[ntp:questions] Befuddled and confused, again...

Dave Baxter spam at goes.nowhere.com
Mon Feb 15 20:45:06 UTC 2010

On 2010-02-14, Dave Baxter <spam at goes.nowhere.com> wrote:
> [quoted text muted]
> I *Need* PPS support, as I have an app that needs mS accruacy.  See:-
> http://www.dxatlas.com/Faros/  for details of what I have running, that 
> needs such data.   Plus, for whatever reason, my ISP (Demon/Thus/C&W) 
> seem unable to provide a stable NTP service these days.

You do not need PPS support. Just use something like gpsd, and the shm
refclock and you will get usec accuracy (not ms accuracy). 

> [quoted text muted]
> "spare and empty" PC, I decided to revisit the FreeBSD version, after 
> all, it only took me 2 days last time to get it going.
> I've been at it (trying to get FreeBSD working again) this time for over 
> 3 weeks!  And am about to lob the thing out of the window.

> Install a prepackaged Linux from one of the distros. don't install X
> or all of the other stuff (openoffice, firefox, etc) to keep the size 
> down.

> Then on either Linux or bsd, you could use chrony instead, and get 
> even better accuracy and much faster convergence, but since you 
> already only want ms accuracy, that might be overkill except for the 
> faster convergence. 

GPSD as in Global Positioning System Diciplined.

Yes, it uses the DCD line (I think) to input the PPS signal from the GPS 
receiver, a Garmin GPS16LVS in this case.  It's all configured and 
working on a Win2k box, with the Meinberg port, but I want that physical 
machine for something else, so I'm trying to get the FreeBSD version 

NTP timekeeping via the internet is not reliable at the mS level, I 
suffer time of day related WAN congestion, sometimes the end to end 
latnecy can be over 1.5 seconds, but no packet loss, so the ISP says 
that's good!   Hence my need for a local NTP source, as 'net based is 
not a viable option for me at this time.

Based on the Meinberg port of NTPD behaviour, the pull in time is not a 
problem, as the thing is left on 24/7 and on a UPS.  If that lot ever 
collapses, then by the time I've got everything else back up and 
pumping, even NTPD has pulled in enough to keep Faros happy(ish.)  (It 
might misidentify the ZL beacon signal's path perhaps, but the others 
will measure OK.

I suspect even Chrony wont tolerate variable network timing either.  Oh, 
it's asymetric and grosly variable ping to ping too, but as there is no 
packet loss, they won't do anything to improve matters as I'm a "home" 
(not busines) user...  After about 6PM local, everything becomes nice 
and fast again, until 9AM the next day.  Traffic shaping by any other 
name, except at weekends!

I still do not know the exact path needed for the Make.conf file.


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