Patent Publication Number: US-10769336-B1

Title: System, method, and computer program product for connecting power supplies in a mixed signal design

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to design simulation, and more specifically, to connecting power supplies in a mixed signal design. 
     DISCUSSION OF THE RELATED ART 
     In order to develop, simulate and test analog and mixed-signal circuit designs, those in the semiconductor and electronic design industry utilize analog-mixed signal extensions (AMS) to such hardware description languages (HDLs) as Verilog and VHDL to describe and define the behavior of the circuit design, Verilog-AMS for Verilog and VHDL-AMS for VHDL. The language extensions not only provide the ability to model the behavior of analog circuitry and digital circuitry, but also allow integration of existing digital designs with analog designs without the need to rewrite the individual designs. For example, Verilog-AMS handles a cross domain connection within a mixed-signal circuit design (e.g., connections between an analog net segment and a digital net segment) by automatically or manually inserting a connect module at the connection point. By doing so, the analog net and digital net are effectively partitioned, allowing each net to be simulated in its respective domain—the analog net in the continuous domain, and the digital net in the discrete domain. Typically, nets in the continuous domain are simulated using a differential equation kernel that calculates solutions to a set of differential equations at discrete points in time. Nets in the discrete domain, on the other hand, are simulated using a discrete event kernel that calculates discrete signal behavior based on events at discrete points in time. Meanwhile, the connect module, usually comprising an analog port connected to the analog net and a digital port connected to the digital net, is charged with converting signals crossing between the two nets. Specifically, the connect module converts the digital logic value from the digital net to an analog voltage for the analog net, or converts an analog voltage from the analog net to a digital logic value for the digital net. 
     In some cases, a special connect module called a bi-directional (e.g., BiDir) connect module is utilized to connect an analog net and a digital net together at a bi-directional connection point. For example, a bi-directional connect module would be used to connect an analog net to a digital net comprising a bi-directional devices or models, such as a switch or a transmission gate. As the name suggests, a bi-directional connect module is capable of converting cross domain signals (e.g., analog voltage to digital logic value, digital logic value to analog voltage) regardless of the direction in which they pass (e.g., from the digital net to the analog net or vice versa). 
     In some cases, it may be necessary to simulate mixed-domain nets which may be connected to Verilog bidirectional primitives (e.g., tran, tranif, etc.) networks. The TRAN network is a model of a circuit containing bi-directional “TRAN” elements that is expressed as a set of Verilog “TRAN” elements and “WIRE” connections. The TRAN network takes input values and processes them to produce outputs, which may be the same as or different from the node values depending on the stability of the network based on the inputs. Outputs that represent new node values replace the old node values, and the TRAN resolution functions can be applied using these “new” node values. 
     As discussed above, the Verilog-AMS language may provide for the insertion of interface elements on ports. These interface elements may provide the interface between the analog and digital segments of a mixed-domain net. In the case of bidirectional interface elements, which are inserted on inout ports, there may be both drivers and receivers inside this interface element, which write and read the digital segment respectively, in addition to the drivers and receivers outside the interface element. As part of the insertion algorithm, the drivers and receivers on the digital segment of the net may be “segregated” into those coming from the interface element and those outside the interface element. The final resolved value of the digital segment may be determined solely by the drivers inside the interface element, while the resolved value seen by the interface element may be determined solely by the drivers outside the interface element (the “normal” drivers). Thus, the interface element may dictate when determining the value. It is helpful to consider this segregation as a process of splitting the net into two nets: one driven by the interface element and one driven by the normal drivers. 
     The algorithm for simulating networks of bidirectional primitives in Verilog may be similar. For example, the drivers of the net may be segregated from the receivers, and fed into the network resolution process. The network resolution then determines a final resolved value of the net in combination with the other inputs to the network. 
     A problem may arise when a net is connected to both a bidirectional interface element and a bidirectional primitive network. Since both objects (i.e., the interface element and the bidirectional primitive network) desire to determine the final resolved value of the net, a conflict arises. Some exiting approaches that attempt to resolve the two algorithms are provided below. The first approach may allow driver/receiver segregation to occur as normal. This may allow the connect module to win in deciding the net resolution. The second approach may involve turning off driver/receiver segregation. This may allow the tran network to dictate when deciding the net resolution. Both of these approaches have been implemented in existing simulators and found to be lacking over some range of usage. 
     For example, in the first approach, since this approach essentially treats the tran network as a normal driver, the output of the interface element may not be fed into the tran network. For the analog to digital case, this is incorrect, since the analog part of the circuit has no effect on the tran network or the digital circuit connected to it. Conversely, in the second approach, driver/receiver segregation may be turned off, so both the drivers and receivers in the interface element may be connected directly to the tran network. However, since we now have two bi-directional entities connected together, we have created a feedback loop, out from the interface element driver, into and back out from the tran network, and into the interface element receiver. Since the digital value being fed back into the interface element affects the analog segment of the net, which in turn affects the digital driver inside the interface element, there is the possibility of creating a latch. As a result, any value driven from the analog segment of the net may latch up on the digital input even if the value driven from analog changes. This may even result in oscillation on the digital segment of the net, depending on the topography of the analog circuit connected to the net in question. 
     Moreover, when modeling in SystemVerilog with four state logic, the designer has bidirectional primitives at his or her disposal such as tran, rtran, etc. No such set of primitives exists for Real Number Modeling (RNM) with SystemVerilog User Defined Nettypes (UDNs). However, the complexity of RNM models means that a small set of built-in primitives is difficult to define and does not cover the breadth of the problems that need to be solved. 
     Further, in a mixed signal design, a block may be switched between different representatives, e.g., Verilog, Verilog-AMS, SPICE, SV-DC, VHDL, VHDL-AMS, etc. The power supply connection is one of the challenges for mixed signal simulation, when switching a block to an analog representative. Since there is a completed power supply network definition in the IEEE1801 standard for digital designs, more mixed signal designers expect to reuse the IEEE1801 specification on mixed signal designs. Accordingly, they may reuse the power net connection specification on the analog blocks, to reduce their configuration work when switching between different representatives. In this way, making the IEEE1801 specification work well on analog blocks becomes a challenge for mixed signal simulation. 
     SUMMARY OF INVENTION 
     In one or more embodiments of the present disclosure, a computer-implemented method for converting between a SystemVerilog user-defined net (“UDN”) and an IEEE supply net. The method may include providing a value conversion table (“VCT”) definition associated with an electronic circuit design. The method may further include mapping, using at least one processor during a simulation, between a SystemVerilog UDN field and a IEEE supply net field. The method may also include converting at least one value between the SystemVerilog UDN field and the IEEE supply net field based upon, at least in part, the VCT definition. 
     One or more of the following features may be included. In some embodiments, the SystemVerilog UDN field may include at least one of a real field and a logic field. In some embodiments, mapping may occur automatically during the simulation. The VCT definition may include power net voltage information. The VCT definition may include power net state information. In some embodiments, converting may include converting between a real value and a power voltage. Converting may include converting between a logic value and a power voltage. Converting may include converting between an integer value and a power voltage. Converting may include converting between a real value and a power state. Converting may include converting between a logic value and a power state. Converting may include converting between an integer value and a power state. 
     In one or more embodiments of the present disclosure, a system for converting between a SystemVerilog user-defined net (“UDN”) and an IEEE supply net. The system may include a computing device having at least one processor configured to provide a value conversion table (“VCT”) definition associated with an electronic circuit design. The at least one processor may be further configured to map, using at least one processor during a simulation, between a SystemVerilog UDN field and a IEEE supply net field. The at least one processor may be configured to convert at least one value between the SystemVerilog UDT field and the IEEE supply net field based upon, at least in part, the VCT definition. 
     One or more of the following features may be included. In some embodiments, at the SystemVerilog UDT field includes at least one of a real field and a logic field. In some embodiments, mapping may occur automatically during the simulation. The VCT definition may include power net voltage information. The VCT definition may include power net state information. In some embodiments, converting may include converting between a real value and a power voltage. Converting may include converting between a logic value and a power voltage. Converting may include converting between an integer value and a power voltage. 
     In one or more embodiments of the present disclosure a method for converting between a SystemVerilog user-defined net (“UDN”) and an IEEE supply net type. The method receiving, via a processor, a user defined conversion between SystemVerilog user-defined net (“UDN”) and an IEEE supply net field. The method may include automatically inserting a DMS IE during a simulation. The method may include converting at least one value during the simulation, based upon at least in part, the user defined conversion. 
     Additional features and advantages of embodiments of the present disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of embodiments of the present disclosure. The objectives and other advantages of the embodiments of the present disclosure may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of embodiments of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of embodiments of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and together with the description serve to explain the principles of embodiments of the present disclosure. 
         FIG. 1  is a diagram depicting an embodiment of a system in accordance with the present disclosure; 
         FIG. 2  is a diagram depicting a bi-directional connect module linking a digital net segment with an analog net segment in accordance with the present disclosure; 
         FIG. 3A-3B  are diagrams depicting analog and mixed-signal circuit design both before and after driver-receiver segregation in accordance with the present disclosure; 
         FIG. 4  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 5  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 6  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 7  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 8  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 9  is a diagram depicting an embodiment of a circuit diagram consistent with an embodiment of the present disclosure; 
