Subversion Repositories darkriscv

/*

 * Copyright (c) 2018, Marcelo Samsoniuk

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 * * Redistributions of source code must retain the above copyright notice, this

 *   list of conditions and the following disclaimer.

 *

 * * Redistributions in binary form must reproduce the above copyright notice,

 *   this list of conditions and the following disclaimer in the documentation

 *   and/or other materials provided with the distribution.

 *

 * * Neither the name of the copyright holder nor the names of its

 *   contributors may be used to endorse or promote products derived from

 *   this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER

 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,

 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

`timescale 1ns / 1ps

// implemented opcodes:

`define LUI     7'b01101_11      // lui   rd,imm[31:12]

`define AUIPC   7'b00101_11      // auipc rd,imm[31:12]

`define JAL     7'b11011_11      // jal   rd,imm[xxxxx]

`define JALR    7'b11001_11      // jalr  rd,rs1,imm[11:0] 

`define BCC     7'b11000_11      // bcc   rs1,rs2,imm[12:1]

`define LCC     7'b00000_11      // lxx   rd,rs1,imm[11:0]

`define SCC     7'b01000_11      // sxx   rs1,rs2,imm[11:0]

`define MCC     7'b00100_11      // xxxi  rd,rs1,imm[11:0]

`define RCC     7'b01100_11      // xxx   rd,rs1,rs2 

`define MAC     7'b11111_11      // mac   rd,rs1,rs2

// not implemented opcodes:

`define FCC     7'b00011_11      // fencex

`define CCC     7'b11100_11      // exx, csrxx

// configuration file

`include "../rtl/config.vh"

module darkriscv

//#(

//    parameter [31:0] RESET_PC = 0,

//    parameter [31:0] RESET_SP = 4096

//) 

(

    input             CLK,   // clock

    input             RES,   // reset

    input             HLT,   // halt

//`ifdef __THREADING__    

//    input             IREQ,  // irq req

//`endif    

    input      [31:0] IDATA, // instruction data bus

    output     [31:0] IADDR, // instruction addr bus

    input      [31:0] DATAI, // data bus (input)

    output     [31:0] DATAO, // data bus (output)

    output     [31:0] DADDR, // addr bus

`ifdef __FLEXBUZZ__

    output     [ 2:0] DLEN, // data length

    output            RW,   // data read/write

`else

    output     [ 3:0] BE,   // byte enable

    output            WR,    // write enable

    output            RD,    // read enable 

`endif

`ifdef SIMULATION

    input         FINISH_REQ,

`endif

    output [3:0]  DEBUG      // old-school osciloscope based debug! :)

);

    // dummy 32-bit words w/ all-0s and all-1s: 

    wire [31:0] ALL0  = 0;

    wire [31:0] ALL1  = -1;

`ifdef __THREADING__

    reg [$clog2(`NTHREADS)-1:0] XMODE = 0;     // thread ptr

`endif

    // pre-decode: IDATA is break apart as described in the RV32I specification

    reg [31:0] XIDATA;

    reg XLUI, XAUIPC, XJAL, XJALR, XBCC, XLCC, XSCC, XMCC, XRCC, XMAC, XRES=1; //, XFCC, XCCC;

    reg [31:0] XSIMM;

    reg [31:0] XUIMM;

    always@(posedge CLK)

    begin

        XIDATA <= XRES ? 0 : HLT ? XIDATA : IDATA;

        XLUI   <= XRES ? 0 : HLT ? XLUI   : IDATA[6:0]==`LUI;

        XAUIPC <= XRES ? 0 : HLT ? XAUIPC : IDATA[6:0]==`AUIPC;

        XJAL   <= XRES ? 0 : HLT ? XJAL   : IDATA[6:0]==`JAL;

        XJALR  <= XRES ? 0 : HLT ? XJALR  : IDATA[6:0]==`JALR;

        XBCC   <= XRES ? 0 : HLT ? XBCC   : IDATA[6:0]==`BCC;

        XLCC   <= XRES ? 0 : HLT ? XLCC   : IDATA[6:0]==`LCC;

        XSCC   <= XRES ? 0 : HLT ? XSCC   : IDATA[6:0]==`SCC;

