wboayue / stable-flight / 38658498873

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Commit Message

Stabilizer clears integrals on an idle setpoint, not zero thrust (#326) (#396)

`CopterGuidance` marks a setpoint `idle` while a piloted throttle
(attitude, rate, absolute attitude, absolute rate) is at or below
`IDLE_THROTTLE` or NaN, and `CopterStabilizer` clears its integrals on
that flag instead of on zero thrust. This follows ArduPilot, which
spools to ground idle on `throttle_zero` in Stabilize
(`ArduCopter/mode_stabilize.cpp:19-40`).

Fixes:
- **In flight:** a zero-thrust tick from the altitude loop (shooting up
past a waypoint) keeps the yaw trim.
- **On the ground:** a stick resting at 0.03 now clears the integrals.
- **Tailsitter:** the back handoff's step goes away (issue comment).

Closes #326

## Changes
- **Core (Breaking):**
- `AttitudeSetpoint`, `RateSetpoint` and `BodyRateSetpoint` gain `idle:
bool`.
  - New `Setpoint::idle()`; it is `false` for `Plane`.
- `with_thrust` keeps the flag, so `ThrustHandoff` and the tailsitter
throttle floor carry it through.
  - The disarmed telemetry setpoint is marked idle.
- **Guidance:** `hold_piloted` returns `(thrust, idle)`, so the idle
rule lives in one place. Waypoint and land setpoints are never idle.
Auto-mode ground idle needs a land detector and is filed as #395
(`TODO(#395)`).
- **Link:** `PROTOCOL_VERSION` goes from 4 to 5, because the `Record`
shape changed.
- **Docs:** `CopterStabilizer` and `CopterGuidance` module docs,
`IDLE_THROTTLE`, `architecture.md`, and both CHANGELOGs.

## Tests
-
`stabilizers::copter::tests::idle_setpoint_keeps_the_integrals_from_winding_up`:
a table over Attitude, Rate and BodyRate × thrust × idle. Thrust 0 or
NaN that isn't idle builds the I terms; an idle setpoint clears them at
any thrust.
-
`stabilizers::copter::tests::zero_thrust_in_flight_keeps_the_yaw_trim`:
the issue's repro. The `shooting_up` waypoint setpoint (thrust 0, not
idle) keeps a built yaw-trim I term.
- `guidance::copter::tests::idle_throttle_marks_the_setpoint_idle`: each
input × throttle {0... (continued)

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