PDP1/pdp1_doc.txt

To:	Users
From:	Bob Supnik
Subj:	PDP-1 Simulator Usage
Date:	15-Nov-2004

			COPYRIGHT NOTICE

The following copyright notice applies to both the SIMH source and binary:

   Original code published in 1993-2004, written by Robert M Supnik
   Copyright (c) 1993-2004, Robert M Supnik

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   ROBERT M SUPNIK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

   Except as contained in this notice, the name of Robert M Supnik shall not
   be used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from Robert M Supnik.

This memorandum documents the PDP-1 simulator.


1. Simulator Files

sim/		scp.h
		sim_console.h
		sim_defs.h
		sim_fio.h
		sim_rev.h
		sim_sock.h
		sim_timer.h
		sim_tmxr.h
		scp.c
		sim_console.c
		sim_fio.c
		sim_sock.c
		sim_timer.c
		sim_tmxr.c

sim/pdp1/	pdp1_defs.h
		pdp1_cpu.c
		pdp1_drm.c
		pdp1_dt.c
		pdp1_lp.c
		pdp1_stddev.c
		pdp1_sys.c

2. PDP-1 Features

The PDP-1 is configured as follows:

device		simulates
name(s)

CPU		PDP-1 CPU with up to 64KW of memory
PTR,PTP		integral paper tape reader/punch
TTY		console typewriter
LPT		Type 62 line printer
DRM		Type 24 serial drum
DRP		Type 23 parallel drum
DT		Type 550 Microtape (DECtape)

The PDP-1 simulator implements the following unique stop conditions:

	- an unimplemented instruction is decoded, and register
	  STOP_INST is set
	- more than IND_MAX indirect addresses are detected during
	  memory reference address decoding
	- more than XCT_MAX nested executes are detected during
	  instruction execution
	- I/O wait, and no I/O operations outstanding (i.e, no I/O
	  completion will ever occur)
	- a simulated DECtape runs off the end of its reel

The PDP-1 loader supports RIM format tapes and BLK format tapes.  If
the file to be loaded has an extension of .BIN, or switch -B is specified,
the file is assumed to be BLK format; otherwise, it defaults to RIM
format.  LOAD takes an optional argument which specifies the starting
address of the field to be loaded:

	LOAD lisp.rim		-- load RIM format file lisp.rim
	LOAD ddt.rim 70000	-- load RIM format file ddt.rim into
				   the field starting at 70000
	LOAD -B macro.blk	-- load BLK format file macro.blk

The DUMP command is not implemented.

2.1 CPU

The only CPU options are the presence of hardware multiply/divide and the
size of main memory.

	SET CPU MDV		enable multiply/divide
	SET CPU NOMDV		disable multiply/divide
	SET CPU 4K		set memory size = 4K
	SET CPU 8K		set memory size = 8K
	SET CPU 12K		set memory size = 12K
	SET CPU 16K		set memory size = 16K
	SET CPU 20K		set memory size = 20K
	SET CPU 24K		set memory size = 24K
	SET CPU 28K		set memory size = 28K
	SET CPU 32K		set memory size = 32K
	SET CPU 48K		set memory size = 48K
	SET CPU 64K		set memory size = 64K

If memory size is being reduced, and the memory being truncated contains
non-zero data, the simulator asks for confirmation.  Data in the truncated
portion of memory is lost.  Initial memory size is 64K.

CPU registers include the visible state of the processor as well as the
control registers for the interrupt system.

	name		size	comments

	PC		16	program counter
	AC		18	accumulator
	IO		18	IO register
	OV		1	overflow flag
	PF		6	program flags<1:6>
	SS		6	sense switches<1:6>
	TA		16	address switches
	TW		18	test word (front panel switches)
	EXTM		1	extend mode
	IOSTA		18	IO status register
	SBON		1	sequence break enable
	SBRQ		1	sequence break request
	SBIP		1	sequence break in progress
	IOH		1	I/O halt in progress
	IOS		1	I/O synchronizer (completion)
	PCQ[0:63]	16	PC prior to last jump or interrupt;
				most recent PC change first
	STOP_INST	1	stop on undefined instruction
	SBS_INIT	1	initial state of sequence break enable
	EXTM_INIT	1	initial state of extend mode
	XCT_MAX		8	maximum XCT chain
	IND_MAX		8	maximum nested indirect addresses
	WRU		8	interrupt character

The CPU can maintain a history of the most recently executed instructions.
This is controlled by the SET CPU HISTORY and SHOW CPU HISTORY commands:

	SET CPU HISTORY		clear history buffer
	SET CPU HISTORY=0	disable history
	SET CPU HISTORY=n	enable history, length = n
	SHOW CPU HISTORY	print CPU history
	SHOW CPU HISTORY=n	print first n entries of CPU history

The maximum length for the history is 65536 entries.

