HINT: Toward an Executable Hardware-Intent Representation Layer for LLM-Driven RTL Generation

2026-08-07

AI Summary

This work addresses the challenge that direct generation of high-quality RTL by large language models (LLMs) often degrades due to tight coupling between microarchitectural decisions and low-level code. To overcome this, the paper introduces HINT—an executable hardware intent intermediate representation that explicitly models microarchitecture, enables pre-RTL verification, and formalizes the RTL refinement contract. By integrating behavioral specifications, an executable oracle, and a staged single-agent workflow, HINT reliably produces protocol-rich, hierarchical RTL. The approach successfully generates synthesizable and specification-compliant RTL for seven operators, achieving up to 86.1% area reduction compared to handcrafted designs and C2RTL baselines, and has been effectively deployed in complex systems including AES, SDC, and the Vortex VPU.

Abstract

Generating implementation-quality RTL with large language models (LLMs) remains difficult because direct generation must resolve microarchitecture while simultaneously producing and debugging low-level code. We present HINT, an executable hardware-intent intermediate representation layer between behavioral specifications or executable oracles and RTL. HINT makes RTL-relevant microarchitecture explicit, supports pre-RTL checking, and supplies explicit RTL-lowering obligations. We evaluate HINT using both a minimal single-agent flow and a full staged workflow. Across seven operator cases, the HINT-mediated route, with no post-synthesis QoR refinement, produces contract-compliant synthesizable RTL on 7/7 cases; Direct C2RTL and C2HLSC apply to five cases and succeed on 5/5 and 1/5, respectively. Under matched Design Compiler synthesis, HINT reduces area by 5.0\%--26.2\% relative to five manual RTL implementations and by 8.9\%--86.1\% relative to five accepted Direct C2RTL results. RealBench AES and SDC, together with a Vortex VPU synthesizing to 561.67k~$μ\mathrm{m}^2$, further demonstrate specification-driven, protocol-rich, memory-rich, and hierarchical designs. In the controlled operator study, the HINT-mediated route shows better observed convergence and avoids the severe implementation-quality degradation seen in several direct-generation results.

Problem

• LLM-driven RTL generation
• microarchitecture resolution
• executable hardware-intent
• implementation-quality RTL
• hardware design automation

Innovation

• HINT
• hardware-intent representation
• LLM-driven RTL generation
• microarchitecture explicitness
• pre-RTL verification