Setting up for the disk writing tests was quite involved. I prepared a memory file of the original sector 0 value for the disk cartridge, from the archive on bitsavers. I set up the most useful signals on the logic analyzer and triple checked that my tool was not going to actually write data onto the drive during the early tests.
First up, I had to verify that the file I created was correctly loaded into RAM on the board. All my testing to date verified that I could write to RAM from data extracted off disk, but now I would use the USB link mechanism. I need a known image to write in order to validate the bitstream sent to the heads.
My logic is not updating RAM from the USB link, either from a file or via direct manipulation of the registers. I set up diagnostics to figure this out. I didn't have much time available today but should have this working imminently.