Linux system time with NTP/Chrony but no PPS

[Mike Tubby]

Dear All,

I have an iMX6 based mobile device with a 4G mobile data connection that 
also has a uBlox MAX-M8W GNSS connected to a three wire serial interface 
(TXD, RXD, GND only) on the processor.  I don't have CTS or DCD for PPS 
input.

GPSD can see uBlox and my main application is fine with this setup, 
however we also want to set/maintain the Linux kernel time using NTP or 
Chrony with remote clocks over the 4G connection and/or a local feed 
from GPSD.

In previous questions Gary has recommended using Chrony over NTP where 
internet connections are intermittent - we're okay with this but haven't 
used Chrony before.

Reading the "how to":

    https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html

it implies that we need PPS as part of the solution - is this the case?

It it possible to use a local peer, i.e. GPSD with SHM, and two remote 
peers over 4G without PPS?

For our application we only need accuracy of better than 0.5 seconds so 
don't think we need custom fudge factors to make the solution work.

Does anyone have hints or a configuration snippet for Chrony or NTP that 
will work with GPSD without PPS?



Regards


Mike