Meridian RXV —  X-Propagation Sign-Off

Palo Alto Networks' Advanced X-Propagation Sign-Off Methodology

X-Propagation Sign-Off

  • Performs accurate audit of design initialization and provides useful debug capability
  • Provides optimization suggestions for adding resets to improve initialization or for reducing number of resets to improve design efficiency
  • Prevents inaccurate RTL simulation by identifying potential X-optimism

Dangerous X

Design language standards define an X as an “unknown” when simulation cannot definitely resolve a signal value. State-of-the-art low-power designs can have several sources of Xs due to switching between power modes. Xs can increase signal transitions and exceed the design’s power budget.

They can also mask bugs in RTL simulation.

Time consuming synthesis-simulation iterations are required to debug the unknowns. Meridian RXV exposes all X-sources up-front at RTL and helps improve design quality by helping to address X-optimism.

Reset Audit

While hardware resets can be used to initialize registers to known values, resetting every flop or latch is challenging. Additionally, every FF in the design may not even need to be initialized, for example—FFs internal to a pipeline. Reset Audit enables understanding the design initialization requirements and status accurately. Meridian RXV provides information about percentage initialization, whether a particular FF is getting initialized, by what mechanism it is initialized, and if some FFs can avoid needing to be explicitly initialized. Formal analysis provides a refined and accurate analysis, and parallel processing is used to scale the runtime performance of formal analysis.

Reset Optimization

After reviewing reset audit information, designers can choose to optimize the design’s reset scheme further. Reset optimizations in Meridian RXV can determine resets needed to be added to increase design initialization percentage and meet the power budget. Additionally, it can also identify FFs that do not need to be explicitly reset to help reduce routing complexity and power consumption. Meridian RXV performs comprehensive formal analysis with parallel processing to provide the most accurate results while balancing runtime requirements.

X-optimism report

Reset Optimization Report

RTL X-Propagation Analysis


Meridian RXV delivers a comprehensive report that highlights how susceptible a design is to the masking of functional bugs due to X-optimism in RTL simulations. All X-sources in the design are automatically identified through structural analysis as well as X-accurate formal reset analysis. The report shows nets in the design that are sensitive to X-optimism due to the propagation of an X from said X-sources, and provides debug information with links to the source code and a trace from each X-Optimism net to a relevant X-source.

Integrated X-Propagation Graphical Debugger

Meridian RXV provides comprehensive reports for review of reset audit, reset optimization and optimism analysis.

It also comes with a powerful integrated graphical interface that shows debug paths, facilitates waivers of X-sources, and provides links for source code navigation.

X-Propagation debug


  • Identifies all X-sources and X-sensitive constructs that might lead to X-propagation and affect design quality
  • Identifies an optimal number of resets needed to be added to improve design initialization
  • Identifies FFs for which resets can be removed to reduce power and routing
  • Minimizes susceptibility to simulation inaccuracy due to X-optimism at RTL
  • Enables easy graphical debugging with integrated source browser, schematics, and VCDs