta s t r uc t u r e s tha t RM S r e qu i r e s
f o r sh a r ed f i l e s .

SVAS(nonpaged_pool)

NPAGEDYN

E.2.5

----

512

Th e S YS B OOT pa r am e t e r I NTS TKPAGE S
i n t e r r up t s t a c k i n p ag e s .
SVAS(int_stack)

g i ves

INTSTKPAGES

the

v a l ue

the

E.2.6

I n c a l c u l a t i ng t h e t o t a l s i z e o f the sys t em pag e
tab l e ,
the
g ua r d pag e s
( p r o te c t i o n
s e t to no a c c e s s ) a t e i th e r e nd o f
t h e i n t e r r up t s t a c k a r e n o t c o un ted .
Th e s e
pag e s c a u s e
a c c e s s v i o l a t i o n e x c e p t i o n s ( a c t ua l l y a n i n te r r up t s ta c k n o t
v a l i d HA LT ) on b o th s t a c k o v e r f l o w a nd s ta c k u nd e r f l o w .
7.

Th e s i ze o f t h e s y s t em c on t r o l b l o c k i s C PU d epe nd en t .
Bo t h
the VAX- 1 1 /7 5 0
a nd t h e VAX- 1 1 /7 8 0 c o n ta i n the a r c h i t e c t u r a l
sys t em c o n t r o l b l o c k ( F i g u r e 2 - 1 , F i g u r e 6 - 3 ) .
In add i t i o n ,
the VAX- 1 1 /7 5 0 s ys tem c o n t r o l b l o c k h a s a s e c o nd pag e d evo ted
to UN I B US i n t e r r up t d i s pa tc h i ng ( F i g u r e 6 - 3 ) .

SVAS(scb)

�

(for t he VAX-11/750)
(for the VAX- 11/780)

E-ll

E.2.7

S I Z E OF SYSTEM VI RTUAL ADDRESS S PAC E
8.

Th e a r e a d evo ted to b a l a n c e s l o t s c ompr i se s mo r e t h a n h a l f o f
s y s tem v i r t ua l ad d r e s s s pa c e i n t yp i c a l c o n f i g u r a t i o n s .
Its
s i ze d e pe nd s o n t h e SYS B OO T p a r ame t e r BALS ETCNT a nd the
s i ze
o f a p r o c e s s h e ad e r i n p ag e s , c a l c u l a ted i n S ec t i o n E . l .
Th e
c o n s t a n t s i z e o f b a l a nc e
s l o t s , mo t i v a ted
i n Ch a pte r 1 1 ,
m a k e s th i s a t r i v i a l c a l c u l a t i o n .
SVAS(balance_slots)

BALSETCNT*PHD(pages)

E.2.8

B e c a us e o f the m u l t i pl i c a t i v e n a t u r e of th i s r e l a t i o n sh i p , i t
i s nec e s s a r y to
r ed uc e
t h e BALS ETCNT p a r am e t e r i n sys t em s
t h a t mus t s u ppo r t a l a r g e p r o c e s s v i r t ua l a d d r e s s spac e .
In
a s i m i l a r f a sh i o n , c o n f i g u r a t i o n s tha t r e qu i r e a l a rg e n um b e r
o f c o n c u r r en t l y r e s i d en t p r o c e s s e s sho u l d u s e a sma l l e r v a l ue
o f VI RTUA L PAG ECNT .
9.

Th e s y s t em h e ad e r i nv o l v e s a c a l c ul a t i o n s i m i l a r to the s i ze
o f the process heade r ,
d e sc r i b ed
i n the
l a s t s ec t i o n .
Howe v e r , t h e r e i s no o p t i m i za t i o n t e c h n i que f o r
empty pag e s
b ec a u s e
the r e
i s no
l a rg e v a r i a t i o n i n wo r k i ng s e t s i ze s .
Th e r e i s a l so no n e ed f o r t h e a n a l og ue to p r o c e s s h e ad e r pag e
a r r a ys b e c a u s e the s ys t em h e ad e r d o e s no t d e sc r i b e a n o b j e c t
t h a t swa p s .
Th e s i z e o f t h e system pag e
t ab l e ,
t h e sys tem
a n a logue
to
process
p ag e
t ab l e s , i s c a l c u l a t ed s e pa r a t e l y
f r om the r e s t o f
the
s ys t em h e ad e r ,
wh i c h h a s a
s impl e
d e pe n d e n c e o n two SYSB OOT p a r am e te r s .
Th e o n l y s y s tem h e ad e r c ompo n e n t i s t h e sys tem e q u i v a l e n t
to
t h e wo r k i ng
set
l i s t a nd the p r o c e s s s e c t i o n t a b l e in the
process head e r .
Th e
s ys t em e qu i v a l en t s
a re
the s ys t em
wo r k i ng
set
l i s t a nd the g l o b a l s e c t i o n t ab l e .
The SYS B OOT
p a r am e t e r s
th a t co n t r o l
the i r
s i zes a re
SYSMWCNT
a nd
G B LS ECT I ONS .

SVAS(sysphd)

�

HD$K_LENGTH + 4*SYSMWCNT
+ 32*GBL SECTIONS + 511

)

E.2.9

512

Th e s y s tem s e c t i o n t a b l e c o n t a i n s s ec t i o n t a b l e e n t r i e s n o t o n l y
fo r
a l l g l o b a l s e c t i o n s b u t a l s o fo r th r e e sys tem s e c t i o n s :
the
e x ec u t i v e i mag e i t s e l f , t h e RM S i m ag e ,
a nd
the
sys t em m e s s ag e
file .
10.

Th e s i ze o f the s ys t em pag e t a b l e d epe nd s o n t h e
s i zes o f the
o th e r
p i ec e s
of
s y s t em
a d d r e s s spac e .
Th e c a l c u l a t i o n o f i t s
s i ze i s d e fe r r ed un t i l the nex t s ec t i o n .

11.

Th e l a s t s i mpl e c a l c ul a t i o n o f a po r t i o n
add r e s s
s pa c e
i nvo l v e s t he
s i ze o f the
g ov e r ned by the SYSB OOT p a r am e t e r G B L PAG E S .

SVAS(gpt)

GBLPAGES + 127
=

128

E-12

of
sys t em v i r t ua l
g l ob a l
pag e t a b l e ,

E.2. 10

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE
E. 2. 2

Sys t em Pag e T ab l e a nd the PFN Da t a B a s e

Th e PFN d a t a b a s e c o n t a i n s a d e sc r i pt i o n o f
e a c h pag e o f
phys i c a l
memo r y .
Howe v e r ,
i t d o e s n o t c o n t a i n i n fo rm a t i o n a b o u t t h e n o npag ed
exec ut i ve .
B e c a us e
the
PFN d a t a
base
i s pa r t of
the n o n pag ed
e x e c u t i v e , i t s s i z e d e pe nd s o n i t s e l f .
Ho we v e r , t h e s i t ua t i o n i s mo r e
c ompl i c a t ed .
Th e sys t em pag e t a b l e , a l so nonpag ed , m a ps t h e PFN d a ta
base .
Th u s t h e s i ze o f the PFN d a ta b a s e d epe nd s o n i t s o wn s i z e i n
two d i f f e r e n t wa ys .
Th e s i g n i f i c a nc e o f t h e n umb e r 1 8 i n the f o l l owi ng
equa t io n
is
that
the r e
a re
18
b yt e s o f i n f o rma t i o n s to r ed f o r e a c h pag e o f phys i c a l
memo r y .
As d e sc r i b ed i n Ch a p t e r 1 1 , e a c h phys i c a l pag e
i s d e sc r i b ed
b y two byte a r r a ys , s i x wo rd a r r a ys , a nd two l ongwo r d a r r a ys .
Bec ause
the two l i n k a r r a ys o ve r l a p t wo o th e r a r r a ys , th i s amo u n t s to a
to t a l
of
18
byt e s o f
i n fo rma t i o n
f o r e a c h phys i c a l p ag e .
Th i s v a l u e i s
r e p r e s e n t ed b y t h e g l o b a l
c o n s t a n t PFN $ C L ENGTH d e f i n ed
by mod u l e
SYS PARAM { o r PARAME T ER ) .

SVAS(pfn) =

18*(PHYSICAL - NO_PFN_DATA) + 511

E.2.11

512

whe r e PHYS I CAL r e p r e se n t s th e s i z e o f phys i c a l memo ry

{

PHYSICAL = minimum size of physical memory , PHYSICALPAGES

}

a n d NO PFN DATA r e p r e se n t s t h e n o npag ed po r t i o n s o f s y s tem s pa c e
a r e not a cco un ted f o r i n t h e PFN d a t a b a s e .

th a t

NO_PFN_DATA = SVAS(nonpaged_exec)
+ SVAS(pfn)
+ SVAS(nonpaged_pool)
+ SVAS(int_stack)
+ SVAS(scb)
+ SVAS(sysphd)
+ SVAS(spt)

Th e no n pag e d po r t i o n o f the e x e c u t i v e i m ag e , SVAS { no npag ed_e x ec ) , i s a
subset o f
SVAS ( sp t r e q )
wh e n c om p u t i ng
the s i z e o f the sys t e m pag e
tab l e .
I ts s i ze i s a c o n s t a n t who s e v a l u e
i s d e te rm i ned whe n t h e
e x ec u t i ve i mag e i s l i n ked .
SVAS(nonpaged_exec) = MMG$AL_PGDCOD - MMG$A_ENDVEC
= 77 pages

No t i c e tha t t h e PFN d a t a b a s e d epend s o n
i t s o wn
s i ze e x p l i c i t l y
( th r o ug h th e N O P F N DATA t e rm ) a n d a l s o impl i c i t l y th r o ug h t h e s i z e o f
t h e sys tem pag e-t a ble ( Eq ua t i o n E . 2 . 1 2 ) .
I n a s i m i l a r f a sh i o n , th e s i z e o f t h e sys tem pag e t ab l e d epend s o n i t s
own
s i ze
e x p l i c i t l y a nd impl i c i t l y t h r o ug h the s i z e o f the PFN d a ta
b a se .
E-1 3

S I Z E OF SYSTEM VI RTUAL ADDRESS SPACE

SVAS(spt)

THE_REST + SVAS(spt) + SVAS(pfn) + 127

E .2.12

128

wh e r e THE R E S T r e p r e s e n t s a l l c on t r i b ut i o n s to
sys tem add r e s s
e x c e pt fo r t h e sys tem pag e t a b l e a nd t h e PFN d a t a b a s e .
THE_REST

E.2.3

s pa c e

SVAS(sptskel)
+ SVAS(sptreq)
+ SVAS(rpb)
+ SVAS(paged_ pool)
+ SVAS(nonpaged_pool)
+ SVAS(int_stack)
+ SVAS(scb)
+ SVAS(balance_slots)
+ SVAS(sysphd)
+ SVAS(gpt)

App r ox i ma t i on Used by SYSBOOT

Fo r some l a rg e v a l ue s o f e i th e r
VI RTUALPAGE CNT o r phys i c a l memo r y
s i ze ,
an
i te r a t i ve c a l c u l a t i o n fo r the s i ze s o f the s e two qua n t i t i e s
d o es n o t c o nve rg e b u t r a th e r o sc i l l a te s a b o u t a s t a b l e so l ut i o n .
To avo i d th i s pro b l em , a s i mp l i f i c a t i o n i n t h e c a l c u l a t i o n
i s m ad e .
Th e n umbe r
o f sys t e m pag e t a b l e e n t r i e s s e t a s i d e fo r the PFN d a ta
b a s e d o es n o t t a k e i n to acco unt the f a c t tha t t h e pag e s occ upi ed by
t h e nonpag ed e x ec u t i v e a r e n o t a c c o un ted fo r in t h e PFN d a ta b a s e .

SVAS(pfn)

18*PHYSICAL + 511

E.2.13

512

Th i s r e l a t i o n r ep l a c e s Equa t i o n E . 2 . 1 1 i n the c a l c ul a t i o n o f the
s i ze
I t a l s o g r ea t l y s i mpl i f i e s Equa t i o n E . 2 . 1 2
of
the sys tem pag e t a b l e .
bec a us e the SVAS { p f n ) t e r m no l o ng e r d epe nd s o n SVAS { spt ) .
I n s t e ad ,
SVAS ( p f n ) i s a c o n s ta n t .
Bec a us e Equa t i o n E . 2 . 1 3 e r r s o n the h ig h s i d e i n a l l o c a t i ng S PTEs f o r
the
PFN d a ta b a se , t h e n um b e r o f S PTEs se t a s i d e fo r the sys t em pag e
t ab l e d o e s n o t u s e Equa t i on E . 2 . 1 2 i t e r a t i v e l y .
I n s tead , the r e
is a
s i ng l e pa s s o n c a l c u l a t i ng t h e s i z e o f t h e s ys t em pag e tabl e .

E-14

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE

SVAS(spt,O)

THE_REST + SVAS(pfn)
128

SVAS(spt)

THE_REST + SVAS(pfn) + SVAS(spt,O) + 127

E.2.14

128

B e c a us e phys i c a l pag e s a r e n o t a l l o c a ted f o r the PFN d a t a b a s e
unt i l
the
s ys t em pag e
t ab l e s i z e
h a s b e e n c a l c u l a t e d , th e r e i s n o l a rg e
wa s te o f phys i c a l memo r y .
Th e o n l y a f f e c t o f the s e t wo a pp r o x i ma t i o n s
m i g h t b e o n e mo r e phys i c a l p ag e a l l o c a t ed f o r t h e sys t e m pag e t a b l e
t h a n i s a bso l u t e l y n e c e s s a r y .
Th i s wo u l d o n l y o c c u r o n
sys t em s wi th
very
l a r g e amoun t s o f m emo r y i n
the
f i r s t p l a c e so the l o s s i s
p r ac t i c a l l y unno t i c ed .

E. 2.4

Reno rma l i za t i on o f S PTREQ

Th e r o und i ng of the s i ze o f the s ys t em pag e t a b l e to the n e x t h i g h e s t
pag e
b o u nd a r y c a n a d d
extra
sys t em p ag e
t a b l e e n t r i e s to tho s e
r e q u i r ed to m a p t h e e n t i r e s ys t em .
Af t e r SYSB OOT h a s
c a l c u l a t ed
the
r e s u l t o f Equa t i o n E . 2 . 1 4 , i t m a ps the l i nked e x e c u t i ve b eg i nn i ng a t
the l o w a d d r e s s e nd o f s ys t em a d d r e s s s pa c e ( 8 0 0 0 0 0 0 0 )
and m a ps
the
d yn a m i c po r t i o n o f s ys t em s pa c e b eg i nn i ng a t t h e h i g h a d d r e s s e nd .
An y pag e s l e f t o v e r a f t e r t h i s m a pp i ng a r e put i n to the po o l o f s ys t em
pag e
t ab l e e n t r i e s l o c a t e d by BOO $G L S PTFREL and B O O $ G L S PTFRE H .
As
S PT E s a r e n e ed ed f o r f u r th e r m a pp i ng ( fo r e x ampl e b y SYSIN I T
to m a p
RMS a nd t h e s ys t em m e s s a g e f i l e o r b y S YSGEN wh e n l o ad i ng d r i v e r s tha t
r e q u i r e a sys tem v i r t ua l pag e n um be r ) , t h e s e pag e s a r e t a k e n f r om
the
po o l .
Onc e the
e nt i r e
s ys t em
is
m a pped , any e x t r a pag e s ( d u e to
r o und i ng as we l l as an o v e r e s t i ma te o f the S PTREQ p a r am e t e r ) r em a i n i n
the po o l o f s ys tem pag e t a b l e e n t r i e s .

E. 3

PHYS I CAL MEMORY REQU I REMENTS OF THE E XECUT IVE

Onc e t h e s i z e s o f t h e v a r i o u s p i e c e s o f s ys tem a d d r e s s s pa c e have b e e n
c a l c u l a ted ,
it
is
po s s i b l e
to
l i s t the
to t a l
phys i c a l m emo r y
r e qu i r em e n ts o f t h e e x e c u t i v e ,
t h e n um b e r o f pag e s t h a t
are
no t
a v a i l a b l e fo r u s e r p r o c e s s e s .

E. 3 . 1

Phys i c a l Memo r y Used b y the Ex e c ut i ve

Ta b l e E - 3 l i s t s e a c h p i e c e o f the n o npag ed e x e c u t i v e
a nd
e i th e r
i ts
i n pag e s o r a n e q ua t i o n n um b e r i n S e c t i o n E . 2 t h a t d e sc r i b e s how
s i ze
i t s s i ze is c ompu ted .

E-15

S I Z E OF S YS TEM VI RTUAL ADDRESS S PACE
Tab l e E - 3
Div i s ion of S y s tem Virtua l Addre s s Space
into Nonpaged and Paged P ie c e s
The
fo l l owi ng
po r t i o n s o f
s ys tem
add r e s s
s pa c e
are
permanen t l y m apped b y SYSB OOT .
The phys i c a l pag e s tha t they
o c c upy a r e n o t a c c o un ted f o r in the PFN d a ta b a s e .
S i ze

I tem
Nonpag ed Po r t i o n o f Execut i v e Imag e

MMG $AL PGDCOD - MMG $A_ENDVEC
( 7 7 pa ge s )

PFN Da t a Ba se

Equa t i o n E . 2 . 1 3

No n pag ed Dynam i c Mem o r y

Equa t i o n E . 2 . 5

In t e r r upt S t a c k

Equa t i o n E . 2 . 6

Sys tem Co n t r o l B l o c k

Equa t i o n E . 2 . 7

Sys tem He ad e r

Eq ua t i o n E . 2 . 9

Sys t em Pag e Ta bl e

Equa t i o n E . 2 . 1 4

Th e fo l l owi ng a r e the pag e ab l e po r t i ons
of
the
execut i v e .
Th e i r to ta l m emo r y c o s t c an n ev e r exc e ed SYSMWCNT .
S i ze

I t em
Sys t em Se rv i c e Vec to r A r e a

3 pag e s

Pa g ed Exec u t ive Ro ut i n e s

MMG $A L PGDC ODEN - MMG $AL_PGDCOD
( 6 7 pa ge s )

RMS Imag e

S i ze o f RMS Imag e
( 1 3 1 pag e s )

Sys tem Me ssage Fi l e

S i ze o f Sys t em Me s sag e Fi l e
( 2 5 7 pag e s )

Pag ed Dynam i c Memory

Equa t i o n E . 2 . 4

Gl obal

Equa t i o n E . 2 . 1 0

Pag e Ta b l e Pag es

Th e fo l l owi ng po r t i o n s o f
s ys tem
add re s s d o
no t
phys i c a l memo ry a c c o un ted fo r i n Equa t i o n E . 2 . 1 4 .
Re a so n

I t em
XDE LTA ,

r equ i r e

U s ua l l y n o t mapped

IN I T , and BUGC HECK

I /0 Spa c e Ma ppi ng

I /O Ad d re s s e s

SVPNs fo r D i sk Dr i v e r s

I /O Ad d re s s e s o r
Do ub l e Ma ppi ng

Ba l anc e Sl o t Area

Proc e s s He ad e r Pag es and
Pag e Tab l e Pag es a r e
cha rged t o proc e s s
wo r k i ng s e t s

E-16

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE
NONPAGED = SVAS(nonpaged_exec)
+ SVAS(rpb)
+ SVAS(pfn)
+ SVAS(nonpaged_pool)
+ SVAS(int_stack)
+ SVAS(scb)
+ SVAS(sysphd)
+ SVAS(spt)

E.3.1

Th i s i n i t i a l s um i s the t o ta l m emo r y r eq u i r emen t o f
the
nonpaged
e x e c u t i v e c od e a nd d a t a t a b l e s .
Th e pag ed e x e c ut i ve ( Ta b l e E - 3 ) a l so
r equ i r e s phys i c a l m emo r y .
Howe v e r , i t i s r ea so na b l e
to
a s s um e
tha t
the
s ys t em wo r k i ng
set
is
full
a t a l l t i m e s s o tha t the phys i c a l
m emo r y r eq u i r em e n ts o f t h e pag ed e x e c ut i v e a r e s i mpl y SYSMWCNT pag e s .
Two f i n a l i t em s mus t b e t a k e n i n t o a c c o un t wh en c a l c u l a t i ng the n umbe r
o f phys i c a l
pag e s used
by
the execut i ve .
Th e SYS B OO T p a r am e t e r s
FRE E L IM a nd MPW L O L IM I T s e t l o w l im i t t h r e sho l d s o n the n umbe r
of
Th e se p a r ame t e r s s h o u l d b e
pag e s o n t h e f r ee a nd mod i f i ed pag e l i s t s .
i nc l ud ed wh e n c a l c u l a t i ng t h e n um be r o f a v a i l ab l e ph ys i c a l pag e s .
MEMORY = NONPAGED + SYSMWCNT + FREELIM + MPW_LOLIMIT

AVAILABLE = PHYSICAL - MEMORY

E.3.2

E.3.3

By wo r k i ng b a c k f r om Equa t i o n E . 3 . 3 , i t
i s po s s i b l e
to o b t a i n
the
n umbe r o f a v a i l a b l e phys i c a l
p ag e s
i n t e rm s o f t h e c o n t e n t s of a
SYSG EN p a r am e t e r f i l e a nd
one more
i np u t pa r am e t e r ,
the
s i ze
of
phys i c a l m em o r y .

E. 3. 2

Sys tem P r o c e s s e s

Wh e n a t t em p t i ng t o a s s e s s the t o t a l m em o r y r equ i r ed by t h e s ys t em , o n e
mo r e
f a c t o r mus t b e t a k e n i n to a c c o un t .
Al l memo r y r e s i d en t sys tem
p ro c e s s e s r e q u i r e a n umbe r of pag e s e qua l to the i r r e spec t i ve wo r k i ng
s e t s i ze s .
Th e s ys tem p r o c e s s e s a r e :
•

J o b Co n t r o l l e r

•

P r i n t Sym b i o n t ( s )

•

E r r o r Log g e r Fo rma t P r o c e s s ( E RRFMT )

•

Ope r a t o r Commun i c a t i o n P r o c e s s ( O PC OM )

•

D i s k AC P ( s )

•

Mag ta pe AC P ( s )

N e t wo r k AC P ( NETAC P )

Remo t e Te r m i n a l AC P ( REMAC P )

( I f any)

( At l e a s t o n e )
( I f any)
( I f any)

E-1 7

( I f any)

S I Z E OF SYSTEM VI RTUAL ADDRESS SPACE
The amo un t o f memo r y r equ i r ed by t h e s e p r o c e s s e s c anno t b e c a l c u l a t e d
in
c l o s ed
f o rm a s the e x e c u t i v e ' s m emo r y r eq u i r em e n t s a r e c a l c u l a te d
f o r s ev e r a l r e a so n s .
•

•
•

Th e memo r y c o n s umed by a p r o c e s s i s
i t s wo r k i ng
s e t s i ze .
Automa t i c
wo r k i ng
s e t s i ze
ad j us tme n t c a u s e s th i s p r o c e s s
( Th i s a s s um e s t h a t the p r o c e s s
a t t r i b u t e to v a r y o v e r t i m e .
i n qu e s t i o n
r e a ches
i ts
wo r k i ng
s e t l i m i t , a r e a so na b l e
a s s umpt i o n f o r s y s t em p r o c e s s e s . )
Th e
wo r k i ng
set o f any
process
in
t h e s ys tem i s r e a d i l y a v a i l a b l e f r om t h e D I S P LAY
u t i l i ty .
Sha r i ng c o n f u s e s the i s s u e .
Howe v e r , t h e SHOW SYSTEM c ommand
l i s t s t h e ph ys i c a l mem o r y used by e a c h p r o c e s s i n the sys tem .
Sys tem p r o c e s s e s c a n b e o u t swa pped , t em po r a r i l y r ed uc i ng
phys i c a l memo r y r e qu i r em e n t s of t ho s e p r oc e s s e s to z e r o .

the

B e c a us e phys i c a l memo r y r eq u i r em e n t s o f s y s tem p r o c e s s e s v a r y o v e r
t i me a nd c a n b e e a s i l y o b ta i n ed f r om a ut i l i ty s uc h a s D I S PLAY o r wi th
t h e SHOW SYSTEM c omma nd , they a r e not i nc l ud ed
in
any e q ua t i o n s
in
t h i s c ha p te r .
Howe v e r ,
the i r
r equ i r em e n t s
sho u l d b e t a ke n i n to
a c c o un t wh e n a n y t ype o f c o n f i g u r a t i o n c a l c ul a t i o n
i s m ad e .
Th i s
a ppe nd i x h a s p r ov i d ed a too l fo r c a l c u l a t i ng t h e memo r y r e qu i r em e n t s
o f t h e e x e c u t i ve , a n umbe r th a t i s n o t s o r e a d i l y a v a i l ab l e .

E.4

S I Z E S OF P I ECES OF P l S PAC E

Mo s t o f t h e p i ec e s o f P1 s pa c e h a v e p r ed e t e rm i n ed s i z e s , b a s ed on
the
c o n t e n t s o f mod u l e
S H E LL
i n the e x e c u t i v e .
Th i s mod u l e i nc l ud e s a
s k e l e to n P l pag e ta b l e tha t i s used wh e n a p r o c e s s i s c r e a t ed
to
set
u p a n i n i t i a l P l pag e ta b l e .
Some pi e c e s o f P 1 s pa c e a r e d yn am i c a l l y c o n f i g u r ed ,
w i th s i ze s
tha t
a r e d e t e rm i n ed by a v a r i e ty o f t e c h n i q ue s .
Tab l e E - 4 l i s t s the p i e c e s
The
fo l l o w i ng
o f P 1 s pa c e a nd h o w t h e s i z e o f e a c h
i s d e te rm i ned .
l i s t i n c l ud e s d e ta i l s a b o u t e a c h d yn am i c po r t i o n o f P 1 spa c e .
L i ke Pl
s pa c e i t s e l f , t h e l i s t moves towa r d l o we r v i r t ua l a d d r e s s e s .
1.

Al l o f the p i e c e s o f P 1 s p a c e f r om the d eb ug g e r symbo l
tab l e
to
th e
c h a nn e l
control
bloc k
tab l e have
the i r
s i zes
d e te r m i n ed by a s s em b l y t i m e pa r am e t e r s i n mod u l e SHELL .
( Th e
spec i a l SYS B OOT pa r am e t e r C HANNE LCNT i s c u r r e n t l y unused . )

Th e P 1 wi ndow to th e
p r o c e s s h e ad e r
i nc l ud e s a l l o f
the
p r o c e s s h e a d e r e x c e p t f o r pag e t a b l e pag e s ( Ta b l e E- 1 ) .
Th e
emp t y pag e s a r e
i n c l ud ed
i n the
Pl
wi nd ow .
Se c t i o n E . 1
r e l a tes
the
s i ze o f
t h e p r o c e s s h e ad e r
to the r e l eva n t
SYSB OOT p a r am e t e r s .

Th e
LOG INOUT i m ag e m a ps
the
s e l ec t ed c omm a nd
l a ng uag e
i n te r pr e t e r i n to P l s pa c e fo r i n t e r a c t i v e a nd b a tch j o bs .
(A
m e r g ed imag e a c t i v a t i o n a c c ompl i s h e s th i s m a pp i ng . ) Th e
s i ze
o f the C L I i m a g e d e t e rm i n e s how m u c h s pa c e i s t a k e n up by the
CLI .

