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DEC-XV-IRSMA-A

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XVM/RSX PART IX
SYSTEM ORGANIZATION AND LISTS

CHAPTER 1
INTRODUCTION TO SYSTEM ORGANIZATION

Under RSX, information about system operation is maintained in a
series of system lists.
These lists contain up-to-date entries
concerning different aspects of RSX activity.
As Tasks are added,
activated, and terminated, the contents of each system list change
automatically to reflect the new status of the system. The user need
not be directly concerned with the organization or updating of system
lists since RSX handles all list operations automatically.
The
discussion which follows relates only to predefined system lists with
listheads in the System Communications Area (SCOM). User Tasks and I/O
Device Handler Tasks can naturally construct and maintain their own
lists.

1.1

THE DEQUE LIST APPROACH

A system list is a linked, double-ended queue known as a deque
(pronounced "deck"). Each deque consists of a listhead (normally
located in the Executive) and a series of list elements or nodes which
are linked in circular fashion by forward and backward pointers. The
listhead consists only of a forward and a backward pointer.
Large
nodes contain forty~seven words in systems with a floating point
processor or forty-one words in systems without such hardware and are
used only in the Partition Block Description List. The PBDL section
describes these nodes. Other deques use small nodes, each of which is
a ten-word entry containing the following:
Contents

Forward pointer (address of the next node)

Backward pointer (address of the previous node)

2-11

Data

A node is simply a chunk of forty-seven (or forty-one) or ten words of
contiguous core.
Nodes in a list are linked only by their pointers
and are not necessarily contiguous. Figure 1-1 illustrates linkage in
a short deque.

IX-l-l

1st node
f

pntr

b pntr

Figure 1-1
A Three-Node Deque
An empty deque consists only of a listhead, as in Figure 1-2.

Figure 1-2
An Empty Deque
1.2

POOL:

POOL OF EMPTY NODES

POOL, the ·Pool of Empty Nodes," is a list of all small (ten-word)
system nodes that are currently unused. These nodes are dynamically
manipulated during system operation to form all of the other lists
that the monitor uses (except the PBDL list, which is formed out of
large nodes).
Nodes are created at system generation and at system reconfiguration
(via the ReF MeR function). Since nodes are used by the Executive and
I/O Handlers, they must reside in the lower 32K of memory.
When a node is needed to expand a list, it is "taken" from the pool.
When a node is no longer needed, it is "returned" to the pool.
"Taken" and "returned" imply no actual movement of data.
Only the
pointers change.

1.3

LPOOL:

POOL OF EMPTY LARGE NODES

LPOOL is a list of all large system nodes that are currently unused.
These large nodes are used to construct partition definition blocks
and are returned to LPOOL when the partition they describe is removed.
LPOOL is created at system generation and may be
on-line reconfiguration (via the ReF MeR function).

extended

LPooL entries are undefined, except for the listhead (in words
1).

Ix-I-2

during
0

and

CHAPTER 2
SYSTEM LISTS

All major system lists have listheads in the Executive System
Communications Area (SCOM). This provides an absolute reference point
to lists by routines not assembled with the Executive. Tasks can also
construct their own lists, with listheads elsewhere.
Table 2-1
summarizes information about each list described in this chapter.

XVM/RSX V1B

IX-2-1

September 1976

Table 2-1
RSX System Lists

System List

Abbreviation

Information Content

Octal
Listhead
Address

Pool of Empty Nodes

POOL

Available small nodes

240

Pool of Empty Large
Nodes

LPOOL

Available large nodes

264

System Task List

STL

All tasks in system

242

Active Task List

ATL

All active tasks in
system

244

Clock Queue

CKQ

Requests for future
task execution and
MARK times

246

Partition Block
Description List

PBDL

All partitions in
system

250

Physical Device List

PDVL

All physical device
units in system

252

System COMMON Blocks
Description List

SCDL

All system COMMON
blocks

254

Task Termination
Notice Request List

TNRL

All abnormal exits of
user-mode tasks

256

I/O Rundown Queue

IORDQ

All tasks requiring
I/O rundown

260

Execute List

EXELH

All tasks to be
executed

276

Batch Job List

JOBI

All batch tasks

323

Small Node Description
List

SNDL

All "partitions" of
small nodes

266

Large Node Description
List

LNDL

All "partitions" of
large nodes

270

MULTIACCESS
Exit Queue

TDV.EQ

All exits of tasks
run under
MULTIACCESS

217

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September 1976

2.1

ATL:

ACTIVE TASK LIST

The Active Task List (ATL) contains information about all active Tasks
the system. This list is ordered by the priority of these active
Tasks and is used to deter.mine Task scheduling under RSX.
Nodes are
added to the Active Task List by the REQUEST System Directive and
deleted by the EXIT Directive. SCHEDULE, RUN, and SYNC Directives do
not directly ent.er new nodes in the ATL. Instead, when the time
specified in these Directives comes due, the Clock Handler requests
the relevant Task.
in

Each node in the ATL consists of the following:
Word

Contents

Forward pointer

Backward pointer

Task name (first half)

Task name (second half)

Task priority, octal

Partition block address

STL node address

Flag and Task status

Start or resumption address

Event Variable address

The meaning of forward (word 0) and backward (word 1) pointers has
already been explained.
The Task name is stored in .SIXBT format.
The Task run priority corresponds either to the default priority set
when the Task was installed or to the value specified in a REQUEST,
SCHEDULE, RUN, or SYNC command,
it must be in the range 1-512,
decimal.
The order in which Tasks are executed is determined by scanning the
Active Task List for the highest priority Task whose status indicates
that it is ready to run. Tasks with the same priority are handled in
the order in which they were entered. The action to be taken is
determined by examdninq the Flag and Task status (word 7). This word
is constructed as follows:

IX-2-3

Bit

Contents

Set when Task is loading into core

1-8

Unused

9-17

Used to indicate Task status

Task status indicates that one of
taken:
Status

the

following

actions

Action

Task image is on disk, if partition is available, flag
the partition as unavailable and proceed to status 2,
otherwise, service the next Task in the ATL

