AndroidAutomotive模块介绍（四）VehicleHal介绍
前言前面的文章中，描述了 Android Automotive 的框架中应用、Framework 层服务等知识，本篇文章将会继续按照 Android Automotive 框架介绍 Vehicle Hal 层服务的内容。
上一篇：AndroidAutomotive模块介绍（三）CarService服务
正文
1、VehicleHal 介绍
本篇文档将对 Andorid Automotive 框架中 VehicleHal 层睁开介绍。VehicleHal 即为车辆硬件抽象层的定义。可以明白为 Android Automotive OS 中的硬件抽象层接口，包罗车辆属性和方法；各厂商制造商会根据定义的 Hal 接口，实现定制化的模块服务。
VehicleHal 是链接 Android Automotive Car Services 与制造商实现车辆控制服务进程的桥梁，通过标准化接口对上层提供服务，对于服务的实现依赖厂商的定制化，可以忽略汽车制造商的详细实现，也就是说 CarService 调用 VehicleHal 定义的标准接口，厂商实现这些接口。
2、VehicleHal 模块功能
2.1 rc 文件
VehicleHal 的代码路径为：android/hardware/interfaces/automotive/vehicle/2.0/default。路径下有 android.hardware.automotive.vehicle@2.0-service.rc 文件，在开机阶段通过此 rc 文件，将 VehicleHal 进程启动，下面来看下 android.hardware.automotive.vehicle@2.0-service.rc 文件的定义
service vendor.vehicle-hal-2.0 /vendor/bin/hw/android.hardware.automotive.vehicle@2.0-service
class hal
user vehicle_network
group system inet
2.2 编译
对于 VehicleHal 的编译，可以对以下两个 Android.bp 文件介绍。
[*]Hidl 接口编译
[*]VehicleHal 服务编译
VehicleHal 定义的 Hal 接口编译介绍，Android.bp 文件路径为：android/hardware/interfaces/automotive/vehicle/2.0，目录结构如下：
ubuntu:android/hardware/interfaces/automotive/vehicle/2.0$ ls -l
total 132
-rw-r--r-- 1 users 375 Nov92022 Android.bp
drwxrwxr-x 5 users 4096 Mar 22 13:55 default
-rw-r--r-- 1 users 2336 Nov92022 IVehicleCallback.hal
-rw-r--r-- 1 users 3665 Nov92022 IVehicle.hal
-rw-r--r-- 1 users 115184 Nov92022 types.hal
下面是 Android.bp 文件的定义：
// This file is autogenerated by hidl-gen -Landroidbp.
hidl_interface {
name: "android.hardware.automotive.vehicle@2.0",
root: "android.hardware",
vndk: {
enabled: true,
},
srcs: [
"types.hal",
"IVehicle.hal",
"IVehicleCallback.hal",
],
interfaces: [
"android.hidl.base@1.0",
],
gen_java: true,
}
编译文件中定义了 android.hardware.automotive.vehicle@2.0 HIDL 接口编译，包罗三个文件 types.hal、IVehicle.hal、IVehicleCallback.hal 文件。
VehicleHal 服务编译介绍，Android.bp 文件路径为：android/hardware/interfaces/automotive/vehicle/2.0/default，目录结构如下：
ubuntu16:android/hardware/interfaces/automotive/vehicle/2.0/default$ ls -l
total 28
-rw-r--r-- 1 users 4705 Nov92022 Android.bp
-rw-r--r-- 1 users155 Nov92022 android.hardware.automotive.vehicle@2.0-service.rc
drwxrwxr-x 4 users 4096 Jun72022 common
drwxrwxr-x 3 users 4096 Jun72022 impl
drwxrwxr-x 2 users 4096 Nov92022 tests
-rw-r--r-- 1 users 1953 Nov92022 VehicleService.cpp
Android.bp 文件定义如下：
// Vehicle reference implementation lib
cc_library {
name: "android.hardware.automotive.vehicle@2.0-manager-lib",
vendor: true,
defaults: ["vhal_v2_0_defaults"],
srcs: [
"common/src/Obd2SensorStore.cpp",
"common/src/SubscriptionManager.cpp",
"common/src/VehicleHalManager.cpp",
"common/src/VehicleObjectPool.cpp",
"common/src/VehiclePropertyStore.cpp",
"common/src/VehicleUtils.cpp",
