mem.cpp

   1 // DGen/SDL v1.15+
   2 // Megadrive C++ module - misc memory
   3
   4 #include <stdio.h>
   5 #include "md.h"
   6 // md.h also has include fm.h
   7
   8 // This is to handle memory accesses outside of ROM and RAM
   9 // e.g. c00000 and a00000 addresses
  10 // REMEMBER NOT TO USE ANY STATIC variables, because they
  11 // will exist thoughout ALL megadrives!
  12
  13 unsigned char md::z80_read(unsigned int a)
  14 {
  15   if (a<0x2000) return z80ram[a&0xffff];
  16
  17
  18   if ((a&0xfffc)==0x4000) // 00 01 02 03 - not sure about reads
  19   {
  20     return myfm_read(a&3);
  21   }
  22
  23   if (a>=0x8000)
  24   {
  25     int addr68k;
  26     addr68k=z80_bank68k<<15;
  27     addr68k+=a&0x7fff;
  28
  29     return misc_readbyte(addr68k);
  30   }
  31
  32   return 0;
  33 }
  34
  35 unsigned short md::z80_port_read(unsigned short a)
  36 {
  37   int ret=0;
  38
  39 //  dprintf("z80 port read %.2x return %.4x\n",a,ret);
  40
  41   return ret;
  42 }
  43 void md::z80_port_write(unsigned short a,unsigned char v)
  44 {
  45 //  dprintf("z80 port write %.2x %.2x\n",a,v);
  46 }
  47
  48
  49 void md::z80_write(unsigned int a,unsigned char v)
  50 {
  51   if ((a&0xfffc)==0x4000) // 00 01 02 03
  52   {
  53     myfm_write(a&3,v,1);
  54     return ;
  55   }
  56   if (a==0x7f11)
  57   { mysn_write(v); return; }
  58
  59   if (a==0x6000)
  60   {
  61     z80_bank68k>>=1;
  62     z80_bank68k+=(v&1)<<8;
  63     z80_bank68k&=0x1ff; // 9 bits and filled in the new top one
  64     return ;
  65   }
  66   if (a<0x2000) { z80ram[a&0xffff]=v; return; }
  67
  68
  69   if (a>=0x8000)
  70   {
  71     int addr68k;
  72     addr68k=z80_bank68k<<15;
  73     addr68k+=a&0x7fff;
  74     misc_writebyte(addr68k,v);
  75     return;
  76   }
  77
  78 //  dprintf("z80 write %.4x %.2x\n",a,v);
  79   return;
  80 }
  81
  82
  83 unsigned md::misc_readbyte(unsigned a)
  84 {
  85   unsigned char ret=0;
  86   a&=0x00ffffff; // in case stars didn't clip to 24-bit bus
  87
  88
  89   // In case it's a rom read after all
  90   if (a<0xa00000) {
  91     // Saveram
  92     if((save_active)     && (save_len) &&
  93        (a >= save_start) && ((a - save_start) < save_len)) {
  94       return saveram[(a^1) - save_start];
  95     }
  96     else if ((signed)(a^1)<romlen) { ret=rom[(a^1)]; goto end; }
  97   }
  98
  99   // In case it's a ram read after all
 100   if (a>=0xe00000) if (a<=0xffffff) { ret=ram[(a^1)&0xffff]; goto end; }
 101
 102   // GFX data read (byte)
 103   if ((a&0xfffffffe)==0x00c00000) // 00 or 01
 104     { ret=vdp.readbyte(); goto end; }
 105
 106
 107   if ((a&0xfffffffc)==0xa04000)
 108   {
 109     ret=myfm_read(a&3); goto end;
 110   }
 111
 112   if ((a>=0xa00000)&&(a<0xa08000))
 113   {
 114     // Read from z80's memory
 115     ret=z80_read(a&0x7fff); goto end;
 116   }
 117
 118   // I/O port access
 119   if ((a&0xfffffe)==0xa10002)
 120   {
 121     if (aoo3_six==3)
 122     {
 123       // Extended pad info
 124       if (aoo3_toggle==0) ret=((pad[0]>>8)&0x30)+0x00;
 125       else ret=((pad[0])&0x30)+0x40+((pad[0]>>16)&0xf);
