signalk-mini

Lightweight low-latency C++ Signal K mini server for Arduino and Linux.

This stage vendors only source trees from the uploaded modules:

• modules/async-event-loop/src
• modules/nmea0183/src
• modules/data-model/src

The main project code is split under src/signalk_mini/.

The mini server base is in signalk_mini/server.hpp. It has one event loop, one mandatory main Signal K TCP server, connector configuration, runtime connection registries, backpressure handling, NMEA line input, typed model updates, and Signal K delta publishing.

Project direction:

• strongly typed internal data model, not Signal K as store
• Signal K as an output adapter layer
• template<typename Real> through core paths
• unit suffixes preserved in data model field names
• ArduinoJson v7 at the JSON/protocol boundary
• Linux daemon configuration uses libconfig .conf, not JSON

Naming

Connectors are configuration entries. They describe a protocol plus transport, such as nmea0183 over udp.

Connections are runtime objects. One connector can create zero, one, or many runtime connections. For example, one TCP server connector can accept many TCP connections. UDP listeners do not create TCP-style connections; they receive datagrams on a socket.

Connector config is separated into common connector identity, access flags, protocol-specific settings, and transport-specific settings. For example, NMEA0183 checksum settings belong to the NMEA0183 protocol block, while UDP listen host/port belong to the UDP transport block.

Defaults

The built-in default connector listens for NMEA0183 UDP datagrams on all local interfaces:

protocol = "nmea0183";
transport = "udp";
listen_host = "0.0.0.0";
listen_port = 10110;

Port 10110 is the de facto NMEA0183-over-IP port used for NMEA0183 navigational data over TCP or UDP. Binding to 0.0.0.0:10110 receives packets sent directly to the host and ordinary IPv4 broadcast packets reaching that interface.

Linux config

Default path:

/etc/signalk-mini/signalk-mini.conf

Example:

examples/linux/signalk-mini.conf

The config has one mandatory main Signal K server and optional connectors. Each connector combines protocol plus transport, for example:

enabled = true;
label = "nmea0183-udp-10110";
protocol = "nmea0183";
transport = "udp";

access: {
  allow_rx = true;
  allow_tx = false;
};

nmea0183: {
  validate_checksum = false;
};

udp: {
  listen_host = "0.0.0.0";
  listen_port = 10110;
  allow_broadcast = true;
};

or:

enabled = true;
label = "nmea0183-serial";
protocol = "nmea0183";
transport = "serial";

access: {
  allow_rx = true;
  allow_tx = false;
};

nmea0183: {
  validate_checksum = true;
};

serial: {
  device = "/dev/ttyUSB0";
  baud = 4800;
};

For NMEA0183, omitted validate_checksum defaults by transport:

• serial: true
• tcp_client, tcp_server, udp: false

Implemented NMEA0183 transports in this stage:

• udp
• tcp_client
• tcp_server
• serial

Build

cmake -S . -B build
cmake --build build --parallel
ctest --test-dir build --output-on-failure

Linux build dependencies: libevent, libconfig, pkg-config.

Default TCP/UDP ports:

• Signal K TCP server: 20223
• NMEA0183 UDP listener: 0.0.0.0:10110