sched: Avoid rescheduling the currently active timer

It's tricky to reschedule the timer irq correctly (due to race
conditions with the irq) and in practice it's very rarely needed.
Handle the special cases in the generic sched.c code so that the board
code doesn't have to handle it.

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

1 files changed, 12 insertions, 30 deletions

diff --git a/src/avr/timer.c b/src/avr/timer.c
index a6da9b4f..06d8845e 100644
--- a/src/avr/timer.c
+++ b/src/avr/timer.c
@@ -39,13 +39,6 @@ timer_set(uint16_t next)
 }
 
 static inline void
-timer_set_clear(uint16_t next)
-{
-    OCR1A = next;
-    TIFR1 = 1<<OCF1A;
-}
-
-static inline void
 timer_repeat_set(uint16_t next)
 {
     // Timer1B is used to limit the number of timers run from a timer1A irq
@@ -78,6 +71,15 @@ timer_init(void)
 }
 DECL_INIT(timer_init);
 
+static void
+timer_shutdown(void)
+{
+    // Reenable timer irq
+    timer_set(timer_get() + 50);
+    TIFR1 = 1<<OCF1A;
+}
+DECL_SHUTDOWN(timer_shutdown);
+
 
 /****************************************************************
  * 32bit timer wrappers
@@ -120,35 +122,15 @@ timer_periodic(void)
     }
 }
 
-#define TIMER_MIN_TICKS 100
-
-// Set the next timer wake time (in absolute clock ticks).  Caller
-// must disable irqs.  The caller should not schedule a time more than
-// a few milliseconds in the future.
-uint8_t
-timer_set_next(uint32_t next)
-{
-    uint32_t cur = timer_read_time();
-    if ((int16_t)(OCR1A - (uint16_t)cur) < 0 && !(TIFR1 & (1<<OCF1A)))
-        // Already processing timer irqs
-        try_shutdown("timer_set_next called during timer dispatch");
-    uint32_t mintime = cur + TIMER_MIN_TICKS;
-    if (sched_is_before(mintime, next)) {
-        timer_set_clear(next);
-        return 0;
-    }
-    timer_set_clear(mintime);
-    return 1;
-}
-
 #define TIMER_IDLE_REPEAT_TICKS 8000
 #define TIMER_REPEAT_TICKS 3000
 
 #define TIMER_MIN_TRY_TICKS 60 // 40 ticks to exit irq; 20 ticks of progress
 #define TIMER_DEFER_REPEAT_TICKS 200
 
-// Similar to timer_set_next(), but wait for the given time if it is
-// in the near future.
+// Set the next timer wake time (in absolute clock ticks) or return 1
+// if the next timer is too close to schedule.  Caller must disable
+// irqs.
 uint8_t
 timer_try_set_next(uint32_t target)
 {