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Companion Protocol

Last Updated: 2026-07-04
Protocol Version: Companion Firmware v1.16.0+

NOTE: This document is still in development. Some information may be inaccurate.

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.

Official Libraries

Please see the following repos for existing MeshCore Companion Protocol libraries.

JavaScript: https://github.com/meshcore-dev/meshcore.js
Python: https://github.com/meshcore-dev/meshcore_py

Important Security Note

All secrets, hashes, and cryptographic values shown in this guide are example values only.

All hex values, public keys and hashes are for demonstration purposes only
Never use example secrets in production
Always generate new cryptographically secure random secrets
Please implement proper security practices in your implementation
This guide is for protocol documentation only

BLE Connection
Packet Structure
Commands
Channel Management
Message Handling
Response Parsing
Example Implementation Flow
Best Practices
Troubleshooting

BLE Connection

Service and Characteristics

MeshCore Companion devices expose a BLE service with the following UUIDs:

Service UUID: 6E400001-B5A3-F393-E0A9-E50E24DCCA9E
RX Characteristic (App → Firmware): 6E400002-B5A3-F393-E0A9-E50E24DCCA9E
TX Characteristic (Firmware → App): 6E400003-B5A3-F393-E0A9-E50E24DCCA9E

Connection Steps

Scan for Devices
- Scan for BLE devices advertising the MeshCore Service UUID
- Optionally filter by device name (typically contains "MeshCore" prefix)
- Note the device MAC address for reconnection
Connect to GATT
- Connect to the device using the discovered MAC address
- Wait for connection to be established
Discover Services and Characteristics
- Discover the service with UUID 6E400001-B5A3-F393-E0A9-E50E24DCCA9E
- Discover the RX characteristic 6E400002-B5A3-F393-E0A9-E50E24DCCA9E
  - Your app writes to this, the firmware reads from this
- Discover the TX characteristic 6E400003-B5A3-F393-E0A9-E50E24DCCA9E
  - The firmware writes to this, your app reads from this
Enable Notifications
- Subscribe to notifications on the TX characteristic to receive data from the firmware
Send Initial Commands
- Send CMD_APP_START to identify your app to firmware and get radio settings
- Send CMD_DEVICE_QUERY to fetch device info and negotiate supported protocol versions
- Send CMD_SET_DEVICE_TIME to set the firmware clock
- Send CMD_GET_CONTACTS to fetch all contacts
- Send CMD_GET_CHANNEL multiple times to fetch all channel slots
- Send CMD_SYNC_NEXT_MESSAGE to fetch the next message stored in firmware
- Setup listeners for push codes, such as PUSH_CODE_MSG_WAITING or PUSH_CODE_ADVERT
- See Commands section for information on other commands

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

BLE Write Type

When writing commands to the RX 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.

MTU (Maximum Transmission Unit)

The default BLE MTU is 23 bytes (20 bytes payload). For larger commands like SET_CHANNEL (50 bytes), you may need to:

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

Companion Frame Size Limits

Firmware transports use MAX_FRAME_SIZE = 176 as the companion frame buffer size.

When an app advertises target protocol version 14 or newer in CMD_DEVICE_QUERY, firmware emits PACKET_FRAME_FRAGMENT for original firmware-to-app companion frames larger than MAX_FRAME_SIZE. Frames up to 176 bytes are sent unchanged. Each emitted fragment is also kept at or below MAX_FRAME_SIZE. Apps that do not advertise version 14 keep the legacy behavior based on the older single-frame transport limit.

Command Sequencing

Critical: Commands must be sent in the correct sequence:

After Connection:
- Wait for BLE connection to be established
- Wait for services/characteristics to be discovered
- Wait for notifications to be enabled
- Now you can safely send commands to the firmware
Command-Response Matching:
- Send one command at a time
- Wait for a response before sending another command
- Use a timeout (typically 5 seconds)
- Match response to command by type (e.g: CMD_GET_CHANNEL → RESP_CODE_CHANNEL_INFO)

Command Queue Management

For reliable operation, implement a command queue.

