Android 2.3 兼容性定義

版權所有 © 2010，谷歌公司。保留所有權利。
compatibility@android.com

目錄

一、簡介

本文檔列舉了手機要兼容 Android 2.3 必須滿足的要求。

“必須”、“不得”、“要求”、“應”、“不應”、“應該”、“不應該”、“推薦”、“可以”和“可選”的使用符合 IETF 標準在 RFC2119 [資源，1 ] 中定義。

在本文檔中，“設備實施者”或“實施者”是指開發運行 Android 2.3 的硬件/軟件解決方案的個人或組織。 “設備實現”或“實現”是這樣開發的硬件/軟件解決方案。

要被視為與 Android 2.3 兼容，設備實現必須滿足此兼容性定義中提出的要求，包括通過引用合併的任何文檔。

如果此定義或第 10 節中描述的軟件測試是沉默的、模棱兩可的或不完整的，則設備實施者有責任確保與現有實施的兼容性。出於這個原因，Android 開源項目 [參考資料，3 ] 是 Android 的參考和首選實現。強烈鼓勵設備實施者盡可能以 Android 開源項目提供的“上游”源代碼為基礎進行實施。雖然假設某些組件可以替換為替代實現，但強烈不鼓勵這種做法，因為通過軟件測試將變得更加困難。實施者有責任確保與標準 Android 實施的完全行為兼容性，包括並超出兼容性測試套件。最後，請注意本文檔明確禁止某些組件替換和修改。

請注意，此兼容性定義的發布是為了與 Android 的 2.3.3 更新相對應，即 API 級別 10。此定義廢棄並取代了 2.3.3 之前的 Android 2.3 版本的兼容性定義。 （也就是說，版本 2.3.1 和 2.3.2 已過時。）未來運行 Android 2.3 的 Android 兼容設備必須配備 2.3.3 或更高版本。

2.資源

1. IETF RFC2119 要求級別： http ://www.ietf.org/rfc/rfc2119.txt
2. Android 兼容性程序概述：http: //source.android.com/compatibility/index.html
3. 安卓開源項目：http: //source.android.com/
4. API 定義和文檔：http: //developer.android.com/reference/packages.html
5. Android 權限參考：http: //developer.android.com/reference/android/Manifest.permission.html
6. android.os.Build 參考：http: //developer.android.com/reference/android/os/Build.html
7. Android 2.3 允許的版本字符串：http: //source.android.com/compatibility/2.3/versions.html
8. android.webkit.WebView類：http: //developer.android.com/reference/android/webkit/WebView.html
9. HTML5：http: //www.whatwg.org/specs/web-apps/current-work/multipage/
10. HTML5 離線功能： http ://dev.w3.org/html5/spec/Overview.html#offline
11. HTML5 視頻標籤： http ://dev.w3.org/html5/spec/Overview.html#video
12. HTML5/W3C 地理定位 API： http ://www.w3.org/TR/geolocation-API/
13. HTML5/W3C 網絡數據庫 API： http ://www.w3.org/TR/webdatabase/
14. HTML5/W3C IndexedDB API： http ://www.w3.org/TR/IndexedDB/
15. Dalvik 虛擬機規範：在 Android 源代碼中可用，位於 dalvik/docs
16. AppWidgets：http: //developer.android.com/guide/practices/ui_guidelines/widget_design.html
17. 通知：http: //developer.android.com/guide/topics/ui/notifiers/notifications.html
18. 應用資源： http ://code.google.com/android/reference/available-resources.html
19. 狀態欄圖標樣式指南：http: //developer.android.com/guide/practices/ui_guideline /icon_design.html#statusbarstructure
20. 搜索管理器：http: //developer.android.com/reference/android/app/SearchManager.html
21. 敬酒：http: //developer.android.com/reference/android/widget/Toast.html
22. 動態壁紙： https ://android-developers.googleblog.com/2010/02/live-wallpapers.html
23. 參考工具文檔（adb、aapt、ddms）：http: //developer.android.com/guide/developing/tools/index.html
24. 安卓apk文件說明：http: //developer.android.com/guide/topics/fundamentals.html
25. 清單文件：http: //developer.android.com/guide/topics/manifest/manifest-intro.html
26. 猴子測試工具： https ://developer.android.com/studio/test/other-testing-tools/monkey
27. Android 硬件功能列表：http: //developer.android.com/reference/android/content/pm/PackageManager.html
28. 支持多屏幕：http: //developer.android.com/guide/practices/screens_support.html
29. android.util.DisplayMetrics：http: //developer.android.com/reference/android/util/DisplayMetrics.html
30. android.content.res.Configuration：http: //developer.android.com/reference/android/content/res/Configuration.html
31. 傳感器坐標空間：http: //developer.android.com/reference/android/hardware/SensorEvent.html
32. 藍牙 API：http: //developer.android.com/reference/android/bluetooth/package-summary.html
33. NDEF 推送協議：http: //source.android.com/compatibility/ndef-push-protocol.pdf
34. MIFARE MF1S503X： http ://www.nxp.com/documents/data_sheet/MF1S503x.pdf
35. MIFARE MF1S703X： http ://www.nxp.com/documents/data_sheet/MF1S703x.pdf
36. MIFARE MF0ICU1： http ://www.nxp.com/documents/data_sheet/MF0ICU1.pdf
37. MIFARE MF0ICU2： http ://www.nxp.com/documents/short_data_sheet/MF0ICU2_SDS.pdf
38. MIFARE AN130511： http ://www.nxp.com/documents/application_note/AN130511.pdf
39. MIFARE AN130411： http ://www.nxp.com/documents/application_note/AN130411.pdf
40. 相機方向 API：http: //developer.android.com/reference/android/hardware/Camera.html#setDisplayOrientation(int)
41. android.hardware.Camera：http://developer.android.com/reference/android/hardware/Camera.html
42. Android 安全和權限參考：http: //developer.android.com/guide/topics/security/security.html
43. 適用於 Android 的應用程序： http ://code.google.com/p/apps-for-android

其中許多資源直接或間接源自 Android 2.3 SDK，並且在功能上與該 SDK 文檔中的信息相同。在任何情況下，如果此兼容性定義或兼容性測試套件與 SDK 文檔不一致，則 SDK 文檔被視為權威。上述參考文獻中提供的任何技術細節都被視為包含在本兼容性定義中。

3. 軟件

Android 平台包括一組託管 API、一組本機 API 和一組所謂的“軟”API，例如 Intent 系統和 Web 應用程序 API。本節詳細介紹了兼容性不可或缺的硬 API 和軟 API，以及某些其他相關的技術和用戶界面行為。設備實現必須符合本節中的所有要求。

3.1.託管 API 兼容性

託管（基於 Dalvik）執行環境是 Android 應用程序的主要載體。 Android 應用程序編程接口 (API) 是暴露給在託管 VM 環境中運行的應用程序的一組 Android 平台接口。設備實現必須提供由 Android 2.3 SDK [參考資料，4 ] 公開的任何已記錄 API 的完整實現，包括所有已記錄的行為。

設備實現不得省略任何託管 API、更改 API 接口或簽名、偏離記錄的行為或包含空操作，除非本兼容性定義明確允許。

此兼容性定義允許設備實現省略某些類型的硬件，其中 Android 包含 API。在這種情況下，API 必須仍然存在並以合理的方式運行。有關此場景的特定要求，請參閱第 7 節。

3.2.軟 API 兼容性

除了第 3.1 節中的託管 API 之外，Android 還包括一個重要的僅限運行時的“軟”API，其形式為 Intents、權限和 Android 應用程序的類似方面，這些方面不能在應用程序編譯時強制執行。本節詳細介紹了與 Android 2.3 兼容所需的“軟”API 和系統行為。設備實現必須滿足本節中提出的所有要求。

3.2.1.權限

設備實現者必須支持並強制執行權限參考頁 [參考資料，5 ] 中記錄的所有權限常量。請注意，第 10 節列出了與 Android 安全模型相關的其他要求。

3.2.2.構建參數

Android API 在android.os.Build類 [ Resources, 6 ] 中包含許多常量，這些常量旨在描述當前設備。為了在設備實現中提供一致的、有意義的值，下表包括對設備實現必須遵守的這些值的格式的額外限制。

