[time-nuts] looking for low-power system for gps ntp timekeeping

David J Taylor david-taylor at blueyonder.co.uk
Mon Jul 1 01:31:13 EDT 2013


From: Dennis Ferguson
[]
You aren't necessarily showing the part where the Raspberry Pi is a bit
weak, though.  How well do clients which receive their time via the
USB ethernet interface do?

The Beaglebone Black has about three advantages going for it in this
application:
[]
For a $5-$10 difference in price for the board I think these are worth it.
The RPI makes a fine, low-power replacement for Intel hardware for this,
but the Beaglebone Black has the raw material to do significantly better at
this than either of them.  The only problem with the Beaglebone is that it
is not as popular as the Raspberry Pi, so making use of the former is going
to require one to do more work on one's own to take advantage of it.

Dennis Ferguson
======================================

Dennis,

I've tested with 75 clients (simulated load) and not seen any problems with 
the Raspberry Pi's own time keeping.  I'll set my FreeBSD PC to look at the 
the three Raspberry Pi cards and report back....

A first report is that the offset is shown as 0.091 ms from one RPi and 
0.065 ms from the second, and 0.056 ms on the third RPi which is operating 
over Wi-Fi.  This is far better than I see from any Internet servers on my 
Cable Modem ISP service.  Jitter is 0.022 and 0.027 ms for the LAN connected 
devices, again much better than the best Internet device which shows 0.110 
ms (at what is the middle of the night for many - 06:00 clock time here).

Here the two units are similarly priced, so you can take your choice.

There is one write-up here:

  https://groups.google.com/forum/#!topic/beagleboard/bU_xZ9tWoiA

for using the BeagleBone Black as an NTP server, but he seems to have an 
offset of -0.281 ms from his PPS source, which is rather high.

Cheers,
David
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk 




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