Embedded operating system (OS)

Embedded and/or integrated systems are in some ways reminiscent of the computers of yesteryear, with their limited resources. This leads to a need for code compactness and optimized use of hardware, which is no longer the case in today's computer systems, where abundant computing and memory resources are the rule. However, let there be no mistake: comparison is not reason, and today's embedded computer systems are often far more powerful than their non-embedded predecessors, but they are also extremely constrained, and the few kilobytes, microseconds or milliwatts that are saved by an ad hoc operating system will always be useful to the application, enabling a device to operate better, safer and longer. Overall, the aim of an operating system is to abstract and share hardware resources to simplify application writing. Modern computer operating systems aim to optimize the user's average response time to a keyboard and mouse, even if this means requiring many resources at any given time to guarantee this objective. In the embedded world, such an objective often makes no sense, as there is no user to speak of, and the rather subjective and poorly formalized notion of acceptable response time is clearly inadequate. Operating systems for embedded systems generally need clearly specified constraints to realize the services they are supposed to provide. These criteria can be related to time performance, for example minimum and maximum interrupt processing latency, maximum memory space requirements, hardware control capacity with a view to low power consumption, and so on. Systems in which an action must be carried out within a predefined period of time, potentially repeatedly, are known as real-time systems. This is particularly important in the embedded world, where controlling the triggering of an air bag or the decoding of a video is only of interest if the action is carried out within the allotted time.

In addition, operating system construction methods have evolved over time, and today only include those parts that are useful both to the application - if this is known in advance, which is often the case - and to the hardware. This allows us to build a "tailor-made" system that maximizes the device's efficiency. As integration poses crucial questions of efficiency and flexibility, integrated systems currently being designed tend to include several (or even many) processors. The management of these many processors, which may be of the same or different types - for example, a general-purpose processor and a signal-processing processor - clearly has an impact on the operating systems intended for on-board use.

Most of today's embedded applications use algorithms that are very demanding in terms of memory resources and computing capacity. As a result, embedded electronic...