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PostPosted: Tue Dec 05, 2017 2:29 pm 
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Joined: Mon Dec 29, 2014 1:46 pm
Posts: 750
Location: New York, NY
Wordtris starts up with copyright screens followed by the title screen / player selection menu. If you select 1 PLAYER, the screen whites out for a moment before the game begins. For part of the white out, the LCD is disabled. Shortly after the LCD is enabled, my emulator detects VRAM writes during PPU mode 3 (rendering the pixels). This occurs from LDI (HL), A calls, a convenient way to blocks of data. It happens at points all over the screen as opposed to the edges, the latter of which would suggest a timing issue. The writes also occur over many frames. I read that when the LCD is enabled, there might be a full white out frame where VRAM is still accessible by the CPU before the PPU engages VRAM. But, as mentioned, this happens over several frames after the LCD is enabled.

Anyway, is this actually an issue with my emulator or do some games attempt VRAM writes at the wrong times? I can't visually see any problems in Wordtris when the writes are blocked.


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PostPosted: Tue Dec 05, 2017 2:40 pm 
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Joined: Sun Mar 27, 2011 10:49 am
Posts: 219
Location: NYC
You can configure BGB to break on invalid VRAM writes (amongst other things), and I've definitely gotten commercial games to trigger the debugger.

I suggest running Wordtris through it and seeing what happens. BGB is pretty accurate.


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