Execute.v

   1 module Execute(
   2         input clk,
   3         input Nrst,     /* XXX not used yet */
   4
   5         input stall,
   6         input flush,
   7
   8         input inbubble,
   9         input [31:0] pc,
  10         input [31:0] insn,
  11         input [31:0] cpsr,
  12         input [31:0] op0,
  13         input [31:0] op1,
  14         input [31:0] op2,
  15         input carry,
  16
  17         output reg outstall = 0,
  18         output reg outbubble = 1,
  19         output reg [31:0] outcpsr = 0,
  20         output reg write_reg = 1'bx,
  21         output reg [3:0] write_num = 4'bxxxx,
  22         output reg [31:0] write_data = 32'hxxxxxxxx
  23         );
  24
  25         reg mult_start;
  26         reg [31:0] mult_acc0, mult_in0, mult_in1;
  27         wire mult_done;
  28         wire [31:0] mult_result;
  29
  30         reg [31:0] alu_in0, alu_in1;
  31         reg [3:0] alu_op;
  32         reg alu_setflags;
  33         wire [31:0] alu_result, alu_outcpsr;
  34         wire alu_setres;
  35
  36         reg next_outbubble;
  37         reg [31:0] next_outcpsr;
  38         reg next_write_reg;
  39         reg [3:0] next_write_num;
  40         reg [31:0] next_write_data;
  41
  42         Multiplier multiplier(
  43                 .clk(clk), .Nrst(Nrst),
  44                 .start(mult_start), .acc0(mult_acc0), .in0(mult_in0),
  45                 .in1(mult_in1), .done(mult_done), .result(mult_result));
  46
  47         ALU alu(
  48                 .clk(clk), .Nrst(Nrst),
  49                 .in0(alu_in0), .in1(alu_in1), .cpsr(cpsr), .op(alu_op),
  50                 .setflags(alu_setflags), .shifter_carry(carry),
  51                 .result(alu_result), .cpsr_out(alu_outcpsr), .setres(alu_setres));
  52
  53         always @(posedge clk)
  54         begin
  55                 if (!stall)
  56                 begin
  57                         outbubble <= next_outbubble;
  58                         outcpsr <= next_outcpsr;
  59                         write_reg <= next_write_reg;
  60                         write_num <= next_write_num;
  61                         write_data <= next_write_data;
  62                 end
  63         end
  64
  65         reg prevstall = 0;
  66         always @(posedge clk)
  67                 prevstall <= outstall;
  68
  69         always @(*)
  70         begin
  71                 outstall = stall;
  72                 next_outbubble = inbubble;
  73                 next_outcpsr = cpsr;
  74                 next_write_reg = 0;
  75                 next_write_num = 4'hx;
  76                 next_write_data = 32'hxxxxxxxx;
  77
  78                 mult_start = 0;
  79                 mult_acc0 = 32'hxxxxxxxx;
  80                 mult_in0 = 32'hxxxxxxxx;
  81                 mult_in1 = 32'hxxxxxxxx;
  82
  83                 alu_in0 = 32'hxxxxxxxx;
  84                 alu_in1 = 32'hxxxxxxxx;
  85                 alu_op = 4'hx;  /* hax! */
  86                 alu_setflags = 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                         if (!prevstall && !inbubble)
  92                         begin
  93                                 mult_start = 1;
  94                                 mult_acc0 = insn[21] /* A */ ? op0 /* Rn */ : 32'h0;
  95                                 mult_in0 = op1 /* Rm */;
  96                                 mult_in1 = op2 /* Rs */;
  97                                 $display("New MUL instruction");
  98                         end
  99                         outstall = stall | ((!prevstall | !mult_done) && !inbubble);
 100                         next_outbubble = inbubble | !mult_done | !prevstall;
 101                         next_outcpsr = insn[20] /* S */ ? {mult_result[31] /* N */, mult_result == 0 /* Z */, 1'b0 /* C */, cpsr[28] /* V */, cpsr[27:0]} : cpsr;
 102                         next_write_reg = 1;
 103                         next_write_num = insn[19:16] /* Rd -- why the fuck isn't this the same place as ALU */;
 104                         next_write_data = mult_result;
 105                 end
