NRF51822蓝牙低能耗应用入门：LED按钮服务示例

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本篇文档是Nordic Semiconductor发布的名为"电子-nRF51822创建一个简单的BLE例程英文版"的应用笔记，主要针对那些希望学习如何在nRF51822芯片上开发蓝牙低功耗（Bluetooth Low Energy, BLE）应用的人群。文档提供了入门级别的指导，强调了对嵌入式C编程的基本了解是必要的。首先，文档概述了BLE功能的一般概念，这是一种专为物联网和通信技术设计的2.4GHz无线通信技术，旨在提供低功耗、连接大量设备的能力，特别适合电池供电设备。nRF51822作为核心硬件，其功能强大且适合此类应用开发。文档的核心部分着重于实现一个简单的例子：LED Button Service。这包括创建自定义服务以及相应的数据交互。用户需要使用以下工具来完成此任务： 1. **nRF51822评估套件**：这是进行实验和原型开发的基础平台。 2. **S110 SoftDevice**：这是一个关键软件组件，提供了蓝牙低功耗协议栈和安全功能。 3. **nRFgo Studio**：一个集成开发环境，用于程序编译、调试和下载到nRF51822。 4. **nRF51 SDK**：软件开发工具包，包含必要的库和驱动，支持各种开发过程。 5. **Keil MDK-ARM**：用于编写和调试C代码的高级集成开发环境，适用于嵌入式系统开发。在实践中，开发者将学习如何设置开发环境，配置硬件，理解和使用S110 SoftDevice，编写服务和特性描述，处理GATT（Generic Attribute Profile）操作，以及调试和测试最终的BLE应用程序。通过这个简单示例，读者将建立起基本的BLE应用开发技能，并为后续更复杂的设计打下坚实基础。文档共分为35页，每一步都细致入微，确保初学者能够逐步掌握。因此，阅读和实践这份应用笔记对于想要进入或扩展蓝牙低功耗领域的人来说，是一项宝贵的资源。

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Creating Bluetooth low energy applications using nRF51822 v1.0

2.1.5 Connection

By definition the Central and Peripheral are in a connection from the first data exchange. When in a

connection, the Central will request data from the Peripheral at specifically defined intervals. This interval is

called the connection interval. It is decided and applied to the link by the Central, but a Peripheral can send

Connection Parameter Update Requests to the Central. The connection interval must be between 7.5 ms

and 4 s according to the Bluetooth Core Specification.

If the Peripheral doesn’t respond to packages from the Central within the time-frame called connection

supervision timeout, the link is considered lost.

It is possible to achieve higher data throughput by transmitting multiple packets in each connection

interval. Each packet transferred can be up to 20 bytes. However, if current consumption is important and a

Peripheral has no data to send, it can choose to ignore a certain number of intervals. The number of ignored

intervals is called the slave latency.

While in a connection, the devices will hop through all the channels in the frequency band, except for the

advertising channels, in a way that is completely transparent to the application.

2.2 Generic Attribute profile (GATT)

GATT is the layer where the data values are actually transferred.

2.2.1 Roles

In addition to the roles in GAP, BLE also defines two roles, a GATT Server and a GATT Client, that are

completely independent of the GAP roles. The concept is the device containing data is a Server, while the

one accessing it is a Client.

2.2.2 GATT hierarchy

A GATT Server organizes data in what is called an attribute table and it is the attributes that contain the

actual data.

Figure 2 GATT overview

For the LED Button example, the Peripheral device (with its LED and button) is in the role of

Server and the Central is in the role of Client.

0x0002

0x0001 SERVICE

Handle UUID Permissions Value

READ HRS

CHAR READ HRM

0x0003 HRM READ/NOTIF 80 bpm

0x0004 DESC READ NOTIFY

Service

Characteristic

Descriptor

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