What is relationship of run_phase and main_phase?

UVM
,
1

I am confused with the relationship of run_phase and main_phase.
so I do a experiment. I used run_phase and main_phase in different component.
when I run the flowing code, I found the code of main_phase in sys_env do not execute. why?
when I add “phase.raise_objection(this);” “phase.drop_objection(this)” into main_phase of sys_env, then uvm prints “sys_env run over”. this result accords with my idea.


`timescale 1ns/1ps

module tb();
   import  uvm_pkg::*;
   `include "uvm_macros.svh"

   class sys_env extends uvm_env;
       `uvm_component_utils(sys_env)
     
       function new(string name, uvm_component parent);
           super.new(name, parent);
       endfunction

       function void build_phase(uvm_phase phase);
           super.build_phase(phase);
       endfunction
   
       task main_phase(uvm_phase phase);
           //phase.raise_objection(this);
           #4ns;
           `uvm_info("ENV", "sys_env run over!", UVM_LOW)
           //phase.drop_objection(this);
       endtask
    endclass
    
    class sys_test extends uvm_env;
       `uvm_component_utils(sys_test)
       sys_env   m_env;

       function new(string name, uvm_component parent);
           super.new(name, parent);
       endfunction

       function void build_phase(uvm_phase phase);
           super.build_phase(phase);
           m_env = sys_env::type_id::create("m_env", this);
       endfunction
   
       task run_phase(uvm_phase phase);
           phase.raise_objection(this);
           #20ns;
           `uvm_info("TEST", "sys_test run over!", UVM_LOW)
           phase.drop_objection(this);
       endtask
    endclass

    initial begin
       $timeformat(-9, 0, "ns", 5);
       run_test("sys_test");
    end
endmodule
2

In reply to ppeezz:

You need to raise an objection in any task-based phase for it to exist for more than 0 time.

BTW, we recommend using just the run_phase. Use sequences to control ordering in your test.

3

In reply to dave_59:

Thanks for your reply, Dave.
I will follow your advice(raise an objection in any task-based phase) in my real project.
but I am really curious with the relationship of run_phase and main_phase(run time phase).
In many papers or UVM spec, they all told me that run_phase and run time phase execute concurrently.
but Compare the above code, why the following code run, uvm can print “TEST” and “ENV” message.
They don’t look like a simple parallel relationship.


`timescale 1ns/1ps
 
module tb();
   import  uvm_pkg::*;
   `include "uvm_macros.svh"
 
   class sys_env extends uvm_env;
       `uvm_component_utils(sys_env)
 
       function new(string name, uvm_component parent);
           super.new(name, parent);
       endfunction
 
       function void build_phase(uvm_phase phase);
           super.build_phase(phase);
       endfunction
 
       task main_phase(uvm_phase phase);
           phase.raise_objection(this);
           #40ns;
           `uvm_info("ENV", "sys_env run over!", UVM_LOW)
           phase.drop_objection(this);
       endtask
    endclass
 
    class sys_test extends uvm_env;
       `uvm_component_utils(sys_test)
       sys_env   m_env;
 
       function new(string name, uvm_component parent);
           super.new(name, parent);
       endfunction
 
       function void build_phase(uvm_phase phase);
           super.build_phase(phase);
           m_env = sys_env::type_id::create("m_env", this);
       endfunction
 
       task run_phase(uvm_phase phase);
           //phase.raise_objection(this);
           #20ns;
           `uvm_info("TEST", "sys_test run over!", UVM_LOW)
           //phase.drop_objection(this);
       endtask
    endclass
 
    initial begin
       $timeformat(-9, 0, "ns", 5);
       run_test("sys_test");
    end
endmodule
4

In reply to ppeezz:

This is because there is kind of a hierarchy of phases. The main_phase is embedded in the run_phase.

5

In reply to dave_59:

Thanks for your reply, Dave.
Is there any paper describing this topic? I want to understand it exactly.

Tks

6

In reply to ppeezz:

Please read the UVM Standard.

7

In reply to dave_59:

In reply to ppeezz:
BTW, we recommend using just the run_phase. Use sequences to control ordering in your test.

Why did you recommend using just run_phase, as sub_phases adds complexity ??

8

In reply to akhil_dv:

Yes, it adds to the complexity. There is no standard definition of what goes in each phase, and that can make coordination with other VIP difficult. It’s easy to look at and maintain the flow of sequences in a test. The phases are there if you find it makes things easier, but the use is not widespread.

9

In reply to dave_59:

Understood. Thank you Dave