2.2 Programmed I/O Devices

2.2.1 Paper Tape Reader (PTR)

The paper tape reader (PTR) reads data from or a disk file.  The POS
register specifies the number of the next data item to be read.  Thus,
by changing POS, the user can backspace or advance the reader.

The paper tape reader supports the BOOT command.  BOOT PTR copies the
RIM loader into memory and starts it running.  BOOT PTR loads into the
field selected by TA<0:3> (the high order four bits of the address
switches).

The paper tape reader implements these registers:

	name		size	comments

	BUF		8	last data item processed
	DONE		1	device done flag
	RPLS		1	return restart pulse flag
	POS		32	position in the input file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape

	end of file	1	report error and stop
			0	out of tape

	OS I/O error	x	report error and stop

2.2.2 Paper Tape Punch (PTP)

The paper tape punch (PTP) writes data to a disk file.  The POS
register specifies the number of the next data item to be written.
Thus, by changing POS, the user can backspace or advance the punch.

The paper tape punch implements these registers:

	name		size	comments

	BUF		8	last data item processed
	DONE		1	device done flag
	RPLS		1	return restart pulse flag
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape

	OS I/O error	x	report error and stop

2.2.3 Console Typewriter (TTY)

The Typewriter is a half-duplex electric typewriter (originally a
Friden Flexowriter, later a Sorobon-modified IBM B).  It has only a
single buffer and a single carriage state but distinct input and
output done and interrupt flags.  The typewriter input (TTY unit 0)
polls the console keyboard for input.  The typewriter output (TTY
unit 1) writes to the simulator console window.

The typewriter implements these registers:

	name		size	comments

	BUF		6	typewriter buffer
	UC		1	upper case/lower case state flag
	RPLS		1	return restart pulse flag
	KDONE		1	input ready flag
	KPOS		32	number of characters input
	KTIME		24	keyboard polling interval
	TDONE		1	output done flag
	TPOS		32	number of characters output
	TTIME		24	time from I/O initiation to interrupt

2.2.4 Type 62 Line Printer (LPT)

The paper line printer (LPT) writes data to a disk file.  The POS
register specifies the number of the next data item to be written.
Thus, by changing POS, the user can backspace or advance the printer.

The line printer can be disabled and enabled with the SET LPT DISABLED
and SET LPT ENABLED commands, respectively.

The line printer implements these registers:

	name		size	comments

	BUF		8	last data item processed
	PNT		1	printing done flag
	SPC		1	spacing done flag
	RPLS		1	return restart pulse flag
	BPTR		6	print buffer pointer
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error
	LBUF[0:119]	8	line buffer

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape or paper

	OS I/O error	x	report error and stop

2.3 Type 550/555 Microtape (DECtape) (DT)

The PDP-1 uses the Type 550 Microtape (later renamed DECtape), a programmed
I/O controller.  PDP-1 DECtape format has 4 18b words in its block headers
and trailers.

DECtapes drives are numbered 1-8; in the simulator, drive 8 is unit 0.
DECtape options include the ability to make units write enabled or write
locked.

	SET DTn WRITEENABLED	set unit n write enabled
	SET DTn LOCKED		set unit n write locked

Units can also be set ENABLED or DISABLED.

The DECtape controller can be disabled and enabled with the SET DT DISABLED
and SET DT ENABLED commands, respectively.

The Type 550 supports PDP-8 format, PDP-11 format, and 18b format DECtape
images.  ATTACH tries to determine the tape format from the DECtape image;
the user can force a particular format with switches:

	-r			PDP-8 format
	-s			PDP-11 format
	-t			18b format

The DECtape controller is a data-only simulator; the timing and mark
track, and block header and trailer, are not stored.  Thus, the WRITE
TIMING AND MARK TRACK function is not supported; the READ ALL function
always returns the hardware standard block header and trailer; and the
WRITE ALL function dumps non-data words into the bit bucket.

The DECtape controller implements these registers:

	name		size	comments

	DTSA		12	status register A
	DTSB		12	status register B
	DTDB		18	data buffer
	DTF		1	DECtape flag
	BEF		1	block end flag
	ERF		1	error flag
	LTIME		31	time between lines
	DCTIME		31	time to decelerate to a full stop
	SUBSTATE	2	read/write command substate
	POS[0:7]	32	position, in lines, units 0-7
	STATT[0:7]	18	unit state, units 0-7
	STOP_OFFR	1	stop on off-reel error

It is critically important to maintain certain timing relationships
among the DECtape parameters, or the DECtape simulator will fail to
operate correctly.

	- LTIME must be at least 6
	- DCTIME needs to be at least 100 times LTIME

Acceleration time is set to 75% of deceleration time.

2.4 Drums

The PDP-1 supported two drums: the Type 23 parallel drum (DRP) and
the Type 24 serial drum (DRM).  Both use device addresses 061-064;
accordingly, only one can be enabled at a time.  By default, the
Type 24 serial drum is enabled, and the Type 23 parallel drum is
disabled.

