Good, somewhat surprising news. I programmed the AVR that is being used for the USB interface and the device attached to a PC on first attempt. So far I haven’t been able to get serial data through it, but just communicating with a PC is fantastic progress. Next steps…

1) Figure out where serial data is being lost
2) I’ll plug in the Disk ][ interface AVR and get some basic operations working
3) I’ll have to finalize and implement the host/Disk ][ communications protocol.