Skip to content

Latest commit

 

History

History
103 lines (73 loc) · 6.62 KB

kconfig.rst

File metadata and controls

103 lines (73 loc) · 6.62 KB
Raw

Project Configuration

Introduction

ESP-IDF uses kconfiglib which is a Python-based extension to the Kconfig system which provides a compile-time project configuration mechanism. Kconfig is based around options of several types: integer, string, boolean. Kconfig files specify dependencies between options, default values of the options, the way the options are grouped together, etc.

For the complete 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 inside sdkconfig file in the project root directory. Based on sdkconfig, application build targets will generate sdkconfig.h file in the build directory, and will make sdkconfig options available to the project build system and source files.

(For the legacy GNU Make build system, the project configuration menu is opened with make menuconfig.)

Using sdkconfig.defaults

In some cases, such as when sdkconfig file is under revision control, the fact that sdkconfig file gets changed by the build system may be inconvenient. The build system offers a way to avoid this, in the form of sdkconfig.defaults file. This file is never touched by the build system, and must be created manually. It can contain all the options which matter for the given application. The format is the same as that of the sdkconfig file. Once sdkconfig.defaults is created, sdkconfig can be deleted and added to the ignore list of the revision control system (e.g. .gitignore file for git). Project build targets will automatically create sdkconfig file, populated with the settings from sdkconfig.defaults file, and the rest of the settings will be set to their default values. Note that the build process will not override settings that are already in sdkconfig by ones from sdkconfig.defaults. For more information, see custom-sdkconfig-defaults.

Kconfig Formatting Rules

The following attributes of Kconfig files are standardized:

  • Within any menu, option names should have a consistent prefix. The prefix length is currently set to at least 3 characters.
  • The indentation style is 4 characters created by spaces. All sub-items belonging to a parent item are indented by one level deeper. For example, menu is indented by 0 characters, the config inside of the menu by 4 characters, the help of the config by 8 characters and the text of the help by 12 characters.
  • No trailing spaces are allowed at the end of the lines.
  • The maximum length of options is set to 40 characters.
  • The maximum length of lines is set to 120 characters.
  • Lines cannot be wrapped by backslash (because there is a bug in earlier versions of conf-idf which causes that Windows line endings are not recognized after a backslash).

Format checker

tools/check_kconfigs.py is provided for checking the Kconfig formatting rules. The checker checks all Kconfig and Kconfig.projbuild files in the ESP-IDF directory and generates a new file with suffix .new with some recommendations how to fix issues (if there are any). Please note that the checker cannot correct all rules and the responsibility of the developer is to check and make final corrections in order to pass the tests. For example, indentations will be corrected if there isn't some misleading previous formatting but it cannot come up with a common prefix for options inside a menu.

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. confgen.py is used by the tool chain to pre-process sdkconfig files before anything else, for example menuconfig, would read them. As the consequence, the settings for old options will be kept and not ignored.
  2. confgen.py 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.
  3. confgen.py post-processes sdkconfig files and generates all build outputs (sdkconfig.h, sdkconfig.cmake, auto.conf) by adding a list of compatibility statements, i.e. value of the old option is set the value of the new option (after modification). This is done in order to not break customer codes where old option might still be used.
  4. configuration-deprecated-options are automatically generated by confgen.py.

Configuration Options Reference

Subsequent sections contain the list of available ESP-IDF options, automatically generated from Kconfig files. Note that depending on the options selected, some options listed here may not be visible by default in the interface of menuconfig.

By convention, all option names are upper case 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 sdkconfig and sdkconfig.h files will have CONFIG_ENABLE_FOO defined. In this reference, option names are also prefixed with CONFIG_, same as in the source code.

inc/kconfig.inc

Customisations

Because IDF builds by default with warn-undefined-variables, when the Kconfig tool generates Makefiles (the auto.conf file) its behaviour has been customised. In normal Kconfig, a variable which is set to "no" is undefined. In IDF's version of Kconfig, this variable is defined in the Makefile but has an empty value.

(Note that ifdef and ifndef can still be used in Makefiles, because they test if a variable is defined and has a non-empty value.)

When generating header files for C & C++, the behaviour is not customised - so #ifdef can be used to test if a boolean config item is set or not.