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// $Id: aeMB_ctrl.v,v 1.3 2007-11-08 14:17:47 sybreon Exp $

//

// AEMB CONTROL 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 $

// Revision 1.2  2007/11/02 19:20:58  sybreon

// Added better (beta) interrupt support.

// Changed MSR_IE to disabled at reset as per MB docs.

//

// Revision 1.1  2007/11/02 03:25:40  sybreon

// New EDK 3.2 compatible design with optional barrel-shifter and multiplier.

// Fixed various minor data hazard bugs.

// Code compatible with -O0/1/2/3/s generated code.

//

module aeMB_ctrl (/*AUTOARG*/

   // Outputs

   rMXDST, rMXSRC, rMXTGT, rMXALT, rMXALU, rRW, rDWBSTB, dwb_stb_o,

   dwb_wre_o,

   // Inputs

   rXCE, rDLY, rIMM, rALT, rOPC, rRD, rRA, rRB, rPC, rBRA, rMSR_IE,

   dwb_ack_i, gclk, grst, gena

   );

   // INTERNAL   

   //output [31:2] rPCLNK;

   output [1:0]  rMXDST;

   output [1:0]  rMXSRC, rMXTGT, rMXALT;

   output [2:0]  rMXALU;

   output [4:0]  rRW;

   output        rDWBSTB;

   input [1:0]    rXCE;

   input         rDLY;

   input [15:0]  rIMM;

   input [10:0]  rALT;

   input [5:0]    rOPC;

   input [4:0]    rRD, rRA, rRB;

   input [31:2]  rPC;

   input         rBRA;

   input         rMSR_IE;

   // DATA WISHBONE

   output        dwb_stb_o;

   output        dwb_wre_o;

   input         dwb_ack_i;

   // SYSTEM

   input         gclk, grst, gena;

   // --- DECODE INSTRUCTIONS

   // TODO: Simplify

   wire          fSFT = (rOPC == 6'o44);

   wire          fLOG = ({rOPC[5:4],rOPC[2]} == 3'o4);

   wire          fMUL = (rOPC == 6'o20) | (rOPC == 6'o30);

   wire          fBSF = (rOPC == 6'o21) | (rOPC == 6'o31);

   wire          fDIV = (rOPC == 6'o22);

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

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

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

   wire          fBRA = fBRU & rRA[3];

   wire          fIMM = (rOPC == 6'o54);

   wire          fMOV = (rOPC == 6'o45);

   wire          fLOD = ({rOPC[5:4],rOPC[2]} == 3'o6);

   wire          fSTR = ({rOPC[5:4],rOPC[2]} == 3'o7);

   wire          fLDST = (&rOPC[5:4]);

   // --- OPERAND SELECTOR ---------------------------------

   wire          fRDWE = |rRW;

   wire          fAFWD_M = (rRW == rRA) & (rMXDST == 2'o2) & fRDWE;

   wire          fBFWD_M = (rRW == rRB) & (rMXDST == 2'o2) & fRDWE;

   wire          fAFWD_R = (rRW == rRA) & (rMXDST == 2'o0) & fRDWE;

   wire          fBFWD_R = (rRW == rRB) & (rMXDST == 2'o0) & fRDWE;

   assign        rMXSRC = (fBRU | fBCC) ? 2'o3 : // PC

                          (fAFWD_M) ? 2'o2: // RAM

                          (fAFWD_R) ? 2'o1: // FWD

                          2'o0; // REG

   assign        rMXTGT = (rOPC[3]) ? 2'o3 : // IMM

                          (fBFWD_M) ? 2'o2 : // RAM

                          (fBFWD_R) ? 2'o1 : // FWD

                          2'o0; // REG

   assign        rMXALT = (fAFWD_M) ? 2'o2 : // RAM

                          (fAFWD_R) ? 2'o1 : // FWD

                          2'o0; // REG

   // --- ALU CONTROL ---------------------------------------

   reg [2:0]      rMXALU;

   always @(/*AUTOSENSE*/fBRA or fBSF or fDIV or fLOG or fMOV or fMUL

            or fSFT) begin

      rMXALU <= (fBRA | fMOV) ? 3'o3 :

                (fSFT) ? 3'o2 :

                (fLOG) ? 3'o1 :

                (fMUL) ? 3'o4 :

                (fBSF) ? 3'o5 :

                (fDIV) ? 3'o6 :

                3'o0;

   end

   // --- RAM CONTROL ---------------------------------------

   reg           rDWBSTB, xDWBSTB;

   reg           rDWBWRE, xDWBWRE;

   assign        dwb_stb_o = rDWBSTB;

   assign        dwb_wre_o = rDWBWRE;

   // --- DELAY SLOT REGISTERS ------------------------------

   reg [31:2]    rPCLNK, xPCLNK;

   reg [1:0]      rMXDST, xMXDST;

   reg [4:0]      rRW, xRW;

   wire          fSKIP = (rBRA & !rDLY);

   always @(/*AUTOSENSE*/fLOD or fSKIP or fSTR or rXCE)

     if (fSKIP | |rXCE) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        xDWBSTB <= 1'h0;

        xDWBWRE <= 1'h0;

        // End of automatics

     end else begin

        xDWBSTB <= (fLOD | fSTR);

        xDWBWRE <= fSTR;

     end

   always @(/*AUTOSENSE*/fBCC or fBRU or fLOD or fRTD or fSKIP or fSTR

            or rRD or rXCE)

     if (fSKIP) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        xMXDST <= 2'h0;

        xRW <= 5'h0;

        // End of automatics

     end else begin

        case (rXCE)

          2'o2: xMXDST <= 2'o1;

          default: xMXDST <= (fSTR | fRTD | fBCC) ? 2'o3 :

                             (fLOD) ? 2'o2 :

                             (fBRU) ? 2'o1 :

                             2'o0;

        endcase

        case (rXCE)

          2'o2: xRW <= 5'd14;

          default: xRW <= rRD;

        endcase

     end // else: !if(fSKIP)

   // --- PIPELINE CONTROL DELAY ----------------------------

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rDWBSTB <= 1'h0;

        rDWBWRE <= 1'h0;

        rMXDST <= 2'h0;

        rRW <= 5'h0;

        // End of automatics

     end else if (gena) begin

        //rPCLNK <= #1 xPCLNK;

        rMXDST <= #1 xMXDST;

        rRW <= #1 xRW;

        rDWBSTB <= #1 xDWBSTB;

        rDWBWRE <= #1 xDWBWRE;

     end

endmodule // aeMB_ctrl