(Ccing the media ML) See my reply below. On Fri, Feb 6, 2015 at 4:36 AM, Yin Ling <birdyin@xxxxxxxxx> wrote: > Hi Ezequiel Garcia, > > Sorry for this bother. We are researcher at University and working on > STK1160 usb connection related solusion. As our system needs multiple > STK1160 to input video data, we plan to use usb Hub to connect > multiple STK1160. Nevertheless, currently only one STK1160 with driver > can be operated by one usb Hub host from the information below, > http://www.linuxtv.org/wiki/index.php/Stk1160_based_USB_2.0_video_and_audio_capture_devices#Known_issues > It wrote that "To one root hub port can connect only one device. Can > connect multiple, but at the same time only one operate. This not an > power supply issue, since the device consumes only 200mA in operation > mode. Number of devices that can simultaneously connect to PC depends > on the amount root hub ports." > > If try to operate multiple STK1160 by one usb Hub, is it possible? > Could you help to provide any hints or technological ways to achieve > this goal? > As far as I can recall, the only constraint is the USB host controller isochronous bandwidth. Given the stk1160 chip streams raw video, and given I have found no way to implement frame size in-chip reduction, your USB host must be able to deal with raw full frames. Roughly speaking you need as much as 20 MB/s for each stk1160 video input. Such throughput is more or less close, to USB2.0 maximum throughput. I hope someone can jump in and correct me if I'm wrong here. > Additionally, if this way is not feasible, we have to work on > capturing 4 channel video data from one STK1160 at the same time. We > have to switch channel to capture each specific channel video data. We > found that if we switch channel with the frequency as 1s, the quality > of images are not well. Do you know how we can capture 4 channel good > quality video data, lower switch frequency? How much it could be? > I think this is a hardware limitation. The stk1160 is not able to capture from the multiple channels simultaneously. I honestly don't recall how it performs when fast switching between channels, but I wouldn't expect much. > As we are very busy with the system, and are confusing with these > problems at this period, we are highly looking forward to receiving > your information. or else, if anyone may knows the solution, could you > help to provide to us as well? > Maybe you can get yourself a video capture device that can stream compressed video? That will certainly reduce the USB bandwidth requirement. Hope this helps! -- Ezequiel García, VanguardiaSur www.vanguardiasur.com.ar -- 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
