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? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
