Started following some tutorial on att85 usi. Downloaded example code from make avr book.

Make AVR Examples/Chapter10_Pulse-Width-Modulation/pwmOnAnyPin/pwmOnAnyPin.c

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+// Quick and dirty demo of how to get PWM on any pin with interrupts
+// ------- Preamble -------- //
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+#include "pinDefines.h"
+
+#define DELAY 3
+
+volatile uint8_t brightnessA;
+volatile uint8_t brightnessB;
+
+// -------- Functions --------- //
+static inline void initTimer0(void) {
+                                 /* must be /64 or more for ISR timing */
+  TCCR0B |= (1 << CS01) | (1 << CS00);
+                                     /* both output compare interrupts */
+  TIMSK0 |= ((1 << OCIE0A) | (1 << OCIE1B));
+  TIMSK0 |= (1 << TOIE0);                 /* overflow interrupt enable */
+  sei();
+}
+
+ISR(TIMER0_OVF_vect) {
+  LED_PORT = 0xff;
+  OCR0A = brightnessA;
+  OCR0B = brightnessB;
+}
+ISR(TIMER0_COMPA_vect) {
+  LED_PORT &= 0b11110000;                    /* turn off low four LEDs */
+}
+ISR(TIMER0_COMPB_vect) {
+  LED_PORT &= 0b00001111;                   /* turn off high four LEDs */
+}
+
+int main(void) {
+  // -------- Inits --------- //
+
+  uint8_t i;
+  LED_DDR = 0xff;
+  initTimer0();
+
+  // ------ Event loop ------ //
+  while (1) {
+
+    for (i = 0; i < 255; i++) {
+      _delay_ms(DELAY);
+      brightnessA = i;
+      brightnessB = 255 - i;
+    }
+
+    for (i = 254; i > 0; i--) {
+      _delay_ms(DELAY);
+      brightnessA = i;
+      brightnessB = 255 - i;
+    }
+
+  }                                                  /* End event loop */
+  return 0;                            /* This line is never reached */
+}