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Verilator v5.048 removed multi-threaded FST tracing and now reports --trace-threads as DEPRECATED. svsim does not pass -Wno-fatal by default, so with TraceKind.Fst(Some(n)) the Verilator build fails. Only pass --trace-fst for FST tracing. Keep the traceThreads parameter for source and binary compatibility, but deprecate it and document that it is ignored. Add a CommandLineSpec test that checks the generated Verilator arguments no longer contain --trace-threads. Assisted-by: Claude Code:claude-opus-5-5
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Summary
Fixes #5335
Verilator v5.048 removed multi-threaded FST tracing (verilator/verilator#7443) and now reports
--trace-threadsas DEPRECATED. svsim doesn't pass-Wno-fatalby default, so withTraceKind.Fst(Some(n))the Verilator build fails. Hamster5295 reported this and traced it toFst.toCompileFlags. This drops the option, as suggested in the issue, instead of checking the Verilator version.Fstnow only emits--trace-fst.traceThreadsis kept for source and binary compatibility, but it's deprecated and documented as ignored.@deprecatedon the parameter alone trips-Werrorbecause the synthetic case class members read it, soFstalso has@nowarn("cat=deprecation"). ConstructingFst(Some(n))doesn't warn.CommandLineSpectest checks that the generated Verilator arguments contain--trace-fstand no--trace-threads. It fails before this change and passes after.Checked with Verilator 5.048 (conda-forge build) and JDK 21:
ChiselSimSpectest "should dump a FST waveform when traceStyle is Fst and enableWaves is used" already usesFst(Some(2)). Before this change it fails with the same DEPRECATED error as the issue; after it, it passes.svsim.cross[2.13].testandsvsim.cross[3].testpass (the VCS spec is ignored, no VCS here).chisel[2.13].test.compile,unipublish[2.13].mimaReportBinaryIssuesand the svsimcheckFormattasks pass.CI installs oss-cad-suite 2023-06-21, which predates Verilator 5.048, so CI doesn't hit this failure.
Not done here: the issue also suggests having ChiselSim store and print the Verilator version it was tested with when the Verilator call fails, like it does for firtool. That's left out to keep this change small; it could be a follow-up PR.
Release Notes
svsim no longer passes
--trace-threadsto Verilator, which fixes FST tracing withTraceKind.Fst(Some(n))on Verilator v5.048 and newer. ThetraceThreadsparameter ofTraceKind.Fstis deprecated and ignored. Multi-threaded FST writing is no longer requested on older Verilator versions either.Development notes
Assisted-by: Claude Code:claude-opus-5-5