I’m not familiar with Chrony. With NTPsec, the PPS driver docs say [0]:
> While this driver can discipline the time and frequency relative to the PPS source, it cannot number the seconds. For this purpose an auxiliary source is required;
And so (with NTPsec), you need to define two sources even though it’s coming from the same device. One for the PPS signal for clock discipline, the other for the clock value.
> It’s unclear to me why there’s so much delay and jitter in the PPS timestamping.
I’ve messed around with this on a couple different GPS chips. I’ve found improvements can be made by increasing the baud rate to the maximum supported. 9600 tends to be the default, but 57600 works a lot better. Also, disable all NMEA sentences except the one you are using. Finally ramp up the update interval to be much more often. The default tends to be every 1000 milliseconds, but 100 milliseconds works better for less jitter. I’ve been using NTPsec, not Chrony, so maybe there are more nuances.
Im just a hobbyist, but I have a bit more details written up here, checkout the poorly designed hamburger menu for some charts and graphs: https://www.developerdan.com/ntp/
I get weird looks when I speak with people about my GPS PPS NTP servers. This is website amazing. Most of it is way beyond my comprehension, but it’s given me a lot to read up on.
Using the same receiver, but with a PPS wire to a GPIO pin on a raspberry pi, I get +/- 5µs jitter.
If you are interested, I have a write up with live graphs in the hamburger menu here: https://www.developerdan.com/ntp