Re: [gpsd-users] Raspberry Pi, GPIO PPS and NTP

[hans mayer]

dear Chris,

but the reason is clear and logical.
the 1PPS comes very exactly witch an interval of 1 second.
the SHM information is generated out of the serial interface
of the gps module. and this is far away to have a
constant interval.

i run a ntp server with a type 22 as clock source and
type 28 as time information.
and SHM driver floats around +- 10 ms while
PPS is about +- 10 us ( micro seconds ) for offset
see attached files.
( i didn't try SHM to bring to an average of 0 )

and of course this reflects the jitter too.


kind regards
hans

--



Am 09.06.2016 09:34, schrieb Chris Hastie:
> On 09/06/16 07:50, Gary E. Miller wrote:
> > > I would like to be able to use ntp's gpsd-ng json driver (type 46).
> > Uh, don't do it.  The only way to make it work properly is undocumented.
> >
> > Wait until it gets properly fixed.  The SHM drivers work better, and
> > work as documented.
>
> Intrigued now :)
>
> I thought I'd try various configurations and see which works best. I've
> had the SHM driver going for about 9 hours now and is producing
> considerably more jitter than my earlier test with NTP's PPS driver.
> This might be because I took the advice in the NTP docs to ignore the
> advice in the gpsd docs to use a minpoll of 4. I've just changed that,
> so I'll see how it goes from here.
>
>
> Cheers
>
> Chris