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Practical Zephyr – West workspaces (Part 6)

By May 15, 2024No Comments

In the previous articles, we used freestanding applications and relied on a global Zephyr installation. In this article, we’ll see how we can use West to resolve global dependencies by using workspace applications. We first explore West without even including Zephyr and then recreate the modified Blinky application from the previous article in a West workspace.

After this article, you should know West not as a meta-tool for build and flash commands, but as a powerful dependency manager for your Zephyr applications. Hopefully – after reading this article – you will no longer create freestanding Zephyr applications but will use West workspaces only.

Table of Contents

Prerequisites

This article is part of the Practical Zephyr article series. In case you haven’t read the previous articles, please go ahead and have a look. This article requires that you’re able to build and flash a Zephyr application to the board of your choice and that you’re familiar with Devicetree.

We’ll be using the development kit for the nRF52840 and the STM32 Nucleo-64 development board, but you can follow along with any target – real or virtual.

Note: This article uses two manifest repositories that are available on GitHub:

Note: While writing this article series, I had to switch from STM’s Nucleo-C031C6 to the Nucleo-F411RE since I broke my C031C6 development kit. Apologies for the subtle switch – but you should be able to follow along with any board.

Creating a workspace from scratch

Let’s start from scratch, without any tools installed. Ok, that might be a bit much – let’s say you have at least git, python and pipenv installed. You can, of course, use pyenv or install directly using pip, whatever works best for you!

$ mkdir workspace
$ cd workspace

Installing west

We’ve been using West a lot now to build, debug and flash our project. It comes bundled with the nRF Connect SDK, so until now, we didn’t have to install it at all. Without sourcing any paths, e.g., from a setup.sh script that we created at the very beginning of this article series, I don’t have West installed:

$ west --version
zsh: command not found: west

The first thing to even get started is therefore installing West, which is available as a python package. Instead of following the official documentation and installing West globally, I’ll be using pipenv to manage an environment for me:

$ pwd
$ path/to/workspace
$ touch Pipfile

In my Pipfile, I can simply add west as a dev-package, since I won’t be needing it for any python application or extension:

[]
url = "https://pypi.org/simple"
verify_ssl = true
name = "pypi"

[dev-packages]
autopep8 = "*"
pylint = "*"
west = "1.2"

[requires]
python_version = "3.11"

All that’s left to do is to install the environment and activate the shell, and we have West available:

workspace $ pip install pipenv
workspace $ pipenv install --dev
workspace $ pipenv shell
(workspace) workspace $ west --version
West version: v1.2.0

In the remainder of this article, I won’t explicitly refer to the python environment or West installation anymore. It is up to you to decide which approach to use, e.g., installing West globally, using pipenv, venv, poetry, or maybe you’re using one Zephyr’s docker images – whatever works best for you!

Adding a manifest

We now want to use West to handle our dependencies: We really want to move on from using a global installation that may or will change at any time, and instead have all of our dependencies managed in our workspace. Zephyr evolves fast and it is therefore very important to have fixed versions of all modules and Zephyr’s source code.

West solves this by using a so-called manifest file, which is nothing else than a list of external dependencies – and then some. West uses this manifest file to basically act like a package manager for your C project, similar to what cargo does with its cargo.toml files for Rust.

Note: Please don’t pin me down for comparing West with cargo. I’m just trying to find some other description than “Swiss Army Knife”.

Note: The complete complete manifest repository used in this section is available on GitHub: practical-zephyr-t2-empty-ws.

West can also be used if you’re not planning to create a Zephyr project. In fact, let’s start with a manifest file that doesn’t include Zephyr at all. For that, we create the file app/west.yml in our workspace folder.

workspace $ mkdir app
workspace $ tree
.
├── app
│   └── west.yml
├── Pipfile
└── Pipfile.lock

The minimal content of our manifest file is the following:

app/west.yml

manifest:
  # lowest version of the manifest file schema that can parse this file’s data
  version: 0.8

Zephyr’s official documentation on West basics calls the workspace folder the “topdir” and our app folder the manifest repository: In an idiomatic workspace, the folder containing the manifest file is a direct sibling of the “topdir” or workspace root directory, and it is a git repository. The folder name app is just a personal preference.

Note: I’m using the term “idiomatic” since there are multiple ways of setting up West workspaces. Placing your manifest file into a folder that is a direct sibling of the workspace is a convention. Nothing stops you from placing your manifest file in a different folder, e.g., deeper within your folder tree. This does, however, have some drawbacks since some of the West commands, e.g., west init, are currently not very customizable, e.g., initializing a workspace using a repository and the -m argument won’t work out-of-the-box.

Feel free to experiment with your version of West. I’m sure there will be some changes in the future, but for now, we focus on the intended or “idiomatic” way of using West.

Let’s initialize the repository for our app folder containing the manifest files:

workspace/app $ git init
Initialized empty Git repository in /path/to/workspace/app/.git/

workspace/app $ tree --dirsfirst -a -L 2 ../
../      # topdir
├── app  # manifest _repository_
│   ├── .git
│   └── west.yml  # manifest _file_
├── Pipfile
└── Pipfile.lock

workspace/app $ git remote add origin git@github.com:lmapii/practical-zephyr-t2-empty-ws.git
workspace/app $ git add --all
workspace/app $ git commit -m "initial commit"
workspace/app $ git push -u origin main

Initializing the workspace

Having everything under version control we can relax and start exploring. First, we finally initialize the West workspace using west init. There are two ways to initialize a West workspace:

  • Locally, using the -l or --local flag: This assumes that your manifest repository already exists in your filesystem, e.g., you already used git clone to populate it in the topdir.
  • Remotely, by specifying the URL to the manifest repository using the argument -m. With this argument, West clones the manifest repository into the topdir for you before initializing the workspace. We’ll see how this works in a later section.

