NAME
        SuperState -- enter supervisor state with user stack

   SYNOPSIS
        oldSysStack = SuperState()
        D0

        aptr superstate(void);

   FUNCTION
        Enter supervisor mode while running on the user's stack. The user
        still has access to user stack variables.  Be careful though, the
        user stack must be large enough to accommodate space for all
        interrupt data -- this includes all possible nesting of interrupts.
        This function does nothing when called from supervisor state.

   RESULTS
        oldSysStack - system stack pointer; save this.  It will come in
                      handy when you return to user state.  If the system
                      is already in supervisor mode, oldSysStack is zero.

   SEE ALSO
        userstate(), supervisor()