         FIG. 10  is a diagram depicting a waveform generated without using the design simulation process of the present disclosure; 
         FIG. 11  is a diagram depicting a waveform generated in accordance with an embodiment of the present disclosure; 
         FIG. 12  is a flowchart depicting operations incorporating the design simulation process in accordance with an embodiment of the present disclosure; 
         FIG. 13  is a schematic depicting an embodiment of a process consistent with an embodiment of the present disclosure; 
         FIG. 14  is a flowchart depicting operations incorporating the design simulation process in accordance with an embodiment of the present disclosure; 
         FIG. 15  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; 
         FIG. 16  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; 
         FIG. 17  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; 
         FIG. 18  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; 
         FIG. 19  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; 
         FIG. 20  is a schematic depicting an embodiment of a value conversion process consistent with an embodiment of the present disclosure; and 
         FIG. 21  is a flowchart depicting operations incorporating a value conversion process in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the disclosure to those skilled in the art. 
     As will be appreciated by one skilled in the art, the present disclosure may be embodied as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present disclosure may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. 
     As used in any embodiment described herein, “circuitry” may include, for example, singly or in any combination, hardwired circuitry, programmable circuitry, state machine circuitry, and/or firmware that stores instructions executed by programmable circuitry. It should be understood at the outset that any of the operations and/or operative components described in any embodiment herein may be implemented in software, firmware, hardwired circuitry and/or any combination thereof. 
     Any suitable computer usable or computer readable medium may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer-usable, or computer-readable, storage medium (including a storage device associated with a computing device or client electronic device) may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device. In the context of this document, a computer-usable, or computer-readable, storage medium may be any tangible medium that can contain, or store a program for use by or in connection with the instruction execution system, apparatus, or device. 
     A computer readable signal medium may include a propagated data signal with computer readable program coded embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations of the present invention may be written in an object oriented programming language such as Java, Smalltalk, C++ or the like. However, the computer program code for carrying out operations of the present invention may also be written in conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     The present invention is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     One or more hardware description languages may be used in accordance with the present disclosures. Some hardware description languages may include, but are not limited to, Verilog, VHDL, and Verilog-AMS. Various other hardware description languages may also be used as well. 
     Referring to  FIG. 1 , there is shown design simulation process  10  and value conversion process  11  that may reside on and may be executed by server computer  12 , which may be connected to network  14  (e.g., the Internet or a local area network). Examples of server computer  12  may include, but are not limited to: a personal computer, a server computer, a series of server computers, a mini computer, and a mainframe computer. Server computer  12  may be a web server (or a series of servers) running a network operating system, examples of which may include but are not limited to: Microsoft® Windows® Server; Novell® NetWare®; or Red Hat® Linux®, for example. (Microsoft and Windows are registered trademarks of Microsoft Corporation in the United States, other countries or both; Novell and NetWare are registered trademarks of Novell Corporation in the United States, other countries or both; Red Hat is a registered trademark of Red Hat Corporation in the United States, other countries or both; and Linux is a registered trademark of Linus Torvalds in the United States, other countries or both.) Additionally/alternatively, the design simulation process  10  and/or value conversion process  11  may reside on and be executed, in whole or in part, by a client electronic device, such as a personal computer, notebook computer, personal digital assistant, or the like. 
     As will be discussed below in greater detail, design simulation process  10  and/or value conversion process  11  may be utilized to simulate an analog and mixed-signal circuit design having a digital circuit segment connected to an analog circuit segment at a connection point. Design simulation process  10  and/or value conversion process  11  may insert a bidirectional interface element at the connection point located between the digital circuit segment and the analog circuit segment. Design simulation process  10  and/or value conversion process  11  may further split the digital circuit segment into a plurality of transistor network models to provide for bi-directional transfer of data between the analog circuit segment and the digital circuit segment. 
     The instruction sets and subroutines of design simulation process  10  and/or value conversion process  11 , which may include one or more software modules, and which may be stored on storage device  16  coupled to server computer  12 , may be executed by one or more processors (not shown) and one or more memory modules (not shown) incorporated into server computer  12 . Storage device  16  may include but is not limited to: a hard disk drive; a solid state drive, a tape drive; an optical drive; a RAID array; a random access memory (RAM); and a read-only memory (ROM). Storage device  16  may include various types of files and file types including but not limited, to hardware description language (HDL) files, which may contain the port type descriptions and executable specifications of hardware blocks. 
     Server computer  12  may execute a web server application, examples of which may include but are not limited to: Microsoft IIS, Novell Webserver™, or Apache® Webserver, that allows for HTTP (i.e., HyperText Transfer Protocol) access to server computer  12  via network  14  (Webserver is a trademark of Novell Corporation in the United States, other countries, or both; and Apache is a registered trademark of Apache Software Foundation in the United States, other countries, or both). Network  14  may be connected to one or more secondary networks (e.g., network  18 ), examples of which may include but are not limited to: a local area network; a wide area network; or an intranet, for example. 
     Server computer  12  may execute an electronic design automation (EDA) application (e.g., EDA application  20 ), examples of which may include, but are not limited to those available from the assignee of the present application. EDA application  20  may interact with one or more EDA client applications (e.g., EDA client applications  22 ,  24 ,  26 ,  28 ) for electronic design optimization. 
     Design simulation process  10  and/or value conversion process  11  may be a stand alone application, or may be an applet/application/script that may interact with and/or be executed within EDA application  20 . In addition/as an alternative to being a server-side process, the design simulation process and/or value conversion process  11  may be a client-side process (not shown) that may reside on a client electronic device (described below) and may interact with an EDA client application (e.g., one or more of EDA client applications  22 ,  24 ,  26 ,  28 ). Further, the design simulation process and/or value conversion process  11  may be a hybrid server-side/client-side process that may interact with EDA application  20  and an EDA client application (e.g., one or more of client applications  22 ,  24 ,  26 ,  28 ). As such, the design simulation process and/or value conversion process  11  may reside, in whole, or in part, on server computer  12  and/or one or more client electronic devices. 
     The instruction sets and subroutines of EDA application  20 , which may be stored on storage device  16  coupled to server computer  12  may be executed by one or more processors (not shown) and one or more memory modules (not shown) incorporated into server computer  12 . 
     The instruction sets and subroutines of EDA client applications  22 ,  24 ,  26 ,  28 , which may be stored on storage devices  30 ,  32 ,  34 ,  36  (respectively) coupled to client electronic devices  38 ,  40 ,  42 ,  44  (respectively), may be executed by one or more processors (not shown) and one or more memory modules (not shown) incorporated into client electronic devices  38 ,  40 ,  42 ,  44  (respectively). Storage devices  30 ,  32 ,  34 ,  36  may include but are not limited to: hard disk drives; solid state drives, tape drives; optical drives; RAID arrays; random access memories (RAM); read-only memories (ROM), compact flash (CF) storage devices, secure digital (SD) storage devices, and a memory stick storage devices. Examples of client electronic devices  38 ,  40 ,  42 ,  44  may include, but are not limited to, personal computer  38 , laptop computer  40 , mobile computing device  42  (such as a smart phone, netbook, or the like), notebook computer  44 , for example. Using client applications  22 ,  24 ,  26 ,  28 , users  46 ,  48 ,  50 ,  52  may access EDA application  20  and may allow users to e.g., utilize design simulation process  10  and value conversion process  11 . 
     Users  46 ,  48 ,  50 ,  52  may access EDA application  20  directly through the device on which the client application (e.g., client applications  22 ,  24 ,  26 ,  28 ) is executed, namely client electronic devices  38 ,  40 ,  42 ,  44 , for example. Users  46 ,  48 ,  50 ,  52  may access EDA application  20  directly through network  14  or through secondary network  18 . Further, server computer  12  (i.e., the computer that executes EDA application  20 ) may be connected to network  14  through secondary network  18 , as illustrated with phantom link line  54 . 
     The various client electronic devices may be directly or indirectly coupled to network  14  (or network  18 ). For example, personal computer  38  is shown directly coupled to network  14  via a hardwired network connection. Further, notebook computer  44  is shown directly coupled to network  18  via a hardwired network connection. Laptop computer  40  is shown wirelessly coupled to network  14  via wireless communication channel  66  established between laptop computer  40  and wireless access point (i.e., WAP)  68 , which is shown directly coupled to network  14 . WAP  68  may be, for example, an IEEE 802.11a, 802.11b, 802.11g, Wi-Fi, and/or Bluetooth device that is capable of establishing wireless communication channel  66  between laptop computer  40  and WAP  68 . Mobile computing device  42  is shown wirelessly coupled to network  14  via wireless communication channel  70  established between mobile computing device  42  and cellular network/bridge  72 , which is shown directly coupled to network  14 . 
     As is known in the art, all of the IEEE 802.11x specifications may use Ethernet protocol and carrier sense multiple access with collision avoidance (i.e., CSMA/CA) for path sharing. The various 802.11x specifications may use phase-shift keying (i.e., PSK) modulation or complementary code keying (i.e., CCK) modulation, for example. As is known in the art, Bluetooth is a telecommunications industry specification that allows e.g., mobile phones, computers, and personal digital assistants to be interconnected using a short-range wireless connection. 
     Client electronic devices  38 ,  40 ,  42 ,  44  may each execute an operating system, examples of which may include but are not limited to Microsoft Windows, Microsoft Windows CE®, Red Hat Linux, or other suitable operating system. (Windows CE is a registered trademark of Microsoft Corporation in the United States, other countries, or both.) 
