FL_HW_IDX
ndesc = FL_HW_IDX(fl->pending);
if (FL_HW_IDX(fl->pidx) == FL_HW_IDX(fl->cidx))
desc_last = FL_HW_IDX(fl->pidx);
desc_start = FL_HW_IDX(fl->pidx + fl->cap - fl->pending);
desc_start = FL_HW_IDX(fl->pidx - fl->pending);