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DEC-15-ODFFA-A

January 1972

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Document:	DOS-15 System Manual
Order Number:	DEC-15-ODFFA-A
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Pages:	173
Original Filename:	http://bitsavers.org/pdf/dec/pdp15/DEC-15-ODFFA-A_DOS15_SysMan.pdf

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DEC-lS-ODFFA-A-D

DOS-IS
SYSTE~1

MAN UAL

FOR ADDITIONAL COPIES OF THIS MANUAL J ORDER THE NUMBER ABOVE FROM THE
PROGRAM LIBRARY J DIGITAL EQUIPMENT CORPORATION J MAYNARD J MASSACHUSETTS

01754

PRICE $10.00

First Printing, January 1972
Second Printing, July 1972

(S)

1972

by Digital Equipment Corporation

The material in this document is for information purposes and is subject to change without
notice.

The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
COP
Computer Lab
Comtex
DEC
OECtape
Dibol

Digital
DNC
Flip Chip
IOAC
Indac
KAlO

LAB-8/e
OMNIBUS
OS/8
PDP
PHA

PS/8
Quickpoint

RAO-8
RSTS
RSX
RTM
SABR
Typeset 8
Unibus

CON~ENTS

PREFACE
CHAPTER 1

DOS OPERATION

CHAPTER 2

THE RESIDENT MONITO~

2.1

INTRODUCTION

2-1

2.2

THE CAL HANDLER

2-2

2.3
2.3.1
2.3.2

lOPS ERROR HANDLER, AND THE EXPANDED ERROR PROCESSOR 2-2
.MED
I
2-2
The Expanded Error ~rocessor
2-6

2-4

THE SYSTEM BOOTST~

2-7

2-5

SYSTEM I/O INITIALIZATION

2-8

2.6
2.6.1
2.6.2

RESIDENT MONITOR TIMING FEATURES
Clock Operation
.TIMER

2-8
2-12
2-12

2.7

THE RESIDENT MONITOR PATCH AREA

2-14

2.8

CONTROL CHARACTERS

2-14

CHAPTER 3

THE NONRESIDENT MONITOR

3.1

INTRODUCTION

3-1

3.2

COMMANDS TO THE NONRESIDENT MONITOR

3-7

3.3

CONSIDERATIONS FOR ADDITIONS TO THE NONRESIDENT
MONITOR

3-7

3.4

QFILE

3- 8

CHAPTER 4

THE SYSTEM LOADER AND THE LINKING LOADER

4-13

4.1

MANUAL BOOTSTRAP

4.2

LOADING SYSTEM PROG~S

4.4

TABLES AND INFORMATION
BLOCKS USED AND BUILT
I
BY LOADERS

4.5

.DAT SLOT MANIPULATION BY THE SYSTEM LOADER

4-15

4.6

BUFFER ALLOCATION BY THE SYSTEM LOADER

4-20

LO~DS
I

AND RESTARTS

4-13

4-15

CHAPTER 5

SYSTEM INFORMATION BLOCKS AND TABLES
II

5.1

CORE-RESIDENT NON-REFRESHED REGISTERS

5-1

5.2
5.2.1
5.2.2
5.2.3

DISK-RESIDENT UNCHANGING BLOCKS
SYSBLK
COMBLK
SGNBLK

5.3

DISK-RESIDENT CHANGING BLOCKS

5-1
5-1
5-1
5-8

5-9

5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.4.6

TEMPORARY TABLES BUILT FROM DISK-RESIDENT
TABLES
The Overlay Table
The Device Table
The Input/Output Communication (IOC) Table
The Device Assignment Table (.DAT)
The User File Directory Table (.UFDT)
The Skip Chain

5-9
5-11
5-11
5-12
5-12
5-12

5.5
5.5.1
5.5.2
5.5.3

TEMPORARY TABLES BUILT FROM SCRATCH
File Buffer Transfer Vector Table
The RCOM Table
The Mass Storage Busy Table

5-12
5-12
5-13
5-13

5.6

RESERVED WORD LOCATIONS

5.4

5-9

5-13

5.7

BOOTSTRAP NON-BOSS BATCH BITS

5-15

CHAPTER 6

FILE STRUCTURES

6.1
6.1.1
6.1.2

DECTAPE FILE ORGANIZATION
Non-Directoried DECtape
Directoried DECtape

6-1
6-1
6-1

6.2
6.2.1
6.2.2
6.2.2.1
6.2.2.2
6.2.2.3
6.2.3
6.2.4

MAGNETIC TAPE
Non-directoried Data Recording (MTF)
Directoried Data Recording (MTA., MTC.)
Magnetic Tape File Directory
User-File Labels
File-Names in Labels
Continuous Operation
Storage Retrieval on File-Structured
Magnetic Tape

6-4
6-5
6-5
6-7
6-9
6-10
6-10

6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.4.1
6.3.4.2
6.3.5
6.3.6
6.3.7

DISK FILE STRUCTURE
. Introduction
User Identification Codes (UIC)
Organization of Specific Files on Disk
Buffers
Commands that Obtain and/or Return BuffE~rs
The Current Set
Pre-allocation
Storage Allocation Tables (SAT's)
Bad Allocation Tables (BAT's)

6-12
6-12
6 ... 12
6-14
6-14
6-14
6-16
6-16
6-17
6-18

6-11

CHAPTER 7
7.1

WRITING NEW I/O DEVICE HANDLERS
I/O DEVICE HANDLERS, AN INTRODUCTION
Setting Up the Skip Chain and API
(Hardware) Channel Registers
Handling the Interrupt

7-1

7.2
7.2.1
7.2.2

API SOFTWARE HANDLERS, An Introduction
Setting Up API Software Channel Registers
Queueing

7-6
7-6
7-7

7.3
7.3.1
7.3.2
7.3.3

WRITING SPECIAL I/O DEVICE HANDLERS
Discussion of Example A by Parts
Example A, Skeleton I/O Device Handler
Example B. Special Device Handler for
AFOIB A/D Converter

7.1.1

CHAPTER 8

7-4

7-5

7-9
7-11
7-12
7-14

BOSS-IS

B.l.l
B.l.2
B.l.3

PROCEDURE FILES
Procedure File Format
Direct Substitution
Example of Procedure File

8-16
8-16
8-19
8-19

B.2

BOSS-15 ACCOUNTING

B-20

8.3

B.PRE

8-21

8.1

APPENDIX A

DECtape 'A' Handler (DTA.)

APPENDIX B

Disk "A" Handlers

APPENDIX C

PROCEDURE FILES

vii

This manual was written for customer ~ystems programmers, DEC Software
I

Specialists, and internal maintenance programmers.

Readers must be

familiar with the DOS User's Manual, DEC-15-MRDA-D.

In addition, chap-

ter 8 requires familiarity with the BOSS Reference Manual, DEC-15-GUDA-D.

CHAPTER 1
DOS OPERATION

The System Manager must use DOSSAV in order to load DOS-IS for the
first time.

The DOS System Generator manual, DEC-15-YWZB-DN12, des-

cribes DOSSAV operation in its appendix.

After successful DOSSAV op-

eration, the System Manager should load the Bootstrap into the highest
bank.

(This tells DOS how many banks it can use.)

The Bootstrap loads

the System Loader, which in turn loads the Nonresident Monitor.

order to ensure a working system, the System Manager should place the
DOS-IS Checkout Package tape (RF.CHK, DEC-lS-CIDA-PA, for RF DECdisk
systems, or RP.CHK, DEC-lS-CTAA-PA, for
the Paper Tape Reader, and type BATCH

RP~2

PR~.

Disk Pack systems) into
Operating instructions

for the Checkout Package, and the tape itself, are distributed as part
of the DOS-IS system.

Once the system has been checked out, the System Manager should use
DOSGEN, the DOS System Generator orogram, to tailor the system to
his needs.

As mentioned in the System Generator manual, a complete

tailoring of the system may also involve use of PATCH, PIP, and
UPDATE.

Commands to the Nonresident Monitor allow temporary modification of
the system, in order to suit the needs of a particular program.

The

Nonresident Monitor modifies the system by changing information in
the .SCOM Table.

The System Loader examines the .SCOM Table, along

with three disk-resident information blocks, SYSBLK, COMBLK and SGNBLK,
and carries out all operations necessary to fulfill the operator's
commands.

The System Loader "builds" the Resident Monitor by relocat-

ing and linking those routines
by the next core load.

indicated by the .SCOM table as needed

The Resident Monitor then retains general con-

trol over the system.

1-1

CHAPTER 2
THE RESIDENT '10NITOR
.

2.1

INTRODUCTION

The Resident Monitor gets its name because it seems resident to the user.
Strictly speaking, however, the only part of the system that is always
resident is the Bootstrap.

There are two parts of the system that are

refreshed only after manual Bootstrap lo&ds and restarts:
Resident :-1onitor Patch Area.

.SCOM and the

Every time an operator or program changes

certain key system parameters, the system will build a new Resident
Monitor from blocks stored on the system device.
The Resident Monitor is the interface between the operator, and the
active devices on one hand, and the program which is running (the
Nonresident Monitor), on the other.

The Resident Monitor always contains

the following routines and tables:
.DAT
.UFDT
(
S
.SCOM
The CAL Handler, which routes all System and I/O
Macro calls
The Startup routine after usinq the Bootstrap
.MED, the Monitor's standard error routine
The Expanded Error Processor, for more flexibility
with error messages
Handlers for the following error conditions:
Nonexistent Memory
Memory Protect
Interrupt-Memory Parity
This
Power-Fail
Chapter
Software API not set up
The Monitor's TRAN routine (different from I/O .TRAN's)
A clock handler
The .GTBUF and GVBUF processor
The CTRL Q processor
The .USER processor
The .OVRLA processor
TTA.
The Resident Monitor's Patch A1ea
Chapter

In addition, the user can request the system to retain certain other
routines in a resident Monitor status:
The CTRL X Feature, including a driver for the VT-IS
The paper Tape or Card Reader Handler for Batch
The Resident Batch code
BOSS-IS also has resident routines, wnich are covered in Chanter 8.

2-1

2.2

THE CAL HANDLER

The CAL instruction transfers control to

re~ister

21, bank

and loads

All DOS I/O and system macros take the form of a CAL instruction (posI

sibly with some code in the low-order bits), and the next sequential
register contains a dispatch code.

Some mabros require more informaI

tion in succeeding registers.

Figure 2-1, Resident Monitor CAL Handler,
I

illustrates the operation of that portion of the Resident Monitor.

-- for legal function
r
code, and for legal .DAT slot. Aside from that, and ensuring the

CAL Handler does only minimal error checkin

The

clock is turned on, the CAL Handler is only a dispatcher to other

routines.
2.3

lOPS ERROR HANDLER, AND THE EXPANDED ERROR PROCESSOR
I

2.3.1

.MED

There are two error processors in the Resident Monitor:

.MED and the

Expanded Error Processor.

Figure 2-2 illustrates those routines.
!

Figure 2-3 shows two subroutines used by th7 error routines.

.MED

(location 3, bank

processes lOPS errors from all device handlers
I

except the disk handlers, and COB., MTF., TTA., and LPA.

Calls to

.MED should take the following form, if not lOPS 4:
I

LAC
DAC*

INFO
(. MED

LAW
JMP*

N
(. MED+I

/ARGUMENT OF ERROR
/ADDRESS OF CAL IS ALREADY IN . MED,
/IF DESIRED
IN IS ERROR CODE ~~N~777. AC MUST BE NEGATIVE.

lOPS 4 messages may take the following form:
LAC
(4
JMS* (.MED

lAC MUST BE POSITIVE

.MED+I contains a JMP to the Monitor Error Diagnostic Routine.
I

above calls to .MED will cause the follOwin? printouts:
IOPSN (contents of .MED)
IOPS4

2-2

The

2.
3.

Loa
ress
Turn clock on, if
on
Deposit minus 1 in register 7, if
= or less than minus two

lOPS ~

~_N________________~The following CAL's

take this path:
.EXIT, .OVRLA, .TlMER
• SETUP, • GTBUF ,
.GVBUF, .GET, &
IOPS2

• PUT

Give control to
proper portion of
the Resident Monitor.

Resident Monitor CAL Handler

Figure 2-1

2-3

Enter from
.MED

Enter from
.SCOM+37

Put recovery PC 1n .MED
Initialization
NOTE:

The Nonresident Monitor HALT and

QDUMP commands will change this loop to

the appropriate action. BOS and Batching Mode abort the $JOB.

(Wait f r a
Contro Char)
N

1.
2.
3.

Echo Command
Restore API, if required
Restore PI

Return
via .MED
Expanded Error Processor
and
Monitor Error Diagnostic Routine
.MED

Figure 2-2

2-4

SETTLE

1.
2.
3.
4.
5.

Store error number
Set up to turn nulls into
spaces, if LINK is set
Turn off PI
wait 110 ms for the teleprinter
to die down
Type Carriage RBTURN, Line Feed

Print "IOPS" and error number,
zero suppressed

Print a space, fol~owed by the
octal contents of .MED, followed
by another space

Print contents of .SCOM+32 (disk
block number)

Resident Monitor Subroutines

Figure 2-3

2-5

2.3.2

The Expanded Error Processor

The disk handlers (except the Bootstrap), CDB., MTF., TTA., and LPA.
use the Expanded Error Processor.

Each error message is "potentially"
I

recoverable by typing CTRL R.

That is, the Resident Monitor always

returns control to the caller upon a CTRL R.
to respond accordingly.

It is up to the caller

All handlers supplied with the system simply

repeat the error message if the error is unrecoverable.
I

The Expanded Error Processor gives the capability of printing additional information after the standard lOPS message.
AC must contain the error number
must be passed, however, via JMS*

As with .MED, the

(~<number<777)

in bits 9-17.
.
(.SCOM+37, not JMP* (.MED+l.

The following information pertains to the message:

Control

LOC+2 must contain

the two's complement of the number of message words to be typed after
the standard "IOPSNN nnnnnn" message.
tive, no message will be printed.
printed as spaces.

If the number is zero or posi-

If the LINK is set, nulls will be

If the LINK is zero, nulls will be ignored.

the AC is positive on calling the expanded error facility, only the
special message will be printed.

The "lOPS" part will be omitted.

The message itself must be packed in .SIXBT.
The following are examples of use of the Expanded Error Processor:

Example a:
UNREC

DAC*

STATUS
(.MED

STL
LAW
JMS*
JMP

/STATUS
/CAL ADDRESS IS NOW OVERWRITTEN
/BY CONTENTS OF STATUS REGISTER
/TURN NULLS INTO SPACES

ERRNUM
(. SCOM+37
UNREC

~ERRNUM <l~~ ~

LAC

/THIS IS AN UNRECOVERABLE ERROR.
/JMP .-1 WILL NOT DO -- EXPANDED
/ERROR PROCESSOR CHANGES THE
/CONTENTS OF .MED.

LAW
-1
.SIXBT IDKAI
UNITNO fI
.SIXBT IFILl
.SIXBT IE'
.SIXBT 'SRC I
The printout from that code will be as follows:
IOPS777 nnnnnn DKA FILE SRC
where nnnnnn is the contents of .MED, and equals the Status Register
B, and ERRNUM was 777.

2-6

PARITY

LAW
STL
JMS*
JMP
LAW

61
/TURNS NULLS INTO SPACES
(.SCOM+37
RETRY

/THIS IS A RECOVERABLE ERROR

-1

.SIXBT 'DTA'
The printout from that code will be as follows:
IOPS61 nnnnnn DTA
where nnnnnn is the contents of .MED, the address of the last CAL,
deposited by the CAL Handler.
2.4

THE SYSTEM BOOTSTRAP

The System Bootstrap is nothing more than a disk driver.

It may load

the System Loader and Resident Monitor from Hardware Readin,
restart.

or manual

All other Bootstrap operations result from the use of the

Monitor TRAN routine.

The Monitor TRAN routine sets up the Bootstrap

to read or write any block or set of contiguous blocks from the disk
to or from any location in core.

Before calling the Bootstrap, the

Monitor TRAN does a .WAIT to all .DAT slots in the Mass Storage Busy
Table, clears all flags, turns off the VT if it was on, and allows the
clock to tick positive, so that it will keep time but not interrupt.
After the Bootstrap has finished, it calls the Monitor Initialization
Routine, which updates the clock and turns on the VT, if necessary.
The Monitor TRAN Routine requires the followinq parameter table:
P ARADU

LOC+ fJ
LOC+l
LOC+.2
LOC+3

BLKNUM
FIRSTA-I
-SIZE
START

/FIRST BLOCK NUMBER
/FIRST ADDRESS OF BUFFER, MINUS ONE
/# OF WORDS TO BE TRANSFERRED IN 2'S COM
/STARTING ADDRESS AFTER DISK I/O
/COMPLETION

The following code illustrates the use of the Monitor TRAN:
UNIT=lfJ~fJfJfJ

/MONITOR TRAN WILL USE UNIT ONEl

.SCOM=l~fJ

LAC
XOR
STL
JMP*

(PARADD
UNIT
(. SCOM+55

/MONITOR TRAN REQUIRES ADDRESS OF
/PARAMETER TABLE IN BITS 3-17 AND
/UNIT NUMBER IN BITS ~-2 OF AC
/NONZERO LINK GIVES TRAN OUT
/.SCOM+55 IS USER ENTRY POINT FOR
/MONITOR TRAN

See also paragraph 5.7.
IDECdisk TRANs ignore unit number, use block number.
2-7

.OVRLA, .EXIT, and manual Q dumps all use the Monitor TRAN routine.
I

Figure 2-4, .OVRLA, .EXIT and CTRL Q, illustrates their operation,
i

and also the Monitor TRAN.
For the RF DECdisk, the user can reference, a specific platter just by
identifying the block number he wants. That is, the block numbers to
not automatically go to zero at the beginning of every platter. The
block numbers and platter relationships are shown below:
I

TABLE 2-1

RF Platter-Block Number Correspondence
I

Platter Number

Block Number

~-1777
2~{i1j1-3777

1
2
3
4

4{i1j1{i1-S777
6j1{i1j1-7777
l{i1j1{i1.0-1l777

l2~.0{i1-l3777

6
7

l4j1~.0-1S777

l6{i1j1{i1-l7777
(All numbers are in octal)
I

2.5

SYSTEM I/O INITIALIZATION
i

There are two routines that do DOS I/O initialization: the startup routine
after Bootstrap manual loads and restarts, and the startup routine
performed after Monitor TRAN's and after a CTRL C, P, T or S for an
error. The startup routine after Bootstrap loads is described in
Figure 4-1, The System Loader Interface Routine. Figure 2-5, Resident
Monitor Initialization, describes the other routine.
1

---

2.6

RESIDENT MONITOR TIMING FEATURES
I

Figure 2-6, The Resident Monitor Clock Routine, describes the Resident
Monitor'S time functions. There are three places in DOS which start
or try to update the clock -- (1) the first-time initialization after
manual Bootstrap loads and restarts, (2) the Resident Monitor Initialization, and (3) the CAL Handler. The following .SCOM registers contain timing information:
i

2-8

.OVP..LA

CAL Entry
.EXIT CAL
Entry
Put System program name into
.SCOM+43,44 (pro
name pointed to
by CAL+2)
Scan Overlay
Table (address in
.SCOM+31) for a
match with the

Put name of the
Nonresident Mon
itor into .SCOM
43 & 44

Entry

Set LINK (.TRAN out)
and set up pointer to .TRAN
parameters for CTRL QAREA

Put contents of .SCOM+72
into .SCOM+7l, and set
AC with unit number
Set up pointer to
parameters

TRAN

Set up unit number ~ and
pointer to TRAN parameters for loading .SYSLD
Clear LINK for .TRAN in

Update .SCOM+31
clear AC and the
LINK (Unit ~, & ~--~
.TRAN in)

(MONITOR

TRAN ROUTINE -- Independent from
device handler .TRAN's)

Store Unit number and
other TRAN parameters
in the Bootstrap

* CLEAR does a .WAIT or a
.INIT to each entry in
the Mass Storage Busy
Table. This precludes
conflicts between disk
I/O performed by the
system disk handler, and
disk lOT's issued by the
Bootstrap, an independent
program. CLEAR also turns
off the clock and PI, and
enables BANK mode.

