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readme.md

PDP-8

Stuff to read

PiDP-8

connecting from mac serial (not wifi)

% ls /dev/tty.usb*
(e.g.) /dev/tty.usbmodem00011

% screen /dev/tty.usbmodem00011

Then linux-log in, then run `pidp8i', and get the '.' prompt for OS/8

^Ad to detach.

return to seesion with pidp8i at prompt

to stop sim

^equit

to restart service

sudo systemctl restart pidp8i

Study

OS 8

OS 8 Books from BitSavers: https://bitsavers.org/pdf/dec/pdp8/os8/

Basics and Overview

Start here to understand what OS-8 is and how it’s structured.

  • OS8_Handbook_Apr1974.pdf
  • DEC-S8-OSRNA-B-D_os8v3DrelN.pdf

User and System

Once you understand the big picture, read the manuals you’ll use most.

  • AA-H607A-TA_OS8_V3D_sysMan.pdf
  • DEC-S8-OSSMB-A-D_OS8_v3ssup.pdf
  • AA-H606A-TA_os8SysgenNotes.pdf

Language, development, and tools

  • AA-H609A-TA_OS8_Language_Reference_Manual_Mar79.pdf
  • AA-D319A-TA_os8DevExt.pdf
  • AA-H608A-TA_os8teco_mar79.pdf

Misc references

  • AA-H610A-TA_os8errMsg_mar79.pdf
  • OS8_V3_Memos_1973.pdf
  • DEC-S8-OSHBA-A_DN4_OS8_Handbook_Update_Sep77.pdf

Stuff

Running Adventure

(courtesy of https://raymii.org/s/articles/Running_ADVENT-on-the-PDP-8-with-SIMH.html)

.R FRTS
*ADVENT
<esc>

(fortran Run Time System)

ghostty --command "./vt2400 /dev/tty.usbmodem00011"

ghostty --device /dev/tty.usbmodem00011 --baud 2400

socat -d -d PTY,raw,echo=0,link=/tmp/pidp8-pty
EXEC:"./vt2400 /dev/tty.usbmodem00011",raw,echo=0

PTY for Ghostty to connect

mkfifo /tmp/pidp8-in mkfifo /tmp/pidp8-out

PiDP-8 → throttled PTY

cat /dev/tty.usbmodem00011 | pv -q -L 240 > /tmp/pidp8-out &

Keyboard → PiDP-8

cat /tmp/pidp8-in > /dev/tty.usbmodem00011 &

^E reset boot rk

https://hackaday.com/2017/08/10/getting-started-with-blinking-lights-on-old-iron/

https://www.youtube.com/watch?v=S2r_GujSc6w

Running adventure

.R FRTS
*ADVENT
<esc>

Running BASIC

EX TICTAC.BA

BASIC OLD TICTAC

a demo(e)

https://www.youtube.com/watch?v=oMRDAD1JNWo

  • Stop
  • (put program in at address 10 (octal))
  • so set switches to 10, and then load address - lights on top line match the switches
  • first instruction. put in HLT opcode is 7402, and DEPosit
    • notice "memory buffer" shows 7402
    • notice "address" shows the address we entered
    • notice the ProgramCounter lights have added 1 binary)
    • (so you could continue to DEP more instructions)
  • now run it by putting in 10 - see the address / top line update
  • press start
    • it ran and halted
    • notice PC ticked over to show next instruction it would run
    • notice OPR light is on - HLT is in the operation category

increment the accumulator. - six instruction, incr the accum five times.

  • 0010 and load address
  • 7001 is the increment accumulator so put that into the switches
  • press DEP five times. (so run it five times
  • then 7402 to halt after the add and DEPosit that
  • let's examine memory
  • 0010 and load address.
  • see what's at that address with EXAMine
    • shows the memory buffer, which is 7001
    • increments the program counter
  • keep EXAM and they're the same, and eventually will get the 7102
  • LOAD ADDR with 0010 still on switches
  • then can press start - what do you expect to happen (accum goes to five very quickly)
  • we can do more interesting things. Go back to 0010 with LOAD ADDR.
  • toggle the SINGLE INSTruction toggle
  • now CONTinue will just execute one instruction
    • notice the program counter is one ahead - might be a pi thing, or maybe not - like it's expected to be one ahead, but it's two ahead, so it's probably preftecthed the next instruction

so now for a loop

  • now for a two-instruction program. increment accumulator, and jump to the beginning

  • go back to 0100 and LOAD ADDR. Turn off SING INST switch

  • 7001 for increment accumulator, DEPosit

  • 5 + address to jump to - so 5010

    • (video showed the instruction jmp lamp lights up. mine did not)

  • now do the examine again

    • 0100 and LOAD ADDr
    • EXAM - see 7001
    • EXAM - see 5010 (I am not seeing the instruction lamps follow along)
    • load address and press start. What do you expect to happen?
      • the accumulator totally fills up, because it's adding and overflowing so fast
      • notice the opr and jmp lamps are flashing
      • video has fetch and execute flashing, but just fetch i sdoing that for me

  • STOP / CONTINUE and see the accumulator have different values

  • put on SING INST

  • CONT CONT CONT

    • see the light bounce between OPR and JMP (increment jump)
    • see the accumulator increment by one

  • say wanted to slow it down?

  • say add a delay loop - one more instruction, ISZ - increment and skip if zero

    • increments a location, if zero, it'll skip the next instruction
    • essentially doing it 4096 times

  • turn off SING INST

  • 0100 and LOAD ADDr

  • 7001 and DEPosit - first instruction, increment acunulator

  • 2___ - increment and skip if zero

    • 2 plus address of what we want to increment.
    • address 3-4 is popular with demos, so do that
    • 2034 DEP

  • next instruction is the jmp for the delay loop, that'll get skipped if the increment wraps around to zero

  • we'll jump (5___) to the increment and set, which happens to be at the address 11. so

    • 5011 DEP
    • that's the inner loop

  • jump back to the beginning

    • 5010 DEP

  • then go to 0010 load addrr, and then exam the program

  • then start, can single

0010: 7001 IAC // accumulator++ 0011: 2034 ISZ 0034 // memory[0034]++, skip next if zero 0012: 5011 JMP 0011 0013: 5010 JMP 0010