mamedev/mame
Oct 2024 – May 2026
5 Months active
Languages Used
C++
Technical Skills
EmulationROM HackingReverse EngineeringC++ DevelopmentDevice emulationLow-level programming
Brian Johnson
PROFILE
Brian Johnson
Worked on the mamedev/mame repository, focusing on enhancing Epson QX-10 emulation through targeted C++ development and low-level programming. Delivered features such as ROM dump integrity verification using CRC and SHA1 checksums, modernized memory layout and banking, and introduced battery-backed semidisk RAM disk support. Addressed hardware accuracy by refining Z80 CPU timing and correcting memory handling bugs, improving both stability and compatibility. Implemented device driver development and error handling to resolve issues with video rendering and hard drive detection. The work emphasized system emulation fidelity, robust memory management, and hardware interaction, resulting in more reliable and accurate emulation environments.
Overall Statistics
Feature vs Bugs
57%Features
Repository Contributions
7Total
Bugs
3
Commits
7
Features
4
Lines of code
641
Activity Months5
Your Network
119 peopleWork History
May 2026
1 Commits • 1 Features
May 1, 2026May 2026 monthly summary for mamedev/mame: Focused on improving Z80 CPU timing accuracy for Epson QX-10 emulation and stabilizing hardware-specific behavior. Implemented an additional wait state in the M1 cycle of the Z80 in the QX-10 system, addressing timing gaps that affected accuracy and compatibility.
1 Commits • 1 Features
May 1, 2026May 2026 monthly summary for mamedev/mame: Focused on improving Z80 CPU timing accuracy for Epson QX-10 emulation and stabilizing hardware-specific behavior. Implemented an additional wait state in the M1 cycle of the Z80 in the QX-10 system, addressing timing gaps that affected accuracy and compatibility.
May 2026
March 2026
2 Commits • 1 Features
Mar 1, 2026March 2026 monthly performance summary for mamedev/mame focusing on business value and technical achievements. Highlights include delivering a semidisk RAM disk for Epson QX enabling battery-backed storage (memory mapping, device definitions, and I/O), and fixing a critical WD1000 hard drive detection bug that caused ID-not-found errors during read/write, improving reliability for QX010 with CR1510 drives. These changes strengthen data integrity, reliability, and emulation fidelity, improving developer and user experience and enabling robust storage options in emulation environments.
March 2026
2 Commits • 1 Features
Mar 1, 2026March 2026 monthly performance summary for mamedev/mame focusing on business value and technical achievements. Highlights include delivering a semidisk RAM disk for Epson QX enabling battery-backed storage (memory mapping, device definitions, and I/O), and fixing a critical WD1000 hard drive detection bug that caused ID-not-found errors during read/write, improving reliability for QX010 with CR1510 drives. These changes strengthen data integrity, reliability, and emulation fidelity, improving developer and user experience and enabling robust storage options in emulation environments.
February 2026
1 Commits • 1 Features
Feb 1, 2026February 2026 — mamedev/mame: Key feature delivery focused on Epson QX-10 emulation memory system modernization. Implemented modern memory layout and banking, VRAM banking for RGB planes, and precise SRAM/ROM mirroring to reflect real hardware. Introduced NVRAM-backed 2K CMOS SRAM persistence and add save-state support via internal state captures. Major bug fix: memory handling issues in epson/qx10.cpp addressed (#14920), improving stability and accuracy. Business impact: higher fidelity QX-10 emulation expands software compatibility and reliability, reducing debugging costs for users and enabling more accurate testing. Technologies demonstrated: C++ memory modeling, banking, VRAM management, NVRAM usage, and save-state integration.
1 Commits • 1 Features
Feb 1, 2026February 2026 — mamedev/mame: Key feature delivery focused on Epson QX-10 emulation memory system modernization. Implemented modern memory layout and banking, VRAM banking for RGB planes, and precise SRAM/ROM mirroring to reflect real hardware. Introduced NVRAM-backed 2K CMOS SRAM persistence and add save-state support via internal state captures. Major bug fix: memory handling issues in epson/qx10.cpp addressed (#14920), improving stability and accuracy. Business impact: higher fidelity QX-10 emulation expands software compatibility and reliability, reducing debugging costs for users and enabling more accurate testing. Technologies demonstrated: C++ memory modeling, banking, VRAM management, NVRAM usage, and save-state integration.
February 2026
November 2024
2 Commits
Nov 1, 2024November 2024 monthly summary for mamedev/mame: Core focus on graphics accuracy and display integrity. Implemented a fix for the Upd7220 video device memory address pitch calculation to correct VRAM read/write pathways, improving rendering accuracy across affected emulated systems. Restored correct QX10 zoom behavior by reverting two commits that disrupted scaling, ensuring visual fidelity for zoomed displays. The fixes reduce rendering artifacts, improve compatibility with software relying on precise memory operations, and preserve hardware-accurate visuals. These efforts contribute to emulator stability and user experience while maintaining robust code health through targeted, well-documented changes.
November 2024
2 Commits
Nov 1, 2024November 2024 monthly summary for mamedev/mame: Core focus on graphics accuracy and display integrity. Implemented a fix for the Upd7220 video device memory address pitch calculation to correct VRAM read/write pathways, improving rendering accuracy across affected emulated systems. Restored correct QX10 zoom behavior by reverting two commits that disrupted scaling, ensuring visual fidelity for zoomed displays. The fixes reduce rendering artifacts, improve compatibility with software relying on precise memory operations, and preserve hardware-accurate visuals. These efforts contribute to emulator stability and user experience while maintaining robust code health through targeted, well-documented changes.
October 2024
1 Commits • 1 Features
Oct 1, 2024Monthly work summary for 2024-10 focusing on business value and technical achievements in mamedev/mame. Highlights include implementing ROM dump integrity verification for Epson QX10 to improve accuracy and reliability of emulation and dumps, along with a concise record of commits and outcomes.
1 Commits • 1 Features
Oct 1, 2024Monthly work summary for 2024-10 focusing on business value and technical achievements in mamedev/mame. Highlights include implementing ROM dump integrity verification for Epson QX10 to improve accuracy and reliability of emulation and dumps, along with a concise record of commits and outcomes.
October 2024
Activity
Loading activity data...
Quality Metrics
Correctness91.4%
Maintainability85.8%
Architecture85.8%
Performance82.8%
AI Usage20.0%
Skills & Technologies
Programming Languages
C++
Technical Skills
C++ DevelopmentC++ developmentC++ programmingDevice emulationEmulationLow-level programmingROM HackingReverse Engineeringdevice driver developmentembedded systemsemulator developmenterror handlinghardware interactionmemory managementsystem emulation
Repositories Contributed To
Overview of all repositories you've contributed to across your timeline