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

Make AVR Examples/Chapter07_Analog-to-Digital-Conversion-I/nightLight/nightLight.c

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+// Quick and dirty adjustable-threshold night-light.
+
+// ------- Preamble -------- //
+#include <avr/io.h>
+#include <util/delay.h>
+#include "pinDefines.h"
+
+uint16_t readADC(uint8_t channel) {
+  ADMUX = (0xf0 & ADMUX) | channel;
+  ADCSRA |= (1 << ADSC);
+  loop_until_bit_is_clear(ADCSRA, ADSC);
+  return (ADC);
+}
+
+int main(void) {
+  // -------- Inits --------- //
+  uint16_t lightThreshold;
+  uint16_t sensorValue;
+  // Set up ADC
+  ADMUX |= (1 << REFS0);                  /* reference voltage on AVCC */
+  ADCSRA |= (1 << ADPS1) | (1 << ADPS0);     /* ADC clock prescaler /8 */
+  ADCSRA |= (1 << ADEN);                                 /* enable ADC */
+
+  LED_DDR = 0xff;
+  // ------ Event loop ------ //
+  while (1) {
+
+    lightThreshold = readADC(POT);
+    sensorValue = readADC(LIGHT_SENSOR);
+
+    if (sensorValue < lightThreshold) {
+      LED_PORT = 0xff;
+    }
+    else {
+      LED_PORT = 0x00;
+    }
+  }                                                  /* End event loop */
+  return 0;                            /* This line is never reached */
+}