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.

## 3 POS Responsibilities

POS is responsible for:

- deterministic reset into known machine state;
- VM initialization 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.

## 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:

```text
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:

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

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

```text
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:

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

## 7 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 initializes the VM/runtime for the cartridge;
4. 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.

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`](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.

## 8 Firmware States

The current firmware state model includes:

- `Reset`
- `SplashScreen`
- `LaunchHub`
- `HubHome`
- `LoadCartridge`
- `GameRunning`
- `AppCrashes`

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

## 9 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.

## 10 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.

## 11 Relationship to Other Specs

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