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PostPosted: Mon Jul 23, 2018 12:32 pm 
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If the goal for the VRC2 and VRC4 submappers was that emulators should not respond to address lines to which the original hardware did not respond, then there need to be at least two more submappers for consistency:

Mapper 85.0: Konami VRC7a/b: ASIC An pin connected to both CPU A3 and CPU A4 (0x18), in other words, "unknown", the default behavior
Mapper 85.1: Konami VRC7b: ASIC An connected to CPU A3 (0x08)
Mapper 85.2: Konami VRC7a: ASIC An connected to CPU A4 (0x10)

Mapper 16.0: Bandai FCG-1/2 or LZ93D50: Mapper responds in the $6000-$FFFF range, may or may not support 256 byte EPROM (denoted by NES 2.0 PRG-NVRAM field), IRQ counter may or may not be latched.
Mapper 16.4: Bandai FCG-1/2: Mapper responds only in the $6000-$7FFF range, no EPROM support, IRQ counter is not latched.
Mapper 16.5: Bandai LZ93D50: Mapper responds only in the $8000-$FFFF range, support for 256 byte EPROM (denoted by NES 2.0 PRG-NVRAM field), IRQ counter is latched.
Note that these are different from kevtris' old proposal that merely disambiguated the save data size and is rightfully deprecated, but did not distinguish the ASIC type.

Also, I noticed that among the discrete mappers, ANROM, UxROM and CNROM have bus-conflict-disambiguating submappers, but not MHROM/GNROM. Was this an oversight, or on purpose because there are supposed to have been bus-conflict-avoiding UxROM and CNROM boards (though I don't know any) but no bus-conflict-avoiding MHROM/GNROM board?

Edit: Mapper 16 proposal modified to not collide with previous deprecated proposal.


Last edited by NewRisingSun on Thu Aug 09, 2018 11:18 am, edited 1 time in total.

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PostPosted: Mon Jul 23, 2018 1:09 pm 
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Yes, discrete logic mappers were only allocated variations as we found they existed.

Submappers were allocated for VRC2/4 because the conflation actually exposed bugs in the lumped emulation (such as Wai Wai World relying on not have 1-screen mirroring, or ... whatever the game is that incorrectly starts writing to the wrong register set during the credits).

But as far as we know, there's no emulation failures due to lumping the two PCB layouts for VRC7.

On the other hand, the difference in IRQ behavior on the Bandai FCG series definitely does warrant something. Unfortunately, kevtris already allocated some redundancy here and has separately made it clear that he's not interested in being told his allocations were redundant.


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PostPosted: Mon Jul 23, 2018 1:17 pm 
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Joined: Thu May 19, 2005 11:30 am
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lidnariq wrote:
Yes, discrete logic mappers were only allocated variations as we found they existed.
I wonder which games used UxROM/CNROM without bus conflicts. The wiki previously mentioned Colorful Dragon as CNROM without bus conflicts, but that one turned out to be a mapper hack, as confirmed by redumps of the original Sachen cartridge and of a Game Doctor FDS disk that matched the Mapper 3 ROM in its PRG/overdumped CHR data. Camerica games are basically UNROM without bus conflicts, but those go as Mapper 71 anyway.
lidnariq wrote:
But as far as we know, there's no emulation failures due to lumping the two PCB layouts for VRC7.
I'd still like to allocate it for consistency as well as neatness and exactness of emulation.
lidnariq wrote:
Unfortunately, kevtris already allocated some redundancy here and has separately made it clear that he's not interested in being told his allocations were redundant.
Do we need to take that older proposal into account? Has any emulator implemented it? I suppose I could change the new submapper numbers to ones not used by that older proposal.


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PostPosted: Mon Jul 23, 2018 9:27 pm 
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The only games we have confirmed that have issues with bus conflict are Cybernoid and Donkey Kong Official Edition. The former requires bitwise AND of CPU value and ROM value to function properly after changing from music to sound effects or vice versa, the latter requires the absence of bus conflicts to work without graphics glitches. Both ROMs can be patched to avoid these issues. Officially both games use Mapper 3/CNROM, which canonically does not have bus conflict prevention hardware. Other games either account for bus conflicts or use hardware which accounts for them.

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PostPosted: Thu Aug 09, 2018 11:17 am 
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Here are test ROMs for the proposed submappers to mappers 16 and 85. The mapper 16 test ROM only tests the address range of the CHR register; it does not test whether the IRQ counter is latched or not, and does not test the EPROM size (i.e. not the deprecated submappers).


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TEST016.7z [1.25 KiB]
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TEST085.7z [1.26 KiB]
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