Linux character Device driver Development Basics (i)--writing simple LED device driver __linux

Now, let's write our own first character device driver--light LEDs. (Imperfect, back to perfect)

Hardware platform: Exynos4412 (FS4412)

Writing the drive is divided into the following steps:

A--View the schematic, data manual, understand the equipment operation method;

B-Find a similar driver in the kernel, develop it as a template, and sometimes need to start from scratch;

C-Implement driver initialization: For example, register the driver with the kernel so that the application can pass in the filename and the kernel will find the appropriate driver;

D--The design of the operation to be implemented, such as open, close, read, write and other functions;

e-To implement interrupt services (interrupts are not required for each device driver);

F--Compile the driver into the kernel or load it with the INSMOD command;

g--test driver;

Here is a light LED driver:

The first step, of course, is to view the manual, view the schematic diagram, find the corresponding register;

To view the manual, the four led registers are:

Led2

Gpx2con 0X11000C40
Gpx2dat 0X11000C44

led3

Gpx1con 0X11000C20
Gpx1dat 0X11000C24

led4 3-4 3-5

Gpf3con 0x114001e0
Gpf3dat 0x114001e4

Here to note : ARM architecture is IO memory, must be mapped ioremap (); Its role is the mapping of physical memory to virtual memory . Using the Writel readl These two functions, the detailed explanation will not be on the back, look at the simple usage first:

Take LED2 as an example, the following is address mapping and reading and writing:

int *pgpx2con  ;
int *pgpx2dat;

Pgpx2con = Ioremap (Gpx2con, 4);
Pgpx2dat = Ioremap (gpx2dat,4);
Readl (Pgpx2con);
Writel (0x01, Pgpx2dat);

Here is the driver, which will be more complete later

#include <linux/module.h> #include <linux/fs.h> #include <linux/cdev.h> #include <linux/device.h
> #include <asm/io.h> #include <asm/uaccess.h> static int major = 250;
static int minor=0;
Static dev_t Devno;
static struct class *cls;

static struct device *test_device; #define GPX2CON 0x11000c40 #define GPX2DAT 0x11000c44 #define GPX1CON 0x11000c20 #define GPX1DAT 0x11000c2
4 #define GPF3CON 0x114001e0 #define GPF3DAT 0x114001e4 static int *pgpx2con;

static int *pgpx2dat;
static int *pgpx1con;

static int *pgpx1dat;
static int *pgpf3con;

static int *pgpf3dat;

void fs4412_led_off (int num); void fs4412_led_on (int num) {switch (num) {case 1:writel (READL (Pgpx2dat) | (
			0x1<<7), Pgpx2dat);
		Break Case 2:writel (Readl (Pgpx1dat) | (			
			0x1<<0), Pgpx1dat);			
		Break Case 3:writel (Readl (Pgpf3dat) | (	
			0x1<<4), Pgpf3dat);
		Break Case 4:writel (Readl (Pgpf3dat) | ( 0X1&LT;&LT;5), Pgpf3daT);	
		Break
			Default:fs4412_led_off (1);
			Fs4412_led_off (2);
			Fs4412_led_off (3);
			Fs4412_led_off (4);
			
	Break 
			} void Fs4412_led_off (int num) {switch (num) {case 1:writel (Readl (Pgpx2dat) & (~ (0x1<<7)), Pgpx2dat);
		Break			
			Case 2:writel (Readl (Pgpx1dat) & (~ (0x1<<0)), Pgpx1dat);			
		Break	
			Case 3:writel (Readl (Pgpf3dat) & (~ (0x1<<4)), Pgpf3dat);
		Break			
			Case 4:writel (Readl (Pgpf3dat) & (~ (0x1<<5)), Pgpf3dat);			
	Break
	} static int Led_open (struct inode *inode, struct file *filep) {//open fs4412_led_off (1);
	Fs4412_led_off (2);
	Fs4412_led_off (3);	
	Fs4412_led_off (4);
return 0;
	static int led_release (struct inode *inode, struct file *filep) {//close fs4412_led_off (1);
	Fs4412_led_off (2);
	Fs4412_led_off (3);	
	Fs4412_led_off (4);
return 0;

