On Wednesday 11 November 2009 18:29:52 Sakari Ailus wrote:
> Hans Verkuil wrote:
> > On Saturday 24 October 2009 23:56:24 Sakari Ailus wrote:
> >> Ivan T. Ivanov wrote:
> >>> Hi Sakari,
> >> Hi,
> >>
> >>> On Fri, 2009-10-23 at 13:18 +0300, Sakari Ailus wrote:
> >> [clip]
> >>>> struct v4l2_event {
> >>>> __u32 count;
> >>>> __u32 type;
> >>>> __u32 sequence;
> >>>> struct timeval timestamp;
> >>> Can we use 'struct timespec' here. This will force actual
> >>> implementation to use high-resolution source if possible,
> >>> and remove hundreds gettimeofday() in user space, which
> >>> should be used for event synchronization, with more
> >>> power friendly clock_getres(CLOCK_MONOTONIC).
> >> Good point. I originally picked timeval since it was used in
> >> v4l2_buffer. The spec tells to use gettimeofday() for system time but
> >> clock skewing is causes problems in video encoding.
> >> clock_getres(CLOCK_MONOTONIC) is free of clock skewing and thus should
> >> be more suitable for this kind of use.
> >>
> >> I also propose to use timespec instead of timeval.
> >>
> >
> > Hi Sakari,
> >
> > What is that status of the event API? It is my impression that it is pretty
> > much finished. Sakari, can you make a final 2.3 RFC? Then Guru can take over
> > and start the implementation.
>
> Ah.
>
> One thing that I was still wondering was that are there use cases where
> other kind of time stamps might be useful? I guess that when the V4L2
> was designed no-one though of the need for time stamps of different
> type. So are there use cases where gettimeofday() style stamps would
> still be better?
If you ever need to relate an event to a specific captured frame, then that
might well be useful. But I can't think of an actual use case, though.
> In that case we might choose to leave it driver's decision to decide
> what kind of timestamps to use and in that case application would just
> have to know. The alternative would be to use union and a flag telling
> what's in there.
>
Let's go with timespec. If we need to add an event that has to relate to
a specific captured frame then it is always possible to add a struct timeval
as part of the event data for that particular event.
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG Telecom
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