[ntp:questions] NMEA driver using common PPSAPI code

Venu Gopal neo.venu at gmail.com
Thu Oct 7 04:36:26 UTC 2010


Hello Dave,

I never used the time1 and time2 flags in the older NMEA driver.
And neither I did with the newer code. As per your suggestion I tried
to use time1 and time2 in the newer code to see if it helps. But it didn't
and instead it made it worse.

My point is simple. If it works with older NMEA driver then it should work
with the newer one too (without the need of using time1 and time2 flags).

I am literally tired of these experiments :-). And I hope to hear if someone
is using
the new driver successfully. This would be my last attempt of using time2
flag
and see if it works. All wanted to check is the significant changes
submitted by
Juergen Perlinger for https://bugs.ntp.org/show_bug.cgi?id=1571.

Thanks & kind regards,
_Venu


On Thu, Oct 7, 2010 at 5:19 AM, Dave Hart <hart at ntp.org> wrote:

> On Wed, Oct 6, 2010 at 09:42 AM, Venu Gopal <neo.venu at gmail.com> wrote:
> > Hello Folks,
> >
> > I tried using time1 and time2 flags but things became worse :-(.
> > Everything works fine with NMEA driver when using local PPSAPI.
> > And I don't need use time1 or time2 flags (set to 0 by default).
>
> I believe you are conflating two separate issues.  At the time the
> NMEA driver had its own PPSAPI code, it used a single fudge for both
> PPSAPI and serial end-of-line timestamp offsets.  Since then, the two
> fudge factors were separated, to allow improved startup behavior by
> bringing the serial timestamp closer to the PPS that is eventually
> used.
>
> If you are switching back and forth between older and newer ntpd to
> test using NMEA-local PPSAPI code, you are also switching between the
> prior and current fudge behaviors.
>
> The short-term goal you should have is to experiment with "fudge
> 127.127.20.x time2 y" varying y to attempt to reduce the size of the
> step when switching from serial timestamps to PPS.  Do this without
> hardpps, at least initially.  You should within a few tries be able to
> get the difference between the two times in the tens of milliseconds
> or better.
>
> I'm pretty confident others are using the newer NMEA code, sine it has
> been that way for well over a year.
>
> Good luck,
> Dave Hart
>



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