ITS 1.5 Reference Manual
Massachusetts Institute of Technology
Artificial Intelligence Laboratory
MAC-M-377
July 1969
Artificial Intelligence
Memo No. 161A
(Revised 161, June 1968)
D. EastlakeAuthor of this memo, R. Greenblatt, J. Holloway, T. Knight, S. Nelson
This reference manual consists of two parts. The first (sections 1
through 6) is intended for those who are either interested in the
ITS 1.5 time sharing monitor for its own sake or who wish to write
machine language programs to run under it. Some knowledge of PDP-6
(or PDP-10) machine language is useful in reading this part. The
second part (sections 7, 8 and 9) describes three programs that
run under ITS. The first program (DDT) is a modified machine
language debugging program that also replaces the "monitor command"
level (where the user is typing directly at the monitor) present
in most time-sharing systems. The remaining two (PEEK and LOCK)
are a status display and a miscellaneous utility program. It
should be remembered that the McCulloch Laboratory PDP-6 and
PDP-10 installation is undergoing continuous software and hardware
development which may rapidly outdate this manual.
* * *
Work reported herein was supported by the Warren McCulloch
Laboratory, an M.I.T. research program sponsored by the Advanced
Research Projects Agency of the Department of Defense under Office
of Naval Research contract number N00014-70-A-0362-0002.
Reproduction of this document, in whole or in part, is permitted
for any purpose of the United States Government.
This manual was transcribed by David Carter from a scanned,
typewritten original between February 27, 2004 and March 10, 2004.
Effort has been put into being as accurate as possible in the
transcription process, but due to the condition of the original,
some errors have no doubt been made. Where there is uncertainty
about a particular character or word, a best guess has been made.
Please send any corrections to dcarter at sigfs dot org,
especially if you have page 19 of the original! The original file
came from
ftp://publications.ai.mit.edu/ai-publications/0-499/AIM-161A.ps so
refer to that if you're in doubt about anything.
This came from http://www.sigfs.org/its-reference/ so you should
check there for any updates. This file is available in PDF, HTML,
ASCII, LaTeX and the original LyX, so hopefully one of those
formats fits your need. If you convert this file to another
widely-used format, please send me a copy so I can post it.
Table of Contents
0.1 Introduction
0.2 Notation Used in this Manual
0.2.1 Numbers
0.2.2 Character Objects and Strings
0.2.3 Bit Positions and Intervals
0.2.4 Internal References
0.2.5 Other Conventions
0.3 Introduction to ITS
0.3.1 Preview of Section 1
0.3.2 Preview of Sections 2 and 3
0.3.3 Preview of Section 4
0.3.4 Preview of Section 5
0.3.5 Preview of Section 6
0.4 Introduction to DDT, PEEK, and LOCK
0.4.1 Preview of DDT
0.4.2 Preview of PEEK and LOCK
0.4.3 Preview of Appendices
Chapter 1 Transmitting Commands to ITS
1.1 Control Z
1.1.1 Control Z on an Idle Teletype
1.1.2 Control Z on an Active Console
1.2 Trapping Instructions
1.2.1 UUO's
1.2.2 Non-UUO Trapping Instructions
Chapter 2 The General Transaction of Input-Output
2.1 Philosophy and Organization
2.2 The .OPEN UUO
2.2.1 File Directories
2.2.2 The Translation Table
2.2.2.1 The .TRANS UUO
2.2.2.2 The .TRANAD UUO
2.2.2.3 The .TRANDL UUO
2.2.3 System Names
2.3 The .IOT UUO
2.3.1 The End of File Condition
2.3.2 The Device Full Condition
2.3.3 Non-Recoverable Data Errors
2.4 The .FDELE UUO
2.5 The .STATUS UUO
2.6 The Input-Output Channel Push Down Facility
2.6.1 The .IOPUSH and .IOPOP UUO's
2.6.2 The .IOPDL UUO
2.7 Miscellaneous Input-Output Related System Calls
2.7.1 The .CLOSE UUO
2.7.2 The .RESET UUO
2.7.3 The .ITYIC UUO
2.7.4 The .ACCESS UUO
Chapter 3 Properties of Particular Devices
3.1 File Structured Devices
3.1.1 The DSK, DKn, and Pnm Devices
3.1.1.1 Links
3.1.2 The UTn Devices
3.1.2.1 The .UDISMT UUO
3.1.2.2 The .ASSIGN and .DESIGN UUO's
3.1.2.3 The .UBLAT UUO
3.1.2.4 The .UTNAM UUO
3.1.2.5 The .UINIT UUO
3.1.3 The COM and SYS Devices
3.2 Unit Character Oriented Devices
3.2.1 The Tnm and TTY Devices
3.2.1.1 The .ATTY and .DTTY UUO's
3.2.1.2 The .LISTEN UUO
3.2.1.3 The Dial Feature
3.2.2 The LPT Device
3.2.3 The PLT Device
3.2.4 The PTP and PTR Device
3.2.4.1 The .FEED UUO
3.2.5 The COD Device
3.3 Robotic Oriented Devices
3.3.1 The NVD, TVC, and VID Devices
3.3.1.1 The .VSCAN and .VSTST UUO's
3.3.2 The OMX Device
3.3.2.1 The .ARMOVE and .ARMOFF UUO's
3.3.3 The IMX Device
3.3.3.1 The .POTSET UUO
3.4 Miscellaneous Devices
3.4.1 The DIS and IDS Devices
3.4.1.1 The .DSTART and .DSTRTL UUO's
3.4.1.2 The .LTPEN UUO
3.4.1.3 The .DCLOSE UUO
3.4.1.4 The .DSTOP UUO
3.4.1.5 The .NDIS UUO
3.4.2 The USR Device
3.4.2.1 The PDP-10
3.4.3 The CLA, CLI, CLO and CLU Devices
3.4.4 The ERR Device
3.4.5 The TPL Device
3.4.6 The NUL Device
Chapter 4 The Procedure
4.1 Philosophy and Organization
4.2 User Interrupts
4.2.1 The .SETM2 UUO
4.2.2 The .DISMISS UUO
4.3 The Core Allocator
4.3.1 The .CORE UUO
4.4 The Scheduler
4.5 The .SUSET UUO
Chapter 5 Procedure Interaction
5.1 The Hierarchical Organization of Procedures
5.1.1 Procedure Creation
5.1.2 Attaching Disowned Procedure Trees
5.1.3 The .UTRAN UUO
5.2 Controls over an Immediately Inferior Procedure
5.2.1 The .UCLOSE UUO
5.2.2 The .DISOWN UUO
5.2.3 The .USET UUO
5.3 Communication to an Immediately Superior Procedure
5.3.1 The .VALUE UUO
5.3.2 The .BREAK UUO
5.4 The .GUN UUO
Chapter 6 Miscellaneous System Calls and Features
6.1 The .LOGIN and .LOGOUT UUO's
6.2 Nonstandard Devices
6.2.1 The .RDSW UUO
6.2.2 The .RD760 and .WR760 UUO's
6.2.3 The .RD710 UUO
6.2.4 The .RD500 UUO
6.3 Various Times and the Date
6.3.1 The .RDTIME UUO
6.3.2 The .RTIME UUO
6.3.3 The .RDATE UUO
6.4 The MAR Feature
6.5 The System Job
6.5.1 The .SUPSET UUO
6.5.2 The System Going Down Feature
6.5.2.1 The .SHUTDN UUO
6.5.2.2 The .DIETIM UUO
6.6 Examining ITS
6.6.1 The .GETSYS UUO
6.6.2 The .GETLOC UUO
6.6.3 The .RSYSI UUO
6.6.4 The .EVAL UUO
6.7 The One Proceed Feature
6.8 Miscellaneous
6.8.1 The .SLEEP UUO
6.8.2 The .GENSYM UUO
6.8.3 The .IOTLSR UUO
6.8.4 The .SETLOC and .IFSET UUO's
6.8.5 The .MASTER UUO
6.8.6 The .REDEF UUO
Chapter 7 DDT
7.1 Introduction
7.1.1 When DDT Starts
7.2 Monitor Mode Commands
7.2.1 Logging In and Out
7.2.2 Inter User Communication
7.2.3 Inferior Procedures
7.2.4 Files and Input-Output
7.2.5 The Control-P Feature
7.2.6 Miscellaneous
7.3 Interrupt Level and Context Tree Commands
7.4 Error Comments
7.5 DDT Mode Commands
Chapter 8 PEEK
8.1 Introduction
8.2 Modes Available
8.3 IO Control
8.4 Miscellaneous
Chapter 9 LOCK
9.1 Introduction
9.2 Commands
Chapter 10 References
Appendix A System Calls in Numeric Order
Appendix B System Calls in Alphabetic Order
Appendix C Available Symbolic Devices in Alphabetic Order
Appendix D System Variables per User
Appendix E Relics of ITS's Past
Appendix F Further Sources of Information on ITS
Appendix G Illustrative Console Output
0.1 Introduction
The reader will find below in section 0.2 a few notes on the
notation used in this manual. This is followed in section 0.3 by
fairly extensive introductory and overview material on the
Incompatible Time Sharing system monitor (ITS), the body of the
information which appears in sections 1 through 6. Then in section
0.4 will be found a brief preview of the information appearing in
sections 7, 8, and 9 about the three programs DDT, PEEK, and LOCK
respectively. The first of these is a modified machine language
debugging program that replaces the "monitor command" level (where
the user is typing directly at the monitor) present in most time
sharing systems. The remaining two are of a status display and
miscellaneous utility nature. These three sections are each fairly
self-contained as opposed to any particular section of the six on
ITS which may be highly interdependent with other ITS sections.
Finally, in section 0.5, appears a summary of the appendices to
this manual.
It should be remembered that Project MAC, AI Group, PDP-6 and
PDP-10 installation is undergoing continuous software and hardware
development that may rapidly outdate this manual. Please direct
all corrections, additions or comments to the author at:
Donald E. Eastlake III,
Room 915,
545 Technology Square,
Cambridge, Mass. 02139
0.2 Notation Used in this Manual
0.2.1 Numbers
All numbers written in arabic numerals are octal except as follows:
1. those part of a name, such as a type "35" teletype
2. those part of the meta-structure of this manual (a page or
section number for example)
3. or those that are floating point, which will always have more
than one digit to the right of the decimal point such as 3.14159
For the meaning of numbers which appear to be floating point with
one digit to the right of the decimal point and which are not
section numbers, see section 0.2.3 below. Numbers that are written
alphabetically are decimal.
0.2.2 Character Objects and Strings
Character objects and strings are usually surrounded by quotation
marks ("") and are relatively clear from context. Non-graphic
characters typed by holding down the control key of a teletype and
striking a graphic are represented by the graphic preceeded by a "^"
as in ^A for "control-A". The special character alt.-mode (or escape
or prefix) is represented by "$".
0.2.3 Bit Positions and Intervals
Bit positions in thirty-six bit words (word length on the PDP-6
and PDP-10) are represented by the concatenation of a digit from 1
through 4, a ".", and a digit from 1 through 9. The first digit is a
quadrant number starting from the right or least arithmetically
significant part of the word. The second digit is a bit number in
the quadrant, also starting from the right or least significant
bit. Thus 1.1 is the lowest bit and 4.9 the sign bit.
Bit intervals are represented by the concatenation of an included
starting bit position, a "--", and an included terminating position.
Thus 3.3--3.1 is the lowest octal digit in the left half of a word.
0.2.4 Internal References
Most internal references in the text of this manual are of the
following form: [App x], [Ref x], and [Sec x]. These refer,
respectively, to the x'th appendix, the x'th item in the section
of this manual entitled "References", and the x'th numbered section
of this manual. Some internal references are written out in less
formality and combined forms are allowed, such as the following,
whose meaning should be evident: [Sec x, y], [App x; Ref x, y], etc.
0.2.5 Other Conventions
UUO's ("UnUsed Operations[Ref 1]) that trap to the system [Sec
1.2.1] to request action by it are frequently referred to as "
system calls". (This should not be confused with the .CALL subclass
of systems calls.) Individually they are written in all capital
letters with a preceding period. The reasons for this is that the
MIDAS [Ref 3] assembler has just these character strings (actually
the first six characters including the period) pre-defined as
symbols. In pronouncing them, the period should be ignored.
The use of the system calls described in this manual is frequently
illustrated by a short excerpt of pseudo-assembly-language. In
such examples, the tag CALL will appear on the line of the system
call in question. Frequently set-up instructions precede the call
to emphasize certain of its properties. They should not be taken
too literally.
0.3 Introduction to ITS
The Incompatible Time Sharing system (ITS) is a control program
tailored to the Project MAC Artificial Intelligence (AI) Group
PDP-6 and PDP-10 installation. It was designed in an attempt to
provide the following potential advantages of a time sharing system:
1. More than one person can perform tasks not requiring all
available computer resources with seeming simultaneity; one
person can similarly perform several tasks.
2. Simple device independent input-output facilities should
relieve the user of having to worry about hardware interface routines.
3. Jobs which would otherwise require excessive continuous blocks
of time can be performed automatically in small parts over long
periods of time at reduced priority.
4. Various debugging and other facilities can be designed-in using
the mechanisms necessary to protect user programs from each other.
To achieve these advantages and the particular goals of Project
MAC's AI Group, which require a high level of sophisticated
service to a limited number of users, ITS is designed with the
following properties:
1. ITS sits in control of the PDP-6 performing most input-output
for and allocating machine resources among various user programs.
2. All user programs reside in core storage so it is possible to
switch between programs with great rapidity and have
sufficiently short quanta to allow character response without
undue inefficiency. (Swapping of programs may soon be added but
it is expected that only dormant programs will be swapped out.)
A user may have many programs running for him "simultaneously".
3. ITS has a minimal direct user command facility to assure users
that they can maintain control over their programs. For the
utmost in flexibility almost all system actions are the result
of systems calls executed by the user's programs.
4. ITS attempts to provide not only simple standardized
input-output and other system calls but also much more complex
and specialized calls which reduce overhead or enable the use of
special devices and features.
MIDAS, a machine language assembler with macro facilities [Ref 3,
10], was chosen for writing ITS because of the resultant
efficiency, flexibility, ease in writing, and ease in debugging.
For information more detailed or more recent than this manual
consult the sources listed in Appendix F.
0.3.1 Preview of Section 1
The user of ITS normally commands a hierarchy of programs in
machine storage organized in an inverted tree. The top procedure
[Sec 7] is initially loaded for him by the system when he informs
it of his presence by typing a ^Z on an idle console [Sec 1.1.1].
All programs may have inferior procedures which they can control.
Almost all commands to the system are machine instructions [App A,
B; Ref 1], which trap to the monitor, executed for the user by his
programs [Sec 1.2]. The only exception is that he may interrupt
the superior procedure of the program with which he is conversing
by typing ^Z [Sec 1.2.1]. By this method the user can return to
his top procedure at which point ^Z's typed on his console are
ignored by the system.
0.3.2 Preview of Sections 2 and 3
The majority of the code in the ITS monitor is devoted to
input-output. It has been organized with such goals in mind as
flexibility, speed, and generality. Simple device-independent
system calls applicable to all devices where they are meaningful,
more complex but efficient calls applicable to most devices, and
specialized system calls enabling nearly full use of some special
devices are all available. Most devices are referenced
symbolically [App C] and procedures may cause symbolic
translations such that an inferior procedure referencing a
particular device will in fact get a different device.
Input-output may be done a character or word per system call or,
for less overhead per character or word, an arbitrary size block
of words may be transferred into or out of the user program's core
with one system call. The user program is not required to have any
buffers in its core image. Many special features relate to
consoles or special devices on the PDP-6 such as eyes, arms and
the DEC 340 display.
0.3.3 Preview of Section 4
A feature of the ITS monitor not frequently found in time sharing
systems and contributing greatly to its flexibility and generally
is that user programs may receive software implemented interrupts
in much the same way that ITS receives hardware interrupts. The
system is so designed that the user is rarely involuntarily
uninterruptable for more than a few hundred microseconds. If the
interrupt is dismissed in a normal manner the non-interrupt
portion of the program can proceed even from the "middle" of a
system call taking an arbitrary amount of time.
The ITS core allocator keeps a record of the status of each 2000
word block of memory and the 200 word sub-blocks into which some
of these are divided. It allocates and de-allocates memory for and
at the request of procedures and system input-output routines.
Most of its complexity is due to the lack of paging on the PDP-6
which makes it sometimes necessary to "shuffle" memory to provide
sufficient contiguous space for a procedure.
A scheduling algorithm is used which tries primarily to equalize
machine time used by each active procedure tree (console) and
secondarily to equalize machine time among those procedures in
each tree. The system variables related to a particular procedure
[App D] used by the scheduler and other parts of ITS are kept in
system memory and do not impinge on the user's core image.
0.3.4 Preview of Section 5
User programs operating within the environment provided by ITS are
organized (as mentioned in section 0.3.2) as inverted tree
hierachies. Superior procedures can retrieve and store words in
their inferior procedures as if they were input-output devices.
There also exists a large set of special system calls for
controlling procedures immediately beneath them and several
special ways that procedures may communicate with their superior
procedure. Buffered communication between arbitrary pairs of
procedures treating each other as input-output devices is also
provided [Sec 3.4.3].
0.3.5 Preview of Section 6
A large number of miscellaneous system calls and features exist
for a variety of purposes. Some provide easy input-output to
devices which do not fit the forms of standard ITS devices. Others
provide the use of certain hardware modifications to the PDP-6
which enable the simulation of certain features of manual control
of the PDP-6 such as address stop [Ref 1]. The remainder are such
minor but necessary functions as login and logout.
A special procedure, known as the system job, exists under ITS. it
performs various low priority functions for the system and can
check constant portions of ITS against a copy in an attempt to
detect some forms of system or hardware failure.
0.4 Introduction to DDT, PEEK, and LOCK
These three programs all run under ITS but are more closely
related to it than most other systems programs. The editor (TECO),
assembler (MIDAS [Ref 3]), list processing language (LISP), etc.
used by the Project MAC AI Group have also been modified to run
under ITS but have very similar non-time-sharing versions. PEEK
and LOCK would generally be meaningless outside ITS and while
there is a non-time-sharing DDT, the version for ITS has been very
extensively modified.
0.4.1 Preview of DDT
DDT originated as a general machine language debugging program on
the Digital Equipment Corporation PDP-1 computer. When the
hierarchical organization of procedures [Sec 5] and logical
simplicity of procedure origination of almost all system actions
[Sec 1.2] had been decided upon, the need for a conversational "
monitor command" program was recognized. An extensively modified
DDT, with commands relating to various ITS features and
modifications so as to be able to control multiple procedures was
the obvious answer. For historic reasons a top level modified DDT
under ITS is known as a "HACTRN".
0.4.2 Preview of PEEK and LOCK
The first of these utility programs, PEEK, is described in section
8 of this manual. It provides periodically updated displays or
printouts of various aspects of the time sharing system's status.
The second and smaller program, LOCK, is described in section 9 of
this manual. It performs a variety of miscellaneous functions,
some related to testing or debugging ITS.
DDT, described in section 7, is the normal means by which the user
may load and transfer control to these programs. Note that the
commands P, Q, and ? have the same meaning for both programs. The
? command causes each of them to print a list of their commands
with short explanations.
0.4.3 Preview of Appendices
The first three appendices to this manual are for cross-reference
and index usage (although important cross-references are
frequently included in the text [Sec 0.2.4]). Appendices A and B
list system calls [Sec 0.2.5, 1.2.1] in numeric and alphabetic
order, respectively, with the number of the manual section most
relevant to the call. Appendix C lists symbolicly referenceable
input-output devices in alphabetic order with the section or
sections most relevant to them.
Appendix D is nearly a direct extract from the source listing of
ITS. It is the initial "dummy" image of the user variable area, one
of which exists for each procedure [Sec 4, 5] in a system.
Appendix E, included for completeness, lists certain system calls
that are being phased out along with their replacements and short
descriptions of their functions.
Appendix F lists persons to consult for further information on ITS.
The last appendix, denominated G, gives a single console session
with ITS as an illustration in which the self documenting features
of DDT, PEEK, and LOCK are exercised.
Transmitting Commands to ITS
See also section 0.3.1.
1.1 Control Z
The only item of input-output data recognized by ITS directly as a
command is the character ^Z when received from an idle teletype or
from an active console, that is a teletype in control of a
procedure tree [Sec 5]. A teletype is a member of the class of
devices that may be consoles, currently either a GE Datanet 760
terminal or a KSR 35/37. Teletypes may also be in use as ordinary
devices (as Tnm instead of TTY [Sec 3.2.1]) in which case ITS
ignores ^Z's typed on them.
1.1.1 Control Z on an Idle Teletype
If the teletype is idle, ^Z normally causes the teletype to become
a console and loads and starts as its top level procedure [Sec
5.1, 7] the dump file named "@ HACTRN" on device SYS, or if not
found there from device UT2 (see section 2.1 for a discussion of
file and device names). The JNAME of a thus initiated procedure is
HACTRN and its UNAME and SNAME are set to the value minus 1 [Sec
2.2.3, 5.1; App D]. This will not happen if there is insufficient
memory available or if too many people type ^Z simultaneously. ITS
will echo a ^Z typed on an idle teletype if and only if it
succeeded in starting a top procedure. If a failure to start a top
procedure is due to a lack of memory, a console free message will
be typed out [Sec 6.5].
1.1.2 Control Z on an Active Console
The effect of ^Z in the second case, that of an active console, is
intended to be such that the user at the console may cause control
of his console to revert to higher level procedures and ultimately
to his top level procedure even in the face of hostile inferiors.
A ^Z typed on an active console is ignored by ITS if the console
is being controlled by its top level procedure. Otherwise it sets
a flag associated with the console so that it may not be assigned
downward in the procedure tree [Sec 3.2.1.1]. This flag is cleared
only by typing any character other than ^Z on the console. ITS
also sets the ^Z interrupt bit, a class on interrupt [Sec 4.2],
for the procedure controlling the console and possible for an
arbitrary number of procedures, each the immediate superior of the
last, extending upward in the tree from the procedure controlling
the console. The condition for each step upward in the procedure
tree is that either the superior to the procedure having its ^Z
interrupts bit set is stopped or the current procedure was found
to already have its ^Z bit on.
Action on ^Z interrupt bits set will be taken in less than one
quantum time when the scheduler [Sec 4.4] next runs.
1.2 Trapping Instructions
With the exception of ^Z all commands to ITS are given by
instructions which trap to the monitor. All valid commands are
from a class of instructions called UUO's which are characterized
by an initial octal digit of 0. These are discussed in section
1.2.1 and listed in Appendices A and B. Section 1.2.2 concerns all
other trapping instructions. It is a useful characteristic of the
PDP-6 and PDP-10 that an identical effective address calculation
is performed on all words fetched as instructions regardless of
their operation code or legality [Ref 1]. Thus indexing and
indirect addressing are available on all trapping instructions.
Interrupts to the monitor as a result of conditions encountered in
the execution of an instruction (such as memory protection
violation, AR overflow, PDF overflow, etc) rather than the type of
instruction are discussed in section 4.2.
