Application Profiles

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After setting up the Bluetooth Controller, the next step is to enable the discovery of the Bluetooth server and facilitate read and write operations. To achieve this, we first need to create Application Profiles, which act as the interface through which clients can interact with the server.\

Implementation

Each profile is defined as a struct where the members depend on the services and characteristics that are implemented . The members also include a GATT Interface , Application ID , and a callback function to handle profile events . In this specific example , each profile is composed by ..

struct gatts_profile_inst {
    esp_gatts_cb_t gatts_cb         ; // Callback Function 
    uint16_t gatts_if               ; // GATTS Interface
    uint16_t app_id                 ; // Application ID 
    uint16_t conn_id                ; // Connection ID 
    uint16_t service_handle         ; // Service Handle
    esp_gatt_srvc_id_t service_id   ; // Service ID
    uint16_t char_handle            ; // Characteristic Handle
    esp_bt_uuid_t char_uuid         ; // Characteristic UUID
    esp_gatt_perm_t perm            ; // Attribute Permission 
    esp_gatt_char_prop_t property   ; // Characteristic Property
    uint16_t descr_handle           ; // Client Characteristic Configuration Descriptor
    esp_bt_uuid_t descr_uuid        ; // Client Characteristic Configuraiton UUID
};

This profile has was designed to have one service and one characteristic , and that the characteristic has one descriptor . Note that the characteristic supports notification or indications, it must implement a client characteristic configuration descriptor ( This ties into the fact that Bluetooth Devices can act as both clients and server ) . which is an additional attribute that describes if the notifications or indications are enabled and defines how the characteristic may be configured by a specific client. This descriptor also has a handle and an UUID.

Storage of Application Profiles

The Application Profiles are stored in an array and corresponding callback functions gatts_profile_a_event_handler() and gatts_profile_b_event_handler() are assigned. Different applications on the GATT client use different interfaces, represented by the gatts_if parameter. For initialization, this parameter is set to ESP_GATT_IF_NONE, which means that the Application Profile is not linked to any client yet.

//User Defined parameters for Statically Allocated Array

#define PROFILE_NUM 2
#define PROFILE_A_APP_ID 0
#define PROFILE_B_APP_ID 1


//Storage using Statically Allocated Array
//
/* One gatt-based profile one app_id and one gatts_if, this array will store the gatts_if returned by ESP_GATTS_REG_EVT */ 
static struct gatts_profile_inst gl_profile_tab[PROFILE_NUM] = {
    [PROFILE_A_APP_ID] = {
        .gatts_cb = gatts_profile_a_event_handler,
        .gatts_if = ESP_GATT_IF_NONE,       /* Not get the gatt_if, so initial is ESP_GATT_IF_NONE */
    },
    [PROFILE_B_APP_ID] = {
        .gatts_cb = gatts_profile_b_event_handler,                   /* This demo does not implement, similar as profile A */
        .gatts_if = ESP_GATT_IF_NONE,       /* Not get the gatt_if, so initial is ESP_GATT_IF_NONE */
    },
};