Overview

Questa X-Check

An undefined signal at a critical control junction in a design, or a register unexpectedly loaded with garbage, can quickly cascade into a perplexing, show-stopping bug. Unfortunately, the handling ‘X’ level signals differ in logic synthesis and simulation.


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An undefined signal at a critical control junction in a design, or a register unexpectedly loaded with garbage, can quickly cascade into a perplexing, show-stopping bug. Unfortunately, the handling ‘X’ level signals differ in logic synthesis and simulation.
Key features

Questa automated X-state verification

The automated Questa X-Check app is designed to automatically employ formal analysis to exhaustively identify ‘X’ propagation issues in your design. Specifically, taking your RTL and a spec of your initialization sequence as input Questa X-Check begins.

Rapidly identify chip-killing X-state issues

X-state verification

An undefined signal at a critical control junction in a design, or a register unexpectedly loaded with garbage, can quickly cascade into a perplexing, show-stopping bug. Unfortunately, the handling ‘X’ level signals differ in logic synthesis and simulation. In the former case, ‘X’ is treated as a “don’t care”; the latter ‘X’ is treated as an “unknown”.

Common X-check verification use cases

Circuit start-up & initialization

  • Verify transition from time 0 to fully up state does not leave ‘X’s that will corrupt critical design elements or states
  • Make sure power-on reset or watchdog circuitry properly reinitialize the whole circuit

Low power-related optimizations

  • Allocate async resets to only the flops that need them

Gate level verification

  • “X unresolved check”–validate the register will land in a predictable logic value in silicon
  • Explain why ‘X’s are suddenly appearing in post-synthesis gate level netlists (due to simulation ‘X’ pessimism)


Formal Verification

Featured white papers

Formal verification

On-demand webinars

View all available Formal Verification video recordings at the Verification Academy.

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Verification Academy

Verification Academy provides the skills necessary to mature an organization's functional verification process capabilities, providing a methodological bridge between high-level value propositions and the low-level details.

Verification Horizons blog

Insight and updates on concepts, values, standards, methodologies, and examples to assist with the understanding of what advanced functional verification technologies can do and how to most effectively apply them.

Verification Horizons

The Verification Horizons publication provides concepts, values, methodologies and examples to assist with the understanding of what advanced functional verification technologies can do and how to most effectively apply them.