PATENT DOCUMENT

Publication Number: US-7956636-B2
Application Number: US-52669108-A
Country: US
Kind Code: B2

Title: Generating test benches for pre-silicon validation of retimed complex IC designs against a reference design

Abstract:
This invention ( 900 ) describes a method that generates and uses a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing a sub-circuit that matches the electrical design module. The invention includes providing ( 902 ) a description of an electrical design module that includes a plurality of ports. In addition, the invention includes providing ( 904 ) a description of an electrical reference model. The invention further includes providing and or creating ( 92 ) one or more implicit defines for the reference modules that appear in hierarchy of the electrical reference model. And, the invention includes providing ( 906 ) a description file that includes one or more instance definitions. The invention parses ( 91 ) the hierarchy of the electrical design model and then processes ( 96 ) the description file. The invention then writes ( 97 ) the test bench.

Claims:
1. A method that generates a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing within its hierarchy a sub-circuit that matches the electrical design module, comprising:
 providing a description of an electrical design module that includes a plurality of ports; 
 providing a description of an electrical reference model that comprises a hierarchy of one or more reference modules where each said reference module comprises a plurality of ports and a plurality of internal wires; 
 providing or creating one or more implicit defines for said reference modules that appear in said hierarchy of said electrical reference model where each said implicit define comprises a path through said hierarchy of said electrical reference model to said module so defined; 
 providing a description file that includes one or more instance definitions, wherein each said instance definition contains a plurality of port definitions, each said port definition contains the name of a port of said electrical design module and a reference connection, said reference connection contains the name of a single implicit define being also the name of a module within said electrical reference model, hence rendering said reference connection independent of its path within said electrical reference model, and the name of said port on said module within said electrical reference model; 
 parsing the hierarchy of said electrical design model; 
 processing said description file; and 
 writing the test bench containing logic to drive each input port of said electrical design module with said port of said reference module to which said output port maps and to check at each clock cycle each output port of said electrical design module against said port of said reference module to which it maps and to record in the test bench that each said plurality of ports of said electrical design module matches its corresponding port of said reference module. 
 
     
     
       2. The method of  claim 1  wherein said implicit defines are generated for each said reference module that appears uniquely in the hierarchy of said electrical reference model. 
     
     
       3. The method of  claim 1  wherein each said port definition within said description file further specifies an encoding function to apply to said reference connection. 
     
     
       4. The method of  claim 1  wherein each said port definition further specifies that said reference connection be delayed by an integral number of clock cycles. 
     
     
       5. The method of  claim 1  wherein each said port definition further specifies that the port on said electrical design model be delayed by an integral number of clock cycles. 
     
     
       6. The method of  claim 1  wherein said reference connection specifies a Boolean combination of one or more reference signals where each said reference signal comprises a signal or port in said electrical reference module. 
     
     
       7. A method that uses a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing within its hierarchy a sub-circuit that matches the electrical design module, comprising:
 providing a description of an electrical design module that includes a plurality of ports; 
 providing a description of an electrical reference model that comprises a hierarchy of one or more reference modules where each said reference module comprises a plurality of ports and a plurality of internal wires; 
 providing or creating one or more implicit defines for said reference modules that appear in said hierarchy of said electrical reference model where each said implicit define comprises a path through said hierarchy of said electrical reference model to said module so defined; 
 providing a description file that includes one or more instance definitions, wherein each said instance definition contains a plurality of port definitions, each said port definition contains the name of a port of said electrical design module and a reference connection, said reference connection contains the name of a single implicit define being also the name of a module within said electrical reference model, hence rendering said reference connection independent of its path within said electrical reference model, and the name of said port on said module within said electrical reference model; 
 parsing the hierarchy of said electrical design model; 
 processing said description file; and 
 writing the test bench containing logic to drive each input port of said electrical design module with said port of said reference module to which said output port maps and to check at each clock cycle each output port of said electrical design module against said port of said reference module to which it maps and to record in the test bench that each said plurality of ports of said electrical design module matches its corresponding port of said reference module. 
 
     
     
       8. The method of  claim 7  wherein said implicit defines are generated for each said reference module that appears uniquely in the hierarchy of said electrical reference model. 
     
