USB driver, interrupt pipe

how to handle polling interval which is defined in USB_ENDPOINT_DESCRIPTOR
for interrupt pipe. Do I need set a timer for it?

 

It is done by the host controller driver.

 

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.

d

 

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.

 

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
controller.

Thanks,
Martin Borve
Windows DDK Support

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