TxDesc
i = roundup2(sizeof(union TxDesc)*RE_TX_BUF_NUM, RE_DESC_ALIGN);
union TxDesc *txptr;
memset(&txptr[i], 0, sizeof(union TxDesc));
union TxDesc *txptr = arg;
union TxDesc *txptr;
union TxDesc *txptr;
union TxDesc *tx_desc; /* 8 bits alignment */