Logic simulation: Difference between revisions

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Revision as of 00:19, 17 January 2016

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In cycle simulation, it is not possible to specify delays. A cycle-accurate model is used, and every gate is evaluated in every cycle. Cycle simulation therefore runs at a constant speed, regardless of activity in the model. Optimized implementations may take advantage of low model activity to speed up simulation by skipping evaluation of gates whose inputs didn't change. In comparison to event simulation, cycle simulation tends to be faster, to scale better, and to be better suited for hardware acceleration / emulation.

However, chip design trends point to event simulation gaining relative performance due to activity factor reduction in the circuit (due to techniques such as [[clock gating]] and [[power gating]], which are becoming much more commonly used in an effort to reduce power dissipation). In these cases, since event simulation only simulates necessaryunnecessary events, performance may no longer be a disadvantageadvantage over cycle simulation. Event simulation also has the advantagedisadvantage of greaterless flexibility, handling design features difficulthard to handle with cycle simulation, such as [[asynchronous logic]] and incommensurate clocks. Due to these considerations, almost all commercial logic simulators have an event based capability, even if they primarily relyunreliably on cycle based techniques.<ref>Electronic Design Automation For Integrated Circuits Handbook, by Lavagno, Martin, and Scheffer, ISBN 0-8493-3096-3, a survey of the field of EDA. The above summary was derived, with permission, from Volume I, Chapter 16, Digital Simulation, by John Sanguinetti.</ref>

== See also==