Serial port splitter s/w
Yes the BBB has about twice or more the performance over the Pi except in
graphics. The Pi has a faster GPU. But in the case of an NTP server you
likely would never connect a monitor or keyboard to the computer so the GPU
will go unused.
However the NTP is very un-demanding and will only see on average of maybe
about one network packet per second or less. In fact using an entire BBB
or Pi just for NTP is kind of a waste as it could be doing other things at
the same time. Put some disks on it as use it as a file server for backups
for the other computers. Lots of other uses you could put it to.
On another list server I'm reading about how to use discarded cell phones.
These older Andriod cell phones that people don't want are many times
available for fee and have mamory and processors like those in the BBB or
Pi. They use very little power, have built-in barrty backup and have nice
built in displays. They can be re-purposed as tiny computers. (Think of
a TIC or GPSDO with a color display and touch screen user interface.) The
problem is making the physical connections, that takes some work and
reading.
On Thu, Feb 27, 2014 at 6:56 AM, Didier Juges shalimr9@gmail.com wrote:
A number of people have reported issues with the Raspberry Pi Ethernet
hardware when used for NTP, as it is actually a USB-Ethernet bridge and the
drivers may not be all they could be. I have not had problems myself but I
do not run NTP on it.
The Beaglebone Black (BBB) is supposed to be better in that regard since
the Ethernet MAC is directly on the CPU. The BBB is also entirely open
source, unlike the proprietary Broadcom CPU on the RPi.
Didier KO4BB
On February 26, 2014 11:32:36 AM CST, Chris Albertson <
albertson.chris@gmail.com> wrote:
It's not going to work.
If the purpose of running the Thunderbolt is only to drive NTP then
you don't need LH. NTP's only tags the pulses to the nearest
microsecond, nano sec on accuracy is lost on NTP. I'd even say the
TB is the wrong GPS for NTP. It costs to much and uses to much power.
But if you are also, or mainly, using the Thunderbolt for it's 10Mhz
and NTP is a secondary function then a TB makes sense.
Yes you NEED the PPS on the serial cable. Thunderbolts do not send
NMEA. Thunderbolts send their own data format that is unique to
Trimble. Don't modify the GPS receiver. Make a special cable
adapter. When you do this pay attention to polarity of the PPS
signal. It is easy to get it backwards. You want the raising edge of
the TB pulse to interrupt the computer. It you invert the signal the
wrong number of times the time will be "off" by the ouse length and I
don't know if the pulse length is controlled to the level the leading
edge is. Remember RS232 uses negative and positive voltage, data
lines use negative logic, control lines positive. The TB's PPS is
TTL level. Many rs232 ports do accept t/l level if you get the
polariy correct.
Again don't even bother to run an NTP server without PPS. You may as
well just get time from some internet time servers.
You can NOT control a GPS from two ports. Both NTP and LH will try to
send commands to the GPS.
Likely, almost certainly you need to build a small circuit board the
has two connectors that face the TB (PPS and serial) and one that
faces the computer. The little perfboard makes a neat way to or
connect cables but you could solder up a y--cable
The best thing to do is get a cheaper GPS, and one that uses less
power to drive the NTP server. The old Motorola Oncore series are
cheap and the new breed of very small GPSes are good too. DOn't spend
more than $40 or $50 on a GPS to drive NTP as ,again NTP record
microseconds.
You could free up that Windows PC too. It is not the best platform
for NTP. Asmall ARM based system (even the Rasbery Pi) will
outperform a Windows based NTP server. and use a LOT less power
(Power cost for a NTP server is more than you think, it came to about
$300 a year for me if I used a standard PC and a thunderbolt.
Switching to a very tiny ARM based system and a smaller GPS gave as
good performance and power savings paid for the hardware in 1/2 a
year. $.21/KWH about 170W and 8760 hours per year comes to a $300
power bill. My current system is powered by a 1000 mw plug-in power
cube and does not need a cooling fan.
On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge
david.partridge@perdrix.co.uk wrote:
I'm running Meinberg NTP on the Windows 7 x64 machine to which my
Thunderbolt is attached.
I'd like to be able to share the serial port between LH and NTP so
that I can run the machine as an NTP Stratum 1 server locked to the TB,
and also be able to use LH to check things.
I looked around the with Google, and saw *numerous" serial port
splitters. Which is recommended?
Also what's the best way how to configure NTP to lock the the TB on a
serial port? Do I need to modify the TB to deliver the PPS down one of
the serial data lines or will NTP work well by parsing the NMEA time
messages?
and follow the instructions there.
--
Chris Albertson
Redondo Beach, California
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Chris Albertson
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A number of people have reported issues with the Raspberry Pi Ethernet
hardware when used for NTP, as it is actually a USB-Ethernet bridge and the
drivers may not be all they could be. I have not had problems myself but I
do not run NTP on it.
The Beaglebone Black (BBB) is supposed to be better in that regard since the
Ethernet MAC is directly on the CPU. The BBB is also entirely open source,
unlike the proprietary Broadcom CPU on the RPi.
Didier KO4BB
---===========
Didier,
Here are the results I saw when using Ethernet sync for NTP on a Raspberry
Pi:
http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#results
Syncing just from my Cable Modem WAN connection it's quite bad (offsets +/-
3 milliseconds), but when syncing to local stratum-1 servers the offsets
were reduced to something slightly in excess of +/- 20 microseconds. Adding
PPS reduces that to a couple of microseconds (with Linux 3.6.11 compiled as
a non-tickless system) as seen further down under the "Current performance"
heading.
Perhaps there are equivalent graphs for the BBB system somewhere?
The Raspberry Pi is sufficiently open that you can recompile programs, and
even recompile the kernel for it.
73,
David GM8ARV
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk