ENETC_TBPIR
ENETC_TXQ_WR4(sc, qid, ENETC_TBPIR, pidx);
ENETC_TXQ_WR4(sc, i, ENETC_TBPIR, 0);
pidx = ENETC_TXQ_RD4(sc, qid, ENETC_TBPIR);