In the second half of the 20th century, with the continuous development of integrated circuits and computers, electronic technology is facing severe challenges. Due to the shortening of the development cycle of electronic technology, the design of ASIC is facing the contradiction between the increasing difficulty and the shortening of the design cycle. In order to solve this problem, we must adopt new design methods and use high-level design tools. In this case, EDA (Electronic Design Automation) emerges as the times require.
With the development of electronic technology and the requirement of shortening the design cycle of electronic system, EDA technology has developed rapidly.
EDA technology takes large-scale programmable logic device as design carrier, hardware description language as the main expression of system logic description, and computer, large-scale programmable logic device development software and experimental development system as design tools. Through relevant development software, it can automatically complete the logic compilation and logicalization from software design to hardware system Simple, logical partition, logic synthesis and optimization, logic layout and routing, logic simulation, adaptation and compilation for specific target chip, logic mapping, programming and downloading, etc., finally forming a new technology of integrated electronic system or special integrated chip.
Along with the development of computer, integrated circuit and electronic system design, EDA technology has gone through three stages: CAD technology developed in 1970s; CAE technology applied in 1980s; EDA technology characterized by hardware description language, system level simulation and synthesis technology appeared in the late 1990s. At this time, EDA tools not only have the function of electronic system design, but also have the function of hardware design It can not only provide system level design capability independent of process and manufacturer, but also have high-level abstract design conception means.
EDA technology involves a wide range and rich content. From the teaching and practical point of view, it mainly includes the following four aspects: (1) large scale programmable logic devices; (2) hardware description language; (3) software development tools; (4) experimental development system. Among them, large-scale programmable logic device is the carrier of electronic system design using EDA technology; hardware description language is the main expression means of electronic system design using EDA technology; software development tool is the intelligent and automatic design tool of electronic system design using EDA technology; experimental development system is the downloader of electronic system design using EDA technology Hardware verification tools.
With the development of modern semiconductor precision machining technology to the deep submicron (0.18 ~ 0.35um) stage, a large number of customized or semi customized ASIC (application specific integrated circuit) devices based on large-scale or ultra large-scale integrated circuit (VLSI) technology have emerged and been widely used, which has greatly promoted the development of electronic technology and products This paper discusses the development process of social informatization. And one of the main foundations supporting this development process is EDA technology.
EDA technology integrates large integrated circuit manufacturing technology, IC drawing design technology, ASIC testing and packaging technology, CPLD / FPGA technology, etc. in terms of hardware; in terms of computer-aided engineering, it integrates CAD, cam, CAT technology and design concepts of multiple computer languages; in terms of modern electronics, it contains more content, Such as digital system design theory, digital signal processing technology, system modeling and optimization technology.
2 programmable logic device
Programmable logic device (PLD) is a new type of integrated circuit developed in recent years. It is the main hardware foundation of current digital system design and the physical implementation tool of hardware programming language HLD. PLD plays an important role in digital system design automation. It can be said that there is no current digital circuit automation without PLD This kind of EDA design mode, which takes programmable logic devices as raw materials and starts from “manufacturing independent chips”, has become the mainstream of current digital system design. If we want to catch up with the most advanced digital system design methods in the world, we need to know and use programmable logic devices.
Digital integrated circuit itself is constantly updated. It has developed from the early electron tubes, transistors, small and medium scale integrated circuits to very large scale integrated circuits (VLSIC) and many ASIC with specific functions. However, with the development of microelectronics technology, the task of designing and manufacturing integrated circuits is not entirely undertaken by semiconductor manufacturers. System designers prefer to design their own ASIC chips, and hope that the design cycle of ASIC will be as short as possible. It is better to design suitable ASL chips in the laboratory and put them into practical application immediately. Therefore, field programmable logic devices (FPLD) appear, among which the most widely used is the field programmable gate array (FPGA) complex programmable logic devices Programming logic device (CPLD).
Programmable logic devices are in the stage of rapid development. The scale of new FPGA / CPLD is bigger and bigger, and the cost is lower and lower. High cost performance makes programmable logic devices play an increasingly important role in the field of hardware design.
The low-end CPLD has gradually replaced the 74 series and other traditional digital components, and the high-end FPGA is constantly seizing the market share of ASIC. Especially at present, most large-scale FPGAs support the organic combination of SOPC and CPU or dspcore, which makes FPGA not only a traditional hardware circuit design means, but also a system level implementation tool.
The four development trends of the next generation programmable logic device hardware can be summarized as follows: the most advanced ASL production process will be more widely used in the programmable logic devices represented by FPGA; more and more high-end FPGA products will contain DSP or CPU processor cores, so that FPGA will gradually transition from the traditional hardware design means to the system level design platform; FPGA contains more and more functions More and more abundant hardip cores are further integrated with traditional ASIC, and some ASIC markets are occupied by structured ASIC technology. The density of low-cost FPGA is higher and higher, and the price is more and more reasonable, which will become the backbone of FPGA development. These four trends can be referred to as advanced technology, processor core, hard core and structured ASIC low-cost devices.
