docs/pyboard/tutorial/amp_skin: Add example for playing large WAV files.

Author: riklaunim

docs/pyboard/tutorial/amp_skin.rst

@@ -69,4 +69,30 @@ Then you can do::
     >>> f = wave.open('test.wav')
     >>> dac.write_timed(f.readframes(f.getnframes()), f.getframerate())
 
-This should play the WAV file.
+This should play the WAV file. Note that this will read the whole file into RAM
+so it has to be small enough to fit in it.
+
+To play larger wave files you will have to use the micro-SD card to store it.
+Also the file must be read and sent to the DAC in small chunks that will fit
+the RAM limit of the microcontroller.  Here is an example function that can
+play 8-bit wave files with up to 16kHz sampling::
+
+    import wave
+    from pyb import DAC
+    from pyb import delay
+    dac = DAC(1)
+
+    def play(filename):
+        f = wave.open(filename, 'r')
+        total_frames = f.getnframes()
+        framerate = f.getframerate()
+
+        for position in range(0, total_frames, framerate):
+            f.setpos(position)
+            dac.write_timed(f.readframes(framerate), framerate)
+            delay(1000)
+
+This function reads one second worth of data and sends it to DAC.  It then waits
+one second and moves the file cursor to the new position to read the next second
+of data in the next iteration of the for-loop.  It plays one second of audio at
+a time every one second.