Zephyr (west module)

Single-node starter on Zephyr via the in-tree zephyr/ west module. nano-ros ships as a Zephyr module — west discovers it from your workspace’s west.yml, drops in a prj.conf Kconfig surface, and the standard west build / west flash flow takes care of the rest.

Contributor path? Building nano-ros’s own Zephyr examples straight from this repository (no west-managed workspace) is covered at Zephyr (contributor). The page below is the canonical user entry.

Just want a working starter? Clone the nano-ros-zephyr-example repo (west init -m …) — a manifest + zenoh talker app pinned to a tested Zephyr, with the same quickstart as below baked in. The steps here explain what it does so you can adapt it to your own workspace.

Prereqs. Run nros setup zephyr --rmw <rmw> once (see Prerequisites below) — it provisions the Zephyr west workspace + Zephyr SDK bits, the emulator, and your RMW’s host daemon into the shared store. No hand-installed Zephyr SDK, west, or cross-toolchain, and no ROS 2 install required. Python: 3.10+ on Zephyr 3.7 LTS, but ≥ 3.12 on Zephyr 4.x (4.x’s find_package(Python3) requires 3.12 — see the version matrix below). nano-ros’s imported west fragment zephyr/west.yml is a manifest-only file — it does NOT pull Zephyr itself; that has to be in your parent manifest (zephyrproject-rtos/zephyr).

Which Zephyr? — 3.7 LTS and 4.x both supported

nano-ros consumes as a module on both the 3.7 LTS line (supported to Jan 2027; the safety-island default) and the current 4.x rolling line. You build against whatever Zephyr your workspace already pins — nano-ros adapts. The two lines differ only in how you select an RMW and apply nano-ros’s Zephyr patches:

native_sim networking uses NSOS (host loopback) on both lines — no TAP/bridge/root. The copy-out, snippet, patch-apply, and dual-line build flows are exercised in CI (contributor lanes just zephyr ci-both, just zephyr check-copy-out).

Project layout

A Zephyr workspace using nano-ros looks like any other Zephyr project — the nano-ros module sits beside Zephyr, your application sits beside both:

my_zephyr_ws/
├── .west/
├── zephyr/                            # cloned by `west init`
├── modules/
│   └── nano-ros/                      # imported via west.yml
└── apps/
    └── my_app/                        # your application
        ├── CMakeLists.txt
        ├── prj.conf                   # Kconfig — selects nros + RMW
        ├── west.yml                   # (optional) per-app manifest
        └── src/
            └── main.c                 # nros user code

The application CMakeLists.txt is a stock Zephyr app — find_package(Zephyr)

• target_sources. No add_subdirectory(<nano-ros>) is needed; the module shell handles it once CONFIG_NROS=y flips on.

A minimal apps/my_app/ looks like this — the shipped examples/zephyr/c/talker/ quoted directly (only the project/class names are trimmed to my_app), so this page can’t drift from the real API surface. It is a stateful C component (a struct + a configure function, RFC-0043 / phase-244.C2) — not a hand-written main() — because the Zephyr typed carrier generates the entry point and calls into the component by identity:

# apps/my_app/CMakeLists.txt
cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(my_app)

set(NANO_ROS_PLATFORM zephyr)
include("${NROS_REPO_DIR}/cmake/NanoRosNodeRegister.cmake")
include("${NROS_REPO_DIR}/cmake/NanoRosVerbs.cmake")

nano_ros_auto_add_library(talker_lib STATIC src/Talker.c)

nros_components_register_node(talker_lib
    PLUGIN my_app::Talker
    EXECUTABLE talker
    SHAPE configure
    TYPED
    DEPLOY zephyr)

// apps/my_app/src/Talker.c
// `talker_configure` creates a raw publisher on `/chatter` + a timer that
// publishes a CDR-encoded Int32 counter each tick. `NROS_C_COMPONENT` emits
// the C-ABI factory/configure the Zephyr typed Entry carrier calls.
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

