A Deep Dive into Integration Methodologies in RISC-V

The integration methodology can significantly affect the performance of dedicated accelerators. This work explores this aspect, considering Keccak, a pivotal hashing standard in Post-Quantum Cryptography (PQC), as a case of study. The paper presents three versions of KRONOS (Keccak RISC-V Optimized eNgine fOr haShing): a loosely coupled memory-mapped accelerator, a tightly coupled approach, and an Instruction Set Extension (ISE). The latter two versions leverage the Core-V eXtension InterFace (CV-X-IF) interface, with and without, respectively, an additional register file to store the Keccak state. Experimental results demonstrate that the tightly coupled integration achieves the highest throughput-to-area ratio (1.070 Mb/(s · LUTs)), outperforming both the loosely coupled (0.937 Mb/(s · LUTs)) and coprocessor-based (0.386 Mb/(s · LUTs)) implementations. This confirms that a tightly integrated accelerator balances resource consumption and performance most effectively.