# Common Development Models

Many development models exist for which you can use the Yocto Project. This chapter overviews simple methods that use tools provided by the Yocto Project:

- System Development: System Development covers Board Support Package (BSP) development and kernel modification or configuration. For an example on how to create a BSP, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide. For more complete information on how to work with the kernel, see the Yocto Project Linux Kernel Development Manual.

- User Application Development: User Application Development covers development of applications that you intend to run on target hardware. For information on how to set up your host development system for user-space application development, see the Yocto Project Application Developer's Guide. For a simple example of user-space application development using the Eclipse IDE, see the "Application Development Workflow" section.

- Temporary Source Code Modification: Direct modification of temporary source code is a convenient development model to quickly iterate and develop towards a solution. Once you implement the solution, you should of course take steps to get the changes upstream and applied in the affected recipes.

- Image Development using Toaster: You can use Toaster to build custom operating system images within the build environment. Toaster provides an efficient interface to the OpenEmbedded build that allows you to start builds and examine build statistics.

- Image Development using Hob: You can use the Hob to build custom operating system images within the build environment. Hob provides an efficient interface to the OpenEmbedded build system.

- Using a Development Shell: You can use a `devshell` to efficiently debug commands or simply edit packages. Working inside a development shell is a quick way to set up the OpenEmbedded build environment to work on parts of a project.

## System Development Workflow

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 number of features that a full-fledged Linux distribution provides. Thus, you can create a much smaller image that is designed to use only the 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 or configuration.

### Developing a Board Support Package (BSP)

A BSP is a collection of recipes that, when applied during a build, results in an image that 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 the "Yocto Project Terms" section.

The remainder of this section presents the basic steps used to create a BSP using the Yocto Project's BSP Tools. Although not required for BSP creation, the `meta-intel` repository, which contains many BSPs supported by the Yocto Project, is part of the example.

For an example that shows how to create a new layer using the tools, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

The following illustration and list summarize the BSP creation general workflow.

1. Set up your host development system to support development using the Yocto Project: See the "The Linux Distribution" and the "The Packages" sections both in the Yocto Project Quick Start for requirements.

2. Establish a local copy of the project files on your system: You need this Source Directory available on your host system. Having these files on your system gives you access to the build process and to the tools you need. For information on how to set up the Source Directory, see the "Getting Set Up" section.

3. Establish the `meta-intel` repository on your system: Having local copies of these supported BSP layers on your system gives you access to layers you might be able to build on or modify to create your BSP. For information on how to get these files, see the "Getting Set Up" section.

4. Create your own BSP layer using the `yocto-bsp` script: 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 and configurations for your BSP. In fact, a BSP is, in itself, a special type of layer. The simplest way to create a new BSP layer that is compliant with the Yocto Project is to use the `yocto-bsp` script. For information about that script, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support (BSP) Developer's Guide.

   Another example that illustrates a layer is an application. 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 OpenEmbedded build system knows about. For more information on layers, see the "Understanding and Creating Layers" section. For more information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

   Five BSPs exist that are part of the Yocto Project release: `genericx86`, `genericx86-64`, `beaglebone` (ARM), `mpc8315e` (PowerPC), and `edgerouter` (MIPS). The recipes and configurations for these five BSPs are located and dispersed within the Source Directory. On the other hand, the `meta-intel` layer contains BSP layers for many supported BSPs (e.g. Crystal Forest, Emenlow, Fish River Island 2, Haswell, Jasper Forest, and so forth). Aside from the BSPs in the `meta-intel` layer, the Source Repositories contain additional BSP layers such as `meta-minnow` and `meta-raspberrypi`.

   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 a BSP by examining any supported BSP found in the `meta-intel` layer inside the Source Directory.

5. Make configuration changes to your new BSP layer: The standard BSP layer structure organizes the files you need to edit in `conf` and several `recipes-*` directories 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. When you run the `yocto-bsp` script, you are able to interactively configure many things for the BSP (e.g. keyboard, touchscreen, and so forth).

6. Make recipe changes to your new BSP layer: Recipe changes include altering recipes (`.bb` files), removing recipes you do not use, and adding new recipes or append files (`.bbappend`) that you need to support your hardware.

7. 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 OpenEmbedded build system in order for it to create your image. You need to get the build environment ready by sourcing an environment setup script (i.e. `oe-init-build-env` or `oe-init-build-env-memres`) and you need to be sure two key configuration files are configured appropriately: the `conf/local.conf` and the `conf/bblayers.conf` file. You must make the OpenEmbedded build system aware of your new layer. See the "Enabling Your Layer" section for information on how to let the build system know about your new layer.

   The entire process for building an image is overviewed in the section "Building an Image" section of the Yocto Project Quick Start. You might want to reference this information.

8. Build the image: The OpenEmbedded build system uses the BitBake tool to build images based on the type of image you want to create. You can find more information about BitBake in the BitBake User Manual.

   The build process supports several types of images to satisfy different needs. See the "Images" chapter in the Yocto Project Reference Manual for information on supported images.

You can view a video presentation on "Building Custom Embedded Images with Yocto" at Free Electrons. After going to the page, just search for "Embedded". You can also find supplemental information in the Yocto Project Board Support Package (BSP) Developer's Guide. Finally, there is helpful material and links on this wiki page. Although a bit dated, you might find the information on the wiki helpful.

### Modifying the Kernel

Kernel modification involves changing the Yocto Project kernel, which could involve changing configuration options as well as adding new kernel recipes. Configuration changes can be added in the form of configuration fragments, while recipe modification comes through the kernel's `recipes-kernel` area in a kernel layer you create.

The remainder of this section presents a high-level overview of the Yocto Project kernel architecture and the steps to modify the kernel. You can reference the "Patching the Kernel" section for an example that changes the source code of the kernel. For information on how to configure the kernel, see the "Configuring the Kernel" section. For more information on the kernel and on modifying the kernel, see the Yocto Project Linux Kernel Development Manual.

#### Kernel Overview

Traditionally, when one thinks of a patched kernel, they think of a base kernel source tree and a fixed structure that contains kernel patches. The Yocto Project, however, employs mechanisms that, in a sense, result in a kernel source generator. By the end of this section, this analogy will become clearer.

You can find a web interface to the Yocto Project kernel source repositories at . If you look at the interface, you will see to the left a grouping of Git repositories titled "Yocto Linux Kernel." Within this group, you will find several kernels supported by the Yocto Project:

- `linux-yocto-3.8` - The stable Yocto Project kernel to use with the Yocto Project Release 1.4. This kernel is based on the Linux 3.8 released kernel.

- `linux-yocto-3.10` - An additional, unsupported Yocto Project kernel used with the Yocto Project Release 1.5. This kernel is based on the Linux 3.10 released kernel.

- `linux-yocto-3.14` - The stable Yocto Project kernel to use with the Yocto Project Releases 1.6 and 1.7. This kernel is based on the Linux 3.14 released kernel.

- `linux-yocto-3.17` - An additional, unsupported Yocto Project kernel used with the Yocto Project Release 1.7. This kernel is based on the Linux 3.17 released kernel.

