Cobalt

A native AT Protocol / Bluesky client for the Nintendo Wii U, built as Aroma homebrew with devkitPro/WUT and SDL2.

Version 0.4.0

Cobalt exists because I looked at a Wii U's weak little PowerPC tri-core and decided that, somehow, it was going to post to Bluesky.

That is not a metaphor for the project. I deliberately wanted to make AT Protocol work on hardware that was never designed for it, and I wanted to do it properly rather than turning the Wii U into a thin browser target.

Cobalt treats the Wii U as the platform it is rather than as a browser target: the TV and GamePad are both first-class displays, with support for normal two-screen use and Off-TV Play.

Cobalt uses Wolfram, my C AT Protocol SDK, for its AT Protocol implementation. The project sits alongside the rest of my mineral and material-named projects and deliberately echoes Channel Blue, the Wii counterpart.

Status

Usable on real hardware.

Cobalt is installed and running on a Wii U, and the core Bluesky workflow is usable end-to-end. Host-side compilation, unit tests, link checks, mock-PDS tests and the desktop simulator provide additional coverage, but they do not replace testing on the console.

Implemented

• TV + GamePad and Off-TV Play
• Diagnostics covering paths, networking, TLS, Wolfram and session state
• App-password sign-in with an on-screen keyboard
• Persistent encrypted sessions and sign-out
• Home timeline with paging, reposts and threads
• Posting, replies, quote posts and reply gates
• Likes and reposts, including undo
• Notifications and mark-as-seen
• Profiles, follows and unfollows
• Followers, following and profile tabs
• Pinned posts
• Avatars
• Post, reply and quote images with alt text
• Link-card previews
• Actor search
• Custom feed browsing
• Read-only lists and list members
• Mute and block, including browsable lists
• Post search

Deliberately not planned

Some Bluesky features do not currently fit Cobalt's Wii U target:

• Video and GIFs — there is no suitable decoder in the current dependency and performance budget.
• Push notifications — there is no modern push service available to a Wii U homebrew application.
• OAuth sign-in — the browser-based redirect flow is not a good fit for this application.

These are platform constraints rather than features merely waiting in the backlog.

Requirements

Cobalt requires a Wii U with Aroma installed. It does not install or facilitate the exploit required to run Aroma.

For networked AT Protocol features, you need a Bluesky app password. Cobalt does not use your normal account password.

Building Cobalt requires:

• devkitPro with devkitPPC and the WUT SDK
• the Wii U SDL2, SDL2_ttf and SDL2_image portlibs
• Wii U curl and mbedTLS
• a sibling checkout of Wolfram
• OpenSSL for generating the per-installation entropy seed

Building

Build Wolfram for Wii U first, then build Cobalt:

git clone https://github.com/ewanc26/wolfram ../wolfram

cd ../wolfram
cmake -S . -B build-wiiu \
  -DCMAKE_TOOLCHAIN_FILE=$PWD/.devdeps/wiiu.cmake \
  -DWOLFRAM_BUILD_WIIU=ON \
  -DWOLFRAM_BUILD_TESTS=OFF \
  -DWOLFRAM_BUILD_EXAMPLES=OFF
cmake --build build-wiiu -j8 --target wolfram

cd ../cobalt
make

Cobalt looks for Wolfram at ../wolfram/build-wiiu by default. Set WOLFRAM_ROOT and WOLFRAM_BUILD to override those paths.

A Cobalt build can technically be produced without Wolfram, but the AT Protocol functionality is then omitted. A normal networked build should therefore have Wolfram available.

Build targets

Command	Purpose
make	Build the Wii U application
make bundle	Build the application and create a per-installation entropy seed
make test	Run the host-side test suite
make cacert	Refresh the bundled TLS trust store
make run	Print the expected installation/push location
make clean	Remove generated build and test output

Installing

The normal WUHB installation is:

sd:/wiiu/apps/cobalt.wuhb

For a complete bundle, make bundle creates:

dist/wiiu/
└── apps/
    ├── cobalt.wuhb
    └── cobalt/
        └── entropy.bin

The entropy seed is generated for that installation and must not be shared between consoles.

