Decode.v

   1 `include "ARM_Constants.v"
   2
   3 module Decode(
   4         input clk,
   5         input stall,
   6         input [31:0] insn,
   7         input [31:0] inpc,
   8         input [31:0] incpsr,
   9         input [31:0] inspsr,
  10         output reg [31:0] op0,
  11         output reg [31:0] op1,
  12         output reg [31:0] op2,
  13         output reg carry,
  14         output reg [31:0] outcpsr,
  15         output reg [31:0] outspsr,
  16
  17         output reg [3:0] read_0,
  18         output reg [3:0] read_1,
  19         output reg [3:0] read_2,
  20         input [31:0] rdata_0,
  21         input [31:0] rdata_1,
  22         input [31:0] rdata_2
  23         );
  24
  25         wire [31:0] regs0, regs1, regs2;
  26         reg [31:0] rpc;
  27         reg [31:0] op0_out, op1_out, op2_out;
  28         reg carry_out;
  29
  30         /* shifter stuff */
  31         wire [31:0] shift_oper;
  32         wire [31:0] shift_res;
  33         wire shift_cflag_out;
  34         wire [31:0] rotate_res;
  35
  36         assign regs0 = (read_0 == 4'b1111) ? rpc : rdata_0;
  37         assign regs1 = (read_1 == 4'b1111) ? rpc : rdata_1;
  38         assign regs2 = rdata_2; /* use regs2 for things that cannot be r15 */
  39
  40         IREALLYHATEARMSHIFT shift(.insn(insn),
  41                                   .operand(regs1),
  42                                   .reg_amt(regs2),
  43                                   .cflag_in(incpsr[`CPSR_C]),
  44                                   .res(shift_res),
  45                                   .cflag_out(shift_cflag_out));
  46
  47         SuckLessRotator whirr(.oper({24'b0, insn[7:0]}),
  48                               .amt(insn[11:8]),
  49                               .res(rotate_res));
  50
  51         always @(*)
  52                 casez (insn)
  53                 `DECODE_ALU_MULT,               /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
  54 //              `DECODE_ALU_MUL_LONG,           /* Multiply long */
  55                 `DECODE_ALU_MRS,                /* MRS (Transfer PSR to register) */
  56                 `DECODE_ALU_MSR,                /* MSR (Transfer register to PSR) */
  57                 `DECODE_ALU_MSR_FLAGS,          /* MSR (Transfer register or immediate to PSR, flag bits only) */
  58                 `DECODE_ALU_SWP,                /* Atomic swap */
  59                 `DECODE_ALU_BX,                 /* Branch and exchange */
  60                 `DECODE_ALU_HDATA_REG,          /* Halfword transfer - register offset */
  61                 `DECODE_ALU_HDATA_IMM,          /* Halfword transfer - register offset */
  62                 `DECODE_LDRSTR_UNDEFINED,       /* Undefined. I hate ARM */
  63                 `DECODE_LDRSTR,                 /* Single data transfer */
  64                 `DECODE_LDMSTM,                 /* Block data transfer */
  65                 `DECODE_BRANCH,                 /* Branch */
  66                 `DECODE_LDCSTC,                 /* Coprocessor data transfer */
  67                 `DECODE_CDP,                    /* Coprocessor data op */
  68                 `DECODE_SWI:                    /* SWI */
  69                         rpc = inpc + 8;
  70                 `DECODE_MRCMCR:                 /* Coprocessor register transfer */
  71                         rpc = inpc + 12;
  72                 `DECODE_ALU:                    /* ALU */
  73                         rpc = inpc + (insn[25] ? 8 : (insn[4] ? 12 : 8));
  74                 default:                        /* X everything else out */
  75                         rpc = 32'hxxxxxxxx;
  76                 endcase
  77
  78         always @(*) begin
  79                 read_0 = 4'hx;
  80                 read_1 = 4'hx;
  81                 read_2 = 4'hx;
  82
  83                 op0_out = 32'hxxxxxxxx;
  84                 op1_out = 32'hxxxxxxxx;
  85                 op2_out = 32'hxxxxxxxx;
  86                 carry_out = 1'bx;
  87
  88                 casez (insn)
  89                 `DECODE_ALU_MULT:       /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
  90                 begin
  91                         read_0 = insn[15:12]; /* Rn */
  92                         read_1 = insn[3:0];   /* Rm */
  93                         read_2 = insn[11:8];  /* Rs */
  94
  95                         op0_out = regs0;
  96                         op1_out = regs1;
  97                         op2_out = regs2;
  98                 end
  99 //              `DECODE_ALU_MUL_LONG:   /* Multiply long */
 100 //              begin
 101 //                      read_0 = insn[11:8]; /* Rn */
 102 //                      read_1 = insn[3:0];   /* Rm */
 103 //                      read_2 = 4'b0;       /* anyus */
 104 //
 105 //                      op1_res = regs1;
 106 //              end
 107                 `DECODE_ALU_MRS:        /* MRS (Transfer PSR to register) */
 108                 begin end
 109                 `DECODE_ALU_MSR:        /* MSR (Transfer register to PSR) */
