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Genesis-Plus-GX/core/genesis.c

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/***************************************************************************************
* Genesis Plus
* Internal Hardware & Bus controllers
*
* Support for SG-1000, Mark-III, Master System, Game Gear, Mega Drive & Mega CD hardware
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2024 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"
#ifdef USE_DYNAMIC_ALLOC
external_t *ext;
#else /* External Hardware (Cartridge, CD unit, ...) */
external_t ext;
#endif
uint8 boot_rom[0x800]; /* Genesis BOOT ROM */
uint8 work_ram[0x10000]; /* 68K RAM */
uint8 zram[0x2000]; /* Z80 RAM */
uint32 zbank; /* Z80 bank window address */
uint8 zstate; /* Z80 bus state (d0 = /RESET, d1 = BUSREQ, d2 = WAIT) */
uint8 pico_current; /* PICO current page */
static uint8 tmss[4]; /* TMSS security register */
/*--------------------------------------------------------------------------*/
/* Init, reset, shutdown functions */
/*--------------------------------------------------------------------------*/
void gen_init(void)
{
int i;
/* initialize Z80 */
z80_init(0,z80_irq_callback);
/* 8-bit / 16-bit modes */
if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)
{
/* initialize main 68k */
m68k_init();
m68k.aerr_enabled = config.addr_error;
/* initialize main 68k memory map */
/* $800000-$DFFFFF : illegal access by default */
for (i=0x80; i<0xe0; i++)
{
m68k.memory_map[i].base = work_ram; /* for VDP DMA */
m68k.memory_map[i].read8 = m68k_lockup_r_8;
m68k.memory_map[i].read16 = m68k_lockup_r_16;
m68k.memory_map[i].write8 = m68k_lockup_w_8;
m68k.memory_map[i].write16 = m68k_lockup_w_16;
zbank_memory_map[i].read = zbank_lockup_r;
zbank_memory_map[i].write = zbank_lockup_w;
}
/* $C0xxxx, $C8xxxx, $D0xxxx, $D8xxxx : VDP ports */
for (i=0xc0; i<0xe0; i+=8)
{
m68k.memory_map[i].read8 = vdp_read_byte;
m68k.memory_map[i].read16 = vdp_read_word;
m68k.memory_map[i].write8 = vdp_write_byte;
m68k.memory_map[i].write16 = vdp_write_word;
zbank_memory_map[i].read = zbank_read_vdp;
zbank_memory_map[i].write = zbank_write_vdp;
}
/* $E00000-$FFFFFF : Work RAM (64k) */
for (i=0xe0; i<0x100; i++)
{
m68k.memory_map[i].base = work_ram;
m68k.memory_map[i].read8 = NULL;
m68k.memory_map[i].read16 = NULL;
m68k.memory_map[i].write8 = NULL;
m68k.memory_map[i].write16 = NULL;
/* Z80 can ONLY write to 68k RAM, not read it */
zbank_memory_map[i].read = zbank_unused_r;
zbank_memory_map[i].write = NULL;
}
if (system_hw == SYSTEM_PICO)
{
/* additional registers mapped to $800000-$80FFFF */
m68k.memory_map[0x80].read8 = pico_read_byte;
m68k.memory_map[0x80].read16 = pico_read_word;
m68k.memory_map[0x80].write8 = m68k_unused_8_w;
m68k.memory_map[0x80].write16 = m68k_unused_16_w;
/* there is no I/O area (Notaz) */
m68k.memory_map[0xa1].read8 = m68k_read_bus_8;
m68k.memory_map[0xa1].read16 = m68k_read_bus_16;
m68k.memory_map[0xa1].write8 = m68k_unused_8_w;
m68k.memory_map[0xa1].write16 = m68k_unused_16_w;
/* initialize page index (closed) */
pico_current = 0;
}
else
{
/* $A10000-$A1FFFF : I/O & Control registers */
m68k.memory_map[0xa1].read8 = ctrl_io_read_byte;
m68k.memory_map[0xa1].read16 = ctrl_io_read_word;
m68k.memory_map[0xa1].write8 = ctrl_io_write_byte;
m68k.memory_map[0xa1].write16 = ctrl_io_write_word;
zbank_memory_map[0xa1].read = zbank_read_ctrl_io;
zbank_memory_map[0xa1].write = zbank_write_ctrl_io;
