The comment is misleading - that register setting seems to kick off the

initial chip NF cal.

sys/dev/ath/ath_hal/ar5416/ar5416_cal.c

@@ -221,6 +221,7 @@ ar5416InitCal(struct ath_hal *ah, const struct ieee80211_channel *chan)
 	 * higher than normal value if DC offset and noise floor cal are
 	 * triggered at the same time.
 	 */
+	/* XXX this actually kicks off a NF calibration -adrian */
 	OS_REG_SET_BIT(ah, AR_PHY_AGC_CONTROL, AR_PHY_AGC_CONTROL_NF);
 	/*
 	 * Try to make sure the above NF cal completes, just so