     Referring now to  FIG. 2 , an embodiment of the present disclosure depicting a bi-directional connect module is provided.  FIG. 2  illustrates a configuration, where analog and mixed-signal circuit design  200  may utilize a bi-directional connect module  202  to connect a digital net segment  204  with an analog net segment  206 . As illustrated, the bi-directional connect module  202  may not only connect the digital net  204  and analog net  206 , but also may provide segregation of the net segments for simulation purposes. The bi-directional connect module may be further configured to convert in both directions simultaneously at any specific time during simulation. 
     Conventionally, in order for a bi-directional connect module to properly account for the influences of an analog net on a digital net, a bi-directional connect module connecting the two nets may implement the concept of driver-receiver segregation (DRS) during mixed-signal simulation. Essentially, during simulation of the analog and mixed-signal circuit design using the driver-receiver segregation, ordinary drivers and ordinary receivers of a digital network (or digital net) connected to the digital port of a bi-directional connect module may be segregated into two net segments with no direct link between them. One segment may be (a) a driver net segment (e.g., driver digital network) connected to digital input port of the bi-directional connect module and comprising the ordinary drivers of the digital network; the other segment may be (b) a receiver net segment (e.g., receiver digital network) connected to the digital output port of the bidirectional connect module and comprising the ordinary receivers of the digital network. By doing so, the bi-directional connect module during mixed-signal simulation can control the link between the driver net segment and receiver net segment such that the contributions of the analog net can be properly and accurately accounted for in the behavior of the digital net.  FIGS. 3A and 3B  illustrate how driver-receiver segregation is typically utilized in simulation of an example analog and mixed-signal circuit. 
     Referring now to  FIG. 3A , an example of an analog and mixed-signal circuit  300  comprising two inverters (I 1  and I 2 ) modeled in the digital (e,g. discrete) domain, and a capacitor modeled in the analog (e,g. continuous) domain is provided. The two inverters comprise digital net segment  302 , while the capacitor comprises analog net segment  304 . Typically, during simulation, a connect module would be inserted between segment  302  and segment  304 , thereby partitioning the two circuit segments and allowing them to be simulated in their respective domains. However, without the use of driver-receiver segregation, as described above, the simulation of the circuit may produce an unexpected and incorrect result. In this specific instance, because the inverters are modeled in the digital domain, and know nothing about the presence of the analog domain due to the net segregation, the digital simulation kernel may propagate a signal from the first inverter I 1  to the second inverter I 2  without accounting for the signal delay induced by the presence of capacitor C 1 . 
     Referring now to  FIG. 3B , an exemplary analog and mixed-signal circuit  350  is provided after insertion of a bi-directional connect module  352  between digital net segment  302  and analog net segment  304 . Driver-receiver segregation (DRS) of the digital net segment  302  may result in a driver net  354  comprising only I 1 , and a receiver net  356  comprising only I 2 . As depicted, the driver net  354  is connected to the digital input port of module  352 , while receiver net  356  is connected to the digital output port of module  352 . By doing so, the connect module  352  is able to propagate the signal from the driver net  354  to the receiver net  356  with the delay attributed from analog net  304 . It should be noted that conventionally, during analog and mixed-signal simulation (even under driver-receiver segregation) (a) the bi-directional connect module may perform digital and analog signal resolution (e.g., cross-domain signal conversion) between the analog circuit segment and the digital circuit segment; and (b) the transmission gate network may remain unaware of the existence of the one or more bi-directional connect modules connected to it. 
     For mixed-signal simulations, the alternative to using a bi-directional mixed-signal interface element (IE) (e.g., bi-directional connect module) would be to manually define the direction of the signal now for every connection. This is the case for SpectreVerilog, where once the direction of a signal has been properly defined, the simulation can insert digital-to-analog and analog-to-digital interface elements (IE&#39;s) accordingly. 
     Unfortunately, neither conventional bi-directional connect modules, nor manually defining the direction of signal flows, may be adequate for mixed-signal simulations when the design comprises bi-directional connection points. With respect to conventional bi-directional connect modules, which are based on driver-receiver segregation (DRS), the simulation cannot perform accurate chip-level verification when an analog net is connected to a digital net through a conventional bi-directional connect module because driver-receiver segregation may: (1) functionally verify a mixed-signal circuit design through simulation of the analog loading effect on digital receivers of the digital net, (2) but does so under the assumption that the circuit design does not contain bidirectional connection points (e.g., bi-directional connect modules). 
     Likewise, manually defining the direction of signal flows at bi-directional connection points may also fail to adequately simulate mixed-signal circuit designs having such connection points because it cannot fully verify the circuit design when the signal is dynamically bi-directional. Furthermore, in existing mixed-signal circuit design simulations, the interface element (IE) may fail to accurately reflect the signal strength from the analog driver, which may lead to additional erroneous simulation results, especially when the digital net is connected to multiple analog drivers. 
     Referring now to  FIG. 4 , an exemplary circuit  400  is provided depicting both a schematic diagram and a Verilog HDL representation. Circuit  400  may include analog wire  402  on the left side of the diagram shown connected to the analog part of the circuit. Analog wire  401  may be connected via a resistor  404  to a digital wire  406 . To interface between these analog and digital parts of the net, an interface element  408  may be provided. The digital wire  406  may then be connected to one terminal of a tran network  410 . 
     Referring now to  FIG. 5 , an exemplary circuit  500  is provided again depicting both a schematic diagram and a Verilog HDL representation. Circuit  500  illustrates the concepts of driver/receiver segregation. In this particular embodiment, the dotted lines may correspond to the split versions of nets which undergo segregation. In the first instance, we see the net “e” has been split as a result of connection to the tran network. In the second instance, we see the net “digital_net” has been split. This has actually been split for two reasons: it is connected to a tran network and also connected to an interface element. This second split net creates a potential problem in that a feedback loop has been created, which can result in the digital and analog nets latching up to a certain value possibly occurring after the drivers have been turned off. 
     Referring now to  FIG. 6 , an exemplary diagram  600  is provided depicting the feedback loop issue identified above in greater detail. In this particular embodiment, the digital port of the interface element is shown in greater detail. With the interrelationships between the digital and analog segments of the net shown, one can clearly see the feedback loop that has been created. This feedback loop may be a direct result of the bidirectional nature of the interface element and the tran network in combination. 
     In some embodiments, the present disclosure may provide for bidirectional transfer of values between the analog and digital parts of the circuit including the tran network. This may result in reasonable accuracy, and does not produce latch up of the signal on the digital side of the interface element. 
     Referring now to  FIG. 7 , an exemplary diagram  700  is provided depicting switchable unidirectional interface element  702 , which may be used to break the problems created by the feedback loop described herein. The bi-directional interface element may be converted into switchable unidirectional element  702 , which may be configured to compare the relative driver strengths of the digital and analog parts of the circuit, and to drive either in to or out of analog based on these strengths. Switchable unidirectional element  702  may include one or more converters, including but not limited to, digital-to-analog converter  704  and analog-to-digital converter  706 . Switchable unidirectional element  702  may further include one or more strength comparators  708 . In this diagram, the strength comparison is being performed between the resolved value of only ordinary drivers  710  to the net and the drive strength of the analog part of the circuit. This analog driver strength may be based on output resistance of a voltage source. An more detailed discussion of the subject matter of  FIG. 7  may be found in U.S. Pat. No. 7,870,518, assigned to the assignee of the subject application, the entire contents of which are incorporated by reference in their entirety. 
     In this way, the interface element may be configured to break the contention between the analog and digital drivers to the net. This may be accomplished by comparing the drive strengths of the digital and analog drivers and allowing the one with the greater strength to win. In some embodiments, additional measures may be taken in the case where the strengths are equal, for example, in driving an X. In this context “digital drivers” may refer to the digital only copy of the tran network which was created. In essence this changes the interface element from a purely bidirectional one to a switchable unidirectional element. 
     Referring now to  FIG. 8 , an exemplary diagram  800  is provided depicting a “shadow tran network”  820 . Diagram  800  includes a bidirectional interface element  802  inserted at the connection point located between the digital circuit segment  803  and the analog circuit segment  801 . Diagram  800  further depicts the digital circuit segment  803  once it has been split into a plurality of transistor network models  812  and  820  to provide for bi-directional transfer of data between the analog circuit segment  801  and the digital circuit segment  803 . 
     In this particular embodiment a new tran network  820  is created which is only driven by the drivers (e.g. driver  830 ) outside of interface element  802 . Thus, instead of merely splitting the net, both the net and its connected tran network  812  are split. For the purposes of the present disclosure, the newly created tran network is referred to as the shadow tran network  820 . In some embodiments, the shadow tran network  820  may only be connected to the ordinary drivers. 
     In this way, the present disclosure may provide a method for expanding the driver/receiver segregation so that it encompasses the tran network itself. Thus, an entire new version of the tran network may be created, which may be connected only to the drivers from the digital circuit. In essence, a “digital-only” version of the tran network which the interface element can use as its digital input, just as the digital drivers are used in the case where no tran network is involved. The shadow tran network may be configured to provide access to a model of the connected tran network as if it were connected to only the digital drivers. In some embodiments, the tran network may be treated as a “net” in the context of driver/receiver segregation by splitting it into two networks. As discussed above, the interface element shown in  FIG. 7  may break the contention between the analog and digital sides of the circuit based on the relative driving strengths of the two sides. 
     In some embodiments, the process of resolving the net and its connected tran network may include one or more of the following operations: 
     1) When the driven value or driven strength from either the shadow tran network  820  or the analog circuit changes, compare the digital drive strength with the analog driver strength; 
     2) If the digital drive strength is greater than the analog drive strength: drive the value from digital into the analog circuit, and drive a Hi-Z out from the interface element into the tran network  812  (D→A); 
     3) If the analog drive strength is greater than the digital drive strength: drive a Hi-Z into the analog circuit, and drive the converted value from analog into the tran network  812  (A→D); 