- `linux-yocto-3.19` - The stable Yocto Project kernel to use with the Yocto Project Release 1.8. This kernel is based on the Linux 3.19 released kernel.

- `linux-yocto-dev` - A development kernel based on the latest upstream release candidate available.

The kernels are maintained using the Git revision control system that structures them using the familiar "tree", "branch", and "leaf" scheme. Branches represent diversions from general code to more specific code, while leaves represent the end-points for a complete and unique kernel whose source files, when gathered from the root of the tree to the leaf, accumulate to create the files necessary for a specific piece of hardware and its features. The following figure displays this concept:

Within the figure, the "Kernel.org Branch Point" represents the point in the tree where a supported base kernel is modified from the Linux kernel. For example, this could be the branch point for the `linux-yocto-3.19` kernel. Thus, everything further to the right in the structure is based on the `linux-yocto-3.19` kernel. Branch points to the right in the figure represent where the `linux-yocto-3.19` kernel is modified for specific hardware or types of kernels, such as real-time kernels. Each leaf thus represents the end-point for a kernel designed to run on a specific targeted device.

The overall result is a Git-maintained repository from which all the supported kernel types can be derived for all the supported devices. A big advantage to this scheme is the sharing of common features by keeping them in "larger" branches within the tree. This practice eliminates redundant storage of similar features shared among kernels.

Keep in mind the figure does not take into account all the supported Yocto Project kernel types, but rather shows a single generic kernel just for conceptual purposes. Also keep in mind that this structure represents the Yocto Project source repositories that are either pulled from during the build or established on the host development system prior to the build by either cloning a particular kernel's Git repository or by downloading and unpacking a tarball.

Upstream storage of all the available kernel source code is one thing, while representing and using the code on your host development system is another. Conceptually, you can think of the kernel source repositories as all the source files necessary for all the supported kernels. As a developer, you are just interested in the source files for the kernel on which you are working. And, furthermore, you need them available on your host system.

Kernel source code is available on your host system a couple of different ways. If you are working in the kernel all the time, you probably would want to set up your own local Git repository of the kernel tree. If you just need to make some patches to the kernel, you can access temporary kernel source files that were extracted and used during a build. We will just talk about working with the temporary source code. For more information on how to get kernel source code onto your host system, see the "Yocto Project Kernel" bulleted item earlier in the manual.

What happens during the build? When you build the kernel on your development system, all files needed for the build are taken from the source repositories pointed to by the `SRC_URI` variable and gathered in a temporary work area where they are subsequently used to create the unique kernel. Thus, in a sense, the process constructs a local source tree specific to your kernel to generate the new kernel image - a source generator if you will.

The following figure shows the temporary file structure created on your host system when the build occurs. This Build Directory contains all the source files used during the build.

Again, for additional information on the Yocto Project kernel's architecture and its branching strategy, see the Yocto Project Linux Kernel Development Manual. You can also reference the "Patching the Kernel" section for a detailed example that modifies the kernel.

#### Kernel Modification Workflow

This illustration and the following list summarizes the kernel modification general workflow.

1. Set up your host development system to support development using the Yocto Project: See "The Linux Distribution" and "The Packages" sections both in the Yocto Project Quick Start for requirements.

2. Establish a local copy of project files on your system: Having the Source Directory on your system gives you access to the build process and tools you need. For information on how to get these files, see the bulleted item "Yocto Project Release" earlier in this manual.

3. Establish the temporary kernel source files: Temporary kernel source files are kept in the Build Directory created by the OpenEmbedded build system when you run BitBake. If you have never built the kernel in which you are interested, you need to run an initial build to establish local kernel source files.

   If you are building an image for the first time, you need to get the build environment ready by sourcing an environment setup script (i.e. `oe-init-build-env` or `oe-init-build-env-memres`). You also need to be sure two key configuration files (`local.conf` and `bblayers.conf`) 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. You can find more information on BitBake in the BitBake User Manual.

   The build process supports several types of images to satisfy different needs. See the "Images" chapter in the Yocto Project Reference Manual for information on supported images.

4. Make changes to the kernel source code if applicable: Modifying the kernel does not always mean directly changing source files. However, if you have to do this, you make the changes to the files in the Build Directory.

5. Make kernel configuration changes if applicable: If your situation calls for changing the kernel's configuration, you can use the `yocto-kernel` script or `menuconfig` to enable and disable kernel configurations. Using the script lets you interactively set up kernel configurations. Using `menuconfig` allows you to interactively develop and test the configuration changes you are making to the kernel. When saved, changes using `menuconfig` update the kernel's `.config` file. Try to resist the temptation of directly editing the `.config` file found in the Build Directory at `tmp/sysroots/<machine-name>/kernel`. Doing so, can produce unexpected results when the OpenEmbedded build system regenerates the configuration file.

   Once you are satisfied with the configuration changes made using `menuconfig`, you can directly compare the `.config` file against a saved original and gather those changes into a config fragment to be referenced from within the kernel's `.bbappend` file.

6. Rebuild the kernel image with your changes: Rebuilding the kernel image applies your changes.

## Application Development Workflow

Application development involves creating an application that you want to run on your target hardware, which is running a kernel image created using the OpenEmbedded build system. The Yocto Project provides an Application Development Toolkit (ADT) and stand-alone cross-development toolchains that facilitate quick development and integration of your application into its runtime environment. Using the ADT and toolchains, you can compile and link your application. You can then deploy your application to the actual hardware or to the QEMU emulator for testing. If you are familiar with the popular Eclipse IDE, you can use an Eclipse Yocto Plug-in to allow you to develop, deploy, and test your application all from within Eclipse.

While we strongly suggest using the ADT to develop your application, this option might not be best for you. If this is the case, you can still use pieces of the Yocto Project for your development process. However, because the process can vary greatly, this manual does not provide detail on the process.

### Workflow Using the ADT and Eclipse

To help you understand how application development works using the ADT, this section provides an overview of the general development process and a detailed example of the process as it is used from within the Eclipse IDE.

The following illustration and list summarize the application development general workflow.

1. Prepare the host system for the Yocto Project: See "Supported Linux Distributions" and "Required Packages for the Host Development System" sections both in the Yocto Project Reference Manual for requirements. In particular, be sure your host system has the `xterm` package installed.

2. Secure the Yocto Project kernel target image: You must have a target kernel image that has been built using the OpenEmbedded build system.

   Depending on whether the Yocto Project has a pre-built image that matches your target architecture and where you are going to run the image while you develop your application (QEMU or real hardware), the area from which you get the image differs.

   - Download the image from `machines` if your target architecture is supported and you are going to develop and test your application on actual hardware.

   - Download the image from `machines/qemu` if your target architecture is supported and you are going to develop and test your application using the QEMU emulator.

   - Build your image if you cannot find a pre-built image that matches your target architecture. If your target architecture is similar to a supported architecture, you can modify the kernel image before you build it. See the "Patching the Kernel" section for an example.

