Interrupt handlers and servers are defined by the Exec Interrupt
structure.  This structure specifies an interrupt routine entry point and
data pointer.  The C definition of this structure is as follows:

    struct Interrupt
    {
        struct Node is_Node;
        APTR        is_Data;
        VOID      (*is_Code)();
    };

Once this structure has been properly initialized, it can be used for
either a handler or a server.