There is no difference between the two methods except that West also clones the repository when using the -m argument to pass the manifest repository URL. Since our manifest repository is initialized already in the app folder, we can initialize the workspace using this local manifest repository:

workspace/app $ west init --local .
=== Initializing from existing manifest repository app
--- Creating /path/to/workspace/.west and local configuration file
=== Initialized. Now run "west update" inside /path/to/workspace.

workspace/app $ tree --dirsfirst -a -L 2 ../
../
├── .west
│   └── config
├── app
│   ├── .git
│   └── west.yml
├── Pipfile
└── Pipfile.lock

When initializing a workspace, West creates a .west directory in the topdir, which in turn contains a configuration file.

workspace/app $ cat ../.west/config
[manifest]
path = app
file = west.yml

The location of the .west folder “marks” the topdir and thus the West workspace root directory. Within this file, we can see that West stores the location and name of the manifest file. Modifying this file – or any file within the .west folder – is not recommended, since some of West’s commands might no longer work as expected.

“west/config” sounds familiar, doesn’t it? If you’ve been following this article series, you might remember that we already encountered the west config command in the very first article: We used the command “west config build.board nrf52840dk_nrf52840” to configure the board for our build so that we didn’t have to pass it as an argument to west build anymore. This does sound suspiciously similar to “west/config”!

Let’s try and see how west config affects our workspace and .west/config:

workspace/app $ west config build.board nrf52840dk_nrf52840
workspace/app $ cat ../.west/config
[manifest]
path = app
file = west.yml

[build]
board = nrf52840dk_nrf52840

Having initialized a West workspace, we can now see that west config by default uses this local configuration file to store its configuration options. West also supports storing configuration options globally or even system-wide. Have a look at the official documentation in case you need to know more.

Let’s get rid of the configuration option and finally run west update as suggested by the output we got in our call to west init:

workspace/app $ west config -d build.board
workspace/app $ cd ../
workspace $ west update
workspace $ # nothing happens

Huh, that was disappointing. west update didn’t do anything – feel free to check your files, nothing changed! The reason for that is quite simple: With west init we already took care of initializing the workspace. Since we don’t have any external dependencies to manage, we have no work for west update.

Adding projects

In your manifest file, you can use the manifest.projects key to define all Git repositories that you want to have in your workspace. Let’s say that we’re planning to use a more modern doxygen documentation for our project and therefore want to add Doxygen Awesome to our workspace. We can add this external dependency as an entry in the manifest.projects key of our manifest file:

app/west.yml

manifest:
  version: 0.8

  projects:
    - name: doxygen-awesome
      url: https://github.com/jothepro/doxygen-awesome-css
      # you can also use SSH instead of HTTPS:
      # url: git@github.com:jothepro/doxygen-awesome-css.git
      revision: main
      path: deps/utilities/doxygen-awesome-css

Every project at least has a unique name. Typically, you’ll also specify the url of the repository, but there are several options, e.g., you could use the remotes key to specify a list of URLs and add specify the remote that is used for your project. You can find examples and a detailed explanation of all available options in the official documentation for the projects key.

With the revision key you can tell West to check out either a specific branch, tag, or commit hash. Without specifying the revision, at the time of writing West defaults to the master branch. Since Doxygen Awesome uses main as a development branch, we have to specify it explicitly.

The path key is also an optional key that tells West the relative path to the topdir that it should use when cloning the project. Without specifying the path, West uses the project’s name as the path. Notice that you’re not allowed to specify a path that is outside of the topdir and thus West workspace.

With that project added, we finally have some work for west update:

workspace $ west update
=== updating doxygen-awesome (deps/utilities/doxygen-awesome-css):
--- doxygen-awesome: initializing
Initialized empty Git repository in /path/to/workspace/deps/utilities/doxygen-awesome-css/.git/
--- doxygen-awesome: fetching, need revision main
...
HEAD is now at 8cea9a0 security: fix link vulnerable to reverse tabnabbing (#127)

Great! Now West populated our dependencies and we have Doxygen Awesome available in the specified path:

workspace $ tree --dirsfirst -a -L 3 --filelimit 8
.
├── .west
│   └── config
├── app
│   ├── .git  [10 entries exceeds filelimit, not opening dir]
│   └── west.yml
├── deps
│   └── utilities
│       └── doxygen-awesome-css
├── Pipfile
└── Pipfile.lock

The folder name deps is again just a personal choice. I have borrowed this convention from Mike Szczys’ talk “Manifests: Project Sanity in the Ever-Changing Zephyr World” from the 2022 Zephyr Developer Summit, and we’ll see why it makes sense to collect your dependencies in just a bit.

In our manifest file, we specified that we want to use the main branch for the doxygen-awesome project. This kind of defeats the purpose of using a manifest to create a stable workspace since we’ll always be checking out the latest version of the repository when using west update. Instead, you’ll typically either specify a tag or even a specific commit in the revision.

At the time of writing, the tag v2.2.1 was the latest release available for doxygen-awesome, pointing at the commit with the shortened hash df83fbf. Let’s update the manifest to use the latest tag:

app/west.yml

manifest:
  version: 0.8

  projects:
    - name: doxygen-awesome
      url: https://github.com/jothepro/doxygen-awesome-css
      revision: v2.2.1
      path: deps/utilities/doxygen-awesome-css

Running west update changes our dependency to the specified revision:

workspace $  west update
=== updating doxygen-awesome (deps/utilities/doxygen-awesome-css):
Warning: you are leaving 2 commits behind, not connected to
any of your branches:

  8cea9a0 security: fix link vulnerable to reverse tabnabbing (#127)
  00a52f6 Makefile: install -tabs.js as well (#122)

If you want to keep them by creating a new branch, this may be a good time
to do so with:

 git branch  8cea9a0

HEAD is now at df83fbf fix rendering error in example class

Looks like the main branch was already two commits ahead of the specified revision!