#include <nros/component.h>

typedef struct {
    _Alignas(8) uint8_t pub[NROS_C_PUBLISHER_STORAGE_SIZE];
    int32_t count;
} talker_t;

static void write_u32_le(uint8_t* p, uint32_t v) {
    p[0] = (uint8_t)v;
    p[1] = (uint8_t)(v >> 8);
    p[2] = (uint8_t)(v >> 16);
    p[3] = (uint8_t)(v >> 24);
}

static void on_tick(void* ctx) {
    talker_t* self = (talker_t*)ctx;
    /* std_msgs/Int32 CDR: 4-byte encapsulation header (CDR_LE) + int32 data. */
    uint8_t buf[8];
    buf[0] = 0x00;
    buf[1] = 0x01;
    buf[2] = 0x00;
    buf[3] = 0x00;
    write_u32_le(buf + 4, (uint32_t)self->count);
    if (nros_cpp_publish_raw(self->pub, buf, sizeof(buf)) == 0) {
        printf("Published: %d\n", (int)self->count);
    }
    self->count++;
}

static nros_ret_t talker_configure(const nros_cpp_node_t* node, void* executor, talker_t* self) {
    self->count = 0;
    int32_t rc = nros_cpp_publisher_create(node, "/chatter", "std_msgs::msg::dds_::Int32_", "",
                                           nros_c_qos_default(), self->pub);
    if (rc != 0) {
        return rc;
    }
    size_t timer_handle;
    return nros_cpp_timer_create(executor, /*period_ms=*/500, on_tick, self, &timer_handle);
}

NROS_C_COMPONENT(talker_t, talker_configure)

See examples/templates/zephyr-byo/app/src/Talker.c for the up-to-date source (this is that BYO starter’s talker, only stripped of its file header comment; the canonical in-tree examples/zephyr/c/talker/ uses the generated typed std_msgs/String bindings instead of raw CDR). Note the nros_cpp_* symbol prefix: those are C-ABI functions from nros-cpp (the cpp is a namespace prefix, not C++ linkage) — a C component links against them directly, and shares the same executor + node as a C++ component would.

prj.conf is the one shown in Configure below — note it needs both CONFIG_NROS_C_API=y and CONFIG_NROS_CPP_API=y: the typed Zephyr carrier that drives this component’s configure is C++, so the nros-cpp header surface must be on the app include path even though Talker.c itself is C.

Prerequisites

nros setup provisions the parts nano-ros owns — the RMW host daemon (zenohd / Micro-XRCE-DDS agent) and the RMW transport submodules (zenoh-pico + mbedtls for zenoh, the cyclonedds fork) — from a pinned index into ${NROS_HOME:-~/.nros}/sdk / the nano-ros checkout. It does not replace Zephyr’s own SDK, and interface codegen still needs the ROS message definitions.

1. Build the in-tree nros CLI (Phase 218, from the nano-ros checkout):

   ./scripts/bootstrap.sh      # builds packages/cli/target/release/nros
   source ./activate.sh        # OR: direnv allow / source ./activate.fish
   

2. Provision the RMW (daemon + transports) from the nano-ros checkout:

   ( cd modules/nano-ros && nros setup zephyr --rmw zenoh )  # zenohd + zenoh-pico + mbedtls
   ( cd modules/nano-ros && nros setup --source px4-rs )     # workspace cargo-load dep
   

3. Install the Zephyr SDK the standard Zephyr way (nros setup does not provide it) and expose it — export ZEPHYR_SDK_INSTALL_DIR=/path/to/zephyr-sdk-<ver> (or register it via the SDK’s setup.sh -c).
4. Message definitions for codegen. The interface codegen resolves a package’s msg/*.msg from NROS_<PKG>_DIR (e.g. export NROS_STD_MSGS_DIR=/opt/ros/humble/share/std_msgs) — point it at a ROS install or any dir holding the .msg files.

