NAME
        AddKBInt -- adds a routine to the keyboard interrupt. (V40)

   SYNOPSIS
        intHandle = AddKBInt(intRoutine, intData);
        D0                   A0          A1

        aptr addkbint(aptr, aptr);

   FUNCTION
        This routine extends the functionality of the keyboard interrupt to
        include intRoutine. Since this is an extention of the normal
        keyboard interrupt all of the keyboard handshaking is handled. The
        keyboard error codes are filtered out and not passed to intRoutine.

        The routine is called whenever the user enters a key on the
        keyboard.

        The routine is called from within an interrupt, so normal
        restrictions apply. The routine must preserve the following
        registers: A2, A3, A4, A7, D2-D7. Other registers are
        scratch, except for D0, which MUST BE SET TO 0 upon
        exit. On entry to the routine, A1 holds 'intData' and A5
        holds 'intRoutine', and D0 contains the rawkey code read
        from the keyboard.

        The routine is not called when a reset is received from the
        keyboard.

        This is a low level function that does not fit the normal Amiga
        multitasking model. The interrupt installed will have no knowledge
        of which window/screen currently has input focus.

        If your program is to exit without reboot, you MUST call remkbint()
        before exiting.

        Only one interrupt routine may be added to the system.  ALWAYS
        check the return value in case some other task has previously
        used this function.

   INPUTS
        intRoutine - the routine to invoke every vblank. This routine should
                     be as short as possible to minimize its effect on overall
                     system performance.
        intData - data passed to the routine in register A1. If more than one
                  long word of data is required this should be a pointer to
                  a structure that contains the required data.

   RESULT
        intHandle - a handle used to manipulate the interrupt, or NULL
                    if it was not possible to attach the routine.

   SEE ALSO
        remkbint()