PPS documentation

Gary E. Miller gem at rellim.com
Sun Feb 26 21:18:42 UTC 2017

Yo Achim!

On Sun, 26 Feb 2017 22:12:59 +0100
Achim Gratz <Stromeko at nexgo.de> wrote:

> Gary E. Miller writes:
> > I do not see anything in that file I disagree with.  Can you be more
> > specific on what you dislike in there?  
> It shouldn't mention a kernel driver that doesn't exist anymore.  PPS
> API is now available in mainline and that code is from the LinuxPPS
> project.

Since I don't see what you are seeing I suggest you send a patch.

> >> It should probably be mentioned that hardpps is not available even
> >> with the PPS API present on most distributions since it is
> >> incompatible with a tickless kernel, something that became standard
> >> somewhere in the 3.x line of Linux kernels ca. 2012.  
> >
> > Ah, no.  KPPS works better on kernels with a tick, but not
> > incompatible with tickless.  And most tickless kernels distributed
> > by distros have the option at boot time to change the tick
> > configuration.  Certainly RasPian is that way.  
> When NO_HZ is configured, you cannot configure CONFIG_NTP_PPS

Now ould you ever, ever, ever want to turn that on!  See my recent email
to Fred.  That option is to send the PPS to the kernel and not use
ntpd at all.

> AFter that ntpd then falls back to non-kernel discipline.

Correct, that is what we always want.  We want to use the kernel 
discipline in ntpd, otherwise there is no point to running ntpd.

With CONFIG_NTP_PPS you attach the PPS wire directly to the kernel and
the kernel does all the work, ntpd is not invovled at all.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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