Digital PDFs

XX-5EB16-4C

1964

17 pages

Original

0.5MB

Document:	PDP-4 Fortran UM
Order Number:	XX-5EB16-4C
Revision:
Pages:	17
Original Filename:	http://bitsavers.org/pdf/dec/pdp4/PDP-4_Fortran_UM.pdf

OCR Text

J-4FT

PDP-4
FORTRAN
USERS' MANUAL

DIGITAL EQUIPMENT CORPORATION

•

MAYNARD, MASSACHUSETTS

PDP-4

FORTRAN

USERS' MANUAL

INTRODUCTION

This manual details standard operating procedures for the several available PDP-4 FORTRAN
systems _ The procedures are standard in the s,ense that they are directed to the person who
wants to write and execute FORTRAN programs with little or no attention paid to the details
of the operation beyond the source language level.

PDP-4 FORTRAN is written for two sig-

nificantly different hardware configurations, the one an exclusively paper-tape configuration
and the other a configuration which includes minimally two logical tape units (either normal
magnetic tape or a dual Micro Tape unit) and an 8K memory.
The principal subsections of the FORTRAN system for paper tape are:
Compiler
Assembler
Operating System
Library.
The compiler accepts input in the FORTRAN language and produces an

output in an inter-

mediate language acceptable to the assembler. The assembler accepts the compi ler output
and produces a binary relocatable version of the program and (in 8K systems) a binary version
of the Iinking loader.

In 4K systems this loader is too large to be kept in memory with the

assembler, and it constitutes an additiona I primary element of the system. When the user is
ready, he loads his main program and any sub-programs, followed by any built-in functions
called from the library. Once the total program is in memory, he loads the operating system and
executes his program. The operating system contains an interpreter for floating point arithmetic, an interpreter for format statements, red tape routines such as fix a floating number and
vice versa, and the I/O routines.

The operating system must be in memory when a

FORTRAN

program is execu ted.

PROCEDURE FOR USING FORTRAN WITH A PDP-4 PAPER TAPE SYSTEM
Since the avai lable memory is small (74, 000 bits), the FORTRAN system for 4K paper tape systems is slightly less flexible than normal systems. "AII format has been omitted as well as Hollerith input. Floating point numbers may be output in "EII format only. About 1400 decimal
locations are available for program and data.

The following procedure, with differences noted, applies equally well to 4K and 8K systems.
In an 8K system about 4600 decimal registers are avai lable for program and data. The bootstrap loader with starting address 7770 (for 4K machines) or 17770 {for 8K machines} is called
the readin mode loader or RIM loader.

Pressing the START switch on the console with the ap-

propriate address in the ADDRESS switches is called RIM "start."
Step 1:

Prepare the programs to be compi led in accordance wi th the conventions
establ ished in the II Summary Description of PDP-·4 FORTRAN. II

Step 2:

Place the paper tape labelled FORTRAN in the reader and RIM "start. II

Step 3:

Place the program to be compi led in the reader (lnd press CONT I NUE. The
punch must be on. FORTRAN wi II punch out the intermediate object tape.

Step 4:

If other programs are to be compi led, repeat step 3. If an accidental error
occurs at any time, such as the punch running out of paper tape before compilation is completed, the compilation procedure may be restarted by replacing the source tape in the reader, putting octal 22 in the ADDRESS
switches, and depressing START.

Step 5:

If an error occurs in the source language, the compiler will type a threeletter plus two-digit code on the teleprinter followed by the current (last
encountered) statement number. See Appendix II for the associated error
conditions. As a rule, a source language error will make any further action
useless. The error must be corrected and the program compiled again.

How-

ever, compilation should be completed to uncover all errors in the same program.

In 8K systems, the compiler will also print the offending line with

the errant charac ter flagged (by Iine feed).
Step 6:

When all necessary compilations have been successfully completed, remove
the output tape(s} from the punch.

Step 7:

Load the FORTRAN Assembler through RIM II start. II

Step 8:

Place the first program to be assembled in the reloder.

If severa I programs

were compiled together they will be separated from each other by a short
length of blank tape. The punch must be on, and the accumulator switches
must be all in the down position.
punch a partial binary output.