/* initialize Z80 memory map */
/* $0000-$3FFF is mapped to Z80 RAM (8K mirrored) */
/* $4000-$FFFF is mapped to hardware but Z80 PC should never point there */
for (i=0; i<64; i++)
{
z80_readmap[i] = &zram[(i & 7) << 10];
}
/* initialize Z80 memory handlers */
z80_writemem = z80_memory_w;
z80_readmem = z80_memory_r;
/* initialize Z80 port handlers */
z80_writeport = z80_unused_port_w;
z80_readport = z80_unused_port_r;
}
/* $000000-$7FFFFF : external hardware area */
if (system_hw == SYSTEM_MCD)
{
/* initialize SUB-CPU */
s68k_init();
s68k.aerr_enabled = config.addr_error;
/* initialize CD hardware */
scd_init();
}
else
{
/* Cartridge hardware */
md_cart_init();
}
}
else
{
/* initialize cartridge hardware & Z80 memory handlers */
sms_cart_init();
/* initialize Z80 ports handlers */
switch (system_hw)
{
/* Master System compatibility mode */
case SYSTEM_PBC:
{
z80_writeport = z80_md_port_w;
z80_readport = z80_md_port_r;
break;
}
/* Game Gear hardware */
case SYSTEM_GG:
case SYSTEM_GGMS:
{
/* initialize cartridge hardware & Z80 memory handlers */
sms_cart_init();
/* initialize Z80 ports handlers */
z80_writeport = z80_gg_port_w;
z80_readport = z80_gg_port_r;
break;
}
/* Master System hardware */
case SYSTEM_SMS:
case SYSTEM_SMS2:
{
z80_writeport = z80_ms_port_w;
z80_readport = z80_ms_port_r;
break;
}
/* Mark-III hardware */
case SYSTEM_MARKIII:
{
z80_writeport = z80_m3_port_w;
z80_readport = z80_m3_port_r;
break;
}
/* SG-1000 hardware */
case SYSTEM_SG:
case SYSTEM_SGII:
case SYSTEM_SGII_RAM_EXT:
{
z80_writeport = z80_sg_port_w;
z80_readport = z80_sg_port_r;
break;
}
}
}
}
void gen_reset(int hard_reset)
{
/* System Reset */
if (hard_reset)
{
/* On hard reset, 68k CPU always starts at the same point in VDP frame */
/* Tests performed on VA4 PAL MD1 showed that the first HVC value read */
/* with 'move.w #0x8104,0xC00004' , 'move.w 0xC00008,%d0' sequence was */
/* 0x9F21 in 60HZ mode (0x9F00 if Mode 5 is not enabled by first MOVE) */
/* 0x8421 in 50HZ mode (0x8400 if Mode 5 is not enabled by first MOVE) */
/* Same value is returned on every power ON, indicating VDP is always */
/* starting at the same fixed point in frame (probably at the start of */
/* VSYNC and HSYNC) while 68k /VRES line remains asserted a fixed time */
/* after /SRES line has been released (13 msec approx). The difference */
/* between PAL & NTSC is caused by the top border area being 27 lines */
/* larger in PAL mode than in NTSC mode. CPU cycle counter is adjusted */
/* to match these results (taking in account emulated frame is started */
/* on line 192 */
m68k.cycles = ((lines_per_frame - 192 + 159 - (27 * vdp_pal)) * MCYCLES_PER_LINE) + 1004;
/* clear RAM (on real hardware, RAM values are random / undetermined on Power ON) */
memset(work_ram, 0x00, sizeof (work_ram));
memset(zram, 0x00, sizeof (zram));
}
else
{
/* when RESET button is pressed, 68k could be anywhere in VDP frame (Bonkers, Eternal Champions, X-Men 2) */
m68k.cycles = (uint32)((MCYCLES_PER_LINE * lines_per_frame) * ((double)rand() / (double)RAND_MAX));
/* reset YM2612 (on hard reset, this is done by sound_reset) */
fm_reset(0);
}
/* 68k M-cycles should be a multiple of 7 */
m68k.cycles = (m68k.cycles / 7) * 7;
/* Z80 M-cycles should be a multiple of 15 */
Z80.cycles = (m68k.cycles / 15) * 15;
/* 8-bit / 16-bit modes */
if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)
{
if (system_hw == SYSTEM_MCD)
