Pulse width measurement

I downloaded the demo program from the website to measure the pulsewidth using TIMER0.

ET0 =1;
EA =1;
TMOD = (TMOD&0xF)| 0x09;  //Set GATE0 bit
while(1)
{
T0_ISR_count=0;
TH0=0;
TL=0;

TR0=1;          //start TIMER0

tdelay(200);   //Test#1
//tdealay(500);   //Test#2


while(!INT0);   //wait for rising edge
while(INT0);    //wait for falling edge
printf("The width pulse is: %ld uSec\n",
(unsigned long) ((TH0<<8) | TL0 | ((unsigned long)T0_ISR_count<<16)));
}
}
//------------------------

void tdelay(unsigned long I) //time delay
{
  int i;
  for (i=0;I;i++);
}

When I tested the code on the real board, changing from
Test#1 to Test#2 (for tdelay function ) above made huge different results !!. I would think that the timer will not run until the INT0 goes HI because the
SMOD bit4 (GATE0) is set.
Could somebody kindly tell me what I did wrong here.
NOTE: on the downloaded file, there was a PRINTF
statement in replace of the tdelay(200) function.
Again, I don't think it is going to make any different
because the TIMER has not been fired yet at that line.

We are using Winbond 77LE532 (11.0592MHZ).

Thanks

Jimmy