src/devices/tech/power/values.jd

page.title=Measuring Power Values
@jd:body

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  <div id="qv">
    <h2>In this document</h2>
    <ol id="auto-toc"></ol>
  </div>
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<p>Device manufacturers must provide a component power profile in
<code>/frameworks/base/core/res/res/xml/power_profile.xml</code>.</p>

<p>To determine values for power profiles, use hardware that measures the power
being used by the device and perform the various operations for which
information is needed. Measure the power use during those operations and compute
the values (deriving differences from other baseline power uses as appropriate).
</p>

<p>As the goal of a power profile is to estimate battery drain appropriately,
power profile values are given in current (amps). The Android framework
multiplies the current by the time for which the subsystem was active and
computes the mAh value, which is then used to estimate the amount of battery
drained by the application/subsystem.</p>

<h2 id="multiple-cpus">Devices with heterogeneous CPUs</h2>

<p>The power profile for devices with CPU cores of heterogeneous architecture
must include the following additional fields:
<ul>
<li>Number of total CPUs for each cluster.</li>
<li>CPU speeds supported by each cluster.</li>
</ul>

<p>To differentiate between active CPUs and supported CPU speeds for each
cluster, append the cluster number to the name of the array. Example:</p>

<pre>
&lt;array name="cpu.active.cluster0"&gt;
&lt;value&gt;200&lt;/value&gt;
&lt;value&gt;300&lt;/value&gt;
&lt;value&gt;400&lt;/value&gt;
&lt;/array&gt;
&lt;array name="cpu.speeds.cluster0"&gt;
&lt;value&gt;600000&lt;/value&gt;
&lt;value&gt;800000&lt;/value&gt;
&lt;value&gt;1200000&lt;/value&gt;
&lt;/array&gt;

&lt;array name="cpu.active.cluster1"&gt;
&lt;value&gt;400&lt;/value&gt;
&lt;value&gt;500&lt;/value&gt;
&lt;value&gt;600&lt;/value&gt;
&lt;/array&gt;
&lt;array name="cpu.speeds.cluster1"&gt;
&lt;value&gt;800000&lt;/value&gt;
&lt;value&gt;1200000&lt;/value&gt;
&lt;value&gt;1400000&lt;/value&gt;
&lt;/array&gt;
</pre>

<h2 id="values">Power values</h2>
<p>The following table describes available power value settings. To view the
sample file in AOSP, see
<a href="https://android.googlesource.com/platform/frameworks/base/+/master/core/res/res/xml/power_profile.xml">power_profile.xml</a>.</p>

<table>
<tr>
  <th>Name</th>
  <th>Description</th>
  <th>Example Value</th>
  <th>Notes</th>
</tr>
<tr>
  <td>none</td>
  <td>Nothing</td>
  <td>0</td>
  <td></td>
</tr>

<tr>
  <td>screen.on</td>
  <td>Additional power used when screen is turned on at minimum brightness.</td>
  <td>200mA</td>
  <td>Includes touch controller and display backlight. At 0 brightness, not the
  Android minimum which tends to be 10 or 20%.</td>
</tr>

<tr>
  <td>screen.full</td>
  <td>Additional power used when screen is at maximum brightness, compared to
  screen at minimum brightness.</td>
  <td>100mA-300mA</td>
  <td>A fraction of this value (based on screen brightness) is added to the
  screen.on value to compute the power usage of the screen.</td>
</tr>

<tr>
  <td>bluetooth.active</td>
  <td>Additional power used when playing audio through Bluetooth A2DP.</td>
  <td>14mA</td>
  <td></td>
</tr>

<tr>
  <td>bluetooth.on</td>
  <td>Additional power used when Bluetooth is turned on but idle.</td>
  <td>1.4mA</td>
  <td></td>
</tr>

<tr>
  <td>wifi.on</td>
  <td>Additional power used when Wi-Fi is turned on but not receiving,
  transmitting, or scanning.</td>
  <td>2mA</td>
  <td></td>
</tr>

<tr>
  <td>wifi.active</td>
  <td>Additional power used when transmitting or receiving over Wi-Fi.</td>
  <td>31mA</td>
  <td></td>
</tr>

