ZephCore/zephcore/ARCHITECTURE.md

ZephCore Architecture Guide

Comprehensive developer reference for the ZephCore codebase — a Zephyr RTOS port of the Arduino MeshCore LoRa mesh networking firmware.

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Table of Contents

1. Project Overview
2. Directory Structure
3. Layer Architecture
4. Core Mesh Engine
5. Radio Subsystem
6. Application Layer
7. Hardware Adapters
8. UI Subsystem
9. Build System
10. Board Matrix
11. Packet Format Reference
12. BLE Protocol Reference
13. Data Storage
14. Key Call Flows

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1. Project Overview

ZephCore is a LoRa mesh networking firmware running on Zephyr RTOS. It supports two device roles:

• Companion: BLE-connected device paired with a phone app. Full contact/channel/message management.
• Repeater: Autonomous headless relay node. CLI administration via authenticated mesh connections or serial UART.

Supported hardware: nRF52840, nRF54L15, ESP32-C3/C6/S3, EFR32MG24 — all with SX1262 or LR1110 LoRa radios.

Upstream Relationship

ZephCore is a port of Arduino MeshCore. The core mesh protocol (Mesh.cpp, Dispatcher.cpp, Packet.cpp, Identity.cpp, Utils.cpp) is shared code. Adapters (adapters/) bridge MeshCore's HAL interfaces to Zephyr APIs. Binary file formats (prefs, contacts, channels) are byte-compatible with Arduino MeshCore.

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2. Directory Structure

zephcore/
├── src/                    # Core mesh engine (shared with Arduino MeshCore)
│   ├── Mesh.cpp            # Routing protocol: flood, direct, dedup, adverts
│   ├── Dispatcher.cpp      # Packet queue, radio scheduling, CAD, duty cycle
│   ├── Packet.cpp          # Packet serialization, hash, wire format
│   ├── Identity.cpp        # Ed25519 key management, ECDH shared secrets
│   ├── Utils.cpp           # AES-ECB encrypt, HMAC-SHA256, MAC
│   ├── StaticPoolPacketManager.cpp  # Fixed-size packet pool (24 slots)
│   ├── main_companion.cpp  # Companion mode entry point + event loop
│   └── main_repeater.cpp   # Repeater mode entry point + event loop
│
├── include/mesh/           # Core interfaces (shared with Arduino MeshCore)
│   ├── Mesh.h, Dispatcher.h, Packet.h, Identity.h, Utils.h
│   ├── MeshCore.h          # Constants: key sizes, packet limits
│   ├── Radio.h             # Abstract radio interface
│   ├── Board.h, Clock.h, RNG.h, RTC.h  # HAL interfaces
│   ├── LoRaConfig.h        # Default radio parameters
│   ├── RadioIncludes.h     # Compile-time radio driver selection
│   ├── SimpleMeshTables.h  # Hash-based packet deduplication
│   └── StaticPoolPacketManager.h  # Fixed pool allocator
│
├── adapters/               # Zephyr HAL implementations
│   ├── radio/              # LoRa radio drivers
│   │   ├── LoRaRadioBase.cpp/h    # Shared TX/RX state machine, noise floor, AGC
│   │   ├── SX126xRadio.cpp/h      # SX1262 adapter (native Zephyr driver)
│   │   ├── LR1110Radio.cpp/h      # LR1110 adapter (patched Zephyr driver)
│   │   ├── radio_common.h         # Shared radio types and constants
│   │   └── lr11xx/                # LR11xx low-level HAL (SPI, GPIO, Semtech SDK)
│   ├── ble/ZephyrBLE.cpp/h        # BLE NUS service, pairing, TX congestion
│   ├── board/ZephyrBoard.cpp/h    # Battery ADC, LEDs, reboot, bootloader
│   ├── clock/                     # Millisecond uptime + software RTC
│   ├── datastore/ZephyrDataStore.cpp/h  # LittleFS persistence
│   ├── gps/ZephyrGPSManager.cpp/h      # GNSS state machine, power mgmt
│   ├── ota/wifi_ota.c/h           # WiFi SoftAP + HTTP firmware upload
│   ├── rng/ZephyrRNG.cpp/h        # Hardware CSPRNG with PRNG fallback
│   ├── sensors/                   # I2C env sensors + power monitors
│   └── usb/                       # USB CDC for companion + repeater
│
├── app/                    # Application layer
│   ├── CompanionMesh.cpp/h       # Phone-connected companion logic
│   ├── RepeaterMesh.cpp/h        # Autonomous repeater logic
│   └── RepeaterDataStore.cpp/h   # Repeater-specific persistence paths
│
├── helpers/                # Shared utilities
│   ├── BaseChatMesh.cpp/h        # Contact/channel/message base class
│   ├── CommonCLI.cpp/h           # Serial/mesh CLI command processor
│   ├── AdvertDataHelpers.cpp/h   # Advertisement wire format encoder/decoder
│   ├── ClientACL.cpp/h           # Authenticated client management
│   ├── TransportKeyStore.cpp/h   # Region transport key cache
│   ├── RegionMap.cpp/h           # Region-based flood filtering
│   ├── ContactInfo.h, ChannelDetails.h, NodePrefs.h  # Data structures
│   ├── RateLimiter.h, IdentityStore.h, StatsFormatHelper.h
│   └── ui/                       # Display, buzzer, input, pages, Doom game
│
├── boards/                 # Board definitions
│   ├── common/             # Shared configs, DTS includes, partition layouts
│   ├── nrf52840/           # RAK4631, WisMesh Tag, T1000-E, ThinkNode M1, etc.
│   ├── nrf54l/             # XIAO nRF54L15
│   ├── esp32/              # LilyGo TLoRa C6, Station G2, XIAO ESP32-C3/C6
│   └── mg24/               # XIAO MG24
│
├── patches/                # Zephyr tree modifications
│   ├── zephyr/             # Unified diffs (SX126x extensions, GNSS, blobs)
│   └── zephyr-new/         # New files (LR11xx Zephyr driver, DTS bindings)
│
├── lib/ed25519/            # Vendored Ed25519 crypto library
├── tools/                  # Formatter (flash erase) + LR1110 firmware updater
├── CMakeLists.txt          # Build orchestration
├── Kconfig                 # All ZephCore configuration options
├── prj.conf                # Base project config
└── west.yml                # West manifest (Zephyr version pin)

