[ntp:questions] ATOM falseticker with flag3 enabled

David Lord snews at lordynet.org
Fri Mar 30 12:29:28 UTC 2012

David Lord wrote:
> A C wrote:
>> On 3/29/2012 03:29, David Lord wrote:
>>> Dave Hart wrote:
>>>> On Thu, Mar 29, 2012 at 02:44, A C <agcarver+ntp at acarver.net> wrote:
>>>>> Without flag3 it appears that ntpd does the heavy lifting but is
>>>>> unable to
>>>>> use the PPS unless a prefer peer is set. With flag3 enabled, PPS is
>>>>> running
>>>>> without a prefer peer.
>>>> Being unable to use the PPS unless either a prefer peer is set or
>>>> another knob is adjusted (see what I quoted earlier) is operating by
>>>> design. The change in operation with flag3 1 seems likely to me to be
>>>> an ntpd bug, which is why I'd like to see a bug report filed. Unless
>>>> I'm missing some design intention, it seems to me PPS should not
>>>> become reachable with no prefer peer regardless of flag3.
>>> On NetBSD-5, i386, I had the PPS marked as falseticker as
>>> from March 2, 2012 when I updated from 4.2.6p3 to 4.2.6p5.
>>> When I went back to 4.2.6p3 the 'o' was back. I hadn't spare
>>> time to investigate and changed config to use only type 20
>>> nmea driver with 4.2.6p5.
>> Interesting, so that's the same OS on two platforms with similar 
>> problems.  Did you happen to also observe your minimum jitter times in 
>> the upgrade?  When I run 4.2.6 my minimum jitter is reported as 
>> 0.061ms.  But in 4.2.7 the minimum jitter is 0.122ms, exactly double 
>> the 4.2.6 value.
>> I'm still tinkering with my configuration to see if I can get ATOM to 
>> stop being a false ticker but no luck yet even though it's still 
>> disciplining the clock.
> Jitter depends on time of day, weather etc. The variations
> doesn't seem to have been altered by the update from 4.2.6p3
> to p5.
> I didn't tinker as something is obviously broken with
> type 22 driver in p5.

Loop_summary averages over 7day
               rms(us)         var
20120123-29      3.85       0.086
20120323-29      6.71       0.353

You might be tempted to draw a wrong conclusion resulting
from update of ntpd from 4.2.6p3 type 20 (nmea) + type 22 (pps)
to 4.2.6p5 with type 20 (nmea + pps).

The running plots of offset for show an extra peak between
0800 and 1300 during the latter period due to the pc being
in direct sun.


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