This ready-to-use code is written for any AVR microcontroller to add some basic UART functions.

AVRserial.c

/****************************************************************************
 Title:     AVR UART library
 Author:    Robert-Maarten Schuurman <[email protected]>  http://rms95.nl/
 Date:      28-06-2013
 Software:  AVR-GCC 3.3 
 Target:    Any AVR device with a single UART and the registers named like
            the ATmega32 (UCSRA-C, UBRRH and UBRRL). By modifying the code
            a bit it is usable for any AVR UART.

 DESCRIPTION
       This file contains a function to set up the UART, to send and
       receive bytes in a polling and non polling way.

       There's also included a printf() function dedicated for the serial
       connection, you can use this function like the normal printf()

 USAGE
       Just include these libraries, and if you need to, also change the
       register names in the c file. At AVR microprocessors with multiple
       UARTs it is usually required to put a number after the register name
       but before the extension of the name: UCSRA --> UCSR0A or UCSR1A.
       
*****************************************************************************/

#include <avr/io.h>
#include <stdarg.h>

/// Initialisation
    void SERIAL_init(int baudrate)
    {
        baudrate = ((F_CPU/(baudrate*8UL))-1);
        UCSRA|=(1<<U2X);
        UCSRB=(1<<RXEN)|(1<<TXEN);
        UCSRC=(1<<URSEL)|(1<<UCSZ0)|(1<<UCSZ1);
        UBRRH=(baudrate >> 8) ;
        UBRRL=baudrate;
    }

/// Data transmission
    void SERIAL_sendByte(char byte)
    {
        while (!SERIAL_sendReady);
        SERIAL_byte = byte;
    }

    char SERIAL_receiveByte()
    {
        return SERIAL_receiveReady?SERIAL_byte:0;
    }

    char SERIAL_receiveBytePoll(unsigned int timeout)
    {
        while (!SERIAL_receiveReady && timeout > 0) {timeout--;};
        return timeout?SERIAL_byte:0;
    }

/// Serial printf
    void SERIAL_printf(const char* format, ...)
    {
        va_list argList;
        va_start(argList, format);
        char *buffer = malloc(SERIAL_printfBuffer);
        vsprintf(buffer, format, argList);
        va_end(argList);
        while(*buffer)
        {
            SERIAL_sendByte(*buffer++);
        }
    }

AVRserial.h

/****************************************************************************
 Title:     AVR UART library
 Author:    Robert-Maarten Schuurman <[email protected]>  http://rms95.nl/
 Date:      28-06-2013
 Software:  AVR-GCC 3.3 
 Target:    Any AVR device with a single UART and the registers named like
            the ATmega32 (UCSRA-C, UBRRH and UBRRL). By modifying the code
            a bit it is usable for any AVR UART.

 DESCRIPTION
       This file contains a function to set up the UART, to send and
       receive bytes in a polling and non polling way.
       
       There's also included a printf() function dedicated for the serial
       connection, you can use this function like the normal printf()

 USAGE
       Just include these libraries, and if you need to, also change the
       register names in the c file. At AVR microprocessors with multiple
       UARTs it is usually required to put a number after the register name
       but before the extension of the name: UCSRA --> UCSR0A or UCSR1A.
       
*****************************************************************************/

#ifndef F_CPU
#define F_CPU 1000000
#endif

#define SERIAL_receiveReady (!!(UCSRA&(1<<RXC)))
#define SERIAL_sendReady (!!(UCSRA&(1<<UDRE)))
#define SERIAL_byte UDR
#define SERIAL_printfBuffer 128

#ifndef SERIAL_H_
#define SERIAL_H_

/// Initialisation
    void SERIAL_init(int baudrate);

/// Data transmission
    void SERIAL_sendByte(char byte);
    char SERIAL_receiveByte();
    char SERIAL_receiveBytePoll(unsigned int timeout);

/// Serial printf
    void SERIAL_printf(const char* format, ...);

#endif