a.c

/*
 * main.c
 *
 * Created: 4/2/2024 11:15:32 AM
 *  Author: DatNgo
 */ 

#include <xc.h>
#include <avr/io.h>
#include <avr/interrupt.h>

typedef unsigned char byte;

#define cbi(REG8, BITNUM) REG8 &= ~(_BV(BITNUM))
#define sbi(REG8, BITNUM) REG8 |= _BV(BITNUM)

#define ITERATION_BORDERLINE 5 // when iteration counts exceed this value, will reset to one and changes the led_state.

byte iteration_count = ITERATION_BORDERLINE;
byte led_state_1 = 0, led_state_2 = 0;

ISR(TIMER0_OVF_vect) {
	// if iteration count is over borderline, set iteration count to one.
	(iteration_count++ > ITERATION_BORDERLINE && !(iteration_count = 1)) &&
		(   // and then
			// shift led_state_1 to left, led_state_2 to right. if both states are zero, reset to initial state.
			(!(led_state_1 <<= 1 + led_state_2 >>= 1)) && (led_state_1 = 0x01, led_state_2 = 0x80)
			// merge both state to PORTB.
			+ (PORTB = led_state_1 | led_state_2)
		)
}

int main(void)
{
	DDRB = 0xff;
	PORTB = 0x00;

	TCCR0 = 0x07;
	sbi(TIMSK, 0);
	sei(); // SREG |= 0x80;
	TCNT0 = 0x00;

    while(1);
}