[time-nuts] chrony vs ntpd

jimlux jimlux at earthlink.net
Sat Oct 28 12:04:25 EDT 2017


Now that I have successfully connected my GPS receiver to my beagle and 
I'm getting pps ticks into the driver, etc. (thanks to info from several 
folks on this list!) the question arises of whether to use ntpd or chrony.

For my particular application, I'm more interested in synchronizing time 
on the local machine, not necessarily being a NTP server - all of my 
beagles have a GPS on them.  Of course, there may be times when a GPS 
doesn't work, or something else comes up where it would be useful for 
one of the machines to "get time" from somewhere else.

What I am doing is using the Beagle to capture RF samples (RTL-SDR) in a 
distributed array, with wireless connections among the nodes.  The 
processing isn't necessarily real-time (maybe later..), for now, it's 
"trigger some seconds of capture at approximately the same time" and 
post process in matlab/octave.

There's all kinds of nondeterministic latency issues with the 
USB/RTL-SDR path, so I'm under no illusion that I can capture samples 
aligned to the 1pps.  However, what I *can* do is generate a "sync 
pulse" from the 1 pps and feed it into the RTL's RF input in some (TBD) way.
And the 1pps might give me a clever way to calibrate the frequency drift 
of the RTLSDR's clock.

Right now, I'm interested in HF signals (so the period is 30 ns at the 
top end, and 500 ns at the bottom end)





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