Latency reduction for CSI/MIPI camera on Jetson Nano

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
1

Dear community,

I am using the following hardware configuration:

  • Jetson Nano with Jetpack 4.6
  • Arducam OV2311 connected via CSI/MIPI

After installing Arducam’s Jetvariety driver, I wrote a C++ program that reads the camera frames using Video4Linux (linux/videodev2.h). After configuring Video4Linux for low-latency (sudo v4l2-ctl -c low_latency_mode=1) I can reach the following “glass-to-software latencies” on average:

  • 15ms at 120fps (8.3ms per frame)
  • 22ms at 80fps (12.5ms per frame)
  • 26ms at 60fps (16.6ms per frame)

These measurements were done with an LED, the Nano’s GPIO, and an oscilloscope. This means there is a latency of more or less two frames between the LED and the C++ program. This observation matches the information I found in this forum and elsewhere on the web. It seems that the driver is buffering something here, although low-latency mode has been enabled.

The question is: (How) Is it possible to further reduce this latency to approximately one frame? The concrete use case is the creation of a camera-based control loop without additional dead time for various industrial use cases.

Thank you very much in advance!
Chris

3

Well, suppose it’s the best result from your result.

Thanks

4

Thank you for your reply. Do you mean that there is no chance for improvement here?

If that is the case, I would still like to understand, where this latency comes from. Because from my understanding, there is no technical reason for this. In other words: Why does the driver (or v4l2 or another component?) “hold back” the frame for the time of an additional frame? Or am I missing something?

Maybe someone here could point me in the right direction. Thanks!

5

Suppose the G2G need to consider the display latency.

6

There is no display latency. The chain looks like this:

LED - Camera - CSI/MIPI - Jetson Nano - C++ program - GPIO

7

Maybe confirm the SOF → EOF in vi2_fops.c to breakdown the latency.

9

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