android平台led开发之硬件抽象层

二,硬件抽象层

 

1,在hardware\libhardware\include\hardware下新建swtled.h文件

swtled.h

#ifndef ANDROID_SWTLED_INTERFACE_H
#define ANDROID_SWTLED_INTERFACE_H

#include <hardware/hardware.h>

__BEGIN_DECLS

//module interface
struct swtled_module_t
{
    struct hw_module_t common;
};

//device interface
struct swtled_device_t
{
    struct hw_device_t common;
    int fd;
    int (*set_on)(struct swtled_device_t* dev,int number);
    int (*set_off)(struct swtled_device_t* dev,int number);
};


#define SWTLED_HARDWARE_MODULE_ID "swtled"
__END_DECLS

#endif

2:在hardware/libhardware/module下新建swtled文件夹并新建swtled.c

#define LOG_TAG "swtledStub"

#include <hardware/hardware.h>
#include <hardware/swtled.h>
#include <fcntl.h>
#include <errno.h>
#include <cutils/log.h>
#include <cutils/atomic.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>


#define LED_ON _IO('k',1)
#define LED_OFF _IO('k',2)

#define DEVICE_NAME "/dev/swt_led"
#define MODULE_NAME "swtled"
#define MODULE_AUTHOR "zc"



//open or close device interface

static int swtled_device_open(const struct hw_module_t* module,const char* name, struct hw_device_t** device);

static int swtled_device_close(struct hw_device_t* device);


//light-on light-off
static int swtled_set_on(struct swtled_device_t* dev,int number);
static int swtled_set_off(struct swtled_device_t* dev,int number);


static int swtled_device_open(const struct hw_module_t* module,const char* name, struct hw_device_t** device)
{

    struct swtled_device_t * dev;
    dev = (struct swtled_device_t*)malloc(sizeof(struct swtled_device_t));
    if (!dev)
    {
     LOGE("Swtled Stub:failed to alloc space");
        return -EFAULT;

    }
    memset(dev,0,sizeof(struct swtled_device_t));
    dev->common.tag = HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = (hw_module_t*)module;
    dev->common.close = swtled_device_close;
    dev->set_on = swtled_set_on;
    dev->set_off = swtled_set_off;

    if ((dev->fd = open(DEVICE_NAME,O_RDWR)) == -1)
    {
        LOGE("Swtled Stub:failed to open /dev/swt_led -- %s.",strerror(errno));
        free(dev);
        return -EFAULT;
    }

    *device = &(dev->common);
    LOGI("Swtled Stub: open /dev/swt_led successfully");

    return 0;
}

static int swtled_device_close(struct hw_device_t* device)
{
    struct swtled_device_t* swtled_device = (struct swtled_device_t*)device;
    if (swtled_device)
    {
        close(swtled_device->fd);
        free(swtled_device);
    }
    return 0;
}


//------------------------------------------------------------------------------
//number: 1: light one 2:light two
//------------------------------------------------------------------------------
static int swtled_set_on(struct swtled_device_t* device,int number)
{
    ioctl(device->fd,LED_ON,number);
    return 0;
}


//------------------------------------------------------------------------------
//number: 1: light one 2:light two
//------------------------------------------------------------------------------
static int swtled_set_off(struct swtled_device_t* device,int number)
{
    ioctl(device->fd,LED_OFF,number);
    return 0;
}



//module method table
static struct hw_module_methods_t swtled_module_methods =
{
    open: swtled_device_open
};



const struct swtled_module_t HAL_MODULE_INFO_SYM = {

    common:
    {
        tag: HARDWARE_MODULE_TAG,
        version_major: 1,
        version_minor: 0,
        id: SWTLED_HARDWARE_MODULE_ID,
        name:MODULE_NAME,
        author: MODULE_AUTHOR,
        methods: &swtled_module_methods,
    }

};

这里主要是通过hw_module_t和hw_device_t结构体形式将内核中led的驱动封装一层,
导出set_on和set_off接口,到时供JNI层的CPP调用。由于权限问题,应用层在打开dev时可能提示permission deny,所以需要修改
system\core\rootdir下的ueventd.rc文件,在其中添加一句

/dev/swt_led 0666 root root

3,在同目录下添加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
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_SRC_FILES := swtled.c
LOCAL_MODULE := swtled.default
include $(BUILD_SHARED_LIBRARY)

4,编译

 (1 进入到gingerbread目录下,执行mmm hardware/libhardware/modules/swtled会

    编译成功后，就可以在out/target/product/generic/system/lib/hw目录下看到swtled.default.so文件了

 

 (2 再执行make snod，使system.img镜像文件中包名硬件抽象模块swtled.default.so