antmicro/verilator
Oct 2024 – Jan 2026
15 Months active
Languages Used
C++PythonSystemVerilogVerilogRST
Technical Skills
AST ManipulationBug FixingBuild SystemsC++C++ DevelopmentCompiler Development
Todd Strader
PROFILE
Todd Strader
Todd Strader contributed to the antmicro/verilator repository, focusing on enhancing simulation reliability, correctness, and performance for Verilog and SystemVerilog workflows. Over 15 months, he delivered features such as scoped random resets, expression coverage analysis, and system function support, while addressing complex bugs in type casting, parameter handling, and wide-width operations. Todd’s work involved deep C++ and Python development, leveraging AST manipulation, regression testing, and compiler optimization techniques. By refining core algorithms and expanding test coverage, he improved standard compliance, determinism, and maintainability, enabling more robust hardware description language simulations and reducing debugging time for downstream users.
Overall Statistics
Feature vs Bugs
41%Features
Repository Contributions
49Total
Bugs
19
Commits
49
Features
13
Lines of code
15,617
Activity Months15
Your Network
75 peopleShared Repositories
75
Zhou ShenMember
Artur BieniekMember
Artur BieniekMember
github actionMember
Aleksander KirykMember
jalcimMember
Thomas AldrianMember
Aliaksei ChapyzhenkaMember
Aleksander KirykMember
Work History
January 2026
2 Commits
Jan 1, 2026January 2026: Verilator stability and correctness improvements focused on simulation timing and type safety. Fixed first-iteration handling by introducing a separate scope and adjusting the evaluation loop to ensure correct initial assignments; improved type assignments for arrays of parameter types in Verilog and added targeted tests validating multiple scenarios. These changes enhance reliability for HDL simulations and downstream tooling, and strengthen regression safety.
2 Commits
Jan 1, 2026January 2026: Verilator stability and correctness improvements focused on simulation timing and type safety. Fixed first-iteration handling by introducing a separate scope and adjusting the evaluation loop to ensure correct initial assignments; improved type assignments for arrays of parameter types in Verilog and added targeted tests validating multiple scenarios. These changes enhance reliability for HDL simulations and downstream tooling, and strengthen regression safety.
January 2026
December 2025
2 Commits • 2 Features
Dec 1, 2025Month: 2025-12. Concise monthly summary focusing on key features delivered, major bugs fixed, overall impact and accomplishments, and technologies/skills demonstrated for antmicro/verilator. The month prioritized performance optimizations and accuracy improvements in tracing and coverage tooling, delivering tangible business value for build speed and quality metrics.
December 2025
2 Commits • 2 Features
Dec 1, 2025Month: 2025-12. Concise monthly summary focusing on key features delivered, major bugs fixed, overall impact and accomplishments, and technologies/skills demonstrated for antmicro/verilator. The month prioritized performance optimizations and accuracy improvements in tracing and coverage tooling, delivering tangible business value for build speed and quality metrics.
November 2025
4 Commits • 1 Features
Nov 1, 2025Month 2025-11: Focused on improving Verilator's correctness, determinism, and robustness. Key features delivered include expression evaluation correctness enhancements with improved coverage analysis distinguishing system vs user-defined functions; major bug fixes to ensure deterministic initialization of Verilator-created variables and to resolve a naming collision with the keyword fdree by using std::free (distinct from system memory deallocation). These changes increase reliability of simulations and reduce runtime issues for downstream users.
4 Commits • 1 Features
Nov 1, 2025Month 2025-11: Focused on improving Verilator's correctness, determinism, and robustness. Key features delivered include expression evaluation correctness enhancements with improved coverage analysis distinguishing system vs user-defined functions; major bug fixes to ensure deterministic initialization of Verilator-created variables and to resolve a naming collision with the keyword fdree by using std::free (distinct from system memory deallocation). These changes increase reliability of simulations and reduce runtime issues for downstream users.
