Re[3]: NTPsec reports excessive jitter from GPSD/KPPS SHM

[Nick Burkitt]

Hi Greg.

Although it appears that gpsd assigns only one shared memory unit for 
PPS devices. So if I declare my PPS device before my GPS device on the 
gpsd command line, I have to configure ntpd to use SHM(0) as the PPS and 
SHM(1), not SHM(2), as the GPS.

-Nick

------ Original Message ------
From: "Nick Burkitt" <address@hidden>
To: "Greg Troxel" <address@hidden>
Cc: address@hidden
Sent: 3/9/2020 10:36:48 AM
Subject: Re[2]: NTPsec reports excessive jitter from GPSD/KPPS SHM

> Hi Greg.
>
> My understanding (if that's not too strong a word) is that gpsd assigns two 
> shared memory units for each device (as declared on the gpsd comman dline). 
> Since I've got only GPS on one device (/dev/ttyACM4), and only PPS on one 
> device (/dev/pps0), gpsd assigns two pairs of shared memory units (0 and 1, 2 
> and 3), and only one half of each pair (0 and 2) is actually used.
>
> -Nick
>
> ------ Original Message ------
> From: "Greg Troxel" <address@hidden>
> To: "Nick Burkitt" <address@hidden>
> Cc: address@hidden
> Sent: 3/9/2020 9:43:07 AM
> Subject: Re: NTPsec reports excessive jitter from GPSD/KPPS SHM
>
> > "Nick Burkitt" <address@hidden> writes:
> >
> > >  # GPS Serial data reference (NTP0)
> > >  refclock shm unit 0 refid GPS noselect
> > >  # GPS PPS reference (NTP1)
> > >  refclock shm unit 2 minpoll 3 maxpoll 3 refid PPS prefer
> >
> > Perhaps this is documented in gpsd, but I wonder why there is unit 0 and
> > unit 2, vs 1.