1.2.1 UUO's
The instruction as instructions or words with an operation code
[Ref 1] of from 000 to 077 normally results in the instruction
word being stored in absolute location 40 modified by having had
its effective address computed and stored in its address field and
its indirect and index fields cleared. The instruction in absolute
location 41 is then executed. Since all ITS system calls utilize
only UUO's 040 through 047 the Project MAC AI Group's PDP-6 has
been modified so that UUO's 001 through 037 and 050 through 077
will trap, as described above, but directly to the user program's
relocated core image with no extra overhead. UUO 000 will also
appear to trap to the user but this occurs via monitor simulation
that checks to see if relocated location 41 directly addresses
(indexing or indirect addressing ignored) a location between 20
and the location 6 less than the top of the user's core image
inclusive. If so, a JSR to that location is simulated. If not, the
user's illegal instruction interrupt bit, a class two interrupt
[Sec 4.2], is turned on and a schedule [Sec 4.4] immediately performed.
Complete lists of system calls appear in numeric order in Appendix
A and in alphabetic order in Appendix B. However, a list
classified by operation code is listed here:
UUO Symbol Description
040 .IOT Executed for each item or block of data transmitted between
a user program and a symbolic input-output device [Sec 2.3].
041 .OPEN Used to initialize input-output between a device and a
program [Sec 2.2].
042 .OPER A class of system calls further decoded by the value of their
effective address.
043 .CALL A class of system calls further decoded by the value of their
accumulator field.
044 .USET Executed by procedures to examine and set some of the system
variables associated with their inferior procedures [Sec 5.2.3].
045 .BREAK Executed by a procedure to signal its superior [Sec 4.3.2].
046 .STATUS Used to ascertain the status of an input-output device, channel,
or transfer [Sec 2.5].
047 .ACCESS Used in input-output to randomly addressable devices [Sec 2.7.4].
ITS system calls were designed to be numerically rather than
symbolically decoded to decrease their cumbersomeness and increase
monitor efficiency.
1.2.2 Non-UUO Trapping Instructions
The only other trapping instructions are those whose first octal
digit is 7 and the instruction JRST with the 10 or 4 bit on in its
accumulator field [Ref 1]. The first of these two includes all
instructions which effect hardware input-output and most of those
affecting the state of the PDP-6 instruction processor (including
user/executive mode). In the second the 10 and 4 bits respectively
dismiss a hardware interrupt and stop the PDP-6. The execution of
any of these trapping instructions causes an illegal instruction
interrupt to the user (a class two interrupt [Sec 4.2]) unless the
user's procedure is in iot-user mode [Sec 5.8.3]. The remaining
way to affect the state of the processor is a JRST instruction
with the 2 bit on in the accumulator field; however, in user mode
this will not effect the state of the user, special or iot-user
[Sec 6.8.3] modes except that it may turn off iot-user mode.
The General Transaction of Input-Output
2.1 Philosophy and Organization
[original document missing page 19 here]
user core image input-output is negligible in comparison to any
significant processing of the data. Using system buffers has the
following advantages:
1. The user may be interrupted, swapped out, moved in core, or
otherwise molested during an .IOT [Sec 2.3] as it is the
software transfer of data between system buffers and his core.
2. Real input-output transfers may proceed without consideration
of the state of the user program they are occuring for as they
are into or out of system controlled memory.
3. Higher memory efficiency is obtained due to the dynamic nature
of major file device buffers. Even for devices with fixed
buffers, such as the line printer, only one large buffer need
exist regardless of how many programs that could use the device
are in the system.
4. User programs need not concern themselves with the size of
physical blocks on devices.
Some devices do not fit this framework very well and system calls
relating to them are not included in section 6. Miscellaneous
calls and special features related to particular symbolic devices
are, however, included under the device in section 3.
2.2 The .OPEN UUO
CALL: .OPEN CHNUM,FILNAM
;error return
;normal return
FILNAM: MODE,,(SIXBIT /DEV/)
SIXBIT /FILNM1/
SIXBIT /FILNM2/
Input-output on a particular channel is initialized by executing a
.OPEN. The channel is numerically specified by the accumulator
field of the .OPEN (CHNUM in the illustration above) and any
previous transfer of that channel is terminated as if by a .CLOSE
[Sec 2.7.1]. If the user is interrupted [Sec 4.2] during a .OPEN
the channel may have been closed and not yet reopened. The
effective address of the .OPEN should point to the first word of a
block of three words in the user's core image which specify a
device, mode, and file. The second two words specify the two file
names (FILNM1 and FILNM2 in the above illustration). As a
convention, the file names are usually thought of as up to six
left-justified sixbit characters rather than thiry-six bit
quantities. Some devices ignore the supplied file names. Other
devices augment the file names by the procedure's system name as
explained in section 2.2.3 below. These properties are indicated
in the device descriptions in section 3. The first word has the
three character sixbit device name in its right half (DEV in the
above illustration) and the direction and mode in its left.
Immediately below are the standard mode bits from this left half.
Bit(s) Meaning
4.9 Always ignored.
4.8-3.4 Device dependant but using zero should be safe.
3.3 \Rightarrow 1Image mode.
\Rightarrow 0ASCII mode, alias character mode.
3.2 \Rightarrow 1Block mode.
\Rightarrow 0Unit mode.
3.1 \Rightarrow 1Output.
\Rightarrow 0Input.
The device and file specified will be altered by entries in the
translation table [Sec 2.2.2] made by either the procedure or any
of its superior procedures. Because of this translation and the
symbolic nature of .OPEN, it is one of the slower ITS system calls.
If the .OPEN is successful it will skip the immediately following
instruction. If not successful it will not skip and will set a "
most recent channel in error" system variable associated with the
procedure to the channel number on which the .OPEN was attempted.
The reason for the failure may be ascertained with a .STATUS [Sec
2.5] or via the ERR device [Sec 3.4.4]. Zero file names are not
allowed on many devices and attempts to use them will cause the
.OPEN to fail. Any .OPEN closes previously opened devices on that
channel whether or not the .OPEN is successful.
2.2.1 File Directories
For devices with true file structure a file directory of the
device may be read by trying to input the file with the name ".FILE.(DIR)"
. If character mode is used, a readable file directory terminated
by a ^L and ^C results. If this pseudo-file is read from the DSK,
DKn, or Pnm device, only files with the system name [Sec 2.2.3] of
the reading procedure will be listed. Both block and unit modes
are available [Sec 2.3]. For non-file devices character input of
this file name will yield the string "NON-DIRECTORY DEVICE".
Attempted binary input will fail (the .OPEN will not skip) except
for the UTn devices [Sec 3.1.2] and the DSK family of devices [Sec
3.1.1, 3.1.3] where an actual device dependant binary of the
directory will be read. For the DSK family of devices a
pseudo-file "M.F.D. (FILE)" is also recognized by the system and
yields a list of the system names [Sec 2.2.3] for which
directories exist on the disk. In general files may be written
with these pseudo-file names and then renamed [Sec 2.4] so their
contents can be read back.
In an ITS-produced readable file directory, an "*" by a file name
indicates the file is inaccessible. This may be due to the fact
that it is just then being written or it may have been deleted
while open for reading and will vanish when closed.
2.2.2 The Translation Table
Entries in the translation table may be made or deleted by any
procedure and have effect only at .OPEN time for the procedure
making the entry and its inferiors. The entry consists of the following:
1. The UNAME and JNAME of the procedure making the entry
2. The JNAME of the procedure it is to apply to ("*" means all JNAME's)
3. Whether it is to apply to input, output, or both
4. Whether its resultant is to be considered final or be retranslated
5. The from device and pair of file names, where "*"s in from
positions match any device or file name
6. The to device and pair of file names, where "*"s in to positions
indicate no substitution
At .OPEN time all entries in the table are examined to see if the
device and file names of the .OPEN and the UNAME and JNAME of the
procedure executing the .OPEN match them. If so and the procedure
which made the entry is the same or superior to the procedure
executing the .OPEN, the substitution for device and file names
specified by the entry is made and unless prohibited by the entry
this process is repeated. Should eight successful and sequential
translations be made the .OPEN will fail leaving a "too many translations"
indication [Sec 2.5] and no further attempt will be made to translate.
2.2.2.1 The .TRANS UUO
CALL: .TRANS FILNAM
;error return
;normal return
FILNAM: MODE,,(SIXBIT /DEV/)
SIXBIT /FILNM1/
SIXBIT /FILNM2/
This system call is expected to point to a three word block in the
same manner as a .OPEN [Sec 2.2]. It normally skips and returns
with the block replaced by its translation (the block pointed to
by a .OPEN is never changed by the execution of the .OPEN). If too
many levels of translation are required it will not skip and the
block will be unchanged.
2.2.2.2 The .TRANAD UUO
CALL: .TRANAD TBLOCK
;error return
;normal return
TBLOCK: UNAME ;UNAME of procedure making & subject to entry
JNAME ;JNAME for procedure subject to entry
ATMIO,,DEV1 ;4.9 = 0 \Rightarrow retranslate
;4.9 = 1 \Rightarrow atomic, don't retranslate
;3.2 = 1 \Rightarrow applies to output .OPEN's
;3.1 = 1 \Rightarrow applies to input .OPEN's
;DEV1 = from device
FN11 ;from file names
FN12
,,DEV2 ;to device
FN21 ;to file names
FN22
This system call makes new entries in the translation table. All
information for the entry is specified by an eight word block
pointed to by the UUO (TBLOCK in the illustration above). Before
trying to insert a new entry in the translation table, this system
call simulates a .TRANDL pointing at the same block to eliminate
redundant entries. If a .TRANAD is successful in creating an entry
it skips. If not, because the first entry in the block is
incorrect or the translation table is full, it returns without skipping.
2.2.2.3 The .TRANDL UUO
This system call deletes entries in the translation table and
normally points at an eight word block identical to the one which
was used by the corresponding .TRANAD. See section 2.2.2.2
immediately above for the contents of this normal block. If may,
if appropriate, modify the ATMIO bits of an entry for both input
and output to delete one or the other. It skips if successful in
deleting an entry or removing one of the directions to which it
applies. If it effects no change in the translation table, it
returns without skipping. It also has a special form where the
first work of the block is zero (not a possible UNAME). In this
case all entries previously made by the procedure doing the
.TRANDL relating to the JNAME in the second word of the block are
deleted. This special form always skips and does not examine the
remaining six words of the block.
2.2.3 System Names
In order to distinguish the files of different users of ITS on
shared devices with common file directories a third file name is
used. This file name is referred to as a procedure's "system name"
or SNAME.
In reading, writing, deleting, etc. files on the DSK and related
devices [Sec 3.1.1] and on the core link devices [Sec 3.4.3], ITS
obtains a third file name from the SNAME [App D] associated with
the procedure. This variable is set, when the procedure is
initially created, to the common UNAME [App D] of the procedure
tree [Sec 5.1] the procedure is in. This is normally the name the
user has logged in as [Sec 5.1] so his procedures will initially
refer to his files. However, a procedure may examine and change
its own SNAME by means of an .SUSET [Sec 4.5] and may examine and
change the SNAME of any of its inferiors with a .USET [Sec 5.2.3].
The system name facility is also used to simulate certain
pseudo-devices as explained in sections 3.1.3 and 3.4.5.
2.3 The .IOT UUO
;unit mode
CALL: .IOT CHNUM,DATLOC
;return
DATLOC: ;place char or word read into or written from
;block mode
CALL: .IOT CHNUM,PNTR
PNTR: --LENGTH,,DATLOC ;pointer, modified during transfer
DATLOC: BLOCK LENGTH ;block read into or written from
All actual data transfers to or from devices being handled via
input-output channels are initiated by .IOT's. The accumulator
field of a .IOT should contain the number of an input-output
channel (CHNUM in the above illustrations) that has been set up
for transfer in a particular mode between the procedure and a
particular device by a successful .OPEN [Sec 2.2]. If the channel
has not been .OPEN'ed the procedure will receive an input-output
channel error interrupt (a class two interrupt [Sec 4.2]). Also
the number of the channel on which the .IOT was attempted will be
remembered as the most recent erroneous channel for use by the ERR
device [Sec 3.4.4]. The effective address of a .IOT is used
somewhat differently depending on whether the channel is open in
unit or block mode.
For unit mode (the first of the two illustrations above) the
effective address points to a word to be written from or read
into. For character unit modes the character is right justified
and the rest of the word is ignored on output and zeroed (except
as mentioned in section 2.3.1 on input. Some devices, which are
classified as input, use the contents of the effective address as
an argument to determine what they will store back (see devices
IMX, VID, and NVD).
Block modes always read or write to a contiguous block of words.
The contents of the effective address of the .IOT is interpreted
as having minus the length of the block in its left half and the
address of the first word in its right half (see second
illustration above). Block mode normally treats each word in the
block identically to the corresponding unit mode except that block
character modes pack five characters of seven bits per word left
adjusted. The block pointer word pointed to by the .IOT is
advanced as the transfer progresses so that if it completes the
left half will be zero and the right half will point to one
greater than the last word processed. If a procedure is
interrupted out of a block mode .IOT the pointer word will reflect
the progress of the transfer when it was interrupted.
Block character input-output from some devices which are naturally
one character at a time is limited to blocks of length 77777 words
or less and the top three bits of the pointer word are used during
the transfer as a character count.
When a .IOT returns to the user without causing an input-output
channel error, the transfer it requested will have been completed
for unit mode input or output or block mode output. For block mode
input, the count in the pointer word will indicate the amount
transferred which may be less than that requested if an end of
file is reached [Sec 2.3.1].
2.3.1 The End of File Condition
For devices on which the end of file while reading condition is
meaningful it is signaled to the user in various ways depending on
the transfer mode. For character devices in the character at a
time mode a ^C will be read with the left half of the word read
into set to minus one. In block character mode the last word will
be filled out with ^C's. Usually the pointer word will not have
counted out as the end of file did not occur on a block boundary.
For word devices, the user must normally determine the logical end
of file from the data being read although physical end of file is
detectable in block mode by the lack of advancement of the pointer
word. On some devices, attempts to read beyond an end of file will
cause the input-output channel to be automatically .CLOSE'ed [Sec
2.7.1] and further .IOT's will cause input-output channel errors
(class two interrupts [Sec 4.2]).
When packed characters are being read from a word device the
physical block is normally filled out with ^C's but some older
files on DEC tape [Sec 3.1.2] are filled out with the character
whose ASCII value is 141 ("a"). The end of file character for a
particular file can be determined after the file has been opened
by putting the number of the input-output channel it is open on in
the accumulator specified by an .EOFC. This channel number will be
replaced with the end of file character for that channel by the
execution of the .EOFC. See following illustration:
MOVEI AC,CHNUM
CALL: .EOFC AC, ;replaces CHNUM in AC with eof character
;return
2.3.2 The Device Full Condition
Attempted output on a full file structured device (UTn, DSK)
results in an input-output channel error (a class two interrupt
[Sec 4.2]) for the outputing procedure. This interrupt will occur
for the .IOT that failed in such a way that it may be successfully
resumed if the procedure's interrupt routine or some other
procedure deletes material from the full device. The channel on
which the error occured is saved by ITS for the ERR device.
2.3.3 Non-Recoverable Data Errors
ITS normally encounters non-recoverable data errors when reading
into its buffer for the user asynchronously with any UUO's by the
user. After a fixed number of attempts it accepts the possible
erroneous data which it will later give to the user if her reads
far enough. It also sets a flag related to the channel so the next
.IOT performed on it will give an input-output channel error
interrupt. The purpose of this flag is to avoid giving the user a
channel error interupt with no indication of which channel it is
on. The user's program may return to the .IOT and continue reading
the file after handling the interrupt.
2.4 The .FDELE UUO
The system call .FDELE is used for deleting and renaming files. It
points at a five word block which, for the three types of
.FDELE's, contain the following:
CALL: .FDELE FBLOCK
;error return
;normal return
;file delete
FBLOCK: ---,,DEV ;device on which to find file
FN1 ;names of file to be deleted
FN2
0 ;zero
--- ;unexamined
;normal file rename
FBLOCK: ---,,DEV ;device on which to find file
FN11 ;old file names
FN12
FN21 ;new file names
FN22
| ;rename of file while open for writing
FBLOCK: --- ;unexamined
CHNUM ;channel on which open
FN1 ;new file names
FN2
An .FDELE on a device that is not truly file structured has no
effect but skips as do all successful effective .FDELE's. If a
.FDELE does not skip the reason for its failue may be determined
with a .STATUS as though the .FDELE had been a failing .OPEN on
channel zero [Sec 2.5].
2.5 The .STATUS UUO
CALL: .STATUS CHNUM,DATLOC
;return
DATLOC: ;location status information is stored in by call
The accumulator field of this system call is the number of an
input-output channel (CHNUM in the above illustration) whose
status word replaces the contents of the effective address (DATLOC
in the above illustration) of the UUO. This status word is
described in detail by the tables below; however, its general
composition is as follows:
* The left half relates to the channel and it set by failing
.OPEN's, failing .FDELE's and input-output channel errors
* The right half relates to the device, if any, open on the
channel and the state of the transfer between it and the user.
Bit(s) Meaning
1.1-1.6 ITS physical device code (see table below).
1.7-1.9 Mode in which device was opened.
2.1 1 \Rightarrow buffering capacity empty.
2.2 1 \Rightarrow buffering capacity full.
2.3-2.9 Device dependent.
3.1-3.6 Set by failing .OPEN's and .FDELE's
3.7-3.9 Set by interpreted display [Sec 3.4.1]
input-output channel errors (see table below).
4.1-4.5 Set by non-display input-output channel
errors (see table below).
4.6-4.9 Always zero.
The following is a table of ITS device codes (note that the 40 bit
indicates that the file names used are significant and the 20 bit
indictes a software device):
Code Symbol Device
1 Tnm Teletype (KSR 35/37).
2 Tnm GE display and keyboard.
3 LPT Line printer.
4 VID Old vidisector ""(TVB).
5 NVD New vidisector ""(TVC).
6 PLT Calcomp plotter.
7 PTP Paper tape punch.
10 IMX Input multiplextor (A-D).
11 OMX Output multiplexor (D-A).
12 PTR Paper tape reader.
13 DIS DEC 340 display.
14 IDS Interpreted display.
15 COD Morse code transmitter.
16 COD Morse code receiver.
21 NUL Null device.
41 UTn DEC tape.
43 DSK 2311 disks.
60 USR A not immediately inferior procedure.
61 USR An inferior procedure.
62 CLx Core link device.
63 --- The directory service [Sec 2.2.1].
64 USR PDP-10 device.
The following is a list of the codes left by failing .OPEN's and .FDELE's:
Code Reason
1 No such device.
2 Wrong direction.
3 Too many translations.
4 File not found.
5 Directory full.
6 Device full.
7 Device not ready.
10 Device not available.
11 Illegal file name.
12 Mode not available.
13 File already exists (attempted rename).
14 Bad channel number (attempted open rename).
15 Link depth limit exceeded (DSK).
16 Pack not mounted (Pnm).
17 Directory not now available.
20 User doesn't exist (DSK or USR).
21 Local service only.
The following are the error codes left by the 340 interpretive
display routines:
Code Meaning
1 Illegal scope mode.
2 Scope hung.
3 More than 2000 words scope buffer.
4 Memory protection violation.
5 Illegal scope operation.
6 Memory protection violation on PDL pointer.
7 Illegal parameter set.
The following are the non-display input-output channel error codes:
Code Meaning
3 Non-recoverable data error on read [Sec 2.3.3].
4 Non-existant sub-device (such as IMX channel [Sec 3.3.3]).
5 Over .IOPOP [Sec 2.6.1].
6 Over .IOPUSH [Sec 2.6.1].
7 Channel does not have a procedure open on it.
8 Channel not open.
9 Device full [Sec 2.3.2].
2.6 The Input-Output Channel Push Down Facility
For greater flexibility in input-output than that available with
the basic input-output channel system [Sec 2.1], a facility is
provided whereby a limited number of input-output transactions may
be stored for later resumption. Meanwhile the channel they were
being effected on may be otherwise utilized.
2.6.1 The .IOPUSH and .IOPOP UUO's
CALL: .IOPUSH CHNUM, ;push channel number CHNUM
;return
CALL: .IOPOP CHNUM, ;pop channel number CHNUM
;return
These instructions treat input-output channels as the PUSH and POP
instructions [Ref 1] do memory locations. A channel may be
.IOPUSH'ed regardless of whether it is open or not and any
transfer in progress on it will be inaccessable until the slot
occupied by the information pushed is .IOPOP'ed (possible by
.IOPDL [Sec 2.6.2]) into a channel (possible different from that
from which it was .IOPUSH'ed). The error status and .ACCESS [Sec
2.7.4] pointer for a channel are also correctly stored and
restored. Executing a .IOPOP into a channel first .CLOSE's the
channel. Each procedure's input-output channel push down list [App
D] has space for eight entries.
2.6.2 The .IOPDL UUO
CALL: .IOPDL ;reset input-output channel pdl
;return
This system call takes no arguments and is intended to reset a
procedure's input-output channel push down list. Entries on a
procedure's input-output channel push down list actually contain
the number of the channel that was pushed to produce the entry.
This information is used only by .IOPDL whose execution is
equivalent to the number of .IOPOP's [Sec 2.6.1] equal to the
number of entries in the procedure's input-output push down list
and which .IOPOP each entry back into the channel from which it
was .IOPUSH'ed.
2.7 Miscellaneous Input-Output Related System Calls
The following system calls relate to most or all devices handled
via input-output channels.
2.7.1 The .CLOSE UUO
CALL: .CLOSE CHNUM, ;close input-output channel
;return
This system call closes the input-output channel whose number
(CHNUM in the above illustration) is in its accumulator field. It
has no effect if the channel is not open. Executing a .IOT on the
channel without reopening it will result in an input-output
channel error. For devices with true file structure it is at close
time that a file with the same name as one being written is deleted.
2.7.2 The .RESET UUO
CALL: .RESET CHNUM, ;reset input-output channel
;return
This system call is intended to reset system buffer pointers so
that buffered data on an input-output channel (specified by the
accumulator field as with CHNUM in the above illustration) will be
ignored. It is currently implemented for the following devices:
Tnm, TTY, LPT, PLT, PTR, TVC, and USR. For the USR device it has
special effects [Sec 3.4.2].
2.7.3 The .ITYIC UUO
MOVEI AC, CHNUM ;set up for channel number CHNUM
CALL: .ITYIC AC, ;get interrupt character
;error return ;none available
;normal return ;got one
It is frequently desirable to examine the characters of an
incoming stream at the interrupt [Sec 4.2] level of a procedure
(for "quit" features, etc.). This system call provides the facility
to read these characters from channels on which devices are open
that will provide appropriate interrupts (TTY and Tnm). The
accumulator referred to by an .ITYIC should have an appropriate
channel number placed on it (see illustration above). The
execution of an .ITYIC will then replace this number with the
character read and skip. If no character is available the .ITYIC
will return without skipping and if an improper channel is
specified the procedure will receive an illegal instruction interrupt.
