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DEC-08-SBAB-D

December 1967

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IDENTIFICATION
Product Code:

DEC-OS-SBAB-D

Product Name:

PDP-8 Disc System Builder

Date Created:

October 27, 1967

Maintainer:

Software Services Group

LIIHARV

DEC-08-SBAB—D

ABSTRACT

This document describes a fast convenient keyboard oriented monitor which will enable the
user

efficiently control the flow of programs through his PDP-8.

The system is modular and open-

ended allowing the user to build the software components required in his environment.

The user may

specify the system device (disc or DECtape), the amount of core, number of disc units available and
the number,

name

and size of his resident system programs.

This is a basic package to which DEC will add FORTRAN, Assembler, Editor,

Peripheral

Interchange Program, DDT, and perhaps other programs, as they become available. The system described here includes all features of the monitor and allows the user full access to the disc as a program

storage medium.
The System Monitor is designed to facilitate user/system communication.

By typing appro-

priate commands to the monitor the user may call the loader from the systems device, save a core image
on

the systems device,

call a saved file into core from the systems device.

PRELIMINARY REQUIREMENTS
PDP-8

(4K)

3 cycle Data Break

DF32 Disc (or TCOl

DECtape)

SYSTEM GENERATION

3.1

Building the Monitor
To load a monitor system on an empty disc or DECtape,

perform the following sequence of

operations.

to fit your

Load RIM Loader

Load Binary Loader

Load BUILD using the Binary Loader

Disable write protect on the desired device; DISC or DTA8

Start at

Answer the questions (underlined) asked by the BUILD Program,

2008

hardware system.
*TYPE SIZE OF CORE

(IN K) ;

*4;
*HIGH SPEED PAPER TAPE?

*YES)

shown below,

DEC-O8-SBAB-D

:DISC OR TAPE? )

:DISC)
:TYPE NUMBER OF DISC UNITS

)

1‘] g

z A

(MAXIMUM I MINUTE DELAY)

Yo:

will get either:

Q»

meaning the monitor and loader are correct or
WRITE ERROR.

If in a disc environment, you get the latter; start over at step a

hardware problems).

(you may have

If you have DECtape, try a new DECtape at step d or try writing timing and

mark tracks on the DECtape and start over.

The builder will ask other questions as necessary allowing

you to tailor your system to the hardware.

3.2

Building the System Library
(section 4.1) and CALL/SAVE description (section 4.2).

Read the LOADER description

Type in appropriate commands as indicated in Loader description. By using the

starting address of 76008 ("ST= 7600"), control is returned to the monitor after load and each program
may be saved.

An example of loader use follows.

.LOADA
A
*IN-R:
t
T

READ ONE TAPE FROM READER

*OPT-2

LOAD IN 2 PASS MODE (PROGRAM REQUIRES

*ST= 7600;

JUMP TO 7600 AFTER LOAD IS FINISHED

LOADER FOUND DEVICE R: IS VALID
USE OF CORE ABOVE 70008)

lTll

LAT/TYPE

< CONTROL > P TO JUMP TO START ADDRESS.

LOAD TAPE FOR PASS 2, TYPE < CONTROL > P.
’

ND OF PASS I TYPE <CONTROL > P

LOADER IS WAITING FOR YOU TO LOAD A TAPE AND
TYPE < CONTROL > P
c.

Save the core

image as described under SAVE/CALL in this document.

exclamation point ('.) after the name.
a

user

program save.

Note the

This means system program as opposed to the normal colon (z) of

(See Appendix A).
Repeat process From step b until you have stored all the desired systems programs.

DEC-08- SBAB- D

OPERATION OF THE DISC SYSTEM

4.1

Loader

4.] .I

General

The loader is a disappearing program allowing paper tape or disc

input.

It loads

in one or two passes and makes all of core available to the user, except the page reserved for the

monitor head
a

(7600-7777).

The user specifies a command list to the loader and the entry point.

After

successful load the loader disappears and enters at the specified starting address.

4.] .2

Operations

From the monitor, type LOAD and wait for *IN —-.

The loader uses either

high or low speed paper tape as specified at build time by the answer to HIGH SPEED PAPER TAPE?

If you specified high speed paper tape either T: or R: is forced to the high speed reader; if you said
no,

both devices are forced to low speed.

This applies only to the loader.

The loader will load up to five separate tapes.
command string in response to *IN —.
“*IN
causes

—

R:,R:,R:)

This is done by typing the appropriate

For example,
"

the loader to expect three separate tapes to be loaded.

each of the three tapes must be read in twice.

"<cr><LF>l"

If the two pass option is specified,

The loader acknowledges each valid input with a

The next typeout is "*OPT —" which expects a l-character answer I
is the number of passes required.

This argument

The one pass loader will not load programs in field 0 above 7000.

