Dear Alan, My comment below: 2011/6/2 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Thu, 2 Jun 2011, Soho Soho123 wrote: > >> >> Soho: in our platform the time precision is 10ms per tick . >> > >> > In a PC, the time precision is between 1 and 10 ms per tick. But PCs >> > also have high-precision timers available; apparently your platform >> > does not. Without high-precision timestamps, there's no way to tell >> > what's causing your latencies to be so large. >> >> >> soho:???? > > If your usbmon timestamps were accurate down to microseconds, I could > tell whether the latency was caused by ehci-hcd, by uvcvideo, or by > something else. > Soho:we have sent you the log from ther other e-mail. you should get that. Could you kindly help to confirm the error condition? thank you very much!!! >> > One other thing you can try: Increase UVC_MAX_PACKETS to 100. >> >> soho: we will try it later. Could you explation the consideration >> about increase uvc max packet? > > With UCV_MAX_PACKETS set to 32, you get an interrupt and have to submit > a new URB every 4 us. That's a pretty high rate. With UVC_MAX_PACKETS > set to 100, an interrupt will occur every 12.5 us. The timing > requirements will be less strict and the overhead of interrupt handling > will be reduced. > > Alan Stern > > Soho: we have do the verification with large UVC_MAX_PACKETS. it seem better for the faster platform. In the faster platform , we do not see submit urb error in a few minutes. But in another platfrom , that is slower, the modification of UVC_MAX_PACKETS is no any effect. the problem is still exist. Our target is to see the cause in slower platform and fixed it if passible.One more question: We take the observation: if we suspected UVC complete function (or UVC device driver is cause). in theory, the urb_actual_length is not fixed, sometimes is shorter and sometimes is longer. So, the time for decode is sometimes is shorter and sometimes is longer. usb_submit_urb is handle by usb code and ehci host driver. Then the time frame for re-submit urb to ehci host is sometimes earlier and sometimes later, right? is there any time inaccuracy in ehci host? -- 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
