Zgen 0.2.0 Released

[Felipe]

An emulator made by Eric Pearson, also known as Pagefault from ZSNES.​

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Genesis​

A Sega Genesis / Mega Drive emulator written in C++17 with SDL3 and Dear ImGui.

What This Project Is​

A desktop emulator with cycle-aware Genesis / Mega Drive hardware emulation:

• Motorola 68000 main CPU (~7.67 MHz)
• Zilog Z80 sound CPU (~3.58 MHz) — passes ZEXDOC conformance suite
• VDP — planes A/B, window, sprites, scrolling, DMA, shadow/highlight, H32/H40, interlace mode 2 (320x448 double-resolution), H-interrupt driven mid-frame splits
• YM2612 6-channel FM synthesis with LFO, SSG-EG, DAC, timers, CH3 special mode
• SN76489 PSG — 3 tone channels + noise
• Memory bus — full 24-bit address space, bank switching, SRAM save support
• Controllers — 3-button and 6-button with TH counter detection

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Project Status​

Playable — boots and runs games reliably. Audio and timing accuracy are under active improvement.

Features​

GUI​

Dear ImGui overlay with a menu bar, draggable windows, and responsive DPI-aware rendering that stays readable in small windows without ballooning in large ones.

• File — open ROM, recent ROMs (last 10), reset, resume, quit
• Settings — video, audio, emulation, and input configuration
• Tools — cheat manager, save state browser
• Help — controls reference, about

Video Settings​

• Display modes: windowed, borderless fullscreen, or exclusive fullscreen
• Exclusive fullscreen resolution selection when SDL reports display modes
• Window size presets (1x-6x, 320x224 base) in windowed mode
• Scaling mode: integer-only, fit, or stretch
• Aspect ratio: auto, 4:3, 16:9, or stretch
• Bilinear filtering toggle
• VSync and frame limiter toggles
• FPS counter with Simple and Detailed profiler modes
• On-screen performance breakdown for emulation, render, swap/present, UI, SDL, audio, and idle time

Audio Settings​

• Buffer size presets (75ms / 150ms / 300ms radio buttons) with fine-tune slider (50–500ms)
• 48 kHz stereo output (respects system sample rate)

Save States​

• 10 slots per game with thumbnail previews (320x224 screenshots)
• Quick save/load hotkeys (F5/F7), slot browser (F6), and slot navigation (F4/F8)
• Full state serialization: CPU, RAM, VDP, audio chips

Cheat Manager​

• Format: FFFFFF:YY (byte) or FFFFFF:YYYY (word)
• Per-cheat enable/disable toggles
• RAM search with known-value and unknown-initial-state workflows
• Result refinement (Changed, Unchanged, Increased, Decreased, Equal To Value, Not Equal To Value)
• Set Once memory editing and Freeze cheat creation from search results
• ROM-sidecar cheat save/load (.cht next to the ROM)
• Real-time freeze application during emulation

Input Rebinding​

• Game controls and emulator hotkeys are rebindable with visual key-capture UI
• Persistent storage (~/.genesis/keybindings.txt)
• Reset to defaults with confirmation

Rendering Backends​

• OpenGL 3.2+ (default) — shader-based framebuffer rendering
• Vulkan 1.0+ (compile-time option) — full swapchain, render pass, and descriptor set pipeline

GitHub - ericpearson/zgen: a genesis emulator

a genesis emulator. Contribute to ericpearson/zgen development by creating an account on GitHub.

github.com

 

[Ikagura]

Will this support 32-X and Sega CD without the need for a Bios? Will it have rewind?

 

[PacGuy]

I saw him hinting about this on X!!! Very exciting. Needs snow animations

 

[Ikagura]

I saw him hinting about this on X!!! Very exciting. Needs snow animations.

Agreed, even if it's not needed it gave older emulators some personality:

At least it was better than Genecyst's blood effect.

 

[PacGuy]

Agreed, even if it's not needed it gave older emulators some personality:
View attachment 161107
At least it was better than Genecyst's blood effect.

Wow I forgot all about Genecyst. That was weird! I agree though, love the personality touches

 

[Ikagura]

Wow I forgot all about Genecyst. That was weird!

This was by the same team behind Nesticle (yeah, they got creative with the names). This tells it was the 90's and DOS.

I agree though, love the personality touches.

Yeah, I also liked Gens' effect when no games were loaded

Sadly I couldn't find any gif of it.

Kega had TV statics which were fine but probably less interesting visually.

 

[Felipe]

An update was released:

What's New​

Audio / Sound​

• Fix YM2612 busy flag: Disabled the overly long busy flag that starved the Z80 sound driver, causing clippy/missing music in games using the GEMS sound driver (Top Gear 2, Gargoyles, and many others)
• Fix Timer B prescaler: Corrected from 8 to 16 FM samples per increment, matching the YM2612 datasheet. Fixes DAC sample playback rate for correct music tempo
• Fix YM2612 status register reads: All addresses in the $4000-$5FFF (Z80) and $A04000-$A04003 (68K) ranges now correctly return the status byte. Previously only $4000 worked, causing games like Mega Turrican to hang on a busy-flag spin loop

CPU Timing​

• Fix M68K instruction timing: Match yacht.txt v1.1 reference for accurate 68000 cycle counts
• Fix 68K quick memory operation timing
• Z80 EI instruction: Properly delays interrupt enable by one instruction, matching real Z80 hardware

Video​

• Fix VDP timing: Correct VPA interrupt delay, HBLANK flag behavior, and pixel output timing

Other​

• Add --debug flag: All diagnostic logging is now gated behind --debug for zero overhead in normal use
• Windows build fix: Add SDL_main entry point and GUI subsystem support

 

[secreto7]

New update

v0.6.5 - Timing, audio, SRAM, and Vulkan builds

Highlights​

• Adds a Windows Vulkan release package alongside the existing Linux, macOS, and Windows OpenGL packages.
• Improves raster timing, FIFO behavior, DMA ordering, and VSRAM latch handling for more stable mid-frame effects.
• Improves Z80, YM2612, and PSG cadence so audio drivers keep advancing during long main-CPU activity and interrupt windows.
• Fixes direct-mapped SRAM access and cartridge startup edge cases that affected save-backed titles.

Emulator Accuracy​

• Panorama Cotton: fixes bottom HUD flash, paused HUD instability, gameplay black-line artifacts, and related cold-boot rendering regressions.
• Top Gear 2: fixes race-screen red-line flashes, black-line artifacts, and left-edge race viewport corruption.
• F1: fixes the PAL race viewport bottom border so bottom garbage is not drawn below the active race image.
• Clue: fixes corrupted menu background pixels after cold boot and Start input.
• Darius: fixes startup BUSACK handling and title-logo FIFO/drop artifacts.
• Flashback: improves intro music cadence by keeping Z80 V-int pulse timing and audio chip clocks aligned.
• OutRun: keeps title-screen rows and sky bands stable in the regression scenes.

 

[Ikagura]

Wait, are they working on both this emulator and Super ZSNES?