Abstract:
Disclosed is a method for translating a SPICE format circuit description to Verilog format, allowing simulation in Verilog format, or verification of prior Verilog to SPICE conversion as required by some simulation programs. The invention may employ identification of SPICE sub circuits, circuit elements, input signals, and output signals; and translation of these to Verilog format wherein signal names and design hierarchy may be maintained. Instance names may be translated to Verilog names easily associated with SPICE instance names. Identification and translation may employ lookup tables, rule sets, specialized field delimiters, naming conventions, other algorithms or combinations thereof. An intermediate file of input and output signals may be created. SPICE node names may be converted to Verilog wire definitions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    a. Field of the Invention  
           [0002]    The present invention pertains to integrated circuit development software and more specifically to translating a circuit description employing a SPICE format to that of a Verilog format.  
           [0003]    b. Description of the Background  
           [0004]    Integrated circuit design may be custom or semi-custom. Semi-custom may employ gate array or standard cell methodologies. Gate array employs a base set of functions fabricated on a semiconductor die that are later interconnected to reflect the function of the design. Interconnection may employ metal, polysilicon or other layers. Standard cell employs a predefined set of cells exhibiting a common dimension that may be placed in rows and blocks, the order determined by functions to be implemented and routing of interconnect between cells or groups of cells. Verilog, a hardware description language, is frequently employed in the design process. Verilog may be used to specify the initial design, to provide input to synthesis tools, and to check post layout operation. At times, the predefined set of cells of a standard cell library may not provide a desired function, or may not provide the speed, size, or power consumption desired. In these circumstances, new cells may be created, or a custom block of logic incorporating the desired function may be designed. The design of the custom block of logic may employ SPICE (Special Programs for Interactive Circuit Elements) to specify and simulate the design. SPICE supports both logical and timing simulation. In order to simulate the whole design that comprises Verilog and SPICE defined elements, Verilog must be converted to SPICE or SPICE must be converted to Verilog. A number of simulation tools require a SPICE format input and tools are provided to convert Verilog to SPICE such that the whole design may be simulated using SPICE. There are not tools that provide SPICE to Verilog conversion, as may be employed to verify Verilog to SPICE conversion, or to allow simulation of a design in Verilog for those simulation tools that support Verilog formats. Further, changes made to SPICE designs are not easily verified. Therefore a new method to convert a SPICE netlist to a Verilog netlist is needed.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention overcomes the disadvantages and limitations of the prior art by providing a system and method of translating a SPICE netlist to Verilog. By mapping SPICE constructs to Verilog constructs, and by mapping SPICE syntax to Verilog syntax, the present invention provides an easy to use, automatic conversion program. Advantageously, the present invention allows SPICE based designs to be converted to Verilog to confirm the accuracy of prior conversion from Verilog to SPICE. SPICE may be required as a simulation input format for some simulation tools. Such tools may be employed to simulate circuits comprising semi-custom and custom components, and may also be employed to simulate circuits comprising analog and digital circuitry, as may be employed in communication systems.  
           [0006]    The present invention therefore may comprise a method for designing an integrated circuit comprising: partitioning a design into a plurality of function blocks; designing a first one of the plurality of function blocks employing Verilog to produce a first block design; designing a second one of the plurality of function blocks employing SPICE to produce a second block design; converting the first block design to SPICE to produce a converted first block design; simulating operation of the converted first block design and the second block design; and translating the converted first block design to Verilog to produce a translated first block design.  
           [0007]    The present invention provides flexibility in the format of simulation such that SPICE designs may be converted to Verilog and simulated in Verilog. Such simulation may comprise testing and fault coverage analysis. Further, a SPICE file that is converted to Verilog may be used as stimulus to another block that is being designed, allowing design and simulation to occur in a single format. Advantageously, the circuit and signal names of the SPICE file may be retained, or may be translated to a form readily associable with the original names such that translated files may easily be compared with the SPICE source file. The hierarchy of the SPICE description may also be maintained, allowing simplified review of circuit structure  
           [0008]    The invention therefore may further comprise a method for translating a SPICE netlist to Verilog comprising: opening a SPICE file; translating “.SUBCKT” instantiations to “module”; translating “.ENDS” statements to “endmodule”; translating SPICE circuit elements to Verilog format; and removing discrete circuit elements.  
