# Preparing for Application Development

In order to develop applications, you need set up your host development system. Several ways exist that allow you to install cross-development tools, QEMU, the Eclipse Yocto Plug-in, and other tools. This chapter describes how to prepare for application development.

## Installing the ADT and Toolchains

The following list describes installation methods that set up varying degrees of tool availability on your system. Regardless of the installation method you choose, you must `source` the cross-toolchain environment setup script before you use a toolchain. See the "Setting Up the Cross-Development Environment" section for more information.

Avoid mixing installation methods when installing toolchains for different architectures. For example, avoid using the ADT Installer to install some toolchains and then hand-installing cross-development toolchains by running the toolchain installer for different architectures. Mixing installation methods can result in situations where the ADT Installer becomes unreliable and might not install the toolchain.

If you must mix installation methods, you might avoid problems by deleting `/var/lib/opkg`, thus purging the `opkg` package metadata

- Use the ADT installer script: This method is the recommended way to install the ADT because it automates much of the process for you. For example, you can configure the installation to install the QEMU emulator and the user-space NFS, specify which root filesystem profiles to download, and define the target sysroot location.

- Use an existing toolchain: Using this method, you select and download an architecture-specific toolchain installer and then run the script to hand-install the toolchain. If you use this method, you just get the cross-toolchain and QEMU - you do not get any of the other mentioned benefits had you run the ADT Installer script.

- Use the toolchain from within the Build Directory: If you already have a Build Directory, you can build the cross-toolchain within the directory. However, like the previous method mentioned, you only get the cross-toolchain and QEMU - you do not get any of the other benefits without taking separate steps.

### Using the ADT Installer

To run the ADT Installer, you need to get the ADT Installer tarball, be sure you have the necessary host development packages that support the ADT Installer, and then run the ADT Installer Script.

For a list of the host packages needed to support ADT installation and use, see the "ADT Installer Extras" lists in the "Required Packages for the Host Development System" section of the Yocto Project Reference Manual.

#### Getting the ADT Installer Tarball

The ADT Installer is contained in the ADT Installer tarball. You can download the tarball into any directory from the Index of Releases, specifically at . Or, you can use BitBake to generate the tarball inside the existing Build Directory.

If you use BitBake to generate the ADT Installer tarball, you must `source` the environment setup script (`&OE_INIT_FILE;` or `oe-init-build-env-memres`) located in the Source Directory before running the BitBake command that creates the tarball.

The following example commands download the Poky tarball, set up the Source Directory, set up the environment while also creating the default Build Directory, and run the BitBake command that results in the tarball `~/yocto-project/build/tmp/deploy/sdk/adt_installer.tar.bz2`:

         $ cd ~
         $ mkdir yocto-project
         $ cd yocto-project
         $ wget &YOCTO_RELEASE_DL_URL;/&YOCTO_POKY_TARBALL;
         $ tar xjf &YOCTO_POKY_TARBALL;
         $ source &OE_INIT_PATH;
         $ bitbake adt-installer

#### Configuring and Running the ADT Installer Script

Before running the ADT Installer script, you need to unpack the tarball. You can unpack the tarball in any directory you wish. For example, this command copies the ADT Installer tarball from where it was built into the home directory and then unpacks the tarball into a top-level directory named `adt-installer`:

         $ cd ~
         $ cp ~/poky/build/tmp/deploy/sdk/adt_installer.tar.bz2 $HOME
         $ tar -xjf adt_installer.tar.bz2

Unpacking it creates the directory `adt-installer`, which contains the ADT Installer script (`adt_installer`) and its configuration file (`adt_installer.conf`).

Before you run the script, however, you should examine the ADT Installer configuration file and be sure you are going to get what you want. Your configurations determine which kernel and filesystem image are downloaded.

The following list describes the configurations you can define for the ADT Installer. For configuration values and restrictions, see the comments in the `adt-installer.conf` file:

- `YOCTOADT_REPO`: This area includes the IPKG-based packages and the root filesystem upon which the installation is based. If you want to set up your own IPKG repository pointed to by `YOCTOADT_REPO`, you need to be sure that the directory structure follows the same layout as the reference directory set up at . Also, your repository needs to be accessible through HTTP.

- `YOCTOADT_TARGETS`: The machine target architectures for which you want to set up cross-development environments.

- `YOCTOADT_QEMU`: Indicates whether or not to install the emulator QEMU.

- `YOCTOADT_NFS_UTIL`: Indicates whether or not to install user-mode NFS. If you plan to use the Eclipse IDE Yocto plug-in against QEMU, you should install NFS.

  To boot QEMU images using our userspace NFS server, you need to be running `portmap` or `rpcbind`. If you are running `rpcbind`, you will also need to add the `-i` option when `rpcbind` starts up. Please make sure you understand the security implications of doing this. You might also have to modify your firewall settings to allow NFS booting to work.

- `YOCTOADT_ROOTFS_<arch>`: The root filesystem images you want to download from the `YOCTOADT_IPKG_REPO` repository.

