Re[2]: NTPsec reports excessive jitter from GPSD/KPPS SHM

[Nick Burkitt]

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.