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This page documents how bluetooth coexistence is supported by ath9k.
Bluetooth coexistence has to be manually enabled when loading ath9k by setting the btcoex_enable module parameter.
modprobe ath9k btcoex_enable=1
Some Atheros cards in both the AR9002 and AR9003 family use this scheme in which WLAN and Bluetooth time-shares their usage of the 2.4 GHz band. Three pins are used in this scheme.
|BT_ACTIVE||BT||Signals that Bluetooth device is expecting TX or RX activity. Provides WLAN with information about when the antenna is being used by Bluetooth.|
|BT_PRIORITY||BT||At the start of BT_ACTIVE, it is asserted to indicate the priority of the Bluetooth activity. Then, this pin indicates the TX/RX status of the Bluetooth activity.|
|WLAN_ACTIVE||WLAN||Indicates when WLAN has taken the antenna.|
BT weights and WLAN weights are programmed in the hardware by the driver. Hardware infers the Bluetooth activity by sampling the BT_ACTIVE signal. Whenever there’s Bluetooth activity, hardware compares the assigned weight of Bluetooth traffic and the current WLAN traffic. If Bluetooth traffic has a lower priority, hardware will continue WLAN traffic, thus stomping on the Bluetooth side (and possible interference on WLAN side as well). If Bluetooth traffic has a higher priority, hardware will abort WLAN traffic and treat it as if there’s collision on-air.