Linux驱动程序开发

1. 设置一个模块

在Linux系统中，每个驱动程序都可以看作是一个独立的模块。驱动开发的第一步是创建一个模块，用来存放驱动的相关代码。

1.1 模块的入口和出口
  
模块的入口和出口是通过函数接口实现的。在Linux中，模块的入口函数需要注册到内核中，以便系统能够加载和卸载该模块。
  
static int __init gec6818_led_init(void){      // 安装驱动  }  static void __exit gec6818_led_exit(void){      // 卸载驱动  }  module_init(gec6818_led_init);  module_exit(gec6818_led_exit);

1.2 模块的描述
  
// 模块描述

#modinfo led_drv.ko

2. 定义一个cdev

cdev是Linux内核中用于描述字符设备的数据结构。在大多数字符设备驱动中，使用cdev模型来实现设备的注册和操作。

static struct cdev led_cdev;

3. 申请设备号

设备号是字符设备驱动的唯一标识符。在Linux系统中，可以通过申请设备号来注册字符设备。

if(led_major == 0){          ret = alloc_chrdev_region(&led_dev_num, led_minor, 1, "led_device");      } else{          led_dev_num = MKDEV(led_major, led_minor);          ret = register_chrdev_region(led_dev_num, 1, "led_device");      }      if(ret < 0){          printk("can not get led device number\n");          return ret;      }

4. 提供文件操作接口

为了让应用程序能够与驱动程序交互，需要定义文件操作接口（file operations）。这些接口包括open、write、release等函数。

4.1 open函数
  
static int gec6818_led_open(struct inode *inode, struct file *filp){      printk("led driver is opening\n");      return 0;  }
  
4.2 write函数
  
static ssize_t gec6818_led_write(struct file *filp, const char __user *buf, size_t len, loff_t *off){      // 接收应用程序写下来的数据，并用这些数据来控制LED灯      // 定义一个数据协议：应用程序写下来的数据有两个字节      // buf[1] -> 某一站灯：8, 9, 10, 11      // buf[0] -> LED灯的状态：1---亮，0---灯灭      ret;      char led_flag[2];      if(len != 2){          return -EINVAL;      }      ret = copy_from_user(led_flag, buf, len);      if(ret < 0){          return -EFAULT;      }      switch(led_flag[1]){          case 8:              // GPIOC17              if(led_flag[0] == 1){                  *(unsigned int *)GPIOCOUT &= ~(1<<17);              } else if(led_flag[0] == 0){                  *(unsigned int *)GPIOCOUT |= (1<<17);              } else{                  return -EINVAL;              }              break;          case 9:              // GPIOC8              if(led_flag[0] == 1){                  *(unsigned int *)GPIOCOUT &= ~(1<<8);              } else if(led_flag[0] == 0){                  *(unsigned int *)GPIOCOUT |= (1<<8);              } else{                  return -EINVAL;              }              break;          case 10:              // GPIOC7              if(led_flag[0] == 1){                  *(unsigned int *)GPIOCOUT &= ~(1<<7);              } else if(led_flag[0] == 0){                  *(unsigned int *)GPIOCOUT |= (1<<7);              } else{                  return -EINVAL;              }              break;          case 11:              // GPIOC12              if(led_flag[0] == 1){                  *(unsigned int *)GPIOCOUT &= ~(1<<12);              } else if(led_flag[0] == 0){                  *(unsigned int *)GPIOCOUT |= (1<<12);              } else{                  return -EINVAL;              }              break;          default:              return -EINVAL;      }      return len;  }
  
4.3 release函数
  
static int gec6818_led_release(struct inode *inode, struct file *filp){      printk("led driver is closing\n");      return 0;  }
  
static const struct file_operations gec6818_led_fops = {      .owner = THIS_MODULE,      .write = gec6818_led_write,      .open = gec6818_led_open,      .release = gec6818_led_release,  };

5. 初始化cdev并将其加入内核

// 4. 初始化cdev      cdev_init(&led_cdev, &gec6818_led_fops);      // 5. 将初始化好的cdev加入内核      ret = cdev_add(&led_cdev, led_dev_num, 1);      if(ret < 0){          printk("cdev add error\n");          unregister_chrdev_region(led_dev_num, 1);          return -EBUSY;      }

6. 创建class和device

// 创建class  led_class = class_create(THIS_MODULE, "led_class");  if(IS_ERR(led_class)){      ret = PTR_ERR(led_class);      printk("led driver class create error\n");      cdev_del(&led_cdev);      unregister_chrdev_region(led_dev_num, 1);      return ret;  }  // 创建device  led_device = device_create(led_class, NULL, led_dev_num, NULL, "led_drv");  if(IS_ERR(led_device)){      ret = PTR_ERR(led_device);      printk("led driver device create error\n");      class_destroy(led_class);      cdev_del(&led_cdev);      unregister_chrdev_region(led_dev_num, 1);      return ret;  }

7. 获取物理地址对应的虚拟地址

// 8. 申请物理内存区  led_res = request_mem_region(0xC001C000, 0x1000, "GPIOC_MEM");  if(led_res == NULL){      printk("request memory error\n");      device_destroy(led_class, led_dev_num);      class_destroy(led_class);      cdev_del(&led_cdev);      unregister_chrdev_region(led_dev_num, 1);      return -EBUSY;  }  // 9. IO内存的动态映射  GPIOC_BASE = ioremap(0xC001C000, 0x1000);  if(GPIOC_BASE == NULL){      printk("ioremap error\n");      release_mem_region(0xC001C000, 0x1000);      device_destroy(led_class, led_dev_num);      class_destroy(led_class);      cdev_del(&led_cdev);      unregister_chrdev_region(led_dev_num, 1);      return -EFAULT;  }  GPIOCOUT = GPIOC_BASE + 0x00; // 0x00  GPIOCOUTENB = GPIOC_BASE + 0x04; // 0x04  GPIOCALTFN0 = GPIOC_BASE + 0x20; // 0x20  GPIOCALTFN1 = GPIOC_BASE + 0x24; // 0x24

8. 通过虚拟地址访问寄存器（裸机方法）

// LED的初始化，通过虚拟地址-->物理地址-->寄存器-->控制GPIO  *(unsigned int *)GPIOCALTFN0 &= ~(3<<24)|(3<<16)|(3<<14));  *(unsigned int *)GPIOCALTFN0 |= (1<<24)|(1<<16)|(1<<14);  *(unsigned int *)GPIOCALTFN1 &= ~(3<<2);  *(unsigned int *)GPIOCALTFN1 |= (1<<2);  *(unsigned int *)GPIOCOUTENB |=((1<<17) + (1<<12) + (1<<8) + (1<<7));  *(unsigned int *)GPIOCOUT |=((1<<17) + (1<<12) + (1<<8) + (1<<7));

思考

如何将一个数的第20位和第10位设置为1，而其他位保持不变？

a |= (1<<20);  a |= (1<<10);

等价于：

a |= ((1<<20) + (1<<10));