simple AVR USART

usart.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sfr_defs.h>

static void		init(uint16_t rate)
{
	UBRR0H = (uint8_t) (rate >> 8); // freq/(16*speed)-1
	UBRR0L = (uint8_t) rate;
	UCSR0A &= ~_BV(U2X0); // unset double speed (optiboot)
	UCSR0B = _BV(RXEN0) | _BV(TXEN0); // enable transmision/reception
	UCSR0C = _BV(UCSZ00) | _BV(UCSZ01); // set 8N1
	UCSR0B |= _BV(RXCIE0); // enable interrupt on char
}

static void		putchr(char c)
{
	loop_until_bit_is_set(UCSR0A, UDRE0); // check if read op is pending
	UDR0 = c; // write char
}

ISR(USART_RX_vect)
{
	char	c;

	c = UDR0; // read char
	if (bit_is_clear(UCSR0A, FE0)) // check for transmission error
	{
		if (c != '\n')
			putchr(c + 1);
		else
			putchr('\n');
	}
}

int 			main(void)
{
	init(103);
	sei();
	for (;;);
	return (0);
}

Thanks for publishing your code snippet. Line 12 helped me a lot!