STMicroelectronics X-CUBE-BLE2 User Manual

UM2666

User manual

Getting started with the X-CUBE-BLE2 Bluetooth Low Energy software expansion for STM32Cube

Introduction

The X-CUBE-BLE2 expansion software package for STM32Cube runs on the STM32 and includes drivers for BlueNRG-2and BlueNRG-2N Bluetooth® low energy devices.

The expansion is built on STM32Cube software technology to ease portability across different STM32 microcontrollers.

The software comes with sample implementations of the drivers running on the X-NUCLEO-BNRG2A1 when connected to a NUCLEO-L476RG board.

Acronyms and abbreviations

1Acronyms and abbreviations

	Table 1. List of acronyms

Acronym	Description
ACI	Application controller interface

ATT	Attribute protocol

BLE	Bluetooth low energy

BSP	Board support package

BT	Bluetooth

GAP	Generic access profile

GATT	Generic attribute profile

GUI	Graphical user interface

HAL	Hardware abstraction layer

HCI	Host controller interface

IDE	Integrated development environment

L2CAP	Logical link control and adaptation protocol

LED	Light emitting diode

LL	Link layer

LPM	Low power manager

MCU	Micro controller unit

PCI	Profile command interface

PHY	Physical layer

SIG	Special interest group

SM	Security manager

SPI	Serial peripheral interface

UUID	Universally unique identifier

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X-CUBE-BLE2 software expansion for STM32Cube

2X-CUBE-BLE2 software expansion for STM32Cube

2.1Overview

The X-CUBE-BLE2 software package expands STM32Cube functionality and provides the Bluetooth Low Energy connectivity.

The key features are:

•Complete middleware to build Bluetooth® low energy applications using BlueNRG-2 and BlueNRG-2N devices

•Easy portability across different MCU families, thanks to STM32Cube

•Numerous examples to aid comprehension of Bluetooth connectivity applications

•Package compatible with STM32CubeMX, can be downloaded from and installed directly into STM32CubeMX

•Free, user-friendly license terms

2.1.1Bluetooth Low Energy

Bluetooth Low Energy is a wireless personal area network technology designed and marketed by Bluetooth SIG. It can be used to develop new innovative applications (fitness, security, healthcare, etc.) using devices which run on coin cell batteries, and can remain indefinetely operative without draining the battery.

2.1.1.1Operating modes

According to the Bluetooth standard specification (version 4.0 and above), Bluetooth Classic and Bluetooth Low Energy can be supported on the same device (dual-mode, also called Bluetooth smart ready).

Instead, a single-mode (Bluetooth smart) device supports the BLE protocol only.

2.1.1.2Software partitioning

A typical BLE system consists of :

•an LE controller, containing a physical layer (PHY) including the radio, a link layer (LL) and a standard host controller interface (HCI)

•a host, containing an HCI and other higher protocol layers (e.g. L2CAP, SM, ATT/GATT and GAP)

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Overview

Figure 1. BLE protocol stack

The host can send HCI commands to control the LE controller. The HCI interface and the HCI commands are standardized by the Bluetooth core specification (refer to the Bluetooth standard for further information).

The PHY layer ensures communication with the stack and data (bits) transmission over-the-air. BLE operates in the 2.4 GHz Industrial Scientific Medical (ISM) band and defines 40 radio frequency (RF) channels with 2 MHz channel spacing.

In BLE, when a device only needs to broadcast data, it transmits the data in advertising packets through the advertising channels. Any device that transmits advertising packets is called advertiser. Devices that aim only at receiving data through the advertising channels are called scanners. Bidirectional data communication between two devices requires them to connect to each other.

BLE defines two device roles at the link layer (LL) for a created connection: the master and the slave. These are the devices that act as initiator and advertiser during the connection creation, respectively.

The host controller interface (HCI) layer provides a standardized interface to enable communication between the host and controller. In BlueNRG-2 and BlueNRG-2N, this layer is implemented through the SPI hardware interface.

In BLE, the main goal of L2CAP is to multiplex the data of three higher layer protocols, ATT, SMP and link layer control signaling, on top of a link layer connection.

The SM layer is responsible for pairing and key distribution, and enables secure connection and data exchange with another device.

