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84-444: SystemVerilog , standardized as IEEE 1800 , is a hardware description and hardware verification language used to model, design , simulate , test and implement electronic systems. SystemVerilog is based on Verilog and some extensions, and since 2008, Verilog is now part of the same IEEE standard . It is commonly used in the semiconductor and electronic design industry as an evolution of Verilog. SystemVerilog started with

168-574: A multi-valued logic system, in which case it may also be called an X value or don't know . In the Verilog hardware description language such values are denoted by the letter "X". In the VHDL hardware description language such values are denoted (in the standard logic package) by the letter "X" (forced unknown) or the letter "W" (weak unknown). An X value does not exist in hardware. In simulation, an X value can result from two or more sources driving

252-433: A state machine . It is sometimes possible that some states that are nominally can't-happen conditions can accidentally be generated during power-up of the circuit or else by random interference (like cosmic radiation , electrical noise or heat). This is also called forbidden input . In some cases, there is no combination of inputs that can exit the state machine into a normal operational state. The machine remains stuck in

336-475: A test bench ). At minimum, a testbench contains an instantiation of the model (called the device under test or DUT), pin/signal declarations for the model's I/O, and a clock waveform. The testbench code is event driven: the engineer writes HDL statements to implement the (testbench-generated) reset-signal, to model interface transactions (such as a host–bus read/write), and to monitor the DUT's output. An HDL simulator —

420-405: A "simulation" netlist with gate-delay information, a "handoff" netlist for post-synthesis placement and routing on a semiconductor die, or a generic industry-standard Electronic Design Interchange Format (EDIF) (for subsequent conversion to a JEDEC -format file). On the other hand, a software compiler converts the source-code listing into a microprocessor -specific object code for execution on

504-421: A concatenation: This sequence matches if the gnt signal goes high one clock cycle after req goes high. Note that all sequence operations are synchronous to a clock. Other sequential operators include repetition operators, as well as various conjunctions. These operators allow the designer to express complex relationships among design components. An assertion works by continually attempting to evaluate

588-407: A condition that a formal logic proving tool must assume to be true . An assertion specifies a property that must be proven true. In simulation , both assertions and assumptions are verified against test stimuli. Property coverage allows the verification engineer to verify that assertions are accurately monitoring the design. Coverage as applied to hardware verification languages refers to

672-485: A derived class gain control of the function. See virtual function for further information. Encapsulation and data hiding is accomplished using the local and protected keywords, which must be applied to any item that is to be hidden. By default, all class properties are public . Class instances are dynamically created with the new keyword. A constructor denoted by function new can be defined. SystemVerilog has automatic garbage collection , so there

756-473: A few years, VHDL and Verilog emerged as the dominant HDLs in the electronics industry, while older and less capable HDLs gradually disappeared from use. However, VHDL and Verilog share many of the same limitations, such as being unsuitable for analog or mixed-signal circuit simulation. Specialized HDLs (such as Confluence) were introduced with the explicit goal of fixing specific limitations of Verilog and VHDL, though none were ever intended to replace them. Over

840-620: A hardware description language. The first hardware description languages appeared in the late 1960s, looking like more traditional languages. The first that had a lasting effect was described in 1971 in C. Gordon Bell and Allen Newell's text Computer Structures . This text introduced the concept of register transfer level , first used in the ISP language to describe the behavior of the Digital Equipment Corporation (DEC) PDP-8 . The language became more widespread with

924-435: A hierarchy of blocks are properly classified as netlist languages used in electric computer-aided design . HDL can be used to express designs in structural, behavioral or register-transfer-level architectures for the same circuit functionality; in the latter two cases the synthesizer decides the architecture and logic gate layout. HDLs are used to write executable specifications for hardware. A program designed to implement

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1008-494: A higher level of abstraction than simulation at the schematic level, and thus increased design capacity from hundreds of transistors to thousands. In 1986, with the support of the U.S Department of Defense, VHDL was sponsored as an IEEE standard (IEEE Std 1076), and the first IEEE-standardized version of VHDL, IEEE Std 1076-1987, was approved in December 1987. Cadence Design Systems later acquired Gateway Design Automation for

