path: root/user/overview/index.rst
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authorChris Johns <>2016-03-09 15:37:31 +1100
committerAmar Takhar <>2016-05-02 20:51:26 -0400
commitc05e43b4a37277384a5d7ae8d38e150e9a38b237 (patch)
tree2715b54a76e7595b973a8d46461ec65168a0db46 /user/overview/index.rst
parentUpdate the POSIX user manual version number. (diff)
User manual, devel install and windows install.
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-Welcome to the :ref:term:`RTEMS` user manual.
+Welcome to the :ref:term:`RTEMS` User Manual.
-This document will attempt to cover every topic required as a user of RTEMS.
+This document covers all the topic required as a user of RTEMS to use the RTEMS
+operating system.
-.. note::
- Developers should look at the :r:url:`devel` for technical information the
+RTEMS, Real-Time Executive for Multiprocessor Systems, is a real-time executive
+(kernel) which provides a high performance environment for embedded
+applications including the following features:
+.. sidebar:: Developers
+ Developers should look at the :r:url:`devel` for technical information the
design and development of RTEMS is located there.
+- multitasking capabilities
+- homogeneous and heterogeneous multiprocessor systems
+- event-driven, priority-based, preemptive scheduling
+- optional rate monotonic scheduling
+- intertask communication and synchronization
+- priority inheritance
+- responsive interrupt management
+- dynamic memory allocation
+- high level of user configurability
+RTEMS provides features found in moderen operating system:
+- file systems
+- networking
+- USB
+- perminante media such as flash disks, cards and USB devices
+Real-time Application Systems
+Real-time application systems are a special class of computer applications.
+They have a complex set of characteristics that distinguish them from other
+software problems. Generally, they must adhere to more rigorous requirements.
+The correctness of the system depends not only on the results of computations,
+but also on the time at which the results are produced. The most important and
+complex characteristic of real-time application systems is that they must
+receive and respond to a set of external stimuli within rigid and critical time
+constraints referred to as deadlines. Systems can be buried by an avalanche of
+interdependent, asynchronous or cyclical event streams.
+Deadlines can be further characterized as either hard or soft based upon the
+value of the results when produced after the deadline has passed. A deadline
+is hard if the results have no value or if their use will result in a
+catastrophic event. In contrast, results which are produced after a soft
+deadline may have some value.
+Another distinguishing requirement of real-time application systems is the
+ability to coordinate or manage a large number of concurrent activities. Since
+software is a synchronous entity, this presents special problems. One
+instruction follows another in a repeating synchronous cycle. Even though
+mechanisms have been developed to allow for the processing of external
+asynchronous events, the software design efforts required to process and manage
+these events and tasks are growing more complicated.
+The design process is complicated further by spreading this activity over a set
+of processors instead of a single processor. The challenges associated with
+designing and building real-time application systems become very complex when
+multiple processors are involved. New requirements such as interprocessor
+communication channels and global resources that must be shared between
+competing processors are introduced. The ramifications of multiple processors
+complicate each and every characteristic of a real-time system.
+Real-time Executive
+Fortunately, real-time operating systems or real-time executives serve as a
+cornerstone on which to build the application system. A real-time multitasking
+executive allows an application to be cast into a set of logical, autonomous
+processes or tasks which become quite manageable. Each task is internally
+synchronous, but different tasks execute independently, resulting in an
+asynchronous processing stream. Tasks can be dynamically paused for many
+reasons resulting in a different task being allowed to execute for a period of
+time. The executive also provides an interface to other system components such
+as interrupt handlers and device drivers. System components may request the
+executive to allocate and coordinate resources, and to wait for and trigger
+synchronizing conditions. The executive system calls effectively extend the
+CPU instruction set to support efficient multitasking. By causing tasks to
+travel through well-defined state transitions, system calls permit an
+application to demand-switch between tasks in response to real-time events.
+By proper grouping of responses to stimuli into separate tasks, a system can
+now asynchronously switch between independent streams of execution, directly
+responding to external stimuli as they occur. This allows the system design to
+meet critical performance specifications which are typically measured by
+guaranteed response time and transaction throughput. The multiprocessor
+extensions of RTEMS provide the features necessary to manage the extra
+requirements introduced by a system distributed across several processors. It
+removes the physical barriers of processor boundaries from the world of the
+system designer, enabling more critical aspects of the system to receive the
+required attention. Such a system, based on an efficient real-time,
+multiprocessor executive, is a more realistic model of the outside world or
+environment for which it is designed. As a result, the system will always be
+more logical, efficient, and reliable.
+By using the directives provided by RTEMS, the real-time applications developer
+is freed from the problem of controlling and synchronizing multiple tasks and
+processors. In addition, one need not develop, test, debug, and document
+routines to manage memory, pass messages, or provide mutual exclusion. The
+developer is then able to concentrate solely on the application. By using
+standard software components, the time and cost required to develop
+sophisticated real-time applications is significantly reduced.
+Open Source
+RTEMS is an open source operating and an open source project. As a user you
+have access to all the source code and we encourage you to work with the source
+code and to integrate the processes used to build tools, the kernel and any 3rd
+party libraries into your project's configuration management processes. The
+RTEMS project is always improving the way it develivers the kernel to you and
+so your feedback is important.
+What we used in the RTEMS project to develop and maintain RTEMS does not
+dictate what you use to develop and maintain your project. You can and should
+select the work-flow that best suites the demands of your project and what you
+are delivering.