mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-09-17 11:54:50 +02:00
265 lines
7.3 KiB
C
265 lines
7.3 KiB
C
/****************************************************************************
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* Genesis Plus
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* Game Genie Hardware emulation
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*
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* Copyright (C) 2009 Eke-Eke (GCN/Wii port)
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*
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* Based on documentation from Charles McDonald
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* (http://cgfm2.emuviews.com/txt/genie.txt)
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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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#include "shared.h"
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static struct
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{
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uint8 enabled;
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uint8 *rom;
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uint16 regs[0x20];
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uint16 old[6];
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uint16 data[6];
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uint32 addr[6];
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} ggenie;
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static unsigned int ggenie_read_byte(unsigned int address);
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static unsigned int ggenie_read_word(unsigned int address);
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static void ggenie_write_byte(unsigned int address, unsigned int data);
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static void ggenie_write_word(unsigned int address, unsigned int data);
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static void ggenie_write_regs(unsigned int offset, unsigned int data);
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void ggenie_init(void)
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{
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memset(&ggenie,0,sizeof(ggenie));
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/* Open Game Genie ROM */
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FILE *f = fopen(GG_ROM,"rb");
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if (!f) return;
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/* store Game Genie ROM above cartridge ROM + SRAM */
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if (cart.romsize > 0x600000) return;
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ggenie.rom = cart.rom + 0x600000;
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/* Load ROM */
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int i = 0;
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while (i < 0x8000)
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{
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fread(ggenie.rom+i,0x1000,1,f);
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i += 0x1000;
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}
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fclose(f);
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#ifdef LSB_FIRST
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/* Byteswap ROM */
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uint8 temp;
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for(i = 0; i < 0x8000; i += 2)
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{
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temp = ggenie.rom[i];
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ggenie.rom[i] = ggenie.rom[i+1];
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ggenie.rom[i+1] = temp;
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}
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#endif
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/* $0000-$7fff mirrored into $8000-$ffff */
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memcpy(ggenie.rom+0x8000,ggenie.rom,0x8000);
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/* set flag */
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ggenie.enabled = 1;
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}
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void ggenie_shutdown(void)
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{
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if (ggenie.enabled)
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{
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ggenie_switch(0);
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ggenie.enabled = 0;
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}
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}
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void ggenie_reset(int hard)
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{
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if (ggenie.enabled)
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{
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if (hard)
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{
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/* clear codes */
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ggenie_switch(0);
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/* reset internal state */
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memset(ggenie.regs,0,sizeof(ggenie.regs));
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memset(ggenie.old,0,sizeof(ggenie.old));
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memset(ggenie.data,0,sizeof(ggenie.data));
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memset(ggenie.addr,0,sizeof(ggenie.addr));
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}
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/* Game Genie ROM is mapped at $000000-$007fff */
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m68k_memory_map[0].base = ggenie.rom;
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/* Internal registers are mapped at $000000-$00001f */
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m68k_memory_map[0].write8 = ggenie_write_byte;
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m68k_memory_map[0].write16 = ggenie_write_word;
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/* Disable registers reads */
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m68k_memory_map[0].read16 = NULL;
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}
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}
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void ggenie_switch(int enable)
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{
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int i;
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if (enable)
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{
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/* enable cheats */
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for (i=0; i<6; i++)
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{
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/* patch is enabled ? */
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if (ggenie.regs[0] & (1 << i))
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{
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/* save old value and patch ROM if enabled */
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ggenie.old[i] = *(uint16 *)(cart.rom + ggenie.addr[i]);
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*(uint16 *)(cart.rom + ggenie.addr[i]) = ggenie.data[i];
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}
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}
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}
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else
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{
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/* disable cheats in reversed order in case the same address is used by multiple patches */
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for (i=5; i>=0; i--)
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{
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/* patch is enabled ? */
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if (ggenie.regs[0] & (1 << i))
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{
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/* restore original ROM value */
