1 page.title=Sensors 2 @jd:body 3 4 <!-- 5 Copyright 2015 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 <div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25 </div> 26 <img style="float: right; margin: 0px 15px 15px 15px;" src="images/ape_fwk_hal_sensors.png" alt="Android Sensors HAL icon"/> 27 28 <p>Android sensors give applications access to a mobile device's underlying physical sensors. They are data-providing virtual devices defined by <a href="{@docRoot}devices/halref/sensors_8h.html">sensors.h</a>, the sensor Hardware Abstraction Layer (HAL).</p> 29 30 <h2 id="what_are_android_sensors">What are Android sensors?</h2> 31 <p>Android sensors are virtual devices that provide data coming from a set of physical sensors: accelerometers, gyroscopes, magnetometers, barometer, humidity, pressure, light, proximity and heart rate sensors.</p> 32 <p>Not included in the list of physical devices providing data are camera, fingerprint sensor, microphone, and touch screen. These devices have their own reporting mechanism; the separation is arbitrary, but in general, Android sensors provide lower bandwidth data. For example, 100hz x 3 channels for an accelerometer versus 25hz x 8 MP x 3 channels for a camera or 44kHz x 1 channel for a microphone.</p> 33 <p>Android does not define how the different physical sensors are connected to the system on chip (SoC).</p> 34 <ul> 35 <li> Often, sensor chips are connected to the SoC through a <a href="sensor-stack.html#sensor_hub">sensor hub</a>, allowing some low-power monitoring and processing of the data. </li> 36 <li> Often, Inter-Integrated Circuit (I2C) or Serial Peripheral Interface 37 (SPI) is used as the transport mechanism. </li> 38 <li> To reduce power consumption, some architectures are hierarchical, with some 39 minimal processing being done in the application-specific integrated 40 circuit (ASIC - like motion detection on the accelerometer chip), and 41 more is done in a microcontroller (like step detection 42 in a sensor hub). </li> 43 <li> It is up to the device manufacturer to choose an architecture based on 44 accuracy, power, price and package-size characteristics. See <a 45 href="sensor-stack.html">Sensor stack</a> for more information. </li> 46 <li> Batching capabilities are an important consideration for power optimization. 47 See <a href="batching.html">Batching</a> for more information. </li> 48 </ul> 49 <p>Each Android sensor has a type representing how the sensor behaves and what 50 data it provides.</p> 51 <ul> 52 <li> The official Android <a href="sensor-types.html">Sensor types</a> are defined in <a href="{@docRoot}devices/halref/sensors_8h.html">sensors.h</a> under the names SENSOR_TYPE_ 53 <ul> 54 <li> The vast majority of sensors have an official sensor type. </li> 55 <li> Those types are documented in the Android SDK. </li> 56 <li> Behavior of sensors with those types are tested in the Android 57 Compatibility Test Suite (CTS). </li> 58 </ul> 59 </li> 60 <li> If a manufacturer integrates a new kind of sensor on an Android device, the 61 manufacturer can define its own temporary type to refer to it. 62 <ul> 63 <li> Those types are undocumented, so application developers are unlikely to use 64 them, either because they dont know about them, or know that they are rarely 65 present (only on some devices from this specific manufacturer). </li> 66 <li> They are not tested by CTS. </li> 67 <li> Once Android defines an official sensor type for this kind of 68 sensor, manufacturers must stop using their own temporary type 69 and use the official type instead. This way, the sensor will be 70 used by more application developers. </li> 71 </ul> 72 </li> 73 <li> The list of all sensors present on the device is reported by the HAL 74 implementation. 75 <ul> 76 <li> There can be several sensors of the same type. For example, two proximity 77 sensors or two accelerometers. </li> 78 <li> The vast majority of applications request only a single sensor of a given type. 79 For example, an application requesting the default accelerometer will get the 80 first accelerometer in the list. </li> 81 <li> Sensors are often defined by <a href="suspend-mode.html#wake-up_sensors">wake-up</a> and <a href="suspend-mode.html#non-wake-up_sensors">non-wake-up</a> pairs, both sensors sharing the same type, but differing by their wake-up 82 characteristic. </li> 83 </ul> 84 </li> 85 </ul> 86 <p>Android sensors provide data as a series of sensor events.</p> 87 <p> Each <a href="hal-interface.html#sensors_event_t">event</a> contains:</p> 88 <ul> 89 <li> a handle to the sensor that generated it </li> 90 <li> the timestamp at which the event was detected or measured </li> 91 <li> and some data </li> 92 </ul> 93 <p>The interpretation of the reported data depends on the sensor type. 94 See the <a href="sensor-types.html">sensor type</a> definitions for details on 95 what data is reported for each sensor type.</p> 96 97 <h2 id="existing_documentation2">Existing documentation</h2> 98 <h3 id="targeted_at_developers">Targeted at developers</h3> 99 <ul> 100 <li> Overview 101 <ul> 102 <li><a href="https://developer.android.com/guide/topics/sensors/sensors_overview.html"> https://developer.android.com/guide/topics/sensors/sensors_overview.html </a></li> 103 </ul> 104 </li> 105 <li> SDK reference 106 <ul> 107 <li> <a href="https://developer.android.com/reference/android/hardware/SensorManager.html">https://developer.android.com/reference/android/hardware/SensorManager.html</a></li> 108 <li><a href="https://developer.android.com/reference/android/hardware/SensorEventListener.html"> https://developer.android.com/reference/android/hardware/SensorEventListener.html</a></li> 109 <li> <a href="https://developer.android.com/reference/android/hardware/SensorEvent.html">https://developer.android.com/reference/android/hardware/SensorEvent.html</a></li> 110 <li><a href="https://developer.android.com/reference/android/hardware/Sensor.html"> https://developer.android.com/reference/android/hardware/Sensor.html</a></li> 111 </ul> 112 </li> 113 <li> StackOverflow and tutorial websites 114 <ul> 115 <li> Because sensors documentation was sometimes lacking, developers resorted to Q&A 116 websites like StackOverflow to find answers. </li> 117 <li> Some tutorial websites exist as well, but do not cover the latest features like 118 batching, significant motion and game rotation vectors. </li> 119 <li> The answers over there are not always right, and show where more documentation 120 is needed. </li> 121 </ul> 122 </li> 123 </ul> 124 <h3 id="targeted_at_manufacturers_public">Targeted at manufacturers</h3> 125 <ul> 126 <li> Overview 127 <ul> 128 <li>This <a href="{@docRoot}devices/sensors/index.html">Sensors</a> 129 page and its sub-pages. </li> 130 </ul> 131 </li> 132 <li> Hardware abstraction layer (HAL) 133 <ul> 134 <li> <a href="{@docRoot}devices/halref/sensors_8h_source.html">https://source.android.com/devices/halref/sensors_8h_source.html</a></li> 135 <li> Also known as sensors.h </li> 136 <li> The source of truth. First document to be updated when new features are 137 developed. </li> 138 </ul> 139 </li> 140 <li> Android CDD (Compatibility Definition Document) 141 <ul> 142 <li><a href="{@docRoot}compatibility/android-cdd.pdf">https://source.android.com/compatibility/android-cdd.pdf</a></li> 143 <li> See sections relative to sensors. </li> 144 <li> The CDD is lenient, so satisfying the CDD requirements is not enough to ensure 145 high quality sensors. </li> 146 </ul> 147 </li> 148 </ul> 149
