smid

smid is a Linux userspace driver for the Silicon Motion USB display path used by portable triple-monitor adapters such as the Triple Aero Pro Max by Aura Displays. One panel is usually driven by normal USB-C DisplayPort Alt Mode; smid drives the two USB-attached panels exposed by the adapter's 090c:0760 USB device.

The driver creates EVDI virtual displays, captures their framebuffers, encodes the required JPEG bands, and sends the adapter protocol over USB. The default runtime path uses VA-API for hardware accelerated JPEG encoding, adaptive JPEG quality, cursor commands, USB recovery, and per-frame dirty detection.

Requirements

• Linux with the EVDI kernel module and libevdi development files
• libusb-1.0, libva, and libva-drm development files
• pkg-config, git, cmake, ninja, a C compiler, and nasm or yasm
• A VA-API JPEG-capable driver for the fast path

The CPU encoder remains available as a fallback, but it uses noticeably more CPU than the VA-API path.

Build

make -j"$(nproc)"

The first build fetches a pinned libjpeg-turbo revision into vendor/libjpeg-turbo and builds a static libturbojpeg.a with SIMD enabled. That vendor checkout is a build artifact, not part of the release source.

Useful cleanup targets:

make clean
make distclean

Permissions

Install local udev rules once:

sudo ./install-udev-rules.sh

The rule grants access to the 090c:0760 USB device and EVDI DRM devices for an active local seat. Log out and back in if the installer adds your user to a new group.

If you have already installed the vendor userspace helper, disable or uninstall that before running smid; both drivers cannot own the same USB device at the same time.

Run

./smid

By default this starts two EVDI streams, enables cursor events, uses direct VA-API JPEG encoding when available, and adapts quality around a 36 MiB/s target.

Common options:

--encoder cpu|direct-vaapi
--jpeg-target-mib-s N
--jpeg-quality N
--jpeg-fixed-quality
--evdi-streams 1|2
--seconds N

Dirty detection uses the tested hash-bands path. The top and bottom bands are hashed independently, and unchanged bands can be represented by a small companion update when the adapter's retained-frame basis is known.

Notes

• The adapter expects each USB display frame as two JPEG bands.
• Cursor updates are sent through native cursor commands instead of repainting the framebuffer.
• USB endpoint recovery keeps the EVDI displays open, so window placement should survive transient adapter reconnects.
• Sequence wrap is handled by reconnecting the USB session and forcing a full refresh.
• Reverse-engineering tools, packet experiments, and capture-analysis helpers have been intentionally excluded from this release tree.

License

MIT License. See LICENSE.