VFB_INTR
st = vfb_read1(sc, VFB_INTR);
vfb_write1(sc, VFB_INTR, st); /* W1C ack */
vfb_write1(sc, VFB_INTR, VFB_INTR_VERT);
vfb_write1(sc, VFB_INTR, 0xff);
vfb_write1(sc, VFB_INTR, 0xff);