West thus takes care of all the projects that we’re using. We can, in fact, delete the entire deps repository and run west update again, and it’ll simply put it back into its specified state. This is also the reason why it makes sense to group external dependencies, e.g., into this deps folder (full credits to Mike Szczys and Golioth): Whenever you’re not working on this project anymore, you can simply delete the deps and .west folders to save disk space (as soon as we’ll add Zephyr this becomes a significant amount of disk space). Once you pick it up again, simply run west init and west update and you’re ready to go.

Note: More complex applications include lots of projects in their manifest hierarchy. Having a single dependency folder deps can also help in your CI builds: E.g., with GitHub actions you can cache your dependency folder and thereby significantly reduce the time required to run west update. The GitHub action used by the practical-zephyr-manifest-repository that we’ll create later in this article uses such a cache for demonstration purposes. Noah Pendleton wrote an excellent article about GitHub actions for NCS applications.

Whatever project structure you’re using, however, is entirely up to you and always subject to personal preference.

Creating a workspace from a repository

In Zephyr’s official documentation for West, the first example call to west init uses the -m argument to specify the manifest repository’s URL. In the previous section, we’ve seen how we can create such a manifest repository and how to use west init --local to initialize the workspace locally.

Instead of initializing a workspace locally, let’s use the manifest file and repository that we’ve created in the previous section and initialize the workspace from scratch using its remote URL. Let’s fire up a new terminal (I’ll be installing West again in a virtual environment) and get started right away:

$ mkdir workspace-m
$ cd workspace-m

workspace-m $ west init -m git@github.com:lmapii/practical-zephyr-t2-empty-ws.git
=== Initializing in /path/to/workspace-m
--- Cloning manifest repository from git@github.com:lmapii/practical-zephyr-t2-empty-ws.git
Cloning into '/path/to/workspace-m/.west/manifest-tmp'...
...
--- setting manifest.path to practical-zephyr-t2-empty-ws.git
=== Initialized. Now run "west update" inside /path/to/workspace-m.

workspace-m $ tree --charset=utf-8 --dirsfirst -a -L 2
.
├── .west
│   └── config
├── practical-zephyr-t2-empty-ws.git
│   ├── .git
│   └── west.yml
├── Pipfile
└── Pipfile.lock

Notice that we no longer specify the current directory in the call to west init using “.”. In fact, the directory – optionally passed as the last argument to west init – is interpreted differently by West when using the --local flag or the -m arguments:

  • With --local, the directory specifies the path to the local manifest repository.
  • Without the --local flag, the directory refers to the topdir and thus the folder in which to create the workspace (defaulting to the current working directory in this case).

Awkward, but this approach is probably used due to legacy reasons. If no --local flag is used and no repository is specified using -m, West defaults to using the Zephyr repository.

The file tree, however, isn’t exactly what we wanted … west init created a folder practical-zephyr-t2-empty-ws.git instead of the folder called app that we’ve had before. Well, there’s no way for West to know that we want the manifest repository to use the folder name app, so it uses the repository’s name instead. How can we change that?

Updating the manifest repository path

The manifest file uses the key manifest.self for configuring the manifest repository itself, meaning that all settings in the manifest.self key are only applied to the manifest repository. The key manifest.self.path can be used to specify the path that West uses when cloning the manifest repository, relative to the West workspace topdir.

Let’s update the west.yml file in the folder that west init cloned for us as follows:

practical-zephyr-t2-empty-ws.git/west.yml

manifest:
  version: 0.8

  # Entries in the `self` key are only applied to the _manifest repository_
  self:
    path: app

  projects:
    - name: doxygen-awesome
      url: https://github.com/jothepro/doxygen-awesome-css
      revision: main
      path: deps/utilities/doxygen-awesome-css

Don’t forget to commit and push the change: We’re passing a URL to west init so West obviously won’t pick up local changes during the workspace initialization.

To reinitialize the workspace, we must remove the .west folder, otherwise west init throws an error telling us that the workspace is already initialized:

workspace-m $ west init -m git@github.com:lmapii/practical-zephyr-t2-empty-ws.git
FATAL ERROR: already initialized in /path/to/workspace-m, aborting.
  Hint: if you do not want a workspace there,
  remove this directory and re-run this command:

  /path/to/workspace-m/.west

Let’s follow the instructions and also remove practical-zephyr-t2-empty-ws.git before reinitializing the workspace:

workspace-m $ rm -rf .west practical-zephyr-t2-empty-ws.git
workspace-m $ west init -m git@github.com:lmapii/practical-zephyr-t2-empty-ws.git
=== Initializing in /path/to/workspace-m
...
--- setting manifest.path to app
=== Initialized. Now run "west update" inside /path/to/workspace-m.

workspace-m $ tree --charset=utf-8 --dirsfirst -a -L 2
.
├── .west
│   └── config
├── app
│   ├── .git
│   └── west.yml
├── Pipfile
└── Pipfile.lock

Now we can run west update and we end up with the same workspace as we got when initializing it locally:

workspace-m $ west update
=== updating doxygen-awesome (deps/utilities/doxygen-awesome-css):
--- doxygen-awesome: initializing
Initialized empty Git repository in /path/to/workspace-m/deps/utilities/doxygen-awesome-css/.git/
--- doxygen-awesome: fetching, need revision v2.2.1
...
HEAD is now at df83fbf fix rendering error in example class

workspace-m $ tree --dirsfirst -a -L 3 --filelimit 8
.
├── .west
│   └── config
├── app
│   ├── .git  [10 entries exceeds filelimit, not opening dir]
│   └── west.yml
├── deps
│   └── utilities
│       └── doxygen-awesome-css
├── Pipfile
└── Pipfile.lock

Locally vs. remotely initialized workspaces

What is the difference between a West workspace that has been initialized locally using the --local flag, or remotely by passing the URL of the manifest repository? As mentioned already, thankfully, the short answer is none.

