Compute a CRC-16/Modbus

main.dart

//import 'dart:ffi';

int crc16Modbus(List<int> bytes){
  const crc16 = 0xA001;
  int crc = 0xFFFF;

  if (false) {
    for (int pos = 0; pos < bytes.length; pos++) {
        crc ^= bytes[pos];     // XOR byte into least sig. byte of crc

        for (int i = 8; i != 0; i--) {     // Loop over each bit

            if ((crc & 0x0001) != 0) { // If the LSB is set
                crc >>= 1;             // Shift right and 
                crc ^= crc16;          // XOR 0xA001
            }
            else {                   // Else LSB is not set
              crc >>= 1;             // Just shift right
            }
         }
      }
  }
  else {
    for(int i=0;i<bytes.length;i++) {
      crc ^= bytes[i];
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
      crc = (crc>>1) ^ (crc16&-(crc&1));
    }
  }
  
  // swap CRC
  return (crc & 0xff) << 8 | crc >> 8;
}

final dalyBmsBleMessages = {
  0x80: "nominal capacity",
  0x81: "cell reference voltage",
  0x82: "boards count",
  0x83: "cell string count board 1",
  0x84: "cell string count board 2",
  0x85: "cell string count board 3",
  0x86: "temp sensors count board 1",
  0x87: "temp sensors count board 2",
  0x88: "temp sensors count board 3",
  0x89: "unknown",
  0x8A: "sleep after",
  0x8B: "cell protection overvoltage L1",
  0x8C: "cell protection overvoltage L2",
  0x8D: "cell protection undervoltage L1",
  0x8E: "cell protection undervoltage L2",
  0x8F: "battery overvoltage L1",
  
  0x90: "battery overvoltage L2",
  0x91: "battery undervoltage L1",
  0x92: "battery undervoltage L2",
  0x93: "battery discharging overcurrent L1",
  0x94: "battery discharging overcurrent L2",
  0x95: "battery charging overcurrent L1",
  0x96: "battery charging overcurrent L2",
  0x97: "battery charging temp too high L1",
  0x98: "battery charging temp too high L2",
  0x99: "battery charging temp too low  L1",
  0x9A: "battery charging temp too low  L2",
  0x9B: "battery discharging temp too high L1",
  0x9C: "battery discharging temp too high L2",
  0x9D: "battery discharging temp too low  L1",
  0x9E: "battery discharging temp too low  L2",
  0x9F: "cell voltage diff threshold alarm L1",
  
  0xA0: "cell voltage diff threshold alarm L2",
  0xA1: "temp sensor diff threshold alarm  L1",
  0xA2: "temp sensor diff threshold alarm  L2",
  0xA3: "cell voltage threshold at balancing is enable",
  0xA4: "voltage diff btw cells that is acceptable",
  0xA5: "rated capacity",
  0xA6: "unknown",
  0xA7: "setup SoC",
  0xA8: "temp MOS protection",
  0xA9: "unknown"
};

void main() {
  
  const table = [

    // == Writes
    
    // -- 8
    [0xd2, 0x06, 0x00, 0x80, 0x01, 0xF4, 0x9B, 0x96],
    [0xd2, 0x06, 0x00, 0x81, 0x0C, 0xB2, 0x4F, 0x34],
    [0xd2, 0x06, 0x00, 0x82, 0x00, 0x01, 0xFB, 0x81],
    [0xd2, 0x06, 0x00, 0x83, 0x00, 0x08, 0x6A, 0x47],
    [0xd2, 0x06, 0x00, 0x84, 0x00, 0x00, 0xDA, 0x40],
    [0xd2, 0x06, 0x00, 0x85, 0x00, 0x00, 0x8B, 0x80],
    [0xd2, 0x06, 0x00, 0x86, 0x00, 0x01, 0xBA, 0x40],
    [0xd2, 0x06, 0x00, 0x87, 0x00, 0x00, 0x2A, 0x40],
    [0xd2, 0x06, 0x00, 0x88, 0x00, 0x00, 0x1A, 0x43],
    // 89
    [0xd2, 0x06, 0x00, 0x8A, 0xFF, 0xFF, 0xBA, 0x33],
    // 8B
    [0xd2, 0x06, 0x00, 0x8C, 0x0E, 0x42, 0xDF, 0xD3],
    // 8D
    [0xd2, 0x06, 0x00, 0x8E, 0x07, 0xD0, 0xF9, 0xEE],
    // 8F
    
    // -- 9
    [0xd2, 0x06, 0x00, 0x90, 0x01, 0x2C, 0x9A, 0x09],
    // 91
    [0xd2, 0x06, 0x00, 0x92, 0x00, 0xA0, 0x3B, 0xFC],
    // 93
    [0xd2, 0x06, 0x00, 0x94, 0x72, 0x42, 0x7F, 0x14],
    // 95
    [0xd2, 0x06, 0x00, 0x96, 0x78, 0x1E, 0XD8, 0x4D],
    // 97
    [0xd2, 0x06, 0x00, 0x98, 0x00, 0x69, 0xDB, 0xA8],
    // 99
    [0xd2, 0x06, 0x00, 0x9A, 0x00, 0x1E, 0x3A, 0x4E],
    [0xd2, 0x06, 0x00, 0x9C, 0x00, 0x69, 0x9A, 0x69],
    // 9D
    [0xd2, 0x06, 0x00, 0x9E, 0x00, 0x0A, 0x7B, 0x80],
    // 9F
    
    // -- A
    [0xd2, 0x06, 0x00, 0xA0, 0x03, 0x20, 0x9B, 0x63],
    // A1
    [0xd2, 0x06, 0x00, 0xA2, 0x00, 0x0F, 0x7B, 0x8F],
    [0xd2, 0x06, 0x00, 0xA3, 0x0C, 0x1C, 0x6E, 0x82],
    [0xd2, 0x06, 0x00, 0xA4, 0x00, 0x32, 0x5A, 0x5F],
    // A5
    // A6
    [0xd2, 0x06, 0x00, 0xA7, 0x03, 0x81, 0xEB, 0x1A],
    [0xd2, 0x06, 0x00, 0xA8, 0x00, 0x57, 0x5A, 0x77],
    // A9, AA, AB, AC, AD, AE, AF
  ];
  
  for (final m in table) {
    final id = m[3];
    final readWrite = m[1] == 6 ? "write" : "read";
    final message = dalyBmsBleMessages[id] ?? "—";


    final write = m.sublist(0, m.length-2);
    final writeCrc = m.sublist(m.length-2);
    final transmitCrc = writeCrc[0]<<8|writeCrc[1];
    final computedCrc = crc16Modbus(write);
    final match = transmitCrc == computedCrc;
    
    print("$readWrite ${m.map((e) => e.toRadixString(16).padLeft(2,'0'))}| computed CRC: ${computedCrc.toRadixString(16).padLeft(2,'0')} ${match ? '🟢':'🔴 should be ${transmitCrc.toRadixString(16).padLeft(2,'0')}'} | $message");
  }
}