        XMCC   <= XRES ? 0 : HLT ? XMCC   : IDATA[6:0]==`MCC;

        XRCC   <= XRES ? 0 : HLT ? XRCC   : IDATA[6:0]==`RCC;

        XMAC   <= XRES ? 0 : HLT ? XRCC   : IDATA[6:0]==`MAC;

        //XFCC   <= XRES ? 0 : HLT ? XFCC   : IDATA[6:0]==`FCC;

        //XCCC   <= XRES ? 0 : HLT ? XCCC   : IDATA[6:0]==`CCC;

        // signal extended immediate, according to the instruction type:

        XSIMM  <= XRES ? 0 : HLT ? XSIMM :

                 IDATA[6:0]==`SCC ? { IDATA[31] ? ALL1[31:12]:ALL0[31:12], IDATA[31:25],IDATA[11:7] } : // s-type

                 IDATA[6:0]==`BCC ? { IDATA[31] ? ALL1[31:13]:ALL0[31:13], IDATA[31],IDATA[7],IDATA[30:25],IDATA[11:8],ALL0[0] } : // b-type

                 IDATA[6:0]==`JAL ? { IDATA[31] ? ALL1[31:21]:ALL0[31:21], IDATA[31], IDATA[19:12], IDATA[20], IDATA[30:21], ALL0[0] } : // j-type

                 IDATA[6:0]==`LUI||

                 IDATA[6:0]==`AUIPC ? { IDATA[31:12], ALL0[11:0] } : // u-type

                                      { IDATA[31] ? ALL1[31:12]:ALL0[31:12], IDATA[31:20] }; // i-type

        // non-signal extended immediate, according to the instruction type:

        XUIMM  <= XRES ? 0: HLT ? XUIMM :

                 IDATA[6:0]==`SCC ? { ALL0[31:12], IDATA[31:25],IDATA[11:7] } : // s-type

                 IDATA[6:0]==`BCC ? { ALL0[31:13], IDATA[31],IDATA[7],IDATA[30:25],IDATA[11:8],ALL0[0] } : // b-type

                 IDATA[6:0]==`JAL ? { ALL0[31:21], IDATA[31], IDATA[19:12], IDATA[20], IDATA[30:21], ALL0[0] } : // j-type

                 IDATA[6:0]==`LUI||

                 IDATA[6:0]==`AUIPC ? { IDATA[31:12], ALL0[11:0] } : // u-type

                                      { ALL0[31:12], IDATA[31:20] }; // i-type

    end

    // decode: after XIDATA

`ifdef __3STAGE__

    reg [1:0] FLUSH = -1;  // flush instruction pipeline

`else

    reg FLUSH = -1;  // flush instruction pipeline

`endif

`ifdef __THREADING__

    `ifdef __RV32E__

        reg [$clog2(`NTHREADS)+3:0] RESMODE = -1;

        wire [$clog2(`NTHREADS)+3:0] DPTR   = XRES ? RESMODE : { XMODE, XIDATA[10: 7] }; // set SP_RESET when RES==1

        wire [$clog2(`NTHREADS)+3:0] S1PTR  = { XMODE, XIDATA[18:15] };

        wire [$clog2(`NTHREADS)+3:0] S2PTR  = { XMODE, XIDATA[23:20] };

    `else

        reg [$clog2(`NTHREADS)+4:0] RESMODE = -1;

        wire [$clog2(`NTHREADS)+4:0] DPTR   = XRES ? RESMODE : { XMODE, XIDATA[11: 7] }; // set SP_RESET when RES==1

        wire [$clog2(`NTHREADS)+4:0] S1PTR  = { XMODE, XIDATA[19:15] };

        wire [$clog2(`NTHREADS)+4:0] S2PTR  = { XMODE, XIDATA[24:20] };

    `endif

`else

    `ifdef __RV32E__

        reg [3:0] RESMODE = -1;

        wire [3:0] DPTR   = XRES ? RESMODE : XIDATA[10: 7]; // set SP_RESET when RES==1

        wire [3:0] S1PTR  = XIDATA[18:15];

        wire [3:0] S2PTR  = XIDATA[23:20];

