:-/

extras/doc/Garmin.md

@@ -0,0 +1,36 @@
+# Garmin Proprietary messages
+
+To use the Garmin Proprietary NMEA message parser, you must enable the following in `NMEAGPS_cfg.h`:
+```
+#define NMEAGPS_PARSE_MFR_ID
+#define NMEAGPS_DERIVED_TYPES
+```
+
+**NeoGPS** implements the following additional NMEA messages:
+
+* $PGRMF - Fix data
+
+You may want to change the configured PGRM messages in `src/Garmin/PGRM_cfg.h`.  It is currently configured to work with the example application, `PGRM.ino`.  `PGRM_cfg.h` has the following configuration items:
+```
+#define GARMINGPS_PARSE_PGRMF
+```
+
+As shown in the PGRM.ino example program, you should use an instance of `GarminNMEA` instead of the typical `NMEAGPS`:
+
+```
+#include <NeoGPS_cfg.h>
+#include <Garmin/GrmNMEA.h>
+#include <GPSTime.h>
+
+   ...
+
+static GarminNMEA gps; // This parses received characters
+static gps_fix    fix;
+```
+
+A few different header files are included, but all other operations are identical.
+
+Notice that the $PGRMF message sets the global variable, `GPSTime::leap_seconds`.  As reported in 
+[Issue #90](https://github.com/SlashDevin/NeoGPS/issues/90), this is required for exact UTC 
+calculations that span dates with different GPS leap seconds 
+(see  [Wikipedia article](http://en.wikipedia.org/wiki/Global_Positioning_System#Leap_seconds)).