Add RTC module example

examples/01_Basic/RTC/RTC.ino

@@ -0,0 +1,35 @@
+// Uses the built in Real Time Clock (RTC) to generate periodic interrupts
+// The RTC can generate periodic interrupts with periods of: 1s, 0.5s, 0.25s, 0.125s .... 30.51µs.
+// The interrupts are syncronized to the RTC. I.e., the 1s interrupt fires exactly at the 1s clock transition
+// If other periods are requested, the library uses the the next longer period. I.e. if
+// you do a setPeriod(0.4s) you get a period of 0.5s.
+//
+// Requires a T4.x board
+
+#include "Arduino.h"
+#include "TeensyTimerTool.h"
+
+using namespace TeensyTimerTool;
+
+PeriodicTimer myRTCtimer(RTC);
+
+void setup()
+{
+    pinMode(LED_BUILTIN, OUTPUT);
+    while (!Serial) {}
+
+    myRTCtimer.begin([] { digitalToggleFast(LED_BUILTIN); }, 25ms);  // blink with 20Hz for 1.5s
+    delay(1500);
+
+    myRTCtimer.stop(); // stop for 2s
+    delay(2000);
+
+    myRTCtimer.setPeriod(0.5s); // blink with 1Hz for 5s
+    delay(5000);
+
+    myRTCtimer.setPeriod(50ms); // blink with 10Hz
+}
+
+void loop()
+{
+}