android從應用層到HRL層調用流程：
1.實現自己的LED燈之HAL層代碼編寫
(1)編寫Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw //動態庫會放在system/lib/hw文件夾中。
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_SRC_FILES := led_hal.c
LOCAL_MODULE := led.default
include $(BUILD_SHARED_LIBRARY)
(2)編寫led_hal.h
#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>
__BEGIN_DECLS
struct led_device_t {
struct hw_device_t common;
int (*led_open)(struct led_device_t* dev);
int (*led_ctrl)(struct led_device_t* dev, int which, int status); //對led 燈進行操作接口。
};
__END_DECLS
#endif // ANDROID_LED_INTERFACE_H
（3）編寫led_hal.c
#define LOG_TAG "LedHal"
#include <hardware/vibrator.h>
#include <hardware/hardware.h>
#include <cutils/log.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <hardware/led_hal.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <utils/Log.h>
static int fd;
/** Close this device */
static int led_close(struct hw_device_t* device)
{
close(fd);
return 0;
}
/** open this device */
static int led_open(struct led_device_t* dev)
{
fd = open("/dev/leds", O_RDWR);
ALOGI("led_open : %d", fd);
if (fd >= 0)
return 0;
else
return -1;
}
//操作ioctl 驅動led 燈。
static int led_ctrl(struct led_device_t* dev, int which, int status)
{
int ret = ioctl(fd, status, which);
ALOGI("led_ctrl : %d, %d, %d", which, status, ret);
return ret;
}
//操作驅動所有的接口。
static struct led_device_t led_dev = {
.common = {
.tag = HARDWARE_DEVICE_TAG,
.close = led_close,
},
.led_open = led_open,
.led_ctrl = led_ctrl,
};
//hal默認方法。
static int led_device_open(const struct hw_module_t* module, const char* id,
struct hw_device_t** device)
{
*device = &led_dev;
return 0;
}
static struct hw_module_methods_t led_module_methods = {
.open = led_device_open,
};
struct hw_module_t HAL_MODULE_INFO_SYM = {
.tag = HARDWARE_MODULE_TAG,
.id = "led",
.methods = &led_module_methods,
};
//把新文件上傳到服務器, 所在目錄:
hardware/libhardware/include/hardware/led_hal.h
hardware/libhardware/modules/led/led_hal.c
hardware/libhardware/modules/led/Android.mk
（4）編譯動態庫
$ mmm hardware/libhardware/modules/led
2.實現自己的HAL Led燈之JNI層代碼編寫：
（1）編寫JNI代碼
com_android_server_LedService.cpp
#define LOG_TAG "LedService"
#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"
#include <utils/misc.h>
#include <utils/Log.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <hardware/led_hal.h>
namespace android
{
static led_device_t* led_device; //led燈設備。
jint ledOpen(JNIEnv *env, jobject cls)
{
jint err;
hw_module_t* module;
hw_device_t* device;
ALOGI("native ledOpen ...");
/* 1. hw_get_module */
err = hw_get_module("led", (hw_module_t const**)&module); //id ＝"led"與 led_hal.c 類的方法HAL_MODULE_INFO_SYM 屬性 .id = "led"一致
if (err == 0) {
/* 2. get device : module->methods->open */
err = module->methods->open(module, NULL, &device);
if (err == 0) {
/* 3. call led_open */
led_device = (led_device_t *)device;
return led_device->led_open(led_device);
} else {
return -1;
}
}
return -1;
}
void ledClose(JNIEnv *env, jobject cls)
{
//ALOGI("native ledClose ...");
//close(fd);
}
//操作led燈
jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
{
ALOGI("native ledCtrl %d, %d", which, status);
return led_device->led_ctrl(led_device, which, status);
}
static const JNINativeMethod methods[] = {
{"native_ledOpen", "()I", (void *)ledOpen},
{"native_ledClose", "()V", (void *)ledClose},
{"native_ledCtrl", "(II)I", (void *)ledCtrl},
};
int register_android_server_LedService(JNIEnv *env)
{
return jniRegisterNativeMethods(env, "com/android/server/LedService",
methods, NELEM(methods));
}
}
（2）修改frameworks/base/services/core/jni/onload.cpp
1）在namespace android {}方法中添加
int register_android_server_LedService(JNIEnv *env);
2）extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved){}方法中添加
register_android_server_LedService(env);
（3）修改 frameworks/base/services/core/jni/Android.mk ：
添加 $(LOCAL_REL_DIR)/com_android_server_LedService.cpp \
（4）把新文件上傳到服務器, 所在目錄:
frameworks/base/services/core/jni/com_android_server_LedService.cpp
（5）編譯：
$ mmm frameworks/base/services //重新打包libandroid_servers.so動態庫。
3.實現自己的HAL Led燈之Service層代碼編寫
（1) 編寫AIDL
1） ILedService.aidl
package android.os;
/** {@hide} */
interface ILedService
{
int ledCtrl(int which, int status);
}
2）把 ILedService.aidl 放入 frameworks/base/core/java/android/os
3）修改 frameworks/base/Android.mk 添加一行
core/java/android/os/IVibratorService.aidl \
+ core/java/android/os/ILedService.aidl \
（2）編譯：mmm frameworks/base
它會生成: ./out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/os/ILedService.java
（3) 編寫LedService.java