18-06-2013, 03:28 PM
Embedded Web Technology: Applying World Wide Web Standards to Embedded Systems
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ABSTRACT
Embedded Systems have traditionally been
developed in a highly customized manner. The user
interface hardware and software along with the
interface to the embedded system are typically unique
to the system for which they are built, resulting in extra
cost to the system in terms of development time and
maintenance effort.
World Wide Web standards have been developed
in the passed ten years with the goal of allowing servers
and clients to interoperate seamlessly. The client and
server systems can consist of differing hardware and
software platforms but the World Wide Web standards
allow them to interface without knowing about the
details of system at the other end of the interface.
Embedded Web Technology is the merging of
Embedded Systems with the World Wide Web.
Embedded Web Technology decreases the cost of
developing and maintaining the user interface by
allowing the user to interface to the embedded system
through a web browser running on a standard personal
computer. Embedded Web Technology can also be used
to simplify an Embedded System’s internal network.
TERMS AND DEFINITIONS
To establish a common base of understanding, the
following definitions will be used:
Client—A logical entity that initiates a request for
data or for an action to take place. A client depends
upon the presence of an associated server to perform
requests. A client may refer to client software, client
hardware, or a combination of the two to implement a
logical client.
Server—A complementary logical entity to a
client. A server listens for client requests and services
those requests, whether the request is for data or for an
action to be performed. A server may refer to server
software, server hardware, or a combination of the two
used to implement a logical server.
EMBEDDED WEB TECHNOLOGY
INTRODUCTION
Embedded Web Technology was developed for the
Fluids and Combustion Facility (FCF) of the
International Space Station (ISS). FCF is being
developed to perform investigations in combustion
science and fluids physics in the microgravity
environment of the ISS. One of the goals of the FCF is
to be able to perform at least 10 investigations in each
discipline per year for 10 to 15 years. In order to meet
this goal, it is important for the software to be adaptable
to changing requirements. One of the areas of concern
is the user interface software that the ISS astronauts
will use to operate the FCF. The challenge facing the
FCF software engineers is that the laptop computer that
the user interface software will operate on is supplied
by the ISS, not FCF. In the event that the ISS decides to
upgrade the laptop computer, the FCF software team
will be required to modify existing user interface code
for a new environment while still developing new code
for possibly the old laptop computer and also the new
laptop computer. The FCF software engineers are also
faced with the task of developing a system that would
accommodate unknown experiments. This scenario can
be extended to any system where the users, hardware
and applications are unknown and the system is
expected to have along life.
OVERVIEW OF THE WORLD WIDE WEB
The World Wide Web is a collection of protocol
standards that are controlled by the World Wide Web
Consortium®. The protocol standards promote evolution
of the World Wide Web and ensure its interoperability.
The key protocol standard behind the World Wide
Web is the Hypertext Transfer Protocol, HTTP,
specified in RFC 2616. HTTP is “an application-level
protocol for distributed, collaborative, hypermedia
information systems.” (RFC 2616).
COMPARISON OF A TYPICAL WEB SERVER
ENVIRONMENT VERSUS AN EMBEDDED,
REAL-TIME ENVIRONMENT
A typical web server runs on a computer that is
running a nonrealtime operating system. The web
server software itself tends to be large and complex and
requires a lot of memory and disk space, on the order of
10 MB or more. The web servers are designed to run on
personal computers and general purpose workstations.
The embedded, real-time environment is much
more restricted. The system generally consists of an
embedded processor running a real-time operating
system and also running a real-time application.
Embedded systems have limited memory and disk
space that is not easily extensible.
TEMPEST FEATURES
The Tempest software, which was written by
software engineers at the NASA Glenn Research Center
in Cleveland, Ohio, is a web server written specifically
for embedded, real-time systems. Tempest was
originally written for the VxWorks® operating system
from Wind Rivers Systems, Inc. and then ported to the
Java™ language so that it can run on any operating
system that has a Java™ Virtual Machine.
Tempest requires fewer memory resources than
web servers written for the typical web server
environment. Memory requirements are under 100 KB,
depending on how it is configured. The amount of disk
space is also under 100 KB with additional space
needed for the files that make up the web pages, images
and applets.
SUMMARY
Embedded Web Technology provides for the
development of an embedded, real-time system that
appears to the users of the system as a node on the
World Wide Web. This capability provides for great
savings by eliminating the need to develop and
distribute user interface software that is platform
specific and somewhat cumbersome to configuration
manage.
Tempest software is a small, flexible web server
that makes it easy to interface to embedded systems. It
also has the potential to be an aid in debugging systems.
Tempest workshops have been held for customers
in the private sector. Customer remote data acquisition
and control applications include medical, telecommunications,
aerospace, factory automation,
instrumentation, automotive, building management and
education.
Tempest is available from the NASA Glenn
Research Center by contacting the Commercial
Technology Office at 216–433–3484.