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The Linux operating system is the fastest growing UNIX-like operating system in the world, with an estimated market size of seven million users and a 1997-1998 growth rate exceeding 200 percent. Linux has become the OS of choice for Web servers, with more than 50-percent market share to date.

Its popularity is based on several factors. If purchased from a reseller, Linux costs about one-tenth as much as comparable UNIX products. If downloaded from any of a number of sources on the Internet, it costs nothing at all. Once considered a mere programmer's toy, Linux is now accepted as a stable and reliable operating system suitable for networks and servers. A major reason for its popularity is its open source code, which gives developers greater control over program development. And finally, Linux is highly portable.

The maturing of Linux is recent enough that support from tool vendors and computer manufacturers is not yet universal, but some major companies have announced support, and more are coming on board every month. For example, Sun Microsystems offers UltraLinux, a version of Linux that supports UltraSPARC workstations and servers, Apple has been supporting Linux on the Power Macintosh since 1996, and Compaq preloads Linux on a number of its servers.

The stability and reliability of Linux have made it attractive to designers of embedded applications, where dependability is crucial. More and more embedded developers are working on desktop PCs, so Linux’s unbloated code (compared to UNIX) is another attraction in a limited development environment.

As a result of Linux’s popularity with embedded developers, more and more programming tool vendors are supporting it. CAD-UL, for example, has just come out with an embedded-optimized C/C++ compiler and toolkit for Linux developers. Many developers now working in Linux have years of experience with C and C++, so it just makes sense to give them tools that will be easy for them to use. This kit enables them to prototype their software code on a Linux-based host platform using C/C++ tools. Equally important is that a number of our customers are already implementing Linux in embedded systems, and of course we have an obligation to support our existing customer base.

Other tool vendors are going the same way. Zentropic Computing has just released a CD with RTLinux installation and development tools, for example.

There is considerable interest in using Linux for a target OS in embedded systems, as well as for host development. Paul Zorfass, embedded analyst with IDC/FTI, says "Linux is in its early stages of evaluation by leading-edge embedded developers. Of interest is its potential as an embedded target-platform operating system. This is still at a very early stage, but it holds promise."

The promise is already being kept. The Real-Time Linux (RTLinux) project at the New Mexico Institute of Mining and Technology has developed an extension to Linux that handles time-critical tasks, and many companies are already using it for real-time embedded applications. RTLinux implements a small hard-real-time kernel with Linux running as just one task within that kernel. Linux, normally non-pre-emptible, runs as the lowest priority and is pre-emptible by higher-priority tasks. In essence, it is a bifurcated system, with strict partitioning of real-time and non-real-time tasks.

For example, data-acquisition applications composed of a simple polling or interrupt-driven real-time task send data through a queue to a Linux process that takes care of logging and display. RTLinux is said to be quite successful for such applications. According to Victor Yodaiken, Chair of the Dept. of Computer Science at the New Mexico Institute of Mining and Technology (Socorro, N.M.) where RTLinux originated, the I/O buffering and aggregation performed by Linux provide a high level of average-case performance while the real-time task meets strict worst-case limited deadlines.

Not everyone is excited by the idea of Linux in embedded systems, however. Luke Dion, Vice President of Lynx Real-Time Systems, Inc. says, "The hurdle for Linux in being used as an embedded target OS is going to be quality and support. A lot of real-time applications are going into systems that are life-critical, such as airplanes and life-support systems in hospitals, or they're business critical in ways where a crash could cost millions of dollars, such as in telecom or banking. These systems require a high level of safety and quality. It's not that Linux couldn't get there, it's just that it's hard to control development of a system that has open sources. Even if the quality is achieved, who is going to provide technical support?"

It's true that there are hurdles to be dealt with. But no new applications in the electronics industry are without problems. Once there is widespread support for an emerging technology, it is only a matter of time until the roadblocks are knocked down. The stability and reliability of Linux appear to be of great potential value in real-time embedded systems, so it is a safe bet that the question of technical support will be worked out somehow, just as its non-pre-emptive character has been solved with RTLinux.

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