bsnes/src/cartridge/header.cpp

#ifdef CARTRIDGE_CPP

void Cartridge::read_header(const uint8_t *data, unsigned size) {
  type        = TypeUnknown;
  mapper      = LoROM;
  dsp1_mapper = DSP1Unmapped;
  region      = NTSC;
  ram_size    = 0;

  has_bsx_slot   = false;
  has_superfx    = false;
  has_sa1        = false;
  has_srtc       = false;
  has_sdd1       = false;
  has_spc7110    = false;
  has_spc7110rtc = false;
  has_cx4        = false;
  has_dsp1       = false;
  has_dsp2       = false;
  has_dsp3       = false;
  has_dsp4       = false;
  has_obc1       = false;
  has_st010      = false;
  has_st011      = false;
  has_st018      = false;

  //=====================
  //detect Game Boy carts
  //=====================

  if(size >= 0x0140) {
    if(data[0x0104] == 0xce && data[0x0105] == 0xed && data[0x0106] == 0x66 && data[0x0107] == 0x66
    && data[0x0108] == 0xcc && data[0x0109] == 0x0d && data[0x010a] == 0x00 && data[0x010b] == 0x0b) {
      type = TypeGameBoy;
      return;
    }
  }

  const unsigned index = find_header(data, size);
  const uint8 mapperid = data[index + Mapper];
  const uint8 rom_type = data[index + RomType];
  const uint8 rom_size = data[index + RomSize];
  const uint8 company  = data[index + Company];
  const uint8 regionid = data[index + CartRegion] & 0x7f;

  ram_size = 1024 << (data[index + RamSize] & 7);
  if(ram_size == 1024) ram_size = 0;  //no RAM present

  //0, 1, 13 = NTSC; 2 - 12 = PAL
  region = (regionid <= 1 || regionid >= 13) ? NTSC : PAL;

  //=======================
  //detect BS-X flash carts
  //=======================

  if(data[index + 0x13] == 0x00 || data[index + 0x13] == 0xff) {
    if(data[index + 0x14] == 0x00) {
      const uint8_t n15 = data[index + 0x15];
      if(n15 == 0x00 || n15 == 0x80 || n15 == 0x84 || n15 == 0x9c || n15 == 0xbc || n15 == 0xfc) {
        if(data[index + 0x1a] == 0x33 || data[index + 0x1a] == 0xff) {
          type = TypeBsx;
          mapper = BSXROM;
          region = NTSC;  //BS-X only released in Japan
          return;
        }
      }
    }
  }

  //=========================
  //detect Sufami Turbo carts
  //=========================

  if(!memcmp(data, "BANDAI SFC-ADX", 14)) {
    if(!memcmp(data + 16, "SFC-ADX BACKUP", 14)) {
      type = TypeSufamiTurboBios;
    } else {
      type = TypeSufamiTurbo;
    }
    mapper = STROM;
    region = NTSC;  //Sufami Turbo only released in Japan
    return;         //RAM size handled outside this routine
  }

  //==========================
  //detect Super Game Boy BIOS
  //==========================

  if(!memcmp(data + index, "Super GAMEBOY2", 14)) {
    type = TypeSuperGameBoy2Bios;
    return;
  }

  if(!memcmp(data + index, "Super GAMEBOY", 13)) {
    type = TypeSuperGameBoy1Bios;
    return;
  }

  //=====================
  //detect standard carts
  //=====================

  //detect presence of BS-X flash cartridge connector (reads extended header information)
  if(data[index - 14] == 'Z') {
    if(data[index - 11] == 'J') {
      uint8 n13 = data[index - 13];
      if((n13 >= 'A' && n13 <= 'Z') || (n13 >= '0' && n13 <= '9')) {
        if(company == 0x33 || (data[index - 10] == 0x00 && data[index - 4] == 0x00)) {
          has_bsx_slot = true;
        }
      }
    }
  }

