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Computer-aided design (CAD) res. Moscow State University of Printing Arts Components of the design process

Automated design is the design carried out by a person when interacting with a computer. The degree of automation can be different, and is estimated by the proportion of design work performed on a computer without human intervention. At = 0, design is called manual, at = 1 - automatic.

A computer-aided design system is an organizational and technical system consisting of a set of design automation tools interacting with departments design organization and performing computer-aided design.

Development of complex design automation tools electronic systems pursues the following goals:

reducing the time and cost of product development and implementation;

reducing the number of design errors;

ensuring the possibility of changing design decisions and reducing the time for checking and testing products.

The tasks solved at various stages of design can be broadly divided into three groups: synthesis and analysis. The task of the analysis is to study the behavior and properties of the system for the given characteristics of the external environment, its components and the structure of the system (or its model). According to general systems theory, synthesis is the process of generating functions and structures that are necessary and sufficient to obtain certain results. By identifying the functions implemented by the system, one defines a certain system about which one knows only what it will do.

In this regard, the stage of synthesis of functions is called abstract synthesis. There are also stages of structural and parametric synthesis. In structural synthesis, the structure of an object is determined - the set of its constituent elements and the ways of their connection with each other (as part of the object and with external environment). Parametric synthesis consists in determining the numerical values of the parameters of the elements for a given structure and operating conditions (i.e., it is necessary to find a point or region in the space of internal parameters in which certain conditions are satisfied).

CAD development is a major scientific and technical challenge. Despite the large labor costs (50-200 qualified specialists), the creation of integrated ARPAs in various fields of technology is a necessity caused by the increasing complexity of design objects. Taking into account the foregoing, it is possible to formulate the basic requirements that the CAD system must satisfy:

1. Have a universal structure that implements the principles of decomposition and hierarchy (block-hierarchical approach). Moreover, design systems at various levels of the hierarchy must be informationally coordinated. Informational consistency means that for sequential design procedures, the output of one of them can be input to another, and no transformation is required.

2. Have a high degree of integration. The degree of integration should be such as to ensure the implementation of the entire design path: from the presentation of the idea to the implementation of the project. An important role for the integration of design tools is played by so-called frameworks (CAD frameworks), which provide both the integration of various design tools and data, and the execution of control functions using a single user interface.

3. Carry out design in real time. Reducing the time required for the interaction of CAD with the user is ensured by the availability of operational technical means of interaction between the developer and the system, the efficiency of design procedures, etc.

4. The CAD structure must be open, ie. have the property of convenience of expanding subsystems while improving it.

5. Have means of control of input and output information.

6. Have a means of automatically making changes to the project.

2. The structure of the CAD hardware and software complex

All hardware and software that make up the basic CAD software can be classified according to their function:

software (MO);

linguistic support (LO);

software (software);

technical support (TO);

information support (IO);

organizational support (OO);

The MO includes: theory, methods, mathematical models, algorithms used in computer-aided design.

LO is represented by a set of languages used in computer-aided design. The main part of LO is the languages of communication between a person and a computer.

Software is a collection of machine programs and related documentation. It is divided into system-wide and applied. System-wide software components are, for example, operating systems, compilers, etc. These software tools are intended for organizing the functioning of hardware, i.e. for planning and managing the computing process.

Application software is created for CAD needs. It is usually presented in the form of application packages (APPs), each of which serves a specific stage of the design process.

TO components are a set of interconnected and interacting technical means (for example, computers, means of transferring, entering, displaying and documenting data) intended for computer-aided design.

IO integrates the data needed for computer-aided design. They can be presented in the form of certain documents on various media containing information of a reference nature about the parameters of the design object, intermediate results, etc.

The main part of IO CAD is a data bank (BND), which is a collection of tools for centralized accumulation and collective use of data in CAD. BND consists of a database (DB) and a database management system (DBMS). DB - the data itself, located in the computer memory and structured in accordance with the rules adopted in this BND. DBMS - a set of software tools that ensure the functioning of the BND. The DBMS is used to record data in the BND, retrieve them at the request of the user and application programs, etc.

The computer-aided design process is a sequential interaction of a large number of software modules. The interaction of modules is manifested mainly in control connections (ordered transitions from the execution of one program module to the execution of another), and information (using the same data in different modules) (see Fig. 1 and 2).

When designing complex systems, it is the problem of informational coordination of various software modules that is significant. There are three main ways to implement links by information:

by passing parameters from the calling program to the called program;

across common areas(exchange zones) of interacting modules;

through the data bank.

The implementation of information links through the transfer of parameters means that either parameters or their addresses are transferred. It is used with a relatively small amount of transmitted data and their simple structure.

Implementation of information links through the exchange area, each module must send data to the exchange area, presenting them in a form acceptable from the standpoint of the requirement of any of the other modules. Since the requirements for the data structure of each module - the data consumer may be different, the method of communication through the exchange zones is relatively easy to implement only with a small and stable number of information links. They are used for software modules within a certain RFP.

