| Re: [chrony-users] Refclock Integration Advice |
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On Mon, 30 Nov 2020, Miroslav Lichvar wrote:
On Mon, Nov 30, 2020 at 03:03:10PM +0000, Chang, Benjamin wrote:
So I managed to switch it to a 50% duty cycle PPS, and it appears to take every pulse now. The LastRX floats between 0 and 2 (seemed like 20 us is too short a pulse).
However, now when I look at the measured offsets, it seems to greatly vary from 100s of ns to 10s of us. Shouldn't it be consistent? According to the datasheet of my PPS (the syncserver S650), it should have ~15 ns accuracy and resolution. When I scoped it on an oscilloscope, it was consistent and not varying.
Almost certainly problems with the interrupt handling by the computer. It
takes a while for the operating system to get to the interrupt, if other
things (disk reads, etc) are hogging the interrupt system. 20us seems a bit
long, but it will depend on your system.
Here is my conf file setup
My ntp server setting: minpoll -6 maxpoll -6
That still makes absolutely no sense. What in the world do you expect to
change in 1/64 of a second. Certainly there is no new time signals coming from
the gps unit.
My PPS: poll 0 prefer trust pps width 0.5
If you use a serial port for the PPS, the stability will depend on how
stable is the interrupt delay. A stability in tens of microseconds is
not unusual. You may get better results if you disable all
power-saving states and set a fixed frequency for the CPU.
If you increase the chrony poll to 3 or 4, the PPS samples will be
filtered using a median filter and that should help with the outliers.
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