This document explains the Espressif IoT Development Framework build system and the concept of “components”
Read this document if you want to know how to organise a new ESP-IDF project.
We recommend using the esp-idf-template project as a starting point for your project.
Using the Build System¶
The esp-idf README file contains a description of how to use the build system to build your project.
An ESP-IDF project can be seen as an amalgamation of a number of components. For example, for a webserver that shows the current humidity, there could be:
- The ESP32 base libraries (libc, rom bindings etc)
- The WiFi drivers
- A TCP/IP stack
- The FreeRTOS operating system
- A webserver
- A driver for the humidity sensor
- Main code tying it all together
ESP-IDF makes these components explicit and configurable. To do that, when a project is compiled, the build environment will look up all the components in the ESP-IDF directories, the project directories and (optionally) in additional custom component directories. It then allows the user to configure the ESP-IDF project using a a text-based menu system to customize each component. After the components in the project are configured, the build process will compile the project.
- A “project” is a directory that contains all the files and configuration to build a single “app” (executable), as well as additional supporting output such as a partition table, data/filesystem partitions, and a bootloader.
- “Project configuration” is held in a single file called sdkconfig in the root directory of the project. This configuration file is modified via
make menuconfigto customise the configuration of the project. A single project contains exactly one project configuration.
- An “app” is an executable which is built by esp-idf. A single project will usually build two apps - a “project app” (the main executable, ie your custom firmware) and a “bootloader app” (the initial bootloader program which launches the project app).
- “components” are modular pieces of standalone code which are compiled into static libraries (.a files) and linked into an app. Some are provided by esp-idf itself, others may be sourced from other places.
Some things are not part of the project:
- “ESP-IDF” is not part of the project. Instead it is standalone, and linked to the project via the
IDF_PATHenvironment variable which holds the path of the
esp-idfdirectory. This allows the IDF framework to be decoupled from your project.
- The toolchain for compilation is not part of the project. The toolchain should be installed in the system command line PATH, or the path to the toolchain can be set as part of the compiler prefix in the project configuration.
An example project directory tree might look like this:
- myProject/ - Makefile - sdkconfig - components/ - component1/ - component.mk - Kconfig - src1.c - component2/ - component.mk - Kconfig - src1.c - include/ - component2.h - main/ - src1.c - src2.c - component.mk - build/
This example “myProject” contains the following elements:
- A top-level project Makefile. This Makefile set the
PROJECT_NAMEvariable and (optionally) defines other project-wide make variables. It includes the core
$(IDF_PATH)/make/project.mkmakefile which implements the rest of the ESP-IDF build system.
- “sdkconfig” project configuration file. This file is created/updated when “make menuconfig” runs, and holds configuration for all of the components in the project (including esp-idf itself). The “sdkconfig” file may or may not be added to the source control system of the project.
- Optional “components” directory contains components that are part of the project. A project does not have to contain custom components of this kind, but it can be useful for structuring reusable code or including third party components that aren’t part of ESP-IDF.
- “main” directory is a special “pseudo-component” that contains source code for the project itself. “main” is a default name, the Makefile variable
SRCDIRSdefaults to this but can be set to look for pseudo-components in other directories.
- “build” directory is where build output is created. After the make process is run, this directory will contain interim object files and libraries as well as final binary output files. This directory is usually not added to source control or distributed with the project source code.
Component directories contain a component makefile -
component.mk. This may contain variable definitions
to control the build process of the component, and its integration into the overall project. See Component Makefiles for more details.
Each component may also include a
Kconfig file defining the component configuration options that can be set via the project configuration. Some components may also include
Makefile.projbuild files, which are special files for overriding parts of the project.
Each project has a single Makefile that contains build settings for the entire project. By default, the project Makefile can be quite minimal.
