Hi,
Scenario:
I have an image sensor with USB highspeed capability which is sending data continuously to the host PC and has a break of sending data periodically for short duration. During this time, the device sends a NAK for the IN token received. In case of the break ,an USB3 xHCI has a way bigger polling delay ( 20 microsecond) than EHCI ( 2 microsecond) before issuing the next IN token.
The snapshot of USB traffic captured in XHCI is attached below. Note that it takes 20.650 microsecond to issue IN token ( packet 10) following NAK ( packet 9)
On the other hand, for EHCI, this delay is much lesser ( 2.184 microsecond) as shown below
I am using Intel XHCI 7 series