Many development models exist for which you can use the Yocto Project. However, for the purposes of this manual we are going to focus on two common ones: System Development and User Application Development. System Development covers Board Support Package (BSP) development and kernel modification. User Application Development covers development of applications that you intend to run on some target hardware. This chapter presents overviews of both system and application models. If you want to reference specific examples of these development models, see BSP Development Example and Kernel Modification Example.

System development involves modification or creation of an image that you want to run on a specific hardware target. Usually when you want to create an image that runs on embedded hardware the image does not require the same amount of features that a full-fledged Linux distribution provides. Thus, you can create a much smaller image that is designed to just use the hardware features for your particular hardware. To help you understand how system development works in the Yocto Project, this section covers two types of image development: BSP creation and kernel modification (see ).

A BSP is a package of recipes that when applied during a build results in an image you can run on a particular board. Thus, the package, when compiled into the new image, supports the operation of the board. For a brief list of terms used when describing the development process in the Yocto Project, see Yocto Project Terms in this manual. The remainder of this section presents the basic steps to create a BSP basing it on an existing BSP that ships with the Yocto Project. You can reference BSP Development Example for a detailed example that uses the Crown Bay BSP as a base BSP from which to start. This illustration and the following list summarizes the BSP creation general workflow. Set up your host development system to support development using the Yocto Project: See The Linux Distributions section and The Packages section both in the Yocto Project Quick Start for requirements. You will also need a release of Yocto Project installed on the host. Establish a local copy of the Yocto Project files on your system: You need to have the Yocto Project files available on your host system. Having the Yocto Project files on your system gives you access to the build process and tools you need. For information on how to get these files, see the Getting Setup section in this manual. Choose a Yocto Project-supported BSP as your base BSP: The Yocto Project ships with several BSPs that support various hardware. It is best to base your new BSP on an existing BSP rather than create all the recipes and configuration files from scratch. While it is possible to create everything from scratch, basing your new BSP on something that is close is much easier. Or, at a minimum, it gives you some structure with which to start. At this point you need to understand your target hardware well enough to determine which existing BSP it most closely matches. Things to consider are your hardware’s on-board features such as CPU type and graphics support. You should look at the README files for supported BSPs to get an idea of which one you could use. A generic Atom-based BSP to consider is the Crown Bay that does not support the Intel® Embedded Media Graphics Driver (EMGD). The remainder of this example uses that base BSP. To see the supported BSPs, go to the Yocto Project download page and click on “BSP Downloads.” Establish a local copy of the base BSP files: Having the BSP files on your system gives you access to the build process and tools you need. For information on how to get these files, see Getting Setup earlier in this manual. Create your own BSP layer: Layers are ideal for isolating and storing work for a given piece of hardware. A layer is really just a location or area in which you place the recipes for your BSP. In fact, a BSP is, in itself, a special type of layer. Consider an application as another example that illustrates a layer. Suppose you are creating an application that has library or other dependencies in order for it to compile and run. The layer, in this case, would be where all the recipes that define those dependencies are kept. The key point for a layer is that it is an isolated area that contains all the relevant information for the project that the Yocto Project build system knows about. The Yocto Project supports four BSPs that are part of the Yocto Project release: atom-pc, beagleboard, mpc8315e, and routerstationpro. The recipes and configurations for these four BSPs are located and dispersed within local Yocto Project files. Consequently, they are not totally isolated in the spirit of layers unless you think of meta-yocto as a layer itself. On the other hand, BSP layers for Crown Bay, Emenlow, Jasper Forest, N450, and Sugar Bay are isolated. When you set up a layer for a new BSP you should follow a standard layout. This layout is described in the Example Filesystem Layout section of the Board Support Package (BSP) Development Guide. In the standard layout you will notice a suggested structure for recipes and configuration information. You can see the standard layout for the Crown Bay BSP in this example by examining the directory structure of the meta-crownbay layer inside the local Yocto Project files. Make configuration and recipe changes to your new BSP layer: The standard BSP layer structure organizes the files you need to edit in conf and several recipes-* within the BSP layer. Configuration changes identify where your new layer is on the local system and identify which kernel you are going to use. Recipe changes include altering recipes (.bb files), removing recipes you don't use, and adding new recipes that you need to support your hardware. Prepare for the build: Once you have made all the changes to your BSP layer there remains a few things you need to do for the Yocto Project build system in order for it to create your image. You need to get the build environment ready by sourcing an environment setup script and you need to be sure two key configuration files are configured appropriately. The entire process for building an image is overviewed in the Building an Image section of the Yocto Project Quick Start. You might want to reference this information. Build the image: The Yocto Project uses the BitBake tool to build images based on the type of image you want to create. You can find more information on BitBake here. The build process supports several types of images to satisfy different needs. When you issue the BitBake command you provide a “top-level” recipe that essentially starts the process off of building the type of image you want. [WRITER'S NOTE: Consider moving this to the Poky Reference Manual.] You can find these recipes in the meta/recipes-core/images and meta/recipes-sato/images directories of your local Yocto Project file structure (Git repository or extracted release tarball). Although the recipe names are somewhat explanatory, here is a list that describes them: Base – A foundational basic image without support for X that can be reasonably used for customization. Core – A foundational basic image with support for X that can be reasonably used for customization. Direct Disk – An image that you can copy directory to the disk of the target device. Live – An image you can run from a USB device or from a CD without having to first install something. Minimal – A small image without a GUI. This image is not much more than a kernel with a shell. Minimal Development – A Minimal image suitable for development work. Minimal Direct Disk – A Minimal Direct Disk image. Minimal RAM-based Initial Root Filesystem – A minimal image that has the initramfs as part of the kernel, which allows the system to find the first “init” program more efficiently. Minimal Live – A Minimal Live image. Minimal MTD Utilities – A minimal image that has support for the MTD utilities, which let the user interact with the MTD subsystem in the kernel to perform operations on flash devices. Sato – An image with Sato support, a mobile environment and visual style that works well with mobile devices. Sato Development – A Sato image suitable for development work. Sato Direct Disk – A Sato Direct Disk image. Sato Live – A Sato Live image. Sato SDK – A Sato image that includes the Yocto Project toolchain and development libraries. Sato SDK Direct Disk – A Sato SDK Direct Disk image. Sato SDK Live – A Sato SDK Live image. You can view a video presentation of the BSP creation process here. You can also find supplemental information in the Board Support Package (BSP) Development Guide. Finally, there is wiki page write up of the example located here you might find helpful.

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