Definition

ISA compliance verification is the architecture-level verification activity that checks whether a CPU implementation is compliant with its Instruction Set Architecture (ISA). In the cited verification-planning context, architecture verification is needed so that software can run seamlessly on the CPU design, and its test plan should cover the ISA-visible behavior of instructions, modes, memory management, interrupts, and other software interfaces. [ISA compliance goal; Architecture-verification scope]

An ISA defines the software-visible features of a CPU, including supported instructions, data types, registers, hardware support for main memory such as virtual memory, memory consistency and addressing modes, and privilege levels. The device that executes the ISA-defined instructions is an implementation of that ISA; the ISA defines how machine code behaves across implementations, enabling binary compatibility despite differing internal designs. [ISA definition and implementation]

Role in CPU verification

ISA compliance verification is part of broader CPU verification. The evidence distinguishes architecture verification from microarchitecture verification and performance verification. Architecture verification focuses on conformance to the ISA, while microarchitecture verification is organized around logical building blocks such as fetch, execution, load/store, and cache units; performance verification focuses on benchmarks and bottlenecks. [CPU verification plan categories]

Because a single CPU test plan is usually insufficient, ISA compliance is typically captured as its own architecture-verification plan. That plan documents both what must be verified and how it will be verified, including stimulus generation, checking mechanisms, and coverage-related properties. [Verification test-plan contents]

Typical verification mechanisms

The evidence describes several mechanisms used in CPU verification that are directly relevant to ISA compliance work:

• simulation-based verification, including constrained-random or coverage-driven approaches;
• selective use of formal verification for specific design areas or special features;
• stimulus infrastructure, randomization controls, sequences, and tests;
• scoreboards, interface assertions, or embedded assertions in RTL or verification components as checking mechanisms;
• coverage properties to assess stimulus quality. [Verification mechanisms]

In the RISC-V CPU-core verification work cited here, the verification environment includes a scoreboard, a Spike instruction-set simulator, and a coverage model, and its experimental evaluation includes an instruction set compliance test, direct tests, benchmarks, and fuzzing. [RISC-V CPU verification components and evaluation]

Relationship to RISC-V compliance testing

For a RISC-V processor, ISA compliance verification includes checking the implementation against RISC-V architectural behavior. The cited RISC-V CPU-core verification work explicitly includes an "Instruction set compliance test" in its experimental evaluation, supporting the relationship between ISA compliance verification and a RISC-V compliance-testing activity. [RISC-V instruction-set compliance testing]