eng: Add glossary terms

Define the following terms:

* assembler language
* C language
* ELF
* interrupt service
* software component
* software unit

Clarify:

* task

Update #3715.

2 files changed, 92 insertions, 3 deletions

diff --git a/eng/glossary.rst b/eng/glossary.rst
index c58e67f..d0fc1eb 100644
--- a/eng/glossary.rst
+++ b/eng/glossary.rst
@@ -1,6 +1,7 @@
 .. SPDX-License-Identifier: CC-BY-SA-4.0
 
 .. Copyright (C) 2017, 2019 embedded brains GmbH (http://www.embedded-brains.de)
+.. Copyright (C) 1988, 1998 On-Line Applications Research Corporation (OAR)
 
 Glossary
 ********
@@ -14,6 +15,19 @@ Glossary
     API
         An acronym for Application Programming Interface.
 
+    assembler language
+        The assembler language is a programming language which can be translated very
+        easily into machine code and data.  For this project assembler languages are
+        restricted to languages accepted by the :term:`GNU` assembler
+        program for the target architectures.
+
+    C language
+        The C language for this project is defined in terms of
+        :term:`C11`.
+
+    C11
+        The standard ISO/IEC 9899:2011.
+
     CCB
         An acronym for Change Control Board.
 
@@ -24,6 +38,10 @@ Glossary
     EARS
         An acronym for Easy Approach to Requirements Syntax.
 
+    ELF
+        An acronym for
+        `Executable and Linkable Format <https://en.wikipedia.org/wiki/Executable_and_Linkable_Format>`_.
+
     GCC
         An acronym for `GNU Compiler Collection <https://gcc.gnu.org/>`_.
 
@@ -34,6 +52,17 @@ Glossary
     GNU
         An acronym for `GNU's Not Unix <https://www.gnu.org/>`_.
 
+    interrupt service
+        An *interrupt service* consists of an
+        :term:`Interrupt Service Routine` which is called with a user
+        provided argument upon reception of an interrupt service request.  The
+        routine is invoked in interrupt context.  Interrupt service requests may have
+        a priority and an affinity to a set of processors.  An *interrupt service* is
+        a :term:`software component`.
+
+    Interrupt Service Routine
+        An ISR is invoked by the CPU to process a pending interrupt.
+
     ISVV
         An acronym for Independent Software Verification and Validation.
 
@@ -44,12 +73,54 @@ Glossary
     RTEMS
         An acronym for Real-Time Executive for Multiprocessor Systems.
 
+    software component
+        This term is defined by ECSS-E-ST-40C 3.2.28 as a "part of a software
+        system".  For this project a *software component* shall be any of the
+        following items and nothing else:
+
+        * :term:`software unit`
+
+        * explicitly defined :term:`ELF` symbol in a
+          :term:`source code` file
+
+        * :term:`assembler language` data in a source code file
+
+        * :term:`C language` object with static storage duration
+
+        * C language object with thread-local storage duration
+
+        * :term:`thread`
+
+        * :term:`interrupt service`
+
+        * collection of *software components* (this is a software architecture
+          element)
+
+        Please note that explicitly defined ELF symbols and assembler language
+        data are considered a software component only if they are defined in a
+        :term:`source code` file.  For example, this rules out symbols
+        and data generated as side-effects by the toolchain (compiler, assembler,
+        linker) such as jump tables, linker trampolines, exception frame information,
+        etc.
+
     software item
         This term has the same meaning as :term:`software product`.
 
     software product
         The *software product* is the :term:`RTEMS` real-time operating system.
 
+    software unit
+        This term is defined by ECSS-E-ST-40C 3.2.24 as a "separately compilable
+        piece of source code".  For this project a *software unit* shall be any of
+        the following items and nothing else:
+
+        * :term:`assembler language` function in a
+          :term:`source code` file
+
+        * :term:`C language` function (external and internal linkage)
+
+        A *software unit* is a :term:`software component`.
+
     source code
         This project uses the *source code* definition of the
         `Linux Information Project <http://www.linfo.org/source_code.html>`_:
@@ -57,5 +128,23 @@ Glossary
         software as it is originally written (i.e., typed into a computer) by a
         human in plain text (i.e., human readable alphanumeric characters)."
 
+    task
+        This project uses the
+        `thread definition of Wikipedia <https://en.wikipedia.org/wiki/Thread_(computing)>`_:
+        "a thread of execution is the smallest sequence of programmed
+        instructions that can be managed independently by a scheduler, which is
+        typically a part of the operating system."
+
+        It consists normally of a set of registers and a stack.  The scheduler
+        assigns processors to a subset of the ready tasks.  The terms task and
+        :term:`thread` are synonym in RTEMS.  The term task is used
+        throughout the Classic API, however, internally in the operating system
+        implementation and the POSIX API the term thread is used.
+
+        A *task* is a :term:`software component`.
+
+    thread
+        This term has the same meaning as :term:`task`.
+
     YAML
         An acronym for `YAML Ain't Markup Language <https://yaml.org/>`_.
diff --git a/eng/req-eng.rst b/eng/req-eng.rst
index 61b82be..a5e615d 100644
--- a/eng/req-eng.rst
+++ b/eng/req-eng.rst
@@ -934,9 +934,9 @@ program may be provided to place Doxygen markup in assembler files.  The
 software architecture is documented via Doxygen groups.  Each Doxygen group
 name should have a project-specific name and the name should be unique within
 the project, e.g.  RTEMSTopLevel\ MidLevel\ LowLevel.  The link from a Doxygen
-group to its parent group is realized through the `@ingroup` special command.
-The link from a Doxygen group or software component to the corresponding
-requirement is realized through a `@satisfy{req}`
+group to its parent group is realized through the ``@ingroup`` special command.
+The link from a Doxygen group or :term:`software component` to the
+corresponding requirement is realized through a ``@satisfy{req}``
 `custom command <http://www.doxygen.nl/manual/custcmd.html>`_
 which needs the identifier of the requirement as its one and only parameter.
 Only links to parents are explicitly given in the Doxygen markup.  The links