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Re: [pwc] Frame buffer underflow

To: Philips Webcam Linux Driver <>
Subject: Re: [pwc] Frame buffer underflow
From: Andrew Cavers <>
Date: Thu, 7 Jul 2005 08:56:57 +0100
List,

Not sure if anybody else here uses PD/PDP/PiDiP software, but if you
do, the fix below will get your pwc webcam working with it. The
problem was that PDP used features very specific to the old pwc/pwcx
driver and was broken with Luc's driver. The changes below basically
edit out all of the pwc-specific stuff and allow PDP to access the
camera like any other.

1. Download the PDP 0.12.4 source from
http://zwizwa.fartit.com/pd/pdp/pdp-0.12.4.tar.gz

2. In the modules/image_io/pdp_v4l.c file, change the following:
 - Comment out (by adding // to the start of the line) lines 49-52,
188-247 and 488-489.
 - Edit lines 781 and 782 with your preferred default width and
height. I don't think you'll need to change this but I only want to
use 160x120.

3. ./configure (with any options); make; make install

Hope this helps some people.

Andrew.

On 7/5/05, Andrew Cavers <> wrote:
> I've been having a similar problem with buffer underflow errors with
> 10.0.7a and 2.6.12 too. The camera works perfectly (apart from the
> colour issues mentioned in another thread) using a program such as
> mplayer to access the stream. However, when I try to access the device
> using Puredata with the PDP plugin, I get the black screen/buffer
> underflow errors.
>
> I posted a message to the Puredata list regarding this issue (thinking
> it was a PDP problem) and someone suggested I revert to the pwc/pwcx
> drivers as they had also been having problems with the new drivers
> from within PD. I'd rather not use the old drivers, but if it solves
> the problem, it solves the problem! I'll report back once I've tried
> that this evening.
>
> Puredata seems to force the camera to run at 320x240 @ 27fps - this
> seems to be at the very limit of what the USB bus can support -
> perhaps this is the root of my problem?
>
> Andrew.
>
> On 7/5/05, Krzysztof Kowalczyk <> wrote:
> > On Tue, Jul 05, 2005 at 01:12:18PM +0200, Luc Saillard wrote:
> > > On Mon, Jul 04, 2005 at 02:01:34PM +0200, Krzysztof Kowalczyk wrote:
> > > > Hi,
> > > > I've tried philips pcvc680k with kernel 2.6.12.2
> > > > and also with 2.6.12.2 with module compiled from pwc-10.0.7a.tar.bz2
> > > > and I've got lots of messages:
> > > >  kernel: pwc Frame buffer underflow (XXXX bytes); discarded.
> > > > with XXXX depending on resolution.
> > > >
> > >
> > > Can you try another application like xawtv ?
> > I've checked with xawtv and got same problems, black image and lots of
> > buffer underflow messages. But additionally I have some output from
> > xawtv:
> >
> > This is xawtv-3.94, running on Linux/i686 (2.6.12.2n)
> > /dev/video0 [v4l2]: no overlay support
> > v4l-conf had some trouble, trying to continue anyway
> > ioctl: VIDIOC_G_STD(std=0xb7f2643cbfc2ed20
> > [PAL_D,PAL_M,PAL_Nc,PAL_60,NTSC_M_JP,?,?,SECAM_D,SECAM_L,?ATSC_8_VSB,ATSC_16_VSB,(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null)]):
> > Invalid argument
> > ioctl: VIDIOC_G_CTRL(id=9963778;value=134558539): Invalid argument
> > ioctl: VIDIOC_S_CTRL(id=9963778;value=134558539): Invalid argument
> > ioctl: VIDIOC_S_CTRL(id=9963776;value=64): Invalid argument
> > ioctl: VIDIOC_S_CTRL(id=9963777;value=32): Invalid argument
> > ioctl: VIDIOC_S_STD(std=0x0 []): Invalid argument
> > v4l2: oops: select timeout
> >
> > > Do you have other usb device on the same bus ? perhaps it's the problem.
> > I don't have any other usb devices connected right now.
> >
> > --
> > Krzysztof Kowalczyk
> >                                http://www.xysio.prv.pl/
> >
> > _______________________________________________
> > pwc mailing list
> > 
> > http://lists.saillard.org/mailman/listinfo/pwc
> >
>
>
> --
> --
> Andrew Cavers
> 
> www.mution.com
>


--
--
Andrew Cavers

www.mution.com
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