v3.5.0 — Betaflight aligned with its own tooling

Same treatment ArduPilot got in v3.4.0, now for Betaflight: cross-checked the
BF path against the firmware itself (src/main/blackbox/blackbox.c) plus
betaflight/blackbox-log-viewer and Plasmatree/PID-Analyzer. Full
item-by-item table in
docs/ALIGNMENT_BETAFLIGHT.md.

Fixed — blackbox_high_resolution was ignored (data corruption)

BF 4.4+ has a blackbox_high_resolution option that logs gyro and setpoint
with an extra digit of precision by multiplying them by 10
(blackbox.c:2313: blackboxHighResolutionScale = high_resolution ? 10.0f : 1.0f).
It applies to gyroADC, gyroUnfilt, rcCommand and setpoint
(blackbox.c:1262-1289); PID term fields are not scaled. The flag is in the
log header, and blackbox-log-viewer divides by it before display.

SmartTune ignored it, so on any high-resolution log:

• gyro / setpoint / rcCommand read 10x too large, and
• the outlier sanitiser — bounded by rate_limits x 1.1 (~2198) — then treated
  every sample above ~220 deg/s real as corruption and interpolated it
  away. The harder the flying, the more of the trace was silently replaced.

Everything downstream (vibration level, step response, filter and PID
recommendations) followed the corrupted signal. The header flag is now parsed
and the four affected field families are descaled; state is reported in
extras["blackbox_info"].

Changed — step response realigned to PID-Analyzer

The BF step response previously followed PTstepcalc.m's published
description (PIDtoolbox; the repo is delisted, so nothing could be verified):
2-second segments, constant-λ regularisation, segment/4 spacing — and no
window function at all. PID-Analyzer, the open and verifiable ancestor of
this algorithm family (and of the WebTools implementation we already match for
ArduPilot), uses np.hanning(self.flen) (PID-Analyzer.py:64). An unwindowed
2-second segment leaks spectrally into the deconvolution and biases the
transfer function being estimated.

Betaflight now delegates to the same verified kernel as ArduPilot
(Hanning window, 1 s frame = framelen, spacing flen/16 = superpos 16,
Gaussian-CDF SNR regularisation at cutfreq 25 Hz, cumsum over resplen
0.5 s), supplying only BF's input gating: peaks in [20, 500] deg/s, which is
exactly PID-Analyzer's low-input response (low_high_mask(max_in, 500)).
⚠️ This moves Betaflight step-response numbers, toward the reference.
info.method is now pid_analyzer_wiener, and info.steady_state /
steady_state_ok report whether the deconvolution converged instead of hiding
a bad curve.

compute_step_response_for_axis() also stops resampling through the IMU path
by default (prefer_imu=False): for Betaflight Actual is gyroADC, so
the old default interpolated one signal onto its own timebase for nothing.

Checked — gyro scaling was already correct

The going-in suspicion was a missing gyro_scale. The viewer does apply one
(flightlog.js:1468), but the firmware writes gyro_scale = 1.0f
(blackbox.c:1513) because gyroADC comes from gyro.gyroADCf[], already in
deg/s — so reading it raw is right and the viewer's formula collapses to
identity. The header value is now recorded
(blackbox_info.gyro_scale_header) so a legacy log where it is not 1.0 is
visible rather than silent.

Added

• extras["gyro_unfiltered"] — the pre-filter gyroUnfilt trace (descaled),
  which is what notch targeting should be derived from. FlightData.gyro stays
  the filtered gyroADC so existing vibration thresholds keep their
  calibration; a --prefilter notch mode is the planned follow-up.
• extras["blackbox_info"]: high_resolution, high_resolution_scale,
  gyro_source, has_unfiltered_gyro, gyro_scale_header.
• max_target_amplitude on the shared step-response kernel (opt-in; ArduPilot
  keeps WebTools' no-upper-gate behaviour).

Tests

• New tests/test_bf_alignment.py (14 cases): high-resolution descaling of
  gyro/setpoint, flag off leaves values alone, a 1500 deg/s manoeuvre no longer
  clipped by the sanitiser, PID terms not descaled, unfiltered gyro exposed
  and descaled, missing-gyroUnfilt reporting, gyro_scale header recorded,
  step response using the windowed kernel, high-input (>500 deg/s) and
  low-amplitude (<20 deg/s) window exclusion, gyro_adc as the default output
  signal, and that the new upper gate stays opt-in for ArduPilot.

Docs

• New docs/ALIGNMENT_BETAFLIGHT.md (sources with commit hashes, firmware line
  references, what was wrong, what was verified correct, every deliberate
  deviation, and how to cross-check a real .bbl against both reference tools).
• New docs/TEST_PLAN_v3.5.md.

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