//--------------------------------------------------------------------------------
// pulse_stretch.sv
// Konstantin Pavlov, pavlovconst@gmail.com
//--------------------------------------------------------------------------------

// INFO --------------------------------------------------------------------------------
// Pulse stretcher/extender module
//   this implementftion uses a simple delay line or counter to stretch pulses
//   WIDTH parameter sets output pulse width
//   if you need variable output poulse width, see pulse_gen.sv module


/* --- INSTANTIATION TEMPLATE BEGIN ---

pulse_stretch #(
  .WIDTH( 8 )
  .USE_COUNTER(0)
) ps1 (
  .clk( clk ),
  .nrst( nrst ),
  .in(  ),
  .out(  )
);

--- INSTANTIATION TEMPLATE END ---*/

module pulse_stretch #( parameter
  WIDTH = 8,
  USE_CNTR = 0      // ==0  - stretcher is implemented on delay line
                    // ==1  - stretcher is implemented on counter
)(
  input clk,
  input nrst,

  input in,
  output out
);


localparam CNTR_WIDTH = $clog2(WIDTH) + 1;

generate

  if ( WIDTH == 0 ) begin
    assign out = 0;

  end else if( WIDTH == 1 ) begin
    assign out = in;

  end else begin
    if( USE_CNTR == '0 ) begin
      // delay line

      logic [WIDTH-1:0] shifter = '0;
      always_ff @(posedge clk) begin
        if( ~nrst ) begin
          shifter[WIDTH-1:0] <= '0;
        end else begin
          // shifting
          shifter[WIDTH-1:0] <= {shifter[WIDTH-2:0],in};
        end // nrst
      end // always

      assign out = (shifter[WIDTH-1:0] != '0);

    end else begin
      // counter

      logic [CNTR_WIDTH-1:0] cntr = '0;
      always_ff @(posedge clk) begin
        if( ~nrst ) begin
          cntr[CNTR_WIDTH-1:0] <= '0;
        end else begin
          if( in ) begin
            // setting counter
            cntr[CNTR_WIDTH-1:0] <= WIDTH;
          end else if( out ) begin
            // decrementing counter
            cntr[CNTR_WIDTH-1:0] <= cntr[CNTR_WIDTH-1:0] - 1'b1;
          end
        end // nrst
      end // always

      assign out = (cntr[CNTR_WIDTH-1:0] != '0);

    end
  end // if WIDTH
endgenerate


endmodule