If the same modules can be included in different design procedures, interact with many modules, then it is advisable to unify the means of information exchange. This unification is carried out using the BND concept. The main feature of the information stored in the BND is its structuredness. Main advantages communication BND are as follows:

The restrictions on the number of serviced design procedures are removed;

Development and modification of the software system is possible;

It is possible to modify the modernization of technical means for storing data without changing the RFP;

Data integrity is ensured.

However, the implementation of information links through the data BND has its own drawbacks, mainly associated with a significant amount of time to search for data in the database.

Rice. 1. The graph reflecting the links for management.

Rice. 2. The graph, reflecting the connection by information.

Rice. 3. Implementation of information links through the DBMS.

3 ... Composition of CAD electronic systems

Modern CAD is a complex hardware and software complex, referred to in scientific and technical literature as a "workstation" (PC).

Rice. 3. The structure of the workstation for the design of electronic systems.

Rice. 4. Structure of CAD software.

4 ... Hierarchical levels of presentation of electronic devices

The main design method using CAD is the block-hierarchical method or the method of decomposing a complex object into subsystems (blocks, nodes, components). In this case, the description of a complex system is divided into hierarchical levels (levels of abstraction) according to the degree of detail in reflecting the properties of the system. At each level of project presentation, there is a concept of a system, a subsystem, an element of the system, the law of functioning of the elements of the system as a whole, and external influences.

It is these concepts that define one or another level of the device representation hierarchy. A subsystem is a part of a system, which is a collection of some of its elements, selected according to a certain functional feature, and is subordinate in its purpose of functioning to a single purpose of functioning of the entire system. An element of a system is understood as its part that performs a certain function (functions) and is not subject to decomposition at a given level of consideration. The indivisibility of an element is a concept, but not physical property of this item. Using the concept of an element, the designer reserves the right to move to another level on the basis of a part or by combining several elements into one.

At the upper hierarchical level, the entire complex object is considered as a set of interacting subsystems. At the next hierarchical level, subsystems are considered separately as systems consisting of some constituent parts (elements), and have a greater detail of description. This hierarchical level is the level of subsystems. The number of levels in the hierarchy is always limited. Levels are characterized by the fact that the set of types of elements from which the design subsystem can be composed is limited. Such a set is called a level basis.

The decomposition method poses serious problems when creating CAD systems:

determination of hierarchy levels and bases for them;

development of software;

mapping from one basis to another, etc.

The method of hierarchical representation of the designed object used by developers electronic circuits and systems, can be based on two ways of representing (describing) elements: structural and behavioral.

The structural method provides for the description of a system element as a set of interconnected elements of a lower level, thereby defining the basis of this level. The structural form of the project hierarchy implies the process of decomposing or dividing the project so that at any level that is selected for modeling, the system model is built as a set of interrelated elements defined for this level. The question immediately arises here: how are these elements defined? Most often they are formed using elements of the next, lower level. Thus, as shown in Fig. 5, the project can be represented in the form of a tree, and different levels the hierarchy of abstractions corresponds to their levels of this tree. At the level of the tree leaves, the behavior of the lowest-level project elements is determined. The behavioral method provides for the description of a system element by input / output dependencies using a certain procedure. Moreover, this description is determined by some own procedure, and is not described using other elements. Therefore, the behavioral model is used to describe the elements of the leaf level of the project tree. Since the behavioral model of a project can exist at any level, different parts of the project can have behavioral descriptions at different levels.

Rice. 5. The project presented in the form of a complete (a) and incomplete (b) tree.

In fig. 5 (a) shows the "complete" project tree, where all behavioral descriptions are generated at the same level. Figure 5 (b) shows a project presented in the form of an incomplete tree, where behavioral descriptions are assigned to different levels. This situation arises because the developer often wants to build and analyze the relationships between system components even before the design is complete. Thus, it is not necessary to have specifications for all system components, for example, at the level of logic gates, in order to be able to monitor the project as a whole for the absence of errors. This control is carried out using multilevel modeling, that is, modeling in which the behavioral descriptions of component models refer to different levels of the hierarchy. An important additional advantage of this approach is that it improves the efficiency of modeling.

From the point of view of the hardware designer, there are six main levels of the hierarchy, shown in Fig. 6.

Rice. 6. Levels of the hierarchy of representation of electronic systems.

These are the system, microcircuit (or IC), register, gate, circuit and topological levels. The figure shows that the hierarchy of presentation levels has the form of a truncated pyramid. The expansion of the pyramid downward reflects an increase in the degree of detail, i.e. the number of elements that must be taken into account when describing the designed device at this level.

Table 1 shows the characteristics of the levels - the elements of the structure and the behavioral representation for each level are indicated.

