biscuit.

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.

Dashboard

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)

Recon tools

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

Tetris on e-ink

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