   For information on pre-built kernel image naming schemes for images that can run on the QEMU emulator, see the "Downloading the Pre-Built Linux Kernel" section in the Yocto Project Quick Start.

3. Install the ADT: The ADT provides a target-specific cross-development toolchain, the root filesystem, the QEMU emulator, and other tools that can help you develop your application. While it is possible to get these pieces separately, the ADT Installer provides an easy, inclusive method. You can get these pieces by running an ADT installer script, which is configurable. For information on how to install the ADT, see the "Using the ADT Installer" section in the Yocto Project Application Developer's Guide.

4. If applicable, secure the target root filesystem and the Cross-development toolchain: If you choose not to install the ADT using the ADT Installer, you need to find and download the appropriate root filesystem and the cross-development toolchain.

   You can find the tarballs for the root filesystem in the same area used for the kernel image. Depending on the type of image you are running, the root filesystem you need differs. For example, if you are developing an application that runs on an image that supports Sato, you need to get a root filesystem that supports Sato.

   You can find the cross-development toolchains at `toolchains`. Be sure to get the correct toolchain for your development host and your target architecture. See the "Using a Cross-Toolchain Tarball" section in the Yocto Project Application Developer's Guide for information and the "Installing the Toolchain" in the Yocto Project Quick Start for information on finding and installing the correct toolchain based on your host development system and your target architecture.

5. Create and build your application: At this point, you need to have source files for your application. Once you have the files, you can use the Eclipse IDE to import them and build the project. If you are not using Eclipse, you need to use the cross-development tools you have installed to create the image.

6. Deploy the image with the application: If you are using the Eclipse IDE, you can deploy your image to the hardware or to QEMU through the project's preferences. If you are not using the Eclipse IDE, then you need to deploy the application to the hardware using other methods. Or, if you are using QEMU, you need to use that tool and load your image in for testing. See the "Using the Quick EMUlator (QEMU)" chapter for information on using QEMU.

7. Test and debug the application: Once your application is deployed, you need to test it. Within the Eclipse IDE, you can use the debugging environment along with the set of user-space tools installed along with the ADT to debug your application. Of course, the same user-space tools are available separately if you choose not to use the Eclipse IDE.

### Working Within Eclipse

The Eclipse IDE is a popular development environment and it fully supports development using the Yocto Project.

This release of the Yocto Project supports both the Kepler and Juno versions of the Eclipse IDE. Thus, the following information provides setup information for both versions.

When you install and configure the Eclipse Yocto Project Plug-in into the Eclipse IDE, you maximize your Yocto Project experience. Installing and configuring the Plug-in results in an environment that has extensions specifically designed to let you more easily develop software. These extensions allow for cross-compilation, deployment, and execution of your output into a QEMU emulation session as well as actual target hardware. You can also perform cross-debugging and profiling. The environment also supports a suite of tools that allows you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

This section describes how to install and configure the Eclipse IDE Yocto Plug-in and how to use it to develop your application.

#### Setting Up the Eclipse IDE

To develop within the Eclipse IDE, you need to do the following:

1. Install the optimal version of the Eclipse IDE.

2. Configure the Eclipse IDE.

3. Install the Eclipse Yocto Plug-in.

4. Configure the Eclipse Yocto Plug-in.

Do not install Eclipse from your distribution's package repository. Be sure to install Eclipse from the official Eclipse download site as directed in the next section.

##### Installing the Eclipse IDE

It is recommended that you have the Kepler 4.3.2 version of the Eclipse IDE installed on your development system. However, if you currently have the Juno 4.2 version installed and you do not want to upgrade the IDE, you can configure Juno to work with the Yocto Project.

If you do not have the Kepler 4.3.2 Eclipse IDE installed, you can find the tarball at . From that site, choose the Eclipse Standard 4.3.2 version particular to your development host. This version contains the Eclipse Platform, the Java Development Tools (JDT), and the Plug-in Development Environment.

Once you have downloaded the tarball, extract it into a clean directory. For example, the following commands unpack and install the downloaded Eclipse IDE tarball into a clean directory using the default name `eclipse`:

         $ cd ~
         $ $ tar -xzvf ~/Downloads/eclipse-standard-kepler-SR2-linux-gtk-x86_64.tar.gz

##### Configuring the Eclipse IDE

This section presents the steps needed to configure the Eclipse IDE.

Before installing and configuring the Eclipse Yocto Plug-in, you need to configure the Eclipse IDE. Follow these general steps:

1. Start the Eclipse IDE.

2. Make sure you are in your Workbench and select "Install New Software" from the "Help" pull-down menu.

3. Select `Kepler - &ECLIPSE_KEPLER_URL;` from the "Work with:" pull-down menu.

   For Juno, select `Juno - &ECLIPSE_JUNO_URL;`

4. Expand the box next to "Linux Tools" and select the `LTTng - Linux Tracing Toolkit` boxes.

5. Expand the box next to "Mobile and Device Development" and select the following boxes:

   - `C/C++ Remote Launch (Requires RSE Remote System Explorer)`

   - `Remote System Explorer End-user Runtime`

   - `Remote System Explorer User Actions`

   - `Target Management Terminal`

   - `TCF Remote System Explorer add-in`

   - `TCF Target Explorer`

6. Expand the box next to "Programming Languages" and select the `C/C++ Autotools Support` and `C/C++ Development Tools` boxes.

7. Complete the installation and restart the Eclipse IDE.

##### Installing or Accessing the Eclipse Yocto Plug-in

You can install the Eclipse Yocto Plug-in into the Eclipse IDE one of two ways: use the Yocto Project's Eclipse Update site to install the pre-built plug-in or build and install the plug-in from the latest source code.

###### Installing the Pre-built Plug-in from the Yocto Project Eclipse Update Site

To install the Eclipse Yocto Plug-in from the update site, follow these steps:

1. Start up the Eclipse IDE.

2. In Eclipse, select "Install New Software" from the "Help" menu.

3. Click "Add..." in the "Work with:" area.

4. Enter `&ECLIPSE_DL_PLUGIN_URL;/kepler` in the URL field and provide a meaningful name in the "Name" field.

   If you are using Juno, use `&ECLIPSE_DL_PLUGIN_URL;/juno` in the URL field.

5. Click "OK" to have the entry added to the "Work with:" drop-down list.

6. Select the entry for the plug-in from the "Work with:" drop-down list.

7. Check the boxes next to `Yocto Project ADT Plug-in`, `Yocto Project Bitbake Commander Plug-in`, and `Yocto Project Documentation plug-in`.

8. Complete the remaining software installation steps and then restart the Eclipse IDE to finish the installation of the plug-in.

###### Installing the Plug-in Using the Latest Source Code

To install the Eclipse Yocto Plug-in from the latest source code, follow these steps:

1. Be sure your development system is not using OpenJDK to build the plug-in by doing the following:

   1. Use the Oracle JDK. If you don't have that, go to and download the appropriate tarball for your development system and extract it into your home directory.