3.2.3.意圖兼容性

Android 使用 Intents 來實現應用程序之間的鬆散耦合集成。本節描述了與設備實現必須遵守的 Intent 模式相關的要求。 “榮譽”意味著設備實現者必須提供一個 Android 活動或服務，指定一個匹配的 Intent 過濾器並綁定到每個指定的 Intent 模式並為每個指定的 Intent 模式實現正確的行為。

3.2.3.1.核心應用意圖

Android 上游項目定義了一些核心應用程序，例如電話撥號器、日曆、通訊錄、音樂播放器等。設備實施者可以用替代版本替換這些應用程序。

但是，任何此類替代版本都必須遵循上游項目提供的相同 Intent 模式。例如，如果設備包含替代音樂播放器，它仍然必須遵循第三方應用程序發出的 Intent 模式來選擇歌曲。

以下應用程序被視為核心 Android 系統應用程序：

• 台鐘
• 瀏覽器
• 日曆
• 計算器
• 聯繫人
• 電子郵件
• 畫廊
• 全球搜索
• 啟動器
• 音樂
• 設置

核心 Android 系統應用程序包括各種被認為是“公共”的 Activity 或 Service 組件。也就是說，屬性“android:exported”可能不存在，或者可能具有值“true”。

對於核心 Android 系統應用之一中定義的每個活動或服務，如果未通過值為“false”的 android:exported 屬性標記為非公共，設備實現必須包含實現相同 Intent 過濾器的相同類型的組件patterns 作為核心的 Android 系統應用程序。

換句話說，設備實現可以取代核心 Android 系統應用程序；但是，如果是這樣，設備實現必須支持由每個被替換的核心 Android 系統應用程序定義的所有 Intent 模式。

3.2.3.2.意圖覆蓋

由於 Android 是一個可擴展的平台，設備實現者必須允許第 3.2.3.1 節中引用的每個 Intent 模式被第三方應用程序覆蓋。上游 Android 開源項目默認允許這樣做；設備實現者不得將特殊權限附加到系統應用程序對這些 Intent 模式的使用，或阻止第三方應用程序綁定到這些模式並承擔對這些模式的控制。該禁令具體包括但不限於禁用“選擇器”用戶界面，該界面允許用戶在處理相同 Intent 模式的多個應用程序之間進行選擇。

3.2.3.3.意圖命名空間

設備實現者不得在 android.* 命名空間中包含任何使用 ACTION、CATEGORY 或其他鍵字符串來支持任何新 Intent 或 Broadcast Intent 模式的 Android 組件。設備實現者不得在屬於另一個組織的包空間中包含任何使用 ACTION、CATEGORY 或其他鍵字符串來支持任何新 Intent 或 Broadcast Intent 模式的 Android 組件。設備實施者不得更改或擴展第 3.2.3.1 節中列出的核心應用程序使用的任何 Intent 模式。

此禁止類似於第 3.6 節中為 Java 語言類指定的禁止。

3.2.3.4.廣播意圖

第三方應用依賴平台廣播某些Intent，通知自身硬件或軟件環境的變化。 Android 兼容設備必須廣播公共廣播 Intent 以響應適當的系統事件。 SDK 文檔中描述了廣播意圖。

3.3.本機 API 兼容性

在 Dalvik 中運行的託管代碼可以調用應用程序 .apk 文件中提供的本機代碼，作為針對相應設備硬件架構編譯的 ELF .so 文件。由於本機代碼高度依賴於底層處理器技術，因此 Android 在 Android NDK 中定義了許多應用程序二進制接口 (ABI)，位於文件docs/CPU-ARCH-ABIS.txt中。如果設備實現與一個或多個定義的 ABI 兼容，它應該實現與 Android NDK 的兼容性，如下所示。

如果設備實現包括對 Android ABI 的支持，它：

• 必須包括對在託管環境中運行的代碼的支持，以使用標準 Java 本機接口 (JNI) 語義調用本機代碼。
• 必須與下面列表中的每個必需庫源代碼兼容（即標頭兼容）和二進制兼容（對於 ABI）
• 必須通過android.os.Build.CPU_ABI API 準確報告設備支持的本機應用程序二進制接口 (ABI)
• 必須僅在文件docs/CPU-ARCH-ABIS.txt中報告最新版本的 Android NDK 中記錄的那些 ABI
• 應使用上游 Android 開源項目中提供的源代碼和頭文件構建

以下本機代碼 API 必須可供包含本機代碼的應用程序使用：

• libc（C 庫）
• libm（數學庫）
• 對 C++ 的最小支持
• JNI接口
• liblog（Android 日誌記錄）
• libz（Zlib 壓縮）
• libdl（動態鏈接器）
• libGLESv1_CM.so (OpenGL ES 1.0)
• libGLESv2.so（OpenGL ES 2.0）
• libEGL.so（本機 OpenGL 表面管理）
• libjnigraphics.so
• libOpenSLES.so（開放聲音庫音頻支持）
• libandroid.so（本機 Android 活動支持）
• 支持 OpenGL，如下所述

請注意，Android NDK 的未來版本可能會引入對其他 ABI 的支持。如果設備實現與現有的預定義 ABI 不兼容，則它絕不能報告對任何 ABI 的支持。

本機代碼兼容性具有挑戰性。出於這個原因，應該重申，非常強烈地鼓勵設備實現者使用上面列出的庫的上游實現來幫助確保兼容性。

3.4.網絡兼容性

許多開發人員和應用程序的用戶界面依賴於android.webkit.WebView類 [ Resources, 8 ] 的行為，因此 WebView 實現必須在 Android 實現之間兼容。同樣，完整、現代的網絡瀏覽器是 Android 用戶體驗的核心。設備實現必須包括與上游 Android 軟件一致的android.webkit.WebView版本，並且必須包括支持 HTML5 的現代瀏覽器，如下所述。

3.4.1. Web 視圖兼容性

Android 開源實現使用 WebKit 渲染引擎來實現android.webkit.WebView 。因為為 Web 渲染系統開發一個全面的測試套件是不可行的，設備實現者必須在 WebView 實現中使用特定的 WebKit 上游構建。具體來說：

• 設備實現的android.webkit.WebView實現必須基於 Android 2.3 的上游 Android 開源樹中的 533.1 WebKit 構建。此版本包括一組特定的 WebView 功能和安全修復程序。設備實現者可以包括對 WebKit 實現的自定義；但是，任何此類自定義不得改變 WebView 的行為，包括呈現行為。
• WebView 報告的用戶代理字符串必須採用以下格式：
  Mozilla/5.0 (Linux; U; Android $(VERSION); $(LOCALE); $(MODEL) Build/$(BUILD)) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1
  • $(VERSION) 字符串的值必須與android.os.Build.VERSION.RELEASE的值相同
  • $(LOCALE) 字符串的值應該遵循國家代碼和語言的 ISO 約定，並且應該引用設備當前配置的區域設置
  • $(MODEL) 字符串的值必須與android.os.Build.MODEL的值相同
  • $(BUILD) 字符串的值必須與android.os.Build.ID的值相同

WebView 組件應該盡可能多地支持 HTML5 [ Resources, 9 ]。至少，設備實現必須支持與 WebView 中的 HTML5 關聯的這些 API 中的每一個：

• 應用程序緩存/離線操作 [資源，10 ]
• <video> 標籤 [ Resources, 11 ]
• 地理定位 [資源, 12 ]

此外，設備實現必須支持 HTML5/W3C webstorage API [參考資料，13 ]，並且應該支持 HTML5/W3C IndexedDB API [參考資料，14 ]。請注意，隨著 Web 開發標準機構轉向支持 IndexedDB 而不是 webstorage，IndexedDB 有望成為未來版本的 Android 中的必需組件。

與所有 JavaScript API 一樣，HTML5 API 必須在 WebView 中默認禁用，除非開發人員通過常用的 Android API 明確啟用它們。

3.4.2.瀏覽器兼容性

設備實現必須包括一個獨立的瀏覽器應用程序，供一般用戶瀏覽網頁。獨立瀏覽器可以基於 WebKit 以外的瀏覽器技術。但是，即使使用備用瀏覽器應用程序，提供給第三方應用程序的android.webkit.WebView組件也必須基於 WebKit，如第 3.4.1 節所述。

