Use of Linux 2.4.18 kernel timer

My kernel is 2.4.18 . The Linux kernel defines a timer structure:

#include

struct timer_list

{

struct list_head list;

unsigned long expires; // Timer expiration time

unsigned long data; // passed as a parameter to the timer processing function

void (*function)(unsigned long);

};

Using this structure, we can easily use the timer in the driver.

1: Timer API function :

Initialize the timer:

void init_timer(struct timer_list * timer);

Add a timer:

void add_timer(struct timer_list * timer);

To delete a timer:

int del_timer(struct timer_list * timer);

Modify the expiration of the timer :

int mod_timer(struct timer_list *timer, unsigned long expires);

2: The general process of using the timer is:

( 1 ) Create a timer and write a timeout timer processing function ;

( 2 ) Assign values ​​to the timer 's expires , data , and function ;

( 3 ) Call add_timer to add the timer to the list;

( 4 ) When the timer expires, the function is executed;

( 5 ) In the program where timer control is involved, call del_timer or mod_timer appropriately to delete the timer or modify the timer 's expiration date .

Three: A simple example (timer.c) :

/******************************************

* Author : Cai Xiaofei *

* Date : November 27, 2008 *

* Name: timer.c *

* Description : This program is used to learn the Linux kernel *

* Basic use of timer *

*****************************************/

#include

#include

#include

#include //jiffies is defined in this header file

#include

#include

struct timer_list mytimer; // define a timer

void mytimer_ok(unsigned long arg)

{

printk("Mytimer is okn");

printk("receive data from timer: %dn",arg);

}

static int __init hello_init (void)

{

printk("hello,worldn");

init_timer(&mytimer); // Initialize the timer

mytimer.expires = jiffies+100; // Set the timeout period, 100 represents 1 second

mytimer.data = 250; // The value passed to the timer timeout function

mytimer.function = mytimer_ok; // Set timer timeout function

add_timer(&mytimer); // Add timer, timer starts to take effect

return 0;

}

static void __exit hello_exit (void)

{

del_timer(&mytimer); // Delete the timer when uninstalling the module

printk("Hello module exitn");

}

module_init(hello_init);

module_exit(hello_exit);

MODULE_AUTHOR("CXF");

MODULE_LICENSE("Dual BSD/GPL");

4: After cross-compilation, put it on the development board:

#insmod timer.o

It can be found that after one second, the timer expiration function is executed, the information is printed, and 250 is also passed correctly.

, haha!

#rmmod timer

The experiment is complete.

Five: Further understanding of the timer:

In the above timer timeout function mytimer_ok(unsigned long arg) , add the following

Code:

mytimer.expires = jiffies+100; // Set the timeout period, 100 represents 1 second

mytimer.function = mytimer_ok; // Set timer timeout function

add_timer(&mytimer); // Add timer, timer starts to take effect

After cross-compilation, put it on the development board

#insmod timer.o

It is found that the mytimer_ok function is executed once every second . This is because every time the timer expires,

It sets a new timeout again, and the new timeout function points to itself, forming a hand-off.

So it will continue to execute.

#rmmod timer

You can uninstall the module, and of course the printing will end. Note that the function keeps printing information because the timer times out.

, which will cause the timer timeout function to keep printing information when you enter the above command. Don't worry about it.

Patiently enter the above command to successfully uninstall.