3.1.2.6 BLE Transparent UART

Introduction

This section will help users create a peripheral device and send/receive characters between 2 connected BLE devices over Microchip proprietary Transparent UART Profile. Peripheral device will be WBZ451 Device and Central device can either be a Smartphone with Light Blue App or another WBZ451 Device. The instructions mentioned below are applicable for a BLE Peripheral device.

Users can choose to just run the precompiled Application Example hex file on the WBZ451 Curiosity 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
WBZ451 Curiosity Board	1
Micro USB cable	1

SDK Setup

Getting Started with Software Development

Software Requirement

TeraTerm

Smartphone App

Light Blue

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_pic32cxbz2_wbz45\apps\ble\building_blocks\peripheral\profiles_services\peripheral_trp_uart\hex" folder
Follow the steps mentioned here

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 "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 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, WBZ451 will start Advertising (connectable), central device (Smartphone or another WBZ451) scanning for these advertisements will connect to the device. In case of using Light Blue App search for “Microchip” and 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 advertisement “Advertising”, connection “BLE Scanning”, “Connected” and “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 central device (Smartphone or another WBZ451) should be entered in the terminal emulator.

Testing

This section assumes that user has programmed the Application Example on the WBZ451 Curiosity Board Demo Experience when using a Smartphone (Light Blue App) as Central Device

Reset the WBZ451 Curiosity board, Open Terminal emulator like Tera Term, select the right COM port@ (Speed: 115200, Data: 8-bit, Parity: none, stop bits: 1 bit, Flow control: none).
Open Light Blue App on your smartphone, Search and select the advertisement with Device Name "Microchip"
To receive data from WBZ451 Curiosity Board (peripheral) device to central device, users need to select the UUID: 49535343-1E4D-4BD9-BA61-23C647249616 and select listen for notifications
Enter "test" on Teraterm and data should be displayed on Light Blue App
To send data from central device to WBZ451 Curiosity Board (peripheral), users need to select the UUID: 49535343-8841-43F4-A8D4-ECBE34729BB3 and select write new value
Enter trp uart on App and data must be displayed on Terminal Window

Demo Experience when using another WBZ451 as Central device. Users can use another WBZ451 Curiosity Board configured as BLE Transparent UART(central) instead of using a Smartphone App as the central device.

Developing the Application from Scratch using the MPLAB Code Configurator

This section explains the steps required 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 MCC Harmony Project. For more details on how to create a new MCC Harmony Project, refer to 2.5 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_pic32cxbz2_wbz45\apps\ble\building_blocks\peripheral\profiles_services\peripheral_trp_uart\firmware\peripheral_trp_uart.X". Users should follow the instructions mentioned here to import the component configuration.
Accept Dependencies or satisfiers, select Yes
Verify if the Project Graph window has all the expected configuration

Note: Make sure that the macro "configUSE_TICKLESS_IDLE" is set to 0. The macro is available in FreeRTOSConfig.h file

#define configUSE_TICKLESS_IDLE 0

Verifying Advertisement,Connection and Transparent UART Profile Configuration

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

Generating a Code

For instructions on generating a code, refer to 14.2 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.

Autogenerated, advertisement data format


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_trsps_handler.c	All Transparent UART Server related Event handlers
ble_trsps.c	All Transparent Server 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_trsps.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_trsps.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 Tip: definitions.h is not specific to just UART peripheral, instead it should be included in all application source files where peripheral functionality will be exercised
User action is required as mentioned 14.1 User Action

Set PUBLIC Device Address

BLE_GAP_SetDeviceAddr(&devAddr);

    BLE_GAP_Addr_T devAddr;
    devAddr.addrType = BLE_GAP_ADDR_TYPE_PUBLIC;
    devAddr.addr[0] = 0xA1;
    devAddr.addr[1] = 0xA2;
    devAddr.addr[2] = 0xA3;
    devAddr.addr[3] = 0xA4;
    devAddr.addr[4] = 0xA5;
    devAddr.addr[5] = 0xA6;

    // Configure device address
    BLE_GAP_SetDeviceAddr(&devAddr);

Starting Advertisement

BLE_GAP_SetAdvEnable(0x01, 0);

Connected & 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_TRSPS_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_TRSPS_SendData() API

uint16_t conn_hdl;// connection handle info captured @BLE_GAP_EVT_CONNECTED event
uint16_t ret;
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_TRSPS_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);

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)
{
   // Pass BLE UART Data transmission target BLE UART Device handling
   APP_UartCBHandler();
}

Receive Data

BLE_TRSPS_EVT_RECEIVE_DATA is the event generated when data is sent from central device
Use the BLE_TRSPS_GetDataLength(p_event->eventField.onReceiveData.connHandle, &data_len; API to extract the length of application data received
BLE_TRSPS_GetData(p_event->eventField.onReceiveData.connHandle, data); API is used to retrieve the data

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

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

  /* TODO: implement your application code.*/
  uint16_t data_len;
  uint8_t *data;
  // Retrieve received data length
  BLE_TRSPS_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_TRSPS_GetData(p_event->eventField.onReceiveData.connHandle, data);
  // Output received data to UART
  SERCOM0_USART_Write(data, data_len);
  // Free memory
  OSAL_Free(data);