Task image is on disk and partition is available,
queue
a disk GET request, using the ATL' s Event Variable
address (word 11), and proceed to status 3

Task waiting for an Event Variable,
if the Event
Variable whose address is in the ATL is nonzero, proceed
to status 4, otherwise, service the next Task in the ATL,
the Event Variable can be specified either by the
Executive while the Task is in status 2 or by the Task
using a WAITFOR System Directive

Task ready to be started or resumed,
set status 5 in
order to save the environment if the Task is interrupted
by the Executive, and start or continue Task execution,
status 4 can be set by the WAIT or RESUME System
Directives

Task was running and interrupted by the
Executive
(environment has been saved in the Task's partition
block), restore environment and return control to the
Task

Task suspended, only the the SUSPEND System Directive
can set this status, no action taken, service the next
Task in the ATL

Task execution suspended so that another Task in same
time slice may use its burst of processing time; after
specified time elapses, latter Task proceeds to status 7
while a Task in status 7 proceeds to 5

IX-2-4

The start or resumption address (word 10) indicates either the initial
entry point for the task, or the address at which the task restarts
after a WAIT or resumes after a SUSPEND. Word 10 is constructed as
follows:
Bit

Contents

Link contents

Execution mode indicator
page mode, 1 = bank mode

Execution mode indicator (level of privilege);
o = exec mode, 1 = user mode

3-17

Start or resumption address

(addressing)~

When a REQUEST MAPPED directive is issued for a task, bits 0 to 8 of
word 11 are initially set to the number of the system LUN to which
task accesses to virtual LUN-2 should be mapped.
In addition,
if a
user number is specified, bits 9 to 13 of word 11 are set to the user
number.
(When a REQUEST directive is issued, word 11 is set to
zero.)
The contents of word 11 can be chanqed as soon as the task
enters a partition, because the contents of word 11 are used only to
initialize the task PBDL node.

XVM/RSX V1B

IX-2-5

September 1976

2.2

CKQ:

CLOCK QUEUE

The Clock Queue (CKQ) is a deque consisting of one node for each
action to be performed at some future time.
It is ordered by the time
at which entered requests come due.
Such actions include the
scheduling
of
tasks
(nodes added by SCHEDULE, RUN and SYNC
directives), the rescheduling of tasks
(nodes added by the clock
interrupt service routine) and the setting of event variables after a
specified elapsed time (nodes added by MARK directives).
Nodes are
removed from the list when the time comes due and no rescheduling has
been specified. Task scheduling nodes can be nullified by CANCEL and
mark-time requests can be nullified by UNMARK.
Each node in the Clock Queue consists of the following:
Word

XVM/RSX VlB

Contents

Forward pointer

Backward pointer

Type indicator
and MARK use)

Unused

Task run priority (for task scheduling
use) or event variable address
(for MARK use)

STL node address (for task scheduling)
use) Or partition block address (for
MARK use)

Schedule interval seconds (for
task scheduling and MARK use)

Schedule interval ticks (for
task scheduling and MARK use)

Reschedule interval seconds (for
task scheduling use)

Reschedule interval ticks (for
task scheduling use)

(for task schedulinq

IX-2-6

September 1976

The type indicator (word 2) can be set to any of the following values:
Type

Meaning

Task scheduling; no rescheduling

Task scheduling; periodic rescheduling

MARK request

Null (result of CANCEL or UNMARK request)

In all nodes except the first, the schedule interval is relative to
the previous node.
The schedule interval in the first node is
relative to the current time and is decremented and examined at each
clock interrupt (i.e., tick). Words 6 and 7 of each Clock Queue node
are used to record the schedule interval. The interval in ticks (word
7) can only be zero when a request comes due at the same time as for
the previous node. This interval can never be greater than the number
of ticks per second (usually 60, but depends on the clock). When the
relevant interval is greater than one second, word 6 of the Clock
Queue node indicates the additional amount of time in whole seconds.
For the convenience of the clock interrupt service routine, both
schedule ticks and schedule seconds are recorded as two's complement
negative numbers. Reschedule seconds and ticks (words 10 and 11) are
set when periodic rescheduling is specified. Both are recorded as
positive numbers.

XVM/RSX V1B

IX-2-7

September 1976

•

2.3

EXELH:

EXECUTE LIST

The Execute List (EXELH) is used to implement the EXECUTE system
directive.
An entry is made in the list when an EXECUTE directive is
issued and is removed by the task FININS when the directive has been
processed.
The EXELH cannot be manipulated directly by the user and
contains no permanent members.
Each node in the EXELH consists of the following:
Word

Contents

Forward Pointer

Backward pointer

Task name

(first half)

Task name

(second half)

Priority

LUN, "alias execute" bit and "deferred execute"
bit

Partition name (first half or 0) or task event
variable address

Partition name

Unused or secondary task name (first half)

Unused or secondary task name

(second half or 0)

(second half)

The task name, secondary task name (if specified) and
(if specified) are stored in .SIXBT format.

partition

name

The task name identifies the created file
in which
resides.
The file extension is assumed to be IMG.

the

image

task

The secondary task name can be used to identify the task when it is
later requested.
The "alias-execute" option
(bit 0 of word 5)
determines whether the secondary task name is used.
Secondary task
names allow more than one copy of an installed task to be uniquely
referenced. This feature is used extensively by MULTIACCESS.
The partition name identifies the memory partition in which the task
will be run.
A partition name of zero specifies the partition
selected at task-building time.
The "deferred-execut~" option (bit 1
of word 5)
determines whether
the specified partition is used or
whether no partition is used.
If no partition is used,
the task is
not requested by FININS (see below) and a special task event variable
is returned to the calling program.
This feature is used primarily by
MULTIACCESS to request tasks later, when the correct partition is
known.
The LUN in word 5 can be associated with any disk
disk) •
XVM/RSX VIB

IX-2-8

(preferably a "user"

September 1976

A node is inserted in EXELH whenever the EXECUTE system directive is
issued.
After
inserting the node, EXECUTE requests a task called
FININS to locate the appropriate created file,
check its partition
characteristics and transfer it to the system disk.
FININS then
inserts a node for this task in the STL, with the "remove-on-exit" bit
(bit I of word 4) set.
Depending on the EXECUTE directive options
specified, FININS configures the STL node with the task name or
secondary task name
(alias-execute option), and with or without
(deferred-execute option) a partition name.
If the deferred-execute option is not specified, FININS requests that
the specified task be run. when the task finishes, the EXIT Processor
sets the ~done" bit (bit 6 of word 4) of the task STL node.
It is the operator's responsibility to periodically run a task called
AUTORM, which removes inactive tasks from the system. A task is
inactive when both the "remove-on-exit" and "done" bits are set in the
related STL node. AUTORM is, thus, an important tool for conserving
space on the system disk.
If the deferred-execute option is specified, FININS does not request
the task to be run.
Instead, FININS returns the address of the task
STL node to the calling program. The address is placed in the task
event variable.
This address is used later to fill in a partition
name when an appropriate partition has been selected.
The task can
then be requested to run.

