Month: 2025-12. Focused on stabilizing Difftest alignment to support a broader set of C++ types and improve code generation reliability. Key deliverables include alignment refinement for Difftest elements to map to supported C++ types, increasing type safety and preventing generation of unsupported signals. This work reduces runtime errors and improves maintainability of the difftest code path. The changes are scoped to OpenXiangShan/difftest and align with the repository’s code-generation roadmap.

May 2025 performance summary for OpenXiangShan development across XiangShan and NEMU. Focused on security/performance enhancements, extension interoperability, and repository alignment with upstream fixes. Implemented Smcsrind extension support with new CSR definitions and refined permission checks, upgraded the rocket-chip submodule for upcoming features, and strengthened privilege checks in the RISC-V emulator, reducing risk of unauthorized access and improving overall reliability.

April 2025 Monthly Summary (OpenXiangShan projects) — Focused on improving trigger accuracy, register validation, and CSR behavior to increase simulation fidelity and hardware validation reliability across riscv-isa-sim and NEMU. Overall, delivered targeted fixes and defensive enhancements that align with the XiangShan CPU constraints (address-based triggers only) and robust performance monitoring, reducing risk of misconfigurations and stabilizing downstream validation workflows.

March 2025 monthly summary for OpenXiangShan/NEMU focused on hardening memory safety around atomic memory operations by implementing safe MMIO validation. This work ensures AMO, load-reserved, and store-conditional instructions execute only within valid physical memory and respect memory protection rules, preventing erroneous access to MMIO regions. The change reduces risk of crashes and undefined behavior, and improves overall emulator correctness and hardware compatibility.

February 2025 monthly summary for OpenXiangShan/NEMU: Delivered Spike Simulator Dependency Upgrade by bumping the Spike submodule in the ready-to-run workflow to a newer commit (72ab2ee31f024705a1dc51b80d05bfa4378a19f3). This upgrade enhances simulation accuracy and stability, enabling more reliable testing, faster iteration cycles, and closer alignment with the latest Spike features. No major bugs fixed this month; focus was on strengthening the test harness and ensuring reproducible results. Overall impact: stronger QA throughput, more reproducible results across local and CI environments, and reduced risk when validating architectural changes. Technologies/skills demonstrated: Git submodule management, external dependency pinning, integration testing with Spike, and cross-repo collaboration.

Monthly summary for 2025-01 focusing on key features, major bugs fixed, business impact, and technologies demonstrated across the XiangShan projects. Highlights include updates to Spike/NEMU references in ready-to-run for improved reliability, new power-management CSRs enabling hardware-level control, and enhanced testing/difftest workflows for better validation parity.

December 2024 monthly summary for OpenXiangShan development efforts focused on strengthening testing fidelity, cross-repo integration, and expanding hardware extension support, all while tightening interrupt/CSR behavior and CI coverage.

November 2024 performance summary for OpenXiangShan platform: delivered foundational correctness improvements, extended ISA extension support, and enhanced observability across NEMU and XiangShan. Upgraded dependencies to align with the NEMU project, consolidated macro definitions for maintainability, and expanded simulation capabilities to accelerate testing of new extensions. These efforts reduce risk, improve compatibility, and boost developer productivity through clearer debugging and validation workflows.

October 2024: Consolidated improvements across the Spike-based simulation stack and NEMU integration to boost stability, compatibility, and verification reliability. Delivered targeted bug fixes and a key submodule upgrade that align spike references with newer toolchains.

September 2024: Delivered targeted fixes and enhancements to OpenXiangShan/riscv-isa-sim to improve correctness, reliability, and maintainability of the RISCV ISA simulator. Focused on crucial control-flow and vector processing paths, with two bug fixes and two feature improvements that reduce risk, streamline maintenance, and enhance vector workflows.

2024-07 monthly summary for OpenXiangShan/riscv-isa-sim focused on FP diff test fidelity and cross-ISA coverage. Delivered targeted features and stability improvements to improve verification reliability, reduce FP-related aborts, and broaden RISC-V ISA coverage. Key outcomes: - Implemented comprehensive FCSR support in Difftest, enabling reading/writing, initialization, and FP state handling (commits include d3439e7bc0139f1da9617668478746f4ffdd7221, 78974f67d42516facc63a584726ff4b3393e00f2, 71092af26c319c8d1fd903e3173f2391fe92e972, b6af90408a5ca344ddf7ea2640110750087ff716, 1186c3010f5395cff130e8810f792619795bcf7f, d9477ffd754afd73774ba3fbb2129108da40c8ee, 4c990a59fc01ac259ea94de0b5cb9ccc629e7c92, d88b7b7c7c579134c0185350f3474c86042af524, 67b5fc1e47d9c1c15084ddc0aea52f48229d122a). - Hardened FCSR writes behind the FP state enable flag (fs) to prevent aborts when fs is Off (commit b28a38bdeedcebebc8483cdd74d637b5040c1db9). - Extended Sdtrig differential testing support with status/register handling, including difftest enablement for Sdtrig CSR components (commits 8803835f052fb3f81e81eb48fd18176feed1f72e, 4b5e4adcb18392c8542a962a249360b18ec9120f, 0042ad7e1d71fb929eb7539c426d644991247898). - Fixed Medeleg unwritable bit when Sdtrig is enabled to ensure correct exception handling (commit edb38c8317d0ac3aa2d2224da74df008af34c69d). - Implemented Difftest trigger/config initialization to align XiangShan CPU with nemu simulator and added ISA strings for ZICNTR and ZIHPM to expand test coverage (commits 2e9148231bf678eb46d5592499dd73c776356692, 215c79fb4ca2f0f0a3b1e4d6074498516fed47ba, 04d11cde25480c47df0297d8623b392345d347ec). Top 3-5 achievements: - FCSR support in Difftest with full read/write mapping and initialization - Safety improvement: FCSR writes gated by FS enable state - Sdtrig difftest extension with status/register handling - Medeleg unwritable bit fix under Sdtrig - Difftest trigger/init configuration and broader ISA coverage Business value: - Improved FP state verification fidelity reduces risk of silent mis-verification, tightening hardware validation loop. - Aligns XiangShan with nemu for more accurate performance and regression testing. - Broader ISA coverage (ZICNTR/ZIHPM) enables more complete validation of the simulator and future releases.