feat(host/steam): M0 — virtual hid-steam UHID device binds + parses (Linux)
Greenfield virtual Steam Deck controller, the Steam analogue of the shipped virtual DualSense. Proves the kernel hid-steam driver binds a /dev/uhid 28DE:1205 device, registers it as a real Steam Deck, and parses our input reports — the go/no-go gate for the full Steam Controller/Deck pipeline. - inject/proto/steam_proto.rs: keeper module — the vendor HID descriptor (one feature report, the sole thing steam_is_valve_interface() checks), the command/feature IDs, serialize_deck_state, and the serial GET_REPORT reply. Unit-tested. - src/bin/steam_uhid_spike.rs: throwaway M0 spike (Linux-only) — opens /dev/uhid, creates the device, services the handshake including UHID_SET_REPORT (which the DualSense backend omits and which hid-steam stalls ~5s/cmd without), and heartbeats a neutral report. - design/steam-controller-deck-support.md: full design + M0–M7 plan; the two walls (Steam Input capture ownership; virtual-Steam recognition) and the fidelity ceiling. Status: M0 GREEN. On-box (headless Ubuntu 26.04, kernel 7.0, no Steam): journalctl -k shows hid-steam binding the device (rebind off hid-generic), "Steam Controller connected", and the kernel creating BOTH a "Steam Deck" gamepad evdev and a "Steam Deck Motion Sensors" IMU evdev (INPUT_PROP_ACCELEROMETER). A layout-agnostic mash-probe drove 23 distinct BTN_* codes through hid-steam -> evdev, proving the input-report parse path. M1 line-checks the exact per-bit report layout against the lab kernel. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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//! M0 recognition spike (THROWAWAY) — `design/steam-controller-deck-support.md` go/no-go gate.
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//!
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//! Opens `/dev/uhid`, creates a virtual `28DE:1205` Steam Deck controller using
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//! [`steam_proto::STEAMDECK_RDESC`], services the kernel handshake (the three event types the
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//! DualSense backend does NOT: `UHID_SET_REPORT` must be answered or `hid-steam` stalls ~5 s/cmd),
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//! answers `steam_get_serial`, heartbeats a neutral Deck report at 125 Hz, and toggles `BTN_A`
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//! every 500 ms so a button event is observable.
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//!
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//! PASS (GO): `dmesg` shows `hid-steam` binding the device; both a gamepad evdev and an IMU evdev
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//! (`INPUT_PROP_ACCELEROMETER`) appear; an evdev reader sees `BTN_A` toggle. Run:
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//! `cargo run -p punktfunk-host --bin steam_uhid_spike -- [seconds]`
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//!
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//! This binary is deleted once M1's `inject/linux/steam_controller.rs` subsumes it.
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#[cfg(target_os = "linux")]
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#[path = "../inject/proto/steam_proto.rs"]
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mod steam_proto;
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#[cfg(target_os = "linux")]
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fn main() -> anyhow::Result<()> {
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use anyhow::Context;
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use std::fs::OpenOptions;
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use std::io::{Read, Write};
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use std::os::unix::fs::OpenOptionsExt;
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use std::time::{Duration, Instant};
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use steam_proto::{
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serial_reply, serialize_deck_state, SteamState, STEAMDECK_PRODUCT, STEAMDECK_RDESC,
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STEAM_REPORT_LEN, STEAM_VENDOR,
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};
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// /dev/uhid event ABI (linux/uhid.h): a u32 `type` then a __packed union (largest member is
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// uhid_create2_req). Field offsets below are union-start (event byte 4) + struct offset.