1092-440: A minimization of logic elements. Direct minimization of logic elements in such circuits was computationally impractical (for large systems) with the computing power available to Ginsburg in 1958. Examples of don't-care terms are the binary values 1010 through 1111 (10 through 15 in decimal) for a function that takes a binary-coded decimal (BCD) value, because a BCD value never takes on such values (so called pseudo-tetrades ); in

1176-471: A packed array's size must be known at compile time (from a constant or expression of constants), the dynamic array size can be initialized from another runtime variable, allowing the array to be sized and resize arbitrarily as needed. An associative array can be thought of as a binary search tree with a user-specified key type and data type . The key implies an ordering ; the elements of an associative array can be read out in lexicographic order. Finally,

1260-445: A physically realizable form, the design database becomes progressively more laden with technology-specific information, which cannot be stored in a generic HDL description. Finally, an integrated circuit is manufactured or programmed for use. Essential to HDL design is the ability to simulate HDL programs. Simulation allows an HDL description of a design (called a model) to pass design verification , an important milestone that validates

1344-464: A property is a factual statement about the expected or assumed behavior of another object. Ideally, for a given HDL description, a property or properties can be proven true or false using formal mathematical methods. In practical terms, many properties cannot be proven because they occupy an unbounded solution space . However, if provided a set of operating assumptions or constraints, a property checker can prove (or disprove) certain properties by narrowing

1428-502: A queue provides much of the functionality of the C++ STL deque type: elements can be added and removed from either end efficiently. These primitives allow the creation of complex data structures required for scoreboarding a large design. SystemVerilog provides an object-oriented programming model. In SystemVerilog, classes support a single-inheritance model, but may implement functionality similar to multiple-inheritance through

1512-450: A result of the efficiency gains realized using HDL, a majority of modern digital circuit design revolves around it. Most designs begin as a set of requirements or a high-level architectural diagram. Control and decision structures are often prototyped in flowchart applications, or entered in a editor. The process of writing the HDL description is highly dependent on the nature of the circuit and

1596-480: A sequence or property. An assertion fails if the property fails. The sequence above will fail whenever req is low. To accurately express the requirement that gnt follow req a property is required: This example shows an implication operator |=> . The clause to the left of the implication is called the antecedent and the clause to the right is called the consequent . Evaluation of an implication starts through repeated attempts to evaluate

1680-473: A signal simultaneously, or the stable output of a flip-flop not having been reached. In synthesized hardware, however, the actual value of such a signal will be either 0 or 1, but will not be determinable from the circuit's inputs. Further considerations are needed for logic circuits that involve some feedback . That is, those circuits that depend on the previous output(s) of the circuit as well as its current external inputs. Such circuits can be represented by

1764-497: A single, general-purpose always block to model different types of hardware structures, each of SystemVerilog's new blocks is intended to model a specific type of hardware, by imposing semantic restrictions to ensure that hardware described by the blocks matches the intended usage of the model. An HDL compiler or verification program can take extra steps to ensure that only the intended type of behavior occurs. An always_comb block models combinational logic . The simulator infers

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1848-426: A suite of debug tools. These allow the user to stop and restart the simulation at any time, insert simulator breakpoints (independent of the HDL code), and monitor or modify any element in the HDL model hierarchy. Modern simulators can also link the HDL environment to user-compiled libraries, through a defined PLI / VHPI interface. Linking is system-dependent ( x86 , SPARC etc. running Windows / Linux / Solaris ), as

1932-571: A union are currently in use. The packed attribute causes the structure or union to be mapped 1:1 onto a packed array of bits. The contents of struct data types occupy a continuous block of memory with no gaps, similar to bitfields in C and C++: As shown in this example, SystemVerilog also supports typedefs , as in C and C++. SystemVerilog introduces three new procedural blocks intended to model hardware : always_comb (to model combinational logic ), always_ff (for flip-flops ), and always_latch (for latches ). Whereas Verilog used

2016-458: A variable will take on all possible values once before any value is repeated. Variables without modifiers are not randomized. In this example, the fcs field is not randomized; in practice it will be computed with a CRC generator, and the fcs_corrupt field used to corrupt it to inject FCS errors. The two constraints shown are applicable to conforming Ethernet frames . Constraints may be selectively enabled; this feature would be required in

2100-432: Is a textual description consisting of expressions, statements and control structures. One important difference between most programming languages and HDLs is that HDLs explicitly include the notion of time. HDLs form an integral part of electronic design automation (EDA) systems, especially for complex circuits, such as application-specific integrated circuits , microprocessors , and programmable logic devices . Due to