The RMW host daemon must be running before an example connects (for zenoh: ZENOH_CONFIG_OVERRIDE='listen/endpoints=["tcp/127.0.0.1:7447"];scouting/multicast/enabled=false' ros2 run rmw_zenoh_cpp rmw_zenohd; the Micro-XRCE-DDS agent for xrce).

Configure

Add nano-ros (and a Zephyr pin — zephyr/west.yml is manifest-only; it does not pull Zephyr itself) to your workspace west.yml:

manifest:
  remotes:
    - name: nano-ros
      url-base: https://github.com/NEWSLabNTU
    - name: zephyr
      url-base: https://github.com/zephyrproject-rtos
  projects:
    - name: zephyr
      remote: zephyr
      revision: v3.7.0          # or your chosen 3.7 LTS / 4.x SHA
      path: zephyr
      import: true               # pulls Zephyr's own modules
    - name: nano-ros
      remote: nano-ros
      revision: nros-v0.5.0      # pin a release tag (west needs SOME
                                 # revision — its default `master` does
                                 # not exist here). `main` works for
                                 # tracking tip, but a tag keeps your
                                 # build reproducible.
      path: modules/nano-ros
      import:
        file: zephyr/west.yml    # pulls nano-ros's transport deps

Then per-application prj.conf:

CONFIG_NROS=y
CONFIG_NROS_C_API=y
CONFIG_NROS_RMW_ZENOH=y                 # bool per RMW: NROS_RMW_{ZENOH,XRCE,CYCLONEDDS}
# (ROS edition is a build-time Cargo feature, NOT a Kconfig symbol — do not set
#  CONFIG_NROS_ROS_EDITION; Zephyr aborts on the undefined symbol.)

# Required for any networked RMW on QEMU / native_sim:
CONFIG_NETWORKING=y
CONFIG_NET_IPV4=y
CONFIG_NET_TCP=y

CONFIG_NROS=y activates the shell, which maps Kconfig values to NANO_ROS_* CMake cache vars and add_subdirectory()s the root nano-ros CMake. NanoRos::NanoRos is linked into your app library transparently.

Build

If your workspace is a fresh manifest-only dir (no .west/), initialise it first so west knows which west.yml is the manifest:

cd my_zephyr_ws
west init -l .                           # one-time; points west at the
                                         # local west.yml in cwd
west update                              # clones nano-ros + Zephyr into the workspace

(If you started from west init -m <remote>, both calls above are already done — go straight to west build below.)

nros build on Zephyr: it hands off, it does not take over

The other platforms let nros build own the build: it generates a cargo or CMake root from your [image.*] declarations and runs the tool. Zephyr is not like that, on purpose.

You own the west workspace and the application. west init / west update populate the workspace, your app carries its own CMakeLists.txt and prj.conf, and west only runs from inside that workspace. None of that is ours to generate — an app’s Kconfig is authored, not derived (RFC-0065 D5).

So for a Zephyr image nros build:

1. resolves the application — the entry package for that image’s board, not the bringup;
2. resolves your Zephyr — $ZEPHYR_BASE, else $NROS_ZEPHYR_WORKSPACE, else an in-tree zephyr-workspace/, else a sibling ../nano-ros-workspace. Note it is a Zephyr that is needed, not a .west/ directory: with ZEPHYR_BASE set, west build runs from anywhere, which is what makes a freestanding application — one outside the west workspace — work;
3. runs west build from there with the image’s overlays (EXTRA_CONF_FILE, APPLICATION_CONFIG_DIR) already applied.

If it cannot find a workspace it does not guess. It prints the command and where to run it:

$ nros build demo_bringup:zephyr
Error: no west workspace found, so `west build` cannot be run for `zephyr`.

Zephyr differs from the other drivers: YOU own the west workspace and the
application, and `west` only runs inside a workspace …

Run this from your west workspace:

    west build -b native_sim/native/64 …/src/zephyr_entry

Point nros at your workspace:

    NROS_ZEPHYR_WORKSPACE=<dir>   # the dir containing zephyr/

That is deliberate and it is the same boundary nros setup --system draws when it composes an install command and prints it rather than running sudo for you: where the tool is yours, nano-ros hands you the command instead of assuming it may act.

