GitHub - yattsu/biscuit: Firmware for the ESP32-C3 SoC Xteink X4 e-paper display reader
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Custom firmware for the Xteink X4 e-paper device. Turns a $70 e-ink reader into a smart device with wireless tools, security features, communication, games, and utilities — while keeping full e-reader functionality. Forked from CrossPoint Reader. All core reading functionality comes from CrossPoint. Biscuit builds on top of it.
What is this Biscuit treats the Xteink X4 as a general-purpose smart device, not just an e-reader. The home screen is a tile-based dashboard with live system info (battery, heap, uptime, WiFi status). Reading is one of eight categories, not the main focus. The 4.26" e-ink display is readable in direct sunlight, retains its image without power, and gives the device days of battery life. Seven physical buttons provide navigation without a touchscreen. WiFi and BLE 5.0 enable wireless tools. A MicroSD card stores everything. Hardware
Spec Value
SoC ESP32-C3 (RISC-V, 160MHz)
RAM 380KB SRAM (no PSRAM)
Flash 16MB
Display 4.26" 800×480 e-ink, 1-bit mono
Input 7 buttons (4 front, 3 side)
WiFi 2.4GHz 802.11 b/g/n
BLE 5.0 (shared radio with WiFi)
Storage MicroSD (FAT32)
Port USB-C (serial + power)
Apps The home screen is a dashboard of eight tiles. Everything lives under one of them.
Tile Purpose
Recon Passive scanning and monitoring — no transmission
Offense Active wireless testing, grouped into Scan → Profile → Attack → Capture
Defense Stealth, detection, and device hardening
Comms Communication and exchange
Tools Crypto, network, productivity, and creative utilities
Games Entertainment
Reader Ebooks, OPDS, reading stats
Settings Preferences, file transfer, system management
Recon — scan and monitor (passive only)
All apps in Recon are read-only — they listen but never transmit.
App What it does
WiFi Scanner Discover APs and connected clients
BLE Scanner Scan BLE devices, browse services and characteristics
Full Sweep Combined WiFi + BLE passive scan
Packet Monitor Monitor WiFi frames with PCAP recording
Probe Sniffer Capture WiFi probe requests
Wardriving Log access points with signal strength
Crowd Density Estimate nearby people via probe request counting
Device Fingerprint Identify device OS from probe request patterns
Vendor Lookup Identify manufacturer by MAC (OUI database on SD)
AP History Log visible access points over time to SD
Network Change Snapshot nearby devices, compare for changes
Perimeter Watch Alert when new devices appear in area
BLE Proximity Track BLE device RSSI
WiFi Heat Map RSSI mapping walkabout
Signal Locator Estimate AP position via RSSI triangulation
Deauth Detector Monitor for deauthentication frame spikes
Offense — active wireless testing Offense opens a 2×2 sub-menu grouped into four phases. A disclaimer must be acknowledged before first use. Scan — target discovery
App What it does
WiFi Scan Discover APs and clients
BLE Scan Discover BLE devices
Full Sweep Combined WiFi + BLE passive scan
Saved Targets Browse cached target database
Profile — target analysis
App What it does
Target Profiler Select and analyze a target
Client Enum Devices connected to target AP
Host Scanner Find devices on local network
Vuln Assessment Check encryption and WPS settings
Signal Locator Estimate AP position from RSSI
Attack — broadcast and testing tools
App What it does
Beacon Test Custom beacon broadcasting
WiFi Test Wireless connectivity testing
Captive Portal Network portal for testing
Beacon Flood Broadcast 30 random SSIDs
SSID
Clone Clone a WiFi AP (open, same channel)
BLE Spam Proximity / Fast Pair / Swift Pair flood
BLE Keyboard HID keyboard emulation (DuckyScript over BLE)
AirTag Test Device location testing
USB Keyboard Wired DuckyScript over USB-C
Capture — review and export
App What it does
Captured Data Handshakes, credentials, PCAPs, BLE logs
Credential Viewer View credentials captured by portal
Probe Log Recorded WiFi probe requests
Scan History Browse previously found targets
Wipe Captures Delete all captured data
Defense — stealth and protect Ghost Mode is the headline entry — it rotates MAC, kills radios, and cleans up state in one action (replacing the old standalone MAC Changer and RF Silence apps).
App What it does
Ghost Mode MAC rotate + RF kill + state cleanup, one shot
Tracker Detector Detect AirTags, SmartTags, and Tiles following you
Security Sweep Scan for cameras, trackers, rogue APs, skimmers
Network Monitor Detect rogue APs and suspicious frames
Emergency SOS SOS beacon (WiFi + BLE + Mesh) with dead man's switch
Phone Tether BLE proximity disconnect alert
Quick Wipe Erase all biscuit data from SD with verification
PIN Security Lock device with PIN, duress PIN for fake profile
Screen Decoy Fake screen to hide activity
SD Encryption Encrypt biscuit data on SD with PIN
Comms — communicate and exchange
App What it does
Mesh Chat ESP-NOW text chat, no WiFi needed, ~200m range, multi-hop relay
SSID Channel Hide short messages in WiFi network names
Contact Exchange Swap contact cards between devices via BLE
Dead Drop Temporary WiFi AP for anonymous file exchange
Bulletin Board Local anonymous message board via WiFi AP
Tools — utilities and productivity A single tile that merges the old Network section with crypto, productivity, tracking, and creative apps.
