I-COR: Instruction-Level Fault Tolerance for Register File in 3-Stage Pipeline RISC-V Processors

Abstract

I-COR is a novel instruction-level fault tolerance mechanism specifically designed to protect the Register File (RF) in simple 3-stage pipeline RISC-V processors. This approach leverages instruction context to selectively introduce redundancy, thereby effectively mitigating soft errors affecting stored register data. The resulting innovation provides high reliability crucial for embedded applications while incurring minimal performance and area overhead compared to traditional full core redundancy methods.

Report

Key Highlights

• I-COR Mechanism: Introduces a specialized instruction-level mechanism named I-COR for achieving high reliability and fault tolerance.
• Target Component: The primary focus of protection is the processor's Register File (RF), which is highly susceptible to transient soft errors and critical for maintaining processor state.
• Architectural Scope: The solution is tailored specifically for resource-constrained 3-Stage Pipeline RISC-V processor architectures, common in deep embedded systems.
• Efficiency Goal: The design prioritizes low overhead, seeking to offer significant reliability improvements without the high area or power costs associated with full hardware redundancy (like Triple Modular Redundancy).
• Error Mitigation: I-COR targets data corruption within the register file caused by single-event upsets (soft errors).

Technical Details

• Instruction-Level Application: Unlike traditional core-level fault tolerance, I-COR applies protection at the granularity of specific instructions, likely those that read or write critical state variables.
• 3-Stage Pipeline Integration: The mechanism is seamlessly integrated into the minimal RISC-V pipeline (typically Instruction Fetch, Decode/Execute, and Write Back).
• Register File Protection: The implementation likely involves adding error correction codes (ECC) or parity bits selectively to register entries, or utilizing instruction duplication/re-execution pathways when critical data is handled.
• Implementation Strategy: To minimize performance impact, the error detection and correction logic must operate efficiently, potentially leveraging unused pipeline slots or minimizing stalls during error handling events.
• RISC-V ISA Context: The design relies on the simplicity and modularity of the RISC-V Instruction Set Architecture (ISA) to efficiently identify and protect critical instruction sequences.

Implications

• Safety-Critical Computing: I-COR significantly enhances the viability of simple, low-power RISC-V cores for safety-critical and high-reliability markets, such as automotive, industrial control, and aerospace embedded systems.
• Cost-Effective Resilience: By implementing fault tolerance at the instruction level rather than requiring full architectural duplication, I-COR lowers the barrier to entry for incorporating resilience into highly constrained designs.
• Expanding RISC-V Adoption: This innovation strengthens the RISC-V ecosystem by providing proven methods for achieving necessary reliability certifications (e.g., ISO 26262), thus accelerating its adoption in areas historically dominated by proprietary or older architectures.
• Pipelined Architecture Optimization: The research provides valuable insights into how fine-grained redundancy can be applied to deeply pipelined processors, offering a template for protecting other critical components in more complex RISC-V designs.