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 */