CrossPlay

E-ink is good at waiting.
So is a chess position, a flashcard, a puzzle you are halfway through.

Releases · What is on it · Identity · Scope

CrossPlay is a fork of CrossPoint for the Xteink X4 Pro and the Seeed reTerminal Sticky. CrossPoint turns the device into an excellent e-reader. CrossPlay keeps all of that and adds the other things a screen that holds still is good at: games you think about rather than react to, spaced-repetition flashcards, comics, and two devices that play together with nothing to set up.

It is a personal fork, built in the open. Upstream lands on a base branch and is merged in continuously. The reading side is CrossPoint's and stays CrossPoint's: the EPUB engine, sync and the file browser are theirs, and the reader's chrome is restyled to match the design language the apps use.

What is on it

Chess	A full engine on the device, or a board between two of them.
Battleship	Lay out a fleet, then hunt someone else's.
Connections	The daily word grid, with an archive of past boards.
Solitaire	Klondike, turned sideways because that is the shape of a tableau.
D&Diagrams	A nonogram whose clues are a dungeon. 64 of them.
Insider	A party game for a table and one device.
Jaipur	The two-player trading game, solo or nearby.
Murdle	A logic grid built through the solver, so you never have to guess.
Checkers	English draughts, where taking is compulsory and the board says so.
Connect Four	Drop a disc, get four in a line. Seven columns, one tap each.
Yahtzee	Thirteen boxes, three rolls a turn, and the Joker rules in full.
Knucklebones	Cult of the Lamb's dice game. Matching dice multiply; yours destroy theirs.
Minesweeper	Tap to dig, hold to flag. The first dig is always safe.
Sudoku	Generated on the device and graded by the technique it needs, not the clues.
Sea Salt	Sea Salt & Paper: collect duos, bet on STOP or LAST CHANCE.
Toy Battle	Nine boards of bases and paths. Hold regions, take medals, solo or nearby.
Forehead	Screen against your forehead, the room shouts clues, sixty seconds.
Trivia	50,000 questions off 42 years of Jeopardy. Read them out, or play alone.
Wavelength	A hidden point on a spectrum, one clue, and the whole table arguing.
Study	Anki decks with the FSRS scheduler, offline.
Hacker News	The front page in a reading serif, articles kept on the card.
xkcd	The archive, packed for the card and drawn one to one.
Get Books	Browse any OPDS catalog and download straight to the card, no computer.
Instapaper	Your read-later queue, synced both ways: reading position and archiving.

Nine of them play over PLAY NEARBY: Chess, Checkers, Connect Four, Yahtzee, Knucklebones, Battleship, Jaipur, Sea Salt and Toy Battle. Put two devices next to each other and they find one another. No pairing screen, no room code, no account, no router, no internet.

Each game's rules, its state machines and the decisions behind them: Checkers · Connect Four · Yahtzee · Knucklebones · Minesweeper · Sudoku · Trivia · Jaipur · Sea Salt · Murdle · Toy Battle. How the two physical buttons are used, and why there are only two: buttons.

Install it

CrossPlay targets two devices: the Xteink X4 Pro and the Seeed reTerminal Sticky, both ESP32-S3 with the same 800x480 panel and capacitive touch. For every other device CrossPoint supports, CrossPoint upstream is the right answer and is excellent.

This runs on real hardware. One tester flashed v1.2.1 and played most of the shelf; the three problems they hit were fixed in v1.2.2. As of v1.3.0 I have an X4 Pro of my own on the desk, and since 2026-08-25 a Sticky next to it, so releases are flashed to both before they ship. That is still a small record: if you flash it, please say what happened, either way.

You do not need to have installed CrossPoint first.

From the browser

Open crossplay.ma-r-s.com/#get in Chrome or Edge on a computer, plug the device in, wake it, and press Install. The page downloads the current release and writes it over USB itself; there is nothing to install first and no command to type. Safari and Firefox have no Web Serial, and no phone or tablet does either, so the button says so rather than failing when pressed.

By hand

1. Download your device's full image from the releases page: crossplay-<version>-x4pro-full.bin for the X4 Pro, crossplay-<version>-sticky-full.bin for the Sticky. Each is the whole firmware: second-stage bootloader at 0x0, partition table at 0x8000, application at 0x10000, in one file.

