feat(espnow): Pi bridge client, binary wire, and espnow-sender firmware
Replace serial/Wi-Fi driver transport paths with WebSocket bridge client, binary espnow_wire delivery, device announce registry, and restructured espnow-sender (AP + broadcast passthrough). Includes docs and tests. Co-authored-by: Cursor <cursoragent@cursor.com>
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docs/espnow-architecture.md
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docs/espnow-architecture.md
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# ESP-NOW transport architecture
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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).
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**On the wire:** binary only (no JSON) for ESP-NOW and Pi↔bridge WebSocket. The Pi web UI and `db/*.json` still use JSON internally.
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## System overview
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| Component | Firmware / path | Role |
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|-----------|-----------------|------|
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| **led-controller** | Raspberry Pi, `src/` | Web app; WebSocket **client** to bridge; device registry; builds binary commands |
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| **Bridge** | [`espnow-sender/`](../espnow-sender/) | WebSocket **server** `/ws`; relays binary ↔ ESP-NOW; max **20** peers (LRU) |
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| **led-driver** | [`led-driver/`](../led-driver/) submodule | Boot **ANNOUNCE** broadcast; applies **GROUPS**, **CMD**, **GROUP_CMD** |
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Configure the Pi in `settings.json`:
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```json
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{
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"bridge_ws_url": "ws://192.168.4.1/ws",
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"wifi_channel": 6
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}
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```
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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** (Pi sends `BRIDGE_CH` on connect; bridge updates AP + ESP-NOW STA).
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---
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## Boot and registration
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1. Driver powers on and sends **ANNOUNCE** to broadcast MAC `ff:ff:ff:ff:ff:ff`.
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2. Bridge receives it and forwards a **WebSocket uplink** frame to the Pi (peer MAC + packet).
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3. Pi **upserts** the device in `db/device.json` (key = 12-char hex MAC).
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4. Pi scans `db/group.json` and builds a **GROUPS** packet.
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5. Pi sends **GROUPS** unicast to that MAC via the bridge.
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6. Driver stores group ids in RAM for **GROUP_CMD** filtering.
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If the Pi or bridge is not up yet, the driver re-sends **ANNOUNCE** periodically until **GROUPS** arrives.
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---
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## Sending presets and commands
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1. UI or API triggers a send (e.g. `POST /presets/send`).
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2. Pi builds one or more **CMD** packets (v2 binary envelope, chunked to ≤250 bytes).
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3. Each packet is wrapped in a **WebSocket downlink** frame (unicast MAC or broadcast).
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4. Bridge forwards on ESP-NOW.
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5. Driver parses and applies (presets, select, brightness, device_config, etc.).
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For a **group**, Pi may send **GROUP_CMD** on broadcast once per chunk; only drivers that belong to that group apply the payload.
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---
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## Packet layers
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### Layer A — WebSocket frame (Pi ↔ bridge)
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| Offset | Size | Field |
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|--------|------|--------|
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| 0 | 1 | `flags` — bit0 = broadcast (`ff:ff:…`); peer ignored if set |
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| 1 | 6 | `peer` — destination MAC (raw bytes) |
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| 7 | … | Full ESP-NOW packet (layer B) |
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**Uplink** (bridge → Pi): same layout; `flags = 0`, `peer` = sender.
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**Ack** (bridge → Pi after downlink): 1 byte — `0x01` ok, `0x00` error.
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### Layer B — ESP-NOW packet (on air)
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| Offset | Size | Field |
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|--------|------|--------|
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| 0 | 1 | Magic `0x4C` (`'L'`) |
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| 1 | 1 | Message type |
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| 2 | … | Body (≤248 bytes so total ≤250) |
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| Type | Value | Direction | Purpose |
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|------|-------|-------------|---------|
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| ANNOUNCE | `0x01` | Driver → broadcast | Boot settings |
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| GROUPS | `0x02` | Pi → driver | Group membership |
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| CMD | `0x03` | Pi → driver | Command (v2 envelope) |
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| GROUP_CMD | `0x04` | Pi → broadcast | Command scoped to one group |
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| BRIDGE_CH | `0x10` | Pi → bridge | Set STA channel 1–11 |
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### Layer C — v2 command envelope (inside CMD / GROUP_CMD)
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Used for presets, select, default, brightness. **No JSON.**
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| Byte | Field |
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|------|--------|
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| 0 | Version `2` |
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| 1 | Brightness wire 0–127 (→ 0–255); `128–255` = unchanged |
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| 2 | `lp` — presets section length |
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| 3 | `ls` — select section length |
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| 4 | `ld` — default section length |
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| 5… | Presets blob (`lp` bytes) |
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| … | Select blob (`ls` bytes) |
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| … | Default blob (`ld` bytes) |
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Optional trailing `0x01` after the envelope in **CMD** means `save` (persist to flash).
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Implementation: [`src/util/binary_envelope.py`](../src/util/binary_envelope.py), [`src/util/espnow_wire.py`](../src/util/espnow_wire.py).
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---
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## Message body reference
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### ANNOUNCE (`0x01`)
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Sender MAC comes from ESP-NOW headers, not the body.
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```
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name_len (u8) | name (utf-8) | num_leds (u16 LE) | color_order (u8) | startup_mode (u8) | brightness (u8) | device_type (u8)
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```
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| `color_order` | `startup_mode` |
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|---------------|----------------|
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| 0=rgb, 1=rbg, 2=grb, 3=gbr, 4=brg, 5=bgr | 0=default, 1=last, 2=off |
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### GROUPS (`0x02`)
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```
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count (u8) | repeat: id_len (u8) | group_id (utf-8)
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```
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Group ids match keys in `db/group.json` (e.g. `"5"`, `"18"`).
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### GROUP_CMD (`0x04`)
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```
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group_id_len (u8) | group_id (utf-8) | v2 envelope | [optional 0x01 save]
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```
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Driver applies only if `group_id` is in its stored list.
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---
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## Size limits and chunking
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- **250 bytes** max per ESP-NOW datagram.
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- Large preset libraries → multiple **CMD** packets from the Pi.
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- Bridge stores at most **20** peer MACs; oldest peer evicted (LRU) when full.
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---
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## Related files
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| Topic | Location |
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|-------|----------|
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| Byte-level spec | [espnow-binary-protocol.md](espnow-binary-protocol.md) |
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| Pi wire codec | [`src/util/espnow_wire.py`](../src/util/espnow_wire.py) |
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| Pi bridge client | [`src/models/bridge_ws_client.py`](../src/models/bridge_ws_client.py) |
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| Bridge firmware | [`espnow-sender/main.py`](../espnow-sender/main.py) |
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| Driver ESP-NOW | [`led-driver/src/espnow_transport.py`](../led-driver/src/espnow_transport.py) |
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