Definition

A Stimulus Graph is a scheduling-control mechanism used by STING, a bare-metal, software-driven test generator for RISC-V. In the provided evidence, STING “uses stimulus graphs to enable user control of the scheduling of both the random and directed tests generated.”

Technical context

Stimulus graphs appear in the context of RISC-V processor verification, where multiple stimulus techniques are needed because random testing and directed testing have complementary strengths and limitations. Random stimuli can explore broad state spaces and expose unanticipated behaviours, but may leave coverage gaps. Directed tests can systematically validate specific ISA features, but may miss subtle corner cases.

Within this combined verification strategy, STING generates both C++-based random streams and ASM-style directed tests. Stimulus graphs provide user-level control over how those generated random and directed tests are scheduled.

Role in STING-based verification

STING includes a programming framework for developing directed tests and can generate constrained-random and directed stimulus. Stimulus graphs are the mechanism identified in the evidence for controlling the scheduling of these generated tests. This makes them part of STING’s approach to combining breadth-oriented random stimulus with precision-oriented directed testing.

Scope of evidence

The provided evidence identifies the purpose of stimulus graphs in STING scheduling control, but does not describe their internal representation, graph semantics, node or edge types, execution algorithm, or syntax.