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byuu 4.0


byuu is an upcoming multi-system emulator that aims to provide the accuracy of higan, with the ease-of-use of bsnes.


It seeks to accomplish this by catering to the common 99% of use cases, rather than higan, which tries to cater to every niche. As such, certain advanced functionality will not be available in byuu; however, the emulator will be significantly easier to use, like bsnes.


Unlike bsnes, byuu will also put accuracy at the forefront, at least at first. This is both to uphold my vision for emulator design, as well because as one person, I cannot possibly hope to maintain dozens of hard forks of each emulator core I have written. This means that byuu will have higher system requirements and less enhancements than bsnes, but it will still aim to offer more features than higan.


Essentially, think of it as the bridge between two extremes. The goal is to build on the success of bsnes, and to offer an easy-to-use interface for all of my emulator cores, rather than just for the SNES alone.


Emulated Systems:

  • Nintendo NES
  • Nintendo SNES
  • Nintendo GameBoy
  • Nintendo GameBoy Color
  • Nintendo GameBoy Advance
  • Sega SG-1000
  • Sega Master System
  • Sega Game Gear
  • Sega Mega Drive
  • NEC TurboGrafx-16
  • NEC SuperGrafx
  • MSX
  • MSX2
  • Bandai WonderSwan
  • Bandai WonderSwan Color
  • Neo Geo Pocket
  • Neo Geo Pocket Color


This release substantially improves PC Engine emulation, fixing 80% of known issues.


Regretfully, this will be my final release. I will be stepping down, and my emulators will be maintained going forward as a team project. I'll have more to say on this in the near future in a separate post.



  • PC Engine: improved IRQ handling significantly
  • PC Engine: fixed T-flag instructions, and implemented all addressing modes for it
  • PC Engine: improved VDP penalty cycle timing
  • PC Engine: always fire Vblank IRQs every frame, regardless of VDW setting
  • PC Engine: add support for STreet Fighter II CE's custom mapper
  • PC Engine: emulated MPR latch used by TMA and TAM instructions
  • PC Engine: randomize various registers and memory at power-on
  • PC Engine: do not allow block moves to read from $ff:0800-17ff
  • PC Engine: always set P.B flag (except when pushing P during BRK)
  • PC Engine: delay PSG synchronization when not needed (~8% speedup for accuracy profile)
  • PC Engine: emulate 4-color background and sprite modes
  • PC Engine: emulate grayscale VCE mode
  • PC Engine: emulate extra scanline VCE mode
  • PC Engine: fixed VRAM->VRAM DMA transfers (was transferring one byte less than it should)
  • PC Engine: improve burst-mode emulation (early VRAM->VRAM termination, etc)
  • PC Engine: add display timing latching to the performance profile's scanline renderer
  • PC Engine: many disassembler improvements
  • PC Engine CD: added skeleton implementation (non-functional)
  • Mega Drive: fix a crash when loading Sonic & Knuckles or the Game Genie without a daughter cartridge connected
  • higan: fix System menu option enabling when "Create New System" is selected
  • icarus: fix typo in save RAM portion of Master System game manifests (was marked as ROM by mistake)
  • byuu: don't show the program icon briefly when loading a new game
  • byuu: focus the viewport after loading games
  • byuu: add trace log path override option
  • byuu: use save path override for SNES save RAM files as well


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