Updating a GATT Value

[Yatekii]

Hi!

So I have my GATT value of a service that I would like to update. Sadly that value always stays at the initial value. Below you can find my update function.

uint32_t ble_pwr_data_update(ble_pwr_t* p_pwr, pwr_data_t pwr_data){
    if (p_pwr == NULL){
        return NRF_ERROR_NULL;
    }

    uint32_t err_code = NRF_SUCCESS;
    ble_gatts_value_t gatts_value;

    // Initialize value struct.
    memset(&gatts_value, 0, sizeof(gatts_value));

    gatts_value.len     = sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = (uint8_t*)&pwr_data;

    // Update databasee.
    err_code = sd_ble_gatts_value_set(p_pwr->conn_handle,
                                        p_pwr->pwr_handles.value_handle,
                                        &gatts_value);
    if (err_code == NRF_SUCCESS){
        // Save new Voltage value.
        p_pwr->pwr_data = pwr_data;
    }else{
        return err_code;
    }

    // Send value if connected and notifying.
    if ((p_pwr->conn_handle != BLE_CONN_HANDLE_INVALID) && p_pwr->is_notification_supported){
        ble_gatts_hvx_params_t hvx_params;

        memset(&hvx_params, 0, sizeof(hvx_params));

        hvx_params.handle = p_pwr->pwr_handles.value_handle;
        hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
        hvx_params.offset = gatts_value.offset;
        hvx_params.p_len  = &gatts_value.len;
        hvx_params.p_data = gatts_value.p_value;

        err_code = sd_ble_gatts_hvx(p_pwr->conn_handle, &hvx_params);
    }
    else{
        err_code = NRF_ERROR_INVALID_STATE;
    }

    return err_code;
}

Do I do this in improper fashion?

(p_pwr->conn_handle != BLE_CONN_HANDLE_INVALID) && p_pwr->is_notification_supported

returns true, so it should also notify. I pulled the value manually tho to be sure. No change.

Thanks for any advice Best wishes Noah

[FormerMember]

I'm not sure if I clearly understand, is the problem that notifications never are transferred (sd_ble_gatts_hvx() )? Or that if you use sd_ble_gatts_value_set(), the value is not updated?

[Yatekii]

The update of the value does not work. Even if I manually request the value (Nordic Developer Mobile App), it doesn't update.

[FormerMember]

To make notifications work, the client (typically central/master) has to enable notifications on the server. This video tutorial part 1 at approximately 19:15 explains data transfer using notifications, I would recommend you to take a look at it.