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Forums > Functional Verification > SystemVerilog

Subject: What is wrong with this code ? I'm trying to use a Queue of classes..
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mirzani
Posts: 0
Online: User is Offline
12/14/2006 1:14 AM   
module top;
timeunit 1ns;

class genfra;
rand bit [31:0] dword1;
rand bit [31:0] dword2;
endclass :genfra

integer success,i,dly;
genfra temp1,temp2;

genfra fifo[$] ;
initial
 begin
temp1=new();
     for(i = 0 ; i < 20 ;i++)
       begin
       success = temp1.randomize();
       success = randomize(dly) with {dly > 2;dly < 5;};
       $display("time=%d.. temp1.dword1 = %08x  ",$time,temp1.dword1);
       $display("time=%d.. temp1.dword2 = %08x  ",$time,temp1.dword2);
       fifo.push_back(temp1);
       #dly;
       end
       $finish;
 end

initial
      begin
      #15;
       forever
       begin
           $display("time=%d..before pop ",$time);
           if(fifo.size())
           begin
           $display("fifo size before pop ",fifo.size());
           temp2=fifo.pop_front();
           $display("time=%d.. temp2.dword1 = %08x  ",$time,temp2.dword1);
           $display("time=%d.. temp2.dword2 = %08x  ",$time,temp2.dword2);
           $display("fifo size after pop ",fifo.size());
           end
           else
            #1;
       end
      end

endmodule


I'm getting the following output.. The 
temp2=fifo.pop_front();
doesn't seem to do what it should.. It prints the last object and doesn't remove it from the queue ..
can someone point out whats wrong!! (see --????? below..)

ncverilog: 05.83-p002: (c) Copyright 1995-2006 Cadence Design Systems, Inc.
TOOL:   ncverilog   05.83-p002: Started on Dec 14, 2006 at 13:49:26 IST
.
.
.
ncsim> run
SVSEED set from command line: 60
time=                   0.. temp1.dword1 = e68182cd
time=                   0.. temp1.dword2 = 0321b106
time=                   4.. temp1.dword1 = 7bd6b7f7
time=                   4.. temp1.dword2 = a9586452
time=                   7.. temp1.dword1 = a51a824a
time=                   7.. temp1.dword2 = c78e9c8f
time=                  10.. temp1.dword1 = 9ba71c37
time=                  10.. temp1.dword2 = 106de120
time=                  13.. temp1.dword1 = 8798120f
time=                  13.. temp1.dword2 = 3b6a8d76
time=                  15..before pop
fifo size before pop           5
time=                  15.. temp2.dword1 = 8798120f --?????
time=                  15.. temp2.dword2 = 3b6a8d76 --?????
fifo size after pop           4
time=                  15..before pop
fifo size before pop           4
time=                  15.. temp2.dword1 = 8798120f --?????
time=                  15.. temp2.dword2 = 3b6a8d76 --?????
fifo size after pop           3
time=                  15..before pop
fifo size before pop           3
time=                  15.. temp2.dword1 = 8798120f
time=                  15.. temp2.dword2 = 3b6a8d76
fifo size after pop           2
time=                  15..before pop
fifo size before pop           2
time=                  15.. temp2.dword1 = 8798120f
time=                  15.. temp2.dword2 = 3b6a8d76
fifo size after pop           1
time=                  15..before pop
fifo size before pop           1
time=                  15.. temp2.dword1 = 8798120f
time=                  15.. temp2.dword2 = 3b6a8d76
fifo size after pop           0
time=                  15..before pop
time=                  16..before pop
time=                  17.. temp1.dword1 = 8e68b41c
time=                  17.. temp1.dword2 = 5e7ba1bc
time=                  17..before pop
fifo size before pop           1
time=                  17.. temp2.dword1 = 8e68b41c
time=                  17.. temp2.dword2 = 5e7ba1bc
fifo size after pop           0
time=                  17..before pop
time=                  18..before pop
time=                  19..before pop
time=                  20..before pop
time=                  21.. temp1.dword1 = 2a916b55
time=                  21.. temp1.dword2 = 0dcdad1b
time=                  21..before pop
fifo size before pop           1
time=                  21.. temp2.dword1 = 2a916b55
time=                  21.. temp2.dword2 = 0dcdad1b
fifo size after pop           0
time=                  21..before pop
time=                  22..before pop
time=                  23..before pop
time=                  24.. temp1.dword1 = bdfc1c7b
time=                  24.. temp1.dword2 = e2a8aec5
time=                  24..before pop
fifo size before pop           1
time=                  24.. temp2.dword1 = bdfc1c7b
time=                  24.. temp2.dword2 = e2a8aec5

.
.
.
 

Thanks..
kameade
Posts: 13
Online: User is Offline
12/14/2006 4:49 AM  
Hello,

I looked at your code and see that you are only calling new() once during the simulation.  So it is only allocating space for one genfra class item.  When you place the item on the queue, you are actually only placing the pointer to genfra.  So it will always remember the last item you randomized.

To fix the problem, move the temp1=new() inside the for-loop.  It will generate a new item every time.

initial
  begin
     for (i=0; i<20; i++)
        begin
           temp1=new();  // MOVE HERE!
            success = temp1.randomize();
  ....

I hope this helps!

Kathleen Meade
mirzani
Posts: 0
Online: User is Offline
12/14/2006 5:24 AM  
Thanks..
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Forums > Functional Verification > SystemVerilog > What is wrong with this code ? I'm trying to use a Queue of classes..


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