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Introduction

Embedded Crosswalk Project (ECP) is the minimal Linux platform that boots a fully-fledged Web application.

In development terms, ECP is actually a Yocto layer where it carefully select components and custom configure them, featuring the Crosswalk Web runtime and Chromium. In particular Chromium here is using Ozone-GBM platform and therefore does not rely on any Linux traditional window system like X11, Wayland, etc, neither graphics toolkits like EFL, Qt. It's a pretty simple and new software stack that the main motivation is to leverage the Web platform (HTML5, CSS, JavaScript and more) as the application platform.

You may want to use the Embedded Crosswalk Project as a backbone for creating a real Web-based Linux distribution to enable IoT (Internet of Things), Wearables, Digital Signage or any other embedded use case.

Contents

  • Design - the architecture behind
  • Howto - set up the system environment, build and run
  • Bugs - what's not working that we need still to catch up and improve
  • Customizing - boot up your own Web app and other hacking
  • Contributing - help develop and send patches
  • License

Design

Alt text

Howto

Important caveat: ECP at the moment works only for x86 (Intel) and modern hardware containing GPU due the Chromium Ozone-GBM architecture. That said, we don't have plans to extend it to any other category of devices. For testing, development and deployment we recommend the MinnowBoard MAX.

This guide will help you to build a bootable image with the Embedded Crosswalk Project. Most of the toolchain needed to build comes from Yocto Poky and it's expected to use just a few of your system's dependencies. We use Ubuntu 14.04 LTS (Trusty Tahr) in particular, but there's no reason to not use any other different system. Besides, make sure you have at least 45 GB of disk space to store all the sources and a few types of images to be built.

Firstly, you will need anyway a couple of your distribution tools and development packages:

$ sudo apt-get install gawk wget git-core diffstat unzip texinfo \
gcc-multilib g++-multilib build-essential chrpath libsdl1.2-dev xterm gyp

then download the needed stuff:

$ mkdir yocto
$ cd yocto/

$ git clone http://git.yoctoproject.org/git/poky
$ git clone http://github.com/crosswalk-project/meta-crosswalk
$ git clone http://github.com/otcshare/meta-crosswalk-embedded

now go to poky and checkout the 'dizzy' branch, which is where the new things are and then jump to its build environment:

$ cd poky/
$ git checkout dizzy
$ source oe-init-build-env

You had no conf/local.conf file so a configuration file has therefore been created for you with some default values, but we need still to add the meta-crosswalk and meta-crosswalk-embedded layers in conf/bblayers.conf - mind to change the lines below with the full path of the directory you are cloning the repos (in our case it was /media/yocto/) :

BBLAYERS ?= " \
/media/yocto/poky/meta \
/media/yocto/poky/meta-yocto \
/media/yocto/poky/meta-yocto-bsp \
/media/yocto/meta-crosswalk-embedded \
/media/yocto/meta-crosswalk \
"

In the conf/local.conf file, set the distro variable from the default (usually "poky") to "crosswalk-embedded", which stands for our custom Yocto distribution:

DISTRO ?= "crosswalk-embedded"

then, set in conf/local.conf the genericx86-64 machine (you could try a different architecture but we haven't yet):

MACHINE ?= "genericx86-64"

besides, still in local.conf we need to pick our simple Web UI to boot the system into. So add this in the same file:

IMAGE_INSTALL_append = " ventus"

Now close the file and let's cook the image:

$ bitbake core-image-crosswalk-embedded

It will take several hours to download much of the dependencies, build and etc. Relax now. If everything goes fine, you will have the following directory with the images built in inside:

$ ls tmp/deploy/images/genericx86-64/*.hddimg
$ tmp/deploy/images/genericx86-64/core-image-crosswalk-embedded-genericx86-64-20141009113028.hddimg
$ tmp/deploy/images/genericx86-64/core-image-crosswalk-embedded-genericx86-64.hddimg

Make sure you have now inserted a USB flash drive, checking the correct file descriptor that Linux will be using with the sudo fdisk -l command. For example in our system it is /dev/sdd, so the following is what we used to flash it:

$ cd tmp/deploy/images/genericx86-64/
$ sudo dd if=core-image-crosswalk-embedded-genericx86-64.hddimg of=/dev/sdd
$ sync 
$ sudo eject /dev/sdd

You are able now to boot the flash drive in your hardware and play around with a couple of examples such as HexGL, Emberwind, WebRTC, WebGL motion detector (using Web cam), Crosswalk, among others. Note that what you are seeing there as a "desktop" is actually the HTML5 & CSS3 window manager Ventus, so don't get confused because nothing you see there is native but Web-based ;)

Bugs

What's not working:

  • Sound
  • Touchpad

Customizing

The first customization that you may want to try is boot up your own Web app instead the example we provide -- note that Crosswalk is a runtime not a regular browser, so you won't get an URL bar to load anything you want. Let's say you want to make an image booting into "myapp", so first you need to install "myapp" and "crosswalk-service" into your image:

IMAGE_INSTALL_append = " crosswalk-service myapp"

Worth to mention that "crosswalk-service" is already included by default in the ECP distribution but "myapp" obviously not. You have two parameters then you may want to set in your Yocto's conf/local.conf. With CROSSWALK_SERVICE_PARAMS, one will able to point to the manifest of "myapp" in the filesystem (or to something online like http://example.com, but you need to make sure that network is up on boot time in this case). Example:

CROSSWALK_SERVICE_PARAMS = "/path/to/myapp/manifest.json"

or simply:

CROSSWALK_SERVICE_PARAMS = "http://example.com"

The other parameter is CROSSWALK_SERVICE_DEBUG. Set this to 1 and the image will boot into the shell, you can call xwalk-service executable manually after logging in. Example:

CROSSWALK_SERVICE_DEBUG = "1"

Contributing

Start discussions by opening issues in github (right menu) and after agreed the necessary changes with the developers, send a pull request. Jump on IRC and chat with other developers; they hang out on Freenode in the #crosswalk channel. Subscribe yourself to the crosswalk-dev mailing list.

License

Embedded Crosswalk Project (ECP) uses the BSD license (check the LICENSE file in the project).

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