Genesis-Plus-GX/source/genesis.c

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2007-08-10 22:34:06 +02:00
/*
Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald
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 *cart_rom; /* cart_rom NEED to be previously dynamically allocated */
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;
uint32 lastbusreqcnt;
uint8 lastbusack;
uint32 genromsize;
static int cpu_sync[512]; /* Z80-68K cycles synchronization table */
#ifdef LSB_FIRST
void bswap(uint8 *mem, int length)
{
int i;
for(i = 0; i < length; i += 2)
{
uint8 temp = mem[i+0];
mem[i+0] = mem[i+1];
mem[i+1] = temp;
}
}
#endif
/*--------------------------------------------------------------------------*/
/* Init, reset, shutdown functions */
/*--------------------------------------------------------------------------*/
void gen_init (void)
{
int i;
#ifdef LSB_FIRST
bswap(cart_rom, genromsize);
#endif
#ifdef NGC
ShadowROM ();
#else
memcpy(shadow_rom,cart_rom,genromsize);
#endif
m68k_set_cpu_type (M68K_CPU_TYPE_68000);
m68k_pulse_reset ();
gen_running = 1;
for (i=0; i<512; i++) cpu_sync[i] = (int)(((double)i * 7.0) / 15.0);
}
void gen_reset (void)
{
/* Clear RAM */
memset (work_ram, 0, sizeof (work_ram));
memset (zram, 0, sizeof (zram));
gen_running = 1;
zreset = 0; /* Z80 is reset */
zbusreq = 0; /* Z80 has control of the Z bus */
zbusack = 1; /* Z80 is busy using the Z bus */
zbank = 0; /* Assume default bank is 000000-007FFF */
zirq = 0; /* No interrupts occuring */
lastbusreqcnt = 0;
lastbusack = 1;
/* Reset the 68000 emulator */
m68k_pulse_reset ();
z80_reset (0);
z80_set_irq_callback (z80_irq_callback);
}
void gen_shutdown (void)
{
}
/*-----------------------------------------------------------------------
Bus controller chip functions
-----------------------------------------------------------------------*/
int gen_busack_r (void)
{
if (zbusack == 0)
{
if ((count_m68k + m68k_cycles_run() - lastbusreqcnt) > 16)
return 0; /* bus taken */
else return (lastbusack&1);
}
else return 1;
}
void gen_busreq_w (int state)
{
int z80_cycles_to_run;
input_raz ();
if (state == 1)
{
/* Bus Request */
lastbusreqcnt = count_m68k + m68k_cycles_run();
lastbusack = zbusack;
if (zbusreq == 0)
{
/* Z80 stopped */
/* z80 was ON during the last 68k cycles */
/* 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);
}
}
else
{
/* Bus released */
if (zbusreq == 1)
{
/* Z80 started */
/* z80 was OFF during the last 68k cycles */
/* we burn the appropriate number of z80 cycles */
z80_cycles_to_run = aim_z80 - cpu_sync[aim_m68k - count_m68k - m68k_cycles_run()];
if (z80_cycles_to_run > 0) count_z80 = z80_cycles_to_run;
}
}
zbusreq = (state & 1);
zbusack = 1 ^ (zbusreq & zreset);
}
void gen_reset_w (int state)
{
zreset = (state & 1);
zbusack = 1 ^ (zbusreq & zreset);
if (zreset == 0)
{
lastbusreqcnt = 0;
lastbusack = 1;
fm_reset();
z80_reset (0);
z80_set_irq_callback (z80_irq_callback);
}
}
void gen_bank_w (int 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;
}