Xbox impulse-trigger release on physical Switch 2 controllers¶

Source audit¶

The parity target is Switch2Connect commit 61ac6642ce12fe7217e38a860b14863b18ca7e28. src/virtual_controller.py defines a 90 ms linear release independently for the left and right Xbox impulse-trigger channels. A positive replacement on a side cancels that side's pending release. Repeated zero updates do not restart the release. Dynamic-frequency mode derives frequency from the instantaneous decayed strength; fixed-frequency mode retains the selected carrier.

The donor resolves this state from its approximately 16.6 ms rumble loop. DS4Windows uses a 16 ms presentation cadence with an exact 90 ms terminal point. The linear state law is transport-independent and uses the canonical microsecond clock.

Ownership and ordering¶

The release is a downstream presentation continuation of one already accepted Xbox CFBK frame. It does not fabricate a new canonical source sequence, ownership epoch, producer lane, or mapping path. This distinction matters: inventing canonical sequence numbers for intermediate decay points would make the next real VIIPER CFBK frame appear stale.

The exact Switch2VirtualFeedbackSession owns the envelope and lazily creates one timer only when an impulse side begins releasing. Each point stages reduced LT/RT amplitudes against the exact current canonical frame, asks the existing feedback runtime for a presentation refresh, and reaches the same Switch2HdRumbleDeliverySink and sole USB/Bluetooth physical writer. Body motors and the other trigger side remain unchanged.

The sink records a separate monotonic presentation revision. An unchanged revision is idempotent. If a physical result is uncertain, the exact prior derived amplitudes, tuning, canonical frame, and delivery epoch are retained and retried before a newer decay point can present. A newer real canonical frame may supersede the uncertain point only through the existing canonical ordering law.

Lifecycle¶

Disabling impulse translation, changing to a non-Xbox feedback path, receiving a terminal Stop, or retiring the virtual session clears the envelope and fences its timer. A superseding delayed frame retains the configured delay; the active release continues only until that newer frame reaches presentation. Session retirement disposes the timer before the sole physical owner emits terminal neutral. A copied callback cannot write afterward.

An explicitly configured rumble delay runs first; the 90 ms release begins when the delayed CFBK frame reaches presentation. If the canonical frame expires before a pending refresh succeeds, the ordinary runtime expiry/neutral path is authoritative.

This is a perceptual translation from Xbox impulse motors to Switch 2 LRA HD rumble. It does not claim waveform identity with an Xbox trigger motor.