Is it possible to change commercial game mappers?

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Pasky
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Is it possible to change commercial game mappers?

Post by Pasky » Thu Jun 05, 2014 12:55 pm

What I mean is, is it possible to change a commercials game mapper to use another? I know this has been done with hacks such as mega man 4, but can this be done to Koei games using the MMC5 mapper and switch it to a more common mapper? Is it one of those things that is possible, but extremely difficult and time consuming? Reason I ask is so that I can play them on the powerpak. Thanks.

tepples
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Re: Is it possible to change commercial game mappers?

Post by tepples » Thu Jun 05, 2014 1:15 pm

Hacking a game from a less sophisticated mapper to a more sophisticated mapper involves replacing the mapper writes with the new mapper's equivalents. Going the other way generally requires a rewrite of the engine because a lot of the features that the engine expects just aren't present.

But then the degree to which games use the more sophisticated mapper can also vary. Some games might only use one or two features. Some 72-pin games might use a sophisticated mapper just because it was cheaper to use Nintendo's MMCs than to get its own ASIC certified, such as Castlevania III which was hacked from Konami's own VRC6 to MMC5 outside Japan. But anything that uses MMC5 ExGrafix is going to be really hard to hack back to MMC3.

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thefox
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Re: Is it possible to change commercial game mappers?

Post by thefox » Thu Jun 05, 2014 3:52 pm

Doesn't loopy's partial MMC5 implementation work? I haven't tested it myself so I don't know what sort of subset of MMC5 features it supports.
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rainwarrior
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Re: Is it possible to change commercial game mappers?

Post by rainwarrior » Thu Jun 05, 2014 5:06 pm

I was under the impression that Loopy's MMC5 mapper supports everything except the expansion sound. (There are only 3 games with MMC5 sound anyway: Just Breed, Metal Slader Glory, Shin-4-Nin Uchi Mahjong.)
http://home.comcast.net/~olimar/NES/mmc5.zip

I'm not at home right now, though, so I can't test.

Pasky
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Re: Is it possible to change commercial game mappers?

Post by Pasky » Fri Jun 06, 2014 2:29 pm

No, it only seems to work for certain games. All Koei games using MMC5 crash.

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loopy
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Re: Is it possible to change commercial game mappers?

Post by loopy » Fri Jun 06, 2014 6:22 pm

All features except sound and vertical split scrolling are (theoretically) implemented. I never did track down what was wrong with those Koei games... seems to be a bug in the sram mapping (?).

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