ATmega 8 - PWM test

Makefile

BUILDDIR=build
BASENAME=pwm_test
MMCU=atmega8


all: clean compile burn

clean:
	rm -f $(BUILDDIR)/$(BASENAME).elf
	rm -f $(BUILDDIR)/$(BASENAME).hex
	rmdir $(BUILDDIR)

compile:
	mkdir -p $(BUILDDIR)
	avr-gcc \
		-mmcu=$(MMCU) \
		-O3 \
		-o $(BUILDDIR)/$(BASENAME).elf \
		$(BASENAME).c
	objcopy \
		-O ihex $(BUILDDIR)/$(BASENAME).elf \
		$(BUILDDIR)/$(BASENAME).hex


burn:
	avrdude \
		-p m8 \
		-P /dev/ttyUSB0 \
		-c avr910 \
		-U flash:w:$(BUILDDIR)/$(BASENAME).hex:a 

pwm_test.c

#define F_CPU 8000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <math.h>

uint8_t pwm(uint8_t x) {
	double fx = (double) x;
	return pow(2.,8.*fx/256.)-1;

}

void set_rgb(uint8_t r, uint8_t g, uint8_t b) {
	OCR2 = pwm(r);
	OCR1A = pwm(g);
	OCR1B = pwm(b);
}

int main (void) {
 
	DDRB = (1<<PB1) | (1<<PB2) | (1<<PB3); // set output pins
	DDRD = 0xff;

	// configure 16 bit counter
	TCCR1A = (1<<WGM10) | (1<<COM1A1) | (1<<COM1B1); // PWM, phase correct, 8 bit.
	TCCR1B = (1<<CS11) | (1<<CS10); // Prescaler 64 = Enable counter

	// configure 8 bit counter
	TCCR2 = (1<<WGM20) | (1<<COM21) | (1<<CS22); // PWM, phase correct, 8 bit.
	
	PORTD = pwm(0xff);

	uint16_t step = 0;
 
	while(1) {
		uint8_t val = step&0xff;
		uint8_t edge = (step>>8)&7;
		PORTD = val;
		step++;

		switch(edge) {
			// black
			case 0: set_rgb(val,      0,        0);        break;
			// red
			case 1: set_rgb(0xff,     val,      0);        break;
			// orange
			case 2: set_rgb(0xff-val, 0xff,     0);        break;
			// yellow
			case 3: set_rgb(0,        0xff,     val);      break;
			// green
			case 4: set_rgb(val,      0xff,     0xff);     break;
			// white
			case 5: set_rgb(0xff,     0xff-val, 0xff);     break;
			// purple
			case 6: set_rgb(0xff-val, 0,        0xff);     break;
			// blue
			case 7: set_rgb(0,        0,        0xff-val); break;
			// black
		}
  	
		_delay_ms(5);

	};
	return 0;
}