---

3. Layer Architecture

┌─────────────────────────────────────────────────┐
│  Phone App (BLE NUS)  or  Serial CLI (USB CDC)  │  External
├─────────────────────────────────────────────────┤
│  CompanionMesh / RepeaterMesh                   │  App Layer
│    ├── BaseChatMesh (contacts, channels, msgs)  │
│    ├── CommonCLI (command processor)            │
│    ├── ClientACL, RegionMap, TransportKeyStore  │
│    └── UI (display, buzzer, buttons)            │
├─────────────────────────────────────────────────┤
│  mesh::Mesh                                     │  Routing
│    ├── Flood routing (path hash accumulation)   │
│    ├── Direct routing (source-routed paths)     │
│    ├── Packet dedup (SimpleMeshTables)          │
│    └── Advert / ACK / Trace / Group dispatch    │
├─────────────────────────────────────────────────┤
│  mesh::Dispatcher                               │  Scheduling
│    ├── TX/RX queue management                   │
│    ├── CAD (channel activity detection)         │
│    ├── Duty cycle enforcement (EU ETSI)         │
│    ├── RX delay (score-based prioritization)    │
│    └── Maintenance (noise floor, AGC reset)     │
├─────────────────────────────────────────────────┤
│  LoRaRadioBase                                  │  Radio HAL
│    ├── SX126xRadio  ──► Zephyr SX126x driver   │
│    └── LR1110Radio  ──► Custom LR11xx driver    │
├─────────────────────────────────────────────────┤
│  Zephyr RTOS (kernel, drivers, BLE, FS, USB)    │  Platform
└─────────────────────────────────────────────────┘

---

4. Core Mesh Engine

4.1 Packet Lifecycle

1. Allocation: StaticPoolPacketManager::allocNew() — fixed pool of 24 Packet objects (no heap)
2. Creation: Mesh::createDatagram(), createAdvert(), createAck(), etc.
3. Queuing: Dispatcher::sendPacket() → PacketManager::queueOutbound() with priority + scheduled time
4. Transmission: Dispatcher::checkSend() → CAD check → serialize → radio->startSendRaw()
5. Release: PacketManager::free() after TX complete or processing done