實現可以在獨立的瀏覽器應用程序中提供自定義用戶代理字符串。

獨立的瀏覽器應用程序（無論是基於上游 WebKit 瀏覽器應用程序還是第三方替代品）應該盡可能多地支持 HTML5 [參考資料，9 ]。至少，設備實現必須支持以下與 HTML5 相關的每個 API：

• 應用程序緩存/離線操作 [資源，10 ]
• <video> 標籤 [ Resources, 11 ]
• 地理定位 [資源, 12 ]

此外，設備實現必須支持 HTML5/W3C webstorage API [參考資料，13 ]，並且應該支持 HTML5/W3C IndexedDB API [參考資料，14 ]。請注意，隨著 Web 開發標準機構轉向支持 IndexedDB 而不是 webstorage，IndexedDB 有望成為未來版本的 Android 中的必需組件。

3.5. API 行為兼容性

每種 API 類型（託管、軟件、本機和 Web）的行為必須與上游 Android 開源項目 [參考資料，3 ] 的首選實現一致。一些特定的兼容性領域是：

• 設備不得更改標準 Intent 的行為或語義
• 設備不得改變特定類型系統組件（例如服務、活動、內容提供者等）的生命週期或生命週期語義
• 設備不得更改標準權限的語義

上面的列表並不全面。兼容性測試套件 (CTS) 測試平台的重要部分的行為兼容性，但不是全部。實施者有責任確保與 Android 開源項目的行為兼容性。出於這個原因，設備實施者應該盡可能使用通過 Android 開源項目提供的源代碼，而不是重新實施系統的重要部分。

3.6. API 命名空間

Android 遵循 Java 編程語言定義的包和類命名空間約定。為確保與第三方應用程序的兼容性，設備實施者不得對這些包命名空間進行任何禁止的修改（見下文）：

• java.*
• javax.*
• 太陽。*
• 安卓。*
• com.android.*

禁止的修改包括：

• 設備實現不得通過更改任何方法或類簽名，或者通過刪除類或類字段來修改 Android 平台上公開公開的 API。
• 設備實現者可以修改 API 的底層實現，但此類修改不得影響任何公開 API 的聲明行為和 Java 語言簽名。
• 設備實現者不得向上述 API 添加任何公開公開的元素（例如類或接口，或現有類或接口的字段或方法）。

“公開暴露的元素”是任何未使用上游 Android 源代碼中使用的“@hide”標記修飾的構造。換句話說，設備實現者不得公開新的 API 或更改上述命名空間中的現有 API。設備實施者可以進行僅限內部的修改，但這些修改不得公佈或以其他方式暴露給開發人員。

設備實施者可以添加自定義 API，但任何此類 API 不得位於其他組織擁有或引用的命名空間中。例如，設備實施者不得將 API 添加到 com.google.* 或類似的命名空間；只有谷歌可以這樣做。同樣，Google 不得將 API 添加到其他公司的命名空間。此外，如果設備實現包含標準 Android 命名空間之外的自定義 API，則這些 API 必須打包在 Android 共享庫中，以便只有明確使用它們（通過<uses-library>機制）的應用才會受到內存使用量增加的影響此類 API。

如果設備實施者提議改進上述包命名空間之一（例如通過向現有 API 添加有用的新功能，或添加新 API），實施者應該訪問 source.android.com 並開始貢獻更改的過程和代碼，根據該站點上的信息。

請注意，上述限制對應於 Java 編程語言中命名 API 的標準約定；本節的目的只是為了加強這些約定，並通過將它們包含在此兼容性定義中來使其具有約束力。

3.7.虛擬機兼容性

設備實現必須支持完整的 Dalvik 可執行 (DEX) 字節碼規範和 Dalvik 虛擬機語義 [參考資料，15 ]。

具有分類為中密度或低密度屏幕的設備實現必須配置 Dalvik 為每個應用程序分配至少 16MB 的內存。具有分類為高密度或超高密度屏幕的設備實現必須配置 Dalvik 為每個應用程序分配至少 24MB 的內存。請注意，設備實現可能會分配比這些數字更多的內存。

3.8.用戶界面兼容性

Android 平台包含一些開發人員 API，允許開發人員掛接到系統用戶界面。設備實現必須將這些標準 UI API 合併到他們開發的自定義用戶界面中，如下所述。

3.8.1.小部件

Android 定義了一種組件類型和相應的 API 和生命週期，允許應用程序向最終用戶公開“AppWidget”[參考資料，16 ]。 Android 開源參考版本包括一個 Launcher 應用程序，該應用程序包含允許用戶從主屏幕添加、查看和刪除 AppWidgets 的用戶界面元素。

設備實施者可以替代參考啟動器（即主屏幕）。替代啟動器應該包括對 AppWidgets 的內置支持，並公開用戶界面元素以直接在啟動器中添加、配置、查看和刪除 AppWidgets。替代啟動器可以省略這些用戶界面元素；然而，如果它們被省略，設備實現者必須提供一個單獨的應用程序，可以從啟動器訪問，允許用戶添加、配置、查看和刪除 AppWidgets。

3.8.2.通知

Android 包含允許開發人員通知用戶重要事件的 API [參考資料，17 ]。設備實施者必須為如此定義的每一類通知提供支持；特別是：聲音、振動、燈光和狀態欄。

此外，實現必須正確呈現 API [ Resources, 18 ] 或狀態欄圖標樣式指南 [ Resources, 19 ] 中提供的所有資源（圖標、聲音文件等）。設備實施者可以為通知提供替代用戶體驗，而不是參考 Android 開源實施所提供的體驗；然而，這樣的替代通知系統必須支持現有的通知資源，如上所述。

3.8.3.搜索

Android 包含 API [ Resources, 20 ]，允許開發人員將搜索合併到他們的應用程序中，並將他們的應用程序數據公開到全局系統搜索中。 Generally speaking, this functionality consists of a single, system-wide user interface that allows users to enter queries, displays suggestions as users type, and displays results. The Android APIs allow developers to reuse this interface to provide search within their own apps, and allow developers to supply results to the common global search user interface.

Device implementations MUST include a single, shared, system-wide search user interface capable of real-time suggestions in response to user input. Device implementations MUST implement the APIs that allow developers to reuse this user interface to provide search within their own applications. Device implementations MUST implement the APIs that allow third-party applications to add suggestions to the search box when it is run in global search mode. If no third-party applications are installed that make use of this functionality, the default behavior SHOULD be to display web search engine results and suggestions.

Device implementations MAY ship alternate search user interfaces, but SHOULD include a hard or soft dedicated search button, that can be used at any time within any app to invoke the search framework, with the behavior provided for in the API documentation.

3.8.4. Toasts

Applications can use the "Toast" API (defined in [ Resources, 21 ]) to display short non-modal strings to the end user, that disappear after a brief period of time. Device implementations MUST display Toasts from applications to end users in some high-visibility manner.

3.8.5. Live Wallpapers

Android defines a component type and corresponding API and lifecycle that allows applications to expose one or more "Live Wallpapers" to the end user [ Resources, 22 ]. Live Wallpapers are animations, patterns, or similar images with limited input capabilities that display as a wallpaper, behind other applications.

Hardware is considered capable of reliably running live wallpapers if it can run all live wallpapers, with no limitations on functionality, at a reasonable framerate with no adverse affects on other applications. If limitations in the hardware cause wallpapers and/or applications to crash, malfunction, consume excessive CPU or battery power, or run at unacceptably low frame rates, the hardware is considered incapable of running live wallpaper. As an example, some live wallpapers may use an Open GL 1.0 or 2.0 context to render their content. Live wallpaper will not run reliably on hardware that does not support multiple OpenGL contexts because the live wallpaper use of an OpenGL context may conflict with other applications that also use an OpenGL context.

Device implementations capable of running live wallpapers reliably as described above SHOULD implement live wallpapers. Device implementations determined to not run live wallpapers reliably as described above MUST NOT implement live wallpapers.

4. Application Packaging Compatibility

Device implementations MUST install and run Android ".apk" files as generated by the "aapt" tool included in the official Android SDK [ Resources, 23 ].

Devices implementations MUST NOT extend either the .apk [ Resources, 24 ], Android Manifest [ Resources, 25 ], or Dalvik bytecode [ Resources, 15 ] formats in such a way that would prevent those files from installing and running correctly on other compatible devices. Device implementers SHOULD use the reference upstream implementation of Dalvik, and the reference implementation's package management system.

