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@chapter Introduction

The purpose of this document is to guide you through the process of

installing a GNU cross development environment to use with RTEMS.

If you are already familiar with the concepts behind a cross compiler and

have a background in Unix, these instructions should provide the bare

essentials for performing a setup of the following items:

@itemize @bullet

@item GNAT/RTEMS Cross Compilation Tools on your host system

@item RTEMS OS for the target host

@item GDB Debugger

@end itemize

The remainder of this chapter provides background information on real-time

embedded systems and cross development and an overview of other

resources of interest on the Internet.  If you are not familiar with

real-time embedded systems or the other areas, please read those sections.

These sections 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.

@section Resources on the Internet

This section describes various resources on the Internet which are of

use to GNAT/RTEMS users.

@subsection RTEMS Mailing List

rtems-users@@OARcorp.com

This mailing list is dedicated to the discussion of issues related

to RTEMS, including GNAT/RTEMS.  If you have questions about RTEMS,

wish to make suggestions, or just want to pick up hints, this is a

good list to subscribe to.  Subscribe by sending an empty mail

message to rtems-users-subscribe@@OARcorp.com.  Messages sent

to rtems-users@@OARcorp.com are posted to the list.

@subsection CrossGCC Mailing List

crossgcc@@cygnus.com

This mailing list is dedicated to the use of the GNU tools in

cross development environments.  Most of the discussions

focus on embedded issues.  Subscribe by sending a message with

the one line "subscribe" to crossgcc-request@@cygnus.com.

The crossgcc FAQ as well as a number of patches and utiliities

of interest to cross development system users are available

at ftp://ftp.cygnus.com/pub/embedded/crossgcc.

@subsection GNAT Chat Mailing List

chat@@gnat.com

This mailing list is dedicated to the general discussion

of GNAT specific issues.  The discussions try to avoid

more general Ada95 language issues which have other

forums.  Subscribe by sending a message with

the one line "subscribe" to chat-request@@gnat.com.