[time-nuts] Beaglebone NTP server

Brian Lloyd brian at lloyd.aero
Thu Dec 11 12:54:04 EST 2014

On Thu, Dec 11, 2014 at 10:46 AM, Jim Lux <jimlux at earthlink.net> wrote:

> Actually, I think my point was that the problems I face at JPL are
> essentially identical to the problems we face at home.  I'm not in the time
> and frequency group (and I don't know that they actually are better off..
> although they do have rooms full of good clocks), so in our areas, we tend
> to have little point solutions to problems.

> It's not like there's a big time/frequency infrastructure with *free*
> spigots from the maser in every lab.  You have to pay for this stuff on
> your project funds, and a lot of times, it seems easier to find a one time
> expense (summer hire intern!) than sign up for a perpetual monthly charge
> plus the infrastructure change cost to pull the fiber/coax.
> We do have NTP, of course. But network drops are about $30-40/month, so in
> a lab, you might decide, hey, I can buy a widget for a few hundred dollars,
> and I'll have a better than NTP time source forever. And if you've got a
> student hire, buying that $200 unit off eBay or Amazon and taping a GPS
> antenna to the window starts to look pretty attractive.
> There's probably more than a 100 (certainly dozens) of little GPS antennas
> all over the lab connected to a bewildering variety of time/frequency
> sources in labs.  Sure, there's a goodly number of TrueTime/Fluke/Pendulum/Symmetricom
> boxes of various vintages and models, but there's also all manner of
> home-grown stuff.

Has anyone there noticed the amount of time and money spent recreating the
same thing over and over? Sure, individually it is cheap but when you do
the same thing hundreds of times, it is no longer a tiny amount. Clearly it
is a common needed service/device that your IT (or whatever) dept could
provide for nearly nothing. Sheesh.

> Which is exactly what we do at work.. Lots of old PCs doing something, but
> there's that "what do we do when the PC fails" question.  Just like at
> home, you've got a limited budget and time available.  Do you stock a
> couple extra BBBs or RPis? That costs money, and you need to have a place
> to store them where you'll be able to find them.

Why not? The freakin' things are down to about $35 for an RPi and $55 for a
BBB. And the price for this is going to go down again. (Well, eventually
fabbing the board and soldering the nearly-free components is going to
define the lower bound in price but the performance can't help but

> Or do you hope that when it fails 5 years hence, you'll have time and
> budget to rebuild?

And in 5 years there will be equivalent or better hardware at the same
price point. Stay in and eat beans for dinner one night to pay for your new
NTP server.

>> So, I am still looking for a straight-forward, "here is a really good way
>> to use a BBB coupled to a GPS 1pps to do NTP," treatise. Better still if
>> someone is using their LTE-lite to do it. It seems like a nice little
>> package for the amateur time-nut for everyday time and frequency keeping.
> Essentially, you want the equivalent of a Microsemi (Symmetricom/TrueTime)
> XL-GPS with the right options for, say, $500 or less.

Well, it is looking like I can do this very nicely for about $250 including
the BBB or RPi, LTE-Lite, and a 1U rack-box. Yes I have to build a buffer
for the 1pps and 10MHz output but that has been covered here very nicely.

> I do too.
> But I'm also not under any illusion that when my homegrown unit fails that
> I'll be able to fix it, or rebuild it for the same price.  It will depend
> on someone having done the redesign using whatever is available then, and
> published the cookbook.

I'm still thinking that the spare RPi or two tucked into the box with the
OS already loaded and configured will go a long way toward making sure I
can recover and keep going for many years. I have a BBB with Debian running
NTP that has been running for about 5 months now without a reboot as just a
local NTP stratum-3 server for my local machines. Works pretty well so I am
satisfied that it is stable to do the job. Once it is started I don't
expect to be doing a lot of OS upgrades. If it only runs NTP and all the
other services/daemons are turned off, it is going to be pretty difficult
to exploit. If it ain't broke, don't fix it.

Brian Lloyd
Lloyd Aviation
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.aero
+1.210.802-8FLY (1.210.802-8359)

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