[time-nuts] RasberryPi, timing and GPS receivers

Chris Albertson albertson.chris at gmail.com
Tue Oct 16 19:07:52 EDT 2012

On Tue, Oct 16, 2012 at 3:26 PM,  <xaos at darksmile.net> wrote:
> Michael,
> Thank you for your most valuable information.
> This is why time-nuts is so amazing!
> My goal is actually two-fold.
> First, I would like to have a NTP server that I can easily
> hook up (well, as easily as possible) without
> dedicadting a Linux server each time.

One does NOT need a dedicated server for NTP.  NTP can run on a linux
system that is also a web and mail server or on e  linux desktop
system that you use for web surfing and web browse ring, just as long
as the box stays running and you don't turn it off.
> My personal use would require 3 separate NTP servers
> because I am a time-nut and stratum 2 is not an option.

What level of accuracy is required?  Don't say "as good as posable"
because that can be quite expensive.  What really do you need?  About
the best you can expect from NTP without exotic hardware is 2 u-sec
level.   But maybe you'd be happy with 2 milli seconds.
> The idea here is to create a smart piggy-back architecture
> where the CPU/Ethernet sits on the bottom
> with (perhaps) a few modules on top of that
> with GPS right on top (let's call it the penthouse).

Remember that you cn buy a fully integrated Intel Atom mainboard that
is a bout 6" square and uses only a few watts for $90. The Atom will
run NTP and mail and web servers and allow web surfing all at the same
time and costs $90 including the soldered down CPU.  It will have a
real RS232 port and a good built-in Eithernet.  These boards don't
require fan cooling.
> For obvious reasons I would put the Power supply
> separately.

Why?  I hate power cubes
> So we are looking for a very small footprint
> NTP server.
> Now, I thought the RasberryPi would be ok
> even though I did not like the limitations you
> mentioned as well. It is very popular.

It is popular for some applications.  But a statum 1 NTP server needs
the PPS from the GPS to go to a hardware interrupt and it needs a
solid Ethernet controller with low latency.
> You mentioned the Olimex olinuxino. Wow!
> This is a thing of beauty indeed!
> https://www.olimex.com/Products/OLinuXino/A13/A13-OLinuXino/

Look at this one:

It is directly usable for NTP with no circuit design or soldering and
the NTP server will run at the few u-sec level while also running as a
file seder, web server and runing LLady Heather inside a virtual
Windows under VMware.  Not heat or fan noise.


Chris Albertson
Redondo Beach, California

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