XVM/RSX V1B

IX-2-S.1

September 1976

2.4

IORDQ:

I/O

RUI~DOtm

QUEUE

The I/O Rundown Queue (IORDQ) is a list of Tasks for which I/O Rundown
must be performed. Whenever a USER-mode Task exits or is aborted, and •
its transfers-pending count is nonzero, the Active Task List node
corresponding to the Task is inserted in the I/O Rundown Task (lORD)
to service the request. Nodes in the I/O Rundown Queue are identical
to those in the Active Task List.

XVH/RSX V1B

IX-2-9

September 1976

2.5

JOBl:

BATCH JOB LIST

The Batch Job List (JOBl) is a system list consisting of two nodes for
each batch job queued in the RSX system. Entries in this list are interpreted by the Batch Processor, and can be listed (printed out) with
the OPR JOB LIST function.
The first node of each JOBI entry consists of:
Word

Contents

Forward pointer
Backward pointer
File name (first half)
File name (second half)
Pointer to the second node
Job file sequence number
Job flags
Job parameters
Date when job was queued
Time (seconds since midnight) when job was queued

1
2

3
4
5
6
7
10
11

The contents of words 2 and 3 (file name) are stored in .SIXBT format.
The file name extension is assumed to be JOB.
The contents of word 6 (job flags) are:
Bit

Name

o
1
2
3

DLTFLG
OPRFLG
FRCFLG
SEQFLG

4
5

HLDFLG

CCLFLG

UFDFLG

8-17

TIMMSK

Meaning
Delete job file after processing
Operator required to run this job
Force this job to run next
Sequence this job (sequenced jobs are run in
the order of submittal)
Reserved
Hold this job until it is released by the operator
Reserved for RSX CCL (concise command language)
Login device, unit and UFD is specified in
CPB words 7 and 10
Job file time limit in minutes (zero implies
that the default value is used)

The contents of word 7 (job parameters) are:
Bit

Name

0-2
3-10
11-17

CLSMSK

XVM/RSX VIB

MEMMSK

Meaning
Job priority class (0 to 7)
Reserved
Minimum core needed to run the job (zero indicates lKi all ones, 127, indicates l28K)

IX-2-l0

September 1976

The contents of word 10 (data) are:
Bit
0-8
9-12
13-17

Contents
Year (from location YR)
Month (from location MO)
Day (from location DA)

The second node of each JOBI entry consists of:
Word

o
1
2

3
4
5
6
7
10
11

contents
Input device and unit
Input UFD
Reserved for listing device and unit
Reserved for listing UFD
Login device and unit
Login UFD
Reserved
Reserved
Reserved
Reserved

UFDs (words 1, 3 and 5) are stored in .SIXBT format. Device and unit
specifications (words 0, 2 and 4) contains a 2-character .SIXBT device
name in bits 0 to 11 and a 6-bit binary unit number in bits 12 to 17.

XVM/RSX VIB

IX-2-ll

September 1976

2.6

LNDT.I:

LARGE NODE

DERCRIPTIO~~

I.IST

The Large Node Description List (LNDL) consists of information on each
"partition" of core containing large nodes. Such areas are not true
partitions, for they are formed from core remaining after ordinary
partitions have been allocated.
Each node in the LNDL consists of the following:
Word

Contents

Forward pointer

Backward pointer

Name of this "partition" of nodes
(first half)

Name of this "partition" of nodes
(second half)

"Partition" base

"Parti tion" size

Unused

The "partition" name is stored in .SIXBT format.

IX-2-12

2.7

PBDL:

PARTITION BLOCK DESCRIPTION LIST

The Partition Block Description List (PBDL) initially
contains
descriptions of all partition blocks generated at System Startup time.
XVM/RSX facilitates
dynamic reconfiguration of partition blocks;
thus the PBDL can change as partitions are added or respecified. With
the RCF MCR Function Task, the user can add large nodes to the pool
for subsequent partition assignment. With Rep, he can add these nodes
to the PBDL itself.
Partition blocks serve a variety of useful
example:

functions

RSX

for

• They contain descriptive information which allows RSX to ensure
that Tasks being installed in the system have been built for
existing partitions.
• They indicate whether partitions are free or occupied.
• They provide the core for the Event Variable and disk GET
Control Table required when loading Tasks from disk into core
partitions.
• They provide an area of core in which the Task's environment
can be saved when the Task is interrupted by the Executive.
• They maintain a count of pending transfers (I/O and mark-time)
to and from a partition so that I/O Rundown can be performed
for Tasks built in USER mode.
• They indicate the location of I/O buffers within partitions.
Each PBDL node consists of the following:
Word

Conte ts

Forward pointer

Backward pointer

Partition name (first half)

Partition name (second half)

Partition base address

Partition size

Task size

Count of pending transfers to/from
this partition

Flags word

Virtual partition size

IX-2-l3

contents

Word

Buffers pointer

Interrupt connect location

DBA Instruction

JMS* .-3 instruction

AC buffer

XR buffer

LR buffer

MQ buffer

se buffer

R1 buffer

R2 buffer

R3 buffer

R4 buffer

R5 buffer

R6 buffer

X10 buffer

Xl1 buffer

Xl2 buffer

X13 buffer

X14 buffer

Xl5 buffer

Xl6 buffer

X17 buffer

L20 buffer (core location 20, CAL
return address)

SKP or NOP

MM register buffer

clock overflow counts

IX-2-l4

Word

Contents

XM clock ticks above overflow count

Task-use count

Pointer to the task-use count word of the task
shared area.
Used whenever the task in this
partition is sharing core.

