REAL-TIME APPLICATION OVERVIEW

Before entering the description of Windows Embedded Compact 7 real-time capabilities, you need a general presentation on time determinism in computer systems. The first section of this chapter introduces important notions such as notifications and latencies and the influence of hardware on computing delays.

Using a sophisticated operating system such as Compact 7 to build a real-time application is not mandatory; numerous real-time systems do not use an operating system. The operating system has an influence on time determinism and may prevent the developer from accessing low-level functionalities. The motivations to use an operating system in a real-time application may come from software engineering constraints such as code portability or functional constraints such as user interface. In such systems, the developer must know the deterministic services of the operating system to build the path to real-time processing.

Time Determinism in an Embedded System

As the term embedded suggests, an embedded system is not dedicated to the same usage as a general purpose computer such as a PC or a server. Most of the systems belonging to this category will never be noticed by the final user; they are inside metal boxes under the car’s hood and react to driver actions, or they are installed in waterproof cabinets next to cell phone antennas to switch voice and data packets.

Embedded systems often interact with their environment; as a consequence they need to ...

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