Jetson Orin Nano UART /dev/ttyTHS0 Not Working

Issue Overview

Users are experiencing issues with the UART communication on the Nvidia Jetson Orin Nano, specifically with the device node /dev/ttyTHS0. The primary symptoms include failure to establish a connection with external devices (e.g., Pixhawk PX4) and receiving error messages such as "Waiting for heartbeat from /dev/ttyTHS0" and "link 1 down" when attempting to run commands like mavproxy.py --master=/dev/ttyTHS0. This issue occurs during setup and when trying to communicate with connected peripherals.

The problem has been reported inconsistently, with some users able to connect via USB but not through UART, leading to interference with other functionalities like RC control. The issue seems prevalent across various JetPack versions, particularly after upgrades, raising concerns about software bugs or configuration errors. Users have also noted that while some configurations work intermittently, others result in complete communication failure.

Possible Causes

1. Hardware Incompatibilities or Defects: Issues could arise from faulty GPIO pins or incorrect wiring connections between the Jetson Orin Nano and external devices.
2. Software Bugs or Conflicts: Upgrades to JetPack versions (e.g., from 4.x to 5.x) may introduce bugs affecting UART functionality.
3. Configuration Errors: Incorrect settings in the device tree or pinmux configurations could prevent proper UART operation.
4. Driver Issues: Incompatibilities or bugs in the drivers associated with the UART interface may lead to communication failures.
5. Environmental Factors: Power supply issues or temperature fluctuations could affect UART performance.
6. User Errors or Misconfigurations: Incorrect baud rates, flow control settings, or service conflicts (e.g., nvgetty.service) may disrupt UART communication.

Troubleshooting Steps, Solutions & Fixes

1. Verify Connections:

   • Ensure correct wiring of TX, RX, and GND pins on the J12 header (Pin 8 for TX, Pin 10 for RX, Pin 9 for GND).
   • Check for loose connections or damaged cables.

2. Check Baud Rate Settings:

   • Confirm that the baud rate is set correctly in both your application and the Jetson settings (common rates include 115200 and 460800).
   • Use commands like stty -F /dev/ttyTHS0 115200 raw -echo to set baud rates.

3. Disable Conflicting Services:

   • Stop and disable the nvgetty.service which may occupy the UART port:

     sudo systemctl stop nvgetty.service
     sudo systemctl disable nvgetty.service
     

4. Test Loopback Functionality:

   • Short TXD/RXD pins on the expansion header and run:

     sudo su
     stty -F /dev/ttyTHS0 115200 raw -echo
     cat /dev/ttyTHS0 &
     echo "test" > /dev/ttyTHS0
     

   • If loopback works but external communication fails, focus on external device settings.

5. Update Firmware and Drivers:

   • Ensure that you are using the latest JetPack version that supports your hardware configuration.
   • Check for firmware updates related to USB and UART functionality.

6. Review Device Tree Settings:

   • Inspect device tree configurations for UART settings; ensure they match expected configurations for your hardware.
   • Use commands like dmesg | grep tty to check if /dev/ttyTHS0 is recognized correctly.

7. Monitor Serial Output:

   • Capture serial console logs for further diagnostics:

     sudo dmesg > dmesg.txt
     

   • Look for any error messages related to UART in the logs.

8. Check Software Dependencies:

   • Ensure that all required libraries and dependencies for your application (like mavproxy.py) are installed correctly.

9. Consider Environmental Factors:

   • Test in different environmental conditions (temperature, power supply stability) if issues persist.

10. Seek Further Assistance:

    • If problems remain unresolved after following these steps, consider posting detailed logs and descriptions of your setup on forums for community support.

By following these structured troubleshooting steps, users can systematically identify and resolve issues related to UART communication on the Nvidia Jetson Orin Nano.