5.1.1.4 BLE Connection

This section helps users to enable scan and connect functionality on the Bluetooth Low Energy central device (WBZ351). To establish a successful Bluetooth Low Energy connection, the advertiser needs to broadcast advertisement packets across the three primary advertisement channels (or a subset of these channels). This allows the devices scanning for advertisers to find and read their advertisement data, the scanner can initiate a connection if advertiser allows it. To demonstrate a Bluetooth Low Energy connection on the WBZ351, two device types are required:

Advertiser (Transmitting Connectable Adv)
Scanner

Users can choose to either run the precompiled Application Example hex file provided on the WBZ351 Curiosity Board or follow the steps to develop the application from scratch.

It is recommended to follow the examples in sequence to understand the basic concepts before progressing to the advanced topics.

Hardware Requirement

Table 5-5. Hardware Prerequisites
S. No.	Tool	Quantity
1	WBZ351 Curiosity Board	2
2	Micro USB cable	2

SDK Setup

Refer to Getting Started with Software Development from Related Links.

Software Requirement

To install Tera Term tool, refer to the Tera Term web page in Reference Documentation from Related Links.

Smartphone Application

None

Programming the Precompiled Hex File or Application Example

Using MPLAB® X IPE:

Central Device – Import and program the precompiled hex file: <Discover Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\central\central_conn\hex folder.
Peripheral Device – Import and program the precompiled hex file: <Discover Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\Peripheral\Peripheral_conn\hex
For detailed steps, refer to Programming a Device in MPLAB® IPE in Reference Documentation from Related Links.

Note: Ensure to choose the correct Device and Tool information.

Using MPLAB® X IDE:

Perform the following the steps mentioned in Running a Precompiled Example. For more information, refer to Running a Precompiled Application Example from Related Links.
Central Device – Open and program the application central_conn.X located in <Discover Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\central\central_conn\firmware.
Peripheral Device – Open and program the application peripheral_conn.X located in <Discover Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\peripheral\peripheral_conn\firmware.
For more details on how to find the Discover path, refer to Download Application Example from Discover in Running a Precompiled Application Example from Related Links.

Demo Description

To experience this demo, users are required to use central_connection and peripheral_connection application examples. The two application example mentioned above demonstrates a Bluetooth Low Energy connection establishment process. An Advertiser (Peripheral) starts connectable, scannable, undirected Bluetooth Low Energy advertisement and the scanner (Central) receives the advertisements and initiates a Bluetooth Low Energy connection. This enables the users to transmit connectable and scannable undirected Bluetooth Low Energy advertisements. The demo application prints the following status messages:

Scanning – At the initiation of the scan process.
Connected! – Upon successful connection.
Disconnected – When the connection is lost, within a terminal emulator interface.

Tera Term Configuration

Baud Rate/Speed – 115200 (as configured in SERCOM configuration)
Parity – None
Data Bits – 8
Stop Bits – 1
Flow Control – None

Testing

Users must use another WBZ351 Curiosity Board configured as peripheral connection, see BLE Connection from Related Links.

This section assumes that a user has already programmed the peripheral_conn and central_conn application on two WBZ351 Curiosity Boards.

Board 1 – WBZ351 Curiosity Board programmed with peripheral_conn.
1. Open TeraTerm and configure as mentioned below:
  Terminal Settings
  - Baud Rate/Speed – 115200 (as configured in SERCOM configuration)
  - Parity – None
  - Data Bits – 8
  - Stop Bits – 1
  - Flow Control – None
2. Reset the board. Upon reset, the Advertising message appears on the Tera Term.
Board 2 – WBZ351 Curiosity Board programmed with central_conn.
1. Open TeraTerm and configure as mentioned below:
  Terminal Settings
  - Baud Rate/Speed – 115200 (as configured in SERCOM configuration)
  - Parity – None
  - Data Bits – 8
  - Stop Bits – 1
  - Flow Control – None
2. Reset the board. Upon reset, the Scanning message appears on the Tera Term.
3. Upon finding peripheral device with public address {0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6} message Found Peer Node will be displayed and a connection request will be initiated Initiating Connection.

Note: Scanner is configured to scan only for 100s. The user must ensure the peer device is advertising.

After connection establishment, both the peripheral device (Board1) and central device (Board2) displays Connected! message on respective terminal windows.

Developing the Application from Scratch using MCC

Follow the steps below to build the application manually:

Note: It is recommended for the new users of the MPLAB Code Configurator to refer MPLAB® Code Configurator (MCC) User’s Guide in Reference Documentation from Related Links.

Create a new harmony project. For more details, see Creating a New MCC Harmony Project from Related Links.
Import Component Configuration - This step helps users to setup the basic components and configuration required to develop this application. The imported file is of format .mc4 and is located in the path <Discover Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\central\central_conn\firmware\central_conn.X.For more details on importing the component configuration, refer to Importing Existing App Example Configuration from Related Links.
Note: Import and export functionality of component configuration helps users to start from a known working setup of MCC configuration.
Accept Dependencies or Satisfiers.
1. If prompted to resolve dependencies or add required modules. Click Yes.
2. MPLAB® MCC automatically adds any required drivers or middleware.
Verify Project Graph.

In Project Graph window, confirm that all expected components are present. For more details, see the following figure.

