AVR Freaks

I try to use Analog Comparator on ATTiny461A. The voltage of the AIN1 changes according to below table.

                       I/P         Normal       Left        Right

AIN0 (Pin 12)  NEG          2.5v         2.5V       2.5V

AIN1 (Pin 11)  POS           2.5V        2.1V       2.6V

AC0                                                  0           1

I wish to compare AIN1 to AIN0. If AIN1 voltage more than AIN0, AC0 to be set.  

I try to get below code work, but there isnt any response on the output pin. i attached the datasheet table. 

#include <avr/io.h>

void port_init()
{
	DDRA |= (1<<PINA6) | (1<<PINA7); //AIN0 AND AIN1 AS INPUT
	DDRB |= (1<<PINB4)| (1<<PINB6);//OUTPUT PINS
}

void AC_Init(){
	ACSRA = 0b00000000;
	ACSRB = 0b00000010; //ain0 as negative input, ain1 as positive

}


int main(void)
{
	port_init();
	AC_Init();
	while (1)
	{
		if ((ACSRA & 0X20) == 1)
		{
			
			PORTB |= (1 << PINB6);  //PINB6 HIGH
			PORTB &= ~(1 << PINB4);  //PINB4 LOW
		}
		else
		{
			PORTB &= ~(1 << PINB6);  //PINB6 LOW
			PORTB |=  (1 << PINB4);  //PINB4 HIGH
		}

	}
}

Is there anything else I need to set on the ACSRA, ACSRB register or ADCSRA register ?

I have try set ADEN to zero, it doesnt work too.  Any help is much appreciated.