黑金使用 計數器 來控制4個LED燈

計數器分別去表示1s、2s、3s、4s這幾個時間，然後實現流水燈

//================================================================================
//  Revision History:
//  Date          By            Revision    Change Description
//--------------------------------------------------------------------------------
//  2017/7/19     meisq          1.0         Original
 
//*******************************************************************************/

`timescale 1ns / 1ps
module led_test
(
    input           clk,           // system clock 50Mhz on board
    input           rst_n,         // reset ,low active
    output          led1,          // led on core board
    output reg[3
 
:0] led            // LED,use for control the LED signal on expansion board
);

assign led1 = led[0];

//define the time counter
reg [31:0]      timer;

// cycle counter:from 0 to 4 sec
always@(posedge clk or negedge rst_n)
begin
    if (rst_n == 1'b0)
        timer <= 32'd0;                     //when the reset signal valid,time counter clearing
 

    else if (timer == 32'd199_999_999)      //4 seconds count(50M*4-1=199999999)
        timer <= 32'd0;                     //count done,clearing the time counter
    else
        timer <= timer + 32'd1;             //timer counter = timer counter + 1
end

// LED control
always@(posedge clk or negedge rst_n)
begin
    if (rst_n == 1'b0)
        led <= 4'b0000;                     //when the reset signal active
    else if (timer == 32'd49_999_999)       //time counter count to 1st sec,LED1 lighten
        led <= 4'b0001;
    else if (timer == 32'd99_999_999)       //time counter count to 2nd sec,LED2 lighten
        led <= 4'b0010;
    else if (timer == 32'd149_999_999)      //time counter count to 3rd sec,LED3 lighten
        led <= 4'b0100;
    else if (timer == 32'd199_999_999)      //time counter count to 4th sec,LED4 lighten
        led <= 4'b1000;
end
endmodule