5. Multimedia Compatibility

Device implementations MUST fully implement all multimedia APIs. Device implementations MUST include support for all multimedia codecs described below, and SHOULD meet the sound processing guidelines described below. Device implementations MUST include at least one form of audio output, such as speakers, headphone jack, external speaker connection, etc.

5.1. Media Codecs

Device implementations MUST support the multimedia codecs as detailed in the following sections. All of these codecs are provided as software implementations in the preferred Android implementation from the Android Open-Source Project.

Please note that neither Google nor the Open Handset Alliance make any representation that these codecs are unencumbered by third-party patents. Those intending to use this source code in hardware or software products are advised that implementations of this code, including in open source software or shareware, may require patent licenses from the relevant patent holders.

The tables below do not list specific bitrate requirements for most video codecs. The reason for this is that in practice, current device hardware does not necessarily support bitrates that map exactly to the required bitrates specified by the relevant standards. Instead, device implementations SHOULD support the highest bitrate practical on the hardware, up to the limits defined by the specifications.

5.1.1. Media Decoders

Device implementations MUST include an implementation of a decoder for each codec and format described in the table below. Note that decoders for each of these media types are provided by the upstream Android Open-Source Project.

5.1.2. Media Encoders

Device implementations SHOULD include encoders for as many of the media formats listed in Section 5.1.1. as possible. However, some encoders do not make sense for devices that lack certain optional hardware; for instance, an encoder for the H.263 video does not make sense, if the device lacks any cameras. Device implementations MUST therefore implement media encoders according to the conditions described in the table below.

See Section 7 for details on the conditions under which hardware may be omitted by device implementations.

In addition to the encoders listed above, device implementations SHOULD include an H.264 encoder. Note that the Compatibility Definition for a future version is planned to change this requirement to "MUST". That is, H.264 encoding is optional in Android 2.3 but will be required by a future version. Existing and new devices that run Android 2.3 are very strongly encouraged to meet this requirement in Android 2.3 , or they will not be able to attain Android compatibility when upgraded to the future version.

5.2. Audio Recording

When an application has used the android.media.AudioRecord API to start recording an audio stream, device implementations SHOULD sample and record audio with each of these behaviors:

• Noise reduction processing, if present, SHOULD be disabled.
• Automatic gain control, if present, SHOULD be disabled.
• The device SHOULD exhibit approximately flat amplitude versus frequency characteristics; specifically, ±3 dB, from 100 Hz to 4000 Hz
• Audio input sensitivity SHOULD be set such that a 90 dB sound power level (SPL) source at 1000 Hz yields RMS of 5000 for 16-bit samples.
• PCM amplitude levels SHOULD linearly track input SPL changes over at least a 30 dB range from -18 dB to +12 dB re 90 dB SPL at the microphone.
• Total harmonic distortion SHOULD be less than 1% from 100 Hz to 4000 Hz at 90 dB SPL input level.

Note: while the requirements outlined above are stated as "SHOULD" for Android 2.3, the Compatibility Definition for a future version is planned to change these to "MUST". That is, these requirements are optional in Android 2.3 but will be required by a future version. Existing and new devices that run Android 2.3 are very strongly encouraged to meet these requirements in Android 2.3 , or they will not be able to attain Android compatibility when upgraded to the future version.

5.3. Audio Latency

Audio latency is broadly defined as the interval between when an application requests an audio playback or record operation, and when the device implementation actually begins the operation. Many classes of applications rely on short latencies, to achieve real-time effects such sound effects or VOIP communication. Device implementations that include microphone hardware and declare android.hardware.microphone SHOULD meet all audio latency requirements outlined in this section. See Section 7 for details on the conditions under which microphone hardware may be omitted by device implementations.

For the purposes of this section:

• "cold output latency" is defined to be the interval between when an application requests audio playback and when sound begins playing, when the audio system has been idle and powered down prior to the request
• "warm output latency" is defined to be the interval between when an application requests audio playback and when sound begins playing, when the audio system has been recently used but is currently idle (that is, silent)
• "continuous output latency" is defined to be the interval between when an application issues a sample to be played and when the speaker physically plays the corresponding sound, while the device is currently playing back audio
• "cold input latency" is defined to be the interval between when an application requests audio recording and when the first sample is delivered to the application via its callback, when the audio system and microphone has been idle and powered down prior to the request
• "continuous input latency" is defined to be when an ambient sound occurs and when the sample corresponding to that sound is delivered to a recording application via its callback, while the device is in recording mode

Using the above definitions, device implementations SHOULD exhibit each of these properties:

• cold output latency of 100 milliseconds or less
• warm output latency of 10 milliseconds or less
• continuous output latency of 45 milliseconds or less
• cold input latency of 100 milliseconds or less
• continuous input latency of 50 milliseconds or less

Note: while the requirements outlined above are stated as "SHOULD" for Android 2.3, the Compatibility Definition for a future version is planned to change these to "MUST". That is, these requirements are optional in Android 2.3 but will be required by a future version. Existing and new devices that run Android 2.3 are very strongly encouraged to meet these requirements in Android 2.3 , or they will not be able to attain Android compatibility when upgraded to the future version.

If a device implementation meets the requirements of this section, it MAY report support for low-latency audio, by reporting the feature "android.hardware.audio.low-latency" via the android.content.pm.PackageManager class. [ Resources, 27 ] Conversely, if the device implementation does not meet these requirements it MUST NOT report support for low-latency audio.

6. Developer Tool Compatibility

Device implementations MUST support the Android Developer Tools provided in the Android SDK. Specifically, Android-compatible devices MUST be compatible with:

• Android Debug Bridge (known as adb) [ Resources, 23 ]
  Device implementations MUST support all adb functions as documented in the Android SDK. The device-side adb daemon SHOULD be inactive by default, but there MUST be a user-accessible mechanism to turn on the Android Debug Bridge.
• Dalvik Debug Monitor Service (known as ddms) [ Resources, 23 ]
  Device implementations MUST support all ddms features as documented in the Android SDK. As ddms uses adb , support for ddms SHOULD be inactive by default, but MUST be supported whenever the user has activated the Android Debug Bridge, as above.
• Monkey [ Resources, 26 ]
  Device implementations MUST include the Monkey framework, and make it available for applications to use.

Most Linux-based systems and Apple Macintosh systems recognize Android devices using the standard Android SDK tools, without additional support; however Microsoft Windows systems typically require a driver for new Android devices. (For instance, new vendor IDs and sometimes new device IDs require custom USB drivers for Windows systems.) If a device implementation is unrecognized by the adb tool as provided in the standard Android SDK, device implementers MUST provide Windows drivers allowing developers to connect to the device using the adb protocol. These drivers MUST be provided for Windows XP, Windows Vista, and Windows 7, in both 32-bit and 64-bit versions.

7. Hardware Compatibility

Android is intended to enable device implementers to create innovative form factors and configurations. At the same time Android developers write innovative applications that rely on the various hardware and features available through the Android APIs. The requirements in this section strike a balance between innovations available to device implementers, and the needs of developers to ensure their apps are only available to devices where they will run properly.

If a device includes a particular hardware component that has a corresponding API for third-party developers, the device implementation MUST implement that API as described in the Android SDK documentation. If an API in the SDK interacts with a hardware component that is stated to be optional and the device implementation does not possess that component:

• complete class definitions (as documented by the SDK) for the component's APIs MUST still be present
• the API's behaviors MUST be implemented as no-ops in some reasonable fashion
• API methods MUST return null values where permitted by the SDK documentation
• API methods MUST return no-op implementations of classes where null values are not permitted by the SDK documentation
• API methods MUST NOT throw exceptions not documented by the SDK documentation

A typical example of a scenario where these requirements apply is the telephony API: even on non-phone devices, these APIs must be implemented as reasonable no-ops.

Device implementations MUST accurately report accurate hardware configuration information via the getSystemAvailableFeatures() and hasSystemFeature(String) methods on the android.content.pm.PackageManager class. [ Resources, 27 ]

7.1. Display and Graphics

Android 2.3 includes facilities that automatically adjust application assets and UI layouts appropriately for the device, to ensure that third-party applications run well on a variety of hardware configurations [ Resources, 28 ]. Devices MUST properly implement these APIs and behaviors, as detailed in this section.

