Initial commit (based on code by Michael Smith).

PCM.c

@@ -0,0 +1,157 @@
+/*
+ * speaker_pcm
+ *
+ * Plays 8-bit PCM audio on pin 11 using pulse-width modulation (PWM).
+ * For Arduino with Atmega168 at 16 MHz.
+ *
+ * Uses two timers. The first changes the sample value 8000 times a second.
+ * The second holds pin 11 high for 0-255 ticks out of a 256-tick cycle,
+ * depending on sample value. The second timer repeats 62500 times per second
+ * (16000000 / 256), much faster than the playback rate (8000 Hz), so
+ * it almost sounds halfway decent, just really quiet on a PC speaker.
+ *
+ * Takes over Timer 1 (16-bit) for the 8000 Hz timer. This breaks PWM
+ * (analogWrite()) for Arduino pins 9 and 10. Takes Timer 2 (8-bit)
+ * for the pulse width modulation, breaking PWM for pins 11 & 3.
+ *
+ * References:
+ *     http://www.uchobby.com/index.php/2007/11/11/arduino-sound-part-1/
+ *     http://www.atmel.com/dyn/resources/prod_documents/doc2542.pdf
+ *     http://www.evilmadscientist.com/article.php/avrdac
+ *     http://gonium.net/md/2006/12/27/i-will-think-before-i-code/
+ *     http://fly.cc.fer.hr/GDM/articles/sndmus/speaker2.html
+ *     http://www.gamedev.net/reference/articles/article442.asp
+ *
+ * Michael Smith <[email protected]>
+ */
+
+#include <stdint.h>
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <avr/pgmspace.h>
+
+#define SAMPLE_RATE 8000
+
+#if defined(ARDUINO) && ARDUINO >= 100
+#include "Arduino.h"
+#else
+#include "WProgram.h"
+#endif
+
+#include "PCM.h"
+
+/*
+ * The audio data needs to be unsigned, 8-bit, 8000 Hz, and small enough
+ * to fit in flash. 10000-13000 samples is about the limit.
+ *
+ * sounddata.h should look like this:
+ *     const int sounddata_length=10000;
+ *     const unsigned char sounddata_data[] PROGMEM = { ..... };
+ *
+ * You can use wav2c from GBA CSS:
+ *     http://thieumsweb.free.fr/english/gbacss.html
+ * Then add "PROGMEM" in the right place. I hacked it up to dump the samples
+ * as unsigned rather than signed, but it shouldn't matter.
+ *
+ * http://musicthing.blogspot.com/2005/05/tiny-music-makers-pt-4-mac-startup.html
+ * mplayer -ao pcm macstartup.mp3
+ * sox audiodump.wav -v 1.32 -c 1 -r 8000 -u -1 macstartup-8000.wav
+ * sox macstartup-8000.wav macstartup-cut.wav trim 0 10000s
+ * wav2c macstartup-cut.wav sounddata.h sounddata
+ *
+ * (starfox) nb. under sox 12.18 (distributed in CentOS 5), i needed to run
+ * the following command to convert my wav file to the appropriate format:
+ * sox audiodump.wav -c 1 -r 8000 -u -b macstartup-8000.wav
+ */
+
+int speakerPin = 11;
+unsigned char const *sounddata_data=0;
+int sounddata_length=0;
+volatile uint16_t sample;
+byte lastSample;
+
+// This is called at 8000 Hz to load the next sample.
+ISR(TIMER1_COMPA_vect) {
+  if (sample >= sounddata_length) {
+    if (sample == sounddata_length + lastSample) {
+      stopPlayback();
+    }
+    else {
+      // Ramp down to zero to reduce the click at the end of playback.
+      OCR2A = sounddata_length + lastSample - sample;
+    }
+  }
+  else {
+    OCR2A = pgm_read_byte(&sounddata_data[sample]);
+  }
+
+  ++sample;
+}
+
+void startPlayback(unsigned char const *data, int length)
+{
+  sounddata_data = data;
+  sounddata_length = length;
+
+  pinMode(speakerPin, OUTPUT);
+
+  // Set up Timer 2 to do pulse width modulation on the speaker
+  // pin.
+
+  // Use internal clock (datasheet p.160)
+  ASSR &= ~(_BV(EXCLK) | _BV(AS2));
+
+  // Set fast PWM mode  (p.157)
+  TCCR2A |= _BV(WGM21) | _BV(WGM20);
+  TCCR2B &= ~_BV(WGM22);
+
+  // Do non-inverting PWM on pin OC2A (p.155)
+  // On the Arduino this is pin 11.
+  TCCR2A = (TCCR2A | _BV(COM2A1)) & ~_BV(COM2A0);
+  TCCR2A &= ~(_BV(COM2B1) | _BV(COM2B0));
+
+  // No prescaler (p.158)
+  TCCR2B = (TCCR2B & ~(_BV(CS12) | _BV(CS11))) | _BV(CS10);
+
+  // Set initial pulse width to the first sample.
+  OCR2A = pgm_read_byte(&sounddata_data[0]);
+
+
+  // Set up Timer 1 to send a sample every interrupt.
+
+  cli();
+
+  // Set CTC mode (Clear Timer on Compare Match) (p.133)
+  // Have to set OCR1A *after*, otherwise it gets reset to 0!
+  TCCR1B = (TCCR1B & ~_BV(WGM13)) | _BV(WGM12);
+  TCCR1A = TCCR1A & ~(_BV(WGM11) | _BV(WGM10));
+
+  // No prescaler (p.134)
+  TCCR1B = (TCCR1B & ~(_BV(CS12) | _BV(CS11))) | _BV(CS10);
+
+  // Set the compare register (OCR1A).
+  // OCR1A is a 16-bit register, so we have to do this with
+  // interrupts disabled to be safe.
+  OCR1A = F_CPU / SAMPLE_RATE;    // 16e6 / 8000 = 2000
+
+  // Enable interrupt when TCNT1 == OCR1A (p.136)
+  TIMSK1 |= _BV(OCIE1A);
+
+  lastSample = pgm_read_byte(&sounddata_data[sounddata_length-1]);
+  sample = 0;
+  sei();
+}
+
+void stopPlayback()
+{
+  // Disable playback per-sample interrupt.
+  TIMSK1 &= ~_BV(OCIE1A);
+
+  // Disable the per-sample timer completely.
+  TCCR1B &= ~_BV(CS10);
+
+  // Disable the PWM timer.
+  TCCR2B &= ~_BV(CS10);
+
+  digitalWrite(speakerPin, LOW);
+}

