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mapper001.cpp
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172 lines (148 loc) · 6.43 KB
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#include "mapper001.hpp"
/**** mapper 001 (MMC1) ****/
void Mapper001::Reset()
{
PRG_RAM_Enable = false;
PRGBankMode = PRGBankMode::FIX_HIGH_BANK;
CHRBankMode = CHRBankMode::SWITCH_4K;
mappedPRGBank32 = 0;
mappedPRGBank16 = 0;
mappedCHRBank8 = 0;
mappedCHRBank4Low = 0;
mappedCHRBank4High = 0;
shiftRegister = 0x00;
}
uint32_t Mapper001::MapReadPRG(uint16_t address, bool &fromRAM)
{
uint32_t mappedAddress = 0x00000000;
if (PRG_RAM_Enable && address >= 0x6000 && address <= 0x7FFF) // 8 KiB PRG RAM (optional)
{
mappedAddress = address & 0x1FFF;
fromRAM = true;
}
else if (address >= 0x8000 && address <= 0xFFFF)
switch (PRGBankMode)
{
case PRGBankMode::SWITCH_32K:
mappedAddress = mappedPRGBank32 * 0x8000 + (address & 0x7FFF); // 0x8000 - 0xFFFF
break;
case PRGBankMode::FIX_LOW_BANK:
if (address <= 0xBFFF) // 0x8000 - 0xBFFF
mappedAddress = 0 * 0x4000 + (address & 0x3FFF);
else // 0xC000 - 0xFFFF
mappedAddress = mappedPRGBank16 * 0x4000 + (address & 0x3FFF);
break;
case PRGBankMode::FIX_HIGH_BANK:
if (address <= 0xBFFF) // 0x8000 - 0xBFFF
mappedAddress = mappedPRGBank16 * 0x4000 + (address & 0x3FFF);
else // 0xC000 - 0xFFFF
mappedAddress = (numBanksPRG - 1) * 0x4000 + (address & 0x3FFF);
break;
}
return mappedAddress;
}
uint32_t Mapper001::MapWritePRG(uint16_t address, uint8_t data, bool &toRAM)
{
static uint8_t shift;
uint32_t mappedAddress = 0x00000000;
if (PRG_RAM_Enable && address >= 0x6000 && address <= 0x7FFF) // 8 KiB PRG RAM (optional)
{
mappedAddress = address & 0x1FFF;
toRAM = true;
}
else if (address >= 0x8000 && address <= 0xFFFF)
{
if (data & 0x80)
{
shiftRegister = 0x00; // writing a byte with bit 7 set clears shift register
shift = 0; // reset shift register
}
else
{
if (shift < 4)
{
shiftRegister = shiftRegister >> 1 | (data & 0x01) << 3; // shift bit 0 of data into 4-bit shift register (LSB)
shift++;
}
else
{
uint8_t internalRegister = shiftRegister | (data & 0x01) << 4; // 5-bit internal register
shiftRegister = 0x00; // writing fifth bit of command clears shift register
shift = 0; // reset shift register
if (!(address & 0x4000) && !(address & 0x2000)) // control register: address 0x8000 - 0x9FFF, bit 14 == 0, bit 13 == 0
{
switch (internalRegister & 0x03)
{
case 0:
mirroringMode = MirroringMode::SINGLE_SCREEN_LOWER;
break;
case 1:
mirroringMode = MirroringMode::SINGLE_SCREEN_UPPER;
break;
case 2:
mirroringMode = MirroringMode::VERTICAL;
break;
case 3:
mirroringMode = MirroringMode::HORIZONTAL;
break;
}
switch ((internalRegister & 0x0C) >> 2)
{
case 0:
case 1:
PRGBankMode = PRGBankMode::SWITCH_32K;
break;
case 2:
PRGBankMode = PRGBankMode::FIX_LOW_BANK;
break;
case 3:
PRGBankMode = PRGBankMode::FIX_HIGH_BANK;
break;
}
if (!(internalRegister & 0x10))
CHRBankMode = CHRBankMode::SWITCH_8K;
else
CHRBankMode = CHRBankMode::SWITCH_4K;
}
else if (!(address & 0x4000) && (address & 0x2000)) // CHR bank 0: address 0xA000 - 0xBFFF, bit 14 == 0, bit 13 == 1
{
mappedCHRBank8 = (internalRegister & 0x1E) >> 1;
mappedCHRBank4Low = internalRegister;
}
else if ((address & 0x4000) && !(address & 0x2000)) // CHR bank 1: address 0xC000 - 0xDFFF, bit 14 == 1, bit 13 == 0
mappedCHRBank4High = internalRegister;
else if ((address & 0x4000) && (address & 0x2000)) // PRG bank and RAM enable: address 0xE000 - 0xFFFF, bit 14 == 1, bit 13 == 1
{
mappedPRGBank32 = internalRegister & 0x0E;
mappedPRGBank16 = internalRegister & 0x0F;
PRG_RAM_Enable = !(internalRegister & 0x10);
}
}
}
}
return mappedAddress;
}
uint32_t Mapper001::MapReadCHR(uint16_t address)
{
uint32_t mappedAddress = 0x00000000;
if (CHRBankMode == CHRBankMode::SWITCH_4K)
if (address <= 0x0FFF) // 0x0000 - 0x0FFF
mappedAddress = mappedCHRBank4Low * 0x1000 + (address & 0x0FFF);
else // 0x1000 - 0x1FFF
mappedAddress = mappedCHRBank4High * 0x1000 + (address & 0x0FFF);
else if (CHRBankMode == CHRBankMode::SWITCH_8K) // 0x0000 - 0x1FFF
mappedAddress = mappedCHRBank8 * 0x2000 + (address & 0x1FFF);
return mappedAddress;
}
uint32_t Mapper001::MapWriteCHR(uint16_t address)
{
uint32_t mappedAddress = 0x00000000;
if (CHRBankMode == CHRBankMode::SWITCH_4K)
if (address <= 0x0FFF) // 0x0000 - 0x0FFF
mappedAddress = mappedCHRBank4Low * 0x1000 + (address & 0x0FFF);
else // 0x1000 - 0x1FFF
mappedAddress = mappedCHRBank4High * 0x1000 + (address & 0x0FFF);
else if (CHRBankMode == CHRBankMode::SWITCH_8K) // 0x0000 - 0x1FFF
mappedAddress = mappedCHRBank8 * 0x2000 + (address & 0x1FFF);
return mappedAddress;
}