NAME
        ObtainQuickVector -- obtain and install a Quick interrupt vector (v39)

   SYNOPSIS
        vector=ObtainQuickVector(interruptCode)
        d0                       a0

        ULONG ObtainQuickVector(APTR);

   FUNCTION
        This function will install the code pointer into the quick interrupt
        vector it allocates and returns to you the interrupt vector that
        your Quick interrupt system needs to use.

        This function may also return 0 if no vectors are available.  Your
        hardware should be able to then fall back to using the shared
        interrupt server chain should this happen.

        The interrupt code is a direct connect to the physical interrupt.
        This means that it is the responsibility of your code to do all
        of the context saving/restoring required by interrupt code.

        Also, due to the performance of the interrupt controller, you may
        need to also watch for "false" interrupts.  These are interrupts
        that come in just after a DISABLE.  The reason this happens is
        because the interrupt may have been posted before the DISABLE
        hardware access is completed.  For example:

        myInt:          move.l  d0,-(sp)        ; Save d0...
                        move.w  _intenar,d0     ; Get interrupt enable state
                        btst.l  #INTB_INTEN,d0  ; Check if pending disable
                        bne.s   realInt         ; If not, do real one...
        exitInt:        move.l  (sp)+,d0        ; Restore d0
                        rte                     ; Return from int...
        ;
        realInt:        ; Now do your int code...  d0 is already saved
                        ; ALL other registers need to be saved if needed
                        ; This includes a0/a1/d0/d1 as this is an interrupt
                        ; and not a function call...
                        ;
                        bra.s   exitInt         ; exit interrupt...

        If your interrupt will not play with system (OS) structures and your
        own structures are safe to play with you do not need to check for
        the disable.  It is only needed for when the system is in disable but
        that "one last interrupt" still got through.

   NOTE
        This function was not implemented fully until V39.  Due to a mis-cue
        it is not safe to call in V37 EXEC.  (Sorry)

   INPUTS
        A pointer to your interrupt code.  This code is not an EXEC interrupt
        but is dirrectly connected to the hardware interrupt.  Thus, the
        interrupt code must not modify any registers and must return via
        an RTE.

   RESULTS
        The 8-bit vector number used for Zorro-III Quick Interrupts
        If it returns 0, no quick interrupt was allocatable.  The device
        should at this point switch to using the shared interrupt server
        method.

   SEE ALSO