AR_NEXT_TBTT
OS_REG_WRITE(ah, AR_NEXT_TBTT, 0); /* no beacons */
OS_REG_WRITE(ah, AR_NEXT_TBTT, TU_TO_USEC(bs->bs_nexttbtt));
return OS_REG_READ(ah, AR_NEXT_TBTT);
OS_REG_WRITE(ah, AR_NEXT_TBTT, TU_TO_USEC(bt->bt_nexttbtt));