4.1.1.5 BLE Transparent UART

Introduction

This document enables users create a central device and send/receive characters between 2 connected BLE devices over Microchip proprietary Transparent UART Profile. The central and peripheral devices in this tutorial are 2 WBZ351devices. The following instructions are applicable for a BLE Central device.

Users of this document can choose to just run the precompiled Application Example hex file on the WBZ351Curiosity board and experience the demo or can go through the steps involved in developing this application from scratch.

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

Hardware Requirement


Tool	Qty
WBZ351Curiosity Board	2
Micro USB cable	2

SDK Setup

Getting Started with Software Development

Software Requirement

TeraTerm

Smartphone App

None

Programming the precompiled hex file or Application Example

Programming the hex file using MPLABX IPE

Precompiled Hex file is located in "<Harmony Content Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\central\profiles_services\central_trp_uart\hex" folder
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 MPLABX IDE

Follow steps mentioned in of Running a Precompiled Example document
Open and program the Application Example "central_trp_uart.x" located in "<Harmony Content Path>\wireless_apps_pic32cxbz3_wbz35\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware" using MPLABX IDE

For more details on how to find the Harmony Content Path, refer to Installing the MCC Plugin

Demo Description

Upon programming the demo application, central device (WBZ351) 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 will print start of the scanning "Scanning",connected "Connected!" and disconnected "Disconnected" state on a terminal emulator like TeraTerm (Speed: 115200, Data: 8-bit, Parity: none, stop bits: 1 bit, 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 WBZ351 Curiosity Board configured as 4.1.2.6 BLE Transparent UART with External Flash OTA

Demo Experience when using 2 WBZ351Curiosity 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 2 WBZ351Curiosity Boards.

Board1 = WBZ351Curiosity Board with peripheral_trp_uart application Programmed

Board2 = WBZ351Curiosity Board with central_trp_uart applicaton Programmed

Board1: Open TeraTerm @ (Speed: 115200, Data: 8-bit, Parity: none, stop bits: 1 bit, Flow control: none). Reset the board. Upon reset, "Advertising" message is displayed on the TeraTerm.

Board 2: Open TeraTerm @ (Speed: 115200, Data: 8-bit, Parity: none, stop bits: 1 bit, Flow control: none). Reset the board. Upon reset, "Scanning" message is displayed on the TeraTerm. 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 (Board1) and central device(Board2) 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 either terminals will immediately be sent to the peer devices

Developing this Application from scratch using MPLAB Code Configurator

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

Note: It is recommended that new users of MPLAB Code Configurator go through the overview.

Create a new MPLAB MCC Harmony Project. For more details, refer to 3.4 Creating a New MCC Harmony Project
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_pic32cxbz3_wbz35\apps\ble\building_blocks\central\profiles_services\central_trp_uart\firmware\central_trp_uart.X".For more details on how to import the component configuration , refer to 13.3 Importing Existing App Example Configuration

Note: Import and Export functionality of component configuration will help users to start from a known working setup of configuration
Accept Dependencies or satisfiers, select Yes
Verify if the Project Graph window has all the expected configuration

Verifying Scan,Connection and Transparent Profile Configuration

Select BLE_Stack component in project graph
Select Transparent Profile component in project graph

Generating Code

For more details on code generation, refer to, 13.2 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

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

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.


Source Files	Usage
app.c	Application 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.c	All GAP, GATT, SMP and L2CAP Event handlers
app_ble\app_trspc_handler.c	All Transparent UART Client related Event handlers
ble_trspc.c	All 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 13.1 User Action
Figure 4-1. Start Scanning

BLE_GAP_SetScanningEnable(true, BLE_GAP_SCAN_FD_ENABLE, BLE_GAP_SCAN_MODE_OBSERVER, 1000);

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 Adverstisements 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);
  }

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

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;// 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();
       }                
  }

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);