Tracer bullet roadmap

First priority is an end-to-end tracer bullet from sensors up to the OpenXR API, with hardware blockers avoided by emulating inputs at defined boundaries. Each stage replaces emulation with real code or hardware, leaving everything above it unchanged.

Emulation points

Three input-side boundaries, from the Monado headset driver data flow. Each one further down removes more of our own code from the test.

Emulation point	What replaces what	Real code exercised	Use it for
Kernel interfaces	vivid / v4l2loopback / vkms stand in for kernel drivers	Capture, trackers, device, core	Capture code: setup, buffers, formats, drop handling
Sinks	A replay source pushes recorded frames and IMU into the tracker sinks	Trackers, device, core	Perception and pose output on real recorded data
`xrt_device`	Monado's simulated device replaces the whole headset driver	Core and apps only	App → runtime → compositor path before any driver exists

Kernel-level emulation exercises everything, but test patterns give SLAM nothing to track. Sink-level replay is the only point where perception runs on meaningful data.
Display side has its own emulation points: vkms at the kernel, or a desktop window at the compositor's output target. Either combines with any input-side option.

Stage 1: Prove the platform

Goal: show the RB5, kernel, Turnip and stock Monado run OpenXR apps. No custom code.

Build Monado for Arch Linux ARM on the RB5 dev kit.
Run it with Monado's simulated device (it ships with Monado and provides a display description and pose), presenting through the Vulkan display target (VK_KHR_display) to the dev kit's HDMI output. HDMI is also a KMS connector, so the panels aren't needed yet.
Run hello_xr, then the Godot launcher.

Exit criteria: apps render through the compositor in direct mode on the RB5, with stable frame pacing.

Stage 2: Headset driver against emulated inputs

Goal: all driver-side code runs end to end without custom hardware.

Driver skeleton

Builder, HMD device, hand-tracking device.
Config loading: source mode, camera-to-tracker mapping, calibration paths.