     
       9. The method of  claim 7  wherein each said port definition within said description file further specifies an encoding function to apply to said reference connection. 
     
     
       10. The method of  claim 7  wherein each said port definition further specifies that said reference connection be delayed by an integral number of clock cycles. 
     
     
       11. The method of  claim 7  wherein each said port definition further specifies that the port on said electrical design model be delayed by an integral number of clock cycles. 
     
     
       12. The method of  claim 7  wherein said reference connection specifies a Boolean combination of one or more reference signals where each said reference signal comprises a signal or port in said electrical reference module. 
     
     
       13. A program storage device readable by a computing device that tangibly embodies a program of instructions executable by the computing device to perform a method that uses a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing within its hierarchy a sub-circuit that matches the electrical design module, comprising:
 providing a description of an electrical design module that includes a plurality of ports; 
 providing a description of an electrical reference model that comprises a hierarchy of one or more reference modules where each said reference module comprises a plurality of ports and a plurality of internal wires; 
 providing or creating one or more implicit defines for said reference modules that appear in said hierarchy of said electrical reference model where each said implicit define comprises a path through said hierarchy of said electrical reference model to said module so defined; 
 providing a description file that includes one or more instance definitions, wherein each said instance definition contains a plurality of port definitions, each said port definition contains the name of a port of said electrical design module and a reference connection, said reference connection contains the name of a single implicit define being also the name of a module within said electrical reference model, hence rendering said reference connection independent of its path within said electrical reference model, and the name of said port on said module within said electrical reference model; 
 parsing the hierarchy of said electrical design model; 
 processing said description file; and 
 writing the test bench containing logic to drive each input port of said electrical design module with said port of said reference module to which said output port maps and to check at each clock cycle each output port of said electrical design module against said port of said reference module to which it maps and to record in the test bench that each said plurality of ports of said electrical design module matches its corresponding port of said reference module. 
 
     
     
       14. The program storage device of  claim 13  wherein said implicit defines are generated for each said reference module that appears uniquely in the hierarchy of said electrical reference model. 
     
     
       15. The program storage device of  claim 13  wherein each said port definition within said description file further specifies an encoding function to apply to said reference connection. 
     
     
       16. The program storage device of  claim 13  wherein each said port definition further specifies that said reference connection be delayed by an integral number of clock cycles. 
     
     
       17. The program storage device of  claim 13  wherein each said port definition further specifies that the port on said electrical design model be delayed by an integral number of clock cycles. 
     
     
       18. The program storage device of  claim 13  wherein said reference connection specifies a Boolean combination of one or more reference signals where each said reference signal comprises a signal or port in said electrical reference module.

Description:
TECHNICAL FIELD 
     The present invention relates to generating test benches for integrated circuit designs. More specifically, the present invention relates to generating test benches for pre-silicon validation of retimed complex IC designs against a reference design. 
     BACKGROUND ART 
     Functional validation (verification) of complex IC designs is an activity that currently consumes a majority of the engineering man-hours for creating a semiconductor design. Verification entails checking the output of a design implementation with that expected by a design reference model. The checking can be either at an abstract level using a high-level reference model, or it can involve checking signals on a cycle-by-cycle basis against a cycle-accurate reference model. The validation process depends upon having two independently-created implementations of the same specification to reduce the probability that a violation of the specification is accepted due to a common-mode failure in both the implementations. 
     This invention pertains to checking a plurality of design modules against a plurality of modules within a cycle-accurate reference model. The use of cycle-accurate reference models is unusual within the industry because:
         1. There is a considerable overhead involved in maintaining a cycle-accurate reference model beyond that for maintaining an abstract reference model. This overhead increases proportionately to the degree of flux of the architectural specification of the design.   2. Implementing a new architecture requires a parallel effort to create a cycle-accurate reference model; this parallel effort has approximately the same degree of difficulty as the implementation being tested for the architecture.   3. In cases where a re-implementation occurs of an existing architecture, the original implementation cannot usually be used as a reference model since there are usually changes to the feature set, such as adding new features or fixing defects, that render the original implementation inaccurate as a reference model.       

