从内核驱动到android app

该文不得作为商业用途,仅为学习积累所用,转载请注明出处:http://blog.csdn.net/callon_h/article/details/51909169


了解android驱动框架:


1.方法1——jni调用底层驱动


在android框架中写入c/c++直接调用底层linux驱动,并向上提供jni接口给应用程序:

从内核驱动到android app_第1张图片

优点:简单易行;

缺点:主要在于驱动程序,由于在linux中需要遵循GPL协议,需要开源,而许多厂商的一些代码不希望开源。


2.方法2——增加硬件抽象层


将驱动程序一分为二,一部分开源在内核中,一部分不开源在android框架中:

从内核驱动到android app_第2张图片



led android驱动:



从这里我们将看到整个应用框架层到底层驱动的走向。首先,无论是哪种方法,我们都需要实现一个linux驱动以供上层访问led资源。


1.linux驱动:

linux的字符设备驱动编写:

从内核驱动到android app_第3张图片

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 



static struct cdev dev;
static dev_t dev_num;


#define GPM4CON 0x110002E0
#define GPM4DAT 0X110002E4

#define LED_ON _IOW('G',0,int)
#define LED_OFF _IOW('G',1,int)

static unsigned int *led_con = NULL;
static unsigned int *led_dat = NULL;


static struct class *led_class = NULL;


static long led_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
		switch(cmd)
		{
				case LED_ON:
				{
						writel(readl(led_dat)& ~(0x1<



2 实现第一种方法:


首先,说明一下为什么使用jni:

1.基于对代码的保护,java相对容易被反编译,而c/c++库反汇编难度较大;

2.可以方便地使用现存的开源库;

3.提高执行效率;

4.java在某些文件操作方面,找不到相关的API,如此处的ioctl.

其次,为什么使用ndk?

ndk提供了一系列的工具,能够帮助开发者快速开发c/c++的动态库,并能自动将.so动态库和java一起打包成apk.

第一种方法的设计思路如下所示:

从内核驱动到android app_第4张图片

在第一步中想要使用javah命令自动产生头文件需要先编写app程序,但是此时的app程序并不需要很完善,只需要提出一个你想要的native接口就好(但是你的android程序必须要Rebuild正确才会正确产生头文件):

package com.led.ndk.example.callon.ndk_led;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;

public class MainActivity extends Activity {

    private CheckBox[] Led = new CheckBox[4];
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Led[0] = (CheckBox)findViewById(R.id.checkbox_led1);
        Led[1] = (CheckBox)findViewById(R.id.checkbox_led2);
        Led[2] = (CheckBox)findViewById(R.id.checkbox_led3);
        Led[3] = (CheckBox)findViewById(R.id.checkbox_led4);
    }

    private void SendCmd(View view)
    {
        for(int i =1; i<5; i++)
        {
            if(Led[i].isChecked())
            {
                cmdLeds(1, i);
            }
            else
            {
                cmdLeds(0, i);
            }
        }
    }

    public native void cmdLeds(int cmd, int arg);
    
}

根据如上简单的app,使用命令:

javah -d jni -classpath 你的sdk目录/platforms/你的平台名/android.jar:你的应用程序/app/build/intermediates/classes/debug/ 你的包名.主类名

如:

javah -d jni -classpath /opt/AndroidSDK/platforms/android-23/android.jar:/home/callon/Downloads/callon_ndk_led/ndk_led/app/build/intermediates/classes/debug/ com.led.ndk.example.callon.ndk_led.MainActivity

此时自动产生出jni文件夹,其中包含头文件com_led_ndk_example_callon_ndk_led_MainActivity.h,头文件比较重要的:

JNIEXPORT void JNICALL Java_com_led_ndk_example_callon_ndk_1led_MainActivity_cmdLeds
  (JNIEnv *, jobject, jint, jint);

这也就是我们编写源文件需要实现的方法名,下面直接编写源文件:

#include "com_led_ndk_example_callon_ndk_led_MainActivity.h"
#include 
#include 
#include 
#include 
#include 
#include 
#include 


#define LED_ON _IOW('G',0,int)
#define LED_OFF _IOW('G',1,int)