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*(uint16 *)(cart.rom + ggenie.addr[i]) = ggenie.old[i];
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}
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}
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}
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}
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static unsigned int ggenie_read_byte(unsigned int address)
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{
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unsigned int data = ggenie.regs[(address >> 1) & 0x1f];
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return ((address & 1) ? (data & 0xff) : ((data >> 8) & 0xff));
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}
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static unsigned int ggenie_read_word(unsigned int address)
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{
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return ggenie.regs[(address >> 1) & 0x1f];
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}
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static void ggenie_write_byte(unsigned int address, unsigned int data)
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{
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/* Register offset */
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uint8 offset = (address >> 1) & 0x1f;
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/* /LWR and /UWR are used to decode writes */
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if (address & 1)
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{
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data = (ggenie.regs[offset] & 0xff00) | (data & 0xff);
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}
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else
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{
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data = (ggenie.regs[offset] & 0x00ff) | ((data & 0xff) << 8);
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}
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/* Update internal register */
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ggenie_write_regs(offset,data);
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}
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static void ggenie_write_word(unsigned int address, unsigned int data)
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{
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/* Register offset */
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uint8 offset = (address >> 1) & 0x1f;
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/* Write internal register (full WORD) */
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ggenie_write_regs(offset,data);
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}
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static void ggenie_write_regs(unsigned int offset, unsigned int data)
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{
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/* update internal register */
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ggenie.regs[offset] = data;
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/* Mode Register */
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if (offset == 0)
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{
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/* MODE bit */
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if (data & 0x400)
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{
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/* $0000-$7ffff reads mapped to Cartridge ROM */
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m68k_memory_map[0].base = cart.rom;
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m68k_memory_map[0].read8 = NULL;
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m68k_memory_map[0].read16 = NULL;
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}
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else
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{
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/* $0000-$7ffff reads mapped to Game Genie ROM */
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m68k_memory_map[0].base = ggenie.rom;
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m68k_memory_map[0].read8 = NULL;
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m68k_memory_map[0].read16 = NULL;
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/* READ_ENABLE bit */
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if (data & 0x200)
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{
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/* $0000-$7ffff reads mapped to Game Genie Registers */
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/* code doing this should execute in RAM so we don't need to modify base address */
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m68k_memory_map[0].read8 = ggenie_read_byte;
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m68k_memory_map[0].read16 = ggenie_read_word;
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}
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}
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/* LOCK bit */
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if (data & 0x100)
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{
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/* decode patch address (ROM area only)*/
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/* note: Charles's doc is wrong, first register holds bits 23-16 of patch address */
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ggenie.addr[0] = ((ggenie.regs[2] & 0x3f) << 16) | ggenie.regs[3];
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ggenie.addr[1] = ((ggenie.regs[5] & 0x3f) << 16) | ggenie.regs[6];
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ggenie.addr[2] = ((ggenie.regs[8] & 0x3f) << 16) | ggenie.regs[9];
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ggenie.addr[3] = ((ggenie.regs[11] & 0x3f) << 16) | ggenie.regs[12];
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ggenie.addr[4] = ((ggenie.regs[14] & 0x3f) << 16) | ggenie.regs[15];
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ggenie.addr[5] = ((ggenie.regs[17] & 0x3f) << 16) | ggenie.regs[18];
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/* decode patch data */
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ggenie.data[0] = ggenie.regs[4];
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ggenie.data[1] = ggenie.regs[7];
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ggenie.data[2] = ggenie.regs[10];
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ggenie.data[3] = ggenie.regs[13];
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ggenie.data[4] = ggenie.regs[16];
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ggenie.data[5] = ggenie.regs[19];
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/* disable internal registers */
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m68k_memory_map[0].write8 = m68k_unused_8_w;
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m68k_memory_map[0].write16 = m68k_unused_16_w;
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/* patch ROM when GG program exits (LOCK bit set) */
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/* this is done here to handle patched program reads faster & more easily */
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/* on real HW, address decoding would be done on each reads */
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ggenie_switch(1);
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}
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else
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{
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m68k_memory_map[0].write8 = ggenie_write_byte;
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m68k_memory_map[0].write16 = ggenie_write_word;
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}
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}
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/* RESET register */
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else if (offset == 1)
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{
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ggenie.regs[1] |= 1;
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}
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}
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