sysprog-basic/btn-pwm-ctrl/main.c

86 lines
1.6 KiB
C

/*
* Use the timers pwm to dim a light on demand.
* The light will change continously until you
* press the button to stop.
*/
#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>
#define PWM_LOW 0
#define PWM_HIGH 96
#define DELAY 25
void change();
typedef enum {
UP,
STOP,
DOWN
} State;
State state = UP;
int brightness = PWM_HIGH;
// code for INT0
ISR(INT0_vect) {
PORTB |= (1 << PORTB5);
state = UP;
}
// code for INT1
ISR(INT1_vect) {
PORTB &= ~(1 << PORTB5);
state = STOP;
}
int main(void) {
// read from D2 and D3, write to D6
DDRD |= (1 << PORTD6);
DDRB = 0xff; // used for internal led only
PORTD |= (1 << PORTD2) | (1 << PORTD3); // pull up D2 and D3
// 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: Fast PWM
// Prescaler: /8
// max: dynamic depending on pushed button
TCCR0A |= (1 << WGM01) | (1 << WGM00); // Fast PWM Mode
OCR0A = brightness; // max value for timer
TCCR0A |= (1 << COM0A1); // set non inverting mode, start initialized
TCCR0B |= (1 << CS02) | (1 << CS00); // enable with prescaler 1024
sei(); // magic interrupt macro
while (1) {
change();
_delay_ms(DELAY);
}
}
void change() {
// start looping through brightnesses
if (state == UP) {
OCR0A = brightness++;
if (brightness >= PWM_HIGH) {
state = DOWN;
}
}
if (state == DOWN) {
OCR0A = brightness--;
if (brightness <= PWM_LOW) {
state = UP;
}
}
}