Debugging Serial Communication on Jetson Orin Nano Developer Kit

Issue Overview

Users are experiencing difficulties when attempting to establish and debug a serial connection between a Jetson Orin Nano Developer Kit and a custom microcontroller. The primary symptoms include:

• Inability to read data from the serial port using standard commands like cat < /dev/ttyTHS0
• Confusion about which UART interface to use (/dev/ttyTHS0 vs /dev/ttyS0)
• Input/output errors when trying to interact with /dev/ttyS0
• Uncertainty about the functionality of echo and cat commands on DMA-enabled UARTs

The issue occurs during the setup and testing of serial communication, impacting the ability to send and receive data between the Jetson Orin Nano and the connected microcontroller.

Possible Causes

1. Incorrect UART interface selection: Using the wrong UART port for the intended connection can lead to communication failures.

2. Ground connection issues: Poor or missing ground connections between devices can cause communication problems.

3. DMA (Direct Memory Access) complications: The presence of DMA on certain UART interfaces may affect traditional debugging methods.

4. Driver incompatibilities: The use of different drivers (e.g., 8250 driver for /dev/ttyS0) may cause unexpected behavior.

5. Incorrect pin connections: Connecting to the wrong pins on the Developer Kit can result in communication failures.

6. Baud rate mismatches: Inconsistent baud rate settings between the Jetson and the microcontroller can prevent successful communication.

Troubleshooting Steps, Solutions & Fixes

1. Verify UART interface selection:

   • For the Jetson Orin Nano Developer Kit, use /dev/ttyTHS0 (UART1) for connections via pins 22 and 32.
   • UART0 is associated with the M.2 Key E connector, not the standard GPIO pins.

2. Check ground connections:

   • Ensure a proper ground connection between the Jetson Orin Nano and the microcontroller.
   • A faulty ground connection can cause communication issues even with correct TX/RX connections.

3. Set up the serial connection:
   Configure the UART interface with the correct parameters:

   stty -F /dev/ttyTHS0 115200 -parity cs8 -cstopb
   

4. Test basic communication:
   Use a simple echo loop to send data:

   while true; do
     echo -e "#something#something\r\n" >> /dev/ttyTHS0
     sleep 1
   done
   

5. Read incoming data:
   Use the cat command to read from the UART:

   cat < /dev/ttyTHS0
   

   Note: This method works for DMA-enabled UARTs on the Jetson Orin Nano.

6. Implement loopback testing:

   • Configure the microcontroller to echo back received data.
   • This helps isolate issues between the Jetson and the microcontroller.

7. Verify pin connections:

   • For UART1 (ttyTHS0), use pin 22 (TX) and pin 32 (RX) on the Jetson Orin Nano Developer Kit.
   • Double-check the pinout in the Developer Kit documentation.

8. Investigate /dev/ttyS0 issues:

   • If encountering Input/output errors with /dev/ttyS0, focus on using /dev/ttyTHS0 instead.
   • The /dev/ttyS0 interface uses a different driver (8250) and may not be suitable for all use cases.

9. Gather system information:
   Run the following command and share the output for further analysis:

   dmesg > dmesg_output.txt
   

10. Check UART mapping:
    Refer to the UART interface mapping for the Orin Nano Developer Kit in the following thread:
    OrinNX : How to check UART is working? – #3 by KevinFFF 18

11. Consider use case requirements:

    • If debugging messages need to be output from UART1 (uarta@3100000), ensure you’re using the correct interface and configuration.
    • Tailor your approach based on whether you need simple debugging or full-featured serial communication.

By following these steps and considering the possible causes, you should be able to establish and debug the serial connection between your Jetson Orin Nano Developer Kit and the custom microcontroller successfully.