Real Intent's Ascent functional verification product now includes an automated solution to ensure X-robust designs, available through the Ascent Path-Based Verification (PBV) product. Explicit and implicit X sources (X assignments in RTL and non-resettable flops, respectively) in the designs can lead to many challenging issues for design verification, such as masking real design errors and causing RTL-to-netlist simulation mismatches.Depending on coding styles, simulation results can be X-pessimistic, which lead to unnecessary unknown values; or X-optimistic, which result in known values when they should have been unknown. Design and verification teams write properties to trap Xs or instrument two-value simulation with random initialisation to avoid X ambiguity in order to detect design errors. However, these approaches take a considerable amount of manual and computational resources without offering the complete confidence of X robustness.
Ascent PBV offers a multi-faceted solution that addresses the problem through structural and formal analysis, as well as by augmenting simulation using Ascent Simportal. Explicit and implicit X sources are automatically detected. Formal techniques are used to prove X-optimism safe designs. Ascent Simportal can augment simulation to detect X-excitation, control X-pessimism and eliminate X-optimism without loss of efficiency. It is an automatic and comprehensive solution that detects and debugs design errors and RTL/netlist simulation mismatches.