{
/* FRES is only asserted on Power ON */
if (hard_reset)
{
/* reset CD hardware */
scd_reset(1);
}
/* reset MD cartridge hardware (only when booting from cartridge) */
if (scd.cartridge.boot)
{
md_cart_reset(hard_reset);
}
}
else
{
/* reset MD cartridge hardware */
md_cart_reset(hard_reset);
}
/* Z80 bus is released & Z80 is reseted */
m68k.memory_map[0xa0].read8 = m68k_read_bus_8;
m68k.memory_map[0xa0].read16 = m68k_read_bus_16;
m68k.memory_map[0xa0].write8 = m68k_unused_8_w;
m68k.memory_map[0xa0].write16 = m68k_unused_16_w;
zstate = 0;
/* assume default bank is $000000-$007FFF */
zbank = 0;
/* TMSS support */
if ((config.bios & 1) && (system_hw == SYSTEM_MD) && hard_reset)
{
int i;
/* clear TMSS register */
memset(tmss, 0x00, sizeof(tmss));
/* VDP access is locked by default */
for (i=0xc0; i<0xe0; i+=8)
{
m68k.memory_map[i].read8 = m68k_lockup_r_8;
m68k.memory_map[i].read16 = m68k_lockup_r_16;
m68k.memory_map[i].write8 = m68k_lockup_w_8;
m68k.memory_map[i].write16 = m68k_lockup_w_16;
zbank_memory_map[i].read = zbank_lockup_r;
zbank_memory_map[i].write = zbank_lockup_w;
}
/* check if BOOT ROM is loaded */
if (system_bios & SYSTEM_MD)
{
/* save default cartridge slot mapping */
cart.base = m68k.memory_map[0].base;
/* BOOT ROM is mapped at $000000-$0007FF */
m68k.memory_map[0].base = boot_rom;
}
}
/* reset MAIN-CPU */
m68k_pulse_reset();
}
else
{
/* RAM state at power-on is undefined on some systems */
if ((system_hw == SYSTEM_MARKIII) || ((system_hw & SYSTEM_SMS) && (region_code == REGION_JAPAN_NTSC)))
{
/* some korean games rely on RAM to be initialized with values different from $00 or $ff */
memset(work_ram, 0xf0, sizeof(work_ram));
}
/* reset cartridge hardware */
sms_cart_reset();
/* halt 68k (/VRES is forced low) */
m68k_pulse_halt();
}
/* reset Z80 */
z80_reset();
/* some Z80 registers need to be initialized on Power ON */
if (hard_reset)
{
/* Power Base Converter specific */
if (system_hw == SYSTEM_PBC)
{
/* startup code logic (verified on real hardware): */
/* 21 01 E1 : LD HL, $E101
25 -- -- : DEC H
F9 -- -- : LD SP,HL
C7 -- -- : RST $00
01 01 -- : LD BC, $xx01
*/
Z80.hl.w.l = 0xE001;
Z80.sp.w.l = 0xDFFF;
Z80.r = 4;
}
/* Master System & Game Gear specific */
else if (system_hw & (SYSTEM_SMS | SYSTEM_GG))
{
/* check if BIOS is not being used */
if ((!(config.bios & 1) || !(system_bios & (SYSTEM_SMS | SYSTEM_GG))))
{
/* a few Master System (Ace of Aces, Shadow Dancer) & Game Gear (Ecco the Dolphin, Evander Holyfield Real Deal Boxing) games crash if SP is not properly initialized */
Z80.sp.w.l = 0xDFF0;
}
}
}
}
/*-----------------------------------------------------------------------*/
/* OS ROM / TMSS register control functions (Genesis mode) */
/*-----------------------------------------------------------------------*/
void gen_tmss_w(unsigned int offset, unsigned int data)
{
int i;
/* write TMSS register */
WRITE_WORD(tmss, offset, data);
/* VDP requires "SEGA" value to be written in TMSS register */
if (memcmp((char *)tmss, "SEGA", 4) == 0)
{
for (i=0xc0; i<0xe0; i+=8)
{
m68k.memory_map[i].read8 = vdp_read_byte;
m68k.memory_map[i].read16 = vdp_read_word;
m68k.memory_map[i].write8 = vdp_write_byte;
m68k.memory_map[i].write16 = vdp_write_word;
zbank_memory_map[i].read = zbank_read_vdp;
zbank_memory_map[i].write = zbank_write_vdp;
}
}
else
{
for (i=0xc0; i<0xe0; i+=8)
{
m68k.memory_map[i].read8 = m68k_lockup_r_8;
m68k.memory_map[i].read16 = m68k_lockup_r_16;
