Gate-Level Simulation X-Pessimism Reduction via Reconvergent Path Correlation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional gate-level simulators and verification techniques exhibit X-pessimism due to their inability to account for correlations between reconvergent paths, leading to inaccurate propagation of indeterminate values and increased uncertainty in signal values, especially during power-up modeling of complex low-power circuits.
Innovation Solution
The system identifies combinational blocks expected to exhibit X-pessimism and modifies the gate-level design by adding correcting blocks or replicating combinational blocks, assigning concrete values to indeterminate inputs, and using unique free input variables to represent sources of indeterminate values, thereby reducing X-pessimism during simulation and verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gate-level simulators propagate indeterminate values through reconvergent paths, then simulation speed is maintained, but measurement precision of signal values deteriorates due to X-pessimism
Solution Approach 1:
The patent introduces a correlation tracking mechanism as an intermediary between the conventional simulator and the indeterminate value propagation. This mechanism tracks correlations between reconvergent paths and uses this information to adjust propagation behavior, thereby improving measurement precision without fundamentally changing the simulator architecture
Solution Approach 2:
The patent dynamically changes the propagation parameter (whether to propagate X values) based on detected correlations in reconvergent paths. When correlations are detected, the system switches from standard propagation to a modified propagation mode that accounts for the correlations, thus improving accuracy adaptively
2Measurement precision
If gate-level simulation accounts for correlations between reconvergent paths, then measurement precision improves, but device complexity increases due to additional tracking mechanisms
Solution Approach 1:
The patent segments the correlation tracking into modular components: correlation detection modules that identify reconvergent paths, correlation storage structures that record relationships, and propagation adjustment modules that apply the tracking information. This segmentation reduces overall system complexity by making each component independent and manageable
3Reliability
If conventional verification techniques are used, then verification speed is maintained, but reliability of verification results deteriorates due to X-pessimism
Solution Approach 1:
The patent performs preliminary correlation analysis before the main verification process. By pre-identifying and storing correlation information in reconvergent paths, the system prepares the data structures needed for accurate verification in advance, allowing the main verification to proceed at normal speed while benefiting from the pre-computed correlation information
Data Source
AI summary
Methods and apparatuses are described for reducing or eliminating X-pessimism in gate-level simulation and/or formal verification. A system can identify a set of reconvergent inputs of a combinational block in a gate-level design. Next, the system can determine whether or not the combinational block is expected to exhibit X-pessimism during gate-level simulation. If the combinational block is expected to exhibit X-pessimism during gate-level simulation, the system can modify the gate-level design to reduce X-pessimism during gate-level simulation. In some embodiments, the system can build a model for the gate-level design by using unique free input variables to represent sources of indeterminate values. The system can then use the model to perform formal verification.