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// $Id: aeMB_bpcu.v,v 1.1 2007-11-02 03:25:39 sybreon Exp $

//

// AEMB BRANCH PROGRAMME COUNTER UNIT

// 

// Copyright (C) 2004-2007 Shawn Tan Ser Ngiap <shawn.tan@aeste.net>

//  

// This library is free software; you can redistribute it and/or

// modify it under the terms of the GNU Lesser General Public License

// as published by the Free Software Foundation; either version 2.1 of

// the License, or (at your option) any later version.

//

// This library is distributed in the hope that it will be useful, but

// WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

// Lesser General Public License for more details.

//  

// You should have received a copy of the GNU Lesser General Public

// License along with this library; if not, write to the Free Software

// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307

// USA

//

// $Log: not supported by cvs2svn $

module aeMB_bpcu (/*AUTOARG*/

   // Outputs

   iwb_adr_o, rPC, rPCLNK, rBRA, rDLY,

   // Inputs

   rMXALT, rOPC, rRD, rRA, rRESULT, rDWBDI, rREGA, rXCE, gclk, grst,

   gena

   );

   parameter IW = 24;

   // INST WISHBONE

   output [IW-1:2] iwb_adr_o;

   // INTERNAL

   output [31:2]   rPC, rPCLNK;

   output          rBRA;

   output          rDLY;

   input [1:0]      rMXALT;

   input [5:0]      rOPC;

   input [4:0]      rRD, rRA;

   input [31:0]    rRESULT; // ALU

   input [31:0]    rDWBDI; // RAM

   input [31:0]    rREGA;

   input [1:0]      rXCE;

   // SYSTEM

   input           gclk, grst, gena;

   // BRANCH

   wire            fRTD = (rOPC == 6'o55);

   wire            fBCC = (rOPC == 6'o47) | (rOPC == 6'o57);

   wire            fBRU = (rOPC == 6'o46) | (rOPC == 6'o56);

   wire [31:0]      wREGA;

   assign          wREGA = (rMXALT == 2'o2) ? rDWBDI :

                           (rMXALT == 2'o1) ? rRESULT :

                           rREGA;

   wire            wBEQ = (wREGA == 32'd0);

   wire            wBNE = ~wBEQ;

   wire            wBLT = wREGA[31];

   wire            wBLE = wBLT | wBEQ;

   wire            wBGE = ~wBLT;

   wire            wBGT = ~wBLE;

   reg             xXCC;

   always @(/*AUTOSENSE*/rRD or wBEQ or wBGE or wBGT or wBLE or wBLT

            or wBNE)

     case (rRD[2:0])

       3'o0: xXCC <= wBEQ;

       3'o1: xXCC <= wBNE;

       3'o2: xXCC <= wBLT;

       3'o3: xXCC <= wBLE;

       3'o4: xXCC <= wBGT;

       3'o5: xXCC <= wBGE;

       default: xXCC <= 1'bX;

     endcase // case (rRD[2:0])

   // DELAY SLOT

   reg             rBRA, xBRA;

   reg             rDLY, xDLY;

   wire            fSKIP = rBRA & !rDLY;

   always @(/*AUTOSENSE*/fBCC or fBRU or fRTD or rBRA or rRA or rRD

            or xXCC)

     if (rBRA) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        xBRA <= 1'h0;

        xDLY <= 1'h0;

        // End of automatics

     end else begin

        xDLY <= (fBRU & rRA[4]) | (fBCC & rRD[4]) | fRTD;

        xBRA <= (fRTD | fBRU) ? 1'b1 :

                (fBCC) ? xXCC :

                1'b0;

        /*

        case (rXCE)

          2'o1: xBRA <= 1'b0;

          default: xBRA <= (fRTD | fBRU) ? 1'b1 :

                           (fBCC) ? xXCC :

                           1'b0;

        endcase // case (rXCE)

         */

     end

   reg [31:2] rPCLNK, xPCLNK;

   always @(/*AUTOSENSE*/fSKIP or rBRA or rPC or rRESULT)

     if (fSKIP) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        xPCLNK <= 30'h0;

        // End of automatics

     end else begin

        xPCLNK <= (rBRA) ? rRESULT[31:2] : rPC;

     end

   // PC Changes - (NXT, BRA, INT)

   reg [31:2]      rIPC, xIPC;

   reg [31:2]      rPC, xPC;

   assign          iwb_adr_o = rIPC[IW-1:2];

   always @(/*AUTOSENSE*/rBRA or rIPC or rRESULT) begin

      xIPC <= (rBRA) ? rRESULT[31:2] : (rIPC + 1);

      /*

      case (rXCE)

        2'o1: xIPC <= 32'h04;

        default: xIPC <= (rBRA) ? rRESULT[31:2] : (rIPC + 1);

      endcase // case (rXCE)

       */

      xPC <= rIPC;

   end

   // SYNC

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rBRA <= 1'h0;

        rDLY <= 1'h0;

        rIPC <= 30'h0;

        rPC <= 30'h0;

        rPCLNK <= 30'h0;

        // End of automatics

     end else if (gena) begin

        rIPC <= #1 xIPC;

        rBRA <= #1 xBRA;

        rPC <= #1 xPC;

        rPCLNK <= #1 xPCLNK;

        rDLY <= #1 xDLY;

     end

   // synopsys translate_off

   // synopsys translate_on

endmodule // aeMB_bpcu