JNIEXPORT void JNICALL Java_com_led_ndk_example_callon_ndk_1led_MainActivity_cmdLeds
  (JNIEnv * env, jobject thiz, jint cmd, jint arg)
{
		int fd;
		int temp_cmd;
		fd = open("/dev/callon_led",O_WRONLY);
		
		if(cmd == 1)
			temp_cmd = LED_ON;
		else
			temp_cmd = LED_OFF;
			
		ioctl(fd, temp_cmd, arg);
		close(fd);
		  	
}

就是一些对内核驱动文件的操作,然后编写Android.mk即makefile:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := callon_ndk_led
LOCAL_SRC_FILES := ndk_led.c
include $(BUILD_SHARED_LIBRARY)
此时,在你的jni文件夹应该有这三个文件了,退到jni文件夹之外,使用命令ndk-build即可:

callon@ubuntu:~/Downloads/callon_ndk_led/jni$ ls
Android.mk  com_led_ndk_example_callon_ndk_led_MainActivity.h  ndk_led.c
callon@ubuntu:~/Downloads/callon_ndk_led/jni$ cd ..
callon@ubuntu:~/Downloads/callon_ndk_led$ ndk-build 
[armeabi] Compile thumb  : callon_ndk_led <= ndk_led.c
[armeabi] SharedLibrary  : libcallon_ndk_led.so
[armeabi] Install        : libcallon_ndk_led.so => libs/armeabi/libcallon_ndk_led.so
callon@ubuntu:~/Downloads/callon_ndk_led$ 

最后一步,完善app:

首先,用Project形式来看我们的app,并在app->src->main下创建一个目录"jniLibs";

然后,将我们.so所在的armeabi目录拷贝到jniLibs目录下;

最后在我们的app代码的最后加上:

static
    {
        System.loadLibrary("callon_ndk_led");
    }

然后Rebuild Project即可!



3 实现第二种方法:


1.HAL程序编写:

从内核驱动到android app_第5张图片

首先在  安卓源代码根目录/hardware/libhardware/modules/下创建自己的hal代码存放路径,如led。

最终编写的文件为:安卓源代码根目录/hardware/libhardware/modules/led/led_hal.c和Android.mk,安卓源代码根目录/hardware/libhardware/include/hardware/led.h。

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define LOG_TAG "callon_led"
static int fd;

static int led_close(struct hw_device_t *device)
{
	struct led_device_t* led = (struct led_device_t*)device;
	free(led);

	close(fd);
	return 0;
}

int led_on(struct led_device_t* dev,int arg)
{
	ioctl(fd,LED_ON,arg);
	return 0;
}

int led_off(struct led_device_t* dev,int arg)
{
	ioctl(fd,LED_OFF,arg);
	return 0;
}

static struct led_device_t led_dev = {
	.led_device = {
		.tag = HARDWARE_DEVICE_TAG,
		.close = led_close,
	},
	.set_on = led_on,
	.set_off = led_off,
};

static int open_led(const struct hw_module_t* module, char const* name,
        struct hw_device_t** device)
{
	*device = &led_dev;
	fd = open("/dev/callon_led",O_RDWR);
	if(fd < 0)
	{
		ALOGD(LOG_TAG, "open device fail!");
		return -1;
	}
	return 0;
}

static struct hw_module_methods_t led_methods = {
    .open =  open_led,
};


struct hw_module_t HAL_MODULE_INFO_SYM = {
    .tag = HARDWARE_MODULE_TAG,
    .id = "led",
    .methods = &led_methods,
};


led.h

#ifndef _HARDWARE_LED_H
#define _HARDWARE_LED_H

#include 

#define LED_ON _IOW('G',0,int)
#define LED_OFF _IOW('G',1,int)

struct led_device_t {
	struct hw_device_t led_device;
	int (*set_on)(struct led_device_t* dev,int arg);//means led_number
	int (*set_off)(struct led_device_t* dev,int arg);
};



#endif  // _HARDWARE_LED_H

Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := led.default

# HAL module implementation stored in
# hw/.default.so
LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_C_INCLUDES := hardware/libhardware
LOCAL_SRC_FILES := led_hal.c
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_MODULE_TAGS := eng

include $(BUILD_SHARED_LIBRARY)

