MAME-NES v2.0 rewrites PPU timing and adds four NTSC alignments

The MAME-NES branch has released its version 2.0, an update focused on NES/Famicom hardware precision. The work thoroughly rewrites the CPU M6502/NES, APU, and PPU timing paths to approach cycle-accurate behavior, doing so without breaking the existing NES/Famicom architecture that MAME already had: the declared goal is to gain fidelity while maintaining compatibility with what exists.

This is not a catalog change or a new interface, but an internal rewrite. The project is published on GitHub under the repository theklap/mame_nes, and the build is distributed as nes.exe.

MAME-NES moves PPU timing out of the APU

The background change is where the PPU clock lives. Previously, PPU timing hung off the APU: each APU tick fired three PPU ticks. In version 2.0, the PPU manages its own timing and no longer depends on the APU.

That decoupling is what opens the door to emulating the four NTSC CPU/PPU timing alignments, something the previous structure did not allow. It is a precision adjustment: it better reproduces how the two chips coordinate in the original hardware, not a convenience feature.

Four NTSC alignments to choose from

The build exposes selection via Tab → Machine Configuration → CPU/PPU Alignment, with phases 0 through 3 or the Random option. Random does not pick purely at random: it chooses an alignment using weighted probabilities. In all cases, the selection takes effect when the machine is rebooted, so the change does not apply hot.

What the tests say

The project claims that all four phases pass the $2007, RMW2007Test, and AccuracyCoin alignment tests. The version notes themselves qualify the rest of the table, with several results marked as pending confirmation:

• Wario Woods: a flicker appears in phase 1.
• read2004.nes: looks correct in phase 0; in phases 1–3 it is missing an initial FF (the author notes this as possibly normal behavior).
• demo_ntsc: correct in all phases.
• scanline.nes: correct in phase 0; in phases 1–3 it shows some corruption (also marked as possibly normal).
• PaletteCorruption.nes: correctly detects the selected phase.
• INC2007Alignment.nes: correctly detects the selected phase.

These notes should be read with caution: they are from the development itself, not an external validation, and some results remain open to interpretation.

What changes for the player

For someone playing today, the value lies in the fidelity of the work, not a list of new games. A CPU/APU/PPU timing path closer to the hardware reduces subtle synchronization errors that affect cycle-sensitive titles. Someone coming from MAME4droid 1.41.2 and its mobile packaging will find something different here: a desktop branch that prioritizes NES precision over convenience features.

What still does not work entirely is listed in the notes themselves: the flicker of Wario Woods in phase 1 and the corruption of scanline.nes in phases 1–3 remain as pending points. The full build can be downloaded from the project’s repository.