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76-433: The Verilog-AMS standard was created with the intent of enabling designers of analog and mixed signal systems and integrated circuits to create and use modules that encapsulate high-level behavioral descriptions as well as structural descriptions of systems and components. Verilog-AMS is an industry standard modeling language for mixed signal circuits. It provides both continuous-time and event-driven modeling semantics, and so

152-448: A DAC which is an example for analog processing which is triggered by a digital signal: The ADC model is reading analog signals in the digital blocks: While the language was initially only supported by commercial companies, parts of the behavioural modeling subset, "Verilog-A" was adopted by the transistor-modeling community. The ADMS translator supports it for open-source simulators like Xyce and ngSPICE. A more complete implementation

228-484: A programming language such as C or ALGOL ; it 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

304-475: 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 —

380-405: 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

456-477: A breakthrough device in 1978, the programmable array logic or PAL. The architecture was simpler than that of Signetics' FPLA because it omitted the programmable OR array. This made the parts faster, smaller and cheaper. They were available in 20-pin 300-mil DIP packages, while the FPLAs came in 28-pin 600-mil packages. The PAL Handbook demystified the design process. The PALASM design software (PAL assembler) converted

532-672: A device called an EPROM eraser. Flash memory is non-volatile, retaining its contents even when the power is switched off. It is stored on floating-gate MOSFET memory cells, and can be erased and reprogrammed as required. This makes it useful in PLDs that may be reprogrammed frequently, such as PLDs used in prototypes. Flash memory is a kind of EEPROM that holds information using trapped electric charges similar to EPROM. Consequently, flash memory can hold information for years, but possibly not as many years as EPROM. As of 2005, most CPLDs are electrically programmable and erasable, and non-volatile. This

608-440: A few hundred logic gates. For bigger logic circuits, complex PLDs or CPLDs can be used. These contain the equivalent of several PALs linked by programmable interconnections, all in one integrated circuit . CPLDs can replace thousands, or even hundreds of thousands, of logic gates. Some CPLDs are programmed using a PAL programmer, but this method becomes inconvenient for devices with hundreds of pins. A second method of programming

684-473: 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

760-403: A grid of logic gates , and once stored, the data doesn't change, similar to that of an ordinary gate array. The term field-programmable means the device is programmed by the customer, not the manufacturer. FPGAs and gate arrays are similar but gate arrays can only be configured at the factory during fabrication. FPGAs are usually programmed after being soldered down to the circuit board, in

836-620: 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

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912-435: 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

988-494: 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

1064-478: A manner similar to that of larger CPLDs. In most larger FPGAs, the configuration is volatile and must be re-loaded into the device whenever power is applied or different functionality is required. Configuration is typically stored in a configuration PROM , EEPROM or flash memory. EEPROM versions may be in-system programmable (typically via JTAG ). The difference between FPGAs and CPLDs is that FPGAs are internally based on look-up tables (LUTs), whereas CPLDs form

1140-445: 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

1216-449: A precise, formal description of an electronic circuit that allows for 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

1292-464: 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

1368-450: 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

1444-456: A separate stream of development was happening. This type of device is based on gate array technology and is called the field-programmable gate array (FPGA). Early examples of FPGAs are the 82S100 array, and 82S105 sequencer, by Signetics, introduced in the late 1970s. The 82S100 was an array of AND terms. The 82S105 also had flip-flop functions. (Remark: 82S100 and similar ICs from Signetics have PLA structure, AND-plane + OR-plane.) FPGAs use

1520-426: 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

1596-403: A voltage across a modified area of silicon inside the chip. They are called antifuses because they work in the opposite way to normal fuses, which begin life as connections until they are broken by an electric current. SRAM, or static RAM, is a volatile type of memory, meaning that its contents are lost each time the power is switched off. SRAM-based PLDs therefore have to be programmed every time

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1672-674: Is because they are too small to justify the inconvenience of programming internal SRAM cells every time they start up, and EPROM cells are more expensive due to their ceramic package with a quartz window. Many PAL programming devices accept input in a standard file format, commonly referred to as ' JEDEC files'. They are analogous to software compilers . The languages used as source code for logic compilers are called hardware description languages , or HDLs. PALASM , ABEL and CUPL are frequently used for low-complexity devices, while Verilog and VHDL are popular higher-level description languages for more complex devices. The more limited ABEL

