On 13/12/2021 21:22, Trent Piepho wrote:
And finally we can have the kernel act on the PPS timestamps itself.
But NTP network traffic might be a bridge too far. Mills describes
this as a "hardpps()". This was added to Linux in 2011 by Alexander
Gordeev, based on Mills' work, but with a different implementation.
This is a "kernel consumer" of PPS timestamps, which can be used to
steer the PLL entirely inside kernel code. It's enabled with the
kernel config option NTP_PPS. One can easily see if this is present
in the kernel via the usual methods. It is often NOT enabled because
it doesn't work with tickless kernels. I do now know if current ntpd
supports this or what it takes to use it with ntpd. I have used it,
but I wrote my own code from scratch to integrate it with a GPS module
to perform time sync without installing either ntpd nor chrony.
Trent,
Thanks for that! I was only aware of a limited subset of that as I came later
to NTP on Linux (it was mostly Windows before), and I understood even less at
the time! Your notes helped clarify things, thanks.
David
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