Question re. feasibility of creating replacement CPU, PPU out of MiSTer NES core

[friendofmegaman]

Hi folks,

With the availability of new NES boards (such as nesessity) one could build a pretty much all new NES with the exception of CPU and PPU. I was wondering if it was possible (and if anyone tried) separating the NES core's CPU and PPU logic into standalone FPGA-based CPU and PPU replacement chips for projects like this.

My naive idea is that, perhaps, this could be done in two smaller and cheaper FPGAs (like Lattice). I was hoping someone better informed could comment on this and perhaps even evaluate the complexity of the project.

Cheers!

PS. I understand that this is not directly related to MiSTer, however if such project was possible, it would only make sense to base it off MiSTer core.

[jca]

It has been done for a Yamaha sound chip. It uses the core developed by Jotego and the board is a tiny board which plugs right into the socket of the original chip. I think it is a Lattice FPGA and it does not need an EEPROM as it retains its programming.

[friendofmegaman]

Interesting, thank you for the information!

It appears that someone implemented a full NES on an ICE40 (github link), so the CPU alone or the PPU alone should be possible as well at least in theory.

[Newsdee]

It is definitely possible, it has been done for the ULA chip for Spectrums, e.g.:

http://blog.retroleum.co.uk/electronics ... nt-module/

As long the FPGA implementation of the component is pin compatible and cycle accurare, it would work.

[jlancaster86]

It would be nice to have new ASICs made as drop-in replacements if that's at all feasible. The clones that already exist have known issues (mainly with sound, if I recall correctly).

If going the FPGA route, wouldn't it make more sense to design an entirely new PCB centered around a singular FPGA? That'd be the ultimate way of reviving a broken NES.