Queue Structure:

Maintain a queue of pending commands
Track which command is currently waiting for a response
Only send next command after receiving response or timeout

Error Handling:

On timeout, clear current command, process next in queue
On error, log error, clear current command, process next

Packet Structure

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

Commands: Sent from app to firmware via RX characteristic
Responses: Received from firmware via TX characteristic notifications
All multi-byte integers: Little-endian byte order (except CayenneLPP which is Big-endian)
All strings: UTF-8 encoding

Most packets follow this format:

[Packet Type (1 byte)] [Data (variable length)]

The first byte indicates the packet type (see Response Parsing).

Commands

1. App Start

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

Command Format:

Byte 0: 0x01
Bytes 1-7: Reserved (currently ignored by firmware)
Bytes 8+: Application name (UTF-8, optional)

Example (hex):

01 00 00 00 00 00 00 00 6d 63 63 6c 69

Response: PACKET_SELF_INFO (0x05)

2. Device Query

Purpose: Query device information.

Command Format:

Byte 0: 0x16
Byte 1: App target protocol version

Example (hex):

16 0E

Set byte 1 to the highest companion protocol version the app understands. Firmware uses this value to decide whether it may emit newer optional frame formats. Apps that support PACKET_FRAME_FRAGMENT should send 0x0E (14) or higher.

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

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 34-49: Secret (16 bytes)

Total Length: 50 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 (16 bytes):

For private channels: 16-byte secret
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)
    [16 bytes of secret]

Note: The 32-byte secret variant is unsupported and returns PACKET_ERROR.

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. Send Channel Data Datagram

Purpose: Send a binary datagram to a channel. Unlike channel text messages, datagrams carry no built-in sender identity and no timestamp — applications needing either must encode them inside the binary payload.

Command Format:

Byte 0:                         0x3E
Byte 1:                         Channel Index (0-7)
Byte 2:                         Path Length (0xFF = flood, otherwise actual path length)
Bytes 3 .. 2+path_len:          Path (omitted when path_len == 0xFF)
Next 2 bytes (little-endian):   Data Type (`data_type`, uint16)
Remaining bytes:                Binary payload (variable length)

Example (flood, DATA_TYPE_DEV, payload A1 B2 C3, channel 1):

3E 01 FF FF FF A1 B2 C3

Data Type / Transport Mapping:

0x0000 (DATA_TYPE_RESERVED) is invalid and rejected with PACKET_ERROR.
0xFFFF (DATA_TYPE_DEV) is the developer namespace for experimenting and developing apps.
Values 0x0001–0xFFFE are available for registered application/community namespaces. See the Registered data_type values table below.

Limits:

Maximum payload length is MAX_CHANNEL_DATA_LENGTH = MAX_FRAME_SIZE - 9 = 163 bytes.
Larger payloads are rejected with PACKET_ERROR (ERR_CODE_ILLEGAL_ARG).

Response: PACKET_OK (0x00) on success, or PACKET_ERROR (0x01) with one of:

ERR_CODE_NOT_FOUND (2) — unknown channel_idx
ERR_CODE_ILLEGAL_ARG (6) — invalid path_len, reserved data_type (0x0000), or payload larger than MAX_CHANNEL_DATA_LENGTH
ERR_CODE_TABLE_FULL (3) — outbound send queue is full; retry later

Inbound datagrams are delivered to the host via RESP_CODE_CHANNEL_DATA_RECV (0x1B); see Receive Channel Data Datagram.

Registered `data_type` values

data_type is an application identifier, not a payload-format identifier. Each registered value identifies an application that owns its own internal payload schemas. The firmware does not inspect payload contents — data_type is transported opaquely.

