text: /*===================================================================*/
  /*                                                                   */
  /*                       Mapper 4 (MMC3)                             */
  /*                                                                   */
  /*===================================================================*/
  
  BYTE  Map4_Regs[ 8 ];
  NES_DWORD Map4_Rom_Bank;
  NES_DWORD Map4_Prg0, Map4_Prg1;
  NES_DWORD Map4_Chr01, Map4_Chr23;
  NES_DWORD Map4_Chr4, Map4_Chr5, Map4_Chr6, Map4_Chr7;
  
  #define Map4_Chr_Swap()    ( Map4_Regs[ 0 ] & 0x80 )
  #define Map4_Prg_Swap()    ( Map4_Regs[ 0 ] & 0x40 )
  
  BYTE Map4_IRQ_Enable;
  BYTE Map4_IRQ_Cnt;
  BYTE Map4_IRQ_Latch;
  BYTE Map4_IRQ_Request;
  BYTE Map4_IRQ_Present;
  BYTE Map4_IRQ_Present_Vbl;
  
  /*-------------------------------------------------------------------*/
  /*  Initialize Mapper 4                                              */
  /*-------------------------------------------------------------------*/
  void Map4_Init()
  {
    /* Initialize Mapper */
    MapperInit = Map4_Init;
  
    /* Write to Mapper */
    MapperWrite = Map4_Write;
  
    /* Write to SRAM */
    MapperSram = Map0_Sram;
  
    /* Write to APU */
    MapperApu = Map0_Apu;
  
    /* Read from APU */
    MapperReadApu = Map0_ReadApu;
  
    /* Callback at VSync */
    MapperVSync = Map0_VSync;
  
    /* Callback at HSync */
    MapperHSync = Map4_HSync;
  
    /* Callback at PPU */
    MapperPPU = Map0_PPU;
  
    /* Callback at Rendering Screen ( 1:BG, 0:Sprite ) */
    MapperRenderScreen = Map0_RenderScreen;
  
    /* Set SRAM Banks */
    SRAMBANK = SRAM;
  
    /* Initialize State Registers */
    for ( int nPage = 0; nPage < 8; nPage++ )
    {
      Map4_Regs[ nPage ] = 0x00;
    }
  
    /* Set ROM Banks */
    Map4_Prg0 = 0;
    Map4_Prg1 = 1;
    Map4_Set_CPU_Banks();
  
    /* Set PPU Banks */
    if ( NesHeader.byVRomSize > 0 )
    {
      Map4_Chr01 = 0;
      Map4_Chr23 = 2;
      Map4_Chr4  = 4;
      Map4_Chr5  = 5;
      Map4_Chr6  = 6;
      Map4_Chr7  = 7;
      Map4_Set_PPU_Banks();
    } else {
      Map4_Chr01 = Map4_Chr23 = 0;
      Map4_Chr4 = Map4_Chr5 = Map4_Chr6 = Map4_Chr7 = 0;
    }
  
    /* Initialize IRQ Registers */
    Map4_IRQ_Enable = 0;
    Map4_IRQ_Cnt = 0;
    Map4_IRQ_Latch = 0;
    Map4_IRQ_Request = 0;
    Map4_IRQ_Present = 0;
    Map4_IRQ_Present_Vbl = 0;
  
    /* Set up wiring of the interrupt pin */
    K6502_Set_Int_Wiring( 1, 1 ); 
  }
  
  /*-------------------------------------------------------------------*/
  /*  Mapper 4 Write Function                                          */
  /*-------------------------------------------------------------------*/
  void Map4_Write( WORD wAddr, BYTE byData )
  {
    NES_DWORD dwBankNum;
  
    switch ( wAddr & 0xe001 )
    {
      case 0x8000:
        Map4_Regs[ 0 ] = byData;
        Map4_Set_PPU_Banks();
        Map4_Set_CPU_Banks();
        break;
  
      case 0x8001:
        Map4_Regs[ 1 ] = byData;
        dwBankNum = Map4_Regs[ 1 ];
  
        switch ( Map4_Regs[ 0 ] & 0x07 )
        {
          /* Set PPU Banks */
          case 0x00:
            if ( NesHeader.byVRomSize > 0 )
            {
              dwBankNum &= 0xfe;
              Map4_Chr01 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          case 0x01:
            if ( NesHeader.byVRomSize > 0 )
            {
              dwBankNum &= 0xfe;
              Map4_Chr23 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          case 0x02:
            if ( NesHeader.byVRomSize > 0 )
            {
              Map4_Chr4 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          case 0x03:
            if ( NesHeader.byVRomSize > 0 )
            {
              Map4_Chr5 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          case 0x04:
            if ( NesHeader.byVRomSize > 0 )
            {
              Map4_Chr6 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          case 0x05:
            if ( NesHeader.byVRomSize > 0 )
            {
              Map4_Chr7 = dwBankNum;
              Map4_Set_PPU_Banks();
            }
            break;
  
