SNUG Austin 2014: Handling Windows of Uncertainty - Reducing False Errors from Variable DUT Timing



A common verification challenge is performing transaction level checks during windows of time when signal values are hard to predict. A testbench may generate predicted values too early or too late relative to the design under test, although the design behavior is nevertheless valid. This generates many false errors, increasing the effort to debug regressions and enhance testbench code. While many solutions exist for solving this problem, most have various deficiencies, typically adding leniency in the checking and increasing code complexity.

This paper proposes a generic window handler as a solution to overcome these issues in many practical situations. The window handler encapsulates timing characteristics of the hard-to-model behavior, reducing complexity of the testbench code without sacrificing rigor in transaction checks. When applied to an example design, this technique eliminated many false errors from simulations, allowing more time to find real bugs and quickly achieving error-free regressions.

( Jeff Vance )

September 23, 2014