SF_CQ_PRODIDX
csr_write_4(sc, SF_CQ_PRODIDX, 0);
cmpprodidx = SF_IDX_LO(csr_read_4(sc, SF_CQ_PRODIDX));
cmpprodidx = SF_IDX_HI(csr_read_4(sc, SF_CQ_PRODIDX));