 126     }
 127     else
 128     {
 129       if (aoo3_toggle==0)
 130       {
 131         if (aoo3_six==4) ret=((pad[0]>>8)&0x30)+0x00+0x0f;
 132         else             ret=((pad[0]>>8)&0x30)+0x00+(pad[0]&3);
 133       }
 134       else ret=((pad[0])&0x30)+0x40+(pad[0]&15);
 135     }
 136     goto end;
 137   }
 138
 139   if ((a&0xfffffe)==0xa10004)
 140   {
 141     if (aoo5_six==3)
 142     {
 143       // Extended pad info
 144       if (aoo5_toggle==0x00) ret=((pad[1]>>8)&0x30)+0x00;
 145       else ret=((pad[1])&0x30)+0x40+((pad[1]>>16)&0xf);
 146     }
 147     else
 148     {
 149       if (aoo5_toggle==0x00)
 150       {
 151         if (aoo5_six==4) ret=((pad[1]>>8)&0x30)+0x00+0x0f;
 152         else             ret=((pad[1]>>8)&0x30)+0x00+(pad[1]&3);
 153       }
 154       else ret=((pad[1])&0x30)+0x40+(pad[1]&15);
 155     }
 156     goto end;
 157   }
 158
 159   if (a==0xa10001)
 160   {
 161     // overseas/pal/disk/0/ md version (0-f) - may make games act different!
 162     if ((country_ver&0xff0)==0xff0)
 163     {
 164       // autodetect country
 165       int headcode=0x80,avail=0;
 166       int i;
 167       for (i=0;i<3;i++)
 168       {
 169         int ch=misc_readbyte(0x1f0+i);
 170              if (ch=='U') avail|=1;
 171         else if (ch=='E') avail|=2;
 172         else if (ch=='J') avail|=4;
 173       }
 174            if (avail&1) headcode=0x80;
 175       else if (avail&2) headcode=0x80;
 176       else if (avail&4) headcode=0x00;
 177       ret=headcode+(country_ver&0x0f) | (pal? 0x40 : 0);
 178     }
 179     else ret=country_ver;
 180     goto end;
 181   }
 182
 183   if (a==0xa11000) {ret=0xff; goto end; }
 184   if (a==0xa11001) {ret=0xff; goto end; }
 185   if (a==0xa11100)
 186   {
 187     ret=z80_online; goto end;
 188   }
 189   if (a==0xa11101) {ret=0x00; goto end; }
 190   if (a==0xa11200) {ret=0xff; goto end; }
 191   if (a==0xa11201) {ret=0xff; goto end; }
 192
 193   // Genecyst style - toggles fifo full/empty
 194   if (a==0xc00004)
 195   {
 196     // This is the genecyst fudge for FIFO full/empty
 197     coo4^=0x03;
 198     ret=coo4; goto end;
 199   }
 200   if (a==0xc00005)
 201   {
 202     // This is the genecyst fudge for in h-blank
 203     //coo5^=0x04;
 204     ret=coo5 | (pal? 1 : 0); goto end;
 205   }
 206
 207   if (a==0xc00008) { ret=calculate_coo8(); goto end; }
 208   if (a==0xc00009) { ret=calculate_coo9(); goto end; }
 209
 210
 211   end:
 212   return ret;
 213 }
 214
 215 void md::misc_writebyte(unsigned a,unsigned d)
 216 {
 217   a&=0x00ffffff; // in case stars didn't clip to 24-bit bus
 218
 219   // Saveram write
 220   if(save_len && !save_prot) if(a >= save_start)
 221     if ((a - save_start) < save_len)
 222       { saveram[(a^1) - save_start] = d; return; }
 223
 224   // In case it's a ram write after all
 225
 226   if (a>=0xe00000) if (a<=0xffffff) { ram[(a^1)&0xffff]=d; return; }
 227
 228   // GFX data write (byte)
 229   if ((a&0xfffffffe)==0x00c00000) // 00 or 01
 230     { vdp.writebyte(d); return; }
 231
 232   if ((a&0xfffffffc)==0xa04000)
 233   {
