proble with altera uart ttyS0

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

}