Add PWM dimming.

main.c

@@ -1,14 +1,61 @@
 #include <avr/io.h>
 #include <util/delay.h>
 
+#define PIN_LED 0b1000;
+
+void init_ports(void) {
+  DDRB = 0x00;
+  DDRC = 0x00;
+  DDRD = 0x00;
+
+  DDRD |= PIN_LED;
+}
+
+void init_pwm(void) {
+  // page 84
+  //  7-6: ouput A, 5-4: output B, 3-2: res, 1-0: waveform
+  TCCR2A = 0b00100011;
+  // 7-6: force output A/B, 5-4: res, 3: waveform, 2-0: clock source
+  TCCR2B = 0b01000001;
+  // duty
+  OCR2B = 0;
+}
+
+void deinit_pwm(void) {
+  TCCR2A = 0;
+  TCCR2B = 0;
+  OCR2B = 0;
+}
+
+void pwm_fade_in(int until, int step) {
+  int i;
+  for (i = 0; i < until; i += step) {
+    OCR2B = i;
+    _delay_ms(0.5);
+  }
+}
+
+void pwm_fade_out(int until, int step) {
+  int i;
+  for (i = OCR2B; i > until; i -= step) {
+    OCR2B = i;
+    _delay_ms(0.25);
+  }
+}
+
 int main(void) {
-  DDRD = 255;
+  init_ports();
 
   while (1) {
-    PORTD = 0b00001000;
-    _delay_ms(100);
-    PORTD = 0;
-    _delay_ms(100);
+    init_pwm();
+    pwm_fade_in(0x7f, 1);
+    _delay_ms(300);
+    OCR2B = 0xff;
+    _delay_ms(150);
+    pwm_fade_out(0, 4);
+    deinit_pwm();
+    PORTD &= ~PIN_LED;
+    _delay_ms(2000);
   }
   return 0;
 }