CC2540/41蓝牙低功耗开发指南：软件与平台详解

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《电子-CC2540/41蓝牙低功耗软件开发者指南》是一份由 Texas Instruments (TI) 出版的文档，版权日期为2010年至2013年，适用于 CC2540/41系列芯片。这份指南主要聚焦于蓝牙低功耗 (Bluetooth Low Energy, BLE) 的软件开发，是针对物联网和通信技术中蓝牙通信的专业参考。该文档首先介绍了蓝牙低功耗协议栈的基本概念，强调了在设计和开发过程中理解这些核心组件的重要性。蓝牙低功耗协议栈包括几个关键部分： 1. **操作系统抽象层 (OSAL)**: OSAL 是软件开发平台的基础，它负责任务初始化、事件管理和处理，以及内存管理。OSAL 提供了统一的接口，使得开发者可以专注于应用逻辑，而无需过多关注底层硬件细节。 2. **硬件抽象层 (HAL)**: HAL 是连接 OSAL 和实际硬件的桥梁，它封装了对 CC2540/41芯片的驱动程序，使得开发者能够轻松地与蓝牙功能进行交互。 3. **蓝牙协议栈**: - **通用访问 profile (GAP)**: GAP 主要处理设备的配对、连接和断开过程，是任何蓝牙低功耗设备的基本组成部分。 - **通用属性 profile (GATT)**: GATT 负责数据存储和检索，支持设备之间的服务发现和属性交换，是实现物联网设备间通信的关键。 4. **软件架构中的应用接口**: - **GATT服务器应用程序API**: 提供了创建和管理服务、特性以及值的方法，以便开发人员可以构建具有特定功能的应用。 - **库文件**: 文档还列出了可供使用的库文件，这些文件包含了蓝牙协议栈的具体实现和配置。 5. **应用示例与角色**: - **GAP角色**: - ** peripheral (设备) **: 设备模式下，设备提供服务并监听连接请求。 - **peripheral/broadcaster (多角色) **: 这种设备同时可以广播其服务信息和接收连接请求。 - **central (中央) **: 中央设备用于寻找、连接和控制其他蓝牙设备。这份指南详细阐述了如何在CC2540/41平台上实现这些功能，并为开发者提供了清晰的开发路径和指导，有助于快速上手并构建高效、兼容的蓝牙低功耗应用。对于那些从事物联网项目，特别是希望通过蓝牙技术实现设备互联的工程师来说，这是一份不可或缺的参考资料。

TI CC254x Bluetooth Low Energy Software Developer’s Guide SWRU271D Version 1.3.1

Note: The OSAL is capable of providing many more services than are covered in this guide,

including message management, timer management, and more; however for many applications

this level of depth is not required. This guide should serve as an introduction to the basic

framework of the OSAL.

Additional information on the OSAL can be found in [1]:

3.1.1 Task Initialization

In order to use the OSAL, at the end of the main function there should be a call to

osal_start_system. This is the OSAL routine that starts the system, and which will call the

osalInitTasks function that is defined by the application. In the SimpleBLEPeripheral project, this

function can be found in the file OSAL_SimpleBLEPeripheral.c.

Each layer of software that is using the OSAL must have an initialization routine that is called from

the function osalInitTasks. Within this function, the initialization routine for every layer of software

is called. As each task initialization routine is called, an 8-bit “task ID” value is assigned to the

task. Note that when creating an application, it is very important that it be added to the end of the

list, such that it has a higher task ID than the others. This is because the priority of tasks is

determined by the task ID, with a lower value meaning higher priority. It is important that the

protocol stack tasks have the highest priority in order to function properly. Such is the case with

the SimpleBLEPeripheral application: its initialization function is SimpleBLEPeripheral_Init, and

it has the highest task ID and therefore the lowest priority.

3.1.2 Task Events and Event Processing

After the OSAL completes initialization, it runs the executive loop checking for task events. This

loop can be found in the function osal_start_system in the file OSAL.c. Task events are

implemented as a 16-bit variable (one for each task) where each bit corresponds to a unique

event. The definition and use of these event flags is completely up to the application.

For example, the SimpleBLEPeripheral application defines a flag in simpleBLEPeripheral.h:

SBP_START_DEVICE_EVT (0x0001), which indicates that the initial start has completed, and

the application should begin. The only flag value which is reserved and cannot be defined by the

application is 0x8000, which corresponds to the event SYS_EVENT_MSG (this event is used for

messaging between tasks, which is covered in section 3.1.3).

