Added support for UART.

emb/uart.cpp

+#include "uart.hpp"
+
+#include "servos.hpp"
+#include "command.h"
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+void initUart()
+{
+    cli();
+    
+    UCSR0A = (1 << U2X0);  // double transmission speed
+    UCSR0B = (1 << RXCIE0) // enable RX complete interrupt
+           | (1 << UDRIE0) // enable data register empty interrupt
+           | (1 << RXEN0)  // enable receiver
+           | (1 << TXEN0); // enable transmitter
+    UCSR0C = (0 << UMSEL01) | (0 << UMSEL00) // asynchronous USART
+           | (0 << UPM01) | (0 << UPM00)     // no parity bit
+           | (0 << USBS0)                    // 1 stop bit
+           | (1 << UCSZ01) | (1 << UCSZ00);  // 8 data bits
+    
+    UBRR0 = 16; // 115.2k baud rate
+    
+    sei();
+}
+
+ISR(USART_RX_vect)
+{
+    uart_add_ch(UDR0);
+}
+
+ISR(USART_UDRE_vect)
+{
+    // nothing to do right now
+}

emb/uart.hpp

+#ifndef UART_H
+#define UART_H
+
+/**
+ * Initialises the UART logic.
+ */
+void initUart();
+
+#endif /* UART_H */