   2. In the shell you are going to do your work, export the location of the Oracle Java as follows:

               export PATH=~/jdk1.7.0_40/bin:$PATH

2. In the same shell, create a Git repository with:

            $ cd ~
            $ git clone git://git.yoctoproject.org/eclipse-poky

3. Be sure to checkout the specific plug-in branch. For example, if you are using Kepler, do the following:

            $ git checkout kepler

4. Change to the `scripts` directory within the Git repository:

            $ cd scripts

5. Set up the local build environment by running the setup script:

            $ ./setup.sh

6. When the script finishes execution, it prompts you with instructions on how to run the `build.sh` script, which is also in the `scripts` directory of the Git repository created earlier.

7. Run the `build.sh` script as directed. Be sure to provide the name of the Git branch along with the Yocto Project release you are using. Here is an example that uses the `&DISTRO_NAME;` branch:

            $ ECLIPSE_HOME=/home/scottrif/eclipse-poky/scripts/eclipse ./build.sh &DISTRO_NAME; &DISTRO_NAME;

   After running the script, the file `org.yocto.sdk-`release`-`date`-archive.zip` is in the current directory.

8. If necessary, start the Eclipse IDE and be sure you are in the Workbench.

9. Select "Install New Software" from the "Help" pull-down menu.

10. Click "Add".

11. Provide anything you want in the "Name" field.

12. Click "Archive" and browse to the ZIP file you built in step eight. This ZIP file should not be "unzipped", and must be the `*archive.zip` file created by running the `build.sh` script.

13. Click through the "Okay" buttons.

14. Check the boxes in the installation window and complete the installation.

15. Restart the Eclipse IDE if necessary.

At this point you should be able to configure the Eclipse Yocto Plug-in as described in the "Configuring the Eclipse Yocto Plug-in" section.

##### Configuring the Eclipse Yocto Plug-in

Configuring the Eclipse Yocto Plug-in involves setting the Cross Compiler options and the Target options. The configurations you choose become the default settings for all projects. You do have opportunities to change them later when you configure the project (see the following section).

To start, you need to do the following from within the Eclipse IDE:

- Choose "Preferences" from the "Windows" menu to display the Preferences Dialog.

- Click "Yocto Project ADT".

###### Configuring the Cross-Compiler Options

To configure the Cross Compiler Options, you must select the type of toolchain, point to the toolchain, specify the sysroot location, and select the target architecture.

- Selecting the Toolchain Type: Choose between `Standalone pre-built toolchain` and `Build system derived toolchain` for Cross Compiler Options.

  - `Standalone Pre-built Toolchain:` Select this mode when you are using a stand-alone cross-toolchain. For example, suppose you are an application developer and do not need to build a target image. Instead, you just want to use an architecture-specific toolchain on an existing kernel and target root filesystem.

  - `Build System Derived Toolchain:` Select this mode if the cross-toolchain has been installed and built as part of the Build Directory. When you select `Build system derived toolchain`, you are using the toolchain bundled inside the Build Directory.

- Point to the Toolchain: If you are using a stand-alone pre-built toolchain, you should be pointing to where it is installed. If you used the ADT Installer script and accepted the default installation directory, the toolchain will be installed in the `&YOCTO_ADTPATH_DIR;` directory. Sections "Configuring and Running the ADT Installer Script" and "Using a Cross-Toolchain Tarball" in the Yocto Project Application Developer's Guide describe how to install a stand-alone cross-toolchain.

  If you are using a system-derived toolchain, the path you provide for the `Toolchain Root Location` field is the Build Directory. See the "Using BitBake and the Build Directory" section in the Yocto Project Application Developer's Guide for information on how to install the toolchain into the Build Directory.

- Specify the Sysroot Location: This location is where the root filesystem for the target hardware resides. If you used the ADT Installer script and accepted the default installation directory, then the location is `/opt/poky/&DISTRO;/sysroots`. Additionally, when you use the ADT Installer script, the same location is used for the QEMU user-space tools and the NFS boot process.

  If you used either of the other two methods to install the toolchain or did not accept the ADT Installer script's default installation directory, then the location of the sysroot filesystem depends on where you separately extracted and installed the filesystem.

  For information on how to install the toolchain and on how to extract and install the sysroot filesystem, see the "Installing the ADT and Toolchains" section in the Yocto Project Application Developer's Guide.

- Select the Target Architecture: The target architecture is the type of hardware you are going to use or emulate. Use the pull-down `Target Architecture` menu to make your selection. The pull-down menu should have the supported architectures. If the architecture you need is not listed in the menu, you will need to build the image. See the "Building an Image" section of the Yocto Project Quick Start for more information.

###### Configuring the Target Options

You can choose to emulate hardware using the QEMU emulator, or you can choose to run your image on actual hardware.

- QEMU: Select this option if you will be using the QEMU emulator. If you are using the emulator, you also need to locate the kernel and specify any custom options.

  If you selected `Build system derived toolchain`, the target kernel you built will be located in the Build Directory in `tmp/deploy/images/machine` directory. If you selected `Standalone pre-built toolchain`, the pre-built image you downloaded is located in the directory you specified when you downloaded the image.

  Most custom options are for advanced QEMU users to further customize their QEMU instance. These options are specified between paired angled brackets. Some options must be specified outside the brackets. In particular, the options `serial`, `nographic`, and `kvm` must all be outside the brackets. Use the `man qemu` command to get help on all the options and their use. The following is an example:

          serial ‘<-m 256 -full-screen>’

  Regardless of the mode, Sysroot is already defined as part of the Cross-Compiler Options configuration in the `Sysroot Location:` field.

- External HW: Select this option if you will be using actual hardware.

Click the "OK" to save your plug-in configurations.

#### Creating the Project

You can create two types of projects: Autotools-based, or Makefile-based. This section describes how to create Autotools-based projects from within the Eclipse IDE. For information on creating Makefile-based projects in a terminal window, see the section "Using the Command Line" in the Yocto Project Application Developer's Guide.

Do not use special characters in project names (e.g. spaces, underscores, etc.). Doing so can cause configuration to fail.

To create a project based on a Yocto template and then display the source code, follow these steps:

1. Select "Project" from the "File -> New" menu.

2. Double click `CC++`.

3. Double click `C Project` to create the project.

4. Expand `Yocto Project ADT Project`.

5. Select `Hello World ANSI C Autotools Project`. This is an Autotools-based project based on a Yocto template.

6. Put a name in the `Project name:` field. Do not use hyphens as part of the name.

7. Click "Next".

8. Add information in the `Author` and `Copyright notice` fields.

9. Be sure the `License` field is correct.

10. Click "Finish".

11. If the "open perspective" prompt appears, click "Yes" so that you in the C/C++ perspective.

12. The left-hand navigation pane shows your project. You can display your source by double clicking the project's source file.

#### Configuring the Cross-Toolchains

The earlier section, "Configuring the Eclipse Yocto Plug-in", sets up the default project configurations. You can override these settings for a given project by following these steps:

1. Select "Change Yocto Project Settings" from the "Project" menu. This selection brings up the Yocto Project Settings Dialog and allows you to make changes specific to an individual project.

