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<html devsite>
<head>
<title>Measuring Power Values</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
{% include "_versions.html" %}
<!--
Copyright 2017 The Android Open Source Project
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<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>
<p>Devices with Bluetooth, modem, and Wi-Fi controllers running Android 7.0 and
higher can provide additional power values obtained from chipset data.</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 (expressed in cpu.clusters.cores).</li>
<li>CPU speeds supported by each cluster.</li>
<li>Active CPU power consumption for each cluster.</li>
</ul>
<p>To differentiate between active CPU power consumption and supported CPU
speeds for clusters, append the cluster number to the name of the array. Cluster
numbers are assigned in the order of CPU cores in the kernel device tree. For
example, in a heterogeneous architecture that has two (2) clusters with four (4)
cores:</p>
<ul>
<li>cluster0 consists of cpu0-3</li>
<li>cluster1 consists of cpu4-7</li>
</ul>
<p>The Android framework uses these CPU core numbers when it reads statistics
from the <code>sysfs</code> files in:
<code>/sys/devices/system/cpu/cpu<number>/cpufreq/stats</code>.
<p>Example of cluster CPUs and speeds:</p>
<pre class="devsite-click-to-copy">
<array name="cpu.active.cluster0">
<value>200</value>
<value>300</value>
<value>400</value>
</array>
<array name="cpu.speeds.cluster0">
<value>600000</value>
<value>800000</value>
<value>1200000</value>
</array>
<array name="cpu.active.cluster1">
<value>400</value>
<value>500</value>
<value>600</value>
</array>
<array name="cpu.speeds.cluster1">
<value>800000</value>
<value>1200000</value>
<value>1400000</value>
</array>
</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>ambient.on</td>
<td>Additional power used when screen is in doze/ambient/always-on mode instead of off.</td>
<td>around 100 mA</td>
<td> - </td>
</tr>
<tr>
<td>screen.on</td>
<td>Additional power used when screen is turned on at minimum brightness.</td>
<td>200 mA</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>100 mA-300 mA</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>wifi.on</td>
<td>Additional power used when Wi-Fi is turned on but not receiving,
transmitting, or scanning.</td>
<td>2 mA</td>
<td> - </td>
</tr>
<tr>
<td>wifi.active</td>
<td>Additional power used when transmitting or receiving over Wi-Fi.</td>
<td>31 mA</td>
<td> - </td>
</tr>
<tr>
<td>wifi.scan</td>
<td>Additional power used when Wi-Fi is scanning for access points.</td>
<td>100 mA</td>
<td> - </td>
</tr>
<tr>
<td>audio</td>
<td>Additional power used when audio decoding/encoding via DSP.</td>
<td>around 10 mA</td>
<td>Used for DSP audio.</td>
</tr>
<tr>
<td>video</td>
<td>Additional power used when video decoding via DSP.</td>
<td>around 50 mA</td>
<td>Used for DSP video.</td>
</tr>
<tr>
<td>camera.avg</td>
<td>Average power use by the camera subsystem for a typical camera
application.</td>
<td>600 mA</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>200 mA</td>
<td> - </td>
</tr>
<tr>
<td>gps.signalqualitybased</td>
<td>Additional power used by GPS based on signal strength. This is a multi-value entry,
one per signal strength, from weakest to strongest.</td>
<td> 30 mA, 10 mA </td>
<td> - </td>
</tr>
<tr>
<td>gps.on</td>
<td>Additional power used when GPS is acquiring a signal.</td>
<td>50 mA</td>
<td> - </td>
</tr>
<tr>
<td>radio.active</td>
<td>Additional power used when cellular radio is transmitting/receiving.</td>
<td>100 mA-300 mA</td>
<td> - </td>
</tr>
<tr>
<td>radio.scanning</td>
<td>Additional power used when cellular radio is paging the tower.</td>
<td>1.2 mA</td>
<td> - </td>
</tr>
<tr>
<td>radio.on</td>
<td>Additional power used when the cellular radio is on. This is a multi-value entry,
one per signal strength (no signal, weak, moderate, strong).</td>
