Unexpected TSC Values in Nvidia Jetson Orin Nano GTE

Issue Overview

Users of the Nvidia Jetson Orin Nano Dev board have reported issues related to unexpected values recorded by the General Timestamp Engine (GTE) during operation. The specific symptoms include:

• Erroneous timestamps: Users observe that the timestamps retrieved from the GTE FIFO do not align correctly with the actual timestamps from the Timestamp Counter (TSC), particularly when multiple events are processed.
• Context of occurrence: This issue primarily arises when the system is configured with an occupancy setting greater than one, leading to delays in reading the GTE FIFO.
• Hardware and software specifications: The problem has been noted in various configurations, particularly with Jetpack versions 5.1.2 and 6.0, and involves settings related to event handling and interrupt service routines (ISRs).
• Frequency: Reports indicate that this issue has persisted for several months, with users expressing frustration over the lack of resolution or updates from Nvidia.
• Impact on user experience: The inaccuracies in timestamping can lead to missed event samples, which significantly affects applications relying on precise timing, such as robotics or real-time data processing.

Possible Causes

Several potential causes for this issue have been identified:

• Hardware limitations: The GTE only records the lower 24 bits of the TSC in FIFO. When multiple events are processed, variations in high bits can lead to incorrect timestamps.
• Software bugs: There may be underlying bugs in how the GTE processes timestamps, particularly when handling multiple events or high occupancy settings.
• Configuration errors: Incorrect settings in the ISR or delays introduced in processing can exacerbate the problem, leading to missed timestamps.
• Driver issues: Outdated or incompatible drivers with specific Jetpack versions might contribute to inconsistencies in timestamp readings.
• User errors: Misconfigurations during setup or operation could lead to unexpected behavior.

Troubleshooting Steps, Solutions & Fixes

To address the issue of unexpected TSC values, users can follow these troubleshooting steps:

1. Verify Configuration Settings:

   • Ensure that occupancy is set to 1 during initial testing to confirm if the problem persists at this setting.

2. Check ISR Implementation:

   • Review and optimize ISR code to minimize delays. Ensure that timestamps are recorded promptly within the ISR.

3. Testing with Different Jetpack Versions:

   • If using Jetpack 6.0 or later, consider reverting to Jetpack 5.1.2 for testing purposes as some users reported fewer issues with earlier versions.

4. Log Analysis:

   • Collect logs from both GTE and TSC during operation to identify discrepancies.
   • Use commands such as dmesg or cat /proc/interrupts to gather relevant system information.

5. Adjust Timing Parameters:

   • Experiment with different timing parameters within your application to see if reducing delays improves timestamp accuracy.

6. Firmware Updates:

   • Check for any available firmware updates for both the Orin Nano and any connected peripherals that might affect performance.

7. Isolation Testing:

   • Test with minimal configurations (e.g., fewer events) to isolate whether the issue is related to system load or specific hardware interactions.

8. Documentation Review:

   • Refer to Nvidia’s official documentation for any notes on known issues or updates regarding GTE functionality.

9. Community Engagement:

   • Engage with community forums for shared experiences and solutions from other developers facing similar challenges.

10. Contact Nvidia Support:

    • If issues persist after following these steps, consider reaching out directly to Nvidia support for further assistance.

Code Snippet Example

To ensure proper timestamp recording within an ISR, a sample code snippet might look like this:

void myISR() {
    uint32_t tsc_value = read_tsc(); // Function to read TSC
    store_timestamp(tsc_value); // Store the timestamp for later use
}

Best Practices

• Regularly update your development environment and tools.
• Maintain clear documentation of your configurations and any changes made during troubleshooting.
• Share findings and solutions within community forums to assist others facing similar issues.

Unresolved Aspects

Despite ongoing investigations, some areas remain unresolved:

• The exact impact of different Jetpack versions on GTE functionality requires further testing.
• Specific hardware interactions that may lead to inconsistent behavior are still being explored by users and developers alike.