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const EVENT_SIZE: usize = 4 + 4372;
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const UHID_DESTROY: u32 = 1;
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const UHID_START: u32 = 2;
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const UHID_STOP: u32 = 3;
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const UHID_OPEN: u32 = 4;
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const UHID_CLOSE: u32 = 5;
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const UHID_OUTPUT: u32 = 6;
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const UHID_GET_REPORT: u32 = 9;
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const UHID_GET_REPORT_REPLY: u32 = 10;
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const UHID_CREATE2: u32 = 11;
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const UHID_INPUT2: u32 = 12;
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const UHID_SET_REPORT: u32 = 13;
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const UHID_SET_REPORT_REPLY: u32 = 14;
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const BUS_USB: u16 = 0x03;
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let seconds: u64 = std::env::args()
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.nth(1)
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.and_then(|s| s.parse().ok())
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.unwrap_or(25);
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let mut fd = OpenOptions::new()
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.read(true)
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.write(true)
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.custom_flags(libc::O_NONBLOCK)
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.open("/dev/uhid")
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.context("open /dev/uhid (are you in the 'input' group?)")?;
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// --- UHID_CREATE2: identity + report descriptor ---
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let put_cstr = |ev: &mut [u8], off: usize, cap: usize, s: &str| {
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let n = s.len().min(cap - 1);
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ev[off..off + n].copy_from_slice(&s.as_bytes()[..n]);
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};
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let mut ev = vec![0u8; EVENT_SIZE];
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ev[0..4].copy_from_slice(&UHID_CREATE2.to_ne_bytes());
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put_cstr(&mut ev, 4, 128, "Punktfunk Steam Deck (M0 spike)"); // name[128]
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put_cstr(&mut ev, 132, 64, "punktfunk/steam/0"); // phys[64]
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put_cstr(&mut ev, 196, 64, "punktfunk-steam-0"); // uniq[64]
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ev[260..262].copy_from_slice(&(STEAMDECK_RDESC.len() as u16).to_ne_bytes()); // rd_size
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ev[262..264].copy_from_slice(&BUS_USB.to_ne_bytes()); // bus
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ev[264..268].copy_from_slice(&STEAM_VENDOR.to_ne_bytes()); // vendor
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ev[268..272].copy_from_slice(&STEAMDECK_PRODUCT.to_ne_bytes()); // product
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ev[272..276].copy_from_slice(&0x0100u32.to_ne_bytes()); // version
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ev[276..280].copy_from_slice(&0u32.to_ne_bytes()); // country
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ev[280..280 + STEAMDECK_RDESC.len()].copy_from_slice(STEAMDECK_RDESC);
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fd.write_all(&ev).context("write UHID_CREATE2")?;
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eprintln!(
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"UHID_CREATE2 -> 28DE:1205 \"Punktfunk Steam Deck (M0 spike)\", {} byte rdesc; running {seconds}s",
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STEAMDECK_RDESC.len()
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);
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let (mut starts, mut opens, mut gets, mut sets, mut outputs) = (0u32, 0u32, 0u32, 0u32, 0u32);
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let mut seq: u32 = 0;
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let mut a_down = false;
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let start = Instant::now();
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let mut last_hb = start;
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let mut last_toggle = start;
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let mut rbuf = vec![0u8; EVENT_SIZE];
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while start.elapsed() < Duration::from_secs(seconds) {
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// Drain all pending kernel events; reply to the handshake (O_NONBLOCK → WouldBlock = empty).