The plain west build below keeps working and is still the primary flow. nros build is the convenience that applies an image’s overlays for you; it never becomes a required layer between you and west.

Starting from nothing: nros new node and nros new entry

A node package is board- and RMW-agnostic — it names no platform, which is what lets the same package be deployed to Linux and to a Cortex-M without an edit:

nros new node talker_pkg

It writes the package and adds the [[component]] row to your bringup. (Use nros new <name> --platform native only for a standalone runnable project — it pins a board crate, so an entry on another platform cannot link it.)

The entry: nros new entry

You do not have to write the entry package by hand:

nros new entry zephyr_entry --platform zephyr

nros new entry: scaffolded ./src/zephyr_entry (7 file(s))
  declared [image.zephyr_entry] in ./src/demo_bringup/system.toml

Next:
  nros sync
  nros build demo_bringup:zephyr_entry --zephyr-workspace <dir>

It writes the package — Cargo.toml, CMakeLists.txt, build.rs, src/lib.rs, prj.conf, prj-zenoh.conf, boards/<board>.conf — and three things outside it that are easy to miss and invisible until they fail:

• the [image.*] block, with board, entry and the conf overlay the entry’s own CMakeLists.txt requires;
• an exclude entry in every enclosing cargo workspace, because a west-built staticlib must not be an ordinary cargo member;
• a path dependency per node package the bringup declares, since the entry links them.

--board, --rmw and --bringup override the defaults (native_sim/native/64, zenoh, and the workspace’s single bringup).

The whole flow, end to end

Five commands, run from your workspace. This is the examples/workspaces/rust transcript, verbatim:

# 0. tell nros where your west workspace is — the directory containing
#    `zephyr/`. On the command line:
#
#      nros build demo_bringup:zephyr --zephyr-workspace /path/to/zephyr-workspace
#
#    or once for the shell, if you would rather not repeat it:
export NROS_ZEPHYR_WORKSPACE=/path/to/zephyr-workspace

# 1. generate the message bindings this workspace's packages depend on.
#    `nros build` refuses with "this workspace has never been synced" until
#    you do — it will not silently build against absent bindings.
nros sync

# 2. build. This resolves the application, applies the image's overlays and
#    runs `west build` for you.
nros build demo_bringup:zephyr

# 3. start the router ROS itself uses — the one `rmw_zenoh_cpp` ships, so it
#    cannot drift from the RMW your ROS 2 nodes use. Separate terminal; it
#    keeps running. Listens on tcp/127.0.0.1:7447.
ros2 run rmw_zenoh_cpp rmw_zenohd

# 4. run the image.
./build/zephyr/zephyr.exe

*** Booting Zephyr OS build v3.7.0 ***
<inf> nros_net_wait: Network ready (NSOS — host kernel sockets)
<inf> rust: rustapp: nros: zephyr workspace entry up (2 nodes)
<inf> rust: talker_pkg: talker publishing chatter seq=0
<inf> rust: talker_pkg: talker publishing chatter seq=1

and from a ROS 2 shell on the same router, the nodes are ordinary ROS nodes:

$ export RMW_IMPLEMENTATION=rmw_zenoh_cpp
$ ros2 topic echo /chatter --once
data: 6
---

Step 3 is not optional and its ORDER does not matter, but the locator does: zenoh-pico is a client, so with no router the image gets

<err> rust: nros: zephyr entry — executor open failed: Transport(ConnectionFailed)

which names no port. Both sides default to tcp/127.0.0.1:7447 — the port rmw_zenohd listens on and a rmw_zenoh_cpp node connects to. Override with CONFIG_NROS_ZENOH_LOCATOR on the image side (via a conf fragment) and ZENOH_CONFIG_OVERRIDE='listen/endpoints=["tcp/127.0.0.1:<port>"]' on the router, and change both.

