GBZ80Core.v

   1 `define REG_A 0
   2 `define REG_B 1
   3 `define REG_C 2
   4 `define REG_D 3
   5 `define REG_E 4
   6 `define REG_F 5
   7 `define REG_H 6
   8 `define REG_L 7
   9 `define REG_SPH 8
  10 `define REG_SPL 9
  11 `define REG_PCH 10
  12 `define REG_PCL 11
  13
  14 `define FLAG_Z 8'b10000000
  15 `define FLAG_N 8'b01000000
  16 `define FLAG_H 8'b00100000
  17 `define FLAG_C 8'b00010000
  18
  19 `define STATE_FETCH                     2'h0
  20 `define STATE_DECODE                    2'h1
  21 `define STATE_EXECUTE           2'h2
  22 `define STATE_WRITEBACK         2'h3
  23
  24 `define INSN_LD_reg_imm8        8'b00xxx110
  25 `define INSN_HALT                               8'b01110110
  26 `define INSN_LD_HL_reg          8'b01110xxx
  27 `define INSN_LD_reg_HL          8'b01xxx110
  28 `define INSN_LD_reg_reg         8'b01xxxxxx
  29 `define INSN_LD_reg_imm16       8'b00xx0001
  30 `define INSN_LD_SP_HL           8'b11111001
  31 `define INSN_PUSH_reg           8'b11xx0101
  32 `define INSN_POP_reg                    8'b11xx0001
  33 `define INSN_LDH_AC                     8'b111x0010     // Either LDH A,(C) or LDH (C),A
  34 `define INSN_LDx_AHL                    8'b001xx010     // LDD/LDI A,(HL) / (HL),A
  35 `define INSN_ALU8                               8'b10xxxxxx     // 10 xxx yyy
  36
  37 `define INSN_reg_A              3'b111
  38 `define INSN_reg_B              3'b000
  39 `define INSN_reg_C              3'b001
  40 `define INSN_reg_D              3'b010
  41 `define INSN_reg_E              3'b011
  42 `define INSN_reg_H              3'b100
  43 `define INSN_reg_L              3'b101
  44 `define INSN_reg_dHL    3'b110
  45 `define INSN_reg16_BC   2'b00
  46 `define INSN_reg16_DE   2'b01
  47 `define INSN_reg16_HL   2'b10
  48 `define INSN_reg16_SP   2'b11
  49 `define INSN_stack_AF   2'b11
  50 `define INSN_stack_BC   2'b00
  51 `define INSN_stack_DE   2'b01
  52 `define INSN_stack_HL   2'b10
  53 `define INSN_alu_ADD            3'b000
  54 `define INSN_alu_ADC            3'b001
  55 `define INSN_alu_SUB            3'b010
  56 `define INSN_alu_SBC            3'b011
  57 `define INSN_alu_AND            3'b100
  58 `define INSN_alu_XOR            3'b101
  59 `define INSN_alu_OR             3'b110
  60 `define INSN_alu_CP             3'b111          // Oh lawd, is dat some CP?