Hardware description language (HDL)
HDI is a language for describing the behavior, structure and data flow of electronic system hardware. At present, hardware description language can be used to design digital electronic system. With the deepening of the research, the use of hardware description language for analog electronic system design or hybrid electronic system design is also being explored.
There are many kinds of hardware description languages, some developed from pascai, and some from CL. Some HDL become IEEE standard, but most of them are enterprise standard. The technical source of HDL development is: before the formation and development of HDL, there were many programming languages, such as assembly, C, Pascal, FORTRAN, Prolog and so on. These languages run on different hardware platforms and operating environments. They are suitable for describing processes and algorithms, but not for hardware description. With the emergence of CAD, people can use computer to carry out the aided design of architecture, clothing and other industries, and the electronic aided design is also developing at the same time. In the use of EDA tools for electronic design, logic diagram, discrete electronic components as the whole more and more complex electronic system design has not adapted. Any EDA tool needs a hardware description language as its working language. These many EDA tool software developers have launched their own HDL language. The most influential hardware description languages in China are ABEL-HDL, Verilog HDL, AHDL and VHDL.
3.1 ABEL-HDL language
This is an early hardware description language. In the design of PLD, the logic function of the designed circuit can be described conveniently and accurately. He supports various expressions of logic circuits, including logic equations, truth tables and state diagrams. Abel language and Verilog language belong to the same description level, but the characteristics of Abel language are far less supported than Verilog. Verilog is developed from integrated circuit design, the language is more mature, and supports many EDA tools. Abel language developed from the early design of programmable logic device (PLD). Abel-hdi is widely used in the logic function design of various programmable logic devices. Because of the independence of its language description, abel-hdi is suitable for the design of programmable devices of various sizes. For example, the DOS version of Abel 3.0 software can describe and design all-round logic including gal, and ABEL-HDL can also be used in large-scale FPGA / CPLD device function design in EDA software such as ispex pert of Latice, Synario of dataio, design direct of vantis, foundation of Xilinx and webpack. Abel-hdi can also simulate the function of the designed logic system. ABEL-HDL design can also be converted to other design environment, such as vhdi, through standard format design. Verilog HDL et al. In the long run, Verilog HDL will be used more than ABEL-HDL, and ABEL-HDL will continue to exist in a small range.
Verilog HDL is a component description language developed on the basis of the most widely used C language. It was first created by phimooorby of GDA (Gateway Design Automation) Company in the end of 1983. At first, only one simulation and verification tool was designed, and then related fault simulation and timing analysis tools were developed. In 1985, moorby launched its third commercial emulator, Verilog XL, and achieved great success, which made Verilog HDL rapidly popularized and applied. In 1989 cadence company acquired GDA company, which made Verilog HDL the exclusive patent of GDA company. In 1990, CAD CE company published Verilog HDL and established LVI to promote Verilog HDL to become IEEE standard, namely IEEE standard 1364-1995.
The biggest feature of Verilog HDL is easy to learn and use. If you have the programming experience of C language, you can quickly learn and master it in a short time. Therefore, you can arrange the content of Verilog HDL to be taught in ASIC design and other related courses. Because HDL language is designed specifically for hardware and system, this arrangement can enable learners to obtain the actual design experience at the same time The experience of the road. In contrast, VHDL learning is more difficult. However, Verilog HDL’s relatively free syntax is easy to cause beginners to make some mistakes, which should be paid special attention to.
Altera hardware description language (AHDL) is a modular high-level language, which is the HDL invented by Altera company. It is very easy to learn and use. People who have learned high-level language can master AHDL in a very short time (such as a few weeks).
AHDL language is fully integrated into MAX + PLUSII / QuartusII system, especially suitable for describing complex combinational logic, group operation, state machine, truth table and parameterized logic. The designer can edit the AHDL source program through MAX + PLUS II or QuartusII software system, and build the output files of simulation, time domain analysis and device programming by compiling the source program.
The statements and elements of AHDL are complete, powerful and easy to use. Designers can use AHDL to direct the whole level of project design files, or mix other types of design files in one level of design, such as Verilog HDL HDL design files. AHDL file is a kind of text file. It can use the text file editor provided by EDA to create text (tdfahdl text design file) and other text editors to create text files. However, due to the special relationship between AHDL and MAX + plus Ⅱ / Quartus Ⅱ, it is recommended that the former be the best one. Designers can easily use MAX + plus Ⅱ / Quartus Ⅱ to edit AHDL text Editing, compiling, debugging and so on, especially in the message processor, the function of automatic error location makes debugging very convenient. Its disadvantage is that it has poor portability and is usually only used in the development system of Altera company.