"common/src/VmsUtils.cpp",
],
local_include_dirs: ["common/include/vhal_v2_0"],
export_include_dirs: ["common/include"],
}
// Vehicle default VehicleHAL implementation
cc_library_static {
name: "android.hardware.automotive.vehicle@2.0-default-impl-lib",
vendor: true,
cflags: ["-Wno-unused-parameter", "-Wno-sign-compare"],
defaults: ["vhal_v2_0_defaults"],
srcs: [
"impl/vhal_v2_0/CommConn.cpp",
"impl/vhal_v2_0/EmulatedVehicleHal.cpp",
"impl/vhal_v2_0/VehicleEmulator.cpp",
"impl/vhal_v2_0/PipeComm.cpp",
"impl/vhal_v2_0/SocketComm.cpp",
"impl/vhal_v2_0/LinearFakeValueGenerator.cpp",
"impl/vhal_v2_0/JsonFakeValueGenerator.cpp",
],
local_include_dirs: ["common/include/vhal_v2_0"],
export_include_dirs: ["impl"],
whole_static_libs: ["android.hardware.automotive.vehicle@2.0-manager-lib"],
shared_libs: [
"libbase",
"libprotobuf-cpp-lite",
],
static_libs: [
"libjsoncpp",
"libqemu_pipe",
"android.hardware.automotive.vehicle@2.0-libproto-native",
],
}
cc_binary {
name: "android.hardware.automotive.vehicle@2.0-service",
defaults: ["vhal_v2_0_defaults"],
init_rc: ["android.hardware.automotive.vehicle@2.0-service.rc"],
vendor: true,
relative_install_path: "hw",
srcs: ["VehicleService.cpp"],
shared_libs: [
"libbase",
"libprotobuf-cpp-lite",
],
static_libs: [
"android.hardware.automotive.vehicle@2.0-manager-lib",
"android.hardware.automotive.vehicle@2.0-default-impl-lib",
"android.hardware.automotive.vehicle@2.0-libproto-native",
"libjsoncpp",
"libqemu_pipe",
],
}
从 Android.bp 的定义中，VehicleHal 的服务名为 android.hardware.automotive.vehicle@2.0-service，启动 rc 文件是 android.hardware.automotive.vehicle@2.0-service.rc，入口文件是 VehicleService.cpp，依赖自定义干系模块重要有 android.hardware.automotive.vehicle@2.0-manager-lib、android.hardware.automotive.vehicle@2.0-default-impl-lib、android.hardware.automotive.vehicle@2.0-libproto-native。
android.hardware.automotive.vehicle@2.0-manager-lib 模块是 common 目录下的文件所编译的内容，重要是 VehicleHal 以是来的模块。
android.hardware.automotive.vehicle@2.0-default-impl-lib 模块是 impl 目录下的文件所编译的内容，重要是 VehicleHal 的功能实现模块。
android.hardware.automotive.vehicle@2.0-libproto-native 模块是 impl/vhal_v2_0/proto 目录下的文件所编译的内容，目录下的文件为 VehicleHalProto.proto 文件，是一种序列化存储数据的方式。
2.3 HIDL 接口
Android Automotive 框架中 Hal 层接口文件有三个，IVehicle.hal、IVehicleCallback.hal 和 types.hal 文件。IVehicle.hal 文件中定义了 Vehicle Hal 对外提供的接口；IVehicleCallback.hal 文件中定义了 VehicleHal 的回调接口；types.hal 文件定义了 Vehicle Hal 的属性定义。
Hidl 文件路径为：android/hardware/interfaces/automotive/vehicle/2.0。
2.3.1 IVehicle.hal
IVehicle.hal 文件中定义了 Vehicle Hal 对外提供的接口，上层 CarService 通过 IVehicle.hal 中定义的接口与 Vehicle Hal 通讯。
package android.hardware.automotive.vehicle@2.0;
import IVehicleCallback;
interface IVehicle {
/**
* Returns a list of all property configurations supported by this vehicle
* HAL.
