Development boards and associated software project examples provided by microcontroller manufacturers are often of great help to engineers when starting a new design. However, after the early stages of a design project are completed, the software provided by the manufacturer may cause some problems when designing further.
There are also many challenges for the design of using a real-time operating system as a platform for application code. For example, there are issues such as how to effectively allocate functions to different parallel tasks, how to design reliable inter-process communication, and how to test the entire software package on hardware.
More and more OEM manufacturers have found that the best way to avoid the above problems is to start new designs using a Linux operating system based on open source, proven, scalable, and able to run on various hardware platforms. The number of Linux operating system transplants on various computer hardware platforms is also second to none.
Linux derivatives are already used in a wide variety of embedded systems, including network routers, mobile phones, building automation controls, televisions, and video game consoles.
Although Linux is widely used and successful, this does not mean that it is easy to use. Linux contains over a million lines of code and operates in a distinctly "Linux way" that may take some getting used to for beginners.
Therefore, the purpose of this article is to help start a new design project using the Linux embedded operating system version-μClinux. This guide will be broken down into five steps. To illustrate the guide, a μClinux project implemented on STMicroelectronics' STM32F429 microcontroller, which uses an ARM Cortex-M4 core with a maximum frequency of 180MHz and uses Emcraft's STM32F429 Discovery Linux Board Support Package (BSP ).
Step 1: Linux Tools and Project Layout
Every embedded software design starts with choosing the right tools.
The tool chain is a set of software development tools that are connected (or linked) together. It includes tools such as the GNU Compiler Collection (GCC), binutils (a set of linkers, assemblers, and other tools for object files and archives). development tools) and glibc (a C function library that provides system calls and basic functions); in some cases, other tools such as compilers and debuggers may also be included.
The tool chain used for embedded development is a cross tool chain, more commonly known as a cross compiler.
GNUBinutils is the first component of the embedded Linux tool chain. GNUBinutils contains two important tools:
●"as", assembler, converts assembly code (generated by GCC) into binary code
●"ld", connector, connects discrete target code segments to libraries or form executable files
The compiler is the second important component of the tool chain. In Embedded Linux, it is called GCC and supports many kinds of microcontroller and processor architectures.
Next is the C function library. It implements Linux's traditional POSIX application programming interface (API), which can be used to develop user-space applications. It interfaces with the kernel through system calls and provides high-level services.
Engineers have several C function library options:
●glibc is an available C function library provided by the open source GNU project. The library is full-featured, portable and compliant with Linux standards.
●Embedded GLIBC (EGLIBC) is a derivative version optimized for embedded systems. Its code is streamlined, supports cross-compilation and cross-testing, and its source code and binary code are compatible with GLIBC.
●uClibc is another C function library that can be used when flash space is limited and/or the memory footprint must be minimal.
The debugger is usually also part of the tool chain, because when debugging the application running on the target machine, a cross-debugger is required. In the field of embedded Linux, GDB is a commonly used debugger.
The above tools are so indispensable, but when they work independently, it will take too long to compile the Linux source code and integrate it into the final image (image). Fortunately, Buildroot automates the process of building a complete embedded system and simplifies cross-compilation by generating any or all of the following tasks:
●Cross-compilation tool chain
●Root file system
●Kernel image
●Boot image
For embedded system designers, it is also convenient to use a tool (utility) aggregation tool, such as BusyBox, which integrates the tools that are usually most needed. According to BusyBox's information page, "It combines tiny versions of many common UNIX tools into a small executable. It provides an alternative to most of the tools you would typically see in tools like GNU fileutils and shellutils. BusyBox The tools in BusyBox are generally less selective than their full-featured GNU counterparts; but the included options provide expected functionality and behavior that is almost identical to that provided by the GNU counterpart. For any small or embedded system, BusyBox provides The environment is quite complete.”
The last important tool is a BSP, which is specially made for the motherboard equipped with the project target MCU or processor.
The BSP includes pre-configured tools, as well as a bootloader to load the operating system onto the motherboard. It also provides source code for the kernel and device drivers (see Figure 1).

