40 lines
867 B
C
40 lines
867 B
C
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/*
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* Use the timer to produce a sound in a speaker.
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*
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* Formular for the frequency:
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* (F_CPU/Prescaler)/(wanted_frequency*2)+1
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*
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* Cut off the decimal part and see which is
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* closer to the wanted frequency.
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*/
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#define F_CPU 16000000UL
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#define __AVR_ATmega328P__
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#include <avr/interrupt.h>
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#include <avr/io.h>
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#include <util/delay.h>
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#define MINUTE 60 * 1000
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const int TIME = 45 * MINUTE;
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ISR(TIMER0_COMPA_vect) { PORTB ^= (1 << PORTB5); }
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int main(void) {
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DDRB = 0xff; // write to B
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DDRD = 0; // read from D
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// Timer 0
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// Mode: Overflow, Interrupt
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// Prescaler: /256
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// max: 70
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TCCR0A |= (1 << WGM01); // CTC Mode
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OCR0A = 70; // max value for timer
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TIMSK0 |= (1 << OCIE0A); // enable interrupt ISR_COMPA_vect
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sei(); // magic interrupt macro
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TCCR0B |= (1 << CS02); // enable with prescaler 256
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while (1) {
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}
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}
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