5.1.1.6 BLE Multilink 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

Smartphone 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\multilink\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_ml_trp_uart.X located in <Harmony Content Path>\wireless_apps_pic32_bz6\apps\ble\building_blocks\central\profiles_services\multilink\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. The central device continues scanning until 100 secs and allows new peripheral devices that are advertising to join. For this example we are going to demonstrate three BLE links

                    ------------------Central Device------------------
                    |                      |                         |
                    |                      |                         |
            Peripheral Device       Peripheral Device        Peripheral Device

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

For more details on changing the device address, refer to the Set PUBLIC Device Address in

BLE Transparent UART from Related Links.

Demo Experience when Using Four PIC32-BZ6 Curiosity Boards, Three Configured as Peripheral and One Configured as Central Device

After connection establishment, both the Peripheral device (Board2/3/4) and Central device (Board1) will display “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 any peripheral device's (Board2,3,4) terminal emulator will appear on central device's (Board1) terminal emulator. Characters entered on central devices terminal emulator will appear on peripheral devices emulator in a round-robin fashion without priority. For example in order to send character “a” to all peripheral devices, “aaa” needs to be entered on terminal emulator of the central device

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\multilink\firmware\central_ml_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 UART 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 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. Initialization routine executed during program initialization can be found in the project files.

Header Files

• ble_gap.h: The header file contains BLE GAP functions and is automatically included in the app.c file.
• ble_trspc.h: The header file associated with APIs 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.

• 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 status 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 secs.

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
  // Filter Devices based of Address, for this example address checking only 2 bytes
  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 = 0x50;
      createConnParam_t.connParams.intervalMax = 0x50;
      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. BLE_GAP_EVT_DISCONNECTED event will be generated when a BLE connection is broken.

Connection and Disconnection Handlers

• 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

• In Multilink application, unique connection handler's will be generated for all the peripheral links

• The disconnect handle associated with the peer peripheral device needs to be removed from the conn_hdl list.

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

  

  // Global Variables
  uint8_t scanAddr[12]; // var to store ASCII address
  extern uint16_t conn_hdl[3];
  extern uint8_t no_of_links;
  
  // Connected Event
  SERCOM0_USART_Write((uint8_t *)"Connected!\r\n", 12);
  conn_hdl[no_of_links] = p_event->eventField.evtConnect.connHandle;
  no_of_links++;      
  
  // Disconnected Event
  SERCOM0_USART_Write((uint8_t *)"Disconnected\r\n", 15);
  uint16_t rmv_conn_hdl = p_event->eventField.evtDisconnect.connHandle;
  uint8_t i = 0;
  for(i = 0; i < no_of_links; i++)
  {
  	if (conn_hdl[i] == rmv_conn_hdl)
                  {
  		uint16_t tmp_hdl = conn_hdl[no_of_links-1];                    
  		conn_hdl[no_of_links-1] = conn_hdl[i];
  		conn_hdl[i] = tmp_hdl;
                  }
  }
  no_of_links--;
  

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", 18);

  

Transmit Data

• Add "APP_MSG_UART_CB" to the generated APP_MsgId_T

  
• 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[3] = {0xFFFF, 0xFFFF, 0xFFFF};// connection handle info captured @BLE_GAP_EVT_CONNECTED event
uint8_t no_of_links;// No of connected peripheral devices
uint8_t i = 0;// link index
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[i], 1, &uart_data);
    i++;
    if(i==no_of_links) i = 0; //reset link index    
}

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

  Note: BLE_TRSPC_Event_T p_event structure stores the information about BLE transparent UART callback functions.

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);