EPA buffer

FMAl, A-sign buffer

FMA2 buffer

FMQl buffer

FMQ2 buffer

JEA and guard-bit buffer

Words 51 to 56 are used only by machines containing floating-point
hardware.
The meaning of forward
(word 0) and backward (word 1)
pointers has already been explained. The partition name (words 2 and
3) must be entered in .SIXBT format. The task size (word 6) is the
amount of a partition available to a task.
Initially, the task size
is less than the partition size (word 5); however, the task size can
be increased by issuing a RAISEB system directive from a MACRO
program.
Because they are memory-protected, tasks built in user mode
are constrained by their size and are prevented by RSX from making
illegal memory references.
The flags word
(10) has several data
fields, which are described below:
Bit

Contents

0-8

Reset to zero unless the task executing in the
partition has mapped LUNs.
If these bits are
nonzero,
LUN references by the task in
the
partition are mapped to system LUNs.
The contents
of bits 0 to 8 specify the system LUN to which
user virtual LUN-2 is mapped.

9-14

User number under MULTIACCESS.

Set if the partition is being
condition that prevents core
partition.

16-17

Shared access characteristics of the partition:

reconfigured;
a
sharing for
the

00 = no core sharing permitted

sharing permitted in read-only fashion

sharing permitted in read/write fashion

When a task is initially made active, the virtual partition size (word
11)
is set equal to its actual size
(word 5).
This size is

XVM/RSX V1B

IX-2-15

September 1976

subsequently decreased each time the task preallocates I/O buffer
space for an I/O handler that uses external I/O buffers (i.e., buffers
created at the top of a task partition). The virtual partition size
can also decrease when I/O buffers are actually allocated. After all
buffers have been reserved, a partition appears virtually smaller to a
task.
This new size is used to determine the task size after a task
has issued a RAISEB directive.

XVM/RSX VIB

IX-2-1S.1

September 1976

When a Task is first activated, the buffers pointer (word 12) is set
to zero, indicating that there are no buffers currently in the
partition. As buffers are created, they are linked together in a
single-ended queue which begins with a pointer address placed in word
12 of the PBDL node.
Buffers LR, MQ, SC, Rl, and R2 (words 21-25) provide core for the
Event Variable and disk GET Control Table required when loading a
disk-resident Task into the partition. These buffers are filled as
follows:
contents
21

Event Variable

Disk Platter number

Disk starting address

Core starting address

Word count

Buffers R3 and R4 (words 26-27) are used as a pointer and counter
respectively by the routine in Significant Event Recognition (embedded
within the executive) which zeroes the partition prior to the loading
of a task.
Buffers Rl, R2, R3, R4, R5 and R6 (words 24-31) are
pseudo-registers used by reentrant system routines. Buffers XlO, XII,
X12, X13, X14, X15, X16, and X17, (words 32-41) are autoincrement
registers 10 through 17. The MM register buffer word (word 44) is
used to store the register which controls XM-15 hardware. Words 45
and 46 save the processor time the task in the partition has used.
The first word of this pair stores the number of XM clock overflows
(one' unit represents 2.62 seconds); while the second word indicates
the XM clock ticks beyond those represented in the overflow count (one
unit represents 10 microseconds). The task use count (word 47) is
incremented
whenever a task is loaded into the partition and
decremented when the task exits.
This word is also incremented
whenever a user mode task begins sharing the partition (via the SHARE
Directive) and decremented whenever such a task terminates core
sharing for the partition or exits. When a user mode task is running
in the partition and begins to share an area of memory, word 50 is set
to point at the task use count word for the node describing the shared
block of memory.
Buffers EPA,FMAl,FMA2,FMQl,FMQ2, and JEA
(words
51-56) are floating-point hardware reg1sters and are present only in
machines which support floating-point hardware. When this hardware is
not available, PBDL nodes are 6 words shorter.
Word 43 of each PBDL node contains a SKP instruction for partition
blocks and a NOP instruction for interrupt service routines. If an
interrupt service routine requires the use of the RSX Register Save
Routine, the interrupt service routine must have an entry-point
address (word 13) and a set of buffers (words 17-42), identical to
those of a partition block. After registers have been saved for an
interrupt service routine, control is transferred to the
word
following the NOP instruction. The Register Save Routine records the
XM clock contents and saves the MM register and
floating-point
registers
(only if floating-point hardware exists on the machine) ,
only for partition blocks, not for interrupt service routines. When a
Task is interrupted by the Executive, control is transferred to word
14 of the appropriate PBDL node so that all relevant registers can be
saved.
IX-2-l6

2.8

PDVL:

PHYSICAL DEVICE LIST

The Physical Device List (PDVL) contains descriptions of all physical
devices operating under RSX. Each PDVL node represents a single unit
of a particular physical device (e.g., Magtape unit 3). This list is
created at System Startup time. PDVL nodes can subsequently be added
by the ADV MeR Function Task but not dynamically deleted.
PDVL nodes are used primarily to provide a listhead for X/O requests
queued for a particular X/O unit. When a Logical unit Number (LUN) is
assigned to a physical unit by means of the REASSXGN MCR Function
Task, the address of the PDVL node corresponding to that physical unit
is placed in the appropriate LUN entry of the Logical Unit Table.
Each PDVL node consists of the following:
Contents

Forward pointer

Backward pointer

Device name (first half)

Device name (second half always 0)