Depress CONTINUE. The assembler will

Step 9:

Depress CONTINUE to finish punching of the binary output. Symbols which
are used in the source program, but never appear on the left hand side of an
arithmetic statement or in an input statement or as the argument of a subroutine call, will be printed with a relative location automatically assigned
by the assembler. Any statement number which is referred to but never used
as a statement label will be printed also.

Step 10:

If a printout of the relative locations of program symbols is desired, put the
least significant (right most) switch of the ACCUMULATOR switches (test
switches) to the up position and press CONTINUE.

If the printout is not

desired, leave the switch in the down position and press CONTINUE to
restore the assembler for the next assembly. For detai Is about the assembly
capabilities of the PDP-4 Assembler see Digital-4-15-S. Many of the operations possible with the FORTRAN Assembler have not been del ineated here.
Should an error occur during the assembly procedure, the Assembler will
print a message on the teleprinter. For a summary see Appendix II. An
error printed by the assembler usually is the result of an original program
error which was not detected by FORTRAN.
Step 11:

If more prpgrams are to be assembled, place the next tape in the reader and
complete step 8.

If several programs were compiled together, be sure that

the blank tape area is under the reader light before continuing.
Step 12:

Remove the assembled programs from the punch. Each program will have its
title punched in readable format at the beginning. Since t~e FORTRAN Assembler is a one-pass assembler I this will be at the physical end of the
punched tape.

Step 13:

Load the FORTRAN linking loader through RIM "start,1I for 4K systems.
Omit this step in an 8K system.

Step'14:

Load the main program through RIM IIstart. II
program be loaded first.

It is important that the main

In an 8K system, the linking loader is punched on

the main program tape only. The loader is a lengthy strip of tape with the
eighth level punched at every frame and is unmistakable once recognized.
Step 15:

Place any sub-programs in the reader (readable title is always the leader),
and load through RIM IIstart. 1I The loader wi II handle the problems of Iinking between programs.

Step 16:

To obtain a printout of the-obsolute locations of sub-program labels put 5
in the ADDRESS switches and depress START.

Should a subroutine call or

library function call not yet be "Satisfied (i .e. not yet loaded), the symbol
will be preceded on the line by a minus sign followed by an address designating the last refe:renced i ink to this symbol.
Step 17:

If no library functions are needed go to step 18.

Place the library tape in

the reader, put 6 in the ADDRESS switches and depress START.

The linking

loader will search i-he library for functions called by the program. When
all the called functions have been loaded, the loader will halt, perhaps
part way through the library tape, displaying in the accumulator lights the
last program address.

In general, overlays of program and common storage

will not be detected by the loader; this responsibility is left to the programmer.
Step 18:

Load the operating system through RIM II start. II

Put octal 22 in the ADDRESS

switches and depress START to execute the progrom.

If paper tape input to

the FORTRAN program is used, this should be reDdy in the reader.
THE FORTRAN SYSTEM
When Micro Tape or normal magnetic tape is available, a FORTRAN oriented job-processing
executive system, called DECSYS, moy be used.
quired.
later.

A minimum of two physical tape units is re-

An int'egral part of DECSYS is the FORTRAN debugging system which is described
The basic jobs which DECSYS can do are detai led in the following paragraph.

The sys-

tem is organizationally open-ended in the sense that its executive list (job list) may readily be
expanded or changed to 5U it the purposes of a given insta Ilation.
The DECSYS Job-List
The convention of the context in which jobs are defined is that two tapes are available, a systems tape and a scratch tape.
may be read.

In general, the systems tape may not be written onJthe scratch

Paragraph headings are control commands and are typed in on the teleprinter.

Get Name - DECSYS will retrieve the named program from the system tape and relinquish control to that program.

Compile N Name, Name, Name; M Name, Name~ - Nand M are both two valued; they
indicate the physical source for the list of programs which follow; 11111 means paper tape, 11211
magnetic tape.

If "copy" is typed before "compile;1 DECSYS will copy the systems tape onto

the scratch tape and append any programs now on paper tape before proceeding.
Either list of names may have one element only, and either may be omitted. If a source designation is not typed, the source is understood to be paper tape. Unless errors occur, the job
will proceed .to the point of execution (load and almost go). Depress CONTI NUE to execute
the program.
All intermediate output is stored on the scratch tape and may be retrieved at any time by again
designating the scratch tape as a systems tape and restarting DECSYS.

If errors occur during

compilation, the compilation will be allowed to proceed although the output will be lost and
DECSYS will automatically restart.

