[TriEmbed] BBB /dev/video0 issues

Wed Jul 8 18:48:58 CDT 2015

BBB has a built in network switch, I have seen data suggesting it should be 
capable of 90Mb/s. I doubt it is the file transfer, unless something else is 
also taking a large chunk of CPU.
USB cameras will usually do  raw at small resolutions, mjpeg at medium 
resolutions, and newer ones h264 for HD type resolutions.  One thing to 
check might be top, to see what if anything is using great amounts of CPU, 
if you are piping it through ffmpeg or something it could be 
changing/transcoding it underneath you.
Another would be check to see if the USB camera is being detected/negotiated 
as USB v1 instead of USB v2 which your camera probably is. Not sure but 
lsusb might give you some of that type of info.

Ken

-----Original Message----- 
From: Alex Davis via TriEmbed
Sent: Wednesday, July 08, 2015 1:33 PM
To: triembed at triembed.org
Subject: Re: [TriEmbed] BBB /dev/video0 issues

Bill,

I've seen USB issues capturing purely still images and from running
whatever 'motion' does (max_framerate set to '5' or less).

I was hoping it was some sort of v4l2 lib issue on 3.8 but I've seen it
on 3.14 as well. I can live with something higher than 3.14 as I am not
using the GPIO and don't care if overlays work or not.

What I was trying to do, briefly, was run motion and have it drop stills
to an NFS export where they could be viewed via a web browser. Does the
BBB hang the ethernet off the USB like the Pi? Maybe there's a bandwidth
issue? Hard to believe that, since the jpeg files are only about 60 KB.

When I get some more free time, I'll run this with the files saved only
to the SD card and wrap it in strace.

On Wed, Jul 8, 2015, at 01:00 PM, triembed-request at triembed.org wrote:
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>    1. Re: BBB USB webcam issues? (Bill Farrow)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 8 Jul 2015 08:27:20 -0400
> From: Bill Farrow <bill at arrowsreach.com>
> To: TriEmbed <triembed at triembed.org>
> Subject: Re: [TriEmbed] BBB USB webcam issues?
> Message-ID:
> <CAPm8Nr3QvZNuqh5ntaTw9LubHxcp4qs26Yau=o3aXCE=2ExVVA at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> I suspect that it is not a power issue, but a bandwidth or CPU
> throughput limitation.
>
> Note that the Logitech C920 webcam is able to stream h.254 video over
> USB, which means the data rate is lower than other video encodings and
> the BBB CPU does not have to do any video compression.
>
> Can you capture still images at higher resolutions ?
>
> What are you doing with the video stream on the BBB ? Are you
> processing it, streaming it over the network, writing to flash ? Each
> one of these will have different resource limitations and potential
> bottlenecks.
>
> Bill
>
> On Tue, Jul 7, 2015 at 10:40 PM, Carl Nobile via TriEmbed
> <triembed at triembed.org> wrote:
> > Alex,
> >
> > Both the BBB and RPi have version 2 USB which specifies 500mA as the 
> > maximum
> > allowed current through a USB connector. The max speed of a USB 2 is 480
> > megabits per second. Here is an interesting addressing some of the issue 
> > you
> > mentioned.
> > http://electronics.stackexchange.com/questions/24700/why-are-usb-devices-slower-than-480-mbit-s
> >
> > Carl
> >
> >
> > On Mon, Jul 6, 2015 at 2:51 PM, Alex Davis via TriEmbed
> > <triembed at triembed.org> wrote:
> >>
> >> Anyone have experience with the BeagleBone Black and USB webcams? In my
> >> experience with v4l2 and UVC USB webcams on the BBB, getting an image
> >> above 320x240 is unreliable and 320x240 or below is occasionally
> >> unreliable. I've seen this on two separate BBBs under 3.8 and 3.14
> >> kernels. It is more reliable if you set the webcam to send a compressed
> >> image stream (JPEG) vs uncompressed (YUV), so it makes me think the
> >> issue is data-rate dependent on the USB bus.
> >>
> >> I am using a Microsoft Lifecam Cinema camera. It is rock-solid on my
> >> Debian laptop running a 3.8 kernel at up to the native 12800x720
> >> resolution.
> >>
> >> I know with the early Raspberry Pi there is an issue with limited USB
> >> current, but I don't think that's the case with the BBB. I use at
> >> minimum a 2A 5V supply, which should be plenty for the BBB and the USB
> >> webcam. Could it be some hardware issue limited to the original 2 GB
> >> eMMC models that I have?
> >>
> >> There isn't much on the web with regards to BBB-specific webcam issues.
> >> I've seen BBB projects using high-end logitech cameras for live
> >> streaming, so it must work for some.
> >>
> >> --
> >> "The theater of noise is proof of our potential."
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> >
> > --
> > -------------------------------------------------------------------------------
> > Carl J. Nobile (Software Engineer)
> > carl.nobile at gmail.com
> > -------------------------------------------------------------------------------
> >
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