First commit - blinking LED.

src/main.cpp

@@ -0,0 +1,24 @@
+#include <Arduino.h>
+
+#ifndef LED_BUILTIN
+# warning Development kit has no built-in LED. Using GPIO4 as default.
+# define LED_BUILTIN 4
+#endif
+
+static uint32_t timeBase = 0;
+
+void setup(void)
+{
+
+    Serial.begin(115200); // prepare serial debug port
+    pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void loop(void)
+{
+
+    if (millis() - timeBase > 500) {
+        timeBase = millis();
+        digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
+    }
+}