ACX_TX_RING_SIZE
error = bus_dmamap_create(sc->sc_dmat, ACX_TX_RING_SIZE, 1,
ACX_TX_RING_SIZE, 0, BUS_DMA_NOWAIT, &rd->tx_ring_dmamap);
error = bus_dmamem_alloc(sc->sc_dmat, ACX_TX_RING_SIZE, PAGE_SIZE,
ACX_TX_RING_SIZE, (caddr_t *)&rd->tx_ring, BUS_DMA_NOWAIT);
rd->tx_ring, ACX_TX_RING_SIZE, NULL, BUS_DMA_WAITOK);
bzero(rd->tx_ring, ACX_TX_RING_SIZE);