<td>1.2 mA</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>bluetooth.controller.idle</td>
<td>Average current draw (mA) of the Bluetooth controller when idle.</td>
<td> - </td>
<td rowspan=4>These values are not estimated, but taken from the data sheet of
the controller. If there are multiple receive or transmit states, the average
of those states is taken. In addition, the system now collects data for
<a href="#le-bt-scans">Low Energy (LE) and Bluetooth scans</a>.<br><br>Android
7.0 and later no longer use the Bluetooth power values for bluetooth.active
(used when playing audio via Bluetooth A2DP) and bluetooth.on (used when
Bluetooth is on but idle).</td>
</tr>
<tr>
<td>bluetooth.controller.rx</td>
<td>Average current draw (mA) of the Bluetooth controller when receiving.</td>
<td> - </td>
</tr>
<tr>
<td>bluetooth.controller.tx</td>
<td>Average current draw (mA) of the Bluetooth controller when transmitting.</td>
<td> - </td>
</tr>
<tr>
<td>bluetooth.controller.voltage</td>
<td>Average operating voltage (mV) of the Bluetooth controller.</td>
<td> - </td>
</tr>
<tr>
<td>modem.controller.sleep</td>
<td> Average current draw (mA) of the modem controller when asleep.</td>
<td> 0 mA </td>
<td rowspan=5>These values are not estimated, but taken from the data sheet of the controller.
If there are multiple receive states, the average of those states is taken. If there are
multiple transmit states, specifying a value for each transmit state is supported
starting in Android {{ androidPVersionNumber}}.</td>
</tr>
<tr>
<td>modem.controller.idle</td>
<td>Average current draw (mA) of the modem controller when idle.</td>
<td> - </td>
</tr>
<tr>
<td>modem.controller.rx</td>
<td>Average current draw (mA) of the modem controller when receiving.</td>
<td> - </td>
</tr>
<tr>
<td>modem.controller.tx</td>
<td>Average current draw (mA) of the modem controller when transmitting at different RF power
levels. This is a multi-value entry with one value per transmit power level.</td>
<td> 100 mA, 200 mA, 300 mA, 400 mA, 500 mA </td>
</tr>
<tr>
<td>modem.controller.voltage</td>
<td>Average operating voltage (mV) of the modem controller.</td>
<td> - </td>
</tr>
<tr>
<td>wifi.controller.idle</td>
<td>Average current draw (mA) of the Wi-Fi controller when idle.</td>
<td> - </td>
<td rowspan=4>These values are not estimated, but taken from the data sheet of
the controller. If there are multiple receive or transmit states, the average
of those states is taken.</td>
</tr>
<tr>
<td>wifi.controller.rx</td>
<td>Average current draw (mA) of the Wi-Fi controller when receiving.</td>
<td> - </td>
</tr>
<tr>
<td>wifi.controller.tx</td>
<td>Average current draw (mA) of the Wi-Fi controller when transmitting.</td>
<td> - </td>
</tr>
<tr>
<td>wifi.controller.voltage</td>
<td>Average operating voltage (mV) of the Wi-Fi controller.</td>
<td> - </td>
</tr>
<tr>
<td>cpu.speeds</td>
<td>This is a multi-value entry that lists each possible CPU speed in KHz.</td>
<td>125000 KHz, 250000 KHz, 500000 KHz, 1000000 KHz, 1500000 KHz</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>3 mA</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>50 mA</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>100 mA, 120 mA, 140 mA, 160 mA, 200 mA</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>3000 mAh</td>
<td> - </td>
</tr>
</table>
<h2 id="le-bt-scans">Low Energy (LE) and Bluetooth scans</h2>
<p>For devices running Android 7.0, the system collects data for Low Energy (LE)
scans and Bluetooth network traffic (such as RFCOMM and L2CAP) and associates
these activities with the initiating application. Bluetooth scans are associated
with the application that initiated the scan, but batch scans are not (and
are instead associated with the Bluetooth application). For an application
scanning for N milliseconds, the cost of the scan is N milliseconds of rx time
and N milliseconds of tx time; all leftover controller time is assigned to
network traffic or the Bluetooth application.</p>
</body>
</html>
|
