57 lines
2.0 KiB
C
57 lines
2.0 KiB
C
/* Direct-digital synthesis */
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// ------- Preamble -------- //
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#include <avr/io.h> /* Defines pins, ports, etc */
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#include <util/delay.h> /* Functions to waste time */
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#include <avr/power.h>
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#include "pinDefines.h"
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#include "fullSine.h"
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static inline void initTimer0(void) {
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TCCR0A |= (1 << COM0A1); /* PWM output on OCR0A */
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SPEAKER_DDR |= (1 << SPEAKER); /* enable output on pin */
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TCCR0A |= (1 << WGM00); /* Fast PWM mode */
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TCCR0A |= (1 << WGM01); /* Fast PWM mode, pt.2 */
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TCCR0B |= (1 << CS00); /* Clock with /1 prescaler */
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}
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int main(void) {
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uint16_t accumulator = 0;
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uint16_t accumulatorSteps = 880; /* approx 440 Hz */
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uint8_t waveStep;
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int8_t pwmValue;
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// -------- Inits --------- //
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clock_prescale_set(clock_div_1); /* CPU clock 8 MHz */
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initTimer0();
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BUTTON_PORT |= (1 << BUTTON); /* pullup on button */
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// ------ Event loop ------ //
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while (1) {
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if (bit_is_clear(BUTTON_PIN, BUTTON)) {
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SPEAKER_DDR |= (1 << SPEAKER); /* enable speaker */
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accumulator += accumulatorSteps; /* advance accumulator */
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waveStep = accumulator >> 8; /* which entry in lookup? */
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pwmValue = fullSine[waveStep]; /* lookup voltage */
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loop_until_bit_is_set(TIFR0, TOV0); /* wait for PWM cycle */
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OCR0A = 128 + pwmValue; /* set new PWM value */
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TIFR0 |= (1 << TOV0); /* reset PWM overflow bit */
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}
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else { /* button not pressed */
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SPEAKER_DDR &= ~(1 << SPEAKER); /* disable speaker */
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}
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} /* End event loop */
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return 0; /* This line is never reached */
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}
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