Th e SYS BOOT p a r am e t e r
C L I SYMTBL d e t e rm i n e s
t h e numbe r o f
d emand
z e r o pag e s t h a t a r e c r e a ted b y LOG INOUT f o r t h e C L I
s ymbo l t a b l e .
E- 1 8

Tab l e E - 4
Deta i l ed Layout o f P l Space
( Va r iable S i z e Portion )

The s i ze o f the f i r s t po r t i o n o f P l s pac e , f r om the user s ta c k to the P l w i ndow to the pro c e s s head er , i s ma i n l y
depend ent on SYSBOOT pa ramete r s . The s i ze s o f e a c h o f these pieces m a y v a r y fo r d i f fe rent sys t ems , d i f fe r en t processes
i n the same system , or even d i ffe r en t imag e s i n the same process .
Item
Low Add ress End o f
Pl Spa c e
Use r Sta c k

G l obal Add re s s o f Po inter
@ PHD$L FREPlVA
( Of fset i n to the
Pro c e s s Head e r )

Fac to rs Tha t
Af fect S i ze

Pro t

own e r

Pag eabl e

Mapped by

Yes

Imag e
Ac t i va to r

Yes

Imag e
Ac t i v a to r

I OS EGMENTS
( L i n k Time Opt ion)

UREW

Yes

Imag e
Ac t i vato r

Si ze of Me ssag e
Sec t i o n

Yes

SET M ESSAGE
Command

CLISYMTB L

URSW

Ye s

LOGINOUT

CLI Imag e Si ze

Yes

LOGINOUT

Si ze o f the
Process Head e r

SRKW

Cod e i n SHELL

STACK
( L i n k Time Opt ion)
=

Ex tra Use r Sta c k Pag es

EXUSRSTK

Image I/0 Segment

@ P IO$GW I I OIMPA + 4
@ CTL$AL=S TACK + ( 3 *4 ) (S )

Bo und ary be tween
Process-Pe rman ent and
Imag e-Spec i f i c Pieces
of P l Space

@ CTL$G L_CTLBASVA ( 1 )

Pe r -Process Mes sag e Sec t i on

@ CTL$G L_PPMSG

C L I Symbol Tab l e
C LI Imag e

@ CTL$AG_C LIM AGE

In i t i a l End o f Pl Spa c e for
Every Pro c ess i n Th i s System

@ MMG$G L_C TLBASVA ( 2 )

P l Wi ndow to Process Head er

@ CTL$G L_PHD

(continued on next page )

Detai l ed Layout of P l Space
( F ixed S i z e Port ion )

The rest o f P1 space i s f i x ed in s i ze and locations fo r a l l possible systems . The si zes o f each o f these pieces are
determined by assembly t ime pa rameters in modul e SHELL . These pieces ' a re impl i c i tl y mapped by the Swapper when the
skeleton P1 pag e tabl es a r e swapped in from the shel l process at the t ime that the process i s c reated .
Global Add ress
Add ress
or
G l obal Add ress o f Po inter
=

Item
Channel Co ntrol Block Table
Process I/O Segment

Si ze in Pag es

Prot

OWner

Pag eabl e

4 pages

UREW

Yes

3 0 pag es

UREW

Yes

7FFE2C OO

4 pag es

Yes

7FFE3400

4 pag es

Yes

7FFE3C O O
7FFE3C O O

1 pag es

Yes

7FFE3E OO

4 pag es

Yes

7FFDE 8 0 0
7FFDFOOO
PI O$G L FMLH
@ CTL$GL-RMSPP
CTL$G L-CCB + 16
7FFDF O O O ( S )
@ CTL$G L=CCBBASE + 1 6 ( S )
=

Pe r-Process Common fo r Users
Pe r-Process Common fo r DIGITAL

CTL$A_COMMON

Compa t i b i l i ty Mode Da ta Pag e

CTL$AG CMEDATA
CTL$AL=CMCNTX

=
=

no t cur rently used
Process Al location Reg ion

7FFE4600

46 pag es

UREW

Yes

Gen e r i c CLI Da ta Pag es

CTL$AL_CLICALBK

7FFEA200

3 pages

URSW

Yes

Image Ac tivato r Sc ratch Pag es

MMG$IMGACTBUF

7FFEA800

8 pag es

. Yes

7FFEB800

4 pages

Yes

7FFECOOO

2 pag es

UREW

Yes

7FFEC 4 0 0

pag e

Yes

7FFEC600

1 pag e

Debugger Co ntext Pag es
Vec to rs fo r User-Wr i tten
System Serv ices and
Pe r-Imag e or Pe r-Process
Messages

CTL$A_DISPVEC

Imag e Header Buffer

MMG$IMGHDRBUF
@ CTL$G L_IMGHDRBF

No Access Gua rd Pag e
Ke rnel Stack

CTL$G L KSTKBAS
7FFEC800 ( S )
@ CTL$AL=STACK + ( - 1 *4 ) ( S )

3 pag es

SRKW

Execut ive Stack

7FFECEOO ( S )
CTL$G L KSPINI
@ CTL$AL=STACK + ( 0 *4 ) ( S )

8 pages

SREW

Yes

Supe rv i so r Stack

7FFEDEOO
@ CTL$AL_STACK + ( 1 *4 ) ( S )

16 pag es

URSW

Yes

P l Po inter Pag e

CTL$G L VECTORS
7FFEFEOO
@ CTL$AL=STACK + ( 2 *4 ) ( S )

1 pag e

URKW

Debugger symbol Table

1 28 pag es

In the g lobal add ress c o l umn , symbo l names pr eced ed by the symbo l @ a r e the add resses o f po inte r s to the spec i f i c
po rt ions o f P l space . Symbo l names wi th no pr eced i ng @ s ign a re the ac tua l add resses o f the areas i n quest i o n .

(S)

Stacks g row towa rd s sma l l e r v i r tua l add resse s . Th i s i s the reason for the seem i ng anomal y i n the addresses and
po i nt e r s that d e l im i t the four pe r-process stacks .
The channel control block tab l e a l so g rows towa rd sma l l e r
v i rtual add resse s .
a.

Gl obal l o c a t i o n CTL$AL STACK i s the address o f a four l ongwo rd a r r a y whose e l ements conta i n the i n i t i a l va l ue s
o f t h e four pe r-process s t a c k po i nte r s . A n a r r ay e l ement c a n b e indexed wi th t h e access m o d e a s an argument . A
f i fth l o ng wo rd , preced i ng the a r ray and accessed wi th an i nd ex of - 1 , l ocates the l ow add ress end o f the ke rnel
stac k .
I n the tab l e , the expl i c i t mul t i pl i cat ions r e f l ect the
add re ss i ng i n l ongwo rd contex t . Tha t i s ,

CTL$AL_STACK +

3 *4

l ocates the beg i nn i ng
o f the user s tac k .

CTL$AL_STACK +

2 *4

l ocates the beg i nn i ng
o f the s upe rv i so r stac k .

CTL$AL_STACK +

1 *4

l ocates the beg i nn i ng
o f the executive stac k .

CTL$AL_STACK +

0 *4

l ocates the beg i nn i ng
o f the k e rnel stac k .

CTL$AL_STACK + -1 * 4

l ocates the end
o f the ke rnel stac k .

mul t i pl i c a t i on

four

tha t

impl i ed

i ndexed

CTL$GL CCB i s the add r e s s o f the channel control b l o c k for channel o . The channe l numbe r returned to the cal l e r
o f the Ass i g n Ch annel sys tem serv i c e ( o r some o ther sys tem serv i c e o r RMS cal l ) i s a neg a t i ve byte index from
th i s loca t ion to the beg i nn i ng o f the channel contr o l b l o c k f o r the sel ec ted channe l .

(1)

The contents o f l oca t ion CTL$G L CTLBASVA l ocate the bound ary between the image-spec i f i c po r t i o n o f P l space ( del eted
at image ex i t by rout ine MMG $IMGRESET) and the process-pe rmanent po r t i on of Pl space .

(2)

The contents o f g l obal l o c a t i o n MMG$GL C TLBASVA l ocate the i n i t i a l s i ze o f P l space , i nc l ud i ng the l i nked exec utive
a nd the P l wi ndow to the proc e s s heade r . Al l processes have th i s a s the i r i n i t i a l s i ze o f Pl s pace . As command
l a ng uage interpr ete r s and o ther dynam i c po r t ions o f Pl space s uch as process-pe rmanent message secti ons a re added ,
l o c a t i o n CTL$GL_CTLBASVA is upd a ted to r e f l ec t the chang e .

S I Z E OF SYSTEM VI RTUAL ADDRESS S PACE
5.

Th e spec i a l SYSBOOT pa r am e t e r I MG I OCNT d e t e rm i n e s the d e f a u l t
n um b e r
o f pag e s th a t a r e c r e a te d by t h e i m ag e a c t i va to r fo r
t h e i m a g e I /O s egmen t , t h e RMS i m pu r e a r e a fo r
f i l e s o pe n ed
d u r i ng the e x ec ut i o n of a spec i f i c i m ag e .
Th e d e f a ul t n um b e r
of
imag e
I /O s eg me n t pag e s c a n
ov e r r i d d en f o r a spe c i f i c i m ag e b y i nc l ud i ng the l i n e
I OS EGM ENT

n , [ [N O ] P O BUFS ]

a s a pa r t o f the l i n k t i m e o p t i o n f i l e .
6.

Th e spe c i a l SYS BOOT pa r am e t e r EXUS RSTK d e t e rm i n e s the n um b e r
of
e x t r a pag e s t h a t a r e a l l o c a te d f o r t h e us e r s t a c k b y the
i mag e a c t i v a to r .
Th e s e pag e s a r e
not
u s ed
for
the
use r
stack .
Ins tead ,
t h e y a r e a t a h i g h e r v i r t ua l a d d r e s s t h a n
t h e i n i t i a l v a l ue o f the u se r s ta c k po i n t e r .
Th e s e p a g e s a l l ow t h e o pe r a t i ng s y s tem to r e c o v e r i f the use r
s t a c k i s c o r r upted .

Th e s i z e o f t h e us e r s t a c k i s d e te rm i n ed by t h e opt i o n
STACK

i n an o p t i o n s f i l e a t l i n k t i m e .
i s twe n t y pa g e s .

Th e d e fa u l t us e r s t a c k s i ze

Be c a us e t h e s t a c k i s a utoma t i c a l l y e x pa nd ed by
the
sys t em ' s
a c c e s s v i o l a t i o n h a nd l e r wh e n the us e r s t a c k o v e r f l o ws , the r e
i s l i t t l e n e ed fo r u s i ng th i s opt i o n .
One po s s i b l e use m i g h t
be
fo r
a n i m a g e th a t r equ i r e s a l a rg e a m o un t o f s ta c k s pa c e
b u t c a n n o t a f fo r d t h e o v e r h e a d r e q u i r ed fo r
a utoma t i c
stac k
e x pa ns i o n a t r un t i m e .

E- 2 2

APPEND I X F
VAX/VMS VE RS I ON 2 . 2 ENHANCEMENTS

Two f unc t i o na l c h a ng e s we r e m a d e
to VAX/VMS w i th
the Ve r s i o n 2 . 2
ma i n t e n a n c e
rel ease .
Th e s e c h a ng e s a l t e r
the
wa y two compo n e n t s
d e sc r i b ed i n th i s m a n ua l o p e r a t e .
Be c a u s e t h e s e c h a ng e s we r e p u t i n t o
the
sys tem wi t h pa t c h e s to the e x e c u t i v e , t h e y we r e r e s t r i c ted i n t h e
c h a ng e s tha t c o u l d b e mad e to the sys t em .
It
is
l i ke l y t h a t
these
c h a ng e s w i l l
a ppe a r i n Ve r s i o n 3 o f VMS i n a s l i g h t l y d i f f e r e n t fo rm
th a n they a ppe a r in Ve r s i o n 2 . 2 .
On e o f the chang e s a d d s a s e c o nd l o o k a s i d e l i s t to t h e nonpag ed
po o l
a l l oc a t i o n s c h eme .
Th e
f i x ed
pa c k e t s i ze
i n th i s s e c o nd l i s t i s
c o n t r o l l ed b y a S YS B OO T p a r am e t e r b u t i s t yp i c a l l y s e t to
5 7 6 bytes .
Th i s c h ang e wa s mad e
to
impr ove DECn e t pe r f o rm a n c e a f t e r i t wa s
d i s c o v e r ed t h a t DECn e t wa s s p e nd i ng
a
c o n s i d e r a b l e amo un t o f
t ime
a l l o c a t i ng DECn e t r e c e i v e b u f f e r s f r om nonpag ed po o l .
Th e s e c o nd chang e a l t e r s t h e t e c h n i que fo r c o un t i ng s l o t s
in a
swa p
f i l e b a s ed
on
the
s i ze
o f the swa p f i l e a nd t h e SYSB OOT pa r am e t e r
WSMAX .
Th i s c h a ng e r emo v e s t h e Ve r s i o n 2 r e s t r i c t i o n o f no mo r e
than
256
p r ocesse s .
Th e n e w uppe r l i m i t o n the num b e r o f p r o c e s s e s tha t
c a n b e c r e a t ed i s 8 1 9 2 .
No t e , h o we ve r , th a t o th e r
sys t em r e so u r c e s
wi l l a l mo s t s u r e l y b e exh a u s ted b e fo r e th i s l i m i t i s r e a c hed .

F. l

S ECOND LOOKAS IDE LIST

I n Ch a pt e r 2 5 , the u s e of two nonpag ed
po o l
a l l o c a t i o n s c h em e s wa s
d i s c us s ed .
Th e I /0 l o o k a s i d e l i s t c o n s i s t ed o f a n umb e r ( I R PC OUN T ) o f
f i x ed s i ze b l o c k s l i nked tog e th e r .
Th i s l i s t wa s e s t ab l i shed b y t h e
i n i t i a l i za t i on code
i n mod u l e
INIT .
Th e no npag ed po o l a l l o c a t i o n
r o u t i n e c h e c k ed the r e qu e s t ed s i z e ag a i n s t t h e s i z e o f a n I/O
r e que s t
pa c k e t .
I f t h e r e qu e s ted s i z e wa s sm a l l e r than o r equa l t o t h e s i z e
o f a n I RP , a n a l l o c a t i o n wa s a t tempted f r om the l o o ka s i d e l i s t ( wi th a
s i ng l e
REMQUE
i n s t r uc t i o n ) .
On l y i f th i s a l l o c a t i o n f a i l ed wa s t h e
mo r e g e n e r a l ( bu t s l owe r ) a l l o c a t i o n r o u t i n e c a l l ed .
Th e Ve r s i o n 2 . 2 e nha n c em e n t e x p a nd s o n t h i s s c h em e o f f i x ed
s i ze
b l o c ks
l i nked
tog e th e r .
Two s pe c i a l SYSB OOT p a r ame te r s c o n t r o l t h e
l i s t pa r ame te r s .
Th e
pa r ame t e r
LRPCNT
( a na l og o u s to
IRPC O UNT )
d e t e rm i n e s
the
n um b e r
o f b l oc k s th a t a r e
s e t a s i d e by the
i n i t i a l i z a t i o n r o u t i n e fo r t h i s s e cond l o o ka s i d e l i s t .
Th e
si ze
of
each block
i s d e t e rm i n ed b y the pa r ame t e r LRPS I Z E ( a n a l o g o u s t o t h e
a s s emb l y t i me c o n s t a n t I RP $ K_L ENGTH ) .

F-1

VAX/VMS VE R S I ON 2 . 2 ENHANC EMENTS
F. l. l

I n i t i a l i za t i o n o f S e c o nd L o o k a s i d e L i s t

Th e i n i t i a l i z a t i o n o f t h i s po o l a r e a i s p e r f o rmed by SYS I N I T .
( Th i s
i s d o n e b e c a u s e i t i s e a s i e r to r e l e a s e a n e w SYS I N I T i m ag e th a n pa tch
t h e I N I T mod u l e in the
e x e c u t i ve
i mag e
SYS . E XE . )
Fi r s t ,
the
s 1 ze
p a r ame t e r
i s max i m i z e d w i t h
I RP $ K L ENGTH .
( I t wo u l d b e us e l e s s to
a l l ow t h e s econd l o o ka s i d e l i s t to h ave a b l o c k s i z e sma l l e r
than
an
I RP . )
Wo r k i ng
und e r the a s s um p t i o n tha t these b l o c ks wi l l b e u s e d b y
D E Cn e t , t h e v a l ue o f LRPS I Z E i s a d d ed to 6 4 ( fo r DECn e t o v e r h e ad ) , and
the
r esul t
is
t r un c a ted
to
a m u l t i pl e of 1 6 .
To p r ev e n t i n t e r n a l
f r ag m e n t a t i o n ( u s e o f t h e s e b l o c k s f o r s i z e r e que s t s much sma l l e r t h a n
the b l o c k s i z e ) ,
th e nonpag ed po o l a l l o c a t i o n r o u t i n e w i l l o n l y u s e
t h i s l i s t i f t h e r eque s t ed s i ze i s b e twe en 8 0 % and 1 0 0 % o f t h e upd a t ed
s i ze .
Th e m i n imum va l ue ( a l s o t r un c a t e d to a m u l t i pl e of 1 6 ) a nd the
u pd a ted p a c k e t s i z e
are
s to r ed
fo r
l ater
use by t h e a l l o c a t i o n
r out ine .
A b l o c k o f n o npag e d po o l i s t a k e n f r om t h e h i gh a d d r e s s e nd
of
the
g e n e r a l n o npag ed po o l a r e a , i mmed i a t e l y p r e c ed i ng the l o c a t i o n po i n t ed
to by t h e c on t e n t s o f E XE $G L S PL I TADR
( Fi g u r e 2 5 -4 ) .
Th i s a r e a
is
t h e n d i v i d ed
i n to e qua l s i z e
b l o c k s ( d e t e rm i n ed b y LRPS I Z E ) .
Th e
r eque s t ed l a rg e pa c k e t c o un t ( LR PCNT ) i s m i n im i zed wi th t h i s c o un t o f
e qua l
s i zed b l oc ks .
Th e s e
b l o c k s a r e t h e n l i n k e d tog e th e r ( wi t h a
s e r i e s o f I N S QUE i ns t r uc t i o n s ) .
Th e bo und a r y b e twe e n the l o w add r e s s
e nd o f
t h i s s e c o nd l o o ka s i d e l i s t a nd t h e g e ne r a l po o l a r e a i s s a v ed
( fo r the d e a l l o c a t i o n r o u t i n e ) .
Th e r e i s a to t a l o f f i v e l o ng wo r d s ( c u r r en t l y l o c a t ed i n the nonpag ed
r e a d /wr i t e pa tch a r e a ) th a t d e sc r i b e th i s s e c o nd l o o k a s i d e l i s t .
Th e y
a re :
Upd a t ed S i ze o f P a c k e t s

( t r un c a ted t o m u l t i pl e o f 1 6 )

8 0 % o f th i s upd a t ed s i ze

( a l so t r un c a ted to m u l t i pl e o f 1 6 )

Fo r wa r d L i n k f o r Lo o k a s i d e L i s t
Ba c kwa r d L i n k f o r Lo o k a s i d e L i s t
Bo und a r y b e t we en S e c o nd Lo o k a s i d e L i s t a nd G e n e r a l Po o l Ar e a

F. l.2

No npag ed Po o l Al l oc a t i o n a nd De a l l o c a t i o n

Wh e n o ne o f the no npag ed
po o l
a l l o c a t i o n r o u t i ne s
is
c a l l ed ,
the
r eque s t ed s i ze i s f i r s t c ompa r ed to the s i z e o f a n I R P , a s b e fo r e .
If
t h i s c h e c k i nd i c a t e s t h a t the r e q u e s ted s i ze i s l a r g e r t h a n a n I R P ,
a
s e c o nd
c h ec k
i s now m ad e .
I f t h e r e que s t e d s i ze i s sma l l e r t h a n the
upd a ted p a c k e t s i z e but l a rg e r t h a n 8 0 % of
the
upd a ted pa c ke t s i z e
( p r e c ompu t ed b y t h e
i n i t i a l i z a t i o n c od e ) ,
t h e n a n a l l oc a t i o n i s
a t t empted f r om t h e s e c o nd l o o k a s i d e l i s t .
I f tha t l i s t i s empt y ,
the
g e n e r a l po o l a l l o c a t i o n r o u t i n e i s c a l l ed .
Wh e n a b l o c k o f memo r y i s d e a l l o c a t e d to nonpag ed
po o l ,
a chec k
is
mad e
to d e te rm i n e wh e th e r i ts a d d r e s s i s l a rg e r than the c o n t e n t s o f
E XE $G L S PL I TADR .
I f s o , t h e b l o c k i s d e a l l o c a t ed to the I /O l o o ka s i d e
l i s t (wi th a n I N S QUE i n s t r uc t i o n ) .
I f the b l o c k l i e s b e twe e n the two
bound a r i e s o f t h e s e c o nd l o o ka s i d e l i s t , then the b l o c k i s d e a l l o c a t ed
to
tha t
l i st
( w i th a n
I N S QU E
i n s t r uc t i o n to a s e c o nd l i s th e ad ) .
F- 2

VAX/VM S VE RS I ON 2 . 2 ENHANC EMENTS
F i n a l l y , i f the b l o c k i s l o c a t ed at a l o we r add r e s s t h a n
t h e s e c o nd
looka s i d e
l i st ,
then
the
block
i s d e a l l o c a ted to the g en e r a l po o l
a rea .

F. 2

CHANGE TO SUPPORT A LARGE NUMBER OF PROC ESSES

I n Ve r s i o n 2 of VM S , t h e swa p f i l e t ab l e e n t r i e s
( S FTE ,
p i c t u r ed
in
Figure 1 1-23 )
t h a t d e sc r i b ed
the
two
po s s i b l e swa p f i l e s we r e
s t a t i c a l l y a l l o c a ted wh e n t h e e x e c u t i v e wa s l i nked .
Th e
bi t map in
e ach
S F TE wa s
1 2 8 b i t s l o ng , l i m i t i ng the n umbe r o f swa p s l o t s i n a
I n a d d i t i o n , t h e s l o t c o un t wa s s to r ed
in a
g i v e n swa p f i l e to 1 2 8 .
byte .

F. 2. 1

Swa p F i l e I n i t i a l i za t i o n

Th e c h a ng ed a l l o c a t i o n s c h e m e i s i m pl eme n ted i n bo th S YS I N I T , fo r
the
d e f a u l t swa p f i l e SWAPF I L E . SYS ,
a nd
in
the
SYSGEN u t i l i t y ,
to
a c commod a te a s e c ond swa p f i l e mad e
k n o wn
to the
s ys t em wi th the
I N S TA L L/SWAPF I LE c omma n d .
Und e r
the c h a ng ed a l l o c a t i o n s c h eme , the
s wa p f i l e s i z e is d i v i d ed b y the wo r k i ng set m a x i m um ( WSMAX )
to g i v e
t h e s l o t c o un t fo r t h e s wa p f i l e b e i ng i n i t i a l i z ed .
I f the s l o t c o u n t
i s no t
l a rg e r
than
128,
n o th i ng
is
c h ang ed
f r om
the Ve r s i o n 2
i mpl em e n t a t i o n .
I f the r e i s r o om fo r mo r e t h a n 1 2 8 s l o t s i n the swa p f i l e , t h e n a n e w
s wa p f i l e t ab l e e n t r y i s a l l o c a ted f r om n o npa g ed po o l .
Th i s S F T E h a s
a n ex t end ed b i tm a p to a c commod a t e the to t a l n umber
of
slots
i n the
file.
Th e a pp r o p r i a t e
en t r y
in
t h e pag e a nd
swa p f i l e vec to r
( F i g u r e 1 1 - 2 2 ) i s upd a te d to l o c a t e the n e w S FTE .
Und e r
the
cur rent
impl em e n ta t i o n ,
t h e s e c o nd
entry
( en t r y 1)
i s upd a t ed f o r a l a rg e
SWAPF I LE . SYS a nd
the
th i r d
entry
( entry 2 )
i s upd a t ed
fo r
an
a d d i t i o na l swa p f i l e .

F.2.2

Process Li m i t s

Onc e the s l o t c o un t i s d e t e r m i n ed a nd the SFTE h a s b e e n a l l o c a t ed a nd
i n i t i a l i z ed ,
t h e uppe r
l i m i t o n t h e n um b e r o f p r o c e s s e s th a t t h e
s y s tem c a n s uppo r t ( s to r ed i n l o c a t i o n S C H$GW PROC L I M ) i s
upd a t ed
as
b e fo r e .
Th e o n l y d i f fe r e nc e
i n th i s s t ep- i s t h e n e w r a ng e th a t i s
a l l o we d b y r emo v i ng t h e l i m i t i m po s e d b y swa p f i l e s l o t c o un t .
No te tha t the p r o c e s s l i m i t i s s t i l l bo unded by t h e SYSB OOT p a r am e t e r
MAXPROC ESS CNT .
Th us ,
i n o rd e r
to c r e a t e a s ys t em th a t s uppo r t s a
l a rg e n um b e r o f p r o c e s s e s , t h r e e s t e p s m u s t b e t a k e n .
•
•
•

A l a r g e s wa p f i l e mus t b e c r e a t ed .
Cu r r e n t
s ug g e s t th a t a m ul t i v o l um e f i l e i s r e qui r ed .
MAXPROC E S S CNT m u s t b e c h a ng ed
p r o c e s s e s tha t a r e r eq u i r ed .

WSMAX s h o u l d b e k e p t
r e a so n a b l y
e f f i c i e n t u s e o f t h e swa p f i l e .

sma l l

F-3

r e f l ec t
to

d i sk

s i ze s

the

n umbe r

al low

the

of
mo s t

VAX/VMS VER S I ON 2 . 2 ENHANCEMENTS
Th e s e th r e e c h a ng e s s i mpl y r emove t h e abso l u t e l i m i t s i mpo s ed by VMS .
Othe r
s ys tem
r e so u r c e s s uc h a s phys i c a l m em o r y , pag e f i l e spa c e , a nd
o th e r s e c o nd a r y s to r ag e a r e a l so r e q u i r ed to r un a sys tem w i th a l a rg e
n umb e r o f proc e s s e s .
L i m i t s i mpo s ed by l a c k o f t h e s e r e s o u r c e s c a nn o t
b e c a l c u l a ted b u t c a n o n l y be d e t e rm i ned
by
l o o k i ng
at a
spe c i f i c
s ys tem c o n f i g u r a t i o n .
A f i n a l c omm e n t i s r e q u i r ed o n t h e a b s o l u t e l i m i t o f
8 1 92 processes
that
e x i s t s i n Ve r s i o n 2 . 2 .
Th e r e i s a n a r c h i t e c t u r a l l i m i t o f 6 5 5 3 6
p r oc e s s e s t h a t c a n ex i s t i n a VM S s ys t em .
Th i s l i m i t
is
i mpo s ed by
the
use
of
a
wo rd w i t h i n
the p r o c e s s ID as a n i nd ex i n to the PC B
v e c to r ( Ch a p t e r 1 7 ) .
Th e Ve r s i o n 2 . 2 enh a n c em e n t e x t end s
the
s wa p
s l o t c o un t wi th i n a s i ng l e swa p f i l e t o th i s a r c h i tec t u r a l l im i t .
Th e
l i m i t o f 8 1 9 2 p r o c e s s e s e x i s t s d ue to the s i ze o f i n t e r n a l
tables
in
the
S HOW
i mag e tha t i mp l em e n t s t h e SHOW/ SYS TEM c omma nd .
( Th i s l a s t
l im i t i s o bv i o u s l y a r t i f i c i a l
a nd w i l l b e e x tend ed
wh e n phys i c a l
r e so u r c e s s uc h a s m emo r y a nd d i s k s i ze r e qu i r e i t . )

F-4

INDEX

$ADJSTK
s e e Ad j us t O u t e r Mo d e
S t a c k Po i n t e r
$ADJWSL
see Ad j u s t Wo r k i ng S e t L i m i t
$A L L OC
s e e Al l o c a t e Dev i c e
$ASC EFC
s e e As s o c i a t e Comm o n Event
Fl ag C l u s t e r
$ASCTIM
s e e Conve r t B i n a r y T i m e
to ASC I I S t r i ng
$ A S S IGN
s e e As s i g n Ch a n n e l
$ B INTIM
see Conve r t AS C I I S t r i ng
to B i n a ry T i me
$ B RDC S T
s e e B r o ad c a s t
$ C ANC E L
s e e C a n c e l I /O o n Ch a n n e l
$ CANEXH
s e e C a n c e l Ex i t Ha nd l e r
$ CANT IM
s e e Ca n c e l T i m e r Reque s t
$ CANWAK
s e e C a n c e l Wa k e up
$ C LREF
see C l e a r Event F l ag
$ CM EXEC
see Ch a ng e Mo d e to
Exec ut ive
$ CMKRN L
s e e Ch a ng e Mo d e to Ke r n e l
$ C NTREG
s e e Co n t r a c t Reg i o n
$ C RE LOG
s e e C r e a t e Log i c a l Nam e
$ C REMBX
s e e C r e a t e Ma i l box
$ C REPRC
s e e C r e a te P r o c e s s
$ C RETVA
s e e C r e a t e Vi r t ua l
Ad d r e s s S pa c e
$ C RMPSC
s e e C r e a t e a nd Ma p Sec t i o n
$ DAC E FC
s e e Di s a s so c i a t e Commo n
Ev e n t Fl ag C l us t e r
$ DALLOC
see De a l l o c a t e Dev i c e
$ DAS SGN
s e e De a s s i g n Ch a n n e l
$ D C LAS T
s e e Dec l a r e AST

$ DC LCMH
see De c l a r e C h a ng e Mo d e o r
Compa t i b i l i ty Mod e Hand l e r
$ DC LEXH
see De c l a r e E x i t Ha nd l e r
$ D E LLOG
see De l e te Log i c a l Name
$ DE LMBX
see De l e te Ma i l b o x
$ D E L PRC
s e e De l e te P r o c e s s
$ D E L TVA
s e e De l e te V i r t ua l
Ad d r e s s Spa c e
$ DGBLSC
s e e De l e te G l o b a l S e c t i o n
$ D LC E FC
s e e De l e t e Commo n Eve n t
Fl ag C l us te r
$ EXIT
s e e Ex i t
$ EXPREG
see Expa nd Reg i o n
$ FAO
s e e Fo rma t t ed ASC I I Ou tput
$ FAOL
see Fo rma t ted ASC I I Ou tput
$ FORC EX
s e e Fo r c e Ex i t
$ G E TC HN
s e e G e t I /O Ch a nn e l
I n fo rm a t i o n
$ G E TDEV
see Get I/O Dev i c e
I n fo rma t i o n
$GETJ P I
s e e G e t Job/P r o c e s s
I n fo rma t i o n
$G E TMSG
see Get Me s sag e
$G ETT IM
s e e Ge t T i me
$ H I BER
see Hi bernate
$ LC KPAG
s e e Lo c k Pag e s i n Memo r y
$ L KWSET
s e e Lo c k Pag e s in Wo r k i ng S e t
$ MGBLSC
s e e Ma p G l o b a l S e c t i o n
$NUMTIM
s e e Conve r t B i n a r y T i me
to Nume r i c T i m e
$ P URGWS
s e e Pu r g e Wo r k i ng S e t
$ P UTM SG
see Put Me s sa g e

Index-1

INDEX
$QIO
s e e Q u e u e I /O Re q u e s t
$ Q I OW
s e e Que ue I/O Re q u e s t
$ READE F
s e e Re a d Ev e n t Fl ag
$ R E S UM E
s e e Re s um e P r o c e s s
$ S C HDWK
s e e S c h e d u l e Wa k e up
$ S ETAST
s e e S e t A S T Enab l e
$ S ETEF
see S e t Ev e n t F l a g
$ S ETEXV
s e e S e t Exc ept i o n Ve c to r
$ S E T IM E
s e e S e t Sys t em T i m e
$ S ET IMR
see Se t T i m e r
$ S ETPRA
s e e S e t Po we r Re c ov e r y AST
$ S ETPR I
s e e S e t Pr i o r i ty
$ S ET PRN
s e e Se t Pr o c e s s Name
$ S E TPRT
s e e S e t P r o tec t i o n o n Pag e s
$ S E T PRV
s e e S e t Pr i v i l eg e s
$ S ETRWM
s e e Se t Re s o u r c e Wa i t Mo d e
$ S ETS FM
s e e S e t Sys tem Se rv i c e
Fa i l u r e Mo d e
$ S E TSWM
s e e S e t Pr o c e s s Swa p Mod e
$ SNDACC
see S e nd Me ssag e to
Ac c o un t i ng Ma n a g e r
$ S NDERR
s e e Send Me s s ag e to
E r r o r Log g e r
$ S NDO PR
s e e S e nd Me ssag e to Ope r a to r
$ SNDSMB
s e e S e nd Me s s ag e to
Sym b i o n t Ma n ag e r
$ S US PN D
s e e S u s pend P r o c e s s
$ TRN LOG
s e e T r a n s l a te Log i c a l Name
$ U LK PAG
s e e Un l o c k Pag e s f r om Mem o r y
$ U LW S E T
s e e Un l o c k Pag e s f r o m
Wo r k i ng S e t
$ UNW IND
see Unw i nd Ca l l S t a c k

