The original Spacewar! game was written for the PDP-1 minicomputer and there were several ports to other architectures.
This port to the PDP-11 architecture was done by Bill Seiler & Larry Bryant in 1974. It was then submitted to DECUS as 11-192.
SPACEWAR on the HP 1332A vector screen.
Click to see video clip:
SPACEWAR on a VR12 vector screen. Has a very nice P7 phosphor that has fantastic after-glow. Actually this type of phosphor was used in the PDP-1 screen which the original SPACEWAR was run on.
Ufortunatley DECUS threw away all the sources many years ago. By luck I got in contact with Bill Seiler and he sent me the source files. The sources were provided to me as scanned documents. With some help the original PDFs were tidied up to help the OCR process. Then I partly OCRed and manually transcribed all files into text files. The files were then then fed into the PAL11-S assembler and numerous errors were detected already when trying to get the files pass the syntax check. Then the output listing files was compared side by side with the original scanned files. Byte for byte were checked and yet more problems were found. Finally during linking a number of issues with global symbols were found. In the end the program assembled and linked correctly.
As a side note there exists at least two more ports of the SPACEWAR game to the PDP-11 architecture (for example this one), but both of those rely on the VT11 vector drawing option which is for example present in the GT40 system. I don't have a VT11 neither a GT40 so this is my best option to get SPACEWAR on a PDP-11.
If you don't want to go down the route of assembling and linking all the source moddules there is an easy solution. Just grab the dddp.dsk image and use the TU58FS tool (or some other TU58 emulator) to serve it to your PDP-11. It contains a bootable DDDP image with a SPACEWAR image binary image. Just type R SPCWAR.LDA and it will run provided you have the AR11 card.
In case you just want to run the binary and not want the fun of building it from scratch, just grab the SPACEWAR.ABS file in the ar11-patch branch (if you have a AR11 board in your machine) and run in from 025424 025432 (please note that this may change since a new build of the code might affect the entrypoint, check the SPACEWAR.MAP file when in doubt). Make sure to also load the IOX binary in the IOX-11 subfolder into memory before starting the SPACEWAR and set the switch regsiter to all zeroes. I have seen that otherwise it gets stuck in the IOX library. Probably a non-zero SR indicate some options to the IOX library, but I haven't investigated that further.
Update: Even easier should be to use the SPACEWARWIOX.LDA binary since it includes the IOX-11 binary and also have the proper transfer address which should make the loader start it directly. Make sure to have the SR set to 0. This binary starts at 1000 if it is loaded using PDP11GUI rather than read from paper tape.
It is possible to assemble the files located in the SRC folder using PAL11-S assembler under SimH PDP-11 simulator. PAL11-S is part of the PDP-11 Paper Tape Software.
First toggle in the bootstrap loader (or use the file TOOLS/simh.ini)
sim> SET CPU 11/05
Disabling XQ
sim> SET CPU 16K
sim>
sim>
sim> ; Disable devices that we don't need
sim> SET HK DISABLE
sim> SET DZ DISABLE
sim> SET RL DISABLE
sim> SET RX DISABLE
sim> SET RP DISABLE
sim> SET RQ DISABLE
sim> SET TM DISABLE
sim> SET TQ DISABLE
sim> SET RK DISABLE
sim>
sim> ; Enable the high-speed paper tape reader/punch
sim> SET PTR ENABLE
sim> SET PTP ENABLE
sim> DEPOSIT 037744 016701
sim> DEPOSIT 037746 000026
sim> DEPOSIT 037750 012702
sim> DEPOSIT 037752 000352
sim> DEPOSIT 037754 005211
sim> DEPOSIT 037756 105711
sim> DEPOSIT 037760 100376
sim> DEPOSIT 037762 116162
sim> DEPOSIT 037764 000002
sim> DEPOSIT 037766 037400
sim> DEPOSIT 037770 005267
sim> DEPOSIT 037772 177756
sim> DEPOSIT 037774 000765
sim> DEPOSIT 037776 177550
sim> ATTACH PTR TOOLS/DEC-11-L2PC-PO.ptap
sim> GO 037744
HALT instruction, PC: 037500 (MOV PC,SP)
sim> D SR 37500
sim> ATTACH PTR TOOLS/dec-uplsa-a-pl.bin
PTR: unit is read only
sim> GO 037500
PAL-11S V003A
*S
Now pressing Ctrl-E allows for attaching the correct input and output virtual paper tapes.
Simulation stopped, PC: 035110 (CMPB R1,#14)
sim> attach ptr SRC/SPCWAR.PAL
sim> attach ptp OBJ/SPCWAR.OBJ
PTP: creating new file
sim> attach lpt LST/SPCWAR.LST
LPT: creating new file
sim> c
Now we are back in the PAL11-S assmebler. But it has alread greated you above with an S(ource) so it won't do that again. Simply type H for input via High-Speed reader. The same for the O(utput). Send L(ist) to the P(rinter) and the T(able) to the T(eletype) output.
