// license:BSD-3-Clause // copyright-holders:Vas Crabb /*************************************************************************** Nintendo Game Boy Memory Bank Controller 2 Low-cost controller for games with modest ROM requirements and save file support. Supports up to 256 KiB ROM (16 16 KiB pages), and has 512 nybbles of internal static RAM. Only A15-A14, A8-A0, D3-D0, and the read/write/RAM select lines are connected to the MBC2 chip, i.e. addresses are effectively masked with 0xC01F and data is effectively masked with 0x0F. 0x0000-3FFF R - Fixed ROM bank, always first page of ROM. 0x4000-7FFF R - Selectable ROM bank, page 1-15 of ROM. 0xA000-A1FF RW - Internal static RAM on low nybble if enabled. Mirrored up to 0xBFFF. 0b0011xxx0xxxx W - Static RAM enable - write 0x0A on low nybble to enable, any other value to disable. 0b0011xxx1xxxx W - Select ROM page mapped at 0x4000. Only low nybble is significant. Writing 0 selects page 1. ***************************************************************************/ #include "emu.h" #include "mbc2.h" #include "cartbase.h" #include "cartheader.h" #include //#define VERBOSE 1 //#define LOG_OUTPUT_FUNC osd_printf_info #include "logmacro.h" namespace bus::gameboy { namespace { class mbc2_device : public mbc_device_base { public: mbc2_device(machine_config const &mconfig, char const *tag, device_t *owner, u32 clock); virtual std::error_condition load(std::string &message) override ATTR_COLD; virtual void unload() override ATTR_COLD; protected: virtual void device_start() override ATTR_COLD; virtual void device_reset() override ATTR_COLD; private: static inline constexpr unsigned RAM_SIZE = 512; u8 ram_mbc_read(address_space &space, offs_t offset); void ram_mbc_write(offs_t offset, u8 data); void ram_mbc_enable(u8 data); void bank_rom_switch(u8 data); std::unique_ptr m_ram_mbc; u8 m_ram_mbc_enable; bool m_battery_present; }; mbc2_device::mbc2_device( machine_config const &mconfig, char const *tag, device_t *owner, u32 clock) : mbc_device_base(mconfig, GB_ROM_MBC2, tag, owner, clock), m_ram_mbc_enable(0U), m_battery_present(false) { } std::error_condition mbc2_device::load(std::string &message) { // first check ROM set_bank_bits_rom(4); if (!check_rom(message)) return image_error::BADSOFTWARE; // decide whether to enable battery backup memory_region *const nvramregion(cart_nvram_region()); if (nvramregion) { if (nvramregion->bytes() != RAM_SIZE) { message = "Unsupported cartridge NVRAM size (only MBC2 internal 512 nybble RAM is supported)"; return std::error_condition(); } m_battery_present = true; logerror("Found 'nvram' region, battery backup enabled\n"); } else if (loaded_through_softlist()) { logerror("No 'nvram' region found, battery backup disabled\n"); m_battery_present = false; } else { // guess based on header u8 const carttype((&cart_rom_region()->as_u8())[cartheader::OFFSET_TYPE]); switch (carttype) { case cartheader::TYPE_MBC2: m_battery_present = false; break; case cartheader::TYPE_MBC2_BATT: m_battery_present = true; break; default: osd_printf_warning( "[%s] Unrecognized cartridge type 0x%02X in header, assuming no battery present\n", tag(), carttype); m_battery_present = false; } osd_printf_verbose( "[%s] Cartridge type 0x%02X in header, battery backup %s\n", tag(), carttype, m_battery_present ? "enabled" : "disabled"); } // install ROM, RAM and handlers install_rom(); cart_space()->install_read_handler( 0xa000, 0xa1ff, 0x0000, 0x1e00, 0x0000, emu::rw_delegate(*this, FUNC(mbc2_device::ram_mbc_read))); cart_space()->install_write_handler( 0xa000, 0xa1ff, 0x0000, 0x1e00, 0x0000, emu::rw_delegate(*this, FUNC(mbc2_device::ram_mbc_write))); cart_space()->install_write_handler( 0x0000, 0x00ff, 0x0000, 0x3e00, 0x0000, emu::rw_delegate(*this, FUNC(mbc2_device::ram_mbc_enable))); cart_space()->install_write_handler( 0x0100, 0x01ff, 0x0000, 0x3e00, 0x0000, emu::rw_delegate(*this, FUNC(mbc2_device::bank_rom_switch))); // load battery backup if appropriate if (nvramregion) battery_load(m_ram_mbc.get(), RAM_SIZE, nvramregion->base()); else if (m_battery_present) battery_load(m_ram_mbc.get(), RAM_SIZE, 0x0f); for (unsigned i = 0U; RAM_SIZE > i; ++i) m_ram_mbc[i] &= 0x0f; // all good return std::error_condition(); } void mbc2_device::unload() { if (m_battery_present) battery_save(m_ram_mbc.get(), RAM_SIZE); } void mbc2_device::device_start() { mbc_device_base::device_start(); m_ram_mbc = std::make_unique(RAM_SIZE); save_pointer(NAME(m_ram_mbc), RAM_SIZE); save_item(NAME(m_ram_mbc_enable)); } void mbc2_device::device_reset() { mbc_device_base::device_reset(); m_ram_mbc_enable = 0U; set_bank_rom(1); } u8 mbc2_device::ram_mbc_read(address_space &space, offs_t offset) { if (m_ram_mbc_enable) return (m_ram_mbc[offset] & 0x0f) | (space.unmap() & 0xf0); else return space.unmap(); } void mbc2_device::ram_mbc_write(offs_t offset, u8 data) { if (m_ram_mbc_enable) m_ram_mbc[offset] = data & 0x0f; } void mbc2_device::ram_mbc_enable(u8 data) { m_ram_mbc_enable = (0x0a == (data & 0x0f)) ? 1U : 0U; LOG( "%s: Internal MBC2 RAM %s\n", machine().describe_context(), m_ram_mbc_enable ? "enabled" : "disabled"); } void mbc2_device::bank_rom_switch(u8 data) { data &= 0x0f; set_bank_rom(data ? data : 1); } } // anonymous namespace } // namespace bus::gameboy DEFINE_DEVICE_TYPE_PRIVATE(GB_ROM_MBC2, device_gb_cart_interface, bus::gameboy::mbc2_device, "gb_rom_mbc2", "Game Boy MBC2 Cartridge")