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authorJoel Sherrill <joel.sherrill@OARcorp.com>1998-04-11 14:54:09 +0000
committerJoel Sherrill <joel.sherrill@OARcorp.com>1998-04-11 14:54:09 +0000
commit5741c943d00d515de7dd489ca0fd7807903e25d3 (patch)
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parent8e8676daae33d27c42ba95ff0a3721316c2245c7 (diff)
downloadrtems-5741c943d00d515de7dd489ca0fd7807903e25d3.tar.bz2
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@@ -21,4 +21,102 @@ essentials for performing a setup of the following items:
@item GDB Debugger
@end itemize
+The remainder of this chapter provides background information on real-time
+embedded systems and cross development. If you are not familiar with either
+of these areas, please read them. This will help familiarize you with the
+types of systems RTEMS is designed to be used in and the cross development
+process used when developing RTEMS applications.
+
+@section Real-Time Embedded Systems
+
+Real-time embedded systems are found in practically every facet of our
+everyday lives. Today's systems range from the common telephone, automobile
+control systems, and kitchen appliances to complex air traffic control
+systems, military weapon systems, an d production line control including
+robotics and automation. However, in the current climate of rapidly changing
+technology, it is difficult to reach a consensus on the definition of a
+real-time embedded system. Hardware costs are continuing to rapidly decline
+while at the same time the hardware is increasing in power and functionality.
+As a result, embedded systems that were not considered viable two years ago
+are suddenly a cost effective solution. In this domain, it is not uncommon
+for a single hardware configuration to employ a variety of architectures and
+technologies. Therefore, we shall define an embedded system as any computer
+system that is built into a larger system consisting of multiple technologies
+such as digital and analog electronics, mechanical devices, and sensors.
+
+Even as hardware platforms become more powerful, most embedded systems are
+critically dependent on the real-time software embedded in the systems
+themselves. Regardless of how efficiently the hardware operates, the
+performance of the embedded real-time software determines the success of the
+system. As the complexity of the embedded hardware platform grows, so does
+the size and complexity of the embedded software. Software systems must
+routinely perform activities which were only dreamed of a short time ago.
+These large, complex, real-time embedded applications now commonly contain
+one million lines of code or more.
+
+Real-time embedded systems have a complex set of characteristics that
+distinguish them from other software applications. Real-time embedded
+systems are driven by and must respond to real world events while adhering to
+rigorous requirements imposed by the environment with which they interact.
+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.
+
+A single real-time application can be composed of both soft and hard
+real-time components. A typical example of a hard real-time system is a
+nuclear reactor control system that must not only detect failures, but must
+also respond quickly enough to prevent a meltdown. This application also has
+soft real-time requirements because it may involve a man-machine interface.
+Providing an interactive input to the control system is not as critical as
+setting off an alarm to indicate a failure condition. However, th e
+interactive system component must respond within an acceptable time limit to
+allow the operator to interact efficiently with the control system.
+
+@section Cross Development
+
+Today almost all real-time embedded software systems are developed in a
+@b{cross development} environment using cross development tools. In the cross
+development environment, software development activities are typically
+performed on one computer system, the @b{host} system, while the result of the
+development effort (produced by the cross tools) is a software system that
+executes on the @b{target} platform. The requirements for the target platform are
+usually incompatible and quite often in direct conflict with the requirements
+for the host. Moreover, the target hardware is often custom designed for a
+particular project. This means that the cross development toolset must allow
+the developer to customize the tools to address target specific run-time
+issues. The toolset must have provisions for board dependent initialization
+code, device drivers, and error handling code.
+
+The host computer is optimized to support the code development cycle with
+support for code editors, compilers, and linkers requiring large disk drives,
+user development windows, and multiple developer connections. Thus the host
+computer is typically a traditional UNIX workstation such as are available
+from SUN or Silicon Graphics, or a PC running either a version of MS-Windows
+or UNIX. The host system may also be required to execute office productivity
+applications to allow the software developer to write documentation, make
+presentations, or track the project's progress using a project management
+tool. This necessitates that the host computer be general purpose with
+resources such as a thirty-two or sixty-four bit processor, large amounts of
+RAM, a monitor, mouse, keyboard, hard and floppy disk drives, CD-ROM drive,
+and a graphics card. It is likely that the system will be multimedia capable
+and have some networking capability.
+
+Conversely, the target platform generally has limited traditional computer
+resources. The hardware is designed for the particular functionality and
+requirements of the embedded system and optimized to perform those tasks
+effectively. Instead of hard driverss and keyboards, it is composed of
+sensors, relays, and stepper motors. The per-unit cost of the target platform
+is typically a critical concern. No hardware component is included without
+being cost justified. As a result, the processor of the target system is
+often from a different processor family than that of the host system and
+usually has lower performance. In addition to the processor families
+targeted only for use in embedded systems, there are versions of nearly every
+general-purpose process or specifically tailored for real-time embedded
+systems. For example, many of the processors targeting the embedded market
+do not include hardware floating point units, but do include peripherals such
+as timers, serial controllers, or network interfaces.
+
+