H
*B H
*L P
*T T
ADBR = 176772 G ADCS = 176770 G AMMO 000216RG
ANGH1 000154RG ANGH2 000202RG ANGL1 000152RG
ANGL2 000200RG ANGMID = 000702 G COMPAR = ****** G
DAC0 = 176750 G DAC1 = 176752 G DAC2 = 176754 G
FIRE = 001440 G FLAG1 000132RG FLAG2 000160RG
GAME1 000222RG GAME2 000224RG GRAVTY = ****** G
GRVFLG 000226RG HIT1 000204RG HIT2 000206RG
MASK = 002100 G PARM = ****** G PC =%000007
POINT = ****** G PTNUM = ****** G PTREP 000230RG
RESET = ****** G RKTSIZ = 007000 G RKT1 = ****** G
RKT2 = ****** G R0 =%000000 R1 =%000001
R2 =%000002 R3 =%000003 R4 =%000004
R5 =%000005 R6 =%000006 R7 =%000007
SHOTS1 000210RG SHOTS2 000212RG SP =%000006
SPCRST 000020RG SPCWAR 000000RG SPC01 000066R
SUNSZ = 004000 G TSPEED 000220RG UPDAT1 = ****** G
UPDAT2 = ****** G WIN 000214RG XDISP1 000150RG
XDISP2 000176RG XSIZE1 000142RG XSIZE2 000170RG
XVELH1 000146RG XVELH2 000174RG XVELL1 000144RG
XVELL2 000172RG YDISP1 000140RG YDISP2 000166RG
YSIZE1 000130RG YSIZE2 000156RG YVELH1 000136RG
YVELH2 000000RG YVELL1 000134RG YVELL2 000162RG
. = 000232R
END ?
So now the assembler want to run the second pass which means that we have to load our virtual source tape again. Press Ctrl-E now to get into SimH.
Simulation stopped, PC: 035464 (BR 35334)
sim> attach ptr SRC/SPCWAR.PAL
sim> c
And then press return when back into the PAL11-S environment.
000000 ERRORS
PAL-11S V003A
*S
Do this for each and every file to produce object files.
Linking involves running the LINK11-S which is similar to how to run the assembler.
sim> SET CPU 11/05
Disabling XQ
sim> SET CPU 16K
sim>
sim> ; Disable devices that we don't need
sim> SET HK DISABLE
sim> SET DZ DISABLE
sim> SET RL DISABLE
sim> SET RX DISABLE
sim> SET RP DISABLE
sim> SET RQ DISABLE
sim> SET TM DISABLE
sim> SET TQ DISABLE
sim> SET RK DISABLE
sim>
sim> ; Enable the high-speed paper tape reader/punch
sim> SET PTR ENABLE
sim> SET PTP ENABLE
sim> DEPOSIT 037744 016701
sim> DEPOSIT 037746 000026
sim> DEPOSIT 037750 012702
sim> DEPOSIT 037752 000352
sim> DEPOSIT 037754 005211
sim> DEPOSIT 037756 105711
sim> DEPOSIT 037760 100376
sim> DEPOSIT 037762 116162
sim> DEPOSIT 037764 000002
sim> DEPOSIT 037766 037400
sim> DEPOSIT 037770 005267
sim> DEPOSIT 037772 177756
sim> DEPOSIT 037774 000765
sim> DEPOSIT 037776 177550
sim> ATTACH PTR TOOLS/DEC-11-L2PC-PO.ptap
sim> GO 037744
HALT instruction, PC: 037500 (MOV PC,SP)
sim> ATTACH PTR TOOLS/dec-11-ulksa-a-pl.bin
PTR: unit is read only
sim> D SR 0
sim> GO 037500
LINK-11S V002A
*I H
*O H
*M P
*T
*B
PASS 1
*
Simulation stopped, PC: 035140 (MOV R5,14(SP))
sim> ATTACH PTP SPACEWAR.ABS
sim> ATTACH LPT SPACEWAR.MAP
sim> ATTACH PTR OBJ/SPCWAR.OBJ
To the linker you specify the I(input) and O(utput) deivce. H (High-speed) reader or L (Low-speed). Load map (M) is either not generated at all if pressing RETURN or by pressing H (High speed punch) or T(teletype), or P(Line Printer). The there are two questions (T and B) how the relocation should be done. Press RETURN for top of memory to both of those.
In this case I have chosen to have the resulting binary to be generated on the paper tape punch and the module map on the line printer.
After this each file is fed into the linker by attaching it to the reader and pressing RETURN at the * prompt. When all object files has been presented to the first pass of the linker you can press U a the * prompt to show the remaining undefined symbols. When all is done press E and the linker will print the load map and then start the seconds pass, requesting the same object files in the same order.
