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Preliminary MBC1 support. Enough to run cpu_instrs.gb to completion. Hurrah!

Browse Source 
Signed-off-by: Adrian.Conlon <adrian.conlon@gmail.com>
This commit is contained in:
Adrian.Conlon 2017-08-24 23:23:40 +01:00
parent 9964070b85
commit ae4106ce5a
2 changed files with 53 additions and 23 deletions
LR35902
inc
Bus.h
src
Bus.cpp

18
LR35902/inc/Bus.h

@ -14,17 +14,9 @@ namespace EightBit {
ROM_MBC1_RAM_BATTERY = 3,
};
enum MbcOneMode {
SixteenEight,
FourThirtyTwo,
};
enum {
TotalLineCount = 154
};
enum {
VideoRam = 0x8000
TotalLineCount = 154,
RomPageSize = 0x4000
};
enum {
@ -189,12 +181,14 @@ namespace EightBit {
bool m_disableBootRom;
bool m_disableGameRom;
bool m_mbc1;
bool m_rom;
bool m_banked;
bool m_ram;
bool m_battery;
MbcOneMode m_mbc1Mode;
bool m_higherRomBank;
bool m_ramBankSwitching;
int m_romBank;
int m_ramBank;

58
LR35902/src/Bus.cpp

@ -5,12 +5,12 @@ EightBit::Bus::Bus()
: Memory(0xffff),
m_disableBootRom(false),
m_disableGameRom(false),
m_mbc1(false),
m_rom(false),
m_ram(false),
m_battery(false),
m_mbc1Mode(SixteenEight),
m_romBank(0),
m_higherRomBank(true),
m_ramBankSwitching(false),
m_romBank(1),
m_ramBank(0),
m_divCounter(256),
m_timerCounter(0),
@ -48,7 +48,7 @@ uint8_t& EightBit::Bus::reference(uint16_t address, bool& rom) {
if ((effective < 0x4000) && gameRomEnabled())
return m_gameRom[effective];
if ((effective < 0x8000) && gameRomEnabled())
return m_gameRom[effective + (m_romBank * 0x4000)];
return m_gameRom[(effective - RomPageSize) + (m_romBank * RomPageSize)];
rom = false;
return m_bus[effective];
}
@ -58,14 +58,50 @@ void EightBit::Bus::Bus_WrittenByte(const AddressEventArgs& e) {
const auto address = e.getAddress();
const auto value = e.getCell();
auto handled = false;
switch (address & 0xe000) {
case 0x0000:
// Register 0: RAMCS gate data
if (m_ram) {
assert(false);
}
break;
case 0x2000:
m_romBank = value & Processor::Mask5;
// Register 1: ROM bank code
if (m_banked && m_higherRomBank) {
assert((address >= 0x2000) && (address < 0x4000));
assert((value > 0) && (value < 0x20));
m_romBank = value & Processor::Mask5;
handled = true;
}
break;
case 0x4000:
// Register 2: ROM bank selection
if (m_banked) {
assert(false);
}
case 0x6000:
m_mbc1Mode = value & Processor::Mask1 ? FourThirtyTwo : SixteenEight;
// Register 3: ROM/RAM change
if (m_banked) {
switch (value & Processor::Mask1) {
case 0:
m_higherRomBank = true;
m_ramBankSwitching = false;
break;
case 1:
m_higherRomBank = false;
m_ramBankSwitching = true;
break;
default:
__assume(0);
}
handled = true;
}
break;
default:
}
if (!handled) {
switch (address) {
case BASE + TAC:
m_timerRate = timerClockTicks();
@ -106,20 +142,20 @@ void EightBit::Bus::checkTimer(int cycles) {
void EightBit::Bus::validateCartridgeType() {
m_rom = m_mbc1 = m_ram = m_battery = false;
m_rom = m_banked = m_ram = m_battery = false;
switch (m_gameRom[0x147]) {
case ROM:
m_rom = true;
break;
case ROM_MBC1:
m_rom = m_mbc1 = true;
m_rom = m_banked = true;
break;
case ROM_MBC1_RAM:
m_rom = m_mbc1 = m_ram = true;
m_rom = m_banked = m_ram = true;
break;
case ROM_MBC1_RAM_BATTERY:
m_rom = m_mbc1 = m_ram = m_battery = true;
m_rom = m_banked = m_ram = m_battery = true;
break;
default:
throw std::domain_error("Unhandled cartridge ROM type");