//======================================================================
//
// novena_clkmgr.v
// ---------------
// Clock and reset implementation for the Cryptech Novena
// FPGA framework.
//
//
// Author: Pavel Shatov
// Copyright (c) 2015, 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 novena_clkmgr
(
input wire gclk_p, // signal from clock pins
input wire gclk_n, //
input wire reset_mcu_b, // cpu reset (async, active-low)
output wire sys_clk, // buffered system clock output
output wire sys_rst_n // system reset output (async set, sync clear, active-low)
);
//
// Wrapper for Xilinx-specific DCM (Digital Clock Managar) primitive.
//
wire gclk; // buffered input clock
wire dcm_reset; // dcm reset
wire dcm_locked; // output clock valid
wire gclk_missing; // missing input clock
novena_dcm_spartan6 #
(
.CLK_OUT_MUL (2), // 2..32
.CLK_OUT_DIV (2) // 1..32
)
dcm_s6
(
.clk_in_p(gclk_p),
.clk_in_n(gclk_n),
.reset_in(dcm_reset),
.gclk_out(gclk),
.gclk_missing_out(gclk_missing),
.clk_out(sys_clk),
.clk_valid_out (dcm_locked)
);
//
// DCM Reset Logic
//
/* DCM should be reset on power-up, when input clock is stopped or when the
* CPU gets reset. Note that DCM requires active-high reset, so the shift
* register is preloaded with 1's and gradually filled with 0's.
*/
reg [15: 0] dcm_rst_shreg = {16{1'b1}}; // 16-bit shift register
always @(posedge gclk or negedge reset_mcu_b or posedge gclk_missing)
//
if ((reset_mcu_b == 1'b0) || (gclk_missing == 1'b1))
dcm_rst_shreg <= {16{1'b1}};
else
dcm_rst_shreg <= {dcm_rst_shreg[14:0], 1'b0};
assign dcm_reset = dcm_rst_shreg[15];
//
// System Reset Logic
//
/* System reset is asserted for 16 cycles whenever DCM aquires lock. Note that system
* reset is active-low, so the shift register is preloaded with 0's and gradually filled
* with 1's afterwards.
*/
reg [15: 0] sys_rst_shreg = {16{1'b0}}; // 16-bit shift register
always @(posedge sys_clk or negedge reset_mcu_b or posedge gclk_missing or negedge dcm_locked)
//
if ((reset_mcu_b == 1'b0) || (gclk_missing == 1'b1) || (dcm_locked == 1'b0))
sys_rst_shreg <= {16{1'b0}};
else if (dcm_locked == 1'b1)
sys_rst_shreg <= {sys_rst_shreg[14:0], 1'b1};
assign sys_rst_n = sys_rst_shreg[15];
endmodule
//======================================================================
// EOF novena_clkmgr.v
//======================================================================
