[ntp:questions] Trimble Resolution T

unruh unruh at physics.ubc.ca
Mon Oct 17 17:45:23 UTC 2011


On 2011-10-17, Chris Albertson <albertson.chris at gmail.com> wrote:
> 2011/10/17 Miguel Gon?alves <mail at miguelgoncalves.com>
>
>>  what are the best (meaning well supported) refclocks today to
>> set up a new server?
>
>
> Likely the GPS with the best PPS is the new Oncore.   But for NTP you don't
> need 5 nanosecond accuracy.   From NTP's point of view 5 nS is not better
> than 50 nS.

In fact it is really hard for a computer to keep to 1us accuracy because
of the delays in interrupt processing. The computer has to recognize the
interrupt, deliver the notification that an interrupt has occured to the
interrupt processing driver, the driver has to then ask the operating
system for the local time to timestamp the interrupt. All that takes
time, and it is hard to keep that under 1us. 

Mind you his question is "which refclock is the most well supported",
not which is most accurate. But I am not at all sure that that is really
his question. The NMEA driver is well supported but, relatively
speaking" horribly inaccurate (ms rather than usec). Similarly many of
the radio clock are well supported, but even less accurate. 


>
>
> Chris Albertson
> Redondo Beach, California



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