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Customizing the Build

Table of contents

Rust configuration flags

The following are flags passed to rustc that influence the build.

  • --cfg espidf_time64

    This is a flag for the libc crate that uses 64-bits (instead of 32-bits) for time_t. This must be set for ESP-IDF 5.0 and above and must be unset for lesser versions.

  • -Zbuild-std=std,panic_abort

    Required for std support. Rust does not provide std libraries for ESP32 targets since they are tier-2/-3.

Features

  • native

    This is the default feature for downloading all tools and building the ESP-IDF framework using the framework's "native" (own) tooling. It relies on build and installation utilities available in the embuild crate.

    The native builder installs all needed tools to compile this crate as well as the ESP-IDF framework itself.

  • pio

    This is a backup feature for installing all build tools and building the ESP-IDF framework. It uses PlatformIO via the embuild crate.

    Similarly to the native builder, the pio builder also automatically installs all needed tools (PlatformIO packages and frameworks in this case) to compile this crate as well as the ESP-IDF framework itself.

    [!WARNING] The pio builder is less flexible than the default native builder in that it can work with only one, specific version of ESP-IDF. At the time of writing, this is V4.3.2.

  • binstart

    Defines the esp-idf entry-point for when the root crate is a binary crate that defines a main function.

  • libstart

    Defines the esp-idf entry-point for when the root crate is a library crate. the root crate is expected to provide a

    #[no_mangle]
fn main() {}

    function.

  • uart0_driver_init

    Enables UART0 to be driven by the driver code, adding buffering support required to read std::io::stdin() from UART0. This is enabled by default.

sdkconfig

The esp-idf makes use of an sdkconfig file for its compile-time component configuration (see the esp-idf docs for more information). This config is separate from the build configuration.

(native builder only) Using cargo-idf to interactively modify ESP-IDF's sdkconfig file

TBD: Upcoming

(pio builder only) Using cargo-pio to interactively modify ESP-IDF's sdkconfig file

To enable Bluetooth, or do other configurations to the ESP-IDF sdkconfig you might take advantage of the cargo-pio Cargo subcommand:

  • To install it, issue cargo install cargo-pio --git https://github.com/ivmarkov/cargo-pio
  • To open the ESP-IDF interactive menuconfig system, issue cargo pio espidf menuconfig in the root of your binary crate project
  • To use the generated/updated sdkconfig file, follow the steps described in the "Bluetooth Support" section

ESP-IDF configuration

There are two ways to configure how the ESP-IDF framework is compiled:

  1. Environment variables, denoted by $VARIABLE;

    The environment variables can be passed on the command line, or put into the [env] section of a .cargo/config.toml file (see cargo reference).

  2. The [package.metadata.esp-idf-sys] section of the Cargo.toml, denoted by field.

    [!NOTE] Configuration can only come from the root crate's Cargo.toml. The root crate is the package in the workspace directory. If there is not root crate in case of a virtual workspace, its name can be specified with the ESP_IDF_SYS_ROOT_CRATE environment variable.

    [!WARNING] Environment variables always take precedence over Cargo.toml metadata.

Note

workspace directory

The workspace directory mentioned here is always the directory containing the Cargo.lock file and the target directory (unless configured otherwise, see the note below about CARGO_TARGET_DIR) where the build artifacts are stored. It can be overridden with the CARGO_WORKSPACE_DIR environment variable, should this not be the right directory.
(See embuild::cargo::workspace_dir for more information).

There is no need to explicitly add a [workspace] section to the Cargo.toml of the workspace directory.

Please note that if you have set CARGO_TARGET_DIR and moved your target directory out of the crate root, then embuild is not able to locate the crate root. This will result in it among other things ignoring your local sdkconfig.defaults. In this case you must declare:

[env]
CARGO_WORKSPACE_DIR = { value = "", relative = true }

in the .cargo/config.toml file, to force it to look in the current directory.

The following configuration options are available:

  • esp_idf_sdkconfig_defaults, $ESP_IDF_SDKCONFIG_DEFAULTS

    A single path or a list of paths to sdkconfig.defaults files to be used as base values for the sdkconfig. If such a path is relative, it will be relative to the workspace directory.

