How to measure pulse width applied in INT0 of Cypress USB FX2 CY7C68013

Hi,

I want to measure the width of the pulse applied in INT0. My code base on the sample of KEIL: http://www.keil.com/download/docs/8051_timer0_pulse.zip.asp

The result printed out in Serial1 window is very strange. For example, when I input 100usec pulse into INT0, but it just print out 3us. (Notes, I run in debug and simulation mode).

#include "fx2.h"
#include "fx2regs.h"
#include <stdio.h>

/*-------------------------------------------
Timer 0 Overflow Interrupt
------------*/
unsigned int T0_ISR_count = 0;

void T0_ISR (void) interrupt 1
{
T0_ISR_count++;
TF0 = 0; // Reset the interrupt request
}

/*-------------------------------------------
MAIN C function
------------*/
void main (void)
{
/*--------------------------------------
Set serial port for 9600 baud at
11.0592 MHz. Note that we use Timer 1
for the baud rate generator.
--------------------------------------*/
SCON0 = 0x50;
TMOD |= 0x20; //Enable bit TMOD5 Timer1: Mode2: 8bit counter with auto-reload
TH1 = 0xFA;
TR1 = 1; //Enable counting on Timer 1
TI = 1;
PCON |= 0x80; //Serial Port 0 mode 3

printf ("\nPulse Width Example Program\n\n");

/*--------------------------------------
Enable interrupts for timer 0.
--------------------------------------*/
ET0 = 1;

/* ET0 - Enable Timer 0 interrupt. ET0 = 0 disables Timer 0 interrupt (TF0).
ET0=1 enables interrupts generated by the TF0 flag.*/

EA = 1;

/*--------------------------------------
Set Timer0 for 16-bit interval timer
mode.
--------------------------------------*/
TMOD = (TMOD & 0xF0) | 0x09;
while (1)
{
/*--------------------------------------
Clear the timer overflow counter and
the timer low and high registers. Then,
start the timer.
--------------------------------------*/
T0_ISR_count = 0; //Clear overflow counter
TH0 = 0;
TL0 = 0;

TR0 = 1; //Enable Timer0 to receive clock in
IT0= 0;// Detect LowLevel at INT0

printf ("\nStart a pulse.\n");

/*--------------------------------------
Wait for the pulse to start.
Then, wait for the pulse to end.
--------------------------------------*/
while (!IE0); // Wait when INT0 low
while (IE0); //and continue to wait when INTO high

/*--------------------------------------
Compute the width of the pulse -- one
clock cycle is 1us for a standard 8051
and display it.
--------------------------------------*/
printf ("The width pulse is: %ld uSec\n",
(unsigned long)((TH0 << 8) | TL0 | ((unsigned long)T0_ISR_count << 16)));
}
}