  61
  62 module GBZ80Core(
  63         input clk,
  64         output reg [15:0] busaddress,   /* BUS_* is latched on STATE_FETCH. */
  65         inout [7:0] busdata,
  66         output reg buswr, output reg busrd);
  67
  68         reg [1:0] state = 0;                                    /* State within this bus cycle (see STATE_*). */
  69         reg [2:0] cycle = 0;                                    /* Cycle for instructions. */
  70
  71         reg [7:0] registers[11:0];
  72
  73         reg [15:0] address;                             /* Address for the next bus operation. */
  74
  75         reg [7:0] opcode;                               /* Opcode from the current machine cycle. */
  76
  77         reg [7:0] rdata, wdata;         /* Read data from this bus cycle, or write data for the next. */
  78         reg rd = 1, wr = 0, newcycle = 1;
  79
  80         reg [7:0] tmp;                                  /* Generic temporary reg. */
  81
  82         reg [7:0] buswdata;
  83         assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
  84
  85         initial begin
  86                 registers[ 0] <= 0;
  87                 registers[ 1] <= 0;
  88                 registers[ 2] <= 0;
  89                 registers[ 3] <= 0;
  90                 registers[ 4] <= 0;
  91                 registers[ 5] <= 0;
  92                 registers[ 6] <= 0;
  93                 registers[ 7] <= 0;
  94                 registers[ 8] <= 0;
  95                 registers[ 9] <= 0;
  96                 registers[10] <= 0;
  97                 registers[11] <= 0;
  98         end
  99
 100         always @(posedge clk)
 101                 case (state)
 102                 `STATE_FETCH: begin
 103                         if (wr)
 104                                 buswdata <= wdata;
 105                         if (newcycle)
 106                                 busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};
 107                         else
 108                                 busaddress <= address;
 109                         buswr <= wr;
 110                         busrd <= rd;
 111                         state <= `STATE_DECODE;
 112                 end
 113                 `STATE_DECODE: begin
 114                         if (newcycle) begin
 115                                 opcode <= busdata;
 116                                 rdata <= busdata;
 117                                 newcycle <= 0;
 118                                 cycle <= 0;
 119                         end else
 120                                 if (rd) rdata <= busdata;
 121                         buswr <= 0;
 122                         busrd <= 0;
 123                         wr <= 0;
 124                         rd <= 0;
 125                         address <= 16'bxxxxxxxxxxxxxxxx;        // Make it obvious if something of type has happened.
 126                         wdata <= 8'bxxxxxxxx;
 127                         state <= `STATE_EXECUTE;
 128                 end
 129                 `STATE_EXECUTE: begin
 130 `define EXEC_INC_PC \
 131         {registers[`REG_PCH], registers[`REG_PCL]} <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
 132 `define EXEC_NEXTADDR_PCINC \
 133         address <= {registers[`REG_PCH], registers[`REG_PCL]} + 1
 134 `define EXEC_NEWCYCLE \
 135         newcycle <= 1; rd <= 1; wr <= 0
 136                         casex (opcode)
 137                         `INSN_LD_reg_imm8: begin
 138                                 case (cycle)
 139                                 0:      begin
 140                                                 `EXEC_INC_PC;
 141                                                 `EXEC_NEXTADDR_PCINC;
 142                                                 rd <= 1;
 143                                         end
 144                                 1: begin
 145                                                 `EXEC_INC_PC;
 146                                                 if (opcode[5:3] == `INSN_reg_dHL) begin
 147                                                         address <= {registers[`REG_H], registers[`REG_L]};
 148                                                         wdata <= rdata;
 149                                                         rd <= 0;
 150                                                         wr <= 1;
 151                                                 end else begin
 152                                                         `EXEC_NEWCYCLE;
 153                                                 end
 154                                         end
 155                                 2: begin
 156                                                 `EXEC_NEWCYCLE;
 157                                         end
 158                                 endcase
 159                         end
 160                         `INSN_HALT: begin
 161                                 `EXEC_NEWCYCLE;
 162                                 /* XXX Interrupts needed for HALT. */
 163                         end
 164                         `INSN_LD_HL_reg: begin
 165                                 case (cycle)
 166                                 0:      begin
 167                                                 case (opcode[2:0])
 168                                                 `INSN_reg_A:    begin wdata <= registers[`REG_A]; end
 169                                                 `INSN_reg_B:    begin wdata <= registers[`REG_B]; end
 170                                                 `INSN_reg_C:    begin wdata <= registers[`REG_C]; end
 171                                                 `INSN_reg_D:    begin wdata <= registers[`REG_D]; end
 172                                                 `INSN_reg_E:    begin wdata <= registers[`REG_E]; end
 173                                                 `INSN_reg_H:    begin wdata <= registers[`REG_H]; end