Table 1 Model Hierarchy

Level	Structural primitives	Formal apparatus for behavioral representation
Systemic	Central processors, switches, channels, buses, storage devices, etc.	Systems analysis, game theory, queuing theory, etc.
Microcircuit	Microprocessors, RAM, ROM, UAPP, etc.	Input-output dependencies, GSA
Register	Registers, ALUs, counters, multiplexers, decoders	Theory of digital automata, truth tables, GSA
Valve	Logic gates, triggers	Algebra of logic, systems of logical equations
Schematic	Transistors, diodes, resistors, capacitors	Theory of electrical circuits, systems of linear, nonlinear, differential equations
Silicic	Geometric Objects	No

In fact lower level, silicon, as basic primitives, geometric shapes are used that represent areas of diffusion, polysilicon and metallization on the surface of a silicon crystal. The combination of these forms, as it were, imitates the process of making a crystal from the point of view of the developer. Here the view is only purely structural (not behavioral).

At the next, higher level, the schematic, the design representation is formed using interconnections of traditional active and passive elements of the electrical circuit: resistors, capacitors, and bipolar and MOS transistors. The connection of these components is used to simulate the behavior of an electrical circuit, expressed in terms of relationships between voltages and currents. Differential equations can be used to describe the behavioral description at this level.

The third level, the level of logic gates, traditionally plays a major role in the design of digital circuits and systems. Here are used such basic elements, as logical gates AND, OR and NOT and various types of flip-flops. The combination of these primitives allows combinational and sequential logic to be processed. The formal apparatus for the behavioral description at this level is Boolean algebra.

Above the gate level in the hierarchy is the register level. The basic elements here are components such as registers, counters, multiplexers, and arithmetic logic units (ALUs). The behavioral representation of the project at the register level is possible using truth tables, state tables and register transfer languages.

Above the register level is the level of microcircuits (or ICs). At the microcircuit level, the elements are components such as microprocessors, main memory devices, serial and parallel ports, and interrupt controllers. Although the boundaries of the microcircuits are also the boundaries of the element models, other situations are possible. So, a set of microcircuits that together form one functional device, can be thought of as a single item. An illustrative example here is the modeling of a bit-modular processor. An alternative option is also possible - when the elements represent separate sections of one microcircuit, for example, at the stage of analysis of technical specifications and decomposition. The main feature here is that the element represents a large block of logic, where for long and often converging data processing paths it is necessary to represent the dependencies of outputs on inputs. As in the case of the elements of the lower levels, the elements of the microcircuit level are not built hierarchically from simpler primitives, but are unified model objects. So, if you need to simulate a serial I / O port (universal asynchronous transceiver, UART), the corresponding model is not built by connecting simpler functional models blocks such as registers and counters, here the UART itself becomes the base model. Models of this type are important to OEMs who purchase ICs from other manufacturers but do not know their internal logic gate level structure as this is usually a secret. The behavioral description of the microcircuit level model is based on the input-output dependence of each specific IS algorithm implemented by this IS. The top level is the system level. The elements of this layer are the processor, memory and switch (bus), etc. The behavioral description at this level includes such basic data and characteristics as, for example, the processor speed in millions of instructions per second (megoflops) or the throughput of the data processing path (bit / s). From table. 1 and the foregoing, it can be seen that the structural or behavioral characteristics of neighboring levels overlap to a certain extent. For example, GAW representation can be used at both the register and chip level. However, the structural representation for both levels is completely different, which is why they are separated. The microcircuit and system level have essentially the same elements, however, they are completely different in their behavioral characteristics. Thus, behavioral models of the IS level allow the computation of detailed individual responses in the form of integer and bit values. And the behavioral representation of the system level is characterized by a serious limitation - it serves primarily to model the throughput of the system or determine the stochastic parameters of the system. In practice, the system-level view of the design is used primarily for comparative evaluation of different architectures. In general, different levels of models should be used if either behavioral or structural requirements are different.

The last concept associated with a hierarchical project view is the so-called project window.

This term denotes a group of levels in the project tree with which each specific developer works. So, the project window for the development of VLSI covers silicon, circuit, gate, register and microcircuit levels. The computer designer, on the other hand, is usually interested in a window covering the gate, register, microcircuit, and system levels. It is the concept of the project window that is the basis for multi-level design. With the increasing complexity of the VLSI, it will become impractical to include the gate level in the project window, since hundreds of thousands of logic gates can be placed on one chip. The register level, while certainly less complex than the gate level, may also contain optional details for those who are only interested in VLSI I / O signals.

Thus, from the point of view of the machine developer, the VLSI itself will become an element of the project.

Rice. 7. An example of the implementation of the presentation levels of a multiprocessor system.

Test work on the topic:

Electronic systems design stages

Design solution - an intermediate description of the designed object, obtained at one or another hierarchical level, as a result of the procedure (corresponding level).

The design procedure is an integral part of the design process. Examples of design procedures are synthesis of a functional diagram of a designed device, modeling, verification, routing of interconnections on a printed circuit board, etc.

Power plant design is divided into stages. A stage is a certain sequence of design procedures. The general sequence of design stages is presented as follows:

· Drawing up technical specifications;

· Project input;

· Architecture design;

· Functional and logical design;

· Schematic design;

· Topological design;

· Production of a prototype;

· Determination of the characteristics of the device.

