My experience with NTP service is that you need to keep it active. If you let it set the clock on the Rpi and then keep running without the internet connection the time on the clock gets pretty far off quite quickly. Like one day later it is way off.
From: John D Hays - K7VE
Sent: Wednesday, December 26, 2018 5:34 PM
Subject: Re: [udrc] Setting up auto time with draws gps
As has been discussed previously. NTP services like chrony slowly adjust the system clock based on information obtained from both ntp servers and refclocks (like the GPS and PPS).
Basil has created a script that verifies time at ~/n7nix/gps/verify_time.sh
The command line to do a quick update of the clock is: sudo chronyc makestep
You can verify your clocks with: chronyc sources -v
The battery backed RTC in the GPS must be set by the GPS once it has acquired the time reference from the satellites.
In my opinion, NTP time synchronization works best if the computer is not powered down and the Raspberry Pi is well suited to continuous operation at low power consumption. With the computer running continuously the chrony daemon can keep the system clock well synchronized whether using the GPS/PPS and/or network connections. (It ignores sources that are not reporting or are way out of sync.)
On Wed, Dec 26, 2018, 16:16 Art - KC7SDA <nouse4anick@... wrote:
i think you have to have the battery installed for the rtc.... it takes a bit to get the signal and then set the clock.