2184-442: Is a variable-width two-state type that works much like logic . Two-state types lack the X and Z metavalues of classical Verilog; working with these types may result in faster simulation. Structures and unions work much like they do in the C programming language . SystemVerilog enhancements include the packed attribute and the tagged attribute. The tagged attribute allows runtime tracking of which member(s) of

2268-412: Is called by the user for randomization of the class variables. The pre_randomize method is called by the randomize method before the randomization and the post_randomize method is called by the randomize method after randomization. The constraint_mode() and the random_mode() methods are used to control the randomization. constraint_mode() is used to turn a specific constraint on and off and the random_mode

2352-461: Is certainly possible to represent hardware semantics using traditional programming languages such as C++ , which operate on control flow semantics as opposed to data flow , although to function as such, programs must be augmented with extensive and unwieldy class libraries . Generally, however, software programming languages do not include any capability for explicitly expressing time, and thus cannot function as hardware description languages. Before

2436-405: Is commonly called SystemVerilog Assertion or SVA. SystemVerilog assertions are built from sequences and properties . Properties are a superset of sequences; any sequence may be used as if it were a property, although this is not typically useful. Sequences consist of boolean expressions augmented with temporal operators . The simplest temporal operator is the ## operator which performs

2520-432: Is growing desire in the industry for a single language that can perform some tasks of both hardware design and software programming. SystemC is an example of such— embedded system hardware can be modeled as non-detailed architectural blocks ( black boxes with modeled signal inputs and output drivers). The target application is written in C or C++ and natively compiled for the host-development system; as opposed to targeting

2604-527: Is no language facility to explicitly destroy instances created by the new operator . Example: Integer quantities, defined either in a class definition or as stand-alone variables in some lexical scope, can be assigned random values based on a set of constraints. This feature is useful for creating randomized scenarios for verification . Within class definitions, the rand and randc modifiers signal variables that are to undergo randomization. randc specifies permutation -based randomization, where

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2688-442: Is not a hardware register. The names "logic" and "reg" are interchangeable. A signal with more than one driver (such as a tri-state buffer for general-purpose input/output ) needs to be declared a net type such as "wire" so SystemVerilog can resolve the final value. Multidimensional packed arrays unify and extend Verilog's notion of "registers" and "memories": Classical Verilog permitted only one dimension to be declared to

2772-541: Is permitted. Enumerated data types ( enums ) allow numeric quantities to be assigned meaningful names. Variables declared to be of enumerated type cannot be assigned to variables of a different enumerated type without casting . This is not true of parameters, which were the preferred implementation technique for enumerated quantities in Verilog-2005: As shown above, the designer can specify an underlying arithmetic type ( logic [2:0] in this case) which

2856-568: Is still in its infancy, but is expected to become an integral part of the HDL design toolset. An HDL is grossly similar to a software programming language , but there are major differences. Most programming languages are inherently procedural (single-threaded), with limited syntactical and semantic support to handle concurrency . HDLs, on the other hand, resemble concurrent programming languages in their ability to model multiple parallel processes (such as flip-flops and adders ) that automatically execute independently of one another. Any change to

2940-446: Is used to represent the enumeration value. The meta-values X and Z can be used here, possibly to represent illegal states. The built-in function name() returns an ASCII string for the current enumerated value, which is useful in validation and testing. New integer types : SystemVerilog defines byte , shortint , int and longint as two-state signed integral types having 8, 16, 32, and 64 bits respectively. A bit type

3024-447: Is used to turn a randomization of a specific variable on or off. The below code describes and procedurally tests an Ethernet frame : Assertions are useful for verifying properties of a design that manifest themselves after a specific condition or state is reached. SystemVerilog has its own assertion specification language, similar to Property Specification Language . The subset of SystemVerilog language constructs that serves assertion

3108-593: The Catapult C tools from Mentor Graphics , and the Impulse C tools from Impulse Accelerated Technologies. A similar initiative from Intel is the use of Data Parallel C++, related to SYCL , as a high-level synthesis language. Annapolis Micro Systems , Inc.'s CoreFire Design Suite and National Instruments LabVIEW FPGA provide a graphical dataflow approach to high-level design entry and languages such as SystemVerilog , SystemVHDL, and Handel-C seek to accomplish

