Problem when I decompile a .OBJ file (Victor 9000 BIOS)

[FreddyV]

Hi,

I am working on the Victor 9000 machine, to rebuild a BIOS and eventually build an XT IDE board for it.

I found the .OBJ Files from the BIOS and the DOS and when I try to decompile them, there are some missing code.

Example:
mov word ptr $S16,bx
mov word ptr $S16 + 00002h,es
db 089h
in al,dx
pop bp

Or :
mov cl,0Fh
mul cl
db 089h
ret

les si,dword ptr JPTR
db 089h
repz mov al,es:[bx+004h]
mov $S31,al

What are those DB 89h opcode ?

Do you know a good OBJ 2 ASM program ?

Thanks

 

[VileR]

How did you decompile? There's OBJASM for one (you can select "B:" and "save" to grab a disk image).

AFAIK on these machines the BIOS is part of MSDOS.SYS, so you could also pull that from a boot disk and let IDA go to town on it.
I guess you've tried the stuff here? - https://web.archive.org/web/20160505170625/http://www.actsirius1.co.uk/pages/issue.htm#OS

 

[FreddyV]

I use this OBJASM, I don't remember where I got it:

; OBJASM version 2.0 released on Jan 3, 1991
; (C) Copyright 1988,1989,1990,1991 by Robert F. Day. All rights reserved

 

[Ruud]

What about disassembling the ROM itself?

 

[VileR]

What about disassembling the ROM itself?

This seems to be one of those machines where the BIOS isn't present on a ROM but loaded from disk when you boot DOS... hence, the MSDOS.SYS suggestion above.

 

[nigwil]

IIRC, even the font is "soft" (loaded from disk) on the VICTOR 9000 (Sirius 1), so the font file should be in MSDOS.SYS too (or as a separate file).