PCM.h

@@ -0,0 +1,63 @@
+/*
+ * speaker_pcm
+ *
+ * Plays 8-bit PCM audio on pin 11 using pulse-width modulation (PWM).
+ * For Arduino with Atmega168 at 16 MHz.
+ *
+ * Uses two timers. The first changes the sample value 8000 times a second.
+ * The second holds pin 11 high for 0-255 ticks out of a 256-tick cycle,
+ * depending on sample value. The second timer repeats 62500 times per second
+ * (16000000 / 256), much faster than the playback rate (8000 Hz), so
+ * it almost sounds halfway decent, just really quiet on a PC speaker.
+ *
+ * Takes over Timer 1 (16-bit) for the 8000 Hz timer. This breaks PWM
+ * (analogWrite()) for Arduino pins 9 and 10. Takes Timer 2 (8-bit)
+ * for the pulse width modulation, breaking PWM for pins 11 & 3.
+ *
+ * References:
+ *     http://www.uchobby.com/index.php/2007/11/11/arduino-sound-part-1/
+ *     http://www.atmel.com/dyn/resources/prod_documents/doc2542.pdf
+ *     http://www.evilmadscientist.com/article.php/avrdac
+ *     http://gonium.net/md/2006/12/27/i-will-think-before-i-code/
+ *     http://fly.cc.fer.hr/GDM/articles/sndmus/speaker2.html
+ *     http://www.gamedev.net/reference/articles/article442.asp
+ *
+ * Michael Smith <[email protected]>
+ */
+
+/*
+ * The audio data needs to be unsigned, 8-bit, 8000 Hz, and small enough
+ * to fit in flash. 10000-13000 samples is about the limit.
+ *
+ * sounddata.h should look like this:
+ *     const int sounddata_length=10000;
+ *     const unsigned char sounddata_data[] PROGMEM = { ..... };
+ *
+ * You can use wav2c from GBA CSS:
+ *     http://thieumsweb.free.fr/english/gbacss.html
+ * Then add "PROGMEM" in the right place. I hacked it up to dump the samples
+ * as unsigned rather than signed, but it shouldn't matter.
+ *
+ * http://musicthing.blogspot.com/2005/05/tiny-music-makers-pt-4-mac-startup.html
+ * mplayer -ao pcm macstartup.mp3
+ * sox audiodump.wav -v 1.32 -c 1 -r 8000 -u -1 macstartup-8000.wav
+ * sox macstartup-8000.wav macstartup-cut.wav trim 0 10000s
+ * wav2c macstartup-cut.wav sounddata.h sounddata
+ *
+ * (starfox) nb. under sox 12.18 (distributed in CentOS 5), i needed to run
+ * the following command to convert my wav file to the appropriate format:
+ * sox audiodump.wav -c 1 -r 8000 -u -b macstartup-8000.wav
+ */
+
+#include <avr/pgmspace.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void startPlayback(unsigned char const *data, int length);
+void stopPlayback();
+
+#ifdef __cplusplus
+}
+#endif