Understanding HDL: The Language of Digital Design

What is HDL?

HDL, namely hardware description language is a specialized computer language. HDL is a specialized programming language designed to facilitate the description of electronic circuits' structure, behaviour, and timing, especially digital logic circuits. HDL plays a crucial role in the development of digital circuits such as processors, motherboards, and CPUs. In addition to aiding in circuit design, HDL also enables the simulation of the circuit and verification of its response. While several HDLs are available, the most commonly used ones are Verilog and VHDL.  

Purpose of HDL

Hardware Description Language (HDL) is a highly versatile and robust methodology for the creation, testing, production, and validation of digital hardware systems. It offers a reliable and efficient means of constructing complex digital circuits and systems, ranging from basic logic gates to advanced microprocessors and application-specific integrated circuits (ASICs). With HDL, one can design and develop intricate digital hardware systems with confidence and precision, ensuring that they meet the highest standards of quality and reliability. Overall, HDL is an essential tool for anyone involved in the design and development of digital hardware systems, be it in a business or academic setting. Design Representation: HDL is a tool for depicting digital hardware designs using text or graphics. It captures the behaviour, structure, and connections of components like logic gates, memory elements, and registers. It helps designers create and communicate designs accurately and efficiently. Simulation and Validation: Hardware designers employ Hardware Description Languages (HDLs) to model and validate their designs prior to physical implementation. To achieve this, they create test benches and apply stimuli to the design to evaluate its functionality, timing, and performance. The process of simulation plays a crucial role in identifying design flaws, and potential issues, and refining the design through iterative improvement. Synthesis and Optimization: Hardware Design often involves the use of Hardware Description Languages (HDLs) in conjunction with synthesis tools. This combination allows for the automatic generation of efficient gate-level representations or netlists. Synthesis is the process of transforming the abstract design into a specific technological implementation, which takes into account various factors such as timing constraints, power requirements, and the target hardware platform. Hardware Implementation: HDL serves as a fundamental basis for designing the physical implementation of a project. It is primarily used as input for various tools such as place-and-route algorithms that ascertain the placement of components on a chip and connection routing. HDL descriptions establish a crucial connection between the design intention and the actual physical realization, making it an indispensable tool for any project. Verification and Debugging: HDLs are instrumental in aiding the development of intricate test benches and verification systems that ensure the accuracy and proper functioning of a design. The debugging functions of HDL tools are crucial as they enable designers to detect and resolve any issues that may arise during the design phase. Documentation and Collaboration: The process of developing hardware designs requires thorough documentation. In this regard, HDL descriptions serve as a crucial tool in representing the design's structure and behaviour in a clear and concise manner. Such documentation facilitates effective collaboration among designers, engineers, and stakeholders, ensuring that the development process runs smoothly and efficiently.  

Types of HDL: Take Verilog and VHDL as An Example

In the realm of Hardware Description Languages (HDLs), there exists a range of options to choose from. However, the two most prominent and widely used HDLs are Verilog and VHDL.

What is Verilog?

Figure 1 Verilog Verilog is a language utilized in digital design to describe the behaviour and structure of electronic systems. This language provides engineers with a means to model, simulate, and verify complex digital circuits before they are physically implemented. Initially developed by Gateway Design Automation in the 1980s and later standardized by IEEE as IEEE 1364, Verilog is now widely recognized as an industry-standard language for digital design and verification. It is supported by a variety of electronic design automation (EDA) tools, which makes it a top pick among hardware designers. Verilog is equipped with an array of features that make the design process more manageable. It supports behavioural modelling, which involves describing the desired functionality of a digital circuit using high-level constructs. The language also enables structural modelling, which allows for smaller modules to be combined into larger designs for increased reusability and scalability. Verilog boasts a comprehensive set of data types and operators, which provide a means for accurately modelling and manipulating data within digital circuits. Additionally, it supports simulation capabilities, which aid in the validation and verification of designs at various levels of abstraction. Verilog's synthesis capabilities permit designers to convert high-level descriptions into a gate-level representation for physical implementation. Furthermore, the language offers features for creating test benches, which enable effective verification and debugging. Overall, Verilog is a powerful and widely adopted language that empowers engineers to efficiently design and verify digital systems, including application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and system-on-chip (SoC) designs. Its various features and capabilities make it an ideal choice for digital design and verification. For more information, please read this article: What is Verilog?: Module, Multiplexer, and Verilog vs. Vhdl  

What is VHDL?

VHDL, also known as VHSIC, is an abbreviation for Very High-speed Integrated Circuit Hardware Description Language. Its primary function is to assist in the development of digital circuits, specifically those of a complicated nature such as Microprocessors and Digital Signal Processors.   Perhaps you're unsure about the distinction between Verilog and VHDL. For your convenience, please read this blog: Verilog vs. VHDL: What are the differences between them  

Designing with HDL

When it comes to designing digital electronic circuits and systems using Hardware Description Language (HDL), taking a systematic approach is crucial. Generally speaking, the process of HDL can be described as follows:

Figure 2 HDL In order to create a digital system, it is imperative to first identify its requirements and specifications. This entails determining the desired functionality, performance benchmarks, and any constraints or limitations that must be taken into account. Subsequently, a high-level architectural design of the system should be developed. This will involve identifying the major components, their interconnections, and the overall structure of the system. Block diagrams or textual descriptions can be utilized to represent the architecture. Once a clear architectural design has been established, the system can be coded using an HDL such as Verilog or VHDL. The HDL constructs should be used to describe the behaviour and structure of the digital components, such as registers, logic gates, and memory elements. It is crucial to adhere to the syntax and guidelines of the chosen HDL. A test bench should be developed in order to simulate and validate the functionality of the HDL design. This will allow any design flaws and corner cases to be identified and will ensure that the design meets the desired requirements. If the design is intended for implementation on specific hardware, synthesis tools should be utilized to convert the HDL description into a gate-level netlist. This process optimizes the design for the target technology, taking into account factors such as area, power, and timing constraints. The physical implementation of the design can then be carried out using the gate-level netlist. This involves activities such as place-and-route, where specific components are mapped to physical locations on the chip, and interconnections are established. Verification at this stage ensures that the physical implementation matches the intended design. Comprehensive testing should then be conducted to validate the functionality, performance, and reliability of the design once implemented. Various test vectors and scenarios should be applied to ensure that the system operates as expected and meets the design requirements. Throughout the design process, it is important to iterate and refine the design based on simulation and testing results. Any issues should be addressed, and the design should be optimized and improved as necessary. Clear and thorough documentation should be maintained throughout the design process. This should include the design specifications, architectural diagrams, HDL code, simulation results, synthesis reports, and any other relevant information. This documentation facilitates collaboration, future reference, and design maintenance. Designers can efficiently create complex digital circuits and systems that meet design requirements while ensuring functionality and reliability by utilizing the power of HDL and following a systematic approach.  

Conclusion

In contemporary digital electronic systems design, Hardware Description Language (HDL) plays a critical role in the creation, modelling, simulation, and execution of intricate circuits. HDL provides a standardized approach that facilitates the early detection of design errors and enables the validation of functionality. Additionally, HDL's flexibility allows for the synthesis of gate-level representations, which facilitate physical implementation on different platforms. Furthermore, HDL fosters design reusability, and collaboration, and drives progress in various industries, including electronics, telecommunications, and aerospace. In essence, HDL ensures the development of efficient and dependable digital circuit designs, making it an essential tool in the advancement of digital technology.