 174                                                 `INSN_reg_L:    begin wdata <= registers[`REG_L]; end
 175                                                 endcase
 176                                                 address <= {registers[`REG_H], registers[`REG_L]};
 177                                                 wr <= 1; rd <= 0;
 178                                         end
 179                                 1:      begin
 180                                                 `EXEC_INC_PC;
 181                                                 `EXEC_NEWCYCLE;
 182                                         end
 183                                 endcase
 184                         end
 185                         `INSN_LD_reg_HL: begin
 186                                 case(cycle)
 187                                 0: begin
 188                                                 address <= {registers[`REG_H], registers[`REG_L]};
 189                                                 rd <= 1;
 190                                         end
 191                                 1: begin
 192                                                 tmp <= rdata;
 193                                                 `EXEC_INC_PC;
 194                                                 `EXEC_NEWCYCLE;
 195                                         end
 196                                 endcase
 197                         end
 198                         `INSN_LD_reg_reg: begin
 199                                 `EXEC_INC_PC;
 200                                 `EXEC_NEWCYCLE;
 201                                 case (opcode[2:0])
 202                                 `INSN_reg_A:    begin tmp <= registers[`REG_A]; end
 203                                 `INSN_reg_B:    begin tmp <= registers[`REG_B]; end
 204                                 `INSN_reg_C:    begin tmp <= registers[`REG_C]; end
 205                                 `INSN_reg_D:    begin tmp <= registers[`REG_D]; end
 206                                 `INSN_reg_E:    begin tmp <= registers[`REG_E]; end
 207                                 `INSN_reg_H:    begin tmp <= registers[`REG_H]; end
 208                                 `INSN_reg_L:    begin tmp <= registers[`REG_L]; end
 209                                 endcase
 210                         end
 211                         `INSN_LD_reg_imm16: begin
 212                                 `EXEC_INC_PC;
 213                                 case (cycle)
 214                                 0:      begin
 215                                                 `EXEC_NEXTADDR_PCINC;
 216                                                 rd <= 1;
 217                                         end
 218                                 1:      begin
 219                                                 `EXEC_NEXTADDR_PCINC;
 220                                                 rd <= 1;
 221                                         end
 222                                 2: begin `EXEC_NEWCYCLE; end
 223                                 endcase
 224                         end
 225                         `INSN_LD_SP_HL: begin
 226                                 case (cycle)
 227                                 0:      begin
 228                                                 tmp <= registers[`REG_H];
 229                                         end
 230                                 1:      begin
 231                                                 `EXEC_NEWCYCLE;
 232                                                 `EXEC_INC_PC;
 233                                                 tmp <= registers[`REG_L];
 234                                         end
 235                                 endcase
 236                         end
 237                         `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
 238                                 case (cycle)
 239                                 0: begin
 240                                                 wr <= 1;
 241                                                 address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
 242                                                 case (opcode[5:4])
 243                                                 `INSN_stack_AF: wdata <= registers[`REG_A];
 244                                                 `INSN_stack_BC: wdata <= registers[`REG_B];
 245                                                 `INSN_stack_DE: wdata <= registers[`REG_D];
 246                                                 `INSN_stack_HL: wdata <= registers[`REG_H];
 247                                                 endcase
 248                                         end
 249                                 1: begin
 250                                                 wr <= 1;
 251                                                 address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
 252                                                 case (opcode[5:4])
 253                                                 `INSN_stack_AF: wdata <= registers[`REG_F];
 254                                                 `INSN_stack_BC: wdata <= registers[`REG_C];
 255                                                 `INSN_stack_DE: wdata <= registers[`REG_E];
 256                                                 `INSN_stack_HL: wdata <= registers[`REG_L];
 257                                                 endcase
 258                                         end
 259                                 2:      begin /* TWIDDLE OUR FUCKING THUMBS! */ end
 260                                 3: begin
 261                                                 `EXEC_NEWCYCLE;
 262                                                 `EXEC_INC_PC;
 263                                         end
 264                                 endcase
 265                         end
 266                         `INSN_POP_reg: begin    /* POP is 12 cycles! */
