#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>

#define UART_MAXSTRLEN 5

#define F_CPU 8000000
#define BAUD 19200
#include <util/setbaud.h>

static volatile bool uart_dataReceived_b = false;
static volatile char uart_data_c[UART_MAXSTRLEN + 1] = {0};

static void uart_transmit( unsigned char data )
{
  while(!(UCSR0A & (1<<UDRE0)));
  UDR0 = data;
}

void uart_init()
{  
  /* Set baud rate */
  UBRR0H = UBRRH_VALUE;
  UBRR0L = UBRRL_VALUE;
  #if USE_2X
    UCSR0A |= (1 << U2X0);
  #else
    UCSR0A &= ~(1 << U2X0);
  #endif
  /* Enable receiver and transmitter */
  UCSR0B |= (1<<RXCIE0)|(1<<RXEN0)|(1<<TXEN0); // RXCIE0: RX Interrupt
  /* Set frame format: 8data, 1stop bit */
  UCSR0C = (1<<UCSZ00)|(1<<UCSZ01);
}

void uart_flush(void)
{
  uint8_t dummy;
  while (UCSR0A & (1<<RXC0))
  dummy = UDR0;
}

void uart_sendString(volatile char *StringPtr)
{
  while(*StringPtr != 0x00)
  {
    uart_transmit(*StringPtr);
    StringPtr++;
  }
}

ISR(USART_RX_vect)
{
  unsigned char nextChar_c;
    static uint8_t uart_dataReceivedLength_u8 = 0;
  // Daten aus dem Puffer lesen
  nextChar_c = UDR0;
  if( false == uart_dataReceived_b )   // wenn uart_string gerade in Verwendung, neues Zeichen verwerfen
  {
      if( (nextChar_c != '\n')
      && (nextChar_c != '\r'))
//      && (UART_MAXSTRLEN > uart_dataReceivedLength_u8))
      {
          uart_data_c[uart_dataReceivedLength_u8] = nextChar_c;
          uart_dataReceivedLength_u8++;
      }
      else
      {
          uart_data_c[uart_dataReceivedLength_u8] = '\0';
            uart_dataReceivedLength_u8 = 0;
//            uart_dataReceived_b = true;
      }
  }
}

int main(void)
{
    uart_init();
    sei();
    uart_sendString("start\n");
    while (1) 
    {
        if(uart_dataReceived_b)
        {
            uart_sendString(uart_data_c);
            uart_dataReceived_b = false;
        }
    }
}