 110                 begin
 111                         read_0 = insn[3:0];     /* Rm */
 112
 113                         op0_out = regs0;
 114                 end
 115                 `DECODE_ALU_MSR_FLAGS:  /* MSR (Transfer register or immediate to PSR, flag bits only) */
 116                 begin
 117                         read_0 = insn[3:0];     /* Rm */
 118
 119                         if(insn[25]) begin     /* the constant case */
 120                                 op0_out = rotate_res;
 121                         end else begin
 122                                 op0_out = regs0;
 123                         end
 124                 end
 125                 `DECODE_ALU_SWP:        /* Atomic swap */
 126                 begin
 127                         read_0 = insn[19:16]; /* Rn */
 128                         read_1 = insn[3:0];   /* Rm */
 129
 130                         op0_out = regs0;
 131                         op1_out = regs1;
 132                 end
 133                 `DECODE_ALU_BX:         /* Branch and exchange */
 134                 begin
 135                         read_0 = insn[3:0];   /* Rn */
 136
 137                         op0_out = regs0;
 138                 end
 139                 `DECODE_ALU_HDATA_REG:  /* Halfword transfer - register offset */
 140                 begin
 141                         read_0 = insn[19:16];
 142                         read_1 = insn[3:0];
 143                         read_2 = insn[15:12];
 144
 145                         op0_out = regs0;
 146                         op1_out = regs1;
 147                         op2_out = regs2;
 148                 end
 149                 `DECODE_ALU_HDATA_IMM:  /* Halfword transfer - immediate offset */
 150                 begin
 151                         read_0 = insn[19:16];
 152                         read_1 = insn[15:12];
 153
 154                         op0_out = regs0;
 155                         op1_out = {24'b0, insn[11:8], insn[3:0]};
 156                         op2_out = regs1;
 157                 end
 158                 `DECODE_ALU:            /* ALU */
 159                 begin
 160                         read_0 = insn[19:16]; /* Rn */
 161                         read_1 = insn[3:0];   /* Rm */
 162                         read_2 = insn[11:8];  /* Rs for shift */
 163
 164                         op0_out = regs0;
 165                         if(insn[25]) begin     /* the constant case */
 166                                 carry_out = incpsr[`CPSR_C];
 167                                 op1_out = rotate_res;
 168                         end else begin
 169                                 carry_out = shift_cflag_out;
 170                                 op1_out = shift_res;
 171                         end
 172                 end
 173                 `DECODE_LDRSTR_UNDEFINED:       /* Undefined. I hate ARM */
 174                 begin
 175                         /* eat shit */
 176                 end
 177                 `DECODE_LDRSTR:         /* Single data transfer */
 178                 begin
 179                         read_0 = insn[19:16]; /* Rn */
 180                         read_1 = insn[3:0];   /* Rm */
 181                         read_2 = insn[15:12];
 182
 183                         op0_out = regs0;
 184                         if(!insn[25] /* immediate */) begin
 185                                 op1_out = {20'b0, insn[11:0]};
 186                                 carry_out = incpsr[`CPSR_C];
 187                         end else begin
 188                                 op1_out = shift_res;
 189                                 carry_out = shift_cflag_out;
 190                         end
 191                         op2_out = regs2;
 192                 end
 193                 `DECODE_LDMSTM:         /* Block data transfer */
 194                 begin
 195                         read_0 = insn[19:16];
 196
 197                         op0_out = regs0;
 198                         op1_out = {16'b0, insn[15:0]};
 199                 end
 200                 `DECODE_BRANCH:         /* Branch */
 201                 begin
 202                         op0_out = {{6{insn[23]}}, insn[23:0], 2'b0};
 203                 end
 204                 `DECODE_LDCSTC:         /* Coprocessor data transfer */
 205                 begin
 206                         read_0 = insn[19:16];
 207
 208                         op0_out = regs0;
 209                         op1_out = {24'b0, insn[7:0]};
 210                 end
 211                 `DECODE_CDP:            /* Coprocessor data op */
 212                 begin
 213                 end
 214                 `DECODE_MRCMCR:         /* Coprocessor register transfer */
 215                 begin
 216                         read_0 = insn[15:12];
 217
 218                         op0_out = regs0;
 219                 end
 220                 `DECODE_SWI:            /* SWI */
 221                 begin
 222                 end
 223                 default:
