1<!-- 2 Copyright 2010 The Android Open Source Project 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15--> 16 17# Compatibility Program Overview # 18 19The Android compatibility program makes it easy for mobile device 20manufacturers to develop compatible Android devices. 21 22# Program goals # 23 24The Android compatibility program works for the benefit of the entire 25Android community, including users, developers, and device manufacturers. 26 27Each group depends on the others. Users want a wide selection of devices 28and great apps; great apps come from developers motivated by a large market 29for their apps with many devices in users' hands; device manufacturers rely 30on a wide variety of great apps to increase their products' value for 31consumers. 32 33Our goals were designed to benefit each of these groups: 34 35- *Provide a consistent application and hardware environment to application 36developers.* 37 Without a strong compatibility standard, devices can vary so 38greatly that developers must design different versions of their applications 39for different devices. The compatibility program provides a precise definition 40of what developers can expect from a compatible device in terms of APIs and 41capabilities. Developers can use this information to make good design 42decisions, and be confident that their apps will run well on any compatible 43device. 44 45- *Enable a consistent application experience for consumers.* 46 If an application runs well on one compatible Android device, it should run well on 47any other device that is compatible with the same Android platform version. 48Android devices will differ in hardware and software capabilities, so the 49compatibility program also provides the tools needed for distribution systems 50such as Google Play to implement appropriate filtering. This means that 51users can only see applications which they can actually run. 52 53- *Enable device manufacturers to differentiate while being 54compatible.* 55 The Android compatibility program focuses on the aspects of 56Android relevant to running third-party applications, which allows device 57manufacturers the flexibility to create unique devices that are nonetheless 58compatible. 59 60- *Minimize costs and overhead associated with compatibility.* 61 Ensuring compatibility should be easy and inexpensive to 62device manufacturers. The testing tool (CTS) is free, open source, and 63available for [download](downloads.html). 64CTS is designed to be used for continuous self-testing 65during the device development process to eliminate the cost of changing your 66workflow or sending your device to a third party for testing. Meanwhile, there 67are no required certifications, and thus no corresponding costs and 68fees. 69 70The Android compatibility program consists of three key components: 71 72- The source code to the Android software stack 73- The Compatilbility Definition Document, representing the "policy" aspect of compatibility 74- The Compatilbility Test Suite, representing the "mechanism" of compatibility 75 76Just as each version of the Android platform exists in a separate branch in 77the source code tree, there is a separate CTS and CDD for each version as 78well. The CDD, CTS, and source code are -- along with your hardware and your 79software customizations -- everything you need to create a compatible device. 80 81# Compatibility Definition Document (CDD) # 82 83For each release of the Android platform, a detailed Compatibility 84Definition Document (CDD) will be provided. The CDD represents the "policy" 85aspect of Android compatibility. 86 87No test suite, including CTS, can truly be comprehensive. For instance, the 88CTS includes a test that checks for the presence and correct behavior of 89OpenGL graphics APIs, but no software test can verify that the graphics 90actually appear correctly on the screen. More generally, it's impossible to 91test the presence of hardware features such as keyboards, display density, 92WiFi, and Bluetooth. 93 94The CDD's role is to codify and clarify specific requirements, and 95eliminate ambiguity. The CDD does not attempt to be comprehensive. Since 96Android is a single corpus of open-source code, the code itself is the 97comprehensive "specification" of the platform and its APIs. The CDD acts as a 98"hub", referencing other content (such as SDK API documentation) that provides 99a framework in which the Android source code may be used so that the end 100result is a compatible system. 101 102If you want to build a device compatible with a given Android version, 103start by checking out the source code for that version, and then read the 104corresponding CDD and stay within its guidelines. For additional details, 105simply examine [the latest CDD](4.1/android-4.1-cdd.pdf). 106 107# Compatibility Test Suite (CTS) # 108 109The CTS is a free, commercial-grade test suite, available for 110[download](downloads.html). 111The CTS represents the "mechanism" of compatibility. 112 113The CTS runs on a desktop machine and executes test cases directly on 114attached devices or an emulator. The CTS is a set of unit tests designed to be 115integrated into the daily workflow (such as via a continuous build system) of 116the engineers building a device. Its intent is to reveal incompatibilities 117early on, and ensure that the software remains compatible throughout the 118development process. 119 120 121# Compatibility Test Suite Verifier (CTS Verifier) # 122The Compatibility Test Suite Verifier (CTS Verifier) is a supplement to the 123Compatibility Test Suite (CTS), available for [download](downloads.html). 124CTS Verifier provides tests for APIs and functions that cannot be tested on a 125stationary device without manual input (e.g. audio quality, accelerometer, etc). 126 127For details on the CTS, consult the [CTS introduction](cts-intro.html). 128