Abstract

To meet stringent automotive safety and security requirements, this work proposes hPMP, an extension to the RISC-V SPMP specification designed for real-time systems. The key innovation enables virtual address redirection for selected memory regions, allowing for easier software development using a large virtual address space. This approach successfully combines the benefits of virtualization flexibility while preserving the fully deterministic behavior essential for real-time microcontrollers.

Report

Analysis Report: Virtual memory for real-time systems using hPMP

Key Highlights

• Novel Memory Protection: The paper introduces hPMP, an extension to the current RISC-V SPMP (Supervisor/Secure Physical Memory Protection) proposal.
• Deterministic Virtualization: The core achievement is enabling address redirection (virtual memory mapping) while maintaining the fully deterministic behavior required by real-time systems, such as automotive microcontrollers.
• Target Market: The innovation is specifically motivated by the stringent safety and security requirements in the automotive sector.
• Hybrid Approach: It seeks to bridge the gap between deterministic, physical address-based protection (MPU) and flexible, virtual address-based protection (MMU).

Technical Details

• Mechanism: hPMP extends RISC-V SPMP by incorporating address redirection capabilities.
• Redirection Scope: Unlike a full MMU, address redirection is only applied to selected address regions, ensuring that the protection logic remains simple and deterministic where required.
• Contrast with MMU: The design avoids the potential non-deterministic overhead typically associated with full Memory Management Units (MMUs) and page table walks.
• Goal: To allow software development to utilize a large virtual address space that is agnostic to the underlying physical address space.

Implications

• RISC-V in Safety-Critical Environments: This development strengthens RISC-V's positioning in high-integrity, safety-critical domains, particularly automotive and industrial control, where determinism is non-negotiable.
• Simplified Software Development: Providing a virtual address space makes software development, integration, and porting easier, especially when dealing with complex system architectures or virtualization layers.
• Hardware Architecture Evolution: hPMP offers a specialized memory protection and mapping primitive for RISC-V that is optimized for hard real-time constraints, potentially accelerating the adoption of RISC-V cores in mixed-criticality systems that cannot tolerate traditional MMU overhead.