33.3.2.5 UPDI Communication Error Handling

The UPDI contains a comprehensive error detection system that provides information to the debugger when recovering from an error scenario. The error detection consists of detecting physical transmission errors like start bit error, parity error, contention error, and frame error, to more high-level errors like access time-out error. See the PESIG bits in UPDI_STATUSB for an overview of the available error signatures.

Whenever the UPDI detects an error, it will immediately transfer to an internal error state to avoid unwanted system communication. In the error state, the UPDI will ignore all incoming data requests, except if a BREAK character is transmitted. The following procedure should always be applied when recovering from an error condition.
  • Send a BREAK character. See 33.3.1.2 BREAK Character for recommended BREAK character handling.
  • Send a SYNCH character at the desired baud rate for the next data transfer. Upon receiving a BREAK the UPDI oscillator setting in UPDI.ASI_CTRLA is reset to the 4 MHz default UPDI clock selection. This affects the baud rate range of the UPDI according to Table 33-2.
  • Do a Load Control Status (LDCS) to UPDI.STATUSB register to read the PESIG field. PESIG gives information about the occurred error, and the error signature will be cleared when read.
  • The UPDI is now recovered from the error state and ready to receive the next SYNCH character and instruction.