Description

   The TPU$TRIGGER_ASYNC_ACTION routine, along with TPU$SPECIFY_
   ASYNC_ACTION routine allow applications to interrupt TPU after
   calling TPU$CONTROL. The command that was specified for this
   facility_index is put on the TPU queue of work items and is
   handled as soon as no other work items are present. This allows
   TPU to complete and stabilize its environment before executing
   the command. This routine must be called after control has been
   passed to TPU via the TPU$CONTROL routine.