UART1 Flow Control Issues on Nvidia Jetson Orin Nano Dev Board

Issue Overview

Users are experiencing issues with the flow control functionality of UART1 on the Nvidia Jetson Orin Nano Dev board. Specifically, UART1 is failing to transmit and receive data, while UART0 operates without problems. The issue arises when users attempt to implement hardware flow control on UART1, configured similarly to UART0. The symptoms include incorrect data transmission and reception, particularly when using specific testing tools like picocom and linux-serial-test. The problem is consistent across different setups, indicating a potential underlying issue with the Nvidia serial driver (serial-tegra.c) or the hardware configuration.

Context

• Symptoms: UART1 does not transmit or receive data; incorrect bytes received when tested.
• Environment: Users tested with L4T version r35.3.1 and various configurations, including custom carrier boards.
• Hardware/Software: Involves pinmux configurations for UART pins and testing with tools like picocom and linux-serial-test.
• Frequency: The issue is reported consistently by multiple users.
• Impact: This affects the ability to use UART1 for communication, particularly in applications requiring reliable flow control.

Possible Causes

1. Hardware Configuration Errors: Incorrect pinmux settings or GPIO configurations may lead to improper operation of UART1.

   • Explanation: If the pin settings for UART1 are not correctly configured, it can prevent proper data transmission.

2. Driver Issues: Potential bugs in the Nvidia serial driver (serial-tegra.c) may cause flow control features to malfunction.

   • Explanation: If the driver does not handle flow control signals correctly, it can lead to data loss or corruption.

3. Software Bugs or Conflicts: Conflicts between different software tools used for testing may result in erroneous outputs.

   • Explanation: Inconsistent behavior across different testing tools might indicate compatibility issues.

4. Environmental Factors: Power supply issues or temperature variations could impact UART performance.

   • Explanation: Insufficient power or overheating can affect the reliability of serial communication.

5. User Errors: Misconfigurations by users in setting up the hardware or software environment.

   • Explanation: Users may overlook specific settings required for proper operation.

Troubleshooting Steps, Solutions & Fixes

Step-by-Step Instructions

1. Verify Pinmux Configuration:

   • Ensure that the pinmux settings for UART1 are correctly set according to specifications. Compare them with working configurations of UART0.

2. Testing Commands:
   Use the following commands to test UART communication:

   # On Orin Nano
   sudo picocom -b 115200 /dev/ttyTHS0 -f h
   
   # On PC
   sudo picocom -b 115200 /dev/ttyUSB0 -f h
   

3. Check Device Mapping:
   Confirm that you are using the correct device files:

   • UART0 should be /dev/ttyTHS1
   • UART1 should be /dev/ttyTHS0

4. Run Loopback Tests:
   Perform loopback tests without enabling hardware flow control to isolate whether the issue is related to flow control settings.

5. Use Alternative Testing Tools:
   If picocom does not yield reliable results, try using minicom or other serial communication tools to verify data integrity.

6. Patch Application:
   Consider applying any patches mentioned in forum discussions that may address known issues with UART functionality:

   # Example command to apply a patch (ensure you have the correct patch file)
   sudo patch < path_to_patch_file.patch
   

7. Monitor GPIO States:
   For RS485 communication, manage GPIO states manually to switch between RX and TX modes if necessary:

   # Set GPIO for RX mode
   echo 0 > /sys/class/gpio/PCC.00/value
   
   # Set GPIO for TX mode
   echo 1 > /sys/class/gpio/PCC.00/value
   

8. Consult Documentation & Updates:
   Regularly check Nvidia’s documentation and forums for updates regarding JetPack versions and known issues related to UART functionality.

Recommended Approaches

• Multiple users reported success using minicom as an alternative tool for testing serial communication.
• Keep an eye on upcoming JetPack releases (e.g., JP6) which may include fixes for these issues.

Unresolved Aspects

• Users are still seeking clarification on whether a specific patch can be applied for JetPack 5.1.1 to resolve these UART issues.
• Further investigation into the behavior of the Nvidia serial driver is needed, particularly concerning flow control functionality.

By following these steps and utilizing community resources, users can better diagnose and potentially resolve their UART1 flow control issues on the Nvidia Jetson Orin Nano Dev board.