2. Plug the device into a computer over USB.

3. Install esptool if you have not (pip install esptool, same on Windows, macOS and Linux) and run the line for your device:

   esptool.py --chip esp32s3 --baud 921600 write_flash 0x0 crossplay-<version>-x4pro-full.bin

   esptool.py --chip esp32s3 --baud 921600 write_flash 0x0 crossplay-<version>-sticky-full.bin

Updating an install you already have

The release also carries firmware.bin, which is the application on its own. That is the file for a device that already has a bootloader, and it needs no cable: Settings -> Check for updates fetches it over Wi-Fi, or you can copy it onto the SD card and choose it from the same screen. The updater matches that exact filename, so do not rename it.

-full.bin is for the USB install only. Do not hand it to the on-device updater: that would be writing a bootloader into a slot meant for the application.

Reflashing without a cable

Settings > System > Developer Mode turns any device into one you can flash over Wi-Fi, including a device that has only ever run shipped releases: it is a setting, not a build flag. Pair once with the six-digit code the screen shows, then every flash after that is one command.

./scripts_local/wifi-flash.sh --pair 123456
./scripts_local/wifi-flash.sh
./scripts_local/wifi-flash.sh --disable

It is off until you turn it on, it says on the panel that the device will not sleep while it is on, and --disable closes it again. It also serves the last panic, its backtrace and the log lines from before the reset at GET /api/dev/crash, which used to need a cable to read. docs/developer-mode.md has the rest, including what protects it.

Two things worth knowing before you start:

• --chip esp32s3, and only these two devices. The X4 and X3 are ESP32-C3: these binaries are not for them and flashing one there is a cross-chip flash. Install CrossPoint on those instead: it is excellent and it is what this is built on. Between the two S3 devices the firmware protects you -- every image carries its board name, and both updaters refuse an image built for the other board.
• Flashing replaces the firmware, not the SD card. Your library, your reading positions and your fonts are files on that card and are left alone. Installing stock CrossPoint over the top puts the device back where it was, which makes this cheap to try. If a flash goes wrong, docs/fix-bricked-xteink.md is the way back.

Try it without a device

crossplay.ma-r-s.com runs the real firmware in the browser: the same src/ and lib/ the device build compiles, put through em++ instead of g++, against an SD card of its own. Click the screen in the hero, or ask for two devices and watch them find each other.

The browser build fakes three things, all documented in site/README.md: the network answers from a snapshot, Study's headword font is the small cut under the big one's name, and sleep is off.

Build it

pio run -e x4pro                 # the firmware
pio run -e simulator_x4_pro      # a desktop simulator, SDL2 + a FreeRTOS shim
./scripts_local/check.sh         # host tests and both builds

Every suite green is the only green; nothing is a known failure.

The apps live in src/apps_local/, which is what keeps the merge with upstream close to conflict-free. It is not the whole diff: the settings screens, the reader's menus and parts of lib/ are reworked too, and those are where a merge conflict will come from if one does. Read LOCAL_SCOPE.md and docs/shelf.md before adding anything, and docs/building-apps.md for how an app is put together.

The website

site/ is static: the landing page, the Study deck installer (Pyodide converting Anki decks in the browser, previewed on the real firmware), their stylesheet and scripts, the assets they name, and the browser build under site/emulator/. See site/README.md for how to serve it (a plain http.server will not do, the threads need COOP/COEP) and what has to be true before it deploys.

Credit and licence

CrossPlay is MIT, like the project it forks, and it is a fork in git's sense as well as in the README's: this repository is a GitHub fork of crosspoint-reader/crosspoint-reader, shares its commit history, and merges every upstream release rather than re-implementing it. It stands on CrossPoint and the FreeInk SDK; upstream's own README is kept at docs/crosspoint-readme.md.

xkcd comics are by Randall Munroe, CC BY-NC 2.5, fetched by the device from xkcd.com. Connections puzzles are the New York Times'; CrossPlay ships none of them and downloads only what you ask for. Type is Jersey 25 and Instrument Serif, both SIL OFL.

Jaipur, Insider, Murdle, Battleship, Connections, Knucklebones, Sea Salt & Paper and Toy Battle are trademarks of their respective owners. Sea Salt & Paper was designed by Bruno Cathala and Theo Riviere and is published by Bombyx. Toy Battle was designed by Paolo Mori and Alessandro Zucchini and is published by Repos Production. CrossPlay implements the games; it is not affiliated with, endorsed by or sponsored by any of them.

Reading positions sync to CrossPoint's own server by default. That is upstream's infrastructure rather than this fork's, inherited so that flashing CrossPlay over CrossPoint does not orphan an existing sync; the address is a setting and can be pointed at any KOSync server.