Static ssize_t led_read (struct file *filep, char __user *buf, size_t len, loff_t *pos) {return 0;} Static ssize_t led_write (struct file *Filep, const char __user *buf, size_t len, loff_t *pos) {int led_num;
	if (len!=4) {return-einval;	
	} if (Copy_from_user (&led_num,buf,len)) {return-efault;
	} fs4412_led_on (Led_num);

	PRINTK ("Led_num =%d \ n", led_num);
return 0; static struct file_operations hello_ops= {. open = Led_open,. Release = Led_release,. Read = Led_read,. WRI

Te = Led_write,};
	static void Fs4412_led_init (void) {Pgpx2con = Ioremap (gpx2con,4);

	Pgpx2dat = Ioremap (gpx2dat,4);
	Pgpx1con = Ioremap (gpx1con,4);

	Pgpx1dat =ioremap (gpx1dat,4);
	Pgpf3con = Ioremap (gpf3con,4);

	Pgpf3dat =ioremap (gpf3dat,4); Writel (Readl (Pgpx2con) & ~ (0xf<<28) | (
	0x1<<28), Pgpx2con); Writel (Readl (Pgpx1con) & ~ (0xf<<0) | (	
	0x1<<0), Pgpx1con); Writel (Readl (Pgpf3con) & ~ (0xff<<16) | (	
0X11&LT;&LT;16), Pgpf3con);	
	static int led_init (void) {int ret;
	Devno = Mkdev (Major,minor);

	ret = Register_chrdev (Major, "led", &hello_ops); CLS = Class_creatE (This_module, "MyClass");
		if (Is_err (CLS)) {Unregister_chrdev (Major, "led");
	Return-ebusy; } Test_device = Device_create (Cls,null,devno,null, "led");//mknod/dev/hello if (Is_err (Test_device)) {Class_destroy (c
		LS);
		Unregister_chrdev (Major, "led");
	Return-ebusy;
	} fs4412_led_init ();
return 0;
	} void Fs4412_led_unmap (void) {Iounmap (Pgpx2con);

	Iounmap (Pgpx2dat);
	Iounmap (Pgpx1con);

	Iounmap (Pgpx1dat);
	Iounmap (Pgpf3con);
Iounmap (Pgpf3dat);
	} static void Led_exit (void) {Fs4412_led_unmap ();
	Device_destroy (CLS,DEVNO);	
	Class_destroy (CLS);
	Unregister_chrdev (Major, "led");
PRINTK ("Led_exit \ n");
} module_license ("GPL");
Module_init (Led_init);
 Module_exit (Led_exit);

Test program:

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

Main ()
{
	int fd,i,lednum;

	FD = open ("/dev/led", O_RDWR);
	if (fd<0)
	{
		perror ("Open fail \ n");
		return;
	}
	for (i=0;i<100;i++)
	{
		lednum=0;
		Write (fd,&lednum,sizeof (int));
		Lednum = i%4+1;
		Write (fd,&lednum,sizeof (int));	
		Sleep (1);
	}
	Close (FD);
}

Makefile

Ifneq  ($ (kernelrelease),)
obj-m:=hello.o
$ (Info "2nd")
else
#KDIR: =/lib/modules/$ ( Shell uname-r)/build
kdir: =/home/xiaoming/linux-3.14-fs4412
pwd:=$ (Shell PWD) all
:
	$ (info) 1st ")
	Make-c $ (kdir) m=$ (PWD) modules arm-none-linux-gnueabi-gcc test.c
	sudo cp Hello.ko a.out/rootfs/ test/clean
:
	rm-f *.ko *.o *.symvers *.mod.c *.mod.o *.order
endif

After the compilation finishes, copy A.out and Hello.ko to the Development Board:

# Insmod Hello.ko

#mknod/dev/hello C 250 0

#./a.out

will see the effect of the happy lantern.

The rear will be perfect for that drive.