   By default, the Cross Compiler Options and Target Options for a project are inherited from settings you provided using the Preferences Dialog as described earlier in the "Configuring the Eclipse Yocto Plug-in" section. The Yocto Project Settings Dialog allows you to override those default settings for a given project.

2. Make your configurations for the project and click "OK". If you are running the Juno version of Eclipse, you can skip down to the next section where you build the project. If you are not working with Juno, you need to reconfigure the project as described in the next step.

3. Select "Reconfigure Project" from the "Project" menu. This selection reconfigures the project by running `autogen.sh` in the workspace for your project. The script also runs `libtoolize`, `aclocal`, `autoconf`, `autoheader`, `automake --a`, and `./configure`. Click on the "Console" tab beneath your source code to see the results of reconfiguring your project.

#### Building the Project

To build the project in Juno, right click on the project in the navigator pane and select "Build Project". If you are not running Juno, select "Build Project" from the "Project" menu. The console should update and you can note the cross-compiler you are using.

#### Starting QEMU in User-Space NFS Mode

To start the QEMU emulator from within Eclipse, follow these steps:

See the "Using the Quick EMUlator (QEMU)" chapter for more information on using QEMU.

1. Expose and select "External Tools" from the "Run" menu. Your image should appear as a selectable menu item.

2. Select your image from the menu to launch the emulator in a new window.

3. If needed, enter your host root password in the shell window at the prompt. This sets up a `Tap 0` connection needed for running in user-space NFS mode.

4. Wait for QEMU to launch.

5. Once QEMU launches, you can begin operating within that environment. For example, you could determine the IP Address for the user-space NFS by using the `ifconfig` command.

#### Deploying and Debugging the Application

Once the QEMU emulator is running the image, you can deploy your application using the Eclipse IDE and then use the emulator to perform debugging. Follow these steps to deploy the application.

1. Select "Debug Configurations..." from the "Run" menu.

2. In the left area, expand `C/C++Remote Application`.

3. Locate your project and select it to bring up a new tabbed view in the Debug Configurations Dialog.

4. Enter the absolute path into which you want to deploy the application. Use the "Remote Absolute File Path for C/C++Application:" field. For example, enter `/usr/bin/programname`.

5. Click on the "Debugger" tab to see the cross-tool debugger you are using.

6. Click on the "Main" tab.

7. Create a new connection to the QEMU instance by clicking on "new".

8. Select `TCF`, which means Target Communication Framework.

9. Click "Next".

10. Clear out the "host name" field and enter the IP Address determined earlier.

11. Click "Finish" to close the New Connections Dialog.

12. Use the drop-down menu now in the "Connection" field and pick the IP Address you entered.

13. Click "Run" to bring up a login screen and login.

14. Accept the debug perspective.

#### Running User-Space Tools

As mentioned earlier in the manual, several tools exist that enhance your development experience. These tools are aids in developing and debugging applications and images. You can run these user-space tools from within the Eclipse IDE through the "YoctoTools" menu.

Once you pick a tool, you need to configure it for the remote target. Every tool needs to have the connection configured. You must select an existing TCF-based RSE connection to the remote target. If one does not exist, click "New" to create one.

Here are some specifics about the remote tools:

- `OProfile`: Selecting this tool causes the `oprofile-server` on the remote target to launch on the local host machine. The `oprofile-viewer` must be installed on the local host machine and the `oprofile-server` must be installed on the remote target, respectively, in order to use. You must compile and install the `oprofile-viewer` from the source code on your local host machine. Furthermore, in order to convert the target's sample format data into a form that the host can use, you must have OProfile version 0.9.4 or greater installed on the host.

  You can locate both the viewer and server from . You can also find more information on setting up and using this tool in the "oprofile" section of the Yocto Project Profiling and Tracing Manual.

  The `oprofile-server` is installed by default on the `core-image-sato-sdk` image.

- `Lttng2.0 ust trace import`: Selecting this tool transfers the remote target's `Lttng` tracing data back to the local host machine and uses the Lttng Eclipse plug-in to graphically display the output. For information on how to use Lttng to trace an application, see and the "LTTng (Linux Trace Toolkit, next generation)" section, which is in the Yocto Project Profiling and Tracing Manual.

  Do not use `Lttng-user space (legacy)` tool. This tool no longer has any upstream support.

  Before you use the `Lttng2.0 ust trace import` tool, you need to setup the Lttng Eclipse plug-in and create a Tracing project. Do the following:

  1. Select "Open Perspective" from the "Window" menu and then select "Tracing".

  2. Click "OK" to change the Eclipse perspective into the Tracing perspective.

  3. Create a new Tracing project by selecting "Project" from the "File -> New" menu.

  4. Choose "Tracing Project" from the "Tracing" menu.

  5. Generate your tracing data on the remote target.

  6. Select "Lttng2.0 ust trace import" from the "Yocto Project Tools" menu to start the data import process.

  7. Specify your remote connection name.

  8. For the Ust directory path, specify the location of your remote tracing data. Make sure the location ends with `ust` (e.g. `/usr/mysession/ust`).

  9. Click "OK" to complete the import process. The data is now in the local tracing project you created.

  10. Right click on the data and then use the menu to Select "Generic CTF Trace" from the "Trace Type... -> Common Trace Format" menu to map the tracing type.

  11. Right click the mouse and select "Open" to bring up the Eclipse Lttng Trace Viewer so you view the tracing data.

- `PowerTOP`: Selecting this tool runs PowerTOP on the remote target machine and displays the results in a new view called PowerTOP.

  The "Time to gather data(sec):" field is the time passed in seconds before data is gathered from the remote target for analysis.

  The "show pids in wakeups list:" field corresponds to the `-p` argument passed to `PowerTOP`.

- `LatencyTOP and Perf`: LatencyTOP identifies system latency, while Perf monitors the system's performance counter registers. Selecting either of these tools causes an RSE terminal view to appear from which you can run the tools. Both tools refresh the entire screen to display results while they run. For more information on setting up and using `perf`, see the "perf" section in the Yocto Project Profiling and Tracing Manual.

#### Customizing an Image Using a BitBake Commander Project and Hob

Within the Eclipse IDE, you can create a Yocto BitBake Commander project, edit the Metadata, and then use Hob to build a customized image all within one IDE.

##### Creating the Yocto BitBake Commander Project

To create a Yocto BitBake Commander project, follow these steps:

1. Select "Other" from the "Window -> Open Perspective" menu and then choose "Bitbake Commander".

2. Click "OK" to change the perspective to Bitbake Commander.

3. Select "Project" from the "File -> New" menu to create a new Yocto Bitbake Commander project.

4. Choose "New Yocto Project" from the "Yocto Project Bitbake Commander" menu and click "Next".

5. Enter the Project Name and choose the Project Location. The Yocto project's Metadata files will be put under the directory `project_location/project_name`. If that directory does not exist, you need to check the "Clone from Yocto Git Repository" box, which would execute a `git clone` command to get the project's Metadata files.

   Do not specify your BitBake Commander project location as your Eclipse workspace. Doing so causes an error indicating that the current project overlaps the location of another project. This error occurs even if no such project exits.

