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Document:	Introduction to RSX-11M
Order Number:	AA-2555D-TC
Revision:	0
Pages:	50
Original Filename:	http://bitsavers.org/pdf/dec/pdp11/rsx11m_s/RSX11M_V3.2_Jun79/1_Introduction/AA-2555D-TC_Introduction_to_RSX-11M_197906.pdf

OCR Text

Introduction to
RSX-11M
Order No. AA-25550-TC

RSX-11M Version 3.2

r-;:::rder additional copies of this document, contact the Software Distribution
~er, Digital Equipment Corporation, Maynard, Massachusetts 01754

digitcJI equipment corporation · maynard, massachusetts

First Printing, May 1974
Revised:
November 1976
Decembe.r 19 7 7
June 1979

The information in this document is subject to change without notice
and should not be construed as a commitment by Digital Equipment
Corporation. Digital Equipment Corporation assumes no responsibility
for any errors that may appear in this document.
The software described in this document is furnished under a
license
and may only be used or copied in accordance with the terms of such
license.
No responsibility is assumed for the use or reliability of software on
equipment that is not supplied by DIGITAL or its affiliated companies.

The postage prepaid READER'S COMMENTS form on the last page of this
document requests the user's critical evaluation to assist us in
preparing future documentation.
The following are trademarks of Digital Equipment Corporation:

DIGITAL
DEC
PDP
DECUS
UNIBUS
COMPUTER LABS
CO MT EX
DDT
DECCOMM
ASSIST-11
VAX
DECnet
DATATRIEVE

DECsystem-lo
DECtape
DIBOL
EDU SYSTEM
FLIP CHIP
FOCAL
IND AC
LAB-8
DECSYSTEM-20
RTS-8
VMS
!AS
TRAX

MAS SB US
OMNIBUS
OS/8
PHA
RSTS
RSX
TYPESET-8
TYPESET-11
TMS-11
ITPS-10
SB!
PDT

4/80-14

·~

CONTENTS
Page
PRE:FACE
CHJl~PTER

RSX-llM AND RSX-llS

1-1

1.1

RSX-llM
RSX-llS

1-1

1.2
2

RSX-llM APPLICATIONS

2-1

2.1

2-1
2-1
2-1
2-2

2 .1. 4
2.2
2.3

REAL-TIME APPLICATIONS
Data Acquisition
Process Monitoring and Control
Manufacturing Monitoring and Control
Laboratory and Medical Data Processing
SUPPORTED LANGUAGES AND PROGRAM DEVELOPMENT
COMPUTER NETWORKS

2-3

REAL-TIME AND MULTIPROGRAMMING OPERATIONS

3-1

3.1
3 .1.1
3 .1. 2
3 .1. 3
3.2
3.2.1

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

3.2.6
3.2.7
3.3
3.3.1
3.3.2
3.3.3

MEMORY ORGANIZATION
Mapped and Unmapped Systems
Partition Types
Subpartitions
EXECUTIVE CONTROL
Task State
Priority
Checkpointing
Round-Robin Scheduling
Swapping
Significant Events
Example of a 16K Unmapped System
SYSTEM DIRECTIVE FUNCTIONS
Event Flags
System Traps
Extended Logical Address Space

3-4
3-5
3-5
3-6
3-6
3-7
3-7
3-8
3-9
3-9
3-10

SYSTEM OPERATION

4-1

2 .1.1
2 .1. 2
2 .1. 3

CHAPTER

3.2.2
3.2.3
3.2.4

3.2.5

CHAPTER

1-1

4.1
THE MCR INTERFACE
4.1.1
External Scheduling of Task Execution
4 .1. 2
Indirect Command Files
4 .1. 3
The MCR Indirect File' Processor
Symbol Value Substitution
4.1.3.1
TERMINAL OPERATION
4.2
Attached Terminals
4.2.1
Slave Terminals
4.2.2
MULTIUSER PROTECTION
4.3
4.3.1
Public and Private Devices
4.4
SYSTEM MAINTENANCE FEATURES
4.4.1
Error Logging
4.4.2
Power Failure Restart

iii

2-2
2-2

3-3

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

CONTENTS
Page
CHAPTER

PROGRAM DEVELOPMENT

5-1

5.1
5.1.1
5.1. 2

5-1
5-1

5.5
5.5.l
5.s.2

EDITING UTILITIES
EDI
EDT
PROGRAMMING LANGUAGES
MACR0-11
BASIC-11
BASIC-PLUS-2
COBOL
CORAL-66
FORTRAN-IV and FORTRAN IV-PLUS
BUILDING THE TASK
RUNNING THE TASK
DEBUGGING THE TASK
ODT
Post Mortem and Snapshot Dumps

FILES AND I/O OPERATIONS

6-l

RSX-llM FILE SYSTEM
FILES-11
6.2.1
File Ownership and Directories
File Protection
6.2.2
6.2.3
File Specifications
6.2.4
File Manipulation
PIP
6.2.4.1
Queue Manager
6.2.4.2
6.3
TASK I/O OPERATIONS
6.3.1
File Control Services (FCS)
6.3.2
Record Management Services (RMS)
6.3.3
Device Independence
6.4
PHYSICAL I/O OPERATIONS

6-l
6-l
6-1

5.2
5.2.1
5.2.2
5.2.3

5.2.4
S.2.5
S.2.6

5.3
5 •. 4

CHAPTER

6.l
6.2

INDEX

5-2
5-3

5-3
5-3
5-4
5-4

s-s
s-s
S-6
S-6

S-6
S-6
5-7

6-2
6-2
6-3
6-3
6-3
6-4
6-4
6-5
6-6
6-6

Index-1
FIGURES

PIGURE

3-1
3-2
5-1
6-1
6-2
6-3

Comparison of Sequential and Concurrent
Execution of Programs
Sample Unmapped System Memory Layout
Steps to Creating a FORTRAN Program
Sequential File Organization
Relative File Organization
Indexed File Organization

3-3
3-8

5-2
6-5
6-5
6-6

PREFACE

MANUAL OBJ:ECTIVES

This manual introduces the basic concepts
RSX-llM and RSX-118 operating systems.

INTJ~llDED

and

capabilities

the

AUDIENCE

To understand the subjects discussed in this manual, readers should
have a general knowledge of computing terms and principles. Previous
knowledge of the RSX-llM or RSX-llS operating system, however, is not
required.

STRUCTURE OF THIS DOCUMENT

The manual contains the following chapters:
1

RSX-llM and RSX-llS

Chapter 2

RSX-llM Applications

Chapter 3

Real-Time and Multiprogramming Operations

ChaptE!r

System Operation

ChaptE~r

ChaptE!r 5

Program Development

Chapter 6

File System and I/O Operations

ASSOlCIATED DOCUMENTS

The RSX-llM/RSX-llS Documentation Directory defines the intended
readership of each manual in the RSX-llM/RSX-llS set and.provides a
brief synopsis of each manual's contents.
For detailed information about PDP-11 hardware,
appropriate PDP-11 processor or peripheral handbook.

refer

the

CHAPTER l
RSX-llM AND RSX-118

1.1

RSX-llM

RSX-·llM is a disk-based operating system for PDP-11 computers that can
be used both as a multiprogramming system and as a real-time system.
The primary function of RSX-llM is quick response to real-time events.
Howeiver, the multiprogramming capability of the system allows you to
combine this real-time activity, with less time-dependent activities
such as program development or text editing.
An RSX-llM system can be anything from a
stand-alone
system
controlling one process (where quick response is the most important
factor) to a multiuser system, supporting program development activity
at several terminals.
Initially, you will receive a minimal RSX-llM host system on whatever
distribution medium you select. You decide what you want your RSX-llM
system to do (choosing from a wide range of hardware and software
options.) You can then create an RSX-llM target system to suit your
exact requirements, using a process called System Generation.
The
combination of hardware and software options you choose is called your
target system configuration.
You can change the configuration at any
System Generation.

time

performing

another

The user interface to RSX-llM is called the Monitor Console Routine
(MCR).
It serves as a channel for communication between the user and
the operating system.

1.2

RSX-US

RSX-·llS is a memory-only version of the RSX~llM operating system. Its
main purpose is to run tasks on a processor that has limited
peripheral devices (tapes and disks). Since RSX-llS does not have a
file! system, checkpointing, nonresident tasks, editors, compilers, or
assemblers, tasks must be written, assembled or compiled, and task
built on an RSX-llM or RSX-llM-PLUS host system before they can run on
an RSX-llS system.
RSX-llS can operate with a minimum of SK words of memory and a maximum
of 124K words.
(This includes space for a 4K Executive; the
remainder is available for user-written tasks.)
RSX-·llS is fully compatible with RSX-llM, both internally and at the
user level. It supports the same I/O driver interface and any drivers
written to run on one system can be incorporated without change to run
on the other.

