Pure C Language In Arduino Uno (Sample Code 2)

test.c

/*
    Compiling and uploading to Arduino Uno (Sample Code 2)
    ======================================================

    avr-gcc -Os -mmcu=atmega328p -c test.c
    avr-gcc -mmcu=atmega328p -o test.elf test.o
    avr-objcopy -O ihex -R .eeprom test.elf test.hex
    avrdude -F -V -c arduino -p ATMEGA328P -P /dev/cu.usbmodem1421 -b 115200 -U flash:w:test.hex

*/
#ifndef F_CPU
#define F_CPU 16000000UL //set frequency
#endif

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

#define MS_DELAY 2000 //2 seconds

int main() {
  DDRB |= _BV(DDB1); //set pin 9 to output
  DDRB |= _BV(DDB0); //set pin 8 to output
  
  for(;;) {
    PORTB |= _BV(PORTB1); //set pin 9 to high
    PORTB &= ~_BV(PORTB0); //set pin 8 to low
    _delay_ms(MS_DELAY); //delay

    PORTB &= ~_BV(PORTB1); //set pin 9 to low
    PORTB |= _BV(PORTB0); //set pin 8 to high
    _delay_ms(MS_DELAY); //delay
  }
  
  return 0;
}