  if(has_bsx_slot) {
    if(!memcmp(data + index, "Satellaview BS-X     ", 21)) {
      //BS-X base cart
      type = TypeBsxBios;
      mapper = BSXROM;
      region = NTSC;  //BS-X only released in Japan
      return;         //RAM size handled internally by load_cart_bsx() -> BSXCart class
    } else {
      type = TypeBsxSlotted;
      mapper = (index == 0x7fc0 ? BSCLoROM : BSCHiROM);
      region = NTSC;  //BS-X slotted cartridges only released in Japan
    }
  } else {
    //standard cart
    type = TypeNormal;

    if(index == 0x7fc0 && size >= 0x401000) {
      mapper = ExLoROM;
    } else if(index == 0x7fc0 && mapperid == 0x32) {
      mapper = ExLoROM;
    } else if(index == 0x7fc0) {
      mapper = LoROM;
    } else if(index == 0xffc0) {
      mapper = HiROM;
    } else {  //index == 0x40ffc0
      mapper = ExHiROM;
    }
  }

  if(mapperid == 0x20 && (rom_type == 0x13 || rom_type == 0x14 || rom_type == 0x15 || rom_type == 0x1a)) {
    has_superfx = true;
    mapper = SuperFXROM;
    ram_size = 1024 << (data[index - 3] & 7);
    if(ram_size == 1024) ram_size = 0;
  }

  if(mapperid == 0x23 && (rom_type == 0x32 || rom_type == 0x34 || rom_type == 0x35)) {
    has_sa1 = true;
    mapper = SA1ROM;
  }

  if(mapperid == 0x35 && rom_type == 0x55) {
    has_srtc = true;
  }

  if(mapperid == 0x32 && (rom_type == 0x43 || rom_type == 0x45)) {
    has_sdd1 = true;
  }

  if(mapperid == 0x3a && (rom_type == 0xf5 || rom_type == 0xf9)) {
    has_spc7110 = true;
    has_spc7110rtc = (rom_type == 0xf9);
    mapper = SPC7110ROM;
  }

  if(mapperid == 0x20 && rom_type == 0xf3) {
    has_cx4 = true;
  }

  if((mapperid == 0x20 || mapperid == 0x21) && rom_type == 0x03) {
    has_dsp1 = true;
  }

  if(mapperid == 0x30 && rom_type == 0x05 && company != 0xb2) {
    has_dsp1 = true;
  }

  if(mapperid == 0x31 && (rom_type == 0x03 || rom_type == 0x05)) {
    has_dsp1 = true;
  }

  if(has_dsp1 == true) {
    if((mapperid & 0x2f) == 0x20 && size <= 0x100000) {
      dsp1_mapper = DSP1LoROM1MB;
    } else if((mapperid & 0x2f) == 0x20) {
      dsp1_mapper = DSP1LoROM2MB;
    } else if((mapperid & 0x2f) == 0x21) {
      dsp1_mapper = DSP1HiROM;
    }
  }

  if(mapperid == 0x20 && rom_type == 0x05) {
    has_dsp2 = true;
  }

  if(mapperid == 0x30 && rom_type == 0x05 && company == 0xb2) {
    has_dsp3 = true;
  }

  if(mapperid == 0x30 && rom_type == 0x03) {
    has_dsp4 = true;
  }

  if(mapperid == 0x30 && rom_type == 0x25) {
    has_obc1 = true;
  }

  if(mapperid == 0x30 && rom_type == 0xf6 && rom_size >= 10) {
    has_st010 = true;
  }

  if(mapperid == 0x30 && rom_type == 0xf6 && rom_size < 10) {
    has_st011 = true;
  }

  if(mapperid == 0x30 && rom_type == 0xf5) {
    has_st018 = true;
  }
}

unsigned Cartridge::find_header(const uint8_t *data, unsigned size) const {
  unsigned score_lo = score_header(data, size, 0x007fc0);
  unsigned score_hi = score_header(data, size, 0x00ffc0);
  unsigned score_ex = score_header(data, size, 0x40ffc0);
  if(score_ex) score_ex += 4;  //favor ExHiROM on images > 32mbits

