Yet another blikenlights program?

[Mark Lawler]

So in my effort to try to learn some PDP-8/I PAL assembly language after getting Oscar's kit built I decided to take something I wrote for my Altair 8800 and IMSAI 8080 replicas and "port" it to the PDP-8/I.  The original started out as hacks on top of the Kill The Bit game as I was trying to learn 8080 assembly.  

Turns out it was more of a rewrite than a port due to the nature of the limited instruction set (and my newly acquired limited knowledge in it).  Whereas the Altair could use the LDAX instruction trick and the IMSAI had Programmed Output LEDs to display desired bit patterns on the panel, on the PiDP-8/I I decided to misuse and abuse the EAE to have the Multiplier Quotient lights handle the output display.  The program would probably be way simpler had I just used the EAE MQ correctly vs treating it only as a display means to an end...  I do have to admit I like the visual appeal of this version much better though given how the Incandescent Lamp Simulator that was added to the PiDP8 works. 

The source is ugly as this is a hack with only week's worth of experience after hours and over the weekend.  It is so bloated I even had to figure out why PAL was generating errors once I crossed a page boundary and then changed my source to fix it with a strategically placed next PAGE command.  I also had to give up on being a purist and using only EDIT midway through development (once the code became too long) and started to use the PIP command to input my source code changes from an outside text editor on the Raspberry Pi.

To input the source, assemble, then run:

     .R PIP

     .MARKBI.PA<TTY:
     <paste source here, press enter after the last '$', and then a ^Z to end the file, then the ESC key to exit PIP and save the code>
     .PAL MARKBI
     .LOAD/G MARKBI

And now the source (sorry for the formatting--old habit of tabs vs spaces didn't go so well for me, perhaps proving the case for spaces? <grin>):

/YET ANOTHER BLICKEN LIGHTS PROGRAM. THIS VERSION IS BASED ON 

/ONE FOR THE IMSAI 8080, BUT USING THE PDP-8'S EAE

/MULTIPLIER QUOTIENT TO SIMPLY DISPLAY THE FRONT PANEL LIGHT

/PANEL PATTERNS (WHEREAS THE IMSAI USED ITS PROGRAMMED OUTPUT

/DISPLAY).

/

/ SW 0: 0 - DOT          | 1 - DASH

/ SW 1: 0 - RIGHT      | 1 - LEFT

/ SW 2: 0 - NORMAL | 1 - BOUNCE

/ SW 3: 0 - NORMAL | 1 - RANDOM (IGNORE OTHERS)

/ SW ALL 1 = TERMINATE AND RETURN TO MONITOR PROGRAM

/

/CREATED JUNE 2022 BY MARK LAWLER

MUY=7405

MQA=7501

MQL=7421

CAM=7621

IR1=10 /DELAY INNER REGISTER

IR2=11 /DELAY OUTER REGISTER

*200

START, CLA CLL /CLEAR ACCUMULATOR AND LINK

JMS GCMD /GET COMMAND FROM SWITCHES

TAD DSPBTS /LOAD UP AND LIGHT UP

MQL /  MQ WITH DISPLAY BITS

JMS DELAY /TAKE A REST SO MQ ISN'T A BLUR

JMS CDSP /COMPUTE NEXT DISPLAY PATTERN

JMP START /LET'S GO DO THIS AGAIN

GCMD, . /ROUTINE TO READ SWITCHES FOR COMMANDS

CLA CLL /CLEAR ACCUMULATOR AND LINK

OSR /READ IN THE SWITCH VALUES

DCA CURSW /STORE AWAY FOR LATER RECALL

TAD CURSW /HAVE THE SWITCH SETTINGS EVEN CHANGED?

CIA         / MAKE THE NUMBER NEGATIVE

TAD LASTSW / AND ADD THE LAST TO IT. IF == 0 NO CHANGE

SZA /HAVE SWITCHES CHANGED SINCE LAST TIME?

