Clarifications about PPS SHM content

[Martin Boissonneault]

Hi all,

I'm curious as to why NTPd would need to have both the GNSS PPS shm and the GNSS serial shm refclocks in the ntp.conf. Wouldn't the PPS shm contain enough time information as collated from GPSd?

I know they both refer to a different point in time (PPS for one, serial for the other one) but I'd think GPSd is smart enough to catch the serial time information and fill in the PPS blanks?

Assumptions:

• GPSd is properly configured,
  
• the GNSS serial sends the right strings, is properly configured, has a PPS signal line properly set up and working,
  
• and both shms give results.
  

In that case, is the serial shm needed by NTPd? I currently think the serial shm use case is for PPS line disconnection or unsynchronized GNSS (in both cases, time won't be great). Are there others?

Thanks,
Martin