The only difference is that for remotely initialized workspaces West clones the repository for you and thus you essentially don’t need to use git clone to obtain the manifest repo used to setup the workspace.

We can also see this in the configuration file .west/config:

workspace-m $ cat .west/config
[manifest]
path = app
file = west.yml

Just like for the locally initialized repository, the [manifest] section points to the manifest file in the app folder. Running west update therefore only checks the contents of the local manifest file. It won’t try to pull new changes in the manifest repository and it also won’t attempt to read the file from the remote.

If there were any changes to the manifest file in the repository, you’ll have to git pull them in your manifest repository – which is a good thing. In fact, west update will never attempt to modify the manifest repository and also states this in the --help information for the update command:

“This command does not alter the manifest repository’s contents.”

Zephyr with West

Having covered the West basics, let’s get back to creating Zephyr applications and put this knowledge into practice.

In this section, we recreate the modified Blinky application that we’ve seen in the previous article, where we failed to compile the application for the STM32 Nucleo-64 development board since we relied upon the sources from a globally installed nRF Connect SDK – which doesn’t include STM32 HAL.

Note: You can find the complete manifest repositories on GitHub: practical-zephyr-manifest-repository.

Application skeleton

Let’s zoom through the usual warm-up to create our application. Go ahead and create the following file tree:

$ tree --dirsfirst -a -L 3
.
└── app
    ├── boards
    │   └── nrf52840dk_nrf52840.overlay
    ├── src
    │   └── main.c
    ├── CMakeLists.txt
    └── prj.conf

As an application, we’re using a modified version of the Blinky sample, where we select the LED node via a newly created /chosen node, and output “Tick” and “Tock” each time the LED is turned on or off:

app/main.c

/** file main.c */

#include 
#include 

#define SLEEP_TIME_MS 1000U
#define LED_NODE      DT_CHOSEN(app_led)

static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED_NODE, gpios);

void main(void)
{
    int err   = 0;
    bool tick = true;

    if (!gpio_is_ready_dt(&led))
    {
        printk("Error: LED pin is not available.n");
        return;
    }

    err = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
    if (err != 0)
    {
        printk("Error %d: failed to configure LED pin.n", err);
        return;
    }

    while (1)
    {
        (void) gpio_pin_toggle_dt(&led);
        k_msleep(SLEEP_TIME_MS);

        if (tick != false) { printk("Tickn"); }
        else { printk("Tockn"); }
        tick = !tick;
    }
}

I’ll again build the application for my nRF52840 Development Kit from Nordic and will only later switch to the STM32 Nucleo-64 development board, so, for now, all I need is the matching nrf52840dk_nrf52840.overlay that specifies the chosen LED node:

app/boards/nrf52840dk_nrf52840.overlay

/ {
    chosen {
        app-led = &led0;
    };
};

The prj.conf remains empty, and the CMakeLists.txt only includes the same old boilerplate to create a Zephyr application with a single main.c source file:

app/CMakeLists.txt

cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

project(
    EmptyApp
    VERSION 0.1
    DESCRIPTION "Modified Blinky application."
    LANGUAGES C
)

target_sources(
    app
    PRIVATE
    src/main.c
)

Trying to run west build shows us that we’re not just missing the Zephyr source code, but we’re also still lacking the Zephyr-specific extension commands, e.g., build:

workspace-m $ west build
usage: west [-h] [-z ZEPHYR_BASE] [-v] [-V] <command> ...
west: unknown command "build"; workspace /path/to/workspace-m does not define this extension command -- try "west help"

As we’ve seen in previous articles, e.g., build and flash are Zephyr-specific extension commands that are not included by a plain West installation. We’ll resolve this in the following sections.

Setting up the manifest repository and file

For our workspace structure, we’re using what’s known as a “T2 star topology”: In such a topology, the manifest repository does not only contain the manifest file(s) but also contains all application files.

We have all of our application code ready in the app folder, so let’s go ahead, create an empty app/west.yml and make the app folder our manifest repository:

$ cd app
$ git init
$ touch west.yml
$ git add --all
$ cd ../

$ tree --dirsfirst -a -L 3
.
└── app  # manifest repository
    ├── .git
    ├── boards
    │   └── nrf52840dk_nrf52840.overlay
    ├── src
    │   └── main.c
    ├── CMakeLists.txt
    ├── prj.conf
    └── west.yml  # manifest file

With this, we can initialize our workspace as follows:

$ west init --local app
=== Initializing from existing manifest repository app
--- Creating /path/to/workspace/.west and local configuration file
=== Initialized. Now run "west update" inside /path/to/workspace.

Before running west update, let’s add Zephyr as a project in manifest.projects just like what we’ve done for the Doxygen-Awesome dependency before:

app/west.yml

manifest:
  version: 0.8

  self:
    path: app

  projects:
    - name: zephyr
      revision: v3.4.0
      url: https://github.com/zephyrproject-rtos/zephyr
      path: deps/zephyr

Running west update clones the Zephyr repository into deps/zephyr and checks out the commit with the tag v3.4.0:

$ west update
=== updating zephyr (deps/zephyr):
--- zephyr: initializing
Initialized empty Git repository in /path/to/workspace/deps/zephyr/.git/
--- zephyr: fetching, need revision v3.4.0
...
HEAD is now at 356c8cbe63 release: Zephyr 3.4.0 release