Value	Constant	Purpose
0x0000	`DATA_TYPE_RESERVED`	Reserved; invalid on send
0x0001 – 0x00FF	—	Reserved for internal use
0x0100 – 0xFEFF	—	Registered application namespaces (see number_allocations.md)
0xFF00 – 0xFFFE	—	Testing/development; no registration required
0xFFFF	`DATA_TYPE_DEV`	Developer/experimental namespace

To register a new application, submit a PR adding a row to the table in docs/number_allocations.md. Internal sub-formats within an allocated application ID are owned by that application and are not tracked in MeshCore firmware or this document.

Receive Channel Data Datagram

Inbound group datagrams (radio-level PAYLOAD_TYPE_GRP_DATA, 0x06) are forwarded to the host as RESP_CODE_CHANNEL_DATA_RECV notifications.

Frame Format (RESP_CODE_CHANNEL_DATA_RECV, 0x1B):

Byte 0:                 0x1B (packet type)
Byte 1:                 SNR (signed int8, scaled ×4 — divide by 4.0 to recover dB)
Bytes 2-3:              Reserved (clients MUST ignore)
Byte 4:                 Channel Index (0-7)
Byte 5:                 Path Length (actual path length when flooded, otherwise 0xFF for direct)
Bytes 6-7:              Data Type (uint16 little-endian)
Byte 8:                 Data Length
Bytes 9 .. 8+data_len:  Payload

Path bytes are not forwarded: Only path_len is reported in the receive frame — the path itself is not copied to the host. There are no path bytes between byte 5 and the data_type field at bytes 6–7, regardless of path_len.

Path Length semantics differ between send and receive:

Direction	`path_len = 0xFF`	`path_len ≠ 0xFF`
Send	Flood the network	Direct route; the encoded path follows (low 6 bits = hash count, top 2 bits + 1 = hash size; on-wire byte count = `hash_count × hash_size`)
Receive	Packet arrived via direct route	Packet was flooded; this is the encoded `pkt->path_len` field as observed (no path bytes follow)

In other words, the meaning of 0xFF is inverted between the two directions, and on receive the field carries metadata only — never a routable path. path_len is an encoded byte (see Packet::isValidPathLen / Packet::writePath in src/Packet.cpp), not a raw byte count.

Note: The device may also emit PACKET_MESSAGES_WAITING (0x83) to notify the host that datagrams are queued; poll with CMD_SYNC_NEXT_MESSAGE (0x0A) to retrieve them.

Parsing Pseudocode:

def parse_channel_data_recv(data):
    if len(data) < 9:
        return None
    snr_byte = data[1]
    snr = (snr_byte if snr_byte < 128 else snr_byte - 256) / 4.0
    channel_idx = data[4]
    path_len = data[5]
    data_type = int.from_bytes(data[6:8], 'little')
    data_len = data[8]
    if 9 + data_len > len(data):
        return None
    payload = data[9:9 + data_len]
    return {
        'snr': snr,
        'channel_idx': channel_idx,
        'path_len': path_len,
        'data_type': data_type,
        'payload': bytes(payload),
    }

7. Get Message

Purpose: Request the next queued message from the device.

Command Format:

Byte 0: 0x0A

Command Format With Fragment ACK (app target version 14+ only):

Byte 0: 0x0A
Byte 1: Flags
Bytes 2-3: ACK Fragment ID (uint16 little-endian)
Byte 4: ACK Fragment Index

Flags:

Bit 0 (0x01): Fragment ACK is present

Example (hex):

0A

Example With Fragment ACK (hex, ACK fragment ID 0x1234, index 1):

0A 01 34 12 01

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_CHANNEL_DATA_RECV (0x1B) for channel data datagrams
PACKET_FRAME_FRAGMENT (0x91) for one fragment of an oversized queued frame when the app advertised target protocol version 14+
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.