3192-574: The Data General Eclipse MV/8000 , and commercial need began to grow for a language that could map well to them. By 1983 Data I/O introduced ABEL to fill that need. In 1985, as design shifted to VLSI, Gateway Design Automation introduced Verilog , and Intermetrics released the first completed version of the VHSIC Hardware Description Language ( VHDL ). VHDL was developed at the behest of

3276-537: The United States Department of Defense 's Very High Speed Integrated Circuit Program (VHSIC), and was based on the Ada programming language , and on the experience gained with the earlier development of ISPS. Initially, Verilog and VHDL were used to document and simulate circuit designs already captured and described in another form (such as schematic files). HDL simulation enabled engineers to work at

3360-498: The design space have been explored . A SystemVerilog coverage group creates a database of "bins" that store a histogram of values of an associated variable. Cross-coverage can also be defined, which creates a histogram representing the Cartesian product of multiple variables. Hardware description language A hardware description language enables a precise, formal description of an electronic circuit that allows for

3444-598: The HDL simulator environment, as the early stage of the design is subject to frequent and major circuit changes. An HDL description can also be prototyped and tested in hardware — programmable logic devices are often used for this purpose. Hardware prototyping is comparatively more expensive than HDL simulation, but offers a real-world view of the design. Prototyping is the best way to check interfacing against other hardware devices and hardware prototypes. Even those running on slow FPGAs offer much shorter simulation times than pure HDL simulation. Historically, design verification

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3528-399: The HDL simulator and user libraries are compiled and linked outside the HDL environment. Design verification is often the most time-consuming portion of the design process, due to the disconnect between a device's functional specification , the designer's interpretation of the specification, and the imprecision of the HDL language. The majority of the initial test/debug cycle is conducted in

3612-568: The abstraction level of hardware design in order to reduce the complexity of programming in HDLs, creating a sub-field called high-level synthesis . Companies such as Cadence , Synopsys and Agility Design Solutions are promoting SystemC as a way to combine high-level languages with concurrency models to allow faster design cycles for FPGAs than is possible using traditional HDLs. Approaches based on standard C or C++ (with libraries or other extensions allowing parallel programming) are found in

3696-432: The antecedent. When the antecedent succeeds , the consequent is attempted, and the success of the assertion depends on the success of the consequent. In this example, the consequent won't be attempted until req goes high, after which the property will fail if gnt is not high on the following clock. In addition to assertions, SystemVerilog supports assumptions and coverage of properties. An assumption establishes

3780-428: The automated analysis and simulation of the circuit. It also allows for the synthesis of an HDL description into a netlist (a specification of physical electronic components and how they are connected together), which can then be placed and routed to produce the set of masks used to create an integrated circuit . A hardware description language looks much like a programming language such as C or ALGOL ; it

3864-428: The code is synthesized. In industry parlance, HDL design generally ends at the synthesis stage. Once the synthesis tool has mapped the HDL description into a gate netlist, the netlist is passed off to the back-end stage. Depending on the physical technology ( FPGA , ASIC gate array , ASIC standard cell ), HDLs may or may not play a significant role in the back-end flow. In general, as the design flow progresses toward

3948-486: The collection of statistics based on sampling events within the simulation. Coverage is used to determine when the device under test (DUT) has been exposed to a sufficient variety of stimuli that there is a high confidence that the DUT is functioning correctly. Note that this differs from code coverage which instruments the design code to ensure that all lines of code in the design have been executed. Functional coverage ensures that all desired corner and edge cases in

4032-411: The creation of extensible, flexible test benches . The string data type represents a variable-length text string . For example: In addition to the static array used in design, SystemVerilog offers dynamic arrays , associative arrays and queues : A dynamic array works much like an unpacked array, but offers the advantage of being dynamically allocated at runtime (as shown above.) Whereas

4116-433: The design's intended function (specification) against the code implementation in the HDL description. It also permits architectural exploration. The engineer can experiment with design choices by writing multiple variations of a base design, then comparing their behavior in simulation. Thus, simulation is critical for successful HDL design. To simulate an HDL model, an engineer writes a top-level simulation environment (called