 224                         $display("Undecoded instruction");
 225                 endcase
 226         end
 227
 228
 229         always @ (posedge clk) begin
 230                 if (!stall)
 231                 begin
 232                         op0 <= op0_out;   /* Rn - always */
 233                         op1 <= op1_out; /* 'operand 2' - Rm */
 234                         op2 <= op2_out;   /* thirdedge - Rs */
 235                         carry <= carry_out;
 236                         outcpsr <= incpsr;
 237                         outspsr <= inspsr;
 238                 end
 239         end
 240
 241 endmodule
 242
 243 module IREALLYHATEARMSHIFT(
 244         input [31:0] insn,
 245         input [31:0] operand,
 246         input [31:0] reg_amt,
 247         input cflag_in,
 248         output reg [31:0] res,
 249         output reg cflag_out
 250 );
 251         wire [5:0] shift_amt;
 252         reg is_arith, is_rot;
 253         wire rshift_cout;
 254         wire [31:0] rshift_res;
 255
 256         assign shift_amt = insn[4] ? {|reg_amt[7:5], reg_amt[4:0]}     /* reg-specified shift */
 257                                    : {insn[11:7] == 5'b0, insn[11:7]}; /* immediate shift */
 258
 259         SuckLessShifter barrel(.oper(operand),
 260                                .carryin(cflag_in),
 261                                .amt(shift_amt),
 262                                .is_arith(is_arith),
 263                                .is_rot(is_rot),
 264                                .res(rshift_res),
 265                                .carryout(rshift_cout));
 266
 267         always @(*)
 268                 case (insn[6:5])
 269                 `SHIFT_LSL: begin
 270                         /* meaningless */
 271                         is_rot = 1'b0;
 272                         is_arith = 1'b0;
 273                 end
 274                 `SHIFT_LSR: begin
 275                         is_rot = 1'b0;
 276                         is_arith = 1'b0;
 277                 end
 278                 `SHIFT_ASR: begin
 279                         is_rot = 1'b0;
 280                         is_arith = 1'b1;
 281                 end
 282                 `SHIFT_ROR: begin
 283                         is_rot = 1'b1;
 284                         is_arith = 1'b0;
 285                 end
 286                 endcase
 287
 288         always @(*)
 289                 case (insn[6:5]) /* shift type */
 290                 `SHIFT_LSL:
 291                         {cflag_out, res} = {cflag_in, operand} << {insn[4] & shift_amt[5], shift_amt[4:0]};
 292                 `SHIFT_LSR: begin
 293                         res = rshift_res;
 294                         cflag_out = rshift_cout;
 295                 end
 296                 `SHIFT_ASR: begin
 297                         res = rshift_res;
 298                         cflag_out = rshift_cout;
 299                 end
 300                 `SHIFT_ROR: begin
 301                         if(!insn[4] && shift_amt[4:0] == 5'b0) begin /* RRX x.x */
 302                                 res = {cflag_in, operand[31:1]};
 303                                 cflag_out = operand[0];
 304                         end else begin
 305                                 res = rshift_res;
 306                                 cflag_out = rshift_cout;
 307                         end
 308                 end
 309                 endcase
 310 endmodule
 311
 312 module SuckLessShifter(
 313         input [31:0] oper,
 314         input carryin,
 315         input [5:0] amt,
 316         input is_arith,
 317         input is_rot,
 318         output wire [31:0] res,
 319         output wire carryout
 320 );
 321
 322         wire [32:0] stage1, stage2, stage3, stage4, stage5;
 323
 324         wire pushbits = is_arith & oper[31];
 325
 326         /* do a barrel shift */
 327         assign stage1 = amt[5] ? {is_rot ? oper : {32{pushbits}}, oper[31]} : {oper, carryin};
 328         assign stage2 = amt[4] ? {is_rot ? stage1[16:1] : {16{pushbits}}, stage1[32:17], stage1[16]} : stage1;
 329         assign stage3 = amt[3] ? {is_rot ? stage2[8:1] : {8{pushbits}}, stage2[32:9], stage2[8]} : stage2;
 330         assign stage4 = amt[2] ? {is_rot ? stage3[4:1] : {4{pushbits}}, stage3[32:5], stage3[4]} : stage3;
 331         assign stage5 = amt[1] ? {is_rot ? stage4[2:1] : {2{pushbits}}, stage4[32:3], stage4[2]} : stage4;
 332         assign {res, carryout} = amt[0] ? {is_rot ? stage5[1] : pushbits, stage5[32:2], stage5[1]} : stage5;
 333
 334 endmodule
 335
 336 module SuckLessRotator(
 337         input [31:0] oper,
 338         input [3:0] amt,
 339         output wire [31:0] res
 340 );
 341
 342         wire [31:0] stage1, stage2, stage3;
 343         assign stage1 = amt[3] ? {oper[15:0], oper[31:16]} : oper;
 344         assign stage2 = amt[2] ? {stage1[7:0], stage1[31:8]} : stage1;
 345         assign stage3 = amt[1] ? {stage2[3:0], stage2[31:4]} : stage2;
 346         assign res    = amt[0] ? {stage3[1:0], stage3[31:2]} : stage3;
 347
 348 endmodule
 349