     Thus, the current invention is useful only when a cycle-accurate implementation of a stable architecture can be used as a reference model for a re-implementation of that architecture. 
     Since validation occupies such a time-consuming portion of the development of complex ICs, it is important to begin the validation process as soon as possible in the design cycle. The present invention greatly facilitates the early testing of design modules by automating the repetitive task of generating test benches. Furthermore, our method uses description files to specify how the testing of a design module is to proceed; these description files act as a precise definition of the interfaces between design modules. 
     This application claims the benefits of the earlier filed U.S. Provisional Application Ser. No. 60/893,028, filed 5 Mar. 2007, which is incorporated by reference for all purposes into this specification. 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     This invention describes a method that generates and uses a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing a sub-circuit that matches the electrical design module. The invention comprises providing a description of an electrical design module that includes a plurality of ports. In addition, the invention includes providing a description of an electrical reference model that comprises a hierarchy of one or more reference modules where each reference module comprises a plurality of ports and a plurality of internal wires. The invention further includes providing and or creating one or more implicit defines for the reference modules that appear in hierarchy of the electrical reference model where each implicit define comprises a path through the hierarchy of the electrical reference model to the module so defined. And, the invention includes providing a description file that includes one or more instance definitions, wherein each instance definition contains a plurality of port definitions, each port definition contains the name of a port of the electrical design module and a reference connection, the reference connection contains the name of a single implicit define being also the name of a module within the electrical reference model and the name of the port on the module within the electrical reference model. The invention parses the hierarchy of the electrical design model and then processes the description file. The invention then writes the test bench containing logic to drive each input port of the electrical design module with the port of the reference module to which it maps and to check at each clock cycle each output port of the electrical design module against the port of the reference module to which it maps and to record in the test bench that each of the plurality of ports of the electrical design module matches its corresponding port of the reference module. 
     Further refining the invention, the implicit defines are generated for each reference module that appears uniquely in the hierarchy of the electrical reference model. In addition, the reference connection comprises the name of an implicit define and the name of an internal wire in the module within the electrical reference model. Further, each said port definition within the description file further specifies an encoding function to apply to the reference connection. Additionally, each port definition further specifies that the reference connection be delayed by an integral number of clock cycles. Further, each port definition further specifies that the port on the electrical design model be delayed by an integral number of clock cycles. And, the reference connection specifies a Boolean combination of one or more reference signals where each reference signal comprises a signal or port in the electrical reference module. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To further aid in understanding the invention, the attached drawings help illustrate specific features of the invention and the following is a brief description of the attached drawings: 
         FIG. 1  illustrates the invention in a typical networked environment. 
         FIG. 2  discloses a test bench to check a unit-level design module against a unit-level reference module. 
         FIG. 3  discloses a test bench to check a unit-level design module against a block-level reference module. 
         FIG. 4  discloses a test bench to check a unit-level design module against a chip-level reference module. 
         FIG. 5  discloses a test bench to check two unit-level design modules against a chip-level reference module. 
         FIG. 6  discloses a test bench in which some ports of design modules are wired together and tested against a chip-level reference module. 
         FIG. 7  discloses a test bench to check a unit-level design module against a reference module with functionality reduced by driving one or more inputs with constant values and the remaining inputs with those of the corresponding reference module in a chip-level reference module. 
         FIG. 8  discloses a test bench to check a block-level design module against a chip-level reference module. 
         FIG. 9A  illustrates the top-level flow chart of the disclosed invention. 
         FIG. 9B  illustrates the process of step  950  of  FIG. 9A . 
         FIG. 10  illustrates the process of step  91  of  FIG. 9B . 
         FIG. 11  illustrates the process of step  96  of  FIG. 9B . 
         FIG. 12  illustrates the process of step  205  of  FIG. 11 . 
         FIG. 13  illustrates the process of step  97  of  FIG. 9B . 
         FIG. 14  illustrates the process of step  411  and step  412  of  FIG. 13 . 
     
