Extras

Light shows, SD card storage, games from the card, and USB accessories.

These live under Settings → SETTINGS, after DISPLAY: PARTY, STORAGE and EXTRAS (with the GB Emulator, listed as LEGACY HANDHELD, and DOOM), plus USB KEYBOARD/MOUSE after KEYBOARD.

Party: music and lights#

Lights and music run while the PARTY window is open and stop when you leave it.

MUSIC: Songs play with beat-synced lights. Choose Pirates, Carmen, Gadget, Kakariko, Techno or Brinstar (the playing song is marked >), or STOP MUSIC. Each voice of the song drives its own LED.
LIGHTS: Choose an effect for all five LEDs. RAINBOW CHASE (default), COLOR WIPE, SPARKLE or BREATHE, and BRIGHTNESS at 10, 20 (default), 35 or 50%. With a song playing, the effect colours the beat.

If the lights can't start you see LED driver unavailable.

Storage: SD cards#

CAT uses a microSD card (External SD). Some CATs also have a built-in 128 MB card (Internal SD); on those that don't, the row reads Internal SD (absent).

Insert and remove cards with CAT switched offCAT can't detect a card being inserted or removed. Put the card in before switching on, and take it out only after POWER DOWN, or after Unmount shows Safe to remove.

Card format: MBR partition table (not GPT), one FAT16, FAT32 or exFAT volume. On a Mac: Disk Utility → View → Show All Devices → select the card → Erase, scheme Master Boot Record, format ExFAT or MS-DOS (FAT).

Page or row	What it does
External SD / Internal SD	Choose a card. Its state shows as Ready, Unformatted, Unmounted, Not mounted or Unavailable.
Browse	Folders (marked [+]) and files, five per page. New folder. Pick an item to Open, Copy to..., Move to..., Rename or Delete...; its size is shown.
Info	Filesystem, label, free space, Rename card (11 characters) and Create game folders (makes `/ROM` and `/SAVE`).
Default: External	Which card the GB Emulator and Doom use.
Mount / Unmount	Start or stop using the card.
Format...	Asks Format External SD? Erases all files. with Cancel first. CAT never formats a card on its own.

When copying or moving, a row cycles what happens if a file already exists: Stop, Skip, Replace or Keep both. Long jobs show Working...; Hold B to cancel stops them (some files may already be done). B goes up a folder, or back a page.

Folders CAT uses: /ROM for GB Emulator games, /SAVE for their saves, and /games/doom/ for Doom.

GB Emulator#

The GB Emulator plays GB and GBC games from the SD card. Copy .gb or .gbc files you have the right to use into /ROM on the card.

Settings → SETTINGS → EXTRAS → LEGACY HANDHELD.
CHOOSE A GAME lists up to 64 games, 10 per page (Previous / Next).
Pick a game. Large games take a few seconds to load.
Play with the D-pad, A, B, START and SELECT; each maps straight to the game's own button.
To quit, hold START and SELECT together for about 1.5 seconds.

With no card or no games you see NO CARTRIDGE FAT32/exFAT SD (MBR). Copy .gb/.gbc games to /ROM. Insert with CAT off..

Saves: games with battery saves are saved to /SAVE when you quit. Saves are matched to the game's contents, so renaming a ROM keeps its save. Save inside the game before quitting.
Game clocks (games with a real-time clock) keep time while CAT is off.
Picture: the 160×144 game picture is scaled up and centred. Screen dimming still applies.
Sound plays through the speaker at the Settings volume.
The mesh keeps running while you play.
Most ordinary cartridges work (ROM-only, MBC1, MBC2, MBC3, MBC5). Special cartridges, such as those with motion sensors, don't.
If the battery reaches 5% during a game, CAT quits the game to save the node, and the game's own save is skipped.

Doom#

The shareware first episode of Doom, played from the SD card.

Put doom1.whx (the compressed shareware data from the CAT release package) in /games/doom/ on the default card, or use the provisioner's "Install Doom to SD". An ordinary .wad file won't work.
Settings → SETTINGS → EXTRAS → DOOM. The window shows the card, then Ready (SD). and Mesh paused in Doom. Hold START+SELECT to exit.
Choose PLAY. CAT saves, then restarts into Doom.

Button	In Doom
D-pad	Move and turn; move through menus
`A`	Fire; accept (Yes)
`B`	Use and open doors; back (No)
`START`	Open or close the Doom menu
`SELECT` + D-pad	Strafe
`SELECT` + `A`	Automap
`SELECT` + `B`	Next weapon
Hold `START` + `SELECT` for 1.5 s	Quit back to CAT

While Doom runs, the mesh is off. Your CAT doesn't receive or relay messages until you quit and it restarts.
Doom saves (8 slots) go to /games/doom/saves/ on the card.
Other messages: Checking game files..., Game files missing. Open SD SETUP. (SD SETUP explains where the file goes), Doom not installed. Update firmware.
A USB keyboard and mouse work in Doom if you switched them on before choosing PLAY: W/S move, A/D strafe, P fire, L use; the mouse turns and its left button fires.
Multiplayer over LoRa is in development.

USB keyboard and mouse#

Settings → SETTINGS → USB KEYBOARD/MOUSE → tick ENABLED, then plug a keyboard, mouse, receiver or small hub into the USB-C port. CAT powers the accessory from its battery.

The status line says what is happening: Switching on..., Plug in a keyboard, mouse or dock., Keyboard and mouse ready., Unplug the computer or charger., Can't power USB. Battery low?, Switched off: nothing plugged in.
Keys: Esc/Tab = Start/Select, P/L = A/B, WASD/arrows = D-pad. In the on-screen keyboard you can type directly (see Typing).
Mouse: a pointer appears; left click is a tap. The wheel and other buttons are ignored, and a real touch always wins.
While it is on, the USB port can't be used for a computer, charging or updates. It switches itself off after 2 minutes with nothing plugged in, and is always off after a restart.
Unplug any computer or charger before switching it on. It refuses to start on a low battery.

NFC tag#

CAT contains a read-only NFC tag. Hold a phone's NFC area against the case for a couple of seconds and it opens https://entropicengineering.com/; NFC apps also show a line with the device ID. The antenna sits deep in the case, so you may need to move the phone around slowly.