The loader disturbs core from 6000 to 7577.

The two pass loader will load programs in all of field 0

except the cells described below.
Cells Excepted

Core Size
4K

7600-7777

8-32K

7574-7777

The two pass loader requires the input tapes be passed through the reader twice.
case

higher fields will be loaded.

In either

In the command string, each field, delimited by commas, contains

device of one binary program and this command string will be identical for one pass or two pass load

of the same program.

The loader asks "*ST=

and expects a one to five digit answer describing, in octal, the

starting address. The highest digit of a five digit number describes the memory extension involved; a
four digit or less string implies field 0.
"

means

jump to

ST:

30200)

”

field 3, address 200.

For example,

DEC-O8- SBAB-D
The loader then types

”

T“ and waits for a tape to be inserted in the reader.

positioned, type <CONTROL>P. The tape is read-in and the loader again types "1

When the tape is
and waits.

The low

speed reader version of the loader halts; press Continue to resume the requested operation. Continue the
above operation until you have matched the number of tapes loaded with the input request.
one more

<CONTROL>P causes the loader to enter at the specified starting address.

<CONTROL>P's are required at the end of pass 1 of a two pass load.
in the following order:

Tape 1, Tape 2, Tape 3.

Errors

4.2

CALL/SAVE

4.2.l

SAVE

then Tape 1,

Note that two

In two pass mode, tapes are loaded

Tape 2, Tape 3.

An illegal checksum causes the loader to type "?" and return to the monitor.

4.l .3

The typing of

Core may be saved on the disc in blocks of

12810 words.

From 1 to 31

(decimal)

blocks may be placed on the disc and the blocks may be contiguous or non-contiguous as specified by
the user.

The syntax is as follows:
.

SAVE u

xxxx{ '. }YYYYY -zzzzz, wwwww;uuuuu)

l—ENTRY

POINT

ONE PAGE SAVE

L————MULTIPLE PAGE SAVE
:

USER PROGRAM

.' SYSTEM PROGRAM

PROGRAM NAME

Any combination of multiple page SAVE and/or single page SAVE requests may be requested,
up to 32

(decimal) requests. Beginning address of a multiple page request must be smaller than the

ending address. All addresses must be in the same field. All addresses are in octal and are one through
five digits where the most significant digit of five is the memory extension.

.SAVE
saves a core

of 20.

CORE:

0 ,

400-6l77;

For example,

20)

image called CORE, as page 0, and all cells from 400 through 6T 77 with an entry point

Extended memory may be saved through the use of a five digit number.

This most significant

digit describes the field to be accessed and no check is made for validity in your system.
in field 7 you must have memory to match the request.
is remembered.

The last non-zero extended field digit entered

The following three examples perform in exactly the same way.
.

SAVE

FOO:10000

SAVE

FOO:30000

SAVE

FOO:10000

If you save

17777; 10200
67777; 10200
7777; 200

DEC—OB-SBAB- D

Only one Field may be saved at a time, and an entry point oF zero causes a return to monitor
at

call time.

4.2.2

SALE

Core may be loaded From the disc by name in the Following ways:

.CALL

XXXXA
1

.xxxx

The Former is used iF a user program is desired.
sired (see

and

At the successful completion oF the "call", control is transFerred to

SAVE).

Only the core specified at save time is disturbed.

the entry point specified at save time.

DETAILS OF OPERATION AND

5.1

Core ConFiguration

STORAGE

The system resides in the top page oF Field 0.
7642.

The latter is used iF a system program is de-

The entry point to the system I/O routine is

The loader, SAVE and CALL can access extended memory.

monitor mode, and user mode.

when the monitor is started.

Two modes are used in the system;

Monitor mode is present when 1C is typed at system program time or

The

means

monitor mode; the "*"

means user

User Time

Monitor Time

System IO +

Monitor Head

I
Monitor

Body
I

l
USER

Figure 1

Core Storage ConFiguration

mode.

(See Figure l).

DEC-08—SBAB-D

The operation of the system after it is built and stored on the disc is described below.

Appendix B shows the bootstrap which must be toggled in to start the system, if‘ the machine core is
cleared or destroyed.
At monitor and SP time the keyboard listens to a TC and returns to the head of the monitor

(top page of field 0).

The system is completely open ended,

the user installation.

The system is built easily on the user's machine from a tutorial system builder

allowing flexibility in system content at

program.

Monitor start is at location 7600 of field 0.

At monitor start the code from 7200 to 7577 is

saved in the first two scratch blocks on the systems device, and the monitor (block 1 and 2) is read into

these cells.
"

Control is transferred to the monitor which types a carriage return, line feed and a

." at the start of any line informs the user that he is communicating with the monitor.

