void setup() {
  // put your setup code here, to run once:
  volatile char *dirf = 0x30;
  volatile char *outf = 0x31;
  volatile long i;
  *dirf = 0x01;
  while(1){
    *outf = 0x01;
    for(i=0;i<100;i++);// by controlling the delay time the led brightness controlled
    *outf = 0x00;
    for(i=0;i<300;i++);// by controlling the delay time the led brightness controlled
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}