device-tree

name	device-tree
title	Device Tree
version	1
status	active
owners	[]
triggers	["device tree","FDT","chosen node","reserved-memory"]
prerequisites	["task-planning","cross-architecture-design","reliability-fault-injection"]
related_docs	["PORTING.md","build/targets/arm64-qemu.toml"]
category	Drivers and hardware
conditional_skills	["arm64-platform-development","boot-protocol-evolution"]
implementation_gates	["Do not implement a generic DT framework before ARM64 boot firmware/handoff strategy is accepted."]
related_milestones	["M1 Dual-Architecture Boot"]
last_verified	{"base_commit":"d21a477","date":"2026-07-16","worktree_dirty":true,"context":"base commit plus uncommitted audit and agent-system worktree"}
description	Use when working on device tree, FDT, chosen node; provides the FinnOS-specific device tree workflow and evidence gates.

Device Tree

1. Name

device-tree (Drivers and hardware; skill maturity: planning-gated).

2. Purpose

Decide and implement validated ARM firmware-description parsing when ARM bring-up requires it.

3. When to use this skill

Use for requests mentioning device tree, FDT, chosen node, reserved-memory, or when a dependency points to this skill. Load only after repository entry and before design or implementation.

4. When not to use this skill

Do not implement a generic DT framework before ARM64 boot firmware/handoff strategy is accepted. Do not load it only because a future FinnOS document mentions the subsystem.

5. Prerequisite skills

• task-planning
• cross-architecture-design
• reliability-fault-injection

Read the full prerequisite closure in topological dependency order. If one cannot be satisfied, move the task to Blocked or Deferred; do not omit the dependency.

Conditional skills:

• arm64-platform-development and boot-protocol-evolution after the firmware policy is accepted

Implementation gates are roadmap/runtime conditions, not additional documents to load automatically:

• Do not implement a generic DT framework before ARM64 boot firmware/handoff strategy is accepted.

6. Authoritative repository references

• PORTING.md
• build/targets/arm64-qemu.toml

Re-read implementation and tests referenced by those documents. The documents establish intent/status boundaries, not runtime proof.

7. Current FinnOS context

No DT policy, parser, blob handoff, or ARM executable exists; QEMU virt requirements remain planned.

Registry verification used base commit d21a477 plus the dirty worktree context "base commit plus uncommitted audit and agent-system worktree" on 2026-07-16. This is not an integrated-revision claim. Reverify after HEAD, active PRs, or relevant source changes.

8. Required inputs

• User request or issue with desired outcome and architecture/profile scope.
• Current git status, recent history, active related issue/PR, and selected roadmap item.
• Relevant implementation, tests, invariants, ADRs, and exact baseline output.
• Toolchain/firmware/hardware versions when behavior crosses those boundaries.

9. Expected outputs

An evidence-backed device tree result with scoped artifacts, tests, documentation, and handoff. Include acceptance evidence, residual limitations, and next dependency rather than only code.

10. Step-by-step workflow

1. Decide DT versus ACPI scope in ADR
2. Validate FDT header/offsets/strings/reservations
3. Parse chosen, memory, CPUs, UART, GIC
4. Translate address/interrupt cells with bounds
5. Test malformed blobs and QEMU fixture
6. Run the narrow regression, then all required subsystem/repository checks.
7. Update canonical docs/status and finish the agent-handoff template.

11. Repository-specific commands

./tools/finn check

Run commands from the repository root. A command listed here is a baseline/gate, not evidence that absent future functionality has a runnable target.

12. Architecture considerations

State shared semantics explicitly; isolate x86-64 and ARM64 mechanisms.

State guest architecture separately from host architecture and emulator model. Maintain a parity row for changed semantics and document intentional differences.

13. Safety constraints

Preserve the boundary described by the current state: No DT policy, parser, blob handoff, or ARM executable exists; QEMU virt requirements remain planned. Apply .agents/checklists/pre-change.md; for kernel, driver, security, architecture, or UI work also apply the matching checklist.

14. Testing requirements

Make Test malformed blobs and QEMU fixture observable with a negative case, then run the narrow and aggregate gates. Do not permanently hard-code test counts; counts belong to dated evidence reports.

15. Documentation requirements

Update the canonical behavior/status document, relevant architecture/reference material, test/build instructions, limitations, and this skill registry if any command, gate, or current-context statement changes.

16. Review checklist

• The workflow proves Decide DT versus ACPI scope in ADR before relying on downstream assumptions.
• The observed baseline and first failing/divergent point are recorded.
• Every prerequisite and roadmap dependency is satisfied or explicitly marked blocked.
• Bounds, ownership, rollback, error paths, and resource limits were reviewed.
• x86-64 and ARM64 semantics are mapped without unsupported parity claims.
• Negative/failure tests exist at the layer that owns the behavior.
• Commands, logs, artifact/profile/architecture, and results are preserved.
• Canonical documentation and affected agent skills agree with behavior.

17. Completion criteria

• All stated outputs exist and remain within the task's scope/non-goals.
• The narrow regression and required repository/subsystem gates pass.
• Acceptance criteria are tied to source, test, runtime, or hardware evidence as appropriate.
• Unknowns and unsupported environments remain explicit; no planned feature is promoted.
• The final diff is reviewed and a structured handoff is complete.

18. Common failure modes

• Starting from an audit statement instead of re-reading changed source and tests.
• Using a successful compile or marker as evidence for a broader subsystem claim.
• Ignoring this skill's current constraint: No DT policy, parser, blob handoff, or ARM executable exists; QEMU virt requirements remain planned.
• Changing shared policy while testing only one architecture or one happy path.
• Losing the exact failing artifact/log by rebuilding before capture.

19. Forbidden shortcuts

• Do not weaken, delete, reorder, or broaden validators merely to make a test pass.
• Do not claim ARM64, physical hardware, userspace, Peony, security, or release support without its own acceptance evidence.
• Do not bypass a named prerequisite by embedding a temporary incompatible abstraction.
• Do not commit target/, build/out/, firmware, credentials, local paths, or unreviewed generated output.
• Do not disregard the roadmap/status gate: Do not implement a generic DT framework before ARM64 boot firmware/handoff strategy is accepted.

20. Handoff requirements

Use .agents/templates/handoff-template.md. Include objective, starting/final Git state, task state, skills used, files, exact commands/results, evidence classification, docs/status changes, unknowns, blockers, risks, next action, and next skills. Distinguish locally verified worktree changes from integrated behavior.

21. Examples

Request: "Work on device tree." Correct response: begin by decide dt versus acpi scope in adr, then validate fdt header/offsets/strings/reservations, and require evidence for test malformed blobs and qemu fixture before changing status. Incorrect response: create a plausible subsystem scaffold and mark the roadmap item complete because it compiles.

22. Skill maintenance notes

Canonical source: .agents/scripts/skill_registry.py. Increment version for material policy/workflow/gate changes, update last_verified only after reinspection, run python3 .agents/scripts/render_skills.py, review generated diffs, then run python3 .agents/scripts/validate.py --all. Follow .agents/GOVERNANCE.md; never hand-edit generated skills.