Hacking up the Psion SIBO SDK DOS debugger

Disclaimer: I have no idea what I’m doing 😀

Whilst poking around in the Psion SIBO SDK debugger (the DOS prog “SDBG.EXE” which appears to be heavily based on the MC400 OS/GUI and is found in the SYS directory after installing the SIBO C SDK) I’ve managed to get some of the MC’s “native apps” running in it 😀

(all screenshots are from SDBG.EXE running in dosbox, “MC native apps” copied from the MC WORD’s System Flash SSD)

The debugger looks like it’s hard-coded to launch the SYS$BOOT.IMG file which attempts to connect to a remote machine via the serial link to debug the processes running on it…

SDBG.EXE launched and waiting to connect to a remote SIBO/EPOC machine

I moved the original SYS$BOOT.IMG file somewhere safe, took the MC’s file manager FLMAN.APP and renamed it to SYS$BOOT.IMG, restarted SDBG.EXE and lo and behold…


Once the file manager is running we can use it to run some of the other MC apps too:

Database running in SDBG.EXE
Test Processor running in SDBG.EXE
Editing OPL in the Text Processor running in SDBG.EXE

Some apps won’t run (both CALC.APP & WORD.APP crash with “Panic 54” which is “Missing external categories in LibLink“) and the OPL translator wont’ translate (even though I copied over SYS$OPLT & SYS$OPLR from the MC’s ROM:: disk).

PANIC 54 when attempting to run CALC.APP or WORD.APP

Once these apps are running locally we can inspect them with the debugger too by running DEBUG.APP and selecting “break into process”:

DEBUG.APP running
DEBUG.APP running

I’m assuming that SDBG.EXE has been written with modified file & window servers (SYS$FSRV and SYS$WSRV) to run on “PC” hardware rather than the SIBO MC and that all the good stuff (ASIC1/2 + ASIC4/5 support) is missing from this code. It would be interesting to see if the shell (SYS$SHLL) from the MC can be swapped into the embedded “ROM” image in SDBG.EXE and actually run.

Poking around with a hex editor shows what looks very similar to the MC400’s ROM dump embedded in the SDBG.EXE file at offset 0x400…

SDBG.EXE on the left, MC400 V2.60F ROM on the right

Published by zedstarr

Chilled out human being, doing techy stuff.

One thought on “Hacking up the Psion SIBO SDK DOS debugger

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