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 <p>The vehicle HAL interface defines the properties OEMs can implement and
 contains property metadata (for example, whether the property is an int and
 which change modes are allowed). The vehicle HAL interface is based on accessing
 (read, write, subscribe) a property, which is an abstraction for a specific
 function.</p>

 <h2 id=interfaces>HAL interfaces</h2>
 <p>The vehicle HAL uses the following interfaces:</p>
 <ul>
 <li><code>vehicle_prop_config_t const *(*list_properties)(..., int*
 num_properties)</code>
 <br>List configuration of all properties supported by the vehicle HAL. Only
 supported properties are used by vehicle network service.
 </li>
 <li><code>(*get)(..., vehicle_prop_value_t *data)</code>
 <br>Read the current value of the property. For zoned property, each zone may
 have different value.</li>
 <li><code>(*set)(..., const vehicle_prop_value_t *data)</code>
 <br>Write a value to property. Result of write is defined per property.</li>
 <li><code>(*subscribe)(..., int32_t prop, float sample_rate, int32_t
 zones)</code>
 <ul>
 <li>Start monitoring a property value change. For zoned property, subscription
 applies to requested zones. Zones = 0 is used to request all zones supported.
 </li>
 <li>Vehicle HAL should call separate callback when the property's value changes
 (=on change) or in const interval (=continuous type).</li>
 </ul></li>
 <li><code>(*release_memory_from_get)(struct vehicle_hw_device* device,
 vehicle_prop_value_t *data)</code>
 <br>Release memory allocated from get call.</li>
 </ul>

 <p>The vehicle HAL uses the following callback interfaces:</p>
 <ul>
 <li><code>(*vehicle_event_callback_fn)(const vehicle_prop_value_t
 *event_data)</code>
 <br>Notifies vehicle property's value change. Should be done only for
 subscribed properties.</li>
 <li><code>(*vehicle_error_callback_fn)(int32_t error_code, int32_t property,
 int32_t operation)</code>
 <br>Return global vehicle HAL level error or error per property. Global error
 causes HAL restart, which can lead to restarting other components (including
 applications).</li>
 </ul>

 <h2 id=properties>Vehicle properties</h2>
 <p>Properties can be read-only, write-only (used to pass information to vehicle
 HAL level), or read and write (support of most properties is optional). Each
 property is uniquely identified by an int32 key and has a predefined type
 (<code>value_type</code>):</p>

 <ul>
 <li><code>INT32</code> (and array), <code>INT64</code>, <code>BOOLEAN</code>,
 <code>FLOAT</code> (and array), string, bytes.</li>
 <li>Zoned type has zone in addition to value.</li>
 </ul>

 <h2 id-=zone_type>Zone types</h2>
 <p>The vehicle HAL defines three zone types:</p>
 <ul>
 <li><code>vehicle_zone</code>
 <br>Zone based on rows.</li>
 <li><code>vehicle_seat</code>
 <br>Zone based on seats.</li>
 <li><code>vehicle_window</code>
 <br>Zone based on windows.</li>
 </ul>
 <p>Each zoned property should use pre-defined zone type. If necessary, you can
 use a custom zone type for each property (for details, see
 <a href=#prop_custom>Handling custom properties</a>).</p>

 <h2 id=prop_config>Configuring a property</h2>
 <p>Use <code>vehicle_prop_config_t</code> to provide configuration information
 for each property. Information includes:</p>
 <ul>
 <li><code>access</code> (r, w, rw)</li>
 <li><code>change_mode</code> (represents how property is monitored: on change vs
 continuous)</li>
 <li><code>min_value</code> (int32, float, int64), <code>max_value</code> (int32,
 float, int64)</li>
 <li><code>min_sample_rate</code>, <code>max_sample_rate</code></li>
 <li><code>permission_model</code></li>
 <li><code>prop</code> (Property ID, int)</li>
 <li><code>value_type</code></li>
 <li><code>zone_flags</code> (represents supported zones as bit flags)</li>
 </ul>
 <p>In addition, some properties have specific configuration flags to represent
 capability.</p>

