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