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Present day designers require deep reasoning methods to analyze circuit
timing. This includes analysis of effects of dynamic behavior (like
glitches) on critical paths, simultaneous switching and identification of
specific patterns and their timings. This paper proposes a novel approach
that uses a combination of symbolic event propagation and temporal
reasoning to extract timing properties of gate-level circuits. The
formulation captures complex situations like trigerring of traditional
false paths and simultaneous switching in a unified symbolic representation
in addition to identifying false paths, critical paths as well as
conditions for such situations. This information is then represented as
an event-time graph. A simple temporal logic on events is proposed that can
be used to formulate a wide class of useful queries for various input
scenarios. These include maximum/minimum delays, transition times,
duration of patterns, etc. An algorithm is developed that retrieves
answers to such queries from the event-time graph. A complete BDD based
implementation of this system has been made. Results on the ISCAS85
benchmarks indicate very interesting properties of these circuits.
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