timer2

timer2/main.c

@@ -0,0 +1,72 @@
+/*
+ * Use the timer to produce a sound in a speaker.
+ *
+ * Formular for the frequency:
+ * (F_CPU/wanted_frequency*2*Prescaler)+1
+ *
+ * Cut off the decimal part and see which is
+ * closer to the wanted frequency.
+ *
+ * Task: Sum at start with 440 Hz, when a button is pushed, sum at 264 Hz. The
+ * other button reverses.
+ */
+#define F_CPU 16000000UL
+#define __AVR_ATmega328P__
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <util/delay.h>
+
+#define SOUND_A 17
+#define SOUND_C 30
+
+#define MINUTE 60 * 1000
+const int TIME = 45 * MINUTE;
+
+int state = 0;
+
+// Timer0 interrupt
+ISR(TIMER0_COMPA_vect) {
+  PORTB ^= (1 << PORTB5); // toggle the speaker
+}
+
+// code for INT0
+ISR(INT0_vect) {
+  OCR0A = SOUND_A;              // max value for timer
+}
+
+// code for INT1
+ISR(INT1_vect) {
+  OCR0A = SOUND_C;              // max value for timer
+}
+
+int main(void) {
+
+  DDRB = 0xff; // write to B
+  DDRD = 0;    // read from D
+
+  PORTD |= (1 << PORTD2) | (1 << PORTD3); // pull up D2 and D3
+  PORTB = 0;  // pull down PORT B
+
+  // enable external interruprs
+  EIMSK |= (1 << INT0);
+  EIMSK |= (1 << INT1);
+
+  // trigger when anything changes
+  EICRA |= (1 << ISC00); // for INT0
+  EICRA |= (1 << ISC10); // for INT1
+
+  // Timer 0
+  // Mode: Overflow, Interrupt
+  // Prescaler: /1024
+  // max: dynamic depending on pushed button
+  TCCR0A |= (1 << WGM01);  // CTC Mode
+  OCR0A = SOUND_C;         // max value for timer
+  TIMSK0 |= (1 << OCIE0A); // enable interrupt ISR_COMPA_vect
+
+  sei(); // magic interrupt macro
+
+  TCCR0B |= (1 << CS02) | (1 << CS00); // enable with prescaler 1024
+  while (1) {
+    // do nothing
+  }
+}