November 2025
October 2025
2 Commits
Oct 1, 2025October 2025 monthly summary for antmicro/verilator: Focus: stabilize Verilator integration and ensure deterministic DFG synthesis; deliver robust tests and maintainable fixes with clear business value. Key features delivered: - Verilator integration fix: correct handling of constant signals in always_ff and proper processing of SenItem node references; regression test added to prevent future regressions. - DFG synthesis determinism fix: replaced unordered_map with a std::map using a custom comparator to order variables by name, ensuring reproducible synthesis results. Major bugs fixed: - Fixed constant-signal handling in always_ff when using Verilator; regression tests added for long-term reliability. - Addressed non-determinism in DFG synthesis by enforcing deterministic symbol order, improving repeatability of synthesis outcomes. Overall impact and accomplishments: - Increased stability and correctness of Verilator integration, reducing time spent diagnosing intermittent failures. - Achieved deterministic DFG synthesis, yielding reproducible build outputs across environments and runs. - Expanded regression coverage, boosting confidence for future changes and releases. Technologies/skills demonstrated: - C++ standard library: strategic replacement of unordered_map with ordered std::map and a custom comparator. - Regression testing and test automation to guard against regressions. - Verilator integration and SystemVerilog constructs (always_ff, SenItem) handling. - Code quality, maintainability, and reproducibility improvements. Business value: - More reliable Verilator-based validation, faster issue diagnosis, and consistent synthesis behavior across CI and developer environments, reducing risk and time-to-market for users.
October 2025
2 Commits
Oct 1, 2025October 2025 monthly summary for antmicro/verilator: Focus: stabilize Verilator integration and ensure deterministic DFG synthesis; deliver robust tests and maintainable fixes with clear business value. Key features delivered: - Verilator integration fix: correct handling of constant signals in always_ff and proper processing of SenItem node references; regression test added to prevent future regressions. - DFG synthesis determinism fix: replaced unordered_map with a std::map using a custom comparator to order variables by name, ensuring reproducible synthesis results. Major bugs fixed: - Fixed constant-signal handling in always_ff when using Verilator; regression tests added for long-term reliability. - Addressed non-determinism in DFG synthesis by enforcing deterministic symbol order, improving repeatability of synthesis outcomes. Overall impact and accomplishments: - Increased stability and correctness of Verilator integration, reducing time spent diagnosing intermittent failures. - Achieved deterministic DFG synthesis, yielding reproducible build outputs across environments and runs. - Expanded regression coverage, boosting confidence for future changes and releases. Technologies/skills demonstrated: - C++ standard library: strategic replacement of unordered_map with ordered std::map and a custom comparator. - Regression testing and test automation to guard against regressions. - Verilator integration and SystemVerilog constructs (always_ff, SenItem) handling. - Code quality, maintainability, and reproducibility improvements. Business value: - More reliable Verilator-based validation, faster issue diagnosis, and consistent synthesis behavior across CI and developer environments, reducing risk and time-to-market for users.
September 2025
1 Commits
Sep 1, 2025September 2025: Delivered enforcement of the IEEE 1800-2023 hierarchical parameter assignment rule in Verilator by introducing a dedicated HIERPARAM error code, updating parameter checking, and aligning tests and documentation with the standard. The change improves standard compliance and error clarity in user workflows.
1 Commits
Sep 1, 2025September 2025: Delivered enforcement of the IEEE 1800-2023 hierarchical parameter assignment rule in Verilator by introducing a dedicated HIERPARAM error code, updating parameter checking, and aligning tests and documentation with the standard. The change improves standard compliance and error clarity in user workflows.
September 2025
August 2025
1 Commits
Aug 1, 2025Concise monthly summary for 2025-08 focusing on business value and technical achievements for the antmicro/verilator project. The primary deliverable this month was a reliability fix for the VPI value-change callbacks, improving simulation stability and reducing flaky test behavior. A regression test was added to prevent regressions and document the behavior.
