YosysHQ/yosys
Oct 2024 – Oct 2025
10 Months active
Languages Used
VerilogC++SystemVerilogMakefileTclYAMLCPython
Technical Skills
hardware description languagetestingverificationDigital DesignFormal VerificationHardware Description Language (HDL)
Jannis Harder
PROFILE
Jannis Harder
Jix contributed to the YosysHQ/yosys repository by engineering features and fixes that advanced formal verification, synthesis, and cross-platform reliability. Over ten months, Jix delivered robust enhancements such as optimized Liberty parsing, improved SVA parsing, and kernel-level bufnorm rewrites, focusing on performance and maintainability. Using C++ and Verilog, Jix refactored core abstractions, streamlined command-line tooling, and strengthened test automation, addressing both backend and API stability. The work included careful handling of hardware description languages, code optimization, and regression testing, resulting in more reliable synthesis flows, faster verification cycles, and improved developer experience across diverse digital design and verification workflows.
Overall Statistics
Feature vs Bugs
68%Features
Repository Contributions
62Total
Bugs
10
Commits
62
Features
21
Lines of code
494,672
Activity Months10
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75 peopleShared Repositories
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Work History
October 2025
2 Commits • 1 Features
Oct 1, 2025October 2025 monthly summary for YosysHQ/yosys focusing on performance optimization and reliable defaults. Key features delivered include an Efficient abc_new pass with bufnorm optimization, and a bug fix for SimPass cycle_width defaults. These changes improved synthesis efficiency by reducing bufnorm helper churn and ensured predictable simulation behavior by restoring the default cycle_width to 10 and clarifying tests. Overall, the work enhanced technology quality, reduced resource usage, and improved test stability, with demonstrated skills in C++ optimization, RTL-aware tuning, regression testing, and clear commit hygiene.
2 Commits • 1 Features
Oct 1, 2025October 2025 monthly summary for YosysHQ/yosys focusing on performance optimization and reliable defaults. Key features delivered include an Efficient abc_new pass with bufnorm optimization, and a bug fix for SimPass cycle_width defaults. These changes improved synthesis efficiency by reducing bufnorm helper churn and ensured predictable simulation behavior by restoring the default cycle_width to 10 and clarifying tests. Overall, the work enhanced technology quality, reduced resource usage, and improved test stability, with demonstrated skills in C++ optimization, RTL-aware tuning, regression testing, and clear commit hygiene.
October 2025
September 2025
31 Commits • 7 Features
Sep 1, 2025September 2025 monthly summary for YosysHQ/yosys focused on delivering robust verification enhancements, improving kernel-level functionality, and stabilizing cross-platform tooling. Highlights include SMTBMC cover-mode skip support, a major RTLIL bufnorm overhaul, and cross-backend integration improvements that collectively raise verification throughput and reliability.
September 2025
31 Commits • 7 Features
Sep 1, 2025September 2025 monthly summary for YosysHQ/yosys focused on delivering robust verification enhancements, improving kernel-level functionality, and stabilizing cross-platform tooling. Highlights include SMTBMC cover-mode skip support, a major RTLIL bufnorm overhaul, and cross-backend integration improvements that collectively raise verification throughput and reliability.
August 2025
5 Commits • 4 Features
Aug 1, 2025August 2025 monthly summary for YosysHQ/yosys focusing on reliability, performance, and developer experience improvements across SVA parsing, edge checking, abstraction controls, kernel port characterization, and CI/CD workflows. Deliverables emphasize business value through faster verification cycles, more precise analysis, and streamlined development pipelines.
5 Commits • 4 Features
Aug 1, 2025August 2025 monthly summary for YosysHQ/yosys focusing on reliability, performance, and developer experience improvements across SVA parsing, edge checking, abstraction controls, kernel port characterization, and CI/CD workflows. Deliverables emphasize business value through faster verification cycles, more precise analysis, and streamlined development pipelines.
August 2025
June 2025
1 Commits • 1 Features
Jun 1, 2025June 2025 monthly summary for YosysHQ/yosys focused on Verilog SVA verification improvements and maintainability. Delivered Verilog SVA Importer enhancement to support the followed-by operator in cover mode, reusing existing implication-operator logic to improve coverage accuracy and compatibility with other SVA implementations. No major bugs fixed this month. Overall impact includes stronger SVA coverage validation, easier downstream verification and synthesis workflows, and improved confidence in cover-mode assertions. Technologies/skills demonstrated include Verilog/SystemVerilog, SVA parsing, code reuse/refactoring, and open-source contribution workflows.
June 2025
1 Commits • 1 Features
Jun 1, 2025June 2025 monthly summary for YosysHQ/yosys focused on Verilog SVA verification improvements and maintainability. Delivered Verilog SVA Importer enhancement to support the followed-by operator in cover mode, reusing existing implication-operator logic to improve coverage accuracy and compatibility with other SVA implementations. No major bugs fixed this month. Overall impact includes stronger SVA coverage validation, easier downstream verification and synthesis workflows, and improved confidence in cover-mode assertions. Technologies/skills demonstrated include Verilog/SystemVerilog, SVA parsing, code reuse/refactoring, and open-source contribution workflows.
