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MaixCDK Development Guidelines and Guidance

General Guidelines

  • Simplicity and Ease of Use: Assume minimal prior experience from users. Minimize required actions and provide simple APIs with comprehensive documentation.

For example, instead of asking users to choose and download a toolchain, it is better to automatically select and download the toolchain based on the chosen platform, reducing the entry barrier.

  • Universality: APIs should be designed to be platform-agnostic and provide consistent abstraction. If this cannot be achieved, reconsider whether the feature should be included.

  • Consistency: Maintain consistent API styles and coding standards.

  • Extensibility: While ensuring core functionality, provide extension interfaces to allow users to add features easily.

  • Depth: Keep APIs simple but document the underlying principles. Open-source as much code as possible to facilitate deeper exploration by users.

Source Code and Binary Files

  • Avoid Using Git Submodules: This facilitates faster downloads for users in China. Even if the main repository is mirrored, submodules still need to be fetched from GitHub, which can be slow for Chinese users.

  • Do Not Store Large Files or Binaries in the Source Code Repository: Storing these will significantly increase the Git repository size. Git is optimized for text files; handle binary files as described below.

  • Automatically Download Third-Party Libraries and Binaries Before Compilation: Define necessary files for download in component.py. During compilation, they will be downloaded to dl/pkgs and extracted to dl/extracted, allowing direct inclusion in CMakeLists.txt, e.g., list(APPEND ADD_INCLUDE "${DL_EXTRACTED_PATH}/sunxi_mpp/sunxi-mpp-1.0.0/include").

The list of files to be downloaded is stored in dl/pkgs_info.json during each build. Users with slow internet connections can manually download these files from official sources or third-party services and place them in dl/pkgs.

  • Do Not Modify Third-Party Libraries: Avoid modifying the source code of third-party libraries to facilitate upgrades. If modifications are necessary, consider applying patches automatically after extraction.

Overview of MaixCDK Architecture

For general application developers, key concepts include:

  • MaixCDK consists of two main parts: MaixCDK (library storage) and project (application code). Official examples and apps are located in MaixCDK/examples and MaixCDK/projects, respectively. You can also create your own projects in MaixCDK/projects.

Alternatively, you can separate the two and set an environment variable MAIXCDK_PATH pointing to the MaixCDK directory, e.g., export MAIXCDK_PATH=/home/xxx/MaixCDK. This allows projects to reside in other locations, such as /home/xxx/projects.

  • Components: Each functional module can be encapsulated as a component, making it easy to include in different applications.

    • For example, the main component in examples/hello_world and various components in components. You can also add custom components, like hello_world/component1.
    • Use the environment variable MAIXCDK_EXTRA_COMPONENTS_PATH to specify additional component paths.
    • Each component includes a CMakeLists.txt file describing its contents, e.g., list(APPEND ADD_INCLUDE "include") for header files, list(APPEND ADD_SRCS "src/hello.c") for source files, and list(APPEND ADD_REQUIREMENTS basic) for dependencies.

  • Kconfig: Provides terminal-based configuration options. Each component can include a Kconfig file for setting options, accessible via maixcdk menuconfig. The configuration is saved in build/config, generating global_config.cmake and global_config.h for use in CMakeLists.txt and C/C++ files.

  • Third-Party Library Integration: There are two recommended methods:

    • Method 1: Specify third-party libraries in the component’s CMakeLists.txt for automatic download during compilation. This is preferred for libraries integrated into MaixCDK.
    • Method 2: Package and publish the library as a Python package on pypi.org with the naming convention maixcdk-xxx. Users can then install it using pip install maixcdk-xxx.

  • Documentation: Located in the docs directory. API documentation is auto-generated from code; do not edit it manually. The application documentation serves as a user guide.

Coding Style

To ensure consistency across MaixCDK and MaixPy APIs, follow these coding style guidelines:

  • Function Names: Use lowercase with underscores, e.g., get_name.
  • Variable Names: Use lowercase with underscores, e.g., file_path.
  • Class Names: Use CamelCase, with common abbreviations in uppercase, e.g., Person, YOLOv2, UART.
  • Macros: Use uppercase with underscores, e.g., MAIXPY_VERSION.
  • Class Member Variables: Use lowercase with underscores without m_ prefix, e.g., name.
  • Private Class Member Variables: Prefix with _, e.g., _name.
  • Using Class Member Variables: Explicitly use this-> for clarity, e.g., this->name.
  • Namespace: Use the maix namespace for all official APIs, with sub-namespaces for different features, e.g., maix::thread, maix::peripheral.
  • Source File Naming: Use lowercase with underscores, e.g., maix_peripheral_uart.cpp. Use .hpp for C++ header files.
  • Comments: Follow Doxygen style for API documentation, as shown in components/basic/include/maix_api_example.hpp.

API Documentation Guidelines

Include the following keywords in your API comments:

  • brief: A brief description of the functionality.
  • param: Detailed parameter descriptions, including value requirements and direction (e.g., param[in] a).
  • return: Detailed return value descriptions.
  • retval: Use this for specific return value explanations, e.g., @retval 0 success.
  • attention: Special considerations for using the API.
  • maixpy: Indicates a MaixPy API, including the package and variable name, e.g., maix.example.
  • maixcdk: Indicates a MaixCDK API.

Follow the guidelines strictly, especially when defining types and default values, to ensure accurate MaixPy API and documentation generation.

API Standardization Suggestions

  • Prefer MaixCDK APIs over direct third-party APIs for better cross-platform compatibility, e.g., use maix_fs.hpp for file operations.
  • Use logging APIs from maix_log.hpp for consistent logging and to manage log levels.
  • Use error handling from maix_err.hpp for consistent error codes and exception handling.
  • For common APIs across modules, define a base class and inherit it in specific implementations, enhancing code reuse and consistency across platforms.