1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
// ***************************************************************************
// ***************************************************************************
// Copyright 2013(c) Analog Devices, Inc.
// Author: Lars-Peter Clausen <lars@metafoo.de>
//
// 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 Analog Devices, Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
// - The use of this software may or may not infringe the patent rights
// of one or more patent holders. This license does not release you
// from the requirement that you obtain separate licenses from these
// patent holders to use this software.
// - Use of the software either in source or binary form, must be run
// on or directly connected to an Analog Devices Inc. component.
//
// THIS SOFTWARE IS PROVIDED BY ANALOG DEVICES "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
// INCLUDING, BUT NOT LIMITED TO, NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED.
//
// IN NO EVENT SHALL ANALOG DEVICES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, INTELLECTUAL PROPERTY
// RIGHTS, 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.
// ***************************************************************************
// ***************************************************************************
/*
* Helper module for synchronizing bit signals from one clock domain to another.
* It uses the standard approach of 2 FF in series.
* Note, that while the module allows to synchronize multiple bits at once it is
* only able to synchronize multi-bit signals where at max one bit changes per
* clock cycle (e.g. a gray counter).
*/
module sync_bits
(
input [NUM_OF_BITS-1:0] in,
input out_resetn,
input out_clk,
output [NUM_OF_BITS-1:0] out
);
// Number of bits to synchronize
parameter NUM_OF_BITS = 1;
// Whether input and output clocks are asynchronous, if 0 the synchronizer will
// be bypassed and the output signal equals the input signal.
parameter ASYNC_CLK = 1;
reg [NUM_OF_BITS-1:0] cdc_sync_stage1 = 'h0;
reg [NUM_OF_BITS-1:0] cdc_sync_stage2 = 'h0;
always @(posedge out_clk)
begin
if (out_resetn == 1'b0) begin
cdc_sync_stage1 <= 'b0;
cdc_sync_stage2 <= 'b0;
end else begin
cdc_sync_stage1 <= in;
cdc_sync_stage2 <= cdc_sync_stage1;
end
end
assign out = ASYNC_CLK ? cdc_sync_stage2 : in;
endmodule
|
