任务
本例中我们实现了一个 led 灯的"呼吸"，而板子上有 4 个 led 灯，我们可以修改代码让 4 个 led 灯的呼吸频率都不同步，大家可以尝试一下。
代码
module breath_led
#(
parameter CNT_1US_MAX = 6'd49,
parameter CNT_1MS_MAX = 10'd999,
parameter CNT_1S_MAX = 10'd999
)
(
input sys_clk,
input sys_rst_n,
output reg 3:0 led_out
);
// 计数器定义
reg 5:0 cnt_1us;
reg 9:0 cnt_1ms;
reg 9:0 cnt_1s 3:0;
reg cnt_1s_en 3:0;
// 1us计数器
always @(posedge sys_clk or negedge sys_rst_n)
if(!sys_rst_n)
cnt_1us <= 6'd0;
else if(cnt_1us == CNT_1US_MAX)
cnt_1us <= 6'd0;
else
cnt_1us <= cnt_1us + 1'b1;
// 1ms计数器
always @(posedge sys_clk or negedge sys_rst_n)
if(!sys_rst_n)
cnt_1ms <= 10'd0;
else if(cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
cnt_1ms <= 10'd0;
else if(cnt_1us == CNT_1US_MAX)
cnt_1ms <= cnt_1ms + 1'b1;
// 为每个LED生成独立的秒计数器和控制逻辑
genvar i;
generate
for (i = 0; i < 4; i = i + 1) begin : led_inst
// 独立的秒计数器，初始相位错开
always @(posedge sys_clk or negedge sys_rst_n)
if(!sys_rst_n)
cnt_1si <= i * 10'd250;
else if(cnt_1si == CNT_1S_MAX && cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
cnt_1si <= 10'd0;
else if(cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
cnt_1si <= cnt_1si + 1'b1;
// 独立的方向标志
always @(posedge sys_clk or negedge sys_rst_n)
if(!sys_rst_n)
cnt_1s_eni <= 1'b0;
else if(cnt_1si == CNT_1S_MAX && cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
cnt_1s_eni <= ~cnt_1s_eni;
// PWM输出控制
always @(posedge sys_clk or negedge sys_rst_n)
if(!sys_rst_n)
led_outi <= 1'b0;
else if((cnt_1s_eni && cnt_1ms < cnt_1si) || (!cnt_1s_eni && cnt_1ms > cnt_1si))
led_outi <= 1'b0;
else
led_outi <= 1'b1;
end
endgenerate
endmodule
引脚限制
=============================================================================
时钟与复位信号约束
=============================================================================
系统时钟输入（50MHz晶振）
set_property PACKAGE_PIN W19 get_ports sys_clk
set_property IOSTANDARD LVCMOS33 get_ports sys_clk
全局复位按键（低电平有效）
set_property PACKAGE_PIN N15 get_ports sys_rst_n
set_property IOSTANDARD LVCMOS33 get_ports sys_rst_n
=============================================================================
LED灯引脚约束
开发板LED为共阳极接法：led_out=0时灯亮，led_out=1时灯灭
=============================================================================
LED0 控制信号
set_property PACKAGE_PIN M21 get_ports {led_out\[0}]
set_property IOSTANDARD LVCMOS33 get_ports {led_out\[0}]
LED1 控制信号
set_property PACKAGE_PIN L21 get_ports {led_out\[1}]
set_property IOSTANDARD LVCMOS33 get_ports {led_out\[1}]
LED2 控制信号
set_property PACKAGE_PIN K21 get_ports {led_out\[2}]
set_property IOSTANDARD LVCMOS33 get_ports {led_out\[2}]
LED3 控制信号
set_property PACKAGE_PIN K22 get_ports {led_out\[3}]
set_property IOSTANDARD LVCMOS33 get_ports {led_out\[3}]