First, the technical development history of modern computers
1. Embedded application in microcomputer era
Electronic digital computer was born in 1946. In the long historical process since then, computers have always been large and expensive equipment to realize numerical calculation in special computer rooms. It was not until the advent of microprocessors in the 1970s that computers experienced historic changes. Microprocessor-based microcomputers are rapidly coming out of the computer room because of their small size, low price and high reliability. Microcomputer based on high-speed numerical calculation ability has aroused the interest of control professionals, and it is required to embed microcomputer into the object system to realize intelligent control of the object system. For example, after electrical and mechanical strengthening, a microcomputer is equipped with various peripheral interface circuits and installed on a large ship to form an autopilot or marine engine condition monitoring system. In this way, the computer lost its original form and general computer functions. In order to be different from the original general computer system, the computer is embedded into the object system to realize the intelligent control of the object system, which is called embedded computer system. Therefore, the embedded system was born in the microcomputer era, and the embedded essence of the embedded system is to embed a computer into an object system, which are the basic starting points for understanding the embedded system.
2. Two branches of modern computer technology.
Because the embedded computer system should be embedded into the object system to realize intelligent control of the object, it has completely different technical requirements and development direction from the general computer system. The technical requirement of general computer system is high-speed and massive numerical calculation; The development direction of technology is the infinite improvement of bus speed and the infinite expansion of storage capacity. The technical requirement of embedded computer system is the intelligent control ability of the object; The development direction of technology is embedded performance, control ability and control reliability closely related to the object system.
In the early days, people reluctantly reformed the general computer system to realize embedded applications in large-scale equipment. However, for many object systems (such as household appliances, instruments and meters, industrial control units), it is impossible to embed into general-purpose computer systems, and the technical development direction of embedded systems and general-purpose computer systems is completely different. Therefore, it is necessary to independently develop general-purpose computer system and embedded computer system, which forms two branches of the development of modern computer technology.
If the appearance of microcomputer makes the computer enter the stage of modern computer development, then the birth of embedded computer system marks that the computer has entered the era of parallel development of general computer system and embedded computer system, which led to the high-speed development of computers at the end of the 20th century.
3. Milestones in the development of the two branches
The specialized development between general-purpose computer system and embedded computer system led to the rapid development of computer technology in the late 20th century and early 20th century. The computer professional field concentrates on developing the software and hardware technology of general computer system, regardless of the embedded application requirements, and the general microprocessor changes rapidly from 286, 386 and 486 to Pentium series; The operating system has rapidly expanded the computer's file processing ability based on high-speed and massive data, making the general computer system enter a perfect stage.
Embedded computer system has embarked on a completely different road, which is the road of single chip development. It mobilized the original manufacturers and professionals in the traditional electronic system field, took over the embedded system originated from the computer field, and undertook the historical task of developing and popularizing the embedded system, so that the traditional electronic system quickly developed into the era of intelligent modern electronic system.
Therefore, the milestone significance of the two branches of modern computer technology development lies in that it not only forms a specialized division of labor in computer development, but also extends the task of developing computer technology to the traditional electronic system field, making computers a powerful tool for human society to enter the era of comprehensive intelligence.
Second, the definition and characteristics of embedded system
If we know the origin and development of embedded (computer) system, we won't have too many misunderstandings about embedded system, but we can define embedded system historically, essentially and universally.
1. Definition of embedded system
According to historical, essential and universal requirements, embedded system should be defined as "special computer system embedded in the target system". Embedded, special and computer system are three basic elements of embedded system. The target system refers to the host system embedded in the embedded system.
2. The characteristics of embedded system
The characteristics of embedded system are different from the definition, which is derived from three basic elements in the definition. Different embedded systems will have different characteristics. Related characteristics of "embeddedness": Because it is embedded in the object system, it must meet the environmental requirements of the object system, such as physical environment (small), electrical/atmospheric environment (reliable), cost (low price) and so on. Characteristics related to "particularity": customization of software and hardware; Minimum software and hardware configuration to meet the requirements of the object. Features related to "computer system": The embedded system must be a computer system that can meet the control requirements of the target system. In view of the above two characteristics, this computer must be equipped with an interface circuit suitable for the target system.
In addition, when understanding the definition of embedded system, don't confuse it with embedded devices. Embedded equipment refers to products and equipment with embedded systems, such as household appliances, instruments, industrial control units, robots, mobile phones, PDA, etc.
3. Types and development of embedded systems
According to the above definition of embedded system, a computer system can be called an embedded system as long as the three elements in the definition are met. Embedded system can be divided into device level (industrial computer), board level (single board, module) and chip level (MCU, SoC).
Some people regard the embedded processor as an embedded system, but because the embedded system is an embedded computer system, such a computer system can only be called an embedded system if the embedded processor is regarded as an embedded application.
Embedded system is closely related to the target system, and its main technical development direction is to meet the requirements of embedded applications and continuously expand the peripheral circuits required by the target system (such as ADC, DAC, PWM, calendar clock, power supply monitoring, program operation monitoring circuit, etc.). ) and form an application system that meets the requirements of the object system. Therefore, embedded system, as a special computer system, should continuously develop into computer application system. Therefore, the defined dedicated computer system can be extended to a computer application system that meets the requirements of the target system.
Thirdly, the independent development path of embedded system.
1. Single chip microcomputer pioneered the independent development of embedded systems.
Although the embedded system originated from the era of microcomputer, the size, price and reliability of microcomputer can not meet the embedded application requirements of most target systems, so the embedded system must take the road of independent development. This road is a chip road. The computer is made on one chip, thus creating the era of single chip microcomputer for independent development of embedded systems.