A <CONTROL>

C(lC), when typed to either the monitor or loader causes an immediate transfer of control to 7600.

rubout typed to the monitor causes a monitor restart without destroying the contents of the scratch blocks
on

the systems device.
Core images may be saved by typing:

one

four character program name.

SAVE NAME:

The dash between

and

n1 -n2, n3; n4 1

where NAME is any

indicates a contiguous save from the

through the page containing n2. Address n3 is comma delimited and indicates a single page save. The entry point
is delineated by a semicolon.
n4
page containing address n1

A list showing the required pages is constructed from the information typed by the operator
and a block requirement count is kept.
a

When the carriage return is typed (allowing the save to begin)

directory name (DN) search is initiated.

the present file; if not,

new

If a file of the name specified is found, it is replaced by

file is created.

A storage availability search finds sufficient available

blocks to satisfy the requirement count generated as the page list was built.
on a

corresponding block list.

Their numbers are stored

These blocks are then filled with the contents of the pages to be saved

until the typed request has been satisfied.

When the save is completed control returns to the start of

the monitor (7600).
A save file may be recovered by typing "CALL NAME

and control is transferred to the entry point specified during the save.

The file is loaded back into core
If the file was designated a

systems program at save time it will be recovered by typing only NAME 2
a

DN search is initiated to find the name specified.

When a program is called,

Associated with the name is the entry point, and

file protection and extension information.

If the DN entry is found to be a save file of the proper mode

(systems or non-systems), calling proceeds.

If not, the call is terminated and control is returned to the

monitor.
to the

When the call is completed (i .e., all of the saved code is back in core) control is transferred

entry point specified at save time.

time to type the request.

The time for a program to be saved or called is less then the

DEC -08- SBAB- D

5 2

Mass Storage Configuration

5.2.1

File Structure

A relatively sophisticated file structure is implemented to allow for automatic

retrieval of storage for use by the system and a requirement for a single DECtape system.
Two types of blocks are present

—

directory name (DN), and storage allocation map (SAM) blocks.

former are described in Figure 3, the latter in Figure 4.

line

unused.

The SAM block is the item

Each DN entry has a SAM number between

A SAM block has a record of

The

All blocks are linked with the end of chain

The top of the SAM block chain is addressed in all DN blocks.

which allows automatic storage retrieval.
means

(See Figure 2.)

25610 pages of

mass

storage (Figure 4).

1-778. A

zero

The first page of

any numbered program is found by searching SAM blocks until an entry with matching number is found.

To add to a file, find a SAM block entry equal to 0, insert the correct SAM number and adjust the

storage block linking.

To delete a block, the DN entry is cleared and the SAM block entries (equal to

the DN number) are zeroed out.

DIRECTORY (BAC K-UP)
MONITOR

LOA DER
FORTRAN

EDITOR
DDT

OTS
PIP

ASSEMBLER

16K

DIRECTORY (NORMAL)

USER

SC RATC H

Figure 2

256

Mass Storage Configuration

DEC—O8-SBAB-D

FIRST SAM BLOCK

NUMBER

<—4 CHARACTER NAME

NAME BLOCK ENTRY

START

ADDRESS

ENTRY

POINT

”—1—“
Extended Memory Bits

PROG. TYPE
00 Source

‘T‘

“—r—'

25 ENTRYS/BLOC K

Binary
10 Fort. Binary

ii Save

System Program

LINK

Figure 3

Directory Name Block

(SIXBIT)

DEC-OB-SBAB-D

SAM BLOCK IMAGE

SAM BLOCK LAYOUT

Block 200

Block 0

Block 201

Block I

Block 202

Block 2

Block 203

Block 3
Block 4

I
I
I

I
|

Block 377

Block I77

‘——-> LINK

LINK

Link to SAM Block 2 w/

Block 400

577

Figure 4

Storage Allocation Mop

DEC-O8-SBAB-D

5.2.2

Disc Configuration

The Disc configuration is shown in

system overlay is located in the last two pages of disc storage.

Figure 5B. The scratch area for

Additional DN and SAM blocks are

added, one each per 32K of disc.
5.2.3

DECtape Configuration

The DECtape configuration (Figure 5A) is logically equivalent to

the disc system but has the SAM and DN blocks ordered differently for

efficiency.

BLOC K
HEAD OF MONITOR

HEAD OF MONITOR

MONITOR

SAM

SCRATCH

SYSTEMS

SCRATCH

SAM

l l

SAM

”F

16K

SYSTEMS

SAM

USER

SAM2
USER

SCRATCH
SCRATCH
LAST

SCRATCH

DEC TAPE

DISC

(A)

(3)
Figure 5

Mass Storage Configuration

l per 32K

additional disc

DEC-O8-SBAB-D

5 3
.

Error Messages
a.