What an image declares

The Zephyr images in examples/workspaces/* are the worked examples:

[image.zephyr]
board = "native_sim/native/64"
entry = "zephyr_entry"          # only when several entries match, see below
conf  = ["prj-zenoh.conf"]      # the RMW overlay this app requires

• conf names the app’s own Kconfig fragments, in order. They are looked for beside the board config dir, then beside the application, then beside the bringup — the app rung matters because a Zephyr app keeps its prj-<rmw>.conf next to the CMakeLists.txt west builds. These entries FATAL_ERROR without an RMW overlay, so the image has to say which one.
• board is the Zephyr board target — and also a name nano-ros must know. See below.
• entry names the application package. Normally leave it out: an entry declares the deploy target it serves — [package.metadata.nros.entry] deploy in Cargo.toml, nano_ros_add_executable(... DEPLOY zephyr) in CMakeLists.txt — and one package usually claims a given board. Set it when several do (realtime-cpp has zephyr_entry and fvp_entry, both DEPLOY zephyr, on the same board, for two images that differ in payload). Deriving there is a coin flip, so nros build refuses and lists the candidates rather than picking one.

If you live in west: west nros

Everything above assumes you stand in your nano-ros workspace and name the Zephyr one. If you work the other way round — inside the west workspace — west already knows where Zephyr is, so it can tell nros for you:

cd ~/zephyr-workspace
west nros build --workspace ~/my_robot demo_bringup:zephyr

No ZEPHYR_BASE, no NROS_ZEPHYR_WORKSPACE, no --zephyr-workspace. Every argument after nros is passed straight through, so anything nros accepts works here unchanged.

It picks up automatically in any workspace whose manifest lists nano-ros — the same route west fvp takes. Two things worth knowing:

• It only exists inside a west workspace. West loads extension commands from the manifest, so from an unrelated directory you get west: unknown command "nros". That is why this is an addition rather than a replacement: it swaps which of the two trees you have to name, trading the Zephyr path (which differs per machine) for your own workspace path (which you chose).
• It never overwrites a ZEPHYR_BASE you set yourself — an exported one is a deliberate choice, and this only fills in a missing answer.

Which boards you can name

board does two jobs from one string: it is passed to west build -b verbatim, and it is looked up in nano-ros’s board catalog, where a descriptor carries a set of names:

names = ["zephyr", "native_sim/native/64"]

So it is not free-form. A board the catalog does not know is refused with the list of ones it does, because the descriptor supplies more than the -b string — the platform, the toolchain, the entry kind, the declared capabilities. There is no safe default for those.

A board is a package — put it in your workspace. Drop an nros-board.toml beside a package’s package.xml and it joins the catalog like any other package in src/:

my_robot/src/
├── talker_pkg/
└── my_board/
    ├── package.xml
    └── nros-board.toml

# src/my_board/nros-board.toml
[[board]]
names = ["my-board"]              # what your images say
west_board = "qemu_cortex_m3"     # what west is given
platform = "zephyr"
toolchain = "stable"
platform_feature = "platform-zephyr"
link_kind = "none"
entry_kind = "zephyr-staticlib"

# src/demo_bringup/system.toml
[image.zephyr]
board = "my-board"

No environment variable, nothing outside the tree, nothing copied into the nano-ros checkout. west_board is what lets the friendly name be the one your workspace uses — leave it out when your board name already is the west board target, which is what the shipped descriptors do.

For a board shared by several workspaces there is no single workspace to put it in, and $NROS_EXTRA_BOARD_PATH still covers that: PATH-style, naming directories shaped like packages/boards/.

nros new board <name> --for-platform zephyr scaffolds the descriptor. Note this is the nano-ros descriptor; an out-of-tree Zephyr board definition (its devicetree and board.yml) is contributed the Zephyr way, through your module’s board_root.