Drawing up technical specifications. The requirements for the designed product, its characteristics are determined, and the technical task for the design is formed.

Project input. Each design stage has its own input means; moreover, many tooling systems provide for more than one way of describing the project.

High-level graphic and text editors for the description of the project of modern design systems are effective. These editors enable the designer to draw a block diagram of a large system, assign models to individual blocks, and interconnect the latter via buses and signal paths. Editors typically automatically associate textual descriptions of blocks and connections with associated graphics, thereby providing a comprehensive system simulation. This allows systems engineers not to change their usual style of work: you can still think, sketching out the flowchart of your project as if on a piece of paper, while at the same time accurate information about the system will be entered and accumulated.

Logic equations or circuit diagrams are often used very well to describe basic interface docking logic.

Truth tables are useful for describing decoders or other simple logic blocks.

Hardware description languages that contain structures such as state machines are usually much more efficient at representing more complex logical functional blocks, such as control blocks.

Architecture design. It represents the design of an EI up to the level of signal transmission to the CPU and memory, memory and efficiency. At this stage, the composition of the device as a whole is determined, its main hardware and software components are determined.

Those. designing an entire system with its high-level representation to check the correctness of architectural solutions is done, as a rule, in cases when it is developed in principle new system and all architectural issues need to be carefully worked out.

In many cases, a complete system design requires the inclusion of both non-electrical components and effects in the structure, in order to test them in a single modeling complex.

As elements of this level are used: processor, memory, controllers, buses. When constructing models and modeling the system, the methods of graph theory, set theory, the theory of Markov processes, the theory of queuing, as well as logical and mathematical means of describing the functioning of the system are used.

In practice, it is envisaged to build a parameterized system architecture and select the optimal parameters for its configuration. Consequently, the corresponding models must also be parameterized. The configuration parameters of the architectural model determine which functions will be implemented in hardware and which in software. Some of the configuration options for hardware include:

· Number, capacity and bandwidth of the system buses;

· Time of access to memory;

· The size of the cache;

· The number of processors, ports, register blocks;

· Capacity of data transfer buffers.

And the software configuration parameters include, for example:

· Parameters of the scheduler;

· Priority of tasks;

· "Garbage disposal" interval;

· The maximum allowable CPU interval for the program;

· Parameters of the memory management subsystem (page size, segment size, as well as the distribution of files on disk sectors;

Media configuration parameters:

· The value of the time-out interval;

· Fragment size;

· Protocol parameters for error detection and correction.

Rice. 1 - Sequence of design procedures for the architectural design phase

In interactive design at the system level, the functional specifications of the system level are first introduced in the form of data flow diagrams, and the types of components for the implementation of various functions are selected (Fig. 1). The main task here is to develop such a system architecture that will satisfy the given functional, speed and cost requirements. Errors at the architectural level are much more expensive than the decisions made during the physical implementation.

Architectural models are important and reflect the logic of the system's behavior and its temporal features, which makes it possible to identify functional problems. They have four important features:

· They accurately represent the functionality of hardware and software components using high-level data abstractions in the form of data streams;

· Architectural models abstractly represent the implementation technology in the form of time parameters. The specific implementation technology is determined by the specific values of these parameters;

· Architectural models contain diagrams that allow many functional blocks to share (share) components;

· These models must be parameterizable, typed, and reusable;

Modeling at the system level allows the developer to evaluate alternative options for system designs in terms of the ratio of their functionality, performance indicators and cost.

A top-down design tool system (ASIC Navigator, Compass Disign Automation) for ASICs and systems.

An attempt to free engineers from designing at the gate level.

Logic Assistant

· Design Assistant;

ASIC Synthesizez (ASIC synthesizer);

· Test Assistant;

It is a unified design and analysis environment. Allows you to create an ASIC specification by entering graphical and textual descriptions of your designs. Users can describe their projects using most high-level input methods, including flowcharts, Boolean formulas, state diagrams, VHDL and Verilog statements, and more. The system software will support these input methods as the basis for the entire subsequent ASIC design process.

The general architecture of the designed ASIC can be represented in the form of interconnected functional blocks without taking into account their physical division. These blocks can then be described in a manner that best suits the particulars of each function. For example, a user can describe control logic using state diagrams, arithmetic function blocks using data processing path diagrams, and algorithmic functions in VHDL. The final description can be a combination of both text and graphic materials and serves as the basis for the analysis and implementation of the ASIC.

The Logic Assistant subsystem converts the resulting specification into behavioral VHDL code. This code can be processed using a third-party VHDL modeling system. Modification of the specification at a behavioral level, makes it possible to make changes and debug at the initial stages of design.

Disign Assistant

Once the specification has been verified, it can be displayed on the ASIC. Initially, however, the user must decide how best to implement such a high-level project. The project description can be mapped onto one or more gate arrays or ICs based on standard elements.

Dising Assistant helps users evaluate a variety of options for optimal implementation. D.A. as directed by the user, determines the estimated crystal size, possible packaging methods, power consumption and the estimated number of logic gates for each decomposition option and for each type of ASIC.

