[ntp:questions] Ignore one server except in extreme conditions?

unruh unruh at invalid.ca
Wed Nov 16 23:59:45 UTC 2011


On 2011-11-16, A C <agcarver+ntp at acarver.net> wrote:
> On 11/15/2011 22:09, Harlan Stenn wrote:
>> And you are sure the PPS signal goes away when your NMEA source is no
>> syncd?
>
> I'm not talking about losing sync on the GPS.  I'm talking about 
> purposefully ignoring the NMEA data because it has a lot more drift than 

Tthe NMEA certainly should not have more drift. Maybe more jitter. 
You should use the nmea for numbering the seconds, and pps for defining
the second start. You do not care that the nmea is 200ms off if you do
not use it for the subsecond timing. 

> the other servers so I'd like ntpd to use only PPS plus Internet when 
> the Internet is available.  If the Internet ceases to be available, fall 
> back to the NMEA.  Obviously if the GPS loses sync at the same time as a 
> loss of the Internet connection then the clock is just going to wander 
> away but would eventually come back when sync/connections are restored.
>
> In my case, I am supplying two different refclocks with the single GPS. 
>   The PPS is being fed through a serial port using the PPS refclock 
> (22).  The NMEA refclock (20) data is coming from a different serial 
> port with no PPS signal and the clock is not configured to us its own 
> PPS routines.



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