7.1.1. Screen Configurations

Device implementations MAY use screens of any pixel dimensions, provided that they meet the following requirements:

• screens MUST be at least 2.5 inches in physical diagonal size
• density MUST be at least 100 dpi
• the aspect ratio MUST be between 1.333 (4:3) and 1.779 (16:9)
• the display technology used consists of square pixels

Device implementations with a screen meeting the requirements above are considered compatible, and no additional action is necessary. The Android framework implementation automatically computes display characteristics such as screen size bucket and density bucket. In the majority of cases, the framework decisions are the correct ones. If the default framework computations are used, no additional action is necessary. Device implementers wishing to change the defaults, or use a screen that does not meet the requirements above MUST contact the Android Compatibility Team for guidance, as provided for in Section 12.

The units used by the requirements above are defined as follows:

• "Physical diagonal size" is the distance in inches between two opposing corners of the illuminated portion of the display.
• "dpi" (meaning "dots per inch") is the number of pixels encompassed by a linear horizontal or vertical span of 1". Where dpi values are listed, both horizontal and vertical dpi must fall within the range.
• "Aspect ratio" is the ratio of the longer dimension of the screen to the shorter dimension. For example, a display of 480x854 pixels would be 854 / 480 = 1.779, or roughly "16:9".

Device implementations MUST use only displays with a single static configuration. That is, device implementations MUST NOT enable multiple screen configurations. For instance, since a typical television supports multiple resolutions such as 1080p, 720p, and so on, this configuration is not compatible with Android 2.3. (However, support for such configurations is under investigation and planned for a future version of Android.)

7.1.2. Display Metrics

Device implementations MUST report correct values for all display metrics defined in android.util.DisplayMetrics [ Resources, 29 ].

7.1.3. Declared Screen Support

Applications optionally indicate which screen sizes they support via the <supports-screens> attribute in the AndroidManifest.xml file. Device implementations MUST correctly honor applications' stated support for small, medium, and large screens, as described in the Android SDK documentation.

7.1.4. Screen Orientation

Compatible devices MUST support dynamic orientation by applications to either portrait or landscape screen orientation. That is, the device must respect the application's request for a specific screen orientation. Device implementations MAY select either portrait or landscape orientation as the default. Devices that cannot be physically rotated MAY meet this requirement by "letterboxing" applications that request portrait mode, using only a portion of the available display.

Devices MUST report the correct value for the device's current orientation, whenever queried via the android.content.res.Configuration.orientation, android.view.Display.getOrientation(), or other APIs.

7.1.5. 3D Graphics Acceleration

Device implementations MUST support OpenGL ES 1.0, as required by the Android 2.3 APIs. For devices that lack 3D acceleration hardware, a software implementation of OpenGL ES 1.0 is provided by the upstream Android Open-Source Project. Device implementations SHOULD support OpenGL ES 2.0.

Implementations MAY omit Open GL ES 2.0 support; however if support is omitted, device implementations MUST NOT report as supporting OpenGL ES 2.0. Specifically, if a device implementations lacks OpenGL ES 2.0 support:

• the managed APIs (such as via the GLES10.getString() method) MUST NOT report support for OpenGL ES 2.0
• the native C/C++ OpenGL APIs (that is, those available to apps via libGLES_v1CM.so, libGLES_v2.so, or libEGL.so) MUST NOT report support for OpenGL ES 2.0.

Conversely, if a device implementation does support OpenGL ES 2.0, it MUST accurately report that support via the routes just listed.

Note that Android 2.3 includes support for applications to optionally specify that they require specific OpenGL texture compression formats. These formats are typically vendor-specific. Device implementations are not required by Android 2.3 to implement any specific texture compression format. However, they SHOULD accurately report any texture compression formats that they do support, via the getString() method in the OpenGL API.

7.2. Input Devices

Android 2.3 supports a number of modalities for user input. Device implementations MUST support user input devices as provided for in this section.

7.2.1. Keyboard

Device implementations:

• MUST include support for the Input Management Framework (which allows third party developers to create Input Management Engines -- ie soft keyboard) as detailed at developer.android.com
• MUST provide at least one soft keyboard implementation (regardless of whether a hard keyboard is present)
• MAY include additional soft keyboard implementations
• MAY include a hardware keyboard
• MUST NOT include a hardware keyboard that does not match one of the formats specified in android.content.res.Configuration.keyboard [ Resources, 30 ] (that is, QWERTY, or 12-key)

7.2.2. Non-touch Navigation

Device implementations:

• MAY omit a non-touch navigation option (that is, may omit a trackball, d-pad, or wheel)
• MUST report the correct value for android.content.res.Configuration.navigation [ Resources, 30 ]
• MUST provide a reasonable alternative user interface mechanism for the selection and editing of text, compatible with Input Management Engines. The upstream Android Open-Source code includes a selection mechanism suitable for use with devices that lack non-touch navigation inputs.

7.2.3. Navigation keys

The Home, Menu and Back functions are essential to the Android navigation paradigm. Device implementations MUST make these functions available to the user at all times, regardless of application state. These functions SHOULD be implemented via dedicated buttons. They MAY be implemented using software, gestures, touch panel, etc., but if so they MUST be always accessible and not obscure or interfere with the available application display area.

Device implementers SHOULD also provide a dedicated search key. Device implementers MAY also provide send and end keys for phone calls.

7.2.4. Touchscreen input

Device implementations:

• MUST have a touchscreen
• MAY have either capacitive or resistive touchscreen
• MUST report the value of android.content.res.Configuration [ Resources, 30 ] reflecting corresponding to the type of the specific touchscreen on the device
• SHOULD support fully independently tracked pointers, if the touchscreen supports multiple pointers

7.3. Sensors

Android 2.3 includes APIs for accessing a variety of sensor types. Devices implementations generally MAY omit these sensors, as provided for in the following subsections. If a device includes a particular sensor type that has a corresponding API for third-party developers, the device implementation MUST implement that API as described in the Android SDK documentation. For example, device implementations:

• MUST accurately report the presence or absence of sensors per the android.content.pm.PackageManager class. [ Resources, 27 ]
• MUST return an accurate list of supported sensors via the SensorManager.getSensorList() and similar methods
• MUST behave reasonably for all other sensor APIs (for example, by returning true or false as appropriate when applications attempt to register listeners, not calling sensor listeners when the corresponding sensors are not present; etc.)

The list above is not comprehensive; the documented behavior of the Android SDK is to be considered authoritative.

Some sensor types are synthetic, meaning they can be derived from data provided by one or more other sensors. (Examples include the orientation sensor, and the linear acceleration sensor.) Device implementations SHOULD implement these sensor types, when they include the prerequisite physical sensors.

The Android 2.3 APIs introduce a notion of a "streaming" sensor, which is one that returns data continuously, rather than only when the data changes. Device implementations MUST continuously provide periodic data samples for any API indicated by the Android 2.3 SDK documentation to be a streaming sensor.

7.3.1. Accelerometer

Device implementations SHOULD include a 3-axis accelerometer. If a device implementation does include a 3-axis accelerometer, it:

• MUST be able to deliver events at 50 Hz or greater
• MUST comply with the Android sensor coordinate system as detailed in the Android APIs (see [ Resources, 31 ])
• MUST be capable of measuring from freefall up to twice gravity (2g) or more on any three-dimensional vector
• MUST have 8-bits of accuracy or more
• MUST have a standard deviation no greater than 0.05 m/s^2

7.3.2. Magnetometer

Device implementations SHOULD include a 3-axis magnetometer (ie compass.) If a device does include a 3-axis magnetometer, it:

• MUST be able to deliver events at 10 Hz or greater
• MUST comply with the Android sensor coordinate system as detailed in the Android APIs (see [ Resources, 31 ]).
• MUST be capable of sampling a range of field strengths adequate to cover the geomagnetic field
• MUST have 8-bits of accuracy or more
• MUST have a standard deviation no greater than 0.5 µT

7.3.3. GPS

Device implementations SHOULD include a GPS receiver. If a device implementation does include a GPS receiver, it SHOULD include some form of "assisted GPS" technique to minimize GPS lock-on time.

