drivers: systick: Improve the logic for detecting counter wrap-around events when exiting low power mode.

drivers/timer/cortex_m_systick.c

@@ -109,6 +109,12 @@ static cycle_t cycle_pre_idle;
 /* Idle timer value before entering the idle state. */
 static uint32_t idle_timer_pre_idle;
 
+/* How many ticks the system was expected to sleep when
+ * idle timer was configured. Used to determine if the
+ * counter overflowed or not.
+ */
+static uint32_t idle_timer_scheduled_sleep_ticks;
+
 /* Idle timer used for timer while entering the idle state */
 static const struct device *idle_timer = DEVICE_DT_GET(DT_CHOSEN(zephyr_cortex_m_idle_timer));
 
@@ -154,25 +160,43 @@ void z_cms_lptim_hook_on_lpm_entry(uint64_t max_lpm_time_us)
 	 * difference in measurements after exiting the idle state.
 	 */
 	counter_get_value(idle_timer, &idle_timer_pre_idle);
+
+	idle_timer_scheduled_sleep_ticks = cfg.ticks;
 }
 
 uint64_t z_cms_lptim_hook_on_lpm_exit(void)
 {
 	/**
 	 * Calculate how much time elapsed according to counter.
 	 */
-	uint32_t idle_timer_post, idle_timer_diff;
+	uint32_t idle_timer_post, idle_timer_diff, idle_timer_top;
+	bool idle_timer_int_pending, idle_timer_wrap;
 
 	counter_get_value(idle_timer, &idle_timer_post);
+	idle_timer_int_pending = counter_get_pending_int(idle_timer) ? true : false;
+	idle_timer_top = counter_get_top_value(idle_timer);
 
 	/**
 	 * Check for counter timer overflow
 	 * (TODO: this doesn't work for downcounting timers!)
 	 */
 	if (idle_timer_pre_idle > idle_timer_post) {
-		idle_timer_diff =
-			(counter_get_top_value(idle_timer) - idle_timer_pre_idle) +
-			idle_timer_post + 1;
+		/* Pre > Post: counter wrapped (overflow occurred) */
+		idle_timer_wrap = true;
+	} else if (idle_timer_pre_idle == idle_timer_post) {
+		/* Pre == Post: consider wrap only if interrupt is pending */
+		idle_timer_wrap = idle_timer_int_pending;
+	} else {
+		/* Pre < Post: normally no wrap; if interrupt pending and the
+		 * expected sleep spans the counter top, treat as wrap.
+		 */
+		idle_timer_wrap = idle_timer_int_pending &&
+			((uint64_t)idle_timer_pre_idle + idle_timer_scheduled_sleep_ticks
+				>= idle_timer_top);
+	}
+
+	if (idle_timer_wrap) {
+		idle_timer_diff = idle_timer_top - idle_timer_pre_idle + idle_timer_post + 1;
 	} else {
 		idle_timer_diff = idle_timer_post - idle_timer_pre_idle;
 	}