[ntp:questions] Using Trimble TSIP under Linux

Chris Adams cmadams at hiwaay.net
Mon Oct 29 00:47:51 UTC 2012

Once upon a time, David Taylor  <david-taylor at blueyonder.co.uk> said:
>I am at the very early stages of building a small stratum-1 NTP server 
>using a Linux box (Raspberry Pi).  A Trimble GPS is connected via USB 
>(yes, I know I will need an interrupt-driven pin for the PPS), and if I 
>install gpsd I can see the output from the GPS with the cgps -s command.

It sounds like you are really trying to run ntpd talking to gpsd, not
directly to the Trimble.  If you are also trying to fetch GPS info,
that'll work, but you'll get better time results by having ntpd talk to
the Trimble.  The reason is that gpsd will configure the TSIP protocol
better for location rather than time service; ntpd configures TSIP into
single-sat mode (once it determines its location, it can keep the clock
with only one satellite in view).

Also, at one time, gpsd didn't initialize enough of TSIP settings after
ntpd talked to the device, and gpsd didn't handle the results (I
submitted patches a while back, but I haven't run gpsd against my
SVeeSix since, so I don't know if they were applied).

If you just want ntpd to talk to the Trimble, use:

server mode 10 minpoll 4 maxpoll 4 prefer

and set up a symlink for /dev/gps0 pointing to your USB device.  For
example, a file in /etc/udev/rules.d with (this works with my 2-port
FTDI USB RS232 adapter with the GPS on the second port):

KERNEL=="ttyUSB*", ATTRS{interface}=="DLP2232M", ATTRS{bInterfaceNumber}=="01", SYMLINK+="gps gps0 refclock-0", MODE:="660", GROUP:="ntp"

I then have my PPS connected to a parallel port (obviously not available
on the Pi, but GPIO is there and Linux has pps-gpio).  I haven't tried
connecting my GPS to my Pi yet.
Chris Adams <cmadams at hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.

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