1.新建hardware/libhardware/include/hardware/led_hal.h檔案：

#ifndef ANDROID_LED_INTERFACE_H
#define ANDROID_LED_INTERFACE_H

#include <stdint.h>
#include <sys/cdefs.h>
#include <sys/types.h>
#include <hardware/hardware.h>

#define LED_HARDWARE_MODULE_ID "led"

struct led_module_t {
    struct hw_module_t common;
};

struct led_device_t {
    struct hw_device_t common;
    int fd;
    int (*led_ctrl)(struct led_device_t* dev, int val);
};

#endif  // ANDROID_LED_INTERFACE_H
 

2.新建hardware/libhardware/modules/led/led_hal.c檔案：

#define LOG_TAG "led_device"

#include <cutils/log.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <hardware/led.h>

int led_ctrl (struct led_device_t *dev, int val)
{
    int ret;

    val = !!val;
    ret = write(dev->fd, &val, 1);
    if (ret < 0) {
        ALOGE("write to /dev/led-dev failed");
        return -EBUSY;
    }

    return 0;
}

int close_led (struct hw_device_t *dev)
{
    struct led_device_t *led_dev = (struct led_device_t *)dev;

    close(led_dev->fd);
    free(led_dev);

    return 0;
}

static int open_led (const struct hw_module_t *module, char const *name,
        struct hw_device_t **device)
{
    int fd;
    struct led_device_t *dev;

    fd = open("/dev/led-dev", O_RDWR);
    if (fd < 0) {
        ALOGE("open /dev/led-dev failed");
        return -EBUSY;
    }

    dev = malloc(sizeof(struct led_device_t));
    if (!dev) {
        ALOGE("malloc failed");
        return -ENOMEM;
    }

    memset(dev, 0, sizeof(*dev));

    dev->fd = fd;
    dev->common.tag = HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = (struct hw_module_t*)module;
    dev->common.close = (int (*)(struct hw_device_t*))close_led;
    dev->led_ctrl = led_ctrl;

    *device = (struct hw_device_t *)dev;
    return 0;
}

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

struct led_module_t HAL_MODULE_INFO_SYM = {
    common: {
        tag:  HARDWARE_MODULE_TAG,
        version_major:  1,
        version_minor:  0,
        id:  LED_HARDWARE_MODULE_ID,
        name:  "led Module",
        author:  "cary.he",
        methods:  &led_module_methods,
    }
};
 

3.新建hardware/libhardware/modules/led/Android.mk:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := led.default
LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_C_INCLUDES := hardware/libhardware
LOCAL_SRC_FILES := led_hal.c
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_MODULE_TAGS := userdebug

編譯：mmm hardware/libhardware/modules/led/
在out/target/product/msm8909/system/lib/hw/下會生成led.default.so檔案。

4.新建frameworks/base/services/core/jni/com_android_server_LedService.cpp檔案：

#define LOG_TAG "LedServiceJNI"
#include "utils/Log.h"

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

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <hardware/hardware.h>  
#include <hardware/led.h>

namespace android
{
struct led_device_t *led_dev;

int led_init(JNIEnv *env, jclass clazz)
{
    int ret;
    struct led_module_t *led_module;

    ret = hw_get_module(LED_HARDWARE_MODULE_ID, (const struct hw_module_t **)&led_module);
    if (ret) {
        ALOGE("hw_get_module failed");
        return -EBUSY;
    }

    ret = led_module->common.methods->open((const struct hw_module_t *)led_module, 
            NULL, (struct hw_device_t **)&led_dev);
    if (ret) {
        ALOGE("led module open failed");
        return -EBUSY;
    }

    return 0;
}

int led_ctrl(JNIEnv *env, jclass clazz, jint val)
{
    int ret;

    ret = led_dev->led_ctrl(led_dev, val);
    if (ret) {
        ALOGE("led_ctrl failed");
        return -EBUSY;
    }

    return 0;
}

void led_close(JNIEnv *env, jclass clazz)
{
    led_dev->common.close((struct hw_device_t *)led_dev);
}

static const JNINativeMethod method_table[] = {
    {"init_native",  "()I",  (void*)led_init },
    {"ctrl_native",  "(I)I", (void*)led_ctrl },
    {"deinit_native", "()V", (void*)led_close},
};

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

5.修改frameworks/base/services/core/jni/onload.cpp檔案，增加函式宣告和呼叫：
    int register_android_server_Watchdog(JNIEnv* env);
    int register_android_server_LedService(JNIEnv *env);

    register_android_server_Watchdog(env);
    register_android_server_LedService(env);

6.修改frameworks/base/services/core/jni/Android.mk檔案，增加一行：
    $(LOCAL_REL_DIR)/com_android_server_PersistentDataBlockService.cpp \
    $(LOCAL_REL_DIR)/com_android_server_LedService.cpp \
    $(LOCAL_REL_DIR)/onload.cpp
編譯：mmm frameworks/base/services
在out/target/product/msm8909/system/lib/下會生成libandroid_servers.so檔案。