$ U PDS EC
s e e Upd a t e Sec t i o n
$WA I T FR
s e e Wa i t fo r S i ng l e
Ev e n t F l ag
$WAKE
s e e Wa k e P r o c e s s
$WFLAND
s e e Wa i t fo r Log i c a l AND
o f Even t Fl ag s
$WFLOR
s e e Wa i t fo r Log i c a l OR
o f Eve n t F l a g s

Abo r t s , 2 - 8 , 7 - 1 0
Tab l e 2-1
Ac c e s s mod e , x x x , 1 - 1 7 , 1 - 1 9 ,
3 - 1 2 , 5 - 2 to S -4 , S - 7 , 7 - 5 ,
7 - 9 , 8 - 1 6 , 8 -2 3 , 1 0- 1 1
F i g ure 1-4
F i g u r e 1 1 -7
Ta b l e 9 - 1
T a b l e 1 1 -1
a nd l og i c a l nam e s , 2 6- 1 , 2 6 -4
Ac c e s s r i g h t s b l oc k ( ARB ) ,
1 7- 3 , 1 8- 2 4
F i g u r e D- 1
F i g u r e D- 2
Tab l e 1 8-1
Ac c e s s v i o l a t i o n e x c e p t i o n ,
2 - 9 , 1 3 -3
T a b l e 2-1
Tab l e 2-2
Ac c o un t n am e , 1 7 - 1 6 , 2 0 -7 , 2 7 - 2
Ta b l e 1 7 - 2
Ac c o un t i ng i n fo rm a t i o n , 5 - 1 1 ,
1 1 - 2 , 2 7-1
Ac c o un t i ng m a n ag e r
( j ob cont r o l l e r ) , 1 9- 3 , 2 7-1
Ta b l e 1 9 - 1
AC P
s e e F i l e s- 1 1 ACP
s e e mag n e t i c tape AC P
s e e n e two r k AC P
ACP BAS E PR I O SYSBOOT p a r am e te r ,
a:: 1 9
AC P DATAC HECK SYSBOOT p a r a m e te r ,
a:: 1 9
AC P D I RCAC HE SYSBOOT p a r am e te r ,
a:: 1 8
AC P E XTCAC HE SYSBOOT pa r am e t e r ,
a::1 9
AC P E XTLIM I T SYS BOOT pa r ame t e r ,
a:: 1 9
AC P F I DCACHE S YSBOOT pa r am e t e r ,
a:: 1 9

I nd ex - 2

INDEX
ACP HDRCAC HE SYSBOOT p a r ame t e r ,
s= l a
AC P MAPCACHE SYSBOOT p a r am e t e r ,
s= l a
AC P MAXREAD SYSB OOT pa r am e te r ,
s=l 9
ACP MULT I PLE SYSBOOT
-pa r am e t e r f l ag ,
B-17
A C P QUOCACHE SYSBOOT p a r am e t e r ,
s= l 9
AC P S HARE SYSB OOT
p a r am e t e r f l ag ,
B-1 7
A C P SWAPFLGS SYS B O OT p a r ame t e r ,
s=l 9
AC P S Y SACC SYSBOOT pa r am e t e r ,
s= l 9
AC P W I N DOW SYSB OOT p a r am e t e r ,
l S- 4 , B- 1 9
ACP WORKS E T SYSBOOT pa r am e t e r ,
s= l 8
AC P WR I TEBAC K SYSB OOT p a r am e t e r ,
s= l 9
Ac t i ve and v a l i d PFN s t a t e ,
1 2-4 , 1 2- 1 9
Figure 1 1-11
Figure 1 2-3
Fig ure 1 2-4
Figure 1 2-5
F i g u r e 1 2-6
Ta b l e 1 4 -4
Ac t i v e t r a n s i t i o n p ag e , 1 2 - 1 8 ,
1 4 -2 6
Ad a p t e r c o n t r o l b l o c k ( ADP )
Figure 6-3
Ad d r e s s t r a n s l a t i o n ,
1 - 1 6 to 1 - 1 7 , 8 - 2 1 , 1 1 - 2 ,
1 2-1 , 1 2-3
Ad d r e s s t r a n s l a t i o n b u f f e r , 8 - 2 8
Ad j u s t S t a c k
s y s tem s e rv i c e ( $ ADJSTK ) ,
1 3 -3 to 1 3 - 4
Ad j u s t Wo r k i ng S e t L i m i t
s y s t em s e rv i c e ( $ ADJWS L ) ,
1 3- 1 0 to 1 3-1 2 , 1 3-1 4 , 1 8- 2 2
Ta b l e 1 3 - 1
A l l o c a t e Dev i c e
s ys t em s e rv i c e ( $ A LLOC ) ,
1 6 - 4 to 1 6 - 5
Ta b l e 2 4 - 2
ALLOC PFN
m od u l e i n s ys t em i m a g e
Ta b l e 1 4 - 3
Al te r na t e s ta r t I /O e n t r y po i n t ,
1 5-9
ALTPR I p r i v i l eg e , 9 - 1 1 , 1 7 -6
An c i l l a r y c o n t r o l p r o c e s s
s e e F i l e s- 1 1 AC P

Anc i l lary contro l proce s s ,

( cont . ) ,

s e e mag n e t i c t a pe ACP
s e e n e two r k AC P
Arg um e n t l i s t , 3 - 5 , 5 - 8 t o 5 - 9
Figure 2-3
Fig ure 2-4
F i g u re 3-2
Figure 3-6
Figure 5-2
Arg um e n t po i n t e r ( AP ) , 2 7 - 7
Ar i t hm e t i c e x c e p t i o n s , 2 - 9
Tab l e 2 - 1
T a b l e 2-2
Ta b l e 2 - 3
As s i g n Channe l
s ys t em s e rv i c e ( $ AS S I GN ) ,
1 6- 1
Ta b l e 2 4 - 2
As s o c i a t e Comm o n Ev e n t
Fl ag C l u s t e r
s ys t em s e rv i c e ( $ ASC E FC ) ,
9-1 , 9- 1 4
Ta b l e 9 - 1
A S S UM E m a c r o , A- 3
AST , 1 - 1 4 , 5 - l
e x e c u t i v e mod e , 3 - 1 2
k e r n e l mod e , 1 3 - 1 4
s pe c i a l ke r n e l mod e
s e e s pe c i a l ke r n e l AST
s upe r v i so r mod e , 2 0 - 9 , 2 0 - 1 4
u s e r mode , 9 - 1 0
AST a rg um e n t l i s t
Figure 5-2
AST c o n t r o l b l o c k ( AC B ) , 5 - 2 ,
5-4 , 5 -1 3 , 1 0- 8 , 1 8- 2 3 , D-3
Figure 5-l
AST d e l i v e r y , 3 - 1 2 , 5 - 6 , 8 - 1 5 ,
8 - 2 3 , 9-5 , 1 0-7 , 1 0 -1 1 ,
1 2-2 9 , 1 3- 3 t o 1 3 -4
Figure 1-5
Ta b l e 4 - 1
Ta b l e 2 4 - 1
A S T d e l i ve r y i n te r r up t , 8 - 1 4 , 2 4 - 5
AST d e l i v e r y s t a c k f a u l t , 2 - 1 3
Ta b l e 2 - 2
A S T e n q ue u i ng , 5 - 2 , 5 - 4 , 8 - 1 ,
8 - 1 0 t o 8 - 1 1 , 8 - 1 3 to 8 - 1 5 ,
2 4 - 5 , 2 7 - 8 to 2 7 - 9
Figure 8-5
AST ex i t pa th , 3 - 1 0 , 5 - 8
Figure 3-4
A S T l ev e l r eg i s t e r ( PR $ A S T LVL } ,
5 - l t o 5 - 2 , 5 - 5 t o 5 -6 , 8 - 2 0 ,
8 - 2 7 to 8 - 2 8 , 1 4 - 2 7
Figure 8-6
Ta b l e 7 - 1
Tab l e 2 3 - 1
A S T pa r am e t e r , 5 - 8 , 5 - 1 0
Figure 5-2

Ind ex- 3

INDEX

AST q u e ue
Figure 5-l
AS TDE L
m od u l e i n s ys t em i m ag e ,
5-4 , 5-9
Asyn c h r o n o us sys tem t r ap
s e e AS T
Atten t i o n AS T , 5 - 1 2 , 9 - 1 3 ,
1 5- 1 2 , 2 4 - 5 , 2 5-7
Au tho r i z a t i o n r ec o rd , 2 0 - 5
F i g u r e 2 0-1
Tabl e 1 3-1
AUTHOR I Z E u t i l i ty
Ta b l e 1 8 - 1
Au t o con f i g u r e o pe r a t i o n , 1 1 - 3 7
AUTOCONF I G URE SYSGEN c omma nd ,
22-9 , 22-18
Ta b l e 2 1 - 1
Ta b l e 2 2 - 3
Automa t i c r e s ta r t , 7 - 7
Au tom a t i c u s e r s t a c k e x pa n s i o n ,
2-9 , 1 3-3
Automa t i c wo r k i ng s e t
s i ze a d j u s tmen t , 5 - 4 , 5 - 1 2 ,
8 -8 , 1 3 - 1 0 , 1 3 - 1 2 , 1 8 - 2 2
Ta b l e 1 3 - 2
AWSMAX SYSBOOT pa r am e te r , 8 - 8 ,
1 3 - 1 4 , B- 1 6
Ta b l e 1 3 - 2
AWSMIN S YS BOOT pa r am e t e r , 8 - 8 ,
1 3 - 1 4 , B- 1 6
Ta b l e 1 3 - 2
AWS T I M E S YS B OOT pa r am e t e r , 8 - 8 ,
1 3 - 1 3 , B- 1 6
Ta b l e 1 3 - 2

BACKTRANS . E XE
Fi gure 1-8
Bad b l o c k h a nd l i ng , 1 5 - 1 , 1 5 - 4
Bad pag e l i s t , 1 1 -1 7
F i g u r e 1 1 -1 1
BAK PFN a r r ay , 1 1 -1 1 , 1 1 -1 6 ,
1 2-4 , 1 2- 6 , 1 2- 1 2 ,
1 2 - 1 4 t o 1 2 -1 5 , 1 2 - 1 7 , 1 2 - 2 6 ,
1 4 -1 1 , 1 4 -1 4 , 1 4 - 2 3
F i g u r e 1 1 -9
F i g ur e 1 1 -1 0
Ta b l e 1 1 - 2
BAK save a r ea i n PHD
F i g u r e 1 1 -8
Ba l a nce s l o t , 1 1 - 2 7 , 1 1 - 3 0 ,
1 4 - 1 1 , 1 4 - 2 0 to 1 4 - 2 3
F i g u r e 1 1 -2 0
Ba l a n c e s l o t a r ea , 2 5 - 1 1 , B-2 3 ,
E-l l
Figure 1-6
F i g u r e 1 2 -8

Balance s l o t area ,

( co nt . ) ,
Figure E-1
Tab l e E - 2
Ta b l e E - 3
BALS E TC NT SYSBO OT pa r am e t e r ,
1 1 - 2 7 , 1 4 - 2 0 , 2 2 - 9 , B-1 5 , E - l l
F i g u r e 1 1- 2 0
F i g u r e 1 1- 2 1
Tabl e 2 2-1
Ta b l e E - 2
BAS IC , 2 - 2
B a t c h j ob , 7 - 5 , 9-1 0 , 2 0- 1 , 2 7-1
Figure 20-2
Ta b l e 9 - 2
BJOBLIM SYSBOOT pa r am e t e r , B- 1 9
B l a c k h o l e pag e , 2 2- 1 0 , 2 3- 1 1
B L I N K PFN a r r a y , 1 1 - 1 7
F i g u r e 1 1- 9
Figure 1 1-1 3
Ta b l e 1 1 - 2
B OO T 5 8
a l te r na t e b o o t s t r a p p r o g r am ,
2 1- 5
Ta b l e 2 1 - 1
Bo o t s t r a p
s e e s ys t em i n i t i a l i za t i o n
Bo o ts t r a p c omma nd f i l e , 2 1 - 6
Bo o t s t r a p d i s k d r i ve r , 7 - 6
Boo t s t r a p I /O r o ut i ne , 2 1 - 1 4 ,
2 2-9
Ta b l e 2 2 - 1
B PT e x c ept i o n
Ta b l e 2 - 1
Ta b l e 2 - 2
B PT i n s t r uc t i o n , 2 1 - 9 , 2 1 - 1 5
B r o ad c a s t
s ys t em se r v i c e ( $ BRDC S T ) ,
1 6-1 6
B r o ad c a s t d e sc r i pto r b l o c k ( BRD )
F i g u r e 1 6 -4
B u f f e red I/O , 5 - 1 0 , 1 6 - 8
B u f f e red I /O c o mpl e t i o n , 1 6 - 9
Bug c he c k , 2 - 1 4 , 2 - 3 1 , 3 - 1 2 ,
7-1 t o 7-2 , 7-4 t o 7-5 , 7-1 2
Figure 3-5
Ta b l e 2 - 1
s e e a l so f a ta l bug chec k
BUGC HEC KFATAL S YS B OOT
pa r am e t e r f l ag ,
7 - 5 to 7 - 6 , B- 1 7
B UGC HK p r i v i l eg e , 7 - 2 , 7 - 5 ,
27-3
BUGRE BOOT SYSBOOT pa r am e te r f l ag ,
7-4 , 7 - 7 , 2 1 - 2 , 2 3-6
Bus r e que s t ( BR ) l evel o n UN I B US ,
6-7
B u s r e q u e s t r ec e i v e vec to r
r eg i s t e r ( BRRVR ) , 6- 1 0 , 2 3 - 1 1
Fi gure 6-3
Byt e i nd ex , x x x i

I nd ex- 4

INDEX

Chann e l a s s ignment ,

( cont . ) ,

r em o t e d ev i c e , 1 6 - 2 t o 1 6 - 3
s po o l ed d ev i c e , 1 6 - 2 t o 1 6 - 3
C a l l f r ame , 2 - 1 , 3 - 4 to 3 - 5 ,
Channel control bloc k ( CCB) ,
5-8 , 1 7-1 8 , 2 0-1 3
5-1 0 , 9-1 5 , 1 6- 1 , 1 6-9
Figure 2-3
Figure 1 1-7
Figure 2-5
F i g u r e 1 6-1
Figure 2-6
F i g u r e 1 6-3
Figure 2-7
Ch a nn e l c on t r o l b l o c k t a b l e
Figure 2-8
F i g u r e 1-7
Figure 3-2
Ta b l e E - 4
Figure 3-6
C h a n n e l d e a s s i g nm e n t , 1 6 - 3
C a l l f r am e c ond i t i o n h a nd l e r ,
Ch a nn e l r eque s t b l o c k ( C RB ) ,
2-18
6 - 7 , 6 - 1 0 to 6 - 1 1
CALLG i n s t r uc t i o n , 5 - 8
Figure 6-3
C a l l i ng mecha n i sm , 1 - 1 0
Figure 6-4
C a l l i ng s t and a rd
Figure 6-5
s e e p r o c ed u r e c a l l i ng s t a nd a rd
F i g u r e 6 -7
CALLx i n s t r uc t i o n , 3 - 1 6
C HANN E LCNT s pe c i a l
Figure 3-2
SYSB OOT pa r am e te r ,
Figure 3-3
B-1 5 , E-1 7
Figure 3-6
C h a r ac t e r d a t a type , 1 - 1 1
C a n c e l I /O o n Ch a nn e l
C h a r a c t e r s t r i ng i n s t r uc t i o n s ,
s y s t e m s e rv i c e ( $ CANC E L ) ,
1-11
1 6- 4 , 1 6- 1 0
C HM E e x c e p t i o n , 1 - 1 4 , 1 - 1 8 ,
C a n c e l T i m e r Re que s t
2 - 7 to 2 - 8 , 3 - 4 , 3- 1 7 , 2 0 - 5
s y s tem s e rv i c e ( $ CANT I M ) ,
Ta b l e 2 - 1
1 0 - 1 0 to 1 0 - 1 1 , 1 8 - 2 2
C a n c e l Wa k e up
C HM E e x c e pt i o n d i spa tc he r ,
s ys tem s e rv i c e ( $ CANWAK ) ,
3 -1 0 , 3-1 3
1 0 -1 0 , 1 0 -1 2
Figure 3-4
C HM E i n s t r uc t i o n , 1 - 1 1 , 1 - 1 8 ,
Ta b l e 9 - 1
3 - 1 , 3 - 4 , 3- 1 6
C a r d r e a d e r d r i ve r
Figure 3-1
Figure 20-2
Figure 3-6
u n so l i c i ted i nput , 2 0 -1 , 2 0 - 4
C HMK e x c e pt i o n , 1 - 1 4 , 1 - 1 8 ,
CAS EW i n s t r uc t i o n , 3 - 5 , 3 - 1 0
2 - 7 , 3 - 4 , 3-1 0 , 3 - 1 7
Figure 3-2
Ta b l e 2 - 1
Figure 3-4
C HMK e x c e pt i o n d i spa tc h e r ,
Figure 3-6
3-1 0 , 3-1 3 , 5-8
C a t c h a l l c ond i t i o n h a nd l e r ,
Figure 3-4
2 - 1 8 , 2 - 3 0 , 1 7 - 1 8 to 1 7 - 1 9 ,
C HMK i n s t r uc t i o n , 1 - 1 1 , 1 - 1 8 ,
20-1 3 , 27-7
3 - 1 , 3 - 4 , 3- 1 6
Cha ng e m o d e d i spa tch e r , 3 - 4 , A-6
Figure 3-1
Figure 3-2
C HMS e x c e p t i o n , 2 - 8 , 2 - 1 3 , 3 - 4
Figure 3-4
Tab l e 2-1
Change mode except i ons
Ta b l e 2 - 2
s e e C HMx e x c e p t i o n s
Ch a nge mode h a nd l e r , 1 8 - 2 3
C HM S e x c ep t i o n h a nd l e r , 3 - 4
C HMU e x c e pt i o n , 2 - 8 , 2 - 1 3 , 3 - 4
C h a nge mode i n s t r uc t i o n s
Ta b l e 2 - 1
s e e C HMx i n s t r uc t i o n
Ta b l e 2 - 2
Ch a ng e Mo d e t o Ex e c u t i v e
C HMU e x c e p t i o n h a nd l e r , 3 - 4
s ys tem s e rv i c e ( $ CMEXE C ) ,
C HMx ex c e p t i o n s , 2 - 7
2 - 3 1 , 3- 1 8 , 2 0 - 5 , A- 1 4
C HMx i n s t r uc t i o n , 1 - 1 1 , 3 - 4 ,
Ch a ng e Mo d e t o Ke r n e l
3-1 3 , 8-1 6 , 8 - 1 8
s ys t em s e rv i c e ( $ CMKRN L ) ,
F i g u r e 1 -4
2 - 3 1 , 3 - 1 8 , A- 1 4
Figure 3-2
C h a ng e -mod e- t o - s upe r v i s o r hand l e r ,
Figure 3-9
2 0-9
C l e a r Eve n t Fl ag
Figure 20-3
sys tem s e rv i c e ( $ C LR E F ) ,
Ch a nn e l a s s i g nm e n t , 1 6 - 1
9-7
n e two r k d ev i c e , 1 6 - 2 t o 1 6 - 3

I nd e x - 5

I NDEX

C LI
s e e c omma nd l a ng uag e i n t e r p r e t e r
s e e DC L c omma nd l a ng uag e
i n t e r p r e te r
s e e MCR c omma nd l a ng uag e
i n te r p r e t e r
C L I d a ta
F i g u r e 1-7
Tab l e E-4
C L I i mag e
Figure 1-7
Tabl e E-4
C L I s ymbo l t a b l e
F i g u r e 1-7
Tab l e E-4
C L I S YMTBL S Y S B O OT p a r am e t e r ,
2 0 - 7 , B- 1 7 , E - 1 7
Tab l e E-4
C l ock t i c ks , 8 - 5
C l u s t e r s i ze , 1 2- 2 0 t o 1 2 - 2 1 ,
1 2- 2 5 t o 1 2- 2 7
Tab l e 1 2-1
C l us te r ed r e ad , 1 2 - 1 9 t o 1 2 - 2 0
C l u s t e r ed w r i te , 1 2 - 2 0
CMEXEC p r i v i l eg e , 3 - 1 8 , 1 8 - 1 1
CMKRNL p r i v i l eg e , 3 - 1 8 , 6 - 1 5 ,
1 8- 1 1
Tab l e 2 2-3
CMODS SDS P
mod u l e i n s ys t em i m ag e ,
3 - 5 , 3 - 1 6 to 3 - 1 7 , 5 - 9
F i g u r e 3-4
C OB O L S TO P s t at em en t , 2 0 - 1 5
Co l d s t a r t
s e e s ys t e m i n i t i a l i z a t i o n
Co l l i d ed p ag e , 1 1 - 1 7 , 1 2 - 2 4 ,
1 2- 3 0
Figure 11-12
Co l l i d ed p a g e wa i t s t a t e ( C O L PG ) ,
8 - 1 1 , 8 - 1 5 to 8 - 1 6 , 8 - 2 7 ,
1 2- 3 0 , 1 3- 5
Figure 8-5
Ta b l e 8 - 1
Tab l e 1 4-2
C OMDRVS UB
mod u l e in s ys tem i m ag e , 5 - 1 3
C omma nd l a ng uag e i n t e r p r e t e r ;
1 - 6 , 2 -1 3 , 2- 3 0 , 3-4 , 1 8 -3 ,
2 0-7 , 2 2 -1 7
F i g u r e 1-2
F i g u r e 1-4
Figure 20-3
Figure 2 0-4
T a b l e 2 1 -1
c omma nd p r o c e s s o r , 2 0 - 1 1 ,
2 0 -1 4
F i g u r e 2 0-3

Command l angu ag e interpr eter ,

( cont . ) ,

m a pp i ng i n to P l s pa c e , 2 0 - 1 ,
2 0 - 5 t o 2 0 -6 , 2 2 -1 5 , E-1 7
F i g u r e 1-7
F i g u r e 2 0-1
F i g u r e 2 0-2
Ta b l e E - 4
C ommon e v e n t b l oc k ( C E B ) , 8 - 1 4 ,
9-1 , 9-7
Figure 9-2
Figure 9-3
mas t e r CEB , 1 1-4 2
Figure 9-4
Figure 9-5
s l av e C E B , 1 1 - 4 2
Figure 9-4
Figure 9-5
C o mmon e v e n t b l o c k l i s t
Ta b l e 8 - 2
C ommon e v e n t b l o c k l i s t m u t ex
Ta b l e 2 4 - 2
C ommon e v e n t f l ag , 9 - 1 , 9 - 6 ,
9 - 8 , 9 - 1 3 to 9 - 1 4
i n sha r ed m emo r y , 9 - 7 ,
9- 1 4 t o 9 -1 5 , 1 1- 3 5 , 1 1-4 2
Figure 9-5
Figure 1 1- 2 5
C ommo n e v e n t f l ag c l u s t e r , 9 - 6
C o mmon e v e n t f l ag wa i t q ue u e s
Figure 9-3
Figure 9-4
C ommon e v e n t f l ag wa i t s ta t e ( C E F ) ,
8 - 9 , 8 - 1 5 , 9 - 5 to 9 - 6
Figure 8-5
Ta b l e 8 - 1
Ta b l e 1 4 - 2
C o mpa t i b i l i ty mod e , A - 9
s e e a l s o RSX- l lM AME
C ompa t i b i l i ty m o d e d a ta pag e ,
B-27
Figure 1-7
Ta b l e E - 4
Compa t i b i l i ty m o d e e x c e p t i o n ,
2-1 3 , 1 8-1 5
Tab l e 2 - 1
Tabl e 2-2
Compa t i b i l i ty m o d e h a nd l e r ,
1 8- 2 3
Compa t i b i l i ty m o d e i m ag e , 1 - 2 4 ,
1 8- 2 , 1 8 - 5 , 1 8-1 5
Figure 1-8
C o mpu t a b l e o u t swa pped p r o c e s s ,
8-8
Compu t a b l e o u t s wa pped
s c h ed u l i ng state ( C OMO ) ,
8 -9 , 1 4 -4
Figure 8-5
Tab l e 8 - 1

I nd ex - 6

I NDEX

Conve r t ASC I I S tr i n g , ( co nt . ) ,
Compu t a b l e r e s i d en t
s c h ed u l i ng s t a t e ( C OM ) ,
s ys tem s e rv i c e ( $ B I N T I M ) ,
8 - 9 , 8 - 2 2 to 8 - 2 3
2 7-1 1
Figure 8-5
C o nv e r t B i n a r y T i m e
Ta b l e 8 - 1
to AS C I I S t r i ng
s y s t em s e rv i c e ( $ ASCT I M ) ,
Ta b l e 1 4 - 2
2 7- 1 1
Compu t a b l e s t a t e q ue u e h e ad e r s
Fi gure 8 -3
Co nve r t B i n a r y T i m e
Compu t e - bo und p r o c e s s , 8 - 5
to Num e r i c T i m e
Cond i t i o n hand l i ng f a c i l i ty , 2 - 1
s ys t em s e rv i c e ( $ N UMT IM ) ,
Cond i t i o n s , 2 - 1
27-1 1
s ee a l so except i o n s
Co py-on- r e f e r e n c e pag e , 1 1 - 4 ,
CONNEC T C ONSOLE SYSGEN c omma nd ,
1 1 - 1 6 , 1 2-3 , 1 2-8
1 5 - 1 8 to 1 5 - 1 9
Figure 1 2-4
C ONNEC T S Y SGEN c omma nd , 1 5 - 2 ,
F i g u r e 1 2-7
2 5- 1 3
C o py-o n - r e f e r e n c e s ec t i o n
Connec t - to - i n t e r r up t m e c h a n i sm ,
F i q u r e 1 1 -7
Figure 18-2
6-1 5
C PU t i m e l i m i t ex p i r a t i o n , 8 - 8
Figure 6-7
Ta b l e 1 4 -3
C ONSOL . S YS , 1 5 - 1 6 , 2 1 - 6 , 2 3 - 4
C PU-d e pe nd ent r o u t i n e ,
Ta b l e 2 1 - 1
2 1 - 1 6 to 2 1 - 1 7 , 2 2 - 9 , 2 2 - 1 1 ,
Con so l e b l o c k s to r ag e d ev i c e ,
1 5 - 1 8 , 2 1 - 5 to 2 1 - 6
A-1 5 t o A- 1 6 , B-1 3
f l o ppy d i s k , 1 5 - 1 6 , 1 5 - 1 9
Figure 22-3
TU58 c a r tr idge , 1 5-1 6 , 1 5-1 8 ,
Ta b l e 2 1 -4
2 1-5
Ta b l e 2 2 -1
Conso l e i n te r f a c e , 1 5 - 1 6
CRDENAB LE SYSBOOT p a r am e t e r f l ag ,
Conso l e p r og r am
B-1 7
Figure 2 1-1
C r e a t e a nd Ma p Sec t i on
C o n so l e t e rm i n a l , 1 5 - 1 8 , 2 2 - 1 0 ,
s ys t em s e rv i c e ( $ C RMPS C ) ,
9 - 1 4 , 1 1 -2 0 , 1 1 - 2 7 , 1 1 - 4 0 ,
B-2
1 2 - 6 , 1 2 -2 4 , 1 3 - 6 , 1 3 - 8 ,
F i g ure 1 5-1
1 8- 8 , 1 8-1 2
C o n t e x t i nd e xed ad d r e s s i ng ,
C r e a t e Log i c a l Name
xxxi , 1- 1 1 , 4-5
s ys t em s e rv i c e ( $ C R E LOG ) ,
Con tex t s w i tch , 8 - 2 0 , 1 4 - 2
2 6- 4
C ONT INUE c omma nd , 2 0 - 1 6
C r e a t e Ma i l box
F i g u r e 2 0-3
s y s t em s e rv i c e ( $ CREMBX ) ,
C ON T INUE S YSGEN c omma nd , 2 2 - 2 3
9 - 1 4 to 9 - 1 5 , 1 6 - 1 1
F i g u r e 2 2 -4
F i g u r e 2 2-5
C r e a t e P-r o c e s s
Ta b l e 2 2 -3
s ys t em s e rv i c e ( $ C R E PRC ) ,
Co n t i n u i ng f r om a n ex c e pt i o n ,
8 - 4 , 1 7 - 1 , 2 0 - 4 to 2 0 - 5
2-2 , 2-2 3
Figure 17-1
C o n t r a c t Reg i o n
Ta b l e 9 - 1
sys tem s e rv i c e ( $ C NTREG ) ,
Ta b l e 9 - 2
Ta b l e 1 3 - 1
1 3-5
Con t r o l mechan i sm s , x x v i i i
Tab l e 1 7- 1
Con t r o l r eg i o n , 1 - 2 2 , 5 - 1 1 , 1 7 - 1
C r e a te Vi r t ua l Add r e s s Spa c e
Fi gure 1-1
s ys tem s e rv i c e ( $ C R E TVA ) ,
Fig ure 1 7-1
1 2- 1 0 , 1 3-2 , 1 8- 8
F i g ure 1 7-6
C TR L/C , 5 - 1 5
see a l so Pl space
C TR L/Y , 5 - 1 5 , 1 8 - 1 7 , 2 0 - 9 ,
Con t r o l l e r i n i t i a l i z a t i o n r o u t i n e ,
2 0-1 4 , 20-16
2 3 -7
C TR L/Y A S T , 5-1 5
Conve r sa t i o n a l b oo t s t r a p ,
F i g u re 20-3
2 1-1 7 , 22-21
C u r r en t p r o c e s s
Ta b l e 2 1 - 2
s c h ed ul i ng s t a t e ( C UR )
C o nve r t ASC I I S t r i ng
Fig u r e 8-5
to B i n a ry T i me
Tab l e 8 - 1

