How to add the descriptions of GATT Primary Service(0x2800) and GATT characteristic?

[zqclzz]

How to add the descriptions of GATT Primary Service(0x2800) and GATT characteristic? Just like the picture below.

[MartinBL]

Hi

You can use sd_ble_gatts_descriptor_add() to add Characteristic User Descriptions to your characteristics.

You can do something like this:

static uint32_t our_descriptor_add(ble_os_t * p_our_service, uint16_t char_handle)
{
    uint32_t   err_code; // Variable to hold return codes from library and softdevice functions
    
    ble_gatts_attr_md_t    attr_md;
    memset(&attr_md, 0, sizeof(attr_md));

    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
    BLE_GAP_CONN_SEC_MODE_SET_NO_ACCESS(&attr_md.write_perm);

    attr_md.vloc    = BLE_GATTS_VLOC_STACK;
    attr_md.rd_auth = 0;
    attr_md.wr_auth = 0;
    attr_md.vlen    = 0;
    
    ble_uuid_t          attr_uuid;
    attr_uuid.uuid      = BLE_UUID_DESCRIPTOR_CHAR_USER_DESC;
    ble_uuid128_t       base_uuid = {0x23, 0xD1, 0x13, 0xEF, 0x5F, 0x78, 0x23, 0x15, 0xDE, 0xEF, 0x12, 0x12, 0x00, 0x00, 0x00, 0x00}; // 128-bit base UUID
    err_code = sd_ble_uuid_vs_add(&base_uuid, &attr_uuid.type);
    APP_ERROR_CHECK(err_code); 
    
    
    uint8_t attr_value[]  = "Your User description";
    const uint16_t attr_len   = sizeof(attr_value);
    
    ble_gatts_attr_t    attr;
    memset(&attr, 0, sizeof(attr));
    
    attr.init_len       = attr_len;
    attr.max_len        = attr_len;
    attr.init_offs      = 0;
    attr.p_value        = attr_value;
    attr.p_attr_md      = &attr_md;
    attr.p_uuid         = &attr_uuid;
    
    err_code = sd_ble_gatts_descriptor_add(char_handle, &attr, &p_our_service->descr_handle);
    APP_ERROR_CHECK(err_code); 
    
    return err_code;
}

Please have a look at e.g. the ble_app_hids_mouse example in e.g. SDK 9.0.0. It shows how to add descriptors like this.

[zqclzz]

Hi, Martin Børs-Lind

I can't find the example how to add descriptors in the ble_app_hids_mouse example . And, what is the ble_os_t and and char_handle in the code you showed above. Can you tell me how to use the "our_descriptor_add()" detailedly?

[MartinBL]

The example is located in "your_sdk_folder\examples\ble_peripheral\ble_app_hids_mouse". The sd_ble_gatts_descriptor_add() function is used in e.g. the rep_char_add() function found in ble_hids.c file.

The code above is copy-pasted from a random example i made. ble_os_t and char_handle are just residues from that example. ble_os_t is a service struct containing data about the service being worked on and char_handle is the handle to the characteristic that you want to add a descriptor to. If you want to use the code above you will have to modify it a bit to fit your particular application.