From Newsgroup: comp.lang.vhdl

David J. A. Koogler wrote in 2019: |--------------------------------------------------------------|
|"John, |
| |
|There is one point in this discussion no has raised yet: There|
|may be several different implementations (bodies) for a given | |specification. |
| |
|In VHDL, a hardware design language which based itself on |
|Ada83 concepts, there is a specification for logic function. |
|The language allows for "architecture behavioral" and |
|"architecture structural" implementations against the | |specification. The "behavioral" implementation defines the |
|defines the behavior of the function as an algorithm (much |
|as you write the function in Ada), while the "structural" | |implementation gives a very precise gate-level or netlist |
|description of the function (how you actually do the function |
|with digital components). I believe there may be a third |
|such "architecture" available to describe an analog |
|(transistor) level description. |
| |
|While Ada does not explicitly provide for parallel | |implementations, you may find many GNAT based projects the |
|use the naming facilities of a GNAT Project File (.gpr) to |
|select different bodies to match certain configurations. |
|For instance, you may want to have one implementation which |
|is a stub and maybe has some tracing statements, and another | |implementation which has the complete algorithm. Another |
|common variation is one implementation for Unix and another |
|for Windows. By using environment variables when launching |
|gprbuild, the user selects which bodies to use. To be |
|complete, you can use the same naming technique for specs |
|as well as bodies. |
| |
|If you look at it in the right way, you can see where Java |
|and Ada interfaces are to do something similar except |
|interfaces allow the user to make a run-time selection not |
|a build-time selection. For my work with small machines, |
|I almost always need just one implementation at run-time |
|so build-time selection is the way I go. |
| |
|Dave Koogler |
|Engineer" | |--------------------------------------------------------------|

VHDL allows as many architectures as an engineer wants for a single specification.
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