April 20, 2022
Callan Multibus 68k computer - Progress, as of 4/20/22
I began working on this February 17, 2022 -- about 2 months ago.
I have spent a lot of my free time over those two months on this project.
That turned out to be a lot more than I expected.
Where am I at now
I can build and run arbitrary C code on the Callan, downloading it over
the 9600 baud serial link. This is somewhat painful, even for executables
that are on the order of 5K in size. No doubt I am spoiled by modern systems.
I have written a driver for the CWC (Callan Winchester controller), i.e. the
hard drive controller. It is unable to read sectors from the disk.
The disk may very well be bad, but that is uncertain.
Troubles along the way
Power supply troubles - I had one supply with a bad -12 volt section.
Then I had a memory card with a shorted +12 bypass capacitor.
RAM troubles - my multibus memory card had a long list of problems.
This was finally solved by giving up on it and switching to a good card.
For unknown reasons, the CPU frequently goes into HALT state.
It is still useful though.
It seems to only do this when the serial port is disconnected.
I can load software and run it more or less indefinitely, but
once I exit my terminal emulator, it tends to go to HALT fairly quickly.
Steps along the way
- Lots of hardware troubleshooting (see above)
- Disassembled and analyzed the boot roms
- Reverse engineered and disassembled HD controller firmware.
- Wrote an S record download tool in Python.
- Wrote drivers for uart and HD controller
- Wrote ram diagnostic
- Wrote HD diagnostic
Feedback? Questions?
Drop me a line!
Tom's Computer Info / tom@mmto.org