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/* $Id: aeMB2_iwbif.v,v 1.5 2008-04-27 19:52:31 sybreon Exp $

**

** AEMB2 EDK 6.2 COMPATIBLE CORE

** Copyright (C) 2004-2008 Shawn Tan <shawn.tan@aeste.net>

**

** This file is part of AEMB.

**

** AEMB 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 3 of the

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

**

** AEMB 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 AEMB. If not, see <http:**www.gnu.org/licenses/>.

*/

/**

 * Instruction Wishbone Interface

 * @file aeMB2_iwbif.v

  * This handles the instruction fetch portion of the pipeline. It

    alternates the PC and performs bubble/branch insertion. Bus

    transactions are independent of the pipeline.

 */

module aeMB2_iwbif (/*AUTOARG*/

   // Outputs

   iwb_adr_o, iwb_stb_o, iwb_sel_o, iwb_wre_o, iwb_cyc_o, iwb_tag_o,

   ich_adr, fet_fb, rpc_if, rpc_ex, rpc_mx, exc_iwb,

   // Inputs

   iwb_ack_i, iwb_dat_i, ich_hit, msr_ex, hzd_bpc, hzd_fwd, bra_ex,

   bpc_ex, gclk, grst, dena, iena, gpha

   );

   parameter AEMB_IWB = 32;

   parameter AEMB_HTX = 1;

   // Wishbone

   output [AEMB_IWB-1:2] iwb_adr_o;

   output                iwb_stb_o;

   output [3:0]   iwb_sel_o;

   output                iwb_wre_o;

   output                iwb_cyc_o;

   output                iwb_tag_o;

   input                 iwb_ack_i;

   input [31:0]   iwb_dat_i;

   //input               iwb_err_i; // bus error exception

   // Cache

   output [AEMB_IWB-1:2] ich_adr;

   input                 ich_hit;

   // Internal

   output                fet_fb;

   output [31:2]         rpc_if,

                         rpc_ex,

                         rpc_mx;

   input [7:5]           msr_ex;

   input                 hzd_bpc,

                         hzd_fwd;

   input [1:0]            bra_ex;

   input [31:2]          bpc_ex;

   output                exc_iwb;

   // SYS signals

   input                 gclk,

                         grst,

                         dena,

                         iena,

                         gpha;

   /*AUTOWIRE*/

   /*AUTOREG*/

   // Beginning of automatic regs (for this module's undeclared outputs)

   reg                  iwb_stb_o;

   reg [31:2]           rpc_if;

   reg [31:2]           rpc_mx;

   // End of automatics

   reg [31:2]           rpc_of,

                        rpc_ex;

   // BARREL

   reg [31:2]           rADR, rADR_;

   wire [31:2]          wPCINC = (rADR + 1); // incrementer

   wire [31:2]          wPCNXT = rADR_;

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rADR <= 30'h0;

        rADR_ <= 30'h0;

        // End of automatics

     end else if (iena) begin

        case ({hzd_fwd,bra_ex[1]})

          2'o0: {rADR} <= #1 {rADR_[AEMB_IWB-1:2]}; // normal increment

          2'o1: {rADR} <= #1 {bpc_ex[AEMB_IWB-1:2]}; // brach/return/break

          2'o2: {rADR} <= #1 {rpc_if[AEMB_IWB-1:2]}; // bubble/hazard

          default: {rADR} <= #1 32'hX;

          //2'o3: rADR <= #1 rpc_if[AEMB_IWB-1:2]; // bubble/hazard

          //2'o3: rADR <= #1 bpc_ex[AEMB_IWB-1:2]; // brach/return/break

        endcase // case ({hzd_fwd,bra_ex[1]})

        rADR_ <= #1 wPCINC;

     end // if (iena)

   assign               ich_adr = rADR;

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rpc_ex <= 30'h0;

        rpc_if <= 30'h0;

        rpc_mx <= 30'h0;

        rpc_of <= 30'h0;

        // End of automatics

     end else begin

        if (dena) begin

           {rpc_mx, // PC PIPELINE

            rpc_ex,

            rpc_of} <= #1 {rpc_ex,

                           rpc_of,

                           rpc_if};

        end

        if (iena) begin

           rpc_if <= #1 rADR;

        end

     end // else: !if(grst)

   // WISHBONE SIGNALS

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        iwb_stb_o <= 1'h0;

        // End of automatics

     end else begin

        iwb_stb_o <= #1 (iwb_stb_o & !iwb_ack_i) | (!iwb_stb_o & !ich_hit);

     end

   assign               iwb_adr_o = rADR;

   assign               iwb_wre_o = 1'b0;

   assign               iwb_sel_o = 4'hF;

   assign               iwb_cyc_o = iwb_stb_o;

   assign               iwb_tag_o = msr_ex[5];

   assign               fet_fb = iwb_stb_o ~^ iwb_ack_i; // no WB cycle      

   // TODO: enable iwb_err_i exception pass-thru

   assign               exc_iwb = 1'b0;

endmodule // aeMB2_iwbif