MeshCore/docs/protocol_guide.md

# MeshCore Device Communication Protocol Guide

This document provides a comprehensive guide for communicating with MeshCore devices over Bluetooth Low Energy (BLE). It is platform-agnostic and can be used for Android, iOS, Python, JavaScript, or any other platform that supports BLE.

## ⚠️ Important Security Note

**All secrets, hashes, and cryptographic values shown in this guide are EXAMPLE VALUES ONLY and are NOT real secrets.** 

- The secret `9b647d242d6e1c5883fde0c5cf5c4c5e` used in examples is a made-up example value
- All hex values, public keys, and hashes in examples are for demonstration purposes only
- **Never use example secrets in production** - always generate new cryptographically secure random secrets
- This guide is for protocol documentation only - implement proper security practices in your actual implementation

## Table of Contents

1. [BLE Connection](#ble-connection)
2. [Protocol Overview](#protocol-overview)
3. [Commands](#commands)
4. [Channel Management](#channel-management)
5. [Secret Generation and QR Codes](#secret-generation-and-qr-codes)
6. [Message Handling](#message-handling)
7. [Response Parsing](#response-parsing)
8. [Example Implementation Flow](#example-implementation-flow)

---

## BLE Connection

### Service and Characteristics

MeshCore devices expose a BLE service with the following UUIDs:

- **Service UUID**: `0000ff00-0000-1000-8000-00805f9b34fb`
- **RX Characteristic** (Device → Client): `0000ff01-0000-1000-8000-00805f9b34fb`
- **TX Characteristic** (Client → Device): `0000ff02-0000-1000-8000-00805f9b34fb`

### Connection Steps

1. **Scan for Devices**
   - Scan for BLE devices advertising the MeshCore service UUID
   - Filter by device name (typically contains "MeshCore" or similar)
   - Note the device MAC address for reconnection

2. **Connect to GATT**
   - Connect to the device using the discovered MAC address
   - Wait for connection to be established

3. **Discover Services and Characteristics**
   - Discover the service with UUID `0000ff00-0000-1000-8000-00805f9b34fb`
   - Discover RX characteristic (`0000ff01-...`) for receiving data
   - Discover TX characteristic (`0000ff02-...`) for sending commands

4. **Enable Notifications**
   - Subscribe to notifications on the RX characteristic
   - Enable notifications/indications to receive data from the device
   - On some platforms, you may need to write to a descriptor (e.g., `0x2902`) with value `0x01` or `0x02`

5. **Send AppStart Command**
   - Send the app start command (see [Commands](#commands)) to initialize communication
   - Wait for OK response before sending other commands

### Connection State Management

- **Disconnected**: No connection established
- **Connecting**: Connection attempt in progress
- **Connected**: GATT connection established, ready for commands
- **Error**: Connection failed or lost

**Note**: MeshCore devices may disconnect after periods of inactivity. Implement auto-reconnect logic with exponential backoff.

### BLE Write Type

When writing commands to the TX characteristic, specify the write type:

- **Write with Response** (default): Waits for acknowledgment from device
- **Write without Response**: Faster but no acknowledgment

**Platform-specific**:
- **Android**: Use `BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT` or `WRITE_TYPE_NO_RESPONSE`
- **iOS**: Use `CBCharacteristicWriteType.withResponse` or `.withoutResponse`
- **Python (bleak)**: Use `write_gatt_char()` with `response=True` or `False`

**Recommendation**: Use write with response for reliability, especially for critical commands like `SET_CHANNEL`.

### MTU (Maximum Transmission Unit)

The default BLE MTU is 23 bytes (20 bytes payload). For larger commands like `SET_CHANNEL` (66 bytes), you may need to:

1. **Request Larger MTU**: Request MTU of 512 bytes if supported
   - Android: `gatt.requestMtu(512)`
   - iOS: `peripheral.maximumWriteValueLength(for:)`
   - Python (bleak): MTU is negotiated automatically

2. **Handle Chunking**: If MTU is small, commands may be split automatically by the BLE stack
   - Ensure all chunks are sent before waiting for response
   - Responses may also arrive in chunks - buffer until complete

### Command Sequencing and Timing

**Critical**: Commands must be sent in the correct sequence:

1. **After Connection**:
   - Wait for GATT connection established
   - Wait for services/characteristics discovered
   - Wait for notifications enabled (descriptor write complete)
   - **Wait 200-1000ms** for device to be ready (some devices need initialization time)
   - Send `APP_START` command
   - **Wait for `PACKET_OK` response** before sending any other commands

2. **Command-Response Matching**:
   - Send one command at a time
   - Wait for response before sending next command
   - Use timeout (typically 5 seconds)
   - Match response to command by:
     - Command type (e.g., `GET_CHANNEL` → `PACKET_CHANNEL_INFO`)
     - Sequence number (if implemented)
     - First-in-first-out queue

