Thursday, 30 January 2014

First thoughts on a flash cart

Tonight I sat down and thought about the flash cart. Bearing in mind that I also require some hardware to analyse the buses and program the cart itself - on both MVS and AES systems - I ended up no less than with six (6) distinct PCB's! I'm also tempted to add MVS->AES and AES->MVS converter functionality as well, but it's by no means definite. I would also stress that this is not a consumer product - at least not in this form - so ease-of-use and price are definitely not factors in my design at this point.

Four (4) of the PCB's are little more than EURO to card-edge and socket adapters for MVS and AES systems, allowing me to plug either cartridge into either system, via the analyser/programmer PCB. Hopefully these will be cheap, 2-layer boards.

The aforementioned analyser/programmer PCB comprises the FPGA and (most likely) an SD card socket for ROM images. It can be configured for use as either a CHA or PRG board. It can also be powered externally for stand-alone operation.

In analyser mode, the PCB plugs into both the MVS/AES motherboard, and a standard MVS/AES cartridge. The FPGA is configured to capture cartridge bus activity and all/any lines as required, using Altera's excellent SignalTap function. It's worth noting that the FPGA PLL's will allow super-sampling to capture asynchronous events. Trace depth is limited by the size of the FPGA.

If it were possible to add converter functionality, it would effectively be done in analyser mode.

In programmer mode, the PCB must be powered externally and is connected only to a flash cart PCB (CHA/PRG). The FPGA is configured with a soft-core processor that reads ROM images from the SD card and programs the memory on the flash cart.

Finally, the flash cart is configured as either a CHA or PRG board, and operates simultaneously? as both an MVS and AES cartridge. The flash cart itself may be plugged into either the analyser/programmer board or into an MVS/AES system via the adapter boards.

I'm thinking I'll need an EP4CE22 or EP3C25 at the very least on the analyser/programmer board, and likely a decent CPLD on the flash cart. EURO connectors would need to be 150-way or equivalent.

Disclaimer: these are all random thoughts put together in a single evening, and may represent impossibly ambitious or technically infeasible goals. But I have to start somewhere!

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