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

 facility_index

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    The facility_index argument represents the asynchronous action to
    be taken. This is the same index passed to the TPU$SPECIFY_ASYNC_
    ACTION routine registering what DECTPU statements to execute.