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Access USB devices from Ruby

LIBUSB is a Ruby binding that gives Ruby programmers access to arbitrary USB devices.

  • libusb is a library that gives full access to devices connected via the USB bus. No special kernel driver is thus necessary for accessing USB devices.
  • This Ruby binding supports the API version 1.0 of libusb. Note that the old "legacy" version 0.1.x of libusb uses a completely different API that is covered by the ruby extension ruby-usb .

LIBUSB for Ruby is covered by the GNU Lesser General Public License version 3.

Features

  • Access to descriptors of devices, configurations, interfaces, settings and endpoints
  • Synchronous and asynchronous communication for bulk, control, interrupt and isochronous transfers
  • Compatibility layer for ruby-usb (API based on libusb-0.1). See USB for description.

Synopsis

See the documentation for a full API description.

require "libusb"

usb = LIBUSB::Context.new
device = usb.devices(:idVendor => 0x04b4, :idProduct => 0x8613).first
device.open_interface(0) do |handle|
  handle.control_transfer(:bmRequestType => 0x40, :bRequest => 0xa0, :wValue => 0xe600, :wIndex => 0x0000, :dataOut => 1.chr)
end

LIBUSB::Context#devices is used to get all or only particular devices. After opening and claiming the LIBUSB::Device the resulting LIBUSB::DevHandle can be used to communicate with the connected USB device by LIBUSB::DevHandle#control_transfer, LIBUSB::DevHandle#bulk_transfer, LIBUSB::DevHandle#interrupt_transfer or by using the LIBUSB::Transfer classes.

A LIBUSB::Device can also be used to retrieve information about it, by using the device descriptor attributes. A LIBUSB::Device could have several configurations. You can then decide of which configuration to enable. You can only enable one configuration at a time.

Each LIBUSB::Configuration has one or more interfaces. These can be seen as functional group performing a single feature of the device.

Each LIBUSB::Interface has at least one LIBUSB::Setting. The first setting is always default. An alternate setting can be used independent on each interface.

Each LIBUSB::Setting specifies it's own set of communication endpoints. Each LIBUSB::Endpoint specifies the type of transfer, direction, polling interval and maximum packet size.

Prerequisites

  • Linux, MacOSX or Windows system with Ruby MRI 1.8.7/1.9/2.0, JRuby or recent version of Rubinius
  • Optionally: libusb or libusbx library version 1.0.8+ :

    • Debian or Ubuntu:
      
    • OS-X: install with homebrew:
      

    or macports:

      
    • Windows: libusb.gem already comes with a precompiled libusb.dll, but you need to install a device driver (see below)

Install

$ gem install libusb

While gem install the system is checked for a usable libusb(x) library installation. If none could be found, a bundled libusb version is built and used, instead.

Latest code can be used in this way:

$ git clone git://github.com/larskanis/libusb.git
$ rake install_gem

Device hotplug support

Support for device hotplugging can be used, if LIBUSB.has_capability?(:CAP_HAS_HOTPLUG) returns true. This requires libusb(x)-1.0.16 or newer on Linux or OS-X. Windows support is still on the way.

A hotplug event handler can be registered with LIBUSB::Context#on_hotplug_event. You then need to call LIBUSB::Context#handle_events in order to receive any events. This can be done as blocking calls (possibly in it's own thread) or by using LIBUSB::Context#pollfds to detect any events to handle.

Usage on Windows

In contrast to Linux, any access to an USB device by LIBUSB on Windows requires a proper driver installed in the system. Fortunately creating such a driver is quite easy with Zadig. Select the interesting USB device, choose WinUSB driver and press "Install Driver". That's it. You may take the generated output directory with it's INI-file and use it for driver installation on other 32 or 64 bit Windows systems.

Cross compiling for Windows

Libusb-gem can be build on a linux or darwin host for the win32 platform, using the mingw cross compiler collection. Libusb is downloaded from source git repo, cross compiled and included in the generated libusb.gem.

Install mingw32. On a debian based system this should work:

$ apt-get install mingw32

On MacOS X, if you have MacPorts installed:

$ port install i386-mingw32-gcc

Download and cross compile libusb for win32:

$ rake cross gem

If everything works, there should be libusb-VERSION-x86-mingw32.gem in the pkg directory.

EventMachine integration

Libusb for Ruby comes with an experimental integration to EventMachine. That API is currently proof of concept - see LIBUSB::Context#eventmachine_register. If you're experienced with EventMachine, please leave a comment.

Resources

Todo

  • stabilize EventMachine interface