[ntp:questions] Re: GPS receiver - driver available?

Hal Murray hmurray at suespammers.org
Wed Aug 13 07:52:02 UTC 2003


>> Does it output NEMA?  PPS?
>
>I don't know.
>
>How would I find out?

I think that should be NMEA - National Marine Electronics Association,
or something close to that.

It's an RS-232 protocol that was designed for marine navigation.
Works OK for (rough) timekeeping too.  Lots of status/quality info.

You will see things like this:

$GPGGA,074148,3726.0859,N,12212.1943,W,1,04,01.77,000000.0,M,-028.1,M,,
$GPRMC,074220,A,3726.0858,N,12212.1936,W,000.1,049.9,130803,015.4,E*61
$GPGGA,074248,3726.0851,N,12212.1934,W,1,04,01.77,000000.0,M,-028.1,M,,
$GPRMC,074324,A,3726.0855,N,12212.1938,W,000.2,017.0,130803,015.4,E*66
$GPGGA,074348,3726.0859,N,12212.1940,W,1,04,01.78,000000.0,M,-028.1,M,,

The stuff before the N and W is my location.  My house isn't moving so
the wander in the bottom bits is the error in receiving the GPS signals.


PPS is Pulse Per Second.  For serious time keeping, you need another
signal in addition to lines of ASCII text.  The PPS signal is generally
connected to one of the modem control signals.  The kernel has a hook
to record the time on an interrupt.

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