Memory Mapper

CPU RAM Regions

MMIOAccess mmio;
StaticRAM  wram(128 * 1024);
StaticRAM  apuram(64 * 1024);
StaticRAM  vram(64 * 1024);
StaticRAM  oam(544);
StaticRAM  cgram(512);

Lo Rom

Cartridge::LoROM: 
map(MapLinear, 0x00, 0x7f, 0x8000, 0xffff, memory::cartrom);
map(MapLinear, 0x80, 0xff, 0x8000, 0xffff, memory::cartrom);
map_generic_sram();

Hi Rom

Cartridge::HiROM:
map(MapShadow, 0x00, 0x3f, 0x8000, 0xffff, memory::cartrom);
map(MapLinear, 0x40, 0x7f, 0x0000, 0xffff, memory::cartrom);
map(MapShadow, 0x80, 0xbf, 0x8000, 0xffff, memory::cartrom);
map(MapLinear, 0xc0, 0xff, 0x0000, 0xffff, memory::cartrom);
map_generic_sram();

Mapping Method

void Bus::map(
  MapMode mode,
  uint8  bank_lo, uint8  bank_hi,
  uint16 addr_lo, uint16 addr_hi,
  Memory &access, unsigned offset, unsigned size
) {
  assert(bank_lo <= bank_hi);
  assert(addr_lo <= addr_hi);

  if(access.size() == -1U) return;

  uint8 page_lo = addr_lo >> 8;
  uint8 page_hi = addr_hi >> 8;
  unsigned index = 0;

  switch(mode) {
    case MapDirect: {
      for(unsigned bank = bank_lo; bank <= bank_hi; bank++) {
        for(unsigned page = page_lo; page <= page_hi; page++) {
          map((bank << 16) + (page << 8), access, (bank << 16) + (page << 8));
        }
      }
    } break;

    case MapLinear: {
      for(unsigned bank = bank_lo; bank <= bank_hi; bank++) {
        for(unsigned page = page_lo; page <= page_hi; page++) {
          map((bank << 16) + (page << 8), access, mirror(offset + index, access.size()));
          index += 256;
          if(size) index %= size;
        }
      }
    } break;

    case MapShadow: {
      for(unsigned bank = bank_lo; bank <= bank_hi; bank++) {
        index += page_lo * 256;
        if(size) index %= size;

        for(unsigned page = page_lo; page <= page_hi; page++) {
          map((bank << 16) + (page << 8), access, mirror(offset + index, access.size()));
          index += 256;
          if(size) index %= size;
        }

        index += (255 - page_hi) * 256;
        if(size) index %= size;
      }
    } break;
  }
}
</pre>



#Sram Mapping
<pre>
void sBus::map_generic_sram() {

    if(memory::cartram.size() == 0 || memory::cartram.size() == -1U) { return; }
    map(MapLinear, 0x20, 0x3f, 0x6000, 0x7fff, memory::cartram);
    map(MapLinear, 0xa0, 0xbf, 0x6000, 0x7fff, memory::cartram);
 
    //research shows only games with very large ROM/RAM sizes require MAD-1 memory mapping of SRAM
    //otherwise, default to safer, larger SRAM address window
   uint16 addr_hi = (memory::cartrom.size() > 0x200000 || memory::cartram.size() > 32 * 1024) ? 0x7fff : 0xffff;
   map(MapLinear, 0x70, 0x7f, 0x0000, addr_hi, memory::cartram);
  if(cartridge.mapper() != Cartridge::LoROM) return;
  map(MapLinear, 0xf0, 0xff, 0x0000, addr_hi, memory::cartram);
}