Return to
user

Put starting address into
location ~, bank ~, and
set the Bootstrap to go to
Monitor Recovery Routine
on exit

Bootstrap

.OVRLA, .EXIT and CTRL Q
I

Figure 2-4
I

2-9

Entry
from
Bootstrap

Entry
from
RESMON

Arrive with exit address in AC

set exit to address in ~

2.
3.
4.

2.
3.

Set up clock so that it
keeps running, but does
not interrupt (ticks
positive)
Clear all flags
Turn off PI and API
Restore cell 4 to transfer
to Error Diagnostic Routine
Set up proper addressing
(Bank or Page), according
to .SCOM+4, bit 7

Update the clock, and allow it to
interrupt
Clear TTY Busy Switch (Clear all
flags ensures no I/O to TTY)
Turn API on or off, depending on
contents of register 6 (The System Loader loads register 6 according to .SCOM+4, bit ~)
Turn on PI

proper
location

Resident Monitor Initialization

Figure 2-5

2-10

Ent.rY frolll
PI or API

Allow clock to tick positive, so it
will not interrupt for an hour

set up the exit from this routine
to go to the .TIMER address in
.SCOM+61, is if it were a JMS instruction. Set high-order bits
of return address with interrupt
information

.SCOM+50
hhmmss
Increment .SCOM+34
Subtract one from

Restore pre-interrupt
conditions

Note:

The Clock Routine will use PI if API i~ busy, or down.
I

The Resident Monitor Clock Routine
•

Fl..gure 2-6

2-11

.SCOM+5~

.SCOM+51
.SCOM+56
.SCOM+6~

.SCOM+6l
.SCOM+73
.SCOM+74

2.6.1

Time of day, in hhmmss (six bits each)
Elapsed time, in ticks
Time limit, in seconds (zero, if no limit)
Time left for .TIMER interrupt (zero, if
.TIMER not in effect)
Address of .TIMER user interrupt routine
Number of ticks left in the next second
Line frequency, in ticks per second

Clock Operation

The Nonresident Monitor's TIME command changes or senses
. SCOM+51 is not used by any system program.
increments it upon each clock tick.

.SCOM+5~ •

The clock handler simply

User programs may deposit a known
I

quantity into .SCOM+51, in order to time events.

The Nonresident

Monitor deposits the argument for a TIMEST command into .SCOM+56.

.SCOM+56 is nonzero, the Resident Monitor will issue an ISZ .SCOM+56
I

command each second, until it reaches zero.

At such a time, the Resi-

dent Monitor will perform a .EXIT.

MICLOG, LOGIN, and LOGOUT clear
I

.SCOM+56.
I

2•6•2

. TIME R

.TIMER allows users to schedule routines for a specified time from
"now".

These routines may return to the interrupted code, if the
I

programmer desires.

.TIMER users should take care that the timeI

dependent code follows certain rules:

When a programmer does not wish to reset the .TIMER mechanism, but wishes to return to the interrupted program, his
code should look like this:

XIT

DAC

SAVEAC

LAC
RAL
LAC
JMP*

/C+l REACHED VIA JMS
/MUST NOT USE NON-REENTRANT CODE
/POSSIBLY USED BY THE INTERRUPTED
/PROGRAM.
(INCLUDES THE CAL IN/STRUCTION)
/RESTORE THE LINK

SAVEAC

/RESTORE THE AC

2-12

When the programmer does wish to reset the .TIMER mechanism,
and return to the interrupted code, his routine should look
like this:
.SCOM=I,0~
CLON=7,0~~44
CLOF=7~fJ~fJ4
INTRVL=-lfJ~

DAC

LAC
DAC*
CLOF
LAC

DAC*
LAC
RAL
LAC
CLON
JMP*

/THIS ROUTINE WILL RUN EVERY
/TICKS

1,0~8+

fJ
SAVEAC

ADDRES
/RETURN TO THE NEXT ROUTINE
( .SCOM+61
/TURN THE CLOCK OFF TO ENSURE NO
/REENTRANCE BEFORE .TlMER RESET AND
/RETURN
/DESIRED INTERVAL IN TWO'S COMPLEMENT
INTRVL
(. SCOM+6fJ
/RESTORE THE LINK
C
SAVEAC

/RESTORE THE AC
/TURN THE CLOCK BACK ON (AFTER NEXT
/INSTRUCTION)

When a programmer does not wish to return to the interrupted
program, he need not save the AC, and he may use the CAL instruction. He should beware of using I/O buffers that may
still be modified by a handler's interrupt section.
In many
cases, a .INIT to an active .DAT slot will terminate I/O.
Teleprinter I/O should be terminated by the following:
XCT*

(.SCOM+35

The user should program a delay of at least llfJ milliseconds
after such an instruction, before he attempts teleprinter I/O.
Note: The interrupt routine will run at the level of the interrupted code, with the same addressing mode and memory protect status. Thus, no debreak and restore is required.

2-13

2.7

THE RESIDENT MONITOR PATCH AREA

There are two types of patch area taken from the space allocated at
assembly time:
1.

That allocated by using PATCH

That allocated when answering the Patch Area
question in system generation

Patch area one is the place for permanent changes to the Resident
Monitor.
core.

It is always refreshed when the System Loader comes into

Patch area two is only refreshed on manual Bootstrap loads

and restarts.

The second area would be appropriate for communication

between successive programs loaded by the System Loader.

This area

should be used because the System Loader refreshes all of core, except the Bootstrap, .SCOM, the CTRL X buffer, and the patch area two.
The combined size is limited by the current assembly at
areas can be initialized, using PATCH.

47~~8.

Both

The important dividing line

between area one and area two is register

l~l

(.SCOM+l) of RESMON.

The way to allocate more space in part one is to increase the value
of register
DOSGEN.

l~l.

The way to change the area in part two is to use

The second part will start at the address in register

The upper bound of the second area will be
of register
2.8

l~l,

l~l.

the sum of the contents

and the number specified to DOSGEN.

CONTROL CHARACTERS

CTRL C, P, R, S, and T are all special characters that interrupt the
current program and transfer control.

The Resident Monitor ignores

CTRL R except after lOPS 4 and any call to the Expanded Error
Processor.

CTRL S always transfers control to the address in

.SCO~+6.

In the case of core-image system programs and EXECUTE, a CTRL Swill
transfer to register zero, and result in an lOPS 3.

The Linking

Loader places the starting address of the first load module into
.SCOM+6.
A .INlT macro to the teleprinter handler will change the address of
either CTRL C, P or T.

The Resident Monitor is always initialized to

2-14

perform a .EXIT after CTRL C, and ignore CTRL P and T.

DDT uses

CTRL T, and CTRL P is ordinarily used by programs for restarts.
MACRO-IS expands .INIT to change the CTRL P address.

If the programmer

expands .INIT without the aid of the assembler, a

in bits zero and

A ~l

in those bits

one of LOC+2 will change the address of CTRL T.
will change the address of CTRL C.

It should be obvious that special

care should be taken with CTRL C.

In addition, modifications to the

CTRL T address should not be made when debugging with DDT.
cases, however, when such modifications are desirable.

There are

In particular,

all zeroes in LOC+2 (2-17) will cause the teleprinter handler to ignore
CTRL C, P, or T.

This address might be used when sensitive code is

being executed, as in DOSGEN.

The following .INIT expansion will

cause the Resident Monitor to ignore CTRL C:
CAL-2&777
1
2~~~~~

2-15

CHAPTER 3
THE NONRESIDENT MONITOR

3.1

INTRODUCTION

The System Loader brings the Nonresident Monitor into core after a
hardware readin, a manual restart, a CTRL C, or a .EXIT.

The RCOM

Table, SGNBLK, SYSBLK and COMBLK are always coresident with the Nonresident Monitor.

This gives the Nonresident Monitor access to all

important system parameters.
The Nonresident Monitor announces its presence by typing DOS-15 VN.A
on the teleprinter.

It remains in core until the operator requests

another system program, or until the operator's command implies a
refreshed configuration of the Resident Monitor is necessary.
The Nonresident Monitor's actions are limited to (1) decoding commands,
(2) manipulating or examining bits and registers in .SCOM,

.DAT, .UFDT,

SYSBLK, COMBLK, and SGNBLK, and (3) calling the System Loader, when
necessary.

The Nonresident Monitor has only one entry, which starts

an initialization section.

Figure 3-1, Nonresident Monitor Initial-

ization, describes that logic.

Every time the System Loader brings

in the Nonresident Monitor, it passes control to the initialization
section.

After initialization, and after all commands that do not

require the

System Loader, the Nonresident Monitor types a $, and

awaits an input line, terminated by a Carriage RETURN or an ALT MODE.
It then examines the first six characters (or those up to the first
blank) and tries to find an entry in the Nonresident Monitor's Command
Table.

If a match is found, control passes to the appropriate routine,

and thence to the next command, or the System Loader.

If the typed

command does not correspond to an entry in the command table, the
Nonresident Monitor temporarily assumes the operator wishes a new
core-image system program, and checks COMBLK for a corresponding entry.
If there is no corresponding entry in COMBLK, the Nonresident Monitor
will type an error message, and await the next command.

If COMBLK

contains a matching entry, the Nonresident Monitor composes a .OVRLA,
and passes control to the System Loader via that .OVRLA.

3-1

ST~RT

1.
2.
3.
4.
5.
6.
7.

Bank bit initialize pointers to SYSBLK, COMBLK and SGNBLK
Determine the number of positive .OAT slots
Save the contents of .OAT-12, in case the user desires LP ON
(restore before leaving Nonresident Monitor)
Save contents of .SCOM+7 -- Nonresident Monitor will use
.SCOM+7 for address of LPA. or TTA.
Change all .UFDT entries that equal BNK or PAG to SYS
Compute addresses of .OAT-2,+I,+5 and +6
Compute address of beginning of I/O Device Table in SGNBLK

Initialize .DAT-2 and
.DAT-3

(next page)
Nonresident Monitor Initialization

Figure 3-1
3-2

(from preceding page)

Clear bit 1 of .SCOM+42
(Nonresident Monitor
.EXIT flag)

(Continue to Command Decoder)

Nonresident Monitor Initialization
(continued)

Figure 3-1 (Cant.)

3-3

3.2

COMMANDS TO THE NONRESIDENT MONITOR

This paragraph discusses legal commands listed in the Nonresident
Monitor's Command Table.

Table 3-1, Effects and Exits for Nonresident

Monitor Commands, describes all commands that do not request a new
program.
There are five entries in the Command Table that load relocatable
system programs.

They are DDT, EXECUTE, GLOAD and LOAD.

The Non-

resident Monitor treats these commands separately, because SYSBLK
does not list them.

All information necessary for loading these pro-

grams resides in the Nonresident Monitor itself.
3.3

CONSIDERATIONS FOR ADDITIONS TO THE NONRESIDENT MONITOR

Programmers should not attempt to add commands to the Nonresident
Monitor unless they have access to a copy of the source code.

The

source code may be purchased from Digital Equipment Corporation,
146 Main Street, Maynard, Massachusetts, under one of the order numbers listed in the footnote.

They should then use the

EDITO~

program

to put in the indicated changes, and reassemble.

New additions to the Nonresident Monitor require the following actions:
1.

Update the Nonresident Monitor's Command Table.
The Command Table is in two parts:
a)

The .SIXBT names of the commands

The corresponding transfer vector

Write the code for the command.

Consider the kind of exit the command will take:
a)

Commands that end with a request for a new
command should end with JMP KLCOM

Commands that re-configure the Nonresident
Monitor should end with JMP NRMEX1.

DECtape

DEC-15-SRDA-Ul

Magtape

Unavail1.ble

3-4

Table 3-1
Effects and Exits
for Nonresident Monitor Commands*
COMMAND

MODIFIER

ACTION TAKEN

EXIT

API

ON
OFF

Set bit ~ of .SCOM+4.
Clear bit ~ of .SCOM+4.

.EXIT
.EXIT

ASSIGN

handler

Check whether handler is available.
If yes, load .DAT slot with proper
handler code.
(The proper loader
will load the handler, and insert
its starting address into the .DAT
slot.

Next
Command

DIC

Load proper slot via a .USER

Next
Command

BANK

ON
OFF

Set bit 11 of .SCOM+4.
Clear bit 11 of .SCOM+4.

Next
Command

BATCH

Set bit ~ and clear bit 2 in location 1777 of the Bootstrap's bank.
If bit 2 of .SCOM+33 is set (i.e.,
if VT is ON) and bit 17 of .SCOM+33
is set (i.e., CTRL X is set for VT),
set bit 1 of .SCOM+33 in order to
tell the Resident Monitor Initialization to start up CTRL X.

.EXIT

Set bits ~ and 2 of location 1777 of
the Bootstrap's bank, and set bit 1
of .SCOM+33 as with BATCH PRo

.EXIT

BUFFS

number

Put number indicated into .SCOM+26,
and set Nonresident Monitor Initialization to leave .SCOM+26 alone.

Next
Command

CHANNEL

7
9

Clear bit 13 of .SCOM+4.
Set bit 13 of .SCOM+4

Next
Command

DATE

date
no date

Enter date into .SCOM+47.
Print date from .SCOM+47.

Next
Command

(and/or)

This table assumes error-free input.

3-5

Table 3-1

(cont.)

Effects and Exits
for Nonresident Monitor Commands

COMMAND
GET
GETP
GETS
GETT
HALF

ACTION TAKEN

EXIT

Set bit ~ of .SCOM+33.
Clear bits f1 and 1 of .SCOM+33.

.EXIT
.EXIT

MODIFIER
Set Section 3.4.

ON
OFF

HALT

If not in BOSS-IS mode, put a HLT
instruction (instead of a JMP) into
the exit from non-IOPS 4 errors to
.MED.
If in BOSS mode, do nothing.

Next
Command

INSTRUCT

none
ERRORS

Print INSALL Table.
Print INSERR Table.

Next
Command

KEEP

ON
OFF

Set bit 16 of .SCOM+42.
Clear bit 16 of .SCOM+42.
Initialize to SGEN default values all entries in .DAT and .UFDT, except
change SCR default values to current
UIC.

Next
Command

Output five spaces after Carriage
RETURNs. After ALT MODE, go to
next command.

Next Command (after
ALT MODE)

Redefine current UIC (. SCOM+4l) .
Clear bit ~ of .SCOM+42, reset variable system parameters to SGEN default values zero .SCOM+S6.

.EXIT

LOGOUT

Set current UIC to SCR.
Set .UFDT
entries to SGEN default parameters.
Deposit zero into .SCOM+42 and S 6.

.EXIT

LOGW

For BOSS-IS, print message.
In all
cases, after a Carriage RETURN, output five spaces.
After ALT MODE,
type four bells tp, and await CTRL P.
After CTRL P, go to next command.

Next Command (after
ALT MODE)

LOG

uic

3-6

Table 3-1 (cant.)
Effects and Exits
for Nonresident Monitor Commands
ACTION TAKEN

EXIT

COMMAND

MODIFIER

ON
OFF

Set bit 3 of .SCOM+42.
Clear bit 3 of .SCOM+42.

.EXIT
.EXIT

MICLOG

mic

Check key with SGNBLK.
If correct,
set bit % of . SC0"1+42 , make "SYS"
the current UIC, and zero . SCO"1+5 6.
If incorrect, ignore command.

Next
Command

PAGE

ON
OFF

Clear bit 11 of .SCOM+4.
Set bit 11 of . SCOM+4.

Next
Command

PROTECT

If n is between fJ and 7, inclusive,
enter it into . SCOM+54.

Next
Corrun and

PUT

See Section 3.4.

QDUMP

Enter MANSAV, the address of the
manual CTRL Q, into the exit from
non-lOPS 4 errors to .MED.

Print the current assignments for
.DAT and .UFDT.
Print the current assignments for
all positive .DAT and .UFDT slots.
Print required .DAT and .UFDT slots,
and the assignments and use for each.

Next
Command

REQUEST

none
USER
prog

.SCOM

Print the information for the current system.

Next
Command
Next
Command

TIME

time
none

Enter time into .SCOM+5,0.
Print time from .SCOM+5.0.

ON
OFF

.EXIT
Set bit 2 of .SCOM+33.
Clear bits 1, 2, and 17 of .SCOM+33.
Execute 7%3.044.

X4K

ON
OFF

Enter 4.f5~~~fJ into .SCOM+2~.
Deposit zero into .SCOM+2.0.

Next
Command

33TTY

ON
OFF

Clear bit 2 of .SCOM+4.
Set bit 2 of . SCOM+4.

.EXIT

3-7

After assembly, the programmer must call PATCH, in
order to make his relocatable binary program absolute.
Commands to PATCH should be as follows:
>DOS15)

>READR

16~77

DOSNRM BIN)

16~77 indicates the highest location the new monitor
can occupy.
(SYSBLK begins at 161~~.)
DOSNRM BIN
happens to be the file name used by program development.
The progranuner may, of course, substitute his
own file name. More information may be found in the
PATCH manual -- DEC-15-YWZB-DN5.

3.4

QFILE

QFILE is a system program that allows users to

(1) store core images

in named files, and (2) retrieve such core images for examination via
DUMP (or possibly for a slow, core-swapping capability).

QFILE imple-

ments the following Resident Monitor system macros and Nonresident
Monitor commands:
.GET, GET, GETP, GETS, GETT,

.PUT and PUT

Users can not obtain QFILE by typing its name to the Nonresident
Monitor.

The Resident Monitor will load QFILE as part of its response

to the commands and macros listed above.
PUT creates a file that contains the data in the CTRL QAREA;
creates a file from the current core image.

.PUT

GET, GETP, GETS, GETT

and .GET all overlay core with the contents of the QAREA or file.
different commands specify different startup locations.)

(The

In addition

to the above capabilities, the Resident Monitor provides the capability
of overlaying core with the contents of the CTRL Q area.

The follow-

ing instructions show how to use that routine:
UNITNO=4~~~f1~
.SCOM=l~~

LAC

START

XOR
JMP*

UNITNO
(. SCOM+6 4

/UNIT FOUR

/STARTING ADDRESS AFTER THE CTRL Q
/GET
/UNIT NUMBER IN HIGH-ORDER THREE BITS
/ADDRESS OF CTRL Q GET ROUTINE

3-8

Figure 3-2, QFILE, and Implementation of GET and PUT Logic, shows
the information flow associated with QFILE.

QFILE uses the follow-

ing registers:
. SCOM+7 , l~
.SCOM+65

.SIXBT Filename and Extension
Command parameters, packed as follows:
Bits ~-2
Bit 8
Bit 9
Bits 15-17

Device unit number
NRM PUT, when set
PUT logic, when set
Function Code

.SCOM+66-71

CTRL Q Area parameters

.DAT-14

File must be on the device assigned
to this .DAT slot.

NOTE
All GET and .GET operations change all
of core, except registers ~ through 4
of bank zero.

3-9

.PUT CAL

store unit number and
function code into

Set bit 9 of .SCOM+65
to indicate .PUT

Store unit number and code into

Store unit number an
function code into

Set bits 8 and 9 of
.SCOM+65 to indicate
NRM PUT

• 5COM+ 65

.SCOM+65

Dump core into CTRL Q area
Bring in QFILE via a .OVRLA

GET

1.
2.

PUT

Transfer core image from CTRL Q area
to named file via Monitor TRAN's and
dump mode .WRITE's

Save .SCOM+65 from the file
Transfer core image file to
crRL Q area via dump mode
.READ's and Monitor TRAN's.

Use function code from file's .SCOM+65
1.
2.

Store correct startup address
Do Monitor TRAM from CTRL Q

Note:

This chart assumes error free input.

QFILE, and Implementation of GET and PUT Logic

Figure 3-2

3-10

CHAPTER 4
THE SYSTEM LOADER AND THE LINKING LOADER

The System Loader is the third major part of the 00S-15 Monitor.
other two are the Resident and Nonresident parts.

