nRF Connect desktop Error: "failed to get descriptor"

[Taoyi]

Hi,

I am trying to use nRF Connect for desktop with a dongle or nrf52 DK to connect with another board. When I want to get the value from the connected board, it would always display this error: "failed to get descriptor", no matter whether using "notify". I cannot read or write anything

 

Could you please tell me how to solve this problem?

Thank you in advance!

Best,

Taoyi

[Simonr]

Hi

What exact changes have been made from the original ble_app_hrs example? Does this error occur on all of the services, or just the body sensor one? Is seems like the body sensor characteristic has been edited somewhat in your example. Can you show me how it is configured as well?

I also see that your init_len and init_value differs from the characteristic parameters of the HRM configuration, try changing these to the values below to see if that helps.

    add_char_params.init_len          = hrm_encode(p_hrs, INITIAL_VALUE_HRM, encoded_initial_hrm);
    add_char_params.p_init_value      = encoded_initial_hrm;

We also have this BLE characteristics tutorial, so if your goal is to add custom characteristics I suggest taking a look at that.

Best regards,

Simon

[Taoyi]

Thanks for your help. This error only happens when the characteristic uses notification and has cccd. I tried your method and it does not work. 
The example I'm using only remove battery level service, and simplify the heart rate function. Here's the related code, and I cannot find the difference of CCCD related part between official example and this one. 

static void services_init(void)
{
ret_code_t err_code;
ble_hrs_init_t hrs_init;
ble_dis_init_t dis_init;
uint8_t body_sensor_location;
nrf_ble_qwr_init_t qwr_init = {0};

qwr_init.error_handler = nrf_qwr_error_handler;
err_code = nrf_ble_qwr_init(&m_qwr, &qwr_init);
APP_ERROR_CHECK(err_code);


/*------------------------------------*/
body_sensor_location = BLE_HRS_BODY_SENSOR_LOCATION_WRIST;
memset(&hrs_init, 0, sizeof(hrs_init));
hrs_init.evt_handler = NULL;
hrs_init.is_sensor_contact_supported = true;
hrs_init.p_body_sensor_location = &body_sensor_location;

hrs_init.hrm_cccd_wr_sec = SEC_OPEN;
hrs_init.bsl_rd_sec = SEC_OPEN;
err_code = ble_hrs_init(&m_hrs, &hrs_init);
APP_ERROR_CHECK(err_code);
/*--------------------END-------------------*/

/*------------------------------*/
memset(&dis_init, 0, sizeof(dis_init));

ble_srv_ascii_to_utf8(&dis_init.manufact_name_str, (char *)MANUFACTURER_NAME);
dis_init.dis_char_rd_sec = SEC_OPEN;
err_code = ble_dis_init(&dis_init);
APP_ERROR_CHECK(err_code);
/*-------------------END-----------------*/
}

uint32_t ble_hrs_init(ble_hrs_t * p_hrs, const ble_hrs_init_t * p_hrs_init)
{
    uint32_t              err_code;
    ble_uuid_t            ble_uuid;
    ble_add_char_params_t add_char_params;
    uint8_t               initial_hrm[9];
	uint8_t               encoded_initial_hrm[MAX_HRM_LEN];
  
    p_hrs->evt_handler                 = p_hrs_init->evt_handler;
    p_hrs->is_sensor_contact_supported = p_hrs_init->is_sensor_contact_supported;
    p_hrs->conn_handle                 = BLE_CONN_HANDLE_INVALID;
    p_hrs->is_sensor_contact_detected  = false;
    p_hrs->rr_interval_count           = 0;
    p_hrs->max_hrm_len                 = MAX_HRM_LEN;

    BLE_UUID_BLE_ASSIGN(ble_uuid, BLE_UUID_HEART_RATE_SERVICE);
    err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY,
                                        &ble_uuid,
                                        &p_hrs->service_handle);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }

    memset(&add_char_params, 0, sizeof(add_char_params));
    add_char_params.uuid              = BLE_UUID_HEART_RATE_MEASUREMENT_CHAR;
    add_char_params.max_len           = MAX_HRM_LEN;
    add_char_params.init_len          = hrm_encode(p_hrs, INITIAL_VALUE_HRM, encoded_initial_hrm);
    add_char_params.p_init_value      = encoded_initial_hrm;
    add_char_params.is_var_len        = true;
	
    add_char_params.char_props.notify = 1;
    add_char_params.cccd_write_access = p_hrs_init->hrm_cccd_wr_sec;
				
		//char_md.p_char_user_desc = (uint8_t *) user_desc;
   // char_md.char_user_desc_size = strlen(user_desc);
   // char_md.char_user_desc_max_size = strlen(user_desc);
		
		
    //Add char
    err_code = characteristic_add(p_hrs->service_handle, &add_char_params, &(p_hrs->hrm_handles));
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }
		
		
		
    if (p_hrs_init->p_body_sensor_location != NULL)
    {
        memset(&add_char_params, 0, sizeof(add_char_params));
        add_char_params.uuid            = BLE_UUID_BODY_SENSOR_LOCATION_CHAR;
        add_char_params.max_len         = sizeof(uint8_t);
        add_char_params.init_len        = sizeof(uint8_t);
        add_char_params.p_init_value    = p_hrs_init->p_body_sensor_location;
        add_char_params.char_props.read = 1;
        add_char_params.read_access     = p_hrs_init->bsl_rd_sec;
				
        err_code = characteristic_add(p_hrs->service_handle, &add_char_params, &(p_hrs->bsl_handles));
        if (err_code != NRF_SUCCESS)
        {
            return err_code;
        }
    }

    return NRF_SUCCESS;
}