Genesis-Plus-GX/source/genesis.c

/***************************************************************************************
 *  Genesis Plus
 *  Genesis internals & Bus controller
 *
 *  Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003  Charles Mac Donald (original code)
 *  Eke-Eke (2007,2008,2009), additional code & fixes for the GCN/Wii port
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 ****************************************************************************************/

#include "shared.h"

uint8 bios_rom[0x10000];  /* BIOS rom */
uint8 work_ram[0x10000];  /* 68K work RAM */
uint8 zram[0x2000];       /* Z80 work RAM */
uint8 zbusreq;            /* /BUSREQ from Z80 */
uint8 zreset;             /* /RESET to Z80 */
uint8 zbusack;            /* /BUSACK to Z80 */
uint8 zirq;               /* /IRQ to Z80 */
uint32 zbank;             /* Address of Z80 bank window */
uint8 gen_running;
int32 resetline;

/*--------------------------------------------------------------------------*/
/* Init, reset, shutdown functions                                          */
/*--------------------------------------------------------------------------*/
void set_softreset(void)
{
  resetline = (int) ((double) (lines_per_frame - 1) * rand() / (RAND_MAX + 1.0));
}

void gen_init(void)
{
  int i;

  /* initialize CPUs */
  m68k_set_cpu_type(M68K_CPU_TYPE_68000);
  m68k_init();
  z80_init(0,0,0,z80_irq_callback);

  /* initialize 68k mapped memory */
  /* $000000-$7fffff is affected to cartridge area (see cart_hw.c) */
  /* $800000-$ffffff is affected to WRAM (see VDP DMA) */
  for (i=0x80; 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;
    zbank_memory_map[i].read    = NULL;
    zbank_memory_map[i].write   = NULL;
  }

  /* initialize 68k memory handlers */
  for (i=0x80; i<0xe0; i++)
  {
    /* illegal area */
    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;
  }

  /* 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;
  zbank_memory_map[0xa0].read   = zbank_lockup_r;
  zbank_memory_map[0xa0].write  = zbank_lockup_w;

  /* 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;

  /* SEGA PICO */
  if (system_hw == SYSTEM_PICO)
  {
    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[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;
    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;
  }

  /* VDP */
  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;
  }
}

void gen_reset(uint32 hard_reset)
{
  if (hard_reset)
  {
    /* Clear RAM */
    memset (work_ram, 0x00, sizeof (work_ram));
    memset (zram, 0x00, sizeof (zram));

    /* TMSS BIOS */
    if (config.bios_enabled == 3)
    {
      m68k_memory_map[0].base = bios_rom;
    }

    count_m68k  = 0;
    count_z80   = 0;
    gen_running = 1;  /* System is running */
    zreset      = 0;  /* Z80 is reset */
    zbusreq     = 0;  /* Z80 has control of the Z bus */
    zbusack     = 1;  /* Z80 is busy using the Z bus */
    zirq        = 0;  /* No interrupts occuring */
    zbank       = 0;  /* Assume default bank is $000000-$007FFF */
  }

  resetline   = -1;

  /* reset CPUs */
  m68k_pulse_reset();
  z80_reset();
  fm_reset();
}

void gen_shutdown(void)
{
  z80_exit();
}

/*-----------------------------------------------------------------------
  Bus controller chip functions                                            
  -----------------------------------------------------------------------*/
void gen_busreq_w(uint32 state)
{
  uint32 z80_cycles_to_run;

  if (state)
  {
    /* Bus Request */
    if (!zbusreq && zreset)
    {
      /* Z80 stopped */
      /* z80 was ON during the last 68k cycles */
      /* we execute the appropriate number of z80 cycles */
      z80_cycles_to_run = line_z80 + ((count_m68k - line_m68k)*7)/15;
      current_z80 = z80_cycles_to_run - count_z80;
      if (current_z80 > 0) count_z80 += z80_execute(current_z80);
    }
  }
  else
  {
    /* Bus released */
    if (zbusreq && zreset)
    {
      /* Z80 started */
      /* z80 was OFF during the last 68k cycles */
      /* we burn the appropriate number of z80 cycles */
      z80_cycles_to_run = line_z80 + ((count_m68k - line_m68k)*7)/15;
      count_z80 = z80_cycles_to_run;
    }
  }

  zbusreq = state;
  zbusack = 1 ^ (zbusreq & zreset);
}

void gen_reset_w(uint32 state)
{
  uint32 z80_cycles_to_run;

  if (state)
  {
    /* stop RESET process */
    if (!zbusreq && !zreset)
    {
      /* Z80 started */
      /* z80 was OFF during the last 68k cycles */
      /* we burn the appropriate number of z80 cycles */
      z80_cycles_to_run = line_z80 + ((count_m68k - line_m68k)*7)/15;
      count_z80 = z80_cycles_to_run;
    }
  }
  else
  {
    /* start RESET process */
    if (!zbusreq && zreset)
    {
      /* Z80 stopped */
      /* z80 was ON during the last 68k cycles */
      /* we execute the appropriate number of z80 cycles */
      z80_cycles_to_run = line_z80 + ((count_m68k - line_m68k)*7)/15;
      current_z80 = z80_cycles_to_run - count_z80;
      if (current_z80 > 0) count_z80 += z80_execute(current_z80);
    }

    /* Reset Z80 & YM2612 */
    z80_reset();
    fm_reset();
  }

  zreset = state;
  zbusack = 1 ^ (zbusreq & zreset);
}

void gen_bank_w (uint32 state)
{
  zbank = ((zbank >> 1) | ((state & 1) << 23)) & 0xFF8000;
}

int z80_irq_callback (int param)
{
  zirq = 0;
  z80_set_irq_line (0, CLEAR_LINE);
  return 0xFF;
}