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/***************************************************************************************
* Genesis Plus
* Backup RAM support
*
* Copyright (C) 2007-2013 Eke-Eke (Genesis Plus GX)
*
* 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"
T_SRAM sram;
/****************************************************************************
* A quick guide to external RAM on the Genesis
*
* The external RAM definition is held at offset 0x1b0 of the ROM header.
*
* 1B0h: dc.b 'RA', %1x1yz000, %abc00000
* 1B4h: dc.l RAM start address
* 1B8h: dc.l RAM end address
* x 1 for BACKUP (not volatile), 0 for volatile RAM
* yz 10 if even address only
* 11 if odd address only
* 00 if both even and odd address
* 01 others (serial EEPROM, RAM with 4-bit data bus, etc)
* abc 001 if SRAM
* 010 if EEPROM (serial or parallel)
* other values unused
*
* Assuming max. 64k backup RAM throughout
****************************************************************************/
void sram_init()
{
memset(&sram, 0, sizeof (T_SRAM));
/* backup RAM data is stored above cartridge ROM area, at $800000-$80FFFF (max. 64K) */
if (cart.romsize > 0x800000) return;
sram.sram = cart.rom + 0x800000;
/* initialize Backup RAM */
memset(sram.sram, 0xFF, 0x10000);
sram.crc = crc32(0, sram.sram, 0x10000);
/* retrieve informations from header */
if ((READ_BYTE(cart.rom,0x1b0) == 0x52) && (READ_BYTE(cart.rom,0x1b1) == 0x41))
{
/* backup RAM detected */
sram.detected = 1;
/* enable backup RAM */
sram.on = 1;
/* retrieve backup RAM start & end addresses */
sram.start = READ_WORD_LONG(cart.rom, 0x1b4);
sram.end = READ_WORD_LONG(cart.rom, 0x1b8);
/* autodetect games with wrong header infos */
if (strstr(rominfo.product,"T-26013") != NULL)
{
/* Psy-O-Blade (wrong header) */
sram.start = 0x200001;
sram.end = 0x203fff;
}
/* fixe games indicating internal RAM as volatile external RAM (Feng Kuang Tao Hua Yuan) */
else if (sram.start == 0xff0000)
{
/* backup RAM should be disabled */
sram.on = 0;
}
/* fixe other bad header informations */
else if ((sram.start > sram.end) || ((sram.end - sram.start) >= 0x10000))
{
sram.end = sram.start + 0xffff;
}
}
else
{
/* autodetect games with missing header infos */
if (strstr(rominfo.product,"T-50086") != NULL)
{
/* PGA Tour Golf */
sram.on = 1;
sram.start = 0x200001;
sram.end = 0x203fff;
}
else if (strstr(rominfo.product,"ACLD007") != NULL)
{
/* Winter Challenge */
sram.on = 1;
sram.start = 0x200001;
sram.end = 0x200fff;
}
else if (strstr(rominfo.product,"T-50286") != NULL)
{
/* Buck Rogers - Countdown to Doomsday */
sram.on = 1;
sram.start = 0x200001;
sram.end = 0x203fff;
}
else if (((rominfo.realchecksum == 0xaeaa) || (rominfo.realchecksum == 0x8dba)) &&
(rominfo.checksum == 0x8104))
{
/* Xin Qigai Wangzi (use uncommon area) */
sram.on = 1;
sram.start = 0x400001;
sram.end = 0x40ffff;
}
else if ((strstr(rominfo.ROMType,"SF") != NULL) && (strstr(rominfo.product,"001") != NULL))
{
/* SF-001 */
sram.on = 1;
if (rominfo.checksum == 0x3e08)
{
/* last revision (use bankswitching) */
sram.start = 0x3c0001;
sram.end = 0x3cffff;
}
else
{
/* older revisions (use uncommon area) */
sram.start = 0x400001;
sram.end = 0x40ffff;
}
}
else if ((strstr(rominfo.ROMType,"SF") != NULL) && (strstr(rominfo.product,"004") != NULL))
{
/* SF-004 (use bankswitching) */
sram.on = 1;
sram.start = 0x200001;
sram.end = 0x203fff;
}
else if (strstr(rominfo.international,"SONIC & KNUCKLES") != NULL)
{
/* Sonic 3 & Knuckles combined ROM */
if (cart.romsize == 0x400000)
{
/* Sonic & Knuckle does not have backup RAM but can access FRAM from Sonic 3 cartridge */
sram.on = 1;
sram.start = 0x200001;
sram.end = 0x203fff;
}
}
/* auto-detect games which need disabled backup RAM */
else if (strstr(rominfo.product,"T-113016") != NULL)
{
/* Pugsy (does not have backup RAM but tries writing outside ROM area as copy protection) */
sram.on = 0;
}
else if (strstr(rominfo.international,"SONIC THE HEDGEHOG 2") != NULL)
{
/* Sonic the Hedgehog 2 (does not have backup RAM) */
/* this prevents backup RAM from being mapped in place of mirrored ROM when using S&K LOCK-ON feature */
sram.on = 0;
}
/* by default, enable backup RAM for ROM smaller than 2MB */
else if (cart.romsize <= 0x200000)
{
/* 64KB static RAM mapped to $200000-$20ffff */
sram.start = 0x200000;
sram.end = 0x20ffff;
sram.on = 1;
}
}
}
unsigned int sram_read_byte(unsigned int address)
{
return sram.sram[address & 0xffff];
}
unsigned int sram_read_word(unsigned int address)
{
address &= 0xfffe;
return (sram.sram[address + 1] | (sram.sram[address] << 8));
}
void sram_write_byte(unsigned int address, unsigned int data)
{
sram.sram[address & 0xffff] = data;
}
void sram_write_word(unsigned int address, unsigned int data)
{
address &= 0xfffe;
sram.sram[address] = data >> 8;
sram.sram[address + 1] = data & 0xff;
}
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