[time-nuts] GPS for ntp

Chris Albertson albertson.chris at gmail.com
Tue Oct 21 12:48:52 EDT 2014

On Tue, Oct 21, 2014 at 6:58 AM, Simon Marsh
> How do you map the timer counter value in to a PPS timestamp ?
> (that is, how do you turn the HW counter value in to what the OS thought the
> time was when the event occured ?)

He is running NTP.   NTP's job is it keep the system time in sync with
a number of "reference clocks".  The 1PPS from a GPS makes a good
reference clock.  It does this by adjusting the RATE of the system
clock to not gain or loose vs. a set of reference clocks over time.
The algorithm is not simple.  The weak link is that the timing is done
in software and in the real world the accuracy is a few microseconds.


Chris Albertson
Redondo Beach, California

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