Genesis-Plus-GX/core/memz80.c

/***************************************************************************************
 *  Genesis Plus
 *  Z80 bus handlers (Genesis & Master System modes)
 *
 *  Support for SG-1000, Mark-III, Master System, Game Gear & Mega Drive ports access
 *
 *  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"


/*--------------------------------------------------------------------------*/
/*  Handlers for access to unused addresses and those which make the        */
/*  machine lock up.                                                        */
/*--------------------------------------------------------------------------*/

INLINE void z80_unused_w(unsigned int address, unsigned char data)
{
#ifdef LOGERROR
  error("Z80 unused write %04X = %02X (%x)\n", address, data, Z80.pc.w.l);
#endif
}

INLINE unsigned char z80_unused_r(unsigned int address)
{
#ifdef LOGERROR
  error("Z80 unused read %04X (%x)\n", address, Z80.pc.w.l);
#endif
  return 0xFF;
}

INLINE void z80_lockup_w(unsigned int address, unsigned char data)
{
#ifdef LOGERROR
  error("Z80 lockup write %04X = %02X (%x)\n", address, data, Z80.pc.w.l);
#endif
  if (!config.force_dtack)
  {
    Z80.cycles = 0xFFFFFFFF;
    zstate = 0;
  }
}

INLINE unsigned char z80_lockup_r(unsigned int address)
{
#ifdef LOGERROR
  error("Z80 lockup read %04X (%x)\n", address, Z80.pc.w.l);
#endif
  if (!config.force_dtack)
  {
    Z80.cycles = 0xFFFFFFFF;
    zstate = 0;
  }
  return 0xFF;
}


/*--------------------------------------------------------------------------*/
/*  Z80 Memory handlers (Genesis mode)                                      */
/*--------------------------------------------------------------------------*/

static void z80_request_68k_bus_access(void)
{
  /* check if 68k bus is accessed by VDP DMA */
  if ((Z80.cycles < dma_endCycles) && (dma_type < 2))
  {
    /* force Z80 to wait until end of DMA */
    Z80.cycles = dma_endCycles;

    /* check if DMA is not finished at the end of current timeframe */
    if (dma_length)
    {
      /* indicate Z80 will still be waiting for 68k bus at the end of current DMA timeframe */
      zstate |= 4;
    }
  }

  /* approximate 68k wait-states during Z80 access to 68k bus (cf https://docs.google.com/document/d/1ST9GbFfPnIjLT5loytFCm3pB0kWQ1Oe34DCBBV8saY8) */
  /* value is adjusted to get ride of graphical glitches in Rick Dangerous 2 title screen when bus refresh delays are also emulated and still get */
  /* "M68K DELAY ON Z80 ROM READ" test "passed" in Ti_'s test ROM (misc_test.bin), although the measured delay value is still slightly too high. */
  m68k.cycles += ((Z80.cycles % 7) + 68);

  /* average Z80 wait-states when accessing 68k bus (cf https://docs.google.com/document/d/1ST9GbFfPnIjLT5loytFCm3pB0kWQ1Oe34DCBBV8saY8) */
  Z80.cycles += (3 * 15);
}

unsigned char z80_memory_r(unsigned int address)
{
  switch((address >> 13) & 7)
  {
    case 0: /* $0000-$3FFF: Z80 RAM (8K mirrored) */
    case 1:
    {
      return zram[address & 0x1FFF];
    }

    case 2: /* $4000-$5FFF: YM2612 */
    {
      return fm_read(Z80.cycles, address & 3);
    }

    case 3: /* $7F00-$7FFF: VDP */
    {
      if ((address >> 8) == 0x7F)
      {
        /* request access to 68k bus */
        z80_request_68k_bus_access();

        /* read from $C00000-$C0FFFF area */
        return (*zbank_memory_map[0xc0].read)(address);
      }
      return z80_unused_r(address);
    }
      
    default: /* $8000-$FFFF: 68k bank (32K) */
    {
      /* request access to 68k bus */
      z80_request_68k_bus_access();

