teensy-core-4.1/teensy4/Blink.cc

// Only for testing with the Makefile - not actually part of the core library

#include <Arduino.h>

int led = 13;

void setup() {
  pinMode(led, OUTPUT);
}

void loop() {
  digitalWrite(led, HIGH);
  delay(1000);
  digitalWrite(led, LOW);
  delay(1000);
}