Minimal Example Makefile¶
PROJECT_NAME := myProject include $(IDF_PATH)/make/project.mk
Mandatory Project Variables¶
PROJECT_NAME: Name of the project. Binary output files will use this name - ie myProject.bin, myProject.elf.
Optional Project Variables¶
These variables all have default values that can be overridden for custom behaviour. Look in
make/project.mk for all of the implementation details.
PROJECT_PATH: Top-level project directory. Defaults to the directory containing the Makefile. Many other project variables are based on this variable. The project path cannot contain spaces.
BUILD_DIR_BASE: The build directory for all objects/libraries/binaries. Defaults to
COMPONENT_DIRS: Directories to search for components. Defaults to $(IDF_PATH)/components, $(PROJECT_PATH)/components and
EXTRA_COMPONENT_DIRS. Override this variable if you don’t want to search for components in the esp-idf & project
EXTRA_COMPONENT_DIRS: Optional list of additional directories to search for components. Components themselves are in sub-directories of these directories, this is a top-level directory containing the component directories.
COMPONENTS: A list of component names to build into the project. Defaults to all components found in the COMPONENT_DIRS directories.
SRCDIRS: Directories under the main project directory which contain project-specific “pseudo-components”. Defaults to ‘main’. The difference between specifying a directory here and specifying it under
EXTRA_COMPONENT_DIRSis that a directory in
SRCDIRSis a component itself (contains a file “component.mk”), whereas a directory in
EXTRA_COMPONENT_DIRScontains component directories which contain a file “component.mk”. See the Example Project for a concrete case of this.
Each project contains one or more components, which can either be part of esp-idf or added from other component directories.
A component is any sub-directory that contains a component.mk file.[#f1]_.
Minimal Component Makefile¶
component.mk file is an empty file(!). If the file is empty, the default component behaviour is set:
- All source files in the same directory as the makefile (
*.S) will be compiled into the component library
- A sub-directory “include” will be added to the global include search path for all other components.
- The component library will be linked into the project app.
See example component makefiles for more complete component makefile examples.
Note that there is a different between an empty
component.mk file (which invokes default component build behaviour) and no
component.mk file (which means no default component build behaviour will occur.) It is possible for a component to have no component.mk file, if it only contains other files which influence the project configuration or build process.
Preset Component Variables¶
The following component-specific variables are available for use inside
component.mk, but should not be modified:
COMPONENT_PATH: The component directory. Evaluates to the absolute path of the directory containing
component.mk. The component path cannot contain spaces.
COMPONENT_NAME: Name of the component. Defaults to the name of the component directory.
COMPONENT_BUILD_DIR: The component build directory. Evaluates to the absolute path of a directory inside $(BUILD_DIR_BASE) where this component’s source files are to be built. This is also the Current Working Directory any time the component is being built, so relative paths in make targets, etc. will be relative to this directory.
COMPONENT_LIBRARY: Name of the static library file (relative to the component build directory) that will be built for this component. Defaults to
The following variables are set at the project level, but exported for use in the component build:
PROJECT_NAME: Name of the project, as set in project Makefile
PROJECT_PATH: Absolute path of the project directory containing the project Makefile.
COMPONENTS: Name of all components that are included in this build.
CONFIG_*: Each value in the project configuration has a corresponding variable available in make. All names begin with
OBJCOPY: Full paths to each tool from the gcc xtensa cross-toolchain.
HOSTAR: Full names of each tool from the host native toolchain.
If you modify any of these variables inside
component.mk then this will not prevent other components from building but it may make your component hard to build and/or debug.
Optional Project-Wide Component Variables¶
The following variables can be set inside
component.mk to control build settings across the entire project:
COMPONENT_ADD_INCLUDEDIRS: Paths, relative to the component directory, which will be added to the include search path for all components in the project. Defaults to
includeif not overridden. If an include directory is only needed to compile this specific component, add it to
COMPONENT_ADD_LDFLAGS: Add linker arguments to the LDFLAGS for the app executable. Defaults to
-l$(COMPONENT_NAME). If adding pre-compiled libraries to this directory, add them as absolute paths - ie $(COMPONENT_PATH)/libwhatever.a
COMPONENT_DEPENDS: Optional list of component names that should be compiled before this component. This is not necessary for link-time dependencies, because all component include directories are available at all times. It is necessary if one component generates an include file which you then want to include in another component. Most components do not need to set this variable.