Now, we have a complete “T2 star topology” workspace, where the Zephyr dependency is placed in a separate deps folder in the topdir (again following the convention presented by Mike Szczys in his talk “Manifests: Project Sanity in the Ever-Changing Zephyr World”):

tree --dirsfirst -a -L 3
.  # topdir
├── .west
│   └── config
├── app  # manifest repository
│   ├── .git
│   ├── boards
│   │   └── nrf52840dk_nrf52840.overlay
│   ├── src
│   │   └── main.c
│   ├── CMakeLists.txt
│   ├── prj.conf
│   └── west.yml  # manifest file
└── deps
    └── zephyr

Since we’ve used this application already in the previous article, we’re pretty sure that it should build. However, building still fails since we didn’t tell West about Zephyr’s extension commands yet:

$ west build --board nrf52840dk_nrf52840 app
usage: west [-h] [-z ZEPHYR_BASE] [-v] [-V] <command> ...
west: unknown command "build"; workspace /path/to/workspace does not define this extension command -- try "west help"

We can fix this by adding the west-commands key to the zephyr project: Zephyr’s West extensions are provided by the file scripts/west-commands.yml in Zephyr’s repository. Using the key west-commands, we can provide a relative path to West extension commands within the project:

app/west.yml

manifest:
  version: 0.8

  self:
    path: app

  projects:
    - name: zephyr
      revision: v3.4.0
      url: https://github.com/zephyrproject-rtos/zephyr
      path: deps/zephyr
      # explicitly add Zephyr-specific West extensions
      west-commands: scripts/west-commands.yml

With the west-commands in place we can re-run west update to try and build our application. Several things can go wrong at this point. Best case, you’ll see the error message below. Otherwise, the build might fail, e.g., because you don’t have CMake installed or because the Zephyr SDK doesn’t match the target:

west build --board nrf52840dk_nrf52840 app
-- west build: generating a build system
Loading Zephyr default modules (Zephyr base).
...
-- ZEPHYR_TOOLCHAIN_VARIANT not set, trying to locate Zephyr SDK
CMake Error at /path/to/workspace/deps/zephyr/cmake/modules/FindZephyr-sdk.cmake:108 (find_package):
  Could not find a package configuration file provided by "Zephyr-sdk"
  (requested version 0.15) with any of the following names:

    Zephyr-sdkConfig.cmake
    zephyr-sdk-config.cmake

  Add the installation prefix of "Zephyr-sdk" to CMAKE_PREFIX_PATH or set
  "Zephyr-sdk_DIR" to a directory containing one of the above files.  If
  "Zephyr-sdk" provides a separate development package or SDK, be sure it has
  been installed.

The error message is quite clear: Zephyr builds require that a toolchain is either installed globally or specified using the ZEPHYR_TOOLCHAIN_VARIANT environment variable. I didn’t do either.

Note: The west-commands is only needed since we’ve not seen the import key yet. I’ve added it explicitly so that you know about this key and how the West extension commands are handled in a manifest file, but you typically don’t need to specify this in your west.yml.

The term “Zephyr SDK” refers to the toolchains that must be provided for each of Zephyr’s supported architectures. With our manifest, we only add Zephyr’s sources to our workspace. The required tools, however, e.g., the GCC compiler for ARM Cortex-M, are not included.

Adding a toolchain

Toolchain management is always a highly opinionated topic, so I’ll try to keep that discussion out of this article. The point is this: West workspaces do not include the required toolchain needed for building your application. This is something that you need to manage yourself, using whatever approach you feel comfortable with:

… or any other approach, is entirely up to you. What you need for building Zephyr applications are:

  • Host dependencies such as python, cmake, ninja, etc., as explained in Zephyr’s Getting Started guide
  • An installation of the Zephyr SDK, containing the architecture specific toolchain. Zephyr’s official documentation includes a dedicated section on the Zephyr SDK and its installation instructions. The Zephyr SDK does not contain Zephyr’s sources!

Note: Yes, the inconsistent use of the term “SDK” is quite annoying. While Zephyr uses SDK exclusively for refering to the toolchain, I’d claim that an SDK typically also includes source code.

The host tools are typically in your $PATH – at least for the executing terminal. For pointing Zephyr’s build process to your installed SDK you can use the two environment variables ZEPHYR_TOOLCHAIN_VARIANT and ZEPHYR_SDK_INSTALL_DIR.

In the first article of this series, we installed the correct SDK for the nRF52840 Development Kit using Nordic’s toolchain manager. This installation contains not only the Zephyr SDK but also the host dependencies that I need for building Zephyr applications for nRF devices.

Since both, the STM32 and the nRF52840, are ARM MCUs, the installed Zephyr SDK already also contains the toolchain for building for the STM32 Nucleo-64 development board. All I need to do is provide the required environment variables.

For that, I could, e.g., use a shell script similar to what we’ve seen in the first article of this series:

app/setup-sdk-nrf.sh

#!/bin/sh

ncs_install_dir="${ncs_install_dir:-/opt/nordic/ncs}"
ncs_bin_version="${ncs_bin_version:-4ef6631da0}"

paths=(
    $ncs_install_dir/toolchains/$ncs_bin_version/bin
    $ncs_install_dir/toolchains/$ncs_bin_version/opt/nanopb/generator-bin
)

# required if dependencies are not installed, see also
# https://docs.zephyrproject.org/latest/develop/getting_started/index.html#install-dependencies
# e.g., "Ninja"
for entry in ${paths[@]}; do
    export PATH=$PATH:$entry
done

# only export the paths to the SDK, no longer export the path to the zephyr installation.
export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
export ZEPHYR_SDK_INSTALL_DIR=$ncs_install_dir/toolchains/$ncs_bin_version/opt/zephyr-sdk

Notice: Zephyr provides environment scripts including a zephyr-env.sh, which you can source in case you’re using Zephyr’s official SDK.

