Duplicate GTE Events on GPIO Rising Edge for Nvidia Jetson Orin Nano

Issue Overview

Users of the Nvidia Jetson Orin Nano development board are experiencing an issue where two Global Timer Events (GTE) are triggered on a single GPIO rising edge. This problem persists across different L4T (Linux for Tegra) versions, including L4T 35.4.1. The issue is critical for applications requiring precise time synchronization between the Jetson and other hardware components.

The duplicate events occur consistently when a GPIO rising edge is detected, potentially affecting the accuracy and reliability of time-sensitive operations. This problem impacts users who rely on GTE for accurate timestamping, particularly in scenarios where the Jetson needs to be synchronized with external devices.

Possible Causes

1. Hardware Timing Discrepancy: The GTE hardware module might be detecting the GPIO rising edge twice due to signal bouncing or internal timing issues.

2. Driver Implementation Bug: The Linux driver responsible for handling GTE events could be incorrectly processing or reporting the GPIO signals.

3. Firmware Misconfiguration: The Jetson’s firmware might be improperly configured, leading to duplicate event generation.

4. Software Race Condition: A race condition in the software stack could be causing the event to be registered twice.

5. GPIO Signal Instability: Electrical noise or signal instability on the GPIO line might be triggering multiple events.

Troubleshooting Steps, Solutions & Fixes

1. Verify Hardware Setup:

   • Ensure proper GPIO connections and use appropriate pull-up/pull-down resistors.
   • Check for any signal integrity issues using an oscilloscope if available.

2. Update L4T and Firmware:

   • Upgrade to the latest L4T version available for the Jetson Orin Nano.
   • Check for any firmware updates that might address GTE-related issues.

3. Implement Software Debouncing:

   • Add a software debounce mechanism to filter out duplicate events:

     import time
     
     last_event_time = 0
     debounce_interval = 0.01  # 10 ms
     
     def gte_event_handler():
         global last_event_time
         current_time = time.time()
         if current_time - last_event_time > debounce_interval:
             # Process the event
             last_event_time = current_time
     

4. Adjust GTE Configuration:

   • Review and modify GTE configuration parameters in the device tree or through sysfs interfaces.
   • Experiment with different sensitivity or threshold settings if available.

5. Kernel Debugging:

   • Enable kernel debugging for GTE and GPIO subsystems.
   • Analyze kernel logs to identify any anomalies in event handling:

     sudo dmesg | grep -i gte
     

6. Test with Different GPIO Pins:

   • Try using different GPIO pins to rule out pin-specific issues.
   • Document the behavior across various pins to identify any patterns.

7. Implement Event Filtering:

   • If software debouncing is not sufficient, implement a more sophisticated event filtering mechanism:

     from collections import deque
     import time
     
     event_queue = deque(maxlen=5)
     min_event_interval = 0.001  # 1 ms
     
     def process_gte_event():
         current_time = time.time()
         if event_queue and current_time - event_queue[-1] < min_event_interval:
             return  # Ignore the event if it's too close to the previous one
         event_queue.append(current_time)
         # Process the valid event
     

8. Consult Nvidia Developer Forums:

   • Post detailed information about the issue, including hardware setup, L4T version, and any debugging logs.
   • Engage with Nvidia developers for potential workarounds or upcoming fixes.

9. Evaluate Alternative Timekeeping Methods:

   • Consider using other hardware timers or synchronization methods if GTE continues to be unreliable.
   • Explore software-based synchronization techniques as a fallback.

10. Monitor Event Frequency:

    • Implement a monitoring system to track GTE event frequency and patterns:

      import time
      
      event_times = []
      monitoring_window = 60  # 60 seconds
      
      def log_gte_event():
          current_time = time.time()
          event_times.append(current_time)
          event_times = [t for t in event_times if current_time - t <= monitoring_window]
          print(f"Events in the last {monitoring_window} seconds: {len(event_times)}")
      

11. Report to Nvidia Support:

    • If the issue persists, compile a comprehensive report including:
      • Detailed hardware configuration
      • L4T version and any relevant software versions
      • Exact steps to reproduce the issue
      • Logs and debugging output
    • Submit the report to Nvidia support for further investigation and potential resolution in future updates.