    Defaults to sdkconfig.defaults.

    In case of the environment variable, multiple elements should be ;-separated.

    [!NOTE] For each defaults file in this list, a more specific file will also be searched and used. This happens with the following patterns and order (least to most specific):

    1. <path>
    2. <path>.<profile>
    3. <path>.<mcu>
    4. <path>.<profile>.<mcu>

    where <profile> is the current cargo profile used (debug/release) and <mcu> specifies the mcu for which this is currently compiled for (see the mcu configuration option below).

    [!WARNING] A setting contained in a more specific defaults file will override the same setting specified in a less specific one. For example, in a debug build, flags in sdkconfig.debug override those in sdkconfig.defaults.

  • esp_idf_sdkconfig, $ESP_IDF_SDKCONFIG

    The sdkconfig file used to configure the esp-idf. If this is a relative path, it is relative to the workspace directory.

    Defaults to sdkconfig.

    [!NOTE] Similar to the sdkconfig.defaults-file a more specific sdkconfig-file will be selected if available. This happens with the following patterns and precedence:

    1. <path>.<profile>.<mcu>
    2. <path>.<mcu>
    3. <path>.<profile>
    4. <path>

     

    [!NOTE] native builder only:
    The cargo optimization options (debug and opt-level) are used by default to determine the compiler optimizations of the esp-idf, however if the compiler optimization options are already set in the sdkconfig they will be used instead.

  • esp_idf_tools_install_dir, $ESP_IDF_TOOLS_INSTALL_DIR

    The install location for the ESP-IDF framework tooling.

    [!NOTE] The framework tooling is either PlatformIO when the pio builder is used, or the ESP-IDF native toolset when the native builder is used (default).

    This option can take one of the following values:

    • workspace (default) - the tooling will be installed or used in <crate-workspace-dir>/.embuild/platformio for pio, and <crate-workspace-dir>/.embuild/espressif for the native builder;

    • out - the tooling will be installed or used inside esp-idf-sys's build output directory, and will be deleted when cargo clean is invoked;

    • global - the tooling will be installed or used in its standard directory (~/.platformio for PlatformIO, and ~/.espressif for the native ESP-IDF toolset);

    • custom:<dir> - the tooling will be installed or used in the directory specified by <dir>. If this directory is a relative location, it is assumed to be relative to the workspace directory;

    • fromenv - use the build framework from the environment

      • native builder: use activated esp-idf environment (see esp-idf docs unix / windows)
      • pio builder: use platformio from the environment (i.e. $PATH)

      and error if this is not possible.

    [!WARNING] Please be extra careful with the custom:<dir> setting when switching from pio to native and the other way around, because the builder will install the tooling in <dir> without using any additional platformio or espressif subdirectories, so if you are not careful, you might end up with both PlatformIO, as well as the ESP-IDF native tooling intermingled together in a single folder.

    [!WARNING] The ESP-IDF git repository will be cloned inside the tooling directory. The native builder will use the esp-idf at idf_path of available.

  • idf_path, $IDF_PATH (native builder only)

    A path to a user-provided local clone of the esp-idf, that will be used instead of the one downloaded by the build script.

  • esp_idf_version, $ESP_IDF_VERSION (native builder only)

    The version used for the esp-idf, can be one of the following:

    • commit:<hash>: Uses the commit <hash> of the esp-idf repository. Note that this will clone the whole esp-idf not just one commit.
    • tag:<tag>: Uses the tag <tag> of the esp-idf repository.
    • branch:<branch>: Uses the branch <branch> of the esp-idf repository.
    • v<major>.<minor> or <major>.<minor>: Uses the tag v<major>.<minor> of the esp-idf repository.
    • <branch>: Uses the branch <branch> of the esp-idf repository.

    Defaults to v4.4.1.

  • esp_idf_repository, $ESP_IDF_REPOSITORY (native builder only)

    The URL to the git repository of the esp-idf, defaults to https://github.com/espressif/esp-idf.git.

