EttusResearch_uhd/fpga/usrp2/gpmc/cross_clock_reader.v

//
// Copyright 2011-2012 Ettus Research LLC
//
// This program 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.
//
// This program 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 cross_clock_reader
    #(
        parameter WIDTH = 1,
        parameter DEFAULT = 0
    )
    (
        input clk, input rst,
        input [WIDTH-1:0] in,
        output reg [WIDTH-1:0] out
    );

    reg [WIDTH-1:0] shadow0, shadow1;
    reg [2:0] count;

    always @(posedge clk) begin
        if (rst) begin
            out <= DEFAULT;
            shadow0 <= DEFAULT;
            shadow1 <= DEFAULT;
            count <= 0;
        end
        else if (shadow0 == shadow1) count <= count + 1;
        else count <= 0;
        shadow0 <= in;
        shadow1 <= shadow0;
        if (count == 3'b111) out <= shadow1;
    end

endmodule //cross_clock_reader