6. Select `Finish` to create the project.

##### Editing the Metadata

After you create the Yocto Bitbake Commander project, you can modify the Metadata files by opening them in the project. When editing recipe files (`.bb` files), you can view BitBake variable values and information by hovering the mouse pointer over the variable name and waiting a few seconds.

To edit the Metadata, follow these steps:

1. Select your Yocto Bitbake Commander project.

2. Select "BitBake Recipe" from the "File -> New -> Yocto BitBake Commander" menu to open a new recipe wizard.

3. Point to your source by filling in the "SRC_URL" field. For example, you can add a recipe to your Source Directory by defining "SRC_URL" as follows:

            ftp://ftp.gnu.org/gnu/m4/m4-1.4.9.tar.gz

4. Click "Populate" to calculate the archive md5, sha256, license checksum values and to auto-generate the recipe filename.

5. Fill in the "Description" field.

6. Be sure values for all required fields exist.

7. Click "Finish".

##### Building and Customizing the Image Using Hob

To build and customize the image using Hob from within the Eclipse IDE, follow these steps:

1. Select your Yocto Bitbake Commander project.

2. Select "Launch Hob" from the "Project" menu.

3. Enter the Build Directory where you want to put your final images.

4. Click "OK" to launch Hob.

5. Use Hob to customize and build your own images. For information on Hob, see the Hob Project Page on the Yocto Project website.

### Workflow Using Stand-Alone Cross-Development Toolchains

If you want to develop an application without prior installation of the ADT, you still can employ the Cross Development Toolchain, the QEMU emulator, and a number of supported target image files. You just need to follow these general steps:

1. Install the cross-development toolchain for your target hardware: For information on how to install the toolchain, see the "Using a Cross-Toolchain Tarball" section in the Yocto Project Application Developer's Guide.

2. Download the Target Image: The Yocto Project supports several target architectures and has many pre-built kernel images and root filesystem images.

   If you are going to develop your application on hardware, go to the `machines` download area and choose a target machine area from which to download the kernel image and root filesystem. This download area could have several files in it that support development using actual hardware. For example, the area might contain `.hddimg` files that combine the kernel image with the filesystem, boot loaders, and so forth. Be sure to get the files you need for your particular development process.

   If you are going to develop your application and then run and test it using the QEMU emulator, go to the `machines/qemu` download area. From this area, go down into the directory for your target architecture (e.g. `qemux86_64` for an Intel-based 64-bit architecture). Download kernel, root filesystem, and any other files you need for your process.

   In order to use the root filesystem in QEMU, you need to extract it. See the "Extracting the Root Filesystem" section for information on how to extract the root filesystem.

3. Develop and Test your Application: At this point, you have the tools to develop your application. If you need to separately install and use the QEMU emulator, you can go to QEMU Home Page to download and learn about the emulator. You can see the "Using the Quick EMUlator (QEMU)" chapter for information on using QEMU within the Yocto Project.

## Modifying Source Code

A common development workflow consists of modifying project source files that are external to the Yocto Project and then integrating that project's build output into an image built using the OpenEmbedded build system. Given this scenario, development engineers typically want to stick to their familiar project development tools and methods, which allows them to just focus on the project.

Several workflows exist that allow you to develop, build, and test code that is going to be integrated into an image built using the OpenEmbedded build system. This section describes two:

- `devtool`: A set of tools to aid in working on the source code built by the OpenEmbedded build system. Section "Using `devtool` in Your Workflow" describes this workflow. If you want more information that showcases the workflow, click here for an excellent presentation by Trevor Woerner that provides detailed background information and a complete working tutorial.

- Quilt: A powerful tool that allows you to capture source code changes without having a clean source tree. While Quilt is not the preferred workflow of the two, this section includes it for users that are committed to using the tool. See the "Using Quilt in Your Workflow" section for more information.

### Using `devtool` in Your Workflow

As mentioned earlier, `devtool` helps you easily develop projects whose build output must be part of an image built using the OpenEmbedded build system. The remainder of this section presents the workflow you would use that includes `devtool`.

Kudos and thanks to Trevor Woerner whose "Yocto Project Developer Workflow Tutorial" paper contributed nicely towards the development of this section.

The workflow considers the entire build process for the image and not just modification of the external source code.

#### Establish the Reference Image

The steps to clone the `poky` Git repository, build out an image, and test it using QEMU are well documented as follows:

- For information on how to set up a local copy of the `poky` repository and on how to build a Yocto Project image, see the "Building an Image" section in the Yocto Project Quick Start.

- For information on how to test an image using QEMU, see the "Using the Quick EMUlator (QEMU)" section.

Before you start making modifications to your project's source code, you should be sure you have the appropriate local repositories and have a base image built using BitBake that you can run on QEMU.

#### Update Your External Source

Part of the development flow using `devtool` of course involves updating your source files. Several opportunities exist in the workflow to extract and work on the files. For now, just realize that you need to be able to have access to and edit files. One obvious solution is to initially extract the code into an isolated area in preparation for modification.

Another option is to use the `devtool modify` command. This command makes use of a "workspace" layer where much of the transitional work occurs, which is needed for setting up Metadata used by the OpenEmbedded build system that lets you build your software. Options (i.e. "-x") exist using `devtool` that enable you to use the tool to extract source code.

#### Use `devtool add` to Integrate Your Code with the Image

The `devtool add` command automatically generates the needed Metadata that allows the OpenEmbedded build system to build your code into the image.

If a package or packages produced by the recipe on which you are working are not already in `IMAGE_INSTALL` for the image, you must add them. The `devtool add` command does not add them for you.
Use the following command form:

         $ devtool add your-project-name path-to-source

Running `devtool add` modifies the `bblayers.conf` that the OpenEmbedded build system uses to build an image. For more information on the `bblayers.conf`, see the "`build/conf/bblayers.conf`" section in the Yocto Project Reference Manual.

Running `devtool add` adds a new workspace layer to the `bblayers.conf` file that is based on your project's location:

         path-to-source/build-directory/workspace-layer

By default, the name of the workspace layer is "workspace".

For details on the workspace layer created in the build-directory, see the "Adding a New Recipe to the Workspace Layer" section.

Running `devtool add` automatically generates your recipe:

         $ cat workspace/recipes/your-project-name/your-project-name.bb
         # Recipe created by recipetool
         # This is the basis of a recipe and may need further editing in order to be fully functional.
         # (Feel free to remove these comments when editing.)
         #
         # Unable to find any files that looked like license statements. Check the accompanying
         # documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
         LICENSE = "CLOSED"
         LIC_FILES_CHKSUM = ""

         # No information for SRC_URI yet (only an external source tree was
         # specified)
         SRC_URI = ""

         DEPENDS = "libx11"
         # NOTE: if this software is not capable of being built in a separate build directory
         # from the source, you should replace autotools with autotools-brokensep in the
         # inherit line
         inherit autotools

         # Specify any options you want to pass to the configure script using EXTRA_OECONF:
         EXTRA_OECONF = ""

Lastly, the `devtool add` command creates the `.bbappend` file:

         $ cat workspace/appends/your-project-name.bbappend
         inherit externalsrc
         EXTERNALSRC = "/path-to-source/your-project-name"

         # initial_rev: commit-ID

#### Build Your Project

You can use BitBake or `devtool build` to build your modified project.

