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一、前言
以STM32为例，打开网络上下载的例程或者是购买开发板自带的例程，都会发现应用层中会有stm32f10x.h或者stm32f10x_gpio.h，这些文件严格来时属于硬件层的，如果软件层出现这些文件会显得很乱。
使用过Linux的童鞋们肯定知道linux系统无法直接操作硬件层，打开linux或者rt_thread代码会发现代码中都会有device的源文件，没错，这就是驱动层。
二、实现原理
原理就是将硬件操作的接口全都放到驱动链表上，在驱动层实现device的open、read、write等操作。当然这样做也有弊端，就是驱动find的时候需要遍历一遍驱动链表，这样会增加代码运行时间。
三、代码实现
国际惯例，写代码先写头文件。rt_thread中使用的是双向链表，为了简单在这我只用单向链表。有兴趣的可以自行研究rt_thread
头文件接口:
本次只实现如下接口，device_open 和device_close等剩下的接口可以自行研究。这样就可以在应用层中只调用如下接口可实现：
/* 驱动注册 */ int cola_device_register(cola_device_t *dev); /* 驱动查找 */ cola_device_t *cola_device_find(const char *name); /* 驱动读 */ int cola_device_read(cola_device_t *dev, int pos, void *buffer, int size); /* 驱动写 */ int cola_device_write(cola_device_t *dev, int pos, const void *buffer, int size); /* 驱动控制 */ int cola_device_ctrl(cola_device_t *dev, int cmd, void *arg);;
头文件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; }; /* 驱动注册 */ int cola_device_register(cola_device_t *dev); /* 驱动查找 */ cola_device_t *cola_device_find(const char *name); /* 驱动读 */ int cola_device_read(cola_device_t *dev, int pos, void *buffer, int size); /* 驱动写 */ int cola_device_write(cola_device_t *dev, int pos, const void *buffer, int size); /* 驱动控制 */ 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; /* 查找任务是否存在 */ 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; } /* 驱动注册 */ 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); } /* 驱动查找 */ 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; } /* 驱动读 */ 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; } /* 驱动写 */ 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; } /* 驱动控制 */ 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; }
硬件注册方式:以LED为例，初始化接口void led_register(void)，需要在初始化中调用。
#include "stm32f0xx.h" #include "led.h" #include "cola_device.h" #define PORT_GREEN_LED GPIOC #define PIN_GREENLED GPIO_Pin_13 /* LED亮、灭、变化 */ #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); }
应用层app代码:
#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状态改变一次 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); }
这样app.c文件中就不需要调用led.h头文件了，rtt就是这样实现的。
四、总结
这样就可以实现软硬件分层了，是不是非常好用！
审核编辑：刘清
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