L515：can't get sensor_timestamp

[popsheng]

---

Required Info
Camera Model	L500
Firmware Version	05.12.10.00
Operating System & Version	Linux 18.04
Kernel Version (Linux Only)	5.4.0-62-generic
Platform	PC
SDK Version	2.41.0
Language	C++
Segment	SLAM

Issue Description

<Describe your issue / question / feature request / etc..>

Hi,
When I run realsense-viewer or rs-save-to-disk with L515, I can't obtain the sensor_timestamp, frame_timestamp can be obtained normally.

• D435i does not have this problem.
• I have patched the linux kernal according to the https://github.com/IntelRealSense/librealsense/blob/master/doc/installation.md

Here is my test code:

uint64_t sensor_timestamp = frame.get_frame_metadata(
     rs2_frame_metadata_value::RS2_FRAME_METADATA_FRAME_TIMESTAMP);

and the log is:

[ERROR] [1612419970.578703243]: An error has occurred during frame callback: metadata not available

Thinks.

[RealSenseSupport]

Hi @popsheng

We have documentation with regards to metadata, here are the links:
https://dev.intelrealsense.com/docs/frame-metadata
https://github.com/IntelRealSense/librealsense/blob/master/doc/frame_metadata.md

Timestamp information:

librealsense/include/librealsense2/hpp/rs_frame.hpp

Line 446 in 8fc9ad2

/**