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What is an Embedded System?
An embedded system is a specialised computing system that is optimised to carry out a single, or very few, dedicated functions. Embedded systems form part of larger devices, or pieces of equipment, with the purpose of controlling a dedicated function within those machines. The pre-determined functionality of an embedded system contrasts with that of a GPP, such as those found in a Personal Computer (PC), whereby a single processor will perform a large number of very varied functions.
A GPP is not designed with any specific task in mind. A desktop computer, for example, can be used to perform a myriad of tasks including document creation and editing, a home entertainment system, an image and video editing system, or an internet terminal. An embedded system is application-specific, and as such can be finely optimised to deliver the chosen characteristics of a given application. Those characteristics could be to provide very high performance in a given area, or low power consumption. It is only by making the system application-specific that allows an embedded system to achieve such performance. A GPP may be able to perform the functions of an embedded system, but is unlikely to achieve the same system performance, and/or power consumption requirements. The generic programmability of a GPP also comes at a cost, with GPPs generally being far more expensive than those used in embedded systems.
Applications
Embedded systems are deployed in a large number of devices across a breadth of fields. An overview of some of the more prominent uses for embedded systems is provided in Figure 9.1.
A number of more specific applications from each of the highlighted fields are provided as follows:
• Telecommunications — Mobile phones, routers, consumer radio and television.
• Medical Electronics — Body scanning devices such as MRI machines, electronic stethoscopes and pacemakers.
• Consumer Electronics — Digital cameras, video games consoles and washing machines.
• Military and Avionics — RADAR and SONAR, guided missile systems, satellite stations and flight navigation systems.
• Transport Systems — Anti-Lock Braking Systems (ABS), air bag deployment, on board entertainment, GPS and satellite navigation systems.
Generic Embedded System Architecture
In general, the architecture of an embedded system follows the architecture outlined in Figure 9.2.
The individual components in Figure 9.2 are defined as follows:
• Processor — This is the ‘brains' of the system. It is programmed to perform the tasks specific to the application of the embedded system.
• Memory Controller — Memory controllers manage the reading and writing of data to and from main memory in an embedded system. Memory controllers reside in on-chip soft cores, providing an interface between the system memory and all other parts of the system.
• Peripherals — These are the components around the central processing unit. Peripherals can be implemented as individual integrated circuits, be contained onchip with the processor, or may reside in an area of programmable logic such as an FPGA.
• System Bus — In an embedded system with multiple buses, the system bus connects the processor, memory controller and other high-speed devices together. As such, it is the bus with the greatest bandwidth in the system.
• Peripheral Bus — The second bus creates two separate sections of the system, allowing two arbiters to control and manage communications across the two buses. This allows devices on the peripheral bus to communicate with each other, even when a high-priority processor-memory transaction is taking place on the system bus.
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