Re: [chrony-users] Setting up Chrony with PPS

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On Sun, Feb 21, 2016 at 07:26:21AM -0800, Deven Hickingbotham wrote:
> I believe the stats that appear below with show that the system problem was
> just poor antenna placement.
> On 2/19/2016 7:46 AM, Miroslav Lichvar wrote:
> >When chronyd has some NTP sources, you may want to tweak the offset
> >value of the SHM refclock so the measured offset as reported in
> >"chronyc sourcestats" is close to zero and the PPS signal can be
> >locked to it properly.
> Given the figures below, how should offset and delay be calculated?

You would adjust the 0.5 offset by 0.148, I'm not sure in which
direction. The goal is to have a smaller offset in the sourcestats
output. But it's not very important as long as the PPS refclock can
"lock" to the NMEA.

> Finally, any other suggestions for how to setup chrony.conf to quickly
> converge to PPS time after startup or acquisition of GPS signal?

If the clock is not too far, that should happen pretty quickly,
few minutes at most.

If the initial offset of the system clock is large (e.g. the board has
no RTC or battery), you might want to add something like "makestep 1.0
1" to the config, so chronyd is allowed to step the clock if the first
measured offset is larger than 1 second.

Miroslav Lichvar

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