Overview

Chiffre is a hardware instrumentation tool by Eldridge et al. It is described in the Logic Fuzzer implementation context as a tool that can automatically instrument hardware systems written in Chisel by leveraging FIRRTL compiler infrastructure for intermediate-representation traversal and transformation.

Role in Logic Fuzzer integration

In the cited Logic Fuzzer work, the authors note that Logic Fuzzer concepts can be implemented directly in RTL, but that a cleaner integration motivated automatic instrumentation support. They implemented a proof-of-concept flow for the BOOM core in which verification engineers could insert Logic Fuzzer congestors by annotating RTL signals with one line of code per congestor. Chiffre was used to automatically break the annotated signal and insert the congestor between the resulting signal endpoints.

FIRRTL and Chisel dependency

Chiffre's instrumentation approach relies on the FIRRTL compiler, which supports passes over a digital circuit's intermediate representation. The cited work states that Chiffre can only work with hardware descriptions written in Chisel; as a result, the proof-of-concept congestor-insertion experiment was limited to the BOOM core.

Limitations noted in the evidence

The available evidence identifies a language/tooling constraint: Chiffre is limited to Chisel-based hardware descriptions. The Logic Fuzzer authors state that they were applying the same concept using other tools capable of transforming IRs generated from Verilog, implying that Chiffre itself was not the tool used for Verilog-generated IR transformation in that context.