0. 测试环境
Linux 2.6.39 AT91SAM9G45
1. 定时器简单的测试例子
#include
#include
MODULE_LICENSE("GPL");
struct timer_list tm;
static int num;
static void func()
{
num++;
mod_timer(&tm, jiffies + HZ);
printk("Hello, timer :%d\n", num);
}
static int timer_init(void)
{
num = 0;
init_timer(&tm);
tm.expires = jiffies + HZ;
tm.function = func;
add_timer(&tm);
return 0;
}
static void timer_exit(void)
{
del_timer(&tm);
printk("remove timer\n");
}
module_init(timer_init);
module_exit(timer_exit);
Makefile
obj-m := timer.o
KERNEL := /Android/linux-2.6.39-android_altus
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNEL) M=$(PWD) modules
.PHONEY:clean
clean:
rm -f *.o *.ko
insmod timer.ko
使用命令cat /proc/kmsg查看效果
2. jiffies和jiffies_64变量定义的位置
http://bbs.chinaunix.net/archiver/tid-1982818.html?page=2
jiffies_64获取的驱动部分代码
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define JIFFIES_64_DEVICE_NODE_NAME "jiffies_64"
#define JIFFIES_64_DEVICE_CLASS_NAME "jiffies_64"
#define JIFFIES_64_DEVICE_FILE_NAME "jiffies_64"
static unsigned long long value_of_jiffies_64;
static dev_t devno;
static struct class *jiffies_64_class;
static struct cdev jiffies_64_dev;
static ssize_t jiffies_64_read(struct file *filp, char __user *buf, size_t size, loff_t *f_pos)
{
if (buf == NULL || size != sizeof(value_of_jiffies_64))
return -EINVAL;
if (value_of_jiffies_64 == 0)
value_of_jiffies_64 = get_jiffies_64();
if (copy_to_user(buf, &value_of_jiffies_64, sizeof(value_of_jiffies_64)))
return -ENOMEM;
memset(&value_of_jiffies_64, 0, sizeof(value_of_jiffies_64));
return 0;
}
static ssize_t jiffies_64_open(struct inode *inode, struct file *filp)
{
return 0;
}
static ssize_t jiffies_64_release(struct inode *inode, struct file *filp)
{
return 0;
}
static struct file_operations jiffies_64_fops = {
.owner = THIS_MODULE,
.open = jiffies_64_open,
.read = jiffies_64_read,
.release = jiffies_64_release,
};
static ssize_t jiffies_64_val_show(struct device *dev, struct device_attribute *attr, char *buf);
static DEVICE_ATTR(val, S_IRUGO | S_IWUSR, jiffies_64_val_show, NULL);
static ssize_t jiffies_64_val_show(struct device *dev, struct device_attribute *attr, char *buf)
{
return snprintf(buf, PAGE_SIZE, "%lld\n", value_of_jiffies_64);
}
static int __init jiffies_64_init(void)
{
int err = -1;
struct device *device = NULL;
err = alloc_chrdev_region(&devno, 0, 1, JIFFIES_64_DEVICE_NODE_NAME);
if (err < 0) {
printk(KERN_ALERT"Failed to alloc char dev region.\n");
goto fail;
}
/* setup cdev */
cdev_init(&jiffies_64_dev, &jiffies_64_fops);
jiffies_64_dev.owner = THIS_MODULE;
err = cdev_add(&jiffies_64_dev, devno, 1);
if (err) {
printk(KERN_ALERT"cdev_add failed.\n");
goto unregister;
}
jiffies_64_class = class_create(THIS_MODULE, JIFFIES_64_DEVICE_CLASS_NAME);
if (IS_ERR(jiffies_64_class)) {
err = PTR_ERR(jiffies_64_class);
printk(KERN_ALERT"Failed to create jiffies_64 class\n");
goto destroy_cdev;
}
device = device_create(jiffies_64_class, NULL, devno, NULL, "%s", JIFFIES_64_DEVICE_FILE_NAME);
if (IS_ERR(device)) {
err = PTR_ERR(device);
printk(KERN_ALERT"Failed to create jiffies_64 device.\n");
goto destroy_class;
}
err = device_create_file(device, &dev_attr_val);
if (err < 0) {
printk(KERN_ALERT"Failed to create attribute val.\n");
goto destroy_device;
}
return 0;
destroy_device:
device_destroy(jiffies_64_class, devno);
destroy_class:
class_destroy(jiffies_64_class);
destroy_cdev:
cdev_del(&jiffies_64_dev);
unregister:
unregister_chrdev_region(devno, 1);
fail:
return err;
}
static void __exit jiffies_64_exit(void)
{
if (jiffies_64_class) {
device_destroy(jiffies_64_class, devno);
class_destroy(jiffies_64_class);
}
cdev_del(&jiffies_64_dev);
unregister_chrdev_region(devno, 1);
}
module_init(jiffies_64_init);
module_exit(jiffies_64_exit);
MODULE_LICENSE("GPL");
jiffies_64获取的应用部分代码
#include
#include
#include
#include
#include
#include
#define DEVICE_NODE_NAME "/dev/jiffies_64"
int main(int argc, char **argv)
{
unsigned long long jiffies_64; /* It's in userspace, so without trouble */
int fd = -1;
fd = open(DEVICE_NODE_NAME, O_RDONLY);
if (fd == -1) {
perror(DEVICE_NODE_NAME);
return -1;
}
read(fd, &jiffies_64, sizeof(jiffies_64));
printf("jiffies_64 = %lld\n", jiffies_64);
close(fd);
return 0;
}
在编译Linux内核，配置时：make menuconfig ---> Kernel hacking --> show timing information on printks
当选中这个选项后，启动内核，会在日志信息前面加上时间戳。
从linux启动信息可以看出，时间精确到微秒(us)。
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