uart.h

#ifndef UART_H
#define UART_H

#define F_CPU 16000000UL
#define BAUD 9600

#include <util/setbaud.h>

static int uart_putchar(char c, FILE *stream);
static int uart_getchar(FILE *stream);
void uart_init(void);

static FILE uart_output = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
static FILE uart_input = FDEV_SETUP_STREAM(NULL, uart_getchar, _FDEV_SETUP_READ);

int uart_putchar(char c, FILE *stream) {
	if (c == '\n') {
		uart_putchar('\r', stream);
	}
	loop_until_bit_is_set(UCSR0A, UDRE0);
	UDR0 = c;
	return 0;
}

int uart_getchar(FILE *stream) {
	loop_until_bit_is_set(UCSR0A, RXC0); /* Wait until data exists. */
	return UDR0;
}

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 */

    // Redirect stdin and stdout so functions like printf and getchar work.
	stdout = &uart_output;
	stdin = &uart_input;
}

#endif // UART_H