| page.title=Overview |
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| <div id="qv-wrapper"> |
| <div id="qv"> |
| <h2>In this document</h2> |
| <ol id="auto-toc"> |
| </ol> |
| </div> |
| </div> |
| |
| <p>Welcome to the Android Platform Development Kit (PDK) Guide! The Android PDK allows partners to port |
| their drivers as well as develop, optimize, and test against an upcoming Android platform release. |
| The Android PDK includes a set of interfaces for the Android hardware abstraction layer (HAL), |
| platform sources for integration, a binary system image, and HAL and integration documentation. |
| In addition, the PDK also ships with the Android Compatibility Test Suite (CTS). |
| </p> |
| |
| <h2 id="arch">Android Low-Level System Architecture</h2> |
| <p>Before you begin porting Android to your hardware, it is important to have an |
| understanding of how Android works at a high level. Because your drivers and HAL code interact |
| with many layers of Android code, this understanding can help you find |
| your way through the many layers of code that are available to you through the AOSP |
| (Android Open Source Project) source tree as well as the PDK. |
| The following diagram shows a system level view of how Android works: |
| </p> |
| |
| <img src="images/system-architecture.png"> |
| |
| <p class="img-caption"><strong>Figure 1.</strong> Android System Architecture</p> |
| |
| <h4>Application framework</h4> |
| <p>This is the level that most application developers concern themselves with. You should be |
| aware of the APIs available to developers as many of them map 1:1 to the underlying HAL |
| interfaces and can provide information as to how to implement your driver. |
| </p> |
| |
| <h4>Binder IPC</h4> |
| <p> |
| The Binder Inter-Process Communication mechanism allows the application framework to |
| cross process boundaries and call into the Android system services code. This basically allows |
| high level framework APIs to interact with Android's system services. At the application framework level, all |
| of this communication is hidden from the developer and things appear to "just work." |
| </p> |
| |
| <h4>System services</h4> |
| <p>Most of the functionality exposed through the application framework APIs must |
| communicate with some sort of system service to access the underlying hardware. Services |
| are divided into modular components with focused functionality |
| such as the Window Manager, Search Service, or Notification Manager. System services are grouped |
| into two buckets: system and media. The system services include things such as the Window or |
| Notification Manager. The media services include all the services involved in playing and |
| recording media. |
| </p> |
| |
| <h4>Hardware abstraction layer (HAL)</h4> |
| <p>The HAL serves as a standard interface that allows the Android system to call into the device |
| driver layer while being agnostic about the lower-level implementations of your drivers and hardware. |
| You must implement the corresponding HAL (and driver) for the particular piece of hardware that your product |
| provides. Android does not mandate a standard interaction between your HAL implementation and your device drivers, so |
| you have free reign to do what is best for your situation. However, you must abide by the contract |
| defined in each hardware-specific HAL interface for the Android system to be able |
| to correctly interact with your hardware. HAL implementations are typically built into |
| shared library modules (<code>.so</code> files). |
| </p> |
| <h4>Linux Kernel</h4> |
| <p>For the most part, developing your device drivers is the same as developing a typical Linux device driver. |
| Android uses a specialized version of the Linux kernel with a few special additions such as |
| wakelocks, a memory management system that is more agressive in preserving memory, |
| the Binder IPC driver, and other features that are important for a mobile embedded platform like Android. |
| These additions have less to do with driver development than with the system's functionality. The PDK |
| does not provide kernel sources, so you must provide your own. You can use any version of the kernel that |
| you want as long as it supports the required features, such as the binder driver. However, we recommend |
| using the latest version of the Android kernel. For the latest Android kernel, see |
| <a href="{@docRoot}source/building-kernels.html" >Building Kernels</a>. |
| </p> |
| |
| |
| <h2 id="pdk">PDK Components</h2> |
| <p>Now that you have a high-level overview of the Android system, we'll go over the PDK and what it provides |
| to port Android to your product. The PDK provides source files needed to implement |
| your product and a platform binary that lets you build a runnable system image. You can then install |
| this barebones image to test your product with the latest builds of Android. The most important source files |
| included in the PDK are located in the:</p> |
| |
| <ul> |
| <li><code>frameworks/native</code> directory</li> |
| <li><code>frameworks/av</code> directory for media, camera, DRM, and the audio framework stack</code></li> |
| <li><code>hardware/libhardware/include/hardware</code> directory for the HAL interfaces </li> |