编译则在  安卓源代码根目录下使用

$ . setenv
$ lunch
$ mmm hardware/libhardware/modules/led/
看到

target SharedLib: led.default (out/target/product/tiny4412/obj/SHARED_LIBRARIES/led.default_intermediates/LINKED/led.default.so)
target Symbolic: led.default (out/target/product/tiny4412/symbols/system/lib/hw/led.default.so)
Export includes file: hardware/libhardware/modules/led/Android.mk -- out/target/product/tiny4412/obj/SHARED_LIBRARIES/led.default_intermediates/export_includes
target Strip: led.default (out/target/product/tiny4412/obj/lib/led.default.so)
Install: out/target/product/tiny4412/system/lib/hw/led.default.so
make: Leaving directory `/opt/Tiny4412/Android/android-5.0.2'

#### make completed successfully (1 seconds) ####

即可,最后产生的就在out/target/product/tiny4412/system/lib/hw/led.default.so了。

我们将system.img重做,这里通过一个脚本./gen-img.sh完成。


2.硬件服务编写:

首先,Service Manager为了解决访问冲突而存在的,在有Service Manager的基础之上,我们的底层需要先编写硬件服务,注册到Service Manager,我们的app才能通过Service Manager获取到服务,操作底层。

从内核驱动到android app_第6张图片


由于涉及到许多目录操作,细化操作后为:

1.创建 ILedService.aidl

仿照 frameworks/base/core/java/android/os/IVibratorService.aidl 

package android.os;

/** {@hide} */
interface ILedService
{
    int LedOpen();
    int LedOn(int arg);
    int LedOff(int arg);
}

2.修改frameworks/base/Android.mk

增加
core/java/android/os/ILedService.aidl \

3.自动生成ILedService.java

mmm frameworks/base/编译自动生成out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/os/ILedService.java

4.创建 LedService.java 实现接口函数

仿照frameworks/base/services/core/java/com/android/server/VibratorService.java 

package com.android.server;

import android.util.Slog;
import android.os.ILedService;

public class LedService extends ILedService.Stub{
    private static final String TAG = "LedService";
    
	public LedService() 
	{
		Slog.d(TAG,"LedService");
	}
    	public int LedOpen() throws android.os.RemoteException
	{
		return native_LedOpen();
	}
    	public int LedOn(int arg) throws android.os.RemoteException
	{
		return native_LedOn(arg);
	}
	public int LedOff(int arg) throws android.os.RemoteException
	{
		return native_LedOff(arg);
	}      
        
	public static native int native_LedOpen();
	public static native int native_LedOn(int arg);
	public static native int native_LedOff(int arg);
}

5.将服务注册到Service Manager当中

修改frameworks/base/services/java/com/android/server/SystemServer.java
参考vibrator修改的地方
LedService led = null;

Slog.i(TAG, "Led Service");
            led = new LedService();
            ServiceManager.addService("led", led);

6.实现com_android_server_LedService.cpp

为什么需要它?因为我们的hal代码并没有提供jni的接口(这里提供了一种新的方法来提供native方法,之前是自动产生头文件然后来实现的)。

根据frameworks/base/services/core/jni/com_android_server_VibratorService.cpp

/*
 * Copyright (C) 2009 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.
 */

#define LOG_TAG "LedService"

#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"

#include 
#include 
#include 

#include 


struct led_device_t *led_dev;

namespace android
{

static jint LedOpen(JNIEnv *env, jobject clazz)
{
	hw_module_t *module;
	hw_device_t *device;	
	hw_get_module("led",(hw_module_t const **)&module);

	module->methods->open(module, NULL, &device);
	
	led_dev = (struct led_device_t*)device;
	return 0;
}

static jint LedOn(JNIEnv *env, jobject clazz, int arg)
{
	led_dev->set_on(led_dev,arg);
	return 0;
}

static jint LedOff(JNIEnv *env, jobject clazz, int arg)
{
    	led_dev->set_off(led_dev,arg);
	return 0;
}

static JNINativeMethod method_table[] = {
    { "native_LedOpen", "()I", (void*)LedOpen },
    { "native_LedOn", "(I)I", (void*)LedOn },
    { "native_LedOff", "(I)I", (void*)LedOff}
};

int register_android_server_LedService(JNIEnv *env)
{
    return jniRegisterNativeMethods(env, "com/android/server/LedService",
            method_table, NELEM(method_table));
}

