PPS documentation

Achim Gratz Stromeko at nexgo.de
Sun Feb 26 21:20:02 UTC 2017

Gary E. Miller writes:
> 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.

Yes it does, if you tell it to.  But it won't on tickless kernels
whether you tell it or not since the kernel doesn't offer that API in
this case.  It should, but it doesn't currently work.

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

That's why ntpd not only knows about this interface, but actively probes
it and switches from it's own PLL to the kernel one and vice versa
according to the result (and whether the PPS source the kernel uses is
still good).

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