Patent Publication Number: US-11030376-B2

Title: Net routing for integrated circuit (IC) design

Description:
BACKGROUND 
     The present invention generally relates to integrated circuits (ICs), and more specifically, to net routing for an IC design. 
     An IC chip may include a large number of electronic components that are fabricated by layering several different materials on a silicon base or wafer. The design of an IC transforms a circuit description into a geometric description which is known as a layout. The process of converting the functional specifications of an electronic circuit into a layout is called the physical design. The objective of physical design is to determine an optimal arrangement of devices in a plane or in a three-dimensional space, and an efficient interconnection or routing scheme between the devices to obtain the desired functionality. 
     An IC chip includes elements, and connections between the elements, formed on a surface of a semiconductor substrate. The IC may include a large number of elements and require complex connections between the elements. Millions of circuits may need to be physically placed and connected on the chip. Placement may be a relatively time consuming process because the actual process of designing, placing, and connecting the circuits on the chip can affect the performance and timing requirements of the chip. Therefore, the design process may be automated by using a computer place and wire circuits into a functional chip. However, automation may sacrifice the performance of the resulting IC chip for the ability to determine a connected circuit in a reasonable amount of computing time. 
     SUMMARY 
     Embodiments of the present invention are directed to net routing for an integrated circuit (IC) design. A non-limiting example computer-implemented method includes receiving a netlist corresponding to a net in an IC design. The method also includes identifying intermediate logic in the net, wherein the intermediate logic is connected between a source and a sink of the net, and wherein the sink is located downstream from the source in the IC design. The method also includes hiding the intermediate logic from the netlist. The method also includes creating a global route in the IC design between the source and the sink of the net without the intermediate logic. The method also includes restoring the intermediate logic to the netlist. The method also includes placing the intermediate logic along the global route. 
     Other embodiments of the present invention implement features of the above-described method in computer systems and computer program products. 
     Additional technical features and benefits are realized through the techniques of the present invention. Embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed subject matter. For a better understanding, refer to the detailed description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The specifics of the exclusive rights described herein are particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the embodiments of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of an example computer system for use in conjunction with one or more embodiments of net routing for an integrated circuit (IC) design; 
         FIG. 2  is a flow diagram of a process for net routing for an IC design in accordance with one or more embodiments of the present invention; 
         FIG. 3A  is a block diagram of components of a system for net routing for an IC design in accordance with one or more embodiments of the present invention; 
         FIG. 3B  is a block diagram of components of a system for net routing for an IC design in accordance with one or more embodiments of the present invention; 
         FIG. 3C  is a block diagram of components of a system for net routing for an IC design in accordance with one or more embodiments of the present invention; 
         FIG. 3D  is a block diagram of components of a system for net routing for an IC design in accordance with one or more embodiments of the present invention; and 
         FIG. 4  depicts a system of a computer system integrated with a manufacturing fabrication plant according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the present invention provide net routing for an integrated circuit (IC) design. An IC may include a relatively large number of nets, each net being described by a netlist in the IC design. Routing of a net in an IC design includes placement of logic gates along a route between the net endpoints (e.g., a source and one or more sinks). The route may be generated between endpoints that are not in the same logic level. In order to generate a route, intermediate logic in the net may be hidden from the netlist in the IC design, and a global route may be created between a source and a sink without the intermediate logic. The hidden logic may then be unhidden and placed along the global route. The hidden logic may include a sequence of latches in some embodiments, as latches may be present in the netlist prior to physical design. 
     Embodiments of routing for IC design may provide routing solutions that comply with timing requirements. Rerouting may be performed to improve timing using an existing netlist. A netlist including a number of latches and a route connecting a source to a sink may be received. The route between the source and the sink may be detached by temporarily disconnecting (or hiding connectivity) any logic gates, such as latches, that are located between the source and a given sink (which may be located in one or more levels downstream from the source). Therefore, in some embodiments, the intermediate logic may include paths containing one or more latches. After disconnecting the latches, the net connected to the source may be connected to the given sink and any intermediate latches and driving nets are temporarily removed from the design. A global route may then be created for the net connecting a source to a downstream sink that takes wiring limitations and numbers of lanes available in the IC design into account. After routing, the removed latches and nets are added back to the netlist, using the created route as guidance for latch placement. The latches may then be legally placed on the global route in a manner than reduces congestion and delay in the IC. 
