Calculation of pixel_clk_hz for device tree

Issue Overview

Users are experiencing confusion regarding the calculation of the pixel_clk_hz for the Nvidia Jetson Orin Nano Dev board when dealing with MIPI frames that include both RAW12 and EMB formats. The specific symptoms include uncertainty about which bits per pixel (bpp) value to use in the calculation when a MIPI frame contains both active pixels (RAW12 with bpp=12) and meta lines (EMB with bpp=8). This issue arises during the configuration of camera sensors within the device tree.

The context of the problem occurs primarily during setup and configuration phases, particularly when users are attempting to integrate camera sensors that utilize different pixel formats. The hardware in question is the Nvidia Jetson Orin Nano Dev board, and the software context involves device tree configurations. The frequency of this issue seems to vary, as it depends on individual user setups and their specific sensor configurations.

This confusion can significantly impact user experience by leading to incorrect configurations, potentially resulting in suboptimal camera performance or failure to initialize the camera correctly.

Possible Causes

• Misunderstanding of Pixel Formats: Users may not fully understand how to interpret the pixel formats (RAW12 vs. EMB) and their implications for clock calculations.

• Incorrect Calculation Method: There may be ambiguity in determining which bpp value to use when both formats are present in a MIPI frame.

• Lack of Documentation: Insufficient clarity in existing documentation regarding multi-format MIPI frames could lead to miscalculations.

• Configuration Errors: Users might incorrectly configure their device trees based on incorrect assumptions about pixel clock calculations.

Troubleshooting Steps, Solutions & Fixes

1. Understand the Calculation Formula:

   • The formula for calculating pixel_clk_hz is:
     $$ \text{pixel_clk_hz} = \text{sensor data rate per lane (Mbps)} \times \text{number of lanes} / \text{bits per pixel} $$

2. Identify the Correct bpp Value:

   • When encountering a MIPI frame containing both RAW12 and EMB, it is recommended to use 12 as the bpp value for calculations, as confirmed by user feedback in the forum discussion.

3. Verify Sensor Data Rate and Lanes:

   • Ensure that you have accurate values for sensor data rate per lane and the number of lanes being used. This information is typically found in the sensor’s datasheet.

4. Test Configuration:

   • After calculating pixel_clk_hz, update your device tree configuration accordingly.
   • Run tests to verify that the camera initializes correctly and operates as expected.

5. Consult Documentation:

   • Refer to Nvidia’s official documentation on camera development for further details on sensor software driver programming.

6. Use Terminal Commands for Debugging:

   • Utilize terminal commands to gather system information about connected devices and their configurations. For example:

     dmesg | grep -i mipi
     

   • This command can help identify if there are any errors related to MIPI devices during boot.

7. Best Practices:

   • Always double-check your calculations and configurations against multiple sources.
   • Engage with community forums or support channels if uncertainties persist, as peer insights can be valuable.

8. Unresolved Aspects:

   • Further investigation may be needed regarding how different sensor configurations might affect clock calculations in more complex setups.
   • Users may benefit from additional examples or case studies illustrating successful implementations involving mixed pixel formats.