To use BitBake, use the following:

         $ bitbake your-project-name

Alternatively, you can use `devtool build`, which is equivalent to `bitbake -c populate_sysroot`. For example:

         $ devtool build your-project-name

#### Build the Image

The final step before testing is to rebuild the base image with your project changes as part of the image. Simply run BitBake again on your image. Here is an example:

         $ bitbake image

#### Testing the Image

Once you have the image, you can test it using QEMU. Here is an example assuming "qemux86":

         $ runqemu qemux86 image

For information on how to test an image using QEMU, see the "Using the Quick EMUlator (QEMU)" section.

### `devtool` Quick Reference

`devtool` has more functionality than simply adding a new recipe and the supporting Metadata to a temporary workspace layer. This section provides a short reference on `devtool` for most of the commands.

#### Getting Help

The easiest way to get help with the `devtool` command is using the `--help` option:

         $ devtool --help
         usage: devtool [-h] [--basepath BASEPATH] [-d] [-q] [--color COLOR]
                   <subcommand> ...

         OpenEmbedded development tool

         optional arguments:
           -h, --help           show this help message and exit
           --basepath BASEPATH  Base directory of SDK / build directory
           -d, --debug          Enable debug output
           -q, --quiet          Print only errors
           --color COLOR        Colorize output (where COLOR is auto, always, never)

         subcommands:
           <subcommand>
             create-workspace   Set up a workspace
             deploy-target      Deploy recipe output files to live target machine
             undeploy-target    Undeploy recipe output files in live target machine
             add                Add a new recipe
             modify             Modify the source for an existing recipe
             extract            Extract the source for an existing recipe
             update-recipe      Apply changes from external source tree to recipe
             status             Show workspace status
             build              Build a recipe
             reset              Remove a recipe from your workspace

         Use devtool <subcommand> --help to get help on a specific command

As directed in the general help output, you can get more syntax on a specific command by providing the command name and using `--help`:

         $ devtool add --help
         usage: devtool add [-h] [--same-dir] [--version VERSION] recipename srctree

         Adds a new recipe

         positional arguments:
           recipename            Name for new recipe to add
           srctree               Path to external source tree

         optional arguments:
           -h, --help            show this help message and exit
           --same-dir, -s        Build in same directory as source (default: False)
           --version VERSION, -V VERSION
                                 Version to use within recipe (PV) (default: None)

#### Adding a New Recipe to the Workspace Layer

Use the `devtool add` command to add a new recipe to the workspace layer. The recipe you add should not exist - `devtool` creates it for you. The source files the recipe uses should exist in an external area.

The following example creates and adds a new recipe named `jackson-2.0` to the workspace layer. The source code built by the recipes resides in `/home/scottrif/sources/jackson`:

         $ devtool add jackson-2.0 /home/scottrif/sources/jackson

For complete syntax, use the `devtool add --help` command.

If you add a recipe and the workspace layer does not exist, the command creates the layer and populates it as follows:

         README - Provides information on what is in workspace layer and how to
                  manage it.

         appends - A directory that contains *.bbappend files, which point to
                   external source.

         conf - A configuration directory that contains the layer.conf file.

         recipes - A directory containing recipes.  This directory contains a
                   folder for each directory added whose name matches that of the
                   added recipe.  devtool places the recipe.bb file
                   within that sub-directory.

Running `devtool add` when the workspace layer exists causes the tool to add the recipe and append files into the existing workspace layer. The `.bbappend` file is created to point to the external source tree.

#### Creating the Workspace Layer

Use the `devtool create-workspace` command to create a new workspace layer in your Build Directory. When you create a new workspace layer, it is populated with the `README` file and the `conf` directory only.

The following example creates a new workspace layer in your current working and by default names the workspace layer "workspace":

         $ devtool create-workspace

For complete syntax, use the `devtool create-workspace --help` command.

You can create a workspace layer anywhere by supplying a pathname with the command. The following command creates a new workspace layer named "new-workspace":

         $ devtool create-workspace /home/scottrif/new-workspace

#### Modifying a Recipe

Use the `devtool modify` command to begin modifying the source of an existing recipe. This command is very similar to the `add` command except that it does not physically create the recipe in the workspace layer because the recipe already exists in an another layer.

The `devtool modify` command extracts the source for a recipe, sets it up as a Git repository if the source had not already been fetched from Git, checks out a branch for development, and applies any patches from the recipe as commits on top. You can use the following command to checkout the source files:

         $ devtool modify -x recipe path-to-source

Using the above command form, the default development branch would be "devtool".

If you want to name a development branch, use the `-b` option with the `-x` option:

         $ devtool modify -x -b branch recipe path-to-source

For complete syntax, use the `devtool modify --help` command.

#### Resetting a Recipe

Use the `devtool reset` command to remove a recipe and its configuration (e.g. the corresponding `.bbappend` file) from the workspace layer. Realize that this command deletes the recipe and the append file. The command does not physically move them for you. Consequently, you must be sure to physically relocate your updated recipe and the append file outside of the workspace layer before running the `devtool reset` command.

If the `devtool reset` command detects that the recipe or the append files have been modified, the command preserves the modified files in a separate "attic" subdirectory under the workspace layer.

For complete syntax, use the `devtool reset --help` command.

#### Updating a Recipe

Use the `devtool update-recipe` command to update your recipe with patches that reflect changes you make to the source files. For example, if you know you are going to work on some code, you could first use the `devtool modify` command to extract the code and set up the workspace. After which, you could modify, compile, and test the code. When you are satisfied with the results you can then run the `devtool update-recipe` to create the patches and update the recipe:

         $ devtool update-recipe recipe

For complete syntax, use the `devtool update-recipe --help` command.

#### Building Your Software

Use the `devtool build` command to cause the OpenEmbedded build system to build your software based on the recipe file. The `devtool build` command is equivalent to `bitbake -c populate_sysroot`. Here is an example:

         $ devtool build recipe

For complete syntax, use the `devtool update-recipe --help` command.
Building your software using `devtool build` is identical to using BitBake to build the software.

#### Deploying Your Software on the Target Machine

Use the `devtool deploy-target` command to deploy the recipe's build output to the live target machine:

         $ devtool deploy-target recipe target

The target is the address of the target machine, which must be running an SSH server (i.e. `user@hostname[:destdir]`).

This command deploys all files installed during the `do_install` task. Furthermore, you do not need to have package management enabled within the target machine. If you do, the package manager is bypassed.

Notes

The `deploy-target` functionality is for development only. You should never use it to update an image that will be used in production.

For complete syntax, use the `devtool deploy-target --help` command.

#### Removing Your Software from the Target Machine

Use the `devtool undeploy-target` command to remove deployed build output from the target machine. For the `devtool undeploy-target` command to work, you must have previously used the `devtool deploy-target` command.

