added simple audio player example

hardware/arduino/sam/libraries/Audio/examples/SimpleAudioPlayer/SimpleAudioPlayer.ino

@@ -0,0 +1,77 @@
+#include <SD.h>
+#include <SPI.h>
+#include <Audio.h>
+
+void setup()
+{
+  // debug output at 115.2K
+  Serial.begin(115200);
+
+  // setup SD-card
+  Serial.print("Initializing SD card...");
+  if (!SD.begin(4)) {
+    Serial.println(" failed!");
+    return;
+  }
+  Serial.println(" done.");
+  // hi-speed SPI transfers
+  SPI.setClockDivider(4);
+
+  // 44100Khz stereo => 88200 sample rate
+  // 100 mSec of prebuffering.
+  Audio.begin(88200, 100);
+}
+
+void loop()
+{
+  int count=0;
+
+  // open wave file from sdcard
+  File myFile = SD.open("fadh.wav");
+  if (!myFile) {
+    // if the file didn't open, print an error and stop
+    Serial.println("error opening fadh.wav");
+    while (true);
+  }
+
+  const int S=1024; // Number of samples to read in block
+  int16_t buffer[S];
+
+  Serial.print("Playing");
+  // until the file is not finished
+  while (myFile.available()) {
+    // read from the file into buffer
+    myFile.read(buffer, sizeof(buffer));
+
+    // Prepare samples
+    int volume = analogRead(2);
+    prepare(buffer, S, volume);
+    // Feed samples to audio
+    Audio.write(buffer, S);
+
+    // Every 100 block print a '.'
+    count++;
+    if (count == 100) {
+      Serial.print(".");
+      count = 0;
+    }
+  }
+  myFile.close();
+
+
+  Serial.println("End of file. Thank you for listening!");
+  while (true) ;
+}
+
+
+void prepare(int16_t *buffer, int S, int volume) {
+  uint16_t *ubuffer = (uint16_t*) buffer;
+  for (int i=0; i<S; i++) {
+    // set volume amplitude (signed multiply)
+    buffer[i] = buffer[i] * volume / 1024;
+    // convert from signed 16 bit to unsigned 12 bit for DAC.
+    ubuffer[i] += 0x8000;
+    ubuffer[i] >>= 4;
+  }
+}
+