Update some comments.

include/nuttx/clock.h

@@ -336,25 +336,28 @@ void clock_resynchronize(FAR struct timespec *rtc_diff);
 #endif
 
 /****************************************************************************
- * Name:  clock_systimer
+ * Name: clock_systimer
  *
  * Description:
  *   Return the current value of the 32/64-bit system timer counter.
+ *
  *   Indirect access to the system timer counter is required through this
  *   function if the execution environment does not have direct access to
  *   kernel global data.
  *
- *   Use of this function is also required to assue atomic access to the
+ *   Use of this function is also required to assure atomic access to the
  *   64-bit system timer.
  *
+ *   NOTE:  This is an internal OS interface and should not be called from
+ *   application code.  Rather, the functionally equivalent, standard
+ *   interface clock() should be used.
+ *
  * Input Parameters:
  *   None
  *
  * Returned Value:
  *   The current value of the system timer counter
  *
- * Assumptions:
- *
  ****************************************************************************/
 
 #if !defined(__HAVE_KERNEL_GLOBALS) || defined(CONFIG_SYSTEM_TIME64)

sched/clock/clock_systimer.c

@@ -67,7 +67,18 @@
  * Name: clock_systimer
  *
  * Description:
- *   Return the current value of the 32/64-bit system timer counter
+ *   Return the current value of the 32/64-bit system timer counter.
+ *
+ *   Indirect access to the system timer counter is required through this
+ *   function if the execution environment does not have direct access to
+ *   kernel global data.
+ *
+ *   Use of this function is also required to assure atomic access to the
+ *   64-bit system timer.
+ *
+ *   NOTE:  This is an internal OS interface and should not be called from
+ *   application code.  Rather, the functionally equivalent, standard
+ *   interface clock() should be used.
  *
  * Input Parameters:
  *   None
@@ -75,8 +86,6 @@
  * Returned Value:
  *   The current value of the system timer counter
  *
- * Assumptions:
- *
  ****************************************************************************/
 
 systime_t clock_systimer(void)