在Android2.3.1下进行HAL层的开发，先参照网上弄了个hello的demo，首先看下HAL层在android系统中的位置：
硬件驱动程序可以看做是在keinel层，HAL封装了硬件驱动，然后再经过JNI接口的封装才能给Java应用程序调用。
HAL层接口封装的具体流程如下：
1）在../Android-2.3.1/hardware/libhardware/include/hardware这个目录下添加hello.h头文件，具体可以参开当前目录下的overlay.h，
/***************************************************
*android_hal_hello_demo
*hello.h
***************************************************/
#ifndef ANDROID_HELLO_INTERFACE_H
#define ANDROID_HELLO_INTERFACE_H
#include <hardware/hardware.h>
__BEGIN_DECLS
#define HELLO_HARDWARE_MODULE_ID "hello"
struct hello_module_t {
struct hw_module_t common;
};
struct hello_device_t {
struct hw_device_t common;
int fd;
int (*get_val)(struct hello_device_t *dev,int val);
int (*set_val)(struct hello_device_t *dev,int val);
};
__END_DECLS;
#endif
2）在../Android-2.3.1/hardware/libhardware/modules这个目录下新建hello文件夹，并在此文件夹中添加hello.c和Android.mk文件，具体可以参考modules目录下overlay文件夹中的内容。
/******************************************************************************
*android_hal_hello_demo
*hello.c
*****************************************************************************/
#include <hardware/hardware.h>
#include <hardware/hello.h>
#include <fcntl.h>
#include <errno.h>
#include <cutils/log.h>
#include <cutils/atomic.h>
#define LOG_TAG "hello_stub"
#define DEVICE_NAME "/dev/hello"
#define MODULE_NAME "Hello"
#define MODULE_AUTHOR "pwzhgx@163.com"
static int hello_device_open(const struct hw_module_t *module,const char *name,struct hw_device_t** device);
static int hello_device_close(struct hw_device_t* device);
static int hello_set_val(struct hello_device_t*dev,int val);
static int hello_get_val(struct hello_device_t *dev,int *val);
static struct hw_module_methods_t hello_module_methods = {
open : hello_device_open
};
struct hello_module_t HAL_MODULE_INFO_SYM = {
common: {
tag: HARDWARE_MODULE_TAG,
version_major: 1,
version_minor: 0,
id: HELLO_HARDWARE_MODULE_ID,
name: MODULE_NAME,
author: MODULE_AUTHOR,
methods: &hello_module_methods,
}
};
static int hello_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device) {
struct hello_device_t* dev;
dev = (struct hello_device_t*)malloc(sizeof(struct hello_device_t));
if(!dev) {
LOGE("Hello Stub: failed to alloc space");
return -EFAULT;
}
memset(dev, 0, sizeof(struct hello_device_t));
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (hw_module_t*)module;
dev->common.close = hello_device_close;
dev->set_val = hello_set_val;
dev->get_val = hello_get_val;
if((dev->fd = open(DEVICE_NAME, O_RDWR)) == -1) {
LOGE("Hello Stub: failed to open /dev/hello -- %s.", strerror(errno));free(dev);
return -EFAULT;
}
*device = &(dev->common);
LOGI("Hello Stub: open /dev/hello successfully.");
return 0;
}
static int hello_device_close(struct hw_device_t* device) {
struct hello_device_t* hello_device = (struct hello_device_t*)device;
if(hello_device) {
close(hello_device->fd);
free(hello_device);
}
return 0;
}
static int hello_set_val(struct hello_device_t* dev, int val) {
LOGI("Hello Stub: set value %d to device.", val);
write(dev->fd, &val, sizeof(val));
return 0;
}
static int hello_get_val(struct hello_device_t* dev, int* val) {
if(!val) {
LOGE("Hello Stub: error val pointer");
return -EFAULT;
}
read(dev->fd, val, sizeof(*val));
LOGI("Hello Stub: get value %d from device", *val);
return 0;
}
/******************************************************************************
*android_hal_hello_demo
*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 := hello.c
LOCAL_MODULE := hello.default
include $(BUILD_SHARED_LIBRARY)
到此HAL层的代码基本已经弄好，接下来就是编译，将其编译成模块.so库文件。