| <li><code>vendor/pdk/data/cts</code> directory for the CTS binaries</li> |
| </ul> |
| </p> |
| <p>In addition, the Android PDK includes the following source directories:</p> |
| <ul> |
| <li>abi</li> |
| <li>bionic</li> |
| <li>bootable</li> |
| <li>build</li> |
| <li>device</li> |
| <li>external (Chromium and Webkit are not included)</li> |
| <li>hardware</li> |
| <li>libnativehelper</li> |
| <li>pdk</li> |
| <li>prebuilt</li> |
| <li>prebuilts</li> |
| <li>system</li> |
| </ul> |
| |
| <p>The PDK also contains documentation that is split into the following sections:</p> |
| <ul> |
| <li><a href="{@docRoot}devices/getting_started.html">Getting Started</a> - Explains how to download |
| the PDK source, how the Android build system works, and how to configure a build for your specific product.</li> |
| <li><a href="{@docRoot}devices/porting.html">Porting</a> - Explains the various HALs provided by Android |
| and the interfaces (C header files) that define them. This section also provides reference documentation |
| for the various HAL interfaces.</li> |
| <li><a href="{@docRoot}devices/debugtune.html">Debugging and Tuning</a> - Explains the debugging and tuning features of the PDK.</li> |
| <li><a href="{@docRoot}devices/tech/index.html">Technical Information</a> - Explains important concepts of the Android platform.</li> |
| </ul> |
| |
| <h3 id="cts">Compatibility Test Suite</h3> |
| <p>CTS binaries for ARM, MIPS, and x86 are provided in the corresponding directories in <code>vendor/pdk/data/cts</code>. Only the ARM |
| variant is Google-verified as there is no Nexus device running on any other architecture. Not all of the CTS tests since the |
| complete Android platform is not present. The following CTS tests should work:</p> |
| |
| <ul> |
| <li>android.bluetooth</li> |
| <li>android.graphics</li> |
| <li>android.graphics2</li> |
| <li>android.hardware</li> |
| <li>android.location</li> |
| <li>android.opengl</li> |
| <li>android.openglperf</li> |
| <li>android.media</li> |
| <li>android.mediastress</li> |
| <li>android.nativemedia.sl</li> |
| <li>android.nativemedia.xa</li> |
| <li>android.net</li> |
| <li>android.renderscript</li> |
| </ul> |
| <p>You can run individual packages such as <code>android.media</code> with:</p> |
| <pre>cts-tradefed run singleCommand cts --skip-device-info --package android.media</pre> |
| </ul> |
| |
| <p>Because the PDK is missing many components compared to a full Android source tree, |
| there is a PDK test plan that is provided with CTS that limits the tests that are ran when using the PDK. You can run |
| this special test plan with the following command:</p> |
| |
| <pre>run cts --plan PDK</pre> |
| |
| <p>CTS is always actively under development, so we expect some tests to fail. CTS results |
| for the Galaxy Nexus are provided for you in the |
| the <code>vendor/pdk/data/cts/</code> directory and will show which tests fail on that |
| device. You can safely ignore the failed tests for your devices as well.</p> |
| |
| <p>See <a href="{@docRoot}compatibility/index.html">Compatibility</a> for more information on CTS.</p> |
| |
| <h2 id="inc-ex">PDK Inclusions and Exclusions</h2> |
| <p>The PDK is a subset of the complete Android source tree and might be missing things that you might need. Here is a list of what the PDK supports |
| and does not support:</p> |
| <ul> |
| <li>Supports building Android apps using the publicly available, standard SDK. Builds with non-public platform APIs are not supported. The JNI build is supported.</li> |
| <li>Supports only <code>en_US</code> locale.</li> |
| <li>Supports only phone layouts. Tablet layouts are not included.</li> |
| <li>Enables support for software navigation buttons by default, which you can disable by setting <code>qemu.jw.mainkeys=1</code>.</li> |
| <li>Builds all binaries with SMP (symmetric multiprocessing) features enabled. This might have a small performance impact on non-SMP CPUs.</li> |
| <li>Includes a minimal amount of Java libraries. Obtain any additional Java libraries from the publicly released Android source tree.</li> |
| <li>Contains a minimum number of applications. Build and install necessary applications as needed.</li> |
| <li>Does not support media streaming.</li> |
| <li>Does not include non-Latin fonts. (set by <code>MINIMAL_FONT_FOOTPRINT</code> variable in <code>BoardConfig.mk</code>). |
| An app might crash if it requires such fonts. </li> |
| <li>Does not support replacing framework resources by using the overlay mechanism. |
| This means all configurations controlled by framework resources are fixed.</li> |
| <li>Does not support NFC</li> |
| <li>Does not support DRM</li> |
| </ul> |
| |
| <h2 id="knownissues">Support and Known Issues</h2> |
| <p> |
| For questions or to report issues related with the PDK, send a message to the <a href="https://groups.google.com/a/google.com/forum/?fromgroups#!forum/android-pdk-feedback">android-pdk@google.com</a> mailing list.</p> |
| |
| <p>The following list describes the known issues with the PDK:</p> |
| <ul> |
| <li>After running the CTS (Compatibility Test Suite), <code>android.process.acore</code> crashes. This is caused by |
| some missing components in PDK and does not affect the operation of CTS tests.</li> |
| </p> |