ecu-tests/docs/05_architecture_overview.md

Architecture Overview

This document provides a high-level view of the framework’s components and how they interact, plus a Mermaid diagram for quick orientation.

For the dynamic wiring — how a test actually reaches a live LinInterface at session start, the fixture topology, and the playbook for adding a new framework component — see 24_test_wiring.md.

Components

Framework core (ecu_framework/)

• Config Loader — ecu_framework/config/loader.py (YAML → dataclasses; re-exported via ecu_framework.config)
• LIN Abstraction — ecu_framework/lin/base.py (LinInterface, LinFrame)
• Mock LIN Adapter — ecu_framework/lin/mock.py
• MUM LIN Adapter — ecu_framework/lin/mum.py (Melexis Universal Master via pylin + pymumclient)
• BabyLIN Adapter — ecu_framework/lin/babylin.py (SDK wrapper → BabyLIN_library.py; DEPRECATED, kept for legacy rigs only)
• LDF Database — ecu_framework/lin/ldf.py (LdfDatabase/Frame over ldfparser; per-frame pack/unpack). Runtime, dynamic. Loaded fresh each session from whatever LDF the config points at. See LDF Database vs Generated LIN API below for why this is paired with the generated layer.
• Flasher — ecu_framework/flashing/hex_flasher.py
• Power Supply (PSU) control — ecu_framework/power/owon_psu.py (serial SCPI + cross-platform port resolver)
• PSU quick demo script — vendor/Owon/owon_psu_quick_demo.py

Hardware test layer (tests/hardware/)

• Project-wide fixtures — tests/conftest.py (config, lin, ldf, flash_ecu, rp)
• Hardware-suite fixtures — tests/hardware/conftest.py (session-scoped, autouse PSU; the bench is powered up once at session start and stays on for every test in the suite)
• MUM-suite fixtures — tests/hardware/mum/conftest.py (session-scoped fio, nad, alm; autouse _require_mum gate and _reset_to_off per-test reset). Tests outside tests/hardware/mum/ cannot see these — that's how PSU-only and BabyLIN-only tests are kept from accidentally requesting MUM fixtures.
• Generic LDF I/O — tests/hardware/frame_io.py (FrameIO — send/receive/pack/unpack for any LDF frame plus raw-bus escape hatches). Stringly-typed at this layer (fio.send("ALM_Req_A", …)); tests use this only for cases the AlmTester facade doesn't model (schema introspection, raw-frame escape hatches, MUM-only send_raw).
• ALM domain helpers — tests/hardware/alm_helpers.py (AlmTester + hand-maintained IntEnum classes). The single contributor-facing API for ALM tests: per-signal readers (read_led_state, read_voltage_status, …), per-action senders (send_color, send_config, …), wait helpers, and cross-frame patterns (assert_pwm_matches_rgb). See 19_frame_io_and_alm_helpers.md.
• Retired layer (kept under deprecated/) — deprecated/gen_lin_api.py + deprecated/_generated/lin_api.py. Was an LDF→Python generator that emitted typed frame/encoding classes; replaced by the hand-maintained surface in alm_helpers.py. See 22_generated_lin_api.md for the historical design.
• PSU settle helpers — tests/hardware/psu_helpers.py (wait_until_settled, apply_voltage_and_settle — measured-rail-then-validation pattern shared by all voltage-changing tests)
• RGB→PWM calculator — vendor/rgb_to_pwm.py (consumed by AlmTester.assert_pwm_*)
• Test templates (not collected) — tests/hardware/_test_case_template.py, tests/hardware/_test_case_template_psu_lin.py

Tests, reporting, artifacts

• Tests (pytest) — modules under tests/{,unit,plugin,hardware}/
• Reporting Plugin — conftest_plugin.py (docstring → report metadata)
• Reports — reports/report.html, reports/junit.xml, reports/summary.md, reports/requirements_coverage.json

