tulip_tx_desc
struct tulip_tx_desc *tx_ring;
sizeof(struct tulip_tx_desc) * TX_RING_SIZE,
tp->tx_ring = (struct tulip_tx_desc *)(tp->rx_ring + RX_RING_SIZE);
tp->tx_ring[i].buffer2 = cpu_to_le32(tp->tx_ring_dma + sizeof(struct tulip_tx_desc) * (i + 1));