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// $Id: aeMB_ibuf.v,v 1.7 2007-11-22 15:11:15 sybreon Exp $

//

// AEMB INSTRUCTION BUFFER

// 

// Copyright (C) 2004-2007 Shawn Tan Ser Ngiap <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/>.

//

// $Log: not supported by cvs2svn $

// Revision 1.6  2007/11/14 23:39:51  sybreon

// Fixed interrupt signal synchronisation.

//

// Revision 1.5  2007/11/14 22:14:34  sybreon

// Changed interrupt handling system (reported by M. Ettus).

//

// Revision 1.4  2007/11/10 16:39:38  sybreon

// Upgraded license to LGPLv3.

// Significant performance optimisations.

//

// Revision 1.3  2007/11/03 08:34:55  sybreon

// Minor code cleanup.

//

// 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_ibuf (/*AUTOARG*/

   // Outputs

   rIMM, rRA, rRD, rRB, rALT, rOPC, rSIMM, xIREG, iwb_stb_o,

   // Inputs

   rBRA, rMSR_IE, rMSR_BIP, iwb_dat_i, iwb_ack_i, sys_int_i, gclk,

   grst, gena

   );

   // INTERNAL

   output [15:0] rIMM;

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

   output [10:0] rALT;

   output [5:0]  rOPC;

   output [31:0] rSIMM;

   output [31:0] xIREG;

   input         rBRA;

   //input [1:0]         rXCE;

   input         rMSR_IE;

   input         rMSR_BIP;

   // INST WISHBONE

   output        iwb_stb_o;

   input [31:0]  iwb_dat_i;

   input         iwb_ack_i;

   // SYSTEM

   input         sys_int_i;

   // SYSTEM

   input         gclk, grst, gena;

   reg [15:0]     rIMM;

   reg [4:0]      rRA, rRD;

   reg [5:0]      rOPC;

   // FIXME: Endian

   wire [31:0]    wIDAT = iwb_dat_i;

   assign        {rRB, rALT} = rIMM;

   // TODO: Assign to FIFO not full.

   assign       iwb_stb_o = 1'b1;

   reg [31:0]    rSIMM, xSIMM;

   wire [31:0]   wXCEOP = 32'hBA2D0008; // Vector 0x08

   wire [31:0]   wINTOP = 32'hB9CE0010; // Vector 0x10

   wire [31:0]   wBRKOP = 32'hBA0C0018; // Vector 0x18

   wire [31:0]   wBRAOP = 32'h88000000; // NOP for branches

   wire [31:0]   wIREG = {rOPC, rRD, rRA, rRB, rALT};

   reg [31:0]    xIREG;

   // --- INTERRUPT LATCH --------------------------------------

   // Debounce and latch onto the positive level. This is independent

   // of the pipeline so that stalls do not affect it.

   reg          rFINT;

   reg [1:0]     rDINT;

   wire         wSHOT = rDINT[0];

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rDINT <= 2'h0;

        rFINT <= 1'h0;

        // End of automatics

     end else if (rMSR_IE) begin

        rDINT <= #1 {rDINT[0], sys_int_i};

        rFINT <= #1 (wIREG == wINTOP) ? 1'b0 : (rFINT | wSHOT);

     end

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

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

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

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

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

   always @(/*AUTOSENSE*/fBCC or fBRU or fIMM or fRTD or rBRA or rFINT

            or wBRAOP or wIDAT or wINTOP) begin

      xIREG <= (rBRA) ? wBRAOP :

               (!fIMM & rFINT & !fRTD & !fBRU & !fBCC) ? wINTOP :

               wIDAT;

   end

   always @(/*AUTOSENSE*/fIMM or rBRA or rIMM or wIDAT or xIREG) begin

      xSIMM <= (!fIMM | rBRA) ? { {(16){xIREG[15]}}, xIREG[15:0]} :

               {rIMM, wIDAT[15:0]};

   end

   // --- PIPELINE --------------------------------------------

   always @(posedge gclk)

     if (grst) begin

        /*AUTORESET*/

        // Beginning of autoreset for uninitialized flops

        rIMM <= 16'h0;

        rOPC <= 6'h0;

        rRA <= 5'h0;

        rRD <= 5'h0;

        rSIMM <= 32'h0;

        // End of automatics

     end else if (gena) begin

        {rOPC, rRD, rRA, rIMM} <= #1 xIREG;

        rSIMM <= #1 xSIMM;

     end

endmodule // aeMB_ibuf