4) Write the vivado code to implement the following functions, display the character string 2017 04 27 ddl in four 7-segment LED circularly at a rate of 0.5 Hz(Assume that your main clock frequency is 100MHz.)

Here is an example Vivado code to implement the given function:

module display(
    input clock,
    output [27:0] seg
);

reg [31:0] counter = 0;
reg [3:0] digit = 0;

always @(posedge clock) begin
    counter <= counter + 1;
    if (counter >= 50000000) begin // 0.5 Hz
        counter <= 0;
        digit <= digit + 1;
        if (digit > 3) begin
            digit <= 0;
        end
    end
end

always @(*) begin
    case (digit)
        0: seg = 28'b0000_0000_0000_0000_0000_0001_0000;
        1: seg = 28'b0000_0000_0000_0000_0000_0000_1111;
        2: seg = 28'b0000_0000_0000_0000_0000_0000_1110;
        3: seg = 28'b0000_0000_0000_0000_0000_0000_1101;
    endcase
end

endmodule

In this module, we have an input `clock` which is the main clock signal with a frequency of 100MHz. We also have an output `seg` which is a 28-bit signal representing the 4 7-segment displays.

We use a counter to keep track of the time and update the `digit` variable every 0.5 seconds (50000000 clock cycles). We use a case statement to assign the correct 7-segment code to `seg` based on the current `digit`.

Assuming that the pins for the 7-segment displays are connected correctly, this code should display the character string "2017 04 27 ddl" in a circular fashion on the 4 displays.