How to implement System verilog Mailbox's Peek behavior using System Verilog Queue?

SystemVerilog
1

I want to implement mailbox peek method’s behavior using queues how to do that ?

2

In reply to Hardik Trivedi:

int que[$]; //queue declaration
...
function int peek();
    while (que.size > 0) begin
        peek = que[0];
    end
endtask
3

In reply to rohitk:
That doesn’t work. You will get an infinite loop when (que.size > 0) is true. You need a task with a wait statement

int que[$]; //queue declaration
...
task peek(output int message);
    wait (que.size > 0)
        message = que[0]; // this assumes you do que.push_back(message)
endtask
4

In reply to dave_59:

thanks for correcting, so final code will look like following:

int que[$]; //queue declaration
...
task peek(output int message);
    wait (que.size > 0
    message = que.pop_front(); // Pop queue content 
    que.push_front(message);   // Push message back in front
endtask
5

In reply to rohitk:
That’s not correct either. You don’t want to be disturbing the queue as other processes may be accessing it as well. My comment about push_back was if you are also implementing a put() task.

6

In reply to dave_59:

Agreed, thanks for correcting again. your original solution works fine as it is.

7

In reply to dave_59:

Hi Dave, If I am not wrong the basic difference between peek and get is that peek method doesn’t delete the element from the mailbox. SO you have used this,
wait (que.size > 0
message = que[0]
But this will always give the zeroth location data right?
Correct me If I am wrong.

Thanks,
Sitesh

8

It will, and that is what peek does.

9

In reply to ocmob:

Yeah but how we can access all the element from the queue.It will always loop the zero’th element I guess.

Here I am attaching my code please have a look.

module test;
  
	int result ,result_1;
    class  mailbox #(type T = bit);
    
    T que [$];
    
    
    
    task put(input T item);
      que.push_back(item);
      
    endtask
    
    task get(output T item);
      wait(que.size > 0);
      item = que.pop_front();
    endtask
    
    task peek(output T item);
      wait(que.size > 0);
      for(int i; i < que.size -1 ;i ++)
        item = que[i];
      $display("item =%0d",item);
    endtask
    
    
  endclass
  
  class A;
    mailbox #(int) mbx;
    rand bit[3:0] data [];
   
    constraint abc {data.size == 10;}
   
    function new();
      mbx = new;
    endfunction
    
  endclass
  
  A a1,a2;
  
  initial begin
    a1 = new();
    a1.randomize ();
    
    foreach(a1.data[i])
      a1.mbx.put(a1.data[i]);
      $display(a1.mbx);
    
    fork 
    //forever begin 
      //a1.mbx.get(result);
      //$display($time,"Result = %0d",result);
      //$display(a1.mbx);
      //#10;
    //end
    
    forever begin 
      a1.mbx.peek(result_1);
      $display($time,"Result_1 = %0d",result_1);
      $display(a1.mbx);
   
    end
    join
    
    
    
  end
  
  
  
endmodule
10

In reply to Sitesh11:
A mailbox has FIFO (First-in First-out) semantics. Since you are using push_back() to put() things on the queue, element 0 of a queue is the first-in element, the oldest. This is the element that both get() and and peek() return.

Your peek() routine returns the newest element.