[新手问题]正反循环流水灯(纯新手)

snakeqx · 发表于 2019-7-3 22:25:46

星期二刚买的板子,开始跟视频学习.
才学到第一课流水灯,学完后自己想改一下,改成可以正反循环流水的.
但是怎么都不对,第一次从右到左流完就结束了.

请各位指点迷津啊. 代码如下

module verilog_test (
input clk,
input rst_n,
output reg[3:0] led
);
// to set up a counter for every 0.2 s
// 1 second / 50MHz = 0.2 / xHz => x = 10MHz
// to hold 10_000_000, it needs 24 bits.
reg [23:0] counter;
reg [1:0] led_status; //to judge the led status
reg direction_flag; //dicide which direction the led flow
parameter CNT_200MS = 24'd10_000_000;
//generate signal with 10MHz (0.2s)
always [url=home.php?mod=space&uid=95564]@[/url] (posedge clk or negedge rst_n) begin
if(!rst_n)
counter <= 24'd0;
else begin
if(counter < CNT_200MS)
counter <= counter + 1'b1;
else
counter <= 24'd0;
end
end
// +/- flow_led
always @ (posedge clk or negedge rst_n) begin
if(!rst_n) begin
// initialize
led_status <= 2'b00;
direction_flag <= 1'b1;
led <= 4'b0001;
end
// every 200ms trigger
else if (counter == CNT_200MS) begin
// status + 1
led_status <= led_status + 1'b1;
// judge status to decide direction
if (led_status == 2'b11)
direction_flag <= ~direction_flag;
else
direction_flag <= direction_flag;
// flow according direction
if (direction_flag)
led = led << 1;
else
led = led >> 1;
end
else
led <= led;
end
endmodule

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snakeqx · 发表于 2019-7-3 22:55:35

本帖最后由 snakeqx 于 2019-7-3 22:58 编辑

我好像明白了. 根据视频介绍:

因为<=的赋值是并发的,而且整个一个always里面都是并发的,所以先全部算右值,再赋值左边.
于是我"错过"了切换的机会, 而下次触发的时候1已经移出范围,导致LED里的值全是0,而且因为没有1了,后面怎么移也不会有1.
我改了一下代码,至少运行正常了.

还请各位能指点一下是不是这样的.

module verilog_test (
input clk,
input rst_n,
output reg[3:0] led
);
// to set up a counter for every 0.2 s
// 1 second / 50MHz = 0.2 / xHz =? x = 10MHz
// to hold 10_000_000, it needs 24 bit.
reg [23:0] counter;
reg [1:0] led_status; //to judge the led status
reg direction_flag; //dicide which direction the led flow
parameter CNT_200MS = 24'd10_000_000 -1'b1;
//generate signal with 10MHz (0.2s)
always @ (posedge clk or negedge rst_n) begin
if(!rst_n)
counter <= 24'd0;
else begin
if(counter < CNT_200MS)
counter <= counter + 1'b1;
else
counter <= 24'd0;
end
end
// +/- flow_led
always @ (posedge clk or negedge rst_n) begin
if(!rst_n) begin
// initialize
led_status <= 2'b01; //////////////////////这里从1开始
direction_flag <= 1'b1;
led <= 4'b0001;
end
// every 200ms trigger
else if (counter == CNT_200MS) begin
// status + 1
led_status <= led_status + 1'b1;
// judge status to decide direction
if (led_status == 2'b11) begin
direction_flag <= ~direction_flag;
led_status <= 2'b01; /////////////////////////只用3位,所以这里回复1
end
else
direction_flag <= direction_flag;
// flow according direction
if (direction_flag)
led = led << 1;
else
led = led >> 1;
end
else
led <= led;
end
endmodule

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[新手问题]正反循环流水灯(纯新手)

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