Mermaid architecture diagram

flowchart TB
  subgraph Tests_and_Pytest [Tests & Pytest]
    T[tests/* (test bodies)]
    CF[tests/conftest.py<br/>config, lin, ldf, flash_ecu, rp]
    HCF[tests/hardware/conftest.py<br/>SESSION psu &#40;autouse&#41;]
    MCF[tests/hardware/mum/conftest.py<br/>fio, alm, nad, _require_mum &#40;autouse&#41;,<br/>_reset_to_off &#40;autouse&#41;]
    PL[conftest_plugin.py]
  end

  subgraph Hardware_Helpers [Hardware-test helpers]
    ALM[tests/hardware/alm_helpers.py<br/>AlmTester + typed IntEnums<br/>&#40;contributor-facing API&#41;]
    FIO[tests/hardware/frame_io.py<br/>FrameIO &#40;low-level, rarely used by tests&#41;]
    RGB[vendor/rgb_to_pwm.py]
    TPL[tests/hardware/_test_case_template*.py<br/>not collected]
  end

  subgraph Retired [Retired &#40;deprecated/&#41;]
    GEN[deprecated/_generated/lin_api.py]
    GENSCRIPT[deprecated/gen_lin_api.py]
  end

  subgraph Framework
    CFG[ecu_framework/config/loader.py]
    BASE[ecu_framework/lin/base.py]
    MOCK[ecu_framework/lin/mock.py]
    MUM[ecu_framework/lin/mum.py]
    BABY[ecu_framework/lin/babylin.py<br/>DEPRECATED]
    LDF[ecu_framework/lin/ldf.py]
    FLASH[ecu_framework/flashing/hex_flasher.py]
    POWER[ecu_framework/power/owon_psu.py<br/>SerialParams, OwonPSU,<br/>resolve_port]
  end

  subgraph Artifacts
    REP[reports/report.html<br/>reports/junit.xml<br/>reports/summary.md]
    YAML[config/*.yaml<br/>test_config.yaml<br/>mum.example.yaml<br/>babylin.example.yaml — deprecated]
    PSU_YAML[config/owon_psu.yaml<br/>OWON_PSU_CONFIG]
    MELEXIS[Melexis pylin + pymumclient<br/>MUM @ 192.168.7.2]
    SDK[vendor/BabyLIN_library.py<br/>platform libs<br/>DEPRECATED]
    OWON[vendor/Owon/owon_psu_quick_demo.py]
    LDFFILE[vendor/*.ldf]
    LDFLIB[ldfparser PyPI]
  end

  T --> CF
  T --> HCF
  T --> MCF
  MCF --> FIO
  MCF --> ALM
  CF --> CFG
  CF --> BASE
  CF --> MOCK
  CF --> MUM
  CF --> BABY
  CF --> FLASH
  HCF --> POWER
  T --> ALM
  T -.rare, low-level.-> FIO
  ALM --> FIO
  GENSCRIPT -.was: read LDF.-> LDFFILE
  GENSCRIPT -.was: emit source.-> GEN
  ALM --> RGB
  TPL -.copy & edit.-> T

  PL --> REP

  CFG --> YAML
  CFG --> PSU_YAML
  MUM --> MELEXIS
  BABY --> SDK
  LDF --> LDFLIB
  LDF --> LDFFILE
  POWER --> PSU_YAML
  T --> OWON
  T --> REP

Data and control flow summary

• Tests use fixtures to obtain config and a connected LIN adapter
• Config loader reads YAML (or env override), returns typed dataclasses
• LIN calls are routed through the interface abstraction to the selected adapter
• Hardware tests sit on top of three helpers: FrameIO (LDF-driven send / receive / pack / unpack for any frame, stringly-typed by frame name), the generated lin_api.py (typed AlmReqA.send(fio, …) wrappers plus LedState/Mode/Update enums, so signal/frame typos become import errors), and AlmTester (ALM_Node domain patterns built on FrameIO and the generated enums). All three are imported as siblings from tests/hardware/ — see docs/19_frame_io_and_alm_helpers.md and docs/22_generated_lin_api.md
• The hardware-suite tests/hardware/conftest.py defines a session-scoped, autouse psu fixture: on benches where the Owon PSU powers the ECU, the supply is opened once at session start, parked at config.power_supply.set_voltage / set_current, and left enabled for every test. Voltage-tolerance tests perturb voltage and restore in finally; they never toggle output. See docs/14_power_supply.md §5.
• Flasher (optional) uses the same LinInterface to program the ECU
• Power supply control (optional) uses ecu_framework/power/owon_psu.py and reads config.power_supply (merged with config/owon_psu.yaml or OWON_PSU_CONFIG when present). The quick demo script under vendor/Owon/ provides a quick manual flow
• Reporting plugin parses docstrings and enriches the HTML report