    
    
     DISCLOSURE OF INVENTION 
     This disclosure describes generating test benches for pre-silicon validation of retimed complex IC designs against a reference design. This disclosure describes numerous specific details in order to provide a thorough understanding of the present invention. One skilled in the art will appreciate that one may practice the present invention without these specific details. Additionally, this disclosure does not describe some well known items in detail in order not to obscure the present invention. 
       FIG. 1  illustrates the use of the present invention in a typical networked environment. The invention is a software program that runs on one or more workstation  10  in a networked environment. The various workstations  10  couple to a network  12  where they may communicate with each other. Additionally, the networked environment may include a shared storage device  14  and a network server  16 . And, the networked environment may couple to the Internet  18 . In addition to being able to operate on one or more workstations  10 , the invention may use the resources of the shared storage device  14  and the network server  16 . The invention may also use resources available through the Internet  18 . One embodiment of the invention uses a LINUX based standalone workstation  10  and uses the interpretive language PERL. One skilled in the arts will appreciate the invention is capable of using other languages for operation and that it may be hosted on other operating systems. 
     The following sections illustrate an exemplary selection of test benches generated using the disclosed invention. The inputs used are the name of a top-level module to be used as a reference model, one or more description files, described below, and optionally, one or more implicit defines. An object of this invention is that all of these test benches can be generated using the same description file(s) for the design module(s) being tested, regardless of which reference model is used for providing stimulus and checking results. 
       FIG. 2  discloses a test bench to check a unit-level design module against a unit-level reference module. The simplest form of a test bench that can be generated using the disclosed invention is to test a unit-level design module against a unit-level reference module. Referring back to  FIG. 2 , the outer boundary represents the generated test bench, which contains instances of reference module B and design module b corresponding to it. The inputs of the test bench drive the inputs of B and the outputs of B are propagated to the outputs of the test bench. Furthermore, the inputs of B are also driven into b so that it sees the identical stimulus. The outputs of both B and b are wired into a checker unit (represented as a check mark within a circle in the figure) to report any mismatches. The thicker lines represent logic generated by the test bench generator, where a box indicates instantiation and a line indicates a wire. To use such a test bench, there must be a unit-level stimulus generator. 
       FIG. 3  discloses a test bench to check a unit-level design module against a block-level reference module, which illustrates a more complex test bench generated with the disclosed invention. In this figure, the reference module B is instantiated within a higher-level module that also instantiates reference module C. The inputs and outputs to the generated test bench match those of the higher-level module. The boxes and wires with thinner lines indicate logic that is present within the higher-level module and not generated by the test bench generator. The test bench generator creates wires to drive the inputs of b either from primary inputs to the test bench or from wires within the reference design that drive B. Similarly, the test bench generator checks the outputs of b against the outputs of those internal wires driven by B in the higher-level design. 
       FIG. 4  discloses a test bench to check a unit-level design module against a chip-level reference module. The natural extension of these test benches is to use the reference model for an entire chip to test a unit-level module in the design as shown schematically in this figure. In fact, conceptually the extensions can go even beyond the chip level, for example, to multiple processors in a symmetric multiprocessing system. 
       FIG. 5  discloses a test bench to check two unit-level design modules against a chip-level reference module. Another way that the test benches can be extended is to allow for testing of multiple design modules independently in the same test bench as illustrated in this figure. This extension uses the same description files for design modules b and c as would be used in their unit-level test benches. 
       FIG. 6  discloses a test bench where some ports of the design modules are wired together and tested against a chip-level reference module. When adjacent modules in a design have both been tested, it can be convenient to produce a test bench in which the outputs of one design module are wired to the inputs of another design module that consume them, as illustrated in this figure. The description files for b and c can be used for generating this test bench without changes, but an additional description file is needed to override the driving of the input ports that are driven from a local instance. 
       FIG. 7  discloses a test bench to check a unit-level design module against a reference module with functionality reduced by driving one or more inputs with constant values and the remaining inputs with those of the corresponding reference module in a chip-level reference module. The purpose of using automatically-generated test benches is to begin testing as early as possible in the design cycle. Sometimes it is desired to begin testing before all the features of the design module have been implemented. If the unimplemented features can be disabled in the corresponding reference module by driving some inputs with constant values (i.e., logic 0 or 1), then the result is a test bench as illustrated in this figure. Here, an additional instance of reference module B, called B′ has been instantiated in the test bench with certain inputs driven from constant values. The outputs of design module b are checked against those of B′. While reference module B may receive inputs that b is unable to handle, module B′ behaves as though those inputs had not occurred so that the outputs of b can be checked. The description file used for testing b against the full design can be used for generating this test bench without changes, but an additional description file is needed to instantiate B′. 