4.2 Packet Structure

Wire format:
  [header: 1B] [transport_codes: 0 or 4B] [path_len: 1B] [path: variable] [payload: variable]

Header byte:
  Bits 0-1: Route type (0=transport_flood, 1=flood, 2=direct, 3=transport_direct)
  Bits 2-5: Payload type (0=REQ .. 15=RAW_CUSTOM)
  Bits 6-7: Version (0=v1)

Path_len byte:
  Bits 0-5: Hash count (0-63 hops)
  Bits 6-7: Hash size mode (0=1B, 1=2B, 2=3B, 3=reserved)

4.3 Payload Types

Type	Value	Description
REQ	0x00	Encrypted request to peer
RESPONSE	0x01	Encrypted response from peer
TXT_MSG	0x02	Encrypted text message
ACK	0x03	4-byte CRC acknowledgment
ADVERT	0x04	Signed identity advertisement
GRP_TXT	0x05	Group channel text message
GRP_DATA	0x06	Group channel data
ANON_REQ	0x07	Anonymous request (includes full pubkey)
PATH	0x08	Path return (source route exchange)
TRACE	0x09	Trace route
MULTIPART	0x0A	Multi-ACK container
CONTROL	0x0B	Control data (zero-hop)
RAW_CUSTOM	0x0F	Raw custom data

4.4 Routing

Flood routing: Packet has no destination path. Each relay node appends its identity hash to path[] and retransmits. Priority decreases with hop count. allowPacketForward() is the gatekeeper.

Direct routing: Packet carries a source-routed path[]. Each relay node checks if the first path hash matches its own identity, removes itself, and forwards. Path is built from previous flood packets' accumulated hashes.

Deduplication: SimpleMeshTables maintains a circular buffer of 128 packet hashes (8 bytes each, SHA-256 truncated) and 64 ACK CRCs. hasSeen() prevents duplicate processing and retransmission.

4.5 Dispatcher Scheduling

The Dispatcher runs a tight loop:

loop():
  1. Check if current TX is complete → release packet, record airtime
  2. Process next inbound packet from queue (if scheduled time has passed)
  3. checkRecv(): Drain radio RX ring buffer
     - Parse raw bytes into Packet
     - Flood packets: compute RX delay based on score → defer or process immediately
     - Direct packets: process immediately
  4. checkSend(): Check outbound queue
     - CAD: if channel busy, retry with random backoff (120-480ms)
     - Duty cycle: if exceeded, defer 5 seconds (admin packets exempt)
     - Final LBT check right before TX (closes timing gap)
     - Serialize and transmit

RX Delay: Flood packets are delayed based on signal quality. High-quality signals (high SNR, short packets) get shorter delays, allowing closer/better relays to retransmit first. Uses a lookup table approximation of 10^(0.85 - score*0.1) - 1 multiplied by airtime.

Duty Cycle: Fixed 1-hour sliding window. Default 10%. Admin packets (REQ, RESPONSE, ANON_REQ, CONTROL) are exempt.

4.6 Maintenance Loop

Called every ~5 seconds from the main event loop:

1. Noise floor calibration: EMA with alpha=1/8, jitter, threshold filtering, warmup
2. RX mode watchdog: Flags error if radio stuck outside RX for >8 seconds
3. AGC reset: Periodic warm sleep + recalibration (configurable interval, default off)

4.7 Encryption

• Peer-to-peer: ECDH shared secret (Curve25519) → AES-128-ECB encrypt → 2-byte HMAC-SHA256 MAC
• Group channels: SHA-256 of channel name → AES key
• Advertisements: Ed25519 signature over (pubkey + timestamp + app_data)
• ACKs: SHA-256(shared_secret + packet_hash) truncated to 4 bytes

---

5. Radio Subsystem

5.1 Class Hierarchy

mesh::Radio (abstract interface)
  └── LoRaRadioBase (shared state machine, ring buffer, noise floor)
        ├── SX126xRadio → Zephyr native SX126x driver + sx126x_ext.h
        └── LR1110Radio → Custom lr11xx_lora.c driver + Semtech HAL

Compile-time selection via CONFIG_ZEPHCORE_RADIO_LR1110 in RadioIncludes.h.

