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authorChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
committerChris Johns <chrisj@rtems.org>2016-11-03 16:58:08 +1100
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+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+.. COMMENT: All rights reserved.
+
+Scheduler Manager
+#################
+
+Introduction
+============
+
+The scheduler manager ...
+
+The directives provided by the scheduler manager are:
+
+- sched_get_priority_min_ - Get Minimum Priority Value
+
+- sched_get_priority_max_ - Get Maximum Priority Value
+
+- sched_rr_get_interval_ - Get Timeslicing Quantum
+
+- sched_yield_ - Yield the Processor
+
+Background
+==========
+
+Priority
+--------
+
+In the RTEMS implementation of the POSIX API, the priorities range from the low
+priority of ``sched_get_priority_min()`` to the highest priority of
+``sched_get_priority_max()``. Numerically higher values represent higher
+priorities.
+
+Scheduling Policies
+-------------------
+
+The following scheduling policies are available:
+
+*SCHED_FIFO*
+ Priority-based, preemptive scheduling with no timeslicing. This is
+ equivalent to what is called "manual round-robin" scheduling.
+
+*SCHED_RR*
+ Priority-based, preemptive scheduling with timeslicing. Time quantums are
+ maintained on a per-thread basis and are not reset at each context switch.
+ Thus, a thread which is preempted and subsequently resumes execution will
+ attempt to complete the unused portion of its time quantum.
+
+*SCHED_OTHER*
+ Priority-based, preemptive scheduling with timeslicing. Time quantums are
+ maintained on a per-thread basis and are reset at each context switch.
+
+*SCHED_SPORADIC*
+ Priority-based, preemptive scheduling utilizing three additional
+ parameters: budget, replenishment period, and low priority. Under this
+ policy, the thread is allowed to execute for "budget" amount of time before
+ its priority is lowered to "low priority". At the end of each replenishment
+ period, the thread resumes its initial priority and has its budget
+ replenished.
+
+Operations
+==========
+
+There is currently no text in this section.
+
+Directives
+==========
+
+This section details the scheduler 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.
+
+.. _sched_get_priority_min:
+
+sched_get_priority_min - Get Minimum Priority Value
+---------------------------------------------------
+.. index:: sched_get_priority_min
+.. index:: get minimum priority value
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <sched.h>
+ int sched_get_priority_min(
+ int policy
+ );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+ - The indicated policy is invalid.
+
+**DESCRIPTION:**
+
+This routine return the minimum (numerically and logically lowest) priority for
+the specified ``policy``.
+
+**NOTES:**
+
+NONE
+
+.. _sched_get_priority_max:
+
+sched_get_priority_max - Get Maximum Priority Value
+---------------------------------------------------
+.. index:: sched_get_priority_max
+.. index:: get maximum priority value
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <sched.h>
+ int sched_get_priority_max(
+ int policy
+ );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``EINVAL``
+ - The indicated policy is invalid.
+
+**DESCRIPTION:**
+
+This routine return the maximum (numerically and logically highest) priority
+for the specified ``policy``.
+
+**NOTES:**
+
+NONE
+
+.. _sched_rr_get_interval:
+
+sched_rr_get_interval - Get Timeslicing Quantum
+-----------------------------------------------
+.. index:: sched_rr_get_interval
+.. index:: get timeslicing quantum
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <sched.h>
+ int sched_rr_get_interval(
+ pid_t pid,
+ struct timespec *interval
+ );
+
+**STATUS CODES:**
+
+On error, this routine returns -1 and sets ``errno`` to one of the following:
+
+.. list-table::
+ :class: rtems-table
+
+ * - ``ESRCH``
+ - The indicated process id is invalid.
+ * - ``EINVAL``
+ - The specified interval pointer parameter is invalid.
+
+**DESCRIPTION:**
+
+This routine returns the length of the timeslice quantum in the ``interval``
+parameter for the specified ``pid``.
+
+**NOTES:**
+
+The ``pid`` argument should be 0 to indicate the calling process.
+
+.. _sched_yield:
+
+sched_yield - Yield the Processor
+---------------------------------
+.. index:: sched_yield
+.. index:: yield the processor
+
+**CALLING SEQUENCE:**
+
+.. code-block:: c
+
+ #include <sched.h>
+ int sched_yield( void );
+
+**STATUS CODES:**
+
+This routine always returns zero to indicate success.
+
+**DESCRIPTION:**
+
+This call forces the calling thread to yield the processor to another
+thread. Normally this is used to implement voluntary round-robin task
+scheduling.
+
+**NOTES:**
+
+NONE