ble_app_uart Tx Characteristics - Read property

Question

Hi, I am using nRF52832 module as connectivity chip (GAP peripheral, GATT server) with ble_app_uart_pca10040_s112 as source. 
 I am using nRF connect app to test data communication. 
 
 The data sent from App is received in my Application chip, I have no issues w.r.t to NUS Rx GATT characteristics (0002). 
 With NUS Tx GATT characteristics (0003) , I would like to use Read property instead of Notify property. After enabling Read in ble_nus_init(), I am not seeing any response in Read value in the nRF connect App. However, with Notify property, I'm getting the desired response. 
 
 I have found similar discussion here . My question is, is it mandatory to use Notify property in order to get received data? 
 If not, how can I get data using only the Read property(as my application demands this way), disabling the Notify property? 
 
 Please help. Thank you in advance.

Yadhu KP · Accepted Answer

Hi, 
 PKANNAN said: Thank you so much for your response. I am able to remove "0x0A" with the hint you have provided. 
 However, I'm still facing issue with read property, even after manual read there is no data seen in Read value. 
 I think I got your problem, correct me if i am wrong. 
 It seems that on the example " ble_app_uart_pca10040_s112" you only changed "add_char_params.char_props.read = 1" in the "ble_nus_init" function, right? 
 if this is the case please understand that the example "ble_app_uart_pca10040_s112" was written to update characterestic value using Notify property, so you need to change this to suit your method. 
 step 1 
 uint32_t ble_nus_init(ble_nus_t * p_nus, ble_nus_init_t const * p_nus_init)
{
 ret_code_t err_code;
 ble_uuid_t ble_uuid;
 ble_uuid128_t nus_base_uuid = NUS_BASE_UUID;
 ble_add_char_params_t add_char_params;

 VERIFY_PARAM_NOT_NULL(p_nus);
 VERIFY_PARAM_NOT_NULL(p_nus_init);

 // Initialize the service structure.
 p_nus->data_handler = p_nus_init->data_handler;

 /**@snippet [Adding proprietary Service to the SoftDevice] */
 // Add a custom base UUID.
 err_code = sd_ble_uuid_vs_add(&nus_base_uuid, &p_nus->uuid_type);
 VERIFY_SUCCESS(err_code);

 ble_uuid.type = p_nus->uuid_type;
 ble_uuid.uuid = BLE_UUID_NUS_SERVICE;

 // Add the service.
 err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY,
 &ble_uuid,
 &p_nus->service_handle);
 /**@snippet [Adding proprietary Service to the SoftDevice] */
 VERIFY_SUCCESS(err_code);

 // Add the RX Characteristic.
 memset(&add_char_params, 0, sizeof(add_char_params));
 add_char_params.uuid = BLE_UUID_NUS_RX_CHARACTERISTIC;
 add_char_params.uuid_type = p_nus->uuid_type;
 add_char_params.max_len = BLE_NUS_MAX_RX_CHAR_LEN;
 add_char_params.init_len = sizeof(uint8_t);
 add_char_params.is_var_len = true;
 add_char_params.char_props.write = 1;
 add_char_params.char_props.write_wo_resp = 1;
 
 
 add_char_params.read_access = SEC_OPEN;
 add_char_params.write_access = SEC_OPEN;

 err_code = characteristic_add(p_nus->service_handle, &add_char_params, &p_nus->rx_handles);
 if (err_code != NRF_SUCCESS)
 {
 return err_code;
 }
 

 // Add the TX Characteristic.
 /**@snippet [Adding proprietary characteristic to the SoftDevice] */
 memset(&add_char_params, 0, sizeof(add_char_params));
 add_char_params.uuid = BLE_UUID_NUS_TX_CHARACTERISTIC;
 add_char_params.uuid_type = p_nus->uuid_type;
 add_char_params.max_len = BLE_NUS_MAX_TX_CHAR_LEN;
 add_char_params.init_len = 3;//sizeof(uint8_t);
 add_char_params.is_var_len = true;
 add_char_params.char_props.read = 1;
 uint8_t value[3];
 value[0] = 'h';
 value[1] = 'a';
 value[2] = 'i';
 add_char_params.p_init_value = value;
 add_char_params.is_value_user = 0;

 add_char_params.read_access = SEC_OPEN;
 add_char_params.write_access = SEC_OPEN;
 add_char_params.cccd_write_access = SEC_OPEN;

 return characteristic_add(p_nus->service_handle, &add_char_params, &p_nus->tx_handles);
 ///**@snippet [Adding proprietary characteristic to the SoftDevice] */
 
} 
 please change your "ble_nus_init" function in ble_nus.c to this , please notice the changes in adding the second characterestic, also i set the initial value as 'hai' so when you first read it, you will see that 
 step 2 
 go to ble_nus_data_send function in ble_nus.c, right now this is only tailored to send new data as Notificaiton, change this to the following. 
 uint32_t ble_nus_data_send(ble_nus_t * p_nus,
 uint8_t * p_data,
 uint16_t * p_length,
 uint16_t conn_handle)
{
 ret_code_t err_code;
 ble_gatts_hvx_params_t hvx_params;
 ble_gatts_value_t gatts_value;
 ble_nus_client_context_t * p_client;

 VERIFY_PARAM_NOT_NULL(p_nus);

 err_code = blcm_link_ctx_get(p_nus->p_link_ctx_storage, conn_handle, (void *) &p_client);
 VERIFY_SUCCESS(err_code);

 if ((conn_handle == BLE_CONN_HANDLE_INVALID) || (p_client == NULL))
 {
 return NRF_ERROR_NOT_FOUND;
 }

 //if (!p_client->is_notification_enabled)
 //{
 // return NRF_ERROR_INVALID_STATE;
 //}

 if (*p_length > BLE_NUS_MAX_DATA_LEN)
 {
 return NRF_ERROR_INVALID_PARAM;
 }

 //memset(&hvx_params, 0, sizeof(hvx_params));
 memset(&gatts_value,0,sizeof(gatts_value));
 //hvx_params.handle = p_nus->tx_handles.value_handle;
 //hvx_params.p_data = p_data;
 //hvx_params.p_len = p_length;
 //hvx_params.type = BLE_GATT_HVX_NOTIFICATION;
 gatts_value.len = *p_length;
 gatts_value.offset = 0;
 gatts_value.p_value = p_data;

 return sd_ble_gatts_value_set(conn_handle, p_nus->tx_handles.value_handle, &gatts_value);
 //return sd_ble_gatts_hvx(conn_handle, &hvx_params);
} 
 now after sending new data from serial terminal, upon reading the characteristic you will get the new values in nRF connect app, if any issue persist let me Know!

ble_app_uart Tx Characteristics - Read property

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