In this script, I’m extending my $PATH for the binaries that come with Nordic’s toolchain installation. This includes cmake, ninja, and all other host tools used by Zephyr. In fact, this installation even contains git and python, but by appending to $PATH, my local installations have precedence over Nordic’s binaries.

Then, I’m setting the ZEPHYR_TOOLCHAIN_VARIANT to zephyr and point ZEPHYR_SDK_INSTALL_DIR to the full path of the toolchain installation. Since I’m still using my own virtual environment, I need to install all Python packages required by Zephyr. Instead of cloning Zephyr as documented in the getting started guide, I can use the locally populated Zephyr installation:

$ pip install -r deps/zephyr/scripts/requirements.txt

Note: Using the above shell script I could actually scrap my virtual python environment, since all dependencies and packages are installed in Nordic’s installation.

Having all tools installed, the build should now pass, or shouldn’t it? Worth a try!

$ source app/setup-sdk-nrf.sh
$ west build --board nrf52840dk_nrf52840 app
-- west build: generating a build system
Loading Zephyr default modules (Zephyr base (cached)).
-- Application: /path/to/workspace/app
...
-- Found host-tools: zephyr 0.16.0 (/opt/nordic/ncs/toolchains/4ef6631da0/opt/zephyr-sdk)
-- Found toolchain: zephyr 0.16.0 (/opt/nordic/ncs/toolchains/4ef6631da0/opt/zephyr-sdk)
...
-- Including generated dts.cmake file: /path/to/workspace/build/zephyr/dts.cmake

warning: USE_SEGGER_RTT (defined at modules/segger/Kconfig:12) was assigned the value 'y' but got
the value 'n'. Check these unsatisfied dependencies: HAS_SEGGER_RTT (=n), 0 (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_USE_SEGGER_RTT and/or look up
USE_SEGGER_RTT in the menuconfig/guiconfig interface. The Application Development Primer, Setting
Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be helpful
too.
...
error: Aborting due to Kconfig warnings

CMake Error at /path/to/workspace/deps/zephyr/cmake/modules/kconfig.cmake:343 (message):
  command failed with return code: 1
Call Stack (most recent call first):
  /path/to/workspace/deps/zephyr/cmake/modules/zephyr_default.cmake:115 (include)
  /path/to/workspace/deps/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:66 (include)
  /path/to/workspace/deps/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:97 (include_boilerplate)
  CMakeLists.txt:2 (find_package)


-- Configuring incomplete, errors occurred!
FATAL ERROR: command exited with status 1: /opt/homebrew/bin/cmake -DWEST_PYTHON=/path/to/workspace/.venv/bin/python -B/path/to/workspace/build -GNinja -S/path/to/workspace/app

The build process was now able to correctly determine the host-tools and toolchains, but the build still failed with an error message that is quite hard to comprehend. Something seems to be missing!

Manifest imports

The build fails since we’re only adding the Zephyr repository as a dependency. This is not enough: The Zephyr repository has its own dependencies, which it lists as projects in its own west.yml file. We can recursively import the required projects from Zephyr using the import key as follows:

app/west.yml

manifest:
  version: 0.8

  self:
    path: app

  projects:
    - name: zephyr
      revision: v3.4.0
      url: https://github.com/zephyrproject-rtos/zephyr
      # the path is no longer needed since we're now using `path-prefix`
      # path: deps/zephyr
      # explicitly adding the Zephyr-specific West extensions is also no longer needed since
      # they are added accordingly with the `import` key.
      # west-commands: scripts/west-commands.yml
      # recursively import Zephyr dependencies
      import:
        path-prefix: deps
        # the `file` key is not strictly needed since `west.yml` is the default value.
        file: west.yml
        name-allowlist:
          - cmsis
          - hal_nordic

We got rid of the path key, since import.path-prefix allows us to define a common prefix for all projects. Using the import.file key, we’re telling West to look for a west.yml file in Zephyr’s repository and also consider the projects and West commands listed there. Notice that by default West looks for a west.yml file when using import and therefore it is not neccessary to provide the import.file entry.

Instead of adding all of Zephyr’s dependencies, we pick the ones we need by their name using the import.name-allowlist key.

Notice: Without name-allowlist we’d instruct West to clone all dependencies, recursively. If you have a quick look at Zephyr’s manifest file west.yml, you’ll see that it has a lot of dependencies. Running west update without limiting the dependencies may take several minutes and lots of disk space!

With this, West recursively imports all allowed dependencies from the zephyr project. The details are explained nicely in the official documentation on “Manifest Imports”.

Running west update, the new dependencies are placed in the deps/modules folder: We specified the deps prefix, whereas the module folder comes from Zephyr’s own west.yml file:

$ tree --dirsfirst -a -L 5
.
├── .west
│   └── config
├── app
│   ├── .git
│   ├── boards
│   │   └── nrf52840dk_nrf52840.overlay
│   ├── src
│   │   └── main.c
│   ├── CMakeLists.txt
│   ├── prj.conf
│   ├── setup-sdk-nrf.sh
│   └── west.yml
├── build  [13 entries exceeds filelimit, not opening dir]
└── deps
    ├── modules
    │   └── hal
    │       ├── cmsis
    │       └── nordic
    └── zephyr  [43 entries exceeds filelimit, not opening dir]

Now, our west build indeed succeeds:

$ west build --board nrf52840dk_nrf52840 app
...

[163/163] Linking C executable zephyr/zephyr.elf
Memory region         Used Size  Region Size  %age Used
           FLASH:       24852 B         1 MB      2.37%
             RAM:        4416 B       256 KB      1.68%
        IDT_LIST:          0 GB         2 KB      0.00%

Notice: In addition to the name-allowlist you can also instruct West to use shallow clones instead of a complete git clone for all its projects. E.g., use west update -o=--depth=1 -n to create shallow clones. Have a look at the help output of west update --help!

