[SLE] GPS Time Standard and Linux NTP

This is a follow-up topic to the NTP thread of a couple weeks ago... for those
of you who may be interested in accessing GPS as a time standard for your
local Suse NTP server, as an alternative to using one of the primary or
secondary external NTP servers. Often folks forget about the GPS alternative.

I have been playing with the Earthmate GPS LT-20 by DeLorme (carried by
BestBuy and others lately). This GPS unit is nicely compatible with Linux
(specifically gpsdrive, and gpsd; both ship with Suse 10) as well as minicom
or other serial terminal emulator. The device does not require M$ software,
nor does it require proprietary drivers.

The device is quite small 6.7cm x 4.5 cm x 1.5 cm, and comes complete with an
attached 1.5 m USB cable. The LT-20 is USB powered, self-contained, and
communicates outbound over USB using the NMEA ascii standard sentences. These
sentences may be parsed by a simple script, or extracted via gpsd via telnet.

The LT-20 uses a twelve channel RF receiver chip from SiGE (SE4100L) and the
GPS micro controller chip from ST Microelectronics (STA2051). Operation is
simple... plug it into an available USB port on your local Suse box and go...

The NMEA output sentences can be accessed via minicom at 4800 baud N81 to
device /dev/ttyUSBx (where x will be 0 for the first device). Otherwise gpsd
can be started after plugging in the unit:

gpsd -p /dev/ttyUSB0

By default gpsd uses port 2947. Accessing the NMEA output is as simple as
running telnet to port 2947 and pressing the 'R' command to receive 'raw'
data.

telnet localhost 2947

... the date and time can be extracted with the 'D' command.

Obviously the beauty of the GPS receiver is to be able to provide global
positioning for navigation, orienteering, etc... but often computer folks
forget that the GPS system is an excellent time standard for a local NTP
server, or other time coordination scheme. The myth is that GPS time can not
be relied upon because of a leap second snafu. This is not true, however. The
failure of GPS time has been in the firmware on GPS receivers (programming
errors) not the GPS system, software, or clocks. Fortunately the LT-20
handles the time correctly. Consequently, the LT-20 can be used with your
Suse linux system as a reliable time standard for your local server without
the need for accessing external NTP servers.





--
Kind regards,

M Harris <><

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