Subversion Repositories raptor64

`include "Raptor64_opcodes.v"

`timescale 1ns / 1ps

//=============================================================================

//        __

//   \\__/ o\    (C) 2011-2013  Robert Finch, Stratford

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@opencores.org

//       ||

//  

//      Raptor64_BranchHistory.v

//

//  

// This source file 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.                                      

//                                                                          

// This source file 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 General Public License for more details.                             

//                                                                          

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

// along with this program.  If not, see <http://www.gnu.org/licenses/>.    

//                                                                          

//

//=============================================================================

//

module Raptor64_BranchHistory(rst, clk, advanceX, xIR, pc, xpc, takb, predict_taken);

input rst;

input clk;

input advanceX;

input [31:0] xIR;

input [63:0] pc;

input [63:0] xpc;

input takb;

output predict_taken;

integer n;

reg [2:0] gbl_branch_hist;

reg [1:0] branch_history_table [255:0];

// For simulation only, initialize the history table to zeros.

// In the real world we don't care.

initial begin

        for (n = 0; n < 256; n = n + 1)

                branch_history_table[n] = 0;

end

wire [7:0] bht_wa = {xpc[7:2],gbl_branch_hist[2:1]};             // write address

wire [7:0] bht_ra1 = {xpc[7:2],gbl_branch_hist[2:1]};            // read address (EX stage)

wire [7:0] bht_ra2 = {pc[7:2],gbl_branch_hist[2:1]};     // read address (IF stage)

wire [1:0] bht_xbits = branch_history_table[bht_ra1];

wire [1:0] bht_ibits = branch_history_table[bht_ra2];

assign predict_taken = bht_ibits==2'd0 || bht_ibits==2'd1;

wire [6:0] xOpcode = xIR[31:25];

wire isxBranchI = (xOpcode==`BEQI || xOpcode==`BNEI ||

                                        xOpcode==`BLTI || xOpcode==`BLEI || xOpcode==`BGTI || xOpcode==`BGEI ||

                                        xOpcode==`BLTUI || xOpcode==`BLEUI || xOpcode==`BGTUI || xOpcode==`BGEUI)

                                ;

wire isxBranch = (isxBranchI || xOpcode==`TRAPcc || xOpcode==`TRAPcci || xOpcode==`BTRI || xOpcode==`BTRR);

// Two bit saturating counter

reg [1:0] xbits_new;

always @(takb or bht_xbits)

if (takb) begin

        if (bht_xbits != 2'd1)

                xbits_new <= bht_xbits + 2'd1;

        else

                xbits_new <= bht_xbits;

end

else begin

        if (bht_xbits != 2'd2)

                xbits_new <= bht_xbits - 2'd1;

        else

                xbits_new <= bht_xbits;

end

always @(posedge clk)

if (rst)

        gbl_branch_hist <= 3'b000;

else begin

        if (advanceX) begin

                if (isxBranch) begin

                        gbl_branch_hist <= {gbl_branch_hist[1:0],takb};

                        branch_history_table[bht_wa] <= xbits_new;

                end

        end

end

endmodule