GMACOMR
mac_write(sc, GMACOMR, 0);
csr = mac_read(sc, GMACOMR);
mac_write(sc, GMACOMR, csr &~ (OMR_SR | OMR_ST));
csr = mac_read(sc, GMACOMR);
mac_write(sc, GMACOMR, csr | OMR_SR | OMR_ST);