GATT Over BR/EDR User Guide

GATT Over BR/EDR allows the GATT protocol, originally part of BLE, to be transmitted and used over classic Bluetooth (BR/EDR), thereby enhancing data rate and device compatibility. This document uses the AirSync service as an example to introduce how to implement GATT over BR/EDR based on the SDK.

Note

  • Directly enable the global macro F_APP_AIRSYNC_SERVICE_SUPPORT, as the following configurations are already included in the SDK.

  1. Configure the ADV_TYPE_FLAGS for BLE advertising without GAP_ADTYPE_FLAGS_BREDR_NOT_SUPPORTED.

    static  uint8_t adv_data[31] =
{
   0x02,
   GAP_ADTYPE_FLAGS,
   GAP_ADTYPE_FLAGS_GENERAL,

   ...
}

  2. The source file and header file for the AirSync service are airsync_ble_service.c and airsync_ble_service.h, respectively. Unlike a regular BLE service, the Attribute flags in the service table need to be configured with ATTRIB_FLAG_BREDR.

    const T_ATTRIB_APPL airsync_ble_service_tbl[] =
{
   /* <<Primary Service>>, 0.. */
   {
      (ATTRIB_FLAG_VALUE_INCL | ATTRIB_FLAG_LE | ATTRIB_FLAG_BREDR),  /* wFlags     */
      {   /* bTypeValue */
            LO_WORD(GATT_UUID_PRIMARY_SERVICE),
            HI_WORD(GATT_UUID_PRIMARY_SERVICE),
            LO_WORD(GATT_UUID_AIRSYNC_SERVICE),      /* service UUID */
            HI_WORD(GATT_UUID_AIRSYNC_SERVICE)
      },
      UUID_16BIT_SIZE,                            /* bValueLen     */
      NULL,                                       /* pValueContext */
      GATT_PERM_READ                              /* wPermissions  */
   },
   ...
};

  3. Add the service in app_ble_service.c and call bt_att_init() to initialize ATT and register the callback.

    #include "bt_att.h"
#include "airsync_ble_service.h"

// add service id
T_SERVER_ID  air_ser_id;

//callback function
void att_callback(uint8_t bd_addr[6], T_BT_ATT_MSG_TYPE msg_type, void *p_msg)
{
   APP_PRINT_INFO1("att_callback msg_type = 0x%x", msg_type);
}

void app_ble_service_init(void)
{
   //init bt att
   bt_att_init(att_callback);

   //add service
   air_ser_id = airsync_add_service((void *)app_profile_callback);
}

  4. Add the SDP table for the AirSync service in app_sdp.c.

    static const uint8_t att_sdp_record[] =
{
   SDP_DATA_ELEM_SEQ_HDR,
   0x2b,
   //attribute SDP_ATTR_SRV_CLASS_ID_LIST
   SDP_UNSIGNED_TWO_BYTE,
   (uint8_t)(SDP_ATTR_SRV_CLASS_ID_LIST >> 8),
   (uint8_t)SDP_ATTR_SRV_CLASS_ID_LIST,
   SDP_DATA_ELEM_SEQ_HDR,
   0x03,
   SDP_UUID16_HDR,
   //According to UUID
   (uint8_t)(0xFEE7 >> 8),
   (uint8_t)(0xFEE7),
   //attribute SDP_ATTR_PROTO_DESC_LIST
   SDP_UNSIGNED_TWO_BYTE,
   (uint8_t)(SDP_ATTR_PROTO_DESC_LIST >> 8),
   (uint8_t)SDP_ATTR_PROTO_DESC_LIST,
   SDP_DATA_ELEM_SEQ_HDR,
   0x13,
   SDP_DATA_ELEM_SEQ_HDR,
   0x06,
   SDP_UUID16_HDR,
   (uint8_t)(UUID_L2CAP >> 8),
   (uint8_t)(UUID_L2CAP),
   SDP_UNSIGNED_TWO_BYTE,
   (uint8_t)(PSM_ATT >> 8),
   (uint8_t)(PSM_ATT),
   SDP_DATA_ELEM_SEQ_HDR,
   0x09,
   SDP_UUID16_HDR,
   (uint8_t)(UUID_ATT >> 8),
   (uint8_t)(UUID_ATT),
   SDP_UNSIGNED_TWO_BYTE,
   //According to service start handle
   0x00,
   0x10,
   SDP_UNSIGNED_TWO_BYTE,
   //According to service end handle
   0x00,
   0x18,
   //attribute SDP_ATTR_BROWSE_GROUP_LIST
   SDP_UNSIGNED_TWO_BYTE,
   (uint8_t)(SDP_ATTR_BROWSE_GROUP_LIST >> 8),
   (uint8_t)SDP_ATTR_BROWSE_GROUP_LIST,
   SDP_DATA_ELEM_SEQ_HDR,
   0x03,
   SDP_UUID16_HDR,
   (uint8_t)(UUID_PUBLIC_BROWSE_GROUP >> 8),
   (uint8_t)(UUID_PUBLIC_BROWSE_GROUP),
};

void app_sdp_init(void)
{

   ......
   bt_sdp_record_add((void *)att_sdp_record);

}

    • For the above SDP table, you need to fill in the start handle and end handle, introducing two methods to obtain the handle:

      • Use the function server_get_start_handle(service id) to get the start handle, and calculate the end handle based on the registered service table.

      • Open the .cfa file in Ellisys Bluetooth Analyzer.exe, select ATT Read Type Transaction, and read the values in sequence 3 in the figure to fill in the initial handle position of the SDP table. If the registered service changes, it needs to be refilled.

        ../../../_images/Gatt_over_bredr_Starting_Handle.png

        Start Handle

        ../../../_images/Gatt_over_bredr_Ending_Handle.png

        End Handle

  5. Call server_ext_send_data() to send Notification/Indication.

    uint16_t conn_handle;
uint16_t cid;
uint8_t cid_num;
for (uint8_t i = 0; i < MAX_BR_LINK_NUM; i++)
{
   if (app_db.br_link[i].used == true)
   {
         gap_chann_get_handle(app_db.br_link[i].bd_addr, 0x10/*BTIF_REMOTE_ADDR_CLASSIC*/, &conn_handle);
         gap_chann_get_cid(conn_handle, 1, &cid, &cid_num);

         server_ext_send_data(conn_handle,
                              cid,
                              airsync_ser_id,
                              2,
                              p_data,
                              data_len,
                              GATT_PDU_TYPE_ANY);
         break;
   }
}
//le notification
server_send_data(conn_id,
                  airsync_ser_id,
                  2,
                  p_data,
                  data_len,
                  GATT_PDU_TYPE_NOTIFICATION);

Note

  • If there is a situation where ATT cannot connect properly, try using HFP to connect and then actively initiate an ATT connection after a delay of approximately 5 seconds by calling bt_att_connect_req().

  • The above AirSync service, transmitted via GATT over BR/EDR, is suitable for Android WeChat Sports, while iOS WeChat Sports can still use BLE.