LDF Database vs Generated LIN API: two layers, one purpose

Historical. The generated LIN API is retired — see the banner in 22_generated_lin_api.md. The comparison below is kept for traceability: the runtime LdfDatabase path is still active (it's what FrameIO calls into); the generated path column describes a code path that now lives under deprecated/. Today, the analog of the right column is the hand-maintained IntEnum classes and method surface in tests/hardware/alm_helpers.py.

There are two pieces of code in this repo whose names both sound like "the LDF module", and a recurring question is why both exist:

Aspect	ecu_framework/lin/ldf.py (LdfDatabase/Frame)	tests/hardware/_generated/lin_api.py
What it is	Runtime wrapper around ldfparser	Source file emitted by scripts/gen_lin_api.py
When it runs	Every test session — parse_ldf(path) is called inside the ldf fixture (tests/conftest.py:92)	Never runs as a parser; it is the parser's output, imported like any other module
What it produces	Frame objects whose .pack(**kw) / .unpack(bytes) route through ldfparser's encode_raw / decode_raw	class AlmReqA, class LedState(IntEnum), etc. — Python literals derived from one LDF
Source of truth	The LDF file on disk at startup	The LDF file at the time gen_lin_api.py was last run (SHA256 in the file header)
Typing model	Stringly-typed (db.frame("ALM_Req_A").pack(AmbLight…=…))	Statically typed (AlmReqA.send(fio, AmbLight…=…))
Failure mode for a missing/renamed frame	KeyError: 'Frame X not found' at test time	ImportError: cannot import name 'X' at collection time, surfaced in CI
Failure mode for an LDF rev	None — it parses whatever is on disk	The in-sync unit test fails when the LDF SHA256 in the header drifts
Layer in the dependency tree	Framework core (ecu_framework/) — knows nothing about specific frame names	Test code (tests/hardware/) — bakes specific frame and signal names in
Lifecycle	Re-parsed each pytest session	Regenerated only on LDF change, then committed
Coupling to ldfparser	Direct (from ldfparser import parse_ldf)	None at runtime; the generator imports it, the generated file does not

The two answer orthogonal questions:

• ecu_framework/lin/ldf.py answers "what bytes go on the wire for this frame right now?" — it has to be dynamic because bit offsets, widths, and init values are properties of whichever LDF the bench loaded, and must be re-validated against that LDF at startup.
• tests/hardware/_generated/lin_api.py answers "what frame and signal names are valid for me to type in test code?" — it has to be static because that question is asked by the IDE, mypy, and pytest's collection step, all of which run before any LDF has been parsed.

If only ecu_framework/lin/ldf.py existed, every test would keep its stringly-typed fio.send("ALM_Req_A", …) calls and its hand-copied LED_STATE_OFF = 0 constants — both of which silently drift when the LDF changes. If only the generated lin_api.py existed, the runtime would have no path from a frame name to the actual byte layout for the currently loaded LDF — and worse, the test bench would happily ship bytes encoded against a stale LDF baked into the generator's last run.

Test-side entry points

Updated. This section originally described three parallel paths including the generated typed-wrapper layer. With the generator retired, the active picture is simpler: tests reach for AlmTester by default, and drop down to FrameIO only for schema introspection or other low-level needs. The diagram below is preserved for reference but the gen_lin_api node represents the now-retired path — see deprecated/.