1-1

RSX-llM AND RSX-llS

Any nonprivileged user task that runs on RSX-llS can run on RSX-llM if
you Task Build the file containing the object modules so that it fits
in the available RSX-llS memory. Tasks that run on RSX-llM can also
run on RSX-llS if they are correctly task built, as long as the tasks
do not include memory management directives (also called Programmed
Logical Address Space or PLAS directives). RSX-llS does not support
dynamic allocation of
system-controlled
partitions
or
memory
management.
The user interface to RSX-llS is Basic MCR (a subset
interface, MCR). It is compatible with MCR.

the

RSX-llM

RSX-llS can also include other system tasks:
1.

The Online Task Loader (OTL), which
fixes tasks in the RSX-llS system.

installs,

loads,

and

The System Image Preservation program (SIP), which
image of the operating system for subsequent use.

saves

The System Activity
terminal
displays
activity.

A subset of File Control Services (FCS) for record
This feature does not include directory support.

Display programs which provide video
of information about RSX-llS system

1-2

devices.

CHAPTER 2
RSX-llM APPLICATIONS

This chapter discusses several real-time jobs that RSX-llM can handle.
It .also introduces RSX-llM program development facilities and network
communications (DECnet).
Real-time events demand immediate and full access to available
computer resources at regular and irregular intervals. When RSX-llM
is not responding to these events, it permits the computer resources
to be used to perform less time-dependent jobs, such as program
development or payroll processing. RSX-llM can immediately preempt
these programs whenever it needs to respond to a real-time event.
Therefore, nonreal-time applications can make up the major work load
for an RSX-llM system, without interfering with the system's real-time
capabilities.

2.1

REAL-TIME APPLICATIONS

The following sections explain
RSX-llM
operations,
for
data
acquisition, process monitoring and control, manufacturing monitoring
and control, and laboratory and medical data processing.

2.1.l

Data Acquisition

Data acquisition refers to the process of collecting physically
generated data in a form that can later be evaluated. A typical data
acquisition application might require a number of programs to respond
to a single burst of data.
RSX-llM multiprogramming allows this
apparently concurrent execution of several programs.
For example,
three separate RSX-llM tasks could process data generated by one
real-time event and recorded on three different devices:
one task
could record data from a spectrometer; another could record data from
a flowmeter; and a third, data from a thermocouple.
RSX-llM provides a rapid response

to external stimuli because the
programs that control peripheral devices are linked directly to the
PDP-11 hardware interrupt vectors. This permits the system to change
rapidly from one device to another and from one task to another.

2.1.2

Process Monitoring and Control

A process control application usually involves first acquiring and
analyzing data, and then returning information based on the analysis.
The information obtained is used to control some actual process.
Oil
refineries and steel rolling mills could perform such process control
activities.
2-1

RSX-llM APPLICATIONS
The signals that the PDP-11 hardware receives from devices that
monitor and control a process are called process inputs. RSX-llM uses
these inputs to monitor many facets of the process, such
as
temperature,
flow
rate, or the amount of raw material used.
Instructions stored in RSX-llM user programs can determine how to keep
the process running properly.
In addition, control optimization
programs can make adjustments based on the relationship of various
parts of the process.
After analyzing all of the data, RSX-llM,
directed by user programs, generates signals called process outputs to
control the valves, switches, and relays that, in turn, control the
process.

2.1.3

Manufacturing Monitoring and Control

RSX-llM tasks can monitor manufacturing operations, test the quality
of products, furnish data to other production systems and inventory
control systems, and manage the flow of work between departments.
Manufacturing data can be collected directly from sensors or entered
manually through terminals dedicated to that use.

2.1.4

Laboratory and Medical Data Processing

Medical and laboratory settings require small computer systems to
perform precisely defined real-time operations. The monitoring of
patients for example, demands instant response to all changes in a
patient's condition.
A PDP-11 connected to monitoring devices can
keep a continual log of the patient's condition, while running other
programs to diagnose symptoms. Other possible laboratory and medical
app1ications include:

2.2

•

X-ray diffraction measurement

•

Gas chromatography

Psychological testing

•

Particle acceleration

SUPPORTED LANGUAGES AND PROGRAM DEVELOPMENT

The real-time activities described above require specialized software
systems
(compilers
or
assemblers).
RSX-llM supports several
programming languages so you can choose the ones most suited to your
parti~ular applications.
These languages include:
e

MACR0-11

•

BASIC-11

•

BASIC-PLUS-2

•

COBOL

CORAL-66

FORTRAN IV or FORTRAN IV-PLUS

2-2

RSX-llM APPLICATIONS
The range of languages that RSX-llM supports allows you to
improve
existing applications and to develop new ones without changing
operating systems.
For example, a company that uses RSX-llM for a
real-time process control application might decide to use the same
system to handle its payroll. All the process control programs may
have been written in FORTRAN IV, not the best language for the payroll
operation. The company could buy the RSX-11 COBOL compiler to use for
developing
payroll programs without significantly affecting the
existing system.

2.3

COMPUTER NETWORKS

You can use an optional software package, DECNET-11,
computer network.

establish

A network connects several computer systems,
communication devices,
and I/O devices. The computer systems, called "nodes," are connected
by hardware, called "physical links."
In addition, DECNET-11 allows:

sharing. Device sharing allows
• Device
connect to and use the peripheral

a DECNET-11 user to
devices of a remotely

located node.

•

File sharing.

•

Program sharing.

File sharing permits you to read
to, and update files on a remotely located node.

from,

write

A loadable program can be transferred to
remotely located node where it can be loaded and executed.

DECNET-11 allows tasks to communicate with each other across nodes,
even if the nodes are geographically remote from each other. A task
executing in one node can send data to a task executing in another
node!. DECNET-11 monitors the data transfer, performing such functions
as error detection.

2-3

CHAPTER 3
REAL-TIME AND MULTIPROGRAMMING OPERATIONS

require

the

•

Memory. Memory is the hardware storage medium in which
executive and user and system programs reside and run.

the

•

Th• Executive. The RSX-llM Executive is the operating
software that directs all program execution.

•

Ua•r and System Programs.
RSX-llM executable programs are
called "tasks." Tasks can either be user-written or supplied
by DIGITAL (system tasks).

RSX-llM real-time and multiprogramming
operations
interaction of the following system elements1

This chapter introduces the memory
combine
to
produce the RSX-llM
facUitieso

3 .1

MEMOR~!

and executive
real-time and

system

facilities that
multiprogramming

ORGANIZATION

A task runs in a contiguous area of memory called a partition.
The
size and location• of these partitions are set at system generation.
Each partition has:

• A name
.
• A defined size
~).

• A f:ixed base address

'-"

• A defined type
The relationship between a task and the partition in which it runs
depends on whether the system is mapped or unmapped, and whether the
partition is system- or user-controlled.

3.1.1

Mapped and Unmapped Systems

RSX-·llM is designed to run on almost all PDP-11 computers. The PDP-11
allows a task to directly address only 32K words of memory. A special
hardware device, a memory management unit, is available to allow you
to use memory larger than 32K words. This unit is available with
PDP-11/23/34/35/40/45/50/55/60/70 processors. The memory management
unit associates addresses used in tasks (virtual addresses) with
actual locations in memory (called physical addresses).
Virtual
addresses can range from O to 32K words, and physical addresses can

3-1

REAL-TIME AND MULTIPROGRAMMING OPERATIONS

range from 0 to 124K words on all processors except the PDP-11/70.
Physical addresses on a PDP-11/70 can range from O to 1920K words.
A PDP-11 system that includes a memory management unit
mapped system. Systems without the unit are unmapped.

called

RSX-llM users create tasks differently, depending on whether the
system is mapped or unmapped •. Before you can run an object module
created by a language compiler or assembler, it must be processed by
the Task Builder.
If the task is to run on an unmapped system, you
must specify to the Task Builder the base address of the partition in
which it is to run. The task cannot run at a base address different
from the address specified in the Task Builder command.
In a mapped system, however, every task has a virtual base address of
O. The memory management unit maps the virtual addresses of a task to
the actual physical addresses in which the task resides. This mapping
is invisible
(transparent) to the person who is running the task.
Therefore, a task in a mapped system can run in any partition large
enough to contain it.
The only exception to this mapping method occurs when a privileged
task is set to run in the memory space allocated to the executive.
Such tasks will not be reloca~ed.

3.1.2

Partition Types

RSX-llM tasks can execute in two types of partitions:
•

System-controlled

•

User-controlled

In a system-controlled partition, which can only be used on a mapped
system, the Executive allocates available space to make room for as
many tasks as possible at one time.
This allocation can involve
shuffling tasks already in memory (resident). The shuffling arranges
available space into a contiguous block large enough to contain a
requested
task.
Only mapped systems contain system-controlled
partitions.

A user-controlled partition is allocated exclusively to one task at a
time.
This type of partition can be used with both mapped and
unmapped systems.

