From: Sami Liedes <sliedes@cc.hut.fi>
Date: Tue, 15 Feb 2011 23:21:38 +0000 (+0200)
Subject: Store the next cycle count where the earliest cycle timer needs to be run.
X-Git-Tag: v1.0a7~42
X-Git-Url: https://git.htl-mechatronik.at/public/?a=commitdiff_plain;h=199a5e98393ec3151eec2464cf97f23ebb65740f;p=sx%2Fsimavr.git

Store the next cycle count where the earliest cycle timer needs to be run.
This speeds up cycle timer processing significantly and almost doubles
the speed of the overall simulation.

Signed-off-by: Sami Liedes <sliedes@cc.hut.fi>
---

diff --git a/simavr/sim/sim_avr.h b/simavr/sim/sim_avr.h
index 6d205d4..32426dd 100644
--- a/simavr/sim/sim_avr.h
+++ b/simavr/sim/sim_avr.h
@@ -156,6 +156,7 @@ typedef struct avr_t {
 	// these timers are one shots, then get cleared if the timer function returns zero,
 	// they get reset if the callback function returns a new cycle number
 	uint32_t	cycle_timer_map;
+	avr_cycle_count_t next_cycle_timer;
 	struct {
 		avr_cycle_count_t	when;
 		avr_cycle_timer_t	timer;
diff --git a/simavr/sim/sim_cycle_timers.c b/simavr/sim/sim_cycle_timers.c
index 57fd058..3bafa5c 100644
--- a/simavr/sim/sim_cycle_timers.c
+++ b/simavr/sim/sim_cycle_timers.c
@@ -33,6 +33,8 @@ void avr_cycle_timer_register(avr_t * avr, avr_cycle_count_t when, avr_cycle_tim
 		return;
 	}
 	when += avr->cycle;
+	if (when < avr->next_cycle_timer)
+		avr->next_cycle_timer = when;
 	for (int i = 0; i < 32; i++)
 		if (!(avr->cycle_timer_map & (1 << i))) {
 			avr->cycle_timer[i].timer = timer;
@@ -60,6 +62,9 @@ void avr_cycle_timer_cancel(avr_t * avr, avr_cycle_timer_t timer, void * param)
 			avr->cycle_timer[i].param = NULL;
 			avr->cycle_timer[i].when = 0;
 			avr->cycle_timer_map &= ~(1 << i);
+			// no need to reset next_cycle_timer; having too small
+			// a value there only causes some harmless extra
+			// computation.
 			return;
 		}
 }
@@ -92,8 +97,15 @@ avr_cycle_timer_status(avr_t * avr, avr_cycle_timer_t timer, void * param)
  */
 avr_cycle_count_t avr_cycle_timer_process(avr_t * avr)
 {
-	if (!avr->cycle_timer_map)
+	// If we have previously determined that we don't need to fire
+	// cycle timers yet, we can do an early exit
+	if (avr->next_cycle_timer > avr->cycle)
+		return avr->next_cycle_timer - avr->cycle;
+
+	if (!avr->cycle_timer_map) {
+		avr->next_cycle_timer = (avr_cycle_count_t)-1;
 		return (avr_cycle_count_t)-1;
+	}
 
 	avr_cycle_count_t min = (avr_cycle_count_t)-1;
 	uint32_t map = avr->cycle_timer_map;
@@ -120,5 +132,6 @@ avr_cycle_count_t avr_cycle_timer_process(avr_t * avr)
 			min = avr->cycle_timer[bit].when;
 		map &= ~(1 << bit);		
 	}
+	avr->next_cycle_timer = min;
 	return min - avr->cycle;
 }