3. **Timing Considerations**:
   - Minimum delay between commands: 50-100ms
   - After `APP_START`: Wait 200-500ms before next command
   - After `SET_CHANNEL`: Wait 500-1000ms for channel to be created
   - After enabling notifications: Wait 200ms before sending commands

**Example Flow**:
```python
# 1. Connect and discover
await connect_to_device(device)
await discover_services()
await enable_notifications()
await asyncio.sleep(0.2)  # Wait for device ready

# 2. Send AppStart
send_command(build_app_start())
response = await wait_for_response(PACKET_OK, timeout=5.0)
if response.type != PACKET_OK:
    raise Exception("AppStart failed")

# 3. Now safe to send other commands
await asyncio.sleep(0.1)  # Small delay between commands
send_command(build_device_query())
response = await wait_for_response(PACKET_DEVICE_INFO, timeout=5.0)
```

### Command Queue Management

For reliable operation, implement a command queue:

1. **Queue Structure**:
   - Maintain a queue of pending commands
   - Track which command is currently waiting for response
   - Only send next command after receiving response or timeout

2. **Implementation**:
```python
class CommandQueue:
    def __init__(self):
        self.queue = []
        self.waiting_for_response = False
        self.current_command = None
    
    async def send_command(self, command, expected_response_type, timeout=5.0):
        if self.waiting_for_response:
            # Queue the command
            self.queue.append((command, expected_response_type, timeout))
            return
        
        self.waiting_for_response = True
        self.current_command = (command, expected_response_type, timeout)
        
        # Send command
        await write_to_tx_characteristic(command)
        
        # Wait for response
        response = await wait_for_response(expected_response_type, timeout)
        
        self.waiting_for_response = False
        self.current_command = None
        
        # Process next queued command
        if self.queue:
            next_cmd, next_type, next_timeout = self.queue.pop(0)
            await self.send_command(next_cmd, next_type, next_timeout)
        
        return response
```

3. **Error Handling**:
   - On timeout: Clear current command, process next in queue
   - On error: Log error, clear current command, process next
   - Don't block queue on single command failure

---

## Protocol Overview

The MeshCore protocol uses a binary format with the following structure:

- **Commands**: Sent from client to device via TX characteristic
- **Responses**: Received from device via RX characteristic (notifications)
- **All multi-byte integers**: Little-endian byte order
- **All strings**: UTF-8 encoding

### Packet Structure

Most packets follow this format:
```
[Packet Type (1 byte)] [Data (variable length)]
```

The first byte indicates the packet type (see [Response Parsing](#response-parsing)).

---

## Commands

### 1. App Start

**Purpose**: Initialize communication with the device. Must be sent first after connection.

**Command Format**:
```
Byte 0: 0x01
Byte 1: 0x03
Bytes 2-10: "mccli" (ASCII, null-padded to 9 bytes)
```

**Example** (hex):
```
01 03 6d 63 63 6c 69 00 00 00 00
```

**Response**: `PACKET_OK` (0x00)

---

### 2. Device Query

**Purpose**: Query device information.

**Command Format**:
```
Byte 0: 0x16
Byte 1: 0x03
```

**Example** (hex):
```
16 03
```

**Response**: `PACKET_DEVICE_INFO` (0x0D) with device information

---

### 3. Get Channel Info

**Purpose**: Retrieve information about a specific channel.

**Command Format**:
```
Byte 0: 0x1F
Byte 1: Channel Index (0-7)
```

**Example** (get channel 1):
```
1F 01
```

**Response**: `PACKET_CHANNEL_INFO` (0x12) with channel details

**Note**: The device does not return channel secrets for security reasons. Store secrets locally when creating channels.

---

### 4. Set Channel

**Purpose**: Create or update a channel on the device.

**Command Format**:
```
Byte 0: 0x20
Byte 1: Channel Index (0-7)
Bytes 2-33: Channel Name (32 bytes, UTF-8, null-padded)
Bytes 34-65: Secret (32 bytes, see [Secret Generation](#secret-generation))
```

**Total Length**: 66 bytes

**Channel Index**:
- Index 0: Reserved for public channels (no secret)
- Indices 1-7: Available for private channels

**Channel Name**:
- UTF-8 encoded
- Maximum 32 bytes
- Padded with null bytes (0x00) if shorter

**Secret Field** (32 bytes):
- For **private channels**: 32-byte secret (see [Secret Generation](#secret-generation))
- For **public channels**: All zeros (0x00)

**Example** (create channel "YourChannelName" at index 1 with secret):
```
20 01 53 4D 53 00 00 ... (name padded to 32 bytes)
    [32 bytes of secret]
```