Adding your own drivers, modules and boards

Everything Zephyr lets you extend, you still extend the Zephyr way. The application CMakeLists.txt is yours (RFC-0065 D5) and nros build runs west build against it, so the extension points are untouched:

Only the last two rows are ours, and they are how an IMAGE differs from its siblings — the module itself is a property of the application, not of one image, so it belongs in the app’s CMakeLists.txt where you would have put it anyway.

nros build passes exactly four things to west of its own — APPLICATION_CONFIG_DIR, EXTRA_CONF_FILE, EXTRA_DTC_OVERLAY_FILE, FILE_SUFFIX, all Zephyr’s own variables — and there is deliberately no image key for arbitrary -D defines. Something your application always needs belongs in its CMakeLists.txt, which keeps one place to look.

Customizing the west command itself

Anything after -- goes to west. west build has two argument zones, and nros build routes each token to the right one using west’s own flag list:

nros build demo_bringup:zephyr -- --pristine        # a west option
nros build demo_bringup:zephyr -- -t run            # build, then run it
nros build demo_bringup:zephyr -- -DMY_OPT=1        # a cmake option
nros build demo_bringup:zephyr -- -p always -DX=1   # both, in one go

which becomes, respectively, the west option zone and the cmake zone:

west build -b <board> <app> -p always -- -DEXTRA_CONF_FILE=… -DX=1

nros build --dry-run prints that line without running it, so you can always see exactly what west is being asked to do — and copy it if you would rather drive west yourself.

Two flags are refused rather than routed, because the image already decides them and a build must not be able to disagree with its own declaration:

$ nros build demo_bringup:zephyr -- --sysbuild
Error: `--sysbuild` is decided by the image, not by the command line.
It comes from the presence of a `sysbuild.conf` beside the application.

Change it there, so one build cannot disagree with the declaration it was
resolved from.

The other is -b/--board, which comes from the image’s board.

Verified by building one. An out-of-tree module with its own Kconfig, a driver source gated on it, a devicetree overlay declaring a node and a binding shipped from the module’s dts_root, added to examples/workspaces/rust’s entry and enabled through the image:

[image.zephyr]
conf = ["prj-zenoh.conf", "prj-user-extra.conf", "user-widget.overlay"]

*** Booting Zephyr OS build v3.7.0 ***
user_extra: out-of-tree driver init, widget-id=42
<inf> rust: rustapp: nros: zephyr workspace entry up (2 nodes)
<inf> rust: talker_pkg: talker publishing chatter seq=0

The driver’s BUILD_ASSERT(DT_NODE_EXISTS(DT_NODELABEL(user_widget))) is what makes that a test rather than a screenshot: without the overlay reaching the build, it fails to compile instead of quietly doing nothing.

A mistake in your module surfaces as Zephyr’s own error, unmediated — a wrong kconfig: path in module.yml reports

ERROR: "kconfig" key in …/extra_module/zephyr/module.yml has value
"../Kconfig" which does not point to a valid Kconfig file.

which is the message you would get from a plain west build, because it is a plain west build.

The transports + px4-rs come from the prerequisites step (west update clones nano-ros but not its submodules). With the Zephyr SDK + NROS_STD_MSGS_DIR exported (also prerequisites), build your app — nros on PATH is auto-resolved as the codegen tool:

# native_sim (POSIX, no QEMU). The 3.7 line needs the NSOS line overlay; apply
# the NSOS patches first (see "apply nano-ros's patches" below).
overlay="$PWD/modules/nano-ros/cmake/zephyr/native-sim-line-3.7.conf"
west build -b native_sim/native/64 apps/my_app -- -DCONF_FILE="prj.conf;$overlay"

# A real board, e.g. Cortex-A9 (no native_sim overlay):
west build -b qemu_cortex_a9 apps/my_app

(Verified end-to-end on a fresh BYO west workspace: this builds to zephyr.exe and runs to Published: 0 against a router started with ZENOH_CONFIG_OVERRIDE='listen/endpoints=["tcp/127.0.0.1:7447"];scouting/multicast/enabled=false' ros2 run rmw_zenoh_cpp rmw_zenohd. On the Zephyr 4.4 line, find_package(Python3) requires ≥ 3.12 and you select the RMW with -S nros-zenoh instead of the overlay.)

