First commit, working build.

lib/Adafruit-GPS-Library/examples/echo/echo.pde

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+// Test code for Adafruit GPS modules using MTK3329/MTK3339 driver
+//
+// This code just echos whatever is coming from the GPS unit to the
+// serial monitor, handy for debugging!
+//
+// Tested and works great with the Adafruit Ultimate GPS module
+// using MTK33x9 chipset
+//    ------> http://www.adafruit.com/products/746
+// Pick one up today at the Adafruit electronics shop 
+// and help support open source hardware & software! -ada
+
+#include <Adafruit_GPS.h>
+#if ARDUINO >= 100
+ #include <SoftwareSerial.h>
+#else
+  // Older Arduino IDE requires NewSoftSerial, download from:
+  // http://arduiniana.org/libraries/newsoftserial/
+// #include <NewSoftSerial.h>
+ // DO NOT install NewSoftSerial if using Arduino 1.0 or later!
+#endif
+
+// Connect the GPS Power pin to 5V
+// Connect the GPS Ground pin to ground
+// If using software serial (sketch example default):
+//   Connect the GPS TX (transmit) pin to Digital 3
+//   Connect the GPS RX (receive) pin to Digital 2
+// If using hardware serial (e.g. Arduino Mega):
+//   Connect the GPS TX (transmit) pin to Arduino RX1, RX2 or RX3
+//   Connect the GPS RX (receive) pin to matching TX1, TX2 or TX3
+
+// If using software serial, keep these lines enabled
+// (you can change the pin numbers to match your wiring):
+#if ARDUINO >= 100
+  SoftwareSerial mySerial(3, 2);
+#else
+  NewSoftSerial mySerial(3, 2);
+#endif
+Adafruit_GPS GPS(&mySerial);
+// If using hardware serial (e.g. Arduino Mega), comment
+// out the above six lines and enable this line instead:
+//Adafruit_GPS GPS(&Serial1);
+
+
+// Set GPSECHO to 'false' to turn off echoing the GPS data to the Serial console
+// Set to 'true' if you want to debug and listen to the raw GPS sentences
+#define GPSECHO  true
+
+// this keeps track of whether we're using the interrupt
+// off by default!
+boolean usingInterrupt = false;
+void useInterrupt(boolean); // Func prototype keeps Arduino 0023 happy
+
+void setup()  
+{    
+  // connect at 115200 so we can read the GPS fast enuf and
+  // also spit it out
+  Serial.begin(115200);
+  Serial.println("Adafruit GPS library basic test!");
+
+  // 9600 NMEA is the default baud rate for MTK - some use 4800
+  GPS.begin(9600);
+  
+  // You can adjust which sentences to have the module emit, below
+  
+  // uncomment this line to turn on RMC (recommended minimum) and GGA (fix data) including altitude
+  GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCGGA);
+  // uncomment this line to turn on only the "minimum recommended" data for high update rates!
+  //GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCONLY);
+  // uncomment this line to turn on all the available data - for 9600 baud you'll want 1 Hz rate
+  //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);
+
+  // the nice thing about this code is you can have a timer0 interrupt go off
+  // every 1 millisecond, and read data from the GPS for you. that makes the
+  // loop code a heck of a lot easier!
+  useInterrupt(true);
+  
+  delay(1000);
+}
+
+// Interrupt is called once a millisecond, looks for any new GPS data, and stores it
+SIGNAL(TIMER0_COMPA_vect) {
+  char c = GPS.read();
+  // if you want to debug, this is a good time to do it!
+  if (GPSECHO)
+    if (c) UDR0 = c;  
+    // writing direct to UDR0 is much much faster than Serial.print 
+    // but only one character can be written at a time. 
+}
+
+void useInterrupt(boolean v) {
+  if (v) {
+    // Timer0 is already used for millis() - we'll just interrupt somewhere
+    // in the middle and call the "Compare A" function above
+    OCR0A = 0xAF;
+    TIMSK0 |= _BV(OCIE0A);
+    usingInterrupt = true;
+  } else {
+    // do not call the interrupt function COMPA anymore
+    TIMSK0 &= ~_BV(OCIE0A);
+    usingInterrupt = false;
+  }
+}
+
+
+void loop()                     // run over and over again
+{
+   // do nothing! all reading and printing is done in the interrupt
+}