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PostPosted: Sun Apr 30, 2006 5:56 pm 
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On most of the commercial games I've tried on my devcarts the PGM ROM will work just fine with no CHR ROM in place except of course the graphics will be pretty hard to follow. On some games such as Xexyz if you don't put in the CHR chip the game either just "hangs" at the "green screen" or later or just doesn't work properly. On these games it seems the main code execution is dependent on the values in the CHR ROM. Has anybody ever seen any code that would account for this?


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PostPosted: Sun Apr 30, 2006 5:59 pm 
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Yeah, it's not unheard-of. SMB comes to mind, it has it's title screen data in CHR-ROM. And Snake Rattle and Roll IIRC had it's music data in CHR-ROM.


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PostPosted: Sun Apr 30, 2006 6:55 pm 
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Memblers wrote:
Yeah, it's not unheard-of. SMB comes to mind, it has it's title screen data in CHR-ROM. And Snake Rattle and Roll IIRC had it's music data in CHR-ROM.

I had problems trying to run SMB with Spy vs. Spy's CHR. It never left the title screen. However, running it without a CHR chip worked fine. Running it on a CHR RAM cart also worked fine. Maybe it's just a coincidence that the values on Spy vs. Spy's CHR caused the game to lock up but the random values on the other cases didn't?


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PostPosted: Fri May 05, 2006 5:45 pm 
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Umm... excuse but... what PGM stands for?

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PostPosted: Fri May 05, 2006 6:08 pm 
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I'm guessing "PGM" is a misreading/misremembering of the more common "PRG", both standing for "program".


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PostPosted: Fri May 05, 2006 9:12 pm 
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Lloyd Gordon wrote:
On most of the commercial games I've tried on my devcarts the PGM ROM will work just fine with no CHR ROM in place except of course the graphics will be pretty hard to follow. On some games such as Xexyz if you don't put in the CHR chip the game either just "hangs" at the "green screen" or later or just doesn't work properly. On these games it seems the main code execution is dependent on the values in the CHR ROM. Has anybody ever seen any code that would account for this?


As others mentioned, it could be looking for data in CHR ROM, or more likely, it is waiting for a sprite 0 hit that never occurs. I've had that happen many times on my FPGA NES. If there's some hardware issue, and sprite 0 is never hit, the game will crash hard.

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