 267                                 case (cycle)
 268                                 0: begin
 269                                                 rd <= 1;
 270                                                 address <= {registers[`REG_SPH],registers[`REG_SPL]};
 271                                         end
 272                                 1: begin
 273                                                 rd <= 1;
 274                                                 address <= {registers[`REG_SPH],registers[`REG_SPL]};
 275                                         end
 276                                 2: begin
 277                                                 `EXEC_NEWCYCLE;
 278                                                 `EXEC_INC_PC;
 279                                         end
 280                                 endcase
 281                         end
 282                         `INSN_LDH_AC: begin
 283                                 case (cycle)
 284                                 0:      begin
 285                                                 address <= {8'hFF,registers[`REG_C]};
 286                                                 if (opcode[4]) begin    // LD A,(C)
 287                                                         rd <= 1;
 288                                                 end else begin
 289                                                         wr <= 1;
 290                                                         wdata <= registers[`REG_A];
 291                                                 end
 292                                         end
 293                                 1: begin
 294                                                 `EXEC_NEWCYCLE;
 295                                                 `EXEC_INC_PC;
 296                                         end
 297                                 endcase
 298                         end
 299                         `INSN_LDx_AHL: begin
 300                                 case (cycle)
 301                                 0: begin
 302                                                 address <= {registers[`REG_H],registers[`REG_L]};
 303                                                 if (opcode[3]) begin    // LDx A, (HL)
 304                                                         rd <= 1;
 305                                                 end else begin
 306                                                         wr <= 1;
 307                                                         wdata <= registers[`REG_A];
 308                                                 end
 309                                         end
 310                                 1:      begin
 311                                                 `EXEC_NEWCYCLE;
 312                                                 `EXEC_INC_PC;
 313                                         end
 314                                 endcase
 315                         end
 316                         `INSN_ALU8: begin
 317                                 if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
 318                                         // fffffffff fuck your shit, read from (HL) :(
 319                                         rd <= 1;
 320                                         address <= {registers[`REG_H], registers[`REG_L]};
 321                                 end else begin
 322                                         `EXEC_NEWCYCLE;
 323                                         `EXEC_INC_PC;
 324                                         case (opcode[2:0])
 325                                         `INSN_reg_A:    begin tmp <= registers[`REG_A]; end
 326                                         `INSN_reg_B:    begin tmp <= registers[`REG_B]; end
 327                                         `INSN_reg_C:    begin tmp <= registers[`REG_C]; end
 328                                         `INSN_reg_D:    begin tmp <= registers[`REG_D]; end
 329                                         `INSN_reg_E:    begin tmp <= registers[`REG_E]; end
 330                                         `INSN_reg_H:    begin tmp <= registers[`REG_H]; end
 331                                         `INSN_reg_L:    begin tmp <= registers[`REG_L]; end
 332                                         `INSN_reg_dHL:  begin tmp <= rdata; end
 333                                         endcase
 334                                 end
 335                         end
 336                         default:
 337                                 $stop;
 338                         endcase
 339                         state <= `STATE_WRITEBACK;
 340                 end
 341                 `STATE_WRITEBACK: begin
 342                         casex (opcode)
 343                         `INSN_LD_reg_imm8:
 344                                 case (cycle)
 345                                 0: cycle <= 1;
 346                                 1: case (opcode[5:3])
 347                                         `INSN_reg_A:    begin registers[`REG_A] <= rdata; cycle <= 0; end
 348                                         `INSN_reg_B:    begin registers[`REG_B] <= rdata; cycle <= 0; end
 349                                         `INSN_reg_C:    begin registers[`REG_C] <= rdata; cycle <= 0; end
 350                                         `INSN_reg_D:    begin registers[`REG_D] <= rdata; cycle <= 0; end
 351                                         `INSN_reg_E:    begin registers[`REG_E] <= rdata; cycle <= 0; end
 352                                         `INSN_reg_H:    begin registers[`REG_H] <= rdata; cycle <= 0; end
 353                                         `INSN_reg_L:    begin registers[`REG_L] <= rdata; cycle <= 0; end
 354                                         `INSN_reg_dHL:  cycle <= 2;
 355                                         endcase
 356                                 2: cycle <= 0;
