Issue.v

   1 `include "ARM_Constants.v"
   2
   3 module Issue(
   4         input clk,
   5         input Nrst,     /* XXX not used yet */
   6
   7         input stall,    /* pipeline control */
   8         input flush,
   9
  10         input inbubble, /* stage inputs */
  11         input [31:0] insn,
  12         input [31:0] inpc,
  13         input [31:0] cpsr,
  14
  15         output reg outstall = 0,        /* stage outputs */
  16         output reg outbubble = 1,
  17         output reg [31:0] outpc = 0,
  18         output reg [31:0] outinsn = 0
  19         /* XXX other? */
  20         );
  21
  22
  23
  24 `ifdef COPY_PASTA_FODDER
  25         /* from page 2 of ARM7TDMIvE2.pdf */
  26         casex (insn)
  27         32'b????000000??????????????1001????:   /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
  28 //      32'b????00001???????????????1001????:   /* Multiply long */
  29         32'b????00010?001111????000000000000:   /* MRS (Transfer PSR to register) */
  30         32'b????00010?101001111100000000????:   /* MSR (Transfer register to PSR) */
  31         32'b????00?10?1010001111????????????:   /* MSR (Transfer register or immediate to PSR, flag bits only) */
  32         32'b????00??????????????????????????:   /* ALU */
  33         32'b????00010?00????????00001001????:   /* Atomic swap */
  34         32'b????000100101111111111110001????:   /* Branch */
  35         32'b????000??0??????????00001??1????:   /* Halfword transfer - register offset */
  36         32'b????000??1??????????00001??1????:   /* Halfword transfer - register offset */
  37         32'b????011????????????????????1????:   /* Undefined. I hate ARM */
  38         32'b????01??????????????????????????:   /* Single data transfer */
  39         32'b????100?????????????????????????:   /* Block data transfer */
  40         32'b????101?????????????????????????:   /* Branch */
  41         32'b????110?????????????????????????:   /* Coprocessor data transfer */
  42         32'b????1110???????????????????0????:   /* Coprocessor data op */
  43         32'b????1110???????????????????1????:   /* Coprocessor register transfer */
  44         32'b????1111????????????????????????:   /* SWI */
  45         default:                                /* X everything else out */
  46         endcase
  47 `endif
  48
  49         /* Flag setting */
  50         reg use_cpsr;
  51         reg [15:0] use_regs;
  52         reg def_cpsr;
  53         reg [15:0] def_regs;
  54
  55         function [15:0] idxbit;
  56                 input [3:0] r;
  57                 if (r == 15)
  58                         idxbit = 0;
  59                 else
  60                         idxbit = (16'b1) << r;
  61         endfunction
  62
  63         wire [3:0] rn = insn[19:16];
  64         wire [3:0] rd = insn[15:12];
  65         wire [3:0] rs = insn[11:8];
  66         wire [3:0] rm = insn[3:0];
  67         wire [3:0] cond = insn[31:28];
  68
  69         wire [3:0] rd_mul = insn[19:16];
  70         wire [3:0] rn_mul = insn[15:12];
  71         wire [3:0] rs_mul = insn[11:8];
  72
  73         wire [3:0] alu_opc = insn[24:21];
  74
  75         function alu_is_logical;
  76                 input [3:0] op;
  77
  78                 case (op)
  79                 `ALU_AND,`ALU_EOR,`ALU_TST,`ALU_TEQ,`ALU_ORR,`ALU_MOV,`ALU_BIC,`ALU_MVN: alu_is_logical = 1;
  80                 default: alu_is_logical = 0;
  81                 endcase
  82         endfunction
  83
  84         function alu_flags_only;
  85                 input [3:0] op;
  86
  87                 case (op)
  88                 `ALU_TST,`ALU_TEQ,`ALU_CMP,`ALU_CMN: alu_flags_only = 1;
  89                 default: alu_flags_only = 0;
  90                 endcase
  91         endfunction
  92
  93         function shift_requires_carry;
  94                 input [7:0] shift;
  95
  96                 case(shift[1:0])
  97                 `SHIFT_LSL: shift_requires_carry = (shift[7:2] == 0);
  98                 `SHIFT_LSR: shift_requires_carry = 0;
  99                 `SHIFT_ASR: shift_requires_carry = 0;
 100                 `SHIFT_ROR: shift_requires_carry = (shift[7:2] == 0);
 101                 endcase
 102         endfunction
 103
 104         always @(*)
 105                 casez (insn)
 106                 32'b????000000??????????????1001????:   /* Multiply -- must come before ALU, because it pattern matches a specific case of ALU */
 107                 begin
 108                         use_cpsr = `COND_MATTERS(cond);
 109                         use_regs = (insn[21] /* accum */ ? idxbit(rn_mul) : 0) | idxbit(rs_mul) | idxbit(rm);
 110                         def_cpsr = insn[20] /* setcc */;
 111                         def_regs = idxbit(rd_mul);
 112                 end
 113 //              32'b????00001???????????????1001????:   /* Multiply long */
