[ntp:questions] Re: PPS source not always being chosen?

David L. Mills mills at udel.edu
Tue Aug 16 01:57:13 UTC 2005

Hans Jørgen,

Say "tinker mindist 0.5". Then find out why the HP driver has such huge 
jitter. The Spectracom and Arbiter GPS drivers usually see jitter in the 
low tens of microseconds. Remember to disable the UART FIFO involved, 
which is highly system dependent. With Solaris and the PPSAPI, this is 
automatic. This might be the case in other systems as well when you 
light up the atom driver.


Hans Jørgen Jakobsen wrote:
> On Mon, 15 Aug 2005 00:11:05 GMT, John Ackermann N8UR wrote:
>>I'm seeing a strange quirk in the selection process of my NTP servers
>>that use refclocks that provide both a serial data timestamp as well as
>>a PPS signal.  I mentioned this some time ago, and with the most recent
>>4.2.0a-20050720 snapshot (running on FreeBSD 5.4), I'm still seeing the
>>same thing.
>>Attached below are the results of ntpq -p showing that the PPS source,
>>while apparently far better in jitter and offset, is being deselected in
>>preference to the serial timestamp source.  That just doesn't seem
>>right.  Is there something in my configuration (sample attached below)
>>that might be causing this?
> I have a look alike config.
> The jitter on the serial signal is causing trouble.
> The NTPD go through the following states:
> 1) GPS_HP gets selected
> 2) After some time PPS gets selected with GPS_HP as providing seconds.
> 3) GPS_HP gets declared insane because of large jitter.
> 4) PPS cannot be used any more.
> 5 goto 1)
> It would be fine if GPS_HP was ONLY used for resolving seconds ambiguity.
> /hjj

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