Genesis-Plus-GX/source/cart_hw/ggenie.c

284 lines
8.5 KiB
C

/****************************************************************************
* Genesis Plus
* Game Genie Hardware emulation
*
* Copyright (C) 2009-2011 Eke-Eke (Genesis Plus GX)
*
* Based on documentation from Charles McDonald
* (http://cgfm2.emuviews.com/txt/genie.txt)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
*
* - Redistributions may not be sold, nor may they be used in a commercial
* product or activity.
*
* - Redistributions that are modified from the original source must include the
* complete source code, including the source code for all components used by a
* binary built from the modified sources. However, as a special exception, the
* source code distributed need not include anything that is normally distributed
* (in either source or binary form) with the major components (compiler, kernel,
* and so on) of the operating system on which the executable runs, unless that
* component itself accompanies the executable.
*
* - Redistributions must reproduce the above copyright notice, this list of
* conditions and the following disclaimer in the documentation and/or other
* materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************************/
#include "shared.h"
static struct
{
uint8 enabled;
uint8 *rom;
uint16 regs[0x20];
uint16 old[6];
uint16 data[6];
uint32 addr[6];
} ggenie;
static unsigned int ggenie_read_byte(unsigned int address);
static unsigned int ggenie_read_word(unsigned int address);
static void ggenie_write_byte(unsigned int address, unsigned int data);
static void ggenie_write_word(unsigned int address, unsigned int data);
static void ggenie_write_regs(unsigned int offset, unsigned int data);
void ggenie_init(void)
{
int i;
FILE *f;
memset(&ggenie,0,sizeof(ggenie));
/* Store Game Genie ROM (32k) above cartridge ROM + SRAM area */
if (cart.romsize > 0x600000) return;
ggenie.rom = cart.rom + 0x600000;
/* Open Game Genie ROM file */
f = fopen(GG_ROM,"rb");
if (f == NULL) return;
/* Load ROM */
for (i=0; i<0x8000; i+=0x1000)
{
fread(ggenie.rom + i, 0x1000, 1, f);
}
/* Close ROM file */
fclose(f);
#ifdef LSB_FIRST
for (i=0; i<0x8000; i+=2)
{
/* Byteswap ROM */
uint8 temp = ggenie.rom[i];
ggenie.rom[i] = ggenie.rom[i+1];
ggenie.rom[i+1] = temp;
}
#endif
/* $0000-$7fff mirrored into $8000-$ffff */
memcpy(ggenie.rom + 0x8000, ggenie.rom, 0x8000);
/* set flag */
ggenie.enabled = 1;
}
void ggenie_shutdown(void)
{
if (ggenie.enabled)
{
ggenie_switch(0);
ggenie.enabled = 0;
}
}
void ggenie_reset(int hard)
{
if (ggenie.enabled)
{
if (hard)
{
/* clear codes */
ggenie_switch(0);
/* reset internal state */
memset(ggenie.regs,0,sizeof(ggenie.regs));
memset(ggenie.old,0,sizeof(ggenie.old));
memset(ggenie.data,0,sizeof(ggenie.data));
memset(ggenie.addr,0,sizeof(ggenie.addr));
}
/* Game Genie ROM is mapped at $000000-$007fff */
m68k_memory_map[0].base = ggenie.rom;
/* Internal registers are mapped at $000000-$00001f */
m68k_memory_map[0].write8 = ggenie_write_byte;
m68k_memory_map[0].write16 = ggenie_write_word;
/* Disable registers reads */
m68k_memory_map[0].read16 = NULL;
}
}
void ggenie_switch(int enable)
{
int i;
if (enable)
{
/* enable cheats */
for (i=0; i<6; i++)
{
/* patch is enabled ? */
if (ggenie.regs[0] & (1 << i))
{
/* save old value and patch ROM if enabled */
ggenie.old[i] = *(uint16 *)(cart.rom + ggenie.addr[i]);