The user can then interactively perform what-if analysis, explore alternative technical solutions with different design decomposition options, or arrange and move standard elements for the case of gate arrays. In this way, the user can find the optimal approach that meets the requirements of the specification.

ASIC Synthesizer

After a specific design option is selected, its behavioral description must be converted to a logic gate level representation. This procedure is very time consuming.

At the gate level, the following can be selected as structural elements: logic gates, flip-flops, and as a means of description - truth tables, logical equations. When using the register level, the structural elements will be: registers, adders, counters, multiplexers, and the description means - truth tables, micro-operation languages, jump tables.

The so-called logical simulation models, or simply simulation models (IM), have become widespread at the functional-logical level. IMs reflect only the external logic and temporal features of the functioning of the designed device. As a rule, in MI, the internal operations and internal structure should not be similar to those that exist in a real device. But the simulated operations and the temporal features of functioning, in the form as they are externally observed, in the MI should be adequate to those that exist in the real device.

Models of this stage are used to check the correctness of the implementation of the specified algorithms for the functioning of a functional or logical circuit, as well as timing diagrams of the device without a specific hardware implementation and taking into account the features of the element base.

This is done using logical modeling methods. Logical modeling means imitation on a computer of the operation of a functional circuit in the sense of advancing information presented in the form of logical values "0" and "1" from the input of the circuit to its output. Checking the functioning of the logic circuit includes both checking the logic functions implemented by the circuit and checking the timing (the presence of critical paths, risks of failure and signal race). The main tasks solved with the help of models of this level are verification of functional and schematic diagrams, analysis of diagnostic tests.

Schematic design is the process of developing electrical schematic diagrams, specifications in accordance with the requirements of the technical assignment. Designed devices can be: analog (generators, amplifiers, filters, modulators, etc.), digital (various logic circuits), mixed (analog-digital).

At the schematic design stage, electronic devices are represented at the schematic level. The elements of this level are active and passive components: resistor, capacitor, inductor, transistors, diodes, etc. A typical circuit fragment (gate, flip-flop, etc.) can also be used as an element of the circuit level. The electronic circuit of the designed product is a combination of ideal components that fairly accurately reflects the structure and elemental composition of the designed product. Ideal circuit components are assumed to be mathematically described with specified parameters and characteristics. The mathematical model of an electronic circuit component is an ODE with respect to variables: current and voltage. The mathematical model of a device is represented by a set of algebraic or differential equations expressing the relationship between currents and voltages in various components of the circuit. Mathematical models of typical fragments of a circuit are called macromodels.

The schematic design stage includes the following design procedures:

Structural synthesis - construction of an equivalent circuit of the designed device

· Calculation of static characteristics involves the determination of currents and voltages in any node of the circuit; analysis of current-voltage characteristics and study of the influence of the parameters of the components on them.

· Calculation of dynamic characteristics consists in determining the output parameters of the circuit depending on changes in internal and external parameters (single-variant analysis), as well as in assessing the sensitivity and degree of dispersion relative to the nominal values of the output parameters depending on the input and external parameters of the electronic circuit (multivariate analysis).

· Parametric optimization, which determines such values of the internal parameters of the electronic circuit that optimize the output parameters.

Distinguish between top-down (top-down) and bottom-up (bottom-up) design. Top-down design executes steps that use higher levels of device representation before steps that use lower hierarchical levels. In bottom-up design, the sequence is reversed.

When looking at the project tree, you can point to two design concepts: bottom-up (bottom-up) and top-down (top-down). Here, the word "top" refers to the root of the tree, and the word "bottom" refers to the leaves. With top-down design, work can begin already when the developer already knows only the functions of the root - and he (or she), first of all, splits the root into some set of primitives of the lower level.

After that, the developer proceeds to work with the underlying level and splits the primitives of this level. This process continues until it comes to the leaf nodes of the project. To characterize top-down design, it is important to note that the breakdown at each level is optimized according to one or another objective criterion. Here the split is not bound by the box of what is already there.

The term bottom-up design is not entirely correct in the sense that the design process still begins with the definition of the root of the tree, but in this case, the partition is carried out taking into account what components are already there and can be used as primitives; in other words, when splitting, the developer has to proceed from what constituent parts will be represented in the leaf nodes. These very "lower" parts will be designed first. Top-down design seems to be the most appropriate approach, but its weakness is that the resulting components are not "standard", which increases the cost of the project. Therefore, a combination of bottom-up and top-down design methods seems to be the most rational.

The vast majority of electronics and computing engineers are projected to use a top-down methodology. They will become, in effect, systems engineers, with a significant portion of their time spent on behavioral product design.

Currently, the design of electronic systems is carried out according to a bottom-up methodology, with the first step in the design process usually entering a description of the circuit at the structural level (obviously at the level of IC and discrete components). After determining the structure, a description of the behavior of this system in one or another language for describing this equipment is introduced and modulation is carried out. In this case, the electronic part of the project is performed manually, that is, without the use of design tools.

