[time-nuts] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is "Good Enough"?

David J Taylor david-taylor at blueyonder.co.uk
Sat Jun 13 02:06:42 EDT 2015


Hi Max!  Thanks for the information, I was wondering if you had documented 
what you did to your Raspberry Pi so that it might be reproducible to 
someone like me (a newcomer time-nut and intermediate Linux user) ... you 
had said:
[]
Thanks so much for your assistance!  Sorry if these questions have been 
posted before, but I am very curious about your setup as it nearly matches 
mine!

    -Randal "r3" of CubeCentral
=======================================

I would also like to know how to best tweak the Raspberry Pi 2 for best
performance as an NTP server. Although I have been using Linux-based
firmware in my routers for several years now, I have never actually
worked In Linux before.

I have gone through several tutorials on compiling a custom kernel, only
one or two have actually ended in a compilation, but then I couldn't
figure out where the kernel and modules were and get them onto the Pi. I
have tried this under Ubuntu x64, Debian x64, and Mint 32 bit. So far
Mint has been the best, I successfully compiled and I found the kernel,
but cannot figure out where the modules are. Anybody suggest a really
nice tutorial for learning this Linux stuff? My experience so far is
really leading me to appreciate Windows.

Thanks
Ed
=======================================

Randal, Ed,

Just in case you missed it, I am also a beginner to Linux, so I documented 
my steps to get NTP working on the Raspberry Pi on my Web site.  There's a 
quick-start guide here:

  http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html

and a more blog-like set of detailed notes here:

  http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html

I hope they may be of some help.  Typically I'm seeing well under 5 
microsecond offsets reported by the RPi themselves:

  http://www.satsignal.eu/mrtg/performance_ntp.php

although with different GPS devices, antennas, and system loads the 
performance does vary.  The polled USB is, perhaps, the main limitation to 
the device as a server on the LAN, although my own tests have shown RMS 
offsets reported by a remote client on a quiet LAN of 39 microseconds and a 
jitter of 38 microseconds.  Likely on a busier LAN the network itself might 
be the limiting factor.

I am no longer convinced that there is a significant gain to to be had by 
recompiling the kernel, now that PPS support for interrupts is included in 
the current Raspbian kernels.  I'm willing to be convinced otherwise, 
though.  Recompiling is a long and painful process, and cross-compiling 
presents further problems!

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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