嵌入式实践教程--Android HAL自定义HAL代码教程

HIDL接口定义

创建hidl目录

在aosp中的hardware/interfaces目录下创建自己的hal目录

mkdir -p hardware/interfaces/qmiller/1.0/default

创建hal文件

在我们刚才创建的hardware/interfaces/qmiller/1.0/目录下新建IQmiller.hal文件,传入string name，返回string类型的result。

package android.hardware.qmiller@1.0;interface IQmiller {helloWorld(string name) generates (string result);};

生产HAL文件

使用hidl-gen工具来处理IQmiller.hal文件，这里可以写成一个shell脚本。

PACKAGE=android.hardware.qmiller@1.0
LOC=hardware/interfaces/qmiller/1.0/default/
make hidl-gen -j4
hidl-gen -o $LOC -Lc++-impl -randroid.hardware:hardware/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE
hidl-gen -o $LOC -Landroidbp-impl -randroid.hardware:hardware/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE

此时的文件树：

hardware/interfaces/qmiller/1.0/
├── default
│   ├── Android.bp
│   ├── Qmiller.cpp
│   └── Qmiller.h
└── IQmiller.hal

然后使用脚本来更新Makefile，自动生成Android,mk, Android.bp

./hardware/interfaces/update-makefiles.sh

此时的文件树：

hardware/interfaces/qmiller/1.0/
├── Android.bp
├── default
│   ├── Android.bp
│   ├── Qmiller.cpp
│   └── Qmiller.h
└── IQmiller.hal

新建两个空文件：

touch hardware/interfaces/qmiller/1.0/default/android.hardware.qmiller@1.0-service.rc
touch hardware/interfaces/qmiller/1.0/default/service.cpp

实现HAL的implementation库

自动生成的Qmiller.h文件,这里介绍的是绑定式HAL，而不是直通式。

#pragma once#include <android/hardware/qmiller/1.0/IQmiller.h>
#include <hidl/MQDescriptor.h>
#include <hidl/Status.h>namespace android::hardware::qmiller::implementation {using ::android::hardware::hidl_array;
using ::android::hardware::hidl_memory;
using ::android::hardware::hidl_string;
using ::android::hardware::hidl_vec;
using ::android::hardware::Return;
using ::android::hardware::Void;
using ::android::sp;struct Qmiller : public V1_0::IQmiller {// Methods from ::android::hardware::qmiller::V1_0::IQmiller follow.Return<void> helloWorld(const hidl_string& name, helloWorld_cb _hidl_cb) override;// Methods from ::android::hidl::base::V1_0::IBase follow.};// FIXME: most likely delete, this is only for passthrough implementations
// extern "C" IQmiller* HIDL_FETCH_IQmiller(const char* name);}  // namespace android::hardware::qmiller::implementation

自动生成的Qmiller.cpp


#include "Qmiller.h"namespace android::hardware::qmiller::implementation {// Methods from ::android::hardware::qmiller::V1_0::IQmiller follow.
Return<void> Qmiller::helloWorld(const hidl_string& name, helloWorld_cb _hidl_cb) {// TODO implementreturn Void();
}// Methods from ::android::hidl::base::V1_0::IBase follow.//IQmiller* HIDL_FETCH_IQmiller(const char* /* name */) {//return new Qmiller();
//}
//
}  // namespace android::hardware::qmiller::implementation

修改Android.bp文件，将-impl改成-service，将cc_library_shared改成cc_library，在-service后面加上vendor名称。

cc_library {name: "android.hardware.qmiller@1.0-service-lzm",relative_install_path: "hw",vendor:true,// FIXME: this should be 'vendor: true' for modules that will eventually be// on AOSP.proprietary: true,srcs: ["Qmiller.cpp",],shared_libs: ["libhidlbase","libutils","android.hardware.qmiller@1.0",],
}

实现service.cpp

#define LOG_TAG   "android.hardware.qmiller@1.0-service-lzm"
#include &lt;hidl/HidlLazyUtils.h&gt;
#include &lt;hidl/HidlSupport.h&gt;
#include &lt;hidl/HidlTransportSupport.h&gt;
#include "Qmiller.h"using ::android::OK;
using ::android::sp;
using ::android::hardware::configureRpcThreadpool;
using ::android::hardware::joinRpcThreadpool;
using ::android::hardware::LazyServiceRegistrar;
using ::android::hardware::qmiller::V1_0::IQmiller;
using ::android::hardware::qmiller::V1_0::implementation::Qmiller;int main(int argc, char* []) {sp<IQmiller> qmiller = new Qmiller;configureRpcThreadpool(1, true);auto registrar = LazyServiceRegistrar::getInstance();if (registrar.registerService(qmiller) != OK) {ALOGE("Could not register service.");return 1;}joinRpcThreadpool();ALOGE("Service exited!");return 1;
}

修改Android.bp

cc_library {name: "android.hardware.qmiller@1.0-service-lzm",relative_install_path: "hw",vendor:true,// FIXME: this should be 'vendor: true' for modules that will eventually be// on AOSP.proprietary: true,srcs: ["Qmiller.cpp",],shared_libs: ["libhidlbase","libutils","android.hardware.qmiller@1.0",],
}
cc_binary{name: "android.hardware.qmiller@1.0-service",defaults: ["hidl_defaults"],relative_install_path: "hw",proprietary: true,srcs: ["service.cpp"],init_rc: ["android.hardware.qmiller@1.0-service.rc"],shared_libs: ["libhidlbase","libhidltransport","libutils","liblog","libhardware","android.hardware.qmiller@1.0","android.hardware.qmiller@1.0-service-lzm",],
}

实现Qmiller.cpp文件

#include "Qmiller.h"
namespace android::hardware::qmiller::implementation {Return<void> Qmiller::helloWorld(const hidl_string& name, helloWorld_cb _hidl_cb) {char buf[100];::memset(buf, 0x00, 100);::snprintf(buf, 100, "Hello World, %s", name.c_str());hidl_string result(buf);_hidl_cb(result);return Void();}} // namespace android::hardware::qmiller::implementation

编译hal

mmm hardware/interfaces/qmiller/1.0/default/

最终会生成一个android.hardware.qmiller@1.0-service-lzm.so, 生成在/vendor/lib64/hw/下。

service.rc

service.cpp会被编译成bin文件，我们需要在系统启动的时候将我们编写的hal服务加进系统。android.hardware.qmiller@1.0-service.rc文件内容如下：

service qmiller_hal_service /vendor/bin/hw/android.hardware.qmiller@1.0-serviceclass haluser systemgroup system

为了让服务器被客户端访问到，还需要在device/xxx/xxx/manifest.xml（不同厂商路径不同）添加如下：

<hal format="hidl"><name>android.hardware.qmiller</name><transport>hwbinder</transport><impl level="generic"></impl><version>1.0<version><interface><name>IQmiller</name><instance>default</instance></interface>
</hal>