     4) The tran network resolution then occurs as normal and the newly resolved values are driven out to the readers of the tran network  812 ; and 
     5) If the drive strengths are equal the driven values are compared—if they are the same, this value is driven to both the analog circuit and the tran network  812 . If they are not the same, then an X is driven to both sides. 
     In some embodiments, the bidirectional interface element described herein may be used in a variety of different applications in addition to the context of tran gate connections. Some of these may include, but are not limited to, standard delay format (SDF) interconnect delays (since this also modifies the drivers of the digital net, it collides with driver/receiver segregation), waveform display (since the interface element “sees” a different set of drivers then the connected digital net, probing or displaying the value of the two different objects can results in different values—this causes confusion among users who do not understand (or care about) the concept of driver/receiver segregation), and “Back-to-back” interface elements (e.g., if one interface element is connected directly to another, they do not “see” each other because they ignore connect drivers). In some embodiments, the use of bidirectional interface elements may permit the disabling of driver/receiver segregation, which may simplify numerous issues. 
     Referring now to  FIG. 9 , an exemplary diagram  900  is provided depicting an additional embodiment of the tran network. Diagram  900  includes L2R connect module  902  and bidirectional connect module  904  having resistor  906  included therebetween. In some embodiments, tran network  908  may be driven on one side by bidirectional connect module  904 , and on the other side by a pure digital driver  910 . The tran network may be stimulated by applying a stimulus from each side and seeing what the resolved values are. In some embodiments, digital driver  910  is assumed to have a higher drive strength than the driver from the bidirectional connect module  904 . The sequence of stimuli applied may include one or more operations. For example, a low voltage may be driven from the analog side and a logic 0 from the digital side. In this case, both sides of the tran network may resolve to 0. A high voltage may be driven from the analog side, which should drive a logic 1 from the bidirectional connect module  904 . The “dig_in” side of the tran network  908  should stay at 0, since the 0 is being driven from dig_out with a stronger drive strength. This should then cause the analog side of bidirectional connect module  904  to float somewhere between a high and low voltage. If a low voltage is driven from the analog side, both sides may resolve to 0. Next, drive a logic 1 from the digital side. Since this has a higher drive strength then the bidirectional connect module  904 , it should cause both sides of the tran network  908  to resolve to 1. This should then cause the analog side of the bidirectional connect module  904  to float somewhere between a high and low voltage. 
     Referring now to  FIG. 10 , an exemplary waveform  1000  is provided depicting the resultant waveform if driver/receiver segregation has been turned off. In particular, look at the time 30 ns. This corresponds to driving a logic 1 from the digital side as discussed above. However, instead of both sides resolving to a logic 1, they go to X. The analog side of the bidirectional connect module also stays at a low voltage. This is because the digital side of the bidirectional connect module has latched up—it is still seeing the old value of logic 0 being driven from the tran network and it is driving it back out to take part in the resolution of the tran network. 
     Referring now to  FIG. 11 , an exemplary waveform  1100  is provided depicting a resultant waveform in accordance with the teachings of the present disclosure. In this particular example, the logic 1 driven from the digital side of the tran network correctly overdrives the 0 from the analog side, both sides of the tran network resolve to 1, and the analog side of the bidirectional connect module goes to a high voltage. 
     Referring now to  FIG. 12 , an exemplary flowchart  1200  depicting operations consistent with the present disclosure is provided. Operations may include inserting a bidirectional interface element at the connection point located between the digital circuit segment and the analog circuit segment ( 1202 ). Operations may further include splitting the digital circuit segment into a plurality of tran networks to provide for bi-directional transfer of data between the analog circuit segment and the digital circuit segment ( 1204 ). Numerous additional operations are also within the scope of the present disclosure. For example, operations may additionally include detecting a change in drive strength of at least one of the shadow transistor network model and the analog circuit segment and comparing a digital drive strength from the shadow transistor network model with an analog drive strength from the analog circuit segment. 
     Referring now to  FIGS. 13-14 , alternative embodiments of a design simulation process  10  are provided. In some embodiments, design simulation process  10  may be configured to create bidirectional real number models in SystemVerilog. As discussed above, when modeling in SystemVerilog with four state logic, the modeler has bidirectional primitives at her disposal like tran, rtran, etc. No such set of primitives exists for Real Number Modeling (RNM) with SystemVerilog User Defined Nettypes (UDNs). However, the complexity of RNM models means that a small set of built-in primitives is difficult to define and does not cover the breadth of the problems that need to be solved. Accordingly, embodiments of design simulation process  10  may be configured to extend the Strength-based Insertion Element (SIE) concept for writing bidirectional connect modules, as discussed above, beyond the role of conversion elements and apply it to solving the more general problem of bidirectional models. 
     Existing approaches do not have a way to model bidirectional devices in SystemVerilog that can handle contention in 0 delay. There are implementations that when contention is detected use a small random delay to see if that contention is real or if it is due to a race condition at the inputs. However, this approach is slow and consumes simulation time (i.e., not 0 delay). The cause of the problem is that SystemVerilog does not provide a mechanism to be sensitive only to the external drivers of a bidirectional port. Thus, once an internal driver is applied that causes contention the port goes to a contention state (e.g., X) and may not recover until all drivers are removed. Also, since the resolved value of a port includes the internal driver, when modeling pass gate like behavior (a→b and b→a), the resolved value of a includes the resolved value of b and subsequently driving the resolved value of a onto b means that b&#39;s value is reflected back on itself causing the resolved value on each side to grow infinitely (e.g., in a feedback loop). 
     Embodiments of design simulation process  10  may allow the user to call the $SIE_input( ) task on any singular SystemVerilog input net port. Referring again to  FIG. 13 , during elaboration of the module port the tool may create a shadow net (e.g., X″ and Y″ in  FIG. 13 ) of the collapsed port net (e.g., X and Y) that is driven with just the net ports drivers outside of the module (e.g., A, B, C) and none of the drivers inside the module. The user can alias the shadow net to a net that is local to the module with the $SIEinput( ) system task that the tool provides. This may allow the module to be sensitive to just changes in the external drivers of its ports such that it can handle contention without latching up. 
     In some embodiments, and to address the immediate problem of allowing users to write bidirectional functional models for nets of user defined nettype, embodiments included herein provide in our SystemVerilog support SIE module ports which may extend the SIE concept discussed above for connectmodules to be leveraged in a more general way to create arbitrary bidirectional models. This may allow the user to model bidirectional behavior like pass gates for nets with arbitrary types. Embodiments of the present disclosure allow for access to just the external drivers of a net and, as such, writing bidirectional models can be done simply and robustly without inherent value latching or performance issues that we have seen with other methods. 
     It should be noted that modeling arbitrary networks of pass gates may not be possible for every resolution function as the pass gate model relies heavily on the resolution behavior of the net. For some resolutions (e.g., wrealavg) it may not be possible to use this methodology to model pass gate like behavior (e.g., wrealavg ports may have different values on each port because the internal driver gets averaged with the external drivers which may be different on each port in a multi driver situation). If the user intends to model pass gate behavior care should be taken in how they craft their resolution function such that it will support their pass gate models. 
     In operation, the use model may similar to the use model for a manually inserted SIE connectmodule with a few differences. For example, the module may not contain any analog ports and the module may not be limited to just two ports like a connectmodule. As stated above the module can have an arbitrary number of digital ports. All inout ports that have a $SIE_input( ) call associated with them will receive additional SIE processing to create a shadow networks. Additionally and/or alternatively, all ports that do not have an associated $SIE_input( ) call associated with them will receive normal SystemVerilog port processing. In some cases, it will be illegal for an siemodule to have a $SIE_input( ) call associated with a port that is not also declared (or has default direction) of inout. Also, all ports that have $SIE input( ) calls associated with them must be nets, it will be illegal to call $SIE_input( ) on a var port. However, normal ports that don&#39;t get SIE processing may have any legal port kind, type, or direction. 
     Also, note that no automatic insertion may take place for siemodules, all instances of an siemodule must be explicitly instantiated in the design just like any other module. 
     In some embodiments, an siemodule may be used to model a wreal pass gate. One popular use model for this feature will be to model real valued pass gates for real nets. Below are a couple of useful pass gate models that can be modeled with SIE ports. For example, a wreal1driver pass gate model may refer to a model for a pass gate that will be useful with wreal1driver nets. The basic functionality is that if the enable is high and only one of the model port is driven then that value is passed to the other side. In the contention case where both ports are driven and the enable is high there may be contention and both sides of the pass gate go to wrealXState. If the enable is low both sides of the pass gate may be isolated from each other (e.g., the pass gate drives out wrealZValue). If the enable is X or Z both sides go to wrealXState. 
     As used herein, a “Connect module” and/or “interface element” may refer to a SystemVerilog model that may interface between nets of different types, handling value conversion and propagation from and to each connected net. The phrase “SIE module” may refer to a module that may model the strength-based interface element algorithm, in other words, the segregation of drivers on an input port into internal and external driver sets and availability of segregated external drivers to the contents of the module. The term “wreal1driver” may refer to a resolution method for a wreal net that allows for only one driver to be active at any time. The term “wrealXstate” may refer to a mapping of the logic domain X state into the real domain, along with conversions between the two domains. The term “wrealZstate” may refer to a mapping of the logic domain Z state into the real domain, along with conversions between the two domains. The term “wrealmax” may refer to a resolution method for a wreal net that resolves to the largest of all driven values. The term “wrealavg” may refer to a resolution method for a wreal net that resolves to the average (arithmetic mean) value of all driven values. The term “inout port” may refer to a port of a SystemVerilog module that contains drivers both internal and external to the module, and allows for resolution of all drivers. The term “nettype” may refer to a SystemVerilog user-defined nettype. 
     One wreal1driver pass gate example is provided below: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                   
                 import cdn_rnm_pkg::*; 
               
