Running the BBB as an NTP server is a breeze and has a couple of
advantages over the Pi. Specifically, on the BBB, the kernel module is
pre-built and configuring the PPS driver is done at runtime using the
device tree. No kernel re-compilation is required to get up and running,
just plug and go on any of the available GPIO. The ethernet interface on
the BBB is also a SoC peripheral so gives much better latency than the
USB ethernet on the Pi. This gives a big improvement if you are using it
to serve time for other NTP clients.
I have one of the Reyax u-blox 8 modules and it works as described,
_but_ be aware that they do not have an external antenna connector. I
found the reception indoors was poor to the point of making it
unuseable, so depending on your circumstances, this could be a major
problem.
E-bay is riddled with GPS modules and pretty much any of them will be
fine for NTP use. For a more off the wall suggestion, I currently have a
BBB hooked up to one of these:
http://www.ebay.com/itm/Mini-U-blox-B39-PCI-5S-1-500-PCI-E-Express-Wireless-Card-GPS-Module-for-MID-Lapt-/201172829176?pt=Radio_Control_Parts_Accessories&hash=item2ed6d5c3f8
A little bit of soldering is required (see here:
http://emerythacks.blogspot.co.uk/2013/01/u-blox-pci-5s-cheap-gps-module-for-your.html),
but what you get is a dirt cheap u-blox 5 module powered at 3.3v
directly by the BBB. It's not cutting edge, and I'm not going to suggest
using one of these to discipline your frequency standard, but for simple
NTP use it works a treat.
No claims are any good without being backed by data, so attached are a
couple of plots showing my NTP performance from the past 4 hours.
'Sheliak' is the BBB with the PCI-5S and 'Albali' is a Pi with an
adafruit ultimate GPS breakout (MTK3339). It's easy to see the heating
coming on at ~6:20, as both servers are out in the open and it's
interesting to see how they both respond to the temperature change. The
scale is in milliseconds, so 5m is showing 5us.
Cheers
Simon
What does everyone think of this GPS module for ntp use? According to the
specsheet, it uses a Ublox Neo-7N.
http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752
I'm thinking about using it for a Beaglebone ntp server. I know there was
some discussion about Beaglebones a while back. Has anyone gotten ntpd
with
PPS and time stamping running on a Beaglebone yet (like on the Soekris
Net4501)?
[]
I have one Beaglebone White that I got cheap, so I have something to get
started with. Later, as I figure out things, I'll buy a few Beaglebone
Blacks.
Joe Gray
W5JG
============================================
Joe,
You might also consider the Raspberry Pi as an NTP server using PPS:
http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
You can get the ublox 7Q in a ready-to-go no=-soldering board here:
http://ava.upuaut.net/store/index.php?route=product/product&path=59_60&product_id=95
I would reckon on sub-100 microsecond timing accuracy with the
Raspberry Pi and kernel-mode PPS, but I've not done any comparison
with the BB.
Cheers,
David
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