only print CRC when it is wrong

firmware/rust1/src/rs485.rs

@@ -534,13 +534,14 @@ impl RS485 {
                             }
                             if let ModbusFrameLength::Length(x) = rx_expected_bytes {
                                 if x == rx_received_bytes {
-                                    let received_crc = rx_char_prev as u16 | ((rx_char as u16) << 8);
                                     let calculated_crc = rxcrc.finalize();
-                                    rxcrc = CRC.digest();
-                                    info!("received_crc: {:04x}, calculated_crc: {:04x}", received_crc, calculated_crc);
+                                    rxcrc = CRC.digest();  // re-init to placate borrow checker
+                                    const CORRECT_CRC: u16 = 0;  // because we include the CRC bytes in our calculation
+                                    if calculated_crc != CORRECT_CRC {
+                                        info!("CRC: {:04x} (should be zero)", calculated_crc);
+                                    }
 
                                     //FIXME In case of CRC mismatch, wait for gap/idle of >=1.5 chars.
-                                    const CORRECT_CRC: u16 = 0;  // because we include the CRC bytes in our calculation
                                     const OUR_ADDRESS: u8 = 1;
                                     if rxbuf[0] == OUR_ADDRESS && calculated_crc == CORRECT_CRC {
                                         txbuf.clear();