Time Synchronization Function

• MartyG

  • November 09, 2020 07:42
  • Edited

  Hi Shingo Ayabe

  The timestamp timings of RealSense camera sensors are generated as frame metadata attributes.  These can be produced by the camera firmware or by the host clock.  The links below describe how metadata is created.

  https://dev.intelrealsense.com/docs/frame-metadata 

  https://github.com/IntelRealSense/librealsense/issues/2188#issuecomment-409985803 

  RealSense also has a feature called External Synchronization (genlock) for external triggering control.

  https://www.intelrealsense.com/depth-camera-external-sync-trigger/ 

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• Shingo Ayabe

  • November 09, 2020 08:09

  Hi MartyG

  Thank you for your quick response!, and I understood that there are several timestamps in the frame metadata and they could be produced from the "Firmware Clock" in the RealSense and PC clock.

  I'd like to know when both of "Firmware Clock" and PC clock will be synchronized from each other.

  Is that at the moment of that the RealSense was connected to its host PC first?

  Or, are they always being synchronized during the RealSense is active from the host PC?

  Do we need to do specific configuration or something other things to keep both clocks always synchronized?

  It would be highly appreciated if you could give me further clarification.

   

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• MartyX Grover

  • November 09, 2020 12:32
  • Edited

  I apologise for the delay in responding further.   Metadata is not one of my specialist subjects, so I will refer you to the official documentation link below to ensure that you are provided with accurate information about when stamping begins.

  https://intelrealsense.github.io/librealsense/doxygen/classrs2_1_1frame.html#a25f71d45193f2f4d77960320276b83f1 

  In regard to syncing hardware and software timestamps, the difficulties of synching hardware timestamps with ones from the host clock are mentioned here:

  https://github.com/IntelRealSense/librealsense/issues/2188#issuecomment-417911161 

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• Shingo Ayabe

  • November 10, 2020 00:29

  Hi MartyG

  Thanks for providing me greatly useful information again!

  I understood it's very difficult to perfectly synchronize the device clock and the PC clock.

  But, I'm assuming slight time deviance between them is acceptable on my use cases this time.

  I'd be very happy if you could give me just one more clarification.

   

  The device clock and the PC clock is basically always synchronized automatically, it's not accurate though.

  Is this correct understanding?

   

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• MartyG

  • November 10, 2020 07:15

  Further research found that device time and system time are aligned when Global Time is enabled.  This function was introduced some months after the comment about the difficulties with clock sync was made.

  https://github.com/IntelRealSense/librealsense/pull/3909 

  https://github.com/IntelRealSense/librealsense/issues/4505#issuecomment-553590316 

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