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MAKING THE CHANGE

From Standalone to Internet Appliance
by Edward Steinfeld

Start ę Internet Appliance Options ę Web Technology ę Cost and Options ę Web Server Inside ę Use Common Components ę Sources and PDF

WEB TECHNOLOGY

Can you hear the pathologist saying, "I donęt want my instruments on the web" or the plant manager stating, "With web access, anyone can shut down my production lines."

The solution is web technology, not the World Wide Web.

Web technology is probably the most widely used computer technology. Nearly every potential user has used a web browser either at work or at home. The user interface looks the same whether it is running on a Unix workstation, iMAC, or PC. The web client software used in the browsers can communicate with any server using the HTTP server protocol. Similarly, the HTML pages displayed can be generated on a variety of systems and still look alike.

As with all technologies, you have choices. The Internet appliance can be a web client, a web server, or both.

WEB CLIENT

The most common web client is the ubiquitous web browser. Embedded web browsers are available from a number of vendors. One of the more popular embedded web browsers comes from the originator of the commercial browser, Spyglass. The purpose of the web browser is to provide a graphical user interface (GUI).

With a web client, the appliance can send and receive data with web servers. The web client has a built-in human interface, doesn't need one, or uses a web browser as the human GUI. Web clients can transfer files using FTP protocol, but, more likely, will use the HTTP protocol. Even within the file transfer protocol, you have choices. The upcoming file format is XML. The Internet appliance can have an XML parser or framer.

Most devices that are being converted to Internet appliances already have human interfaces, the front panels. Some of the more complex devices have an embedded kernel with its own GUI. Also, only a few of these devices need to communicate with AOL, CNET, or Yahoo. These devices have a limited and unique requirementęto display specific data and control the device. Most embedded web browsers have heavy memory requirements and processor loading. Some need GUI compatibility, which would mandate the use of an embedded web browser. This will be shown later.

The embedded web client, sans browser, is an underused Internet application. It has a small memory footprint, yet has most of the power of a web server. It communicates with web servers by requesting or sending objects. The memory requirement of an embedded web client is about 12 KB of ROM and RAM.

There are few companies currently offering embedded web clients. Allegro Software Development began shipping its web client software a few months ago. It is being used in a telecommunications tester and a time-and-attendance terminal. Ebs, Inc. has had an embedded web client on its list for a long time, with the price tag TBD.

The common way to make a device into an Internet appliance is with the use of an embedded web server. The embedded web server communicates with other web servers and user-provided web browsers.

WEB SERVER

The embedded web server delivers HTML-formatted graphic pages to web browsers and communicates with other web servers on the local network or the Internet. These graphic pages can display the data normally seen on the front panel of the instrument, and accept user input to control or setup the device. Most of the embedded web servers can be incorporated with their HTML pages in under 100 KB of ROM and RAM.

What follows is the implementation of an Internet appliance using an embedded web server. The costs and memory sizes listed are based on the Allegro Software Development RomPager products. There are competitive offerings from Treck, Prism, Spyglass, and others. Many RTOS vendors have alliances with the vendors of embedded web servers. Most embedded web servers, such as the Allegro RomPager, are provided as C sources, without run-time royalties.

The key to using a web browser is the ability to display dynamic or changing data on the remote browser. This capability is provided by the embedded web servers. In order to display this dynamic data and change pages on the fly, you need a run-time HTML page parser, such as the Allegro SoftPages product.

Most embedded web servers can be incorporated as an addition to the embedded application that is used to control the instrument. A kernel or RTOS may be used but is not necessary. The RomPager embedded web server engine is invoked with only a few lines of code (see Listing 1).

Whether or not you need a RTOS is determined by the implementation of your instrument. It isnęt required to run an embedded web server. The Allegro toolkits come with make files for all popular RTOSs. If you do not use an embedded kernel or RTOS, the integration is simple. The code required for integration is shown in Listing 1. Products, such as the Allegro Internet products, come with make files for all popular embedded kernels, operating systems, and TCP/IP software stacks. Moreover, they are processor independent.

The end user can make the Internet appliance proactive by adding embedded e-mail. The appliance can send an e-mail message to the responsible person when the appliance needs service. They can also use e-mail to download new software. And finally, each end user needs a web browser (although most already have them).

Using web technology provides the Internet appliance with a common network interface, user interface, and a connection to any platform or user. It is inexpensive to develop, and the user does not have to be an Internet guru to make it happen.

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