該文不得作為商業(yè)用途，僅為學(xué)習(xí)積累所用，轉(zhuǎn)載請注明出處：http://blog.csdn.net/callon_h/article/details/51909169

了解android驅(qū)動框架：
1.方法1——jni調(diào)用底層驅(qū)動

在android框架中寫入c/c++直接調(diào)用底層linux驅(qū)動，并向上提供jni接口給應(yīng)用程序：

優(yōu)點(diǎn)：簡單易行；

缺點(diǎn)：主要在于驅(qū)動程序，由于在linux中需要遵循GPL協(xié)議，需要開源，而許多廠商的一些代碼不希望開源。

2.方法2——增加硬件抽象層

將驅(qū)動程序一分為二，一部分開源在內(nèi)核中，一部分不開源在android框架中：

led android驅(qū)動：

從這里我們將看到整個應(yīng)用框架層到底層驅(qū)動的走向。首先，無論是哪種方法，我們都需要實(shí)現(xiàn)一個linux驅(qū)動以供上層訪問led資源。

1.linux驅(qū)動：

linux的字符設(shè)備驅(qū)動編寫：

#include#include#include#include#include#include#include#includestatic?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<<arg),?led_dat);
						break;		
				}
					
				case?LED_OFF:
				{
						writel(readl(led_dat)|?(0x1<<arg),?led_dat);
						break;		
				}
					
				default:
				{
						return?-EINVAL;		
						break;
				}
			
		}
	
		return?0;
}

static?struct?file_operations?led_fops?=?{
		.owner?=?THIS_MODULE,
		.unlocked_ioctl?=?led_ioctl,
};

static?void?hw_init()//GPM4_0-3
{
			//1.2.1?映射地址
			led_con?=?ioremap(GPM4CON,4);
			led_dat?=?ioremap(GPM4DAT,4);
			
			//1.2.2?設(shè)置為輸出狀態(tài)
			writel((readl(led_con)&?~0xffff)?|?0x1111,?led_con);
			
			//1.2.3?設(shè)置為高電平
			writel(readl(led_dat)|0xf,?led_dat);
	
}


static?int?led_init()
{
	??//1.1?cdev字符設(shè)備初始化
		//1.1.1?分配cdev結(jié)構(gòu)(靜態(tài)分配)?
		
		//1.1.2?初始化cdev結(jié)構(gòu)
		alloc_chrdev_region(&dev_num,0,1,"callon_led");
		cdev_init(&dev,?&led_fops);
		dev.owner?=?THIS_MODULE;
		
		//1.1.3?注冊cdev結(jié)構(gòu)?
		cdev_add(&dev,dev_num,1);
		
		//1.2?硬件初始化
		hw_init();
		
		//1.3?創(chuàng)建設(shè)備文件
		//1.3.1?創(chuàng)建類
		led_class?=?class_create(THIS_MODULE,"callon_led");
		
		//1.3.2?創(chuàng)建設(shè)備
		device_create(led_class,NULL,dev_num,NULL,"%s","callon_led");
		
		printk("init?led?device?is?OK!n");
		return?0;
}

static?void?led_exit()
{
		device_destroy(led_class,dev_num);
		class_destroy(led_class);
	
		iounmap(led_dat);
		iounmap(led_con);
		
		cdev_del(&dev);
		unregister_chrdev_region(dev_num,1);
}




module_init(led_init);
module_exit(led_exit);

2 實(shí)現(xiàn)第一種方法：

首先，說明一下為什么使用jni：

1.基于對代碼的保護(hù)，java相對容易被反編譯，而c/c++庫反匯編難度較大；

2.可以方便地使用現(xiàn)存的開源庫；

3.提高執(zhí)行效率；

4.java在某些文件操作方面，找不到相關(guān)的API，如此處的ioctl.

其次，為什么使用ndk？

ndk提供了一系列的工具，能夠幫助開發(fā)者快速開發(fā)c/c++的動態(tài)庫，并能自動將.so動態(tài)庫和java一起打包成apk.