The increasing complexity of the designed systems leads to the fact that developers practically lose the ability to intuitively analyze the project, that is, to evaluate the quality and characteristics of the system design specification. And modeling at the system level using architectural models (as the first step in the top-down design process) provides such an opportunity.

In the case of top-down design, the two bottom-up design steps described above are performed in reverse order. Top-down design focuses on the behavioral representation of the system being developed, rather than its physical or structural representation. Naturally, the end result of the top-down design is also a structural or schematic representation of the project.

The point here is that top-down design requires system architecture models, and bottom-up design requires structural models.

Benefits (for all CAD systems):

1) A top-down design methodology serves as a prerequisite for parallel design: the coordinated development of hardware and software subsystems.

2) The implementation of the method of top-down design is facilitated by means of logical synthesis. These tools provide the transformation of logical formulas into physically realizable descriptions of the level of logical gates.

Thereby:

The physical implementation is simplified

Efficient use of design time

Technological templates are effectively used

However, for complex projects with a scale of several hundred thousand logic gates, it is desirable to be able to optimize globally through system-level modeling and analysis.

3) The top-down design methodology is based on the fact that the specification of the project is automatically created according to the initial functional requirements. It is functional requirements that are the initial component in the design of complex systems. Due to this, such an approach can reduce the likelihood of an inoperative system. In many cases, the failure of a designed system is caused by a mismatch between functional requirements and design specifications.

4) Another potential benefit of top-down design is that it allows the development of effective tests for design verification and validation, as well as test vectors for inspection of manufactured products.

5) The results of modeling at the system level can serve as the basis for a quantitative assessment of the project already at the initial stages of design. At later stages, logic gate-level modeling is required for design verification and validation. A homogeneous design environment will allow you to compare the simulation results obtained in the first and subsequent stages of design.

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Algorithmic methods are widely used to measure and calculate the parameters of mathematical models of radio components in computer-aided design systems for electronic circuits. Electronic computers are used for their design.

Optimization of management in various spheres of human activity. Classification of automated information management systems. Design methods and stages of development. Structural scheme, amount of memory, equipment for output and display of information.

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Electronic systems design stages

Design solution - an intermediate description of the designed object, obtained at one or another hierarchical level, as a result of the procedure (corresponding level).

The design procedure is an integral part of the design process. Examples of design procedures are the synthesis of the functional diagram of the designed device, modeling, verification, routing of interconnections on printed circuit board etc.

Power plant design is divided into stages. A stage is a certain sequence of design procedures. The general sequence of design stages is presented as follows:

preparation of technical specifications;

project input;

architecture design;

functional and logical design;

circuit design;

topological design;

production of a prototype;

determination of the characteristics of the device.

Drawing up technical specifications. The requirements for the designed product, its characteristics are determined, and the technical task for the design is formed.

Project input. Each design stage has its own input means; moreover, many tooling systems provide for more than one way of describing the project.

High-level graphic and text editors of the project description are effective. modern systems design. These editors enable the designer to draw a block diagram of a large system, assign models to individual blocks, and interconnect the latter via buses and signal paths. Editors typically automatically associate textual descriptions of blocks and connections with associated graphics, thereby providing a comprehensive system simulation. This allows systems engineers not to change their usual style of work: you can still think, sketching out the flowchart of your project as if on a piece of paper, while at the same time accurate information about the system will be entered and accumulated.

Logic equations or circuit diagrams are often used very well to describe basic interface docking logic.

Truth tables are useful for describing decoders or other simple logic blocks.

Hardware description languages that contain structures such as state machines are usually much more efficient at representing more complex logical functional blocks, such as control blocks.

Those. designing an entire system with a high-level representation of it to check the correctness of architectural solutions is done, as a rule, in cases where a fundamentally new system is being developed and all architectural issues need to be carefully worked out.

In many cases, a complete system design requires the inclusion of both non-electrical components and effects in the structure, in order to test them in a single modeling complex.

number, bit width and throughput system bus;

memory access time;

cache size;

number of processors, ports, register blocks;

capacity of data transfer buffers.

And the software configuration parameters include, for example:

scheduler parameters;

priority of tasks;

garbage disposal interval;

the maximum allowable CPU interval for the program;

parameters of the memory management subsystem (page size, segment size, as well as the distribution of files on disk sectors;

Media configuration parameters:

the value of the timeout interval;

fragment size;

protocol parameters for error detection and correction.

Rice. 1 - Sequence of design procedures for the architectural design phase

They accurately represent the functionality of hardware and software components using high-level data abstractions in the form of data streams;

architectural models abstractly represent the implementation technology in the form of temporal parameters. Specific technology implementations define specific values for these parameters;

architectural models contain schematics that allow many functional blocks to share (share) components;

these models must be parameterizable, typed, and reusable;

Modeling at the system level allows the developer to evaluate alternative options for system designs in terms of their relationship functionality, performance indicators and cost.

A top-down design tool system (ASIC Navigator, Compass Disign Automation) for ASICs and systems.

