Wei Dongshan uboot_kernel_root file system study notes 5.4~5.5-Lesson 005_Character device driver_Section 004~005__Character device driver LED driver_Operation LED

A few knowledge points of writing actual driver

1. Virtual address mapping-ioremap function/iounmap

Virtual address and MMU:

eg：
分配地址代码gpio_va = ioremap(0x56000000, 0x100000);//0x56000000起始地址，0x100000长度
释放地址代码iounmap(gpio_va);//

2. Value transfer between user program and driver

eg:
char __user *buf；//用户空间变量
static unsigned char key_val;//内核空间变量
//向用户程序传值函数
copy_to_user(buf, &key_val, count);//count表示字符长度
//向内核空间传值函数
copy_from_user(&key_val,buf,count)

3. User program main function entry parameter description

int argc: The number of parameters passed in. eg: When calling the program, the input ./app onis two parameters
char **argv: the character array stored by the incoming parameter.

int main(int argc, char **argv)

4. Use of
   minor device number The function corresponding to the minor device number is controlled by the driver's open/read/write function. See the full source code:JZ2440V3\drivers_and_test\leds

(1) Usage of driver open function

//struct inode *inode：次设备号
static int first_drv_open(struct inode *inode, struct file *file)
{
	//获取次设备号，其对应的功能由驱动程序控制
	int minor = MINOR(inode->i_rdev);
	return 0;
}

(2) Usage of driver init The
following code iis the sub-device number, and the name of the sub-device number is 100ask_led%d.

for (i = 0; i < LED_NUM; i++)
	device_create(led_class, NULL, MKDEV(major, i), NULL, "100ask_led%d", i); /* /dev/100ask_led0,1,... */

(3) After the development board is loaded with the driver program, a /dev/folder corresponding to each minor device number appears in the directory

5. top command The
   top command is a commonly used performance analysis tool under Linux, which can display the resource occupancy status of each process in the system in real time, similar to the task manager of Windows.