#include <avr/io.h>
#include <util/delay.h>

/*

Blinks two LEDs; one on B1 and one on B0.

Assumes negative PINs of LEDs are connected to the AVR micro-controller.
Positive pins are connected through resistors to VCC.
 
As a result, all logic is inverted from previous versions.

A 1K resistor works well for most LEDs.
Decrease if too dim.

*/

#define LED_ON(port, nr) port &= ~(1 << (nr))
#define LED_OFF(port, nr) port |= (1 << (nr))

int main(void) {
    DDRB = 255U; // Make all PB* -- PORT B -- pins output
    PORTB = 0xFF; // turn all PB* -- PORT B -- pins off.
    
    while (1) {
        LED_ON(PORTB, PB0);
        _delay_ms(200);
        LED_ON(PORTB, PB1);
        _delay_ms(100);
        LED_OFF(PORTB, PB0);
        _delay_ms(200);
        LED_OFF(PORTB, PB1);
        _delay_ms(2500); // 2.5 seconds off
    }
}