3.4 VHDL language
VHDL (very high speed integrated circuit hardware description language) is a very high speed integrated circuit hardware description language. The US Department of defense developed VHDL in the late 1980s. The VHDL working group established in June 1981 proposed a HDL that can meet various requirements of electronic design and can be used as an industrial standard. In the third quarter of 1983, JBM company, TJ company and internetrics company signed a contract to form a development group, whose task is to propose the language version and develop the software environment. In 1986, IEEE began to work and discuss VHDL language standard. It took more than a year. In December 1987, IEEE Std 1076-1987 [irm87] passed the standard review and announced its implementation. In 1993, VHDL was revised to form a new standard, namely IEEE Std 1076-1993 [irm93].
The language has complete design technology, flexible method, independent of manufacturing process and easy to share programming, so it has become the mainstream of hardware description language and standard hardware description language. The VHDL program is written into the programmable chip to make ASIC chip. Because of its short development cycle and more convenient, it will replace the single-chip control circuit in a large range and become the main melody of the future digital circuit design. Due to the rapid progress of semiconductor programming technology, VHDL can provide high-order circuit description language, so that complex circuits can easily and quickly reach the design specifications through the circuit mode of VHDL editor. VHDL circuit description language can cover a wide range, and can be applied to the needs of different levels of design engineers. From ASIC design to PCB system design, VHDL circuit description language can be used, so VHDL circuit design has undoubtedly become a necessary tool for hardware design engineers. At present, VHDL language has become the most commonly used tool for FPGA / CPLD programming.
VHDL is an important component of EDA, which provides a good way to design digital system with the help of computer. VHDL has many advantages in hardware description, which can be used for description, simulation, synthesis and debugging from gate level, circuit level to system level. By using VHDL’s rich simulation statements and library functions, the early design of large-scale system can be simulated at a high level far away from the gate level, so as to help designers determine the feasibility of the whole design structure and function. The powerful behavior description ability and program structure of VHDL enable it to support the decomposition of large-scale design and reuse the existing design. Using VHDL to design the hardware of the system is relatively independent. There is no process related information embedded in the design. The description of the hardware has nothing to do with the specific process technology and hardware structure. When the description of gate level or above passes the simulation test, the design can be mapped into different processes with corresponding tools, which makes the target devices of hardware implementation have a wide selection range, and there is no adverse effect between modifying circuit and modifying process or selecting devices. VHDL Standard Specification, syntax is more strict, using VHDL design is easy to reuse communication, VHDL has generic description statements and subroutine calls and other functions, so that the designer of the completed design, do not have to change the source program, just change the generic parameters or functions, can change the size and structure of the design. VHDL is recommended as the national standard of hardware description language for electronic design automation in 1995. VHDL has become a standardized hardware description language widely recognized and promoted by EDA tools and IC manufacturers in the world. Mastering VHDL and using VHDL to design electronic circuits is a basic skill and powerful tool for technology competition.
EDA software plays an extremely important role in the application of EDA technology. The core of EDA is to use computer to realize the automation of circuit design, so the support of EDA tool software based on computer environment is essential.
There are many kinds of EDA software, which have been applied in our country: PSpice, PCAD, PROTEL, viewlogic, mentor, graphics, Synopsys, cadence, Edison, Tina and so on. Most of the software can be used for circuit design and simulation, FCB automatic layout and routing, output a variety of netlist files, share data with other manufacturers’ software, and so on. According to their main functions and application fields, they can be divided into electronic circuit design tools, simulation tools, PCB design software, IC design software, PID design tools and other EDA software. Among them, IC design and PID design represent the development level of today’s electronic technology and are widely used software types in this industry.
At present, IC design tools are developing rapidly, and the IC field itself has developed to the stage of ASIC (application specific integrated circuit) chip design. Famous IC software suppliers are cadence, synopsysl Avanti and agilenti.
PLD is a kind of digital integrated circuit whose logic function is constructed by users according to their needs. Its design method is to generate the corresponding object file by means of EDA software, schematic diagram, Boolean expression, hardware description language and other methods. Finally, it is realized by the target device with programmer or download cable. At present, the representative PLD manufacturers in the world are Altera, Xilinx and lattice. Some small and simple PLD design tools are mainly provided by device manufacturers, while some powerful and large-scale PLD design tools are developed by software companies and device manufacturers. For example, MAX + PLUS II and quatus II of Altera company, and synaptic of lattice company. Because of the university cooperation program implemented by Altera company, most of the engineering R & D personnel contact MAX + PLUS II and quatus II most early in the University, and the development tools of MAX + PLUS II and quatus II are friendly and easy to operate, so they are more easily accepted by R & D personnel.
