NAME
        SetIntVector -- set a new handler for a system interrupt vector

   SYNOPSIS
        oldInterrupt = SetIntVector(intNumber, interrupt)
        D0                          D0         A1

        struct interrupt *setintvector(ulong, struct interrupt *);

   FUNCTION
        This function provides a mechanism for setting the system interrupt
        vectors.  These are non-sharable; setting a new interrupt handler
        disconnects the old one.  Installed handlers are responsible for
        processing, enabling and clearing the interrupt.  Note that interrupts
        may have been left in any state by the previous code.

        The IS_CODE and IS_DATA pointers of the interrupt structure will
        be copied into a private place by Exec.  A pointer to the previously
        installed interrupt structure is returned.

        When the system calls the specified interrupt code, the registers are
        setup as follows:

            D0 - scratch
            D1 - scratch (on entry: active
                          interrupts -> equals INTENA & INTREQ)

            A0 - scratch (on entry: pointer to base of custom chips
                          for fast indexing)
            A1 - scratch (on entry: Interrupt's IS_DATA pointer)

            A5 - jump vector register (scratch on call)
            A6 - Exec library base pointer (scratch on call)

            all other registers must be preserved

   INPUTS
        intNum - the Paula interrupt bit number (0..14).  Only non-chained
                 interrupts should be set.  Use addintserver() for server
                 chains.
        interrupt - a pointer to an interrupt structure containing the
                 handler's entry point and data segment pointer.  A NULL
                 interrupt pointer will remove the current interrupt and
                 set illegal values for IS_CODE and IS_DATA.

                 By convention, the LN_NAME of the interrupt structure must
                 point a descriptive string so that other users may
                 identify who currently has control of the interrupt.

   RESULT
        A pointer to the prior interrupt structure which had control
        of this interrupt.

   SEE ALSO
        addintserver(),exec/interrupts.i,hardware/intbits.i