Author: Beijing University of Aeronautics and Astronautics He Limin
Abstract: The embedded system was born in the microelectronics era and has experienced a long-standing single-chip road. Seeking scientific definitions to embedded systems, you must understand the development history of embedded systems, define embedded systems in accordance with historical, intrinsic, and universality, and distinguish between definitions and characteristics. Due to embedded system applications, the extensive development path of the object system and the single-chip technology, enabling embedded system applications in two models, from the discipline construction, can be uniformly embedded.
Keywords: embedded system development history embedded system definition application mode high and low application
Currently, in the field of embedded system applications, many people don't know what is embedded system. Some people have worked for more than ten years of single-chip application, and I don't know that the microcontroller is a most typical embedded system; it is also the characteristics of the embedded system when explaining what is embedded system. I often don't know the cloud. Therefore, it is necessary to understand the origin of the embedded system from the perspective of the disciplinary construction from the perspective of the discipline system from the perspective of the contemporary development history.
1 History of technology development of modern computers
(1) Embedded application began in the microcomputer era
The electronic digital computer was born in 1946. In its subsequent historical process, the computer is always supported in special machine rooms to achieve large-scale expensive devices for numerical calculations. Until the 1970s, the appearance of microprocessors, the computer had historic changes. Microprocessor-based microprocessor is small, cheap, high reliability characteristics, quickly walk out of machine room; microcomputer based on high-speed numerical decision capabilities, the intelligent level has caused interest in control professionals, requirement The microcontrol is embedded in an object system to realize the intelligent control of the object system. For example, a microcomputer is reinforced, mechanically reinforced, and configure a variety of peripheral interface circuits, and mounted to a large ship to constitute an automatic driver or a turbine state monitoring system. In this way, the computer lost the original morphology and general computer function. In order to distinguish the original general-purpose computer system, the embedded computer system is implemented in the object system, referred to as an embedded computer system. Therefore, the embedded system is born in the microcomputer era, the embedded nature of the embedded system is embedded in an object system, which is to understand the basic starting point of the embedded system.
(2) Two big branches of modern computer technology
Since the embedded computer system is embedded in the object system, it is realized that the intelligent control of the object is achieved, so it has a technical requirements and technological development direction with the general-purpose computer system.
The technical requirements of the general computer system are high-speed, massive calculations; the direction of technology is an unlimited increase in bus speed, and the storage capacity is infinitely expanded. The technical requirements of the embedded computer system are intelligent control capabilities of the object; the technical development direction is the reliability of embedded performance, control capabilities and control of the subject system.
In the early days, people were difficult to modify the general-purpose computer system, and embedded applications were implemented in large equipment. However, for numerous object systems (such as household appliances, instrumentation, industrial control units ...), it is unable to embed universal computer systems, and the technology development direction of embedded systems and general computer systems is completely different. Therefore, universal computers must be developed independently. System and embedded computer system, which form two major branches of modern computer technology development.
If the appearance of the microcomputer enables the computer to enter the modern computer development stage, the birth of the embedded computer system is marked, and the computer has entered the era of two major branches of the general computer system and the embedded computer system, causing 20 At the end of the century, the computer's rapid development period.
(3) Milestones for the development of two big branches
The development of the specialized division of labor of the universal computer system and the embedded computer system, leading to the rapid development of computer technology at the end of the 21st century. Computer professional field concentrates on the development of universal computer systems soft, hardware technology, does not have to take care of embedded applications, universal microprocessors quickly from 286, 386, 486 to Pentium series; operating system quickly expand computer based on high-speed massive data file processing Ability, enabling universal computer systems into the perfect stage. The embedded computer system has embedded a completely different path, which is a single-chip road. It mobilized the manufacturers and professionals from the original traditional electronic system, which received embedded systems originated in the computer field, assabbed to develop and popularize the historical tasks of the embedded system, and quickly develop traditional electronic systems to intelligence. Modern electronic system era.
Therefore, the two branches of modern computer technology have also formed not only the professional division of labor of computer development, but also expands the task of developing computer technology to the field of electronic system, making computers into comprehensive human society. Powerful tools in the intelligent era.
