Hardware Description Language - Design Using HDL

Design Using HDL

As 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 state-diagram editor. The process of writing the HDL description is highly dependent on the nature of the circuit and 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 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 dangling ports or shorted outputs. This process aids in resolving errors before 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, this 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 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.