The

The Resident and

Nonresident Monitors communicate with the System Loader by manipulating certain .SCOM registers.

When comm&nds to either part imply a

new configuration is needed, that part sets up the appropriate .SCOM
registers, and passes control to the System Bootstrap via the Monitor
TRAN routine.

The Bootstrap then loads the System Loader into high

core, and gives it control.
The System Loader examines the .SCOM registers, and loads a fresh copy
of the Resident Monitor, including any features that the user wishes
to be resident, such as the CTRL X feature.
desired system program and
tion.

a~l

It will also load the

handlers required by the new configura-

In addition, it will allocate all required buffers.

The Non-

resident Monitor is treated like any other core-image system program.
The System Loader never loads user programs.

It only loads core-image

system programs, the Linking Loader and Execute.
user

The latter two load

programs~

The System Loader uses two device handlers to interface with the disk:
the System Bootstrap, and the System Loader Disk Handler (DKL.).

OKL.

arrives in core along with SYSBLK, COMBLK and SGNBLK, as well as the
loader itself.

The Bootstrap loads core image programs only.

The OKL.

takes care of relocatable programs and any handlers loaded by the
System Loader.

Those include all handlers for core-image system programs,

the Linking Loader's own handlers, and any needed by the Execute file.
The Linking Loader loads some handlers needed by user programs it links.
There are two parts to the System Loader:
and the System Loader proper (.SYSLD).
Loader Interface.

the System Loader Interface,

Figure 4-1 describes the System

Figure 4-2 describes the System Loader Proper, and

Figure 4-3 describes the Linking Loader.

4-1

Turn on the clock
Initialize
First free reg.SCOM+~
ister below the
Bootstrap
SGEN default
.SCOM+4
Bit zero set, i
.SCOM+2~
extra 4K: rest
zero
.SCOM+33 VT & HALF, as
per SGEN
.SCOM+74 Line frequency
-Mov to hi hest bank

2.
3.
4.
5.
6.
7.
8.
9.
l~.

11.

Zero .SCOM+36, to indicate no entries in
Busy Table
Move Resident Monitor into lower core
Set up:
Jump to Skip Chain
CAL* error
Legal CAL jump
Turn API on or off, depending on bit ~ of .SCOM+4 (set=on)
Bank bit initialize Resident Monitor to talk to the
Bootstrap, and load .SYSLD into the proper bank upon a
subsequent .EXIT or .OVRLA.
Initialize the Bootstrap with the proper lOPS 4 address for
disk not ready
Calculate the Skip Chain from SGNBLK
Set all API channel registers to point to lOPS 3 (with the
exception of the clock interrupt) and all software levels
to point to lOPS 3~
Put transfer vector to .DAT slots into .SCOM+23
Put number of positive ~DAT slots into .SCOM+24
Put pointer to .UFDT+~ .into .SCOM+25

.TRAN image _of .OAT
and • UFDT out to
block 37 of the system device unit

.TRAN image of .OAT
and • UFDT in from
block 37 of the system device unit ~
1.
2.
3.

Zero .OAT-7 (i.e., not yet set up)
set up .DAT-2 and .DAT-3 for TTA.
Update .SCOM+l and +2 to point
just-above the Skip Chain, .DAT
and .UFDT

Next Page
System Loader Initialization
Figure 4-1

4-2

From Preceding Page

1.
2.
3.
4.
5.

Put number of system device's "A" handler (DKA. or DPA.)
into .SCOM+57
Set up tabbing for current teleprinter
Set .SCOM+2~ to initial state (as in first t~e initialization)
Set up for CTRL Q -- ignore Q-dumps if RF system and QAREA too
small, or nonexistent
Setup for lOPS errors upon the followinG interrupts:
Nonexistent Memory
(lOPS 31)
Memory Protect Violation
(lOPS32)
Memory Parity Error
(lOPS33)
Power Fail Not Set Up
(lOPS34)

Y -- Non-BOSS Batch
Set up for the
proper input
device (CD or PR)

19-

nore input until $JOB
N~tP~e

System Loader Initialization

Figure 4-1 (Cont.)
4-3

From Preceding Page
1. Set up CTRL C to clear the Batch Switch (bit 1 of 17777
of the Bootstrap)
2. set up CTRL T to abort current job, and start the Batch
Monitor looking for the next $JOB line
3. Relocate proper batch handler (PR or CD) to low core

4. Put handler entry point into .DAT-2
5. Set lOPS errors to abort job -- effectively a CTRL T
6. Set up all batch device .DAT slots to refer to the handler currently in core. That is, only one batch input
device is allowed at anyone time
7. Clear $JOB read switch (bit 1 of Bootstrap 17777)
8. Perform .INIT to .DAT-2

1.
2.
3.

Relocate Resident BOSS
and link it to the DOS
Resident Monitor
Patch DOS Resident Monitor to accomodate BOSS
Set bits 14, 15 and 17
of .SCOM+42, to tell
.SYSLD to set up .DAT-7
and +6

Relocate and
link CTRL X
code, and give
proper buffer

Set up linkages between
CTRL X code and the
Resident Monitor

Next Page
System Loader Initialization

Figure 4-1 (Cont.)
4-4

From Preceding Page

Allocate the number of buffers
indicated by .SCOM+26
2. Set up File Buffers Transfer
Vector Table pointer, in .sCOM+3~
3. Store one of the following codes
into .SCOM+6:
LOAD
l~~~~~
GLOAD
3~~~~~
DDT
4~~~~~
DDTNS
5~~~~~
4. Zero .SCOM+5
~

__________________

Tell .SYSLD by setting
.SCOM+ll to XCS (avoids
two handlers in core for
same device)

____________

~2.

Allocate number of
buffers indicated
by .SCOM+26
Set up File Buffers
Transfer Vecter
Table in .SCOM+3~
Set .SCOM+6 = m

(Loading a Core-Image Program)
1. Find entry in SYSBLK and COMBLK
2. Build Overlay Table from information in COMBLK, and set .SCOM+31 to
first word in the table
3. Store the number of overlays in the overlay processor of the Resident
Monitor

1. Store the list of active .DAT slots derived from COMBLK in the System Loader
command area, just below the ~ootstrap,
and delimit the list with a zero
2. If the Nonresident Monitor was not the
last program, restore .SCOM+26 ~default
3. Allocate space for, and set up .SCOM+3~
to point to the File Buffers Transfer
Vector Table

Next age
System Loader Initialization

Figure 4-1
4-5

(Cont.)

From Preceding Page

1.
2.

Zero .SCOM+6
Put 1
into .SCOM+5

Move the RCOM Table to position below
the Bootstrap
Build the IOC Table

System Loader Initialization

Figure 4-1

4-6

(Cont.)

1.
2.
3.
4.

set up for Page or Bank Mode
Set up .DAT-7 for the System Loader disk handler COXA. or OPA.)
Clear free core, and initialize bank bits in pointers to the Bootstrap
Make a Mass Storage Busy Table consisting of one entry

1.
2.

Change XCS to XCT
Allow reading of
EXECUTE file by the
System Loader Handler

Clear memory bank pointers of banks that
do not exist

Load handlers into extra 4k,

Put System Device's code into
.DAT+~, to allow subsequent
insertion into .DAT-7
Next Page
The System Loader

Figure 4-2
4-7

From Preceding Page

EXECUTE

coreimage

1. Translate the handler code from radix

to .SIXBT
2. Do .USER to .UFOT-7, using "lOS"
3. Do .INIT and .SEEK to .OAT-7, in order
to get the handler file
4. Load handler via .OAT-7, and close .OAT-7
5~

N --

Note: Subroutine IOPROS accepts
.OAT slots as input. If the indicated .OAT slot contains zero,
the slot is unassigned, and IOPROS
returns. If not zero, IOPROS checks----------~
whether the desired handler has already been loaded. If the handler
is in core, IOPROS loads the .OAT
slot with the handler's starting address and returns. If the handler has
not been loaded, the handler code is made
an unresolved .GLOBL, to be satisfied
by the loop that follows immediately.
The System Loader

Figure 4-2 (Cant.)

4-8

not

1. Set up Mass storage Rusy

Table Entries for all
active .OAT slots
2. Set .SCOM+l to first free
location in core--often
becomes first location of
EXECUTE

From Preceding Page

Load and relocate EXECUTE or the Linking
Loader, and place starting address into
.SCOM+5

1.
2.

set up Mass Storage Busy table with
one entry per active .DAT slot
Move the IOC table from the System
Loader's area (just beneath the
Bootstrap) to the Linking Loader's
area

set .SCOM+2 and +3 to delimit free core

dress in
SCOM+5

1.
2.
3.

Allocate all necessary buffers
If the system has an extra 4K,
put the first free address beneath
the handlers into .SCOM+2~
Update first free location in core
shown in .SCOM+2 -- .OVRLA updates
the first free address beneath the
Bootstrap, .SCOM+3

Exit via
.OVRLA
Note:

Subroutine BaseKl does the following, if loading a program under BOSS-15:
(1) .USER to .UFDT-7, (2) .SEEK to .DAT-7 for PRCFIL PRC.
The System Loader

Figure 4-2
4-9

(Cont.)

STARr

1.
2.
3.

Clear all of core above the loader, including the extra 4K, if present, and
excluding the Bootstrap ,
Initialize the Load Table with the first free address in every bank or page
Indicate all core below the address in .SCOM+2 as not free
Compute transfer vectors to .OAT-l, -3, -4, -5, and -7, and a pointer to
.UFDT-l
Save the contents of .UFDT-l

Load DDT and set the
symbol flag, if not
ODTNS

Type appropriate
name, and await
command string

1.
2.
3.

Check for P, G and C switc es
Translate all file names after left arrow into .SIXBT, pad with blanks,
and store in symbol table
After ALT MODE, load to end-of-file each file on .DAT-4, and put starting
address of the first file (i.e., not DDT) into .SCOM+6

After every end of tape, type tp
and await CTRL P -- continue
until number of tapes equals the
number of commas, plus one

Next Page
The Linking Loader

Figure 4-3

4-10

From Preceding Page
Check Symbol Table for handlers
needed, and load them from .DAT
-1, using lOS as a UIC; exit if
ille al .DAT
desired

NOTE:
During the library searches
diagrammed on this page, the
Linking Loader tests for
more unresolved .GLOBL's after each resolution. Whenever there are no more unresolved .GLOBL's, the Linking
Loader halts its library
searches, and goes directly
to the COMMON area allocation
code (next to the last box
on this page). Thus, the
libraries are never searched
more than is necessary.

Check Symbol Table for any
unresolved .GLOBL's

1.
2.
3.

Do .SEEK to LIBRS BIN on .DAT-S
Read through user's library and
load any program units that satisfy any .GLOBL's
Read to end of library file, if
still unresolved .GLOBL's

If any unresolved .GLOBL's, try to
program units in the system
library (.LIBR BIN) on .DAT-l

~----------~~------------~find

Scan Symbol Table for Common Blocks,
and allocate space and set pointers,
as needed. If any unresolved .GLOBL's
seek matches in the Common Blocks

Exit to the~______-1 Print LOAD3 error
Nonresident
message
Monitor
~------------------

Next Page
The Linking Loader
Figure 4-3 (Cont.)

4-11

From Preceding Page

Set .SCOM+2 below all
of the Loader's handlers, and the Loader
itself

set .SCOM+2 above the
Loader's highest handler -- no handler is
overlayed

Allocate the Mass Storage Busy Table,
with the number of entries equal the
sum of the active .DAT slots, minus
one -- i.e., the two .DAT slots for
the teleprinter are omitted, and one for
.DAT-7 is added

GLOAD

LOAD

Put lowest address of
the Symbol Table into
.SCOM+II, and the highest into .SCOM+2 -DDT will recalculate
.SCOM+2

The Linking Loader

Figure 4-3

4-12

(Cont.)

4.1

MANUAL BOOTSTRAP LOADS AND RESTARTS

Manual Bootstrap loads and restarts bring blocks
device into the lowest bank.

~-36

of the system

These blocks contains the Resident Moni-

tor, the System Loader Interface Routine, and SYSBLK, COMBLK and SGNBLK.
Figure 4-4 illustrates the core load after manual Bootstrap loads and
restarts.

The Interface sets up

.SCOM+~,

2~,

27, 33, 54 and 74

from SGNBLK values determined at system generation time, and then
transfers the whole core image of the Interface to the Bootstrap's
bank.
bank

(DOS requires 16K, because this bank must be different from
~.)

At all other times, the Bootstrap loads the System Loader

into its own bank.

This preserves the image of .SCOM, part two of

the Resident Monitor patch
4.2

~ea,

and the CTRL X buffer.

LOADING SYSTEM PROGRAMS

The System Loader Interface Routine gets control in the highest bank,
either by a transfer from the lowest bank, or by load from the Bootstrap.

After setting up for the System Loader Proper (.SYSLD), accord-

ing to the program to be loaded and the settings of certain SCOM registers, the Interface Routine brings it in as a complete overlay.

Figure

4-5 illustrates the core configuration of the Interface when it is
in the highest bank.

(The addresses provided are for a 16K system.)

The System Loader loads handlers from the lowest part of free core up,
with the exception that the extra 4K is filled first, if it exists.
Core image system programs are usually loaded just beneath the Bootstrap
(always in the highest bank).

Such core images must be wholely within

the top bank of core, and above register 17 of that bank.

Figure 4-6

illustrates the core maps for system programs.

Whenever the Linking Loader is loaded (LOAD, GLOAD, DDT, and DDTNS) ,
the System Loader loads all handlers for .DAT slots -1, -4, and -5,
and then loads the Linking Loader itself.
Linking Loader.)

(DDT is loaded by the

Figure 4-7 illustrates the core maps for the Linking

Loader.
For EXECUTE, the System Loader loads EXECUTE's handler, and reads the
EXECUTE file, in order to determine the active .DAT slots.

The System

Loader then loads all the handlers required, and sets up the .DAT
slots.

Figure 4-8 illustrates core maps for EXECUTE.

4-13

16K. 24K. 32K

16K, 24K. 32K

BOOTSTRAP

BOOTSTRAP
.SCOM

.sCOM
.ReOM TABLE
37500 (16K)
SGNBLK

UNUSED

37100 (16K)
SYS3LK and COMBLK
36100 (16K)
17500
SYSTEM LOADER INTERFACE
(overlayed by .SYSLD)

3 SYSTEM BLOCKS
16100

SYSTEM LOADER INTERFACE
RESIDENT MONITOR IMAGE

20100 (16K)

16K, 24K. 32K

RESIDENT MONITOR
BOOTSTRAP

.SCOM
100

.SCOM+3·

.SCOM+l.2 •

DDT, IF PR ESENT
RESIDENT MONITOR

15-0663

• A s the In1erhce moves code down, It Inere
ments .SCOM+l and +2.

15-0664

LOADED PROGRAMS

Figure 4-4

ON DDT LOADS. SYMBOLS
ARE MOVED INTO THE
LOWEST PART OF FREE CORE.

Bootstrap Load

Figure 4-5

SYMBOL TABL E
SYMBOLS AND PROGRAMS BUILD
TOWARD EACH OTHER.

Standard
Interface Load
.SCOM+2·

LINKING LOADER"

LOADER HANDLERS
16K, 24K, 32K

.SCOM+l

BOOTSTRAP
BUFFER POOL
.SCOM

16K. 24K, 32K
BOOTSTRAP

SYSTEM PROGRAM

.SCOM

BUFFER POOL
TRANSFER VECTORS

(THIS AREA IS USED BY CORE
IMAGES. SOME ROOM UNDERNEATH
THE BOOTSTRAI' MAY BE LEFT
FREE FOR COMMUNICATION
BETWEEN CORE IMAGES IN AN
OVERLAY STRUCTURE.
CORE IMAGES MUST BE BK OR
LESS.)

OVERLAY SYSTEM
BLANK COMMON

RESIDENT MONITOR
.SCOM+3

·Placement of .SCOM+2 depends on relative
positions of the Linking Loader and its handlers .
.SCOM+3

FREE CORE

When control is nansfertad to loaded program,
SCOM.2 and +3 bracket 1ree core

FREE CORE

15-0660
.SCOM+2

.SCOM+2

Figure 4-7

EXECUTE

HANDLERS, BUFFERS

.SCOM+l

Linking

Loader

All HANDLERS REQUIRED

BUFFER POOL
TRANSFER VECTORS
BUFFER POOL
OVERLAY TABLE
BUFFER POOL
TRA'IISFE R VECTORS
DEVICE TABLE
.SCOM+l

RESIDENT MONITOR

15- 0662

Figure 4-6

15-0661

Figure 4-8

System
Program Load

Execute

4-14

BOSS-IS Mode operation requires the system "A" handler be assigned to
.DAT-7.

This requires a sleight of hand on the part of the System

Loader, which needs the "L" handler on .DAT-7.

It therefore loads

the "A" handler as if it were assigned to .DAT+P', and transfers the
set up .DAT slot ~ contents to .DAT-7 before transferring control to
the program being loaded.

.DAT+~

is then restored to its original

status.
4.4

TABLES AND INFORMATION BLOCKS USED AND BUILT BY LOADERS

The System Loader uses SYSBLK, COMBLK, SGNBLK, block 37 of the system
device,

.SCOM, the RCOM Table, the IOC Table, the Device Table, the

Mass Storage Busy Table, the File Buffers Transfer Vector Table, the
Overlay Table,

.DAT, .UFDT and three bits in the Bootstrap.

Tables

4-I, 4-I1 and 4-II1 describe how the Loaders use these blocks and tables.

4.5

.DAT SLOT MANIPULATION BY THE SYSTEM LOADER

The System Loader maintains the .DAT slot device handler assignments
as they were the last time the Nonresident Monitor was in core.

The

Loader saves the .DAT and .UFDT on the system device whenever the
Nonresident Monitor was the last program. in core.

Thereafter, the

Loader refreshes .DAT and .UFDT from the image on the disk.

If KEEP

is off, the Nonresident Monitor's initialization routine restores the
.DAT and .UFDT to default values.

When loading core-image system programs, the System Loader determines
the active .DAT slots by examining COMBLK.

When loading EXECUT, the

System Loader sets up .DAT-4, and any active slots indicated by the
Execute file itself.

wnen loading the Linking Loader, the System

Loader sets up .DAT-l, -4, and -5.

The Linking Loader will set up other

other active .DAT slots according to the .IODEV commands in the assembly of the program units being loaded.

Both the System Loader and the Linking Loader set up .DAT slots in
this manner:

(In the following procedure, "loader" refers to either

one. )

4-15

Table 4-1
I

Tables and Block?
Used by the Loaders
I

USE

LOCATION

SYSBLK

The System Loader obtains Monitor TRAN
parameters from SYSBLK when it builds

16S99 of
.SYSLD's bank

COMBLK

Indicates number of buffers required,
the active .DAT slots, and the names

171~f1

SGNBLK

Default settings for .SCOM registers,
number of words per buffer, size of
Resident Monitor's patch area (part
two), Skip Chain, .DAT and .UFDT default contents, and handler information.

16199 of
.SYSLD's bank

Block 37
of the System Device

Image of .DAT and .UFDT, when last program was loaded (excluding the Nonresident Monitor).

. SCOM Table

See Table 4-11 .

RCOM Table

Moved for use by the Nonresident Monitor. 175f1f1 of the
highest bank

laC Table

Built by Interface Routine for .SYSLD
itself.

Just beneath
the System
Loader

Device
Table

Built by Interface Routine if loading
PIP, or if PIP is among the overlays
listed in COMBLK

Just above
.SCOM+l

Mass Storage
Busy Table

Built by the System Loader itself.

Pointed to by
.SCOM+62

File Buffers
Transfer Vector Table

Allocated by the Interface Routine, and
initialized by it for non-core Image
programs. System Loader proper initializes for core-image programs.