3.1.3

Subpartitions

A user-controlled partition may be subdivided into as many as seven
nonoverlapping subpartitions. Like the main partition, a subpartition
can contain only one task at a time. Since the subpartitions occupy
the same physical memory as the main partition, tasks cannot be
simultaneously resident in both the
main
partition
and
any
subpartitions.
However, since the subpartitions can each contain a
task, up to seven tasks can run together within a main partition.
Subpartitioning reclaims large storage areas in unmapped s~stems. For
example, when a large task that requires a main partition is no longer
active or can be checkpointed, subpartitioning allows the space to be
used by a number of smaller real-time tasks.

3-2

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
3.2

EXECUTIVE CONTROL

The RSX-llM Executive allocates CPU time to various system and user
tasks.
The Central Processing Unit (CPU) is the part of the computer
that actually carries out instructions provided by system or user
tasks; only one task at a time can control the CPU. Multiprogramming
is possible because task execution almost always involves more than
CPU usage.
A real-time task that initiates a process and then waits
for the process to complete may not need CPU time while it is waiting.
Therefore, while one task waits for an event to complete, the
Executive gives control of the CPU to another task. This happens so
rapidly that many individual users seem to have control of the CPU at
the same time (apparent concurrency; see Figure 3-1.)

CONCURRENT EXECUTION

SEQUENTIAL EXECUTION

!------,___.
t=ROGRAM A ., _

ELAPSED TIME

--------.i

_..,.i--- PROGRAM B --*4-PROGRAM C

1 - - - - 1 1.-. .

ELAPSED TIME - - - - 1 1....
,,

PROGRAM A

PROGRAM B

KEY

D
~

PROGRAM C

DISKTIME

CPUTIME

TERMINAL TIME

Figure 3-1 Comparison of Sequential
and Concurrent Execution of Programs
Figure 3-1 illustrates the advantages of multiprogramming. When tasks
A, B, and C run in a system without multiprogramming, they run one
after the other. Task A reads some information from disk, operates on
it, and generates a report.
Task B performs some computation,
generates a message, performs some more computation, and writes the
result to disk.
Task C performs some computation, reads some
information from disk, performs additional computation, and writes the
result to disk. While one part of the system, such as the disk drive,
is busy, other parts, such as the CPU, are idle.

3-3

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
A different sequence of operations is possible if the three tasks run
concurrently in a multiprogramming system. The CPU, disk drive, and
terminal are active simultaneously; and the concurrent execution of
the three tasks takes less time than the sequential execution of the
same tasks.
In RSX-llM, the Executive coordinates the execution of all tasks in
memory to achieve both efficient use of system resources and rapid
response to real-time demands. The following factors affect the way
this coordination works:

• Task state

• Priority
• Checkpointin9
• Round-robin 1chedulin9
• swapping
• Significant events

.,--.1

Task State

3.2.1

When you install a task (by issuing an MCR command from a terminal)
the system records information about the task in the System Task
Direct'ory (STD). The STD is a table that the Executive creates and
updates to keep track of all the tasks it knows about. The parameters
recorded in the STD include the name and size of the task, the disk
address at which the task starts, and the name of the partition in
which the task is to run.
An installed task is defined as a task that has an entry in the STD.
It is neither resident in memory nor competing for system resources.
The Executive considers the task to be inactive until a running task
or a command issued from a terminal requests the Executive to activate
it. Therefore the Executive recognizes two task states:
•

Dormant. A dormant task is one that has been installed but is
not running.

•

Active. An active task is an installed task that is running.
It remains active until it exits, terminates, or is aborted,
when it returns to a dormant state.
An active task can be either ready-to-run or blocked.
•

Ready-to-run. A ready-to-run task competes with other
tasks for CPU time on the basis of the task's
priority. The ready-to-run task with the highest
priority obtains CPU time and becomes the current
task.

•

Blocked. A blocked task is unable to compete for CPU
time because it needs access to some resource (memory,
a file, a device, etc.) that is not available.

The distinction between dormant tasks and active tasks is important in
RSX-llM.
A dormant task requires very little memory. However, when
the task is needed to service a real-time event, the Executive can
quickly introduce it into active competition for the system resources.

3-4

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
An installed task's STD entry enables this quick response because it
contains all the parameters the system needs to retrieve the task.
NotE! that the number of installed dormant tasks can far exceed the
number of active tasks.
When the Executive receives a request from a terminal or another
to activate a dormant task, it does the following:
•

Allocates required memory resources

•

Brings the task into memory

•

Places the task in active
tasks for system resources

competition

with

other

task

resident

If the partition in which a task is to be installed is fully occupied
and no other task in that partition can be checkpointed, the newly
installed task is placed in a queue by priority with other activated
tasks, each waiting for space to become available in its partition.
At this point, the task is blocked.

3.2.,2

Priority

Active tasks compete for system resources on the basis of priority and
resource availability.
The priority of a task is determined by a
number assigned to the task when it is built, when it is installed, or
when it is running.
Task priorities can be established by both
privileged and nonprivileged users. However, only privileged users
can run tasks created at a high priority. The priority is in the
ran9e 1 to 250(10), where a higher number indicates a higher priority.
The ready·-to-run task with the highest priority gains control of the
CPU.. When that task becomes blocked (waiting for an I/O transfer to
complete, for example), the Executive looks for the ready-to-run task
with the next highest priority.
In an RSX-llM system that mixes real-time tasks with other jobs, the
real-time tasks should be assigned higher priority numbers. This
arrangement ensures that the real-time tasks receive CPU time ahead of
the less time-dependent tasks.
For examplE!, the text editors commonly used in program development
spend much of their time waiting for terminal I/O to complete. During
these waiting periods, the editors are in a blocked state.
However,
when the I/O finishes, the user wants a rapid response to his or her
next request. To gain this response, the system manager can assign a
priority to the text editors that is higher than more CPU-dependent
tasks like the Task Builder or the Assembler.

3.2.3

Checkpointing

Checkpointing allows tasks hot currently resident in memory to gain
control of the CPU.
In some instances, an installed task cannot
compete for the processor because the partition in which it was
installed is fully occupied. If the partition contains a task that
has a lower priority and is checkpointable, the Executive can move
that task out of memory to make room for the higher priority task.
This process is called checkpointing.
When the latter task is
finished,
the
checkpointed
task is reactivated and continues
processing from the point at which it was interrupted.

3-5

REAL-TIME AND MULTIPROGRAMMING OPERATIONS

To be checkpointable, tasks require a space on disk equal to the size
of the task or its partition. While a checkpointed task is stored in
this space, a higher priority task occupies memory. Checkpoint space
is allocated either statically at _Task Build time or dynamically at
runtime.
When submitting a compiled or assembled program to the Task Builder,
you can specify that checkpoint space be allocated in the task image.
Therefore, checkpoint space is always available on disk while the task
is running, whether or not the Executive actually needs to checkpoint
the task. This is called static allocation of checkpoint space:
the
location and size of the area do not change unless the object module
is task built with different parameters.
Dynamic allocation of checkpoint space allows a more efficient use of
disk storage. Instead of reserving disk space for each checkpointable
task -- space which may not be needed
checkpoint files can be
created on disk to contain all checkpointed tasks. The size of the
files depends on an estimation of the checkpoint space required on the
system at any given time. When the system allocates checkpoint space
dynamically, tasks do not need to be built as checkpointable.
The
user determines whether a task is checkpointable when it is installed.
Then, when the Executive needs to checkpoint a task, it determines
that the task is checkpointable and rolls it out to a checkpoint file.
The main drawback to dynamic allocation of checkpoint space is that
space in a checkpoint file may not always be available.

3.2.4

Round-Robin Scheduling

When several tasks have equal priorities, the Executive tends to give
CPU time more often to those tasks that appear first in the STD queue.
(Entries with equal priorities appear in the STD in the order in which
the
tasks were installed.) However, RSX-llM provides a system
generation option called round-robin
scheduling.
This
option
periodically rotates tasks of equal priority within the STD. The
overall effect of the round-robin scheduler is to distribute use of
the CPU more evenly because each equal priority task has its turn to
be at the head of the queue.

