Croc: An End-to-End Open-Source Extensible RISC-V MCU Platform to Democratize Silicon

Abstract

Croc is an end-to-end, free and open-source RISC-V microcontroller platform designed to democratize silicon access and bridge the gap between education and semiconductor innovation. The platform features a streamlined OS synthesis flow built around the extensible CVE2 core (RV32I(EMC)), allowing students to define and implement custom Instruction Set Architecture extensions. Croc's viability is demonstrated by the MLEM tapeout in IHP's 130 nm node and its planned adoption by ETH Zurich for a large-scale curricular VLSI class involving up to 80 students.

Report

Croc: An End-to-End Open-Source Extensible RISC-V MCU Platform

Key Highlights

• Silicon Democratization: Croc is positioned as an end-to-end (silicon to software) free and open-source platform specifically designed to increase the influx of skilled chip designers, supporting goals outlined in various national and international "Chips Acts."
• Educational Focus: The platform is explicitly targeted at hands-on teaching and curriculum development, offering unconstrained access to the design, the design automation tools, and the implementation technology.
• Validated Tapeout: The platform's feasibility was proven by MLEM, a successful tapeout in IHP's open 130 nm node, which was completed in a compressed timeframe of eight weeks by a team of just two students.
• Curricular Adoption: ETH Zurich will utilize Croc in its spring 2025 VLSI class, where approximately 80 students will produce numerous application-specific integrated circuit (ASIC) layouts and complete up to five student-led System-on-Chip (SoC) tapeouts.

Technical Details

• Core Architecture: Croc utilizes the industry-proven, open-source CVE2 core.
• ISA Support: The core implements the RV32I(EMC) instruction set architecture (ISA).
• Extensibility: A major feature is the ability for students to define and implement their own ISA extensions, crucial for custom hardware acceleration and innovation.
• Implementation Flow: The platform provides a streamlined and fully open-source (OS) synthesis and implementation flow.
• Technology Node: The MLEM tapeout was fabricated using IHP's open 130 nm node.
• Open Resources: All associated lecture notes and exercises are made available under a Creative Commons license.

Implications

• Lowering Barriers to Entry: By providing a complete, open-source path from design files to physical silicon (including implementation flow and educational material), Croc significantly lowers the barrier for universities and self-educators to engage in practical VLSI and ASIC design.
• Fostering RISC-V Customization: The extensibility feature encourages deep learning of the RISC-V ISA and promotes practical development of custom application-specific hardware.
• Scalable Education Model: The deployment at ETH Zurich demonstrates a high-throughput educational model capable of training a large number of students in practical chip design and preparing them for real-world tapeout processes.
• Community Growth: Croc contributes a high-quality, proven, open-source MCU platform to the broader hardware architecture ecosystem, fulfilling the promise of RISC-V's open nature for foundational educational tools.