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# Companion Protocol
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-- **Last Updated**: 2026-01-03
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+- **Last Updated**: 2026-03-08
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- **Protocol Version**: Companion Firmware v1.12.0+
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> NOTE: This document is still in development. Some information may be inaccurate.
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@@ -100,7 +100,7 @@ When writing commands to the RX characteristic, specify the write type:
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### MTU (Maximum Transmission Unit)
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-The default BLE MTU is 23 bytes (20 bytes payload). For larger commands like `SET_CHANNEL` (66 bytes), you may need to:
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+The default BLE MTU is 23 bytes (20 bytes payload). For larger commands like `SET_CHANNEL` (50 bytes), you may need to:
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1. **Request Larger MTU**: Request MTU of 512 bytes if supported
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- Android: `gatt.requestMtu(512)`
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@@ -167,16 +167,16 @@ The first byte indicates the packet type (see [Response Parsing](#response-parsi
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**Command Format**:
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```
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Byte 0: 0x01
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-Byte 1: 0x03
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-Bytes 2-10: "mccli" (ASCII, null-padded to 9 bytes)
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+Bytes 1-7: Reserved (currently ignored by firmware)
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+Bytes 8+: Application name (UTF-8, optional)
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```
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**Example** (hex):
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```
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-01 03 6d 63 63 6c 69 00 00 00 00
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+01 00 00 00 00 00 00 00 6d 63 63 6c 69
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```
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-**Response**: `PACKET_OK` (0x00)
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+**Response**: `PACKET_SELF_INFO` (0x05)
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---
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@@ -216,8 +216,6 @@ Byte 1: Channel Index (0-7)
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**Response**: `PACKET_CHANNEL_INFO` (0x12) with channel details
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-**Note**: The device does not return channel secrets for security reasons. Store secrets locally when creating channels.
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-
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---
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### 4. Set Channel
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@@ -229,10 +227,10 @@ Byte 1: Channel Index (0-7)
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Byte 0: 0x20
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Byte 1: Channel Index (0-7)
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Bytes 2-33: Channel Name (32 bytes, UTF-8, null-padded)
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-Bytes 34-65: Secret (32 bytes)
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+Bytes 34-49: Secret (16 bytes)
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```
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-**Total Length**: 66 bytes
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+**Total Length**: 50 bytes
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**Channel Index**:
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- Index 0: Reserved for public channels (no secret)
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@@ -243,16 +241,18 @@ Bytes 34-65: Secret (32 bytes)
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- Maximum 32 bytes
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- Padded with null bytes (0x00) if shorter
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-**Secret Field** (32 bytes):
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-- For **private channels**: 32-byte secret
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+**Secret Field** (16 bytes):
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+- For **private channels**: 16-byte secret
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- For **public channels**: All zeros (0x00)
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**Example** (create channel "YourChannelName" at index 1 with secret):
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```
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20 01 53 4D 53 00 00 ... (name padded to 32 bytes)
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- [32 bytes of secret]
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+ [16 bytes of secret]
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```
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+**Note**: The 32-byte secret variant is unsupported and returns `PACKET_ERROR`.
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+
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**Response**: `PACKET_OK` (0x00) on success, `PACKET_ERROR` (0x01) on failure
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---
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@@ -304,9 +304,9 @@ Byte 0: 0x0A
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---
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-### 7. Get Battery
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+### 7. Get Battery and Storage
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-**Purpose**: Query device battery level.
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+**Purpose**: Query device battery voltage and storage usage.
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**Command Format**:
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```
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@@ -318,7 +318,7 @@ Byte 0: 0x14
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14
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```
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-**Response**: `PACKET_BATTERY` (0x0C) with battery percentage
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+**Response**: `PACKET_BATTERY` (0x0C) with battery millivolts and storage information
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---
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@@ -346,7 +346,7 @@ Byte 0: 0x14
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1. **Set Channel**:
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- Fetch all channel slots, and find one with empty name and all-zero secret
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- Generate or provide a 16-byte secret
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- - Send `CMD_SET_CHANNEL` with name and secret
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+ - Send `CMD_SET_CHANNEL` with name and a 16-byte secret
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2. **Get Channel**:
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- Send `CMD_GET_CHANNEL` with channel index
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- Parse `RESP_CODE_CHANNEL_INFO` response
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@@ -360,7 +360,7 @@ Byte 0: 0x14
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### Receiving Messages
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-Messages are received via the RX characteristic (notifications). The device sends:
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+Messages are received via the TX characteristic (notifications). The device sends:
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1. **Channel Messages**:
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- `PACKET_CHANNEL_MSG_RECV` (0x08) - Standard format
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@@ -544,10 +544,10 @@ Byte 1: Error code (optional)
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Byte 0: 0x12
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Byte 1: Channel Index
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Bytes 2-33: Channel Name (32 bytes, null-terminated)
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-Bytes 34-65: Secret (32 bytes, but device typically only returns 20 bytes total)
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+Bytes 34-49: Secret (16 bytes)
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```
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-**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.