Switching boards

With our workspace set up and our knowledge about Zephyr’s imports, we’re ready to add support for the STM32 Nucleo-64 development board. The first thing we need is an overlay file to specify the /chosen LED node:

app/boards/nucleo_f411re.overlay

/ {
    chosen {
        app-led = &green_led_2;
    };
};

Knowing that we’re still missing the STM32 HAL, we can look it up in Zephyr’s west.yml file:

$ grep stm32 deps/zephyr/west.yml -A 2 --ignore-case
    - name: hal_stm32
      revision: c865374fc83d93416c0f380e6310368ff55d6ce2
      path: modules/hal/stm32
      groups:
        - hal

The STM32 HAL is part of the project hal_stm32, which we can now add to our allow-list in the manifest file:

app/west.yml

manifest:
  version: 0.8

  self:
    path: app

  projects:
    - name: zephyr
      revision: v3.4.0
      url: https://github.com/zephyrproject-rtos/zephyr
      import:
        path-prefix: deps
        name-allowlist:
          - cmsis
          - hal_nordic
          - hal_stm32 # <-- added STM32 HAL

Running west update, West populates the stm32 HAL in the expected folder deps/modules/hal/stm32:

$ west update
$ tree --dirsfirst -a -L 5
.
├── .west
│   └── config
├── app
└── deps
    ├── modules
    │   └── hal
    │       ├── cmsis
    │       ├── nordic
    │       └── stm32
    └── zephyr  [43 entries exceeds filelimit, not opening dir]

Building the application for the STM32 development kit now succeeds as expected:

$ west build --board nucleo_f411re app --pristine
...

[159/159] Linking C executable zephyr/zephyr.elf
Memory region         Used Size  Region Size  %age Used
           FLASH:       18726 B       512 KB      3.57%
             RAM:        4352 B       128 KB      3.32%
        IDT_LIST:          0 GB         2 KB      0.00%

Connecting the development kit to my computer, I should now be able to program the application, right? Let’s try:

$ west flash
-- west flash: rebuilding
ninja: no work to do.
-- west flash: using runner openocd
FATAL ERROR: required program openocd not found; install it or add its location to PATH

Oh, the STM32 development kit uses a different runner than the nRF52840 development kit: Nordic’s development kits use jlink, whereas this development kit uses openocd.

Thus, you don’t only need the host tools and Zephyr SDK for your target, but also all other supporting tools, such as Nordic’s command line tools or in this case openocd. On my computer, a simple brew install open-ocd fixes this problem, and I’m able to flash the application to the device.

In a more serious setup, your entire toolchain should be maintained in a much better way, but – as promised – I won’t try to tell how you should do that – it’s entirely up to you.

Zephyr as dependency

When browsing allowed imports, we’ve seen that Zephyr has dependencies. What we haven’t seen yet, is that Zephyr itself can be a dependency: Depending on your application, you might make use of some frameworks or SDKs that in turn depend on Zephyr and thus list it as project in their own west.yml file.

E.g., looking at the GitHub repository the nRF Connect SDK, we find that Nordic uses their own fork of the official Zephyr repository and has it listed as a project in the SDK’s west.yml file:

https://github.com/nrfconnect/sdk-nrf/blob/main/west.yml

manifest:
  projects:
    - name: zephyr
      repo-path: sdk-zephyr
      revision: 90a72daae2c8715d760d974a7d294aa2eb6b38c4
      import:
        name-allowlist:
          - TraceRecorderSource
          - canopennode
          - chre
          - ...

Another example is the Golioth Zephyr SDK, which lists the official Zephyr repository as a project in their west-zephyr.yml manifest:

https://github.com/golioth/golioth-zephyr-sdk/blob/main/west-zephyr.yml

manifest:
  projects:
    - name: zephyr
      revision: v3.5.0
      url: https://github.com/zephyrproject-rtos/zephyr
      import: true

These dependencies are something that you need to handle yourself since West ignores projects that have already been defined in other files. E.g., if you define Zephyr as a project in your manifest file, and after add Golioth’s Zephyr SDK, then the Zephyr project in the west-zephyr.yml file of the Golioth SDK is ignored.

It is your responsibility to ensure that the projects are compatible – or deal with resolving differences in case they are not. West doesn’t do that for you.

For some applications, it can therefore be beneficial to maintain multiple manifest files: E.g., when building for devices from Nordic, you may want to use the sdk-nrf as a project in your manifest file instead of adding “vanilla” Zephyr.

This may be tedious but is necessary and not a downside of using Zephyr: If you were to switch MCUs or if you’d be including a big SDK in any other firmware project, you’d also have to ensure compatibility. West manifests simply make this explicit, reproducible, and manageable.

Working on projects

Even though we mostly ignored the inner workings of West, there’s one thing that you need to be aware of when working with West workspaces: Except for the manifest repository, West creates and controls a Git branch named manifest-rev in each project and thus for all dependencies.

E.g., let’s have a look at the deps/zephyr repository that we cloned using West for the modified Blinky application in the section “Zephyr with West”:

$ cd deps/zephyr
$ git status
HEAD detached at refs/heads/manifest-rev
nothing to commit, working tree clean

We’re not on Zephyr’s main branch nor are we on a detached head at a specific revision – we’re on the manifest-rev branch that is maintained by West.

This is done for all projects in a manifest. The manifest repository itself is not affected since – as we’ve seen before – West does not touch the manifest repository. This behavior is also explained in the official documentation.

For all other projects, however, West creates and manages its own manifest-rev branch. It is important that you do not modify the manifest-rev branch and that you don’t push it to your remote since West recreates and resets the manifest-rev branch on each execution of west update command. Any changes would be lost.