An attempt to free engineers from designing at the gate level.

Logic Assistant

Design Assistant;

ASIC Synthesizez (ASIC synthesizer);

The Logic Assistant subsystem converts the resulting specification into behavioral VHDL code. This code can be processed using a third-party VHDL modeling system. Modification of the specification at the behavioral level, makes it possible to make changes and debug on initial stages design.

Disign Assistant

Dising Assistant helps users evaluate a variety of options for optimal implementation. D.A. determines the estimated crystal size as directed by the user, possible ways packaging, power consumption and the estimated number of logic gates for each decomposition option and for each type of ASIC.

ASIC Synthesizer

After a specific design option is selected, its behavioral description must be converted to a logic gate level representation. This procedure is very time consuming.

This is done using logical modeling methods. Logical modeling means imitation on a computer of the operation of a functional circuit in the sense of advancing information presented in the form of logical values "0" and "1" from the input of the circuit to its output. Checking the functioning of the logic circuit includes both checking the logic functions implemented by the circuit and checking the timing (the presence of critical paths, risks of failure and signal race). The main tasks solved using models of this level are verification of functional and schematic diagrams, analysis of diagnostic tests.

The schematic design stage includes the following design procedures:

structural synthesis - construction of the equivalent circuit of the designed device

calculation of static characteristics involves the determination of currents and voltages in any node of the circuit; analysis of current-voltage characteristics and study of the influence of the parameters of the components on them.

the calculation of dynamic characteristics consists in determining the output parameters of the circuit depending on changes in the internal and external parameters (single-variant analysis), as well as in assessing the sensitivity and the degree of dispersion relative to the nominal values of the output parameters depending on the input and external parameters of the electronic circuit (multivariate analysis).

parametric optimization, which determines the values of the internal parameters of the electronic circuit that optimize the output parameters.

The point here is that top-down design requires system architecture models, and bottom-up design requires structural models.

Benefits (for all CAD systems):

1) A top-down design methodology serves as a prerequisite for parallel design: the coordinated development of hardware and software subsystems.

Thereby:

simplifies the physical implementation

efficient use of design time

technology templates are effectively used

However, for complex projects with a scale of several hundred thousand logic gates, it is desirable to be able to optimize globally through system-level modeling and analysis.

4.1. Definition, purpose, purpose

By definition, CAD is an organizational and technical system consisting of a set of design automation tools and a team of specialists from departments design organization performing computer-aided design of an object that is the result of an activity design organization [ , ].

From this definition, it follows that CAD is not a means of automation, but a system of human activities in the design of objects. Therefore, design automation as a scientific and technical discipline differs from the usual use of computers in design processes in that it deals with the issues of building a system, and not a set of individual tasks. This discipline is methodological in that it summarizes features that are common to different specific applications.

The ideal scheme of CAD functioning is shown in Fig. 4.1.

Rice. 4.1.

This scheme is ideal in the sense of full compliance with the wording according to existing standards and inconsistency with actually operating systems, in which not all design work is performed using automation tools and not all designers use these tools.

Designers, as the definition suggests, are CAD. This statement is quite legitimate, since CAD is a computer-aided design system, not an automated design system. This means that some of the design operations can and always will be performed by humans. At the same time, in more advanced systems, the proportion of work performed by a person will be less, but the content of these works will be more creative, and the role of a person in most cases will be more responsible.

From the definition of CAD it follows that the purpose of its operation is design. As already mentioned, design is a process of information processing, which ultimately leads to obtaining a complete picture of the designed object and methods of its manufacture.

In the practice of manual design, a complete description of the designed object and methods of its manufacture contains a product design and technical documentation... For the condition of computer-aided design, the name has not yet been legalized final product design, containing data about the object, and the technology of its creation. In practice, it is still called the "project".

Design is one of the most challenging types of human intellectual work. Moreover, the process of designing complex objects is beyond the power of one person and is carried out by a creative team. This, in turn, makes the design process even more complex and difficult to formalize. To automate such a process, you need to clearly know what it really is and how it is performed by developers. Experience shows that the study of design processes and their formalization were given to specialists with great difficulty, therefore design automation everywhere was carried out in stages, sequentially covering all new design operations... Accordingly, new systems were created step by step and old systems were improved. The more parts a system is split into, the more difficult it is to correctly formulate the initial data for each part, but the easier it is to optimize.

Design automation object are the work, the actions of a person that he performs in the design process. And what they design is called object of design.

A person can design a house, a car, technological process, industrial product. The same objects are designed to design CAD. At the same time, CAD products (CAD I) and CAD technological processes (CAD TP).

Hence, design objects are not objects of design automation... In production practice object of design automation is the whole set of actions of designers who develop a product or technological process, or both, and formalizing the results of developments in the form of design, technological and operational documentation.

By dividing the entire design process into steps and operations, you can describe them using specific mathematical methods and define tools for automating them. Then it is necessary to consider the highlighted design operations and automation tools in a complex and find ways to pair them in unified system that meets the set goals.

