Illegal Opcode Injection
ConceptIllegal opcode injection is a constrained-random processor-verification technique in which an instruction-generation model deliberately selects an unassigned opcode value to make an operation illegal, enabling exception-testing scenarios.
First seen 5/28/2026
Last seen 5/29/2026
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Overview
Illegal opcode injection is a stimulus-generation technique used in constrained-random microprocessor verification. The technique deliberately creates an instruction operation with an opcode value that is not assigned by the processor ISA, causing the operation to be illegal so that the processor's exception behavior can be tested.
Modeling approach
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2 connectionsThe opcode class supports an ILLEGAL kind to inject illegal opcodes for exception testing.
Illegal opcode injection is used to trigger and test exception handling in processor verification.
CITATIONS
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[1] Processors support exceptions for conditions such as illegal opcodes and watchpoints. Applying constrained-random verification to microprocessors
[2] The operation/opcode class can add an ILLEGAL operation kind to its enumerated kind property. Applying constrained-random verification to microprocessors
[3] When the operation kind randomizes to ILLEGAL, the generator uses a random unassigned opcode value to make the operation illegal for exception testing. Applying constrained-random verification to microprocessors
[4] Constraint blocks in the instruction model can be independently controlled to obey or violate processor rules and thereby create exception-triggering cases. Applying constrained-random verification to microprocessors