4200-432: The designer's preference for coding style. The HDL is merely the 'capture language', often beginning with a high-level algorithmic description such as a C++ mathematical model. Designers often use scripting languages such as Perl to automatically generate repetitive circuit structures in the HDL language. Special text editors offer features for automatic indentation, syntax-dependent coloration, and macro -based expansion of

4284-527: The donation of the Superlog language to Accellera in 2002 by the startup company Co-Design Automation. The bulk of the verification functionality is based on the OpenVera language donated by Synopsys . In 2005, SystemVerilog was adopted as IEEE Standard 1800-2005. In 2009, the standard was merged with the base Verilog (IEEE 1364-2005) standard, creating IEEE Standard 1800-2009. The SystemVerilog standard

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4368-623: The embedded CPU, which requires host-simulation of the embedded CPU or an emulated CPU. The high level of abstraction of SystemC models is well suited to early architecture exploration , as architectural modifications can be easily evaluated with little concern for signal-level implementation issues. However, the threading model used in SystemC relies on shared memory , causing the language not to handle parallel execution or low-level models well. In their level of abstraction, HDLs have been compared to assembly languages . There are attempts to raise

4452-485: The entity/architecture/signal declaration. The HDL code then undergoes a code review, or auditing. In preparation for synthesis, the HDL description is subject to an array of automated checkers. The checkers report deviations from standardized code guidelines, identify potential ambiguous code constructs before they can cause misinterpretation, and check for common logical coding errors, such as floating ports or shorted outputs. This process aids in resolving errors before

4536-528: The example above to generate corrupt frames. Constraints may be arbitrarily complex, involving interrelationships among variables, implications, and iteration. The SystemVerilog constraint solver is required to find a solution if one exists, but makes no guarantees as to the time it will require to do so as this is in general an NP-hard problem ( boolean satisfiability ). In each SystemVerilog class there are 3 predefined methods for randomization: pre_randomize, randomize and post_randomize. The randomize method

4620-627: The exploding complexity of digital electronic circuits since the 1970s (see Moore's law ), circuit designers needed digital logic descriptions to be performed at a high level without being tied to a specific electronic technology, such as ECL , TTL or CMOS . HDLs were created to implement register-transfer level abstraction, a model of the data flow and timing of a circuit. There are two major hardware description languages: VHDL and Verilog . There are different types of description in them: "dataflow, behavioral and structural". Example of dataflow of VHDL: HDLs are standard text-based expressions of

4704-411: The function output does not matter. An input that is known never to occur is a can't-happen term . Both these types of conditions are treated the same way in logic design and may be referred to collectively as don't-care conditions for brevity. The designer of a logic circuit to implement the function need not care about such inputs, but can choose the circuit's output arbitrarily, usually such that

4788-425: The introduction of System Verilog in 2002, C++ integration with a logic simulator was one of the few ways to use object-oriented programming in hardware verification. System Verilog is the first major HDL to offer object orientation and garbage collection. Using the proper subset of hardware description language, a program called a synthesizer, or logic synthesis tool , can infer hardware logic operations from

4872-653: The introduction of DEC's PDP-16 RT-Level Modules (RTMs) and a book describing their use. At least two implementations of the basic ISP language (ISPL and ISPS) followed. ISPS was well suited to describe relations between the inputs and the outputs of the design and was quickly adopted by commercial teams at DEC, and by several research teams in the US and among its allies in the North Atlantic Treaty Organization ( NATO ). The RTM products never succeeded commercially and DEC stopped marketing them in

4956-424: The language statements and produce an equivalent netlist of generic hardware primitives to implement the specified behaviour. Synthesizers generally ignore the expression of any timing constructs in the text. Digital logic synthesizers, for example, generally use clock edges as the way to time the circuit, ignoring any timing constructs. The ability to have a synthesizable subset of the language does not itself make

5040-490: The left of the variable name. SystemVerilog permits any number of such "packed" dimensions. A variable of packed array type maps 1:1 onto an integer arithmetic quantity. In the example above, each element of my_pack may be used in expressions as a six-bit integer. The dimensions to the right of the name (32 in this case) are referred to as "unpacked" dimensions. As in Verilog-2001 , any number of unpacked dimensions

5124-510: The mid-1980s, as new methods grew more popular, more so very-large-scale integration (VLSI). Separate work done about 1979 at the University of Kaiserslautern produced a language called KARL ("KAiserslautern Register Transfer Language"), which included design calculus language features supporting VLSI chip floorplanning and structured hardware design. This work was also the basis of KARL's interactive graphic sister language ABL, whose name

