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Access USB devices from Ruby via libusb-1.x

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README.md

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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 {LIBUSB::Device#open_interface 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:

      $ sudo apt-get install libusb-1.0-0-dev
      
    • OS-X: install with homebrew (note the x):

      $ brew install libusbx
      

      or macports:

        $ port install libusb
      
    • 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 libusbx 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
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