[time-nuts] Beaglebone NTP server

Jim Lux jimlux at earthlink.net
Thu Dec 11 13:44:59 EST 2014

On 12/11/14, 9:54 AM, Brian Lloyd wrote:
> 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.
> 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.

Nothing in an institutional environment is provided for nearly nothing. 
The *actual cost* to provide a network drop is very close to the 
$30/month my project gets charged (there's armies of auditors checking 
this stuff).

There's also the phenomenon (applicable to hobbyist and business alike) 
of "different kinds of money and resources".  As a hobbyist, I pay for 
hardware, but my time is (sort of) free, at least in the sense that I 
don't have to write a check to myself for the time I spend.  I do pay an 
opportunity cost in the sense that time I spend stringing coax across my 
roof to the antenna is time that I can't spend on something else which 
potentially is remunerative.

Similarly, in business, there's a difference between "project funds" and 
"infrastructure funds".  Likewise, a big difference between "capital" 
and "expenses", and local situations and project stuff might push one 
one way or another.  For NASA, each year stands alone, too, subject to 
the vagaries of Congress and the Executive Branch: just because you have 
funding this year does not mean that your project will be funded next 
year, even if it's a multiyear project.

A 50k project isn't going to be able to buy a $100k Vector Network 
Analyzer; they're going to rent one for a few thousand a month.  A $10M 
project lasting 3 years might say, hey, we'll spend 100k in the first 
year, rather than 100k spread over 3 years as monthly rental fees.

Or, more timenuts-ish.. Do I buy a $5k box from MicroSemi, put it in the 
rack and go? Do I buy $500 in parts and $1000 in student intern? Do I 
spend $3000 in facilities costs to run a fiber drop to my lab from the 
maser, the purchase costs of the local cleanup loop and buffers, and 
then pay whatever the monthly fee is to keep that fiber alive and my 
share of the maser cost?  (I actually don't know if the maser cost is 
shared by the users, or paid for by an institutional support account.. 
But for things like network drops, clean rooms, antenna ranges, ESD 
inspections, you pay as you use it)

It kind of depends on what my needs are.  There are relatively few 
things I might do that need the maser, and I might just drag my test 
article up the hill to the frequency and timing lab for a few weeks and 
pay the labor costs of the FTL folks to do it, and for the rest of the 
time when all I need is "reasonably clean quartz oscillator that is 
disciplined" I use my local GPSDO (whether XL-GPS or homebrew).

that's why lists like this are so useful.. Homebrew is more common than 
some might expect in a research lab environment.  And there's an 
undeniable benefit in "rolling your own" to develop the skill sets.

I am MUCH better suited to making the make/buy/rent decision because 
I've had practical experience getting a GPSDO working, using a truetime 
box, and hooking up that cleanup loop from Wenzel to the maser spigot, 
and subsequently trying to make ADEV/Phase noise measurements with all 
manner of equipment.

So some of that "do it over and over" rather than "institutionally 
provided" might be viewed not as paying too much for the ultimate 
service, but as a training and educational expense.

This is particularly important as the folks coming out of school are 
increasingly specialized (due to the increasing breadth of what might 
get covered in a EE or CS degree), and many may not know which end of 
the soldering iron gets hot, just because it's not something they ever 
had to do.

>> 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
> increase.)

But you also need to stock all the other parts, the GPS receiver, etc. 
So you're really looking at something like a few hundred bucks/copy. 
And that's a box that has to find a home on a shelf and have someone 
remember where it is and what's in it, and to make sure that those spare 
parts aren't scavenged for some other project.

And that there is actually the physical room to store them.  Every year, 
we have to justify the existence of such boxes, because we're all total 
pack-rats, and you never know when you might need that old slotted line, 
or that piece of unistrut, or that odd shaped piece of waveguide.

While there's not an actual dollar price associated with storage space, 
if we were left to our own devices, we'd have no room left in the labs 
because the shelves would be overflowing with 40 years of spares.

So we try only to keep things that might get used in, say, the next 10 
years, or for which there is a specific use anticipated.

This kind of thing applies to my garage as well as work, except that at 
home, I get to be the sole decision maker of "keep vs throw away", 
constrained only by the physical space available. If I have that shoebox 
with the RPi and GPS receivers in it, do I throw away that S-100 serial 
port card to make room for it?

>> 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.

But you'll need to redesign for that equivalent or better hardware. It 
is *unlikely* that it will be a drop in replacement, which is sort of my 

You're depending on either a speculative future development/porting 
expense, or that the kindness of strangers will provide a cookbook 
solution that you can assemble.

>> 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.

Yep... and that's way cool.

>> 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.

How do you know it's the RPi that will break?  Do you also spare the 
LTE-Lite? and the buffer amplifier?

So it starts to add up..  An extra $250 today (plus storage space) in 
exchange for some speculative redevelopment and $250 in a few years?

My own preference, today, is for the latter... I'd rather learn about 
the new technology when the time arises

(My wife, the MBA,  would probably say, "put the $250 in some investment 
vehicle and in 5 years you'll have enough to pay for the new hardware 
AND to pay for someone to hook it up")

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