9 Replies Latest reply on Mar 19, 2014 7:39 AM by allan_intel

    Why does XHCI host controller take a lot of time compared to EHCI to issue an IN token to a device following a NAK?

    Mudabir_Kabir

      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)

      Untitled1.png

      On the other hand, for EHCI, this delay is much lesser ( 2.184 microsecond) as shown below

      Untitled2.png

       

      I am using Intel XHCI 7 series