**Response**: `PACKET_OK` (0x00) on success, `PACKET_ERROR` (0x01) on failure

---

### 5. Send Channel Message

**Purpose**: Send a text message to a channel.

**Command Format**:
```
Byte 0: 0x03
Byte 1: 0x00
Byte 2: Channel Index (0-7)
Bytes 3-6: Timestamp (32-bit little-endian Unix timestamp, seconds)
Bytes 7+: Message Text (UTF-8, variable length)
```

**Timestamp**: Unix timestamp in seconds (32-bit unsigned integer, little-endian)

**Example** (send "Hello" to channel 1 at timestamp 1234567890):
```
03 00 01 D2 02 96 49 48 65 6C 6C 6F
```

**Response**: `PACKET_MSG_SENT` (0x06) on success

---

### 6. Get Message

**Purpose**: Request the next queued message from the device.

**Command Format**:
```
Byte 0: 0x0A
```

**Example** (hex):
```
0A
```

**Response**: 
- `PACKET_CHANNEL_MSG_RECV` (0x08) or `PACKET_CHANNEL_MSG_RECV_V3` (0x11) for channel messages
- `PACKET_CONTACT_MSG_RECV` (0x07) or `PACKET_CONTACT_MSG_RECV_V3` (0x10) for contact messages
- `PACKET_NO_MORE_MSGS` (0x0A) if no messages available

**Note**: Poll this command periodically to retrieve queued messages. The device may also send `PACKET_MESSAGES_WAITING` (0x83) as a notification when messages are available.

---

### 7. Get Battery

**Purpose**: Query device battery level.

**Command Format**:
```
Byte 0: 0x14
```

**Example** (hex):
```
14
```

**Response**: `PACKET_BATTERY` (0x0C) with battery percentage

---

## Channel Management

### Channel Types

1. **Public Channels** (Index 0)
   - No secret required
   - Anyone with the channel name can join
   - Use for open communication

2. **Private Channels** (Indices 1-7)
   - Require a 16-byte secret
   - Secret is expanded to 32 bytes using SHA-512 (see [Secret Generation](#secret-generation))
   - Only devices with the secret can access the channel

### Channel Lifecycle

1. **Create Channel**:
   - Choose an available index (1-7 for private channels)
   - Generate or provide a 16-byte secret
   - Send `SET_CHANNEL` command with name and secret
   - **Store the secret locally** (device does not return it)

2. **Query Channel**:
   - Send `GET_CHANNEL` command with channel index
   - Parse `PACKET_CHANNEL_INFO` response
   - Note: Secret will be null in response (security feature)

3. **Delete Channel**:
   - Send `SET_CHANNEL` command with empty name and all-zero secret
   - Or overwrite with a new channel

### Channel Index Management

- **Index 0**: Reserved for public channels
- **Indices 1-7**: Available for private channels
- If a channel exists at index 0 but should be private, migrate it to index 1-7

---

## Secret Generation and QR Codes

### Secret Generation

For private channels, generate a cryptographically secure 16-byte secret:

**Pseudocode**:
```python
import secrets

# Generate 16 random bytes
secret_bytes = secrets.token_bytes(16)

# Convert to hex string for storage/sharing
secret_hex = secret_bytes.hex()  # 32 hex characters
```

**Important**: Use a cryptographically secure random number generator (CSPRNG). Do not use predictable values.

### Secret Expansion

When sending the secret to the device via `SET_CHANNEL`, the 16-byte secret must be expanded to 32 bytes:

**Process**:
1. Take the 16-byte secret
2. Compute SHA-512 hash: `hash = SHA-512(secret)`
3. Use the first 32 bytes of the hash as the secret field in the command

**Pseudocode**:
```python
import hashlib

secret_16_bytes = ...  # Your 16-byte secret
sha512_hash = hashlib.sha512(secret_16_bytes).digest()  # 64 bytes
secret_32_bytes = sha512_hash[:32]  # First 32 bytes
```

This matches MeshCore's ED25519 key expansion method.

### QR Code Format

QR codes for sharing channel secrets use the following format:

**URL Scheme**:
```
meshcore://channel/add?name=<ChannelName>&secret=<32HexChars>
```

**Parameters**:
- `name`: Channel name (URL-encoded if needed)
- `secret`: 32-character hexadecimal representation of the 16-byte secret

**Example** (using example secret - NOT a real secret):
```
meshcore://channel/add?name=YourChannelName&secret=9b647d242d6e1c5883fde0c5cf5c4c5e
```

**Alternative Formats** (for backward compatibility):

1. **JSON Format**:
```json
{
  "name": "YourChannelName",
  "secret": "9b647d242d6e1c5883fde0c5cf5c4c5e"
}
```
*Note: The secret value above is an example only - generate your own secure random secret.*

2. **Plain Hex** (32 hex characters):
```
9b647d242d6e1c5883fde0c5cf5c4c5e
```
*Note: This is an example hex value - always generate your own cryptographically secure random secret.*

