mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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99 lines
3.2 KiB
C
99 lines
3.2 KiB
C
/***************************************************************************************
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* Genesis Plus
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* Backup RAM support
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*
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* Copyright (C) 2007, 2008, 2009 Eke-Eke (GCN/Wii port)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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****************************************************************************************/
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#include "shared.h"
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T_SRAM sram;
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/****************************************************************************
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* A quick guide to SRAM on the Genesis
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*
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* The SRAM definition is held at offset 0x1b0 of the ROM header.
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*
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* 1B0h: dc.b 'RA', %1x1yz000, %00100000
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* 1B4h: dc.l RAM start address
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* 1B8h: dc.l RAM end address
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* x 1 for BACKUP and 0 If not BACKUP
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* yz 10 if even address only
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* 11 if odd address only
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* 00 if both even and odd address
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*
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* Assuming max. 64k SRAM / Battery RAM throughout
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****************************************************************************/
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void sram_init()
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{
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memset (&sram, 0, sizeof (T_SRAM));
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memset (&sram.sram[0], 0xFF, 0x10000);
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sram.crc = crc32 (0, &sram.sram[0], 0x10000);
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if ((READ_BYTE(cart_rom,0x1b0) == 0x52) && (READ_BYTE(cart_rom,0x1b1) == 0x41))
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{
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/* retrieve informations from headezr */
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sram.detected = 1;
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sram.start = READ_WORD_LONG(cart_rom, 0x1b4);
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sram.end = READ_WORD_LONG(cart_rom, 0x1b8);
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/* fixe some bad header informations */
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if ((sram.start > sram.end) || ((sram.end - sram.start) >= 0x10000))
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sram.end = sram.start + 0xffff;
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sram.start &= 0xfffffffe;
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sram.end |= 1;
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}
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else
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{
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/* default SRAM region */
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sram.start = 0x200000;
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sram.end = 0x20ffff;
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}
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/* set SRAM ON by default when ROM is not mapped */
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if (genromsize <= sram.start)
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{
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sram.on = 1;
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sram.write = 1;
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}
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/* Some games with bad header or specific configuration */
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if (strstr(rominfo.product,"T-113016") != NULL)
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{
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/* Pugsy (try accessing unmapped area for copy protection) */
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sram.on = 0;
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sram.write = 0;
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}
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else if ((strstr(rominfo.product,"T-26013") != NULL) && (rominfo.checksum == 0xa837))
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{
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/* Psy-O-Blade (bad header) */
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sram.on = 1;
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sram.write = 1;
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sram.start = 0x200001;
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sram.end = 0x203fff;
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}
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else if (((realchecksum == 0xaeaa) || (realchecksum == 0x8dba)) && (rominfo.checksum == 0x8104))
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{
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/* Xin Qigai Wangzi, aka Beggar Prince (no header, use uncommon area) */
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sram.on = 1;
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sram.write = 1;
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sram.start = 0x400000;
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sram.end = 0x40ffff;
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}
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}
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