Re: (bisected) Logitech C920 (uvcvideo) stutters since 3.9

Paulo Assis
2014-11-05T10:14:07Z

Hi,

2014-11-04 23:32 GMT+00:00 Sakari Ailus <sakari.ailus@iki.fi>:
> Sakari Ailus wrote:
>> yavta does, for example, print both the monotonic timestamp from the buffer
>> and the time when the buffer has been dequeued:
>>
>> <URL:http://git.ideasonboard.org/yavta.git>
>>
>> $ yavta -c /dev/video0
>>
>> should do it. The first timestamp is the buffer timestamp, and the latter is
>> the one is taken when the buffer is dequeued (by yavta).

I've done exaclty this with guvcview, and uvcvideo timestamps are
completly unreliable, in some devices they may have just a bit of
jitter, but in others, values go back and forth in time, making them
totally unusable.
Honestly I wouldn't trust device firmware to provide correct
timestamps, or at least I would have the driver perform a couple of
tests to make sure these are at least reasonable: within an expected
interval (maybe comparing it to a reference monotonic clock) or at the
very least making sure the current frame timestamp is not lower than
the previous one.

Regards,
Paulo

>
> Removing the uvcvideo module and loading it again with trace=4096 before
> capturing, and then kernel log would provide more useful information.
>
> --
> Sakari Ailus
> sakari.ailus@iki.fi