### QR Code Generation

**Steps**:
1. Generate or use existing 16-byte secret
2. Convert to 32-character hex string (lowercase)
3. URL-encode the channel name
4. Construct the `meshcore://` URL
5. Generate QR code from the URL string

**Example** (Python with `qrcode` library):
```python
import qrcode
from urllib.parse import quote
import secrets

channel_name = "YourChannelName"
# Generate a real cryptographically secure secret (NOT the example value)
secret_bytes = secrets.token_bytes(16)
secret_hex = secret_bytes.hex()  # This will be a different value each time

# Example value shown in documentation: "9b647d242d6e1c5883fde0c5cf5c4c5e"
# DO NOT use the example value - always generate your own!

url = f"meshcore://channel/add?name={quote(channel_name)}&secret={secret_hex}"
qr = qrcode.QRCode(version=1, box_size=10, border=5)
qr.add_data(url)
qr.make(fit=True)
img = qr.make_image(fill_color="black", back_color="white")
img.save("channel_qr.png")
```

### QR Code Scanning

When scanning a QR code:

1. **Parse URL Format**:
   - Extract `name` and `secret` query parameters
   - Validate secret is 32 hex characters

2. **Parse JSON Format**:
   - Parse JSON object
   - Extract `name` and `secret` fields

3. **Parse Plain Hex**:
   - Extract only hex characters (0-9, a-f, A-F)
   - Validate length is 32 characters
   - Convert to lowercase

4. **Validate Secret**:
   - Must be exactly 32 hex characters (16 bytes)
   - Convert hex string to bytes

5. **Create Channel**:
   - Use extracted name and secret
   - Send `SET_CHANNEL` command

---

## Message Handling

### Receiving Messages

Messages are received via the RX characteristic (notifications). The device sends:

1. **Channel Messages**:
   - `PACKET_CHANNEL_MSG_RECV` (0x08) - Standard format
   - `PACKET_CHANNEL_MSG_RECV_V3` (0x11) - Version 3 with SNR

2. **Contact Messages**:
   - `PACKET_CONTACT_MSG_RECV` (0x07) - Standard format
   - `PACKET_CONTACT_MSG_RECV_V3` (0x10) - Version 3 with SNR

3. **Notifications**:
   - `PACKET_MESSAGES_WAITING` (0x83) - Indicates messages are queued

### Contact Message Format

**Standard Format** (`PACKET_CONTACT_MSG_RECV`, 0x07):
```
Byte 0: 0x07 (packet type)
Bytes 1-6: Public Key Prefix (6 bytes, hex)
Byte 7: Path Length
Byte 8: Text Type
Bytes 9-12: Timestamp (32-bit little-endian)
Bytes 13-16: Signature (4 bytes, only if txt_type == 2)
Bytes 17+: Message Text (UTF-8)
```

**V3 Format** (`PACKET_CONTACT_MSG_RECV_V3`, 0x10):
```
Byte 0: 0x10 (packet type)
Byte 1: SNR (signed byte, multiplied by 4)
Bytes 2-3: Reserved
Bytes 4-9: Public Key Prefix (6 bytes, hex)
Byte 10: Path Length
Byte 11: Text Type
Bytes 12-15: Timestamp (32-bit little-endian)
Bytes 16-19: Signature (4 bytes, only if txt_type == 2)
Bytes 20+: Message Text (UTF-8)
```

**Parsing Pseudocode**:
```python
def parse_contact_message(data):
    packet_type = data[0]
    offset = 1
    
    # Check for V3 format
    if packet_type == 0x10:  # V3
        snr_byte = data[offset]
        snr = ((snr_byte if snr_byte < 128 else snr_byte - 256) / 4.0)
        offset += 3  # Skip SNR + reserved
    
    pubkey_prefix = data[offset:offset+6].hex()
    offset += 6
    
    path_len = data[offset]
    txt_type = data[offset + 1]
    offset += 2
    
    timestamp = int.from_bytes(data[offset:offset+4], 'little')
    offset += 4
    
    # If txt_type == 2, skip 4-byte signature
    if txt_type == 2:
        offset += 4
    
    message = data[offset:].decode('utf-8')
    
    return {
        'pubkey_prefix': pubkey_prefix,
        'path_len': path_len,
        'txt_type': txt_type,
        'timestamp': timestamp,
        'message': message,
        'snr': snr if packet_type == 0x10 else None
    }
```

### Channel Message Format

**Standard Format** (`PACKET_CHANNEL_MSG_RECV`, 0x08):
```
Byte 0: 0x08 (packet type)
Byte 1: Channel Index (0-7)
Byte 2: Path Length
Byte 3: Text Type
Bytes 4-7: Timestamp (32-bit little-endian)
Bytes 8+: Message Text (UTF-8)
```

