PPS documentation

Fred Wright fw at fwright.net
Sun Feb 26 20:42:37 UTC 2017

On Sun, 26 Feb 2017, Gary E. Miller wrote:
> On Sun, 26 Feb 2017 14:29:59 +0100
> Achim Gratz <Stromeko at nexgo.de> wrote:
> > 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.
> Can you be more specific on a kernel that does not work?

>From drivers/pps/Kconfig:

config NTP_PPS
	bool "PPS kernel consumer support"
	depends on !NO_HZ_COMMON
	  This option adds support for direct in-kernel time
	  synchronization using an external PPS signal.

	  It doesn't work on tickless systems at the moment.

There's no reason in principle why it can't work on tickless kernels, but
the current implementation is deficient.

Fred Wright

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