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.

The record time is stored for each level as a 2-byte integer in big endian in units of hundredths of a second followed by two bytes of checksum. The checksum is computed as follows (where ^ is XOR):

record[2] = 0x55 ^ record[0];
record[3] = 0xFF ^ record[0] ^ record[1] ^ record[2];

For example, if the record value is 0x00E4554E, the time is 0x00E4 = 228 = 22.8 seconds.
Checksum verifies because 0x00 ^ 0x55 = 0x55, and 0xFF ^ 0x00 ^ 0xE4 ^ 0x55 = 0x4E

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.

// helper function for checksum update routine below
static u8 ComputeChecksumByte(u8 *data) // 80205760
{
   u8 cksum = 0;
   u8 key;
   for (int i = 0; i < 33; i++) {
      for (int j = 7; j >= 0; j--) {
         if (cksum & 0x80) {
            key = 0x85;
         } else {
            key = 0x00;
         }
         cksum = cksum << 1;
         if (i == 0x20) {
            cksum = cksum & 0xFF;
         } else {
            u8 mask = data[i] & (1 << j);
            u8 bit = mask ? 1 : 0;
            cksum |= bit;
         }
         cksum = cksum ^ key;
      }
   }
   return cksum;
}
 
// usually called with base address of EEPROM data and length = 0x100
// this will update checksum at eeprom[0x100 - 4]
u8 UpdateChecksum(u8 *eeprom, int length) // 801F2C84
{
   u8 cksum[4];
   int blocks = (length + 0x7F) >> 7;
   // zero out existing EEPROM checksum and local buffer
   for (int i = 0; i < 4; i++) {
      cksum[i] = 0;
      eeprom[length + i - 4] = 0;
   }
   if (blocks > 0) {
      for (int i = 0; i < blocks; i++) {
         for (int j = 0; j < 4; j++) {
            int offset = (i << 7) + (j << 5);
            if (offset < length) {
               u8 ckbyte = ComputeChecksumByte(eeprom + offset);
               cksum[j] += (ckbyte & 0xFF);
            }
         }
      }
   }
   // copy the checksum into the EEPROM data
   for (int i = 0; i < 4; i++) { // 801F2C84
      eeprom[length + i - 4] = cksum[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”