Anatomy of What You Just Built

Two packages, two roles. Everything you add to this project later is another package with one of these roles, or a few more lines in the bringup. The shape never changes; it only gains packages.

If you come from ROS 2, each role is something you already know:

The node package: the code

A node package is one node, as a library. It has no main() and names no board:

src/sensor_node/
├── Cargo.toml          # a library crate; dependencies only
├── package.xml         # ROS package manifest: std_msgs is declared here
└── src/lib.rs          # the Talker: a 1 s timer that publishes on /chatter

lib.rs declares what the node creates (a publisher, a timer) and what its callback does. Message types come from package.xml’s dependencies and are generated during the build; you never write them by hand.

The same node builds for any board. Nothing in this package says mps2-an385, zenoh or serial: those are the bringup’s.

The bringup package: what runs where

src/sensor_node_bringup/ holds no code, only package.xml and system.toml:

[system]
name = "sensor_node"
rmw = "zenoh"                        # which middleware
ros_edition = "humble"               # which ROS 2 your peers run
domain_id = 0

[[component]]                        # which nodes run
pkg = "sensor_node"
class = "sensor_node::Talker"
name = "sensor_node"

[image.baremetal]                    # one block per thing you deploy
board = "mps2-an385-baremetal"
locator = "serial/UART_0#baudrate=115200"

Every configuration choice lives here, never in a node package. Moving the talker to another board is a new [image.*] block; switching middleware is the rmw line. Neither touches src/sensor_node/.

The launch file: generated until you need one

ROS 2 projects describe what to start in a launch file. This bringup has no launch/ directory, so nros run generated one from the [[component]] rows, after the first build. To see it:

cat build/nros/launch/sensor_node_bringup/launch/system.launch.xml

When you need what only a launch file can say (a parameter, a remap, a launch argument), add launch/system.launch.xml to the bringup and it replaces the generated one. The file is the ROS 2 launch XML schema, so a launch file from another ROS 2 project pastes in unchanged.

The entry: the binary, also generated

There is no entry package under src/. nros run (and nros build) reads each [image.*] block and generates the entry for it under build/: a main() that constructs each component, applies the launch file’s parameters, and runs them on one executor. Running the entry is launching the system; there is no separate ros2 launch step.

What is yours and what is generated

Everything under src/ is yours to edit and commit. build/ holds everything derived: generated message code, the launch file, the resolved system and the entry. Nothing in build/ is committed; if you can regenerate it, it does not belong in git.

Next

• Your own message package
• Growing your workspace: a second node, a second board, a launch file.
• First Node in C or C++: the same node package in another language.

Design background

RFC-0121 D1 to D3.