JMP GCMD0 / YES: LET'S GO DO SOMETHING USEFUL

JMP GCMDE / NO: LET'S GET OUT OF HERE

GCMD0, /SWITCHES CHANGED -- GRAB AND EXECUTE COMMAND

CLA CLL

TAD CURSW /WHAT WERE THOSE SWITCH SETTINGS AGAIN?

DCA LASTSW /STORE THAT THEY'VE CHANGED

TAD CURSW /WHAT WERE THOSE SWITCH SETTINGS AGAIN?

CMA /TEST FOR 7777?

SNA / NO: EXAMINE SWITCH SETTINGS MORE

JMP I [7600 / YES: EXIT TO MONITOR PROGRAM

CMA /WHAT WERE THOSE SWITCH SETTINGS AGAIN?

AND (0001 /DISPLAY A DOT OR A DASH?

SNA / IT WAS THE DASH

        JMP GCMD1 / IT WAS THE DOT

CLA CLL

TAD DASH /LOAD THE DASH

DCA DSPBTS / STORE IT

JMP GCMD2 / AND TEST NEXT SWITCH

GCMD1,  TAD DOT /LOAD THE DOT

DCA DSPBTS / STORE IT

GCMD2,  TAD LASTSW /ARE WE GOING TO THE LEFT OR TO THE RIGHT?

AND (0002

DCA DIR /STORE OUR DIRECTION

GCMD3,  TAD LASTSW /DO WE WANT TO BOUNCE IN KITT MODE?

AND (0004

DCA BOUNCE /STORE IF WE BOUNCE OR NOT

GCMD4,  TAD LASTSW /DO WE WANT RANDOM BITS?

AND (0010

DCA RANDOM /STORE IF WE WANT RANDMOM BITS OR NOT

GCMDE, JMP I GCMD /RETURN TO CALLER

CDSP, . /ROUTINE TO COMPUTE NEXT DISPLAY PATTERN

CLA CLL /CLEAR AC AND LINK

TAD RANDOM /CHECK FOR RANDOM BITS

SNA /ARE WE RANDOMIZING?

        JMP CDSP1 / NO: CALC OUR NEXT ROTATION

JMS GETRND / YES: TEE UP THE NEXT RANDOM NUMBER

DCA DSPBTS /      STORE IT FOR DISPLAY

JMP I CDSP /      AND RETURN TO CALLER

CDSP1,  JMS ROT /TIME TO ROTATE SINCE NOT RANDOM

JMP I CDSP /AND RETURN TO CALLER

GETRND, 0                    /ROUTINE GENERATES A RANDOM NUMBER

CLA CLL /CLEAR AC & AL; RN RETURNED IN AC

TAD LRNDMQ /LOAD THE LAST RANDOM MQ VALUE

MQL /STORE THAT IN THE MQ AS NEXT SEED        

TAD LSTRND        /GET THE LAST RANDOM VALUE

MUY 5545 /MULTIPLY BY 2917 BASE 10

TAD RNDADD /SUM IN RANDOM NUMBER ADDEND

DCA LSTRND /SAVE RANDOM NUMBER FOR NEXT TIME

CLA CLL

MQA /STORE WHAT IS IN MQ

DCA LRNDMQ /LATER AS OUR NEXT SEED VALUE

TAD LSTRND /CALLER EXPECTS RND VAL IN AC

JMP I GETRND /RETURN TO CALLER

ROT, . /MOVE THE DOT/DASH TO LEFT OR RIGHT

CLA CLL /CLEAR AC AND LINK

TAD DSPLNK /WAS THE LINK SET IN PREVIOUS ROTATE?

SZA / NO: SKIP NEXT INSTRUCTION

CML / YES: SET THE LINK BEFORE WE DO NEXT ROTATE

CLA /CLEAR THE AC

TAD DIR /LOAD THE DIRECTION WE ARE SUPPOSED TO ROTATE

SNA / !=0 SO GOING RIGHT

JMP ROTL / ==0 SO GOING LEFT

ROTR, CLA 

TAD DSPBTS

RAR /SHIFT RIGHT ONE BIT

JMP ROTE /GO SAVE THE RESULTS

ROTL, CLA 

TAD DSPBTS

RAL /SHIFT LEFT ONE BIT

ROTE, DCA DSPBTS /SAVE THE RESULTS

SZL         /IS THE LINK SET?

