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Project Configuration

[TOC]

Overview

This document defines the organization of the program and project specific files needed by Zephyr EC projects.

The goals of the project organization include:

  • Minimize code duplication, allowing multiple projects to share common configuration options and devicetree nodes.
  • Define the set of files required by each project.
  • Define the best practices for devicetrees.

Glossary

  • program: The name of a Chromebook reference design. The program includes all Chromebooks based on a single AP SoC, such as Intel MeteorLake, Qualcomm 7c G3, or AMD Mendocino. The program corresponds to a single board overlay in the ChromeOS SDK. The term baseboard is often used as a synonym for program.

  • project: The name of a specific Chromebook model or variant. All Chromebook programs contain at least one project which serves as the reference design(s) for the program. The reference project may or may not use the same name as the program. For example, the reference project for the skyrim program is also called skyrim. The corsola program included two reference projects, kingler and krabby. For the legacy ECOS builds, board was used as a synonym for project.

This document uses bold to highlight the terms program and project to reference the definitions above.

Directory Structure

The zephyr/program contains the program and project configuration files for all Zephyr based EC builds.

zephyr/program directory

Each program has it's own subdirectory under zephyr/program.

zephyr/program/
├── brya/
├── corsola/
├── herobrine/
├── intelrvp/
├── it8xxx2_evb/
├── minimal/
├── nissa/
├── npcx_evb/
├── rex/
├── skyrim/
└── trogdor/

The zephyr/program/minimal program contains example EC projects that demonstrate how to build a Zephyr EC with the minimum feature set enabled. These projects require only a working UART on the target board.

zephyr/program/<program>/ Directory Overview

Each program subdirectory contains a subdirectory foreach each project, including a subdirectory for the reference project.

The minimum configuration for a program named skyrim with just a single reference project, also named skyrim, is shown below.

zephyr/program/skyrim/
├── include/
│   └── <program headers>.h
├── skyrim/
│   ├── include/
│   │   └── <project headers>.h
│   ├── src/
│   │   └── <project sources>.c
│   ├── CMakeLists.txt
│   ├── project.conf
│   └── project.overlay
├── src/
│   └── <program sources>.c
├── BUILD.py
├── CMakeLists.txt
├── Kconfig
├── program.conf
└── <devicetrees>.dtsi

zephyr/program/<program>/ Directory Details

Description of the files and directories found directly in the level directory. Note that all paths are relative to the zephyr/program/ directory.

  • <program>/: Top level directory for the program. skyrim is the program name in the example above.
  • <program>/include/: Directory containing the header files common to all projects in the program. Use of program level includes is discouraged. Instead, consider creating a generic driver that can be shared across all programs.
  • <program>/src/: Directory containing the C source files common to all projects in the program.
  • <program>/BUILD.py: Defines which projects can be made from this directory.
  • <program>/CMakeLists.txt: CMake file for the program.
  • <program>/Kconfig - Defines new Kconfig options, used by all projects in the program.
  • <program>/program.conf - Sets the default Kconfig settings for all projects.
  • <program>/<devictrees>.dtsi - One or more devicetree files, organized by the hardware module or EC feature. See the Devicetree Best Practices section for additional information.
  • <program>/<project>/: Top level directory for the <project>. Create a separate directory for each project defined by the program.

zephyr/program/<program>/<project>/ Directory Details

Each project provides the following files. Note that all paths are relative to the zephyr/program/<program>/ directory.

  • <project>/include/: The project may optionally provide a public include directory, but this is discouraged. There are some exceptions where the legacy EC code expects the project to define a public header, such as the keyboard_customization.h file.
  • <project>/src/: Directory containing the C source files specific to the project.
  • <project>/CMakeLists.txt: CMake file for the project.
  • <project>/project.conf: Kconfig settings for the project.
  • <project>/project.overlay: Main devicetree overlay for the project.

Creation of custom C source files specific to the program or project is discouaraged. You can usually project manage project specific settings with Kconfig and devicetree changes only.

Note that program and project custom C files are still subject to the same unit test requirements. So all custom C files also require that you write tests.