**V3 Format** (`PACKET_CHANNEL_MSG_RECV_V3`, 0x11):
```
Byte 0: 0x11 (packet type)
Byte 1: SNR (signed byte, multiplied by 4)
Bytes 2-3: Reserved
Byte 4: Channel Index (0-7)
Byte 5: Path Length
Byte 6: Text Type
Bytes 7-10: Timestamp (32-bit little-endian)
Bytes 11+: Message Text (UTF-8)
```

**Parsing Pseudocode**:
```python
def parse_channel_message(data):
    packet_type = data[0]
    offset = 1
    
    # Check for V3 format
    if packet_type == 0x11:  # V3
        snr_byte = data[offset]
        snr = ((snr_byte if snr_byte < 128 else snr_byte - 256) / 4.0)
        offset += 3  # Skip SNR + reserved
    
    channel_idx = data[offset]
    path_len = data[offset + 1]
    txt_type = data[offset + 2]
    timestamp = int.from_bytes(data[offset+3:offset+7], 'little')
    message = data[offset+7:].decode('utf-8')
    
    return {
        'channel_idx': channel_idx,
        'timestamp': timestamp,
        'message': message,
        'snr': snr if packet_type == 0x11 else None
    }
```

### Sending Messages

Use the `SEND_CHANNEL_MESSAGE` command (see [Commands](#commands)).

**Important**: 
- Messages are limited to 133 characters per MeshCore specification
- Long messages should be split into chunks
- Include a chunk indicator (e.g., "[1/3] message text")

---

## Response Parsing

### Packet Types

| Value | Name | Description |
|-------|------|-------------|
| 0x00 | PACKET_OK | Command succeeded |
| 0x01 | PACKET_ERROR | Command failed |
| 0x02 | PACKET_CONTACT_START | Start of contact list |
| 0x03 | PACKET_CONTACT | Contact information |
| 0x04 | PACKET_CONTACT_END | End of contact list |
| 0x05 | PACKET_SELF_INFO | Device self-information |
| 0x06 | PACKET_MSG_SENT | Message sent confirmation |
| 0x07 | PACKET_CONTACT_MSG_RECV | Contact message (standard) |
| 0x08 | PACKET_CHANNEL_MSG_RECV | Channel message (standard) |
| 0x09 | PACKET_CURRENT_TIME | Current time response |
| 0x0A | PACKET_NO_MORE_MSGS | No more messages available |
| 0x0C | PACKET_BATTERY | Battery level |
| 0x0D | PACKET_DEVICE_INFO | Device information |
| 0x10 | PACKET_CONTACT_MSG_RECV_V3 | Contact message (V3 with SNR) |
| 0x11 | PACKET_CHANNEL_MSG_RECV_V3 | Channel message (V3 with SNR) |
| 0x12 | PACKET_CHANNEL_INFO | Channel information |
| 0x80 | PACKET_ADVERTISEMENT | Advertisement packet |
| 0x82 | PACKET_ACK | Acknowledgment |
| 0x83 | PACKET_MESSAGES_WAITING | Messages waiting notification |
| 0x88 | PACKET_LOG_DATA | RF log data (can be ignored) |

### Parsing Responses

**PACKET_OK** (0x00):
```
Byte 0: 0x00
Bytes 1-4: Optional value (32-bit little-endian integer)
```

**PACKET_ERROR** (0x01):
```
Byte 0: 0x01
Byte 1: Error code (optional)
```

**PACKET_CHANNEL_INFO** (0x12):
```
Byte 0: 0x12
Byte 1: Channel Index
Bytes 2-33: Channel Name (32 bytes, null-terminated)
Bytes 34-65: Secret (32 bytes, but device typically only returns 20 bytes total)
```

**Note**: The device may not return the full 66-byte packet. Parse what is available. The secret field is typically not returned for security reasons.

**PACKET_DEVICE_INFO** (0x0D):
```
Byte 0: 0x0D
Byte 1: Firmware Version (uint8)
Bytes 2+: Variable length based on firmware version

For firmware version >= 3:
Byte 2: Max Contacts Raw (uint8, actual = value * 2)
Byte 3: Max Channels (uint8)
Bytes 4-7: BLE PIN (32-bit little-endian)
Bytes 8-19: Firmware Build (12 bytes, UTF-8, null-padded)
Bytes 20-59: Model (40 bytes, UTF-8, null-padded)
Bytes 60-79: Version (20 bytes, UTF-8, null-padded)
```

