tillitis-key/hw/application_fpga/rtl/clk_reset_gen.v

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//======================================================================
//
// clk_reset_gen.v
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// -----------
// Clock and reset generator used in the Tillitis Key 1 design.
// This module instantiate the internal SB_HFOSC clock source in the
// Lattice ice40 UP device. It then connects it to the PLL, and
// finally connects the output from the PLL to the global clock net.
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//
//
// Author: Joachim Strombergson
// Copyright (C) 2022 - Tillitis AB
// SPDX-License-Identifier: GPL-2.0-only
//
//======================================================================
`default_nettype none
module clk_reset_gen #(parameter RESET_CYCLES = 200)
(
output wire clk,
output wire rst_n
);
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//----------------------------------------------------------------
// Registers with associated wires.
//----------------------------------------------------------------
reg [7 : 0] rst_ctr_reg = 8'h0;
reg [7 : 0] rst_ctr_new;
reg rst_ctr_we;
reg rst_n_reg = 1'h0;
reg rst_n_new;
wire hfosc_clk;
wire pll_clk;
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//----------------------------------------------------------------
// Concurrent assignment.
//----------------------------------------------------------------
assign rst_n = rst_n_reg;
//----------------------------------------------------------------
// Core instantiations.
//----------------------------------------------------------------
/* verilator lint_off PINMISSING */
// Use the FPGA internal High Frequency OSCillator as clock source.
// 00: 48MHz, 01: 24MHz, 10: 12MHz, 11: 6MHz
SB_HFOSC #(.CLKHF_DIV("0b10")
) hfosc_inst (.CLKHFPU(1'b1),.CLKHFEN(1'b1),.CLKHF(hfosc_clk));
// Use a PLL to generate a new clock frequency based on the HFOSC clock.
SB_PLL40_CORE #(
.FEEDBACK_PATH("SIMPLE"),
.DIVR(4'b0000), // DIVR = 0
.DIVF(7'b0101111), // DIVF = 47
.DIVQ(3'b101), // DIVQ = 5
.FILTER_RANGE(3'b001) // FILTER_RANGE = 1
) pll_inst (
.RESETB(1'b1),
.BYPASS(1'b0),
.REFERENCECLK(hfosc_clk),
.PLLOUTCORE(pll_clk)
);
// Use a Global Buffer to distribute the clock.
SB_GB gb_inst (
.USER_SIGNAL_TO_GLOBAL_BUFFER (pll_clk),
.GLOBAL_BUFFER_OUTPUT (clk)
);
/* verilator lint_on PINMISSING */
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//----------------------------------------------------------------
// reg_update.
//----------------------------------------------------------------
always @(posedge clk)
begin : reg_update
rst_n_reg <= rst_n_new;
if (rst_ctr_we)
rst_ctr_reg <= rst_ctr_new;
end
//----------------------------------------------------------------
// rst_logic.
//----------------------------------------------------------------
always @*
begin : rst_logic
rst_n_new = 1'h1;
rst_ctr_new = 8'h0;
rst_ctr_we = 1'h0;
if (rst_ctr_reg < RESET_CYCLES) begin
rst_n_new = 1'h0;
rst_ctr_new = rst_ctr_reg + 1'h1;
rst_ctr_we = 1'h1;
end
end
endmodule // reset_gen
//======================================================================
// EOF reset_gen.v
//======================================================================