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/******************************************************************************

 This Source Code Form is subject to the terms of the

 Open Hardware Description License, v. 1.0. If a copy

 of the OHDL was not distributed with this file, You

 can obtain one at http://juliusbaxter.net/ohdl/ohdl.txt

 Description: Branch prediction module

 Generates a predicted flag output and compares that to the real flag

 when it comes back in the following pipeline stage.

 Signals are deliberately not named after the pipeline stage they belong to,

 in order to keep this module generic.

 Copyright (C) 2013 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>

 ******************************************************************************/

`include "mor1kx-defines.v"

module mor1kx_branch_prediction

  #(

    parameter OPTION_OPERAND_WIDTH = 32

    )

   (

    input       clk,

    input       rst,

    // Signals belonging to the stage where the branch is predicted.

    input       op_bf_i,

    input       op_bnf_i,

    input [9:0] immjbr_upper_i,

    output      predicted_flag_o,

    // Signals belonging to the stage where the branch is resolved.

    input       prev_op_brcond_i,

    input       prev_predicted_flag_i,

    input       flag_i,

    // Branch misprediction indicator

    output      branch_mispredict_o

    );

   // Compare the real flag with the previously predicted flag and signal a

   // misprediction in case of a mismatch.

   assign branch_mispredict_o = prev_op_brcond_i &

                                (flag_i != prev_predicted_flag_i);

   // Static branch prediction - backward branches are predicted as taken,

   // forward branches as not taken.

   assign predicted_flag_o = op_bf_i & immjbr_upper_i[9] |

                             op_bnf_i & !immjbr_upper_i[9];

endmodule