**Parsing Pseudocode**:
```python
def parse_device_info(data):
    if len(data) < 2:
        return None
    
    fw_ver = data[1]
    info = {'fw_ver': fw_ver}
    
    if fw_ver >= 3 and len(data) >= 80:
        info['max_contacts'] = data[2] * 2
        info['max_channels'] = data[3]
        info['ble_pin'] = int.from_bytes(data[4:8], 'little')
        info['fw_build'] = data[8:20].decode('utf-8').rstrip('\x00').strip()
        info['model'] = data[20:60].decode('utf-8').rstrip('\x00').strip()
        info['ver'] = data[60:80].decode('utf-8').rstrip('\x00').strip()
    
    return info
```

**PACKET_BATTERY** (0x0C):
```
Byte 0: 0x0C
Bytes 1-2: Battery Level (16-bit little-endian, percentage 0-100)

Optional (if data size > 3):
Bytes 3-6: Used Storage (32-bit little-endian, KB)
Bytes 7-10: Total Storage (32-bit little-endian, KB)
```

**Parsing Pseudocode**:
```python
def parse_battery(data):
    if len(data) < 3:
        return None
    
    level = int.from_bytes(data[1:3], 'little')
    info = {'level': level}
    
    if len(data) > 3:
        used_kb = int.from_bytes(data[3:7], 'little')
        total_kb = int.from_bytes(data[7:11], 'little')
        info['used_kb'] = used_kb
        info['total_kb'] = total_kb
    
    return info
```

**PACKET_SELF_INFO** (0x05):
```
Byte 0: 0x05
Byte 1: Advertisement Type
Byte 2: TX Power
Byte 3: Max TX Power
Bytes 4-35: Public Key (32 bytes, hex)
Bytes 36-39: Advertisement Latitude (32-bit little-endian, divided by 1e6)
Bytes 40-43: Advertisement Longitude (32-bit little-endian, divided by 1e6)
Byte 44: Multi ACKs
Byte 45: Advertisement Location Policy
Byte 46: Telemetry Mode (bitfield)
Byte 47: Manual Add Contacts (bool)
Bytes 48-51: Radio Frequency (32-bit little-endian, divided by 1000.0)
Bytes 52-55: Radio Bandwidth (32-bit little-endian, divided by 1000.0)
Byte 56: Radio Spreading Factor
Byte 57: Radio Coding Rate
Bytes 58+: Device Name (UTF-8, variable length, null-terminated)
```

**Parsing Pseudocode**:
```python
def parse_self_info(data):
    if len(data) < 36:
        return None
    
    offset = 1
    info = {
        'adv_type': data[offset],
        'tx_power': data[offset + 1],
        'max_tx_power': data[offset + 2],
        'public_key': data[offset + 3:offset + 35].hex()
    }
    offset += 35
    
    lat = int.from_bytes(data[offset:offset+4], 'little') / 1e6
    lon = int.from_bytes(data[offset+4:offset+8], 'little') / 1e6
    info['adv_lat'] = lat
    info['adv_lon'] = lon
    offset += 8
    
    info['multi_acks'] = data[offset]
    info['adv_loc_policy'] = data[offset + 1]
    telemetry_mode = data[offset + 2]
    info['telemetry_mode_env'] = (telemetry_mode >> 4) & 0b11
    info['telemetry_mode_loc'] = (telemetry_mode >> 2) & 0b11
    info['telemetry_mode_base'] = telemetry_mode & 0b11
    info['manual_add_contacts'] = data[offset + 3] > 0
    offset += 4
    
    freq = int.from_bytes(data[offset:offset+4], 'little') / 1000.0
    bw = int.from_bytes(data[offset+4:offset+8], 'little') / 1000.0
    info['radio_freq'] = freq
    info['radio_bw'] = bw
    info['radio_sf'] = data[offset + 8]
    info['radio_cr'] = data[offset + 9]
    offset += 10
    
    if offset < len(data):
        name_bytes = data[offset:]
        info['name'] = name_bytes.decode('utf-8').rstrip('\x00').strip()
    
    return info
```

**PACKET_MSG_SENT** (0x06):
```
Byte 0: 0x06
Byte 1: Message Type
Bytes 2-5: Expected ACK (4 bytes, hex)
Bytes 6-9: Suggested Timeout (32-bit little-endian, seconds)
```

**PACKET_ACK** (0x82):
```
Byte 0: 0x82
Bytes 1-6: ACK Code (6 bytes, hex)
```

### Error Codes

**PACKET_ERROR** (0x01) may include an error code in byte 1:

| Error Code | Description |
|------------|-------------|
| 0x00 | Generic error (no specific code) |
| 0x01 | Invalid command |
| 0x02 | Invalid parameter |
| 0x03 | Channel not found |
| 0x04 | Channel already exists |
| 0x05 | Channel index out of range |
| 0x06 | Secret mismatch |
| 0x07 | Message too long |
| 0x08 | Device busy |
| 0x09 | Not enough storage |

**Note**: Error codes may vary by firmware version. Always check byte 1 of `PACKET_ERROR` response.

### Partial Packet Handling

BLE notifications may arrive in chunks, especially for larger packets. Implement buffering:

