Docs: Power reorganization with sentence casing for headers and 80 char limit enforced.
Adding power profile value for camera flashlight. Minor tweaks.
Bug: 20951506, 22409074
Change-Id: Ideedaf2ac9ec099dd8a326d098ebc3408350e631
diff --git a/src/devices/tech/power/device.jd b/src/devices/tech/power/device.jd
new file mode 100644
index 0000000..985b9c0
--- /dev/null
+++ b/src/devices/tech/power/device.jd
@@ -0,0 +1,250 @@
+page.title=Measuring Device Power
+@jd:body
+
+<!--
+ Copyright 2015 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>
+
+<p>You can determine device power consumption for Android devices that include a battery fuel gauge
+such as a Summit SMB347 or Maxim MAX17050 (available on many Nexus devices). Use the in-system
+gauge when external measurement equipment is not available or is inconvenient to
+connect to a device (such as in mobile usage).</p>
+
+<p>Measurements can include instantaneous current, remaining charge, battery capacity at test start
+and end, and more depending on the supported properties of the device (see below). For best
+results, perform device power measurements during long-running A/B tests that use the same device
+type with the same fuel gauge and same current sense resistor. Ensure the starting battery charge
+is the same for each device to avoid differing fuel gauge behavior at different points in the
+battery discharge curve.</p>
+
+<p>Even with identical test environments, measurements are not guaranteed to be of high absolute
+accuracy. However, most inaccuracies specific to the fuel gauge and sense resistor are consistent
+between test runs, making comparisons between identical devices useful. We recommend running
+multiple tests in different configurations to identify significant differences and relative power
+consumption between configurations.</p>
+
+<h2 id="power-consumption">Reading power consumption</h2>
+
+<p>To read power consumption data, insert calls to the API in your testing code.</p>
+
+<pre>
+import android.os.BatteryManager;
+import android.os.ServiceManager;
+import android.content.Context;
+BatteryManager mBatteryManager =
+(BatteryManager)Context.getSystemService(Context.BATTERY_SERVICE);
+Long energy =
+mBatteryManager.getLongProperty(BatteryManager.BATTERY_PROPERTY_ENERGY_COUNTER);
+Slog.i(TAG, "Remaining energy = " + energy + "nWh");
+</pre>
+
+<h2 id="avail-props">Available properties</h2>
+
+<p>Android supports the following battery fuel gauge properties:</p>
+
+<pre>
+BATTERY_PROPERTY_CHARGE_COUNTER Remaining battery capacity in microampere-hours
+BATTERY_PROPERTY_CURRENT_NOW Instantaneous battery current in microamperes
+BATTERY_PROPERTY_CURRENT_AVERAGE Average battery current in microamperes
+BATTERY_PROPERTY_CAPACITY Remaining battery capacity as an integer percentage
+BATTERY_PROPERTY_ENERGY_COUNTER Remaining energy in nanowatt-hours
+</pre>
+
+<p>Most properties are read from kernel power_supply subsystem attributes of similar names.
+However, the exact properties, resolution of property values, and update frequency
+available for a specific device depend on:</p>
+
+<ul>
+<li>Fuel gauge hardware, such as a Summit SMB347 or Maxim MAX17050.</li>
+<li>Fuel gauge-to-system connection, such as the value of external current sense resistors.</li>
+<li>Fuel gauge chip software configuration, such as values chosen for average current computation
+intervals in the kernel driver.</li>
+</ul>
+
+<p>For details, see the properties available for <a href="#nexus-devices">Nexus devices</a>.</p>
+
+<h2 id="maxim-fuel">Maxim fuel gauge</h2>
+
+<p>When determining battery state-of-charge over a long period of time, the Maxim fuel gauge
+(MAX17050, BC15) corrects for coulomb-counter offset measurements. For measurements made over a
+short period of time (such as power consumption metering tests), the fuel gauge does not make
+corrections, making the offset the primary source of error when current measurements are too small
+(although no amount of time can eliminate the offset error completely).</p>
+
+<p>For a typical 10mOhm sense resistor design, the offset current should be better than 1.5mA,
+meaning any measurement is +/-1.5mA (PCBoard layout can also affect this variation). For example,
+when measuring a large current (200mA) you can expect the following:</p>
+
+<ul>
+<li>2mA (1% gain error of 200mA due to fuel gauge gain error)</li>
+<li>+2mA (1% gain error of 200mA due to sense resistor error)</li>
+<li>+1.5mA (current sense offset error from fuel gauge)</li>
+</ul>
+
+<p>The total error is 5.5mA (2.75%). Compare this to a medium current (50mA) where the same error
+percentages give a total error of 7% or to a small current (15mA) where +/-1.5mA gives a total
