On Wed, 23 Aug 2017, Martin Oprešnik wrote:
> Hi,
>
> What happens when you try to use the fourth camera?
>
> I'm sorry I forgot to write whet the actual problem is. Error message is
> "No space left on device". Based on what I read this means there it
> can't allocate enough bandwidth.
>
> Using this command (cat /sys/kernel/debug/usb/devices | grep "B: "), I
> could see bandwidth allocation if cameras are connected to USB 2.0, but
> not if connected to 3.0 port. With this command and usbtop I created
> this table.
>
> +-------------+----------+----------------------+----------------+
> | Resolution | Name | Bandwidth allocation | Transfer rate |
> +-------------+----------+----------------------+----------------+
> | 1280x720 | 720p | 256us | up to ~1.4Mb/s |
> | 1600x896 | | 424us | up to ~1.7Mb/s |
> | 1920x1080 | Full HD | 488us | up to ~1.8Mb/s |
> +-------------+----------+----------------------+----------------+
>
> On USB 2.0 port there is 800us available bandwidth, that means i could
> run cameras in this modes:
> -3 cameras in 720p (used 96% of bandwidth)
> -one camera in 720p and one camera in FullHD
>
> On USB 3.0 port I can run cameras in same formats as on USB 2.0 and
> additionally
> -one camera in FullHD and one camera in 1600x896
>
> I currently don't have 4 cameras, but I suppose that if we can make
> cameras to work on higher resolutions, I could add more cameras.
> Cameras are connected trough TP-LINK 3.0 USB hub (Model: UH720), but
> there is no difference if I connect one camera directly and other over hub.
Your bandwidth calculations do not take into account the USB keyboard
and the OM device (whatever that is). They use up a significant
fraction of the total bandwidth.
Try plugging those two devices into USB-2 ports (or into a hub that
is plugged into a USB-2 port) while plugging the cameras all into USB-3
ports (or into a hub that is plugged into a USB-3 port), and see if
that helps at all.
And try to avoid nesting hubs deeply; you're better off plugging
multiple hubs each into a separate controller than all of them through
a single hub into a single controller.
Alan Stern
> Then while running with 3 cameras, make a copy of
> /sys/kernel/debug/usb/devices and post the copy.
>
> I added attachment.
>
> Also, what version of the kernel are you using?
>
> Linux odroid 4.9.38
>
> and which host controller? (xhci, ehci, ohci, uhci)
>
> Using this code:
> struct v4l2_capability caps = {};
> if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &caps))
> {
> perror("Querying Capabilities");
> return 1;
> }
>
> printf( "Driver Caps:\n"
> " Driver: \"%s\"\n"
> " Card: \"%s\"\n"
> " Bus: \"%s\"\n"
> " Version: %d.%d\n"
> " Capabilities: %08x\n",
> caps.driver,
> caps.card,
> caps.bus_info,
> (caps.version>>16)&&0xff,
> (caps.version>>24)&&0xff,
> caps.capabilities);
> It says "usb-xhci-hcd.2.auto-1.1.1.4".
>
> On 23. 08. 2017 08:04, Felipe Balbi wrote:
> > Hi,
> >
> > Alan Stern<stern@xxxxxxxxxxxxxxxxxxx> writes:
> >> On Tue, 22 Aug 2017, Martin Oprešnik wrote:
> >>
> >>> Hello,
> >>>
> >>> we are working on a project, where we need multiple cameras connected to
> >>> embedded computer. For computer we have chosen odroid XU4 and for
> >>> cameras Logitech C920. We need at least 5 cameras running with 720p. The
> >>> problem we have is allocated USB bandwidth (cameras are using
> >>> isochronous transfer). Currently we can run 3 cameras on 720p. Image is
> >>> transferred in h264 compressed format. Writing on disk is done directly
> >>> trough memory map using V4L2 api and files on disk are really small and
> >>> using usbmon/wireshark shows ~1104kB/s (there should be a lot of USB
> >>> bandwidth left).
> >> What happens when you try to use the fourth camera?
> >>
> >>> I tried same setups on my laptop and I don't get any better results, so
> >>> I suspect there is some space for improvement in software and it's not
> >>> odroid's fault. I tried changing different parameters in uvcvideo driver
> >>> and I think only wMaxPacketSize is affecting bandwidth allocation. And
> >>> changing that is reflected in non working camera.
> >>> Now I don't know enough about USB and linux kernel to work around this
> >>> problem and I would be very happy if you could give me some help or
> >>> directions.
> >>> If I should provide some additional information, I'll be happy to add it.
> >>>
> >>> I am looking forward to hearing from you.
> >> Please try the following. First, mount a debugfs filesystem:
> >>
> >> mount -t debugfs none /sys/kernel/debug
> >>
> >> Then while running with 3 cameras, make a copy of
> >> /sys/kernel/debug/usb/devices and post the copy.
> >>
> >> Also, what version of the kernel are you using?
> > and which host controller? (xhci, ehci, ohci, uhci)
> >
>
>
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