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PostPosted: Sun May 10, 2009 4:02 am 
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Is it theoretically possible to make a cartridge with a mapper that would use 1K of the NES's PPU RAM as CHR RAM, and have the other 1K as a single screen mirrored nametable?

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PostPosted: Sun May 10, 2009 7:43 am 
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Yep, connect: VRAM_CE to GND and VRAM_A10 to PPU_A13.


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PostPosted: Sun May 10, 2009 6:16 pm 
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Great, assign it a mapper number and let the competitions begin :)

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PostPosted: Sun May 10, 2009 6:34 pm 
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How would the PRG switching work? Or are you talking 32 KiB max PRG?

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PostPosted: Sun May 10, 2009 6:58 pm 
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What's wrong with ANROM (as long as you don't use more than 1KiB of CHR-RAM or switch name tables)?


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PostPosted: Sun May 10, 2009 7:05 pm 
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A mapper that grounds VRAM_CE mirrors the 64 tiles eight times in the pattern tables. A*ROM doesn't.


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PostPosted: Sun May 10, 2009 7:10 pm 
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But that doesn't mean you can't make a "PRG-only board" compatible game. Can't people be trusted to not use more than 64 tiles? It should be easy to verify.


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PostPosted: Sun May 10, 2009 7:46 pm 
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kyuusaku wrote:
Can't people be trusted to not use more than 64 tiles?

Until your code depends on tile $27 showing the same as tile $67.

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PostPosted: Sun May 10, 2009 7:52 pm 
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tepples wrote:
Until your code depends on tile $27 showing the same as tile $67.

Then do the same as we already do to represent games that have less than 16KB of PRG-ROM in iNES form: replicate the data. Use the same 1KB of CHR 8 times. <-- THIS DOESN'T MAKE SENSE, AS WE'RE TALKING ABOUT RAM, NOT ROM. SO YEAH, WE MIGHT NEED A NEW MAPPER NUMBER...


Last edited by tokumaru on Sun May 10, 2009 8:50 pm, edited 1 time in total.

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PostPosted: Sun May 10, 2009 7:59 pm 
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Except of course when your game animates tiles, and expects the mirrors to be updated as well each frame for whatever reason :roll:


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PostPosted: Sun May 10, 2009 8:49 pm 
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Don't mind my stupidity. I forgot we were talking about RAM, not ROM. I'm sleepy...


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PostPosted: Sun May 10, 2009 8:53 pm 
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Don't mind my comment, it was sarcasm ;)


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PostPosted: Mon May 11, 2009 4:07 pm 
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Why only 1 screen mirroring? Why not map the 2kB over the PPU's entire address space so that you can trade off CHR-RAM and nametable RAM ?

P.S. There's a little ~game called Escape From Pong which is a 1kB PRG-ROM and CHR-RAM -- it currently pretends to be a 16kB NROM game with CHR-RAM, but this is technically invalid.


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PostPosted: Mon May 11, 2009 7:15 pm 
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lidnariq wrote:
Why only 1 screen mirroring? Why not map the 2kB over the PPU's entire address space so that you can trade off CHR-RAM and nametable RAM ?

Because you can't tell the NES to just skip parts of a nametable without using heavy sprite 0 or palette wizardry.

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P.S. There's a little ~game called Escape From Pong which is a 1kB PRG-ROM and CHR-RAM -- it currently pretends to be a 16kB NROM game with CHR-RAM, but this is technically invalid.

It's not invalid if you treat mapper 0 with CHR RAM as an undersize BNROM, just like ordinary NROM is an undersize CNROM, and CNROM is an undersize GNROM.


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PostPosted: Tue May 12, 2009 10:09 am 
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tepples wrote:
lidnariq wrote:
Why only 1 screen mirroring? Why not map the 2kB over the PPU's entire address space so that you can trade off CHR-RAM and nametable RAM ?

Because you can't tell the NES to just skip parts of a nametable without using heavy sprite 0 or palette wizardry.

I imagine that scrolling would be a big pain.

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It's not invalid if you treat mapper 0 with CHR RAM as an undersize BNROM, just like ordinary NROM is an undersize CNROM, and CNROM is an undersize GNROM.

I always thought that it'd make more sense to treat mapper 0 with CHR-RAM as an undersize UNROM. I believe Nestopia said my ROM was corrupted when I tried that though, it wouldn't take less than 128KB or PRG-ROM.


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