* U
* E
PASS 2
*
Simulation stopped, PC: 035122 (ADD #34662,R2)
sim> ATTACH PTR FPMP-11/FPMP-11-SPACEWAR.OBJ
sim> c
When you supplied the last file you should be greated with another linker startup message.
LINK-11S V002A
*I
Then you know that all is good and there should be a binary file and map file generated.
The first time I tried to run the linker was not succesful. After feeding all source modules unfortunatley I got two undefined symbols.
sim> c
* U
$ICI
$ICO
*
These two subroutines are from the FPMP-11 package. Just adding one of the two pre-made FPMP-11 object files does not resolve the two undefined symbols. FPMP-11 documentation.
Reading the manual a bit more revealed that the reason is that the two premade object files just contain a subset of the FPMP-11 package, not the $ICI and $ICO modules! To get those into the build one has to add a special file with defines for two variables used by the conditional build of the FPMP-11 packaged. By feeding this file
;******************************************************
;
; CONDITIONAL SWITCHES
; FOR FPMP-11 PACKAGE
; WHEN USED WITH SPACE WAR
;
CND$24=1
CND$25=1
.EOT
before the six FPMP-11 source files I had a tailor made object paper tape with just the $ICI and $ICO symbols defined!
Please note that the SPCWAR module has to be the first module and the POINT module the last module. See comments further below. All the other modules comes inbetween including the FPMP-11 library built previously.
This new object tape was then fed first into the linker, followed by all the 19 object paper tapes of SPACE WAR ending with the module POINT which has to be the last module. And indeed the link completeted without any unresolved symbols this time.
This was the resulting MODULE MAP from LINK11-S:
* U
* E
LOAD MAP
TRANSFER ADDRESS: 000001
LOW LIMIT: 025424
HIGH LIMIT: 037460
**********
MODULE SPCWAR
SECTION ENTRY ADDRESS SIZE
<. ABS.> 000000 000000
< > 025424 000232
ADBR 170402
ADCS 170400
AMMO 025642
ANGH1 025600
ANGH2 025626
ANGL1 025576
ANGL2 025624
ANGMID 000702
DAC0 170412
DAC1 170414
DPCS 170410
ERASE 010000
FIRE 001440
FLAG1 025556
FLAG2 025604
GAME1 025646
GAME2 025650
GRVFLG 025652
HIT1 025630
HIT2 025632
MASK 002100
PTREP 025654
RKTSIZ 007000
SHOTS1 025634
SHOTS2 025636
SPCRST 025444
SPCWAR 025424
SUNSZ 004000
TSPEED 025644
WIN 025640
XDISP1 025574
XDISP2 025622
XSIZE1 025566
XSIZE2 025614
XVELH1 025572
XVELH2 025620
XVELL1 025570
XVELL2 025616
YDISP1 025564
YDISP2 025612
YSIZE1 025554
YSIZE2 025602
YVELH1 025562
YVELH2 025610
YVELL1 025560
YVELL2 025606
**********
MODULE CHAR
SECTION ENTRY ADDRESS SIZE
< > 025656 000302
CHAR 025656
**********
MODULE CHRTAB
SECTION ENTRY ADDRESS SIZE
< > 026160 000606
CHRTAB 026160
**********
MODULE COMPAR
SECTION ENTRY ADDRESS SIZE
< > 026766 000444
COMPAR 026766
**********
MODULE EXPLOD
SECTION ENTRY ADDRESS SIZE
< > 027432 000330
EXPLOD 027432
EXPREP 027550
EXPX 027556
EXPY 027560
**********
MODULE GRAVTY
SECTION ENTRY ADDRESS SIZE
< > 027762 000450
GRAVTY 027762
**********
MODULE MULPLY
SECTION ENTRY ADDRESS SIZE
< > 030432 000304
MULPLY 030432
**********
MODULE PARM
SECTION ENTRY ADDRESS SIZE
< > 030736 001214
PARM 030736
**********
MODULE PWRUP
SECTION ENTRY ADDRESS SIZE
< > 032152 000106
**********
MODULE RESET
SECTION ENTRY ADDRESS SIZE
< > 032260 000206
CENTER 040000
ORBIT 000400
RESET 032260
RES01 032446
**********
MODULE RKT1
SECTION ENTRY ADDRESS SIZE
< > 032466 000160
RKT1 032466
**********
MODULE RKT2
SECTION ENTRY ADDRESS SIZE
< > 032646 000142
RKT2 032646
**********
MODULE SCORE
SECTION ENTRY ADDRESS SIZE
< > 033010 000266
SCORE 033010
**********
MODULE SINCOS
SECTION ENTRY ADDRESS SIZE
< > 033276 000462
SINCOS 033276
**********
MODULE SLINE
SECTION ENTRY ADDRESS SIZE
< > 033760 000140
SLINE 033760
**********
MODULE SUN
SECTION ENTRY ADDRESS SIZE
< > 034120 000304
SUN 034120
**********
MODULE UPDAT1
SECTION ENTRY ADDRESS SIZE
< > 034424 000372
UPDAT1 034424
**********
MODULE UPDAT2
SECTION ENTRY ADDRESS SIZE
< > 035016 000372
UPDAT2 035016
**********
MODULE FPMP11
SECTION ENTRY ADDRESS SIZE
< > 035410 000640
$ERR 036212
$ERRA 036222
$ERVEC 036242
$ICI 035416
$ICO 035722
$OCI 035410
$OCO 035714
$POLSH 036206
$V20A 036206
**********
MODULE POINT
SECTION ENTRY ADDRESS SIZE
< > 036250 001210
POINT 036250
PTNUM 036456
PASS 2
*
And it also resulted a 7323 byte file in Absolute Binary format! From the load map one can deduce the starting address of the binary. 025424 in this case.
