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Re: [pwc] VIDIOCPWCRUSER

To: Philips Webcam Linux Driver <>
Subject: Re: [pwc] VIDIOCPWCRUSER
From:
Date: Fri, 13 Jan 2006 11:25:45 +0100
> > yesterday i found out that if i remove the ioctl to VIDIOCPWCRUSER 
> > everything
> > works like normal. so it seems this is a problem with PWC.
> 
> I don't understand your bug report ... is it a bug or a normal feature ?

that's the question :)

> pwc driver don't call the restore setting, it's the application that use it.

indeed. 
i'm the author of PDP (http://zwizwa.goto10.org/pd/pdp) and Packet
Forth (http://zwizwa.goto10.org/darcs/libpf)
both have pwc support, and for newer cameras there's a strange behaviour..

let me be more specific: i have 2 cameras.
(A) Philips PCVC730K (ToUCam Fun)/PCVC830 (ToUCam II)
(B) Logitech QuickCam 4000 Pro USB

camera (A) works perfectly for all the versions of pwc that i've used,
from somewhere around 8.x upto and including the newest version 
10.0.11-unofficial.

camera (B) seems to not like the VIDIOCPWCRUSER ioctl. more specifically,
if i call this ioctl after opening the device for the 2nd time 
(open-close-open),
every 2 seconds there is a 'flash' in the image, after which the AGC oscillates
for a moment and the image becomes stable again.

this behaviour for camera (B) has been there since 9.0, which is the lowest 
version
i used that supports camera (B).

now, this behaviour occurs only after the video device is opened/closed once. 
unplugging the camera, or unloading/reloading the module seems to reset
the behaviour, in which case the VIDIOCPWCRUSER seems to work without problems.

> So perhaps it's a problem in your application. 

maybe. if so, i don't know what i'm doing wrong.
i had a look at the pwc-ctrl.c driver source, and it seems the IOCTL 
implementation is fairly simple, so i can't imagine anything being wrong
with that.


i've also had this report from a Packet Forth user:

| I got myself a webcam connected to my machine. It's a "Logitech 
| Quickcam for Notebooks Pro".  Works wonderful!
| There's also a little bit of weird behavior with this, since it's
| resetting the exposure of my webcam every second or so (goes dark for
| about three frames). Not the same in xawtv or effectv...

which seems to be the same behaviour as my camera (B)

my v4l code is in v4l.c at
http://zwizwa.goto10.org/darcs/libpf/plugins/v4l/

you can try for yourself:

wget http://zwizwa.goto10.org/darcs/libpf/libpf.tar.gz
tar zxf libpf.tar.gz

        ( change the if(1) to if(0) in libpf/plugins/v4l/v4l.c on line 226
          see also line 201 )

cd libpf
. bootstrap
mkdir d
cd d
../configure --enable-debug
make local


bin/pf ../demo/tv.pf
bye
bin/pf ../demo/tv.pf


the second time you run it should produce the bug.

hope this helps
tom

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