If errors occur during assembly, however, normal assembly

is allowed to continue.
DECSYS will return control to the programmer in the assembly error mode with the following
eventualities possible:
Cancel!

DECSYS wi II restart

Symbols~

DECSYS will print output symbol definitions.

Change ~

DECSYS will prefix the lines typed following "change" to
the intermediate language and reassemble.

Print ~

DECSYS will print a listing of the assembly input.

Ignore!

DECSYS will ignore the error and continue the job.

Assemble N Name, Name, Name; M Name, Name ~ - The remarks about N, M, and the lists
made in the previous section apply here.

If "copy" precedes lIassemble, II DECSYS wi II copy

the systems tape onto the scratch tape and append a II paper tape programs before proceeding.
Assembly procedure will follow the path outlined in the preceding section.
Execute Name - DECSYS will search the systems tape for the named program including subprograms called by it and proceed to the point of execution. Depress CONTINUE to execute
the program.

Edit - DECSYS will retrieve the editing program and relinquish control to it. English language
sources either in FORTRAN or assembly (machine) language serve as input.
Debugging in the FORTRAN System
An integral part of DECSYS is the FORTRAN debug mode.
word IIdebug ll is typed.

In place of II comp ile,ll the control

FORTRAN is then switched into the debug mode and the compi led pro-

gram includes entries to the Debug routine incorporated in the (debug) opsys. All executable
statement numbers are available as labels to the debugging program. When the point of ex~
ecution is reached and DECSYS is in the debug mode, the programmer may type:
XXX

LIST

TRACE

XXX

MUST

XXX

Where XXX is a statement number, III ist ll is a I ist of variables to be printed out when the assoc iated statement number is encountered, II trace ll wi II cause the printout of the last five
statement numbers encountered when the designated statement number occurs, and IImust ll
designates a statement number which must be encountered in a reasonable time or else an error
halt should occur. Whenever the debug program is in control, i.e . just after a printout, its
II Iive II Iist of debug commands may be a Itered •

APPENDIX I

DIAGNOSTICS

The following diagnostics may be printed during compi lations. Each diagnostic is identified by
a three-letter name, and a two-digit number.

In addition, when using an 8K compiler, the

offending statement will be printed, with a I ine feed after the last character processed. For
all errors, except those which indicate storage capacity exceeded, processing will continue.
For both systems, the diagnostic error print (below) will be followed by the current statement
number.

Name

Number

Why
CONTROL STATEMENT

CON

Illegal Control Statement. The statement
will be ignored.

Upper case character in Control Statement.
The statement wi II be ignored.
COMMON STATEMENT

COM

Illegal entry in list. The entry will be ignored.

Symbol appears twice in COMMON.
The second occurrence will be ignored.
ASSIGN

ASG

N not a fixed point number. Attempt to use
it anyway. This will probably result in an
undefined symbol at assembly.

SUB

Number not followed by to.
ment.

Ignore the state-

No fixed point variable. Use the variable as
fixed point.

Illega I format - variable.
the statement.

Ignore the rest of

SUBROUTINE AND FUNCTION
Name not a variable. Compi Ie anyway.

Name

Number

'Nhy

Dummy symbol not a variable. Treat as a
symbol.

Dummy symbol used twice. Use anyway.
Will result in a multiple symbol definition
at assembly.
DIMENSION

DIM

Array name not a variable. Treat as a variable.

Array dimensioned hvice.

Dimension not a fixed point number.
cess anyway.

Process anyway.
Pro-

DO ST A TEME NT

First two letters not lido. II

Ignore statement.

No statement number.

No end test va lue spec ified.

Too many characters.
characters.

Process anyway.
Process anyway.

Ignore excessive

ILLEGAL FORMAT

ILF

Non-statement number at left margin.
cess as statement number.

Pro-

Missing left parenthesis. Assume present.

Missing right parenthesis.

Missing left parenthesis. Assume present.

Missing right parenthesis. Assume present.

Comma missing in go to. Assume present.

Variable missing in ,arithmetic statements,
ignore second opera tor.

Illegal device number in input or output
statement. Process anyway •

Illegal format in accept statement.
statement.

Illegal format statement number in an I/O
statement. Process anyway.

Assume present.

Ignore

Name

Number

Why

Extra right parenthesis.

