[ntp:questions] basic questions about the leapsecond

Unruh unruh-svam at physics.ubc.ca
Tue Dec 16 19:18:18 UTC 2008


"David J Taylor" <david-taylor at blueyonder.neither-this-part.nor-this-bit.co.uk> writes:

>Unruh wrote:
>> "David J Taylor"
>[]
>>> In view of the popularity of the GPS18-LVC it's a pity that the
>>> driver support for the leap second isn't better, but I appreciate
>>> that being able to test once every few years doesn't make things any
>>> easier!
>>
>> As far as I can see, the GPS18-LVC unit does NOT warn of leapseconds.
>> There is absolutely nothing the driver can do if the information is
>> not supplied by
>> the GPS unit.

>Yes, that was poorly worded - I meant "shouldn't NTP note the leap-second 
>flags from the other Internet upstream servers, and base its whole second 
>values on those sources during a leap-second update, using just the PPS 
>part of the GPS signal?"  The would appear to apply to any GPS source 
>which is PPS + NMEA....

That is what it appears to do. I have three sources, a GPS PPS source (via
the shm driver which has no leapsecond warning), and two outside sources,
one a level 1 and the other a level 2 source (which is a pretty flakey
source, and is never the preferred source) The other level 1 source,
although separated from me by 45ms round trip has an offset at the .1ms
level (as compared with the PPS)

And my system is showing the leap second warning. 


ntpq> rv
assID=0 status=4964 leap_add_sec, sync_telephone, 6 events,
event_peer/strat_chg,
version="ntpd 4.2.4p4 at 1.1520-o Fri Mar 14 06:59:25 UTC 2008 (1)",
processor="i686", system="Linux/2.6.24.7-desktop-2mnb", leap=01,
stratum=1, precision=-20, rootdelay=0.000, rootdispersion=0.433,
peer=48639, refid=PPS,
reftime=ccf27d17.96467b01  Tue, Dec 16 2008 11:16:39.587, poll=4,
clock=ccf27d25.491436a5  Tue, Dec 16 2008 11:16:53.285, state=4,
offset=0.009, frequency=212.452, jitter=0.001, noise=0.001,
stability=0.000, tai=0





>David 




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