1. Compile / install the driver
- In the Linux system, the driver usually kernel module program structure to be encoded. Therefore, compile / install a driver, its essence is to compile / install a kernel module. The following sample code is copied to a Linux system:
- memdev.c
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
int dev1_registers[5];
int dev2_registers[5];
struct cdev cdev;
dev_t devno;
/*文件打开函数*/
int mem_open(struct inode *inode, struct file *filp)
{
/*获取次设备号*/
int num = MINOR(inode->i_rdev);
if (num==0)
filp->private_data = dev1_registers;
else if(num == 1)
filp->private_data = dev2_registers;
else
return -ENODEV; //无效的次设备号
return 0;
}
/*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{
return 0;
}
/*读函数*/
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
int ret = 0;
int *register_addr = filp->private_data; /*获取设备的寄存器基地址*/
/*判断读位置是否有效*/
if (p >= 5*sizeof(int))
return 0;
if (count > 5*sizeof(int) - p)
count = 5*sizeof(int) - p;
/*读数据到用户空间*/
if (copy_to_user(buf, register_addr+p, count))
{
ret = -EFAULT;
}
else
{
*ppos += count;
ret = count;
}
return ret;
}
/*写函数*/
static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
int ret = 0;
int *register_addr = filp->private_data; /*获取设备的寄存器地址*/
/*分析和获取有效的写长度*/
if (p >= 5*sizeof(int))
return 0;
if (count > 5*sizeof(int) - p)
count = 5*sizeof(int) - p;
/*从用户空间写入数据*/
if (copy_from_user(register_addr + p, buf, count))
ret = -EFAULT;
else
{
*ppos += count;
ret = count;
}
return ret;
}
/* seek文件定位函数 */
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{
loff_t newpos;
switch(whence) {
case SEEK_SET:
newpos = offset;
break;
case SEEK_CUR:
newpos = filp->f_pos + offset;
break;
case SEEK_END:
newpos = 5*sizeof(int)-1 + offset;
break;
default:
return -EINVAL;
}
if ((newpos<0) || (newpos>5*sizeof(int)))
return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
/*文件操作结构体*/
static const struct file_operations mem_fops =
{
.llseek = mem_llseek,
.read = mem_read,
.write = mem_write,
.open = mem_open,
.release = mem_release,
};
/*设备驱动模块加载函数*/
static int memdev_init(void)
{
/*初始化cdev结构*/
cdev_init(&cdev, &mem_fops);
/* 注册字符设备 */
alloc_chrdev_region(&devno, 0, 2, "memdev");
cdev_add(&cdev, devno, 2);
}
/*模块卸载函数*/
static void memdev_exit(void)
{
cdev_del(&cdev); /*注销设备*/
unregister_chrdev_region(devno, 2); /*释放设备号*/
}
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);- Makefile (note the kernel source code should be changed to your own path):
obj-m := memdev.o
KDIR := /home/S4_a/part3/lesson3/lesson-2440/linux-mini2440
all :
make -C $(KDIR) M=$(PWD) CROSS_COMPILE=arm-linux- ARCH=arm
clean:
rm -f *.o *.ko *.order *.symvers *.mod.c
- Compile:
- #make
- Memdev.ko copied to the development board and then installs:
- #insmod memdev.ko
2. Create a device file
- This figure may be known by the application of the device driver is accessed through the device file to carry out, the device as a media file as the applications and device drivers linked together.
- By character device file, the application can use the corresponding character device driver to control the character device .
- Create a character device file, there are two general ways:
- 1. Use the mknod: mknod / dev / filename c major number minor device numbers
- It has four parameters, the first is the name of a character device file needs to be created, small c for character device file, the major number to establish a connection and device drivers, they need to use the same major number, so how View device number mendev driver uses just installed it? Development board input: #cat proc / Devices
- 2 shows the information, the first column is the major number, the second column is the name of the device driver. It should be 253, the minor number of non-negative number can be taken, it is generally between 0 and 255.
- Now we create a file in the device development board (device file name and existing conflicts can not):
- #mknod /dev/memdev0 c 253 1
- And then view the dev: #ls / dev
- 2. Create function (subsequent description) in the driver
- 1. Use the mknod: mknod / dev / filename c major number minor device numbers
3. Access Device
- The device file is actually a memory operation because the actual hardware device access, and ultimately all access to device registers, the memory access in a few units to achieve the same effect.
- Write an application to access the device files:
- Write device: write_mem.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd = 0;
int src = 2013;
fd = open("/dev/memdev0", O_RDWR);
write(fd, &src, sizeof(int));
close(fd);
return 0;
}
- Reading equipment: read_mem.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd = 0;
int dst = 0;
fd = open("/dev/memdev0", O_RDWR);
read(fd, &dst, sizeof(int));
printf("dst is %d\n",dst);
return 0;
}
- Using the arm-linux-gcc compiler generated files are copied to the development board, and then executed, if an error is found:
- ~bin/sh: ./write_mem not found
- In fact, this is not write_mem can not find the file, but it relies on the library can not be found, you can use:
- #arm-readelf -d write_mem
- -d indicates that the query dynamic link library to view it depends on the library
- This method is time 2 minutes, 1 is a copy of the libraries it depends lib directory development board, the connector 2 with static at compile time:
- #arm-linux-gcc -static write_mem.c -o write_mem
- Reading equipment: read_mem.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd = 0;
int dst = 0;
fd = open("/dev/memdev0", O_RDWR);
read(fd, &dst, sizeof(int));
printf("dst is %d\n",dst);
return 0;
}
