src/devices/tech/power/mgmt.jd

page.title=Power Management
@jd:body

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    <h2>In this document</h2>
    <ol id="auto-toc"></ol>
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<p>Battery life is a perennial user concern. To extend battery life, Android
continually adds new features and optimizations to help the platform optimize
the off-charger behavior of applications and devices.</p>
<p>The Android 6.0 release includes the following improvements to battery life:
</p>

<ul>
<li><b><a href="#app-standby">App Standby</b></a>. The platform can now place
unused applications in App Standby mode, temporarily restricting network access
and deferring syncs and jobs for those applications.</li>
<li><b><a href="#doze">Doze</b></a>. The platform now enters a state of deep
sleep (periodically resuming normal operations) if users have not actively used
their device (screen off and stationary) for extended periods of time. As this
feature requires the platform to detect the stationary state, it is available
only on devices that implement the significant motion detection APIs in the
Sensor HAL. Doze dramatically improves battery life.</li>
<li><b><a href="#exempt-apps">Exemptions</b></a>. System apps and cloud
messaging services preloaded on a device are typically exempted by default. App
developers can intent their applications into this setting. Users can also
exempt applications from App Standby and Doze via Settings > Battery >
Battery optimization > All apps and then selecting the app to turn off (or back
on) optimization.</li>
</ul>
<p>The following sections describe these improvements.</p>

<h2 id="app-standby">App Standby</h2>
<p>App Standby extends battery life by deferring background network activity
and jobs for applications the user is not actively using.</p>

<h3 id="app-standby-life">App Standby lifecycle</h3>
<p>The platform detects inactive applications and places them in App Standby
until the user begins actively engaging with the application.</p>

<table>
<tbody>
<tr>
<th width=33%>Detection</th>
<th width=33%>During App Standby</th>
<th width=33%>Exit</th>
</tr>

<tr>
<td><p>The platform detects an application is inactive when the device is not
charging <strong>and</strong> the user has not launched the application directly
or indirectly for a specific amount of clock time as well as a specific amount
of screen-on time. (Indirect launches occur when a foreground app accesses a
service in a second app.)</p></td>
<td><p>The platform prevents applications from accessing the network more than
once a day, deferring application syncs and other jobs.</p></td>
<td><p>The platform exits the app from App Standby when:</p>
<ul>
<li>Application becomes active.</li>
<li>Device is plugged in and charging.</li>
</ul>
</td>
</tr>
</tbody>
</table>

<p>Active applications are unaffected by App Standby. An application is active
when it has:</p>
<ul>
<li>A process currently in the foreground (either as an activity or foreground
service, or in use by another activity or foreground service), such as
notification listener, accessibility services, live wallpaper, etc.</li>
<li>A notification viewed by the user, such as in the lock screen or
notification tray.</li>
<li>Explicitly been launched by the user.</li>
</ul>
<p>An application is inactive if none of the above activities has occurred for
a period of time.
</p>

<h3>Testing App Standby</h3>
<p>You can manually test App Standby using the following ADB commands:</p>

<pre>
$ adb shell dumpsys battery unplug
$ adb shell am set-idle packageName true
$ adb shell am set-idle packageName false
$ adb shell am get-idle packageName
</pre>

<h2 id="doze">Doze</h2>

<p>Doze extends battery life by deferring application background CPU and
network activity when a device is unused for long periods.</p>

<p>Idle devices in Doze periodically enter a maintenance window, during which
apps can complete pending activities (syncs, jobs, etc.). Doze then resumes sleep
for a longer period of time, followed by another maintenance window. The
platform continues the Doze sleep/maintenance sequence, increasing the length of
idle each time, until a maximum of a few hours of sleep time is reached. At all
times, a device in Doze remains aware of motion and immediately leaves Doze
if motion is detected.</p>

<p>System services (such as telephony) and other preloaded services/apps are
exempted from Doze by default. Users can also exempt specific applications from
Doze in the Settings menu. By default, Doze is <b>disabled</b> in the Android
Open Source Project (AOSP). For details on enabling Doze, see
<a href="#integrate-doze">Integrating Doze</a>.</p>

<h3 id="doze-reqs">Doze requirements</h3>

<p>Doze support requires the following:</p>
<ul>
<li>Device implements the
<a href="http://source.android.com/devices/sensors/sensor-types.html#significant_motion">significant
motion detector (SMD) APIs</a> in the Sensor HAL. Devices that do not implement
these APIs cannot support Doze.</li>
<li>Device has a cloud messaging service, such as
<a href="https://developers.google.com/cloud-messaging/">Google Cloud Messaging
(GCM).</a> This enables the device to know when to wake from Doze.</li>
</ul>

<h3 id="doze-life">Doze lifecycle</h3>

<p>The Doze lifecycle begins when the platform detects the device is idle and
ends when the device exits Doze mode.</p>

