multiplexer toggle coverage

Technique

Multiplexer toggle coverage is a hardware-fuzzing coverage technique associated with monitoring multiplexer behavior in RTL designs to guide exploration. The available evidence ties the technique to RFUZZ, but also notes practical limits: monitoring multiplexers in complex designs can introduce excessive performance overhead, and RFUZZ-style approaches are described as tightly coupled to Chisel HDL.

First seen 5/28/2026

Last seen 6/8/2026

Evidence 5 chunks

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Overview

Multiplexer toggle coverage is a coverage-guidance technique for hardware fuzzing that centers feedback on multiplexer activity in a design. In the processor-fuzzing literature, multiplexer-focused feedback is motivated by the role of multiplexers and their selection logic in exposing control-state behavior during RTL simulation.

A closely related processor-fuzzing metric, DIFUZZRTL's register coverage, monitors value changes in registers that control multiplexer selection signals. The stated intuition is that values in those registers can represent unique states in the processor finite-state machine (FSM), so guiding a fuzzer with that feedback can help explore additional FSM states.

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NEIGHBORHOOD

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RELATIONSHIPS

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RFUZZ ← implements 90% 2e

RFUZZ uses multiplexer toggle coverage as its hardware coverage metric.

Hardware fuzzing part of → 85% 1e

Multiplexer toggle coverage is a coverage metric used in hardware fuzzing.

RFUZZ ← uses 90% 1e

RFUZZ uses multiplexer toggle coverage for hardware fuzzing.

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RFUZZ IMPLEMENTS Extracted graph relationship

CITATIONS

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[1] DIFUZZRTL-style register coverage monitors value changes in registers that control multiplexer selection signals, with the intuition that such values represent processor FSM states and can guide exploration of additional states. ProcessorFuzz: Processor Fuzzing with Control and

[2] Monitoring multiplexers in complex designs can introduce excessive performance overhead. ProcessorFuzz: Processor Fuzzing with Control and

[3] RFUZZ and related work by Li et al. are described as highly coupled to Chisel HDL, limiting applicability. ProcessorFuzz: Processor Fuzzing with Control and

[4] In processor fuzzing, RTL simulation can be compared with ISA simulation, and a difference in execution output indicates a potential processor bug. ProcessorFuzz: Processor Fuzzing with Control and