pub trait Sys {
fn read(&mut self, addr: u16) -> Option<u8>;
fn write(&mut self, addr: u16, val: u8) -> Option<()>;
fn set_sync(&mut self, _set: bool) { ... }
fn poll_nmi(&mut self) -> bool { ... }
fn peek_nmi(&self) -> bool { ... }
fn nmi_length(&self) -> NmiLength { ... }
fn irq(&self) -> bool { ... }
}