    `else

        reg [4:0] RESMODE = -1;

        wire [4:0] DPTR   = XRES ? RESMODE : XIDATA[11: 7]; // set SP_RESET when RES==1

        wire [4:0] S1PTR  = XIDATA[19:15];

        wire [4:0] S2PTR  = XIDATA[24:20];

    `endif

`endif

    wire [6:0] OPCODE = FLUSH ? 0 : XIDATA[6:0];

    wire [2:0] FCT3   = XIDATA[14:12];

    wire [6:0] FCT7   = XIDATA[31:25];

    wire [31:0] SIMM  = XSIMM;

    wire [31:0] UIMM  = XUIMM;

    // main opcode decoder:

    wire    LUI = FLUSH ? 0 : XLUI;   // OPCODE==7'b0110111;

    wire  AUIPC = FLUSH ? 0 : XAUIPC; // OPCODE==7'b0010111;

    wire    JAL = FLUSH ? 0 : XJAL;   // OPCODE==7'b1101111;

    wire   JALR = FLUSH ? 0 : XJALR;  // OPCODE==7'b1100111;

    wire    BCC = FLUSH ? 0 : XBCC; // OPCODE==7'b1100011; //FCT3

    wire    LCC = FLUSH ? 0 : XLCC; // OPCODE==7'b0000011; //FCT3

    wire    SCC = FLUSH ? 0 : XSCC; // OPCODE==7'b0100011; //FCT3

    wire    MCC = FLUSH ? 0 : XMCC; // OPCODE==7'b0010011; //FCT3

    wire    RCC = FLUSH ? 0 : XRCC; // OPCODE==7'b0110011; //FCT3

    wire    MAC = FLUSH ? 0 : XMAC; // OPCODE==7'b0110011; //FCT3

    //wire    FCC = FLUSH ? 0 : XFCC; // OPCODE==7'b0001111; //FCT3

    //wire    CCC = FLUSH ? 0 : XCCC; // OPCODE==7'b1110011; //FCT3

`ifdef __THREADING__

    `ifdef __3STAGE__

        reg [31:0] NXPC2 [0:`NTHREADS-1];       // 32-bit program counter t+2

    `endif

    `ifdef __RV32E__

        reg [31:0] REG1 [0:16*`NTHREADS-1];       // general-purpose 16x32-bit registers (s1)

        reg [31:0] REG2 [0:16*`NTHREADS-1];       // general-purpose 16x32-bit registers (s2)

    `else

        reg [31:0] REG1 [0:32*`NTHREADS-1];       // general-purpose 32x32-bit registers (s1)

        reg [31:0] REG2 [0:32*`NTHREADS-1];       // general-purpose 32x32-bit registers (s2)    

    `endif

`else

    `ifdef __3STAGE__

        reg [31:0] NXPC2;       // 32-bit program counter t+2

    `endif

    `ifdef __RV32E__

        reg [31:0] REG1 [0:15];   // general-purpose 16x32-bit registers (s1)

        reg [31:0] REG2 [0:15];   // general-purpose 16x32-bit registers (s2)

    `else

        reg [31:0] REG1 [0:31];   // general-purpose 32x32-bit registers (s1)

        reg [31:0] REG2 [0:31];   // general-purpose 32x32-bit registers (s2)

    `endif

`endif

    reg [31:0] NXPC;        // 32-bit program counter t+1

    reg [31:0] PC;                   // 32-bit program counter t+0

    // source-1 and source-1 register selection

    wire signed   [31:0] S1REG = REG1[S1PTR];

    wire signed   [31:0] S2REG = REG2[S2PTR];

    wire          [31:0] U1REG = REG1[S1PTR];

    wire          [31:0] U2REG = REG2[S2PTR];

    // L-group of instructions (OPCODE==7'b0000011)

`ifdef __FLEXBUZZ__

    wire [31:0] LDATA = FCT3[1:0]==0 ? { FCT3[2]==0&&DATAI[ 7] ? ALL1[31: 8]:ALL0[31: 8] , DATAI[ 7: 0] } :

                        FCT3[1:0]==1 ? { FCT3[2]==0&&DATAI[15] ? ALL1[31:16]:ALL0[31:16] , DATAI[15: 0] } :