2.7.4 The .ACCESS UUO
CALL: .ACCESS CHNUM,LOC ;set channel pointer to value LOC
;return
This system call is intended to be used in accessing randomly
addressable devices. A pointer is associated with each
input-output channel which is set to the effective address of a
.ACCESS executed with the channel's number (CHNUM in the above
illustration) in its accumulator field. This pointer is set to
zero whenever the channel is closed. Currently this pointer
influences only the USR device [Sec 3.4.2] but it is hoped that
random access will be added to the disk [Sec 3.1.1] routines soon.
Properties of Particular Devices
Properties and system calls related to particular devices handled
via input-output channels are discussed below. Lower case letters
in a device name indicate that there are several devices
distinguished by numeric digits in their place. The phrase "all
standard modes" in descriptions below implies that all combinations
of ASCII/image and unit/block modes are available and that ASCII
mode implies seven bit ASCII characters and image mode thirty-six
bit binary words.
3.1 File Structured Devices
3.1.1 The DSK, DKn, and Pnm Devices
These symbolic devices represent IBM 2311 units attached to the
PDP-6. These disks are characterized by interchangable disk packs.
A single logical directory is maintained by the system for the
entire disk volume. Files are identified by two names [Sec 2.2]
and a system name [Sec 2.2.3]. If a file is being read, which of
the above symbolic device names is used is entirely immaterial.
There are some special aspects to reading directories from these
devices as explained in section 2.2.1.
If a file is being written, the DSK device will physically write
it on a particular drive whose number is assembled into the
system. In contrast the DKn device will write the file on the n'th
drive. The Pnm device will try to write on a pack with a
particular two digit number.
The actual directory for these devices consists of a master
directory for each drive and a user directory for each system name
that has been used to write files on the disk. The maximum number
of user directories is one hundred. The maximum number of files
per user is not fixed as the area in a users directory, used to
describe the location of the blocks each file consists of is
dynamically allocated. When as is occasionally necessary a garbage
collection, to compact the information in a user directory,
occurs, the system job [Sec 2.5] prints out a message on its
teletype. This warning was added when the garbage collector was
less reliable than it now is. The master directory for a drive is
read in the first time the drive is referenced. A copy is written
back out whenever the disks are idle and the master directory has
been changed since it was last written out. User directories are
read in when first referenced. If a currently nonexistant user
directory is referenced to write it will be created. If
rereferenced to read, a special open lose [Sec 2.5] will indicate
this to the user. User directories are copied out whenever the
disks are idle and they have been changed since last copied out. A
user directory in memory may be erased if no files are open in it,
a current copy has been written out, and a core request provokes
the core allocator [Sec 4.3] to examine the status of an area of
memory including the buffer.
The IBM 2311 interface transfers information directly to memory in
units of 2000 words. Dynamically allocated buffers in system
memory are used for input and output. The capacity of each pack is
about thirty times that of a reel of DEC tape [Sec 3.1.2].
3.1.1.1 Links
CALL: .FDELE FBLOCK
;error return
;normal return
FBLOCK: 200000,,[SIXBIT /DSK/]
SIXBIT /FFNAM1/
SIXBIT /FFNAM2/
SIXBIT /TFNAM1/
SIXBIT /TFNAM2/
SIXBIT /TSNAME/
A special feature of the disk device is that users may establish
symbolic links. If the call illustrated above has been executed,
then an attempt to read the file FFNAM1 FFNAM2 with the system
name [Sec 2.2.3] that was being used by the procedure that
established the link will actually refer to file TFNAM1 TFNAM2
with the system name TSNAME. A link may refer to another link and
so on for up to eight levels. Attempting to write or delete
through a link writes on top of or deletes the link rather than
the file it refers to.
3.1.2 The UTn Devices
The devices UT1, UT2, UT3 and UT4 represent the four DEC tape
drives on the PDP-6. They are true file structured devices under
ITS with all standard modes available. Data is dynamically
buffered by ITS for both input and output. The file directory of a
tape is read in by the system and retained when a drive is
referenced and there is no directory being retained for it. An
updated directory will be written out on a particular tape
whenever the directory has been changed, no files are open on the
tape, and no data transfers are in progress on any drive. Files on
UTn do not have a system name [Sec 2.2.3] associated with them.
Directories can be excised from core only by the .UDISMT UUO.
3.1.2.1 The .UDISMT UUO
MOVEI AC,TAPEN
CALL: .UDISMT AC,
;error return
;normal return
This system call, if successful, causes a DEC tape's file
directory to be excised from core and the tape to be physically
demounted. The drive number must be in the accumulator specified
by the UUO. Manually removing tapes or switching drive numbers of
drives for which ITS is retaining a directory may result in
out-of-date file entries left on tapes and directories for one
tape being written on another.
A .UDISMT skips if and only if successful. It will fail if any
files are open on the tape. If a file is opened, deleted, or
renamed on a tape while the tape is being dismounted by ITS the
dismount will be aborted and the tape retained.
3.1.2.2 The .ASSIGN and .DESIGN UUO's
MOVEI AC,TAPEN
CALL: .ASSIGN AC,
;error return
;normal return
MOVEI AC,TAPEN
CALL: .DESIGN AC,
;error return
;normal return
These system calls are to enable a user to protect against other
users accidentally referencing his DEC tape to write or delete a
file or rename [Sec 3.1.2.4] the tape. Both specify the drive
numbers as the contents of their specified accumulator. The
.ASSIGN UUO skips if successful and results in attempts to write
on the designated drive failing unless the writing procedure has
the same system name [Sec 2.2.3] as the UNAME of the procedure
that executed the .ASSIGN. For a procedure in a disowned tree [Sec
5.2.2], an .ASSIGN will be treated as an illegal instruction. An
.ASSIGN will fail only if the drive is already assigned. The
.DESIGN UUO skips if successful and causes the drive to be
unassigned. It fails if the drive is already unassigned or
assigned to a different user. A drive may also be .DESIGN'ed by a
.UDISMT [Sec 3.1.2.1] and the .ASSIGN'ing of a drive does not
protect against other users dismounting it.
3.1.2.3 The .UBLAT UUO
MOVEI AC,TAPEN
CALL: .UBLAT AC,
;error return
;normal return
This system call is intended for reading non-MAC format [Ref 4]
(such as DEC format) DEC tapes. The contents of the specified
accumulator must be a drive number for which ITS is not retaining
a directory. If a directory is already being retained, the .UBLAT
will fail and return without skipping. (The user might try first
.UDISMT'ing the drive.)
If successful, the .UBLAT skips. Instead of attempting to read in
the directory from the tape mounted on the specified drive, ITS
internally marks the drive so that its contents may not be changed
(no writes, deletes, or renames). At this point a successful .OPEN
of the tape may be executed with any file name and all blocks of
the tape will be read consecutively. Thus the tape may only be
referenced to read the file containing the entire contents or to
.UDISMT [Sec 3.1.1] it.
3.1.2.4 The .UTNAM UUO
MOVE AC,[(SIXBIT /lll/),,TAPEN
CALL: .UTNAM AC,
;error return
;normal return
This system call changes the three character tape name of a
particular DEC tape. The tape drive number must be specified in
the right half of the specified accumulator. The call will fail
and return without skipping if there is no such drive or if the
drive is in .UBLAT mode [Sec 3.1.2.3] or .ASSIGN'ed [Sec 3.1.2.2]
to another user. Otherwise it modifies the tape's directory
(reading it in if necessary) so as to have a tape name
corresponding to the left half of the accumulator specified by the
call and skips on return.
3.1.2.5 The .UINIT UUO
MOVE AC,TAPEN
CALL: .UINIT AC,
;error return
;normal return
This system call initializes the directory for the DEC tape on the
drive whose number is the contents of the accumulator it
specifies. The tape must have been .ASSIGN'ed [Sec 3.1.2.2] to the
user doing the .UINIT. If successful the .UINIT skips on
returning. If the specified drive is nonexistant or the tape on it
is not .ASSIGN'ed to the user doing the .UINIT, it returns without skipping.
3.1.3 The COM and SYS Devices
The device SYS is used for storage of systems programs and the "
message of the day" [Sec 7.1.1]. It is currently those files on
device DSK with system name SYS. Reading or writing device SYS
causes one to reference DSK as though one's system name were
momentarily SYS. The device COM is used for commonly used user
files and the mail feature [Sec 7.2.1, 7.2.2]. In a manner similar
to device SYS it is DSK with system name COMMON.
3.2 Unit Character Oriented Devices
3.2.1 The Tnm and TTY Devices
Device T00 is the console teletype. Devices T11 through T14 (the
two digits are treated as an octal number) are GE Datanet 760
terminals with a character only display and keyboard. Devices T01
through T10 are available for more teletype and teletype-like
hardware and are read and written through the Knight Teletype
Kludge. Device TTY for a particular procedure is the console
controlling the procedure tree it is on. All input-output to these
devices is in ASCII characters and the "image" mode [Sec 2.2] has
special meanings. Further detail on which Tnm is "where" is given in
the following table (as of July 14, 1969):
Tnm Location
T0 Main console (by PDP-6).
T1 Advanced Remote Display Station.
T2 Outside line (or 1479 depending on switch).
T3 Robot console.
T4 PDP-10 console.
T5 System console (by line printer).
T6 Inside line 1425.
T7 Inside line 1474 (or outside depending on switch) 15cps.
T10 Spare.
T11 GE console by plotter.
T12 GE console on 8th floor.
T13 GE console by air conditioner.
T14 GE console by ham rig (in far corner).
T15up Nonexistent.
A procedure may not open its console by referring to it as Tnm for
the corresponding n and m. Only one procedure at a time may have a
teletype open as a device rather than a console. The procedure
with T00 opened as a console (TTY) and that actually has control
of it [Sec 3.2.1.1] can always seize the DEC 340 display [Sec 3.4.1].
Image mode output to KSR 35/37's is very straight forward and just
sends the character to the teletype unmodified. ASCII mode differs
only in the following:
1. The character whose value is 33 is printed as a "$".
2. Other characters with a value less than 40 that are not format
effectors or bell are printed as a "~" followed by the character
with an ASCII value 100 greater.
3. Tab is simulated with spaces.
4. The "delete" character doesn't type out.
5. New line is simulated for a carriage return.
Output to GE terminals is the same as ASCII mode output to KSR
35/37's except for the following:
1. All line feeds (12) are ignored.
2. A ^L (form feed) clears the screen.
3. An automatic new line is inserted if the right margin is touched.
4. An " \ulcorner " as displayed by the GE terminal, is used instead of a "~" prefix.
5. Output beyond the bottom of the output area wraps around and
overwrites from the top of the output area which does not
include the bottom three lines unless the first input .OPEN [Sec
2.2] had the 3.4 mode bit on.
6. Finally, if the output is in image mode only, the character ^T
will allow overwriting starting from the top of the output area
without clearing the screen or wrapping off the bottom.
For all the above output modes, adding block mode only affects
individual character processing by causing ^C's that are output to
be ignored.
Input to keyboards (which are all full duplex) is buffered by ITS
in relatively small fixed size buffers. Striking a key when this
input buffer is full results only in a ^G (bell) (or "?" on a GE
terminal) being output as echo. Any input when the keyboard is not
in use, except ^Z [Sec 1.1.1], is ignored by ITS. Procedures may
enable interrupts (class three) due to non-empty input buffers
[Sec 4.2] and also examine the input characters at interrupt time
with .ITYIC [Sec 2.7.3].
Image mode input is characterized by no ITS-supplied echo and no
modofication of the character codes unless open mode [Sec 2.2] bit
3.5 ("old mode") is also on, in which case lower case KSR 37
characters are transformed to upper case KSR 35 characters.
ASCII mode input provides echo in approximately the same manner as
outputing the characters in ASCII mode. Procedure output has
higher priority than echo output. On GE terminals input is
normally echoed in the bottom three lines unless the 3.4 open mode
bit was on, in which case characters are echoed where output is
appearing except that a few characters are not echoed at all. In
ASCII mode input, the characters whose values are 175 and 176 are
input and echoed as if they were the character whose value is 33.
Having open mode bit 3.5 on has the same effect for ASCII mode
input as it did for image mode input. In general, all of the
various mode bits affecting input are obtained from the first
input .OPEN [Sec 2.2] executed by a procedure for a particular
teletype. For all the above input modes, adding block mode results
in input until the block input pointer runs out or until a ^C is
typed at which point the .IOT [Sec 2.3] being executed terminates
as on an end of file [Sec 2.3.2].
Any input or output TTY .OPEN by a procedure that has never had
control of a console will fail. Any input or output .IOT or .OPEN
executed on a TTY device by a procedure that has had control of
the device while it is actually being controlled by another
procedure [Sec 3.5.1] will hang until the executing procedure
regains the device.
The device dependent .STATUS [Sec 2.5] bits for the teletype
devices are as follows:
Bit Meaning
2.3 Channel open in "DDT "mode (3.4 mode bit).
2.4 A console (TTY device) open on this channel.
2.5--2.9 If channel open for output:
Current line number if a GE console.
2.5--2.9 If channel open for input:
2.5 Indicates some characters have been seen at
interrupt and not main program level.
2.8 Teletype is at the 340 [Sec 3.4.1] or a 340 slave.
2.9 Teletype is local, not dial in.
3.2.1.1 The .ATTY and .DTTY UUO's
CALL: .ATTY CHNUM,
;error return
;normal return
CALL: .DTTY CHNUM,
;error return
;normal return
These system calls enable procedures in a single console
controlled procedure tree to transfer control of their console
between each other. The execution of either by a procedure that
does not have control of the console, because it was taken away by
a higher procedure's execution of a .DTTY, will hang until it
regains control. The accumulator field of each must specify a
channel (CHNUM in the above illustration) on which an immediate
inferior procedure is open [Sec 3.4.2]. An .ATTY will pass control
of the console to this open procedure unless the procedure
executing the .ATTY has control of the teletype by taking it from
some deeper inferior along the same procedure tree branch in which
case it reverts to the procedure from which it came. An .ATTY will
hang instead of doing the above if the last character typed on the
console was a ^Z. A .DTTY retrieves control of the console from
some inferior to the procedure executing it.
Both of these calls skip if successful. An .ATTY will fail to skip
only if no inferior is open on the channel it specifies. A .DTTY
will fail to skip if no inferior is open on the channel it
specifies or if the procedure executing it never had control of
the console or never gave control away. All other conditions
blocking the success of either system call cause them to hang.
3.2.1.2 The .LISTEN UUO
CALL: .LISTEN AC,
;error return
;normal return
This system call is usable only on the console a procedure is
associated with. It will hang if control of the console [Sec
3.2.1.1] has been taken away from the procedure executing it and
if all procedure output has not been typed. It then returns with
the number of buffered input characters in the specified
accumulator. If the procedure has never had control of the console
or is in a disowned tree [Sec 5.2.2] zero will be returned.
3.2.1.3 The Dial Feature
A feature is available under ITS that allows procedures to dial
calls on the two dataphone lines now available. Caution should be
exercised in using this feature if one is using the system over
one of these lines. The computer may "hang-up" in a more literal
sense than usual.
MOVEI AC,[440600+DIALN,,DLBUF]
CALL: .DIAL AC,
;error return
;normal return
DLBUF: 010201,,020202
100506,,101000
The .DIAL call is used to initially associate a procedure with a
dialer and to actually request dialing on the dataphone line
associated with the dialer. The accumulator specified by the call,
AC in the above example, should contain a byte pointer directly
addressing a byte within the user's core image. Indirect
addressing and indexing are ignored and in fact the index field is
used to specify the dialer number, DIALN in the above example.
This corresponds to a teletype as follows:
Dialer Teletype
0 T07
1 T06
The .DIAL will have no effect and return without skipping if any
of the following conditions hold:
1. A nonexistant dialer is specified.
2. The teletype associated with the dialer is in use by a
procedure other than the dialing procedure.
3. The associated teletype is not in use but the dialer is
assigned (by the execution of a .DIAL not yet followed by a
.HANGUP (see below)) to a procedure other than the dialing procedure.
If the .DIAL skips in returning it will have set up variables in
the system to that dialing will proceed asynchronously with the
procedure's execution. The byte string, which specifies what is to
be dialed, can not be more than five words long. These words are
transfered to the system by the .DIAL and dialing will be
unaffected by the user's subsequent modification of his image of
these words. However a later .DIAL without an intervening .DIALW
or .HANGUP (see below) will simply overwrite these words and may
cause garbled dialing.
As dialing proceeds, each byte is examined in succession. A zero
byte indicates the end of bytes to be processed. A byte whose
value is between one and ten causes a similar number of dial
pulses to be sent. Interdigital pauses are automatically inserted
after each digit. Bytes with a value larger than ten cause a pause
in dialing of as many tenths of a second as the byte's value minus ten.
A special means is provided to send the "break" signal. If the
accumulator specified by a .DIAL is zero except possibly for the
index field (where the dialer number is specified), then a "break"
will be sent after a .DIALW has been simulated to avoid garbling
any dialing in progress.
CALL: .DIALW DIALN,
;error return
;normal return
This call refers to the dialer specified by its accumulator field
(DIALN in the above example). It has no effect and returns without
skipping if the dialer has not been assigned to the .DIALW'ing
procedure by a successful .DIAL (see above). Otherwise it returns
and skips after requested dialing by the dialer is complete.
CALL: .HANGUP DIALN,
;error return
;normal return
This call refers to the dialer specified by its accumulator field
(DIALN in the above example). It has no effect and returns without
skipping if the dialer has not been assigned to the .HANGUP'ing
procedure by a successful .DIAL (see above). Otherwise it returns
and skips after hanging up the line for at least three seconds and
freeing the dialer so it is no longer assigned to any procedure.
3.2.2 The LPT Device
A six hundred line per minute Data Products, Inc. line printer
with one hundred and twenty print positions and sixty four
printing characters is available for character output as device
LPT. The ASCII/image mode bit [Sec 2.2] is ignored in .OPEN's on
device LPT but either single ASCII characters or blocks of packed
characters may be output as indicated by the block/unit mode bit.
The following "transformations" are made to the output text:
1. Lower case characters are made upper case.
2. Characters beyond the one hundred and twentieth print position
are ignored.
3. Format effectors (except for vertical tab) are simulated as for
a model 35 teletype, thus overprinting can be accomplished by
using carriage return without line feed.
4. Characters with an ASCII value below 40 other than the
simulated format effectors and character 33, which is printed as
a "$", are printed as a "~" followed by the character whose ASCII
value is 100 greater.
Only one procedure may have the LPT device open at one time but it
may be open on more than one channel. Procedures in disowned trees
are blocked from opening the LPT device but it will not be taken
away from a procedure as the procedure is disowned [Sec 5.2.2].
(Disowned procedures may use the TPL [Sec 3.4.5] device.) A fixed
1000 word buffer in ITS is used for output to this device.
The device dependent .STATUS [Sec 2.5] bits for the LPT device
have in the 2.2-2.9 field the current character position in the
print line. This count starts at zero at the left margin.
3.2.3 The PLT Device
A CalComp model 565 plotter [Ref 9] is available via "character"
output to device PLT. Available with the same modal restrictions
as the LPT device [Sec 3.2.2], it is also similar to that device
in that it may only be open by one procedure at a time but may be
open on more than one channel. A fixed 200 word area is used in
ITS to buffer output.
Only the right most six bits of characters output to the PLT
device have effect. They are as follows:
Bit Effect if a one
1.1 drum down
1.2 drum up
1.3 carriage right
1.4 carriage left
1.5 pen up
1.6 pen down
3.2.4 The PTP and PTR Device
The PTP and PTR devices represent, respectively, the sixty three
and a third character per second paper tape punch and four hundred
character per second photoelectric paper tape reader on the PLP-6
[Ref 1]. They are similar to the LPT and PLT devices [Sec 3.2.2,
3.2.3] in that only one procedure may have each open at one time
but that procedure may have the device open on more than one
channel possibly in different modes. Also output or input is
buffered in ITS in fixed areas of 20 and 100 words, respectively.
These devices differ from the LPT and PLT devices in that all
standard modes [Sec 4] are available and the following special
mode. If in a successful .OPEN for one of these devices, the 3.4
mode bit [Sec 2.2] is on then the 3.3 mode bit is ignored, the 3.2
mode bit must indicate unit mode, and all eight paper tape
channels may be written or read from or into the eight rightmost
bits of the word addresses by each .IOT [Sec 2.3] executed.
3.2.4.1 The .FEED UUO
CALL: .FEED CHNUM,
;error return
;normal return
This system call checks to see if the PTP device is open on the
channel it specifies (CHNUM above). If not, it returns without
skipping. If so, it causes one line of blank tape to be punched
and skips.
3.2.5 The COD Device
This is a character output device that may be used in block or
unit mode but not any form of image mode and not by more than one
procedure at a time. It causes transmission of low power FM Morse
code at a frequency just off the bottom of the FM broadcast band.
Characters for which there is no standard Morse code (such as line
feed) are ignored except that the speed it set by characters whose
value is greater than 137 to approximately, seventy five divided
by the difference between the character value and 137, words per
minute. It tries to interrupt on the input-output channel it is
open on when the fixed buffer in ITS it uses is almost empty.
3.3 Robotic Oriented Devices
3.3.1 The NVD, TVC, and VID Devices
The VID and NVD devices are somewhat similar to the IMX device
[Sec 3.9] in that they may be open by any number of procedures,
have block and unit modes, and "functional" word input where the
quantity read is a function of the contents. They differ in that
the ASCII/image .OPEN mode bit [Sec 2.2] is ignored and they
represent vidissectors. The initial contents of words input into
should be the coordinates of a point in the field of view of the
particular vidissector at which it is desired to know the light
intensity. This contents will be replaced by a function of said
intensity. The exact form of these words and the use of any device
dependent .OPEN mode bits [Sec 2.2] is listed in the table below.
Item VID NVD
X 2.3--1.1 4.5-3.2
Y 4.3--3.1 2.5-1.2
value 1.8--1.1 (reciprocal of intensity)
4.9-3.3 (normalized floating reciprocal intensity)
2.1-1.1 (integar logarithm reciprocal intensity)
(too 400 3.1 (overflow)
dark) 3.2 (dim cut off)
dead --1 4000000
modes 3.6--3.4 (340 intensity)
3.5-3.4 (confidence level)
3.8-3.6 (dim cut off level)
The VID device is of little use as it is a lower quality subset of
the NVD device. The deflection signals for the VID device come
from the DEC 340 display [Sec 3.4.1] whose use will be degraded by
using device VID.
The TVC device is the same as the NVD device except that it should
be opened on two channels, one for output and one for input. Words
with coordinates in them are output on one channel and stored in a
fixed length buffer in system memory. There they are replaced by
ITS, at its interrupt level, with the response word shown above
(value). They may be read, in the same order as output, on the
input channel. Unlike most devices, a block mode .IOT outputting
to the TVC device when its buffer is full will not hang up but
return with the block .IOT pointer word pointing at the first word
not transferred.
3.3.1.1 The .VSCAN and .VSTST UUO's
(Some of this section is taken from Reference 13.)
PTABLE: WBIT,,VCONO ;+0
--LENGTH,,ARRAY ;+1
XRES,,YRES ;+2
R1 ;+3
R2 ;+4
C1 ;+5
R3 ;+6
R4 ;+7
C2 ;+10
P1 ;+11
P2 ;+12
ARRAY: BLOCK LENGTH
This system call allows the user to read the light intensity at an
array of points with low overhead and, if desired, overlapped computation.
