Android底层开发（二）之HAL层 第二步

1

HAL程序必须要一个HAL-MODULE-INFO——SYM（hw_module_t）变量，有了这个才能被Android系统调用。类似于（C函数的main()和linux驱动程序的init()函数）

2 HAL编程是三个关键结构体：

struct hw_module_t; （HAL模块 中）

struct hw_module_methods_t; （入口函数 小）

struct hw_device_t; （HAL设备 大）

这几个数据结构是在Android工作目录/hardware/libhardware/include/hardware/hardware.h文件中定义.

3 源程序

3.1 leds_hal.h

#include <hardware/hardware.h>

#include <fcntl.h>

#include <cutils/log.h>

struct led_module_t

{

struct hw_module_t hw_module;

};

struct led_control_device_t

{

struct hw_device_t hw_device;

int (*set_on)(struct led_control_device_t *dev, int32_t led);

int (*set_off)(struct led_control_device_t *dev, int32_t led);

};

#define LED_HARDWARE_MODULE_ID "led_hal"

3.2 leds_hal.c

#include "leds_hal.h"

int dev_file = 0;

int led_on(struct led_control_device_t *dev, int32_t led)

{

return ioctl(dev_file, 1, led);

}

int led_off(struct led_control_device_t *dev, int32_t led)

{

return ioctl(dev_file, 0, led);

}

int led_device_close(struct hw_device_t* device)

{

struct led_control_device_t* ctx = (struct led_control_device_t*) device;

if (ctx)

{

free(ctx);

}

close(dev_file);

return 0;

}

static int led_device_open(const struct hw_module_t* module, const char* name,

struct hw_device_t** device)

{

struct led_control_device_t *dev;

dev = (struct led_control_device_t *) malloc(sizeof(*dev));

memset(dev, 0, sizeof(*dev));

dev->hw_device.tag = HARDWARE_DEVICE_TAG;

dev->hw_device.version = 0;

dev->hw_device.module = (struct hw_module_t*) module;

dev->hw_device.close = led_device_close;

dev->set_on = led_on;

dev->set_off = led_off;

//*device = &dev->hw_device;

*device = (hw_device_t*)dev;

dev_file = open("/dev/leds", O_RDWR);

if (dev_file < 0)

{

LOGI("LED Stub: open /dev/leds fail.");

}

else

{

LOGI("LED Stub: open /dev/leds success .");

}

//leds_init_gpm();

return 0;

}

static struct hw_module_methods_t led_module_methods =

{ open: led_device_open };

struct led_module_t HAL_MODULE_INFO_SYM =

{ hw_module:

{ tag: HARDWARE_MODULE_TAG, version_major: 1, version_minor: 0, id

: LED_HARDWARE_MODULE_ID,

name: "Sample LED HAL Stub",

author: "Lining",

methods: &led_module_methods,

}

};

4 Android.mk文件与分析

第一步：

HAL模块属于android系统的一部分，HAL需要很多的Android的头文件和共享库，采用办法如下：建立链接

ln -s /root/drivers/ch09/leds_hal/ /working/android2.3.4_src/hardware/leds_hal

第二步 采用mm命令编译

Android.mk文件如下：

LOCAL_PATH := $(call my-dir) //返回当前路径

include $(CLEAR_VARS) //清楚...变量

LOCAL_PRELINK_MODULE := false

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw

//编译出来的.so文件存放地方

LOCAL_SHARED_LIBRARIES := liblog //本次编译要链接动态库文件liblog.so文件

LOCAL_SRC_FILES := leds_hal.c

LOCAL_MODULE :=led_hal.default //编译生成led_hal.default.so

LOCAL_MODULE_TAGS := eng

include $(BUILD_SHARED_LIBRARY) //编译器负责

第三步：把生成的led_hal.default.so传入开发板的/system/lib/hw中。