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Genesis-Plus-GX/source/cd_hw/cd_cart.c

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/***************************************************************************************
* Genesis Plus
* CD compatible ROM/RAM cartridge support
*
* Copyright (C) 2012 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
*
* - Redistributions may not be sold, nor may they be used in a commercial
* product or activity.
*
* - Redistributions that are modified from the original source must include the
* complete source code, including the source code for all components used by a
* binary built from the modified sources. However, as a special exception, the
* source code distributed need not include anything that is normally distributed
* (in either source or binary form) with the major components (compiler, kernel,
* and so on) of the operating system on which the executable runs, unless that
* component itself accompanies the executable.
*
* - Redistributions must reproduce the above copyright notice, this list of
* conditions and the following disclaimer in the documentation and/or other
* materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************************/
#include "shared.h"
/*--------------------------------------------------------------------------*/
/* backup RAM cartridge (max. 512KB) */
/*--------------------------------------------------------------------------*/
static unsigned int cart_ram_read_byte(unsigned int address)
{
/* LSB only */
if (address & 1)
{
return scd.cartridge.area[(address >> 1) & scd.cartridge.mask];
}
return 0xff;
}
static unsigned int cart_ram_read_word(unsigned int address)
{
return (scd.cartridge.area[(address >> 1) & scd.cartridge.mask] | 0xff00);
}
static void cart_ram_write_byte(unsigned int address, unsigned int data)
{
/* LSB only */
if (address & 1)
{
scd.cartridge.area[(address >> 1) & scd.cartridge.mask] = data;
}
}
static void cart_ram_write_word(unsigned int address, unsigned int data)
{
scd.cartridge.area[(address >> 1) & scd.cartridge.mask] = data & 0xff;
}
/*--------------------------------------------------------------------------*/
/* backup RAM cartridge ID */
/*--------------------------------------------------------------------------*/
static unsigned int cart_id_read_byte(unsigned int address)
{
/* LSB only */
if (address & 1)
{
return scd.cartridge.id;
}
return 0xff;
}
static unsigned int cart_id_read_word(unsigned int address)
{
return (scd.cartridge.id | 0xff00);
}
/*--------------------------------------------------------------------------*/
/* backup RAM cartridge write protection */
/*--------------------------------------------------------------------------*/
static unsigned int cart_prot_read_byte(unsigned int address)
{
/* LSB only */
if (address & 1)
{
return scd.cartridge.prot;
}
return 0xff;
}
static unsigned int cart_prot_read_word(unsigned int address)
{
return (scd.cartridge.prot | 0xff00);
}
static void cart_prot_write_byte(unsigned int address, unsigned int data)
{
/* LSB only */
if (address & 1)
{
int i;
if (data & 1)
{
/* cartridge is write enabled */
for (i=0x60; i<0x70; i++)
{
m68k.memory_map[i].write8 = cart_ram_write_byte;
m68k.memory_map[i].write16 = cart_ram_write_word;
zbank_memory_map[i].write = cart_ram_write_byte;
}
}
else
{
/* cartridge is write protected */
for (i=0x60; i<0x70; i++)
{
m68k.memory_map[i].write8 = m68k_unused_8_w;
m68k.memory_map[i].write16 = m68k_unused_16_w;
zbank_memory_map[i].write = zbank_unused_w;
}
}
scd.cartridge.prot = data;
}
}
static void cart_prot_write_word(unsigned int address, unsigned int data)
{
int i;
if (data & 1)
{
/* cartridge is write enabled */
for (i=0x60; i<0x70; i++)
{
m68k.memory_map[i].write8 = cart_ram_write_byte;
m68k.memory_map[i].write16 = cart_ram_write_word;
zbank_memory_map[i].write = cart_ram_write_byte;
}
}
else
{
/* cartridge is write protected */
for (i=0x60; i<0x70; i++)
{
m68k.memory_map[i].write8 = m68k_unused_8_w;
m68k.memory_map[i].write16 = m68k_unused_16_w;
zbank_memory_map[i].write = zbank_unused_w;
}
}
scd.cartridge.prot = data & 0xff;
}
/*--------------------------------------------------------------------------*/
/* ROM/RAM cartridge initialization */
/*--------------------------------------------------------------------------*/
void cd_cart_init(void)
{
int i;
/* System boot mode */
if (scd.cartridge.boot)
{
/* disable backup RAM cartridge when booting from cartridge (Mode 1) */
scd.cartridge.id = 0;
}
else
{
/* enable 512K backup RAM cartridge when booting from CD (Mode 2) */
scd.cartridge.id = 6;
}
/* RAM cartridge enabled ? */
if (scd.cartridge.id)
{
/* disable cartridge backup memory */
memset(&sram, 0, sizeof (T_SRAM));
/* clear backup RAM */
memset(scd.cartridge.area, 0x00, sizeof(scd.cartridge.area));
/* backup RAM size mask */
scd.cartridge.mask = (1 << (scd.cartridge.id + 13)) - 1;
/* enable RAM cartridge write access */
scd.cartridge.prot = 1;
/* RAM cartridge ID register (read-only) */
for (i=0x40; i<0x60; i++)
{
m68k.memory_map[i].base = NULL;
m68k.memory_map[i].read8 = cart_id_read_byte;
m68k.memory_map[i].read16 = cart_id_read_word;
m68k.memory_map[i].write8 = m68k_unused_8_w;
m68k.memory_map[i].write16 = m68k_unused_16_w;
zbank_memory_map[i].read = cart_id_read_byte;
zbank_memory_map[i].write = zbank_unused_w;
}
/* RAM cartridge memory */
for (i=0x60; i<0x70; i++)
{
m68k.memory_map[i].base = NULL;
m68k.memory_map[i].read8 = cart_ram_read_byte;
m68k.memory_map[i].read16 = cart_ram_read_word;
m68k.memory_map[i].write8 = cart_ram_write_byte;
m68k.memory_map[i].write16 = cart_ram_write_word;
zbank_memory_map[i].read = cart_ram_read_byte;
zbank_memory_map[i].write = cart_ram_write_byte;
}
/* RAM cartridge write protection register */
for (i=0x70; i<0x80; i++)
{
m68k.memory_map[i].base = NULL;
m68k.memory_map[i].read8 = cart_prot_read_byte;
m68k.memory_map[i].read16 = cart_prot_read_word;
m68k.memory_map[i].write8 = cart_prot_write_byte;
m68k.memory_map[i].write16 = cart_prot_write_word;
zbank_memory_map[i].read = cart_prot_read_byte;
zbank_memory_map[i].write = cart_prot_write_byte;
}
}
else
{
/* initialize ROM cartridge */
md_cart_init();
/* when booting from CD, cartridge is mapped to $400000-$7FFFFF */
if (!scd.cartridge.boot)
{
for (i=0; i<0x40; i++)
{
m68k.memory_map[i+0x40].base = m68k.memory_map[i].base;
m68k.memory_map[i+0x40].read8 = m68k.memory_map[i].read8;
m68k.memory_map[i+0x40].read16 = m68k.memory_map[i].read16;
m68k.memory_map[i+0x40].write8 = m68k.memory_map[i].write8;
m68k.memory_map[i+0x40].write16 = m68k.memory_map[i].write16;
zbank_memory_map[i+0x40].read = zbank_memory_map[i].read;
zbank_memory_map[i+0x40].write = zbank_memory_map[i].write;
}
}
}
}
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