[LinuxPPS] gpio-pps synchronisation -> discarded by intersection algorithm

[Chris Albertson]

I just made that mistake too.   Best to use the PPS support that is inside
the NMEA driver, Don't use "Atom".      NMEA is typically a large fraction
of a second "off" the second as it can take a longish type to transmit all
that ASCII data.      Do PPS in the same driver and this gets fixed.

Now I have one question:   How do you physically connect to GPIO.  I've
only used serial PPS.   What other ways are there to connect a pulse to
Linux PPS?



On Mon, Jan 9, 2012 at 10:42 AM, Miroslav Lichvar <mlichvar at redhat.com>wrote:

> On Mon, Jan 09, 2012 at 06:52:07PM +0100, Thomas Smits wrote:
> > NTP starts selecting GPS NMEA driver and PPS for synchronisation, but
> > I get "discarded by intersection algorithm" quite soon.
> > Then both sources are discarded.
> >
> >      remote       refid       st t when poll reach   delay   offset
>  jitter
> >
> ==============================================================================
> > xGPS_NMEA(0)     .GPS.         0 l   16   16  377    0.000   7.888  5.425
> > xPPS(0)          .PPS.         0 l   15   16  377    0.000   347.025
>  1.741
>
> > config:
> > >>>>>>>>>>>>>>
> > server 127.127.20.0 mode 17 minpoll 4 maxpoll 4 prefer
> > server 127.127.22.0 mode 1 minpoll 4 prefer
> > fudge 127.127.22.0 flag3 1 flag2 0 refid NMEA
>
> What ntp version is that? I think only the NMEA source should have the
> prefer keyword. You can also try to use just the NMEA source alone
> with the flag1 set to 1 and /dev/gpspps0.
>
> I'm curious if you can get better jitter than 1 us (the best result
> I've seen with PPS on serial port).
>
> --
> Miroslav Lichvar
>
> _______________________________________________
> LinuxPPS mailing list
> LinuxPPS at ml.enneenne.com
> http://ml.enneenne.com/cgi-bin/mailman/listinfo/linuxpps
> Wiki: http://wiki.enneenne.com/index.php/LinuxPPS_support
>



-- 

Chris Albertson
Redondo Beach, California
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://ml.enneenne.com/pipermail/linuxpps/attachments/20120109/6be27cc4/attachment.htm