原文网址：http://www.2cto.com/kf/201304/202040.html

时隔多日，终于都抽出时间来写blog了。废话不多说，接着上一篇，这里将介绍如何编写HAL层（硬件抽象层）对应的JNI方法。

这里提到的都是在ICS源码里编译的。

1、定义JNI层接口
进入到android-4.0.4_r1.2/hardware/libhardware/include/hardware目录，并创建 ttt.h 文件，内容如下：

[cpp]
#ifndef ANDROID_TTT_INTERFACE_H  
#define ANDROID_TTT_INTERFACE_H  
#include <hardware/hardware.h>  
 
__BEGIN_DECLS 
 
// 定义模块ID  
#define HELLO_HARDWARE_MODULE_ID    "ttt"  
 
// 硬件模块结构体  
struct ttt_module_t{ 
    struct hw_module_t common; 
}; 
 
// hardware interface struct  
struct ttt_device_t{ 
    struct hw_device_t common; 
    int fd; 
    int(*set_val)(struct ttt_device_t* dev, int val); 
    int(*get_val)(struct ttt_device_t* dev, int* val); 
}; 
 
__END_DECLS 
 
 
#endif

#ifndef ANDROID_TTT_INTERFACE_H
#define ANDROID_TTT_INTERFACE_H
#include <hardware/hardware.h>

__BEGIN_DECLS

// 定义模块ID
#define HELLO_HARDWARE_MODULE_ID "ttt"

// 硬件模块结构体
struct ttt_module_t{
    struct hw_module_t common;
};

// hardware interface struct
struct ttt_device_t{
 struct hw_device_t common;
 int fd;
 int(*set_val)(struct ttt_device_t* dev, int val);
 int(*get_val)(struct ttt_device_t* dev, int* val);
};

__END_DECLS

#endif

2、实现JNI层接口功能
进入到android-4.0.4_r1.2/frameworks/base/services/jni目录，并创建com_android_server_TTTService.cpp文件，其内容如下：

[cpp]
#define LOG_TAG     "TTTService"  
 
#include "jni.h"  
#include "JNIHelp.h"  
#include "android_runtime/AndroidRuntime.h"  
#include <utils/misc.h>  
#include <utils/Log.h>  
#include <hardware/hardware.h>  
#include <hardware/ttt.h>  
#include <stdio.h>  
 
namespace android 
{ 
    struct ttt_device_t* ttt_device = NULL; 
 
    // through the HAL interface to set the register value  
    static void ttt_setVal(JNIEnv* env, jobject clazz, jint value){ 
        int val = value; 
        LOGI("TTT JNI: set value %d to device.", val); 
        if(!ttt_device){ 
            LOGI("TTT JNI: device is not open."); 
            return; 
        } 
 
        ttt_device->set_val(ttt_device, val); 
    } 
 
    // through the HAL interface to read the register value  
    static jint ttt_getVal(JNIEnv* env, jobject clazz){ 
        int val = 0; 
        if(!ttt_device){ 
            LOGI("TTT JNI: device is not open."); 
            return val; 
        } 
        ttt_device->get_val(ttt_device, &val); 
 
        LOGI("TTT JNI: get value %d from device.", val); 
 
        return val; 
    } 
 
    // through the HAL interface to open the hardware device  
    static inline int ttt_device_open(const hw_module_t* module, struct ttt_device_t** device){ 
        return module->methods->open(module, HELLO_HARDWARE_MODULE_ID, (struct hw_device_t**)device); 
    } 
 
    // throught the hardware module ID to load the HAL module and open the device  
    static jboolean ttt_init(JNIEnv* env, jclass clazz){ 
        ttt_module_t* module; 
 
        LOGI("TTT JNI: initializing..."); 
        if(hw_get_module(HELLO_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0){ 
            LOGI("TTT JNI: ttt stub found."); 
            if(ttt_device_open(&(module->common), &ttt_device) == 0){ 
                LOGI("TTT JNI: ttt device is open."); 
                return 0; 
            } 
            LOGE("TTT JNI: failed to open ttt device."); 
            return -1; 
        } 
 
