KeysCheck

KeysCheck is a CardputerZero utility that shows every key currently held down, using labels a person can read such as A, SHIFT, SPACE, FN, and SYM.

It is intentionally a viewer. The input layer keeps Linux's raw EV_KEY.code values; only the screen translates each code into a label. KeysCheck does not turn key combinations into characters, shortcuts, or Fn/Sym layer results.

Behavior and privacy

• EV_KEY.value=1 presses a code and value=0 releases it.
• Repeat events (value=2) do not change the pressed-key set.
• Keys that were already held when the app starts are included.
• After Linux reports dropped events, the complete pressed-key state is read again.
• Multiple input sources are tracked independently, so releasing one does not clear a matching key still held on another.
• KeysCheck has no network feature, analytics, account, or persistent key log. State exists only in memory while the app runs.

On CardputerZero, automatic discovery accepts the confirmed built-in keyboard device named tca8418c. This excludes HDMI and infrared input devices that also advertise keyboard keys. A specific device may be selected at configure time with -DAPP_KEY_INPUT_DEVICE=/dev/input/eventN.

The label table is CardputerZero-specific. Unknown Linux key codes remain visible as KEY N instead of being discarded.

Font

No font file is stored in this repository or package. KeysCheck loads JetBrains Mono Regular from the operating system with FreeType. CardputerZero uses:

/usr/share/fonts/truetype/jetbrains-mono/JetBrainsMono-Regular.ttf

The Debian package depends on fonts-jetbrains-mono. For development, set KEYSCHECK_FONT_FILE=/absolute/path/JetBrainsMono-Regular.ttf at runtime or -DAPP_SYSTEM_FONT_FILE=... at configure time. If the font is absent, the app logs a warning and uses LVGL's built-in fallback.

Desktop build

Requirements are CMake 3.25 or newer, Ninja, a C++17 compiler, SDL2, libpng, FreeType, and zlib. A first configure also needs internet access to fetch the pinned LVGL and fmt sources.

On macOS with Apple Silicon:

brew install cmake ninja sdl2 libpng freetype
cmake --preset darwin-arm64
cmake --build --preset darwin-arm64-dbg
./build/darwin-arm64/Debug/keyscheck

On Ubuntu or Debian:

sudo apt install cmake ninja-build g++ libsdl2-dev libpng-dev libfreetype6-dev zlib1g-dev
cmake --preset linux-x86-64
cmake --build --preset linux-x86-64-dbg
./build/linux-x86-64/Debug/keyscheck

The desktop simulator accepts the computer keyboard and mouse clicks on its CardputerZero keypad. Losing window focus releases simulator-held state to prevent stuck keys.

Tests

After configuring a desktop preset:

ctest --test-dir build/darwin-arm64 -C Debug --output-on-failure

Replace the build directory with build/linux-x86-64 on Linux.

CardputerZero package

The cross build requires CMake 3.25 or newer, Ninja, and an AArch64 GNU cross compiler (aarch64-linux-gnu-gcc and aarch64-linux-gnu-g++). Run:

cmake --workflow --preset cp0-cross-package

The first build downloads the CardputerZero BSP v0.0.4 and verifies its SHA-256 before extraction. LVGL and fmt are fetched at pinned commits. The resulting package is written to dist/.

Install over an existing ADB connection:

adb push dist/KeysCheck_0.2.0_harrison1_arm64.deb /tmp/KeysCheck.deb
adb shell sudo dpkg -i /tmp/KeysCheck.deb

Uninstall with:

adb shell sudo apt remove keyscheck

Installing or removing a Debian package requires administrative package-manager permission, but the installed application itself runs as the normal APPLaunch user. It installs no root systemd service. That user must have read access to the selected /dev/input/event* node and access to the framebuffer (or configured DRM device).

Project layout

• src/platform/: raw input state and Linux evdev adapter
• src/view/: human-readable labels and the 320×170 screen
• src/app/: application lifecycle, font discovery, and desktop simulator
• tests/: input-state and label tests
• cmake/: CardputerZero toolchain and Debian packaging
• assets/images/: desktop shell artwork and the single 256×256 launcher icon

Open-source information

KeysCheck is licensed under the MIT License. It was derived from the CardputerZero Template at commit d28fb262685a, whose notice is preserved. LVGL and {fmt} are pinned build dependencies. JetBrains Mono is a system dependency and is not redistributed. See third-party notices for details.

Contributions are welcome under the contribution guide. Report security issues using the private process in the security policy. Release changes are recorded in the changelog.