Added time tracking.

emb/time.cpp

+#include "time.hpp"
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+
+static uint32_t millis;
+
+void initTime()
+{
+    cli();
+    
+    TCCR0A = (1 << WGM01);              // CTC mode, TOP = OCRA
+    TCCR0B = (1 << CS01) | (1 << CS00); // 64th prescaler
+    OCR0A = 249;                        // set TOP for 1 kHz interrupts
+    TIMSK0 = (1 << OCIE0A);             // enable compare A interrupt
+    
+    sei();
+}
+
+uint32_t getCurrentMillis()
+{
+    return millis;
+}
+
+ISR(TIMER0_COMPA_vect)
+{
+    millis++;
+}

emb/time.hpp

+#ifndef TIME_H
+#define TIME_H
+
+#include <stdint.h>
+
+/**
+ * Initialises time.
+ */
+void initTime();
+
+/**
+ * Gets the number of milliseconds since program start.
+ */
+uint32_t getCurrentMillis();
+
+#endif /* TIME_H */