proble with altera uart ttyS0

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hi all 

i have problem with altera uart0 when i send char it's ok but µclunix stop run , my function  int uart_altera_test() { char* msg = "c";  int fp;  char prompt = 0;  fp = open ("/dev/ttyS0", O_RDWR | O_NONBLOCK); //Open file for reading and writing   if (fp < 0)  {  printf( "error open %.\n", fp);  }  else  {     if( write(fp, msg ,sizeof(char)) < 0)  {  printf("error write UART file.\n");  }  fclose (fp);  printf("Closing the UART file.\n");  }  return 0 }