265 lines
12 KiB
Text
265 lines
12 KiB
Text
The build structure of the Espressif IoT Development Framework explained.
|
|
|
|
An ESP-IDF project can be seen as an almagation of a number of components.
|
|
For example, for a webserver that shows the current humidity, we would
|
|
have:
|
|
- The ESP32 base libraries (libc, rom bindings etc)
|
|
- The WiFi drivers
|
|
- A TCP/IP stack
|
|
- The FreeRTOS operating system
|
|
- A webserver
|
|
- A driver for an 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
|
|
SDK directories, the project directories and optionally custom other component
|
|
directories. It then allows the user to configure compile-time options using
|
|
a friendly text-based menu system to customize the SDK as well as other components
|
|
to the requirements of the project. After the components are customized, the
|
|
build process will compile everything into an output file, which can then be uploaded
|
|
into a board in a way that can also be defined by components.
|
|
|
|
A project in this sense is defined as a directory under which all the files required
|
|
to build it live, excluding the SDK files and the toolchain. A simple project
|
|
tree looks like this:
|
|
|
|
- myProject/ - build/
|
|
- components/ - component1/ - Makefile
|
|
- Kconfig
|
|
- src1.c
|
|
- component2/ - Makefile
|
|
- Kconfig
|
|
- src1.c
|
|
- main/ - src1.c
|
|
- src2.c
|
|
- Makefile
|
|
|
|
|
|
As we can see, a project consists of a components/ subdirectory containing its
|
|
components as well as one or more directories containing the project-specific
|
|
sources; by default a single directory called 'main' is assumed. The project
|
|
directory will also have a Makefile where the projects name as well as optionally
|
|
other options are defined. After compilation, the project directory will contain
|
|
a 'build'-directory containing all of the objects, libraries and other generated
|
|
files as well as the final binary.
|
|
|
|
Components also have a Makefile containing various definititions influencing
|
|
the build process of the component as well as the project it's used in, as
|
|
well as a Kconfig file defining the compile-time options that are settable
|
|
by means of the menu system.
|
|
|
|
|
|
Project makefile variables that can be set by the programmer:
|
|
PROJECT_NAME: Mandatory. Name for the project
|
|
BUILD_DIR_BASE: Set the directory where all objects/libraries/binaries end up in.
|
|
Defaults to $(PROJECT_PATH)/build
|
|
COMPONENT_DIRS: Search path for components. Defaults to the component/ directories
|
|
in the SDK path and the project path.
|
|
COMPONENTS: A list of component names. Defaults to all the component found in the
|
|
COMPONENT_DIRS directory
|
|
EXTRA_COMPONENT_DIRS: Defaults to unset. Use this to add directories to the default
|
|
COMPONENT_DIRS.
|
|
SRCDIRS: Directories under the project dir containing project-specific sources.
|
|
Defaults to 'main'. These are treated as 'lite' components: they do not have
|
|
include directories that are passed to the compilation pass of all components and
|
|
they do not have a Kconfig option.
|
|
|
|
|
|
Component makefile variables that can be set by the programmer:
|
|
COMPONENT_ADD_INCLUDEDIRS: Relative path to include directories to be added to
|
|
the entire project
|
|
COMPONENT_PRIV_INCLUDEDIRS: Relative path to include directories that are only used
|
|
when compiling this specific component
|
|
COMPONENT_DEPENDS: Names of any components that need to be compiled before this component.
|
|
COMPONENT_ADD_LDFLAGS: Ld flags to add for this project. Defaults to -l$(COMPONENT_NAME).
|
|
Add libraries etc in the current directory as $(abspath libwhatever.a)
|
|
COMPONENT_EXTRA_INCLUDES: Any extra include paths. These will be prefixed with '-I' and
|
|
passed to the compiler; please put absolute paths here.
|
|
COMPONENT_SRCDIRS: Relative directories to look in for sources. Defaults to '.', the current
|
|
directory (the root of the component) only. Use this to specify any subdirectories. Note
|
|
that specifying this overwrites the default action of compiling everything in the
|
|
components root dir; to keep this behaviour please also add '.' as a directory in this
|
|
list.
|
|
COMPONENT_OBJS: Object files to compile. Defaults to the .o variants of all .c and .S files
|
|
that are found in COMPONENT_SRCDIRS.
|
|
COMPONENT_EXTRA_CLEAN: Files that are generated using rules in the components Makefile
|
|
that also need to be cleaned
|
|
COMPONENT_BUILDRECIPE: Recipe to build the component. Optional. Defaults to building all
|
|
COMPONENT_OBJS and linking them into lib(componentname).a
|
|
COMPONENT_CLEANRECIPE: Recipe to clean the component. Optional. Defaults to removing
|
|
all built objects and libraries.
|
|
COMPONENT_BUILD_DIR: Equals the cwd of the component build, which is the build dir
|
|
of the component (where all the .o etc files should be created).
|
|
|
|
|
|
These variables are already set early on in the Makefile and the values in it will
|
|
be usable in component or project Makefiles:
|
|
CC, LD, AR, OBJCOPY: Xtensa gcc tools
|
|
HOSTCC, HOSTLD etc: Host gcc tools
|
|
LDFLAGS, CFLAGS: Set to usable values as defined in SDK Makefile
|
|
PROJECT_NAME: Name of the project, as set in project makefile
|
|
PROJECT_PATH: Path to the root of the project folder
|
|
COMPONENTS: Name of the components to be included
|
|
CONFIG_*: Values set by 'make menuconfig' also have corresponding Makefile variables.
