Problem with interrup on P89C557E4

Hi, i'm having a problem with the interrupt routine for timer 0 on the P89C557E4 Philips chip.
The interrupt routine doesn't work when running the program. when i simulate it, it works fine.
below is the code:

#include <reg557.h>
#define TIMER0_COUNT 0xDC11 /* 10000h - ((11,059,200 Hz / (12 * FREQ)) - 17) */
static unsigned timer0_tick; /* timer tick variable */
/*------------------------------------------------------------------------------
static void timer0_isr (void);
This function is an interrupt service routine for TIMER 0. It should never
be called by a C or assembly function. It will be executed automatically
when TIMER 0 overflows.
------------------------------------------------------------------------------*/
static void timer0_isr (void) interrupt 1 using 1
{
/*------------------------------------------------
Stop Timer 0, adjust the timer 0 counter so that
we get another interrupt in 10ms, and restart the
timer.
------------------------------------------------*/
TR0 = 0; /* stop timer 0 */
TL0 = TL0 + (TIMER0_COUNT & 0x00FF);
TH0 = TH0 + (TIMER0_COUNT >> 8);
TR0 = 1; /* start timer 0 */
/*------------------------------------------------
Increment the timer tick. This interrupt should
occur approximately every 10ms. So, the resolution
of the timer will be 100Hz not including interrupt
latency.
------------------------------------------------*/
//timer0_tick++;
CMSR4 = 0;
}
/*------------------------------------------------------------------------------
void timer0_initialize (void);
This function enables TIMER 0. TIMER 0 generates a synchronous interrupt
once every 100Hz.
------------------------------------------------------------------------------*/
void timer0_initialize (void)
{
EA = 0; /* disable interrupts */
timer0_tick = 0;
TR0 = 0; /* stop timer 0 */
TMOD &= ~0x0F; /* clear timer 0 mode bits */
TMOD |= 0x01; /* put timer 0 into 16-bit no prescale */
TL0 = (TIMER0_COUNT & 0x00FF);
TH0 = (TIMER0_COUNT >> 8);
PT0 = 0; /* set low priority for timer 0 */
ET0 = 1; /* enable timer 0 interrupt */
TR0 = 1; /* start timer 0 */
EA = 1; /* enable interrupts */
}
/*------------------------------------------------------------------------------
unsigned timer0_count (void);
This function returns the current timer0 tick count.
------------------------------------------------------------------------------*/
unsigned timer0_count (void)
{
unsigned t;
EA = 0;
t = timer0_tick;
EA = 1;
return (t);
}
/*------------------------------------------------------------------------------
void timer0_delay (
unsigned count);
This function waits for 'count' timer ticks to pass.
------------------------------------------------------------------------------*/
void timer0_delay (
unsigned count)
{
unsigned start_count;
start_count = timer0_count (); /* get the starting count */
while ((timer0_count () - start_count) <= count) /* wait for count "ticks" */
{
}
}
void main (void)
{
timer0_initialize();
while (1)
  {
CMSR4 = !CMSR4;
//timer0_delay( 1 );
  }
}