This the full transcript on how to link the SPACEWARWIOX.LDA binary. At the B prompt give 1000 to indicate that the starting address should be 1000 octal.
$ ~/simh/BIN/pdp11
PDP-11 simulator V4.0-0 Beta git commit id: f1a6d538
sim> do TOOLS/simh.ini
Disabling XQ
HALT instruction, PC: 037500 (MOV PC,SP)
sim> ATTACH PTR TOOLS/dec-11-ulksa-a-pl.bin
sim> D SR 0
sim> GO 037500
LINK-11S V002A
*I H
*O H
*M P
*T
*B 1000
PASS 1
*
Simulation stopped, PC: 035122 (ADD #34662,R2)
sim> attach ptp SPACEWARWIOX.LDA
PTP: creating new file
sim> attach LPT SPACEWARWIOX.MAP
LPT: creating new file
sim> ATTACH PTR OBJ/SPCWAR.OBJ
sim> c
*
Simulation stopped, PC: 035042 (MOV (SP)+,R5)
sim> ATTACH PTR FPMP-11/FPMP-11-SPACEWAR.OBJ
sim> c
*
Simulation stopped, PC: 035036 (CLR R4)
sim> ATTACH PTR OBJ/CHAR.OBJ
sim> c
*
Simulation stopped, PC: 035104 (CMPB R1,#14)
sim> ATTACH PTR OBJ/CHRTAB.OBJ
sim> c
*
Simulation stopped, PC: 035110 (BHI 35354)
sim> ATTACH PTR OBJ/COMPAR.OBJ
sim> c
*
Simulation stopped, PC: 035450 (JSR R4,35462)
sim> ATTACH PTR OBJ/EXPLOD.OBJ
sim> c
*
Simulation stopped, PC: 035054 (MOV (SP)+,R0)
sim> ATTACH PTR OBJ/GRAVTY.OBJ
sim> c
*
Simulation stopped, PC: 035122 (ADD #34662,R2)
sim> ATTACH PTR OBJ/MULPLY.OBJ
sim> c
*
Simulation stopped, PC: 035140 (MOV R5,14(SP))
sim> ATTACH PTR OBJ/PARM.OBJ
sim> c
* ATTACH PTR OBJ/PWRUP.OBJ\\\\\\\\\\\\\\\\\\\\\\\\
Simulation stopped, PC: 035342 (ADD (SP)+,PC)
sim> ATTACH PTR OBJ/PWRUP.OBJ
sim> c
*
Simulation stopped, PC: 035026 (MOV R3,-(SP))
sim> ATTACH PTR OBJ/RESET.OBJ
sim> c
*
Simulation stopped, PC: 035342 (ADD (SP)+,PC)
sim> ATTACH PTR OBJ/RKT1.OBJ
sim> c
*
Simulation stopped, PC: 035056 (RTI)
sim> ATTACH PTR OBJ/RKT2.OBJ
sim> c
*
Simulation stopped, PC: 035460 (BR 35330)
sim> ATTACH PTR OBJ/SCORE.OBJ
sim> c
*
Simulation stopped, PC: 032100 (BIT (R0)+,@4(SP))
sim> ATTACH PTR OBJ/SINCOS.OBJ
sim> c
*
Simulation stopped, PC: 035110 (BHI 35354)
sim> ATTACH PTR OBJ/SLINE.OBJ
sim> C
*
Simulation stopped, PC: 035336 (MOVB 34641(R1),(SP))
sim> ATTACH PTR OBJ/SUN.OBJ
sim> C
*
Simulation stopped, PC: 035332 (ASL R1)
sim> ATTACH PTR OBJ/UPDAT1.OBJ
sim> C
*
Simulation stopped, PC: 035336 (MOVB 34641(R1),(SP))
sim> ATTACH PTR OBJ/UPDAT2.OBJ
sim> C
*
Simulation stopped, PC: 035100 (MOVB (R5)+,R1)
sim> ATTACH PTR IOX-11/dec-11-xioxa-a.obj
sim> C
* U
POINT
PTNUM
*
Simulation stopped, PC: 035162 (BLE 35332)
sim> ATTACH PTR OBJ/POINT.OBJ
sim> C
* U
* E
PASS 2
*
Simulation stopped, PC: 035046 (MOV (SP)+,R3)
sim> ATTACH PTR OBJ/SPCWAR.OBJ
sim> C
*
Simulation stopped, PC: 035460 (BR 35330)
sim> ATTACH PTR FPMP-11/FPMP-11-SPACEWAR.OBJ
sim> C
*
Simulation stopped, PC: 035150 (BLE 35332)
sim> ATTACH PTR OBJ/CHAR.OBJ
sim> C
*
Simulation stopped, PC: 035150 (BLE 35332)
sim> ATTACH PTR OBJ/CHRTAB.OBJ