The effective address of a .VSCAN should point at an eleven word
block of parameters defining the points to be scanned, the
locations to read into, the mode they are to be read in, and
whether the call should hang until the scan is through. The effect
of the parameters, in order, is described below.
The first word has in its right half the control bits for the
vidisector as in section 3.3.1 for NVD. The sign bit, if a one,
causes the .VSCAN to hang until the scan is over. If a zero,
computation by the .VSCAN'ing user may procede while the scanning
proceeds at ITS's interrupt level.
The second word should be similar to a block mode .IOT [Sec 2.3]
pointer word. Its right half should point to the beginning of an
array to be read into in the response format of NVD in section
3.3.1. Its left half should be a negative count equal to or
larger, in magnitude, than the number of points being scanned. (If
in the above illustration either PTABLE+12 or ARRAY+LENGTH-1 were beyond the users memory
bound, the .VSCAN would be treated as an illegal instruction.)
The third word has in its left and right halves, as eighteen bit
integers, the "X" and "Y" resolution or number of points to be scanned
in each direction.
The remaining nine parameters, which are fixed point quantities
with the binary point between 2.9 and 3.1, define where the XRES
by YRES points lie in vidissector coordinates according to the
following ALGOL program:
FOR Y1<--0 STEP 1 UNTIL YRES--1 DO
BEGIN
Y2<--(2*Y1+1)/(2*YRES)
FOR X1<--0 STEP 1 UNTIL XRES--1 DO
BEGIN
X2<--(2*X1+1)/(2*XRES)
TEMP<--P1*X2+P2*Y2+1
X<--(R1*X2+R2*Y2+C1)/TEMP
Y<--(R3*X2+R4*Y2+C2)/TEMP
ARRAY(Y1*XRES+X1)<--SCAN(X,Y)
END
END
A .VSCAN will hang up until the NVD device is free. This device is
then seized, not to be released until the scan is over or aborted.
A scan is only aborted if the procedure it is being executed for
is reset [Sec 3.4.2] or its core size reduced so as to exclude the
array being read into (ARRAY in the above illustrations) or by .VSTST.
MOVSI AC,1 ;or 0 or 400000
CALL: .VSTST AC,
;return
This system call allows later control of and sensing by a
procedure that has overlapped computation with a .VSCAN. It is
illegal if executed when another procedure is .VSCAN'ing. If the
contents of the specified accumulator is positive, the .VSTST
hangs till the scan is over. If the contents of the specified
accumulator is negative, any scan in progress is aborted. If the
contents of the specified accumulator is zero, the user's location
then being stored into by the scan, if any, replaces it.
3.3.2 The OMX Device
A multiplexed digital to analog converter on the PDP-6 is
available via word output to the OMX device [Ref 5, 6]. Block and
unit modes are available and the "ASCII/image" mode bit [Sec 2.2]
has a special significance explained below. Each word output
should have the desired channel number in bits 4.9-4.4 and the
value to be converted in bits 4.3-3.1. Thus channel numbers range
from zero to 77 and values from zero to 7777. These output
channels decay exponentially with some large time constant so ITS
stores the current desired value for each channel and outputs them
every half second as long as the OMX device is open by some
procedure. Output in "ASCII" mode immediately affects the channel as
well as storing a value to be output periodically. Slightly less
overhead occurs in "image" mode which only stores a value in ITS and
may have no effect for up to half a second. Any number of users
may have the OMX device open, possibly on more than one channel
and possible in different modes. Current OMX channel assignments
are as follows:
Channel Effect
0--31 Unused.
32 NVD iris.
33 NVD focus.
34 NVD mirror.
35-55 Unused.
56 TVB pan.
57 TVB tilt.
60 MA3 hand extend.
61 MA3 hand rotate.
62 MA3 hand grasp.
63 Cannon lens zoom (MA3 hand finger #1).
64 Cannon lens focus (MA3 hand finger #2).
65 MA3 hand tilt.
66 Alles hand grip.
67 Alles hand tilt.
70 Alles hand extend.
71 Alles hand rotate.
72 AMF arm wrist roll.
73 AMF arm wrist yaw.
74 TDR horizontal.
75 AMF arm horizontal.
76 AMF arm vertical.
77 AMF arm swing.
3.3.2.1 The .ARMOVE and .ARMOFF UUO's
(Some of this section is taken from Reference 13.)
MOVE AC,[--LENGTH,,ARMBLK]
CALL: .ARMOVE AC,
;normal return
;test successful return
ARMBLK: BLOCK LENGTH
This system call allows one procedure at a time to exercise
special control over several digital to analog multiplexor
channels [Sec 3.3.2]. It provides acceleration and velocity
limiting, software limit stops, and conversion from joint number
to multiplexor channel.
To avoid certain timing problems, the transmission of commands to
the multiplexor control routines in ITS is noninterruptable (but
for a limited length of time as only a limited number of commands
may be transmitted). Each command is a single word in a block
pointed at by the contents of the accumulator specified in the
call. The format of these words is as follows:
Bits Significance
4.9--4.4 joint number
4.3--3.7 command
3.6 unused
3.5 indirect
3.4--3.1 index
2.9--1.1 address or operand
The currently available joint addresses are as follows:
Address Significance
0 AMF swing
1 AMF vertical
2 AMF horizontal
3 AMF yaw (inoperative)
4 Alles hand tilt
5 Alles hand grip
6 Alles hand rotate
7 Alles hand extend
10 AMF roll (inoperative)
The currently available commands are as follows:
Command Significance
0 set destination
1 set velocity limit
2 test magnitude of position error
3 test magnitude of velocity
The operand is computed by adding the contents of the specified
index register (if any) to the right half of the command. The
result is masked to 13 bits. If the indirect bit is a one, the
right half of the word addressed is used as the operand. No
further indexing or indirecting is interpreted.
The test commands are "true" if the quantity tested exceeds the
operand. If any tests are "true" the .ARMOVE will skip.
CALL: .ARMOFF
;return
The multiplexor control routines are activated by the first
.ARMOVE and are turned off by an .ARMOFF or killing the
.ARMOVE'ing procedure.
An .ARMOVE is illegal if:
1. The arm is in use by another user.
2. The block extends above the user's memory bound.
3. An indirect reference is out of bounds.
4. An unused command code or joint number is specified.
5. The block is over 100 words long.
3.3.3 The IMX Device
A multiplexed analog to digital converter attached to the PDP-6 is
available via word input from the IMX device [Ref 5, 6]. Block and
unit modes are available but the "ASCII/image" mode bit [Sec 2.2]
has a special significance explained below. Each word input into
must initially contain a number from zero to 177. This number will
be replaced with the twelve bit digitalization of the analog
quantity associated with the multiplexor channel of the same
number. If it is desired to read in values converted at each .IOT
[Sec 2.4] time then device IMX should be opened in "ASCII" mode.
Opening device IMX in "image" mode causes ITS to continuously read
all input multiplexor channels into system core a minimum of about
ten times a second. Executing a .IOT on a channel opened in this
manner will result in values up to one tenth of a second old but
without the overhead necessary to read in new values. Any number
of procedures may have the IMX device open, possibly on different
channels and possibly in different modes. Current IMX channel
assignments are as follows:
Channel Input function
0--21 Unused.
22 MA3 hand extend.
23 MA3 hand rotate.
24 MA3 hand grasp.
25 Cannon lens zoom (MA3 hand finger #1).
26 Cannon lens focus (MA3 hand finger #2).
27 MA3 hand tilt.
30--32 Unused.
33 NVD iris.
34 NVD focus.
35 NVD mirror.
36 Rhomboidal test table pot A.
37 Rhomboidal test table pot B.
40 Rhomboidal test table pot C.
41 Rhomboidal test table pot D.
42 Pot box upper left.
43 Pot box upper right.
44 Pot box lower right.
45 Pot box lower left.
46--57 Unused.
60 TDR output.
61 Alles hand tilt.
62 Alles hand extend.
63 Alles hand rotate.
64 Alles hand grasp.
65 AMF arm wrist roll.
66 AMF arm wrist yaw.
67--70 AMF arm horizontal high resolution.
71 AMF arm horizontal absolute position.
72--73 AMF arm swing high resolution.
74 AMF arm swing absolute position.
75--76 AMF arm vertical high resolution.
77 AMF arm vertical absolute position.
100--111 Unused.
112 Joy stick X.
113 Joy stick Y.
114--131 Unused.
132 TVC pot box one (manual iris control).
133 TVC pot box two (manual focus control).
134 TVC pot box three.
135 TVC pot box four.
136 TVC pot box five.
137 TVC pot box six.
140 New pot box pot one.
141 New pot box pot two.
142 New pot box pot three.
143 New pot box pot four.
144 New pot box pot five.
145 New pot box pot six.
146 New pot box pot seven.
147 New pot box pot eight.
150--155 Unused.
156 Pot box two, one.
157 Pot box two, two.
160 Pot box two, three.
161 Pot box two, four.
162 Pot box two, five.
163 Pot box two, six.
164 Pot box two, seven.
165 Pot box two, eight.
166 Joy stick console pot ten.
167 Joy stick console pot nine.
170 Joy stick console pot eight.
171 Joy stick console pot seven.
172 Joy stick console pot six.
173 Joy stick console pot five.
174 Joy stick console pot four.
175 Joy stick console pot three.
176 Joy stick console pot two.
177 Joy stick console pot one.
3.3.3.1 The .POTSET UUO
(some of this section is taken from Reference 13.)
CALL: .POTSET PTABLE
;return
PTABLE: BLOCK 4*NUMENTRIES
0
This call gives the user a flexible means of controlling program
parameters via the input multiplexor. A maximum of 20 simultaneous
connections between pots and variables is permitted. Each may be
variable fixed or floating point. If fixed point, it may be an
arbitrary byte within a word. The user may specify a mapping from
pot values to variable values by giving an upper and lower limit.
These may be inverted to give a backward mapping. Two types of
control are provided, absolute and incremental. In absolute mode,
the true pot position sets the value. This may be useful for
positioning displayed objects with a joystick. The incremental
mode permits a variable or set of variables to be changed slightly
without causing a discontinuous jump in their values. The value is
unchanged at connect time, but rotating the pot adds its scaled
increment to the variable. Turning it down in the bottom third, or
up in the top third of the pot's range causes a faster change so
as to keep the control near center. The increase in gain is
inhibited at low speeds to prevent drift due to noise.
The address of the call points to a table of pot connection (or
disconnect) specifications. This table consists of blocks of 4
words, followed by a zero word. The block format is as follows:
Location Variable
F00+0 Multiplexor channel,,control bits (see below)
F00+1 Byte specification (see below),,variable address
F00+2 Lower limit (value at pot = 0)
F00+3 Upper limit (value at pot = 100000)
The control bits are as follows:
Bit Meaning
2.9 \Rightarrow 1disconnect pot
\Rightarrow 0connect pot
1.2 \Rightarrow 1absolute
\Rightarrow 0incremental
1.1 \Rightarrow 1floating
\Rightarrow 0fixed
The byte specification should be in machine byte pointer format
(no index or indirect allowed) for a partial word and may be zero
for a full word.
A .POTSET call is illegal if:
1. The user tries to connect a pot already in use by another user.
2. The table is more than twenty blocks long.
3. An attempt is made to connect a pot when twenty pots are
already connected.
4. The address exceeds the user's memory bound.
A pot is disconnected when:
1. The user disconnects it with a .POTSET.
2. The user reduces his memory bound below the address the pot controls.
3. The job is killed.
3.4 Miscellaneous Devices
3.4.1 The DIS and IDS Devices
The DEC 340 display [Ref 1] differs significantly from all other
devices usable in ITS. In order to maintain an image on the
display it is necessary to repeatedly output to it a list of
display words. This list must be stored in main memory and the
various means of using the display may be divided into those that
maintain this list in system memory (discussed in this section)
and those that allow the list to be maintained in the user's core
image [Sec 3.4.1.1].
Only one procedure at a time may use the 340 display and in only
one of its three modes (as symbolic device DIS, as symbolic device
IDS, or via the .DSTART and .STRTL UUO's). If the display is free,
any procedure may seize it by executing a proper .OPEN on device
DIS or IDS or by executing a .DSTART or .DSTRTL UUO. If the
display is in use, however, a procedure will succeed in any of the
above UUO's only if it is the procedure that has the display or it
has control of device T00 as a console [Sec 3.5]. If the second
case applies, the channels, if any, on which the other procedure
had the DIS or IDS open will be modified to the corresponding
(block or unit) NUL device [Sec 3.4] output. .CLOSE'ing [Sec
2.8.1] all input-output channels in which device DIS or IDS are
open is the same as executing a .DCLOSE [Sec 3.4.1.3].
The DIS symbolic device allows the user to output single or packed
blocks of ASCII characters in ASCII mode and single or blocks of
340 display list half words [Ref 1] in image mode. This device may
be open on more than one channel at a time in possibly different
modes. If the user outputs characters and then halfwords, ITS will
automatically insert intervening items to cause the display to
escape to parameter mode. If the user outputs half words and then
character, ITS assumes that he has inserted items to cause the
display to escape to parameter mode. A display list produced by
output to the DIS device will start by setting the 340 display
intensity to 7, its x and y coordinates to zero and 7000, and its
scale to one larger than the 3.4-3.5 field of .OPEN mode bits [Sec
2.2] used unless that field is 3 in which case the scale is set to
zero. Lines of character output that extend beyond the right edge
of the screen will wrap around and continue, superimposed on their
beginning, from the left. Lines of character output that extend
beyond the bottom of the screen similarly continue from the top.
The amount of display information created by DIS output may not
exceed 2000 words. After that, further output is ignored. The
stored information created by output to the DIS device may be
deleted to accept new information by outputting a ^T or ^L (form
feed) character. In the latter case, this action will be delayed
for a few seconds.
The IDS symbolic device allows the user to use a semi-idealized
display. This device is known as the interpreted display since the
user writes "instructions" to be executed by a display processor
which are then interpreted by ITS simulating the processor and
creating a 340 display list to actually display. The IDS device
may only be opened in unit output mode and what the user outputs
to it is the location, in the user core image, for the display
processor to start "executing".
.IOT DISCHN,PC
...
FC: STRTLC ;location to start
;updated during execution
Almost all error conditions encountered during this "execution"
cause interrupts to the user [Sec 4.2]. The simulated display
processor has a push down list facility with its push down list
pointer in the user's location 43. The information to be sent by
the .IOT'ing [Sec 2.4] of each starting location to the IDS device
is normally terminated by the display processor POPJ'ing to zero.
Frequently this is made to happen by over popping by the display
processor. The information stored by the IDS device is currently
limited to 2000 words. If the 340 display is being run by the IDS
device when a .IOT is executed on it, the display will stop and
the stored information will be over-written. If the 340 display is
not being run, output from simulation is appended to that already
present. Whether the 340 display is started at the end of the
simulation initiated by a .IOT is determined by a display
processor parameter that may be set during simulation.
Instructions for the IDS simulated display processor are thiry-six
bit words interpreted as five left justified ASCII characters if
bit 1.1 is zero. If bit 1.1 is a one, bits 1.4--1.6 are
interpreted as the following commands:
1.4--1.6 Command Other fields
0 Illegal.
1 Point. 4.9--3.4 Y, 3.3--1.7 X, 1.2 intensify.
2 Rel vector. 4.9--3.4 Y, 3.3--1.7 X, 1.2 intensify.
3 Increment. 5 left justified 5 bit fields each:
1.1--1.2 length
1.3 intensify
1.4--1.6 direction (clockwise from vertical).
4 See below. 1.7--1.9 subcommand function.
5 Abs vector. 4.9--3.4 Y, 3.3--1.7 X, 1.2 intensify.
6 Illegal.
7 Illegal.
1.7--1.9 Function Other fields
0 Illegal.
1 PUSHJ. 4.9--3.1 address.
2 POPJ. 4.9--3.1 address.
3 JRST. 4.9--3.1 address.
4 POP. 4.9--3.1 address.
5 PUSH. 4.9--3.1 address.
6 See below. 2.3--2.9 parameter to set from 4.9--3.1.
7 Illegal.
2.3--2.9 Parameter
0 Illegal.
1 Start mode (nonzero means start after .IOT).
2 Character scale.
3 Increment mode.
4 Vector scale.
5 All scales.
6 Coordinate of left edge of displayed area.
7 Coordinate of bottom edge of displayed area.
10--77 Illegal.
3.4.1.1 The .DSTART and .DSTRTL UUO's
CALL: .DSTART DPNTR
;error return
;normal return
DPNTR: --LENGTH,,DISLIST--1
DISLIST: BLOCK LENGTH
CALL: .DSTRTL PHTRL
;error return
;normal return
PHTRL: DPNT2+1,,.+1
DPNT2+1,,0
DPNT2: --LENGTH,,DISLIST
DISLIST: BLOCK LENGTH
These UUO's enable the user to display lists that are in his core
image. The execution of either attempts to seize the 340 display
and skips only if successful.
A .DSTART should point at a location that will always contain
either a BLK0 [Ref 1] type output pointer, if one block of data is
to be displayed, or the first word of a linked list of display
blocks. In this linked list, the right half of each entry points
to the next entry, or, if zero, indicated the end of the list. The
left half of each word should be positive and is a pointer to a
BLK0 pointer or is ignored if it is zero or points to a zero word.
.DSTRTL differs from .DSTART only in that, if it is used to
display a list of blocks, the left halves of its linked list words
are interpreted as pointing to the word after not a BLK0 pointer
but a regular block mode output pointer [Sec 2.4].
3.4.1.2 The .LTPEN UUO
MOVE AC,[CONTROL]
MOVEM AC,LBLOCK
CALL: .LTPEN LBLOCK
;return
LBLOCK: BLOCK 6
The 340 display is equipped with a light pen that causes a
hardware interrupt when the light intensity it sees increases
suddenly as when a spot is displayed under it. The display also
stops when this occurs and its current coordinates can be read in
by the PDP-6. The user may enable software interrupts (class
three) to his procedures when the light pen is seen and he has the
display seized [Sec 4.2].
This system call enabled the user with the display seized to read
information about where the light pen has been seen and the state
of the current transfer to the display. Results are returned in
the contents of the effective address and following five
locations. The contents of the effective address also acts as an
argument. If bit 4.9 is zero the rest is ignored. But if bit 4.9
is a one then bit 3.1 will cause the .LTPEN to hang until the
light pen has been seen at least once and bit 1.1 will be used to
set the multiple sighting mode. If this mode is on, the light pen
may be seen many times while a display block is displayed once. If
this mode is off (zero) the light pen may be seen only once and
ignored thereafter for each display of a display block.
The six words returned to the user are as follows:
1. The actual word DATAI'ed [Ref 1] from the 340 display at the
time of the last light pen interrupt.
2. The number of times the light pen was seen since the last .LTPEN.
3. The sum of the y coordinates at the points the light pen was
seen since the last .LTPEN.
4. The corresponding sum of x coordinates.
5. The current linked list pointer.
6. The current BLK0 pointer.
3.4.1.3 The .DCLOSE UUO
CALL: .DCLOSE
;return
This system call releases the 340 display if executed by the user
who has the display seized, closing any channels on which it is
open. Otherwise it does nothing.
3.4.1.4 The .DSTOP UUO
CALL: .DSTOP
;return
This system call stops the 340 display, but does not release it,
if executed by the user who has the display seized. Otherwise it
does nothing. It is intended for use in conjunction with the
.DSTART or .DSTRTL UUO.
3.4.1.5 The .NDIS UUO
MOVEI AC,69.
CALL: .NDIS AC,
;error return
;normal return
This system call is intended for use in taking pictures of 340
displays. It sets a display control variable from the contents of
the accumulator it specifies. This variable has no effect if it is
negative but if zero it inhibits display completely and if
positive it is decremented by one each time the current display
block or list of blocks is displayed. This call skips unless
executed by a procedure that does not have the display assigned to it.
3.4.2 The USR Device
The USR device actually represents procedures. A successful .OPEN
[Sec 2.2] executed on device USR will either create a new
procedure [Sec 5.1.1], attach a disowned procedure tree [Sec
5.1.2], associate with the input-output channel on which it was
executed an existant procedure or allow the user access to the
PDP-10's memory [Sec 3.4.2.1]. The file names are the UNAME and
JNAME of the procedure being .OPEN'ed. Only immediate inferiors
may be .OPEN'ed to write into but any procedure may be examined.
If an inferior procedure has been opened, it may be destroyed by a
.UCLOSE [Sec 5.2.1] but will be entirely unaffected by a .CLOSE
[Sec 2.7.1] executed on the channel. The same procedure may be
open on more than one channel of its superior, possibly in
different modes. It is as first .OPEN time that an interrupt bit
[Sec 5.1.3] is assigned by ITS to a procedure. The number of
inferior procedures a procedure may have is currently limited to eight.
The 3.3 mode bit [Sec 2.2] is ignored in .OPEN's on device USR but
both block and unit modes are available. Executing .IOT's on
channels opened on device USR results in the transfer of a
thirty-six bit binary word or words between the procedures. The
location in the .OPEN'ed procedure of the first word to be
transferred is specified by the .ACCESS [Sec 2.7.5] pointer
associated with the input-output channel on which the transfer is
occuring. Each word transferred advances the appropriate pointer
by one even in unit mode which ITS treats internally as blocks of
length one. An attempt to read a word beyond the core allocated
[Sec 4.3] will result in a class two interrupt [Sec 4.2] but in a
similar attempt to write (possible only for an immediate inferior)
ITS will attempt to extend the procedure's core image and and
interrupt will result only if more core is unobtainable.
Executing a .RESET [Sec 2.7.2] on a channel with an inferior
procedure open on it is equivalent to executing a .UCLOSE and then
a .OPEN to recreate the procedure (with reset variables, one 2000
word block of cleared core, etc.) but with less overhead.
3.4.2.1 The PDP-10
An .OPEN on device USR with a second file name of "PDP10" may be
made, in all the modes allowed for regular procedures, to access
the memory of the PDP-10. .IOTs attempting to read or write the
PDP-10's accumulators will be ineffective and read or write the
core locations shadowed by the accumulators. Attempting to
reference above the PDP-10's memory will result in illegal user
address interrupts. Only the procedures of one procedure tree may
have the PDP-10 open at a time, possibly on more than one channel
at a time in different modes.
Attempts to set or read variables for the PDP-10 "inferior" are
ignored except that 40000 will be read as its memory bound. A
.RESET executed on a channel on which the PDP-10 is open will
clear its memory.
3.4.3 The CLA, CLI, CLO and CLU Devices
These symbolic devices enable arbitrary pairs of procedures to
talk to each other as buffered input-output devices. Each file on
any of these "core link" devices represents a 200 word area, most of
which is buffer, which may be simultaneously open for reading,
writing, both or neither. The files are identified by two regular
file names and a system name [Sec 2.2, 2.2.3]. Only one procedure
at a time may have a core link open to write or read on one
channel. All standard modes are available.
The CLO (Core Link Open) device may be used to open any core link
file and (whether reading or writing) will create one if none
exists with the name used. The CLU (Core Link Use) device is
identical except that an .OPEN on it will fail if the referenced
file does not already exist.
