//////////////////////////////////////////////////////////////////////////////
// SPDX-FileCopyrightText: 2021 , Dinesh Annayya                          
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// SPDX-License-Identifier: Apache-2.0
// SPDX-FileContributor: Created by Dinesh Annayya <dinesha@opencores.org>
//
//////////////////////////////////////////////////////////////////////
////                                                              ////
////  clock skew adjust                                          ////
////                                                              ////
////  This file is part of the YIFive cores project               ////
////  https://github.com/dineshannayya/yifive_r0.git              ////
////  http://www.opencores.org/cores/yifive/                      ////
////                                                              ////
////  Description                                                 ////
////      This block is useful for global clock skew adjustment   ////
////      logic implementation:                                   ////
////        clk_out = (sel=0) ? clk_in :                          ////
////                  (sel=1) ? clk_d1 :                          ////
////                  (sel=1) ? clk_d2 :                          ////
////                  .....                                       ////
////                  (sel=15)? clk_d15 :clk_in                   ////
////                                                              ////
////     Note: each d* indicate clk buf delay                     ////
////                                                              ////
////                                                              ////
////  To Do:                                                      ////
////    nothing                                                   ////
////                                                              ////
////  Author(s):                                                  ////
////      - Dinesh Annayya, dinesha@opencores.org                 ////
////                                                              ////
////  Revision :                                                  ////
////    0.0 - 29th Feb 2021, Dinesh A                             ////
////          Initial version                                     ////
///
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2000 Authors and OPENCORES.ORG                 ////
////                                                              ////
//// This source file may be used and distributed without         ////
//// restriction provided that this copyright statement is not    ////
//// removed from the file and that any derivative work contains  ////
//// the original copyright notice and the associated disclaimer. ////
////                                                              ////
//// 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 2.1 of the License, or (at your option) any   ////
//// later version.                                               ////
////                                                              ////
//// This source 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 Lesser General Public License for more ////
//// details.                                                     ////
////                                                              ////
//// You should have received a copy of the GNU Lesser General    ////
//// Public License along with this source; if not, download it   ////
//// from http://www.opencores.org/lgpl.shtml                     ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
// Clock-in is east pad direction
// clock out give in other three direction for better placement
/////////////////////////////////////////////////////////////////////
module clk_skew_adjust(clk_in, sel, clk_out);
  input  clk_in;
  output clk_out;
  input [3:0] sel;
  wire in0;
  wire in1;
  wire in2;
  wire in3;
  wire in4;
  wire in5;
  wire in6;
  wire in7;
  wire in8;
  wire in9;
  wire in10;
  wire in11;
  wire in12;
  wire in13;
  wire in14;
  wire in15;

  wire clk_d1;
  wire clk_d2;
  wire clk_d3;
  wire clk_d4;
  wire clk_d5;
  wire clk_d6;
  wire clk_d7;
  wire clk_d8;
  wire clk_d9;
  wire clk_d10;
  wire clk_d11;
  wire clk_d12;
  wire clk_d13;
  wire clk_d14;
  wire clk_d15;

  wire d00;
  wire d01;
  wire d02;
  wire d03;
  wire d04;
  wire d05;
  wire d06;
  wire d07;
  wire d10;
  wire d11;
  wire d12;
  wire d13;
  wire d20;
  wire d21;
  wire d30;


  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_1  (.A(clk_in),  .X(clk_d1));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_2  (.A(clk_d1),    .X(clk_d2));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_3  (.A(clk_d2),    .X(clk_d3));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_4  (.A(clk_d3),    .X(clk_d4));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_5  (.A(clk_d4),    .X(clk_d5));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_6  (.A(clk_d5),    .X(clk_d6));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_7  (.A(clk_d6),    .X(clk_d7));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_8  (.A(clk_d7),    .X(clk_d8));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_9  (.A(clk_d8),    .X(clk_d9));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_10 (.A(clk_d9),    .X(clk_d10));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_11 (.A(clk_d10),   .X(clk_d11));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_12 (.A(clk_d11),   .X(clk_d12));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_13 (.A(clk_d12),   .X(clk_d13));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_14 (.A(clk_d13),   .X(clk_d14));
  sky130_fd_sc_hd__clkdlybuf4s15_2 clkbuf_15 (.A(clk_d14),   .X(clk_d15));


  // Tap point selection
  assign in0  = clk_in;
  assign in1  = clk_d1;
  assign in2  = clk_d2;
  assign in3  = clk_d3;
  assign in4  = clk_d4;
  assign in5  = clk_d5;
  assign in6  = clk_d6;
  assign in7  = clk_d7;
  assign in8  = clk_d8;
  assign in9  = clk_d9;
  assign in10 = clk_d10;
  assign in11 = clk_d11;
  assign in12 = clk_d12;
  assign in13 = clk_d13;
  assign in14 = clk_d14;
  assign in15 = clk_d15;


  // first level mux - 8
  sky130_fd_sc_hd__mux2_1 u_mux_level_00 ( .X (d00) , .A0 (in0),  .A1(in1),  .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_01 ( .X (d01) , .A0 (in2),  .A1(in3),  .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_02 ( .X (d02) , .A0 (in4),  .A1(in5),  .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_03 ( .X (d03) , .A0 (in6),  .A1(in7),  .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_04 ( .X (d04) , .A0 (in8),  .A1(in9),  .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_05 ( .X (d05) , .A0 (in10), .A1(in11), .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_06 ( .X (d06) , .A0 (in12), .A1(in13), .S(sel[0]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_07 ( .X (d07) , .A0 (in14), .A1(in15), .S(sel[0]));

  // second level mux - 4
  sky130_fd_sc_hd__mux2_1 u_mux_level_10 ( .X (d10) , .A0 (d00), .A1(d01), .S(sel[1]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_11 ( .X (d11) , .A0 (d02), .A1(d03), .S(sel[1]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_12 ( .X (d12) , .A0 (d04), .A1(d05), .S(sel[1]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_13 ( .X (d13) , .A0 (d06), .A1(d07), .S(sel[1]));

  // third level mux - 2
  sky130_fd_sc_hd__mux2_1 u_mux_level_20 ( .X (d20) , .A0 (d10), .A1(d11), .S(sel[2]));
  sky130_fd_sc_hd__mux2_1 u_mux_level_21 ( .X (d21) , .A0 (d12), .A1(d13), .S(sel[2]));

  // fourth level mux - 1
  sky130_fd_sc_hd__mux2_4 u_mux_level_30 ( .X (d30) , .A0 (d20), .A1(d21), .S(sel[3]));


  assign clk_out = d30;

endmodule