The following variable only works for components that are part of esp-idf itself:
COMPONENT_SUBMODULES: Optional list of git submodule paths (relative to COMPONENT_PATH) used by the component. These will be checked (and initialised if necessary) by the build process. This variable is ignored if the component is outside the IDF_PATH directory.
Optional Component-Specific Variables¶
The following variables can be set inside
component.mk to control the build of that component:
COMPONENT_PRIV_INCLUDEDIRS: Directory paths, must be relative to the component directory, which will be added to the include search path for this component’s source files only.
COMPONENT_EXTRA_INCLUDES: Any extra include paths used when compiling the component’s source files. These will be prefixed with ‘-I’ and passed as-is to the compiler. Similar to the
COMPONENT_PRIV_INCLUDEDIRSvariable, except these paths are not expanded relative to the component directory.
COMPONENT_SRCDIRS: Directory paths, must be relative to the component directory, which will be searched for source files (
*.S). Defaults to ‘.’, ie the component directory itself. Override this to specify a different list of directories which contain source files.
COMPONENT_OBJS: Object files to compile. Default value is a .o file for each source file that is found in
COMPONENT_SRCDIRS. Overriding this list allows you to exclude source files in
COMPONENT_SRCDIRSthat would otherwise be compiled. See Specifying source files
COMPONENT_EXTRA_CLEAN: Paths, relative to the component build directory, of any files that are generated using custom make rules in the component.mk file and which need to be removed as part of
make clean. See Source Code Generation for an example.
COMPONENT_OWNBUILDTARGET& COMPONENT_OWNCLEANTARGET: These targets allow you to fully override the default build behaviour for the component. See Fully Overriding The Component Makefile for more details.
CFLAGS: Flags passed to the C compiler. A default set of
CFLAGSis defined based on project settings. Component-specific additions can be made via
CFLAGS +=. It is also possible (although not recommended) to override this variable completely for a component.
CPPFLAGS: Flags passed to the C preprocessor (used for .c, .cpp and .S files). A default set of
CPPFLAGSis defined based on project settings. Component-specific additions can be made via
CPPFLAGS +=. It is also possible (although not recommended) to override this variable completely for a component.
CXXFLAGS: Flags passed to the C++ compiler. A default set of
CXXFLAGSis defined based on project settings. Component-specific additions can be made via
CXXFLAGS +=. It is also possible (although not recommended) to override this variable completely for a component.
FLAGS_basenameallows you to set compilation flags to apply to a single source file only. For example, this can useful for disabling warnings in a single upstream source file. The
basenameportion is the directory (relative to
COMPONENT_PATH) and the base filename (without extension) of the source file. For example, if a file inside
library/alpha/widget.cthen you can set variable
FLAGS_library/alpha/widget := -DTESTto pass the TEST macro when compiling this source file only.
Each component can also have a Kconfig file, alongside
component.mk. This contains contains
configuration settings to add to the “make menuconfig” for this component.
These settings are found under the “Component Settings” menu when menuconfig is run.
To create a component KConfig file, it is easiest to start with one of the KConfig files distributed with esp-idf.
For an example, see Adding conditional configuration.
Build Process Internals¶
Top Level: Project Makefile¶
- “make” is always run from the project directory and the project makefile, typically named Makefile.
