[time-nuts] In search of ways to improve Raspberry Pi stratum 1server

David J Taylor david-taylor at blueyonder.co.uk
Mon Jan 12 10:25:21 EST 2015

Hi all,

This is my first post to the list. I have a Raspberry Pi B+ and a HAB 
Supplies U-Blox Max-M8Q set in stationary mode connected to a Virgin Media 
Superhub (broadband router) by a 0.5m cat7 ethernet cable. The GPS is 
attached to the Pi's GPIO and has an external active antenna placed on an 
inside window sill. The Pi is running Raspbian on a fast Class10 microSD 
card and has a kernel (Linux raspberrypi 3.12.35 #1 PREEMPT Sun Jan 11 
17:40:22 GMT 2015 armv6l GNU/Linux) rebuilt to disable tickless, enable PHY 
timestamping and enable all appropriate PPS options, and has NTP 
4.2.8p1-beta5 compiled with:
I've tried using Banana Pi and Beaglebone Black SBCs and have also used 
u-blox Max-7Q and Trimble Copernicus II GPS breakout boards with no 
improvement (The Banana Pi is the best but is stuck on the Allwinner 3.4 
kernel, which I'm not thrilled about), leading me to believe the roadblock 
to a more precise clock lies in my less than ideal antenna setup, but my 
questions are: can I improve upon this and, if so, how? Have I made any 
obvious errors? I'm relatively new to this and would appreciate any advice I 
can get.



I see approximately the same here, with the exception of those systems using 
a kernel which /is/ tickless where the jitter is a factor of about two 
worse.  I can see anything wrong.

I couldn't face recompiling the kernel another time, and have asked that 
nohz=no  be accepted by the stock kernel, particularly now that it includes 
PPS support.

Based on plotting the jitter with MRTG the Raspberry Pi cards perform at 
least as well as an Intel Atom system running Linux.


The Intel system did work rather better with FreeBSD, so it would be 
interesting to know whether the Raspberry Pi is capable of improved 
performance using that OS.  I would be most interested to know the outcome.

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

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