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…

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:

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).

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

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…