      /* read from 68k banked area */
      address = zbank | (address & 0x7FFF);
      if (zbank_memory_map[address >> 16].read)
      {
        return (*zbank_memory_map[address >> 16].read)(address);
      }
      return READ_BYTE(m68k.memory_map[address >> 16].base, address & 0xFFFF);
    }
  }
}


void z80_memory_w(unsigned int address, unsigned char data)
{
  switch((address >> 13) & 7)
  {
    case 0: /* $0000-$3FFF: Z80 RAM (8K mirrored) */
    case 1: 
    {
      zram[address & 0x1FFF] = data;
      return;
    }

    case 2: /* $4000-$5FFF: YM2612 */
    {
      fm_write(Z80.cycles, address & 3, data);
      return;
    }

    case 3: /* Bank register and VDP */
    {
      switch(address >> 8)
      {
        case 0x60: /* $6000-$60FF: Bank register */
        {
          gen_zbank_w(data & 1);
          return;
        }

        case 0x7F: /* $7F00-$7FFF: VDP */
        {
          /* request access to 68k bus */
          z80_request_68k_bus_access();

          /* write to $C00000-$C0FFFF area */
          (*zbank_memory_map[0xc0].write)(address, data);
          return;
        }

        default:
        {
          z80_unused_w(address, data);
          return;
        }
      }
    }

    default: /* $8000-$FFFF: 68k bank (32K) */
    {
      /* request access to 68k bus */
      z80_request_68k_bus_access();

      /* write to 68k banked area */
      address = zbank | (address & 0x7FFF);
      if (zbank_memory_map[address >> 16].write)
      {
        (*zbank_memory_map[address >> 16].write)(address, data);
        return;
      }
      WRITE_BYTE(m68k.memory_map[address >> 16].base, address & 0xFFFF, data);
      return;
    }
  }
}

/*--------------------------------------------------------------------------*/
/*  Unused Port handlers                                                    */
/*                                                                          */
/*  Ports are unused when not in Mark III compatibility mode.               */
/*                                                                          */
/*  Genesis games that access ports anyway:                                 */
/*    Thunder Force IV reads port $BF in it's interrupt handler.            */
/*                                                                          */
/*--------------------------------------------------------------------------*/

unsigned char z80_unused_port_r(unsigned int port)
{
#if LOGERROR
  error("Z80 unused read from port %04X (%x)\n", port, Z80.pc.w.l);
#endif
  if (system_hw == SYSTEM_SMS)
  {
    unsigned int address = (Z80.pc.w.l - 1) & 0xFFFF;
    return z80_readmap[address >> 10][address & 0x3FF];
  }
  return 0xFF;
}

void z80_unused_port_w(unsigned int port, unsigned char data)
{
#if LOGERROR
  error("Z80 unused write to port %04X = %02X (%x)\n", port, data, Z80.pc.w.l);
#endif
}

/*--------------------------------------------------------------------------*/
/* MegaDrive / Genesis port handlers (Master System compatibility mode)     */
/*--------------------------------------------------------------------------*/

void z80_md_port_w(unsigned int port, unsigned char data)
{
  switch (port & 0xC1)
  {
    case 0x01:
    {
      io_z80_write(1, data, Z80.cycles + PBC_CYCLE_OFFSET);
      return;
    }

    case 0x40:
    case 0x41:
    {
      psg_write(Z80.cycles, data);
      return;
    }

    case 0x80:
    {
      vdp_z80_data_w(data);
      return;
    }

    case 0x81:
    {
      vdp_z80_ctrl_w(data);
      return;
    }

    default:
    {
      port &= 0xFF;

      /* write FM chip if enabled */
      if ((port >= 0xF0) && (config.ym2413 & 1))
      {
        fm_write(Z80.cycles, port, data);
        return;
      }

      z80_unused_port_w(port, data);
      return;
    }
  }
}

unsigned char z80_md_port_r(unsigned int port)
{
  switch (port & 0xC1)
  {
    case 0x40:
    {
      return ((vdp_hvc_r(Z80.cycles - 15) >> 8) & 0xFF);
    }

    case 0x41:
    {
      return (vdp_hvc_r(Z80.cycles - 15) & 0xFF);
    }

    case 0x80:
    {
      return vdp_z80_data_r();
    }

    case 0x81:
    {
      return vdp_z80_ctrl_r(Z80.cycles);
    }

    default:
    {
      port &= 0xFF;

      if ((port == 0xC0) || (port == 0xC1) || (port == 0xDC) || (port == 0xDD))
      {
        return io_z80_read(port & 1);
      }

      /* read FM chip if enabled */
      if ((port >= 0xF0) && (config.ym2413 & 1))
      {
        return fm_read(Z80.cycles, port);
      }

      return z80_unused_port_r(port);
    }
  }
}


/*--------------------------------------------------------------------------*/
/* Game Gear port handlers                                                  */
/*--------------------------------------------------------------------------*/

void z80_gg_port_w(unsigned int port, unsigned char data)
{
  switch(port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      port &= 0xFF;

      if (port < 0x07)
      {
        if (system_hw == SYSTEM_GG)
        {
          io_gg_write(port, data);
          return;
        }
      }

