FPGA新起点V1开发板（十）——按键控制LED

module key_led(
    input            sys_clk,
    input            rst_n,
    input      [3:0] key,
    
    output reg [3:0] led
    
);

// reg define
reg [23:0] cnt;
reg [1:0]  led_ctrl;

//0.2s计数器
always @ (posedge sys_clk or negedge rst_n) begin
    if(!rst_n)
        cnt <= 24'd0;
    else
        if(cnt < 24'd1000_0000)
            cnt <= cnt + 1'b1;
        else
            cnt <= 24'd0;

end

//每隔0.2s改变的四个状态
always @ (posedge sys_clk or negedge rst_n) begin
    if(!rst_n)
        led_ctrl <= 2'b0;
    else
        if(cnt == 24'd1000_0000)
            led_ctrl <= led_ctrl + 1'b1;
        else
            led_ctrl <= led_ctrl;

end

//按键控制
always @ (posedge sys_clk or negedge rst_n) begin
    if(!rst_n)
        led <= 4'b0000;
    else
        if(key[0] == 1'b0)
            case(led_ctrl)
                2'd0 : led <= 4'b1000;
                2'd1 : led <= 4'b0100;
                2'd2 : led <= 4'b0010;
                2'd3 : led <= 4'b0001;
            endcase
        else if(key[1] == 1'b0)
            case(led_ctrl)
                2'd0 : led <= 4'b0001;
                2'd1 : led <= 4'b0010;
                2'd2 : led <= 4'b0100;
                2'd3 : led <= 4'b1000;
            endcase
        else if(key[2] == 1'b0)
            case(led_ctrl)
                2'd0 : led <= 4'b1111;
                2'd1 : led <= 4'b0000;
                2'd2 : led <= 4'b1111;
                2'd3 : led <= 4'b0000;
            endcase
        else if(key[3] == 1'b0)
            led <= 4'b1111;
        else
            led <= 4'b0000;

end

endmodule