1748-461: 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

1824-432: 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

1900-607: Is now available through OpenVAF. The post-SPICE simulator Gnucap was designed in accordance with the standard document, and its support for Verilog-AMS for both the simulator level and the behavioral modeling is growing. Hardware description language In computer engineering , a hardware description language ( HDL ) is a specialized computer language used to describe the structure and behavior of electronic circuits , usually to design application-specific integrated circuits (ASICs) and to program field-programmable gate arrays (FPGAs). A hardware description language enables

1976-564: Is often used for historical reasons, but for new designs VHDL is more popular, even for low-complexity designs. For modern PLD programming languages, design flows, and tools, see FPGA and reconfigurable computing . A device programmer is used to transfer the Boolean logic pattern into the programmable device. In the early days of programmable logic, every PLD manufacturer also produced a specialized device programmer for its family of logic devices. Later, universal device programmers came onto

2052-486: Is significant because it was the basis for the field programmable logic array produced by Signetics in 1975, the 82S100. ( Intersil actually beat Signetics to market but poor yield doomed their part.) In 1974 GE entered into an agreement with Monolithic Memories (MMI) to develop a mask-programmable logic device incorporating the GE innovations. The device was named programmable associative logic array or PALA. The MMI 5760

2128-425: Is similar to a ROM concept, however a PLA does not provide full decoding of a variable and does not generate all the minterms as in a ROM. PAL devices have arrays of transistor cells arranged in a "fixed-OR, programmable-AND" plane used to implement "sum-of-products" binary logic equations for each of the outputs in terms of the inputs and either synchronous or asynchronous feedback from the outputs. MMI introduced

2204-568: 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

2280-442: Is suitable for analog, digital, and mixed analog/digital circuits. It is particularly well suited for verification of very complex analog, mixed-signal and RF integrated circuits. Verilog and Verilog/AMS are not procedural programming languages, but event-based hardware description languages (HDLs). As such, they provide sophisticated and powerful language features for definition and synchronization of parallel actions and events. On

2356-492: Is to solder the device to its printed circuit board, then feed it with a serial data stream from a personal computer. The CPLD contains a circuit that decodes the data stream and configures the CPLD to perform its specified logic function. Some manufacturers, such as Altera and Atmel (now Microchip) , use JTAG to program CPLDs in-circuit from .JAM files. While PALs were being developed into GALs and CPLDs (all discussed above),

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2432-593: 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

2508-574: 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

2584-537: 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

2660-601: The in-circuit programming technique. Lattice GALs combine CMOS and electrically erasable (E ) floating gate technology for a high-speed, low-power logic device. A similar device called a PEEL (programmable electrically erasable logic) was introduced by the International CMOS Technology (ICT) corporation. Sometimes GAL chips are referred as simple programmable logic device (SPLD), analogous to complex programmable logic device (CPLD) below. PALs and GALs are available only in small sizes, equivalent to

2736-598: 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

2812-399: 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

2888-473: The PAL was the generic array logic device, or GAL, invented by Lattice Semiconductor in 1985. This device has the same logical properties as the PAL but can be erased and reprogrammed. The GAL is very useful in the prototyping stage of a design, when any bugs in the logic can be corrected by reprogramming. GALs are programmed and reprogrammed using a PAL programmer, or, in the case of chips that support it, by using

2964-525: The TMS2000, was programmed by altering the metal layer during the production of the IC. The TMS2000 had up to 17 inputs and 18 outputs with 8 JK flip-flops for memory. TI coined the term programmable logic array for this device. A programmable logic array (PLA) has a programmable AND gate array, which links to a programmable OR gate array, which can then be conditionally complemented to produce an output. A PLA

3040-726: The Verilog-AMS committee was a single language for both analog and digital design, however due to delays in the merger process it remains at Accellera while Verilog evolved into SystemVerilog and went to the IEEE. Verilog/AMS is a superset of the Verilog digital HDL, so all statements in digital domain work as in Verilog (see there for examples). All analog parts work as in Verilog-A . The following code example in Verilog-AMS shows

3116-507: The XC157, a mask-programmed gate array with 12 gates and 30 uncommitted input/output pins. In 1970, Texas Instruments developed a mask-programmable IC based on the IBM read-only associative memory or ROAM. This device, the TMS2000, was programmed by altering the metal layer during the production of the IC. The TMS2000 had up to 17 inputs and 18 outputs with 8 JK flip-flops for memory. TI coined

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3192-568: 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

3268-438: The circuit is switched on. This is usually done automatically by another part of the circuit. An EPROM memory cell is a MOSFET (metal-oxide semiconductor field-effect transistor, or MOS transistor) that can be switched on by trapping an electric charge permanently on its gate electrode. This is done by a PAL programmer. The charge remains for many years and can only be removed by exposing the chip to strong ultraviolet light in