7.3.4. Gyroscope

Device implementations SHOULD include a gyroscope (ie angular change sensor.) Devices SHOULD NOT include a gyroscope sensor unless a 3-axis accelerometer is also included. If a device implementation includes a gyroscope, it:

• MUST be capable of measuring orientation changes up to 5.5*Pi radians/second (that is, approximately 1,000 degrees per second)
• MUST be able to deliver events at 100 Hz or greater
• MUST have 8-bits of accuracy or more

7.3.5. Barometer

Device implementations MAY include a barometer (ie ambient air pressure sensor.) If a device implementation includes a barometer, it:

• MUST be able to deliver events at 5 Hz or greater
• MUST have adequate precision to enable estimating altitude

7.3.7. Thermometer

Device implementations MAY but SHOULD NOT include a thermometer (ie temperature sensor.) If a device implementation does include a thermometer, it MUST measure the temperature of the device CPU. It MUST NOT measure any other temperature. (Note that this sensor type is deprecated in the Android 2.3 APIs.)

7.3.7. Photometer

Device implementations MAY include a photometer (ie ambient light sensor.)

7.3.8. Proximity Sensor

Device implementations MAY include a proximity sensor. If a device implementation does include a proximity sensor, it MUST measure the proximity of an object in the same direction as the screen. That is, the proximity sensor MUST be oriented to detect objects close to the screen, as the primary intent of this sensor type is to detect a phone in use by the user. If a device implementation includes a proximity sensor with any other orientation, it MUST NOT be accessible through this API. If a device implementation has a proximity sensor, it MUST be have 1-bit of accuracy or more.

7.4. Data Connectivity

Network connectivity and access to the Internet are vital features of Android. Meanwhile, device-to-device interaction adds significant value to Android devices and applications. Device implementations MUST meet the data connectivity requirements in this section.

7.4.1. Telephony

"Telephony" as used by the Android 2.3 APIs and this document refers specifically to hardware related to placing voice calls and sending SMS messages via a GSM or CDMA network. While these voice calls may or may not be packet-switched, they are for the purposes of Android 2.3 considered independent of any data connectivity that may be implemented using the same network. In other words, the Android "telephony" functionality and APIs refer specifically to voice calls and SMS; for instance, device implementations that cannot place calls or send/receive SMS messages MUST NOT report the "android.hardware.telephony" feature or any sub-features, regardless of whether they use a cellular network for data connectivity.

Android 2.3 MAY be used on devices that do not include telephony hardware. That is, Android 2.3 is compatible with devices that are not phones. However, if a device implementation does include GSM or CDMA telephony, it MUST implement full support for the API for that technology. Device implementations that do not include telephony hardware MUST implement the full APIs as no-ops.

7.4.2. IEEE 802.11 (WiFi)

Android 2.3 device implementations SHOULD include support for one or more forms of 802.11 (b/g/a/n, etc.) If a device implementation does include support for 802.11, it MUST implement the corresponding Android API.

7.4.3. Bluetooth

Device implementations SHOULD include a Bluetooth transceiver. Device implementations that do include a Bluetooth transceiver MUST enable the RFCOMM-based Bluetooth API as described in the SDK documentation [ Resources, 32 ]. Device implementations SHOULD implement relevant Bluetooth profiles, such as A2DP, AVRCP, OBEX, etc. as appropriate for the device.

The Compatibility Test Suite includes cases that cover basic operation of the Android RFCOMM Bluetooth API. However, since Bluetooth is a communications protocol between devices, it cannot be fully tested by unit tests running on a single device. Consequently, device implementations MUST also pass the human-driven Bluetooth test procedure described in Appendix A.

7.4.4. Near-Field Communications

Device implementations SHOULD include a transceiver and related hardware for Near-Field Communications (NFC). If a device implementation does include NFC hardware, then it:

• MUST report the android.hardware.nfc feature from the android.content.pm.PackageManager.hasSystemFeature() method. [ Resources, 27 ]
• MUST be capable of reading and writing NDEF messages via the following NFC standards:
  • MUST be capable of acting as an NFC Forum reader/writer (as defined by the NFC Forum technical specification NFCForum-TS-DigitalProtocol-1.0) via the following NFC standards:
    • NfcA (ISO14443-3A)
    • NfcB (ISO14443-3B)
    • NfcF (JIS 6319-4)
    • NfcV (ISO 15693)
    • IsoDep (ISO 14443-4)
    • NFC Forum Tag Types 1, 2, 3, 4 (defined by the NFC Forum)
  • MUST be capable of transmitting and receiving data via the following peer-to-peer standards and protocols:
    • ISO 18092
    • LLCP 1.0 (defined by the NFC Forum)
    • SDP 1.0 (defined by the NFC Forum)
    • NDEF Push Protocol [ Resources, 33 ]
  • MUST scan for all supported technologies while in NFC discovery mode.
  • SHOULD be in NFC discovery mode while the device is awake with the screen active.

  (Note that publicly available links are not available for the JIS, ISO, and NFC Forum specifications cited above.)

  Additionally, device implementations SHOULD support the following widely-deployed MIFARE technologies.

  • MIFARE Classic (NXP MF1S503x [ Resources, 34 ], MF1S703x [ Resources, 35 ])
  • MIFARE Ultralight (NXP MF0ICU1 [ Resources, 36 ], MF0ICU2 [ Resources, 37 ])
  • NDEF on MIFARE Classic (NXP AN130511 [ Resources, 38 ], AN130411 [ Resources, 39 ])

  Note that Android 2.3.3 includes APIs for these MIFARE types. If a device implementation supports MIFARE, it:

  • MUST implement the corresponding Android APIs as documented by the Android SDK
  • MUST report the feature com.nxp.mifare from the android.content.pm.PackageManager.hasSystemFeature() method. [ Resources, 27 ] Note that this is not a standard Android feature, and as such does not appear as a constant on the PackageManager class.
  • MUST NOT implement the corresponding Android APIs nor report the com.nxp.mifare feature unless it also implements general NFC support as described in this section

  If a device implementation does not include NFC hardware, it MUST NOT declare the android.hardware.nfc feature from the android.content.pm.PackageManager.hasSystemFeature() method [ Resources, 27 ], and MUST implement the Android 2.3 NFC API as a no-op.

  As the classes android.nfc.NdefMessage and android.nfc.NdefRecord represent a protocol-independent data representation format, device implementations MUST implement these APIs even if they do not include support for NFC or declare the android.hardware.nfc feature.

  7.4.5. Minimum Network Capability

  Device implementations MUST include support for one or more forms of data networking. Specifically, device implementations MUST include support for at least one data standard capable of 200Kbit/sec or greater. Examples of technologies that satisfy this requirement include EDGE, HSPA, EV-DO, 802.11g, Ethernet, etc.

  Device implementations where a physical networking standard (such as Ethernet) is the primary data connection SHOULD also include support for at least one common wireless data standard, such as 802.11 (WiFi).

  Devices MAY implement more than one form of data connectivity.

  7.5. Cameras

  Device implementations SHOULD include a rear-facing camera, and MAY include a front-facing camera. A rear-facing camera is a camera located on the side of the device opposite the display; that is, it images scenes on the far side of the device, like a traditional camera. A front-facing camera is a camera located on the same side of the device as the display; that is, a camera typically used to image the user, such as for video conferencing and similar applications.

  7.5.1. Rear-Facing Camera

  Device implementations SHOULD include a rear-facing camera. If a device implementation includes a rear-facing camera, it:

  • MUST have a resolution of at least 2 megapixels
  • SHOULD have either hardware auto-focus, or software auto-focus implemented in the camera driver (transparent to application software)
  • MAY have fixed-focus or EDOF (extended depth of field) hardware
  • MAY include a flash. If the Camera includes a flash, the flash lamp MUST NOT be lit while an android.hardware.Camera.PreviewCallback instance has been registered on a Camera preview surface, unless the application has explicitly enabled the flash by enabling the FLASH_MODE_AUTO or FLASH_MODE_ON attributes of a Camera.Parameters object. Note that this constraint does not apply to the device's built-in system camera application, but only to third-party applications using Camera.PreviewCallback .

