Arm64 tick timer fixes

arch/arm64/src/common/arm64_arch_timer.c

@@ -244,6 +244,7 @@ static int arm64_tick_start(struct oneshot_lowerhalf_s *lower,
 {
   struct arm64_oneshot_lowerhalf_s *priv =
     (struct arm64_oneshot_lowerhalf_s *)lower;
+  uint64_t next_cycle;
 
   DEBUGASSERT(priv != NULL && callback != NULL);
 
@@ -252,10 +253,11 @@ static int arm64_tick_start(struct oneshot_lowerhalf_s *lower,
   priv->callback = callback;
   priv->arg = arg;
 
-  /* Set the timeout */
+  next_cycle =
+    arm64_arch_timer_count() / priv->cycle_per_tick * priv->cycle_per_tick +
+    ticks * priv->cycle_per_tick;
 
-  arm64_arch_timer_set_compare(arm64_arch_timer_count() +
-                               priv->cycle_per_tick * ticks);
+  arm64_arch_timer_set_compare(next_cycle);
   arm64_arch_timer_set_irq_mask(false);
 
   return OK;
@@ -418,4 +420,4 @@ void arm64_arch_timer_secondary_init()
   arm64_arch_timer_enable(true);
 #endif
 }
-#endif
+#endif

drivers/timers/arch_alarm.c

@@ -116,26 +116,34 @@ static void udelay_coarse(useconds_t microseconds)
 static void oneshot_callback(FAR struct oneshot_lowerhalf_s *lower,
                              FAR void *arg)
 {
-  clock_t now = 0;
+  clock_t now;
+  ONESHOT_TICK_CURRENT(g_oneshot_lower, &now);
 
 #ifdef CONFIG_SCHED_TICKLESS
-  ONESHOT_TICK_CURRENT(g_oneshot_lower, &now);
   nxsched_alarm_tick_expiration(now);
 #else
-  clock_t delta;
+  /* Start the next tick first, in order to minimize latency. Ideally
+   * the ONESHOT_TICK_START would also return the current tick so that
+   * the retriving the current tick and starting the new one could be done
+   * atomically w. respect to a HW timer
+   */
 
-  do
-    {
-      clock_t next;
+  ONESHOT_TICK_START(g_oneshot_lower, oneshot_callback, NULL, 1);
 
+  /* It is always an error if this progresses more than 1 tick at a time.
+   * That would break any timer based on wdog; such timers might timeout
+   * early. Add a DEBUGASSERT here to catch those errors. It is not added
+   * here by default, since it would break debugging. These errors
+   * would occur due to HW timers possibly running while CPU is being halted.
+   */
+
+  /* DEBUGASSERT(now - g_current_tick <= 1); */
+
+  while (now - g_current_tick > 0)
+    {
+      g_current_tick++;
       nxsched_process_timer();
-      next = ++g_current_tick;
-      ONESHOT_TICK_CURRENT(g_oneshot_lower, &now);
-      delta = next - now;
     }
-  while ((sclock_t)delta <= 0);
-
-  ONESHOT_TICK_START(g_oneshot_lower, oneshot_callback, NULL, delta);
 #endif
 }
 

sched/semaphore/sem_tickwait.c

@@ -100,8 +100,9 @@ int nxsem_tickwait(FAR sem_t *sem, uint32_t delay)
 
   if (delay == 0)
     {
-      /* Return the errno from nxsem_trywait() */
+      /* Timed out already before waiting */
 
+      ret = -ETIMEDOUT;
       goto out;
     }
 
@@ -149,7 +150,7 @@ int nxsem_tickwait(FAR sem_t *sem, uint32_t delay)
 
 int nxsem_tickwait_uninterruptible(FAR sem_t *sem, uint32_t delay)
 {
-  clock_t end = clock_systime_ticks() + delay;
+  clock_t end = clock_systime_ticks() + delay + 1;
   int ret;
 
   for (; ; )