请用verilog帮我写一个由八个八段数码管显示的倒计时器项目，按位显示

好的，以下是一个简单的由八个八段数码管显示的倒计时器项目的Verilog代码，它会按位显示倒计时器的数值：

module countdown_timer(
    input clk,
    input reset,
    output reg [7:0] seg_a,
    output reg [7:0] seg_b,
    output reg [7:0] seg_c,
    output reg [7:0] seg_d,
    output reg [7:0] seg_e,
    output reg [7:0] seg_f,
    output reg [7:0] seg_g,
    output reg [7:0] dp
);

reg [24:0] counter = 25_000_000; // 1秒钟的计数器
reg [23:0] countdown = 60_000; // 60秒倒计时计数器
reg [3:0] digit = 4'b1111; // 当前显示的数码管位数，初始设置为8位数码管

always @(posedge clk) begin
    if (reset) begin
        counter <= 25_000_000;
        countdown <= 60_000;
        digit <= 4'b1111;
    end else begin
        counter <= counter - 1;
        if (counter == 0) begin
            counter <= 25_000_000;
            countdown <= countdown - 1;
            if (digit == 4'b0000) begin
                digit <= 4'b1111;
            end else begin
                digit <= digit - 1;
            end
        end
    end
end

always @(countdown) begin
    case (digit)
        4'b1111: begin // 显示倒计时的个位数
            seg_a <= (countdown % 10 == 0) ? 8'h40 : 8'h3f;
            seg_b <= (countdown % 10 == 1 || countdown % 10 == 4) ? 8'h06 : 8'h5b;
            seg_c <= (countdown % 10 == 0 || countdown % 10 == 1 || countdown % 10 == 7) ? 8'h3f : 8'h06;
            seg_d <= (countdown % 10 == 0 || countdown % 10 == 1 || countdown % 10 == 7) ? 8'h06 : 8'h5b;
            seg_e <= (countdown % 10 == 1 || countdown % 10 == 2 || countdown % 10 == 3 || countdown % 10 == 7) ? 8'h5b : 8'h4f;
            seg_f <= (countdown % 10 == 0 || countdown % 10 == 1 || countdown % 10 == 7) ? 8'h3f : 8'h66;
            seg_g <= (countdown % 10 == 0) ? 8'h40 : 8'h5f;
            dp <= 8'h00;
        end
        4'b1110: begin // 显示倒计时的十位数
            seg_a <= ((countdown / 10) % 10 == 0) ? 8'h40 : 8'h3f;
            seg_b <= ((countdown / 10) % 10 == 1 || (countdown / 10) % 10 == 4) ? 8'h06 : 8'h5b;
            seg_c <= ((countdown / 10) % 10 == 0 || (countdown / 10) % 10 == 1 || (countdown / 10) % 10 == 7) ? 8'h3f : 8'h06;
            seg_d <= ((countdown / 10) % 10 == 0 || (countdown / 10) % 10 == 1 || (countdown / 10) % 10 == 7) ? 8'h06 : 8'h5b;
            seg_e <= ((countdown / 10) % 10 == 1 || (countdown / 10) % 10 == 2 || (countdown / 10) % 10 == 3 || (countdown / 10) % 10 == 7) ? 8'h5b : 8'h4f;
            seg_f <= ((countdown / 10) % 10 == 0 || (countdown / 10) % 10 == 1 || (countdown / 10) % 10 == 7) ? 8'h3f : 8'h66;
            seg_g <= ((countdown / 10) % 10 == 0) ? 8'h40 : 8'h5f;
            dp <= (digit == 4'b1110) ? 8'h01 : 8'h00; // 显示小数点
        end
        4'b1101: begin // 显示冒号
            seg_a <= 8'h00;
            seg_b <= 8'h00;
            seg_c <= 8'h00;
            seg_d <= 8'h00;
            seg_e <= 8'h00;
            seg_f <= 8'h00;
            seg_g <= (countdown % 2 == 0) ? 8'h00 : 8'h02;
            dp <= 8'h00;
        end
        4'b1100: begin // 显示倒计时的百位数
            seg_a <= ((countdown / 100) % 10 == 0) ? 8'h40 : 8'h3f;
            seg_b <= ((countdown / 100) % 10 == 1 || (countdown / 100) % 10 == 4) ? 8'h06 : 8'h5b;
            seg_c <= ((countdown / 100) % 10 == 0 || (countdown / 100) % 10 == 1 || (countdown / 100) % 10 == 7) ? 8'h3f : 8'h06;
            seg_d <= ((countdown / 100) % 10 == 0 || (countdown / 100) % 10 == 1 || (countdown / 100) % 10 == 7) ? 8'h06 : 8'h5b;
            seg_e <= ((countdown / 100) % 10 == 1 || (countdown / 100) % 10 == 2 || (countdown / 100) % 10 == 3 || (countdown / 100) % 10 == 7) ? 8'h5b : 8'h4f;
            seg_f <= ((countdown / 100) % 10 == 0 || (countdown / 100) % 10 == 1 || (countdown / 100) % 10 == 7) ? 8'h3f : 8'h66;
            seg_g <= ((countdown / 100) % 10 == 0) ? 8'h40 : 8'h5f;
            dp <= (digit == 4'b1100) ? 8'h01 : 8'h00; // 显示小数点
        end
        // 以此类推，根据当前显示的数码管位数依次设置显示的数码管的值
        // ...
        4'b0000: begin // 所有数码管都不显示
            seg_a <= 8'h00;
            seg_b <= 8'h00;
            seg_c <= 8'h00;
            seg_d <= 8'h00;
            seg_e <= 8'h00;
            seg_f <= 8'h00;
            seg_g <= 8'h00;
            dp <= 8'h00;
        end
    endcase
end

endmodule

这个倒计时器每次启动时会从60秒开始倒计时，并且会按位显示倒计时器的数值。倒计时结束后，所有的数码管都会被清零。您可以根据需要修改计数器的初始值和倒计时结束后的显示值。