For fragmented queued frames, apps that advertised target protocol version 14+ must ACK the previous fragment in the next CMD_SYNC_NEXT_MESSAGE request before the firmware advances to the next fragment. If the ACK is missing or does not match the last sent fragment, the firmware repeats that fragment. After the app ACKs the last fragment, the firmware removes the original queued frame and returns the next queued frame or PACKET_NO_MORE_MSGS.

8. Get Battery and Storage

Purpose: Query device battery voltage and storage usage.

Command Format:

Byte 0: 0x14

Example (hex):

Response: PACKET_BATTERY (0x0C) with battery millivolts and storage information

Channel Management

Channel Types

Public Channel
- Uses a publicly known 16-byte key: 8b3387e9c5cdea6ac9e5edbaa115cd72
- Anyone can join this channel, messages should be considered public
- Used as the default public group chat
Hashtag Channels
- Uses a secret key derived from the channel name
- It is the first 16 bytes of sha256("#test")
- For example hashtag channel #test has the key: 9cd8fcf22a47333b591d96a2b848b73f
- Used as a topic based public group chat, separate from the default public channel
Private Channels
- Uses a randomly generated 16-byte secret key
- Messages should be considered private between those that know the secret
- Users should keep the key secret, and only share with those you want to communicate with
- Used as a secure private group chat

Channel Lifecycle

Set Channel:
- Fetch all channel slots, and find one with empty name and all-zero secret
- Generate or provide a 16-byte secret
- Send CMD_SET_CHANNEL with name and a 16-byte secret
Get Channel:
- Send CMD_GET_CHANNEL with channel index
- Parse RESP_CODE_CHANNEL_INFO response
Delete Channel:
- Send CMD_SET_CHANNEL with empty name and all-zero secret
- Or overwrite with a new channel

Message Handling

Receiving Messages

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

Channel Messages:
- PACKET_CHANNEL_MSG_RECV (0x08) - Standard format
- PACKET_CHANNEL_MSG_RECV_V3 (0x11) - Version 3 with SNR
Contact Messages:
- PACKET_CONTACT_MSG_RECV (0x07) - Standard format
- PACKET_CONTACT_MSG_RECV_V3 (0x10) - Version 3 with SNR
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:

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:

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).

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

Terminology

This document uses a spec-level naming convention (PACKET_*) for bytes the firmware sends back to the host. In the firmware source these same values are split across two #define families by purpose:

RESP_CODE_* — direct replies to a command (e.g. RESP_CODE_CHANNEL_DATA_RECV = PACKET_CHANNEL_DATA_RECV = 0x1B).
PUSH_CODE_* — asynchronous notifications not tied to a specific command (e.g. PUSH_CODE_MSG_WAITING = PACKET_MESSAGES_WAITING = 0x83).

Byte values are authoritative; names are aliases. When reading firmware source, RESP_CODE_X / PUSH_CODE_X correspond to this doc's PACKET_X of the same numeric value.

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
0x1B	PACKET_CHANNEL_DATA_RECV	Channel data datagram
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)
0x91	PACKET_FRAME_FRAGMENT	Fragment of a larger frame

Parsing Responses

PACKET_FRAME_FRAGMENT (0x91, app target version 14+):

Firmware emits this wrapper only when the app has advertised target protocol version 14 or newer in CMD_DEVICE_QUERY, and only when an original companion frame is larger than MAX_FRAME_SIZE (176 bytes). Frames up to 176 bytes are sent unchanged.

Queued messages are stored by the firmware as full logical companion frames. The firmware chooses the delivery format when the app polls CMD_SYNC_NEXT_MESSAGE: apps that advertised protocol version 14+ receive oversized queued frames as PACKET_FRAME_FRAGMENT; older apps receive the same legacy truncated single-frame form they received before fragmentation support. Queued fragments require ACKs via CMD_SYNC_NEXT_MESSAGE; the firmware repeats the last sent fragment until the app acknowledges it.

