Lpc2000

the problem is i can only enter the interrupt 
funciton once,then never enter the function again.
are there any problems with my program?
anyone can give me a suggestion?


#include "config.h"
unsigned int  result[20];
unsigned char channelx[20];

void __irq IRQ_ADC(void)
{
   unsigned int  value   = 0x0000;       //result of the ADC converter
   unsigned char channel = 0x00;         //the channel
   unsigned char i	       = 0;	
   value        = ADDR;  //read the result and clear the DONE sign
   channel      = (value>>0x18)&0x07; //get the channel
   value        = (value>>6)&0x03ff;  //convert the ADC result
   if(channel == 0x00)                //switch the channel
       	ADCR = ADCR&0xFFFFFF00|0x02;   
    else if(channel == 0x01)
       	ADCR = ADCR&0xFFFFFF00|0x04;
    else if(channel == 0x02)
      	ADCR = ADCR&0xFFFFFF00|0x08;
    else if(channel == 0x03)
      	ADCR = ADCR&0xFFFFFF00|0x01;
    channelx[i]  = channel;
	result[i]    = value;
	i++;	
	if(i<20)             //whether get 20 result ?
		i++;
	else
		i = 0;
	VICVectAddr0 = 0;    //clear the IRQ function address
}

int main(void)
{
    PINSEL1 	 = 0x01400000;//connect the pin to adc
    ADCR    	 = 0x00201501;//setup the ADCR only use the ain0
    ADCR		 = ADCR|0x00010000;//use burst model
    VICIntSelect = 0x00000000;      //
    VICVectCntl0 = 0x32;
    VICVectAddr0 = (int)IRQ_ADC;    //address of the IRQ function
    VICIntEnable = 0x00040000;      //enamble the ADC interrupt
    while(1)
    {
	;                           //wait for the interrupt
     }
	return(0);
}