Tuesday, 29 April 2014

Decisions, decisions...

First; I simply haven't had the time to finish soldering up the MVS adapter, though I have almost finished the MVS Cartridge adapter. It's not difficult, but tedious, given that the pair of MVS adapters have 1,080 pins between them. Plus I've also been competing for time in the lab and, unfortunately, real work gets priority for some reason!

I've had a few questions both here and elsewhere on the make-up of my planned flash cartridge. Given that I've decided it would be prudent to design it in parallel with the analyser/programmer PCB, I really need to sort that out ASAP if I'm going to move ahead with the project in the short term, which I certainly plan to do.

Initially I was planning on designing a pure flash cartridge, which required programming via the analyser/programmer PCB but would then subsequently be a non-volatile, instant-on Neo Geo cartridge. It would have capacity for (at most) a single commercial title, and certainly not designed to be a general multi-cart.

The primary reason for this is that I wanted a simple, quick-to-prototype design that wouldn't get bogged down in the design decision stage. The cartridge would initially allow me to run my own home-brew software on real MVS & AES boards, run any commercial title on the NGPACE motherboard (for testing), and finally allow me to write software to assist in the development and testing of the NGPACE motherboard project.

The 'product' spin would incorporate the programmer on-board and/or utilise some form of volatile memory that could be programmed on-the-fly from, say, SD card. It does increase the risk somewhat of the 2nd spin, but I do believe that most of the challenge in this phase is getting the actual cartridge bus right and the non-ROM functions of the cartridge working for all commercial titles.

There is some temptation to go straight to this version of the board - it would allow faster turn-around times on writing and running software of course - but that is perhaps not important with the ability to do much of the work under software emulation. It's also worthy to note that if the flash cartridge does not require the programmer PCB, then there's very little point in designing the analyser board (at significant expense).

What would be interesting however, is the possibility of using RAM-based sprite memory and (also) providing access via the 68K bus. The up-shot of all this would be to provide a sort of bit-map memory, not unlike the MSX has, for example. The trick is accommodating sufficient CPU access bandwidth to make it truly useful, which I believe could be done with faster modern RAM.

That would open up all sorts of possibilities on the system, in particular porting some classic arcade and computer games. One might argue that it's then no longer a Neo Geo, but I would argue that several consoles in the past have used cartridges with additional hardware to enhance the system's capabilities.

Either way, my initial focus is finishing the assembly of and testing the MVS adapters, then moving on to the design of the other PCB's ASAP. So there's a good chance I'll simply stick with my original plan of a simple flash-only cartridge, and get the next phase done-and-dusted before the next millennium.

No comments:

Post a Comment