MEC_NEXTTX
bus_space_write_8(st, sh, MEC_TX_RING_PTR, MEC_NEXTTX(nexttx));
i = MEC_NEXTTX(i), sc->sc_txpending--) {
firsttx = MEC_NEXTTX(sc->sc_txlast);
nexttx = MEC_NEXTTX(sc->sc_txlast);