# ESP-NOW transport architecture

This document describes how **led-controller**, the **bridge ESP32**, and **led-driver** devices work together. Wire-level byte layouts are in [espnow-binary-protocol.md](espnow-binary-protocol.md).

**Pi ↔ bridge WebSocket:** v1 **devices envelope** (JSON) — see [espnow-sender/msg.json](../espnow-sender/msg.json). **ESP-NOW over the air:** JSON driver payloads (≤250 bytes) or legacy binary (`0x4C` wire). The Pi web UI and `db/*.json` use JSON internally.

## System overview

![Three-node ESP-NOW architecture](images/espnow/system-overview.svg)

| Component | Firmware / path | Role |
|-----------|-----------------|------|
| **led-controller** | Raspberry Pi, `src/` | Web app; WebSocket **client** to bridge (auto-reconnect); device registry; builds devices envelope |
| **Bridge** | [`espnow-sender/`](../espnow-sender/) | WebSocket **server** `/ws`; routes envelope per MAC; max **20** peers (LRU) |
| **led-driver** | [`led-driver/`](../led-driver/) submodule | Boot **ANNOUNCE** broadcast; applies **GROUPS**, **CMD**, **GROUP_CMD** |

Configure the Pi in `settings.json`:

```json
{
  "bridge_ws_url": "ws://192.168.4.1/ws",
  "wifi_channel": 5
}
```

Connect the Pi to the **bridge access point** (SSID = bridge `name` in `/settings.json`, default IP **192.168.4.1**). All nodes must use the same 2.4 GHz **channel**: set `wifi_channel` in the bridge and each led-driver `/settings.json` (applied at boot on those devices). The Pi stores `wifi_channel` in its own `settings.json` for alignment (restart led-controller after changing).

---

## Boot and registration

![Boot and registration sequence](images/espnow/boot-sequence.svg)

1. Driver powers on and sends **ANNOUNCE** to broadcast MAC `ff:ff:ff:ff:ff:ff`.
2. Bridge receives it and forwards a **WebSocket uplink** frame to the Pi (peer MAC + packet).
3. Pi **upserts** the device in `db/device.json` (key = 12-char hex MAC).
4. Pi scans `db/group.json` and sends a **groups** envelope (`set_groups: true`) unicast to that MAC.
5. Driver stores group ids in RAM (`device_groups`) for filtering.
6. Pi bridge client **reconnects** automatically if the WebSocket drops (2 s backoff).

If the Pi or bridge is not up yet, the driver re-sends **ANNOUNCE** periodically until **GROUPS** arrives.

---

## Devices envelope (Pi → bridge)

```json
{
  "v": "1",
  "dv": {
    "ff:ff:ff:ff:ff:ff": {
      "p": { "2": { "p": "on", "c": ["#FFFFFF"], "a": true } },
      "s": ["2", 0],
      "g": ["5", "18"],
      "sg": false,
      "sv": true
    }
  }
}
```

Short wire names (long names still accepted on receive): `dv`=devices, `p`=presets, `s`=select (`["preset_id", step?]` — no device name), `g`=groups, `sg`=set_groups, `sv`=save, `df`=default; preset fields `p/c/d/b/a/bg/n1…`.

| `set_groups` | Destination | Bridge | Driver |
|--------------|-------------|--------|--------|
| `true` | any | Unicast only (expand `ff:ff:…` to all known peers) | `groups_replace`, then apply body |
| `false` | `ff:ff:ff:ff:ff:ff` | ESP-NOW air broadcast | Apply only if device is in `groups` |
| `false` | specific MAC | Unicast | Same group filter |

Legacy raw payloads (binary wire or plain v1 JSON without `devices`) are still **broadcast** by the bridge.

## Sending presets and commands

1. UI or API triggers a send (e.g. `POST /presets/push`).
2. Pi builds a **devices envelope** (or legacy binary) and sends it on the bridge WebSocket.
3. Bridge routes each MAC entry to unicast or ESP-NOW broadcast per `set_groups`.
4. Driver `process_data` applies presets, select (`[preset_id, step?]`; legacy name map still accepted), brightness, etc.

