This chapter introduces the Yocto Project and gives you an idea of what you need to get started. You can find enough information to set up your development host and build or use images for hardware supported by the Yocto Project by reading The Yocto Project Quick Start. The remainder of this chapter summarizes what is in the Yocto Project Quick Start and provides some higher-level concepts you might want to consider.

The Yocto Project is an open-source collaboration project focused on embedded Linux development. The project currently provides a build system, which is sometimes referred to as "Poky", and provides various ancillary tools suitable for the embedded developer. The Yocto Project also features the Sato reference User Interface, which is optimized for stylus driven, low-resolution screens. You can use the Yocto Project, which uses the BitBake build tool, to develop complete Linux images and associated user-space applications for architectures based on ARM, MIPS, PowerPC, x86 and x86-64. While the Yocto Project does not provide a strict testing framework, it does provide or generate for you artifacts that let you perform target-level and emulated testing and debugging. And, if you are an Eclipse IDE user, you can install an Eclipse Yocto Plug-in to allow you to develop within that familiar environment.

Here is what you need to get set up to use the Yocto Project: Host System: You should have a reasonably current Linux-based host system. You will have the best results with a recent release of Fedora, OpenSUSE, or Ubuntu as these releases are frequently tested against the Yocto Project and officially supported. You should also have about 100 gigabytes of free disk space for building images. Packages: The Yocto Project requires certain packages exist on your development system (e.g. Python 2.6 or 2.7). See "The Packages" section in the Yocto Project Quick start for the exact package requirements and the installation commands to install them for the supported distributions. Yocto Project Release: You need a release of the Yocto Project. You can get set up with local Yocto Project files one of two ways depending on whether you are going to be contributing back into the Yocto Project source repository or not. Regardless of the method you use, this manual refers to the resulting hierarchical set of files as "the Yocto Project files" or "the Yocto Project file structure." Tarball Extraction: If you are not going to contribute back into the Yocto Project, you can simply download the Yocto Project release you want from the website’s download page. Once you have the tarball, just extract it into a directory of your choice. For example, the following command extracts the Yocto Project 1.1 release tarball into the current working directory and sets up the Yocto Project file structure with a top-level directory named poky-1.1: $ tar xfj poky-edison-6.0.tar.bz2 This method does not produce a Git repository. Instead, you simply end up with a local snapshot of the Yocto Project files that are based on the particular release in the tarball. Git Repository Method: If you are going to be contributing back into the Yocto Project, you should use Git commands to set up a local Git repository of the Yocto Project files. Doing so creates a Git repository with a complete history of changes and allows you to easily submit your changes upstream to the project. The following transcript shows how to clone the Yocto Project files' Git repository into the current working directory. The command creates the repository in a directory named poky. For information on the Yocto Project and Git, see the "Git" section. $ git clone git://git.yoctoproject.org/poky Initialized empty Git repository in /home/scottrif/poky/.git/ remote: Counting objects: 116882, done. remote: Compressing objects: 100% (35987/35987), done. remote: Total 116882 (delta 80651), reused 113045 (delta 77578) Receiving objects: 100% (116882/116882), 72.13 MiB | 2.68 MiB/s, done. Resolving deltas: 100% (80651/80651), done. For another example of how to set up your own local Git repositories, see this wiki page, which describes how to create both poky and meta-intel Git repositories. Linux Yocto Kernel: If you are going to be making modifications to a supported Linux Yocto kernel, you need to establish local copies of the source. This setup involves creating a bare clone of the Linux Yocto kernel and then cloning that repository. You can create the bare clone and the copy of the bare clone anywhere you like. For simplicity, it is recommended that you create these structures outside of the Yocto Project files' Git repository. As an example, the following transcript shows how to create the bare clone of the linux-yocto-3.0 kernel and then create a copy of that clone. When you have a local Linux Yocto kernel Git repository, you can reference that repository rather than the upstream Git repository as part of the clone command. Doing so can speed up the process. In the following