        LOGE("TTT JNI: failed to get ttt stub module."); 
        return -1; 
    } 
 
    // JNI methods table  
    static const JNINativeMethod method_table[] = { 
        {"init_native", "()Z", (void*)ttt_init}, 
        {"setVal_native", "(I)V", (void*)ttt_setVal}, 
        {"getVal_native", "()I", (void*)ttt_getVal}, 
    }; 
 
    // regist JNI method  
    int register_android_server_TTTService(JNIEnv* env){ 
        return jniRegisterNativeMethods(env, "com/android/server/TTTService", method_table, NELEM(method_table)); 
    } 
};

#define LOG_TAG     "TTTService"

#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"
#include <utils/misc.h>
#include <utils/Log.h>
#include <hardware/hardware.h>
#include <hardware/ttt.h>
#include <stdio.h>

namespace android
{
    struct ttt_device_t* ttt_device = NULL;

// through the HAL interface to set the register value
    static void ttt_setVal(JNIEnv* env, jobject clazz, jint value){
        int val = value;
        LOGI("TTT JNI: set value %d to device.", val);
        if(!ttt_device){
            LOGI("TTT JNI: device is not open.");
            return;
        }

ttt_device->set_val(ttt_device, val);
    }

// through the HAL interface to read the register value
    static jint ttt_getVal(JNIEnv* env, jobject clazz){
        int val = 0;
        if(!ttt_device){
            LOGI("TTT JNI: device is not open.");
            return val;
        }
        ttt_device->get_val(ttt_device, &val);

LOGI("TTT JNI: get value %d from device.", val);

return val;
    }

// through the HAL interface to open the hardware device
    static inline int ttt_device_open(const hw_module_t* module, struct ttt_device_t** device){
        return module->methods->open(module, HELLO_HARDWARE_MODULE_ID, (struct hw_device_t**)device);
    }

// throught the hardware module ID to load the HAL module and open the device
    static jboolean ttt_init(JNIEnv* env, jclass clazz){
        ttt_module_t* module;

LOGI("TTT JNI: initializing...");
        if(hw_get_module(HELLO_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0){
            LOGI("TTT JNI: ttt stub found.");
            if(ttt_device_open(&(module->common), &ttt_device) == 0){
                LOGI("TTT JNI: ttt device is open.");
                return 0;
            }
            LOGE("TTT JNI: failed to open ttt device.");
            return -1;
        }

LOGE("TTT JNI: failed to get ttt stub module.");
        return -1;
    }

// JNI methods table
    static const JNINativeMethod method_table[] = {
        {"init_native", "()Z", (void*)ttt_init},
        {"setVal_native", "(I)V", (void*)ttt_setVal},
        {"getVal_native", "()I", (void*)ttt_getVal},
    };

// regist JNI method
    int register_android_server_TTTService(JNIEnv* env){
        return jniRegisterNativeMethods(env, "com/android/server/TTTService", method_table, NELEM(method_table));
    }
};

3、添加JNI初始化调用
修改android-4.0.4_r1.2/frameworks/base/services/jni目录下的 onload.cpp 文件，在 JNI_OnLoad函数中的return之前添加下面一句：

[cpp]
register_android_server_TTTService(env);

register_android_server_TTTService(env);同时，在该文件中的namespace中添加下面一句声明：

[cpp]
int register_android_server_TTTService(JNIEnv* env);

int register_android_server_TTTService(JNIEnv* env);

这样，在系统初始化时，就会调用register_android_server_TTTService方法来加载JNI方法了。

4、添加编译JNI的配置
修改android-4.0.4_r1.2/frameworks/base/services/jni目录下的 Android.mk 文件，在 LOCAL_SRC_FILES 变量中添加下面一行：

