custom instruction verification

Concept

Custom instruction verification is the verification effort required when adding application-specific instructions to a processor, especially in RISC-V designs. Evidence indicates that custom instructions increase verification scope because teams must re-verify impacted functionality and check for unintended effects on pipeline control, ALU conflicts, cache behavior, load-store paths, SoC integration, workloads, security, power, and performance.

First seen 5/27/2026

Last seen 5/27/2026

Evidence 1 chunks

Wiki v1

WIKI

Overview

Custom instruction verification is the process of validating processor behavior after adding custom instructions or other application-specific features. In RISC-V contexts, custom instructions are attractive because the architecture can be modified for specific applications, but each added feature increases verification effort and complexity. Teams must re-verify affected behavior and ensure the addition does not negatively affect the rest of the design, especially when the change touches pipeline control, ALU conflicts, cache behavior, or load-store paths.

Verification strategy

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CITATIONS

8 sources

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[1] Custom instructions increase verification scope and require re-verification of impacted functionality, especially around pipeline control, ALU conflicts, cache behavior, and load-store paths. RISC-V Microarchitecture Verification Approaches

[2] Formal verification is useful for exhaustively exploring input combinations against ISA-specified behavior, while simulation is needed for full processor modules, SoC integration, and software execution on the device under test. RISC-V Microarchitecture Verification Approaches

[3] Processor teams commonly compare implemented behavior against a reference model, and differences between RTL and the reference require engineering analysis when specifications are not precise. RISC-V Microarchitecture Verification Approaches

[4] Verification is never truly complete; a practical standard is that residual risk is manageable, and coverage alone is insufficient for processor verification. RISC-V Microarchitecture Verification Approaches

[5] Processor verification must consider instruction sequences and dynamic pipeline events, and RISC-V custom instruction work requires understanding microarchitecture, SoC effects, and workloads. RISC-V Microarchitecture Verification Approaches

[6] Virtual prototypes, simulation acceleration, and hardware prototyping are critical validation techniques that can help detect unintended power or performance tradeoffs. RISC-V Microarchitecture Verification Approaches

[7] Security- and safety-sensitive products may require stricter verification, including fault injection and diagnostic coverage analysis such as ISO 26262 functional-safety approaches. RISC-V Microarchitecture Verification Approaches

[8] Running real software workloads for extended periods is a useful heuristic when exhaustive verification is impossible, and real software can expose issues not found by other EDA checks or formal proofs. RISC-V Microarchitecture Verification Approaches