obdash/ARCHITECTURE.md

ford-obd — Architecture & Roadmap

Plan for growing the terminal obd_reader.py into a graphical Windows scan tool for the 6.0L Power Stroke, on a shared headless core.

Vision

A desktop app with:

• a PID browser (searchable list, live values) on the side,
• a flexible graph workspace — overlay many metrics on one plot, split into a grid of single-metric plots, or show gauges (one metric each),
• purpose-built perspectives: Cranking, Driving, Diagnostics (DTCs), Logging,
• a Ford DTC database behind the codes page,
• session record + playback so intermittent faults can be reviewed offline.

The constraint that shapes everything: ELM327 bandwidth

The ELM327 is a one-request-at-a-time link: each Mode-22 round-trip is ~40–150 ms over the CH340, so total throughput is ~7–15 PID reads/sec, shared across the whole UI. Consequences baked into the design:

• A prioritized polling scheduler owns the link. The active view subscribes the PIDs it needs at the rates it needs (cranking = ICP fast, ignore the rest).
• Acquisition runs off the UI thread; the GUI only reads the store.
• Per-PID rates and dead-PID parking keep the sample rate from collapsing.
• A faster adapter (OBDLink SX/MX+, STN chip — batched PIDs, faster protocols) multiplies throughput; the link layer is abstracted so either works.

Layers

        +------------------- GUI (PySide6 + pyqtgraph) -------------------+
        |  PID browser | Graph workspace | Perspectives | DTC page | Log  |
        +--------------------------------|-------------------------------+
                         reads only      |  (Qt thread)
        +--------------------------------v-------------------------------+
        |                         obdcore (headless)                      |
        |  PollScheduler  --reads-->  ElmLink / MockLink  --serial-->  PCM |
        |       |  pushes samples                                          |
        |       v                                                          |
        |  TimeSeriesStore  <--- CsvRecorder / replay_csv                  |
        |  PidRegistry (verified PIDs)   DtcDatabase                       |
        +-----------------------------------------------------------------+

obdcore is pure data/IO — no Qt, no curses — so it's shared by the terminal tool, the GUI, and tests.

obdcore modules (built, tested)

Module	Responsibility
link.py ElmLink	ELM327 serial: init, protocol negotiate, Mode-01/22 reads, ATRV, DTC read/clear. Returns raw bytes.
mock.py MockLink	Synthetic crank (ICP ramp, FICM ~48V, batt sag) — same interface; powers tests + GUI dev with no truck.
registry.py PidRegistry	Verified Ford 6.0 PID table (corrected addresses + scaling + confidence) and subscription presets. DtcDatabase seeds the code DB.
scheduler.py PollScheduler	Prioritized round-robin polling; per-PID Hz; derived channels; dead-PID park/revive. tick() is test-drivable with a fake clock.
store.py TimeSeriesStore	Per-PID ring buffers + min/max; CsvRecorder (long format) + replay_csv for record/playback.

Tests: tests/test_obdcore.py — decoders vs real truck bytes, crank ramp + peak capture, derived BOOST, dead-PID parking, record/replay round-trip.

Data model

• Pid: key, name, mode (01/22/atrv/derived), pid hex, nbytes, decode fn, unit, group, vmin/vmax, confidence (verified|doc|tentative), deps (for derived), notes.
• Channel: rolling (t, value) + session min/max.
• Derived/virtual channels: e.g. BOOST = MAP − BARO; later ICP_error = ICP_DES − ICP, FICM_sag = FICM_M − FICM_V.

GUI plan (PySide6 + pyqtgraph)

• Left dock: QTreeView PID browser grouped by system (fuel/ficm/air/…), live value + confidence badge, checkbox to add to the focused panel.
• Central workspace: dockable/tabbed panels. Panel types:
  • Overlay plot — many PIDs, multiple Y-axes (pyqtgraph ViewBox linking).
  • Split grid — one plot per PID.
  • Gauge — radial/linear single metric with warn/crit bands. Drag a PID from the browser onto a panel to add it.
• Perspectives (saved layouts):
  • Cranking — ICP big readout + 500-psi firing line + peak-hold + trace (port of terminal --crank).
  • Driving — boost (MGP), EOT, ECT, EBP, load, RPM, IPR, FICM, trans temp.
  • Diagnostics — DTC read/clear (guarded) + freeze frame, joined to the Ford DTC DB (description, causes, no-start relevance).
  • Logging/Playback — record a session; scrub/replay through the graphs.
• Settings — COM port, baud, protocol, per-PID rates, units (psi/°F vs kPa/°C), dark/night theme.
• Bottom status — adapter, protocol, port voltage, dropped-response rate.

Honest 6.0 data-stream limits

Two commonly-wanted gauges are not in the stock 6.0 PCM stream from the OBD port and need aftermarket sensors:

• Engine oil PRESSURE — only ICP (injection oil) + EOT (oil temp) exist; lube pressure is an idiot-light switch, not a PID.
• EGT — only EBP (exhaust back pressure) exists; exhaust gas temperature is an add-on pyrometer.

Plan: present what the PCM exposes; design an aux-input path so external sensors (e.g. a serial/analog EGT/oil-PSI module) can feed extra channels later.

Additional features (backlog)

• Session record + playback/scrub (highest value; foundation already in store).
• Bi-directional tests: KOEO/KOER self-tests, injector buzz, cylinder contribution/balance.
• Alarms + min/max hold per PID (EOT>230°F, ICP<500 cranking).
• Timeline annotations ("started cranking", "stabbed throttle").
• Computed channels (ICP error, FICM sag).
• Multi-vehicle profiles + per-truck DTC history.
• Export/report (CSV/PDF, graph screenshots, one-click "share state").
• PID discovery scan in GUI (the brute-scan, auto-add hits).
• Units toggle, night theme, big-touch cab mode.

Roadmap

• P0 — core (this commit): obdcore package + tests + this doc. Next: migrate obd_reader.py to import obdcore (remove the duplicated ELM/PID logic) so terminal + GUI share one source of truth.
• P1 — GUI shell: PySide6 window, connect dialog, PID browser, one overlay plot fed by the scheduler/store. Validate against MockLink first.
• P2 — panels + perspectives: split plots, gauges, Cranking + Driving views.
• P3 — diagnostics: DTC read/clear page + Ford DTC DB (built by the cross-verified workflow, same method as the PID hunt).
• P4 — record/playback + alarms + computed channels.
• P5 — packaging: PyInstaller one-file .exe (+ CH340 driver note), optional code-signing; OBDLink/STN fast-path support.

Dependencies

• Runtime (core): pyserial.
• GUI: PySide6, pyqtgraph, numpy.
• Dev: pytest, pyinstaller.