 <h2 id=zone_prop>Handling zone properties</h2>
 <p>A zoned property is equivalent to a collection of multiple properties where
 each sub property is accessible by specified zone value.</p>
 <ul>
 <li><code>get</code> call for zoned property always includes zone in request, so
 only the current value for the requested zone should be returned.</li>
 <li><code>set</code> call for zoned property always includes zone in request, so
 only the requested zone should be changed.</li>
 <li><code>subscribe</code> call includes flags of all zones subscribed. Events
 from un-subscribed zones should not be reported.</li>
 </ul>

 <h3 id=get>Get calls</h3>
 <p>During initialization, the value for the property may not be available yet as
 the matching vehicle network message has not yet been received. In such cases,
 the <code>get</code> call should return <code>-EAGAIN</code>. Some properties
 (such as HVAC) have separate on/off power property. Calling <code>get</code> for
 such a property (when powered off) should return a special value
 <code>(VEHICLE_INT_OUT_OF_RANGE_OFF/VEHICLE_FLOAT_OUT_OF_RANGE_OFF)</code>
 rather than returning an error.</p>
 <p>In addition, some properties (such as HVAC temperature) can have a value to
 indicate it is in max power mode rather than in specific temperature value. In
 such cases, use special values to represent such state.</p>
 <ul>
 <li>VEHICLE_INT_OUT_OF_RANGE_MAX/MIN</li>
 <li>VEHICLE_FLOAT_OUT_OF_RANGE_MAX/MIN</li>
 </ul>

 <p>Example: get HVAC Temperature</p>
 <img src="../images/vehicle_hvac_get.png" alt="Vehicle HAL get HVAC example">
 <p class="img-caption"><strong>Figure 1</strong>. Get HVAC temperature (CS =
 CarService, VNS = VehicleNetworkService, VHAL = Vehicle HAL)</p>

 <h3 id=set>Set calls</h3>
 <p>A <code>set</code> call is an asynchronous operation involving event
 notification after a requested change is made. In a typical operation, a
 <code>set</code> call leads to making a change request across vehicle network.
 When the change is performed by the electronic control unit (ECU) owning the
 property, the updated value is returned through vehicle network and the vehicle
 HAL sends an updated value as an event to vehicle network service (VNS).</p>
 <p>Some <code>set</code> calls may require initial data to be ready but during
 initialization, such data may not be available yet. In such cases, the
 <code>set</code> call should return <code>-EAGAIN</code>. Some properties with
 separate power on /off should return <code>-ESHUTDOWN</code> when the property
 is powered off and set cannot be done.</p>
 <p>Until <code>set</code> is made effective, <code>get</code> does not
 necessarily return the same value as what is set. The exception is a property
 with change mode of <code>VEHICLE_PROP_CHANGE_MODE_ON_SET.</code> This property
 notifies change only when it is set by external component outside Android (for
 example, clock properties such as <code>VEHICLE_PROPERTY_UNIX_TIME</code>).</p>

 <p>Example: set HVAC Temperature</p>
 <img src="../images/vehicle_hvac_set.png" alt="Vehicle HAL set HVAC example">
 <p class="img-caption"><strong>Figure 2</strong>. Set HVAC temperature (CD =
 CarService, VNS = VehicleNetworkService, VHAL = Vehicle HAL)</p>

 <h2 id=prop_custom>Handling custom properties</h2>
 <p>To support partner-specific needs, the vehicle HAL allows custom properties
 that are restricted to system apps. Use the following guidelines when working
 with custom properties:</p>
 <ul>
 <li>Key should be in [<code>VEHICLE_PROPERTY_CUSTOM_START,
 VEHICLE_PROPERTY_CUSTOM_END</code>] range. Other ranges are reserved for future
 extension; using such ranges can cause conflicts in future Android releases.</li>
 <li>Use only defined <code>value_type</code>. BYTES type allows passing raw
 data, so this is enough in most cases. Sending big data frequently through
 custom properties can slow down the whole vehicle network access, so be careful
 when you add a big payload.</li>
 <li>Add access policy into <code>vendor_vns_policy.xml</code> (otherwise, all
 access will be rejected).</li>
 <li>Access via <code>VendorExtensionManager</code> (for Java components) or
 via Vehicle Network Service API (for native). Do not modify other car APIs as it
 can lead to compatibility issues in the future.</li>
 </ul>