Core link "files" have some peculiar properties. When writing a core
link, a procedure will hang if the buffer is full and will write
an end-of-file mark outside of the data stream when it closes the
channel it has the file open on. However, opening and writing
again the same file name essentially pushes a new block of data
into the pipeline to be removed by a reading procedure. A
procedure reading a core link can not read past an end-of-file and
must close and reopen the file if it suspects that there is more
to follow. If a reading procedure closes a core link before
encountering an end-of-file, remaining information until the
end-of-file is ignored. Core link "files" cease to exist only if
empty and open for neither reading nor writing or not empty and
not open for from two to four minutes. In the later case they are
expunged by the system job [Sec 6.5] to unclutter the system.
The CLI (Core Link Interrupt) device may only be opened to write.
The two file names specified should be the UNAME and JNAME [Sec
5.1] of a procedure in the system with the CLI interrupt [Sec 4.2]
enabled. If ther is no existing core link with the file names and
system name used, the .OPEN will succeed in creating a link and
interrupting the specified procedure. In addition ITS inserts in
the created link two words of information as the start of the
first file. These are the UNAME and JNAME of the .OPEN'ing procedure.
The CLA (Core Link Answer) device is to be used in response to a
CLI interrupt. It may only be opened for reading and scans through
all existing links for one with file names the same as the UNAME
and JNAME [Sec 5.1] of the procedure doing the CLA open. If one is
found not already open for reading, the .OPEN succeeds.
3.4.4 The ERR Device
This device, by a mechanism similar to that used for the "directory device"
[Sec 2.2.1], allows the user to input a character string
explaining whatever error indication there may be in a .STATUS
word [Sec 2.5].
The first file name specified on an .OPEN on device ERR must
numerically be either 1, 2 or 3. If it is 1, the status of the
last input-output channel on which there was an error will be
analyzed. If it is a 2, the bottom four bits of the second file
name specify which input-output channel to examine. If a 3, the
second file name is treated as the .STATUS word to analyze.
3.4.5 The TPL Device
This device allows a user to output a file to be line printed [Sec
3.2.2] at some later time when the line printer is free and such
print out has not been inhibited [Sec 6.5.1]. In a manner similar
to the COM and SYS [Sec 3.1.3], this device refers to files on the
disk with system name ".LPTR.". However, renames are ignored on the
TPL device and, while reads work normally, on writes the supplied
file names are ignored. Instead, the UNAME of the procedure
writing is used as the first file name and a counter of how many
files have been written on the TPL device in the current system
run is used as the second file name.
Files written on the TPL device are printed out by the system job
[Sec 6.5] when the line printer is free. A significant length of
time (up to two minutes) is left between non-TPL line printer use
and TPL print out and between successive TPL output to allow local
users to seize and use the line printer directly.
3.4.6 The NUL Device
This device has all standard modes and is a high speed infinite
sink on output and source of zeros on input.
The Procedure
See also section 0.3.3.
4.1 Philosophy and Organization
The use of ITS is entirely procedure oriented. Almost all system
actions are caused by trapping instructions [Sec 1.2; App A, B]
executed by user programs that are hierarchially organized [Sec
5.1]. A large number of variables [App D; Sec 4.5] is associated
with each procedure by the ITS system. These variables are stored
in the system and do not impinge on the user's core image.
These procedures are run for short fixed lengths of time or until
they become unrunnable (whichever comes sooner) in an order
determined by the scheduler [Sec 4.4]. The scheduler also handles
software interrupts to the user [Sec 4.2]. When in execution, user
programs run with the PDP-6 in user mode [Sec 1.2.2] which enabled
protection and relocation hardware that ITS sets in accordance
with the length [Sec 4.3] and location in absolute memory of the
particular procedure's core image.
The following are among the advantages of this storage of user variables:
1. No effort by a user's procedure to randomize its core image can
effect system variables related to the procedure and thus erase
evidence of system malfunction or lack of malfunction.
2. A procedure's core image may be easily swapped out without
significant reduction in information concerning it of interest
to the system or the necessity to retain some portion of it.
4.2 User Interrupts
ITS provides software implemented interrupts to the user program
similar to the hardware interrupts it receives. Only one level of
interrupt is simulated but this makes little difference due to the
ease with which the user can inhibit or enable various types of
interrupt [Sec 4.2.1] and may also re-enable interrupts without
immediately or ever returning to the location his program was
interrupted from.
Each procedure has in system memory two interrupt enable mask
words, two interrupt request words, and a flag indicating
interrupt level status [App D]. Various conditions that can cause
interrupts are assigned bits in these interrupt request words.
These conditions are divided into three classes according to
severity as follows:
1. Class one conditions, the most severe, can not be enabled. They
always cause the "interrupted" program to be stopped and its
superior procedure to receive an interrupt.
2. Class two conditions are of moderate severity. They may be
enabled to interrupt the user but if they occur while not
enabled or while the user's interrupt level flag indicates he is
currently processing an interrupt, he will be stopped and his
superior procedure interrupted.
3. Class three conditions are the least severe and may also be
enabled to interrupt the user. While not enabled they have no
effect. If enabled and they occur while the user's interrupt
level flag indicates he is free to receive interrupts he will
not be interrupted but if the user's flag indicates he is not
free they will be stored in the interrupt request words to be
presented to the user as soon as he allows unless reset with an
.SUSET [Sec 4.5].
In cases mentioned above (for class one and two) when a
procedure's superior is interrupted, the particular bit used to
interrupt the immediately superior procedure is in its second
interrupt request word. A bit is assigned by ITS to that inferior
at the time it was created [Sec 5.1.3] and can be read with a
.USET [Sec 5.2.3].
When conditions that would cause a procedure's superior to be
interrupted occur in a top level procedure one of two things may
happen. If the procedure tops a console controlled tree, a new
HACTRN will be loaded (as in section 1.1) and all inferior
procedures will be lost. If the procedure tops a disowned tree
[Sec 5.2.2] it will be immediately stopped and when next attached
[Sec 5.1.2] by a job tree the attaching procedure will be
appropriately interrupted.
ITS determines that it should actually interrupt a procedure when
it schedules [Sec 4.4], or the procedure executes a .DISMISS [Sec
4.2.2], or .SUSET [Sec 4.5] of the PICLR variable if there are
corresponding bits on in one or both of the procedure's interrupt
request and mask words and its interrupt level flag (PICLR)
indicates interrupts are enabled. ITS examines the contents of the
procedure's location 42 to see if its direct address (indexing and
indirect addressing ignored) is between location 20 and the
location 6 less than the top of the user's core image, inclusive.
If not, the user receives a class one interrupt for a bad location
42. If so, the user's appropriate interrupt word (first word has
higher priority than the second), containing bits on for
interrupts the user is being presented with, is placed in the word
directly addressed by the user's location 42 and bit 4.9 of that
location is turned on if second word requests are stored. The
interrupt request word stored is then cleared to receive further
interrupts. The user's interrupt level flag is also set to inhibit
further interrupts. Finally a JSR [Ref 1] is simulated to a
location one greater than that in which the interrupts were just
stored. The normal manner to return from an interrupt is with a
.DISMISS [Sec 4.2.2].
The following is a list of word one interrupt bits:
Bit(s) Class Condition
1.1 3 Character typed at console [Sec 3.2.1].
1.2 1 ^Z typed [Sec 1.1.2].
1.3 1 Bad location 42.
1.4 3 AR overflow [Ref 1].
1.5 2 Display list memory protection violation [Sec 3.4.1].
1.6 2 Illegal instruction.
1.7 3 System going down in 5 minutes [Sec 6.5.2].
1.8 1 .VALUE executed [Sec 5.3.1].
1.9 2 Input-output channel error. This interrupt always occurs
at an .IOT [Sec 2.3] or .OPER [Sec 1.2.1] that refers, with
its ac field, to the channel on which the error occured. For
more exact cause of interrupt use a .STATUS [Sec 2.6] or
the ERR device [Sec 3.4.4].
2.1 2 Memory protection violation on reference to inferior procedure [Sec 3.4.2].
2.2 1 .BREAK executed [Sec 5.3.2].
2.3 1 Return from single instruction proceed [Sec 6.7].
2.4 3 Slow clock (every half second).
2.5 2 Memory protection violation [Ref 1].
2.6 2 MAR interrupt [Sec 6.4].
2.7 3 Light pen [Sec 3.4.1.2].
2.8 3 PDL overflow [Ref 1].
2.9 3 Not used.
3.1--4.8 --- Not used
4.9 --- Indicates rest of bits to be interpreted as below.
In the second word of interrupt requests, bits 3.1-3.8 represent
inferior procedures [Sec 5.1.3] and bits 1.1--2.7 represents
input-output channels [Sec 2.1] with 1.1 for channel zero.
Interrupts occur from inferior procedures as described above for
class one or two interrupts to the inferiors while an input-output
channel will try to interrupt if there is buffered teletype [Sec
3.2.1] input on the channel. These buffered characters may be
examined at the interrupt level with .ITYIC [Sec 2.7.3].
4.2.1 The .SETM2 UUO
A procedure can examine and modify all of the five variable words
associated with interrupts to it by means of the .SUSET UUO [Sec
4.5]. When a procedure is first created [Sec 5.1.1] or has a
.RESET executed on it [Sec 3.4.2] all of these five variables are
zero except PICLR which is set to minus one. For the mask (MSKST
and MSKST2) and request (PIRQC and IFPIR) words a one bit
represents an enabled interrupt of pending request and a zero
represents an inhibited interrupt or lack of request. ITS will
ignore attempts by the user to enable a class one interrupt (first
word mask bits 1.2, 1.3, 2.2, and 2.3). To avoid certain timing
errors, special .SUSET means (APIRQ and IPIRQ) are provided to
turn on or off bits in the first request word without affecting
other bits in that word.
The procedure's interrupt level flag (PICLR) can also be read or
set. Its zero state indicated that interrupts are inhibited and
class two interrupts become fatal. If nonzero, interrupts are
enabled. ITS sets this variable to minus one when it executes a
.DISMISS from a user, but when a user attempts to set it the word
he stores there with .SUSET will be shifted right thirty five
places. Thus the user can set his PICLR to either zero or one
depending on the sign bit of the word he stores. As a result he
can enable interrupts (even in the middle of his "interrupt routine"
in a manner distinguishable from the automatic enablement
performed by ITS or inhibit interrupts.
The above discussion also applies to examining and modifying these
variables in inferiors with .USET [Sec 5.2.3].
To avoid certain timing problems there is a special UUO by which a
procedure may set both its mask words at once as follows:
MOVE AC,[MASKW1] ;set up first word of mask bits
MOVE AC+1,[MASKW2] ;set up second word of mask bits
CALL: .SETM2 AC, ;set both mask vars from AC & AC+1
;return
4.2.2 The .DISMISS UUO
LOC 42
JSR TSINT
TSINT: 0 ;interrupt bits stored here
0 ;loc interrupted from stored here
... ;interrupt routine
...
...
CALL: .DISMISS TSINT+1 ;returns to where interrupted from
This system call provides the normal means to return to an
interrupted routine. It simultaneously re-enables interrupts and
transfers to the location addressed by the right half of the
contents of its effective address, restoring flags from the left
half. This is normally, but not necessarily, the pseudo-JSR word
stored by ITS as it simulates an interrupt. If there are pending
conditions in the user's interrupt request words he will be
immediately re-interrupted.
4.3 The Core Allocator
The core allocator consists of a single special procedure, called
the core job, that does most of the work and various routines that
signal to it their interest in acquiring or releasing core.
An internal map of the status of every 2000 word block of memory
exists in the system and is maintained by the core allocator. The
majority of the complexity of the core allocator is not due to
maintaining this table but to the actions it must sometimes take
to relocate input-output buffers and other occupants of core when
a procedure wishes to expand. The lack of paging on the PDP-6
makes it sometimes neccessary to "shuff'le" core to make a
sufficient contiguous block.
Each 2000 word block must, except for two transient states, be
devoted to one of the following uses:
1. Part of a procedure's core image (ITS code and variables appear
as core allocated for the system job [Sec 6.5]).
2. A disk buffer or directory [Sec 3.1.1].
3. A display buffer.
4. Unused.
5. Further divided into 200 word blocks. These 200 word blocks are
used for core link device buffers [Sec 3.4.3] or for DEC tape
buffers or directories [Sec 3.1.2].
A procedure may request more or less core by means of a .CORE [Sec
4.3.1] and determine its memory bound without making protection
violations with a .SUSET [Sec 4.5]. Other than the .CORE UUO a
procedure's memory bound may be affected only by its destruction,
when all blocks in its core image are marked free, or a .USET [Sec
5.2.3] or .IOT on device USR [Sec 3.4.2] executed by its immediate superior.
4.3.1 The .CORE UUO
CALL: .CORE NUMBLK
;error return
;normal return
This system call requests for the procedure executing it as many
2000 word blocks as the value of its effective address except that
if this value is zero it will be treated as if it were one. If and
only if the .CORE is successful it skips. Only a .CORE to acquire
more core may fail. If it does and a more than one block increase
was being requested, some smaller number than requested may have
been obtained.
4.4 The Scheduler
The scheduler runs when a quantum time-out occurs or when the
physically running procedure encounters a blocking condition or
causes an interrupt by some program action (memory protection
violation, PDL overflow, etc.). The scheduler decides which
procedure should run next by an examination of the variables [App
D] in the system for each procedure. It simultaneously performs
those modifications of these variables necessary to provide the
simulated interrupt feature [Sec 4.2].
For those procedures that have their stop word (USTP [App D])
zero, their runnability is determined by a variable known as the
flush instruction (FLSINS) which is set when the procedure becomes
blocked. If this variable is zero the procedure is runnable. if
nonzero it is executed with the procedure's EPDL2 variable [App D]
loaded into ITS symbolic accumulator T. If the instruction skips
then the procedure is runnable and has just become unblocked. If
the flush instruction does not skip the procedure is still blocked.
The next procedure to be run is picked from among the runnable
procedures by a scan which considers two "resource" variables per
procedure. Both of these are quantized approximations to
exponential decays toward proportions of machine time. The JTMU
variable is associated with a particular procedure while the
UTMPTR variable pointer for that procedure points to a quantity
similar to JTMU maintained for all procedures in one console
controlled tree. During the scan to select the next procedure to
run, a procedure will be preferred to the best so far if its
console tree has used less time recently than that of the best so
far or its console tree has used exactly the same amount and the
procedure has used less time recently. Exceptions to this are that
a procedure is always preferred to the best so far if it has used
less than one eighth as much time recently and never preferred if
it has used more than eight times as much. Also the procedure, if
any, that has seized the .MASTER [Sec 6.8.5] facility is given
double priority and disowned procedures are given one eighth
priority unless they have the line printer (device LPT) assigned
to them or are running in executive mode when scheduled.
All disowned [Sec 5.1] job's UTMPTR's point to a single word which
is given less resource than that for a normal console tree. The
systems job [Sec 5.5] and core job [Sec 4.3] have UTAPTR's to
seperate words given the same priority as a normal tree.
The general properties of this scheduling system can be described
as follows:
1. Machine time is normally equally divided between consoles and
then between all the procedures running for each console.
2. Machine time used by a procedure is integrated with decay (time
constant about seven seconds) so
(a) a procedure that is frequently blocked for a short period of
time (compared with a quantum, currently one fifteenth of a
second) should receive equal service with a pure compute job and
(b) an interactive program called on infrequently by a user is
essentially guaranteed good service as it starts to think of a
reply but can not, on average, use more time than a pure
compute job.
4.5 The .SUSET UUO
CALL: .SUSET [DIRECTION+VARIABLE,,DATLOC]
;return
DATLOC: ;location read into or written from
Procedures may examine and modify some of their system variables
[App D] by means of this system call. The contents of its
effective address (a constant in the illustration above) is viewed
as two half words. The right half should point at the word from
which the variable is to be set or into which the variable is to
be read. The left half specifies by its top bit (4.9) whether the
variable is to be read (zero) or written (one) and by the value of
its remaining bits which system variable. The following table
lists permissible values:
Name Value Type Variable
UPC 0 07 Program counter word [Ref 1].
VALUE 1 17 Contents of effective address of most recent .VALUE [Sec 5.3.1].
TTY 2 05 Status relative to console [Sec 3.2.1].
FLSIMS 3 01 Blocking condition [Sec 4.4].
UNAME 4 05 UNAME [Sec 3.4.2].
JNAME 5 07 JNAME [Sec 3.4.2].
MASK 6 17 Interrupt mask word [Sec 4.2].
USTP 7 03 Stop word (usually only bit 4.7 can be written) [Sec 4.4].
PIRQC 10 17 First interrupt request word [Sec 4.2].
IMTS 11 01 Bit used to interrupt superior [Sec 5.1.3]].
MEMT 12 07 Memory bound [Sec 4.3], first location it would be
illegal to reference.
SV40 13 05 Last executed UUO trapping to system [Sec 1.2.1].
IPIRQ 14 17 Interrupt request word (written by an IORM).
APIRQ 15 17 Interrupt request word (written by an ARDCAM).
SNAME 16 17 System name [Sec 2.2.3].
PICLR 17 17 Interrupt level status word [Sec 4.2].
MARA 20 17 MAR register and control bits [Sec 6.4].
MARPC 21 17 Program counter at last MAR interrupt [Sec 6.4].
UUOH 22 05 Program counter word at last system UUO.
UIND 23 05 User index.
RUNT 24 05 Total run time in 4.069 microsecond units.
MSK2 25 17 Interrupt mask word two [Sec 4.2].
IFPIR 26 17 Interrupt request word two [Sec 4.2].
APRC 27 05 Disowned and processor cono status.
SV60 30 05 Saved absolute location 60.
31--77 00 Unused.
IOC 100+N 01 Input-output channel word for channel N.
IOS 120+N 01 Status word for input-output channel N.
IOP 140+N 01 Nth word of input-output channel push down list
[Sec 2.6], two words per entry.
In the above table the 1.3 bit on in the type column implies that
the variable can be read with .SUSET and the 1.4 bit implies it
can be written with .SUSET. The other type bits relate to the
.USET UUO [Sec 5.2.3].
Pre-defined symbols are available in the MIDAS assembler
consisting of a "." followed by an "R" for read or a "S" for set
followed by the string in the name column of the above table for
all its entries.
Procedure Interaction
See also section 0.3.4 and 3.4.2.
5.1 The Hierarchical Organization of Procedures
All procedures operating under ITS are members of a tree structure
recorded in the system by associating with each a pointer to its
immediate superior. If this pointer is minus one it indicates that
the procedure tops a tree. These trees may be of two types, those
under the control of a console and those that are disowned [Sec 5.2.2].
Console "controlled" trees have had their top level procedure
automatically loaded by ITS [Sec 1.1]. Since procedures may
control their inferiors and the most that the user can do in
appealing for aid when confronted with recalcitrant programs is to
cause his console to converse with higher level procedures [Sec
1.1.2], he is actually at the mercy of this top level program. It
is currently a DDT expanded by the addition of new commands
related to time sharing [Sec 7]. About the only restrictions
deliberately inserted in it relate to logging in [Sec 6.1].
Disowned procedure trees differ from console controlled trees only
in the following ways:
1. The have no console associated with them.
2. Class one interrupts in a top level procedure are handled
differently [Sec 4.2].
3. They are scheduled with lower priority [Sec 4.4].
4. Certain system calls, when executed in them, are treated as
illegal instructions.
5. Certain input-output devices are not accessible by them.
There exist a variety of means for procedures immediately above
and below each other to interact [Sec 5.2, 5.3]. Procedures may
also affect any procedure beneath them in the procedure tree by
means of input-output translation table entries [Sec 2.2.2] and an
arbitrary pair of procedures may converse treating each other as
input-output devices [Sec 3.4.3].
Among the advantages of the above system of procedure organization
are the following:
1. The highest level command processor (the top level procedure of
a console controlled tree) may vary arbitrarily from user to
user. In actual operation it is normal to see a HACTRN's whose
inferior procedure variables and symbol tables much exceed their code.
2. New versions of the highest level command processor may be
introduced simply by writing a file on the dik with no
interruption to system continuity.
3. New versions of the highest level command processor may be
easily and safely debugged by loading them as inferior
procedures. In this position they can exercise all their normal
functions except logging in and out.
4. It is not necessary to make every effort to remove all bugs
from the highest level command processor for fear that the
system may be destroyed by them, a consideration often
inhibiting more complex and powerful command languages. A fatal
error simply results in the program being reloaded.
5. Users have great generality in creating command levels of their own.
6. Multi-task programs may be organized in a consistent manner.
Items 1, 2 and 4 above argue to various extents against pure
procedures as does their inherent speed inefficiency. Having to
maintain seperate copies of the highest level command processor
for each user is not that significant a disadvantage if one
considers the amount of each copy's core image unique to each user
and that while not in actual use they could be swapped out of the system.
5.1.1 Procedure Creation
Procedures may be created only by typing ^Z on an idle teletype
[Sec 1.1.1] or by executing a .OPEN [Sec 2.2] on device USR [Sec
3.4.2]. In the second case, which is discussed here, there are
strict requirements on the "file name" used in the .OPEN. The first
file name, which will be the UNAME of the created procedure, must
be the same as the UNAME of the procedure executing the .OPEN. The
second file name, which will be the JNAME of the created
procedure, must be different from the JNAME of all jobs then in
existence that have the UNAME being used. A procedure may have a
maximum of eight directly inferior procedures. A newly created
procedure will have one 2000 word block of cleared memory and all
of its system variables initialized.
5.1.2 Attaching Disowned Procedure Trees
The only case in which a successful .OPEN [Sec 2.2] on device USR
[Sec 3.4.2] may be executed to provide an inferior procedure (as
opposed to opening a procedure for examination only) with a first
file name different from the UNAME of the procedure executing the
.OPEN is that in which the top procedure of a disowned tree is
being opened. This type of .OPEN will be treated as an illegal
instruction if executed by a procedure in a disowned tree. If not
and the opening procedure has less than eight inferiors the open
will succeed and ITS will modify the UNAME of the opened procedure
and its inferior tree to agree with the opening procedure. It will
then take each UNAME JNAME pair in the attached tree and make it
unique by incrementing the JNAME part if necessary.
5.1.3 The .UTRAN UUO
CALL: .UTRAN FBLOCK
;error return ;no inferior found for int bit
;normal return ;inferior found
FBLOCK: INTBIT,, ;UNAME stored here by call
0 ;JNAME stored here by call
When a procedure is first created by a .OPEN, ITS assigns to it a
bit for use in interrupts [Sec 4.2] to its superior procedure
different from that for any other inferior procedure its superior
may have. Since inferior procedures can only be directly
controlled when open on input-output channels, the loss of the
name of an inferior by its superior while it was not open would
result in complete loss of communication. Although procedures that
have inferiors normally keep close track of their names and
interrupt bits as read by .USET's [Sec 5.2.3], this system call
has been provided to translate from particular interrupt bit to
name of inferior. The left half of the contents of the effective
address must have only the appropriate interrupt bit on. If a
corresponding inferior procedure is found, the .UTRAN skips and
the UNAME and JNAME of the inferior are stored in the two words
after the word containing the interrupt bit. If not corresponding
inferior is found the .UTRAN will fail to skip and the two
locations after the location it effectively addresses will be unmodified.