      /* full address range is decoded by Game Gear I/O chip (fixes G-LOC Air Battle) */
      else if ((port == 0x3E) || (port == 0x3F))
      {
        io_z80_write(port & 1, data, Z80.cycles + SMS_CYCLE_OFFSET);
        return;
      }

      z80_unused_port_w(port, data);
      return;
    }

    case 0x40:
    case 0x41:
    {
      psg_write(Z80.cycles, data);
      return;
    }

    case 0x80:
    {
      vdp_z80_data_w(data);
      return;
    }

    case 0x81:
    {
      vdp_sms_ctrl_w(data);
      return;
    }

    default:
    {
      z80_unused_port_w(port & 0xFF, data);
      return;
    }
  }
}

unsigned char z80_gg_port_r(unsigned int port)
{
  switch(port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      port &= 0xFF;

      if (port < 0x07)
      {
        if (system_hw == SYSTEM_GG)
        {
          return io_gg_read(port);
        }
      }

      return z80_unused_port_r(port);
    }

    case 0x40:
    {
      return ((vdp_hvc_r(Z80.cycles) >> 8) & 0xFF);
    }

    case 0x41:
    {
      return (vdp_hvc_r(Z80.cycles) & 0xFF);
    }

    case 0x80:
    {
      return vdp_z80_data_r();
    }

    case 0x81:
    {
      return vdp_z80_ctrl_r(Z80.cycles);
    }

    default:
    {
      port &= 0xFF;

      /* full address range is decoded by Game Gear I/O chip */
      if ((port == 0xC0) || (port == 0xC1) || (port == 0xDC) || (port == 0xDD))
      {
        return io_z80_read(port & 1);
      }

      return z80_unused_port_r(port);
    }
  }
}


/*--------------------------------------------------------------------------*/
/* Master System port handlers                                              */
/*--------------------------------------------------------------------------*/

void z80_ms_port_w(unsigned int port, unsigned char data)
{
  switch (port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      /* full address range is decoded by 315-5297 I/O chip (fixes Super Tetris / Power Boggle Boggle) */
      if ((region_code != REGION_JAPAN_NTSC) || ((port & 0xFE) == 0x3E))
      {
        io_z80_write(port & 1, data, Z80.cycles + SMS_CYCLE_OFFSET);
        return;
      }

      z80_unused_port_w(port & 0xFF, data);
      return;
    }

    case 0x40:
    case 0x41:
    {
      psg_write(Z80.cycles, data);
      return;
    }

    case 0x80:
    {
      vdp_z80_data_w(data);
      return;
    }

    case 0x81:
    {
      vdp_sms_ctrl_w(data);
      return;
    }

    default:
    {
      /* check if YM2413 chip is enabled */
      if (config.ym2413 & 1)
      {
        if (region_code == REGION_JAPAN_NTSC)
        {
          /* 315-5297 I/O chip decodes full address range */
          port &= 0xFF;

          /* internal YM2413 chip */
          if ((port == 0xF0) || (port == 0xF1))
          {
            fm_write(Z80.cycles, port, data);
            return;
          }

          /* Audio control register (315-5297 I/O chip specific) */
          if (port == 0xF2)
          {
            /*  D1 D0
                -----
                0  0 : enable only PSG output (power-on default)
                0  1 : enable only FM output
                1  0 : disable both PSG & FM output
                1  1 : enable both PSG and FM output
            */
            psg_config(Z80.cycles, config.psg_preamp, ((data + 1) & 0x02) ? 0x00 : 0xFF);
            fm_write(Z80.cycles, 0x02, data);
            io_reg[6] = data;
            return;
          }
        }
        else if (!(port & 4))
        {
          /* external FM board */
          fm_write(Z80.cycles, port, data);
          return;
        }
      }

      z80_unused_port_w(port & 0xFF, data);
      return;
    }
  }
}

unsigned char z80_ms_port_r(unsigned int port)
{
  switch (port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      return z80_unused_port_r(port & 0xFF);
    }

    case 0x40:
    {
      return ((vdp_hvc_r(Z80.cycles) >> 8) & 0xFF);
    }

    case 0x41:
    {
      return (vdp_hvc_r(Z80.cycles) & 0xFF);
    }

    case 0x80:
    {
      return vdp_z80_data_r();
    }

    case 0x81:
    {
      return vdp_z80_ctrl_r(Z80.cycles);
    }

    default:
    {
      if (region_code == REGION_JAPAN_NTSC)
      {
        /* 315-5297 I/O chip decodes full address range */
        port &= 0xFF;