sim> C
*
Simulation stopped, PC: 035120 (BNE 35352)
sim> ATTACH PTR OBJ/COMPAR.OBJ
sim> C
*
Simulation stopped, PC: 035120 (BNE 35352)
sim> ATTACH PTR OBJ/EXPLOD.OBJ
sim> C
*
Simulation stopped, PC: 035034 (CLR R3)
sim> ATTACH PTR OBJ/GRAVTY.OBJ
sim> C
*
Simulation stopped, PC: 035112 (MOVB (R5)+,R2)
sim> ATTACH PTR OBJ/MULPLY.OBJ
sim> C
*
Simulation stopped, PC: 035100 (MOVB (R5)+,R1)
sim> ATTACH PTR OBJ/PARM.OBJ
sim> C
*
Simulation stopped, PC: 035114 (BIT #177770,R2)
sim> ATTACH PTR OBJ/PWRUP.OBJ
sim> C
*
Simulation stopped, PC: 035154 (BLE 35346)
sim> ATTACH PTR OBJ/RESET.OBJ
sim> C
*
Simulation stopped, PC: 035154 (BLE 35346)
sim> ATTACH PTR OBJ/RKT1.OBJ
sim> C
*
Simulation stopped, PC: 035154 (BLE 35346)
sim> ATTACH PTR OBJ/RKT2.OBJ
sim> C
*
Simulation stopped, PC: 035040 (MOV R0,PC)
sim> ATTACH PTR OBJ/SCORE.OBJ
sim> C
*
Simulation stopped, PC: 035154 (BLE 35346)
sim> ATTACH PTR OBJ/SINCOS.OBJ
sim> C
*
Simulation stopped, PC: 035162 (BLE 35332)
sim> ATTACH PTR OBJ/SLINE.OBJ
sim> C
*
Simulation stopped, PC: 035066 (JSR R0,35022)
sim> ATTACH PTR OBJ/SUN.OBJ
sim> C
*
Simulation stopped, PC: 035022 (MOV R1,-(SP))
sim> ATTACH PTR OBJ/UPDAT1.OBJ
sim> C
*
Simulation stopped, PC: 035032 (MOV R5,-(SP))
sim> ATTACH PTR OBJ/UPDAT2.OBJ
sim> C
*
Simulation stopped, PC: 035126 (MOVB (R2),R3)
sim> ATTACH PTR IOX-11/dec-11-xioxa-a.obj
sim> C
* ATTACH PTR OBJ/POINT.OBJ\\\\\\\\\\\\\\\\\\\\\\\\
Simulation stopped, PC: 035150 (BLE 35332)
sim> ATTACH PTR OBJ/POINT.OBJ
sim> C
LINK-11S V002A
*I
Simulation stopped, PC: 035112 (MOVB (R5)+,R2)
sim> DETACH PTP
sim> DETACH PTR
sim> DETACH LPT
sim>
If you feed the wrong module in the second pass this message will be shown. Just feed the correct module and try again.
Simulation stopped, PC: 035046 (MOV (SP)+,R3)
sim> ATTACH PTR OBJ/SLINE.OBJ
sim> C
?LOAD SINCOS NEXT!
The Abolute loader format can specify the starting address so that when the loader loads the tape (or file) into memory it will automatically jump to the starting address. This is done by specifying the starting address on the .END directive. I modified the SPCWAR.PAL file to include the starting symbol SPCWAR.
The SPACE WAR program make use of the IOX-11 package for teletype IO, which means that this has to be loaded before the SPACE WAR program. Since the IOX package make use of the IOT instruction for all operations there is no linking needed. But the address of the IOX package has to not collide with the SPACE WAR program itself address space wise. It appears that the IOX-11 pacakge is fixed at 015100. There are no instruction on how to assemble the package and a try in PAL-11S results in 245 errors. The IOX-11 package is an absolute binary and is loaded by the abolute loader as most other programs.
