So, I have started debugging the new CPU board. Amazingly, the first time I powered it up it booted to the sign-on message. It got stuck there, so I hooked up the logic analyzer to see where it was at in the code. As I suspected, it was getting hung up trying to access the new floppy controller. Although the i82078 (the new controller) is register-compatible with the uPD765 (the original DSS-1 controller), it needs to be initialized quite differently. I’m hoping to have a fix for it this week.
Once the floppy is working, the next task will be getting the new USB controller up and running. The firmware that FTDI supplies is supposed to be compatible with the VNC-1 command set, but things are rarely ever that easy 😀