5.2 Controls over an Immediately Inferior Procedure
See also section 3.2.1.1.
5.2.1 The .UCLOSE UUO
CALL: .UCLOSE CHNUM,
;return
Procedures may be destroyed only by the execution of a .LOGOUT
[Sec 6.1] or a .UCLOSE. The second of these two system calls,
which is discussed here, destroys the inferior procedure open on
the channel specified by its accumulator field (CHNUM in the above
illustration) and the entire procedure subtree of which this
inferior is the top procedure. If an inferior is not open on the
channel, the .UCLOSE'ing procedure will receive an input-output
channel error interrupt. .CLOSE's [Sec 2.7.1] are automatically
effected on all channels of all destroyed procedures and any
system resources they claim are surrendered (by possibly
simulating a .DCLOSE, .HANGUP, and/or .MASTER). In order to kill
certain cancerous types of procedure subtrees it has been found
necessary to implement this system call such that it first stops
all procedures in the subtree and then destroys them.
5.2.2 The .DISOWN UUO
CALL: .DISOWN CHNUM,
;return
This system call requires that an inferior procedure be open on
the channel specified by its accumulator field (CHNUM in the above
illustration) or the .DISOWN'ing procedure will receive an
input-output channel error interrupt. It causes this open
procedure to become the top procedure of a disowned tree [Sec 5.1]
and in the process closes all channels on which the disowning
procedure has it open. A procedure in a disowned tree that tries
to execute this system call will be unsuccessful and receive an
illegal instruction interrupt [Sec 4.2] as will a procedure trying
to disown a subtree that controls the tree's console [Sec 3.2.1.1].
5.2.3 The .USET UUO
CALL: .USET,[DIRECTION+VARIABLE,,DATLOC]
;return
DATLOC: ;location read into or set from
This system call was created to allow a procedure to set and read
many of the system variables [App D] associated with its inferiors
and to read variables associated with other procedures. When
executed its accumulator field must contain the number of a
channel (CHNUM in the above illustration) on which a procedure
open or the .USET'ing procedure will receive an input-output
channel error interrupt. Otherwise it is very similar to .SUSET
[Sec 4.5]. Reading is allowed if the 1.1 bit is on in the type
column of the table in section 4.5. Setting is allowed for
immediate inferiors if the 1.2 bit is on in that table.
5.3 Communication to an Immediately Superior Procedure
5.3.1 The .VALUE UUO
CALL: .VALUE ARGLOC
;return if restarted
ARGLOC: ARG ;transmitted to superior procedure
A procedure executing this system call receives a class one
interrupt [Sec 4.2] stopping it and interrupting its superior
procedure. The contents of the effective address is saved in a
system variable associated with the procedure [App D] so its
superior can easily retreive it with a .USET [Sec 5.2.3].
5.3.2 The .BREAK UUO
CALL: .BREAK ARG1,ARG2
;return if restarted
The accumulator field and effective address of this UUO are
ignored by ITS. A procedure executing it receives a class one
interrupt [Sec 4.2] stopping it and interrupting its superior procedure.
5.4 The .GUN UUO
MOVEI AC,USRINDEX
CALL: .GUN AC,
;failure return
;normal return
This system call, intended for use as a last resort, allows any
procedure in a console controlled tree to expunge another tree
from the system. The procedure specifies the tree to by .GUN'ed
down by the user index (see section 8.2, mode N) of its top
procedure. This is used instead of the normally unique UNAME JNAME
pair so that easy reference may be had to procedures not logged in
[Sec 6.1]. The contents of the accumulator specified by a .GUN
must be the user index (can be read with .USET) of a top level
[Sec 5.1] procedure other than the system job [Sec 6.5] or core
job [Sec 4.3]. If the procedure executing the .GUN is in a
disowned tree it will receive an illegal instruction interrupt.
The .GUN skips if successful at which point the system job will
have been informed of the tree it is desired to expunge, which
action the system job will, in due course, perform, also typing
out an appropriate message. If the above restrictions on the
specified user index are not met the .GUN will return without skipping.
Miscellaneous System Calls and Features
See also section 0.3.5.
6.1 The .LOGIN and .LOGOUT UUO's
These two system calls are the only ones that are effective only
at the top level.
CALL: .LOGOUT
;return if not top level
.LOGOUT has no effect and simply returns from the system to the
instruction following if not executed in a top level procedure. It
causes the procedure tree in whose top procedure it is executed in
to be expunged from the system. It works for both console
controlled trees and disowned trees. Since the normal means to
create [Sec 5.1.1] and destroy [Sec 5.2.1] a procedure under ITS
are calls in a superior procedure, the special case of the top
level procedure must be handled differently as it is by ^Z [Sec
1.1.1] and .LOGOUT.
MOVE AC,[SIXBIT /NAME/]
CALL: .LOGIN AC,
;error return
;normal return
.LOGIN is not restricted to top level procedures by ITS but rather
by HACTRN, the top level procedure ITS automatically loads [Sec
7]. A .LOGIN represents an attempt by a procedure to set its UNAME
to the contents of the accumulator specified. This is allowed by
ITS only if the procedures's current UNAME is minus one (as the
UNAME of initial HACTRN's is set) and the desired UNAME is neither
zero, minus one, nor the UNAME of an extant console controlled
tree. The success of a .LOGIN is signalled by its skipping. HACTRN
will not open inferior procedures for a user until he has
successfully logged in at which point his inferior procedures will
have UNAME's dooming future .LOGIN's in that tree to failure.
6.2 Nonstandard Devices
6.2.1 The .RDSW UUO
CALL: .RDSW AC,
;return
This system call reads (DATAI's [Ref 1]) the contents of the data
switches on the PDP-6's console into the specified accumulator.
6.2.2 The .RD760 and .WR760 UUO's
CALL: .RD760 AC,
;return
CALL: MOVE AC,[BITS]
.WR760 AC,
;return
These system calls respectively read the data register (DATAI) of
the device whose PDP-6 device number is 760 into the specified
accumulator and output (DATAC) from the specified accumulator to
the data register of the device [Ref 1]. The bits in the data
register of this device are usually used for temporary direct
control or sense hookups. Currently the bottom six bits control
lights on the hand of the AMF arm [Sec 3.3.2].
6.2.3 The .RD710 UUO
CALL: .RD710 AC,
;return
The real time clock, which ITS currently uses to time user quanta,
has, as well as an interval timing counter, a clock counter which
is neither set or stopped by ITS. This system call reads into the
specified accumulator a word whose bottom twenty four bits are
this clock counter. It is incremented once every 4.069 microseconds.
6.2.4 The .RD500 UUO
CALL: .RD500 AC,
;return
This call reads (DATAI's) into the specified accumulator from
device 500. This device is purported to be or become yet another
kind of clock. See Paul DeCoriolis for more information.
6.3 Various Times and the Date
6.3.1 The .RDTIME UUO
CALL: .RDTIME AC,
;return
This system call reads into the specified accumulator the internal
system time which is a word set to zero when a system is first
loaded and is incremented every thirtieth of a second thereafter.
This quantity is useful in conjunction with .SLEEP [Sec 6.8.1].
6.3.2 The .RTIME UUO
CALL: .RTIME AC,
;return
After the system has determined real (24 hour system) time, it
maintains this internally as a number in units of one half second
since the last midnight. This system call reads into the specified
accumulator in sixbit characters this time in pairs of digits,
reading from the left, hours, minutes, and seconds. If the time
has not yet been determined, minus one will be read.
6.3.3 The .RDATE UUO
CALL: .RDATE AC,
;return
After the system has determined the calendar date, it maintains it
internally as a word with sixbit characters in it. These
characters are all numeric. The first two are the last two digits
of the year, the next two are the month number, and the last two
digits are the day of the month. This system call reads this word
into the specified accumulator. If the date has not yet been
determined, minus one will be read. In the current implementation,
the date being determined implies that the time [Sec 6.3.2] has
been determined. The date is correctly incremented every midnight.
6.4 The MAR Feature
In order to simulate the address stop facility of the PDP-6 in a
time shared mode, it was decided to introduce a new hardware
register, the MAR register, to cause interrupts when a particular
location was addressed by the computer. To increase the
flexibility of this feature, three control bits were added which
further define the interrupt condition given that a memory address
match has occurred.
Among the system variables [App D] kept by ITS for each procedure
are its MAR register contents and control bits. These are loaded
into the hardware as the user is started. Since the MAR feature is
intended primarily as a debugging aid, it causes a class two
interrupt [Sec 4.2] and a .USET [Sec 5.2.3] is used to set it from
DDT [Sec 7] more frequently than a procedure sets its own with an
.SUSET [Sec 4.5].
.USET and .SUSET take the right half of the word set from as the
new address to be put in the MAR register and the low three bits
of the left half as control bits as follows:
Bit Meaning (one state)
3.3 Interrupt if data read or written is negative
3.2 Interrupt if data read or written is positive
3.1 Interrupt only on a write
At this time, attempts to differentiate read cycles on the basis
of sign will fail as, due to a timing error, the data always
appears positive. If a write cycle is interrupted on, the
protected location will have been modified when the interrupt is processed.
When an MAR interrupt occurs, further MAR interrupts are disabled
until the MAR is again set. A .SUSET or .USET may be used to read
the word stored by the JSR at the system's processor interrupt
channel location when the last MAR interrupt occurred.
Although, for their own safety, some parts of executive code
inhibit MAR interrupts, it is quite possible for the user to cause
some system calls to interrupt to the user, on reference to his
core image where his MAR is pointing. The program counter word
stored by the JSR at the user's location 42 [Sec 4.2] will be the
location in his core image of the offending system call. The word
read by a .SUSET or .USET will be an executive program counter
word showing the absolute location at which the system call first
attempted to reference the user's protected location.
6.5 The System Job
There are various tasks ITS would like to perform, most of which
include input-output or waiting indefinite periods of time, which
would be inconvenient to implement directly due to the procedure
originated orientation of almost all system routines. Because of
this a procedure was synthesized, known as the system job, that is
actually a part of the monitor and always runs in executive mode.
To aid in debugging ITS a feature was added to the system job so
that when it had no other tasks to perform it would compare
constant parts of ITS against a copy it makes initially [Sec
6.5.1]. The following are some of the other tasks the system job performs:
1. Does .CORE's [Sec 4.3.1] for ITS to make room for more blocks
of user variables or for the system job's copy of constant parts
of ITS.
2. Prints messages on the system console whenever an effective
.SETLOC, .GUN, .IOTLSR, .LOGIN, .LOGOUT, or .OPEN for output or
.FDELE on device SYS is executed.
3. Prints messages on the system console when a parity error,
unrequested change in teletype priority interrupt channel
allocation, memory excessively full condition, or garbage
collection of DSK user directory is detected.
4. Initially determines the 24 hour time and calendar date [Sec
6.3.2, 6.3.3].
5. Prints a message on all teletypes when the system is first loaded.
6. Outputs a "CONSOLE FREE" message on any teletype when it is no
longer open by any procedure.
7. Various tasks related to the system going down feature [Sec
6.5.2] and TPL device [Sec 3.4.5].
6.5.1 The .SUPSET UUO
MOVEI AC,2
CALL: .SUPSET AC,
;return
The system job is partially controlled by ITS through a word in
system memory. Bits to the left of 2.8 in this system word
represent requests for some transient action. In the right half
the bottom two bits (1.1--1.2) are currently used. Bit 1.1
controls the system checking feature. If this bit is on, the
system job makes a copy of the constant parts of ITS and procedes
to spend its spare time checking the areas it copied against the
copy. If a discrepency occurs, a message is printed and the copy
corrected. If this bit is off, the system job will destroy any
copy it may have, freeing that memory and most of the fraction of
the machine time the system job uses when in checking mode.
Bit 1.2 affects the TPL device [Sec 3.4.5]. If it is on, TPL use
of the LPT device is inhibited. Furthermore if a TPL file is being
printed when this bit is turned on, it will be deleted, output
will be aborted, and the LPT device freed.
The .SUPSET system call enables the user to control the system
checking bit by XOR'ing [Ref 1] bits 1.1--2.8 of the specified
accumulator into the system job control word and returning the
resulting value in the specified accumulator. It also types out a
message on the system job console like the message for .SETLOC.
6.5.2 The System Going Down Feature
To provide an orderly means for the termination of the operation
of ITS, a special feature has been added. It is activated by
setting absolute location 37 negative (either with the PDP-6
console keys [Ref 1] or a .SETLOC [Sec 3.8.4]) or using .SHUTDN
[Sec 6.5.2.1]. After a negative location 37 is noticed, all
procedures for which it is enabled will receive a system going
down interrupt [Sec 4.2] and all free teletypes have an
appropriate message typed on them. Then a five minute timer is
started and new console trees started [Sec 1.1.1] will be given a
system going down interrupt right after they are created.
When the timer times out or when the number of console controlled
trees in which successful .LOGIN's [Sec 6.1] have been executed
goes to zero, all trees are forcably logged out and a message
typed on all teletypes. All DEC tapes [Sec 3.1.2] for which the
system is retaining a directory are flapped.
6.5.2.1 The .SHUTDN UUO
MOVE AC, [TIME]
CALL: .SHUTDN AC,
;error return
;normal return
This system call, which is illegal for procedures in a disowned
tree, is a request for the system to go down [Sec 6.5.2] in as
many thirtieths of a second as the contents of the specified
accumulator. If an amount less than five minutes is specified, it
will be treated as though it had been five minutes. If the system
is already going down in less time than specified, this call will
be ignored and return without skipping.
If the system is going down in a longer time than specified or not
going down at all the call will succeed and skip. It will cause a
system going down interrupt to all enabled procedures and start a
timer for the specified length of time. New console trees created
thereafter [Sec 1.1.1] will also receive a system going down
interrupt when created. If the time till system death passes
through five minutes, all enabled procedures will be interrupted again.
The conditions for and actions on actual death are as in section 6.5.2.
6.5.2.2 The .DIETIM UUO
CALL: .DIETIM AC,
;return
This system call sets its specified accumulator to minus one if
the then running ITS is not going down [Sec 6.5.2]. If it is, the
accumulator is set to the maximum time till system death in
thirtieths of a second.
6.6 Examining ITS
6.6.1 The .GETSYS UUO
MOVE AC,[--LENGTH,,DATLOC]
MOVE AC+1,[SIXBIT /AREA/]
CALL: .GETSYS AC,
;error return
;normal return
DATLOC: BLOCK LENGTH ;area read into
This system call enables a procedure to receive copies of various
internal monitor areas in such a way that the data in those areas
must be consistent. The specified accumulator contains a pointer
word as for a block mode .IOT [Sec 2.3]. If the left half of the
accumulator is zero, the block is treated as running to the end of
the user's core image. The location following the specified
accumulator contains, in left justified sixbit, the area requested
as follows:
Sixbit Area
TRANS Translation table [Sec 2.2.2].
GETS List of things which can be requested with .GETSYS.
DEVS List of available symbolic input-output devices [App C].
MEMORY Memory allocation tables [Sec 4.3].
UTAPE DEC tape routine variables [Sec 3.1.2].
CLINK Core link variables [Sec 3.4.3].
CALLS List of symbols in squoze [Ref 3] for system calls [App A]
and .SUSET [Sec 4.5] left halves and their values.
DSYMS Symbol table for ITS.
IMPX Area input multiplextor cycled into [Sec 3.3.3].
OMPX Area output multiplexor cycled from [Sec 3.3.2].
USERS User variables for all procedures [App D].
USER User variables for particular user specified by UNAME and
JNAME in locations two and three greater than the specified
accumulator [App D]. If user not found location containing
UNAME will be zeroed.
Interrupts are inhibited to a sufficient extent that the data
obtained can not be inconsistent due to the area's modification
while being transferred to the user. A successful .GETSYS will
skip. One that fails, due to non-recognition of its sixbit word or
insufficient memory specified by its pointer word, will not skip
and in the former case the sixbit word will be zeroed.
6.6.2 The .GETLOC UUO
MOVE AC,[ABSLOC,,DATLOC]
CALL: .GETLOC AC,
;return
DATLOC: 0 ;contents of ABSLOC stored here
This system call simply transfers the contents of the absolute
location pointed to by the left half of the specified accumulator
to the user's relative location pointed to by the right half. If
the right half points beyond the user's memory bound he will
receive an illegal instruction interrupt [Sec 4.2].
6.6.3 The .RSYSI UUO
CALL: .RSYSI AC,
;return
This system call reads into the specified accumulator the sixbit
representations of the second file name of the symbolic file that
was assembled to produce the running version of ITS.
6.6.4 The .EVAL UUO
MOVE AC,[SQUOZE sym]
CALL: .EVAL AC,
;error return
;normal return
The .EVAL system call allows a user to easily look up symbols in
high core DDT's table of system symbols. The "squoze" code [Ref 3]
for the symbol should be put in the accumulator specified. If the
symbol is not found, the call will return without skipping. If it
is found its value will be placed in the specified accumulator and
the call will skip on returning.
6.7 The One Proceed Feature
The Project MAC AI Group PDP-6 has been modified so that there
exists a mode in which it executes one instruction and then traps.
This mode is properly stored when an interrupt occurs and is
restored by JRST 2, [Ref 1]. For users it causes a class one
interrupt and is expected to be used by superior (such as DDT [Sec
7] procedures by .USET'ing [Sec 5.2.3] the 3.9 bit of their
inferior's program counter word. There is coding in ITS such that
all system calls will appear to be single instructions using this
mode. While in this mode a user interrupt may be serviced and the
user's status, including this mode, will be restored by a normal
.DISMISS [Sec 4.2.2].
6.8 Miscellaneous
6.8.1 The .SLEEP UUO
MOVE AC,[TIME]
CALL: .SLEEP AC,
;return eventually
This system call allows a procedure to stop running, while
remaining interruptable, by either specifying a length of time to
remain quiescent or a particular time to wake up. If the specified
accumulator contains a positive number it is considered the length
of time, in thirtieths of a second, that the procedure wishes to
sleep. If the specified accumulator contains a negative number
then the procedure will sleep until the magnitude of system time
(as read by .RDTIME [Sec 6.3.1]) is greater than the magnitude of
this negative number. When a .SLEEP returns, the accumulator
specified will be zero, but if a program is interrupted out of
either type of .SLEEP the accumulator will be seen to contain the
appropriate negative number.
6.8.2 The .GENSYM UUO
CALL: .GENSYM AC,
;return
This system call returns in the specified accumulator a valid
sixbit file-name-like symbol that will be unique among those
returned by .GENSYM's for a particular system run.
6.8.3 The .IOTLSR UUO
MOVSI AC,400000 ;or 0 to release
CALL: .IOTLSR AC,
;return
Procedures run by ITS in IOT-user mode may execute hardware
input-output instructions which would otherwise be ineffective and
trap to the monitor. This system call sets the IOT-user status of
the procedure executing it from the sign bit of the specified
accumulator. If this bit is a one the procedure will attempt to
enter IOT-user mode. If it is not currently in IOT-user mode it
will enter it and a message will be output by the system job [Sec
6.5] unless the procedure is in a disowned tree in which case it
will receive an illegal instruction interrupt [Sec 4.2]. If this
bit is a zero, the procedure will not be in IOT-user mode after
the .IOTLSR.
6.8.4 The .SETLOC and .IFSET UUO's
MOVE AC,[DATLOC,,ABSLOC]
CALL: .SETLOC AC,
;return
DATLOC: ... ;data from here written in ABSLOC
The .SETLOC system call treats the specified accumulator as two
half word pointers. It takes the contents of the relative user
location pointed to by the left half and places it in the absolute
location pointed to by the right half and causes the system job to
output an appropriate message [Sec 6.5] unless the procedure
executing it is in a disowned tree in which case the procedure
will receive an illegal instruction interrupt [Sec 4.2].
MOVE AC,[DATBLK,,ABSLOC]
CALL: .IFSET AC,
;error return
;normal return
DATBLK: TESTWD ;tested against c(ABSLOC)
SETWRD ;set into ABSLOC if test succeeds
The .IFSET system call is very similar to .SETLOC. The left half
of its accumulator, however, points to a two word block. It first
compares the first of these two words against the specified
absolute location. If they are not equal, it returns immediately
without skipping. If they are equal, it proceeds as for .SETLOC
but sets from the second word of the block and skips on returning.
Going to the extra effort to use .IFSET is much safer of you think
there is some chance that the absolute location you are setting
may be moved by the core allocator.
6.8.5 The .MASTER UUO
MOVSI AC,400000 ;or 0 to release
CALL: .MASTER AC,
;error return
;normal return
ITS has a specified feature whereby one procedure can receive
peferential treatment. It will be scheduled [Sec 4.4] with twice
the priority of a normal procedure (running in competition with a
second running job, it would reach an equilibrium where it was
using twice as much machine time) and is given preference in the
use of the DEC 340 display [Sec 3.4.1].
To request this status a procedure should execute a .MASTER with
the 4.9 bit of the specified accumulator a one. It will succeed,
and the .MASTER will skip, if no procedure has the facility seized
or if the procedure executing the .MASTER has control [Sec
3.2.1.1] of teletype T00 (the "main console" in front of the 340
display). If the later case, the facility may be removed from
another procedure having it. A failing .MASTER returns without skipping.
The facility may be released by executing a .MASTER with the
specified accumulator having bit 4.9 zero. This always skips even
if the procedure does not have the facility to release.
6.8.6 The .REDEF UUO
MOVEI AC,SYMBLK
CALL: .REDEF AC,
;error return
;normal return
SYMBLK: SQUOZE BITS,sym
VALUE
This system call allows the user to define, redefine, and delete
system symbols from high core DDT's symbol table. It is illegal
for a procedure in a disowned procedure tree. The accumulator
specified by it should contain a pointer to a two word block. The
first word in this block should be the "squoze" code [Ref 3] for the
symbol to be affected. The second word is the new value for a
define (the symbol is not currently in the table) or redefine (the
symbol currently is in the table). A delete request is indicated
by having all four squoze flag bits (BITS in the above
illustration) on. The call skips if successful. It can fail only
on an attempt to define a new symbol when there is no more room
above the time sharing system.
DDT
See also section 0.4.1.
7.1 Introduction
DDT is a general purpose machine language debugging program that
has been extensively modified to act as a supervisory procedure in
ITS. It is automatically loaded by ITS [Sec 1.1.1] when a user
informs ITS of his presence at an idle teletype. All further
requests of the system by the user, until he logs out, are by
means of trapping instructions [Sec 1.2] executed for the user,
possibly as a result of characters he types in, by DDT or
procedures inferior [Sec 5.1] to and under the control of DDT. The
current binary of DDT exists as the file "@ HACTRN" on device SYS
[Sec 3.1.3]. For historic reasons, a top level DDT is known as a
HACTRN (pronounced hack-tran).
The initial command structure of DDT provided single character
debugging commands of limited mnemonicity. This structure was
badly strained by the introduction of time-shared related
commands. Then a new set of multi-letter commands was introduced.
This set was expanded with the thought of providing all the most
frequently used commands that did not relate to machine language
debugging. Since a beginning or transient user might wish to use
only these mnemonic commands, a mode switch was added to DDT.