August 2025
1 Commits
Aug 1, 2025Concise monthly summary for 2025-08 focusing on business value and technical achievements for the antmicro/verilator project. The primary deliverable this month was a reliability fix for the VPI value-change callbacks, improving simulation stability and reducing flaky test behavior. A regression test was added to prevent regressions and document the behavior.
July 2025
2 Commits • 1 Features
Jul 1, 2025July 2025: Focused on correctness and reliability of wide-width operations in Verilator. Delivered critical bug fix for mis-optimization of wide non-blocking assignments, with regression tests ensuring correct value assignments for wide N-B blocks. Improved coverage tracking for wide ternary operations by introducing separate interface instances for sequential, combinational, and assign statements, with updated tests reflecting structural changes. These changes enhance simulation accuracy for wide-width designs and reduce regression risk, supported by strengthened test coverage and clearer separation of contexts. Technologies demonstrated include C++, AST-level analysis, regression testing, and interface specialization.
2 Commits • 1 Features
Jul 1, 2025July 2025: Focused on correctness and reliability of wide-width operations in Verilator. Delivered critical bug fix for mis-optimization of wide non-blocking assignments, with regression tests ensuring correct value assignments for wide N-B blocks. Improved coverage tracking for wide ternary operations by introducing separate interface instances for sequential, combinational, and assign statements, with updated tests reflecting structural changes. These changes enhance simulation accuracy for wide-width designs and reduce regression risk, supported by strengthened test coverage and clearer separation of contexts. Technologies demonstrated include C++, AST-level analysis, regression testing, and interface specialization.
July 2025
June 2025
7 Commits • 3 Features
Jun 1, 2025June 2025 monthly summary for antmicro/verilator: Delivered critical correctness fixes and expanded test coverage, strengthening simulation accuracy and developer experience. Key improvements include major bug fixes in type/casting and parameter handling, improvements to random reset initialization, enhanced test coverage for unsupported features, and updated FPGA initial values documentation. These contributions reduce risk for users validating complex SystemVerilog designs and enable more robust FPGA/ASIC verification workflows.
June 2025
7 Commits • 3 Features
Jun 1, 2025June 2025 monthly summary for antmicro/verilator: Delivered critical correctness fixes and expanded test coverage, strengthening simulation accuracy and developer experience. Key improvements include major bug fixes in type/casting and parameter handling, improvements to random reset initialization, enhanced test coverage for unsupported features, and updated FPGA initial values documentation. These contributions reduce risk for users validating complex SystemVerilog designs and enable more robust FPGA/ASIC verification workflows.
May 2025
7 Commits • 1 Features
May 1, 2025Month: May 2025 — Key features delivered: Scoped random resets and seed generation for Verilator, enabling scoped randomization of signals and MurmurHash64A-based seed with scope and salt for deterministic initialization. Major bugs fixed: Fixes to Verilator type casting and concatenation handling; GCC 10 linker error resolved via constexpr s_threadBoxWidth; Packed arrays handling improvements and fixes with improved type resolution, array cast handling, and parsing deductions. Overall impact: Improved simulation stability, determinism, and Verilator correctness; better compatibility with modern toolchains; expanded regression test coverage (t_concat_casts tests and packed array tests) reducing debugging time. Technologies/skills demonstrated: C++, Verilator internals, test-driven development, regression testing, seed generation using MurmurHash64A, and robust handling of packed arrays and Verilog constructs.
7 Commits • 1 Features
May 1, 2025Month: May 2025 — Key features delivered: Scoped random resets and seed generation for Verilator, enabling scoped randomization of signals and MurmurHash64A-based seed with scope and salt for deterministic initialization. Major bugs fixed: Fixes to Verilator type casting and concatenation handling; GCC 10 linker error resolved via constexpr s_threadBoxWidth; Packed arrays handling improvements and fixes with improved type resolution, array cast handling, and parsing deductions. Overall impact: Improved simulation stability, determinism, and Verilator correctness; better compatibility with modern toolchains; expanded regression test coverage (t_concat_casts tests and packed array tests) reducing debugging time. Technologies/skills demonstrated: C++, Verilator internals, test-driven development, regression testing, seed generation using MurmurHash64A, and robust handling of packed arrays and Verilog constructs.
