STM32WBA Bluetooth® LE – Serial communication

1. Serial communication profile

Serial communication applications are proprietary applications used to exchange data entered on the UART of each board.

SerialCom applications are named BLE_SerialCom_Central and BLE_SerialCom_Peripheral: One board is configured as central using BLE_SerialCom_Central. The other board is configured as peripheral using BLE_SerialCom_Peripheral.

Both boards support data transfer by sending L2CAP data through a COC (Connection Oriented Channel) link.

• Open VT100 terminals on client and server sides.
• Connect to ST-LINK via the COM port @115200 bauds/s, 8 data bits, with no parity and 1 stop bit:
  

Bluetooth® Serial port configuration

• Configure the terminal with local echo settings:
  

Bluetooth® Terminal setup

• No service is added.​
  

Once a Bluetooth® LE link is established, a Connection Oriented Channel (COC) is established.
Data are exchanged through the COC link.

The SerialCom projects provided within the STM32CubeWBA MCU Package are described below:

Bluetooth® LE SerialCom projects & STM32WBA

Bluetooth® LE SerialCom Peripheral project & Smartphone

Example of COC link establishment between a SerialCom central (STM32WBA or Smartphone) & a SerialCom peripheral (STM32WBA)

Example of COC exchanged data between a SerialCom peripheral (STM32WBA) & a SerialCom central (STM32WBA or Smartphone)

1.1. On board buttons configuration

Button configuration for Bluetooth® Low Energy SerialCom Applications on Nucleo-WBA55CG boards
Application Condition B1 Click B1 Long Press B2 Click B2 Long Press B3 Click B3 Long Press SerialCom Peripheral Idle Connected Send data Mode Toggle / Clear Sec db Slave Sec Req / / / SerialCom Central Idle Connected Starts scan then connects Send data Mode Toggle / Clear Sec db Pairing request / - Update connection interval /

2. Requirements

2.1. Software and Hardware requirements

For software and hardware requirements refer to STM32WBA Build BLE Project wiki page.

2.2. Collector applications compatibility

The STM32CubeWBA SerialCom peripheral application is compatible with the following collector:

• STM32CubeWBA and SerialCom central application.

3. STM32WBA SerialCom peripheral description

3.1. Project directory

The "BLE_SerialCom_Peripheral" application is available by downloading STM32CubeWBA MCU Package.

Refer to How to Build a Bluetooth® LE project wiki page for project directory information.

3.2. Project description

3.2.1. Structure

Software project structure with the most important parts:

SerialCom peripheral project structure
Main applicative part files Services management Bluetooth® LE libraries Link Layer System integration files WARNING: Do not modify the files in the Middlewares folder

3.2.2. Application initialization

The application initialization steps are described below:

SerialCom peripheral project initialization

Initialize the system (HAL, clocks, peripherals) Infinite loop for run mode Initialize the BSP, Power Mode, trace, memory manager, NVM Wait for initialization done Initialize the Bluetooth® LE Host Stack Initialize the Bluetooth® LE GATT level Initialize the Bluetooth® LE GAP level Reset the number of registered handler Initialize the context Manage the COC link establishment Initialize Rx UART to process data from terminal

3.2.3. GAP and GATT initialization and interaction

SerialCom peripheral software module interaction

and The Bluetooth® LE SerialCom peripheral application initialization is done within app_ble.c.

• Starts the Bluetooth® LE stack:
  • Initializes the device as peripheral.
  • Configures and starts advertising: ADV parameters, local name, UUID - APP_BLE_init()
• Calls the services controller initialization SVCCTL_Init() - svc_ctl.c
• Manages the GAP event - SVCCTL_App_Notification().
  • EVT_LE_CONN_COMPLETE provides information of the connection interval, the slave latency, and the supervision timeout.
  • EVT_LE_CONN_UPDATE_COMPLETE provides information about the new connection.
  • EVT_DISCONN_COMPLETE communicates link disconnection and its reason to the application.
  • EVT_ENCRYPT_CHANGE communicates link encryption to the application.

The Services management is done by the service controller, svc_ctl.c:

• Initializes the number of the registered handler - SVCCTL_SvcInit()
• Manages events - SVCCTL_UserEvtRx()- from the Bluetooth® LE Host Stack and redirects them to the gap event handler - SVCCTL_App_Notification

The application level of the SerialCom peripheral is done with coc_peripheral_app.c:

• Initializes the application context.
• Manages the COC link establishment.

Initializes Rx UART to process data from the terminal.

