On Tuesday 28 July 2009 07:43:41 Rogier Wolff wrote:
> On Mon, Jul 27, 2009 at 04:49:14PM +0200, Laurent Pinchart wrote:
> > On Monday 27 July 2009 16:45:32 Rogier Wolff wrote:
> > > On Mon, Jul 27, 2009 at 04:34:19PM +0200, Laurent Pinchart wrote:
> > > > Could you load the driver with trace=255 and have a look at the
> > > > kernel log ? It might get pretty verbose.
> > >
> > > I can.
> > >
> > > Here is the log of the insmod. I'm not at the machine right now, so I
> > > can't expect the "live video" over the internet to work to my display
> > > here at work.
> >
> > It's the "live video" log that I'm interested in :-) Please send it when
> > you'll have physical access to your machine.
>
> Here is the rest:
>

[snip]
> <4>[52260.448521] VIDIOC_STREAMON<7>uvcvideo: uvc_v4l2_ioctl
> <4>[52260.451712] VIDIOC_DQBUF<7>uvcvideo: Dropping payload (error bit set).
> <7>[52260.941626] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941628] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941630] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941631] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941632] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941633] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941634] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941636] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941637] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941638] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941639] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941641] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941642] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941643] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941644] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941645] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941647] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941648] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941649] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941650] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941651] uvcvideo: Dropping payload (error bit set).
> <7>[52260.941653] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981622] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981624] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981625] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981627] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981628] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981629] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981630] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981632] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981633] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981634] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981635] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981637] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981638] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981639] uvcvideo: Dropping payload (error bit set).
> <7>[52260.981640] uvcvideo: Dropping payload (error bit set).
> <7>[52261.101630] uvcvideo: Frame complete (EOF found).
> <7>[52261.101641] uvcvideo: Dequeuing buffer 0 (3, 22930 bytes).
> <7>[52261.101702] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.101705] VIDIOC_QBUF<7>uvcvideo: Queuing buffer 0.
> <7>[52261.127126] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.127131] VIDIOC_DQBUF<7>uvcvideo: Frame complete (EOF found).
> <7>[52261.221642] uvcvideo: Dequeuing buffer 1 (3, 22682 bytes).
> <7>[52261.221688] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.221689] VIDIOC_QBUF<7>uvcvideo: Queuing buffer 1.
> <7>[52261.234064] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.234069] VIDIOC_DQBUF<7>uvcvideo: Frame complete (EOF found).
> <7>[52261.341653] uvcvideo: Dequeuing buffer 2 (3, 25734 bytes).
> <7>[52261.341711] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.341714] VIDIOC_QBUF<7>uvcvideo: Queuing buffer 2.
> <7>[52261.354175] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.354181] VIDIOC_DQBUF<7>uvcvideo: Frame complete (EOF found).
> <7>[52261.461651] uvcvideo: Dequeuing buffer 3 (3, 25702 bytes).
> <7>[52261.461702] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.461704] VIDIOC_QBUF<7>uvcvideo: Queuing buffer 3.
> <7>[52261.474363] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.474368] VIDIOC_DQBUF<7>uvcvideo: Frame complete (EOF found).
> <7>[52261.581655] uvcvideo: Dequeuing buffer 0 (3, 27500 bytes).
> <7>[52261.581705] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.581707] VIDIOC_QBUF<7>uvcvideo: Queuing buffer 0.
> <7>[52261.594133] uvcvideo: uvc_v4l2_ioctl
> <4>[52261.594139] VIDIOC_DQBUF<7>uvcvideo: Frame complete (EOF found).
> <7>[52261.701659] uvcvideo: Dequeuing buffer 1 (3, 27352 bytes).
> <7>[52261.701709] uvcvideo: uvc_v4l2_ioctl
> ...
> [ and this repeats. ]
> ...

I can't see anything wrong there. Video data is transferred from the webcam to 
the driver and then to the application. What exactly goes wrong on the 
application side ?

> <4>[52270.667558] VIDIOC_STREAMOFF<7>uvcvideo: uvc_v4l2_release
>
> What I don't understand is the 120ms interval between the buffers
> getting queued. I had expected 30ms intervals....

Not too surprising, most webcams have auto-exposure turned on by default and 
reduce the frame rate in low light conditions.

Regards,

Laurent Pinchart

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