May 2025
1 Commits • 1 Features
May 1, 2025May 2025: Key feature delivered in YosysHQ/yosys: Add -move-to-cell option to the -wire rename operation, enabling cells to be named after the wires they drive. This required refactoring of wire naming logic to support multi-dimensional wires and port connections, plus automated tests validating the new option. No major bugs reported this month. Overall impact: improved readability and maintainability of netlists, reduced manual renaming effort, and faster debugging. Technologies demonstrated: code refactoring, command-line tool integration, test automation, and robust handling of multi-dimensional wires and port connections.
1 Commits • 1 Features
May 1, 2025May 2025: Key feature delivered in YosysHQ/yosys: Add -move-to-cell option to the -wire rename operation, enabling cells to be named after the wires they drive. This required refactoring of wire naming logic to support multi-dimensional wires and port connections, plus automated tests validating the new option. No major bugs reported this month. Overall impact: improved readability and maintainability of netlists, reduced manual renaming effort, and faster debugging. Technologies demonstrated: code refactoring, command-line tool integration, test automation, and robust handling of multi-dimensional wires and port connections.
May 2025
April 2025
11 Commits • 2 Features
Apr 1, 2025April 2025 performance and stability month for YosysHQ/yosys: Delivered major Liberty parsing enhancements and activation-pattern optimizations, plus a FormalFF memory emission bug fix. These changes improve throughput for large designs, reduce runtime errors, and strengthen the stability of the SAT/sharing flow, with caching enabling faster re-runs and more reliable memory emission under -declockgate.
April 2025
11 Commits • 2 Features
Apr 1, 2025April 2025 performance and stability month for YosysHQ/yosys: Delivered major Liberty parsing enhancements and activation-pattern optimizations, plus a FormalFF memory emission bug fix. These changes improve throughput for large designs, reduce runtime errors, and strengthen the stability of the SAT/sharing flow, with caching enabling faster re-runs and more reliable memory emission under -declockgate.
February 2025
7 Commits • 3 Features
Feb 1, 2025February 2025: Yosys development focusing on RTLIL index handling, abstract command enhancements, and formal verification documentation. Delivered robust wire index conversions, extended abstraction capabilities, and improved verification readiness across the repository.
7 Commits • 3 Features
Feb 1, 2025February 2025: Yosys development focusing on RTLIL index handling, abstract command enhancements, and formal verification documentation. Delivered robust wire index conversions, extended abstraction capabilities, and improved verification readiness across the repository.
February 2025
December 2024
2 Commits
Dec 1, 2024December 2024 monthly summary for YosysHQ/yosys: Focused on stabilizing the Tcl API, improving macOS compatibility, and tightening parameter handling. Consolidated changes reduced cross-platform build friction, improved API correctness, and delivered clearer error messaging, contributing to higher reliability for Tcl-based workflows and easier maintenance.
December 2024
2 Commits
Dec 1, 2024December 2024 monthly summary for YosysHQ/yosys: Focused on stabilizing the Tcl API, improving macOS compatibility, and tightening parameter handling. Consolidated changes reduced cross-platform build friction, improved API correctness, and delivered clearer error messaging, contributing to higher reliability for Tcl-based workflows and easier maintenance.
November 2024
1 Commits • 1 Features
Nov 1, 2024November 2024 monthly summary for repository YosysHQ/yosys focused on delivering a targeted optimization in the formal verification workflow. Delivered a feature that enhances clock gating handling within the FormalFF pass, plus accompanying tests to ensure correctness and regression safety.
1 Commits • 1 Features
Nov 1, 2024November 2024 monthly summary for repository YosysHQ/yosys focused on delivering a targeted optimization in the formal verification workflow. Delivered a feature that enhances clock gating handling within the FormalFF pass, plus accompanying tests to ensure correctness and regression safety.
November 2024
October 2024
1 Commits • 1 Features
Oct 1, 2024Month 2024-10: Focused on strengthening test coverage for critical extraction functionality in YosysHQ/yosys, delivering a dedicated test case for extract_fa and validating gcd-related behavior during synthesis and verification. This work improves reliability of the synthesis pipeline, enables faster regression feedback, and provides a solid base for future coverage expansion.
October 2024
1 Commits • 1 Features
Oct 1, 2024Month 2024-10: Focused on strengthening test coverage for critical extraction functionality in YosysHQ/yosys, delivering a dedicated test case for extract_fa and validating gcd-related behavior during synthesis and verification. This work improves reliability of the synthesis pipeline, enables faster regression feedback, and provides a solid base for future coverage expansion.
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Quality Metrics
Correctness89.6%
Maintainability86.4%
Architecture85.4%
Performance82.8%
AI Usage20.2%
Skills & Technologies
Programming Languages
CC++MakefilePythonShellSystemVerilogTclVerilogYACCYAML
Technical Skills
ABI CompatibilityAPI DevelopmentBackend DevelopmentBufferingBug FixingBuild SystemBuild System ConfigurationBuild SystemsC ProgrammingC++C++ DevelopmentC++ developmentCI/CDCharacter EncodingCode Analysis
Repositories Contributed To
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