Re: [chrony-dev] [PATCH v2 2/2] refclock: Add a new "tai" option

[Chris Perl <cperl@xxxxxxxxxxxxxx>]

On Wed, Oct 11, 2017 at 10:55 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
>
> On Tue, Oct 10, 2017 at 01:23:21PM -0400, Chris Perl wrote:
> > +  if (instance->tai) {
> > +    tai_offset = REF_GetTaiOffset(sample_time);
>
> It turned out, this doesn't actually handle the case I mentioned
> before. We want to get the offset for the reference time, not the
> local system time. For instance, if chronyd was started with local
> clock in year 2000, it should apply the current TAI-UTC offset and not
> the one from 2000. It seems this requires two separate calls of
> REF_GetTaiOffset(). One to get an approximate reference time in UTC
> and then get the actual TAI-UTC offset.
>
> I'll apply your patches with some minor modifications and add the
> improved conversion in a separate commit.
>
> Thanks!

Ah.  Thanks.

> > +    if (!tai_offset) {
> > +      DEBUG_LOG("refclock sample ignored unknown TAI offset");
> > +      return 0;
> > +    }
> > +
> > +    /* REF_GetTaiOffset returns the number of leap seconds that have
> > +       been inserted into UTC.  To get from TAI to UTC, we have to
> > +       remove those seconds from the sample */
>
> Strictly speaking, the offset between TAI and UTC is not the number of
> leap seconds that have been applied so far. The offset already started
> at 10. I'll just remove the comment.

Right, sorry.  I was trying to come up with a decent comment for why
we were subtracting rather than adding.  If you think its unnecessary,
that is fine by me.

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