JMP ROTE1 / YES: GO TO STORING LINK IS NOW SET

CLA / NO: STORE THAT THE LINK 

DCA DSPLNK /     IS NOW CLEAR

JMP I ROT /RETURN TO CALLER

ROTE1, CLA /STORE THAT THE LINK

IAC         / HAD BEEN SET WITH THAT 

DCA DSPLNK / LAST ROTATE

TAD BOUNCE /SINCE WE HIT END, DO WE CHANGE DIRECTIONS?

SNA         / YES: WE'LL NEED TO CHANGE DIRECTIONS

JMP I ROT / NO: RETURN TO CALLER

CLA

TAD DIR /WHAT DIRECTION WERE WE GOING?

SZA         / YES: WERE GOING LEFT

JMP ROTE2 / NO: WERE GOING RIGHT

CLA /NOW START GOING RIGHT

IAC

JMP ROTE3

ROTE2,  CLA /NOW START GOING LEFT

ROTE3, DCA DIR /STORE OUR NEW DIRECTION,IGNORING DIR SWITCH

JMP I ROT /RETURN TO CALLER

DSPBTS, 0 /BIT PATTERN WE ARE DISPLAYING IN MQ

DSPLNK, 0 /DISPLAY VALUE OF LINK

DOT, 1 /WHAT A DOT SHOULD LOOK LIKE

DASH, 7 /WHAT A DASH SHOULD LOOK LIKE

CURSW,  0 /CURRENT SWITCH SETTINGS

LASTSW, -1 /LAST SWITCH SETTINGS

DIR, 0 /DIRECTION: 0=LEFT; !0=RIGHT (CALL ME LAZY)

BOUNCE, 0 /KITT MODE: 0=OFF; !0=ON

RANDOM, 0 /RANDOM BITS: 0=OFF; !0=ON

LSTRND, 0 /LAST RANDOM NUMBER 

LRNDMQ, 541 /LAST RANDOM MQ

RNDADD, 541               /353 BASE 10

DELAYV, -400 /OUTLOOP DELAY 

PAGE

DELAY, . /DELAY ROUTINE SO WE CAN SEE WHAT IS GOING ON

CLA CLL /CLEAR AC AND LINK

TAD DELAYV /LOAD OUTER LOOP COUNT

DCA IR2 / AND STOR IT

DELAYO, ISZ IR2 /OUTER DELAY LOOP. DONE?

JMP DELAYI         / NO: DO THE INNER LOOP

JMP I DELAY / YES: RETURN TO CALLER

DELAYI, ISZ IR1 /INNER DELAY LOOP. DONE?

JMP DELAYI / NO: DO NEXT INNER LOOP

JMP DELAYO / YES: DO NEXT OUTER LOOP

$

Enjoy!  My next project will be to add some text instructions to display on the terminal.  Looks like the PiDP-8 simulator's rendition of PAL and MAC supports TEXT, but perhaps not TEXTZ?  So much more to dig into and learn...

Best,

-Mark

[Steve Tockey]

Mark,

Just for fun (and as yet another example of PAL-8 blinkenlight programming), a rite of passage when I first programmed PDP-8s in 1975-1976 was to write a kind of one dimensional Pong. Two players, one on the left side (Switch Register bit 0) and one on the right side (Switch Register bit 11). Flipping your switch on was like swinging your paddle. You couldn't swing too early, nor too late. Given the size of the PiDP-8/i front panel and switches, I updated the code to use the keyboard instead. The left player can use a set of keys on the left side of the keyboard, the player on the right similarly. See the attached source code for which keys work for which player. It keeps score in binary in the MQ.

Code-wise, the trickiest thing might be that it uses interrupts rather than polled I/O. Otherwise, I would hope it's straightforward.

There are a lot of other PDP-8 blinkenlight programs, if you're interested.

Cheers,

-- steve