>
> Laurent
>
> >
> > Hi Ravi,
> >
> > On Wednesday 27 March 2013 10:43:24 B, Ravi wrote:
> > > Hi
> > >
> > > I am observing issue while streaming video from usb camera connected
> to
> > host
> > > controller based on mentor graphics. The issue is root caused that
> there
> > > are huge SOF gaps seen between the two isochronous IN token issued by
> > host
> > > controller. This is due to fact, significant amount of time is spent
> in
> > uvc
> > > callback function handler. Due to this next request programmed is
> > delayed
> > > leads to this failure of video streaming. I have measured time taken
> by
> > uvc
> > > callback function is in range minimum of 11 microsecond to maximum of
> > 3318
> > > microsecond. Looks like callback handler doing some processing and
> > takes
> > > more time to return rather than giveback immediately. Need your help
> to
> > > understand why uvc callback handler takes much time, if it does any
> > > processing can it move to different task context and return
> immediately,
> > > this will reduce the latency.
> >
> > I'm surprised by that large delay. A quick look at the UVC URB
> completion
> > handler (I assume you're talking about the host driver, not the gadget
> > driver)
>
> Thanks for reply, Yes, I am using the musb host controller driver
> (driver/usb/musb).
>
> > doesn't show any significant source of delay. You will likely need to
> > profile
> > the code to find out where the problem comes from.
>
> I have profiled by adding timestamp before and after the
> usb_hcd_giveback_urb() @ drivers/usb/musb/musb_host.c and found the
> microsecond delay is ranging from 11usec to 3318usec while capturing video
> stream frames of resolution 640x480 from usb camera.
>
> static void musb_giveback(struct musb *musb, struct urb *urb, int status)
> __releases(musb->lock)
> __acquires(musb->lock)
> {
> + struct timeval st, et, t;
> + int is_isoc;
> .....
> + if (is_isoc)
> + do_gettimeofday(&st); /* get start time */
> usb_hcd_giveback_urb(musb_to_hcd(musb), urb, status);
> + if (is_isoc) {
> + do_gettimeofday(&et); /* get end time */
> + t.tv_sec = et.tv_sec - st.tv_sec;
> + t.tv_usec = et.tv_usec - st.tv_usec;
> + gtime[gIndex++ % MAX_LOG_TIME] = t; /* compute diff time
> */
> + }
>
> Anything I miss here?
>
> You should also make
> > sure
> > that no other IRQ handler on the system keeps IRQs disabled for a long
> > time.
Some more debugging, Most of the time spend in stream->decode() function in uvc_video_complete() callback handler.
--
Ravi B
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