簡介

led燈成本很低，操控簡單，在嵌入式產品中不可或缺，可以作為除錯標識，狀態指示等等，高階用法還可以作為呼吸燈進一步增強其美觀性。本章介紹只控制led燈的亮滅，tiny4412開發板有四個LED燈在核心板上供使用者操作，led燈亮滅靠cpu IO口輸出電平，具體操控看實際電路。

電路圖

在tiny4412開發板上，led燈電路如下：

與CPU連線如下：

可以看到CPU相應引腳輸出相關電平，就可以控制燈的亮滅，cpu引腳輸出低電平led燈亮，接下來就是操作相關暫存器，這些暫存器與GPM4相關，一個是控制暫存器，一個是資料暫存器。
命令暫存器

資料暫存器

驅動程式碼

//驅動程式碼
#include<linux/kernel.h>
#include<linux/module.h>
#include<linux/init.h>
#include <asm/io.h>
#include <asm/uaccess.h>

#include<linux/fs.h>
#include<linux/cdev.h>
#include<linux/kdev_t.h>
#include<linux/slab.h>
#include<linux/device.h> //增加自動建立裝置標頭檔案
 

#include<linux/uaccess.h>
//定義字元裝置結構體
static struct cdev *leddriver_cdev;
//定義裝置號（包含主次）
static dev_t leddriver_num=0;
//定義裝置類
static struct class *leddriver_class;
//定義裝置結構體
static struct device *leddriver_device;
//定義錯誤返回型別
static int  err;
//定義裝置名稱
#define LEDDRIVER_NAME "myled"

#define GPM4CON_ADDR 0x110002E0 
 

#define GPM4DAT_ADDR 0X110002E4

static volatile unsigned long *gpm4con=NULL;  
static volatile unsigned long *gpm4dat=NULL;

#define GPM4CON *gpm4con
#define GPM4DAT *gpm4dat


static

ssize_t leddriver_read(struct file *file, char __user *usr, size_t size, loff_t *loft)
{
    unsigned char LED_STATUE;


 copy_from_user(&LED_STATUE,usr,1);
 printk("leddriver read is %d\r\n",LED_STATUE);

  switch(LED_STATUE)
    {
 case 10:GPM4DAT |= (0x1<<0);break;
 case 11:GPM4DAT &=~(0X1<<0);break;
 case 20:GPM4DAT |= (0x1<<1);break;
 case 21:GPM4DAT &=~(0X1<<1);break;
 case 30:GPM4DAT |= (0x1<<2);break;
 case 31:GPM4DAT &=~(0X1<<2);break;
 case 40:GPM4DAT |= (0x1<<3);break;
 case 41:GPM4DAT &=~(0X1<<3);break;

  }

  return 0;
}

ssize_t leddriver_write (struct file *file, const char __user *usr, size_t size, loff_t *loft)
{
  printk("leddriver write is ok\r\n");
  return 0;
}

int leddriver_open (struct inode *node, struct file *file)
{
  printk("files open is success\r\n");
  return 0;
}

int leddriver_release (struct inode *node, struct file *file)
{
  printk("leddriver close is success\r\n");
  return 0;
}

//檔案操作函式結構體
static struct file_operations leddriver_fops={
.owner=THIS_MODULE,
    .open=leddriver_open,
    .release=leddriver_release,
    .read=leddriver_read,
    .write=leddriver_write,
};

static __init int ldedriver_init(void)
{
//分配字元裝置結構體，前面只是定義沒有分配空間
leddriver_cdev=cdev_alloc();
//判斷分配成功與否
if(leddriver_cdev==NULL)
{
  err=-ENOMEM;
  printk("leddriver alloc is err\r\n");
  goto err_leddriver_alloc;
}

//動態分配裝置號
err=alloc_chrdev_region(&leddriver_num, 0, 1, LEDDRIVER_NAME);
//錯誤判斷
if(err<0)
{
  printk("alloc leddriver num is err\r\n");
  goto err_alloc_chrdev_region;
}

//初始化結構體
cdev_init(leddriver_cdev,&leddriver_fops);

//驅動註冊
err=cdev_add(leddriver_cdev,leddriver_num,1);
if(err<0)
{
  printk("cdev add is err\r\n");
  goto err_cdev_add;
}

//建立裝置類
leddriver_class=class_create(THIS_MODULE,"led_class");
  err=PTR_ERR(leddriver_class);
  if(IS_ERR(leddriver_class))
    {
printk("leddriver creat class is err\r\n");
goto err_class_create;
  }


//建立裝置
  leddriver_device=device_create(leddriver_class,NULL, leddriver_num,NULL, "leddevice");
 err=PTR_ERR(leddriver_device);
    if(IS_ERR(leddriver_device))
        {
printk("leddriver device creat is err \r\n");
goto err_device_create;
    }
//led燈暫存器配置
    gpm4con=ioremap(GPM4CON_ADDR, 4);
    gpm4dat=ioremap(GPM4DAT_ADDR, 4);

    GPM4CON &= ~(0XFFFF<<0);
    GPM4CON |= (0x1111<<0);
    GPM4DAT |= (0XF<<0);

printk("leddriver init is success\r\n");
return 0;

err_device_create:
class_destroy(leddriver_class);
err_class_create:
 cdev_del(leddriver_cdev);
err_cdev_add:
unregister_chrdev_region(leddriver_num, 1);

err_alloc_chrdev_region:
kfree(leddriver_cdev);

err_leddriver_alloc:
return err;

}

static __exit void leddriver_exit(void)
{
    //取消對映
    iounmap(gpm4con);
    iounmap(gpm4dat);

  device_destroy(leddriver_class,leddriver_num);
  class_destroy(leddriver_class);
  cdev_del(leddriver_cdev);
  unregister_chrdev_region(leddriver_num, 1);
  printk("leddriver is exit\r\n");
}


module_init(ldedriver_init);
module_exit(leddriver_exit);
MODULE_LICENSE("GPL");

app程式碼

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc,char *argv[])
{
  unsigned char LED_STATUE,shi;
  int ge;

  int led_fp;

  led_fp = open(argv[1],O_RDWR);
 // LED_STATUE=(unsigned char)atoi(argv[2]);
 while(1)
    {
  for(shi=1;shi<=4;shi++)
    {
      for(ge=1;ge>=0;ge--)
        {
      LED_STATUE=shi*10+ge;
      read(led_fp,&LED_STATUE,1);
      sleep(1);
    }
    }
    }
  close(led_fp);
}

Makefile

KERN_DIR = /zhangchao/linux3.5/linux-3.5
all:
    make -C $(KERN_DIR) M=`pwd` modules
cp:
    cp ./* /zhangchao/rootfs/zhangchao
clean:
    make -C $(KERN_DIR) M=`pwd` modules clean
    rm -rf modules.order
obj-m += led.o

說明
雖然呼叫read write函式，來實現對燈的控制，並不符合函式操作規範，這裡的led燈並不能看做是一個檔案操作，並沒有體現出linux一切皆檔案，並不符合標準的檔案操作方法，規範化寫法將在後面給出。