  7.5.2. Front-Facing Camera

  Device implementations MAY include a front-facing camera. If a device implementation includes a front-facing camera, it:

  • MUST have a resolution of at least VGA (that is, 640x480 pixels)
  • MUST NOT use a front-facing camera as the default for the Camera API. That is, the camera API in Android 2.3 has specific support for front-facing cameras, and device implementations MUST NOT configure the API to to treat a front-facing camera as the default rear-facing camera, even if it is the only camera on the device.
  • MAY include features (such as auto-focus, flash, etc.) available to rear-facing cameras as described in Section 7.5.1.
  • MUST horizontally reflect (ie mirror) the stream displayed by an app in a CameraPreview, as follows:
  • If the device implementation is capable of being rotated by user (such as automatically via an accelerometer or manually via user input), the camera preview MUST be mirrored horizontally relative to the device's current orientation.
  • If the current application has explicitly requested that the Camera display be rotated via a call to the android.hardware.Camera.setDisplayOrientation() [ Resources, 40 ] method, the camera preview MUST be mirrored horizontally relative to the orientation specified by the application.
  • Otherwise, the preview MUST be mirrored along the device's default horizontal axis.
  • MUST mirror the image data returned to any "postview" camera callback handlers, in the same manner as the camera preview image stream. (If the device implementation does not support postview callbacks, this requirement obviously does not apply.)
  • MUST NOT mirror the final captured still image or video streams returned to application callbacks or committed to media storage

  7.5.3. Camera API Behavior

  Device implementations MUST implement the following behaviors for the camera-related APIs, for both front- and rear-facing cameras:

  1. If an application has never called android.hardware.Camera.Parameters.setPreviewFormat(int), then the device MUST use android.hardware.PixelFormat.YCbCr_420_SP for preview data provided to application callbacks.
  2. If an application registers an android.hardware.Camera.PreviewCallback instance and the system calls the onPreviewFrame() method when the preview format is YCbCr_420_SP, the data in the byte[] passed into onPreviewFrame() must further be in the NV21 encoding format. That is, NV21 MUST be the default.
  3. Device implementations SHOULD support the YV12 format (as denoted by the android.graphics.ImageFormat.YV12 constant) for camera previews for both front- and rear-facing cameras. Note that the Compatibility Definition for a future version is planned to change this requirement to "MUST". That is, YV12 support is optional in Android 2.3 but will be required by a future version. Existing and new devices that run Android 2.3 are very strongly encouraged to meet this requirement in Android 2.3 , or they will not be able to attain Android compatibility when upgraded to the future version.

  Device implementations MUST implement the full Camera API included in the Android 2.3 SDK documentation [ Resources, 41 ]), regardless of whether the device includes hardware autofocus or other capabilities. For instance, cameras that lack autofocus MUST still call any registered android.hardware.Camera.AutoFocusCallback instances (even though this has no relevance to a non-autofocus camera.) Note that this does apply to front-facing cameras; for instance, even though most front-facing cameras do not support autofocus, the API callbacks must still be "faked" as described.

  Device implementations MUST recognize and honor each parameter name defined as a constant on the android.hardware.Camera.Parameters class, if the underlying hardware supports the feature. If the device hardware does not support a feature, the API must behave as documented. Conversely, Device implementations MUST NOT honor or recognize string constants passed to the android.hardware.Camera.setParameters() method other than those documented as constants on the android.hardware.Camera.Parameters . That is, device implementations MUST support all standard Camera parameters if the hardware allows, and MUST NOT support custom Camera parameter types.

  7.5.4. Camera Orientation

  Both front- and rear-facing cameras, if present, MUST be oriented so that the long dimension of the camera aligns with the screen's long dimension. That is, when the device is held in the landscape orientation, a cameras MUST capture images in the landscape orientation. This applies regardless of the device's natural orientation; that is, it applies to landscape-primary devices as well as portrait-primary devices.

  7.6. Memory and Storage

  The fundamental function of Android 2.3 is to run applications. Device implementations MUST the requirements of this section, to ensure adequate storage and memory for applications to run properly.

  7.6.1. Minimum Memory and Storage

  Device implementations MUST have at least 128MB of memory available to the kernel and userspace. The 128MB MUST be in addition to any memory dedicated to hardware components such as radio, memory, and so on that is not under the kernel's control.

  Device implementations MUST have at least 150MB of non-volatile storage available for user data. That is, the /data partition MUST be at least 150MB.

  Beyond the requirements above, device implementations SHOULD have at least 1GB of non-volatile storage available for user data. Note that this higher requirement is planned to become a hard minimum in a future version of Android. Device implementations are strongly encouraged to meet these requirements now, or else they may not be eligible for compatibility for a future version of Android.

  The Android APIs include a Download Manager that applications may use to download data files. The Download Manager implementation MUST be capable of downloading individual files 55MB in size, or larger. The Download Manager implementation SHOULD be capable of downloading files 100MB in size, or larger.

  7.6.2. Application Shared Storage

  Device implementations MUST offer shared storage for applications. The shared storage provided MUST be at least 1GB in size.

  Device implementations MUST be configured with shared storage mounted by default, "out of the box". If the shared storage is not mounted on the Linux path /sdcard , then the device MUST include a Linux symbolic link from /sdcard to the actual mount point.

  Device implementations MUST enforce as documented the android.permission.WRITE_EXTERNAL_STORAGE permission on this shared storage. Shared storage MUST otherwise be writable by any application that obtains that permission.

  Device implementations MAY have hardware for user-accessible removable storage, such as a Secure Digital card. Alternatively, device implementations MAY allocate internal (non-removable) storage as shared storage for apps.

  Regardless of the form of shared storage used, device implementations MUST provide some mechanism to access the contents of shared storage from a host computer, such as USB mass storage or Media Transfer Protocol.

  It is illustrative to consider two common examples. If a device implementation includes an SD card slot to satisfy the shared storage requirement, a FAT-formatted SD card 1GB in size or larger MUST be included with the device as sold to users, and MUST be mounted by default. Alternatively, if a device implementation uses internal fixed storage to satisfy this requirement, that storage MUST be 1GB in size or larger and mounted on /sdcard (or /sdcard MUST be a symbolic link to the physical location if it is mounted elsewhere.)

  Device implementations that include multiple shared storage paths (such as both an SD card slot and shared internal storage) SHOULD modify the core applications such as the media scanner and ContentProvider to transparently support files placed in both locations.

  7.7. USB

  Device implementations:

  • MUST implement a USB client, connectable to a USB host with a standard USB-A port
  • MUST implement the Android Debug Bridge over USB (as described in Section 7)
  • MUST implement the USB mass storage specification, to allow a host connected to the device to access the contents of the /sdcard volume
  • SHOULD use the micro USB form factor on the device side
  • MAY include a non-standard port on the device side, but if so MUST ship with a cable capable of connecting the custom pinout to standard USB-A port

  8. Performance Compatibility

  Compatible implementations must ensure not only that applications simply run correctly on the device, but that they do so with reasonable performance and overall good user experience. Device implementations MUST meet the key performance metrics of an Android 2.3 compatible device defined in the table below:

  Metric	Performance Threshold	Comments
  Application Launch Time	The following applications should launch within the specified time. Browser: less than 1300ms MMS/SMS: less than 700ms AlarmClock: less than 650ms	The launch time is measured as the total time to complete loading the default activity for the application, including the time it takes to start the Linux process, load the Android package into the Dalvik VM, and call onCreate.
  Simultaneous Applications	When multiple applications have been launched, re-launching an already-running application after it has been launched must take less than the original launch time.

  9. Security Model Compatibility

  Device implementations MUST implement a security model consistent with the Android platform security model as defined in Security and Permissions reference document in the APIs [ Resources, 42 ] in the Android developer documentation. Device implementations MUST support installation of self-signed applications without requiring any additional permissions/certificates from any third parties/authorities. Specifically, compatible devices MUST support the security mechanisms described in the follow sub-sections.

  9.1. Permissions

  Device implementations MUST support the Android permissions model as defined in the Android developer documentation [ Resources, 42 ]. Specifically, implementations MUST enforce each permission defined as described in the SDK documentation; no permissions may be omitted, altered, or ignored. Implementations MAY add additional permissions, provided the new permission ID strings are not in the android.* namespace.

  9.2. UID and Process Isolation

  Device implementations MUST support the Android application sandbox model, in which each application runs as a unique Unix-style UID and in a separate process. Device implementations MUST support running multiple applications as the same Linux user ID, provided that the applications are properly signed and constructed, as defined in the Security and Permissions reference [ Resources, 42 ].

