bumping up file size

Discussion of development of software for any "obsolete" computer or video game system.
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coinheaven
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Joined: Sat Sep 17, 2005 12:26 pm

bumping up file size

Post by coinheaven » Thu Mar 05, 2020 9:44 am

I have a rom that is 48k and want to bump it up to 64k or 128k, anybody know how can i do this? thanks

pwnskar
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Re: bumping up file size

Post by pwnskar » Thu Mar 05, 2020 10:23 am

You'll have to use bank swapping in order to expand your rom. MMC3 is a popular mapper that supports this: https://wiki.nesdev.com/w/index.php/MMC3

The NES can only access 32kb of PRG-ROM and 32kb of CHR-ROM by default. To get around this limitation "mappers" were developed and put into the circuitry of game carts. The idea is you tell the mapper which parts of your rom will be adressable by the NES and switch it around in code for when different parts are needed.

lidnariq
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Re: bumping up file size

Post by lidnariq » Thu Mar 05, 2020 11:27 am

pwnskar wrote:
Thu Mar 05, 2020 10:23 am
The NES can only access 32kb of PRG-ROM and 32kb of CHR-ROM by default.
8kb of CHR-ROM.

Everything else you said is true.

(That said, if the game is already 48KB, it must be some non-zero mapper already.)

coinheaven
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Re: bumping up file size

Post by coinheaven » Thu Mar 05, 2020 12:04 pm

oh, sorry for the confusion, it's an sg-1000 rom that i am trying to put on a master system board. i was hoping to put it on a 27c512 eprom. i have bumped up nes chr and prg files using the copy /b in dos but i never had to bump up something i can't just double. thanks!

lidnariq
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Re: bumping up file size

Post by lidnariq » Thu Mar 05, 2020 12:33 pm

If I remember correctly, in this case you can just ignore the uppermost 16Kb, but you'll need extra logic so that the ROM is enabled whenever A15 or A14 is low. (Which exact signals you have access to depend on what physical console you're using - see smspowerwiki:Japanese SMS Cartridge)

Oziphantom
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Re: bumping up file size

Post by Oziphantom » Thu Mar 05, 2020 11:16 pm

This is a Nintendo forum, you would be better of asking at https://www.smspower.org/forums/

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TmEE
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Re: bumping up file size

Post by TmEE » Thu Mar 05, 2020 11:20 pm

48KB is max size without mappers on SMS. For anything bigger the game will have to use one (perhaps the standard SMS mapper that most games use) but the game itself needs to be hacked to support that and that probably is not trivial by any means.

tepples
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Re: bumping up file size

Post by tepples » Thu Mar 05, 2020 11:53 pm

If you don't want to spring for a mapper quite yet, the other option is improving the game's data compression so you can free more space in the same 48 KiB ROM. I concede that this might not be so viable if the data is already packed as tightly as, say, 144p Test Suite for Game Boy. But I can offer some compression tips if you're interested.

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