     Multiple levels of logic may be identified and hidden from a netlist to enable routing between a source and a sink. The source may be in a first logic level and the sink (or sinks) may be in one or multiple different logic levels downstream. The logic levels to be temporarily hidden are identified (e.g., by saving of latch names), such that connectivity is preserved, and are removed from the netlist. The same names may be maintained for the latches during hiding and unhiding, and when placing the latches in the global route, in order to maintain latches as part of the original netlist. A global route is then determined as if the source and sinks are directly connected, without the hidden logic. The global route is defined by the location of the source and the sink. Therefore, the global route may take a best path chosen by the router. For example, the global route may extend through available wiring in a hierarchical block in the IC, in which the latches may not be placed. Once the global route is created the hidden logic is added back to the netlist. The global route may be manipulated such that portions of the route are added to appropriate respective logic level nets in order to accommodate the unhidden intermediate logic. Placement of latches or other removed logic is performed on the original netlist using the global route. Latches may be moved along the global route to determine an appropriate location for each latch based on timing and delay constraints (e.g., to ensure balanced latches), while keeping the latches in the same order as in the original route from the netlist. 
     Turning now to  FIG. 1 , a computer system  100  is generally shown in accordance with an embodiment. The computer system  100  can be an electronic, computer framework comprising and/or employing any number and combination of computing devices and networks utilizing various communication technologies, as described herein. The computer system  100  can be easily scalable, extensible, and modular, with the ability to change to different services or reconfigure some features independently of others. The computer system  100  may be, for example, a server, desktop computer, laptop computer, tablet computer, or smartphone. In some examples, computer system  100  may be a cloud computing node. Computer system  100  may be described in the general context of computer system executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types. Computer system  100  may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices. 
     As shown in  FIG. 1 , the computer system  100  has one or more central processing units (CPU(s))  101   a ,  101   b ,  101   c , etc. (collectively or generically referred to as processor(s)  101 ). The processors  101  can be a single-core processor, multi-core processor, computing cluster, or any number of other configurations. The processors  101 , also referred to as processing circuits, are coupled via a system bus  102  to a system memory  103  and various other components. The system memory  103  can include a read only memory (ROM)  104  and a random access memory (RAM)  105 . The ROM  104  is coupled to the system bus  102  and may include a basic input/output system (BIOS), which controls certain basic functions of the computer system  100 . The RAM is read-write memory coupled to the system bus  102  for use by the processors  101 . The system memory  103  provides temporary memory space for operations of said instructions during operation. The system memory  103  can include random access memory (RAM), read only memory, flash memory, or any other suitable memory systems. 
     The computer system  100  comprises an input/output (I/O) adapter  106  and a communications adapter  107  coupled to the system bus  102 . The I/O adapter  106  may be a small computer system interface (SCSI) adapter that communicates with a hard disk  108  and/or any other similar component. The I/O adapter  106  and the hard disk  108  are collectively referred to herein as a mass storage  110 . 
     Software  111  for execution on the computer system  100  may be stored in the mass storage  110 . The mass storage  110  is an example of a tangible storage medium readable by the processors  101 , where the software  111  is stored as instructions for execution by the processors  101  to cause the computer system  100  to operate, such as is described herein below with respect to the various Figures. Examples of computer program product and the execution of such instruction is discussed herein in more detail. The communications adapter  107  interconnects the system bus  102  with a network  112 , which may be an outside network, enabling the computer system  100  to communicate with other such systems. In one embodiment, a portion of the system memory  103  and the mass storage  110  collectively store an operating system, which may be any appropriate operating system, such as the z/OS or AIX operating system from IBM Corporation, to coordinate the functions of the various components shown in  FIG. 1 . 
