code has been entered, no more keys must be pressed for 0.5 seconds</span>
<span class="comment"> * before the lock is opened.</span>
<span class="comment"> *</span>
<span class="comment"> * This is an example that shows two things:</span>
<span class="comment"> * - how to implement a code lock key input mechanism, and</span>
<span class="comment"> * - how to implement a sequential timed routine.</span>
<span class="comment"> *</span>
<span class="comment"> * The program consists of two protothreads,