 114                 32'b????00010?001111????000000000000:   /* MRS (Transfer PSR to register) */
 115                 begin
 116                         use_cpsr = `COND_MATTERS(cond) || (insn[22] == 0) /* Source = CPSR */;
 117                         use_regs = 0;
 118                         def_cpsr = 0;
 119                         def_regs = idxbit(rd);
 120                 end
 121                 32'b????00010?101001111100000000????:   /* MSR (Transfer register to PSR) */
 122                 begin
 123                         use_cpsr = `COND_MATTERS(cond);
 124                         use_regs = idxbit(rm);
 125                         def_cpsr = 1;
 126                         def_regs = 0;
 127                 end
 128                 32'b????00?10?1010001111????????????:   /* MSR (Transfer register or immediate to PSR, flag bits only) */
 129                 begin
 130                         use_cpsr = `COND_MATTERS(cond);
 131                         use_regs = insn[25] ? 0 : idxbit(rm);
 132                         def_cpsr = 1;
 133                         def_regs = 0;
 134                 end
 135                 32'b????00??????????????????????????:   /* ALU */
 136                 begin
 137                         use_cpsr = `COND_MATTERS(cond) | (!insn[25] /* I */ && shift_requires_carry(insn[11:4]));
 138                         use_regs =
 139                                 (insn[25] /* I */ ? 0 :
 140                                         (insn[4] /* shift by reg */ ?
 141                                                 (idxbit(rs) | idxbit(rm)) :
 142                                                 (idxbit(rm)))) |
 143                                 (((alu_opc != `ALU_MOV) && (alu_opc != `ALU_MVN)) ? idxbit(rn) : 0);
 144                         def_cpsr = insn[20] /* S */ | alu_is_logical(alu_opc);
 145                         def_regs = alu_flags_only(alu_opc) ? 0 : idxbit(rd);
 146                 end
 147                 32'b????00010?00????????00001001????:   /* Atomic swap */
 148                 begin
 149                         use_cpsr = `COND_MATTERS(cond);
 150                         use_regs = idxbit(rn) | idxbit(rm);
 151                         def_cpsr = 0;
 152                         def_regs = idxbit(rd);
 153                 end
 154                 32'b????000100101111111111110001????:   /* Branch */
 155                 begin
 156                         use_cpsr = `COND_MATTERS(cond);
 157                         use_regs = idxbit(rm);
 158                         def_cpsr = 0;   // don't care, we'll never get there
 159                         def_regs = 0;
 160                 end
 161                 32'b????000??0??????????00001??1????:   /* Halfword transfer - register offset */
 162                 begin
 163                         use_cpsr = `COND_MATTERS(cond);
 164                         use_regs = idxbit(rn) | idxbit(rm) | (insn[20] /* L */ ? 0 : idxbit(rd));
 165                         def_cpsr = 0;
 166                         def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
 167                 end
 168                 32'b????000??1??????????00001??1????:   /* Halfword transfer - immediate offset */
 169                 begin
 170                         use_cpsr = `COND_MATTERS(cond);
 171                         use_regs = idxbit(rn) | (insn[20] /* L */ ? 0 : idxbit(rd));
 172                         def_cpsr = 0;
 173                         def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
 174                 end
 175                 32'b????011????????????????????1????:   /* Undefined. I hate ARM */
 176                 begin
 177                         use_cpsr = 0;
 178                         use_regs = 0;
 179                         def_cpsr = 0;
 180                         def_regs = 0;
 181                 end
 182                 32'b????100?????????????????????????:   /* Block data transfer */
 183                 begin
 184                         use_cpsr = `COND_MATTERS(cond);
 185                         use_regs = idxbit(rn) | (insn[20] /* L */ ? 0 : insn[15:0]);
 186                         def_cpsr = insn[22];    /* This is a superset of all cases, anyway. */
 187                         def_regs = (insn[21] /* W */ ? idxbit(rn) : 0) | (insn[20] /* L */ ? insn[15:0] : 0);
 188                 end
 189                 32'b????101?????????????????????????:   /* Branch */
 190                 begin
 191                         use_cpsr = `COND_MATTERS(cond);
 192                         use_regs = 0;
 193                         def_cpsr = 0;
 194                         def_regs = 0;
 195                 end
 196                 32'b????110?????????????????????????:   /* Coprocessor data transfer */
 197                 begin
 198                         use_cpsr = `COND_MATTERS(cond);
 199                         use_regs = idxbit(rn);
