I remember learning in my embedded programming class about state machines and how certain states cannot be reached.<p>In the lab, I accounted for every possible valid state with a transition out to another state.<p>I left my microcontroller running when I went to get lunch, came back and it was frozen. I did a dump, and discovered it was idling in a state that has no entry into it, and because I had no exit, it would just sit there.<p>I &#x27;fixed&#x27; the problem by adding a transition to reset the controller from every state that shouldn&#x27;t be reached.