          /* Set ROM Banks */
          case 0x06:
            Map4_Prg0 = dwBankNum;
            Map4_Set_CPU_Banks();
            break;
  
          case 0x07:
            Map4_Prg1 = dwBankNum;
            Map4_Set_CPU_Banks();
            break;
        }
        break;
  
      case 0xa000:
        Map4_Regs[ 2 ] = byData;
  
        if ( !ROM_FourScr )
        {
          if ( byData & 0x01 )
          {
            InfoNES_Mirroring( 0 );
          } else {
            InfoNES_Mirroring( 1 );
          }
        }
        break;
  
      case 0xa001:
        Map4_Regs[ 3 ] = byData;
        break;
  
      case 0xc000:
        Map4_Regs[ 4 ] = byData;
        Map4_IRQ_Latch = byData;
        break;
  
      case 0xc001:
        Map4_Regs[ 5 ] = byData;
        if ( PPU_Scanline < 240 )
        {
            Map4_IRQ_Cnt |= 0x80;
            Map4_IRQ_Present = 0xff;
        } else {
            Map4_IRQ_Cnt |= 0x80;
            Map4_IRQ_Present_Vbl = 0xff;
            Map4_IRQ_Present = 0;
        }
        break;
  
      case 0xe000:
        Map4_Regs[ 6 ] = byData;
        Map4_IRQ_Enable = 0;
  			Map4_IRQ_Request = 0;
        break;
  
      case 0xe001:
        Map4_Regs[ 7 ] = byData;
        Map4_IRQ_Enable = 1;
  			Map4_IRQ_Request = 0;
        break;
    }
  }
  
  /*-------------------------------------------------------------------*/
  /*  Mapper 4 H-Sync Function                                         */
  /*-------------------------------------------------------------------*/
  void Map4_HSync()
  {
  /*
   *  Callback at HSync
   *
   */
    if ( ( /* 0 <= PPU_Scanline && */ PPU_Scanline <= 239 ) && 
         ( PPU_R1 & R1_SHOW_SCR || PPU_R1 & R1_SHOW_SP ) )
    {
  		if( Map4_IRQ_Present_Vbl ) {
  			Map4_IRQ_Cnt = Map4_IRQ_Latch;
  			Map4_IRQ_Present_Vbl = 0;
  		}
  		if( Map4_IRQ_Present ) {
  			Map4_IRQ_Cnt = Map4_IRQ_Latch;
  			Map4_IRQ_Present = 0;
  		} else if( Map4_IRQ_Cnt > 0 ) {
  			Map4_IRQ_Cnt--;
  		}
  
  		if( Map4_IRQ_Cnt == 0 ) {
  			if( Map4_IRQ_Enable ) {
  				Map4_IRQ_Request = 0xFF;
  			}
  			Map4_IRQ_Present = 0xFF;
  		}
  	}
  	if( Map4_IRQ_Request  ) {
  		IRQ_REQ;
  	}
  }
  
  /*-------------------------------------------------------------------*/
  /*  Mapper 4 Set CPU Banks Function                                  */
  /*-------------------------------------------------------------------*/
  void Map4_Set_CPU_Banks()
  {
    if ( Map4_Prg_Swap() )
    {
      ROMBANK0 = ROMLASTPAGE( 1 );
      ROMBANK1 = ROMPAGE( Map4_Prg1 % ( NesHeader.byRomSize << 1 ) );
      ROMBANK2 = ROMPAGE( Map4_Prg0 % ( NesHeader.byRomSize << 1 ) );
      ROMBANK3 = ROMLASTPAGE( 0 );
    } else {
      ROMBANK0 = ROMPAGE( Map4_Prg0 % ( NesHeader.byRomSize << 1 ) );
      ROMBANK1 = ROMPAGE( Map4_Prg1 % ( NesHeader.byRomSize << 1 ) );
      ROMBANK2 = ROMLASTPAGE( 1 );
      ROMBANK3 = ROMLASTPAGE( 0 );
    }
  }
  
