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PostPosted: Tue Jun 21, 2016 5:10 pm 
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Formerly Fx3
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Location: Brazil
The "PPU race condition" occurs when a Y-increment triggers after a $2006 (second) write, which should win. Games that are affected by this thing are Mega Man 5, The Simpsons - Bart vs Space Mutants, Kick Master, among others.

A way of fixing it is to put a flag that indicates a $2006 2nd write. If this flag is raised on Y-increment, the increment won't occur after PPU cycle 254 (or 255 depending of how you're counting cycles).

I wonder if this is a real condition... or an obscure timing bug in emulators.


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PostPosted: Tue Jun 21, 2016 5:35 pm 
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With the flag does it still pass all the test ROMs in addition to fixing all the games?


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PostPosted: Wed Jun 22, 2016 3:48 am 
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Should be quite easy to write a test rom for this, someone should definitely make it and test on a real console.


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PostPosted: Wed Jun 22, 2016 7:01 pm 
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No problems. Sprite zero tests are OK, including overflow bit and MMC3 IRQs.


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