e1000_adv_tx_desc
tsize = roundup2(txr->num_tx_desc * sizeof(union e1000_adv_tx_desc),
sizeof(union e1000_adv_tx_desc) * txr->num_tx_desc);
union e1000_adv_tx_desc *txd = NULL;
txd = (union e1000_adv_tx_desc *)&txr->tx_base[i];