Confusing fork ~ join(any,none) behavior

SystemVerilog
,
1

Hello,

I’m trying to understand fork ~join_none statmenet.




module disable_fork;
  
  initial begin
    $display("-----------------------------------------------------------------");
    
    fork
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-1 of fork-1 Started");
        #5;
        $display($time,"\tProcess-1 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
    	$display("-----------------------------------------------------------------");
      	$display($time,"\tAfter a0");
    	$display("-----------------------------------------------------------------");
    
      begin
        $display($time,"\tProcess-2 of fork-1 Started");
        #20;
        $display($time,"\tProcess-2 of fork-2 Finished");
      end
        $display("-----------------------------------------------------------------");
      	$display($time,"\tAfter a1");
    	$display("-----------------------------------------------------------------");
    join_any
    
        $display("-----------------------------------------------------------------");
    	$display($time,"\tAfter fork1");
    	$display("-----------------------------------------------------------------");
    
    //-------------------
    //fork-2
    //-------------------    
    fork
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-3 of fork-1 Started");
        #5;
        $display($time,"\tProcess-3 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-4 of fork-1 Started");
        #20;
        $display($time,"\tProcess-4 of fork-2 Finished");
      end
    join_none    
    
  //  disable fork;
      
    $display("-----------------------------------------------------------------");
      $display($time,"\tAfter disable-fork");
    $display("-----------------------------------------------------------------");
  
    
      fork
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-5 of fork-1 Started");
        #5;
        $display($time,"\tProcess-5 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-6 of fork-1 Started");
        #20;
        $display($time,"\tProcess-6 of fork-2 Finished");
      end
      join_any
    
    fork
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-7 of fork-1 Started");
        #5;
        $display($time,"\tProcess-7 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-8 of fork-1 Started");
        #20;
        $display($time,"\tProcess-8 of fork-2 Finished");
      end
    join_any
    
  end  
endmodule

there are some fork~join_any and fork~join_none statements.
And I can get the below results.


-----------------------------------------------------------------
                   0	Process-1 of fork-1 Started
-----------------------------------------------------------------
-----------------------------------------------------------------
                   0	After fork1
-----------------------------------------------------------------
-----------------------------------------------------------------
                   0	After disable-fork
-----------------------------------------------------------------
                   0	Process-5 of fork-1 Started
                   0	Process-6 of fork-1 Started
                   0	Process-3 of fork-1 Started
                   0	Process-4 of fork-1 Started
                   0	After a0
-----------------------------------------------------------------
                   0	Process-2 of fork-1 Started
-----------------------------------------------------------------
                   0	After a1
-----------------------------------------------------------------
                   5	Process-1 of fork-2 Finished
                   5	Process-5 of fork-2 Finished
                   5	Process-7 of fork-1 Started  <----- why consumed time 5?
                   5	Process-8 of fork-1 Started  <----- why consumed time 5?
                   5	Process-3 of fork-2 Finished
                  10	Process-7 of fork-2 Finished
                  20	Process-6 of fork-2 Finished
                  20	Process-4 of fork-2 Finished
                  20	Process-2 of fork-2 Finished
                  25	Process-8 of fork-2 Finished

But I coundn’t undersatnd

                   5	Process-7 of fork-1 Started
                   5	Process-8 of fork-1 Started

they are supposed to start in 0 time not 5. it also implemented as process-5,process-6 so I expected 7 and 8 also will happen 0 time but it does not.
Could you guide me how to implement and undersatnd in multiple fork ~ join( none, any)?

2

In reply to UVM_LOVE:


module disable_fork;
 
  initial begin
    $display("-----------------------------------------------------------------");
 
    fork    //First fork block
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-1 of fork-1 Started");
        #5;
        $display($time,"\tProcess-1 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
    	$display("-----------------------------------------------------------------");
      	$display($time,"\tAfter a0");
    	$display("-----------------------------------------------------------------");
 
      begin
        $display($time,"\tProcess-2 of fork-1 Started");
        #20;
        $display($time,"\tProcess-2 of fork-2 Finished");
      end
        $display("-----------------------------------------------------------------");
      	$display($time,"\tAfter a1");
    	$display("-----------------------------------------------------------------");
    join_any
 
        $display("-----------------------------------------------------------------");
    	$display($time,"\tAfter fork1");
    	$display("-----------------------------------------------------------------");
 
    //-------------------
    //fork-2
    //-------------------    
    fork          //second fork block
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-3 of fork-1 Started");
        #5;
        $display($time,"\tProcess-3 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-4 of fork-1 Started");
        #20;
        $display($time,"\tProcess-4 of fork-2 Finished");
      end
    join_none    
 
  //  disable fork;
 
    $display("-----------------------------------------------------------------");
      $display($time,"\tAfter disable-fork");
    $display("-----------------------------------------------------------------");
 
 
      fork    //Third Fork block
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-5 of fork-1 Started");
        #5;
        $display($time,"\tProcess-5 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-6 of fork-1 Started");
        #20;
        $display($time,"\tProcess-6 of fork-2 Finished");
      end
      join_any
 
    fork  //Fourth Fork block.
      //-------------------
      //Process-1
      //-------------------
      begin
        $display($time,"\tProcess-7 of fork-1 Started");
        #5;
        $display($time,"\tProcess-7 of fork-2 Finished");
      end
      //-------------------
      //Process-2
      //-------------------
      begin
        $display($time,"\tProcess-8 of fork-1 Started");
        #20;
        $display($time,"\tProcess-8 of fork-2 Finished");
      end
    join_any
 
  end  
endmodule



    5	Process-7 of fork-1 Started
    5	Process-8 of fork-1 Started

You are getting above result because.,
Firstly All Four Fork blocks are inside begin end so these fork blocks are sequential .
Then Inside third fork block there are 2 process running parallely, According Fork-Join_any block control will come out of that block only after completion of any one process, So third fork block will complete after execution of both the statement in begin-end i.e., @5.
Because All the fork join blocks are sequential After third fork block task is completed only fourth fork block is starting executed **Hence you are getting p7 and p8 started @5
**