|
|
|
|
For components, there also are these defines:
|
|
COMPONENT_PATH: Absolute path to the root of the source tree of the component we're
|
|
compiling
|
|
COMPONENT_LIBRARY: The full path to the static library the components compilation pass
|
|
is supposed to generate
|
|
|
|
|
|
How this works:
|
|
The Make process is always invoked from the project directory by the
|
|
user; invoking it anywhere else gives an error. This is what happens if
|
|
we build a binary:
|
|
|
|
The Makefile first determines how it was included. It determines it was
|
|
included as a project file in this case and will continue to figure out
|
|
various paths as well as the components available to it. It will also
|
|
collect the ldflags and includes that the components specify they need.
|
|
It does this by running a dummy Make on the components with a target that
|
|
will output these values.
|
|
|
|
The Makefile will then create targets to build the lib*.a libraries of
|
|
all components and make the elf target depend on this. The targets
|
|
invoke Make on the makefiles of the components in a subshell: this way
|
|
the components have full freedom to do whatever is necessary to build
|
|
the library without influencing other components. By default, the
|
|
component includes the utility makefile $(SDK_PATH)/make/component.mk.
|
|
This provides default targets and configurations that will work
|
|
out-of-the-box for most projects.
|
|
|
|
For components that have parts that need to be run when building of the
|
|
project is done, you can create a file called Makefile.projbuild in the
|
|
component root directory. This file will be included in the main
|
|
Makefile. For the menu, there's an equivalent: if you want to include
|
|
options not in the 'components' submenu, create a Kconfig.projbuild and
|
|
it will be included in the main menu of menuconfig. Take good care when
|
|
(re)defining stuff here: because it's included with all the other
|
|
.projbuild files, it's possible to overwrite variables or re-declare
|
|
targets defined in the SDK makefile/Kconfig and other .projbuild files
|
|
|
|
|
|
WRITING COMPONENT MAKEFILES
|
|
|
|
A component consists of a directory which doubles as the name for the
|
|
component: a component named 'httpd' lives in a directory called 'httpd'
|
|
Because components usually live under the project directory (although
|
|
they can also reside in an other folder), the path to this may be
|
|
something like /home/myuser/projects/myprojects/components/httpd .
|
|
|
|
One of the things that most components will have is a Makefile,
|
|
containing instructions on how to build the component. Because the
|
|
build environment tries to set reasonable defaults that will work most
|
|
of the time, a component Makefile can be pretty small. At the absolute
|
|
minimum, it will just include the SDK component makefile, which adds
|
|
component functionality:
|
|
|
|
----8<----
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
This will take all the .c and .S files in the component root and compile
|
|
them into object files, finally linking them into a library.
|
|
Subdirectories are ignored; if your project has sources in subdirectories
|
|
instead of in the root of the component, you can tell that to the build
|
|
system by setting COMPONENT_SRCDIRS:
|
|
|
|
----8<----
|
|
COMPONENT_SRCDIRS := src1 src2
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
This will compile all source files in the src1/ and src2/ subdirectories
|
|
instead.
|
|
|
|
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 hardcode the objects to be compiled by
|
|
manually setting the COMPONENT_OBJS variable to the name of the
|
|
objects that need to be generated:
|
|
|
|
----8<----
|
|
COMPONENT_OBJS := file1.o file2.o thing/filea.o thing/fileb.o anotherthing/main.o
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
This can also be used in order to conditionally compile some files
|
|
dependent on the options selected in the Makefile:
|
|
|
|
Kconfig:
|
|
----8<----
|
|
config FOO_ENABLE_BAR
|
|
bool "Enable the BAR feature."
|
|
help
|
|
This enables the BAR feature of the FOO component.
|
|
---->8----
|
|
|
|
Makefile:
|
|
----8<----
|
|
COMPONENT_OBJS := foo_a.o foo_b.o $(if $(CONFIG_FOO_ENABLE_BAR),foo_bar.o foo_bar_interface.o)
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
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.
|
|
|
|
----8<----
|
|
COMPONENT_EXTRA_CLEAN := logo.h
|
|
|
|
graphics_lib.o: logo.h
|
|
|
|
logo.h: $(COMPONENT_PATH)/logo.bmp
|
|
bmp2h -i $^ -o $@
|
|
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
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.
|
|
|
|
|
|
This will work just fine, but there's one last cosmetic improvement that
|
|
can be done. The SDK make system tries to make the make process somewhat
|
|
easier on the eyes by hiding the commands (unless you run make with the
|
|
V=1 switch) and this does not do that yet. Here's an improved version
|
|
that will output in the same style as the rest of the make process:
|
|
|
|
----8<----
|
|
COMPONENT_EXTRA_CLEAN := test_tjpgd_logo.h
|
|
|
|
graphics_lib.o: logo.h
|
|
|
|
logo.h: $(COMPONENT_PATH)/logo.bmp
|
|
$(vecho) BMP2H $@
|
|
$(Q) bmp2h -i $^ -o $@
|
|
|
|
include $(SDK_PATH)/make/component.mk
|
|
---->8----
|
|
|
|
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 build system entirely by setting COMPONENT_OWNBUILDTARGET and
|
|
possibly COMPONENT_OWNCLEANTARGET and defining your own build- and clean
|
|
target. The build target can do anything as long as it creates
|
|
$(COMPONENT_LIBRARY) for the main file to link into the project binary,
|
|
and even that is not necessary: if the COMPONENT_ADD_LDFLAGS variable
|
|
is set, the component can instruct the linker to do anything else as well.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|