X19-Core: Purdue ROV ZeroMQ & Protobuf System

This repository hosts the core communication, sensing, and control architecture for the Purdue ROV X-19 underwater vehicle. The system uses ZeroMQ (ZMQ) for low-latency inter-process communication and Protocol Buffers (Protobuf) for type-safe, cross-language serialization (C++ and Python).

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📂 Codebase Directory Layout

X19-Core/
├── config/                  # Configuration files (ports, address bindings)
├── src/                    # Communication wrappers & middleware
│   ├── cpp/                 # C++ wrapper library
│   └── python/              # Python wrapper library (python.messaging package)
│       └── messaging/
│           ├── publisher.py
│           └── subscriber.py
├── nodes/                   # Independent executable nodes
│   ├── cpp/                 # C++ nodes (thrusters, pid controls, etc.)
│   └── python/              # Python nodes (video, pilot control, etc.)
├── proto/                   # Protobuf message schemas
├── scripts/                 # Utility scripts (setup, compilation)
├── testing/                 # Validation and testing scripts
├── run.sh                   # Main runner shortcut script
└── MVPs.md                  # Development checklist & milestones

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⚙️ Setup & Installation

1. System & Python Dependencies

Prerequisites include the Protobuf Compiler (protoc), ZeroMQ development headers, and Python 3.

Run the automated setup script to provision your system:

./scripts/setup.sh

(This installs protobuf-compiler and libzmq3-dev via apt-get, and builds the Python dependencies defined in requirements.txt into your virtual environment).

2. Compile Protobuf Schemas

Compile your .proto files in the proto/ directory to generate C++ and Python bindings:

./scripts/compile_protos.sh

This outputs compiled bindings directly to src/protocols/cpp and src/protocols/python.

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🚀 Running the Code

Use the root run.sh script to execute your code with the correct python paths set:

# Run the hello_pub test node
./run.sh

# Recompile protobuf schemas AND run the hello_pub test node
./run.sh -p

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🛠️ Messaging Wrapper API

To make writing nodes simple and robust, lightweight wrappers wrap ZMQ sockets into easy-to-use classes.

Python API

1. Publisher (python.messaging.Publisher)

Creates a ZMQ PUB socket that serializes and publishes Protobuf messages on a specific topic.

from src.python.messaging import Publisher
from src.protocols.python import telemetry_pb2

# Initialize publisher (binds to address by default)
publisher = Publisher(address="tcp://127.0.0.1:5555", topic="telemetry")

# Create and publish a Protobuf message
msg = telemetry_pb2.SensorData(depth=1.24)
publisher.publish(msg)

# Clean up
publisher.close()

• __init__(address: str, topic: str, bind: bool = True)
  • address: ZMQ address endpoint (e.g., tcp://*:5555).
  • topic: Topic name string.
  • bind: Binds socket to the port if True; connects if False.
• publish(proto_message)
  • Serializes the Protobuf class instance and publishes it.
• close()
  • Closes the underlying ZMQ socket.

2. Subscriber (core.messaging.Subscriber)

Creates a ZMQ SUB socket that connects to a publisher, subscribes to a topic, and parses incoming Protobuf payloads.

from src.python.messaging import Subscriber
from src.protocols.python import telemetry_pb2

def telemetry_callback(data):
    print(f"Received depth: {data.depth}")

# Initialize subscriber (connects to address by default)
subscriber = Subscriber(
    address="tcp://127.0.0.1:5555",
    topic="telemetry",
    message_type=telemetry_pb2.SensorData,
    callback=telemetry_callback
)

# Process a single incoming message (timeout in milliseconds)
subscriber.spin_once(timeout_ms=100)

# Clean up
subscriber.close()

• __init__(address: str, topic: str, message_type, callback, bind: bool = False)
  • address: Target publisher endpoint (e.g., tcp://127.0.0.1:5555).
  • topic: Subscribed topic string.
  • message_type: Protobuf class type used to deserialize payloads.
  • callback: Callback function signature def callback(message).
  • bind: Binds socket if True; connects if False.
• spin_once(timeout_ms: int)
  • Polls the socket. If data is available, it deserializes the payload and invokes the callback. Returns True if processed, otherwise False.
• close()
  • Closes the underlying ZMQ socket.

3. Running The Code

• set python path to dir root

export PYTHONPATH=<project_root>

• run publisher using virtual env first

./.venv/bin/python ./testing/hello_pub.py 

• run subscriber using virtual env next

./.venv/bin/python ./testing/hello_sub.py 

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📹 Video Streaming & ZMQ IP Discovery

X19-Core contains the camera acquisition and low-latency H.264 RTSP streaming pipeline for the ROV cameras.

┌──────────────────────────────────────────────────────────────────┐
│                   X19-Core Video Subsystem                       │
│                                                                  │
│  1. get_ip.py (ZMQ Subscriber on port 5556)                      │
│     - Connects to tcp://<SURFACE_IP>:5556 on topic 'surface_ip'  │
│     - Deserializes Protobuf payload: telemetry_pb2.test(msg=ip)  │
│                                                                  │
│  2. V4L2 Device Auto-Discovery                                   │
│     - Runs 'v4l2-ctl --list-devices'                             │
│     - Detects attached exploreHD / Arducam / Intel cameras       │
│                                                                  │
│  3. FFmpeg RTSP Streamers (videos_launch.py)                     │
│     - Spawns background FFmpeg process for each camera           │
│     - Encodes H.264 / MJPEG video with zerolatency preset        │
│     - Pushes RTSP stream to rtsp://<SURFACE_IP>:8554/camera<N>   │
└──────────────────────────────────────────────────────────────────┘

Video Nodes in src/python/videos/:

• get_ip.py: ZMQ subscriber node listening for Surface IP broadcast. Once IP is received, triggers camera discovery and starts streaming processes.
• videos_launch.py: Low-latency FFmpeg RTSP camera streamer node (--ip, --device, --camera-number).
• cv_camera_connect.py: DepthAI camera RTSP streamer node for OAK/DepthAI hardware.

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🌐 Network Ports & Field Deployment Guide

When running on the Raspberry Pi connected to the Surface Topside Laptop via Ethernet/tether network:

Port	Protocol	Target Node	Purpose
5555	ZMQ (TCP)	Surface Telemetry	Receives telemetry packets on topic telemetry
5556	ZMQ (TCP)	Surface IP Publisher	Receives Surface IP broadcast on topic surface_ip
8554	RTSP (TCP)	Go2RTC Server	Pushes RTSP camera streams to Surface media server

Running on Raspberry Pi (Hardware Network Setup):

1. On Surface Topside Laptop: Start the go2rtc_node.py (or run ./launch --field). Note the Surface laptop IP address (e.g. 192.168.1.100).
2. On Raspberry Pi (X19-Core): Launch get_ip.py pointing to the Surface laptop's IP address:

   python3 src/python/videos/get_ip.py --surface-address tcp://192.168.1.100:5556

   Or export the environment variable:

   export SURFACE_ZMQ_ADDRESS="tcp://192.168.1.100:5556"
   python3 src/python/videos/get_ip.py