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.
Thanks,
Neil.
===================================
Neil,
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.
http://www.satsignal.eu/mrtg/performance_ntp.php
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.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: [email protected]
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