linux系統的驅動層實現原理

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?
#include?
?
?
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?
#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);
}

這樣app.c文件中就不需要調用led.h頭文件了，rtt就是這樣實現的

四、總結

這樣就可以實現軟硬件分層了，是不是非常好用！

編輯：黃飛

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