[cpp]
com_android_server_TTTService.cpp \

com_android_server_TTTService.cpp \这里是添加编译配置。

5、开始编译
[cpp]
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# . build/envsetup.sh  
including device/moto/stingray/vendorsetup.sh 
including device/moto/wingray/vendorsetup.sh 
including device/samsung/crespo4g/vendorsetup.sh 
including device/samsung/crespo/vendorsetup.sh 
including device/samsung/maguro/vendorsetup.sh 
including device/samsung/smdkc110/vendorsetup.sh 
including device/samsung/smdkv210/vendorsetup.sh 
including device/samsung/torospr/vendorsetup.sh 
including device/samsung/toro/vendorsetup.sh 
including device/samsung/tuna/vendorsetup.sh 
including device/ti/panda/vendorsetup.sh 
including sdk/bash_completion/adb.bash 
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# . build/envsetup.sh
including device/moto/stingray/vendorsetup.sh
including device/moto/wingray/vendorsetup.sh
including device/samsung/crespo4g/vendorsetup.sh
including device/samsung/crespo/vendorsetup.sh
including device/samsung/maguro/vendorsetup.sh
including device/samsung/smdkc110/vendorsetup.sh
including device/samsung/smdkv210/vendorsetup.sh
including device/samsung/torospr/vendorsetup.sh
including device/samsung/toro/vendorsetup.sh
including device/samsung/tuna/vendorsetup.sh
including device/ti/panda/vendorsetup.sh
including sdk/bash_completion/adb.bash
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#[cpp] view plaincopyprint?root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm frameworks/base/services/jni 
============================================ 
PLATFORM_VERSION_CODENAME=REL 
PLATFORM_VERSION=4.0.4 
TARGET_PRODUCT=full 
TARGET_BUILD_VARIANT=eng 
TARGET_BUILD_TYPE=release 
TARGET_BUILD_APPS= 
TARGET_ARCH=arm 
TARGET_ARCH_VARIANT=armv7-a 
HOST_ARCH=x86 
HOST_OS=linux 
HOST_BUILD_TYPE=release 
BUILD_ID=IMM76I 
============================================ 
make:进入目录'/home/brantyou/workspace/android-4.0.4_r1.2' 
target thumb C++: libandroid_servers <= frameworks/base/services/jni/com_android_server_HelloService.cpp 
target thumb C++: libandroid_servers <= frameworks/base/services/jni/com_android_server_TTTService.cpp 
target thumb C++: libandroid_servers <= frameworks/base/services/jni/onload.cpp 
make: *** 没有规则可以创建“out/target/product/generic/obj/SHARED_LIBRARIES/libandroid_servers_intermediates/LINKED/libandroid_servers.so”需要的目标“out/target/product/generic/obj/lib/libsystem_server.so”。 停止。 
make:离开目录“/home/brantyou/workspace/android-4.0.4_r1.2” 
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm frameworks/base/services/jni
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=4.0.4
TARGET_PRODUCT=full
TARGET_BUILD_VARIANT=eng
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
TARGET_ARCH_VARIANT=armv7-a
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=IMM76I
============================================
make:进入目录'/home/brantyou/workspace/android-4.0.4_r1.2'
target thumb C++: libandroid_servers <= frameworks/base/services/jni/com_android_server_HelloService.cpp
target thumb C++: libandroid_servers <= frameworks/base/services/jni/com_android_server_TTTService.cpp
target thumb C++: libandroid_servers <= frameworks/base/services/jni/onload.cpp
make: *** 没有规则可以创建“out/target/product/generic/obj/SHARED_LIBRARIES/libandroid_servers_intermediates/LINKED/libandroid_servers.so”需要的目标“out/target/product/generic/obj/lib/libsystem_server.so”。 停止。
make:离开目录“/home/brantyou/workspace/android-4.0.4_r1.2”
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#
矮油~~~这里出错了，提示没有找到 libsystem_server.so 文件。
执行下面的命令，生成 libsystem_server.so 文件：

[cpp]
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make libsystem_server

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make libsystem_server生成之后的提示：

[cpp]
Install: out/target/product/generic/system/lib/libvorbisidec.so 
Install: out/target/product/generic/system/lib/libstagefright_yuv.so 
Install: out/target/product/generic/system/lib/libdrmframework.so 
Install: out/target/product/generic/system/lib/libchromium_net.so 
Install: out/target/product/generic/system/lib/libstagefright_amrnb_common.so 
Install: out/target/product/generic/system/lib/libstagefright_enc_common.so 
Install: out/target/product/generic/system/lib/libstagefright_avc_common.so 
Install: out/target/product/generic/system/lib/libstagefright.so 
Install: out/target/product/generic/system/lib/libstagefright_omx.so 
Install: out/target/product/generic/system/lib/libmediaplayerservice.so 
Install: out/target/product/generic/system/lib/libinput.so 
Install: out/target/product/generic/system/lib/libsystem_server.so 
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#

