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外部模块（Out-of-Tree）

外部模块为开发人员提供了一种便捷的机制，可以管理/分组他们想要添加（或更新）PX4固件的专有模块。 外部模块可以使用与内部模块相同的includes，并可以通过uORB与内部模块交互。

本主题说明如何将外部（“out of tree”）模块添加到PX4编译中。

我们鼓励您尽可能将更改贡献给 PX4！

用法

要创建外部模块：

• 创建外部目录目录以对外部模块进行分组：
  • This can be located anywhere outside of the PX4-Autopilot tree.
  • It must have the same structure as PX4-Autopilot (i.e. it must contain a directory called src).
  • 稍后我们使用EXTERNAL_MODULES_LOCATION来引用此目录。
• 将现有模块（例如examples/px4_simple_app）复制到外部目录，或直接创建新模块。
• Rename the module (including MODULE in CMakeLists.txt) or remove it from the existing PX4-Autopilot cmake build config. This is to avoid conflicts with internal modules.

• 在外部目录中添加文件 CMakeLists.txt ，内容为：

  set(config_module_list_external
      modules/<new_module>
      PARENT_SCOPE
      )
  

• 在 modules/<new_module>/CMakeLists.txt 中添加一行 EXTERNAL px4_add_module()，例如：

  px4_add_module(
    MODULE modules__test_app
    MAIN test_app
    STACK_MAIN 2000
    SRCS
      px4_simple_app.c
    DEPENDS
      platforms__common
    EXTERNAL
    )
  

Out-of-Tree uORB Message Definitions

uORB messages can also be defined out-of-tree. For this, the $EXTERNAL_MODULES_LOCATION/msg folder must exist.

• 将所有新消息定义放在 $EXTERNAL_MODULES_LOCATION/msg 目录中。 这些新的树外消息定义的格式与任何其他 uORB 消息定义 的格式相同。

• 将以下内容添加文件$EXTERNAL_MODULES_LOCATION/msg/CMakeLists.txt：

  set(config_msg_list_external
      <message1>.msg
      <message2>.msg
      <message3>.msg
      PARENT_SCOPE
      )
  

其中<message#>.msg是要处理并用于生成uORB消息的uORB消息定义文件的名称。

The out-of-tree uORB messages will be generated in the same locations as the normal uORB messages. The uORB topic headers are generated in <build_dir>/uORB/topics/, and the message source files are generated in <build_dir>/msg/topics_sources/.

The new uORB messages can be used like any other uORB message as described here.

树外的uORB消息定义不能与任何普通的uORB消息具有相同的名称。

Building External Modules and uORB Messages

Execute make px4_sitl EXTERNAL_MODULES_LOCATION=<path>.

Any other build target can be used, but the build directory must not yet exist. If it already exists, you can also just set the cmake variable in the build folder.

For subsequent incremental builds EXTERNAL_MODULES_LOCATION does not need to be specified.