环境配置、内核配置、字符型驱动设备

配置交叉编译环境

arm-linux-gcc -v交叉编译

1、将版本配置为4.4.3

2、内核一部分

外设（时钟配置、GPIO、串口）

3、配置环境（将板载设置为2440）

ubuntu下查看函数原码

ctag -R 路径
设置完成后进主

函数将光标停在函数名字处按Ctrl + }可跳转至函数 Ctrl + t回到原位置

配置内核

出现异常

sudo apt-get install u-boot-tools

用下面这个命令下载一个u-boot-tools

完成之后重新将uImage下载至板子上

每次配置完（make menuconfig）后要编译+拷贝到tftpboot下

字符设备驱动程序

1、框架格式

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>


int _init first_dirver_init(void)
{
    printk("first_dirver_init OK\n");
}

void _exit first_dirver_exit(void)
{
    printk("first_dirver_exit OK\n");
}

module_init(first_dirver_init);
module_exit(first_dirver_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("QuJunjie");

2、第一种编译流程（使用Makefile编译）

若需要添加文件，只需在Makefile中添加一个目标文件即可

3、加入驱动

4、将模块加载到板子上验证程序

第二种编译流程

函数接口

int register_chardev( unsigned int major, const char *name, const struct file_operations *fops)

设备号：设备编号（在内核中区分设备的一个数）

主设备号（driver）：驱动程序本身

子设备号（device）：使用了驱动程序的设备

注：同一个主设备号可能有多个子设备号，不允许有多个同名的主设备号，同一个主设备号不能有多个相同的设备

参数：

major：主设备号

name：设备名字

fops：结构体（file_operations）指针

struct file_operations {
   struct module *owner;
   loff_t (*llseek) (struct file *, loff_t, int);
   ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
   ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
   ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
   ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
   int (*readdir) (struct file *, void *, filldir_t);
   unsigned int (*poll) (struct file *, struct poll_table_struct *);
   int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
   long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
   long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
   int (*mmap) (struct file *, struct vm_area_struct *);
   int (*open) (struct inode *, struct file *);
   int (*flush) (struct file *, fl_owner_t id);
   int (*release) (struct inode *, struct file *);
   int (*fsync) (struct file *, struct dentry *, int datasync);
   int (*aio_fsync) (struct kiocb *, int datasync);
   int (*fasync) (int, struct file *, int);
   int (*lock) (struct file *, int, struct file_lock *);
   ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
   unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
   int (*check_flags)(int);
   int (*flock) (struct file *, int, struct file_lock *);
   ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
   ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
   int (*setlease)(struct file *, long, struct file_lock **);
};

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>

#define DEVICE_MAJOR 200
#define DEVICE_NAME "first_driver"

int  first_driver_open(struct inode *node, struct file *fp)
{
    printk("first_driver_open OK\n");
    return 0;
}

ssize_t first_driver_read(struct file *fp, char __user *user_buffer, size_t len, loff_t *offset)
{
    printk("first_driver_read OK\n");
    return 0;
}

ssize_t first_driver_write(struct file *fp, const char __user *user_buffer, size_t len, loff_t *offset)
{
    printk("first_driver_write OK\n");
    return 0;
}

int first_driver_release(struct inode *node, struct file *fp)
{
    printk("first_driver_release OK\n");
    return 0;
}

static struct file_operations fops = 
{
    .owner = THIS_MODULE,
    .open = first_driver_open,
    .read = first_driver_read,
    .write = first_driver_write,
    .release = first_driver_release
};

int __init first_dirver_init(void)
{
    register_chrdev(DEVICE_MAJOR, DEVICE_NAME, &fops);
    printk("first_dirver_init OK\n");
    return 0;
}

void __exit first_dirver_exit(void)
{
    unregister_chrdev(DEVICE_MAJOR, DEVICE_NAME);
    printk("first_dirver_exit OK\n");
}

module_init(first_dirver_init);
module_exit(first_dirver_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("QuJunjie");