5.2 LoRaRadioBase State Machine

TX Flow:

1. startSendRaw() → cancel RX → configure TX → copy to buffer → async send → wake TX wait thread
2. TX wait thread blocks on semaphore, polls completion signal (5s timeout)
3. On DIO1 TX_DONE interrupt → signal raised → restart RX → update stats

RX Flow:

1. lora_recv_async() with callback
2. ISR writes to 8-slot SPSC ring buffer (drops NEW packet on overflow)
3. Main thread drains via recvRaw()

Config Caching: Avoids redundant lora_config() calls. Fast-path for TX↔RX transitions when only direction differs.

5.3 Noise Floor EMA

Algorithm in triggerNoiseFloorCalibrate():

• Random 0-500ms jitter to break phase-lock with interference
• 4 RSSI samples per tick, take minimum
• Threshold filter: reject samples ≥ floor + 14dB (after 8-tick warmup)
• Periodic bypass: every 8th tick accepts unconditionally
• EMA: floor += round_nearest((sample - floor) / 8), clamped to [-120, -50] dBm

5.4 LR1110 Driver Errata Workarounds

The custom lr11xx_lora.c driver handles several LR1110 firmware bugs:

• CMD_ERROR IRQ: Benign error flag on several write commands — cleared silently
• RX buffer drift: Buffer base shifts 4 bytes per packet → clear_rxbuffer() after every RX
• Header error: Can shift buffer pointer → standby before RX restart
• DIO1 stuck HIGH: 5-cycle detection → full hardware reset + recovery
• RX duty cycle broken: 23-40% packet loss → disabled, always continuous RX

5.5 Default Radio Parameters

Parameter	Default	Notes
Frequency	869.618 MHz	EU 869.4-869.65 MHz band (500mW ERP allowed)
Bandwidth	62 kHz
Spreading Factor	8
Coding Rate	4/8
Preamble	16 symbols
TX Power	22 dBm	Clamped by CONFIG_ZEPHCORE_MAX_TX_POWER_DBM

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6. Application Layer

6.1 Class Hierarchy

mesh::Mesh
├── BaseChatMesh (contacts, channels, messages, connections)
│   └── CompanionMesh (BLE protocol, phone sync, offline queue, ACK tracking)
└── RepeaterMesh (ClientACL, RegionMap, CLI, rate limiting, neighbor tracking)

6.2 CompanionMesh

Handles the binary BLE protocol with ~60 command opcodes. Key features:

• Offline queue: 16-frame circular buffer with peek/confirm pattern (survives BLE drops)
• ACK tracking: 8-slot table, computes expected ACK = SHA256(secret + hash)[0:4]
• Contact iteration: Streaming protocol with lastmod filtering for incremental sync
• Lazy write batching: Dirty contacts/channels flush after 5-second delay
• Protocol versioning: V2/V3 frame format negotiation with phone app
• Ed25519 signing: 3-phase flow (start→data→finish) for signing up to 8KB
• Flood scope: Transport key filtering for region-scoped sends

6.3 RepeaterMesh

Autonomous operation features:

• Authentication: Password-based login with timestamp replay protection (120s window)
• Permission levels: GUEST(0), READ_ONLY(1), READ_WRITE(2), ADMIN(3)
• Region filtering: RegionMap with transport key matching per flood packet
• Rate limiting: 4 requests per 120s (discovery), 4 per 180s (anonymous)
• Neighbor tracking: 16-slot table with RSSI/SNR/name/timestamp
• Temporary radio params: tempradio command with auto-revert timer

6.4 CommonCLI Commands

System: ver, board, reboot, start dfu, start ota, erase Config: set name/freq/radio/tx/flood.max/password/..., corresponding getters GPS: gps on/off/setloc/advert Sensors: sensor get/set/list Stats: stats-core/stats-radio/stats-packets, clear stats Power: powersaving on/off

