Embedded system (device that can operate independently)
The embedded system is composed of hardware and software. It is a device that can operate independently. The software content only includes the software operating environment and its operating system. The hardware content includes many aspects including signal processor, memory, communication module, etc. Compared with the general computer processing system, the embedded system has a big difference, it can not realize the large-capacity storage function, because there is no matching large-capacity medium, most of the storage media used are E- PROM, EEPROM, etc., the software part uses API programming interface as the core of the development platform.
Definition
Embedded system is a dedicated computer system that is application-centric, based on modern computer technology, and can flexibly tailor software and hardware modules according to user needs (function, reliability, cost, volume, power consumption, environment, etc.).
The main points are summarized:
Application-centric: Emphasize that the goal of embedded systems is to meet the specific needs of users. For most complete embedded systems, users can directly enjoy their functions when turning on the power, without secondary development or only a small amount of configuration operations.
Specificity: Most of the application scenarios of embedded systems have higher requirements for reliability and real-time performance. This determines that the dedicated system serving specific applications is the mainstream mode of embedded systems. It does not emphasize the Do not emphasize the universality and scalability of the system. This kind of specialization usually also leads to the embedded system being a final system with tightly integrated software and hardware, because this can more effectively improve the reliability of the entire system and reduce costs, and make it have a better user experience.
With modern computer technology as the core: the most basic support technology for embedded systems, roughly including integrated circuit design technology, system structure technology, sensing and detection technology, embedded operating system and real-time operating system technology, highly reliable software development technology for resource-constrained systems, system formal specification and verification technology, communication technology, low power consumption technology, data analysis in specific application fields, signal processing and control optimization technology, etc., they are formed by integrating the basic principles of computers into specific special equipment An embedded system.
Software and hardware can be tailored: Embedded systems are aimed at so many application scenarios, and bring extremely different design index requirements (functional performance, reliability, cost, power consumption), so that it is difficult to have a set of solutions to meet in reality all system requirements, therefore, according to different requirements, flexible tailoring of software and hardware, and the establishment of a final system that meets the requirements is an inevitable technical route for the development of embedded technology.
Development process
The real development of embedded computers was after the advent of microprocessors. In November 1971, the arithmetic unit and the controller circuit were successfully integrated, and the first microprocessor was launched. After that, various manufacturers successively introduced 8-bit and 16-bit microprocessors. Systems based on these microprocessors are widely used in the fields of instrumentation, medical equipment, robots, and household appliances. The extensive application of microprocessors has formed a broad embedded application market. Computer manufacturers have begun to provide users with OEM products in a large number of plug-ins, and then users can choose a set of suitable CPU boards, memory boards and various types according to their needs. The I/O plug-in board constitutes a dedicated embedded computer system and embeds it in its own system equipment.
In the 1980s, with the improvement of the level of microelectronics technology, integrated circuit manufacturers began to integrate the microprocessors, I/O interfaces, A/D converters, D/A converters, and serial The line interface, RAM, ROM and other components are all integrated into a VLSI, thereby manufacturing a microcontroller designed for I/O, which is commonly known as a single-chip microcomputer. The single-chip microcomputer has become a rookie emerging in the embedded computer. In the 1990s, driven by huge demands for distributed control, flexible manufacturing, digital communications, and information appliances, embedded systems developed rapidly. DSP products for real-time signal processing algorithms are developing in the direction of high speed, high precision, and low power consumption. The 21st century is an era in which networks are prevalent, and the application of embedded systems to various networks is an important direction for its development.
The development of embedded systems has roughly gone through the following three stages:
The first stage: the early stage of embedded technology. The embedded system exists in the form of a programmable controller with a simple function special computer or a single-chip microcomputer as the core, and has functions such as monitoring, servo, and equipment indication. This system is mostly used in various industrial controls and weapons and equipment such as aircraft and missiles.
The second stage: marked by high-end embedded CPU and embedded operating system. The main feature of this-stage system is the emergence of highly reliable, low-power embedded CPUs in computer hardware, such as ARM, PowerPC, etc., and supports the operating system, and supports the development and operation of complex applications.
The third stage: Marked by chip technology and Internet technology. The rapid development of microelectronics technology, SOC (System on Chip) makes embedded systems smaller and smaller, but their functions are getting stronger and stronger. At present, most embedded systems are still isolated from the Internet, but with the development of the Internet and the increasingly close integration of Internet technology with information appliances, industrial control technology, etc., embedded technology is entering a period of rapid development and widespread application.
Features
The hardware and software of the embedded system must be selected according to specific application tasks, with power consumption, cost, volume, reliability, and processing capacity as indicators. The core of an embedded system is system software and application software. Due to the limited storage space, the software code is required to be compact, reliable, and have strict requirements for real-time performance.
From the perspective of composition, the embedded system is a computer system that integrates software and hardware and can work independently; from the appearance, the embedded system is like a "programmable" electronic "device"; from the functional point of view, it It is a controller that controls the target system (host object) and makes it intelligent. From the different perspectives of users and developers, compared with ordinary computers, embedded systems have the following characteristics.
(1) Strong specificity. Since the embedded system is usually oriented to a specific application, the hardware and software of the embedded system, especially the software, are designed for a specific user group and usually have a certain specificity.
