Jetson Orin Nano SPI Communication Issues

Issue Overview

Users have reported issues with SPI communication on the Jetson Orin Nano Dev board, particularly when using similar code that worked without problems on the Jetson Nano. The primary symptoms include receiving garbage data during SPI reads, which correlates inconsistently with the expected incoming values. This problem occurs despite successful verification of SPI functionality through loopback tests and confirmed clock cycles during chip select (CS) assertions. Users have noted that specific SPI devices, such as the AD7927 ADC, require precise timing configurations, including MOSI alignment to the falling edge and reading MISO data on the rising edge.

The issue seems to manifest inconsistently, with some users successfully operating other SPI ports while encountering failures on specific ports under identical conditions. The impact on user experience is significant, as it hampers the expected functionality of applications relying on accurate data from SPI devices.

Possible Causes

1. Hardware Incompatibilities: Differences in hardware design between the Jetson Nano and Jetson Orin Nano could lead to timing discrepancies affecting SPI communication.
2. Software Bugs or Conflicts: Changes in driver implementations between different kernel versions may introduce bugs affecting how SPI transactions are handled.
3. Configuration Errors: Incorrectly set parameters in the device tree (DTB) or other configuration files can lead to improper functioning of SPI.
4. Driver Issues: Variations in driver behavior between the two platforms could cause differences in how data is transmitted and received.
5. Environmental Factors: Power supply variations or temperature fluctuations may affect signal integrity during communication.
6. User Errors or Misconfigurations: Misalignment of expected timing settings or improper initialization of SPI parameters can lead to unexpected behavior.

Troubleshooting Steps, Solutions & Fixes

1. Verify Device Tree Settings:

   • Check that the device tree settings for nvidia,rx-clk-tap-delay and nvidia,tx-clk-tap-delay are correctly configured for your specific setup.
   • Use the command:

     dtc -I fs -O dts -o extracted.dts /proc/device-tree
     

     to extract and verify current device tree settings.

2. Inspect Clock Signal Integrity:

   • Use an oscilloscope to analyze the SCLK signal from the Orin Nano compared to that from the Jetson Nano to identify any degradation or timing issues.

3. Adjust Timing Parameters:

   • Experiment with different values for nvidia,rx-clk-tap-delay and nvidia,tx-clk-tap-delay based on observations from successful configurations on Jetson Nano.
   • Example adjustments:

     nvidia,rx-clk-tap-delay = <0x07>;
     nvidia,tx-clk-tap-delay = <0x00>;
     

4. Check Power Supply:

   • Ensure that all components are receiving adequate power; use commands like:

     sudo busybox devmem 0x03230004
     

     to check power status at specified memory addresses.

5. Examine Data Transmission Order:

   • Inspect your code for any discrepancies in how data is being sent and received. For example, ensure that byte order is consistent across both platforms.
   • Adjust your code if necessary to swap bytes if you observe differences in behavior.

6. Test with Different Configurations:

   • Isolate the issue by testing with different SPI devices or configurations to determine if the problem is device-specific or configuration-related.

7. Driver Updates:

   • Ensure you are using the latest drivers compatible with your version of JetPack; consider rolling back to a previous version if instability persists.

8. Documentation and Community Support:

   • Refer to NVIDIA’s documentation for any updates regarding driver changes or known issues between Jetson Nano and Orin Nano.
   • Engage with community forums for additional insights or similar experiences shared by other users.

9. Log Analysis:

   • Collect logs using:

     dmesg > dmesg_log.txt
     

     Analyze these logs for any error messages related to SPI transactions.

10. Recompile with Debug Options (if necessary):

    • If issues persist, consider recompiling your kernel with debug options enabled to gather more detailed information about what might be going wrong during SPI transactions.

By following these steps, users should be able to diagnose and potentially resolve the issues they are experiencing with SPI communication on the Jetson Orin Nano Dev board.