#include <avr/io.h>
//this library has the AVR's functions

#include <util/delay.h> 
//This library has some utilities, only the delay utility is used here

#define output(directions,pin) (directions |= pin)
 // set port direction for output

#define set(port,pin) (port |= pin) 
// set port pin (setting its value to 1)


#define PWM_delay() _delay_us(25) // PWM delay=25 MicroSeconds

#define led_port PORTA  //the led is connected to a pin from the pins of port A
#define led_direction DDRA 
#define led (1 << PA7) // PA7 is connected to the led


int main(void) {
   //
   // main
   //
   unsigned char count, pwm;
   //Making two variables will be used in the main loop
 
   // set clock divider to /1
   //

   CLKPR = (1 << CLKPCE);
//
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   // initialize LED pins
   //
   set(led_port, led);
   output(led_direction, led);

   //
   // main loop
   //
   while (1) {
      //
      // off -> red
      //
      for (count = 0; count < 255; ++count) {
         clear(led_port,led);
         for (pwm = count; pwm < 255; ++pwm)
            PWM_delay();
         set(led_port,led);
         for (pwm = 0; pwm < count; ++pwm)
            PWM_delay();
         }
         for (count = 255; count > 0; --count) {
         clear(led_port,led);
         for (pwm = count; pwm < 255; ++pwm)
            PWM_delay();
         set(led_port,led);
         for (pwm = 0; pwm < count; ++pwm)
            PWM_delay();
         }
   }
}