VMS Help DECTPU, TPU$SPECIFY_ASYNC_ACTION, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The TPU$SPECIFY_ASYNC_ACTION routine, along with TPU$TRIGGER_
    ASYNC_ACTION, allow applications to interrupt DECTPU after
    calling TPU$CONTROL. The specified DECTPU statement is compiled
    and saved.

    This routine must be called after TPU$INITIALIZE. It will not
    complete successfully if keystroke journaling is enabled.