       FIG. 8  discloses a test bench to check a block-level design module against a chip-level reference module. Eventually, the design modules are composed hierarchically into higher-level modules (blocks). When the modules to be tested (b and c in this example) are instantiated within a higher-level design module, there is no reason to drive their inputs directly. However, the disclosed invention uses the description files to generate checkers for the design modules by propagating the values from the internal wires driven by the design modules to the test bench for comparison against those of the reference model. These checkers can be created with no change to the description files that would be used for doing unit-level checking. 
     In the above examples, the description files have no dependence upon what the reference model is except that the reference model must contain modules of the appropriate type. In addition, the above examples all assume that there is a perfect correspondence between a reference module and a design module. In practice, this is often not the case. 
     An important innovation of the disclosed invention is the use of implicit defines to make the description file for a design module independent of the reference model. The inputs are the name of the top-level module to be used as a reference model, a list of one or more description files, and an optional list of one or more implicit defines. Each description file contains the information needed to provide a correspondence between a design file and a plurality of locations in the reference file against which the design file is to be checked. Each location within the reference model may be a network (a\k\a wire), a register, or a port of some module. Each location within the reference model is referenced using the implicit define for the module within the reference model that contains the location. 
       FIG. 9A  illustrates the top-level flow chart of the disclosed invention. A user of the disclosed invention first provides  902  a description of an electrical design module that includes a plurality of ports. The user next provides  904  a description of an electrical reference model, which comprises a hierarchy of one or more reference modules where each reference module comprises a plurality of ports and a plurality of internal wires. Additionally, the user provides, or the invention creates,  92  one or more implicit defines for the reference modules that appear in the hierarchy of the electrical reference model where each implicit define comprises a path through the hierarchy of the electrical reference model to the module so defined. Next, the user provides  906  a description file that includes one or more instance definitions, wherein each instance definition contains a plurality of port definitions, each port definition contains the name of a port of the electrical design module and a reference connection, the reference connection contains the name of a single implicit define being also the name of a module within the electrical reference model and the name of the port on the module within the electrical reference model. 
       FIG. 9B  illustrates the process of step  950  of  FIG. 9A . Here, the disclosed invention traverses  91  the module hierarchy of the reference model. During this traversal, it keeps track, for every module encountered, of the complete hierarchical paths of the instances.  FIG. 10 , discussed below, further elaborates this step. Referring back to  FIG. 9B , the disclosed invention searches  92  through each module that was encountered in traversing  91  the module hierarchy of the reference model and, if there is a unique instance of the module, the invention creates an implicit define that associates the path to the unique instance with the name of the module. The invention also establishes an implicit define for each element of the optional list of implicit defines specified as an input to the invention where the list is used for providing implicit defines for multiply instanced modules in the reference model as needed to test the design module(s). The invention additionally in step  92  initializes the list file_list to contain the names of the definition files that were given in the input and the list path_list to contain one empty string for every element of the list file_list. The two lists, file_list and path_list, are maintained in parallel, with the elements of path_list giving the path within the test bench to the instances of the modules represented by the corresponding elements of file_list. Initially, all instances are at the top level of the test bench, which is why the list path_list contains an empty string for each. 
     Next, the disclosed invention checks in step  94  whether list file_list is empty. If it is, the invention proceeds to step  97  to write the test bench file. If it is not, the invention continues to step  95 , which removes the first element of list file_list and assigns it to variable next_file and also removes the first element of list path_list and assigns it to variable next_path. The invention then continues to step  96 , where it processes the description file next_file with path next_path and returns to step  94 .  FIG. 11  further illustrates step  96 , and  FIG. 13  further illustrates step  97 . 
       FIG. 10  illustrates in more detail the traversing of step  91  of  FIG. 9B . In step  101 , the disclosed inventions initializes the list mods_to_parse of modules that need to be parsed to contain a single element, the name of the top-level module of the reference model and the list path_list 2  to contain a single element which is an empty string. The two lists mods_to_parse and path_list 2  are maintained in parallel, with the elements of path_list 2  giving the path within the reference model to the modules represented by the corresponding elements of mods_to_parse. 
     In step  102 , the invention checks to see if the list mods_to_parse is empty, which it will not be the first time through. If the list mods_to_parse is empty, the invention is finished with step  91 . If the list mods_to_parse is not empty, the invention proceeds to step  103  where it removes the first element of list mods_to_parse, assigning it to variable mod and removes the first element of list path_list 2  and assign it to the variable path. Next, the invention initializes the list inst_list to contain the instance names of all the instances contained in module mod. 
     In step  105 , the invention checks whether the list inst_list is empty. If it is, then the invention has finished processing module mod and goes back to step  102  to check for any additional modules to parse. If the list inst_list is not empty, the invention continues on to step  106 , which does the following:
         1. Remove the first element of inst_list and assign it to the variable inst.   2. Assign the module of which instance inst is an instance to the variable inst_mod.   3. Add path.inst to the list of instances of module inst_mod (the period (.) is omitted if the variable path is the empty string).   4. Append inst_mod to the list mods_to_parse and append path.inst to the list path_list 2  (again omitting the period if the variable path is the empty string).   5. The invention then goes back to step  105  to check for any additional instances within inst_mod.       