---

## Packet layers

![Packet layer stack](images/espnow/packet-layers.svg)

### Layer A — WebSocket frame (Pi ↔ bridge)

| Offset | Size | Field |
|--------|------|--------|
| 0 | 1 | `flags` — bit0 = broadcast (`ff:ff:…`); peer ignored if set |
| 1 | 6 | `peer` — destination MAC (raw bytes) |
| 7 | … | Full ESP-NOW packet (layer B) |

**Uplink** (bridge → Pi): same layout; `flags = 0`, `peer` = sender.

**Ack** (bridge → Pi after downlink): 1 byte — `0x01` ok, `0x00` error.

### Layer B — ESP-NOW packet (on air)

| Offset | Size | Field |
|--------|------|--------|
| 0 | 1 | Magic `0x4C` (`'L'`) |
| 1 | 1 | Message type |
| 2 | … | Body (≤248 bytes so total ≤250) |

![Message types](images/espnow/message-types.svg)

| Type | Value | Direction | Purpose |
|------|-------|-------------|---------|
| ANNOUNCE | `0x01` | Driver → broadcast | Boot settings |
| GROUPS | `0x02` | Pi → driver | Group membership |
| CMD | `0x03` | Pi → driver | Command (v2 envelope) |
| GROUP_CMD | `0x04` | Pi → broadcast | Command scoped to one group |
| BRIDGE_CH | `0x10` | Pi → bridge | Set STA channel 1–11 |

### Layer C — v2 command envelope (inside CMD / GROUP_CMD)

Used for presets, select, default, brightness. **No JSON.**

| Byte | Field |
|------|--------|
| 0 | Version `2` |
| 1 | Brightness wire 0–127 (→ 0–255); `128–255` = unchanged |
| 2 | `lp` — presets section length |
| 3 | `ls` — select section length |
| 4 | `ld` — default section length |
| 5… | Presets blob (`lp` bytes) |
| … | Select blob (`ls` bytes) |
| … | Default blob (`ld` bytes) |

Optional trailing `0x01` after the envelope in **CMD** means `save` (persist to flash).

Implementation: [`src/util/binary_envelope.py`](../src/util/binary_envelope.py), [`src/util/espnow_wire.py`](../src/util/espnow_wire.py).

---

## Message body reference

### ANNOUNCE (`0x01`)

Sender MAC comes from ESP-NOW headers, not the body.

```
name_len (u8) | name (utf-8) | num_leds (u16 LE) | color_order (u8) | startup_mode (u8) | brightness (u8) | device_type (u8)
```

| `color_order` | `startup_mode` |
|---------------|----------------|
| 0=rgb, 1=rbg, 2=grb, 3=gbr, 4=brg, 5=bgr | 0=default, 1=last, 2=off |

### GROUPS (`0x02`)

```
count (u8) | repeat: id_len (u8) | group_id (utf-8)
```

Group ids match keys in `db/group.json` (e.g. `"5"`, `"18"`).

### GROUP_CMD (`0x04`)

```
group_id_len (u8) | group_id (utf-8) | v2 envelope | [optional 0x01 save]
```

Driver applies only if `group_id` is in its stored list.

---

## Size limits and chunking

- **250 bytes** max per ESP-NOW datagram.
- Large preset libraries → multiple **CMD** packets from the Pi.
- Bridge stores at most **20** peer MACs; oldest peer evicted (LRU) when full.

---

## Related files

| Topic | Location |
|-------|----------|
| Byte-level spec | [espnow-binary-protocol.md](espnow-binary-protocol.md) |
| Pi wire codec | [`src/util/espnow_wire.py`](../src/util/espnow_wire.py) |
| Pi bridge client | [`src/models/bridge_ws_client.py`](../src/models/bridge_ws_client.py) |
| Bridge firmware | [`espnow-sender/main.py`](../espnow-sender/main.py) |
| Driver ESP-NOW | [`led-driver/src/espnow_transport.py`](../led-driver/src/espnow_transport.py) |