Oversized live push frames, such as raw packet data, control data, and RF log data, may also be emitted as PACKET_FRAME_FRAGMENT when the app advertised protocol version 14+. Live push frames up to MAX_FRAME_SIZE are sent unchanged for v14 apps. Live push fragments are not ACKed by CMD_SYNC_NEXT_MESSAGE.

Each fragment frame is also capped to MAX_FRAME_SIZE (176 bytes). With the 10-byte fragment header, the maximum chunk size is 166 bytes.

The fragment payload contains a chunk of the original companion frame, including that original frame's byte 0. Apps must reassemble all chunks with the same Fragment ID, then parse the reconstructed bytes as the original companion frame.

Byte 0: 0x91
Bytes 1-2: Fragment ID (uint16 little-endian)
Byte 3: Fragment Index (0-based)
Byte 4: Fragment Count
Byte 5: Original Frame Type (copy of reconstructed byte 0)
Bytes 6-7: Original Frame Length (uint16 little-endian)
Bytes 8-9: Chunk Offset in original frame (uint16 little-endian)
Bytes 10+: Chunk bytes

Fragment IDs are scoped to the current device connection/session and may wrap. Apps should discard incomplete fragment sets on disconnect, timeout, duplicate metadata mismatch, or if the accumulated chunks do not exactly match the advertised original frame length.

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 34-49: Secret (16 bytes)

Note: The device returns the 16-byte channel secret in this response.

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)
Byte 80: Client repeat enabled/preferred (firmware v9+)
Byte 81: Path hash mode (firmware v10+)

Parsing Pseudocode:

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 Voltage (16-bit little-endian, millivolts)
Bytes 3-6: Used Storage (32-bit little-endian, KB)
Bytes 7-10: Total Storage (32-bit little-endian, KB)

Parsing Pseudocode:

def parse_battery(data):
    if len(data) < 3:
        return None
    
    mv = int.from_bytes(data[1:3], 'little')
    info = {'battery_mv': mv}
    
    if len(data) >= 11:
        info['used_kb'] = int.from_bytes(data[3:7], 'little')
        info['total_kb'] = int.from_bytes(data[7:11], 'little')
    
    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, no null terminator required)

Parsing Pseudocode:

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: Route Flag (0 = direct, 1 = flood)
Bytes 2-5: Tag / Expected ACK (4 bytes, little-endian)
Bytes 6-9: Suggested Timeout (32-bit little-endian, milliseconds)

PACKET_ACK (0x82):

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

Error Codes

PACKET_ERROR (0x01) carries a single-byte error code in byte 1. Values match the ERR_CODE_* constants defined in examples/companion_radio/MyMesh.cpp:

Code	Constant (firmware)	Description
1	`ERR_CODE_UNSUPPORTED_CMD`	Unknown or unsupported command byte / sub-command
2	`ERR_CODE_NOT_FOUND`	Target not found (channel, contact, message, etc.)
3	`ERR_CODE_TABLE_FULL`	Internal queue or table is full — retry later
4	`ERR_CODE_BAD_STATE`	Operation not valid in current device state (e.g. iterator already running)
5	`ERR_CODE_FILE_IO_ERROR`	Filesystem or storage I/O failure
6	`ERR_CODE_ILLEGAL_ARG`	Invalid argument (bad length, out-of-range value, reserved field, etc.)

Note: Error codes may vary by firmware version. Always check byte 1 of PACKET_ERROR response, and treat unknown codes as generic errors.

Frame Handling

BLE implementations enqueue and deliver one protocol frame per BLE write/notification at the firmware layer.

