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This paper introduces a spec-driven approach to hardware evolution that refines new feature requests into executable contracts for RTL version iteration, rather than generating RTL from scratch. By organizing the evolution process into four stages鈥擲pecify, Plan, Implement, and Validate鈥攖he authors leverage contract-centered formulations to ensure that legacy designs can be updated while maintaining their validated behavior. The results from a case study on a TPU datapath block demonstrate the effectiveness of this method in achieving functional convergence under a reviewed contract, highlighting its potential for semantic version evolution in trusted hardware designs.
Executable contracts can transform how we evolve legacy hardware, ensuring validated designs adapt without starting from scratch.
Hardware development is inherently evolutionary: major revisions typically begin by changing intended behavior and then updating a previously validated implementation, rather than regenerating RTL from scratch. Yet most recent LLM-based hardware research still frames the task primarily as prompt-to-RTL generation, offering limited support for semantic version evolution of trusted legacy designs. We present spec-driven hardware evolution, a contract-centered formulation for RTL version iteration. Instead of treating a new feature request as a direct prompt for RTL generation, we refine it into a reviewed executable contract for the next version. This contract specifies what must hold at the externally visible transactional level through a behavior-level reference together with explicit observation and checking semantics, while leaving how the change is realized in RTL to the evolution process. Based on this formulation, we organize hardware evolution into four stages: Specify, Plan, Implement, and Validate. After contract approval, the remaining stages proceed automatically: Plan derives cross-version semantic deltas and localizes affected RTL regions, aided by mutation-based semantic probing; Implement and Validate then perform legacy-aware RTL update under proof-guided checking and iterative repair. We evaluate the framework on a controlled version-evolution case study of a representative TPU datapath block under data-format changes. The results support the feasibility of contract-driven hardware evolution and demonstrate that the proposed backend workflow can effectively drive validated legacy RTL toward next-version functional convergence under a reviewed executable contract. An anonymous artifact for reproducibility is available at https://anonymous.4open.science/r/SDHE-3A6C.