};


7.注册native接口

在frameworks/base/services/core/jni/onload.cpp中添加

int register_android_server_LedService(JNIEnv* env);

register_android_server_LedService(env);

8.修改Android.mk

在frameworks/base/services/core/jni/Android.mk中加入自己写的com_android_server_LedService.cpp

$(LOCAL_REL_DIR)/com_android_server_LedService.cpp \

9.mmm frameworks/base/services/编译

Copying: out/target/common/obj/JAVA_LIBRARIES/services_intermediates/classes.dex
target Jar: services (out/target/common/obj/JAVA_LIBRARIES/services_intermediates/javalib.jar)
Install: out/target/product/tiny4412/system/framework/services.jar
make: Leaving directory `/opt/Tiny4412/Android/android-5.0.2'

#### make completed successfully (50 seconds) ####

其中碰到一阵错误,非常无语:

make: Entering directory `/opt/Tiny4412/Android/android-5.0.2'
make: *** No rule to make target `frameworks/base/services/core/.java', needed by `out/target/common/obj/JAVA_LIBRARIES/services.core_intermediates/classes-full-debug.jar'.  Stop.
make: Leaving directory `/opt/Tiny4412/Android/android-5.0.2'

#### make failed to build some targets (1 seconds) ####
直接不往下编译,直接报错,非常难找错误,最后发现由于LedService.java的 文件名多了个空格。出现这种错误一定要耐心,一定是某个小地方出错的。

最后继续使用./gen-img.sh完成system.img的编译,烧写进开发板,为写应用程序做准备。


3.应用程序设计:

package com.led.hal.example.callon.callonhalled;

import android.os.RemoteException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import android.os.ILedService;
import android.os.ServiceManager;

public class MainActivity extends AppCompatActivity {

    private CheckBox[] Led = new CheckBox[4];
    private ILedService iLedService = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Led[0] = (CheckBox)findViewById(R.id.checkbox_led1);
        Led[1] = (CheckBox)findViewById(R.id.checkbox_led2);
        Led[2] = (CheckBox)findViewById(R.id.checkbox_led3);
        Led[3] = (CheckBox)findViewById(R.id.checkbox_led4);
        iLedService = ILedService.Stub.asInterface(ServiceManager.getService("led"));
        try {
            iLedService.LedOpen();
        }catch(RemoteException e){
            e.printStackTrace();
        }
    }

    private void SendCmd(View view)
    {
        for(int i =1; i<5; i++)
        {
            if(Led[i].isChecked()) {
                try {
                    iLedService.LedOn(i);
                }catch (RemoteException e){
                    e.printStackTrace();
                }
            }
            else {
                try {
                    iLedService.LedOff(i);
                }catch (RemoteException e){
                    e.printStackTrace();
                }
            }
        }
    }
}
程序其实很简单,但是涉及到android 中隐藏类的使用,我们的ILedService和ServiceManager其实都是隐藏类,你编译不过去的,添加相应的jar包才可以,参考

http://blog.csdn.net/wukunting/article/details/5788196

首先拷贝out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes.jar到工程下

然后AndroidStudio中File->Project Structure点击其中的'+'->选择Import .JAR/.AAR Package->选择classes.jar->Finish

继续在Project Structure下选择app->Dependencies->选择'+'->Module Dependency->选择'classes'即可。

这时候整个源码都好了,但是下载速度会很慢,改善基于frameworks设计的app下载和运行速度的方案:

1.修改build.gradle(Module:app)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.led.hal.example.callon.callonhalled"
        minSdkVersion 21
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
        multiDexEnabled true
    }

    dexOptions {
        javaMaxHeapSize "4g"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.2.0'
    compile project(':classes')
    compile 'com.android.support:multidex:1.0.0'
}
2.修改AndroidManifest.xml

在application下增加

android:name="android.support.multidex.MultiDexApplication"

最后下载运行吧!



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