mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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222 lines
7.4 KiB
C
222 lines
7.4 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) 2007-2013 Eke-Eke (Genesis Plus GX)
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*
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* Redistribution and use of this code or any derivative works are permitted
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* provided that the following conditions are met:
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*
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* - Redistributions may not be sold, nor may they be used in a commercial
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* product or activity.
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*
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* - Redistributions that are modified from the original source must include the
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* complete source code, including the source code for all components used by a
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* binary built from the modified sources. However, as a special exception, the
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* source code distributed need not include anything that is normally distributed
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* (in either source or binary form) with the major components (compiler, kernel,
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* and so on) of the operating system on which the executable runs, unless that
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* component itself accompanies the executable.
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*
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* - Redistributions must reproduce the above copyright notice, this list of
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* conditions and the following disclaimer in the documentation and/or other
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* materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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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 external RAM on the Genesis
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*
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* The external RAM definition is held at offset 0x1b0 of the ROM header.
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*
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* 1B0h: dc.b 'RA', %1x1yz000, %abc00000
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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 (not volatile), 0 for volatile RAM
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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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* 01 others (serial EEPROM, RAM with 4-bit data bus, etc)
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* abc 001 if SRAM
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* 010 if EEPROM (serial or parallel)
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* other values unused
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*
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* Assuming max. 64k backup 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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/* backup RAM data is stored above cartridge ROM area, at $800000-$80FFFF (max. 64K) */
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if (cart.romsize > 0x800000) return;
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sram.sram = cart.rom + 0x800000;
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/* initialize Backup RAM */
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memset(sram.sram, 0xFF, 0x10000);
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sram.crc = crc32(0, sram.sram, 0x10000);
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/* retrieve informations from header */
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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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/* backup RAM detected */
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sram.detected = 1;
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/* enable backup RAM */
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sram.on = 1;
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/* retrieve backup RAM start & end addresses */
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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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/* autodetect games with wrong header infos */
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if (strstr(rominfo.product,"T-26013") != NULL)
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{
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/* Psy-O-Blade (wrong header) */
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sram.start = 0x200001;
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sram.end = 0x203fff;
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}
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/* fixe games indicating internal RAM as volatile external RAM (Feng Kuang Tao Hua Yuan) */
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else if (sram.start == 0xff0000)
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{
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/* backup RAM should be disabled */
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sram.on = 0;
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}
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/* fixe other bad header informations */
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else if ((sram.start > sram.end) || ((sram.end - sram.start) >= 0x10000))
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{
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sram.end = sram.start + 0xffff;
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}
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}
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else
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{
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/* autodetect games with missing header infos */
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if (strstr(rominfo.product,"T-50086") != NULL)
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{
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/* PGA Tour Golf */
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sram.on = 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 (strstr(rominfo.product,"ACLD007") != NULL)
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{
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/* Winter Challenge */
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sram.on = 1;
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sram.start = 0x200001;
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sram.end = 0x200fff;
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}
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else if (strstr(rominfo.product,"T-50286") != NULL)
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{
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/* Buck Rogers - Countdown to Doomsday */
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sram.on = 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 (((rominfo.realchecksum == 0xaeaa) || (rominfo.realchecksum == 0x8dba)) &&
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(rominfo.checksum == 0x8104))
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{
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/* Xin Qigai Wangzi (use uncommon area) */
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sram.on = 1;
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sram.start = 0x400001;
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sram.end = 0x40ffff;
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}
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else if ((strstr(rominfo.ROMType,"SF") != NULL) && (strstr(rominfo.product,"001") != NULL))
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{
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/* SF-001 */
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sram.on = 1;
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if (rominfo.checksum == 0x3e08)
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{
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/* last revision (use bankswitching) */
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sram.start = 0x3c0001;
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sram.end = 0x3cffff;
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}
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else
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{
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/* older revisions (use uncommon area) */
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sram.start = 0x400001;
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sram.end = 0x40ffff;
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}
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}
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else if ((strstr(rominfo.ROMType,"SF") != NULL) && (strstr(rominfo.product,"004") != NULL))
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{
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/* SF-004 (use bankswitching) */
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sram.on = 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 (strstr(rominfo.international,"SONIC & KNUCKLES") != NULL)
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{
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/* Sonic 3 & Knuckles combined ROM */
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if (cart.romsize == 0x400000)
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{
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/* Sonic & Knuckle does not have backup RAM but can access FRAM from Sonic 3 cartridge */
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sram.on = 1;
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sram.start = 0x200001;
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sram.end = 0x203fff;
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}
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}
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/* auto-detect games which need disabled backup RAM */
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else if (strstr(rominfo.product,"T-113016") != NULL)
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{
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/* Pugsy (does not have backup RAM but tries writing outside ROM area as copy protection) */
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sram.on = 0;
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}
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else if (strstr(rominfo.international,"SONIC THE HEDGEHOG 2") != NULL)
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{
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/* Sonic the Hedgehog 2 (does not have backup RAM) */
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/* this prevents backup RAM from being mapped in place of mirrored ROM when using S&K LOCK-ON feature */
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sram.on = 0;
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}
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/* by default, enable backup RAM for ROM smaller than 2MB */
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else if (cart.romsize <= 0x200000)
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{
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/* 64KB static RAM mapped to $200000-$20ffff */
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sram.start = 0x200000;
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sram.end = 0x20ffff;
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sram.on = 1;
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}
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}
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}
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unsigned int sram_read_byte(unsigned int address)
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{
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return sram.sram[address & 0xffff];
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}
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unsigned int sram_read_word(unsigned int address)
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{
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address &= 0xfffe;
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return (sram.sram[address + 1] | (sram.sram[address] << 8));
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}
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void sram_write_byte(unsigned int address, unsigned int data)
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{
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sram.sram[address & 0xffff] = data;
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}
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void sram_write_word(unsigned int address, unsigned int data)
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{
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address &= 0xfffe;
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sram.sram[address] = data >> 8;
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sram.sram[address + 1] = data & 0xff;
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}
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