FrameIO deliberately has no static dependency on ecu_framework/lin/ldf.py (its only ecu_framework import is LinInterface + LinFrame from lin/base.py), so the ldf it receives can be any object with a .frame(name) method.

flowchart TB
  T[test code]

  subgraph Paths[three independent ways to address a frame]
    GEN["gen_lin_api typed wrapper<br/>AlmReqA.send&#40;fio, ...&#41;<br/>compile-time name check"]
    FIO["FrameIO stringly-typed<br/>fio.send&#40;'ALM_Req_A', ...&#41;<br/>per-instance frame cache"]
    LDFDIRECT["LdfDatabase directly<br/>ldf.frame&#40;'ALM_Req_A'&#41;.pack&#40;...&#41;<br/>returns bytes, no I/O"]
  end

  T --> GEN
  T --> FIO
  T --> LDFDIRECT

  GEN -.delegates.-> FIO
  FIO -.duck-typed lookup.-> LDFOBJ[ldf-like object<br/>currently LdfDatabase]
  LDFDIRECT --> LDFOBJ
  LDFOBJ --> LDFPARSER[ldfparser - bit layout]

  FIO --> LIN[LinInterface.send / receive]
  LDFDIRECT -->|caller invokes lin.send<br/>with the packed bytes| LIN
  LIN --> WIRE[wire]

What each path buys you:

• gen_lin_api — compile-time name validation. Typo a frame or signal name and the IDE / mypy / pytest collection rejects it before any LDF is read. Delegates the actual packing to fio.send.
• FrameIO — stringly-typed I/O over the wire. Caches frame lookups, supports raw escape hatches (send_raw / receive_raw) that bypass the LDF object entirely.
• LdfDatabase directly — schema-only access. Useful when a test wants to inspect frame layout, pack a buffer without sending, or hand the bytes to a non-FrameIO transport.

The LDF object (currently LdfDatabase) is consumed by both FrameIO and any direct-use code path. FrameIO's use is via injection — it never imports LdfDatabase and can be tested against a stub. The next section explains what "duck-typed" means in this codebase and why it matters architecturally.

Removing any of the three entry points collapses a distinct affordance:

• Drop gen_lin_api → tests keep stringly-typed fio.send("ALM_Req_A", …) and hand-copied state constants, both of which silently drift when the LDF changes.
• Drop FrameIO → every test that wants high-level I/O has to wire LinInterface + LDF lookup + pack/unpack itself.
• Drop direct LdfDatabase usage → tests can no longer pack a frame without sending it, or inspect frame metadata without an I/O attempt.

Duck typing: how the polymorphism actually works

Both architectural seams above (FrameIO's ldf injection, the lin fixture's adapter selection) rely on duck typing rather than static type hierarchies. The Python idiom is:

If it walks like a duck and quacks like a duck, it's a duck.

Translation: Python doesn't check what type of object you pass — it just calls the methods you call and trusts they work. If they do, the object is "duck enough." The contract is the shape of the methods used, not the class.

Example 1: FrameIO and the ldf parameter

Look at tests/hardware/frame_io.py line 44:

class FrameIO:
    def __init__(self, lin: LinInterface, ldf) -> None:
        self._lin = lin
        self._ldf = ldf

Two parameters, two very different contracts:

• lin carries an annotation (LinInterface). That's a nominal contract: a type checker expects an instance of that class (or a subclass).
• ldf has no annotation at all. Anything is accepted at the call site.

Then on line 65 FrameIO uses ldf exactly once, this way:

f = self._ldf.frame(name)

That single method call — .frame(name) returning something with .id, .pack(**signals), .unpack(bytes), and .length — is the contract. Anything with that surface works:

• The real LdfDatabase (production)
• A unit-test stub (class _StubLdf: def frame(self, n): return _StubFrame(n))
• A future schema source (cached JSON, in-memory dict, etc.)

grep will confirm: frame_io.py never writes from ecu_framework.lin.ldf import LdfDatabase, never writes isinstance(ldf, LdfDatabase). The module is structurally unaware of LdfDatabase. That's what "no static dependency" meant in the previous section's diagram label duck-typed lookup.