**Implementation**:
```python
class PacketBuffer:
    def __init__(self):
        self.buffer = bytearray()
        self.expected_length = None
    
    def add_data(self, data):
        self.buffer.extend(data)
        
        # Check if we have a complete packet
        if len(self.buffer) >= 1:
            packet_type = self.buffer[0]
            
            # Determine expected length based on packet type
            expected = self.get_expected_length(packet_type)
            
            if expected is not None and len(self.buffer) >= expected:
                # Complete packet
                packet = bytes(self.buffer[:expected])
                self.buffer = self.buffer[expected:]
                return packet
            elif expected is None:
                # Variable length packet - try to parse what we have
                # Some packets have minimum length requirements
                if self.can_parse_partial(packet_type):
                    return self.try_parse_partial()
        
        return None  # Incomplete packet
    
    def get_expected_length(self, packet_type):
        # Fixed-length packets
        fixed_lengths = {
            0x00: 5,  # PACKET_OK (minimum)
            0x01: 2,  # PACKET_ERROR (minimum)
            0x0A: 1,  # PACKET_NO_MORE_MSGS
            0x14: 3,  # PACKET_BATTERY (minimum)
        }
        return fixed_lengths.get(packet_type)
    
    def can_parse_partial(self, packet_type):
        # Some packets can be parsed partially
        return packet_type in [0x12, 0x08, 0x11, 0x07, 0x10, 0x05, 0x0D]
    
    def try_parse_partial(self):
        # Try to parse with available data
        # Return packet if successfully parsed, None otherwise
        # This is packet-type specific
        pass
```

**Usage**:
```python
buffer = PacketBuffer()

def on_notification_received(data):
    packet = buffer.add_data(data)
    if packet:
        parse_and_handle_packet(packet)
```

### Response Handling

1. **Command-Response Pattern**:
   - Send command via TX characteristic
   - Wait for response via RX characteristic (notification)
   - Match response to command using sequence numbers or command type
   - Handle timeout (typically 5 seconds)
   - Use command queue to prevent concurrent commands

2. **Asynchronous Messages**:
   - Device may send messages at any time via RX characteristic
   - Handle `PACKET_MESSAGES_WAITING` (0x83) by polling `GET_MESSAGE` command
   - Parse incoming messages and route to appropriate handlers
   - Buffer partial packets until complete

3. **Response Matching**:
   - Match responses to commands by expected packet type:
     - `APP_START` → `PACKET_OK`
     - `DEVICE_QUERY` → `PACKET_DEVICE_INFO`
     - `GET_CHANNEL` → `PACKET_CHANNEL_INFO`
     - `SET_CHANNEL` → `PACKET_OK` or `PACKET_ERROR`
     - `SEND_CHANNEL_MESSAGE` → `PACKET_MSG_SENT`
     - `GET_MESSAGE` → `PACKET_CHANNEL_MSG_RECV`, `PACKET_CONTACT_MSG_RECV`, or `PACKET_NO_MORE_MSGS`
     - `GET_BATTERY` → `PACKET_BATTERY`

4. **Timeout Handling**:
   - Default timeout: 5 seconds per command
   - On timeout: Log error, clear current command, proceed to next in queue
   - Some commands may take longer (e.g., `SET_CHANNEL` may need 1-2 seconds)
   - Consider longer timeout for channel operations

5. **Error Recovery**:
   - On `PACKET_ERROR`: Log error code, clear current command
   - On connection loss: Clear command queue, attempt reconnection
   - On invalid response: Log warning, clear current command, proceed

---

## Example Implementation Flow

### Initialization

```python
# 1. Scan for MeshCore device
device = scan_for_device("MeshCore")

# 2. Connect to BLE GATT
gatt = connect_to_device(device)

# 3. Discover services and characteristics
service = discover_service(gatt, "0000ff00-0000-1000-8000-00805f9b34fb")
rx_char = discover_characteristic(service, "0000ff01-0000-1000-8000-00805f9b34fb")
tx_char = discover_characteristic(service, "0000ff02-0000-1000-8000-00805f9b34fb")

# 4. Enable notifications on RX characteristic
enable_notifications(rx_char, on_notification_received)

# 5. Send AppStart command
send_command(tx_char, build_app_start())
wait_for_response(PACKET_OK)
```

### Creating a Private Channel

```python
# 1. Generate 16-byte secret
secret_16_bytes = generate_secret(16)  # Use CSPRNG
secret_hex = secret_16_bytes.hex()

# 2. Expand secret to 32 bytes using SHA-512
import hashlib
sha512_hash = hashlib.sha512(secret_16_bytes).digest()
secret_32_bytes = sha512_hash[:32]

# 3. Build SET_CHANNEL command
channel_name = "YourChannelName"
channel_index = 1  # Use 1-7 for private channels
command = build_set_channel(channel_index, channel_name, secret_32_bytes)

# 4. Send command
send_command(tx_char, command)
response = wait_for_response(PACKET_OK)

# 5. Store secret locally (device won't return it)
store_channel_secret(channel_index, secret_hex)
```

