Please excuse my probably newbie question …
I have a Pi running GPSD and I see the input from the AdaFruit Ultimate GPS, and I see the PPS input as well (ppstest). I have NTP running, and I’m using the SHM driver.
I found an article that talks about the SHM driver having 3 units, so I’ve setup my server statements to use all 3. 127.127.28.0 / 127.127.28.1 / 127.127.28.2
NTP is happy with unit 2 (*), and has selected unit 1 as the secondary (+), and does not like unit 0 (x).
The GPS is being read from /dev/ttyAMA0
The PPS is via GPIO4 and /dev/pps0
I’ve loaded the GPSD config to reach both devices.
Honestly, I have no idea what each of the units means. How do I know which is the GPS time hacks, and which is the PPS hacks? I can’t find any good description of what the different units are.
I’m using the distribution versions of GPSD (3.17) and NTP (4.2.8P12) - not from GIT or any other sources.