<tr>
  <td>wifi.scan</td>
  <td>Additional power used when Wi-Fi is scanning for access points.</td>
  <td>100mA</td>
  <td></td>
</tr>

<tr>
  <td>dsp.audio</td>
  <td>Additional power used when audio decoding/encoding via DSP.</td>
  <td>14.1mA</td>
  <td>Reserved for future use.</td>
</tr>


<tr>
  <td>dsp.video</td>
  <td>Additional power used when video decoding via DSP.</td>
  <td>54mA</td>
  <td>Reserved for future use.</td>
</tr>

<tr>
  <td>camera.avg</td>
  <td>Average power use by the camera subsystem for a typical camera
  application.</td>
  <td>600mA</td>
  <td>Intended as a rough estimate for an application running a preview
  and capturing approximately 10 full-resolution pictures per minute.</td>
</tr>

<tr>
  <td>camera.flashlight</td>
  <td>Average power used by the camera flash module when on.</td>
  <td>200mA</td>
  <td></td>
</tr>


<tr>
  <td>gps.on</td>
  <td>Additional power used when GPS is acquiring a signal.</td>
  <td>50mA</td>
  <td></td>
</tr>

<tr>
  <td>radio.active</td>
  <td>Additional power used when cellular radio is transmitting/receiving.</td>
  <td>100mA-300mA</td>
  <td></td>
</tr>

<tr>
  <td>radio.scanning</td>
  <td>Additional power used when cellular radio is paging the tower.</td>
  <td>1.2mA</td>
  <td></td>
</tr>

<tr>
  <td>radio.on</td>
  <td>Additional power used when the cellular radio is on. Multi-value entry,
  one per signal strength (no signal, weak, moderate, strong).</td>
  <td>1.2mA</td>
  <td>Some radios boost power when they search for a cell tower and do not
  detect a signal. Values can be the same or decrease with increasing signal
  strength. If you provide only one value, the same value is used for all
  strengths. If you provide two values, the first is used for no-signal, the
  second value is used for all other strengths, and so on.</td>
</tr>

<tr>
  <td>cpu.speeds</td>
  <td>Multi-value entry that lists each possible CPU speed in KHz.</td>
  <td>125000KHz, 250000KHz, 500000KHz, 1000000KHz, 1500000KHz</td>
  <td>The number and order of entries must correspond to the mA entries in
  cpu.active.</td>
</tr>

<tr>
  <td>cpu.idle</td>
  <td>Total power drawn by the system when CPUs (and the SoC) are in system
  suspend state.</td>
  <td>3mA</td>
  <td></td>
</tr>

<tr>
  <td>cpu.awake</td>
  <td>Additional power used when CPUs are in scheduling idle state
  (kernel idle loop); system is not in system suspend state.</td>
  <td>50mA</td>
  <td>Your platform might have more than one idle state in use with differing
  levels of power consumption; choose a representative idle state for longer
  periods of scheduler idle (several milliseconds). Examine the power graph on
  your measurement equipment and choose samples where the CPU is at its lowest
  consumption, discarding higher samples where the CPU exited idle.</td>
</tr>

<tr>
  <td>cpu.active</td>
  <td>Additional power used by CPUs when running at different speeds.</td>
  <td>100mA, 120mA, 140mA, 160mA, 200mA</td>
  <td>Value represents the power used by the CPU rails when running at different
  speeds. Set the max speed in the kernel to each of the allowed speeds and peg
  the CPU at that speed. The number and order of entries correspond to the
  number and order of entries in cpu.speeds.</td>
</tr>

<tr>
  <td>cpu.clusters.cores</td>
  <td>Number of cores each CPU cluster contains.</td>
  <td>4, 2</td>
  <td>Required only for devices with <a href="#multiple-cpus">heterogeneous CPU
  architectures</a>. Number of entries and order should match the number of
  cluster entries for the cpu.active and cpu.speeds. The first entry represents
  the number of CPU cores in cluster0, the second entry represents the number of
  CPU cores in cluster1, and so on.</td>
</tr>

<tr>
  <td>battery.capacity</td>
  <td>Total battery capacity in mAh.</td>
  <td>3000mAh</td>
  <td></td>
</tr>
</table>