Subversion Repositories s80186

// Copyright Jamie Iles, 2017

//

// This file is part of s80x86.

//

// s80x86 is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// s80x86 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 s80x86.  If not, see .

module SegmentOverride(input logic clk,

                       input logic reset,

                       input logic next_instruction,

                       input logic force_segment,

                       input logic bp_is_base,

                       input logic segment_override,

                       input logic [1:0] microcode_sr_rd_sel,

                       output logic [1:0] sr_rd_sel);

reg [1:0] override;

reg override_active;

always_comb begin

    if (force_segment || segment_override)

        sr_rd_sel = microcode_sr_rd_sel;

    else if (override_active)

        sr_rd_sel = override;

    else if (bp_is_base)

        sr_rd_sel = SS;

    else

        sr_rd_sel = microcode_sr_rd_sel;

end

always_ff @(posedge clk or posedge reset) begin

    if (reset) begin

        override_active <= 1'b0;

        override <= 2'b00;

    end else if (next_instruction) begin

        override_active <= 1'b0;

        override <= 2'b00;

    end else if (segment_override) begin

        override <= microcode_sr_rd_sel;

        override_active <= 1'b1;

    end

end

endmodule