I nd ex - 7

I NDEX

D a t a s t r uc t u r e d e f i n i t i o n s ,
xx i x
DC L c o mmand l a ng uag e i n te r p r e t e r ,
3-4 , 20-9
Tabl e 1 -1
D e a l l oc a te Dev i c e
s y s tem s e rv i c e ( $ DALLOC ) ,
1 6 - 4 to 1 6 - 5 , 1 8 - 2 2
D e a s s i g n Ch a n n e l
s y s tem s e rv i c e ( $ DA S SGN ) ,
1 6- 3 , 1 8 - 2 1
D e bug b oo t s t r a p
s e e Imag e S t a r tup
DEBUG c omma nd , 2 - 1 3 , 2 - 3 0 ,
1 8 - 1 7 , 2 0 -1 6
F i g ur e 2 0-3
D E BUG e x c e pt i o n ( S S $_D EBUG ) ,
2-1 3
Tabl e 2-2
D e bug g e r , 1 - 2 4 , 2 - 3 0 , 1 3 - 1 6 ,
1 8 - 1 , 1 8 - 1 6 to 1 8 - 1 7
F i g u r e 1-8
D e b ug g e r s ymbo l t a b l e
F i g u r e 1-7
Tabl e E-4
D e c ima l o v e r f l ow e x c ep t i o n
Ta b l e 2 - 3
Dec l a r e AST
s ys tem s e rv i c e ( $ DC LAS T ) ,
5-1 , 5-4 , 5-8
D e c l a r e Ch a ng e Mo d e o r
Compa t i b i l i ty Mo d e Ha nd l e r
s ys tem s e rv i c e ( $ DC LCMH ) ,
2-1 3 , 3-4
D e c l a r e E r r o r Log Ma i l bo x
s y s tem s e rv i c e ( $ D E R LMB ) ,
7 - 3 to 7 - 4
D E Cn e t , 1 5 - 1 1
D e f a ul t d i r e c to r y s t r i ng ,
1 7-1 6 , 2 0 -7
Ta b l e 1 7 - 2
D E FBOO . CMD , 2 1 - 6 to 2 1 - 7
D E FMBXB UFQUO SYS BOOT p a r am e t e r ,
1 6 - 1 1 , B- 1 6
D E FMB XMXMSG S YS B OOT p a r am e t e r ,
1 6 - 1 2 , B- 1 6
D E FMB XN UMMSG S Y S B O OT p a r am e t e r ,
B-1 6
D E FPR I S YS B OOT pa r am e t e r , 1 4 -4 ,
B- 1 9
D e l e t e Comm o n Ev e n t F l ag C l u s t e r
s ys t em s e rv i c e ( $ D LC E FC ) ,
9-2
Tabl e 9 - 1
D e l e t e G l o b a l Sec t i o n
s ys tem s e rv i c e ( $ DGB LS C ) ,
1 1-2 0 , 1 3-9

D e l e t e Log i c a l Name
s ys tem s e rv i c e ( $ D E L LOG ) ,
1 8- 2 3 , 2 6-4
D e l e t e Ma i l box
s ys t em s e rv i c e ( $ D E LM B X ) ,
1 6-1 6
De l e te Process
s ys tem s e rv i c e ( $ D E L PRC } ,
5 - 1 1 , 1 9 - 1 , 1 9- 6 ,
2 0 - 8 to 2 0 - 9 , 2 4 - 9
Ta b l e 9 - 1
Ta b l e 9 - 2
De l e t e Vi r t ua l Ad d r e s s Spa c e
s ys tem s e rv i c e ( $ D E LTVA ) ,
1 3 -5 , 1 9- 5
Demand z e r o pag e , 1 1 - 7 , 1 2 - 3 ,
1 2- 1 0 , 1 3-2
F i g u r e 1 1-3
F i g u r e 1 2-4
Demand ze r o pag e ( g l o ba l ) , 1 1 - 2 3
Demand z e r o s ec t i o n , 1 8 - 8
F i g u r e 1 1 -7
F i g ur e 1 8-2
F i g u r e 1 8-4
D e pth a rg um e n t i n m e c h a n i sm a r r a y ,
2-1 8
Figure 2-5
D E TAC H p r i v i l eg e , 1 7 - 1
Tab l e 1 7 -3
D ev i c e a l l o c a t i o n , 1 6 - 5
D ev i c e d e a l l o c a t i o n , 1 6 - 5
De v i c e d r i v e r , 1 - 4 , 2 - 3 1 ,
4 - 2 to 4 - 4 , 4 - 7 , 5 - 1 4 , 6 - 7 ,
7 - 1 , A- 1 6
F i g u r e 1 - 2·
Figure 1-5
Figure 6 -3
F i g u r e 6 -4
Tab l e 2 2 -3
De v i c e e r r o r s , 7 - 1
D ev i c e i n t e r r upt s e r v i c e r o u t i n e ,
1- 1 5 , 4 - 4
Figure 1-5
De v i c e t i me o u t , 1 0 - 4 , 1 0 - 1 0
D I AGN O S E p r i v i l eg e , 7 - 4
D i ag n o s t i c s upe r v i so r , 2 1 -8 ,
21-1 1
Tab l e 2 1 - 2
D IALTYPE SYS BOOT p a r am e t e r , B - 1 7
D i r e c t I /0 , 5 - 1 0 , 1 6 - 8
D i r e c t I /O c om p l e t i o n , 1 6 - 8
D i r e c t I /O c o un t , 1 3 - 5 , 1 4 - 8 ,
1 4 -1 4
D i r e c t l y v e c to r ed
UN IBUS d ev i c e i n te r r upts ,
6-7
Figure 2-1
Figure 6-2

I nd e x - 8

INDEX

ERRFMT proc e s s , ( co nt . ) ,
D i s a s so c i a t e Common Eve n t
Fl ag C l us t e r
wa ke up c a l l , 7 - 3
s ys tem s e rv i c e ( $ DAC EFC ) ,
E RRLOG . SYS
9-2 , 1 8- 2 2
s e e e r r o r l og f i l e
D i s k d r iver , 1 5-1
E r r o r c o d e c o r r ec t i o n ( EC C ) ,
D I SMOUNT
1 5 - 1 t o 1 5 -2
s e e v o l um e d i smo un t u t i l i ty
E r r o r l og e n t r y , 7 - 1 1 t o 7 - 1 2 ,
D i s pl a c em e n t m o d e a d d r e s s i ng ,
2 3-1 1
A-2
Ta b l e 7 - 1
D I S PLAY u t i l i t y , 1 - 7 , 8 - 3 , E - 1 7
E r r o r l og f i l e , 7 - 1 , 7 - 3
Ta b l e 1 - 1
E r r o r l og ma i l box , 7 - 3 , 1 8 - 2 2
s ta t i s t i c s , B - 4 , B- 1 2
E r r o r l og m e s s a g e b u f f e r , 7 - 7 ,
DM C- 1 1 c ommun i c a t i o n s d ev i c e ,
7 - 9 , 2 7 - 3 to 2 7 - 4
1 5- 1 2
E r r o r l og r epo r t g e n e r a to r ( S Y E ) ,
F i g u r e 1 5 -3
7-1 , 7- 3 , 27-3
Do ub l e m a pp i ng of I /0 b u f f e r pag e s E r r o r l og r o ut i n e s , 2 4 -4 ,
1 5- 1 9
2 7 - 3 to 2 7 -4
DR 3 2
E r r o r l ogg i ng , 6- 1 0 , 7 - 1 ,
Ta b l e 6 - 1
7 - 6 to 7 - 7 , 2 7 - 3
DR 3 2 i n t e r r upt s e r v i c e r o u t i n e ,
Ta b l e 2 - 2
6-1 3
E s t a b l i sh i ng a c o nd i t i o n h a nd l e r ,
Figure 6-5
2-2 , 2-1 6
DR 7 8 0 i n t e r f a c e
Ev en t f l ag , 8 - 1 , 9 - 1 ,
Ta b l e 2 2 -2
9- 1 3 to 9 - 1 4 , 1 0 - 1 0 , 1 2 - 2 9
D S B INT m a c r o , 2 4 -1 , A- 1 3
s e t t i ng , 1 0 - 8 , 1 6 - 9 , 2 4 - 7 ,
Figure 24-1
2 7 - 8 ' 2 7 -1 0
Dump f i l e , 7 - 7 , 2 2 -1 3 , 2 2 - 1 6
Even t f l ag wa i t , 1 6 -6
Ta b l e 2 1 - 1
Ev e n t f l ag wa i t ma s k , 8 - 1 0
Dum p f i l e h ead e r b l o c k , 7 - 7 , 7 - 9
E v e n t f l ag wa i t s t a t e s , 9 - 4
Ta b l e 7 - 1
Ev e n t f l ag wa i t s y s t em s e rv i c e s
DUM PB UG SYS BOOT pa r am e t e r f l ag ,
( $WA I TFR , $WFLAND , o r $WFLOR) ,
7 - 4 , 7 - 7 , B- 1 7
9-4
Dyn am i c m em o r y a l l o c a t i o n ,
E XC E PT I ON
x x i x , 1 - 6 , 1 - 2 1 , 2 5 -1
m od u l e i n s ys t em imag e ,
F i g u r e 2 5 -1
2-1 2 , 2- 1 4 , 27-4
F i g u r e 2 5-2
Ta b l e 2 - 2
Dyn am i c m emo r y d e a l l o c a t i o n ,
Ex c ept i o n d i s pa tch e r , 3 - 4
2 5- 2
Ex c e pt i o n hand l e r , 1 8 - 2 3
Fig u re 2 5 -1
e x ec u t i v e mode , 2 0 -6
F i g u r e 2 5 -3
E x c ept i o n n ame
Dyn am i c S Y S B OOT pa r am e t e r s ,
F i g u r e 2-2
1 3-1 2 , 22-2 5
E x c e p t i o n se rv i c e r o u t i n e ,
1 -1 2 , 1-1 5
Ex c ept i o n v e c t o r s , 2 - 1 7
E
Ex c e pt i o n s , 1- 1 4 , 1 - 1 7 , 2 - 1 ,
7-1 , 7-9
Emp t y pag e s i n the p r o c e s s h e ad e r ,
F i gure 1-5
1 1-1 1
F i g u r e 2-1
F i g u r e 1 1 -1
see a l so c o nd i t i o n s
ENB INT m a c r o , 2 4 -1
Ex c l u s i v e wr i t e r f l ag
Figure 24-1
to $ U PDSEC s ys tem s e rv i c e ,
En t r y ma s k , 3 - 1 , 3 - 5 , 5 - 8
Figure 3-1
1 3-1 0
Figure 3-9
EXE $ E XCMSG
Ta b l e 2 - 3
r o u t i ne i n s ys t e m i m ag e ,
ERRFMT p r o c e s s , 7 - 1 t o 7 - 4 ,
2 7 - 4 , 2 7 -7
E XE $NAM P I D
2 2-1 3 , 2 2 -1 7 , 24-4 ,
2 7 - 3 to 2 7 -4
r o u t i ne i n s ys t em imag e ,
Ta b l e 1 - 1
9 - 8 , 1 7 - 1 2 , A- 1 2 , A- 1 4
Execut ive , x xx i
Ta b l e 2 1 -1

I nd ex - 9

INDEX

F L I N K PFN a r r a y , 1 1 - 1 7
Ex e c u t i v e a c c e s s m od e , 3 - 1
F i g u r e 1 1 -9
Figure 1-4
F i g u r e 1 1 -1 3
Ta b l e 3 - 1
Ta b l e 1 1 - 2
Ex e c u t i v e d a ta a r e a s , x x i x
F l o a t i ng ove r f l o w e x c ep t i o n
Ex e c u t i v e mode e x c e p t i o n , 2 - 3 1
Ta b l e 2 - 3
E x e c u t i v e s tac k
F l o a t i ng und e r f l o w e x c ep t i o n
Figure 1-7
Ta b l e 2 - 3
Ta b l e E - 4
F l o a t i ng / d e c i m a l d i v i d e b y z e r o
Ex i t
except ion
s ys tem s e rv i c e ( $ E XI T ) ,
Ta b l e 2 - 3
7 - 5 , 9 - 1 0 , 1 7 -1 9 , 2 0 - 6 ,
Fo r c e Ex i t
2 0 - 9 , 2 0 -1 4 , 2 0 -1 6
s ys tem s e rv i c e ( $ F ORC EX ) ,
Figure 20-3
5-4 ' 5-1 2 , 9-1 0
Tabl e 9-1
Tab l e 9-1
E X I T c o mmand , 2 0 -1 6
Ta b l e 9 - 2
F i g u r e 2 0-3
Fo r k b l oc k ( FKB } , 5 - 1 3 , 2 4 - 5 ,
E X I T S Y S G E N c omma nd , 2 2 - 2 3
D- 5
Ta b l e 2 2 - 3
Figure 4-2
E x pa nd Reg i o n
Figure 6-3
s ys t em s e rv i c e ( $ E XPREG } ,
Fo r k d i s pa tc h i ng , 5 - 1 3
1 2 - 1 0 , 1 3 - 2 to 1 3 - 3 , 1 3 - 6 ,
Tab l e 4 - 1
1 8-1 1
Fo r k pr oc e s s i ng , 1 - 1 5 ,
E x te r n a l ad a pte r , 2 1 - 7 , 2 1 - 9 ,
4-3 to 4 - 5 , 2 4 - 3 , 2 4-6
2 2 -1 , 2 2-8 , 2 2-1 0 , 2 3-6
Figure 1-5
E XTRAC PU S YS B OOT p a r am e t e r ,
Fo r k que ue , 4 - 5 , 2 4 - 5
8-8 , B-1 6
E XUS RSTK s pe c i a l SYSBOOT pa r am e t e r Fo rma t ted AS C I I O u t p u t
s ys tem s e rv i c e ( $ FAO ) ,
B- 1 5 , E - 21
27-7 , 27-11
Tab l e E - 4
Fo rma t t i ng s uppo r t , 2 7 -1 0
F ORTRAN , 2 - 2
F ORTRAN PA US E s t a tem e n t , 2 0 - 1 5
F
F r am e po i n t e r ( FP ) , 1 7 - 1 8 , 2 0 - 1 3
F r e e pag e a v a i l a b l e s ys t em e v e n t ,
FAB ( F i l e Ac c e s s B l o c k ) , 3 - 1 2
8-1 6
Fac i l i ty c o d e s , 2 7 - 6 , C- 9
F
r
e
e pag e l i s t , 8 - 1 1 , 1 1 - 7 ,
Fa t a l b ug c h e c k , 7 - 5 , 8 - 2 3 ,
1 1 -1 4 , 1 1- 1 7 , 1 2-4 , 1 2-6 ,
2 3 -6 , 2 4 - 6 , A- 1 4
1 2 -1 0 , 1 2 - 1 5 , 1 4 - 2 0 , 1 4 - 2 4
F i g u r e 8 -7
F i g u re 1 1 -1 1
Ta b l e 1 5 -1
Figure 1 1-1 3
Fa u l ts , 2-8 , 2 - 2 3 , 8 - 1 6
Figure 1 2-3
Ta b l e 2 - 1
Figure 1 2-5
Ta b l e 2 - 3
Figure 1 2-6
FDT r o u t i n e , 4 - 2 , 4 - 7 , 1 1 - 3 4 ,
F
r
e
e
pag e wa i t s t a t e ( FPG ) ,
1 5 -4 , 1 6 -7 , 2 4 - 7
8 - 1 1 , 8 - 1 5 to 8 - 1 6 , 8 - 2 7 ,
F i g u r e 1 5 -1
1 2-3 0
FFS i n s t r uc t i o n , 8 - 2 6
Figure 8-5
F i g u r e 8 -7
Tabl e 8 - 1
F i l e sys tem ( U I C ) p r o t e c t i o n ,
Ta b l e 1 4 - 2
1-20
FRE
E
L I M SYSB OOT p a r am e t e r ,
Ta b l e 1 - 1
1
4
1 , 1 4 - 4 , 2 2 - 1 0 , B- 1 7 , E - 1 6
F I LE READ
Ful l d upl ex t e rm i n a l o pe r a t i o n ,
m od u l e i n s ys t em i m ag e ,

21-1 4
F i l e s- 1 1 , 2 1 - 8 , 2 1 - 1 4
F i l e s- 1 1 ACP , 1 - 6 , 4 - 3 , 1 5 - 1 ,
1 5 - 4 to 1 5 - 5 , 1 8 - 2 , 2 1 - 1 4 ,
2 2-1 3 , 2 2 - 1 7 , 2 4 - 7
Ta b l e 1 - 1
Ta b l e 2 1 - 1
Ta b l e 2 4 -2

G B L PAG E S SYSBOOT pa r am e te r ,
B-1 4 , E-l l
G B LS ECT I ONS SYSBO OT p a r am e te r ,
B-1 4 , E -l l
Ta b l e E - 2

I nd ex - 1 0

INDEX

G e n e r a l p u r po s e r eg i s te r s ,
8 - 2 0 , 8 - 2 7 to 8 - 2 8
Figure 8-6
Ta b l e 7 - 1
Ta b l e 2 3 - 1
G e t I /O Ch a n n e l I n f o rma t i o n
s ys t em s e rv i c e ( $ G E TC HN ) ,
1 6- 1 9
G e t I /0 Dev i c e I n fo rma t i o n
s ys t em s e rv i c e ( $ G ETDEV) ,
1 6-1 9
G e t Job/ P r o c e s s I n f o rma t i o n
s ys t em s e rv i c e ( $G E TJ P I ) ,
5-l , 5-4 , 5- 1 1 , 9-1 , 9-6 ,
1 8- 2 1 , 2 7 -7
Ta b l e 9 - 1
s e e a l s o imag e c o un t e r
wi l d c a rd s uppo r t , 2 7 - 1 0
G e t Me s s ag e
s ys t em s e rv i c e ( $ G E TM SG ) ,
27-4 , 2 7-6
Get Time
s ys t em s e rv i c e ( $ G E TTIM ) ,
1 0 -4
G l o b a l p ag e , 1 1 - 1 ,
1 1 - 1 9 to 1 1 - 2 0
a nd i n swa p , 1 4 - 2 5
and o u t swa p , 1 4 - 1 4
a nd pag e f a u l t s , 1 2 -1 2 , 1 2 - 1 5
c o py-o n- r e f e r e nc e , 1 2 -1 0 ,
1 2-1 6
r ead-only
Figure 1 1-1 2
r e ad/wr i t e
Figure 1 1-1 2
G l o b a l p ag e t ab l e , 1 1 - 4 ,
1 1 - 2 3 to 1 1 - 2 6 , 2 5 -1 1 , B - 2 3
Figure 1-6
Figure 1 1-1 7
Figure 1 1-18
Figure 1 1-19
F i g u r e 1 4 -2
Figure 1 4-3
Fig ure 1 4 -4
Figure 14-5
Figure 1 4-6
F i g u r e 1 4 -7
F i g u r e E-1
Tab l e 1 2- 1 1
Ta b l e E - 2
Tab l e E-3
G l o b a l pag e t ab l e e n t r y , 1 1 - 4 ,
1 1 - 2 3 , 1 1 - 2 5 to 1 1 - 2 6 , 1 2 - 1 2 ,
1 2- 1 5 , 1 2-1 7 , 1 3-7 , 1 3- 9 ,
1 4 -2 6
Figure 1 1-17
F i g u r e 1 1- 1 8
Figure 1 1-19

( co nt . ) ,
F i g u r e 1 2 -4
F i g u r e 1 2-6
F i g u r e 1 2 -7
F i g u r e 1 8-5
Ta b l e 1 4 - 5
G l o b a l pag e t a b l e i nd e x , 1 1 - 4 ,
1 1 - 2 6 , 1 2- 1 2 , 1 2-1 5 , 1 2-1 7 ,
1 3-7 , 1 3-9 , 1 4 - 2 5 to 1 4 -2 6
F i g u r e 1 1 -3
F i g u r e 1 1 -1 9
F i g u r e 1 2 -4
F i g u r e 1 2-6
F i g u r e 1 2 -7
F i g u r e 1 8-5
Tab l e 1 4 -5
G l obal sect ion , 9-1 , 9-1 4 ,
1 1 -4 , 1 3 -1 , 1 3- 6 , 1 8 - 2 , 1 8- 1 1
F i g u r e 1 1 -7
F i g u r e 1 8 -2
F i g u r e 1 8-5
a nd $ U PDSEC s ys tem s e rv i c e ,
1 2-2 9
i n sha r ed memo r y , 9 - 1 4 ,
1 1 - 3 5 , 1 1 - 3 9 , 1 3 -6 to 1 3-7
Fig ure 1 1-2 5
m a pp i ng , 9 - 1 4
G l oba l sec t i o n c re a t i o n , 1 3-7
G l oba l sec t i o n d e l e t i on , 1 3- 9
G l o b a l s e c t i o n d e sc r i pto r ( G S D ) ,
1 1 - 2 0 to 1 1 - 2 1 ,
1 1 - 2 5 to 1 1 - 2 6 , 1 1 - 4 0 , 1 3 - 7 ,
1 3 - 9 , 2 5 - 1 1 , D- 6
F i g u r e 1 1 -1 4
F i g u r e 1 1 -1 6
F i g u r e 1 1 -1 8
f o r PFN ma pp i ng , 1 3 - 8
Figure 1 1-1 4
i n sha r ed memo r y , 9 - 1 8 , 1 3 - 8
Figure 11-2 5
Figure 11-27
G l o b a l se c t i o n d e sc r i p t o r l i s t
Ta b l e 8 - 2
G l o b a l s e c t i o n d e sc r i p to r
l i st mutex
Ta b l e 2 4 - 2
G l ob a l sec t ion t a b l e , 1 1 -2 1 ,
1 1-2 5 , E-l l
F i g u r e 1 1 -1 5
F i g u r e 1 1 -1 8
G l ob a l s e c t i o n t a b l e e n t r y ,
1 1 - 2 0 to 1 1 -2 1 , 1 1 - 2 5 , 1 1 - 3 0 ,
1 1 - 4 0 , 1 2 - 1 2 , 1 3 - 7 to 1 3 - 9 ,
1 4-1 1
F i g u r e 1 1 -1 5
F i g u r e 1 1 -1 6
F i g u r e 1 1 -1 8
F i g u r e 1 8 -5

Global page tabl e entry ,

Index- 1 1

INDEX

G l o b a l s ec t i o n tab l e i nd e x ,
1 1- 2 3 , 1 1-2 6 , 1 2-1 2 ,
1 2 - 1 4 t o 1 2- 1 5 , 1 2 - 1 7 ,
1 4-2 5 t o 1 4-2 6
F i g u r e 1 2-4
F i g u r e 1 2-6
F i g u r e 1 2 -7
G r o up , 9 - 1 1
G r o up l og i c a l name t a b l e , 8 - 1 4 ,
2 5-1 1 , 2 6- 1 , 2 6 - 3
Figure 26-1
Figure 26-2
Ta b l e 8 - 2
G r o up l og i c a l name t ab l e m u t ex
Ta b l e 2 4 -2
GROUP p r i v i l eg e , 1 - 2 0 , 9 - 8 ,
9 - 1 1 , 1 0 - 1 1 , 1 9- 1
Ta b l e 9 - 1
G R PNAM p r i v i l eg e , 2 6 - 4

I /0 c o mpl e t i on , 4 - 1 ,
5 - l to 5 - 2 , 5 - 4 , 5 - 1 0 , 9 - 6 ,
1 1 -1 8 , 1 2- 3 0
Ta b l e 8 - 3
I /0 c o mpl e t i o n A S T , 1 6 - 6
I /0 c ompl e t i o n n o t i f i c a t i o n ,
1 6- 6
I /O d a t a b a s e m u t ex
Ta b l e 2 4 - 2
I /0 f un c t i o n c od e , 1 2 - 1 9
I /O po s t p r o c e s s i ng , 1 - 1 5 , 4 - 3 ,
4 -7 , 5 - 1 0 , 1 2 - 2 0 , 1 2 - 2 4 ,
1 2-2 8 , 1 5-4 t o 1 5- 5 , 1 6-8 ,
2 4 - 3 , 2 4 -7
F i g ure 1-5
Ta b l e 4 - 1
I /O po s tp r o c e s s i ng q u e ue , 4 - 7
I /O r e que s t , 1 - 1 5
I /O r e que s t pa c k e t ( I R P ) , 5 - 4 ,
5-1 3 , 1 2-1 9
I /O s t a t us b l oc k , 5 - 1 0 , 1 6 -6
I /O s ub s ys t em , x x v i i i , 1 - 4 ,
H
1-1 0 , 1 1-3 2
Ha r d wa r e c l o c k , 6 - 1 , 1 0 - 1
Figure 1-2
Figure 1-5
I /0 s yn c h r o n i z a t i o n , 9 - 1
i n t e r r upt s e r v i c e r o u t i ne ,
I JO B L I M SYS BOOT pa r am e t e r , B - 1 9
4 - 6 , 8 - 5 , 1 0-1 , 1 0- 3 ,
Imag e , 1 - 1 , 1 - 3
1 0- 5 t o 1 0-6 , 2 3-7 , 2 4-4
Figure 1-8
Ta b l e 1 0 - 1
Imag e ac t i v a t i o n , 1 3 - 6 , 1 8 - 1 ,
Ta b l e 1 3 - 2
2 0-1 3
Ha r d wa r e c o n t ex t , 1 - 1 , 1 - 1 1 ,
F i g u r e 2 0- 3
1 -1 8 , 5-2 , 5-1 1 , 8-1 , 8-2 0 ,
Ta b l e 9 - 2
8-22
Imag e a c t i va to r , 1 - 3 , 3 - 1 4 ,
Figure 1-1
1 3-2 , 1 3 -6 , 1 7-18
Ha r d wa r e i n t e r r upt s , 1 - 1 1 , 1 - 1 8
F i g u r e 1-7
Figure 6-2
F i g u r e 1-8
s e e a l so d ev i c e i n te r r upt
F i g u r e 3-8
s e rv i c e r o u t i n e
Figure 1 8-9
Ha r d wa r e PCB
Ta b l e 1 8 - 1
s e e h a r d wa r e p r o c e s s
Ta b l e E - 4
cont rol block
Imag e c o u n te r , 2 7 - 9
Ha r d wa r e p r o c e s s c o nt r o l b l o c k ,
Imag e e x e c u t i o n , 1 - 6
xxxi , 1-1 , 1-3 , 1-1 8 , 5-2 ,
Imag e ex i t , 7 - 5 , 1 3 - 2 , 1 3 -1 0 ,
5-5 , 8 -2 1 , 8-2 3 , 9-5 , 1 4-2 2 ,
1 8- 1 8
1 4 - 2 7 , D- 1 0
Imag e f i l e , 1 1 - 4 , 1 1 - 1 1 , 1 1 - 3 5 ,
F i g u re 1 - 1
1 2 - 3 t o 1 2 - 4 , 1 2- 6 , 1 2 - 2 6 ,
Figure 8 -6
1 3-6 , 1 8- 5
F i g u r e 1 1 -2
Figure 1 8-1
Ta b l e D-3
Imag e h e ad e r , 1 8 - 5
see a l so p r oc e s s c o n t r o l b l o c k
Figure 1 8-1
H i b e r na t e P r o c e s s
Imag e h e ad e r b u f f e r
s ys tem s e rv i c e ( $ B I B E R ) ,
F i g u r e 1-7
8 -1 1 , 8 - 1 5 , 9-9
Ta b l e E - 4
Ta b l e 9 - 1
Imag e I / O s egmen t , 1 - 2 4 , 1 8 - 8 ,
Ta b l e 9 - 2
1 8- 2 1
H i b e r n a t e wa i t s ta t e s ( H I B a nd H I B O )
F i g u r e 1-7
8 -1 5 , 9 - 9
Figure 1 8-9
Figure 8-5
Ta b l e E - 4
Ta b l e 8 - 1
Tab l e 1 4 - 2

I nd ex - 1 2

I NDEX

I N S QUE i n s t r uc t i o n , 4 - 3
I NS TA L L SYSGEN c omma nd , 1 1 - 3 2 ,

Imag e i n s ta l l ed wi t h p r i v i l eg e ,
1 8-1 1

Imag e r e s e t
r o u t i ne i n s ys t em i m ag e ,
1 3- 2 ,

1 4-1 2

I N S TA L L u t i l i ty , 1 - 7 , 1 1 - 4 0 ,
1 3- 7 , 1 8-2 to 1 8 - 3 , 1 8- 1 2 ,

1 3-1 2

F i g u r e 1 8-9
T a·b l e 1 8 - 1
Tab l e E-4
Imag e r e s e t o pe r a t i o n , 1 8 - 2 1
Imag e r un d o wn , 7 - 4 , 1 3 - 1 0 ,
1 8- 2 0 , 2 0 - 9 , 2 0 -1 3 to 2 0 -1 4 ,
2 3-8 ,

27-9

14-22

20-1 3

F i g u r e 1 8-7
Imag e s t a r t up , 2 - 3 0 , 1 3 - 1 4
F i g u r e 1-8
Imag e t e rm i n a t i o n , 2 0 - 1 4
Imag e - s pe c i f i c m e s sag e s e c t i o n ,