                                        DATAI;

`else

    wire [31:0] LDATA = FCT3==0||FCT3==4 ? ( DADDR[1:0]==3 ? { FCT3==0&&DATAI[31] ? ALL1[31: 8]:ALL0[31: 8] , DATAI[31:24] } :

                                             DADDR[1:0]==2 ? { FCT3==0&&DATAI[23] ? ALL1[31: 8]:ALL0[31: 8] , DATAI[23:16] } :

                                             DADDR[1:0]==1 ? { FCT3==0&&DATAI[15] ? ALL1[31: 8]:ALL0[31: 8] , DATAI[15: 8] } :

                                                             { FCT3==0&&DATAI[ 7] ? ALL1[31: 8]:ALL0[31: 8] , DATAI[ 7: 0] } ):

                        FCT3==1||FCT3==5 ? ( DADDR[1]==1   ? { FCT3==1&&DATAI[31] ? ALL1[31:16]:ALL0[31:16] , DATAI[31:16] } :

                                                             { FCT3==1&&DATAI[15] ? ALL1[31:16]:ALL0[31:16] , DATAI[15: 0] } ) :

                                             DATAI;

`endif

    // S-group of instructions (OPCODE==7'b0100011)

`ifdef __FLEXBUZZ__

    wire [31:0] SDATA = U2REG; /* FCT3==0 ? { ALL0 [31: 8], U2REG[ 7:0] } :

                        FCT3==1 ? { ALL0 [31:16], U2REG[15:0] } :

                                    U2REG;*/

`else

    wire [31:0] SDATA = FCT3==0 ? ( DADDR[1:0]==3 ? { U2REG[ 7: 0], ALL0 [23:0] } :

                                    DADDR[1:0]==2 ? { ALL0 [31:24], U2REG[ 7:0], ALL0[15:0] } :

                                    DADDR[1:0]==1 ? { ALL0 [31:16], U2REG[ 7:0], ALL0[7:0] } :

                                                    { ALL0 [31: 8], U2REG[ 7:0] } ) :

                        FCT3==1 ? ( DADDR[1]==1   ? { U2REG[15: 0], ALL0 [15:0] } :

                                                    { ALL0 [31:16], U2REG[15:0] } ) :

                                    U2REG;

`endif

    // C-group not implemented yet!

    wire [31:0] CDATA = 0;        // status register istructions not implemented yet

    // RM-group of instructions (OPCODEs==7'b0010011/7'b0110011), merged! src=immediate(M)/register(R)

    wire signed [31:0] S2REGX = XMCC ? SIMM : S2REG;

    wire        [31:0] U2REGX = XMCC ? UIMM : U2REG;

    wire [31:0] RMDATA = FCT3==7 ? U1REG&S2REGX :

                         FCT3==6 ? U1REG|S2REGX :

                         FCT3==4 ? U1REG^S2REGX :

                         FCT3==3 ? U1REG<U2REGX?1:0 : // unsigned

                         FCT3==2 ? S1REG<S2REGX?1:0 : // signed

                         FCT3==0 ? (XRCC&&FCT7[5] ? U1REG-U2REGX : U1REG+S2REGX) :

                         FCT3==1 ? U1REG<<U2REGX[4:0] :

                         //FCT3==5 ? 

// maybe the $signed solves the problem for MODELSIM too! needs to be tested!

//`ifdef MODEL_TECH        

//                         FCT7[5] ? -((-U1REG)>>U2REGX[4:0]; // workaround for modelsim

//`else

                         FCT7[5] ? $signed(S1REG>>>U2REGX[4:0]) : // (FCT7[5] ? U1REG>>>U2REG[4:0] : 

//`endif                        

                                   U1REG>>U2REGX[4:0];

`ifdef __MAC16X16__

    // MAC instruction rd += s1*s2 (OPCODE==7'b1111111)