Install: out/target/product/generic/system/lib/libvorbisidec.so
Install: out/target/product/generic/system/lib/libstagefright_yuv.so
Install: out/target/product/generic/system/lib/libdrmframework.so
Install: out/target/product/generic/system/lib/libchromium_net.so
Install: out/target/product/generic/system/lib/libstagefright_amrnb_common.so
Install: out/target/product/generic/system/lib/libstagefright_enc_common.so
Install: out/target/product/generic/system/lib/libstagefright_avc_common.so
Install: out/target/product/generic/system/lib/libstagefright.so
Install: out/target/product/generic/system/lib/libstagefright_omx.so
Install: out/target/product/generic/system/lib/libmediaplayerservice.so
Install: out/target/product/generic/system/lib/libinput.so
Install: out/target/product/generic/system/lib/libsystem_server.so
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# 好了，这个问题解决了，我们继续编译这个JNI。

[cpp]
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm frameworks/base/services/jni 
============================================ 
PLATFORM_VERSION_CODENAME=REL 
PLATFORM_VERSION=4.0.4 
TARGET_PRODUCT=full 
TARGET_BUILD_VARIANT=eng 
TARGET_BUILD_TYPE=release 
TARGET_BUILD_APPS= 
TARGET_ARCH=arm 
TARGET_ARCH_VARIANT=armv7-a 
HOST_ARCH=x86 
HOST_OS=linux 
HOST_BUILD_TYPE=release 
BUILD_ID=IMM76I 
============================================ 
make:进入目录'/home/brantyou/workspace/android-4.0.4_r1.2' 
target SharedLib: libandroid_servers (out/target/product/generic/obj/SHARED_LIBRARIES/libandroid_servers_intermediates/LINKED/libandroid_servers.so) 
target Symbolic: libandroid_servers (out/target/product/generic/symbols/system/lib/libandroid_servers.so) 
target Strip: libandroid_servers (out/target/product/generic/obj/lib/libandroid_servers.so) 
Install: out/target/product/generic/system/lib/libandroid_servers.so 
make:离开目录“/home/brantyou/workspace/android-4.0.4_r1.2” 
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm frameworks/base/services/jni
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=4.0.4
TARGET_PRODUCT=full
TARGET_BUILD_VARIANT=eng
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
TARGET_ARCH_VARIANT=armv7-a
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=IMM76I
============================================
make:进入目录'/home/brantyou/workspace/android-4.0.4_r1.2'
target SharedLib: libandroid_servers (out/target/product/generic/obj/SHARED_LIBRARIES/libandroid_servers_intermediates/LINKED/libandroid_servers.so)
target Symbolic: libandroid_servers (out/target/product/generic/symbols/system/lib/libandroid_servers.so)
target Strip: libandroid_servers (out/target/product/generic/obj/lib/libandroid_servers.so)
Install: out/target/product/generic/system/lib/libandroid_servers.so
make:离开目录“/home/brantyou/workspace/android-4.0.4_r1.2”
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#很好，这一次已经顺利的编译完了。

下面我们需要重新打包这个 system.img，包我们编写的JNI方法包含进去：

[cpp]
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make snod 
============================================ 
PLATFORM_VERSION_CODENAME=REL 
PLATFORM_VERSION=4.0.4 
TARGET_PRODUCT=full 
TARGET_BUILD_VARIANT=eng 
TARGET_BUILD_TYPE=release 
TARGET_BUILD_APPS= 
TARGET_ARCH=arm 
TARGET_ARCH_VARIANT=armv7-a 
HOST_ARCH=x86 
HOST_OS=linux 
HOST_BUILD_TYPE=release 
BUILD_ID=IMM76I 
============================================ 
make snod: ignoring dependencies 
Target system fs image: out/target/product/generic/system.img 
out/target/product/generic/system.img total size is 44107008 
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make snod
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=4.0.4
TARGET_PRODUCT=full
TARGET_BUILD_VARIANT=eng
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
TARGET_ARCH_VARIANT=armv7-a
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=IMM76I
============================================
make snod: ignoring dependencies
Target system fs image: out/target/product/generic/system.img
out/target/product/generic/system.img total size is 44107008
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# 这样就成功的把我们编写的JNI打包到 system.img中了。

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