Hi Soho and Alan, Sorry for the late reply. On Tuesday 31 May 2011 17:53:03 Soho Soho123 wrote: > Dear Laurent, > =========================================================================== > Let me explain my problem again. > We use MJPG-streamser to test IP Cam function. the network interface > is WiFi. WebCam is using UVC driver. > We have the issue is the stream will disconnect in a few minutes on > our embedded system. > the reason is : the call back function of uvc urb complete can not > re-submit urb successfully. The error code is "-EFBIG". EHCI driver > think the urb submit is too late. > the ip cam test condition is 1280x720 30 fps via WiFi(802.11n). > the call back function seems take more cpu cycles when itd_complete, > because it decode data and re-submit urb . the call back function is > included in ehci irq path. it may increase irq latency. > Do you have idea about : > is it "must" decode data in uvcvideo complete call back function? > is it "must" re-submit urb in uvcvideo complete call back function? The URB completion callback performs the following operations. - Header decoding. Every UVC packet starts with a header that contains a couple of bit flags. Those flags are processed to detect image boundaries and errors. - Data copy. If the packet contains payload data (as opposed to packets with a header only), the payload is copied to another buffer. Whether the device will send many small isochronous packets or few big ones is entirely up to the device, but in the end the same amount of data will be copied. At most 3070 bytes will be copied per URB. - Video buffer completion. If the driver detects that a frame is complete, it will wake tasks waiting on the buffer. This can't really be optimized without removing URB processing from interrupt context completely. I could just queue the URB buffers to a list and process them in a workqueue. URBs could then be resubmitted faster, with another buffer. However, if the platform isn't fast enough, the URB completion callback will run out of buffers and will thus loose data. How much time are drivers allowed to spend in the URB completion callback ? Why does the EHCI driver require very low latency there ? If the URB is resubmitted too late, why can't it just be queued for the next (micro-)frame ? -- Regards, Laurent Pinchart -- 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