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7. Hardware Adapters

7.1 BLE (adapters/ble/)

• Nordic UART Service (NUS) with AUTHEN permissions (forces pairing)
• Passkey-based MITM pairing, runtime configurable PIN
• TX congestion control: queue (12 frames) + overflow buffer + retry + timeout watchdog
• Fast/slow advertising switching with post-disconnect flap prevention
• DLE (Data Length Extension) to 251 bytes
• Interface coexistence: BLE vs USB, one active at a time

7.2 DataStore (adapters/datastore/)

• Internal: LittleFS on flash (/lfs)
• External: Optional LittleFS on QSPI (/ext) with auto-migration
• Prefs: 93-byte binary format, Arduino-compatible, field-by-field I/O
• Contacts: 152-byte records, stored on external flash if available
• Channels: 68-byte records (4 pad + 32 name + 32 secret)
• Blobs: Fixed-size records with LRU eviction by timestamp

7.3 GPS (adapters/gps/)

• State machine: OFF → ACQUIRING → STANDBY (with warm standby on supported hardware)
• 3 consecutive good fixes (≥4 satellites) required before reporting
• Multi-constellation: GPS+GLONASS+Galileo+BeiDou with fallback
• T1000-E: Complex 6-GPIO power sequencing with VRTC preservation
• Repeater mode: 48-hour wake interval for time sync only
• GPS time blocks phone time sync for 2 hours after last fix

7.4 USB (adapters/usb/)

• CompanionUSB: V3-framed CDC (little-endian 16-bit length prefix + payload)
• RepeaterUSB: Minimal CDC with 1200-baud DFU touch detection
• Both share message queues with BLE adapter (transport-agnostic mesh layer)

7.5 Board (adapters/board/)

• Battery ADC with optional regulator-gated voltage divider, 8-sample average
• UF2 bootloader entry via GPREGRET magic (0x57 = UF2, 0xA8 = BLE DFU)
• TX LED bracketing for LoRa transmissions
• Bootloader version detection via flash memory scan

---

8. UI Subsystem

8.1 Architecture

Event-driven, no dedicated thread. All UI work on Zephyr work queues.

Hardware buttons → Zephyr input subsystem → Longpress filter → Multi-tap filter
    → ui_input_cb() → page navigation / action dispatch → schedule_render()
        → render_work (50ms OLED / 200ms EPD debounce) → CFB framebuffer → display

8.2 Pages

Companion (11 pages): Messages, Recent, Radio, Bluetooth, Advert, GPS, Buzzer, Sensors, Offgrid, DFU, Shutdown

Repeater (3 pages): Status, Radio, Shutdown

8.3 Multi-Tap Input

Single button, up to 4 taps within 400ms window:

• 1 tap → Page next
• 2 taps → Flood advert
• 3 taps → Buzzer toggle
• 4 taps → GPS toggle (immediate, no delay)

8.4 Buzzer

Non-blocking RTTTL parser on dedicated work queue. Predefined melodies for startup, shutdown, messages, ACKs. 2-second safety watchdog auto-silences on work queue stall.

8.5 Doom Easter Egg

Wolf3D-style raycaster on OLED: textured walls, 2 enemy types, shooting, HUD. Bypasses CFB, writes directly to display. ~1.7KB RAM, ~5KB flash. Enabled via CONFIG_ZEPHCORE_EASTER_EGG_DOOM. Triple-press ENTER on Messages page to activate.

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9. Build System

9.1 Config Layering

prj.conf (base: console, logging)
  → boards/common/zephcore_common.conf (ALL boards: BLE, crypto, FS, LoRa, sensors)
    → boards/common/<platform>_common.conf (nrf52/esp32/nrf54l/mg24 specifics)
      → boards/<mcu>/<board>/board.conf (board-specific pins, features)
        → [optional] repeater.conf, prod.conf (user extras, LAST = highest priority)

9.2 Key Kconfig Choices

• Role: ZEPHCORE_ROLE_COMPANION (default) vs ZEPHCORE_ROLE_REPEATER
• Radio: ZEPHCORE_RADIO_NATIVE (SX126x, default) vs ZEPHCORE_RADIO_LR1110
• Features: Display, buzzer, buttons, multi-tap, Doom (auto-enabled from DT)