There is a "monitor mode" in which only the multi-letter commands
are available besides a few interrupt level commands that are
unaffected by mode. In "DDT mode" all of the single character
debugging commands are also available.
Section 7.2 below gives more information on monitor mode and
describes almost all monitor mode commands. Section 7.3 describes
the few interrupt mode commands in HACTRN and section 7.4 explains
how DDT tells the user about error conditions. The information in
these three sections should be more than enough to enable
extensive use of ITS, particularly the conversational and
interpretive programs avaiable under it (such as TECO, LISP and STRING).
The remaining section (7.5) gives information on finding out about
DDT mode commands. These would be important to someone developing
a machine language program.
7.1.1 When DDT Starts
When a new copy of DDT is started, it types out certain useful
information. If output is to a GE Datanet 760 console, it first
clears the screen. Then it types out "DDT.xxx." where xxx is the
version number of the DDT so that bugs can be correctly matched to
version. Then, if ITS is in the system going down mode [Sec
6.5.2], a message indicating its remaining life span is output.
Finally, if a file named "SYSTEM MAIL" is found on device SYS [Sec
3.1.3], it is typed out.
7.2 Monitor Mode Commands
When in monitor mode [Sec 7.1], DDT indicates its readiness to
accept a command by typing out a ":". At this point the user can
type a series of letters followed by a break character (normally
space or carriage return). DDT looks up this symbol (or its first
six letters if longer) in a table of monitor mode commands. A user
may also type a comment that will be ignored by DDT in or before
this string by beginning and ending it with an "^$" (alt.-mode). No "^$"
s may be embedded in the comment. If the symbol is found, control
is transferred to a routine associated with it which may perform
immediate actions or wait for more information to be typed by the
user. At any time during the typing of a command, the user can
abort and start over by typing a rubout.
If the string (say "llll") after the ":" is not found in DDT's command
table, it looks for a file called "TS llll" on device SYS [Sec
3.1.3]. If not found an error comment [Sec 7.4] to that effect is
output. If found, an inferior procedure is created, this file
loaded into the inferior core image, and it is then started. The
effect is as though the following [Sec 7.2] were typed:
:JOB llll
:LOAD SYS: TS llll
except that symbols for the program are not loaded into DDT from
the file and the normal effects of :LOAD on the current file and
device names in DDT is absent.
7.2.1 Logging In and Out
:LOGIN uname
This command takes as its argument the "uname" that the user wishes
to log in with [Sec 6.2]. A "?" will be typed out and the command
will be ineffective if someone is already logged in with that
name. For ease in accessing his disk files, a user should use a
consistent UNAME.
At the time the user logs in, DDT looks for a file names "uname MAIL"
on device COM [Sec 3.1.3]. If not found, no action is taken by
DDT. If found, DDT types it out, deletes the file "uname OMAIL", if
any, on device COM, and renames the "uname MAIL" file as "uname OMAIL".
:LOGOUT
This command expunges all of the user's procedures from the system
including the user's HACTRN [Sec 6.1]. The teletype the user was
typing on will become free and a message to that effect will be
typed out on it by the system job [Sec 6.5]. DDT also deletes the
file "uname OMAIL" on device COM at this time (where "uname) is the
name the user logged in as).
7.2.2 Inter User Communication
:MAIL uname string...^C
This command takes as its first argument the user name of someone
who uses ITS and as its second argument a string terminated by a "^C"
. The command prefixes the string to the file "uname MAIL" on device
COM [Sec 3.1.3] if such a file exists. If no such file exists, one
is created with the string as its contents. This file is presented
to the specified user when he logs in [Sec 7.2.1]. The user can
rubout individual characters while typing the string or cancel the
command by typing enough rubouts.
:BUG string...^C
This command is intended for use in reporting bugs in systems
software. It is identical to ":MAIL SYS string...^C".
:SEND uname string...^C
This command takes arguments like :MAIL above but attempts to send
the message string supplied to the user specified in a direct
manner so that, if he is logged in, his HACTRN will type the
string out on his console. If he is not logged in, DDT will type
out "(MAIL)" and perform the actions specified under :MAIL above.
:GAG number
This command enables a user to gag messages that other users may
attempt to send the him with :SEND (above). It takes a numeric
argument that is bit decoded as per the table below.
Bit Source
1.1 Other user's inferiors.
1.2 Other user's HACTRN's.
1.3 Your inferiors.
1.4 Your HACTRN (yourself).
If a bit is on it inhibits messages from the source listed. If
off, messages are not inhibited. The initial state is :GAG 1.
The current implementation gives no way to tell if a message sent
was gagged by the intended receiver.
7.2.3 Inferior Procedures
:JOB {jname}
This command may be followed by an optional job name [Sec 5.1]. If
there is an inferior procedure with this JNAME it will be selected
by HACTRN as its "current job" (possibly attaching a disowned tree
[Sec 5.1.2]). Many commands in DDT affect the current job only as
this changes infrequently and one would not want to respecify it
with each command. If there is no inferior with the specified
name, one will be created [Sec 5.1.1] and selected as the current job.
The job names SYS and PDP10 are special. The first allows the user
limited access to absolute core. The second allows full access to
the core image of the PDP-10 [Sec 3.4.2.1] to one user.
If no argument is supplied to :JOB it attempts to select some job
different from the current one and types out "jname$J" to inform the
user it has selected job "jname". If there is no current or other
job, nothing it typed out. If the current job is the only inferior
of HACTRN it will be reselected. If other inferiors exist one is
selected in such a way that all inferiors are cycled through by
successive :JOB's with no argument.
:KILL
This command obliterates [Sec 5.2.1] the current job and all its
inferiors if it is an immediate inferior. If not an immediate
inferior the variable space for it in HACTRN is reclaimed and
logical pointers to it obliterated. In either case a :JOB with no
argument is then simulated to minimize the time during which there
is no current job.
:LISTJ
This command lists all of the inferiors of which HACTRN is aware.
An "*" is printed before the current job, if any. After each job
will be a character indicating its state as follows:
Character Status
-- Just created or loaded.
R Running.
P Procedable from random interrupt.
Bn Procedable from breakpoint n [Sec 7.5].
W Interrupt/message to HACTRN pending.
After this letter is the user index of the procedure (see section
8.2, mode N). An example of :LISTJ output appears in Appendix G.
:DISOWN
This command disowns [Sec 5.2.2] the current job, deselecting it,
expunging all information about it in HACTRN, and simulating a
:JOB with no argument.
:LOAD {file specification}
This command attempts to load a file into the current job. HACTRN
has a current device, system name [Sec 2.2.3], and pair of file
names which it will use if nothing is specified after a command
taking a file argument. This current file is initially device DSK,
file name "@ BIN", and the system name the user logged in as [Sec
7.2.1]. Various fields can appear in the file specification
distinguished by their terminating character. A "dev:" field sets
the device to "dev". An "sname;" sets the system name to "sname". A
field terminated by a space or carriage return (the later
indicating the end of the file specification) is treated
differently depending on how many of this type of field have been
seen. The first, if any, such becomes the first file name. The
second, if any, becomes the second file name. A third, if
supplied, becomes the device name (as if followed by a ":") and
indicates the end of the file specification.
:DUMP {file specification}
This command dumps the current job as a file optionally specified
as in :LOAD above.
:START {number}
This command starts the current job, giving it control of the
user's console [Sec 3.2.1.1]. If no argument is supplied it is
started at the last place it was started with a :START. if not
:START'ed before then at the assembled-in starting address that
was read in as the program was loaded. If no starting address was
supplied a "?" is typed out.
If a numeric argument is supplied, the job is started at the
specified address which is stored away for future :START's without argument.
:CONFIX{UE}
This restarts the current job if it is stopped and gives it
control of the user's console. It can be used to continue after
returning to HACTRN with a "^Z" [Sec 1.1.2].
:PROCED
This command restarts the current job if it is stopped but leaves
HACTRN in control of the user's console. Using this command the
user can easily get several inferiors running at the same time.
7.2.4 Files and Input-Output
:PRINT {file specification}
This command treats a file as ASCII characters and prints it out.
It accepts an optional file specification as described under :LOAD
[Sec 7.2.3] above.
:DELETE {file specification}
This command deletes [Sec 2.4] a file. It takes an optional file
specification as described under :LOAD [Sec 7.2.3] above.
:LISTF {device name}
This command lists the files on HACTRN's current device or the
device specified as an argument [Sec 2.2.1].
:FLAP number
This command must be followed by the number of a DEC tape drive.
It causes the tape on the specified drive to by physically
demounted and its directory to be excised from ITS [Sec 3.1.2.1].
:LINK {file name pair} sname; fnam1 fnam2
This command creates a link [Sec 3.1.1.1] under HACTRN's current
system name to the file "fname1 fname2" under system name "sname". The
link's file name is also "fnam1 fnam2" unless the optional file
names shown above are supplied.
7.2.5 The "Control-P" Feature
DDT has a feature which is designed to reduce the need to
repeatedly type the same or very similar file names at different
systems programs. For historic reasons this is called a "Control-P"
feature. This feature is implemented using a block of four
locations in DDT. These are deposited in the core image of a newly
loaded inferior by the execution of certain DDT mode [Sec 7.5]
commands and certain of the commands explained below. The
locations set in an inferior and their significance are as follows:
Location Significance
50 First file name.
51 New second file name.
52 Current second file name.
53 Old second file name.
:CR
This command reads in a file name as for :LOAD [Sec 7.2.3]. It
puts the first file name read in the DDT word to be deposited in
location 50. It puts the second file name in the DDT word to be
deposited in location 52 and the second file name incremented in
the word to be deposited in location 51. It clears the word to be
deposited in 53 and finally loads, deposits in 50 through 53, and
starts a copy of TECO, the normal ITS editing program, as for a
:TECO [Sec 7.2] except for the depositing in 50 through 53.
:ED
This command increments the file name in the location to be put in
51 and then puts the incremented file name back after moving what
was there into the location to be put in 52 and similarly moving
that word into the location to be put into 53. it then loads,
deposits in, and starts a copy of TECO, the normal ITS editor, as
for a :TECO [Sec 7.2] except for the depositing in 50 through 53.
:ST
This command simply reads a file name and does the same thing with
it as :CR (described above) except it does not load or start a TECO.
7.2.6 Miscellaneous
:?
This command lists all important monitor mode commands with a
short explanation of each. An example is shown in Appendix G.
:DDT
This command switches HACTRN to DDT mode [Sec 7.1].
:MON
This command switches HACTRN to monitor mode [Sec 7.1].
:XFILE {file specification}
This command reads the file, optionally specified as for :LOAD
[Sec 7.2.3] above, and, treating it as ASCII, executes it as
HACTRN commands.
:SYNLOD
Mostly useful in conjunction with DDT mode [Sec 7.5] commands,
this command loads symbols only for the current job. It takes an
optional file specification as for :LOAD [Sec 7.2.3] above.
:ERR
Mostly useful in conjunction with DDT mode [Sec 7.5] commands,
this command interprets the last quantity typed out by HACTRN as a
.STATUS [Sec 2.5] word using the ERR device [Sec 3.4.4].
7.3 Interrupt Level and Context Tree Commands
There are six single character commands to HACTRN that are
interpreted at its interrupt level or at its top level in a manner
independent of and not affecting the context in which they occur.
They are presented in alphabetic order below. Two provide the user
with the ability to "silence" any particular output of his HACTRN
and abort it from a hung state. The remaining four control where
HACTRN's output goes.
Character Effect
^B Attempts to seize the line printer [Sec 3.2.2]. If successful, causes HACTRN output
to be printed.
^E Releases the line printer [Sec 3.2.2] and stops HACTRN output from being printed.
^G Interpreted at the interrupt level, this command causes HACTRN to abort from
whatever it is doing, type out ""QUIT?, and wait for new commands. This command
should only be used when necessary (ie HACTRN seems to be permanently hung
up) as there is almost no protection from interrupting out of embarrasing places where
variables are out of phase, etc. All buffered type in and out is also reset [Sec 2.7.2].
^S This character is interpreted at both interrupt and top level. It inhibits HACTRN output,
also doing a type out reset [Sec 2.7.2], between these two interpretations. Thus ""^S
is a much less drastic step than ""^G (above) to be used when the only trouble is that
HACTRN is being somewhat long winded. It re-enables output when HACTRN gets
around to it at the top level.
^V This command causes HACTRN output to be typed. It is the initial state.
^W This command stops HACTRN output from being typed.
7.4 Error Comments
DDT used to have two error comments, "U" and "?". The first of these
is typed out when an undefined symbol is evaluated, usually when
it is terminated by a non-symbol-constituent. The second was typed
out for all other errors. it has been significantly augmented.
Errors in attempting to open, rename, or delete a file are
indicated by the comment produced by the ERR device [Sec 3.4.4]
followed by the symbolic name of the device and a question mark.
In the case of an input-output error interrupt from an .IOT or
.OPER, a special check is made to see if the error is device full
on the input-output channel on which dumps are written. If so, the
partial dump is deleted and an appropriate message output.
Otherwise, the following error comment is output.
n, m, p, IOC?
where n is the error number, m the input-output channel on which
it occurred, and p the location of the offending .IOT or .OPER.
For other errors indicated by interrupts the following is output:
n, p, INT?
where n is a number with the interrupt bits on and p is the
location interrupted from.
Other error comment listed in the following table:
Output Meaning
NML? Interrupt from unknown inferior.
TMJ? Attempt to have too many inferiors.
CKS? Checksum error on load.
EOF? Unexpected end-of-file on read.
CFT? Unable to assign console to inferior.
COR? Can't get more core.
JOB? No current job.
UNF? DEC tape unflappable.
DSK? Disown failed.
TMS? Too many undefined symbols.
ILUUC? Illegal UUO executed in DDT.
LOGIN? You are not logged in.
7.5 DDT Mode Commands
Monitor mode commands may also be used in DDT mode. It is simply
necessary for the user to type the initial ":". For further
information on DDT mode commands, references 2, 7 and 8 of this
memo are recommended. Also one might try next year's edition of
this memo.
PEEK
8.1 Introduction
PEEK is a utility program operating under ITS. It enables a user
to monitor a variety of aspects of the time sharing system by
providing periodically updated display output or periodic
character string output to teletype or line printer. Commands to
PEEK are single letters sometimes preceded by numeric arguments.
When initially started, PEEK is in N, or normal, mode [Sec 8.2].
If the uder is on a GE console [Sec 3.2.1] PEEK will initially
start outputing by typing (which, on a GE console, is effectively
displaying). If the user is on a teletype, PEEK will try to seize
the 340 display [Sec 3.4.1] and either display on the 340 or type
its output depending on whether it succeeds or fails,
respectively. This may be disconcerting if you are at a teletype
not in view of the 340 because it will appear that the PEEK is
just sitting there. This can be rectified with the ^N command [Sec 8.3].
The first line of all pages output by PEEK is as follows:
ITS xxx PEEK yyy mm/dd/yy hh:mm:ss
where xxx is the version number of the system in use [Sec 6.5.3],
yyy is the version number of the PEEK in use (so bugs can be
matched to exact version), and mm/dd/yy is the date and hh:mm:ss
the time according to ITS [Sec 6.3.2, 6.3.3]. If any core or disk
parity errors have occured during the current system run, a second
line is displayeed listing the number of each. The last line of
all pages displayed on the 340 by PEEK is a list of mode commands
which can be given by light-penning [Sec 3.4.1.2] them with
effects identical to typing them.
All characters typed at PEEK are interpreted at its interrupt
level and have effect, if any, immediately. Characters that are
not commands, digits, or ^Z are completely ignored. Digits are
accumulated as an octal number until a non-digit is typed at which
time the accumulated number is made available (if the non-digit is
a command taking a numeric argument) and reset.
The amount of memory occupied by PEEK varies with mode but the
present minimum is three memory blocks (a total of 5000 words).
8.2 Modes Available
The particular subset of the time sharing system's status being
output by PEEK is controlled by its mode. Initially PEEK is in N
mode but it may be changed to any of those listed below by typing
the letter indicated or light penning [Sec 3.4.1.2] it if PEEK is
displaying on the 340. Unless otherwise specified the output
repetition rate for those modes is the standard rate initially set
to 5 seconds delay after end of page output before starting on the
next update. This is variable by the user with the Z command [Sec 8.4].
D This mode outputs system supplied directories [Sec 2.2.1] for the disk
device [Sec 3.1.1]. The directory output will list only those files for the
system name [Sec 2.2.3] of the PEEK. If the PEEK is running as an
inferior of DDT [Sec 7], this system name may be easily changed by a
DDT command. If output is to the 340 display, the user directory is
preceded by a list of the extant user directories which may be
individually light penned to change PEEK's system names and select a
different directory to display.
G This mode lists the sixbit symbols recognized by .GETSYS [Sec 6.6.1]
in the system in use. Output is updated after a ten second delay.
H Only available with the 340 display, this mode outputs a graph of
memory with different memory users [Sec 4.3] on different vertical
levels and location represented by horizontal coordinate.
I The symbolic devices implemented in the system in use [App A, B] are
listed by this mode. Output is updated after a ten second delay.
M This mode is somewhat reminiscent of H mode. It lists all memory users
and the amount of memory they are using in decreasing order. An ""* is
also output by stopped jobs as are the characters for special resources
being used by any job (see table below).
V This is the most frequently used mode of PEEK. It tries to give a snapshot
of the status of all user jobs in the system. Different amounts of information
are displayed depending on the particular output device in use, but in all
cases the following additional information is output:
1. Above the list of user jobs, the number of free blocks (each
2000 words) of memory (MEMFR), the number of areas that are
allocated for user variable [App D] (USRRI), and the number of
user programs that were runnable last schedule time (RNABLU);
2. Below the list of user jobs, the number of blocks of memory
occupied by user programs (USR MEM) (the sum of this figure and
MEMFR is not constant due to dynamic IO buffers), the total
percentage of machine time being used by the listed programs
(USR TIM) (less than one hundred due to scheduling and other
overhead), the amount of time that the running system has been
up (STIME), and the total amount of machine time used by users
that have logged out (LOUTIN).
Between the two sets of information described above, there is one
line of information for each procedure in the system topped by a
title line which provides a heading for each column of
information. The first item on the line for any particular
procedure will be the user index of the procedure, a number that
uniquely refers to it (see mode V). The second item will be either
the UNAME for top level procedures and the JNAME for inferiors or
the UNAME, JNAME, and SNAME for each procedure depending on the
line width of the output device. This second item also portrays
the existant procedure tree structure in that each procedure not
at the top level is an inferior of the nearest procedure above it
whose name is not indented as far.
Other items include an exponential approximation to the percentage
of machine time the procedure has been receiving, the number of
core blocks it is occupying, a column labeled "TTY" that has a "T"
concatenated with the console number opposite procedures
controlling a console, various letters immediately after the "TTY"
column for system resources controlled by the procedure (see the
table below), and a column labelled "STATUS". The character string
opposite a procedure in the STATUS column should be interpreted as follows:
1. A leading "*" indicates that the procedure is processing a
software interrupt [Sec 4.2].
2. RUN indicates that the program is running in user mode.
3. A pair of numbers separated by an "!" indicates that the
procedure is stopped.
4. Most other strings represent a system call (with S used for the
very common .SLEEP call) or input-output device and type of transfer.
(a) If preceded by a "+" the procedure is running in executive
move performing the call or input-output.
(b) If not it is hung on the call or input-output.
T The contents of the system translation table [Sec 2.2.2] is output.
U This mode displays the status of the DEC tape drives [Sec 3.1.2]
and of the open DEC tape files. For the normal user, the most
useful information per tape is the drive number in the leftmost
column and the DIR variable in the next to rightmost (UTASS)
column. If the DIR variable is minus one, ITS is not retaining a
directory for that drive and a tape mounted on it could be removed
manually. Otherwise it is the absolute location of the directory.
The per open file information includes the names of the procedure
using the file, its direction, and the number of buffers (200 words
each) currently being used for the file by the system.
V This mode command should be proceeded by the user index (see
mode K above) of some user. It displays many of his user variables
[App D] and the channel word and status word for each of his
input-ouput channels [Sec 2.1, 2.5]. If output is to the 340 or line
printer, the contents of the selected user's accumulators are also
output.
X This mode outputs the digitalization of all the multiplexed analog to
digital input channels [Sec 3.3.3] and the value being output on each
of the multiplexed digital to analog channels [Sec 3.3.2].
Y This mode outputs system supplied [Sec 2.2.1] directories for DEC
tapes. It shoud be proceeded by a drive number.
? This mode outputs a list and brief explanation of PEEK's commands.
An example of its use is included in Appendix G. Output is updated
after a ten second delay.
The following are the system resource letters used in modes N and
M above:
C Indicates that the procedure is now or was the last
to use the core allocator.
D Indicates that the procedure has seized control of the DEC
340 display.
F Indicates that the procedure has control of the COD device.
I This letter can be present for more than one procedure. It
indicates that the procedure it appears with is in ""IOT-user
mode [Sec 6.8.3].
L Indicates that the procedure has control of the line printer.
M Indicates that the procedure has seized the .MASTER
[Sec 6.8.5] facility.
P Indicates that the procedure has seized control of the plotter.
R Indicates that the procedure has control of the paper tape reader.
T Indicates that the procedure has control of the paper tape punch.
10 Indicates that the user has the PDP-10 core image open on
device USR [Sec 4.3.2.1].
8.3 IO Control
PEEK will output to only one device at a time. The initial device
is chosen as explained in section 8.1. All of the following four
commands for changing PEEK's output device also cause PEEK to
immediately restart output for its current mode [Sec 8.2]:
^B This switches output to the line printer if it is available.
If not available the output device will be unchanged.
^E This command will terminate PEEK output to the line
printer and cause it to either type or display its output.
^N This command terminates 340 display output, starts
typed output, and sets a flag in PEEK that is cleared
only by the ^Y command. This flag inhibits PEEK's
attempts to seize the 340 as described in section 8.1
^Y PEEK will attempt to seize the 340 display for output
on receipt of this command. If it is unsuccessful, output
will revert to typing. In any case the flag mentioned
under ^N above is cleared.
8.4 Miscellaneous
The following are miscellaneous PEEK commands:
P If the PEEK is running under DDT [Sec 7], this command
will return control of the user's console to DDT but leave
PEEK running and, if the 340 display or line printer is
selected, producing output. It uses .VALUE to return the
string ""^P as a command to DDT.
Q If the PEEK is running under DDT [Sec 7], this command
will destroy the PEEK it is typed at and return control of
the user's console to DDT. It uses .VALUE to return the
string ""$^X. as a command to DDT.
Z This command should be preceded by a small number. It
sets the standard update delay to as many seconds [Sec 8.2].
! This command will probably go away when swapping is
added to the system. Under normal circumstances it will
cause the procedure tree in which is found the pEEK it is
typed at to be replaced by a single newly loaded PEEK at the
top level. This saves memory if several people want to leave a
PEEK at a single console running for their joint enlightenment.
A top level PEEK will commit suicide if a ^Z is typed at it.
LOCK
9.1 Introduction
LOCK is a utility program operating under ITS performing a
multitude of infrequently required tasks. Its name derives from
the fact that the function it was originally written for was to "lock"
and "unlock" teletypes (see the + and -- commands [Sec 9.2]). Most
of LOCK's commands are single characters.