3.3. How to use the Bluetooth® Low Energy SerialCom Peripheral application

Once the BLE SerialCom Peripheral application is installed on the STM32WBA platform, use BLE SerialCom Central application on STM32WBA platform or a Smartphone.

• Open a VT100 terminal on the central and peripheral sides via the ST-Link Com port, @115200 bauds, 8 data bits, no parity and 1 stop bit:
  

Bluetooth® Serial Port Peripheral write data

Bluetooth® Serial Port Central receive data

• Press B1 on the central to scan, connect and establish the COC link. When the link is ready, the CONNECTION READY message is displayed.
  
• Enter data on UART, on the peripheral or central side. Check that the peer device receives data correctly.
  

Pressing B2 while not connected allows to clear the security database. Pressing B2 while connected allows to send peripheral security request.

There are two different modes to send messages from an STM32WBA: Send button or Real time.

In terminal, when you type the message:

• Send button mode, data are sent when LF is sent
• Real time mode, each character is immediately sent.
  

Pressing B1 on peripheral side allows data send mode changing.

3.4. UART debug trace

The debug log via UART interface ensures the application project is traced.

To enable the traces within the project, enable them within app_conf.h as described below:

/**
 * Enable or Disable traces in application
 */
#define CFG_DEBUG_APP_TRACE         (1)

SerialCom Peripheral - Initialization phase

Connected Phase

==>> Start Ble_Hci_Gap_Gatt_Init function Success: hci_reset command Success: aci_hal_write_config_data command - CONFIG_DATA_PUBADDR_OFFSET Public Bluetooth Address: 00:80:e1:2a:7e:6e Success: aci_hal_write_config_data command - CONFIG_DATA_IR_OFFSET Success: aci_hal_write_config_data command - CONFIG_DATA_ER_OFFSET Success: aci_hal_set_tx_power_level command Success: aci_gatt_init command Success: aci_gap_init command Success: aci_gatt_update_char_value - Device Name Success: aci_gatt_update_char_value - Appearance Success: hci_le_set_default_phy command Success: aci_gap_set_io_capability command Success: aci_gap_set_authentication_requirement command Success: aci_gap_configure_whitelist command ==>> End Ble_Hci_Gap_Gatt_Init function ==>> aci_gap_set_discoverable - Success ==>> Success: Start Fast Advertising

>>== HCI_LE_CONNECTION_COMPLETE_SUBEVT_CODE - Connection handle: 0x0001 - Connection established with @:00:80:e1:2a:7e:9d - Connection Interval: 50.00 ms - Connection latency: 0 - Supervision Timeout: 5000 ms BLE_SVC_L2CAP_Conn_Update(), Successfully >>== HCI_LE_CONNECTION_UPDATE_COMPLETE_SUBEVT_CODE - Connection Interval: 45.00 ms - Connection latency: 0 - Supervision Timeout: 10000 ms >>== ACI_L2CAP_COC_CONNECT_VSEVT_CODE ==>> aci_l2cap_coc_connect_confirm : Success Success: change MTU >>== MTU_size = 247 >>== CONNECTION READY

4. STM32WBA SerialCom Central example description

4.1. Project directory

The "BLE_SerialCom_Central" application is available by downloading STM32CubeWBA MCU Package

Refer to How to Build a Bluetooth® LE project wiki page for project directory information.

4.2. Project description

4.2.1. Structure

Software project structure with the most important parts:

SerialCom central project structure
Main applicative part files Services management Bluetooth® LE libraries Link Layer System integration files WARNING: Do not modify the files in Middlewares folder

4.2.2. Application initialization

The different steps of the application initialization are described below:

SerialCom central project initialization

Initialize the system (HAL, clocks, peripherals) Infinite loop for run mode Initialize the BSP, Power Mode, trace, memory manager, NVM Wait for initialization done Initialize the Bluetooth® LE Host Stack Initialize the Bluetooth® LE GATT level Initialize the Bluetooth® LE GAP level Reset the number of registered handler Initialize Gatt Client Application Manage COC link establishment Initialize Rx UART to process data from terminal

4.2.3. GAP and GATT initialization and interaction

SerialCom central software module interaction

and The Bluetooth LE SerialCom central application initialization is done within app_ble.c

