printf mit Atmega128 über uart0

Ich versuche mit Printf_P Strings über den Uart auszugeben, hatte damit
aber bislang nur wenig Erfolg.
Das Ganze soll interruptgesteuert und gepuffert ablaufen.
Hoffentlich kann mir hier jemand noch einen Rat geben wo der Fehler
steckt...

Ich benutze WinAVR-20030913 und AVR Studio 4.07 und folgenden Code:


#include <avr/io.h>
#include <avr/signal.h>
#include <avr/interrupt.h>
#include <stdio.h>
#include <avr/pgmspace.h>

#define UART_BUF_SIZE    40

char character = 'H';
char string[]  = "ello World!";

/* uart globals */
volatile unsigned char uart_txd_buf_cnt;
volatile unsigned char *uart_txd_in_ptr, *uart_txd_out_ptr;
volatile unsigned char uart_txd_buffer[UART_BUF_SIZE];



SIGNAL(SIG_UART0_DATA)
/* signal handler for uart data buffer empty interrupt */
{
    if (uart_txd_buf_cnt > 0) {
        outp(*uart_txd_out_ptr, UDR0);          /* write byte to data
buffer */
        if (++uart_txd_out_ptr >= uart_txd_buffer + UART_BUF_SIZE) /*
Pointer wrapping */
            uart_txd_out_ptr = uart_txd_buffer;
        if(--uart_txd_buf_cnt == 0)             /* if buffer is empty:
*/
            cbi(UCSR0B, UDRIE0);                /* disable UDRIE int
*/
    }
}

int uart_putchar(char c)
{
    if (uart_txd_buf_cnt<UART_BUF_SIZE) {
        cli();
        uart_txd_buf_cnt++;
        *uart_txd_in_ptr = c;                   /* put character into
buffer */
        if (++uart_txd_in_ptr >= uart_txd_buffer + UART_BUF_SIZE) /*
pointer wrapping */
            uart_txd_in_ptr = uart_txd_buffer;
        sbi(UCSR0B, UDRIE0);                    /* enable UDRIE int */
        sei();
        return 0;
    }
    else
        return 1;                             /* buffer is full */
}

unsigned char uart_putstr(char s[])
{
    char  *c  = s;

  while (PRG_RDB(c))
        if (0 == uart_putchar(PRG_RDB(c)))
            c++;

    return 0;
}

int main(void)
{

/* initialize uart */
  // USART initialization
  // Communication Parameters: 8 Data, 1 Stop, No Parity
  // USART Receiver: On
  // USART Transmitter: On
  // USART Baud rate: 38400
  UCSR0A=0x00;
  UCSR0B=((1<<RXCIE) | (1<<RXEN) | (1<<TXEN));
  // USART Mode: Asynchronous
  UCSR0C=0x86;
  UBRR0L=0x19;
  UBRR0H=0x00;

    uart_txd_in_ptr  = uart_txd_out_ptr = uart_txd_buffer;
    uart_txd_buf_cnt = 0;


fdevopen(uart_putchar,NULL,0);
sei();

printf_P(character);
printf_P(string);


while (1) { };

return 0;
}