/***********************************************************
 * 
 * Blink a LED using register approach.
 * (c) 2018-2024 Tomas Fryza, MIT license
 *
 * Developed using PlatformIO and AVR 8-bit Toolchain 3.6.2.
 * Tested on Arduino Uno board and ATmega328P, 16 MHz.
 * 
 ***********************************************************/

/* Defines ------------------------------------------------*/
#define LED_GREEN PB5   // AVR pin where green LED is connected
#define SHORT_DELAY 250 // Delay in milliseconds
#ifndef F_CPU
# define F_CPU 16000000 // CPU frequency in Hz required for delay
#endif

/* Includes -----------------------------------------------*/
#include <avr/io.h>     // AVR device-specific IO definitions
#include <util/delay.h> // Functions for busy-wait delay loops


/* Function definitions -----------------------------------*/
/***********************************************************
 * Function: Main function where the program execution begins
 * Purpose:  Toggle one LED and use delay library.
 * Returns:  none
 ***********************************************************/
int main(void)
{
    // Set pin as output in Data Direction Register
    DDRB = DDRB | (1 << LED_GREEN);
    // Set pin LOW in Data Register (LED off)
    PORTB = PORTB & ~(1 << LED_GREEN);

    // Infinite loop
    while (1)
    {
        // Pause several milliseconds
        _delay_ms(SHORT_DELAY);
        // Invert LED in Data Register
        PORTB = PORTB ^ (1 << LED_GREEN);
    }

    // Will never reach this
    return 0;
}