# ATO ↔ TrainSim interface (v1)

Standalone. No ETCS. No ATP. JSON over HTTP.

Base URL (TrainSim): `http://trainsim:8080`

## TrainSim → ATO reads

`GET /train/state`

```json
{
  "speed_mps": 0.0,
  "position_m": 0.0,
  "track_length_m": 1000.0,
  "sim_running": false
}
```

## ATO → TrainSim writes

`POST /train/actuate`

```json
{
  "traction_pct": 0,
  "brake_pct": 0
}
```

Percent 0–100. Do not send both > 0 (TrainSim clamps brake wins).

`POST /sim/start` — start physics tick (empty body)

`POST /sim/stop` — pause physics (empty body)

Optional (TrainSim logs only): `POST /train/doors` `{ "command": "open" | "close" }`

## ATO configuration (env)

| Variable | Meaning |
|----------|---------|
| `TRAINSIM_URL` | TrainSim base URL |
| `TARGET_SPEED_MPS` | Cruise target (default 10) |
| `TICK_MS` | Control period (default 100) |