 200                         def_cpsr = 0;
 201                         def_regs = insn[21] /* W */ ? idxbit(rn) : 0;
 202                 end
 203                 32'b????1110???????????????????0????:   /* Coprocessor data op */
 204                 begin
 205                         use_cpsr = `COND_MATTERS(cond);
 206                         use_regs = 0;
 207                         def_cpsr = 0;
 208                         def_regs = 0;
 209                 end
 210                 32'b????1110???????????????????1????:   /* Coprocessor register transfer */
 211                 begin
 212                         use_cpsr = `COND_MATTERS(cond);
 213                         use_regs = insn[20] /* L */ ? 0 : idxbit(rd);
 214                         def_cpsr = 0;
 215                         def_regs = insn[20] /* L */ ? idxbit(rd) : 0;
 216                 end
 217                 32'b????1111????????????????????????:   /* SWI */
 218                 begin
 219                         use_cpsr = `COND_MATTERS(cond);
 220                         use_regs = 0;
 221                         def_cpsr = 0;
 222                         def_regs = 0;
 223                 end
 224                 default:                                /* X everything else out */
 225                 begin
 226                         use_cpsr = 1'bx;
 227                         use_regs = 16'bxxxxxxxxxxxxxxxx;
 228                         def_cpsr = 1'bx;
 229                         def_regs = 16'bxxxxxxxxxxxxxxxx;
 230                 end
 231                 endcase
 232
 233         /* Condition checking logic */
 234         reg condition_met;
 235         always @(*)
 236                 casez(insn[31:28])
 237                 `COND_EQ:       condition_met = cpsr[`CPSR_Z];
 238                 `COND_NE:       condition_met = !cpsr[`CPSR_Z];
 239                 `COND_CS:       condition_met = cpsr[`CPSR_C];
 240                 `COND_CC:       condition_met = !cpsr[`CPSR_C];
 241                 `COND_MI:       condition_met = cpsr[`CPSR_N];
 242                 `COND_PL:       condition_met = !cpsr[`CPSR_N];
 243                 `COND_VS:       condition_met = cpsr[`CPSR_V];
 244                 `COND_VC:       condition_met = !cpsr[`CPSR_V];
 245                 `COND_HI:       condition_met = cpsr[`CPSR_C] && !cpsr[`CPSR_Z];
 246                 `COND_LS:       condition_met = !cpsr[`CPSR_C] || cpsr[`CPSR_Z];
 247                 `COND_GE:       condition_met = cpsr[`CPSR_N] == cpsr[`CPSR_V];
 248                 `COND_LT:       condition_met = cpsr[`CPSR_N] != cpsr[`CPSR_V];
 249                 `COND_GT:       condition_met = !cpsr[`CPSR_Z] && (cpsr[`CPSR_N] == cpsr[`CPSR_V]);
 250                 `COND_LE:       condition_met = cpsr[`CPSR_Z] || (cpsr[`CPSR_N] != cpsr[`CPSR_V]);
 251                 `COND_AL:       condition_met = 1;
 252                 `COND_NV:       condition_met = 0;
 253                 default:        condition_met = 1'bx;
 254                 endcase
 255
 256         /* Issue logic */
 257 `define STAGE_EXECUTE   0
 258 `define STAGE_MEMORY    1
 259 /* Once it's hit writeback, it's essentially hit the regfile so you're done. */
 260         reg cpsr_inflight [1:0];
 261         reg [15:0] regs_inflight [1:0];
 262
 263         reg waiting_cpsr;
 264         reg waiting_regs;
 265         wire waiting = waiting_cpsr | waiting_regs;
 266
 267         initial
 268         begin
 269                 cpsr_inflight[0] = 0;
 270                 cpsr_inflight[1] = 0;
 271                 regs_inflight[0] = 0;
 272                 regs_inflight[1] = 0;
 273         end
 274
 275         always @(*)
 276         begin
 277                 waiting_cpsr = use_cpsr & (cpsr_inflight[0] | cpsr_inflight[1]);
 278                 waiting_regs = |(use_regs & (regs_inflight[0] | regs_inflight[1]));
 279
 280                 outstall = waiting && !inbubble;        /* Happens in an always @*, because it is an exception. */
 281         end
 282
 283         /* Actually do the issue. */
 284         always @(posedge clk)
 285         begin
 286                 cpsr_inflight[0] <= cpsr_inflight[1];   /* I'm not sure how well selects work with arrays, and that seems like a dumb thing to get anusulated by. */
 287                 cpsr_inflight[1] <= (waiting || inbubble || !condition_met) ? 0 : def_cpsr;
 288                 regs_inflight[0] <= regs_inflight[1];
 289                 regs_inflight[1] <= (waiting || inbubble || !condition_met) ? 0 : def_regs;
 290
 291                 if (waiting)
 292                 begin
 293                         $display("ISSUE: Stalling instruction %08x because %d/%d", insn, waiting_cpsr, waiting_regs);
 294                 end
 295
 296                 outbubble <= inbubble | waiting | !condition_met;
 297                 outpc <= inpc;
 298                 outinsn <= insn;
 299         end
 300 endmodule