Anyone else's UART RX (serial input) stopped working? - Printable Version

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Anyone else's UART RX (serial input) stopped working? - pion - 03-23-2022

I installed and was happily running OpenBSD on my RockPro64 v2.1 for many months. At some point I needed to wipe and reinstall everything. When I attached the serial console as usual, I realized that I was only ever able to get serial output FROM the board, but was no longer ever able to send any serial TO the board.

I have performed all of the expected troubleshooting steps many, many times to figure out what the heck I'm doing wrong:
  • rechecked TX, RX, and GND connections
  • rechecked serial terminal baudrate and settings (correct because I'm getting good serial output)
  • swapped out different FTDI USB-serial cables
  • confirmed I was able to use the same FTDI cable to send and receive on a different SBC
  • connected both TX and RX lines to an oscilloscope (with serial decoding) to monitor that I was, indeed, sending and receiving valid serial data to/from the board

At this point I'm starting to think that I must either have inadvertently shorted the UART RX pin to something bad and blown the OC/OV/ESD protection in the silicon, or maybe there is even a manufacturing defect.

As my next debugging step I was going to start writing firmware to manually read the RX pin and see if it picks up signal changes, but I wanted to check with folks here and see if anyone has encountered this and/or if someone can suggest an easier debugging strategy.

Thanks much!

RE: Anyone else's UART RX (serial input) stopped working? - foresto - 04-07-2022

Could it be that the RockPro64's unusually high default bit rate is a little too fast for the UART you're using to handle reliably?

Could it be that you need a shorter (or otherwise better) serial cable to handle such a high speed?

I wouldn't expect either of those situations to cause trouble in only one direction, but you never know. It might be worth configuring the serial port for 19200 just to see if it helps. I had to do that until I bought a more expensive serial/USB adapter.