        if (port == 0xF2)
        {
          /* D7-D5 : C-SYNC counter (not emulated)
             D4-D2 : Always zero
             D1 : Mute control bit 1
             D0 : Mute control bit 0
          */
          return io_reg[0x06] & 0x03;
        }

        if ((port == 0xC0) || (port == 0xC1) || (port == 0xDC) || (port == 0xDD))
        {
          /* read I/O ports if enabled */
          if (!(io_reg[0x0E] & 0x04))
          {
            return io_z80_read(port & 1);
          }
        }

        return z80_unused_port_r(port);
      }
      else
      {
        uint8 data = 0xFF;

        /* read FM board if enabled */
        if (!(port & 4) && (config.ym2413 & 1))
        {
          data = fm_read(Z80.cycles, port);
        }

        /* read I/O ports if enabled */
        if (!(io_reg[0x0E] & 0x04))
        {
          data &= io_z80_read(port & 1);
        }

        return data;
      }
    }
  }
}

/*--------------------------------------------------------------------------*/
/* Mark III port handlers                                                   */
/*--------------------------------------------------------------------------*/

void z80_m3_port_w(unsigned int port, unsigned char data)
{
  switch (port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      z80_unused_port_w(port & 0xFF, data);
      return;
    }

    case 0x40:
    case 0x41:
    {
      psg_write(Z80.cycles, data);
      return;
    }

    case 0x80:
    {
      vdp_z80_data_w(data);
      return;
    }

    case 0x81:
    {
      vdp_sms_ctrl_w(data);
      return;
    }

    default:
    {
      /* write to FM sound unit (FM-70) if enabled */
      if (!(port & 4) && (config.ym2413 & 1))
      {
        fm_write(Z80.cycles, port, data);

        /* FM output control "register" */
        if (port & 2)
        {
          /* PSG output is automatically disabled (resp. enabled) by FM sound unit hardware if FM output is enabled (resp. disabled) */
          psg_config(Z80.cycles, config.psg_preamp, (data & 0x01) ? 0x00 : 0xff);
        }
        return;
      }

      z80_unused_port_w(port & 0xFF, data);
      return;
    }
  }
}

unsigned char z80_m3_port_r(unsigned int port)
{
  switch (port & 0xC1)
  {
    case 0x00:
    case 0x01:
    {
      return z80_unused_port_r(port & 0xFF);
    }

    case 0x40:
    {
      return ((vdp_hvc_r(Z80.cycles) >> 8) & 0xFF);
    }

    case 0x41:
    {
      return (vdp_hvc_r(Z80.cycles) & 0xFF);
    }

    case 0x80:
    {
      return vdp_z80_data_r();
    }

    case 0x81:
    {
      return vdp_z80_ctrl_r(Z80.cycles);
    }

    default:
    {
      /* read FM sound unit (FM-70) if enabled */
      if (!(port & 4) && (config.ym2413 & 1))
      {
        /* I/O ports are automatically disabled by FM sound unit hardware */
        return fm_read(Z80.cycles, port);
      }

      /* read I/O ports   */
      return io_z80_read(port & 1);
    }
  }
}


/*--------------------------------------------------------------------------*/
/* SG-1000 port handlers                                                     */
/*--------------------------------------------------------------------------*/

void z80_sg_port_w(unsigned int port, unsigned char data)
{
  switch(port & 0xC1)
  {
    case 0x40:
    case 0x41:
    {
      psg_write(Z80.cycles, data);

      /* Z80 !WAIT input is tied to SN76489AN chip READY pin (held low for 32 clocks after each write access) */
      Z80.cycles += (32 * 15);
      return;
    }

    case 0x80:
    {
      vdp_z80_data_w(data);
      return;
    }

    case 0x81:
    {
      vdp_tms_ctrl_w(data);
      return;
    }

    default:
    {
      z80_unused_port_w(port & 0xFF, data);
      return;
    }
  }
}

unsigned char z80_sg_port_r(unsigned int port)
{
  switch (port & 0xC1)
  {
    case 0x80:
    {
      return vdp_z80_data_r();
    }

    case 0x81:
    {
      return vdp_z80_ctrl_r(Z80.cycles);
    }

    case 0xC0:
    case 0xC1:
    {
      return io_z80_read(port & 1);
    }

    default:
    {
      return z80_unused_port_r(port & 0xFF);
    }
  }
}