Mapper 1 CHR issues

Discuss emulation of the Nintendo Entertainment System and Famicom.

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Myself086
Posts: 158
Joined: Sat Nov 10, 2018 2:49 pm

Mapper 1 CHR issues

Post by Myself086 »

I'm starting to implement mappers into my Nes emulator and I'm using Zelda 1 to test out mapper 1 support. PRG banks are fine but CHR banks give me a lot of trouble. I got the text to load by starting CHR banks at $778f in the Rom file but everything else is still garbage and this address doesn't make sense. I tried searching the sequence of bytes for the "0" character but only one match was found.

I'm using resources from: https://wiki.nesdev.com/w/index.php/MMC1

I tried searching about this issue but I couldn't find anything.
WedNESday
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Re: Mapper 1 CHR issues

Post by WedNESday »

Zelda 1 doesn't have any CHR ROM banks. It uses CHR RAM instead.
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tokumaru
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Re: Mapper 1 CHR issues

Post by tokumaru »

When a game uses CHR-RAM (CHR pages specified as 0 in the iNES header), your emulator shouldn't load any CHR data automatically. Instead, give the game 8KB (or more if specified in an NES 2.0 mapper) of empty RAM in the CHR area that the game code itself will populate it with tiles.
Myself086
Posts: 158
Joined: Sat Nov 10, 2018 2:49 pm

Re: Mapper 1 CHR issues

Post by Myself086 »

Thanks for the information. It's fixed now and everything else that I need to fix for this game seems very straight forward.
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