Pointed to by
.SCOM+39

Overlay
Table

Built by the Interface Routine

Pointed to by
.SCOM+31

.DAT
and
.UFDT

Image stored and restored from block 37
of the System Device. The System Loader
loads all handlers for core-image programs and EXECUTE Files, and sets up
the appropriate .DAT slots. The System
Loader also loads handlers assigned to
.DAT-l, -4, and -5 when loading the
Linking Loader, and .DAT-7 and +6 for
BOSS-IS.

Pointed to by
.SCOM+23 and
.SCOM+2S

BOOTSTRAP

Bits fI, I, and 2 of location 17777 in
the Bootstrap's bank used for Batch (nonBOSS) information.

NAME

down, in
.SYSLD's bank

l.0f1 of 1st bank

4-16

Table 4-11
.SCOM REGISTERS USED BY THE SYSTEM LOADER
.SCOM+

Description of Use by the System Loader

Set in first-time initialization routine.
Used to locate
the System Loader Conunand Area, which is just below the
Bootstrap.

System Loader Interface routine updates this indication
of the first free register above the Resident Monitor
each time it moves a piece down to low core.

The Interface and .SYSLD itself continually update this
indication of the first free location as they move code
and build tables.

Updated as with .SCOM+2. Last free location in core.

First Time Initialization routine sets this register according to a SGNBLK parameter.
Refer to Table 4-III.

Interface Routine stores code of program to be loaded
.SYSLD uses .SCOM+S for starting address
into .SCOM+S.
when loading EXECUT or LOAD. The .OVRLA routine loads
.SCOM+S with starting address of the Monitor Recovery
The Bootstrap transfers to the address in
Routine.
.SCOM+S after all its operations.

Interface Routine stores codes for DDT, DDTNS, LOAD and
GLOAD into . SCOM+6.
For other programs, the Interface
Routine zeroes . SCOM+6.

.SYSLD saves contents of .DAT-I in .SCOM+7, when loading
the Linking Loader. When loading EXECUT, .SCOM+7 contains the first three characters of the Execute file's
name. Contains .DAT-12 when loading Nonresident Monitor.

If!

.SYSLD saves contents of .DAT-4 in SCOM+l,0, when loading
the Linking Loader. When loading EXECUT, .SCOM+l,0 contains the second three characters of the Execute file's
name.

.SYSLD saves contents of .DAT-5 in .SCOM+ll, when loading
the Linking Loader. When loading EXECUT, .SCOM+ll contains the extension of the Execute file's name.
(The
Interface routine sets .SCOM+ll to XCS, telling .SYSLD
that EXECUT will be using the system device.
.SYSLD
then restores .SCOM+ll to XCT.)

1215

The Interface routine initializes these transfer vectors
for API software levels to point to SERR, an error routine
that will produce an IOPS3,0.

16,
17

Unaffected.

4-17

Table 4-II (Cont'd)
.SCOM+

Description of Use by the System Loader

2)1

Bit zero set in first time initialization, if system contains an extra 4K.
If the system does contain an extra
4K, the System Loader will load handlers in that page -from the bottom up -- when loading a core-image program.
Whenever there is an extra 4K, the System Loader will
update bits 3-17 with the address of the first free cell
in the extra 4K.

Unaffected.

The Interface Routine refreshes this pointer to .DAT.

The Interface Routine refreshes this indication of the
number of positive .DAT slots.

The Interface Routine refreshes this pointer to .UFOT+.0'.

When the Nonresident Monitor was the last program, the
System Loader allocates the number of buffers indicated
by the contents of .SCOM+26.
If the Nonresident Monitor
was not the last program, the System Loader restores
.SCOM+26 to the default value if program to be loaded is
core image. Otherwise, untouched.

The first time initialization routine sets this indication of the number of words per file buffer.

The Initialization Routine loads this pointer to the
File Buffer Transfer Vector Table.

When loading a core-image program, the Interface Routine
loads .SCOM+31 with the pointer to the Overlay Table, or
with zero, if there is none.

Unaffected.

See Interface Routine table, to determine how that routine
reacts to the bits in . SCOM+33.

34, 35

Unaffected.

System Loader loads wi th the number of active . OAT slots
assigned to the system device.

37-42

Unaffected.

43, 44

Contains name of the program to be loaded.

45-56

Unaffected.

System Loader loads with the number of entries in the
Mass Storage Busy Table.

6)1, 61

Unaffected.

System Loader loads with the address of the first entry
in the r.~ass Storage Busy Table.

63-

Unaffected.

4-18

Table 4-II1
Use of .SCOM+4 by the System Loader
Bit
0

If set, place "API ON n constant into ~~~~~6.
If clear, place "API OFF n constant in same register.

Ignored.

If set, change the Resident Monitor so it will tab
with the KSR 35/37 tabbing mechanism.

Loader will set this bit, if loading the Nonresident
Monitor; clear it otherwise.

4-6

Ignored.

Loader sets this bit if bit 11 is cleared, and loadOtherwise clear.
ing the Linking Loader or Execute.

Sets or clears, after comparing current core size
(known by location of Bootstrap, and status of bit ~,
.SCOM+2,0) with SGNBLK parameter. Also, modifies
Resident Monitor to give IOPS77 after attempts to use
CTRL Q.

9, 10

Ignored

Indicates whether to clear or set bit 7 , when loading
Linking Loader or Execute.

12-17

Ignored

4-19

Each .OAT slot will contain a handler number -- either the
system default, or one inserted via an ASSIGN command to
the Nonresident Monitor.
This handler number is the relative location of the handler name in the IOC Table, which
the Interface Routine builds.
(The IOC Table contains
handler names in Radix 5~.)
.

For each active .OAT slot, the loader uses the handler
number in that slot to find the name in the IOC table, and
converts the name to .SIXBT.

If the handler is already in core, the loader simply inserts
the starting address of the handler into the .OAT slot.

If the handler is not yet in core, the loader does a .SEEK
to lOS for the handler, reads it into core, relocates it,
and places the starting address of the handler into the
.DAT slot.

The System Loader always sets up .OAT-2 and -3.

(It reserves .OAT-7

for its own use.)

When not in non-BOSS Batch Mode, -2 is assiqned
I

to TTA.

In non-BOSS Batch Mode, the batch input device goes to -2.

If loading the Nonresident Monitor and bit three of .SCOM+42 is set,
I

the System Loader will set up .DAT-12 for the LPA, if it is in the
I

system, or else for TTA.

If in BOSS mode ,I the Nonresident Moni tor

assigns LPA. to .OAT+6, and the System Loader assigns .DAT-7 to the
system device "A" handler.
handlers are in core.

The System Lo~der then ensures that both

The Resident BOSS set up routine subsequently

routes all .DAT slots connected to TTA. to Resident BOSS.
I

4.6

BUFFER ALLOCATION BY THE SYSTEM LOAD~R

The System Loader allocates space for buffers equal to the contents
of .SCOM+26 times the contents of .SCOM+27.

The first time initial-

ization routine sets .SCOM+27 to the standard number of locations per
buffer.

Before the Nonresident Monitor does an .OVRLA to a software

system program, it checks whether a BUFFS command has been issued.
If so, it leaves .SCOM+26 as is.

If not, it uses the default number

of buffers for that program, as shown in SYSBLK.

4-20

CHAPTER 5
SYSTEM INFORMATION BLOCKS AND TABLES

5.1

CORE-RESIDENT NON-REFRESHED REGISTERS

The .SCOM table, the Bootstrap and the resident Patch Area are the
only registers not refreshed by the System Loader.

Table 5-I de-

scribes the .SCOM Table.
5.2

DISK-RESIDENT UNCHANGING BLOCKS: SYSBLK, COMBLK AND SGNBLK
I

SYSBLK, COMBLK and SGNBLK occupy blocks 34, 35, and 36

(octal) on the

system device

(unit zero).

SYSBLK and COMBLK (blocks 34 and 35) contain

the parameters for loading all core image system programs.
I

tains all the other information needed to run DOS.

SGNBLK con-

All three arrive

in core along with the Resident Monitor and the System Loader Interface, and start at location

l61~~

of the highest bank.

The Nonresident

Monitor and System Loader use them, and DOSGEN and PATCH modify them,
when necessary.
5.2.1

SYSBLK

SYSBLK contains the parameters required for implementation of .OVRLA
to any system program, or any of the system program overlays.
The order of entries in SYSBLK is unimportant, except for the first
three permanent entries:

RESMON,

.SYSLD, and fQAREA.

of SYSBLK contains the block address
first free word after itself.
5.2.2

The first word

(the unrelocated address) of the

Figure 5-1 describes SYSBLK.

COMBLK

COMBLK contains information the System Loader and the Nonresident
Monitor need to remember about the current core-image system programs.
The last location in COMBLK (that is, location 377 of block 35) contains the block address of the first entry in COMBLK.

The remainder

of COMBLK consists of variable-length entries associated with the
system programs.

The Nonresident Monitor searches COMBLK when it

finds no match for a typed command in its own Command Table.
5-1 illustrates the organization of COMBLK.
5-1

Figure

The System Generator adds

TABLE 5-1
.SCOM Registers

BIT

MEANING

First register below the Bootstrap (set by the
System Loader Interface)

First register above the Resident Monitor (set by
the System Loader Interface)

Lowest free register available for storage (set
by the System Loader or the Linking Loader)

Highest free register available for storage (set
by the System Loader, the Linking Loader or DDT)

Initialized from SGNBLK values by the IIfirst time
section of the System Loader Interface Routine,
and by the LOGIN, LOGOUT and MICLOG logic of the
Nonresident Monitor; modified by the Nonresident
Monitor, unless otherwise indicated.
~

= 1

API is available.

= 1

EAE is available

(always set)

2 = 1

Teleprinter is Model 35 or 37

3 = 1

Nonresident Monitor is in core

4,5
6

Reserved

= 1

9-Channel Magnetic Tape System

7 = 1

Page Mode Operation

8 = 1

QAREA inadequate for current core size (set by
the System Loader Interface Routine)

= 1

DOS disk file structure (always set)

1.0 = 1

RB~9

11 = 1

Bank Mode System

12,13

Line Printer Line Size:
~9

)11
1.0
11

14 = 1
15- 17

disk is system device.

No Line Printer
8~ Characters
12.0 Characters
132 Characters

Background/Foreground System (always clear)
Drum size (ignored -- DOS does not support drum)

5-2

TABLE 5-1 (Cont'd)
I

REGIS~ER
5
6

MEANING

BIT

Core Image System Program starting address.
fJ

= 1

DDT in core.

= 1

GLOAD

= 1

DDTNS
User program starting address.

3-17

When using the Linking Loader, . SCOM+7 , 10 and 11
contain the handler numbers for handlers needed by
the Linking Loader in . DAT -1, -4, and -5 respectively.

7-11

When using EXECUTE, 7-11 contain the .SIXBT representation of the name and extension of the Execute
File.
When using QFILE (for implementation of .GET, .PUT
and the Nonresident Monitor GET and PUT commands),
7-11 contain the .SIXBT representation of the name
and extension of the core image file.
12

API Level 4 service routine entry point

API Level 5

API Level 6

API Level 7

Program Counter on Keyboard Interrupts.

AC on Keyboard Interrupts.

2fJ

fJ
3-17

= 1

2fJK or 28K system.
First free address in top page.

Magtape Status Register.

Reserved for Magtape Handler.

Pointer to .DAT+,0.

Number of positive .DAT slots.

Pointer to .UFDT+fJ.

Number of buffers.

Number of words per buffer.

3fJ

Pointer to Buffer Transfer Vector Table.

5-3

TABLE 5-1 (Cont'd)

REGISTERS

BIT

MEANING

Pointer to first entry in the Overlay Table (zero,
if none).

Bad block number on lOPS

CTRL X status register.

Y1 = 1

and 72.

HALF ON

= 1

Display Buffer already set up.

= 1

VT ON

17 = 1

If VT ON, display mode is on.

If in BOSS mode, elapsed time in seconds.

Instruction to clear TT Busy Switch.

Number of Entries in the Mass Storage Busy Table.

Entry point for Expanded Error Processor.

JMP to Expanded Error Processor.

The logged-in UIC.

Bit Register.
~

MICLOG successful.

= 1

.EXIT from Nonresident Monitor.

= 1
3 _. 1

.OVRLA from Nonresident Monitor.

4 = 1
5

= 1

6-13
14

Dump core on calls to .MED (except lOPS 4) .
Halt on calls to .MED (except lOPS 4) .
Unused.

= 1

15 = 1
16

LP ON -- LPA to .DAT-12 when loading Nonresident
Monitor.

= 1

17 = 1

Set up .DAT+6 (used by BOSS Mode).
Load System Device Handler into .DAT-7.
KEEP-ON.
BOSS Mode.

43,44

.SIXBT Representation of the name of the core
image system program to be loaded (if any).

45,46

.SIXBT Representation of the name of the Nonresident Monitor

5-4

TABLE 5-1 (Cont'd)

REGISTERS

BIT

MEANING

Date

(MMDDYY)

5f1

Time

(HHMMSS)

Elasped time, in ticks.

BOSS Bit Register

fl = 1

BOSSl5 Mode.

= I

Control Card Read by user, 5/7 ASCII image saved
in first block of NRBOSS.

Resident BOSS reached "EOF" on run time file

3 = I

User exceeded time estimate.

= I

I/O CAL to go to TTY.

= I

Terminal lOPS error by user.

QDUMP to be given to user on lOPS errors.

7 = 1
8

Operator abort (Control T) .
Job active.

9 = 1

Exit from BOSSl5 Mode.

1.0' = 1

User tried to do a .PUT.
a listing given on LP.

11 = 1

User tried to do a .GET.

Not defined.

14-16
17 = 1

(RTF) .

Core will be dumped and

. SYSLD error number .
Job abort.

Reserved for CTRL X code.

Default Protection Code.

Entry to Monitor TRAN routine.

Two's complement of time limit, in seconds (zero,
if no limit) .

System Device Code, for use by the Linking Loader.

6fl

Number of ticks until clock interrupt specified
in last . TIMER (zero, if .TlMER not in use).

5-5

TABLE 5-1
REGISTER

(Cont'd)

BIT

MEANING

. TIMER address.

Address of the first word in the Mass Storage Busy
Table.

Numl;>er of words per Mass Storage Busy Table Entry.

JMP to CTRL Q GET routine.

QFILE Communication Register.

First Block of the CTRL Q Area.

Starting Address minus one of the CTRL Q Area.

Two's complement of number of word in Qdump

Starting Address after DUMP or GET.

Starting Address after CTRL Q.

TWo's cOIrlplement of the number of ticks left in the
next second.

TWo's complement of the line frequency ..

Number of RTF Lines

76-1~5

(for BOSS Mode).

Unused.

5-6

Word #

Value

Description

flfJf1nnn

Pointer to first free word after SYSBLK
(There is one set of seven words/core
image program.)

7N+l
7N+2
7N+3

.SIXBT
.SIXBT
nnnnnn

7N+4

flfIf1fJnn

7N+5

addres

7N+6
7N+7

~nnnnn

·
·

·
·
·

S
B
L

•• K

addres

Name of System Program or overlay
Number of first block on system device
occupied by this program or overlay.
Number of blocks occupied by this program or overlay
Thirteen-bit first address for this
program or overlay
Program size
Thirteen-bit starting address for this
program or overlay

·
·
~---------------. -----------------------------------------------------·

(free area)

~---------~;;---l-;:;;;;~;-----~::::-:~-:::~:-::-~~::-::::~-~~:-:~::--5fJl
592
5fJ3

5f14

.SIXBT
.SIXBT
.SIXBT
.SIXBT

595

~f1fJfJ~2

.. C

.OAT&777
'-..OAT&777

596
5fJ7

51fl

f1f1~fl95

511
512
513
514

.SIXBT
.SIXBT
0-< 9f19fJfJl

Name of this system program

Number of buffers required by this program (Note that his program has no overlays. )
.OAT slot for this program

.OAT&777

2
'-

777

case, Ifl)
Name of this system program (leftjustified and zero-filled)
Name of an overlay (left-justified and
zero-filled) -- overlays are optional
Number of buffers required by this system program (Bits fJ-6 = f1 means the end
of any overlay names. This is why program and overlay names must be leftjustified.)
Active .OAT slot
Active .OAT slot (Note: 777777 for a .DAT
slot means all positive .OAT slots.)
Number of words for this entry (in this
case, 5)

Pointer to first word in COMBLK (equals
count from first word in SYSBLK). The
two contiguous blocks on the system device that hold SYSBLK and COMBLK are
treated by the system as one large block.
In this case, COMBLK happens to start at
location 5f1f1 of the two blocks combined.
Figure 5-1
SYSBLK and COMBLK
5-7

names of core-image system programs by making them the new first entry.
In this way, SYSBLK and COMBLK build toward the center.
5.2.3

SGNBLK

SGNBLK (block 36 on the system device) contains all the system parameters not directly associated with core-image system programs.

The

bulk of SGNBLK is concerned with r/o (.OAT slots, .UFDT slots, Skip
Chain Order, Handlers, and skip rOT codes and mnemonics).

The first

few registers hold such important system information as the system device,

.SCOM+4 contents, and so on.

The very first word in SGNBLK

points to the block address of the first free word after SGNBLK.

The

next entry is an offset word indicating the total length (including
itself) of the miscellaneous system parameter table to follow.

This

table includes the size of the .DAT and the size of the skip chain.
The end of the handler and skip rOT table is the first free entry of
the block.
The .DAT slot table corresponds to the legal range of .DAT slots,
with the maximum negative set to -15 and the maximum positive set to
a number not to exceed 77 • The .DAT slots are in the form in which
8
they appear when the Nonresident Monitor is in core.
That is, the
unit number is in bits
justified in bits 3-17.

~-2,

and the number of the handler right-

The handler number for the first handler in

the Device Handler-Skip rOT Table is zero, for the pseudo-handler NON.
TTA. is one, and so on.

The constant l~~~~~ indicates a fixed or il-

legal .DAT slot (such as -2, -3, and ~).

DOSGEN will not modify such

slots.
The .UFD Table is

m one-to-one correspondence with the .DAT slot Table.

An entry of .SIXBT 'UIC' indicates that the logged in UIC is to be substituted for the name urc in the table.

An entry of .srXBT 'SYS' in-

dicates BNK or PAG is to be substituted, in accordance with the current
addressing mode.

Otherwise, the contents of each location will be the

.srXBT representation of the corresponding .UFD slot.
The Skip Chain Table lists the system skip lOT's in order.

A negative

skip (one that skips on "off", not "on") is represented in one's complement.

Not all skips in the handler Skip lOT Table

low) need to be included in the Skip Chain Table.

5-8

(described be-

The Device Handler/Skip lOT Table contains all the handler nameS and
skip lOT numbers and mnemonics for each I/O device identified to the
system.

Every such device has an entry in the table.

A handler name

must be exactly three characters in length, with the last character
not an octal digit.
characters.

The

The device code for a device is exactly two

first two characters of each handler name for a de-

vice must be the device code.

This fact is essential for understand-

ing the format of a device entry, since the device code is never
stored as such in an entry, but is inferred from the device handler
name.

The typical entry for a device is the following:
1.

The first words of an entry contain the handler names
for a device in .SIXBT. Each handler name is different, and the end of the list of handlers is determined
by a word with zeros in bits ~-5 (the first character
position).

The word that terminated the list of handler names
contains the number of skip lOT's for the device.
For each skip lOT, there are three words in the table:
two for the skip mnemonic and one for the actual code.

The next device entry follows the last skip for the previous device.
Handlers may be entered without any skips, but no devices may be
entered without at least one handler name.
the organization of SGNBLK.

Figure 5-2 illustrates

Appendix D of SGEN-DOS Utility Programs,

DEC-lS-YWZB-DNI2, lists SGNBLK, SYSBLK and COMBLK, as they are supplied
by Digital Equipment Corporation.
5.3

DISK-RESIDENT CHANGING BLOCKS

The System Loader uses block 37 of the system device to store an image
of .DAT and .UFDT.