(2) Miniaturization of volume. The embedded computer integrates many tasks completed by the board in a general-purpose computer system into the chip, thereby facilitating miniaturization and embedding the embedded system into the target system.
(3) Good real-time performance. Embedded systems are widely used in production process control, data acquisition, transmission and communication and other occasions. They are mainly used to control host objects, so there are more or less real-time requirements for embedded systems. For example, the real-time requirements for embedded systems in weapons and control systems in certain industrial control devices are extremely high. Some systems do not have very high real-time requirements, such as handheld computers that have developed relatively fast in recent years. But in general, real-time is a universal requirement for embedded systems, and an important indicator that designers and users should focus on.
(4) Good cutability. From the perspective of the specific characteristics of embedded systems, embedded system suppliers should provide a variety of hardware and software as alternatives, and strive to achieve higher performance on the same silicon chip area, so that they can be more specific More competitive in the application.
(5) High reliability. Because the computing tasks undertaken by some embedded systems involve important matters such as the critical quality of the accused product, personal equipment safety, and even national secrets, and the host objects of some embedded systems work in unattended situations, such as in high-risk situations. The monitoring device in the harsh industrial environment and harsh outdoor environment. Therefore, compared with ordinary systems, embedded systems have extremely high requirements for reliability.
(6) Low power consumption. Many embedded systems host small application systems, such as mobile phones, MP3s, digital cameras, etc. It is impossible for these devices to be equipped with AC power supplies or large-capacity power supplies, so low power consumption has always been the goal pursued by embedded systems .
(7) The embedded system itself does not have the ability of self-development, and must be developed with the help of a general-purpose computer platform. After the design of an embedded system is completed, ordinary users usually have no way to modify the program or hardware structure, and must have a set of development tools and environment to proceed.
(8) Embedded systems are usually realized by the method of "software and hardware co-design". Early embedded system design methods often adopted the "hardware first" principle, that is, under the condition of only roughly estimating the software task requirements, the hardware design and implementation are carried out first, and then the software design is carried out on this hardware platform. If the traditional design method is adopted, once a problem is found in the test and the design needs to be modified, the entire design process will be repeated, which will have a great impact on the cost and design cycle. The design of the system depends to a large extent on the experience of the designer. Since the 1990s, with the development of related technologies such as electronics and chips, a software and hardware co-design method has emerged in the design and implementation of embedded systems, that is, the use of unified methods and tools to describe, synthesize and verify software and hardware. Under the guidance of system goals and requirements, through the comprehensive analysis of system software and hardware functions and existing resources, the software and hardware architecture is collaboratively designed to maximize the system's software and hardware capabilities and avoid all kinds of problems caused by independent design of the software and hardware architecture. Disadvantages, get high-performance, low-cost optimized design.
System composition
From the perspective of external characteristics, an embedded system is usually a fully functional software and hardware integrated system that can run independently without relying on other external devices.
Embedding method
The embedded system works by embedding the CPU in the target system or controlled system. But in different embedded systems, the form and degree of embedding are different. According to the closeness of the connection between the embedded system and the general-purpose computer, the embedded form can be divided into a fully embedded mode and a semi-embedded mode.
Fully embedded
If the fully embedded method is adopted, the embedded system (or its core functions) can work independently without relying on a general-purpose computer system. Typical examples include mobile phones, MP4s, and car GPS navigation systems. The embedded system adopting the fully embedded mode has the following characteristics.
(1) It has an independent processor system and a complete input/output system, which can independently complete the functions of the system.
(2) The high-end CPU supports embedded operating systems and can develop complex applications.
(3) Generally, it is a portable handheld device, and its working environment is generally unattended, mobile space, high altitude or other environments with harsh conditions.
(4) The power supply method is generally battery-powered. In some cases, it can also be directly powered by city power 220V. The conversion and voltage stabilizing circuit are designed by the system. Higher-end devices often combine the two power supply modes, allowing users to use them more flexibly.
(5) The fully embedded method is suitable for any occasion where general-purpose computers are not suitable, such as consumer electronics, household appliances, communication network equipment, industrial control, intelligent instruments, battlefield electronic countermeasures, aerospace weapons, etc., and its application range is very wide.
Semi-embedded
If a semi-embedded method is adopted, the embedded system (or its core function) needs to be combined with a general-purpose computer system to work normally. Typical examples include medical B-ultrasound systems and PCI card-based data acquisition systems. The embedded system adopting the semi-embedded mode has the following characteristics.
(1) Generally, there is no independent processor, but the CPU of a general-purpose computer system is used to complete calculation and/or control functions; sometimes even with its own independent processor, the processor only completes some limited specific functions, and does not have Control the functions of the entire system.
(2) The embedded system is only a part of the whole system and can only complete part of the functions of the whole system, while other functions need to be completed on a general-purpose computer. General-purpose computers use their rich software and hardware resources to provide a friendly man-machine interface and powerful data processing capabilities.
(3) The function of the embedded system is embodied in the collection of front-end data and the execution of the control of the controlled object. The functions of data analysis, processing and storage are completed by a general-purpose computer system.
(4) Embedded systems generally use various standardized bus forms to connect with general-purpose computers. Typical examples are PCI bus, USB bus, etc. Simple embedded systems can also be connected through serial ports.
(5) The embedded system is connected to a general-purpose computer as a peripheral, so it is generally necessary to provide a standard driver for the embedded system in a general-purpose computer.