第一種方法的設(shè)計(jì)思路如下所示：

在第一步中想要使用javah命令自動產(chǎn)生頭文件需要先編寫app程序，但是此時的app程序并不需要很完善，只需要提出一個你想要的native接口就好（但是你的android程序必須要Rebuild正確才會正確產(chǎn)生頭文件）：

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);
????
}

根據(jù)如上簡單的app，使用命令：

javah -d jni -classpath 你的sdk目錄/platforms/你的平臺名/android.jar:你的應(yīng)用程序/app/build/intermediates/classes/debug/ 你的包名.主類名

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

此時自動產(chǎn)生出jni文件夾，其中包含頭文件com_led_ndk_example_callon_ndk_led_MainActivity.h，頭文件比較重要的：

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

這也就是我們編寫源文件需要實(shí)現(xiàn)的方法名，下面直接編寫源文件：

#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);
		??	
}

就是一些對內(nèi)核驅(qū)動文件的操作，然后編寫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)

此時，在你的jni文件夾應(yīng)該有這三個文件了，退到j(luò)ni文件夾之外，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$?ndk-build?
[armeabi]?Compile?thumb??:?callon_ndk_led??libs/armeabi/libcallon_ndk_led.so
callon@ubuntu:~/Downloads/callon_ndk_led$

最后一步，完善app：

首先，用Project形式來看我們的app，并在app->src->main下創(chuàng)建一個目錄"jniLibs"；

然后，將我們.so所在的armeabi目錄拷貝到j(luò)niLibs目錄下；

最后在我們的app代碼的最后加上：

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

然后Rebuild Project即可！

3 實(shí)現(xiàn)第二種方法：
1.HAL程序編寫：

首先在 ?安卓源代碼根目錄/hardware/libhardware/modules/下創(chuàng)建自己的hal代碼存放路徑，如led。

最終編寫的文件為：安卓源代碼根目錄/hardware/libhardware/modules/led/led_hal.c和Android.mk，安卓源代碼根目錄/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)

編譯則在 ?安卓源代碼根目錄下使用

$?.?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，最后產(chǎn)生的就在out/target/product/tiny4412/system/lib/hw/led.default.so了。

我們將system.img重做，這里通過一個腳本./gen-img.sh完成。

2.硬件服務(wù)編寫：

首先，Service Manager為了解決訪問沖突而存在的，在有Service Manager的基礎(chǔ)之上，我們的底層需要先編寫硬件服務(wù)，注冊到Service Manager，我們的app才能通過Service Manager獲取到服務(wù)，操作底層。

由于涉及到許多目錄操作，細(xì)化操作后為：

1.創(chuàng)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.自動生成ILedService.java

mmm frameworks/base/編譯自動生成out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/os/ILedService.java

4.創(chuàng)建 LedService.java 實(shí)現(xiàn)接口函數(shù)

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.將服務(wù)注冊到Service Manager當(dāng)中 修改frameworks/base/services/java/com/android/server/SystemServer.java
參考vibrator修改的地方

LedService?led?=?null;

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

6.實(shí)現(xiàn)com_android_server_LedService.cpp

為什么需要它？因?yàn)槲覀兊膆al代碼并沒有提供jni的接口（這里提供了一種新的方法來提供native方法，之前是自動產(chǎn)生頭文件然后來實(shí)現(xiàn)的）。

根據(jù)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#includestruct?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.注冊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中加入自己寫的com_android_server_LedService.cpp

$(LOCAL_REL_DIR)/com_android_server_LedService.cpp?

9.mmm frameworks/base/services/編譯

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)?####

其中碰到一陣錯誤，非常無語：

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)?####

直接不往下編譯，直接報錯，非常難找錯誤，最后發(fā)現(xiàn)由于LedService.java的文件名多了個空格。出現(xiàn)這種錯誤一定要耐心，一定是某個小地方出錯的。

最后繼續(xù)使用./gen-img.sh完成system.img的編譯，燒寫進(jìn)開發(fā)板，為寫應(yīng)用程序做準(zhǔn)備。

3.應(yīng)用程序設(shè)計(jì)：

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();
????????????????}
????????????}
????????}
????}
}

程序其實(shí)很簡單，但是涉及到android 中隱藏類的使用，我們的ILedService和ServiceManager其實(shí)都是隱藏類，你編譯不過去的，添加相應(yīng)的jar包才可以，參考

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

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

然后AndroidStudio中File->Project Structure點(diǎn)擊其中的'+'->選擇Import .JAR/.AAR Package->選擇classes.jar->Finish

繼續(xù)在Project Structure下選擇app->Dependencies->選擇'+'->Module Dependency->選擇'classes'即可。

這時候整個源碼都好了，但是下載速度會很慢，改善基于frameworks設(shè)計(jì)的app下載和運(yùn)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"

最后下載運(yùn)行吧！