Mega Man X on a CX4 cart. Advice needed.

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Arthrimus
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Joined: Wed Nov 27, 2019 11:37 am

Mega Man X on a CX4 cart. Advice needed.

Post by Arthrimus » Wed Nov 27, 2019 11:47 am

Hello everybody. I'm trying to get a Mega Man X, X2 and X3 multi cart up and running. From a hardware perspective I already know what I have to do to accomplish this, as I have already designed a couple of flash memory adapters for CX4 and built X2 and X3 multicarts. The issue I'm trying to solve seems like a software problem more than anything. I have a CX4 cart with X flashed to it, and the game boots using an unmodified rom. The problem is that the sprites are all garbled, which I'm assuming has to do with something about how the CX4 addresses the rom differently than the SNES does on a simple low rom cart.

I assume that the rom would simply need to be patched to correct where the graphics are addressed from to match the CX4, but unfortunately I have never done any rom hacking before and I really don't know where to begin. Has anyone attempted something like this before? If so can someone point me in the right direction? I'd really appreciate it. Thanks.

EDIT: I've done more testing and I now have a better idea of what needs to be done to get this working. My adapter is wired so that the CE# for the first mask rom on an X2 cartridge controls A20 on the flash chip. This allows X2 or X3 to run from a single 16mbit chip rather than X2's original 2 mask rom setup.

If I wire A20 of the flash chip to RA20 on the CX4 then I do not get garbled graphics and everything works normally. So what I would like to know is if it would be possible to patch an MMX rom to behave like the X2 rom where CE# controls A20 instead of RA20 controlling A20? If it's possible to do this as a patch it would be a lot cleaner from a hardware perspective. Thanks.

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