Apps should treat each characteristic write/notification as exactly one companion protocol frame
Apps should still validate frame lengths before parsing
For app target protocol version 14+, apps should accept unfragmented firmware-to-app frames up to MAX_FRAME_SIZE (176 bytes) and PACKET_FRAME_FRAGMENT frames up to the same size
Future transports or firmware revisions may differ, so avoid assuming fixed payload sizes beyond the negotiated protocol behavior
Apps that send target protocol version 14+ in CMD_DEVICE_QUERY must handle PACKET_FRAME_FRAGMENT and reassemble the original companion frame before normal parsing

Response Handling

Command-Response Pattern:
- Send command via RX characteristic
- Wait for response via TX characteristic (notification)
- Match response to command using sequence numbers or command type
- Handle timeout (typically 5 seconds)
- Use command queue to prevent concurrent commands
Asynchronous Messages:
- Device may send messages at any time via TX characteristic
- Handle PACKET_MESSAGES_WAITING (0x83) by polling GET_MESSAGE command
- Parse incoming messages and route to appropriate handlers
- Validate frame length before decoding
Response Matching:
- Match responses to commands by expected packet type:
  - APP_START → PACKET_SELF_INFO
  - 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, PACKET_CHANNEL_DATA_RECV, or PACKET_NO_MORE_MSGS
  - SEND_CHANNEL_DATA → PACKET_OK or PACKET_ERROR
  - GET_BATTERY → PACKET_BATTERY
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
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

# 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, "6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
rx_char = discover_characteristic(service, "6E400002-B5A3-F393-E0A9-E50E24DCCA9E")
tx_char = discover_characteristic(service, "6E400003-B5A3-F393-E0A9-E50E24DCCA9E")

# 4. Enable notifications on TX characteristic
enable_notifications(tx_char, on_notification_received)

# 5. Send AppStart command
send_command(rx_char, build_app_start())
wait_for_response(PACKET_SELF_INFO)

Creating a Private Channel

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

# 2. 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_16_bytes)

# 3. Send command
send_command(rx_char, command)
response = wait_for_response(PACKET_OK)

# 4. Store secret locally
store_channel_secret(channel_index, secret_hex)

Sending a Message

# 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(rx_char, command)
response = wait_for_response(PACKET_MSG_SENT)

Receiving Messages

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(rx_char, build_get_message())

Best Practices

Connection Management:
- Implement auto-reconnect with exponential backoff
- Handle disconnections gracefully
- Store last connected device address for quick reconnection
Secret Management:
- Always use cryptographically secure random number generators
- Store secrets securely (encrypted storage)
- Never log or transmit secrets in plain text
Message Handling:
- Send CMD_SYNC_NEXT_MESSAGE when PUSH_CODE_MSG_WAITING is received
- Implement message deduplication to avoid displaying the same message twice
Channel Management:
- Fetch all channel slots even if you encounter an empty slot
- Ideally save new channels into the first empty slot
Error Handling:
- Implement timeouts for all commands (typically 5 seconds)
- Handle RESP_CODE_ERR responses appropriately

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 and check error code
Timeout: Increase timeout value or try again

Message Issues

Messages not received: Poll GET_MESSAGE command periodically
Duplicate messages: Implement message deduplication using timestamp/content as a unique id
Message truncation: Send long messages as separate shorter messages

38 KiB Raw Blame History

Companion Protocol

Official Libraries

Important Security Note

Table of Contents

BLE Connection

Service and Characteristics

Connection Steps

BLE Write Type

MTU (Maximum Transmission Unit)

Companion Frame Size Limits

Command Sequencing

Command Queue Management

Packet Structure

Commands

1. App Start

2. Device Query

3. Get Channel Info

4. Set Channel

5. Send Channel Message

6. Send Channel Data Datagram

Registered data_type values

Receive Channel Data Datagram

7. Get Message

8. Get Battery and Storage

Channel Management

Channel Types

Channel Lifecycle

Message Handling

Receiving Messages

Contact Message Format

Channel Message Format

Sending Messages

Response Parsing

Terminology

Packet Types

Parsing Responses

Error Codes

Frame Handling

Response Handling

Example Implementation Flow

Initialization

Creating a Private Channel

Sending a Message

Receiving Messages

Best Practices

Troubleshooting

Connection Issues

Command Issues

Message Issues

38 KiB

Raw Blame History

Registered `data_type` values