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PostPosted: Thu Jan 28, 2016 3:16 am 
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If you check the attached file, you'll see a strange effect in SMB running in my environment. SMB is the only title that's affected and I've tried quite a few. It looks like it's attribute-related, but only under certain conditions somehow.
I've checked attribute/nametable-mirroring, it seems okay.
Anyone got a quick feeling like "aha, he's doing this wrong"?


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File comment: Titlescreen of SMB with bugs
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PostPosted: Thu Jan 28, 2016 10:56 am 
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Don't know offhand what would be causing this particular problem. But step 1 is to determine whether this is a PPU or CPU problem.

Do the attribute tables look correct in memory and are just being displayed incorrectly? (PPU problem)

Or are the attribute tables themselves incorrect? (CPU problem)

Or it might be a mirroring issue. Is your PPU getting the attributes from the wrong NT?


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PostPosted: Thu Jan 28, 2016 1:05 pm 
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Looks like the attributetable is bad when I check. My CPU core passes the nestest.nes CPU-test, so.. To be continued..

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PostPosted: Thu Jan 28, 2016 3:51 pm 
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Maybe the CPU is writing the correct values to $2006/2007, but they're being moved to the wrong place??


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PostPosted: Wed Feb 03, 2016 1:51 pm 
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Still bothered with this bug. Doesn't seem to be PPU-related. Wrong data is stored in RAM.. I've got other issues in "Ice Climber", wrong data is also stored in RAM which is used for leveldata, I suspect the issues are related..
It's difficult tracking the code backwards on what's going wrong.. How reliable are the CPU test ROMS out there? I pass the tests I've tried but this problem isn't obviously caught..

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PostPosted: Wed Feb 03, 2016 5:57 pm 
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oRBIT2002 wrote:
Looks like the attributetable is bad when I check. My CPU core passes the nestest.nes CPU-test, so.. To be continued..


Try this one too: http://blargg.8bitalley.com/nes-tests/instr_test-v4.zip

My emulator passed nestest.nes but this one found a problem and I was able to fix it.


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PostPosted: Thu Feb 04, 2016 1:40 pm 
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Thanks for the tip, this fixed the problem! I already thought I've been running these tests but this one obviously was different.

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PostPosted: Thu Feb 04, 2016 2:15 pm 
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So, what exactly was wrong about your CPU implementation that caused such bugs? You know, to keep this thread relevant for future readers.


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PostPosted: Thu Feb 04, 2016 7:34 pm 
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Glad you got it working! I'd also be interested in knowing what it was.


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PostPosted: Thu Feb 04, 2016 11:42 pm 
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My <ROL zeropage> & <LSR zeropage> implementation was flawed. Strange that other test-ROMs didn't find this..

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