Actually I am wondering roughly the same thing. Can you hook up several
USB cameras/capture devices (AverTV for example) at one and have them
recognized as devices.
Michael
On Wednesday, April 11, 2001, at 02:38 PM, Rich Drewes wrote:
Hello,
I've been unable to get two USB CPIA cameras to work reliably on the
same machine at more or less the same time. Either camera (/dev/video0
or /dev/video1) will work fine by itself when the other camera is not
being used--the problem arises when trying to use them at or near the
same time. While it is possible to open /dev/video0 and /dev/video1
simultaneously, if one device is in the middle of a VIDIOCMCAPTURE then
opening the other device fails with a "device or resource busy error".
If I coordinate the device openings to work around this problem (that
is, not starting captures until both devices are successfully opened),
then things fail if one card tries to do a VIDIOCMCAPTURE while the
other is already doing a capture. I haven't found any V4L api docs
anywhere that indicate that doing two captures at once on separate
devices from separate processes is not permitted.
I have experimented with protecting the actual capture with a shared
memory semaphore so two processes never try to do a capture at the same
time. This seems to work mostly, though there are enough lingering
problems that I suspect that this may not be a proper solution. Does
anyone have a recommended approach? Has anyone else gotten two USB cams
working on the same machine reliably? If so, under what kernel/v4l
driver version?
I am on kernel 2.4.0. The cameras are generic USB CPIA cameras made by
Ezonics. I have used a variety of test programs to explore the error
behavior, but my main test environment is two "motion" processes (, each
process controlling a camera. I have seen the same behavior with two
concurrent gqcam processes as well, but it usually takes longer to
manifest the problem with gqcam since gqcam spends a lot of time waiting
between successive VIDIOCMCAPTURE calls and therefore the probability of
both processes trying to do a VIDIOCMCAPTURE at the same time is lower.
Eventually, however, an error will occur.
Any suggestions will be appreciated.
Rich
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