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brewpi/components/pid/TODO.md
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jensandClaude Sonnet 4.6 2845051350 Refresh design-backlog docs after Pot's gain/theta cleanup
Drop the now-stale "config.json.templ/.sim still carry dead
Model.kn/Plant.kn keys" note (they were deleted), note that Pot now
always starts at theta_amb (no separate initial-temp param) and that
dropping the gain (efficiency) factor entirely is a partial realism
regression, not just a fix. Point the config-validation item at the
gain key that's still dead in config.json.sim. Also update demo_sud.py
to match the Pot params Pot.__init__ actually reads.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-06-19 18:37:03 +02:00

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# components/pid design backlog
Findings from a design review, refreshed against the current state of
`master` after the Kalman-filter removal and Smith-predictor rewrite (see
git history for `temp_controller.py`/`temp_controller_smith.py`).
- [x] **FSM thresholds aren't configurable.** Moved into an optional
`TempCtrl.Thresholds` config section (`HoldIdle`, `HoldHeat`,
`IdleHeat`, `IdleHold`, `HeatHold`, `HeatIdle`), merged over
`DEFAULT_THRESHOLDS` (now in `temp_controller_base.py`, formerly
`tc_constants.py`) so existing configs without the section keep
working unchanged.
- [x] **matplotlib imported at module level in production code.**
`temp_controller.py`, `temp_controller_smith.py`, and `kalman.py`
used to `from matplotlib.pyplot import ...` just to support their
`__main__` self-test plots. The plotting demos (and `kalman_eval.py`)
moved to `scripts/demos/pid/demo_*.py`; production modules no longer
import matplotlib.
- [x] **Three Kalman filters share one tuning.** No longer applicable:
`temp_controller_smith.py` was rewritten to drop Kalman filtering
entirely (see below), so there's no shared tuning to split anymore.
- [x] **`Pid.scale()` is a gain-scheduling hack, not anti-windup.**
Fixed: removed `Pid.scale()`/`self.k` entirely. `Pid.process(err, d,
scale=1.0)` now takes the gain multiplier as a plain per-call
argument instead of mutable state, so there's nothing to go stale
across a `reset()`. `temp_controller*.py` compute `hold_scale =
1.0/heatrate_soll_set if heatrate_soll_set > 0 else 1.0` themselves
and pass it through `process_pid(theta_err, heatrate_err,
hold_scale)` — the overshoot-compensation scheduling logic now lives
entirely in the temp controller, not the generic `Pid` block.
- [ ] **No automated tests.** `tests/components/pid/` was added once
(stdlib `unittest`, no pytest) covering FSM transitions, anti-windup
clamping, and Kalman convergence, but was removed again before the
Kalman-filter removal/Smith rewrite, so none of the current
`temp_controller*.py` behavior (backward-difference + low-pass
filtered heat rate, the two-model Smith correction) has test
coverage. This drives a physical heater — worth re-adding.
- [ ] **`set_model_power` isn't defined on every controller, but
`brewpi.py` wires it unconditionally.** `brewpi.py` always does
`heater.set_on_changed("power_set", tc.set_model_power)` regardless
of `Controller.pid_type`. Only `temp_controller_smith.py` (the Smith
predictor) defines `set_model_power`; `temp_controller.py` (`"Normal"`)
does not, so starting the server with `"pid_type": "Normal"` crashes
at wiring time with `AttributeError: 'TempController' object has no
attribute 'set_model_power'`. Either add a no-op `set_model_power` to
`TempControllerBase`, or only wire it when the configured controller
actually exposes a model to feed.
- [ ] **Config access is unchecked `dict[key]` everywhere.**
`params['Hold']`, `params['Td']`, etc., throughout, with no schema
validation at load time. We already hit this bug class once
(`config.json.sim`'s `gain`/`Model` nesting mismatch). A small
schema/dataclass validation layer at config-load would surface
errors immediately instead of mid-`__init__` — and would have caught
the dead `TempCtrl.Kalman` / `Model.kn` / `Plant.kn` keys that used
to sit unused in `config.json.templ`/`.sim` (since deleted) and the
`Model.gain`/`Plant.gain` keys still doing the same in
`config.json.sim` right now — `Pot` dropped `gain` entirely, see
`components/plant/TODO.md`.
- [ ] **`kalman.py` is now dead code in production.** Neither
`temp_controller.py` nor `temp_controller_smith.py` uses `Kalman`
anymore; the only remaining references are
`scripts/demos/pid/demo_kalman.py` and `demo_kalman_eval.py`. Decide
whether to keep it as a documented standalone filtering example or
delete it along with the demos.