9.3 Patches

Patch	Risk	Purpose
0001-lora-lr11xx-build	LOW	Integrates LR11xx driver into Zephyr LoRa build
0003-lora-sx126x-native	HIGH	~400 lines: DIO1 work queue, errata workarounds, extension API
0005-gnss-air530z-easy	MEDIUM	EASY ephemeris + removes PM (prevents deadlocks)
0006-blobs-py	LOW	Fix west blobs fetch KeyError

9.4 Flash Partition Layouts

nRF52840 SD v6: SoftDevice 152KB → App 696KB → LFS 128KB → UF2 48KB nRF52840 SD v7: SoftDevice 156KB → App 692KB → LFS 128KB → UF2 48KB ESP32 (4MB): Boot + App → NVS 8KB → LFS 184KB nRF54L15: MCUboot 64KB → App 1272KB → NVS 8KB → LFS 84KB

---

10. Board Matrix

Board	SoC	Radio	GPS	Display	Buzzer	Buttons	QSPI	Max Contacts
RAK4631	nRF52840	SX1262	gnss-nmea	-	-	-	-	350
WisMesh Tag	nRF52840	SX1262	Air530Z	-	Yes	1+multitap	-	350
T1000-E	nRF52840	LR1110	AG3335	-	Yes	1+multitap	-	350
ThinkNode M1	nRF52840	SX1262	Air530Z	EPD 200x200	Yes	2+multitap	2MB	510
Wio Tracker L1	nRF52840	SX1262	L76K	OLED 128x64	Yes	5-way joy	2MB	510
Ikoka Nano 30dBm	nRF52840	SX1262+PA	-	-	-	-	-	350
XIAO nRF54L15	nRF54L15	SX1262	-	-	-	-	-	450
XIAO ESP32-C3	ESP32-C3	SX1262	-	-	-	-	-	300
XIAO ESP32-C6	ESP32-C6	SX1262	-	-	-	-	-	300
LilyGo TLoRa C6	ESP32-C6	SX1262	-	-	-	-	-	300
Station G2	ESP32-S3	SX1262+PA	UART1	OLED 128x64	-	1 button	-	350
XIAO MG24	EFR32MG24	SX1262	-	-	-	-	-	350

---

11. Packet Format Reference

Wire Format

Byte 0: Header
  [1:0] Route type: 0=transport_flood, 1=flood, 2=direct, 3=transport_direct
  [5:2] Payload type (see table in §4.3)
  [7:6] Version (0=v1)

If transport route (bit 0 or both bits set):
  Bytes 1-4: transport_codes[2] (2x uint16_t LE)

Next byte: path_len
  [5:0] Hash count (number of hops)
  [7:6] Hash size mode (0→1B, 1→2B, 2→3B)

Next N bytes: path[] (hash_count × hash_size bytes)

Remaining bytes: payload (type-specific)

Advert Payload

[32B pubkey] [4B timestamp LE] [64B Ed25519 signature] [0-32B app_data]

app_data format (AdvertDataHelpers):
  Byte 0: type(3:0) | flags(7:4)
    flags: bit4=lat/lon, bit5=feat1, bit6=feat2, bit7=name
  [optional 8B: lat(float) + lon(float)]
  [optional 2B: features1]
  [optional 2B: features2]
  [remaining: name string]

Encrypted Datagram (REQ/RESPONSE/TXT_MSG)

[1B dest_hash] [1B src_hash] [encrypted_payload + 2B MAC]

encrypted_payload (after AES-128-ECB decrypt):
  For TXT_MSG: [4B timestamp] [1B txt_type] [text...]
    txt_type: 0=plain, 1=cli_data, 2=signed_plain

---

12. BLE Protocol Reference

Frame Format

Raw binary over BLE NUS. Each frame: [1B opcode] [payload...] Over USB CDC: V3 framing: [2B LE length] [1B opcode] [payload...]

