prometeu-runtime/docs/specs/runtime/12-firmware-pos-and-prometeuhub.md

Firmware - POS and PrometeuHub

Domain: firmware and system orchestration Function: normative

This chapter defines the firmware layer of the PROMETEU machine.

It covers:

• machine authority above the VM;
• POS responsibilities;
• Hub responsibilities;
• firmware states and cartridge launch flow.

1 Firmware Scope

The PROMETEU firmware is composed of two cooperating layers:

• PrometeuOS (POS): the machine authority responsible for boot, VM/runtime orchestration, peripherals, crash handling, and system-level policy;
• PrometeuHub: the launcher/UI layer that runs over POS and uses the system window model.

The VM does not own the machine lifecycle. Firmware does.

2 Terms

• Host: the real platform that drives the core loop and presents output.
• POS: system firmware/core authority.
• PrometeuHub: launcher and system UI running over POS.
• PVM: the VM subsystem that executes cartridge bytecode.
• Cartridge: the executable package loaded by firmware.
• AppMode: cartridge mode, currently Game or System.
• Logical frame: execution unit completed when the app reaches FRAME_SYNC.
• Host tick: the host-driven outer update tick.
• Process: technical execution owned by POS lifecycle.
• Task: navigable presence associated with an app flow.
• Window: visual presence for a shell/system task when that task is represented by the system window model.
• WindowOwner: ownership marker for a system window. The v1 owners are Hub, Task(TaskId), and Overlay.
• Shell task window: a WindowManager window whose owner is WindowOwner::Task(TaskId).
• Games root: a host-provided local directory used by Hub/Home to discover Game directory cartridges.
• Library entry: an internal catalog record retained by Hub/SystemOS for a discovered cartridge.
• Foreground visual owner: the single machine owner whose visual output may be presented at a given time.
• Paused: a Game-visible lifecycle event/state. The Game may observe it and prepare for foreground loss.
• Suspended: an OS-owned scheduler/runtime state. A suspended Game remains resident but does not receive normal gameplay ticks, normal Game input, or frame pacing.
• VM session: the POS-owned mutable execution context for one VM-backed process. It contains the VM instance and per-session runtime state.

3 POS Responsibilities

POS is responsible for:

• deterministic reset into known machine state;
• VM session creation, initialization, activation, and teardown for cartridge execution;
• input latching and logical-frame budgeting;
• peripheral reset/orchestration;
• fault capture and crash-flow transition;
• return to Hub after app exit or crash.

At the VM boundary, POS must preserve:

• logical-frame semantics;
• FRAME_SYNC as the canonical frame boundary;
• deterministic transition from host tick to VM slice execution.

Firmware must not treat a single global VM object as the canonical execution owner for all cartridges. The firmware state machine orchestrates macro-state; POS/session services own VM-backed process context.

4 PrometeuHub Responsibilities

PrometeuHub is responsible for:

• presenting available apps;
• reading cartridge metadata needed for launch decisions;
• deciding launch behavior based on AppMode;
• managing the system window surface for system-mode apps.
• presenting the host-provided local games library when --games-root <dir> is configured;
• emitting system-owned launch actions for selected Home entries.

The Hub does not execute bytecode directly. It always delegates execution setup to POS.

For v1, the local games library is Game-only. Hub/Home must not expose Shell or System cartridges from the games root. The internal library entry must retain the loaded manifest data, title, app_id, app_version, the cartridge path, and discovery metadata such as a timestamp or equivalent discovery marker.

The Home UI may display only title, app_id, and app_version. Path and operational metadata may remain internal.

5 App Modes

Game

Game-mode cartridges:

• transition firmware into the game-running state;
• run as the active app flow;
• present through the main frame path.
• run as fullscreen firmware sessions;
• are not WindowManager windows.

System

System-mode cartridges:

• are initialized by POS;
• are integrated into the Hub/window environment;
• do not replace the firmware state with the game-running path.
• are represented as shell task windows when they expose a visual shell presence.

6 Task-Owned Shell Windows

The shell window contract separates execution, navigation, and visual presence:

Process = technical execution
Task = navigable presence
Window = visual presence of the task

For shell/system apps managed by the window model, the visible shell presence must be a WindowManager window owned by WindowOwner::Task(TaskId).

Hub windows are not shell task windows. Overlay windows are not shell task windows in this v1 contract. Overlay/modal policy, minimization, app switching, dock behavior, background services, and complex multi-window semantics are future contracts and are not defined here.

Game cartridges must not be represented as WindowManager windows. They remain fullscreen sessions driven by GameRunningStep.

For v1, ShellRunningStep continues a shell task only while both conditions are true:

TaskState::Foreground
+
focused window owner == WindowOwner::Task(task_id)

The runtime query for the focused-window ownership predicate is:

os.windows().focused_window_belongs_to_task(task_id)

If a foreground shell task loses its eligible focused window, ShellRunningStep must close the task through SystemOS lifecycle before returning to Hub:

Shell task loses its eligible focused window
    -> os.lifecycle().close_task(task_id)
    -> TaskState::Closed
    -> ProcessState::Stopped
    -> FirmwareState::HubHome

7 Foreground Stack and Game Pause

The v1 foreground contract is single-owner:

• exactly one foreground visual owner exists at a time;
• at most one Game may be resident;
• at most one Shell app may be foreground;
• Hub/Home is the root Shell owner and back-stack controller.

