The implementation I had suggested at first is a fairly literal interpretation of the RE'd MMC3C schematic that Furrtek did by tracing decapped images of the chip (the IRQ stuff is in the last page).rainwarrior wrote: ↑Wed Nov 02, 2022 11:08 am So, it isn't quite the filter you suggested in your first post on this thread. I did try it like that, but never found a successful result with it.
So, it should be pretty much how the A12 filter is supposed to work.
But, yeah, that doesn't account for external factors such as the FPGA having different logic levels or extra noise that isn't present on a standalone MMC3 board. Using a faster clock for the pre-filter should get rid of really fast transients while keeping behavior such as the pre-render scanline causing jitter in Wario's Woods in some CPU-PPU alignments.
I seem to remember that lidnariq had measured some kind of delay between when the MMC3 registers an IRQ internally and when it actually asserts the IRQ line... or something to that end. Not sure how relevant that'd be here.rainwarrior wrote: ↑Wed Nov 02, 2022 11:08 am The main thing the filter should be affecting is the specific onset timing. Unfortunately I don't know if anyone has made a test ROM that can measure MMC3 IRQ timing directly (Blargg's tests seem agnostic to a little bit of delay), but the real MMC3 carts I have on hand vs. this implementation look visually identical to me in terms of horizontal positioning.
rainwarrior wrote: ↑Wed Nov 02, 2022 1:42 pm Attempt #7. I've found zero issues testing with many games.