Power Gated Circuit Verification via Compositional Reasoning
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Solution Overview
Problem
The increasing complexity of power gated circuit designs poses challenges in verifying their functionality, particularly in ensuring that power gating does not affect the overall circuit behavior when disabled, and existing methods struggle to efficiently check for sequential and compositional equivalence.
Innovation Solution
A method involving the creation of a power gated circuit version with disabled power gating for sequential equivalence checks and partitioning the circuit into functional blocks for compositional conditional equivalence verification, using circular reasoning to compose individual block equivalences into total circuit equivalence, while employing observers to monitor and ensure minimal assumptions about interface behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power gating is enabled in circuit designs to reduce power consumption, then energy efficiency is improved, but verification complexity increases due to the need to ensure functional equivalence between power-gated and non-power-gated versions
Solution Approach 1:
The verification process is segmented into two independent phases: (1) structural equivalence checking to verify that the power-gated and non-power-gated circuits have identical logic structures, and (2) sequential equivalence checking to verify that the circuits produce identical outputs for all valid input sequences. This segmentation allows each phase to focus on specific aspects of equivalence, reducing overall verification complexity while maintaining power savings through power gating.
2Reliability
If existing verification methods are used to check sequential equivalence in power gated circuits, then verification can be performed, but the process becomes computationally expensive and time-consuming
Solution Approach 1:
The methodology performs preliminary structural equivalence checking before conducting sequential equivalence checking. By first verifying that the logic structures are identical and eliminating structurally different cases, the subsequent sequential equivalence checking operates on a reduced problem space, significantly reducing verification time while maintaining complete accuracy for detecting functional differences.
3Use of energy by moving object
If power gating is implemented in functional blocks, then power consumption is reduced, but ensuring that interface behavior assumptions hold becomes more difficult
Solution Approach 1:
The methodology introduces interface behavior assumptions as intermediary conditions that mediate between the power-gated functional blocks and their interfaces. These assumptions capture the expected behavior of neighboring blocks and are automatically verified as part of the sequential equivalence checking process, making interface behavior verification systematic and automated rather than difficult and manual.
Data Source
AI summary
A novel and useful method of functional verification of power gated designs by compositional reasoning. The method of the present invention performs a sequential equivalence check between the power gated design and a version of itself in which power gating is disabled. A compositional approach is first used to look for conditional equivalence of each functional block of the circuit (and its corresponding functional block with power gating disabled) under a suitable set of assumptions, guaranteed by the neighboring functional blocks. Circular reasoning rules are then employed to compose the conditional equivalences proved on the individual functional blocks back into total equivalence on the whole circuit.