example, the bare clone is named linux-yocto-3.0.git, while the copy is named linux-yocto-3.0: $ git clone --bare git://git.yoctoproject.org/linux-yocto-3.0 linux-yocto-3.0.git Initialized empty Git repository in /home/scottrif/linux-yocto-3.0.git/ remote: Counting objects: 2123870, done. remote: Compressing objects: 100% (341338/341338), done. remote: Total 2123870 (delta 1778780), reused 2107534 (delta 1762583) Receiving objects: 100% (2123870/2123870), 445.72 MiB | 2.06 MiB/s, done. Resolving deltas: 100% (1778780/1778780), done. Now create a clone of the bare clone just created: $ git clone linux-yocto-3.0.git linux-yocto-3.0 Initialized empty Git repository in /home/scottrif/linux-yocto-3.0/.git/ Checking out files: 100% (36898/36898), done. The poky-extras Git Repository: The poky-extras Git repository contains metadata needed to build the kernel image. In particular, it contains the kernel .bbappend files that you edit to point to your locally modified kernel source files and to build the kernel image. Pointing to these local files is much more efficient than requiring a download of the source files from upstream each time you make changes to the kernel. It is good practice to create this Git repository inside the Yocto Project files Git repository. Following is an example that creates the poky-extras Git repository inside the Yocto Project files Git repository, which is named poky in this case: $ cd ~/poky $ git clone git://git.yoctoproject.org/poky-extras poky-extras Initialized empty Git repository in /home/scottrif/poky/poky-extras/.git/ remote: Counting objects: 543, done. remote: Compressing objects: 100% (483/483), done. remote: Total 543 (delta 144), reused 307 (delta 39) Receiving objects: 100% (543/543), 520.55 KiB, done. Resolving deltas: 100% (144/144), done. Supported Board Support Packages (BSPs): Similar considerations exist for BSPs. You can get set up for BSP development one of two ways: tarball extraction or with a local Git repository. Regardless of the method you use, the Yocto Project uses the following BSP layer naming scheme: meta-<BSP_name> where <BSP_name> is the recognized BSP name. Here are some examples: meta-crownbay meta-emenlow meta-n450 Tarball Extraction: You can download any released BSP tarball from the same download site used to get the Yocto Project release. Once you have the tarball, just extract it into a directory of your choice. Again, this method just produces a snapshot of the BSP layer in the form of a hierarchical directory structure. Git Repository Method: If you are working with a Yocto Project files Git repository, you should also set up a meta-intel Git repository. Typically, you set up the meta-intel Git repository inside the Yocto Project files Git repository. For example, the following transcript shows the steps to clone the meta-intel Git repository inside the poky Git repository. $cd poky $ git clone git://git.yoctoproject.org/meta-intel.git Initialized empty Git repository in /home/scottrif/poky/meta-intel/.git/ remote: Counting objects: 1325, done. remote: Compressing objects: 100% (1078/1078), done. remote: Total 1325 (delta 546), reused 85 (delta 27) Receiving objects: 100% (1325/1325), 1.56 MiB | 330 KiB/s, done. Resolving deltas: 100% (546/546), done. The same wiki page referenced earlier covers how to set up the meta-intel Git repository. Eclipse Yocto Plug-in: If you are developing applications using the Eclipse Integrated Development Environment (IDE), you will need this plug-in. See the "Setting up the Eclipse IDE" section in the Yocto Application Development Toolkit (ADT) User’s Guide for more information.

The build process creates an entire Linux distribution, including the toolchain, from source. For more information on this topic, see the "Building an Image" section in the Yocto Project Quick Start. The build process is as follows: Make sure you have the Yocto Project files as described in the previous section. Initialize the build environment by sourcing a build environment script. Optionally ensure the conf/local.conf configuration file is set up how you want it. This file defines the target machine architecture and other build options. Build the image using the BitBake command. If you want information on Bitbake, see the user manual at . Run the image either on the actual hardware or using the QEMU emulator.

Another option you have to get started is to use pre-built binaries. This scenario is ideal for developing software applications to run on your target hardware. To do this, you need to install the stand-alone Yocto Project cross-toolchain tarball and then download the pre-built kernel that you will boot in the QEMU emulator. Next, you must download and extract the target root filesystem for your target machine’s architecture. Finally, you set up the environment to emulate the hardware and then start the QEMU emulator. You can find details on all these steps in the "Using Pre-Built Binaries and QEMU" section of the Yocto Project Quick Start.