AR5K_TIMER0
v = ath5k_hw_reg_read(ah, AR5K_TIMER0);
ath5k_hw_reg_write(ah, 0, AR5K_TIMER0);
ath5k_hw_reg_write(ah, next_beacon, AR5K_TIMER0);
nbtt = ath5k_hw_reg_read(ah, AR5K_TIMER0);