linux内核之高精度定时器
低精度定时器在一些特殊场合不能达到定时要求,故引出高精度定时器;
struct hrtimer结构体
高精度定时器在内核中是以struct hrtimer结构体对象表示:
头文件: linux/krtimer.h
struct hrtimer {
struct timerqueue_node node;
ktime_t _softexpires;
enum hrtimer_restart (*function)(struct hrtimer *);//计时器到期回调函数
struct hrtimer_clock_base *base;//指向计时器基数的指针;
u8 state; //状态信息
u8 is_rel;//若计时器已启用,则设置;
u8 is_soft;//在软中断上下文中设置hrtimer是否过期;
};ktime_t
高精度定时器是以ktime_t来定义时间的;
操作函数如下:
typedef s64 ktime_t;
//将秒和纳秒转ktime_t
ktime_t ktime_set(const s64 secs, const unsigned long nsecs);
//ktime转微秒
s64 ktime_to_us(const ktime_t kt);
//ktime转毫秒
s64 ktime_to_ms(const ktime_t kt);
//纳秒转ktime
ktime_t ns_to_ktime(u64 ns);
//毫秒转ktime
ktime_t ms_to_ktime(u64 ms);其中最核心的就是function回调函数,定时到期后自动调用,需要用户实现;
常用函数
/* 作用:初始化高精度定时器
参数1：需要初始化的高精度定时器
参数2：要使用的时钟,种类如下:
#define CLOCK_REALTIME 0
#define CLOCK_MONOTONIC 1
#define CLOCK_PROCESS_CPUTIME_ID 2
#define CLOCK_THREAD_CPUTIME_ID 3
#define CLOCK_MONOTONIC_RAW 4
#define CLOCK_REALTIME_COARSE 5
#define CLOCK_MONOTONIC_COARSE 6
#define CLOCK_BOOTTIME 7
#define CLOCK_REALTIME_ALARM 8
#define CLOCK_BOOTTIME_ALARM 9
其中CLOCK_MONOTONIC最常用,表示自系统开机以来的单调递增时间;
参数3:时间模式;取值如下:
enum hrtimer_mode {
HRTIMER_MODE_ABS = 0x00,//绝对时间;
HRTIMER_MODE_REL = 0x01,//相对时间;
HRTIMER_MODE_PINNED = 0x02,//计时器绑定到CPU,仅在启动定时器时考虑;
HRTIMER_MODE_SOFT = 0x04,//计时器回调将会在软中断上下文中执行;
HRTIMER_MODE_ABS_PINNED = HRTIMER_MODE_ABS | HRTIMER_MODE_PINNED,
HRTIMER_MODE_REL_PINNED = HRTIMER_MODE_REL | HRTIMER_MODE_PINNED,
HRTIMER_MODE_ABS_SOFT = HRTIMER_MODE_ABS | HRTIMER_MODE_SOFT,
HRTIMER_MODE_REL_SOFT = HRTIMER_MODE_REL | HRTIMER_MODE_SOFT,
HRTIMER_MODE_ABS_PINNED_SOFT = HRTIMER_MODE_ABS_PINNED | HRTIMER_MODE_SOFT,
HRTIMER_MODE_REL_PINNED_SOFT = HRTIMER_MODE_REL_PINNED | HRTIMER_MODE_SOFT,
};
*/
void hrtimer_init(struct hrtimer *timer, clockid_t clock_id, enum hrtimer_mode mode);
/*
作用:启动定时器
参数1：高精度定时器;
参数2:设置的到期时间;
参数3:参数3:时间模式，同hrtimer_init中;
*/
void hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode);
//修改到期时间为 从现在开始的interval时间
u64 hrtimer_forward_now(struct hrtimer *timer, ktime_t interval);
//取消定时器
int hrtimer_cancel(struct hrtimer *timer);
示例:
#include
#include
#include
struct hrtimer timer;
enum hrtimer_restart hrtimer_func(struct hrtimer *t)
{
printk("----hrtimer_func----\n");
//实现循环定时
hrtimer_forward_now(t, ktime_set(5,1000));
return HRTIMER_RESTART;
}
static int __init test_drv_init(void)
{
hrtimer_init(&timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
timer.function = hrtimer_func;
hrtimer_start(&timer, ktime_set(1,1000), HRTIMER_MODE_REL);
printk("----test_drv_init----\n");
return 0;
}
static void __exit test_drv_exit(void)
{
hrtimer_cancel(&timer);
printk("----test_drv_exit----\n");
}
module_init(test_drv_init);
module_exit(test_drv_exit);
MODULE_LICENSE("GPL");