Later on I learnt that IOX-11 is supposed to be built with PAL-11A instead of PAL-11S. PAL-11A reads the two files directly after each other. There are a number of .EOT directives that will give a EOF? prompt in the assembler. Just pressing CR will feed to the next section. The idea behind this is that if one want to modify the start address of join other source files this can be done at these points. However I wanted to make a single SPACEWAR binary with IOX builtin that is loaded into the machine. Thus I needed to use PAL-11S which is used for the rest of SPACEWAR. There are some things that differ since PAL-11S is a relocating assembler and PAL-11A is a absolute assembler. I had to add .CSECT and .ASECT directives to the source. I also combined the module into one source file.
With this in place it was possible to re-link the entire package.
I thought it would be good to have a disk image with the SPACEWAR binary loaded. Using the xxdpdir utilities bye Dan North I added the binary to the image. The image with the SPACEWAR binary is provided as a TU58 disk image, dddp.dsk. The image has a XXDP+ system on it.
The intention is that it should be possible to simply do a RUN SPCWAR.LDA from the XXDP+ prompt but it does not appear to work. It gets stuck inside the IOX-library waiting for something, at least when testing this in SIMH. But if I halt the SIMH simulator and do a RESET command followed by GO 1000, it is actually runs. So somehow the RESET command in SimH circumvents the problem. I have not figured out how to solve this. I was thinking that a RESET instructon could do the same thing. But haven't tried it yes.
It suddenly occured to me that the reason for not working was a simple as interrupts. The XXDP monitor runs with interrups disabled. The RESET command and the START switch on the real machine resets interrup level. By lowering the priority level of the CPU it worked just fine. The dddp.dsk is a TU58 image which is bootable. A simple RUN SPCWAR.LDA will start SPCWAR. For my own use I will make a CAPS-11 cassette and possibly also a TADP cassette with the SPCWAR.LDA binary.
With the SPACEWAR binary on the dddp.dsk it is possible to boot a PDP-11 into the XXDP monitor with a second serial card using a TU58 emulator. This second serial port has to be setup with base address 176500 and vector 300. Make sure it is set to 8 bits without parity. Jörg Hoppe has designed a such an emulator which is combined with a method for downloading the bootstrap using the console emulator called tu58fs.
Start an emulation process over /dev/ttyUSB0 running at 9600 bps for drive 0 in readonly mode using dddp.dsk image
tu58fs -p /dev/ttyUSB0 -b 9600 -d 0 r dddp.dsk
Command to download and start a boostrap process over /dev/ttyUSB1 running at 2400 bps using a m9301 board in the pdp-11.
tu58fs -p /dev/ttyUSB1 -b 2400 --boot m9301 1
When XXDP has greeted you with a startup message and you got the . prompt it is possible to simply run the binary. It takes some time to loads since it does this over a 9600 bps serial line so have a bit of patience.
.RUN SPCWAR.LDA
After a while SPACEWAR will start.
All this made it possible to build a new SPACEWAR binary with the IOX library built in and also have the autostart feature. The new binary is called SPACEWARWIOX.LDA. The extension .LDA is to signify that it should be possible to use this from any PDP-11 oprating system that is able to load abolute binary files. For example XXDP is able to handle .LDA files and I think CAPS-11 and DOS-11 too.
sim> SET CPU 11/05
Disabling XQ
sim> SET CPU 16K
sim>
sim> ; Disable devices that we don't need
sim> SET HK DISABLE
sim> SET DZ DISABLE
sim> SET RL DISABLE
sim> SET RX DISABLE
sim> SET RP DISABLE
sim> SET RQ DISABLE
sim> SET TM DISABLE
sim> SET TQ DISABLE
sim> SET RK DISABLE
sim>
sim> ; Enable the high-speed paper tape reader/punch
sim> SET PTR ENABLE
sim> SET PTP ENABLE
sim> DEPOSIT 037744 016701
sim> DEPOSIT 037746 000026
sim> DEPOSIT 037750 012702
sim> DEPOSIT 037752 000352
sim> DEPOSIT 037754 005211
sim> DEPOSIT 037756 105711
sim> DEPOSIT 037760 100376
sim> DEPOSIT 037762 116162
sim> DEPOSIT 037764 000002
sim> DEPOSIT 037766 037400
sim> DEPOSIT 037770 005267
sim> DEPOSIT 037772 177756
sim> DEPOSIT 037774 000765
sim> DEPOSIT 037776 177550
sim> ATTACH PTR TOOLS/DEC-11-L2PC-PO.ptap
sim> GO 037744
HALT instruction, PC: 037500 (MOV PC,SP)
sim> d sr 0
sim> ATTACH PTR IOX-11/dec-11-xioxa-a-pb.bin
sim> GO 037500
HALT instruction, PC: 037712 (BR 37514)
sim> ATTACH PTR SPACEWAR.ABS
sim> GO 037500
HALT instruction, PC: 037712 (BR 37514)
sim> GO 034604
SPACE WAR
ANY CHANGES? (YES-NO)
Y
WANT A SUN WITH GRAVITY? (YES-NO)
Y
WANT REAPPEARING PHOTON TORPEDSOES? (YES-NO)
Y
INPUT # OF TORPEDOS RKTS WILL HAVE. STD=64
64
INPUT # OF HITS TO DESTROY A RKT STD=32
32
INPUT SPEED OF TORPEDOES. STD=16000
16000
HALT instruction, PC: 000042 (BIC R4,SP)
sim>
So why is it halting? There is a Non existing memory (NXM) handler installed by the IOX-11 package.