<table>
<tbody>
<tr>
<th width=33%>Detection</td>
<th width=33%>During Doze</th>
<th width=33%>Exit</th>
</tr>
<tr>
<td><p>The platform detects a device is idle when:</p>
<ul>
<li>Device is stationary (using significant motion detector).</li>
<li>Device screen is off for some amount of time.</li>
</ul>
<p>Doze mode does not engage when the device is plugged into a power charger.
</p>
</td>
<td><p>The platform attempts to keep the system in a sleep state, periodically
resuming normal operations during a maintenance window then returning the device
to sleep for longer repeating periods. During the sleep state, the following
restrictions are active:</p>
<ul>
<li>Apps not allowed network access.</li>
<li>App wakelocks ignored.</li>
<li>Alarms deferred. Excludes alarm clock alarms and alarms set using
<code>setAndAllowWhileIdle()</code>. This exemption is intended for apps (such
as Calendar) that must show event reminder notifications.</li>
<li>Wi-Fi scans not performed.</li>
<li>SyncAdapter syncs and JobScheduler jobs deferred until the next maintenance
window.</li>
<li>Apps receiving SMS and MMS messages are put on a temporary whitelist so
they can complete their processing.</li>
</ul>
</td>
<td><p>The platform exits the device from Doze when it detects:</p>
<ul>
<li>User interaction with device.</li>
<li>Device movement.</li>
<li>Device screen turns on.</li>
<li>Imminent AlarmClock alarm.</li>
</ul>
<p>Notifications do not cause the device to exit from Doze.</p>
</td>
</tr>
</tbody>
</table>

<h3 id="doze-interactions">Interaction with App Standby</h3>
<ul>
<li>Time spent in Doze does not count towards App Standby.</li>
<li>While the device is in Doze, idle applications are allowed to perform normal
operations at least once a day.</li>
</ul>

<h3 id="integrate-doze">Integrating Doze</h3>
<p>To enable Doze for a device, perform the following tasks:</p>

<ol>
<li>Confirm the device supports
<a href="http://source.android.com/devices/sensors/sensor-types.html#significant_motion">SENSOR_TYPE_SIGNIFICANT_MOTION
</a>. If the device does not support this sensor, it cannot support Doze.</li>
<li>Confirm the device has a cloud messaging service installed.</li>
<li>In the device overlay config file
<code>overlay/frameworks/base/core/res/res/values/config.xml</code>, set
<code>config_enableAutoPowerModes</code> to <b>true</b>:
<pre>
bool name="config_enableAutoPowerModes"&gt;true&lt;/bool&gt;
</pre>
<br>In AOSP, this parameter is set to false (Doze disabled) by default.<br>
</li>
<li>Confirm that preloaded apps and services:
<ul>
<li>Use the new
<a href="https://developer.android.com/preview/behavior-changes.html#behavior-power">power-saving
optimization guidelines</a>. For details, see <a href="#test-apps">Testing and
optimizing applications</a>.
<p><b>OR</b></p>
<li>Are exempted from Doze and App Standby. For details, see
<a href="#exempt-apps">Exempting applications</a>.</li>
</ul>
</li>
<li>Confirm the necessary services are exempted from Doze.</a>
</li>
</ol>

<h4 id="test-apps">Testing and optimizing applications</h4>
<p>Test all applications (especially preloaded applications) in Doze mode. For
details, refer to
<a href="https://developer.android.com/preview/testing/guide.html#doze-standby">Testing
Doze and App Standby</a>.</p>

<p class="note"><b>Note</b>: MMS/SMS/Telephony services function independently
of Doze and will always wake client apps even while the device remains in Doze
mode.</p>

<h2 id="exempt-apps">Exempting applications</h2>
<p>You can exempt applications from being subject to Doze or App Standby.</p>

<p class="warning"><b>Warning</b>: Do not exempt apps to avoid testing and
optimizing. Unnecessary exemptions undermine the benefits of Doze and App
Standby and can compromise the user experience, so we strongly suggest
minimizing such exemptions as they allow applications to defeat beneficial
controls the platform has over power use. If users become unhappy about the
power consumption of these apps, it can lead to frustration, bad experiences
(and negative user reviews for the app), and customer support questions. For
these reasons, we strongly recommend that you do not exempt third-party
applications and instead exempt only cloud messaging services or apps with
similar functions.</p>

<p>Apps exempted by default are listed in a single view within the Settings >
Battery menu. This list is used for exempting the app from both Doze and App
Standby modes. To provide transparency to the user, the Settings menu
<b>MUST</b> show all exempted applications.</p>

<p>Users can manually exempt apps using the Settings menu. However, users cannot
unexempt any application or service that is exempted by default in the system
image.</p>