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
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
|
//======================================================================
//
// alpha_clkmgr.v
// ---------------
// Clock and reset implementation for the Cryptech Alpha
// FPGA framework.
//
//
// Author: Pavel Shatov
// Copyright (c) 2016, 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 alpha_clkmgr
(
input wire gclk, // signal from clock pin
output wire sys_clk, // buffered system clock output
output wire sys_rst_n // system reset output (async set, sync clear, active-low)
);
//
// Parameters
//
parameter CLK_OUT_MUL = 20.0;
parameter CLK_OUT_DIV = 20.0;
//
// Wrapper for Xilinx-specific MMCM (Mixed Mode Clock Manager) primitive.
//
wire gclk_int; // buffered input clock
wire mmcm_reset; // reset input
wire mmcm_locked; // output clock valid
wire gclk_missing; // input clock stopped
clkmgr_mmcm #
(
.CLK_OUT_MUL (CLK_OUT_MUL), // 2..64
.CLK_OUT_DIV (CLK_OUT_DIV) // 1..128
)
mmcm
(
.clk_in (gclk),
.reset_in (mmcm_reset),
.gclk_out (gclk_int),
.gclk_missing_out (gclk_missing),
.clk_out (sys_clk),
.clk_valid_out (mmcm_locked)
);
//
// MMCM Reset Logic
//
/* MMCM should be reset on power-up and when the input clock is stopped.
* Note that MMCM requires active-high reset, so the shift register is
* preloaded with 1's and then gradually filled with 0's.
*/
reg [15: 0] mmcm_rst_shreg = {16{1'b1}}; // 16-bit shift register
always @(posedge gclk_int or posedge gclk_missing)
//
if ((gclk_missing == 1'b1))
mmcm_rst_shreg <= {16{1'b1}};
else
mmcm_rst_shreg <= {mmcm_rst_shreg[14:0], 1'b0};
assign mmcm_reset = mmcm_rst_shreg[15];
//
// System Reset Logic
//
/* System reset is asserted for 16 cycles whenever MMCM aquires lock. Note
* that system reset is active-low, so the shift register is preloaded with
* 0's and gradually filled with 1's.
*/
reg [15: 0] sys_rst_shreg = {16{1'b0}}; // 16-bit shift register
always @(posedge sys_clk or posedge gclk_missing or negedge mmcm_locked)
//
if ((gclk_missing == 1'b1) || (mmcm_locked == 1'b0))
sys_rst_shreg <= {16{1'b0}};
else if (mmcm_locked == 1'b1)
sys_rst_shreg <= {sys_rst_shreg[14:0], 1'b1};
assign sys_rst_n = sys_rst_shreg[15];
endmodule
//======================================================================
// EOF alpha_clkmgr.v
//======================================================================
|