2 Definition and characteristics of embedded systems
If we understand the origin and development of the embedded (computer) system, we will not have too much misunderstandings to the embedded system, and can define the embedded systems in history, essentially, and universally.
(1) Definition of embedded system
According to historical, intrinsic, universality requirements, embedded systems should be defined as: "Special Computer Systems embedded in the object system." "Embedd", "Specialty" and "Computer System" are three basic elements of the embedded system. The object system refers to the host system embedded in the embedded system.
(2) Features of embedded systems
The characteristics of the embedded system are different from the definition, which is derived from three basic elements in the definition. Different embedded systems have a difference.
The related features of "embedded": Since it is embedded in the object system, the environmental requirements of the object system must be met, such as physical environment (small), electrical / atmosphere environments (reliable), cost (cheap) and other requirements.
related features of "Specialty": Soft, hardware cropping; the minimum soft, hardware configuration, etc. satisfying the subject requirements.
related to "Computer System": The embedded system must be a computer system that meets the object system control requirements. Extremely educed with the upper two features, such a computer must be configured with an interface circuit that is adapted to an object system.
In addition, do not confuse the embedded device when understanding the embedded system definition. The embedded device refers to a product, apparatus, such as an embedded system, for example, a single-chip household appliance, instrumentation, industrial control unit, robot, mobile phone, PDA, etc.
(3) Types and development of embedded systems
In accordance with the definition of the above-described embedded system, it is a embedded system as long as the computer system that is defined in the definition is satisfied. The embedded system can be divided into device-level (single board, module), chip level (MCU, SOC).
Some people regard the embedded processor as an embedded system, but because the embedded system is an embedded computer system, only the embedded processor constitutes a computer system and as an embedded application, such a computer The system can be referred to as an embedded system.
The embedded system is closely related to the object system. The main technological development direction is to meet the embedded application requirements, and continuously expand the peripheral circuit required by the object system (such as ADC, DAC, PWM, calendar clock, power monitoring, program operation monitoring circuit, etc. ), Forming an application system that meets the requirements of the object system. Therefore, the embedded system acts as a dedicated computer system to continue to develop to the computer application system. Therefore, the dedicated computer system in the definition can be introduced into a computer application system required by the object system.
3 Independent Development Roads of Embedded Systems (1) MCU creates an independent development path of embedded systems.
Although the embedded system originated in the microcomputer era, however, the volume, price and reliability of the microcomputer can meet the embedded application requirements of the majority of object systems, so the embedded system must take an independent development path. This road is the chipping path. Do your computer on a single chip, creating a single-chip year-developer era of embedded systems.
When exploring the development path of the microcontroller, there have been two modes, ie "σ mode" and "innovative mode". "Σ mode" is essentially a general purpose computer direct chipping mode, which is integrated on a chip, constitutes a single chip, and constitutes a single chip; "Innovation mode" is fully composed of embedded applications. Requires a new architecture, microprocessor, instruction system, bus mode, management mode, etc., which meet the embedded application requirements. Intel's MCS-48, MCS-51 is a single-chipful embedded system (single chip microcomputer) developed in the innovative model. The MCS-51 is a fully comprehensive embedded system based on the MCS-48 exploration. History proves that "innovation mode" is the correct road of embedded systems independently develops, and the architecture of MCS-51 has also become a typical structural system for single-piece embedded systems.
(2) History of technology development of single chip microcomputer
The microcontroller was born in the end of the 1970s, and I experienced the three stages of SCM, MCU, SOC.
The SINGLE mini computer (Single Chip Microcomputer) is mainly to seek the best architecture of the best single-piece embedded system. "Innovation Mode" has been successful, laid the development path of SCM and General Computer. Intel companies are not available on the road of creating embedded systems.
MCU is the micro controller unit, the main technological development direction is: continuous expansion of various peripheral circuits and interface circuits required by the object system, highlight the intelligent control capability of the object. It is related to the object system. Therefore, the development of MCU will inevitably, in electrical, electronic technology manufacturers. From this perspective, Intel gradually fades out of the development of MCUs and its objective factors. In the development of MCU, the most famous manufacturers have a number of Philips.
