NTPsec leap second experience

[Hal Murray]

Stromeko at nexgo.de said:
> What I was getting at was that I've had quite good holdover performance
> (<1ms over 47 hours) that I wasn't really expecting to see from something as
> cheap as the rasPi and my improvised "ovenization" (which really is just a
> cardboard box and some bubble wrap plus running sha512sum on two of the
> rasPi cores to keep it at the desired temperature).  If NTP would have had
> some feedforward loop to keep the frequency offset adjusted during holdover
> that might have resulted in <30µs deviation over that same period of time.
> In general I'd expect that feedforward compensation could improve NTP
> performance by about one order of magnitude. 

What do you mean by "feedforward"?

ntpd works out the "drift" of the clock it is using.  The system time usually 
traces back to a crystal.  Sometimes there is smearing in there to reduce 
EMI.  (or dance under the regulations)

The actual frequency of a low cost crystal tracks temperature.  Details 
depend on all sorts of things.

Until you have a stable clock, perhaps by keeping the temperature constant, 
everything else is lost in the noise.


How much does your drift change over the day when your system is operating 
normally?


There is a wonderful paper on this area:

NTP temperature compensation
Mark Martinec, 2001-01-08 
  https://www.ijs.si/time/temp-compensation/


-- 
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