5.1.1.5 BLE Transparent UART

Recommended Readings

1. Getting Started with Application Building Blocks – See Building Block Examples from Related Links.

2. Getting Started with Peripheral Building Blocks – See Central Devices from Related Links.

3. See BLE Connection from Related Links.
4. See BLE Transparent UART from Related Links.
5. See BLE Multilink Transparent UART from Related Links.

6. BLE Software Specification – See MPLAB® Harmony Wireless BLE in Reference Documentation from Related Links.

Hardware Requirement

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.

Smart phone App

None

Programming the Precompiled Hex File or Application Example

Using MPLAB® X IPE:

1. Central Device – Import and program the precompiled hex file: <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\central\profiles_services\central_trp_uart\precompiled_hex .
2. Peripheral Device – Import and program the precompiled hex file: <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\Peripheral\profiles_services\peripheral_trp_uart\precompiled_hex.
3. 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:

1. Perform the following the steps mentioned in Running a Precompiled Example. For more information, refer to Running a Precompiled Application Example from Related Links.
2. Central Device – Open and program the application central_trp_uart.X located in <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware.
3. Peripheral Device – Open and program the application peripheral_trp_uart.X" located in <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\peripheral\profiles_services\peripheral_trp_uart\firmware.

4. For more details on how to find the Harmony Content Path, refer to Installing the MCC Plugin from Related Links.

Demo Description

Upon programming the demo application, central device (PIC32-BZ6) will start scanning for near by peripheral devices to connect. After a connection has been made data can be sent back and forth over UART between the two devices that are connected.

Demo application prints the status messages “Scanning” at the initiation of the scan process, “Connected!” upon successful connection, and “Disconnected” when the connection is lost, within a terminal emulator interface.

Application data to be sent to the connected peripheral device must be entered in the terminal emulator.

Testing

Users must use another PIC32-BZ6 Curiosity Board configured as Peripheral Transparent UART, see BLE Transparent UART from Related Links.

Experience the Demo using two PIC32-BZ6 Curiosity boards configured as Peripheral and Central device.

This section assumes that a user has already programmed the “peripheral_trp_uart” and “central_trp_uart” application on two PIC32-BZ6 Curiosity Boards.

1. Board 1 – PIC32-BZ6 Curiosity Board Programmed with “peripheral_trp_uart”
   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

      For terminal setup configuration, go to Setup>Terminal.

      For Serial port setup and connection, go to Setup>Serial Port.

      

   2. Reset the board, Upon reset, “Advertising” message is displayed on the Tera Term.
2. Board 2 – PIC32-BZ6 Curiosity Board Programmed with “central_trp_uart”
   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

      For terminal setup configuration, go to Setup>Terminal.

      For Serial port setup and connection, go to Setup>Serial Port.

      
   2. Reset the board. Upon reset, “Scanning” message is displayed on the TeraTerm.
   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”.

After connection establishment, both the peripheral device (Board 1) and central device (Board 2) displays “Connected!” message on respective terminal windows.

Users can now start sending data back and forth between the central and peripheral device using the terminal emulator. Characters entered on either terminals will immediately be sent to the peer devices

Developing this Application from Scratch using MCC

1. Create a new harmony project. For more details, see Creating a New MCC Harmony Project from Related Links.
2. Import component configuration - This step helps users setup the basic components and configuration required to develop this application. The imported file is of format .mc3 and is located in the path <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware\central_trp_uart.X.
   Note: Import and export functionality of Harmony component configuration will help users to start from a known working setup of MCC configuration.
3. Accept dependencies or satisfiers when prompted.
4. Verify if the project graph window has all the expected configuration.

   

Verifying Scan,Connection and Transparent Profile Configuration

1. Select BLE Stack component in project graph, to open component configuration and configure as illustrated in the following figure.

   

2. Select Transparent Profile component in project graph, to open component configuration and configure as illustrated in the following figure.

   

Generating 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. Initialization routine executed during program initialization can be found in the project files.

Header Files

• ble_gap.h: This header file contains BLE GAP functions and is automatically included in the app.c file

• ble_trspc.h: This header file associated with API’s and structures related to BLE Transparent Client functions for application user.

Function Calls

MCC generates and adds the code to initialize the BLE Stack GAP, GATT, L2CAP and SMP in APP_BleStackInit() function.

• APP_BleStackInit() is the API that will be called inside the Applications 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.

• ble_trspc.h in app.c, BLE Transparent UART Server related API's are available here

• osal/osal_freertos_extend.h in app_trsps_handler.c, OSAL related API's are available here

• 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.

• 

// 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 Applications initialstate - APP_STATE_INIT in app.c. Scan duration is 100 seconds.

