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Project Configuration

:link_to_translation:`zh_CN:[中文]`

Introduction

The esp-idf-kconfig package that ESP-IDF uses is based on kconfiglib, which is a Python extension to the Kconfig system. Kconfig provides a compile-time project configuration mechanism and offers configuration options of several types (e.g., integers, strings, and boolens). Kconfig files specify dependencies between options, default values of options, the way options are grouped together, etc.

For the full list of available features, please see Kconfig and kconfiglib extentions.

Project Configuration Menu

Application developers can open a terminal-based project configuration menu with the idf.py menuconfig build target.

After being updated, this configuration is saved in the sdkconfig file under the project root directory. Based on sdkconfig, application build targets will generate the sdkconfig.h file under the build directory, and will make the sdkconfig options available to the project build system and source files.

Using sdkconfig.defaults

In some cases, for example, when the sdkconfig file is under revision control, it may be inconvenient for the build system to change the sdkconfig file. The build system offers a solution to prevent it from happening, which is to create the sdkconfig.defaults file. This file is never touched by the build system, and can be created manually or automatically. It contains all the options which matter to the given application and are different from the default ones. The format is the same as that of the sdkconfig file. sdkconfig.defaults can be created manually when one remembers all the changed configuration, or it can be generated automatically by running the idf.py save-defconfig command.

Once sdkconfig.defaults is created, sdkconfig can be deleted or added to the ignore list of the revision control system (e.g., the .gitignore file for git). Project build targets will automatically create the sdkconfig file, populate it with the settings from the sdkconfig.defaults file, and configure the rest of the settings to their default values. Note that during the build process, settings from sdkconfig.defaults will not override those already in sdkconfig. For more information, see :ref:`custom-sdkconfig-defaults`.

Kconfig Format Rules

Format rules for Kconfig files are as follows:

  • Option names in any menus should have consistent prefixes. The prefix currently should have at least 3 characters.
  • The unit of indentation should be 4 spaces. All sub-items belonging to a parent item are indented by one level deeper. For example, menu is indented by 0 spaces, config menu by 4 spaces, help in config by 8 spaces, and the text under help by 12 spaces.
  • No trailing spaces are allowed at the end of the lines.
  • The maximum length of options is 40 characters.
  • The maximum length of lines is 120 characters.

Note

The help section of each config in the menu is treated as reStructuredText to generate the reference documentation for each option.

Format Checker

kconfcheck tool in esp-idf-kconfig package is provided for checking Kconfig files against the above format rules. The checker checks all Kconfig and Kconfig.projbuild files given as arguments, and generates a new file with suffix .new with some suggestions about how to fix issues (if there are any). Please note that the checker cannot correct all format issues and the responsibility of the developer is to final check and make corrections in order to pass the tests. For example, indentations will be corrected if there is not any misleading formatting, but it cannot come up with a common prefix for options inside a menu.

The esp-idf-kconfig package is available in ESP-IDF environments, where the checker tool can be invoked by running command python -m kconfcheck <path_to_kconfig_file>.

For more information, please refer to esp-idf-kconfig package documentation.

Backward Compatibility of Kconfig Options

The standard Kconfig tools ignore unknown options in sdkconfig. So if a developer has custom settings for options which are renamed in newer ESP-IDF releases, then the given setting for the option would be silently ignored. Therefore, several features have been adopted to avoid this:

  1. kconfgen is used by the tool chain to pre-process sdkconfig files before anything else. For example, menuconfig would read them, so the settings for old options is kept and not ignored.
  2. kconfgen recursively finds all sdkconfig.rename files in ESP-IDF directory which contain old and new Kconfig option names. Old options are replaced by new ones in the sdkconfig file. Renames that should only appear for a single target can be placed in a target-specific rename file sdkconfig.rename.TARGET, where TARGET is the target name, e.g., sdkconfig.rename.esp32s2.
  3. kconfgen post-processes sdkconfig files and generates all build outputs (sdkconfig.h, sdkconfig.cmake, and auto.conf) by adding a list of compatibility statements, i.e., the values of old options are set for new options after modification. If users still use old options in their code, this will prevent it from breaking.
  4. :ref:`configuration-deprecated-options` are automatically generated by kconfgen.

Configuration Options Reference

Subsequent sections contain the list of available ESP-IDF options automatically generated from Kconfig files. Note that due to dependencies between options, some options listed here may not be visible by default in menuconfig.

By convention, all option names are upper-case letters with underscores. When Kconfig generates sdkconfig and sdkconfig.h files, option names are prefixed with CONFIG_. So if an option ENABLE_FOO is defined in a Kconfig file and selected in menuconfig, then the sdkconfig and sdkconfig.h files will have CONFIG_ENABLE_FOO defined. In the following sections, option names are also prefixed with CONFIG_, same as in the source code.

.. include-build-file:: inc/kconfig.inc