3.1.1.5 BLE Transparent UART

Getting Started

Getting Started with Central Building Blocks

BLE Connection

Introduction

This section enables users create a central device and send/receive characters between two connected BLE devices over Microchip proprietary Transparent UART Profile. The central and peripheral devices in this tutorial are two WBZ451 devices. The following instructions are applicable for a BLE Central device.

Users can choose to run the precompiled application example .hex file on the WBZ451 Curiosity Board and experience the demo or go through the steps involved in developing this application from scratch.

Recommendation is to follow the examples in order, by learning the basic concepts first and then progressing to the more advanced topics.

Recommended Reading

  1. BLE Software Specification

  2. BLE Connection(central)

Hardware Requirement

Table 3-7. Hardware Requirement
Tool Qty
WBZ451 Curiosity Board2
Micro USB cable2

SDK Setup

Software Requirement

Smart phone App

None

Programming the Precompiled Hex File or Application Example

Programming the .hex File using MPLAB X IPE

  1. Central Device – Precompiled .hex file is located in "<Harmony Content Path>\wireless_apps_pic32cxbz2_wbz45\apps\ble\building_blocks\central\profiles_services\central_trp_uart\hex" folder
  2. Peripheral Device – Precompiled .hex file is located in "<Harmony Content Path>\wireless_apps_pic32cxbz2_wbz45\apps\ble\building_blocks\Peripheral\profiles_services\peripheral_trp_uart\hex" folder
  3. For more details on the steps, go to Programming A Device
Note: Users must choose the correct Device and Tool information

Programming the Application using MPLAB X IDE

  1. Follow steps mentioned in the Running a Precompiled Example section.
  2. Central Device – Open and program the application example "central_trp_uart.X" located in "<Harmony Content Path>\wireless_apps_pic32cxbz2_wbz45\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware" using MPLAB X IDE
  3. Peripheral Device – Open and program the application example "peripheral_trp_uart.X" located in "<Harmony Content Path>\wireless_apps_pic32cxbz2_wbz45\apps\ble\building_blocks\peripheral\profiles_services\peripheral_trp_uart\firmware" using MPLAB X IDE

For more details on finding the Harmony content path, refer to Installing the MCC Plugin

Demo Description

Upon programming the demo application, central device (WBZ451) 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.

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

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

Testing

Users must use another WBZ451 Curiosity Board configured as BLE Transparent UART (Peripheral).

Experience the Demo using two WBZ451 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 WBZ451 Curiosity Boards.

  1. Board 1 – WBZ451 Curiosity Board Programmed with “peripheral_trp_uart”
    1. Open TeraTerm and configure as mentioned below:
      Terminal Settings
      • Baud Rate/Speed – 921600 (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

      Figure 3-39. Tera Term Settings
    2. Reset the board, Upon reset, "Advertising" message is displayed on the Tera Term.
  2. Board 2 – WBZ451 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".
Note: Scanner is configured to scan only for 100 seconds. The user must ensure the peer device is advertising
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
Figure 3-40. Tera Term Logs

Developing this Application from Scratch using MCC

This section explains the steps required by a user to develop this application example from scratch using MCC

Note: It is recommended that new users of MCC to go through the overview.

  1. Create a new MPLAB MCC Harmony Project. For more details, refer to Creating a New MCC Harmony Project

  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_pic32cxbz2_wbz45\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware\central_trp_uart.X".
    For more details on importing the component configuration , refer to Importing Existing App Example Configuration
    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, select Yes
  4. Verify if the project graph window has all the expected configuration. as illustrated in the following figure:
    Figure 3-41. Project Graph

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.

    Figure 3-42. BLE Stack Configuration

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

    Figure 3-43. Transparent Profile Configuration

Generating Code

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

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
Figure 3-44. Project File
The OSAL, RF System, BLE System initialization routine executed during program initialization can be found in the project files. This initialization routine is automatically generated by the MCC
Figure 3-45. initialization.c
The BLE stack initialization routine executed during Application Initialization can be found in project files. This initialization routine is automatically generated by the MCC. This call initializes and configures the GAP, GATT, SMP, L2CAP and BLE middleware layers.
Figure 3-46. app_ble.c
Table 3-8. Source Files
Source Files Usage
app.cApplication State machine, includes calls for Initialization of all BLE stack (GAP,GATT, SMP, 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.cAll GAP, GATT, SMP and L2CAP Event handlers
app_ble\app_trspc_handler.cAll Transparent UART Client related Event handlers
ble_trspc.cAll Transparent Client Functions for user application
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

  • 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

  • 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.
  • User action is required as mentioned User Action
    Figure 3-47. 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 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)
  {
      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);
  }
Figure 3-48. app_ble_handler.c

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);
    Figure 3-49. 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", 18);
Figure 3-50. Scan Timeout Event

Transmit Data

  • Add APP_MSG_UART_CB to the generated APP_MsgId_T in app.h
    Figure 3-51. Transmit Data
  • 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_BLE_STACK_LOG)
     {
     // Pass BLE LOG Event Message to User Application for handling
     APP_BleStackLogHandler((BT_SYS_LogEvent_T *)p_appMsg->msgData);
      }
      else if(p_appMsg->msgId==APP_MSG_UART_CB)
      {
       // Transparent UART Client Data transfer Event
       APP_UartCBHandler();
       }                
  }
Figure 3-52. app.c
Figure 3-53. app.c
Figure 3-54. app.c

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);
Figure 3-55. app_trspc_handler.c

For more details on exercising various other BLE functionalities refer to, BLE Stack API section.

For more details, refer to BLE Multilink Transparent UART section.