Device attach flag

Device unit number

Device request queue (deque
listhead) - forward pointer

Device request queue (deque
listhead) - backward pointer

Trigger Event variable address

Assign inhibit and files open flag

The meaning of forward (word 0) and backward (word 1) pointers has
already been explained.
The two-letter device name (words 2-3) is
stored in .SXXBT format, e.g., .SXXBT "DT@@@@". When a physical device
unit is attached, the device attach flag (word 4) is filled with the
address of the appropriate entry in the Attach Flag Table.
The
referenced AFT entry contains the address of the System Task List
(STL) node which describes the Task requesting attachment. The device
attach flag is set by the reentrant "Attach LUN and Device" subroutine
(ALAD) and may be cleared by the reentrant "Detach LUN and Device"
subroutine (DLAO), by the reentrant "Detach LON and Device and Empty
Queue" Subroutine (DMTQ), or by the REASSIGN MCR Function Task.
PDVL node words 6 and 7 form the I/O request queue listhead for the
particular device unit. Nodes may be entered in this queue by various
forms of the QUEUE I/O Directive or by the I/O Rundown Task.
Nodes
are taken from the queue (de-queued) by the X/O Device Handler Task
which services the I/O unit described in the node.
IX-2-17

The Trigger Event Variable address (word 10) is initially set to zero.
When
an
I/O
Device
Handler Task is loaded into core, the
initialization of this Task serves to set the word to the address of
the Task's Trigqer Event Variable. The Handler then passes control by
issuing a W~TFOR System Directive which suspends execution until the
Event Variable is set to same nonzero value (e.g., until a request is
entered in the I/O request queue).
The assign inhibit flag (word 11) is normally set to zero.
The
REASSIGN MCR Function Task can set bit 0 of this word nonzero to
indicate that it has removed the Trigger Event Variable address (word
10) from the relevant PDVL node and has requested the I/O Device
Handler Task which services the described unit to DISCONNECT & EXIT
(I/O function code 777 at priority 514). I/O Handlers can set bit I of
this word to inform REASSIGN that the Handler has open files.
The
source of the setting is indicated by the following:
Contents

Set by REASSIGN

Set by Handler with open files

2-17

Unused

IX-2-1S

2.9

SCDL:

SYSTEM COMMON BLOCKS DESCRIPTION LIST

The System COMMON Blocks Description List (SCDL) contains descriptions
of all COMMON blocks in the system. The COMMON blocks and the list
which describes them are initially created at System Sta~~up ~~~~
Because ~l/RSX now facilitates dynmaic reconfiguration
crn~ON
blocks by means of the RCF MCR Function Task, the SCDL can change as
COMMON blocks are added or respecified. This list is used by the
INSTALL MCR Function Task and the COMMON Communicator Handler Task.

·of

E~ch

SCDL node consists of the following:
Word

Contents

Forward pointer

Backward pointer

COMMON block name (first half)

COMMON block name (second half)

Unused

COMMON block base address

·6

COMMON block size

Unused

Flags

Task Use Count

The meaning of forward (word 0) and backward (word 1) pointers
has
already been explained. The COMMON block name (words 2-3) is stored
in .SIXBT format. The flags word (10) has only three bits currently
defined.
Their meaning is identical to the same bits of word 10 of
PBDL nodes. If bits 16 and 17 contain zeroes, the System Common Block
can not be shared by a user mode task. If these bits contain 01, the
System Common Block can be shared in a read only fashion. ~~en these
bits contain 10, user mode tasks can share the System Common Block in
either a read only or read/write fashion. Whenever the System COMMON
Block is being reconfigured, bit 15 of the Flags word is set to
disable core sharing by User mode tasks.
The task use count (word 11) is incremented whenever a user mode task
begins sharing the System Common Block and decremented whenever such a
task terminates core sharing for the System Common Block or exits.

IX-2-l9

2.10

SNDL:

Sl.fALL NODE DESCRIPTION' LIST

The Small Node Description List (SNDL) consists of information on each
"partition" of core containing small nodes. Such areas are not true
partitions, for they are formed from core remaining after ordinary
partitions have been allocated.
Each SCDL node consists of the following:

Word

Contents

Forward pointer

Backward pointer

Name of this "partition" of nodes
(first half)

Name of this "partition" of nodes
(second half)

"Partition" base

"Partition" size

Unused

The "partition" name (words 2-3) is stored in .SIXBT format.

IX-2-20

2.11

STL:

SYSTEM TASK LIST

The System Task List (STL) is a directory containing information about
all Tasks installed in the system. Nodes are added to this list when
a Task is installed and deleted when a Task is removed from the
system. Each node consists of the following:
Contents

Forward pointer

Backward pointer

Task name (first half)

Task name (second half)

Flags and default priority

Partition block address

Disk address

Size of resident image
Task size (and XVM hardware flags
for USER mode tasks)

Task entry point

The meaning of forward (word 0) and backward (word 1) pointers has
already been explained. The Task name (words 2-3) is stored in .SXXBT
format (right-filled with zeros). The flags and default priority word
(4) is constructed as follows:

IX-2-21

Contents

Set when Task active

Set to signal -remove on exit-

Set when Task disabled

Set when Task fixed in core

Set when partition lost
through reconfiguration

Set when reconfiguration
in progress

-Done- bit; set when Task has exited

Unused

8-17

Task's default priority

The disk address (word 6) is an l8-hi t ~"ord \vhich points to the starting disk location of the Task image. Because task 1~ages
start on
block boundaries, bits 11-17 of the di~k address are knm·m to he zeros.
Hence the relevant disk platter number can overlay the 1mv-order eight
bits of word 6.
The task size (word 10) indicates the core required to run on the Task
and several XVM hardware flags for USER mode tasks. If the Task has
been created in EXEC mode
(unprotected and unrelocated) with no
overlays, the Task size is identical to the size of the resident image
(word 7). If the Task has been created in USER mode
(protected and
relocated), the size must be a mUltiple of 256 (decimal); this is a
consequence of the memory protection increment.
Hence, bits 10-17 of the task size for USER mode tasks are known to be
zero.
Therefore, the ~~ hardware flags can overlay bits 10-13 of
this word.
For USER mode tasks, word 10 has the following format:
Bit

Contents

0-9

Task size

Unused

11-12

Set when wide indirect addressing is in effect
(XVr"l mode)

Set when task can issue lOT instructions

IX-2-22

The task entry point (word 11) has the
Bit

followin~

format:

Contents

o if the task is built not to reauire the
floating-point processor (FPP), 1 if FPP
required