     Additional input/output devices are shown as connected to the system bus  102  via a display adapter  115  and an interface adapter  116  and. In one embodiment, the adapters  106 ,  107 ,  115 , and  116  may be connected to one or more I/O buses that are connected to the system bus  102  via an intermediate bus bridge (not shown). A display  119  (e.g., a screen or a display monitor) is connected to the system bus  102  by a display adapter  115 , which may include a graphics controller to improve the performance of graphics intensive applications and a video controller. A keyboard  121 , a mouse  122 , a speaker  123 , etc. can be interconnected to the system bus  102  via the interface adapter  116 , which may include, for example, a Super I/O chip integrating multiple device adapters into a single integrated circuit. Suitable I/O buses for connecting peripheral devices such as hard disk controllers, network adapters, and graphics adapters typically include common protocols, such as the Peripheral Component Interconnect (PCI). Thus, as configured in  FIG. 1 , the computer system  100  includes processing capability in the form of the processors  101 , and, storage capability including the system memory  103  and the mass storage  110 , input means such as the keyboard  121  and the mouse  122 , and output capability including the speaker  123  and the display  119 . 
     In some embodiments, the communications adapter  107  can transmit data using any suitable interface or protocol, such as the internet small computer system interface, among others. The network  112  may be a cellular network, a radio network, a wide area network (WAN), a local area network (LAN), or the Internet, among others. An external computing device may connect to the computer system  100  through the network  112 . In some examples, an external computing device may be an external webserver or a cloud computing node. 
     It is to be understood that the block diagram of  FIG. 1  is not intended to indicate that the computer system  100  is to include all of the components shown in  FIG. 1 . Rather, the computer system  100  can include any appropriate fewer or additional components not illustrated in  FIG. 1  (e.g., additional memory components, embedded controllers, modules, additional network interfaces, etc.). Further, the embodiments described herein with respect to computer system  100  may be implemented with any appropriate logic, wherein the logic, as referred to herein, can include any suitable hardware (e.g., a processor, an embedded controller, or an application specific integrated circuit, among others), software (e.g., an application, among others), firmware, or any suitable combination of hardware, software, and firmware, in various embodiments. 
       FIG. 2  shows a process flow diagram of a method  200  for net routing for an IC design in accordance with one or more embodiments of the present invention. Method  200  of  FIG. 2  may be implemented in conjunction with any appropriate computer system, such as computer system  100  of  FIG. 1 . Embodiments of method  200  may be implemented in software  111 , and may operate on data stored in mass storage  110  and/or system memory  103 . In block  201  of method  200 , a netlist corresponding to a selected net from an IC design is received. The IC design may include a plurality of nets including the selected net. The net may include endpoints (i.e. a source and one or more sinks), and any appropriate number and type of intermediate components, including but not limited to latches. The source may be in a first logic level of the IC design, and the sink (or sinks) may be in one or multiple different logic levels downstream in the IC design in some embodiments. In block  202 , any intermediate latches located between the source and the sink in the selected net are identified and hidden from the netlist. For each hidden latch, a name of the latch and the network connectivity of the latch may be saved in block  202  based on the latch being removed from the netlist. 
     In block  203 , a global route is determined directly between the source and the sink(s) in the IC design using any available wire tracks in the IC design. The global route may take wiring limitations and numbers of lanes available in the IC design into account. The global route may extend through a hierarchical object, like a unit, a macro, or an intellectual property (IP) unit in the IC design. The hierarchical object may include gates that are configured such that additional gates or latches may not be able to be placed inside the hierarchical object. The hierarchical object may be described as a placement blockage in the IC design. For a current level of the hierarchy, the hierarchical object may be a forbidden area where no gate is permitted to be placed. 