When exploring the development path of single chip microcomputer, there have been two modes, namely "σ mode" and "innovation mode". "Sigma mode" is essentially a general-purpose computer direct chip mode, which cuts the basic units in the general-purpose computer system and integrates them on a chip to form a single chip. "Innovation Mode" designs a brand-new architecture, microprocessor, instruction system, bus mode and management mode according to the requirements of embedded applications. MCS-48 and MCS-5 1 of Intel Corporation are monolithic embedded systems (monolithic microcomputers) developed according to innovative modes. MCS-5 1 is an integrated embedded system based on MCS-48. History has proved that "innovation mode" is the correct way for independent development of embedded systems, and the architecture of MCS-5 1 has therefore become a typical architecture of monolithic embedded systems.
2. The development history of single chip microcomputer technology
Single-chip microcomputer was born in the late 1970s and has gone through three stages: SCM, MCU and SoC.
1.SCM is the stage of single chip microcomputer, which mainly seeks the best architecture of embedded system in the best single chip form. The success of "innovation mode" has laid a completely different development path between single chip microcomputer and general computer. Intel has made great contributions to the independent development of embedded systems.
2.MCU is the stage of microcontroller unit, and its main technical development direction is to expand all kinds of peripheral circuits and interface circuits that meet the requirements of embedded applications and highlight the intelligent control ability of its objects. The fields it involves are all related to the object system, so the important task of developing MCU inevitably falls on the electrical and electronic technology manufacturers. From this point of view, Intel's gradual fading out of MCU also has its objective factors. In the development of MCU, the most famous manufacturer is Philips.
With its great advantages in embedded applications, Philips Company has rapidly developed MCS-5 1 from a single chip microcomputer to a microcontroller. Therefore, when we review the development path of embedded systems, don't forget the historical achievements of Intel and Philips.
3. Single-chip microcomputer is the independent development path of embedded system, and the important factor to develop to MCU stage is to seek the biggest solution of application system on chip; Therefore, the development of dedicated single-chip microcomputer naturally forms the trend of SoC. With the development of microelectronic technology, ic design and EDA tools, the design of single chip microcomputer application system based on SoC will have great development. Therefore, the understanding of MCU can be extended from MCU and MCU to MCU application system.
Four, two application modes of embedded system
The embedded application characteristics of embedded system determine its interdisciplinary characteristics. As the connotation of computer, people in the computer field are required to devote themselves to the research of its architecture, software technology and engineering application. However, in order to understand the control requirements of the object system and realize the control mode of the system, we must have professional knowledge in the object field. Therefore, from the historical process of embedded system development and the diversity of embedded applications, we can understand two objectively formed application modes.
1. Two objectively existing application modes
Embedded computer system originated in the era of microcomputer, but soon entered the era of independent development of single chip microcomputer. In the era of single-chip microcomputer, embedded system quickly entered the field of traditional electronic technology in the form of devices, and realized the intelligentization of traditional electronic system with electronic technology application engineers as the main body, but the computer professional team did not really enter the field of single-chip microcomputer application. Therefore, electronic technology application engineers are engaged in the application development of single chip microcomputer with their accustomed electronic technology application mode. The most important characteristics of this application mode are: the underlying nature and randomness of software and hardware; The close correlation of professional knowledge of object system; Lack of computer engineering design methods.
Although in the era of single-chip microcomputer, computer specialty faded out of the field of embedded system, with the arrival of post-PC era, network and communication technology developed; At the same time, the software and hardware technology of embedded system has been greatly improved, which has opened up a broad world for computer professionals to intervene in embedded system applications. With the intervention of computer professionals, computer application mode has obvious characteristics of computer engineering application, that is, non-embedded underlying applications based on embedded system software and hardware platform, mainly network and communication.
2. The coexistence and complementarity of the two application modes.
Because the biggest, widest and lowest application of embedded system is the intelligent transformation of traditional electronic technology, the application mode of electronic system with strong electronic system design color will exist for a long time, mainly based on the electronic technology team familiar with the object, with the least cost of embedded system software and hardware, mainly based on 8-bit computers.
In addition, computer professionals will be more and more involved in embedded system applications, but due to the gap in object expertise, their application fields will focus on network, communication, multimedia, business electronics and so on, and it is impossible to replace the original embedded applications of electronic engineers in control, instrumentation, machinery, electronics and so on. Therefore, these two objective application modes will coexist for a long time and complement 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 characteristics of circuit system, basic peripheral circuit design method and basic requirements of object system from electronic system design mode.
3. High-end and low-end applications of embedded systems
Because the embedded system has a long independent development path of single chip microcomputer, most of them are based on 8-bit single chip microcomputer, which realizes the lowest embedded system application and has obvious characteristics of electronic system design mode. Most of the developers engaged in the application of single chip microcomputer are electronic system engineers in the target system field. In addition, the appearance of single-chip microcomputer immediately left the computer professional field and entered the electronic system field as an "intelligent" device, without introducing the concept of "embedded system". Therefore, many people engaged in the application of single-chip microcomputer do not understand the relationship between single-chip microcomputer and embedded system. When it comes to the field of "embedded system", they are often understood as the computer professional field, which is based on 32-bit embedded processors and engaged in network, communication, multimedia and other applications. In this way, "single chip microcomputer" and "embedded system" have formed two independent terms that are common in embedded systems. However, because "single chip microcomputer" is a typical and independently developed embedded system, it should be unified as "embedded system" from the perspective of discipline construction. Considering the characteristics of the underlying application of the original single-chip microcomputer electronic system, the application of embedded system can be divided into high-end and low-end. The original single-chip microcomputer application can be understood as the low-end application of embedded system, which means its underlying nature and tight coupling with the target system.