*(uint16 *)(cart.rom + ggenie.addr[i]) = ggenie.data[i];
}
}
}
else
{
/* disable cheats in reversed order in case the same address is used by multiple patches */
for (i=5; i>=0; i--)
{
/* patch is enabled ? */
if (ggenie.regs[0] & (1 << i))
{
/* restore original ROM value */
*(uint16 *)(cart.rom + ggenie.addr[i]) = ggenie.old[i];
}
}
}
}
static unsigned int ggenie_read_byte(unsigned int address)
{
unsigned int data = ggenie.regs[(address >> 1) & 0x1f];
return ((address & 1) ? (data & 0xff) : ((data >> 8) & 0xff));
}
static unsigned int ggenie_read_word(unsigned int address)
{
return ggenie.regs[(address >> 1) & 0x1f];
}
static void ggenie_write_byte(unsigned int address, unsigned int data)
{
/* Register offset */
uint8 offset = (address >> 1) & 0x1f;
/* /LWR and /UWR are used to decode writes */
if (address & 1)
{
data = (ggenie.regs[offset] & 0xff00) | (data & 0xff);
}
else
{
data = (ggenie.regs[offset] & 0x00ff) | ((data & 0xff) << 8);
}
/* Update internal register */
ggenie_write_regs(offset,data);
}
static void ggenie_write_word(unsigned int address, unsigned int data)
{
/* Register offset */
uint8 offset = (address >> 1) & 0x1f;
/* Write internal register (full WORD) */
ggenie_write_regs(offset,data);
}
static void ggenie_write_regs(unsigned int offset, unsigned int data)
{
/* update internal register */
ggenie.regs[offset] = data;
/* Mode Register */
if (offset == 0)
{
/* MODE bit */
if (data & 0x400)
{
/* $0000-$7ffff reads mapped to Cartridge ROM */
m68k_memory_map[0].base = cart.rom;
m68k_memory_map[0].read8 = NULL;
m68k_memory_map[0].read16 = NULL;
}
else
{
/* $0000-$7ffff reads mapped to Game Genie ROM */
m68k_memory_map[0].base = ggenie.rom;
m68k_memory_map[0].read8 = NULL;
m68k_memory_map[0].read16 = NULL;
/* READ_ENABLE bit */
if (data & 0x200)
{
/* $0000-$7ffff reads mapped to Game Genie Registers */
/* code doing this should execute in RAM so we don't need to modify base address */
m68k_memory_map[0].read8 = ggenie_read_byte;
m68k_memory_map[0].read16 = ggenie_read_word;
}
}
/* LOCK bit */
if (data & 0x100)
{
/* decode patch address (ROM area only)*/
/* note: Charles's doc is wrong, first register holds bits 23-16 of patch address */
ggenie.addr[0] = ((ggenie.regs[2] & 0x3f) << 16) | ggenie.regs[3];
ggenie.addr[1] = ((ggenie.regs[5] & 0x3f) << 16) | ggenie.regs[6];
ggenie.addr[2] = ((ggenie.regs[8] & 0x3f) << 16) | ggenie.regs[9];
ggenie.addr[3] = ((ggenie.regs[11] & 0x3f) << 16) | ggenie.regs[12];
ggenie.addr[4] = ((ggenie.regs[14] & 0x3f) << 16) | ggenie.regs[15];
ggenie.addr[5] = ((ggenie.regs[17] & 0x3f) << 16) | ggenie.regs[18];
/* decode patch data */
ggenie.data[0] = ggenie.regs[4];
ggenie.data[1] = ggenie.regs[7];
ggenie.data[2] = ggenie.regs[10];
ggenie.data[3] = ggenie.regs[13];
ggenie.data[4] = ggenie.regs[16];
ggenie.data[5] = ggenie.regs[19];
/* disable internal registers */
m68k_memory_map[0].write8 = m68k_unused_8_w;
m68k_memory_map[0].write16 = m68k_unused_16_w;
/* patch ROM when GG program exits (LOCK bit set) */
/* this is done here to handle patched program reads faster & more easily */
/* on real HW, address decoding would be done on each reads */
ggenie_switch(1);
}
else
{
m68k_memory_map[0].write8 = ggenie_write_byte;
m68k_memory_map[0].write16 = ggenie_write_word;
}
}
/* RESET register */
else if (offset == 1)
{
ggenie.regs[1] |= 1;
}
}