mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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94 lines
3.2 KiB
C
94 lines
3.2 KiB
C
/***************************************************************************************
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* Genesis Plus 1.2a
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* 68k memory from VDP handler
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*
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* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald (original code)
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* modified by Eke-Eke (compatibility fixes & additional code), GC/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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unsigned int vdp_dma_r(unsigned int address)
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{
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int offset = address >> 19;
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switch (m68k_readmap_16[offset])
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{
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case ROM:
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if (svp) address -= 2;
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return *(uint16 *)(rom_readmap[offset] + (address & 0x7ffff));
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case UMK3_HACK:
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return *(uint16 *)(&cart_rom[offset << 19] + (address & 0x7ffff));
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case SVP_DRAM:
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address -= 2;
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return *(uint16 *)(svp->dram + (address & 0x1fffe));
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case SVP_CELL:
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address -= 2;
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switch (address >> 16)
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{
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case 0x39:
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address >>= 1;
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address = (address & 0x7001) | ((address & 0x3e) << 6) | ((address & 0xfc0) >> 5);
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return ((uint16 *)svp->dram)[address];
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case 0x3A:
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address >>= 1;
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address = (address & 0x7801) | ((address & 0x1e) << 6) | ((address & 0x7e0) >> 4);
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return ((uint16 *)svp->dram)[address];
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default:
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return 0xffff;
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}
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case SYSTEM_IO:
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/* Z80 area */
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/* Return $FFFF only when the Z80 isn't hogging the Z-bus.
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(e.g. Z80 isn't reset and 68000 has the bus) */
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if (address <= 0xa0ffff) return (zbusack ? *(uint16 *)(work_ram + (address & 0xffff)) : 0xffff);
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/* The I/O chip and work RAM try to drive the data bus which
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results in both values being combined in random ways when read.
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We return the I/O chip values which seem to have precedence, */
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if (address <= 0xa1001f)
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{
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int temp = io_read((address >> 1) & 0x0f);
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return (temp << 8 | temp);
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}
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/* All remaining locations access work RAM */
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return *(uint16 *)(work_ram + (address & 0xffff));
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case SRAM:
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if (address <= sram.end) return *(uint16 *)(sram.sram + (address - sram.start));
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return *(uint16 *)(rom_readmap[address >> 19] + (address & 0x7ffff));
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case EEPROM:
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if (address == (eeprom.type.sda_out_adr & 0xfffffe)) return eeprom_read(address, 1);
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return *(uint16 *)(rom_readmap[address >> 19] + (address & 0x7ffff));
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case J_CART:
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return jcart_read();
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default:
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return *(uint16 *)(work_ram + (address & 0xffff));
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}
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}
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