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138 lines
3.4 KiB
C++
138 lines
3.4 KiB
C++
#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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#include "sample.h"
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#define LED_PIN 13
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#define SPEAKER_PIN 11
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#define KNOB_1 (0)
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#define KNOB_2 (1)
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#define KNOB_3 (2)
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#define INPUT_3 (3)
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volatile uint16_t sample;
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volatile uint16_t loop_start;
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volatile uint16_t loop_length;
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volatile uint16_t index_bounds;
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volatile uint16_t loop_overflow;
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volatile boolean gate;
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volatile boolean gate_prev;
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byte lastSample;
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void startPlayback()
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{
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pinMode(SPEAKER_PIN, OUTPUT);
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// Set up Timer 2 to do pulse width modulation on the speaker 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(&sound_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(&sound_data[sound_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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TIMSK1 &= ~_BV(OCIE1A); // Disable playback per-sample interrupt.
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TCCR1B &= ~_BV(CS10); // Disable the per-sample timer completely.
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TCCR2B &= ~_BV(CS10); // Disable the PWM timer.
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digitalWrite(SPEAKER_PIN, LOW);
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}
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void setup()
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{
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pinMode(LED_PIN, OUTPUT);
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digitalWrite(LED_PIN, HIGH);
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startPlayback();
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loop_start = 0;
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loop_length = sound_length;
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gate = false;
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gate_prev = false;
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}
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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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{
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if(sample >= index_bounds)
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{
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sample = loop_start;
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}
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else if((sample < loop_start) &&
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(sample >= loop_overflow))
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{
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sample = loop_start;
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}
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else if((gate == true) &&
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(gate_prev == false))
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{
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sample = loop_start;
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}
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else
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{
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OCR2A = pgm_read_byte(&sound_data[sample % sound_length]);
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}
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gate_prev = gate;
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sample++;
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}
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void loop()
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{
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loop_start = analogRead(KNOB_1) / 1024.0 * sound_length;
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loop_length = (analogRead(KNOB_2) + 1) / 1024.0 * sound_length;
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OCR1A = (512.0 / (analogRead(KNOB_3) + 1)) * (F_CPU / SAMPLE_RATE);
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gate = analogRead(3) >> 9; // 10 bits in. gate < 512 == off, gate >= 512 == on
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// can be up to 2x sound length. the more you know.
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index_bounds = loop_start + loop_length;
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// this will set the overflow length. take the loop overflow into account when checking the loop boundaries
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if(index_bounds > sound_length)
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{
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loop_overflow = index_bounds - sound_length;
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}
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else
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{
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loop_overflow = 0;
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}
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}
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