1. Field of the Invention
The present invention relates to the field of electronic design automation (EDA). More specifically, the present invention relates to integrated circuit modeling having timing information associated therewith for use with EDA systems for the design of integrated circuit devices.
2. Related Art
Rapid growth in the complexity of modern electronic circuits has forced electronic circuit designers to rely upon computer programs to assist and automate most steps of the integrated circuit design process. Typical circuits today contain hundreds of thousands or millions of individual pieces or xe2x80x9ccells.xe2x80x9d These designs are much too large for a circuit designer or even an engineering team of designers to manage effectively manually. To automate the design and fabrication of integrated circuit devices, the field of electronic design automation (EDA) has been developed which uses computer aided design (CAD) tools and systems.
Typically, CAD tools function in part by decomposing the overall desired behavior of the integrated circuit into simpler functions which can be represented as functional cells by the CAD tool. The CAD tool generates netlists including cells, logic gates and connections between them which perform the desired circuit behavior. Netlists can represent the integrated circuit in different levels of abstraction depending on the CAD function being performed, such as the behavior level, the structural level and the gate level. However, the high level design (HDL) description is typically the starting point for CAD tools because the HDL description file describes the behavior of the integrated circuit.
FIG. 1 illustrates a prior art EDA process 100. An HDL description 101 of an integrated circuit is received by a logic synthesis process 102. Process 102 first generates a technology independent netlist (including cells) based on the HDL description 101 and then generates a technology dependent netlist (including gates) based on a specified process technology library 103. The technology specific library 103 includes specific information regarding the cells of the selected process technology.
Optimization processes 104 are then applied to the technology dependent netlist so that specified design constraints 105 (e.g., area constraints and timing, power and other performance related constraints) can be maintained in the resultant design. Optimization 104 is the process of mapping one representation of functionality for an electronic circuit to another. The representation may be in terms of a circuit netlist (an abstract interconnection of electronic components), a circuit layout (an interconnection of components and their associated physical placement and wiring), or an abstract functional description which simply describes the function the circuit should perform without fully specifying circuit details. In general, optimization attempts to improve some aspect of the functionality of a circuit, e.g., its speed, its size, its power consumption, or some other circuit parameter. The goal of the optimization processes 104 is to select a functionally equivalent cell or group of cells that can be used to replace an existing cell where the replacement reduces the area of the integrated circuit or improves its performance (e.g., speed, power dissipation, etc.). The xe2x80x9cDesign Compiler,xe2x80x9d which is commercially available from Synopsys, Inc. of Mountain View, Calif., is an example of an automated circuit optimizer 104.
Circuit simulation 106 of FIG. 1 is used to determine if the modifications performed by the optimization process satisfy the given design constraints 105. Circuit simulation 106 can also be used to test if the netlist operates in the proper logical manner. At step 108 of FIG. 1, if the netlist satisfies the given design constraints 105 and logical simulation verifies, it is used to fabricate a physical integrated circuit device. Step 108 typically includes automatic coarse and fine placement processes where the cells of the netlist are spatially placed in the substrate area. Then, interconnections between the cells are routed in an automatic routing process.
The steps outlined in process 100 can be very process intensive thereby consuming large amounts of computer time and computer resources. For this reason, it is typical for large integrated circuit designs to be broken down into separate circuit blocks with each block independently being subjected to one or more of the steps of process 100. xe2x80x9cCharacterizationxe2x80x9d refers to the process of setting up distinct circuit blocks of a large circuit design to be optimized independently, outside of the whole integrated circuit design. For instance, assume a circuit design, E, contains circuit blocks A, B, C, and D. Circuit E has specified timing constraints and timing exceptions. Characterization automatically generates timing constraints and exceptions which are appropriate for the optimization of blocks A, B, C and D, independently. When optimizing the blocks using characterization, the optimization tool 104 (FIG. 1) need only load and process one block at a time. This decreases the demand of the tool on the computer resources. After the blocks have been optimized, they are then re-assembled back into circuit E. One example of the characterization described above is the xe2x80x9ccharacterizexe2x80x9d command found in the above referenced Design Compiler tool from Synopsys, Inc. of Mountain View, Calif.
Modeling is another tool used in EDA processes to reduce the demand on computer resources when designing integrated circuits. Modeling represents a circuit block in a more compact form so that it requires less computer memory resources to represent and also so that it requires less processor time to process. Usually, models achieve their smaller memory requirements by omitting details about the original block in the model. Because details are omitted from them, models cannot be used as a universal replacement for a circuit block. Usually models can only be used for very specific purposes. Prior art models contain a limited amount of information about the circuit block they replace. For instance, prior art models contain the circuit block size, the name and physical position of the pins of the circuit block, the pin""s imposed electrical capacitance, the pin""s imposed electrical current (drive), the arrival time at a circuit block""s output and the required time at a circuit block""s input. Although useful for some applications, the above described models do not model timing exceptions and therefore these models are not appropriate for use in general applications such circuit optimization.
