xilinx/xc7/tests/counter/counter_pynqz1.v

module top (
    input  wire clk,
    input  wire [1:0] sw,
    input  wire [3:0] btn,
    output wire [3:0] led,
    output wire led4_b,
    output wire led4_g,
    output wire led4_r,
    output wire led5_b,
    output wire led5_g,
    output wire led5_r
);

	localparam BITS = 4;
	localparam LOG2DELAY = 18;

	reg [BITS+LOG2DELAY-1:0] counter = 0;

    IBUF clk_ibuf(.I(clk),      .O(clk_ibuf));
    BUFG clk_bufg(.I(clk_ibuf), .O(clk_b));

	always @(posedge clk_b) begin
		counter <= counter + 1;
	end

	assign led = counter >> LOG2DELAY;
endmodule