[ntp:questions] Re: Question on loopstats and PPS

Mauro Fiacco Mauro.Fiacco at ipaccess.com
Thu Dec 15 11:00:18 UTC 2005


The PPS signal is derived from an _unsynchronised_ rubidium source. It
provides a 1sec pulse signal which is interfaced to the serial port of
the server (/dev/cuaa0 on freeBSD) (no time infos are available)

I do not use refclocks, I let the kernel to discipline the oscillator
(The only thing on the conf file is "enable pps")

I have also slightly modified the ntp_loopfilter.c file such that the
PLL is not used, only the FLL correction (I modified the status passed
to the kernel).

One could use the as preferred clock (not much choise

The system works well; however, it is difficult to quantify how good it
is. The frequency error on loopstats refers to the PC oscillator.

Thanks again.



On Thu, Dec 15, 2005 at 04:14:42AM -0600, Hal Murray wrote:
> Date: Thu, 15 Dec 2005 04:14:42 -0600
> From: Hal Murray <hmurray at suespammers.org>
> To: questions at lists.ntp.isc.org
> Subject: [ntp:questions] Re: Question on loopstats and PPS

> >I am tryng to evaluate how good is my NTP server. It runs freeBSD and
> >uses a rubidium PPS signal to discipline the frequency (no time
> >correction).

> How are you connecting it up and/or what's in your conf file?
> Which refclock are you using?

> I didn't know NTP could do what I think you are describing.

> The PPS driver (refclock_atom) expects the PPS signal to
> arrive on the second boundary.  It needs some other source
> of time (a server marked prefer) to know which second the
> PPS signal matchs.
Mauro Fiacco 

ip.access Ltd                      
URL: www.ipaccess.com  

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