Testing ntpd and/or timing from gpsd

[Hal Murray]

esr at thyrsus.com said:
>> This seems like a good opportunity for an experiment.  What do you have in 
>> the way of a place to stand while can monitor other NTP servers?
> The Pi might be it.  I have it set up to monitor four pool servers with
> noselect.  I get output like this: 

Begin rant...

If you are going to be playing this game, you need a few toys.  The primary 
one is a PC with a real serial port and a good GPS receiver.

You can use a Pi with GPS to monitor other systems, but the Ethernet on USB 
that limits the resolution of what you can measure.  It's probably good 
enough for watching sites on the Internet and/or your ISP connection.  It's 
probably not good enough if you are interested in the difference due to using 
the kernel PLL.

Another good example is the offset from PPS over USB.  It's a whole lot 
simpler to measure that if you have a place to stand.


You can use an old PC.  Their main problem is that they eat a lot of power 
and make a lot of heat and noise.

Some old laptops have serial ports.  Sometimes they are on docking stations 
or whatever you call them.

You can get ATOM systems that don't take much power.

The high cost route is things like:
  http://www.mini-box.com/site/index.html
I got the Intel D2500CCE because it had 2 serial ports.
  http://www.mini-box.com/Intel-D2500CCE-Mini-ITX-Motherboard
I don't like any of their boxes - no flow-through cooling,
but I haven't found anything better.

The low cost route is eBay.  I've gotten several Dell FX-160 boxes for under 
$100.  They are fanless.  (not really, there is a tiny fan under the disk)  
You want the hold-upright stand for cooling - or fake something.  They are 
available for roughly $15.  You want a disk - it takes a special bracket.  It 
might work to run from a USB thumb drive.  They come with 2 versions of CPU.  
The 330 has 2 hyperthreaded cores so it looks like 4 CPUs at 1.6 GHz.  It 
only takes a few minutes to configure, build, and check ntpsec.  (without 
documentation)

I'll say more about either if anybody wants.

There are probably other brands/models available.  I haven't spotted any 
obvious good ones.  Many of the no-fan systems don't have serial ports.  
Please let me/us know if you find one you like.

There may be good ARM systems, but I don't have any experience with any of 
them.


For a GPS unit, the best deal is probably the Sure board.  Some soldering 
required.  Adding the PPS to the serial port isn't very hard.  Getting it on 
the USB port involves tiny pins, but that isn't necessary.


-- 
These are my opinions.  I hate spam.