auto CPU::read(uint16 addr) -> uint8 {
  if(io.oamdmaPending) {
    io.oamdmaPending = false;
    read(addr);
    oamdma();
  }

  while(io.rdyLine == 0) {
    r.mdr = bus.read(io.rdyAddrValid ? io.rdyAddrValue : addr);
    step(rate());
  }

  r.mdr = bus.read(addr);
  step(rate());
  return r.mdr;
}

auto CPU::write(uint16 addr, uint8 data) -> void {
  bus.write(addr, r.mdr = data);
  step(rate());
}

auto CPU::lastCycle() -> void {
  io.interruptPending = ((io.irqLine | io.apuLine) & ~r.p.i) | io.nmiPending;
}

auto CPU::nmi(uint16& vector) -> void {
  if(io.nmiPending) {
    io.nmiPending = false;
    vector = 0xfffa;
  }
}

auto CPU::oamdma() -> void {
  for(uint n : range(256)) {
    uint8 data = read(io.oamdmaPage << 8 | n);
    write(0x2004, data);
  }
}

auto CPU::nmiLine(bool line) -> void {
  //edge-sensitive (0->1)
  if(!io.nmiLine && line) io.nmiPending = true;
  io.nmiLine = line;
}

auto CPU::irqLine(bool line) -> void {
  //level-sensitive
  io.irqLine = line;
}

auto CPU::apuLine(bool line) -> void {
  //level-sensitive
  io.apuLine = line;
}

auto CPU::rdyLine(bool line) -> void {
  io.rdyLine = line;
}

auto CPU::rdyAddr(bool valid, uint16 value) -> void {
  io.rdyAddrValid = valid;
  io.rdyAddrValue = value;
}