               
                   
                 module wreal1driver_pass_gate(inout wreal1driver a, 
               
               
                   
                 inout wreal1driver b, wire en); 
               
               
                   
                  real aVal, bVal; 
               
               
                   
                  real aOut, bOut; 
               
               
                   
                 initial 
               
               
                   
                  begin 
               
               
                   
                  $SIE input(a, aVal); 
               
               
                   
                  $SIE input(b, bVal); 
               
               
                   
                  aOut = ′wrealZState; 
               
               
                   
                  bOut = ′wrealZState; 
               
               
                   
                 end 
               
               
                   
                 always @(aVal, bVal, en) 
               
               
                   
                  begin 
               
               
                   
                   //en is high so the pass gate is open 
               
               
                   
                   if(en===1) 
               
               
                   
                    begin 
               
               
                   
                     if(aVal ===′wrealZState) 
               
               
                   
                      begin 
               
               
                   
                       // a is Z so we pass b to a 
               
               
                   
                       aOut = bVal; 
               
               
                   
                       bOut = ′wrealZ State; 
               
               
                   
                      end 
               
               
                   
                     else if(bVal === ′wrealZState) 
               
               
                   
                      begin 
               
               
                   
                       // b is Z so pass a to b 
               
               
                   
                       bOut = aVal; 
               
               
                   
                       aOut = ′wrealZState; 
               
               
                   
                      end 
               
               
                   
                     else 
               
               
                   
                      begin 
               
               
                   
                       // both a and b are nonZ so we have contention 
               
               
                   
                 and output X 
               
               
                   
                       aOut = ′wrealXState; 
               
               
                   
                       bOut = ′wrealXState; 
               
               
                   
                      end 
               
               
                   
                     end 
               
               
                   
                    else if(en===0) 
               
               
                   
                     begin 
               
               
                   
                      // en is low so we aren”t passing values. just 
               
               
                   
                 drive Z 
               
               
                   
                      aOut = ′wrealZState; 
               
               
                   
                      bOut = ′wrealZState; 
               
               
                   
                     end 
               
               
                   
                    else 
               
               
                   
                     begin 
               
               
                   
                      // en is X or Z so output X 
               
               
                   
                      aOut = ′wrealXState; 
               
               
                   
                      bOut = ′wrealXState; 
               
               
                   
                     end 
               
               
                   
                    end 
               
               
                   
                   // assign the pass values to the port so they are 
               
               
                   
                 visible to external receivers 
               
               
                   
                    assign a = aOut; 
               
               
                   
                    assign b = bOut; 
               
               
                   
                    endmodule 
               
               
                   
               
            
           
         
       
     
     As used herein, a wrealmax pass gate model may refer to a model for a pass gate that may be useful with wrealmax nets. In some embodiments, the basic functionality is that if the enable is high the largest real value is passed to the smaller value. If the enable is low both sides of the pass gate are isolated from each other (the pass gate drives out wrealZValue). If the enable is X or Z both sides go to wrealXState. 
     One realms pass gate example is provided below: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                   
                 import cdn_rnm_pkg::*; 
               
               
                   
                   
                 module wrealmax_pass_gate(inout wrealmax a, inout 
               
               
                   
                   
                 wrealmax b, wire en); 
               
               
                   
                   
                  real aVal, bVal; 
               
               
                   
                   
                  real aOut, bOut; 
               
               
                   
                   
                  initial 
               
               
                   
                   
                  begin 
               
               
                   
                   
                   $SIE input(a, aVal); 
               
               
                   
                   
                   $SIE input(b, bVal); 
               
               
                   
                   
                   aOut = ′wrealZ State; 
               
               
                   
                   
                   bOut = ′wrealZState; 
               
               
                   
                   
                  end 
               
               
                   
                   
                 always @(aVal, bVal, en) 
               
               
                   
                   
                  begin 
               
               
                   
                   
                   //en is high so the pass gate is open 
               
               
                   
                   
                   if(en===1) 
               
               
                   
                   
                    begin 
               
               
                   
                   
                     if((aVal ===′wrealZState) || (bVal === 
               
               
                   
                   
                  ′wrealXState)) 
               
               
                   
                   
                      begin 
               
               
                   
                   
                       // a orb or both are X so pass X to both sides 
               
               
                   
                   
                       aOut = ′wrealXState; 
               
               
                   
                   
                       bOut = ′wrealXState; 
               
               
                   
                   
                      end 
               
               
                   
                   
                     else if(aVal &gt; bVal) 
               
               
                   
                   
                      begin 
               
               
                   
                   
                       // a is greater than b so pass a to b 
               
               
                   
                   
                       bOut = aVal; 
               
               
                   
                   
                       aOut = ′wrealZ State; 
               
               
                   
                   
                      end 
               
               
                   
                   
                     else 
               
               
                   
                   
                      begin 
               
               
                   
                   
                       // b is greater than or equal to a so pass b to a 
               
               
                   
                   
                       aOut = ′bVal; 
               
               
                   
                   
                       bOut = ′wrealZState; 
               
               
                   
                   
                      end 
               
               
                   
                   
                      end 
               
               
                   
                   
                     else if(en===0) 
               
               
                   
                   
                      begin 
               
               
                   
                   
                       // en is low so we aren”t passing values, just 
               
               
                   
                   
                 drive Z 
               
               
                   
                   
                       aOut = ′wrealZ State; 
               
               
                   
                   
                       bOut = ′wrealZState; 
               
               
                   
                   
                      end 
               
               
                   
                   
                     else 
               
               
                   
                   
                      begin 
               
               
                   
                   
                       // en is X or Z so output X 
               
               
                   
                   
                       aOut = ′wrealXState; 
               
               
                   
                   
                       bOut = ′wrealXState; 
               
               
                   
                   
                      end 
               
               
                   
                   
                     end 
               
               
                   
                   
                    // assign the pass values to the port so they are 
               
               
                   
                   
                   visible to external receivers 
               
               
                   
                   
                    assign a = aOut; 
               
               
                   
                   
                    assign b = bOut; 
               
               
                   
                   
                    endmodule 
               
               
                   
                   
               
            
           
         
       
