Hi Ravi, On Wednesday 27 March 2013 10:43:24 B, Ravi wrote: > Hi > > I am observing issue while streaming video from usb camera connected to host > controller based on mentor graphics. The issue is root caused that there > are huge SOF gaps seen between the two isochronous IN token issued by host > controller. This is due to fact, significant amount of time is spent in uvc > callback function handler. Due to this next request programmed is delayed > leads to this failure of video streaming. I have measured time taken by uvc > callback function is in range minimum of 11 microsecond to maximum of 3318 > microsecond. Looks like callback handler doing some processing and takes > more time to return rather than giveback immediately. Need your help to > understand why uvc callback handler takes much time, if it does any > processing can it move to different task context and return immediately, > this will reduce the latency. I'm surprised by that large delay. A quick look at the UVC URB completion handler (I assume you're talking about the host driver, not the gadget driver) doesn't show any significant source of delay. You will likely need to profile the code to find out where the problem comes from. You should also make sure that no other IRQ handler on the system keeps IRQs disabled for a long time. -- 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
