将模拟模块纳入形式化验证,提前发现芯片设计缺陷。
Analogous Alignments: Digital "Formally" meets Analog
- 把模拟行为模型融入形式化验证流程,实现数模混合电路的统一验证。
- 在合理时间内完成全覆盖验证,早期发现多个设计漏洞。
- 解决状态空间爆炸和数模不兼容难题,适合芯片验证工程师参考。
现代系统级芯片(SoC)复杂度持续上升,快速交付可靠芯片面临挑战,尤其在测试芯片中,时间至关重要。预硅功能验证占产品开发周期大半,传统方法常导致芯片无法工作,引发昂贵的重制。为提前验证,形式化验证可全面检查设计,提升可信度。本文聚焦于包含数字与模拟模块的混合信号IP的实用形式化验证,提出将模拟行为模型引入形式化验证框架的新方法。该方法通过元建模自动生成验证属性,结合FPV、CSR验证与连接性检查等技术,有效应对状态空间爆炸、形式化工具与模拟模型不兼容等挑战,采用k-归纳法缓解问题。最终在合理时间内完成全覆盖验证,并早期发现多个错误,使验证过程更具迭代性与有效性。
原文摘要 · Abstract (English)
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.
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