usb or video4linux problem

From: christophe barbé (christophe.barbe.ml@online.fr)
Date: Thu Jan 24 2002 - 22:28:57 EST

I send a mail few days ago about a problem with a usb webcam (Dlink
DCS100). I see the same thing with various webcam apps (gnomemeeting,
gqcam, camstream, xawtv, ...). So clearly it's not a user-level problem.
It can be a hardware one but i'm convinced it is not (or in the OHCI
chip in my toshiba satellite 2520cds).

With all app I can see the stream but suddenly it freezes.
Because of the following output from xawtv when the problem occurs:

v4l: timeout (got SIGALRM), hardware/driver problems?
ioctl: VIDIOCSYNC(0): Appel système interrompu

I have checked out the code and the interesting part in drv1-v4l.c is :

    alarms=0;
    alarm(SYNC_TIMEOUT);

 retry:
    if (-1 == (rc = xioctl(h->fd,VIDIOCSYNC,h->buf_v4l+frame))) {
   if (errno == EINTR && !alarms)
       goto retry;
    }

From which I conclude that SYNC_TIMEOUT could be to small. The value is
3 secondes which seems to be quite enough. To be sure I've tried with 30
and got the same thing.

So It's a justified timeout because the nextframe will never be there.
usbview sees the webcam before and after the problem.
Restarting the app is enough to get the stream.

I'm convinced that it's a problem with OHCI.
I think it's a soft problem because I can trigger it with cpu/io
activity.

What can I do to go further ?

Christophe 

-- 
Christophe Barbé <christophe.barbe@ufies.org>
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People that hate cats will come back as mice in their next life.
--Faith Resnick
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