- `YOCTOADT_TARGET_SYSROOT_IMAGE_<arch>`: The particular root filesystem used to extract and create the target sysroot. The value of this variable must have been specified with `YOCTOADT_ROOTFS_<arch>`. For example, if you downloaded both `minimal` and `sato-sdk` images by setting `YOCTOADT_ROOTFS_<arch>` to "minimal sato-sdk", then `YOCTOADT_ROOTFS_<arch>` must be set to either `minimal` or `sato-sdk`.

- `YOCTOADT_TARGET_SYSROOT_LOC_<arch>`: The location on the development host where the target sysroot is created.

After you have configured the `adt_installer.conf` file, run the installer using the following command. Be sure that you are not trying to use cross-compilation tools. When you run the installer, the environment must use a host `gcc`:

         $ cd ~/adt-installer
         $ ./adt_installer

Once the installer begins to run, you are asked to enter the location for cross-toolchain installation. The default location is `/opt/poky/<release>`. After either accepting the default location or selecting your own location, you are prompted to run the installation script interactively or in silent mode. If you want to closely monitor the installation, choose “I” for interactive mode rather than “S” for silent mode. Follow the prompts from the script to complete the installation.

Once the installation completes, the ADT, which includes the cross-toolchain, is installed in the selected installation directory. You will notice environment setup files for the cross-toolchain in the installation directory, and image tarballs in the `adt-installer` directory according to your installer configurations, and the target sysroot located according to the `YOCTOADT_TARGET_SYSROOT_LOC_<arch>` variable also in your configuration file.

### Using a Cross-Toolchain Tarball

If you want to simply install a cross-toolchain by hand, you can do so by running the toolchain installer. The installer includes the pre-built cross-toolchain, the `runqemu` script, and support files. If you use this method to install the cross-toolchain, you might still need to install the target sysroot by installing and extracting it separately. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

Follow these steps:

1. Get your toolchain installer using one of the following methods:

   - Go to and find the folder that matches your host development system (i.e. `i686` for 32-bit machines or `x86_64` for 64-bit machines).

     Go into that folder and download the toolchain installer whose name includes the appropriate target architecture. The toolchains provided by the Yocto Project are based off of the `core-image-sato` image and contain libraries appropriate for developing against that image. For example, if your host development system is a 64-bit x86 system and you are going to use your cross-toolchain for a 32-bit x86 target, go into the `x86_64` folder and download the following installer:

              poky-eglibc-x86_64-core-image-sato-i586-&DISTRO;.sh

   - Build your own toolchain installer. For cases where you cannot use an installer from the download area, you can build your own as described in the "Optionally Building a Toolchain Installer" section.

2. Once you have the installer, run it to install the toolchain. You must change the permissions on the toolchain installer script so that it is executable.

   The following command shows how to run the installer given a toolchain tarball for a 64-bit x86 development host system and a 32-bit x86 target architecture. The example assumes the toolchain installer is located in `~/Downloads/`.

            $ ~/Downloads/poky-eglibc-x86_64-core-image-sato-i586-&DISTRO;.sh

   If you do not have write permissions for the directory into which you are installing the toolchain, the toolchain installer notifies you and exits. Be sure you have write permissions in the directory and run the installer again.

   Once the tarball is expanded, the cross-toolchain is installed. You will notice environment setup files for the cross-toolchain in the directory.

### Using BitBake and the Build Directory

A final way of making the cross-toolchain available is to use BitBake to generate the toolchain within an existing Build Directory. This method does not install the toolchain into the default `/opt` directory. As with the previous method, if you need to install the target sysroot, you must do that separately as well.

Follow these steps to generate the toolchain into the Build Directory:

1. Source the environment setup script `&OE_INIT_FILE;` located in the Source Directory.

2. At this point, you should be sure that the `MACHINE` variable in the `local.conf` file found in the `conf` directory of the Build Directory is set for the target architecture. Comments within the `local.conf` file list the values you can use for the `MACHINE` variable.

   You can populate the Build Directory with the cross-toolchains for more than a single architecture. You just need to edit the `MACHINE` variable in the `local.conf` file and re-run the BitBake command.

3. Run `bitbake meta-ide-support` to complete the cross-toolchain generation.

   If you change out of your working directory after you `source` the environment setup script and before you run the BitBake command, the command might not work. Be sure to run the BitBake command immediately after checking or editing the `local.conf` but without changing out of your working directory.

   Once the BitBake command finishes, the cross-toolchain is generated and populated within the Build Directory. You will notice environment setup files for the cross-toolchain in the Build Directory in the `tmp` directory. Setup script filenames contain the strings `environment-setup`.

   Be aware that when you use this method to install the toolchain you still need to separately extract and install the sysroot filesystem. For information on how to do this, see the "Extracting the Root Filesystem" section.

## Setting Up the Cross-Development Environment

Before you can develop using the cross-toolchain, you need to set up the cross-development environment by sourcing the toolchain's environment setup script. If you used the ADT Installer or hand-installed cross-toolchain, then you can find this script in the directory you chose for installation. The default installation directory is the `&YOCTO_ADTPATH_DIR;` directory. If you installed the toolchain in the Build Directory, you can find the environment setup script for the toolchain in the Build Directory's `tmp` directory.

