Blast Corps uses a 512 byte EEPROM in the cartridge to save game state of levels unlocked, record times, and tutorials given. A copy of the EEPROM data is stored at 80364A40 in RAM.

There is a time recorded for each level as an 4-byte unsigned integer in big endian in units of 1/655360 of a second. To convert these values to seconds, divide the value by 655360. e.g., if the value is 0x00E4554E = 14964046, then 14964046/655360 = 22.8 seconds.

The 4-byte checksum at 0xFC is computed using functions that are stored in the hd_front_end_text.raw gzip file. The UpdateChecksum/801F2C84 function takes a pointer to the start of the EEPROM data in A0 and an offset to compute the checksum over and store result in A1. It uses helper function ComputeChecksumByte/80205760 to compute each round.

u8 ComputeChecksumByte(u8 *data) // 80205760
{
   u8 cksum = 0;
   u8 key;
   for (int i = 0; i < 33; i++) { // 80205760
      for (int j = 7; j >= 0; j--) { // 80205760
         if (cksum & 0x80) {
            key = 0x85;
         } else {
            key = 0x00;
         }
         cksum = cksum << 1;
         if (i == 0x20) {
            cksum = cksum & 0xFF;
         } else { // 80205760
            u8 mask = data[i] & (1 << j);
            u8 bit = mask ? 1 : 0;
            cksum |= bit;
         }
         cksum = cksum ^ key;
      }
   }
   return cksum;
}
 
u8 UpdateChecksum(u8 *eeprom, int length) // 801F2C84
{
   u8 buf[4]; // sp28-sp2B
   int blocks = (length + 0x7F) >> 7;
   // zero out existing EEPROM checksum and local buffer
   for (int i = 0; i < 4; i++) { // .Lproc_801F2C84_28: 801F2CAC
      buf[i] = 0;
      eeprom[length + i - 4] = buf[i];
   } // 801F2CE8
   if (blocks > 0) {
      for (int i = 0; i < blocks; i++) { //.Lproc_801F2C84_78:
         for (int j = 0; j < 4; j++) { //.Lproc_801F2C84_7C:
            int offset = (i << 7) + (j << 5);
            if (offset < length) {
               u8 cksum = ComputeChecksumByte(eeprom + offset);
               buf[j] += (cksum & 0xFF);
            }
         }
      }
   }
   // copy the checksum into the EEPROM data
   for (int i = 0; i < 4; i++) { // .Lproc_801F2C84_F8:
      eeprom[length + i - 4] = buf[i];
   }
   return 0;
}

The EEPROM functions are all stored in the hd_front_end_text.raw gzip file. In the (U) (1.0) ROM, these are inflated to 0x801E7000.

The EEPROM can be cleared by holding the 'Start' button while the during reset and startup of the game. You will then be prompted to “Erase Saved Game”