 /// The states of a traffic light
 typedef enum : unsigned
 {
-  DISABLE,    // off
   STOP,       // red
   STOP_GO,    // red and yellow
   GO,         // green

void input()
{
  // S1 pressed = allow the FSM to continue
  if (shield.buttonS1Pressed())
    tick = true;

  // S2 pressed = "asynchronously" reset the FSM
  if (shield.buttonS2Pressed())
    state = DISABLE;
}

/** 

void output()
{
  static unsigned ledBitmask = 0;
  switch (state)
  {
    case STOP:
      ledBitmask = RED;
      break;