When the OSAL detects an event for a task, it will call that task’s event processing routine. The

layer must add its event processing routine to the table formed by the array of function pointers

called tasksArr (located in OSAL_SimpleBLEPeripheral.c in the example). You will notice that

the order of the event processing routines in tasksArr is identical to the order of task ID’s in the

osalInitTasks function. This is required in order for events to be processed by the correct

software layer.

In the case of the SimpleBLEPeripheral application, the function is called

SimpleBLEPeripheral_ProcessEvent. Note that once the event is handled and if it is not

removed from the event flag, the OSAL will continue to call the task’s process event handler. As

can be seen in the SimpleBLEPeripheral application function

SimpleBLEPeripheral_ProcessEvent, after the START_DEVICE_EVT event occurs, it returns

the 16-bit events variable with the SBP_START_DEVICE_EVT flag cleared.

It is possible for any layer of the software to set an OSAL event for any other layer, as well as for

itself. The simplest way to set up an OSAL event is to use the osal_set_event function (prototype

in OSAL.h), which immediately schedules a new event. With this function, you specify the task ID

(of the task that will be processing the event) and the event flag as parameters.

Another way to set an OSAL event for any layer is to use the osal_start_timerEx function

(prototype in OSAL_Timers.h). This function operates just like the osal_set_event function. You

select task ID of the task that will be processing the event and the event flag as parameters;

however for a third parameter in osal_start_timerEx you input a timeout value in milliseconds.

The OSAL will set a timer, and the specified event will not get set until the timer expires.

3.1.3 Heap Manager

TI CC254x Bluetooth Low Energy Software Developer’s Guide SWRU271D Version 1.3.1

OSAL provides basic memory management functions. The osal_mem_alloc function serves as a

basic memory allocation function similar to the standard C malloc function, taking a single

parameter determining the number of bytes to allocate, and returning a void pointer. If no memory

is available, a NULL pointer will be returned. Similarly, the osal_mem_free function works similar

to the standard C free function, freeing up memory that was previously allocated using

osal_mem_alloc.

The pre-processor define INT_HEAP_LEN is used to reserve memory for dynamic allocation.

To see how much memory you typically need, you can set the pre-processor define

OSALMEM_METRICS=TRUE in the project options. After a stress test of the application where

you send as many messages, have as many clients as you will in the worst case, remembering to

use bonding and encryption during the test if that’s applicable, you can look at the value of the

variable memMax in OSAL_Memory.c to see how much memory was ever allocated at the same

time. This figure could be used as a guideline for lowering INT_HEAP_LEN if necessary, but

thorough testing is needed, as the heap is used by the BLE stack.

3.1.4 OSAL Messages

OSAL also provides a system for different subsystems of the software to communicate with each

other by sending or receiving messages. Messages can contain any type of data and can be any

size. To send an OSAL message, first the memory must be allocated by calling the

osal_msg_allocate function, passing in the length of the message as the only parameter. A

pointer to a buffer containing the allocated space will be returned (you do not need to use

osal_mem_alloc when using osal_msg_allocate). If no memory is available, a NULL pointer will

be returned. You can then copy the data into the buffer. To send the message, the

osal_msg_send should be called, with the destination task for the message indicated as a

parameter.

The OSAL will then signal the receiving task that a message is arriving by setting the

SYS_EVENT_MSG flag for that task. This causes the receiving task’s event handler function to

be called. The receiving task can then retrieve the data by calling osal_msg_receive, and can

process accordingly based on the data received. It is recommended that every OSAL task have a

local message processing function (the simpleBLEPeripheral application’s message processing

function is simpleBLEPeripheral_ProcessOSALMsg) that decides what action to take based on

the type of message received. Once the receiving task has completed processing the message, it

must deallocate the memory using the function osal_msg_deallocate (you do not need to use

osal_mem_free when using osal_msg_deallocate).

3.2 Hardware Abstraction Layer (HAL)

The Hardware Abstraction Layer (HAL) of the CC2540/41 software provides an interface of

abstraction between the physical hardware to and the application and protocol stack. This allows

for the development of new hardware (such as a new PCB) without making changes to the

protocol stack or application source code. The HAL includes software for the SPI and UART

communication interfaces, ADC, keys, and LED’s etc. The HAL drivers that are provided support

the following hardware platforms:

• SmartRF05EB + CC2540EM

• SmartRF05EB + CC2541EM

• CC2540 Keyfob

• CC2541 Keyfob

• CC2541 SensorTag

• CC2540 USB Dongle

When developing with a different hardware platform, it might be necessary to modify the HAL

source for compatibility.

More information on the HAL API can be found in [2].

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