For a quick sanity check that the module is wired correctly:

west build -t menuconfig                 # confirm CONFIG_NROS=y is visible

Rust applications

Two things differ for a Rust app (C/C++ apps skip this section):

1. The Rust crate’s [lib] must be named rustapp (crate-type = ["staticlib"]) — a zephyr-lang-rust contract: its rust_cargo_application() links librustapp.a. The Cargo package name is free.

2. Generate the interface crates + the [patch.crates-io] wiring for YOUR layout — do not copy an in-repo example’s .cargo/config.toml: its ../../../../packages/core/... paths are repo-relative and break in a copied-out app. From your app dir, run (after the Prerequisites nros setup, which provides the codegen toolchain + message sources):

   nros generate-rust --generate-config \
       --nano-ros-path "$PWD/../../modules/nano-ros/packages/core"
   

   This writes generated/<pkg>/ (the message crates) and a .cargo/config.toml whose [patch.crates-io] points the nros-* crates at your modules/nano-ros/packages/core/* and the generated interfaces at generated/*. Adjust --nano-ros-path to your workspace’s modules/nano-ros/packages/core (the dir holding nros-core, nros-node, …). The example apps’ committed .cargo/config.toml is for the in-tree build only.

Run

# 1. Start the router (ROS's `rmw_zenohd` — nano-ros ships no router
#    of its own) on port 7447, the port your app's Kconfig default
#    picks up (CONFIG_NROS_ZENOH_LOCATOR defaults to
#    "tcp/127.0.0.1:7447"; change either side to match):
ZENOH_CONFIG_OVERRIDE='listen/endpoints=["tcp/0.0.0.0:7447"];scouting/multicast/enabled=false' \
    ros2 run rmw_zenoh_cpp rmw_zenohd &

# 2. Boot the app from your BYO west workspace:
# QEMU Cortex-A9:
west build -t run
# native_sim:
./build/zephyr/zephyr.exe

# 3. Verify from stock ROS 2 in another terminal. Match the message
# type to the app you booted: the canonical in-tree talker publishes
# std_msgs/String; the raw BYO Talker.c shown above publishes
# std_msgs/Int32.
source /opt/ros/humble/setup.bash
export RMW_IMPLEMENTATION=rmw_zenoh_cpp
# Talker publishes best-effort; stock `ros2 topic echo` defaults to
# RELIABLE, so the QoS-mismatched echo silently delivers nothing.
# Force best-effort to receive:
ros2 topic echo /chatter std_msgs/msg/String --qos-reliability best_effort   # in-tree talker
# ros2 topic echo /chatter std_msgs/msg/Int32 --qos-reliability best_effort  # BYO my_app

Contributors: nano-ros’s own zephyr talker has a matching in-tree recipe for the canonical native_sim build path — see Per-Platform Contributor Lanes.

The Zephyr boot banner runs first, then the talker fires: the canonical in-tree talker prints Publishing: 'Hello World: 1', Publishing: 'Hello World: 2', … (Rust + C + C++ all count from 1, matching the official ROS 2 demo talker); the raw BYO Talker.c above prints Published: 0, Published: 1, …

Readiness signal. On native_sim, expect the first publish line (Publishing: 'Hello World: 1' for the in-tree talker; Published: 0 for the BYO app) within 5 seconds of boot (or ./build/zephyr/zephyr.exe); on qemu_cortex_a9 expect it within ~15 seconds (QEMU cold boot + Zephyr init). If no publish line in 30 seconds:

1. Confirm CONFIG_NROS=y lit up via west build -t menuconfig; without it the module shell never add_subdirectory’s nano-ros.
2. Check CONFIG_NETWORKING=y, CONFIG_NET_IPV4=y, CONFIG_NET_TCP=y in prj.conf — Zephyr networking is opt-in.
3. Confirm zenohd reachable from the simulated network (Slirp needs 10.0.2.2:7447 on QEMU; native_sim uses host loopback).
4. See Troubleshooting — First 10 Minutes.

