[ntp:questions] Can NTP sync within 1ms

William Unruh unruh at invalid.ca
Tue Apr 29 16:15:36 UTC 2014

On 2014-04-29, Rob <nomail at example.com> wrote:
> William Unruh <unruh at invalid.ca> wrote:
>> The problem is not the electronics, it is the response of the system to
>> the interrupt. That interrupt processing time is in the usec range.
> This does not really matter when it is constant.
> And my experience is that the jitter on the PPS refclock is usually
> 0, 1 or 2us when I check it.

That sounds like 100% variability. And the serial port level converter
time delay is much more constant. 
Also look at the jitter when the system is heavily loaded with disk
input/output or network load. 

> On a newer server that has just been configured for this task it is
> the same:
>      remote           refid      st t when poll reach   delay   offset  jitter
> oPPS(0)          .PPS.            0 l   16   16  377    0.000   -0.001   0.001
> (the GPSDO is still synchronizing, things may be even better after that)

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