Be sure to run the environment setup script that matches the architecture for which you are developing. Environment setup scripts begin with the string "`environment-setup`" and include as part of their name the architecture. For example, the toolchain environment setup script for a 64-bit IA-based architecture installed in the default installation directory would be the following:

         &YOCTO_ADTPATH_DIR;/environment-setup-x86_64-poky-linux

## Securing Kernel and Filesystem Images

You will need to have a kernel and filesystem image to boot using your hardware or the QEMU emulator. Furthermore, if you plan on booting your image using NFS or you want to use the root filesystem as the target sysroot, you need to extract the root filesystem.

### Getting the Images

To get the kernel and filesystem images, you either have to build them or download pre-built versions. You can find examples for both these situations in the "A Quick Test Run" section of the Yocto Project Quick Start.

The Yocto Project ships basic kernel and filesystem images for several architectures (`x86`, `x86-64`, `mips`, `powerpc`, and `arm`) that you can use unaltered in the QEMU emulator. These kernel images reside in the release area - and are ideal for experimentation using Yocto Project. For information on the image types you can build using the OpenEmbedded build system, see the "Images" chapter in the Yocto Project Reference Manual.

If you are planning on developing against your image and you are not building or using one of the Yocto Project development images (e.g. `core-image-*-dev`), you must be sure to include the development packages as part of your image recipe.

Furthermore, if you plan on remotely deploying and debugging your application from within the Eclipse IDE, you must have an image that contains the Yocto Target Communication Framework (TCF) agent (`tcf-agent`). By default, the Yocto Project provides only one type pre-built image that contains the `tcf-agent`. And, those images are SDK (e.g.`core-image-sato-sdk`).

If you want to use a different image type that contains the `tcf-agent`, you can do so one of two ways:

- Modify the `conf/local.conf` configuration in the Build Directory and then rebuild the image. With this method, you need to modify the `EXTRA_IMAGE_FEATURES` variable to have the value of "tools-debug" before rebuilding the image. Once the image is rebuilt, the `tcf-agent` will be included in the image and is launched automatically after the boot.

- Manually build the `tcf-agent`. To build the agent, follow these steps:

  1. Be sure the ADT is installed as described in the "Installing the ADT and Toolchains" section.

  2. Set up the cross-development environment as described in the "Setting Up the Cross-Development Environment" section.

  3. Get the `tcf-agent` source code using the following commands:

              $ git clone http://git.eclipse.org/gitroot/tcf/org.eclipse.tcf.agent.git
              $ cd agent

  4. Modify the `Makefile.inc` file for the cross-compilation environment by setting the `OPSYS` and `MACHINE` variables according to your target.

  5. Use the cross-development tools to build the `tcf-agent`. Before you "Make" the file, be sure your cross-tools are set up first. See the "Makefile-Based Projects" section for information on how to make sure the cross-tools are set up correctly.

     If the build is successful, the `tcf-agent` output will be `obj/$(OPSYS)/$(MACHINE)/Debug/agent`.

  6. Deploy the agent into the image's root filesystem.

### Extracting the Root Filesystem

You must extract the root filesystem if you want to boot the image using NFS or you want to use the root filesystem as the target sysroot. For example, the Eclipse IDE environment with the Eclipse Yocto Plug-in installed allows you to use QEMU to boot under NFS. Another example is if you want to develop your target application using the root filesystem as the target sysroot.

To extract the root filesystem, first `source` the cross-development environment setup script and then use the `runqemu-extract-sdk` command on the filesystem image. For example, the following commands set up the environment and then extract the root filesystem from a previously built filesystem image tarball named `core-image-sato-sdk-qemux86-2011091411831.rootfs.tar.bz2`. The example extracts the root filesystem into the `$HOME/qemux86-sato` directory:

         $ source $HOME/toolchain_dir/environment-setup-i586-poky-linux
         $ runqemu-extract-sdk \
            ~Downloads/core-image-sato-sdk-qemux86-2011091411831.rootfs.tar.bz2 \
            $HOME/qemux86-sato

In this case, you could now point to the target sysroot at `$HOME/qemux86-sato`.

## Optionally Building a Toolchain Installer

As an alternative to locating and downloading a toolchain installer, you can build the toolchain installer if you have a Build Directory.

You can build the toolchain installer using `bitbake meta-toolchain`. This method requires you to still install the target sysroot by installing and extracting it separately. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

A final method of building the toolchain installer exists that has significant advantages over the previous method. This method results in a toolchain installer that contains the sysroot that matches your target root filesystem. To build this installer, use the `bitbake image -c populate_sdk` command.

Remember, before using any `bitbake` command, you must source the build environment setup script (i.e. `&OE_INIT_FILE;` or `oe-init-build-env-memres`) located in the Source Directory and you must make sure your `conf/local.conf` variables are correct. In particular, you need to be sure the `MACHINE` variable matches the architecture for which you are building and that the `SDKMACHINE` variable is correctly set if you are building a toolchain designed to run on an architecture that differs from your current development host machine (i.e. the build machine).

When the BitBake command completes, the toolchain installer will be in `tmp/deploy/sdk` in the Build Directory.