86 lines
2.3 KiB
C
86 lines
2.3 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 "macros.h"
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#include "fullSine.h"
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static inline void initTimer0(void){
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set_bit(TCCR0A, COM0A1); /* PWM output on OCR0A */
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set_bit(SPEAKER_DDR, SPEAKER); /* enable output on pin */
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set_bit(TCCR0A, WGM00); /* Fast PWM mode */
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set_bit(TCCR0A, WGM01); /* Fast PWM mode, pt.2 */
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set_bit(TCCR0B, CS00); /* Clock with /1 prescaler */
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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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set_bit(SPEAKER_DDR, SPEAKER); /* enable output on pin */
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clear_bit(LED_PORT, LED0);
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}
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else {
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clear_bit(SPEAKER_DDR, SPEAKER); /* disable output on pin */
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set_bit(LED_PORT, LED0);
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}
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}
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static inline void initLED(void){
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set_bit(LED_DDR, LED0); /* LED on for diagnostics */
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set_bit(LED_PORT, LED0);
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_delay_ms(100);
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clear_bit(LED_PORT, LED0);
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}
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int main(void){
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volatile uint16_t accumulator0;
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volatile uint16_t accumulator1;
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volatile uint16_t tuningWord0;
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volatile uint16_t tuningWord1;
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volatile uint16_t mixer;
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// -------- Inits --------- //
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clock_prescale_set(clock_div_1); /* CPU clock 8 MHz */
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initLED();
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initTimer0();
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set_bit(BUTTON_PORT, BUTTON); /* pullup on button */
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set_bit(SPEAKER_DDR, SPEAKER); /* speaker output */
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tuningWord0 = 440*2; /* Dial tone frequencies */
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tuningWord1 = 350*2;
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// ------ Event loop ------ //
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while(1){
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loop_until_bit_is_set(TIFR0, TOV0); /* wait until overflow bit set */
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set_bit(TIFR0, TOV0); /* writing set should reset... */
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// Note that this bit has to be pretty fast... we have only 256 cycles to
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// set the next value in OCR0A, or we may hear a glitch
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accumulator0 += tuningWord0; /* take tuningWord steps forward */
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accumulator1 += tuningWord1; /* take tuningWord steps forward */
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mixer = fullSine[(uint8_t) (accumulator0 >> 8)]; /* add together */
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mixer += fullSine[(uint8_t) (accumulator1 >> 8)];
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OCR0A = 128 + (mixer >> 1); /* divide by 2, the fast way */
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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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