The PDP-15 distributions at GitHub comes with two software packages:
- A very simple application is "Paper Tape FOCAL",
- the other contains a disk-based operation system "XVM/DOS" and the multi-user capable "XVM/RSX" .
If you want to write own programs, you need a MACRO-15 assembler or a PDP-15 FORTRAN. There are no cross-assemblers running on modern hardware, so XVM/DOS is used to development a small assembler program.
Paper tape FOCAL
FOCAL is a BASIC-like interpretative arithmetic language. It can be run from a paper tape strip without need for any additional software. In this it resembles the BASIC ROM interpreters of early micro computers (PET, Apple II): here the ROM is made from paper holes instead of transistor cells.
To boot the PDP-15 from papertape just execute the "pdp15_focal" batch file. Normally pressing the READ IN key is necessary, but we're cheating here, for your convenience.
The manual is "Focal Programming Manual PDP-15 Systems (Oct 1970, DEC-15-KJZB-D).pdf".
http://www.ibm.com/developerworks/library/os-emulatehistory/ has a simple demo. They enter and run this program:
*01.10 ASK "WHAT YEAR WERE YOU BORN?", BORN
*01.20 ASK "WHAT YEAR IS IT?", YEAR
*01.30 SET AGE=YEAR-BORN
*01.40 TYPE "YOU ARE ", AGE-1, " OR ", AGE, " YEARS OLD.", !
*GO
WHAT YEAR WERE YOU BORN?:1964
WHAT YEAR IS IT?:2010
YOU ARE 45.0000 OR 46.0000 YEARS OLD.
*
Not too impressive, but at least the math is correct. See here a walk-through:
XVM/DOS - editing and assembling
This software package is the one distributed with SimH itself. Primary focus for them is booting XVM/RSX, with RSX/DOS only acting as boot step. But since I still panic when I see the "MCR>" prompt, I choose XVM/DOS as development environment.
The XVM/DOS is quite mystic too, but not too complex. Docs are all at bitsavers. Here we need:
- XVM-DOS USERS MANUAL (Jan 1976, DEC-XV-ODMAA-A-D).pdf
- Programmer's Reference Manual PDP-15 Utility Programs (Oct 1969, DEC-15-YWZA-D).pdf
- PDP-15 MACRO-15 ASSEMBLER PROGRAMMER'S REFERENCE MANUAL (Oct 1969, DEC-15-AMZA-D).pdf
So now follow me stumbling through the pits of a completly unkown user shell (PDP-15 old-timers, please don't laugh!)
A login is possible, but not necessary.
File handling: DIR, DELETE, RENAME
There's no "DIR" command. To list files, PIP must be used:
$PIP
PIP XVM V1A000
>L TT_SY
01-JAN-79
DIRECTORY LISTING (SCR)
110710 FREE BLKS
10 USER FILES
320 USER BLKS
BUILD XCT 1 13-JAN-99
BUILD XCU 33 13-JAN-99
CODE SRC 105 13-JAN-99
RSXPAT XCT 1 13-JAN-99
RSXPAT XCU 1 13-JAN-99
RSX BAT 153 13-JAN-99
HALT SRC 1 01-JAN-88
CLOSE HAL 1 01-JAN-88
>^C
XVM/DOS V1A000
$
There is also no RENAME nor a DELETE under XVM/DOS. These can be called from within the editor!
Editing texts
The text editor is line oriented, of course. There is an EDIT mode to issue commands, and an INSERT mode to write text. Features like BLOCK mode, INPUT file and OUTPUT file are there to deal with devices like tape, and with limited memory usage.
Call:
$EDIT
EDITOR XVM V1A000
>
Most commands in EDIT mode have a single-letter form:
| Command |
Short |
Description |
| DELETE | CALL DELETE INPUT <filename> <ext> Note the space between <filename> and <ext>A file is deleted from disk. Works only before any editing command! |
|
| RENAME |
CALL RENAME INPUT <filename1> <ext1> <filename2> <ext2> |
|
| OPEN |
OPEN <filename> <ext> |
|
| CLOSE | CLOSE [<filename> <ext>] Saves a file to disk. The name can be changed. |
|
| QUIT | ^C | Exit editor. |
| INSERT | <CR> | In EDIT mode, the ENTER key switches to INSERT mode. Then text can be typed |
| EDIT | <CR> ^P |
Ctrl-P leaves the INSERT mode, back to EDIT mode. Also does a single <CR>: you can not simply enter empty lines. |
| TOP | T | Make the top most line current (goto the virtual line before the first one) |
| NEXT <n> | N <n> | Go down n lines. To goto an absolute line number, use T N <line#> |
| PPRINT | P | Display current line |
| PRINT <n> | P <n> | List (print) the <n> next lines, new current lin is last printed. |
| INSERT | I <text> | Insert a new line <text> after the current line. Notice the <space> after "I". |
| REPLACE | R <text> | Replace the current line with <text>. Notice the <space> after "R". |
| DELETE | D | Delete the current line |
Running the MACRO-15 assembler
Call:
$MACRO
MACRO XVM V1A000
>
After the ">" prompt, a "command string" must be entered. It is of the form
<OPTION> <OPTION>←<filename>
Options are single letters separated by spaces. Interesting ones:
L create listing
N number lines decimal
A print symbols
And yes, the ASR-33 teletype had an "←" symbol on its keyboard, don't you have one?
