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

  1. #1

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

    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

  2. #2

    Default

    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/20160505...s/issue.htm#OS
    int10h.org :: :: :: blog

  3. #3

    Default

    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

  4. #4

    Default

    What about disassembling the ROM itself?
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  5. #5

    Default

    Quote Originally Posted by Ruud View Post
    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.
    int10h.org :: :: :: blog

  6. #6
    Join Date
    Jun 2009
    Location
    Hobart, Tasmania, Australia
    Posts
    163

    Default

    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).

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