Cobalt can also be loaded in Cemu for development. Cemu is useful for broad application and UI checks, but it does not reproduce every GamePad, networking, TLS or hardware condition of a real Wii U.

Authentication and storage

Cobalt authenticates with Bluesky app passwords through com.atproto.server.createSession.

Persistent state is kept under:

File	Contents
sd:/wiiu/apps/cobalt/session.dat	Encrypted PDS session
sd:/wiiu/apps/cobalt/device.key	Per-installation encryption key
sd:/wiiu/apps/cobalt/entropy.bin	Per-installation entropy seed
sd:/wiiu/apps/cobalt/cobalt.log	Debug log

Signing out overwrites the session and key before removing them.

The session encryption is deliberately limited by the Wii U's security model: the homebrew environment provides no application-accessible keystore, so the key lives alongside the encrypted session. It protects against incidental exposure of the session file, not someone who has the whole SD card.

Entropy

The Wii U's available mbedTLS entropy source is not suitable for Cobalt's cryptographic needs. Cobalt therefore provisions 64 bytes of entropy per installation and uses its own deterministic generator for subsequent draws, while also providing the required entropy to Wolfram and its TLS transport.

The seed is rotated on boot. A missing seed prevents network authentication rather than silently falling back to weaker randomness.

TLS trust store

The Wii U curl port does not provide a system certificate store that Cobalt can rely on. The build therefore fetches a Mozilla CA bundle into romfs/cacert.pem.

The bundle is generated rather than committed, so it can be refreshed as the Mozilla trust set changes:

make cacert

An offline build can still complete without the bundle, but HTTPS requests will fail certificate verification on the console.

Testing

There is no complete Wii U emulator in Cobalt's workflow, so the repository keeps platform-independent checks on the build machine and uses the real console for hardware-specific behaviour.

make test

This runs the host compile sweep, Wolfram link check when a host Wolfram build is available, and the unit tests.

The test suite covers platform-independent logic including credential storage, service URL handling, keyboard text handling, feed and notification parsing, post layout, image-cache behaviour and other application logic. The Wolfram configuration is also syntax-checked when a sibling Wolfram checkout is available.

Additional checks are available when the corresponding Wolfram host build is present:

make -C tests e2e
make -C tests snapshot
make -C tests sim

The live simulator runs the real application and renderer in two Wii U-sized windows against a mock PDS. It is useful for UI work without a console, but complements rather than replaces hardware testing.

See tests/README.md for the host-test requirements and individual targets.

Repository layout

src/
├── main.c        entry point and frame loop
├── app/          screens and application state
├── ui/           rendering, theme and on-screen keyboard
├── input/        VPAD and controller input
├── net/          Wii U network status and HTTP
├── atproto/      Wolfram-backed session and protocol integration
├── cache/        credential storage
└── util/         logging, paths, entropy and time handling
tools/             asset generation and trust-store fetching
tests/             host checks, unit tests and simulator
romfs/             bundled application data and fonts

AGENTS.md contains the deeper architectural notes and platform constraints behind the implementation.

Accessibility

The GamePad is a first-class display and input surface, including touch input and a dedicated on-screen keyboard.

Image alt text is surfaced directly in the UI because Wii U homebrew does not provide Cobalt with a usable system screen reader. Images with alt text are marked with an explicit ALT badge, and the focused post can display the first image's alt text as a caption.

Contributing

See CONTRIBUTING.md before making changes. Keep changes focused, preserve the existing platform architecture, and run the relevant host-side checks before opening a pull request.

Licence

Cobalt is licensed under the GNU Affero General Public License v3.0. See LICENSE.

Bundled fonts and icon assets have their own licences where applicable; see romfs/FONTS.md for attribution and licence details.