     In block  204 , the latches that were hidden from the netlist in block  202  are unhidden and added back to the netlist of the selected net (i.e., the original netlist is restored). The latches are then placed along the global route that was determined in block  203 . The latches are reconnected to the netlist in order based on the latch names and connectivity that were saved in block  202 . The global route may be divided into a number of segments corresponding to a number of latches in the net, and a segment may be assigned to the net driven by each latch. In block  205 , the placement of the latches on the global route is legalized, and slack in the net is balanced. A multi-dimensional optimization algorithm may be used in block  205  to move the latches to legal positions, in order to meet timing constraints and balance slack amongst the latches. The latches may be moved along the global route to legal positions if the global route may be preserved while meeting timing constraints. If the global route may not be preserved, the global route may be modified as needed in block  205  to meet timing constraints and balance slack in the net, and the latches may be moved along Steiner distances to legal positions. 
     Method  200  of  FIG. 2  may be repeated for any appropriate number of nets in an IC design. When it is determined that all nets in the IC design are appropriately routed (for example, according to method  200  of  FIG. 2 ), a physical chip may be fabricated based on the IC design. Fabrication of a physical chip based on the IC design is discussed in further detail below with respect to  FIG. 4 . 
     The process flow diagram of  FIG. 2  is not intended to indicate that the operations of the method  200  are to be executed in any particular order, or that all of the operations of the method  200  are to be included in every case. Additionally, the method  200  can include any suitable number of additional operations. 
       FIGS. 3A-D  show block diagrams of components of systems  300 A-D for net routing for an IC design in accordance with one or more embodiments of the present invention.  FIGS. 3A-D  are discussed with reference to method  200  of  FIG. 2 . System  300 A of  FIG. 3A  illustrates an embodiment of a selected net that may be received in block  201  of method  200 . The system  300 A includes a source  301 , sink  302 , and intermediate logic comprising latches  303 A-B. System  300 B of  FIG. 3B  illustrates removal of the intermediate latches  303 A-B from the selected net, as is performed in block  202  of  FIG. 2 . As shown in  FIG. 3B , source  301  and sink  302  are directly connected. Information regarding the intermediate latches  303 A-B, including names and connectivity, may be saved based on hiding of the intermediate latches  303 A-B. System  300 C of  FIG. 3C  illustrates an embodiment of creation of a global route  305  that connects with source  301  to the sink  302  in the IC design without the intermediate latches  303 A-B, according to block  203  of  FIG. 2 . As shown in system  300 C, the global route  305  includes available wiring that is located over, but outside of, a hierarchical object  304  of the IC design, which may represent but is not limited to a unit, a macro, or an IP unit in the IC design. In some embodiments, the global route may extend through the hierarchical object if the hierarchical object has available wiring tracks that are visible from the outside of the hierarchical object. The hierarchical object  304  may include any appropriate number of gates located inside the object, such that additional gates or latches may not be able to be placed inside the hierarchical object  304 . 
     System  300 D of  FIG. 3D  illustrates an embodiment of latch placement according to blocks  204  and  205  of  FIG. 2 . The latches  303 A-B are added back into the netlist of the selected net and placed along the global route  305 , based on global route segments  306 A-C, which correspond to, or form, global route  305 . The placement of the latches  303 A-B on the global route segments  306 A-C is legalized, and slack in the net is balanced. A multi-dimensional optimization algorithm may be used to move the latches to legal positions along the global route  305  (by, for example, modifying the lengths of any of global route segments  306 A-C), in order to meet timing constraints and balance slack amongst the latches in the net. A longer global route segment between two latches may correspond to higher slack. The latches may be moved along the global route  305  to legal positions if the global route may be preserved while meeting timing constraints. If the global route  305  may not be preserved, the global route may be modified as needed (e.g., by changing the lengths of any of global route segments  306 A-C) to meet timing constraints and balance slack in the net, and the latches may be moved along Steiner distances to legal positions. 
