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===== ath9k bluetooth coexistence =====

This page documents how [[en/users/Documentation/Bluetooth-coexistence|bluetooth coexistence]] is supported by ath9k. 

===== Supported Coexistence Schemes =====

  * [[en/users/Documentation/Bluetooth-coexistence|2-wire]] 
  * [[en/users/Documentation/Bluetooth-coexistence|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. 

<code>modprobe ath9k btcoex_enable=1</code>

===== 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.