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gameboy.c: improved accuracy of the emulation for MBC2

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games [Tauwasser]

out of whatsnew: also improved the name of some flags, clarifying their meaning.
This commit is contained in:
etabeta78 2015-06-02 11:27:11 +02:00
parent 3ae2668e4f
commit 99b58a5c0c
2 changed files with 17 additions and 20 deletions
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33
src/emu/bus/gameboy/mbc.c
View File

@ -368,8 +368,7 @@ WRITE8_MEMBER(gb_rom_mbc1_device::write_bank)
m_ram_bank = data & 0x3;
break;
case 0x6000: // MBC1 Mode Register
default:
m_mode = (data & 0x1) ? MODE_4M_256k : MODE_16M_8k;
m_mode = (data & 0x1) ? MODE_4M_256k : MODE_16M_64k;
break;
}
}
@ -399,31 +398,29 @@ WRITE8_MEMBER(gb_rom_mbc1_device::write_ram)
READ8_MEMBER(gb_rom_mbc2_device::read_rom)
{
if (offset < 0x4000)
return m_rom[rom_bank_map[m_latch_bank] * 0x4000 + (offset & 0x3fff)];
else
if (offset & 0x4000) /* RB1 */
return m_rom[rom_bank_map[m_latch_bank2] * 0x4000 + (offset & 0x3fff)];
else /* RB0 */
return m_rom[rom_bank_map[m_latch_bank] * 0x4000 + (offset & 0x3fff)];
}
WRITE8_MEMBER(gb_rom_mbc2_device::write_bank)
{
if (offset < 0x2000)
m_ram_enable = ((data & 0x0f) == 0x0a) ? 1 : 0;
else if (offset < 0x4000)
{
// 4bits only
data &= 0x0f;
// bank = 0 => bank = 1
if (data == 0)
data = 1;
// the mapper only has data lines D3..D0
data &= 0x0f;
// The least significant bit of the upper address byte must be 1
if (offset & 0x0100)
m_latch_bank2 = (m_latch_bank2 & 0x100) | data;
// the mapper only uses inputs A15..A14, A8 for register accesses
switch (offset & 0xc100)
{
case 0x0000: // RAM Enable Register
m_ram_enable = (data == 0x0a) ? 1 : 0;
break;
case 0x0100: // ROM Bank Register
m_latch_bank2 = (data == 0x00) ? 0x01 : data;
break;
}
}
// 1 bank only??
READ8_MEMBER(gb_rom_mbc2_device::read_ram)
{
if (!m_ram.empty() && m_ram_enable)

4
src/emu/bus/gameboy/mbc.h
View File

@ -37,7 +37,7 @@ class gb_rom_mbc1_device : public gb_rom_mbc_device
public:
enum {
MODE_16M_8k = 0, /// 16Mbit ROM, 8kBit RAM
MODE_16M_64k = 0, /// 16Mbit ROM, 64kBit RAM
MODE_4M_256k = 1, /// 4Mbit ROM, 256kBit RAM
};
@ -47,7 +47,7 @@ public:
// device-level overrides
virtual void device_start() { shared_start(); save_item(NAME(m_mode)); };
virtual void device_reset() { shared_reset(); m_mode = MODE_16M_8k; };
virtual void device_reset() { shared_reset(); m_mode = MODE_16M_64k; };
virtual void set_additional_wirings(UINT8 mask, int shift) { m_mask = mask; m_shift = shift; } // these get set at cart loading
virtual DECLARE_READ8_MEMBER(read_rom);