Re: USB2.0 [EHCI] Issue : EHCI interrupt endpoints transfer is taking above 600 microsec on USB 2.0 host

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On Tue, May 22, 2012 at 09:45:46AM +0530, Aman Bansal wrote:
> Dear Alan and Sarah,
> We have USB 2.0 embedded device as well as embedded USB 2.0 host.
> We have implemented a gadget driver on the device as well as USB client
> driver on host which uses interrupt endpoints for IN and OUT transfer.
> We are facing a problem with usb_submit_urb time taken for completion  on
> the interrupt end-point.
> In our implementation with EHCI controller and linux-3.0.20:
> The time interval on USB host between calling usb_submit_urb and its
> completion callback invocation on interrupt endpoints
> takes around 636 microseconds as compared to 28 microseconds for bulk
> endpoint.

What was the interval set to on the interrupt URB?

> Is there any timing issue with interrupt transfer in ehci host controller
> or some other aspect related to interrupt transfers?
> Is there any way I can improve interrupt transfer latency between my host
> and device ?

Have you looked at a bus trace of your host controller to see when it
actually sends the interrupt transfer and compared to the USB mon trace
of when it was submitted and completed?

Sarah Sharp
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