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diff --git a/contrib/ntp/html/driver20.htm b/contrib/ntp/html/driver20.htm new file mode 100644 index 0000000..e6a4bd2 --- /dev/null +++ b/contrib/ntp/html/driver20.htm @@ -0,0 +1,131 @@ +<HTML> +<HEAD> + <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + <META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]"> + <TITLE>Generic NMEA GPS Receiver +</TITLE> +</HEAD> +<BODY> + +<H3> +Generic NMEA GPS Receiver</H3> + +<HR> +<H4> +Synopsis</H4> +Address: 127.127.20.<I>u</I> +<BR>Reference ID: <TT>GPS</TT> +<BR>Driver ID: <TT>GPS_NMEA</TT> +<BR>Serial Port: <TT>/dev/gps<I>u</I></TT>; 4800 baud, 8-bits, no parity +<BR>Features: <TT>tty_clk</TT> +<H4> +Description</H4> +This driver supports GPS receivers with the <TT>$GPRMC</TT> NMEA output string. +The driver expect the receiver to be set up to transmit a <TT>$GPRMC</TT> +message every second. + +<P>The accuracy depend on the receiver used. Inexpesive GPS models are +available with a claimed PPS signal accuracy of 1 <FONT FACE="Symbol">m</FONT>s +or better relative to the broadcast signal. However, in most cases the +actual accuracy is limited by the precision of the timecode and the latencies +of the serial interface and operating system. + +<P>The $GPRMC message that the GPS transmits look like this: +<PRE>$GPRMC,POS_UTC,POS_STAT,LAT,LAT_REF,LON,LON_REF,SPD,HDG,DATE,MAG_VAR,MAG_REF*CC<cr><lf> + + POS_UTC - UTC of position. Hours, minutes and seconds. (hhmmss) + POS_STAT - Position status. (A = Data valid, V = Data invalid) + LAT - Latitude (llll.ll) + LAT_REF - Latitude direction. (N = North, S = South) + LON - Longitude (yyyyy.yy) + LON_REF - Longitude direction (E = East, W = West) + SPD - Speed over ground. (knots) (x.x) + HDG - Heading/track made good (degrees True) (x.x) + DATE - Date (ddmmyy) + MAG_VAR - Magnetic variation (degrees) (x.x) + MAG_REF - Magnetic variation (E = East, W = West) + CC - Checksum (optional) + <cr><lf> - Sentence terminator.</PRE> +The driver will send a <TT>$PMOTG,RMC,0000*1D<cr><lf></TT> message +each time a <TT>$GPRMC</TT> string is needed. This is not needed on most +GPS receivers because they automatically send the <TT>$GPRMC</TT> string +every second and will only work on GPS receivers that understand the <TT>$PMOTG</TT> +string. Others will just ignore it. +<H4> +Setting up the Garmin GPS-25XL</H4> +Switch off all output with by sending it the following string. +<PRE>"$PGRMO,,2<cr><lf>"</PRE> +Now switch only $GPRMC on by sending it the following string. +<PRE>"$PGRMO,GPRMC,1<cr><lf>"</PRE> +On some systems the PPS signal isn't switched on by default. It can be +switched on by sending the following string. +<PRE>"$PGRMC,,,,,,,,,,,,2<cr><lf>"</PRE> + +<H4> +Monitor Data</H4> +The $GPRMC string that is used is written to the clockstats file. +<H4> +Fudge Factors</H4> + +<DL> +<DT> +<TT>time1 <I>time</I></TT></DT> + +<DD> +Specifies the time offset calibration factor, in seconds and fraction, +with default 0.0.</DD> + +<DT> +<TT>time2 <I>time</I></TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>stratum <I>number</I></TT></DT> + +<DD> +Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD> + +<DT> +<TT>refid <I>string</I></TT></DT> + +<DD> +Specifies the driver reference identifier, an ASCII string from one to +four characters, with default <TT>GPS</TT>.</DD> + +<DT> +<TT>flag1 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag2 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag3 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag4 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + + +<P>Additional Information + +<P><A HREF="refclock.htm">Reference Clock Drivers</A></DL> + +<HR> +<ADDRESS> +David L. Mills (mills@udel.edu)</ADDRESS> + +</BODY> +</HTML> |