May 2025
April 2025
1 Commits • 1 Features
Apr 1, 2025April 2025 monthly summary for antmicro/verilator focusing on business value and technical achievements. Delivered feature: Verilog system function support in the V3EmitV emitter, enabling accurate emission of system function calls for $sampled, $rose, $fell, and $stable. Included AST visitor integration and regression test updates. The change is captured in commit 7336b9ebfc391bfa5e612f208d3ab496d8bbf722 (Add V3EmitV support for sampled value functions (#5931)).
April 2025
1 Commits • 1 Features
Apr 1, 2025April 2025 monthly summary for antmicro/verilator focusing on business value and technical achievements. Delivered feature: Verilog system function support in the V3EmitV emitter, enabling accurate emission of system function calls for $sampled, $rose, $fell, and $stable. Included AST visitor integration and regression test updates. The change is captured in commit 7336b9ebfc391bfa5e612f208d3ab496d8bbf722 (Add V3EmitV support for sampled value functions (#5931)).
March 2025
2 Commits • 1 Features
Mar 1, 2025March 2025 monthly summary for antmicro/verilator: delivered improvements to expression coverage, fixed edge-cases around eligibility, and expanded tests to ensure robustness. These changes improved coverage accuracy and reduced miscounts of non-persistent objects, contributing to higher verification confidence and more reliable metrics.
2 Commits • 1 Features
Mar 1, 2025March 2025 monthly summary for antmicro/verilator: delivered improvements to expression coverage, fixed edge-cases around eligibility, and expanded tests to ensure robustness. These changes improved coverage accuracy and reduced miscounts of non-persistent objects, contributing to higher verification confidence and more reliable metrics.
March 2025
February 2025
5 Commits • 2 Features
Feb 1, 2025February 2025 focused on expanding Verilator’s verification capabilities and improving the Verilog emitter. Deliveries include substantial V3EmitV enhancements, the introduction of expression coverage analysis, and targeted bug fixes with regression test updates. These changes strengthen verification coverage, reduce risk in hardware validation, and accelerate QA cycles for Verilator users.
February 2025
5 Commits • 2 Features
Feb 1, 2025February 2025 focused on expanding Verilator’s verification capabilities and improving the Verilog emitter. Deliveries include substantial V3EmitV enhancements, the introduction of expression coverage analysis, and targeted bug fixes with regression test updates. These changes strengthen verification coverage, reduce risk in hardware validation, and accelerate QA cycles for Verilator users.
December 2024
7 Commits • 1 Features
Dec 1, 2024December 2024 monthly summary for antmicro/verilator focusing on core reliability, parameter handling, VPI integration, and test infrastructure. Key features delivered center on Verilator Core Improvements: Parameter Resolution, VPI Handling, Tests, and Documentation, with an emphasis on stabilizing parameter access for imported parameters and arrays, improving VPI name processing, and expanding regression coverage. Notable commits drive these improvements and fixes, including parsing and access fixes and test improvements: fix imported array assignment literals; demonstrate unsupported scoped pattern array init; fix interface bracketed array parameter access; fix VPI + SYMRSVDWORD intersection; execute t_emit_accessors; reduce test_regress VPI copypasta; and documentation updates for SYMRSVDWORD and VPI. Major bugs fixed include: imported array assignment literals, interface bracketed array parameter access, and VPI/SYMRSVDWORD intersection issues, complemented by streamlined test execution and cleanup of test macro duplication. Overall impact: Increased reliability of Verilator’s parameter resolution and VPI behavior, expanded regression test coverage, and clearer, updated documentation. These changes reduce risk for users relying on parameterized imports and VPI interfaces and improve maintainability of the core. Technologies/skills demonstrated: Verilator internals (core), C++/system programming, Verilog/VPI interfaces, regression testing, test macro refactoring, and technical documentation."
