[ntp:questions] pps coming in, not received by ntpd

folkert folkert at vanheusden.com
Tue Jul 2 19:40:08 UTC 2013

> > []
> >> To timestamp the pps, you have to have some module (ie kernel level)
> >> timestamp process. shmpps, gpsd, the kernel pps, write your own,....
> >
> > Thanks for the information, Bill.  My only additional comment is that 
> > the code to timestamp the PPS /can/ be in user-mode, although 
> > kernel-mode is preferable.  Additional Linux modules are /not/ required.
> ?? To timestamp the interrupt, you need kernel land. Ie, you need a
> module. Now you can use one of the modules others have written or you
> can write your own. But userland cannot get any sort of accuracy trying
> to figure out when and if a hardware line has been pulled up or not.

Well from userspace I get a jitter of only 10us on an rpi. Yes, I
totally agree that from kernel it would be better (in fact: is) but for
the moment it works for me :-) (too much hassle to recompile the kernel
and ntpd)

Folkert van Heusden

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