    [!NOTE] When the pio builder is used, it is possible to achieve something similar to ESP_IDF_VERSION and ESP_IDF_REPOSITORY by using the platform_packages PlatformIO option as follows:

    ESP_IDF_PIO_CONF="platform_packages = framework-espidf @ <git-url> [@ <git-branch>]"

    The above approach however has the restriction that PlatformIO will always use the ESP-IDF build tooling from its own ESP-IDF distribution, so the user-provided ESP-IDF branch may or may not compile. The current PlatformIO tooling is suitable for compiling ESP-IDF branches derived from versions 4.3.X and 4.4.X.

  • $ESP_IDF_GLOB[_XXX]_BASE and $ESP_IDF_GLOB[_XXX]_YYY

    A pair of environment variable prefixes that enable copying files and directory trees that match a certain glob mask into the native C project used for building the ESP-IDF framework:

    • ESP_IDF_GLOB[_XXX]_BASE specifies the base directory which will be glob-ed for resources to be copied

    • ESP_IDF_GLOB[_XXX]_BASE_YYY specifies one or more environment variables that represent the glob masks of resources to be searched for and copied, using the directory designated by the ESP_IDF_GLOB[_XXX]_BASE environment variable as the root. For example, if the following variables are specified:

      • ESP_IDF_GLOB_HOMEDIR_BASE=/home/someuser
      • ESP_IDF_GLOB_HOMEDIR_FOO=foo*
      • ESP_IDF_GLOB_HOMEDIR_BAR=bar* ... then all files and directories matching 'foo*' or 'bar*' from the home directory of the user will be copied into the ESP-IDF C project.

      Note also that _HOMEDIR in the above example is optional, and is just a mechanism allowing the user to specify more than one base directory and its glob patterns.

  • $ESP_IDF_PIO_CONF_XXX (pio builder only)

    A PlatformIO setting (or multiple settings separated by a newline) that will be passed as-is to the platformio.ini file of the C project that compiles the ESP-IDF.

    Check the PlatformIO documentation for more information as to what settings you can pass via this variable.

    [!NOTE] This is not one variable, but rather a family of variables all starting with ESP_IDF_PIO_CONF_. For example, passing ESP_IDF_PIO_CONF_1 as well as ESP_IDF_PIO_CONF_FOO is valid and all such variables will be honored.

  • esp_idf_cmake_generator, $ESP_IDF_CMAKE_GENERATOR (native builder only)

    The CMake generator to be used when building the ESP-IDF.

    If not specified or set to default, Ninja will be used on all platforms except Linux/aarch64, where (for now) the Unix Makefiles generator will be used, as there are no Ninja builds for that platform provided by Espressif yet.

    Possible values for this environment variable are the names of all command-line generators that CMake supports with spaces and hyphens removed.

  • mcu, $MCU

    The MCU name (i.e. esp32, esp32s2, esp32s3 esp32c3, esp32c2, esp32h2, esp32c5, esp32c6, esp32p4).

    If not set this will be automatically detected from the cargo target.

    [!WARNING] Older ESP-IDF versions might not support all MCUs from above.

  • esp_idf_components, $ESP_IDF_COMPONENTS (native builder only)

    The (;-separated for the environment variable) list of esp-idf component names that should be built. This list is used to trim the esp-idf build. Any component that is a dependency of a component in this list will also automatically be built.

    Defaults to all components being built.

    [!NOTE]
    Some components must be explicitly enabled in the sdkconfig.
    Extra components must also be added to this list if they are to be built.

Example

An example of the [package.metadata.esp-idf-sys] section of the Cargo.toml.

[package.metadata.esp-idf-sys]
esp_idf_tools_install_dir = "global"
esp_idf_sdkconfig = "sdkconfig"
esp_idf_sdkconfig_defaults = ["sdkconfig.defaults", "sdkconfig.defaults.ble"]
# native builder only
esp_idf_version = "branch:release/v4.4"
esp_idf_components = ["pthread"]

Extra ESP-IDF components

It is possible to let esp-idf-sys compile extra ESP-IDF components and generate bindings for them.

This is possible by adding an object to the package.metadata.esp-idf-sys.extra_components array of the Cargo.toml. esp-idf-sys will honor all such extra components in the root crate's and all direct dependencies' Cargo.toml.

