pcjs/apps/pdp11/boot/bootstrap/README.md

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PDP-11 Bootstrap Loader

The blog post "PDP-11 Paper Tape BASIC" describes the Bootstrap Loader, a small program used to load the Absolute Loader, which in turn loads the PDP-11 BASIC Paper Tape.

Here's what the Bootstrap Loader looks like:

Location  Instruction
 037744     016701
 037746     000026
 037750     012702
 037752     000352
 037754     005211
 037756     105711
 037760     100376
 037762     116162
 037764     000002
 037766     037400
 037770     005267
 037772     177756
 037774     000765
 037776     177550

Using a PDPjs machine such as the PDP-11/20 Test Machine with Debugger, the Bootstrap Loader is easily entered with a single Debugger "edit" command:

e 037744 016701 000026 012702 000352 005211 105711 100376 116162 000002 037400 005267 177756 000765 177550

You can immediately disassemble the code using u 037744 040000:

037744: 016701 000026          MOV   26(PC),R1              ; @037776
037750: 012702 000352          MOV   #352,R2
037754: 005211                 INC   @R1
037756: 105711                 TSTB  @R1
037760: 100376                 BPL   037756
037762: 116162 000002 037400   MOVB  2(R1),37400(R2)
037770: 005267 177756          INC   177756(PC)             ; @037752
037774: 000765                 BR    037750
037776: 177550                 .WORD 177550

I also pasted the disassembled code into a listing file, BOOTSTRAP-16KB.LST, and ran FileDump to produce a BOOTSTRAP-16KB.JSON that can be pre-loaded into any machine:

filedump --file=BOOTSTRAP-16KB.lst --format=octal --output=BOOTSTRAP-16KB.json

To run the Bootstrap Loader, set the PC to 037744 and start the machine:

r pc=037744
g