The xe2x80x9cmodelxe2x80x9d command of the Design Compiler from Synopsys, Inc. and the xe2x80x9cextract_modelxe2x80x9d command of PrimeTime from Synopsys, Inc. create models from circuit blocks. U.S. Pat. No. 5,790,830, issued Aug. 4, 1998, by Russell B. Segal and entitled xe2x80x9cExtracting Accurate and Efficient Timing Models of Latch-Based Designsxe2x80x9d describes one form of modeling. These models can be used in a circuit to evaluate the timing. These models are appropriate for replacing prepackaged circuit blocks which are self contained. However, these models are not appropriate to general applications such as use in optimization because, among other shortcomings, they do not model timing exceptions.
Accordingly, what is needed is a method and system for providing a more effective circuit block model. What is needed further is a more effective and efficient optimization process. The present invention provides these advantages. These and other advantages of the present invention not specifically mentioned above will become clear within discussions of the present invention presented herein.
Embodiments of the present invention as described herein are drawn to solutions to problems posed by the optimization and analysis of large circuits. When circuits get large, they place a large burden on optimization and analysis tools which try to process them. In particular, the tools require increasing large amounts of computer memory and processor time to process the circuits. Often, computers are not large or fast enough to handle the task. Some technologies have been developed in the past to solve this problem, but they do not provide a complete solution. The embodiments of the present invention provide a more complete solution to the above problems.
Integrated circuit models are described herein having associated timing and tag information therewith for use with electronic design automation to effectively model timing exception information. The present invention includes a circuit block model which allows automated circuit optimization to be performed on extremely large circuits without the need to load all of the details of the circuit into computer memory. The circuit models of the present invention effectively model timing information including timing exception information. The model of the present invention is associated with command data structure, e.g., composed of textual commands (in one implementation), that describes arrival and required tags (which model exceptions) that are associated with the boundary of the original circuit block that is modeled. Specifically, for the input pins of a circuit to be modeled, the present invention writes out a command defining each unique required tag associated with an input pin and also writes out commands associating each required tag with its input pin. For the output pins of a circuit to be modeled, the present invention writes out a command defining each unique arrival tag associated with an output pin and also writes out commands associating each arrival tag with its output pin. The tag, arrival and required times are then associated with the model, along with other information. By saving the pertinent arrival and required tags (as associated times) at the circuit block boundary, timing exceptions are thereby effectively and efficiently modeled using the present invention.
The present invention also includes various circuit optimization processes (e.g., block and top optimization, bottle optimization and in-context optimization) that utilize the above described circuit model with exception information. These circuit optimizations can be used for incremental optimization of a large circuit. Optimizations using the above circuit models can be performed very efficiently and effectively and are particularly well suited for large integrated circuit designs.
Specifically, embodiments of the present invention include a computer readable memory unit of a computer controlled EDA system having stored therein a circuit model for representing a circuit block of an integrated circuit design, the circuit model comprising: a first set of commands which are arrival tag definitions and required tag definitions corresponding to timing exception paths which cross the boundary of the circuit block; a second set of commands defining associations between respective input pins of the circuit model and required tag values defined for the respective input pins, wherein the required tag values reference the required tag definitions of the first set of commands; and a third set of commands defining associations between respective output pins of the circuit model and arrival tag values defined for the respective output pins, wherein the arrival tag values reference the arrival tag definitions of the first set of commands. Embodiments include the above and wherein the first, second and third set of commands of the circuit model are textual commands. Embodiments include the above and wherein the arrival tag definitions and the required tag definitions are based on defined virtual clocks.
Embodiments also include a method of creating a circuit model representing a circuit block of an integrated circuit design, the method comprising the steps of: generating and storing a shell by copying a portion of the circuit block; generating and storing first commands which are arrival tag definitions and required tag definitions corresponding to timing exception paths which cross the boundary of the circuit block; generating and storing second commands that define associations between respective input pins of the circuit model and required tag values defined for the respective input pins, wherein the required tag values reference the required tag definitions of the first commands; and generating and storing third commands that define associations between respective output pins of the circuit model and arrival tag values defined for the respective output pins, wherein the arrival tag values reference the arrival tag definitions of the first commands; and creating the circuit model by associating the first, second and third commands with the shell. Embodiments include the above and wherein the first, second and third set of commands of the circuit model are textual commands.