PPS documentation

Fred Wright fw at fwright.net
Sun Feb 26 21:13:31 UTC 2017

On Sun, 26 Feb 2017, Gary E. Miller wrote:
> On Sun, 26 Feb 2017 12:42:37 -0800 (PST)
> Fred Wright <fw at fwright.net> wrote:
> > From drivers/pps/Kconfig:
> >
> > ---------------------------------------------------------------------
> > config NTP_PPS
> Oh, that interface.  NTP does not use that interface at all.  If you are
> going to connect your PPS directly to the kernel then you do not use ntpd
> at all.

It can be enabled via some flags bits in ntp.conf (IIRC only in the
relevant refclock driver(s)), which may or may not have survived the
ntp.org->ntpsec transformation.  It's not a full replacement for ntpd,
since it doesn't provide coarse-time synchronization.  The NTP
documentation claims that ntpd's own discipline works better, though I'm
skeptical that that's true in *all* cases.

> Image if the kernel and ntpd where both trying to steer the clock with
> slightly different input data and control loops...

But supposedly ntpd knows when it's using that feature.

Fred Wright

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