* 返回此车辆HAL支持的所有属性配置的列表
*/
getAllPropConfigs() generates (vec<VehiclePropConfig> propConfigs);
/**
* Returns a list of property configurations for given properties.
*
* If requested VehicleProperty wasn't found it must return
* StatusCode::INVALID_ARG, otherwise a list of vehicle property
* configurations with StatusCode::OK
* 返回给定属性的属性配置列表。
* 如果请求的车辆属性没有找到，它必须返回StatusCode::INVALID_ARG，否则返回一个车辆属性配置列表，StatusCode::OK
*/
getPropConfigs(vec<int32_t> props)
generates (StatusCode status, vec<VehiclePropConfig> propConfigs);
/**
* Get a vehicle property value.
*
* For VehiclePropertyChangeMode::STATIC properties, this method must always
* return the same value always.
* For VehiclePropertyChangeMode::ON_CHANGE properties, it must return the
* latest available value.
*
* Some properties like RADIO_PRESET requires to pass additional data in
* GET request in VehiclePropValue object.
*
* If there is no data available yet, which can happen during initial stage,
* this call must return immediately with an error code of
* StatusCode::TRY_AGAIN.
* 获取车辆属性值。
* 对于 VehiclePropertyChangeMode::STATIC 的属性值，此方法会返回同一个值，不会改变。
* 对于 VehiclePropertyChangeMode::ON_CHANGE 的属性值，此方法会返回最新值。
*/
get(VehiclePropValue requestedPropValue)
generates (StatusCode status, VehiclePropValue propValue);
/**
* Set a vehicle property value.
*
* Timestamp of data must be ignored for set operation.
*
* Setting some properties require having initial state available. If initial
* data is not available yet this call must return StatusCode::TRY_AGAIN.
* For a property with separate power control this call must return
* StatusCode::NOT_AVAILABLE error if property is not powered on.
* 设置车辆属性值。
* 特殊场景：
* 设置一些属性值需要其初始状态可用，如果初始状态不可用，需要返回 StatusCode::TRY_AGAIN。
* 设置单独电源控制的属性，如果属性未上电，需要返回 StatusCode::TRY_AGAIN。
*/
set(VehiclePropValue propValue) generates (StatusCode status);
/**
* Subscribes to property events.
*
* Clients must be able to subscribe to multiple properties at a time
* depending on data provided in options argument.
*
* @param listener This client must be called on appropriate event.
* @param options List of options to subscribe. SubscribeOption contains
* information such as property Id, area Id, sample rate, etc.
* 订阅属性
* 客户端可以一次订阅多个属性，这取决于 options 定义的参数。
* 参数 SubscribeOptions 包含 属性id、区域id、采样率 等信息。
*/
subscribe(IVehicleCallback callback, vec<SubscribeOptions> options)
generates (StatusCode status);
/**
* Unsubscribes from property events.
*
* If this client wasn't subscribed to the given property, this method
* must return StatusCode::INVALID_ARG.
* 取消订阅属性
* 如果客户端在此前没有对此属性进行订阅，则返回 StatusCode::INVALID_ARG。
*/
unsubscribe(IVehicleCallback callback, int32_t propId)
generates (StatusCode status);
/**
* Print out debugging state for the vehicle hal.
*
* The text must be in ASCII encoding only.
