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memory.cpp
198 lines (187 loc) · 4.22 KB
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memory.cpp
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#include "gb.h"
#include <memory>
#include <cassert>
//http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory-Banking
struct MBC {
u8* rom;
u32 romLength;
u32 romOffset;
u32 romBank;
u32 ramOffset;
u8 cartType;
bool mode;
u8 ram[0x2000];
} g_mbc;
u16 g_memBreakpoint = 0xFFFF;
bool g_hitMemBreakpoint = false;
void initMemoryBanks(u8* rom, u32 romLength)
{
g_mbc.rom = rom;
g_mbc.romLength = romLength;
g_mbc.romOffset = 0x4000;
g_mbc.romBank = 0;
g_mbc.ramOffset = 0x0000;
g_mbc.cartType = rom[0x147];
g_mbc.mode = false;
memset(g_mbc.ram, 0, sizeof(g_mbc.ram));
}
u8 readMemory(u16 loc)
{
if (loc >= 0x4000 && loc <= 0x7FFF)
{
//ROM (switched bank)
return g_mbc.rom[g_mbc.romOffset + (loc & 0x3FFF)];
}
else if (loc >= 0xA000 && loc <= 0xBFFF)
{
//RAM (switched bank)
return g_mbc.ram[g_mbc.ramOffset + (loc & 0x1FFF)];
}
else if (loc >= 0xE000 && loc <= 0xFDFF)
{
//shadow of working RAM (excluding final 512 bytes)
return gb.memory[loc - 0x1000];
}
else if (loc >= 0xFF00 && loc < 0xFF80)
{
switch (loc)
{
case 0xFF00://Joypad R/W
return gb.joypadInput;
case 0xFF40://LCDC
return gb.gpu.lcdcStatus;
case 0xFF44://LY
return gb.gpu.scanline;
case 0xFF45://LYC
return gb.gpu.scanlinecompare;
case 0xFF0F://Interrupt Flag
return gb.interruptFlag.value;
default:
return 0;
}
}
else if (loc < 0xFFFF)
{
return gb.memory[loc];
}
else//0xFFFF Interrupt Enable
{
return gb.interruptReg.value;
}
}
u16 readMemory16(u16 loc)
{
return (readMemory(loc) << 8) | readMemory(loc + 1);
}
#include <cassert>
void writeMemory(u16 loc, u8 val)
{
if (loc == g_memBreakpoint)
g_hitMemBreakpoint = true;
if (loc <= 0x1FFF)
{
//External RAM switch
}
else if (loc >= 0x2000 && loc <= 0x3FFF)
{
// ROM Bank
switch (g_mbc.cartType)
{
case 1:
case 2:
case 3:
val &= 0x0F;
if (!val) val = 1;
g_mbc.romBank = (g_mbc.romBank & 0x60) + val;
g_mbc.romOffset = g_mbc.romBank * 0x4000;
break;
default:
assert(false);
break;
}
}
else if (loc >= 0x4000 && loc <= 0x5FFF)
{
// RAM Bank
switch (g_mbc.cartType)
{
case 1:
case 2:
case 3:
if (g_mbc.mode)
{
//RAM mode: set RAM bank
g_mbc.ramOffset = (val & 3) * 0x2000;
}
else
{
//ROM mode: set high bits of ROM bank
g_mbc.romBank = (g_mbc.romBank & 0x1F) + ((val & 3) << 5);
g_mbc.romOffset = g_mbc.romBank * 0x4000;
}
break;
default:
assert(false);
break;
}
}
else if (loc >= 0x6000 && loc <= 0x7FFF)
{
switch (g_mbc.cartType)
{
case 2:
case 3:
g_mbc.mode = val & 1;
break;
default:
assert(false);
break;
}
}
else if (loc >= 0xA000 && loc <= 0xBFFF)
{
// External RAM
g_mbc.ram[g_mbc.ramOffset + (loc & 0x1FFF)] = val;
}
else if (loc >= 0xE000 && loc <= 0xFDFF)
{
//shadow of working RAM (excluding final 512 bytes)
gb.memory[loc - 0x1000] = val;
}
else if (loc >= 0xFF00 && loc < 0xFF80)
{
switch (loc)
{
case 0xFF00://Joypad R/W
gb.joypadInput = val;
break;
case 0xFF40://LCDC
gb.gpu.lcdcStatus = val;
break;
case 0xFF45://LYC
gb.gpu.scanlinecompare = val;
break;
case 0xFF0F://Interrupt Flag
gb.interruptFlag.value = val;
break;
case 0xFF46://DMA register
gb.gpu.dmaRegister = val;
break;
default:
break;
}
}
else if (loc < 0xFFFF)
{
gb.memory[loc] = val;
}
else//0xFFFF Interrupt Enable
{
gb.interruptReg.value = val;
}
}
void writeMemory16(u16 loc, u16 val)
{
writeMemory(loc, val >> 8);
writeMemory(loc + 1, val & 0xFF);
}