6502tinymachines

N6 plan: the picture

Written before the code (2026-09-06), the way P3's plan was. The sketch (docs/nes-end-to-end-v0_2.md, section 3, N6) asks for two things: the PPU ladder's DotFrame into ntsc-crt's NES source with the Rung C decode by default and the CRT stages on, and a gate that compares the console's picture with a real console's through the same capture procedure ntsc-crt's M4 uses, on a colour-bars cartridge in both, with tolerances stated before measuring.

What exists

  • ntsc-crt (v0.2.3) has every stage: ntsc-source-nes encodes a DotFrame to composite samples, direct synthesis like the PPU; ntsc-decode has the three-line comb (Rung C) with the NES-native weights; ntsc-crt has the beam, scanlines, persistence, mask and geometry; ntsc-wasm's NesPipeline is the plain-Rust encode and decode the browser page runs, frame after frame with the subcarrier phase carried by parity (CompositeFrame::next_origin). Its bridge is wasm-only behind a cfg, so the console uses it natively.
  • ntsc-source-cap reads a captured waveform into the same frame type (sync, burst lock, sinc resample, DC re-referenced) and carries the capture-card model M4 proved the roundtrip on; its score-real-region example scores a flat region of a real capture against the same colour synthesized, both sides decoded identically.
  • The console (N5) produces DotFrames with the parity the PPU ran, and its plumbing gate holds each to the standalone PPU's.
  • Captures on hand: five records of Super Mario Bros. and Duck Hunt from the real console (M4). No bars capture yet, and no ROM for either game here. full_palette.nes (blargg, NROM) paints every palette entry as bars and runs on the console; 240pee.nes has SMPTE bars but is mapper 2, out of the console's scope.

Steps

  1. The picture through the console. nes-console gains picture: a Picture that takes the console's frames in order, encodes each with the NES source at the phase the previous frame left, decodes on Rung C, and optionally runs the CRT stages; ntsc-crt pinned by tag, the same nes-bus underneath. run-rom gains CRT=out.ppm (the displayed picture) beside its palette dump.

    Gate (tests/picture.rs): a console frame through the picture is byte for byte what the standalone PPU's frame from the same world is through the same picture (the seam adds nothing, now past the encoder), and the phase the picture carries across the console's real parity sequence is what ntsc-grid's arithmetic gives that sequence (the odd frame's short line moves the phase; the console must pass the parity, not just the dots). A mutation (the parity forced Even) must go red on the second.

  2. The capture path, machine half. An example capture-score runs a ROM in the console, encodes its frames, and either reads a real capture (the .u8/.wav the M4 tools read, at the recorder's rate) or runs the frames through ntsc-crt's capture-card model (synthetic, at the same rate), recovers it the way M4 does, and scores named flat regions against the console's own synthesis through the identical decoder: luma, hue, saturation. With full_palette.nes and the synthetic capture the whole path closes on this machine; the real capture of the same ROM on the real box is the bench item.

    Tolerances, stated now. Synthetic roundtrip (the card model's own noise and 5 ppm): luma within 0.01, hue within 1.0 degree, saturation within 5 percent of the synthesis, on every flat region scored; a miss fails. Real capture: recorded beside the synthetic figures and NOT held, because M4's one scored real region already reads 28 percent hot in saturation for a reason the sketch's section 5 assigns to the bench (probe versus DAC); a hue or luma miss beyond the synthetic tolerance is named.

  3. The report (docs/n6-report.md): the picture, the gate's figures, the capture path's synthetic figures per region, the real capture's status, and what stays for the bench.

Not in N6

Wall-clock pacing and the drift policy (N8, with the shell). The CRT parameters stay ntsc-crt's authored ones; nothing here fits them.

Pulled at build time from nes/docs/n6-plan.md; the repository is the one copy.