• Start the Bluetooth® LE stack - initialize the device as peripheral - configure and start advertising: ADV parameters, local name, UUID - APP_BLE_init()
• Call the services controller initialization SVCCTL_Init() - svc_ctl.c
• Manage the GAP event - SVCCTL_App_Notification()
  • EVT_LE_CONN_COMPLETE - provides information of the connection interval, slave latency, supervision timeout
  • EVT_LE_CONN_UPDATE_COMPLETE - provides new information about the connection
  • EVT_DISCONN_COMPLETE - informs the application about the link disconnection and the reason
  • EVT_ENCRYPT_CHANGE - informs the application weather the link is encrypted

The Services management is done by the service controller, svc_ctl.c

• Initialize the number of registered handler - SVCCTL_SvcInit()
• Manage events - SVCCTL_UserEvtRx()- from the Bluetooth® LE Host Stack and redirect them to the gap event handler - SVCCTL_App_Notification

The application level of the SerialCom central is done with gatt_client_app.c:

• Initialize Gatt Client Application
• Manage COC link establishment
• Initialize Rx UART to process data from terminal

4.3. How to use the Bluetooth® Low Energy SerialCom central application

Once the BLE SerialCom Central application is installed on the STM32WBA platform, use BLE SerialCom Peripheral application on other STM32WBA.

• Open a VT100 terminal on central and peripheral sides via the ST-Link Com Port (Connection is displayed as ST Link), @115200 bauds, 8 data bits, no parity and 1 stop bit:
  

• Press B1 on the central side to scan, connect and establish COC. Once the link is ready, the CONNECTION READY message is displayed.
  
• Enter data on the central or the peripheral side, and check that data are correctly received on peer device.
  

There are two different modes to send messages from an STM32WBA: Send button or Real time.

In terminal, when you type the message:

• Send button mode, data are sent when LF is sent
• Real time mode, each character is immediately sent.
  

Pressing B1 on central when device is connected allows data send mode changing.

Pressing B2 while not connected allows to clear the security database. Pressing B2 while connected allows to send pairing request.

Pressing B3 while connected allows to send connection update.

4.4. UART debug trace

Traces are enabled within the project, in app_conf.h as described below:

/**
 * Enable or Disable traces in application
 */
#define CFG_DEBUG_APP_TRACE         (1)

Debugger can also be supported by enabling it within app_conf.h as described below:

/**
 * User interaction
 * When CFG_LED_SUPPORTED is set, LEDS are activated if requested
 * When CFG_BUTTON_SUPPORTED is set, the push button are activated if requested
 * When CFG_DBG_SUPPORTED is set, the debugger is activated
 */
[...]
#define CFG_DBG_SUPPORTED                       (1)

SerialCom Central - Initialization phase

Press B1. The Connected Phase starts.

==>> Start Ble_Hci_Gap_Gatt_Init function Success: hci_reset command Success: aci_hal_write_config_data command - CONFIG_DATA_PUBADDR_OFFSET Public Bluetooth Address: 00:80:e1:2a:7e:9d Success: aci_hal_write_config_data command - CONFIG_DATA_IR_OFFSET Success: aci_hal_write_config_data command - CONFIG_DATA_ER_OFFSET Success: aci_hal_set_tx_power_level command Success: aci_gatt_init command Success: aci_gap_init command Success: aci_gatt_update_char_value - Appearance Success: aci_gap_set_io_capability command Success: aci_gap_set_authentication_requirement command Success: aci_gap_configure_whitelist command ==>> End Ble_Hci_Gap_Gatt_Init function -- CENTRAL INITIALIZED

