Added interrupt support

Added interrupt support to shield_sdlog sketch

examples/shield_sdlog/shield_sdlog.ino

@@ -26,6 +26,11 @@ Adafruit_GPS GPS(&mySerial);
 /* set to true to only log to SD when GPS has a fix, for debugging, keep it false */
 #define LOG_FIXONLY false  
 
+// 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
+
 // Set the pins used
 #define chipSelect 10
 #define ledPin 13
@@ -46,14 +51,14 @@ uint8_t parseHex(char c) {
 
 // blink out an error code
 void error(uint8_t errno) {
-/*
+  /*
   if (SD.errorCode()) {
-    putstring("SD error: ");
-    Serial.print(card.errorCode(), HEX);
-    Serial.print(',');
-    Serial.println(card.errorData(), HEX);
-  }
-  */
+   putstring("SD error: ");
+   Serial.print(card.errorCode(), HEX);
+   Serial.print(',');
+   Serial.println(card.errorData(), HEX);
+   }
+   */
   while(1) {
     uint8_t i;
     for (i=0; i<errno; i++) {
@@ -72,7 +77,7 @@ void setup() {
   // for Leonardos, if you want to debug SD issues, uncomment this line
   // to see serial output
   //while (!Serial);
-  
+
   // connect at 115200 so we can read the GPS fast enough and echo without dropping chars
   // also spit it out
   Serial.begin(115200);
@@ -82,10 +87,10 @@ void setup() {
   // make sure that the default chip select pin is set to
   // output, even if you don't use it:
   pinMode(10, OUTPUT);
-  
+
   // see if the card is present and can be initialized:
   if (!SD.begin(chipSelect, 11, 12, 13)) {
-  //if (!SD.begin(chipSelect)) {      // if you're using an UNO, you can use this line instead
+    //if (!SD.begin(chipSelect)) {      // if you're using an UNO, you can use this line instead
     Serial.println("Card init. failed!");
     error(2);
   }
@@ -102,11 +107,13 @@ void setup() {
 
   logfile = SD.open(filename, FILE_WRITE);
   if( ! logfile ) {
-    Serial.print("Couldnt create "); Serial.println(filename);
+    Serial.print("Couldnt create "); 
+    Serial.println(filename);
     error(3);
   }
-  Serial.print("Writing to "); Serial.println(filename);
-  
+  Serial.print("Writing to "); 
+  Serial.println(filename);
+
   // connect to the GPS at the desired rate
   GPS.begin(9600);
 
@@ -121,39 +128,80 @@ void setup() {
 
   // Turn off updates on antenna status, if the firmware permits it
   GPS.sendCommand(PGCMD_NOANTENNA);
-  
+
+  // 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);
+
   Serial.println("Ready!");
 }
 
-void loop() {
-  char c = GPS.read();
-  if (GPSECHO)
-     if (c)   Serial.print(c);
 
+// Interrupt is called once a millisecond, looks for any new GPS data, and stores it
+SIGNAL(TIMER0_COMPA_vect) {
+  char c;
+  while (mySerial.available())
+  {
+    c = GPS.read();
+    // if you want to debug, this is a good time to do it!
+#ifdef UDR0
+    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. 
+#endif
+  }
+}
+
+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() {
+  char c;
+  while (mySerial.available())
+  {
+    c = GPS.read();
+    if (GPSECHO)
+      if (c)   Serial.print(c);
+  }
+  
   // if a sentence is received, we can check the checksum, parse it...
   if (GPS.newNMEAreceived()) {
     // a tricky thing here is if we print the NMEA sentence, or data
     // we end up not listening and catching other sentences! 
     // so be very wary if using OUTPUT_ALLDATA and trying to print out data
     //Serial.println(GPS.lastNMEA());   // this also sets the newNMEAreceived() flag to false
-        
+
     if (!GPS.parse(GPS.lastNMEA()))   // this also sets the newNMEAreceived() flag to false
       return;  // we can fail to parse a sentence in which case we should just wait for another
-    
+
     // Sentence parsed! 
     Serial.println("OK");
     if (LOG_FIXONLY && !GPS.fix) {
-        Serial.print("No Fix");
-        return;
+      Serial.print("No Fix");
+      return;
     }
 
     // Rad. lets log it!
     Serial.println("Log");
-    
+
     char *stringptr = GPS.lastNMEA();
     uint8_t stringsize = strlen(stringptr);
     if (stringsize != logfile.write((uint8_t *)stringptr, stringsize))    //write the string to the SD file
-      error(4);
+        error(4);
     if (strstr(stringptr, "RMC"))   logfile.flush();
     Serial.println();
   }
@@ -161,3 +209,4 @@ void loop() {
 
 
 /* End code */
+