PPS documentation

Eric S. Raymond esr at thyrsus.com
Sun Feb 26 14:20:25 UTC 2017

Achim Gratz <Stromeko at nexgo.de>:
> The kernel PPS documentation in docs/kernpps.txt still mentions PPSkit as
> the PPS API provider on Linux.  PPSkit has not seen a release since 2007
> and was replaced with the integration of LinuxPPS into the mainline
> kernel somewhere in 2009.

OK, I can delete the text about PPSkit and the remainder still makes sense.

> 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.

I just grepped for hardpps and found a world of previously
undocumented complications.

By 'hardpps' do you mean the RFC1589 facility?

Are there really two *different* APIs for kernel PPS, one defined by
RFC2783 and one by RFC1589, or is the RFC2783 implemented in terms of
RFC1589 on systems that have the latter?

How is RFC2783 implemented on a tickess kernel?
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