crc16

crc16.c

static uint16 crc16(uint16 crc, uint8 val) {
  const uint16 poly = 0x1021;
  uint8 cnt;

  for (cnt = 0; cnt < 8; cnt++, val <<= 1)
  {
    uint8 msb = (crc & 0x8000) ? 1 : 0;

    crc <<= 1;
    if (val & 0x80)  crc |= 0x0001;
    if (msb)         crc ^= poly;
  }

  return crc;
}

static uint16 crcCalc(uint8 *data, uint8 len) {
  uint16 crc = 0;
  for (uint8 idx = 0; idx < len; idx++) {
    crc = crc16(crc, data[idx]);
  }
 
  // IAR note explains that poly must be run with value zero for each byte of crc.
  crc = crc16(crc, 0);
  crc = crc16(crc, 0);

  return crc;
}