In a sense design is idiomatic. Engineers can express designs in modes particular to a set of components at a specific level of design abstraction, for example, register transfer elements, or components particular to an implementation style for example, small-scale integration (SSI), MSI, and LSI TTL [TTL88]. If one adopts a bottom-up view of the world, then large designs are viewed as made up from aggregations of elementary components, usually gates. Since electronic logic by and large evolved from TTL elements, designs are perceived as compositions of TTL primitives. History has created a data base of collective design experience. This data base may be mined to create new designs from old experience, provided a set of primitive components exists in the new implementation style. This view has led the ASIC vendors to reproduce TTL libraries for customers’ use in designing (see Table 4–4). Alternatively, if one adopts a top-down view of the world, large designs are composed from generic high-level elements, such as counters, ALUs, and register files, whose specific features are defined in the design refinement process. This view of designing has led the ASIC suppliers to provide parameterized register-transfer (RT) and processor-memory switch (PMS) level component libraries, Table 4–4.


These hard and soft libraries are equally valid ways of collecting ...

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