CAS_MAC_EXCESS_COLL_CNT
bus_space_write_4(t, h, CAS_MAC_EXCESS_COLL_CNT, 0);
v = bus_space_read_4(t, mac, CAS_MAC_EXCESS_COLL_CNT) +
bus_space_write_4(t, mac, CAS_MAC_EXCESS_COLL_CNT, 0);