Minimal Pub/Sub Example

A minimal publisher/subscriber example using the Eclipse S-CORE middleware (score::mw::com). It demonstrates the full IPC lifecycle over shared memory (SHM):

• Publisher — offers a MotorAngle service, continuously sends angle_deg samples at 20 Hz (sinusoidal 90° amplitude at 1 Hz).
• Subscriber — discovers the service, subscribes to the motor_angle event, and prints each received sample via an event-driven receive handler (no polling).
• TorqueSubscriber — subscribes to a MotorTorque service and prints torque_nm samples; intended as a companion to the example_scorePubSub MATLAB External Mode example where Simulink publishes MotorTorque.

For a detailed walkthrough of the manual build process, prerequisites, and how the patching works, see README_advanced.md.

Repository layout

minimal_score_pubsub_cmake/
├── datatype.h / datatype.cpp      # MotorAngle/MotorTorque structs + Interface/Proxy/Skeleton
├── publisher.cpp                  # Service skeleton: offers and sends MotorAngle samples
├── subscriber.cpp                 # Service proxy: finds, subscribes, receives MotorAngle samples
├── torque_subscriber.cpp          # Service proxy: subscribes to MotorTorque (published by Simulink)
├── etc/
│   └── mw_com_config.json         # Service instance manifest (SHM binding, event slots)
├── build/
│   └── score_mw_sysroot/          # Middleware sysroot (headers, libs, CMake config)
├── setup_score_sysroot.sh         # Builds the middleware sysroot (auto-applies patches)
├── build_and_deploy.sh            # Interactive build + deploy script (recommended entry point)
├── toolchain-arm64.cmake          # ARM64 cross-compilation toolchain file
├── CMakeLists.txt                 # CMake build configuration
└── README.md

Prerequisites

• Bazel 8.x
• C++17-capable compiler (GCC or Clang)
• Linux host (shared memory IPC)

For ARM64 cross-compilation (e.g. Raspberry Pi 5), you also need the aarch64-linux-gnu cross-toolchain. See README_advanced.md for setup instructions.

Tested communication repo commit: 1e03b3110c120ae3f9aff07a366ba8c99cf267d3 (2026-05-06 — Adding clang-tidy checks) If the upstream repo has been updated past this commit, the sysroot patches in setup_score_sysroot.sh may need updating. See the Troubleshooting section.

Quick start — build_and_deploy.sh

The recommended way to build (and optionally deploy to a remote target) is via the interactive script:

./build_and_deploy.sh

The script will guide you through:

1. Target architecture (x86 or arm)
2. Linking mode (static or shared)
3. Whether to (re)build the middleware sysroot, and which communication repo to use
4. Whether to clean the Bazel cache before building
5. Whether to deploy the binaries to a remote SSH target

Non-interactive usage

# ARM static build, no deploy
./build_and_deploy.sh --arch=arm --link=static --deploy=no

# ARM static build, skip sysroot rebuild, deploy to Pi
./build_and_deploy.sh --arch=arm --link=static --skip-sysroot \
    --deploy=yes --target=pi@192.168.1.10

# ARM shared build, deploy to Pi, fully non-interactive
./build_and_deploy.sh --arch=arm --link=shared --clean-cache=no \
    --deploy=yes --target=pi@192.168.1.10 -y

All options:

Option	Description
--arch=x86|arm	Target architecture
--link=static|shared	Linking mode
--comm-repo=PATH	Path to eclipse-score/communication repo
--skip-sysroot	Skip rebuilding the middleware sysroot
--clean-cache=yes|no	Clean Bazel cache before sysroot build
--deploy=yes|no	Deploy to remote target after build
--target=USER@HOST	SSH target (e.g. pi@192.168.1.10)
--deploy-dir=PATH	Remote deploy directory (default: ~/score_pubsub)
-y, --yes	Accept all defaults non-interactively
-h, --help	Show help and exit

Run

After building, open two terminals on the target device (or locally for x86):

Terminal 1 — Publisher:

cd ~/score_pubsub
./publisher etc/mw_com_config.json

[Publisher] Service offered. Sending data...
[Publisher] Sent motor angle [deg]: 0
[Publisher] Sent motor angle [deg]: 27.5664
...