When designing a complex object, various design operations are repeated many times. This is due to the fact that design is a naturally developing process. It begins with the development of a general concept of the designed object, on its basis - draft design... Further approximate solutions (estimates) draft design are specified at all subsequent design stages. In general, such a process can be represented as a spiral. On the lower turn of the spiral is the concept of the projected object, on the top - the final data on the projected object. On each turn of the spiral, from the point of view of information processing technology, identical operations are performed, but in an increasing volume. Hence, instrumental automation tools repetitive operations may be the same.

It is very difficult to practically solve in full the task of formalizing the entire design process, however, if at least part of the design operations is automated, it will still justify itself, since it will allow to develop the created CAD system in the future on the basis of more advanced technical solutions and with lower resource costs ...

In general, for all stages of product design and manufacturing technology, the following main types of typical information processing operations can be distinguished:

search and selection from various sources of the necessary information;
analysis of the selected information;
performing calculations;
making design decisions;
registration of design solutions in a form convenient for further use (at subsequent stages of design, during the manufacture or operation of the product).

Automation of the listed information processing operations and information management processes at all stages of design is the essence of the functioning of modern CAD systems.

What are the main features of computer-aided design systems and their fundamental differences from the "task-based" methods of automation?

The first characteristic feature is the opportunity an integrated solving a general design problem, establishing a close connection between particular problems, i.e., the possibility of intensive exchange of information and interaction not only of individual procedures, but also of design stages. For example, in relation to the technical (design) design stage of CAD, RES allows solving the problems of layout, placement and routing in close relationship, which should be embedded in the hardware and software of the system.

With regard to systems of a higher level, we can talk about the establishment of a close information communication between schematic and technical design stages. Such systems make it possible to create radio-electronic means that are more efficient in terms of a set of functional, design and technological requirements.

The second difference between CAD RES is interactive mode design in which continuous process dialogue"man-machine". No matter how complex and sophisticated the formal design methods are, no matter how powerful the computing power is, it is impossible to create complex equipment without the creative participation of a person. Design automation systems, according to their concept, should not replace the designer, but act as a powerful tool for his creative activity.

The third feature of CAD RES is the possibility simulation radio-electronic systems in working conditions close to real ones. Simulation modeling makes it possible to predict the reaction of the designed object to a variety of perturbations, allows the designer to "see" the fruits of his labor in action without prototyping. The value of this CAD feature lies in the fact that in most cases it is extremely difficult to formulate a system efficiency criterion RES. Efficiency is associated with a large number of requirements of a different nature and depends on a large number of REM parameters and external factors. Therefore, in complex design problems, it is almost impossible to formalize the procedure for finding the optimal solution based on the criterion of complex efficiency. Simulation modeling allows testing different options decisions and choose the best one, and do it quickly and take into account all sorts of factors and indignations.

The fourth feature is the significant complication of software and information support design. We are talking not only about a quantitative, volumetric increase, but also about ideological complication, which is associated with the need to create communication languages between the designer and the computer, developed data banks, information exchange programs between constituent parts systems, design programs. As a result of the design, new, more advanced REMs are created, which differ from their analogues and prototypes in higher efficiency due to the use of new physical phenomena and principles of functioning, more perfect element base and structure, improved designs and progressive technological processes.

4.2. Principles of creating computer-aided design systems for structures and technology

When creating CAD systems, they are guided by the following system-wide principles:

Principle inclusions consists in the fact that the requirements for the creation, operation and development of CAD are determined by a more complex system, which includes CAD as a subsystem. Such complex system maybe, for example, an integrated system ASNI - CAD - process control system of an enterprise, CAD industry, etc.
Principle systemic unity provides for ensuring the integrity of the CAD system due to the connection between its subsystems and the functioning of the CAD control subsystem.
Principle complexity requires the coherence of the design of individual elements and the entire object as a whole at all stages of design.
Principle informational unity predetermines information consistency individual subsystems and CAD components. This means that in the means of providing CAD components should use uniform terms, symbols, conventions, problem-oriented programming languages and ways of presenting information, which are usually established by the appropriate regulatory documents... The principle of information unity provides, in particular, the placement of all files used repeatedly in the design of various objects in data banks. Due to the information unity, the results of solving one problem in CAD without any rearrangement or processing of the obtained data arrays can be used as initial information for other design problems.
Principle compatibility is that languages, codes, information and specifications structural links between subsystems and CAD components should be coordinated so as to ensure the joint functioning of all subsystems and to preserve open structure CAD in general. So, the introduction of any new hardware or software in CAD should not lead to any changes in the tools already in use.
Principle invariance provides that CAD subsystems and components should be as universal or typical as possible, that is, invariant to the designed objects and industry specifics. This is, of course, not possible for all CAD components. However, many components, for example, optimization programs, processing data arrays, and others, can be made the same for different technical objects.

As a result of the design, new, more advanced RES are created, which differ from their analogues and prototypes in higher efficiency due to the use of new physical phenomena and principles.