pub const REG_COUNT: usize = 0x18;Expand description
Number of register slots tracked: $4000-$4017 inclusive.
$4014 (OAM DMA) and $4016 (controller strobe) are inside the range and
are NOT APU registers. They are tracked anyway rather than punched out: the
range is what the bus already classifies as EventKind::ApuWrite, keeping
one contiguous index space costs two slots, and a hole would be a permanent
invitation to off-by-one arithmetic at every call site.