How to collect value from multiple characteristics in the client?

[Taoyi]

Hi, 

I am working on the client program to retrieve the value from 4 characteristics at the same time using notifications. I have already done with the server program. Using nrf connect to connect with my program, it looks like this:

I would like to collect the value from these four characteristics using notifications. Here' s the code to update 4 characteristic data on server:

void ble_eeg_update_4ch(ble_eeg_t *p_eeg) {
  //packet 1:
  uint32_t err_code;
  if (p_eeg->conn_handle != BLE_CONN_HANDLE_INVALID && p_eeg->ads1299_current_configuration[4] != 0xE1) {
    uint16_t hvx_len = EEG_PACKET_LENGTH;//The length is 60
    ble_gatts_hvx_params_t const hvx_params = {
        .handle = p_eeg->eeg_ch1_handles.value_handle,
        .type = BLE_GATT_HVX_NOTIFICATION,
        .offset = 0,
        .p_len = &hvx_len,
        .p_data = p_eeg->eeg_ch1_buffer,
    };
    err_code = sd_ble_gatts_hvx(p_eeg->conn_handle, &hvx_params);
  }
  if (err_code == NRF_ERROR_RESOURCES) {
    NRF_LOG_INFO("sd_ble_gatts_hvx() ERR/RES: 0x%x\r\n", err_code);
  }
  //Packet 2
  if (p_eeg->conn_handle != BLE_CONN_HANDLE_INVALID && p_eeg->ads1299_current_configuration[5] != 0xE1) {
    uint16_t hvx_len = EEG_PACKET_LENGTH;//The length is 60
    ble_gatts_hvx_params_t const hvx_params = {
        .handle = p_eeg->eeg_ch2_handles.value_handle,
        .type = BLE_GATT_HVX_NOTIFICATION,
        .offset = 0,
        .p_len = &hvx_len,
        .p_data = p_eeg->eeg_ch2_buffer,
    };
    err_code = sd_ble_gatts_hvx(p_eeg->conn_handle, &hvx_params);
  }
  if (err_code == NRF_ERROR_RESOURCES) {
    NRF_LOG_INFO("sd_ble_gatts_hvx() ERR/RES: 0x%x\r\n", err_code);
  }

  //Packet 3
  if (p_eeg->conn_handle != BLE_CONN_HANDLE_INVALID && p_eeg->ads1299_current_configuration[6] != 0xE1) {
    uint16_t hvx_len = EEG_PACKET_LENGTH;//The length is 60
    ble_gatts_hvx_params_t const hvx_params = {
        .handle = p_eeg->eeg_ch3_handles.value_handle,
        .type = BLE_GATT_HVX_NOTIFICATION,
        .offset = 0,
        .p_len = &hvx_len,
        .p_data = p_eeg->eeg_ch3_buffer,
    };
    err_code = sd_ble_gatts_hvx(p_eeg->conn_handle, &hvx_params);
  }
  if (err_code == NRF_ERROR_RESOURCES) {
    NRF_LOG_INFO("sd_ble_gatts_hvx() ERR/RES: 0x%x\r\n", err_code);
  }

  //Packet 4
  if (p_eeg->conn_handle != BLE_CONN_HANDLE_INVALID && p_eeg->ads1299_current_configuration[7] != 0xE1) {
    uint16_t hvx_len = EEG_PACKET_LENGTH;//The length is 60
    ble_gatts_hvx_params_t const hvx_params = {
        .handle = p_eeg->eeg_ch4_handles.value_handle,
        .type = BLE_GATT_HVX_NOTIFICATION,
        .offset = 0,
        .p_len = &hvx_len,
        .p_data = p_eeg->eeg_ch4_buffer,
    };
    err_code = sd_ble_gatts_hvx(p_eeg->conn_handle, &hvx_params);
  }
  if (err_code == NRF_ERROR_RESOURCES) {
    NRF_LOG_INFO("sd_ble_gatts_hvx() ERR/RES: 0x%x\r\n", err_code);
  }
}

 

Question:

1. Do you have examples that have multiple characteristics that need notifications in one service? I read the code of ble_app_hrs_c, but this program is not what I want.

2. If I can get retrieve these 4 characteristics data on the client, how to differentiate them?

[tesc]

Hi,

In the ble event, the handle in the ble_gattc_evt_hvx_t data structure is the attribute handle which identifies the characteristic. (Not to be confused with the connection handle, which is found in the ble_gattc_evt_t structure that holds the ble_gattc_evt_hvx_t structure in its params.hvx field.)

