ath9k bluetooth coexistence#

This page documents how bluetooth coexistence is supported by ath9k.

Supported Coexistence Schemes#

2-wire
3-wire
MCI (Message-Based Coexistence Interface)

Enabling bluetooth coexistence#

Bluetooth coexistence has to be manually enabled when loading ath9k by setting the btcoex_enable module parameter.

modprobe ath9k btcoex_enable=1

Cards supporting BTCOEX#

2-wire (two-chip cards with separate WLAN and BT)#

* WB197 ( AR9287 + AR3011 )

3-wire (two-chip cards with separate WLAN and BT)#

* WB195 ( AR9285 + AR3011 )
* WB225 ( AR9485 + AR3012 )

MCI (SoC-type cards with integrated WLAN and BT)#

* WB222 ( based on AR9462 )
* WB335 ( based on AR9565 )

3-wire scheme details#

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.

PIN	Driven by	Details
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.

PTA (Packet Traffic Arbitration ) Algorithm#

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.