hi, your problem is not related to de-facto bandwidth use but with bandwidth allocation. The uvc driver follows the uvc specification: The driver selects an alternate setting for the Isochronous endpoint that satisfies the bandwidth requirements for the negotiated video stream. The bandwidth requirement depends on the stream resolution,rate and format (think YUV or MJPEG...) and is reported by the camera. This is where the problem lies: Especially when you select a compressed format (for high resolutions and rates this is usually the case.), the camera reports a very conservative estimate on the minimum bandwidth required. This effectively prohibits multiple streams. One workaround is to estimate the bandwidth yourself. For uncompressed streams a quirk exists: http://www.ideasonboard.org/uvc/faq/#faq7 For mjpeg stream there is a patch (not written by me) here: https://gist.githubusercontent.com/mkassner/10134241/raw/5ea34a0269d5b4bc12ec3ee466238cf82000e29d/mjepg_bandwidth.patch I would really like to integrate the patch. I think I will do some writeup and submit a clean version. On Wed, Mar 18, 2015 at 7:50 AM, dongdong zhang <dongguangit@xxxxxxxxx> wrote: > Using kernel 3.2.0 on ti am3354 , > Kernel 2.6.35.7 on samsung s5pv210, > Kernel 3.0.8 on samsung s5pv210, > Linux ubuntu 3.13.0-24-generic #46-Ubuntu SMP Thu Apr 10 19:08:14 UTC > 2014 i686 i686 i686 GNU/Linux > Ubuntu 14.04 on x86 > > I find it impossible to > start motion with two UVC cameras: > > uvcvideo: Failed to submit URB 0 (-28). > Error starting stream. > VIDIOC_STREAMON: No space left on device > ioctl(VIDIOCGMBUF) - Error device does not support memory map > When using one UVC camera with the same configuration it works fine. > Is there a limitation in the UVC driver regarding simultaneous camera. > > > Lowering the resolution on both two cameras to the minimum (160x120) > open simultaneously doesn't > help. However with the same camera of two UVC at 1280x720 open > simultaneously on windows xp software platform it works fine. > So it doesn't seem to be a USB bandwidth problem > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
