crc = modbus_serial_rtu_crc(0xFFFF, &slave_addr, sizeof(slave_addr));
crc = modbus_serial_rtu_crc(crc, buffer, buffer_size);
result = serial_write_blocking(serial, &crc, sizeof(crc), 0);
if (result < 0)
crc = modbus_serial_rtu_crc(0xFFFF, &slave_addr, sizeof(slave_addr));
crc = modbus_serial_rtu_crc(crc, buffer, buffer_size);
result = serial_write_blocking(serial, &crc, sizeof(crc), 0);
if (result < 0)