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commit a255c99eb8a13197dc1a93b1910a4fd5d6268332
Author: ouyangxiangzhen <ouyangxiangz...@xiaomi.com>
AuthorDate: Tue Apr 1 20:09:40 2025 +0800
sched/wdog: Add CONFIG_TIMER_ADJUST_USEC.
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 <ouyangxiangz...@xiaomi.com>
---
sched/Kconfig | 10 ++++++++++
sched/sched/sched_timerexpiration.c | 17 +++++++++++++++++
2 files changed, 27 insertions(+)
diff --git a/sched/Kconfig b/sched/Kconfig
index aa7a41c667..840871b26a 100644
--- a/sched/Kconfig
+++ b/sched/Kconfig
@@ -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
diff --git a/sched/sched/sched_timerexpiration.c
b/sched/sched/sched_timerexpiration.c
index 1d268877cd..6fe5ba0b35 100644
--- a/sched/sched/sched_timerexpiration.c
+++ b/sched/sched/sched_timerexpiration.c
@@ -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).
