Dedicated Digital Processors: Methods in Hardware/Software Co-Design

3

Hardware Design Using VHDL

3.1 HARDWARE DESIGN LANGUAGES

As already noted in section 1.2, circuits composed of building blocks can be understood as a special way to realize algorithms in hardware and be specified by means of the algorithmic notation found in programming languages. For the design of digital systems (and for real-time programming) the timing behavior of the execution of operations is important (see section 1.4), in particular, the timing of the events of changing signal levels. For the purpose of defining digital hardware structures, including their timing, hardware design languages (HDL) have emerged that as well as defining the operations to be performed also specify their timing. A common HDL is VHDL, others are Verilog, ELLA [69], and extended versions of standard languages like C, e.g. System C [70], and Handel-C which goes back to [29].

For a long time, hardware designers drew circuit diagrams (‘schematics’) showing the interconnection of components (gates, registers, processors, etc.), using special shapes or annotations to distinguish the different building blocks. This is adequate for showing the structure of a design, and can be supported by using a graphics editor for schematic entry. It does not cover the specification of the timing behavior as a basis of timing simulations and verification. Algorithms are read more easily from a textual representation, and sometimes a hardware description is only given up to the point of specifying its behavior (the ...