Android framework HAL(HIDL)

brief description

When you use different hardware devices (such as cameras, sensors, audio devices, etc.) in the Android system, you need to HALcommunicate with the hardware abstraction layer ( ). HALis an intermediate layer that acts as a bridge between hardware and applications. However, due to different hardware devices, the HAL interface will also vary between different hardware. This is where Android HALInterface Definition Language ( HIDL) comes in.

HIDLAllows developers to define their own interfaces for each hardware device. These interfaces define the functions and characteristics of the hardware device, including input parameters, return values, and exceptions. Using these interfaces, applications can communicate directly with hardware devices without knowing specific hardware details. In Android, HIDLis widely used to HALcommunicate with .

It Android Project Treblewas proposed in , and android Owas pushed comprehensively in . The purpose of designing HIDLthis mechanism is to isolate the framework ( )framework from , so that the framework part can be directly overwritten and updated without recompiling .HALHAL

HIDLIt is actually used for inter-process communication ( Inter-process Communication，IPC). Inter-process communication can be called Bindercall ( Binderized). For libraries that must be linked into a process, passthoughmode (but not supported in Java).

official introduction

Write code

AospCreate a directory in the code directory ( hardware/interfaces/stksensor/1.0for 1.0version-related, you can check the version management concept on the official website ),

1. Create a new fileIStksensor.hal

package android,[email protected];

improt IStksensorCallBack;

interface IStksensor {
    setCallBack(IStksensorCallBack callback);
    write(string data) generates (bool res);
    init() generates (MyResult result);
};

2. Create UDT(user-defined type),types.hal

package [email protected];

enum ResultCode : int32_t {
    UNKNOWN = -1,
    ERROR = 0,
    OK = 1,

};

struct MyResult{
    ResultCode resultCode;
    string msg;
};

3. Create a new file callback fileIStksensorCallBack.hal

package [email protected];

interface IStksensorCallBack {
	passData(uint32_t data) generates (MyResult result);
};

Use hidl-gen to generate related files

Execute the following command in the terminal to set the temporary variable

PACKAGE=[email protected]
LOC=hardware/interfaces/stksensor/1.0/default

AOSPExecute the files in the hidl-gengenerated defaultdirectory in the root directory of the source codec++

hidl-gen -o $LOC -Lc++-impl -randroid.hardware:hardware/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE

AOSPExecute the files in the hidl-gengenerated defaultdirectory in the root directory of the source codeAndroid.bp

hidl-gen -o $LOC -Landroidbp-impl -randroid.hardware:hardware/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE

Executing in AOSPthe root directory of the source code ./hardware/interfaces/update-makefiles.shwill generate the files hardware/interfaces/stksensor/1.0/in the directoryAndroid.bp

Implement the interface code

Modification hardware/interfaces/stksensor/1.0/default/Stksensor.cpp, the implementation here is simply to print the log

// FIXME: your file license if you have one

#include "Stksensor.h"
#include <log/log.h>

namespace android::hardware::stksensor::implementation {

// Methods from ::android::hardware::stksensor::V1_0::IStksensor follow.
Return<void> Stksensor::setCallBack(const sp<::android::hardware::stksensor::V1_0::IStksensorCallBack>& callback) {
    // TODO implement
	ALOGE("stksensor service have called the funtion of setCallBack");
    return Void();
}

Return<::android::hardware::stksensor::V1_0::ResultCode> Stksensor::write(const hidl_string& data) {
    // TODO implement
	ALOGE("stksensor service have called the funtion of write");
    return ::android::hardware::stksensor::V1_0::ResultCode {};
}

Return<void> Stksensor::init(init_cb _hidl_cb) {
    // TODO implement
	ALOGE("stksensor service have called the funtion of init");
    return Void();
}


// Methods from ::android::hidl::base::V1_0::IBase follow.

//IStksensor* HIDL_FETCH_IStksensor(const char* /* name */) {
    //return new Stksensor();
//}
//
}  // namespace android::hardware::stksensor::implementation

Add startup service

1. When hardware/interfaces/stksensor/1.0/default/creatingservice.cpp

#define LOG_TAG "[email protected]"
#include <hidl/HidlTransportSupport.h>
#include <log/log.h>


using android::hardware::configureRpcThreadpool;
using android::hardware::joinRpcThreadpool;
using android::hardwara::stksensor::V1_0::IStksensor;
using android::hardware::stksensor::V1_0::implementation::Stksensor;
using namespace android;


int main() {
    configureRpcThreadpool(1, true);
	sp<IStksensor> service = new Stksensor();
    status_t status = service->registerAsService("stksensor"); 
    if (status != OK) {
		ALOGE("Error registering stksensor as service: %d", status);
        return status;
    }
	ALOGE("Ok to registering stksensor as service");
    joinRpcThreadpool();

    return 1;
}

2. hardware/interfaces/stksensor/1.0/default/Create [email protected]a startup script

service stksensor-hal-1-0 /vendor/bin/hw/[email protected]
    class hal
    user system
    group system

3. In the hardware/interfaces/stksensor/1.0/default/created[email protected]vintf

<manifest version="1.0" type="device">
    <hal format="hidl">
        <name>android.hardware.stksensor</name>
        <transport>hwbinder</transport>
        <version>1.0</version>
        <interface>
            <name>IStksensor</name>
            <instance>stksensor</instance>
        </interface>
    </hal>
</manifest>

Modify the compilation script

1. Modify againhardware/interfaces/stksensor/1.0/default/Android.bp

// FIXME: your file license if you have one

cc_library_shared {
    // FIXME: this should only be -impl for a passthrough hal.
    // In most cases, to convert this to a binderized implementation, you should:
    // - change '-impl' to '-service' here and make it a cc_binary instead of a
    //   cc_library_shared.
    // - add a *.rc file for this module.
    // - delete HIDL_FETCH_I* functions.
    // - call configureRpcThreadpool and registerAsService on the instance.
    // You may also want to append '-impl/-service' with a specific identifier like
    // '-vendor' or '-<hardware identifier>' etc to distinguish it.
    name: "[email protected]",
    relative_install_path: "hw",
    // FIXME: this should be 'vendor: true' for modules that will eventually be
    // on AOSP.
    proprietary: true,
    srcs: [
        "Stksensor.cpp",
        "StksensorCallBack.cpp",
    ],
    shared_libs: [
        "libhidlbase",
        "libutils",
        "[email protected]",
    ],
}

cc_binary {
    name: "[email protected]",
    relative_install_path: "hw",
    defaults: ["hidl_defaults"],
    proprietary: true,
    init_rc: ["[email protected]"],
	vintf_fragments: ["[email protected]"],
    srcs: [
        "SerialPort.cpp",
        "service.cpp",
    ],
    shared_libs: [
        "libbase",
        "liblog",
        "libdl",
        "libutils",
        "libhardware",
        "libhidlbase",
        "libhidltransport",
        "[email protected]",
    ],
}

2. device/$your_company/$SOC/device.mkAdding

PRODUCT_PACKAGES += \
    [email protected] \
    [email protected]

current stksensordirectory structure

stksensor/
└── 1.0
    ├── Android.bp
    ├── default
    │   ├── Android.bp
    │   ├── [email protected]
    │   ├── [email protected]
    │   ├── service.cpp
    │   ├── StksensorCallBack.cpp
    │   ├── StksensorCallBack.h
    │   ├── Stksensor.cpp
    │   └── Stksensor.h
    ├── IStksensorCallBack.hal
    ├── IStksensor.hal
    └── types.hal

Note: Some avcpermissions will be reported, you need to add them yourself