sim> e 0-200
0: 000000
2: 000000
4: 015604
6: 000340
10: 000000
12: 000000
14: 000000
16: 000000
20: 015256
22: 000340
24: 032662
26: 000340
30: 000000
32: 000000
34: 000000
36: 000000
40: 000000
42: 040406
44: 000000
46: 000000
50: 000000
52: 000000
54: 000000
56: 000000
60: 016040
62: 000200
64: 016672
66: 000200
70: 016132
72: 000200
74: 017056
76: 000200
Location 4 is the NXM trap handler and the handler is located at address 15604. Then there are handlers for the paper taper reader, the tty keybaord and printer etc.
A breakpoint in SimH at that address show that the SP is pointing to
sim> break 15604
sim> go 034604
SPACE WAR
ANY CHANGES? (YES-NO)
Y
.
.
.
Breakpoint, PC: 015604 (JSR R0,15220)
sim> e sp
SP: 034600
Now checking the stack at this SP value:
sim> e 34600
34600: 034632
So the Stack contain the PC of the next instruction after the one causing the NXM trap.
e -m 34624-34700
34624: MOV #401,176770
34632: MOV 35020,35010
34640: MOV 35020,35012
34646: MOV 35022,35014
34654: MOV 35022,35016
34662: CLR 36456
34666: JSR PC,32770
34672: MOV #34734,R2
34676: JSR PC,35342
So the offending instruction is the one at 34624 which is trying to reference the ADCS register at address 176770. And since this device is not implemented in SimH this address will not respond and thus the NXM trap!
The code at 15604 will subsequently make a JMP to address 40 where the HALT instruction is executed. Thus stopping the processor.
15600: JMP 40
15604: JSR R0,15220
15610: CLR R0
15612: MOV 14(SP),R1
15616: BR 15600
Then when I had installed the correct hardware and patched the source to use AR11 it still failed. Then I discovered that the stackpointer is initialized with the SPCWAR symbol. Meaning that it grows downwards from that point. Not having the SPCWAR module as the first module will then be a problem since the stack will overwrite the code. I.e. The SPCWAR module has to be the first module and the POINT module has to be that last module. Otherwise the order is of no importance.
Since I don't have any AD01 neither any AA11 subsystem for my PDP-11 and the objective is to have the program running on as like hardware as possible I have to modify it to the hardware I do have, which is the AR11. One obvious benefit of the AR11 is that it is a single HEX module compared with the AD01 and AA11 which are bulky rack-mount system units as big as the computer it self (PDP-11/10).
One disadvantage is that the AR11 is 10 bit only, meaning that som small changes has to be done to handle 12 vs 10 bits.
One obvious difference is that the AR11 make use of completely different IO address. The definitions of the DAC0, DAC1, DAC2, ADCS and ADBR has to change. The use of DAC2 is a little bit peculiar. The DAC2 is used for the Z-axis of the X-Y-scope and the only bit that is used is the MSB which is changed from off to on and the off to signify a dot. The AR11 doesn't have a third DAC at all. Instead it have one single bit called Intensify in the control status register. It makes sense to use this bit instead. But at least the character drawing routine in CHAR.PAL will turn on Z-axis and then change the X and Y coordinates when drawing a character. When done with each character it will switch off the Z-axis. This means that the intensify pulse cannot be used. Instead one of the logical signals will be used to control the Z-axis.
Another issue is that the oscilloscope screens requires certain time to deflect the beam. The AR11 include a functionality that when setting the intensify bit it will delay the acutual intensify operation 20 us and then issue a 2 us pulse. The AR11 will then signal back a DONE flag to indicate that next dot can be painted on screen. The SPACEWAR code does not wait for any DONE flag but draws as fast as the CPU can. This may be ok for a PDP-11/10 but might be to fast for a 11/45? And it may be too fast for certain oscilloscope hardware but OK for others.
