嵌入式底层开发和应用层开发,嵌入式系统分层

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 <string.h>#include <stdbool.h>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 <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！

五、代码下载链接

gitlib:https://gitee.com/schuck/cola_os