Static MASK_WRITE_DELAY 

pub static MASK_WRITE_DELAY: AtomicU8

v2.0 Phase 6 (mc-ppu-subpos): the analog $2001 PPUMASK write delay.

In PPU dots. TriCNES applies a $2001 write 2-3 dots after the CPU write (PPU_Update2001Delay, sub-dot alignment dependent); this emulator’s reload sits one dot later than that plus the existing 1-dot render gate, so the effective default is 4. Runtime-tunable (an atomic) so the exact phase can be swept against the BG Serial In / Stale BG Shift keys without rebuilding. Only consulted under mc-ppu-subpos.