Problem with Phase Firing Angle in dimmer circuit

#include <mega8535.h>
#include <delay.h>

// External Interrupt 0 service routine
interrupt [EXT_INT0] void ext_int0_isr(void)
{
    PORTB=0x00;
    delay_ms(5);  // firing triac 6 ms after zero cross detected
    PORTB=0x01;   
    delay_us(1);  // firing pulse width 1 us
    PORTB=0x00;
}

void main(void)
{

PORTB=0x00;
DDRB=0x01;        // PORTB.0 as output

GICR|=0x40;       // INT0
MCUCR=0x01;
MCUCSR=0x00;
GIFR=0x40;

// Global enable interrupts
#asm("sei")

while (1)
      {
      }
}

ISR ()
{
check Ext Int flag
{
enable timer
}

Check timer overflow flag
{
set output like PORTB=0x01;
}
} 
 
main()
{
}

#include <mega8535.h>
#include <delay.h>

// External Interrupt 0 service routine
interrupt [EXT_INT0] void ext_int0_isr(void)
{
    PORTD.0 = 0;              //initially triac off
    TCCR1B = 0x02;
}

// Timer1 output compare A interrupt service routine
interrupt [TIM1_COMPA] void timer1_compa_isr(void)
{
    TCNT1H=0x00;
    TCNT1L=0x00;
    PORTD.0 = 1;
    delay_us(100);
    PORTD.0 = 0;
    TCCR1B=0x00;
}


// Declare your global variables here

void main(void)
{

PORTD=0x00;
DDRD=0x01;


// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 1500.000 kHz
// Mode: Normal top=0xFFFF
// OC1A output: Discon.
// OC1B output: Discon.
// Noise Canceler: Off
// Input Capture on Falling Edge
// Timer1 Overflow Interrupt: Off
// Input Capture Interrupt: Off
// Compare A Match Interrupt: On
// Compare B Match Interrupt: Off
TCCR1A=0x00;
TCCR1B=0x02;
TCNT1H=0x00;
TCNT1L=0x00;
ICR1H=0x00;
ICR1L=0x00;
OCR1AH=0x1D;                  // 5ms prescaller:8, crystal;12MHz  ==>(5/1000)*(12000000/8)=7500 in hex 1D4C
OCR1AL=0x4C;
OCR1BH=0x00;
OCR1BL=0x00;

// External Interrupt(s) initialization
// INT0: On
// INT0 Mode: Falling Edge
// INT1: Off
// INT2: Off
GICR|=0x40;
MCUCR=0x02;
MCUCSR=0x00;
GIFR=0x40;

// Timer(s)/Counter(s) Interrupt(s) initialization
TIMSK=0x10;

// Analog Comparator Input Capture by Timer/Counter 1: Off
ACSR=0x80;
SFIOR=0x00;


// Global enable interrupts
#asm("sei")


while (1)
      {
      // Place your code here

      }
}