 234     myfm_write(a&3,d,1);
 235     return;
 236   }
 237
 238   if (a==0xc00011)
 239   {
 240     mysn_write(d); return;
 241   }
 242
 243   if (a==0xa11100)
 244   {
 245 //d8 (W) 0: BUSREQ CANCEL
 246 //       1: BUSREQ REQUEST
 247     if (d==1) z80_online=0;
 248     else z80_online=1;
 249     return;
 250   }
 251   if (a==0xa11101) return;
 252   if (a==0xa11200)
 253   {
 254     if (d==0)
 255       mz80reset();
 256     return;
 257   }
 258   if (a==0xa11201) return;
 259
 260   if ((a>=0xa00000)&&(a<0xa08000))
 261   {
 262     // Write into z80's memory
 263     z80_write(a&0x7fff,d);
 264     return;
 265   }
 266
 267   // I/O port access
 268   if (a==0xa10003)
 269   {
 270     if (aoo3_six>=0 && (d&0x40)==0 && aoo3_toggle ) aoo3_six++;
 271
 272     if (aoo3_six>0xc00000) aoo3_six&=~0x400000;
 273     // keep it circling around a high value
 274
 275     if (d&0x40) aoo3_toggle=1; else aoo3_toggle=0;
 276     aoo3_six_timeout=0;
 277     return;
 278   }
 279   if (a==0xa10005)
 280   {
 281     if (aoo5_six>=0 && (d&0x40)==0 && aoo5_toggle ) aoo5_six++;
 282
 283     if (aoo5_six>0xc00000) aoo5_six&=~0x400000;
 284     // keep it circling around a high value
 285
 286     if (d&0x40) aoo5_toggle=1; else aoo5_toggle=0;
 287     aoo5_six_timeout=0;
 288     return;
 289   }
 290   // Saveram status (thanks Steve :)
 291   if(a==0xa130f1)
 292   {
 293     // Bit 0: 0=rom active, 1=sram active
 294     // Bit 1: 0=writeable,  1=write protect
 295     save_active = d & 1;
 296     save_prot   = d & 2;
 297   }
 298 }
 299
 300 unsigned md::misc_readword(unsigned a)
 301 {
 302   unsigned int ret=0;
 303
 304   a&=0x00ffffff; // in case stars didn't clip to 24-bit bus
 305
 306   if ((a&0xfffffffc)==0x00c00000) // 00 or 02
 307   {
 308     ret=vdp.readword();
 309     goto end;
 310   }
 311
 312   // else pass onto readbyte
 313   ret =misc_readbyte(a)<<8;
 314   ret|=misc_readbyte(a+1);
 315   goto end;
 316
 317   end:
 318   return ret;
 319 }
 320
 321 void md::misc_writeword(unsigned a,unsigned d)
 322 {
 323   a&=0x00ffffff; // in case stars didn't clip to 24-bit bus
 324
 325   // GFX data write (word)
 326   if ((a&0xfffffffc)==0x00c00000) // 00 or 02
 327   {
 328     vdp.writeword(d);
 329     return;
 330   }
 331
 332   if ((a&0xfffffffc)==0x00c00004) // 04 or 06
 333   {
 334     if (coo_waiting)
 335     {
 336       // Okay completed the vdp command
 337       coo_cmd|=d; coo_waiting=0;
 338
 339       vdp.command(coo_cmd);
 340       return;
 341     }
 342     if ((d&0xc000)==0x8000)
 343     {
 344       int addr; addr=d>>8; addr&=0x1f;
 345       if (vdp.reg[addr]!=(d&0xff))
 346       {
 347         // Store dirty information down to 1byte level in bits
 348         int byt,bit;
 349         byt=addr; bit=byt&7; byt>>=3; byt&=0x03;
 350         vdp.dirt[0x30+byt]|=(1<<bit); vdp.dirt[0x34]|=8;
 351       }
 352       vdp.reg[addr]=d&0xff;
 353       return;
 354     }
 355     coo_cmd=d<<16; coo_waiting=1;
 356     return;
 357   }
 358
 359   // else pass onto writebyte
 360   misc_writebyte(a,d>>8);
 361   misc_writebyte(a+1,d&255);
 362 }
 363