On Fri 2017-03-10 10:37:21, Steve Longerbeam wrote: > Hi Hans, > > On 03/10/2017 04:03 AM, Hans Verkuil wrote: > >On 10/03/17 05:52, Steve Longerbeam wrote: > >>Add a new FRAME_INTERVAL_ERROR event to signal that a video capture or > >>output device has measured an interval between the reception or transmit > >>completion of two consecutive frames of video that is outside the nominal > >>frame interval by some tolerance value. > > > >Reading back what was said on this I agree with Sakari that this doesn't > >belong here. > > > >Userspace can detect this just as easily (if not easier) with a timeout. > > > > > Unfortunately measuring frame intervals from userland is not accurate > enough for i.MX6. > > The issue here is that the IPUv3, specifically the CSI unit, can > permanently lose vertical sync if there are truncated frames sent > on the bt.656 bus. We have seen a single missing line of video cause > loss of vertical sync. The only way to correct this is to shutdown > the IPU capture hardware and restart, which can be accomplished > simply by restarting streaming from userland. > > There are no other indicators from the sensor about these short > frame events (believe me, we've exhausted all avenues with the ADV718x). > And the IPUv3 DMA engine has no status indicators for short frames > either. So the only way to detect them is by measuring frame intervals. > > The intervals have to be able to resolve a single line of missing video. > With a PAL video source that requires better than 58 usec accuracy. > > There is too much uncertainty to resolve this at user level. The > driver is able to resolve this by measuring intervals between hardware > interrupts as long as interrupt latency is reasonably low, and we > have another method using the i.MX6 hardware input capture support > that can measure these intervals very accurately with no errors > introduced by interrupt latency. Requiring < 58 usec interrupt latency for correct operation is a little too optimistic, no? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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