Docs: Porting new sensors content to site.
Bug: 17410055
Change-Id: Ice1a842e90f1c644b1bc94727383ad7c095cc650
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+page.title=Power consumption
+@jd:body
+
+<!--
+ Copyright 2014 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.
+-->
+<div id="qv-wrapper">
+ <div id="qv">
+ <h2>In this document</h2>
+ <ol id="auto-toc">
+ </ol>
+ </div>
+</div>
+
+<h2 id="low_power_sensors">Low-power sensors</h2>
+<p>Some sensor types are defined as being low power. Low-power sensors must
+ function at low power, with their processing done in the hardware. This means
+ they should not require the SoC to be running. Here are some low-power sensor
+ types:</p>
+<ul>
+ <li> Geomagnetic rotation vector </li>
+ <li> Significant motion </li>
+ <li> Step counter </li>
+ <li> Step detector </li>
+ <li> Tilt detector </li>
+</ul>
+<p>They are accompanied by a low-power (<img src="images/battery_icon.png"
+width="20" height="20" alt="Low power sensor" />) icon in the <a
+href="sensor-types.html#composite_sensor_type_summary">Composite sensor type
+summary</a> table.</p>
+<p>These sensor types cannot be implemented at high power as their primary benefit
+ is low battery use. These sensors are expected to be activated for very long
+ periods, possibly 24/7. It is better to not implement a low-power sensor at all
+ rather than implement it as high power, as it would cause dramatic battery
+ drain.</p>
+<p>Composite low-power sensor types, such as the step detector, must have their
+ processing conducted in the hardware.</p>
+<p>See the CDD for specific power requirements, and expect tests in CTS to
+ verify those power requirements.</p>
+<h2 id="power_measurement_process">Power measurement process</h2>
+<p>The power is measured at the battery. For values in milliWatts, we use the
+ nominal voltage of the battery, meaning a 1mA current at 4V must be counted as
+ 4mW.</p>
+<p>The power is measured when the SoC is asleep, and averaged over a few seconds
+ of the SoC being asleep, so that periodic spikes in power from the sensor chips
+ are taken into account.</p>
+<p>For one-shot wake-up sensors, the power is measured while the sensor doesn’t
+ trigger (so it doesn’t wake the SoC up). Similarly, for other sensors, the
+ power is measured while the sensor data is stored in the hardware FIFO, so the
+ SoC is not woken up.</p>
+<p>The power normally is measured as a delta with when no sensor is activated.
+ When several sensors are activated, the delta in power must be no greater than
+ the sum of the power of each activated sensor. If an accelerometer consumes
+ 0.5mA and a step detector consumes 0.5mA, then activating both at the same time
+ must consume less than 0.5+0.5=1mA.</p>