  9.3. Filesystem Permissions

  Device implementations MUST support the Android file access permissions model as defined in as defined in the Security and Permissions reference [ Resources, 42 ].

  9.4. Alternate Execution Environments

  Device implementations MAY include runtime environments that execute applications using some other software or technology than the Dalvik virtual machine or native code. However, such alternate execution environments MUST NOT compromise the Android security model or the security of installed Android applications, as described in this section.

  Alternate runtimes MUST themselves be Android applications, and abide by the standard Android security model, as described elsewhere in Section 9.

  Alternate runtimes MUST NOT be granted access to resources protected by permissions not requested in the runtime's AndroidManifest.xml file via the <uses-permission> mechanism.

  Alternate runtimes MUST NOT permit applications to make use of features protected by Android permissions restricted to system applications.

  Alternate runtimes MUST abide by the Android sandbox model. Specifically:

  • Alternate runtimes SHOULD install apps via the PackageManager into separate Android sandboxes (that is, Linux user IDs, etc.)
  • Alternate runtimes MAY provide a single Android sandbox shared by all applications using the alternate runtime.
  • Alternate runtimes and installed applications using an alternate runtime MUST NOT reuse the sandbox of any other app installed on the device, except through the standard Android mechanisms of shared user ID and signing certificate
  • Alternate runtimes MUST NOT launch with, grant, or be granted access to the sandboxes corresponding to other Android applications.

  Alternate runtimes MUST NOT be launched with, be granted, or grant to other applications any privileges of the superuser (root), or of any other user ID.

  The .apk files of alternate runtimes MAY be included in the system image of a device implementation, but MUST be signed with a key distinct from the key used to sign other applications included with the device implementation.

  When installing applications, alternate runtimes MUST obtain user consent for the Android permissions used by the application. That is, if an application needs to make use of a device resource for which there is a corresponding Android permission (such as Camera, GPS, etc.), the alternate runtime MUST inform the user that the application will be able to access that resource. If the runtime environment does not record application capabilities in this manner, the runtime environment MUST list all permissions held by the runtime itself when installing any application using that runtime.

  10. Software Compatibility Testing

  The Android Open-Source Project includes various testing tools to verify that device implementations are compatible. Device implementations MUST pass all tests described in this section.

  However, note that no software test package is fully comprehensive. For this reason, device implementers are very strongly encouraged to make the minimum number of changes as possible to the reference and preferred implementation of Android 2.3 available from the Android Open-Source Project. This will minimize the risk of introducing bugs that create incompatibilities requiring rework and potential device updates.

  10.1. Compatibility Test Suite

  Device implementations MUST pass the Android Compatibility Test Suite (CTS) [ Resources, 2 ] available from the Android Open Source Project, using the final shipping software on the device. Additionally, device implementers SHOULD use the reference implementation in the Android Open Source tree as much as possible, and MUST ensure compatibility in cases of ambiguity in CTS and for any reimplementations of parts of the reference source code.

  The CTS is designed to be run on an actual device. Like any software, the CTS may itself contain bugs. The CTS will be versioned independently of this Compatibility Definition, and multiple revisions of the CTS may be released for Android 2.3. Device implementations MUST pass the latest CTS version available at the time the device software is completed.

  MUST pass the most recent version of the Android Compatibility Test Suite (CTS) available at the time of the device implementation's software is completed. (The CTS is available as part of the Android Open Source Project [ Resources, 2 ].) The CTS tests many, but not all, of the components outlined in this document.

  10.2. CTS Verifier

  Device implementations MUST correctly execute all applicable cases in the CTS Verifier. The CTS Verifier is included with the Compatibility Test Suite, and is intended to be run by a human operator to test functionality that cannot be tested by an automated system, such as correct functioning of a camera and sensors.

  The CTS Verifier has tests for many kinds of hardware, including some hardware that is optional. Device implementations MUST pass all tests for hardware which they possess; for instance, if a device possesses an accelerometer, it MUST correctly execute the Accelerometer test case in the CTS Verifier. Test cases for features noted as optional by this Compatibility Definition Document MAY be skipped or omitted.

  Every device and every build MUST correctly run the CTS Verifier, as noted above. However, since many builds are very similar, device implementers are not expected to explicitly run the CTS Verifier on builds that differ only in trivial ways. Specifically, device implementations that differ from an implementation that has passed the CTS Verfier only by the set of included locales, branding, etc. MAY omit the CTS Verifier test.

  10.3. Reference Applications

  Device implementers MUST test implementation compatibility using the following open-source applications:

  • The "Apps for Android" applications [ Resources, 43 ].
  • Replica Island (available in Android Market; only required for device implementations that support with OpenGL ES 2.0)

  Each app above MUST launch and behave correctly on the implementation, for the implementation to be considered compatible.

  11. Updatable Software

  Device implementations MUST include a mechanism to replace the entirety of the system software. The mechanism need not perform "live" upgrades -- that is, a device restart MAY be required.

  Any method can be used, provided that it can replace the entirety of the software preinstalled on the device. For instance, any of the following approaches will satisfy this requirement:

  • Over-the-air (OTA) downloads with offline update via reboot
  • "Tethered" updates over USB from a host PC
  • "Offline" updates via a reboot and update from a file on removable storage

  The update mechanism used MUST support updates without wiping user data. Note that the upstream Android software includes an update mechanism that satisfies this requirement.

  If an error is found in a device implementation after it has been released but within its reasonable product lifetime that is determined in consultation with the Android Compatibility Team to affect the compatibility of third-party applications, the device implementer MUST correct the error via a software update available that can be applied per the mechanism just described.

  12. Contact Us

  You can contact the document authors at compatibility@android.com for clarifications and to bring up any issues that you think the document does not cover.

  Appendix A - Bluetooth Test Procedure

  The Compatibility Test Suite includes cases that cover basic operation of the Android RFCOMM Bluetooth API. However, since Bluetooth is a communications protocol between devices, it cannot be fully tested by unit tests running on a single device. Consequently, device implementations MUST also pass the human-operated Bluetooth test procedure described below.

  The test procedure is based on the BluetoothChat sample app included in the Android open-source project tree. The procedure requires two devices:

  • a candidate device implementation running the software build to be tested
  • a separate device implementation already known to be compatible, and of a model from the device implementation being tested -- that is, a "known good" device implementation

  The test procedure below refers to these devices as the "candidate" and "known good" devices, respectively.

  Setup and Installation

  1. Build BluetoothChat.apk via 'make samples' from an Android source code tree.
  2. Install BluetoothChat.apk on the known-good device.
  3. Install BluetoothChat.apk on the candidate device.

  Test Bluetooth Control by Apps

  1. Launch BluetoothChat on the candidate device, while Bluetooth is disabled.
  2. Verify that the candidate device either turns on Bluetooth, or prompts the user with a dialog to turn on Bluetooth.

  Test Pairing and Communication

  1. Launch the Bluetooth Chat app on both devices.
  2. Make the known-good device discoverable from within BluetoothChat (using the Menu).
  3. On the candidate device, scan for Bluetooth devices from within BluetoothChat (using the Menu) and pair with the known-good device.
  4. Send 10 or more messages from each device, and verify that the other device receives them correctly.
  5. Close the BluetoothChat app on both devices by pressing Home .
  6. Unpair each device from the other, using the device Settings app.

  Test Pairing and Communication in the Reverse Direction

  1. Launch the Bluetooth Chat app on both devices.
  2. Make the candidate device discoverable from within BluetoothChat (using the Menu).
  3. On the known-good device, scan for Bluetooth devices from within BluetoothChat (using the Menu) and pair with the candidate device.
  4. Send 10 or messages from each device, and verify that the other device receives them correctly.
  5. Close the Bluetooth Chat app on both devices by pressing Back repeatedly to get to the Launcher.

  Test Re-Launches

  1. Re-launch the Bluetooth Chat app on both devices.
  2. Send 10 or messages from each device, and verify that the other device receives them correctly.

  Note: the above tests have some cases which end a test section by using Home, and some using Back. These tests are not redundant and are not optional: the objective is to verify that the Bluetooth API and stack works correctly both when Activities are explicitly terminated (via the user pressing Back, which calls finish()), and implicitly sent to background (via the user pressing Home.) Each test sequence MUST be performed as described.