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megadrive.c
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megadrive.c
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#include <stdio.h>
#include <string.h>
#include "m68k/m68k.h"
#include "z80.h"
#include "VDP.h"
#include "input.h"
/*
* Megadrive memory map as well as main execution loop.
*/
unsigned char ROM[0x400000];
unsigned char RAM[0x10000];
unsigned char ZRAM[0x2000];
const int MCLOCK_NTSC = 53693175;
const int MCYCLES_PER_LINE = 3420;
int lines_per_frame = 262; /* NTSC: 262, PAL: 313 */
int cycle_counter = 0;
void set_rom(unsigned char *buffer, size_t size)
{
memset(ROM, 0, 0x400000);
memset(RAM, 0, 0x10000);
memset(ZRAM, 0, 0x2000);
memcpy(ROM, buffer, size);
}
unsigned int read_memory(unsigned int address)
{
unsigned int range = (address & 0xff0000) >> 16;
if (range <= 0x3f)
{
/* ROM */
return ROM[address];
}
else if (range == 0xa0)
{
/* Z80 space */
if (address >= 0xa00000 && address < 0xa04000)
{
return ZRAM[address & 0x1fff];
}
return 0;
}
else if (range == 0xa1)
{
/* I/O and registers */
if (address >= 0xa10000 && address < 0xa10020)
{
return io_read_memory(address & 0x1f);
}
else if (address >= 0xa11100 && address < 0xa11300)
{
return z80_ctrl_read(address & 0xffff);
}
return 0;
}
else if (range >= 0xc0 && range <= 0xdf)
{
/* VDP */
return vdp_read(address);
}
else if (range >= 0xe0 && range <= 0xff)
{
/* RAM */
return RAM[address & 0xffff];
// RAM
}
printf("read(%x)\n", address);
return 0;
}
void write_memory(unsigned int address, unsigned int value)
{
unsigned int range = (address & 0xff0000) >> 16;
if (range <= 0x3f)
{
/* ROM */
ROM[address] = value;
return;
}
else if (range == 0xa0)
{
/* Z80 space */
if (address >= 0xa00000 && address < 0xa04000)
{
ZRAM[address & 0x1fff] = value;
}
return;
}
else if (range == 0xa1)
{
/* I/O and registers */
if (address >= 0xa10000 && address < 0xa10020)
{
io_write_memory(address & 0x1f, value);
return;
}
else if (address >= 0xa11100 && address < 0xa11300)
{
z80_ctrl_write(address & 0xffff, value);
return;
}
return;
}
else if (range >= 0xc0 && range <= 0xdf)
{
/* VDP */
return;
}
else if (range >= 0xe0 && range <= 0xff)
{
/* RAM */
RAM[address & 0xffff] = value;
return;
}
printf("write(%x, %x)\n", address, value);
return;
}
unsigned int m68k_read_memory_8(unsigned int address)
{
return read_memory(address);
}
unsigned int m68k_read_memory_16(unsigned int address)
{
unsigned int range = (address & 0xff0000) >> 16;
if (range >= 0xc0 && range <= 0xdf)
{
return vdp_read(address);
}
else
{
unsigned int word = read_memory(address)<<8 | read_memory(address+1);
return word;
}
}
unsigned int m68k_read_memory_32(unsigned int address)
{
unsigned int longword = read_memory(address) << 24 |
read_memory(address+1) << 16 |
read_memory(address+2) << 8 |
read_memory(address+3);
return longword;
}
void m68k_write_memory_8(unsigned int address, unsigned int value)
{
write_memory(address, value);
return;
}
void m68k_write_memory_16(unsigned int address, unsigned int value)
{
unsigned int range = (address & 0xff0000) >> 16;
if (range >= 0xc0 && range <= 0xdf)
{
vdp_write(address, value);
}
else
{
write_memory(address, (value>>8)&0xff);
write_memory(address+1, (value)&0xff);
}
}
void m68k_write_memory_32(unsigned int address, unsigned int value)
{
m68k_write_memory_16(address, (value>>16)&0xffff);
m68k_write_memory_16(address+2, (value)&0xffff);
return;
}
/*
* The Megadrive frame, called every 1/60th second
* (or 1/50th in PAL mode)
*/
void frame()
{
extern unsigned char vdp_reg[0x20], *screen;
extern unsigned int vdp_status;
extern int screen_width, screen_height;
int hint_counter = vdp_reg[10];
int line;
cycle_counter = 0;
screen_width = (vdp_reg[12] & 0x01) ? 320 : 256;
screen_height = (vdp_reg[1] & 0x08) ? 240 : 224;
vdp_clear_vblank();
memset(screen, 0, 320*240*3); /* clear the screen before rendering */
for (line=0; line < screen_height; line++)
{
m68k_execute(2560+120);
if (--hint_counter < 0)
{
hint_counter = vdp_reg[10];
if (vdp_reg[0] & 0x10)
{
m68k_set_irq(4); /* HInt */
//m68k_execute(7000);
}
}
vdp_set_hblank();
m68k_execute(64+313+259); /* HBlank */
vdp_clear_hblank();
m68k_execute(104);
vdp_render_line(line); /* render line */
}
vdp_set_vblank();
m68k_execute(588);
vdp_status |= 0x80;
m68k_execute(200);
if (vdp_reg[1] & 0x20)
{
m68k_set_irq(6); /* HInt */
}
m68k_execute(3420-788);
line++;
for (;line < lines_per_frame; line++)
{
m68k_execute(3420); /**/
}
}