[time-nuts] Comparing the BeagleBone Black & Raspberry Pi asNTP servers

[David J Taylor]

Folks,

Many thanks for all your comments.  I am now undertaking tests with the 
stripped-down "Console" build of the OS.  With both the RPi and the BBB I 
started with what the typical user might install rather than any special 
version (indeed, it's built into the BBB).  It seems that while many 
services are enabled and run by default on the BBB, this is not so on the 
RPi, and hence the great difference in CPU load.  Early results are that 
this does not make a lot of difference to what NTP on the card reports, but 
it does significantly affect the view from outside, i.e. what an NTP client 
might see from an NTP server.

Specific replies:

Graham:
The other thing that will help is getting rid of the cape-manager system you 
are using, that is file i/o based.  There is a lot of file scanning going on 
that is not useful in time critical applications.

Yes, but I have no idea how to do that.  There seems to be a peculiarity in 
that with the full OS gpsd works as expected, but it doesn't start 
automatically with the console OS.  It does run when started by hand, and I 
have used dpkg-reconfigure to try and make it auto-start.  For the moment, I 
will leave that as one of the BBB's unexplained mysteries!

Attila, Mike:
You will see that I have taken your advice and used the console OS.  Likely 
I will not use the BBB for much else as the RPi 2 is more powerful and has a 
much wider support base.

Attila:
Thanks for the pointer to the pre-built buildroot images, but they note: 
"Since that time, BBB support was merged upstream, so this is really, really 
old. Please, please, don't use this in new projects."  I'm really only 
interested in what they typical user might download or find pre-installed.

Chris:
Yes, the two  /etc/ntp.conf  are identical, with the possible exception of a 
leapsecond file not yet being configured for the BBB.

Paul:
The patch antenna on the Adafruit does work here much of the time, but it is 
smaller than the patch in the magnetic mount antenna I ended up using. 
Compared to the naked Adafruit module, a ublox M8Q module and mag mount 
antenna is noticeably better for indoor use here, and on RPi cards other 
than the one in this test I've switched to these units:

  http://ava.upuaut.net/store/index.php?route=product/product&path=59_60&product_id=117

Paul:
I agree that the table could be improved, but rather than remove information 
I have emboldened that for the two servers which the client is testing.  The 
table is due for a full update once today's running is completed without 
interruption.

Wolfgang:
I agree with your comments, but I am comparing more "out-of-the-box" rather 
than special builds etc.  To show how things changed between the two OS 
versions I added a comparison here:

  http://www.satsignal.eu/ntp/BBB-vs-RPi.html#OS-comparison

Many thanks all for your help.  Tomorrow I will update the table, and I'm 
sure that the BBB will win out under both measures.

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