Setting up a new program

To set up a new EC program, create a new directory under zephyr/program with the organization shown below. Note that for this example, the new program is called "my_program", and the reference project is called "my_reference_project".

Tip - Copy one the projects defined by the minimal program to start with the bare miminimum of features required to boot the Zephyr EC appliation. Then follow the steps in the detailed in Creating a New Zephyr EC Project.

zephyr/program/my_program/
├── my_reference_project/
│   ├── CMakeLists.txt
│   ├── project.conf
│   └── project.overlay
├── BUILD.py
├── CMakeLists.txt
├── Kconfig
└── program.conf

An in-depth example of each file is given below:

BUILD.py

BUILD.py is a Python-based config file for setting up your reference board and the associated variants. The name BUILD.py is important and case-sensitive: zmake searches for files by this name.

When BUILD.py is sourced, the following two globals are defined:

  • here: A pathlib.Path object containing the path to the directory BUILD.py is located in.
  • register_project: A function which informs zmake of a new project to be built. Your BUILD.py file needs to call this function one or more times.

register_project takes the following keyword arguments:

  • project_name (required): The name of the project (typically the Google codename). This name must be unique amongst all projects known to zmake, and zmake will error if you choose a conflicting name.

  • zephyr_board (required): The name of the EC chip used. Note: the concept of a Zephyr board does not align with the ChromeOS concept of a board. The Zephyr build system requires a set of devicetree and Kconfig files under under boards/${ARCH}/${ZEPHYR_BOARD_NAME}. For the Zephyr EC application, the EC chip is mapped onto the Zephyr board organization. Supported zephyr_boards include:

    • mec1727: Microchip MEC1727, 416 KiB RAM, 512 KiB flash
    • npcx7: Nuvoton NPCX7m7FC, 384 KiB, 512 KiB flash
    • npcx9m3f: Nuvoton NPCX9m3F, 320 KiB RAM, 512 KiB flash
    • npcx9m7f: Nuvoton NPCX9m7F, 384 KiB RAM, 1 MiB flash
    • it81202bx: ITE IT81202, 60 KiB RAM, 1 MiB flash
    • it81302bx: ITE IT81302, 60 KiB RAM, 1 MiB flash

  • supported_toolchains (required): A list of the toolchain names supported by the build. Valid values are:

    • coreboot-sdk: only supported in the chroot
    • host: used for unit and integration tests
    • llvm: only supported in the chroot
    • zephyr: only supported outside the chroot

  • output_packer (required): An output packer type which defines which builds get generated, and how they get assembled together into a binary.

  • modules (optional): A list of module names required by the project. The default, if left unspecified, is to use all modules known by zmake. Generally speaking, there is no harm to including unnecessary modules as modules are typically guarded by Kconfig options, so the only reason to set this is if your project needs to build in a limited environment where not all modules are available.

  • dts_overlays (optional): A list of files which should be concatenated together and applied as a Zephyr device-tree overlay. The recommended setting is to select the project specific devicetree overlay file.

    dts_overlays=[here / project_name / "project.overlay"]

  • kconfig_files (optional): A list of files that contain the Kconfig settings for the project. The recommended setting is select the program configuration file followed by the project configuration file.

    kconfig_files=[here / "program.conf", here / <project> / "project.conf",]

  • project_dir (optional): The path to where CMakeLists.txt and Kconfig can be found for the project, defaulting to here.

Note that most projects will not want to call register_project directly, but instead one of the helper functions, which sets even more defaults for you:

  • register_host_project: Define a project which runs in the chroot (not on hardware).
  • register_raw_project: Register a project which builds a single .bin file, no RO+RW packing, no FMAP.
  • register_binman_project: Register a project which builds RO and RW sections, packed together, and including FMAP.
  • register_npcx_project: Just like register_binman_project, but expects a file generated named zephyr.npcx.bin for the RO section with Nuvoton's header.

You can find the implementation of these functions in zephyr/zmake/zmake/configlib.py.

BUILD.py files are auto-formatted with black. After editing a BUILD.py file, please run black BUILD.py on it.