9-1 ,

27-5

I MG I OCNT s p e c i a l SYSB OOT p a r am e t e r ,
B-1 5 ,

!NIT

E-2 1

A- l l
F ig u r e 1 1-2 2
F i g u r e 22- 1
Figure 22-2
F i g u r e 2 2- 3
Ta b l e 2 1 - 1
Tab l e 2 1 - 3
Ta b l e 2 1 - 4
Ta b l e 2 2 - 1
s e e a l so vo l um e i n i t i a l i z a t i o n
u t i l i ty
I N I TADP
mod u l e in s ys tem i m ag e ,
2 2-1 0

I n i t i a l q u a n t um
Tab l e 1 4 - 2
I n i t i a l q u a n t um f l ag , 8 - 5 , 1 4 - 7
I n n e r a c c e s s mo d e , x x x i
Fi g u r e 1-4
I n p u t s ym b i o n t , 2 0 - 4
Fi g u r e 2 0-2
Tab l e 1 - 1

9-1 3

I n t e r p r o c e sso r c omm un i c a t i o n ,
9-1 4 ,

1 1-35

I n t e r r up t d i sp a tc h b l oc k
6-7 ,

m o d u l e i n s y s t em i m ag e ,
xxxi , 7-6 , 1 0-3 , 1 1-32 ,
1 1 - 3 5 , 1 5-9 , 1 7-1 3 , 2 1 - 1 8 ,
2 2 -1 , 2 2 -3 , 2 5 -7 , 2 5 -1 0 ,

1 4 -2 6

I n swa p o pe r a t i o n , 1 1 - 3 5 , 1 4 - 2 1
Figure 8-5
Figure 14-5
Figure 1 4- 6
Figure 14-7
Tab l e 1 4 - 5
I n t e g e r d i v i d e b y z e r o e x c e pt i o n
Tabl e 2-3
I n t eg e r ove r f l o w e x c e p t i o n
Tab l e 2 - 3
I n t e r a c t i v e j ob , 7 - 5 ,
8 - 4 to 8 - 5 , 9 - 1 0 , 2 0 - 1 , 2 0 - 5
Figure 20-1
I n t e r l o c k ed i n s t r uc t i o n s , 1 1 - 3 7
I n t e r p r o c e s s c ommun i c a t i o n ,

1 8- 8

1 7-1 6 ,

14-24 ,

I n swa p o f the pr o c e s s h e ad e r ,

Figure 1 8-1
F i g u r e 1 8-2
F i g u r e 1 8-3
F i g u r e 1 8- 4
F i g ur e 1 8- 5
Imag e S t a r t up
s ys tem s e rv i c e ( $ I MG S TA ) ,
1 8 -1 7 ,

2 5 -1 3

Tab l e 1 -1
Tab l e 1 8-1
Tab l e 2 1 -1
I n s t r uc t i o n b u f f e r , A- 5
I n swa p o f the p r o c e s s b o d y ,

Figure 20-3
Ta b l e 9 - 2
Imag e s ec t i o n , 1 1 - 1 1
Imag e s e c t i o n d e sc r i pt o r , 1 3 - 6 ,
1 8- 5 ,

22-1 8 ,

( I DB ) ,

6-1 1

Figure 6-3
Figure 6-4
Figure 6-5
Figure 6-7
I n t e r r up t pr i o r i t y l ev e l
s e e I PL
I n t e r r upt s e r v i c e r o u t i n e ,
1 - 1 2 to 1-1 3
Figure 6-7
I n t e r r up t s t ac k , 1 - 1 4 , 1 - 1 7 ,
5-2 , 6-4 , 8-2 7 , 23-1 ,
2 5 - 1 1 , B- 2 3 , E - 1 0
Figure 1-6
Figure 6-1
F i g u r e 21-2
Figure E-1
Ta b l e 4 - 1
Ta b l e 2 3 - 1
Ta b l e E - 2
Ta b l e E - 3

2 3-6 ,

I n t e r r up t s ta c k po i n t e r r eg i s te r
( PR $ I S P )
Ta b le 2 1 - 3
Ta b l e 2 3 - 1

I nd e x - 1 3

I NDEX

I n t e r r up t s , 1 - 1 7 , 2 4 - 1
s e e a l s o h a rd wa r e i n t e r r up t s
s e e a l so s o f twa r e i n t e r r up t s
I n t e rva l t im e r , 1 0 - 1
I N TSTKPAG E S SYSBOOT pa r am e t e r ,
B-1 5 , E-1 0
Tab l e E-2
I OTA s pe c i a l SYS B O OT p a r am e t e r ,
5 - 1 1 , 8 - 5 , B- 1 6
I P L , 1 - 1 1 , 1 - 1 7 to 1 - 1 8 , 2 - 8 ,
3-1 0 , 4 - 1 , 4-4 , 6 - 1 , 8 - 1 3 ,
2 4-1
F i g u r e 2 4-1
Tab l e 4 -1
v a l ue d e f i n i t i o n s , D- 2 3
I PL 0 , 1 3- 1 4
I P L 2 ( I P L $ ASTDE L ) , 1 - 1 4 ,
4 - 3 , 5 - l , 5- 6 , 5 - 9 , 8 - 1 5 ,
9-1 0 , 1 2- 1 , 1 3-1 5 , 1 7-1 6 ,
24-5 , 24-9 , 2 5-7
Ta b l e 4 - 1
Tab l e 2 4-1
I PL
3 ( I PL $ S C H ED ) , 8 - 1 8 , 8 - 2 0
I P L 4 ( I PL $ I O PO S T ) , 4 - 3 , 4 - 7 ,
5 - 1 0 , 1 6 - 8� 2 4 - 7
Ta b l e 4 - 1
I PL 6 ( I PL $_QUE UEAST ) , 5 - 1 3 ,
24-5
I P L 7 ( I PL $ S YNC H ) , 1 - 1 1 ,
1-2 0 , 5-6 , 5- 1 0 ,
5-1 3 to 5 -1 4 , 8-2 0 ,
8 - 2 2 to 8 - 2 3 , 9 - 8 , 1 3 - 1 4 ,
1 4 -2 3 , 1 7-7 , 1 8 - 2 2 , 1 9 - 5 ,
2 4 - 3 , 2 4 - 5 , 2 5 - 7 , 2 5 - 1 1 , A- 1 2
Fig ure 8-7
F i g u r e 1 4 -1
T a b l e 2 4 -1
I PL 7 ( I PL $ T I M E R ) , 4 - 6
Ta b l e 4 -T
s o f twa r e i n t e r r up t , 1 0 - 6
I PL 8 - 1 1 , 2 4 -4 , 2 4 -6
T a b l e 2 4 -1
I P L 1 1 ( I PL $ MA I LB OX ) , 1 5 - 1 3 ,
2 5-7
T a b l e 2 5 -1
I PL 1 6-3 1 , 6-1
I P L 2 0 -2 3 , 5 - 1 3 t o 5 - 1 4 , 6 - 6 ,
2 4 -4
Tab l e 2 4-1
I PL 2 4 ( I P L $ HWC LK ) , 4 - 4 , 1 0 - 5 ,
2 3-7 , 2 4 - 4
Ta b l e 2 4 -1
I PL 3 0 , 2 3 - 1
I PL 3 1 ( I P L $ POWE R ) ,
7 - 2 to 7 - 3� 7 - 1 0 to 7 - 1 1 ,
2 4 -4 , 2 5 -7
Tab l e 2 4-1
T a b l e 2 5 -1
I PL r eg i s te r ( PR $ I P L ) , 2 4 - 1
F i g u r e 2 4 -1

I RP e x t e n s i o n , 1 6 - 8
I RPC OUNT SYSBOOT p a r am e t e r ,
2 5 - 9 , 2 5 - 1 3 , B - 1 5 , F- 1
! SAM f i l e , 3 - 1 2

Job , 1 - 1 , 1 - 4
F i g u r e 1 7- 2
F i g u r e 1 9- 1
JOB c a rd ( $J OB ) , 9 - 1 1 , 2 0 - 5
Job con t ro l l e r , 3 - 4 , 2 0 -1 ,
2 2 - 1 3 , 2 2 - 1 7 , 2 7 - 1 to 2 7 - 2
Figure 20-1
F i g u r e 2 0- 2
Ta b l e 1 - 1
Tabl e 2 1- 1
ma i l bo x , 2 0 - 1 , 2 2 - 1 5 , 2 7 - 2 ,
B-2
F i gure 2 0-1
F i g u r e 2 0- 2
J o b i n fo rma t i o n b l o c k ( J I B ) ,
1 - 3 to 1 - 4 , 1 7 - 1 to 1 7 - 2 ,
1 9- 5 , 2 2 - 1 5 , 2 7 - 8 , D-7
Figure 1-1
Figure 1 7- 1
Figure 1 7-2
Figure 1 7-6
F i g u r e D-1
Ta b l e 1 7 - 4

Ke rnel , 1-4
Ke rnel access mode , 1 -1 6 , 3-1 ,
8 -2 7 , 1 4-2
F i g u r e 1-4
Tabl e 3 - 1
K e r n e l mode ex c e p t i o n , 2 - 3 1
K e r n e l s t ac k , 1 - 1 7 , 6 - 4 , 8 - 2 3 ,
1 1 -7 , 1 2-3
F i g u re 1-7
Figure 6-1
Figure 1 2-2
Tabl e 4-1
Ta b l e 1 7 - 5
Ta b l e E - 4
K e r n e l - s t a c k -n o t-va l i d e x c ep t i o n ,
2 - 7 to 2 - 8
Ta b l e 2 - 1
K F I LSTCNT S Y S B O OT p a r am e t e r ,
B-1 4
Known f i l e e n t r y , 1 8 - 1 2
F i g u r e 1 8- 6
Known f i l e en t r y t a b l e , 2 5 - 1 3
Ta b l e 8 - 2 ·
Known f i l e e n t r y t a b l e m u tex
Ta b l e 2 4 - 2

I nd ex - 1 4

I NDEX

K n own f i l e h e ad e r
F i g ur e 1 8-6
K nown imag e , 1 - 7 , 1 8 - 2 , 1 8 - 1 2 ,
1 8- 1 5
Table 2 1-1
K S RVE X I T , 3 - 1 0 , 3 - 1 3 , 3 - 1 7
F i g ur e 3-2
Figure 3-4
Figure 3-5
F i g u r e 3 -7
Figure 3-8
s e e a l s o SRVE X I T

LAMAPREGS S YS BOOT pa r am e t e r ,
B- 1 7
L a s t c h a nc e c o nd i t i o n h a nd l e r ,
2- 1 8 , 1 3-4
L a s t c h a n c e e x c e p t i o n v e c to r ,
2 - 1 8 , 1 7- 2 0 , 1 8 - 2 3 , 2 0 - 1 3
L a ye r ed p r o d uc t s
Fi gure 1-2
L D PC TX i n s t r uc t i o n , 1 - 1 1 , 1 - 1 9 ,
8 - 2 3 , 8 - 2 6 to 8 - 2 8 , 1 1 - 3
Figure 8-7
L e s s p r i v i l eg ed a c c e s s m o d e , A-8
see o u t e r a c c e s s mode
L I B $ E S TAB L I S H
Run-T i m e L i b r a r y p r o c ed u r e ,
2-1 6
L I B $ FR E E VM
Run-T i m e L i b r a r y p r o c ed u r e ,
1 3 -6
L I B $G E T VM
Run=T i m e L i b r a r y p r o c ed u r e ,
1 2 -1 0 , 1 3 - 6
L I B $ I N I T IA L I Z E
Run-T i m e L i b r a r y p r o c ed u r e
Figure 1 8-7
L I B $ R EVE RT
Run-T i m e L i b r a r y p r o c ed u r e ,
2-17
L I B $ S I GNAL
Run-T i m e L i b r a r y p r o c ed u r e ,
2 -1 2 , 2- 1 4 , 2 7-4 , 2 7-7
Figure 2-3
Figure 2-4
L I B $ S TO P
Run-T i m e L i b r a r y p r o c ed u r e
Figure 2-3
Figure 2-4
L I B . M LB , 7 - 1 2 , A- 2 , A- 4 , D- 1
L i nk e r opt i o n , 1 2-2 4 , E - 2 1
L OAD S YSGEN c omma nd , 2 5 - 1 3
Lo c a l e v e n t f l ag , 9 - 1

Loc a l e v e n t f l ag wa i t s t a t e s
( L EF a nd L E F O ) ,
3-1 2 , 8-9 , 8-1 5 , 9-5 to 9-6
Figure 8-5
Ta b l e 8 - 1
Ta b l e 1 4 - 2
Lo c k pag e i n m emo r y b i t
i n WSLE
Figure 11-5
Lo c k pag e i n wo r k i ng s e t b i t
i n WSLE
Figure 11-5
Lo c k Pag e s i n Memo r y
s ys t em s e rv i c e ( $ LC K PAG ) ,
11-1 0 , 1 3 -1 5
Ta b l e 1 3 - 1
Lo c k Pag e s i n Wo r k i ng S e t
s ys t em s e rv i c e ( $ L KWS E T ) ,
1 1 -8 , 1 3 - 1 5 , A- 1 2
Ta b l e 1 3 - 1
Lo c k i ng a mut e x
f o r r ea d a c c e s s , 2 4 - 9
f o r wr i t e a c c e s s , 2 4 - 9
Lo c k i ng I /0 b u f f e r pag e
i n to memo r y ,
1 6-8
Lo c k i ng pag e s , 1 1 - 1 6 , 1 1 - 1 8 ,
1 1 -3 4
Lo c k i ng pag e s i n the wo r k i ng s e t ,
1 3 -1 5
LOCKRETRY s p e c i a l SYSB OOT
pa r am e t e r ,
B-1 7
L OG I O p r i v i l eg e , 1 0 - 4
Log Tc a l b l o c k n um b e r , 1 1 - 1 1
Log i c a l n ame b l o c k ( L OG ) , 1 6 - 1 1
F i g u r e 1 6 -1
Figure 16-3
F ig u r e 26 -1
Figure 26-2
Ta b l e A- 1
Log i c a l n ame c r e a t i o n , 2 6 - 4
Log i c a l n am e s ys t em s e rv i c e s ,
8-14
Log i c a l n ame t r a n s l a t i o n , 9 - 1 4 ,
11-3 9 , 26-5
Log i c a l n ame s , x x i x , 1 - 6 ,
9-1 , 9- 1 4 , 26-1
a nd a s so c i a t ed m a i l bo x ,
16-1 2 , 2 6-3
Log i n c ommand f i l e , 2 0 -7
Figure 20-1
LOG I NO UT i m ag e , 2 0 - 1 ,
2 0 - 4 to 2 0 - 5 , 2 2 - 1 5 , E - 1 7
F i g u r e 2 0 -1
Figure 20-2
Figure 20-3

I nd ex - I S

INDEX

LOGINOUT image ,

2 0 - 1 , ( co nt . ) ,
Tab l e 1 - 1
Ta b l e 1 3 - 1
Ta b l e 1 8 - 1
Ta b l e 2 1 - 1
Ta b l e E - 4
Log o u t o pe r a t i o n , 2 0 - 8
Longwo r d i nd ex , x x x i
Lo o ka s i d e l i s t , 5 - 3 , 1 6 - 7 ,
2 2 - 8 , 2 5 - 9 to 2 5 - 1 0 , F- 1
F i g u r e 2 5 -4
Ta b l e 2 5 -1
T a b l e 2 5- 2
L RPC NT S Y S B O OT p a r am e t e r , F - 1
LRPS I Z E S Y S B OOT pa r am e te r , F - 1
L S I - 1 1 conso l e proce sso r ,
1 5- 1 6 , 2 1 -6

MA7 8 0 i n t e r r upt s e rv i c e r o u t i n e ,
6-1 3 , 9-7
F i g u r e 6-6
MA7 8 0 s h a r ed mem o r y , 7 - 9 , 9 - 1 4 ,
1 1-1 , 1 1- 3 5
Tab l e 6 -1
Tabl e 2 2-2
Ma c h i ne c h e c k , 2 - 7 to 2 - 8 , 6 - 1 ,
7 - 1 to 7 - 2 , 7 - 9
Ta b l e 2 - 1
Tab l e 2-2
M a c h i ne c h e c k c od e , 7 - 1 0 t o 7 - 1 1
Ma c h i ne c h e c k r ecove r y b l oc k ,
7-1 2
Ma g n e t i c t a pe AC P , 1 - 6
Ta b l e 1 - 1
Ma g n e t i c t a pe d r i v e r , 1 5 - 6
MA I L u t i l i ty
Ta b l e 1 - 1
Ma i l bo x c r e a t i o n , 1 6 - 1 1 , 2 6 - 3
F i g u r e 1 6 -1
F i g u r e 1 6-3
Ma i l bo x d ev i c e , 9 - 1 , 9 - 1 3 ,
1 5 - 1 1 , 2 2 - 1 0 , B- 2
i n s h a r ed memo r y ,
9 - 1 4 to 9 - 1 5 , 1 1 - 3 5 , 1 1 - 4 2 ,
1 6-1 3
Figure 11-2 5
Ma i l bo x d r i v e r , 5 - 1 5 , 9 - 1 3 ,
1 5- 1 2
Ma i l bo x l og i c a l name , 1 6 - 1 2 ,
26-3
Ma i l bo x m e s sag e b l o c k
F i g u r e 1 5 -4
Ma i l bo x r ea d o pe r a t i o n , 1 5 - 1 3
Ma i l bo x un i t c o n t r o l b l o c k ,
9-1 5 , 11-42
F i g u r e 1 6 -1
F i g u r e 1 6-3

Ma i l bo x wr i te o pe r a t i o n , 1 5 - 1 5
Map Global Sec t i on
s ys t em s e rv i c e ( $ MG B LS C ) ,
9-1 4 , 1 1 -2 0 , 1 1-2 7 ,
1 3 - 6 to 1 3 - 8 , 1 8 - 1 2
M a pp i ng r eg i s te r s
i n MBA o r UBA , 1 1 - 3 4
MAS SBUS a d a p t e r , 6 - 4
Tab l e 6 - 1
Ta b l e 2 2 - 2
i n t e r r up t s e r v i c e r o u t i n e ,
6-1 0
Figure 6-4
MAXBUF SYS BOOT p a r am e t e r , B-1 6
MAXPR INTSYM B SYSBOOT p a r am e t e r ,
B-1 9
MAXPROC ES SCNT SYSBOOT p a r am e t e r ,
1 4 -1 2 , 1 7 - 9 , 2 2 - 1 6 , B - 1 4 , F- 3
Figure 1 1-21
Ta b l e 2 2 - 1
MCHECK7 5 0
mod u l e i n s ys t em i m ag e , 7 - 1 0
M C HECK7 8 0
mod u l e i n s ys t em i m ag e , 7 - 1 1
M C R c omma nd l a ng uag e i n t e r pr e t e r ,
3-4 , 2 0 - 9
Ta b l e 1 - 1
M DAT
mod u l e i n s ys t e m i m ag e ,
B-1 , B-7
MDL s t r uc t u r e d e f i n i t i o n l a ng uag e ,
x x i x , A- 1 7 , D- 1
Ta b l e A- 1
Ta b l e A - 2
Ta b l e A- 3
M e c ha n i sm a r r a y , 2 - 1 6 , 2 - 1 8 ,
2-2 3
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Mem o r y m a n ag em e n t , x x v i i i , 1 - 4 ,
1-1 0
Figure 1-2
Memo r y m a n ag em e n t e n a b l i ng ,
2 1 -1 8 , 2 2 -1
F i g u r e 2 2- 2
Memo r y m a n ag em e n t I /O r e que s t s
Ta b l e 1 2 - 1
Mem o r y m a n ag em e n t pag e p r o t ec t i o n ,
1 -1 0 , 1-1 6 , 1 -1 9 , 1 1 - 4 , 2 7- 1 0
Figure 1 1-3
Tab l e 1 1 -1
Memo r y m a n ag em e n t wa i t s t a te s ,
8-1 1 , 8-1 6
Memo r y r e s i d e n t p r o c e s s , 8 - 1
Memo r y ROM p r og r am , 2 1 - 7
Tab l e 2 1 - 1

I nd ex - 1 6

INDEX

Memo ry s i z i ng operation ,

Mod i f i ed pag e wr i t i ng , 8 - 8 ,

2 1-7

Me r g ed i m a g e a c t i v a t i o n , 1 8 - 2 ,

8 -1 1 ,

2 2-1 5
Table 2 1-1

Me s s ag e v e c to r s
Figure 1-7
Tab l e E-4
M FY L O L IM I T SYSB OOT pa r am e t e r ,
E-= 1 6

1 1-1 1 ,

M I NWS C NT SYS BOOT pa r am e t e r ,
1 3-1 2 ,

1 7-1 5 ,

B- 1 5

Ta b l e 1 3 - 1
M i s c e l l a ne o us wa i t s t a t e ( MWA I T ) ,
8 - 1 1 , 8 - 1 5 to 8 -1 6 , 1 3- 5 , 2 7- 9
F igure 8-5
Tabl e 8 -1
Tab l e 8 -2
Tab l e 1 4 -2
m u t ex wa i t
Ta b l e 8 - 2
Tab l e 2 4 -2
r e s o u r c e wa i t
Ta b l e 8 - 2
s e e a l s o m u t ex wa i t
s e e a l s o r e so u r c e wa i t
Mo d i f i ed pag e l i s t , 1 1 - 7 ,
1 1 -1 4 , 1 1-1 7 , 1 1-3 5 , 1 2-6 ,
1 2 - 8 , 1 2 -2 5 , 1 2-2 8 , 1 4 -2 1 ,
14-24
F igure 1 1-1 1
F igure 1 2-3
F igure 1 2-4
Figure 1 2-5
F igure 1 2-8
l owe r l i m i t t h r esho l d , 1 2 - 2 9 ,
1 4-8 , 1 4-2 1
uppe r l i m i t t h r esho l d , 1 4 - 8 ,
1 4-2 1

Mod i f i ed page wr i te c l u s te r i ng ,
1 2-2 5

F igure 1 2-8
Mod i f i ed pag e wr i te c o m pl e t i o n ,
1 2 -2 5 ,

1 2- 2 8

1 1-2 3 ,
1 2-20

1 1-3 0 ,

Mod i f i ed pag e wr i te r , 1 1 - 2 0 ,
1 1-3 5 ,

1 2-6 ,

Tab l e 9 -2
Tab l e 1 2-1
Mod i f i ed pag e wr i te r a r r a ys ,
1 1-32 ,

22-9 , 25-1 3
Figure 1 1-24
F igure 1 2-8
Tab l e 1 2 -1
Tab l e 2 2-1

Mod i f i ed pag e wr i te r P T E a r r a y ,
1 1-35

1 2-2 5 ,

1 4- 2 ,

1 4-8

Mod i f y b i t
Figure 1 2-3
Fig u r e 1 2 -4
Figure 1 2-5
Figure 1 2-7
i n t h e pag e t a b l e e n t r y ,

20-6 ,

1 1 -1 6 ,

1 2- 4 ,

1 2 -2 9

Figure 1 1- 3
i n the PFN S TATE a r r a y ,
1 1-1 1 , 1 1-1 6 ,
1 2 - 6 to 1 2 - 8 ,

1 1- 1 8 ,
1 4 - 1 3 to 1 4 - 1 5

i n wo r k i ng s e t l i s t e n t r y
Figure 1 1-5
Mo r e pr i v i l eg ed a c c e s s m o d e
Tab l e 1 1 - 1
s e e i nn e r a c c e s s m o d e
MOUNT
s e e vo l ume moun t u t i l i ty
Mo un t ed v o l um e l i s t , 2 5 - 1 1 ,
2 5- 1 3

MOVC 5 i n s t r uc t i o n , 1 2 - 1 0
M·o vcx i n s t r uc t i o n , 2 1 - 1 4
M PW H I L IM SYS BOOT p a r am e t e r ,
14 - 9 ,

B-1 5

14-9 ,

2 2-1 0 ,

M PW LOL IMIT SYSBOOT p a r am e t e r ,
B-1 5

M PW PR I O s p e c i a l S Y S B OOT
pa r am e t e r ,
B-1 6

Tab l e 1 2 - 1
Ta b l e 1 4 - 1
M PW WRTC LUSTER S Y S B OOT p a r am e t e r ,
ll- 3 5 , 1 2 - 2 6 , 1 2 - 2 8 to 1 2 - 2 9 ,
B- 1 5

Figure 1 1-24
Tab l e 2 2 - 1
M u l t i pl y a c t i ve s i g n a l s , 2 - 2 0 ,
2-2 8

Figure 2-6
Figure 2-8
MUTEX
mod u l e i n sys t em i m ag e , 2 4 - 9
M u t e x wa i t s ta t e ( MWA I T ) , 8 - 1 4 ,
2 4-9 to 2 4-1 0
Ta b l e 2 4 - 2
Mu t ua l e x c l us i o n s em a pho r e ( Mu t ex ) ,
1-2 1 ,
24-7 ,

3 -1 2 , 8 -1 4 ,
2 6 -4 , D-9
Figure 3-5
F i g u r e 2 4 -2

8-1 6 ,

24-1 ,

MWA I T s t a te ( m i s c e l l an e o u s wa i t )
s e e m i s c e l l a n e o u s wa i t
s e e m u t ex wa i t
s e e r e s o u r c e wa i t

Index- 1 7

INDEX

N
Nam i ng conv e n t i o n s , C - 1
N a t i v e m o d e i mag e , 1 - 2 4
Figure 1-8
N E TDR IVER
F i g u r e 1 5 -3
N E TM B X p r i v i l eg e
Ta b l e 1 7 - 3
N e two r k AC P ( N E TAC P ) , 1 5 - 1 2
F i g u r e 1 5 -3
Ta b l e 1 - 1
N e two r k d ev i c e , 1 5 -1 1
N JO B L I M S YS BOOT p a r am e t e r , B- 1 9
No a c c e s s p ag e , 1 - 2 4
Figure 1-8
No a c c e s s p r o c t e c t i o n c od e
Ta b l e 1 1 -1
N OACNT p r i v i l eg e
Ta b l e 1 7 - 3
N OAUTOC ONF I G s p e c i a l SYSB OOT
pa r am e t e r f l ag ,
B-1 7
N O C LOC K s pe c i a l SYSBOOT
p a r am e t e r f l ag ,
B-1 7
N OC LUS TER s pe c i a l S YS B OOT
pa r am e t e r f l ag ,
8-1 7
N o n pa g e d d yn am i c m emo r y , 1 - 2 1 ,
S - 3 , S - 7 , 5 - 9 to 5 - 1 0 , 8 - 1 4 ,
9 - 1 , 1 0 -7 , 1 0 - 1 0 , 1 0 - 1 2 ,
1 1 -3 0 , 1 1 -3 4 , 2 2-5 , 2 5-1 ,
25-1 3 , 8-2 3 , E-1 0
F i g u r e 1-6
F i g u r e 2 1 -2
F i g u r e 2 5 -4
F i g u r e E-1
Ta b l e 8 - 2
Ta b l e 2 2 -1
T a b l e 2 5 -1
T a b l e 2 5 -2
Ta b l e E - 2
Ta b l e E - 3
a l l o c a t i o n , 1 6 -7 , 2 2 - 5 ,
F- 1 to F - 2
d ea l l oc a t i o n , 2 4 - 5 , F- 2
N o n pa g ed po o l
s e e n o n pa g ed d yn am i c m em o r y
N PAG EDYN SYS BOOT pa r am e t e r ,
2 5- � 3 , B- 1 5 , E - 1 0
Tab l e E-2
N u l l d ev i c e , 1 5 - 1 1 , 2 2 - 1 0 , B- 2
Nul l process , 1 -1 5 , 8-3 , 1 1-3 2 ,
2 2 - 8 , B-7
N u l l p r o c e s s PC B , 1 7 - 1 2
F i g u r e 1 7 -3

O PC C RASH p r og r am , 7 - 7
O PC OM p r o c e s s , 2 2 -1 3 , 2 2 - 1 7 ,
27-3
Ta b l e 1 - 1
Ta b l e 2 1 - 1
ma i l box , 2 2 -1 5 , 2 7 - 3 , B-2
O PE R p r i v i l eg e , 1 0 - 4
O p e r a to r c ommun i c a t i o n s , 2 7 - 3
O u t e r a cc e s s mo d e , x x x i , 1 7 -1 8
Figure 1-4
O u t s wa p o f p r o c e s s b od y , 1 4 - 1 � ,
1 4 -1 5
O u t s wa p o f p r o c e s s h e ad e r ,
1 4 - 2 0 to 1 4 - 2 1
O u t s wa p o pe r a t i o n , 1 1 - 3 5 , 1 4 -1 3
Figure 8-5
F i g u r e 1 4 -2
F i g u r e 1 4 -3
F i g u r e 1 4 -4
Ta b l e 1 4 -4
O u t s wa pped p r o c e s s , 8 - 1
Own e r a c c e s s m o d e f i e l d
i n t h e pag e t ab l e e n t r y ,
1 1-4 , 1 3-1
F i g u r e 1 1 -3

P O ba s e r eg i s t e r ( PR $ P OB R ) ,
8 - 2 0 , 8 - 2 6 to 8 - 2 8 , 1 1 - 3 4 ,
2 1 -1 8 , 2 2-2 , 2 3-5
Figure 8-6
F i g u r e 1 1 -2
F i g u r e 2 2 -1
Ta b l e 7 - 1
Ta b l e 2 1 - 4
Ta b l e 2 3 -1
PO l eng th r eg i s t e r ( PR $ P O LR ) ,
8 - 2 0 , 8 - 2 6 to 8 - 2 8 , l l- 3 ,
2 1 -1 8 , 2 2 -2
F i g u r e 8-6
F i g u r e 1 1 -2
F i g u r e 2 2 -1
Ta b l e 7 - 1
Tabl e 2 1 -4
Ta b l e 2 3 -1
PO p a g e tab l e , 1 - 3 , 1 1 - 1 , 1 1 - 3 ,
1 4 - 2 2 , 2 2 - 1 to 2 2 - 2
Figure 1 1-1
F i g u r e 1 1-2
Ta b l e E - 1
P O s pa c e , 1 - 1 6 , 1 1 - 3
P O s pa c e l a yo u t , 1 - 2 4
P O -o n l y i m ag e , 1 8 - 3 , 1 8 -1 1

