libMVCI — an open J2534 driver for the Mini-VCI USB adapter

Cross-platform implementation of the SAE J2534 PassThru API for the common FTDI FT232R–based Mini‑VCI / "M‑VCI" diagnostic cable, so the hardware you own can be used with standard J2534 diagnostic software — including on Linux and macOS, where no vendor driver exists.

Platform	Output	Serial backend	Crypto backend
Linux	libMVCI.so	termios (/dev/ttyUSBx)	OpenSSL libcrypto
macOS	libMVCI.dylib	termios (/dev/cu.usbserial-*)	CommonCrypto (system)
Windows	MVCI32.dll (x86), MVCI64.dll (x64)	FTDI D2XX (ftd2xx.dll, loaded at runtime)	Windows CNG (BCrypt)

Built with CMake; the library lands in the build tree (e.g. build/). See BUILD.md.

Why this exists — interoperability

This project was created for interoperability. The "M‑VCI" cable ships with a closed, Windows‑only J2534 DLL, which means owners of the hardware cannot use it with J2534 tools on Linux, nor with their own software, and have no documentation of how the device communicates.

libMVCI is an independent, re‑implementation of the publicly‑observable J2534 interface and the cable's serial wire protocol, written so that:

• the same physical adapter works across operating systems (notably Linux);
• it can be used as a drop‑in J2534 provider for existing diagnostic applications; and
• the device's behaviour is documented and not locked to one vendor's binary.

It contains no vendor code — only an original implementation that speaks the same wire protocol.

Status

• ✅ ISO14230 / KWP2000 (K‑line) — connect, message filters, SET_CONFIG, fast‑init, and OBD request/response are implemented and tested on a vehicle (live PID reads; works as a J2534 provider for Toyota Techstream over K‑line).
• ⬜ ISO15765 / CAN — not yet implemented. CAN ECUs are not yet reachable.
• The wire framing (DES‑based) and session handling are fully implemented and identical across all platforms; only the protocol/transport/crypto backends differ per OS, selected at compile time.

Hardware

FTDI FT232R, USB VID 0x0403 / PID 0x6001, USB description M-VCI (115200 8N1). On Linux it enumerates through the kernel ftdi_sio driver as /dev/ttyUSBx; on macOS through Apple's FTDI VCP driver as /dev/cu.usbserial-*; on Windows it is opened directly through ftd2xx.dll. No libusb dependency exists.

Building

CMake is the cross-platform build (Linux, macOS, Windows). See BUILD.md for per-platform notes and how to consume MVCI from another CMake project.

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
ctest --test-dir build            # codec self-test, no hardware needed

On Windows, build a specific architecture with the bundled presets (from the matching Native Tools Command Prompt, or by selecting the preset in your IDE):

cmake --preset win64   &&  cmake --build --preset win64   :: MVCI64.dll
cmake --preset win32   &&  cmake --build --preset win32   :: MVCI32.dll

Reuse it from another CMake project — either vendored:

add_subdirectory(external/libmvci)
target_link_libraries(your_target PRIVATE libmvci)

or installed:

find_package(libmvci CONFIG REQUIRED)
target_link_libraries(your_target PRIVATE libMVCI::libmvci)

Using it

The library exports the standard J2534 PassThru* functions, so any J2534 host application can load it.

• Windows: register/point your tool at MVCI32.dll (32‑bit hosts) or MVCI64.dll (64‑bit). It opens the adapter by its USB description M-VCI.
• Linux: load libMVCI.so. Tell it which serial node to use via the pName argument to PassThruOpen, or the MVCI_PORT environment variable (default /dev/ttyUSB0). Add yourself to the dialout group for port access.
• macOS: load libMVCI.dylib. Same as Linux, but the FTDI VCP node is /dev/cu.usbserial-* (MVCI_PORT default /dev/cu.usbserial).

The MVCI session layer can also be used directly via #include <mvci/serial.h> (see test/mvci_test.c for an example: handshake → connect → fast‑init → read PIDs).

Layout

include/mvci/    public headers      ->  #include <mvci/j2534.h>, <mvci/serial.h>
src/             sources + private headers (io.h, compat.h, mvci.def)
test/            mvci_test.c — cross-platform self-test + live harness
docs/            protocol specification (PROTOCOL.md)
cmake/           package-config template (libmvciConfig.cmake.in)
CMakeLists.txt   cross-platform build
CMakePresets.json  win32/win64 + default build presets
build/           build output (generated)

Documentation

The wire protocol and frame format are specified in docs/PROTOCOL.md.

License

LICENSE.md

Disclaimer

This is an independent, unofficial project for interoperability with hardware the user already owns. It is not affiliated with, authorised by, or endorsed by Toyota, XHorse, FTDI, or any J2534 software vendor. All product and company names and trademarks are the property of their respective owners. Provided as‑is, with no warranty; use at your own risk.