76 lines
2.5 KiB
Verilog
76 lines
2.5 KiB
Verilog
// ***************************************************************************
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// ***************************************************************************
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// Copyright 2014 - 2017 (c) Analog Devices, Inc. All rights reserved.
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//
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// This core is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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// A PARTICULAR PURPOSE.
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//
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// Redistribution and use of source or resulting binaries, with or without modification
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// of this file, are permitted under one of the following two license terms:
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//
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// 1. The GNU General Public License version 2 as published by the
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// Free Software Foundation, which can be found in the top level directory of
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// the repository (LICENSE_GPL2), and at: <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
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//
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// OR
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//
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// 2. An ADI specific BSD license as noted in the top level directory, or on-line at:
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// https://github.com/analogdevicesinc/hdl/blob/master/LICENSE_ADIBSD
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// This will allow to generate bit files and not release the source code,
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// as long as it attaches to an ADI device.
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//
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// ***************************************************************************
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// ***************************************************************************
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`timescale 1ns/100ps
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module ad_sysref_gen (
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input core_clk,
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input sysref_en,
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output reg sysref_out
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);
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// SYSREF period is multiple of core_clk, and has a duty cycle of 50%
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// NOTE: if SYSREF always on (this is a JESD204 IP configuration),
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// the period must be a correct multiple of the multiframe period
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parameter SYSREF_PERIOD = 128;
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localparam SYSREF_HALFPERIOD = SYSREF_PERIOD/2 - 1;
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reg [ 7:0] counter;
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reg sysref_en_m1;
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reg sysref_en_m2;
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reg sysref_en_int;
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// bring the enable signal to JESD core clock domain
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always @(posedge core_clk) begin
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sysref_en_m1 <= sysref_en;
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sysref_en_m2 <= sysref_en_m1;
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sysref_en_int <= sysref_en_m2;
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end
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// free running counter for periodic SYSREF generation
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always @(posedge core_clk) begin
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if (sysref_en_int) begin
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counter <= (counter < SYSREF_HALFPERIOD) ? counter + 1 : 0;
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end else begin
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counter <= 0;
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end
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end
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// generate SYSREF
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always @(posedge core_clk) begin
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if (sysref_en_int) begin
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if (counter == SYSREF_HALFPERIOD) begin
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sysref_out <= ~sysref_out;
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end
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end else begin
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sysref_out <= 1'b0;
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end
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end
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endmodule
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