3.2.5

Swapping

Another problem arises when several active tasks with equal priorities
compete for partition space in memory. A task cannot normally cause
the Executive to checkpoint another task of the same or higher
priority.
Therefore a task of equal or lower priority could be
prevented from accessing memory.
Swapping enables the Executive to checkpoint tasks with similar
priorities
in
and
out
of
memory.
(The
tasks
must
be
checkpointable.) When a task begins to run, the Executive adds a
"swapping priority" to the task's normal running priority. The
Executive then decrements the swapping priority (which eventually has
a negative value) as the task runs. When the sum of the decremented
swapping priority and the task's running priority creates an actual
priority less than that of a competing task, the Executive checkpoints
the running task to make room for the competing task.
The Executive
then places the checkpointed task at the end of the queue of active
tasks competing for memory.
(The swapping priority only affects
allocation of space in partitions. It does not affect CPU scheduling
or I/O dispatching, which are governed solely by the task's running
priority.)
3-6

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
Significant Events

3.2.6

Certain occurrences called significant events cause the Executive to
reevaluate the eligibility of all active tasks to run. When a
significant event occurs, the Executive scans the queue of active
Significant
tasks and runs the highest priority ready-to-run task.
events include the following:

3.2.7

•

An I/O completion

•

A task exit

•

The removal of an entry from a clock queue

•

The execution of some system directives issued by a task

•

The execution of the round-robin scheduler

Example of a 16K Unmapped System

Figure 3-2 shows a possible layout of memory for a 16K unmapped
system.
The BK Executive region consists of a system-controlled
partition,
the
RSX-llM
Executive,
device
drivers,
and
a
us~r-controlled partition called SYSPAR.
In this example,
SYSPAR contains the file system
(FllACP).
The
Monitor Console Routine
(MCR) and the Task Termination Notification
routine (TKTN).
Since the FllACP is checkpointable and has a
lower
priority than MCR or TKTN, MCR or TKTN can cause the Executive to
chec~:point the FllACP.
The higher priority task can then take over
the system resources.
The exact lc)cation and size of FllACP, MCR, and TKTN are determined at
system generation.
The BK User region consists of a user-controlled main partition called
PAR8F: and three subpartitions, SUBA, SUBB, and SUBC. PAR8K contains
program development facilities such as language processors and the
Task BuildE~r.
These tasks usually have a
low priority and are
check:pointable.
SUBA, SUBB, and SUBC are available for real-time tasks.
If one of the
real-time tasks
in these partitions needs the CPU and has a higher
priority than the task currently occupying the main partition,
the
task .in the main partition is checkpointed.
If multiple tasks in SYSPAR are ready to run, control of
determined by task priority.

3-7

the

CPU

REAL-TIME AND MULTIPROGRAMMING OPERATIONS

16K

SUBC

2K
SUBB

User
Region

PAR

SUBA

SYSPAR
2K
6K
Executive
Region

RSX-11M
EXECUTIVE

Figure 3-2

3~3

Sample Unmapped System Memory Layout

SYSTEM DIRECTIVE FUNCTIONS

A system directive is a request from a task to the Executive to
perform an operation.
System and user tasks use some directives to
control the execution and interaction of taskse
The execution of
other
system
directives
causes
significant events to occur.
Therefore, directly or indirectly, system directives affect the way
the Executive shares system resources among concurrently active tasks.
System directives enable tasks to:
•

Obtain task and system information

•

Measure time intervals

•

Perform I/O functions

•

Manipulate logical and virtual address space

•

Suspend and resume execution

•

Request the execution of another task

•

Exit

3-8

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
System directives allow tasks to
including:

use

•

Event flags

•

System traps

•

Extended logical address space

3.3.l

some

major

RSX-llM

features,

Event Flags

Significant events affect Executive management of task execution and
allow tasks to coordinate internal task activity and communicate with
otheir tasks. For example, a task can issue a system directive to
assoGiate an event flag with a specific significant event. When that
event occurs, the Executive sets the flag.
Therefore, a task can
determine whether the event has occurred by testing the state of the
flag ..
Ninety-six event flags are available to enable tasks to distinguish
one event from another.
Each event flag has a corresponding event
flag number. The first 32 flags are local to each individual task and
are set or cleared as a result of the task's operation. The second 32
flags are called System Global Event flags and can be used by any
task..
The third flags are called Group Global event flags and are
available to all of the users in a single user group (such as
(303, ••• ]).
Tasks must use global flags to communicate with other tasks, since one
task cannot refer to another task's local flags.

3.3.2

System Traps

System traps transfer control within the system and provide tasks with
the means to monitor and react to events. The Executive initiates
system traps when certain events occur.
The trap then transfers
control from the running task to routines associated with the event.
This gives the task the opportunity to service the event by entering a
user-written routine.
There are two kinds of system traps:
•

Synchronous System Traps (SSTs). SSTs detect events directly
associated with the execution of task instructions. They are
"synchronous" because they always occur at the same point in
the program. The running task controls when the trap occurs.
For example, an illegal instruction causes an SST to occur.

•

Asynchronous System Traps (ASTs).
ASTs detect significant
events
that
occur
"asynchronously"
during the task's
execution; that is, the task has no control over the precise
time that the event occurs. For example, the completion of an
I/O transfer causes an AST to occur.

To use system traps, a task issues system directives that establish
entry points for user-written routines to respond to the event. Entry
points for SSTs are specified in a single table. AST entry points are
set by individual directives for each kind of AST. When a trap
occurs, the task automatically enters the appropriate routine (if its
entry point is specified).

3-9

REAL-TIME AND MULTIPROGRAMMING OPERATIONS
Extended Logical Address Space

3~3.3

An RSX-llM task specifies an address in a 16-bit word.
The largest
address that can be expressed in a 16-bit word is 65,536 bytes or
32,768 words (commonly referred to as 32K words). Therefore,
a task
can directly address only 32K words.
To avoid limiting the size of a
task to its addressing capability, a task can use overlays that are
defined
at Task Build time,
or it can use memory management
directives.
An overlaid task is arranged into segments:
a root segment, which
is
always
in memory when the task is active, and overlay segments, which
can be read into memory as required.
The segments concurrently in
memory cannot exceed 32K words.
Memory management (PLAS) directives allow task segments resident
in
memory to exceed 32K words.
The directives use the KTll memory
management hardware to map task virtual addresses to different logical
addresses.
Therefore, the task can reside entirely in memory and map
its virtual addresses to different physical addresses.
RSX-llM uses three kinds of address space:

•

Physical address space.

•

Logical address space.

•

Virtual address space.

Physical address space consists of
the actual physical memory in which tasks reside and execute.
Logical address space
is the total
amount of physical address space to which the task has access
rights.

Virtual address space corresponds to
the 32K of addresses that the task can explicitly specify in a
16-bit word.
If a task does not use memory management
directives,
its logical and virtual address space are exactly
the same.
If a task does use these directives, it can map its
virtual addresses to different parts of its logical address
space. The net effect is to allow a task's logical address
space to exceed 32K.

The memory management directives also allow a task to expand its
logical address space dynamically while it runs.
In other words, a
task can access logical addresses that are n6t part of its static task
image.
This expansion is accomplished when a task issues directives
that create a new region of logical space and then map a
range of
virtual addresses to the newly created region. A task can also map
virtual addresses to logical areas that are part of another task.
The
other task's logical addresses then become part of the original task's
logical address space.
The ability to map to virtual addresses also allows tasks to
interact
by using shared regions of memory.
For example, a running task can
create a new region of logical address space and writes a large amount
of data to it. Other tasks can then access that data by mapping some
of their virtual addresses to the same region.
Interacting tasks also
allow a greater number of common routines.
Moreover tasks can map to
required routines when they run rather than link to them at Task Build
time.

3-10

CHAPTER 4
SYSTEM OPERATION

RSX··llM

operating procedures vary from one system to
another,
on the function of the computer and the hardware options it
supports.
A laboratory may have a PDP-11/10 used for one real-time
application with only one disk and one terminal. A lab technician
might oversee this computer system as one of many laboratory duties.
In contrast,
a manufacturer may have a PDP-11/70 that performs a
process control
job, all the company's accounting and
payroll
applications, as well as substantial program development.
Such a
system could have a dozen or more terminals and numerous disk and
magnetic tape drives.
A system of this size requires a full-time
operator to maintain the equipment and manage the use of the system.

dep•~nding

Although an RSX-llM system may not require a full-time computer
operator, someone must know how to operate RSX-llM.
The term
"operator" refers to anyone who interfaces with or oversees RSX-llM.
This chapter discusses some basic concepts required to operate an
RSX·-llM system.
Most of the concepts apply to all systems;
however,
som1e features (multiuser protection, for example) are optional and may
not be present on your system.

4.1

THE MCR INTERFACE

You can communicate with RSX-llM by entering commands at a
terminal.
The terminal sends the commands to the Monitor Console Routine (MCR)
processor, which either executes the commands itself or activates a
system- or user-written task to execute the commands.
MCR commands allow an operator to:
•

Start up the system

•

Manage peripheral devices

•

Control task execution

•

Obtain system and task information

•

Activate system- or user-written
from the terminal

tasks

that

request

input

An operator uses MCR commands to establish the base of installed
tasks,
which the Executive,
active tasks, and further MCR commands
manipulate in later operations.
To restrict the use of commands that directly
affect
system
performance, RSX-llM considers some MCR commands and command options
to be privileged. You can issue a privileged command only from a
privileged terminal.
4-1

SYSTEM OPERATION
4.1.1

External Scheduling of Task Execution

An important MCR function is the external scheduling of
task
execution.
This type of scheduling works in conjunction with the
Executive's priority-driven internal scheduling of active tasks.
The
operator can include time parameters with the command that activates
an installed task. The time parameters request the Executive to run a
task:
•

At a specified time from the current moment

•

At a specified time from clock unit synchronization

•

At an absolute time of day

•

Immediately

All of these time options are available with or without periodic
rescheduling. RSX-llM also supports an unlimited number of programmed
timers for each task in the system. The user task can create its own
timer, which the Executive then decrements at regular intervals. When
the timer reaches zero, the Executive sets an event flag or generates
an Asynchronous System Trap (AST) that passes control back to a task.