I n d ex- 1 8

INDEX

P l b a s e r eg i s t e r ( PR $ P l B R ) ,
8 - 2 0 , 8 - 2 6 to 8 - 2 8 , 1 1 - 3
Figure 8-6
F i g u r e 1 1-2
Ta b l e 7 - 1
Tab l e 2 3 -1
P l l e ngth r eg i s t e r ( PR $_P l LR ) ,
8 - 2 0 , 8 - 2 6 to 8 - 2 8 , 1 1 - 3
Figure 8-6
F i g u r e 1 1 -2
Ta b l e 7 - 1
Tab l e 2 3-1
P l p a g e tab l e , 1 - 3 , 1 1 - 1 , 1 1 - 3 ,

Pag e f i l e , 1 1- 4 ,
1 2- 3 ,

A- 1 0 ,

E-1 7

1-1 6 ,

s e e a l s o c o n t r o l r eg i o n
P l s pa c e l a yo u t , 1 - 2 2 , A- 1 7
Figure 1-7
Ta b l e E - 4
P l w i ndow t o t h e p r oc e s s h e ad e r ,
1 1-8 , 1 4 - 2 2 to 1 4-2 3 , 1 7 -1 5 ,
Figure 1-7
Ta b l e E - 4
Pa f e f a u l t
s e e a l s o t r a n s l a t i o n- no t-va l i d
f a ul t
Pa g e a nd s wa p f i l e v e c to r , 1 1 - 3 0
Page faul t , 1 -1 4 , 1 1 - 4 , 1 1 -7 ,
1 2 -1 ,

24-6

F i g u r e 1 2-2
f o r g l o b a l pag e s , 1 2 - 1 2
f r om an i mag e f i l e , 1 2 - 3
f r om the f r e e pag e l i s t , 1 2 - 7
f r om t h e pag e f i l e , 1 2 - 1 2
Pag e f a u l t h a nd l e r , 1 - 4 , 1 - 1 0 ,
1 - 1 5 , 8 - 2 7 , 1 1- 1 , 1 1- 4 , 1 1 -7 ,
1 1 - 1 7 , 1 2 - 1 , 1 3 - 7 , 1 4 - 2 , A- 6
Figure 1-2
Figure 1-3
Figure 1-5
Ta b l e 1 4 - 1
P a g e fa u l t r e a d e r r o r , 2 - 1 3
Ta b l e 2 - 2

Pag e f a u l t wa i t s ta t e ( P FW ) ,
8 -1 1 , 8-1 5 to 8 -1 6 , 8 - 2 7 ,
12-4 ,

12-2 4 ,

Figure 8-5
Ta b l e 8 - 1
Ta b l e 1 4 - 2

1 2- 3 0 ,

1 3-5

2 2- 1 6

1 4-1 1 ,

2 2-1 6

1 1-4 ,

1 1-1 6 ,

1 2-2 1 ,

8-1 6 ,

1 2-2 4 ,

1 2- 3 0

1 3-5

pag e t a b l e e n t r y f o rm a t
F i g u r e 1 1-3
Figure 1 1-10
F i g u r e 1 2- 5
P a g e r ea d compl e t i o n sys tem eve n t ,

B-2 4

27-9

2 2- 1 3 ,

Figure 1 1- 2 2
P a g e f i l e i nd ex
Figure 1 1- 1 0
P a g e f i l e v i r t ua l b l o c k n um b e r ,

Figure 1 1-1
Figure 1 1 -2
Tab l e E-1
P l po i n t e r pag e , 1 1 - 7 , 2 3 - 8 ,

1 1 -3 ,

1 1-3 0 , 1 1-3 5 ,
1 2-1 2 , 1 2-2 6 ,

Tab l e 2 1 - 1
Ta b l e 2 2 - 3
P a g e f i l e b i tm a p , 1 1 - 3 0 , 2 5 - 1 3
Figure 1 1- 2 2
Page f i l e con t r o l b loc k , 1 1- 3 0 ,

1 4-22

Figure 1-7
F i g u r e 2 6- 1
Tab l e 1 7 - 5
Ta b l e E - 4
P l s pa c e , 1 - 3 , 1 - 1 4 ,

1 2-8 ,

Tab l e 8 - 3
P a g e t ab l e e n t r y , 1 1 - 2 , 1 1 - 4 ,
1 2- 1 , 1 2-3 to 1 2 - 4 , 1 2-7
Figure 11-3
Tab l e 1 1- 1
Ta b l e 1 4 - 5
P a g e t ab l e pag e , 1 2 - 2 0
P a g e type c od e
i n PFN TYPE a r r a y
Figure 11-12
i n WS LE
Figure 11-5
Pag ed d yn am i c memo r y , 1 - 2 1 ,
13-7 ,
B- 2 2 ,

2 5 -1 , 2 5 -1 1 ,
E- 1 0
F i g u r e 1 -6
Figure 2 6-1

2 6-4 ,

F i gure E-1
Tab l e 8-2
Tab l e 2 5-1
Tab l e 2 5-2
Ta b l e E - 2
Tab l e E-3
P a g ed d yn am i c mem o r y m u t e x
Ta b l e 2 4 - 2
P a g ed po o l
s e e pag ed d yn am i c memo r y
PAG EDYN S Y S B OOT p a r am e t e r ,
25-1 3 ,

B-1 5 ,

E-1 0

Ta b l e E - 2
PAG E FAU LT
mod u l e i n s ys t em i m age
Tab l e 1 4 - 3
PAG E F I LE . SYS , 1 1 - 3 0
Figure 1 1- 2 2
PAG E F I LS I Z E s p e c i a l SYSB OOT
p a r am e t e r ,
B-1 5

Pa g e r
s e e pag e f a u l t h a nd l e r

I nd ex - 1 9

INDEX

Pa g e r I /0 , 1 - 1 0 , 1 2 - 4 , 1 2 - 1 9
F i g u r e 1-3
PAG F I LC NT s pe c i a l SYSB OOT
pa r am e te r ,
B-1 5
Pag i ng f i l e quo t a , 1 3 - 3
PAGTB L PF C s pec i a l S Y S B O OT
pa r am e te r ,
1 2- 2 1 , B- 1 4
Pa r am e t e r f i l e s , 7 - 5 , 2 2 - 1 9 ,
2 2 -' 2 3
F i g u r e 2 2-4
F i g u r e 2 2- 5
Ta b l e 2 2 - 3
a nd SYSB OOT , 2 2- 1 9
a nd SYSGEN , 2 2 - 2 3
Pa s swo rd , 2 0 - 6
PAS SWORD c a rd ( $ PAS SWORD ) , 2 0 - 5
PC B
s e e h a r d wa r e p r o c e s s c o n t r o l
block
see proc ess c on t r o l b loc k
PC B s t a t u s vec to r ( PC B $ L S TS ) ,
8-5 , 8-1 1 , 8-1 3 , 9-1 1 Tabl e 9-2
Ta b l e 1 7 - 3
PC B v e c to r , 1 1 - 2 7 , 1 7 - 7 , 1 7 - 9 ,
2 2 - 8 , 2 5 -1 3 , 2 7 - 1 0
Figure 1 1- 2 1
F i g u r e 1 7-3
F i gu r e 1 7-4
Ta b l e 2 2 - 1
PDAT
mod u l e in s ys t em i m ag e ,
1 - 1 6 , 2 2 -8 , B- 8
Pe r -p r o c e s s c ommon a r e a
F i g u r e 1-7
Ta b l e E - 4
Pe r -p r o c e s s m e s sag e s e c t i o n ,
1 7-1 6
F i g u r e 1-7
Ta b l e E - 4
Pe r -p r o c e s s s t a c k po i n t e r s ,
8 - 2 0 , 8 - 2 7 to 8 - 2 8
F i gure 8-6
Tab l e 7 - 1
Ta b l e 2 3 -1
Pe r i od i c sys t e m s ub r o u t i n e , 1 0 - 9
Figure 1 0-1
T a b l e 1 0 -1
PFCDEFAULT SYSB OOT pa r am e t e r ,
1 2 - 2 1 , 1 2 - 2 4 , B- 1 4
Ta b l e 1 2 - 1
P F N d a t a b a se , 1 - 4 , 1 1 - 1 , 1 1 -7 ,
1 1 - 1 4 , 1 2- 4 , 1 2-1 5 , 1 4 -1 5 ,
2 1 - 1 7 , 2 5 - 1 1 , B- 2 2 , E - 1 0 ,
E-1 2 to E-1 3
F i g ure 1-6
F igure 11-9
Figure 1 2-3

PFN data ba se , ( cont . ) ,
Figure 1 2-4
Figure 1 2-5
Figure 1 4-2
Figure 14-3
F i gu r e 1 4-4
Figure 14-5
F i g ur e 1 4 - 6
Figure 14-7
Figure 21-2
Figure E-1
Ta b l e 1 1 - 2
Ta b l e 1 4 -1
Ta b l e E-2
Ta b l e E-3
PFN l i n k a r r a y s , 1 1 - 1 7
F i gure 1 1-9
Figure 1 1- 1 3
Tab l e 1 1 - 2
PFN mapp i ng , 1 3 - 6 , 1 3 - 8
PFN t r a ns i t i o n s ta te s , 1 1 - 7 ,
1 2-1 5 , 1 2-2 5 , 1 4 - 2 0
s e e a l s o i nd i v i d ua l s t a t e n a m e s
PFNMAP p r i v i l eg e , 6 - 1 5 , 1 3 - 6
P FRATH S Y S B O OT pa r am e t e r , 8 - 8 ,
1 3 - 1 4 , 8- 1 6
Ta b l e 1 3- 2
PFRATL S Y S BOOT pa r am e te r , 8 - 8 ,
1 3 -1 4 , 8- 1 6
Ta b l e 1 3 - 2
PFRATS s pec i a l SYS800T pa r ame t e r ,
B-1 6
Ph ys i c a l memo r y , 1 1 - 1 4
a m o un t us ed by the sys t em ,
E-1 4
Ph ys i c a l m emo r y c o n t e n t s , 7 - 7 ,
7-9
Phys i c a l m emo r y d e sc r i pt o r s , 7 - 9
Ta b l e 7 - 1
Phys i c a l m emo r y l ayo u t
Figure 21-2
Phys i c a l m emo r y s i z e , x x i x
Ph ys i c a l pag e a l l o c a t i o n ,
1 2 - 1 0 , 1 2 -1 4
Phys i c a l pag e d e l e t i o n , 1 1 - 1 7
PHYS ICALPAG E S spe c i a l SYSB OOT
pa r am e t e r ,
B- 1 6 , E-1 2
P IC
s e e po s i t i o n i nd e pe nd e n t c o d e
PL/I , 2 - 2
POO L PAG ING S Y S B OOT pa r am e t e r f l a g ,
2 2 -8 , B- 1 7
P O P L pseud o i n s t r uc t i o n
F i g u r e A- 1
Po s i t i o n i nd e pend ent c o d e , 1 - 2 4
Figure 1-8
POSTEF
mo d u l e in s ys t em i m ag e , 9 - 6

I nd ex - 2 0

INDEX

P o we r fa i l , 2 - 7 ,

5-1 2 ,

P r i v a t e sect i o n , 1 3-1 , 1 3-6 ,

6-1 ,

1 8-8

7-2 ,

2 3-1
Tabl e 2-1
Ta b l e 2 3 - 1

Figure 18-2
Figure 18-3
P r i v a t e sect i on c re a t i on , 1 3- 6
P r i v i l eg e e nh a n c eme n t s , 1 8 - 1 2
P r i v i l eg e d i m ag e , 1 - 7
Figure 1-2
Figure 1-4
Ta b l e 1 - 1
Ta b l e 2 1 - 1
P r i v i l eg e d i n s t r uc t i o n e x c e p t i o n
Ta b l e 2 - 1
Ta' b l e 2 - 2
P r i v i l eg e d i n s t r uc t i o n s , 1 - 1 1
P r i v i l eg e d l i b r a r y v e c to r ( P LV ) ,

i n t e r r upt s e r v i c e r o u t i n e ,
2 3 -1

Ta b l e 2 1 - 3
Powe r r e c o v e r y , 5 - 1 2 ,

8-8 ,

21-2 ,

2 3-1
Tabl e 2 1 - 3
Tabl e 2 3-1

e r r o r l og e n t r y , 2 3 - 6
s e e a l so r e s t a r t r o u t i n e
Po we r r e c ov e r y A S T , 5 - 1 2 , 1 4 - 9 ,
1 8-2 1 ,

2 3-1 ,

23-6 ,

23-8

Ta b l e 9 - 2
d e l i ve r y , 2 3-8
P Q L Dq u o t a SYSB OOT pa r am e t e r s ,
1 7- 8 ,

B-1 8

1 7- 1 5 ,

E-3

1 7- 8 ,

B-1 8

3-1 4

P Q L DW SDEFAULT SYS BOOT p a r am e t e r ,
F i g u r e 1 1-1
Ta bl e 1 3 -1
Ta b l e E - 1
P QL DWS QUOTA S Y S B OOT pa r am e t e r
Ta b l e 1 3 - 1
P QL Mquo ta SYSBOOT pa r am e t e r s ,
P Q L MWSDE FAULT SYS BOOT p a r am e t e r
Ta b l e 1 3 - 1
P QL MW SQU OTA SYSB OOT pa r am e t e r
Ta b l e 1 3 - 1
P R $ I C C S r eg i s t e r , 1 0 - 1 , 1 0 - 3 ,
10- 6

Tabl e 1 0-1
P R $ I C R r eg i s t e r , 1 0 - 3 , 1 0 - 5
Ta b l e 1 0 - 1
P R $ MAPEN r eg i s t e r , 2 2 - 3 , 2 3 - 5
Fi gure 22-2
P R $ N I C R r eg i s t e r , 1 0 - 1 , 1 0 - 3 ,

2 3- 9
Tabl e 1 5-1
P r e empt i o n , 8 - 4

21-7 ,

23-5 ,

P r i m a r y b o o t s t r a p p r og r am ( VM B ) ,
7 - 6 , 7 - 9 , 2 1 - 5 , 2 1 - 7 , A- l l
Figure 21-1
Ta b l e 2 1 - 1
Ta b l e 2 1 -2
Ta b l e 2 1 - 3
P r ima ry except i o n vec to r , 2 - 1 8 ,
18-2 3 ,

20-6

e x ec u t i v e m o d e , 2 - 3 1
k e r n e l mod e , 2 - 3 1
P r i n t s ymb i o n t
Ta b l e 1 - 1
P r i v a t e pag e , 1 2 - 3

2-2 1

5-8

P r o c ed u r e c a l l i ng s t a nd a r d ,
1-1 2 ,

2-1 ,

1-2 1 ,

2 5 -1 ,

5-8

F i g u r e 2-4
P r o c ed u r e e n t r y ma s k
see entry mask
Process , 1-1 , 8 - 1
P r o c e s s a l l oc a t i o n r eg i o n ,
2 5 -1 1 ,

26-4 ,

B- 2 7

Figure 1-7
F i g u r e 2 6 -1
Ta b l e 1 7 - 5
Ta b l e 2 5 - 1
Tab l e 2 5 - 2
Tab l e E - 4
Proc ess contex t , 1- 1 3 , 1 -1 7 ,
5-1 0 t o 5-1 1 , 8 -1 6 , 9-9 ,

1 0- 5

Ta bl e 1 0 -1
P R $ TXDB r eg i s t e r , 7 - 7 ,
l S- 1 6 to 1 5 - 1 7 , 2 1 - 2 ,

Figure 3-9
P r i v i l eg ed p r o c e s s , 3 - 1 8
P r i v i l eg e d s h a r e a b l e i mag e ,
3 - 1 3 to 3 - 1 4 , 1 8 - 3
Figure 3-8
Figure 3-9
PRM C EB p r i v i l eg e
Ta b l e 9 - 1
P RMMBX p r i v i l eg e , 1 6 - 1 1 , 1 6 - 1 6
P r o c ed u r e , 1 - 1 0 , 1 - 1 2 , 1 - 1 4 ,

1 2-2 , 1 3-1 4 ,
2 2-1 3 , 2 4 - 7 ,
Figure 1-1
Tab l e 1 7 - 1

1 6-7 , 1 9- 1 ,
2 7 - 8 to 2 7 - 9

P r o c ess c ont r o l , 1 - 6 , 9 - 1 , 9-8
P r o c e ss c ont r o l b l oc k , x x x i ,
1-3 , 5-5 , 8-1 , 8-9 ,
8 - 2 2 to 8 - 2 3 , 8 - 2 6 ,
1 7 - 1 to 1 7 - 2 , 1 9 - 5 ,
2 7 - 8 , A-1 0 , D - 9
Figure 1-1
Figure 5-l
Figure 8 -1
Figure 9-1
Figure 9-3
Figure 1 1-21

Index- 2 1

9-8 ,
22-1 5 ,

INDEX
Proc e s s control block ,
Figure 1 7-1
Figure 1 7-2
Figure 17-5
Figure 1 7-6
F i g u r e 1 9- 1
F i g u r e D- 2
Ta b l e 7 - 1
Ta b l e 9 - 2
Ta b l e 1 7 - 4
Ta b l e 1 8 - 1
Ta b l e D - 2

( cont . )

P r oc e s s heade r ,
Tab l e 1 7- 5
Tab l e 1 8 - 1
T a b l e D- 3
Tabl e E -1

con f ig u r a t i o n , 1 7- 1 3
f i x ed s i z e po r t i o n , 1 1 - 2 ,
1 1 -7 ,

9-1 4 ,

11-3 2 ,

1-6 ,
1 4-2 ,

Figure 8-5
Figure 1 7-1
Figure 1 8-9
Tab l e 8 -3
d e t a ch e d p r o c e s s , 1 7 - 6 to 1 7 - 7
Figure 1 7- 1
s ub p r o c es s , 1 7 - 2 , 1 7 - 6 t o 1 7 - 7
Process d e l e t i o n , xxvi i i , 1-6 ,
5 - 1 1 , 7 - 5 , 8 - 9 to 8 - 1 1 ,
8-1 4 to 8 -1 5 , 8 -2 7 , 9-8 ,
9-1 0 ,
24-5 ,

1 7- 1 8 , 1 8 -1 8 ,
2 4-9 , 27-9
Figure 8-5
Ta b l e 8 - 3
Ta b l e 1 4 - 3
Ta b l e 2 4 - 1
s ub p r o c e s s , 1 9- 3
Figure 1 9- 1

1 9- 1 ,

P r o c e s s h e ad e r , x x i x , 1 - 3 ,
1-1 6 , 5-1 1 , 8-8 , 1 0-6 , 1 1-1 ,
1 1-4 , 1 1-7 , 1 1-2 0 , 1 1-2 7 ,
1 4 - 1 0 , 1 7 - 1 , 2 7 - 9 , A- 1 0 , D - 1 4
Figure 1-1
Figure 1 1-1
Figure 1 1-2
Fig ure 1 1 -4
Figure 1 1-6
F i g u r e 1 1-8
Figure 1 1-2 0
F i g u r e 1 4 -2
F i g u r e 1 4 -3
F i g u r e 1 4 -4
F i g u r e 1 4-5
F i g u r e 1 4-6
F i g u r e 1 4 -7
Fi g u r e 1 7-1
Figure 1 7-6
Ta b l e 9 - 2

1 1-2 ,

1 1- 1 1 ,

1 4 -1 1 ,

1 1-27 ,

1 4-2 0

11-27 ,

1 1-3 0 ,

E-3

Figure 1 1-1
Figure 1 1-8
Ta b l e E - 1
P r o c e s s h e ad e r vec to r , 2 2 - 8
Tab l e 2 2- 1
P r o c e s s h e ad e r v e c to r a r r a y s ,

8-28

Ta b l e 2 1 - 3
Ta b l e 2 3 - 1
P r oc ess c re a t i o n , xxv1 1 1 ,

1 7-1 4

Tab l e 1 7- 5
Tab l e E - 1
s i ze , 1 1 - 2 7 , 2 1 - 1 7 , E - 1
Tab l e E- 1
P r o c e s s h e a d e r pag e a r r a ys ,

s e e a l s o h a rd wa r e p r o c e s s
c o nt r o l b lo c k
Process control block
b a se r eg i s t e r ( PR $ PC B B ) ,
x x x i , 8 - 2 1 t o 8 - 2 3� 8 - 2 6 ,

8-9 , 9-8 ,
21-1 7

( cont . ) ,

Figure 1 1-2 1
p r o c e ss i nd ex a r r a y , 1 1 - 2 7
r e f e r en c e c o un t a r r a y , 1 1 - 2 7
P r o c e s s h e ad e r vec to r i nd ex ,
1 1-3 5

Figure 1 1-2 0
Figure 1 1-2 1
Figure 1 1- 2 4
P r o c e s s I /O s egmen t , 2 0 - 6 , B - 2 7
Figur e 1-7
Ta b l e 1 7 - 5
Tab l e E-4
Process I D , 1-3 , 5-1 4 , 9-8 ,
1 0 - 1 1 t o 1 0 - 1 2 , 1 6 -7 , 1 6- 1 0 ,
17-7 ,

1 7- 9 ,

2 5-1 1 ,

26-1

2 7-7 ,

F-4

Figure 1 7-4
Tab l e 1 2 - 1
P r o c e s s i nd ex , 2 7 - 1 0 , F - 4
Figure 1 1-21
F i g u r e 1 7- 4
P r o c e s s l og i c a l name t a b l e ,
Figure 26-1
Figure 2 6-2
P r o c e s s n am e , 1 - 3 , 9 - 8 , 9 - 1 0 ,
1 7- 5 ,

27-7

P r o c e s s o u t s wa pp i ng , 8 - 1 1
P r o c e s s pag e t a b l e , 1 1 - 2 ,
1 4-1 0 ,

1 4 -1 5 ,

F i g u r e 1 1-1 9
Figure 1 4-2
Figure 1 4-3
Figure 1 4-4
Figure 1 4-5
Figure 1 4-6
Figure 1 4-7
Tabl e 1 2- 1 1
Ta b l e 1 4 - 1
Tab l e 1 4- 5

I nd ex- 2 2

1 4 -2 4 ,

1 8-1 , 1 8 - 5

INDEX

P r o c e ss pag e t ab l e e n t r y , 1 2 - 4 ,
1 2 - 1 2 , 1 2- 1 7 , 1 3 - 6 to 1 3 - 7 ,
1 3-9
P r o c e s s pe rm a n e n t f i l e , 1 8 - 2 1 ,
2 0-6 , 2 0- 8
F i g u r e 2 0-1
F i g u r e 2 0- 2
P r o c e ss p r i o r i t y , 1 - 3 , 4-7 ,
8-1 , 8-3 , 8-8 , 9-6 , 9-1 0 ,
1 2 - 3 0 to 1 2 - 3 1 , 1 4 - 4 , 1 4 - 8 ,
1 7- 6 , 2 4 - 1 0 , 2 7 - 2
Figure 8-2
F i g u r e 1 4 -1
Ta b l e 1 2 -1
Ta b l e 1 4 -1
Ta b l e 1 4 -2
a s s o c i a t e d boo s t , 1 0 -8
base , 8 - 3 , 8-1 9 , 8 - 2 3 , 9-1 1 ,
1 6-7 , 2 0 -7
cur r ent , 8-3 , 8 -1 9 ,
8 - 2 2 to 8 - 2 3 , 9 - 1 1
d yn am i c ad j us tm e n t ,
8 - 3 to 8 - 5 , 8 - 1 8 , 1 2 - 2 4
Figure 8-2
Ta b l e 8 - 3
Ta b l e 1 2- 1
no rma l r ang e , 8 - 3 t o 8 - 4 , 2 4 - 9
r e a l - t i m e r a ng e , 8 - 3 , 8 - 1 9 ,
8 - 2 3 , 2 4 -9
P r o c e s s p r i v a t e pag e
Figure 1 1-1 2
P r o c e ss p r i v a t e s ec t i o n , 1 2 - 2 9
P r o c e s s p r i v i l eg e s , 1 - 3 , 1 - 1 3 ,
1-1 9 , 9-8 , 1 6-7 , 1 7- 5 , 1 7 -1 7 ,
1 8-1 1 , 1 8- 2 2 t o 1 8- 2 3 , 2 0-7 ,
2 2-1 3
Ta b l e 1 7 - 2
Ta b l e 1 8 - 1
p r i v i l eg e m a s k , 2 7 - 2
s e e a l s o i nd i v i d ua l
p r i v i l eg e n am e s
P r o c e s s quo ta b l o c k ( PQB ) ,
1 7 - 1 to 1 7 - 2 , 1 7 - 1 6
F i g u r e 1 7-1
F i g u r e 1 7-6
Ta b l e 1 7 - 2
P r o c e s s quo ta s , 1 - 3 , 1 - 1 3 ,
1 - 2 0 , 1 7- 6 , 1 7- 8 , 2 0 -7 , 2 2 - 1 3
Tabl e 1 3 -1
Ta b l e 1 7 -4
d ed uc t i b l e quo ta s , 1 7 - 9
Ta b l e 1 7 - 4
nond ed uc t i b l e quo ta s
Ta b l e 1 7- 4
poo l ed quo ta s , 1 - 4 , 1 7 - 9
F i g u r e 1 7- 1
F i g u r e 1 7- 2
Ta b l e 1 7 -4
P r o c e ss r un d o wn , 1 8 - 2 0 , 1 9 - 3
Tab l e 9 - 2

P r o c ess sch ed ul i ng s t a t e s , 4 -7 ,
8 - 1 , 8 - 1 5 to 8 - 1 6 , 8 - 2 7
Ta b l e 8 - 1
Tab l e 1 4 -2
see a l so i nd i v i d ua l s t a t e n am e s
P r o c e s s sec t ion , 1 1-1 1
P r o c e s s s ec t i o n t ab l e , 1 1 - 2 ,
1 1 -4 , 1 1 - 1 1 , 1 7 - 1 4 , E - 3
Figure 1 1-1
Figure 1 1-6
Ta b l e 1 7 - 5
Ta b l e E-1
P r o c ess s e c t i o n tab l e e n t r y ,
1 1 -4 , 1 1 - 1 1 , 1 1 - 3 0 ,
1 3 - 5 to 1 3 -6 , 1 4 - 1 1
Figure 1 1-6
Figure 11-7
Figure 1 1- 1 0
F i g u r e 1 8- 3
P r o c e s s s ec t i o n tab l e i nd ex ,
1 1 -4 , 1 1 - 1 1 , 1 1 - 1 6 ,
1 2 - 3 to 1 2 -4 , 1 2 - 7 to 1 2 - 8 ,
1 2 - 2 1 , 1 3 -6 , 1 4 - 2 6
Figure 1 1-3
F i g u r e 1 2- 3
F i g u r e 1 2 -4
F i g u r e 1 8-3
P r oc ess s t r uc t ur e , 1 - 1 8
P r oc e ss s uspe n s i o n , 5 - l , 5 - 1 0 ,
9-9
P r o c e s s-pe r ma n e n t m e s sag e s ec t i o n ,
27-5
P r o c e sso r p r io r i ty
s e e I PL
P r o c esso r r eg i st e r s
s e e i nd i v i d u a l r eg i s t e r nam e s
P r o c e s so r s ta t us l o ng wo r d ( PS L ) ,
1 - 1 4 , 4 - 2 , 6 - 1 , 8 - 2 0 , 2 4 -1
F i g u r e 1 2- 2
P r o c esso r s ta t us wo r d ( PSW )
F i g u r e 3-7
Ta b l e 2 - 3
PROC SECTCNT SYS B O OT pa r ame t e r ,
1 3 - 1 2 , B-1 5 , E - 3
Figure 1 1-1
Ta b l e E - 1
PROC STRT
modul e in s ys t em i m ag e ,
2 - 3 0 , 3 - 1 3 , 1 7 - 1 , 1 7 -1 6 ,
2 0 - 1 2 , 2 0 - 1 4 , A- 1 0 , A- 1 2
F i g u r e 1 7-6
F i g u r e 2 0 -4
Ta b l e 1 7 - 1
Ta b l e 1 8 -1
Tab l e E-4
P r og r am d ev e l o pm e n t too l s
Figure 1-2
P rotect ion code
i n t h e pag e t ab l e e n t r y , 1 1 - 4
Figure 1 1-3

I nd e x- 2 3

I NDEX

PSWAPM p r i v i l eg e , 9 - 1 1 ,
1 3 - 1 5 to 1 3 - 1 6
Ta b l e 9 - 1
Ta b l e 1 7 -3
PTE PFN a r r ay , 1 1 - 1 6 to 1 1 - 1 7 ,
1 1 - 3 0 , 1 2 -4 , 1 2 -7 ,
1 2- 1 4 to 1 2 - 1 5 , 1 2- 1 7 , 1 2 - 2 5 ,
1 3- 5
Figure 1 1-9
Figure 1 1-2 0
Ta b l e 1 1 - 2
P u r g e Wo r k i ng S e t
sys tem s e rv i c e ( $ P URGWS ) ,
1 2-6 , 1 3-1 4
P u t Me s sag e
sys tem s e rv i c e ( $ P UTM SG ) ,
1 7-1 9 , 27-4 , 2 7-6

Q ua n t um end , 4 - 6 , 5 - 4 , 5 - 1 2 ,
8 - 4 to 8 - 5 , 1 0 - 6 to 1 0 -7 ,
1 3 -1 0 , 1 3 -1 3
Ta b l e 8 - 3
Ta b l e 9 - 2
Ta b l e 1 3 -2
Ta b l e 1 4 - 3
Q UANTUM SYSBOOT pa r am e t e r , 8 - 5 ,
B-1 5
Q u e ue I /0 Reque s t
sys tem s e rv i c e ( $ Q I O ) , 5 - l ,
5-4 , 5 - 8 , 5 - 1 3 , 8 - 9 , 8 - 1 5 ,
9 - 4 , 9 - 1 3 , 1 5 - 4 , 1 6 -6 ,
1 6-1 9 , 24-7
Q u e u e I /0 Reque s t a nd
Wa i t fo r Eve n t F l ag
sys tem s e rv i c e ( $ Q I OW ) , 1 6 - 6
Q u e u e i n s t r uc t i o n s , 1 - 1 1 , 4 - 3 ,
1 1 - 3 7 , 2 5 -9 , 2 5 -1 1

