PDP11 Coding - with SIMH, and some Linux tools

software, computerhistory
Page content

If you want to write code for a PDP11 CPU or PDP11 machine, you need some environment to do so. I have only parts of a PDP11 machine and cannot simply use this to write code. So I tried several ways:

  • Using SIMH emulator to emulate a PDP11 machine, boot up some PDP11 Operating System (RT11) and use the available tools from that OS
  • Using native Linux executables that allow for assemble and link valid PDP11 executables
  • Using Gnu GCC toolchain for bare metal programming

The SIMH emulator way is described in this document further below. The two other paths are described in additional documents.

See assembler.html for further information

Using Gnu GCC toolchain for bare metal programming

See this document for further information

Build SIMH

Get SIMH from https://github.com/simh/simh. Build only PDP incarnations, search for ALL target in makefile and comment all unneeded emulator incarnations.

Then start build with make. Executables are created in directory BIN.

Set up an emulation that boots RT-11 operating system

To execute the MACRO-11 macro assembler from DEC, the operating system RT-11 can be used as base.

Install RT-11 as described here: http://decuser.blogspot.com/2015/12/tutorial-setting-up-rt-11-v53-on-simh.html The page has a link to an old RT-11 image and also the same can be found here http://simh.trailing-edge.com/software.html.

Update: above link may be gone, I have some with close content here: https://www.computercollection.net/wp-content/uploads/2019/11/BuildRT11TU58Image-20191004.txt

If you become confused with the strange editor “EDIT”, there is some help in this file https://fjkraan.home.xs4all.nl/comp/miniminc/rt11_edit.txt

Try coding

After following the steps described in the blogpost-Link, the simulation can be started with:

pdp11 boot.ini

My boot.ini has the content:

set cpu 11/23+ 256K
set tto 8b
attach LPT lpt.txt
set rl0 writeenabled
set rl0 rl02
attach rl0 RT-11_V5.3_BIN_RL02_WORKING
set rl1 writeenabled
set rl1 rl02
attach rl1 storage.dsk
set rl1 badblock
boot rl0

The decuser link mentioned has a nice hello world test to do the edit, assemble, link, run cycle for the first time Their hello world;

.TYPE HELLO.MAC
    .TITLE HELLO
.MCALL .PRINT,.EXIT   ; TELL ASSEMBLER I WANT THESE TWO FROM SYSMAC.SML

START:  .PRINT #HELLO ; CALL OS FUNCTION TO PRINT STRING, ADDRESS HELLO
        .EXIT         ; CALL OS FUNCTION TO TERMINATE THE PROGRAM

HELLO: .ASCIZ /HELLO, WORLD/ ; AN ASCII STRING ENDING WITH A ZERO BYTE

.END START

PDP Assembler information

PDP11 Assembler Tutorial - https://www.chibiakumas.com/pdp11/

RT11

THE PDP-11 HOW-TO BOOK - http://www.skrenta.com/pdpbook.txt

RT11 Editor hints - https://fjkraan.home.xs4all.nl/comp/miniminc/rt11_edit.txt

RT–11 Quick Reference Manual