[Jetson Orin Camera] Why does TSC calibration need to be used to obtain the timestamp of GMSL Camera, while USB Camera does not need TSC calibration?

[deeptalkcamera]

Platform and hardware: Use the Jetson orin platform, connect D457 through GMSL or USB, and open the RGB camera.

Demo code for obtaining timestamp:

Abnormal and Issue：
When using GMSL to connect to the camera，“monotonic_time_ms” is DQBUF time, sensor “timestamp” is expected to be earlier than this time point. But the actual log shows that the value of “timestamp” is actually larger than the value of “monotonic_time_ms”. Obviously, this is a problem.
Based on this problem, I asked NV supporters and they gave me a solution, which requires TSC calibration:

clock_gettime() | NVIDIA Docs

However, when connected to USB, the timestamp itself is smaller than monotonic_time_ms, so TSC calibration is not required.

Therefore, we are curious about why the timestamps obtained by these two connection methods are different.

[ShaneCCC]

The GMSL camera is RCE firmware to assign the timestamp(TSC time) while receive SOF/EOF from sensor but USB camera is using the system time instead of RCE system time that’s why cause the different.

Thanks