 106 //              `DECODE_ALU_MUL_LONG,   /* Multiply long */
 107                 `DECODE_ALU_MRS,        /* MRS (Transfer PSR to register) */
 108                 `DECODE_ALU_MSR,        /* MSR (Transfer register to PSR) */
 109                 `DECODE_ALU_MSR_FLAGS,  /* MSR (Transfer register or immediate to PSR, flag bits only) */
 110                 `DECODE_ALU_SWP,        /* Atomic swap */
 111                 `DECODE_ALU_BX,         /* Branch */
 112                 `DECODE_ALU_HDATA_REG,  /* Halfword transfer - register offset */
 113                 `DECODE_ALU_HDATA_IMM:  /* Halfword transfer - immediate offset */
 114                 begin end
 115                 `DECODE_ALU:            /* ALU */
 116                 begin
 117                         alu_in0 = op0;
 118                         alu_in1 = op1;
 119                         alu_op = insn[24:21];
 120                         alu_setflags = insn[20] /* I */;
 121
 122                         if (alu_setres) begin
 123                                 next_write_reg = 1;
 124                                 next_write_num = insn[15:12] /* Rd */;
 125                                 next_write_data = alu_result;
 126                         end
 127
 128                         next_outcpsr = alu_outcpsr;
 129                 end
 130                 `DECODE_LDRSTR_UNDEFINED,       /* Undefined. I hate ARM */
 131                 `DECODE_LDRSTR,         /* Single data transfer */
 132                 `DECODE_LDMSTM,         /* Block data transfer */
 133                 `DECODE_BRANCH,         /* Branch */
 134                 `DECODE_LDCSTC,         /* Coprocessor data transfer */
 135                 `DECODE_CDP,            /* Coprocessor data op */
 136                 `DECODE_MRCMCR,         /* Coprocessor register transfer */
 137                 `DECODE_SWI:            /* SWI */
 138                 begin end
 139                 default:                /* X everything else out */
 140                 begin end
 141                 endcase
 142         end
 143 endmodule
 144
 145 module Multiplier(
 146         input clk,
 147         input Nrst,     /* XXX not used yet */
 148
 149         input start,
 150         input [31:0] acc0,
 151         input [31:0] in0,
 152         input [31:0] in1,
 153
 154         output reg done = 0,
 155         output reg [31:0] result);
 156
 157         reg [31:0] bitfield;
 158         reg [31:0] multiplicand;
 159         reg [31:0] acc;
 160
 161         always @(posedge clk)
 162         begin
 163                 if (start) begin
 164                         bitfield <= in0;
 165                         multiplicand <= in1;
 166                         acc <= acc0;
 167                         done <= 0;
 168                 end else begin
 169                         bitfield <= {2'b00, bitfield[31:2]};
 170                         multiplicand <= {multiplicand[29:0], 2'b00};
 171                         acc <= acc +
 172                                 (bitfield[0] ? multiplicand : 0) +
 173                                 (bitfield[1] ? {multiplicand[30:0], 1'b0} : 0);
 174                         if (bitfield == 0) begin
 175                                 result <= acc;
 176                                 done <= 1;
 177                         end
 178                 end
 179         end
 180 endmodule
 181
 182 module ALU(
 183         input clk,
 184         input Nrst,     /* XXX not used yet */
 185
 186         input [31:0] in0,
 187         input [31:0] in1,
 188         input [31:0] cpsr,
 189         input [3:0] op,
 190         input setflags,
 191         input shifter_carry,
 192
 193         output reg [31:0] result,
 194         output reg [31:0] cpsr_out,
 195         output reg setres
 196 );
 197         wire [31:0] res;
 198         wire flag_n, flag_z, flag_c, flag_v, setres;
 199         wire [32:0] sum, diff, rdiff;
 200         wire sum_v, diff_v, rdiff_v;
 201
 202         assign sum = {1'b0, in0} + {1'b0, in1};
 203         assign diff = {1'b0, in0} - {1'b0, in1};
 204         assign rdiff = {1'b0, in1} + {1'b0, in0};
