From e57ab2a7bfb69c0ef9b5b7fa8e53e20a500e7c6c Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Thu, 25 Oct 2012 13:42:10 -0700
Subject: [PATCH] altos: Provide ao_task_alarm_tick to reduce per-tick cost

Cache the next wakeup time and check that before jumping to the task
code.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 src/core/ao_task.c | 20 ++++++++++----------
 src/core/ao_task.h |  1 +
 src/stm/ao_timer.c |  3 ++-
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/core/ao_task.c b/src/core/ao_task.c
index 985c37fa..0411fbdd 100644
--- a/src/core/ao_task.c
+++ b/src/core/ao_task.c
@@ -114,6 +114,8 @@ ao_task_validate_alarm_queue(void)
 #define ao_task_validate_alarm_queue()
 #endif
 
+uint16_t	ao_task_alarm_tick;
+
 static void
 ao_task_to_alarm_queue(struct ao_task *task)
 {
@@ -126,6 +128,7 @@ ao_task_to_alarm_queue(struct ao_task *task)
 		}
 	}
 	ao_list_append(&task->alarm_queue, &alarm_queue);
+	ao_task_alarm_tick = ao_list_first_entry(&alarm_queue, struct ao_task, alarm_queue)->alarm;
 	ao_task_validate_alarm_queue();
 }
 
@@ -133,6 +136,10 @@ static void
 ao_task_from_alarm_queue(struct ao_task *task)
 {
 	ao_list_del(&task->alarm_queue);
+	if (ao_list_is_empty(&alarm_queue))
+		ao_task_alarm_tick = 0;
+	else
+		ao_task_alarm_tick = ao_list_first_entry(&alarm_queue, struct ao_task, alarm_queue)->alarm;
 	ao_task_validate_alarm_queue();
 }
 
@@ -154,10 +161,7 @@ void
 ao_task_check_alarm(uint16_t tick)
 {
 	struct ao_task	*alarm, *next;
-	int		i;
 
-	if (ao_num_tasks == 0)
-		return;
 	ao_list_for_each_entry_safe(alarm, next, &alarm_queue, struct ao_task, alarm_queue) {
 		if ((int16_t) (tick - alarm->alarm) < 0)
 			break;
@@ -173,6 +177,7 @@ ao_task_init(void)
 	uint8_t	i;
 	ao_list_init(&run_queue);
 	ao_list_init(&alarm_queue);
+	ao_task_alarm_tick = 0;
 	for (i = 0; i < SLEEP_HASH_SIZE; i++)
 		ao_list_init(&sleep_queue[i]);
 }
@@ -264,14 +269,9 @@ ao_task_validate(void)
 		}
 	}
 }
-#else
-#define ao_task_validate()
-#endif
+#endif /* DEBUG */
 
-#else
-#define ao_task_to_run_queue(task)
-#define ao_task_to_alarm_queue(task)
-#endif
+#endif /* HAS_TASK_QUEUE */
 
 void
 ao_add_task(__xdata struct ao_task * task, void (*start)(void), __code char *name) __reentrant
diff --git a/src/core/ao_task.h b/src/core/ao_task.h
index b3f152a0..049f69a7 100644
--- a/src/core/ao_task.h
+++ b/src/core/ao_task.h
@@ -82,6 +82,7 @@ ao_add_task(__xdata struct ao_task * task, void (*start)(void), __code char *nam
 
 #if HAS_TASK_QUEUE
 /* Called on timer interrupt to check alarms */
+extern uint16_t	ao_task_alarm_tick;
 void
 ao_task_check_alarm(uint16_t tick);
 #endif
diff --git a/src/stm/ao_timer.c b/src/stm/ao_timer.c
index d69035f8..e07625d8 100644
--- a/src/stm/ao_timer.c
+++ b/src/stm/ao_timer.c
@@ -44,7 +44,8 @@ void stm_tim6_isr(void)
 		stm_tim6.sr = 0;
 		++ao_tick_count;
 #if HAS_TASK_QUEUE
-		ao_task_check_alarm((uint16_t) ao_tick_count);
+		if (ao_task_alarm_tick && (int16_t) (ao_tick_count - ao_task_alarm_tick) >= 0)
+			ao_task_check_alarm((uint16_t) ao_tick_count);
 #endif
 #if AO_DATA_ALL
 		if (++ao_data_count == ao_data_interval) {
-- 
2.30.2