Hardware description language in the context of Programming code

In computer engineering, logic synthesis is a process by which an abstract specification of desired circuit behavior, typically at register transfer level (RTL), is turned into a design implementation in terms of logic gates, typically by a computer program called a synthesis tool. Common examples of this process include synthesis of designs specified in hardware description languages, including VHDL and Verilog. Some synthesis tools generate bitstreams for programmable logic devices such as PALs or FPGAs, while others target the creation of ASICs. Logic synthesis is one step in circuit design in the electronic design automation, the others are place and route and verification and validation.

In computer science, an abstract machine is a theoretical model that allows for a detailed and precise analysis of how a computer system functions. It is similar to a mathematical function in that it receives inputs and produces outputs based on predefined rules. Abstract machines vary from literal machines in that they are expected to perform correctly and independently of hardware. Abstract machines are "machines" because they allow step-by-step execution of programs; they are "abstract" because they ignore many aspects of actual (hardware) machines. A typical abstract machine consists of a definition in terms of input, output, and the set of allowable operations used to turn the former into the latter. They can be used for purely theoretical reasons as well as models for real-world computer systems. In the theory of computation, abstract machines are often used in thought experiments regarding computability or to analyse the complexity of algorithms. This use of abstract machines is fundamental to the field of computational complexity theory, such as with finite state machines, Mealy machines, push-down automata, and Turing machines.

A field-programmable gate array (FPGA) is a type of configurable integrated circuit that can be repeatedly programmed after manufacturing. FPGAs are a subset of logic devices referred to as programmable logic devices (PLDs). They consist of a grid-connected array of programmable logic blocks that can be configured "in the field" to interconnect with other logic blocks to perform various digital functions. FPGAs are often used in limited (low) quantity production of custom-made products, and in research and development, where the higher cost of individual FPGAs is not as important and where creating and manufacturing a custom circuit would not be feasible. Other applications for FPGAs include the telecommunications, automotive, aerospace, and industrial sectors, which benefit from their flexibility, high signal processing speed, and parallel processing abilities.

A FPGA configuration is generally written using a hardware description language (HDL) e.g. VHDL, similar to the ones used for application-specific integrated circuits (ASICs). Circuit diagrams were formerly used to write the configuration.

An application-specific integrated circuit (ASIC /ˈeɪsɪk/) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficiency video codec. Application-specific standard product chips are intermediate between ASICs and industry standard integrated circuits like the 7400 series or the 4000 series. ASIC chips are typically fabricated using metal–oxide–semiconductor (MOS) technology, as MOS integrated circuit chips.

As feature sizes have shrunk and chip design tools improved over the years, the maximum complexity (and hence functionality) possible in an ASIC has grown from 5,000 logic gates to over 100 million. Modern ASICs often include entire microprocessors, memory blocks including ROM, RAM, EEPROM, flash memory and other large building blocks. Such an ASIC is often termed a SoC (system-on-chip). Designers of digital ASICs often use a hardware description language (HDL), such as Verilog or VHDL, to describe the functionality of ASICs.

A computer language is a formal language for humans to communicate with a computer, not a natural language. In earlier days of computing (before the 1980s), the term was used interchangeably with programming language, but today, used primarily for taxonomy, is a broader term that encompasses languages that are not programming in nature. Sub-categories (with possibly contended hierarchical relationships) include:

• Construction
  • Programming – for controlling computer behavior
    • Command – for controlling the tasks of a computer, such as starting programs
    • Query – for querying databases and information systems
    • Transformation – for transforming the text of a formal language into text that meets a specific goal
  • Structural
    • Configuration – for writing configuration files
    • Data exchange – examples: JSON, XML
    • Markup – for annotating a document in a way that is syntactically distinguishable from the text, such as HTML
    • Page description – for describing the appearance of a printed page in a higher level than an actual output bitmap
    • Style sheet – for expressing the presentation of structured documents, such as CSS
• Modeling – for designing systems
  • Architecture description – for describing and representing system architecture
  • Hardware description – for modeling integrated circuits
• Simulation – for simulating
• Specification – for describing what a system should do

In digital circuit design, register-transfer level (RTL) is a design abstraction which models a synchronous digital circuit in terms of the flow of digital signals (data) between hardware registers, and the logical operations performed on those signals.

Register-transfer-level abstraction is used in hardware description languages (HDLs) like Verilog and VHDL to create high-level representations of a circuit, from which lower-level representations and ultimately actual wiring can be derived. Design at the RTL level is typical practice in modern digital design.

VHDL (VHSIC Hardware Description Language) is a hardware description language that can model the behavior and structure of digital systems at multiple levels of abstraction, ranging from the system level down to that of logic gates, for design entry, documentation, and verification purposes. The language was developed for the US military VHSIC program in the 1980s, and has been standardized by the Institute of Electrical and Electronics Engineers (IEEE) as IEEE Std 1076; the latest version of which is IEEE Std 1076-2019. To model analog and mixed-signal systems, an IEEE-standardized HDL based on VHDL called VHDL-AMS (officially IEEE 1076.1) has been developed.

Verilog, standardized as IEEE 1364, is a hardware description language (HDL) used to model electronic systems. It is most commonly used in the design and verification of digital circuits, with the highest level of abstraction being at the register-transfer level. It is also used in the verification of analog circuits and mixed-signal circuits, as well as in the design of genetic circuits.

In 2009, the Verilog standard (IEEE 1364-2005) was merged into the SystemVerilog standard, creating IEEE Standard 1800-2009. Since then, Verilog has been officially part of the SystemVerilog language. The current version is IEEE standard 1800-2023.

Open-source hardware (OSH, OSHW) consists of physical artifacts of technology designed and offered by the open-design movement. Both free and open-source software (FOSS) and open-source hardware are created by this open-source culture movement and apply a similar concept to a variety of components. It is sometimes, thus, referred to as free and open-source hardware (FOSH), meaning that the design is easily available ("open") and that it can be used, modified and shared freely ("free"). The term usually means that information about the hardware is easily discerned so that others can make it – coupling it closely to the maker movement. Hardware design (i.e. mechanical drawings, schematics, bills of material, PCB layout data, HDL source code and integrated circuit layout data), in addition to the software that drives the hardware, are all released under free/libre terms. The original sharer gains feedback and potentially improvements on the design from the FOSH community. There is now significant evidence that such sharing can drive a high return on investment for the scientific community.

It is not enough to merely use an open-source license; an open source product or project will follow open source principles, such as modular design and community collaboration.

In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware (typically a system under design) with another piece of hardware, typically a special purpose emulation system. The emulation model is usually based on a hardware description language (e.g. Verilog) source code, which is compiled into the format used by emulation system. The goal is normally debugging and functional verification of the system being designed. Often an emulator is fast enough to be plugged into a working target system in place of a yet-to-be-built chip, so the whole system can be debugged with live data. This is a specific case of in-circuit emulation.

Sometimes hardware emulation can be confused with hardware devices such as expansion cards with hardware processors that assist functions of software emulation, such as older daughterboards with x86 chips to allow x86 OSes to run on motherboards of different processor families.