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+**Note**: The device returns the 16-byte channel secret in this response.
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**PACKET_DEVICE_INFO** (0x0D):
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```
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@@ -562,6 +562,8 @@ Bytes 4-7: BLE PIN (32-bit little-endian)
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Bytes 8-19: Firmware Build (12 bytes, UTF-8, null-padded)
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Bytes 20-59: Model (40 bytes, UTF-8, null-padded)
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Bytes 60-79: Version (20 bytes, UTF-8, null-padded)
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+Byte 80: Client repeat enabled/preferred (firmware v9+)
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+Byte 81: Path hash mode (firmware v10+)
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```
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**Parsing Pseudocode**:
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@@ -587,9 +589,7 @@ def parse_device_info(data):
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**PACKET_BATTERY** (0x0C):
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```
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Byte 0: 0x0C
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-Bytes 1-2: Battery Level (16-bit little-endian, percentage 0-100)
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-
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-Optional (if data size > 3):
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+Bytes 1-2: Battery Voltage (16-bit little-endian, millivolts)
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Bytes 3-6: Used Storage (32-bit little-endian, KB)
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Bytes 7-10: Total Storage (32-bit little-endian, KB)
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```
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@@ -600,14 +600,12 @@ def parse_battery(data):
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if len(data) < 3:
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return None
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- level = int.from_bytes(data[1:3], 'little')
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- info = {'level': level}
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+ mv = int.from_bytes(data[1:3], 'little')
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+ info = {'battery_mv': mv}
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- if len(data) > 3:
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- used_kb = int.from_bytes(data[3:7], 'little')
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- total_kb = int.from_bytes(data[7:11], 'little')
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- info['used_kb'] = used_kb
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- info['total_kb'] = total_kb
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+ if len(data) >= 11:
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+ info['used_kb'] = int.from_bytes(data[3:7], 'little')
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+ info['total_kb'] = int.from_bytes(data[7:11], 'little')
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return info
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```
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@@ -629,7 +627,7 @@ Bytes 48-51: Radio Frequency (32-bit little-endian, divided by 1000.0)
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Bytes 52-55: Radio Bandwidth (32-bit little-endian, divided by 1000.0)
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Byte 56: Radio Spreading Factor
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Byte 57: Radio Coding Rate
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-Bytes 58+: Device Name (UTF-8, variable length, null-terminated)
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+Bytes 58+: Device Name (UTF-8, variable length, no null terminator required)
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```
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**Parsing Pseudocode**:
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@@ -680,9 +678,9 @@ def parse_self_info(data):
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**PACKET_MSG_SENT** (0x06):
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```
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Byte 0: 0x06
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-Byte 1: Message Type
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-Bytes 2-5: Expected ACK (4 bytes, hex)
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-Bytes 6-9: Suggested Timeout (32-bit little-endian, seconds)
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+Byte 1: Route Flag (0 = direct, 1 = flood)
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+Bytes 2-5: Tag / Expected ACK (4 bytes, little-endian)
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+Bytes 6-9: Suggested Timeout (32-bit little-endian, milliseconds)
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```
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**PACKET_ACK** (0x82):
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@@ -710,89 +708,32 @@ Bytes 1-6: ACK Code (6 bytes, hex)
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**Note**: Error codes may vary by firmware version. Always check byte 1 of `PACKET_ERROR` response.
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-### Partial Packet Handling
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-
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-BLE notifications may arrive in chunks, especially for larger packets. Implement buffering:
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-
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-**Implementation**:
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-```python
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-class PacketBuffer:
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- def __init__(self):
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- self.buffer = bytearray()
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- self.expected_length = None
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-
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- def add_data(self, data):
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- self.buffer.extend(data)
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-
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- # Check if we have a complete packet
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- if len(self.buffer) >= 1:
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- packet_type = self.buffer[0]
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-
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- # Determine expected length based on packet type
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- expected = self.get_expected_length(packet_type)
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-
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- if expected is not None and len(self.buffer) >= expected:
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- # Complete packet
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- packet = bytes(self.buffer[:expected])
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- self.buffer = self.buffer[expected:]
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- return packet
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- elif expected is None:
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- # Variable length packet - try to parse what we have
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- # Some packets have minimum length requirements
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- if self.can_parse_partial(packet_type):
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- return self.try_parse_partial()
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-
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- return None # Incomplete packet
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-
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- def get_expected_length(self, packet_type):
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- # Fixed-length packets
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- fixed_lengths = {
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- 0x00: 5, # PACKET_OK (minimum)
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- 0x01: 2, # PACKET_ERROR (minimum)
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- 0x0A: 1, # PACKET_NO_MORE_MSGS
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- 0x14: 3, # PACKET_BATTERY (minimum)
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- }
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- return fixed_lengths.get(packet_type)
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-
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- def can_parse_partial(self, packet_type):
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- # Some packets can be parsed partially
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- return packet_type in [0x12, 0x08, 0x11, 0x07, 0x10, 0x05, 0x0D]
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-
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- def try_parse_partial(self):
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- # Try to parse with available data
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- # Return packet if successfully parsed, None otherwise
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- # This is packet-type specific
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- pass
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-```
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+### Frame Handling
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-**Usage**:
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-```python
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-buffer = PacketBuffer()
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+BLE implementations enqueue and deliver one protocol frame per BLE write/notification at the firmware layer.