### Sending a Message

```python
# 1. Build channel message command
channel_index = 1
message = "Hello, MeshCore!"
timestamp = int(time.time())
command = build_channel_message(channel_index, message, timestamp)

# 2. Send command
send_command(tx_char, command)
response = wait_for_response(PACKET_MSG_SENT)
```

### Receiving Messages

```python
def on_notification_received(data):
    packet_type = data[0]
    
    if packet_type == PACKET_CHANNEL_MSG_RECV or packet_type == PACKET_CHANNEL_MSG_RECV_V3:
        message = parse_channel_message(data)
        handle_channel_message(message)
    elif packet_type == PACKET_MESSAGES_WAITING:
        # Poll for messages
        send_command(tx_char, build_get_message())
```

### QR Code Sharing

```python
import secrets
from urllib.parse import quote

# 1. Generate QR code data
channel_name = "YourChannelName"
# Generate a real secret (NOT the example value from documentation)
secret_bytes = secrets.token_bytes(16)
secret_hex = secret_bytes.hex()

# Example value in documentation: "9b647d242d6e1c5883fde0c5cf5c4c5e"
# DO NOT use example values - always generate your own secure random secrets!

url = f"meshcore://channel/add?name={quote(channel_name)}&secret={secret_hex}"

# 2. Generate QR code image
qr = qrcode.QRCode(version=1, box_size=10, border=5)
qr.add_data(url)
qr.make(fit=True)
img = qr.make_image(fill_color="black", back_color="white")

# 3. Display or save QR code
img.save("channel_qr.png")
```

---

## Best Practices

1. **Connection Management**:
   - Implement auto-reconnect with exponential backoff
   - Handle disconnections gracefully
   - Store last connected device address for quick reconnection

2. **Secret Management**:
   - Always use cryptographically secure random number generators
   - Store secrets securely (encrypted storage)
   - Never log or transmit secrets in plain text
   - Device does not return secrets - you must store them locally

3. **Message Handling**:
   - Poll `GET_MESSAGE` periodically or when `PACKET_MESSAGES_WAITING` is received
   - Handle message chunking for long messages (>133 characters)
   - Implement message deduplication to avoid processing the same message twice

4. **Error Handling**:
   - Implement timeouts for all commands (typically 5 seconds)
   - Handle `PACKET_ERROR` responses appropriately
   - Log errors for debugging but don't expose sensitive information

5. **Channel Management**:
   - Avoid using channel index 0 for private channels
   - Migrate channels from index 0 to 1-7 if needed
   - Query channels after connection to discover existing channels

---

## Platform-Specific Notes

### Android
- Use `BluetoothGatt` API
- Request `BLUETOOTH_CONNECT` and `BLUETOOTH_SCAN` permissions (Android 12+)
- Enable notifications by writing to descriptor `0x2902` with value `0x01` or `0x02`

### iOS
- Use `CoreBluetooth` framework
- Implement `CBPeripheralDelegate` for notifications
- Request Bluetooth permissions in Info.plist

### Python
- Use `bleak` library for cross-platform BLE support
- Handle async/await for BLE operations
- Use `asyncio` for command-response patterns

### JavaScript/Node.js
- Use `noble` or `@abandonware/noble` for BLE
- Handle callbacks or promises for async operations
- Use `Buffer` for binary data manipulation

---

## Troubleshooting

### Connection Issues
- **Device not found**: Ensure device is powered on and advertising
- **Connection timeout**: Check Bluetooth permissions and device proximity
- **GATT errors**: Ensure proper service/characteristic discovery

### Command Issues
- **No response**: Verify notifications are enabled, check connection state
- **Error responses**: Verify command format, check channel index validity
- **Timeout**: Increase timeout value or check device responsiveness

### Message Issues
- **Messages not received**: Poll `GET_MESSAGE` command periodically
- **Duplicate messages**: Implement message deduplication using timestamps/hashes
- **Message truncation**: Split long messages into chunks

### Secret/Channel Issues
- **Secret not working**: Verify secret expansion (SHA-512) is correct
- **Channel not found**: Query channels after connection to discover existing channels
- **Channel index 0**: Migrate to index 1-7 for private channels

---

## References

- MeshCore Python implementation: `meshcore_py-main/src/meshcore/`
- BLE GATT Specification: Bluetooth SIG Core Specification
- ED25519 Key Expansion: RFC 8032

---

**Last Updated**: 2025-01-01
**Protocol Version**: Based on MeshCore v1.36.0+