 <h2 id=prop_hvac>Handling HVAC properties</h2>
 <p>You can use the vehicle HAL to control HVAC by setting HVAC-related
 properties. Most HVAC properties are zoned properties, but a few are non-zoned
 (global) properties. Example properties defined include:</p>
 <ul>
 <li><code>VEHICLE_PROPERTY_HVAC_TEMPERATURE_SET</code>
 <br>Set temperature per zone.</li>
 <li><code>VEHICLE_PROPERTY_HVAC_RECIRC_ON</code>
 <br>Control recirculation per zone).</li>
 </ul>
 <p>For full list of HVAC properties, search for
 <code>VEHICLE_PROPERTY_HVAC_*</code> in <code>vehicle.h</code>.</p>

 <h2 id=prop_sensor>Handling sensor properties</h2>
 <p>Vehicle HAL sensor properties represent real sensor data or policy
 information such as driving status. Some sensor information (such as driving
 status and day/night mode) is accessible by any app without restriction as the
 data is mandatory to build a safe vehicle application. Other sensor information
 (such as vehicle speed) is more sensitive and requires specific permissions that
 users can manage.</p>
 <p>Supported sensor properties include:</p>
 <ul>
 <li><code>DRIVING_STATUS</code>
 <br>Should support. Represents allowed operations in the current driving state.
 This information is used to block unsafe applications while driving.</li>
 <li><code>NIGHT_MODE</code>
 <br>Should support. Determines day/night mode of display.</li>
 <li><code>GEAR_SELECTION/CURRENT_GEAR</code>
 <br>Gear selected by driver vs. actual gear.</li>
 <li><code>VEHICLE_SPEED</code>
 <br>Vehicle speed. Protected with permission.</li>
 <li><code>ODOMETER</code>
 <br>Current odometer reading. Protected with permission.
 </li>
 <li><code>FUEL_LEVEL</code>
 <br>Current fuel level in %.</li>
 <li><code>FUEL_LEVEL_LOW</code>
 <br>Fuel level is low or not (boolean).</li>
 </ul>

   </body>
 </html>
	<html devsite>
	<head>
	<title>Vehicle Properties</title>
	<meta name="project_path" value="/_project.yaml" />
	<meta name="book_path" value="/_book.yaml" />
	</head>
	<body>
	<!--
	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>The vehicle HAL interface defines the properties OEMs can implement and
	contains property metadata (for example, whether the property is an int and
	which change modes are allowed). The vehicle HAL interface is based on accessing
	(read, write, subscribe) a property, which is an abstraction for a specific
	function.</p>

	<h2 id=interfaces>HAL interfaces</h2>
	<p>The vehicle HAL uses the following interfaces:</p>
	<ul>
	<li><code>vehicle_prop_config_t const (list_properties)(..., int*
	num_properties)</code>
	<br>List configuration of all properties supported by the vehicle HAL. Only
	supported properties are used by vehicle network service.
	</li>
	<li><code>(get)(..., vehicle_prop_value_t data)</code>
	<br>Read the current value of the property. For zoned property, each zone may
	have different value.</li>
	<li><code>(set)(..., const vehicle_prop_value_t data)</code>
	<br>Write a value to property. Result of write is defined per property.</li>
	<li><code>(*subscribe)(..., int32_t prop, float sample_rate, int32_t
	zones)</code>
	<ul>
	<li>Start monitoring a property value change. For zoned property, subscription
	applies to requested zones. Zones = 0 is used to request all zones supported.
	</li>
	<li>Vehicle HAL should call separate callback when the property's value changes
	(=on change) or in const interval (=continuous type).</li>
	</ul></li>
	<li><code>(release_memory_from_get)(struct vehicle_hw_device device,
	vehicle_prop_value_t *data)</code>
	<br>Release memory allocated from get call.</li>
	</ul>

	<p>The vehicle HAL uses the following callback interfaces:</p>
	<ul>
	<li><code>(*vehicle_event_callback_fn)(const vehicle_prop_value_t
	*event_data)</code>
	<br>Notifies vehicle property's value change. Should be done only for
	subscribed properties.</li>
	<li><code>(*vehicle_error_callback_fn)(int32_t error_code, int32_t property,
	int32_t operation)</code>
	<br>Return global vehicle HAL level error or error per property. Global error
	causes HAL restart, which can lead to restarting other components (including
	applications).</li>
	</ul>