Step 2: Boot Sequence, Clock System, Memory and Serial Interface
The typical embedded Linux startup sequence is as follows:
1) The bootloader firmware (U-Boot in the example project) runs in the target MCU's built-in flash memory (no external memory required), and after power-on/reset, performs all necessary initialization work, including setting up the serial port and using Memory controller for external memory (RAM) access.
2) U-Boot can transfer the Linux image from external Flash to external RAM and transfer control to the kernel entry point in RAM. Linux images can be compressed to save flash space at the expense of decompression time at boot time.
3) Linux boots and installs a RAM-based file system (initramfs) as the root file system. When the project is built, the Initramfs is populated with the required files and directories and then simply linked to the kernel.
4) Under the Linux kernel, execute /sbin/init. The /sbin/init program initializes the system according to the description of the configuration file in /etc/inittab.
5) Once the initialization process completes run-level execution and commands in /sbin/init, it starts a login process.
6) The execution of the shell initialization file /etc/profile marks the completion of the startup process.
You can significantly shorten startup time and improve overall performance by enabling in-place execution (ExecuteInPlace—XIP), which is a method of executing code from flash memory. Typically, Linux code is loaded from flash memory to external memory and then executed from the external memory. By executing from flash memory, less memory is required because this copying step is no longer required, and read-only memory no longer takes up program space.
The above is the detailed content of Several steps for embedded Linux project development. For more information, please follow other related articles on the PHP Chinese website!

linux设备节点是应用程序和设备驱动程序沟通的一个桥梁;设备节点被创建在“/dev”,是连接内核与用户层的枢纽,相当于硬盘的inode一样的东西,记录了硬件设备的位置和信息。设备节点使用户可以与内核进行硬件的沟通,读写设备以及其他的操作。

区别:1、open是UNIX系统调用函数,而fopen是ANSIC标准中的C语言库函数;2、open的移植性没fopen好;3、fopen只能操纵普通正规文件,而open可以操作普通文件、网络套接字等;4、open无缓冲,fopen有缓冲。

端口映射又称端口转发,是指将外部主机的IP地址的端口映射到Intranet中的一台计算机,当用户访问外网IP的这个端口时,服务器自动将请求映射到对应局域网内部的机器上;可以通过使用动态或固定的公共网络IP路由ADSL宽带路由器来实现。

在linux中,交叉编译是指在一个平台上生成另一个平台上的可执行代码,即编译源代码的平台和执行源代码编译后程序的平台是两个不同的平台。使用交叉编译的原因:1、目标系统没有能力在其上进行本地编译;2、有能力进行源代码编译的平台与目标平台不同。

在linux中,eof是自定义终止符,是“END Of File”的缩写;因为是自定义的终止符,所以eof就不是固定的,可以随意的设置别名,linux中按“ctrl+d”就代表eof,eof一般会配合cat命令用于多行文本输出,指文件末尾。

在linux中,可以利用“rpm -qa pcre”命令判断pcre是否安装;rpm命令专门用于管理各项套件,使用该命令后,若结果中出现pcre的版本信息,则表示pcre已经安装,若没有出现版本信息,则表示没有安装pcre。

linux查询mac地址的方法:1、打开系统,在桌面中点击鼠标右键,选择“打开终端”;2、在终端中,执行“ifconfig”命令,查看输出结果,在输出信息第四行中紧跟“ether”单词后的字符串就是mac地址。

在linux中,rpc是远程过程调用的意思,是Reomote Procedure Call的缩写,特指一种隐藏了过程调用时实际通信细节的IPC方法;linux中通过RPC可以充分利用非共享内存的多处理器环境,提高系统资源的利用率。


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

SublimeText3 Mac version
God-level code editing software (SublimeText3)

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

Zend Studio 13.0.1
Powerful PHP integrated development environment
