   cycle += 1;
 
   // Wait for falling edge on clock pin
+#if defined(SQUARE_WAVE_CLOCK)
   while (clkPin.is_set()) yield();
+#endif
   ledPin.clear();
 }

#include "Cosa/Trace.hh"
#include "Cosa/IOStream/Driver/UART.hh"

// Set the real-time clock
// #define SET_TIME

// The real-time device, latest start and sample time in ram
DS1307 rtc;

OutputPin ledPin(Board::LED);

// Clock pin
#if defined(SQUARE_WAVE_CLOCK)
#if defined(ARDUINO_PRO_MICRO)
InputPin clkPin(Board::D0);
#else
InputPin clkPin(Board::D2);
#endif
#else
Watchdog::Clock clock;
#endif

void setup()