Note

By only specifying the bindings_header field, one can extend the set of esp-idf bindings that were generated from src/include/esp-idf/bindings.h. To do this you need to create a *.h header file in your project source, and reference that in the bindings_header variable. You can then include extra esp-idf header files from there.

An extra component can be specified like this:

[[package.metadata.esp-idf-sys.extra_components]]
# A single path or a list of paths to a component directory or directory 
# containing components.
# 
# Each path can be absolute or relative. Relative paths will be relative to the
# folder containing the defining `Cargo.toml`.
# 
# **This field is optional.** No component will be built if this field is absent, though
# the bindings of the `[Self::bindings_header]` will still be generated.
component_dirs = ["dir1", "dir2"] # or "dir"

# The path to the C header to generate the bindings with. If this option is absent,
# **no** bindings will be generated.
#
# The path can be absolute or relative. A relative path will be relative to the
# folder containing the defining `Cargo.toml`.
#
# This field is optional.
bindings_header = "bindings.h"

# If this field is present, the component bindings will be generated separately from
# the `esp-idf` bindings and put into their own module inside the `esp-idf-sys` crate.
# Otherwise, if absent, the component bindings will be added to the existing
# `esp-idf` bindings (which are available in the crate root).
#
# To put the bindings into its own module, a separate bindgen instance will generate
# the bindings. Note that this will result in duplicate `esp-idf` bindings if the
# same `esp-idf` headers that were already processed for the `esp-idf` bindings are
# included by the component(s).
#
# This field is optional.
bindings_module = "name"

and is equivalent to

[package.metadata.esp-idf-sys]
extra_components = [
    { component_dirs = [ "dir1", "dir2" ], bindings_header = "bindings.h", bindings_module = "name" }
]

Conditional compilation

The esp-idf-sys build script will set rustc cfgs available for its sources.

Important

If an upstream crate also wants to have access to the cfgs it must:

  • have esp-idf-sys as a dependency, and

  • propagate the cfgs in its build script with

    embuild::build::CfgArgs::output_propagated("ESP_IDF").expect("no esp-idf-sys cfgs");

    using the embuild crate.

The list of available cfgs:

  • esp_idf_comp_{component}_enabled for each component

  • esp_idf_version="{major}.{minor}"

  • esp_idf_version_full="{major}.{minor}.{patch}"

  • esp_idf_version_major="{major}"

  • esp_idf_version_minor="{minor}"

  • esp_idf_version_patch="{patch}"

  • esp_idf_{sdkconfig_option}

    Each sdkconfig setting where {sdkconfig_option} corresponds to the option set in the sdkconfig lowercased and without the CONFIG_ prefix. Only options set to y will get a cfg.

  • {mcu}

    Corresponds to the mcu for which the esp-idf is compiled for.

More info

If you are interested in how it all works under the hood, check the build.rs build script of this crate.

ESP32-C6/ESP32-P4 preliminary support

The ESP32-C6 and the upcoming ESP32-P4 are the first Espressif chips that support the "A" (atomic) extension of the RISCV specification. As such, they do not work with the existing riscv32imc-esp-espidf target, and instead need a new one (to be upstreamed to Rust) called riscv32imac-esp-espidf.

Until the target is upstreamed, you can use the following custom target:

{
    "arch": "riscv32",
    "cpu": "generic-rv32",
    "data-layout": "e-m:e-p:32:32-i64:64-n32-S128",
    "eh-frame-header": false,
    "emit-debug-gdb-scripts": false,
    "env": "newlib",
    "features": "+m,+a,+c",
    "is-builtin": false,
    "linker": "riscv32-esp-elf-gcc",
    "llvm-target": "riscv32",
    "max-atomic-width": 64,
    "os": "espidf",
    "panic-strategy": "abort",
    "relocation-model": "static",
    "target-family": [
      "unix"
    ],
    "target-pointer-width": "32",
    "vendor": "espressif"
  }

Save the target somewhere (perhaps in the root of your binary crate) under the name riscv32imac-esp-espidf.json and when building with cargo, pass it with --target riscv32imac-esp-espidf.json.