    // 

    // 0000000 01100 01011 100 01100 0110011 xor a2,a1,a2

    // 0000000 01010 01100 000 01010 0110011 add a0,a2,a0

    // 0000000 01100 01011 000 01010 1111111 mac a0,a1,a2

    // 

    // 0000 0000 1100 0101 1000 0101 0111 1111 = 00c5857F

    wire signed [15:0] K1TMP = S1REG[15:0];

    wire signed [15:0] K2TMP = S2REG[15:0];

    wire signed [31:0] KDATA = K1TMP*K2TMP;

`endif

    // J/B-group of instructions (OPCODE==7'b1100011)

    wire BMUX       = BCC==1 && (

                          FCT3==4 ? S1REG< S2REGX : // blt

                          FCT3==5 ? S1REG>=S2REG : // bge

                          FCT3==6 ? U1REG< U2REGX : // bltu

                          FCT3==7 ? U1REG>=U2REG : // bgeu

                          FCT3==0 ? !(U1REG^S2REGX) : //U1REG==U2REG : // beq

                          /*FCT3==1 ? */ U1REG^S2REGX); //U1REG!=U2REG); // bne

                                    //0);

    wire        JREQ = (JAL||JALR||BMUX);

    wire [31:0] JVAL = JALR ? DADDR : PC+SIMM; // SIMM + (JALR ? U1REG : PC);

`ifdef SIMULATION

    `ifdef __PERFMETER__

        integer clocks=0, running=0, load=0, store=0, flush=0, halt=0;

    `ifdef __THREADING__

        integer thread[0:`NTHREADS-1];

        integer i;

        initial for(i=0;i!=`NTHREADS;i=i+1) thread[i] = 0;

    `endif

        always@(posedge CLK)

        begin

            if(!XRES)

            begin

                clocks = clocks+1;

                if(HLT)

                begin

                         if(SCC)        store = store+1;

                    else if(LCC)        load  = load +1;

                    else                halt  = halt +1;

                end

                else

                begin

                    if(FLUSH)

                    begin

                        flush=flush+1;

                    end

                    else

                    begin

        `ifdef __THREADING__

                        for(i=0;i!=`NTHREADS;i=i+1)

                                thread[i] = thread[i]+(i==XMODE?1:0);

        `endif

                        running = running +1;

                    end

                end

                if(FINISH_REQ)

                begin

                    $display("****************************************************************************");

                    $display("DarkRISCV Pipeline Report:");

                    $display("core0  clocks: %0d",clocks);

                    $display("core0: running %0d%%",100.0*running/clocks);

         `ifdef __THREADING__

                    for(i=0;i!=`NTHREADS;i=i+1) $display("  thread%0d: running %0d%%",i,100.0*thread[i]/clocks);

         `endif

                    $display("core0:  halted %0d%% (%0d%% load, %0d%% store, %0d%% busy)",

                        100.0*(load+store)/clocks,

                        100.0*load/clocks,

                        100.0*store/clocks,

                        100.0*halt/clocks);

                    $display("core0: stalled %0d%%",100.0*flush/clocks);

                    $display("****************************************************************************");

                    $finish();

                end

            end

        end

    `else

        $finish();

    `endif

`endif

    always@(posedge CLK)

    begin

        RESMODE <= RES ? -1 : RESMODE ? RESMODE-1 : 0;

        XRES <= |RESMODE;

`ifdef __3STAGE__

            FLUSH <= XRES ? 2 : HLT ? FLUSH :        // reset and halt                              

                               FLUSH ? FLUSH-1 :

                               (JAL||JALR||BMUX) ? 2 : 0;  // flush the pipeline!

`else

        FLUSH <= XRES ? 1 : HLT ? FLUSH :        // reset and halt

                       (JAL||JALR||BMUX);  // flush the pipeline!

`endif

`ifdef __RV32E__

        REG1[DPTR] <=   XRES ? (RESMODE[3:0]==2 ? `__RESETSP__ : 0)  :        // reset sp

`else

        REG1[DPTR] <=   XRES ? (RESMODE[4:0]==2 ? `__RESETSP__ : 0)  :        // reset sp

`endif

                       HLT ? REG1[DPTR] :        // halt

                     !DPTR ? 0 :                // x0 = 0, always!

