FXP_NEXTTX
sc->sc_txdirty = FXP_NEXTTX(lasttx);
sc->sc_txlast = FXP_NEXTTX(sc->sc_txlast);
i = FXP_NEXTTX(i), sc->sc_txpending--) {
htole32(FXP_CDTXADDR(sc, FXP_NEXTTX(i)));
mcsp->link_addr = htole32(FXP_CDTXADDR(sc, FXP_NEXTTX(sc->sc_txlast)));
nexttx = FXP_NEXTTX(sc->sc_txlast);