Fix #22 by adding 1hz and 5hz position fix update commands. Update ec…

…ho example to show command usage.

Adafruit_GPS.h

@@ -29,9 +29,15 @@ All text above must be included in any redistribution
 #endif
 
 // different commands to set the update rate from once a second (1 Hz) to 10 times a second (10Hz)
+// Note that these only control the rate at which the position is echoed, to actually speed up the
+// position fix you must also send one of the position fix rate commands below too.
 #define PMTK_SET_NMEA_UPDATE_1HZ  "$PMTK220,1000*1F"
 #define PMTK_SET_NMEA_UPDATE_5HZ  "$PMTK220,200*2C"
 #define PMTK_SET_NMEA_UPDATE_10HZ "$PMTK220,100*2F"
+// Position fix update rate commands.
+#define PMTK_API_SET_FIX_CTL_1HZ  "$PMTK300,1000,0,0,0,0*1C"
+#define PMTK_API_SET_FIX_CTL_5HZ  "$PMTK300,200,0,0,0,0*2F"
+// Can't fix position faster than 5 times a second!
 
 
 #define PMTK_SET_BAUD_57600 "$PMTK251,57600*2C"

examples/echo/echo.pde

@@ -70,12 +70,18 @@ void setup()
   //GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_ALLDATA);
 
   // Set the update rate
+  // Note you must send both commands below to change both the output rate (how often the position
+  // is written to the serial line), and the position fix rate.
   // 1 Hz update rate
   //GPS.sendCommand(PMTK_SET_NMEA_UPDATE_1HZ);
+  //GPS.sendCommand(PMTK_API_SET_FIX_CTL_1HZ);
   // 5 Hz update rate- for 9600 baud you'll have to set the output to RMC or RMCGGA only (see above)
   GPS.sendCommand(PMTK_SET_NMEA_UPDATE_5HZ);
+  GPS.sendCommand(PMTK_API_SET_FIX_CTL_5HZ);
   // 10 Hz update rate - for 9600 baud you'll have to set the output to RMC only (see above)
+  // Note the position can only be updated at most 5 times a second so it will lag behind serial output.
   //GPS.sendCommand(PMTK_SET_NMEA_UPDATE_10HZ);
+  //GPS.sendCommand(PMTK_API_SET_FIX_CTL_5HZ);
 
   // Request updates on antenna status, comment out to keep quiet
   GPS.sendCommand(PGCMD_ANTENNA);