2.4.1 Type 24 Serial Drum (DRM)

The serial drum (DRM) implements these registers:

	name		size	comments

	DA		9	drum address (sector number)
	MA		16	current memory address
	DONE		1	device done flag
	ERR		1	error flag
	WLK		32	write lock switches
	TIME		24	rotational latency, per word
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

Drum data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.4.2 Type 23 Parallel Drum (DRP)

The parallel drum (DRP) implements these registers:

	name		size	comments

	TA		12	track address
	RDF		5	read field
	RDE		1	read enable flag
	WRF		5	write field
	WRF		1	write enable flag
	MA		16	current memory address
	WC		12	word count
	BUSY		1	device busy flag
	ERR		1	error flag
	TIME		24	rotational latency, per word
	STOP_IOE	1	stop on I/O error


Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

Drum data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.5 Symbolic Display and Input

The PDP-1 simulator implements symbolic display and input.  Display is
controlled by command line switches:

	-a			display as ASCII character
	-c			display as FIODEC character string
	-m			display instruction mnemonics

Input parsing is controlled by the first character typed in or by command
line switches:

	' or -a			ASCII character
	" or -c			three character FIODEC string
	alphabetic		instruction mnemonic
	numeric			octal number

Instruction input uses modified PDP-1 assembler syntax.  There are six
instruction classes: memory reference, shift, skip, operate, IOT, and
LAW.

Memory reference instructions have the format

	memref {I} address

where I signifies indirect reference.  The address is an octal number in
the range 0 - 0177777.

Shift instructions have the format

	shift shift_count

The shift count is an octal number in the range 0-9.

Skip instructions consist of single mnemonics, eg, SZA, SZS4.  Skip
instructions may be or'd together

	skip skip skip...

The sense of a skip can be inverted by including the mnemonic I.

Operate instructions consist of single mnemonics, eg, CLA, CLI.  Operate
instructions may be or'd together

	opr opr opr...

IOT instructions consist of single mnemonics, eg, TYI, TYO.  IOT
instructions may include an octal numeric modifier or the modifier I:

	iot modifier

The simulator does not check the legality of skip, operate, or IOT
combinations.

Finally, the LAW instruction has the format

	LAW {I} immediate

where immediate is in the range 0 to 07777.

2.6 Character Sets

The PDP-1's first console was a Frieden Flexowriter; its character encoding
was known as FIODEC.  The PDP-1's line printer used a modified Hollerith
character set.  The following table provides equivalences between ASCII
characters and the PDP-1's I/O devices.  In the console table, UC stands
for upper case.

		 PDP-1			   PDP-1
ASCII		console	 		line printer

000 - 007	none			none
bs		075			none
tab		036			none
012 - 014	none			none
cr		077			none
016 - 037	none			none
space		000	       		000
!		{OR} UC+005		none
"		UC+001			none
#		{IMPLIES} UC+004	none
$		none			none
%		none			none
&		{AND} UC+006		none
'		UC+002			none
(		057			057
)		055			055
*		{TIMES} UC+073		072
+		UC+054			074
,		033			033
-		054			054
.		073			073
/		021			021
0		020			020
1		001			001
2		002			002
3		003			003
4		004			004
5		005			005
6		006			006
7		007			007
8		010			010
9		011			011
:		none			none
;		none			none
<		UC+007			034
=		UC+033			053
>		UC+010			034
?		UC+021			037
@		{MID DOT} 040		{MID DOT} 040
A		UC+061			061
B		UC+062			062
C		UC+063			063
D		UC+064			064
E		UC+065			065
F		UC+066			066
G		UC+067			067
H		UC+070			070
I		UC+071			071
J		UC+041			041
K		UC+042			042
L		UC+043			043
M		UC+044			044
N		UC+045			045
O		UC+046			046
P		UC+047			047
Q		UC+050			050
R		UC+051			051
S		UC+022			022
T		UC+023			023
U		UC+024			024
V		UC+025			025
W		UC+026			026
X		UC+027			027
Y		UC+030			030
Z		UC+031			031
[		UC+057			none
\		{OVERLINE} 056		{OVERLINE} 056
]		UC+055			none
^		{UP ARROW} UC+011	{UP ARROW} 035
_		UC+040			UC+040
`		{RT ARROW} UC+020	036
a		061			none
b		062			none
c		063			none
d		064			none
e		065			none
f		066			none
g		067			none
h		070			none
i		071			none
j		041			none
k		042			none
l		043			none
m		044			none
n		045			none
o		046			none
p		047			none
q		050			none
r		051			none
s		022			none
t		023			none
u		024			none
v		025			none
w		026			none
x		027			none
y		030			none
z		031			none
{		none			none
|		UC+056			076
}		none			none
~		UC+003			013
del		075			none