The monitor protects the user from himself to the extent that it recognizes incorrect

syntax in input command strings.
a

Any errors discovered are remembered and at the time the user types

carriage return the monitor signals them with a ”?"
b.

The command decoder notifies the user of the following errors,

by typing the key

letter shown opposite the offending condition.
No such inputs

Illegal input characters

miscellaneous error
condition

Directory full
System I/O failure
Excessive inputs or outputs

means a

m U-o

The local errors are described in the write-ups for each system program.

Monitor time read/write errors cause a halt to occur.

hardware failure,

Persistence of this condition

the system I/O routine tries to read and write three times before it gives

up.

SPECIAL REQUIREMENTS INSTRUCTIONS OR FORMATS

6.l

Command Strings
The command string structure for the PDP-8 Disc

communicate with the system.

System software enables the user to easily

The punctuation of the input is as described below.

monitor mode

system program mode
‘

<CONTROL> C Request to return to monitor
=

carriage return

‘lP

<CONTROL> P.

<RO> Go back to start of input string.

Proceed with next operation.

Device Names

separator between device and file name

R
Rubout

6.2

devices in list

DECtape if disc and DECtape are on system [ X= unit number 0-7]
System (disc or DECtape)
High-speed paper tape
Teletype (low-speed paper tape)

Not implemented

DEC—08-SBAB-D

The command decoder used by all system programs asks one to three questions:
a.

OUTPUT in the Form "*OUT-"

INPUT in the form "*IN-",

OPTIONS or SWITCHES in the form "*OPT-"

Each system program may chose to use any or all of these options when it enters the command
decoder.

The user may type in one output device,

one

option (any character, which is transmitted in

ASCII to the using program) and a string of one or more input devices.
Each system program using the command decoder must tell it the type of file being dealt

with, i.e., Binary, Fort. Bin., or ASCII.
Some examples of command strings are shown below.

*IN
*IN

—

*OUT
*OPT

S:SAM A

S:FOOZ,R:)
D7:BAR
R

—

*TYPE SIZE OF CORE (IN

*4
*HIGH SPEED PAPER TAPE?

*YES
*DISC OR TAPE?

*DISC
*TYPE NUMBER OF DISC UNITS
*

*l
.

LOAD

*IN-R:

Typical System Builder Output

*OPT-Z

Figure 6

ST= 7600
Hi?
.

SAVE FORT10-7577;45ll
LOAD

*IN-R:
l

*OPT-l
ST= 7600
H
.

SAVE PAL.l 0-3400;24l
LOAD

*IN-R:
i

*OPT-Z
ST= 7600
NH
.

SAVE DDT! 5000—7577;5400

DEC-08— SBAB- D

APPENDIXA

SAVE

SYNTAX

FOR

STANDARD

.SAVE

FORT.l 0

SAVE

PAL.‘

SAVE DDT'.

—

PDP-8

7577; 4511

3400; 241

5000

.SAVE LODT.‘ 1000
.

SAVE HODT.I 7000

SAVE MAC8'. 0

.SAVE FOTS!

LOAD 200, SET SWITCHES+ RUN.

SYSTEM

7577; 5400

1577,- 1000
7577; 7000

7577; 2041*

6200; 200

PROGRAMS

DEC-08-SBAB-D

APPENDIXB
BOOTSTRAP

DISC BOOTSTRAP
0200
0201

0202

0203
0204

0205
0206
0207

021 0
021 I

021 2
0213
021 4
021 5

/ 7600
/661 5
/1 21 5
/361 3
/1 21 2
/3614
/6603
/6622
/ 5207
/ 5600
/ 7576
/ 7750
/7751
/ 7577

/CLA
/DEAL
/TAD 215
/DCA I 213
/TAD 212
/DCA 1 214
/DMAR
/DFSC
/JMP 207
/JMP I 200
/WC
/CA

DECTAPE BOOTSTRAP

(See TCOI System Bootstrap)

LOADERS

DEC-OB—SBAB-D

APPENDIX C

CALLING

SEQUENCE

(SYSTEM ROUTINE)

CALLING SEQUENCE
JMS I SYSIO

/ CELL "SYSIO" POINTS TO I/O

FUNCT

/ SEE PARA. II

BLOCK

/ BLOCK TO BE ACCESSED

CORE

/ LOW ORDER CORE ADDRESS

LINK

/ FILLED BY WRITE, USED BY READ

ERROR

/ ERROR RETURNS HERE
/ NORMAL RETURN HERE

FUNCTION CELL
BITS O-I

UNUSED

BITS 2

=0, NORMAL,- =1, RETURN AT END OF

READ/WRITE TO (ADDRESS + I IN
ERROR RETURN.
BITS 3-5

UNIT NO.

BITS 6-8

MEMORY FIELD

BITS 9-H

FUNCTION; READ

(IF DECTAPE)

3, WRITE