cpp-LIN

C++ LIN bus library — RELAY-conformant, ISO 26262 ASIL-B.

Overview

cpp-LIN is a production-quality C++ implementation of the LIN (Local Interconnect Network) protocol, following the RELAY specification v1.11. It is the C++ sibling of go-LIN and is patterned after cpp-CAN.

Features

• Virtual bus — in-process, thread-safe LIN bus for testing and simulation
• LDF parser — parse LIN Description Files (.ldf), decode signals
• Master node — schedule table runner with configurable slot timing
• Slave node — publish response payloads for specific LIN frame IDs
• E2E safety — End-to-End protection (10-byte header, CRC-16/CCITT-FALSE)
• RELAY adapter — exposes any IBus as a relay::INode for cross-protocol routing
• CLI — cpp-lin-cli binary for RELAY conform/interop test harness integration
• ISO 26262 ASIL-B — full requirements traceability via .fusa-reqs.json

Quick Start

# Clone
git clone https://github.com/SoundMatt/cpp-LIN.git
cd cpp-LIN

# Build (requires CMake >= 3.21, C++17)
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel

# Test
ctest --test-dir build --output-on-failure

# CLI
./build/cli/cpp-lin-cli version
./build/cli/cpp-lin-cli capabilities

Architecture

include/lin/
  channel.hpp        — Chan<T>: bounded, thread-safe FIFO
  relay.hpp          — RELAY v1.11 types (Protocol, Message, INode, …)
  lin.hpp            — IBus, IMasterBus, Frame, Filter, free functions
  virtual/bus.hpp    — In-process virtual LIN bus
  safety/e2e.hpp     — E2E Protector / Receiver
  ldf/parser.hpp     — LDF file parser / signal decoder
  master/node.hpp    — Master schedule runner
  slave/node.hpp     — Slave response publisher

src/
  relay.cpp          — RELAY type implementations
  lin.cpp            — PID, checksum, validation, RELAY adapter
  virtual/bus.cpp    — Virtual bus implementation
  safety/e2e.cpp     — CRC-16 and E2E framing
  ldf/parser.cpp     — LDF tokeniser and parser
  master/node.cpp    — Master node run loop
  slave/node.cpp     — Slave node

cli/
  main.cpp           — CLI entry point (version/capabilities/status/convert)
  json.hpp           — JSON helpers

tests/               — Catch2 unit tests (≥ 70% line coverage enforced)
testdata/            — RELAY spec test vectors
docker/              — Dockerfile + docker-compose.yml

LIN Protocol Notes

Property	Value
Max frame ID	0x3F (6-bit)
Max data length	8 bytes
Diagnostic request ID	0x3C
Diagnostic response ID	0x3D
Classic checksum	Data bytes only
Enhanced checksum	PID + data bytes
Diagnostic frames	Classic checksum only

Protected Identifier (PID):

P0 = ID0 ^ ID1 ^ ID2 ^ ID4        (bit 6)
P1 = NOT(ID1 ^ ID3 ^ ID4 ^ ID5)   (bit 7)

RELAY Integration

cpp-LIN exposes a RELAY v1.11 INode adapter:

#include <lin/lin.hpp>
#include <lin/virtual/bus.hpp>

auto bus = std::make_shared<lin::virt::Bus>();
auto node = lin::adapt(bus);
// node is a relay::INode* — plug it into any RELAY router

The CLI exposes the RELAY test harness interface:

relay conform ./build/cli/cpp-lin-cli --strict
relay interop --protocol LIN ./build/cli/cpp-lin-cli

E2E Safety

#include <lin/safety/e2e.hpp>

lin::safety::Config cfg{.data_id = 0x0042, .source_id = 0x0001};
lin::safety::Protector prot(cfg);
lin::safety::Receiver recv(cfg);

std::vector<uint8_t> payload = {0x01, 0x02, 0x03};
auto protected_msg = prot.protect(payload);
auto unwrapped = recv.unwrap(protected_msg);   // throws E2EError on failure

LDF Parser

#include <lin/ldf/parser.hpp>
#include <fstream>

std::ifstream f("example.ldf");
auto db = lin::ldf::parse(f);

auto& fr = db->frame(0x10);   // frame by ID
auto decoded = db->decode(0x10, {0xAB, 0xCD});  // signal values

ISO 26262 ASIL-B

All requirements are tracked in .fusa-reqs.json. Every source file carries // fusa:req REQ-XXX-NNN annotations; every test file carries // fusa:test REQ-XXX-NNN annotations. The CI pipeline runs cpfusa qualify to enforce ASIL-B traceability coverage.

See SAFETY_PLAN.md for the full safety plan.

Contributing

See CONTRIBUTING.md. All commits require a DCO sign-off:

git commit -s -m "feat: your change"

License

Mozilla Public License 2.0 — see LICENSE.

Copyright (c) 2026 Matt Jones. All rights reserved.