In contrast to PEEK [Sec 8], which interprets commands at the
interrupt level, commands to LOCK are read at the main program
level. Thus commands will in general have no effect before
previous commands have been completed. In fact, some commands
cause a change in the state of LOCK such that following letters
are interpreted as arguments.
LOCK occupies only one block (2000 words) of memory except after
the "T" command.
9.2 Commands
The following are the current LOCK commands:
+ This command should be preceeded by a teletype number
[Sec 3.2.1]. The LOCK will try to open the specified
teletype as an input-output device. it will be successful only
if the teletype is not in use. If it successful, the teletype will
become impervious to ^Z's so no user can log in on it. LOCK
will type out an appropriate message on the now locked
teletype, and LOCK will type a ""W to the LOCK user. If the
LOCK fails in opening the teletype it will type an ""L at the
LOCK user.
-- This command should be preceeded by a teletype number. If
LOCK has the specified teletype locked (see ""+ above) it will
unlock it and type out an ""*. Otherwise it will type a ""?.
_ This command should be preceded by the octal code for a
character. LOCK will type out the character represented in image
mode [Sec 3.2.1]. This is useful for determining the reaction of a
console to various codes.
G This command should be preceded by the user index [Sec 8.2, see
mode N] of the top procedure in a tree that the user wishes to
obliterate. It must be followed by the characters ""UN. If the user
deviates from this sequence, a ""? will be typed and LOCK will
listen for a new command. If the user does not deviate the system
job [Sec 6.5] forceably logs out [Sec 5.4] the tree and types out a
message on the system job teletype.
I A series of magic characters must be typed at a model 37 teletype
to allow its use in full duplex, the mode assumed by most programs
operating under ITS. This command causes LOCK to type the
requisite characters in image mode [Sec 3.2.1].
K This command must be immediately followed by the characters ""ILL
(see G above) and should be preceded by a number. It will activate the
system going down feature [Sec 6.5.2] with a time limit of five or the
number preceding the command minutes, whichever is larger.
O When it receives this command, LOCK will permanently go into a mode
where characters typed at it are echoed as their ASCII values in octal. To
ultimately escape from LOCK in this mode, the user should use ^Z [Sec
1.1.2].
P If LOCK is running under a DDT [Sec 7], this command causes control
of a user's console to revert to it. The command uses .VALUE to return
a null string.
Q If LOCK is running under a DDT [Sec 7], this command causes control
of a user's console to revert to his DDT and his LOCK to be destroyed.
Note that this will unlock all teletypes previously locked (see ""+ above)
by the destroyed LOCK as destroying a procedure closes all its channels.
It uses .VALUE to return the string "":KILL.
S This command complements the run status of the system checking feature
of the system job [Sec 6.5.1]. It will type out the resultant state as either
""START or ""STOP.
T This command causes complex and nonterminating gyrations on the part
of the LOCK it is typed at and the procedures the LOCK will create as a
result of this command. Its purpose is to test the core allocator [Sec 4.3]
and other components of the ITS system. Its casual use is not
recommended.
? This command causes LOCK to type out an up-to-date list of its commands
with a brief explanation of each. An example appears in Appendix G.
References
1. Digital Equipment Corporation
Programmed-Data-Processor-6 Handbook (P-65)
August 1964, DEC, Maynard, Massachusetts.
2. Digital Equipment Corporation
DDT (DEC-6-0-UP-DDT-U4-FP-ACT00),
April 1965, DEC, Maynard, Massachusetts.
3. Peter R. Samson
MIDAS (MAC-M-279, AI-90)
October 1965, Project MAC memo.
4. Peter R. Samson
MAC PDP-6 DEC-tape File Structure (MAC-M-249, AI-82)
Project MAC memo.
5. Michael D. Beeler
[untitled] (AI-128)
March 1967, MAC AI group memo.
6. Michael D. Beeler
IO Test (AI-144)
October 1967, MAC AI group memo.
7. Digital Equipment Corporation
DDT-10 (DEC-10-CDDB-D)
June 1958, DEC, Maynard, Massachusetts.
8. Thomas F. Knight
A Multiple Procedure DDT (AI-147)
January 1958, MAC AI group memo.
9. John T. Holloway
Output to the PDP-6 Calcomp Plotter (AI-104)
August 1966, MAC AI group memo.
10. Donald E. Eastlake III
PDP-6 Software Update (Revised AI-118)
June 1967, MAC AI group memo.
11. Donald E. Eastlake III
ITS 1.4 Reference Manual (MAC-C-377, AI-161)
June 1968, MAC memo.
12. Donald E. Eastlake III
PEEK and LOCK (MAC-M-367, AI-169)
November 1968, MAC memo.
13. Stewart Nelson, Michael Levitt
Robot Utility Functions (AI-172)
February 1969, MAC AI Group memo.
System Calls in Numeric Order
(correct as of ITS version 528)
Name Number Section
.IOT UUO 040 2.3
.OPEN UUO 041 2.2
.OPER UUO 042 1.2.1
.ITYI .OPER 1 App E
.LISTE .OPER 2 3.2.1.2
.SLEEP .OPER 3 6.8.1
.SETMS .OPER 4 App E
.SETM2 .OPER 5 4.2.1
.LOGIN .OPER 6 6.1
.CLOSE .OPER 7 2.7.1
.UCLOS .OPER 10 5.2.1
.ATTY .OPER 11 3.2.1.1
.DTTY .OPER 12 3.2.1.1
.IOPUS .OPER 13 2.6.1
.IOPOP .OPER 14 2.6.1
.DCLOS .OPER 15 3.4.1.3
.DSTOP .OPER 16 3.4.1.4
.RDTIM .OPER 17 6.3.1
.RDSW .OPER 20 6.2.1
.GUN .OPER 21 5.4
.UDISM .OPER 22 3.1.2.1
.GETSY .OPER 23 6.6.1
.RD500 .OPER 24 6.2.4
.GETLO .OPER 25 6.6.2
.SETLO .OPER 26 6.8.4
.DISOW .OPER 27 5.2.2
.RD760 .OPER 30 6.2.2
.WR760 .OPER 31 6.2.2
.GEHSY .OPER 32 6.8.2
.LOGOU .OPER 33 6.1
.GSNAM .OPER 34 App E
.WSNAM .OPER 35 App E
.UPISE .OPER 36 App E
.RESET .OPER 37 2.7.3
.ARMOV .OPER 40 3.3.2.1
.WMAR .OPER 41 App E
.RRTIM .OPER 42 App E
.ASSIG .OPER 43 3.1.2.2
.DESIG .OPER 44 3.1.2.2
.RTIME .OPER 45 6.3.2
.RDATE .OPER 46 6.3.3
.RD710 .OPER 47 6.2.3
.EOFC .OPER 50 2.3.1
.IOTLS .OPER 51 6.8.3
.RSYSI .OPER 52 6.6.3
.SUPSE .OPER 53 6.5.1
.UBLAT .OPER 56 3.1.2.3
.IOPDL .OPER 57 2.6.2
.ITYIC .OPER 60 2.7.3
.MASTE .OPER 61 6.8.5
.VSTST .OPER 62 3.3.1.1
.DIAL .OPER 63 3.2.1.3
.DIALW .OPER 64 3.2.1.3
.HANGU .OPER 65 3.2.1.3
.DIETI .OPER 66 6.5.2.2
.SHUTD .OPER 67 6.5.2.1
.ARMOP .OPER 70 3.3.2.1
.NDIS .OPER 71 3.4.1.5
.FEED .OPER 72 3.2.4.1
.EVAL .OPER 73 6.6.4
.REDEF .OPER 74 6.8.6
.ITSET .OPER 75 6.8.4
.UTNAM .OPER 76 3.1.2.4
.UINIT .OPER 77 3.1.2.5
.CALL UUO 043 1.2.1
.DISMI .CALL 1, 4.2.2
.TRANS .CALL 2, 2.2.2.1
.TRANA .CALL 3, 2.2.2.2
.VALUE .CALL 4, 5.3.1
.UTRAN .CALL 5, 5.1.3
.CORE .CALL 6, 4.3.1
.TRAND .CALL 7, 2.2.2.3
.DSTAR .CALL 10, 3.4.1.1
.FDELE .CALL 11, 2.4
.DSTRT .CALL 12, 3.4.1.1
.SUSET .CALL 13, 4.5
.LTPEN .CALL 14, 3.4.1.2
.VSCAN .CALL 15, 3.3.1.1
.POTSE .CALL 16, 3.3.3.1
.USET UUO 044 5.2.3
.BREAK UUO 045 5.3.2
.STATU UUO 046 2.5
.ACCES UUO 047 2.7.4
System Calls in Alphabetic Order
(correct as of ITS version 528)
Name Number Section
.ACCES UUO 047 2.7.4
.ARMOF .OPER 70 3.3.2.1
.ARMOV .OPER 40 3.3.2.1
.ASSIG .OPER 43 3.1.2.2
.ATTY .OPER 11 3.2.1.1
.BREAK UUO 045 5.3.2
.CALL UUO 043 1.2.1
.CLOSE .OPER 7 2.7.1
.CORE .CALL 6, 4.3.1
.DCLOS .OPER 15 3.4.1.3
.DESIG .OPER 44 3.1.2.2
.DIAL .OPER 53 3.2.1.3
.DIALW .OPER 64 3.2.1.3
.DIETI .OPER 66 6.5.2.2
.DISMI .CALL 1, 4.2.2
.DISOW .OPER 27 5.2.2
.DSTAR .CALL 10, 3.4.1.1
.DSTOP .OPER 16 3.4.1.4
.DSTRT .CALL 12, 3.4.1.1
.DTTY .OPER 12 3.2.1.1
.EOFC .OPER 50 2.3.1
.EVAL .OPER 73 6.6.4
.FDELE .CALL 11, 2.4
.FEED .OPER 72 3.2.4.1
.GENSY .OPER 32 6.8.2
.GETLO .OPER 25 6.6.2
.GETSY .OPER 23 6.6.1
.GSNAM .OPER 34 App E
.GUN .OPER 21 5.4
.HANGU .OPER 65 3.2.1.3
.IFSET .OPER 75 6.8.4
.IOPDL .OPER 57 2.6.2
.IOPOP .OPER 14 2.6.1
.IOPUS .OPER 13 2.6.1
.IOT UUO 040 2.3
.IOTLS .OPER 51 6.8.3
.ITYI .OPER 1 App E
.ITYIC .OPER 60 2.7.3
.LISTE .OPER 2 3.2.1.2
.LOGIN .OPER 5 6.1
.LOGOU .OPER 33 6.1
.LTPEN .CALL 14, 3.4.1.2
.MASTE .OPER 61 6.8.5
.NDIS .OPER 71 3.4.1.5
.OPEN UUO 041 2.2
.OPER UUO 042 1.2.1
.POTSE .CALL 16, 3.3.3.1
.RD500 .OPER 24 6.2.4
.RD710 .OPER 47 6.2.3
.RD760 .OPER 30 6.2.2
.RDATE .OPER 46 6.3.3
.RDSW .OPER 20 6.2.1
.RDTIM .OPER 17 6.3.1
.REDEF .OPER 74 6.8.6
.RESET .OPER 37 2.7.3
.RRTIM .OPER 42 App E
.RSYSI .OPER 52 6.6.3
.RTIME .OPER 45 6.3.2
.SETLO .OPER 26 6.8.4
.SETM2 .OPER 5 4.2.1
.SETMS .OPER 4 App E
.SHUTD .OPER 67 6.5.2.1
.SLEEP .OPER 3 6.8.1
.STATU UUO 046 2.5
.SUPSE .OPER 53 6.5.1
.SUSET .CALL 13, 4.5
.TRANA .CALL 3, 2.2.2.2
.TRAND .CALL 7, 2.2.2.3
.TRANS .CALL 2, 2.2.2.1
.UBLAT .OPER 56 3.1.2.3
.UCLOS .OPER 10 5.2.1
.UDISM .OPER 22 3.1.2.1
.UINIT .OPER 77 3.1.2.5
.UPISE .OPER 36 App E
.USET UUO 044 5.2.3
.UTNAM .OPER 76 3.1.2.4
.UTRAN .CALL 5, 5.1.3
.VALUE .CALL 4, 5.3.1
.VSCAN .CALL 15, 3.3.1.1
.VSTST .OPER 62 3.3.1.1
.WMAR .OPER 41 App E
.WR760 .OPER 31 6.2.2
.WSNAM .OPER 35 App E
Available Symbolic Devices in Alphabetic Order
(correct as of ITS version 528)
Device Type Section
CLA 5 3.4.3
CLI 3 3.4.3
CLO 7 3.4.3
CLU 7 3.4.3
COD 6 3.2.5
COM 7 3.1.3
DIS 2 3.4.1
DKn 7 3.1.1
DSK 7 3.1.1
ERR 4 3.4.4
IDS 2 3.4.1
IMX 4 3.3.3
LPT 2 3.2.2
NUL 6 3.4.6
NVD 6 3.3.1
OMX 2 3.3.2
PLT 2 3.2.3
Pnm 7 3.1.1
PTP 2 3.2.4
PTR 4 3.2.4
SYS 7 3.1.3
Tnm 6 3.2.1
TPL 7 3.4.5
TTY 6 3.2.1
TVC 6 3.3.1
USR 6 3.4.2
UTn 7 3.1.2
VID 6 3.3.1
System Variables per User
(correct as of ITS version 528)
ICCHNM: REPEAT 20,0 ;input-output channel assignment words
;right half, index into IOTTB, CLSTB
;left half, device dependent
SIOCHN: BLOCK LUIOP ;input-output channel push down list
SIOCP: SIOCHN--1 ;pointer into input-output push down list
IOCHST: BLOCK 20 ;input-output channel status for channels at IOCHNM
;3.1--4.9 input-output status
;1.1--2.9 .ACCESS pointer
UPC: 0 ;stores program counter when not running
UPR: 0 ;user protection and relocation registers
MEMTOP: 0 ;six less than first illegal location
RMEMT: 0 ;first illegal location
CORRQ: --1 ;request to core job
;1.1--1.8 number of blocks, 3.1--4.8 user requested for
;4.9=0 means request present, 4.9=0 means no request
ACOS: BLOCK 15 ;swap out accumulators
AC15S: 0 ;commonly referenced swap out accumulator
AC16S: 0 ;commonly referenced swap out accumulator
AC17S: 0 ;commonly referenced swap out accumulator
UUO: ;the following three locations swapped in & out of
;UEXIT, UUOH, etc with user
SUEXIT: JRST 2,@UUOH ;user UUO exit instruction
SUUOH: 0 ;contents of @41 (absolute)
SAC17P: MOVEM U, ;accumulator 17 in user's shadow memory
SV40: 0 ;last interrupting UUO
;(contents of 40 when user out)
SV60: 0 ;contents of 60 when user out
AC14P: 0 ;points to accumulator 14 in shadow memory
AC15P: 0 ;points to accumulator 15 in shadow memory
AC16P: 0 ;points to accumulator 16 in shadow memory
40P: 0 ;points to user's relative location 40
41P: 0 ;points to user's relative location 41
APRC: APRCHN ;right half is cono to processor
;4.9 implies user is in a disowned tree
;4.8 implies user being .UCLOS'ed
;4.7 user has been cored zero
;4.6 core request pending on this user
;4.1--4.4 number of last channel on which an
;error occurred
USTP: 0 ;stop word
;zero implies runnable
;4.9 stopped to be moved by core allocator
;4.8 general core allocator stop bit
;4.7 controlled by superior procedure
;4.6 special bit, see URMEMT & UMEMEX
;1.1--2.9 count of transient reasons to be stopped
PIRQC: 0 ;pending first word interrupts
MSKST: 0 ;interrupt enable mask for PIRQC
IFPIR: 0 ;second wod of interrupt requests
;3.8--3.1 inferior procedure interrupts
;2.7--1.1 input-output channel interrupts
;1.1 for channel 1, etc.
MSKST2: 0 ;second word interrupt enable mask
PICLR: 0 ;interrupt level status flag
SUPPRO: 0 ;pointer and interrupt bit to superior procedure
;--1 for top level procedure
FLSINS: 0 ;blocking condition instruction
;zero implies runnable
UFINAL: 0 ;nonzero implies finalization required to interrupt
RPCL: 0 ;0 implies no RPCLosering in progress
;0,,n RPLSR'ing user n
;--1,,n being RPCLSR'ed by user n
UNAME: 0 ;user name
;This word for each procedure is copied from the
;UNAME of the procedure that creates it (see USR
;device). For an initial top level procedure it is --1 but
;is modified by .LOGIN. It is the same for all procedures
;in a tree.
JNAME: 0 ;job name
;Each logged in procedure has a unique UNAME,
;JNAME pair. The JNAME of an initial top level
;job is ""HACTRN. For other jobs it is the second
;file name specified in the .OPEN on the USR device
;that creates them.
USYSNM: 0 ;current system name
;This variable is initially set equal to the procedure's
;UNAME. It can be read or set by the procedure or its
;superior (.SUSET, .USET). It is used as the third file
;name on certain shared devices.
USYSN1: 0 ;system name used inside disk routines
;This variable is normally equal to USYSNM but see
;devices COM, SYS and TPL.
TTYTEL: 0 ;console assignment for this procedure
UQUAN: 0 ;quantum time
UTRNTM: 0 ;total run time
UTMPTR: 0 ;pointer to procedure tree resource word
JTMU: 0 ;procedure resource word
IOTLSR: 0 ;4.9 a one implies iot-user mode
;4,5--4.3 MAR conditions
;2.9--1.1 contents of MAR register
UMARPC: 0 ;program counter at last MAR interrupt
VALUE: 0 ;contents of effective address of last .VALUE
UOUT: 0 ;4.9=1 \Rightarrow user not completely in core
;4.8 in transit in
;4.7 in transit out
;4.6 ref to disk in progress
;4.5 back in core but needs to be blessed before starting
;1.1--1.9 core blocks needed for swap in
USRPDL: --LUPDL,,UPDL--1 ;push down list pointer for system calls
UPDL: BLOCK LUPDL--2 ;push down list area for system calls
EPDL1: 0 ;link depth for 2311 routines
EPDL: 0 ;temporarily saves accumulator B for ACORE
EPDL2: 0 ;temporarily saves accumulator T for FLSINS
Relics of ITS's Past
The following system calls, while still effective as of ITS
version 523, can be expected to ultimately disappear. They are
redundant, more specialized, older versions of their replacements.
Name Number Replacement Function
.ITYI .OPER 1 .ITYIC Read interrupt level characters from open TTY device, if any.
.SETMS .OPER 4 .SUSET Set own user variable MSKST.
.GSNAM .OPER 34 .SUSET Read own user variable USYSNM.
.WSNAM .OPER 35 .SUSET Set own user variable USYSNM.
.UPISE .OPER 36 .SUSET Set own user variable PICLR.
.WMAR .OPER 41 .SUSET Set own user variable IOTLSR.
.RRTIM .OPER 42 .SUSET Read own user variable UTRNTM.
Further Sources of Information on ITS
Information further than or more recent than that contained in
this manual may usually be obtained by consulting the symbolic
listings of ITS, DDT, PEEK, or LOCK. The following persons may
also be helpful:
Donald E. Eastlake III
Jerry S. Freiberg
Richard D. Greenblatt
Thomas F. Knight
John T. Holloway
Stewart B. Nelson
Frederick H.G. Wright II
Illustrative Console Output
The following pages are a sample console session with ITS
illustrating several features documented in this memo.
\uparrow Z
DDT.198.
:LOGIN DE
:PEEK!
\uparrow N
ITS 530 PEEK 142 07/14/69 00:22:15
PARITY ERRORS: DISK = 11 CORE = 0
MEMFR=267 USRMI=11 RNABLU=2
I= U-JNAME STATUS TTY CORE %TIM
0 SYS TYO T5 25 0%
1 CORE UUO ? 0 1%
3 PEEK +GETSY T4 C 5 3%
10 MS EOAMIC RUN DISOWN 20 91%
USR MEM= 60 USR TIM= 97%
STIME = 7:03:22 LOUTIM = 0
?
ITS 530 PEEK 142 07/14/69 00:22:58
MODE CONTROL:
D DISK DIRECTORY
G AVAILABLE .GETSYS'S
H MEMORY GRAPH (340 ONLY)
I AVAILABLE IO DEVICES
M MEMORY USE LIST
N NORMAL MODE
T TRANSLATION ENTRIES
U DEC TAPE STATUS
V SINGLE USER (PRECEDE BY INDEX)
X MULTIPLEXORS MODE
Y DEC TAPE DIRECTORY (PRECEDE BY #)
? EXPLANATION MODE
IO CONTROL:
\uparrow B USE LINE PRINTER
\uparrow E STOP USING LINE PRINTER
\uparrow Y USE 340
\uparrow N STOP USING 340
OTHER:
P PROCEED BUT RETURN TTY TO DDT
Q QUIT
Z SET DOZE IN SECONDS
! STAND ALONE
Q
$ \uparrow X.
:LOCK!
LOCK.39
\leftarrow ?
+ LOCK TTY (PRECEDE BY #)
- UNLOCK TTY (")
\leftarrow OUTPUT CHARACTER WITH ASCII VALUE # (")
GUN KILL USER WITH # INDEX (")
I INITIALIZE A MODEL 37 TTY
KILL SYSTEM DOWN IN # MINUES (")
O OUTPUT CHARACTERS IN OCTAL
P RETURN TO DDT
Q VALRET AN $ \uparrow X.
S COMPLEMENT RUN STATUS OF SYS JOB
T TEST CORE ALLOCATOR
? LIST COMMANDS
\leftarrow Q
$ \uparrow X.
:?
? = LIST MODE COMMANDS
DISOWN = DISOWN CURRENT JOB
LOGOUT = AUTO-EXPUNGE
SYMLOD = LOAD SYMBOLS ONLY
XFILE = EXECUTE FILE AS DDT COMMANDS
CR = ENTER TECO AND CREATE FILE
ED = ENTER TECO AND EDIT
LOAD = LOAD FROM FOLLOWING FILE INTO CURRENT JOB
DUMP = DUMP INTO " " FROM " "
KILL = KILL CURRENT JOB
LOGIN = LOGIN AS FOLLOWING NAME
SEND = SEND MESSAGE
GAG = CONTROL RECEIPT OF MESSAGES
BUG = DOCUMENT BUG
MAIL = ADD TO USER'S MAIL FILE
JOB = CREATE OR SELECT JOB
LISTJ = LIST JOBS
FLAP = FLAP DECTAPE, FOLLOW BY DRIVE #
LISTF = LIST FILES
DELETE = DELETE FILE
PRINT = PRINT FILE
LINK = CREATE LINK
ERR = IOC ERROR STATUS
DDT = ENTER DDT MODE
MON = ENTER MONITOR MODE
START = START INFERIOR
CONTIN = CONTINUE GIVING INF. TTY
PROCED = PROCEDE INF., LEAVE TTY WITH DDT
WALLP = \uparrow B TO SPECIFIED FILE
:LOGOUT
ITS 530 CONSOLE 4 FREE. 00:25:57