No problem: the "←" is today displayed as the underline "_".
So an assembler call may look like this (the program "HALT SRC" contains only a single HALT opcode):
$MACRO
MACRO XVM V1A000 >A L N_HALT END OF PASS 1
PAGE 1 HALT SRC
1 / DEMO PROGRAM: JUST A HALT
2 00100 A .LOC 100
3 00100 A 740040 A HLT
4 000000 A .END
SIZE=00101 NO ERROR LINES
PAGE 2 HALT SRC
.CLEAR MACRO .CLOSE MACRO .DLETE MACRO .ENTER MACRO
.EXIT MACRO .FSTAT MACRO .GET MACRO .GTBUF MACRO
.GVBUF MACRO .INIT MACRO .MTAPE MACRO .MTRAN MACRO
.OVRLA MACRO .PUT MACRO .RAND MACRO .READ MACRO
.RENAM MACRO .RTRAN MACRO .SEEK MACRO .SETUP MACRO
.SYSID MACRO .TIMER MACRO .TRAN MACRO .USER MACRO
.WAIT MACRO .WAITR MACRO .WRITE MACRO .XVMOF MACRO
.XVMON MACRO
MACRO XVM V1A000
>
The "running light program"
Now that we can assemble, the "Hello world" of BlinkenLight panels is next. It loads the pattern of the DATA switches into the accumulator AC, then shifts it right and HALTS. On CONT another shift is done, and so on.
/ "RUNNING LIGHT" PROGRAM
/ ROTATES THE PATTERN OF THE DATA SWITCHES RIGHT ON EACH CONT
/ SET REGISTER SELECT TO "AC" TO SEE PATTERN.
/ TRY "CONT" WITH AUTO REPEAT!
.LOC 100 / SET POSITION IN MEMORY
START LAS / LOAD DATA SWITCHES INTO AC
LOOP RAR / ROTATE AC AND LINK RIGHT
HLT / WAIT FOR CONT
JMP LOOP / AGAIN
.END
Assembling - a complete walk-through
1. Boot
PDP-15 simulator V4.0-0 Beta REALCONS git commit id: $Format:
Listening on port 2311
Searching realcons controller "PDP15" ...
Connecting to host localhost ...
REALCONS PDP15, host="localhost", host panel="PDP15", interval = 1 msec, connected, boot image filename not set, nodebug,
panel BlinkenBoards driver hardware state = ACTIVE,
server info=
Server info................: PanelsimPDP15_app v1.00
Server program name........: blinkenbone.panelsim.panelsimPDP15.PanelsimPDP15_app
Server command line options: --width 1000 --repeat_rate 8 --register_select 10
To boot XVM/RSX, type "RSX" and press enter at the XVM/DOS "$" prompt.
To return to XVM/DOS, type "DOS" and press enter at the RSX MCR prompt.
To access the extra terminals, telnet to 127.0.0.1 on port 2311 and press Ctrl-T
to bring up the login prompt.
To log off MULTIACCESS, use the TDV command "OFF".
XVM/DOS V1A000
ENTER DATE (MM/DD/YY) - 01/01/79
PAGE MODE 128K API ON XVM ON SCR
$
2. Edit
$EDIT
EDITOR XVM V1A000
>CALL DELETE INPUT LIGHT SRC
>
INPUT
/ "RUNNING" LIGHT PROGRAM
/ ROTATES THE PATTERN OF THE DATA SWITCHES RIGHT ON EACH CONT
.LOC 100
LAS / LOAD DATA SWITCHES INTO ACCUMULATOR AC
LOOP RAR / ROTATE AC AND LINK RIGHT
HLT / WAIT FOR CONT
JMP LOOP / AGAIN
.END
EDIT
>CLOSE LIGHT
EDITOR XVM V1A000
>EXIT
XVM/DOS V1A000
$
We saved the new file as "LIGHT SRC".
