[time-nuts] chrony vs ntpd

Hal Murray hmurray at megapathdsl.net
Sat Oct 28 17:05:16 EDT 2017

I don't know much about chrony.

jimlux at earthlink.net said:
> 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. 

If you are running on Linux, you can get easy access to the PPS info via 
something like:
  $ cat /sys/devices/virtual/pps/pps0/assert
The stuff in front of the # is the time, the stuff after is the pulse count.

So you can setup something to collect the offset and see how well whatever 
you are using is working.

If you want to test the non-PPS mode, you can setup your ntpd/chronyd to not 
use it.  The same measuring software will continue to collect data.

On most OSes, there are 2 ways to use the PPS.  There is an API to read the 
info.  You can use that as a source of time to steer your clock with the same 
sort of logic that you would use if you are getting time from a NTP server.  
Usually it works better because of reduced jitter.  Or, you can set a mode 
bit in the kernel and it will make the adjustments while you sit back and 

On Linux, the kernel mode is not available if your kernel is built with the 
tickless scheduler.  You have to build your own kernel...

These are my opinions.  I hate spam.

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