  /*-------------------------------------------------------------------*/
  /*  Mapper 4 Set PPU Banks Function                                  */
  /*-------------------------------------------------------------------*/
  void Map4_Set_PPU_Banks()
  {
    if ( NesHeader.byVRomSize > 0 )
    {
      if ( Map4_Chr_Swap() )
      { 
        PPUBANK[ 0 ] = VROMPAGE( Map4_Chr4 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 1 ] = VROMPAGE( Map4_Chr5 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 2 ] = VROMPAGE( Map4_Chr6 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 3 ] = VROMPAGE( Map4_Chr7 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 4 ] = VROMPAGE( ( Map4_Chr01 + 0 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 5 ] = VROMPAGE( ( Map4_Chr01 + 1 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 6 ] = VROMPAGE( ( Map4_Chr23 + 0 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 7 ] = VROMPAGE( ( Map4_Chr23 + 1 ) % ( NesHeader.byVRomSize << 3 ) );
        InfoNES_SetupChr();
      } else {
        PPUBANK[ 0 ] = VROMPAGE( ( Map4_Chr01 + 0 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 1 ] = VROMPAGE( ( Map4_Chr01 + 1 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 2 ] = VROMPAGE( ( Map4_Chr23 + 0 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 3 ] = VROMPAGE( ( Map4_Chr23 + 1 ) % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 4 ] = VROMPAGE( Map4_Chr4 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 5 ] = VROMPAGE( Map4_Chr5 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 6 ] = VROMPAGE( Map4_Chr6 % ( NesHeader.byVRomSize << 3 ) );
        PPUBANK[ 7 ] = VROMPAGE( Map4_Chr7 % ( NesHeader.byVRomSize << 3 ) );
        InfoNES_SetupChr();
      }
    }
    else
    {
      if ( Map4_Chr_Swap() )
      { 
  #if 0
        PPUBANK[ 0 ] = VRAMPAGE0( 0 );
        PPUBANK[ 1 ] = VRAMPAGE0( 1 );
        PPUBANK[ 2 ] = VRAMPAGE0( 2 );
        PPUBANK[ 3 ] = VRAMPAGE0( 3 );
        PPUBANK[ 4 ] = VRAMPAGE1( 0 );
        PPUBANK[ 5 ] = VRAMPAGE1( 1 );
        PPUBANK[ 6 ] = VRAMPAGE1( 2 );
        PPUBANK[ 7 ] = VRAMPAGE1( 3 );
  #else
        PPUBANK[ 0 ] = CRAMPAGE( 0 );
        PPUBANK[ 1 ] = CRAMPAGE( 1 );
        PPUBANK[ 2 ] = CRAMPAGE( 2 );
        PPUBANK[ 3 ] = CRAMPAGE( 3 );
        PPUBANK[ 4 ] = CRAMPAGE( 4 );
        PPUBANK[ 5 ] = CRAMPAGE( 5 );
        PPUBANK[ 6 ] = CRAMPAGE( 6 );
        PPUBANK[ 7 ] = CRAMPAGE( 7 );
  #endif
        InfoNES_SetupChr();
      } else {
  #if 0
        PPUBANK[ 0 ] = VRAMPAGE1( 0 );
        PPUBANK[ 1 ] = VRAMPAGE1( 1 );
        PPUBANK[ 2 ] = VRAMPAGE1( 2 );
        PPUBANK[ 3 ] = VRAMPAGE1( 3 );
        PPUBANK[ 4 ] = VRAMPAGE0( 0 );
        PPUBANK[ 5 ] = VRAMPAGE0( 1 );
        PPUBANK[ 6 ] = VRAMPAGE0( 2 );
        PPUBANK[ 7 ] = VRAMPAGE0( 3 );
  #else
        PPUBANK[ 0 ] = CRAMPAGE( 0 );
        PPUBANK[ 1 ] = CRAMPAGE( 1 );
        PPUBANK[ 2 ] = CRAMPAGE( 2 );
        PPUBANK[ 3 ] = CRAMPAGE( 3 );
        PPUBANK[ 4 ] = CRAMPAGE( 4 );
        PPUBANK[ 5 ] = CRAMPAGE( 5 );
        PPUBANK[ 6 ] = CRAMPAGE( 6 );
        PPUBANK[ 7 ] = CRAMPAGE( 7 );
  #endif
        InfoNES_SetupChr();
      }
    }    
  }
  