[ntp:questions] Re: Using NTP with Trimble Acutime Synchronization Kit

Bjorn Gabrielsson bg at lysator.liu.se
Mon Dec 5 21:58:22 UTC 2005


"John Kennedy" <john.kennedyjr1 at us.army.mil> writes:

> After speaking with a Trimble Rep for quite some time, he assured me
> that using the Trimble conversion box (has 2 outputs port A = Passive,
> port B active) using Port A, we could essentially connect 3 PC's to it
> using a special cable that is basically a Y-cable.

Sure you can usually let 3 serial ports listen to a RS232 signal. I do
it at home and in the lab. But its not something I would deliver to a
defence customer... It will usually work, but its _not_ RS232
compliant. Take a look at, 

        http://www.rs485.com/rs485spec.html

or check with your EE engineer.

> The rep said that
> Port A only sends a High/Low message out to the GPS antenna in order to
> stimulate the antenna to send back an NTP type message. 

So, 3 computers would toggle the GPS event input? Three senders are
even more out of spec and would hardly work on RS232.

The usage of the event input is like this

 start    t0 = read_computer_time()
          toggle_event_input()
          t0_check=read_computer_time()
          check that (t0-t0_check) is small

          t0_gps = receive_gps_time_on_portA()

          time_error = t0 - t0_gps

          adjust computer clock to minimize time_error

          goto start

The time (t0_gps) received from the GPS, is not usable on any other
computer than the one that toggled the event input signal.


>  With respect to the driver for NTP, according
> to information on the NTP4.x for windows NT documentation from
> www.eecis.udeledu/~mills/ntp/html/build/hints/winnt.html website, the
> palisade gps driver is already built into the code. 

Was the palisade driver maintained, or (only) general ntp for windows?

Good luck!

--

        Björn




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