75 lines
2.2 KiB
C
75 lines
2.2 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/interrupt.h>
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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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#include "USART.h"
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volatile uint16_t accumulator;
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volatile uint16_t tuningWord;
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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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TIMSK0 |= (1 << TOIE0); /* Overflow interrupt */
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sei(); /* Enable interrupt */
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}
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ISR(TIMER0_OVF_vect) {
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accumulator += tuningWord; /* take tuningWord steps forward */
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/* lookup and set output */
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OCR0A = 128 + fullSine[(uint8_t) (accumulator >> 8)];
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}
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static inline void pollButton(void) {
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if (bit_is_clear(BUTTON_PIN, BUTTON)) {
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SPEAKER_DDR |= (1 << SPEAKER); /* enable output on pin */
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LED_PORT &= ~(1 << LED0);
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}
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else {
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SPEAKER_DDR &= ~(1 << SPEAKER); /* disable output on pin */
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LED_PORT |= (1 << LED0);
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}
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}
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int main(void) {
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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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initUSART();
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BUTTON_PORT |= (1 << BUTTON); /* pullup on button */
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LED_DDR |= (1 << LED0); /* LED on for diagnostics */
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LED_PORT |= (1 << LED0);
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_delay_ms(100);
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LED_PORT &= ~(1 << LED0);
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SPEAKER_DDR |= (1 << SPEAKER);
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tuningWord = 880;
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transmitByte((uint8_t) tuningWord >> 2); /* approx value in Hz */
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// ------ Event loop ------ //
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while (1) {
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pollButton();
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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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