REG_DNLISTPTR
paddr = GET32(REG_DNLISTPTR);
PUT32(REG_DNLISTPTR, paddr);
paddr = GET32(REG_DNLISTPTR);
if ((r->r_avail < r->r_count) && (GET32(REG_DNLISTPTR) != 0)) {
PUT32(REG_DNLISTPTR, sc->ex_txring.r_head->ed_descaddr);