Gain and Pain of a Reliable Delay Model

TL;DR

This paper evaluates the Involution Delay Model (IDM) as a more accurate alternative to inertial delay in digital circuit simulation, demonstrating its close match to analog simulations and revealing inertial delay's shortcomings.

Contribution

It provides an experimental analysis of IDM's behavioral coverage and overhead in complex circuits, supporting its integration into modern simulation tools.

Findings

IDM closely matches analog SPICE simulations.

Inertial delay fails to capture certain malicious behaviors.

IDM offers a viable upgrade for digital timing simulations.

Abstract

State-of-the-art digital circuit design tools almost exclusively rely on pure and inertial delay for timing simulations. While these provide reasonable estimations at very low execution time in the average case, their ability to cover complex signal traces is limited. Research has provided the dynamic Involution Delay Model (IDM) as a promising alternative, which was shown (i) to depict reality more closely and recently (ii) to be compatible with modern simulation suites. In this paper we complement these encouraging results by experimentally exploring the behavioral coverage for more advanced circuits. In detail we apply the IDM to three simple circuits (a combinatorial loop, an SR latch and an adder), interpret the delivered results and evaluate the overhead in realistic settings. Comparisons to digital (inertial delay) and analog (SPICE) simulations reveal, that the IDM delivers very fine-grained results, which match analog simulations very closely. Moreover, severe shortcomings of inertial delay become apparent in our simulations, as it fails to depict a range of malicious behaviors. Overall the Involution Delay Model hence represents a viable upgrade to the available delay models in modern digital timing simulation tools.