 205         assign sum_v = (in0[31] ^~ in1[31]) & (sum[31] ^ in0[31]);
 206         assign diff_v = (in0[31] ^ in1[31]) & (diff[31] ^ in0[31]);
 207         assign rdiff_v = (in0[31] ^ in1[31]) & (rdiff[31] ^ in1[31]);
 208
 209         always @(*) begin
 210                 res = 32'hxxxxxxxx;
 211                 setres = 1'bx;
 212                 flag_c = cpsr[`CPSR_C];
 213                 flag_v = cpsr[`CPSR_V];
 214                 case(op)
 215                 `ALU_AND: begin
 216                         result = in0 & in1;
 217                         flag_c = shifter_carry;
 218                         setres = 1'b1;
 219                 end
 220                 `ALU_EOR: begin
 221                         result = in0 ^ in1;
 222                         flag_c = shifter_carry;
 223                         setres = 1'b1;
 224                 end
 225                 `ALU_SUB: begin
 226                         {flag_c, result} = diff;
 227                         flag_v = diff_v;
 228                         setres = 1'b1;
 229                 end
 230                 `ALU_RSB: begin
 231                         {flag_c, result} = rdiff;
 232                         flag_v = rdiff_v;
 233                         setres = 1'b1;
 234                 end
 235                 `ALU_ADD: begin
 236                         {flag_c, result} = sum;
 237                         flag_v = sum_v;
 238                         setres = 1'b1;
 239                 end
 240                 `ALU_ADC: begin
 241                         {flag_c, result} = sum + {32'b0, cpsr[`CPSR_C]};
 242                         flag_v = sum_v | (~sum[31] & result[31]);
 243                         setres = 1'b1;
 244                 end
 245                 `ALU_SBC: begin
 246                         {flag_c, result} = diff - {32'b0, (~cpsr[`CPSR_C])};
 247                         flag_v = diff_v | (diff[31] & ~result[31]);
 248                         setres = 1'b1;
 249                 end
 250                 `ALU_RSC: begin
 251                         {flag_c, result} = rdiff - {32'b0, (~cpsr[`CPSR_C])};
 252                         flag_v = rdiff_v | (rdiff[31] & ~result[31]);
 253                         setres = 1'b1;
 254                 end
 255                 `ALU_TST: begin
 256                         result = in0 & in1;
 257                         flag_c = shifter_carry;
 258                         setres = 1'b0;
 259                 end
 260                 `ALU_TEQ: begin
 261                         result = in0 ^ in1;
 262                         flag_c = shifter_carry;
 263                         setres = 1'b0;
 264                 end
 265                 `ALU_CMP: begin
 266                         {flag_c, result} = diff;
 267                         flag_v = diff_v;
 268                         setres = 1'b0;
 269                 end
 270                 `ALU_CMN: begin
 271                         {flag_c, result} = sum;
 272                         flag_v = sum_v;
 273                         setres = 1'b0;
 274                 end
 275                 `ALU_ORR: begin
 276                         result = in0 | in1;
 277                         flag_c = shifter_carry;
 278                         setres = 1'b1;
 279                 end
 280                 `ALU_MOV: begin
 281                         result = in1;
 282                         flag_c = shifter_carry;
 283                         setres = 1'b1;
 284                 end
 285                 `ALU_BIC: begin
 286                         result = in0 & (~in1);
 287                         flag_c = shifter_carry;
 288                         setres = 1'b1;
 289                 end
 290                 `ALU_MVN: begin
 291                         result = ~in1;
 292                         flag_c = shifter_carry;
 293                         setres = 1'b1;
 294                 end
 295                 endcase
 296
 297                 flag_z = (result == 0);
 298                 flag_n = result[31];
 299
 300                 cpsr_out = setflags ? {flag_n, flag_z, flag_c, flag_v, cpsr[27:0]} : cpsr;
 301         end
 302 endmodule