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STIMSMITH

InstrGen (Instruction Generator)

Tool WIKI v1 · 5/30/2026

InstrGen is documented here as an instruction-generation tool role for processor verification. The available evidence describes instruction generators that produce long or endless instruction streams, including a static random generator and a Coverage-guided Aging variant used in cross-level processor verification.

Overview

InstrGen (Instruction Generator) is a tool entity associated with the role of an instruction stream generator. In the available evidence, instruction generators are discussed in the context of cross-level processor verification, where the generated workload is treated as an endless instruction stream rather than as isolated test cases. This makes adaptive generation important, because readjustment after each individual run is not available in the same way as it is for finite test cases.

Generator behavior described in the evidence

The evidence contrasts two instruction-generation strategies:

  • A random test generator, described as a re-implementation of an earlier test generator and as already having strong bug-hunting capability.
  • A Coverage-guided Aging test generator, which extends random generation with feedback intended to improve coverage distribution.

The random generator uses a static randomized test strategy that does not change over time. The paper reports that this strategy can favor particular test-state spaces. In a cross-coverage comparison, it produced large peaks for some combinations of instruction groups while other combinations were almost never executed.

By contrast, the Coverage-guided Aging generator produced weaker peaks, executed every instruction-group combination considered in the reported cross coverage, and achieved a more regular coverage distribution. The study reports that Coverage-guided Aging helped close coverage gaps and also exposed an additional micro-architectural bug in an already heavily tested industrial processor.

Use in processor verification

The evaluated setting records how often coverage points are executed, with coverage points defined as a cross product of instruction groups. The experiment also used deterministic random sources initialized with the same cryptographic seed so that instruction generators could be aligned to the same near-future instruction count.

A reported bug involved the execute FIFO of a pipeline no longer receiving further instructions. The issue was triggered because the test-bench adapter emptied the pipeline only when a valid instruction executed; too many invalid instructions in succession could therefore expose the failure.

Relationship to instruction streams

InstrGen implements the concept of an Instruction Stream Generator. The cited evidence supports this role by describing instruction generators operating over an endless instruction stream and comparing strategies for producing instruction sequences during processor verification.

LINKED ENTITIES

1 links
Instruction Stream Generator IMPLEMENTS

CITATIONS

6 sources
6 citations
[1] The available evidence discusses instruction generators in cross-level processor verification, including an endless instruction-stream setting where adjustment over time is important. Cross-Level Processor Verification via
[2] The random generator is described as a re-implementation of a prior test generator with strong bug-hunting capability, but it can favor specific test-state spaces because its randomized strategy is static. Cross-Level Processor Verification via
[3] In the reported cross-coverage results, the random generator produced substantial peaks and gaps across combinations of instruction groups, while Coverage-guided Aging produced a more balanced distribution with all groups visibly executed. Cross-Level Processor Verification via
[4] Coverage points in the study are defined as a cross product of instruction groups, and deterministic random sources initialized with the same cryptographic seed were used to provide the same random sequences. Cross-Level Processor Verification via
[5] The case study reports that Coverage-guided Aging closed gaps, achieved a more regular coverage distribution, and found another intricate micro-architectural bug in an already heavily tested industrial processor. Cross-Level Processor Verification via
[6] The reported bug involved pipeline execute-FIFO behavior and could be triggered when too many invalid instructions occurred in succession because the test-bench adapter emptied the pipeline only after valid instruction execution. Cross-Level Processor Verification via