Analogous Alignments: Digital "Formally" meets Analog

TL;DR

This paper presents a novel formal verification approach for mixed-signal IPs, integrating analog behavioral models into digital verification to improve early bug detection and verification efficiency.

Contribution

It introduces 'Analogous Alignments', a method for seamlessly incorporating analog models into formal digital verification setups, addressing compatibility and complexity challenges.

Findings

Successfully verified mixed-signal IPs with early bug detection.

Mitigated state-space explosion using k-induction techniques.

Achieved comprehensive verification within reasonable timeframes.

Abstract

The complexity of modern-day System-on-Chips (SoCs) is continually increasing, and it becomes increasingly challenging to deliver dependable and credible chips in a short time-to-market. Especially, in the case of test chips, where the aim is to study the feasibility of the design, time is a crucial factor. Pre-silicon functional verification is one of the main contributors that makes up a large portion of the product development cycle. Verification engineers often loosely verify test chips that turn out to be non-functional on the silicon, ultimately resulting in expensive re-spins. To left-shift the verification efforts, formal verification is a powerful methodology that aims to exhaustively verify designs, giving better confidence in the overall quality. This paper focuses on the pragmatic formal verification of a mixed signal Intellectual Property (IP) that has a combination of digital and analog blocks. This paper discusses a novel approach of including the analog behavioral model into the formal verification setup. Digital and Analog Mixed-Signal (AMS) designs, which are fundamentally different in nature, are integrated seamlessly in a formal verification setup, a concept that can be referred to as "Analogous Alignments". Our formal setup leverages powerful formal techniques such as FPV, CSR verification, and connectivity checks. The properties used for FPV are auto-generated using a metamodeling framework. The paper also discusses the challenges faced especially related to state-space explosion, non-compatibility of formal with AMS models, and techniques to mitigate them such as k-induction. With this verification approach, we were able to exhaustively verify the design within a reasonable time and with sufficient coverage. We also reported several bugs at an early stage, making the complete design verification process iterative and effective.