avr: Introduce optimized timer_is_before()

Provide hand-coded assembler for timer_is_before() on AVR as that code
is used frequently in the time-critical timer dispatch loop and gcc
doesn't do a good job at compiling that comparison code.  Remove the
no longer needed waketime+1 hack from reschedule_timer().

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/sched.c b/src/sched.c
index 7a68db86..cae2f819 100644
--- a/src/sched.c
+++ b/src/sched.c
@@ -127,9 +127,9 @@ sched_del_timer(struct timer *del)
 static struct timer *
 reschedule_timer(struct timer *t)
 {
+    uint32_t waketime = t->waketime;
     struct timer *pos = t->next;
-    uint32_t minwaketime = t->waketime + 1;
-    if (!timer_is_before(pos->waketime, minwaketime))
+    if (timer_is_before(waketime, pos->waketime))
         // Timer is still the first - no insertion needed
         return t;
 
@@ -142,7 +142,7 @@ reschedule_timer(struct timer *t)
             // micro optimization for AVR - reduces register pressure
             asm("" : "+r"(prev) : : "memory");
         pos = pos->next;
-        if (!timer_is_before(pos->waketime, minwaketime))
+        if (timer_is_before(waketime, pos->waketime))
             break;
     }
     t->next = pos;