Terminal 2 — Subscriber:

cd ~/score_pubsub
./subscriber etc/mw_com_config.json

[Subscriber] Service found. Connecting...
[Subscriber] Received motor angle [deg]: 0
[Subscriber] Received motor angle [deg]: 27.5664
...

Terminal 3 — Torque Subscriber (used with the example_scorePubSub MATLAB External Mode example):

cd ~/score_pubsub
./torque_subscriber etc/mw_com_config.json

[TorqueSubscriber] Received motor torque [Nm]: 0.5
...

Stop any process with Ctrl+C.

How it works

Concept	This example
Service interface	MotorAngleInterface<Trait> — declares the motor_angle_ event
Data type	MotorAngle — plain struct with float angle_deg
Publisher side	MotorAngleSkeleton::Create() → OfferService() → Allocate() → Send()
Subscriber side	MotorAngleProxy::FindService() → Create() → Subscribe() → SetReceiveHandler()
Torque subscriber	MotorTorqueProxy::FindService() → Create() → Subscribe() → SetReceiveHandler()
Torque data type	MotorTorque — plain struct with float torque_nm; published by Simulink in example_scorePubSub
Transport	Shared memory (SHM), configured in etc/mw_com_config.json
Config	instanceSpecifier: score/examples/MotorAngle, serviceId: 6432, eventId: 3
Torque config	instanceSpecifier: score/examples/MotorTorque (see etc/mw_com_config.json)

Troubleshooting

Sysroot build fails after a git pull on the communication repo

The patches applied by setup_score_sysroot.sh were tested against a specific commit. If the upstream repo has moved past it, the build may fail with compile or Bazel errors.

First, pin to the tested commit and retry:

git -C ~/score/communication checkout 1e03b3110c120ae3f9aff07a366ba8c99cf267d3
./setup_score_sysroot.sh ~/score/communication --cpu=arm64

If that succeeds, the issue is a newer upstream change. See README_advanced.md — Patch maintenance for how to update the patches for the new commit.

ERROR: no such package 'platforms'

The platforms/ directory is missing from the communication repo. Run the sysroot script once — it will copy it automatically from the bundled platforms/ in this repo:

./setup_score_sysroot.sh ~/score/communication --cpu=arm64

error: could not convert … from 'StdVariantType' to 'VariantType'

The tracing_runtime.cpp patch is needed but was not applied. Delete the communication repo's Bazel cache and re-run the sysroot script (it will patch and rebuild):

bazel -C ~/score/communication clean
./setup_score_sysroot.sh ~/score/communication --cpu=arm64

undefined reference to score::os::Path::Default

The @score_baselibs//score/os/utils:path target is missing from the fat library. This is fixed in setup_score_sysroot.sh — make sure you have the latest version of the script and rebuild the sysroot.

syntax error at '\': expected expression in MODULE.bazel

A previous run left literal \n sequences in MODULE.bazel (shell quoting issue). Fix:

python3 - ~/score/communication/MODULE.bazel <<'EOF'
import sys
path = sys.argv[1]
with open(path) as f: src = f.read()
src = src.replace('\\n', '\n')
with open(path, 'w') as f: f.write(src)
print("Fixed")
EOF

Then re-run the sysroot script.

Binaries run but no data is received

• Ensure publisher and subscriber use the same mw_com_config.json.
• Both processes must run as the same user (shared memory permissions).
• On a remote target: verify the config was deployed to etc/mw_com_config.json relative to the working directory, and run from inside the deploy directory:

  cd ~/score_pubsub && ./publisher etc/mw_com_config.json

Shared library not found on target (error while loading shared libraries)

The libmw_com.so was not installed to a system library path. Either:

# Option A — install system-wide (requires sudo on target)
sudo cp libmw_com.so /usr/local/lib/
sudo ldconfig

# Option B — set LD_LIBRARY_PATH at runtime
LD_LIBRARY_PATH=~/score_pubsub ./publisher etc/mw_com_config.json