LED1秒間隔で点灯/消灯しつつシリアルエコー

char led_pin = 13;
boolean led_stat = true;

void setup(){
  Serial.begin(9600);
  pinMode(led_pin, true);
}

void loop(){
  delay(1000);
  digitalWrite(led_pin, led_stat = !led_stat);
  Serial.print("led: ");
  if(led_stat) Serial.println("on");
  else Serial.println("off");
  if(Serial.available()){
    Serial.print("echo: ");
    while(Serial.available()) Serial.write(Serial.read());
    Serial.println("");
  }
}