Книга: Real-Time Concepts for Embedded Systems
1.1.4 Defining the Embedded System
1.1.4 Defining the Embedded System
Some texts define embedded systems as computing systems or devices without a keyboard, display, or mouse. These texts use the “look” characteristic as the differentiating factor by saying, “embedded systems do not look like ordinary personal computers; they look like digital cameras or smart toasters.” These statements are all misleading.
A general definition of embedded systems is: embedded systems are computing systems with tightly coupled hardware and software integration, that are designed to perform a dedicated function. The word embedded reflects the fact that these systems are usually an integral part of a larger system, known as the embedding system. Multiple embedded systems can coexist in an embedding system.
This definition is good but subjective. In the majority of cases, embedded systems are truly embedded, i.e., they are “systems within systems.” They either cannot or do not function on their own. Take, for example, the digital set-top box (DST) found in many home entertainment systems nowadays. The digital audio/video decoding system, called the A/V decoder, which is an integral part of the DST, is an embedded system. The A/V decoder accepts a single multimedia stream and produces sound and video frames as output. The signals received from the satellite by the DST contain multiple streams or channels. Therefore, the A/V decoder works in conjunction with the transport stream decoder, which is yet another embedded system. The transport stream decoder de-multiplexes the incoming multimedia streams into separate channels and feeds only the selected channel to the A/V decoder.
In some cases, embedded systems can function as standalone systems. The network router illustrated in Figure 1.2 is a standalone embedded system. It is built using a specialized communication processor, memory, a number of network access interfaces (known as network ports), and special software that implements packet routing algorithms. In other words, the network router is a standalone embedded system that routes packets coming from one port to another, based on a programmed routing algorithm.
The definition also does not necessarily provide answers to some often-asked questions. For example: “Can a personal computer be classified as an embedded system? Why? Can an Apple iBook that is used only as a DVD player be called an embedded system?”
A single comprehensive definition does not exist. Therefore, we need to focus on the char-acteristics of embedded systems from many different perspectives to gain a real under-standing of what embedded systems are and what makes embedded systems special.
Оглавление книги
- 1.1.1 Embedded Systems in the Home Environment
- 1.1.2 Embedded Systems in the Work Environment
- 1.1.3 Embedded Systems in Leisure Activities
- 1.1.4 Defining the Embedded System
- 1.1.5 Embedded Processor and Application Awareness
- 1.1.6 Hardware and Software Co-Design Model
- 1.1.7 Cross-Platform Development
- 1.1.8 Software Storage and Upgradeability
- Chapter 4: Introduction To Real-Time Operating Systems
- 4.3 Defining an RTOS
- 5.2 Defining a Task
- 7.2 Defining Message Queues
- 4.4.4 The Dispatcher
- About the author
- Chapter 7. The state machine
- Appendix E. Other resources and links
- Example NAT machine in theory
- Using Double Quotes to Resolve Variables in Strings with Embedded Spaces
- The final stage of our NAT machine
- Compiling the user-land applications