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Details regarding use of NDISASM

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Jeff Parsons 2015-04-06 16:25:48 -07:00 • committed by jeffpar
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24
devices/pc/bios/compaq/deskpro386/README.md
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@ -63,17 +63,33 @@ while the /PGM should be connected to INPUT HIGH VOLTAGE. So I wired pin 27 (/P
worked perfectly. The NYC Resistor article implied that every *active low* pin should be connected to GND, but apparently
there are exceptions to that general rule.
Producing Source Code with NDISASM
Producing BIOS Source Code
---
From the current directory, I ran:
In the current directory, I ran NDISASM (the disassembler included with NASM):
ndisasm -o0x8000 -se105h -se05ah -se6ffh -sf025h -sf8aah private/1988-01-28.rom > 1988-01-28.nasm
Then I ran the TextOut command, with the *--nasm* option, to clean up the code:
The `-o0x8000` argument is required to "org" the file at the proper starting address, but the `-s` arguments
are optional; they simply establish a few sync points within the ROM image that save a little cleanup effort, by
preventing disassembly in the middle of instructions.
Then I ran the PCjs [TextOut](/modules/textout/lib/) command, with the *--nasm* option, to prepare the code for reassembly:
node ~/Sites/pcjs/modules/textout/bin/textout --file=1988-01-28.nasm --nasm > t.nasm
mv t.nasm 1988-01-28.nasm
The result, [1988-01-28.nasm](1988-01-28.nasm), can then be reassembled:
The result, [1988-01-28.nasm](1988-01-28.nasm), after a small amount of manual cleanup, can now be successfully reassembled:
nasm -f bin 1988-01-28.nasm -l 1988-01-28.lst -o 1988-01-28.rom
However, it does NOT produce a binary identical to the original ROM, in part because of instruction ambiguities (ie,
instructions that can be assembled multiple ways).
It's possible that reassembled ROM may still work, but more research is required.
One interesting section of the Compaq DeskPro ROM is this string at offset 0xE002:
db 'AUTHORS CAB93GLB93RWS93DJC93NPB(C)Copyright COMPAQ Computer Corporation 1982,83,84,85,86'
Anyone care to take a stab at what `CAB93GLB93RWS93DJC93NPB` means? I've already confirmed that
[Google](https://www.google.com/?gws_rd=ssl#q=CAB93GLB93RWS93DJC93NPB) doesn't know.