5. Digital system hierarchy based on EDA technology
The emergence of EDA (Electronic Design Automation) technology makes the analysis and design method of digital system change fundamentally. There are three basic design methods: direct design, top-down design and bottom-up design. Direct design is to take the design as a whole and design it as a single circuit module, which is suitable for small and simple design. However, some large-scale digital logic systems with complex functions are suitable for top-down or bottom-up design. The top-down design method is to start from the overall requirements of the design and divide the design into different functional sub modules from top to bottom. Each module completes a specific function. This design method first determines the design of the top-level module, and then carries out the detailed design of the sub module. In the design of the sub module, the existing modules in the library or the real modules preserved in the design process can be called Example. The bottom-up approach is the opposite of the top-down approach.
In the EDA design of digital system, the hierarchical method is often used to describe the design by modules and layers. The design describing the total function of the system is the top-level design, and the design describing the smaller unit of the system is the bottom-level design. The whole design process can be understood as a series of transformation process from the top-level abstract description of hardware to the bottom-level structure description, until the realizable hardware unit description is finally obtained. The hierarchical design method is relatively free. It can be designed from top to bottom or from bottom to top. It can be designed with schematic input and HDL at any level.
5.1 bottom up design method
The central idea of the button to up design method is that first of all, according to the test and analysis of the whole system, each function block is connected into a complete system, each independent function module is composed of logic units, and each combination and sequential logic unit is composed of basic gates.
The characteristics of the button to up design method are as follows: calling the logic gate unit directly from the underlying logic library; conforming to the traditional design habits of hardware engineers; lacking the grasp of the overall performance of the whole electronic system in the underlying design; having completed the whole system, it is more difficult to modify and the design cycle is longer; with the improvement of the design scale and system complexity, this method is more effective The disadvantages are more prominent.
The traditional design method of digital system is generally bottom-up, that is, first determine the structure and function of the circuit modules or components that constitute the lowest layer of the system, and then according to the functional requirements of the main system, make them into larger functional blocks, so that their structure and function meet the requirements of the high-level system, and so on, until the EDA design of the whole target system is completed.
5.2 top down design method
The main idea of top-down design method is: the system layer is a top-level module including input and output, which is expressed by system level and behavior description, and completes the simulation and performance analysis of the whole system; the whole system is further composed of various functional modules, and each module is expressed by more detailed behavior description; the mapping from EDA comprehensive tool to process library is completed.
The characteristics of top-down design method: combined with simulation means, the performance of the target system can be mastered from the beginning; with the design level going down, the performance parameters of the system will be further refined and confirmed; the relevant parameters can be adjusted in time according to the needs, so as to ensure the correctness of the design results and shorten the design cycle; when the scale is larger, the performance parameters of the system will be further refined and confirmed The advantages of the method are more obvious; it needs to rely on the support of EDA design tools and expensive basic investment; the logic aggregation and the realization of the later design process need the support of accurate process library.
The design method of modern digital system is generally top-down hierarchical design method, that is, starting from the overall requirements of the whole system, the system design content is gradually refined from top to bottom, that is, the whole system is divided into several functional modules, and finally the design of the whole system is completed.
In the field of electronic design, top-down hierarchical design method is possible only when EDA technology has been developed rapidly and applied maturely. The effective application of top-down hierarchical design method must be based on powerful EDA tools, HDL which integrates system description, behavior description and structure description, and advanced ASIC manufacturing technology And CPLD / FPGA development technology. Nowadays, the top-down hierarchical design method has been the preferred design method of EDA technology and the main design method of CPLD / FPGA development.
EDA technology provides the possibility for the expression and application of modern digital system theory and design. It is not a branch of a discipline, but a comprehensive discipline. EDA technology breaks the barrier between computer software and hardware, which is the combination of software technology and hardware realization, design efficiency and product performance. It represents the development direction of digital electronic design technology and application technology.
EDA technology can be widely used in scientific research, teaching and the development of new electronic products. EDA technology is the product of the combination of electronic design and computer, which greatly promotes the development of the former. At present, EDA technology is developing rapidly. In EDA technology development, mainly concentrated in the United States and other western developed countries, new EDA tools emerge in endlessly. Japan, South Korea and other Asian countries also attach great importance to the development of EDA technology. China’s EDA technology is far behind the developed countries in both development and application, which is also the overall status quo of China’s information technology integrated circuit industry. EDA technology is also the key training content of “national information technology shortage talent training project” of the software and integrated circuit promotion center of the Ministry of information industry. In order to realize the development of China from a world manufacturing power to a world technology power, the majority of the power companies have made great progress Sub engineers should speed up learning and application, improve their competitiveness and adapt to the rapid development of EDA technology.
Editor in charge: Tzh