7 Commits • 1 Features
Dec 1, 2024December 2024 monthly summary for antmicro/verilator focusing on core reliability, parameter handling, VPI integration, and test infrastructure. Key features delivered center on Verilator Core Improvements: Parameter Resolution, VPI Handling, Tests, and Documentation, with an emphasis on stabilizing parameter access for imported parameters and arrays, improving VPI name processing, and expanding regression coverage. Notable commits drive these improvements and fixes, including parsing and access fixes and test improvements: fix imported array assignment literals; demonstrate unsupported scoped pattern array init; fix interface bracketed array parameter access; fix VPI + SYMRSVDWORD intersection; execute t_emit_accessors; reduce test_regress VPI copypasta; and documentation updates for SYMRSVDWORD and VPI. Major bugs fixed include: imported array assignment literals, interface bracketed array parameter access, and VPI/SYMRSVDWORD intersection issues, complemented by streamlined test execution and cleanup of test macro duplication. Overall impact: Increased reliability of Verilator’s parameter resolution and VPI behavior, expanded regression test coverage, and clearer, updated documentation. These changes reduce risk for users relying on parameterized imports and VPI interfaces and improve maintainability of the core. Technologies/skills demonstrated: Verilator internals (core), C++/system programming, Verilog/VPI interfaces, regression testing, test macro refactoring, and technical documentation."
December 2024
November 2024
1 Commits
Nov 1, 2024Month: 2024-11. Focused on stabilizing Verilator's interface/struct pattern interactions in antmicro/verilator. Delivered a targeted bug fix and regression test to prevent pattern collisions, improving robustness and reliability for downstream users. Implemented additional test coverage to ensure proper instantiation and usage of structs within interfaces. This work enhances model correctness, reduces downstream debugging time, and strengthens maintainability of the Verilator codebase.
November 2024
1 Commits
Nov 1, 2024Month: 2024-11. Focused on stabilizing Verilator's interface/struct pattern interactions in antmicro/verilator. Delivered a targeted bug fix and regression test to prevent pattern collisions, improving robustness and reliability for downstream users. Implemented additional test coverage to ensure proper instantiation and usage of structs within interfaces. This work enhances model correctness, reduces downstream debugging time, and strengthens maintainability of the Verilator codebase.
October 2024
5 Commits
Oct 1, 2024Month: 2024-10 — Focused on stability, correctness, and test coverage in antmicro/verilator. Implemented five critical bug fixes across AST handling, Verilog semantics, and output generation, all with regression tests. Key outcomes: improved safety and non-fatal error handling, robust output grouping, and enhanced enum/name formatting. Technologies demonstrated include C++ core changes, regression testing, and Verilator internals work, contributing to safer simulations and reduced risk in large designs.
5 Commits
Oct 1, 2024Month: 2024-10 — Focused on stability, correctness, and test coverage in antmicro/verilator. Implemented five critical bug fixes across AST handling, Verilog semantics, and output generation, all with regression tests. Key outcomes: improved safety and non-fatal error handling, robust output grouping, and enhanced enum/name formatting. Technologies demonstrated include C++ core changes, regression testing, and Verilator internals work, contributing to safer simulations and reduced risk in large designs.
October 2024
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Quality Metrics
Correctness89.0%
Maintainability84.0%
Architecture82.2%
Performance77.2%
AI Usage20.8%
Skills & Technologies
Programming Languages
C++PythonRSTSystemVerilogVerilog
Technical Skills
AST ManipulationAST TraversalBug FixingBuild SystemsC++C++ DevelopmentC++ developmentCode AnalysisCode CoverageCode GenerationCode RefactoringCompiler DesignCompiler DevelopmentCompiler ErrorsCompiler Optimization
Repositories Contributed To
Overview of all repositories you've contributed to across your timeline