Execution-mode indicator (addressing); 0
page mode, 1 = bank mode

Execution-mode indicator (level of privilege);
o = exec mode, 1 = user mode

3-17

XVM/RSX V1B

•

Task entry point; absolute address if exec
mode, address relative to partition base if
user mode

IX-2-23

September 1976

2.12

I
•

TNRL:

TASK TERMINATION NOTICE REQUEST LIST

The Task Termination Notice Request List (TNRL) records all abnormal
exits of tasks except those requested under MULTIACCESS.
Such exits
can occur when the task
issues a bad CAL instruction, makes a
memory-protect violation or makes a nonexistent memory reference.
Task execution can also be halted by the ABORT MCR Function task,
but
ABORT does not result in a new TNRL entry.
Entries can also be made in the TNRL when I/O rundown
is performed.
If the transfers-pending count is still nonzero after transfers to and
from a task partition have supposedly stopped, the
I/O Rundown task
enters a node into the TNRL.
Termination notices are stored in the TNRL and output on
associated with the Monitor Console Routine (LUN-3).
dequeued from the TNRL by a task named TNTERM.

the device
Notices are

Each TNRL node consists of the following:
Word

Contents

Forward pointer

Backward pointer

Task name

(first half)

Task name

(second half)

Termination indicator

PC at termination or transferspending count

AC at termination or unused

XR at termination or unused

Unused

The meaning of forward (word 0) and backward
(word 1)
pointers has
already been explained.
The task name (words 2 and 3) must be entered
in .SIXBT format.
The termination indicator (word 4)
identifies the
reason for task termination in the following way:

XVM/RSX VIB

IX-2-24

September 1976

Value

XVM/RSX VIB

Meaning

Memory-protect violation

Nonexistent memory reference

Bad CAL instruction

Nonzero transfers-pending count

IX-2-2S

September 1976

2.13

TDV.EQ:

MULTIACCESS EXIT QUEUE

The MULTIACCESS Exit Queue (TDV.EQ) records all exits of tasks running
under the MULTIACCESS Monitor. A node is entered in the TDV.EQ when a
task running under MULTIACCESS exits via either the EXIT directive or
an abnormal exit.
For normal exits, the node entered into the TDV.EQ is identical to the
task node in the Active Task List, except that word 11 of the ATL node
contains zero.
For abnormal exits (as a
result of a bad CAL, a
memory-protect violation, etc.), the node entered into the TDV.EQ is
identical to a TNRL entry, except that word 11 of the TDV.EC node is
set to +1.
The node format chanoes related to word 11 distinquish
between normal and abnormal task exits in the MULTIACCESS Exit Queue.
Nodes can be entered into the TDV.EQ by the EXIT directive,
the I/O
Rundown task,
the Bad Cal Processor and the Memory Protection
Interrupt Routine.
Entries in the TDV.EO can be removed by only the
MULTIACCESS EXIT processor.

XVM/RSX V1B

IX-2-26

SepteIDber 1976

CHAPTER 3
SYSTEM COMMUNICATION REGISTERS

The previous chapter summarizes Executive listhead locations for all
system lists described. This chapter details the full set of system
pointers and parameters that can be absolutely referenced by any
exec-mode task.
These pointers and parameters make up the System
Communications Area (SCOM), which begins at octal location 100 in the
Executive. A listing of SCOM follows:
Location
(octal)

Address
Tag

100

Contents
PlEDTN

Explanation
EDIT number. Bits 0 to 2 = 1 to
indicate part one of two-part
source code.

Reentrant System Calls
101
102
103
104
105
106

Rl
R2
R3
R4
R5
R6

FACLB
JMP
JMP
L20
0
0

SAPI
CALDSP

R6, XIO
to
X17, and
RI
to
location 20 are registers used by
reentrant
routines. When task
switching occurs, these registers
(as well as the AC, XR, etc. ) are
Rl to R4 are
saved and restored.
initially set up for bootstrap
loading.

Entry to Reentrant System Subroutines (via JMS)
107

112

XVM/RSX V1B

NADD

NOEL

0
• INH
JMP

Add node to deque •

••

NADDE
Delete node from deque •
NDELE

IX-3-1

September 1976

•

Location
(octal)
115

Address
Tag
PENP

Contents

o
.INH
JMP

I
120

PICK

I
123

SNAM

126

SPRI

131

134

SAVE

REST

the

Pick a node from the
a deque.

head

deque

for

a given name.

.-1
SNAME

o
LAC
JMP

frow

PICKE

o
LAC
JMP

Pick
an ewpty node
Pool of Empty Nodes.
PENPE

o
.INH
JMP

Explanation

• -1

Search deque for
insert a node •

priority

and

SPRIE

Save
registers
of interrupted
program (inhibit interrupts) .

. INH
JMP

SAVV

JMP

RSR

Restore registers and return to
the
interrupted
program. The
SCOM
entry
is
provided for
tasks; the system uses RSR.

Current Task Pointer
135

CURTSK

ATKL

When a task is current (running),
CURTSK contains the address of
the task ATL node.

System Parameters

•

136

CSIZE

57777

Maximum core address (set by
System Configurator).

137

DSIZE

-1

Maximum disk platter number
(set
by the System Configurator). A
negative number indicates "Cold
Start Image" for "RSX Restore".

140

TPS

Clock ticks per second.

141

CTPS

777704

Two's complement of TPS.

142

LUTPI

LUT

Pointer to the beginning
Logical Unit Table.

143

LUTP2

LUT+NLU-l

Pointer to the end of the Logical
Unit Table.

144

AFTPl

AFT

Pointer to the beginning
Attach Flag Table.

XVM/RSX VIB

IX-3-2

the

September 1976

Location
(octal)

Address
Tag

Contents

Explanation

145

AFTP2

AFT+NLU-l

Pointer to the end of the
Flag Table.

146

NTSC5E

D60

Number
of
ticks
clock-generated
events.

147

BATWD

Word used by RSX BATCH.

Directives rejected due to
pool.

Unused.

Attach

separating
significant

System Error Log
150

SE.EP

151

empty

152

SE.DR

Number of disk retries
an error.

153

SE.DF

Number of disk failures.

