15 、FPGA之纯PL流水灯实验

实验基本目的:实验手册PL的流水灯,基本流程参考手册;

逻辑代码解析:

module PL_Led(
           clk,
           rst_n,
           led

       );

input clk;
input rst_n;
output [3:0] led;

reg [0:27] cnt;
reg [3:0] led_reg;
always@(posedge clk or negedge rst_n)
    if (!rst_n)
    begin
        cnt<=28'h0000;
    end
    else if (cnt== 28'h17D_7840) //50MHZ*0.5s
    begin
        cnt<=28'h0000;
    end
    else
    begin
        cnt<=cnt+1'b1;
    end

always@(posedge clk or negedge rst_n)
    if(!rst_n)
    begin
        led_reg<=4'b0001;
    end
    else if (cnt==28'h17D_7840)
    begin
        led_reg<={led_reg[0],led_reg[3:1]};  //  1 000 0100 0010 0001
    end

assign led = led_reg;

endmodule

主要解析一下 

else if (cnt== 28'h17D_7840) //50MHZ*0.5s

FPGA的开发板的时钟是50MHZ, 计算是1/50MHZ=0.02us秒

逻辑代码中,每累加1次需要0.02us, 需要0.5s进行一次led灯变化,侧需要0.5s/0.02us次

0.5s/0.02us=0.5s/(1/50MHZ)=0.5s*50MHZ=0.5*50*1000*1000HZ=25000000=0x17D7840次

set_property PACKAGE_PIN M15 [get_ports {led[3]}]
set_property PACKAGE_PIN G14 [get_ports {led[2]}]
set_property PACKAGE_PIN M17 [get_ports {led[1]}]
set_property PACKAGE_PIN G15 [get_ports {led[0]}]
set_property PACKAGE_PIN K17 [get_ports clk]
set_property PACKAGE_PIN E17 [get_ports rst_n]
set_property IOSTANDARD LVCMOS33 [get_ports {led[3]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[2]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[1]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[0]}]
set_property IOSTANDARD LVCMOS33 [get_ports clk]
set_property IOSTANDARD LVCMOS33 [get_ports rst_n]

create_clock -period 20.000 -name clk -waveform {0.000 10.000} [get_ports clk]

约束文件