On 29/10/2012 00:06, Kennedy, Paul wrote:
Hi Dave,
read through this thread and there does not seem to be any reference to
the good work by the folks at:
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=41&t=1970&start=150
There are several folks with the pi running as an ntp server. I have had
a unit in soak test over a month now without hitch.
some notes:
1. I did use not gpsd. Instead I use direct PPS + Serial RS232 off the
GPIO bus. I used the Sure gps as it has the 3.3v serial output which is
all the GPIO bus will accept. 5V from a Trimble will cook your pi (been
there already)
2. I have a USB GPS as secondary, but the serial has not missed a beat
3. I needed the patched kernel which handles the pps on GPIO pin16 -
this was the most curly part.
4. I had to recompile ntpd so it would display a few more decimal places
of precision (nice). The biggest step out I have noted is a few
microseconds. Generally it is good +/- 2 microsecs.
5. I made a couple of web pages so I could keep an eye on it (and the
raw inputs) in a browser. http://secondthoughts.no-ip.org/ntp
6. You can see the raw data from both the serial (NMEA) and GPIO (PPS)
at: http://secondthoughts.no-ip.org/ntp/page-ntpqc.php
7. I also expose the live output of ntpq-p and my current ntp.conf file
at that link, so you can see for yourself the stability.
The thing that I really like about the pi is the low power and silence.
All of a sudden, I can run an ntp server, host web pages, and develop
using 2 watts of power.
I heard a rumour the ethernet port on the pi is serviced as part of the
USB port, and has a 1 millisecond interrupt interval. I tried to read
up on this, and did see something to that effect, but it is still very
vague to me. So although the pi's clock is good to a couple of
microsoconds (for more than a month) It really needs some testing to see
if the ethernet is the achilles heal. Not much fun having a very stable
server if it cannot serve very accurately! (that is the important bit of
this mail ;-)
regards
pk
Paul, thanks for that. Yes, I have been looking through that thread and
it is encouraging to know that others have got it working but much of it
was over my head, and some of it sufficiently different to what I'm
doing that I wasn't sure it was relevant. Your example uses the serial
from the GPS whereas I'm using gpsd (which appears to work).
Perhaps I need a recompiled NTP with the ATOM driver added, but this is
something I have only done on FreeBSD, and I don't know the precise
instructions for the Raspberry Pi variant of Linux. I'm not even sure
how to check whether the ATOM driver /is/ part of the NTP I have.
1 ms Ethernet: Whether it proves anything or not I don't know, but the
plots of offset every 5 minutes look better than "millisecond" level:
http://www.satsignal.eu/mrtg/performance_raspi-1.php
--
Cheers,
David
Web: http://www.satsignal.eu
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