I ended up using the ERASE (12) bit in the display status register to control the Z-axis. It is a open collector signal so there need to be a pull up resistor in the end of the line at the Z-input of the scope. I also discovered that the AA11 subsystem is 2's complment while the AR11 is not. So besides shifting the output value two steps to the right to make it fit into a ten bit number I also had to add 512 to the number before sending it off to the D/A converter.
The AD01 is 10 bit so there were very few changes appart from changing addresses, except for one thing. The AR11 has to be put into unipolar mode since the potentiometers of the joysticks are fed from the internal 5V source of the board.
All adaptations for the AR11 went into a branch called ar11-patch. Make sure to get that one.
This is basically almost only parts ordered from Aliexpress.
- 2-axis potentiometer Joystick switch 201 Series. Model M1 with B cap.
- New Arcade Push Button Durable Multicade MAME Jamma Game Long Switch - Red
- Waterproof Plastic Enclosure Box Electronic Project Instrument Case Electrical Project Box Outdoor Junction Box Housing. Product properties: 115 x 90 x 55mm + White
- Cable bending protection.
Each cable going from the connector has +5V, GND and Angle and Acceleration. I used a cable with three pairs and individual sheilding for each pair. The pairs are:
- +5V and GND
- Accleration and GND
- Angle and GND.
The fire button is connected to short circuit the acceleration potentiometer to the 5V supply. It is importtant to use a joystick typ that is not full range. The M1 model goes from 1.8k to 3.2k. Thus short-circuiting the viper to 5V when at the lowest position of the viper in the joystick is not a problem. The Model M1 linked to above is this non-full range type. However if you choose model M2 you get into trouble. Then you could add a resistor, maybe 1k or 2k in each end of the potentiometer to avaoid short-circuitng the 5V to ground. So be careful when selecting the joystick.
The use of the model M1 is perhaps to a very good idea. The 1.8kOhm to 3.2kOhm range is very narrow which means that you are not getting the full dynamic range of the A/D converter for acceleration and turning left/right. I am now using a model M2 with 5kOhm total range and in addition to that I have 2.4kOhm resistors in each end of the potentiometer.
I used 47217-000LF/48254-000LF contact elements and 65043-015LF contact housings. The cable is a three pair shieled cable for the Joysticks and the X, Y and Z inputs. An extra cable of simpler type was used for the intensify signal in case I ever wanted to use it.
| Pin | Signal | Connect to |
|---|---|---|
| A | WRITH THRU L | NC |
| B | DISP CH02 L | Pull up to 5V in the scope end + Z input of scope |
| C | ERASE L | NC |
| D | INTESIFY | Optional Z input if the standard point plotting mechanism of the AR11 is to be used for other purposes. |
| E | NON-STORE L | NC |
| F | X OUT | Scope X input |
| H | ERASE RET L | NC |
| J | Y OUT | Scope Y input |
| K | Analog ground | ground for X and Y twisted pair. Including shield |
| L | A/D CH 17 input | NC |
| M | Analog ground | NC |
| N | A/D CH 16 input | NC |
| P | Logic ground | Z - axis pair ground and sheild |
| R | A/D CH 15 input | NC |
| S | Logic ground | Intensify Z- axis pair return and shield (optional) |
| T | A/D CH 14 input | NC |
| U | EXT AD ST L | NC |
| V | A/D CH 13 input | NC |
| W | Analog ground | NC |
| X | A/D CH 12 input | NC |
| Y | Analog ground | NC |
| Z | A/D CH 11 input | NC |
| AA | Analog ground | NC |
| BB | A/D CH 10 input | NC |
| CC | Analog ground | NC |
| DD | A/D CH 7 input | NC |
| EE | Analog ground | Joystick 2 Acceleration pot ground and shield |
| FF | A/D CH 6 input | NC |
| HH | Analog ground | Joystick 2 Angle pot ground and shield |
| JJ | A/D CH 5 input | NC |
| KK | Analog ground | Joystick 1 Acceleration pot ground and shield |
| LL | A/D CH 4 input | NC |
| MM | Analog ground | Joystick 1 Angle pot ground and shield |
| NN | A/D CH 3 input | Joystick 2 Acceleration pot viper |
| PP | -14V HQ | NC |
| RR | A/D CH 2 input | Joystick 2 Angle pot viper |
| SS | +14V HQ | NC |
| TT | A/D CH 1 input | Joystick 1 Acceleration pot viper |
| UU | +5V output | Power to feed joysticks and pull-up resistor for Z-axis |
| VV | A/D CH 0 input | Joystick 1 Angle pot viper |
Over time the 40 pin connector with crimped contact elemnts started to become a problem. It was bulky and thick and hard to get in and out the machine. I designed a breakout board that attached via a 40 pin flat cable instead. This breakout board has three connectors. One for each joustick and one for the screen.
