Effective use of don't cares requires solving several theoretical and practical problems. The theoretical problems are caused by a need to have all tools in a methology use a consistent semantics of don't cares, so as to guarantee correctness of the final implementation. Several common meanings of don't care will be considered and their respective conditions for design correctness will be derived. Several practical problems involving one kind of don't care, where design correctness can be guaranteed, will be discussed. These practical issues include: specifying don't cares in a language description, deriving them during high-level synthesis, and optimizing logic in their presence. Experimental results showing the impact of don't cares on logic quality are presented.
By: D. Brand, R.A. Bergamaschi and L. Stok
Published in: RC20127 in 1995
LIMITED DISTRIBUTION NOTICE:
This Research Report is available. This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and specific requests. After outside publication, requests should be filled only by reprints or legally obtained copies of the article (e.g., payment of royalties). I have read and understand this notice and am a member of the scientific community outside or inside of IBM seeking a single copy only.
Questions about this service can be mailed to reports@us.ibm.com .