Extra characters in statement.
sive charac ters.

Comma missing in repetitive element in I/O
list. Assume present.

Illegal format in I/O list element.
a II characters to next comma.

Ignore exces-

Ignore

ILLEGAL CHARACTER

ICH

Illegal character. The character will be ignored.

Illegal upper case character. Treat as lower
case.

No more characters after an illegal one.
CALL DIT MORSE. Cannot proceed.

DIT

Immediately
2

Wrong place in table

Dispatch number too big

Too many caPs

Illegal cal

Too many exits.

If any of the errors labeled DIT occurs, please note any pertinent
data and send to DEC-Programming Group.
UFX

UNSEEN FIXED POINT
Empty or punctuation. Statement done, or a
punctuation character. Process as if it were
fixed poinL

Floating point quantity, treat as fixed point.

Not a fixed point constant. Treat as if it
were.
FORMAT STATEMENT

FOR

Character missing.

Illegal format.
ment.

Ignore remainder of state-

Name

Number

Why

Characters missing.
statement.

Illegal control chanacter.

Illegal punctuation ..

Letter other than, I, F, E, X, H.
remainder of statement.

N too large in H.

Ignore remainder of
Process anyway.

Ignore

ILLEGAL FUNCTIO'N USAGE

IFU

Function name on left side outside function
definition.
STORAGE CAPACIlrV EXCEEDED

SCE

Processing may not proceed.
Pol ish stack exhausted.

Table exceeded.

Symbol generator exhausted.

Table exceeded.

Statement too long.

Push down stack exceeded.
dais) •

(too many nested

APPENDIX II

ERROR MESSAGES (FORTRAN ASSEMBLER)

With the exception of ~ (storage capacity exceeded) and ~ (illegal parity), assembly continues after the error message nas been printed, unless assembling a Iibrary tape.

An error

message may occur in one of three formats.
Format A
ERR VALl

SYM VAL2

Format A is used to indicate errors in the redefinition of symbols.

ERR is a three letter mnemonic

for the particular error. VALl is the old octal value of the symbol SYM. VAL2 is the value of
the new definition attempted. Whether the symbol was redefined depends upon the particular
error.
ERR

Meaning

mdt

The symbol was redefined with a comma.

rsp

A permanent symbol was redefined.

rda

An attempt to redefine a symbol was made.
The symbol was not redefined.

Format B
ERR OCT SYM
The general error message is printed in Format B. ERR indicates the particular error.
the octal address at which the error occurred.

OCT is

SYM is the symbolic address at which the error

occurred.
ERR

Meaning

ifp

Illegal format in parameter assignment

ifc

Illegal format in a comma assignment

ifq

Illegal format in library list

ify

Illegal format in internal declaration

tms

Toomany symbols in internal declaration

liq

Illegal term punctuation in library list

mdt

The value and address disagree in an address
assignment.

tua

Too many undefined symbols in an address as, signment.

ift

Illegal format in an absolute address assignment

I it

Illegal terminator in a pundef or external list

ifl

Illegal format in a Eundef or external list

ifs

Illegal format in a ~art

ifi

Illegal format in an input pseudo instruction

see

Storage capac i ty exceeded

Ins

non-symbol in a pundef list

Format C
ERR OCT SYM CAUSE
Format C is an expanded version of Format B. CAUSE is additional information to help the
programmer ascertain the cause of the error ~

For example, in the case of an error caused by

an undefined symbol, the symbol wi II be printed.
Meaning

ERR

CAUSE

i Ip

character

Illegal parity (place correct character in
ACS and "continue")

ust

symbol

Undefined symbol in a start or pause

uaa

symbol

Undefined symbol in an absolute address
assignment

upa

symbol

Undefined symbol in a parameter assignment

ich

character

Illegal character

sys

symbol

Already defined s.ymbol in internal declaration

---

Undefined Symbol Assignment
At the end of assembly, before the loader is punched, the undefined symbols and their definitions wi II be printed.

Each undefined symbol which was used in a storage word wi II be defined

as the address of a register at the end of the, program, and the definition printed.

If the sym-

bol was not used in a storage word, then just the symbol will be printed and the symbol will
not be defined. An example of the latter is a symbol which appears to the right in a parameter assignment, but nowhere else.

6017

Printed in U.S.A.

1.5-2/64