CMakeLists.txt

This file, should at minimum contain the following:

cmake_minimum_required(VERSION 3.20.1)

find_package(Zephyr REQUIRED HINTS "${ZEPHYR_BASE}")
project(**project**)

If your program provides any C files, add them to your program CMake file using zephyr_library_sources().

zephyr_library_sources("src/my_program_source.c")

For your project C files, create <project>/CMakeLists.txt and use add_subdirectory() to include the project CMake file.

add_subdirectory("my_reference_project")

Add the requires zephyr_library_souces() calls to the <project>/CMakeLists.txt file.

If your program or project provides a public header, make the include directory visible to rest of the code using cros_ec_library_include_directories().

cros_ec_library_include_directories("include")

Kconfig

If certain projects need project-specific C files or ifdefs, the only way to do so is to create a Kconfig file with the options schema you want, and use it to toggle the inclusion of certain files.

The file must end with a single line that reads source "Kconfig.zephyr". Note that this file is optional, so it's recommended to only include it if you really need it.

program.conf

program.conf has default Kconfig settings for all projects defined for the program. The format is KEY=VALUE, as typical for Kconfig.

project.conf

project.conf has the Kconfig settings for a single project. The format is KEY=VALUE, as typical for Kconfig.

Kconfig settings in project.conf take precedence over the Kconfig settings from program.conf.

project.overlay

project.overlay is the main devicetree overlay for the project. The project.overlay contains the following components:

  • One or more #include statements to add devicetrees defined by the program into project.
  • /delete-node/ statements to remove specific devicetree nodes defined by the program devicetrees.
  • New devicetree nodes for project specific settings that are not provided by any program devicetrees.

Tip: After building your project, you can view the final devicetree in the file build/zephyr/<project>/build-ro/zephyr/zephyr.dts.

Setting up a new variant of an EC program

Unlike our legacy EC, there are no files or directories to copy and paste to setup a new variant in Zephyr code.

Simply add a register_project-based call to the existing BUILD.py for your reference board.

Below is an example of how programs may wish to structure this in BUILD.py:

# Copyright 2021 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

def register_variant(project_name, chip="it8xx2", extra_dts_overlays=()):
    return register_binman_project(
        project_name=project_name,
        zephyr_board=chip,
        dts_overlays=[
            here / "base_power_sequence.dts",
            here / "i2c.dts",
            **extra_dts_overlays,
        ],
    )


# Reference board
register_variant(
    project_name="asurada",
    extra_dts_overlays=[here / "reference_gpios.dts"],
)

# Variants
register_variant(
    project_name="hayato",
    extra_dts_overlays=[here / "hayato_gpios.dts"],
)

If a project is going to be a simple variant of another project (e.g., project bar is exactly identical to project foo but has just a few device-tree/Kconfig changes), you can spin a new variant using the return value of the register functions:

foo = register_variant(project_name="foo")
bar = foo.variant(
    project_name="bar",
    dts_overlays=[here / "bar_extras.dts"],
)

With this simple variant syntax, lists (like Kconfig files and DTS overlays) are concatenated. This means it's not possible to remove files during variant registration for this syntax, so it's only recommended for the simple case.

Devicetree Best Practices

Below are the best practices for devicetree organization:

  • Split the devicetree across multiple files, organized by the functional block. This organization applies to the shared program devicetrees only.

    • FW_CONFIG
    • GPIOs
    • I2C
    • Interrupts
    • Keyboard
    • LEDs
    • Sensors
    • Thermal (fans and temperature sensors)
    • USB-C

  • When creating program, usually with a single reference project, add the shared devicetree files in the program directory, separated by the functional area noted above.

  • Each project creates a project.overlay file, and uses #include statements to add shared devicetree files from the program directory. An example project.overlay for the skyrim project is shown below.

