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：

[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 inte易做图ce 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 inte易做图ce 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 inte易做图ce 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 inte易做图ce 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 inte易做图ce 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;

&nb

补充：移动开发 , Android ,