Being aware how West manages projects is especially important if you’re using West in a “T3 forest topology” or, e.g., if you’re using a separate repository for shared code. E.g., we could add the following shared/dummy project to our workspace:

manifest:
  # --snip--
  projects:
    # --snip--
    - name: dummy
      revision: main
      url: git@github.com:lmapii/practical-zephyr-t2-dummy.git
      path: shared/dummy

In case you need to update such a shared dependency, make sure to push the changes to a new or existing branch, but don’t commit to the manifest-rev branch. Also, after running west update, make sure to switch back to your working branch.

This sounds brittle, but it really isn’t. It isn’t that easy to lose changes to files with a west update. Let’s see this in action. In case you want to follow along, add your own dummy repository to the manifest – I’ll be using the above project in my west.yml – a dummy repository that contains an empty test.txt file:

# after adding the "dummy" project to west.yml, update the project
$ west update
$ tree --dirsfirst -a -L 4 --filelimit 10 -I hal
.
├── .west
│   └── config
├── app
├── deps
│   ├── modules
│   └── zephyr
└── shared
    └── dummy
        └── test.txt

West does not checkout the repository’s main branch as specified in the with the revision: main entry in the manifest file, but instead uses the local manifest-rev branch mentioned before:

$ cd shared/dummy
$ git status
On branch manifest-rev
nothing to commit, working tree clean
$ cd ../../ # workspace root

Without checking out a new branch, I can modify the contents of test.txt and run west update. The changes won’t be lost and west update succeeds since the changes are not in conflict with any incoming change:

$ echo 123-test >> shared/dummy/test.txt
$ west update
...
=== updating dummy (shared/dummy):
--- dummy: fetching, need revision main
From github.com:lmapii/practical-zephyr-t2-dummy
 * branch            main       -> FETCH_HEAD
M       test.txt
HEAD is now at c8deb58 initial commit
...

$ cat shared/dummy/test.txt
123-test

The output of west update shows me that I have in fact local changes to test.txt, but it doesn’t reset the file. The changes are not lost.

Since we’re using main as revision for this dependency (e.g., since we’re still very much in development), it could happen that someone else is writing to test.txt, e.g., the value not-a-test. (let’s not discuss using development branches etc., I’m just showing West’s behavior). Trying to run west update with an incoming change leads to an error – the local changes are still not lost:

$ west update
...
=== updating dummy (shared/dummy):
--- dummy: fetching, need revision main
remote: Enumerating objects: 5, done.
remote: Counting objects: 100% (5/5), done.
remote: Total 3 (delta 0), reused 3 (delta 0), pack-reused 0
Unpacking objects: 100% (3/3), 229 bytes | 57.00 KiB/s, done.
From github.com:lmapii/practical-zephyr-t2-dummy
 * branch            main       -> FETCH_HEAD
error: Your local changes to the following files would be overwritten by checkout:
        test.txt
Please commit your changes or stash them before you switch branches.
Aborting
...
ERROR: update failed for project dummy

OK, time to really try and mess things up: Let’s assume we had a long day and we simply forgot that we’re changing things in a repository managed by West. We’re changing things in test.txt and commit the changes to the local manifest-rev branch:

$ cd shared/dummy
$ git add test.txt
$ git commit -m "an honest mistake"
[detached HEAD 8de0853] an honest mistake
 1 file changed, 1 insertion(+)

Running west update we can indeed see that we’re about to lose the commit:

cd ../../
$ west update
...
=== updating dummy (shared/dummy):
--- dummy: fetching, need revision main
From github.com:lmapii/practical-zephyr-t2-dummy
 * branch            main       -> FETCH_HEAD
Warning: you are leaving 1 commit behind, not connected to
any of your branches:

  8de0853 an honest mistake

If you want to keep it by creating a new branch, this may be a good time
to do so with:

 git branch  8de0853

HEAD is now at d22a413 updated test.txt
...

Whoops! Git is telling us that we’re about to leave behind a commit and at the same time tells us that nothing is lost yet: We can recover the lost change in a new branch by using the proposed command:

$ cd shared/dummy
$ git branch recover-an-honest-mistake 8de0853
$ git checkout recover-an-honest-mistake
Previous HEAD position was c8deb58 initial commit
Switched to branch 'recover-an-honest-mistake'
$ cat test.txt
this-is-a-test.123-test%

Whew! A close call, but even after commiting to our local manifest-rev branch the changes are not lost an can be restored as instructed by the command line output.

Keep in mind that all projects in a West manifest are managed entirely by West. If you’re working on those repositories, use dedicated branches. After every West update, double-check that you’re still working on the correct branch and do not commit to the manifest-rev branch.

Have a look at the official documentation for west update. There, you’ll find a detailed description of the entire update procedure, including some options that allow you to selectively update projects.

Conclusion

In this article, we’ve seen how we can use West to manage our dependencies, including some of its pitfalls and limitations. Exploring the Zephyr application we have also seen, that managing dependencies can still be complicated in case you’re dealing with projects that have the same dependencies, e.g., other SDKs that use different versions of Zephyr as dependency.

We also managed to build an application for MCUs from different vendors: This is possible in Zephyr, though it may take a bit more effort than advertised – at least in case you’re dealing with a professional application. Personally, I still think that Zephyr is a great step forward: Switching MCUs or supporting multiple targets always includes efforts, but with Zephyr, the efforts are predictable and manageable.

This article marks the end of the Practical Zephyr series: I hope that I could get you past the steep section of Zephyr’s learning curve, towards a more enjoyable and reasonable experience. There’s still a ton to explore!

A big Thank You to the team at Memfault for their patience, the reviews, the invaluable feedback for these articles, and for maintaining the Interrupt blog!

Further reading

We’ve only covered the surface of what West can do for you. I very warmly recommend at least skimming through the following resources:

Finally, have a look at the files in the example repositories used throughout this article:

Benjamin Cabé