[NES] Added support for MMC4 (mapper 10)

[Molorius]

Tested on an English patched "Fire Emblem (J).nes". I didn't test this very much, but there are no visible problems in the first area of the game.

[OtherCrashOverride]

I will review and test it. The commit message should start with the system name "[NES]".

[OtherCrashOverride]

Looks good. I can take the patch as-is and add bitmasks to the map10_write (0x0f and 0x1f masks) later or you can include them in this pull request. Let me know which is preferred.

[edit] BTW, the pull request topic doesn't matter. Its the actual commit message in the pull request that should start with "[NES]".

[Molorius]

I don't see where the bitmasks need to be applied, but feel free to add them.

My mistake, the commit message is now properly edited.

[OtherCrashOverride]

For future reference, this how I think it should be based on: https://wiki.nesdev.com/w/index.php/MMC4

/* Used when tile $FD/$FE is accessed */
static void mmc10_latchfunc(uint32 address, uint8 value)
{
   if (0xFD == value || 0xFE == value)
   {
        if (!address)
        {
            latch[0] = value;
            mmc_bankvrom(4, 0x0000, regs[value == 0xfd ? 0 : 1]);
        }
        else
        {
            latch[1] = value;
            mmc_bankvrom(4, 0x1000, regs[value == 0xfd ? 2 : 3]);
        }
   }
}

/* mapper 10: MMC4 */
/* MMC4: Fire Emblem */
static void map10_write(uint32 address, uint8 value)
{
   switch ((address & 0xF000) >> 12)
   {
   case 0xA:
      mmc_bankrom(16, 0x8000, value & 0x0f);
      break;

   case 0xB:
      regs[0] = value & 0x1f;
      //if (0xFD == latch[0])
         mmc_bankvrom(4, 0x0000, regs[0]);
      break;

   case 0xC:
      regs[1] = value & 0x1f;
      //if (0xFE == latch[0])
         mmc_bankvrom(4, 0x0000, regs[1]);
      break;

   case 0xD:
      regs[2] = value & 0x1f;
      //if (0xFD == latch[1])
         mmc_bankvrom(4, 0x1000, regs[2]);
      break;

   case 0xE:
      regs[3] = value & 0x1f;
      //if (0xFE == latch[1])
         mmc_bankvrom(4, 0x1000, regs[3]);
      break;

   case 0xF:
      if (value & 1)
         ppu_mirror(0, 0, 1, 1); /* horizontal */
      else
         ppu_mirror(0, 1, 0, 1); /* vertical */
      break;

   default:
      break;
   }
}

There are only 3 games using this mapper: http://bootgod.dyndns.org:7777/search.php?ines=10

I will just include the patch as-is and others can refer back to this info.