    /* Copyright 2021 The ChromiumOS Authors
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/* Skyrim program common DTS includes */
#include "../adc.dtsi"
#include "../fan.dtsi"
#include "../gpio.dtsi"
#include "../i2c.dtsi"
#include "../interrupts.dtsi"
#include "../keyboard.dtsi"
#include "../motionsense.dtsi"
#include "../usbc.dtsi"

/* Skyrim project node overrides */
/* ... */

Managing project specific settings

When the project needs to make changes to the shared devicetree files, there are two strategies:

  • For small changes, add the /delete-node/ attribute to the project.overlay file to remove the specific devices and devicetree nodes from the project final devicetree.
  • For larger changes, remove the corresponding #include statements from the project.overlay file. Then,dDirectly add any required nodes to the project.overlay file.

In both cases, the shared devicetree file in the program directory is not changed.

Small Devicetree Changes

Examples of small devicetree changes include:

  • Change the I2C peripheral address of a device.
  • Changing USB-C related chips.
  • Changing motionsense properties, such as the odr and ec-rate properties.
  • Overriding a specific property of a node - for instance modifying the pinctrl-0 property to adjust the EC pins connected to a device driver.

The example below demonstrates how to define a device in a program devicetree file and then override the setting in the project.overlay file.

  • The herobrine program defines the TCPC at I2C address 0xb in the file zephyr/program/herobrine/i2c.dtsi. This I2C address is valid for the herobrine, evoker, and villager projects while the hoglin project needs to change the I2C address to 0x1b.

    /* zephyr/program/herobrine/i2c.dtsi */

&i2c1_0 {
  status = "okay";
  /* ... */
  tcpc_port0: ps8xxx@b {
    compatible = "parade,ps8xxx";
    reg = <0xb>;
  };
};

  • The hoglin project.overlay file deletes the TCPC node at address 0xb and creates a new node at address 0x1b. The node name “tcpc_port0” is kept the same, so any references to this node name do not change, such as the USB-C port configuration.

    /* zephyr/program/herobrine/hoglin/project.overlay */

#include “../i2c.dtsi”

&i2c1_0 {
  /delete-node/ ps8xxx@b;
  tcpc_port0: ps8xxx@1b {
    compatible = "parade,ps8xxx";
    reg = <0x1b>;
  };
};

While it is also possible to change a device’s I2C address by directly overriding the reg property, this should not be done. Changing only the reg property causes a mismatch between the node name, ps8xxx@b, and the actual device address, 0x1b.

Your project.overlay file can also directly override properties defined by the program devicetree files.

  • The skyrim program sets the I2C clock frequency for first I2C bus to fast (400 KHz). 
    /* zephyr/program/skyrim/i2c.dtsi */
&i2c0_0 {
  status = "okay";
  label = "I2C_TCPC0";
  clock-frequency = <I2C_BITRATE_FAST>;
  pinctrl-0 = <&i2c0_0_sda_scl_gpb4_b5>;
  pinctrl-names = "default";
};
  • Override the I2C clock frequency to fast-plus (1 MHz) in the winterhold project.overlay. 
    /* zephyr/program/skyrim/winterhold/project.overlay */
#include "../i2c.dtsi"
&i2c0_0 {
  clock-frequency = <I2C_BITRATE_FAST_PLUS>;
};

Large Devicetree Changes

For large devicetree changes, the preference is to copy the relevant devicetree fragment into the project.overlay file and edit the fragment directly.

Examples of large devicetree changes (or changes that don’t benefit from using the /delete-node/ attribute) include:

  • GPIOs - specifically the “named-gpios” node. This integrates better with the arbitrage and the pinmap utility, which auto-generates the EC GPIO settings based on schematic data.
  • Changes to the motionsense sensor types. Currently x86 architectures impose a fixed ordering for the accelerometers and gryoscopes when accessed through the LPC memory map (see the EC_MEMMAP_ACC_DATA). Deleting nodes changes the order of the children under the motionsense-sense node and causes the test hardware.SensorAccel to fail. Copy the motionsense nodes into the project.overlay file and modify as required.
  • LED policies - generally each OEM/ODM defines unique LED policies for their designs to establish differentiation for their brand. There is little value to creating common LED policies for all projects in the program.
  • Batteries - batteries also are generally specific to the OEM/ODM. Define the project batteries directly in the project.overlay file.