Need Help: Digitally Controlled Triac (Phase Firing Angle Application)

[ArdyNT]

I built the following code to control the TRIAC's firing delay.

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

 unsigned char buf[10];
 volatile unsigned int ldr1;
 volatile unsigned int ldr2;
 volatile unsigned int ldr3;

 unsigned int count = 0;

 volatile unsigned int x = 2;
 volatile unsigned int y = 2;
 volatile unsigned int z = 2;
    
 // Alphanumeric LCD functions
 #include <lcd.h>
 #asm
 .equ __lcd_port=0x15 ;PORTC
 #endasm


 // External Interrupt 0 service routine
 interrupt [EXT_INT0] void ext_int0_isr(void)
 {
    // Start  Timer 0
    TCCR0 = 0x02;
 }

 // Timer 0 overflow interrupt service routine
 interrupt [TIM0_OVF] void timer0_ovf_isr(void)
 {
    // Local variables initialization
    static uint8_t pulse_flag = 0;
    
    // Reinitialize Timer 0 value
    TCNT0=0xD3;
    
    // Increment count every 50 us
    count++; 
    
    // Front lamp
    if(count == x)
        {
            PORTB.0 = 0;
        }
    else
        if(count == x + 1)
            {
                PORTB.0 = 1;
                pulse_flag++;
            }
                
    // Middle lamp        
    if(count == y)
        {
            PORTB.1 = 0;
        }
    else
        if(count == y + 1)
            {
                PORTB.1 = 1;
                pulse_flag++;
            }

    // Back lamp
    if(count == z)
        {
            PORTB.2 = 0;
        }
    else
        if(count == z + 1)
            {
                PORTB.2 = 1;
                pulse_flag++;
            }
     
    // Stop timer when all pulses have completed
    if(pulse_flag == 3)
        {
            // Clear flag
            pulse_flag = 0;
             
            // Stop the timer
            TCCR0 = 0;
                  
            // Clear count
            count = 0; 
        }  
 }


#define ADC_VREF_TYPE 0x40

 // Read the AD conversion result
 unsigned int read_adc(unsigned char adc_input)
 {
    ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
    
    // Delay needed for the stabilization of the ADC input voltage
    delay_us(10);
    
    // Start the AD conversion
    ADCSRA|=0x40;
    
    // Wait for the AD conversion to complete
    while ((ADCSRA & 0x10)==0);
    ADCSRA|=0x10;
    return ADCW;
 }


 void main(void)
 {
    // Input/Output Ports initialization
    // Port A initialization
    // Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In 
    // State7=P State6=P State5=P State4=P State3=P State2=P State1=P State0=P 
    PORTA=0xFF;
    DDRA=0x00;

    // Port B initialization
    // Func7=Out Func6=Out Func5=Out Func4=Out Func3=Out Func2=Out Func1=Out Func0=Out 
    // State7=1 State6=1 State5=1 State4=1 State3=1 State2=1 State1=1 State0=1 
    PORTB=0xFF;
    DDRB=0xFF;

    // Port C initialization
    // Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In 
    // State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=T 
    PORTC=0x00;
    DDRC=0x00;

    // Port D initialization
    // Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In 
    // State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=T 
    PORTD=0x00;
    DDRD=0x00;

    // Timer/Counter 0 initialization
    // Clock source: System Clock
    // Clock value: 1500.000 kHz
    // Mode: Normal top=0xFF
    // OC0 output: Disconnected
    TCCR0=0x02;
    TCNT0=0xD3;
    OCR0=0x00;

    TCCR1A=0x00;
    TCCR1B=0x00;
    TCNT1H=0x00;
    TCNT1L=0x00;
    ICR1H=0x00;
    ICR1L=0x00;
    OCR1AH=0x00;
    OCR1AL=0x00;
    OCR1BH=0x00;
    OCR1BL=0x00;

    ASSR=0x00;
    TCCR2=0x00;
    TCNT2=0x00;
    OCR2=0x00;

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

    // Timer(s)/Counter(s) Interrupt(s) initialization
    TIMSK=0x01;

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

    // ADC initialization
    // ADC Clock frequency: 750.000 kHz
    // ADC Voltage Reference: AVCC pin
    // ADC High Speed Mode: Off
    // ADC Auto Trigger Source: ADC Stopped
    ADMUX=ADC_VREF_TYPE & 0xff;
    ADCSRA=0x84;
    SFIOR&=0xEF;

    // Alphanumeric LCD initialization
    // Connections are specified in the
    // Project|Configure|C Compiler|Libraries|Alphanumeric LCD menu:
    // RS - PORTC Bit 0
    // RD - PORTC Bit 1
    // EN - PORTC Bit 2
    // D4 - PORTC Bit 4
    // D5 - PORTC Bit 5
    // D6 - PORTC Bit 6
    // D7 - PORTC Bit 7
    // Characters/line: 16
    lcd_init(16);

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

    while (1)
      {
        ldr1=read_adc(0);
        
        ldr2=read_adc(1);
        
        ldr3=read_adc(2);

        
        // Shorten the firing delay
        if((PORTB.0 == 1) && (ldr1 <= 450))
        {
            if(x > 1)
                {  
                    x = x - 1;
                }
        }
        
        // Increase the firing delay
        if((PORTB.0 == 1) && (ldr1 >= 600))
        {
            if(x < 280)
                { 
                    x = x + 1;
                }
        }
           
        // Shorten the firing delay
        if((PORTB.1 == 1) && (ldr2 <= 450))
        {
            if(y > 1)
                {
                    y = y - 1;
                }
        }
        
        // Increase the firing delay
        if((PORTB.1 == 1) && (ldr2 >= 600))
        {
            if(y < 280)
                {
                    y = y + 1;
                }
        }
          
        // Shorten the firing delay
        if((PORTB.2 == 1) && (ldr3 <= 450))
        {
            if(z > 1)
                {
                    z = z - 1;
                }
        }
           
        // Increase the firing delay
        if((PORTB.2 == 1) && (ldr3 >= 600))
        {
            if(z < 280)
                {
                    z = z + 1;
                }
        }
      }
 }

This code is working already but somehow it works for a very short period only (maybe less than one minute and then error until I RESTART/plug the power off).

I've been checked it several times but I don't know what is the mistake here???
I've re-built my hardware also, but the problem still the same.

Please help me...