     The user in the initial step up of the invention provides  906  a description file that contains one or more instance definitions, each of which contains a plurality of port definitions. An instance definition directs the test bench generation method to place an instance in the test bench. The instance can be either an instance of a design module to be tested or an instance of a reference module against which instances of design modules can be tested. ( FIG. 7  provides an example of instancing a reference module.) In one embodiment of the disclosed invention, the instance definition can specify a plurality of matching functions to define a reference connection for a plurality of ports (for the definition of a reference connection). In another embodiment of the disclosed invention, the instance definition can specify a plurality of sub-instances of a design module whose outputs should be checked. In a further embodiment of the invention, the instance definition can specify a plurality of checks for internal locations within the design module. 
     The port definition for an input port describes how the port is to be driven during testing, unless the instance definition represents a sub-instance of a higher level instance that is being processed, in which case the port definition for the input port is ignored. The port definition for an output port describes how the port is to be checked during testing. 
     A port definition contains the following information:
         1. A /name/ for which port is being defined, corresponding to one of the named ports of the design module.   2. A /reference connection/, which establishes a correspondence between the port of the design module and its equivalent in a reference module, which is referred to using an implicit define.
           A. In one embodiment of the invention, the reference connection can be a Boolean combination of one or more locations within one or more reference modules and the Boolean constants 0 and 1.   B. In another embodiment of the invention, the reference connection for an input port of the design module can be the output port of a different design module for which an instance definition also exists. This embodiment produces a test bench as illustrated in  FIG. 6 .   
           3. In one embodiment of the invention an /encoding function/ which specifies how the reference connection is to be encoded to correspond to the port of the design module.   4. In one embodiment of the invention, a /phase/ which specifies on which phase of a multi-phased clock the port of the design module should be driven or checked for input or output ports, respectively.   5. In one embodiment of the invention, a /reference delay/ which specifies by how many clock cycles the reference connection must be delayed to correspond to the port of the design module.   6. In one embodiment of the invention, a /design delay/ which specifies by how many clock cycles the port of the design module must be delayed to correspond to the reference connection.       