Scan Results and initiating a BLE Connection

• BLE_GAP_EVT_ADV_REPORT event is generated upon finding Advertisements on legacy channels

• BLE connection can be initiated by using the API BLE_GAP_CreateConnection(&createConnParam_t;

  // 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) ||
    (p_event->eventField.evtAdvReport.addr.addr[0] == 0xB1 && p_event->eventField.evtAdvReport.addr.addr[1] == 0xB2) ||
    (p_event->eventField.evtAdvReport.addr.addr[0] == 0xC1 && p_event->eventField.evtAdvReport.addr.addr[1] == 0xC2))
{
    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; 
    createConnParam_t.connParams.intervalMax = 0x10; 
    createConnParam_t.connParams.latency = 0;
    createConnParam_t.connParams.supervisionTimeout = 0x48; 
    SERCOM0_USART_Write((uint8_t *)"Initiating Connection\r\n", 23);
    BLE_GAP_CreateConnection(&createConnParam_t);
}

Connected and Disconnected Events

• In app_ble_handler.c "BLE_GAP_EVT_CONNECTED" event will be generated when a BLE connection is completed.

Connection Handler

• Connection handle associated with the peer peripheral device needs to be saved for data exchange after a BLE connection

• p_event->eventField.evtConnect.connHandle has this information

  // Global variable
  extern uint16_t conn_hdl;
  
  // Connected event
  SERCOM0_USART_Write((uint8_t *)"Connected\r\n", 11);
  conn_hdl = p_event->eventField.evtConnect.connHandle;
  
  // Disconnected event
  SERCOM0_USART_Write((uint8_t *)"Disconnected\r\n", 14);
  

  

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);

Transmit Data

• Add APP_MSG_UART_CB to the generated APP_MsgId_T in app.h

  

• BLE_TRSPC_SendData(conn_hdl , 1, &data); is the API to be used for sending data towards the central device
  Note: The precompiled application example uses a UART callback to initiate the data transmission upon receiving a character on UART.

Example Implementation for Transmitting the received data over UART using the BLE_TRSPC_SendData API

uint16_t conn_hdl;// connection handle info captured @BLE_GAP_EVT_CONNECTED event
uint8_t uart_data;
void uart_cb(SERCOM_USART_EVENT event, uintptr_t context)
{
  APP_Msg_T   appMsg;   
  // If RX data from UART reached threshold (previously set to 1)
  if( event == SERCOM_USART_EVENT_READ_THRESHOLD_REACHED )
  {
    // Read 1 byte data from UART
    SERCOM0_USART_Read(&uart_data, 1);

    appMsg.msgId = APP_MSG_UART_CB;
    OSAL_QUEUE_Send(&appData.appQueue, &appMsg, 0);     
  }
}
void APP_UartCBHandler()
{
    // Send the data from UART to connected device through Transparent service
    BLE_TRSPC_SendData(conn_hdl, 1, &uart_data);     
}

////////////////////////////////////////////////////////////////////////////////////

  // Register call back when data is available on UART for Peripheral Device to send
  // Enable UART Read
  SERCOM0_USART_ReadNotificationEnable(true, true);
  // Set UART RX notification threshold to be 1
  SERCOM0_USART_ReadThresholdSet(1);
  // Register the UART RX callback function
  SERCOM0_USART_ReadCallbackRegister(uart_cb, (uintptr_t)NULL);

////////////////////////////////////////////////////////////////////////////////////

//If msg received in Queue, handle the Queue message based on msgID
if (OSAL_QUEUE_Receive(&appData.appQueue, &appMsg, OSAL_WAIT_FOREVER))
  {
    if(p_appMsg->msgId==APP_MSG_BLE_STACK_EVT)
    {
     // Pass BLE Stack Event Message to User Application for handling
     APP_BleStackEvtHandler((STACK_Event_T *)p_appMsg->msgData);
     }
      else if(p_appMsg->msgId==APP_MSG_UART_CB)
      {
       // Transparent UART Client Data transfer Event
       APP_UartCBHandler();
       }                
  }

Receive Data

• BLE_TRSPC_EVT_RECEIVE_DATA is the event generated when data is sent from central device

• Users need to use the BLE_TRSPC_GetDataLength(&data_len) API to extract the length of application data received

• BLE_TRSPC_GetData(&conn_hdl, data); API is used to retrieve the data, conn_hdl is the value obtained from Connection Handler section

Example Implementation for printing the received data from peripheral device over UART

  /* TODO: implement your application code.*/
    uint16_t data_len;
    uint8_t *data;
    // Retrieve received data length
    BLE_TRSPC_GetDataLength(p_event->eventField.onReceiveData.connHandle, &data_len);
    // Allocate memory according to data length
    data = OSAL_Malloc(data_len);
    if(data == NULL)
    break;
    // Retrieve received data
    BLE_TRSPC_GetData(p_event->eventField.onReceiveData.connHandle, data);
    // Output received data to UART
    SERCOM0_USART_Write(data, data_len);
    // Free memory
    OSAL_Free(data);

Where to go from Here

See BLE Multilink Transparent UART from Related Links.