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5208-503: The new blocks restrict assignment to a variable by allowing only one source, whereas Verilog's always block permitted assignment from multiple procedural sources. For small designs, the Verilog port compactly describes a module's connectivity with the surrounding environment. But major blocks within a large design hierarchy typically possess port counts in the thousands. SystemVerilog introduces concept of interfaces to both reduce

5292-543: The part of the designer; compared to a traditional schematic layout, synthesized RTL netlists were almost always larger in area and slower in performance . A circuit design from a skilled engineer, using labor-intensive schematic-capture/hand-layout, would almost always outperform its logically-synthesized equivalent, but the productivity advantage held by synthesis soon displaced digital schematic capture to exactly those areas that were problematic for RTL synthesis: extremely high-speed, low-power, or asynchronous circuitry. Within

5376-534: The pictures, the circuit computing the lower left bar of a 7-segment display can be minimized to a b + a c by an appropriate choice of circuit outputs for dcba = 1010…1111 . Write-only registers , as frequently found in older hardware, are often a consequence of don't-care optimizations in the trade-off between functionality and the number of necessary logic gates. Don't-care states can also occur in encoding schemes and communication protocols . "Don't care" may also refer to an unknown value in

5460-461: The power-up state or can be moved only between other can't-happen states in a walled garden of states. This is also called a hardware lockup or soft error . Such states, while nominally can't-happen, are not don't-care, and designers take steps either to ensure that they are really made can't-happen, or else if they do happen, that they create a don't-care alarm indicating an emergency state for error detection , or they are transitory and lead to

5544-425: The process and emphasizing automation, reuse, and validation. Don%27t-care term In digital logic , a don't-care term (abbreviated DC , historically also known as redundancies , irrelevancies , optional entries , invalid combinations , vacuous combinations , forbidden combinations , unused states or logical remainders ) for a function is an input-sequence (a series of bits) for which

5628-416: The process's input automatically triggers an update in the simulator's process stack. Both programming languages and HDLs are processed by a compiler (often called a synthesizer in the HDL case), but with different goals. For HDLs, "compiling" refers to logic synthesis ; the process of transforming the HDL code listing into a physically realizable gate netlist . The netlist output can take any of many forms:

5712-410: The program that executes the testbench — maintains the simulator clock, which is the master reference for all events in the testbench simulation. Events occur only at the instants dictated by the testbench HDL (such as a reset-toggle coded into the testbench), or in reaction (by the model) to stimulus and triggering events. Modern HDL simulators have full-featured graphical user interfaces , complete with

5796-403: The redundancy of port-name declarations between connected modules, as well as group and abstract related signals into a user-declared bundle. An additional concept is modport , which shows the direction of logic connections. Example: The following verification features are typically not synthesizable, meaning they cannot be implemented in hardware based on HDL code. Instead, they assist in

5880-486: The rights to Verilog-XL, the HDL simulator that would become the de facto standard of Verilog simulators for the next decade. The introduction of logic synthesis for HDLs pushed HDLs from the background into the foreground of digital design. Synthesis tools compiled HDL source files (written in a constrained format called RTL) into a manufacturable netlist description in terms of gates and transistors . Writing synthesizable RTL files required practice and discipline on

5964-1016: The same goal, but are aimed at making existing hardware engineers more productive, rather than making FPGAs more accessible to existing software engineers . It is also possible to design hardware modules using MATLAB and Simulink using the MathWorks HDL Coder tool or DSP Builder for Intel FPGAs or Xilinx System Generator (XSG) from Xilinx . The two most widely used and well-supported HDL varieties used in industry are Verilog and VHDL . Several projects exist for defining printed circuit board connectivity using language based, textual-entry methods. Among these, new approaches have emerged that focus on enhancing readability, reusability, and validation. These modern methodologies employ open-source design languages specifically tailored for electronics, adopting declarative markup to specify what circuits should achieve. This shift integrates software development principles into hardware design, streamlining

6048-411: The scope of the variable. Static variables are created at the start of the program's execution and keep the same value during the entire program's lifespan, unless assigned a new value during execution. Any variable that is declared inside a task or function without specifying type will be considered automatic. To specify that a variable is static place the " static " keyword in the declaration before