4.1.2

Indirect Command Files

An indirect command file contains a list of commands exclusive to, and
interpretable by, a single task. The interpreting task is usually an
RSX-llM system program, such as MCR, PIP, the MACR0-11 Assembler, or
the Task Builder.
To execute the commands in indirect files, the user enters a file
specifier preceded by an at symbol (@) in response to a prompt from
the appropriate task.
For example, to execute a
enter:
MAC

file

containing

only

MACR0-11

commands,

@INPT.CMD

The MACR0-11 Assembler then executes the commands in INPT.CMD.
Indirect files can invoke other indirect files;
depth varies with each task.

4.1.3

the

maximum

nesting

The MCR Indirect File Processor

Most tasks read and respond to commands contained in an indirect file
as if the commands were entered directly from a terminal. MCR,
however, has an indirect file processor that interprets indirect
commands.
An MCR indirect command file can contain both MCR commands
and commands (or directives) to the indirect file processor itself.
MCR optionally displays on the entering terminal all of the commands
executed from the indirect command file.
The indirect file processor first reads the command file
and
interprets each command line either as a command to be passed to MCR
or as a request for action by the indirect file processor itself.
Directives to the indirect file processor are distinguished by a
period (.) as the first character in the line.

4-2

SYSTEM OPERATION

The MCR indirect file processor also enables the user to define
symbols.
These symbols can subsequently be tested to control the
operntion of the indirect command file. The symbols consist of 1 to 6
ASCII characters that can be a true or false value, an octal or
decimal number, or a character string. The first directive to specify
a symbol defines that symbol; subsequent references test, compare, or
rede:Eine it.

4.1.3.1 Symbol Value Substitution - The symbols described above are
used in directives to the indirect file processor. Indirect MCR
commands can use the values assigned to string symbols by replacing a
normal parameter (for example, a device-unit) with the symbol name
enclosed in single quotation marks (for example, 'DEV'). The indirect
file processor replaces the symbol name enclosed in single quotation
marks with the string value assigned to the symbol.
When the
processor encounters a single quote, it treats the subsequent text, up
to the second single quote, as a symbol. The processor searches the
table of symbols for the corresponding string value and substitutes it
in the indirect command line before the line is interpreted.

4 •2

TERMIN.~L

OPERATION

In RSX-llM, a variable number of terminals can operate concurrently.
In addition, each terminal operates independen~ly of others in the
system so that each can run a different task.
In a system that
suppc,rts multiuser protection a user must log onto a terminal before
issuing further commands. In nonmultiuser protection systems, a user
can issue commands whenever the terminal displays an appropriate
prompt.
In multiuser protection systems, individual
users
are
either
privileged or nonprivileged;
when a user logs on, the terminal
assumes the privilege status of that user. In nonmultiuser protection
systems, however, a terminal's privilege status is determined at
system generation. After system generation, a user can issue an MCR
command at a privileged terminal to modify the privilege status of any
other terminal connected to the system. The privilege status of a
t~rminal
determines what commands you will be able to issue from that
terminal.

4.2.1

Attached Terminals

RSX-llM permits tasks to solicit input from a specific terminal or
terminals.
While the task is receiving input, the terminal is
attached to it. Thus, all of the terminal's output goes directly to
the attached task, with one exception. The exception is a <CTRL/C>
character (the C key typed while pressing the CTRL key). This command
gains the attention of MCR and allows you to issue one MCR command.
Note that attaching to the terminal is a function of the task rather
than the user.
Some applications require that a user be denied access to MCR.
In
that case, a task can attach to the terminal with a special
subfunction that causes the system to generate an AST whenever someone
enters unsolicited input, including <CTRL/C>, from the attached
terminal.

4-3

SYSTEM OPERATION

Slave Terminals

4.2.2

RSX-llM also permits you to dedicate a terminal exclusively to one or
more specific tasks, using an MCR command or special I/O functions in
the task.
A terminal restricted in this way is called a slave terminal.
The
difference between a slave and attached terminal is that the system
ignores all unsolicited inp~t from a slave terminal, including
<CTRL/C>.
Until the user issues an MCR command from a privileged
terminal to delete the slave status, the terminal can only be used to
communicate with the task soliciting input. A task can also issue an
I/O function to delete the slave status of a terminal.
Slave
terminals are often dedicated to critical real-time applications.

4.3

MULTIUSER PROTECTION

Multiuser protection, a system generation option, allows you to
monitor and control individual users of an RSX-llM system. A system
manager assigns a User Identification Code (UIC) to each user.
The
UIC determines whether the user is privileged or nonprivilege~. UICs
in groups less than or equal to 10(8) are privileged. Those in groups
numbered above 10(8) are nonprivileged. When logging on a terminal,
the user supplies a last name or UIC and a password. The system then
checks that the password matches the last name or UIC, and sets the
terminal's privilege status, according to the UIC.

4.3.1

Public and Private Devices

Multiuser protection systems allow both privileged and nonprivileged
users to issue MCR commands to allocate a device (a disk drive, for
example) as the user's private device. Allocating the device prevents
other nonprivileged users from accessing it, although privileged users
can still access it.
A nonprivileged user can use a device allocated to him or her to
perform MCR functions that are privileged in nonmultiuser systems.
These functions include preparing a disk or magnetic tape for use by
the RSX-llM file system and putting the disk or tape online and
off line.
Multiuser protection systems also allow a privileged user to make
certain devices public.
Public devices cannot be allocated to
individual users. When a line printer is public, for example, all
users have equal access to it.

4.4

4.4.1

SYSTEM MAINTENANCE FEATURES

Error Logging

RSX-llM provides an error logging subsystem as a system generation
option for systems that are 24K words or larger. The error logging
subsystem monitors the reliability of system hardware.
Routines in
the Executive and specific Error Logging tasks share control of Error
Logging.

4-4

SYSTEM OPERATION
The error logging task
(ERRLOG)
continually records
information
detected by the Executive or device drivers about hardware errors,
regardless of whether the error was recoverable (soft).
At user-determined intervals, another task, (PSE) can be run to format
the error information so that reports can be generated on some or all
of these errors.
Finally, the report generating task
(SYE)
produces reports on the
errors you select.
You can generate a wide variety of reports from
the data that Error Logging collects.
For example, you can specify a
report to cover a certain time period, a certain device or group of
devices, or a certain type of error. You can also request a
report
that contains only information on individual errors, only summary
information, or both.
The Executive automatically retries operations involving recoverable
errors.
However, you could be unaware that the error occurred, if it
was recovered, unless your system included Error Logging.
In summary, the Error Logging subsystem:
•

Gathers information from
about hardware errors

•

Stores the information in a file

•

Formats the information to produce an error report

•

Generates a report according to the user's specification

4.4.2

the

Executive

and

device

drivers

Power Failure Restart

handle
RSX-llM includes a power failure
restart
routine
to
intermittent short-term power fluctuations with minimal loss of
service or data. The routine operates in four phases:
•

When power begins to fail, the CPU traps to the Executive,
which stores register contents and halts system operations
with very little damage.

•

When power is restored, the Executive restores the preserved
state of the system, including the stored registers.

•

The Executive then reactivates the device drivers that were
active at the time of the power failure at their power-fail
entry points.
~rivers can be reactivated either:
1.

Whenever power fails, or

Only when power fails while the driver is
I/O request.

processing

The drivers can then restore their own state (repeat
transfer, for example).
•

an
I/O

The Executive then determines if any user tasks requests
notification of power failure.
(User tasks do this by
issuing a system directive that requests an AST on power
recovery.)
The Executive initiates ASTs for those tasks that
requested them.

4-5

CHAPTER 5
PROGRAM DEVELOPMENT

Program development on an RSX-llM system usually requires four steps:
l.

Creating a source file, using an RSX-llM editing program

Compiling or assembling the source file into an object
module, using an RSX-llM-supported compiler or assembler

Task Building (linking) the object module
create an executable unit called a task

Running the task

If errors occur in the program, it is necessary to add a
debugging the program.

modules

fifth

step:

This chapter describes some of the system resources available to
create, run, and debug RSX-llM tasks. Figure 5-1 summarizes the steps
invc)lved in creating a FORTRAN program.

5 .1

EDITIING UTILITIES

RSX·-llM provides two interactive utility programs to create and edit
sou1rce files. They are EDT (the DIGITAL Standard Editor) and EDI (the
line text editor). Some features of these editors are described
below.
The RSX-11 Utilities Manual contains complete information on
EDT and EDI.
··~

5.1.1

EDI

EDI uses buffers in operations to create and edit text files.
These
buffers control the amount of data EDI accesses at a time. It reads a
line or group of lines from an input file into an EDI buffer and
permits the user to edit the material in the buffer from the terminal.
When the material is edited, another terminal command can write the
data to a new file and read in another group of lines.