- The project makefile sets
PROJECT_NAMEand optionally customises other optional project variables
- The project makefile includes
$(IDF_PATH)/make/project.mkwhich contains the project-level Make logic.
project.mkfills in default project-level make variables and includes make variables from the project configuration. If the generated makefile containing project configuration is out of date, then it is regenerated (via targets in
project_config.mk) and then the make process restarts from the top.
project.mkbuilds a list of components to build, based on the default component directories or a custom list of components set in optional project variables.
- Each component can set some optional project-wide component variables. These are included via generated makefiles named
component_project_vars.mk- there is one per component. These generated makefiles are included into
project.mk. If any are missing or out of date, they are regenerated (via a recursive make call to the component makefile) and then the make process restarts from the top.
- Makefile.projbuild files from components are included into the make process, to add extra targets or configuration.
- By default, the project makefile also generates top-level build & clean targets for each component and sets up app and clean targets to invoke all of these sub-targets.
- In order to compile each component, a recursive make is performed for the component makefile.
To better understand the project make process, have a read through the
project.mk file itself.
Second Level: Component Makefiles¶
- Each call to a component makefile goes via the
component_wrapper.mkis called with the current directory set to the component build directory, and the
COMPONENT_MAKEFILEvariable is set to the absolute path to
component_wrapper.mksets default values for all component variables, then includes the component.mk file which can override or modify these.
COMPONENT_OWNCLEANTARGETare not defined, default build and clean targets are created for the component’s source files and the prerequisite
COMPONENT_LIBRARYstatic library file.
component_project_vars.mkfile has its own target in
component_wrapper.mk, which is evaluated from
project.mkif this file needs to be rebuilt due to changes in the component makefile or the project configuration.
To better understand the component make process, have a read through the
component_wrapper.mk file and some of the
component.mk files included with esp-idf.
Debugging The Make Process¶
Some tips for debugging the esp-idf build system:
V=1to the make arguments (or setting it as an environment variable) will cause make to echo all commands executed, and also each directory as it is entered for a sub-make.
make -wwill cause make to echo each directory as it is entered for a sub-make - same as
V=1but without also echoing all commands.
make --trace(possibly in addition to one of the above arguments) will print out every target as it is built, and the dependency which caused it to be built.
make -pprints a (very verbose) summary of every generated target in each makefile.
For more debugging tips and general make information, see the GNU Make Manual.
Overriding Parts of the Project¶
For components that have build requirements that must be evaluated in the top-level
project make pass, you can create a file called
Makefile.projbuild in the
component directory. This makefile is included when
project.mk is evaluated.
For example, if your component needs to add to CFLAGS for the entire
project (not just for its own source files) then you can set
CFLAGS += in Makefile.projbuild.
Makefile.projbuild files are used heavily inside esp-idf, for defining project-wide build features such as
esptool.py command line arguments and the
bootloader “special app”.
Makefile.projbuild isn’t necessary for the most common component uses - such as adding include directories to the project, or LDFLAGS to the final linking step. These values can be customised via the
component.mk file itself. See Optional Project-Wide Component Variables for details.
Take care when setting variables or targets in this file. As the values are included into the top-level project makefile pass, they can influence or break functionality across all components!
This is an equivalent to Makefile.projbuild for component configuration KConfig files. If you want to include
configuration options at the top-level of menuconfig, rather than inside the “Component Configuration” sub-menu, then these can be defined in the KConfig.projbuild file alongside the
Take care when adding configuration values in this file, as they will be included across the entire project configuration. Where possible, it’s generally better to create a KConfig file for component configuration.
Example Component Makefiles¶
Because the build environment tries to set reasonable defaults that will work most of the time, component.mk can be very small or even empty (see Minimal Component Makefile). However, overriding component variables is usually required for some functionality.
Here are some more advanced examples of
Adding source directories¶
By default, sub-directories are ignored. If your project has sources in sub-directories
instead of in the root of the component then you can tell that to the build
system by setting
COMPONENT_SRCDIRS := src1 src2
This will compile all source files in the src1/ and src2/ sub-directories instead.