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-def on_notification_received(data):
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- packet = buffer.add_data(data)
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- if packet:
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- parse_and_handle_packet(packet)
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-```
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+- Apps should treat each characteristic write/notification as exactly one companion protocol frame
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+- Apps should still validate frame lengths before parsing
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+- Future transports or firmware revisions may differ, so avoid assuming fixed payload sizes for variable-length responses
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### Response Handling
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1. **Command-Response Pattern**:
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- - Send command via TX characteristic
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- - Wait for response via RX characteristic (notification)
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+ - Send command via RX characteristic
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+ - Wait for response via TX characteristic (notification)
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- Match response to command using sequence numbers or command type
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- Handle timeout (typically 5 seconds)
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- Use command queue to prevent concurrent commands
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2. **Asynchronous Messages**:
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- - Device may send messages at any time via RX characteristic
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+ - Device may send messages at any time via TX characteristic
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- Handle `PACKET_MESSAGES_WAITING` (0x83) by polling `GET_MESSAGE` command
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- Parse incoming messages and route to appropriate handlers
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- - Buffer partial packets until complete
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+ - Validate frame length before decoding
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3. **Response Matching**:
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- Match responses to commands by expected packet type:
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- - `APP_START` → `PACKET_OK`
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+ - `APP_START` → `PACKET_SELF_INFO`
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- `DEVICE_QUERY` → `PACKET_DEVICE_INFO`
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- `GET_CHANNEL` → `PACKET_CHANNEL_INFO`
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- `SET_CHANNEL` → `PACKET_OK` or `PACKET_ERROR`
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@@ -825,16 +766,16 @@ device = scan_for_device("MeshCore")
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gatt = connect_to_device(device)
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# 3. Discover services and characteristics
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-service = discover_service(gatt, "0000ff00-0000-1000-8000-00805f9b34fb")
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-rx_char = discover_characteristic(service, "0000ff01-0000-1000-8000-00805f9b34fb")
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-tx_char = discover_characteristic(service, "0000ff02-0000-1000-8000-00805f9b34fb")
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+service = discover_service(gatt, "6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
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+rx_char = discover_characteristic(service, "6E400002-B5A3-F393-E0A9-E50E24DCCA9E")
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+tx_char = discover_characteristic(service, "6E400003-B5A3-F393-E0A9-E50E24DCCA9E")
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-# 4. Enable notifications on RX characteristic
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-enable_notifications(rx_char, on_notification_received)
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+# 4. Enable notifications on TX characteristic
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+enable_notifications(tx_char, on_notification_received)
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# 5. Send AppStart command
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-send_command(tx_char, build_app_start())
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-wait_for_response(PACKET_OK)
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+send_command(rx_char, build_app_start())
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+wait_for_response(PACKET_SELF_INFO)
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```
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### Creating a Private Channel
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@@ -844,21 +785,16 @@ wait_for_response(PACKET_OK)
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secret_16_bytes = generate_secret(16) # Use CSPRNG
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secret_hex = secret_16_bytes.hex()
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-# 2. Expand secret to 32 bytes using SHA-512
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-import hashlib
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-sha512_hash = hashlib.sha512(secret_16_bytes).digest()
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-secret_32_bytes = sha512_hash[:32]
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-
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-# 3. Build SET_CHANNEL command
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+# 2. Build SET_CHANNEL command
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channel_name = "YourChannelName"
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channel_index = 1 # Use 1-7 for private channels
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-command = build_set_channel(channel_index, channel_name, secret_32_bytes)
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+command = build_set_channel(channel_index, channel_name, secret_16_bytes)
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-# 4. Send command
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-send_command(tx_char, command)
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+# 3. Send command
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+send_command(rx_char, command)
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response = wait_for_response(PACKET_OK)
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-# 5. Store secret locally (device won't return it)
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+# 4. Store secret locally
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store_channel_secret(channel_index, secret_hex)
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```
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@@ -872,7 +808,7 @@ timestamp = int(time.time())
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command = build_channel_message(channel_index, message, timestamp)
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# 2. Send command
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-send_command(tx_char, command)
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+send_command(rx_char, command)
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response = wait_for_response(PACKET_MSG_SENT)
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```
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@@ -887,7 +823,7 @@ def on_notification_received(data):
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handle_channel_message(message)
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elif packet_type == PACKET_MESSAGES_WAITING:
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# Poll for messages
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- send_command(tx_char, build_get_message())
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+ send_command(rx_char, build_get_message())
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```
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---
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