[ntp:questions] false ticker after GPS coldreset

Jakob Bohm jb-usenet at wisemo.com
Tue Oct 31 18:55:28 UTC 2017


On 31/10/2017 18:17, William Unruh wrote:
> On 2017-10-31, valizadeh65 at gmail.com <valizadeh65 at gmail.com> wrote:
>> i have a ntp server based on Raspberry Pi3 with PPS (from u-blox6 ). i have also added a hardware clock to this system.
>>
>>
>> SOME times there is a large offset(3-18 sec) on the SHM (ntp driver 28).
> 
> What program is delivering the time to the SHM? gpsd?
> 
>> i did some experiments and figured out it is related to "leap seconds".
> 
> No idea how it could be related to leap seconds. Leap seconds are only one
> second and that almost never happens. Is your gps broken?

He is obviously talking about the total accumulated leap seconds since
either IAT start (37) or GPS start (28).  Because the GPS satellites
broadcast TAI+19s every 1.5 seconds, but UTC-(TAI+19) every 12.5
minutes, many GPS receivers provide TAI+19 or TAI between power up and
reception of the offset.  Theoretically, something on the computer could
detect this and get the proper offset from the leap-seconds file, but
few implementations have that particular ability.


Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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