6132-461: The sensitivity list to be all variables from the contained statements: An always_latch block models level-sensitive latches. Again, the sensitivity list is inferred from the code: An always_ff block models synchronous logic (especially edge-sensitive sequential logic ): Electronic design automation (EDA) tools can verify the design's intent by checking that the hardware model does not violate any block usage semantics. For example,

6216-519: The simplest, smallest, fastest or cheapest circuit results ( minimization ) or the power-consumption is minimized. Don't-care terms are important to consider in minimizing logic circuit design, including graphical methods like Karnaugh–Veitch maps and algebraic methods such as the Quine–McCluskey algorithm . In 1958, Seymour Ginsburg proved that minimization of states of a finite-state machine with don't-care conditions does not necessarily yield

6300-415: The solution space. The assertions do not model circuit activity, but capture and document the designer's intent in the HDL code. In a simulation environment, the simulator evaluates all specified assertions, reporting the location and severity of any violations. In a synthesis environment, the synthesis tool usually operates with the policy of halting synthesis upon any violation. Assertion based verification

6384-419: The structure of electronic systems and their behaviour over time. Like concurrent programming languages, HDL syntax and semantics include explicit notations for expressing concurrency . However, in contrast to most software programming languages , HDLs also include an explicit notion of time, which is a primary attribute of hardware. Languages whose only characteristic is to express circuit connectivity between

6468-455: The target microprocessor. As HDLs and programming languages borrow concepts and features from each other, the boundary between them is becoming less distinct. However, pure HDLs are unsuitable for general purpose application software development, just as general-purpose programming languages are undesirable for modeling hardware. Yet as electronic systems grow increasingly complex, and reconfigurable systems become increasingly common, there

6552-443: The type, e.g., " static int x; ". The " automatic " keyword is used in the same way. Enhanced variable types add new capability to Verilog's "reg" type: Verilog-1995 and -2001 limit reg variables to behavioral statements such as RTL code . SystemVerilog extends the reg type so it can be driven by a single driver such as gate or module. SystemVerilog names this type "logic" to remind users that it has this extra capability and

6636-527: The underlying semantics of the language statements and simulate the progress of time provides the hardware designer with the ability to model a piece of hardware before it is created physically. It is this executability that gives HDLs the illusion of being programming languages , when they are more precisely classified as specification languages or modeling languages . Simulators capable of supporting discrete-event (digital) and continuous-time (analog) modeling exist, and HDLs targeted for each are available. It

6720-409: The use of so-called "interface classes" (identical in concept to the interface feature of Java). Classes can be parameterized by type , providing the basic function of C++ templates . However, template specialization and function templates are not supported. SystemVerilog's polymorphism features are similar to those of C++: the programmer may specifically write a virtual function to have

6804-431: The years, much effort has been invested in improving HDLs. The latest iteration of Verilog, formally known as IEEE 1800-2005 SystemVerilog, introduces many new features (classes, random variables, and properties/assertions) to address the growing need for better test bench randomization, design hierarchy, and reuse. A future revision of VHDL is also in development , and is expected to match SystemVerilog's improvements. As

6888-533: Was a laborious, repetitive loop of writing and running simulation test cases against the design under test. As chip designs have grown larger and more complex, the task of design verification has grown to the point where it now dominates the schedule of a design team. Looking for ways to improve design productivity, the electronic design automation industry developed the Property Specification Language . In formal verification terms,

6972-904: Was an initialism for "A Block diagram Language". ABL was implemented in the early 1980s by the Centro Studi e Laboratori Telecomunicazioni ( CSELT ) in Torino, Italy, producing the ABLED graphic VLSI design editor. In the mid-1980s, a VLSI design framework was implemented around KARL and ABL by an international consortium funded by the Commission of the European Union. By the late 1970s, design using programmable logic devices (PLDs) became popular, although these designs were primarily limited to designing finite-state machines . The work at Data General in 1980 used these same devices to design

7056-539: Was subsequently updated in 2012, 2017, and most recently in December 2023. The feature-set of SystemVerilog can be divided into two distinct roles: The remainder of this article discusses the features of SystemVerilog not present in Verilog-2005 . There are two types of data lifetime specified in SystemVerilog: static and automatic . Automatic variables are created the moment program execution comes to

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