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) -- balbi -- 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
