[ntp:questions] Re: soekris 4501 that won't settle

Richard B. Gilbert rgilbert88 at comcast.net
Tue Mar 21 15:23:57 UTC 2006


Joshua Coombs wrote:
> My nanobsd testbed has decided to drive me up a wall.  When I set it 
> loose, it starts hunting for a pll adjustment value, swinging wider and 
> wider with each period.  When I last restarted ntpd to try a conf 
> change, it was varying the pll freq by 40ppm over the course of one of 
> it's sweeps.
> 
> Plotting the adjustment value over time generates a lovely sine wave 
> with a static period but an exponentially growing amplitude centered on 
> -25ppm.
> 
> The box is running FreeBSD 6.1B4, and I've alternated between the base 
> included ntpd (4.2.0a) and the 4.2.1RC and both show the same behavior.  
> I was initially locking the poll interval at 2048 seconds as this is a 
> test setup and I both wanted to verify the stability of the 4501 and 
> keep from abusing the remote servers I was using.  I've lowered it to 
> 512 seconds to see if that improves things...
> 
> Any suggestions on where to look for the cause?  I picked 4501s based on 
> PHK's write-ups covering their excellent timekeeping abilities, and am 
> not seeing it in practice so I'd like to know where I err'd.
> 
> Joshua Coombs


Probably by locking the poll interval.  There are excellent reasons, 
involving stability, behind the default values for MINPOLL and MAXPOLL. 
  Configuring NTP with the default values is not considered server 
abuse.   Server abuse is polling at 1 second intervals!!

If you try the defaults, your box should synch up nicely and increase 
its poll interval to the value that gives the best stability.  If you 
are using a good server and a good network connection it should probably 
go to 512 or 1024 seconds and stay there as long as conditions don't 
change.

You neglected to say what you are trying to synchronize with and that 
may be relevant.  FWIW, PHK was using GPS reference clocks on his 
Soekris boxes.




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