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I use ntpd with GPS NMEA with PPS as follows

server 127.127.20.0 mode 18 minpoll 4 maxpoll 4 prefer
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 flag4 0 time2 0.475
  • flag1 enables PPS signal processing of /dev/gpspps0 implicitly
  • flag2 captures rising or falling edge
  • flag3 uses ntpd clock or kernel discipline

I have read about that flag2 could be used for polarity issues with the serial port. So if there is no problem with that I should use rising edge. Or are there any issues about a steeper edge in the falling case?

Should I use ntp clock or kernel discipline? What's the difference? I've read that min/maxpoll 4 and ntp clock discipline is better then kernels due to a median algorithm. Is that also correct?

I set time2 so that ntpd synchronizes faster in the beginning right? Should I set time1 - how? I didn't get that point out of the documentation.

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    What's your goal? What are you trying to achieve? – Ladadadada Oct 20 '14 at 23:02
  • @Ladadadada I want to use this time in an astronomical application. I have already set low_latency for the serial port. I try to achieve to get the most accurate/best configuration . My goal with this question is that anyone verify my assumptions or correct me. – wenzul Oct 20 '14 at 23:13

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