       FIG. 11  further illustrates step  96  of processing the description file. In addition,  FIG. 11  also illustrates the process that encompasses all the above embodiments. In step  201 , the invention opens the description file next_file (which was set in step  95 ) and initializes the list inst_list to contain all the instance definitions from description file next_file. In step  202 , the invention checks whether list inst_list is empty. If it is, the invention goes to step  212 . If it is not, the invention goes to step  203 . In step  203 , the invention removes the first element of inst_list and assigns it to variable inst. The invention assigns the string next_path.inst to variable inst_path except that it omits the period (.) if the variable next_path, which was set in step  95 , is empty. The invention then continues to step  204 , where it checks if the instance definition specified a matching function to match ports of the design module to be instanced with ports of some reference instance. If there is no matching function, the invention goes directly to step  206 . If there is a matching function, the invention proceeds to step  205 , which applies the matching function as illustrated in more detail in  FIG. 12 , after which the invention continues to step  206 . In step  206 , the invention initializes list port_list to the set of port definitions that the instance definition for instance inst contains and proceeds to step  207 . Step  207  asks whether the list port_list is empty. If it is, then the invention proceeds to step  209 . If it is not, then the invention goes to step  208  instead. In step  208 , the invention removes the first element of the list port_list and assign it to variable port. The invention then records all the information from the port definition associated with port into the test bench&#39;s database record for the instance inst_path and port of instance inst_path and returns back to step  207 . Next, step  209  initializes the list subinst_list to contain all the sub-instance definitions contained by the instance definition for inst, if allowed by the embodiment of the invention, and proceeds to step  210 . In step  210 , the invention checks whether the list subinst_list is empty. If it is, the invention returns back to step  202 , otherwise the invention proceeds to step  211 . Step  211  performs the following operations: (1) it removes the first element of list subinst_list and assigns it to the variable subinst; (2) it appends the name of the module of which subinst is a type to the list file_list for later processing; and (3) it appends inst_path to the list path_list. It then returns to Step  210 . Finally, step  212  closes the file next_file. 
     In one embodiment of the disclosed invention, a matching function can be used to eliminate much of the manual effort in establishing a correspondence between the ports of the design module and the ports of some corresponding module in the reference module, as illustrated by step  204  and step  205  of  FIG. 11 . 
       FIG. 12  illustrates the method of step  205  of  FIG. 11 . In Step  301 , the invention gets the list of ports of the instance inst and put it into the list design_ports. The matching function m specifies a reference instance using an implicit define against which instance inst should be matched; then, the invention puts the name of this reference instance into variable ref_inst and proceeds to step  302  and determines if list design_ports is empty; if it is, the invention ends and returns to the prior level. If not, the invention proceeds to step  303 . Step  303  removes the first element of list design_ports and assigns it to the variable design_port. Then the list of ports of reference instance ref_inst is put into list ref_ports and the invention goes to step  304 , which asks whether the list ref_ports has been fully processed. If it has, the invention returns to step  302 . If it has not, then the invention goes on to step  305 . In step  305 , the invention assigns the next unprocessed element of list ref_ports to the variable ref_port and continues to step  306 , in which the invention determines if the design port design_port matches reference port ref_port. The procedure for answering this question is dependent upon the embodiment of the disclosed invention. The simplest procedure requires an exact match between the port names. A slightly more complex procedure checks whether one of the ports is a prefix or suffix of the other. More complicated matching functions are certainly possible, perhaps involving insertion of underscore characters or changing character from upper case to lower case or /vice versa/. Regardless of the matching function used by a particular embodiment of the invention, if the design port design_port does not match reference port ref_port, control reverts to step  304 ; otherwise the invention goes to step  307 . In step  307 , the invention records a correspondence to port ref_port of reference instance ref_inst into the test bench record for port design_port of instance inst_path and return to step  302 . 
       FIG. 13  illustrates step  97  of  FIG. 9B . To create a test bench file, the invention starts in step  401  by writing a module header for the test bench module. The port list of the test bench module exactly matches that of the reference model. The invention also writes an instance of the reference module into the test bench module with its ports wired to those of the test bench module. The invention proceeds to step  402 , which asks whether all the instances recorded in the test bench record in step  208  of  FIG. 11  and step  307  of  FIG. 12  have been processed. If they have, then the invention goes to step  403 , which writes the end of the test bench module. If they have not, the invention executes step  404 , which assigns the next unprocessed instance to the variable next_inst and goes on to step  405 , which checks if all the ports of instance next_inst have been processed. If they have, the invention proceeds to step  406 ; otherwise the invention proceeds to step  408 . Step  406  asks whether instance next_inst is a sub-instance of one of the design modules in an embodiment of the disclosed invention that allows sub-instances. If it is not, then the invention proceeds to step  407 , which writes an instance of instance next_inst