1 page.title=Power Profiles for Android 2 @jd:body 3 4 <!-- 5 Copyright 2015 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 <div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"></ol> 23 </div> 24 </div> 25 26 <p>Battery use information is derived from battery use statistics and power profile values.</p> 27 28 <h2 id="usage-statistics">Battery use statistics</h2> 29 30 <p>The framework automatically determines battery use statistics by tracking how long device 31 components spend in different states. As components (Wi-Fi chipset, cellular radio, Bluetooth, GPS, 32 display, CPU) change states (OFF/ON, idle/full power, low/high brightness, etc.), the controlling 33 service reports to the framework BatteryStats service. BatteryStats collects information over time 34 and stores it for use across reboots. The service doesnt track battery current draw directly, 35 but instead collects timing information that can be used to approximate battery 36 consumption by different components.</p> 37 38 <p>The framework gathers statistics using the following methods:</p> 39 40 <ul> 41 <li><strong>Push</strong>. Services aware of component changes push state changes to the 42 BatteryStats service.</li> 43 <li><strong>Pull</strong>. For components such as the CPU use by apps, the framework 44 automatically pulls the data at transition points (such as starting or stopping an activity) to 45 take a snapshot.</li> 46 </ul> 47 48 <p>Resource consumption is associated with the application using the resource. When multiple 49 applications simultaneously use a resource (such as wakelocks that prevent the system from 50 suspending), the framework spreads consumption across those applications, although not necessarily 51 equally.</p> 52 53 <p>To avoid losing use statistics for a shutdown event, which may indicate battery power 54 consumption problems (i.e. shutdown occurs because the battery reached zero remaining capacity), 55 the framework flashes statistics approximately every 30 minutes.</p> 56 57 <p>Battery use statistics are handled entirely by the framework and do not require OEM 58 modifications.</p> 59 60 <h2 id="profile-values">Power profile values</h2> 61 62 <p class="caution"><strong>Caution:</strong> Device manufacturers must provide a component power 63 profile that defines the current consumption value for the component and the approximate battery 64 drain caused by the component over time. This profile is defined in 65 <a href="https://android.googlesource.com/platform/frameworks/base/+/master/core/res/res/xml/power_profile.xml">platform/frameworks/base/core/res/res/xml/power_profile.xml</a>. 66 For guidance on these settings, see <a href="{@docRoot}devices/tech/power/values.html">Power Values</a>.</p> 67 68 <p>Within a power profile, power consumption is specified in milliamps (mA) of current draw at a 69 nominal voltage and can be a fractional value specified in microamps (uA). The value should be the 70 mA consumed at the battery and not a value applicable to a power rail that does not correspond to 71 current consumed from the battery.</p> 72 73 <p>For example, a display power profile specifies the mA of current required to keep the display on 74 at minimum brightness and at maximum brightness. To determine the power cost (i.e the battery 75 drained by the display component) of keeping the display on, the framework tracks the time spent at 76 each brightness level, then multiplies those time intervals by an interpolated display brightness 77 cost.</p> 78 79 <p>The framework also multiplies the CPU time for each application by the mA required to run the 80 CPU at a specific speed. This calculation establishes a comparative ranking of how much battery an 81 application consumes by executing CPU code (time as the foreground app and total time including 82 background activity are reported separately).</p> 83