+error of 10%.</p>
+
+<p>For best results, we recommend measuring greater than 20mA. Gain measurement errors are
+systematic and repeatable, enabling you to test a device in multiple modes and get clean relative
+measurements (with exceptions for the 1.5mA offset).</p>
+
+<p>For +/-100uA relative measurements, required measurement time depends on:</p>
+
+<ul>
+<li><b>ADC sampling noise</b>. The MAX17050 with its normal factory configuration produces +/-1.5mA
+sample-to-sample variation due to noise, with each sample delivered at 175.8ms. You can expect a
+rough +/-100uA for a 1 minute test window and a clean 3-sigma noise less than 100uA (or 1-sigma
+noise at 33uA) for a 6 minute test window.</li>
+<li><b>Sample Aliasing because of load variation</b>. Variation exaggerates errors, so for samples
+with variation inherent in the loading, consider using a longer test window.</li>
+</ul>
+
+<h2 id="nexus-devices">Supported Nexus devices</h2>
+
+<h5 id="nexus-5">Nexus 5</h5>
+
+<table>
+<tbody>
+<tr>
+<th>Model</th>
+<td>Nexus 5</td>
+</tr>
+<tr>
+<th>Fuel Gauge</th>
+<td>Maxim MAX17048 fuel gauge (ModelGauge™, no coulomb counter)</td>
+</tr>
+<tr>
+<th>Properties</th>
+<td>BATTERY_PROPERTY_CAPACITY</td>
+</tr>
+<tr>
+<th>Measurements</th>
+<td>The fuel gauge does not support any measurements other than battery State Of Charge to a
+resolution of %/256 (1/256th of a percent of full battery capacity).</td>
+</tr>
+</tbody>
+</table>
+
+
+<h5 id="nexus-6">Nexus 6</h5>
+
+<table>
+<tbody>
+<tr>
+<th>Model</th>
+<td>Nexus 6</td>
+</tr>
+<tr>
+<th>Fuel Gauge</th>
+<td>Maxim MAX17050 fuel gauge (a coulomb counter with Maxim ModelGauge™ adjustments), and a 10mohm
+current sense resistor.</td>
+</tr>
+<tr>
+<th>Properties</th>
+<td>BATTERY_PROPERTY_CAPACITY<br>
+BATTERY_PROPERTY_CURRENT_NOW<br>
+BATTERY_PROPERTY_CURRENT_AVERAGE<br>
+BATTERY_PROPERTY_CHARGE_COUNTER<br>
+BATTERY_PROPERTY_ENERGY_COUNTER</td>
+</tr>
+<tr>
+<th>Measurements</th>
+<td>CURRENT_NOW resolution 156.25uA, update period is 175.8ms.<br>
+CURRENT_AVERAGE resolution 156.25uA, update period configurable 0.7s - 6.4h, default 11.25 secs.<br>
+CHARGE_COUNTER (accumulated current, non-extended precision) resolution is 500uAh (raw coulomb
+counter read, not adjusted by fuel gauge for coulomb counter offset, plus inputs from the ModelGauge
+m3 algorithm including empty compensation).<br>
+CHARGE_COUNTER_EXT (extended precision in kernel) resolution 8nAh.<br>
+ENERGY_COUNTER is CHARGE_COUNTER_EXT at nominal voltage of 3.7V.</td>
+</tr>
+</tbody>
+</table>
+
+
+<h5 id="nexus-9">Nexus 9</h5>
+
+<table>
+<tbody>
+<tr>
+<th>Model</th>
+<td>Nexus 9</td>
+</tr>
+<tr>
+<th>Fuel Gauge</th>
+<td>Maxim MAX17050 fuel gauge (a coulomb counter with Maxim ModelGauge™ adjustments), and a 10mohm
+current sense resistor.</td>
+</tr>
+<tr>
+<th>Properties</th>
+<td>BATTERY_PROPERTY_CAPACITY<br>
+BATTERY_PROPERTY_CURRENT_NOW<br>
+BATTERY_PROPERTY_CURRENT_AVERAGE<br>
+BATTERY_PROPERTY_CHARGE_COUNTER<br>
+BATTERY_PROPERTY_ENERGY_COUNTER</td>
+</tr>
+<tr>
+<th>Measurements</th>
+<td>CURRENT_NOW resolution 156.25uA, update period is 175.8ms.<br>
+CURRENT_AVERAGE resolution 156.25uA, update period configurable 0.7s - 6.4h, default 11.25 secs.<br>
+CHARGE_COUNTER (accumulated current, non-extended precision) resolution is 500uAh.<br>
+CHARGE_COUNTER_EXT (extended precision in kernel) resolution 8nAh.<br>
+ENERGY_COUNTER is CHARGE_COUNTER_EXT at nominal voltage of 3.7V.<br>
+Accumulated current update period 175.8ms.<br>
+ADC sampled at 175ms quantization with a 4ms sample period. Can adjust duty cycle.</td>
+</tr>
+</tbody>
+</table>
+
+
+<h5 id="nexus-10">Nexus 10</h5>
+
+<table>
+<tbody>
+<tr>
+<th>Model</th>
+<td>Nexus 10</td>
+</tr>
+<tr>
+<th>Fuel Gauge</th>
+<td>Dallas Semiconductor DS2784 fuel gauge (a coulomb counter), with a 10mohm current sense
+resistor.</td>
+</tr>
+<tr>
+<th>Properties</th>
+<td>BATTERY_PROPERTY_CAPACITY<br>
+BATTERY_PROPERTY_CURRENT_NOW<br>
+BATTERY_PROPERTY_CURRENT_AVERAGE<br>
+BATTERY_PROPERTY_CHARGE_COUNTER<br>
+BATTERY_PROPERTY_ENERGY_COUNTER</td>
+</tr>
+<tr>
+<th>Measurements</th>
+<td>Current measurement (instantaneous and average) resolution is 156.3uA.<br>
+CURRENT_NOW instantaneous current update period is 3.5 seconds.<br>
+CURRENT_AVERAGE update period is 28 seconds (not configurable).<br>
+CHARGE_COUNTER (accumulated current, non-extended precision) resolution is 625uAh.<br>
+CHARGE_COUNTER_EXT (extended precision in kernel) resolution is 144nAh.<br>
+ENERGY_COUNTER is CHARGE_COUNTER_EXT at nominal voltage of 3.7V.<br>
+Update period for all is 3.5 seconds.</td>
+</tr>
+</tbody>
+</table>
\ No newline at end of file