SP_UPPER_BASE_COUNT
ad_write(&sc->sc_ad1848, SP_UPPER_BASE_COUNT, 0xff);
ad_write(sc, SP_UPPER_BASE_COUNT, blksize >> 8);
ad_write(sc, SP_UPPER_BASE_COUNT, blksize >> 8);
ad_write(&sc->sc_ad1848, SP_UPPER_BASE_COUNT, 0xff);