ATmega128 RS232 Komunikation

#include <stdio.h> 

#include <stdlib.h>

#include <avr\io.h> 

#include <avr/interrupt.h> //for the interupts for receiving via UART

#include <string.h> //for building strings of characters

#include <avr/pgmspace.h>  //for PSTR for handling the location of characters

//Set the baud rate of the communication

#define BAUD 9600UL      // Baudrate

// Berechnungen

#define UBRR_VAL ((F_CPU+BAUD*8)/(BAUD*16)-1)   // clever runden

#define BAUD_REAL (F_CPU/(16*(UBRR_VAL+1)))     // Reale Baudrate

#define BAUD_ERROR ((BAUD_REAL*1000)/BAUD) // Fehler in Promille, 1000 = kein Fehler.

#if ((BAUD_ERROR<990) || (BAUD_ERROR>1010))

  #error Systematischer Fehler der Baudrate grösser 1% und damit zu hoch! 

#endif

//Four variables for buffering of received messages

  volatile char c; //The temp place to dump the character we just received

  volatile char buffer[30]; // The array holding the characters that have been sent

  volatile int bufferlocation; //The current location in the buffer

  volatile int bufferflag; //A flag to tell whether there is complete data in the buffer to be processed

//Declare the location of the stream for the output

  void uart_printchar(char c, FILE *stream){

    // Wait until UDR ready

      while(!(UCSR0A & (1 << UDRE0)));

        UDR0 = c;    // send character

  }

//USART RX interrupt this code is executed when we recieve a character

  ISR(USART0_RX_vect){        

    c = UDR0; //Read the value out of the UART buffer

    buffer[bufferlocation] = c; //Dump that value out into the buffer array

    bufferlocation++;  //Increment the bufferlocation so its ready to write next time

    if (c == 13) //Number 13 is carrage return

      bufferflag = 1; //If its a carriage return then mark the string as ready to process

  }

int BaudRateRegister;

int main(void){ 

//---------------Start of Initalisation---------------

//Configure the UART registers

  UCSR0B = ((1<<RXCIE0)|(1<<RXEN0)|(1<<TXEN0));

    //RXCIE0 Enable interupt after recieved

    //RXEN0 Reciever enabled

    //TXEN0 Transmit enabled

  UCSR0C = ((1<<UCSZ00)|(1<<UCSZ01));

    //UCSZ00 and UCSZ01 use 8 bit character size

//Set the baud rate 

  BaudRateRegister=F_CPU/16/BAUD-1;

  UBRR0H=((BaudRateRegister>>8)&0x00FF);

  UBRR0L=(BaudRateRegister&0x00FF); 

//Define and initialise stream used for printing to uart

  FILE uart_str = FDEV_SETUP_STREAM(uart_printchar, NULL, _FDEV_SETUP_RW);

//Redirect stdout, so that printf() knows where to go

  stdout = &uart_str;

//Enable interrupts  

  sei();  

//---------------End of Initalisation---------------

  printf_P(PSTR("..."));

  printf_P(PSTR("Running"));

  printf_P(PSTR("BaudRateRegister set to %u\n"),BaudRateRegister);

  printf_P(PSTR("Wait"));

//Start of infinate while loop

   while(1){

    if (bufferflag == 1){ 

      printf_P(PSTR("Got instruction"));

      bufferflag = 0; //Reset the buffer flag to say its been processed

      bufferlocation =0; //Restart the buffer location

    }

   }

//End of infinate while loop

}

//End of main routine