arch/arm64: Fix clock drift from tick timer.

In the previous implementation, when the current timer count just exceeds the next tick time, it will still cause clock drift. This commit fixed clock drift by using the abosolute ticks (clock_systime_tick() + ticks).

Signed-off-by: ouyangxiangzhen <ouyangxiangzhen@xiaomi.com>

arch/arm64/src/common/arm64_arch_timer.c

@@ -51,6 +51,8 @@
 #define ARM_ARCH_TIMER_PRIO                 IRQ_DEFAULT_PRIORITY
 #define ARM_ARCH_TIMER_FLAGS                IRQ_TYPE_LEVEL
 
+#define ARM_ARCH_TIMER_UNINITIALIZED_TICK   ((UINT64_MAX / TICK_PER_SEC) + 1)
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
@@ -286,9 +288,14 @@ static int arm64_tick_start(struct oneshot_lowerhalf_s *lower,
 
   priv->running = this_cpu();
 
-  next_cycle =
-    arm64_arch_timer_count() / priv->cycle_per_tick * priv->cycle_per_tick +
-    ticks * priv->cycle_per_tick;
+  /* When we first set the timer, we should get the current tick */
+
+  if (g_current_tick == ARM_ARCH_TIMER_UNINITIALIZED_TICK)
+    {
+      lower->ops->tick_current(lower, &g_current_tick);
+    }
+
+  next_cycle = (g_current_tick + ticks) * priv->cycle_per_tick;
 
   arm64_arch_timer_set_compare(next_cycle);
   arm64_arch_timer_set_irq_mask(false);
@@ -381,6 +388,8 @@ struct oneshot_lowerhalf_s *arm64_oneshot_initialize(void)
   priv->cycle_per_tick = arm64_arch_timer_get_cntfrq() / TICK_PER_SEC;
   tmrinfo("cycle_per_tick %" PRIu64 "\n", priv->cycle_per_tick);
 
+  g_current_tick = ARM_ARCH_TIMER_UNINITIALIZED_TICK;
+
   /* Attach handler */
 
   irq_attach(ARM_ARCH_TIMER_IRQ,

drivers/timers/arch_alarm.c

@@ -37,15 +37,19 @@
 #define CONFIG_BOARD_LOOPSPERUSEC    ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000)
 
 /****************************************************************************
- * Private Data
+ * Public Data
  ****************************************************************************/
 
-static FAR struct oneshot_lowerhalf_s *g_oneshot_lower;
-
 #ifndef CONFIG_SCHED_TICKLESS
-static clock_t g_current_tick;
+clock_t g_current_tick;
 #endif
 
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static FAR struct oneshot_lowerhalf_s *g_oneshot_lower;
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
@@ -117,6 +121,8 @@ static void oneshot_callback(FAR struct oneshot_lowerhalf_s *lower,
                              FAR void *arg)
 {
   clock_t now;
+  clock_t diff;
+  clock_t chase;
   ONESHOT_TICK_CURRENT(g_oneshot_lower, &now);
 
 #ifdef CONFIG_SCHED_TICKLESS
@@ -128,6 +134,8 @@ static void oneshot_callback(FAR struct oneshot_lowerhalf_s *lower,
    * atomically w. respect to a HW timer
    */
 
+  diff           = now - g_current_tick;
+  g_current_tick = now;
   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.
@@ -139,11 +147,11 @@ static void oneshot_callback(FAR struct oneshot_lowerhalf_s *lower,
 
   /* DEBUGASSERT(now - g_current_tick <= 1); */
 
-  while (now - g_current_tick > 0)
+  for (chase = 0; chase < diff; chase++)
     {
-      g_current_tick++;
       nxsched_process_timer();
     }
+
 #endif
 }
 

include/nuttx/timers/arch_alarm.h

@@ -30,6 +30,14 @@
 #include <nuttx/config.h>
 #include <nuttx/timers/oneshot.h>
 
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+#ifndef CONFIG_SCHED_TICKLESS
+extern clock_t g_current_tick;
+#endif
+
 /****************************************************************************
  * Public Function Prototypes
  ****************************************************************************/

sched/semaphore/sem_tickwait.c

@@ -150,7 +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 + 1;
+  clock_t end = clock_systime_ticks() + delay;
   int ret;
 
   for (; ; )