           [0009]    The present advantage provides the flexibility of format that allows developers to employ a wider range of simulation tools while maintaining verification of the converted design. The method of the present invention may be employed in a batch process, providing automatic conversion. The aforementioned flexibility of format may allow greater utilization of resources by providing a choice to simulate using SPICE or to simulate using Verilog. 
       
    
    
     DESCRIPTION OF THE FIGURES  
       [0010]    In the figures,  
         [0011]    [0011]FIG. 1 is an overview of a design process.  
         [0012]    [0012]FIG. 2 depicts Verilog to SPICE conversion and combined design simulation using SPICE.  
         [0013]    [0013]FIG. 3 depicts Verilog to SPICE conversion, SPICE to Verilog translation for verification, and combined design simulation using SPICE.  
         [0014]    [0014]FIG. 4 depicts SPICE to Verilog translation and combined design simulation using Verilog.  
         [0015]    [0015]FIG. 5 is a flowchart of a SPICE to Verilog translation process. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    [0016]FIG. 1 is an overview of an integrated circuit design process. Process  100  begins at step  102  where a function specification for a design is received. At step  104 , the design may be partitioned into functional blocks. At step  106 , logic design of the blocks partitioned in step  104  is performed. Logic design may employ pre-defined circuits such as counters and registers that are provided with a design library. Logic design may employ a hardware descriptive language such as Verilog. Verilog is a Hardware Description Language; a textual format for describing electronic circuits and systems. Applied to electronic design, Verilog may be used for verification through simulation, for timing analysis, for test analysis (testability analysis and fault grading) and for logic synthesis. Verilog HDL is an IEEE standard—number 1364. Through Verilog, the designer may select circuit elements and define the interconnection between elements. At step  106 , it may be determined that custom design is desired to meet a design goal such as speed, power, circuit size, or other parameter. Custom design may be performed at step  108  and may employ software simulation tools such as SPICE. Once a design for one block or a plurality of blocks is completed, the process advances to step  110  where the design is simulated. At step  110 , Verilog files may be converted to SPICE to allow simulation with custom logic. Simulation may employ a stimulus file that provides a sequence of input signals, allowing the designer to check operation of the block or blocks. The steps of block design  106 , custom design  108 , and simulation  110  may be reiterative in that a design may be altered to correct errors or to achieve implementation goals. At step  112 , the design may be synthesized wherein the circuit description provided through Verilog or other hardware descriptive language is converted to logic gates. The logic gates may be selected from a logic library such as a standard cell library. For each type of function defined in the design, such as AND, OR and other gates, there are commonly a plurality of versions of each function wherein versions may vary in speed, power, output drive, or other characteristics. Post synthesis simulation  114  may employ SPICE values for custom logic and may employ parameters associated with the logic gates selected in step  112  to provide a more accurate estimation of performance. The step  114  simulation may include comparison with design goals and may result in repetition of previous steps to meet design goals. The process then continues at step  116  where routing and physical layout of the design is performed. Post layout simulations (not depicted) may be performed to confirm correct design operation. The process ends at step  118 .  
         [0017]    [0017]FIG. 2 depicts Verilog to SPICE conversion and combined design simulation using SPICE. Verilog design  202  is input to Verilog to SPICE converter  204 . Verilog to SPICE converter  204  may employ software such as v21vs from Mentor Graphics Corporation that has headquarters at 8005 SW Boeckman Road, Wilsonville, Oreg. 97070. Custom design  206 , in a SPICE format, may be combined with the output of Verilog to SPICE converter  204  to produce combined design  208  that then may be simulated in SPICE format at step  210 . Simulation  210  may employ programs such as Timemill from Synopsys Corporation, headquartered at 700 East Middlefield Rd. Mountain View, Calif. 94043. Simulation  210  may comprise analog, digital or mixed signal simulation.  
         [0018]    [0018]FIG. 3 depicts Verilog to SPICE conversion, SPICE to Verilog translation for verification, and combined design simulation using SPICE. Verilog design  302  is input to Verilog to SPICE converter  304 . Custom design  310 , in a SPICE format, may be combined with the output of Verilog to SPICE converter  304  to produce combined design  312  that may be simulated in SPICE format at step  314 . The output of Verilog to SPICE converter  304  may be input to SPICE to Verilog translator  306 . Verilog design  302  and the output of SPICE to Verilog translator  306  are supplied to conversion verification  308  where the accuracy of Verilog to SPICE conversion may be checked.  