         $ devtool undeploy-target recipe target

The target is the address of the target machine, which must be running an SSH server (i.e. `user@hostname`).
For complete syntax, use the `devtool undeploy-target --help` command.

### Using Quilt in Your Workflow

Quilt is a powerful tool that allows you to capture source code changes without having a clean source tree. This section outlines the typical workflow you can use to modify source code, test changes, and then preserve the changes in the form of a patch all using Quilt.

Tip

With regard to preserving changes to source files if you clean a recipe or have `rm_work` enabled, the workflow described in the "Using `devtool` in Your Workflow" section is a safer development flow than than the flow that uses Quilt.

Follow these general steps:

1. Find the Source Code: Temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.

2. Change Your Working Directory: You need to be in the directory that has the temporary source code. That directory is defined by the `S` variable.

3. Create a New Patch: Before modifying source code, you need to create a new patch. To create a new patch file, use `quilt new` as below:

            $ quilt new my_changes.patch

4. Notify Quilt and Add Files: After creating the patch, you need to notify Quilt about the files you plan to edit. You notify Quilt by adding the files to the patch you just created:

            $ quilt add file1.c file2.c file3.c

5. Edit the Files: Make your changes in the source code to the files you added to the patch.

6. Test Your Changes: Once you have modified the source code, the easiest way to your changes is by calling the `do_compile` task as shown in the following example:

            $ bitbake -c compile -f package

   The `-f` or `--force` option forces the specified task to execute. If you find problems with your code, you can just keep editing and re-testing iteratively until things work as expected.
   All the modifications you make to the temporary source code disappear once you run the `do_clean` or `do_cleanall` tasks using BitBake (i.e. `bitbake -c clean package` and `bitbake -c cleanall package`). Modifications will also disappear if you use the `rm_work` feature as described in the "Building an Image" section of the Yocto Project Quick Start.

7. Generate the Patch: Once your changes work as expected, you need to use Quilt to generate the final patch that contains all your modifications.

            $ quilt refresh

   At this point, the `my_changes.patch` file has all your edits made to the `file1.c`, `file2.c`, and `file3.c` files.

   You can find the resulting patch file in the `patches/` subdirectory of the source (`S`) directory.

8. Copy the Patch File: For simplicity, copy the patch file into a directory named `files`, which you can create in the same directory that holds the recipe (`.bb`) file or the append (`.bbappend`) file. Placing the patch here guarantees that the OpenEmbedded build system will find the patch. Next, add the patch into the `SRC_URI` of the recipe. Here is an example:

            SRC_URI += "file://my_changes.patch"

### Finding Temporary Source Code

You might find it helpful during development to modify the temporary source code used by recipes to build packages. For example, suppose you are developing a patch and you need to experiment a bit to figure out your solution. After you have initially built the package, you can iteratively tweak the source code, which is located in the Build Directory, and then you can force a re-compile and quickly test your altered code. Once you settle on a solution, you can then preserve your changes in the form of patches. If you are using Quilt for development, see the "Using Quilt in Your Workflow" section for more information.

During a build, the unpacked temporary source code used by recipes to build packages is available in the Build Directory as defined by the `S` variable. Below is the default value for the `S` variable as defined in the `meta/conf/bitbake.conf` configuration file in the Source Directory:

         S = "${WORKDIR}/${BP}"

You should be aware that many recipes override the `S` variable. For example, recipes that fetch their source from Git usually set `S` to `${WORKDIR}/git`.
The `BP` represents the base recipe name, which consists of the name and version:

         BP = "${BPN}-${PV}"

The path to the work directory for the recipe (`WORKDIR`) is defined as follows:

         ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}

The actual directory depends on several things:

- `TMPDIR`: The top-level build output directory
- `MULTIMACH_TARGET_SYS`: The target system identifier
- `PN`: The recipe name
- `EXTENDPE`: The epoch - (if `PE` is not specified, which is usually the case for most recipes, then `EXTENDPE` is blank)
- `PV`: The recipe version
- `PR`: The recipe revision

As an example, assume a Source Directory top-level folder named `poky`, a default Build Directory at `poky/build`, and a `qemux86-poky-linux` machine target system. Furthermore, suppose your recipe is named `foo_1.3.0.bb`. In this case, the work directory the build system uses to build the package would be as follows:

         poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0

Now that you know where to locate the directory that has the temporary source code, you can use a Quilt as described in section "Using Quilt in Your Workflow" to make your edits, test the changes, and preserve the changes in the form of patches.

## Image Development Using Toaster

Toaster is a web interface to the Yocto Project's OpenEmbedded build system. You can initiate builds using Toaster as well as examine the results and statistics of builds. See the Toaster User Manual for information on how to set up and use Toaster to build images.

## Image Development Using Hob

The Hob is a graphical user interface for the OpenEmbedded build system, which is based on BitBake. You can use the Hob to build custom operating system images within the Yocto Project build environment. Hob simply provides a friendly interface over the build system used during development. In other words, building images with the Hob lets you take care of common build tasks more easily.

For a better understanding of Hob, see the project page at on the Yocto Project website. If you follow the "Documentation" link from the Hob page, you will find a short introductory training video on Hob. The following lists some features of Hob:

- You can setup and run Hob using these commands:

           $ source oe-init-build-env
           $ hob

- You can set the `MACHINE` for which you are building the image.

- You can modify various policy settings such as the package format with which to build, the parallelism BitBake uses, whether or not to build an external toolchain, and which host to build against.

- You can manage layers.

- You can select a base image and then add extra packages for your custom build.

- You can launch and monitor the build from within Hob.

## Using a Development Shell

When debugging certain commands or even when just editing packages, `devshell` can be a useful tool. When you invoke `devshell`, source files are extracted into your working directory and patches are applied. Then, a new terminal is opened and you are placed in the working directory. In the new terminal, all the OpenEmbedded build-related environment variables are still defined so you can use commands such as `configure` and `make`. The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses `devshell` on a target named `matchbox-desktop`:

         $ bitbake matchbox-desktop -c devshell

This command spawns a terminal with a shell prompt within the OpenEmbedded build environment. The `OE_TERMINAL` variable controls what type of shell is opened.

For spawned terminals, the following occurs:

- The `PATH` variable includes the cross-toolchain.

- The `pkgconfig` variables find the correct `.pc` files.

- The `configure` command finds the Yocto Project site files as well as any other necessary files.

Within this environment, you can run configure or compile commands as if they were being run by the OpenEmbedded build system itself. As noted earlier, the working directory also automatically changes to the Source Directory (`S`).

When you are finished, you just exit the shell or close the terminal window.

It is worth remembering that when using `devshell` you need to use the full compiler name such as `arm-poky-linux-gnueabi-gcc` instead of just using `gcc`. The same applies to other applications such as `binutils`, `libtool` and so forth. BitBake sets up environment variables such as `CC` to assist applications, such as `make` to find the correct tools.

It is also worth noting that `devshell` still works over X11 forwarding and similar situations.