二．設計一數字鐘系統，要求如下：

1. 有基礎的實時數字鐘功能，即時，分，秒的正常顯示模式。（24小時制）

2. 可對系統用手動方式校準，設計兩個按鍵，按動校時鍵，時計數器加一，按動校分鍵，則電路處於校分狀態。

3. 整點報時，要求在59分50秒，52秒，54秒，56秒和58秒發出一個低音訊號，00分00秒發出一個高音訊號。

源程式如下：

module clock (clk,reset,hour_g,hour_d,minute_g,minute_d,second_g,second_d,add_s,add_f,lowalarm,highalarm);  
input         clk,reset,add_s,add_f;
output[3:0]   hour_g,hour_d,minute_g,minute_d,second_g,second_d;
reg[3:0]      hour_g,hour_d,minute_g,minute_d,second_g,second_d;
wire          cout_s,cout_m;
reg[3:0] jishi;
output lowalarm,highalarm;//低音和高音訊號
reg lowalarm;
wire highalarm;
always @(posedge clk)
begin
  if(!reset) second_d<=0;
  else if(second_d==9)
    second_d<=0;
  else
    second_d<=second_d+1;
end

always @(posedge clk)
begin
  if(!reset) second_g<=0;
  else if(second_d==9)
    begin
      if(second_g==5)
        second_g<=0;
      else
        second_g<=second_g+1;
    end
  end
assign cout_s=((second_d==9)&&(second_g==5))?1:0;

always @(posedge clk)
begin
  if(!reset)
        minute_d <= 0;
  else if(cout_s)
    begin
     if(minute_d==9)
        minute_d <= 0;
     else 
        minute_d <=minute_d+1;
    end
end

always @(posedge clk)
begin
  if(!reset)
    minute_g <= 0;
  else if(cout_s)
    begin
    if(minute_d==9)
      begin
      if(minute_g==5)
        minute_g <= 0;
      else 
        minute_g<= minute_g+1;
      end
    end
end

assign cout_m = ((minute_d==9)&&(minute_g==5))?1:0;

always @(posedge clk)
begin
  if(!reset)
        hour_d <= 0;
  else if(cout_m&&cout_s)
  begin
    if((hour_d==3)&&(hour_g==2))
      hour_d<=0;
    else
       if(hour_d==9)
        hour_d <=0;
       else
        hour_d <= hour_d + 1;
  end
end

always @(posedge clk)
begin
  if(!reset)
        hour_g <= 0;
  else if(cout_m&&cout_s)
  begin
      if((hour_d==3)&&(hour_g==2))
        hour_g <= 0;
      else if(hour_d==9)
        hour_g<=hour_g+1;
  end
end

always @(posedge clk)
begin
    if(add_s)
      begin
        if((hour_d==3)&&(hour_g==2))
          begin
            hour_g<=0;
            hour_d<=0;
          end
        else
          if(hour_d==9)
            begin
              hour_d<=0;
              hour_g<=hour_g+1;
            end
          else
            hour_d<=hour_d+1;
      end
    end
    
    always @(posedge clk)
    begin
     if(add_f)
        begin
          if((minute_d==9)&&(minute_g==5))
            begin
              minute_d<=0;
              minute_g<=0;
            end
          else 
            if(minute_d==9)
              begin
                minute_d<=0;
                minute_g<=minute_g+1;
              end
            else
              minute_d<=minute_d+1;
        end
      end
      
      always @(posedge clk)
      begin
        if(!reset) 
        begin
        lowalarm<=0;
        jishi<=1;
        end
        else
          if((minute_g==5)&&(minute_d==9))
            begin
              if(second_g==5)
                begin
                  if((second_d==1)||(second_d==3)||(second_d==5)||(second_d==7))
                    lowalarm<=1;
                  else
                    begin
                    lowalarm<=0;
                    jishi<=jishi+1;
                    end
                end
          if(second_g==4&&second_d==9)
            lowalarm<=1;
            end  
      end
        
        assign highalarm=((minute_g==0)&&(minute_d==0)&&(second_g==0)&&(second_d==0))?1:0;
  
endmodule
 

`timescale 1ns/1ns
module clock_tb();
  reg clk,reset;
  wire[3:0] hour_g,hour_d,minute_g,minute_d,second_g,second_d;
  wire lowalarm,highalarm;
  reg add_s,add_f;
  clock u1(.clk(clk),.reset(reset),.hour_g(hour_g),.hour_d(hour_d),.minute_g(minute_g),
            .minute_d(minute_d),.second_g(second_g),.second_d(second_d),.add_s(add_s),.add_f(add_f),.lowalarm(lowalarm),.highalarm(highalarm));
  parameter DELY=100;
  always #(DELY/2) clk=~clk;
  initial
  begin
    clk=0;add_s=0;add_f=0;reset=0;
    #150 reset=1;
    #(DELY*100000) add_s=1;
    #DELY add_s=0;
    #(DELY*5) add_f=1;
    #DELY add_f=0;
    #DELY $finish;
  end
endmodule