     
     Embodiments of design simulation process  10  may use a shadow network with just the external drivers that the user can access in their model. This allows the model to recover from contention in 0 delay and to pass just the external resolved value eliminating any feedback issues. As discussed above, embodiments included herein may use only the external drivers to model the bidirectional behavior. 
     As discussed above, embodiments of design simulation process  10  may be configured to generate a bidirectional device model, such as a pass-gate, based upon, at least in part, at least two discrete time circuit segments. It should be noted that the example of a pass-gate is provided merely by way of example. Embodiments included herein allow for the modeling of a real valued discrete time approximation of a continuous time device. In some embodiments, the insertion element may be between two discrete time circuit segments, for example. 
     In some embodiments, one or more interface elements tmay connect two discrete time circuits that have different value representations. For example, a discrete time circuit that represents its value with a 4-state logic value (discrete value domain) and a discrete time circuit that represents its value as a real value (continuous value domain). 
     In some embodiments, the insertion elements included herein may translate from one domain to another (e.g., discrete &lt;-&gt; continuous, discrete &lt;-&gt; discrete, continuous &lt;-&gt; continuous, etc.). The insertion elements may be responsible for translating between domains (either time, value, or both). Additionally and/or alternatively, these may be unidirectional or bidirectional. 
     In some embodiments, the bidirectional SIE models may be configured to provide a modeling tool for modeling bidirectional behavior in a single discrete time domain (value may be continuous). 
     Referring also to  FIG. 14 , an embodiment of design simulation process  10  is provided. The process may include inserting  1402  a bidirectional interface element at the connection point located between the discrete domain segment and the continuous domain segment. The method may also include splitting  1404  the discrete domain segment into a plurality of transistor network models to provide for bi-directional transfer of data between the continuous domain segment and the discrete domain segment, wherein at least one of the plurality of transistor network models utilizes only one or more drivers external to a module. 
     Embodiments of design simulation process  10  may provide numerous advantages over existing technologies. For example, using the teachings of the present disclosure the system may recover from contention in all cases and in zero delay to avoid any unwanted feedback issues. Moreover, embodiments of design simulation process  10  have been shown to achieve higher performance than any conventional solutions such as SystemVerilog, for example. 
     Referring now to  FIGS. 15-21 , embodiments consistent with value conversion process  11  are provided. Embodiments included herein may provide a power network connection of a SystemVerilog real number model in an IEEE1801 mixed signal simulation. As discussed above, in a mixed signal design, a block may be switched between different representations, e.g., Verilog, Verilog-AMS, SPICE, SV-DC, VHDL, VHDL-AMS, etc. The power supply connection is one of the challenges for mixed signal simulation, for example, when switching a block to an analog representative. Since there is a completed power supply network definition in the IEEE1801 standard for digital designs, more mixed signal designers expect to reuse the IEEE1801 specification on mixed signal designs. Accordingly, they may reuse the power net connection specification on the analog blocks, to reduce their configuration work when switching between different representatives. In this way, making the IEEE1801 specification work well on analog blocks becomes a challenge for mixed signal simulation. Embodiments included herein may incorporate the SystemVerilog Real Number Mode (SV-RNM) with user defined nettype (SV-UDN), and may be configured to apply an IEEE1801 power supply connection on the SV-RNM of mixed signals design. 
     In the IEEE1801 standard, there is a predefined net type (e.g., supply_net type) in a package such as those associated with the Unified Power Format (“UPF”). This type may be configured to model electrical values as a combination of two values: a state value and a voltage value, which together constitute the IEEE1801 supply network. 
     During a low power intent simulation, this IEEE1801 supply network could be connected with the supply net of an HDL design by one or more commands (e.g., connect_supply_net), if the HDL net is defined as logic or the type supply_net type discussed above. A user could then define a value conversion table by one or more commands (e.g., create_upf2hdl_vct), to specify a conversion from IEEE1801 supply net to the HDL logic supply net. Additionally and/or alternatively, a command (e.g., create_hdl2upf_vct) may be used to specify a conversion from an HDL logic supply net to IEEE1801 supply net. 
     However, the above approach may not work well for SV-RNM in mixed signal simulations since in the SV-RNM, the user would typically prefer to use a User Defined Nettype (“UDT”) to model the analog signal. The UDT could be a structure with multiple elements, not limited in two values with type “enum” for state value and type “integer” for voltage value. Embodiments of the value conversion process  11  described herein may be configured to connect this User Defined Net (UDN) in an HDL context to IEEE1801 supply net and apply a value conversion. 
     In existing approaches, in order to run a power intent simulation and comply with the IEEE1801 standard, a user may have to use the IEEE1801 supply net type in their SV-RNM, which is a limitation for the user. As an alternative, the user also could modify their models and convert the SV-UDN in HDL scope to the IEEE1801 supply net type. However, this introduces additional work for the user. And this effort would be meaningless when reusing the models in a non-power intent simulation. 
     Accordingly, embodiments included herein may provide an automatic approach to apply a field mapping between SV-UDN elements and IEEE1801 supply net type elements, as well as the corresponding value conversion. 
     Table 1 provided below illustrates an embodiment consistent with value conversion process  11 . This example may be configured to resolve the power net connection between an SV-UDN and an IEEE1801 supply network. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 HDL source code 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 # HDL definition 
               
               
                   
                   
                 module ana1(en, vdd); 
               
               
                   
                   
                  output MyUDT vdd; 
               
               
                   
                   
                  T vdd_reg; 
               
               
                   
                   
                  .. 
               
               
                   
                   
                 endmodule 
               
               
                   
                   
                 module ana2(vdd); 
               
               
                   
                   
                  input MyUDT vdd; 
               
               
                   
                   
                  . . . 
               
               
                   
                   
                 endmodule 
               
               
                   
                   
                 module dut(en); 
               
               
                   
                   
                  input wire en; 
               
               
                   
                   
                  wrap_ana1 i_anal(.en(en)); 
               
               
                   
                   
                  wrap_ana2 i_ana2( ); 
               
               
                   
                   
                 endmodule 
               
               
                   
                   
               
            
           
         
       
     
     Table 1 shows an example of HDL source code. Here, there are two instances of SV-RNM, namely, “i_ana1” and “i_ana2”, under top module “udt”. In this example, the supply port “vdd” of these two instances are defined with SV-UDT (“MyUDT”). Here, the net connection is not defined in HDL scope. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 IEEE1801 specification 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 # IEEE1801 specification 
               
               
                   
                   
                 create_supply_net UVDD 
               
               
                   
                   
                 create_supply_net UVDD1 
               
               
                   
                   
                 connect_supply_net UVDD -ports {i_ana1/vdd} 
               
               
                   
                   
                 connect_supply_net UVDD1 -ports {i_ana2/vdd} 
               
               
                   
                   
                 create_power_switch SW \ 
               
               
                   
                   
                  -output_supply_port {OUT UVDD1} \ 
               
               
                   
                   
                  -input_supply_port {IN UVDD} \ 
               
               
                   
                   
                  . . . 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 above shows the IEEE1801 specification. Here, there are two IEEE1801 power supply nets that have been defined, namely, “UVDD” and “UVDD1”, and they are connected through the power switch (“SW”). The power supply net (“UVDD”) is connected with the HDL signal (“i_ana1/vdd”) and the power supply net (“UVDD1”) is connected with the HDL signal (“i_ana2/vdd”). 
     Referring also to  FIG. 15 , an example of a mixed signal design  1500  for IEEE1801 simulation is provided. Based on the IEEE1801 specification, the simulation tool needs to setup the supply net connection on HDL signals, as is shown in  FIG. 15 . To implement the connection between the IEEE1801 supply net and SV-UDN, a mechanism to apply the field/value mapping between the elements of the IEEE1801 supply net type and SV-UDT may be employed. 
     In some embodiments, the SV-UDT may include one or more elements to represent the power state and voltage values. For example: 
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Example of SV-UDT with real and integer elements 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 # SV-UDT definition 
               
               
                   
                   
                 typedef struct { 
               
               
                   
                   
                   real V; 
               
               
                   
                   
                   integer status; 
               
               
                   
                   
                  } T; 
               
               
                   
                   
                  function automatic T Tsum 
               
               
                   
                   
                  . . .  
               
               
                   
                   
                  endfunction 
               
               
                   
                   
                  nettype T wTsum with Tsum; 
               
               
                   
                   
               
            
           
         
       
     
     In this SV-UDT definition, there are two elements (e.g., “status” and “v”) to model state value with type integer (or logic) and a voltage value with type real. 
     For this scenario, and referring also to  FIG. 16 , value conversion process  11  may be configured to extend the IEEE1801 VCT definition and power net connection mechanism, to apply a field mapping and value conversion directly. 
     In some situations, the SV-UDT may include multiple elements, but cannot find the specific element that represents the power state or voltage values. For example: 
     
       
         
           
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Example of SV-UDT with multiple elements 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 # SV-UDT definition 
               
               
                   
                   
                 typedef struct { 
               
               
                   
                   
                  real V; 
               
               
                   
                   
                  real I; 
               
               
                   
                   
                  real R; 
               
               
                   
                   
                 } EEstruct; 
               
               
                   
                   
                 nettype EEstruct EEnet with res_EE 
               
               
                   
                   
               
            
           
         
       
     
     In this SV-UDT definition, there are three elements (e.g., “V”, “I” and “R”) to model an analog signal. 
     For this scenario, and referring now to  FIG. 17 , value conversion process  11  may be configured to insert a connect module on the boundary of IEEE1801 supply net and SV-UDN. Accordingly, a user may specify the resolution function inside the connect module to resolve the value. 
     In some embodiments, value conversion process  11  may provide one or more IEEE1801 extensions for an SV-UDN connection. For example, an extension on a VCT definition. In the IEEE1801 standard, there are two commands namely, “create_hdl2upf_vct” and “create_upf2hdl_vct” that may be used to specify user defined value conversion tables. 
     In some embodiments, the “create_hdl2upf_vct” command defines a VCT from an HDL logic type to the state type of the supply net value when that value is propagated from HDL port to a UPF supply net. 
     Table 5 provided below shows the syntax of the IEEE1801 command “create_hdl2upf_vct”: 
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 IEEE1801 create hdl2upf_vct_command 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_hdl2upf_vct vct_name -hdl_type {&lt;vhdl | sv&gt; [typename]}\ 
               
               
                   
                              -table {{from_value to_value}*} 
               
               
                   
               
            
           
         
       
     
     In this example, the “vct_name” provides a name for the value conversion table for later use with the connect_supply_net command. The “-hdl_type” specifies the HDL type for which the value conversions are defined. For a VHDL net, the net type could be Bit, std_[u]logic, Boolean, or Subtypes of std_[u]logic. For the SystemVerilog net, the net type could be reg/wire, Bit, Logic. The “-table” defines the 1:1 conversion from HDL logic value to the UPF partially on and on/off states. The values are consistent with the HDL type values. 
     Embodiments of value conversion process  11  may be used to extend this command for a SystemVerilog Real Number Model. Accordingly, the user may specify the UDT field name in the field “typename”, to indicate the field mapping and specify the value conversion on the table “{from_value to_value}”, to indicate the value mapping. 
     In some embodiments, the datatype of the SV-UDT element could be real (e.g., real, shortreal, realtime), logic (e.g., bit, logic, reg, byte), integer (e.g., int, shortint, longint). The value conversion may occur, for example, in some or all of the following scenarios: 
     In some embodiments, value conversion process  11  may enable a conversion from a real value to an IEEE1801 power voltage, for example: 
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Conversion from real value to power voltage 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_hdl2upf_vct VCTR2V -hdl_type {sc wTsum.V} \ 
               
