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sched/wdog: Add CONFIG_TIMER_ADJUST_USEC.

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This commit added CONFIG_TIMER_ADJUST_USEC to support the time compensation for wdog timer. Normally, timer event cannot triggered on exact time due to the existence of interrupt latency. Assuming that the interrupt latency is distributed within [Best-Case Execution Time, Worst-Case Excution Time], we can set the timer adjustment value to the BCET to reduce the latency.

Signed-off-by: ouyangxiangzhen <ouyangxiangzhen@xiaomi.com>
This commit is contained in:
ouyangxiangzhen 2025-04-01 20:09:40 +08:00 • committed by Xiang Xiao
parent 8e65375365
commit a255c99eb8
2 changed files with 27 additions and 0 deletions
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10
sched/Kconfig
View file

@ -150,6 +150,16 @@ config USEC_PER_TICK
This value should never be less than the underlying resolution of
the timer. Error may ensue.
config TIMER_ADJUST_USEC
int "System timer tick adjustment (microseconds)"
default 0
---help---
This value is added to the absolute tick set to the system timer.
This is used to compensate for interrupt latency in real-time
systems where the event required to be triggered on exact time.
The default value of 0 means that no adjustment is made. E.g.
5 means for each timer being set will be fired 5 microseconds earlier.
if !SCHED_TICKLESS
config SYSTEMTICK_EXTCLK

17
sched/sched/sched_timerexpiration.c
View file

@ -407,6 +407,23 @@ static clock_t nxsched_timer_start(clock_t ticks, clock_t interval)
}
#endif
/* Normally, timer event cannot triggered on exact time
* due to the existence of interrupt latency.
* Assuming that the interrupt latency is distributed within
* [Best-Case Execution Time, Worst-Case Excution Time],
* we can set the timer adjustment value to the BCET to
* reduce the latency.
* After the adjustment, the timer interrupt latency will be
* [0, WCET - BCET].
* Please use this carefully, if the timer adjustment value is not
* the best-case interrupt latency, it will immediately fired
* another timer interrupt, which may result in a much larger timer
* interrupt latency.
*/
interval = interval <= (CONFIG_TIMER_ADJUST_USEC / USEC_PER_TICK) ? 0 :
interval - (CONFIG_TIMER_ADJUST_USEC / USEC_PER_TICK);
#ifdef CONFIG_SCHED_TICKLESS_ALARM
/* Convert the delay to a time in the future (with respect
* to the time when last stopped the timer).