Counter-example: what static typing would look like

If FrameIO had been written nominally, it would be:

from ecu_framework.lin.ldf import LdfDatabase

class FrameIO:
    def __init__(self, lin: LinInterface, ldf: LdfDatabase) -> None:
        ...

The consequences:

• frame_io.py would carry a hard module-level dependency on ecu_framework/lin/ldf.py.
• A unit test could no longer pass a stub without subclassing LdfDatabase or monkey-patching.
• The frame_io → ecu_framework/lin/ldf.py edge in the architecture diagram would represent a real coupling.

The codebase deliberately avoided that — the ldf parameter being untyped is intentional, not an oversight.

Example 2: the lin fixture and adapter polymorphism

The same idiom drives the LIN adapter swap. tests/conftest.py:34 returns something annotated as LinInterface:

@pytest.fixture(scope="session")
def lin(config: EcuTestConfig) -> Iterator[LinInterface]:
    if   config.interface.type == "mock":    lin = MockBabyLinInterface(...)
    elif config.interface.type == "mum":     lin = MumLinInterface(...)
    elif config.interface.type == "babylin": lin = BabyLinInterface(...)
    ...

This case has a nominal anchor (LinInterface is an abc.ABC declaring the required methods), but the day-to-day swap is duck-typed in spirit: tests call lin.send(frame) / lin.receive(...) without caring which concrete adapter is underneath. All three quack .send() / .receive() identically, so one YAML config switch reroutes every test in the suite without touching a single test body.

Why this matters

Two practical wins, both load-bearing in this codebase:

1. Swappability. A new adapter (CAN, FlexRay, a different LIN master) only needs to expose the same method surface. No edits to FrameIO, no edits to tests.
2. Testability. Unit tests pass minimal stubs — tests/unit/test_mum_adapter_mocked.py builds fake pylin / pymumclient objects with just enough method surface to exercise the adapter, never importing the real Melexis stack.

The Python idiom in play: EAFP

The supporting philosophy has a name: EAFP, "Easier to Ask Forgiveness than Permission." Instead of:

if isinstance(ldf, LdfDatabase) and hasattr(ldf, "frame"):
    f = ldf.frame(name)
else:
    raise TypeError(...)

…you just write:

f = ldf.frame(name)

…and let Python raise AttributeError at the point of misuse. The other half of the idiom is LBYL, "Look Before You Leap" — the explicit-checks style. Python idiomatically prefers EAFP because it composes better with duck typing: you don't need to enumerate every valid type, only the behaviours.

The trade-off

Duck typing is not free. Two costs to be aware of:

• Implicit contracts. The type signature ldf tells you nothing. A reader has to scan the method body to learn that .frame(name), .id, .pack(), .length are required. Mitigated here by the injection happening in one place (the fio fixture) so the duck shape is easy to track.
• Runtime, not compile-time, errors. A misshaped duck blows up at the call site, not at construction. Type checkers can't catch it. Mitigated here by the limited number of concrete duck-shapes in the codebase — there's really only LdfDatabase, and the fixture wires it in centrally.

The codebase accepts those costs in exchange for the swappability and testability wins above. The LinInterface abstract base class is the formal seam where the team chose to spend annotation effort; the ldf slot is where the team chose to keep things light.

Extending the architecture

• Add new bus adapters by implementing LinInterface
• Add new ECU-domain helpers next to AlmTester (e.g. BcmTester) on top of FrameIO; share fixtures via tests/hardware/conftest.py (or a per-adapter conftest like tests/hardware/mum/conftest.py)
• When the LDF changes (new frame, renamed signal, new encoding-type row): add or update the corresponding read_* / send_* method (and, if needed, a new IntEnum) in tests/hardware/alm_helpers.py. This is the maintenance pact that replaced the retired generator
• Add new bench instrument controllers next to OwonPSU under ecu_framework/power/ or a new ecu_framework/instruments/ package, expose them as session-scoped fixtures
• Add new report sinks (e.g., JSON or a DB) by extending the plugin