m68k.memory_map[i].write8 = m68k_lockup_w_8;
m68k.memory_map[i].write16 = m68k_lockup_w_16;
zbank_memory_map[i].read = zbank_lockup_r;
zbank_memory_map[i].write = zbank_lockup_w;
}
}
}
void gen_bankswitch_w(unsigned int data)
{
/* check if BOOT ROM is loaded */
if (system_bios & SYSTEM_MD)
{
if (data & 1)
{
/* enable cartridge ROM */
m68k.memory_map[0].base = cart.base;
}
else
{
/* enable internal BOOT ROM */
m68k.memory_map[0].base = boot_rom;
}
}
}
unsigned int gen_bankswitch_r(void)
{
/* check if BOOT ROM is loaded */
if (system_bios & SYSTEM_MD)
{
return (m68k.memory_map[0].base == cart.base);
}
return 0xff;
}
/*-----------------------------------------------------------------------*/
/* Z80 Bus controller chip functions (Genesis mode) */
/* ----------------------------------------------------------------------*/
void gen_zbusreq_w(unsigned int data, unsigned int cycles)
{
if (data) /* !ZBUSREQ asserted */
{
/* check if Z80 is going to be stopped */
if (zstate == 1)
{
/* resynchronize with 68k */
z80_run(cycles);
/* enable 68k access to Z80 bus */
m68k.memory_map[0xa0].read8 = z80_read_byte;
m68k.memory_map[0xa0].read16 = z80_read_word;
m68k.memory_map[0xa0].write8 = z80_write_byte;
m68k.memory_map[0xa0].write16 = z80_write_word;
}
/* update Z80 bus status */
zstate |= 2;
}
else /* !ZBUSREQ released */
{
/* check if Z80 is going to be restarted */
if (zstate == 3)
{
/* resynchronize with 68k (Z80 cycles should remain a multiple of 15 MClocks) */
Z80.cycles = ((cycles + 14) / 15) * 15;
/* disable 68k access to Z80 bus */
m68k.memory_map[0xa0].read8 = m68k_read_bus_8;
m68k.memory_map[0xa0].read16 = m68k_read_bus_16;
m68k.memory_map[0xa0].write8 = m68k_unused_8_w;
m68k.memory_map[0xa0].write16 = m68k_unused_16_w;
}
/* update Z80 bus status */
zstate &= 1;
}
}
void gen_zreset_w(unsigned int data, unsigned int cycles)
{
if (data) /* !ZRESET released */
{
/* check if Z80 is going to be restarted */
if (zstate == 0)
{
/* resynchronize with 68k (Z80 cycles should remain a multiple of 15 MClocks) */
Z80.cycles = ((cycles + 14) / 15) * 15;
/* reset Z80 & YM2612 */
z80_reset();
fm_reset(cycles);
}
/* check if 68k access to Z80 bus is granted */
else if (zstate == 2)
{
/* enable 68k access to Z80 bus */
m68k.memory_map[0xa0].read8 = z80_read_byte;
m68k.memory_map[0xa0].read16 = z80_read_word;
m68k.memory_map[0xa0].write8 = z80_write_byte;
m68k.memory_map[0xa0].write16 = z80_write_word;
/* reset Z80 & YM2612 */
z80_reset();
fm_reset(cycles);
}
/* update Z80 bus status */
zstate |= 1;
}
else /* !ZRESET asserted */
{
/* check if Z80 is going to be stopped */
if (zstate == 1)
{
/* resynchronize with 68k */
z80_run(cycles);
}
/* check if 68k had access to Z80 bus */
else if (zstate == 3)
{
/* disable 68k access to Z80 bus */
m68k.memory_map[0xa0].read8 = m68k_read_bus_8;
m68k.memory_map[0xa0].read16 = m68k_read_bus_16;
m68k.memory_map[0xa0].write8 = m68k_unused_8_w;
m68k.memory_map[0xa0].write16 = m68k_unused_16_w;
}
/* stop YM2612 */
fm_reset(cycles);
/* update Z80 bus status */
zstate &= 2;
}
}
void gen_zbank_w (unsigned int data)
{
zbank = ((zbank >> 1) | ((data & 1) << 23)) & 0xFF8000;
}
/*-----------------------------------------------------------------------*/
/* Z80 interrupt callback */
/* ----------------------------------------------------------------------*/
int z80_irq_callback (int param)
{
return -1;
}
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