jgnes

Note: This emulator has been largely obsoleted by the NES core in my multi-system emulator, but this emulator does still support a few features that one does not:

• A configurable Gaussian blur filter, which is not accurate to any TV but does smooth out the image with some "fancy" blur
• The entirety of the web frontend; jgenesis has a web frontend, but it doesn't support NES and there's no support for input configuration

---

A cross-platform NES emulator. Has a native frontend built using SDL2 as well as a web frontend that compiles to WASM and runs in the browser.

Feature Status

Implemented:

• Cycle-based 6502 CPU emulation, PPU emulation (graphics), and APU emulation (audio)
• The most commonly used cartridge boards (aka mappers)
  • NROM
  • The most common NROM variants (UxROM / CNROM / AxROM)
  • MMC1
  • MMC3/MMC6
• Some less commonly used cartridge boards
  • MMC2/MMC4
  • MMC5 including expansion audio
  • Konami VRC2 / VRC4 / VRC6 / VRC7, including VRC6 expansion audio and VRC7 expansion audio
  • Sunsoft 5A / 5B / FME-7, including 5B expansion audio
  • Codemasters unlicensed board
  • Color Dreams unlicensed board
  • Bandai FCG-1 / FCG-2 / LZ93D50
    • The LZ93D50 variant that uses the Datach Joint ROM system is not implemented (iNES mapper 157)
  • Namco 108 / 129 / 163 / 175 / 340, including 163 expansion audio
  • NAMCOT-3425 / NAMCOT-3446 / NAMCOT-3453
  • Jaleco JF-11 / JF-14
  • GxROM
  • BNROM
  • NINA-001
• P1 & P2 input with support for keyboard input and DirectInput gamepad input
• Support for 3 different forced aspect ratios (NTSC, 1:1 pixel aspect ratio, 4:3 screen aspect ratio), plus an option for stretched/none
• Overscan customization
• A GPU-backed renderer based on wgpu with an option for integer upscaling + linear interpolation, producing a sharp but clean image even at higher resolutions and non-8:7 aspect ratios
• Save & load state
• Fast forward with a configurable speed multiplier (very CPU-intensive at higher multipliers; my i5-1240P laptop maxes out between 5x and 6x speed)
• Rewind
• Support for both NTSC and PAL releases

Not Implemented:

• A handful of unofficial CPU opcodes that are buggy/unstable and do not do anything useful (specifically $93, $9B, and $9F)
• Cycle-accurate rendering effects of enabling rendering mid-scanline
• DMC DMA cycle stealing and dummy reads, an obscure hardware quirk that affects very very few if any games
• Color palette customization; the NES hardware directly outputs an NTSC video signal rather than RGB pixel grids, so any mapping from NES colors to RGB colors is an approximation at best
• Lots of more obscure cartridge boards
• Support for any controller port peripherals (e.g. the Zapper)

Crate Structure

• jgnes-proc-macros: Custom derive macros used in jgnes-core.
• jgnes-core: The emulation core. Has few dependencies and requires external code to drive it. Uses callbacks for rendering frames, playing audio, polling for input, and writing save files.
• jgnes-renderer: Code for the GPU-backed renderer, as well as some common configuration code that is shared by both renderers.
• jgnes-native-driver: Emulator driver that uses SDL2 to handle everything related to video/audio/input, with an option to use either the GPU renderer or an SDL2 software renderer for rendering emulator output into the window.
• jgnes-cli: A command-line interface that invokes jgnes-native-driver.
• jgnes-gui: A graphical user interface that invokes jgnes-native-driver.
• jgnes-web: An experimental WASM+WebGL2 frontend for jgnes-core that runs in the browser. Uses winit to create the frame and jgnes-renderer to render emulator output.

Requirements

Rust

This project requires the latest stable version of the Rust toolchain to build. See link for installation instructions.

SDL2

This project requires SDL2 core headers to build.

Linux (Debian-based):

sudo apt install libsdl2-dev

Windows:

• https://github.com/libsdl-org/SDL/releases

GTK3 (Linux GUI only)

On Linux only, the GUI requires GTK3 headers to build.

Linux (Debian-based):

sudo apt install libgtk-3-dev

Build & Run

To build the CLI and run for a given NES ROM file:

cargo run --release --bin jgnes-cli -- -f /path/to/file.nes

To view all CLI args:

cargo run --release --bin jgnes-cli -- -h

To build and run the GUI:

cargo run --release --bin jgnes-gui

Test ROM Results

CPU Test ROMs

Test	Result	Failure Reason
blargg_nes_cpu_test5/cpu.nes	✅
blargg_nes_cpu_test5/official.nes	✅
branch_timing_tests/1.Branch_Basics.nes	✅
branch_timing_tests/2.Backward_Branch.nes	✅
branch_timing_tests/3.Forward_Branch.nes	✅
cpu_dummy_reads/cpu_dummy_reads.nes	✅
cpu_dummy_writes/cpu_dummy_writes_oam.nes	✅
cpu_dummy_writes/cpu_dummy_writes_ppumem.nes	✅
cpu_exec_space/test_cpu_exec_space_apu.nes	✅
cpu_exec_space/test_cpu_exec_space_ppuio.nes	✅
cpu_interrupts_v2/cpu_interrupts.nes	✅
cpu_timing_test6/cpu_timing_test.nes	✅
instr_test-v5/all_instrs.nes	✅
instr_test-v5/official_only.nes	✅
instr_timing/instr_timing.nes	✅

