USB driver, interrupt pipe

Discussion in 'Windows Vista Drivers' started by Alan, Jul 6, 2003.

  1. Alan

    Alan Guest

    how to handle polling interval which is defined in USB_ENDPOINT_DESCRIPTOR
    for interrupt pipe. Do I need set a timer for it?
    Alan, Jul 6, 2003
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  2. It is done by the host controller driver.
    Alexander Grigoriev, Jul 6, 2003
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  3. the actual polling is done by the host controller, but you will need the
    appropriate URB pended at the controller level for it to actually be able to
    read data from the device. Walter Oney's book goes into a good amount of
    detail as to what must be done.

    Doron Holan [MS], Jul 6, 2003
  4. Alan

    Tim Roberts Guest

    If I may offer one additional tidbit that isn't necessarily obvious at
    first glance...

    If there is no URB queued up in the host controller at the time your
    interrupt or isoch pipe's frame comes around, the host controller does not
    issue the IN or OUT token, so your device will not see any activity. When
    I started with USB, I assumed that the packets were being scheduled and
    transferred with the contents were dropped, but that is not the case.
    Tim Roberts, Jul 8, 2003
  5. Alan

    Martin Borve Guest

    Also note that the host controller driver may use a smaller period than
    specified in the endpoint descriptor, which is legal per the USB spec. For
    Windows, the max period will be 32 (micro)frames. On an ECHI controller
    the period may actually be changed to every frame for some devices, if
    there are a lot of devices that use interrupt endpoints attached to the

    Martin Borve
    Windows DDK Support

    This posting is provided "AS IS" with no warranties, and confers no rights.
    Martin Borve, Jul 23, 2003
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