Re: Nanosecond precision with refclock SOCK

On Mon, Jan 15, 2024 at 6:32 PM Miroslav Lichvar <[email protected]>
wrote:

>
> > the actual system time).  But the offset will be wrong by a small number
> of
> > seconds if the system clock is so far in the past that leap seconds other
> > than the latest one intervened: I don't think that matters.
>
> That will cause an error in the initial step of the clock and it will
> take longer to stabilize.
>

In computing the initial step, how does chrony handle leap seconds?

There are two ways of computing offsets:
- subtracting the TAI times (so that it is really the number of seconds
that elapse between the system time and the true time)
- subtracting the POSIX times (so leap seconds are ignored)

When the offset is small, I am assuming the first way is right (otherwise
you would get discontinuities). But if the system offset is a long time in
the past (so that chrony is doing a step), does chrony expect the first or
the second? The first would require chrony to have knowledge of all past
leap seconds.

Or am I misunderstanding something here?

The sample time in the SOCK needs to be in the system time (UTC),
> otherwise it will be rejected as invalid.
>

Right: I'm doing that.

> I compute the leap flags based on the true time: if the true time occurs
> on
> > a day that ends with a leap second, then I set the leap flags. Or should
> I
> > be setting them if the true time is some number of hours before the end
> of
> > the day that ends with a leap second?
>
> The leap should be set until the leap happens, starting up to 24 hours
> before.
>

What does "until the leap happens" mean exactly? Does that mean that adding
the offset to the system time gives a time that is < 24:00:00 on the day of
the leap second (i.e. the leap second is over)? Or is it until the leap
second starts?

James