Other disk-resident changing blocks are the storage

Allocation Table and the Bad Allocation Table.

These tables are de-

scribed in Chapter 6.
5.4
5.4.1

TEMPORARY TABLES BUILT FROM DISK-RESIDENT TABLES
The Overlay Table

The System Loader builds the Overlay Table from the entries in SYSBLK
referenced by a core-image system program's entry in COMBLK.

That is,

the Overlay Table contains an entry for the system program itself, and
one for each of its overlays.
entry in the Overlay Table.

Figure 5-3 illustrates the format of an
The first entry in the Overlay Table is

5-9

Location

Value

yr
1
2

flIlflnnn

IlIlJ1nnn
f14l3f1f1
f142Ilflfl

flflflf1l5
flIlflnnn

5
6
7
lfl
11
12
13
14
15

flJ1nnnn
7777nn

flIlflnnn

nnnnnn
nnnnnn
nnnnnn
nnnnnn
.SIXBT
nnnnnn

flIlJ1Ilfln

·
53
54

flJ1f1nnn
.SIXBT

III

.SIXBT
nnnnnn

112

·
·
137
l4f1

·
·
·
·

·
·
·
·
·
·
·
·
·
·
·
·
312

nnnnnn
.SIXBT

·
·

.SIXBT
.SIXBT

··

.SIXBT

J1Jlflflfl3

nnnnnn
nnnnnn
nnnnnn
. SIXBT

Description
Pointer to first free entry in SGNBLK
Number of miscellaneous parameters
Size of .DAT plus size of .UFDT = (number of positive .DAT slots+l6) *2.
(Initial value is 2~ positive .DAT slots.)
Number of skips in Skip Chain
System device code in .SIXBT
Original contents of .SCOM+4
Original contents of .SCOM+29
Number of words per buffer (.SCOM+27)
Default number of buffers (.SCOM+26)
Monitor Identification Code
Information on VT and CTRL X (.SCOM+33)
Default files protection code (.SCOM+54)
Size of the Resident Monitor Patch Area
Minus the number of clock ticks in a second (-74
for 69 hz, -62 for 59 hz.)
Device assignments for the .DAT (made by handler
numbers).
(Termination at 53 assumes 29 positive
slots. )
UIC assignments for the .UFDT.
I I I assumes 2J1 positive slots.)

(Termination at

Skip Chain Table (Negative skips in one's complement.)
(Termination at 137 assumes 22 skips in
chain. )
The last part of the SGNBLK is the Device HandlerSkip lOT Table. Each entry starts with the .SIXBT
representations of all handlers for a particular
device.
(First two characters equal device code,
for all handlers.)
Zeros in the first six bits
of a word indicate the end of the handler names,
and says that the rest of the word contains the
number of skips for this entry's device. The skip
lOT's follow immediately. As above, one's complement skips indicate negative skips. Note, however,
the confusing fact that a one's complement of a
skip rOT is a positive number. Thus, 7yrnnn complemented is 97nnnn .

flfIfIJlfll

nnnnnn

·
·
·

SGNBLK ends at 312, in the DOS-15 system distributed by Digital Equipment Corporation.

Figure 5-2
SGNBLK

5-10

pointed to by .SCOM+31.

.SCOM+31 will contain zero, if there are no

entries in the Overlay Table.

This will occur during Linking Loader

or EXECUTE loads •
. OVRLA is the only Monitor function that looks at the Overlay Table.
If the .OVRLA processor finds a match to the .OVRLA argument in the
Overlay Table, it uses the parameters listed in the table to bring
it in via a Monitor TRAN.

Note that this bypasses the System Loader,

and does not change the handler load.

Thus, the overlay must use only

those .DAT slots required by the original program, the one listed in
COMBLK.
If the .OVRLA processor does not find a match in the Overlay Table, it
calls in the System Loader, which searches COMBLK for the requested
program.

This type of overlay request does not require that .DAT slot

assignments be the same.
all of

On the other hand, the System Loader refreshes

core except .SCOM, etc.

is more difficult.

Thus, communication between overlays

The resident patch area, however, can be used for

this purpose.
5.4.2

The Device Table

The Device

Table is built by the System Loader interface whenever PIP

is being loaded, or when PIP is listed in COMBLK among the overlays
for a program.

It is located just above the register pointed to by

• SCOM+I , and has an entry for each positive .DAT slot.

If a slot has

an assigned device, the low-order twelve bits of the corresponding
entry in the Device Table will contain the device's code, in .SIXBT.
Bit 3 is set when the slot is busy.

If no device is assigned to a

slot, the corresponding entry in the Device Table will contain zero.
5.4.3

The Input/Output Communication (IOC) Table

The System Loader Interface builds the IOC Table and locates i t just
below the first register of the System Loader.

It contains an entry

for each handler in the system, in the order that they appear in
SGNBLK.

The entries themselves contain the handler name in Radix

5~.

The System Loader and the Linking Loader use the handler number supplied by the Nonresident Monitor to index down the IOC Table.
use

the contents of the entry for a .SEEK to the lOS UIC.

5-11

They

5.4.4

The Oevice Assignment Table (.DAT)

The Device Assignment Table makes the association between logical and
physical devices.

The Monitor knows its location by the contents of

.SCOM+23, which points to the zeroth entry in the Table.
are found by indexing on the contents of .SCOM+23.

Specific slots

The number of nega-

tive slots is fixed at 15 ' The number of positive slots is specified
S
by .SCOM+24, and may be any positive number less than 1~~8. It is
specified at system generation time.
The Nonresident Monitor places the handler number in the low order
bits and the unit number in the high order bits.
ler number from SGNBLK.

It derives the hand-

As mentioned above, the System Loader and

the Linking Loader subsequently use the IOC Table to determine the
handler name.

After either loader has loaded and relocated a handler,

it places the handler's starting address in all .OAT slots that reference that handler.
bits.

The unit number remains in the high-order three

Slots with no handler (NON) contain

zero~

Active .OAT slots

are designated by COMBLK, for core-image system programs, and by .IODEV
pseudo-ops for the Linking Loader and EXECUTE.
The User File Directory Table (.UFDT)

5.4.5
.UFDT+~

is offset from

.DAT+~

(pointed to by .SCOM+23) by the sum of

the positive and negative .OAT slots. Each .DAT slot has a corresponding .UFOT slot. UIC's in the .UFDT are packed in .SIXBT. The address
of

.UFDT+~

5.4.6

is stored in .SCOM+25.

The Skip Chain

contains a jump to the beginning of the Skip

The Skip Chain is defined during System Generation, is located

in SGNBLK, and is rebuilt every time the System Loader is called in.
The System Generator Manual (DEC-15-YWZB-DN12) describes considerations
for constructing the Skip Chain.
5.5

TEMPORARY TABLES BUILT FROM SCRATCH

5.5.1

File Buffer Transfe+ Vector Table

The System Loader allocates space for the buffer pool, and creates the
File Buffer Transfer Vector Table.

.SCOM+30 points to the first entry

5-l2

in the table, and the number of entries is specified by .SCOM+26.
Each entry in the table contains the address of a buffer, or its one's
complement.

Negative addresses indicate a busy buffer.

Since refer-

ences to buffers must be indirect anyway, buffers are allocated without regard to bank boundaries.
5.5.2

The RCOM Table

The Nonresident Monitor requires certain information about the Resident Monitor that does not warrant reserving additional .SCOM registers.
The System Loader therefore puts this information into the RCOM table,
whenever it is loading the Nonresident Monitor.
at register
5.5.3

175~~

The RCOM Table starts

of the highest bank.

The Mass Storage Busy Table

Entries in this table are allocated by the System Loader or the Linking Loader.

The Mass Storage Busy Table is pointed to by .SCOM+62 .

• SCOM+63 contains the number of words per entry in the table, and
.SCOM+36 contains the current number of entries.

Generally speaking,

there are as many entries in the Busy Table as there are active .OAT
slots, although the disk handlers are the only ones that currently
refer to the Busy Table.
The .INIT command to a disk handler establishes a Busy Table entry.
The .CLOSE command
ponding entry.

(or the Rewind

.~TAPE

command) deletes the corres-

Figure 5-4 illustrates a typical Busy Table Entry_

The first word of an active entry in the Busy Table contains the .OAT
slot in bits 9-17.

The disk handlers save information about the UFO

current for this .OAT slot in the Mass Storage Busy Table.

They save

information about the file current to the .OAT slot (if any) in the
buffer pointed to by word 1 of the Busy Table Entry.

More information

on the disk handlers and file structure is contained in Chapter 6.

5.6

RESERVED WORD LOCATIONS

Word locations

through 77 are dedicated systems locations and can-

not be employed by the user.

The contents of these locations are

described in Table 5-5.

5-13

Word i
N,N+l

.SIXBT name of Overlay

N+2

First block number

N+3

First address, minus 1

N+4

Size, in two's complement

N+5

Fifteen-bit starting address

Contents

Table 5-3
Word #
N
N+l
N+2
N+3
N+4

Overlay Table
Contents

Device Type~_2' Unit Number _ , Write Check ,.DAT _
3 5
6
9 l7
Buffer Address, or {O, if none allocated
Three-character UIC
First UFD block for this UIC
UFD Entry size for files in this UFD
Table 5-4

Mass Storage Busy Table Entry

ADDRESS

USE
Stores the contents of the extended PC, link, extend
mode status, and memory protect status during a program interrupt

EEM (for PDP-9 compatibility)

JMP to Skip Chain

.MED, entry to Monitor Error Diagnostic routine

JMP to error handler

Stores system type (Bank or Page) indicator during
Teletype interrupts

Used for API ON/OFF indicator

Stores real time clock count

10-17

Autoindex registers

Stores the contents of the extended PC, link, mode
status, and memory protect status on a CAL instruction.

JMP to CAL handler

22-37

Seven pairs of word counter-current address registers
for use with 3-cycle I/O device data channels.

40-77

Store unique entry instructions for each of 32 10 automatic priority interrupt channels
Table 5-5

Reserved Address Locations

5-14

5.7

BOOTSTRAP NON-BOSS BATCH BITS

The high-order three bits of word 17777 in the Bootstrap are reserved
for the Moniter, and have the following meanings:
Bit ~

Bit 1

Bit 2

In non-BOSS Batch Mode

Not in non-BOSS Batch

$JOB ASCII line or card just read by batch device

Last line or card not $JOB

Batch device is card reader

Batch device is paper tape reader

5-15

CHAPTER 6
FILE STRUCTURES

6.1

DECTAPE FILE ORGANIZATION

DECtape can be treated either as a directoried or non-directoried
device.
6.1.1

Non-Directoried DECtape

A DECtape is said to be non-directoried when it is treated as magnetic
tape by issuing the .MTAPE commands: REWIND, BACKSPACE, followed by
.READ or .WRITE.

No directory of identifying information of any kind

is recorded on the tape.

A block of data (255

word maximum), exactly
10
as presented by the user program, is transferred into the handler buffer and recorded at each .WRITE command.

A .CLOSE terminates record-

ing with a software end-of-file record consisting of two words:

001005,

776773

Because braking on DECtape allows for tape roll, staggered recording
of blocks is employed in DOS to avoid constant turnaround or timeconsuming back and forth motion of physically sequential block recording.

When recorded as a non-directoried DECtape, block ~ is the

first block recorded in the forward direction.

Thereafter, every fifth

block is recorded until the end of the tape is reached, at which time
recording, also staggered, begins in the reverse direction.
passes over the tape are required to record all 1100
6.1.2

Five

blocks.

Directoried DECtape

Just as a REWIND or BACKSPACE command declares a DECtape to be nondirectoried, a .SEEK or .ENTER implies that a DEC tape is to be considered directoried.

A directory listing of any such DECtape is

available via the (L)ist command in PIP.

A fresh directory may be

recorded via the N or S switch in PIP.
The directory of all DECtapes except system tapes occupies all
words of block

1~~8.

It is divided into two sections:

Directory Bit Map and (2) a 340

(1) a 40 8 word

word Directory Entry Section.

6-1

4~~8

The Directory Bit Map defines block availability.
cated for each DECtape block (llOOS bits

One bit is allo-

= 408 words).

When set to 1,

the bit indicates that the DECtape block is occupied and may not be
used to record new information.
The Directory Entry Section provides for a maximum of 5610 files on
a DECtape.

Each file on the DECtape has a four-word entry.

Each

entry includes the three-word file name and extension, a pointer to
the first DECtape block of the file, and a file active or present bit.
Figure 6-1 illustrates the DECtape directory.
Word

° U-'" Block

Block

1~77

Entry

1-----------

- - --

Directory
Bit Map

Directory
Entry
Section

f--------------- --Entry
55l~

377

r;
Wd.

5 6

I
I

Name

I
I

File Name Extension

11 12
File

Note: Nulls (0) fill
in short file names.
A file name extension
is not absolutely
necessary.

Data Link (First File Block)
Sign Bit:

1 = File Active

A DIRECTORY ENTRY

Figure 6-1
DECtape Directory
Additional file information is stored in blocks 71 through 77 of every
directoried DECtape.

These are the File Bit Map Blocks.

For each file

in the directory, a 40S-word File Bit Map is reserved in block 71
through 77.

The bit maps are contiguous, and the Nth file uses the

6-2

th
.
N
bit map. Each block is divided into eight File Bit Map Blocks. A
File Bit Map specifies the blocks occupied by that particular file and
provides a rapid, convenient method to perform DECtape storage retrieval for deleted or replaced files.

Note that a file is never de-

leted until the new one of the same name is completely recorded on
the .CLOSE of the new file.

When a fresh directory is written on

DECtape, blocks 71 through 100 are always indicated in the Directory
Bit Map as occupied.

Figure 6-2 illustrates DEC tape file bit maps.

Block 718

Bit Map for File ~

Block 728

Bit Map for File 7
B1t Map for File 8
Bit Map for File 15l~

Bit Map for File 48l~

Block 778

Bit Map for File 56l~

Figure 6-2
DECtape File Bit Map Blocks

Staggered recording (at least every fifth block) is used on directoried
DECtapes, where the first block to be recorded is determined by examination of the Directory Bit Map for a free block.

The first block is

always recorded in the forward direction; thereafter, free blocks are
chosen which are at least five beyond the last one recorded.

The last

word of each data block recorded contains a data link or pointer to
the next block in the file.

When turnaround is necessary, recording

proceeds in the same manner in the opposite direction.
turnaround is determined by examining the data link.

When reading,
If reading has

been in the forward airection, and the data link is smaller than the
last block read, turnaround is required.

If reverse, a block number

greater than the last block read implies turnaround.
A software end-of-file record (001005, 776773) terminates every file.
The data link of the final block is 777777.

6-3

Data organization for each I/O medium is a function of the data modes.
On directoried DECtape there are two forms in which data is recorded:
(1) packed lines - lOPS ASCII, lOPS Binary, Image Alphanumeric, and
Image Binary, and (2) dump mode data - Dump Mode.
In

rops or Image Modes, each line (including header) is packed into

the DECtape buffer.

In lOPS Binary, a 2's complement checksum is com-

puted and stored in the second word of the header.

When a .WRITE

which will exceed the remaining buffer capacity is encountered, the
buffer is output, after which the new record is placed in the empty
buffer.

words, including header, because
10
of the data link and even word requirement of the header word pair
count.

No record may exceed 254

An end-of-file is recorded on a .CLOSE.

It is packed in the same

manner as any other line.

In Dump Mode, the word count is always taken from the I/O macro.
a word count is specified which is greater than 255

(note that space

for the data link must be allowed for again), the DECtape handler will
transfer 255

word increments into the DECtape buffer and from there
10
to DECtape.
If some number of words less than 255
remain as the
10
final element of the Dump Mode .WRITE, they will be stored in the DECtape buffer, which will then be filled on the next .WRITE, or with an
EOF if the next command is .CLOSE.

DECtape storage is thus optimized

in Dump Mode since data is stored back-to-back.
6.2

See Appendix A.

MAGNETIC TAPE

DOS provides for industry-compatible magnetic tape as either a directoried or non-directoried medium.

The magnetic tape handlers com-

municate with a single TC-59D Tape Control unit (TCU).

Up to eight

magnetic tape transports may be associated with one TCU; these may
include any combination of transports TU-IOA or Band TU-30A or B.
There are a number of major differences between magnetic tape and DECtape or Disk; these differences affect the operation of the device
handlers.

Magnetic tape is well suited for handling data records of

variable length.
fashion.

Such records, however, must be treated in serial

The physical position of any record may be defined only in

relation to the preceding record.

Three techniques available in I/O

operations to block-addressable devices are not honored by the magnetic
tape handlers:

6-4

The user cannot specify physical block numbers for
transfer.
In processing I/O requests that have block
numbers in their argument lists (i.e., .TRAN) the
handler ignores the block-number specification.

The only area open for output transfers in the directoried environment is that following the logical end
of tape.

Only a single file may be open for transfers (either
input or output) at any time on a single physical unit.

6.2.1

Non-directoried Data Recording (MTF)

MTF is intended to satisfy the requirements of the FORTRAN programmer
while still providing the assembly language programmer maximum freedom
on the design of his tape format.

MTF writes out a record to the tape

each time the main program issues a .WRITE.

The length of the record

is always two times the word pair count in the header word pair.

FlOPS

records are always as long as the buffer size returned on a .INIT (up
to 256

.INIT.

MTF returns a standard buffer size of 377 , after a
8
The FORTRAN user may dynamically change this size, however,
words).

via the following instructions.
(FORTRAN STATEMENTS)

(MACRO STATEMENTS)

SETMTB
CALL SETMTB (ISIZE)
BUFSIZ
START

6.2. 2

.TITLE SETMTB
.GLOBL .DA, MTBSIZ, SETMTB
$I
.DA
JMS*
START
JMP
$I
BUFSIZ
LAC*
(any buffer size)
MTBSIZ
DAC*
SETMTB
JMP*
.END

Directoried Data Recording (MTA., MTC.)

The programmer can make the fullest possible use of those features
peculiar to magnetic tape by using MTF.

On the other hand, MTF does

not offer the powerful file-manipulation facilities available in the
system.

Directoried I/O allows device independence, and extensive

use of the storage medium with a minimum of effort.

6-5

Every block recorded by MTA.

(with the exception of end-of-file markers,

which are hardware-recorded) includes a two-word Block Control Pair
and not more than 255

words of data.
10
records from one or more .WRITE's.

The data will contain the

The Block Control Pair serves three functions:
acter of the

it specifies the char-

block (label, data, etc.), provides a word count for the

block, and gives an IS-bit block checksum.

The Block Control Pair has

the following format:
Word 1:
Bits 0 through 5: Block Identifier (BI).
This 6-bit byte
specifies the block type. Values of BI may range from 0
to 77 R• Current legal values of BI, for all user files,
are as follows:
BI Value

Block Type SEecified

User-File Header Label

User-File Trailer Label

User-File Data Block

Bits 6 through 17: Block Word Count (BWC). This 12-bit
byte holds the 2's complement of the total number of words
in the block (including the Block Control pair). Legal
values of BWC range from -3 to -401 .
S
Word 2:
Bits 0 through 16: Block Checksum. The Block Checksum is
the full-word, unsigned, 2's complement sum of all the
data words in the block and word 1 of the Block Control
Pair.

5 6

BCP WORD I

N TOTAL WORDS
IN BLOCK
N- 2 DATA
WORDS

Figure 6-3
Block Format, File-Structured Mode

6-6

One of the main file functions of MTA. and MTC. is that of identifying
and locating referenced files.

This is carried out by two means:

first, names of files recorded are stored in a file directory at the
beginning of the tape; and second, file names are contained in the
file's header and trailer labels.
6.2.2.1

Magnetic Tape File Directory

The directory, a single-block file (and the only unlabeled file on any
file-structured tape), consists of the first recorded data block on
the tape. It is a 257
a.

word block with the following characteristics:

Block Control Pair (words I and 2)
Word 1
Block Identifier

74 8 = File Directory Data Block

Block Word Count

-401

8 =

7377 •
8

Word 2:
Block Checksum:

As described above.

