INES Mapper 116

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These boards appear to have been researched by CaH4e3. They're used for some chinese games and bootlegs. He has described them in fceu-mm sources as:

* SL12 Protected 3-in-1 mapper hardware (VRC2, MMC3, MMC1)
* the same as 603-5052 board (TODO: add reading registers, merge)
* SL1632 2-in-1 protected board, similar to SL12 (TODO: find difference)

The following PCBs are listed as examples:

* Garou Densetsu Special (G0904.PCB, Huang-1, GAL dip: W conf.)
* Kart Fighter (008, Huang-1, GAL dip: W conf.)
* Somari (008, C5052-13, GAL dip: P conf., GK2-P/GK2-V maskroms)
* Somari (008, Huang-1, GAL dip: W conf., GK1-P/GK1-V maskroms)
* AV Mei Shao Nv Zhan Shi ()
* Samurai Spirits (Full version) (Huang-1, GAL dip: unk conf. GS-2A/GS-4A maskroms)
* Contra Fighter (603-5052 board, C5052-3, GAL dip: unk conf. SC603-A/SCB603-B maskroms)

These documents were verified by implementation into bizhawk based solely on the fceu-mm sources. FCEUX also possesses fceu-mm's sources for this mapper.

This equipment is much simpler to operate than you might expect, considering that it is a combination of VRC2 + MMC3 + MMC1. The supervisor register controls which mapper's address and IRQ outputs and write enable inputs are enabled:

 Range,Mask:   $4100-7FFF, $4100
   $4100:  [.... .CMM]
     MM = Mapper mode
          %00 = VRC2b
          %01 = MMC3
          %10, %11 = MMC1
      C = 256K CHR ROM base (AV Girl Fighting uses this)

This control register supposedly occupies the WRAM address range, so there can be no WRAM. However, it only answers to $41xx.

The Mapper mode bits control which of the mapper circuits are connected to the NES. All of the PRG-based registers and IRQ signals are connected or disconnected accordingly. This means that in order to configure one of the mapper circuits, it must be connected.

The VRC2 is wired as a VRC2b. Though Konami games using VRC mappers write to only the canonical address of each port, games using this mapper such as Garou Densetsu Special tend to rely on being able to write to mirrors of $8xxx, $9xxx, and $Axxx. And SOMARI-W depends on the CHR bank registers being $FF at power on.

The MMC3 acts exactly as a stock TxROM. It has not been determined which MMC3 variant this MMC3 is acting as. Fceu-mm makes it seem as if the mmc3 CHR regs must be initialized at power-on in a certain pattern; it is unknown why this would be important.

The MMC1 acts exactly as a stock SxROM. Fceu-mm contained "hacky hacky" logic to do a reset of sorts on the MMC1 whenever the low bit of $41xx's address was set, claiming it was necessary for SOMARI-W.

The C bit of the m116's control reg controls CHR ROM A18, which provides a CHR ROM base offset for the VRC2 and MMC3 modes. Whether and how this applies to the MMC1 mode has not been tested.