 357                                 endcase
 358                         `INSN_HALT: begin
 359                                 /* Nothing needs happen here. */
 360                                 /* XXX Interrupts needed for HALT. */
 361                         end
 362                         `INSN_LD_HL_reg: begin
 363                                 case (cycle)
 364                                 0: cycle <= 1;
 365                                 1: cycle <= 0;
 366                                 endcase
 367                         end
 368                         `INSN_LD_reg_HL: begin
 369                                 case (cycle)
 370                                 0:      cycle <= 1;
 371                                 1:      begin
 372                                                 case (opcode[5:3])
 373                                                 `INSN_reg_A:    begin registers[`REG_A] <= tmp; end
 374                                                 `INSN_reg_B:    begin registers[`REG_B] <= tmp; end
 375                                                 `INSN_reg_C:    begin registers[`REG_C] <= tmp; end
 376                                                 `INSN_reg_D:    begin registers[`REG_D] <= tmp; end
 377                                                 `INSN_reg_E:    begin registers[`REG_E] <= tmp; end
 378                                                 `INSN_reg_H:    begin registers[`REG_H] <= tmp; end
 379                                                 `INSN_reg_L:    begin registers[`REG_L] <= tmp; end
 380                                                 endcase
 381                                                 cycle <= 0;
 382                                         end
 383                                 endcase
 384                         end
 385                         `INSN_LD_reg_reg: begin
 386                                 case (opcode[5:3])
 387                                 `INSN_reg_A:    begin registers[`REG_A] <= tmp; end
 388                                 `INSN_reg_B:    begin registers[`REG_B] <= tmp; end
 389                                 `INSN_reg_C:    begin registers[`REG_C] <= tmp; end
 390                                 `INSN_reg_D:    begin registers[`REG_D] <= tmp; end
 391                                 `INSN_reg_E:    begin registers[`REG_E] <= tmp; end
 392                                 `INSN_reg_H:    begin registers[`REG_H] <= tmp; end
 393                                 `INSN_reg_L:    begin registers[`REG_L] <= tmp; end
 394                                 endcase
 395                         end
 396                         `INSN_LD_reg_imm16: begin
 397                                 case (cycle)
 398                                 0:      cycle <= 1;
 399                                 1:      begin
 400                                                 case (opcode[5:4])
 401                                                 `INSN_reg16_BC: registers[`REG_C] <= rdata;
 402                                                 `INSN_reg16_DE: registers[`REG_E] <= rdata;
 403                                                 `INSN_reg16_HL: registers[`REG_L] <= rdata;
 404                                                 `INSN_reg16_SP: registers[`REG_SPL] <= rdata;
 405                                                 endcase
 406                                                 cycle <= 2;
 407                                         end
 408                                 2: begin
 409                                                 case (opcode[5:4])
 410                                                 `INSN_reg16_BC: registers[`REG_B] <= rdata;
 411                                                 `INSN_reg16_DE: registers[`REG_D] <= rdata;
 412                                                 `INSN_reg16_HL: registers[`REG_H] <= rdata;
 413                                                 `INSN_reg16_SP: registers[`REG_SPH] <= rdata;
 414                                                 endcase
 415                                                 cycle <= 0;
 416                                         end
 417                                 endcase
 418                         end
 419                         `INSN_LD_SP_HL: begin
 420                                 case (cycle)
 421                                 0: begin
 422                                                 cycle <= 1;
 423                                                 registers[`REG_SPH] <= tmp;
 424                                         end
 425                                 1: begin
 426                                                 cycle <= 0;
 427                                                 registers[`REG_SPL] <= tmp;
 428                                         end
 429                                 endcase
 430                         end
 431                         `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
 432                                 case (cycle)
 433                                 0: begin
 434                                                 {registers[`REG_SPH],registers[`REG_SPL]} <=
 435                                                         {registers[`REG_SPH],registers[`REG_SPL]} - 1;
 436                                                 cycle <= 1;
 437                                         end
 438                                 1:      begin
 439                                                 {registers[`REG_SPH],registers[`REG_SPL]} <=
 440                                                         {registers[`REG_SPH],registers[`REG_SPL]} - 1;
 441                                                 cycle <= 2;
 442                                         end
 443                                 2:      cycle <= 3;
 444                                 3:      cycle <= 0;
 445                                 endcase
 446                         end
