Commit Graph
2 Commits
Author SHA1 Message Date
enricobuehler d996449a82 fix(host/pads): a virtual pad at rest said it was in free fall
G14, unblocked by the frame measurement in efb7f991 — the plan deliberately left this
one alone until the up axis was known, on the grounds that a confidently wrong constant
would be worse than an obviously wrong zero. It is known now.

A virtual DualSense, DualShock 4 or Steam Deck that had received no motion reported
acceleration `[0, 0, 0]`. That is not "no data": zero proper acceleration means free
fall, which is a definite claim about the physical world and one that is never true of
a controller sitting on a desk or held in someone's hands — both read 1 g up. Anything
that interprets the accelerometer gets a confident wrong answer rather than a boring
right one.

It is worst exactly where it is least visible. A pad with no gyro at all — an X-Box
controller forwarded as a DualSense, which is what "Automatic" does for anything not
Sony or Valve — never sends motion, so it sits on that neutral for the entire session,
telling every game that reads it that the controller is falling. `switch_proto` has
always done this correctly on its own up axis, which is what made the gap visible in the
first place.

Which axis, and why it took a measurement. The wire is a unit passthrough into the
virtual pad's report, so the wire's up axis is the pad's own, and on 2026-08-07 a real
DualSense read over raw HID put `+0.997 g` on report axis 1 at rest, in a frame pinned
the same session as (Right, Up, Backward). So `MOTION_NEUTRAL_ACCEL` is `[0, 10000, 0]`
— NOT the z-up the notes had assumed from `switch_proto`'s documentation, which is why
guessing would have shipped a backend confidently disagreeing with the hardware.

The constant lives in punktfunk-core beside the units it is expressed in, and every
backend derives from it rather than restating it. The Deck's neutral in particular goes
through `steam_remap::motion_wire_to_deck`, the same rescale a real sample takes, so the
neutral and the live path can never end up with two opinions about what 1 g is — its
`hid-steam` resolution stays in exactly one place. The DS4 needs no separate change: it
reuses `DsState`.

`switch_proto` is deliberately NOT touched, and the test says so. It is a different
device on a different driver, its up axis is its own, and nobody has measured its frame
— aligning it to the DualSense for consistency would be the same unmeasured guess this
commit exists to avoid, just in the other direction.

Non-vacuity proven both ways rather than assumed. Moving the up axis to slot 2 (the old
z-up assumption) fails on the wire constant itself, which is what makes the measurement
load-bearing rather than decorative; reverting both neutrals to `[0, 0, 0]` fails on the
DualSense assertion with the message naming the defect. Each backend is checked in ITS
OWN units, because hard-coding "1 g" three times is how the halves of a unit contract
drift apart.

Gate (Linux CI image): fmt, build, `clippy --locked --all-targets -D warnings` across
punktfunk-core / pf-inject / pf-client-core, and both test suites — green, with
`Running tests/motion_contract.rs` and the new case's own `... ok` line observed in the
log rather than inferred from a green exit (`cargo test` stops after the first failing
binary, so a green-looking run can mean the contract test never executed at all).
2026-08-07 19:07:30 +02:00
enricobuehler 4834c2ee51 fix(host/pads): DualShock 4 gyro ran 40× fast, and no pad ever stopped turning
Phase 1 of the gyro program (design/gyro-program.md, G1-G5) — the five
correctness fixes under it. Gyro aim integrates angular velocity over time, so
each of these is not a cosmetic wrongness: a wrong scale is every rotation being
the wrong size, a wrong clock is every rotation being integrated against a
fictional dt, and a stale sample is rotation that never happened.

G1 — the DualShock 4 calibration blob. A Sony pad does not assume a motion
scale, it reads one out of a fixed calibration feature report. Ours declared
0.5 LSB per °/s and 8192 LSB/g while the wire delivers 20 and 10000, so every
DS4-type session decoded gyro 40× too fast and acceleration 1.22× hot — since
the backend shipped. The blob now states the wire's own units (the DualSense
blob's numbers, deliberately: both pads consume the identical wire sample). Its
interleaved per-axis order is NOT a bug and stays: the virtual pad declares
BUS_USB, where interleaved is the correct layout; grouped is Bluetooth's.

The same blob lives a second time in the UMDF driver, which is a separate WDK
workspace that cannot depend on pf-inject — one wrong table in two files, where
fixing one reads as fixing it. Both are fixed, and the DS4 feature reports now
live in dualshock4_proto beside the DualSense's rather than in the Linux
backend, so there is one canonical copy to point at.

Field hosts keep the old blob until they update the host package.

G2 — the gate that would have caught it. Nothing pinned any backend's
declaration against the wire, so tests/motion_contract.rs now applies the
CONSUMER's arithmetic (the kernel's, and SDL's, which differ) to each backend
and asserts the result lands back on the wire constants — for the DualSense and
DS4 blobs, and for the Deck and Switch Pro rescales. It also parses the driver's
Rust source and re-derives the units from THAT, so the two copies cannot drift.
Verified non-vacuous both ways: re-introducing the old blob fails with "declares
a fractional 32/64 LSB per °/s", and reverting only the driver's copy fails with
"the UMDF driver's DS4_FEATURE_CALIBRATION has drifted from pf-inject's".

The wire units themselves move to punktfunk_core::input::gamepad, referenced by
the client's capture scale, the Deck/Switch rescales, and the probe — whose
at-rest vector said 16384 (a driver's number, not the wire's) and now says 1 g.

G3 — real sensor clocks. The DualSense advanced its sensor timestamp by +1 raw
unit per report (0.33 µs — a frozen clock) and the DS4 by a flat +188 (~1 ms)
regardless of the real 4-8 ms cadence. Anything integrating rate × dt off that
field got nonsense. All four backends now stamp elapsed monotonic time in their
own units via a shared SensorClock, anchored to the pad's first report so an
irregular publish loop cannot make it drift, and truncated to the field width —
which reproduces the wrap real hardware does.

G4 — motion is level-triggered and had no watchdog. merge_frame preserves the
last sample and the heartbeat re-emits it, so a feed that stops leaves the pad
rotating forever — and with G3's honest clock, at a dt that keeps growing.
Rumble and the pen plane each have an idle timeout; motion now has one too, at
100 ms. Angular velocity only: acceleration is kept, because gravity is
legitimately persistent and blanking it reads as free-fall. The SDL client
parks its gyro at zero when a slot closes, which is the case we can flush
rather than wait out. (The Apple half of this rides in PR #88.)

G5 — a pad returning inside the 300 ms replug grace keeps the same device and
skips the create path, so a different controller inherits the previous one's
touch contact and rotation — and a pad with no gyro never sends a sample to
correct it. sweep() now reports re-claims separately from drops, and the manager
clears the rich plane on one. Rich fields only: rumble and hidout dedup
deliberately survive a removal.

Gates (Linux, CI image): fmt, build, clippy --all-targets -D warnings over
pf-inject/punktfunk-core/punktfunk-probe/pf-client-core, and the test suites —
110 pf-inject unit + 6 contract + 29 pf-client-core gamepad, all green.
Not yet verified on glass; the on-glass sign/scale session is G16.
2026-08-07 12:47:26 +02:00