Philips develops MCS-51 from single-chip microcomputer to microcontrollers in its huge advantage in embedded applications. Therefore, when we review the road of embedded systems, don't forget the historical merits of Intel and Philips.
MCU is an independent development path of embedded systems, an important factor developed to the MCU stage, is to seek the maximization solution on the chip; therefore, the development of special single-chip microcomputer has naturally formed SOC trend. With the development of microelectronics, IC design, EDA tools, SOC-based single-chip application system design will have a large development. Therefore, the understanding of the microcontroller can extend from a single-chip microcomputer, a single chip microcontroller to a single-chip application system.
4 two application modes of embedded systems
The embedded application characteristics of the embedded system determines its multi-discipline crossing. As the consolidation of the computer, the computer sector is required to involve its architecture, software technology, engineering application research. However, understand the control requirements of the object system, and implement system control mode must have expertise in the field. Therefore, from the historical process of the development of embedded systems, and in the diversity of embedded applications, you can understand the objective application modes.
(1) Two application modes of objective existence
The embedded computer system originated from the microcomputer era, but quickly entered the era of separately developed single-chip microcomputer. In the single-chip old era, the embedded system quickly entered the traditional electronic technology field in the field of the device, and the electronic technology application engineer is the main body, and the intelligence of traditional electronic systems, and the computer professional team did not truly enter the microcontroller application. Therefore, the electronic technology application engineer is engaged in the application development of single-chip microcomputer with its own habitual electronic technology application model. This most important feature of this application mode is: soft, hardware underlayer and randomness; close correlation of subject system professional technology; lack of computer engineering design methods. Although in the single-chip old age, computer majors have fallen out of the field of embedded system, but with the arrival of the PC era, the network, communication technology has developed; at the same time, the embedded system is soft and hardware technology has greatly improved, for the computer Professionals involved in embedded system applications have opened up a broad world. The intervention of computer professionals, the formation of computer application models with obvious engineering application features based on embedded systems soft, hardware platform, network, communication-based non-embedded underlying applications.
(2) Corporation and complement of two application modes
Due to the largest and most wide-level application of embedded systems, it is intelligent transformation in the field of traditional electronic technology. Therefore, the electronic technology team specializing in the subject is mainly, with the least embedded system soft, hardware overhead, 8-bit machine is main, electronic system application model with strong electronic system design color will exist for a long time. In addition, computer professionals will increasingly involving embedded system applications, but they are separated from subject expertise. The application field will focus on network, communications, multimedia, business electronics, etc., it is impossible to replace the original electronic engineer. Embedded applications in control, instrumentation, mechanical electronics, etc. Therefore, the objective existence of two application modes will have a long time to replenish each other in different fields. Electronic system design mode should learn computer engineering methods and embedded system software technology from computer application design mode; computer application design mode should understand the circuit system characteristics of embedded system applications, basic peripheral circuit design methods and Basic requirements for the object system, etc.
(3) High and low ends of embedded system applications
Due to the independent development path of a single single-chip microcomputer due to the embedded system, most of the 8-bit microcontroller is achieved, and the most underlying embedded system application has a significant electronic system design model. Most of the microcontroller application developers are an electronic system engineer in the field of object system. In addition, the appearance of single-chip microcomputer is immediately separated from the computer professional field, and the "intelligent" device enters the electronic system area, and does not bring "embedded system." "concept. Therefore, many people engaged in single-chip applications, do not understand the relationship between single-chip microcomputer and embedded systems, often understand the field of computer professional, based on 32-bit embedded processors, engaged in network, Application of communication, multimedia, etc. Thus, "MCU" and "embedded system" form two independent nouns in the embedded system. However, due to the "microcontroller" is a typical, independently developed embedded system, from the perspective of discipline construction, it should be unified as "embedded system". Taking into account the primary application characteristics of the original single-chip electronic system, the embedded system can be applied into high-end and low ends, and the original microcontroller is applied to the low-end application of the embedded system, and the meaning of its underlayer and the tightening with the object system. coupling.
