f4pga-examples/xc7/counter_test/counter_zynq.v

module top (
    input wire clk,
    output wire [3:0] led
);

  wire [63:0] emio_gpio_o;
  wire [63:0] emio_gpio_t;
  wire [63:0] emio_gpio_i;

  wire clk_bufg;
  BUFG BUFG (
      .I(clk),
      .O(clk_bufg)
  );

  wire en_counter = ~emio_gpio_o[0];
  wire count_direction = ~emio_gpio_o[1];
  reg [31:0] counter = 0;

  always @(posedge clk_bufg) begin
    if (en_counter)
      if (count_direction) counter <= counter + 1;
      else counter <= counter - 1;
  end

  assign led = counter[27:24];

  // The PS7
  (* KEEP, DONT_TOUCH *)
  PS7 PS7 (
      .EMIOGPIOO (emio_gpio_o),
      .EMIOGPIOTN(emio_gpio_t),
      .EMIOGPIOI (emio_gpio_i)
  );


endmodule