5-1

PROGRAM DEVELOPMENT

EDITOR

>FOR
COMPILER

---E:J
USER

OBJECT
MODULE

SYSTEM
LIBRARIES

>TKB
ONLINE
DEBUGGING
TOOL

TASK
BUILDER
........

TASK BUILDER
MAP
.......

.......

........

......

TASK IMAGE

SYMBOL
DEFINITION
FILE

>RUN

Figure 5-1

5.1.2

Ala~

EXECUTING
TASK

POST MORTEM
DUMP

Steps to Creating a FORTRAN Program

EDT

EDT permits you to create and modify text files or source programs, on
either a line or character basis. EDT also permits you to edit large
files without breaking them up into smaller sections.
Features of EDT include:
•

English language commands

•

Video or hard copy display

•

Online documentation of error conditions

•

File and buffer I/O

•

Maneuverable cursor (in character mode) and line
line mode)

5-2

pointer

(in

PROGRAM DEVELOPMENT
5.2

PROGRAMMING LANGUAGES

RSX-llM supports several programming languages, including:
•

MACH0-11

•

BASIC-11

•

BASIC-PLUS-2

•

COBOL

•

CORAL-66

FORTRAN IV AND FORTRAN IV-PLUS

Source programs must be created according to the requirements of the
language you are using.
MACR0-11 is the only language that is
distributed as part of the RSX-llM system.
Compilers or assemblers
for other languages are optional and must be purchased separately.

5.2.1

MACR<>-11

The MACR0-11 assembly language lets the programmer work directly with
the PDP-11 hardware.
MACR0-11 also allows the programmer to define
sections of code called macros with dummy values and to invoke them to
generate repetitive coding sequences.
The MACR0-11 assembler includes the following features:

5.2.2:

•

Program and command
functions

line

control

assembly

and

•

Specification of input and output device and file names

•

Error listing on output device

•

Formatted, alphabetized symbol table

•

Optional cross-reference symbol listing

•

Relocatable object modules

•

Global symbols to link separate object modules

•

Conditional assembly directives

•

Program section (.PSECT) directives

•

user-defined macros and macro libraries

•

System macro library

•

Indirect command files to control the assembly process

listing

BASIC-11

BASIC-11 is an easy-to-learn
abbre·vi at ions,
and
familiar
operaitions.

language that
mathematical

5-3

uses English words,
symbols
to perform

PROGRAM DEVELOPMENT

The BASIC-11 interpreter performs functions handled
compiler, and Task Builder for other languages.

the

editor,

Special features of BASIC-11 include:
•

Immediate executions of programs after input

•

Immediate mode operation for debugging programs and use
desk calculator

ASCII files compatible with FORTRAN

•

PRINT USING statement for formatting output

e String manipulation functions and dynamic allocation of string
storage
•

User-defined functions

•

CALL statements to pass data to assembly language subroutines

•

Graphics and laboratory peripheral support

5.2.3

BASIC-PLUS-2

BASIC-PLUS-2 is a compiled language that combines the execution speed
of a compiler with the ease of use and familiarity of BASIC-11. The
language is an extension of BASIC
used
in
many
commercial
applications.
Special features of BASIC-PLUS-2 include:

5.2.4

•

Virtual arrays

•

Enhanced string manipulation capability

•

Long variable names

•

Complete matrix functionality

•

IF ••• THEN ••• ELSE statements

•

ON ERROR GOTO statements

•

Statement modifiers

•

User-defined functions

•

Multistatement lines and multiline statements

COBOL

COBOL provides rapid
applications.
Source
COBOL-74.

data processing,
programs conform

5-4

primarily for
commercial
to the ANSI standard for

PROGRAM DEVELOPMENT
PDP-11 COBOL features beyond the ANSI standard include:
•

CALL sequences for external subroutines

•

String and substring manipulation capabilities

•

MERGE utility to combine ODS files

•

Reformatting utility to reformat source files

•

Report generator

5.2 • .S

CORAL-66

CORAL 66 is a high-level block-structured language, which performs
and
commercial
assembly
language
operations
in
industrial
applications.
The CORAL-66 compiler provides:
e

BYTE, LONG (32-bit integer) and DOUBLE 64-bit floating
numeric types

•

Generation of reentrant code at the procedure level

•

CORAL 66 programs can run on any RSX-llS system that
the Extended Instruction Set (EIS)

•

Programs can optionally select target PDP-11 instruction set

•

Optional code optimization

•

Option to check the bounds of array variables

•

Conditional compilation of defined parts of source code

•

INCLUDE keyword to
user-defined files

5.2.6

.'-'.

incorporate

CORAL

source

point)

includes

code

from

FORTH.AN-IV and FORTRAN IV-PLUS

RSX-llM supports two versions of PDP-11 FORTRAN:
FORTRAN-IV and
FORTRAN IV--PLUS. Both versions of FORTRAN meet the specifications of
ANSI Standard FORTRAN and include substantial extensions to those
speci.fications. The major differences betweeen the two FORTRANs are:
code,

which

FORTRAN IV-PLUS produces highly optimized
executes in less time than FORTRAN-IV code.

FORTRAN IV-PLUS can use the floating-point processor option.

FORTRAN IV-PLUS can produce shareable code.

Both FORTRAN language processors consist of a compiler and an Object
Time System (OTS)~
The OTS is a set of object modules that can be
Task Built with user programs to perform mathematical functions and to
detect errors when the program runs.

~·

RSX-llM also provides a set
control
subroutines
that
requirements.

of optional FORTRAN callable
meet Instrument Standard of

5-5

process
America

PROGRAM DEVELOPMENT
5.3

BUILDING THE TASK

The Task Builder creates an image called a task by linking one or more
object modules.
This image can then be installed and run, using MCR
commands.
The modules usually include the object module created by a
compiler or assembler,
and object modules containing system or user
library routines.
The Task Builder:
•

Links object modules

•

Resolves references to system
modules

•

Allocates virtual address space to the task

•

Produces an optional Task Builder map that describes memory
allocation, object modules, and global symbol references

•

Produces an optional Symbol Definition File

•

Builds an overlaid task

•

Maps the task to shared regions of memory

5.4

user

libraries

object

RUNNING THE TASK

To run a task on an RSX-llM system,
instructs the system to:

issue an MCR

RUN

command,

•

Locate the task image on the disk where it is stored

•

Load a copy of the image into memory

•

Execute the task

which

The RUN command includes options to run tasks at an exact time of day,
at a specific time
increment,
or at a time increment from another
clock parameter (at the next hour, minute,
second,
or clock tick}.
The command also permits you to
run the task immediately or to
install, run, and remove the task with one command.

5.5

DEBUGGING THE TASK

RSX-llM provides two system features
that can help programmers to
diagnose errors in programs.
The Online Debugging Tool (ODT} lets you
debug MACRO programs interactively, and the Post Mortem and Snapshot
Dump (PMD) analyzes data when a user task terminates abnormally.

5.5.1

ODT

ODT is an online debugging program which is incorporated into
when it is Task Built.

task

An ODT breakpoint allows the user to run and debug the task at the
same time.
The task runs to a predetermined point, the breakpoint.
There, the task stops and the user can examine and modify the contents
of task registers before continuing to run the task.
5-6

PROGRAM DEVELOPMENT
ODT permits the user to:
•

Print the contents of any memory location,
in octal,
and
examine them at the terminal.
(These contents can later be
altered with the RSX-llM Patch utility.)

•

Search for specific bit patterns in the object file.

•

Search for words that reference a specific word in the
f ifo.

•

Fill a block with a designated value.

object

Post Mortem and Snapshot Dumps

5.5.2

The RSX-llM PMD task provides a dump of a task's registers when the
task term}nates execution abnormally, or when a user program requests
a snapshot of the registers during task execution.
Programmers can
use these dumps to debug a program offline, when the program does not
use ODT.
PMD dumps provide the following information:
•

The task name and reason for the dump

•

The contents of the task's registers,
counter at the time of the dump

•

The devices and files being used at the time of the dump

•

The status bits, event flags, and I/O count for the task

•

The terminal that ran the task

•

The device and physical address of the task

•

The task's virtual memory allocation, in
bytes, RADIX-SO, or ASCII

5-7

stack,

octal

and

words,

program

octal

CHAPTER 6
FILES AND I/O OPERATIONS

This chapter introduces the RSX-llM file
basic aspects of I/O operations.

6.1

system

and

describes

some

RSX-llM FILE SYSTEM

In RSX-llM terminology:

6.2

•

A file is an owner-named area on a volume.

•

A volume is a magnetic medium that RSX-llM can recognize, such
as a disk, a DECtape, or a magnetic tape.