154

SE.AD

Number of times the loading of a
task was aborted due to a disk
failure.

155

SE.AP

Number of times the scheduling of
a task was aborted due to an
empty pool.

Reserved.

MAXJOB

QJBLM7

Maximum number of jobs allowed in
the job queue (default is 15) •

160

SSM

Seconds since midnight.

161

DSR

Count of days running.

162
163
164
165

TT
SS
MM
HH

0
0
0
0

Time of day
Time of day
Time of day
Time of day

166
167
170

MO
DA
YR

1
1
106

Date
Date
Date

156
157

following

Time Values

ticks.
seconds.
minutes.
hours.

month.
day.
year.

MCR (Monitor Console Routine) Communications
171

MCRRI

MCR Request Inhibit Flag:

o = CTRL/C

type-in will
the
request
of
Dispatcher ( ••• MCR) •

XVM/RSX V1B

IX-3-3

cause
MCR

September 1976

Location
(octal)

172

Address
Tag

IFAC

I
174

FAC

Contents

Explanation
+1

CTRL/C has been typed once
and
..• MeR or MCR function
task should be active.

-1

CTRL/C has been typed twice
or more. MCR Dispatcher is
not requested.
Some
MCR
functions use the -1 state
as a request for premature
termination.

0
JMP*

(IFACE

Entry point to the subroutine;
read a line and then initialize
the FAC subroutine.

0
JMP*

(FACE

Entry point to the subroutine;
fetch a character.

Terminal Handler Parameters
176

TTYNUM

the
Number of
terminals
on
machine
(set
by
the System
Configurator) •

177

TTYRQT

TTWD07

Pointer to the beginning of a
table
with
one-word entries,
which in turn points to the I/O
Request Queue of each physical
terminal.

200

TTMCTT

Unit number (set by REASSIGN)
the MCR terminal (LUN-2).

201

TTTDTT

Unit number (set by REASSIGN)
the TDV terminal (LUN-12).

202

TTWDOO

Pointer to terminal unit 0 status
register

203

TTWD06

Pointer to terminal unit 0 output
register

204

TTK.EV

Pointer to
terminal
unit
keyboard event variable.

205

TTYS

Maximum number of terminals
(an
assembly parameter; usually 6).

206

TTTGEV

Terminal handler
variable address.

Warm-start flag.
Set to 777777
by " ••• SAV" prior to saving an
image of core on the disk.

trigger

event

Disk Parameters
207

XVM/RSX V1B

WARMFL

IX-3-4

september 1976

Location
(octal)
210

Address
Tag
RFACTB

Contents
0

o
o

Explanation
Number of words allocated.
Disk platter number.
Disk address.
These three words are the control
table
used by the disk file
handlers to allocate up to eight
blocks on the disk.
Whenever
••. SAV is
called,
it
first
deal locates these blocks before
recording a core image on the
disk.

213

GRLINK*

Pointer to BEGIN block.

214

GRSDFL*

Shutdown flag

215

GRQPTR*

Pointer to RPLO in the UFG task.

216

GRQFLG*

Pointer to RPLQ in the
task.

217
220

TDV.EQ

221

MA.UCA

Pointer to base address of first
MULTIACCESS user context area;
zero if
MULTIACCESS
is
not
running.

222

MA.LOF

Current task LUN offset.

223

MA.UN

Current task user number.

224

MA.BLU

Base system LUN
user LUN space.

MULTIACCESS

225

MA.ELU

Final system LUN
user LUN space.

MULTIACCESS

226

MA.CT

MULTIACCESS CTRL/T flags word.

227

MA.CY

MULTIACCESS CTRL/Y flags word.

230

MA.CST

Pointer to MULTIACCESS
and status table.

231

XSIZE

Set by the System Configurator to
indicate the first location above
the top of the Executive.

232

PATRN

Holding word for
show.

233

CENTR

Defines bit sinks and sources for
the RSX light show.

234

LMAGIC

SWHA

Instruction to provide motion
the newly generated bits.

shut down).

RASP

UFG

MULTIACCESS Exit Queue listhead.

.-1

the

RSX

control

light

1These SCOM words are reserved for the RASP software package.

XVM/RSX VIB

IX-3-S

September 1976

Location
(octal)

Address
Tag

Contents

Explanation

Hardware Existence Flags
235

PRHDWE

NOP

Set to a SKP by the
System
Configurator if it detects that
the memory-protect and relocate
hardware exists.

236

FPHDWE

NOP

Set to a SKP by the
System
Configurator
if it detects that
the FP hardware exists.

XVM/RSX V1B

IX-3-5.1

September 1976

Location
(octal)

Address
Tag

Contents

Explanation

POOL Size

237

PLSZ

Initial size (number of nodes)
in the Pool of Empty Nodes (set
by the System Configurator, but
not dynamically updated).

System Deque Listheads

240

POOL

BPL
EPL

Pool of Empty Nodes.

242

STKL

MCR
SCF

System Task List.

244

ATKL

DSK
SFG

Active Task List.

246

CKQ

Clock Queue.

.-1
250

PBDL

·• -1

Partition Block
Description List •

252

PDVL

DSKO
TTOO

Physical Device List.

254

SCDL

·• -1

System COMMON Blocks
Description List •

256

TNRL

• -1

Task Termination Notice
Request List •

260

IORDQ

I/O Rundown Queue.

.-1
262

HTL*

Wait-Task List (used by
RASP for Task-swapping) •

• -1
264

LPOOL

·.-1

Pool of Empty Large Nodes.

266

SNDL

·.-1

Small Node Description List.

270

LNDL

Large Node Description List.

.-1
272

EXECT

EXECUTE Control Table.

273

274

.SIXBT "FIN-

275

.SIXBT "INS"

*These SCOH words are reserved for the RASP Software Package.
XVM/RSX V1B

IX-3-6

September 1976

Location
(octal)
276

Address
Tag

Contents

EXELH

277

Explanation
EXECUTE listhead.

.-1

Task Exit
300

RETX

CAL

301

SYSDSK

HINF code of system disk.

302

RKDISK

Highest unit number of
or -1.

disks

303

RPDISK

Highest unit number of
or -1.

disks

304

LUFDI

LUNUFD

Pointer to beginning of
table.