	<h2 id=properties>Vehicle properties</h2>
	<p>Properties can be read-only, write-only (used to pass information to vehicle
	HAL level), or read and write (support of most properties is optional). Each
	property is uniquely identified by an int32 key and has a predefined type
	(<code>value_type</code>):</p>

	<ul>
	<li><code>INT32</code> (and array), <code>INT64</code>, <code>BOOLEAN</code>,
	<code>FLOAT</code> (and array), string, bytes.</li>
	<li>Zoned type has zone in addition to value.</li>
	</ul>

	<h2 id-=zone_type>Zone types</h2>
	<p>The vehicle HAL defines three zone types:</p>
	<ul>
	<li><code>vehicle_zone</code>
	<br>Zone based on rows.</li>
	<li><code>vehicle_seat</code>
	<br>Zone based on seats.</li>
	<li><code>vehicle_window</code>
	<br>Zone based on windows.</li>
	</ul>
	<p>Each zoned property should use pre-defined zone type. If necessary, you can
	use a custom zone type for each property (for details, see
	<a href=#prop_custom>Handling custom properties</a>).</p>

	<h2 id=prop_config>Configuring a property</h2>
	<p>Use <code>vehicle_prop_config_t</code> to provide configuration information
	for each property. Information includes:</p>
	<ul>
	<li><code>access</code> (r, w, rw)</li>
	<li><code>change_mode</code> (represents how property is monitored: on change vs
	continuous)</li>
	<li><code>min_value</code> (int32, float, int64), <code>max_value</code> (int32,
	float, int64)</li>
	<li><code>min_sample_rate</code>, <code>max_sample_rate</code></li>
	<li><code>permission_model</code></li>
	<li><code>prop</code> (Property ID, int)</li>
	<li><code>value_type</code></li>
	<li><code>zone_flags</code> (represents supported zones as bit flags)</li>
	</ul>
	<p>In addition, some properties have specific configuration flags to represent
	capability.</p>

	<h2 id=zone_prop>Handling zone properties</h2>
	<p>A zoned property is equivalent to a collection of multiple properties where
	each sub property is accessible by specified zone value.</p>
	<ul>
	<li><code>get</code> call for zoned property always includes zone in request, so
	only the current value for the requested zone should be returned.</li>
	<li><code>set</code> call for zoned property always includes zone in request, so
	only the requested zone should be changed.</li>
	<li><code>subscribe</code> call includes flags of all zones subscribed. Events
	from un-subscribed zones should not be reported.</li>
	</ul>

	<h3 id=get>Get calls</h3>
	<p>During initialization, the value for the property may not be available yet as
	the matching vehicle network message has not yet been received. In such cases,
	the <code>get</code> call should return <code>-EAGAIN</code>. Some properties
	(such as HVAC) have separate on/off power property. Calling <code>get</code> for
	such a property (when powered off) should return a special value
	<code>(VEHICLE_INT_OUT_OF_RANGE_OFF/VEHICLE_FLOAT_OUT_OF_RANGE_OFF)</code>
	rather than returning an error.</p>
	<p>In addition, some properties (such as HVAC temperature) can have a value to
	indicate it is in max power mode rather than in specific temperature value. In
	such cases, use special values to represent such state.</p>
	<ul>
	<li>VEHICLE_INT_OUT_OF_RANGE_MAX/MIN</li>
	<li>VEHICLE_FLOAT_OUT_OF_RANGE_MAX/MIN</li>
	</ul>

	<p>Example: get HVAC Temperature</p>
	<img src="../images/vehicle_hvac_get.png" alt="Vehicle HAL get HVAC example">
	<p class="img-caption"><strong>Figure 1</strong>. Get HVAC temperature (CS =
	CarService, VNS = VehicleNetworkService, VHAL = Vehicle HAL)</p>