Specifying source files¶
The standard component.mk logic adds all .S and .c files in the source
directories as sources to be compiled unconditionally. It is possible
to circumvent that logic and hard-code the objects to be compiled by
manually setting the
COMPONENT_OBJS variable to the name of the
objects that need to be generated:
COMPONENT_OBJS := file1.o file2.o thing/filea.o thing/fileb.o anotherthing/main.o COMPONENT_SRCDIRS := . thing anotherthing
COMPONENT_SRCDIRS must be set as well.
Adding conditional configuration¶
The configuration system can be used to conditionally compile some files
depending on the options selected in
config FOO_ENABLE_BAR bool "Enable the BAR feature." help This enables the BAR feature of the FOO component.
COMPONENT_OBJS := foo_a.o foo_b.o ifdef CONFIG_FOO_BAR COMPONENT_OBJS += foo_bar.o foo_bar_interface.o endif
See the GNU Make Manual for conditional syntax that can be used use in makefiles.
Source Code Generation¶
Some components will have a situation where a source file isn’t supplied with the component itself but has to be generated from another file. Say our component has a header file that consists of the converted binary data of a BMP file, converted using a hypothetical tool called bmp2h. The header file is then included in as C source file called graphics_lib.c:
COMPONENT_EXTRA_CLEAN := logo.h graphics_lib.o: logo.h logo.h: $(COMPONENT_PATH)/logo.bmp bmp2h -i $^ -o $@
In this example, graphics_lib.o and logo.h will be generated in the current directory (the build directory) while logo.bmp comes with the component and resides under the component path. Because logo.h is a generated file, it needs to be cleaned when make clean is called which why it is added to the COMPONENT_EXTRA_CLEAN variable.
Because logo.h is a generated file, it needs to be cleaned when make clean is called which why it is added to the COMPONENT_EXTRA_CLEAN variable.
Adding logo.h to the
graphics_lib.o dependencies causes it to be
graphics_lib.c is compiled.
If a a source file in another component included
logo.h, then this
component’s name would have to be added to the other component’s
COMPONENT_DEPENDS list to ensure that the components were built
Embedding Binary Data¶
Sometimes you have a file with some binary or text data that you’d like to make available to your component - but you don’t want to reformat the file as C source.
You can set a variable COMPONENT_EMBED_FILES in component.mk, giving the names of the files to embed in this way:
COMPONENT_EMBED_FILES := server_root_cert.der
Or if the file is a string, you can use the variable COMPONENT_EMBED_TXTFILES. This will embed the contents of the text file as a null-terminated string:
COMPONENT_EMBED_TXTFILES := server_root_cert.pem
The file’s contents will be added to the .rodata section in flash, and are available via symbol names as follows:
extern const uint8_t server_root_cert_pem_start asm("_binary_server_root_cert_pem_start"); extern const uint8_t server_root_cert_pem_end asm("_binary_server_root_cert_pem_end");
The names are generated from the full name of the file, as given in COMPONENT_EMBED_FILES. Characters /, ., etc. are replaced with underscores. The _binary prefix in the symbol name is added by objcopy and is the same for both text and binary files.
For an example of using this technique, see examples/04_https_request - the certificate file contents are loaded from the text .pem file at compile time.
Fully Overriding The Component Makefile¶
Obviously, there are cases where all these recipes are insufficient for a
certain component, for example when the component is basically a wrapper
around another third-party component not originally intended to be
compiled under this build system. In that case, it’s possible to forego
the esp-idf build system entirely by setting COMPONENT_OWNBUILDTARGET and
possibly COMPONENT_OWNCLEANTARGET and defining your own targets named
target. The build target can do anything as long as it creates
$(COMPONENT_LIBRARY) for the project make process to link into the app binary.
(Actually, even this is not strictly necessary - if the COMPONENT_ADD_LDFLAGS variable is set then the component can instruct the linker to link other binaries instead.)