RAB ( Re c o rd Ac c e s s B l oc k ) , 3 - 1 2
Read a c c e s s i b i l i t y , 3 - 5
Read Ev e n t Fl ag
sys tem s e rv i c e { $ R EADE F ) ,
9-7
R e a d i n prog r e s s
PFN t r a n s i t i o n s ta t e , 8 - 1 1 ,
1 2 - 4 , 1 2 -1 4 , 1 2 - 1 7 , 1 3 - 5
Figure 1 1-1 1
F i g ur e 1 2- 3
Figure 1 2-4
Figure 1 2-5
Figure 1 2- 6
F i g u r e 1 2-7
Ta b l e 1 4 -4

Rea l - t i m e b i tm a p
Ta b l e 2 2 - 1
R EALT I M E S PTS S Y S B O OT pa r am e t e r ,
6 - 1 6 , 2 2 - 8 , B- 1 7 , E - 9
Tab l e 2 2 - 1
Ta b l e E - 2
Reco rd m a n ag em e n t s e rv i c e s
s e e RM S
R EFCNT PFN a r r a y ,
1 1 - 1 8 to 1 1 - 1 9 , 1 1 - 3 4 , 1 2 - 4 ,
1 2 -6 , 1 2 - 1 4 to 1 2 - 1 5
F i g u r e 1 1-9
Ta b l e 1 1 - 2
Reg i s t e r s ave m a s k
see entry mask
RE I i n s t r uc t i o n , 1 - 1 1 , 1 - 1 7 ,
2-8 , 2 -1 8 , 2-2 3 , 3-1 0 , 3 -1 7 ,
4 - 2 , 4 - 6 , 5 - l to 5 - 2 ,
5-6 to 5 - 7 , 5 - 9 , 6 - 1 to 6 - 2 ,
6-9 , 8 -2 3 , 8 -2 6 , 8- 2 8 , 1 7-1 8 ,
1 8 - 1 5 , 1 8 - 1 9 , 2 0 -7 , 2 3 -7 ,
2 4 - 1 , A-8
F i g u r e 1-4
F i g u r e 2-3
F i g u r e 3-2
Figure 3-5
Figure 3-6
Figure 3-8
Figure 6-3
Figure 6-4
Figure 6-5
Figure 6-6
Figure 6-7
Figure 8-7
Ta b l e 2 3 -1
Re l e a se pend i ng
PFN t r a n s i t i o n s ta t e , 1 2 - 6 ,
1 2-8
Figure 1 1- 1 1
F i g u re 1 2-3
Figure 1 2-4
Figure 1 2-5
RE LOAD S YSGEN c omma nd , 1 5 - 9
Remo t e t e rm i n a l AC P
Tab l e 1 - 1
REMQUE i n s t r uc t i o n , 4 - 3
REPLY
Tab l e 1 - 1
REQUEST
Ta b l e 1-1
RESALLOC s pe c i a l SYS B O OT p a r am e t e r
f l ag , B - 1 7
Re s c h ed u l i ng i n t e r r upt , 1 - 1 5 ,
4 - 4 , 4 - 7 , 8 - 2 0 , 8 - 2 7 , 9- 6 ,
9 - 1 1 , 1 4 -4 , 2 4 -1 0
Figure 1-5
Ta b l e 4 - 1
Re s c h ed u l i ng i n te r r upt hand l e r
Figure 8-7

I ndex- 2 4

INDEX

Re se r ved add r e s s i ng mod e e x c ept i o n
Ta b l e 2 - 1
Ta b l e 2 - 2
Re se rved i ns t r uc t i o n ex c e pt i o n ,
2 - 1 4 , 7 - 4 to 7 - 5
Ta b l e 2 - 1
Ta b l e 2 - 2
Re s e rved ope r a nd e x c e pt i o n , 2 - 8
Ta b l e 2 - 1
Ta b l e 2 - 2
Re s i d en t computa b l e proc e ss , 8 - 9
Re s i g n a l l i ng a n e x c e pt i o n , 2 - 2 ,
2-2 3
e x ampl e o f
Figure 2-6
Re so u r c e a l l o c a t i o n , 1 - 2 0
Re so u r c e c on t r o l , 1 - 1 9
Re so u r c e wa i t mod e , 1 9 - 2
Ta b l e 1 7 - 3
Re so u r c e wa i t s ta t e ( MWA I T } ,
8 - 1 3 , 1 2-3 1 , 1 9-6 , 2 4-1 1
R E S TAR . CMD , 2 3 - 4
Re s t a r t pa r am e t e r b l o c k ( R PB ) ,
7 - 9 , 2 1 -7 , 2 1 -9 ,
2 1 - 1 4 to 2 1 - 1 5 ,
2 2 - 8 to 2 2 - 1 0 , 2 3 -1 ,
2 3 -3 to 2 3 -4 , 2 3 - 9 , B- 2 2 ,
D- 1 8 , E - 9
Figure 1-6
Figure 21-1
Figure E-1
Ta b l e 2 1 - 3
Ta b l e 2 2 - 1
Ta b l e 2 3 - 1
Ta b l e E - 2
Re s t a r t r o u t i n e , 2 2 - 8 t o 2 2 - 9
Ta b l e 2 1 - 3
s e e a l s o powe r r ecove r y
Re s t a r t a b i l i ty , 2 - 8
R e s ume P r o c e s s
s y s t em s e rv i c e ( $ R E S UM E } ,
5 - 1 1 , 8 - 1 1 , 9 - 9 to 9 - 1 0 ,
1 9- 2
Tabl e 8 - 3
Ta b l e 9 - 1
Ta b l e 9 - 2
R E T i n s t r uc t i o n , 1 - 1 4 , 2 - 2 4 ,
3 - 1 , 3- 1 0 , 3 - 1 3 , 3 - 1 7 , 5 - 8
F i g u r e 3-1
F i g ure 3-2
F i g u r e 3-3
Figure 3-5
F i g u r e 3-6
Figure 3-8
Figure 3-9
RMS , 1 - 6 , 1- 1 2 , 3 - 1 , 8 - 1 0 , 9 - 4 ,
9-1 3
Figure 1-2
Figure 1-4
Ta b l e 1 - 1

R M S d i spa tch e r , 3 - 1 0
Figure 3-6
RMS e r r o r d e tec t i o n , 3 - 1 3
RMS imag e , 1 1 - 2 1 , 2 2 - 1 , 2 2 - 1 3 ,
2 2 - 1 6 to 2 2- 1 7 , A�1 s
F i g ur e 1 - 6
Figure E-1
Tabl e 1 2 - 1
Ta b l e 2 1 - 1
Tabl e E - 2
Ta b l e E - 3
R M S r und own , 1 9- 2 , 2 0 - 6 , 2 0 - 9 ,
2 0 -1 4
RMS s e rv i c e v e c to r
Figure 3-6
RM S se r v i c e s
Ta b l e 3 - 1
R M S s ynch ron i za t i o n
F i g u r e 3 -1
Ta b l e 3 - 1
RM S DFMBC SYSBOOT pa r am e t e r ,
a= 1 s
RM S DFMBFHSH S Y S B OOT pa r am e t e r ,
a=1 s
RM S DFMBFIDX S Y S B OOT pa r ame t e r ,
a=1 s
RM S D FMBFRE L S Y S BOOT p a r am e te r ,
a=1 s
RMS DFMBFSDK SYS BO OT pa r am e t e r ,
a=1 s
RM S DFMBFSMT S Y S B OOT pa r am e te r ,
a= 1 s
RMS DFMBFSUR S YS BOOT p a r am e t e r ,
a= 1 s
RMS S HARE u t i l i ty , 2 2 - 1 8 , 2 5 - 1 3 ,
E-1 0
Ta b l e 2 1 - 1
Ro und rob i n sched u l i ng ,
8 - 4 to 8 - 5
RSE
modul e i n s ys t em i mag e ,
8 -5 , 8-1 7
Ta b l e 1 4 - 3
RSX- 1 1M AME , 1 8 - 2 , 1 8 - 1 5 , A- 9
Figure 1-8
s e e a l so c om pa t i b i l i ty mod e
RSX . EXE
Figure 1-8
RT-1 1 boo ts t r a p , 2 1 -6
Run- T i m e L i b r a r y , 1 - 2 4
Figure 1-2
Figure 1-8
Rund own
s ys t em s e rv i c e ( $ R UNDWN ) ,
1 8- 2 0
s e e imag e r und own
s e e p r o c e s s r und o wn
RX O l f l oppy d i s k , 2 1 - 6

I nd e x- 2 5

INDEX

S B I E RRENA B L E SYSBOOT
pa r am e t e r fl ag ,
B-1 7
S c a t t e r/ga t he r , 1 1 - 3 4
S C BVE C TOR
m o d u l e in s ys tem imag e ,
2 1-1 7
S C HED
m od u l e in system imag e ,
8 -2 0 , 8 - 2 2
S c h e d u l e Wa k e up
s ys tem s e rv i c e ( $ S C HDW K ) ,
1 0 - 1 0 to 1 0 -1 1
F i g u r e 1 0 -1
Ta b l e 9 - 1
S c h e d ul ed wa ke up , 1 0 -1 , 1 0 - 7 ,
1 0-9
S c h ed u l e r , 1 - 1 0 , 4 - 8 , 5 - 1 1 ,
8-1 , 1 2-2 4 , 1 2-3 0 , 1 4-2 7 ,
1 7-7 , 2 2-1 0 , 2 4-5
Figure 1-2
Figure 1 4-1
S c h e d u l i ng , x x v i i i , 1 - 6 , 8 - 1 ,
1 3- 5 , 2 4- 3
i n swa p s c h ed ul i ng , 1 4 - 4 , 1 4 - 2 2
o u t swa p sched ul i ng , 1 4 -4 ,
1 4-1 3
swa p sc h ed ul i ng , 1 4 -2
S c h e d u l i ng s t a t e t r an s i t i o n s
Figure 8-5
S DAT
mod u l e in s ys t em i m ag e ,
8 - 9 , 8 - 2 2 , B- 5
S e a r ch f o r c ond i t i o n h and l e r
Fig u r e 2-4
F i g u r e 2-5
F i g u r e 2-6
S e c o nd a r y b o o t s t r a p p r og r a m
( S YS B OOT ) ,
x xx i , 7 - 6 , 2 1 - 1 1 , 2 1 - 1 5 , A- l l
F i g u r e 2 1- 1
F i g u r e 2 2- 2
F i g u r e 2 2- 4
Tabl e 2 1 -1
Ta b l e 2 1 - 4
Tabl e 2 2 -3
T ab l e 2 2-4
S e c o nd a r y e x cept i o n v e c t o r ,
2-1 8 , 1 8- 2 3
S e c t i on t ab l e e n t r y
s e e g l o b a l s e c t i o n t ab l e e n t r y
s e e p r o c e s s s ec t i o n t a b l e e n t r y
S e l f - r e l a t i ve q ue ue , 1 1 - 3 7
S e nd Me s s ag e t o Ac c o un t i ng Ma n ag e r
s ys te m s e rv i c e ( $ SNDACC ) ,
2 7- 1

S e nd Me s s ag e t o E r r o r Logg e r
s ys te m s e rv i c e ( $ S NDERR ) ,
7 - 2 , 2 7- 3
S end Me s s a g e to Ope r a to r
s y s t e m s e rv i c e ( $ S NDO PR ) ,
2 7- 3
S e nd Me s s ag e t o Sym b i o n t Ma n ag e r
s ys t e m s e rv i c e ( $ SNDSMB ) ,
2 7- 2
Figure 2 0-2
Sense cha rac te r i s t i c s $ Q I O
f un c t i o n c od e ( 1 0 $ S EN S E C HAR ) ,
1 6- 1 9
S e n s e mod e $ Q I 0
f un c t i o n c o d e ( I O $_S EN S EMODE ) ,
1 6- 1 9
S e qu e n c e n umbe r v e c to r , 2 2 - 8 ,
2 5- 1 3
Ta b l e 2 2 - 1
S ET ACC O UNT ING c omma n d , 2 7 - 1
Set AST Enable
s y s t e m s e rv i c e ( $ S E TAST ) ,
5-6 , 9-1 1
Ta b l e 9 - 1
S ET c omma nd , 1 - 7
T ab l e 1 - 1
S e t Ev e n t F l ag
s ys t em s e rv i c e ( $ S ET E F ) , 9 - 6
S e t E x c ept i o n Ve c to r
s ys te m s e rv i c e ( $ S ETEXV ) ,
2-1 7
S ET M E S SAGE c omma nd , 2 7 - 5
Ta b l e E - 4
S ET N OC ONTROL Y c omma nd , 2 0 -1 4
S e t Powe r Re c ove r y AST
s ys te m s e rv i c e , 1 4 - 9
sys t em s e rv i c e ( $ S E TPRA ) ,
2 3 -8
Ta b l e 9 - 1
Ta b l e 9 - 2
S e t P r i o r i ty
s ys t e m s e rv i c e ( $ S E TPR I ) ,
8 - 3 t o 8 - 4 , 9 - 1 0 to 9 - 1 1
Ta b l e 8 - 3
Ta b l e 9 - 1
S e t P r i v i l eg e s
s ys te m s e rv i c e ( $ S ETPRV ) ,
1 8- 2 4
Ta b l e 1 8 - 1
S e t P r o c e ss Name
s ys t e m s e rv i c e ( $ S E TPRN ) ,
9-11
Ta b l e 9 - 1
S ET PROC E S S/PR I OR I TY c omma nd ,
8 -3 t o 8 -4
S ET PROC E S S / PR I VI L EG E S c omma nd ,
1 8- 2 6

I nd ex - 2 6

INDEX

S e t P r o t e c t i o n o n Pag e s
s y s tem s e rv i c e ( $ S ETPRT ) ,
1 3-1 6
S e t Re s o u r c e Wa i t Mo d e
s y s tem s e rv i c e ( $ S ETRWM ) ,
8 - 1 3 , 9-1 1
Ta b l e 9 - 1
Ta b l e 9 - 2
S e t Swa p Mo d e
s ys tem s e rv i c e ( $ S ETSWM ) ,
9 - 1 1 , 1 3 - 1 5 to 1 3 - 1 6
Ta b l e 9 - 1
Ta b l e 9 - 2
S E T SYSGEN c omma nd , 2 2 - 1 9 ,
2 2- 2 3 , 2 2-2 5
F i g u r e 2 2-4
F i g ur e 2 2- 5
Ta b l e 2 2 - 3
S e t S y s t em Se r v i c e Fa i l u r e Mo d e
s ys t em s e rv i c e ( $ S ETSFM) ,
3 - 1 7 , 9- 1 1
Ta b l e 9 - 1
Ta b l e 9 - 2
S e t Sys t em T i m e
s ys tem s e rv i c e ( $ S E T IM E ) ,
1 0 - 3 to 1 0 - 5 , 2 2 -1 5
Ta b l e 1 0 - 1
Set T i m e r
s ys tem se rv i c e ( $ S E T IM R ) ,
5 - l , 5-4 , 5 - 8 ,
1 0 - 7 to 1 0 - 8 , 1 0 - 1 0 to 1 0 - 1 2
S ET U I C c omma nd
Ta b l e 1 8 - 1
S ET WORK ING S E T c omma nd , 1 3 - 1 2
Ta b l e 13- 1
S ET WORK I NG S ET/QUOTA c omma nd ,
1 1-8
S ET I PL m a c r o , 2 4 - 1
F i g ure 2 4-1
S E TPRV p r i v i l eg e , 1 7 - 5 , 1 8 - 2 6
S ETTIME SYSBO OT pa r am e t e r f l ag ,
2 2 - 1 5 , B-1 7
S h a r ea b l e i m ag e , 1 8 - 1 2
Ta b l e 2 1 - 1
S h a r ed f i l e s , 9 - 1
S h a r ed m emo r y
1 a yo u t , 1 1 - 3 7
phys i c a l l ayo u t
Figure 1 1-2 5
Sh a r ed m emo r y c ommo n d a ta pag e ,
1 1- 3 8
F i g ure 1 1- 2 5
Ta b l e 1 1 - 3
Sh a r ed m emo r y c ommo n ev e n t b l oc k
Figure 9-4
Sh a r ed memo r y c o n t r o l b l o c k ,
1 1- 3 8
Figure 1 1- 2 6

S h a r ed memo r y m a i l box
c o n t r o l b l oc k ,
9 - 1 5 , 1 1 -4 2 , 1 6-1 3
F i g ur e 1 6-2
Figure 1 6-3
S HE L L
modul e i n s ys tem i mag e ,
1 -2 2 , 2-3 1 , 1 4 -2 , 2 1- 1 7 ,
2 5 - 1 1 , B- 2 4 , B- 2 6 , E - 1 7
F i g ure 2 6-1
Ta b l e 1 7 - 1
Ta b l e E - 4
She l l p r o c e s s , 1 1 - 3 2 , 1 4 - 1 2 ,
1 7 - 1 , 1 7 -1 2 , 2 2 - 5 , A- 1 2
F i g ur e 1 1- 2 2
F i g u r e 1 7- 5
Ta b l e 1 3 - 1
Ta b l e 1 7 - 5
Ta b l e E-4
S HMEM p r i v i l eg e , 1 6 - 1 1
Sho r t l i t e r a l s , 1 - 1 1
S HOW c omma nd , 1 - 7
Ta b l e 1 - 1
S HOW SYSGEN c ommand , 2 2 - 1 9
Ta b l e 2 2 - 3
SHOW SYSTEM c ommand , 8 - 3 , 1 0 - 4 ,
E - 1 7 , F-4
S HRCNT PFN a r r a y , 1 1 - 1 9 ,
1 2-1 4 t o 1 2-1 5 , 1 3- 1 5 ,
1 4-1 4 t o 1 4-1 5
Figure 1 1-9
Tab l e 1 1 - 2
S HUTDOWN . COM , 7 - 7
S i g n a l a r ra y , 2-8 , 2-1 8 , 2 - 2 3
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Tab l e 2 - 2
S K I PW S L s pe c i a l S Y S B O OT p a r am e t e r ,
1 2 - 1 8 to 1 2- 1 9 , 1 4 - 1 0 , 1 4 - 2 6 ,
B-1 6
Sm i th so n i a n I n s t i t u t i o n
a s t r onom i c a l c a l end a r , 1 0- 3
S OFT INT m a c r o , 4 - 2
S o f twa r e c o n t e x t , 1 - 1 , 1 - 3
Fi gure 1-1
So f t wa r e d e t e c t ed e x c e p t i o n ,
2-1 4
So f t wa r e i n t e r r up t r eq ue s t
r eg i s t e r ( PR $ S I RR )
Figure 4-1
F i g u r e 4 -1 , 4 - 1

I nd ex - 2 7

INDEX

So f twa r e i n te r r up t s umma r y
r eg i s t e r ( PR $ S I S R )
Figure 4-1
F i g u r e 4 -1 , 4 - 1
Ta b l e 2 1 - 3
Ta b l e 2 3 - 1
So f twa r e i n t e r r up t s , 1 - 1 1 ,
1 -1 5 , 1 -1 8 , 4-1 , 5-6 , 5 -1 3 ,
8 -1 8 , 2 4-6
Figure 1-5
F i g u r e 2-1
Ta b l e 4 -1
So f twa r e PC B
s e e p r o c e s s c on t r o l b l o c k
So f twa r e p r i o r i ty
s ee p r o c e s s p r i o r i ty
So f twa r e t i me r , 4 - 5 , 1 0 - 6
Figure 1-5
i n t e r r up t s e r v i c e r o u t i n e ,
4-4 , 4-6 , 1 0-1 , 1 0-6 , 1 3-1 4
Ta b l e 4 -1
So f twa r e- d e t e c t ed e x c e p t i o n s ,
2 -1 2
S p e c i a l k e r ne l AST , 5 - 3 ,
5 - 5 to 5 - 6 , 5 - 9 to 5 - 1 2 ,
9 - 9 to 9 - 1 0 , 1 2 -2 5 ,
1 2 - 2 8 to 1 2 -2 9 ,
1 6 - 9 to 1 6- 1 0 , 1 9- 1 t o 1 9- 2 ,
2 3 - 8 , 2 4 - 5 , 2 4 -7 , 2 7 - 8 to 2 7 - 9
Ta b l e 1 2- 1
S PT R E Q SYS BOOT p a r am e te r , B - 1 5 ,
E-9 , E-1 4
Ta b l e E - 2
S PTSKE L
modul e i n s ys t em i m ag e , E - 9
S RVE X I T , 3 - 1 0 , 3 - 1 3 , 3 - 1 7
F i g u r e 3 -2
F i g u r e 3-4
Figure 3-5
Figure 3-6
Figure 3-7
Figure 3-8
s e e a l s o KSRVE X I T
S S $ C ONT INUE
s ee c o n t i n u i ng f r om a n ex c e p t i o n
S S $ RES IGNAL
s ee r e s i g na l l i ng an e x c e p t i o n
Sta ck ove r f l ow, 2-9
S TARDEF . MDL , A- 3 t o A - 4 , A- 1 8 ,
D-1
Ta b l e D- 1
S TARLET . M LB , A- 2 , A- 4 , D - 1
S t a r t up c ommand f i l e , 2 2- 1 ,
2 2 - 9 , 2 2 - 1 3 , 2 2- 1 7 to 2 2 - 1 8
Ta b l e 2 1 - 1
S TARTU P . C OM , 2 5 - 1 3

S TATE PFN a r r ay , 1 1 - 7 , 1 1 - 1 6 ,
1 1 - 1 8 , 1 1 - 2 3 , 1 2 - 4 , 1 2- 6 ,
1 2-1 9
F i g u r e 1 1-9
F i g u r e 1 1-1 1
F i g u r e 1 1-1 3
Ta b l e 1 1 - 2
S t a t e q ue ue s , 8 - 9
S T O P c omma nd , 2 0 - 1 6
F i g u r e 2 0-3
S t r i ng f o rm a t t i ng s e rv i c e s ,
1-6 , 3-1
S t r uc t u r e t ype c o d e s
Ta b l e D-4
S UBM I T c omma nd , 2 0 - 1 , 2 0 - 4
F i g u r e 2 0-2
S u b s c r i pt r ang e a r i th me t i c t ra p
Ta b l e 2 - 3
S upe rv i so r a c c e s s m od e , 2 0 - 5 ,
20-7
Figure 1-4
S up e rv i so r m o d e e x c e p t i o n , 2 - 3 1
S up e rv i so r s ta c k
F i g u r e 1-7
Ta b l e E - 4
S u spend P r o c e s s
s y s tem s e rv i c e ( $ S US PN D ) ,
5-1 0 , 8 -1 1 , 8 -1 5 ,
9 - 9 to 9 - 1 0
Tab l e 9 - 1
Ta b l e 9 - 2
S u s pend s pe c i a l k e r n e l AST
Ta b l e 9 - 2
S u s pend wa i t s ta t e s
( S US P a nd S U S PO ) ,
5- 1 1 , 8 - 1 5 to 8 - 1 6 ,
9 - 9 to 9 - 1 0 , 2 7 - 9
Figure 8-5
Ta b l e 8 - 1
Ta b l e 1 4 - 2
SVPC TX i n s t r uc t i o n , 1 - 1 1 , 1- 1 9 ,
5- 1 1 , 8 - 2 2 , 8 - 2 6 to 8 - 2 8 , 1 9- 5
Figure 8-7
Swa p f i l e , 1 1 - 7 , 1 1 - 3 0 , 1 1 - 3 5 ,
1 2-2 6 , 2 2 -1 3 , 2 2- 1 6
Ta b l e 2 1 - 1
Ta b l e 2 2 - 3
i n i t i a l i za t i o n , F - 3
Swa p f i l e b i tm a p
F i g u r e 1 1-2 3
Swa p f i l e t ab l e
Fi g u r e 1 7-5
Swa p f i l e t ab l e e n t r y , 1 1 - 3 0 ,
1 1 - 3 2 , 1 4 - 1 1 , 1 7 - 1 3 , 2 2- 5 , F- 3
F i g u r e 1 1- 2 2
Figure 1 1-2 3
Figure 1 7-5

I nd ex- 2 8

INDEX

Swa p s l o t , 1 4 - 1 2 , 1 7 - 7 , 1 9 - 5
F i g u r e 1 7-5
SWAPF I LE
mod u l e i n s y s t e m i m ag e ,
1 1-3 0 , 1 1-32
SWAPF I LE . SYS , 1 1 - 3 2 , 1 4 - 1 2
F i g u r e 1 1- 2 2
F i g u r e 1 7- 5
Swa ppe r I /O , 1 - 1 0 , 1 1 - 3 4 ,
1 2- 1 9 , 1 4-1 1
Figure 1-3
Swa ppe r m a p , 1 1 - 3 2 , 1 1 - 3 4 ,
1 4 - 1 0 , 1 4 - 1 2 t o 1 4 -1 3 , 1 4 - 1 5 ,
1 4-2 4 , 2 2- 9 , 2 5-1 3
F i g u r e 1 1- 2 4
F i g u r e 1 4-2
F i g u r e 1 4-3
F i g u r e 1 4 -4
Figure 1 4-5
F i g u r e 1 4 -6
F i g u r e 1 4 -7
Ta b l e 1 2 - 1
Tab l e 2 2 - 1
Swa ppe r p r oc e s s , 1 - 4 , 1 - 1 0 ,
1 - 1 5 t o 1 - 1 6 , 8 - 8 to 8 - 9 ,
8 - 1 5 , 1 1 - 1 , 1 1 -7 , 1 1 - 1 1 ,
1 1-1 7 , 1 1 - 3 2 , 1 4 -1 t o 1 4-2 ,
1 7 - 1 , 1 7 - 1 3 , 2 2- 8 , 2 2- 1 3 ,
A- 1 2 , B - 7
Figure 1-2
Figure 1-3
F i g u r e 1 4 -1
Tab l e 9 - 2
Ta b l e 1 2 -1
T a b l e 1 4 -1
Ta b l e 1 4 -3
Ta b l e 1 7 - 1
Ta b l e 2 1 - 1
wa k e up c a l l , 8 - 8 , 8 - 1 8
Swa ppe r ' s P O b a s e r eg i s t e r , 2 2- 9
Swa pp i ng , 1 4 -1
SWP PR I O s p e c i a l SYSBOOT
p a r am e t e r ,
B- 1 6
Tab l e l 2 - l
Ta b l e 1 4 - 1
SWPFA I L s pe c i a l SYS B OO T
p a r am e t e r ,
1 4 - 8 , B- 1 6
SWPF I LCNT s p e c i a l SYS B OOT
p a r am e te r ,
B-1 5
SWPRATE s p e c i a l SYSB OOT
p a r am e t e r ,
1 4 - 4 , B- 1 6
SWPVBN PFN a r r ay , 1 1 - 2 0 , 1 1 - 3 5 ,
1 2-2 6 , 1 4 -1 4 , 1 4 - 2 4
F i g u r e 1 1 -9
T a b l e 1 1 -2

SYE
see e r r o r l og r epo r t g en e r a to r
Symb i on t m a n ag e r
( j o b control l e r ) , 27-2
Symbo l n am i ng c onven t i o n s ,
x x i x , C-1
Symbo l i c d ebug g e r , 2 2 - 1 8
s e e d e b ug g e r
Sync h r o n i z a t i o n , x x ix , 1 - 6 ,
1- 1 1 , 1-1 8 , 1 - 2 0 ,
9- 1 3 t o 9 - 1 4 , 1 1 - 3 7 , 2 4 - 1 ,
2 5-7
Ta b l e 2 4 - 1
SYS $ CALL HAND L , 2 - 2 6 , 2 - 2 8
F i g ure 2 - 6
F i g u r e 2-7
F i g u r e 2-8
SYS $ C OMMAND , 2 0 - 6 , 2 0 - 8
Figure 20-1
Figure 20-2
SYS $ D I SK , 1 7 - 6 , 1 7 - 1 8
Tab l e 1 7- 2
SYS $ ERROR , 9 - 1 4 , 1 7 - 6 ,
1 7 - 1 8 to 1 7 - 1 9 , 2 0 - 6 , 2 0 - 8 ,
2 7 -6 to 2 7 -7
Figure 20-1
Figure 20-2
Ta b l e 1 7 - 2
SYS $ IN PUT , 9 - 1 4 , 1 7 - 6 , 1 7 - 1 8 ,
2 0 -6 , 2 0 -8
Figure 20-1
Figure 20-2
Ta b l e 1 7 - 2
S YS $ 0UTPU T , 9- 1 4 , 1 7 - 6 ,
1 7- 1 8 to 1 7 - 1 9 , 2 0 - 6 , 2 0 - 8 ,
2 7 -6 to 2 7 -7
Figure 20-1
Figure 20-2
Ta b l e 1 7 - 2
SYS . EXE
s e e sys tem i mag e f i l e
SYS . STB
s e e s ys t em s ym b o l t ab l e
SYS B OOT
s e e s e c o nd a r y b oo t s t r a p p r og r am
SYS B OO T a nd pa r a m e t e r f i l e s ,
2 2- 1 9
SYSB OOT p a r ame te r s , x x i x ,
x x x i , 1 0-5 , 1 1-1 , 2 1-1 5 ,
2 1 - 1 7 , B- 1 4 , E- 1
Ta b l e 1 7 -1
T a b l e 2 2- 4
Ta b l e E-2
see a l s o i nd i v i d ua l
pa r a m e t e r n am e s
SYS C OMMON
mod u l e in s ys t e m i m ag e ,
1 0 -7 , 1 0 - 9 , B-8
F i g ur e 2 6-1

