[time-nuts] An embedded NTP server

James Harrison james at talkunafraid.co.uk
Wed Jan 2 20:25:54 UTC 2013


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On 02/01/2013 20:05, David J Taylor wrote:
> James,
> 
> You might be interested in my write-up:
> 
> http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
> 
> and its performance:
> 
> http://www.satsignal.eu/mrtg/performance_ntp.php
> 
> I was playing with RasPi-1 today to see whether a different
> (navigation) GPS receiver or system configuration would make any
> difference to the oscillatory nature of the offset, hence the big
> step around 11:00 when the card was restarted after an hour's power
> down.  RasPi-2 with a timing GPS receiver looks better, and it
> should have an identical configuration to RasPi-1 (except that the
> USB port is being sent data).
> 
> Cheers, David

Interesting stuff indeed - the timing receiver certainly looks much
more stable, which is to be expected.

I'm not seeing quite as much stability on my Pi/setup -
http://i.imgur.com/6L8ur.png is the munin-measured kernel offset for
the last day. I've only been running it for a few days but I'd have
thought the clock loop should've stabilized a bit more than it has at
present. Could be that this particular GPS receiver isn't managing
very well at all to give particularly precise PPS pulses, which is
possible given it's a navigational receiver. The datasheet specifies a
60nsec accuracy but it's unclear if that relates to the 1PPS output.

Once this one's been running for a few more days I should have some
more interesting graphs; I'm getting one of my home boxes set up with
Graphite so I can push more detailed statistics and information to
that from the RPi about NTP etc and get a better feel for what's going on.

Cheers,
James
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