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+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. COMMENT: This is the chapter from the RTEMS POSIX 1003.1b API User's Guide that
+.. COMMENT: documents the services provided by the timer @c  manager.
+
+Clock Manager
+#############
+
+Introduction
+============
+
+The clock manager provides services two primary classes of services.  The first
+focuses on obtaining and setting the current date and time.  The other category
+of services focus on allowing a thread to delay for a specific length of time.
+
+The directives provided by the clock manager are:
+
+- clock_gettime_ - Obtain Time of Day
+
+- clock_settime_ - Set Time of Day
+
+- clock_getres_ - Get Clock Resolution
+
+- sleep_ - Delay Process Execution
+
+- usleep_ - Delay Process Execution in Microseconds
+
+- nanosleep_ - Delay with High Resolution
+
+- gettimeofday_ - Get the Time of Day
+
+- time_ - Get time in seconds
+
+Background
+==========
+
+There is currently no text in this section.
+
+Operations
+==========
+
+There is currently no text in this section.
+
+Directives
+==========
+
+This section details the clock manager's directives.  A subsection is dedicated
+to each of this manager's directives and describes the calling sequence,
+related constants, usage, and status codes.
+
+.. _clock_gettime:
+
+clock_gettime - Obtain Time of Day
+----------------------------------
+.. index:: clock_gettime
+.. index:: obtain time of day
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    int clock_gettime(
+        clockid_t        clock_id,
+        struct timespec *tp
+    );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+   - The tp pointer parameter is invalid.
+ * - ``EINVAL``
+   - The clock_id specified is invalid.
+
+**DESCRIPTION:**
+
+**NOTES:**
+
+NONE
+
+.. _clock_settime:
+
+clock_settime - Set Time of Day
+-------------------------------
+.. index:: clock_settime
+.. index:: set time of day
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    int clock_settime(
+        clockid_t              clock_id,
+        const struct timespec *tp
+    );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+   - The tp pointer parameter is invalid.
+ * - ``EINVAL``
+   - The clock_id specified is invalid.
+ * - ``EINVAL``
+   - The contents of the tp structure are invalid.
+
+**DESCRIPTION:**
+
+**NOTES:**
+
+NONE
+
+.. _clock_getres:
+
+clock_getres - Get Clock Resolution
+-----------------------------------
+.. index:: clock_getres
+.. index:: get clock resolution
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    int clock_getres(
+        clockid_t        clock_id,
+        struct timespec *res
+    );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+   - The res pointer parameter is invalid.
+ * - ``EINVAL``
+   - The clock_id specified is invalid.
+
+**DESCRIPTION:**
+
+**NOTES:**
+
+If ``res`` is ``NULL``, then the resolution is not returned.
+
+.. _sleep:
+
+sleep - Delay Process Execution
+-------------------------------
+.. index:: sleep
+.. index:: delay process execution
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <unistd.h>
+    unsigned int sleep(
+        unsigned int seconds
+    );
+
+**STATUS CODES:**
+
+This routine returns the number of unslept seconds.
+
+**DESCRIPTION:**
+
+The ``sleep()`` function delays the calling thread by the specified number of
+``seconds``.
+
+**NOTES:**
+
+This call is interruptible by a signal.
+
+.. _usleep:
+
+usleep - Delay Process Execution in Microseconds
+------------------------------------------------
+.. index:: usleep
+.. index:: delay process execution
+.. index:: delay process execution
+.. index:: usecs delay process execution
+.. index:: microsecond delay process execution
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    useconds_t usleep(
+        useconds_t useconds
+    );
+
+**STATUS CODES:**
+
+This routine returns the number of unslept seconds.
+
+**DESCRIPTION:**
+
+The ``sleep()`` function delays the calling thread by the specified number of
+``seconds``.
+
+The ``usleep()`` function suspends the calling thread from execution until
+either the number of microseconds specified by the ``useconds`` argument has
+elapsed or a signal is delivered to the calling thread and its action is to
+invoke a signal-catching function or to terminate the process.
+
+Because of other activity, or because of the time spent in processing the call,
+the actual length of time the thread is blocked may be longer than the amount
+of time specified.
+
+**NOTES:**
+
+This call is interruptible by a signal.
+
+The Single UNIX Specification allows this service to be implemented using the
+same timer as that used by the ``alarm()`` service.  This is *NOT* the case for
+*RTEMS* and this call has no interaction with the ``SIGALRM`` signal.
+
+.. _nanosleep:
+
+nanosleep - Delay with High Resolution
+--------------------------------------
+.. index:: nanosleep
+.. index:: delay with high resolution
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    int nanosleep(
+        const struct timespec *rqtp,
+        struct timespec       *rmtp
+    );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINTR``
+   - The routine was interrupted by a signal.
+ * - ``EAGAIN``
+   - The requested sleep period specified negative seconds or nanoseconds.
+ * - ``EINVAL``
+   - The requested sleep period specified an invalid number for the nanoseconds
+     field.
+
+**DESCRIPTION:**
+
+**NOTES:**
+
+This call is interruptible by a signal.
+
+.. _gettimeofday:
+
+gettimeofday - Get the Time of Day
+----------------------------------
+.. index:: gettimeofday
+.. index:: get the time of day
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <sys/time.h>
+    #include <unistd.h>
+    int gettimeofday(
+        struct timeval  *tp,
+        struct timezone *tzp
+    );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` as appropriate.
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EPERM``
+   - ``settimeofdat`` is called by someone other than the superuser.
+ * - ``EINVAL``
+   - Timezone (or something else) is invalid.
+ * - ``EFAULT``
+   - One of ``tv`` or ``tz`` pointed outside your accessible address space
+
+**DESCRIPTION:**
+
+This routine returns the current time of day in the ``tp`` structure.
+
+**NOTES:**
+
+Currently, the timezone information is not supported. The ``tzp`` argument is
+ignored.
+
+.. _time:
+
+time - Get time in seconds
+--------------------------
+.. index:: time
+.. index:: get time in seconds
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+    #include <time.h>
+    int time(
+        time_t *tloc
+    );
+
+**STATUS CODES:**
+
+This routine returns the number of seconds since the Epoch.
+
+**DESCRIPTION:**
+
+``time`` returns the time since 00:00:00 GMT, January 1, 1970, measured in
+seconds
+
+If ``tloc`` in non null, the return value is also stored in the memory pointed
+to by ``t``.
+
+**NOTES:**
+
+NONE