tests/asicworld/code_hdl_models_lfsr_updown.v

   1 `define WIDTH 8
   2 module lfsr_updown (
   3 clk       ,   // Clock input
   4 reset     ,   // Reset input
   5 enable    ,   // Enable input
   6 up_down   ,   // Up Down input
   7 count     ,   // Count output
   8 overflow      // Overflow output
   9 );
  10
  11  input clk;
  12  input reset;
  13  input enable;
  14  input up_down;
  15
  16  output [`WIDTH-1 : 0] count;
  17  output overflow;
  18
  19  reg [`WIDTH-1 : 0] count;
  20
  21  assign overflow = (up_down) ? (count == {{`WIDTH-1{1'b0}}, 1'b1}) :
  22                                (count == {1'b1, {`WIDTH-1{1'b0}}}) ;
  23
  24  always @(posedge clk)
  25  if (reset)
  26     count <= {`WIDTH{1'b0}};
  27  else if (enable) begin
  28     if (up_down) begin
  29       count <= {~(^(count & `WIDTH'b01100011)),count[`WIDTH-1:1]};
  30     end else begin
  31       count <= {count[`WIDTH-2:0],~(^(count &  `WIDTH'b10110001))};
  32     end
  33  end
  34
  35 endmodule