Each opendevice() must eventually be matched by a call to closedevice().

All I/O requests must be complete before closedevice().  if any requests
are still pending, abort them with abortio().

   if (!(CheckIO(TimerIO)))
       {
       AbortIO(TimerIO);    /* Ask device to abort any pending requests */
       }
   WaitIO(TimerIO);         /* Clean up */
   CloseDevice((struct IORequest *)TimerIO);  /* Close Timer device */