Verifying Scan and Connection Configuration

Open the Project Graph
1. In MPLAB® X IDE, with MCC open, locate the Project Graph tab. In the Project Graph tab, the user can see all the components and their relationships to the project.
Select the BLE Stack Component
1. Click on the BLE Stack component in project graph. This opens the “BLE Stack” component Configuration Options tab.
2. In the “BLE Stack” Configuration Options tab, the user can set the parameters as per the requirement illustrated in the following figure.
  Figure 5-32. BLE Stack Configuration

Generating a Code

For more details on code generation, refer to MPLAB Code Configurator (MCC) Code Generation from Related Links.

Files and Routines Automatically generated by the MCC

After generating the program source from MCC interface by clicking Generate Code, the BLE configuration can be found in the following project directories.

Initialization routines for OSAL, RF System, and BLE System are auto-generated by the MCC. See OSAL Libraries Help in Reference Documentation from Related Links.

The user can find the BLE stack initialization routine executed during application initialization in the project files. The MCC automatically generates this initialization routine. This call initializes and configures the GAP, GATT, SMP, L2CAP and BLE middleware layers.

Configuration for scanning extended advertisements is auto-generated.

Table 5-6. Source Files
Source Files	Usage
`app.c`	Application State machine, includes calls for Initialization of all BLE stack (GAP,GATT, SMP and L2CAP) related component configurations
`app_ble\app_ble.c`	Source Code for the BLE stack related component configurations, code related to function calls from `app.c`
`app_ble\app_ble_handler.c`	All GAP, GATT, SMP and L2CAP Event handlers
Note: `app.c` is autogenerated and has a state machine based Application code sample. Users can use this template to develop their application.

Header Files
- ble_gap.h: This header file contains BLE GAP functions and is automatically included in the app.c file.
Function Calls
- MCC generates and adds the code to initialize the BLE Stack GAP, GATT, L2CAP and SMP in the APP_BleStackInit() function.
- APP_BleStackInit() is the API that will be called inside the application’s Initial state APP_STATE_INIT in app.c.

User Application Development

Include

Include the user action. For more information, refer to User Action from Related Links.
definitions.h in all the files where UART will be used to print debug information.
Note: definitions.h is not specific to just UART peripheral, instead it must be included in all application source files where peripheral functionality will be exercised.
Start Scanning
```
// Scanning Enabled
BLE_GAP_SetScanningEnable(true, BLE_GAP_SCAN_FD_ENABLE, BLE_GAP_SCAN_MODE_OBSERVER, 1000);
// Output the state string to UART
SERCOM0_USART_Write((uint8_t *)"Scanning \r\n", 11);
```
This API is called in the application’s Initial state, APP_STATE_INIT, in app.c. The scan duration is 100 seconds.
Figure 5-36. app.c

Scan Results and Initiating a BLE connection

BLE_GAP_EVT_ADV_REPORT event in app_ble_handler.c is generated upon finding advertisements on legacy channels.

The user can initiate a BLE connection by using the BLE_GAP_CreateConnection(&createConnParam_t); API.

  // code snippet to filter scan results and initiate connection
  if (p_event->eventField.evtAdvReport.addr.addr[0] == 0xA1 && p_event->eventField.evtAdvReport.addr.addr[1] == 0xA2)
  {
      SERCOM0_USART_Write((uint8_t *)"Found Peer Node\r\n", 17);
      BLE_GAP_CreateConnParams_T createConnParam_t;
      createConnParam_t.scanInterval = 0x3C; // 37.5 ms
      createConnParam_t.scanWindow = 0x1E; // 18.75 ms
      createConnParam_t.filterPolicy = BLE_GAP_SCAN_FP_ACCEPT_ALL;
      createConnParam_t.peerAddr.addrType = p_event->eventField.evtAdvReport.addr.addrType;
      memcpy(createConnParam_t.peerAddr.addr, p_event->eventField.evtAdvReport.addr.addr, GAP_MAX_BD_ADDRESS_LEN);
      createConnParam_t.connParams.intervalMin = 0x10; // 20ms
      createConnParam_t.connParams.intervalMax = 0x10; // 20ms
      createConnParam_t.connParams.latency = 0;
      createConnParam_t.connParams.supervisionTimeout = 0x48; // 720ms
      SERCOM0_USART_Write((uint8_t *)"Initiating Connection\r\n", 23);
      BLE_GAP_CreateConnection(&createConnParam_t);
  }

Connected and Disconnected Events
- All the possible GAP, GATT, SMP and L2CAP Event handlers are available in the app_ble_handler.c file, the users can implement application code to denote Connection state here. BLE_GAP_EVT_CONNECTED event is generated after a successful BLE connection with peripheral device.
```
// Connected EVT
SERCOM0_USART_Write((uint8_t *)"Connected!\r\n", 12);
//Disconnected EVT
SERCOM0_USART_Write((uint8_t *)"Disconnected\r\n", 15);
```
  Figure 5-38. app_ble_handler.c
Scan Timeout Event
- In app_ble_handler.c, BLE_GAP_EVT_SCAN_TIMEOUT event is generated when BLE scan duration expires.
```
SERCOM0_USART_Write((uint8_t *)"Scan Completed\r\n", 17);
```
  Figure 5-39. app_ble_handler.c
Note: The users can exercise various other BLE Advertisement functionalities using the BLE Stack APIs. For more information, refer to BLE Stack in Reference Documentation from Related Links.