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

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

@@ -0,0 +1,67 @@
+/*
+   Capacitive touch sensor demo
+*/
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+#include <avr/power.h>
+#include "pinDefines.h"
+#include "USART.h"
+
+#define SENSE_TIME   50
+#define THRESHOLD    12000
+
+// -------  Global Variables ---------- //
+volatile uint16_t chargeCycleCount;
+
+// ------- Functions -------- //
+
+void initPinChangeInterrupt(void) {
+  PCICR |= (1 << PCIE1);    /* enable Pin-change interrupts 1 (bank C) */
+  PCMSK1 |= (1 << PC1);   /* enable specific interrupt for our pin PC1 */
+}
+
+ISR(PCINT1_vect) {
+  chargeCycleCount++;                             /* count this change */
+
+  CAP_SENSOR_DDR |= (1 << CAP_SENSOR);                  /* output mode */
+  _delay_us(1);                                      /* charging delay */
+
+  CAP_SENSOR_DDR &= ~(1 << CAP_SENSOR);                /* set as input */
+  PCIFR |= (1 << PCIF1);             /* clear the pin-change interrupt */
+}
+
+
+int main(void) {
+  // -------- Inits --------- //
+  clock_prescale_set(clock_div_1);                       /* full speed */
+  initUSART();
+  printString("==[ Cap Sensor ]==\r\n\r\n");
+
+  LED_DDR = 0xff;
+  MCUCR |= (1 << PUD);                          /* disable all pullups */
+  CAP_SENSOR_PORT |= (1 << CAP_SENSOR);    /* we can leave output high */
+
+  initPinChangeInterrupt();
+
+  // ------ Event loop ------ //
+  while (1) {
+
+    chargeCycleCount = 0;                             /* reset counter */
+    CAP_SENSOR_DDR |= (1 << CAP_SENSOR);     /* start with cap charged */
+    sei();                            /* start up interrupts, counting */
+    _delay_ms(SENSE_TIME);
+    cli();                                                     /* done */
+    if (chargeCycleCount < THRESHOLD) {
+      LED_PORT = 0xff;
+    }
+    else {
+      LED_PORT = 0;
+    }
+    printWord(chargeCycleCount);                    /* for fine tuning */
+    printString("\r\n");
+
+  }                                                  /* End event loop */
+  return 0;                            /* This line is never reached */
+}