uint8 ram_read(uint16 addr);
  void ram_write(uint16 addr, uint8 data);

  uint8 port_read(uint8 port);
  void port_write(uint8 port, uint8 data);

  uint8 op_busread(uint16 addr);
  void op_buswrite(uint16 addr, uint8 data);

  void op_io();
  uint8 op_read(uint16 addr);
  void op_write(uint16 addr, uint8 data);