For examples on how to handle this, please have a look at the client service implementations in <sdk folder>/components/ble/ble_services (the folders ending in "_c"). Typically there is an on_hvx() function that checks the handle, e.g. for the battery service client in ble_bas_c.c:

/**@brief     Function for handling Handle Value Notification received from the SoftDevice.
 *
 * @details   This function handles the Handle Value Notification received from the SoftDevice
 *            and checks whether it is a notification of the Battery Level measurement from the peer. If
 *            it is, this function decodes the battery level measurement and sends it to the
 *            application.
 *
 * @param[in] p_ble_bas_c Pointer to the Battery Service Client structure.
 * @param[in] p_ble_evt   Pointer to the BLE event received.
 */
static void on_hvx(ble_bas_c_t * p_ble_bas_c, ble_evt_t const * p_ble_evt)
{
    // Check if the event is on the link for this instance.
    if (p_ble_bas_c->conn_handle != p_ble_evt->evt.gattc_evt.conn_handle)
    {
        return;
    }
    // Check if this notification is a battery level notification.
    if (p_ble_evt->evt.gattc_evt.params.hvx.handle == p_ble_bas_c->peer_bas_db.bl_handle)
    {
        if (p_ble_evt->evt.gattc_evt.params.hvx.len == 1)
        {
            ble_bas_c_evt_t ble_bas_c_evt;
            ble_bas_c_evt.conn_handle = p_ble_evt->evt.gattc_evt.conn_handle;
            ble_bas_c_evt.evt_type    = BLE_BAS_C_EVT_BATT_NOTIFICATION;

            ble_bas_c_evt.params.battery_level = p_ble_evt->evt.gattc_evt.params.hvx.data[0];

            p_ble_bas_c->evt_handler(p_ble_bas_c, &ble_bas_c_evt);
        }
    }
}

Regards,
Terje

[Taoyi]

Also, I 'm trying to enable 4 notifications after discovering the characteristics. The functions are:

static uint32_t cccd_configure(uint16_t conn_handle, uint16_t cccd_handle, bool enable)
{
    uint8_t buf[BLE_CCCD_VALUE_LEN];
    buf[0] = enable ? BLE_GATT_HVX_NOTIFICATION : 0;
    buf[1] = 0;
    ble_gattc_write_params_t const write_params =
    {
        .write_op = BLE_GATT_OP_WRITE_REQ,
        .flags    = BLE_GATT_EXEC_WRITE_FLAG_PREPARED_WRITE,
        .handle   = cccd_handle,
        .offset   = 0,
        .len      = sizeof(buf),
        .p_value  = buf
    };
    return sd_ble_gattc_write(conn_handle, &write_params);
}
//functions of ch1, ch2, ch3, ch4 are same
uint32_t ble_eeg_ch1_c_tx_notif_enable(ble_eeg_uarts_c_t * p_ble_uarts_c)
{
    VERIFY_PARAM_NOT_NULL(p_ble_uarts_c);
    if ( (p_ble_uarts_c->conn_handle == BLE_CONN_HANDLE_INVALID)
       ||(p_ble_uarts_c->handles.eeg_ch1_tx_cccd_handle == BLE_GATT_HANDLE_INVALID)
       )
    {
        return NRF_ERROR_INVALID_STATE;
    }
		
    return cccd_configure(p_ble_uarts_c->conn_handle,p_ble_uarts_c->handles.eeg_ch1_tx_cccd_handle, true);
}
// in the main.c:

static void ble_uarts_c_evt_handler(ble_eeg_uarts_c_t * p_ble_uarts_c, ble_eeg_uarts_c_evt_t const * p_ble_uarts_evt)
{
    ret_code_t err_code;

    switch (p_ble_uarts_evt->evt_type)
    {
        case BLE_UARTS_C_EVT_DISCOVERY_COMPLETE:
            NRF_LOG_INFO("Discovery complete.");
            err_code = ble_uarts_c_handles_assign(p_ble_uarts_c, p_ble_uarts_evt->conn_handle, &p_ble_uarts_evt->handles);
            APP_ERROR_CHECK(err_code);
            //Enable Notify
            err_code = ble_eeg_ch1_c_tx_notif_enable(p_ble_uarts_c);
            APP_ERROR_CHECK(err_code);
			NRF_LOG_INFO("Enabel notification of the Channel 1 Char");
			
			err_code = ble_eeg_ch2_c_tx_notif_enable(p_ble_uarts_c);
            APP_ERROR_CHECK(err_code);
			NRF_LOG_INFO("Enabel notification of the Channel 2 Char");
				
		    err_code = ble_eeg_ch3_c_tx_notif_enable(p_ble_uarts_c);
            APP_ERROR_CHECK(err_code);
			NRF_LOG_INFO("Enabel notification of the Channel 3 Char");
						
			err_code = ble_eeg_ch4_c_tx_notif_enable(p_ble_uarts_c);
            APP_ERROR_CHECK(err_code);
			NRF_LOG_INFO("Enabel notification of the Channel 4 Char");
            NRF_LOG_INFO("Connected to device with EEG Service.");
            break;

        case BLE_UARTS_C_EVT_NUS_TX_EVT:
            uart_chars_print(p_ble_uarts_evt->p_data, p_ble_uarts_evt->data_len);
            break;

        case BLE_UARTS_C_EVT_DISCONNECTED:
            NRF_LOG_INFO("Disconnected.");
            scan_start();
            break;
    }
}

However, when it tries to enable the notifications of ch1~4, it is said there's a fatal error. How to enable these four characteristics correctly?

Thank you!

[tesc]

Hi,

What error code do you get, and from what function call? (It sounds like it is from ble_eeg_ch4_c_tx_notif_enable(), can you confirm or correct that assumption?) This will usually point towards what kind of error you are seeing.

Regards,
Terje

[Taoyi]

I have already solved this. Thank you!