I nd ex - 2 9

INDEX

SYSDE F . MDL , A-3 to A-4� A- 1 8 ,
D-1
Ta b l e D-1
SYSGEN a nd pa r am e t e r f i l e s ,
22-23
SYSGEN u t i l i ty , 1 - 7 , 6 - 7 , 6 - 1 0 ,
6-1 3 , 1 1- 3 2 , 1 1 -3 7 ,
2 2 - 1 8 to 2 2- 1 9 , A- 1 6 , F- 3
F i g ur e 1 1-2 2
F i g u r e 2 2- 5
Ta b l e 1 - 1
Ta b l e 2 1 -1
Ta b l e 2 2 -3
Ta b l e 2 2-4
SYS I N IT p r o c e s s , 7 - 7 , 1 0 - 3 ,
1 1 - 3 0 , 1 1 - 1 2 , 1 4 -1 2 , 1 8 -2 ,
2 1 - 1 8 , 2 2- 1 , 2 2 -1 3 , 2 2- 2 3 ,
2 7 - 4 , A- 1 1 , F- 3
Figure 1 1-22
F i g u r e 2 2- 4
Tab l e 2 1 -1
SYS LOAVEC
mod u l e i n sys t em i m ag e ,
2 2- 1 1
F i g u r e 2 2- 3
Ta b l e 2 2- 1
SYS LOAx xx . EXE , 2 1 - 1 6 , 2 2 - 1 1
Tab l e 2 2 -1
SYSMAR . MAR , A- 3
SYSMWCNT SYS BOOT p a r am e t e r ,
B-1 5 , E-1 1 , E-1 6
Ta b l e 1 3 -1
Ta b l e E - 2
Ta b l e E - 3
SYSNAM p r i v i l eg e , 2 6 - 4
SYS PAG I NG S YSBOOT p a r am e t e r f l ag ,
2 1 - 1 8 , 2 2-5 , B-1 7
SYS PARAM
m o d u l e i n s ys t em i m ag e ,
B - 1 4 , B- 2 0
SYS PFC s pe c i a l SYSBOOT p a r am e t e r ,
B- 1 4
Ta b l e 1 2 -1
Sys tem , XXX
Sys t em b a se r eg i s t e r ( PR $_S B R ) ,
21-1 8
Figure 21-2
F i g u r e 2 2- 1
Tab l e 2 1 -3
Ta b l e 2 1 -4
Ta b l e 2 3 -1
Sys tem c o n t e x t , 1 - 1 3 , 1 5 - 1 9
Sys t em c o n t r o l b l o c k , 1 - 1 4 ,
1-1 7 , 2-4 , 2-8 , 3-4 , 4-1 ,
6 - 1 , 6 - 3 to 6 - 4 , 6 - 9 , 2 1 - 9 ,
2 1 - 1 5 , 2 2 - 5 , 2 3 -1 , B-2 3 , E - 1 0
F i g u r e 1-6
F i g u r e 2-1
F i g u r e 6 -1
F i g u r e 6 -2

System control block ,

( cont . )

Figure 6-3
Figure 6-4
Figure 6-5
Figure 6-6
Figure 21-1
Figure 2 1-2
Figure E-1
Ta b l e 2 2 - 2
Ta b l e E - 2
Ta b l e E - 3
s i ze , 2 1 - 1 7
S y s t em c o n t r o l b l o c k
b a s e r eg i s t e r ( PR $_S C B B ) ,
6-4 , 2 2-5
Figure 2-1
Figure 6-2
F i g u r e 2 1- 1
Figure 21-2
Ta b l e 2 1 - 3
Ta b l e 2 3 - 1
Sys t em c o n t r o l b lo c k v e c to r ,
7-1 1
Figure 6-1
S y s t em c r a sh e s
s e e b ug ch e c k
s e e f a t a l b ug ch e c k
Sy s t em d i s k d r i v e r , 2 1 - 1 7
Ta b l e 2 1 - 4
Ta b l e 2 2- 1
Sy s t em d ump a na l y z e r ( S DA ) ,
x x i x , 7 - 6 , 7 - 9 , 8 - 3 , 2 5- 3 ,
A- 1 6
Ta b l e 1 - 1
Ta b l e 2 2- 1
Sy s t em d ump f i l e , 7 - 9
Sys t em even t , 8 - 1 5 , 9 - 6
Sy s t em even t r epo r t i ng , 8 - 1 7
Ta b l e 8 - 3
Sy s t em h e ad e r , 1 1 - 2 0 , 1 3 - 7 ,
1 3 -9 , 2 1 - 1 7 , 2 2 - 1 7 , 2 5 - 1 1 ,
B- 2 3 , E - l l
Figure 1-6
Figure 1 1-1 5
Figure 11-18
Figure 21-2
F i g u r e E-1
Tab l e 2 2- 1
Ta b l e E - 2
Ta b l e E - 3
S y s t em i d en t i f i c a t i o n r eg i s t e r
( PR $ S I D ) ,
2 1 - 9 , 2 1 - 1 6 , 2 2- 1 1
Sy s t em i m ag e f i l e ( SYS . EXE ) ,
xx i x , 1-1 6 , 7-6 , 1 0-5 ,
1 1 - 2 1 , 2 1 - 1 5 , 2 1 - 1 7 to 2 1 - 1 8 ,
2 2- 1 0
Figure 1-6
F i g u r e 1 7- 5
F i g u r e 2 2- 4

I nd ex- 3 0

INDEX

( SY S . E XE ) { cont . ) , Sy s t em s e rv i c e d i spa tc h i ng , 3 - 1
S y s t em s e rv i c e f a i l u r e e x c e p t i o n ,
F i g u r e 2 2- 5
2-1 3 , 3-1 2 , 9 -1 0 , 1 8- 2 3
Figure E-1
Ta b l e 2 - 2
Ta b l e 1 2 - 1
Ta b l e 1 7 - 3
Tab l e 1 7 - 1
Sys t em s e rv i c e v e c to r , 3 - 1 ,
Ta b l e 2 1 - 1
Ta b l e 2 1 - 4
8-1 6 , 2 1 -1 8 , B-1
Tab l e E - 2
F i g u r e 1-6
Sys t em i n i t i a l i za t i o n , x x v 1 1 1 ,
Figure 3 -1
7 - 1 , 1 0 - 3 to 1 0 -4 , 2 4 - 4 , 2 5 - 7
F i g ur e 3 -2
F i g u r e 2 5 -1
Figure 3-3
Tab l e 2 - 1
F i g ur e E - 1
Ta b l e 1 0 - 1
Ta b l e 3 - 1
Sys t em l eng th r eg i s t e r ( PR $_S LR ) ,
Ta b l e E - 2
Ta b l e E - 3
1 1-2 5 , 21-1 8
Ta b l e 2 1 - 3
S y s t em s e rv i c e s , 1 - 1 0 , 1 - 1 2 ,
Ta b l e 2 1 - 4
1 - 1 4 , 3 -1
Tab l e 2 3 - 1
Figure 1-2
Sys t em l og i c a l n am e t a b l e ,
Figure 1-4
Ta b l e 3 - 1
8 - 1 4 , 2 5 - 1 1 , 2 6 -1
s e e a l s o i nd i v i d ua l s e rv i c e n am e s
F i g u r e 2 6 -1
Sys t em sh utd own , 7 - 6
F i g u r e 2 6-2
Ta b l e 8 - 2
S ys t em s ymbo l t a b l e ( S Y S . STB ) ,
Sys t em l og i c a l name t ab l e m u t ex
1-6 , 1-9 , 1 8-1 1
Tab l e 2 4 - 2
Ta b l e 1 - 1
Sys t em m a p f i l e ( S YS . MAP ) , A- 1 4
sys tem t ime , 1 0 - 1 , 1 0 - 3 , 2 3 - 6 ,
Sys t em m e ssag e f i l e , 1 1 - 2 1 ,
2 4 - 4 , 2 7- 1 1
2 2 - 1 , 2 2 - 1 3 , 2 2 - 1 6 to 2 2 - 1 7 ,
Ta b l e 7 - 1
2 7 - 4 to 2 7 - 5
Ta b l e 1 0 - 1
Figure 1-6
u pd a t i ng , 1 0 - 5 t o 1 0 - 6
S ys t em v e r s i o n n um b e r
Figure E-1
Ta b l e 1 2 - 1 1
Ta b l e 7 - 1
Sys t em v i r t ua l add r e s s s pa c e ,
Ta b l e 2 1 - 1
xx i x , 1-1 4 , 2 1-1 5 , 2 1- 1 7
Ta b l e E - 2
l ayo u t , 1 - 2 1 , A- 1 7
Ta b l e E - 3
Figure 1-6
Sys t em o v e rv i ew , x x v 1 1 1
Figure E-1
Sys t em pag e t a b l e , 7 - 9 ,
Ta b l e E - 2
1 1 - 2 4 to 1 1 - 2 5 , 2 1 - 1 5 , 2 2- 1 ,
s i ze , 2 2- 2 5 , E - 5
2 2 - 3 , 2 5- 1 1 , B- 2 3 ,
S y s t em wo r k i ng s e t , 1 3 - 9 , E - l l
E-l l t o E-1 2
Sys t em wo r k i ng s e t l i st , 1 1 - 2 1
Figure 1-6
F i gu r e 1 1-1 5
F i g u r e 1 1-1 7
Figure 1 1- 1 8
Figure 21-2
S YS U I C SYSBOOT p a r am e t e r , B - 1 6
F i g u r e 2 2-1
S YSWA I T
Figure E-1
m o d u l e i n s ys t em i m ag e , 8 - 2 7
Ta b l e 1 2 - 1 1
Tab l e 1 4 - 3
Ta b l e E - 2
Ta b l e E - 3
s i ze , 2 1 -1 7
Sys t em pag e t a b l e e n t r y
T
u s e d b y d i s k d r i v e r , 1 5- 2 ,
T
e
rm
i
n
a
l
d
r
i
v
e
r
,
5-1 5 , 1 5-7 ,
1 5- 1 9
2 1 -1 7 , 2 2-9
Sy s t em PC B , 1 1 - 2 0
F i gu r e 1 5-1
Sys t em p r o c e s s , 2 2 - 1 , 2 2- 1 3
F i g u r e 1 5- 2
Tab l e 1 - 1
F i g ur e 2 0-1
Sys t em s e c t i o n t ab l e e n t r y ,
Ta b l e 2 1 - 4
2 2- 5 , 2 2 -1 7
Ta b l e 2 2- 1
F i g u r e 1 1-1 6
u n so l i c i te d i np u t , 2 0 - 1
Ta b l e 1 2 - 1

System ima g e f i l e

I nd e x - 3 1

INDEX

Te rm i n a l I /0
F i g u r e 1 5-1
Te rm i n a t i o n h a nd l e r , 1 8 - 18 ,
1 8- 2 3
F i g u r e 1 8·- 8
e x e c u t i v e mode , 1 7 - 1 8
s up e r v i so r mode , 7 - 5 , 2 0 - 9 ,
2 0 -1 3
F i g u r e 2 0-3
use r mode , 7 - 5
Te rm i n a t i o n h a nd l e r c on t r o l b l o c k
Figure 1 8-8
Te rm i n a t i o n m a i l bo x , 1 9- 5
Te rm i n a t i o n ma i l bo x m e s s a g e ,
1 9-3
Ta b l e 1 9 - 1
T i m e -o f-y e a r c l o c k , 1 0 - 1 , 1 0 - 3 ,
23-6
T i me-o f-y e a r r eg i s t e r ( PR $ TODR ) ,
1 0 - 3 to 1 0 -4 , 2 2 - 1 5
Ta bl e 1 0 -1
T i me r ex p i r a t i o n , 4 - 6 , 5 - 2 , 9 - 6
T i m e r que ue , 4 - 6 , 1 0 - 4 t o 1 0 -7 ,
1 0- 1 1 t o 1 0 - 1 2 , 2 3 - 6
T i m e r que ue e l em e n t ( TQE ) , 4 - 6 ,
5 - 4 , 1 0 - 6 to 1 0 - 8 ,
1 0 -1 0 t o 1 0 -1 2
F i g u r e 1 0 -1
T i m e r r e q ue s t , 9- 1 , 1 0 - 7 to 1 0 - 8
Figure 1 0-1
T i m e r se r v i c e s , 1 - 6
T IM E SCHDL
mod u l e in s ys t em i m a g e ,
1 0-5 to 1 0 -6
Tab l e 1 4 - 3
TM PMBX p r i v i l eg e , 1 6 - 1 1
TR n umbe r
Ta b l e 6 - 1
T r a c e pend i ng e x c e p t i o n
Tab l e 2 - 1
Tab l e 2 - 2
T r a c e ba c k f a c i l i ty , 1 - 2 4 , 2 - 3 0 ,
1 8- 1 , 1 8 - 1 6 , 1 8 - 1 8
Figure 1-8
Tr a c k o f f s e t r ecove r y , 1 5 - 3
T r a n s fe r a d d r e s s a r r a y , 1 8 - 1 6
Figure 1 8-7
T r a n s i t i o n pag e
Figure 1 1-3
Figure 1 1-17
Figure 1 2-3
F i g u r e 1 2-4
Figure 1 2-5
F i g u r e 1 2-7
Ta b l e 1 4 - 4
T r a n s l a t e Lo g i c a l Name
s ys t em s e rv i c e ( $ TRN LOG ) ,
9- 1 4 , 2 6 - 5

T r a n s l a t i o n-no t-va l i d f a u l t ,
1 - 1 5 t o 1 - 1 6 , 2-7
F i g u r e 1-5
F i g u r e 1 2-1
Ta b l e 2 - 1
s e e a l so pag e f a u l t
T r a ps , 2 - 8 , 2 - 2 3
Tabl e 2-1
Ta b l e 2 - 3
T T l o g i c a l n am e , 1 7 - 1 8
TTY B U F SYS BOOT p a r am e t e r , B - 1 8
TTY-D E F C HAR SYSBOOT pa r am e t e r ,
s= l 8
TTY OWNE R SYSBOOT p a r am e t e r ,
s= l 8
TTY PROT SYS BOOT p a r am e t e r , B - 1 8
TTY-S PE E D SYS BOOT p a r am e t e r ,
s= l 8
TTY TYPA HDS Z SYSBOOT pa r am e t e r ,
s= l 8
TTYSCANDE LTA SYSB OOT p a r am e t e r ,
1 0 -1 0 , B-1 7
TU58 c a r t ridge
s e e c o n s o l e b l o c k s to r ag e d ev i c e
TYPE PFN a r r ay , 1 1 - 1 7 , 1 2 - 3 0 ,
1 4-1 3
F i g u r e 1 1-9
F i g u r e 1 1- 1 2
Ta b l e 1 1 - 2
Typ e - a h e a d b u f f e r , 1 5 - 1 1

UAFALTERNATE SYSBOOT
pa r am e t e r f l ag ,
2 2 - 1 6 , B-1 7
UIC
s e e us e r i d e n t i f i c a t i o n c od e
Un expe c t e d sys tem s e rv i c e
except ion
( bug c h e c k c o d e ) , 2 - 3 1
UN I B US a d a pt e r , 6 - 4
Ta b l e 6 - 1
T ab l e 2 2 - 2
UN I B U S a d a pt e r i n t e r r upt , 6 - 9
UN I B US d ev i c e i n t e r r up t , 6 - 1 5
UN I B US d ev i c e
i n t e r r up t s e r v i c e r o u t i n e
F i g u r e 6 -3
U N I B U S I /0 p ag e , 6 - 1 5
UN I B US i n t e r r up t d i spa tc h i ng ,
6-1 6
UN I B US v e c to r s , 6 - 7
Un i t c on t r o l b l o c k { UC B ) , 5 - 1 3 ,
6-9 , 6-1 1
F igur e 6-3
Figure 6 -4
F ig u r e 6-5
F ig u r e 6 -7

I nd ex - 3 2

INDEX

U n i t i n i t i a l i za t i o n r o u t i n e ,
2 3 -7
U n l o c k Pag e s f rom Mem o ry
s ys t em s e rv i c e ( � U LK PAG ) ,
1 3 -1 6
U n l o c k Pag e s f rom Wo r k i ng Se t
sys t em s e rv i c e ( $ U LW S ET ) ,
1 3-1 6
U n l o c k i ng a m u t e x , 2 4 - 1 0
U n l o c k i ng I /0 b u f f e r pag e , 1 6- 8
U n so l i c i ted i np u t , 5 - 1 5
U n so l i c i ted MAS SB U S i n t e r r up t ,
6-1 1
U n so l i c i ted UN I B U S i n t e r r up t ,
6-9
U nw i nd C a l l S t a c k
s ys t em s e rv i c e ( $ UNW I ND ) ,
2-2 4 , 2-26
F i g u r e 2-7
F i g u r e 2-8
Unwi nd i ng the c a l l s t ac k , 2 - 2 ,
2-2 4
Upd a t e S e c t i o n
s ys t em s e rv i c e ( $ U PDS EC ) ,
5-4 , 1 1 -4 0 , 1 2- 2 0 ,
1 2 - 2 8 to 1 2 - 2 9 , 1 3 - 8 , 1 3 - 1 0
Ta b l e 1 2 - 1
U S E SYSG EN c omma nd , 2 2 - 1 9 , 2 2- 2 3
F i g u r e 2 2- 4
F i g u r e 2 2- 5
Ta b l e 2 2 - 3
U s e r a c c e s s m od e , 2 0 -1 3
Figure 1-4
U s e r a ut ho r i za t i o n f i l e , 8 - 4 ,
9-1 1
Tab l e 9 - 2
U s e r i d en t i f i c a t i o n c od e ( U I C ) ,
1 -2 0 , 2 0-7 , 2 7 -2
F i g u r e 1 1-1 4
U s e r n am e , 1 7 - 1 6 , 2 0 -6 to 2 0 - 7 ,
2 7-2
Tab l e 1 7 - 2
U s e r s t ac k , 1 - 2 4 , 1 8 - 8 , 1 8 - 1 1 ,
18-21
Figure 1-7
F i g u r e 1 8-9
Ta b l e E - 4
U s e r -wr i t t e n d ev i c e d r i v e r , A- 1 4
U s e r -wr i t t e n s y s t e m s e rv i c e ,
3 -1 3 , 1 7 - 1 6 , 1 8 - 2 1 , A- 1 4
Figure 1-7
Figure 3-8
Ta b l e E - 4
U t i l i ty p r og r am s
Figure 1-2

Va l i d b i t
i n t h e pag e t ab l e e n t r y , 1 1 - 4
F i g ure 1 1- 3
va r i ab l e l eng th b i t f i e l d
i ns t r uc t i o n s , 1 - 1 1
Va r i ab l e l eng th b i t f i e l d s , 1 - 1 1
Ta b l e A- 3
VAX a r c h i t e c t u r e , 1 - 1 0 , 2 - 1 ,
3-1 3 , 4-1 , 4 - 4 , 5 - l , 6-1 ,
8 - 2 6 , 1 1 - 3 7 , 2 4 - 4 , 2 4 -6
VAX- 1 1 c a l l i ng s t a nd a rd
s e e p r o c ed u r e c a l l i ng s tand a rd
VAX- 1 1 l i n k e r
Ta b l e 1 8 - 1
VAX- 1 1 /7 5 0 , 6 - 4 , 6 - 7 , 6 - 1 0 ,
6 -1 6 , 7-7 , E-1 0
F i g u r e 2-1
F i g ur e 6-2
F i g ur e 6-3
Ta b l e 7 - 1
VAX- 1 1 /7 5 0 bo o t b l oc k p r og r am ,
2 1-1 , 2 1-5
Ta b l e 2 1 - 1
VAX- 1 1 /7 5 0 bo o t s t r ap , 2 1 - 1
Ta b l e 2 1 - 1
VAX- 1 1 /7 5 0 c o n so l e , 1 5 - 1 6
VAX- 1 1 /7 5 0 c o n so l e p r og r a m ,
2 1-1 to 2 1-2 , 2 3-3
Ta b l e 2 1 - 1
VAX- 1 1 /7 5 0 d ev i c e ROM ,
2 1 - 1 to 2 1 - 2
VAX- 1 1 /7 5 0 ma c h i ne chec k , 7 - 1 0
VAX- 1 1 /7 5 0 powe r r ec o v e r y , 2 3 - 3
VAX- 1 1 /7 5 0 po we r -o n a c t i o n swi t c h ,
2 3- 3
VAX- 1 1 /7 5 0 sys t em c o n t r o l b l o c k
Ta b l e E - 2
VAX- 1 1 /7 5 0 UN I BU S
i n t e r r up t s e r v i c e r o u t i n e , 6 - 7
VAX- 1 1 /7 8 0 , 6 - 4 t o 6 - 5 ,
6 - 9 to 6 - 1 0 , 6 - 1 6 , 7 - 7 , E- 1 0
Figure 2-1
F i gure 6-3
Ta b l e 2 - 3
Ta b l e 7 - 1
VAX- 1 1 /7 8 0 boo t s t r a p , 2 1 - 6
Ta b l e 2 1 - 1
VAX- 1 1 /7 8 0 c o n so l e , 1 5 - 1 6
VAX- 1 1 /7 8 0 ma c h i ne c h ec k , 7 - 1 1
VAX- 1 1 /7 8 0 memo r y ROM p r og r am
Tab l e 1 5 - 1
VAX- 1 1 /7 8 0 powe r r e c ov e r y , 2 3 - 4
VAX- 1 1 /7 8 0 s y s t em c o n t r o l b lo c k
Ta b l e E - 2
VAX- 1 1 /7 8 0 UN I B US a d a pte r
i n t e r r upt s e r v i c e r o u t i n e ,
6 - 9 , A-6

I nd ex- 3 3

INDEX

Wa k e P r o c e s s
s ys t em s e rv i c e ( $WAK E ) ,
8-1 , 8 - 1 1 , 8-1 5 , 9-9
Tabl e 8 - 3
Tab l e 9 - 1
Ta b l e 9 - 2
Wa rm s ta r t
s e e powe r r ec ove r y
WCSx x x . PAT , 2 1 - 6 , 2 3 - 4
Wi nd ow b i t
i n t h e pag e t ab l e e n t r y , 1 3- 8
Figure 11-3
W i nd ow c o nt r o l b l o c k , 1 1 - 1 1 ,
1 1- 3 0 , 1 5- 4
F i g u r e 1 1-7
F i g u r e 1 1-1 6
F i g u r e 1 1,- 2 2
F i g u r e 1 1- 2 3
W i nd ow t u r n , 1 5 - 6
Wo rd i nd ex , x x x i
Wo r k i ng s e t , 5 - 1 1 , 1 1 - 1 8 , 1 3 - 1
Wo r k i ng s e t l im i t , 1 3 - 1 2
Wo r k i ng s e t l i s t , 1 1 - 1 , 1 1 - 7 ,
1 2-4 , 1 4 -1 0 , 1 4-1 5 , 1 4-2 4 ,
1 7- 1 4 to 1 7 - 1 5 , E - 3
Fi g u r e 1 1-1
F i g ur e 1 1-4
F i g u r e 1 2-3
F i g u r e 1 2-4
F i g ur e 1 2-5
F i g u r e 1 4-2
F i g u r e 1 4-3
F i g u r e 1 4-4
F i g u r e 1 4-5
Fi g u r e 1 4 -6
F i g u r e 1 4-7
Ta b l e 1 3 - 1
Ta b l e 1 4 - 1
w
Ta b l e 1 4 - 5
Wa i t fo r event f l ag
Ta b l e 1 7 - 5
s y s t e m s e rv i c e s
Ta b l e E - 1
( $WA I TFR , WF LAND , a nd $WFLOR ) ,
a nd i t s u s e i n pag i ng , 1 2 - 1 7
8-1 8
d yn am i c po r t i o n , 1 2 -1 8 ,
Wa i t f o r Log i c a l AND o f E v e n t F l ag s
1 3 -1 2 , 1 3-1 5
sys t em s e rv i c e ( $WFLAND ) ,
Figure 11-4
8-9 , 9-6
l o c k ed po r t i o n , 1 3 - 1 5
Ta b l e 9 - 1
Fi gure 1 1-4
Ta b l e 9 - 2
u s e d u r i ng i n s wa p , 1 4 - 2 4
Wa i t f o r Lo g i c a l OR o f Ev e n t F l ag s
u s e d u r i ng o u t swa p , 1 4 - 1 3
sys t em s e rv i c e ( $WFLOR ) ,
Wo r k i ng s e t l i s t e n t r y , 1 1 - 1 0 ,
8-9 , 9-6
1 2-1 7 , 1 3 -5 , 1 4 -1 0 , 1 4 - 2 6
Ta b l e 9 - 1
F i g u r e 1 1-5
Ta b l e 9 - 2
Wo r k i ng s e t quo t a , 1 3 - 1 2
Wa i t f o r S i ng l e E v e n t F l ag
F i g u r e 1 1 -4
sys t em s e rv i c e ( $WA I TFR ) ,
Wo
r
k
i ng se t r ep l a c eme n t a l g o r i thm ,
8 - 9 , 8-1 5 , 9 - 5 , 1 6- 6
1 1-8 , 1 1-1 8 , 1 2-1 7
Tabl e 9 -1
Wo r k i ng s e t s i ze , 1 3 -3
Wa i t s ta t e que u e h ea d e r s
F i g u r e 1 1 -4
Fi g u r e 8 - 4
Ta b l e 1 3 - 1
Wa i t s t a t e s , 8 - 1 , 8 - 4 , 8 - 9

VAX- 1 1 /7 8 0 UN I B US powe r f a i l ,
2 2 - 1 0 , 2 3 -1 1
Vi r t ua l add r e s s , 1 2 - 1 , 1 2 - 3
V i r t ua l a d d r e s s f o rm a t
F i g u r e 1 2 -1
Vi r t ua l add r e s s s pa c e , 1 3 - 1
Vi r t ua l add r e s s s pa c e c r e a t i o n ,
1 3 -2
Vi r t ua l a d d r e s s s pa c e d e l e t i o n ,
8- 1 1 , 1 2-6 , 1 3- 2 , 1 3 -4
V i r t ua l a d d r e s s s pa c e d e sc r i p t i o n ,
1 - 1 , 1 - 3 to 1 - 4 , 1 - 1 3 , 1 1 - 1
F i g u r e 1-1
V i r t ua l b l o c k n um be r , 1 1 - 1 1
Vi r t ua l I /0 f un c t i o n , 1 5 - 4
VI RTUA L PAG E CNT S Y S B O OT pa r am e t e r ,
1 1 - 3 , 1 3 - 3 t o 1 3 - 4 , B- 1 5 ,
E-3 , E-1 1 , E-1 3
F i g u r e 1 1- 1
Tab l e E - 1
VMB
s e e p r i m a r y b o o t s t r a p p r og r am
VM OUNT
s e e v o l um e m o un t u t i l i ty
VM S , X X X
Vo l ume d i smoun t u t i l i ty , 7 - 2
Ta b l e 1 - 1
Vo l um e i n i t i a l i za t i o n u t i l i ty ,
xxxi
Ta b l e 1 - 1
Vo l um e m o un t u t i l i ty , 1 - 7 ,
7 - 1 to 7 - 2 , 2 6 - 3
Ta b l e 1 - 1
Ta b l e 2 4 -2

I nd ex - 3 4

INDEX

Working s e t s i z e ,

( cont . ) ,

a ut ho r i zed q uo ta
Ta b l e 1 3 - 1
d e f a ul t
Tab l e 1 3 - 1
q uo t a
Ta b l e 1 3 - 1
WOR LD p r i v i l eg e , 1 - 2 0 , 9 - 8 ,
9 -1 1 , 1 0-1 1 , 1 9-1
Tab l e 9 - 1
W r i t a b l e c on t r o l s to r e
Figure 6-1
Wr i t a b l e s ec t i o n , 1 1 - 4
WR I TAB L E S YS spec i a l SYSBOOT
pa r am e t e r f l ag ,
B-17
W r i t e b u f f e r pa c k e t
F i g u r e 1 6- 5
Wr i t e c om p l e t i o n
w i th $ U PD S E C , 1 2 - 2 9
Wr i t e i n p r og r e s s
PFN t r a n s i t i o n s ta t e , 1 2 - 6 ,
1 3-5
F i g u r e 1 1-1 1
F i g u r e 1 2- 3
F i g u r e 1 2-5
WR I T E SYSGEN c omma nd , 2 2 - 2 5
F i g u r e 2 2- 5
Ta b l e 2 2 - 3
WRI TEB OOT u t i l i ty , 2 1 - 5
WSDEC SYSB OOT pa r am e t e r , 8 - 8 ,
1 3 - 1 4 , B- 1 6
Ta b l e 1 3 - 2

WS INC S Y S BOOT p a r am e t e r , 8 - 8 ,
1 3 - 1 3 to 1 3 -1 4 , B - 1 6
Ta b l e 1 3 - 2
WS LX P F N a r r ay , 1 1 - 1 1 , 1 1 - 2 0 ,
1 2-4 , 1 4-1 1 , 1 4 - 2 3
F i g u r e 1 1- 9
Tab l e 1 1 - 2
W S LX s a v e a r e a i n PHD
Fig ure 1 1-8
WSMAX S YSBOOT pa r am e te r , 1 1 - 3 2 ,
1 1 -3 4 , 1 3 -1 2 , 1 4 -1 2 , 1 7- 1 5 ,
2 2- 1 0 , 22-1 6 , B-1 5 , E- 3 , F-1 ,
F-3
Figure 1 1-1
Figure 1 1- 2 3
Figure 1 1-2 4
Ta b l e 1 3 - 1
Ta b l e 2 2 - 1
Ta b l e E - 1

XDE LTA , 2 1 - 9 , 2 1 - 1 5 ,
Ta b l e 2 - 1
Ta b l e 4 - 1
Ta b l e 2 1 - 2
XFC i n s t r uc t i o n
Ta b l e 2 - 1
Ta b l e 2 - 2

I nd ex - 3 5

2 2- 5 , 2 3-1 1

VAX/VMS Interna l s and Data S truc tures
AA- K 7 8 5A-TE
READER ' S COMMENTS

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BSSG PUBLI CATIONS ZK1 -3/J3-5
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