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/***************************************************************************
snesobc1.c
File to handle emulation of the SNES "OBC-1" add-on chip.
Original C++ code by byuu.
Byuu's code is released under GNU General Public License
version 2 as published by the Free Software Foundation.
The implementation below is released under the MAME license
for use in MAME, MESS and derivatives by permission of the author.
***************************************************************************/
#include "includes/snes.h"
static int obc1_address;
static int obc1_offset;
static int obc1_shift;
static READ8_HANDLER( obc1_read )
{
UINT16 address = offset & 0x1fff;
UINT8 value;
switch (address)
{
case 0x1ff0:
value = snes_ram[obc1_offset + (obc1_address << 2) + 0];
break;
case 0x1ff1:
value = snes_ram[obc1_offset + (obc1_address << 2) + 1];
break;
case 0x1ff2:
value = snes_ram[obc1_offset + (obc1_address << 2) + 2];
break;
case 0x1ff3:
value = snes_ram[obc1_offset + (obc1_address << 2) + 3];
break;
case 0x1ff4:
value = snes_ram[obc1_offset + (obc1_address >> 2) + 0x200];
break;
default:
value = snes_ram[address];
break;
}
return value;
}
static WRITE8_HANDLER( obc1_write )
{
UINT16 address = offset & 0x1fff;
UINT8 temp;
switch(address)
{
case 0x1ff0:
snes_ram[obc1_offset + (obc1_address << 2) + 0] = data;
break;
case 0x1ff1:
snes_ram[obc1_offset + (obc1_address << 2) + 1] = data;
break;
case 0x1ff2:
snes_ram[obc1_offset + (obc1_address << 2) + 2] = data;
break;
case 0x1ff3:
snes_ram[obc1_offset + (obc1_address << 2) + 3] = data;
break;
case 0x1ff4:
temp = snes_ram[obc1_offset + (obc1_address >> 2) + 0x200];
temp = (temp & ~(3 << obc1_shift)) | ((data & 0x03) << obc1_shift);
snes_ram[obc1_offset + (obc1_address >> 2) + 0x200] = temp;
break;
case 0x1ff5:
obc1_offset = (data & 0x01) ? 0x1800 : 0x1c00;
snes_ram[address & 0x1fff] = data;
break;
case 0x1ff6:
obc1_address = data & 0x7f;
obc1_shift = (data & 0x03) << 1;
snes_ram[address & 0x1fff] = data;
break;
default:
snes_ram[address & 0x1fff] = data;
break;
}
}
static void obc1_init( void )
{
obc1_offset = (snes_ram[0x1ff5] & 0x01) ? 0x1800 : 0x1c00;
obc1_address = (snes_ram[0x1ff6] & 0x7f);
obc1_shift = (snes_ram[0x1ff6] & 0x03) << 1;
}
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