Thought I'd give a quick update on the state of this project, since it's been about a month since I tested the adapters on real Neo Geo hardware.
Whilst it has been very busy for me at work, and I haven't had free blocks of time that have been significant enough to do much on this particular aspect of the project, my colleague has voluntarily taken up the torch and is working on schematic capture of the programmer/analyzer board.
He has designed the voltage level shifting for the board, added the Cyclone III and today, the RS-232 port. There isn't a lot more to add to the schematic design; the SD card, FPGA configuration device and the power supplies probably comprise the rest of the board. The real work here is in the layout, and ensuring that the design is adequate for flash cart programming. To this end, it would be prudent to design the flash cartridge circuit before committing this PCB to manufacture.
I also believe the proposed FPGA will be adequate to enable MVS->AES converter functionality!
I have actually started to code up the FPGA HDL projects for each configuration of the board; whilst I'll require completely different projects for the CHA & PRG personalities, I'm hoping to get away with a single project (configured at run-time) for the programmer & analyzer functions. The FPGA will have a simple NIOS (soft-core CPU) and will likely be running FatFs to read files from the SD card - hopefully I won't require any external SRAM to run the programmer software. Again, it would be prudent to finish this design before manufacturing any boards!
