SystemVerilog note(2)

SV - OOP Concepts (object-oriented programming)

Reference:

http://www.verificationguide.com/p/systemverilog-classes_23.html

class

A class is a description of some group of things that have something in common

<1>. Construct

class sv_class; //class properties
  int x;
  task set(int i); x = i;
  endtask 
  function int get();
    return x;
  endfunction
endclass; //class properties
  int x;
  task set(int i); x = i;
  endtask 
  function int get();
    return x;
  endfunction
endclass

module sv_constructor;
sv_class class_1; // create handle  1class_1 = new(); // construct object
sv_class class_1; // create handle  1class_1 = new(); // construct object
endmodule

class只有经过了new()函数才真正开辟了内存，否则只是一个空的、没有实际存在, 若在class中未实现new()函数，

则会有系统默认new()

<2>. 'This' keyword

Solve ambiguity when the class can faction has the same variable name:

class packet;
  //class properties
  bit [31:0] addr;
  bit [31:0] data;
  bit        write;
  string     pkt_type;
  //constructor
  function new(bit [31:0] addr,data,bit write,string pkt_type);
    this.addr  = addr;
    this.data  = data;
    this.write = write;
    this.pkt_type = pkt_type;
  endfunction
 
  //method to display class prperties
  function void display();
    $display("---------------------------------------------------------");
    $display("\t addr  = %0h",addr);
    $display("\t data  = %0h",data);
    $display("\t write = %0h",write);
    $display("\t pkt_type  = %0s",pkt_type);
    $display("---------------------------------------------------------");
  endfunction
endclass

<3>. Classes Inheritance

You can use a child class to access parents class:

If two functions in the child class and parents class have the same function name. The function in the parent class will be overridden. Add "super" to the child function can solve this problem

class parent_class;
  bit [31:0] addr;
  function display();
    $display("Addr = %0d",addr);
  endfunction
endclass
 
class child_class extends parent_class;
  bit [31:0] data;
  function display();
    super.display();
    $display("Data = %0d",data);
  endfunction 
endclass
 
module inheritence;
  initial begin
    child_class c=new();
    c.addr = 10;
    c.data = 20;
    c.display();
  end
endmodule

Randomization and Constraints

module test_rand;
typedef enum{SM, MED, LRG}, trans_len // SM = 0, MED = 1, LRG = 2;
class transaction;
rand bit [19:0] addr;
rand tras_len len;
rand bit [3:0] byte_len
rand bit wr_or_ed_b;

constraint c1{wr_or_ed_b -> len !=LRG;}
constraint c2{(len==SM) -> (byte_len <=4;)}
constraint c3{(len==MED) -> (byte_len >4 && byte_len <= 8;)}
virtual function string tostring()
return sformat("%5H: %s %d bytes", addr,(wr_or_rd_b)?"WR":"RD", byte_len);
endfunction
endclass

Threads and Inter-Process

<1>. For-Join

Sequential statements are placed inside a begin/end block and executed in sequential order within the block. However, the blocks themselves are executed concurrently. Verilog statements outside any processing block are interpreted as concurrent statements and different procedural blocks execute concurrently.

Fork-Join will start all the processes inside it parallel and wait for the completion of all the processes.

module fork_join;
  initial begin    
    fork
      //Process-1
      begin
        $display($time,"\tProcess-1 Started");
        #5;
        $display($time,"\tProcess-1 Finished");
      end
      //Process-2
      begin
        $display($time,"\tProcess-2 Started");
        #20;
        $display($time,"\tProcess-2 Finished");
      end
    join
    $finish;
  end
endmodule

Result:            0 Process-1 Started
                       0 Process-2 Started
                       5 Process-1 Finished
                       20 Process-2 Finished

• Fork-Join_any will be unblocked after the completion of any of the Process.
• Fork-Join_none: Processes inside the fork-join_none block will be started at the same time, fork block will not wait for the completion of Process inside the fork-join_none.

<2>. Mailbox

A mailbox is a communication mechanism that allows messages to be exchanged between processes

Allow generator and driver running asynchronously and independently.

syntax： mailbox m = new(); //Unbounded             mailbox m = new(5); //bounded

new()	Create a mailbox
put()	Place a message in a mailbox
try_put()	Try to place a message in a mailbox without blocking
get() /peek()	Retrieve a message from a mailbox (peek only make copy)
try_get() /try_peek()	Try to retrieve a message from a mailbox without blocking
num()	Return the number of messages in the mailbox

<3>. Synchronization - Events & Semaphores

Events are static objects useful for synchronization between the process.

module events_ex;
  event ev_1; //declaring event ev_1
  initial begin
    fork        
      
      begin        //process-1, triggers the event
        #40;
        $display($time,"\tTriggering The Event");
        ->ev_1;   //trigger
      end
     
      begin        //process-2, wait for the event to trigger
        $display($time,"\tWaiting for the Event to trigger");
        @(ev_1.triggered);   //wait for trigger
        $display($time,"\tEvent triggered");
      end
    join
  end
endmodule

Result:  0 Waiting for the Event to trigger

             40 Triggering The Event
             40 Event triggered

Semaphores are used for shared resources access control.

new()	Create a semaphore with a specified number of keys
get()	Obtain one or more keys from the bucket
put()	Return one or more keys into the bucket
try_get()	Try to obtain one or more keys without blocking

module semaphore_ex;
  semaphore sema; //declaring semaphore sema
  initial begin
    sema=new(1); //creating sema with '1' key
    fork
      display(); //process-1
      display(); //process-2
    join
  end
 
  //display method
  task automatic display();
    sema.get(); //getting '1' key from sema
    $display($time,"\tCurent Simulation Time");
    #30;
    sema.put(); //putting '1' key to sema
  endtask
endmodule

Result:  0 Current Simulation Time
             30 Current Simulation Time