Cycle Accuracy
Emulation perfection
Cycle-accurate emulation reproduces original hardware behaviour at the CPU cycle level, enabling perfect compatibility at the cost of performance.
Overview
Cycle-accurate emulation replicates original hardware at the most granular level: every CPU cycle, every memory access timed exactly as the real machine behaved. This matters because games and demos often exploited precise timing—raster effects, copy protection, and tricks that only work with exact timing. Cycle accuracy trades performance for perfect compatibility.
Fast facts
- Definition: emulation matching original timing exactly.
- Requirement: much more CPU power than high-level emulation.
- Benefit: near-perfect compatibility.
- Examples: bsnes/higan, Mesen, VICE.
- Tradeoff: slower than less accurate emulators.
Why it matters
When timing is critical:
- Raster effects: require exact scanline timing.
- Copy protection: timing-based checks.
- Demo effects: exploit hardware quirks.
- Edge cases: games that barely worked on real hardware.
Emulator examples
Cycle-accurate implementations:
- bsnes/higan: SNES accuracy focus.
- Mesen: NES with cycle accuracy.
- VICE: Commodore cycle precision.
- Analogue systems: FPGA hardware matching.