G16 step 1, and the second half of what 9e9bb9f4 started. That commit fixed the SIGN
of acceleration (Apple reports the gravity vector, pointing down; a pad reports proper
acceleration, pointing up). This fixes the FRAME, which is a separate defect and was
never going to show up as an inverted axis — it shows up as roll where the game reads
yaw.
The wire is a unit passthrough. `dualsense_proto::write_report` puts gyro[0..3] and
accel[0..3] straight into the virtual pad's report bytes 16.. and 22.., in order, with
no permutation — the same slots a real DualSense fills. So the frame the wire is
DEFINED in is the pad's own report frame, and forwarding GameController's x/y/z
unconverted was speaking a different language with the same vocabulary.
Both frames measured 2026-08-07 from ONE physical DualSense on one desk, read twice —
over raw HID and through GameController — so this is two readings of the same
controller in the same orientations rather than two documents:
DualSense report frame: (Right, Up, Backward) axis 0 pitch, 1 yaw, 2 roll
GameController frame: (Right, Forward, Up)
Right is already slot 0; Up is GC's z and moves to slot 1; slot 2 wants Backward, which
is GC's y negated. Hence (x, z, -y), applied to gyro AND acceleration because it is a
change of basis and both live in that basis.
Notable: the wire's documented naming was right all along — gyro[0]=pitch, [1]=yaw,
[2]=roll is exactly what the hardware does. And Android needs no remap at all: it
forwards the pad's own axis order un-remapped, which is correct. Its old reading was
purely the scale bug f6de620f fixed. Only Apple was converting nothing.
How the hardware frame was established, since a wrong frame here is invisible. Gravity
at rest put +0.997 g on axis 1. Yaw clockwise-from-above drove axis 1 negative (98% of
the rotation), pitch nose-down drove axis 0 negative (100%), roll right-side-down drove
axis 2 negative (95%) — plain right-hand rule, and (a0 x a1 = a2) confirms the triad is
right-handed. The accelerometer then corroborated the gyro's assignment independently:
under pitch-down axis 2 rose 0.160 -> +0.339 (nose down raises the back, so world-up
gains a Backward component) and under roll-right-down axis 0 went +0.021 -> -0.197,
while yaw left acceleration untouched. Two different physical quantities agreeing on
one triad.
Apple's frame took four attempts, and the failures are worth recording because each was
a different way to be confidently wrong:
- peak |w| over a window containing BOTH the tip-down and the return stroke can record
the return, with the opposite sign. Yaw (a continuous one-way spin) was unaffected;
pitch and roll were exactly the two that disagreed with everything else.
- reading `gravity + userAcceleration` when `hasGravityAndUserAcceleration` is FALSE
yields a constant (0,0,1) in every orientation. It looks like data. The tell is that
it never moves. The client's own else-branch on `m.acceleration` is the correct read
and is what the instrument now mirrors.
- `da/dt = -w x a` holds only for gravity, so testing it during vigorous waving — when
`m.acceleration` carries inseparable linear acceleration — fits nothing.
The frame that survived all of that: static poses, three of them, three repetitions
each. Nose-down moved axis 1 by -0.635 (so axis 1 is Forward), right-side-down moved
axis 0 by -0.686 (so axis 0 is Right), flat put +0.99 on axis 2 (Up). That conclusion
holds whether or not the acceleration negation is right, because negating flips the
measured vector and the physical direction it represents together.
Confidence, stated honestly. The accelerometer half is solid: nine pose measurements,
and mapping the flat pose through gives (+0.005, +0.992, +0.192) against the hardware's
own (+0.021, +0.997, +0.160) — all three components, including the small tilt term that
is what distinguishes this mapping from the five other permutations that also put
gravity on slot 1. That the gyro shares the frame unmodified rests on a weaker
measurement: a gravity-dominated consistency test that preferred (+x,+y,+z) by 1.22x,
which is a margin, not a landslide. It is corroborated by the yaw reading (the one
rotation measured without the return-stroke ambiguity) agreeing with right-hand rule in
that frame, and by the peak-vs-return mechanism explaining the two that did not. A
device-side confirmation is still owed and is listed below.
The tests carry the measurements, not just the conclusion. Resting gravity is asserted
against BOTH readings of that pose; each rotation is asserted to reach the slot the wire
reads it from; and two properties guard the shape rather than the numbers — that the
conversion is an isometry (a basis change may not stretch anything) and that it
preserves handedness. That last one matters most: a permutation with the wrong number of
sign flips is a REFLECTION, which looks plausible axis by axis and inverts every
rotation. Mutation-checked: dropping only the negation fails 6 assertions across 4 of
the 5 cases, the handedness test among them.
Owed, and not claimed done: on-glass re-verification through a real iOS device, together
with the two already owed on that rig (the 9e9bb9f4 sign fix and the Android
calibration read) — one pass covers all three. G14's DualSense neutral acceleration is
now unblocked by this measurement (1 g on slot 1, not the z-up the notes assumed) but is
deliberately left to its own change; and that constant must NOT be propagated to
switch_proto, which is a different device whose frame nobody has measured.
Gate: macOS `swift build` + the full suite (215 tests, 5 skipped, 0 failures) with the
five new cases observed in the run's own output, and the iOS-triple typecheck green.
enricobuehler
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