               
                   
                   
                       -table {{real_expression real_value} ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTR2V” may be defined for SV-UDN element “wTsum.V”. If the value of element “wTsum.V” makes the “real_expression” true, then the “real_value” may be applied on the voltage of IEEE1801 power supply net. Otherwise, the original value of element “wTsum.V” may be propagated to the voltage of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may enable a conversion from a logic value and a power voltage. For example, in some cases, there is no real value defined in SV-UDT to describe the power voltage. A conversion from a logic value to a power voltage is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Conversion from logic value to power voltage 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_hdl2upf_vct VCTR2V -hdl_type {sv wTsum.Status } \ 
               
               
                   
                          -table { {logic_value real_value} ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTL2V” may be defined for SV-UDN element “wTsum. Status”. If the value of element “wTsum. Status” equals to “logic_value”, then the specified “real_value” may be applied on the state of IEEE1801 power supply net. Otherwise, the value “wrealXState” may be propagated to the voltage of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may enable a conversion between an integer value and power voltage. In some cases, there is no real value defined in SV-UDT to describe the power voltage. As such, a conversion from an integer value to a power voltage is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Conversion from integer value to power voltage 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_hdl2upf_vct VCTI2V -hdl_type {sv wTsum.Status } \ 
               
               
                   
                       -table { { integer_expression real_value} ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTI2V” may be defined for SV-UDN element “wTsum. Status”. If the value of element “wTsum. Status” makes the “integer_expression” true, then the specified “real_value” may be applied on the state ofIEEE1801 power supply net. Otherwise, the value “wrealXState” may be propagated to the voltage of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may enable a conversion between a real value to an IEEE1801 power state. In some cases, there is no integer value defined in SV-UDT to describe the power state. As such, a conversion from a real value to a power state is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 9 
               
               
                   
               
               
                 Conversion from real value to power state 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_hdl2upf_vct VCTR2V -hdl_type {sv wTsum.V } \ 
               
               
                   
                   
                      -table { { real_expression power_state } ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTR2S” may be defined for an SV-UDN element “wTsum.V”. If the value of element “wTsum.V” makes the “real_expression” true, then the specified “power_state” may be applied on the state of IEEE1801 power supply net. Otherwise, the state “UNDETERMINED” may be propagated to the state of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may enable a conversion between a logic value and an IEEE1801 power state. For example: 
     
       
         
           
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Conversion from logic value to power state 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_hdl2upf_vct VCTL2S -hdl_type {sv wTsum.Status } \ 
               
               
                   
                         -table { { logic_value power_state } ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTL2S” may be defined for a SV-UDN element “wTsum. Status”. If the value of element “wTsum. Status” equals to “logic_value”, then the specified “power_state” may be applied on the state of IEEE1801 power supply net. Otherwise, the state “UNDETERMINED” will be propagated to the state of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may enable a conversion between an integer value and an IEEE1801 power state. For example: 
     
       
         
           
               
             
               
                 TABLE 11 
               
               
                   
               
               
                 Conversion from integer value to power state 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_hdl2upf_vct VCTI2S -hdl_type {sv wTsum.Status} \ 
               
               
                   
                   
                      -table { { logic_expression power_state } ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTI2S” may be defined for SV-UDN element “wTsum. Status”. If the value of element “wTsum.Status” makes the “integer_expression” true, then the specified “power_state” may be applied on the state of IEEE1801 power supply net. Otherwise, the state “UNDETERMINED” may be propagated to the state of IEEE1801 power supply net. 
     In some embodiments, value conversion process  11  may include an extension for upf2hdl VCT. For example, the “create upf2hdl_vct” command may define a VCT for the supply_net_type.state value, when that value is propagated from a UPF supply net into a logic port defined in an HDL. 
     
       
         
           
               
             
               
                 TABLE 12 
               
               
                   
               
               
                 IEEE1801 create_upf2hdl_vct command 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_upf2hdl_vct vct_name -hdl_type {&lt;vhdl | sv&gt; [typename]} \ 
               
               
                   
                              -table {{from_value to_value}*} 
               
               
                   
               
            
           
         
       
     
     Table 12 shows the syntax of the IEEE1801 command “create_upf2hdl_vct”. In this example, the “vct_name” provides a name for the value conversion table for later use with the connect_supply_net command. The “-hdl_type” may specify the HDL type for which the value conversions are defined. For a VHDL net, the net type could be Bit, std_[u]logic, Boolean, or Subtypes of std_[u]logic. For the SystemVerilog net, the net type could be reg/wire, Bit, Logic. The “-table” may define the 1:1 conversion from UPF supply net states to an HDL logic value. The values may be consistent with the HDL type values. 
     Embodiments of value conversion process  11  included herein may, extend this command for a SystemVerilog Real Number Model. Accordingly, a user may specify the UDT field name in the field “typename”, to indicate the field mapping; and specify the value conversion on the table “{from_value to_value}”, to indicate the value mapping. The datatype of SV-UDT element could be real (e.g., real, shortreal, realtime), logic (e.g., bit, logic, reg, byte), integer (e.g., int, shortint, longint). 
     In some embodiments, value conversion process  11  may enable a conversion between an IEEE1801 power voltage and a real value. For example: 
     
       
         
           
               
             
               
                 TABLE 13 
               
               
                   
               
               
                 Conversion from power voltage to real value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_upf2hdl_vct VCTV2R -hdl_type {sc wTsum.V} \ 
               
               
                   
                   
                      -table { { real_expression real_value } ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTV2R” may be defined for SV-UDN element “wTsum.V”. If the voltage value of the IEEE1801 power net makes the “real_expression” true, then the “real_value” may be applied on the element “wTsum.V”. Otherwise, the original voltage value of IEEE1801 power supply net may be propagated to the element “wTsum.V”. 
     In some embodiments, value conversion process  11  may enable a conversion between a power voltage to a logic value. In some cases, there is no power state specified in IEEE1801 supply net, the logic value element defined in SV-UDT depends on power voltage. As such, a conversion from power voltage to logic value is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 14 
               
               
                   
               
               
                 Conversion from power voltage to logic value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_upf2hdl_vct VCTV2L -hdl_type {sv wTsum.Status } \ 
               
               
                   
                        -table { { real_expression logic_value } ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTV2L” may be defined for SV-UDN element “wTsum.Status”. If the voltage value of IEEE1801 power supply net makes the “real_expression” true, then the then the specified “logic value” may be applied on the element “wTsum.Status”. Otherwise, the logic value “X” may be propagated to the element “wTsum. Status”. 
     In some embodiments, value conversion process  11  may enable a conversion between a power voltage and an integer value. In some cases, there is no power state specified in the IEEE1801 supply net, the integer value element defined in SV-UDT depends on power voltage. A conversion from power voltage to integer value is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 15 
               
               
                   
               
               
                 Conversion from power voltage to integer value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_upf2hdl_vct VCTV2I -hdl_type {sv wTsum.Status } \ 
               
               
                   
                       -table { { real_expression integer_value } ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTV2I” may be defined for SV-UDN element “wTsum.Status”. If the voltage value of IEEE1801 power supply net makes the “real_expression” true, then the specified “integer value” may be applied on the element “wTsum.Status”. Otherwise, the integer value “0” may be propagated to the element “wTsum. Status”. 
     In some embodiments, value conversion process  11  may enable a conversion between an IEEE1801 power state and a real value. In some cases, the real value element defined in SV-UDT depends on power state. A conversion from a power state to a real value is needed. For example: 
     
       
         
           
               
             
               
                 TABLE 16 
               
               
                   
               
               
                 Conversion from power state to real value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_upf2hdl_vct VCTS2V -hdl_type {sv wTsum.V } \ 
               
               
                   
                   
                        -table { { power_state real_value } ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTS2V” may be defined for SV-UDN element “wTsum.V”. If the state value of IEEE1801 power supply net equals to “power_state”, then the specified “real_value” may be applied on the element “wTsum.V”. Otherwise, the value “‘wrealXState” may be propagated to the element “wTsum.V”. 
     In some embodiments, value conversion process  11  may enable a conversion between an IEEE1801 power state and a logic value. For example: 
     
       
         
           
               
             
               
                 TABLE 17 
               
               
                   
               
               
                 Conversion from power state to logic value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 create_upf2hdl_vct VCTS2L -hdl_type {sv wTsum.Status} \ 
               
               
                   
                         -table { { power_state logic_value } ... } 
               
               
                   
               
            
           
         
       
     
     In this example, the VCT “VCTS2L” may be defined for SV-UDN element “wTsum. Status”. If the state value of IEEE1801 power net equals to “power_state”, then the specified “logic_value” may be applied on the element “wTsum. Status”. Otherwise, the logic_value “X” may be propagated to the element “wTsum. Status”. 
     In some embodiments, value conversion process  11  may enable a conversion between an IEEE1801 power state and an integer value. For example: 
     
       
         
           
               
             
               
                 TABLE 18 
               
               
                   
               
               
                 Conversion from power state to integer value? 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 create_upf2hdl_vct VCTS2I -hdl_type {sv wTsum.Status} \ 
               
               
                   
                   
                        -table { { power_state integer_value } ... } 
               
               
                   
                   
               
            
           
         
       