*
* Performance requirements:
*
* The HAL must return from this call in less than 10ms. This call must avoid
* deadlocks, as it may be called at any point of operation. Any synchronization
* primitives used (such as mutex locks or semaphores) must be acquired
* with a timeout.
*
* 打印车辆的调试状态。
*/
debugDump() generates (string s);
};
2.3.2 IVehicleCallback.hal
IVehicleCallback.hal 文件定义了 VehicleHal 的回调对象，上层 CarService 通过注册此回调对象以监听属性是否改变。VehicleHal 通过回调对象返回状态给到客户端。
package android.hardware.automotive.vehicle@2.0;
interface IVehicleCallback {
/**
* Event callback happens whenever a variable that the API user has
* subscribed to needs to be reported. This may be based purely on
* threshold and frequency (a regular subscription, see subscribe call's
* arguments) or when the IVehicle#set method was called and the actual
* change needs to be reported.
*
* These callbacks are chunked.
*
* @param values that has been updated.
* 当需要报告客户端订阅的变量时，就会调用此回调函数。
* 这可能基于常规按频率上报或者客户端调用 IVehicle#set 函数时调用。
*/
oneway onPropertyEvent(vec<VehiclePropValue> propValues);
/**
* This method gets called if the client was subscribed to a property using
* SubscribeFlags::EVENTS_FROM_ANDROID flag and IVehicle#set(...) method was called.
*
* These events must be delivered to subscriber immediately without any
* batching.
*
* @param value Value that was set by a client.
* 如果客户端使用 SubscribeFlags::EVENTS_FROM_ANDROID 标志订阅属性，并且调用 IVehicle#set 函数，则回调此方法。
*/
oneway onPropertySet(VehiclePropValue propValue);
/**
* Set property value is usually asynchronous operation. Thus even if
* client received StatusCode::OK from the IVehicle::set(...) this
* doesn't guarantee that the value was successfully propagated to the
* vehicle network. If such rare event occurs this method must be called.
*
* @param errorCode - any value from StatusCode enum.
* @param property - a property where error has happened.
* @param areaId - bitmask that specifies in which areas the problem has
* occurred, must be 0 for global properties
* 设置属性通常是异步操作，客户端调用 IVehicle#set 函数到接收到 StatusCode::OK 的返回值，也不能保证此属性成功传播到车辆网络，如果发生这种低概率的事件，则回调此方法。
* @ errorCode：StatusCode 枚举中的任何值。
* @ property：发生错误的属性。
* @ areaId：指定问题发生在哪个区域的位掩码，对于全局属性必须为 0。
*/
oneway onPropertySetError(StatusCode errorCode,
int32_t propId,
int32_t areaId);
};
2.3.3 types.hal
types.hal 中定义了 VehicleHal 的属性、结构等数据。
2.3.3.1 车辆属性 VehiclePropertyType
下面列举 types.hal 中定义的 VehiclePropertyType 属性：
package android.hardware.automotive.vehicle@2.0;
/**
* Enumerates supported data type for VehicleProperty.
* 枚举 VehicleProperty 支持的数据类型。
* Used to create property ID in VehicleProperty enum.
* 用于在 VehicleProperty enum 中创建属性 ID。
*/
enum VehiclePropertyType : int32_t { // VehicleProperty 的类型是 string、bool、还是 int32 等等
STRING = 0x00100000,
BOOLEAN = 0x00200000,
INT32 = 0x00400000,
INT32_VEC = 0x00410000,
INT64 = 0x00500000,
INT64_VEC = 0x00510000,
FLOAT = 0x00600000,
FLOAT_VEC = 0x00610000,
BYTES = 0x00700000,
/**
* Any combination of scalar or vector types. The exact format must be
* provided in the description of the property.
*/
MIXED = 0x00e00000, // 这两个主要就是 VehicleProperty 用来进行或运算的。
MASK = 0x00ff0000
};
2.3.3.2 车辆区域属性 VehicleArea
下面是 types.hal 中定义的车辆区域属性：
/**
* Vehicle Areas
* Used to construct property IDs in the VehicleProperty enum.
