SAB_PVR_DTR_A
SAB_WRITE(sc, SAB_PCR, ~(SAB_PVR_DTR_A | SAB_PVR_DTR_B));
SAB_WRITE(sc, SAB_PVR, SAB_PVR_DTR_A | SAB_PVR_DTR_B | SAB_PVR_MAGIC);
sc->sc_pvr_dtr = SAB_PVR_DTR_A;