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[/] [forwardcom/] [trunk/] [debouncer.sv] - Blame information for rev 20

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1 20 Agner
//////////////////////////////////////////////////////////////////////////////////
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// Engineer: Agner Fog
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//
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// Create date:    2020-05-03
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// Last modified:  2020-12-15
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// Module name:    debounce
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// Project name:   ForwardCom soft core
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// Tool versions:  Vivado 2020.1
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// License:        CERN-OHL-W v. 2 or later
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// Description:    Push button debouncer
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//
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// Input from one or more pushbuttons is filtered to remove contact noise.
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// buttons_out is 1 when buttons_in is stable at 1 over a period.
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// buttons_out is 0 when buttons_in is stable at 0 over a period.
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// pulse_out is 1 for one clock cycle when the button is pressed
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//
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//////////////////////////////////////////////////////////////////////////////////
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// pushbutton debouncer
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module debounce
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#(parameter num=2)                     // number of buttons to debounce
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(
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    input clock,                       // system clock 50 - 100 MHz
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    input [num-1:0]     buttons_in,    // input from pushbutton
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    output reg[num-1:0] buttons_out,   // debounced output
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    output reg[num-1:0] pulse_out      // a single pulse of 1 clock duration when button is pressed
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);
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reg [19:0] count = 0;                  // clock divider
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reg [2:0] shift [num-1:0];             // shift registers
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genvar i;
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generate
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for (i=0; i
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    always_ff @(posedge clock) begin
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        pulse_out[i] <= 0;
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        count <= count + 1;                             // divide clock by 2**20
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        if (count == 0) begin
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            shift[i] <= {shift[i][1:0], buttons_in[i]}; // serial in parallel out shift register
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            if (shift[i] == 3'b111) begin               // accept as stable high after 3 consecutive high samples
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                if (buttons_out[i] == 0) begin
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                    pulse_out[i] <= 1;                  // set pulse_out high only in the first clock cycle after button press is stable
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                end
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                buttons_out[i] <= 1;                    // button is stable high
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            end else if (shift[i] == 3'b000) begin      // accept as stable low after 3 consecutive low samples
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                buttons_out[i] <= 0;                    // button is stable low
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            end
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        end
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    end
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end
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endgenerate
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endmodule
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