module led_breath_v3(
    input clk,rst_n,
    output [3:0] led
);

    wire [3:0] ctrl_en;
    
    time_ctrl u0(
    .clk(clk),
    .rst_n(rst_n),
    .ctrl_en(ctrl_en)
    );
    
    led_breath_v2 L0(
    .clk(clk),
    .rst_n(ctrl_en[0]),
    .led(led[0])
    );
    led_breath_v2 L1(
    .clk(clk),
    .rst_n(ctrl_en[1]),
    .led(led[1])
    );
    led_breath_v2 L2(
    .clk(clk),
    .rst_n(ctrl_en[2]),
    .led(led[2])
    );
    led_breath_v2 L3(
    .clk(clk),
    .rst_n(ctrl_en[3]),
    .led(led[3])
    );
    
endmodule

module time_ctrl(
    input clk,
    input rst_n,
    output reg [3:0] ctrl_en
    );
    
    parameter T1 = 100_000_000;    //2s
    parameter T2 = 200_000_000;    //4s
    parameter T3 = 300_000_000;    //6s
    
    reg [28:0] cnt;
    
    
    //counter
    always @(posedge clk,negedge rst_n)
        begin
            if(!rst_n)
                cnt <= 0;
            else
                if(cnt < T3 - 1)
                    cnt <= cnt + 1;
                else
                    cnt <= cnt;
        end
        
    
    //turn on led 1 by 1
    always @(posedge clk,negedge rst_n)
        begin
            if(!rst_n)
                ctrl_en <= 0;
            else
                if(cnt == T3 - 1)
                    ctrl_en <= 4'b1111; //4 led all on
                else
                    if(cnt >= T2 - 1)
                        ctrl_en <= 4'b0111; //3 led all on
                    else
                        if(cnt >= T1 - 1)
                            ctrl_en <= 4'b0011; //2 led both on
                        else
                            ctrl_en <= 4'b0001; //1 led  on
        end
    
endmodule