LUN

305

LUFD2

LUNUFD+NLU-l

Pointer to end of LUN UFD table.

306

DUFDI

UFDDSK

Pointer to beginning of disk
table.

307

DUFD2

UFDDSK+20

Pointer to end of disk UFD table.

310

DSAFLG

DSACPL

Address of flag for DSA, showing
whether a bit map is in core.

311

REMBLK

Starting block of REMOVE chain of
blocks.

312

TIMFLG

When
zero,
task
timing
is
disabled;
when nonzero, task
timing
is
enabled
and
the
contents of TIMFLG points to the
task timing control table.

313

RIGHT

37700

Bit mask for bits shifted right.

314

LEFT

760017

Bit mask for bits shifted left.

315

SLITIM

Two's complement of the number of
ticks that a time-sliced task
should be allowed to run.

316

SLIHR

Highest slicing priority.

317

Slilr

Two's
complement
slicing priority.

DSADKC

Address of GET/PUT control
for DSA.

320

XVM/RSX V1B

(10)

A one-word reentrant task used to
force
active
tasks to exit,
(e.g., if aborted).

IX-3-7

UFD

lowest
table

September 1976

Location
(octal)

Address
Tag

Contents

Explanation

321

SPYI

SPYBLK

Pointer to start of Spy area.

322

SPY2

SPYBLK+ll

Pointer to end of Spy area.

323

JOBI

324

JOB2

Header of batch job list.

.-1

Entry to Reentrant Routines for I/O Handler Tasks
325

ALAD

DLAD

DQRQ

VAJX

lOCO

350

PABF

ALBF

DABF

DMTQ

XVM/RSX V1B

RPACTO

o
o
o

Verify and adjust to a l7-bit
value an I/O transfer
parameter.
Decrement the transfers-pending
count.
Preallocate an I/O buffer.

.-1
PABFl

Allocate an I/O buffer.
.-1
ALBFl

Deallocate an I/O buffer.
.-1
DABFI

o
LAC
JMP

364

.-1
IOCDI

a
LAC
JMP

361

.-1
VAJXl

o
LAC
JMP

356

Dequeue an I/O request.
.-1
DQRQl

o
LAC
JMP

353

Unused

o
LAC
JMP

Detach LUN and device unit from
the indicated task.

ATDT

o
LAC
JMP

345

.-1

o
LAC
JMP

342

Unused.

336

Attach LUN and device unit to
the indicated task •

ATDT

o
LAC
STL
JMP

337

• -1

331
332

o
LAC
CLL
JMP

.-1
DMTQl

Deallocate LUN and device unit,
then empty an I/O request queue
of all the requests made by the
indicated task.
Allocate/deallocate control
table for RP unit o.

IX-3-8

September 1976

Location
(octal)

Address
Tag

367

RPACTl

0
0
0

Allocate/deallocate control
table for RP unit 1.

372

RPACT2

0
0

Allocate/deallocate control
table for RP unit 2.

Explanation

contents

0
375

RPACT3

Allocate/deallocate control
table for RP unit 3.

0
0
0

400

RPACT4

403

RPACT5

Allocate/deallocate control
table for RP unit 4.

0
0

Allocate/deallocate control
table for RP unit 5.

0
406

RPACT6

411

RPACT7

0
0
0

Allocate/deallocate control
table for RP unit 6.

Allocate/deallocate control
table for RP unit 7.

0
0
414

RKACTO

Allocate/deallocate control
table for RK unit o.

0
417

RKACTl

Allocate/deallocate control
table for RK unit 1.

0
0

422

RKACT2

0
0
0

Allocate/deallocate control
table for RK unit 2.

425

RKACT3

0
0
0

Allocate/deallocate control
table for RK unit 3.

430

RKACT4

Allocate/deallocate control
table for RK unit 4.

0
433

RKACT5

Allocate/deallocate control
table for RK unit 5.

0
0

436

RKACT6

Allocate/deallocate control
table for RK unit 6.

0
0

441

RKACT7

Allocate/deallocate control
table for RK unit 7.'

0
0

IX-3-9

Address
Tag

Location
(octal)

444

447

NDELXR

DQAB

XVM/RSX V1B

Contents
0
.INH
JMP
0
.INH
JMP

Explantion
Delete node to which XR points.

NDLXRE
Dequeue an I/O request if (and
only if) it is an ABORT request.
DOABI

IX-3-10

September 1976

INDEX

Nodes, 1-1, 1-2

Active Task List (ATL) , 2-3
AUTORM, 2-8.1

Partition blocks, 2-13
Partition Block Description
List (PBDL), 2-13
Physical Device List (PDVL),
2-17
POOL, 1-2, 3-6

Batch Job List (JOBl), 2-10
Buffers, 2-16

Clock handler, 2-3
Clock Queue (CKQ), 2-6
Current task pointer, 3-2
RASP SCaM words, 3-6
Reentrant routines for I/O
handler tasks, 3-8
Reentrant system calls, 3-1
RSX system lists, 2-2

Deque list, 1-1
Disk parameters, 3-4

Execute List (EXELH), 2-8

FININS, 2-8.1

Hardware existence flags, 3-5.1

I/O handler tasks, reentrant
routines for, 3-8
I/O Rundown Queue (IORDQ), 2-9

SCaM (System Communications Area),
2-1, 3-1
Small Node Description Lists
(SNDL), 2-20
System COMMON Blocks Description
List (SCDL), 2-19
System Communications Area (SCaM),
2-1
System deque listheads, 3-6
System error log, 3-3
System parameters, 3-2
System pointers, 3-1
System Task List (STL), 2-21

Task exit, 3-7
Task status, 2-4
Task Termination Notice Request
List (TNRL), 2-24
Terminal handler parameters, 3-4
Time values, 3-3

Large Node Description List
(LNDL), 2-12
Listheads, 2-8
LPOOL (Pool of Empty Large
Nodes), 1-2

MCR (Monitor Console Routine)
communications, 3-3
MULTIACCESS Exit Queue (TDV.EQ),
2-26

XVM/RSX VIB

IX-Index-l

September 1976