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b05f236d13
-Otherwise we can't do sync reset anywhere -glitch on exit from reset? Do we care? Everything is static -Need to check this again!
127 lines
4.1 KiB
Verilog
127 lines
4.1 KiB
Verilog
// ###############################################################
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// # FUNCTION: Synchronous clock divider that divides by integer
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// ###############################################################
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module clock_divider(/*AUTOARG*/
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// Outputs
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clkout, clkout90,
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// Inputs
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clkin, divcfg, reset
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);
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input clkin; // Input clock
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input [3:0] divcfg; // Divide factor
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input reset; // Counter init
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output clkout; // Divided clock phase aligned with clkin
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output clkout90; // Divided clock with 90deg phase shift with clkout
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reg clkout_reg;
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reg [7:0] counter;
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reg [7:0] divcfg_dec;
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reg [3:0] divcfg_reg;
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reg divcfg_change;
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wire div2_sel;
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wire div1_sel;
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wire posedge_match;
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wire negedge_match;
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wire posedge90_match;
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wire negedge90_match;
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reg clkout90_div4;
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reg clkout90_div2;
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// ###################
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// # Decode divcfg
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// ###################
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always @ (divcfg[3:0])
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casez (divcfg[3:0])
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4'b0001 : divcfg_dec[7:0] = 8'b00000010; // Divide by 2
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4'b0010 : divcfg_dec[7:0] = 8'b00000100; // Divide by 4
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4'b0011 : divcfg_dec[7:0] = 8'b00001000; // Divide by 8
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4'b0100 : divcfg_dec[7:0] = 8'b00010000; // Divide by 16
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4'b0101 : divcfg_dec[7:0] = 8'b00100000; // Divide by 32
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4'b0110 : divcfg_dec[7:0] = 8'b01000000; // Divide by 64
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4'b0111 : divcfg_dec[7:0] = 8'b10000000; // Divide by 128
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default : divcfg_dec[7:0] = 8'b00000000; // others
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endcase
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//Divide by two special case
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assign div2_sel = divcfg[3:0]==4'b0001;
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assign div1_sel = (divcfg[3:0]==4'b0000) | reset;
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//Edge change detector (no need for synchronizer)
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always @ (posedge clkin or posedge reset)
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if(reset)
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divcfg_change <=1'b0;
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else
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begin
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divcfg_change <= (divcfg_reg[3:0]^divcfg[3:0]);
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divcfg_reg[3:0] <=divcfg[3:0];
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end
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always @ (posedge clkin or posedge reset)
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if(reset)
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counter[7:0] <= 8'b000001;
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else if(posedge_match | divcfg_change)
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counter[7:0] <= 8'b000001;// Self resetting
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else
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counter[7:0] <= (counter[7:0] + 8'b00000001);
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assign posedge_match = (counter[7:0]==divcfg_dec[7:0]);
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assign negedge_match = (counter[7:0]=={1'b0,divcfg_dec[7:1]});
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assign posedge90_match = (counter[7:0]==({2'b00,divcfg_dec[7:2]}));
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assign negedge90_match = (counter[7:0]==({2'b00,divcfg_dec[7:2]} +
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{1'b0,divcfg_dec[7:1]}));
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always @ (posedge clkin or posedge reset)
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if(reset)
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clkout_reg <= 1'b0;
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else if(posedge_match)
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clkout_reg <= 1'b1;
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else if(negedge_match)
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clkout_reg <= 1'b0;
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assign clkout = div1_sel ? clkin : clkout_reg;
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always @ (posedge clkin or posedge reset)
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if(reset)
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clkout90_div4 <= 1'b0;
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else
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clkout90_div4 <= posedge90_match ? 1'b1 :
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negedge90_match ? 1'b0 :
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clkout90_div4;
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always @ (negedge clkin or posedge reset)
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if(reset)
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clkout90_div2 <= 1'b0;
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else
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clkout90_div2 <= negedge_match ? 1'b1 :
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posedge_match ? 1'b0 :
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clkout90_div2;
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assign clkout90 = div2_sel ? clkout90_div2 : clkout90_div4;
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endmodule // clock_divider
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/*
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Copyright (C) 2013 Adapteva, Inc.
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Contributed by Andreas Olofsson <support@adapteva.com>
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program (see the file COPYING). If not, see
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<http://www.gnu.org/licenses/>.
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*/
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