•

An operator is
system.

anyone

who

uses

maintains

the

RSX-llM

FILES-11

FILES-11 is an RSX-llM system task that oversees the storage and
handling of files on volumes.
Files-11 volumes are magnetic media
that have been specially formatted with an MCR command called
Initi.alize Volume (INITVOL). Volumes that are not in FILES-11 format
are described as foreign volumes.
Although FILES-11 cannot access
these foreign volumes directly, the Files Exchange Utility (FLX)
translates files from the foreign DOS or RT-11 format to FILES-11
format.
User tasks can also perform I/O operations on foreign
volumes, without using FILES-11. This is often necessary to handle
real-time applications.

6.2.l

File Ownership and Directories

The information that follows applies primarily to systems having
multiuser protection.
On nonmultiuser protection systems, users do
not have a password or UIC to identify their files.
However, they can
create UFDs with an MCR UFD command.
When a user receives authorization to use a multiuser protection
system and is given a UIC and a password, he or she also acquires a
default UFD. The default UFD, which has the same number as the UIC,
is in the format [g,m]. The user's group number is g, and the member
number within that group is m.
·

6-1

FILES AND I/O OPERATIONS

The UFO provides protection for user and system files on the system.
A user can use a file name that has already been used in another UFO
and the system will recognize it as the file of that name associated
with that UFO.
For example:
[303,33]CAT.MSE is not the same file as [303,13]CAT.MSE
All of the UFOs on a volume are listed in the volume's Master File
Directory
(MFD).
The name of the UFD in the MFD is a combination of
the group and member numbers, along with a file
type of
.DIR.
for
example, the UFD [303,12] becomes 303012.DIR in the MFD.
Both the MFD and the UFO contain the names of files as well as
pointers to each file's header. The file header contains information
about the physical location of the file segments.

File Protection

6.2.2

To access a file, you must know the UFO in which it is listed and
satisfy the conditions in a protection mask associated with the file.
The mask specifies four types of access allowed to four user groups.
The four types of access are:
•

Read access - user group indicated can read the file

•

Write access - user group indicated can write to the file

•

Extend access - user group indicated can extend the length
the file

•

Delete access - user group indicated can delete the file

The four user groups are:
•

System -- Tasks and users with a privileged UIC

•

Owner

•

Group
Tasks and users whose UIC is in the same group as the
file's owner

•

World -- All other tasks and users

Tasks and users running under the owner's UIC

File Specifications

6~2.3

To refer to a file in an RSX-llM command line, use a file specifier in
the following format:
volume: [g,m]filename.filetype;versionnumber
volume:
The volume holding the volume that contains the file.
[g,m]
The UFO in which the file is listed (the file owner).

6-2

FILES AND I/O OPERATIONS
f ilen.ame
The name of the file, as it appears in the UFO.
f iletype
An abbreviation describing the file's contents.
vers i.onnumbE!r
A number that differentiates between several copies of
file.

the

same

The file system uses the information in the file specification to
retrieve the file as directed by the command line in which the
speci.fication occurs. The same file specification is used with all
RSX-llM tasks, including compilers, editors, and the Task Builder.

6.2.4

File Manipulation

The Files-11 system disguises differences between files on different
types of volumes and enables you to transfer files from one type of
volume to another, without knowing how the file was originally
formc:1tted.
Before Files-11 can access a file, the volume containing the file must
be known to the system. Issue an MCR Mount command to perform this
operation.
Once the required volumes are ready, the user can
manipulate files with system utilities or user-written tasks. The
following sections describe some of the system utilities.

6.2.4.l PIP - The most commonly used file manipulation utility is the
Peripheral Interchange Program (PIP). The major functions of PIP are:

~·

•

Copying files from one Files-11 device to another

•

Deleting and Purging files

•

Renaming files

•

Listing User File Directories

6.2.4.2 Queue Manager - The Queue Manager and the associated Print
command handle the orderly operation of the line printer or other
despooling device. The Queue Manager maintains lists of files to be
printed and sends the files to the printer, usually in chronological
order. The Print command places the names of files in queues.
The major functions of the Queue Manager are to:
•

Control the operation of the system line printer or despooling
device

•

Control the format of line printer output. (for example, output
on special forms or standard line printer paper)

•

Prevent files from
monopolizing
printer
interrupting other line printer operations

6-3

resources

FILES AND I/O OPERATIONS
6.3

TASK I/O OPERATIONS

User tasks running on RSX-llM can
subroutines:

access

•

File Control services (FCS)

•

Record Management Services (RMS)

•

RMS-llK (a separate option that
files)

data

with

three

allows

you

use

sets

indexed

FCS and RMS software are to individual files what FILES-11 software is
to entire volumes. As discussed previously, FILES-11 routines oversee
the storage and handling of files on volumes. FCS and RMS, on the
other hand, oversee the storage and handling of data within each file.
They provide access to individual files,
impose logical structures
upon them, and maintain the integrity of the data they contain.
Through FCS or RMS, tasks access files on FILES-11 volumes and process
their contents, using either block-oriented or record-oriented I/O
operations.
Block-oriented operations treat files as arrays of
equal-sized
structures called virtual blocks.
The size of virtual blocks in a
file is determined by the type of volume containing the file. On disk
volumes, virtual blocks in all files always contain 512 bytes. On
ANSI-compatible magnetic tapes, in contrast, the user can specify
block sizes other than 512 bytes.
Record-oriented I/O operations treat files as collections of logical
records. The size of individual records is specified by the user.
(See the RSX I/O Operations Reference Manual for more
FCS and RMS.)

6.3.l

information

File Control Services (FCS)

•

FCS routines let you read and write files on FILES-11 structured
devices and process files as logical records.
You can write a
collection of data to a file in a way that allows it to be retrieved
at will.
You do not have to know anything about the format in which
the data was written. Therefore, FCS is transparent (invisible) when
you are using it.
FCS views the contents of a file as a continuous sequence of user
records
(see Figure 6-1).
The size of individual records is
determined by the user rather than by the physical medium.
FCS provides two access modes for storing and retrieving individual
records.
Sequential
mode stores successive records physically
adjacent to previous records and retrieves records, based on this
adjacency.
Random mode is permitted only for disk files containing
equal sized records. In this mode, tasks can read and write records
by specifying their relative position in the file.

6-4

FILES AND I/O OPERATIONS

Record Management Services (RMS)

6.3~2

RMS routines let you read and write files in one of three ways:
•

Relative

•

Sequential

•

Indexed

In sequential file organization (see Figure 6-1) records appear in the
same order in which they were created.
End of File

Record

Figure 6-1

Record

Sequential File Organization

In relative file organization, RMS creates a series of fixed-size
record cells.
The cells are numbered according to their location
relcttive to the beginning of the file. Each cell can contain a single
record.
However, empty cells can be interspersed among cells
containing records.
Figure 6-2 illustrates the structure of a
relc1tive f:ile.

'-'1

Cell No.:

[:c,ard

Record
2

Figure 6-2

4
Record
4

999

1000

Record

~-EMPTY~

999

Relative File Organization

The optional RMS-llK software permits a third type of file structure:
indexed file organization. Unlike the physical ordering of records in
a sequential file, or the relative ordering in relative files, indexed
file! organization is transparent to the program using it. Keys in the
recc1rds of the file, established by RMS-llK, determine the placement
of records in an indexed file. These keys, unique character strings
that appear in every record of the file, tell the operating system
where to look for the next record.
Figure 6-3 illustrates the
structure of an indexed file.

6-5

FILES AND I/O OPERATIONS

KEY DEFINITION

•----PRIMARY INDEX (Employee Name)---ABLE

ABLE

ELM AV

24379

....

JONES

: MAIN ST :

Figure 6-3

6.3.3

SMITH

19724

SMITH

HOLT RD :

35888

Indexed File Organization

Device Independence

RMS and FCS allow RSX-llM programmers to write code independent of the
physical characteristics of devices. Therefore, the programmer does
not have to know what devices the program will eventually use for
its
I/O operations.
Note,
however,
the requirement that random access
mode can be used only on disk files.
A program performs I/O on
Logical Unit Numbers (LUNs) that the programmer or operator assigns to
specific devices ahead of time.
An operator can subsequently issue an MCR command to change the
physical device used for I/O if the device fails, for example. This
command will redirect all I/O intended for one device to another of
the same type.
This redirection has no effect on LUN assignments;
FCS or RMS changes the LUNs transparent to the programmer.
You can also use logical devices to associate LUNs with physical
devices.
A task can assign a LUN to a logical device and then issue
an MCR command to associate the logical device name with a physical
device unit.
A logical device name does not correspond to a physical
device until a device is explicitly assigned to it.

