SC_CB
status = SC_CB(sc, sc->sc_next_cb - 1)->cb_status;
status = SC_CB(sc, n)->cb_status;
cmd = SC_CB(sc, n)->cb_cmd;
status = SC_CB(sc, n)->cb_status;
struct iee_cb *cb = SC_CB(sc, sc->sc_next_cb);
cb = SC_CB(sc, sc->sc_next_cb + 1);