Active File Count (Word 3, Bits 9 through 17) 9-bit one's
complement count of the active file names present in the
File Name Entry Section {described below} •

Total File Count (Word 3, Bits 0 through 8) 9-bit one's
complement count of all files recorded on the tape, including both active and inactive files, but not the file
directory block.

File Accessibility Map (Words 4 through 17): The File
Accessibility Map is an array of 252~0 contiguous bits
beginning at bit 0 of word 4 and end~ng as bit 17 of
word 17. Each of the bits in the Accessibility Map refers to a single file recorded on tape. The bits are
assigned relative to the zeroth file recorded; that is,
bit 0 of word 4 refers to the first file recorded; bit
1, word 4, to the second file recorded; bit 0, word 6,
to the 37 10 th file recorded; and so on, for a possible
total of 252 10 files physically present.
A file is only accessible for reading if its bit in the
Accessibility Map is set to one. A file is made inaccessible for reading (corresponding bit = 0) by a .DLETE
of the file, by a .CLOSE (output) of another file of the
same name, or by a . CLEAR. A file is made accessible for
reading (corresponding bit = 1) by a .CLOSE (output) of
that file.
Operations other than those specified above
have no effect on the File Accessibility Map.

6-7

BIT POSITION

·3

17
BEGINNING

OF' TAPE
Bep {

FILE

COUNTS

:::: :

WORD 3

FILE
DIRECTORY

WORD 4

FILE
ACCESSIBILITY
MAP

FILE # 1
(INACTIVE)
WORD 16
WORD 17
WORD

FI LE #2
(ACTIVE)

WORD 21

FIL E
NAME
ENTRY,
SECTION

FILE #3
(INACTIVE)

WORD 24
FILE #4
(ACTIVE)

FI LE #5
(ACTIVE)

WORD 257

END OF TAPE

09-0232

Figure 6-4a. Format of the
File Directory Data Block,
showing relationship of active
and inactive files to file name
entries and to Accessibility Map

Figure 6-4b. Format of filestructured tape, showing
directory block and data
files.

6-8

File Name Entry Section (Words 18 through 257): The File
Name Entry Section, beginning at word 18 of the directory block, includes successive 3-word file name entries
for a possible maximum of 80 entries. Each accessible
file on the tape has an entry in this section. Entries
consist of the current name and extension of the referenced file in .SIXBT (left-adjusted and, if necessary,
zero-filled) .
The position of a file name entry relative to the beginning of the section reflects the position of its accessibility bit in the map.
That bit, in turn, defines the
position of the referenced file on tape with respect to
other (active or inactive) files physically present. Only
active file names appear in the entry section, and accessibility bits for all inactive files on the tape are always
set to zero; accessibility bits for all active files are
set to one.
To locate a file on the tape having a name that occupies
the second entry group in the File Name Entry Section,
the handler must (a) scan the Accessibility Map for the
second appearance of a I-bit, then (b) determine that bit's
location relative to the start of the map.
That location
specifies the position of the referenced file relative to
the beginning of the tape. The interaction of the File
Name Entry Section and the Accessibility Map are shown
in Figure 6-4.

6.2.2.2

User-File Labels

Associated with each file on tape is one label, the header label.
precedes the first data block of the file.
in length.

Each label is 27

Label format is shown in Figure 6-5.

5 6

WORD I

"'7"'745

BCP

WORD 2

CHECKSUM

WORD 3

777 XXX

WORD 4

000000

FILE

NAME

WORD 5

:J]

WORD 2 6 , a C = t - - - -_ _ _
WORD 27 , 0

Figure 6-5
User-File Header Label

6-9

For~at

RESERVED

words

6.2.2.3

File-Names in Labels

The handler will supply the contents of the file-name fields
in labels.

(Word 3)

These are used only for control purposes during the execu-

tion of .SEEK's.

The name consists simply of the two's complement of

the position of the recorded file's bit in the Accessibility Map; the
"name" of the first file on tape is 777777, that of the third file is
777775, and so on.

A unique name is thus provided for each file physi-

cally present on the tape.

Since there may be a maximum of 252

10
present, legal file-name values lie in the range 777777 to 777404.
6.2.3

files

Continuous Operation

Under certain circumstances, it is possible to perform successive I/O
transfers without incurring the shut-down delay that normally takes
place bet. . 'een blocks.

The handler stacks transfer requests, and thus

ensures continued tape motion, under the following conditions:
a.

The I/O request must be received by the CAL handler before a previously-initiated I/O transfer has been completed.

The unit number must be identical to that of the previously initiated I/O transfer.

The I/O request must be one of those listed below to
ensure successful comoletion.
The handler in processing requests in conti~uous mode depends on receiving
control at the CAL level in order to respond to I/O
errors.
The functions for which continuous operation
lS attempted include only the following:
1.
2.

. Jv1TAPE
. READ

3•

. WRITE

.TRAN

With ~TA, more than one logical record may be in a physical
block, so tape motion may stop if fewer successive .READ's
or .WRITE's are issued than there are records in a block.

The previously-requested transfer must be completed without error.
In general, successive error-free READ's
(WRITE's) to the same transport will achieve non-stop
operation.
The following examples illustrate this principle.
Example 1:
SLOT = 1
INPUT = 0
BLOKNO = 0
READl
READ2
RETURN

Successful Continued Operation

.TRAN SLOT, INPUT, BLOCKNO, BUFF1, 257
.TRAN SLOT, INPUT, BLOCKNO, BUFF2, 257
JMP READl

6-10

The program segment in Example 1 will most probably keep the referenced transport (.DAT slot 1) up to speed.

The probability decreases

as more time elapses between READl and READ2, and between READ2 and
RETURN.

Each .TRAN request causes an implicit .WAIT until its opera-

tion is completed.
Example 2:

Unsuccessful Continued Operation

SLOT = 1
INPUT = 0
BLOKNO = 0
READ
STOP
RETURN
The program

.TRAN SLOT, INPUT, BLOKNO, BUFF, 257
.WAIT SLOT
JMP READ

segment in Example 2 will not keep the tape moving because

the .WAIT at location STOP prevents control from returnina to location
READ until the transfer first initiated at READ has bee~ completed.
Example 3:
SLOTl
SLOT2
INPUT
BLOKNO
READI
READ2
RETURN

Unsuccessful Continued Operation

I
2

o
= 0
.TRAN SLOTI, INPUT, BLOKNO, BUFFI, 257
.TRAN SLOT2, INPUT, BLOKNO, BUFF2, 257
JMP READI

This program segment will not provide non-stop operation because of
the differing unit
6.2.4

specificatio~

at READl and READ2.

Storage Retrieval on File-Structured Magnetic Tape

The use of a file accessibility ~ap as well as block identifiers in
Magtape file directories makes it almost impossible to retrieve the
area of a deleted file from a magnetic tape.
deletion command (i.e.,

.DLETE) removes the name of the object file

from the file directory, and clears
Accessibility

The execution of the

tli'2

corresponding bi t in tl"'.e File

~ap.

The only circumstance under which a file area may be easily retrieved
is when the deleted file is also the last file physically on the tape.
Under these conditions, the handler can retrieve the area occupied by
the deleted file when the next .ENTER executed.

.WRI~E -

.CLOSE sequence is

Users may also copy the active files to another device, re-

new the directory, and recopy the files.

6-11

6.3

DISK FILE STRUCTURE

6.3.1

Introduction

The DOS-IS disk file structure is in some ways analogous to DECtape
file structure.

Ordinarily, each disk user has a directory which

points to named files,

just as each DECtape has a directory.

The DEC-

tape has only one directory, but the disk has as many directories as
users have cared to establish.

A single user's disk directory might

correspond to a single DECtape directory.

single disk file's size

is also limited only by the available space, as is true with DECtape.
Whereas DECtape directories may only reference a maximum of 56

files,
10
however, the number of files associated with anyone directory on the

disk is limited only by the available disk space.
The DECtape directory is in a known location -- at block 100.

Since

the disk may have a variable number ,of directories, the Monitor must
know how to find each user's directory.

It therefore maintains a

Haster File Directory (MFD) at a known location l , and the Master File
Directory points to each User File Directory (UFD).

DOS-IS allows

only those users who know the Master Identification Code to have access to any protected UFD's within the MFD.
the I-'fFD.

6.3.2

Figure 6-6 illustrates

Appendix B is a flowchart of the Disk "A" Handlers.

User Identification Codes

(UIC)

The Monitor finds User File Directories by seeking associated User
Identification Codes
Directory.

(UIC's), which are all listed in the Master File

The UIC is a three-character code that is necessary for

all non-.TRAN I/O to the disk.
ences.

.TRAN macros use no directory refer-

A programmer may operate under as many UIC's as he wishes,

vided all are unique and none is reserved 2 .

pro-

He may establish a new

User File Directory by (1) logging in his new UIC to the Monitor via
the LOGIN command,

calling PIP, and (3) issuing an N

DK command.

This establishes a new User File Directory, or refreshes

(wipes clean)

(2)

an old directory under that UIC.

(.ENTER will also create a new MFD

entry and/or a UFD, if none exists.)

Figure 6-7, User File Directory,

illustrates the organization of a UFD.
10n the RF disk, the first block of the MFD is located at block 1777.
On the RP disk, the first block of the MFD is located at block 47~4~.
2The following are reserved UIC's:
CTP.

@@@, ???, PAG, BNK, SYS, lOS,

6-12

Description

Contents

Word #

777777

Dummy UIC used by system.

nnnnnn

Bad Allocation Table's first block number,
or 777777, if there is none. \

nnnnnn

SYSBLK's first block number, or -1, if
there is none.

4 - 2 + b I kn lL'1l

·
··
4N

··

MFD entry size in bits ~-2, plus the block
number of the first submap

··.SIXBT

4N+I

nnnnnn

4N+2

P.0+ M

4N+3

spare

376

nnnnnn

377

nnnnnn

··

UIC for this UED
Block number for the first block of this
UFD or 777777, if no UFD exists (as after
PIP's NL...IDK)}
Protection code in bit .0, plus the UFD
entry size for each file
Unused at this writing
I

Pointer to previous MFD block, or 777777
if none.
Pointer to next MFD block, or 777777 if
none.
Figure 6-6

Master File Directory
Word #

Contents

Description

··
8N

··.SIXBT

8N+l
8N+2
8N+3

· SIXBT
.SIXBT
T.04-blknum

8N+4
8N+5

nnnnnn
ribptr

8N+6

P~_l+ribwrd

8N+7

crdate

Name of this file
and its
extension
Truncation code in bit .0, plus the number
of tre first. block of the file
Number of blocks in this file
Pointer to the first block of the Retrieval
Information Block
Protection code in bits .0-1, plus the
first word in ribptr used by the RIB-- if
the last block of the file has room for
the RIB, the handlers will put it there,
and load word 8N+6 accordingly.
~ate of file's creation -mmddyy (yy modulo 7.0)

376
377

nnnnnn
nnnnnn

Pointer to previous block, or 777777 if none
Pointer to next UFD block, or 777777 if none

Figure 6-7
User File Directory
6-13

6.3.3

Organization of Specific Files on Disk

The Disk Handlers write out files in almost the same way that a DECtape handler does.
backward link.

Disk file blocks, however, have a forward and

(Non-dump records are therefore limited to lengths

of 254

words.)
Further, upon receipt of a .CLOSE I/O macro, the disk
10
handlers fill out a Retrieval Information Block (RIB). The RIB performs the same functions as the file bitmap on DECtape, and also associates the logical sequence of blocks in the file with the physical
locations of the blocks on the disk.

The disk handler uses the RIB to

implement .RTRAN commands and to delete files.

Figure 6-8, The Retrieval

Information Block, illustrates a RIB.
After a user has created a disk file he can access logical records
sequentially via .READ commands,

just as with DECtape files.

He can

also access physical blocks of that file by referencing relative block
numbers in the .RTRAN command.

(The .RTRAN commands require the file

be opened with the .RAND command.)
6.3.4

Buffers

The handlers break buffers from the pool into three parts:
Information (about 4~8 words)~
pre-allocated blocks
(3) data buffer

(1) File

(2) the Block List -- addresses of

(between 4 and 253l~ addresses, inclusive), and

(2561~

words) .

Figure 6-9, Disk Buffer, illustrates

the breakdown of disk buffers.

6.3.4.1

Commands That Obtain And/or Return Buffers

The following commands obtain buffers from the pool, and return them
immediately after execution:
.DLETE
.RENAM
. CLEAR
The following commands obtain a buffer from the pool and do not return
it until a subsequent .CLOSE is performed:
• FSTAT
.ENTER
.SEEK
• RAND

*This number is determined by assembly parameters.
6-14

Contents

Description

nnnnnn

Total number of blocks described by this
physical block.

1
2

nnnnnn
nnnnnn
nnnnnn

First data block pointer.
Second data block pointer.
Third data block pointer.

Word #

376

·
·
·nnnnnn

377

nnnnnn

Pointer to previous RIB block or -1 if no
previous RIB block.
Pointer to next RIB block or -1 if no
next RIB block.

th
t h .
* Zero
word of the RIB may not be zero
word of physlcal block.
This occurs whenever the entire RIB will fit in the last data
block of the file.
Figure 6-8
Retrieval Information Block

4° 8 Words*

}

File Information becomes
'Current Set' when file active
(see 6.3.4.2).

More than 3 and
less than 377
8
words

Addresses of Preallocated
Blocks (Block List or Temp
List or TLIST)

•
Data Buffer

4008 Words

*This is not a fixed number.
different for RP and RF.

It is

Figure 6-9
Disk Buffer

6-15

The following commands return a buffer to the pool, if any was allocated.
.INIT
.CLOSE
.MTAPE (rewind)
6.3.4.2

The Current Set

The handlers retain information about the last file and .OAT slot
processed in an internal storage area.

This area is called the

"Current Set", and is swapped back to the file's buffer whenever a
command to a different file is used.

Thus,

.WRITE to .OAT slot A
.WRITE to .OAT slot B
will swap the Current Set, but •••
• WRITE to .OAT slot A
.TRAN to .OAT slot A
.WRITE to .OAT slot A
will not swap the Current Set.
6.3.5

Pre-allocation

The handlers pre-allocate blocks on the disk upon all .ENTER commands,
I

and whenever sufficient .WRITE commands have been issued to use up the
pre-allocated blocks.

The number of pre-allocated blocks will be the

minimum of the number of free blocks on the device and the number of
address slots available in the Temp List (block list).
When the handlers pre-allocate blocks, they fill out the bit maps, and
immediately fill out the RIB and write i t out in one of the pre-allocated

blocks.
Upon a .CLOSE command, the handlers give back unused blocks, and reI

write the RIB.

6-16

The number of blocks in the Block List depends on the size of the
buffer, which is determined at system generation by setting the buffer
size.

The larger the Block List, the faster will be output.

Smaller

Block Lists may give more efficient allocation of core and disk space.
Smaller buffers save core.

Further, the number of pre-allocated blocks

may affect concurrently opened files on a disk that is tight for space.
Thus, if the Block List is sixty entries long, and there are forty
blocks left on the disk, a .ENTER to .OAT slot will pre-allocate all
forty, leaving none for any subsequent .ENTER's to different .OAT
slots.
lOPS 70 will occur when there are less than four free blocks on the
disk when a handler tries to pre-allocate blocks.

6.3.6

Storage Allocation Tables (SAT's)

The disk handlers use a Storage Allocation Table, in order to distinguish between allocated and free blocks.

If more than one physical

block is required, the individual blocks are called Submaps.
Unlike OECtape, the Storage Allocation Table is never held in core.
When the handlers wish to preallocate some blocks, they read in the
required Submap, and write out the updated one.
Storage Allocation blocks use the following format:

WORD ~
WORD I
WORD 2
WORD 3

WORD 376
WORD 377

Total blocks on the disk
Number of blocks described
by this Submap
Number of blocks occupied
in this Submap
First word of the bit map
(eighteen blocks per word)

Pointer to previous Submap
(or 777777)
Pointer to next Submap
(or 777777)

The bit maps refer to blocks in numerical order.

Thus, bit

of word

three of a Submap will refer to block N, bit I will refer to block N+I,
and so on.

The block is free if the corresponding bit

equals~.

Start-

ing and ending block numbers for all Submaps are retained in the handlers.

The first Submap, however, starts with block zero.

6-17

6.3.7

Bad Allocation Tables

(BAT's)

Occasionally, a particular block on the disk will not record data correctly.

In such instances, the handlers should be prevented from using

the bad blocks.

Accordingly, PIP maintains a Bad Allocation Table.

Whenever a user updates that table, PIP will set the appropriate bit
in the Storage Allocation Table.

The block is thus made unavailable.

Refer to PIP manual (DEC-lS-VWZB-DN13) for more information.

6-18

CHAPTER 7
WRITING NEW I/O DEVICE HANDLERS

This chapter contains information essential for writing new I/O device handlers to work in DOS.
7.1

I/O DEVICE HANDLERS,

INTRODUCTION

All communications between user programs and I/O device handlers are
made via CAL instructions followed by an argument list.
Handler in the Monitor

The CAL

(Figure 2-1) performs preliminary setups,

checks the CAL calling sequence, and transfers control via a JMP*
instruction to the entry point of the device handler.

When the con-

trol transfer occurs (see Figures 7-1 and 7-2), the AC contains the
address of the CAL in bits 3 through 17 and bits 0, 1, and 2 indicate
the status of the Link, Bank/Page mode, and Memory Protect, respectively, at the time of the CAL.

Note that the content of the AC at

the time of the CAL is not preserved when control is returned to the
user.
On machines that have an API, the execution of a CAL instruction automatically raises the priority to the highest software level (level 4).
Control passes to the handler while it is still at level 4, allowing
the handler to complete its non-reentrant procedures before debreaking
(DBK) from level 4.

This permits the handler to receive reentrant

calls from software levels higher than the priority of the program
that contained this call.

Device handlers which do not contain re-

entrant procedures (including all handlers supplied with DOS) may avoid
system failure caused by inadvertent reentries by remaining at level
4 until control is returned to the user.
If the non-reentrant method is used, the debreak and restore (DBR)
instruction should be executed just prior to the JMP* which returns
control to the user, allowing debreak from level 4 and restoring the
conditions of the Link, Bank/Page mode, and Memory Protect.

Any lOT's

issued at the CAL level ·(level 4 if API present, mainstream if no API)
should be executed immediately before the
DBR
JMP*

7-1

USER PROGRAM
{

LOC+.0
LOC+I

CAL ARG.
CODE

LOC+N

NXT INST

.
.

MONITOR

DEVICE HANDLER

IOPS6

Initialize Handler and
return buffer size

Ignored

Issue .SETUP for each
PI skip or API entry
vector

RETURN

to user
at LOC+N

CAL Entry to Device Handler

Figure 7-1
7-2

PI
ENTRY

1.
2.

API
ENTRY

via
JMS f6
Skip Chain
JMP* {INT
1.
2.

Save AC
Save location f6
(including P.C.
LINK and Memory
Protect)
Turn I/O ON

via
JMS* API Device Address
(Le., JMS* (INT)

Save AC
Retain at INT the
P. C., LINK and
Memory Protect
If first time
through, Nap all
PI commands

Test for other errors~ indicate error in header pair

Reset
{e.q., clear I/O
Busy Switch

Restore PI if PI interrupt
and Debreak and Restore

Return via
stored
P. C.

PI and API Entries to Device Handlers

Figure 7-2

7-3

exit sequence in oreer to ensure tEat the exit takes place-before the
interrupt from the issued lOT occurs.
The CAL instruction must not be used at any level (API or PIC) that
might interrupt a CAL. A CAL at such a level will destroy the content
of location 00020 for the previous CAL.

Care must also be taken when executing CALs at level 4.

For example,

a routine that is CALed from level 4 must know that if a debreak (DBR
or DBK) is issued, control will return to the calling program (which
had been at level 4) at a level lower than level 4.
7.1.1

Setting Up the Skip Chain and API (Hardware) Channel Registers

When the Monitor is loaded, the Program Interrupt (PI) Skip chain and
the Automatic Priority Interrupt (API) channels are set up to handle
the TTY keyboard and printer and clock interrupts only.

