Write on the page with your pen. After a pause, the diary drinks your ink — your words fade into the paper — the page thinks for a moment, and an answer writes itself back in a flowing hand, stroke by stroke, then fades away.

No screen glow, no keyboard, no chat UI. Just ink appearing on paper.

This is the diary from the demo.

You need a reMarkable Paper Pro in developer mode with a launcher installed. If that sounds like a lot, it isn't — remagic walks you through turning on developer mode and sets up everything with one command. Come back here, drop riddle in, and start writing to Tom.

Already have xovi + AppLoad? Download the latest release — a ready-to-drop bundle, no compiler needed — or build from source.

1. Grab riddle-appload-aarch64.zip from the latest release and unzip it.
2. Copy the folder to your tablet: scp -O -r riddle root@10.11.99.1:/home/root/xovi/exthome/appload/
3. Add an API key: cp oracle.env.example oracle.env in that folder and put your RIDDLE_OPENAI_KEY in it (any OpenAI-compatible key). Or skip it to use pi.
4. In AppLoad: tap Reload, then The Diary. Write, and rest your pen.

⚠️ This modifies your device. It runs as root, stops the vendor UI (in takeover mode), and drives the e-ink engine directly. It has only been tested on a reMarkable Paper Pro (ferrari, aarch64, OS 3.26–3.27). It may not work on other models or OS versions, and you use it entirely at your own risk. Not affiliated with reMarkable AS. Keep SSH access working before you install anything — that is your escape hatch.

 pen (raw evdev, full 4096-level pressure, hardware event rate)
   │ strokes
   ▼
 riddle ── idle 2.8s → commit page → PNG ──► oracle (resident LLM process,
   │                                          streams reply sentence-by-sentence)
   ▼ strokes (Dancing Script → skeletonized to single-pixel pen paths)
 display backend
   ├── qtfb        — windowed, inside xochitl (AppLoad app)
   └── quill       — full takeover: xochitl stopped, vendor e-ink engine
                     driven directly for instant ink (lowest latency there is)

• riddle/ — the app (Rust). Pen input, ink surface, handwriting synthesis (rasterize → Zhang-Suen thinning → stroke tracing → animated replay), the oracle process manager, and both display backends.
• quill/ — the takeover display host (C/C++). An epfb-re-style QImage-constructor interposition shim over the vendor libqsgepaper.so waveform engine, exposed as a small C ABI (quill_init / quill_buffer / quill_swap) that riddle links against with --features takeover. Includes scribble, a minimal pen-to-glass latency demo.

The diary's replies come from a vision LLM that reads your handwriting from the committed page (sent as an inline PNG). There are two backends, chosen at startup — pick whichever you have:

Set an API key and riddle talks straight to an OpenAI-compatible /chat/completions endpoint. Works with OpenAI, OpenRouter, Groq, a local server — anything that speaks the format. No extra software on the tablet.

export RIDDLE_OPENAI_KEY="sk-..."                       # required
export RIDDLE_OPENAI_BASE="https://api.openai.com/v1"   # optional (default)
export RIDDLE_OPENAI_MODEL="gpt-4o-mini"                # optional; must see images

Any vision-capable model works. Example with OpenRouter:

export RIDDLE_OPENAI_KEY="$OPENROUTER_API_KEY"
export RIDDLE_OPENAI_BASE="https://openrouter.ai/api/v1"
export RIDDLE_OPENAI_MODEL="openai/gpt-4o-mini"

Verify your setup before launching the diary:

riddle --oracle-test path/to/handwriting.png   # prints the streamed reply

Measured ~0.9–1.1 s to first ink on-device. The HTTPS is built into riddle (pure-Rust, no extra libraries).

If you already run pi, riddle will use a resident pi --mode rpc process kept warm (Node + your subscription auth loaded once), so each turn pays only model latency. Used automatically when RIDDLE_OPENAI_KEY is not set.

Both stream the reply sentence-by-sentence, so the quill starts writing seconds before the model finishes. The persona prompt lives in riddle/src/oracle.rs.

Cross-compiled from x86_64. Two flavours:

Requires xovi + AppLoad on the device.

cd riddle
cargo build --release --target aarch64-unknown-linux-gnu

Install to /home/root/xovi/exthome/appload/riddle/ with external.manifest.json, appload-launch.sh, and the binary.

Requires the reMarkable SDK toolchain (~/rm-sdk-3.26) because the linked vendor Qt libs need its glibc, and libqsgepaper.so pulled from your own device (it is proprietary and not distributed here):

cd quill && ./build.sh          # pulls libqsgepaper.so from the device over ssh,
                                # builds libquill.so + scribble
cd ../riddle && ./build-takeover.sh

Deploy libquill.so to /home/root/quill/ and riddle-takeover to /home/root/riddle/riddle, plus scripts/riddle-takeover.sh. Launching via AppLoad (appload-launch.sh) detaches into a transient systemd unit, stops xochitl, runs the diary, and always restores xochitl on exit — exit with the power button, a 5-finger tap, or SIGTERM. If anything wedges: ssh root@10.11.99.1 'systemctl start xochitl'.

The reply hand is Dancing Script (SIL OFL 1.1 — see riddle/fonts/OFL.txt).

MIT for everything in this repository (see LICENSE). The vendor libraries it interposes (libqsgepaper.so, Qt) are not included and must come from your own device/SDK.