     
     In this example, the VCT “VCTS2I” may be defined for SV-UDN element “wTsum. Status”. If the state value of IEEE1801 power net equals to “power_state”, then the specified “integer_value” may be applied on the element “wTsum.Status”. Otherwise, the integer value “0” may be propagated to the element “wTsum. Status”. 
     Embodiments of value conversion process  11  included herein may include, in whole or in part, a real expression in the VCT definition. The real type element could be defined with datatype “real”, “shortreal”, “realtime”. The real expression may include a comparison operator and a threshold value. 
     In some embodiments, the operator may include, but is not limited to, “&gt;=”, “&gt;”, “&lt;”, “&lt;=” (Relational), “==”, “!=” (Logical equality), “===”, “!==” (Case equality), etc. In some embodiments, the case equality operators (“===” and “!==”) may be followed by “‘wrealXState” and “‘wrealZState” only. The equality on real value means that the value may be the same for a system. The user may be responsible for factoring any tolerance in the comparison. 
     In some embodiments, the value could be a real number or “‘wrealXState”/“‘wrealZState”. The variable or parameter in HDL code may not be supported in some cases. 
     In some embodiments, the order or weighting of the map list may be similar to that outlined below, which is provided merely by way of example. 
     In some embodiments, the mapping that includes equality operator “==” or “===” may take the highest priority. For example: {{&gt;=0.2 PARTIAL ON} {==0.5 OFF}} (the power supply net is in “OFF” state instead of “PARTIAL_ON”, if the real value is 0.5). 
     In some embodiments, the mapping that includes the greatest threshold value for operator “&gt;“/”&gt;=”, or the lowest threshold value for operator “&lt;“/”&lt;=” may take higher priority. For example: {{&gt;=1.0 FULL_ON} {&gt;=0.5 PARTIAL_ON}} (the power supply net is in “FULL_ON” state instead of “PARTIAL_ON”, if the real value is greater than 1.0). 
     For example: {{&lt;=0.8 PARTIAL ON} {&lt;=0.2 OFF} } (the power supply net is in “OFF” state instead of “PARTIAL_ON”, if the real value is lower than 0.2). And there may be error out if the lowest threshold value for operator “&gt;“/”&gt;=” is less than the greatest threshold value for operator “&lt;“/”&lt;=”. For example: {{&gt;=0.2 PARTIAL ON}{&lt;=0.5 OFF} } (error out, since power net status cannot be determined if the real value is between 0.2 and 0.5). 
     In some embodiments, the mapping that includes an inequality operator “!=” or !==” may take the lowest priority; For example: {{&gt;=0.2 PARTIAL_ON} {!=1.2 OFF} }(the power supply net is in “PARTIAL_ON” state instead of “OFF”, if the real value is greater than 1.2). Otherwise, the default state “UNDETERMINED” will be taken. For example: {{&gt;=0.8 PARTIAL_ON} {&lt;=0.5 OFF}}))(the power supply net state is “UNDETERMINED”, if the real value is greater than 0.5 and less than 0.8). 
     In some embodiments, value conversion process  11  included herein may include an integer expression in the VCT definition. The integer type element could be defined with datatype “int”, “shortint”, “longint”. The integer expression contains a comparison operator and a threshold value. 
     In some embodiments, the operator may include, but is not limited to, “&gt;=”, “&gt;”, “&lt;”, “&lt;=” (Relational), “==”, “!=” (Logical equality), etc. The variable or parameter in HDL code may not be supported in some cases. 
     In some embodiments, the order and/or weighting of the map list may include, but is not limited to the following. The mapping that have equality operator “==” may take the highest priority; For example: {{&gt;=10 PARTIAL_ON} {==5 OFF}} (the power supply net is in “OFF” state instead of “PARTIAL_ON”, if the integer value is 5). 
     In some embodiments, the mapping that has the greatest threshold value for operator “&gt;“/”&gt;=”, or the lowest threshold value for operator “&lt;“/”&lt;=” may take higher priority; For example: {{&gt;=10 FULL_ON} {&gt;=5 PARTIAL_ON}} (the power supply net is in “FULL_ON” state instead of “PARTIAL_ON”, if the integer value is greater than 10). For example: {{&lt;=8 PARTIAL_ON} {&lt;=2 OFF} }(he power supply net is in “OFF” state instead of “PARTIAL_ON”, if the integer value is lower than 2). And there may be error out if the lowest threshold value for operator “&gt;“/”&gt;=” is less than the greatest threshold value for operator “&lt;“/”&lt;=”. For example: {{&gt;=2 PARTIAL ON}{&lt;=5 OFF} } (error out, since power net status cannot be determined if the integer value is between 2 and 5). 
     In some embodiments, the mapping that includes inequality operator “!=” or !==” may take the lowest priority; For example: {{&gt;=2 PARTIAL_ON} {!=12 OFF}}(the power supply net is in “PARTIAL_ON” state instead of “OFF”, if the integer value is greater than 12). Otherwise, the default state “UNDETERMINED” may be taken. For example: {{&gt;=8 PARTIAL_ON} {&lt;=5 OFF}}(*the power supply net state is “UNDETERMINED”, if the integer value is greater than 5 and less than 8). 
     In some embodiments, for the real_value in VCT definition the value should be a real number. Additionally and/or alternatively, for the logic_value in VCT definition the value should be a 4-state logic value: 1/0/X/Z. For the integer value in VCT definition the value should be an integer number. For the state_value in VCT definition the value should be a power state value: OFF, UNDETERMINED, PARTIAL_ON, or FULL_ON. 
     Referring to Table 19 below an example of the supply connection specification is provided. 
     
       
         
           
               
             
               
                 TABLE 19 
               
               
                   
               
               
                 IEEE1801 command “connect_supply_net” 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 connect_supply_net net_name [-elements element_list ] \ 
               
               
                   
                   
                  [-ports port_list] [-pg_type pg_type_list]* \ 
               
               
                   
                   
                  [-vct vct_name]\ 
               
               
                   
                   
                  [-cells cell_list] [-domain domain_name] 
               
               
                   
                   
               
            
           
         
       
     
     In some embodiments, the “connect_supply_net” command may be configured to connect a supply net to the specified ports. As shown in Table 19, a user could specify the hierarchical HDL port name in the “port_list” of option “-ports”, and specify the VCT in option “-vct”. 
     In some embodiments, and referring also to  FIG. 18 , an extension for an IEEE supply connection may be provided. Accordingly, value conversion process  11 , may extend this command for SystemVerilog Real Number Model. Using the “-ports port list” a user may specify any SystemVerilog net with user defined net type in the “port list”. The simulation tool may trace the actual driver of the net automatically. If there is an HDL driver detected, the connection may be treated as “HDL driving UPF”, and the VCT defined by command “create_hdl2upf_vct” is needed. Otherwise, the connection may be treated as “UPF driving HDL”, and the VCT defined by command “create upf2hdl_vct” is needed. Using the “-vct vct name” a user could specify the user defined VCT for the supply connection. Since the conversion may occur on multiple elements of SystemVerilog user defined net type, multiple VCT for different element fields could be specified on same supply net. 
     In some embodiments, value conversion process  11  may provide error checking for supply connection. For example, there would be error out in one or more scenarios. These may include, but are not limited to, situations where there are multiple VCTs specified on same element of SV-UDN, but in different direction of conversion or there are multiple VCTs specified on voltage element of IEEE1801 supply net type, for the conversion from HDL signal to IEEE1801 supply net. Additionally and/or alternatively, there may be multiple VCTs specified on stage element of IEEE1801 supply net type, for the conversion from HDL signal to IEEE1801 supply net and/or multiple VCTs specified on same element of SV-UDN, for the conversion from IEEE1801 supply net to HDL signal. 
     Referring now to  FIG. 19 , an example of IE insertion for supply connection is provided. In some cases, it may be difficult to locate the SV-UDT fields that represent the power state and voltage specifically. A detailed resolution function is necessary to convert the value between the SV-UDT fields and IEEE1801 power state/voltage fields. In this way, embodiments included herein may provide another solution to allow the user to describe the resolution functions for SV-UDN to IEEE1801 supply net type connection, and IEEE1801 supply type to SV-UDN connection.  FIG. 19  illustrates the supply net connection with IE insertion. The power net connectivity may be described in IEEE1801 power intent file, but there is no VCT specified for the connection on port “i_ana1/vdd” and “i_ana2/vdd”. For this situation, the tool will pick up connect module that compiled in design, and insert it on the boundary of HDL SV-UDN and IEEE1801 power nets. The connect module “UDT2UPF” may be defined for net type conversion from SV-UDT to IEEE1801 supply net. The connect module “UPF2UDT” is defined for net type conversion from IEEE1801 supply net to SV-UDT. 
     Referring also to  FIG. 20 , an embodiment that may be used in processing an SV-UDN power net connection is provided. This schematic is provided merely by way of example and is meant to provide an example consistent with one or more embodiments of value conversion process  11 . Numerous other embodiments are also within the scope of the present disclosure. 
     Embodiments included herein may be configured to allow users easily to reuse the IEEE1801 power intent specification with some minor modifications for mixed signal simulation. Based on that, the tool could setup up power supply network automatically and connect with SV-RNM models. This solution may resolve the challenge of power supply connectivity in mixed signal simulation. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present disclosure without departing from the spirit or scope of the present disclosure. Thus, it is intended that embodiments of the present disclosure cover the modifications and variations provided they come within the scope of the appended claims and their equivalents.