Thursday, 27 November 2014

Quick update

As mentioned, the re-think has reduced the PCB design count from 3 to 1.

This does make the cartridge configuration of the adapters obsolete, unfortunately. Whilst the PCB's themselves won't be wasted (same PCB for cartridge and system adapters) there's a few connectors that may be.

After taking a closer look at the protection and bank switching on the existing commercial cartridges, it soon became clear that an all-encompassing design would require an FPGA capable of snooping and/or routing almost every pin on the cartridge bus. So I've decided to scrap the analyzer/programmer PCB and have the flash cartridge capable of analyzing the bus and also programming itself.

The prototype design will be over-engineered somewhat; I want to address the Neo Geo technical issues without a half-baked design getting in the way. There may be scope for a limited run of this design, but it will be expensive. In any case I'd look at possibly two (2) products from this - a cheaper, cut-down Homebrew Edition that is suited to testing and playing homebrew titles only, and the full-blown Pro Gamer Edition that could, well, play any Neo Geo title.

I've also included some SRAM on the design, for the purpose of experimenting with dynamic sprite tile data. This would in effect allow for a bitmap display mode, opening up all sorts of possibilities for ports from other platforms (Defender, anyone?)

As for progress, all the devices have been specified and chosen, and schematic capture is under way. On the firmware side, the FPGA projects have been mapped out at the top level and a NIOS core has been added to the PRG project - mainly to gauge adequacy of the chosen FPGA.

I'm hoping things will progress quickly from here, as the design really is simple, and it's possible we could have the PCB's ready for manufacture this calendar year! It's not going to be a cheap process as they will need to be assembled externally, so timing may also depend on available funds.

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