3344-428: 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

3420-433: 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

3496-432: 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

3572-601: The desired function. Compared to fixed logic devices, programmable logic devices simplify the design of complex logic and may offer superior performance. Unlike for microprocessors , programming a PLD changes the connections made between the gates in the device. PLDs can broadly be categorised into, in increasing order of complexity, simple programmable logic devices (SPLDs) , comprising programmable array logic , programmable logic array and generic array logic ; complex programmable logic devices (CPLDs) ; and field-programmable gate arrays (FPGAs) . In 1969, Motorola offered

3648-623: 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

3724-463: The engineers' Boolean equations into the fuse pattern required to program the part. The PAL devices were soon second-sourced by National Semiconductor, Texas Instruments and AMD. After MMI succeeded with the 20-pin PAL parts, AMD introduced the 24-pin 22V10 PAL with additional features. After buying out MMI (1987), AMD spun off a consolidated operation as Vantis , and that business was acquired by Lattice Semiconductor in 1999. An improvement on

3800-485: 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

3876-627: 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

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3952-564: The fixed-function microprocessor takes less space on the chip than a part of the programmable gate array implementing the same processor, leaving more space for the programmable gate array to contain the designer's specialized circuits. A PLD is a combination of a logic device and a memory device. The memory is used to store the pattern that was given to the chip during programming. Most of the methods for storing data in an integrated circuit have been adapted for use in PLDs. These include: Silicon antifuses are connections that are made by applying

4028-425: 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

4104-653: 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

4180-424: 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

4256-464: The logic functions with sea-of-gates (e.g. sum of products ). CPLDs are meant for simpler designs while FPGAs are meant for more complex designs. In general, CPLDs are a good choice for wide combinational logic applications, whereas FPGAs are more suitable for large state machines such as microprocessors . Using the same technology as EPROMs , EPLD s have a quartz window in the package that allows them to be erased on exposure to UV light. Using

4332-510: 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

4408-587: The other hand, many actions defined in HDL program statements can run in parallel (somewhat similar to threads and tasklets in procedural languages, but much more fine-grained). However, Verilog/AMS can be coupled with procedural languages like the ANSI C language using the Verilog Procedural Interface of the simulator, which eases testsuite implementation, and allows interaction with legacy code or testbench equipment. The original intention of

4484-543: 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

4560-491: The process and emphasizing automation, reuse, and validation. Programmable logic device A programmable logic device ( PLD ) is an electronic component used to build reconfigurable digital circuits . Unlike digital logic constructed using discrete logic gates with fixed functions, the function of a PLD is undefined at the time of manufacture. Before the PLD can be used in a circuit it must be programmed to implement

4636-416: 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:

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4712-408: The processor. Designing self-altering systems requires that engineers learn new methods, and that new software tools be developed. PLDs are being sold now that contain a microprocessor with a fixed function (the so-called core ) surrounded by programmable logic. These devices let designers concentrate on adding new features to designs without having to worry about making the microprocessor work. Also,

4788-410: 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

4864-486: 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

4940-1016: 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

5016-450: The same technology as EEPROMs , EEPLDs can be erased electrically. An erasable programmable logic device ( EPLD ) is an integrated circuit that comprises an array of PLDs that do not come pre-connected; the connections are programmed electrically by the user. Most GAL and FPGA devices are examples of EPLDs. These are microprocessor circuits that contain some fixed functions and other functions that can be altered by code running on

5092-415: 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

5168-419: 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

5244-455: 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

5320-416: The term programmable logic array (PLA) for this device. In 1971, General Electric Company (GE) was developing a programmable logic device based on the new programmable read-only memory (PROM) technology. This experimental device improved on IBM's ROAM by allowing multilevel logic. Intel had just introduced the floating-gate UV EPROM so the researcher at GE incorporated that technology. The GE device

5396-527: 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

5472-431: 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

5548-533: 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,

5624-904: 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

5700-407: Was completed in 1976 and could implement multilevel or sequential circuits of over 100 gates. The device was supported by a GE design environment where Boolean equations would be converted to mask patterns for configuring the device. The part was never brought to market. In 1970, Texas Instruments developed a mask-programmable IC based on the IBM read-only associative memory or ROAM. This device,

5776-509: Was the first erasable PLD ever developed, predating the Altera EPLD by over a decade. GE obtained several early patents on programmable logic devices. In 1973 National Semiconductor introduced a mask-programmable PLA device (DM7575) with 14 inputs and 8 outputs with no memory registers. This was more popular than the TI part but the cost of making the metal mask limited its use. The device

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