Here is interesting topic about NTP on Raspberry PI (typical usage of
ARM and Linux bread on top of it)
http://www.synclab.org/?tag=testing
Basically, TCP stack on ARM usually come from one source - its a Adam
Dunken TCP stack. Then its is MII part and the hardware which doing
Ethernet. In my opinion, MCU (ARM) could provide excellent Ethernet
functions. However its far from serious dedicated ethernet controllers
we could see in enterprise servers.
Regards,
V.P.
On 2014-02-26 12:32, Chris Albertson 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
<[email protected]> 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?
Many thanks
David Partridge
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--
WBW,
V.P.
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