WIP: checkpoint Wii native IMU and upstream IR bridge

Pause Wii pointing work with firmware 0.33-wii-trace installed. Preserve the pinned libogc IR pipeline, calibrated native IMU, software BOOTSEL, and standard camera sensitivity trial.

Tracking instability, tracking loss, and ineffective vertical movement remain unresolved. Level-2 camera filtering is not hardware-qualified. Nine targeted regression tests pass; firmware and persistent storage were verified after flashing.

tools/switch2_usb_probe/native_imu.h

@@ -0,0 +1,99 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Encode one native mode-0 IMU block. Inputs use the native-right body frame;
+// quaternion wxyz rotates body vectors into the reference frame. Quaternion
+// scale/sign do not matter. Finite acceleration saturates at signed Q28 limits.
+// Invalid inputs leave output untouched; counter and elapsed must fit 12 bits.
+bool probe_native_imu_pack(const float quaternion_wxyz[4], const float accel_g[3],
+                           uint16_t counter_ticks, uint16_t elapsed_ticks,
+                           int16_t temperature_raw, uint8_t output[30]);
+
+#ifdef __cplusplus
+}
+
+struct ProbeNativeMotionSample {
+    bool accel_valid = false;
+    bool gyro_valid = false;
+    uint32_t accel_sequence = 0;
+    uint32_t gyro_sequence = 0;
+    uint32_t accel_us = 0;
+    uint32_t gyro_us = 0;
+    float accel_g[3]{};
+    float gyro_dps[3]{};
+};
+
+// Core 0 only. Call update even when sensors are unavailable, and consult ready
+// before using the orientation. Sequence identities, not polling, admit samples;
+// repeated sequences cannot refresh timestamps or contribute to calibration.
+// Startup requires the user to rest the controller: constant rotation about
+// gravity is indistinguishable from an unknown gyro bias without another sensor.
+// Fresh near-1g acceleration corrects tilt drift after startup. Heading remains
+// gyro-derived unless a reliable optical heading observation is supplied.
+class ProbeNativeMotion {
+public:
+    void reset();
+    void update(uint32_t now_us, uint32_t connection_generation,
+                const ProbeNativeMotionSample& sample);
+    // Call after update, using a full observed sensor-bar pair (never inferred).
+    // Positive optical yaw means aim-right, the negative reference-world turn.
+    // The first sample in each optical generation anchors the current heading;
+    // it supplies neither absolute world yaw nor an absolute console cursor.
+    void observe_optical_heading(uint32_t now_us, uint32_t reference_generation,
+                                 uint32_t sequence, uint32_t sample_us,
+                                 float yaw_radians, bool valid);
+    bool ready() const { return ready_; }
+    const float* quaternion() const { return quaternion_; }
+    const float* acceleration() const { return acceleration_; }
+    const float* bias() const { return bias_; }
+
+private:
+    void invalidate();
+    void clear_candidate();
+    bool initialize_orientation();
+    bool integrate(const float gyro_dps[3], uint32_t elapsed_us);
+    bool correct_gravity(uint32_t elapsed_us);
+    bool normalize_orientation();
+
+    bool have_generation_ = false;
+    bool have_update_ = false;
+    bool seen_accel_sequence_ = false;
+    bool seen_gyro_sequence_ = false;
+    bool have_accel_ = false;
+    bool have_gyro_ = false;
+    bool candidate_ = false;
+    bool ready_ = false;
+    bool have_optical_generation_ = false;
+    bool seen_optical_sequence_ = false;
+    bool have_optical_reference_ = false;
+    bool have_optical_sample_ = false;
+    uint32_t connection_generation_ = 0;
+    uint32_t update_us_ = 0;
+    uint32_t accel_sequence_ = 0;
+    uint32_t gyro_sequence_ = 0;
+    uint32_t accel_us_ = 0;
+    uint32_t gyro_us_ = 0;
+    uint32_t candidate_us_ = 0;
+    uint32_t gyro_count_ = 0;
+    uint32_t accel_count_ = 0;
+    uint32_t optical_generation_ = 0;
+    uint32_t optical_sequence_ = 0;
+    uint32_t optical_sample_us_ = 0;
+    float optical_reference_radians_ = 0.0f;
+    float gyro_variation_ = 0.0f;
+    float accel_variation_ = 0.0f;
+    float quaternion_[4]{1.0f, 0.0f, 0.0f, 0.0f};
+    float acceleration_[3]{};
+    float gyro_dps_[3]{};
+    float bias_[3]{};
+    float mean_gyro_[3]{};
+    float mean_accel_[3]{};
+    float gravity_reference_[3]{};
+};
+#endif