[time-nuts] more of a time distribution question

Hal Murray hmurray at megapathdsl.net
Thu Mar 30 16:43:34 EDT 2017

jimlux at earthlink.net said:
> I've got a bunch (a pack?) of beaglebones that are connected via  ethernet
> (wired) and I want them to be (roughly) synchronized. 

How rough?

> Running NTP (in some flavor) would be the obvious approach, but I'm in  an
> environment where there's no "outside" connectivity.. Could I make  one of
> the beaglebones be the NTP server, and the others be the clients? 

Yes.  Search for orphan mode.  I've never tried it.  Let e know if you can't 
figure out how to make it work and I'll use that as an excuse to learn more.

> (I've seen some "add a GPS to a Rpi to make a NTP server" projects, and  I
> could probably leverage that)

That should work.  I haven't found a GPS with PPS for the beaglebone.  What 
level of accuracy do you want?  If you only need 100 ms or so, then a normal 
junk GPS (no PPS) on USB should work.

There is at least one GPS+PPS over USB.  The GPS breakout board plus FTDI USB 
2.0 breakout with a few wires gives you PPS with improved accuracy.  (Not 
great, just 8x better than PPS over old/slow USB.)  I got mine from Sparkfun.

> I've also got a laptop (a mac, as it happens).. what's involved in  making
> *that* be a NTP server (e.g. the Mac might get its time from a  NTP server
> at some higher stratum, and then it propagates it down). 

That should work too.  I don't know much about the Mac environment.  If it's 
running a normal-enough ntpd it is already a server and you don't have to do 
anything.  If not, you will have to build/install your own and/or poke holes 
in the firewall rules.

These are my opinions.  I hate spam.

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