examples: Add DAC loop mode example.

examples/Advanced/DAC_Loop/Dac_Loop.ino

@@ -0,0 +1,41 @@
+// This examples shows how to use the DAC in loop mode. In loop mode the
+// DAC starts automatically after all buffers are filled, and continuously
+// cycle through over all buffers.
+#include <Arduino_AdvancedAnalog.h>
+
+AdvancedDAC dac1(A12);
+
+void setup() {
+    Serial.begin(9600);
+
+    while (!Serial) {
+
+    }
+
+    // Start DAC in loop mode.
+    if (!dac1.begin(AN_RESOLUTION_12, 16000, 32, 16, true)) {
+        Serial.println("Failed to start DAC1 !");
+        while (1);
+    }
+
+    // Write all buffers.
+    uint16_t sample = 0;
+    while (dac1.available()) {
+        // Get a free buffer for writing.
+        SampleBuffer buf = dac1.dequeue();
+
+        // Write data to buffer.
+        for (int i=0; i<buf.size(); i++) {
+            buf.data()[i] = sample;
+        }       
+
+        // Write the buffer to DAC.
+        dac1.write(buf);
+        sample += 256;
+    }
+}
+
+
+void loop() {
+  // In loop mode, no other DAC functions need to be called.
+}