[time-nuts] Beaglebone NTP server

Simon Marsh subscriptions at burble.com
Thu Dec 11 03:41:58 EST 2014

On 11/12/2014 04:15, Chris Albertson wrote:
> Those sub 1 u-second numbers are very good.  They argue for using the BBB
> as an NTP server but I wonder if it really is the best.   I think the
> numbers that matter are measures of the close on the computers who use your
> BBB as a server.  In other words the goal is to synchronize a set of
> computers.  Can The little BBB push accurate time out to a set of user
> computers and keep then in sync better then some other NTP server platform?

The BBB scores over the Pi here in having real hardware ethernet instead 
of USB ethernet.

Better, the BBB has hardware support for IEEE1588 timestamping so you 
can ditch NTP and distribute time using the BBB as a PTP grandmaster. 
The software is mature, but unfortunately a kernel rebuild is required 
to enable the appropriate drivers.

The attached graph shows an overnight test using two BBBs connected via 
a normal (i.e. non-IEEE1588) gigabit switch. The offset graphed is as 
reported by PTP on the slave, the black line is a moving 100 point 
average and the scale is in ns. The stddev offset over the period is 
about 260ns.



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