         [0019]    [0019]FIG. 4 depicts SPICE to Verilog translation and combined design simulation using Verilog. Custom logic  404 , in SPICE format, is input to SPICE to Verilog translator  406 . Verilog design  402  is combined with the output from SPICE to Verilog translator  406  to produce combined design  408  that may be simulated in Verilog format at step  410 .  
         [0020]    [0020]FIG. 5 is a flowchart of a SPICE to Verilog translation process. The translation process  500  begins with SPICE netlist  502  that is opened and read in at step  504 . Table 1 below lists an example SPICE file input and Table 2 below lists an example Verilog file output. At step  506 , instantiations of the heading “SUBCKT” are translated to “module”. A circuit name, and input and output signal names, may follow the “SUBCKT” heading. The circuit name may be identified as the first work following “SUBCKT” and may be utilized as the module name. Input and output signal names follow the circuit name and may be may be employed in the Verilog output file. For example, the “SUBCKT INV_CHAIN Z A” line of table 1 may be employed to generate the “module INV_CHAIN (Z, A)” entry listed in table 2. Retaining the circuit name and input and output signal names allows simplified association of the SPICE input file with the Verilog output file. Alternately, new circuit and signal names may be introduced in the translation process. At step  508 , “ENDS” statements are translated to “endmodule”. At step  510 , “x” elements are translated to Verilog format. The ‘x’ elements may comprise an instance name, signal nodes, and a circuit element descriptor. For example, the “XINV3 2 3 INV” line listed in table 1 may be translated to the “INV INV3 (.Z(3), .A(2)):” line listed in table 2. The translation of instance names (“XINV1” to “INV1” in the above example), may employ simple truncation of a leading “x” in element names, or may employ renaming. Renaming may be total or in part and may employ a lookup table, an algorithm, or rules to define the instance name. Advantageously, the present invention allows the hierarchy of the SPICE design and signal name associations to be maintained. The signal node names of the SPICE file may be employed to define wires in Verilog, and to specify signal connections to Verilog circuit elements. As may be observed in table 2, the signal nodes listed in table 1 are defined as wires. The circuit element descriptor may be translated to Verilog syntax. IN the examples of tables 1 and 2, INV is used for both SPICE and Verilog syntax. At step  512 , discrete circuit elements, such as resistors, capacitors, transistors, and inductors, for example, are removed. At step  514 , the modified file is written out to produce Verilog structured netlist  516 .  
                         TABLE 1                       EXAMPLE SPICE INPUT                                    .SUBCKT INV_CHAIN Z A           XINV1 1 A INV           XINV2 2 1 INV           XINV3 3 2 INV           XINV4 4 3 INV           XINV5 Z 4 INV           .ENDS           .SUBCKT INV Z A           MP1 Z A VDD VDD W=1U L=0.25U           MN1 Z A VSS VSS W=0.5U L=0.25U           .ENDS                      
 
         [0021]    [0021]                         TABLE 2                       EXAMPLE VERILOG OUTPUT                                    module INV_CHAIN (Z, A);           output Z;           input A;           wire 1;           wire 2;           wire 3;           wire 4;           INV INV1 (.Z(1), .A(A));           INV INV2 (.Z(2), .A(1));           INV INV3 (.Z(3), .A(2));           INV INV4 (.Z(4), .A(3));           INV INV5 (.Z(Z), .A(4));           endmodule                        
         [0022]    The above example is illustrative of one embodiment of the present invention. A Perl code listing of an embodiment of the invention is shown in Appendix A. References to SPICE include any hardware description language compliant with IEEE SPICE standards. The above description need not be implemented in the exact order described. Other methods may be employed to achieve equivalent results. Naming conventions may be employed to simplify the translation process. For example, SPICE files may be formatted such that only input signals begin with the letter “I” and that only output signals begin with the letter “O”. Additionally, signals may be more easily identified through predefined delimiters. For example, a plus sign may be used to delimit and indicate input signals and a minus sign may be used to delimit and indicate output signals.  
         [0023]    As described, the present invention provides a quick and convenient method that allows a designer to verify the accuracy of conversion of Verilog designs to SPICE, and to convert SPICE designs to Verilog for simulation using Verilog. As previously noted, the translation provided by the present invention also provides greater flexibility in the simulation tools that may be employed.  
         [0024]    The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light in the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.