** START GENERAL DISCOVERY (SCAN) ** --- ST MANUFACTURER data BlueSTv2 -- COC peripheral detected, db addr 0x00:80:E1:2A:7E:6E >>== ACI_GAP_PROC_COMPLETE_VSEVT_CODE -- GAP_GENERAL_DISCOVERY_PROC completed ==>> Success: Create connection to SC_WBAxx >>== ACI_GAP_PROC_COMPLETE_VSEVT_CODE >>== HCI_LE_CONNECTION_COMPLETE_SUBEVT_CODE - Connection handle: 0x0001 - Connection established with @:00:80:e1:2a:7e:6e - Connection Interval: 50.00 ms - Connection latency: 0 - Supervision Timeout: 5000 ms GATT services discovery Success: aci_l2cap_connection_parameter_update_resp command Success: aci_hal_set_radio_activity_mask command Fail  : aci_l2cap_connection_parameter_update_resp command ACI_ATT_READ_BY_GROUP_TYPE_RESP_VSEVT_CODE - ConnHdl=0x0001 1/2 short UUID=0x1801, handle [0x0001 - 0x0004], GENERIC_ATTRIBUTE_SERVICE_UUID found 2/2 short UUID=0x1800, handle [0x0005 - 0x000B], GAP_SERVICE_UUID found PROC_GATT_DISC_ALL_PRIMARY_SERVICES services discovered Successfully DISCOVER_ALL_CHARS ConnHdl=0x0001 ALLServiceHandle[0x0001 - 0x000B] ACI_ATT_READ_BY_TYPE_RESP_VSEVT_CODE - ConnHdl=0x0001 ConnHdl=0x0001, number of value pair = 3 1/3 short UUID=0x2A05, Properties=0x0020, CharHandle [0x0002 - 0x0003], GATT SERVICE_CHANGED_CHARACTERISTIC_UUID charac found 2/3 short UUID=0x2A00, Properties=0x000A, CharHandle [0x0006 - 0x0007], GAP DEVICE_NAME charac found 3/3 short UUID=0x2A01, Properties=0x0002, CharHandle [0x0008 - 0x0009], GAP APPEARANCE charac found ACI_ATT_READ_BY_TYPE_RESP_VSEVT_CODE - ConnHdl=0x0001 ConnHdl=0x0001, number of value pair = 1 1/1 short UUID=0x2A04, Properties=0x0002, CharHandle [0x000A - 0x000B] All characteristics discovered Successfully DISCOVER_ALL_CHAR_DESCS [0x0001 - 0x000B] >>== HCI_LE_CONNECTION_UPDATE_COMPLETE_SUBEVT_CODE - Connection Interval: 45.00 ms - Connection latency: 0 - Supervision Timeout: 10000 ms ==>> Start Connection Oriented Channel Success: aci_l2cap_coc_connect command ACI_ATT_FIND_INFO_RESP_VSEVT_CODE - ConnHdl=0x0001 reset - UUID & handle - CHARACTERISTIC_UUID=0x2803 CharStartHandle=0x0002 UUID=0x2A05, handle=0x0003, found GATT SERVICE_CHANGED_CHARACTERISTIC_UUID Descriptor UUID=0x2902, handle=0x0002-0x0003-0x0004, Service Changed found PRIMARY_SERVICE_UUID=0x2800 handle=0x0005 reset - UUID & handle - CHARACTERISTIC_UUID=0x2803 CharStartHandle=0x0006 >>== ACI_L2CAP_COC_CONNECT_CONFIRM_VSEVT_CODE ==>> Connection Oriented Channel established MTU exchanged size = 247 Success: set data length command >>== MTU_size = 247 >>== CONNECTION READY ACI_ATT_FIND_INFO_RESP_VSEVT_CODE - ConnHdl=0x0001 UUID=0x2A00, handle=0x0007, found GAP DEVICE_NAME_UUID reset - UUID & handle - CHARACTERISTIC_UUID=0x2803 CharStartHandle=0x0008 UUID=0x2A01, handle=0x0009, found GAP APPEARANCE_UUID reset - UUID & handle - CHARACTERISTIC_UUID=0x2803 CharStartHandle=0x000A UUID=0x2A04, handle=0x000B All characteristic descriptors discovered Successfully ServiceChangedCharDescHdl =0x0004 All notifications enabled successfully

5. STM32WBA SerialCom peripheral with ST BLE Toolbox smartphone app

Required: phone with Android 10 or newer.

ST BLE ToolBox is a user-friendly application which interacts with and debugs ST Bluetooth®LE devices.

ST BLE Toolbox screenshots about the COC feature

On ST BLE Toolbox, when clicking on a device corresponding to an ST board with a firmware ID SerialCom Peripheral (0x87), a "COC" button appears (next to the "Connect" button).

After accepting the pairing with the device (which is mandatory), a special page for COC appears. This means the L2CAP socket has been created and you can now receive and send data via the L2CAP channel.

Messages sent by the board will immediately appear in the chat.

2 different modes can be used to send messages from the phone: Send button and Real time.

In Send button mode, you can type your message in the text field at the bottom of the chat, then sending this message by clicking on the "Send" button.

In the Real time mode, each character you write is immediately sent.

You can erase all messages by clicking on "Clear".

Data format:
When sending the message "hello", what is actually sent is 0x 05 00 68 65 6C 6C 6F.

• 0x 05 00 is the length of the message in little endian (05 00 in little endian => 00 05 => 5 => number of letters of "hello").
  
• 0x 68 65 6C 6C 6F is "hello" in ascii ("h" = 0x68, "e" = 0x65, "l" = 0x6C, "o" = 0x6F).