Key Command Opcodes (phone → device)

Opcode	Name	Payload
0x01	CMD_SEND_TXT_MSG	contact_idx + text
0x03	CMD_GET_CONTACTS	[optional 4B lastmod filter]
0x06	CMD_GET_SELF_INFO	(none)
0x07	CMD_SET_SELF_INFO	type + name + lat + lon
0x0B	CMD_GET_MSG_WAITING	(none)
0x0C	CMD_CONFIRM_MSG	(none)
0x11	CMD_SET_PREF	pref_key + value
0x12	CMD_DEVICE_QUERY	(none)
0x15	CMD_SEND_SELF_ADVERT	(none)
0x20	CMD_NEGOTIATE_VER	target_version

Push Notifications (device → phone, async)

Code	Name
0x80	PUSH_CODE_ADVERT
0x82	PUSH_CODE_SEND_CONFIRMED
0x83	PUSH_CODE_MSG_WAITING
0x8A	PUSH_CODE_NEW_ADVERT

---

13. Data Storage

File Paths

Path	Content	Format
/lfs/_main.id	Node identity	64B private key + 32B public key
/lfs/new_prefs	Preferences	93B binary (Arduino-compatible)
/lfs/contacts3 or /ext/contacts3	Contacts	152B × N records
/lfs/channels2 or /ext/channels2	Channels	68B × N records
/lfs/adv_blobs or /ext/adv_blobs	Advert cache	Fixed-size blob records
/lfs/repeater/acl	Client ACL	136B × N records
/lfs/repeater/regions2	Region map	Header + 164B × N entries

Preferences Binary Layout (93 bytes)

Offset  Size  Field
0       4     airtime_factor (float)
4       32    node_name
36      4     (padding)
40      8     node_lat (double)
48      8     node_lon (double)
56      4     freq (float)
60      1     sf
61      1     cr
62      1     client_repeat
63      1     manual_add_contacts
64      4     bw (float)
...     ...   (see CommonCLI.cpp loadPrefs/savePrefs for full layout)
92      1     rx_boost (ZephCore extension)

---

14. Key Call Flows

14.1 Receiving a LoRa Packet → Application

DIO1 interrupt → Zephyr lora driver → async RX callback
  → LoRaRadioBase::rxCallbackStatic() → SPSC ring buffer write → _rx_cb()
    → k_event_post(MESH_EVENT_LORA_RX) → main thread wakes
      → Dispatcher::loop() → checkRecv() → drain ring buffer
        → tryParsePacket() → score + airtime calc
          → flood: calcRxDelay() → queue inbound or process immediately
          → direct: process immediately
            → Mesh::onRecvPacket() → decrypt → dispatch by type
              → BaseChatMesh::onPeerDataRecv() → onMessageRecv()
                → CompanionMesh: writeFrame() to phone or queueOfflineMessage()

14.2 Sending a Text Message

Phone sends CMD_SEND_TXT_MSG via BLE NUS
  → CompanionMesh::handleProtocolFrame()
    → BaseChatMesh::sendMessage(contact, text)
      → composeMsgPacket(): ECDH secret → AES encrypt → MAC
      → if contact has path: trySendDirect()
      → else: sendFlood()
        → Mesh::sendFlood() → mark seen → queue outbound
          → Dispatcher::checkSend() → CAD check → duty cycle check → LBT → startSendRaw()

14.3 Repeater Forwarding a Packet

Dispatcher::checkRecv() → Mesh::onRecvPacket()
  → flood packet, not for us
    → routeRecvPacket() → allowPacketForward()
      → RepeaterMesh checks: disable_fwd? flood_max? region filter?
        → if allowed: append self hash to path, ACTION_RETRANSMIT_DELAYED
          → re-queued outbound with priority = hop count

14.4 Noise Floor Calibration Cycle

main event loop (every 5s) → Dispatcher::maintenanceLoop()
  → radio->triggerNoiseFloorCalibrate(threshold)
    → guards: in RX? TX active? duty cycle? mid-receive?
    → random 0-500ms jitter
    → read 4 RSSI samples, take min
    → first sample: seed directly
    → warmup (<8 ticks): accept unconditionally
    → periodic bypass (every 8th): accept unconditionally
    → otherwise: reject if sample ≥ floor + 14dB
    → EMA: floor += round((sample - floor) / 8)
    → clamp [-120, -50] dBm