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

Make AVR Examples/Chapter08_Hardware-Interrupts/helloInterrupt/helloInterrupt.c

@@ -0,0 +1,45 @@
+/*
+
+Demo of using interrupts for doing what they do best --
+two things at once.
+
+Flashes LED0 at a fixed rate, interrupting whenever button is pressed.
+
+ */
+
+// ------- Preamble -------- //
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+#include "pinDefines.h"
+
+ISR(INT0_vect) {         /* Run every time there is a change on button */
+  if (bit_is_clear(BUTTON_PIN, BUTTON)) {
+    LED_PORT |= (1 << LED1);
+  }
+  else {
+    LED_PORT &= ~(1 << LED1);
+  }
+}
+
+void initInterrupt0(void) {
+  EIMSK |= (1 << INT0);                                 /* enable INT0 */
+  EICRA |= (1 << ISC00);                /* trigger when button changes */
+  sei();                          /* set (global) interrupt enable bit */
+}
+
+int main(void) {
+  // -------- Inits --------- //
+  LED_DDR = 0xff;                                   /* all LEDs active */
+  BUTTON_PORT |= (1 << BUTTON);                              /* pullup */
+  initInterrupt0();
+
+  // ------ Event loop ------ //
+  while (1) {
+
+    _delay_ms(200);
+    LED_PORT ^= (1 << LED0);
+
+  }                                                  /* End event loop */
+  return 0;                            /* This line is never reached */
+}