mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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170 lines
4.4 KiB
C
170 lines
4.4 KiB
C
/*
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Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald
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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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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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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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#include "shared.h"
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uint8 *cart_rom; /* cart_rom NEED to be previously dynamically allocated */
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uint8 work_ram[0x10000]; /* 68K work RAM */
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uint8 zram[0x2000]; /* Z80 work RAM */
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uint8 zbusreq; /* /BUSREQ from Z80 */
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uint8 zreset; /* /RESET to Z80 */
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uint8 zbusack; /* /BUSACK to Z80 */
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uint8 zirq; /* /IRQ to Z80 */
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uint32 zbank; /* Address of Z80 bank window */
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uint8 gen_running;
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uint32 lastbusreqcnt;
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uint8 lastbusack;
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uint32 genromsize;
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static int cpu_sync[512]; /* Z80-68K cycles synchronization table */
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#ifdef LSB_FIRST
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void bswap(uint8 *mem, int length)
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{
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int i;
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for(i = 0; i < length; i += 2)
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{
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uint8 temp = mem[i+0];
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mem[i+0] = mem[i+1];
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mem[i+1] = temp;
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}
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}
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#endif
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/*--------------------------------------------------------------------------*/
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/* Init, reset, shutdown functions */
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/*--------------------------------------------------------------------------*/
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void gen_init (void)
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{
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int i;
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#ifdef LSB_FIRST
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bswap(cart_rom, genromsize);
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#endif
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#ifdef NGC
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ShadowROM ();
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#else
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memcpy(shadow_rom,cart_rom,genromsize);
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#endif
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m68k_set_cpu_type (M68K_CPU_TYPE_68000);
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m68k_pulse_reset ();
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gen_running = 1;
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for (i=0; i<512; i++) cpu_sync[i] = (int)(((double)i * 7.0) / 15.0);
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}
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void gen_reset (void)
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{
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/* Clear RAM */
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memset (work_ram, 0, sizeof (work_ram));
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memset (zram, 0, sizeof (zram));
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gen_running = 1;
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zreset = 0; /* Z80 is reset */
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zbusreq = 0; /* Z80 has control of the Z bus */
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zbusack = 1; /* Z80 is busy using the Z bus */
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zbank = 0; /* Assume default bank is 000000-007FFF */
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zirq = 0; /* No interrupts occuring */
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lastbusreqcnt = 0;
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lastbusack = 1;
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/* Reset the 68000 emulator */
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m68k_pulse_reset ();
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z80_reset (0);
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z80_set_irq_callback (z80_irq_callback);
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}
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void gen_shutdown (void)
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{
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}
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/*-----------------------------------------------------------------------
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Bus controller chip functions
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-----------------------------------------------------------------------*/
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int gen_busack_r (void)
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{
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if (zbusack == 0)
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{
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if ((count_m68k + m68k_cycles_run() - lastbusreqcnt) > 16)
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return 0; /* bus taken */
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else return (lastbusack&1);
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}
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else return 1;
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}
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void gen_busreq_w (int state)
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{
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int z80_cycles_to_run;
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input_raz ();
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if (state == 1)
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{
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/* Bus Request */
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lastbusreqcnt = count_m68k + m68k_cycles_run();
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lastbusack = zbusack;
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if (zbusreq == 0)
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{
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/* Z80 stopped */
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/* z80 was ON during the last 68k cycles */
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/* we execute the appropriate number of z80 cycles */
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z80_cycles_to_run = aim_z80 - cpu_sync[aim_m68k - count_m68k - m68k_cycles_run()];
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if (z80_cycles_to_run > 0) z80_run(z80_cycles_to_run);
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}
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}
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else
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{
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/* Bus released */
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if (zbusreq == 1)
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{
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/* Z80 started */
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/* z80 was OFF during the last 68k cycles */
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/* we burn the appropriate number of z80 cycles */
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z80_cycles_to_run = aim_z80 - cpu_sync[aim_m68k - count_m68k - m68k_cycles_run()];
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if (z80_cycles_to_run > 0) count_z80 = z80_cycles_to_run;
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}
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}
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zbusreq = (state & 1);
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zbusack = 1 ^ (zbusreq & zreset);
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}
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void gen_reset_w (int state)
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{
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zreset = (state & 1);
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zbusack = 1 ^ (zbusreq & zreset);
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if (zreset == 0)
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{
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lastbusreqcnt = 0;
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lastbusack = 1;
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fm_reset();
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z80_reset (0);
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z80_set_irq_callback (z80_irq_callback);
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}
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}
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void gen_bank_w (int state)
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{
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zbank = ((zbank >> 1) | ((state & 1) << 23)) & 0xFF8000;
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}
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int z80_irq_callback (int param)
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{
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zirq = 0;
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z80_set_irq_line (0, CLEAR_LINE);
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return 0xFF;
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}
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