The Skip

Chain contains the other skip lOT instructions, but indirect jumps to
an error routine result if a skip occurs, as follows:
SKPDrA
SKP
JMP* INTI
SKP LPT
SKP
JMP* INT2
SKPTTI
SKP
JMP TELINT

/Skip if DECtape flag.
/INTI contains error address.
/Skip if line printer flag.
/INT2 contains error address.
/Skip if teleprinter flag.
/TO teleprinter interrupt handler

All unused API channels, memory protect, memory parity, and powerfail,
also contain JMPrs to the error address.
When a device handler is called for the first time in a core load, it
must call a Monitor routine (.SETUP) to set up its skip(s) in the Skip
Chain, or its API channel, prior to performing any I/O functions.

7-4

The calling sequence is as follows:
CAL N

16
SKP lOT
DEVINT
(normal return)
7.1.2

API channel register 40 through 77 (see User's
Handbook Vol. 1, for standard channel assignments) ,
/0 if device not connected to API.
/.SETUP function code.
/Skip lOT for this device.
/Address of interrupt handler.

Handling the Interrupt

DE'TINT exists in the device handler in the following format to allow
for either API or PI interrupts.

ONLYI

LAC
DAC
DAC
DAC
JMP
DAC
LAC*
DAC

(NOP
DEVION
DEVIOF
IGNRPI
COMMON
DEVAC

IGNRPI

JMP
JMP
DAC
LAC
DAC
JMP

COMMON
DEVPIC
DEVAC
DEVINT
DEVOUT
ONLYI

COMMON
DEVION

DEVCF
ION

DEVIOF

IOF

DEVPIC

DEVINT

/LEAVE PI ALONE, WHEN API IS RUNNING
/THESE REGISTERS
/ARE AVAILABLE
/THIS IS ONCE ONLY CODE
/SAVE AC

(fJ
DEVOUT

/SAVE PC, LINK, ADDRESSING MODE AND
/MEMORY PROTECT
/PI ENTRY
/API ENTRY; SAVE AC
/SAVE PC, LINK, ADDRESSING MODE AND
/API IS OPERATING, SO LEAVE PI ALONE.
/PI INTERRUPTS ARE NOT POSSIBLE, BE/CAUSE .SETUP EFFECTIVELY NOP'S PI
/SKIPS.
/CLEAR DEVICE DONE FLAG.
IPI ALLOWS INTERRUPTS; API DOES A NOP.

/API DOES NOP; PI TURNS 10 OFF TO ENSURE
/NON-REENTRANCE AFTER ISSUING lOT'S.

DEVIOT

/DISMISS ROUTINE

DVSWCH

LAC
ION
DBR
JMP*

DEVAC
DEVOUT

/RESTORE AC.
/ION OR NOP.
/DEBREAK AND RESTORE CONDITIONS
/OP LINK, ADDRESSING MODE AND MEMORY
/PROTECT.

If the Index, Autoincrement, or EAE registers are used by the I/O device handler, it is necessary to save and restore them.

7-5

.SETUP allows either API or PI, but not both for a single device.

The

System Generator Manual gives the method for incorporating nE~W handlers
and associated Skip Chain entries into the Monitor.
7.2

API SOFTWARE LEVEL HANDLERS, An Introduction

The information presented in the following paragraphs assumes that the
reader is familiar with the system input/output considerations described
in the PDP-IS User's Handbook Vol. 1.
7.2.1

Setting

Up API Software Level Channel Registers

When th.3 Monitor is loaded, the API software-level channel registers
(40 through 43) are initialized to
JMS*
JMS*
JMS*
JMS*

.SCOM+12
.SCOM+13
.SCOM+14
.SCOM+1S

/LEVEL 4
/LEVEL 5
/LEVEL 6
/LEVEL 7

where .SCOM is equal to absolute location 000100 and .SCOM+12 through
.SCOM+15 (000112 through 000115) each contains the address of an error
routine.
Therefore, prior to requesting any interrupt at these software priority
levels, the user must modify the contents of the .SCOM registers so
that they point to the entry point of the user's software level handlers.
Example:
.SCOM=lOO
LAC

DAC*

(LV5INT
(. SCOM+ 13

/ set level 5 entry.

LVSINT exists in the user's area in the following format:
LV5INT

0
/PC,LINK,BANK/PAGE MODE,MEM.PROT.
DAC
SAV4AC /SAVE AC
/SAVE INDEX, AUTO INCREMENT AND EAE REGISTERS, IF LEVEL 5
/ROUTINES USE THEM AND LOWER LEVEL ROUTINES ALSO USE THEM.
/SAVE MQ AND STEP COUNTER, IF SYSTEM HAS EAE AND IT IS USED
/AT DIFFERENT LEVELS.
/RESTORE SAVED REGISTERS.
DBR
/DEBREAK FROM LEVEL 5 AND RESTORE
JMP*
LVSINT
/L, BANK/PAGE MODE, MEM. PROT.
7-6

7.2.2

Queueing

High priority/high data rate/short access routines cannot perform complex calculations based on unusual conditions without holding off
further data input.

To perform the calculations, the high priority

program segment must initiate a lower priority (interruptable) segment
to perform the calculations.

Since many data handl~ng routines would

generally be requesting calculations, there will exist a queue of calculation jobs waiting to run at the software level.

Each data handling

routine must add its job request to the appropriate queue

(taking care

to raise the API priority level as high as the highest level that
manipulates the queue before adding the request) and issue an interrupt
request (ISA) at the corresponding software priority level.

The general

flow chart, Figure 7-4, depicts the structure of a software handler
involved with queued requests.
Care must be taken about which routines are called when a software
level request is honored; that is, if a called routine is "open"
(started but not completed) at a lower level, it must be reentrant, or
errors will results.
NOTE
The DOS hardware I/O device handlers do not
reentrant procedures and must not be reentered from higher levels.

~ontain

Resident handlers for Power Fail, Memory Parity,
nonexistent memory violation, and Memory Protect
violation have been incorporated into the system
and effect an lOPS error message if the condition
is detected.
The user can, via a .SETUP, tie his
own handler to these skip lOT or API channel registers.

7-7

LV5INT
SAVE PC, LINK, AC,
AUTO-INDEX REGS,
MQ, STEP COUNTER
AND CONDITIONS
OF EXTENDED MODE
AND MEMORY PROTECT

>-'1--~---1 RESTORE SAVED

REGISTERS

RAISE TO HIGHEST
LEVEL THAT
MANIPULATES
LEVEL 5 QUEUE

15-0094

Figure 7-4
Structure of API Software Level Handler

7-8

7.3

WRITING SPECIAL I/O DEVICE HANDLERS

This section contains information prepared specifically to aid those
users who plan to write their own special I/O device handlers for DOS.
DOS is designed to enable users to incorporate their own device handlers.

Precautions should be taken when writing the handler however,

to ensure compatibility with the Monitor.
Here is a summary of handler operation.

The handler is entered via a

JMP* from the Monitor as a result of a CAL instruction.

The contents

of the AC contain the address of the CAL in bits 3 through 17.

Bit 0

contains the Link, bit 1 contains the Bank/Page Mode status, and bit 2
contains the Memory Protect status.

The previous contents of the AC

and Link are lost.
In order

to show the steps required in writing an I/O device handler,

a complete handler (Example B) was developed with the aid of a skeleton
handler (Example A).

In addition, Appendices A and B are complete

flowcharts of the DTA and DKA handlers.

The skeleton handler

is a non-reentrant type (discussed briefly at the beginning of this
chapter) and uses the Debreak and Restore Instruction (DBR) to leave
the handler at software priority level 4 or at a hardware level for
interrupt servicing (if API), and restore the status of the Link,
Example A is referenced by part

Bank/page Mode, and Memory Protect.

numbers to illustrate the development of Example B, a finished Analogto-Digital Converter (ADC) I/O Handler.
Example B was written for the Type

AF~lB

The ADC handler shown in
Analog to Digital Converter.

This handler is used to read data from the ADC and store it in the
user's I/O buffer.
The reader, while looking at the skeleton of a specialized handler
as shown in Example A, should make the following decisions about his
own handler.

(The decisions made in this case are in reference to

developing the ADC handler):
a.

Services that are required of the handler (flags,
rece~v~ng or s~nd~ng of data, etc.) - By looking
at the ADC lOT's shown in the Reference Manual, it
can be seen that there are three lOT instructions
to be implemented.
These instructions are:
Skip
if Converter Flag Set, Select and Convert, and Read
Converter Buffer.

7-9

The only service the ADC handler performs is that of
receiving data and storing it in user specified areas.
This handler will have a standard 256-word buffer.
b.

Data Modes used (for example, lOPS ASCII, etc.) Since there is only one format of input from the
Type AFOIB ADC, mode specification is unnecessary in
Example C.

Which I/O macros are needed for the handler's specific
use; that is, .INIT, .CLOSE, .READ, etc. For an ADC,
the user would be concerned with four of the macros.

(1)

.INIT would be used to set up the associated API channel register or the interrupt
skip lOT sequence in the Program Interrupt
Skip Chain. This is done by a CAL (N) as
shown in Part III of Example A, where (N)
is the channel address.

(2)

.READ is used to transfer data from the ADC.
When the .READ macro is issued, the ADC
handler will initiate reading of the specified number of data words and then return
control to the user. The analog input data
received is in its raw form.
It is up to
the programmer to convert the data to a
usable format.

(3)

.WAIT detects the availability of the user's
buffer area and ensures that the I/O transfer is completed.
It would be used to ensure
a complete transfer before processing the requested data.

(4)

.WAITR detects the availability of the user's
buffer area as in (3) above.
If the buffer
is not available, control is returned to a
user specified address, which allows other
processing to continue.

Implementation of the API or PIC interrupt serViCE! routine
Example A shows an API or PIC interrupt service routine
that handles interrupts, processes the data and initiates new data requests to fully satisfy the .READ macro
request. Note that the routin~s in Example A will operate with or without API.
Example B uses the routi.nes
exactly as they are shown in Example A.
During the actual writing of Example B, considerat:ion was
given to the implementation of the I/O macros in t:he new
handler in one of the following ways:
(1)

Execute the function in a manner appropriate
to the given device as discussed in(c).
.INIT,
• READ, .WAIT, and .WAITR were implemented into
the ADC handler (Example B) under the subroutine
names ADINIT, ADREAD,· ADWAIT (.WAIT and .WAITR).
Wait for completion of previous I/O.
(Example B
shows the setting of the ADUND switch in the ADREAD
subroutine to indicate I/O underway.)
7-10

(2)

Ignore the function if meaningless to the device.
See Example B (.FSTAT results in JMP ADIGN2) in
the dispatch table DSPCH. For ignored macros,
the return address must be incremented in some
cases, depending upon the number of arguments
following the CAL (see Chapter 3).

(3)

Issue an error message in the case wher~ it is
not possible to perform the I/O function - (An
example would be trying to execute a
.ENTER on
the paper tape reader.)
In Example B, the handler
jumps to DVERR6 which returns to the Monitor with
a standard error code in the AC.

After the handler has been written and assembled, the Monitor must then
be modified to recognize the new handler.

This is accomplished by the

use of the System Generator Program (DOSGEN)described in the DECl5-YWZB-DN12 manual.
W~en

the system generation is complete, the PIP program (refer to

DEC-15-YWZA-DN13) must be used to add the new handler to the lOS UFD.
At this time, the user is ready to use his specialized device handler
in the DOS-IS system.
7.3.1

Discussion of Example A by Parts
Part 1

Stores CAL pointer and argument pointer, and
picks up function code from argument string.

Part 2

By getting proper function code in Part 1 and
adding a JMP DSPCH, the CAL function is dispatched to the proper routine.

Part 3

This is the .SETUP CAL used to set up the PI
skip chain or the API channel register.

Part 4

Shows the API and PI handlers.
these be used as shown.

Part 5

This area reserved for processing interrupt and
performing any additional I/O.

Part 6

Interrupt dismiss routine.

Part 7

Increments argument pointer in bypassing arguments of ignored macro CAL's.

7-11

It is suggested

7.3.2

Example A, Skeleton I/O Device Handler

ICAL ENTRY RnUTINE
.'CLOBL DEV.
.MfO-3
DEV.
OAC
OVCALP
DV4RGP
OAe
iS~
OVARGP
OV1RGP
L.Ae*
(1'1711
AND
DVARGP
is!
,.AO
(JMP 05PCH
IjSI'C~

IMUST BE or rORM A.A,
I,MEO (MONITOR ERROR OIAGNOSTIC)
ISAVE eAL POINTER
IANO ARGUMENT POfNTER
IPOINTS TO rUNCTtON CODE
IGET CODE
IRE MOVE U~IT NO
APPLICABLE
IPOINTS TO C'~.2

Ole

OSIDCH

IOISPATCH WIT'"'
IMODIF'IEO JUMP

JM'JMP
JMP
JMP
JMP

OVINIT
OVF'SAT
DV5EEK
DV[NTR
OVCLER
DVCLOS
DVM TAP
DVREAO

11 •• !NIT

JMFI

JMII
JMIt

JMIt
JMP
JM~

12 • IF'STAT, .OL.[T[, fRENAM
13 • • SEEK

I' = ,ENTER
,CLEAR
II.

16 • ,CL.OSE
17 :; .MTAP[

11~ • • REAO
111 = ,wRITE
112 :I ,WAIT
113 • ,TRAN

DVI.IRTE

OVWAIT
OV'RAN

IILLEGAL 'UNCTIONS IN ABovE ,.APLE COOED AS.
I

JMP

IrUNCT!ON
~V£RR6

~onE
LA~

JMFJ*

OV£RR6

ERROR
IERROR CODE 6

ITO MON!TO~

(,MEO.1

IOATA MoaE ERROR
nVERR1 LAW
,
Jf!H'*
(,MED.!

IERROR eOOE. 7
ITO ~ON!TOR

IOEVICE NOT REAOY
DVERR4 LAC
(RETURN

( I

IRETURN (AODRESS IN ~ANO~ER)
ITO RETURN To ~~£N NOT READY
ICONDITION HAS B[EN REMOVED

MED

IERROR CODE •
ITO MONITOR

(.MEO"1
11/0 UNO£RWAY LOOP

nVBUSV

IBREAK ~ROM LEVEL 4

IJB~

JMp'.

II-OOP o~ CAL.

DVCAL.F"

INORMAL RETURN rROM CA~
DVCI<

IBREAK FROM LEVLr 4
IRE TURN APT;R CAL AND
IARGUMENT STRING

DBR

JM"*

DVARGF'

IT~E OVINST ROUT)~[ MUST INCLUDE
IA .SETUP CALLINr, SEQUENCE roR

7-12

IE'C~ rLAG
I'NO/O~ PI

CnNNECTEO TO API
ACAT SGEN TIME).
ITHE SETUP CALLING SEQUENCE IS.

CAL

DVINIT

= API C~ANNE~ REGISTER

1(4~

~77),

N m 0lr

~OT

CONNECTE~

ITO API
IIOPS rUNCTION CODE
ISKIP lOT TO TEST THE FLAG
IADD~ESS 0' INTERRUPT
I~AND~rR (PI O~ A~I)

16
SI<PloT
08 V I r-I T
IT~lS

SPACE MAY BE USED roR 1/0 SUBROUTINES

IINTERRUpT HANOLER rOR API OR "'1
LAC
(NOP
DAC
DEvION
OAC
DEVIor
DAC
OVSWCH

nN~Y1

DAe

DVPIC

~vrNT

I GNRP I

JMP
DAC

COMMON
DEVAC

LAC.

nAC
JMP

DVOUT
COMMON

JMP

nAe

LAC
OAe
IGNRPI

JMP

COMMON
IjEvION

DEvcr

ISAVE AC
ISAVE'PC. ~lNK, ~ANK/PAGE MODE
lAND MEMORY PROT[eT

DEVPIC
OEVAC
DEVINT
DEVOUT
ONlYl

IPl ENTRY

IAPI ENTRY. SAVE AC
ISAVEI PC, ~INK. BANK/PAGE HOOE
l"1EMORY PROTECT
IL,EAVE PI ,CONE
IENABlE PI OR NOP
IENAR~E PI OR NOP

yON

ITHIS AI THE AREA DEVOTED TO PROCESSING INTERRUpT AND
IPERFORMtNG ANV ADDITIONAL 1/0 DES!RED,
fJEVIOf

IDISABLE

DR NnP
BErORE INTF-RRUPT
IrROM T~IS lOT OCCURS

rOF"

DEVIoT

IOIMISS~L

IINTERRUpT ~ANOLrR DISMISS RoUTE
LAC
OEVAC
IRESTORE AC
DVSWCIoI t O~I
ItON OP NOP
InE8REAK AND RESTORE
DBR
I~!~K. BANK/PAGE MODE, MEMORY
JMI'.
OEVOUT
IPROTECT
~VOJSM

IIr TH[ HANDLER USES THE AUTaINCREMENT • INDEX

lOR EAE

THEIR CONTENTS
BE SAVED AND RESTORED, FUNCTIONS
IPOSSIBLV IGNORED SHOULD CONTAIN
IPROPER tNOEXING TO BYPASS
ICAl ARGu~ENT STRING
REGl~T[RS.

ISIolOU~O

ICODE '0 BYPASS

IG~ORED

FUNCTIONS

!)VIGN2

rS2

JMP

OVARGP

DVCK

7-13

7.3.3

Example B. Special Device Handler for AFOIB AID Converter

PACE

~"'1

IAOC

701301 A
701304 A

:3
4

HANO~E~

ADSF'-?013f2l1
AOSC:a7013f2l4

701.312 A

6
7

~DRB-101312

8
4400210 A
~HHH!'03 A

121

....J

I
t-'
~

12
13
14
15
16
17
18

- 19
20

21
22
23
24
25
26
27
28
29
30

31
32
33
34

ISKIP IF CONVERSJO~ FLAG IS SET
ISELECT AND CONvrHT CAOC ~L4G IS CLEARED
,. ND A CON VER S I 0 ~1 I 5 Hoil TI • LIS ED)
IREAD CONV£RTE~ RUfF"ER INTO AC ANO CLEAR F'LAC

IOX-tSl
.MED=J

,GL.OBI.

ADC,

IHEO (MONITOR ERROR DIAGNOSTIC)

I
01{1~0~

R 0401521 R

0421151 R
(1 '" ~ 0 2 R 4 4 0151 R
~'0003 R 220151 R
D0~el4 R 440151 R
(:; e 0 0 5 .R .3 4 2115 4 R
vi 0t"06 q 040001 R
~HH"el?-R 740040 A
:110010 R 600021 R
~1~011 R 600074 R
;~L?l012 R 600074 R
e,e~13 R 6('121023 R
1-'10014 R 6210023 R
~0015 ~ 600075 R
0e1C'116 ~ 600075 R
r'~017 R 600051 R
~~002~ ~ 600023 R
0e10"1

'70021

AOC.

R 600rlJ44

OSPCH

OAe
DAe
lOX
LAC-

AOCALP
AOARGP
ADARGP

tOlC
TAD
OAC

AOARGP

JMP
JMP
JMP
JMP
JMP
JMP
JMP
JMP
JMP
JMP
JMP

00"'22 R 600023 R

AOARC;P

IsAvr CAL POINTER
lAND ARGUMENT POINTER
IPOINTS TO 'UNCTION COOE
lelT CODE
IPOINTS TO CAL. 2

fJMP DSPCM

OSPCIo!

