使用RL-ARM为ARM微控制器构建应用的入门指南

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RL-ARM 是一款专为基于 ARM 处理器的微控制器设计的应用构建工具，它允许开发者在实时操作系统 (RTOS) 的支持下开发高效、实时的软件应用。本文档针对的是 Keil 公司提供的 Getting Started 指南，适用于使用 ARM 处理器的微控制器平台。该指南旨在引导用户快速上手 RL-ARM，并利用 Keil µVision（一个集成开发环境，IDE）以及 MDK-ARM（μVision 针对 ARM 设备的版本）来构建应用程序。文档强调，所有信息可能会根据需要不时更新，不构成制造商的承诺。使用软件必须遵守许可协议或非披露协议中的条款，未经授权不得复制或传输，除非在协议允许的情况下。用户可以为备份目的制作一份软件副本，但任何手册内容未经书面许可，均不得以任何形式或通过任何手段进行复制或传播，包括但不限于复印、录音或信息存储和检索系统，除非用于个人用途。值得注意的是，Keil、Keil Software Logo、μVision、MDK-ARM、RL-ARM、ULINK 和 Device Database 是 ARM Limited 和 ARM Germany GmbH 的商标或注册商标，而 Microsoft® 和 Windows™ 则是 Microsoft 公司的商标。这表明在使用这些工具时，应尊重知识产权，并确保遵循相关的法律要求。在实际操作中，Getting Started 指南将覆盖以下关键知识点： 1. **平台兼容性**：明确指出哪些型号的 ARM 处理器和微控制器与 RL-ARM 和 Keil µVision 集成良好，确保选择正确的开发环境。 2. **安装和配置**：指导用户如何下载、安装和配置 RL-ARM，以及如何设置开发环境，包括所需的 SDK、库和驱动程序。 3. **项目创建**：演示如何使用 MDK-ARM 创建新项目，设置工程类型、硬件设备和编译选项。 4. **编程语言支持**：介绍支持的编程语言，如 C 和 C++，以及可能的嵌入式汇编语言，以及如何编写和调试代码。 5. **RTOS集成**：讲解如何在实时操作系统（如 RTX Kernel）环境中工作，包括任务调度、中断管理、内存管理和同步机制。 6. **调试和测试**：提供调试工具的使用方法，如 ULink 接口，以及如何进行单元测试和系统级测试。 7. **性能优化**：分享如何优化代码以提高处理速度和内存效率，以及如何处理低功耗和资源受限的环境。 8. **安全和质量保证**：讨论如何遵循最佳实践，确保软件的安全性和可靠性，如代码审查和静态分析。 9. **许可证和法律注意事项**：再次强调使用软件时的法律义务，确保用户了解并遵守相关规定。通过阅读这份 Getting Started 指南，开发者将能够充分利用 RL-ARM 和 Keil µVision 这些强大的工具，为他们的 ARM 微控制器项目实现高效的软件开发流程。

16 Chapter 2. Developing With an RTOS

Chapter 2. Developing With an RTOS

In the course of this chapter we will consider the idea of using RTX, the Keil

small footprint RTOS, on an ARM processor-based microcontroller. If you are

used to writing procedural-based C code on microcontrollers, you may doubt the

need for such an operating system. If you are not familiar with using an RTOS in

real-time embedded systems, you should read this chapter before dismissing the

idea. The use of an RTOS represents a more sophisticated design approach,

inherently fostering structured code development, which is enforced by the

RTOS Application Programming Interface (API).

The RTOS structure allows you to take an object-orientated design approach

while still programming in C. The RTOS also provides you with multithreaded

support on a small microcontroller. These two features create a shift in design

philosophy, moving us away from thinking about procedural C code and flow

charts. Instead, we consider the fundamental program tasks and the flow of data

between them. The use of an RTOS also has several additional benefits, which

may not be immediately obvious. Since an RTOS-based project is composed of

well-defined tasks, using an RTOS helps to improve project management, code

reuse, and software testing.

The tradeoff for this is that an RTOS has additional memory requirements and

increased interrupt latency. Typically, RTX requires between 500 Bytes and

5KBytes of RAM and 5KBytes of code, but remember that some of the RTOS

code would be replicated in your program anyway. We now have a generation of

small, low-cost microcontrollers that have enough on-chip memory and

processing power to support the use of an RTOS. Developing using this

approach is therefore much more accessible.

Getting Started

This chapter first looks at setting up an introductory RTOS project for ARM7,

ARM9, and Cortex-M based microcontrollers. Next, we will go through each of

the RTOS primitives and explain how they influence the design of our

application code. Finally, when we have a clear understanding of the RTOS

features, we will take a closer look at the RTOS configuration file.

20 Chapter 2. Developing With an RTOS

not to add the function entry and exit code. This code would normally manage

the native stack. Since the RTX scheduler handles this function, we can safely

remove this code. This saves both code and data memory and increases the

overall performance of the final application.

An RTOS-based program is made up of a number of tasks, which are controlled

by the RTOS scheduler. This scheduler is essentially a timer interrupt that allots

a certain amount of execution time to each task. So task1 may run for 100ms

then be de-scheduled to allow task2 to run for a similar period; task 2 will give

way to task3, and finally control passes back to task1. By allocating these slices

of runtime to each task in a round-robin fashion, we get the appearance of all

three tasks running in parallel to each other.

Conceptually we can think of each task as performing a specific functional unit

of our program, with all tasks running simultaneously. This leads us to a more

object-orientated design, where each functional block can be coded and tested in

isolation and then integrated into a fully running program. This not only imposes

a structure on the design of our final application but also aids debugging, as a

particular bug can be easily isolated to a specific task. It also aids code reuse in

later projects. When a task is created, it is allocated its own task ID. This is a

variable, which acts as a handle for each task and is used when we want to

manage the activity of the task.

OS_TID id1, id2, id3;

Task Control Block Task Stack

Priority & State Context

Task

In order to make the task-switching process happen, we have the code overhead

of the RTOS and we have to dedicate a CPU hardware timer to provide the

RTOS time reference. For ARM7 and ARM9 this must be a timer provided by

the microcontroller peripherals. In a Cortex-M microcontroller, RTX will use the

SysTick timer within the Cortex-M processor. Each time we switch running

tasks the RTOS saves the state of all the task variables to a task stack and stores

the runtime information about a

task in a Task Control Block. The

“context switch time”, that is, the

time to save the current task state

and load up and start the next task,

is a crucial value and will depend

on both the RTOS kernel and the

design of the underlying hardware.

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使用RL-ARM为ARM微控制器构建应用的入门指南

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