SMB1 MMC3 Conversion - Scanline IRQ problem

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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SMB1 MMC3 Conversion - Scanline IRQ problem

Post by Nalwonk » Tue Mar 02, 2021 4:56 am

I've been working on an MMC3 conversion of Super Mario Bros. as the basis for larger hacking projects.

I've been having no end of problems with converting the top status bar from a sprite 0 hit to an IRQ, mostly by trying to copy what was done with the SMB2 fds to mmc3 conversion, but I find the source files for that to be difficult to decipher at times, so I'm almost certainly missing things.

It seems to be mostly working now, but something in the castle victory code is causing it to break. Whenever I grab the axe, the screen mostly flips to the other nametable, with graphical errors making it look like the IRQ isn't firing on the correct frame, though it does appear to be. I recorded a video of the issue:

Does anyone know what the problem might be?

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