2023.7.15 linux 高分定时器 hrtimer

High-resolution timers (hrtimers) 高分辨率计时器纳秒级的，内核配置：CONFIG_HIGH_RES_TIMERS　　 ktime_t

头文件：　　　　#include <linux/hrtimer.h>

初始化：　　 void hrtimer_init(struct hrtimer *timer, clockid_t which_clock, enum hrtimer_mode mode);

which_clock？

1，CLOCK_REALTIME: This selects the real-time time—that is, the wall time. If the system time changes, it can affect this timer.

2，CLOCK_MONOTONIC: This is an incremental time, not affected by system changes. However, it stops incrementing when the system goes to sleep or suspends.

3，CLOCK_BOOTTIME: The running time of the system. Similar to CLOCK_ MONOTONIC, the difference is that it includes sleep time. When suspended, it will still increase.

mode?

enum hrtimer_restart callback(struct hrtimer *h); 这个callback的返回值就2个：HRTIMER_NORESTART 或者HRTIMER_RESTART 前一种类似单次任务，后类似定期任务

高分计时器前移： u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval) ；now是从什么时间开始，interval 是前移多少。

从现在now开始前移有一个专门的函数：u64 hrtimer_forward_now(struct hrtimer *timer, ktime_t interval)　　；

启动计时器： int hrtimer_start(struct hrtimer *timer, ktime_t time, const enum hrtimer_mode mode); #mode represents the timer expiry mode, and it should be either HRTIMER_MODE_ABS for an absolute time value or HRTIMER_MODE_REL for a time value relative to now. 　　time就是到期时间、

ktime_t 与秒毫秒纳秒的转换函数：

ktime_t ktime_set(const s64 secs, const unsigned long nsecs);

ktime_t ns_to_ktime(u64 ns);

ktime_t ms_to_ktime(u64 ms);

s64 ktime_to_ns(const ktime_t kt)；

s64 ktime_to_us(const ktime_t kt)；

ktime_t ktime_sub(const ktime_t lhs, const ktime_t rhs);

ktime_t ktime_add(const ktime_t add1, const ktime_t add2);

ktime_t ktime_add_ns(const ktime_t kt, u64 nsec);

停止或取消定时器：

int hrtimer_cancel(struct hrtimer *timer);

int hrtimer_try_to_cancel(struct hrtimer *timer);