# Specification v1.0 decisions (frozen 2026-09-14)

This record closes every open item in `HUMAN_REVIEW.md` and every `review_flags` entry in
`configs/rpi5_hardware_facts.json`, so the hardware specification (`rpi5_hardware_facts.json` 1.0) and the action
schema (`action_vocabulary.json` 1.0, `training_data.schema.json`) can be frozen for training.
`configs/spec_lock.json` holds their SHA-256 hashes; `scripts/training_readiness.py` fails if they change without a new
version.

**Rule used for every decision.** The 85,118 labels in dataset release `gpio_llm_v1` already follow the conservative
option (refuse, clarify, or leave out of the labels). v1.0 keeps that option unless an authoritative source settles the
question. Changing a decision needs a new facts or vocabulary version, regenerated labels and a new release.

## Hardware facts

| ID | Item | Decision for v1.0 | Evidence and reasoning |
|---|---|---|---|
| D-01 | PWM on GPIO14/15 | **Not taught; validator and simulator reject PWM on GPIO14/15.** | RP1 Table 4 lists `PWM0[2]`/`PWM0[3]` on GPIO14/15 (function a0), shared with GPIO18/19 (a3). The Raspberry Pi documentation lists hardware PWM only on GPIO12, 13, 18 and 19. GPIO14/15 are also the default UART0 TX/RX pins. |
| D-02 | Current limit figure (`F-GPIO-CURRENT`) | **Used only for loads of 200 mA or more; no borderline (16-50 mA) labels.** | The figure is a general documentation figure, not an RP1 characterisation; RP1 drive settings top out at 12 mA. |
| D-03 | RP1 alternate-function table (`F-ALT-TABLE`) | **Resolved: verified.** | All 252 cells (GPIO0-27 x a0-a8) match RP1 peripherals datasheet RP-008370-DS-1, including every blank cell (checked 2026-09-14). |
| D-04 | Short-circuit refusal (`F-DRIVE-NOT-LIMIT`) | **Keep refusing outputs wired straight to GND or 3V3.** | The documentation's pad-control section says drive strength is not a current limit and the pad behaves as a voltage source; the principle holds for any GPIO, so Pi 5 applicability does not change the decision. |
| D-05 | Default pull per GPIO | **Never stated in labels; the simulator reads an unpulled, unstimulated input as undefined; the hardware layer must set pulls explicitly.** | The documentation says most GPIOs have a default pull defined by the peripheral datasheet; RP1 reset values say "varies", and no per-pin table was collected. |
| D-06 | RP1-only alternate functions (I2C0/2/3 elsewhere, UART1-4, GPCLK, I2S, DPI...) | **Out of scope: no positive or negative labels; pins that have them are excluded from "unsupported" negatives.** | Present in RP1 Table 4, but OS and overlay support on the Pi 5 was not verified. |

## Policies

| ID | Policy | Decision for v1.0 |
|---|---|---|
| D-07 | `P-RESERVED-GPIO` | GPIO0/1 (ID EEPROM) are refused with `reserved_gpio`. The documentation reserves them for advanced use; refusing is the safe default for a voice/text assistant. |
| D-08 | `P-QUESTIONS` | Informational questions return `report_error` / `no_hardware_action`. An answer action is future vocabulary work (2.0). |
| D-09 | `P-DEVICE-SIGNAL` | "Device connected to GPIO N" is controlled as a signal line. **Hardware-layer requirement:** inductive or high-current loads must sit behind a driver or relay module; the controller must not assume otherwise. |
| D-10 | `P-ACTION-VOCAB` | Shell commands, code execution and I2C/SPI/UART payload transfers are refused (`unsupported_operation`). `sensor_read` stays reserved until bus-sensor semantics are specified. |
| D-11 | `P-PIN-NUMBERING` | "GPIO N", "pin N" and "BCM N" mean BCM GPIO N. Physical pins need "physical/header/board pin". Labels never use "pin N" for N = 28-40. |
| D-12 | Active-high default | "Turn on / activate" means HIGH unless the request says the device is active-low. Active-low relay boards must be declared in context or wording. |
| D-13 | Hedged or free-choice pins | "GPIO 27 or GPIO 16, whichever" returns `ask_clarification`; the model never picks a pin. |

## Out of scope for v1.0 (documented gaps)

- Borderline electrical cases (for example 20 mA loads or unusual 3.3 V logic families).
- Waiting for an input edge ("wait until the button is pressed"): no action exists.
- Timing precision limits (microsecond pulses, maximum PWM frequency): only logical bounds (> 0, integer milliseconds) are taught.
- Bus devices (I2C addresses, SPI modes, UART baud rates).

## Changing the specification

1. Bump `version` in the facts or vocabulary file and add a changelog entry.
2. Regenerate and revalidate the dataset (`scripts/build_all.sh`), then build a new release version.
3. Update `configs/spec_lock.json` with `python3 scripts/training_readiness.py --relock` and record the decision here.