AOINIT
AOIGN2
AOIGN2
ADERR6

AOERR6
AOlGN1
AOICN1
ADREAD
AOER~6

AOWAIT
AD£RR6

IOlsPATC~ IIIIITH

IMOOIF"JED JU~p
11-,tNIT
12-.rSTAT,.DLETE"RE~AM

13-.SEEI(
14:,ENTER
IS-,CLEAR
16-,Cl.OSF:
11-,MTAPE
11 lch .READ
111=.WRITE
11 2 =,W AIT
11 J :, TRAto.J

IILLEGAL
I

rUNCTIO~S

JMP
.EJECT

IN ABOVE TAaLE COOED AS
.OERR6

PAGE

47
48
49
5V"

?Ie'1

44
45
46

35
36

38
39
40
41
42
43

-...J

51
52
53
54
55

IFUNCTtON COoE ERROR
;'~023
.~0~24

76kj0~6

62k?1':>S

'0~2~
:~ ~ 2 6

R 76V"e:Z7

"0027

R 620 1 ? 5 R

IEr<QOR Ct'JDE 6
~
t,MED.l ITO MONYTOR
J"1P*
IDATA HODE ERROR
ADERR7
IERRnR cnDE 7
LAW
7

(,MEw.l ITO MONITOR
J""P*
ITHE ADINT RtUTl~E HUST INCLUDE A .SETUP
If OR EACH fL~G ASSOCtAT[O ~IT~ T~E orVlcr

AOINIl'

i,'ete.30 R 2\?112l1?6 R

; l~ ~ 3 1 ~ 0 6 ell 5 1 R
("r?!C'!32 ~ 44~151 R
~~03J

R 0~0057 A

AOCMOO

~~20J4
'~0035
~0?l36

R
R
~

00"'016 A
7~1301 A
el210111 R

ADCKS'~

,~ 0 0 3 7 R 2 " ~ 0 41
0~04~

L.AC

(256

1ST AND ARr, HU~· F ~ ~ 5 I t f-~

OA.C*

ADARGP
ADARGP

IRLTlJRN t T TO USER

040033 R
~. 21 0 4 1 R 6 ~ ~ 12! 4 2 R

CAL
16

AOUND
ADWC
AOWI'CT

LAC
DAC
JMP

I 5 1 : A P J cIi A 1\i ~.~ l L,
I • SET uP I 0 P S r II 'H; T I ') \. (: 0 nF:

.+2

lADe SKIP lOT
IAPOR. i') F I ~JT [ R ~ U p T
ISlT~UP ONCE O~LV
IsKIP SET.UP CODE IF
I.I~ITS AH[ DO~.E

AOC~CD

AOSTUP

.1~H'!42
(~0"'4~

R 1400.S] R
R 600015 R

AOC ROUTINE CLEARS 1'0

ADS TOP

OiM
JMP

UNorR~AV

SwtTC~

AOUNfJ

ADIG'.l

IR[TURN

I
IT~E PRE v ,OUS TAc;5 Pl THE CAL ARE A Aq( USED J:OR
ISTORAGE DURING THE' ACTUAL ,REAo F'UNCTID~'

I
IADCKSM

IS FrR STORI'~GT~E CHECKSUM
IAOCBP IS THr CURRENT BurFER POI~TER
I.OLRHP IS THE LINE RUFfER HfAD[Q POINTER
IAOUND IS POR PEvlCE UNDERwAV SwrTCH
IAOWC Is USEO AS T~E COUNTlR
IAOWPC' IS USEO TO STORE CU~RENT WORD COUNT

~0R~

I
I

'1
72

(LJrCI~'AL)

ADsf
40 C l~! i

ISTO~

66
67
68
69

IIUX TO ptTURN Rurr SI7[

IDX

AOCBP

A[)ARGP

.nL,B~p

60
63
64

lOX
.DEC
,OCT

lAltJ

440151 R

58
59

ADERR6

.EJECT

PAGE
16

'H~1

R 2~0el37 R
~ 7412~0 A
:'-0046 R 60kl!075 R
~0044

00et45

80
61

rele47 R 703344 A
[.,,/21050 R 620150 R

82
8J
84
8!5
86
87

--.J

AOREAO

.OUND
AOIGN1
~OaP

ADeAlP

0012155 R 220150 R

LAC

AOLJNf')

SlAfCMA
JMP
ADBUSV
DAC
ADUND
LAC*
ADCAU'
t70e0
AND
SlA
JMP
AOERf17
ADARGP
LAC·
OAe
AOCAP
OAC
ADI.BIo4P
lOX
ADARGP
;.DARr';P
LAC·

l~0e152

[-10056 R 500157
001'157 R 7402"0
~e~60 R 6021025
,)0"'61 R 220151
v.HH'l62 R "40035
~'0C'163 R 040036
(7:0~64 R 440151
~;'0065 R 220151

I-"
0"1

~ 2~003' R
R 740201 A
~0Q!53 R 600047 R
00054 R k'l40el37 R

00051

89
90

93
94
95
96
97
98
99

LAC
SNA
Jt.1P
11/0 UNOERWAY
A081JSY OBR
JfIo1P·
I
I

ADWAIT

R
A
R
R
R
R
R
R

\?0et66 R 0~0040 R
~1006' R 140~41 R

DAC

DiM
lOX

O~M

AOWC
AowPCT

IcHECK TO SEE lr 1/0 IS UNDERWAY
Ilf NOT SET IT wITH .. 1
lIT WAS ~ET,GO BACK TO CAL
IsE TIT
ILOOK AT MODE
IslTS 6~8 Or\lY
11 0 P S Bp.I ARy?
INO. ERROR
IGEr ~lNE BurrER HEADER POINTER
ISTORE

IA~SO

5TnRE IT rOR LATER 4EAOER
IINcREMr\T ARG. POINTER
IGET ~L.R.W.C(2'S CO~P)
ISTORE IT IN WORD COUNTER
IlERn WOPO COUNT REG.
IlERO C~rCK5u~ REG.
IGET PAST HEADER PAIR
INOW POI~TING AT 8EGINNING or
IBUrPER
ISTA~T UP ~EVICE

~/0~70

R 14",e~~4 R

100

r~((I~71

R 440035 R

1~1

(~0"'72

1~3
1~4

o~073
~~ 0 0 7 4

R 70131'4

105

',HH"75 R703344 A

1~6

r10(~76

R 620151 R

18~EAK F~OM LEVEL 4
ADARr,P IR£TURN AFT[~ CAL
JMP*
IINTERRUPT HANDL[R FOR API OR PIr

1f(!9

(~0~77

R 20e160 R

O\ll..Y1

110
111

.~0100

R 040117 R

1"'2

1"'7
108

112
113
114

115
116
117
118

440035 R

lOX
ADSC

4 4 01 5 1 R

ADCKSM
ADC8p
AOCBP

AOIGN2
ADIGN1

IDx

ADARGP

lINeR. rnR ExIT

D8R

c'0101 R
[~ ~ 1 0 2
\.~ 01 0 :3
:~ ~a 2' 4
d~)105

~40142

e4 et 1 4 5 R

DAC

DAe

R 0 4 011 5 R
~

6 C'J 011 6 R

':'0106

R 04~153
R 22~161

C"(('107

R ~40152 R

R
R

LAC
DAC
QAC

ADCPIC

JMP
DAC
LAC·
DAC
.EJECT

(NOP

ADCION
AOCO~.!T

ADSWCH
TG~~ RPI
cOMMON
A['lCAC
r el )

ADCOIIT

ISAVE .AC
ISAVE PC,~INK,fx. ManE
IMEM.PROT,

PAGE

119
1221

1:57
1:58

:' 0 1 33

R 500 1 6 2

139

,"~134
~01.35

122
123
124
125
126
127
'128

129
130

I
r--'
---l

0~1.

R
R
R
R
R
R
1~0116 R 101312 A
00117 R 7et0042 A
~012~ R 060035 R
00121 R 44~035 R
iJe122 R 440041 R
V'~123 R 340034 R
~~ 012 4 R 0 4 ~ 0 3 4 R
/0125 R 44eet40 R
00126 R 60el142 P
\/1 ~H 2 7 '1 2 0 0 0 4 1 R
(\~'1~h~ R 7402'30 A
?~131 R 1420,3121 A
00132 R 740020 A

1~1

---l

131
132
133
134
1:55

136

140

141
142

143
144

145
146
147
148
3,49

150

0~110 ~ 600116
00111 ~ 6C'1eJ105
021112 ~ 04~153
021113 ~ 2~0111
02'114 R 040152
10115 R 6210077

R
0600.36 R

R 440036 R
:HH 36 R 3 4 ~ " 3 4 R
~~0137 R 060036 R
~014e

R 140(('37 R
R 6 e: 0 14 4 R
;1014:? R 7"HH'H~2 A
~. 01 4 1

/10143

7013e4 A

JMP

4DCINT

cor-HH1N

JM~

ADCPIC

DAC
LAC

ADCAC

DAC

IGNRPI
COMMON

JMP
AORt3

ADCION

ION

ADCII\T
ADcnUT
rNLY1

IplC ENTPY
IAPI ENTRY.SAVl he
ISAVE Pc,~t~K.lx.~ODE
IMl~l. pROT
I REl\ D Co'.: VERTER PUf F'" ER

lOX

An~PCT

IENARLE ~Ic rOR OT~E~ OEVICES
1ST ORE QATA t~ USER ~UfrER
IIt'vC. BUfF'[R POPHfR
lINe. !,.JapO PAIR COLJJTER

TAD

AOI:KSM

I AUD CH ECKSU~1

r)AC
1S2

ADCKSM
AOWC

II~

!jAClOX

JMI'
LAC

AOCBP
ADCBP

ADCO',j T

ISTORE IT
110 COMPLETE
INO KEEp Go P,lG

AD\.roIPCT

lyES, COMPUTE WORO C'JUNT PA! R

ADeAC

IRISTORE AC

IMAy BE rDD
S~~A
ITO TOP ~ALF'
~AR
IMAKE Wr'J. PRS.
(377e00 18 8ITS ONLY
ANO
.DI.,8HP
ISTORE I~ ~EAOER #1
OAC·
10)(
ADLBHP lINe, To STORE CKSUt.1
TAO
ADCKSM IADO WORn PAIR COUNT
ISTORE I~ ~EAOER #2
DAC·
AOL.8~P
DiM
ICLEAR OEVICF UNnERwAV
ADUNO
JMP
ADOIC:;M l£xIT
An Co 'J T lOP'
IOlSA81..E PIC O~ ~~OP
AOSC
18lrORE rNTERRupr fR~M THIS lOT OCCURS
IINTERRUPT HANDLr R DISMISS RTE
lAC

r0144 R 200153 R

AODISM

LA.C
,EJECT

PAGE

I
I--'
00

01211

15j

0e'145 R 7~0~42 A

152

r"146 R 1213344
f~0141 R 620152
;10150 R 000t'H?0
'lC'l151 R 0~00012'
00152 R "00000
00153 R 0~02100

1~3

-...,J

154
155
156

157

A
R
A
A
A
A

158

ADSWCH

ION

lION OR

D8R

IOlBREAK A~O RESTORE
ILINK,EX.MOO[,MEM,PROT
lAUD CAL P~II\jTE~
lAUD ARGUMr~T PJINTER
IPC,l.,rM,MP
lAC SAVEr ~E~E

JMP*

AOCALP

AOARGP

AOCOUT
ADCAC

159

00e1'HH~

~0154

A
R 600007 R *L

-~~-0-155 R0-0Ql-0~4
~H3156 R 0004fllel

.ENU

J. *l

A *L
00151 R e010e0 A *L
10160 R 140000 A *L
~0161 R 00000~ A *L
00162 R J77000 A *L
SIlE:t001b3
NO tRROR LINES

ADCOUT

~,OP

PAGf
ADARGP

I
I-'
\.0

CROSS REF"ERENCE

(;(

:10151

13
96

14
104

106

155*

fl?l*

149

157.

88
1eeJ
122
LH~

101

127

128

131

141

AD8LJSY

rH'l47

AOeAC
ADCALP

~015:~

115

86
121

G1015'1

A.Or.:SP

\1?73~

AOCtNT
ADCION
AD Ct< S~I

:10 t 11

t;4*
55

?l0e34

l1r
53 ..

ADe~l(1[1

~0Vl3~

S20

ADC(HH

0014;:>

123
12i1

153

156.

ADCPIC

111
117
11S-

145.

,A2!15;"
0017.1';
:1 el ~ 0 ('

133

ADCOIIT

r?1 4 4

ADl"JISM

144

AOER~6

00~23

2-3

12 G
14924

A[)rRr~7

41 II-

A(11GNl
AOIGN2
AOtNJT

0J"'2~

"1[i1(7,7~

~~~~74

r"2'k~2?

46.

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42

CHAPTER 8
BOSS-IS

BOSS enables DOS users with a card reader and a line printer to run
jobs sequentially, with a minimum of operator intervention.

BOSS sup-

ports a subset of the DOS system programs, and adds a line editor, its
own resident and nonresident routines (called Resident BOSS and Nonresident BOSS), and the Procedure Files.
cedure Files.

Paragraph 8.1 describes Pro-

Figure 8-1 shows which monitor supports each system

program.
The DOS programs run by BOSS are identical to those run by DOS.

Ex-

ceptions are the Resident and Nonresident Monitors, which are explained later.

BOSS expands the information on Control Cards into

a series of commar.ds in the format expected by the DOS system programs.

Nonresident BOSS does this command expansion, and stores the

expanded commands in a disk file, the Run Time File (RTF).
programs expect to communicate with

Since DOS

operator at a teleprinter, BOSS

feeds the expanded commands to the programs via .DAT slots assigned
to TTA.

•

In BOSS mode, therefore, BOSS attaches .DAT-2 to the Run Tlme

File, and directs most teleprinter output to the Line Printer.

Pro-

grams can force I/O to the teleprinter by setting bit 4 in .SCOM+S2,
and proceding with macros directed to TTA.
Wher.ever bit

of .SCOM+S2 is set, the System Loader Interface attaches

the Resident BOSS code to the Resident Monitor.

The

main purposes

of Resident BOSS are to (1) ensure that BOSS will retain control of
the teleprinter,

(2) feed commands to programs via the Run Time File,

(3) properly route internal Monitor commands, such as .EXIT, .GET and
.PUT, and (4) direct teleprinter output to the Line Printer~

Figure

8-2 illustrates the connections between the DOS Resident Monitor and
the BOSS Resident Monitor that accomplish these changes.

Figure 8-3,

the flowchart for Resident BOSS, further describes Resident BOSS.
Resident BOSS communicates with Nonresident BOSS by

TRANing informa-

tion to and from the first block of Nonresident BOSS.

Nonresident

BOSS gains control on all error conditions, such as IOPS, operator
abort, Time Estimate exceeded, and after a BOSS15
is a flowchart of Nonresident BOSS.

8-1

command.

Figure 8-4

BOSS

DOS
DOSGEN
FOCAL

RESIDENT
MONITOR
NONRESIDENT
MONITOR

DDT
EDIT

SYSTEM
LOADER

NONRESIDENT
BOSS
RESIDENT
BOSS

LINKING LOADER
co
I

BOOTSTRAP
PIP
CHAIN & EXECUTE
FORTRAN

TKB

PATCH

B.PRE
PROCEDURE
FILES

8TRAN
89TRAN

15-0658

Figure 8-1, BOSS/DOS Intersection

RESIDENT BOSS15 INTERFACE TO RESIDENT MONITOR
AND USER PROGRAM OR SYSTEM PROGRAM
- - - - PROGRAM CONTROL
-

--- -

""IF aDUMP WAS SPECIFIED THEN THE Dl!MP
WILL TAKE PLACE BEFORE GOING TO
RESIDENT BOSS15

INFORMATION FU7W

NOTE: SEE RESIDENT BOSS FLOW CHARTS
FOR DET AI LS.

&--

lOPS ERROR FROM
1/0 HANDLER OR USER

~
lOPS 4
RETURN

r----

--1

RESIDENT BOSS15

I
I

EXPANDED
ERROR
PROCESSOR

NORMAL
lOPS
ERROR
PROCESSOR

I
I

lOPS 4
IF USER "CAL" WAS
NOT A.READ

I
1

INFO TO & FROM DISK

I
I
INPUT
FROM TTY

--1-1

TELETYPE
HANDLER

I :

~~~-~-~------~------~-+-------------~lTTYPED

I :

~--t~-----~--l
L.. _ _ _ _ _ --.J

.-------~
I~~~~1:0L
I~~

I DATA

I
-,

_________ ......J

:
I
I

BACK FROM

o
I
I

DATX

CARD READER
HANDLER

A
1"cAL" ENTRY
TOTTY
HANDLER

NORMAL
CARD
DATA

.READ

.WRITE
3
OR ANY OAT ASSIGN TO TTY

.READ
·2

"USER OR SYSTEM PROGRAM

'NOT NON·RES BOSS15

15-0659

Figure

8-3

8-2

lOPS Error
Routine:
EXITLT

Expanded
lOPS Error
Routine

Control Q
Processing,
via .SCOM+72

BOSS~

(JMS Entry)

Store error data in
Resident BOSS .ERR,
.MED, and in the address pointed to by
.SCOM+37
Go to CTRL
Q Routine:
MANSAV

Monitor TRAN in the first block of
onresident BOSS, starting at
C (.SCOM+2)

Startinq at C(.SCOM+2) + 44 8 , transfer lOPS error data to core image of
block

Monitor TRAN"block out
to first block of Nonresident BOSS

Points within the Resident Monitor which transfer control to Resident
RESIDENT BOSS - 15

Figure 8-3
8-4

BOSS - 15

DAT3.B

(.DAT-3 or any .DAT slot
assigned to TTA.)

DAT2.B

Using caller's buffer address and
word count, compose a .READ to
.DAT-7, the run time file (RTF)
on the system 4evice
1.
Compose a .WRITE
to .DAT+6, using
caller's data

Clear bit 4 or
.SCOM+52
Make sure teleprinter is not
busy

Issue .READ to .DAT-7, and await
completion

m~e

Move user's buffer (minus the
header word pair) to Resident
BOSS (always 428 words)

Issue .WRITE to .DAT+6 (the
Line printer) and wait for
completion

Processing for I/O Macros addressed to .DAT slots -2 or -3, or any slot assigned to TTA.

Points within the Resident Monitor which transfer control to Resident BOSS - 15
RESIDENT BOSS - 15

Figure 8-3
8-5

(cont.~.

.EXIT
processing
EXITA

TIME OUT
processing
TIMGON

Operator
Abort tT

.PUT and .GET
Processing
BOSS2

TTDDTR

.SCOM+52

Set bit 11 in .SCOM+52

Set bit 17 in .SCOM+52

Set up .SCOM+43 & 44 to
bring in the Nonresident
Monitor
B.EXT¢

Monitor TRAN first block of Nonresident BOSS
starting at C(.SCOM+2),

in the Mass
Busy Table entries

cessor at
EXITA + 1
Points within the Resident Monitor which transfer control to Resident BOSS - 15
RESIDENT BOSS - 15
8-3 (cont.)

~igure

8-6

start Address 42~
Execute bank bit initializat10n code

Save value of TIME OUT clock, and disable it
Disable CTRL C and set up CTRL T address; save contents
of .SCOM+42, set MICLOG bit and clear user bit

and delete all files in

Set .UFDT -15 and -14 to
the CTP UFD named PRCFIL PRC

Perform .ENTER on .DAT-IS for PRCFIL PRC; set line count

Save current logged-in UIC in~: force
"CTP" to be logged-in UIC

Save system device code 1n 0.11

Set bit zero of .SCOM+S2

word AC.STA

Set bit 17 in

Set bit 2 in Job status word
Print, "END OF RUN TIME FILE
REACHED BY USER" on the LP
Next Page
Nonresident BOSS
I

Figure 8-4
8-7

From Preceding Page

• PUT

Neither

Print on Line Printer,
"USER DID A .PUT"
Set bit 11 in
Status word

Print on Line Printer,
"ILLEGAL .GET BY USER"

set bit 6

Status Word

Print on
"LOAD ERROR •••••••••• "

Set bit 3 in Job Status Word

Print on
ESTIMATE

Set bit 7 in Job status Word
Print on LP, "OPERATOR ABORT"

"TIME

Nonresident BOSS

Figure 8-4
8-8

(cont.)