The Android twin of `pf-client-core`'s pad_audio: drain the host's per-pad
DualSense streams, Opus-decode haptics (kind 0) and speaker (kind 1), interleave
into the pad's own 4-channel layout, and render on the pad itself.
Every other client hands that stream to the platform's audio graph. Android
cannot: AOSP's UsbAlsaManager denylists the DualSense's output by VID/PID, so
the kernel enumerates the pad's playback node and the framework discards it —
`hasOutput: false`, nothing for setPreferredDevice to target, /dev/snd closed by
SELinux, and UsbRequest rejects non-bulk/interrupt endpoints. So this drives the
pad's isochronous endpoint directly via uac-host on the descriptor Java owns.
That is measured, not assumed. On a Nothing Phone (3): the claim succeeds
unprivileged, the gamepad and the pad's microphone both keep working, and the
underrun-free floor is 4 ms — holding under eight-core load with the SoC in
severe thermal throttling. The renderer runs at 6 ms, one step of headroom,
because the same measurement found transient events that are not depth-dependent.
Structured to the crate's own convention: the mixer and PLC are ungated so they
compile and unit-test in the host workspace (8 tests), while everything touching
an Android-only dependency is cfg'd to android. Two details worth review:
- The kinds arrive on different cadences (5 ms vs 10 ms), so each has its own
write cursor and both shift together on overflow — a haptics-only session
renders with a silent speaker pair instead of stalling on a kind that will
never arrive, and the two can never skew.
- An unrecognised kind is dropped rather than folded into the coil pair. A
`min(1)` clamp would have rendered a future kind straight into the actuators.
Lifecycle mirrors MicCapture: dropping the handle joins the thread, and
nativeStopPadAudio returns only once it has, so Kotlin may close the
UsbDeviceConnection as soon as it returns and not before.
usbfs-iso/uac-host enter as git dependencies pinned by revision — a transport
under a real-time deadline should move when we choose. They become version
dependencies once published to crates.io.
enricobuehler
b5f91d50bb