Systemverilog (Green Book) Chapter 3-Process Blocks and Methods

A lot of code needs to be written to do the design verification machine, most of which are used in tasks and functions. Systemverilog adds a lot of improvements in this regard, making it closer to the C language, which makes the writing of code easier, especially in the handling of parameter transfer.

• In Systemverilog, process blocks and their methods are divided by domain, and are divided into hardware and software parts . The specific contents are as follows:

 The test questions for the function parameter type are as follows:

typedef    struct{
    bit    [1:0] cmd;
    bit    [7:0] addr;
    bit    [31:0] data;
} trans;

function    automatic void op_copy(trans t,trans s);
    
    t = s;

endfunction


initial begin
    trans s;
    trans t;
    s.cmd = 'h1;
    s.addr = 'h10;
    s.data = 'h100;
    op_copy(t,s);
    t.cmd = 'h2;
end

Question: What are the final values ​​of the three member variables {cmd, addr, data} in t?

{‘h2,'h0,'h0}

Due to the function parameters, the default direction is input, here the trans t variable is regarded as an input variable. Therefore, the function of assignment is realized by calling the op_copy function. Since the direction of the outgoing value is not determined, the result is 0.

 

• In systemverilog, we divide the life cycle into automatic and static.

• 

  The scope design problems for static variables and dynamic variables are as follows:

• function automatic int auto_cnt(input a);
      int cnt = 0;
      cnt +=a;
      return cnt;
  endfunction
  
  
  function static int auto_cnt(input a);
      static int cnt = 0;
      cnt +=a;
      return cnt;
  endfunction
  
  function int auto_cnt(input a);
      static int cnt = 0;
      cnt +=a;
      return cnt;
  endfunction
  
  initial begin
      $display("@1 auto_cnt = %0d",auto_cnt(1));
      $display("@2 auto_cnt = %0d",auto_cnt(1));
      $display("@1 auto_cnt = %0d",static_cnt(1));
      $display("@2 auto_cnt = %0d",static_cnt(1));
      $display("@1 def_cnt = %0d",def_cnt (1));
      $display("@2 def_cnt = %0d",def_cnt (1));
  end
  
  
  

  Solution: For the first function, if it is defined as automatic, its contents are all dynamic variables. Therefore, after each call, the original value will be restored to 0;

  • For the second function, if it is defined as static, its contents are all static variables. Therefore, after each call, it will increment;

  • For the third function, all functions in the module are static functions by default , and the variables in the functions are static variables . However, in most cases, we hope that the functions in the module are dynamic functions, which is more in line with software requirements.