[PATCH rtems-docs v3] c-user: Update references to rtems_task_wake_after

[Kinsey Moore]

rtems_task_wake_after takes a parameter in terms of a count of clock
ticks and not a measure in a subunit of seconds. This updates
documentation to reflect that. This also makes obvious the caveat about
the first tick wait not being a whole tick and points the user at a
replacement for better accuracy.

Updates #4772
---
 c-user/scheduling-concepts/background.rst |  8 +++----
 c-user/task/directives.rst                | 27 ++++++++++++++---------
 c-user/task/introduction.rst              |  4 ++--
 c-user/task/operations.rst                |  6 ++---
 4 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/c-user/scheduling-concepts/background.rst b/c-user/scheduling-concepts/background.rst
index 1fe7089..38b77ee 100644
--- a/c-user/scheduling-concepts/background.rst
+++ b/c-user/scheduling-concepts/background.rst
@@ -160,7 +160,7 @@ Manual Round-Robin
 
 The final mechanism for altering the RTEMS scheduling algorithm is called
 manual round-robin.  Manual round-robin is invoked by using
-the ``rtems_task_wake_after`` directive with a time interval of
+the ``rtems_task_wake_after`` directive with a ``ticks`` parameter of
 ``RTEMS_YIELD_PROCESSOR``.  This allows a task to give up the processor and be
 immediately returned to the ready chain at the end of its priority group.  If
 no other tasks of the same priority are ready to run, then the task does not
@@ -243,7 +243,7 @@ of the following conditions:
   option and the requested semaphore is unavailable.
 
 - The running task issues a ``rtems_task_wake_after`` directive which blocks
-  the task for the given time interval.  If the time interval specified is
+  the task for the given count of ticks.  If the count of ticks specified is
   zero, the task yields the processor and remains in the ready state.
 
 - The running task issues a ``rtems_task_wake_when`` directive which blocks the
@@ -280,8 +280,8 @@ conditions:
 - A running task issues a ``rtems_semaphore_release`` directive which releases
   the semaphore on which the blocked task is waiting.
 
-- A timeout interval expires for a task which was blocked by a call to the
-  ``rtems_task_wake_after`` directive.
+- The requested count of ticks has elapsed for a task which was blocked by a
+  call to the ``rtems_task_wake_after`` directive.
 
 - A timeout period expires for a task which blocked by a call to the
   ``rtems_task_wake_when`` directive.
diff --git a/c-user/task/directives.rst b/c-user/task/directives.rst
index c082b51..ea2337a 100644
--- a/c-user/task/directives.rst
+++ b/c-user/task/directives.rst
@@ -1475,16 +1475,16 @@ The following constraints apply to this directive:
     \clearpage
 
 .. index:: rtems_task_wake_after()
-.. index:: delay a task for an interval
-.. index:: wake up after an interval
+.. index:: delay a task for a count of clock ticks
+.. index:: wake up after a count of clock ticks
 
 .. _InterfaceRtemsTaskWakeAfter:
 
 rtems_task_wake_after()
 -----------------------
 
-Wakes up after an interval in :term:`clock ticks <clock tick>` or yields the
-processor.
+Wakes up after a count of :term:`clock ticks <clock tick>` have occurred or
+yields the processor.
 
 .. rubric:: CALLING SEQUENCE:
 
@@ -1495,16 +1495,16 @@ processor.
 .. rubric:: PARAMETERS:
 
 ``ticks``
-    This parameter is the interval in :term:`clock ticks <clock tick>` to delay
+    This parameter is the count of :term:`clock ticks <clock tick>` to delay
     the task or :c:macro:`RTEMS_YIELD_PROCESSOR` to yield the processor.
 
 .. rubric:: DESCRIPTION:
 
-This directive blocks the calling task for the specified ``ticks`` of clock
-ticks if the value is not equal to :c:macro:`RTEMS_YIELD_PROCESSOR`.  When the
-requested interval has elapsed, the task is made ready.  The clock tick
-directives automatically updates the delay period.  The calling task may give
-up the processor and remain in the ready state by specifying a value of
+This directive blocks the calling task for the specified ``ticks`` count of
+clock ticks if the value is not equal to :c:macro:`RTEMS_YIELD_PROCESSOR`. When
+the requested count of ticks have occurred, the task is made ready.  The clock
+tick directives automatically update the delay period.  The calling task may
+give up the processor and remain in the ready state by specifying a value of
 :c:macro:`RTEMS_YIELD_PROCESSOR` in ``ticks``.
 
 .. rubric:: RETURN VALUES:
@@ -1516,7 +1516,12 @@ up the processor and remain in the ready state by specifying a value of
 
 Setting the system date and time with the :ref:`InterfaceRtemsClockSet`
 directive and similar directives which set :term:`CLOCK_REALTIME` have no
-effect on a :ref:`InterfaceRtemsTaskWakeAfter` blocked task.
+effect on a :ref:`InterfaceRtemsTaskWakeAfter` blocked task.  The delay until
+first clock tick will never be a whole clock tick interval since this directive
+will never excute exactly on a clock tick.  Applications requiring use of a
+clock (CLOCK_REALTIME or CLOCK_MONOTONIC) instead of clock ticks should make
+use of `clock_nanosleep()
+<https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_nanosleep.html>`_.
 
 .. rubric:: CONSTRAINTS:
 
diff --git a/c-user/task/introduction.rst b/c-user/task/introduction.rst
index 6f5ff4d..4a41acd 100644
--- a/c-user/task/introduction.rst
+++ b/c-user/task/introduction.rst
@@ -84,8 +84,8 @@ and administer tasks. The directives provided by the Task Manager are:
 * :ref:`InterfaceRtemsTaskMode` - Gets and optionally sets the mode of the
   calling task.
 
-* :ref:`InterfaceRtemsTaskWakeAfter` - Wakes up after an interval in
-  :term:`clock ticks <clock tick>` or yields the processor.
+* :ref:`InterfaceRtemsTaskWakeAfter` - Wakes up after a count of :term:`clock
+  ticks <clock tick>` have occurred or yields the processor.
 
 * :ref:`InterfaceRtemsTaskWakeWhen` - Wakes up when specified.
 
diff --git a/c-user/task/operations.rst b/c-user/task/operations.rst
index 6308d7b..438eea5 100644
--- a/c-user/task/operations.rst
+++ b/c-user/task/operations.rst
@@ -75,9 +75,9 @@ Delaying the Currently Executing Task
 -------------------------------------
 
 The ``rtems_task_wake_after`` directive creates a sleep timer which allows a
-task to go to sleep for a specified interval.  The task is blocked until the
-delay interval has elapsed, at which time the task is unblocked.  A task
-calling the ``rtems_task_wake_after`` directive with a delay interval of
+task to go to sleep for a specified count of clock ticks.  The task is blocked
+until the count of clock ticks has elapsed, at which time the task is unblocked.
+A task calling the ``rtems_task_wake_after`` directive with a delay of
 ``RTEMS_YIELD_PROCESSOR`` ticks will yield the processor to any other ready
 task of equal or greater priority and remain ready to execute.
 
-- 
2.30.2