3. Is the new source file there?
$PIP
PIP XVM V1A000
>L TT_SY
01-JAN-79
DIRECTORY LISTING (SCR)
110707 FREE BLKS
11 USER FILES
321 USER BLKS
BUILD XCT 1 13-JAN-99
BUILD XCU 33 13-JAN-99
CODE SRC 105 13-JAN-99
RSXPAT XCT 1 13-JAN-99
RSXPAT XCU 1 13-JAN-99
RSX BAT 153 13-JAN-99
HALT SRC 1 01-JAN-88
LIGHT SRC 1 01-JAN-79
CLOSE HAL 1 01-JAN-88
>^C
XVM/DOS V1A000
$
Yes, LIGHT SRC is there!
4. Assemble
$MACRO
MACRO XVM V1A000
>L_LIGHT
END OF PASS 1
PAGE 1 LIGHT SRC
/ "RUNNING" LIGHT PROGRAM
/ ROTATES THE PATTERN OF THE DATA SWITCHES RIGHT ON EACH CONT
/ SET REGISTER SELECT TO "AC" TO SEE PATTERN.
/ TRY "CONT" WITH AUTO REPEAT!
00100 A .LOC 100
00100 A 750004 A LAS / LOAD DATA SWITCHES INTO ACCUMULATOR AC
00101 A 740020 A LOOP RAR / ROTATE AC AND LINK RIGHT
00102 A 740040 A HLT / WAIT FOR CONT
00103 A 600101 A JMP LOOP / AGAIN
000000 A .END
SIZE=00104 NO ERROR LINES
MACRO XVM V1A000
>^C
XVM/DOS V1A000 $
Entering and starting the LIGHT program
Now that we have the binary code of LIGHT, we must enter it into memory. This will destroy the XVM/DOS memory image, but never mind.
From the listing we can see that the SimH commands would be:
sim> deposit 100 750004
sim> deposit 101 740020
sim> deposit 102 740040
sim> deposit 103 600101
But we use the panel now!
| Step | Switches | Cmd switch | Description |
| 1. | Preparation | ||
| 1.1. | STOP | Stop program execution, if running | |
| 1.2. | REG GROUP inactive REGISTER SELECT = "OA" |
Display memory address ("operand address") on REGISTER lamps | |
| 2. | Enter data into memory | ||
| 2.1. | ADDRESS = 000100 DATA = 750004 |
DEPOSIT THIS | Set memory word at 100 to 750004 See image below |
| 2.2. | DATA = 740020 | DEPOSIT NEXT | Set memory word at 101 to 740020 |
| 2.3. | DATA = 740040 | DEPOSIT NEXT | Set memory word at 102 to 740040 |
| 2.4. | DATA = 600101 | DEPOSIT NEXT | Set memory word at 103 to 600101 |
| 3. | Verify data in memory | ||
| 3.1. | ADDRESS = 000100 | EXAMINE THIS | Verify word at 100 on MEMORY BUFFER lamps: 750004 |
| 3.2. | EXAMINE NEXT | Verify word at 101 | |
| 3.3. | EXAMINE NEXT | Verify word at 102 | |
| 3.4. | EXAMINE NEXT | Verify word at 103 | |
| 4. | Run | ||
| 4.1. | REG GROUP inactive REGISTER SELECT="AC" |
Display accumulator "AC" on LINK and REGISTER lamps | |
| 4.2. | DATA = pattern | Select a data pattern to shift | |
| 4.3. | ADDRESS = 000100 | START | Start program at address 100. It HALTs at PC=103 and shows the shifted pattern. (Set REGISTER SELECT = "PC" to verifyOA |
| 4.4. | CONT | Next shift, and HALT again, and so on. | |
Deposit 750004 into address 100
Debugging with Single Step
You can set SING INST and single step through the program with CONT. You have to set the REGISTER SELECT knob to "PC" to see the program counter changing. It should go 101, 102, 103, 101, 102, 103, .... on each CONT.
More fun: REPEAT
You can use the REPEAT feature to automatically fireing CONT events with varying frequency. This works in normal mode and with SING INST!
Just set REPT active and keep CONT pressed !
Excercises to the reader
- Change the "LIGHT" program from a running dot into a binary counter.
- Enter and run the "Hello World" program in the attachement.
pdp15_hello.lst -- PDP-15 assembler listing for a \"Hello World\" program.