* 用于在VehicleProperty enum中构造属性id。
*
* Some properties may be associated with particular vehicle areas. For
* example, VehicleProperty:DOOR_LOCK property must be associated with
* particular door, thus this property must be marked with
* VehicleArea:DOOR flag.
* 某些属性可能与特定车辆区域相关。例如，VehicleProperty:DOOR_LOCK 属性必须与特定的门相关联，因此该属性必须标记为 VehicleArea: door 标志。
*
* Other properties may not be associated with particular vehicle area,
* these kind of properties must have VehicleArea:GLOBAL flag.
* 其他属性可能不与特定的车辆区域相关联，这些属性必须具有VehicleArea:GLOBAL标志。
*
* Area: An area represents a unique element of an AreaType.
* For instance, if AreaType is WINDOW, then an area may be FRONT_WINDSHIELD.
*
* AreaID: An AreaID is a combination of one or more areas,
* and is represented using a bitmask of Area enums. Different AreaTypes may
* not be mixed in a single AreaID. For instance, a window area cannot be
* combined with a seat area in an AreaID.
*
* Rules for mapping a zoned property to AreaIDs:
*- A property must be mapped to an array of AreaIDs that are impacted when
* the property value changes.
*- Each element in the array must represent an AreaID, in which, the
* property value can only be changed together in all the areas within
* an AreaID and never independently. That is, when the property value
* changes in one of the areas in an AreaID in the array, then it must
* automatically change in all other areas in the AreaID.
*- The property value must be independently controllable in any two
* different AreaIDs in the array.
*- An area must only appear once in the array of AreaIDs. That is, an
* area must only be part of a single AreaID in the array.
*
* Global Property: A property that applies to the entire car
* and is not associated with a specific area. For example, FUEL_LEVEL,
* HVAC_STEERING_WHEEL_HEAT.
*
* Rules for mapping a global property to AreaIDs:
*- A global property must not be mapped to AreaIDs.
*/
enum VehicleArea : int32_t {
GLOBAL = 0x01000000, // 全局区域
/** WINDOW maps to enum VehicleAreaWindow */
WINDOW = 0x03000000, // 窗户区域
/** MIRROR maps to enum VehicleAreaMirror */
MIRROR = 0x04000000, // 反光镜区域
/** SEAT maps to enum VehicleAreaSeat */
SEAT = 0x05000000, // 座椅区域
/** DOOR maps to enum VehicleAreaDoor */
DOOR = 0x06000000, // 车门区域
/** WHEEL maps to enum VehicleAreaWheel */
WHEEL = 0x07000000, // 车轮区域
YFVehicleAreaTire = 0x08000000,
MASK = 0x0f000000,
};
2.3.3.3 车辆属性分组范例 VehiclePropertyGroup
下面是 types.hal 中定义的车辆属性分组范例：
/**
* Enumerates property groups.
* 车辆属性分组枚举
*
* Used to create property ID in VehicleProperty enum.
* 用于在VehicleProperty enum中创建属性ID。
*/
enum VehiclePropertyGroup : int32_t { // AndroidO 之后的 treble，用于区分 android 原生的 property 和厂商的 property。
/**
* Properties declared in AOSP must use this flag.
* AOSP 原生的属性标志
*/
SYSTEM = 0x10000000,
/**
* Properties declared by vendors must use this flag.
* 厂商自定义的属性标志
*/
VENDOR = 0x20000000,
MASK = 0xf0000000,
};
2.3.3.4 车辆属性 VehicleProperty
下面是 types.hal 中定义的车辆属性
/**
* Declares all vehicle properties. VehicleProperty has a bitwise structure.
* Each property must have:
*- a unique id from range 0x0100 - 0xffff
*- associated data type using VehiclePropertyType
*- propert
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