CNROM (mapper 3) graphical glitches

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CNROM (mapper 3) graphical glitches

Post by lord_Chile » Sat Feb 24, 2018 7:14 am


Im developing a nes emulator. I can run NROM and UxROM succesfully. CNROM seems easy, and i can "play" CNROM games but all my CNROMS (circus charlie, friday13th and more) are experimenting graphical problems (glitches). I think my routine (8kb bankswitching is Ok)...

Only one detail. Im not using pointers for it, so im doing bankswitching by "copying 8kb chunks" to vram. Could be it?

So in your experience, Why CNROMS could experiment graphical glitches?
Good day to nesdev people. Lord..
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UTFSM Sansano programmer.. lord_Chile
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Re: CNROM (mapper 3) graphical glitches

Post by na_th_an » Sat Feb 24, 2018 2:01 pm

I'm no expert, but being a developer which has used CNROM extensively, maybe it has to do with the fact that bankswitching can be done *at any time*, even during rendering, as it doesn't involve writing to the PPU at all. What kind of glitches are you getting? Maybe the 8Kb copies are taking longer than expected during a tight and timing sensitive routine such as generating the display?

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Re: CNROM (mapper 3) graphical glitches

Post by MottZilla » Mon Feb 26, 2018 9:41 pm

Post a picture if possible. Your banking routine could be flawed or your rendering. Copying data is not a good idea. It's possible you are copying over and corrupting data maybe. Or post code from some of your routines.

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