Zephyr 4.x build gotchas.

• Could NOT find Python3 ... required is at least "3.12" — 4.x needs Python ≥ 3.12. Provision one without sudo (e.g. uv venv --python 3.12 .venv312 && uv pip install west -r zephyr/scripts/requirements.txt) and run west through it (.venv312/bin/python -m west build ...), so the ROS descriptor-codegen subprocess still uses the system ROS Python.
• attempt to assign the value ... to the undefined symbol ETH_NATIVE_POSIX — that symbol was renamed ETH_NATIVE_TAP in 4.x; the version-aware NSOS overlay handles it (contributors: the in-tree just zephyr build-one recipe applies it automatically).

Zephyr 4.x: select the RMW with a snippet

On 4.x, nano-ros ships west snippets so you pick the RMW on the build line instead of hand-writing the overlay:

west build -b native_sim/native/64 -S nros-cyclonedds apps/my_app
#                                   ^^^^^^^^^^^^^^^^^^^  nros-zenoh | nros-cyclonedds | nros-xrce

The snippet (shipped via the module’s snippet_root) carries the RMW-common Kconfig — equivalent to merging prj-<rmw>.conf. The prj-<rmw>.conf / -DCONF_FILE path still works (and is the only option on 3.7).

nano-ros patches into your workspace

nano-ros needs a few patches to Zephyr’s native_sim NSOS driver (recvmsg, IPv4-multicast) so the host-loopback-based examples work. Both supported lines (3.7 LTS and 4.x) take the same path — nros setup zephyr reads zephyr/patches.yml and applies each patch against the workspace’s Zephyr tree, sha256-checked. No extra step on your side beyond the provisioning command (already run during Prerequisites).

To re-apply (e.g. after a west update reset the tree):

nros setup zephyr --rmw zenoh

(Earlier nano-ros revisions documented a west patch apply flow on 4.x — that required a workspace-side west extension that doesn’t ship with stock Zephyr. Phase 208.D.7 / E.9 unified both lines on the provisioner. Cyclone-DDS-on-Zephyr patches stay baked into the pinned cyclonedds submodule, not delivered through patches.yml.)

Copy out an example as your starting point

The examples/zephyr/<lang>/<role>/ dirs are copy-out clean — copy one into your own app tree and it builds against the nano-ros module with no reference back into the nano-ros repo:

cp -r modules/nano-ros/examples/zephyr/c/talker apps/my_app
# cyclonedds examples need the host idlc + the ROS message dirs:
export NROS_STD_MSGS_DIR=/opt/ros/humble/share/std_msgs   # PKG_DIR contract
west build -b native_sim/native/64 -S nros-zenoh apps/my_app

Cyclone idlc and the descriptor-gen scripts are located via the module’s exported cache vars (NROS_CYCLONE_IDLC, NROS_CYCLONE_SCRIPTS_DIR, NROS_CYCLONE_CMAKE_DIR); message-package dirs come from NROS_<PKG>_DIR env (defaulting to /opt/ros/humble/share/<pkg>). No /opt/ros or repo-relative paths are baked into the example.

See the zephyr/ module dir + its Kconfig for the canonical in-repo surface.

GitHub source

• Zephyr module shell: zephyr/
• Worked examples: examples/zephyr/rust/, examples/zephyr/c/, examples/zephyr/cpp/
• Module manifest: zephyr/module.yml
• Kconfig surface (canonical post-Phase-208.D.7 fold — every CONFIG_NROS* symbol the doc cites lives here): zephyr/Kconfig
• Patches applied by nros setup zephyr (the west patch flow on this page was retired in Phase 208.E.9): zephyr/patches.yml

Next

• Pick a real board (Nordic, NXP, STM32, …): swap -b <board> and add a board-specific overlay to your prj.conf.
• Cyclone DDS on Cortex-A/R: see the DDS section of Choosing an RMW Backend for the required Kconfig deltas.
• Build nano-ros’s own Zephyr examples without west: Zephyr (contributor).