Bluetooth GPS for timekeeping?

[Frank Mayhar]

On Tue, 2005-08-09 at 14:51 -0400, David Gilbert wrote:
> But ... since there are long patches of time where I'm not mobile, I
> was wondering if anyone had looked at using a Bluetooth GPS for
> timekeeping.  Has anyone also ever had an ntp server sometimes use a
> GPS and othertimes use other servers ... depending on the availability
> of the GPS?

The former would depend strongly on the characteristics of the Bluetooth
protocols, at least when it comes to accuracy.  Keeping time to the
half-second or so would be pretty easy, I would guess.

The latter is the way it already works.  Just configure other peers in
your ntp.conf along with your GPS, viz:

pps /dev/pps0 assert hardpps
server 127.127.41.0 prefer      # GPSClock
fudge  127.127.41.0 stratum 0
fudge 127.127.41.0 time1 -1.0
peer 127.127.22.0               # PPS refclock
fudge 127.127.22.0 stratum 0 flag3 1  # name it as a good clock
peer 128.9.176.30               # timekeeper.isi.edu
peer 164.67.62.194              # tick.ucla.edu
peer 63.149.208.50              # nist1.datum.com
peer 192.43.244.18              # time.nist.gov
peer 206.223.0.15               # tick.exit.com

That's the configuration for tock.exit.com.  It uses the GPSClock if
it's available, otherwise it falls back to the best of the other
tickers.
-- 
Frank Mayhar frank at exit.com     http://www.exit.com/
Exit Consulting                 http://www.gpsclock.com/
                                http://www.exit.com/blog/frank/