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while let Ok(n) = fd.read(&mut rbuf) {
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if n < 4 {
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break;
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}
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match u32::from_ne_bytes([rbuf[0], rbuf[1], rbuf[2], rbuf[3]]) {
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UHID_START => {
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starts += 1;
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eprintln!(" <- UHID_START");
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}
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UHID_OPEN => {
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opens += 1;
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eprintln!(" <- UHID_OPEN (a consumer opened the evdev/hidraw)");
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}
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UHID_STOP => eprintln!(" <- UHID_STOP"),
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UHID_CLOSE => eprintln!(" <- UHID_CLOSE"),
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UHID_OUTPUT => {
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outputs += 1;
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let sz = u16::from_ne_bytes([rbuf[4100], rbuf[4101]]) as usize;
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eprintln!(
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" <- UHID_OUTPUT ({sz} bytes, head={:02X?})",
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&rbuf[4..4 + sz.min(8)]
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);
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}
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UHID_GET_REPORT => {
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gets += 1;
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let id = u32::from_ne_bytes([rbuf[4], rbuf[5], rbuf[6], rbuf[7]]);
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let rnum = rbuf[8];
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let reply = serial_reply("PUNKTFUNK01");
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let mut out = vec![0u8; EVENT_SIZE];
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out[0..4].copy_from_slice(&UHID_GET_REPORT_REPLY.to_ne_bytes());
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out[4..8].copy_from_slice(&id.to_ne_bytes()); // id
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out[8..10].copy_from_slice(&0u16.to_ne_bytes()); // err = 0
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out[10..12].copy_from_slice(&(reply.len() as u16).to_ne_bytes()); // size
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out[12..12 + reply.len()].copy_from_slice(&reply);
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fd.write_all(&out).context("write GET_REPORT_REPLY")?;
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eprintln!(" <- UHID_GET_REPORT (rnum={rnum}) -> replied serial");
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}
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UHID_SET_REPORT => {
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sets += 1;
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let id = u32::from_ne_bytes([rbuf[4], rbuf[5], rbuf[6], rbuf[7]]);
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let rnum = rbuf[8];
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let cmd = rbuf[12]; // data[0] = the Steam command id
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let mut out = vec![0u8; EVENT_SIZE];
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out[0..4].copy_from_slice(&UHID_SET_REPORT_REPLY.to_ne_bytes());
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out[4..8].copy_from_slice(&id.to_ne_bytes()); // id
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out[8..10].copy_from_slice(&0u16.to_ne_bytes()); // err = 0 (ack)
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fd.write_all(&out).context("write SET_REPORT_REPLY")?;
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eprintln!(" <- UHID_SET_REPORT (rnum={rnum}, cmd=0x{cmd:02X}) -> ack err=0");
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}
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other => eprintln!(" <- UHID event type {other}"),
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}
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}
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// Heartbeat the current state at ~125 Hz (a real Deck streams continuously; silence reads
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// as an unplug to the kernel/SDL).
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if last_hb.elapsed() >= Duration::from_millis(8) {
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last_hb = Instant::now();
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seq = seq.wrapping_add(1);
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let mut st = SteamState::neutral();
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if a_down {
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// M0 parse-path probe: mash every button byte so SOME BTN_* fires regardless of the
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// exact (M1-confirmed) per-bit mapping — proves hid-steam parses our state reports.
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st.b8 = 0xFF;
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st.b9 = 0xFF;
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st.b10 = 0xFF;
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st.b13 = 0xFF;
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st.b14 = 0xFF;
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}
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let mut r = [0u8; STEAM_REPORT_LEN];
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serialize_deck_state(&mut r, &st, seq);
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let mut out = vec![0u8; EVENT_SIZE];
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out[0..4].copy_from_slice(&UHID_INPUT2.to_ne_bytes());
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out[4..6].copy_from_slice(&(r.len() as u16).to_ne_bytes()); // input2.size
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out[6..6 + r.len()].copy_from_slice(&r); // input2.data
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fd.write_all(&out).context("write UHID_INPUT2")?;
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}
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// Toggle BTN_A every 500 ms so an evdev reader sees a key event.
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if last_toggle.elapsed() >= Duration::from_millis(500) {
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last_toggle = Instant::now();
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a_down = !a_down;
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eprintln!("BTN_A -> {}", if a_down { "DOWN" } else { "UP" });
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}
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std::thread::sleep(Duration::from_millis(1));
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}
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let mut out = vec![0u8; EVENT_SIZE];
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out[0..4].copy_from_slice(&UHID_DESTROY.to_ne_bytes());
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let _ = fd.write_all(&out);
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eprintln!(
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"UHID_DESTROY. handshake counts: START={starts} OPEN={opens} GET_REPORT={gets} SET_REPORT={sets} OUTPUT={outputs}"
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);
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Ok(())
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}
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#[cfg(not(target_os = "linux"))]
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fn main() {
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eprintln!("steam_uhid_spike: Linux-only (needs /dev/uhid + the hid-steam kernel driver)");
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}
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