path: root/rtl/clkmgr_reset_gen.v

//======================================================================
//
// clkmgr_reset_gen.v
// ------------------
// System reset generator.
//
//
// Author: Pavel Shatov
// Copyright (c) 2019, NORDUnet A/S All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// - Redistributions of source code must retain the above copyright
//   notice, this list of conditions and the following disclaimer.
//
// - Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the
//   documentation and/or other materials provided with the distribution.
//
// - Neither the name of the NORDUnet nor the names of its contributors may
//   be used to endorse or promote products derived from this software
//   without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================

module clkmgr_reset_gen
(
    input  clk_in,
    input  locked_in,
    output reset_n_out
);

    //
    // Parameter
    //
    parameter integer SHREG_WIDTH = 16;

    //
    // Shift Register
    //
    (* SHREG_EXTRACT="NO" *)
    (* EQUIVALENT_REGISTER_REMOVAL="NO" *)
    reg [SHREG_WIDTH-1:0] sys_rst_shreg = {SHREG_WIDTH{1'b0}};

    always @(posedge clk_in or negedge locked_in)
        //
        if (!locked_in) sys_rst_shreg <= {SHREG_WIDTH{1'b0}};
        else            sys_rst_shreg <= {sys_rst_shreg[SHREG_WIDTH-2:0], 1'b1};

    assign reset_n_out = sys_rst_shreg[SHREG_WIDTH-1];

endmodule

//======================================================================
// EOF clkmgr_reset_gen.v
//======================================================================