Add uart functions from https://github.com/tuupola/avr_demo

src/uart.c

@@ -0,0 +1,40 @@
+#include <avr/io.h>
+#include <stdio.h>
+
+#ifndef F_CPU
+#define F_CPU 16000000UL
+#endif
+
+#ifndef BAUD
+#define BAUD 9600
+#endif
+#include <util/setbaud.h>
+
+/* http://www.cs.mun.ca/~rod/Winter2007/4723/notes/serial/serial.html */
+
+void uart_init(void) {
+    UBRR0H = UBRRH_VALUE;
+    UBRR0L = UBRRL_VALUE;
+    
+#if USE_2X
+    UCSR0A |= _BV(U2X0);
+#else
+    UCSR0A &= ~(_BV(U2X0));
+#endif
+
+    UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); /* 8-bit data */ 
+    UCSR0B = _BV(RXEN0) | _BV(TXEN0);   /* Enable RX and TX */    
+}
+
+void uart_putchar(char c, FILE *stream) {
+    if (c == '\n') {
+        uart_putchar('\r', stream);
+    }
+    loop_until_bit_is_set(UCSR0A, UDRE0);
+    UDR0 = c;
+}
+
+char uart_getchar(FILE *stream) {
+    loop_until_bit_is_set(UCSR0A, RXC0);
+    return UDR0;
+}

src/uart.h

@@ -0,0 +1,9 @@
+void uart_putchar(char c, FILE *stream);
+char uart_getchar(FILE *stream);
+
+void uart_init(void);
+
+/* http://www.ermicro.com/blog/?p=325 */
+
+FILE uart_output = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
+FILE uart_input = FDEV_SETUP_STREAM(NULL, uart_getchar, _FDEV_SETUP_READ);