[ntp:questions] Mixing .20 and .22 for a PPS signal

[John Thurston]

I'm not new to ntpd, but am trying to understand it (and its use with 
GPS signals) better. In this case, I'm working with ntpd 4.2.8p10 on 
several Pis running minimal raspbian, with MTK3339-based GPS receivers.

What I'm trying to understand better is the interaction of the 
127.127.20.u and 127.127.22.u drivers.

I've quieted my GPS module so it sends only $GPGGA sentences at 9600 
baud. With that, I find it with:
   server 127.127.20.0 mode 0x12
To grab the PPS signal, I can then:
   fudge 127.127.20.0 flag1 1

But I can alternatively grab the PPS signal from the .22 driver with:
   server 127.127.22.0

How are these two methods of grabbing the PPS signal different, and why 
might one method be preferred over another?



-- 
    Do things because you should, not just because you can.

John Thurston    907-465-8591
John.Thurston at alaska.gov
Department of Administration
State of Alaska