The minimal supported navigation cycle is:

Game foreground
    -> Home request
    -> Game pause notification
    -> Game suspended by SystemOS after a bounded budget
    -> Hub/Home foreground
    -> optional Shell foreground
    -> Shell close returns to Hub/Home
    -> same Game resume/foreground-restore notification
    -> Game foreground after a valid current-epoch render submission

Paused is cooperative and visible to the Game. Suspended is imposed by SystemOS. The Game may react to pause/resume, but it must not control whether the OS suspends or resumes its VM.

When Home is requested during Game execution, SystemOS must notify the Game and grant a short bounded pause budget. After the budget, SystemOS may suspend the VM even if the Game did not cooperate. While suspended, the Game must not receive normal gameplay ticks, normal Game input, or frame pacing.

When returning to the same Game, SystemOS must reactivate the VM and send a resume or foreground-restore notification before visual foreground is restored. The Game may remain internally paused while it synchronizes. Hub/Shell remains visible until the resumed Game publishes a valid render submission for the current ownership epoch.

Input pending for the Game must be cleared or barriered across pause/resume boundaries. Game audio pauses with the Game VM in v1. Independent background audio, real background execution, multiple resident Games, multiple foreground Shells, and direct Game-to-Game switching are outside this contract.

The resident Game VM session remains allocated while Hub or Shell is foreground. It preserves Game VM state but is not execution-eligible except for the bounded pause handoff and later foreground resume. A VM-backed Shell has a separate VM session. A native Shell has no VM session.

8 Cartridge Load Flow

Current high-level flow:

1. POS receives a cartridge to load;
2. asset manager is initialized from the cartridge asset table, preload list, and packed asset bytes;
3. POS creates or selects the VM session for the cartridge;
4. POS initializes the session-owned VM/runtime for the cartridge;
5. launch behavior branches by AppMode:
   • Game -> transition to the game-running firmware state;
   • System -> create/focus a Hub window and return to the Hub state.

If VM initialization fails, firmware transitions to the crash path.

For v1, POS must enforce at most one resident Game session. Selecting the same resident Game from Home resumes that session. Selecting a different Game while a resident Game exists is outside the v1 foreground contract and must not create a second resident Game session. VM-backed Shell loading creates a distinct Shell session and must not overwrite resident Game VM state.

POS selects the cartridge and its execution context, but the cartridge's initial callable is not chosen by firmware metadata. Execution starts from the cartridge boot protocol defined in 13-cartridge.md, currently func_id = 0.

When Home launches a discovered Game entry, the request is a system-owned action from PrometeuHub to POS/firmware. Firmware must load the selected cartridge through the normal cartridge loader and transition to LoadCartridge on success. This path must not use a guest syscall and must not reintroduce userland run_cart.

If the selected cartridge cannot be loaded, firmware must leave or return the machine in the Hub/Home flow and record the failure through diagnostics or logging. A polished Home error surface is not required by v1.

9 Firmware States

The current firmware state model includes:

• Reset
• SplashScreen
• LaunchHub
• HubHome
• LoadCartridge
• GameRunning
• ShellRunning
• AppCrashes

These states express machine orchestration above the VM. They are not guest-visible bytecode states.

10 Execution Contract

For game-mode execution, firmware/runtime coordination preserves:

• input latched per logical frame;
• execution in host-driven slices until FRAME_SYNC;
• present only when a logical frame completes;
• no frame present when budget ends before FRAME_SYNC.

This keeps the machine model deterministic and observable.

11 Crash Handling

Firmware owns terminal fault presentation.

When a terminal app fault occurs:

• POS captures the crash report;
• firmware leaves normal app execution flow;
• the machine transitions to AppCrashes.

Crash handling is outside the guest VM execution model.

12 Desktop Smoke Validation

The foreground contract can be smoke-tested on the desktop host with:

cargo run --release -p prometeu-host-desktop-winit -- --run test-cartridges/stress-console
cargo run --release -p prometeu-host-desktop-winit -- --games-root test-cartridges

Expected behavior:

• direct --run still boots the selected Game without using a guest cartridge switching API;
• --games-root starts in Home and launches Games through the Home library;
• while a Game is running, Esc opens Home/SystemOS without entering the guest pad input surface;
• the Game is paused, then suspended after the bounded SystemOS budget;
• Home remains foreground while the Game is resident;
• launching and closing a Shell app returns to Home without losing the resident Game;
• a VM-backed Shell advances its own VM session and does not tick the suspended resident Game session;
• returning to the same Game resumes it through the foreground lifecycle and waits for current-epoch Game rendering before visual Game presentation.

13 Relationship to Other Specs

• 02-vm-instruction-set.md defines the VM subsystem run by firmware.
• 09-events-and-concurrency.md defines the frame-boundary model used by firmware.
• 13-cartridge.md defines cartridge structure and metadata consumed by firmware.
• 14-boot-profiles.md defines startup target selection.