APU Test ROMs

Test	Result	Failure Reason
apu_test/apu_test.nes	✅
blargg_apu_2005.07.30/01.len_ctr.nes	✅
blargg_apu_2005.07.30/02.len_table.nes	✅
blargg_apu_2005.07.30/03.irq_flag.nes	✅
blargg_apu_2005.07.30/04.clock_jitter.nes	✅
blargg_apu_2005.07.30/05.len_timing_mode0.nes	✅
blargg_apu_2005.07.30/06.len_timing_mode1.nes	✅
blargg_apu_2005.07.30/07.irq_flag_timing.nes	✅
blargg_apu_2005.07.30/08.irq_timing.nes	✅
blargg_apu_2005.07.30/09.reset_timing.nes	✅
blargg_apu_2005.07.30/10.len_halt_timing.nes	✅
blargg_apu_2005.07.30/11.len_reload_timing.nes	❌	#5: Reload during length clock when ctr > 0 should be ignored
dmc_dma_during_read4/dma_2007_read.nes	❌	DMC DMA dummy reads not implemented
dmc_dma_during_read4/dma_2007_write.nes	✅
dmc_dma_during_read4/dma_4016_read.nes	❌	DMC DMA dummy reads not implemented
dmc_dma_during_read4/double_2007_read.nes	❌	DMC DMA dummy reads not implemented
dmc_dma_during_read4/read_write_2007.nes	✅
sprdma_and_dmc_dma/sprdma_and_dmc_dma.nes	❌	DMC DMA cycle stealing not implemented
sprdma_and_dmc_dma/sprdma_and_dmc_dma_512.nes	❌	DMC DMA cycle stealing not implemented

PPU Test ROMs

Test	Result	Failure Reason
blargg_ppu_tests_2005.09.15b/palette_ram.nes	✅
blargg_ppu_tests_2005.09.15b/power_up_palette.nes	❌	#2: Palette differs from table
blargg_ppu_tests_2005.09.15b/sprite_ram.nes	✅
blargg_ppu_tests_2005.09.15b/vbl_clear_time.nes	✅
blargg_ppu_tests_2005.09.15b/vram_access.nes	✅
oam_read/oam_read.nes	✅
ppu_open_bus/ppu_open_bus.nes	❌	#3: Decay value should become zero by one second
ppu_read_buffer/test_ppu_read_buffer.nes	✅
ppu_vbl_nmi/ppu_vbl_nmi.nes	✅
sprite_hit_tests_2005.10.05/01.basics.nes	✅
sprite_hit_tests_2005.10.05/02.alignment.nes	✅
sprite_hit_tests_2005.10.05/03.corners.nes	✅
sprite_hit_tests_2005.10.05/04.flip.nes	✅
sprite_hit_tests_2005.10.05/05.left_clip.nes	✅
sprite_hit_tests_2005.10.05/06.right_edge.nes	✅
sprite_hit_tests_2005.10.05/07.screen_bottom.nes	✅
sprite_hit_tests_2005.10.05/08.double_height.nes	✅
sprite_hit_tests_2005.10.05/09.timing_basics.nes	✅
sprite_hit_tests_2005.10.05/10.timing_order.nes	✅
sprite_hit_tests_2005.10.05/11.edge_timing.nes	✅
sprite_overflow_tests/1.Basics.nes	✅
sprite_overflow_tests/2.Details.nes	✅
sprite_overflow_tests/3.Timing.nes	✅
sprite_overflow_tests/4.Obscure.nes	✅
sprite_overflow_tests/5.Emulator.nes	✅
vbl_nmi_timing/1.frame_basics.nes	✅
vbl_nmi_timing/2.vbl_timing.nes	✅
vbl_nmi_timing/3.even_odd_frames.nes	✅
vbl_nmi_timing/4.vbl_clear_timing.nes	✅
vbl_nmi_timing/5.nmi_suppression.nes	✅
vbl_nmi_timing/6.nmi_disable.nes	✅
vbl_nmi_timing/7.nmi_timing.nes	✅

Mapper-Specific Test ROMs

Test	Result	Failure Reason
mmc3_test_2/1-clocking.nes	✅
mmc3_test_2/2-details.nes	✅
mmc3_test_2/3-A12_clocking.nes	✅
mmc3_test_2/4-scanline_timing.nes	✅
mmc3_test_2/5-MMC3.nes	✅
mmc3_test_2/6-MMC3_alt.nes	❌	#2: IRQ shouldn't be set when reloading to 0 due to counter naturally reaching 0 previously

Reset Test ROMs

Test	Result	Failure Reason
apu_reset/4015_cleared.nes	✅
apu_reset/4017_timing.nes	✅
apu_reset/4017_written.nes	✅
apu_reset/irq_flag_cleared.nes	✅
apu_reset/len_ctrs_enabled.nes	✅
apu_reset/works_immediately.nes	✅
cpu_reset/ram_after_reset.nes	✅
cpu_reset/registers.nes	✅

Screenshots