Latency OAK-D-FFC USB vs OAK-D-CM4 Ethernet

Matthieu

Hello,

We are using a OAK-D-FFC board to stream depth and multiple 1080p H264 videos using the USB 3.1 port to our main computer.

We have other constraints what could be solved by using an OAK-D-CM4 like design. In that case, we would use the RPI ethernet port for connexion to stream video flux from the camera to the main computer.

However I'm a bit concerned by the potential additionnal delay it can bring.

Solution 1: camera ==FFC=> Oak-D ==USB 3.1==> main compter

Solution 2: camera ==FFC-like==> Oak-D ==???==> RPI ==Ethernet==> main computer

As we are doing mobile robotics, delay is very critical and we have to keep as small as possible. I guess the solution 2 is worst but I don't know if that's a significant difference (i.e adding >1ms delay).

Do you have information or at least a gut feeling to share about that ?

Thanks

jakaskerl

Hi Matthieu
I'd always suggest using USB over Ethernet for OAK devices since it has much higher bandwidth and lower latency. Solution 2 will have a higher latency since you are counting on RPI to process encoded streams fast enough. The CM4 is mainly designed to run in standalone mode - which is good for your application if you discard the main computer part and do decision making on the RPI.
If you really need to view (and process?) data on the main PC as well then I suggest going for a standard POE models without a raspberry pi.

Thanks,
Jaka

Matthieu

Thanks for your answser, that's pretty clear.

Just to let you know, I'm considering a CM4 not because we need ethernet but rather because we need additional GPIO. But maybe there is a few of them accessible directly from the OAK module or board ?

jakaskerl

Hi Matthieu
In that case, CM4 is clearly better. And if you intend to run processing on the cm4, that's fine. You can then display the frames on the host machine as well, but they will likely have delay.

Thanks,
Jaka