                     AUIPC ? PC+SIMM :

                      JAL||

                      JALR ? NXPC :

                       LUI ? SIMM :

                       LCC ? LDATA :

                  MCC||RCC ? RMDATA:

`ifdef __MAC16X16__

                       MAC ? REG2[DPTR]+KDATA :

`endif

                       //CCC ? CDATA : 

                             REG1[DPTR];

`ifdef __RV32E__

        REG2[DPTR] <=   XRES ? (RESMODE[3:0]==2 ? `__RESETSP__ : 0) :        // reset sp

`else

        REG2[DPTR] <=   XRES ? (RESMODE[4:0]==2 ? `__RESETSP__ : 0) :        // reset sp

`endif

                       HLT ? REG2[DPTR] :        // halt

                     !DPTR ? 0 :                // x0 = 0, always!

                     AUIPC ? PC+SIMM :

                      JAL||

                      JALR ? NXPC :

                       LUI ? SIMM :

                       LCC ? LDATA :

                  MCC||RCC ? RMDATA:

`ifdef __MAC16X16__

                       MAC ? REG2[DPTR]+KDATA :

`endif

                       //CCC ? CDATA : 

                             REG2[DPTR];

`ifdef __3STAGE__

    `ifdef __THREADING__

        NXPC <= /*XRES ? `__RESETPC__ :*/ HLT ? NXPC : NXPC2[XMODE];

        NXPC2[XRES ? RESMODE[$clog2(`NTHREADS)-1:0] : XMODE] <=  XRES ? `__RESETPC__ : HLT ? NXPC2[XMODE] :   // reset and halt

                                      JREQ ? JVAL :                            // jmp/bra

                                                 NXPC2[XMODE]+4;                   // normal flow

        XMODE <= XRES ? 0 : HLT ? XMODE :        // reset and halt

                            JAL ? XMODE+1 : XMODE;

                     //XMODE==0/*&& IREQ*/&&(JAL||JALR||BMUX) ? 1 :         // wait pipeflush to switch to irq

                 //XMODE==1/*&&!IREQ*/&&(JAL||JALR||BMUX) ? 0 : XMODE;  // wait pipeflush to return from irq

    `else

        NXPC <= /*XRES ? `__RESETPC__ :*/ HLT ? NXPC : NXPC2;

            NXPC2 <=  XRES ? `__RESETPC__ : HLT ? NXPC2 :   // reset and halt

                         JREQ ? JVAL :                    // jmp/bra

                                NXPC2+4;                   // normal flow

    `endif

`else

        NXPC <= XRES ? `__RESETPC__ : HLT ? NXPC :   // reset and halt

              JREQ ? JVAL :                   // jmp/bra

                     NXPC+4;                   // normal flow

`endif

        PC   <= /*XRES ? `__RESETPC__ :*/ HLT ? PC : NXPC; // current program counter

    end

    // IO and memory interface

    assign DATAO = SDATA; // SCC ? SDATA : 0;

    assign DADDR = U1REG + SIMM; // (SCC||LCC) ? U1REG + SIMM : 0;

    // based in the Scc and Lcc   

`ifdef __FLEXBUZZ__

    assign RW      = !SCC;

    assign DLEN[0] = (SCC||LCC)&&FCT3[1:0]==0;

    assign DLEN[1] = (SCC||LCC)&&FCT3[1:0]==1;

    assign DLEN[2] = (SCC||LCC)&&FCT3[1:0]==2;

`else

    assign RD = LCC;

    assign WR = SCC;

    assign BE = FCT3==0||FCT3==4 ? ( DADDR[1:0]==3 ? 4'b1000 : // sb/lb

                                     DADDR[1:0]==2 ? 4'b0100 :

                                     DADDR[1:0]==1 ? 4'b0010 :

                                                     4'b0001 ) :

                FCT3==1||FCT3==5 ? ( DADDR[1]==1   ? 4'b1100 : // sh/lh

                                                     4'b0011 ) :

                                                     4'b1111; // sw/lw

`endif

`ifdef __3STAGE__

    `ifdef __THREADING__

        assign IADDR = NXPC2[XMODE];

    `else

        assign IADDR = NXPC2;

    `endif

`else

    assign IADDR = NXPC;

`endif

    assign DEBUG = { XRES, |FLUSH, SCC, LCC };

endmodule