  if(score_lo >= score_hi && score_lo >= score_ex) {
    return 0x007fc0;
  } else if(score_hi >= score_ex) {
    return 0x00ffc0;
  } else {
    return 0x40ffc0;
  }
}

unsigned Cartridge::score_header(const uint8_t *data, unsigned size, unsigned addr) const {
  if(size < addr + 64) return 0;  //image too small to contain header at this location?
  int score = 0;

  uint16 resetvector = data[addr + ResetVector] | (data[addr + ResetVector + 1] << 8);
  uint16 checksum    = data[addr + Checksum   ] | (data[addr + Checksum    + 1] << 8);
  uint16 complement  = data[addr + Complement ] | (data[addr + Complement  + 1] << 8);

  uint8 resetop = data[(addr & ~0x7fff) | (resetvector & 0x7fff)];  //first opcode executed upon reset
  uint8 mapper  = data[addr + Mapper] & ~0x10;                      //mask off irrelevent FastROM-capable bit

  //$00:[000-7fff] contains uninitialized RAM and MMIO.
  //reset vector must point to ROM at $00:[8000-ffff] to be considered valid.
  if(resetvector < 0x8000) return 0;

  //some images duplicate the header in multiple locations, and others have completely
  //invalid header information that cannot be relied upon.
  //below code will analyze the first opcode executed at the specified reset vector to
  //determine the probability that this is the correct header.

  //most likely opcodes
  if(resetop == 0x78  //sei
  || resetop == 0x18  //clc (clc; xce)
  || resetop == 0x38  //sec (sec; xce)
  || resetop == 0x9c  //stz $nnnn (stz $4200)
  || resetop == 0x4c  //jmp $nnnn
  || resetop == 0x5c  //jml $nnnnnn
  ) score += 8;

  //plausible opcodes
  if(resetop == 0xc2  //rep #$nn
  || resetop == 0xe2  //sep #$nn
  || resetop == 0xad  //lda $nnnn
  || resetop == 0xae  //ldx $nnnn
  || resetop == 0xac  //ldy $nnnn
  || resetop == 0xaf  //lda $nnnnnn
  || resetop == 0xa9  //lda #$nn
  || resetop == 0xa2  //ldx #$nn
  || resetop == 0xa0  //ldy #$nn
  || resetop == 0x20  //jsr $nnnn
  || resetop == 0x22  //jsl $nnnnnn
  ) score += 4;

  //implausible opcodes
  if(resetop == 0x40  //rti
  || resetop == 0x60  //rts
  || resetop == 0x6b  //rtl
  || resetop == 0xcd  //cmp $nnnn
  || resetop == 0xec  //cpx $nnnn
  || resetop == 0xcc  //cpy $nnnn
  ) score -= 4;

  //least likely opcodes
  if(resetop == 0x00  //brk #$nn
  || resetop == 0x02  //cop #$nn
  || resetop == 0xdb  //stp
  || resetop == 0x42  //wdm
  || resetop == 0xff  //sbc $nnnnnn,x
  ) score -= 8;

  //at times, both the header and reset vector's first opcode will match ...
  //fallback and rely on info validity in these cases to determine more likely header.

  //a valid checksum is the biggest indicator of a valid header.
  if((checksum + complement) == 0xffff && (checksum != 0) && (complement != 0)) score += 4;

  if(addr == 0x007fc0 && mapper == 0x20) score += 2;  //0x20 is usually LoROM
  if(addr == 0x00ffc0 && mapper == 0x21) score += 2;  //0x21 is usually HiROM
  if(addr == 0x007fc0 && mapper == 0x22) score += 2;  //0x22 is usually ExLoROM
  if(addr == 0x40ffc0 && mapper == 0x25) score += 2;  //0x25 is usually ExHiROM

  if(data[addr + Company] == 0x33) score += 2;        //0x33 indicates extended header
  if(data[addr + RomType] < 0x08) score++;
  if(data[addr + RomSize] < 0x10) score++;
  if(data[addr + RamSize] < 0x08) score++;
  if(data[addr + CartRegion] < 14) score++;

  if(score < 0) score = 0;
  return score;
}

#endif