printf retarget.c - data aborts

Hello,

I work with the AT91RM9200.

I have some problems with the retarget-function for the implementation of printf. It works but sometimes I get a data abort - maybe if the buffer for printf function is too small???

that's my function to transmit printf messages to the usart

int COM1_1_sendchar(int ch)
{
        if (ch == '\n')  {                              /* Check for CR */
        while (!(COM1_1->US_CSR & AT91C_US_TXRDY));      /* Wait for Empty Tx Buffer */
    //  COM1_1->US_THR = '\r';                       /* Output CR */
                AT91F_US_PutChar (COM1_1,'\r');
        }
        while (!(COM1_1->US_CSR & AT91C_US_TXRDY));      /* Wait for Empty Tx Buffer */
        return (COM1_1->US_THR = ch);                        /* Transmit Character */
}

retarget.c

#include <stdio.h>
#include <rt_misc.h>
#include <AT91RM9200.H>
#pragma import(__use_no_semihosting_swi)

extern int COM1_1_sendchar (int ch);    /* in usart.c */

struct __FILE { int handle; /* Add whatever you need here */ };
FILE __stdout;
FILE __stdin;

int fputc(int ch, FILE *f) {

  return (COM1_1_sendchar(ch));
}


int ferror(FILE *f) {
  /* Your implementation of ferror */
  return EOF;
}


void _ttywrch(int ch) {
  COM1_1_sendchar(ch);
}

void _sys_exit(int return_code) {
label:  goto label;  /* endless loop */
}

I hope somebody have a idea - because the problem with the data abort is not always but very often

best regards
Johannes