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一、前言

以STM32為例，打開網絡上下載的例程或者是購買開發板自帶的例程，都會發現應用層中會有stm32f10x.h或者stm32f10x_gpio.h，這些文件嚴格來時屬于硬件層的，如果軟件層出現這些文件會顯得很亂。

使用過Linux的童鞋們肯定知道linux系統無法直接操作硬件層，打開linux或者rt_thread代碼會發現代碼中都會有device的源文件，沒錯，這就是驅動層。

二、實現原理

原理就是將硬件操作的接口全都放到驅動鏈表上，在驅動層實現device的open、read、write等操作。當然這樣做也有弊端，就是驅動find的時候需要遍歷一遍驅動鏈表，這樣會增加代碼運行時間。

三、代碼實現

國際慣例，寫代碼先寫頭文件。rt_thread中使用的是雙向鏈表，為了簡單在這我只用單向鏈表。有興趣的可以自行研究rt_thread

頭文件接口:

本次只實現如下接口，device_open 和device_close等剩下的接口可以自行研究。這樣就可以在應用層中只調用如下接口可實現：

/*
    驅動注冊
*/
int cola_device_register(cola_device_t *dev);
/*
    驅動查找
*/
cola_device_t *cola_device_find(const char *name);
/*
    驅動讀
*/
int cola_device_read(cola_device_t *dev,  int pos, void *buffer, int size);
/*
    驅動寫
*/
int cola_device_write(cola_device_t *dev, int pos, const void *buffer, int size);
/*
    驅動控制
*/
int cola_device_ctrl(cola_device_t *dev,  int cmd, void *arg);;

頭文件cola_device.h：

#ifndef _COLA_DEVICE_H_
#define _COLA_DEVICE_H_
 
 
enum LED_state
{
    LED_OFF,
    LED_ON,
    LED_TOGGLE,
 
};
 
typedef struct cola_device  cola_device_t;
 
struct cola_device_ops
{
    int  (*init)   (cola_device_t *dev);
    int  (*open)   (cola_device_t *dev, int oflag);
    int  (*close)  (cola_device_t *dev);
    int  (*read)   (cola_device_t *dev, int pos, void *buffer, int size);
    int  (*write)  (cola_device_t *dev, int pos, const void *buffer, int size);
    int  (*control)(cola_device_t *dev, int cmd, void *args);
 
};
 
struct cola_device
{
    const char * name;
    struct cola_device_ops *dops;
    struct cola_device *next;
};
 
/*
    驅動注冊
*/
int cola_device_register(cola_device_t *dev);
/*
    驅動查找
*/
cola_device_t *cola_device_find(const char *name);
/*
    驅動讀
*/
int cola_device_read(cola_device_t *dev,  int pos, void *buffer, int size);
/*
    驅動寫
*/
int cola_device_write(cola_device_t *dev, int pos, const void *buffer, int size);
/*
    驅動控制
*/
int cola_device_ctrl(cola_device_t *dev,  int cmd, void *arg);
 
#endif

源文件cola_device.c：

#include "cola_device.h"
#include < string.h >
#include < stdbool.h >
 
 
struct cola_device *device_list = NULL;
 
/*
    查找任務是否存在
*/
static bool cola_device_is_exists( cola_device_t *dev )
{
    cola_device_t* cur = device_list;
    while( cur != NULL )
    {
        if( strcmp(cur- >name,dev- >name)==0)
        {
            return true;
        }
        cur = cur- >next;
    }
    return false;
}
 
 
static int device_list_inster(cola_device_t *dev)
{
    cola_device_t *cur = device_list;
    if(NULL == device_list)
    {
        device_list = dev;
        dev- >next   = NULL;
    }
    else
    {
        while(NULL != cur- >next)
        {
            cur = cur- >next;
        }
        cur- >next = dev;
        dev- >next = NULL;
    }
    return 1;
}
 
/*
    驅動注冊
*/
int cola_device_register(cola_device_t *dev)
{
    if((NULL == dev) || (cola_device_is_exists(dev)))
    {
        return 0;
    }
 
    if((NULL == dev- >name) ||  (NULL == dev- >dops))
    {
        return 0;
    }
    return device_list_inster(dev);
 
}
/*
    驅動查找
*/
cola_device_t *cola_device_find(const char *name)
{
    cola_device_t* cur = device_list;
    while( cur != NULL )
    {
        if( strcmp(cur- >name,name)==0)
        {
            return cur;
        }
        cur = cur- >next;
    }
    return NULL;
}
/*
    驅動讀
*/
int cola_device_read(cola_device_t *dev,  int pos, void *buffer, int size)
{
    if(dev)
    {
        if(dev- >dops- >read)
        {
            return dev- >dops- >read(dev, pos, buffer, size);
        }
    }
    return 0;
}
/*
    驅動寫
*/
int cola_device_write(cola_device_t *dev, int pos, const void *buffer, int size)
{
    if(dev)
    {
        if(dev- >dops- >write)
        {
            return dev- >dops- >write(dev, pos, buffer, size);
        }
    }
    return 0;
}
/*
    驅動控制
*/
int cola_device_ctrl(cola_device_t *dev,  int cmd, void *arg)
{
    if(dev)
    {
        if(dev- >dops- >control)
        {
            return dev- >dops- >control(dev, cmd, arg);
        }
    }
    return 0;
}

硬件注冊方式:以LED為例，初始化接口void led_register(void)，需要在初始化中調用。

#include "stm32f0xx.h"
#include "led.h"
#include "cola_device.h"
 
 
#define PORT_GREEN_LED                 GPIOC                   
#define PIN_GREENLED                   GPIO_Pin_13              
 
/* LED亮、滅、變化 */
#define LED_GREEN_OFF                  (PORT_GREEN_LED- >BSRR = PIN_GREENLED)
#define LED_GREEN_ON                   (PORT_GREEN_LED- >BRR  = PIN_GREENLED)
#define LED_GREEN_TOGGLE               (PORT_GREEN_LED- >ODR ^= PIN_GREENLED)
 
 
static cola_device_t led_dev;
 
static void led_gpio_init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOC, ENABLE);
    GPIO_InitStructure.GPIO_Pin = PIN_GREENLED;                            
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;                     
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;                  
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                     
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;                  
    GPIO_Init(PORT_GREEN_LED, &GPIO_InitStructure);
    LED_GREEN_OFF;
}
 
static int led_ctrl(cola_device_t *dev, int cmd, void *args)
{
    if(LED_TOGGLE == cmd)
    {
        LED_GREEN_TOGGLE;
    }
    else 
    {
        
    }
    return 1;
}
 
 
static struct cola_device_ops ops =
{
    .control = led_ctrl,
};
 
void led_register(void)
{
    led_gpio_init();
    led_dev.dops = &ops;
    led_dev.name = "led";
    cola_device_register(&led_dev);
}

應用層app代碼:

#include < string.h >
#include "app.h"
#include "config.h"
#include "cola_device.h"
#include "cola_os.h"
 
static task_t timer_500ms;
static cola_device_t *app_led_dev;
 
//led每500ms狀態改變一次
static void timer_500ms_cb(uint32_t event)
{
    cola_device_ctrl(app_led_dev,LED_TOGGLE,0);
}
 
void app_init(void)
{
    app_led_dev = cola_device_find("led");
    assert(app_led_dev);
    cola_timer_create(&timer_500ms,timer_500ms_cb);
    cola_timer_start(&timer_500ms,TIMER_ALWAYS,500);
}