本章節(jié)簡介：

可以在任意時刻啟動，可以重復啟動，延時時長可調(diào)，單位可切換（ms/us），在50MHz時鐘下的延時范圍是1ms-85899ms/1us-85899us。

源代碼和modelsim仿真代碼：

moduledelay



//#(parameterN)//可以延時N*1ms/us



(inputclk,rst_n,

inputstart,//start上升沿有效

inputdelay_unit,//延時單位，high:ms/low:us

outputfinish,finish_pose);//finish上升沿有效

regstart_reg0,start_reg1;//start兩級緩存，用于邊沿檢測

regfinish_reg0,finish_reg1;//finish兩級緩存

reg[31:0]cnt;//固定32位寬計數(shù)

reg[31:0]cnt_full;

regrestart;//重新開始

wirestart_pose,full;

always@(posedgeclkornegedgerst_n)

begin

if(!rst_n)

begin

cnt<=?32'd0;

???????????????????cnt_full?<=?32'd10;?//避免一開始finish置位

???????????????????restart?<=?1'b0;

???????????????????start_reg0?<=?1'b0;?start_reg1?<=?1'b0;?

???????????????????finish_reg0?<=?1'b0;?finish_reg1?<=?1'b0;

???????????????end

???????????else

??????????????begin

??????????????????start_reg0?<=?start;?start_reg1?<=?start_reg0;

??????????????????finish_reg1?<=?finish_reg0;??

??????????????????/**檢測計時單位**/

??????????????????if(delay_unit)??

?????????????????????cnt_full?<=?32'd50_000*2-32'd2;??//計時2ms??實際例化時用N代替:?32'd50_000*N-32'd2

??????????????????else

?????????????????????cnt_full?<=?32'd50*2-32'd2;??????//計時2us

?????????????????/***************/

????????????????/**是否重新開始**/

????????????????if(start_pose)??//檢測到起始時刻?

????????????????????restart?<=?1'b1;??

???????????????/****計時完成****/

???????????????else?if(full)??//延時結束

??????????????????begin

??????????????????????cnt?<=?32'd0;??//cnt歸零

??????????????????????finish_reg0?<=?1'b1;??//finish響應

??????????????????????restart?<=?1'b0;

??????????????????end

?????????????/***************/

?????????????/****計時開始****/

?????????????else?if(restart)?

????????????????begin

????????????????????finish_reg0?<=?1'b0;????//新一輪延時finish復位

????????????????????cnt?<=?cnt+1'b1;

????????????????end

???????????/***************/

???????????/**等待新一輪計時**/

???????????else?

??????????????begin

??????????????????cnt?<=?cnt;

??????????????????finish_reg0?<=?finish_reg0;

??????????????????restart?<=?restart;

??????????????end

????end??

end

?

??assign?start_pose?=?(~start_reg1&start_reg0)?1'b1:1'b0;??//start上升沿檢測

??assign?finish_pose?=?(~finish_reg1&finish_reg0)?1'b1:1'b0;??//finish上升沿檢測

??assign?full?=?(cnt_full-cnt==0)?1'b1:1'b0;???//檢測是否計滿



??assign?finish?=?finish_reg0;



endmodule



/**************************************************************************************************/?????????????????????????????????????/***************************************modelsim********************************************/??



`timescale?1ns/1ps

module?delay_tb();

???reg?clk,rst_n;

???reg?start;

???wire?finish,finish_pose;

??

??delay?delay_u0

??(.clk(clk),

???.rst_n(rst_n),

???.start(start),

???.delay_unit(1'b1),

???.finish(finish),

???.finish_pose(finish_pose));

???//defparam?delay_u0.N?=?2;?//延時2ms

??

??initial

????begin

clk?=?1'b0;

????????rst_n?=?1'b0;

????????start?=?1'b0;

#1000?rst_n?=?1'b1;

#4010?start?=?1'b1;?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????#50?????start?=?1'b0;????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????end



??always?#10?clk?=?~clk;

endmodule

思路：

start端口給上升沿啟動延時，延時結束端口finish置位（重新啟動延時后復位）、finish的上升沿檢測在模塊內(nèi)部已做好（端口finish_pose），直接調(diào)用即可，端口delay_unit置高選擇ms，置低選擇us，#（參數(shù)N ）“是計時時長，例如計時8ms：”N = 8， .delay_unit（1'b1）“，實際例化時只需”defparam 例化名.N = 數(shù)值”。因為modelsim無法識別這種調(diào)用，所以直接用數(shù)值代替N進行測試。邊沿檢測會消耗兩個時鐘周期，所以cnt_full需要減2，并且將finish_reg0直接連到finish輸出端口而不是用finish_reg1連接完成。

延時2ms測試的起始時刻（5010ns）和結束時刻（2005010ns）：