What does "Data Fragment" mean in a USBVIDEO COMMIT packet?

asked 2022-11-10 14:04:31 +0000

jnagy gravatar image

I am trying to understand the streaming negotiation process between the host and a UVC camera but am seeing an element in the COMMIT packet of negotiation called "Data Fragment" in Wireshark and cannot find reference to this element in the USB 3.2 or UVC 1.5 specification. What does this "Data Fragment" represent? Looking at the negotiation of my webcam, it is 26 bytes long.

My understanding on the negotiation process is that the host will request a specific format and frame that is specified in the USB device's descriptors and then use GET MAX, GET MIN, and GET CUR to get the usable parameters of interfaces and entities before using a SET CUR to set a specific value. This culminates with a COMMIT request which signals the end of negotiation and configures the camera. For whatever values were set during negotiation. I don't see where a data chunk would fit into this process because the GET and SET requests are capable of configuring every element.


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