Hi,
I'm porting an application which uses the uvc video driver for a logitech
webcam
from Ubuntu 8.04 LTS to Ubuntu 10.04 LTS.
In the 8.04 release, there was some mismatch in the UVC driver from the V4L2
driver for a few of the ioctl values. The V4L2 headers had:
#define V4L2_CID_EXPOSURE_AUTO (V4L2_CID_CAMERA_CLASS_BASE+1)
#define V4L2_CID_EXPOSURE_ABSOLUTE (V4L2_CID_CAMERA_CLASS_BASE+2)
#define V4L2_CID_EXPOSURE_AUTO_PRIORITY (V4L2_CID_CAMERA_CLASS_BASE+3)
But the uvcvideo driver expected:
#define V4L2_CID_EXPOSURE_AUTO (V4L2_CID_PRIVATE_BASE+10)
#define V4L2_CID_EXPOSURE_ABSOLUTE (V4L2_CID_PRIVATE_BASE + 11)
#define V4L2_CID_EXPOSURE_AUTO_PRIORITY (V4L2_CID_PRIVATE_BASE+14)
I found these values in the private header files that came with the luvcview
software, and similar defines in the logitech libwebcam source, which also had
a
comment "Old uvcvideo pre-r178 control IDs"
See
here: http://svn.quickcamteam.net/svn/qct/webcam-tools/trunk/libwebcam/compat.h
My desired camera behavior is to allow the camera to control aperture as
necessary to handle lighting conditions, but my application must run at a fixed
frame rate (30fps, set elsewhere), so it must not change the frame rate. By
experimenting & reading sources mentioned above, I finally found that if I did:
request.id = (V4L2_CID_PRIVATE_BASE+10);
request.value = 8;
if (ioctl(fd, VIDIOC_S_CTRL, &request) < 0) {
...
}
request.id = (V4L2_CID_PRIVATE_BASE+14);
request.value = 0;
if (ioctl(fd, VIDIOC_S_CTRL, &request) < 0 {
...
}
I achieved the desired effect. Note that 8 is not defined in
v4l2_exposure_auto_type, but I'm not the only person who's used it,
see http://forums.quickcamteam.net/showthread.php?tid=1227 for an example of
where it seems to mean aperture priority.
OK, fine, but under Ubuntu 10.04, the ioctls above return EINVAL. So I figured
it was time to use the correct request values in the requests. So I tried:
request.id = V4L2_CID_EXPOSURE_AUTO;
request.value = V4L2_EXPOSURE_APERTURE_PRIORITY;
if (ioctl(fd, VIDIOC_S_CTRL, &request) < 0) {
... I end up here with "Input / Output Error" errno ...
}
request.id = V4L2_CID_EXPOSURE_AUTO_PRIORITY;
request.value = 0;
if (ioctl(fd, VIDIOC_S_CTRL, &request) < 0 {
...
}
No luck - initially I thought it worked, but after trying in a darkened room
and
bright sunlight and rebooting to clear out the current values in the driver, I
see that it is no longer adapting to the lighting conditions, although it does
seem to be correctly pinned to the framerate I set. Also, the
V4L2_CID_EXPOSURE_AUTO ioctl() always returns "I/O error" - I have tried
various
values for the request.value - 0, 1, 3, 8, etc. without any success.
I see other people have reported similar issues in the past, but I see no
resolution, for
example:
http://lists.berlios.de/pipermail/linux-uvc-devel/2008-March/003251.html -
for example in that thread this is mentioned:
enum v4l2_exposure_auto_type { V4L2_EXPOSURE_MANUAL = 0,
V4L2_EXPOSURE_AUTO = 1, V4L2_EXPOSURE_SHUTTER_PRIORITY = 2,
V4L2_EXPOSURE_APERTURE_PRIORITY = 3 };
But in my V4L2 headers, MANUAL = 1, and AUTO = 0.
I also tried the VIDIOC_S_EXT_CTRLS flavor of setting the exposure values, but
no luck - same I/O error.
Any idea on how I can set V4L2_CID_EXPOSURE_AUTO on uvcvideo driver in Ubuntu
10.04 LTS without getting an Input/Output error?
Thanks,
Ben
Ben Mesander
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