NesSweepUnit
StructSource: AudioTypes.h
Description
NES APU sweep unit state for the PULSE channels.
Mirrors the $4001 / $4005 sweep register pair. Operates on the 11-bit timer period (NES PULSE NTSC = 111860.8 / (timer+1) Hz). Clocks at half-frame rate (120 Hz NTSC mode 0); on each tick the unit computes a target period, evaluates the muting conditions, and optionally updates timer from the target.
The muting flag is evaluated CONTINUOUSLY (the "NES bug" from https://www.nesdev.org/wiki/APU_Sweep) — even when sweepEnabled is false or shift is 0, the dispatcher still computes the target and updates muted. The hot path (PULSE generation) checks muted per-sample and gates the output to 0.
That continuous evaluation is scoped to voices that opted in via unitEnabled. Without that gate the rule period < 8 would fire on the default timer == 0, so merely starting the frame counter would silence every PULSE voice driven by the legacy float frequency path. See unitEnabled below.
Default state: all fields zero / false. The canonical track never enables NES mode, so the rendered PCM is byte-for-byte identical. Hito 2 M6.