Hi Michael,
The Linux UVC driver doesn't support reading directly from the device
(yet). Only the streaming I/O method (using mmap) is supported. You can
test your webcam with luvcview.
Thanks for the feedback. I had tried a few other utilities to read from
/dev/vide0, but they were giving me errors as well. I thought that cat(1)
would be the simplest way to demonstrate the problem, but I guess not :-)
When I try using the luvcview utility, the error messages I'm seeing are:
[EMAIL PROTECTED] ~/luvcview-20060920]$ ./luvcview
uvcview version 0.1.7
Video driver: x11
A window manager is available
video /dev/video0
Unable to set format: 5.
Init v4L2 failed !! exit fatal
And in dmesg, I see:
[17357520.848000] uvcvideo: Trying format 0x47504a4d (MJPG): 320x240.
[17357520.848000] uvcvideo: Using default frame interval 6.6 us
(15.0
fps). [17357521.148000] uvcvideo: Failed to query (1) UVC control 1 (unit
0) : -110 (exp. 26).
Welcome to the Logitech hardware bug victims club. You are experiencing a
know hardware problem for which no proper solution exists yet. A patch has
been posted some times ago on this list. Depending on how much your computer
is affected by the bug, it might help you.
Looking at the luvcview-20060920/v4l2uvc.c file, the codepath that
generates the Unable to set format error is:
/* set format in */
memset(vd-fmt, 0, sizeof(struct v4l2_format));
vd-fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
vd-fmt.fmt.pix.width = vd-width;
vd-fmt.fmt.pix.height = vd-height;
vd-fmt.fmt.pix.pixelformat = vd-formatIn;
vd-fmt.fmt.pix.field = V4L2_FIELD_ANY;
ret = ioctl(vd-fd, VIDIOC_S_FMT, vd-fmt);
if (ret 0) {
printf(Unable to set format: %d.\n, errno);
goto fatal;
}
Which I thought that may be an indication that I needed to use the -f
or -s command line arguments to change the requested format or size to
something that may be better supported by my camera, so I tried a number
of different permutations with:
for f in yuv jpg; do
for s in 1024x576 1280x960 160x120 176x144 320x240 352x288 432x240 \
480x360 512x288 640x360 640x480 704x576 864x480 960x720; do
./luvcview -f $f -s $s -o ~/foo
done
done
However, none of them appeared to be successful.
Searching around for the Failed to query error message that appeared in
dmesg seems to suggest that I may be hitting a Logitech hardware bug :-(
Exactly :-( You might be lucky with the so-called reset patch. Please search
the list archive.
Best regards,
Laurent Pinchart
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