     It is to be understood that the block diagrams of  FIGS. 3A-D  are not intended to indicate that the systems  300 A-D are to include all of the components shown in  FIGS. 3A-D . Rather, the systems  300 A-D can include any appropriate fewer or additional components not illustrated in  FIGS. 3A-D  (e.g., nets, sources, sinks, intermediate logic, latches, IC components, global routes, global route segments, hierarchical objects, additional memory components, embedded controllers, functional blocks, connections between functional blocks, modules, inputs, outputs, etc.). Further, the embodiments described herein with respect to systems  300 A-D may be implemented with any appropriate logic, wherein the logic, as referred to herein, can include any suitable hardware (e.g., a processor, an embedded controller, or an application specific integrated circuit, among others), software (e.g., an application, among others), firmware, or any suitable combination of hardware, software, and firmware, in various embodiments. 
     In some embodiments, a semiconductor layout (or IC design) can be generated using the computer system  400  shown in  FIG. 4 . The computer system  400  has one or more software applications  402  configured to function and implement operations as discussed herein. For example, software applications  402  may include one or more routines for net routing for an IC design. A semiconductor layout can be constructed by the software application  402  of the computer  400  according to method  200  of  FIG. 2  as described above to build the semiconductor device (e.g., an integrated circuit). The computer  400  is configured to guarantee design rule cleanliness (i.e., pass) for the semiconductor device before and/or without requiring a design rule check. The software applications  402  include, integrate, are coupled to, and/or function as electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD). Electronic design automation is a category of software tools for designing electronic systems such as integrated circuits and printed circuit boards. The tools work together in a design flow that chip designers use to design and analyze entire semiconductor chips. In some implementations, the computer  400  is coupled to, integrated with, and/or part of the fabrication equipment  485  at the manufacturing fabrication plant  480  (so as to communicate with and/or control operations of the fabrication equipment  485 ) to thereby fabricate semiconductor device(s)  490  as depicted in  FIG. 4 , as understood by one skilled in the art. The computer  400  includes one or processors  406  configured to execute one or more software applications  402  in memory  404 . The computer  400  receives input of a design  470  for the semiconductor device  490 , and the computer  400  is configured to develop/form the semiconductor layout for the semiconductor device in order to build the semiconductor device. The semiconductor layout is a physical design released to the manufacturing fabrication (Fab) plant  480  and physically fabricated by the fabrication equipment  485  to produce the semiconductor device  490 . The manufacturing fabrication plant  480  builds the photo mask from the semiconductor layout as a physical design, and then builds the actual product using the photo mask. The product is an integrated circuit (i.e., semiconductor device  490 ) on a wafer according to the semiconductor layout (physical design). There may be numerous integrated circuits on a wafer, and each integrated circuit may be diced into an individual chip. 
     Various embodiments of the invention are described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. 
     One or more of the methods described herein can be implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     For the sake of brevity, conventional techniques related to making and using aspects of the invention may or may not be described in detail herein. In particular, various aspects of computing systems and specific computer programs to implement the various technical features described herein are well known. Accordingly, in the interest of brevity, many conventional implementation details are only mentioned briefly herein or are omitted entirely without providing the well-known system and/or process details. 
     In some embodiments, various functions or acts can take place at a given location and/or in connection with the operation of one or more apparatuses or systems. In some embodiments, a portion of a given function or act can be performed at a first device or location, and the remainder of the function or act can be performed at one or more additional devices or locations. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. 
     The diagrams depicted herein are illustrative. There can be many variations to the diagram or the steps (or operations) described therein without departing from the spirit of the disclosure. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term “coupled” describes having a signal path between two elements and does not imply a direct connection between the elements with no intervening elements/connections therebetween. All of these variations are considered a part of the present disclosure. 
     The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. 
     Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms “a plurality” are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term “connection” can include both an indirect “connection” and a direct “connection.” 
     The terms “about,” “substantially,” “approximately,” and variations thereof, are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of ±8% or 5%, or 2% of a given value. 
     The present invention may be a system, a method, and/or a computer program product at any possible technical detail level of integration. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention. 
     The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: 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), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire. 
     Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device. 
     Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, configuration data for integrated circuitry, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++, or the like, and procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions 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 any type of network, including 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). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instruction by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention. 
     Aspects of the present invention are described herein 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 readable program instructions. 
     These computer readable 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 readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments described herein.