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.
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
.)
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 :ref:`custom-sdkconfig-defaults`.
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, theconfig
inside of the menu by 4 characters, the help of theconfig
by 8 characters and the text of thehelp
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).
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.
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:
confgen.py
is used by the tool chain to pre-processsdkconfig
files before anything else, for examplemenuconfig
, would read them. As the consequence, the settings for old options will be kept and not ignored.confgen.py
recursively finds allsdkconfig.rename
files in ESP-IDF directory which contain old and newKconfig
option names. Old options are replaced by new ones in thesdkconfig
file.confgen.py
post-processessdkconfig
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.- :ref:`configuration-deprecated-options` are automatically generated by
confgen.py
.
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.
.. include-build-file:: inc/kconfig.inc
Because IDF builds by default with :ref:`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.