into the test bench file and goes to step  402 . If it is, then there is no need to create an instance, since the instance which instantiates next_inst will already contain the wiring information for it, so the invention proceeds directly to step  402 . If step  405  determined that there are unprocessed ports of instance next_inst, then the invention assigns the next unprocessed port to the variable next_port in step  408  and proceeds to step  409 , which asks whether port next_port of instance next_inst is an input port. If it is not, the invention goes to step  412 , otherwise the invention proceeds to step  410 , which asks whether instance next_inst is a sub-instance of a design module in an embodiment of the invention that allows sub-instances. If it is a sub-instance, the invention ignores input wires, since the invention will not create an instance of next_inst in the test bench, and proceeds to step  405 . If it is not a sub-instance, the invention goes to step  411 , which creates reference wires for port next_port of instance next_inst and then returns to step  405 . Step  412  creates reference wires for comparing against output port next_port of instance next_inst and goes to step  413 . The process used by step  411  and step  412  is described in  FIG. 14 . In step  413 , the invention writes a wire for output port next_port of instance next_inst into the test bench file. For an embodiment of the invention that supports design delays, the invention then write a series of latches to delay the output by the design delay for port next_port of instance next_inst. For an embodiment of the invention that supports shifting signals to the correct phase of a multi-phased clock, the invention then writes the logic to shift the delayed output signal to the correct phase. Finally, the invention writes the logic to check the phase-shifted, encoded, delayed reference signal created in step  412  against the phase-shifted, delayed output signal. Finally, the invention returns to step  405 . 
       FIG. 14  illustrates the process of step  411  and step  412  of  FIG. 13 . In this step  501 , the invention writes a wire from the reference port corresponding to port next_port of instance next_inst. For an embodiment of the invention that supports reference delays, the invention then write a series of latches to delay the reference wire by the reference delay for port next_port of instance next_inst. For an embodiment of the invention that supports encoding reference signals to correspond to design signals, the invention then writes the logic to encode the delayed reference wire. For an embodiment of the invention that supports shifting signals to the correct phase of a multi-phased clock, the invention then writes the logic to shift the encoded, delayed reference wire to the correct phase. 
     To summarize, this invention describes a method that generates and uses a test bench for verifying an electrical design module in semiconductor manufacturing against an electrical reference model containing a sub-circuit that matches the electrical design module. The invention comprises providing a description of an electrical design module that includes a plurality of ports. In addition, the invention includes providing a description of an electrical reference model that comprises a hierarchy of one or more reference modules where each reference module comprises a plurality of ports and a plurality of internal wires. The invention further includes providing and or creating one or more implicit defines for the reference modules that appear in hierarchy of the electrical reference model where each implicit define comprises a path through the hierarchy of the electrical reference model to the module so defined. And, the invention includes providing a description file that includes one or more instance definitions, wherein each instance definition contains a plurality of port definitions, each port definition contains the name of a port of the electrical design module and a reference connection, the reference connection contains the name of a single implicit define being also the name of a module within the electrical reference model and the name of the port on the module within the electrical reference model. The invention parses the hierarchy of the electrical design model and then processes the description file. The invention then writes the test bench containing logic to drive each input port of the electrical design module with the port of the reference module to which it maps and to check at each clock cycle each output port of the electrical design module against the port of the reference module to which it maps and to record in the test bench that each of the plurality of ports of the electrical design module matches its corresponding port of the reference module. 
     Further refining the invention, the implicit defines are generated for each reference module that appears uniquely in the hierarchy of the electrical reference model. In addition, the reference connection comprises the name of an implicit define and the name of an internal wire in the module within the electrical reference model. Further, each said port definition within the description file further specifies an encoding function to apply to the reference connection. Additionally, each port definition further specifies that the reference connection be delayed by an integral number of clock cycles. Further, each port definition further specifies that the port on the electrical design model be delayed by an integral number of clock cycles. And, the reference connection specifies a Boolean combination of one or more reference signals where each reference signal comprises a signal or port in the electrical reference module. 
     Other embodiments of the present invention will be apparent to those skilled in the art after considering this disclosure or practicing the disclosed invention. The specification and examples above are exemplary only, with the true scope of the present invention being determined by the following claims.

Metadata:
Filing Date: 20080302
Publication Date: 20110607
Grant Date: 20110607
Priority Date: 20070305
Inventors: NODINE MARK H
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F30/33", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F30/33", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 39739041