printf() function not working

hi, i compiled the sample progarm given by keil named RTX_ex1... i just included the printf() function to indicate which task running but when i debug its not printing in any of the serial terminal....
description:
os =rtx
processor=LPC2124

CODE:

#include <RTL.h>
#include <stdio.h>

OS_TID id1, id2;

__task void task1 (void);
__task void task2 (void);

__task void task1 (void)

{

id1 = os_tsk_self ();

id2 = os_tsk_create (task2, 1);

for (;;)

{

printf("task 1 running");

os_evt_set (0x0004, id2);

os_evt_wait_or (0x0004, 0xffff);

os_dly_wait (5);

}

}

__task void task2 (void)

{

for (;;)

{

printf("task 2 running");

os_evt_wait_or (0x0004, 0xffff);

os_dly_wait (2);

os_evt_set (0x0004, id1);

}

}

int main (void)

{

os_sys_init (task1);

}