At the highest level of the core BLE stack, the GAP specifies device roles, modes and procedures for the discovery of devices and services, the management of connection establishment and security. In addition, GAP handles the initiation of security features. The BLE GAP defines four roles with specific requirements on the underlying controller: Broadcaster, Observer, Peripheral and Central.

The ATT protocol allows a device to expose certain pieces of data, known as attributes, to another device. The ATT defines the communication between two devices playing the roles of server and client, respectively, on top of a dedicated L2CAP channel. The server maintains a set of attributes. An attribute is a data structure that stores the information managed by the GATT, the protocol that operates on top of the ATT. The client or server role is determined by the GATT, and is independent of the slave or master role.

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STMicroelectronics X-CUBE-BLE2 User Manual

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Overview

The GATT defines a framework that uses the ATT for the discovery of services, and the exchange of characteristics from one device to another. GATT specifies the structure of profiles. In BLE, all pieces of data that are being used by a profile or service are called characteristics. A characteristic is a set of data which includes a value and properties.

2.1.1.3Profiles and services

The BLE protocol stack is used by the applications through its GAP and GATT profiles. The GAP profile is used to initialize the stack and setup the connection with other devices. The GATT profile is a way of specifying the transmission - sending and receiving - of short pieces of data known as attributes over a Bluetooth smart link.

All current Low Energy application profiles are based on GATT. The GATT profile allows the creation of profiles and services within these application profiles.

Figure 2. Structure of a GATT-based profile

In this example, the profile is created with the following services:

•GAP service, which has to be always set up

•health thermometer service

•device information service

Each service consists of a set of characteristics defining the service and the type of data it provides as part of the service. In the above example, the health thermometer service contains the following characteristics:

•temperature measurement

•temperature type

•intermediate temperature

•measurement interval

Each characteristic details the data type and value, and is defined by attributes (at least, two for characteristic): the main attribute (0x2803) and a value attribute that actually contains the data. The main attribute defines the value attribute handle and UUID.

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Architecture

2.1.1.4State machine

Figure 3. State machine during BLE operations

During normal operation, a BLE device can be in the following states:

•Standby: does not transmit or receive packets.

•Advertising: broadcasts advertisements in advertising channels. The device transmits advertising channel packets and possibly listens and answers to, triggered by the advertising channel packets.

•Scanning: looks for advertisers. The device is listening for advertising channel packets from advertising devices.

•Initiating: the device initiates connection to the advertiser and is listens to advertising channel packets from specific device(s) and responds to these packets to initiate a connection with another device.

•Connection: connection has been established and the device is transmitting or receiving:

–the initiator device plays the master role, that is, it communicates with the device in the slave role and defines timings of transmission;

–the advertiser device plays the slave role, that is, it communicates with a single device in the master role.

2.2Architecture

This software is a fully compliant expansion for STM32Cube enabling development of applications using the Bluetooth Low Energy connectivity.

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Folders

The software is based on the hardware abstraction layer for the STM32 microcontroller, STM32CubeHAL. The package extends STM32Cube by providing complete middleware for the Bluetooth Low Energy expansion board and several sample applications.

The software layers used by the application software to access the BlueNRG-M2SP module expansion board are:

•The STM32Cube HAL driver layer provides a simple, generic and multi-instance set of APIs (application programming interfaces) to interact with the upper layers (application, libraries and stacks). It includes generic and extension APIs and is based on a generic architecture which allows the layers built on it (such as the middleware layer) to implement their functionalities without dependence on the specific hardware configuration of a given Microcontroller Unit (MCU). This structure improves library code reusability and guarantees high portability across other devices.

•The Board Support Package (BSP) layer provides supporting software for the peripherals on the STM32 Nucleo board, except for the MCU. It has a set of APIs to provide a programming interface for certain boardspecific peripherals (e.g. the LED, the user button etc.) and allow identification of the specific board version.

Figure 4. X-CUBE-BLE2 software architecture

Application	Applications

	Middleware	BLE
	Hardware	STM32Cube Hardware Abstraction Layer (HAL)
	Abstraction	STM32Cube Hardware Abstraction Layer (HAL)
	Abstraction

STM32 Nucleo expansion boards

X-NUCLEO-BNRG2A1 (Connect)

Hardware

STM32 Nucleo development board

2.3Folders

Figure 5. X-CUBE-BLE2 package folder structure

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+ 15 hidden pages

UM2666 - Rev 2 - July 2020	www.st.com
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