6.4

PHYSICAL I/O OPERATIONS

Physical I/O operations involve the transmission of data between main
memory and connected peripheral devices.
In RSX-llM a connected
device cannot be operated unless there is software in memory for
that
device type. This software can be either an I/O driver or a user task
that connects directly to a hardware vector associated with the
device.
An I/O driver performs functions that enable physical I/O operations
to occur.
Drivers for most device types are built into the Executive
at system generation. RSX-llM includes drivers for all the supported
devices.
In addition, RSX-llM permits user-written I/O drivers for
nonstandard devices.
This capability is essential for
real-time
applications that communicate directly with devices such as production
or laboratory equipment (refer to the RSX-llM Guide to Writing an I/O
Driver for more information).

6-6

FILES AND I/O OPERATIONS
Some systems have devices that are used infrequently.
To avoid
wasting memory with permanent drivers that are seldom used, you can
select a system generation option to allow drivers to be loaded and
unloaded.
An alternative approach to drivers is the connect-to-interrupt vector
facility provided by the RSX-llM Executive. Using this facility, the
user task itself can receive the hardware interrupts generated through
hardware vectors dedicated to the device.

6-7

INDEX

ANSI, 5-5
Applications,
data acquisition, 2-1
laboratory and medical, 2-2
manufacturing monitor and
control, 2-2
process monitoring and
control, 2-1
.real-time, 2-1
Assemblers, 2-2
AS T' 3-9' 4-2

EDI, 5-1
EDT, 5-1, 5-2
ERRLOG, 4-5
Error log preformatter task
(PSE), 4-5
Error log report generating
task (SYE) , 4-5
Error logging subsystem, 4-4,
4-5
Error logging,
and device drivers, 4-5
and executive, 4-5
Errors,
recoverable, 4-5
Event flags,
group global, 3-9
local, 3-9
system global, 3-9
Executive, 3-1, 3-3, 3-4, 3-5
internal task scheduling, 4-2
Executive region, 3-7
Extended Logical Address Space,
3-10

B
'•

"-'

BASIC-11, 2-2, 5-3, 5-4
BASIC-PLUS-2, 2-2, 5-3, 5-4

c
Central Processing Unit (CPU),
3-3
Checkpoint, 3-5
Checkpoint files, 3-6
Checkpoint space,
dynamic allocation of, 3-6
static allocation of, 3-6
Checkpointing, 3-5, 3-7
Clock queue, 3-7
COBOL, 2-2, 5-3, 5-4
Compilers, 2-2
Computer languages, 2-2
Computer network, 2-3
CORAL-66, 2-2, 5-3, 5-5
CPU, 3-3

F
FCS I 1-2' 6-4
random files, 6-4
sequential files, 6-4
File, 6-1
File Control Services (FCS} ,
1-2' 6-4
File Exchange Utility (FLX} ,
6-1
File organization,
indexed, 6-5
relative, 6-5
sequential, 6-5
File ownership, 6-1
File protection, 6-2
File sharing, 2-3
File specifications, 6-2
FILES-11, 6-1, 6-4
Floating Point Processor, 5-5
FLX, 6-1
FORTRAN,
Floating Point Processor, 5-5
Process Control Subroutines,
5-5
FORTRAN IV, 2-2, 5-2, 5-5
FORTRAN IV-PLUS, 2-2, 5-3, 5-5

D
DEC Standard Editor (EDT), 5-2
DECNET-11,
device sharing, 2-3
file sharing, 2-3
program sharing, 2-3
Device independence, 6-6
Device sharing, 2-3
Device,
allocation of, 4-4
independence, 6-6
peripheral, 1-1
private, 4-4
public, 4-4
Directories,
User File (UFOS) , 6-1
DOS, 6-1
Dump,
Post Mortem (PMD), 5-7
Snapshot, 5-6, 5-7

H
Hardware interrupt vectors, 2-1
Host system, 1-1

Index-1

INDEX

0
I/O,
block oriented, 6-4
record oriented, 6-4
I/O driver, 6-6
I/O operations, 6-7
Indirect command files, 4-2
Initialize Volume (INITVOL), 6-1
INITVOL, 6-1
Interpreter, 5-4

L
Line Text Editor (EDI), 5-1, 5-2
Link, 5-1
Loadable program, 2-3
Logical address space, 3-10
Logical records, 6-4
Logical Unit Number (LUN), 6-6
LUN I 6-6

M
MACR0-11 Assembler, 2-2, 5-3
Mapped system, 3-1, 3-2
Master File Directory (MFD),
6-2
MCR, 1-4, 4-1
Indirect File Processor, 4-2
INITVOL command, 6-1
MOUNT command, 6-3
privileged commands, 4-1
RUN command, 5-6
symbol value substitution,
4-3
task scheduling, 4-2
user interface, 1-2
Memory, 3-1
partitions, 3-1
Memory layout, 3-7
Memory management unit, 3-1, 3-2
Memory Management Directives
(PLAS), 3-1, 3-10
MFD, 6-2
Monitor Console Routine (MCR),
1-1, 4-1
Multiprogramming, 1-1, 2-1, 3-3
Multiuser protection systems,
4-3, 4-4, 6-1

N
Network communication, 2-3
Nodes, 2-3
Nonmultiuser protection systems,
4-3
Nonprivileged users, 4-3

Object module, 3-2, 5-1
Object Time System (OTS), 5-5
ODT,
breakpoint, 5-6
Online Debugging Tool (ODT) , 5-6
Online Task Loader (OTL) , 1-2
Operating system,
disk based, 1-1
memory only, 1-1
multiuser, 1-1
real-time, 1-1
stand-alone, 1-1
Operator, 4-1, 6-1
OTL, 1-2

p
Partition, 3-1
types of, 3-2
Partitions,
characteristics of, 3-1
dynamic allocation, 1-2
mapped, 3-1, 3-2
subpartitions of, 3-2
system-controlled, 3-1, 3-2
unmapped, 3-1, 3-2
user-controlled, 3-1, 3-2
Password, 6-1
Peripheral Interchange Program
(PIP) I 6-3
Physical address space, 3-10
Physical addresses, 3-2
Physical links, 2-3
PIP, 6-3
PLAS Directives, 1-2
Power failure restart, 4-5
Print despooling device, 6-3
Priority, 3-5
swapping, 3-6
Privileged command, 4-1
Privileged terminal, 4-1
Privileged users, 3-5
Process inputs, 2-2
Process outputs, 2-2
Program development, 2-2 , 2-3 , 5-1
Program sharing, 2-3
Programmed Logical Address
Space (PLAS), 1-2, 3-10
Programming languages, 5-3
Programs,
concurrent execution of, 3-3
sequential execution of, 3-3
Protection,
delete access, 6-2
extend access, 6-2
mask, 6-2
read access, 6-2
write access, 6-2
PSE, 4-5

Index-2

INDEX

Q
Queme Manager, 6-3

R
Rec:ord Management Services
(RMS), 6-4, 6-5
RMS, 6-5
RMS-llK, 6-4
Round-rob:ln scheduling, 3-6
RSX-llS,
c:ompatibility with RSX-llM, 1-1
I/O Driver, 1-1
RSX-llM, 1-1
RT-·11, 6-1

s
Shareable code, 5-5
Significant event, 3-7
SIP, 1-2
Source file, 5-1, 5-3
SS'I~ I 3-9
STD, 3-4
STD Queue,, 3-6
Subpartitions, 3-2
Swapping, 3-6
SYE: I 4-5
Synchronous System Trap "(SST),
3-9
SYSPAR, 3·-7
System configuration, 1-1
System controlled partition, 3-2
System directive functions, 3-7,
3-8, 3-9
System generation,
:RSX-llS, 1-2
:RSX-llM, 1-1, 3-7
System Image Preservation
Program (SIP), 1-2
System programs, 3-1
System Task Directory (STD) , 3-4
System traps,
asynchronous (ASTS), 3-9
synchronous (SSTS), 3-9

Task execution,
external scheduling, 4-2
Task Image,
static, 3-10
Task priority,
Task Builder, 3-5
text editors, 3-5
Task,
activation of, 3-5
active, 3-4
base address of, 3-2
blocked, 3-4
concurrent execution, 2-1,
3-3, 4-3
debugging of, 5-6
dormant, 3-4
I/O Operations, 6-4
installed, 3-4
overlaid, 3-10
privileged, 3-2
ready-to-run, 3-4
resident, 3-2
state of, 3-4
Tasks, 1-1, 3-1
installed, 3-4
real-time, 3-5
Terminals,
attached, 4-3
operation of, 4-3
privileged, 4-1
slave, 4-4

u
UFO, 6-1
UIC, 4-4
Unmapped system, 3-2
User group,
group, 6-2
owner, 6-2
system, 6-2
world, 6-2
User Identification Code (UIC),
4-4
User programs, 3-1
User region, 3-7

T
Target system configuration,
1-1
Task, 5-1
Task Builder, 3-2, 5-1, 5-6

v
Virtual address space, 3-1, 3-10
Virtual addresses, 3-1
Virtual blocks, 6-4

Index-3

Introduction to RSX-llM
AA-25550-TC

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