Security & crypto
App What it does
Authenticator TOTP 2FA codes, fully offline
TOTP QR Show a 2FA code as a scannable QR
Password Manager Encrypted credentials stored on SD
Medical Card Emergency medical info persistent on e-ink
Stego Notes Hide text inside BMP images
Network
App What it does
WiFi Connect Join a WiFi network
WiFi Scanner APs, signal, channels
Host Scanner Find devices on local network
Ping Ping a host or IP address
DNS Lookup Resolve domain names
HTTP Client Send GET/POST requests
mDNS Browser Discover local services
Productivity
App What it does
Clock NTP clock, stopwatch, pomodoro timer
Calculator Basic calculator
QR Generator Generate QR codes from text
Morse Code Encode and decode morse
Unit Converter Convert between measurement units
Cipher Tools ROT13, Caesar, Vigenere, XOR
OTP Generator One-time pad random number pages
Tracking & logging
App What it does
Event Logger Timestamped notes with WiFi location tagging
Flashcards Study decks loaded from CSV on SD
Habit Tracker Daily habit checklist with streak tracking
Breadcrumb Trail Record and retrace your path using WiFi fingerprints
Vehicle Finder Find your parked car via WiFi fingerprint matching
Transit Alert Alert when approaching a saved transit stop
Creative
App What it does
Etch-A-Sketch Draw on the e-ink screen, save as BMP
Barcode Generator Code 128 / Code 39 / EAN-13
Key Copier Draw key profiles from bitting codes
WiFi QR Share Share WiFi credentials as a QR code
File Browser Browse and view files on SD card
Countdown Big countdown timer
Games
Casino (slots, blackjack, roulette, coin flip, higher/lower, loot box), Minesweeper, Sudoku, Chess (with bot), Snake, Tetris, Maze, Dice Roller, Game of Life, Voronoi, Matrix Rain.
Reader
App What it does
Open Book Browse and open an ebook
Recent Books Continue where you left off
OPDS Browser Download books from OPDS servers
Reading Stats Pages read, books completed, streaks
Browse Files File manager for the SD card
Full EPUB 2/3 rendering, KOReader Sync, and Calibre wireless transfer are inherited from CrossPoint. Settings — system and configuration Promoted to a top-level tile from the old System section.
App What it does
Settings Display, reader, controls, system configuration
WiFi Transfer Upload/download files via WiFi (STA, AP, or Calibre)
USB Storage Share the SD card as a USB mass-storage drive
Task Manager View heap, uptime, and activity stack
Battery Battery level with history graph
Device Info Chip, flash, RAM, firmware, WiFi, screen info
Background Radio state, SD status, active timers
Automation WiFi geofence triggers and scheduled tasks
Themes Three UI themes, selectable in Settings:
Classic — original CrossPoint style Lyra — rounded elements, modern feel (default) Military — inverted headers, sharp corners, dashed separators, uppercase labels
SD card structure /biscuit/ portals/ # HTML templates for captive portal ducky/ # DuckyScript files for HID keyboard pcap/ # Packet captures scans/ # Network scan results logs/ # WiFi/BLE scan logs, AP history, event logs drawings/ # Etch-A-Sketch saved BMPs trails/ # Breadcrumb trail data snapshots/ # Network change snapshots flashcards/ # Flashcard decks (CSV) creds.csv # Captured portal credentials medical.dat # Medical card info totp.dat # TOTP authenticator secrets (encrypted) casino.dat # Casino credits habits.dat #
Habit tracker data security.dat # PIN hashes automation.dat # Automation rules oui.txt # IEEE OUI vendor database (user-provided)
Installing Web flasher (recommended)
Connect your Xteink X4 via USB-C data cable (not charge-only) Wake the device by pressing Power Go to https://xteink.dve.al/ and flash the firmware
To revert to stock firmware, use the same site or press "Swap boot partition" at https://xteink.dve.al/debug. Manual git clone --recursive https://github.com/yattsu/biscuit cd biscuit pio run --target upload Development Prerequisites
PlatformIO Core or VS Code + PlatformIO IDE Python 3.8+ USB-C data cable Xteink X4
Building # Windows PowerShell $env:PYTHONUTF8=1 pio run -j 16 # Linux / macOS pio run -j 16 Adding translations Translations live in lib/I18n/translations/. Each language is a YAML file. Add or edit strings, then regenerate: python3 scripts/gen_i18n.py lib/I18n/translations lib/I18n/ See i18n docs for details. Debugging python3 -m pip install pyserial colorama matplotlib python3 scripts/debugging_monitor.py The debug monitor shows color-coded logs and a real-time memory graph. Architecture The firmware uses an activity-based UI architecture. Every screen is an Activity subclass with onEnter(), loop(), render(), and onExit(). Activities are managed by ActivityManager (push/pop/replace). WiFi and BLE share one radio, arbitrated by RadioManager. See architecture docs for the full overview. Upstream Biscuit tracks CrossPoint Reader as upstream. To sync: git remote add upstream https://github.com/crosspoint-reader/crosspoint-reader.git git fetch upstream git merge upstream/master Credits Built on CrossPoint Reader by the CrossPoint contributors. CrossPoint was inspired by diy-esp32-epub-reader by atomic14. License MIT