MRAA简介
MRAA（读作 em-rah）是用C语言编写的低级别通用库。 MRAA旨在提取与平台（比如英特尔、Galileo 或Edison 开发板）基本 I/O 功能访问和控制相关的详细信息，并将其转化为单个、简洁的 API。
MRAA可作为Linux通用输入/输出(GPIO) 设备顶端的转换层。尽管Linux提供丰富的基础设施来控制GPIO，其用于处理GPIO的通用指令也非常标准，但使用难度相对较大。根据定义，不同平台之间存在差异，他们拥有不同的功能、针脚编号和GPIO类型。例如，更换平台后，GPIO 针脚可能无法支持相同类型的功能。某个特定平台可能根本没有针脚。另外，GPIO在平台上的配置方式也取决于不同因素。例如，一种 GPIO 针脚使用模式可能会影响其他针脚的其他使用模式，或影响其他针脚的使用。因此，MRAA可降低程序开发的复杂度，因为它可与其他软件一起使用来创建独立于平台的代码。
注：尽管MRAA可用于编写独立于平台的代码，开发人员仍然负责确保代码足够耐用，以适应平台的各种局限性。
MRAA安装
通常情况下，我们可以直接安装mraa库，通过访问github可以获取mraa的源码、示例以及安装方法，本文以Ubuntu 20.04的为例来说明安装过程。首先在shell控制台中输入如下指令
sudo add-apt-repository ppa:mraa/mraa sudo apt-get install libmraa-dev
安装的路径默认是usr/lib/x86_64-linux-gnu/libmraa.so，通过上述方法也可以在ARM Linux上尝试安装。
说明：github的安装指令有很多条，由于我需要的是C++库，所以只需要安装libmraa-dev即可
MRAA交叉编译
如果在上述方法无法安装成功，可自行编译源码。本文介绍使用交叉编译工具编译mraa库
1、下载mraa源码，从github上自行下载
2、下载交叉编译链，操作方法可参考《玩转DragronBoard 410c系列之四：Linux系统搭建ARM应用开发环境》
3、下载cmake，运行平台选择Linux，也可以使用Windows平台，我会在后面的文章讲解，本文使用的是Linux平台。
4、安装mraa依赖环境，下图是官方资料说明的依赖环境，我们不编译java、swing版本，所以下图中的依赖统统不安装！只要使用apt-get install build-essential安装基本的依赖即可，安装环境需要root权限。
1、修改CMakeLists.txt文件。由于我们只编译C++版本的mraa库，所以需要修改CMakeLists.txt文件，修改记录如下图所示，需要编译的模块标记“ON”，经过测试发现“ONEWIRE”必须标记为“ON”。
2、运行cmake-gui，填入mraa源码路径及编译后存储路径
3、然后点击“Configure”，弹出如下页面时选择“交叉编译”
4、操作系统填“Linux”，处理器填“arm”，编译器选择交叉编译工具中的gcc和g++，目标根路径也按照下图填写
5、点击“Finish”，弹出如下图所示页面
6、此时点击“Generate”按钮，则自动完成编译，如果需要安装，在Build输入“make install”指令，该指令需要root权限如下图所示
到此，mraa交叉编译完成，编译后的动态库为libmraa.so，默认路径为/usr/local/lib/libmraa.so，头文件默认路径为/usr/local/include/mraa。如果需要移植到ARM 开发板只需要将so文件和头文件复制过去即可。
总结
这篇文章主要介绍mraa的交叉编译流程，生成的动态库可以在ARN Linux上使用。附件是我编译好的动态库，有需要的可以下载。
立即下载
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