Definition and development of embedded systems
Author: Beijing University of Aeronautics and Astronautics He Limin
Original link: http://tech.ccidnet.com/pub/Article/c302_a197693_p1.html
First, the history of modern computer technology
1. Beginning an embedded application in the micro-machine era
In 1946, the electronic digital computer was born in 1946. In the long history of history, the computer is always supported in a special machine room to realize a large-scale expensive device for numerical calculation. 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 achieved that the intelligent control of the object is achieved, so it has a technical requirement and technology development direction with the general 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 phase, 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, which leads to the end of the 20th century. High speed development period of the computer.
3. Milestones for the development of two big branches
The development of the specialized division of labor of the general computer system and the embedded computer system has led to the rapid development of computer technology at the end of the 20th 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 milestone of the two major branches of modern computer technology is that it not only has formed a professional division of labor development, but also expands the task of computer technology to the field of traditional electronic system, so that the computer has become comprehensive intelligence into human society. Powerful tools in the times. Second, the 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 for embedded systems, and can define the embedded systems in historical, 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. Related Features with "Embedd": 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), etc. Related Features with "Specialty": Soft, hardware's tailoring; to meet the minimum soft, hardware configuration, etc. of object requirements. Related Features with "Computer System": The embedded system must be a computer system that meets 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, when it is understood that the embedded system is defined, do not confuse the embedded device. 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
According to the definition of the above-described embedded system, the embedded system can be referred to as a computer system that satisfies the three elements of the definition. 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 since the embedded system is an embedded computer system, only the embedded processor constitutes a computer system and as an embedded application, such a computer system is only It 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.), Form a 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.
Third, an independent development path of embedded systems
1. MCU has created an independent development path of embedded systems
Although the embedded system originates from the microcomputer era, however, the volume, price, and reliability of the microcomputer cannot 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, namely "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 single chip was born in the late 1970s, and the three stages of SCM, MCU, SOC were experienced.
1. SCM is the Single Chip Microcomputer phase, 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.
2. MCU is the micro controller unit, the main technical development direction is: continuous expansion of various peripheral circuits and interface circuits required by the object system, highlight the intelligent control capabilities of their objects. 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 has developed MCS-51 rapidly developing MCS-51 from single-chip microcomputers 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.
3. Single chip microcomputer is an independent development path of embedded systems, an important factor in the development of the MCU stage is to seek the maximum solution to the application system 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.
Fourth, two application modes of the embedded system
The embedded application characteristics of the embedded system determine its multi-discipline crossing features. 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. Objective existence of two application modes
The embedded computer system originated from the microcomputer era, but quickly entered the era of independent development. 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 fade out in 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 computer professionals Interventional 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. Coal and complementary application mode
Due to the largest and most wide-level application of the embedded system, the intelligent transformation in the field of traditional electronic technology, therefore, with the professional electronic technology team of the subject, with the least embedded system soft, hardware overhead, 8-bit The machine is main, the 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-chip microcomputer due to the embedded system, most of them are based on 8-bit microcontrollers, achieving the most underlying embedded system applications, with significant electronic system design model features. 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
