drivers: timer: nrf_rtc_timer: Prevent prolonged timeout setting

CC setting algorithm is handling a case when CC is too soon (next
tick from now). It was setting CC to one tick further in the future
if that was detected. Step was repeated if counter incremented during
setting CC and CC was behind the counter because of risk of setting
CC too late. In certain scenarios we might spend a lot of time in
that loop, especially if optimization is turned off. Test shown that
loop was executed dozens of time (up. to 700us). To prevent
prolonged execution whenever CC setting fails we set CC to one more
tick further in future.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>

Author: nordic-krch

drivers/timer/nrf_rtc_timer.c

@@ -233,6 +233,7 @@ static uint32_t set_absolute_alarm(int32_t chan, uint32_t abs_val)
 	uint32_t now2;
 	uint32_t cc_val = abs_val & COUNTER_MAX;
 	uint32_t prev_cc = get_comparator(chan);
+	uint32_t tick_inc = 2;
 
 	do {
 		now = counter();
@@ -251,12 +252,16 @@ static uint32_t set_absolute_alarm(int32_t chan, uint32_t abs_val)
 			k_busy_wait(19);
 		}
 
-		/* If requested cc_val is in the past or next tick, set to 2
-		 * ticks from now. RTC may not generate event if CC is set for
-		 * 1 tick from now.
+		/* RTC may not generate event if CC is set for 1 tick from now.
+		 * Because of that if requested cc_val is in the past or next tick,
+		 * set CC to further in future. Start with 2 ticks from now but
+		 * if that fails go even futher. It may fail if operation got
+		 * interrupted and RTC counter progressed or if optimization is
+		 * turned off.
 		 */
 		if (counter_sub(cc_val, now + 2) > COUNTER_HALF_SPAN) {
-			cc_val = now + 2;
+			cc_val = now + tick_inc;
+			tick_inc++;
 		}
 
 		event_clear(chan);