 447                         `INSN_POP_reg: begin    /* POP is 12 cycles! */
 448                                 case (cycle)
 449                                 0:      begin
 450                                                 cycle <= 1;
 451                                                 {registers[`REG_SPH],registers[`REG_SPL]} <=
 452                                                         {registers[`REG_SPH],registers[`REG_SPL]} + 1;
 453                                         end
 454                                 1:      begin
 455                                                 case (opcode[5:4])
 456                                                 `INSN_stack_AF: registers[`REG_F] <= rdata;
 457                                                 `INSN_stack_BC: registers[`REG_C] <= rdata;
 458                                                 `INSN_stack_DE: registers[`REG_E] <= rdata;
 459                                                 `INSN_stack_HL: registers[`REG_L] <= rdata;
 460                                                 endcase
 461                                                 {registers[`REG_SPH],registers[`REG_SPL]} <=
 462                                                         {registers[`REG_SPH],registers[`REG_SPL]} + 1;
 463                                                 cycle <= 2;
 464                                         end
 465                                 2:      begin
 466                                                 case (opcode[5:4])
 467                                                 `INSN_stack_AF: registers[`REG_A] <= rdata;
 468                                                 `INSN_stack_BC: registers[`REG_B] <= rdata;
 469                                                 `INSN_stack_DE: registers[`REG_D] <= rdata;
 470                                                 `INSN_stack_HL: registers[`REG_H] <= rdata;
 471                                                 endcase
 472                                                 cycle <= 0;
 473                                         end
 474                                 endcase
 475                         end
 476                         `INSN_LDH_AC: begin
 477                                 case (cycle)
 478                                 0:      cycle <= 1;
 479                                 1: begin
 480                                                 cycle <= 0;
 481                                                 if (opcode[4])
 482                                                         registers[`REG_A] <= rdata;
 483                                         end
 484                                 endcase
 485                         end
 486                         `INSN_LDx_AHL: begin
 487                                 case (cycle)
 488                                 0:      cycle <= 1;
 489                                 1:      begin
 490                                                 cycle <= 0;
 491                                                 if (opcode[3])
 492                                                         registers[`REG_A] <= rdata;
 493                                                 {registers[`REG_H],registers[`REG_L]} <=
 494                                                         opcode[4] ? // if set, LDD, else LDI
 495                                                         ({registers[`REG_H],registers[`REG_L]} - 1) :
 496                                                         ({registers[`REG_H],registers[`REG_L]} + 1);
 497                                         end
 498                                 endcase
 499                         end
 500                         `INSN_ALU8: begin
 501                                 if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
 502                                         /* Sit on our asses. */
 503                                         cycle <= 1;
 504                                 end else begin          /* Actually do the computation! */
 505                                         case (opcode[5:3])
 506                                         `INSN_alu_ADD: begin
 507                                                 registers[`REG_A] <=
 508                                                         registers[`REG_A] + tmp;
 509                                                 registers[`REG_F] <=
 510                                                         { /* Z */ ((registers[`REG_A] + tmp) == 0) ? 1'b1 : 1'b0,
 511                                                           /* N */ 0,
 512                                                           /* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
 513                                                           /* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
 514                                                           registers[`REG_F][3:0]
 515                                                         };
 516                                         end
 517                                         default:
 518                                                 $stop;
 519                                         endcase
 520                                 end
 521                         end
 522                         endcase
 523                         state <= `STATE_FETCH;
 524                 end
 525                 endcase
 526 endmodule
 527
 528 `timescale 1ns / 1ps
 529 module TestBench();
 530         reg clk = 0;
 531         wire [15:0] addr;
 532         wire [7:0] data;
 533         wire wr, rd;
 534         reg [7:0] rom [2047:0];
 535
 536         initial $readmemh("rom.hex", rom);
 537         always #10 clk <= ~clk;
 538         GBZ80Core core(
 539                 .clk(clk),
 540                 .busaddress(addr),
 541                 .busdata(data),
 542                 .buswr(wr),
 543                 .busrd(rd));
 544         assign data = rd ? rom[addr] : 8'bzzzzzzzz;
 545 endmodule