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PostPosted: Sat Aug 25, 2018 3:01 am 
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A Mesen version with support for the additional fields in this proposal has now been released for some time, so I wonder if the proposal should be considered accepted and added to the wiki.


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PostPosted: Sat Sep 01, 2018 8:46 am 
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Is there any interest in using the upper nybble of Byte 12 or 14 that would allow for the designation of expansion audio with hardware not orignally intended for that hardware? This might come into play if a homebrew author makes a game that runs off Mapper 4 but uses VRC6 sound. Or there is an interesting pirate version of a particular game that left expansion audio data writes in the game but the cartridge hardware does not support. You could designate the upper nybble like this :

0 - No expansion audio
1 - VRC6
2 - VRC6 Alt
3 - VRC7
4 - Sunsoft 5B
5 - Namco 163
6 - FDS
7 - MMC5
8 - uDP7756
9 - uDP7755
10 - M50805
11 - UM5100
12-15 reserved for future use

I know that the 16-byte header is running out of bits, but maybe this is worth considering.

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PostPosted: Sat Sep 01, 2018 9:08 am 
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You cannot just add any particular sound chip support to any existing mapper because of address space collision. For example, VRC6 uses Addresses $9000-$9003, $A000-$A002, $B000-$B002 with an address mask of $F003, while the MMC3 uses the same address range with an address mask of $E001. Even if you emulated each with the narrowest of address masks, the same address would still map to a register in both chips. You would have to thoroughly redraw each chip's address map for this two work, and the information on how this would be done cannot be conveyed by merely specifying the presence of an additional sound chip, as it would have to be mapper-specific. Multiple expansion sound chip support barely works in NSF players, and only because NSF players do not emulate entire mappers, only the small subset dealing with sound generation. If a homebrew cart wants to use a hybrid mapper combining features of several legacy mappers, it should assign a new mapper number for that, instead of using precious header space.


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PostPosted: Sat Sep 01, 2018 10:50 am 
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Great Hierophant wrote:
Is there any interest in using the upper nybble of Byte 12 or 14 that would allow for the designation of expansion audio with hardware not orignally intended for that hardware?

No. Just create a new mapper for this. Using these 4 bits in the header creates a nonsensical combinatorial explosion with every single mapper. This has no existing use cases. If you want to experiment with these combinations, hack an emulator, or build the cartridge. When you've got something worth emulating, come back and propose the mapper for that particular combination.


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PostPosted: Sat Sep 01, 2018 10:59 am 
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I understand now, it just simply won't work without defining new hardware and therefore should use a new mapper. :roll: Running an NSF and running a game are different things.

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