Also, these lines

Code
	membank("rom")->set_base(memregion("boot")->base());
	membank("ram_0000")->set_base(m_ram.get() + 0x0000);
	membank("ram_1800")->set_base(m_ram.get() + 0x1800);
	membank("ram_4000")->set_base(m_ram.get() + 0x4000);
	membank("ram")->set_base(m_ram.get());


...map the various RAM views in bank 0 to their correct places in the full 64K in bank 1.