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.
Regards
Ravi B
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