mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-12 13:55:07 +01:00
79 lines
2.5 KiB
C
79 lines
2.5 KiB
C
/****************************************************************************
|
|
* Genesis Plus 1.2a
|
|
*
|
|
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
|
|
*
|
|
* SRAM MANAGER
|
|
***************************************************************************/
|
|
|
|
#include "shared.h"
|
|
|
|
T_SRAM sram;
|
|
|
|
/****************************************************************************
|
|
* A quick guide to SRAM on the Genesis
|
|
*
|
|
* This is based on observations only - it may be completely wrong!
|
|
*
|
|
* The SRAM definition is held at offset 0x1b0 of the ROM header.
|
|
* From looking at several ROMS, an ID appears:
|
|
*
|
|
* 0x1b0 : 0x52 0x41 0xF8 0x20 0x00200001 0x0020ffff
|
|
*
|
|
* Assuming 64k SRAM / Battery RAM throughout
|
|
****************************************************************************/
|
|
void SRAM_Init ()
|
|
{
|
|
memset (&sram, 0, sizeof (T_SRAM));
|
|
memset (&sram.sram[0], 0xFF, 0x10000);
|
|
sram.crc = crc32 (0, &sram.sram[0], 0x10000);
|
|
|
|
if ((cart_rom[0x1b0] == 0x52) && (cart_rom[0x1b1] == 0x41))
|
|
{
|
|
sram.on = 1;
|
|
sram.write = 1;
|
|
sram.detected = 1;
|
|
sram.start = READ_WORD_LONG(cart_rom, 0x1b4);
|
|
sram.end = READ_WORD_LONG(cart_rom, 0x1b8);
|
|
|
|
/* some games have incorrect header informations */
|
|
if ((sram.start > sram.end) || ((sram.end - sram.start) >= 0x10000))
|
|
sram.end = sram.start + 0xffff;
|
|
sram.start &= 0xfffffffe;
|
|
sram.end |= 1;
|
|
|
|
/* game using serial EEPROM as external RAM */
|
|
if (sram.end - sram.start < 2) EEPROM_Init();
|
|
}
|
|
else
|
|
{
|
|
/* set SRAM memory region by default */
|
|
sram.start = 0x200000;
|
|
sram.end = 0x20ffff;
|
|
|
|
/* set SRAM ON by default if game is smaller than 2M */
|
|
if (genromsize <= 0x200000)
|
|
{
|
|
sram.on = 1;
|
|
sram.write = 1;
|
|
}
|
|
|
|
/* some games using EEPROM don't have the correct header */
|
|
EEPROM_Init();
|
|
}
|
|
}
|