Add experimental reMarkable 1/rM2 windowed build (rm1 feature)

[sliekens]

Summary

Optional reMarkable 1 / rM2 support alongside unchanged default Paper Pro builds. Compiles with --features rm1 for armv7 windowed AppLoad/qtfb; default aarch64 targets are untouched.

What changes

• rm1 cargo feature — 1404×1872 display, Wacom digitizer, FBFMT_RM2FB, no quill takeover
• qtfb / evdev wire layouts — keyed off target_pointer_width (32 vs 64 bit), not product
• Pen input — Wacom axis rotation map, AppLoad qtfb-shim-32bit via launch script, qtfb pen fallback when evdev grab fails
• Windowed mode polish — footstep stamps (takeover-only upstream experiment) disabled in qtfb; tighter touch+pressure filtering to avoid stray ink
• Build / install — build-rm1.sh, external.manifest.rm1.json, appload-launch-rm1.sh, README section

Tested on

reMarkable 1.0, OS 3.22.0.64, xovi arm32 + AppLoad v0.4.2, OpenAI HTTP oracle.

Not included

quill takeover, 5-finger quit, power-button sleep — Paper Pro / takeover only.

[Copilot]

Pull request overview

Adds an experimental reMarkable 1 / rM2 windowed (qtfb) build path gated behind a new rm1 Cargo feature, while keeping the default Paper Pro build behavior unchanged.

Changes:

• Introduces rm1 feature flags for resolution, framebuffer format, and digitizer handling (Wacom vs Paper Pro marker).
• Updates qtfb and evdev parsing to handle 32-bit vs 64-bit ABI layout differences via target_pointer_width.
• Adds armv7 build/install artifacts (build script, AppLoad launcher, external manifest) and documents the new workflow.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
riddle/src/qtfb.rs	Adds ABI-dependent parsing helpers for init reply and userinput messages (32-bit vs 64-bit layout).
riddle/src/pen.rs	Adds rm1 Wacom ranges, 32/64-bit input_event parsing, and rm1 axis-to-screen rotation mapping.
riddle/src/main.rs	Changes raw-pen selection logic and gates the “footstep stamp” experiment behind takeover mode.
riddle/src/fb.rs	Makes screen dimensions feature-dependent (Paper Pro vs rm1/rm2).
riddle/src/display.rs	Selects qtfb fmt/geometry per feature and tweaks refresh mode for rm1.
riddle/scripts/appload-launch-rm1.sh	New AppLoad launcher that preloads the 32-bit qtfb shim for rm1/rm2 windowed mode.
riddle/external.manifest.rm1.json	New AppLoad manifest for the rm1/rm2 windowed bundle.
riddle/Cargo.toml	Adds rm1 feature and updates crate description to mention optional windowed build.
riddle/build-rm1.sh	New cross-build script producing a dist-rm1/ bundle for tablet install.
riddle/.cargo/config.toml	Adds armv7 linker configuration.
README.md	Documents the experimental rm1/rm2 windowed build steps and constraints.
.gitignore	Ignores the riddle/dist-rm1/ build output directory.

Comments suppressed due to low confidence (1)

riddle/src/qtfb.rs:107

• recv may return fewer than 32 bytes; the code only checks n <= 0 and then parses fixed offsets. If the init reply is short (or malformed), this can mis-parse shm_key/shm_size and attempt to open/mmap the wrong segment. Add a minimum-length check keyed off the ABI before calling parse_init_reply.

        let mut reply = [0u8; 32];
        let n = unsafe { libc::recv(fd, reply.as_mut_ptr() as *mut libc::c_void, 32, 0) };
        if n <= 0 {
            unsafe { libc::close(fd) };
            return Err(io::Error::new(

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