4.5 PIC32CXBZ3/WBZ35 Three-Wire PTA Coexistence Design

PIC32CXBZ3/WBZ35 provides the Three-Wire Packet Traffic Arbitration (PTA) WLAN coexistence solution.

This coexistence solution provides three pins to exchange coordinating information between BT and WLAN. When a BT request (BT_ACTIVE=1) is received, the Wi-Fi device compares this external priority (BT_PRIORITY) request against the internal Wi-Fi priority to grant BT (WLAN_ACTIVE=0) or Wi-Fi (WLAN_ACTIVE=1)

The three pins are defined as:

• BT_ACTIVE: This output pin is to tell that BT is using the RF resources. The signal is high when BT is asking and accessing the RF. The signal is low when BT is not using the RF.
• BT_PRIORITY: This output pin is to tell the BT priority request. The signal is high when there is a high-priority BT request. The signal is low when there is a low priority request.
• WLAN_ACTIVE: This input pin brings in the information about when the WLAN activities are taking place. The signal is high when WLAN is using the RF resources. The signal is low when WLAN is not using the RF.
  1. Coexistence Scenarios using PTA signal

     Scenario 1: Wi-Fi device grants BT device’s Request.

     The BT device wants to use BT RF. It raises a request and waits for WLAN grants to access RF.

     • T1: BT device raises the request by asserting BT_ACTIVE signal and BT_PRIORITY level before accessing BT RF active.
     • T2: Wi-Fi device grant the request by setting WLAN_ACTIVE to low. BT device access BT RF activities execution continuously.

     

     Scenario 2: Wi-Fi device rejects BT device’s request.

     The BT device wants to use BT RF. It raises a request and WLAN rejects the request.

     • T2: Wi-Fi device rejects the grant by asserting WLAN_ACTIVE signal. BT device stops the ongoing BT RF preparation.
     • T3: BT device de-asserts both BT_ACTIVE and BT_PRIORITY signals after stopping the BT RF preparation.

       

     Scenario 3: Wi-Fi device aborts the ongoing BT RF activity by raising WLAN_ACTIVE signal.

     The BT device is using BT RF. Wi-Fi raises a request and waits for BT to grant the RF access.

     • T9: BT device aborts the ongoing BT RF activity after detecting the WLAN_ACTIVE signal is asserted.
     • T8: BT device de-asserts both BT_ACTIVE and BT_PRIORITY signals after detecting the WLAN_ACTIVE signal is asserted.

       

     The following table summarizes the timing values:

     Timing	Minimum (us)	Maximum (us)
     T1	––	100
     T2	75	80
     T3	120	160
     T8	––	100
     T9	––	45

  2. Hardware Information:

     The following dedicate GPIOs are assigned as PTA Pins, once the PTA feature is enabled..

     PTA Pin Function	GPIO Pin
     BT_ACTIVE	PA3
     BT_PRIORITY	PA9
     WLAN_ACTIVE	PA8

     48 pin package IC and WBZ351 provided MCC settings to enable PTA feature.
  3. Software Design Information

  

  Users can enable this feature through the MCC settings provided in BLE stack.
  • PTA APIs in BLE_Stack library

    Two APIs are designed in BLE_Stack library.

    • BT_SYS_PtaInit – It is called within APP_PtaInit() to enable BLE stack PTA feature.
    • BT_SYS_PtaWlanActiveIrqHandler – It is called within APP_PtaWlanActiveIrqHandler() to handle WLAN_ACTIVE signal.
  • MCC Code Generation
    The following MCC configurations apply when BLE MCC component PTA option is enabled.

    • Includes PA3, PA9 and PA8 gpio setup in plib_gpio.c
    • Including app_pta_handler.c and app_pta_handler.h to project.
    • Generate application template code to call APP_PtaInit() in APP_BleStackInitAdvance().
    • The PTA feature will be enabled automatically through the above generated code
  • BT Request Priority Design

    Other Bluetooth activities are of high priority, with exceptions like Bluetooth scanning, packets advertising and RSSI measurements for channel classification.