Android 驱动开发系列四

 

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：

#ifndefANDROID_TTT_INTERFACE_H#defineANDROID_TTT_INTERFACE_H#include <hardware/hardware.h>__BEGIN_DECLS// 定义模块ID#defineHELLO_HARDWARE_MODULE_ID"ttt"// 硬件模块结构体struct ttt_module_t{    struct hw_module_t common;};// hardware interface structstruct 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：

#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：

register_android_server_TTTService(env);

同时，在该文件中的namespace中添加下面一句声明：

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：

    com_android_server_TTTService.cpp \

这里是添加编译配置。

5、开始编译

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# . build/envsetup.sh including device/moto/stingray/vendorsetup.shincluding device/moto/wingray/vendorsetup.shincluding device/samsung/crespo4g/vendorsetup.shincluding device/samsung/crespo/vendorsetup.shincluding device/samsung/maguro/vendorsetup.shincluding device/samsung/smdkc110/vendorsetup.shincluding device/samsung/smdkv210/vendorsetup.shincluding device/samsung/torospr/vendorsetup.shincluding device/samsung/toro/vendorsetup.shincluding device/samsung/tuna/vendorsetup.shincluding device/ti/panda/vendorsetup.shincluding sdk/bash_completion/adb.bashroot@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=RELPLATFORM_VERSION=4.0.4TARGET_PRODUCT=fullTARGET_BUILD_VARIANT=engTARGET_BUILD_TYPE=releaseTARGET_BUILD_APPS=TARGET_ARCH=armTARGET_ARCH_VARIANT=armv7-aHOST_ARCH=x86HOST_OS=linuxHOST_BUILD_TYPE=releaseBUILD_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.cpptarget thumb C++: libandroid_servers <= frameworks/base/services/jni/com_android_server_TTTService.cpptarget thumb C++: libandroid_servers <= frameworks/base/services/jni/onload.cppmake: *** 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：

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

生成之后的提示：

Install: out/target/product/generic/system/lib/libvorbisidec.soInstall: out/target/product/generic/system/lib/libstagefright_yuv.soInstall: out/target/product/generic/system/lib/libdrmframework.soInstall: out/target/product/generic/system/lib/libchromium_net.soInstall: out/target/product/generic/system/lib/libstagefright_amrnb_common.soInstall: out/target/product/generic/system/lib/libstagefright_enc_common.soInstall: out/target/product/generic/system/lib/libstagefright_avc_common.soInstall: out/target/product/generic/system/lib/libstagefright.soInstall: out/target/product/generic/system/lib/libstagefright_omx.soInstall: out/target/product/generic/system/lib/libmediaplayerservice.soInstall: out/target/product/generic/system/lib/libinput.soInstall: out/target/product/generic/system/lib/libsystem_server.soroot@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。

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm frameworks/base/services/jni============================================PLATFORM_VERSION_CODENAME=RELPLATFORM_VERSION=4.0.4TARGET_PRODUCT=fullTARGET_BUILD_VARIANT=engTARGET_BUILD_TYPE=releaseTARGET_BUILD_APPS=TARGET_ARCH=armTARGET_ARCH_VARIANT=armv7-aHOST_ARCH=x86HOST_OS=linuxHOST_BUILD_TYPE=releaseBUILD_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.somake: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：

root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make snod============================================PLATFORM_VERSION_CODENAME=RELPLATFORM_VERSION=4.0.4TARGET_PRODUCT=fullTARGET_BUILD_VARIANT=engTARGET_BUILD_TYPE=releaseTARGET_BUILD_APPS=TARGET_ARCH=armTARGET_ARCH_VARIANT=armv7-aHOST_ARCH=x86HOST_OS=linuxHOST_BUILD_TYPE=releaseBUILD_ID=IMM76I============================================make snod: ignoring dependenciesTarget system fs image: out/target/product/generic/system.imgout/target/product/generic/system.img total size is 44107008root@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。

 

这章到此结束，下一章将介绍，如何基于JNI接口编写对应的服务和编写对应的Android程序来访问服务。