source: avrstuff/libs/usart/usart.c@ 6390cc3

/* AVR USART acces functions - stolen from Extreme Electronics */

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

#ifndef BAUD
        #error You must define BAUD to use libuart.
#endif

#ifdef __AVR_ATmega128__
// FIXME there are two USARTs in this case and we should be able to drive either
#define UBRRH UBRR0H
#define UBRRL UBRR0L
#define UCSRA UCSR0A
#define UCSRC UCSR0C
#define UCSRB UCSR0B
#define UDR   UDR0
#endif

//This function is used to initialize the USART
void USARTInit()
{
        //Set Baud rate
        #include <util/setbaud.h>
        UBRRH = UBRRH_VALUE;
        UBRRL = UBRRL_VALUE;
        #if USE_2X
                UCSRA |= (1 << U2X);
        #else
                UCSRA &= ~(1 << U2X);
        #endif

        /*Set Frame Format
          >> Asynchronous mode
          >> No Parity
          >> 1 StopBit
          >> char size 8
          */
#ifdef __AVR_ATtiny2313__
        UCSRC = (1 << UCSZ1) | (1 << UCSZ0);
#elif defined __AVR_ATmega128__
        UCSRC = (3 << UCSZ0);
#else
        UCSRC = (1 << URSEL) | (3 << UCSZ0);
#endif

        //Enable The receiver and transmitter
        UCSRB = (1 << RXEN) | (1 << TXEN);
}


//This fuction writes the given "data" to
//the USART which then transmit it via TX line
void USARTWriteChar(char data)
{
        //Wait untill the transmitter is ready
        while(!(UCSRA & (1<<UDRE)))
        {
                //Do nothing
        }

        //Now write the data to USART buffer

        UDR=data;
}


//This function is used to read the available data
//from USART. This function will wait untill data is
//available.
char USARTReadChar()
{
        //Wait untill a data is available
        while(!(UCSRA & (1<<RXC)))
        {
                //Do nothing
        }

        //Now USART has got data from host
        //and is available is buffer

        return UDR;
}


void USARTWriteHex(unsigned char i)
{
        unsigned char k = i>>4;
        if (k <=9) k+='0';
        else k+=('A'-10);

        USARTWriteChar(k);

        k = i&0xF;
        if (k <=9) k+='0';
        else k+=('A'-10);

        USARTWriteChar(k);
}