Bluetooth Low Energy Introduction

1. Introduction

Bluetooth low energy, also known as BLE (Bluetooth), is presented in the 4.0 specification

BLE is divided into two types of devices

-Singlemode (Single-mode): Logo for "bluetooth? smart"-Dual Mode (Dual-mode):   logo for"bluetooth? Smart ready"

Tip: The traditional Bluetooth logo is "bluetooth?"

BLE is compatible with traditional Bluetooth as shown

It can be seen that the rules of communication between them are as follows (Bluetooth refers to traditional Bluetooth, below):

Smart Ready:smart ready, Bluetooth, Smartbluetooth:   Smart Ready, Bluetoothsmart:       Smart Ready, Smart

2. Protocol stack

BLE protocol stack as shown

BLE protocol stack consists of controller and host two parts
Profile and service based on Gap and GATT
The application protocol defines the service it uses, whether it is the sensor end or the receiving end
Define the role of GATT (Server/client) and the role of Gap (Peripheral/central)

In a single-chip scenario, the controller and host, profile, and application are all in the same chip
In Network controller mode, controller and host run on the device, but profile and application on other devices, such as PC or other microcontroller, can be operated via UART, USB
In dual-chip mode, the controller is running on one of the controllers, while host, profile, and application are running on the other controller

The 1-phy:1mbps adaptive frequency hopping GFSK operates in the 2.4GHz band.
2-LL:RF controller, control device in preparation (standby), broadcast (advertising), listening/scanning (scanning), initialization (initiating), connection (connected) One of the 5 states
3-HCI: For the interface layer, the host to provide software application interface (API), external hardware control interface, can be through the serial port, SPI, USB to achieve device control
4-L2CAP: Provides data encapsulation services for the upper layer, allowing logical end-to-end datacom
5-SM: Provides pairing and key distribution services for secure connectivity and data exchange
6-GAP: An interface that communicates directly with an application or configuration file (Profiles), handling device discovery and connection-related services. Also handles initialization of security features
7-att: Export specific data (called attributes) to other devices
8-gatt: Defines the structure of the service framework and configuration files (profiles) that use Att. All data communications in BLE are subject to the GATT

3. Link Layer (LL) 3.1 Link state machine link layer operations can be described as link state machines
The link state machine has the following five kinds of states

-Standby state: Prepare, not transmit or receive packets-advertising state: Broadcast, advertiser, send advertising channel packets, accept response from Scanner-Scann ING State: monitor/scan, scanner, monitor advertising channel packets-initiating State from Advertiser: Initialize, initiator, listen for ADV from special device Ertising channel packets and initializing connection-Connection state: Connection, two roles: Master role (from initiator entry)/slave role (from Advertiser)

Link state machine only allowed in one of five states
The link layer can have multiple link state machines, but at least one of the advertising/scanning states is supported

A device in master role can communicate with multiple slave role ticks
Devices in slave role can only communicate with devices that are in master role

Shows the combination of allowed and forbidden link state machines and roles

3.2-bit sequence (bit ordering)

In the link layer specification, the PDU bit sequence is specified as little Endian format

3.3 Device Address

The device address can be a public address or a random address, with a length of

-Public Address: 48-bit Universal LAN MAC addresses with IEEE 802-2001 standard

-Random Address: Detailed requirements can be referenced in the specification

3.4 Physical channel (physical channel)

The BLE RF channel is defined as two kinds: advertising and data

-Advertising channel: Use 3 RF channels to discover the device, initialize the connection and broadcast the data-the database channel:        use up to 37 RF channels for communication between two connected devices

The corresponding relationship between the RF channel and the Advertising/data Channel index

Bluetooth Low Energy Introduction