Decode.v

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