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jwestfall69 / neogeo-diag-bios

Disassembly of smkdan's Neo Geo Diagnostics BIOS with added features
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Make testing of boards with SM1 bypass possible #37

Closed zardam closed 5 months ago

zardam commented 5 months ago

I have a MV1A slot with a defective SM1 mask ROM, causing missing sound in some games. With SM1 chip removed and a "SM1 bypass" mod installed (wiring SM1 CE pin to the Z80 wait pin), the diagnostic BIOS complains about a problem with the Z80 communication (expected), but pressing start to use the test cart M1 ROM fails, as the Z80 cannot come back to SM1 ROM at some point.

This patch enables to switch to M1 on the test cart, but do the test as if run on a MV1B without SM1 ROM.

jwestfall69 commented 5 months ago

So your issue is you want to disable the SM1 OE/CRC checks because you have your weird mod installed which forces the z80 to stall when accessing the SM1?

zardam commented 5 months ago

Yes, exactly.

Finding a replacement for SM1 seems hard (SOP-32 packaging on this board), and this mod is very simple and working perfectly with all the games I tested so far. Maybe there is a better option that I'm not aware of ?

jwestfall69 commented 5 months ago

Sorry for the delay, been busy with other stuff.

When you have a chance can you test this version of the bios

https://www.mvs-scans.com/misc/sp1-sm1-skip1.bin

It has the same C+D causes SM1 tests to be skipped as your patch did but I wanted to go about doing it another way.

thanks

zardam commented 5 months ago

Thank you for this version. It is working on my modded board, testing with C+D completes correctly.

jwestfall69 commented 5 months ago

I've commit my changes, going to close this pull request.