Calculate FX3/CX3 latency in Video Streaming Design - KBA223271

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Question:

How can we roughly calculate the latency introduced by FX3/CX3 in the video streaming design?

 

Answer:
The latency can be estimated roughly using the information in the following table.

Device

MIPI Block

FX3 48KB Buffer Filling Time

USB (~ 300 MBps)

Total Latency

FX3

NA

614.4 µs

48KB/300=160 µs

774.4 µs

CX3

30us

614.4 µs

48KB/300=160 µs

804.4 µs

The results in this table are obtained based on the following:

  • CX3: input:1080p@30 fps, RAW10 output: USB3.0. The latency time is the time between the input and the output in this case.
  • FX3: input:1080p@30 fps, 32-bit parallel output: USB3.0. The latency time is the time between the input and the output in this case.

Note:

  1. We considered 1080p@30 fps for calculation in this case. Each line will take 33.33ms / 1080=30μs.  
  2. The number of lines for the 48-KB buffer should be (48*1024) / (1920*10/8) = 20.48
  3. Buffer filling time should be line time* No. of lines in a buffer =  30*20.48=614.4μs

For other resolutions, frame rates, and buffer size configuration, the results are different. However, it can be calculated in the same way as shown above.