	<h3 id=set>Set calls</h3>
	<p>A <code>set</code> call is an asynchronous operation involving event
	notification after a requested change is made. In a typical operation, a
	<code>set</code> call leads to making a change request across vehicle network.
	When the change is performed by the electronic control unit (ECU) owning the
	property, the updated value is returned through vehicle network and the vehicle
	HAL sends an updated value as an event to vehicle network service (VNS).</p>
	<p>Some <code>set</code> calls may require initial data to be ready but during
	initialization, such data may not be available yet. In such cases, the
	<code>set</code> call should return <code>-EAGAIN</code>. Some properties with
	separate power on /off should return <code>-ESHUTDOWN</code> when the property
	is powered off and set cannot be done.</p>
	<p>Until <code>set</code> is made effective, <code>get</code> does not
	necessarily return the same value as what is set. The exception is a property
	with change mode of <code>VEHICLE_PROP_CHANGE_MODE_ON_SET.</code> This property
	notifies change only when it is set by external component outside Android (for
	example, clock properties such as <code>VEHICLE_PROPERTY_UNIX_TIME</code>).</p>

	<p>Example: set HVAC Temperature</p>
	<img src="../images/vehicle_hvac_set.png" alt="Vehicle HAL set HVAC example">
	<p class="img-caption"><strong>Figure 2</strong>. Set HVAC temperature (CD =
	CarService, VNS = VehicleNetworkService, VHAL = Vehicle HAL)</p>

	<h2 id=prop_custom>Handling custom properties</h2>
	<p>To support partner-specific needs, the vehicle HAL allows custom properties
	that are restricted to system apps. Use the following guidelines when working
	with custom properties:</p>
	<ul>
	<li>Key should be in [<code>VEHICLE_PROPERTY_CUSTOM_START,
	VEHICLE_PROPERTY_CUSTOM_END</code>] range. Other ranges are reserved for future
	extension; using such ranges can cause conflicts in future Android releases.</li>
	<li>Use only defined <code>value_type</code>. BYTES type allows passing raw
	data, so this is enough in most cases. Sending big data frequently through
	custom properties can slow down the whole vehicle network access, so be careful
	when you add a big payload.</li>
	<li>Add access policy into <code>vendor_vns_policy.xml</code> (otherwise, all
	access will be rejected).</li>
	<li>Access via <code>VendorExtensionManager</code> (for Java components) or
	via Vehicle Network Service API (for native). Do not modify other car APIs as it
	can lead to compatibility issues in the future.</li>
	</ul>

	<h2 id=prop_hvac>Handling HVAC properties</h2>
	<p>You can use the vehicle HAL to control HVAC by setting HVAC-related
	properties. Most HVAC properties are zoned properties, but a few are non-zoned
	(global) properties. Example properties defined include:</p>
	<ul>
	<li><code>VEHICLE_PROPERTY_HVAC_TEMPERATURE_SET</code>
	<br>Set temperature per zone.</li>
	<li><code>VEHICLE_PROPERTY_HVAC_RECIRC_ON</code>
	<br>Control recirculation per zone).</li>
	</ul>
	<p>For full list of HVAC properties, search for
	<code>VEHICLE_PROPERTY_HVAC_*</code> in <code>vehicle.h</code>.</p>

	<h2 id=prop_sensor>Handling sensor properties</h2>
	<p>Vehicle HAL sensor properties represent real sensor data or policy
	information such as driving status. Some sensor information (such as driving
	status and day/night mode) is accessible by any app without restriction as the
	data is mandatory to build a safe vehicle application. Other sensor information
	(such as vehicle speed) is more sensitive and requires specific permissions that
	users can manage.</p>
	<p>Supported sensor properties include:</p>
	<ul>
	<li><code>DRIVING_STATUS</code>
	<br>Should support. Represents allowed operations in the current driving state.
	This information is used to block unsafe applications while driving.</li>
	<li><code>NIGHT_MODE</code>
	<br>Should support. Determines day/night mode of display.</li>
	<li><code>GEAR_SELECTION/CURRENT_GEAR</code>
	<br>Gear selected by driver vs. actual gear.</li>
	<li><code>VEHICLE_SPEED</code>
	<br>Vehicle speed. Protected with permission.</li>
	<li><code>ODOMETER</code>
	<br>Current odometer reading. Protected with permission.
	</li>
	<li><code>FUEL_LEVEL</code>
	<br>Current fuel level in %.</li>
	<li><code>FUEL_LEVEL_LOW</code>
	<br>Fuel level is low or not (boolean).</li>
	</ul>

	</body>
	</html>