Constrained-random instruction stream generation (ISG)

Technique

Constrained-random instruction stream generation (ISG) is a hardware design verification technique that automatically generates random instruction sequences under constraints to exercise a processor implementation. It is used alongside the RISC-V International compliance suite and directed tests as part of typical RISC-V processor verification plans, with the Google open-source project riscv-dv being a notable example implementation.

First seen 9/24/2026

Last seen 9/24/2026

Evidence 1 chunks

Wiki v1

WIKI

Constrained-random instruction stream generation (ISG)

Constrained-random instruction stream generation (ISG) is a stimulus-generation technique used in processor hardware design verification (DV). Rather than hand-writing individual test cases, an ISG tool automatically produces streams of instructions whose contents and structure are bounded by user-defined constraints, allowing a verification team to broadly exercise the RTL under test while still keeping the generated sequences within legal and interesting regions of the instruction-set space.

Role in RISC-V processor verification

READ FULL ARTICLE →

NEIGHBORHOOD

No graph connections found for this entity yet. It may appear in future ingestion runs.

explore full graph →

RELATIONSHIPS

3 connections

riscv-dv ← implements 93% 1e

The Google riscv-dv project functions as a constrained-random instruction stream generator for RISC-V verification.

Instruction Stream Generator (ISG) extends → 84% 1e

Constrained-random ISG is presented as a specific form of ISG testing, indicating it is a specialization of the broader ISG technique.

Directed tests compares with → 78% 1e

Both directed tests and constrained-random ISG tests are listed as alternative stimulus inputs used in processor verification plans.

LINKED ENTITIES

3 links

riscv-dv IMPLEMENTS Extracted graph relationship

Instruction Stream Generator (ISG) EXTENDS Extracted graph relationship

Directed tests COMPARES_WITH Extracted graph relationship

CITATIONS

4 sources

4 citations — click to collapse

[1] Typical processor verification plans include rigorous testing of the RTL with comparison to a golden reference model, using a range of stimulus inputs such as the RISC-V International Association Compliance suite, directed tests, and constrained random Instruction Stream Generator (ISG) tests. Imperas Leading RISC-V CPU Reference Model for Hardware Design Verification Selected by Mellanox

[2] An example of a constrained-random ISG for RISC-V is the Google open-source project known as Google RISC-V DV-ISG at https://github.com/google/riscv-dv. Imperas Leading RISC-V CPU Reference Model for Hardware Design Verification Selected by Mellanox

[3] By using the RISC-V reference model in a side-by-side configuration with the target RTL, it is possible to run step-and-compare analysis either interactively or in automated regression tests for continuous integration. Imperas Leading RISC-V CPU Reference Model for Hardware Design Verification Selected by Mellanox

[4] RISC-V as an open ISA permits many configuration and options for processor implementation and microarchitectural features, in addition to extension with custom instructions. Imperas Leading RISC-V CPU Reference Model for Hardware Design Verification Selected by Mellanox